Biodiesel production using immobilized enzyme-current state and future perspective

近年来由于化石燃料的全球性短缺、原油价格的过度上涨和环境问题的加剧致使生物柴油的生产迅速增长。生物柴油生产的关键反应是化学或生物催化的转酯反应,酶催化的转酯反应与化学催化相比有相对节能、副产物甘油易回收及适合高含量游离脂肪酸油脂作为底物等明显优势。本文综述了固定化脂肪酶生产生物柴油的现状及最新进展,包括生物柴油的原料、脂肪酶的来源、酶的固定化技术、甲（乙）醇及甘油对脂肪酶的失活作用,展望了固定化脂肪酶生产生物柴油的未来前景。     

本质安全化设计在硝酸氧化醇工艺中的应用

硝酸氧化醇的反应大多为强放热反应,具有很高的反应热失控危险性。本文在本质安全原理的指导下,结合工艺热危险性分析理论,提出通过适当提高反应温度、改变反应混合性以及强化反应器加料模式3种设计方案来降低硝酸氧化仲辛醇反应工艺的危险性,改善工艺本质安全化水平。同时,根据本质安全评估指标及赋值方式,构建出本质安全化设计影响度的评估模型,并利用该模型验证了3种设计方案对于提高该工艺本质安全化程度的合理性。结果表明：适当提高反应温度、改变反应混合性、强化反应器加料模式分别使该工艺的本质安全化程度提高了约11.7%、12.8%、10.7%。同时,本文提出的3个设计方案在提高该工艺本质安全化程度上主要体现在“最小化”和“缓和”这两个本质安全原理上。     

化工过程本质安全评估方法研究进展与展望

可持续性发展已经成为社会、生态和经济发展的关键。可持续制造的发展道路需要平衡环境、社会和经济各方面。本质安全设计是减少风险、实现化学工业可持续发展的最有效的方法之一,本质安全设计可以永久性地消除或减少化工过程中涉及的危害。本文综述了本质安全的历史发展、本质安全四大原则的概念、本质安全四大原则应用的使用潜力、本质安全设计评估工具,并系统介绍了本质安全设计评估方法的研究进展和存在的问题,包括基于参数的得分索引本质安全方法、基于参数的数值索引本质安全方法、基于图示的本质安全方法、基于风险分析的本质安全方法和基于多目标评价的本质安全方法,分析比较了各种方法的优缺点,并对本质安全评估方法的未来发展和完善提出了一些见解。     

Study of step-growth polymerizations using epoxy-carboxy reaction

Summary Due to its importance in the fields of block-polycondensation and chemical modification, we carried out a study of the epoxy-carboxy reaction on models (3-phenoxy-1,2-epoxy propane and dodecanoic acid) in the bulk; this reaction was catalyzed either by a tertiary amine (N,N-dimethyldodecylamine) or a chromium chelate (chromium diisopropylsalicylate). Whatever the catalytic system we observed an isomerization of the hydroxy-ester (secondary-primary alcohol) plus transesterification reactions when the catalyst was an amine. The contribution of transesterification reactions is limited when the catalyst is a chromium derivative.     

Process intensification with biocatalysts: dynamic kinetic resolution and fluorous phase switch with continuous extraction

Kinetic resolution of racemates with the help of enzymes has become a widely adopted method for the synthesis of chiral intermediates and compounds with biological activity. However, the inherent limitation to 50% yield of any one stereoisomer restricts the use of this method in industrial practice, when only one of the stereoisomers is required. The yield can theoretically be improved to 100% through either a chemical reaction, which inverts the stereochemistry at the optical active center, or through racemization of the unwanted isomer, followed by additional enzymatic resolution. The combination of the racemization of the slower reacting stereoisomer with kinetic resolution in a one-pot reaction is termed dynamic resolution. We describe the dynamic resolution of secondary alcohols through enzymatic stereoselective transesterification and heterogeneously catalyzed racemization of the alcohol over several zirconia-containing catalysts. In order to facilitate the separation of the products, we used a fluorous phase-switching technique coupled with fluorous extraction. The continuous extraction in a membrane contactor allows for facile recovery of the fluorous tagged species in a scaleable operation. The unoptimized scheme offers over 90% conversion with ca. 75% enantiomeric excess (e.e.).     

