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Distribution Equilibrium of Citric Acid between Aqueous Solutions and Tri-n-octylamine-Impregnated Macroporous Resins
Abstract
In this paper, experiments were conducted on equilibrium distribution of citric acid between aqueous solutions and tri-n-octylamine (TOA)-impregnated resins in the 288-318 K temperature range. Analysis of the results showed that the sorption of citric acid could be explained by the formation of acid-TOA complexes in the resin phase with the general composition (H3A)p(TOA)qBAR. Mole fraction of the complexes formed in the resin phase as a function of citric acid concentration in the aqueous solution was obtained. The effect of temperature on equilibrium distribution was also studied, and the apparent thermodynamic data for sorption reactions were determined. Finally, the distribution of citric acid between aqueous solutions and the resins impregnating with a mixture of TOA and bis(2-ethylhexyl)phosphoric acid was examined.
... Already a lot of research has been done in this field for removal of traces of metals from aqueous streams [2][3][4]. Lately, the EIR technology has been extended for recovery of organic compounds, like phenols [5], flavonoids [6], carboxylic acids [7][8][9][10], amino acids [11,12], and antibiotics (spiramycin [13]). In the present research, we investigate the removal of aldehydes from diluted aqueous streams using EIR technology, which has, Nomenclature Symbols n amount of substance, mol C concentration, mol/l K r reaction equilibrium constant, l/mol K ph physical partitioning ratio D overall distribution ratio, defined by Eq. ...
... The impregnation procedure is based on the procedure published by Juang et al. [7]. Amberlite XAD-16 was first cleaned with acetone and n-hexane and then dried under vacuum at 60°C, while MPP and Stamypor were cleaned only with acetone. ...
The performance of Extractant Impregnated Resin (EIR) technology for extraction of aldehydes from aqueous solutions has been investigated. The extraction capabilities of several different aliphatic and aromatic primary amines towards aldehydes were tested and compared. Aliphatic amines showed high affinity. The most promising extractant, Primene® JM-T, was immobilized in a porous particle. As a solid support three different macroporous adsorbents were tested, XAD-16, MPP and Stamypor. Their capacities for the removal of aldehydes were compared with the non-impregnated resin and the resin impregnated with the non-reactive solvent. It was shown that the addition of a reactive extractant can increase the adsorption capacity of an otherwise poor adsorbent for several orders of magnitude. The capacity for the removal of aldehydes was increased with the increase of amine loading on the particle. Temperature influence on the sorption of benzaldehyde on fully impregnated MPP was studied. It was shown that with temperature increase, sorption capacity is increased. The stability of EIRs regarding the loss of the extractant due to the leakage in water was also studied. It was shown that immobilization reduces the extractant’s solubility in water. Sorption kinetics was investigated for fully impregnated XAD-16 and MPP. The modified shrinking core model was used to determine the rate controlling step and it was shown that this sorption is most likely controlled by both chemical reaction and diffusion in the particle.
This paper provides a bibliography of the 1995 journal literature for adsorptive and membrane-type separations. The references are taken from the 50 most important chemical engineering journals. This paper provides an update to the literature as provided in previous bibliographic papers (Ray 1990a, 1991, 1994, 1995, 1996). A bibliography of the chemical engineering journal literature from 1967–1988 has been published by the author (Ray 1990b), and can provide access to a wider range of topics. A complete bibliographic listing of the chemical engineering journal literature from 1989 to 1995 (with subsequent six-monthly updates) is available on a CD-ROM database and full details can be obtained from the author.
The papers included have been divided into the following subject groups: theory; design data; adsorbents; PSA and cyclic systems, and applications; liquid-phase adsorption; ion exchange, chromatography, etc.; membranes; and membrane-type separations.
A process for the separation and the concentration of citric acid was developed within the context of clean technology. It is based on the liquid-liquid phase equilibrium thermodynamic of a system containing salt, which indicates the liquid-liquid extraction process using electrolyte mixed solvent, as potentially attractive to recover citric acid from its fermentation broth. Experimental ternary and quaternary liquid-liquid equilibrium data were obtained in this work and the electrolyte activity coefficient model parameters were calculated from them. The ASPEN PLUS process commercial simulator was used for calculating the thermodynamic parameters, for simulating and for optimizing the process developed.
Solvent impregnated resins (SIRs) were evaluated for the recovery of pyridine derivatives from an aqueous waste-stream containing also acetic acid and succinonitrile. For this purpose, a new solvent was developed, synthesized and impregnated in Amberlite XAD4. Sorption studies were used to determine the capacity, selectivity and the mass-transfer rate. A high capacity of 21 g 4-cyanopyridine (CP) per kg SIR was found, with very high selectivity toward CP over the other solutes of at least 570. A modified Langmuir equation could describe the equilibrium sorption isotherm. Both the linear driving force model and a Fickian diffusion model were evaluated. The Fick-model described both regeneration and loading best. The CP-diffusivity through the solvent phase was estimated at 6.53 · 10−13 ± 2.5% m2 s−1. The model was validated using fixed-bed column experiments. The R2 values for this model ranged between 0.94 at a flow rate of 5 mL/min and 0.99 at a flow rate of 1 mL/min during the loading cycle. Due to mass-transfer limitations the breakthrough profiles were broad and breakthrough occurred after 5 or 23 bed volumes, for flow rates of 5 and 1 mL/min, respectively. Both acetic acid and succinonitrile broke through immediately due to the very high CP-selectivity of the SIR.
The broad application of itaconic acid in synthetic resins, fibers, plastics, rubbers, surfactants, and oil additives has resulted in an increased demand for this product. As an end step of biobased itaconic acid production, a suitable downstream recovery procedure using Aspergillus terreus as a study model was analyzed. Here we present preliminary work to integrate fungal fermentation with in-stream product recovery (ISPR) using pertraction for itaconic acid. Based on prior knowledge and an initial solvent screening, solvent extraction using 2-methyl tetrahydrofuran (2m-THF) was selected as the preferred technique for recovering itaconic acid.1,2
The removal of pyridine derivatives from wastewater streams is of high environmental importance due to their toxicity and poor biodegradability. Conventional separation technologies such as adsorption and extraction cannot be applied effectively due to the difficulties in regeneration of adsorbents and entrainment of the solvent. The use of solvent impregnated resins (SIRs) in fixed bed operation is proposed as alternative to these technologies, combining the advantages of adsorption and liquid–liquid extraction in a single unit operation. Solvents for SIR technology should have a high capacity for pyridines and negligible solubility in water to prevent rapid loss of solvent. In this study, a solvent is designed for the removal of model compound 4-cyanopyridine from an aqueous stream. COSMO-RS was used and evaluated as solvent design tool. Results show that COSMO-RS is able to qualitatively predict the capacities of the solvents. The optimized solvent was a 1:1 mixture of (E)-3-bromo-4-(3-ethylhept-1-en-1-yl)phenol and (Z)-3-bromo-4-(3-ethylhept-1-en-yl)phenol. The distribution coefficient was 254, corresponding to a SIR capacity of 44 g/kg which was 4.5 times higher than the commercially available solvent 4-nonylphenol with a comparably low aqueous solubility of 9.3 ppm.
