| The main purpose of corn stalk depolymerization is to change or remove all kinds of structure and/or chemical barrier enhance cellulose enzymolysis rate and the transformation effect,which is the key and core of produce all sorts of the cellulose chemical and cellulose ethanol.The method of physical coupling with chemical was used to deal with the corn stalk,and the depolymerization effect was evaluated by relevant parameter.It is further to enzymatic hydrolysis,solid acid catalytic hydrolysis and catalytic hydrogenation so that to provide effective way for the further use of straw polymer structure,the results were given as follows:(1)The aim of this study was to investigate the molecular structure of corn stalk after depolymerization with 5%H2SO4 or 5%NaOH solution.The change of structure,chemical composition and thermal property of corn stalk were comparatively analyzed and characterizated.The results showed that treatment with dilute acid or alkali removed most of hemicellulose and some lignin in corn stalk as compared to those of the untreated stalk.The crystallinity of the tested stalk was increased from 51.8%to 63.5%and 67.0%.The coupling method of 1.0%NaOH/2.0%H2SO4 and 2.0%H2SO4/1.0%NaOH was obtained the high glucan yield(80%-88%),and the hemicellulsoe was effective removal and the rate of removal reach 71%-90%,the lignin rate was reach 12%,the content of xylose was reach 6.9mg/ml in the hydrolysate.The content of total sugar yield was reached 20mg/ml when the cellulose as the substrate in the enzymatic hydrolysis process with 72 h.Meanwhile,the content of total sugar yield can obtain 19 mg/ml when the pretreated sample of 1.0%NaOH/2.0%H2SO4 as the substrate.The result showed that it has a significant relationship between the depolymerization processes and the enzyme hydrolysis.It can provide a good environment for preparation of fuel ethanol in the process of fermentation.After depolymerization corn stalk with acid or alkali,the surface morphology become loose,appeared holes and cracks and the thermal stability increased.These results suggest that dilute acid and alkali have a certain depolymerization to the molecular structure of corn stalk,but the depolymerization effect of dilute alkali is better than that of dilute acid in terms of delignification.(2)A combinative pretreatment technology of steam explosion(SE)and alkali was applied to enhance hydrogenolysis conversion of corn stalk into polyol with Ni-W2C or Fe-Mn-K catalyst.The results showed that treatments corn stalk with 0.4 MPa SE and alkali removed 84.16 wt%of hemicellulose and 71.83 wt%of lignin and thereby increased the cellulose content from 31.54 to 80.41 wt%.But the glucose loss was insignificant during pretreatment.The TGA,SEM,FT-IR result showed that the surface morphology become loose,appeared holes and cracks after depolymerization corn stalk,the thermal stability increased,the absorption peak of hemicelluloses and lignin was effective removed in the process of depolymerization.Data from catalytic hydrogenolysis showed that pretreatment corn stalk with 0.4 MPa SE and alkali improved the yield of polyol,and about 20.38 wt%of ethylene glycol and 52.36 wt%of glycerol were produced after catalysis with Ni-W2C/(coconut shell activated carbon,CSAC).Based on the yield of polyol,the catalytic performance of Ni-W2C/CSAC was significantly better than those of Ni-W2C/(coal-based activated carbon)and Fe-Mn-K/(amorphous carbon).(3)The results showed that the coupled pretreatment of NaOH+O3 was achieved a higher conversion rate(>60%),pentosane removal rate(>80%)and delignification rate(>80%)than that of untreated sample in the pretreatment experiments.Additionally,in the experiment of solid acid catalysis,the catalytic effect of AC-SO3H and CD552 was best,followed by GO-SO3H and the HY zeolite solid acid catalyst.The total sugar yield was reached 35%when the NaOH+O3 pretreated sample was catalyzed by AC-SO3H.The total sugar yield was 28%when the 03 pretreated sample was catalyzed by CD552.Additionally,the total sugar yield was over 50%when the extracted hemicellulose sample was catalyzed by CD552.The result showed that the reaction of hemicellulose degradation for xylose is the approach of catalytic hydrolysis.Catalytic effect at 120 ℃ was significantly lower than that at 140℃.(4)In this research,the effects of combined severity parameters(CSP),response surface methodology(RSM),and separation factor(SF)on the recovery and/or removal rate of main fraction for acid-catalyzed hydrolysis of corn stalk were defined and investigated.The results demonstrated that the content change of pentosan,AIL,ASL and SFG-L was more evaluated by CSP.The findings also suggest that both CSP0 and CSP1 parameters are more sensitive to reaction temperature compared to acid loading and hydrolysis time.The optimization experiment of acid depolymerization corn stalk was showed that the maximum total sugar yield(44.31 wt%)was obtained from corn stalk after hydrolysis with 2.05 wt%of acid catalysis at 113.17 0C for 61.69 min(CSP0= 1.80)while the high glucan recovery(88.02%),de-pentosane rate(97.21%),and SF of solid phase fraction were obtained with CSP0 range of 1.14-2.18(CSP1 range of 1.80-2.82).The findings suggest that CSP1 can be used to more efficiently evaluate the separation degree of glucan with lignin(SFG-L)than CSP0.The acid-catalyzed hydrolysis of com stalk has an advantage of high solid-liquid phase recovery and CSP can be used to describe the effect of acid hydrolysis.(5)The content change of xylose and acetic acid in the hydrolysate not showed regularity with the increasing the pKa when the hydrolysis experiments were proceeded by different homogeneous acid catalyst.However,the content change of glucose and arabinose was decrease with the pKa increasing.Meanwhile,the solid phase content of xylan and acid insoluble lignin was decrease with pKa increasing,too.It can better evaluate the content of polysaccharide in the solid phase composition and the content of monosaccharide and by-product content in liquid phase when the same kind of acid was used under the different depolymerization factor.Including pretreatment of hydrochloric acid can obtained higher glucan yield. |
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