Catalytic Conversion Of Cellulose Into Ethylene Glycol And Its Separation By New-type Membranes

The ever-diminishing reserves of fossil energy resources and increasing levels of energy consumption will ultimately result in global energy shortages and serious environmental problems.The conversion of biomass into chemicals and fuels would play an important role in averting these problems.As a potential substitution of fossil energy resources,cellulose is a natural macromolecule compounds,it is widespread,renewable,resourceful and nonedible.During the past decade,using cellulosic biomass to synthesize bulk quantities of high-valuechemicals and fuels has attracted increasing attentions.Among the variety of chemical conversion reported for cellulose,its catalytic transformation to ethylene glycol?EG?under hydrothermal condition represents a very potential process because of its high atomic economy,value-added products and large market demands.However,due to inter-and intra-molecular hydrogen bonding network,effectively depolymerizing cellulose under mild conditions presents a challenge.Second,control of the catalytic products is complicated because of the thermal instabilities of cellulose-derived sugars.Third,raw lignocellulosic materials should be considered as the feedstock to reduce costs.In addition,it is also urgent to develop advanced technologies for separation and purification of the EG product.Therefore,to deal with above issues,this dissertation can be decided into following parts:1.As promising and environmentally friendly catalyst,a low concentration of phosphotungstic acid was used to promote the hydrolysis of cellulose and the cleavage of C-C bond in the water-soluble oligosaccharides and glucose,and the hydrogenation reaction was catalyzed by Ru/AC catalyst,the microcrystalline cellulose was completely converted over a mixed catalystconsisting of a low concentration of phosphotungstic acid?PTA??0.03wt%?and Ru/ACvia an one-pot hydrothermal reaction,with an ethylene glycolyield up to 53.1%under optimal conditions.Then,the stability and reusability of the PTA-Ru/AC were studied,the results showed that the catalytic activity of the mixed catalyst gradually decreased with increasing reaction runs,which was mainly ascribed to the aggregation of Ru/AC particles,and the coverage of active sites of Ru due to the strong adsorption effect and/or coking effect.Finally,cellobiose was used as a model feedstock for a comparative study on the reaction pathways of the cellulose conversion by HPLC-MS,and the results revealed that catalytic conversion of cellobiose consisted of at least three important parallel reactions under the present hydrothemal conditions,which also were most likely involed during the catalytic converison of cellulose for EG production.2.A Ru-WO₃/Graphene catalyst was successfully synthesized via a hydrothermal reduction method,which wasthen studied using XRD,IR,TG,SEM,EDX and TEM.This catalyst composed of numerous WO₃ nanorods and Ru particles deposited ontographene nanosheets,which was found to be a very efficient catalyst for catalytic conversion of cellulose for EG production,and effects of various conditions on the reaction performance were investigated,under the optimal conditions,and the EG yield was as high as 57.5%,with cellulose was completely converted,the stability and deactivation mechanism of Ru-WO₃/Graphene during EG production were also discussed.3.Cassava residues were proposed as a feedstock to replace cellulose for EG production,various mixed catalysts consisting of Ru/AC and a tungsten species were used for the conversion of cassava residues,and the effects of various reaction conditions on the catalytic performance were investigated.Among these catalysts,Ru/AC-H₂WO₄ showed the highest EG yield of 53.1% at 245?after 60 min.Moreover,the stability and reusability study of the binary catalyst showed that the catalytic activity of the Ru/AC-H₂WO₄ catalyst gradually decreased with increasing run cycles,and the EG yield was lower than 50% after 4 reaction cycles.Based on the XRD analysis,the deactivation mechanism of Ru/AC-H₂WO₄ was comfirmed to the fact that,Ca and Fe ions in the feedstock reacted with tungsten compounds,and formed insoluble CaWO₄ and FeWO₄ under the hydrothermal conditions,resulting in reduced activity of the W compound in the binary catalyst.4.As a new crystalline porous material,covalent organic frameworks?COF?were studied as a potential membrane material for molecular separation.COF-1 was synthesized via the solvothermal method,and thenstudied byXRD?FT-IR?BET?SEM?TEM?AFM?TG.It was confirmed that COF-1 consisted of lamellar structure,with an average pore size and surface area of 0.7nm and 710m²/g,respectively,and had excellent thermal stability up to 450? in a nitrogen atmosphere.COF-1 membranes were fabricated on the surface of severalsupports using COF-1 nanosheets as building blocks,which were prepared viathe sonication treatment to COF-1 particles.Finally,single-gas permeance through the COF-1 membrane was investigated,and the membranes showed extremely permeable H₂ performance and excellent thermal stability.5.ACOF-1with improved water-stability was successfullysynthesized via the solvothermal synthesis,and the properties were studied by XRD?FT-IR?BET?SEM?TEM?AFM?TG.It was confirmed that ACOF-1consisted of lamellar structure,with an average surface area and pore size of ACOF-1 are 819m²/g and 1.22 nm,respectively,and hadexcellent thermal stability up to 320?in a nitrogen atmosphere.ACOF-1 membrane was formed on the surface of ceramic tube using ACOF-1 nanosheets as building blocks,which were prepared viathe sonication treatment to ACOF-1 particles in methylbenzene solution.Finally,ACOF-1 membrane was used to study onseparation and purification of EG from waterby pervaporation technology,the results showed that the ACOF-1 membrane had a flux of 0.139kg/?m²h?and separation factor of 552 in the pervaporation of EG-water?90wt%?mixtures at 50?,and holda better separation performances and stability.