Intensification of enzymatic conversion of glucose to lactic acid by reactive extraction

Lactic acid is an important commercial product and extracting this out of aqueous solution is a growing requirement in fermentation-based industries and recovery from waste streams. The design of an amine extraction process requires (i) equilibrium and (ii) kinetic data for the acid-amine (solvent) system used. Equilibria and kinetics for lactic acid extraction by Alamine 336 in octanol as a diluent have been determined and compared with other diluents studied earlier. An approach for extracting the lactic acid by a long-chain tertiary amine, which is in the dispersed phase as a liquid ion exchanger (LIX), is presented. A mathematical model for slurry phase reactor with glucose in the continuous aqueous phase, the amine with a diluent in the dispersed phase and the immobilized enzyme as the solid catalyst, has been developed using equilibrium and kinetic data for reactive extraction. Effects of various parameters affecting the conversion of glucose have been discussed. The model has been solved for batch and semi-batch modes. It has been shown that the semi-batch mode yields approximately five times higher productivity than batch mode.     

Extraction of protactinium from acid media using Aliquat 336

Solvent extraction studies on protactinium were carried out from hydrofluoric acid, hydrochloric acid, and a mixture of hydrochloric and hydrofluoric acids using Aliquat 336 and ²³¹Pa. The extraction of protactinium from hydrofluoric acid (0.025–10 M) decreased with increasing acid concentration and was less than 10% above 5 M. The extraction from hydrochloric acid (0.5–8 M) started only above 4 M and increased with increasing acid concentration. The extraction of protactinium from a mixture containing hydrochloric acid (0.5–8 M) and 0.03 M hydrofluoric acid decreased with increasing acid concentration reached to a minimum at about 2 M and then increased with increasing acid concentration. At low acidity, extraction of protactinium from hydrofluoric acid was higher compared to hydrochloric acid and the mixture of hydrochloric and hydrofluoric acids. Nitric acid (10 M) and hydrofluoric acid (10 M) were suitable for quantitative recovery of protactinium from organic phase. The extraction of ²³¹Pa from real thorium lean raffinate of thorium–uranium extraction process was studied using optimized extraction conditions.     

Studies on Transport of Anionic Complex of Plutonium From Nitric Acid Medium across ALIQUAT 336/n-Paraffin Liquid Membrane

The present studies deal with the application of the supported liquid membrane (SLM) technique for the separation and purification of plutonium from other impurities in nitric acid medium using anion exchanger Aliquat 336 (a quaternary ammonium salt)/ n-paraffin as a carrier. The effects of feed acidity, stripping agent, and membrane pore size and membrane thickness on the transport behavior of anionic complex of plutonium have been studied in detail. An attempt has been made to establish the mechanism for plutonium transport and model the physicochemical transport of plutonium across SLM. Transport of anionic complex of plutonium increased with increase in carrier concentration upto 10% (w/v), while with further increase in carrier concentration, decrease in transport of plutonium was observed. The PTFE membrane with 0.45 µm pore size and 80 µm thickness was found to be most suitable for the transport of plutonium. The effect of membrane thickness indicates that the transport phenomenon is diffusion controlled. Transport behavior of plutonium, uranium, and other fission products from actual feed solution of ion exchange method obtained in PUREX process was also tested and the result clearly indicates that Aliquat 336 has high selectivity for plutonium and it can be used for the separation and purification of plutonium by the supported liquid membrane technique.     

Equilibria and Kinetics of Extraction of Citric Acid from Aqueous Solutions in Alamine 336–Cyclohexanone System

Abstract

Equilibria and kinetics for the extraction of citric acid by Alamine 336 in cyclohexanone as diluent are reported. The theory of extraction accompanied by a chemical reaction has been used to obtain the intrinsic kinetics of extraction of citric acid by Alamine 336 in cyclohexanone. The reaction has been found to be first order in both Alamine 336 and citric acid with a rate constant of 8.8×10^?3 m³ kmol^?1 s^?1.     

Zirconium and Hafnium Separation,Part 1. Liquid/Liquid Extraction in Hydrochloric Acid Aqueous Solution with Aliquat 336

Abstract

The extraction of zirconium and hafnium from aqueous HCl solutions by means of Aliquat 336 in organic diluents was systematically studied. The following three aspects were discussed: the extraction dependence on HCl, the Aliquat 336 concentrations, and the nature of diluents. Both of the metals were stripped with deionized water and the influence of phase ratio on the efficiency of the stripping has been investigated. The stoichiometry of the extracted Zr and Hf species from single metal ion were studied and a possible extraction mechanism for the Zr‐Hf mixture is discussed in the light of the results obtained.     

