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Abstract
Advances in Synthesis Gas: Methods, Technologies and Applications: Syngas Products and Usage considers the applications and usages of syngas for producing different chemical materials such as hydrogen, methanol, ethanol, methane, ammonia, and more. In addition, power generation in fuel cells, or in combination with heat from syngas, as well as iron reduction with economic and environmental challenges for syngas utilization are described in detail.
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Catalyst systems for the conversion of synthesis gas, which are tolerant to fluctuating CO/CO2 gas compositions, have great potential for process-technical applications, related to the expected changes in the supply of synthesis gas. Copper-based catalysts usually used in the synthesis of methanol play an important role in this context. We investigated the productivity characteristics for their application in direct dimethyl ether (DME) synthesis as a function of the CO2/CO x ratio over the complete range from 0 to 1. For this purpose, we compared an industrial Cu/ZnO/Al2O3 methanol catalyst with a self-developed Cu/ZnO/ZrO2 catalyst prepared by a continuous coprecipitation approach. For DME synthesis, catalysts were combined with two commercial dehydration catalysts, H-FER 20 and γ-Al2O3, respectively. Using a standard testing procedure, we determined the productivity characteristics in a temperature range between 483 K and 523 K in a fixed bed reactor. The combination of Cu/ZnO/ZrO2 and H-FER 20 provided the highest DME productivity with up to 1017 gDME (kgCu h)-1 at 523 K, 50 bar and 36 000 mlN (g h)-1 and achieved DME productivities higher than 689 gDME (kgCu h)-1 at all investigated CO2/CO x ratios under the mentioned conditions. With the use of Cu/ZnO/ZrO2//H-FER 20 a promising operating range between CO2/CO x 0.47 and 0.8 was found where CO as well as CO2 can be converted with high DME selectivity. First results on the long-term stability of the system Cu/ZnO/ZrO2//H-FER 20 showed an overall reduction of 27.0% over 545 h time on stream and 14.6% between 200 h and 545 h under variable feed conditions with a consistently high DME selectivity.
Homo-acetogens are microbes that have the ability to grow on gaseous substrates such as H2/CO2/CO and produce acetic acid as the main product of their metabolism through a metabolic process called reductive acetogenesis. These acetogens are dispersed in nature and are found to grow in various biotopes on land, water and sediments. They are also commonly found in the gastro-intestinal track of herbivores that rely on a symbiotic relationship with microbes in order to breakdown lignocellulosic biomass to provide the animal with nutrients and energy. For this motive, the fermentation scheme that occurs in the rumen has been described equivalent to a consolidated bioprocessing fermentation for the production of bioproducts derived from livestock. This paper reviews current knowledge of homo-acetogenesis and its potential to improve efficiency in the rumen for production of bioproducts by replacing methanogens, the principal H2-scavengers in the rumen, thus serving as a form of carbon sink by deviating the formation of methane into bioproducts. In this review, we discuss the main strategies employed by the livestock industry to achieve methanogenesis inhibition, and also explore homo-acetogenic microorganisms and evaluate the members for potential traits and characteristics that may favor competitive advantage over methanogenesis, making them prospective candidates for competing with methanogens in ruminant animals.
Mesoporous gamma-alumina nanoparticles were synthesized using a green and sustainable approach. To this end, the Morus alba leaves were utilized as a biotemplate. Various treatment and infiltration parameters including wetting condition and temperature were employed to find out the best synthetic method. The nano alumina could further be used as a catalyst in various processes. Hence, conventional structural characterization techniques were employed to analyze nano alumina structure, including X-ray powder diffraction (XRD), N2 adsorption/desorption, and field emission scanning electron microscopy (FESEM). The presence of two prominent peaks in XRD patterns confirmed the formation of cubic γ-Al2O3 in all samples. In addition, the FESEM results showed a regular porous structure for treated leaves and exhibited the replication of leaves morphology in the samples. The acidity of the optimum nano alumina sample determined through temperature-programmed desorption of ammonia (NH3-TPD) technique. The temperature-programmed reduction of hydrogen (H2-TPR) proved the reduction of Al.
Graphical Abstract
The necessity of alleviating the environmental challenges associated with the steam-methane reforming (SMR) process has paved the way towards the utilization of clean alternative processes for the production of syngas and hydrogen. In this regard, auto-thermal chemical looping reforming (a-CLR) of methane has emerged as one of the most promising and energy-efficient alternatives. The current research is devoted to the feasibility study of an a-CLR process performed in a network of large-scale packed-bed reactors via a dynamic mathematical model. Here it is demonstrated that the large furnace of the conventional SMR process could be eliminated in the proposed a-CLR system at the expense of a 0.22 abatement in the yield of syngas. Further, based on the proposed cyclic design of the a-CLR process, for the continuous production of syngas a network of packed-bed reactors with seven and five furnace-free reactors in parallel are required for the high-capacity case, i.e. 184 tubes, and the low-capacity case, i.e. 115 tubes, respectively. The auto-thermal operation is not achievable completely in the high-capacity a-CLR case. However, by decreasing the total capacity by 38%, it is conceivable to fully cover the total heat demand in the low-capacity a-CLR case. Utilizing the optimum values of the inlet temperature and steam to carbon ratio as well as the initial oxidation degree in the optimized a-CLR case leads to a 17% enhancement in the methane conversion and also a 0.64 rise in the syngas yield in comparison with the non-optimized a-CLR case.
Graphic Abstract
The inevitable nexus between energy use and CO2 emission necessitates the development of sustainable energy systems. The conversion of CO2 to CH4 using green H2 in power-to-gas applications in such energy systems has attracted much interest. In this context, the present study provides a thermodynamic insight into the effect of water removal on CO2 conversion and irreversibility within a CO2 methanation reactor. A fixed-bed reactor with one intermediate water removal point, representing two reactors in series, was modeled by a one-dimensional pseudo-homogeneous model. Pure CO2 or a mixture of CO2 and methane, representing a typical biogas mixture, were used as feed. For short reactors, both the maximum conversion and the largest irreversibilities were observed when the water removal point was located in the middle of the reactor. However, as the length of the reactor increased, the water removal point with the highest conversion was shifted towards the end of the reactor, accompanied by a smaller thermodynamic penalty. The largest irreversibilities in long reactors were obtained when water removal took place closer to the inlet of the reactor. The study discusses the potential benefit of partial water removal and reactant feeding for energy-efficient reactor design.
