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Assessing the performance of commercial and biological gas hydrate inhibitors using nuclear magnetic resonance microscopy and a stirred autoclave
... Na-CMC changed the hydrate formation conditions, indicating that it has properties of a thermodynamic inhibitor with efficiency 350 times more than methanol. They also investigated the effect of the molecular weight of Na-CMC (90,250, and 700 kDa) on the hydrate formation process. They found that the inhibitor with a molecular weight of 90 kDa showed the best performance at concentrations of 0.005, 0.01 and 0.05 wt%. ...
... However, about 10 percent of the big cages were not fully filled in the case of AFP-III. Moreover, Daraboina et al. [250] determined the efficiency of magnetic resonance imaging (MRI) test to check out the utility of biological (type I and III AFPs) and chemical (H1W85281) inhibitors on hydrate growth or nucleation of mixed natural gas (CH 4 /C 2 H 6 /C 3 H 8 ) at the microscopic and local scales. In addition, they compared the results with the macroscopic size data achieved via more-common gas uptake tests applying a stirred cell. ...
Gas hydrate formation is one of the most serious challenges for flow assurance in oil and gas transportation pipelines as it causes severe safety, environmental, and economic problems for the oil and gas industry. The upstream petroleum industry has been using kinetic hydrate inhibitors (KHIs) for more than 25 years to prevent gas hydrate blockage in flow lines. One or more water-soluble polymers with both hydrophilic and hydrophobic functions are the major constituents of current commercial KHI formulations. However, most KHIs are not biodegradable, cheap, and eco-friendly oilfield production chemicals. Even though most KHIs have low bioaccumulation, acute toxicity, and poor biodegradability. As a result, the long-term chronic toxicity from partially decomposed compounds is a concern if they are disposed into the environment. Therefore, it is necessary to develop cheaper and greener KHIs. In this report, all efforts to produce KHIs with higher biodegradability are reviewed. It is made clear that not all classes of purportedly “green” chemicals are easily biodegradable or non-toxic. A thorough analysis is provided on the function of traditional and novel additives utilized to prevent hydrate formation at different conditions depending on their resources. The research seeks to present a comprehensive view of the structural properties of bio-based KHIs, with a particular emphasis on their key concerns, obstacles and future prospects in hydrate mitigation technologies.
... The experiment was considered complete when the cell pressure and temperature remained stable for 2-3 h without change. The total lag time for the kinetic experiment was approximately 8.0 h, and each experiment was repeated three times, with the average value being used [63]. ...
... In practice, it is defined as the time spent forming a detectable volume of large hydrate nuclei (in the liquid phase). However, because of the crystallization process, induction time is probabilistic [63]. As a result, all tests are repeated three times, with the average value taken into account. ...
The present work deals with evaluating the dual-functional gas hydrate impact of tetramethylammonium chloride (TMACl) in the presence of different CO2-CH4 content mixed gas hydrate systems (30%CO2 + 70%CH4, 50%CO2 + 50%CH4, and 70%CO2 + 30%CH4). A custom-made high-pressure gas hydrate reactor was used to acquire the temperature–pressure loops for the studied systems in the absence/presence of different concentrations of aqueous TMACl solutions via T-Cycle and isochoric constant cooling method for both THI and KHI investigations, respectively. The electrolyte-based thermodynamic model was also applied to validate the obtained HLwVE results for all the studied systems. The obtained results revealed that TMACl acts dual-functional (thermodynamic and kinetic) hydrate inhibitor for high CO2 content gas systems. The increased concentration of TMACl induces more shifts in HLwVE data with maximum variation attained at10 wt% concentration up to 1.46 K for a high CO2 content methane system owing to the increased hydrogen bonding ability of TMACl. Moreover, TMACl delayed the hydrate formation up to 1.4 and1.5 folds for 274.0 and 277.0 K conditions for high CO2 content mixed gas systems. Moreover, the applied electrolyte-based model could predict the HLwVE data of TMACl in the presence of a mixed gas system within the AAE value of 0.1 % for all the studied mixed gas systems. Furthermore, the KHI performance of TMACl was also compared with commercial inhibitor, i.e., polyvinyl pyrrolidone (PVP), and obtained comparable results. Therefore, the acquired dual-functional results (THI = 1.46 K, KHI = 1.5-fold delay) signpost that TMACl can efficiently work as a potential dual-functional hydrate inhibitor for CO2 enriched mixed gas systems.
... The temperature is regulated by refrigerant that is circulated around the cell and the coolant temperature. Sensors measure temperature and pressure (Lee et al., 2005;Jensen et al., 2011;Daraboina et al., 2011Daraboina et al., , 2013Lee and Englezos, 2006;Dholabhai et al., 1987). 3. Ball Stop Rocker Rig (RR): These rigs are widely used to test KHIs performance by the industry. ...
... A cooling fluid is filled outside the pipe, which is cooled/ heated by a heat exchanger (Azarinezhad-mohammadi, 2010;Peytavy et al., 2008;Turner et al., 2005;Lund et al., 1996). 5. Pipe Wheels or Wheel Loop: This setup consists of pipe wheels that are rotated to simulate the transport through a pipeline by creating relative motion between the fluid and wheel (Lippmann et al., 1995;Oskarsson et al., 2005;Ke and Kelland, 2016;Kelland et al., 2006b). 6. Microscopic level and Molecular-level: Differential scanning calorimeter and magnetic resonance imaging are used to study hydrate inhibition at a micro level, while Raman spectroscopy, X-ray diffraction as well as nuclear magnetic resonance spectroscopy is employed to study hydrates at a molecular level Long et al., 2019;Farhadian et al., 2019;Daraboina et al., 2013;Wan et al., 2019b;Uchida et al., 2003;Lafond et al., 2012). ...
This paper briefly reviews gas hydrate nucleation, dissociation, and hydrate inhibition by kinetic hydrate inhibitors (KHIs). The drawbacks of traditional inhibitors and the testing methods for evaluating KHIs are presented. More than 80 tests done on 46 different KHIs based on acrylamide are presented. The KHIs are homopolymers and copolymers of acrylamide and other groups such as hydroxy, hydrazide, amino, acrylate, maleimide, sulfonic acid, acrylic acid, and lactam. The tests are grouped such that they had the same equipment type, test procedure, gas type, initial pressure and polymer concentration. The top KHIs in each group are identified and presented.
... Hence it is also quite clear that, IPDI-based WPUU was a more effective inhibitor than HDI-based WPUU since it delayed nucleation by a factor of 14.87 and HDI-based WPUU delayed by a factor of 10.99 (in 1 wt% low molecular weight samples) in comparison with pure water. In these conditions (2 °C and 9 MPa) the induction time for water + Anti-Freeze Protein (AFP) systems formed with AFP-III and AFP-I was reported as 8 and 24 min, respectively 34 . Also it is reported that, in 274.15 ...
... The induction time of each sample solution was measured during three parallel experiments and their scattering values due to the stochastic nature of nucleation were averaged. The induction time for hydrate formation in pure water measured at 2 °C and 9 MPa in our work (which is equal to 2 minutes) coincides well with literature data (also is equal to 2 minutes) 34 , and confirm reliability of our measurements. ...
A facile, new and promising technique based on waterborne polymers for designing and synthesizing kinetic hydrate inhibitors (KHIs) has been proposed to prevent methane hydrate formation. This topic is challenging subject in flow assurance problems in gas and oilfields. Proposed technique helps to get KHIs with required number and distance of hydrophilic and hydrophobic groups in molecule and good solubility in water. The performance of these new KHIs was investigated by high pressure micro-differential scanning calorimeter (HP-μDSC) and high-pressure autoclave cell. The results demonstrated the high performance of these inhibitors in delay the induction time (10–20 times) and reduce the hydrate growth rate (3 times). Also they did not increase hydrate dissociation temperature in comparison with pure water and show thermodynamic inhibition as well. Inhibition effect of synthesized polymers is improved with the increase of concentration significantly. Since this is the first report of the use of waterborne polymers as kinetic hydrate inhibitor, we expect that KHIs based on waterborne-based polymers can be a prospective option for preventing methane hydrate formation.
... Daraboina et al. investigated the formation kinetics of CH 4 /C 2 H 6 / C 3 H 8 hydrate in the presence of kinetic inhibitors using 1 H MRI [175]. ...
... Their experiments shown that hydrate nucleation and growth were delayed significantly in the presence of inhibitors, which also demonstrated that MRI is a useful tool for the visualization and evaluation of the performance of kinetic inhibitors on gas hydrate formation. They further proposed that the MRI technique may be beneficial for further investigation on the distinct mechanisms of inhibitor performance [175]. By incorporating 4 types of large molecules guest substances (LMGS) in CH 4 system, Susilo et al. reported the hydrate formation and dissociation kinetics for s-H hydrates via MRI using ice particles of 1.3 µm [172]. ...
... Recently, researchers reported that chemicals such as KHIs may influence gas hydrate morphology; various shapes and porosity are found within each hydrate structure (structure I or structure II). [11][12][13][14][15][16][17]. Therefore, even with similar thermodynamic conditions, dissociation of hydrate plugs can be significantly influenced by the presence of chemicals, such as KHIs. ...
