Conversion of Ligno Cellulose to Biofuel

Introduction

Perhaps the most serious issue confronting the world is the vitality emergency. The cost of oil significantly raised in 1973, making an oil emergency. Vitality utilization has expanded relentlessly as the total populace has developed and more nations have turned out to be industrialized. The petroleum products, including unrefined petroleum, coal and flammable gas are the significant assets to satisfy the expanded vitality needs. As generally accepted, the fossil energies will be depleted soon (Wyman, 2001). The world right now expends 30 billion barrels of oil for each year; Colin (2003) gauges that oil stores will turn out to be rare by the 2050s. Since oil is a nonrenewable asset, there is a dire need to look for elective vitality sources that are limitless.

In late decades, a worldwide consciousness of the expanding CO₂ fixation levels in the environment and worry for an Earth-wide temperature boost prompted the plan of the Kyoto Protocol in 1997 which has driven numerous nations to make the duty to diminish the outflow of CO₂. One method for diminishing CO₂ discharges could be substitution of petroleum derivatives with sustainable power sources.

The improvement of elective fuel and vitality sources has in this way turned into an overall research need as of late. Biofuels are powers delivered from biomass. These powers are for the most part as bioalcohols, biodiesel, biogas and different synthetic compounds delivered from biomass. The two primary biofuels are biodiesel and bioethanol. Among those, bioethanol created by bioconversion of lignocellosic biomass is being viewed as one of the most encouraging option biofuels. The decision of lignocellulose to bioethanol transformation ought to be settled based on generally speaking financial aspects (most minimal cost), condition (least poisons) and vitality (higher productivity), i.e., exhaustive procedure advancement and streamlining are as yet required to make the procedure monetarily practical. The expanding oil cost and negative effect of non-renewable energy sources on the earth are empowering the utilization of lignocellulosic materials to help address vitality issues (Di Nasso et al., 2011).

There are numerous favorable circumstances of biofuels over petroleum derivatives that make the elective fuel source an appealing choice now and later on. The principle bit of leeway of biofuels is that they are considered 'carbon unbiased' by certain individuals. This is on the grounds that the carbon dioxide discharged during the ignition of biofuels is equivalent to the sum that absorbed during photosynthesis (Kheshgi et al., 2000) bringing about no net increment to CO2 levels. In this manner, they don't add to a worldwide temperature alteration. Utilization of biofuels discharges no sulfur and has much lower particulate and poisonous outflows, especially when contrasted and other fluid transportation fills (Scott and Wyman, 2004). Bioethanol generation can give an appealing course to discard dangerous lignocellosic squanders, for example, stalks, stovers and leaves of farming yields. Biofuels are sustainable power source (produced using natural materials and even natural waste, there is for all intents and purposes an endless measure of biofuels accessible), cheap to deliver and decrease reliance on remote oils.

Ethanol is one of the most encouraging biofuels that can be utilized to substitute fuel for tomorrow's transportation vehicles. Fuel ethanol is mostly utilized as an oxygenated fuel added substance. The higher octane number of the fuel blend, when it contains ethanol, lessens the requirement for poisonous, octane-upgrading added substances, for example, methyl tertiary butyl ether. Because of the oxygen in ethanol particles, there is likewise a decrease of carbon monoxide discharge and non-combusted hydrocarbons (Hu et al., 2008).

Fig. 1. Basic principles of a biorefinery (Kamm and Kamm, 2004)

Fig. 2. Lignocellulosic feedstock biorefinery (Kamm and Kamm, 2004; Van Dyne et al, 1999)

2. Methods

2.1. Materials

Air-dried ground corn stover was supplied by the National Renewable Energy Laboratory (NREL, Golden, CO). The corn stover (Zea mays) which includes stalks, leaves, tassel, husks, and cobs from Pioneer 34M95 was harvested in Wray, northeastern Colorado in 2002. The harvested corn stover was washed by distilled water and air-dried at ambient temperature, and then screened to a nominal size of 9-35 mesh. The prepared corn stover was stored in the refrigerator at 4ºC. The composition of corn stover was determined by our lab following the chemical analysis and testing standard method developed by NREL [31]. The mass fraction of each component in the untreated corn stover was 34.2 % glucan, 22.3 % xylan, 1.6 % galactan, 3.1 % arabinan, 12.2 % lignin (acid insoluble + acid soluble), 3.9 % acetate, 6.2 % sucrose, 1.6 % protein, 4.0 % uronic acid, 1.2 % ash, and 10.7 % other extractives. Cellulase enzyme, GC 220 (Genencor International Inc., Lot No #301-04232-162) and Multifect-Xylanase (Genencor International Inc., Lot. #301-04021-015) were provided by Genencor International. The average activities of cellulase (GC-220) and xylanase (Multifect) were 45 FPU/ml and 8000 GXU/ml, respectively. The β-glucosidase enzyme, Novozyme 188 (Novo Inc., lot no. 11K1088), was purchased from Sigma-Aldrich (St. Louis, MO). Activity of Novozyme 188 was 750 cellobiase unit (CBU)/ml. The microorganism used for SSF was Saccharomyces cerevisiae ATCC® 200062 (NREL-D5A), which is a SERI strain genetically improved from Red Star baker's yeast. The growth media was YP medium. The mass fractions of yeast extract (Sigma cat. No. Y-0500) and peptone (Sigma cat. No. P-6588) in YP medium were 10 and 20 g/l respectively.

2.2. Experimental setup and Operation

Corn stover was treated with 15% NH4OH solution (WNH3 =15%) in glass media bottles (Fischer Cat# 06-414-1C) at 60 °C for 24 h. Solid-to-liquid ratio was kept at 1:10. The source of ammonia was 29.5% of ammonium hydroxide (Fisher Cat# A669C). This was diluted to 15% NH4OH solution (WNH3 =15%) with deionized (DI) water and used for the treatment. After the completion of treatment, the solids and liquids were separated by fluted filter paper (Fisher Cat# 09-790-14F), and solids were washed with DI water using vacuum filter until the wash water had a neutral pH. Solid cakes were dried in the air until the moisture content of samples reached approximately 10% (drying conditions: ambient temperature and 48-72 h of drying time) and stored in the refrigerator for the second-stage hot water treatment.