A biorefinery approach for castor biodiesel

IRAN -- Chemical engineers from Iran have found a way to produce biodiesel from castor oil without the need for extra petrochemical methanol, using a biorefinery set-up.

Producing biodiesel from vegetable oils is not completely renewable, as the standard transesterification process requires the use of methanol, which is usually produced from petrochemical sources. The researchers, Hamed Bateni and Keikhosro Karimi from Isfahan University of Technology, found from studies that bioethanol could be used instead, and used the concept of a biorefinery, which can produce multiple products from one feedstock, much like a petroleum refinery produces many products from crude oil.

They selected the castor plant as it can grow in very poor conditions, such as on wasteland. They first extracted the castor oil from dried seeds, and retained the plant residue, including the seedcake, stems and leaves.

The plant residue was first milled to obtain a standard-size substrate, before being subjected to an alkaline pre-treatment using 8% w/v sodium hydroxide to remove lignin and hemicellulose, before being fermented with a strain of yeast under anaerobic conditions, achieving an ethanol yield of 71%. The ethanol produced was then used in a transesterification reaction to make biodiesel from the castor oil. The optimum biodiesel yield of 85% was achieved at a temperature of 62.5˚C with an ethanol:oil ratio of 0.29:1 and a reaction time of 3.46h. 1 kg of castor plant makes 149.6g of biodiesel and a minimum of 30.1 g of bioethanol.

“This study showed that the castor plant can be comprehensively exploited using a biorefinery approach for biodiesel and ethanol production in which no extra alcohol out of the process was necessary for the biodiesel unit,” the researchers say.

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