The Preparation Of Molybdenum Trioxide Catalysts And Its Application On During The Coal Pyrolysis Process

The effect of temperature on pyrolysis reaction was examined in a dual-stagefixed bed reactor. The optimum pyrolysis temperature of coal in the dual-stage fixedbed reactor was600oC, in order to obtain much more pyrolysis coal tar. The onlineGC490showed that the main component of pyrolysis gas were carbon monoxide,carbon dioxide, methane, hydrogen and little amounts of C2and C3gases.In the current paper, a series of molybdenum trioxide catalysts were preparedby an volumetric impregnation method with the γ-Al2O3beads as the carrier，theinfluence of catalysts on coal pyrolysis was conducted in a dual-stage fixed bedreactor. The results showed that the yield of pyrolysis coal tar was highest, reaching32.6%, when the active ingredient was12wt%. Moreover the effect ofdesulfurization for pyrolysis coal tar was best, resulting the ratio of sulfur in tar tosulfur in coal decreased8.81%. The main components of coal tar were phenolic,alcohols, carboxylic acids, aldehydes, ketones, aliphatic and aromatic compounds,and so on by FT-IR analysis. And the density of peach of FT-IR spectra increased asthe active ingredient amount increasing, indicating that molybdenum trioxidecatalysts were conducive to improve the content of light molecule compound.Elemental analysis of pyrolysis tar showed that O/C and H/C molar ratio of coal tarincreased as the load the amount of the active ingredient increased, indicating thatmolybdenum trioxide catalysts had the ability to redistribute element oxygen contentin pyrolysis products, during the catalytic pyrolysis process. And they have theeffect of hydrogenation and making coal tar lightweight.In this article, the new catalysts and catalysts attended experiments werecharacterized by specific surface area measurements (BET), X-ray diffraction(XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy(SEM) coupled with energy dispersive X-Ray spectroscopy (EDX), testifying that the specific surface area (SBET) and pore volume (Vp) of catalysts were around250m2/g and0.45cm3/g, respectively. The valence state of molybdenum was+6,amorphous molybdenum trioxide was loaded onto the surface of Al2O3beads,special crystal structure was not formed on the surface of catalysts. The particle sizeof molybdenum trioxide was smaller than carrier characterizing by SEM, whichwould provide more reaction sites for catalytic pyrolysis reaction. Results of EDXand XRD for catalysts attended reactions showing that sulfur was found on thecarrier and catalysts after attending pyrolysis experiments and there were obviousdiffraction peaks of molybdenum disulfide. The sulfur amount was highest, reaching2.46%, when the active ingredient was12wt%. The XPS results showed that theexist state of sulfur and molybdenum was molybdenum disulfide. Resultsindicating that the molybdenum trioxide catalysts had the ability of desulfurization.By comparing and analyzing the coal tar which before and after catalyticpyrolysis, the results showing that the amount of phenolic compounds increasing12.95%, the amount of aliphatic hydrocarbon increasing2.63%, the amount ofhexane insoluble materials decreasing12.62%, the amount of aromatichydrocarbons decreasing3.13%. Therefore, the molybdenum trioxide catalysts hadthe effect on promoting the coal pyrolysis, and increasing the content of phenolicand aromatic compounds, improving the commercial value of coal tar.