Natural gas based hydrogen production with carbon capture and storage is referred to as blue hydrogen. If substantial amounts of CO2 from natural gas reforming are captured and permanently stored, such hydrogen could be a low-carbon energy carrier. However, recent research raises questions about the effective climate impacts of blue hydrogen from a life cycle perspective. Our analysis sheds light on the relevant issues and provides a balanced perspective on the impacts on climate change associated with blue hydrogen. We show that such impacts may indeed vary over large ranges and depend on only a few key parameters: the methane emission rate of the natural gas supply chain, the CO2 removal rate at the hydrogen production plant, and the global warming metric applied. State-of-the-art reforming with high CO2 capture rates combined with natural gas supply featuring low methane emissions does indeed allow for substantial reduction of greenhouse gas emissions compared to both conventional natural gas reforming and direct combustion of natural gas. Under such conditions, blue hydrogen is compatible with low-carbon economies and exhibits climate change impacts at the upper end of the range of those caused by hydrogen production from renewable-based electricity. However, neither current blue nor green hydrogen production pathways render fully “net-zero” hydrogen without additional CO2 removal.
The catalytic performance of Ni, Co, and Ni–Co-based catalysts on Al2O3 support are investigated in the dry methane reforming reaction. Besides, the influence of La or Y promoters on catalytic activity and structural properties of synthesized catalysts are examined in this paper. The prepared catalysts are characterized using N2 Adsorption/Desorption, FESEM, EDX, and XRD techniques. Higher average CH4 and CO2 conversions, as well as hydrogen yield, are obtained using Ni-Co catalyst with equal weight ratios. This could be the result of better dispersion of active sites according to the FESEM images and thus higher BET surface area of this catalyst compared with other un-promoted ones. Although the addition of La does not enhance the catalytic activity and structural properties of the 9Ni–9Co/Al2O3 sample, the presence of Y2O3 particles has a positive effect on both mentioned catalyst features. The maximum CH4 conversion of 99.39%, CO2 conversion of 92.38%, H2 yield of 86.20% and H2/CO molar ratio of 1.50 are achieved using 5Y–9Ni–9Co/Al2O3 at 700 °C. Besides, this catalyst shows lower deposited coke and higher stability compared with other promoted/un-promoted catalysts. The comparison between the activity of 5Y–9Ni–9Co/Al2O3 and industrial 18%Ni/Al2O3 during 11 h DRM shows that although 18%Ni/Al2O3 has higher conversions at first 9 h, its activity is decreased more than 5Y–9Ni–9Co/Al2O3 due to the coke deposition.
Herein, MIL-53(Al)@TiO2 photocatalyst with high photocatalytic performance in the presence of visible light was favorably fabricated using a solvothermal method. Characterization of MIL-53(Al)@TiO2 was carried out by Fourier transformation infrared (FTIR), X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the ultraviolet visible diffused reflectance spectra (DRS), and energy-dispersive X-ray (EDX) analyses, and its photocatalytic activity for the degradation of methylene blue (MB) dye was investigated. Compared with MIL-53(Al) and TiO2, the photocatalytic activity of MIL-53(Al)@TiO2 composite under visible light irradiation was improved. This improvement is attributed to the strategy used in composite synthesis without blocked of any hole by TiO2 nanoparticles. The synthesized MIL-53(Al)@TiO2 nanocomposite degraded 95% of the MB in 240 min without any electron acceptor, while the decolorization of dye by MIL-53(Al) and TiO2 was 51% and 79%, respectively. The data also indicated that the dye degradation by MIL-53(Al)@TiO2 followed first-order kinetic with high correlation coefficient (0.9927).
Micro-reactor (MR) technology is known as an alternative technique for producing materials in a more sustainable way. The advantages of micro-reactors and membrane separation which are combined in membrane micro-reactors (MMR) listed as improved heat and mass transfer, high surface area to volume ratio, enhanced catalytic efficiency with no equilibrium limitation, flexibility in reactor design, a short distance of molecular diffusion as well as high operational safety. The restriction of low production capacity of micro-reactors can be easily solved by using parallel micro-channels in a reactor chip. This mini-review represents firstly the definition of micro-reactors as well as the advantages and disadvantages of membrane micro-reactors. Furthermore, the theoretical basics of membrane micro-reactors and their fabrication methods are presented. At last, the application of catalytic membrane micro-reactors in different processes is given especially in biofuel production. The achieved results of previous researches for hydrogen and other fuels production show better performance of catalytic MMRs in terms of reaction conversion and coke deposition compared with convectional reactors at the same reaction conditions.
The dry reforming of CH4 (with CO2) at 800 °C under 1 MPa to synthesis gas and the synthesis of dimethyl ether (DME) from synthesis gas were combined. A Ni/(MgO)3·Al2O3 catalyst derived from Mg3Ni3Al2(OH)16CO3·xH2O hydrotalcite precursor showed a CH4 conversion of 85.4% after 5 min on stream for the dry reforming. The CH4 conversion decreased to 70.1% after 15 h on stream because the carbonaceous deposit formed during the reaction covered the active sites of Ni/(MgO)3·Al2O3 catalyst. The deactivated Ni/(MgO)3·Al2O3 catalyst was refreshed by calcining in air at 800 °C and subsequently reducing in H2. A mechanical mixed catalyst containing Cu/(ZnO)3·Al2O3 and Cs2.5H0.5PW12O40 (denoted as Cu/(ZnO)3·Al2O3 + Cs2.5) was used for the DME synthesis from syngas. Cu/(ZnO)3·Al2O3 + Cs2.5 showed a CO conversion of 38.5% and a DME selectivity of 63.8% at 260 °C under 1 MPa. A stable activity of Cu/(ZnO)3·Al2O3 + Cs2.5 had been maintained over 30 h in the DME synthesis. A two-stage process was designed for the DME synthesis from CH4 and CO2. Two fixed-bed reactors filled with Ni/(MgO)3·Al2O3 were connected in parallel (switching between reaction and refresh) for the CH4 dry reforming. A fixed-bed reactor filled with Cu/(ZnO)3·Al2O3 + Cs2.5 was connected in series with the two reactors filled with Ni/(MgO)3·Al2O3 to produce DME. The conversion of CH4 was kept at above 80% and the yield of DME was kept at above 20% after 30 h on stream for the DME synthesis from CH4 and CO2.