Ligand exchange chromatography (LEC) using physically impregnated N-hexadecyl-l-hydroxyproline on commercially available RP-18 column is applied for the preparative separation of amino acid racemic mixtures. The equilibrium dispersive model was used for the mathematical prediction of the separation process. The experimental determination of the model parameters is discussed. Using the multi-component competitive Langmuir adsorption isotherm the mathematical model was able to predict the preparative separation behaviour of low concentrated feed solutions of amino acid racemats. The calculated profiles very well predict the break-through experiments (adsorption and desorption) as well as the injection experiments. At a high concentrated feed overloading effects in the break-through adsorption experiments were detected and a discussion on model limits is given.
The selective removal of pyridine derivatives by solvent impregnated resins has been studied. A solvent impregnated resin consists of a macro-porous particle that is impregnated with a solvent. This technology allows the use liquid–liquid extraction in fixed-bed operation, and prevents problems like entrainment and irreversible emulsification. 4-Cyanopyridine was chosen as model pyridine derivative, and 4-nonylphenol was used as solvent. The aim of this study was to select the most suitable resin for this application. While in the literature there are mainly two types of resins used, MPP and Amberlite XAD type, a comparative study has not yet been conducted. In this study, a series of resins were impregnated with the solvent and applied in sorption experiments to study on the effect of the resin properties on the capacity, selectivity and mass-transfer rates of the solvent impregnated resins. It was found that the capacity could be estimated accurately with the previously developed liquid–liquid extraction equilibrium model. Additionally, the selectivity was determined by the solvent properties, and hardly affected by the resin matrix. The mass-transfer rates were primarily determined the by particle diameter, whereas the effect of the porosity is small. On the basis of the results it was established that Amberlite XAD4 had the best combination of capacity, mass-transfer rate, mechanical strength, selectivity and pressure drop over a fixed-bed column and was therefore chosen for a more detailed study. The results showed that the breakthrough curve is broad due to mass-transfer limitations. The loading cycle of the column could be described with great accuracy using the mathematical model developed in this study. Regeneration of the column could be performed efficiently with a pH-swing using hydrochloric acid at a pH of 1. The fixed bed column was percolated with 7000 bed volumes of aqueous solutions varying in composition. No reduction in the capacity was observed which demonstrated that the SIR consisting of Amberlite XAD4 and 4-nonylphenol is highly stable.
Many wastewaters as well as aqueous solutions used for hydrometallurgical extractions have multiple toxic heavy metals: some are present as cations; others are present as anions. This research is directed toward extracting multiple heavy metallic species simultaneously into an appropriate mixed solvent and then recovering and concentrating such heavy metals into appropriate aqueous stripping solutions. Heavy metals of interest are Cu(II), Cr(VI), Zn(II), Hg(II), etc. Such processes have been carried out in a nondispersive fashion in microporous hydrophobic hollow fiber membrane-based devices containing multiple sets of fibers. The results will be presented, and the basis of the observed synergism will be discussed. The advantages of such extraction-stripping processes will be pointed out.
Equilibrium and mass transfer data for the extraction of valeric acid from aqueous solutions containing less than 2.5 wt% of acid with a macroporous fresh resin, Amberlite XAD‐4, and containing tri‐N‐butyl phosphate (TBP) at 25°C are reported. An equilibrium model, which takes into account the valeric acid physical adsorption by the resin (Freundlich isotherm) and the reactive extraction with the TBP inside the pores, provided a good correlation of experimental data. Valeric acid extraction rates were comparatively faster under the initial conditions of higher TBP concentration in the resin and lower concentration of acid in the aqueous phase. Intraparticle effective diffusivities were determined using a homogeneous mass‐transfer model. A heterogeneous diffusion model which considers parallel diffusion of the TBP–valeric acid complex in the organic phase inside the particle pores and surface diffusion of the valeric acid in the polymeric structure of the resin was employed to derive the pore diffusivity and solid surface diffusivity. Both diffusivities were of the same order of magnitude (10 m/s) showing that both diffusion paths in parallel make significant contributions to the intraparticle mass transfer of valeric acid in the extractant‐impregnated resins (EIR).
The phase equilibria of α-phenylglycine in sodium hydroxide solutions at pH=11 and 12 with the extractant trialkylmethylammoniumchloride (Tomac) dissolved in kerosene and toluene and with Amberlite XAD-4 resin coated with Tomac at 30°C is reported.The extraction of α-phenylglycine and co-extraction of hydroxyl ions take place simultaneously by ion exchange reactions with the extractant. Phase equilibria are discussed as a function of α-phenylglycine concentration, pH of the aqueous phase and Tomac concentration either in the organic phase or in resin phase. An equilibrium model, which considers the hydroxyl ion co-extraction, has been used for the correlation of the equilibrium data.
MTBE removal from groundwater is difficult. State-of-the-art processes such as air stripping or adsorption can have significant drawbacks, like high energy consumption, low capacity and low selectivity. This is why the alternative technology of solvent impregnated resins is investigated. The extractant used is 3-iodophenol diluted with propylbenzene. From solids screening and impregnation experiments macroporous polypropylene (MPP) particles appear as a suitable solid support. The MTBE capacity of impregnated MPP is lower than that of a carbonaceous resin, but the selectivity of the SIR between MTBE and humic acid is significantly higher. Solvent impregnated resin (SIR) regeneration can be easily achieved with hot gas.
