Kinetic studies on lipase-catalyzed acetylation of 2-alkanol with vinyl acetate in organic solvent

Lipase-catalyzed acetylation of 2-alkanol with vinyl acetate has been studied kinetically using Burkholderia cepacia lipase (BCL), enantiomerically pure (R)- and (S)-2-alkanols and different organic solvents. The rate equation was derived by the steady state method for the simplified mechanism. The second order rate constants (k(R) and k(S)) for (R)- and (S)-2-alkanols were evaluated from the slopes of the double reciprocal plots, v(-1) vs. [2-alkanol](-1), where v is the initial rate of the reaction. The log k(R) value increased with the solvent hydrophobicity log P, where P is a partition coefficient of a given solvent between octanol and water. The log k(S) value also increased with log P except the bulky solvents such as 1,4-dioxane and cyclohexane, in which the rates were faster than those expected from the log k(S) vs. log P plot. The slope of log k(S) vs. log P plot was larger than that for (R)-2-alkanol. Thus, log E (E=k(R)/k(S): enantioselectivity) decreased with log P except the bulky solvents. The rate constants and the enantioselectivity were different depending on the structure (carbon number CN) of 2-alkanol. The log E vs. CN plot was minimized at CN=8 and 10 and the log k(S) vs. CN plot maximized at CN=8 and 10. In contrast the log k(R) vs. CN plot showed a different feature from the log E vs. CN plot. These facts suggest that dependence of E on CN is more strongly affected by the reactivity of (S)-2-alkanol than that of (R) isomer in this acetylation.     

填充床电催化反应器制备甘露醇研究

自制了DSA电极为阳极,纯镍板为阴极馈电极,阳离子交换膜为隔膜,阴极室填充雷尼镍催化剂的填充床电化学反应器。在雷尼镍填充床电化学反应器中电还原果糖合成甘露醇,考察了雷尼镍用量、阴极馈电极电流强度、果糖起始浓度、槽电压、搅拌速度、支持电解质等因素对电还原反应的影响。结果表明:在无支持电解质存在下,当果糖起始浓度为2.0mol/L,阴极室中雷尼镍填充质量与果糖质量比为3,阴极馈电极电流强度为7A,通电量为2F/mol,槽电压为6V,搅拌速度150r/min,果糖的转化率可达97.68%,采用填充床电化学反应器制备甘露醇,反应效率高,可简化后续产品的提纯过程。     

Emulsion polymerization of vinyl acetate in a tubular loop reactor

A study was conducted on the emulsion polymerization of vinyl acetate using a loop reactor. Among the variables studied were the agitation, that is, the Reynold's number, and the effect of the presence of silver ions on the reaction rate. The molecular weight and molecular weight distribution of the polymer were determined as well as its particle size. The results are compared with earlier work done in a batch, a continuous tubular, and in a tubular loop reactor. © 1994 John Wiley & Sons, Inc.     

Radiation-induced emulsion polymerization of vinyl acetate in a pilot plant reactor I. Recycle flow reactor

A number of successful radiation polymerization of vinyl acetate in emulsion have been carried out in a modular stainless steel flow pilot plant. In a recycle mode, the system was utilized for extremely accurate kinetic measurements and experimental verification of model restrictions such as plug flow, lack of post irradiation effects and differential reactor behavior. Experimental conditions were explored to minimize contaminant, primarily oxygen, inhibition, and the tendency for this formulation, essentially an adhesive, to build up on the reactor walls. Industrial scaleup of such a prototype system appears attractive.     

The radiation-induced emulsion copolymerization of vinyl chloride with vinyl acetate in an engineering flow system

A flow reactor system was used to study the radiation-induced emulsion copolymerization of vinyl chloride with vinyl acetate. The emulsion was recirculated from a stirred vessel through transfer lines to a tubular reactor located within a high-intensity Co-60 source. The effects of physical chemical variables such as soap concentration, phase ratio, reaction temperature and residence time distribution on the molecular weight properties were investigated. The rate of copolymerization was found to be proportional to the 0.17 power of the soap concentration. Variation of the monomer-water ratio produced no significant change in rate. The rate increased with an increase in temperature over the range 5–50°C, while the average molecular weights of the copolymer increased with decreasing polymerization temperature. The molecular weight distribution in this engineering system was found to be essentially similar to those produced in a batch system.     