Graphic Abstract
A two-step process combining CH4 dry reforming to syngas and DME synthesis from syngas was designed for the DME synthesis from CH4 and CO2. The conversion of CH4 was kept at above 80% and the yield of DME was kept at above 20% after 30 h on stream in the two-stage process
Hydrogen is often viewed as an important energy carrier in a future decarbonized world. Currently, most hydrogen is produced by steam reforming of methane in natural gas (“gray hydrogen”), with high carbon dioxide emissions. Increasingly, many propose using carbon capture and storage to reduce these emissions, producing so‐called “blue hydrogen,” frequently promoted as low emissions. We undertake the first effort in a peer‐reviewed paper to examine the lifecycle greenhouse gas emissions of blue hydrogen accounting for emissions of both carbon dioxide and unburned fugitive methane. Far from being low carbon, greenhouse gas emissions from the production of blue hydrogen are quite high, particularly due to the release of fugitive methane. For our default assumptions (3.5% emission rate of methane from natural gas and a 20‐year global warming potential), total carbon dioxide equivalent emissions for blue hydrogen are only 9%‐12% less than for gray hydrogen. While carbon dioxide emissions are lower, fugitive methane emissions for blue hydrogen are higher than for gray hydrogen because of an increased use of natural gas to power the carbon capture. Perhaps surprisingly, the greenhouse gas footprint of blue hydrogen is more than 20% greater than burning natural gas or coal for heat and some 60% greater than burning diesel oil for heat, again with our default assumptions. In a sensitivity analysis in which the methane emission rate from natural gas is reduced to a low value of 1.54%, greenhouse gas emissions from blue hydrogen are still greater than from simply burning natural gas, and are only 18%‐25% less than for gray hydrogen. Our analysis assumes that captured carbon dioxide can be stored indefinitely, an optimistic and unproven assumption. Even if true though, the use of blue hydrogen appears difficult to justify on climate grounds.
Background
Rhodospirillum rubrum is a purple non-sulphur bacterium that produces H 2 by photofermentation of several organic compounds or by water gas-shift reaction during CO fermentation. Successful strategies for both processes have been developed in light-dependent systems. This work explores a dark fermentation bioprocess for H 2 production from water using CO as the electron donor.
Results
The study of the influence of the stirring and the initial CO partial pressure ( p CO ) demonstrated that the process was inhibited at p CO of 1.00 atm. Optimal p CO value was established in 0.60 atm. CO dose adaptation to bacterial growth in fed-batch fermentations increased the global rate of H 2 production, yielding 27.2 mmol H 2 l ⁻¹ h ⁻¹ and reduced by 50% the operation time. A kinetic model was proposed to describe the evolution of the molecular species involved in gas and liquid phases in a wide range of p CO conditions from 0.10 to 1.00 atm.
Conclusions
Dark fermentation in R. rubrum expands the ways to produce biohydrogen from CO. This work optimizes this bioprocess at lab-bioreactor scale studying the influence of the stirring speed, the initial CO partial pressure and the operation in batch and fed-batch regimes. Dynamic CO supply adapted to the biomass growth enhances the productivity reached in darkness by other strategies described in the literature, being similar to that obtained under light continuous syngas fermentations. The kinetic model proposed describes all the conditions tested.
The steel industry is an important engine for sustainable growth, added value, and high-quality employment within the European Union. It is committed to reducing its CO2 emissions due to production by up to 50% by 2030 compared to 1990′s level by developing and upscaling the technologies required to contribute to European initiatives, such as the Circular Economy Action Plan (CEAP) and the European Green Deal (EGD). The Clean Steel Partnership (CSP, a public–private partnership), which is led by the European Steel Association (EUROFER) and the Euro-pean Steel Technology Platform (ESTEP), defined technological CO2 mitigation pathways com-prising carbon direct avoidance (CDA), smart carbon usage SCU), and a circular economy (CE). CE approaches ensure competitiveness through increased resource efficiency and sustainability and consist of different issues, such as the valorization of steelmaking residues (dusts, slags, sludge) for internal recycling in the steelmaking process, enhanced steel recycling (scrap use), the use of secondary carbon carriers from non-steel sectors as a reducing agent and energy source in the steelmaking process chain, and CE business models (supply chain analyses). The current paper gives an overview of different technological CE approaches as obtained in a dedi-cated workshop called “Resi4Future—Residue valorization in iron and steel industry: sustaina-ble solutions for a cleaner and more competitive future Europe” that was organized by ESTEP to focus on future challenges toward the final goal of industrial deployment.
Formaldehyde is a primary chemical in the manufacturing of various consumer products. It is synthesized via partial oxidation of methanol using a mixed oxide iron molybdate catalyst (Fe2(MoO4)3–MoO3). This is one of the standard energy-efficient processes. The mixed oxide iron molybdate catalyst is an attractive commercial catalyst for converting methanol to formaldehyde. However, a detailed phase analysis of each oxide phase and a complete understanding of the catalyst formulation and deactivation studies is required. It is crucial to correctly formulate each oxide phase and influence the synthesis methods precisely. A better tradeoff between support and catalyst and oxygen revival on the catalyst surface is vital to enhance the catalyst’s selectivity, stability, and lifetime. This review presents recent advances on iron molybdate’s catalytic behaviour for formaldehyde production—a deep recognition of the catalyst and its critical role in the processes are highlighted. Finally, the conclusion and prospects are presented at the end.
In this work, the modification of Ni/SBA-16 oxygen carrier (OC) with yttrium promoter is investigated. The yttrium promoted Ni-based oxygen carrier was synthesized via co-impregnation method and applied in chemical looping steam methane reforming (CL-SMR) process, which is used for the production of clean energy carrier. The reaction temperature (500–750 °C), Y loading (2.5–7.4 wt. %), steam/carbon molar ratio (1–5), Ni loading (10–30 wt. %) and life time of OCs over 16 cycles at 650 °C were studied to investigate and optimize the structure of OC and process temperature with maximizing average methane conversion and hydrogen production yield. The synthesized OCs were characterized by multiples techniques. The results of X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) of reacted OCs showed that the presence of Y particles on the surface of OCs reduces the coke formation. The smaller NiO species were found for the yttrium promoted OC and therefore the distribution of Ni particles was improved. The reduction-oxidation (redox) results revealed that 25Ni-2.5Y/SBA-16 OC has the highest catalytic activity of about 99.83% average CH4 conversion and 85.34% H2 production yield at reduction temperature of 650 °C with the steam to carbon molar ratio of 2.
This work aims to evaluate the potential to produce synthetic nitrogen fertilizers from sugarcane bagasse in São Paulo state, Brazil. An ammonia synthesis plant with biomass gasification at atmospheric pressure is fed with residual sugarcane bagasse from one or more sugarcane mills. Three energy resources, namely syngas, electricity or natural gas are used as utility fuel, in order to partially or totally decarbonize the production of ammonia. Two scenarios were analyzed, the alternative one considering bagasse surplus from the mill for ammonia production, and the conventional one, with no bagasse surplus, aiming to separately generate electricity to the grid in the sugar cane mill and produce ammonia by using a typical steam methane reforming plant. The analysis also includes the transportation of surplus bagasse from a first sugarcane mill 20 km far from the ammonia plant localization. In turn, the ammonia plant proposed settles nearby a second sugarcane mill with milling capacity of 10 Mt/y, reportedly the world's largest milling capacity. As a result, an ammonia production of 1235 tNH3/day is estimated. If a discount rate of 8% and no carbon taxes are considered, the net present value of the scenarios with biomass gasification decreased by 39 to 52% compared to the conventional scenario, whereas the modified internal rate of return ranges from 14.5-19.1%. Regarding the unit exergy cost of ammonia, an increase from 54 to 100% is expected when biomass gasification scenarios are compared to the conventional one. Finally, 1.6 MtCO2/y can be avoided by using the residual bagasse as feedstock in the ammonia plant, a reduction in 75% of the CO2 emitted when compared to the typical application of simply using it as energy input in the sugarcane cogeneration plant.