... Therefore, even with similar thermodynamic conditions, dissociation of hydrate plugs can be significantly influenced by the presence of chemicals, such as KHIs. However, there is still very limited research to investigate KHIs impact on gas hydrate dissociation [11][12][13][14][15]. Furthermore, there is no published work with explicit images to provide insight as to how gas hydrates blockages dissociate under the presence of KHIs. ...
This paper presents new gas hydrate equilibrium data's for C2H6 (structure I) and CH4 + C3H8 (structure II) with and without the presence of sodium chloride. Macroscopic observation of gas hydrate dissociation under the presence of kinetic hydrate inhibitor (KHI) is also presented and compared with cells that have no inhibitor. All the experiments are conducted with a synthetic natural gas utilizing a newly fabricated isochoric rocking cell apparatus. Results of experimental gas hydrate equilibria data agrees with thermodynamic software (CSMGem). Macroscopic observation work shows that the presence of KHI slows down gas hydrate dissociation compared to cells with no inhibitor.
... Also, the addition of AFP was found to change the hydrate crystal morphology from octahedral to plate-like. Daraboina et al. found that fish AFPs show significant inhibition for various types of gas hydrates [185,186,190]. It was reported that the efficiency of the protein is better than that of PVCap [29]. ...
... Therefore, the transferability of results from lab scale experiments to field conditions is expected to remain a significant challenge in the short term [151,237,238]. In order to fill this gap and to assess the performance of KHIs under field conditions, research has now moved towards evaluation of KHIs in presence of mixture of gases instead of single component gases [108,184,190,229,[239][240][241]. ...
... If this nucleation delay time is greater than the retention time of the fluids in the risk zone, then hydrate formation can be effectively controlled. These KHIs are also known to alter crystal growth rates after nucleation [2,6,[11][12][13][14][15]. Most KHIs are polymer based components while recent studies have shown that some antifreeze proteins and amino acids can also delay hydrate formation significantly [12,13,[15][16][17][18][19][20]. ...
... If this nucleation delay time is greater than the retention time of the fluids in the risk zone, then hydrate formation can be effectively controlled. These KHIs are also known to alter crystal growth rates after nucleation [2,6,[11][12][13][14][15]. Most KHIs are polymer based components while recent studies have shown that some antifreeze proteins and amino acids can also delay hydrate formation significantly [12,13,[15][16][17][18][19][20]. The application of these KHIs in the field depends on many factors such as gas composition, flow rate, gas/ oil ratio, oil composition, sub cooling, pipeline size, water cut, salinity, other chemical injections, cost etc. ...
... Briefly, the bestadopted mechanisms are molecular diffusion, thermal or Soret diffusion, Brownian diffusion, shear dispersion, and gravity settling (refer to Figure 5). 74−76 Molecular diffusion was found to be the best governing mechanism for the deposition of wax particles, wherein wax deposition starts with forming a 3-D network of incipient wax−oil gel layer on the inner wall of the To understand hydrate−fluid interfacial behavior Challenging to simulate the field conditions To study the cohesive and adhesive forces of microscopic solids Understand the agglomeration of hydrates in multiphase flowlines (for quantitative ranking of AAs performance) In situ Raman spectroscopy 61,62 Deliver evidence for hydrate growth mechanism in presence of LDHIs Limited to quantitative insights on the structure elucidation and cage occupancy Hydrate structure elucidation Acoustic levitation apparatus 63 Unique apparatus to measure the hydrate nucleation and morphological observations of freely suspended water droplets in a high-pressure gas phase Shear nontrivial to control Enables visual monitoring of single particle growth Only single-cell systems 1 H nuclear magnetic resonance imaging (MRI) 64,65 Unique tool for the visualization and evaluation of the performance of kinetic inhibitors ...
... As expected [59][60][61], the hydrate film velocities in the presence of PVP are lower than those for pure water. It has been proposed that the presence of PVP decreases hydrate growth rates because PVP can adsorb to the hydrate crystals and sterically hinder crystal growth [12,18,44,48,49,62,63]. ...
With a single apparatus and very short experimentation times, we have assessed phase equilibria, apparent kinetics and morphology of methane gas hydrates in the presence of thermodynamic inhibitors ethane-1,2-diol (MEG) and sodium chloride (NaCl); and kinetic hydrate inhibitor polyvinyl-pyrrolidone (PVP). Tight, local temperature control produced highly repeatable crystal morphologies in constant temperature systems and in systems subject to fixed temperature gradients. Hydrate-Liquid-Vapor (HLV) equilibrium points were obtained with minimal temperature and pressure uncertainties ( u T avg = 0 . 13 K and u p = 0 . 005 MPa). By applying a temperature gradient during hydrate formation, it was possible to study multiple subcoolings with a single experiment. Hydrate growth velocities were determined both under temperature gradients and under constant temperature growth. It was found that both NaCl and MEG act as kinetic inhibitors at the studied concentrations. Finally, insights on the mechanism of action of classical inhibitors are presented.
... It is defined in practice as the time occupied for the formation of a detectable volume of sizeable hydrate nuclei (in the liquid phase) [45]. However, the induction time appears to be the probabilistic phenomenon due to the crystallization process [46]. Therefore all the experiments are repeated for three times, and the average value is taken into account. ...
... The crystals were altered from octahedral to more elongated platy form. Daraboina et al. used fish AFPs to inhibit the formation of various types of gas hydrates [119,120,124]. They compared the inhibition performance of fish AFPs with PVCap and concluded the former to be more efficient [58]. ...
Recent advances in gas hydrate research mainly focus on dual function gas hydrate inhibitors (DF-GHIs). DF-GHIs exhibit dual behavior of shifting the hydrate dissociation curve to lower temperatures and higher pressures as well as hindering or delaying the nucleation. The main focus of this review is to discuss all the possible factors that can induce dual functionality in gas hydrate inhibitors (GHIs). In this regard, this review summarizes the latest developments, classification, evaluation techniques and experimental findings of GHIs. The experimental data of different research groups is critically analyzed and systematically evaluated in terms of average depression temperature (ΔŦ) and relative inhibition power (RIP). The ΔŦ and RIP is calculated from existing experimental data. The studies in this field will give more knowledge at both academic and industrial level for the development of economical, efficient and biodegradable DF-GHIs.
... Magnetic resonance imaging (MRI) is also another method being used for monitoring kinetics of hydrate crystallization (Baldwin et al. 2009, Bagherzadeh et al. 2011, Xue et al. 2012. Daraboina et al. (2013) examined the performance of both chemical and biological kinetic inhibitors by MRI. In addition, the results have been compared to the common device, which was stirred autoclave. ...
Ice-like crystal compounds, which are formed in low-temperature and high-pressure thermodynamic conditions and composed of a combination of water molecules and guest gas molecules, are called gas hydrates. Since its discovery and recognition as the responsible component for blockage of oil and gas transformation line, hydrate has been under extensive review by scientists. In particular, the inhibition techniques of hydrate crystals have been updated in order to reach the more economically and practically feasible methods. So far, kinetic hydrate inhibition has been considered as one of the most effective techniques over the past decade. This review is intended to classify the recent studies regarding kinetic hydrate inhibitors, their structure, mechanism, and techniques for their performance evaluation. In addition, this communication further analyzes the areas that are more in demand to be considered in future research.
... The most common of them are rocking cell 150 and high-pressure cell or autoclaves 166,167 or both in combination being used. 168,169 Techniques such as nuclear magnetic resonance (NMR) microscopy 160 and NMR combined techniques such as in situ powder X-ray diffraction, 170 highperformance differential scanning calorimetry 53 (HP-DSC), and ultrasonic testing techniques 171 have all been used to study the impact of KHIs on the hydrate nucleation and growth kinetics. KHIs have also been evaluated on a larger setup by means of high-pressure flow loops by Talaghat et al. 172 High pressure automated lag time apparatus (HP-ALTA) is another technique that has been recently adopted for the purpose of studying hydrate formation. ...
Clathrate hydrates are crucial from the point of view of flow assurance, future energy resource as well as promising innovative and sustainable applications such as gas separation, CO2 sequestration, district and data centre cooling and seawater desalination and natural gas storage. Although proof of concept has been demonstrated, significant progress is necessary in order to achieve industrial level validation and commercialization. Most of the applications possess a common requirement of enhanced kinetics in formation and dissociation. There is a need for a broader understanding of hydrate nucleation mechanisms, cause-effect relations and investigation techniques. The stochastic nature of hydrate nucleation, confounding cause-effect relations and spatial-temporal scales have made it even more challenging to study nucleation. The use of hydrate promoters, novel reactor configurations such as porous media in a packed bed, use of nanoparticles and hydrogels necessitates us to obtain further insights about clathrate nucleation. This review provides an in-depth analysis about the characteristics of clathrate hydrate nucleation and the techniques adopted for studying nucleation from an application-oriented perspective and enables further development of clathrate technology towards future applications.
... The experimental system is shown in Fig. 1 The MRI system (Varian, Inc., Palo Alto, CA, USA) is used for visualizing methane hydrate formation and dissociation process. MRI can just acquire images of the 1 H contained in liquid water [11] but 1 H in in solid hydrae can't be acquired by MRI [12,13]. The MRI system operating at a resonance of 400 MHz and the magnetic field intensity is 9.4 T. MRI images were constructed using a spin echo multi-slice pulse sequence (SEMS) [14,15], and the experimental parameters are: echo time (TE) 13.82 ms, repetition time (TR) 560 s, image data matrix 128 128, field of view (FOV) 30 mm 30 mm with 4.0 mm thickness. ...