Non-isothermal lipase-catalyzed kinetic resolution in a packed bed reactor: Modeling, simulation and miniplant studies

A rigorous model is developed for the exothermic kinetic resolution of 1-methoxy-2-propanol with vinyl acetate catalyzed by immobilized Candida antarctica lipase B in a packed bed reactor. The non-isothermal two-dimensional heterogeneous model takes into account the coupled mass and energy balances, the uneven flow distribution and irreversible ping-pong bi-bi kinetics with competitive substrate inhibition by both enantiomers. This model is based on kinetic parameters, which were estimated in earlier work. The model simulation is validated with experimental results obtained in a fully automated modular miniplant and is shown to be capable of predicting the key parameters needed for process design of a kinetic resolution, the enantiomeric excess and the extent of conversion at a given superficial velocity.     

Radiation-induced emulsion ploymerization of vinyl acetate in a pilot plant reactor II. Kinetics

The recycle flow reactor pilot plant, described in Part I of this series, has been used to study some kinetic and other features of the emulsion polymerization of vinyl acetate. In particular, the dependence of the rate on the emulsifier concentration was determined and found to be 0.38 ± 0.09. Separate batch experiments were in reasonable agreement as 0.29 ± 0.10. The effects of temperature, dose rate, and agitation rate were also determined and were in agreement with most of the literature values.     

Polystyrene recycling processes by dissolution in ethyl acetate

This study evaluated the thermal, morphological, chemical, and mechanical properties of virgin and recycled polystyrene. The recycling process was carried out by dissolution of polystyrene (extruded and crystal) in ethyl acetate, followed by two processes for solvent removal: vaporization by direct contact with water at 85 °C in a tubular evaporator and vaporization during the extrusion process. For the samples produced by solvent evaporation in the tubular evaporator, there was practically no degradation on polymer chain, neither reduction in glass transition temperature. For the samples produced by solvent evaporation during the extrusion, a polymer chain degradation was noted by reduction in molar weight and in glass transition temperature. The FTIR evaluation suggests that polymer oxidative degradation, in both samples, was more pronounced in the extruded sample. The removal of plasticizing additives could be evidenced by the glass transition temperature increase in the recycled samples produced in the tubular evaporator. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46208.     

Production of structured lipids by lipase-catalyzed interesterification in a flat membrane reactor

The application of membrane technology to the enzymatic production of specific structured lipids has been investigated in this work. Membrane screening was carried out in a membrane diffusion cell. Twenty-six flat membranes of different materials were tested using rapeseed oil and capric acid. The suitable membranes were selected in terms of higher fatty acid and lower rapeseed oil permeation rates. The stability of membranes and the effect of fatly acid chain length on effluent fluxes were also investigated. Reaction experiments were carried out in a membrane reactor between medium-chain triacylglycerols and n−3 polyunsaturated fatty acids (PUFA) from fish oil. Lipozyme IM was used as the biocatalyst. The incorporation of PUFA into medium-chain triacylglycerols was increased by about 15% in a PUFA 90-h reaction by simultaneous separation of the released medium-chain fatty acids, compared to no separation under the same reaction conditions. It has thus clearly been demonstrated that membrane-assisted separation improved the incorporation of acyl donors into oils beyond the reaction equilibrium defined by the original substrate concentration.     

Production of specific-structured triacylglycerols by lipase-catalyzed interesterification in a laboratory-scale continuous reactor

A laboratory-scale continuous reactor was constructed for production of specific structured triacylglycerols containing essential fatty acids and medium-chain fatty acids (MCFA) in the sn-2 and sn-1,3 positions, respectively. Different parameters in the lipase-catalyzed interesterification were elucidated. The reaction time was the most critical factor. Longer reaction time resulted in higher yield, but was accompanied by increased acyl migration. The concentration of the desired triacylglycerol (TAG) in the interesterification product increased significantly with reaction time, even though there was only a slight increase in the incorporation of MCFA. Increased reactor temperature and content of MCFA in the initial reaction substrate improved the incorporation of MCFA and the yield of the desired TAG in the products. Little increase of acyl migration was observed. Increasing the water content from 0.03 to 0.11% (w/w substrate) in the reaction substrate had almost no effect on either the incorporation or the migration of MCFA, or on the resulting composition of TAG products and their free fatty acid content. Therefore, we conclude that the water in the original reaction substrate is sufficient to maintain the enzyme activity in this continuous reactor. Since the substrates were contacted with a large amount of lipase, the reaction time was shorter compared with a batch reactor, resulting in reduced acyl migration. Consequently, the purity of the specific structured TAG produced was improved. Interesterification of various vegetable oils and caprylic acid also demonstrated that the incorporation was affected by the reaction media. Reaction conditions for lipase-catalyzed synthesis of specific structured TAG should be optimized according to the oil in use. Presented in part at Food Science Conference, Copenhagen, Denmark, January 30–31, 1997.     

