Research On Preparation Of Fuel Ethanol And Comprehensive Utilization Of Rice Hull

Since the 20th century, the rapid development of modern industry and transp ortation industry, driving global energy, food and growing environmental crisis, which makes human beings in the 21st century faces unprecedented challenges. Facing the increasing depletion of conventional fossil energy and the rapid deterioration of the environment, many countries shift their focus on large-scale development and utilization of clean energy as a renewable resource. The first generation of fuel ethanol primarily produced from corn, wheat and other grain crops as raw material, gradually loses its advantage by a tightening situation of world food security. The second generation of biofuel, such as the non-grain ethanol, cellulosic ethanol and biodiesel, becomes the direction of biomass energy industry development in the future, as it follows the line of "not fight for ground with food, not fight for food with people".Cellulosic ethanol is considered to be the best alternative liquid fuel, and becomes the focus of industrial biotechnology research by its ecological benefits. At the present stage, the results of research and industrial test bring human beings the hope of developping cellulosic ethanol. However, a series of problems, such as the efficiency of cellulose hydrolysis, hydrolysis waste pollution, harmful substances affecting the activity of yeast in hydrolysis liquid, energy consumption of the production process......., lead to the high cost of cellulosic ethanol production, troubles in industrial production, and result in a low state of cellulosic ethanol research and industrial development.In this paper, I attempt to find a new way to product biomass ethanol to solve existing problems. The method of preparing xylose and residues (Ⅰ) by hydrolyzing hemicellulose solves the problem of the yeast activity affected by xylose. The way to obtain glucose and residue (Ⅱ) by hydrolyzing from residues (Ⅰ) with concentrated acid under normal pressure and low temperature, can inprove the efficiency of cellulose hydrolysis. Silica from rice hull ash can be dissolved in alkali liquid to preparate sodium silicate solution and residue (Ⅲ), which is used in neutralizing sugar and acid solution. The neutralization can solve the cost problem by producing glucose solution, which can be directly fermented to ethanol, and collecting nano-silica. Incineration of residue (Ⅱ) and (Ⅲ) to preparate nano-silica, can make the final residue being fully utilized. In this way, we obtain a new comprehensive, low-carbon and green technology of preparating fuel ethanol and utilizing rice hulls.The major elements are as follows:Firstly, I obtained glucose solution from the agricultural waste rice hull, through a pretreatment of dilute sulphuric acid and the hydrolysis of concentrated sulphuric acid. The suitable condition of the pretreatment is in the boiling solution with 6% dilute sulphuric acid for 5 h, and the ratio of H2SO4 solution volume (mL) to the rice hull mass (g) is 10:1, hemicellulose hydrolysis rate is 18.6%(mhemicellulose/mrice hull) The optimum hydrolysis conditions are as follows:the concentration of H2SO4 is 72% (wt.%), the temperature is 50℃, the ratio of H2SO4 solution volume(mL) to the rice hull mass(g) is 10:1 and the time is 5 minutes, the glucose yield rate reaches 45.6% (mcellulose/mrice hull afer pretreatment)Secondly, I studied the influence on the separation of the solution with the sugar and acid through the ion exclusion chromatography and neutralization. The ion exclusion chromatography is represented as a small pilot phase of separation of sugar and acid experimental methods. The suitable operating conditions are as follows:the resin used in the column is cation ion-exchange resin, with particle diameter 0.1-0.2 mm, and the resin column height of 1 m. When the feeding and elution flow speed are both 10 mL/min, the glucose rate is 96% and the sulphuric acid rate is 65% at 80℃. In neutralization, the alkaline solution is sodium silicate solution, and the methods are as follows:the concentration of sodium hydroxide solution was 15%(wt.%), and the liquid (sodium hydroxide solution) to solid (rice hull ash) ratio (v/m) was 5:1, the boiling time is 2 hours, the silica rate is 64%. The acid solution is dropped into the flask which contained alkaline solution with a speed of 1 mL/min, the ratio of the amount of alkaline solution to sugar and acid solution is approximately 2:1 (v/v), and the glucose rate is 95%. The concentration of glucose solution from these two methods are measured by ultraviolet spectrophotometer (UV-VIS) could be up to 0.1 g/mL.Thirdly, I studied silica, lignin and sodium sulfate crystals from the hydrolysis of concentrated sulphuric acid and the separation of the sugar and acid separately. This experimental is mainly designed to study the size, shape and dispersion of the nano-silica. With the optimum acid hydrolysis conditions, the silica particle incinerated from hydrolyzed residue is spherical, monodisperse with the size about 100nm; while, after neutralization the silica particle is with the size about 30nm, spherical, and better dispersion. There is a small amount of acid soluble lignin precipitated from the sulphuric acid hydrolysis process of cellulose. The increase of phenolic hydroxyl number after phenolation of rice hull acid-insoluble lignin proved more active site of lignin to react with phenol. When the weight rate of lignin and phenol is 1:6, the volume rate of H2SO4 and water is 9:6, reaction temperature is 80, and reaction time is 4 hours, the highest yield of lignin/phenol is 104%(m lignin/phenol /m pheno).The phenolic resin obtained by modified lignin performed well in the infrared, ultraviolet-resistant, hydrophobic moisture, heat and other properties. The by-product sodium sulfate is test the relationship of the crystal morphology and the formation.Fourthly, the glucose solution hydrolyzed from cellulose is eventually fermented to be ethanol. The fermentation bacteria selected in this experiment is Angel Yeast, which is a kind of commercial yeast. The optimal situations are as follows:the concentration of glucose solution is 10%, m glucose:m yeast=10:1, pH=6.8, reaction time is 60 h, and temperature is 34℃, the ethanol rate is 67.0%(m ethanol= m glucose)Finally, I summarize a method to comprehensively utilize rcie hull. The systematic comparison of rice hulls and rice bran proved that this method can be carried out in a similar application of biomass.