Preparation And Catalytic Properties Of Porous Carbon Based Solid Acids

Acid catalysts are widely used in chemical industry.More than 15 million tons of sulfuric acid are consumed to produce various chemical products annually,which caused energy waste,environmental pollution and large amounts of harmful waste for the tedious treatment.Heterogeneous catalysts such as solid acids have received much attention due to their easy separation,reusability,and ease post-treatment.Many solid acids studied such as cation exchange resins,clay minerals,metal oxide solid acids,solid superacids,and heteropolyacids were studied.Compared with traditional solid acids,carbon-based solid acids have high acid density,good thermal stability,reusability,and low preparation costs,which are good substitutes for sulfuric acid and traditional solid acids.Limited by the low surface area,high polarity,the mass transfer of conventional carbon-based solid acids was quite difficult.Therefore,there is an urgent need for green and efficient methods for preparing porous carbon-based solid acids.In this thesis,porous carbon-based solid acid catalysts with high surface area and high catalytic performance were prepared using carboxylate salts porogenesis,molten salt method,and etching methods respectively.The structure of the solid acids could be adjusted by biomass raw materials and preparation conditions.The main studies include:（1）Using sucrose as raw material,different carboxylate salts such as tartrate,citrate,and oxalate were used as porogenic agents.The porous carbon intermediates were prepared by carbonization,then the desired carbon based solid acids were prepared by sulfonation to introduce sulfonic acid groups.The results showed that S=O stretching absorption at 1040 cm^-1in the FT-IR spectrum,indicating the introduction of the sulfonic acid group.The esterification conversion of the carbon-based solid acids prepared by the carboxylate-salt-porogen method was over95%.The optimal catalyst preparation condition was as follow:carbonization temperature 400℃,a carbonization time 10 h,sulfonation temperature 140℃and sulfonation time 12 h.The catalytic activities for18 aliphatic and aromatic acetals（ketals）synthesis were investigated with the high conversion of over 90%.The novel carbon-based solid acids maintained high catalytic activity after reusing for 10 times.（2）Porous tissue-like carbon-based solid acids were synthesized by the ZnCl₂molten salt template method using water moss as raw material.The S=O absorption at1040 cm^-1in the FT-IR spectrum indicated the introduction of sulfonic acid groups.The novel sulfonic acid-based solid acid catalyst has special tissue-like structure with a thickness of about 20 nm and a length and width greater than 10μm.The surface area can reach 372 m²/g with an acid value of 2.53 mmol/g.The specific tissue-like structure provided easily accessible acidic sites,which assured the high catalytic activity.The reaction condition for biodiesel synthesis was optimized.The best reaction condition was as follow:3.02 g methanol,waste oil 5 g,reaction temperature70℃and the catalyst amount 0.04 g.Both the free fatty acids and triglycerides could be converted to biodiesel simultaneously with an overall yield of 99.1%.The recycled activity of the catalyst was also investigated,and the catalyst maintained high catalytic activity after reused for 10 times.（3）To further increase the catalytic activity of the carbon-based solid acids,biomass pampas grass stick with specific microtube structure of was used as raw material.The pampas grass stick was etched to remove the instable amorphous cellulose structure using the alkali-urea system（sodium hydroxide-thiourea-urea system）.Porous microtube carbon-based solid acids were prepared by optimizing etching process.The effects of etching solvent,solvent dosage,etching time,and etching temperature were investigated by orthogonal experiments.The results showed that the optimal dissolution conditions for the alkali-urea system were as follow:The etchant ratio was 12:7:7,the mass fraction of reed was 3%,the etching time was 60min,and the etching temperature was 20℃.The carbon-based solid acids were prepared by carbonization at 600℃for 6 h and sulfonation at 150℃for 12 h.The porous microtube carbon based solid acid had high catalytic activity for esterification and acetalization.The reuse of the catalysts was also investigated with high catalytic activity after 10 times.