The Research Of Lignocellulosic Hydrolysis Process And Kinetics By Extremely-low Acid

With the depletion of fossil resources, lignocellulose as the feedstockto manufacture fuel ethanol has received great attention all over the world.China, as a big agricultural country, has great potential in fuel ethanolmanufacturing. The key of bioethanol producing is how to hydrolyzecellulose into fermentable sugars efficiently. The extremely low acidhydrolysis (acid concentration below to0.1wt%) has become the focus ofresearch because of the advantages of itself such as low erosion toreaction equipment, good catalytic effect and hydrolysis effect. Therefore,in this paper, the process of lignocellulose hydrolysis to produce reducingsugar under the extremely low acid condition has been studied and theresults were as followed.(1) Taking rice straw (Hubei province, China) as the research object,the effect of stirring rate, acid concentration, liquid-solid ratio,temperature as well as resident time on reducing sugar yields was studied.The optimal condition of straw hydrolysis was obtained at the conditionof the stirring rate500r/min,0.05wt%sulfuric acid concentration,15:1liquid-solid ratio (solid3g/liquid45mL),210℃and10min. The reducingsugar yield was30.05%;(3) The reducing sugar concentrations and yields were determinedafter the hydrolysis of15kinds of lignocellulose at each optimalhydrolysis conditions. It was found that no matter the different kinds oflignocellulose in the same areas or the same kind of lignocellulose indifferent areas, the concentrations and yields were significantly different.The hydrolysis efficiency of rice straw, corn straw in Heilongjiangprovince and wheat straw in Shandong province were much batter thanthat of cotton straw and rape straw.(4) By HPLC, the main hydrolysis products of lignocellulose wereglucose, fructose and xylose. The xylose peak area was much greater,which indicated that the hydrolysis of hemicellulose was much thorough. By analyses of SEM, there were some irregular pores distributed on thesurface of residue after hydrolysis. By TG analysis, the TG and DTGcurve were basically corresponded with that of lignocellulose samples,however, the highest decomposition temperature of residues were higherthan that of samples, which indicated that there mostly existed cellulosein residues. In addition, the determinations of cellulose crystallinity byFTIR and X-diffraction method showed that the crystalline structures ofcellulose were not completely destructed by hydrolysis.(5) During the process of lignocellulose hydrolysis under extremelylow acid and high temperature conditions, the biomass particles was seenas dense spherical, and as the hydrolysis preceded, these particles wouldgradually shrink to the center of the sphere. According to the theory aboutheterogeneous reaction, the external diffusion could be ignored in thehigh-speed stirring reactor, and the diffusion resistance of reactants andproducts mainly existed in the laminar sublayer of particle surface.Basing on the theory above, the shrinking model of lignocellulosehydrolysis was established. Comparison between the calculated resultsfrom the equations and original experimental data proved that the set ofkinetics model could satisfactorily verbalize the dilute acid hydrolysisbehavior of lignocellulose. The calculation by the model showed thatmore uniform particles there are and smaller their size is, the higherreducing sugar concentration could reach.