Modification of poly(ethylene ether carbonate) polyols by transesterification

Poly(ethylene ether carbonate) polyols are the reaction products of alkylene carbonates or alkylene oxides and CO₂ with alcoholic initiators. These polyols can be modified with aliphatic hydroxyl compounds by transesterification reactions. The modifier becomes chemically bound into the polymer during reaction and modifies the properties of the polyol. The extent of reaction is very easy to follow by size exclusion chromatography. Molecular weight is controlled by the molecular weight of the reactants and by their stoichiometry. This transesterification process is compared to the previously described transesterification/advancement process. The transesterification process has the advantage of using milder temperature conditions and runs at ambient pressures. Therefore, modifiers can be used in the transesterification process that are unstable or undergo different chemistry under the reaction conditions of the transesterification/advancement process. Although the modifiers used in the transesterification/advancement process must be less volatile than DEG, more volatile modifiers can be used in the transesterification process. The two processes compliment each other, allowing the preparation of a wide variety of modified poly(ethylene ether carbonate) polyols. These polyols are useful in polyurethane applications.     

Soybean Meal Retains Its Nutritional Value as an Animal Feed Following in Situ Transesterification

The lipid-depleted meal transesterified soybean meal (TSM) coproduct of the in situ transesterification of soybeans to produce biodiesel, and a reference commercial hexane-extracted soybean meal (HSM), were investigated as poultry feeds. In situ transesterification removed 95 % of the lipid from soybean flakes without destroying amino acids or affecting caloric content. Trypsin inhibitor in TSM was successfully denatured by a steam/heat treatment. Two groups of broiler chicks, each consisting of 300 birds (20/pen), were fed diets whose soy meal component was either TSM or HSM. A block design was used, a ‘block’ consisting of two adjacent pens, one receiving TSM and the other HSM. Starter formulation was fed from day 1 to 21 and grower formulation from day 22 to the end of the study on day 42. Chicks accepted both the TSM and HSM diets. No acute toxicities occurred. Over the course of the study weight gain, feed consumption and feed efficiency were comparable (p ≥ 0.05) between the two test groups. Mortalities in the group receiving TSM exceeded those in the HSM group (6.8 vs. 3.4 %), but did not reach statistical significance. Histological examination of the livers of 40 birds sacrificed at the end of the study showed no evidence of pathology in either dietary group. Soybean meal subjected to in situ transesterification is an acceptable component of poultry diets.     

Dynamics and Control of a Biodiesel Transesterification Reactor

Biodiesel transesterification reactors resemble the heart of any biodiesel manufacturing plant. These reactors involve a highly complex set of chemical reactions and heat transfer characteristics. The high nonlinearity inherent in the dynamics of these reactors requires an efficient process control algorithm to handle the variation of operational process parameters and the effect of process disturbances efficiently. In this work, a multi‐model adaptive control strategy is considered for achieving the goal mentioned above. In order to implement the adaptive controller, a rigorous mechanistic model of the biodiesel transesterification reactor was developed and validated with published experimental results. The validated model was analyzed for stability and nonlinearity. The analysis revealed that the system is stable. However, its high nonlinearity necessitates an advanced control strategy to be considered. The input‐output relationship between the effective process variables was studied and the control system synthesis revealed a two‐by‐two control system. Two adaptive control loops were then designed and tuned to optimize the performance of the controller. Finally, a comparison with conventional controllers revealed the superiority of the new control system in terms of set‐point tracking and disturbance rejection. The results of this work prove that an adequately designed adaptive control system can be used to improve the performance of the transesterification reactor.     

Selection of Direct Transesterification as the Preferred Method for Assay of Fatty Acid Content of Microalgae

Assays for total lipid content in microalgae are usually based on the Folch or the Bligh and Dyer methods of solvent extraction followed by quantification either gravimetrically or by chromatography. Direct transesterification (DT) is a method of converting saponifiable lipids in situ directly to fatty acid methyl esters which can be quantified by gas chromatography (GC). This eliminates the extraction step and results in a rapid, one-step procedure applicable to small samples. This study compared the effectiveness of DT in quantifying the total fatty acid content in three species of microalgae to extraction using the Folch, the Bligh and Dyer and the Smedes and Askland methods, followed by transesterification and GC. The use of two catalysts in sequence, as well as the effect of reaction water content on the efficiency of DT were investigated. The Folch method was the most effective of the extraction methods tested, but comparison with DT illustrated that all extraction methods were incomplete. Higher levels of fatty acid in the cells were obtained with DT in comparison with the extraction-transesterification methods. A combination of acidic and basic transesterification catalysts was more effective than each individually when the sample contained water. The two-catalyst reaction was insensitive to water up to 10% of total reaction volume. DT proved a convenient and more accurate method than the extraction techniques for quantifying total fatty acid content in microalgae.     

How to Make Inherent Safety Practice a Reality

In recent years there has been an increased effort to develop inherently safer chemical processes, focusing on changing the process to eliminate hazards, rather than accepting the hazards and developing add‐on features to control them. This paper discusses design approaches to inherently safer processing, including examples of inherent safety principles. The paper also presents a state‐of‐the‐art review of the initiatives taken by various groups and agencies worldwide to promote inherent safety, and the tools developed to measure inherent safety for chemical processes. The discussion concludes with thoughts on why inherent safety is not yet a routine practice for accomplishing risk reduction, and suggestions for ways to make it routine (with reference to a brief case study).     