The black liquor is a byproduct of the kraft pulping process that contains more than half of the exergy content in the total woody biomass fed to the digester, representing a key supply of renewable energy to the pulping process. In this work, the conventional scenario of the black liquor use (i.e., concentration and combustion) is compared with the black liquor upgrading (via) gasification process for ammonia production in terms of economics, exergy efficiency and environmental impact. The combined energy integration and exergy analysis is used to identify the potential improvements that may remain hidden to the energy analysis alone, namely, the determination and mitigation of the process irreversibility. As a result, the exergy efficiencies of the conventional and the integrated cases average 40% and 42%, respectively, whereas the overall emission balance varies from 1.97 to −0.69 tCO2/tPulp, respectively. The negative CO2 emissions indicate the environmental benefits of the proposed integrated process compared to the conventional kraft pulp mill.
Formaldehyde-based chemistry plays a significant role in the production of different materials. In this work, attempts have been made to revamp a silver catalyzed formaldehyde plant by applying membrane technology. The conventional silver catalyst packed bed reactor was replaced by a shell and tube membrane reactor. A steady-state one-dimensional model was applied to evaluate the performance of the proposed membrane process. The model was validated with experimental results from the plant.
The effects of various parameters including reactor pressure, feed temperature, and membrane thickness on the membrane reactor were investigated. Results showed that the effect of feed temperature on production rates was negligible. The increase in pressure and decrease in membrane thickness, however, leads to increase products. The simultaneous production of 100 tonnes/day of formalin 37% (37 wt% formaldehyde in water) and 500 kg/day pure hydrogen achieved by the proposed process. Furthermore, the exiting reactor temperature can be reduced to 420 °C which is significantly lower than the conventional method (650 °C).
Pallets are crucial in the logistics infrastructure system of various industries and manufacturing companies. They are made of wood and used to store various large and heavy goods. However, pulp and paper manufacturing companies undergo material shortages to make wooden pallets. Therefore, this study aimed to apply the 3-R concept (Reduce, Reuse, Recycle) to deal with pallet shortages at the companies. After several experiments, the researcher developed three techniques based on the 3-R concept with the closed-loop system: (1) repairing and (2) reusing waste pallets from/to customers, (3) using Finger Glued-Laminate's products provided internally as raw materials for pallets; all three met several mandatory criteria of strength and design in a pallet. This research aimed to help companies make policies and strategies related to applying the 3-R concept to deal with pallet shortages. If the pallet quantity can meet the company's needs, it will improve the logistics process quality and deliver the products to consumers right on schedule.
The first investigation of La-promoted Co/Al2O3 catalysts in Ethylene Glycol-CO2 conversion (EGCC) for syngas (H2 + CO) production was conducted in this work. Co/Al2O3 catalysts modified with different La promoter loadings (1, 3, and 5%) were generated through sequential incipient wetness impregnation technique and employed for EGCC. The physicochemical attributes of the generated catalysts were examined via Brunauer-Emmett-Teller (BET), H2 temperature-programmed reduction (H2-TPR), X-ray diffraction (XRD), Raman, and temperature-programmed oxidation (TPO). 3%La-promoted catalyst owned the largest specific surface area, smallest Co crystallite size of 9.8 nm, and lowest reduction temperature among the promoted catalysts. These excellent properties resulted in the highest catalytic performance on the 3%La-promoted catalyst (i.e., C2H6O2 conversion = 77.6 %, CO2 conversion = 43.1 %, H2 yield = 75.3 %, and CO yield = 76.8 %). The significant reduction in carbon deposition of the 3%La-promoted catalyst was due to the La capability in eliminating deposited carbon via the formation of intermediate lanthanum dioxycarbonate, La2O2CO3.
Due to the important role of ammonia as a fertilizer in the agricultural industry and its promising prospects as an energy carrier, many studies have recently attempted to find the most environmentally benign, energy efficient, and economically viable production process for ammonia synthesis. The most commonly utilized ammonia production method is the Haber-Bosch process. The downside to this technology is the high greenhouse gas emissions, surpassing 2.16 kgCO2-eq/kg NH3 and high amounts of energy usage of over 30 GJ/tonne NH3 mainly due to the strict operational conditions at high temperature and pressure. The most widely adopted technology for sustainable hydrogen production used for ammonia synthesis is water electrolysis coupled with renewable technologies such as wind and solar. In general, a water electrolyzer requires a continuous supply of pretreated water with high purity levels for its operation. Moreover, for production of 1 tonne of hydrogen, 9 tonnes of water is required. Based on this data, for the production of the same amount of ammonia through water electrolysis, 233.6 million tonnes/yr of water is required. In this paper, a critical review of different sustainable hydrogen production processes and emerging technologies for sustainable ammonia synthesis along with a comparative life cycle assessment of various ammonia production methods has been carried out. We find that through the review of each of the studied technologies, either large amounts of GHG emissions are produced or high volumes of pretreated water is required or a combination of both these factors occur.
Nowadays, we face a series of global challenges, including the growing depletion of fossil energy, environmental pollution, and global warming. The replacement of coal, petroleum, and natural gas by secondary energy resources is vital for sustainable development. Hydrogen (H2) energy is considered the ultimate energy in the 21st century because of its diverse sources, cleanliness, low carbon emission, flexibility, and high efficiency. H2 fuel cell vehicles are commonly the end-point application of H2 energy. Owing to their zero carbon emission, they are gradually replacing traditional vehicles powered by fossil fuel. As the H2 fuel cell vehicle industry rapidly develops, H2 fuel supply, especially H2 quality, attracts increasing attention. Compared with H2 for industrial use, the H2 purity requirements for fuel cells are not high. Still, the impurity content is strictly controlled since even a low amount of some impurities may irreversibly damage fuel cells’ performance and running life. This paper reviews different versions of current standards concerning H2 for fuel cell vehicles in China and abroad. Furthermore, we analyze the causes and developing trends for the changes in these standards in detail. On the other hand, according to characteristics of H2 for fuel cell vehicles, standard H2 purification technologies, such as pressure swing adsorption (PSA), membrane separation and metal hydride separation, were analyzed, and the latest research progress was reviewed.
The new Monsanto Company acetic acid process employs a rhodium-based homogeneous liquid-phase catalyst which promotes methanol carbonylation in high selectivity and at low pressures. This article describes some of the chemistry involved in this process, with particular emphasis on the role played by rhodium complexes in the catalytic cycle.
