Research On Pretreatment Of Rice Husk And Extraction Process Of Xylan From Pretreated Rice Husk

Rice is the main food crops in our courtry, it contains 20 per cent of husk, so ricehusk is the most considerable reproducible agricultural resource in our courtry. Themain component of the rice husk are cellulose, hemicellulose, lignin, and ash.Exploitation and utilization of rice husk has become a hotspot at home and abroad. Atpresent, the main utilization of rice husk include hydrolysis fermentation of fibercompoments in the way of alcohol, furfural, and rice husk ash manufacturing sodiumsilicate, adsorbent and so on. Because the solid network structure of rice husk isdifficult to decompose, pretreatment become the key step of its utilization. In thisthesis, the pretreatment technology of rice husk and the process of xylan extractionfrom rice husk were studied, the main research contents and results are as follows :Popcorn machine was first used to pretreat rice husk and was compared with thefollowing methods, including: 3%NaON, 3%NH3·H2O, 3%H2SO4, boiled in5%NH3·H2O, microwave. The main components of the rice husk and pretreated ricehusk were determined and analyzed with SEM, and the total sugar content of the ricehusk after enzymatic hydrolysis were compared, the results showed that the totalsugar content of the rice husk after pretreated increased by 395.55%, 177.53%,168.62%, 130.16%, 50.61%, 258.50%, respectively. The pretreatment of blasting bypopcorn machine and microwave treatment due to the relatively low cost, and greenenvironmental protection, can be enlarged to the industrialized production.Further tests using microwave cooperate with NaOH solution was used topretreat rice husk. Compare to the unpretreat rice husk, the rice husk pretreated onlyby microwave, the rice husk pretreated only by NaOH solution, and the rice huskpretreated by microwave cooperate with NH3·H2O. The rice husk that pretreated bymicrowave cooperate with NaOH is the easiest to be decomposed by enzyme. Theeffects of NaOH concentration, microwave power, irradiation time and solid-to-liquidratio on the net yields of the sugars of enzymatic hydrolysis of rice husk were studiedin single factor experiments. Subsequently, a regrssion model for net yields of thesugars was established using a Box-Behnken design involving the above four factorsat three levels and based on the model, response surface analysis was carried out tofind out the optimum levels of these four factors. The results indicated that theoptimum conditions were NaOH concetration of 1.5%, microwave power of 650 w,irradiation time of 16 min and solid-to-liquid ratio of 1:12. The rice husk treated under such conditions, can be hydrolyzed by the enzyme to get 56.24% sugars.Xylooligosaccharide is a kind of functional oligosaccharides, can be used to thefood, chemical, medical and other industries. Using rice husk for preparation ofxylooligosaccharides can get economic benefit. The premise work ofxylooligosaccharides preparation is the extraction of xylan. Response surfacemethodology was used to optimize the conditions for alkaline extraction of xylanfrom rice husk, and the rice husk was pretreatmented by microwave before use. Theeffects of extraction tempeature, NaOH concentration, solid-to-liquid ratio andextraction time on the yield of xylan were studied in single factor experiments.Subsequently, a regrssion model for the yield of xylan was established using a centralcomposite design involving the above four factors at five levels and based on themodel, response surface analysis was carried out to find out the optimum levels ofthese four factors. The results indicated that the optimum extraction conditions weretemperature of 69.81℃, NaOH concetration of 10.7%, solid-to-liquid ratio of 1:12.96,and extraction time of 5.13 h. Under such conditions, the experimental yield of xylanwas 76.57%.