Rapid transesterification of soybean oil with phase transfer catalysts

Biodiesel is a renewable, non-toxic and biodegradable alternative fuel for compression ignition engines. Biodiesel is produced mainly through base-catalyzed transesterification of animal fats or vegetable oils. However, the conventional base-catalyzed transesterification is characterized by slow reaction rates at both initial and final reaction stages limited by mass transfer between polar methanol/glycerol phase and non-polar oil phase.In our study we used phase transfer catalysts (PTCs) to facilitate anion transfer between polar methanol/glycerol phase and non-polar oil phase to speed up transesterification. The benefits of transesterification by PTCs include no need for expensive aprotic solvents, potentially simpler scaleup and higher activity (shorter reaction time). Various PTCs were investigated for base-catalyzed transesterification. Experimental results showed that base-catalyzed transesterification was enhanced with an effective PTC, indicated by the formation of high methyl ester (ME) content within a relatively short time. Individual operating variables such as molar ratios of methanol to oil, total OH⁻ to oil, PTC to base catalyst and agitation including ultrasound were investigated for transesterification with PTC. Product analyses showed that ME content higher than 96.5 wt.% was achieved after only 15 min of rapid transesterification with PTC (tetrabutylammonium hydroxide or tetrabutylammonium acetate as PTC, MeOH/oil molar ratio of 6, total OH⁻/oil molar ratio of 0.22, PTC/KOH molar ratio of 1 and 60 °C). Free and total glycerol contents in the final product from 15 min rapid transesterification with PTC were lower than maximum allowable limits in the standard specification for biodiesel.     

High pressure enhances activity and selectivity of Candida rugosa lipase immobilized onto silica nanoparticles in organic solvent

High hydrostatic pressure has been increasingly utilized to improve functions of enzymes, and most of such studies are currently focused on free enzymes in aqueous solution or organic solvent. In this work, Candida rugosa lipase (CRL) was immobilized onto silica nanoparticles and its activity and enantioselectivity in organic solvent were evaluated at high pressures under different water activities. The application of high hydrostatic pressures (50–200 MPa) led to improved activities of immobilized CRL for transesterification of (R)-1-phenylpropan-2-ol with vinyl acetate by 4–6 folds. Additionally the immobilization of CRL resulted in a significant change of selectivities, shifting the enantiomeric excess from the (R)- towards (S)-1-phenylpropan-2-yl acetate product at atmospheric pressure. The application of high pressures led to either enantiomeric excess towards (R)-1-phenylpropan-2-yl or no enantiomeric selectivity, depending on the water activities in the organic solvent and the level of pressures. The interesting behaviour of immobilized CRL under high pressures offers new opportunities to modulate enzyme functions through combination of high pressures and enzyme immobilization.     

A Transesterification Double Step Process — TDSP for biodiesel preparation from fatty acids triglycerides

This study introduces a two consecutive steps basic–acid transesterification process, (denominated Transesterification Double Step Process — TDSP) for biodiesel production from vegetable oils. The process involves homogeneous consecutive basic–acid catalysis steps and is characterized by formation of well-defined phases, easy separation procedures, high reaction velocity and high conversion efficiency. The proposed TDSP is different in relation to other traditional two-step procedures which normally include acid esterification followed by basic transesterification, or enzymatic or even supercritical transesterification conditions. The biodiesel (fatty acid methyl esters) was analyzed by standard biodiesel techniques in addition to ¹H-NMR, indicating high quality and purity biodiesel products. The transesterification of sunflower and linseed oils resulted in oil conversions higher than 97% corresponding to yields of 85%. A probable reaction mechanism responsible for the process is presented.     

Hydroxyl content and refractive index determinations on transesterified soybean oil

Biodiesel, a promising alternative diesel fuel, is produced by transesterification of vegetable oils or animal fats with methanol. One of the main problems in the industrial application of the transesterification process is how to determine the conversion of oils to methyl esters. In this work, a quick analytical method was developed for monitoring the transesterification reaction of soybean oil with methanol. The conversion of oils to methyl esters could be determined by applying a simple linear correlation with hydroxyl content of the transesterified mixture or refractive index of the product. The results were in agreement with the values measured by ¹H NMR spectroscopy. Compared with existing chromatographic and other methods, this method for monitoring the transesterification of vegetable oils with methanol is simple, rapid, and inexpensive and is especially suitable for process control purposes.     

