Knowledge Management System Of Guangzhou Institute of Energy Conversion, CAS
| 酶法合成生物柴油的研究 | |
| Alternative Title | A research on enzymatic biodiesel production |
| 罗文 | |
| Thesis Advisor | 袁振宏 |
| 2007-06-08 | |
| Degree Grantor | 中国科学院广州能源研究所 |
| Place of Conferral | 广州能源研究所 |
| Degree Name | 硕士 |
| Keyword | 生物柴油 脂肪酶 固定化 转酯化 动力学机制 |
| Abstract | 随着能源大量消耗以及环境日益恶化，开发可替代石油的燃料，保护人类赖以生存的自然环境成了目前人类面临的严峻问题。生物柴油是一种可再生、可生物降解、无毒的清洁能源，从而受到世界各国青睐。目前，产业应用的生物柴油生产工艺为化学酸碱法，工艺较成熟，但存在醇用量大和环境污染的问题，本文采用的酶法合成生物柴油则可以克服化学法的这些缺点。作者对Candiada sp. 99-125脂肪酶进行了固定化，以自制固定化酶为催化剂考察了合成生物柴油的工艺，研究了生物柴油酶促转酯化反应的动力学机制，探讨了生物柴油理化性质与组分的关系。初步结论如下： 1.游离酶经固定化后，提高了酶稳定性。固定化酶热稳定性升高，最适温度为40~45 ℃，比游离酶最适反应温度（40 ℃）范围变宽，且相对活力升高；随着温度的增加，游离酶酶活一直下降，而固定化酶活力在轻微的增加后才下降；固定化酶在pH大于8的偏碱性条件下的稳定性以及有机溶剂稳定性也大大提高。 2.游离酶经固定化后，提高了酶催化性能。以菜籽油为原料，采用自制固定化粗酶粉为催化剂的转酯化工艺，石油醚（60-90℃）为溶剂，以油醇摩尔比1：1，40℃下反应时间30小时，生物柴油转化率达到86%。 3.反应产物甘油会吸附到固定化酶载体的表面，而导致酶活的下降。在最佳条件下反应30小时后，清洗并离心去除酶表面的甘油后继续反应4小时，反应转化率提高3%。 4.生物柴油有序机制动力学模型所反映的脂肪酶催化转酯化反应机理过程，比乒乓机制更精确。转酯化历程可描述为：酰基供体（油脂底物）与酶结合形成酰基酶复合物（E.S），此复合物发生异构形成另一二元复合物，再与第二反应物（醇）形成三元复合物，此三元复合物发生异构，形成另一三元复合物，然后依次释放出产物甘油和脂肪酸酯。 5.在反应过程中，醇对酶产生抑制作用，且为竞争性抑制。在底物三甘酯浓度较小的范围内，醇抑制作用较为显著，反应初速度相对较高。随底物三甘酯浓度的升高，产生醇抑制所需要的醇浓度也相应较高。 6.冷滤点主要与生物柴油中的饱和脂肪酸甲酯含量有关，而受不饱和脂肪酸甲酯含量的影响较小。以地沟油为原料合成的生物柴油，其熔点较高的饱和脂肪酸甲酯含量较高，冷滤点相应较高。 7.生物柴油的十六烷值、黏度与其脂肪酸甲酯组分碳链长度、双键数及相应组分含量有关。碳链长度的增加引起生物柴油黏度与十六烷值升高，双键数的增加能使黏度与十六烷值降低。采用黏度预测模型能较好的预测生物柴油黏度。 |
| Other Abstract | At present, the global huge consumption of energy and environmental degradation are becoming more and more serious, so it is urgent for mankind to protect nature and develop alternate fuel. Derived from vegetable oils or animal fats, biodiesel is a fuel consisting of alkyl esters of fatty acids. It is attracting increasing attention as an alternative, non-toxic, biodegradable and renewable diesel fuel. The enzymatic synthesis of biodiesel has been becoming more and more attractive because it overcomes some drawbacks of chemical synthesis. In this study, the immobilization process of lipase was studied and experiments on the biodiesel production catalyzed by this immobilized lipase were performed.Also the kinetics of the transesterification to biodiesel was also studied. The results were listed as follows: 1)lipase from Candida sp. 99-125 was immobilized on aminated controlled pore glass surfaces by the cross-linking process. The optimal conditions for immobilization were obtained. After immobilization, the thermal stability, pH stability（when pH＞8）and tolerance to organic solvents of lipase was improved apparently. 2)Preparation of biodiesel by transesterification from rapeedseed oil catalyzed by lipase was discussed. It was found that methanol-to-oil molar ratio, kind of organic sovlent, volume of solvent, reaction time, water content and glycerol content had important effects on biodiesel yield. 86% biodiesel yield was achieved under the optimal conditions. The half-life of immobilized lipase was longer than 390 hours. 3)The product glycerin was absorbed to the surface of controlled pore glass carrier, which decreased enzyme activity. After 30 hours' reaction under the optimal conditions, the carrier was cleaned and centrifuged to remove the glycerin. The cleaned carrier was returned to the above reaction solution and the reaction continued for 4h. The conversion rate can be improved by 3%. 4)Established an accurate and complex kinetic model for the transesterification to biodiesel, namly, Ordered Bi-Bi mechanism which was proved to better simulate the reaction with comparison to classical Ping-Pong Bi-Bi mechanism. The reaction sequence is as follows: According to the Ordered Bi-Bi mechanism, the acyl donor (triglyceride) first binds with the enzyme and forms an acyl-enzyme complex (E.S). The second reactant (alcohol) then combines with (E.S) to form ternary complex. This ternary complex then isomerizes to another ternary complex, which sequently releases the product of glycerol and fatty acid ester. 5)Only the inhibition of alchol on lipase, which was competitive, was observed in the transesterification to biodiesel. At low triglyceride concentration, alcohol inhibition was significant and the initial rate of reaction was high. Much higher alcohol concentrations were required for inhibition to take place at high substrate concentrations. 6)Cold filter plugging point was impacted mainly by saturated fatty acid ester components, little by unsaturated fatty ester. High content of saturated fatty acid ester with high melting point made high cold filter plugging point of hogwash-oil-biodiesel. 7)Cetane number and viscosity were affected by chain length, numbers of double bond and content of fatty acid ester. Viscosity and cetane number increased with chain length and with increasing degree of saturation. Kinematic viscosity of biodiesel could be well predicted by a logarithmic equation for viscosity. |
| Pages | 82 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.giec.ac.cn/handle/344007/4011 |
| Collection | 中国科学院广州能源研究所 |
| Recommended Citation GB/T 7714 | 罗文. 酶法合成生物柴油的研究[D]. 广州能源研究所. 中国科学院广州能源研究所,2007. |
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