Catalytic Conversion of Cellulose to Platform Chemicals Using Heteropolyanion-based Ionic Liquids

Author:Song Chang Hua

Supervisor:li xue hui


Degree Year:2019





Biomass is the only renewable carbon source in the natural world,considering as a sustainable and benign substitute for petroleum.Today,the catalytic process research on conversion of biomass with high efficiency and selectivity to platform chemicals and their mechanism studies have received considerable attentions from the government and academia.However,it is noteworthy that some inherent drawbacks of severe reaction conditions,low yields of target products and poor catalyst recyclability are big challenges for current technologies of biomass utilization,due to its complicated structure and chemical bonding.Cellulose is the top component of biomass,which means the efficient and clean conversion of cellulose for selective production of chemicals is of significance for the green valorization of biomass.However,the aforementioned bottlenecks are even severer in the cellulose conversion,due to the presence of inter-and intra-molecular hydrogen bonding in the stabilized twofold-helix conformation of cellulose.In this work,based on the process intensification and reaction coupling,a series of heteropolyanion-based ionic liquids(IL-POM)catalyst functioned with acidity,oxidizability and self-separation with temperature control have been devised.The IL-POMs and catalytic systems were further adjusted for the efficient conversion of cellulose to target products such as levulinic acid,levulinate esters and formic acid.Meanwhile,the interaction between the structure and properties of the catalysts and their catalytic performances were studied in detail,expecting to resolving the key scientific problems such as the mechanism of reaction coupling for both cellulose transformation and process,as well as the catalytic mechanism.The main contents of this dissertation are as follows:(1)An efficient one-pot approach for the production of levulinate ester from cellulose is demonstrated using IL-POM catalysts based on PW12O403-anion with alcohols as the promoters and solvents.The relationships between the structure,acidic strength,and solubility of the IL-POM in methanol and the catalytic performance were studied intensively.It is indicated that the hydrolysis rate of cellulose is enhanced by the rapid in situ esterification of the generated levulinic acid with the alcohol promoter,which allows the insolubility of cellulose encountered in biomass conversion to be overcome.A cellulose conversion of 100%could be achieved with a 71.4%yield of methyl levulinate over the catalyst[PyPS]3PW12O40[PyPS=1-(3-sulfopropyl)pyridinium]at 150 oC for 5 h.Furthermore,the present process exhibits high feedstock adaptability for typical carbohydrates and desirable reusability.(2)One-pot production of formic acid from cellulose using IL-POM catalysts based on PMo10V2O405-anion with H2O2 as the oxidant in aqueous phase is investigated.The relationship between the acidic strength and redox property of IL-POM catalysts and their catalytic performance were discussed in detail.Cellulose can be completely converted over the catalyst[PyPS]5PMo10V2O40 at 150 oC for 5 h with the yields of formic acid,acetic acid and CO2 of 77.6,7.2 and 14.8%respectively.Meanwhile,the present reaction system is adaptable for varying carbohydrates and can be reused up to 5 times.The oxidation mechanism of formation of formic acid from cellulose was further studied,indicating that the5.2:1 molar ratio of n(formic acid)/n(CO2)in the resulting products was obtained viaα-scission and electron-oxygen transfer mechanism.(3)PMo10V2O405-anion based IL-POM catalysts were further modified with metal cations(Co2+,Ni2+,Cu2+and Zn2+)and then applied in the one-pot conversion of cellulose to formic acid with O2 as the oxidant.The relationship between the effect of metal cations on the acidic strength and redox property of IL-POM catalysts and their catalytic performance were studied intensively.The conversion of cellulose is up to 100%at 150 oC for 5 h under 1.5Mpa O2 over[PyPS]4Cu0.5PMo10V2O40 catalyst,accompanied with the yield of formic acid,acetic acid and lactic acid of 66.0,7.0 and 15.1%respectively.Meanwhile,the present reaction system is adaptable for typical biomass and can be reused up to 7 times.