The depletion of fossil fuels and global warming have incentivized research into alternative and ecologically benign fuels. Among the most promising options being investigated is the production of hydrogen from biomass. This work investigated the kinetic modeling of the reduction zone for hydrogen production from a wide range of biomass types and conducted a theoretical comparison between various gasification agents (air, steam, and air/steam). The proposed model helps to ascertain the best biomass and agent for attaining the highest hydrogen yield and the lowest environmental contamination in terms of detrimental CO2 emissions. The results show that steam gasification of plastic provides the highest hydrogen yield and that rubber could be considered the most environmentally friendly biomass. Biomass gasification is widely regarded as an efficient method for providing renewable energy source. A kinetic model was developed to investigate the relationship between hydrogen‐rich syngas production and gasification parameters. The model helps predict the best biomass and agent for the highest hydrogen yield and the lowest environmental contamination in terms of CO2 emissions.
The CH4 tri-reforming process can contribute to mitigating CO2 emissions and enables the formation of syngas with different H2/CO ratios. Ni catalysts supported on CeO2 were synthesized by hydrothermal and ionothermal methods and were applied in methane tri-reforming reactions with GHSV of 48,000 mL/g.h, at atmospheric pressure and temperature of 800 °C. The catalytic activity in the tri-reforming reaction was enhanced by changing the morphological properties of the catalyst by appropriate selection of the amount of ionic liquid used in the synthesis procedure. Changing the composition resulted in methane conversion increasing from 60 % to 95 % and carbon dioxide conversion increasing from 40 % to 55 %. Increased Ni dispersion was related to the oxygen vacancies on the Ni-Ce surface, which created interfacial active sites. The results of XANES combined with XPS revealed that a partial reduction of Ni species contributed to high hydrogen yields, due to the distribution of active sites over the catalyst surface. These sites remained active during 5 h, demonstrating the positive effect of the ionic liquid used in the CeO2 synthesis. In addition, post-reaction characterization results showed Ni re-oxidation on the ceria support produced without ionic liquid.
The main objective of this work was to study refuse-derived fuels (RDF) and high-density polyethylene (HDPE) upgrading by pyrolysis of blends of these materials with wood. The study considered three operational conditions: cracking temperature, heating rate, and different wt.% of RDF and HDPE. The results demonstrate that the cracking temperature of 500 °C and the faster heating rates increased the liquid yield for RDF blends. On the other hand, HDPE blends favor gas production at 550 °C and faster heating rates, which enhance the process operativity because polymeric materials generate waxes and are reduced beneath such conditions. Finally, produced gas LHV increases as RDF and HDPE were added. For example, the LHV of the produced gas only with wood at 550 °C and 20 °C/min was 10.34 MJ/m³ and with 25 wt% HDPE was 14.82 MJ/m³.
Background: The Rist diagram is useful for predicting changes in blast furnaces when the operating conditions are modified. In this paper, we revisit this methodology to provide a general model with additions and corrections. The reason for this is to study a new concept proposal that combines oxygen blast furnaces with Power to Gas technology. The latter produces synthetic methane by using renewable electricity and CO 2 to partly replace the fossil input in the blast furnace. Carbon is thus continuously recycled in a closed loop and geological storage is avoided.
Methods: The new model is validated with three data sets corresponding to (1) an air-blown blast furnace without auxiliary injections, (2) an air-blown blast furnace with pulverized coal injection and (3) an oxygen blast furnace with top gas recycling and pulverized coal injection. The error is below 8% in all cases.
Results: Assuming a 280 t HM /h oxygen blast furnace that produces 1154 kg CO2 /t HM , we can reduce the CO 2 emissions between 6.1% and 7.4% by coupling a 150 MW Power to Gas plant. This produces 21.8 kg/t HM of synthetic methane that replaces 22.8 kg/t HM of coke or 30.2 kg/t HM of coal. The gross energy penalization of the CO 2 avoidance is 27.1 MJ/kg CO2 when coke is replaced and 22.4 MJ/kg CO2 when coal is replaced. Considering the energy content of the saved fossil fuel, and the electricity no longer consumed in the air separation unit thanks to the O 2 coming from the electrolyzer, the net energy penalizations are 23.1 MJ/kg CO2 and 17.9 MJ/kg CO2 , respectively.
Discussion: The proposed integration has energy penalizations greater than conventional amine carbon capture (typically 3.7 – 4.8 MJ/kg CO2 ), but in return it could reduce the economic costs thanks to diminishing the coke/coal consumption, reducing the electricity consumption in the air separation unit, and eliminating the requirement of geological storage.
Co-Co2C catalyst has attracted much attention as the catalyst for higher alcohols synthesis due to comparatively high C2+OH selectivity. Herein, oxygen vacancies boosted Co-Co2C catalysts were fabricated via an in-situ reduction and topochemical carbonization process of La0.9K0.1CoxFe1-xO3/ZrO2. The results indicated that abundant oxygen vacancies were introduced into perovskite with the addition of Fe into the B site of perovskite. Under syngas atmosphere, part of Co⁰ was topochemical carbonized into Co2C, and Co-Co2C/LaFeO3-ZrO2 catalyst promoted by oxygen vacancies and K2O-La2O3 could be fabricated. No CO adsorption behaviors on Co2C were detected by in-situ CO-DRIFT and a linear correlation between alcohol selectivity and surface oxygen vacancies was observed, which verified that oxygen vacancies were the key active sites for alcohols formation on Co-Co2C catalyst. TPD results indicated that oxygen vacancies provided additional adsorption sites for CO and adjusted the adsorption forms of CO. Under the synergism effect between Co, Co2C and oxygen vacancies, Co-Co2C catalyst with abundant oxygen vacancies exhibited an excellent alcohol selectivity of 57.1 % and an outstanding stability. This work not only verified the in-situ conversation process of perovskite during reduction and reaction, but also revealed the catalytic mechanism of oxygen vacancies promoted Co-Co2C catalyst for higher alcohol synthesis.
Syngas fermentation is a promising technology for bioalcohols production even though some produced volatile fatty acids (VFA) may remain unconsumed in the effluent. The present research explored the production of polyhydroxyalkanoates (PHA) from the remaining VFA of the syngas fermentation effluents in fed-batch bioreactors so that bioalcohols and biopolymers could be obtained in a combined way. In order to perform these PHA accumulation tests, two different syngas fermentation effluents, composed mainly of a mixture of VFA and alcohols, were used as substrate. Those effluents were characterized by different nitrogen availabilities, one being N-rich and the other N-limited. A mixed microbial culture (MMC) with a maximum PHA storage ability of 53.6% was used as inoculum. The microorganisms of the MMC mainly consumed the VFA rather than the alcohols, allowing the latter to accumulate as end product, besides PHA. However, when the N-rich effluent was used as substrate, the consumption rate of alcohols was 20 times higher (0.040 Cmmol-Alcohol Cmmol-X⁻¹ h⁻¹) compared to the N-limited effluent (0.002 Cmmol-Alcohol Cmmol-X⁻¹ h⁻¹). Despite not observing large differences in the maximum amount of accumulated PHA (40.5 – 41.5%), there was a decrease in the PHA content after reaching its maximum peak when the N-rich effluent was used as substrate. This trend was not observed with the N-limited effluent, in which the maximum PHA peak exactly matched with the end of the experiment.
