Catalytic Methanolysis Of Rice Straw Powder Over Supported KF

Alcoholysis is an effective method of clean and efficient utilization of biomass, from which the bio-oils(BOs) produced can be used to obtain value-added chemicals. In the work,methanol was used for liquefaction of rice straw powder under microwave-assisted or supercritical conditions with supported KF as catalyst(KF/Al2O3, KF/Ca O or KF/zeolite). The yields and chemical components of BOs were investigated to study the mechanism of depolymerization of RSP.Optimization of preparation process of catalysts and process of methanolysis were conducted taken YL as an evaluation index. The optimum condition of preparation process of catalysts is: KF content 20%, calcination temperature of KF/Al2O3 and KF/zeolite 500 o C and KF/Ca O 600 o C. The optimum condition of methanolysis is: reaction temperature 75 o C for microwave-assisted methanolysis(MAM) and 300 oC for supercritical methanolysis(SCM),reaction time 30 min and catalyst dosage 5% for both.Under microwave-assisted conditions, sequential and catalytic methanolysis were respectively conducted to reveal the patterns of depolymerization. Sterols are the most abundant group component in BO from the first-stage MAM, while phthalic acid esters are the main components in both the second and third stage with relative content(RC) of nearly 50%.In total, 66 compounds were identified in BOs from catalytic MAM, comparing to 23 compounds from non-catalytic condition. The supported KF improved the formation of ketones,ethers, esters and aliphatic hydrocarbon. The most plentiful components in BO from KF/Al2O3-,KF/Ca O- and KF/zeolite- catalytic MAM are sterols, ketones(with RC of 65.7%) and furan derivate, respectively.Under supercritical conditions, sequential and catalytic methanolysis were also conducted respectively. Methanolysis in different temperatures revels that the distribution of group components in BOs exists some regularity. Within certain temperature range, the growth of temperature contributes to the formation of ketones, ethers and phenols. Above this temperature, repolymerization occur among some of compounds with small molecule. On the other hand, higher YL and more species of compounds were obtained from catalytic SCM than that from non-catalytic condition and the maximum YL achieved when using KF/zeolite. In BOs from catalytic SCM at 260 oC, 82 compounds were detected, most of which are esters.Besides, all the supported KF promoted the generation of ketones, esters and silicon-containing compounds. Meanwhile, in BOs from catalytic SCM at 300 o C, in total, 172 compounds were identified and prominently more than 64 from the non-catalytic condition. Keones are the maingroup components when using KF/Al2O3 and KF/Ca O, while phenols are the most abundant using KF/zeolite. All supported KF facilitated the formation of ketones, esters and phenols and KF/zeolite also contributed to that of alcohols, esters and aromatic hydrocarbons. Higher YL were achieved from the second stage of KF/Ca O-catalytic SCM at 300 o C and phenols are the most abundant components in the BO, comparing to the non-catalytic situation from which the dominant compounds are tetramethyl orthosilicate(with RC of 65.2%) and hexamethyl diorthosilicate. The sillicon-containing compounds are attributed to the reaction of supercritical methanol and phytoliths in RSP.In this work, supported KF perform desired catalytic character in both MAM and SCM.The catalyst is proposed to promote the dissociation of methanol to CH3O-, which subsequently attack the C-O bridged bonds between sugar rings in cellulose and hemicellulose and aromatic rings in lignin, generating more compounds with small molecule.