Pyrolysis of fermented mass containing microbial oil in a fixed-bed reactor for production of biodiesel

Abstract

In our previous work, steam-exploded wheat straw has been used to produce microbial oil by solid-state fermentation for the purpose of exploring a potential oil resource for the production of biodiesel. After solid-state fermentation the oil content of the dry fermented mass was 10.2%. In the present work, this dry fermented mass was pyrolyzed in a fixed-bed reactor in order to convert the microbial oil to biodiesel. The maximum liquid product yield of 43.2% was obtained at the conditions of final temperature of 500 °C, heating rate of 40 °C/min and sweep gas flow rate of 40 cm 3/min (N 2). The liquid product was extracted with n-hexane and separated to n-hexane soluble fraction and n-hexane insoluble fraction. The two fractions were analyzed using GC/MS, respectively. The main compositions of n-hexane insoluble fraction were water, methanol, 1-hydroxy-2-propanone, furfural and acetic acid. The main compounds of the n-hexane soluble fraction were n-hexadecanoic acid, hexadecanoic acid methyl ester, 9-octadecenoic acid methyl ester, phenol and 4-methyl-phenol. The conversion rates of hexadecanoic acid methyl ester and 9-octadecenoic acid methyl ester can be increased by pyrolysis with catalyst permutit, the former increased from 6.3 to 30.0% and the latter increased from 4.2 to 10.3% with a catalyst ratio of 20% (w/w). It can be speculated that during pyrolysis, the fatty acid methyl esters were produced by transesterification of microbial oil with methanol which was another pyrolysis product of the fermented mass. This research found that the fatty acid methyl esters, which are used as biodiesel, can be produced by pyrolysis of the oleaginous materials for the first time, hence providing a potential way for the production of biodiesel by pyrolysis instead of the traditional processing of oil extraction and transesterification.