萃取-酯交换耦合法制备生物柴油过程催化剂应用研究进展

Recent development in application of catalyst to biodiesel production by coupling extraction and transesterification

传统的生物柴油生产过程通常包括油脂提取、提纯精炼、酯化/酯交换等步骤,需要消耗大量的能源与化学品。萃取-酯交换耦合技术是近年来开发的一种简单有效、具有较大应用潜力的生物柴油制备方法,该方法直接以含油固体为原料,以短链醇等作为萃取溶剂和酯交换反应试剂,油脂萃取与酯化/酯交换反应同时进行,提高了生产效率,降低了生产成本,减少了环境污染。萃取-酯交换耦合法中催化剂的选择是反应能否实现高效转化的关键。酯交换反应的催化剂种类繁多,但大多数针对的原料是浸提过的液体油脂,较少用来催化固体原料原位酯交换反应。笔者综述了近年来萃取-酯交换耦合技术制备生物柴油的研究进展,包括酸催化法、碱催化法、离子液体催化法、超临界法和生物酶法,探讨了各种方法的优缺点,同时提出了萃取-酯交换耦合法制备生物柴油过程中催化剂制备与应用方面需要解决的主要问题及今后的发展方向。

The production of biodiesel traditionally involves multiple stages, including oil extraction, purification and subsequent esterification or transesterification etc., which costs large quantities of energy and chemicals. The in-situ extraction and esterification/transesterification, also known as reactive extraction, is a simple but effective biodiesel production method developed in recent years and is considered to have big application potential. In the reactive extraction process, extraction and esterification/transesterification occur simultaneously with some short-chain alcohols like methanol adopted as extraction solvent and transesterification reagent, and the solid oil-bearing material contacts with alcohol directly instead of reacting with pre-extracted oil and is directly converted into biodiesel. Thus this process can greatly improve the production efficiency, and reduce cost and environmental impact. The selection of catalyst in the reactive extraction is the key factor to obtain high conversion efficiency. There are various catalysts used in transesterification, but most of them are used to catalyze the processed liquid oil rather than reactive extraction. In this paper, the catalytic methods of reactive extraction in biodiesel production including acid catalysis, alkali catalysis, ionic liquid catalysis, supercritical technology and enzyme catalysis are reviewed, and their advantages and disadvantages are discussed. In reactive extraction, acidic catalyst is more favorable than alkali catalyst because the free fatty acid of oil feedstock prohibits the use of alkali catalyst and leads to problems such as soap formation and difficulty in product separation. However, the use of homogeneous acidic catalyst requires neutralization and separation from the reaction mixture and leads to environmental problems relating to the use of solvents and energy. By contrast, the reactive extraction by using solid catalysts has lower operational costs and is more environmentally compatible. Moreover, the main existing problems and development trends in the preparation and application of catalyst for the preparation of biodiesel by coupling extraction and transesterification are introduced.