The recovery of organic acids from aqueous solutions using ion-exchanger-impregnated resins has been investigated. The key parameters for process design are equilibria, mass transfer kinetics and loss of the liquid ion exchanger (bleeding). The maximum bleeding was observed when the resin was used for the first time. The ion exchanger concentration in the aqueous phase decreases to a final concentration lower than 1mg/L after the first usage. The equilibria of citric and tartaric acid have been investigated for the different macroporous resins XAD4 and XAD16 impregnated with tri-n-octylamine (TOA). A modified Langmuir isotherm taking the loading of ion exchanger TOA on the resin into account is able to describe the equilibrium in both test systems in dependence of the temperature. Experiments in a stirred vessel have been carried out to characterize the intraparticular mass transfer. The results have been used to predict the effective pore diffusion coefficient using the tortuosity.
Over the last 50 years petroleum has become the primary feedstock for industrial organic chemical production. Over the next 50 years it is anticipated that there will be a growing use of renewable feedstocks in chemical manufacturing. In this review, the motivations for developing alternatives to petro-chemicals are discussed, and we highlight exciting advances in biotechnology that promise to make biomass-based feedstocks more attractive in the future. We argue that separations remain a key bottleneck to the recovery of organic chemicals from renewable resources. Finally, we consider our research to understand the mechanistic interactions responsible for adsorption onto polymeric adsorbents. We provide examples illustrating how knowledge of hydrogen-bonding interactions can be exploited for separating chemicals from renewable resources. We especially focus on oxygenated aromatic compounds (OACs) that are abundant in biomass-based feedstocks.
The rates for the sorption of citric acid from relatively concentrated aqueous solutions (0.05∼0.2 mol/dm3) with macroporous resins containing tri-n-octylamine (TOA) were measured in finite bath. Experiments were carried out as functions of citric acid concentration in the aqueous phase, TOA concentration in the resin phase, and temperature. It was shown that the kinetic data could be well described by the Elvoich equation. Rate equations for the sorption processes were obtained and the activation energy was also determined.
Experiments were conducted on equilibrium distribution of citric acid between relatively concentrated aqueous solutions and macroporous resins containing tri-n-octylamine (TOA). The equilibrium data were well described by the Langmuir isotherm equation. Chemical model analysis of the results showed that the sorption could be also explained by the formation of an acid-amine complex with general composition (acid)(TOA)q in the resin phase. The loss of amine from the impregnated resins and the effect of temperature on equilibrium distribution were also discussed.
The liquid ion‐exchanger tricaprylylmethylammonium chloride (TCMAC) is used for the preparation of solvent impregnated resins (SIR). The sorption of the model amino acid L‐phenylalanine (L‐Phe) is studied for different solid supports (XAD16, XAD1180, DELOXAN HAP, SIPERNAT D10, IRC50, and Lewatit MP500) under varied initial conditions (volume‐to‐mass ratio, phenylalanine concentration, and ion‐exchanger loading). For comparison, the equilibria of five other amino acids (histidine, tryptophane, tyrosine, arginine, and proline), differing mainly in their hydrophobicity and pI values, is also investigated. The equilibrium sorption of amino acids on SIR is modelled by taking the hydroxide ion co‐extraction into account.
The application of extractants in whole-cell biocatalysis can have a positive impact on industrial fermentations, in terms of productivity, total amount of product produced, and cell growth. When a product is continuously removed from the microorganism surroundings, product inhibition will be diminished. The strategy is exemplified using phenol as the product and the extractant is selected for solvent-impregnated resins, which can prevent emulsification problems that are commonly encountered in in situ extractive recovery of fermentation products. A systematic approach for selection of superior extractants in whole-cell biocatalysis is discussed in this paper. Three criteria are taken into account, namely, extractant toxicity (log Po/w values), product selectivity, and extractant regeneration.
Since the concept of solvent impregnated resins was introduced in the early 1980s, the technique has been applied to a limited amount of applications. The main disadvantage of the resins was that the amount of solvent inside was limited to approximately 1.5 ml/g polymer. A new generation of solvent impregnated resins is introduced. These capsules can contain up to 11.8 ml solvent/g polymer and were prepared using a modified dry impregnation technique. Due to the high solvent loading, the capacity per volume of capsule for extracting products from aqueous phases is therefore dramatically increased.
The focus of this investigation is the development of a solvent impregnated resin for phenol removal from dilute aqueous solutions. Using a solvent impregnated resin (SIR) eliminates the problem of emulsification encountered in liquid–liquid extraction. Impregnated MPP particles and impregnated XAD16 particles are successfully used for phenol extraction. Impregnated MPP particles are preferred, as impregnated XAD16 particles show less mechanical strength and are more expensive. Impregnated MPP particles perform better compared to other synthetic adsorbents and basic ion exchangers. The maximum phenol capacity of impregnated MPP particles with 0.99 mol Cyanex 923 kg−1 SIR is 4.1 mol kg−1 SIR (386 mg g−1 SIR) and of MPP particles containing 1.47 mol Cyanex 923 kg−1 SIR it is 5.08 mol kg−1 SIR (478 mg g−1 SIR). The regenerability of impregnated MPP particles is easy and complete, and the particles are stable during several cycles. The equilibrium constants for the extraction of phenol are determined as Kchem = 37 L mol−1 and Kphys = 18 (mol L−1) (mol L−1)−1. With these values the SIR isotherms can be satisfactorily described.The results indicate that SIR technology is a promising alternative for the conventional phenol removal technologies at low phenol concentration levels.
Interest in the development of solvent-impregnated resins (SIRs) and their applications for the separation of metal ions and organic compounds from water in the form of a hybrid polymeric adsorbent material has intensified over the past thirty years. SIRs are particulate adsorbers that possess a combination of the advantageous features of both liquid–liquid extraction and ion exchange and this renders them applicable to a wide range of potential liquid–solid separation and recovery processes. This paper reviews the extensive published literature on methods of synthesis of SIRs, attempts to stabilize hybrid solvent-impregnated resins and various applications of SIRs.
Microorganisms are generally sensitive to high concentrations of products that they excrete. Such product inhibition and toxicity effects can significantly be reduced by the integration of fermentations with separation technologies to remove the products continuously. Cost-calculations are required to select the preferred integration method. This paper presents a shortcut calculation method that provides easy interpretable results to assist the reader in making rational design choices. The method distinguishes four main cost categories, being capital and operational expenditure for both fermentation and product recovery. We have applied these cost correlations to the production of three typical bio-based bulk chemicals. The results show the origin of the most significant costs in the investigated integrated bio-processes. The presented method can be used to direct future research efforts and might assist in evaluating the impact of integrated product recovery techniques on total production costs of bio-chemicals.