Natural gas hydrate is a clean energy source with significant potential. It's significant to elucidate the formation and dissociation properties of natural gas hydrate during exploitation process. In this study, methane hydrate reformation under dynamic conditions was simulated to provide essential data for hydrate safe and efficient exploitation. The changes of vessel pressure, methane hydrate saturation (Sh) and residual water saturation (RWS) were measured and analyzed. Residual water distribution is illustrated by images obtained by magnetic resonance imaging (MRI). The experimental results indicated that an optimum gas velocity exist to maximize hydrate generation under a certain initial water saturation when constant velocity of methane was injected into the porous media. Compared to downward methane, upward methane is more likely to cause structure changes of porous medium and the structure changes can’t recover after hydrate dissociation. Comparing the axial residual water distribution porous media during the process of hydrate formation and decomposition, the axial residual water distribution in formation process is more non-uniform than that in dissociation process. Moreover, the hydrate dissociation boundaries moving from vessel wall to core can be observed by MRI images. This study provides important basic data for natural gas hydrate exploitation.
... Several new techniques are under development in order to replace or improve conventional methods (methanol injection, temperature increase) for hydrates -plugging prevention. Several chemical and biologic kinetic inhibitors have been developed and investigated as alternative solutions to these traditional thermodynamic inhibitors [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Some compounds naturally found in sea water and reservoir fluids also act as inhibitors [25,26]. ...
... Several AFPs from fish and plants have been investigated as kinetic hydrates inhibitors using various techniques and these AFPs showed to inhibit structure I and structure II hydrate formation [9][10][11][12][13][14][15]. However, hyperactive insect AFPs can act as strong potential hydrate inhibitors and are not yet studied. ...
Gas hydrates are crystalline, ice-like solids which can form from water and small molecules such as those present in natural gas. They form at low temperatures and moderate to high pressures, conditions frequently encountered in the oil and gas industry. Excessive formation of gas hydrates causes blockage of pipelines with subsequent loss of production. Several techniques are applied to avoid gas hydrate formation, but relatively recently, low dosage kinetic hydrate inhibitors (KHIs) have been developed. Despite the success of these compounds at very low concentrations, their poor biodegradability has prompted a search for new environmentally friendly hydrate inhibitors. Antifreeze proteins (AFPs) have been shown to be promising candidates for gas hydrate formation. In particular, certain insect AFPs express very high antifreeze activity (their ability to prevent ice from forming when cooled). Here we show that an insect antifreeze protein from the longhorn beetle, Rhagium mordax (RmAFP1), the most potent protein yet found for freezing inhibition, can inhibit methane hydrates as effectively as the synthetic polymeric inhibitor polyvinylpyrrolidone (PVP). In high pressure Rocking Cell experiments, onset hydrate nucleation temperatures and growth profiles showed highly repeatable results. RmAFP1 clearly showed inhibition of hydrates compared to amino acids (L-valine and L-threonine) and the protein Bovine Serum Albumin (BSA). This indicates that proteins or amino acids do not generally inhibit hydrate formation. The performance of RmAFP1 shows promising results as a new green KHI and could serve as the prototype for further development and increased production of green hydrate inhibitors.
... The effect of KHIs on gas hydrate formation has been studied extensively under different conditions and by using various experimental approaches. [20][21][22][23][24][25][26][27][28] In this work, a highpressure cell in conjunction with a rotational rheometer is used to assess the performance of two commercial kinetic inhibitors under more realistic conditions including: multicomponent gas mixture, high driving force, presence of sodium chloride, and liquid hydrocarbon (n-heptane). To the best of our knowledge, the following is the first study that evaluates the performance of kinetic inhibitors by direct Correspondence concerning this article should be addressed to P. Englezos at peter.englezos@ubc.ca. ...
Methane clathrates on continental margins contain the largest stores of hydrocarbons on Earth, yet the role of biomolecules in clathrate formation and stability remains almost completely unknown. Here we report new methane clathrate-binding proteins (CbpAs) of bacterial origin discovered in metagenomes from gas clathrate-bearing ocean sediments. CbpAs show similar suppression of methane clathrate growth as the commercial gas clathrate inhibitor polyvinylpyrrolidone and inhibit clathrate growth at lower concentrations than antifreeze proteins (AFPs) previously tested. Unlike AFPs, CbpAs are selective for clathrate over ice. CbpA3 adopts a non-globular, extended structure with an exposed hydrophobic surface, and, unexpectedly, its TxxxAxxxAxx motif common to AFPs is buried and not involved in clathrate binding. Instead, simulations and mutagenesis suggest a bipartite interaction of CbpAs with methane clathrate, with the pyrrolidine ring of a highly conserved proline residue mediating binding by filling empty clathrate cages. The discovery that CbpAs exert such potent control on methane clathrate properties implies that biomolecules from native sediment bacteria may be important for clathrate stability and habitability.
The kinetics of hydrate formation has followed different paths depending on the goals of a particular community of researchers. Much of the initial work on hydrate kinetics came from the need to understand processes important for industry such as hydrate plug control in pipelines and seawater desalination with gas hydrates. Engineering researchers first developed models of hydrate processes based on activated chemical kinetics. Following a phase transition model, we present the classical theory of homogeneous and heterogeneous nucleation. Models of hydrate processes based on such considerations are still emerging, and their description takes account of theory, experimental data, and computer modeling studies. Other aspects related to kinetics that are presented include modifiers of kinetics, metastability, morphology, and molecular simulations of kinetic processes.
Technologies for preventing hydrate blockage play an important role in oil and gas production, transportation and processing. In this paper, a fully visual rocking cell was used to study the effects of water cut, surface wettability and kinetic inhibitors (PVCap, apple pectin and three ionic liquids) on gas hydrate nucleation, growth and blockage. The amount of water converted to hydrates reached the highest when the water cut was about 60%. The evolution process of hydrate was observed by CCD camera, including initial crystallization, water film condensation, forming the hydrate bed, and the top blockage. The hydrophilic surface can reduce the nucleation rate of hydrate to some extent, but it can not reduce the final hydrate production. The hydrophobic surface can increase the formation rate of hydrate and the amount of water converted to hydrates, but the pipe blockage did not occur because it is difficult for hydrate to adhere to the pipe wall. In terms of induction time, the inhibition to structure II hydrate of 0.2 wt% apple pectin was similar to that of PVCap, and the inhibition of high concentration apple pectin decreased because of its low solubility. Apple pectin can delay the formation rate of hydrate, but will not change the final production of hydrate. [HMIM]BF4 and [EMIM]Cl can make hydrate disperse evenly in water and prevent pipeline blockage, which play a role like anti-agglomerates. From the inhibition effects of cations and anions on hydrates, the order was as follows: Cl⁻ > BF4⁻, [HMIM]⁺ > [EMIM]⁺. This study might provide a basis for hydrate plugging prevention.
Kinetic inhibitor-amino acid exhibits a promising advantage in preventing the hydrate formation. In this work, adsorption behaviors of amino acid including glycine, serine and valine on methane hydrate surface are investigated by the density functional theory (DFT). It is found that the nitrogen/oxygen and hydrogen atoms in hydrophilic groups of amino acid prefer to attach the hydrogen and oxygen atoms of water molecules in hydrate simultaneously to achieve a more stable adsorption mode. The adsorption energy of hydrophobic groups is lower than that of hydrophilic groups. Meanwhile, molecular dynamics (MD) simulations are carried out to analyze the inhibition effect of glycine, serine and valine. It is observed that the strongest interaction appears between the hydrophilic groups of serine and methane hydrate surface. The hydrophobic group-methyl of valine weakens the interaction of amino and carboxyl groups with water molecules, whereas increases the disturbance of water molecules.
This review highlights the performance of biopolymers in the petroleum industry. It summarizes the recent developments in biopolymers as Kinetic Hydrate Inhibitors (KHIs), their selection criteria, current experimental findings, and inhibition mechanism. The experimental data of various research groups are analyzed critically and assessed systematically in terms of nucleation time, nucleation temperature, hydrate growth rate, gas consumed during hydrate formation, average depression temperature (ΔT) and percentage relative inhibition strength (%RIS). The available experimental data is differentiated based on driving force i.e. sub-cooling temperature. Recent studies in this field have provided more understanding in the development of economical, effective and biodegradable KHIs for both academics and industrial applications.
Inorganic substances and most organic compounds would be excluded from the crystalline hydrate structure. The phenomenon and mechanism of organic exclusions were firstly simulated and in-situ observed with CO2 hydrate formation in this study. The results showed that organic macromolecules could not be trapped in the hydrate structure, and formed a concentration gradient of dissolved organic from the growth front of CO2 hydrate into the aqueous solution. This study demonstrated the hydrate-based technology would be a promising method for organic wastewater treatment.
