A novel constant interfacial area cell for determining the extraction kinetics of Er(III) from chloride medium

A novel constant interfacial area cell (NCIAC), by spatially separating the agitation from liquid flow circulation of organic and aqueous two phases, was suggested to obtain detailed kinetic data for Er(III) extraction from chloride medium by 2-ethyl-hexyl-phosphonic acid mono-(2-ethylhexyl) ester (EHEHPA). Different from the traditional Lewis cell and the constant interfacial area cell with laminar flow, the concentrations of Er(III) in organic and aqueous two phases were uniform, and the stability of the interfacial area between the two phases could be controlled effectively. Therefore, the special requirements for the design of agitators in the traditional Lewis cell and the constant interfacial area cell for minimizing the influence of diffusion resistance could be avoided. Experimental results indicated that the extraction kinetics was mainly affected by the aqueous flow rate, interfacial area between organic and aqueous two phases, and the aqueous pH values. An extraction kinetic equation was suggested based on the experimental data.     

Lipase made active in hydrophobic media

Enzymes are distinguished from other catalysts by their high substrate specificity. This is a great asset when one wants to apply them for syntheses of various compounds. Their usage, however, generally is limited to hydrophilic reaction media, because they usually are not soluble and active in hydrophobic media. Recently, we have been able to make various enzymes soluble and active in highly hydrophobic organic solvents. The key to this success is the chemical modification of enzymes with an amphipathic synthetic polymer, polyethylene glycol. The activated polymers can be attached to enzymes in aqueous buffer solutions, and once enzymes are modified they become soluble and active in various organic solvents such as benzene, toluene and cholorinated hydrocarbons and exhibit high enzymic activities in these organic solvents. Modified hydrolytic enzymes catalyzed the reverse reaction of hydrolysis in organic solvents. The modified lipase catalyzed various ester synthesis reactions. Because the reactions were conducted in the pure solvent system, it also was possible to study the kinetics and the substrate specificity for ester synthesis reaction. It also catalyzed the polymerization of a hydroxy group containing carboxylic acid due to the bifunctional nature. The modified lipase catalyzed ester exchange between an ester and an alcohol, between an ester and a carboxylic acid and between two esters in organic solvents. When the two substrates for ester exchange were liquid, the reaction could take place without organic solvents. The modified lipase catalyzed an ester exchange reaction between trilaurin and triolein when dissolved in these substrates. Dilauroyl-monooleoylglycerol and monolauroyl-dioleoyl-glycerol were formed from these two substrates in the presence of the modified lipase. The modified enzyme was extremely thermostable in its substrates. In the ester synthesis and ester exchange reactions, a trace amount of water was necessary for expression of the enzymic activity. It is suggested that the amphipathic polymer molecules retained water in close proximity to the enzyme. Presented at the symposium “The Biology, Biochemistry and Technology of Lipase” at the 78th annual meeting of the American Oil Chemists’ Society held May 17–21, 1987, in New Orleans, Louisiana.     

异辛醇-甲苯萃取盐湖卤水中硼酸的动力学

引言 硼及其化合物在国民经济中用途极为广泛[1],但是我国主要的硼原料之一硼镁矿石却日趋枯竭,于是开发液体硼矿资源--含硼盐湖卤水成为当务之急.近年来杨卉芃等[2]、李文强[3]、杨存道等[4]分别以沉淀法、离子交换法和结晶法对盐湖卤水提硼工艺进行了研究,并取得了一定的成果.     

Study of auto-accelerated reactions in heterogeneous liquid/liquid mixture: Reaction products effects on mass transfer kinetics

The alkaline hydrolysis of aromatic esters exhibits auto-accelerated kinetics when performed under two phase conditions. This auto-acceleration behavior is linked to reaction products effects (surfactant and co-solvent) on mass transfer kinetics. The co-solvent increases the equilibrium concentration of organic compounds in aqueous solution, while the surfactant modifies the mass transfer coefficient and interfacial area. In this research work, the selected reaction is the alkaline hydrolysis of methyl benzoate carried out in a calorimetric reactor Mettler RC1 in isothermal semi-batch mode. The parameters estimation of mass transfer and chemical kinetics has been conducted using thermal power profile. Two functions—giving the evolution during reaction of the mass transfer coefficient and the equilibrium concentration—are proposed accordingly to surfactant and co-solvent concentrations.     

