The Study Of Fractionation Of Corncob Lignocellulose

Biomass (lignocellulose) is considered to be the only sustainable resource ofproviding gas, liquid and solid fuels and chemical products on a large scale. Corncobis a cheap and renewable lignocellulosic resource, It is of great importance tofractionate corncob lignocellulose and converted them into value added products. Thefollowing works have been done in the thesis:1. The contents of the three major components of corncob lignocellulose, whichis cellulose, hemicellulose and lignin, were determined firstly. Then the pretreatmentof the corncob by dilute sulfuric acid solution were investigated and the effects ofreaction temperature, reaction time and solid-liquid ratio on the lignocelluloseproperties were studied with a fixed dilute sulfuric acid concentration of0.92%. Theresults show that the hemicellulose content decreased72.7%under the condition ofacid concentration of0.92%, reaction temperature of120℃, the reaction time of60min and solid-liquid ratio of1:8. It has been found that the dilute sulfuric acidsolution pretreatment process has little impact on the cellulose and lignin components.The SEM and XRD analysis results indicated that the microstructure of corncoblignocellulose changed to a certain extent after dilute sulfuric acid treatment. Porousand loose domains can be found on the surface of corncob lignocellulose. Changesoccurred both in the crystallized region and the amorphous region and the breakingstrength of the amorphous region was higher than the crystallized region with dilutesulfuric acid treatment.2. Formic acid/acetic acid aqueous solution was used as the solvent to fractionatecorncob lignocellulose. The orthogonal test analysis was used to study the effects ofprocess factors include the formic acid/acetic acid/H2O ratio，reaction temperature andreaction time on the separation efficiency and properties of the three components. Theoptimum conditions for components separation were established:①For the cellulose,the solvent ratio of formic acid/acetic acid/H2O is2/5/3, reaction time is3hours andthe temperature is60℃.②For the hemicellulosem, the solvent ratio of formicacid/acetic acid/H2O is2/5/3, the temperature is60℃and reaction time is2hours.③For the lignin component, the ratio of formic acid/acetic acid/H2O is3/5/2, thetemperature is100℃and reaction time is4hours. FTIR and XRD analysis were used to verify the structure and properties of the obtained samples. It was found that thebasic structures of the hemicellulose and lignin kept unchanged while the crystallinityof cellulose decreased as the ratio of formic acid in the solution increased.3. The Response Surface Methodology (RSM) analysis was used to study thelignin separation and extraction conditions in detail. The sequence of operating factorsthat affect the lignin yield was found to be: reaction temperature> proportion ofsolvent> reaction time. The optimized condition with formic acid/acetic acid/H2Oratio of4/5/1(V/V/V),91℃and4h was established and the lignin yield reached70.16%. The complex structures of the obtained lignin were further characterized byFTIR, UV, TG and1HNMR. The results showed that the lignin was composed ofguaiacyl unit (G), syringyl unit (S) and p-hydroxyphenyl unit (H) and displayed theβ-O-4connecting style. The lignin remained almost unchanged in structure with highpurity. The thermogravimetric analysis showed that the lignin extracted with organicacid queous solution was thermally stable. Extracting the lignin component fromcorncob with organic acid aqueous solution was proved to be an efficient method tofractionate lignocellulose.