To develop a new solvent-impregnated resin (SIR) system for removal of phenols from water, the complex formation of dimethyldodecylamine N-oxide (DMDAO), trioctylamine N-oxide (TOAO), and tris(2-ethylhexyl)amine N-oxide (TEHAO) with phenol (PhOH) and thiophenol (PhSH) is studied. To this end we use isothermal titration calorimetry (ITC) and quantum chemical modeling (on B3LYP/6-311G(d,p)-optimized geometries: B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), MP2/6-311+G(d,p), and spin component scaled (SCS) MP2/6-311+G(d,p); M06-2X/6-311+G(d,p)//M06-2X/6-311G(d,p), MP2 with an extrapolation to the complete basis set limit (MP2/CBS), as well as CBS-Q). The complexes are analyzed in terms of structural (e.g., bond lengths) and electronic elements (e.g., charges). Furthermore, complexation and solvent effects (in benzene, toluene, and mesitylene) are investigated by ITC measurements, yielding binding constants K, enthalpies ΔH(0), Gibbs fre energies ΔG(0), and entropies ΔS(0) of complex formation, and stoichiometry N. The ITC measurements revealed strong 1:1 complex formation between both DMDAO-PhOH and TOAO-PhOH. The binding constant (K=1.7-5.7×10(4) M(-1)) drops markedly when water-saturated toluene was used (K=5.8×10(3) M(-1)), and π-π interaction with the solvent is shown to be relevant. Quantum mechanical modeling confirms formation of stable 1:1 complexes with linear hydrogen bonds that weaken on attachment of electron-withdrawing groups to the amine N-oxide moiety. Modeling also showed that complexes with PhSH are much weaker than those with PhOH, and in fact too weak for ITC determination. CBS-Q incorrectly predicts equal or even higher binding enthalpies for PhSH than for PhOH, which invalidates it as a benchmark for other calculations. Data from the straightforward SCS-MP2 method without counterpoise correction show very good agreement with the MP2/CBS values.
Life sciences will be one of the decisive factors in the 21st century. A major part of this field is the so-called white biotechnology, also known as industrial biotechnology. White biotechnology is an emerging field where bio-chemicals are produced using micro-organisms. However, the production of bio-chemicals is severely inhibited due to toxicity of the product towards the host-organism. Therefore, it is necessary to remove the products from the micro-organisms’ environment. One approach for achieving this is applying so-called in-situ product removal. In this thesis solvent impregnated resins are added to a fermentation broth as an in-situ product removal tool. These particles contain an organic phase able to selectively extract a certain product from an aqueous phase such as fermentation broths.
To develop a new solvent-impregnated resin (SIR) system for the removal of phenols and thiophenols from water, complex formation by hydrogen bonding of phosphine oxides and phosphates is studied using isothermal titration calorimetry (ITC) and quantum chemical modeling. Six different computational methods are used: B3LYP, M06-2X, MP2, spin component-scaled (SCS) MP2 [all four with 6-311+G(d,p) basis set], a complete basis set extrapolation at the MP2 level (MP2/CBS), and the composite CBS-Q model. This reveals a range of binding enthalpies (DeltaH) for phenol-phosphine oxide and phenol-phosphate complexes and their thio analogues. Both structural (bond lengths/angles) and electronic elements (charges, bond orders) are studied. Furthermore, solvent effects are investigated theoretically by the PCM solvent model and experimentally via ITC. From our calculations, a trialkylphosphine oxide is found to be the most promising extractant for phenol in SIRs, yielding DeltaH=-14.5 and -9.8 kcal mol(-1) with phenol and thiophenol, respectively (MP2/CBS), without dimer formation that would hamper the phenol complexation. In ITC measurements, the DeltaH of this complex was most negative in the noncoordinating solvent cyclohexane, and slightly less so in pi-pi interacting solvents such as benzene. The strongest binding is found for the dimethyl phosphate-phenol complex [-15.1 kcal mol(-1) (MP2/CBS)], due to the formation of two H-bonds (P=OH-O- and P-O-HO-H); however, dimer formation of these phosphates competes with complexation of phenol, and would thus hamper their use in industrial extractions. CBS-Q calculations display erroneous trends for sulfur compounds, and are found to be unsuitable. Computationally relatively cheap SCS-MP2 and M06-2X calculations did accurately agree with the much more elaborate MP2/CBS method, with an average deviation of less than 1 kcal mol(-1).
Tri-n-ocytlamine oxide (TOAO) is evaluated as alternative to the state-of-the-art phenol extractants tri-n-octylphosphine oxide (TOPO) and Cyanex 923. Liquid¿liquid equilibrium experiments show that TOAO in 1,3-dimethylnaphthalene achieves higher phenol distribution coefficients in an extractant concentration range of 0.1¿1.25 mol L¿1 than respective TOPO/1,3-dimethylnaphthalene or Cyanex 923/1,3-dimethylnaphthalene solutions. In a solvent impregnated resin (SIR) application, the SIRs impregnated with TOAO/1,3-dimethylnaphthalene have a higher phenol capacity than the SIRs impregnated with Cyanex 923/1,3-dimethylnaphthalene. Regeneration of the SIRs with alkaline solution of pH 13 shows that both SIRs maintain a constant phenol capacity during at least seven cycles. Based on these observations TOAO can be considered as a better alternative to Cyanex 923
To develop a new solvent-impregnated resin system for the removal of phenols from water the complex formation of triisobutylphosphine sulfide (TIBPS), tributylphosphate (TBP), and tri-n-octylphosphine oxide (TOPO) with a series of phenols (phenol, thiophenol, 3-chlorophenol, 3,5-dichlorophenol, 4-cyanophenol, and pentachlorophenol) was studied. The investigation of complex formation between the extractants and the phenols in the solvent toluene was carried out using liquid-liquid extraction, isothermal titration calorimetry (ITC), and quantum chemical modeling (B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and MP2/6-311++G(2d,2p)//B3LYP/6-311G(d,p)). The equilibrium constant (binding affinity, Kchem), enthalpy of complex formation (DeltaH), and stoichiometry (N) were directly measured with ITC, and the entropy of complexation (DeltaS) was derived from these results. A first screening of K chem toward phenol revealed a very high binding affinity for TOPO, and very low binding affinities for the other extractants. Modeling results showed that although 1:1 complexes were formed, the TIBPS and TBP do not form strong hydrogen bonds. Therefore, in the remainder of the research only TOPO was considered. Kchem of TOPO for the phenols in toluene increased from 1,000 to 10,000 M(-1) in the order phenol < pentachlorophenol < 3-chlorophenol < 4-cyanophenol approximately 3,5-dichlorophenol (in line with their pKa values, except for pentachlorophenol) in the absence of water, while the stoichiometric ratio remained 1:1. In water-saturated toluene, the binding affinities are lower due to co-complexation of water with the active site of the extractant. The increase in binding affinity for TOPO in the phenol series was confirmed by a detailed ab initio study, in which Delta H was calculated to range from -10.7 kcal/mol for phenol to -13.4 kcal/mol for 4-cyanophenol. Pentachlorophenol was found to behave quite differently, showing a DeltaH value of -10.5 kcal/mol. In addition, these calculations confirm the formation of 1:1 H-bonded complexes.