Kinetic study of the hydrolysis of two formate esters held in a single organic drop

The rising drop technique was used to study the kinetics of the alkaline hydrolysis of two formate esters; n-butylformate and iso-amylformate in toluene formed the organic phase, whilst aqueous sodium hydroxide was used as the continuous phase. The effects of ester and alkali concentrations on the rate of the hydrolysis were studied. The order of the reaction was found to change with respect to the concentration of both reactants. Cetyltrimethylammoniumbromide (CTAB) was used as a possible catalyst for this liquid–liquid hydrolysis. When CTAB was added to the aqueous phase, enhancement of reaction was observed, whilst its addition to the organic phase caused inhibition of the hydrolysis. It is suggested that the enhancement of the reaction is due to the interaction of micelles in proximity to the interface while the inhibition is probably due to chemical blocking of the interface by adsorbed molecules of ionized CTAB.     

Equilibrium and kinetic studies on the extraction and stripping of uranium(VI) from nitric acid medium into tri-phenylphosphine oxide using a single drop column technique

Equilibrium and kinetic studies have been carried out on the extraction of uranium(VI) from aqueous nitrate medium into tri-phenylphosphine oxide (TPPO). It was found that uranium extraction by TPPO was suitable in toluene as diluent than cyclohexane and chloroform. Kinetic studies were carried out using a single drop column method. Reaction orders were determined with respect to uranium and nitric acid concentrations in the aqueous phase and TPPO concentrations in the organic phase. It was found that the extraction kinetics could be explained in terms of an aqueous phase interfacial reaction accompanied by diffusion through the interface. Sodium hydroxide solution is suitable for stripping uranium from TPPO in toluene.     

MASS TRANSFER OF SULFURIC ACID BY TRIOCTYLAMINE THROUGH A SUPPORTED LIQUID MEMBRANE

The extraction of sulfuric acid in a supported-liquid membrane (SLM) process, and the kinetics of extraction and stripping of sulfuric acid in a cell of constant interfacial area by trioctylamine (TOA)/kerosene solvent were investigated. The kinetics of extraction and stripping were determined by examining the effects of the operating variables. The extraction rate is a function of the activity of sulfuric acid and the concentration of TOA; the stripping rate is a function of the concentration of trioctylamine sulfate salts in the organic solution. A generalized transport model, which included the film diffusion of sulfuric acid in the aqueous phase, the membrane diffusion within the SLM, and the interfacial chemical reaction, was built. The permeability of sulfuric acid through the SLM using TOA as a mobile carrier was determined. The rate-determining step of the extraction of sulfuric acid through a SLM was analyzed using the data obtained from the experiments of extraction kinetics and the mass transfer in the aqueous phase. Diffusion within the membrane dominates the process of extraction process of sulfuric acid by TOA through a SLM.     

Alcoholysis of waste fats with 2‐ethyl‐1‐hexanol using Candida antarctica lipase A in large‐scale tests

Commercial native lipase A from Candida antarctica was used to produce alkyl esters through the alcoholysis of (waste) fats with 2‐ethyl‐1‐hexanol. The process was carried out in batch stirred tank reactors (from 100 mL up to 3000 L). The content of alkyl esters in reaction mixtures was determined by gradient HPLC using an evaporative light scattering detector and the reaction progress was controlled by determining the ratio of the palmitic acid ester peak area to the oleic acid ester peak area in HPLC chromatograms. The results show that alcoholysis is the favoured reaction in presence of excess water and water‐insoluble alcohols in comparison with hydrolysis (fatty acid content <5%). The optimum amount of water for the alcoholysis was found to be 80–100% of the amount of fat. In the presence of low quantities of water both alcoholysis and hydrolysis are slow. Conversion rate increases with increasing temperature to 65–70 °C. Based on these results a large‐scale test to produce 3000 L of alkyl ester (to be used as lubricant coolant) was carried out. The experiments have proved that alcoholysis is completed after about 7–10 h depending on temperature.     

HYDROLYSIS OF ETHYL-2-BROMOISOBUTYRATE ESTER IN AN ALKALINE SOLUTION

The hydrolysis of ethyl-2-bromoisobutyrate in an alkaline solution/organic solvent two-phase medium as well as the effect of quaternary ammonium salt (e.g., tetrabutylammonium bromide) on the hydrolysis of ethyl-2-bromoisobutyrate were investigated in this work. The proposed mechanism for the hydrolysis of ethyl-2-bromoisobutyrate was verified based on experimental analysis. Both the bromo-alkyl (Br-C bond) and ester (-COOR) functional groups of ethyl-2-bromo-isobutyrate hydrolyze into alcohol and acid. Several reaction steps for the hydrolysis of these bromo-alkyl and ester functional groups were developed and discussed. A kinetic model of each reaction step was developed in which the rate expression was derived. The intrinsic rate constants of the reactions were determined from the experimental hydrolyzing data of ethyl-2-bromoisobutyrate using curving fitting. The effects of the reaction conditions on the conversion of reactants were investigated in detail. The results indicated that the conversion of reactants is highly dependent on the concentration of alkaline compound in the aqueous solution. An optimum value of alkaline concentration to produce a maximum conversion of reactant was obtained. Moreover, the conditions for reducing the hydrolysis of halo ester by adding sodium carbonate are recommended.     

