Preparation,Characterization And Catalytic Properties Of Several Kinds Of Sulfonated Biomass Carbon Solid Acid Catalysts

With the continuous development of our society,the environmental issues have received more and more attention.Meanwhile,the green chemistry has been gradually proposed and promoted.As green catalysts with high activity,strong selectivity,and easy recycling,the solid acids can be used in various catalytic reactions.The promotion and use of solid acid can effectively solve the problems caused by the traditional liquid acids such as the equipment corrosion,difficult recycling and waste liquid pollution.As a kind of renewable resource,biomass has attracted gradually attention.For example,quite a few scholars have focused on biomass-based carbon solid acid.These catalysts have the advantages of low cost,abundant sources,pollution-free,and renewablity.Once the solid acid catalysts are commercialized in the field of biofuel synthesis,it can not only reduce environmental pollution and alleviate energy pressure,but also reduce the production costs and promote the sustainable social development.In this thesis,the sulfonated biomass carbon solid acid catalysts were prepared by using several types of biomass waste as raw materials,concentrated sulfuric acid as sulfonating agent and phosphoric acid as activator,respectively.Considering of various analytical characterization results and their catalytic performance in ethyl levulinate synthesis,the effects of different preparation conditions on the acid density and catalytic performance of the as-prepared catalysts were investigated,and the catalytic reaction conditions were further optimized.The specific works were as follows:?1?Sulfonated biomass carbon solid acid catalysts were prepared with a“precalcination-pyrolysis carbonization-hydrothermal sulfonation”method from loofah sponge,pine needle and corn stalk,respectively.The results showed that these catalysts maintained an amorphous carbon structure and had good thermal stability.Under the present experimental conditions;the optimal preparation conditions of sulfonium loofah sponge-based carbon were carbonization temperature 600?,carbonization time 90 min,sulfonation temperature 160?,and sulfonation time 18 h;the optimal preparation conditions of pine needle-based carbon were carbonization temperature 700?,carbonization time 90 min,sulfonation temperature 160?,and sulfonation time 15 h;and the optimal preparation conditions of corn stalk-based carbon were carbonization temperature 600?,carbonization time 120 min,sulfonation temperature 140?,and sulfonation time 18 h.When used as catalysts for the synthesis of ethyl levulinate,the optimal reaction conditions were reaction temperature 80?,ethanol to levulinic acid molar ratio 5.0,catalyst dosage 5.0 wt%,and reaction time 8 h.Under the optimized conditions,the conversions of levulinic acid can reach 92%,96%and 94%over the aforementioned sulfonated biomass carbon catalysts,respectively.Moreover,the reused catalysts can be easily regenerated by a sulfonation process.However,the reusabilities of these catalysts were not ideal,and the catalytic activity decreased significantly after repeated use for 5 times.?2?In order to enhance the reusability of the aforementioned catalysts,the sulfonated pine needle-and corn stalk-based porous carbon catalysts were prepared by using a“low temperature pyrolysis carbonization-hydrothermal sulfonation”procedure with phosphoric acid as activator,respectively.The results showed that the activation of phosphoric acid not only optimized the pore structure of the corresponding catalysts,but also greatly improved the recycle ability.In addition,the strategy eliminated the aforementioned pre-carbonization step and significantly reduced the carbonization temperature,leading to the low enery cost.Under the present experimental conditions,the optimal preparation conditions of pine needle-based porous carbon were carbonization temperature 300?,carbonization time 150 min,sulfonation temperature 160?,sulfonation time 18 h,and phosphoric acid solution dosage 30 mL.The corresponding catalyst prepared under the conditions had a high specific surface area(S_BET=396 m²/g)and a large total pore volume?V_p=0.235 cm³/g?.The optimal preparation conditions of corn stalk-based porous carbon were carbonization temperature 300?,carbonization time 150 min,sulfonation temperature 140?,sulfonation time 15 h,and phosphoric acid solution dosage 30 mL.The corresponding catalyst had a specific surface area of 426 m²/g and a total pore volume of 0.233 cm³/g.Under the aforementioned optimal reaction conditions,these catalysts maintained the catalytic activity of the corresponding unactivated sulfonated carbon.After repeated usage for 5 times,the conversion of levulinic acid had not significantly reduced,indicating that they possessed excellent reusabilities.Overall,in this thesis,different biomass wastes were used as carbon sources to prepare sulfonated biomass-based carbon solid acid catalysts with high catalytic activity and excellent resuseablity.The results have certain academic significance and potential application prospects for reducing the preparation cost of solid acid catalysts,improving the utilization of biomass waste,reducing environmental pollution and synthesis fuel additive-ethyl levulinate.