Study On Combination Of Steam Explosion And Microwave Irradiation Pretreatment Of Corn Stover

Sustainable production of bioethanol from lignocellulosic biomass is one of themost suitable alternatives to fossil fuels. Pretreatment is a key procedure for practicalfeedstock conversion processes. In order to promote the development of bioethanolindustry, it is very important to study and optimize pretreatment processes.In this study, based on comprehensive consideration of the characteristics ofsteam explosion and microwave irradiation pretreatment, a novel pretreatment processnamed combination of steam explosion and microwave irradiation （SE-MI）pretreatment was proposed in order to increase the enzymatic digestibility and sugaryield of pretreated materials. The new process was used for pretreat corn stover, and itwas studied and optimized systematiclly.In this article, a set of SE-MI pretreatment equipment was established, and thedistribution of temperature, pressure, steam flow rate and microwave irradiationintensity in pretreatment reactor were numerical simulated. The results showed thatthe suitable amount of materials was100⁴00g in15L reactor.The enzymatic hydrolysis yields of materials obtained by SE-MI pretreatmentwere much higher than that obtained by steam explosion pretreatment. However, thesolid yields were slightly lower for the former, which resulted in the total sugar yieldsonly slightly higher than that of the latter. When reaction temperature wasrespectively for170℃and190℃, and reaction time was5min, the total sugar yieldof SE-MI pretreatment was respectively for52.34g and69.95g per100g total sugar,which was increased by1.58g and1.66g per100g total sugar respectively comparedto steam explosion pretreatment.Properly increasing reaction temperature and reaction time could significantlyenhance SE-MI pretreatment efficiency. Under190℃reaction temperature and10min reaction time, or200℃reaction temperature and5min reaction time, the totalsugar yield after SE-MI pretreatment was relatively high, which achieved74.64g and75.25g per100g total sugar respectively.Microwave irradiation could greatly decrease the crystallinity of materials, butmerely caused the enzymatic hydrolysis yields and total sugar yields slightly increase.The crystallinity of biomass for SE-MI pretreatment with microwave effect was 37.7⁴2.0%, which was15.6¹9.9%lower than that without microwave effect, andthe decrease of which was more significant at higher reaction temperature. Therefore,low microwave power and short microwave irradiation time were favorable forSE-MI pretreatment when considering sugar yield and energy consumptioncomprehensively.Reaction temperature, reaction time and the amount of material in reactor hadmost significant effect on SE-MI pretreatment. The SE-MI process was optimized byorthogonal experiments, and the optimum pretreatment condition was:1⁶mmparticle size,20%moisture content,200℃reaction temperature,5min reaction time,540W microwave power, and200g materials （in15L reactor）. At this condition, thetotal sugar yield was81.31g/100g total sugar in feedstock, and the minimumapplicable enzyme loading of cellulase was15FPU/g glucan. Although the total sugaryield achieved by SE-MI process was lower than that achieved by acid catalyzedsteam explosion pretreatment of corn stover, which was commonly used currently, thenew process possess competitiveness on environmental protection, process operationand cost, as additional acid catalyst （such as SO₂or surfuric acid） was not need to beadded.