超临界流体技术制备生物柴油的研究进展

概述了生物柴油的制备方法,即直接混合法、微乳法、热裂解法和酯交换法。重点介绍了酯交换法中的超临界制备方法的研究进展,对其制备方法、反应机理及动力学、各个因素对反应的影响进行了深入的阐述。     

Reaction Kinetics and Mechanisms for Hydrolysis and Transesterification of Triglycerides on Tungstated Zirconia

Hydrolysis and transesterification are two reactions which can occur during the synthesis of biodiesel. An Investigation of the mechanistic pathways in hydrolysis and transesterification were carried out at a relatively high temperature (100–130 °C) and moderate pressures (120–180 psi) with tricaprylin and water for hydrolysis or methanol for transesterification using a tungstated zirconia catalyst in a batch reactor. It was found that upon increasing the concentration of TCp, the reaction rates for both hydrolysis and transesterification increased at all conditions. In contrast, water inhibited the reaction rate of hydrolysis by poisoning the active sites. For transesterification, the apparent reaction order of methanol evolved from positive to negative as the concentration of methanol relative to TCp increased. Using a reaction model discrimination procedure, it was found that hydrolysis on WZ could be successfully described by an Eley–Rideal single site mechanism with adsorbed TCp reacting with bulk phase water. The mechanistic pathway for transesterification also seems to follow a similar mechanism, identical to the one previously proposed for transesterification on a solid acid catalyst (SiO₂-supported Nafion-SAC-13) at lower temperature (60 °C).     

酯交换法合成碳酸二甲酯研究

通过酯交换法，以甲醇和碳酸丙烯酯（ＰＣ）为原料，反应精馏合成碳酸二甲酯，筛选出最佳催化剂，确定了其用量，考察了原料配比等对反应转化率的影响，研究结果表明，催化剂ＣＨＳ－１和ＣＨＳ－２催化效果较好，其较佳用量为０．４％～０．５％（相对于甲醇的质量）甲醇与ＰＣ的质量比为８～１０，反应停留时间为４０ｍｉｎ～６０ｍｉｎ本文报道的酯交换工艺具有一定的工业应用价值。     

碳酸二甲酯酯交换反应制碳酸甲乙酯研究进展

碳酸甲乙酯是一种重要的化工原料,市场潜力巨大。相对于传统制备方法,酯交换法制备碳酸甲乙酯具有明显优势。综述碳酸二甲酯酯交换反应合成碳酸甲乙酯的路线,对比碳酸二甲酯分别与乙醇和碳酸二乙酯进行反应的特点,表明碳酸二甲酯与乙醇反应需要解决产物分离的问题,而碳酸二甲酯和碳酸二乙酯酯交换反应则需要提高转化率。两种方法均具有良好的发展前景。     

The General Applicability of in Situ Transesterification for the Production of Fatty Acid Esters from a Variety of Feedstocks

We previously described a method for fatty acid methyl ester (FAME) production wherein acylglycerol transesterification was achieved by reacting flaked full fat soybeans with alkaline methanol to create a product that met ASTM specifications for biodiesel. In the present work we explore the general applicability of this approach, termed in situ transesterification, to feedstocks other than soybeans. Materials investigated were distillers dried grains with solubles (DDGS), which is a co-product of the production of ethanol from corn, and meat and bone meal (MBM), a product of animal rendering. For both feedstocks, reaction conditions giving maximum lipid transesterification were predicted by statistical experimental design and response surface regression analysis, and then verified experimentally. Successful transesterification was achieved at ambient pressure and 35 °C. For DDGS, partial drying markedly reduced the methanol requirement to achieve a high degree (91.1% of maximum theoretical) of transesterification. Elevated reaction temperatures (to 55 °C was explored) caused little or no shortening of the time to completion. Protein was not removed from the DDGS during this treatment. For MBM, drying was not required to achieve a high degree (93.3%) of transesterification. The remaining meal retained approximately 90% of the protein originally present. Coupled with the previous work with soybeans, the data presented here indicate that in situ transesterification is generally applicable to lipid-bearing materials, which could substantially increase the supply of biodiesel. Mention of brand or firm names does not constitute an endorsement by the US Department of Agriculture over others of a similar nature not mentioned.     

Monitoring the transesterification reaction with laser spectroscopy

The production of biodiesel is rapidly expanding around the world, making it more important to produce this fuel with more energy efficiency. In this paper, we observed a series of transesterification reactions of soy bean oil and methyl alcohol catalyzed by potassium hydroxide. The observations were made using a non-invasive optical technique. This technique is useful to indicate the endpoint of a transesterification reaction or to determine when this reaction is reaching the state of chemical equilibrium. This study made it possible to improve the follow-up of the transesterification reaction, by optimizing the reaction time with a better monitoring system.