Gas clathrates are both a resource and a hindrance. They store massive quantities of natural gas but also can clog natural gas pipelines, with disastrous consequences. Eco-friendly technologies for controlling and modulating gas clathrate growth are needed. Type I Antifreeze Proteins (AFPs) from cold-water fish have been shown to bind to gas clathrates via repeating motifs of threonine and alanine. We tested whether proteins encoded in the genomes of bacteria native to natural gas clathrates bind to and alter clathrate morphology. We identified putative clathrate-binding proteins (CBPs) with multiple threonine/alanine motifs in a putative operon (cbp) in metagenomes from natural clathrate deposits. We recombinantly expressed and purified five CbpA proteins, four of which were stable, and experimentally confirmed that CbpAs bound to tetrahydrofuran (THF) clathrate, a low-pressure analog for structure II gas clathrate. When grown in the presence of CbpAs, THF clathrate was polycrystalline and plate-like instead of forming single, octahedral crystals. Two CbpAs yielded branching clathrate crystals, similar to the effect of Type I AFP, while the other two produced hexagonal crystals parallel to the [1 1 1] plane, suggesting two distinct binding modes. Bacterial CBPs may find future utility in industry, such as maintaining a plate-like structure during gas clathrate transportation.
Antifreeze proteins (AFPs) are polypeptides produced by plants, animals, and microorganisms that allow them to survive at temperatures below zero. These compounds were first identified in 1969 by DeVries in the blood of fishes living in frozen sea areas and were named antifreeze proteins because they lowered the freezing point of the fish’s blood below the freezing point of sea water without significantly increasing the osmotic pressure. Antifreeze proteins can halt the formation of large ice crystals associated with recrystallization during frozen storage and thawing, and their potential as a food additive have been investigated in the recent years. Initially the use of AFPs was limited to ice cream products, but now meat, frozen dough, fruit, and vegetables are also among the products investigated. There are many research results about the successful application of AFPs in the freezing and thawing of food. However, in the future commercial use of these proteins will most likely be influenced by various factors such as isolation and purification, thermal stability, price, chemical synthesis, and development in molecular biology. This chapter describes the studies on the use of AFPs in food, as well as the dietary sources of these proteins, their use in foods, their toxicity, and the factors that influence their use.
Gas hydrates are ice-like solid compounds of small gas molecules and water which form at low temperature and high pressure and are the major flow assurance problem in the global oil and gas industry. In this chapter the use of antifreeze proteins as gas hydrate inhibitors is explored. A variety of methods for hydrate management are mentioned and test methods for low dosage hydrate inhibitors are considered in detail. A review of current research into antifreeze proteins as hydrate inhibitors follows. Based on the current state-of-the-art it is concluded that antifreeze proteins may be effective hydrate inhibitors; however, testing needs to be performed on more realistic reservoir fluids than has currently been done. Economic production of antifreeze proteins in large amounts is also a necessary step to allow their adoption in the field. Finally the mechanism of inhibition of antifreeze proteins, at least for hydrates, is not well understood. This could be a fruitful area of future research.
The dissociation kinetics of CO2 hydrate are investigated by molecular dynamics (MD) simulation in the presence of thermodynamic inhibitor glycine (5wt%, 10wt%, 15wt%, 20wt%) and kinetic inhibitor glucose (1.2wt%, 2.0wt%, 3.8wt %). The molecular dynamics simulations are performed at 273.15 K and 3 MPa under the isothermal-isobaric (NPT) ensemble. The configuration, radial distribution functions, mean square displacement, and density are analyzed respectively. It is found that the dissociation rate of CO2 hydrate is increased in the presence of two inhibitors. The optimal concentration of glycine is 10wt% and that is 1.2wt% for glucose. The results indicate different mechanisms for two inhibitors. Glycine accumulates on the solid-liquid surface of the initial structure, and the clathrate hydrate structure is destroyed due to the aggregation of hydroxyl (-OH) and amidogen (-NH2) with water hydrogen bond in the hydrate structure. While glucose accelerates the dissociation of hydrates because of the synergistic effect of steric hindrance, owing to its ring-shaped structure and the disruption of functional groups.
In this work sulfonated chitosan (SCS) was introduced as a promising green kinetic methane hydrate and corrosion inhibitor to overcome the incompatibility problem between inhibitors. Evaluation of hydrate inhibition performance of SCS with high-pressure autoclave and micro-differential scanning calorimeter revealed that hydrate formation was delayed 14.3 ± 0.2 times and amount of hydrate formed was decreased to 30 % compared to water. The weight loss experiments showed that SCS provides corrosion inhibition efficiency of 95.6 ± 0.1 at 5000 ppm concentration. SCS is able to increase polarization resistance and decrease corrosion current density according to electrochemical measurements. Study of surface morphology by SEM-EDX and profilometer showed that SCSs suppress corrosion rate and reduce the surface roughness of carbon steel. Quantum chemical study confirmed that the pendant groups caused by chitosan modification interact with carbon steel surface. The findings of this research can provide new opportunities to develop biodegradable materials as KHIs/CIs for flow assurance in oil and gas pipelines.
Antifreeze proteins are a kind of proteins which can protect organisms at subfreezing temperatures by inhibiting the growth of ice crystals, they are becoming increasingly attractive as a kind of biological kinetic hydrate inhibitors (KHIs). In this work, the inhibition effect of an antifreeze protein (mSA-RmAFP1) on synthetic natural gas (SNG) hydrate nucleation in the case of existing salts and crude oil was investigated using a rocking cell apparatus. In addition, three kinds of environment friendly KHIs (starch, chitosan and glycine) as well as a commercial inhibitor (PVP) were tested for comparison. The results showed that 2250 p.m. mSA-RmAFP1 can inhibit SNG hydrate nucleation more effectively than PVP in various systems (pure water, salt water, salt water + 15 vol% crude oil). Starch, chitosan and glycine present weak inhibition ability on SNG hydrate nucleation. The inhibition strength of various chemicals can be ranked as follows: starch < chitosan < glycine < PVP < mSA-RmAFP1. The SNG hydrate crystal growth and decomposition process were investigated, it was found that mSA-RmAFP1 can decrease the SNG hydrate growth rate and production as well as the onset decomposition temperature. However, PVP increased the SNG hydrate production and onset decomposition temperature. For investigating if the results have dependence on experimental apparatus, the performance of various inhibitors were tested using a micro differential scanning calorimeter (DSC). It was found that the results are consistent with those obtained from the rocking cell apparatus. This study can provide detailed research information on the application of AFPs and contribute to understand hydrate formation and decomposition behavior for the system containing KHIs in realistic conditions.
The expression of anti-freeze proteins (AFPs) on the Escherichia coli using the cell surface display (CSD) strategy was investigated to determine the feasibility of the method as a potential application of kinetic hydrate inhibitors. Monomers to hexamers of type II and III AFPs were displayed on the surfaces of bacterial cells. The kinetic inhibition performance of the AFPs on the synthetic natural gas hydrate formation was tested. The displayed AFPs exhibited higher KHI effectiveness with the increase in the number of peptides attached to the cells. In addition, best KHI performance of the AFPs could be achieved with higher dosages of the cultures when the concentration of the inducer is optimized, regardless of AFP type. Only a small portion of AFPs in the cell cultures exhibited considerable KHI performance, which implies that the CSD could be an effective strategy, reducing the cost for the production and purification of the AFPs.
Antifreeze proteins (AFPs) are characterized by their ability to protect organisms from subfreezing temperatures. They constitute a class of promising candidates as environmentally kinetic hydrate inhibitors (KHIs). In this study, the effectiveness of an insect cell expressed novel monomeric streptavidin fusion protein version of Rhagium mordax RmAFP1 antifreeze protein (mSA-RmAFP1), and four amino acids (histidine, lysine, tyrosine and proline), on CH4 hydrate nucleation, growth and decomposition was investigated using a rocking cell apparatus, then compared with the commercial inhibitors Polyvinylpyrrolidone (PVP) and Luvicap Bio. It was found that CH4 hydrate nucleation and growth exhibited good repeatable results under experimental conditions. The results showed that 2250 ppm mSA-RmAFP1 can inhibit CH4 hydrate nucleation as effectively as PVP at the same concentration. The histidine, lysine, tyrosine and proline exhibited weak inhibition effect on CH4 hydrate nucleation. The mSA-RmAFP1 decreased CH4 hydrate growth rate and production in the fresh and memory solutions. The CH4 hydrate formed in the solutions containing various tested KHIs present slightly lower onset decomposition temperatures than the non-inhibited system under experimental conditions. The promising performance of the insect cell expressed mSA-RmAFP1 could promote the further development of green hydrate inhibitors. The production of this protein through insect cell line fermentation provides a platform for the future production and optimization of AFPs for hydrate inhibition.
Phase equilibria, kinetic, and morphology studies of gas hydrates require separate pieces of equipment and experimentation times in the order of days. Recently, we designed a reactor that allows for tight control of the crystallization temperature. Coupled with a novel method, this reactor can screen the crystal morphology, phase equilibria, and apparent kinetics of gas hydrates. Compared to traditional multi‐trial methods, the main advantage of this method is that only a single experiment, completed in the order of hours, is required to assess (1) the change in hydrate growth velocity with respect to temperature, (2) the H‐L‐V equilibrium temperature at the experimental pressure, and (3) the change in crystal morphology with respect to driving force. Using this 3‐in‐1 method, methane hydrate growth and dissociation was studied in the presence of 4 commercial inhibitors. Phase equilibria, kinetics, and morphology were obtained for all hydrate systems with inhibitors. The standard uncertainty for the H‐L‐V equilibrium temperature was 0.05 K and for pressure 0.005 MPa. The apparent rates of growth were measured for all systems (standard uncertainty was 0.008 mm·s–1) and the difference between the inhibited systems and the pure system was very clear. Crystal habits varied considerably among inhibitors and radically with respect to the uninhibited system. Overall, we present an innovative technology to assess the morphology, kinetics, and thermodynamics of hydrate forming systems with a single apparatus. Furthermore, with little time investment, small sample sizes can be used to obtain replicates with minimum temperature and pressure uncertainties. This article is protected by copyright. All rights reserved.
