Study On Pretreatment Of Poplar By Temperature-Pressure Division Controlled Explosion

Steam explosion technology is a method of pretreating lignocellulosic material by high temperature and high pressure steam.The component separation and structural change could be achieved by instantaneous pressure release.Steam explosion can improve the utilization rate of lignocellulosic materials.The temperature of traditional steam explosion was controlled by the pressure of steam,so temperature and pressure cannot be controlled separately.This research studied a new method,namely temperature-pressure division controlled explosion method.Steam and compressed air would be introduced during the explosion process.The operating temperature can be controlled by the partial pressure of steam,while operating pressure could be adjusted by changing partial pressure of compressed air,so the operating temperature and pressure would be controlled separately.Steam explosion has a stronger degradation effect on hemicellulose,but a relatively weak degradation effect on cellulose.In order to better degrade hemicellulose,the poplar was impregnated with oxalic acid before explosion.In this research,poplar chips impregnated with oxalic acid were pretreated by the temperature-pressure division controlled explosion method.The effects of oxalic acid proportion,reaction temperature,reaction time and explosion pressure on the contents of cellulose,hemicellulose and lignin in the samples after explosion were investigated respectively,and the optimal explosion conditions were found.The properties of samples after explosion were characterized by scanning electron microscope(SEM),fourier transform infrared spectrometer(FTIR),X-ray diffraction(XRD)and thermogravimetric analyzer(TGA).The results showed that after explosion at the optimal conditions(1.5%oxalic acid,210?,9 min and 2.8 MPa),the cellulose relative content was 63.8%,the hemicellulose relative content was 0.8%and the lignin relative content was 25.3%.Compared with the poplar raw material,the cellulose relative content increased by 49.8%after explosion.The content of hemicellulose was reduced by 95.9%.and the removal was sufficient.The lignin content decreased by 10.9%.After the explosion pretreatment,the structure of poplar was damaged,and the closely arranged fibers were torn into single fibers or the fiber bundle structure.Meanwhile,the crystallinity increased from 50.6%to 64.6%after explosion.Enzymatic hydrolysis of poplar and samples after explosion was conducted using cellulose.The glucose concentration and glucose conversion rate in the enzymatic hydrolysis solution were analyzed.The properties of enzymatic hydrolysis products were characterized by fourier transform infrared spectrometer(FTIR),X-ray diffraction(XRD)and thermogravimetric analyzer(TGA).The results showed that,after hydrolyzing for 96 hours,the glucose concentration and conversion rate of poplar were 4.5 g/L and 20.7%.The glucose concentration in the enzymolysis solution was increased to 25.7 g/L and enzymatic conversion rate of the tradition samples after explosion was increased to 85.7%.As to the temperature-pressure division controlled samples after explosion,the glucose concentration in the enzymolysis solution and enzymatic conversion rate were 22.1 g/L and 74.8%,respectively.After pretreated by Acid impregnated temperature-pressure division controlled explosion method,the glucose concentration in the enzymolysis solution and enzymatic conversion rate of product were 20.5 g/L and 71.9%,respectively.Therefore,the enzymatic conversion rate of poplar was the poorest,however,traditional steam samples after explosion has the best enzymatic conversion rate.Due to the destruction of poplar structure,the enzyme and cellulose fibers were increased,thus improving the efficiency of enzymatic hydrolysis.Hemicellulose was extracted from different explosion liquid,and characterized by gel permeation chromatography(GPC),fourier transform infrared spectrometer(FTIR),X-ray diffraction(XRD)and thermogravimetric analyzer(TGA).The results show that the molecular weight of hemicellulose decreases with explosion strength increases.