The performance of extractant impregnated resin (EIR) technology for chiral separation of amino-alcohols has been investigated. Phenylglycinol was selected as an archetype model enantiomer and azophenolic crown ether was used as a versatile enantioselective extractant. 1-Phenyloctane was selected as a suitable solvent for this application because of its very low solubility in water. The extraction system was first evaluated by liquid-liquid equilibrium experiments. It was shown that crown ether dissolved in 1-phenyloctane has an intrinsic selectivity of 11.5. However, due to very low solubility of phenylglycinol in 1-phenyloctane, the overall capacity of the crown ether solution in 1-phenyloctane is limited. The extractant solution was immobilized in macroporous polypropylene particles. Competitive sorption isotherms were obtained from batch experiments and successfully described with a predictive model based on the complexation constants and partitioning ratios, either obtained from literature or from independent experiments. The equilibrium selectivity of these EIRs approaches the intrinsic selectivity for low phenylglycinol concentrations. The dynamic behaviour and stability of the system were examined in column experiments. Breakthrough profiles as well as the elution curves of the R enantiomer are less sharp than those of the S enantiomer proving that the R enantiomer is strongly retained on the column. Separation of phenylglycinol enantiomers is favoured by using lower feed flow rates. The column was regenerated by water with only atmospheric carbon dioxide dissolved which proved to be sufficient. After several cycles the breakthrough profiles remain unchanged suggesting that these EIRs will be sufficiently stable.
The sustainable production of fine/bulk chemicals is often hampered by product toxicity and inhibition to the producing micro-organisms. Consequently, the product must be removed from the micro-organisms' environment. To achieve this, so-called solvent-impregnated resins (SIRs) as well as commercial resins have been added to a Pseudomonas putida S12TPL fermentation that produces phenol as a model compound from glucose. The SIRs contained an ionic liquid which extracts phenol effectively. It was observed that the addition of these particles resulted in an increased phenol production of more than a fourfold while the commercial resin (XAD-4) which is widely used in aromatic removal from aqueous phases, only gave a 2.5-fold increase in volumetric production.
The separation methods which are used in the hydro-metallurgical field are reviewed and compared. Some processes in solvent extraction in use for recovery of crucial metals which are important to the U.S. defense and economy are presented. Various commercial extractants are reviewed and categorized. Other methods such as liquid membranes and ion exchange resins used for dilute metal ions separation are summarized. These methods are compared with solvent extraction. Problems to overcome in the further development of these separation methods are also identified and discussed in this paper.
Distribution data of citric acid between an aqueous solution and a xylene solution of tri-n-octylamine (TOA) were measured in the 283-323 K temperature range. The complexes formed in the organic phase were determined and the equilibrium constants for the formation of these complexes were evaluated. In addition, the apparent thermodynamic data and the mole fraction of each complex present in the organic phase were calculated. When citric acid was extracted with a mixture of TOA and di (2-ethylhexyl) phosphoric acid (D2EHPA), the synergistic and antagonistic effects, depending on either the excess TOA over D2EHPA or the excess D2EHPA over TOA, were also observed and discussed.
Column sorption of citric acid from aqueous solutions using tri-n-octylamine (TOA)-impregnated macroporous resins was studied at 298 K. The breakthrough curves were measured as a function of the feed flow rate, citric acid concentration in the feed solution, TOA concentration in the resin phase, and type of resin. It was found that the type of resin played a most important role in determining the saturated capacity under comparable conditions. The desorption of citric acid from loaded resins was also evaluated with various eluants, including HCl, HNO3, H2SO4, and Na2CO3
In this paper, the rates of the extraction of citric acid from aqueous solutions with tri-n-octylamine dissolved in xylene were measured using a stirred membrane-based cell in the 298 similar to 328 K temperarature range. It was found that, under the conditions studied, both forward extraction and back-extraction processes were mainly controlled by chemical reactions occurring at the interface on the organic side, The intrinsic rate constants for the formation and dissociation of the acid complexes were determined and a possible reaction mechanism was proposed. The effect of temperature on the reaction kinetics was also investigated and the activation energies were thus obtained.
The extraction of lactic, tartaric, succinic, and citric acids from aqueous solutions by trioctylamine (TOA, R3N) was investigated under various conditions.As a result, it was found that the concentration of acid in the organic phase increases with increasing aqueous acid concentration and this tendency is little influenced at different TOA concentrations. The log-log plots of distribution ratio vs. [TOA] revealed the following power dependence: 0.5~1 for lactic acid, for tartaric and succinic acids, and for citric acid. Hence the extraction of organic acids by TOA is expressed by the equilibrium equation HnA(aq) MR3N(org)⇄(R3N)mHnA(org) where n and m=1 for lactic acid, n=2 and m=1~2 for tartaric and succinic acids, and n=3 and m=1~3 for citric acid. The formation of the organic species is also supported by infrared spectral results. Moreover the temperaturedependence of distribution ratio indicates that the extraction of organic acids decreases with increasing temperature. © 1985, The Japan Society for Analytical Chemistry. All rights reserved.
The three-phase extraction process, a modification of reactive extraction, has been investigated for its applicability in the separation of organic acids from fermentation broth. It has been compared with reactive extraction, liquid membrane permeation, and supercritical fluid extraction.These processes are based on the use of amine extractants, which have to be dissolved in nonpolar solvents, for the extraction of carboxylic acids, hydroxycarboxylic acids, and aminocarboxylic acids.This paper considers the comparison of the above-mentioned processes. Furthermore, the extractability of acids from synthetic aqueous solutions and fermented broths has been compared. Principal consideration has been paid to the extraction of lactic acid, gluconic acid, citric acid, and L-leucine.
