Study On The Catalytic Conversion Of Cellulose Into Ethylene Glycol By Mesoporous Tungsten-containing Materials And The Dehydration Of Product

With the rapid development of human society,the world's energy consumption has increased dramatically.The shortage of fossil energy and severe environmental problems have caused the world's energy structure to be changed.The healthy development of the renewable resource industry is particularly important.Ethylene glycol?EG?is an essential industrial raw material produced by traditional petrochemical routes.In the long term,the production of ethylene glycol from renewable carbohydrates is a highly competitive and promising technology,which complements traditional petroleum-based glycol production routes.The development of inexpensive and high efficient catalysts has always been a core issue in cellulose catalytic conversion.Meanwhile,exploring the adaptability of other cellulose-rich materials in hydrothermal catalytic systems is also an important research topic.The separation and purification of catalytic products by energy-saving and high-efficiency methods is beneficial to further improve the market competitiveness of biomass technology.In this thesis,the catalyst structure design and improvement were firstly carried out.Two catalysts of K-WO₃ and S-WO₃ with ordered mesoporous structure were synthesized by using mesoporous silica molecular sieve as template.SEM,XRD,TEM,FT-IR,NH₃-TPD and other techniques were used to prove that they have regular pore structure with pore sizes of 10.3 nm and 5.5 nm,respectively.The results of hydrothermal conversion of cellulose indicated that such mesoporous materials had high reactivity.When the catalyst dosage was adjusted to 10%,and the complete conversion of cellulose was achieved by reacting at 245?for 60 min,and the yield of EG were about 58.9%and 62.1%,respectively.In addition,two inexpensive doped tungsten mesoporous silica molecular sieve catalysts W-K and W-S were prepared by in-situ synthesis.Such catalysts also maintained the original pores and morphology of mesoporous silica.The specific surface areas of the two catalysts could reach to 664.7 m²/g and 793.2 m²/g,respectively.The acidity and reactivity of the molecular sieves after doping were significantly improved,and the EG yield of 55.3%and55.4%were obtained.The catalyst dosage and the Si/W in the framework had a significant effect on their catalytic performance.In the catalyst recycle test,the tungsten oxide attached on the surface of the molecular sieves was dissolved and lost.The tungsten atoms in the framework of SiO₂ were more stable in hydrothermal system.In order to further broaden the range of raw material selection,this thesis explored the effect of pulp used in paper industry for the catalytic conversion of EG.The results showed that the fine cellulose powder of wood pulp obtained by HCl prehydrolysis and spray drying under mild conditions had excellent catalytic activity and the yield of EG was 62.7%under optimal conditions.After pre-hydrolyzed pulp with H₂SO₄,the ash content of the pulp fine cellulose was as high as 39.1%,and the main component was Na₂SO₄.The waste pulp only obtained 76.0%of feedstock conversion and 11.1%of EG yield.The quantitative addition method proved that the inorganic salts in waste pulp fibers caused serious deactivation of the tungsten-based catalysts and limited the formation of EG.In order to explore the high-efficiency and energy-saving product separation method,based on the pervaporation technology,the inorganic membrane is used to dehydrate the high concentration EG/water system.A hydrophilic ZSM-5 membrane was prepared via seeding method on the surface of ceramic tube.The ZSM-5 membrane has excellent thermal stability and good gas separation performance at 200-500?.The membrane flux was greatly affected by the temperature and the concentration of the feed liquid.In the range of EG concentration from 80%-90%at 40-80?,the membrane flux is 50-250 g/m²·h,and the water content in permeate was 92.1%-97.5%.The graphene oxide?GO?membrane was prepared on the surface of the ceramic tube supporter by dip-coating method.Several characterization methods were used to verify the excellent membrane forming performance of GO.A continuous defect-free GO membrane with a thickness about 600 nm was formed.The dehydration application of EG showed superior separation performance of GO membrane compared to ZSM-5 membrane.In the stability test,GO membrane flux was 440-520 g/m²·h,and the water content in permeate was higher than 98.0%.Thermodynamic analysis confirmed that the temperature could significantly increase the driving force of the membrane for increasing membrane flux.In addition,the in-situ XRD was used to analyze the influence of temperature on GO membrane in different solvent environments.The in-suit XRD results showed that the temperature decreased the GO layer spacing,which led to the decreas permeability of GO membrane.The increased differential pressure driving force of the membrane during heating was proven as the dominant factor in increasing membrane flux.