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USAGE OF POTASSIUM METHOXIDE IN METHANOL AND POTASSIUM TERT-BUTOXIDE IN TERT-BUTANOL AS CATALYSTS IN INTERESTERIFICATION OF RAPESEED OIL

Elīna Sīle

Abstract

Biodiesel is well known alternative energy source to conventional fossil fuels. The most common production method of biodiesel is vegetable oil transesterification with methanol, which leads to glycerol formation. Increasing worldwide production of biodiesel causes considerable surplus of glycerol. To solve this problem, biodiesel production method from vegetable oil via interesterification is topical, via interesterification gycerol can be replaced with by-product, which is not necessary to separate from the biodiesel. Triacetin additives up to 10 wt%, for example, can be included into biodiesel formulation. Interesterification reaction is a reversible three step reaction and its proceeding, as well as the influence of different side reactions strongly depend not only on reaction variables but also on the catalytic system used. The current paper involves comparison of rapeseed oil intereserification reactions carried out with methyl acetate in the presence of two different catalytic systems ? potassium methoxide in methanol (MeOK/MeOH) and potassium tert-butoxide in tert-butanol (BuOK/BuOH). Research results showed that MeOK/MeOH catalyst system allows obtain high content of fatty acid methyl esters (FAME was up to 91 wt%), however glycerol layer also forms and triacetin content is poor (<3 wt%). Second, BuOK/BuOH catalyst system, prevented much higher triacetin content (up to 12.4 wt%), but maximum content of FAME was lower (69 wt%) than that in the case of potassium metoxide. In the presence of BuOK/BuOH catalytic system FAME content increased with COMR until maximum FAME content was reached, then no further significant changes in FAME production with increasing COMR were observed. In the presence of MeOK/MeOH catalyst FAME production increased with increasing COMR. Triacetin formation strongly depended on used COMR value. The highest triacetin content was reached at COMR 0.05 in both cases. Comparing biodiesel properties of the obtained mixtures, mixture obtained in the presence of MeOK/MeOH had better conformity to biodiesel standards.

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DOI resolver: doi.org/10.5593/sgem2018/4.1/s17.099

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