Preparation of biodiesel by supercritical reaction
In recent years, biodiesel has become a research hotspot as a green and renewable energy source.The supercritical method is favored because of its fast reaction speed, high conversion rate, no need for catalyst, and simple separation. The continuous supercritical methanol method can greatly improve production efficiency and biodiesel quality. Based on the two processes of continuous supercritical extraction and transesterification, this paper proposes a supercritical extraction-transesterification reaction coupling process, which realizes the direct production of biodiesel from oily raw materials with local materials, which is of great significance to the industrialization of biodiesel .
The extraction temperature is 40C, the CO2 flow rate is 2 L/min, the n-hexane flow rate is 0.4 ml/min, the reaction pressure is 20 MPa, and the transesterification reaction temperature is 250-350C. The supercritical coupling reaction and the supercritical extraction reaction are compared. The results are shown in Figure 1. It is shown that as the reaction temperature increases, the coupling reaction yield also increases. This is because increasing the temperature aggravates molecular motion, promotes molecular diffusion, and facilitates the reaction, which is consistent with the law of simple esterification. It can be found that in the coupling of supercritical CO2 extraction with or without co-solvent and supercritical transesterification, adding n-hexane can not only increase the rate of the extraction stage, but also facilitate the transesterification reaction and increase the yield of methyl esters. This may be Because the n-hexane in the extraction stage enters the transesterification stage together with the oil, it can be miscible with alcohol and oil, and acts as a co-solvent under high temperature and high pressure, making the reactants contact more fully, thereby increasing the yield.