Pilot technology of ethanol production from oat hulls for subsequent conversion to ethylene

Abstract

Complete cycle of ethylene production from oat hulls as widespread agricultural waste was studied on a pilot scale. The cycle involved mechano-chemical, biotechnological and catalytic units. The oat hulls were pretreated with a 2%(w/w) sodium hydroxide solution in a setup consisting of a rotary-pulsating apparatus and a 100-L vessel to produce a pulp containing 90.3% of hydrolyzables. Simultaneous saccharification and fermentation of oat hull pulp with delayed inoculation (dSSF) into ethanol using commercial enzymes CelloLux-A and BrewZyme-BGX and non-GMO yeast Saccharomyces cerevisiae was carried out in 63-L reactor. At a solid loading of 33.3g/L, the yield of reducing sugars was 97.9% on overall hydrolyzables basis. The ethanol yield during dSSF at a solid loading of 60g/L was as high as 95g ethanol/kg oat hulls. The produced raw-ethanol sample contained low impurities of methanol, propanol and alkali metals. The rectified ethanol samples were used for dehydration to ethylene with the overall production index as high as 38–51g ethylene/kg oats hulls. A negative impact of the propanol and alkali metals impurities in the rectified ethanol on conversion and selectivity to ethylene were observed. Being purified from organic impurities, ethanol was dehydrated with higher conversion and selectivity to ethylene. When the ethanol samples that contain less than 0.02g/L organic and no sodium impurities were used in ethanol dehydration process, the yield of ethylene was as high as 56g ethylene/kg oats hulls. In this work, 12kg of oat hulls was converted to 1.21kg 94%(w/w) ethanol, which was then converted to 0.62kg 99.5% ethylene; this is the first experimental study devoted to the production of ethylene from oat hulls on a pilot scale.