A kinetic inhibitor of methane hydrate formation was developed on the basis of amphiphilic polyurethane. The efficiency of the new reagent was evaluated in a high-pressure reactor with agitation by measuring the time for the beginning of hydrate formation and the change of pressure in the system. The results show the excellent inhibiting effect of amphiphilic polyurethane in increasing the induction time (by 15 times) and reducing the growth rate of hydrates (by 2.5 times) compared with a system with pure water In addition, the urethane-based inhibitor did not show significant growth of methane hydrates after nucleation.
Worldwide energy demand has been increased in last few decades, and it is expected that it will increase up to 50% by the end of next decade. Oil and gas were major sources of energy in past, and it is expected that it will remain the primary source of energy in next few decades. Therefore, efforts are being made to upgrade drilling, completion, workover, and production operations to maximize the oil recovery at a lower cost. In last few decades, water-soluble polymers have been extensively used in different gas and oilfield applications. In the present chapter, we discuss the various types of polymeric systems that have been applied in various oilfield applications. These applications are mainly enhanced oil recovery, drilling fluids, and kinetic gas hydrate inhibition. Properties required for each application are also discussed and related to the chemical structure of the polymer.
Natural gas hydrates easily form in pipelines, causing potential safety issues during oil and gas production and transportation. Injecting gas hydrate inhibitors is one of the most effective methods for preventing gas hydrate formation or aggregation. However, some thermodynamic hydrate inhibitors are toxic and harmful to the environment, whereas degradation of kinetic inhibitors is difficult. Therefore, environmentally friendly and easily biodegradable novel green inhibitors have been proposed and investigated. This paper provides a short but systematic review of the inhibitory performance of amino acids, antifreeze proteins, and ionic liquids. For different hydrate formation systems, the influences of the inhibitor type, structure, and concentration on the inhibitory effects are summarized. The mechanism of green inhibitors as kinetic inhibitors is also discussed. The progress described here will facilitate further developments of such green inhibitors for gas hydrate formation.
While kinetic hydrate inhibitors (KHIs) have seen increasing use in the hydrocarbon production industry as a cost effective hydrate mitigation strategy, there is still a lack of understanding concerning inhibition mechanisms and the underlying factors, which influence this. For example, little is known about the effect of gas composition even though this plays a major role, with lean acid gases presenting a particular challenge to KHIs. In this study, a Crystal Growth Inhibition (CGI) method previously developed in-house has been used to examine the effect of acidic gases on KHI performance. Using poly-n-vinylcaprolactam (PVCap) as the KHI, the effect of CO2 and H2S on different gas mixtures has been measured in detail for pressures up to ∼14.0MPa. In addition, the effect of a low pH resulting from hydrochloric, acetic and citric acids on PVCap methane hydrate inhibition has been investigated for comparison. Based on experimental results and thermodynamic modelling, it is concluded that hydrate growth from dissolved gas - a significant factor for water miscible H2S and CO2 - does not appear to play a major role in KHI performance. Likewise, a pH reduction itself does not seem to have a notable influence. Instead, results point to changes in cage occupancy patterns/guest gas composition a function of pressure as having the greatest effect on KHI inhibition, potentially by changing the strength of polymer absorption on different hydrate crystal faces.
In the present work, the effect of new structures of amino acids is studied for prevention of hydrate formation in the carbon dioxide–water system. These amino acids consist of L-proline (as amino acid with nonpolar side chain), L-serine and L-glutamine (as amino acids with polar side chain), and L-histidine (as amino acid with charged side chain). The inhibition effects of these amino acids were compared with glycine, L-threonine, and poly-N-vinylpyrrolidone (PVP). Experiments were performed in the concentration range of 0.5–2 wt.%. Investigation on the experimental results shows that inhibition properties of amino acids in an aqueous solution was due to hydrophobicity, the net charge of amino acid, and electrically charge of the side chain. Based on the experimental results, the ranking of amino acids (to decrease the hydrate growth rate) is as follows: L-histidine > glycine > L-proline ≈ L-serine ≈ L-threonine > L-glutamine, although the inhibition effect of some amino acids is not significant. In addition, the inhibition effects of these amino acids are quantitatively described by the chemical affinity model. The predicted results confirm that some of the applied amino acids decrease CO2 hydrate formation rate.
This paper presents the macroscopic observation of catastrophic gas hydrate growth during a shut-in, cold start-up and flowing conditions, simulating a natural gas transmission line operation. All experiments are conducted with a fixed simulated natural gas composition to form structure II gas hydrate with 11 K subcooling in the isochoric rocking cells. In order to simulate inhibited test systems, a formulated copolymer of vinylpyrolidone and vinylcaprolactam (PVP/PVCap) is included in some of the cells studied. Detailed macroscopic images and interpretation of pressure (P) and temperature (T) data are used to present our findings. It is found that production profiles such as different shut-in time and the mechanism of mass transfer of water from the bulk water phase to gas hydrate phase influence the gas hydrate growth in distinctive ways. Moreover, the capillary force in the gas hydrate structure may provide a greater driving force to promote gas hydrate growth than the diffusion rate of gases into the bulk water phase under shut-in and cold-start up conditions. Additionally, the number of critical nuclei formed during the initial stage of gas hydrate growth may influence the type of bulk gas hydrate present in the system at a later stage, i.e., finely dispersed hydrates or a slush type of gas hydrate.
The development of polymeric and oligomeric chemical additives that can control the nucleation and growth of gas hydrates remains a topic of major research interest, with important implications for energy security and the environment. In this paper we present a molecular dynamics study of eight different oligomeric compounds that have been proposed as potential kinetic inhibitors for methane hydrate. The results show that statistically significant variations in hydrate formation, induced by the chemical additive, can be observed within a relatively modest series of molecular dynamics simulations, thus opening the way for computational screening for optimal additives to control hydrate formation. One amino acid oligomer, asparagine, was found to be more active than a number of synthetic inhibitors, including PVCap.
We present a new method to observe the kinetics of methane hydrate formation by the simultaneous application of macroscopic and microscopic measurements. In a stirred tank stabilized under two different subcooling conditions, both the consumption rate of methane by water and in situ Raman spectra were measured with time. According to our observations, an abrupt decline in the intensity of the Raman peak of dissolved methane coincided with an increase in the intensity of the Raman peak of methane that occupies the large cages of the hydrate at the beginning of hydrate formation. The occupancy of the small cages only occurred after a considerable delay from the nucleation point, whereas the occupancy of the large cages occurred throughout the growth period. Thus, the early stage of hydrate growth shows a strong preference of the dissolved methane to occupy the large cages.
Low dosage kinetic hydrate inhibitors are employed as alternatives to expensive thermodynamic inhibitors to manage the risk of hydrate formation inside oil and gas pipelines. These chemicals need to be tested at appropriate conditions in the laboratory before deployment in the field. A high pressure micro differential scanning calorimeter HP-μDSC VII (Setaram Inc.) containing two 50 cc high pressure cells (maximum operating pressure 40 MPa; temperature range-40 to 120 °C) was employed to observe methane hydrate formation and decomposition in the presence of hyperactive antifreeze protein from Rhagium mordax (RmAFP) and biodegradable synthetic kinetic inhibitor Luvicap Bio. A systematic capillary dispersion method was used, and this method enhanced the ability to detect the effect of various inhibitors on hydrate formation with small quantities. The presence of RmAFP and Luvicap Bio influence (inhibit) the hydrate formation phenomena significantly. Luvicap Bio (relative strength compared to buffer: 13.3 °C) is stronger than RmAFP (9.8 °C) as a nucleation inhibitor. However, the presence RmAFP not only delays hydrate nucleation but also reduces the amount of hydrate formed (20%-30%) after nucleation significantly. Unlike RmAFP, Luvicap Bio promoted the amount of hydrate formed after nucleation. The superior hydrate growth inhibition capability and predictable hydrate melting behavior compared to complex, heterogeneous hydrate melting with Luvicap Bio shows that RmAFP can be a potential natural green kinetic inhibitor for hydrate formation in pipelines.
A series of poly(β-peptoid)s, specifically poly(N-alkyl-β-alanine) homopolymers and copolymers with various N-alkyl substituents, have been synthesized. The activity of poly(β-peptoid)s as kinetic hydrate inhibitors (KHIs) was studied for the first time. Gas hydrate inhibition was studied in high-pressure rocking cells using a synthetic natural gas blend to promote the formation of gas hydrate structure II. The best gas hydrate kinetic inhibition was observed with poly(N-ethyl-β-alanine)-co-N-propyl-β-alanine) with a molecular weight of 4075 Da. The structure-activity relationship (SAR) observed in this investigation confirms the notion that, for water-soluble polymers, the presence of larger aliphatic side chains leads to improved kinetic inhibition. Two isomeric forms of poly(N-ethyl-β-alanine)-co-N-propyl-β-alanine) were studied, a random copolymer and a block copolymer. The random isomeric form performed better than the block analogue. This fact suggests that the correct molecular spacing of the monomeric units is required for best kinetic hydrate inhibition. To our knowledge, this is the first report comparing the KHI performance of random and block copolymers of the same molecular weight and empirical formula.
