Novel Ozonation Technique to Delignify Wheat Straw for Biofuel Production

Abstract

Production of ethanol from lignocellulosic biomass is a promising alternative source of energy because this world is in need of a low cost, renewable and sustainable green energy source. Canada is among the top ten producers of wheat in the world with a capability of producing around 37.52 million tons of wheat straw per year. Hence, wheat straw could be a potential source of energy. Ozone was supposed to break down physical and chemical structure of lignin and hence make cellulose present in wheat straw more accessible for a conversion reaction. However, it was observed in our experimental work that without pretreatment of wheat straw, ozone did not produce the expected effects in the reaction with wheat straw. In spite of conducting the experiments under vigorous conditions only 13 % of lignin removal was achieved. The proposed technique, which is a strategic use of water and ozone, has overcome the problem of slow reaction of ozone with wheat straw. Through this technique, around 90% acid insoluble lignin (AIL) removal was achieved by controlling parameters such as reaction time, flow rate of ozone-oxygen feed stream, ozone concentration in ozone-oxygen feed stream, water contents and particle size. The maximum AIL (90%) was obtained at flow rates of 4L/min, 2L/min and 1L/min at reaction times 90, 120 and 180 minutes, respectively, with 2% wt ozone concentration in ozone-oxygen stream. Other factors supported maximum lignin removal were water contents at 3 times of the dry weight of wheat straw and at 0.5 mm particle size of wheat straw. It was also noted that excessive ozonation caused repolymerization of lignin by-products. The obtained results demonstrated that ozonation of wheat straw using the proposed technique was practical, easy to manage for the removal of lignin and it may be considered as an alternative method for delignification of biomass in production of biofuel.