Production of specific-structured triacylglycerols by lipase-catalyzed interesterification in a laboratory-scale continuous reactor

A laboratory-scale continuous reactor was constructed for production of specific structured triacylglycerols containing essential fatty acids and medium-chain fatty acids (MCFA) in the sn-2 and sn-1,3 positions, respectively. Different parameters in the lipase-catalyzed interesterification were elucidated. The reaction time was the most critical factor. Longer reaction time resulted in higher yield, but was accompanied by increased acyl migration. The concentration of the desired triacylglycerol (TAG) in the interesterification product increased significantly with reaction time, even though there was only a slight increase in the incorporation of MCFA. Increased reactor temperature and content of MCFA in the initial reaction substrate improved the incorporation of MCFA and the yield of the desired TAG in the products. Little increase of acyl migration was observed. Increasing the water content from 0.03 to 0.11% (w/w substrate) in the reaction substrate had almost no effect on either the incorporation or the migration of MCFA, or on the resulting composition of TAG products and their free fatty acid content. Therefore, we conclude that the water in the original reaction substrate is sufficient to maintain the enzyme activity in this continuous reactor. Since the substrates were contacted with a large amount of lipase, the reaction time was shorter compared with a batch reactor, resulting in reduced acyl migration. Consequently, the purity of the specific structured TAG produced was improved. Interesterification of various vegetable oils and caprylic acid also demonstrated that the incorporation was affected by the reaction media. Reaction conditions for lipase-catalyzed synthesis of specific structured TAG should be optimized according to the oil in use. Presented in part at Food Science Conference, Copenhagen, Denmark, January 30–31, 1997.     

氯乙烯-醋酸乙烯酯共聚糊树脂中醋酸乙烯酯含量的测定

采用红外光谱法测定了氯乙烯-醋酸乙烯酯共聚糊树脂中醋酸乙烯酯的含量,并与热重法、化学分析法等分析方法进行了比较。指出氯乙烯-醋酸乙烯酯共聚糊树脂中醋酸乙烯酯含量的多种测定方法各有其特点,需要根据实际情况选用;红外光谱法快速、准确,可满足企业科研和生产所需。     

Emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate using nonionic emulsifiers in loop reactor

Batch emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate (VAc/2EHA = 90 : 10) was initiated by the thermal initiators ammonium persulfate and potassium persulfate at 70°C in the presence of nonylphenol ethoxylates with varying chain lengths and poly(vinyl alcohol). VAc–2EHA copolymer latexes were synthesized as two different series in a loop reactor. The first series was initiated by ammonium persulfate, and the second series was initiated by potassium persulfate. The influence of the counterions or initiators and chain lengths of a nonionic emulsifier on the properties of VAc–2EHA copolymer latexes were determined by measuring the viscosities, weight‐average molecular weights, number‐average molecular weights, molecular weight distribution, and surface tension of latexes to air. The results for the copolymer latexes indicated that some of their physicochemical properties increased with increasing chain length of the nonionic emulsifier, but some of them followed a different trend for the two initiators. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1380–1384, 2005     

Experimental study of acetone removal by packed-bed dielectric barrier discharge reactor

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was developed for acetone removal. The effects of packing materials were investigated in terms of discharge characteristics, removal efficiency and byproducts formation. The identification of organic byproducts was conducted. The results indicated the presence of packing materials enhanced the energy density and exhibited a positive effect on acetone removal, while high oxygen concentration inhibited the removal of acetone. The formations of byproducts were significantly reduced in the presence of packing materials. The degradation pathways and mechanisms were discussed, showing CH₃ radicals played a crucial role in the acetone degradation process.     