In recent years, the possibility of merging technologies for waste recovery such as those based on syngas fermentation and chain elongation has been studied for the production of medium chain fatty acids (MCFAs) and bioalcohols, in an attempt to integrate the concept of circular economy in the industry. Nevertheless, one of the main issues of this approach is the pH mismatch between acetogens and chain elongating microorganisms. This work reports, for the first time, the suitability of a co-culture of C. aceticum and C. kluyveri metabolizing syngas at near neutral pH in stirred tank bioreactors. For this purpose, bioreactor studies were carried out with continuous syngas supply. In the first experiment, maximum concentrations of n-butyrate and n-caproate of 7.0 and 8.2 g/L, respectively, were obtained. In the second experiment, considerable amounts of n-butanol were produced as a result of the reduction, by C. aceticum, of the carboxylates already formed in the broth. In both experiments, ethanol was used as an exogenous electron agent at some point. Finally, batch bottle assays were performed with a pure culture of C. aceticum grown on CO in presence of n-butyrate to assess and confirm its ability to produce n-butanol, reaching concentrations up to 951 mg/L, with a n-butyrate conversion efficiency of 96%, which had never been reported before in this species. Therefore, this work contributes to the state of the art, presenting a novel system for the bioproduction of MCFAs by combining syngas fermentation and chain elongation at near neutral pH, as opposed to the acidic pH range used in all previously reported literature.
Selective synthesis of higher alcohols from syngas conversion is highly desirable, but still very challenging. Here, focusing on the commonly used CuCoAl (CCA) catalyst, we attempted to reconcile the capability of the non-dissociation of CO species and the activation of H2 through adding ZnO modified ZrO2 composite into the catalyst for the promotion of higher alcohols synthesis. Under the guidance of such concept, a series of CCA|ZnO/ZrO2 (m: n) modified catalysts (m: n, represent the mass ratio of ZnO to ZrO2) were prepared by mortar-mixing CuCoAl and ZnO/ZrO2 components (2/1 wt ratio). It was found that the CCA|ZnO/ZrO2 (4:1) catalyst showed a highest total alcohols (ROH) selectivity of 42.6 wt% with excellent C2+OH/ROH fraction of 83.7% among the investigated catalysts. The surface [H*]/[C*] ratio of CCA|ZnO/ZrO2 catalysts, as revealed by (CO + H2)-TPD-MS results, increased with the rise of ZnO/ZrO2 ratio. Moreover, the CCA|ZnO/ZrO2 (4:1) catalyst with moderate [H*]/[C*] ratio could acquire the highest ROH selectivity and best space time yield of total alcohols (STYROH) due to that the balance of relative amount of CO*, CHx* and H* species provided the more probability of CnHx*-CO* coupling reaction for higher alcohols synthesis, rather than the hydrogenation reaction of CHx* or CnHx* species and water gas shift reaction.
This chapter is focused on the application of nanofluid in drug delivery systems and disease treatment. Nanofluids can increase the mass and heat transfer through the different media. Repairing or regenerating the damaged cells, human organs, and tissues is based on different technologies, for example, drug delivery, tissue engineering, etc. Biological function components like the nanostructure materials are one of the main essential parts of human-related technologies. In this case, many functional nanomaterials and nanofluids have been investigated for drug delivery systems, gene therapy, tissue engineering, and cancer therapy. However, in this chapter, a review of the applications and different types of nanomaterials are revealed.
Acetobacterium woodii was able to produce high concentrations of acetic acid, i.e., > 20 g/L, from CO2, in the presence of H2 as an energy source, which was favoured by maintaining a near-optimal pH of 7.8 in an automated bioreactor. This allows the mitigation of CO2 emissions for their conversion to acetic acid, which was then further used to produce lipids (single cell oils) by Rhodosporidium toruloides in the next assay. The yeast, grown on acetic acid, efficiently accumulated lipids in A. woodii’s medium, and further improved bioconversion would result in a highly promising process. Acetic acid inhibitory studies performed with R. toruloides, at different initial concentrations of the acid, using the fermented broth of A. woodii grown on CO2, showed that the yeast maintained a constant growth rate and substrate consumption rate up to acid concentrations of 15 g/L. Both rates remained roughly constant at higher initial acetic acid concentrations; except for a more extended lag phase observed in batch assays before the yeast entered in its exponential growth phase.
Biomass is a renewable and potentially carbon-neutral energy source and can be a promising alternative to fossil fuels in the ironmaking industry. Pulverised biomass injection (PBI) is the most promising technology to use biomass-based materials in ironmaking blast furnaces (BFs). This paper reviews key aspects of recent research relating to biomass combustion in the raceway region: experimental studies, numerical studies, and the application of the research findings to optimise BF practice. In the experimental part, the pretreatment of raw biomass to produce pyrolysed biochar products for improving applicability in BFs is reviewed. The properties of raw biomass and biochar are compared with the main requirements for injection into BFs, and the process tests that have been employed at lab- and pilot-scales are reviewed. In the modelling part, a comprehensive overview of mathematical modelling of biomass combustion in BFs is presented, ranging from turbulent flow to heat transfer and mass transfer, as well as key reaction models for simulating the lower part of the BF. With respect to the application of the research, in-furnace phenomena understanding, operation optimisation, and facility design are reviewed, including the co-firing of biomass and coal. In addition, heat and mass balance modelling has been used to demonstrate the operating window of feasible operations using PBI. Life cycle assessment has been reviewed to demonstrate PBI's environmental credentials. Based on the aspects reviewed, conclusions have been drawn on the strengths, limitations, and outlook of PBI studies. This paper offers a comprehensive review of the combustion of biomass in BFs and should prove useful for process understanding, design and optimisation towards green ironmaking technology.
