| Energy is the foundational material for human society to survive and develop. Its seriousshortage and related environmental problems have received extensive attention of allcountries in the world. So the preparation of fuel ethanol is an irresistable trend withrenewable biomass material.The cotton production in China is in front of world. Cotton stalks, which mainly containrich bast fibre and lignocellulose, have special plant morphology and structure betweenwoody plants and herbs. To fully utilize cotton stalks as a feedstock for fuel ethanolproduction has great potential for development. Four steps are employed in converting thelignocellulose to fuel ethanol: pretreatment, hydrolysis, fermentation and separation. Cottonstalks, which have higher lignification degree and complex structure, need to increase thesurface area of them through proper pretreatment to improve efficiency of enzymatichydrolysis in order to maximize the ethanol fermentationTherefore the pretreatments of dilute sulfuric acid (H2SO4), ultrasonic-assisted alkali(NaOH), high pressure-assisted alkali for conversion of cotton stalks to ethanol wereinvestigated in the study. And the experimental indicators contain weightlessness rate,cellulose content, lignin content. Then the microstructure of before and after processing wereinvestigated through the Scanning Electronic Microscopy, Fourier Transform Infraredspectrum and X-ray diffraction. Finally the enzymatic hydrolysis and ethanol fermentationtest of cotton stalks with different pretreatment was investigated in the study. The mainresearch results as follow:The tested factors showed significant influence on the contents of xylose in the dilutesulfuric acid treated stalks following the order of sulfuric acid volume fraction> treating time> treating temperature. The optimal pretreatment conditions were determined: reactiontemperature133.5℃, time2.0h, sulfuric acid volume fraction3.5%, and the xylose yield was6.865g/L. And the cellulose content was50.50%, being26.73%higher than untreated cottonstalks. Through the observation of SEM images of before and after processing, the resultsshowed that dilute acid pretreatment can break the crystalline structure of cellulose efficientlyand reduce the bondage of lignin. The treating time and sodium hydroxide concentration showed significant influence onthe contents of cellulose in the ultrasonic-assisted alkali treated stalks following the order oftreating time> sodium hydroxide concentration> liquid to solid ratio. The optimumconditions were obtained at ultrasonic power420W, sodium hydroxide3.5%, processing time90min, and liquid to solid ratio21:1. And the cellulose content was58.02%, being45.60%higher than untreated cotton stalks. Images of Scanning Electronic Microscopy showed thatmost hemicellulose and part of lignin were dissolved out of the stalk during the pretreatmentand thus the crystalline structure o was efficiently broken. Overall, application of ultrasonicwave showed significant effect on the alkali pretreatment of cotton stalk.The tested factors showed significant influence on the contents of cellulose in the highpressure-assisted alkali treated stalks following the order of processing pressure> sodiumhydroxide concentration> treating time. The optimum conditions were obtained at processingpressure130kPa, sodium hydroxide3.0%, processing time40min. And the cellulose contentwas64.20%, being61.10%higher than untreated cotton stalks. Images of Scanning ElectronicMicroscopy showed that most hemicellulose and lignin were dissolved out of the stalk and itshowed remarkable effect on the pretreatment of cotton stalk.FT-IR and X-ray diffraction showed that the cotton stalks after pretreatment there is nonew functional groups and the crystal type has no change. Thus the compact structure wasefficiently broken.In addition, the enzymatic hydrolysis of cotton stalks with different pretreatment wasinvestigated in the study. The results showed that the sugar yield was44.44%, being11.47%higher than the original value with the high pressure-assisted alkali pretreatment and theresults were achieved when pH of sodium acetate buffer was5.0, substrate concentration was2%, the amount of enzyme used was550U/gof dry pretreated biomass, and the samples wereincubated at48℃for24h with120rpm.Finally, the ethanol fermentation of different enzymatic liquid with pretreatment wasinvestigated. The results showed that the ethanol yield was45.96%, being57.40%higher thanthe untreated with the high pressure-assisted alkali pretreatment. And it is significantly higherthan the ethanol yield with dilute sulfuric acid (27.44%) and ultrasonic-assisted alkali(33.17%) pretreatment.The above research have shown that high pressure-assisted alkali treated stalks has thebest effect. That make most hemicellulose and lignin were dissolved out of the stalk, brokethe crystalline structure of cellulose efficiently and reduce the bondage of lignin and itshowed remarkable effect on the pretreatment of cotton stalk. And it is advantageous to theenzyme hydrolysis test and ethanol fermentation. |
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