Kinetics and the difference for extraction of praseodymium and neodymium from nitrate aqueous solution by[A336] [NO3] using the single drop technique

The kinetics and the difference for Pr(Ⅲ) and Nd(Ⅲ) extraction from nitrate aqueous solution using trialkylmethylammonium nitrate([A336][NO_3]) as extractant were investigated by the single drop technique.The dependence of the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) on the concentrations of free Pr(Ⅲ) and Nd(Ⅲ)ions, the concentrations of Na NO_3 and H~+in aqueous solutions, and the concentrations of [A336][NO_3] in kerosene solutions were discussed and the corresponding extraction rate equations for Pr(Ⅲ) and Nd(Ⅲ) were obtained. These equations demonstrated that the reaction rate constant of Pr(Ⅲ) with [A336][NO_3] was double than that of Nd(Ⅲ). The effect of the addition of diethylenetriaminepentaacetic acid(DTPA) on the difference in the extraction rate of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] was also investigated. It was revealed that the difference in the complex formation rates of Pr(Ⅲ) and Nd(Ⅲ) with DTPA made a significant impact on the difference in the extraction rates of Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3]. The ratio of extraction rates of Pr(Ⅲ) to Nd(Ⅲ) with[A336][NO_3] was in proportion to the ratio of complex formation rates of Pr(Ⅲ) to Nd(Ⅲ) with DTPA. The extraction rate difference for Pr(Ⅲ) and Nd(Ⅲ) with [A336][NO_3] increased due to a higher complex formation rate constant of DTPA with the free and un-complexed Nd(Ⅲ) ions in the aqueous nitrate solution than that with Pr(Ⅲ) ions. Therefore, the addition of DTPA in the aqueous nitrate solution is an effective method to intensify the separation of Pr(Ⅲ) and Nd(Ⅲ) in kinetics. The study on the extraction mechanism indicated that both the extraction of Pr(Ⅲ) and Nd(Ⅲ) by [A336][NO_3] were diffusion controlled, and the reactions obeyed SN2 mechanism. The present work highlights a possible approach to strengthen the kinetic separation of Pr(Ⅲ) and Nd(Ⅲ).     

Extraction Selectivity of a Quaternary Alkylammonium Salt for Trivalent Actinides over Trivalent Lanthanides: Does Extractant Aggregation Play a Role?

The extraction behavior of a quaternary alkylammonium salt extractant was investigated for its selectivity for trivalent actinides over trivalent lanthanides in nitrate and thiocyanate media. The selectivity was evaluated by solvent extraction experiments through radiochemical analysis of ²⁴¹Am and ^152/154Eu. Solvent extraction distribution and slope-analysis experiments were performed with americium(III) and europium(III) with respect to the ligand (nitrate and thiocyanate), extractant, and metal (europium only) concentrations. Further evaluation of the equilibrium expression that governs the extraction process indicated the appropriate use of the saturation method for estimation of the aggregation state of quaternary ammonium extractants in the organic phase. From the saturation method, we observed an average aggregation number of 5.4 ± 0.8 and 8.5 ± 0.9 monomers/aggregate for nitrate and thiocyanate, respectively. Through a side-by-side comparison of the nitrate and thiocyanate forms, we discuss the potential role of the aggregation in the increased selectivity for trivalent actinides over trivalent lanthanides in thiocyanate media.     

季铵盐(Aliquat 336)萃取对氨基苯磺酸的特性研究

利用季铵盐(Aliquat 336)为反应剂,在较宽的pH值条件下,研究了对氨基苯磺酸稀溶液的萃取相平衡特性;测定了反应剂浓度、稀释剂种类、盐的存在以及溶液pH值对反应萃取平衡分配系数的影响;提出了反应剂与对氨基苯磺酸负离子的阴离子交换反应机理,建立了平衡分配系数D值的表达式。结果表明,极性稀释剂不利于对氨基苯磺酸的萃取,惰性稀释剂能提供较大的萃取平衡分配系数,其顺序为:苯>四氯化碳>氯仿>正辛醇;盐的存在会降低Aliquat 336的萃取效率;与三烷基胺(Alamine 336)相比,Aliquat 336具有更宽的pH值适用范围。     

三烷基胺与二（2-乙基己基）磷酸协同萃取对氨基苯酚

引　言随着现代工业的发展及环境保护标准的严格实施 ,对极性有机物稀溶液的分离和工业废水的治理提出了更高的要求 ,而萃取技术在该领域已进行了较为广泛的研究 ,并进行了工业应用 .由于废水体系的复杂性 ,尤其是含多官能团的极性有机物废水 ,在采用萃取方法进行废水预处理时强化萃取能力是十分必要的 .自 195 6年Blake[1] 提出协同萃取以来 ,由于它兼具物理萃取和化学萃取的优点 ,具有更高的选择性和高效性 ,已成功地用于金属的萃取分离中 .协同萃取用于极性有机物稀溶液的分离多见于物理萃取 ,例如乙酸丁酯与苯乙酮协萃苯酚[2 ] 、乙酸…