Study Of Biodiesel Preparation By Acid Catalysts

Petroleum crisis and environmental pollution accelerate the development of renewable and environmentally friendly alternative energy sources like biodiesel. However, the expensive cost of oil and fat restricts its usage and commercialization. Low cost feedstocks oil usually contains a great deal of free fatty acids (FFA), which influences the transesterification via alkali catalytic process and its subsequent separating process. The acidic catalytical esterification of FFA with lower alcohols such as methanol is commonly used to reduce the acid value of a high acid value feedstock. Conventional liquid acid catalysts cause not only more side reaction, but also device erosion and vast acidic waste water emission, which results in environment problems. Solid acid catalyst is an environmentally friendly technology as it is easy to be recovered and separated from product.Transesterification reaction of peanut oil with methanol using p-toluene sulfonic acid as catalysts was studied. The preferable reaction condition of one-step acid-catalyzed transesterification and effect of two-step acid-catalyzed transesterification was investigated. The process of transesterification was affected by amount of catalysts, molar ratio of alcohol to oil, reaction time and reaction temperature, etc. The results showed that the yield of biodiesel could be achieved 93.6%, while the molar ratio of methanol to oil, the amount of catalysts, reaction time and reaction temperature were 10:1, 0.5% (based on weight of fatty oil), 1.5 hours and 150℃, respectively. The yield of biodiesel reached 97.9% in two-step acid-catalyzed transesterification, while the molar ratio of methanol to oil, the amount of catalysts, reaction time and reaction temperature were 14:1, 0.5% (based on weight of fatty oil), 4.0 hours and 150℃, respectively.A variety of solid acid catalysts were screened in the transesterification of soybean oil with methanol. The results showed that Hβ-molecular sieve had the highest activity. Upon this catalyst, the reaction parameters were investigated. The reaction condition of one-step acid-catalyzed transesterification by Hβ-molecular sieve under methanol subcritical condition was investigated. The yield of biodiesel could be achieved more than 90%, when raw material used the high acid value oil which transferred naphthenate in soybean oil, the molar ratio of methanol to oil, the amount of catalyst (based on weight of fatty oil) , reaction temperature and reaction tome were 12.5:1, 5%, 300℃and 2.0 hours, respectively. For reducing the mol ratio of methanol to the oil remarkably, the glycerin was separated and the oils were transesterified continuously, which was called di-transesterification. The results showed that the yield of biodiesel in di-transesterification could be achieved 98%.The biodiesel prepared by catalysis of Hβ-molecular sieve with a high acid value need to caustic washing. The results showed that Na2CO3 was better than NaOH in caustic washing of biodiesel. In order to avoid impact of hydrolysis and oxidation of biodiesel in long time storage, the acid value of biodiesel exceeded acid value standard of biodiesel of 0.8 mg KOH·g-1. Amount of solid Na2CO3 to biodiesel should more than the theoretical amount. When the molar concentration of Na2CO3 solution was 0.75mol·L-1, the yield of caustic washed biodiesel could be achieved 93.8%.When the lipid feedstocks with high acid value was transesterifi and esterified with methanol via Hβ-molecular sieve catalyst, the water produced in erterification mixed with superfluous methanol, which resulted in the difficulty in the recovery of methanol. Glycerin can be used to esterify the fatty acids in lipid feedstocks and the produced water can be removed easily in the esterifiction because of the higher boiling point of glycerin, which superfluous methanol in transesterification is free water and the recovery of methanol is inexpensive. The esterifiction of organic acids were studied with naphthenic acid (acid value 134mg KOH·g-1) and glycerin. The results showed that the conversion of naphthenic acid could be achieved 98% when the molar ratio of methanol to naphthenic acid, reaction time, reaction temperature were 0.66:1, 3.0 hs, 250℃and free catalysts, respectively.