超临界乙醇技术原理研究与运用进展

Progresses of Principle Research and Application for Supercritical Ethanol

综述了超临界乙醇在制备生物柴油中的主要技术,分析了在酯交换反应、酯化反应、液化反应制生物油以及生物油加氢升级中的原理及应用。研究表明,超临界乙醇的酯交换反应过程由三个连续可逆的反应组成,水和CO_2均能提高反应速率。在酯化过程中,乙醇、酸的浓度对过程存在显著影响,此外,动力学模型表明酸存在催化效应,因此水解及油酸本身存在酸催化效应及自催化作用。超临界乙醇被广泛用于生物质的液化过程,过程主要存在:(1)生物质裂解;(2)油份重整(涉及酯交换及酯化反应等);(3)结焦或结聚;(4)小分子组分气化;及(5)气体间相互反应等典型反应等;且升高温度有利于液化;液化过程中醇与水表现出协同作用。此外,在生物油的加氢升级过程中,超临界乙醇不仅作为一种良好的反应介质,也作为反应物与生物油中的酸类物质发生酯化反应,降低生物油的酸度,提高生物油的热值。因此,超临界乙醇在生物燃料的制备与升级中具有良好的应用前景。

The paper reviews the main technology of the production of biodiesel in supercritical ethanol, analyzing the mechanism and application in transesterification, esterification reaction, the liquefaction of biomass for bio-oil and the hydrogenation process of bio-oil upgrading. Studies have shown that the process of transesterification in supercritical ethanol included a sequence of three consecutive and reversible reactions, of which the reaction rate could be improved by addition of water and CO2. The concentration of alcohol and acid has a significant influence on the process of esterification because there is acid-catalyzed and self-catalyzed effect in hydrolysis and oleic acid which is indicated by dynamic model. Supercritical ethanol technology is widely used in the liquefaction of biomass, which mainly include（1） pyrolysis of biomass,（2） oil reforming（involve the reactions of transesterification and esterification）,（3） coking,（4） gasification of small molecular components and（5） the interactions between the gas. Additionally, high temperature is conducive to the liquefaction of biomass,and alcohol had a synergistic effect with water in the process. In the hydrogenation process of bio-oil upgrading, the supercritical ethanol not only is an excellent reaction medium, but also reacts with the acids in bio-oil by esterification which could decrease the acidity and improve the heating value of bio-oil. Therefore, the supercritical ethanol has a good application prospect in the production of biofuel and upgrading of bio-oil.