HYDROLYSIS OF ETHYL-2-BROMOISOBUTYRATE ESTER IN AN ALKALINE SOLUTION

The hydrolysis of ethyl-2-bromoisobutyrate in an alkaline solution/organic solvent two-phase medium as well as the effect of quaternary ammonium salt (e.g., tetrabutylammonium bromide) on the hydrolysis of ethyl-2-bromoisobutyrate were investigated in this work. The proposed mechanism for the hydrolysis of ethyl-2-bromoisobutyrate was verified based on experimental analysis. Both the bromo-alkyl (Br-C bond) and ester (-COOR) functional groups of ethyl-2-bromo-isobutyrate hydrolyze into alcohol and acid. Several reaction steps for the hydrolysis of these bromo-alkyl and ester functional groups were developed and discussed. A kinetic model of each reaction step was developed in which the rate expression was derived. The intrinsic rate constants of the reactions were determined from the experimental hydrolyzing data of ethyl-2-bromoisobutyrate using curving fitting. The effects of the reaction conditions on the conversion of reactants were investigated in detail. The results indicated that the conversion of reactants is highly dependent on the concentration of alkaline compound in the aqueous solution. An optimum value of alkaline concentration to produce a maximum conversion of reactant was obtained. Moreover, the conditions for reducing the hydrolysis of halo ester by adding sodium carbonate are recommended.     

Penicillin G extraction by amberlite LA-2—a study of interfacial reaction kinetics by interfacial tension measurements

The concentration of reactants at an interface cannot be determined directly. The concentration at the interface has been estimated by measuring the interfacial tension at the interface between two immiscible solutions. An aqueous phase, de-ionised water containing penicillin G, and an organic phase containing amberlite LA-2 were used as a typical system to study the kinetics of interfacial reaction. The interfacial tension was measured by a spinning-drop tensiometer at 25 ± 0·1°C. The interfacial tension was found to correlate well with the concentrations of penicillin G, Amberlite, LA-2 and proton in each respective phase.     

异戊醇从氯化物-磷酸体系中萃取盐酸的动力学

采用上升液滴法研究异戊醇萃取盐酸的动力学,考察二相接触面积、水相中初始盐酸、磷酸浓度对盐酸萃取速率的影响,以比较磷酸和盐酸的萃取行为。实验结果表明,盐酸的初始正向萃取速率与二相界面积无关,随水相初始盐酸、磷酸浓度的增大而增大,异戊醇萃取盐酸可能属相内反应控制模式。水相中盐酸的存在促进磷酸的萃取,用较高浓度的工业盐酸分解开阳磷矿有利于湿法磷酸的分离和净化。经非线性最小二乘法回归实验数据,得出25℃时异戊醇萃取盐酸的动力学方程,其决定性指标为0.993 9,速率常数的相对标准偏差为7.69%。     

固体酸催化酯水解制备有机膦酸

以SO_4~(2-)/M_xO_y型固体酸作为水解催化剂,对2-膦酸丁烷-1,2,4-三羧酸五甲酯水解制备2-膦酸丁烷-1,2,4-三羧酸(PBTCA)的反应进行了研究,探讨了催化剂加入量、水酯比、反应温度以及反应时间对水解转化率的影响,确定了反应的最佳工艺条件。结果表明,以SO_4~(2-)/M_xO_y型固体酸催化水解PBTC五甲酯,能有效缩短水解反应时间,提高产品质量,并且催化剂活性高、用量少,产品经~(31)PNMR谱测定,PBTCA物质的量分数达91.6%。     

Sugar ester-modified lipase for the esterification of fatty acids and long-chain alcohols

The esterification reaction of a long-chain fatty acid and a fatty alcohol with a surfactant-modified lipase in a microaqueousn-hexane system was studied. Various lipases from different sources were first modified with a surfactant of the sugar ester type to improve their dispersibility in apolar organic solvents. This enzyme modification technique converted inactive crude lipases to highly active biocatalysts for the esterification of long-chain fatty acids and fatty alcohols in a microaqueous n-hexane system. The hydrophilic-lipophilic balance value and chainlength of the fatty acid residue of the fatty acid sugar ester, used for modifying the lipases, significantly influenced the amount of precipitated lipase that was dissolved in the aqueous solution, the protein content of the lipase-surfactant complex and its esterification activity.     