Certain organisms survive low temperatures using a range of physiological changes including the production of antifreeze proteins (AFPs), which have evolved to adsorb to ice crystals. Several of these proteins have been purified and shown to also inhibit the crystallization of clathrate hydrates. They have been found to be effective against structure II (sII) hydrates formed from the liquid tetrahydrofuran, sI and sII gas hydrates formed from single gases, as well as sII natural gas hydrates using a mixture of three gases, as assessed using a variety of instrumentation including stirred reactors, differential scanning calorimetry, nuclear magnetic resonance, Raman spectroscopy and X-ray powder diffraction. For the most part, AFPs are equal or more effective than the commercial kinetic hydrate inhibitor (KHI) polyvinylpyrolidone, even under field conditions where saline and liquid hydrocarbons are present. Enclathrated gas analysis has revealed that the adsorption of AFPs to the hydrate surface is distinct from tested commercial KHIs, and results in properties that should make these proteins more valuable in some field applications. Efforts to overcome the difficulties of recombinant protein production are ongoing but in silico models of AFP adsorption to hydrates may offer the opportunity to design commercial KHIs for hydrocarbon recovery and transport with all the attributes of these AFP ‘green inhibitors’ including their benefits for human and environmental safety.
The formation of hydrate plugs in oil and gas pipelines is a serious industrial problem and recently there has been an increased interest in the use of alternative hydrate inhibitors as substitutes for thermodynamic inhibitors like methanol. We show here that antifreeze proteins (AFPs) possess the ability to modify structure II (sII) tetrahydrofuran (THF) hydrate crystal morphologies by adhering to the hydrate surface and inhibiting growth in a similar fashion to the kinetic inhibitor poly-N-vinylpyrrolidone (PVP). The effects of AFPs on the formation and growth rate of high-pressure sII gas mix hydrate demonstrated that AFPs are superior hydrate inhibitors compared to PVP. These results indicate that AFPs may be suitable for the study of new inhibitor systems and represent an important step towards the development of biologically-based hydrate inhibitors.
Kinetic experiments were performed on a methane-water system in the presence of Type-I Antifreeze Proteins (AFPs) in order to elucidate their effectiveness as kinetic hydrate inhibitors, specifically their effect on the hydrate growth period. The results were compared to experiments done with a classical polymeric kinetic hydrate inhibitor, N-vinylpryrrolidone-co-N-vinylcaprolactam [poly(VP/VC)] at the same pressure, temperature and weight percent conditions. As well, a series of experiments was conducted on poly(VP/VC) to examine the effect of concentration on hydrate growth inhibition. Experiments were performed at temperatures between 275.15 and 279.15 K and pressures between 5800 and 7200 kPa. The effect of the polymer on the hydrate growth profile was examined as well as the effect of temperature and pressure on the performance of the polymer and the protein.
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In the oil and gas industry there is ample motivation for moving toward greener kinetic inhibitors of gas hydrates as many of those used today suffer from poor biodegradability. In this work, we have investigated experimentally whether ice-structuring proteins (ISPs) found in fish and insect, assumed biodegradable, are capable of inhibiting the growth of methane hydrate (a structure I hydrate). The ISPs investigated were type III HPLC12 (originally identified in ocean pout) and ISP type III found in meal worm (Tenebrio molitor). These were compared to polyvinylpyrrolidone (PVP) a well-known kinetic hydrate inhibitor. The results revealed that adding ISP in sufficient amounts caused the appearance of an initial nonlinear growth period. At a certain point during the growth process the growth pattern changed to linear which is identical to the growth observed for methane hydrate in the absence of inhibitors. The profile of the nonlinear growth was concentration-dependent but also dependent on the stirring rate. ISP type III HPLC12 decreased the growth rate of methane hydrate during the linear growth period by 17−75% at concentrations of 0.01−0.1 wt % (0.014−0.14 mM) while ISP from Tenebrio molitor and PVP decreased the growth rate by 30% and 39% at concentrations of 0.004 wt % (0.005 mM) and 0.1 wt % (0.1 mM), respectively. Considering the low concentration of Tenebrio molitor ISP used, these results indicate that ISP from Tenebrio molitor is the most effective hydrate inhibitor among those investigated. Thermal hysteresis ice formation experiments revealed that ISP from Tenebrio molitor causes higher thermal hysteresis for ice formation compared to type III ISP identified in ocean pout while PVP did not cause thermal hysteresis. This indicates that there might be a direct relationship between ISP performance for ice and hydrate inhibition, and that thermal hysteresis experiments can be used to screen ISPs as kinetic inhibitors.
Clathrate hydrates or gas hydrates are solid solutions. Water molecules are linked through hydrogen bonding and create cavities (host lattice) that can enclose a large variety of molecules (guests). There is no chemical bonding between the host water molecules and the enclosed guest molecule. The clathrate hydrate crystal may exist at temperatures below as well as above the normal freezing point of water. Clathrate hydrates have been a source of problems in the energy industry because the conditions at which oil and gas are produced, transported, and processed are frequently suitable for clathrate hydrate formation. Naturally occurring clathrate hydrates in the earth, containing mostly methane, are regarded as a future energy resource. These methane hydrates, however, are potentially threatening to the global environment if they decompose due to the greenhouse effect. Several innovative separations based on clathrate hydrate formation with applications in a variety of industrial sectors have been examined in the laboratory and pilot-plant stage. This paper reviews the status of current knowledge on clathrate hydrates. The emphasis is on the aspects related to technological problems and opportunities that arise from the artificial or natural formation and decomposition of clathrate hydrates. However, a description of the fundamentals of formation, properties, and structure is also presented, and aspects related to the molecular simulation are discussed. Studies on calorimetric properties, orientational disorder, guest-guest interactions, and nuclear magnetic resonance are not reviewed, but literature references are made. Clathrate hydrates arouse great interest within chemical and petroleum engineering, chemistry, earth, and environmental sciences.
A synthetic natural gas mixture composed of methane, ethane, and propane in a batch reactor was used to form gas hydrates in the presence of two commercial, chemical kinetic inhibitors, polyvinylpyrrolidone (PVP) and H1W85281, and one biological inhibitor, antifreeze protein type III (AFP-III). Powder X-ray diffraction and nuclear magnetic resonance spectroscopy showed that structure II hydrates dominated, as expected, but in the presence of the chemical inhibitors, structure I was also present. Raman spectroscopy confirmed the complexity and the heterogeneity of the guest composition within these hydrates, which was also consistent with the gas analysis obtained using gas chromatography. However, in the presence of AFP-III, hydrates appeared to be relatively homogeneous structure II hydrates, with weaker evidence of structure I. When individual gas cage occupancies were calculated, both classes of inhibitors reduced large cage methane occupancy by 25%. With the chemical inhibitors, these large cage methane guests appeared to be substituted by ethane, likely resulting in a decreased driving force for hydrate production. In contrast to the near full occupancy of large cages with these inhibitors, almost 10% of the large cages were not filled when hydrates were formed in the presence of AFP-III, likely contributing to the easy decomposition of such hydrates seen in other studies. Therefore, hydrates formed in the presence of these two classes of inhibitors appear to be distinct, and as a consequence, their inhibition mechanisms, as well their practical utility in the field, are likely to be marked by important differences.
A newly fabricated, stirred reactor was used to investigate hydrate inhibition and decomposition in the presence of two commercial, chemical kinetic inhibitors, polyvinylpyrrolidone (PVP) and H1W85281, as well as two antifreeze proteins (AFPs), type I and type III. The longest induction times and the slowest growth rates were observed with HIW8581, with the fastest growth recorded for PVP. Type I AFP (AFP-I) was a more effective inhibitor, with respect to induction time and growth, than either PVP or type III AFP (AFP-III). Complete hydrate decomposition occurred earlier in the presence of any of the inhibitors compared to water controls. However, depending on the type of inhibitor present during crystallization, hydrate decomposition profiles were distinct, with a longer, two-stage decomposition profile in the presence of the chemical kinetic inhibitors (PVP and H1W85281). The fastest, single-stage decompositions were characteristic of hydrates in experiments with either of the AFPs. These results argue that thought must be given to inhibitor-mediated decomposition kinetics in screens and designs of potential kinetic inhibitors. This is a necessary, practical consideration for industry in cases when, because of long shut in periods, hydrate formation may be unavoidable, even when inhibitors are utilized.
The effect of kinetic inhibitors, both chemical (PVP and H1W85281) and biological (type III antifreeze protein), on natural gas hydrate formation was investigated using high pressure differential scanning calorimetry (HP-DSC). The presence of inhibitors decreased the overall formation of methane/ethane/propane hydrate compared to systems without added inhibitors. As well, all of the inhibitors significantly delayed hydrate nucleation as compared to water controls. However, the two classes of inhibitors were distinguished by the formation of hydrates with different stabilities. A single hydrate melting peak was seen with the antifreeze protein (AFP), and this was consistent after recrystallization. In contrast, multiple hydrate melting events, some indicating the formation of hydrate structures with high stability, were observed in the presence of the chemical inhibitors, and these varied depending on the crystallization cycle. This heterogeneity suggests that the use of these chemical inhibitors (PVP and H1W85281) may present a special challenge to operators depending upon the gas mixture and environmental conditions and that AFPs may offer a more predictable, efficacious solution in these cases.
