Study On Preparation And Catalytic Performances Of Biomass Char Sulfonic Acids

Biomass is renewable resource originating from photosynthesis, which is widely existed and possesses numerous varieties on the earth. It can be transformed either to energy or new materials for human life. It has both economic benefits and social significance to research on novel methods for biomass transformation and reinforce utilization of biomass resources, so that modern industry will no longer absolutely depend on the mineral resources.This thesis has focused on the development of new catalytic materials, and methods for transformation of biomass resources into solid sulfonic acid materials. A new method, sulfuric acid catalyzed charring-sulfonation, has been proposed. Char materials were obtained via biomass dehydration catalyzed by sulfuric acid, which could be further sulfonated to produce biomass char sulfonic acids. The preparation conditions via sulfuric acid catalyzed charring-sulfonation using several different kinds of biomass resources as raw materials have been investigated systematically. Based on the pyrolysis technology, experiments were designed to obtain new char materials with polycyclic aromatic ring structure. The transformation of bamboo or pine to char sulfonic acid was achieved via low temperature pyrolytic charring-sulfonation. The structures of biomass char and char sulfonic acid were characterized and catalytic performances of biomass char sulfonic acids were evaluated by acidic catalytic probe reactions, such as esterification, condensation, acetalization etc. Comparisons of two "charring-sulfonation" methods have been studied. The main contents are as follows:1. The development of biomass transformation theories and technologies were reviewed, and mechanism researches on pyrolysis were summarized from the point view of reaction kinetics and products formation. Meanwhile, the process of catalytic application in organic synthesis of typical sulfonic acid resin and inorganic-organic sulfonic acid functionized mesoporous silica materials were summarized. And the recent researches on preparation of solid sulfonic acid from biomass raw materials were also described. 2. A new concept "biomass char sulfonic acid" has been proposed. It is believed that new char materials with sulfonic acid groups attached to graphite-liked structure or polycyclic aromatic rings can be prepared by charring and sulfonation from biomass resources including carbohydrate, plant fiber, herbaceous or woody plant. In order to clearly show their sources, structures and functions, it could be generally called as "biomass char sulfonic acid".3. With the hint of using catalysts in organic reactions, biomass transformation methods by acidic catalytic dehydration were explored. First, using sulfuric acid as a catalyst for dehydration charring process, an efficient novel method for biomass utilization was established, namely sulfuric acid catalyzed charring-sulfonation. Second, traditional pyrolysis technology was modified and improved low temperature pyrolytic charring-sulfonation was proposed for biomass transformation. Bamboo char sulfonic acid was prepared via low temperature pyrolytic charring-sulfonation pretreated bamboo sawdusts with H₃PO₄ or ZnCl₂ solution.4. Application of sulfuric acid catalyzed charring-sulfonation was investigated along varieties of biomass resources. The raw materials chosen to give biomass char sulfonic acids include carbohydrate like glucose, sucrose and starch, natural fiber like cotton fiber, herbaceous plant like bamboo sawdusts, woody plant like pine (pine needle, pine bark, pine cone, and pine sawdusts). All these biomass char sulfonic acids were obtained via sulfuric acid catalyzed charring-sulfonation. Otherwise, bamboo char sulfonic acid and pine char suifonic acids were also prepared via low temperature pyrolytic charring-sulfonation. Effect of charring conditions and sulfonation conditions on acid capacity of biomass char sulfonic acid were investigated by orthogonal experiment or single factor experiments.5. Structure and acid capacity of biomass char and biomass char sulfonic acid from both methods were characterized. The results of XRD analysis showed that all samples were amorphous chars. N₂ adsorpsion-desorption and SEM images indicated the limited surface area and pore volume. Therefore, char materials and sulfonated chars had no mesoporous structures. FTIR analysis identified that the obtained char materials had polycyclic aromatic rings with many oxygen-containing groups, and sulfonic acid groups substituted for active hydrogen atoms at the edge of aromatic rings to anchor in char framework. Results of TG-DTG analysis showed that the sulfonic acid groups can not be decomposed up to 200°C. The results of EA analysis and acid-base titration indicated acid capacities of most biomass char sulfonic acids reached 1.0 mmol g^-1 and they reached 2.0 mmol g^-1 prepared under optimal preparation condition. Hydrothermal stability of cotton char sulfonic acid was investigated and acid capacity of it decreased from 2.16 mmol g^-1 to 1.78 mmol g^-1. Still, good catalytic activity of the cotton char sulfonic acid was observed.6. The catalytic application of biomass char sulfonic acids were investigated in series of organic acidic catalytic reactions. Glucose char sulfonic acid catalyzed esterification of alcohol and acetic acid. Surcose char sulfonic acid was used to catalyze alcoholysis of cyclohexene oxide. Starch char sulfonic acid catalyzed self-condensation of cyclohexanone. The esterification of alcohol and acetic acid were also used to test the catalytic activity and hydrothermal stability of cotton char sulfonic acid. Bamboo char sulfonic acids via sulfuric acid catalyzed charring-sulfonation were applied in synthesis of chalones, and those from pyrolytic charring-sulfonation catalyzed acetalization of aldehydes or ketones. Pine char sulfonic acids from both methods catalyzed the condensation of benzaldehyde and 2-naphthol. Experimental results indicated that each biomass char sulfonic acid can efficiently catalyze the probe reactions, and high reactant conversion ratio and main product selectivity were observed. Compared to sulfonic acid resin, it showed comparable or superior catalytic activity under the same reaction conditions.