Bioethanol is one of the most important renewable fuels due to the economic and environ­mental benefits of its use. The use of bioethanol as an alternative motor fuel has been steadi­ly increasing around the world for the number of reasons. 1) Fossil fuel resources are declining, but biomass has been recognized as a major reasons World renewable energy source. 2) Greenhouse gas emissions is one of the most important challenges in this century because of fossil fuel consumption, biofuels can be a good solution for this problem. 3) Price of petroleum in global market has raising trend. 4) Petroleum reserves are limited and it is monopoly of some oil-importing countries and rest of the world depends on them. 5) Also known petroleum reserves are estimated to be depleted in less than 50 years at the present rate of consumption. At present, in compare to fossil fuels, bioethanol is not produced eco­nomically, but according to scientific predictions, it will be economical about 2030.

Biomass commonly gathers from agricultural, industrial and urban residues. The wastes used for bioethanol production are classified in three groups according to pretreatment process in sugary, starchy and lignocellulosic biomasses. Lignocellulosic biomass, including forestry residue, agricultural residue, yard waste, wood products, animal and human wastes, etc., is a renewable resource that stores energy from sunlight in its chemical bonds. Lignocellulosic biomass typically contains 50%-80% (dry basis) carbohydrates that are poly­mers of 5C and 6C sugar units. Lignocellulosic biomasses such as waste wood are the most promising feedstock for producing bioethanol.

Bioconversion of lignocellulosic biomass to ethanol is significantly hindered by the structur­al and chemical complexity of biomass, which makes these materials a challenge to be used as feedstock for cellulosic ethanol production. Cellulose and hemicellulose, when hydro­lyzed into their component sugars, can be converted into ethanol through well-established fermentation technologies. However, sugars necessary for fermentation are trapped inside the crosslinking structure of the lignocellulose.

Conventional methods for bioethanol production from lignocellulosic biomasses take three steps: pretreatment (commonly acid or enzyme hydrolyses), fermentation, distillation. Pretreat­ment is the chemical reaction that converts the complex polysaccharides to simple sugar. pretreatment of biomass is always necessary to remove and/or modify the surrounding ma­trix of lignin and hemicellulose prior to the enzymatic hydrolysis of the polysaccharides (cellulose and hemicellulose) in the biomass. Pretreatment refers to a process that converts lignocellulosic biomass from its native form. In general, pretreatment methods can be classi­fied into three categories, including physical, chemical, and biological pretreatment. In this step, biomass structure is broken to fermentable sugars. This project focused on chemically and biologically pretreatment. For example: this project shows the effect of sulfuric acid, hy­drochloric acid and acetic acid with different concentration by different conditions also shows the effect of cellulase enzyme by different techniques. Then fermentation step in which there are a series of chemical or enzymatic reactions that converted sugar into etha­nol. The fermentation reaction is caused by yeast or bacteria, which feed on the sugar such as Saccharomyces cerevisae. After that, distillation step in which the pure ethanol is separated from the mixture using distiller which boil the mixture by heater and evaporate the mixture to be condensate at the top of the apparatus to produce the ethanol from joined tube.

The way to manufacture bioethanol is basically the same as that of liquor. Generally, saccha — rinity material such as sugar and starchy material such as rice and corn are saccharified (Figure 5-7), fermented and distilled till absolute ethanol whose alcoholicity is over 99.5%. It is technically possible to manufacture ethanol from cellulosic material such as rice straw or wood remains.