Study On Hydrodeoxygenation And Co-hydrogenation Process Of Coal Tar And Bio-oil

Medium and low temperature coal tar contains a large amount of oxygen-containing compounds,which are mainly monocyclic and condensed phenols.These phenolic compounds are themselves rich in aromatic hydrocarbon resources.If they are excessively hydrogenated to produce fuel oil,it will cause a serious waste of aromatic resources.When bio-oils are used to produce fuel oil products,they also face the problem of hydrodeoxygenation.Moreover,unsaturated fatty acids may easily cause deactivation by coking during hydrodeoxygenation at high temperatures.Therefore,this paper studied a selective hydrodeoxygenation catalyst to enable the phenolic compounds in coal tar to obtain a product with a high aromatic content after hydrodeoxygenation.In addition,co-hydrodeoxygenation reaction of coal tar and bio-oil under commercial Co-Mo/?-Al₂O₃ catalyst was carried out to study the regularity of interactive influence under different processes.Firstly,the binary metal Ni-M?M=Ce?Co?Sn and Fe?catalyst with SiO₂ as the support was prepared by the method of incipient impregnation.These catalysts were characterized and analyzed by BET?XRD?H₂-TPR?NH₃-TPD?XPS and other technologies,and evaluated for hydrodeoxygenation on a small fixed-bed on p-cresol as a model compound.The study found that the addition of the binary metal Ce enhanced the acidity of the catalyst and at the same time enhanced the dispersibility of the active metal Ni.In addition,due to the large difference in the electronegativity between Ce and Ni,Ce increased the electron cloud density of nickel and activated the cleavage of the Caromatics-O bond of p-cresol.Moreover,the addition of Ce disrupted the continuous arrangement of nickel atoms,thereby hindered the adsorption of aromatic rings of phenols,which leaded to the improvement of the selectivity of the DDO reaction path for hydrodeoxygenation of phenols.The added Sn formed a Ni₃Sn crystal with Ni,which changed the priority of hydrogenation of the p-cresol group which leading to the improvement of the HYD reaction path.Twenty-seven groups of hydrogenation experiments at different temperatures,LHSVs and pressures were conducted with crude phenol oil from a plant in northern Shaanxi as raw materials.Based on the above experimental results,the reaction network and kinetic model of the mixed phenolic compounds were established.The verification test confirmed that the relative error of content of phenol,unsaturated hydrocarbon and saturated hydrocarbon in the product by the model was less than 5%,indicating that the model had high reliability.Secondly,the selective hydrodeoxygenation of p-cresol model by supported Ni₂P catalysts with different supports was prepared and studied.The smaller interaction between the silicon oxide support and the oxide precursors of Ni and P resulted in easier formation of Ni₂P active phase and higher dispersion.The catalyst with Q10 as the support had a smaller grain size and a higher degree of dispersion,which enhanced the breaking of the Caromatic-O bond,resulting in a strong selectivity of the DDO reaction path for p-cresol hydrogenation.The selectivity of toluene in the product reached 71.8%.However,catalysts with silicon oxide as a carrier were easily deactivated due to phosphorus loss.Thirdly,according to the types of compounds in coal tar,the corresponding model compounds were selected for co-hydrogenation experiments with bio-oil.In the experiment,under non-hydrogen conditions,the dehydrogenation-hydrogen transfer process was found to increase the conversion rate of hydrodeoxygenation of fatty acids in bio-oils when the bio-oils were co-hydrogenated with the model compounds like tetralin,decalin and 9,10-dihydrophenanthrene.Under hydrogen atmosphere,the conversion of fatty acid was significantly increased when the bio-oil co-hydrogenated with tetrahydronaphthalene,9,10 dihydrophenanthrene,butanol and1-naphthol,and the content of C18 alkane in the product increased.Mixed phenols and dephenolized oil were obtained by alkaline extraction of coal tar.Coal tar is extracted by alkaline solution to obtain mixed phenol and dephenolized oil.The conversion of fatty acids in bio-oil was improved when the bio-oil co-hydrodeoxygenated with mixed phenols.Hydrogenated dephenolized oil promoted the conversion of fatty acids to a greater extent than dephenolized oil when co-hydrodeoxygenated with bio-oil,and inhibited coking for catalyst more effectively.Finally,on the basis of the study of model compounds,the co-hydrogenation law of coal tar and bio-oil under two processes was as follow:Process A used the raw materials mixed with coal tar and bio-oil in co-hydrogenation reaction.It is concluded that when the addition amount of bio-oil in the raw material was within the range of30-40%,the conversion of fatty acid and the degree of unsaturation of the hydrogenation product was higher,but it was cause more serious coking.Process B used a two-stage reaction design:coal tar was fed through the inlet of reactor I,and biological grease was fed through the inlet of reactor II.The main reactions in reactor I were the hydrodeoxygenation of oxygenated compounds and the hydrosaturation of aromatic hydrocarbons in coal tar.The main reactions in Reactor II were the catalytic hydrodeoxygenation of bio-oil?the role of a catalyst?and hydrogen donating-hydrodeoxygenation?the role of hydrogen donating of hydrogenated coal?.In addition,Process B was considered to be a better co-hydrogenation process of coal tar and bio-oil due to the more flexible reaction conditions and product distribution of the two reactors.In this dissertation,the problem of selective hydrodeoxygenation in coal tar to produce more BTX was studied experimentally and theoretically.The idea of co-hydrogenation of coal tar and bio-oil provided some experimental data and theoretical basis for improving the quality of coal tar hydrogenation products and bio-oil hydrogenation products,and at the same time provided a certain reference value for industrial co-hydrogenation production.