Study On The Two-Stage Hydrothermal Auto-catalyic And Strengthened Pretreatment Process Of Cassava Straw

Cassava straws are favourable lignocellulosic materials,which contain more than 40% of cellulose and hemicellulose.But they are mainly used for incineration or discarding,resulting in the waste of resources and environmental pollution.In recent years,with the development of co-metabolism technique of C-5 and C-6 sugars,the two-stage hydrothermal acto-catalytic and strengthened pretreatment technology was firstly in this work proposed for cassava straws.Based on the hydrothermic reaction characteristics of hemicellulose and cellulose components in cassava straws under subcritical conditions,the study was carried out on the two stage hydrothermal pretreatments of cassava straws,in order to increase the yield of C-5 and C-6 sugars maximally.The effects of different pretreated conditions on the formation rules of C-5 sugars(xylose + arabinose),C-6 sugars(glucose),byproducts such as acetic acid,lactic acid,formic acid,furfural and 5-HMF(5-hydroxymethylfurfural)were investigated.The suitable pretreated conditions for two stage hydrothermal pretreatments of cassava straw were determined.In the first stage,under the condition of reaction temperature of 180 °C and the reaction time of 60 min,the yiled of C-5 sugars in the pretreated liquid was 68.49 %,and that of C-6 sugars in the enzymatic hydrolysis liquid was 45.62%.In the second stage,at the reaction temperature of 200 °C and for the reaction time of 20 min,the yield of C-6 sugar in the enzymatic hydrolysis liquid reached to 81.02 %.On the basis of two stage hydrothermal pretreatments of cassava straws,the two-stage auto-catalytic pretreatment technology as firstly proposed to treat cassava straw,the part of self produced riched acids by reused as pretreated liquid to strengthen the pretreated process.The experimently results displayed that under the suitable pretreatment conditions in first stage: the acid concentration in the pretreated liquid was 0.93 wt%,the pH value was 3.90,the reaction temperature was 180 °C and the reaction time was 60 min,and the single-pass yield of C-5 sugars in the pretreated liquid reached to 81.12 %.The suitable pretreatment conditions in second stage: the reaction temperature at 200 °C and the reaction time for 20 min,the yield of C-6 sugars in the enzymatic hydrolysis reaction was reached to 88.60 % after the two stage acto-catalytic pretreatments,and the acidity had little effect on the second stage pretreatment.In this work,various byproduct organic acids were used to strengthen the pretreatment technologies,and the effects of different kinds of organic acids on the hydrolysis of hemicellulose were investigated under the same pretreated acidic strength.The mixted ratio of three kinds of acetic acid,lactic acid and formic acid was also optimized,and the multi-factor model of central response curved surface was established.The optimum conditions were obtained: reaction temperature was 180 °C,reaction time was 60 min,using the mixture of 1.03 wt% acetic acid,0.83 wt% lactic acid and 1.13 wt% formic acid,the C-5 sugars yield reached 90.12%,which was in agreement with the proved experiment,the real yield of C-5 sugars was 89.06%.In addition,the kinetic model for three kinds of organic acid catalyzed hydrolysis process of cassava straw was established,the corresponding rate conatants and activation energy under different temperatures were compared.And the suitable reaction temperature of multiple acid catalyzed hydrolysis of cassava straw was in the range from 160 to 180 °C.