硫酸氢钠催化合成十六烷二酸二乙酯的研究

以十六烷二元酸与乙醇为原料,采用硫酸氢钠做催化剂合成十六烷二元酸二乙酯。考察了原料的摩尔比、反应时间、催化剂量和带水剂对酯化收率的影响。通过分析实验结果,得出反应的最佳条件:醇酸摩尔比7∶1,催化剂量为二元酸质量的5%,带水剂环己烷为酸醇总质量的15%,回流反应时间5h,酯化的最高收率可达94.5%。硫酸氢钠重复使用4次后酯化收率为80.7%。     

Linear polyesters. Products of interfacial polycondensation of bis(4-hydroxyphenyl) ether with isomeric phthaloyl chlorides

New polyesters were obtained by interfacial polycondensation of bis(4-hydroxyphenyl) ether with phthaloyl, isophthaloyl, and terephthaloyl chlorides. The initial reaction conditions were as follows: the aqueous to organic phase ratio 1 : 1, reaction temperature 25°C, the rate of chloride addition about 10 min, and molar ratio of the reagents diol/acid dichloride 1 : 1.1, benzene-hexane as an organic phase. To determine the optimal conditions for interfacial polycondensation, the influence of the following factors on yield and value of reduced viscosity were studied: organic phase, excess of sodium hydroxide as an acceptor of HCl, contribution of benzyltriethylammonium chloride as a catalyst, and contribution of an emulsifier, Mersolan. The structure of all polyesters was determined by elemental analysis and infrared spectra. Initial decomposition and initial intensive decomposition temperature were defined by the curves of thermogravimetric analysis. Some mechanical and electrical properties of isophthaloyl polyester, only partly soluble in organic solvents, were determined.     

Kinetics of Forward Extraction of Boric Acid from Salt Lake Brine by 2-Ethyl-1,3-hexanediol in Toluene Using Single Drop Technique

The kinetics of forward extraction of boric acid from salt lake brine by 2-ethyl-1,3-hexanediol in tolu-ene was investigated using the single drop technique. The factors affecting the extraction rate include interfacial area between aqueous phase and organic phase, initial concentration of boric acid in aqueous phase, initial concen-tration of 2-ethyl-1,3-hexanediol in organic phase, and extraction temperature. The experimental results show that the extraction rate increases with the increase of the initial concentration of boric acid and 2-ethyl-1,3-hexanediol, interfacial area of two phases, and temperature. With the temperature-dependence study, it is showed that the ex-traction is a diffusion-controlled process. The kinetic equation is presented for pH 1.0 in the aqueous phase and temperature of 318 K.     

Wax ester-synthesizing activity of lipases

The synthesis/hydrolysis of wax esters was studied in an aqueous solution using purified rat pancreatic lipase, porcine pancreatic carboxylester lipase, and Pseudomonas fluorescens lipase. The equilibrium between wax ester synthesis and hydrolysis favored ester formation at neutral pH. The synthesizing activities were measured using free fatty acid or triacylglycerol as the acyl donor and an equimolar amount of long-chain alcohol as the acyl acceptor. When oleic acid and hexadecanol emulsified with gum arabic were incubated with these lipases, was ester was synthesized, in a dose- and time-dependent manner, and the apparent equilibrium ratio of palmityl oleate/free oleic acid was about 0.9/0.1. These lipases catalyzed the hydrolysis of palmityl oleate emulsified with gum arabic, and the apparent equilibrium ratio of palmityl oleate/free oleic acid was also about 0.9/0.1. The apparent equilibrium ratio of wax ester/free fatty acid catalyzed by lipase depended on incubation pH and fatty alcohol chain length. When equimolar amounts of trioleoylglycerol and fatty acyl alcohol were incubated with pancreatic lipase, carboxylester lipase, or P. fluorescens lipase, wax esters were synthesized dose-dependently. These results suggest that lipases can catalyze the synthesis of wax esters from free fatty acids or through degradation of triacylglycerol in an aqueous medium.     

Interaction between reverse micelles as a key factor governing back-extraction of proteins and its control systems

The interfacial transport processes of proteins from a reverse micellar phase to an aqueous phase have been investigated focusing on micellar-micellar interaction. The proteins solubilized into reverse micelles were back-extracted to the aqueous phase depending on the concentration of reverse micelles in organic phase. This fact seems to suggest the importance of micellar-micellar interactions in back-extraction processes. The interactions induced by various alcohol addition and temperature change could be evaluated easily and quantitatively by the percolation phenomena in reverse micellar systems (RVMS). The interactions were influenced considerably by the presence of small amount of alcohol and temperature in the RVMS. The addition of alcohols promotes the back-extraction of proteins depending on their species and concentrations. In particular, the alcohols that suppress the cluster formation of reverse micelles, remarkably improve the back-extraction processes. With a small amount of alcohol (20 mM OctOH), Bovine carbonic anhydrase (CAB) can be back-extracted completely from reverse micelles to aqueous solution at the optimal temperature, in which the so high concentration of salt is not necessary.