Study On Efficient Conversion Of Biomass Model Compounds Into Value-added Chemicals/Fuels

With the depletion of non-renewable fossil energy and excess emission of CO₂,which leading to the global warming,much attention was paid to the exploitation of renewable and clean energy.Biomass is the most important renewable energy.Not only energy,but also the elements of carbon,hydrogen and oxygen are provided,which could be catalytically transformed into high valuable chemicals and fuels.Thus,utilization of biomass is of essential research value.In this study,the model compounds of the most abundant biomass?carbohydrates?and new generation of biomass energy compounds?microalgae?were studied.And several novel methods of converting them to value-added chemicals/fuels were developped.Firstly,the reduction of glucose into high valuable polyols?1,2-propanediol,1,2-butanediol and glycol?with the in situ hydrogen from metal and water under hydrothermal condition was investigated.Among the different metals and catalysts,Zn and Pd/C gave the best yields of polyols?48%?and the selectivity of 1,2-propanediol?69.4%?after 30 min at 250^oC.Then,this study investigated the intermediates and the catalysts in the conversion of glucose to 1,2-propanediol.The possible mechanism was provided as following:glucose isomerized to fructose at first,and the cleavage of C-C bond through retro-aldol reaction and reduction leaded to acetol,which was reduced to1,2-propanediol at last.The in-situ formed ZnO worked as a synergistic catalyst with Pd/C and was the key catalyst in the cleavage of C-C in fructose.Secondly,we tried to convert carbohydrates into alkyl lactates in one pot with metal salts.After investigating different metal salts with various ionic radius,we found that Zn²⁺had the best catalytic effect.The best yields of ethyl lactate and methyl lactate from glucose are 47.7%and 50.8%,respectively.However,the yields of ethyl lactate from fructose and sucrose could reach 51.7%and 47.5%,separately,which were the best results from carbohydrates so far.Meanwhile,according to the intermediates and IR of the reactants with Zn²⁺,the possible mechanism was provided.At last,the activation energy of the conversion of glucose to 1,2-propanediol with different metal ions was investigated,the activation energy of the conversion of glucose to 1,2-propanediol with Zn²⁺could be obviously reduced.Although a small amount of Zn²⁺was added in the reaction,the recycle of Zn²⁺is not easy,which could lead to the environmental pollution.Thus,heterogeneous Lewis acid catalysts were developed to convert carbohydrates into ethyl lactate.After screening the solid Lewis acid and the supporters,ZnO/H-ZSM-5 gave the best yield of ethyl lactate,40.5%.Meanwhile,the preparation of ZnO/H-ZSM-5 are quite easy and ZnO/H-ZSM-5 was stable in ethanol with easy recycle.According to the BET and Pyridine-IR,the strong Lewis acidity and the supporter of ZnO were response to the high yield of ethyl lactate.A small amount of water added could improve the yield of ethyl lactate,while the leaching of ZnO was observed.And the leaching of ZnO might be the main reason for the decrease of yield of ethyl lactate with water in the recycling experiments.Thirdly,we tried to get long-chain alkanes,which were widly used as substitutes for diesel,by decarboxylation of microalgae model compounds?fatty acid?without hydrogen.A series of catalysts with Ni were prepared and tested under hydrothermal condition.The Ni catalyst with smaller particle size could give a better yield of long-chain alkane.Ni/ZnO/AlO_n-500 with 6.5 nm particle size of Ni gave the best result,55%yield of long-chain alkane.According to XRD,the particle size of Ni increased which might be response to the decrease of the yield of long-chain alkane with the recycled catalyst.And the possible mechanism of the reaction was provided according to the distribution of products.In conclusion,several biomass model compounds?carbohydrates and fatty acid?were successfully converted to value-added chemicals and fuels with simple metal catalyst.Complicated catalysts,toxic reagent and high purity hydrogen were avoided.This study provided several novel methods for the efficient,economical and green utilization of biomass.