Study On The Preparation Of Bamboo Carbon-based Solid Acid And Its Catalytic Properties In The Hydrolysis Of Cellulose

Cellulose is one of the most abundant renewable natural resources in the world.The effective use of cellulose for either fuel or chemical productions is of great significance to the environmental benign development and,therefore,has received more and more attention in recent years.The hydrolyzation of cellulose to produce glucose has been investigated by many research groups worldwide.The carbon-based solid acids prepared by using different biomasses were often studied as the catalysts for catalytic hydrolysis of cellulose in the literature,because of their easy separation and weak corrosion to the equipment.However,there were still some common disadvantages of these kinds of solid acids.Both the specific surface area and the sulfonic acid amount of these catalysts given in the literature were relatively small,which limited the contact between the cellulose molecule and active site of the catalyst,and led to a relatively low conversion of cellulose and low yield of glucose.To overcome these drawbacks,the preparation of carbon-based solid acid from bamboo and its modification by chemical impregnation were studied in this work.The effects of preparation conditions on the sulfonic acid amount,structure and catalytic performance of the catalyst were investigated systematically.The mechanism for the impregnation modification was also explored:?1?The bamboo carbon-based solid acids were prepared in two different ways.In the first way,bamboo powder was carbonized directly and followed by a sulfonation.Under the optimal conditions,the obtained catalyst gave a sulfonic acid amount of0.810 mmol/g,and when applied to the hydrolysis of cellulose at 150 ^oC it gave a glucose yield of 28.4%.In the second one,bamboo powder was first impregnated in a sodium hydroxide solution and followed by carbonization and sulfonation.After optimizing the conditions,the catalyst generated had a sulfonic acid amount as high as0.939 mmol/g,and it acquired a glucose yield of 45.0%at the same hydrolysis conditions.It is found that the impregnation of bamboo powder in sodium hydroxide solution led to an apparent improvement of the catalytic performance of the bamboo carbon-based solid acid.?2?The microstructure of carbon-based solid acid was characterized by the TG,FT-IR,BET,XRD and SEM.The results indicated that the catalyst was composed of amorphous aromatic carbon sheets with a degree of graphitization,in which distributed some irregular mesoporous structure and loaded with-SO₃H,-COOH and-OH groups.In addition,catalyst was thermal stable below 210 ^oC,and the impregnation modified catalyst showed better stability than the non-modified one.It was noted that the impregnation could promote the porous structure of the bamboo carbon during carbonization,which in return effectively increased specific surface area of the catalyst.The degree of graphitization of catalysts prepared by using various impregnation agents was different.It led to different number of active site that could be substituted by-SO₃H and,therefore,resulted in different amount of sulfonic acid in the catalyst.The catalyst prepared by sodium hydroxide impregnation gave the highest amount of sulfonic acid,and exhibited the best catalytic performance in the hydrolysis of cellulose.It was shown that the modification of the catalytic activity was related not only to the increase of the acid amount of catalyst,but also to its modification of the porous structure.?3?The mechanism for the preparation of impregnation modified catalyst showed that the sodium hydroxide solution impregnation could promote the pyrolysis and carbonization of bamboo powder.The reason was that the acetyl groups and partial?-glycosidic bonds in hemicelluloses,and the partial methoxy groups of the side chains of lignin could be decomposed during alkaline treatment.The cellulose,hemicellulose and lignin structures in bamboo powder underwent dehydration condensation to form aromatic ring structure during carbonization,in which some functional groups such as hydroxyl and ether bond were broken and disappeared,while the cyclic C-O-C bond still existed.Subsequently,the active hydrogen Ar-H on aromatic carbon atom of bamboo carbon underwent a substitution reaction with sulfuric acid?Ar-H+H₂SO₄?Ar-SO₃H+H₂O?during sulfonation,in which the sulfonic acid group was successfully loaded into bamboo carbon,and the amount of sulfonic acid group was related to the number of active hydrogen.