Solvent-impregnated resins (SIR) containing di-(2,4,4-trimethylpentyl)phosphinic acid (DTMPPA) were prepared by adsorption of the organophosphorus extractant into Amberlite XAD-2 polymeric macroporous support. The distribution of DTMPPA between the aqueous phase and resin phase was determined as a function of both pH and loading of the organophosphorus extractant on the resin. The distribution ratio of the organophosphorus compound was obtained after determining the total phosphorus concentration in the aqueous phase by coupled plasma atomic emission spectroscopy. The data were analyzed numerically by the program LETAGROP-DISTR, in order to determine the distribution constant KD, the aggregation constant Kn, and the acidity constant Ka. Moreover, in order to clarify the interactions between the polymeric adsorbent and the extractant, Fourier transform infrared spectroscopy studies have been carried out. Finally the distribution of DTMPPA dissolved in toluene has been compared with its distribution in Amberlite XAD-2.
Experiments were conducted on the equilibrium distribution of divalent zinc between hydrochloric acid medium and macromolecular resin containing tri-n-octylamine (TOA) as an active component. The sorption of zinc on the impregnated sorbent can be expressed by the following stoichiometric relation: ZnCl2(aq.) + 2R3NHCl(s.)↔(R3NH)2ZnCl4(s.) where the equilibrium constant was found to be 3.59 × 105 kg-sorbent ·dm3/mol2. Furthermore the separation of zinc and copper in aqueous solution by use of the sorbent was examined in a batch operation with hydrochloric acid concentrations over 5M. It was found that the sorbent gives high selective separation of zinc to copper, and they can be separated satisfactorily from a 1.0 mol/dm3 hydrochloric acid solution. The applicability of the TOA-impregnated sorbent to column operation is also reported.
Several carboxylic acids are prominent commercial products, and their number and importance will probably grow. Getting these acids out of aqueous solution is necessary in petrochemical manufacture, fermentation, and the environmentally and economically important recovery from waste streams. In this paper, the authors discuss the methods possible to extract acids such as citric, lactic, and succinic from complex mixtures. Carboxylic acids are also readily made by fermentation and are among the most attractive substances that could be manufactured from biomass. Branches of this cycle lead to acetic, lactic, propionic, and formic acids, among others. Carboxylic acids are promising intermediates in a bioprocessing complex, because the oxygen of the biomass is placed in a form that is useful for further reaction with many other products. Citric acid is manufactured on a large scale by fermentation, and lactic and fumaric acids, among others, were manufactured that way in the past.
This work examines the chemistry of solvent extraction by long-chain amines for recovery of carboxylic acids from dilute aqueous solution. Long-chain amines act as complexing agents with the acid, which facilitates distribution of the acid into the organic phase. The complexation is reversible, allowing for recovery of the acid from the organic phase and regeneration of the extractant. Batch extraction experiments were performed to study the complexation of acetic, lactic, succinic, malonic, fumaric, and maleic acids with Alamine 336, an aliphatic, tertiary amine extractant, dissolved in various diluents. Results were interpreted by a ''chemical'' model, in which stoichiometric ratios of acid and amine molecules are assumed to form complexes in the solvent phase. From fitting of the extraction data, the stoichiometry of complexes formed and the corresponding equilibrium constants were obtained. The results of the model were combined with infrared spectroscopic experiments and results of past studies to analyze the chemical interactions that are responsible for extraction behavior. The information from the equilibrium studies was used to develop guidelines for large-scale staged extraction and regeneration schemes. A novel scheme, in which the diluent composition is shifted between extraction and regeneration, was developed which could achieve both high solute recovery and high product concentration. 169 refs., 57 figs., 15 tabs.
The extraction of Zn(II), Cu(II) and Cd(II) from nitrate solutions at 0.1 M ionic strength by impregnated resins containing di(2-ethylhexyl)phosphoric acid has been studied at 25 °C.The distribution coefficient was determined as a function of both pH and extractant concentration in the resin phase. The data were analyzed graphically using the slope analysis method, and numerically using the program LETAGROP-DISTR. The composition of the extracted species in the resin phase has been determined.Analysis of the results showed that the extraction of these metal ions can be explained assuming the formation of metal complexes in the resin phase with a general composition ML2(HL) q where q takes different values depending on the metal. An extraction reaction is proposed and the extraction constants of these species are given.Finally, a comparison between the extraction of Zn(II), Cu(II) and Cd(II) by di(2-ethylhexyl)phosphoric acid into Amberlite XAD2 and the extraction using organic solvents has been made.
Studies have been conducted on the sorption characteristics of palladium (II) from hydrochloric acid media with a macromolecular resin containing tri-n-octylamine (TOA). Sorption equilibrium of Pd (II) on the TOA-impregnated sorbent can be expressed by a simple ion-exchange reaction between a tetrachloro complex of Pd (II) in the aqueous phase and an amine salt in the sorbent as follows:where the equilibrium constant was found to be 6.98x10 kg/dm.The elution of Pd (II) from the metal-loaded sorbent was also examined. Elution can be attained with either hydrochloric acid or aqueous ammonia: in particular, the latter gave a high elution ratio even at a concentration less than 1M. The effect of the pore diameter of the macromolecular resins on the Pd(II) sorption was also studied and two methods for preparating impregnated sorbent were examined.
Solvent impregnated resins (SIR) containing di-(2-ethylhexyl)-phosphoric acid (DEHPA) were prepared by adsorption of the organophosphorous extractant into Amberlite XAD2 polymeric macroporous adsorbent. Extractant adsorption on the polymer was studied as a function of both the nature of the organic solution and the extractant concentration used. The retention and interactions of the extractant on the polymeric matrix was studied by FTIR spectroscopy.The distribution of DEHPA between the aqueous phase and resin phase was determined as a function of both pH and loading of the organophosphorous extractant on the resin. The distribution ratio of the organophosphorous compound was obtained after determining phosphorous by coupled plasma atomic emission spectroscopy. The data have been analyzed numerically by the program LETAGROP-DISTR, in order to determine the distribution constant KD, the aggregation constant Kn and the acidity constant Ka
Coextraction of water during extraction of succinic acid by Alamine 336 in different diluents has been measured. The amounts of coextracted water lie in the same order as the solubilities of water in the diluents without amine present. Water coextraction with different acids follows the order fumaric > malonic > maleic = succinic > lactic > acetic. The effects of temperature on extraction of succinic and lactic acids by Alamine 336 with chloroform and methyl isobutyl ketone (MIBK) diluents have been measured. Enthalpies and entropies of complex formation have been derived from the results and are interpreted in terms of the differences in interactions among the species involved. Two approaches for regeneration through back-extraction into an aqueous phase are considered.