The formation of methane hydrate in an unconsolidated bed of silica sand was investigated and spatially resolved by employing the magnetic resonance imaging technique. Different sand particle size ranges (210–297, 125–210, 88–177, and <75 μm) and different initial water saturations (100, 75, 50, and 25%) were used. It was observed that hydrate formation in such porous media is not uniform, and nucleation of hydrate crystals occurs at different times and different positions inside the bed. Also, hydrate formation was found to be faster in a bed with lower water content and smaller particle size. Decomposition of hydrate by thermal stimulation at constant volume showed that the dissociation front moves radially inward starting from the external surface of the hydrate formation vessel.
Use of low-dosage hydrate inhibitors in oil and gas field applications has been limited mainly because there are uncertainties related to their efficiency in preventing hydrate formation or because of environmental restrictions. Another question that normally arises in connection with use of low-dosage hydrate inhibitors is how they interact with other (than water) compounds normally found in oil and gas production pipelines. In this work three different experimental approaches to obtain hydrate induction times have been tested for structure I and II hydrate. All experiments were conducted in a high-pressure stirred cell. The results suggest that by adding small amounts of impurities to the hydrate-forming system a significant improvement in the reproducibility of induction times can be obtained. Adding salt and heptane to the system (as a simple model for seawater and a light crude) was found to increase the hydrate formation rate. Ice-structuring protein type III identified in the ocean pout, a biological inhibitor, was added to the various hydrate-forming systems to investigate its potential as a low-dosage hydrate inhibitor. As a reference, polyvinylcaprolactam, a well-known and quite effective kinetic inhibitor was used. The ice-structuring protein was found to outperform polyvinylcaprolactam for both structure I and structure II hydrate, suggesting that ice-structuring proteins hold a promising potential as environmentally friendly kinetic hydrate inhibitors.
The effect of kinetic inhibitors on the morphology of methane structure I hydrate was observed using a high pressure sapphire crystallizer. Two kinetic inhibitors were studied, poly(VP/VC), a lactam ring copolymer of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap), and type-I antifreeze protein (AFP). The experiments were performed at temperatures ranging from 274.2 to 275.2 K and pressures from 4200 to 7200 kPa. The experiments were conducted on three droplets simultaneously (a pure water droplet, a droplet containing 0.01 mol/m3 poly(VP/VC), and a droplet containing 0.01 mol/m3 AFP). The morphology and translucency were compared and found to vary significantly due to the presence of kinetic inhibitors. Hydrates formed under a higher driving force had dendrite formation on all but the AFP droplet. Low driving force experiments produced noticeably smoother surfaces on all droplets compared to high driving force experiments. Translucency also varied with AFP and poly(VP/VC) having the appearance of thinner films. Hydrate decomposition was also studied. The pure water droplet had the fastest rate of decomposition, followed by the droplet containing the AFP. The poly(VP/VC) droplet has a visible hydrate skin for a substantially longer period of time than the pure water and the AFP droplet.
The kinetics of hydrate formation and decomposition are explained as understood to date. The formation and decomposition phenomena are complex. Hydrate formation is viewed as a crystallization process that includes the nucleation and growth processes. Hydrate nucleation is an intrinsically stochastic process that involves the formation and growth of gas-water clusters to critical sized, stable hydrate nuclei. Hydrate growth process involves the growth of stable hydrate nuclei as solid hydrates. Hydrate decomposition is a sequence of lattice destruction and gas desorption processes. The process of heat transfer during hydrate decomposition is analogous to nucleate boiling phenomena. The focus of this work is to present the various perspectives on the kinetic processes at a conceptual level. Key issues for research in this area are identified and some possible directions for future work are suggested.
The formation of gas hydrates in gas and oil subsea pipelines often results in blockage and shutdown of these pipelines. Modern control methods depend on understanding the mechanisms through which gas hydrates form. This paper reviews our recent studies of clathrate hydrate formation and inhibition mechanisms using neutron diffraction, differential scanning calorimetry (DSC) and a multiple cell photo-sensing instrument. The structural transformations of water around methane during methane hydrate formation have been studied using neutron diffraction with isotope substitution over the temperature range 4–18 °C and at pressures of 3.4–14.5 MPa. The hydration sphere around methane in the liquid only changes significantly when methane hydrate is formed, with the water shell in the crystalline hydrate being about 1 Å larger than the shell in the liquid. The hydration shell is disordered during methane hydrate formation, with ordering of solvent separated methane molecules occurring only when hydrate has formed. The effects of the addition of three low dosage hydrate inhibitors, PVP, VC-713 and QAB on THF hydrate formation at the surface and in bulk solution have been examined. The QAB inhibitor exhibits the greatest hydrate crystal growth control, while VC-713 is most effective at inhibiting hydrate nucleation. Insight into the perturbations on host and guest molecules due to the presence of these inhibitor molecules has been obtained.
An intrinsic kinetic model with only one adjustable parameter is proposed for the formation of methane and ethane gas hydrates. Experimental formation data were obtained in a semi-batch stirred tank reactor. The experiments were conducted at four temperatures from 274 to 282 K and at pressures ranging from 0.636 to 8.903 MPa. The kinetic model is based on the crystallization theory, while the two-film theory model is adopted for the interfacial mass transfer. Experiments were performed at various stirring rates to define the kinetic regime. The study reveals that the formation rate is proportional to the difference in the fugacity of the dissolved gas and the three-phase equilibrium fugacity at the experimental temperature. This difference defines the driving force which incorporates the pressure effects. The gas consumption rate is also proportional to the second moment of the particle size distribution. The rate constants indicate a very weak temperature dependence.
Formation of methane hydrate in Bentheim sandstone was monitored in situ with magnetic resonance imaging (MRI). Sequestration of CO2 in hydrate accumulations was achieved by exposing the hydrate to liquid CO2. The spontaneous exchange of methane with CO2 within the hydrate structure was monitored by MRI. The process of CO2–CH4 exchange in hydrates without the addition of heat or melting hydrate has the potential as a viable strategy for thermodynamically stable long term CO2-sequestration, with the added benefit of associated natural gas production. The MRI proved to give excellent information about the spatial distribution of the hydrate growth, the rate of the hydrate formation and the rate of the CO2–CH4 exchange. A standardized and reliable data analysis software package was developed to handle the huge amount of MRI-generated data.
A Seafloor Process Simulator (SPS) has been used for mesoscale experiments investigating the nature of hydrate nucleation and dissociation. The SPS is a 72 L vessel which establishes the pressures and temperatures required for methane and carbon dioxide hydrate stability. This paper describes the experiments that have been performed in the SPS and have been duplicated in the smaller Parr vessel (450 mL). It was found that experiments in the SPS resulted in hydrates consistently forming at lower overpressures and in shorter induction times than equivalent experiments in the Parr vessel. The variability of pressure and/or induction time for hydrate formation was not eliminated by using the SPS, but it appeared to be less dramatic (small coefficients of variation) when compared with a 450 mL Parr vessel. Based on the experiments performed using the SPS this reduction in overpressure and/or induction time required for the accumulation of hydrates may be attributed to increased bubble surface area, increased gas concentration, increased lifetime of bubbles, increased total volume of the SPS, or a combination of the above. Mesoscale experiments, such as those in the SPS, may perhaps be more representative of hydrate accumulation in the natural environment.
After obtaining experimental data of CO(2) hydrate formation and dissociation in a porous medium using magnetic resonance imaging (MRI), the purpose of this study was to analyze the different dissociation rate of CO(2) hydrate using two heating rates. Images were obtained by using a fast spin-echo sequence, and the field of view was set to 40×40×40 mm. The vessel pressure was monitored during hydrate formation and dissociation, which was used to compare with MRI mean intensity. The result indicated that the MRI could visualize hydrate formation and dissociation, and the MRI mean intensity of water was in good agreement with the vessel pressure changes. The hydrate formation and dissociation rates were also quantified using the MRI mean intensity of water. The experimental results showed that the higher heating rate caused the rapid hydrate dissociation.
Tetrahydrofuran (THF) hydrate has long been used as a substitute for methane hydrate in laboratory studies. This article investigated the formation and dissociation characteristics of THF hydrate in porous media simulated by various-sized quartz glass beads. The formation and dissociation processes of THF hydrate are observed using magnetic resonance imaging (MRI) technology. The hydrate saturation during the formation is obtained based on the MRI data. The experimental result suggests that the third surface has an effect on hydrate formation. THF hydrate crystals lean to form on the glass beads and in their adjacent area as well as from the wall of the sample container firstly. Furthermore, as the pore size diminishes, or as the formation temperature decreases, the nucleation gets easier and the formation processes faster. However, the dissociation rate is mostly dependent on the dissociation temperature rather than on the pore size.