Gasification is one of the most efficient techniques for sustainable hydrogen production from biomass. In this study, a comparative performance analysis of the gasification process using various types of biomass materials was undertaken via thermodynamic approach. Air, steam, and air/steam as the traditional gasifying agents were applied to provide an opportunity to choose the most proper agent in the process. This paper also evaluates the environmental impacts of the process in terms of CO 2 emission by using Aspen Energy Analyzer. The effects of agent to biomass molar ratio, agent inlet temperature, moisture content of biomass material, and gasification temperature were estimated based on the producer gas compositions, hydrogen yield and heating values. The results indicate that the highest hydrogen yield (0.074 g H 2 /g biomass) was obtained in the steam gasification of plastic, while air gasification of paper generates the lowest one. It was also observed that manure is the most beneficial from environmental perspectives, while tire and plastic have the highest contribution to CO 2 emission and consequently global warming. The higher values of hydrogen production and LHV of produced gas are associated respectively with using steam, air/steam, and air as the gasification agents. The lowest value of CO 2 emission is obtained for air, air/steam, and steam as the gasifying agents, respectively.
Biomass Chemical Looping Gasification (BCLG) is an autothermic gasification process that provides pure syngas for many applications, including liquid biofuels production. Finding low-cost materials that can be used in the process is a key issue, especially when they come from waste. In this sense, LD Slag is a by-product of the steel industry used as an oxygen carrier in Chemical Looping Combustion with good results. This work investigates the use of LD Slag as oxygen carrier in a continuous 1.5 kWth BCLG unit. The effect of the main operational variables (temperature, oxygen-to-fuel and steam-to-biomass ratios) and the use of CO2 instead of steam as gasification agent were analysed. LD slag allowed the process with high biomass conversions, Xb > 90%, carbon conversion efficiencies, ηcc > 90%, and syngas yields, Y ≈ 0.66 Nm³/kg of dry biomass, at conditions corresponding to autothermal operation. A lifetime of 300 h under reducing conditions was inferred and agglomeration problems were never detected. LD slag can be considered a suitable material for BCLG since it is possible to obtain high-quality syngas at autothermal conditions from different types of biomass with low tar generation and CO2 emissions.
Selectively converting syngas to target hydrocarbon products is highly desired but challenging. In this issue of Chem Catalysis, Liu, Zhu, and co-workers report a (CZA + Al2O3)/N-ZSM-5(97) dual-bed catalyst for direct syngas conversion to gasoline, with which they achieved C5–11 selectivity as high as 80.6% at 86.3% CO conversion with no deactivation in 110 h.
Methane reforming allows the production of synthesis gas (syngas) which is an important gas mixture feedstock for the production of chemicals and energy carriers. Steam reforming of methane (SRM) and partial oxidation of methane (POM) have been deployed at large industrial scale, while dry reforming of methane (DRM) and more recently tri-reforming of methane (TRM) are intensively studied. TRM simultaneously combines SRM, POM and DRM in a unique process and allows overcoming several weaknesses of each individual methane reforming process: e.g. regulation of the molar ratio of H2/CO by controlling feed composition; adaptation to the variation in biogas composition as renewable resource. TRM process strongly requires a solid catalyst. To date, the design of efficient TRM catalysts remains a challenge. This work reviews recent achievements on the development of catalysts for TRM, and provides a guideline for future work related to TRM catalysts.
The influence of the carbon source on the metabolism and growth of Clostridium aceticum was investigated, supplying either CO or fructose as sole carbon source. The acid and solvent production patterns were determined under either autotrophic or heterotrophic conditions, elucidating the effect of pH on the substrate's bioconversion pattern. The highest maximum specific growth rate was observed with CO, under the organism's optimal growth conditions, reaching 0.052 h⁻¹ and an acetic acid concentration of 18 g·L⁻¹. The production of 4.4 g·L⁻¹ ethanol was also possible, after medium acidification, during CO bioconversion. Conversely, formic acid inhibition was observed during fructose fermentation under optimal growth conditions. In the latter experiments, it was not possible to stimulate solvent production when growing C. aceticum on fructose, despite applying the same medium acidification strategy as with CO, showing the selective effect of the carbon source (autotrophic vs heterotrophic) on the metabolic pattern and solventogenesis.
In this study, projections and current status of municipal solid waste generation worldwide and its collection, final destination, and waste-to-energy technologies are reviewed. Firstly, an overview of waste generation worldwide is presented comparing income levels and the material composition of residues in several regions. This paper focused on contrasting Brazil and Portugal in terms of waste production and its management from generation to disposal or treatment. Furthermore, it is presented a summary of leading waste-to-energy technologies such as incineration, anaerobic digestion, gasification, pyrolysis, co-combustion, co-gasification, among others. Technical aspects of these thermo-chemical, biological, and physic-chemical processes for the production of biofuels such as biogas, syngas, biodiesel, and hydrogen-enriched gases are presented. Additionally, current aspects of the waste-to-energy market are exposed regarding the major players, investments, and expectations for the future of this activity with the elaboration of SWOT analyses. Finally, a review of greenhouse gases emissions worldwide is presented, specifically from Brazil and Portugal, as well as some consequences of these pollutant gases on the society and the environment and which are the main technologies for carbon dioxide capturing and sequestration as promising solutions for lower pollutant gases concentration in the atmosphere. This review paper aims to provide information for the management of municipal solid waste in Brazil and Portugal considering the mutual objective of meeting sustainable development goals.
In an increasing demand of renewable energy resources, fuel cell represents the highly efficient, clean and sustainable energy conversion source. Broadly speaking, fuel cell can be divided into six different categories according to the types of electrolyte and fuels used. Each type of fuel cells has their own advantages and disadvantages. Among them, solid oxide fuel cell (SOFC) gains significant attentions due to their high efficiency, cost-effectiveness and the possibility to utilize variety of fuels other than hydrogen such as hydrocarbons, coal gas etc. As name implies, SOFC uses solid electrolyte for their operation. Indeed, in medium and large power requirement sectors, SOFC are highly suitable. In the present review article, recent advances and future perspectives of SOFC have been discussed via reviewing the literature over last five years. Most of the available review articles discussed the literature in terms of specific SOFC component such as anode, cathode, electrolytes and so on. In contrast, herein the literatures have been reviewed in the context of two types of SOFC stack designs i.e. planar and tubular that have been immensely used to fabricate efficient SOFC devices. Furthermore, fundamental of SOFC operation and its typical I–V characteristics and SOFC designs are also discussed in detail. Furthermore, preparation techniques for planar and tubular SOFC are briefly described. Finally, some of the recent trends in SOFC technology along with challenges and future perspectives are presented in this review article
Utilizing the greenhouse gas CO2 as a feedstock in chemical processing can offer alternative solutions to long-term storage. In this study, a systematic analysis of methanol synthesis performance was analyzed based on both thermodynamic equilibrium and kinetic models using captured CO2 and syngas produced from biogas as feedstock. Using reactor inlet temperature as a parameter, it was found that methanol yield can be enhanced by increasing residential time from increased reactor diameter. The longer reactor can increase the residential time but a large pressure drop caused a decrease in methanol yield. Due to the exothermic reaction nature, methanol yield from an adiabatic reactor is lower than that from the isothermal reactor due to temperature rise. From the results obtained for CO2 hydrogenation, methanol yield can be enhanced by water removal. The CO2 conversion was found to increase with increased reaction temperature due to methanol and carbon monoxide productions. Using CO and CO2 as limiting species, high combined CO and CO2 conversion can be obtained from syngas with low CO2/H2 and high CO/H2 ratios. However, methanol production per mole of H2 depends on the H2 utility instead of combined CO and CO2 conversion. Finally, syngas produced from biogas by using combined dry and steam reforming reactions was used as the feedstock for the methanol synthesis. To obtained the syngas composition suggested from industrial applications, CH4 and H2O were added in the combined reforming process. With higher CH4 content in the biogas, higher methanol production and lower water production can be obtained. With an increased recycle ratio for unreacted syngas, methanol production can be enhanced.
