| The preparation of biodiesel from vegetable oil by transesterification with methanol, the purification of the glycerin and the identification of vitamin E homologues were studied. Transesterification were carried out by the acid catalysis and alkali catalysis. Vegetable oil with higher acid number should be esterified before the transesterification by alkali catalysis to reduce the content of free fatty acids, which is favorable to achieve high yield of fatty acid methyl ester and for purification of glycerin. The esterification and transesterification could be carried out simultaneously in the preparation of biodiesel by acid catalysis with higher vegetable oils. The results showed that the conversion rate of free fatty acids is 95.5% in the esterification of palm oil when the quantity of catalyst (H2SO4), the mol ratio of methanol to the oil, reaction time and reaction temperature were 0.5% (based on the oil), 8:1, 60 minutes and 65℃, respectively, and the acid number of the palm oil was reduced from 22mg KOH/g to 1mg KOH/g, which is appropriate for transesterification by alkali catalysis.For the transesterification of vegetable oils, the yield of fatty acid methyl ester could be achieved to more than 96.0% when the quantity of catalyst (NaOH), the mol ratio of methanol to the oil, reaction time and reaction temperature were 0.5% (based on the oil), 8:1, 30 minutes and 65℃, respectively. The content of water in the transesterification by alkali catalysis influenced the yield of fatty acid methyl ester seriously, and the yield of fatty acid methyl ester was reduced to 90.0% below when the content of water in the oils or the catalyst is 1.5%(based on the oils), which is the causation of hydrolysis of esters by the alkali catalysis.For reducing the quantity of catalyst and 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 fatty acid methyl ester could be achieved to 95.3% when the total quantity of catalyst (H2SO4), the total mol ratio of methanol to the oil, reaction time and reaction temperature were 1.0% (based on the oil), 20:1, 4 hours and 150℃, respectively.The effect of acid number of the oils to the yield of fatty acid methyl ester was studied. The results showed that the yield of fatty acid methyl ester of the di-transesterification was achieved to 98.4 %, in which the acid number of the oil, total quantity of catalyst (H2SO4), the total mol ratio of methanol to the oil, reaction time and reaction temperature were120mg KOH/g, 1.0% (based on the oil), 20:1, 4 hours and 150℃, respectively. And this showed that the inexpensive vegetable oils with higher acid number could be used to prepare biodiesel by H2SO4 catalysis. The corrosion was studied preparatively in the transesterification by H2SO4 catalysis and the results showed that the corrosion rate was 1.1mm per year for 304# stainless steel in 0.35% H2SO4- butanol solution at 125℃and 12 hours.The GC/MS technology was used to identify the compositions of the biodiesels from palm oil and cottonseed oil. The results indicated that the compositions of the biodiesel from cottonseed oil were mainly methyl cetylate, methyl linoleate and methyl oleate, which the percentages were 22.23%, 50.18% and 18.09%, respectively. And the main compositions of the biodiesel from palm oil were methyl cetylate, methyl oleate and methyl stearate, which the percentages were 40.3%, 50.07% and 7.02%, respectively.Two kinds of commercial vitamin E were analyzed by GC/MS technology. The compositions of the vitamin E (Tianjin) were mainly tocopherols, tocotrienol and squalene, which the percentages were 71.80%, 7.81% and 2.97%, respectvely. Otherwise the compositions of the vitamin E from palm oils (Malaysia) were mainly tocoenol/tocopherols, tocopherols and squalene, which the percentages were 53.27%, 5.86% and 9.56%, respectively. And so the vitamin E from palm oils was more effective to eliminate the radicals in bodys.
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