Recombinant antifreeze proteins (AFPs), representing a range of activities with respect to ice growth inhibition, were investigated for their abilities to control the crystal formation and growth of hydrocarbon hydrates. Three different AFPs were compared with two synthetic commercial inhibitors, poly-N-vinylpyrrolidone (PVP) and HIW85281, by using multiple approaches, which included gas uptake, differential scanning calorimetry (DSC) temperature ramping, and DSC isothermal observations. A new method to assess the induction period before heterogeneous nucleation and subsequent hydrate crystal growth was developed and involved the dispersal of water in the pore space of silica gel beads. Although hydrate nucleation is a complex phenomenon, we have shown that it can now be carefully quantified. The presence of AFPs delayed crystallization events and showed hydrate growth inhibition that was superior to that of one of the benchmark commercial inhibitors, PVP. Nucleation and growth inhibition were shown to be independent processes, which indicates a difference in the mechanisms required for these two inhibitory actions. In addition, there was no apparent correlation between the assayed activities of the three AFPs toward hexagonal ice and the cubic structure II (sII) hydrate, which suggests that there are distinctive differences in the protein interactions with the two crystal surfaces.
The effect of Type I antifreeze protein (AFP) from winter flounder on the formation of propane hydrate and methane hydrate was studied. We show that the formation of both hydrates is inhibited significantly, with both nucleation and crystal growth being affected. Also, AFP showed the so-far unique ability to eliminate the ldquomemory effectrdquo in the reformation of gas hydrate. We have proposed a mechanism involving the interference of AFP with heterogeneous nucleation and subsequent growth of the hydrates. It is also shown that a number of samples must be studied in order to obtain meaningful statistics, and that magnetic resonance imaging provides a novel way of studying the nucleation and growth of hydrate in multiple droplets. ? 2006 American Institute of Chemical Engineers AIChE J, 2006
Abstract: We have used 1H magnetic resonance microimaging to probe both methane and carbon dioxide hydrate formation processes inside dispersed water droplets. When bulk techniques such as gas uptake measurements are used for determining the kinetics of hydrate formation, these show a gradual conversion to hydrate, suggesting a relatively homogeneous process that might be modeled using a set of intrinsic kinetic parameters. The spatially resolved microimaging measurements show that in fact the conversion to hydrate is quite inhomogeneous, some drops converting quickly, others requiring hours or days. This indicates that the observation of gradual conversion in bulk samples only arises as a result of averaging over many local environments. Quantitative measurements of kinetic processes in subvolumes of a larger sample suggests that the smaller the volume observed, the more inhomogeneous the process appears to be. When hydrate-coated water droplets in 3,5,5-trimethylpentane are converted to hydrate, there is evidence that nucleation can take place well away from the hydrate coating, with the hydrate sometimes growing in discrete steps before drops are completely converted. The results obtained indicate that in the quiescent systems studied here the definition of intrinsic kinetic parameters will be difficult, if possible at all, because of a stochastic component that competes with more gradual conversion processes.
The effect of Type I fish antifreeze protein (AFP) from the winter flounder, Pleuronectes americanus (Walbaum), (WfAFP) on the formation of tetrahydrofuran (THF) clathrate hydrate was studied by observing changes in THF crystal morphology and determining the induction time for nucleation. AFP retarded THF clathrate-hydrate growth at the tested temperatures and modified the THF clathrate-hydrate crystal morphology from octahedral to plate-like. AFP appears to be even more effective than the kinetic inhibitor, polyvinylpyrrolidone (PVP). Recombinant AFP from an insect, a spruce budworm, Choristoneura fumiferana (Clem.), moth, (Cf) was also tested for inhibition activity by observation of the THF-hydrate-crystal-growth habit. Like WfAFP, CfAFP appeared to show adsorption on multiple THF-hydrate-crystal faces. A protein with no antifreeze activity, cytochrome C, was used as a control and it neither changed the morphology of the THF clathrate-hydrate crystals, nor retarded the formation of the hydrate. Preliminary experiments on the inhibition activity of WfAFP on a natural gas hydrate assessed induction time and the amount of propane gas consumed. Similar to the observations for THF, the data indicated that WfAFP inhibited propane-hydrate growth. Taken together, these results support our hypothesis that AFPs can inhibit clathrate-hydrate growth and as well, offer promise for the understanding of the inhibition mechanism.
PACS No.: 87.90ty
Crystallization of water or water-encaged gas molecules occurs when nuclei reach a critical size. Certain antifreeze proteins (AFPs) can inhibit the growth of both of these, with most representations conceiving of an embryonic crystal with AFPs adsorbing to a preferred face, resulting in a higher kinetic barrier for molecule addition. We have examined AFP-mediated inhibition of ice and clathrate hydrate crystallization, and these observations can be both explained and modeled using this mechanism for AFP action. However, the remarkable ability of AFPs to eliminate „memory effect‟ (ME) or the faster reformation of clathrate hydrates after melting, prompted us to examine heterogeneous nucleation. The ubiquitous impurity, silica, served as a model nucleator hydrophilic surface. Quartz crystal microbalance-dissipation (QCM-D) experiments indicated that an active AFP was tightly adsorbed to the silica surface. In contrast, polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap), two commercial hydrate kinetic inhibitors that do not eliminate ME, were not so tightly adsorbed. Significantly, a mutant AFP (with no activity toward ice) inhibited THF hydrate growth, but not ME. QCM-D analysis showed that adsorption of the mutant AFP was more similar to PVCap than the active AFP. Thus, although there is no evidence for „memory‟ in ice reformation, and the structures of ice and clathrate hydrate are distinct, the crystallization of ice and hydrates, and the elimination of the more rapid recrystallization of hydrates, can be mediated by the same proteins. Other Other
Magnetic resonance imaging was used to monitor and quantify methane hydrate formation and exchange in porous media. Conversion of methane hydrate to carbon dioxide hydrate, when exposed to liquid carbon dioxide at 8.27 MPa and approximately 4 degrees C, was experimentally demonstrated with MRI data and verified by mass balance calculations of consumed volumes of gases and liquids. No detectable dissociation of the hydrate was measured during the exchange process.
The inhibition activities of two antifreeze proteins (AFPs) on the formation of tetrahydrofuran (THF) clathrate hydrate have been tested. AFPs from fish (wfAFP) and insect (CfAFP) changed the morphology of growing THF hydrate crystals. Also, both AFPs showed higher activities in inhibiting the formation THF hydrate than a commercial kinetic inhibitor, poly(vinylpyrrolidone) (PVP). Strikingly, both AFPs also showed the ability to eliminate the "memory effect" in which the crystallization of hydrate occurs more quickly after the initial formation. This is the first report of molecules that can inhibit the memory effect. Since the homogeneous nucleation temperature for THF hydrate was measured to be 237 K, close to that observed for ice itself, the action of kinetic inhibitors must involve heterogeneous nucleation. On the basis of our results, we postulate a mechanism for heterogeneous nucleation, the memory effect and its elimination by antifreeze proteins.
Clathrate hydrates are of great importance in many aspects. However, hydrate formation and dissociation mechanisms, essential to all hydrate applications, are still not well understood due to the limitations of experimental techniques capable of providing dynamic and structural information on a molecular level. NMR has been shown to be a powerful tool to noninvasively measure molecular level dynamic information. In this work, we measured nuclear magnetic resonance (NMR) spin lattice relaxation times (T1's) of tetrahydrofuran (THF) in liquid deuterium oxide (D2O) during THF hydrate formation and dissociation. At the same time, we also used magnetic resonance imaging (MRI) to monitor hydrate formation and dissociation patterns. The results showed that solid hydrate significantly influences coexisting fluid structure. Molecular evidence of residual structure was identified. Hydrate formation and dissociation mechanisms were proposed based on the NMR/MRI observations.
Kinetics of gas hydrate formation. Part I. Kinetics of ethane gas hydrate formation. Part II Kinetics of natural gas hydrate formation. Report GRI-80/0100, Order no
- Pr Bishnoi
- Vsyniauskas
Bishnoi PR, Vsyniauskas A. Kinetics of gas hydrate formation. Part I. Kinetics of ethane gas hydrate formation. Part II. Kinetics of natural gas hydrate formation. Report GRI-80/0100, Order no. PB82-138868, Avail NTIS; 1980: p. 45.
New developments in the science of clathrate hydrates
- Ja Ripmeester
- Ratcliffe
- K Udachin
- I Moudrakovski
- Lu
- S Alavi
Ripmeester JA, Ratcliffe CI, Udachin K, Moudrakovski I, Lu HL, Alavi S, et al. New developments in the science of clathrate hydrates. Abstr Pap Am Chem Soc 2009:237.
Hydrate growth rate profiles in (a) MRI and (b) autoclave experiments. [12] Englezos P. Clathrate hydrates
- Fig
Fig. 6. Hydrate growth rate profiles in (a) MRI and (b) autoclave experiments.
[12] Englezos P. Clathrate hydrates. I EC Res 1993;32:1251–74.
Gas hydrate crystal growth and decomposition
- Ca Koh
- S Nyburg
- Ak Soper
- S Parker
- Re Westacott
- J Creek
- S Subramanian
Koh CA, Nyburg S, Soper AK, Parker S, Westacott RE, Creek J, Subramanian S.
Gas hydrate crystal growth and decomposition. In: Abstracts of papers, 223rd
ACS national meeting, Orlando, FL, United States; April 7–11, 2002: FUEL-111.