填充床反应器中酶法合成生物蜡酯

研究了填充床式反应器酶法合成生物蜡酯的生产工艺。以大豆油、十六醇为原料,在石油醚体系中,使用实验室自制的固定化Candida sp.99-125为催化剂。对操作参数,如填充高度、进料速度、固定化酶用量、底物摩尔比进行了研究。结果表明,固定化酶质量为47 g,填充高度40 cm（内径3.5 cm）,油醇摩尔比1∶2.4,以4 mL/min速度进料保留时间4 h,产率可达83%。固定化酶在使用16批时,产率仍保持在70%以上。同时,对于填充床的填充方式作了初步探索。     

Miniemulsion and macroemulsion copolymerization of vinyl acetate with vinyl versatate

The miniemulsion and macroemulsion polymerization of vinyl acetate with vinyl versatate in batch and semibatch systems was investigated. Vinyl versatate was added either as an emulsion with the vinyl acetate, or as a neat liquid stream. In the batch runs, there is a poor dispersion of vinyl versatate during the nucleation period for the runs in which the vinyl versatate was added neat at the beginning of the polymerization. This led to smaller particles, lower polymerization rate, and different polymer composition evolution when compared with runs in which the vinyl versatate was emulsified with the vinyl acetate. In seeded semibatch runs, residual surfactant in the seed latex, along with the propensity for homogeneous nucleation in vinyl acetate emulsions, resulted in continuing nucleation during the entire semibatch interval. The polymerization rate was primarily affected by monomer feed rate rather than the feeding mode. The effect of monomer feeding mode on copolymer composition was weak when the semibatch feed rate was low, indicating some level of vinyl versatate mass transfer resistance. In all runs, only one glass transition temperature was observed, indicating effective copolymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2219–2229, 2002     

乙酸乙烯酯的微波加热聚合

对乙酸乙烯酯甲醇溶液在微波加热条件下的聚合反应进行了研究,讨论了微波聚合条件、引发剂浓度、溶剂浓度和种类对聚合产物的转化率和分子量的影响。聚合物可以在较短时间内获得。且在同样的实验条件下,用不同的溶剂获得的聚合物的分子量不同。     

Simulation of temperature peak attenuation by catalyst dilution in a tubular packed-bed reactor

Temperature peak attenuation is an important problem for safe process control. Simulations of the axial temperature and product progression in stationary ammonia synthesis with different axial catalyst dilutions have been carried out. It is demonstrated that the requirement of temperature peak attenuation together with a maximum product yield can be met by an optimal catalyst dilution profile at the entrance of the bed.     

Activity and deactivation of a catalyst for vinyl acetate synthesis in an industrial fluidized reactor

The synthesis of vinyl acetate from acetylene and acetic acid has been carried out using two industrial fluidized reactors. Both reactors have an inverted conical shape with a conical angle of 3°20′, and the diameter of the base is 3.28 m. Both have a production capacity of 50 ton/day. An activated carbon supported zinc acetate catalyst of 0.4 mm in average diameter is used.In order to investigate the optimum fluidizing and reaction conditions with the above industrial reactors, a series of operational tests have been carried out over a period of two years.As a result of such operation tests, it has been confirmed that the subject catalyst is free from hysteresis, because, in the operational tests using the catalysts with the same activity level, it shows the same reaction activity under the same reaction conditions, irrespective of the procedure for setting such reaction conditions. Further, it is considered that the rule of additivity of catalyst activity can be applied to this reaction system, because the subject catalyst shows a reaction activity corresponding to its mixing ratio, when using mixtures of catalysts with different activity levels.In these operational tests, we have introduced a method to calculate space time yield (STY) values at a certain past time point, under such conditions that STY changes on standing by a deterioration of catalyst activity. We measured the STY at a certain time point under certain reaction conditions and continued the operation under the same conditions. Several days later, we measured the STY under the same reaction conditions and, then, proceeded with the operational tests under different reaction conditions and measured the STY again. The STY under the latter reaction conditions at the first time point can be estimated by multiplying the ratio of STY actually measured, just before and after changing reaction conditions, and the STY value measured at the first time point.