Methanation is a potential large-scale option for CO2 utilization, and it is one of the solutions for decreasing carbon emission and production of synthetic green fuels. However, the CO2 conversion is limited by thermodynamics in conventional reaction conditions. However, around 100% conversion can be obtained using sorption enhanced CO2 methanation according to Le Chatelier’s principle, where water is removed during the reaction using zeolite as a sorbent. In this work 5%Ni5A, 5%Ni13X, 5%NiL and 5%Ni2.5%Ce13X bifunctional materials with both catalytic and water adsorption properties were tested in a fixed bed reactor. The overall performance of the bifunctional materials decreased on going from 5%Ni2.5%Ce13X, 5%Ni13X, 5%Ni5A, to 5%NiL. The CO2 conversion and CH4 selectivity were approaching 100% during prolonged stability testing in a 100 reactive adsorption – desorption cycles test for 5%Ni2.5%Ce13X, and only a slight decrease of the water uptake capacity was observed.
Substitution of fossil fuels by sustainable practices must be rapidly implemented to mitigate the impacts of climate change. The conversion of biomass into combustible gas is investigated in a microwave-induced plasma reactor using pure steam as the plasma working gas for the first time. The optimum results are achieved at the highest forward microwave power of 6 kW with biomass carbon conversion efficiency over 98% and complete biomass energy recovery in syngas. Unreacted steam is simply condensed out, leading to the production of a syngas with low inert dilution and high calorific value in the range 10.5-12 MJ/Nm³. The syngas produced is rich in hydrogen, exceeding 60% by volume. The proposed process could aid in the transition to a carbon neutral economy as it has the potential to efficiently convert biomass to syngas that can be used for the sustainable generation of fuels, chemicals and energy.
Carbon monoxide preferential oxidation (CO-PROX) is regarded as a promising strategy to remove trace amount of CO in H2-rich stream. Herein, atomically dispersed Au catalysts with different Au contents supported on cerium-zirconium solid solution supports were obtained by a deposition-precipitation method. The optimal catalyst, with 0.02 wt% Au, exhibits nearly 100% CO conversion and 50% CO2 selectivity for CO-PROX reaction under PEMFC working temperature range (80 − 120 ℃) and remains catalytically stable after 72 h testing at 80 ℃. The superior catalytic performances are attributed to the strong adsorption of CO and the low energy barrier of CO oxidation reaction, as well as the weak H2 adsorption and dissociation over highly dispersed Au single atoms, as supported by density functional theory calculations. Furthermore, combining characterization and experimental results, it is concluded that although catalysts are atomically dispersed, their performances can be adjusted by the synergetic interaction between neighboring Au single atoms.
In this work, the rotating liquid sheet (RLS) contactor was designed and introduced as a new gas-liquid contactor with many benefits compared to conventional technologies for CO2 absorption from CO2/N2 gas mixtures using aqueous SiO2 and ZnO nano solutions as physical absorbents. To evaluate the performance of the RLS system, a helical slot in the wall of central tube was used to provide a high interfacial contact area between gas and liquid phases. The nanofluids were directly exposed to the gas stream to investigate the impact of different operational parameters including tube rotation rate, nanoparticles concentration, gas flow rate and CO2 concentration in the inlet stream. Obtained results clearly revealed that, tube rotation could enhance the characteristics of mass transfer from the gas stream to the liquid phase. Moreover, increasing the gas flow rate and CO2 inlet concentration resulted in the capture efficiency to decrease. Also, the absorption flux improves with increasing of the gas flow rate, while it first increases and then decreases with increment of CO2 inlet concentration. Ultimately, the CO2 absorption measurements confirmed that separation enhances significantly in presence of nanoparticles so that the ZnO nanofluids are more effective than SiO2 nanofluids at the all experimental conditions.
A techno-economic analysis is performed, assessing the production costs of Fischer-Tropsch syncrude and waxes of carbon number C20+. The products are obtained from the gasification of digestate from anaerobic digestion inside a dual fluidized bed gasifier (3.11 MWth). The results are compared against the same system fed with lignocellulosic biomass. The syngas is cleaned from impurities and conditioned to reach the desired H2/CO molar ratio of 1.8 at the inlet of the Fischer-Tropsch reactor. The Fischer-Tropsch products distribution is based on experimental data of a cobalt-based catalyst. Two process configurations are studied: (1) the Fischer-Tropsch off-gas are employed to produce electricity; (2) the off-gas are recirculated to the gasifier for enhanced wax production. Co-production of steam is also investigated. The results show an advantageous production of Fischer-Tropsch compounds utilizing digestate over wood biomass. The highest plant efficiency (i.e., biomass-to-liquid fuel) of 56.3% is reached with digestate feedstock and off-gas recirculation, outputting 61.5 kgwax/tdig. The minimum wax production cost is of 3.04 €/kgwax, assuming 7.5% discount rate and 25-years plant operation.
In the present study, hydrogen-rich syngas production via integrated configuration of pyrolysis and air gasification processes of different algal biomass is investigated at relevant industrial condition. A comprehensive steady state equilibrium simulation model is developed using Aspen Plus software, to investigate and evaluate the performance of pyrolysis and air gasification processes of different algal biomass (Algal waste, Chlorella vulgaris, Rhizoclonium sp and Spirogyra). The model can be used as a predictive tool for optimization of the gasifier performance. The developed process consists of three general stages including biomass drying, pyrolysis and gasification. The model validation using reported experimental results for pyrolysis of algal biomass indicated that the predicted results are in good agreement with experimental data. The effect of various operational parameters, such as gasifier temperature, gasifier pressure and air flow rate on the gas product composition and H2/CO was investigated by sensitivity analysis of parameters. The achieved optimal operating condition to maximize the hydrogen and carbon monoxide production as the desirable products were as follows: gasifier temperature of 600 °C, gasifier pressure of 1 atm and air flow rate of 0.01 m³/h.