Study On The Preparation Of Sulfonated Carbon Material From Bamboo And Its Acidic Catalytic Properties

Solid acid catalyst with its advantages such as high efficiency for many kinds of reactions, high selectivity and easy to be separated for recycling use is a green and environmental friendly catalyst. The use of solid acid catalyst has found a feasible and effective solution to the problems such as the corrosion of equipment, difficulty in recycling use and large amount of liquid wastage, encountered in the use of liquid acid (for example, sulfuric acid, hydrochloric acid and phosphoric acid) and has become a research focus in the catalytic field. Biomass is an abundant, renewable and environmentally friendly resource. Using biomass especially those wasted biomass such as wastes produced during manufacture of bamboo and wood materials, wasted shell, as raw material in preparation of solid acids can not only promote comprehensive utilization of biomass resource, but also reduce the production cost of solid acid, which favors popularizing solid acids in industrial application.Sulfonated carbon material was prepared by one pot simultaneous carbonization and sulfonation method using bamboo powder, wasted material in bamboo manufacture, as main raw material, and p-toluenesulfonic acid monohydrate as sulfonating agent, and the preparing conditions of the catalyst were investigated systematically. At the same time catalysts were also prepared using cellulose and lignin as raw materials and their catalytic performance was also compared, and the differences of cellulose and lignin in simultaneous carbonization and sulfonation process from bamboo was investigated as well. In addition, comparison in catalytic performance between sulfonated carbon derived from bamboo and other catalysts was conducted. Finallly the sulfonated carbon material was applied in different esterification reactions and dehydration reaction of fructose to 5-hydoxymethylfurfural. The main results and conclusions were as follows:(1) Sulfonated carbon material was synthesized by one pot simultaneous carbonization and sulfonation method using wasted bamboo powder as raw material and p-toluenesulfonic acid monohydrate as sulfonating agent. Esterification of acetic acid with n-butanol was used as a standard reaction for the evaluation of the catalysts. The influence of preparing conditions such as weight ratio of p-toluenesulfonic acid monohydrate to bamboo powder, carbonization and sulfonation temperature, time, and air treatment, to the catalytic performance of catalyst were discussed systematically in combination with different characterization techniques. The proper preparing condition was obtained as follows:weight ratio ofp-toluenesulfonic acid monohydrate to bamboo powder 0.8, simultaneous carbonization and sulfonation temperature 180 ℃, reaction time 18 h and 180 ℃ hot air treatment for 6 h. Among them the procedure of hot air treatment was crucial for the development of surface functional groups such as OH and COOH of the catalyst during the preparation process. Those functional groups can stabilize the strong acid sites of the catalyst (SO3H groups) during the the preparation process, thus improving the catalytic activity of the catalyst. Additionally catalyst SBC(0.8/180/18) prepared under the proper preparation condition was compared with SLiC(0.8/180/18) and SCeC(0.8/180/18) prepared under the similar condition but using lignin and cellulose, respectively, as raw materials. It was discovered that during simultaneous carbonization and sulfonation process ligin was easier to be carbonized, affording material with higher carbon content but lower sulfonic acid group density, cellulose was more difficult to be carbonized, affording material with lower carbon content but higher sulfonic acid group density, and bamboo contains both lignin and cellulose, affording material with carbon content close to the material derived from cellulose and with sulfonation extent between the material derived from cellulose and that from lignin. Moreover, the hollow porous structure of bamboo was almost destroyed during the severe simultaneous carbonization and sulfonation process. However, SBC(0.8/180/18) still possesses a surface area of 1.2 m2·g-1, and compact carbon structure was formed during simultaneous carbonization and sulfonation process of both lignin and cellulose, resulting in the materials derived from both lignin and cellulose with lower surface area, which was below the lower limit of detection of the apparatus. Due to the reasons mentioned above,61.8%,61.3% and 29.1% conversions of n-butanol were achieved with selectivities all above 99.5% when SBC(0.8/180/18), SCeC(0.8/180/18) and SLiC(0.8/180/18) were applied in the esterification of acetic acid with n-butanol, respectively. Thus the activity order of those catalysts was as follows:SBC(0.8/180/18) was close but slightly higher than SCeC(0.8/180/18), and much higher than SLiC(0.8/180/18). After that SBC(0.8/180/18) was compared with TSBC prepared by traditional carbonization and subsequently sulfonation method and SulBC prepared by one-pot simultaneous carbonization and sulfonation method using concentrated sulfuric acid as sulfonating agent, and