Bioconversion of hazelnut shell using near critical water pretreatment for second generation biofuel production

Abstract

The global energy deficiency and depletion of fossil fuels have raised concerns leading to a wide scale examination of alternative and renewable energy sources. Lignocellulosic biomass that is one of the renewable energy sources has major potential in the world and it has a wide variety of sources including agricultural residues such as cotton stalk, corn stover, wheat straw, etc. Including over 65% cellulose and hemicelluloses content, these materials can be hydrolyzed into monomeric sugars and then can be converted into biofuels and other industrial products.The main objective of this study is bioethanol production with bioconversion of lignocellulosic biomass, namely hazelnut shell. In order to efficiently utilize this raw material for ethanol production by degrading the lignocellulosic structure, an effective pretreatment is required. LHW, a near critical water pretreatment method, is chosen for this particular research due to its unique environmental and economic properties. The experiment design was prepared with Response Surface Estimation Method (RSM) by Design Expert software. The experiment parameters were selected as temperature (100–200 °C), pressure (80–200 bar) and flow rate (2–8 ml/min). The optimum condition (OC) for the process was determined as 138 °C, 2 ml/min and 200 bar according to the Dinitrosaliclic acid (DNS) method. Additionally, in order to achieve maximum ethanol concentration, the condition producing maximum reducing sugar content is determined. Separated hydrolysis and fermentation (SHF) process was used for bioethanol production. Enzymatic hydrolysis was conducted with a part of solid residue obtained from the maximum ethanol condition (MEC) for bioethanol production. MEC is 200 °C, 2 ml/min and 200 bar. Under MEC, at the end of the fermentation process maximum ethanol yield was 44.89% with 0.5 g of solid loading.The main purpose of the study is to determine the effects of different solid loading rates in the enzymatic hydrolysis stage of SHF process to ethanol production as a result of fermentation. There are several pretreatment methods for this process. It is concluded that the superior qualities of LHW pretreatment in means of environmental friendliness, non-toxic and non-corrosive byproducts, water usage instead of other chemical additives, degradation of lignocellulosic structure and low cost were suitable for the intended purpose of bioethanol production using hazelnut shell.