| With the development and progress of human society, the shortage of fossil resourceshas become an indisputable fact. Considering the unsustainability of petrochemicalresources and the limitation of renewable energy like solar, nuclear and wind etc, biomassenergy has received great attention all over the world. China, as a big agricultural country,has great potential to develop biomass energy. The key of biomass energy development ishow to hydrolyze cellulose and hemicellulose into fermentable sugars efficiently which canbe used to manufacturing bio-ethanol. Therefore, in this paper, cotton straw, as thefeedstock, was hydrolyzed in alcohol-water mixture, which provided the possibility for theimprovement of reducing sugar concentration and the theoretical basis for the furtherresearch the process of lignocellulose hydrolysis.In this work, the operation conditions of lignocellulose hydrolysis by alcohol-watermixed solvent were studied under the intermittent process. The hydrolysis of powderedcotton straw was conducted with a self-designed batch reactor. The content of reducingsugar was detected by DNS method, while the degradation products of reducing sugar werequalitatively analyzed by GC–MS. By using SEM analysis, infrared spectrum analysisand material component analysis, the solid residue was investigated from the changes ofmorphology and microscopic. The volume ratio of alcohol-water mixed solvent, type ofalcohol (carbon chain length and hydroxyl amount), reaction temperature, reaction timeand concentration of sulfuric acid were investigated in this research. The results showedthat at the same temperature and time, the addition of ethanol would benefit the biomassconversion and inhibit the degradation of reducing sugar. However, the high volume ratioof ethanol could conversely reduce the generation rate of reducing sugar. The longer thecarbon chains length and the more the hydroxyl amount, the better the reaction would be.The rate of biomass conversion and the concentration of reducing sugar in the hydrolysisby isopropyl alcohol and ethylene glycol mixed solvents were higher than that byethanol-water mixed solvent. When the temperature reached190℃, the pressure reached1.5MPa and the volume ratio of ethanol-water mixed solvent reached30%, the biomass conversion rate and reducing sugar concentration were46.23%and11.77g/L respectively,while under the same conditions with pure water as solvent, the biomass conversion rateand reducing sugar concentration were41.97%and8.68g/L respectively.Moreover, through the analysis of the solid residue of cotton stalk after hydrolysis indifferent ethanol volume ratios by scanning electron microscopy (SEM), it was found thatthe straw seriously damaged at the ethanol volume ratio of30%. Infrared spectra analysisshowed that the solid crystallinity values of the solid residues were lower than that of rawmaterial, which means the addition of ethanol during hydrolysis process decreased thecrystallinity values of straw. Component analysis found that the contents of cellulose andhemicellulose in the solid were significantly decreased after hydrolysis. The results ofthese three analyses were consistent. GC-MS results showed that the organic acids weregenerated during the pure water hydrolysis, and disappeared during the mixed solventhydrolysis, but the esters appeared at the same time.Finally, under operation condition, the kinetic model was established basing on theprocess of cotton straw hydrolysis, and the kinetic parameters were calculated. However,the comparison between the calculated results from the equations and originalexperimental data showed that the set of kinetics model could not satisfactorily verbalizehydrolysis behavior of lignocellulose. Therefore, the model needed to be further modified. |
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