the following results were obtained:TSBC had the highest surface area of 93.5 m2·g-1 due to the preservation of the hollow porous structure of bamboo, with carbon content similar to SBC(0.8/180/18), but lower sulfonic acid group density than SBC(0.8/180/18), and SulBC had the lowest surface area of 0.3 m2·g-1 due to the destruction of the hollow porous structure of bamboo during the simultaneous carbonization and sulfonation process, with lowest carbon content and sulfonic acid group density. Due to the reasons mentioned above the activity order of those catalysts in the esterification of acetic acid with n-butanol was as follows: SBC(0.8/180/18)>TSBC>SulBC. Finally, the preparation mechanism of sulfonated carbon from bamboo was proposed as follows:bamboo was carbonized under high temperature with the aid of p-toluenesulfonic acid, and sulfonic acid groups were introduced at the same time when amorphous carbon was formed. After air treatment to promote the generation of surface functional groups such as carboxyl group and hydroxyl group sulfonated carbon catalyst derived from bamboo was finally achieved. During the preparing process p-toluenesulfonic acid not only acted as an efficient sulfonating agent, but aslo was indispensable for carbonization.(2) In order to further investigate the catalytic performance of the sulfonated carbon derived from bamboo SBC(0.8/180/18), it was applied in the esterification of n-butanol with acetic acid. The influences of reaction time, temperature and catalyst amount as well as molar ratio of acid to alcohol on production of n-butyl acetate were investigated systematically.91.8% conversion of n-butanol with 99.5% selectivity to ester was obtained under the following condition:reaction temperature 80 ℃, reaction time 4 h, molar ratio of acid to alcohol 3.5 and catalyst amount 10% weight of n-butanol. Above 80% conversion of n-butanol could still be reached after the catalyst was used for 5 times. Active component analysis of catalyst during reusability tests revealed that loss of active component occur during the first usage of catalyst while no obvious loss of active component is observed during subsequent usages, which accounts for the stable catalytic activity of the catalyst during 4 subsequent usages. Additionally, the catalyst demonstrated comparable or superior catalytic activity in comparison with Amberlyst-15 when applied in other esterification reaction systems, which suggested that the sulfonated carbon catslyst has good prospect in industrial application.(3) In order to further investigate the catalytic performance of catalyst SBC(0.8/180/18) in the synthesis of n-butyl acetate and obtain the kinetic data for the synthesis of ethyl acetate, we investigated the reaction kinetics of esterification of n-butanol with acetic acid under suitable catalyst concentration (46.95 g·L-1,5.5% weight of the total reaction mass) and proper range of reaction temperature (323.2-363.2 K) after eliminating the internal and external diffusions, and obtained the parameters of kinetic model, which were as follows:the pre-exponential factor k<j 8.84×108 L·mol-1·min-1, the activation energy Ea 79.01 kJ·mol-1. Moreover the obtained kinetic equation was also verified in the experimental temperature range with maximum absolute value of relative deviation being 9.6% and average relative deviations under different temperatures being no more than 3.9%.(4) In order to expand the application scople of catalyst SBC(0.8/180/18), it was further applied in the catalytic dehydration reaction system of fructose to 5-hydroxymethylfurfural (5-HMF). The influence of solvent, reaction time and temperature as well as catalyst amount on the yield of 5-HMF were fully investigated. 92.1%yield of 5-HMF was obtained under the following conditions:reaction temperature 140℃ , concentration of fructose 0.08 g·mL-1, catalyst amont 10% weight of fructose, reaction time 1 h, using dimethylsulfoxide (DMSO) and tetrahydrofuran (THF) (volume ratio of DMSO/THF 7/3) mixture as solvent, which was superior to commercial ion exchange resin Amberlyst-15 under the same reaction condition (5-HMF yield 81.6%). The catalyst maintained high stability and 84.3% yield of 5-HMF could still be reached in the fifth usage of the catalyst. Moreover active component analysis of catalyst during reusability tests revealed that loss of active component occur during the first usage of catalyst while no obvious loss of active component is observed during subsequent usages, which accounts for the high stability of the catalyst during 4 subsequent usages. Kinetic study of SBC (0.8/180/18) promoted fructose dehydration to 5-HMF was conducted and showed that the reaction follow pseudo-first order kinetics with the pre-exponential factor of 1.40×106 h-1 and the activation energy of 43.57 kJ·mol-1, which further indicated that sulfonated carbon derived from bamboo, i.e., SBC (0.8/180/18), can effectively lower the activation energy of the reaction and lead to a higher reaction rate. All of those results confirmed that catalyst SBC(0.8/180/18) has high activity, good stability in the catalytic dehydration reaction system of fructose to 5-HMF and also the intrinsic value in industrial application.