The results of the mass action law analysis are combined with the results from spectroscopic studies to analyze chemical interactions involved in the complexation of carboxylic acids with amine extractants in various diluents. Infrared spectroscopic studies were performed on anhydrous solutions of succinic, maleic, and fumaric acids to compare the effect of rigidity and configuration on complex stoichiometry. Dicarboxylic acids that form intramolecular hydrogen bonds are inhibited from forming (1,2) and (2,2) complexes. The results from the mass action law analysis and spectroscopic studies of previous investigators indicate that formation of the (1,1) complex involves ion-pair or hydrogen-bond formation between the acid and the amine, while (2,1) complex formation involves hydrogen bonding between the carboxyl of the second acid and the carboxylate of the first.
Studies have been made of the extraction of acetic, lactic, succinic, malonic, fumaric, and maleic acids by Alamine 336, an aliphatic, tertiary amine extractant, dissolved in various diluents. The results were interpreted by a 'chemical modeling' approach, in which the stoichiometries of acid-amine complexes and corresponding equilibrium constants which best represent the experimental results were determined. The acids studied differed in pKa and in the presence or absence of functional groups other than the primary carboxyl group. Diluents were chosen from different chemical classes - electron donating, electron accepting, polar, and nonpolar - so as to examine the effects of diluent-complex interactions.
The separation of zinc and copper from aqueous sulfate solutions using bis(2-ethylhexyl)phosphoric acid-impregnated hydrophobic macroporous resin has been examined in either batch or continuous operation. This resin could be successfully impregnated by the modified dry method. It was found that the impregnated resin gives high selective separation of zinc to copper, and they can be satisfactorily separated from 0.5 mol/dm3 (Na,H)SO4 aqueous solution.
Equilibrium studies were thermodynamically made for the sorption of divalent copper and zinc ions from aqueous sulfate solutions with bis(2-ethylhexyl)phosphoric acid-impregnated hydrophobic macroporous resins, by employing either Bromley or the simplified Pitzer equations to estimate the stoichiometric activity coefficient of various species in the aqueous phase. The mechanisms of copper and zinc sorption were found to be the same as those of the solvent extraction. The operating lifetime of the impregnated resin and the influence of preparation method on the impregnation capacity, as well as the effects of aqueous ionic strength and temperature on the sorption equilibrium, were also examined.
Extraction of citric acid from aqueous solutions with TAA, a mixture of tertiary aliphatic amines, dissolved in 1-octanol/n-heptane mixtures, and coextraction of water have been studied as a function of acid, amine, and octanol concentrations at different temperatures. Using a "chemical modeling" approach, two complexes [acid.amine.h11H2O and acid.(amine)2.h12H2O] have been assumed to exist in the organic phase, and the corresponding equilibrium constants, apparent enthalpies, and entropies of complex formation have been evaluated. The overall equilibrium constants, beta'11 and beta'12, and hydration numbers, h11 and h12, have been correlated with the concentration of amine and with various properties of the mixed solvents. The solubility of water in acid-free organic phase has been found to be the best fitting parameter. According to IR spectra, the amine-acid interaction is represented by an equilibrium between the extreme types of an H-bond ("neutral" O-H...NR3 and ionic O-...H-+NR3). A mathematical model of acid extraction and water coextraction has been formulated.
Experimental data are reported for the adsorption of four carboxylic acids onto a macroreticular resin (Amberlite XAD-2) from dilute aqueous solutions. Acetic, propionic, n-butyric, and n-hexanoic acids were studied at 278, 298, and 323 K. The data, which cover a concentration range from 10 -2 to 10 -4 M, were fitted with a Chebyshev rational approximation polynomial. The data for the acids that were completely miscible in water were successfully correlated by using a modified form of the adsorption potential theory.
Surface diffusivities of benzaldehyde in liquid‐filled pores of Amberlite particles (polystyrene) were measured at 25°C using water as a solvent. For particles of different surface areas but chemically similar pore surfaces, the intrinsic surface diffusivity D s ' was about the same, but the relative importance of surface to pore‐volume diffusion increased with surface area. For a single type of particle, the adsorption capacity was decreased about twenty‐fold by adding up to 19 mole % methanol to the solvent. This was accompanied by an increase in D s ' from 1.2 × 10 ⁻⁸ to 1.2 × 10 ⁻⁷ cm ² /s. These results were interpreted in terms of a two‐step theory for surface migration: (1) formation of a vacant site on the adsorbent surface followed by (2) movement of the adsorbate molecule into the site by breaking the surface‐adsorbate bond. The theory predicts that surface transport will be large when the surface area is high and that the D s ' will be large when the heat of adsorption is low, and when the bond between solvent molecules and the surface is weak.
In our studies the surface contribution to intraparticle transport was as much as 20 times the contribution due to pore‐volume diffusion. This ratio increases as the concentration of adsorbate in the liquid decreases.
Tertiary amines are effective extractants for citric acid. The effect of diluents on the extraction is very important since it affects the distribution of citric acid, the selectivity and the phase separation properties. The distribution coefficient for citric acid is strongly temperature dependent. This makes it possible to strip the acid into water at a higher temperature. Alamine 336 dissolved in a nonpolar diluent is a suitable solvent. Pilot plant runs show that the process is technically feasible.
Various mathematical models of amine extraction of tribasic weak acid were developed and compared with equilibrium data on the distribution of citric acid between water and solution of trialkylamine in MIBK. It has been found that the two suggested mechanisms of extraction (distribution of non-dissociated portion of acid × distribution of dissociated portion of acid) are equivalent, as far as the fit of the model is concerned the only difference being in the values of equilibrium constants. Two amine : acid complexes in the organic phase have been assumed (1 : 1, 2 : 1), their hydration numbers being 4 and 1, respectively. The non-ideality of the aqueous phase was neglected in the concentration range of interest. The non-ideality of the organic phase was expressed both in terms of aggregation and hydration (exponential correction using hydration numbers). The best fit was obtained using a combination of the aggregation and hydration corrections.
Techniques for possible higher and rapid production of citric acid from the well known industrial medium i.e. molasses has
been reported using Aspergillus niger. This includes optimization of the total reducing sugar (TRS) and nutrients like nitrogen
and phosphorous. The long and unproductive lag periods normally associated with this type of fermentation has been reduced.
These strategies are discussed in detail.
Distribution of citric acid between water and trialkylamine C7-C9 dissolved in 7 various diluents (p-xylene, toluene, benzene, MIBK, 1-octanol, methylene chloride, chloroform) was studied. Using a “chemical modeling” approach two acid: amine complexes, ACID. AMINE and ACID. (AMINE)2, have been assumed to exist in the organic phase in the case of proton-donating diluents (octanol, chloroform, methylene chloride), while the complexes ACID. AMINE and (ACID)2(AMINE)3 have been suggested in the case of aromatics and MIBK. The estimated values of overall extraction constants, K11, K12 and K23, were correlated with solvatochromic parameters of the diluents according to the linear solvation energy relationship (LSER). Using this correlation the extractability of citric acid can be predicted for a wide range of diluents or their mixtures. The coextraction of water with acid was explained in terms of the corrected physical solubility of water, w*, and hydration coefficients, h11, h12 and h23. The values of hydration coefficients were also correlated with the solvatochromic parameters of the diluents.
The extraction of Zn(II), Cu(II) and Cd(II) from nitrate solutions at 0.1 ionic strength by impregnated resins containing di-(2,4,4-trimethylpentyl)phosphonic acid (HL) has been studied at 25°C. The distribution coefficient of the metal ion was determined as a function of both pH and extractant concentration in the resin phase, and the data were analyzed graphically using the slope analysis method and numerically using the program LETAGROP-DISTR. Analysis of the results showed that the extraction of these metal ions can be explained by the formation of metal complexes in the resin phase with a general composition ML2(HL)q where the value of q depends on the metal. Extractions reactions are proposed and the extraction constants of these reactions are presented. Finally, a comparison between the extraction of Zn(II), Cu(II) and Cd(II) with di-(2,4,4-trimethylpentyl)phosphinic acid sorbed into Amberlite XAD-2 and the extraction using an organic solvent as Isopar H has been made.
Impregnated resins containing di-(2,2,4-trimethylpentyl)phosphinic acid (Cyanex 272) were prepared by adsorption of the extractant into Amberlite XAD-2 polymeric adsorbant.The distribution of Cyanex 272 between the aqueous and resin phase was studied as a function of pH and loading of the organophosphorous extractant on the resin. The concentration of organophosphorous compound was determined by ICP.XAD-2-Cyanex 272 impregnated resins were tested for the recovery and separation of Zn(II), Cd(II) and Cu(II) from aqueous solutions. The distribution coefficient of Zn(II), Cd(II) and Cu(II) between the aqueous phase and the resin phase were determined under different conditions. The separation factors between the three metal ions are sufficiently large to allow effective separation of Zn from Cd (100%) and Cu (90%). The selective recovery of Zn(II) from aqueous solutions has been carried out by using SIR as the column stationary phase. The retained metal ions were released from the resin quantitatively by elution with hydrochloric acid solutions at the correct concentration for each metal ion.
Within the framework of a program aiming to improve the existing extractive recovery technology of fermentation products, the state of the art is critically reviewed. The acids under consideration are propionic, lactic, pyruvic, succinic, fumaric, maleic, malic, itaconic, tartaric, citric, and isocitric, all obtained by the aerobic fermentation of glucose via the glycolytic pathway and glyoxylate bypass. With no exception, it is the undissociated monomeric acid that is extracted into carbon-bonded and phosphorus-bonded oxygen donor extractants. In the organic phase, the acids are usually dimerized. The extractive transfer process obeys the Nernst law, and the measured partition coefficients range from about 0.003 for aliphatic hydrocarbons to about 2 to 3 for aliphatic alcohols and ketones to about 10 or more for organophosphates. Equally high distribution ratios are measured when long-chain tertiary amines are employed as extractants, forming bulky salts preferentially soluble in the organic phase.
Solvent Extraction and Adsorption by Extracting Resins of Phenol. Huadong Huagong Xueyuan Xuebao
- H Q Gao
- Y F Su
Gao, H. Q.; Su, Y. F. Solvent Extraction and Adsorption by
Extracting Resins of Phenol. Huadong Huagong Xueyuan
Xuebao 1991, 17 (3), 249-254.
Separation of Citric Acid from Fermenation Broth with a Neutral Polymeric Adsorbent. US Patent US 4
- S Kulprathipanja
- T Sato
- H Watanabe
Kulprathipanja, S. Separation of Citric Acid from Fermenation Broth with a Neutral Polymeric Adsorbent. US Patent US 4,-720,579, 1988. Sato, T.; Watanabe, H.; Nakamura, H. Extraction of Lactic, Tartaric, Succinic, and Citric Acids by Trioctylamine. Bunseki Kagaku 1985,34, 559-563.
Process for the Extraction of Organic Acids from Aqueous Solution. Eur. Patent Appl
- A M Baniel
- J Horacek
Baniel, A. M. Process for the Extraction of Organic Acids from Aqueous Solution. Eur. Patent Appl. EP 49,429, 1982. Baniel, A. M.; Gonen, D. Production of Citric Acid. US Patent US 4,994,609, 1991. Bizek, V.; Horacek, J.;
Process for the Extraction of Organic Acids from Aqueous Solution
- A M Baniel
Baniel, A. M. Process for the Extraction of Organic Acids from
Aqueous Solution. Eur. Patent Appl. EP 49,429, 1982.
Separation of Citric Acid from Fermenation Broth with a Neutral Polymeric Adsorbent
- S Kulprathipanja
Kulprathipanja, S. Separation of Citric Acid from Fermenation
Broth with a Neutral Polymeric Adsorbent. US Patent US 4,-720,579, 1988.
Preparation and Study of the Retention and Distribution of the Extractant on the Resin. Solvent Extr. Zon Exch
- I Acid
Acid. I. Preparation and Study of the Retention and Distribution
of the Extractant on the Resin. Solvent Extr. Zon Exch. 1994a,
12 (2), 349-369.
- A M Baniel
- D Gonen
Baniel, A. M.; Gonen, D. Production of Citric Acid. US Patent US
4,994,609, 1991.