Catalyst aging in a process for liquefaction and hydrodesulfurization of coal

Abstract

Aged CoO/Mo08/Si0.JA1203 catalyst pellets, used in a pilot plant for the single-stage liquefaction and hydrodesulfurization of coal, were analyzed with an electron microprobe and scanning electron microscope. The results demonstrate the occurrence of catalyst aging processes which could lead to bed plugging and pore mouth blocking. Department of Chemical EngineeringUniversity of Delaware Newark, Delaware 1971 1 SCOPETo meet the need for new sources of clean fuels, procalytic hydrodesulfurization of the derived liquids. In some of these processes, the liquefaction and catalytic hydrodesulfurization take place in a single reactor. CONCLUSIONS AND SIGNIFICANCEPellets of the hydroprocessing catalyst used in the Synthoil process (sulfided CoO/Mo03/Si02/A1203) accumulated inorganic and organic contaminants both on the exterior surface and in the pore mouths. The inorganic (carbon free) deposit found in the upstream end of the fixed-bed reactor has been identified as primarily ferrous sulfide, Fe14S15. This material covered 50 to 7@% of the catalyst's peripheral surface and penetrated into the catalyst pores to a depth of about 100 pm. The total aceumulated deposit caused a reduction in catalyst surface area and pore volume. The inorganic deposit found in the downstream end of the reactor was mainly aluminum and silicon and covered 10 to 20% of the catalyst's peripheral surface. Titanium penetrated about 150 pm into the pores. All of these deposits caused a 40% loss of pore volume. These results imply that deposition in coal hydroprocessing reactors could lead to bed plugging and pore mouth blocking.Conversion of coal to clean liquid fuels can be accomplished by processes being developed for liquefaction ( a reductive depolymerization of the organic coal matrix) followed by catalytic hydroprocessing of the derived liquid, which removes sulfur and increases the H/C ratio.The liquefaction and hydroprocessing steps typically have been carried out in separate stages, with interstage removal of the mineral matter of the coal. Alternatively, in processes such as Synthoil (Yavorsky, 1973), both liquefaction and hydroprocessing are carried out in a single reactor. The fixed-bed reactor of the Synthoil process is fed with a slurry of coal in coal derived liquid which flows concurrently with hydrogen through a preheater, reaching a temperature of about 720°K at a pressure of 1 . 4~1 0~ N/m2. The organic coal matrix is largely liquefied in the preheater, and the resultant gas-liquid-solid mixture flows through a packed-bed reactor containing particles of CoO/Mo03/SiOz/A1203 hydrodesulfurization catalyst. Highly turbulent flow is used with the intention of preventing plugging of the catalyst bed by deposition of inorganic material, coke, and unconverted coal.Correspondence concerning this paper should be addressed to J. J. Stanulonie.The research described here was undertaken to evaluate catalyst aging in reactors used for coal liquefaction and hydroprocessing. The aging problem is unidentified in the literature, but data from a S...

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Catalytic removal of sulfur, nitrogen, and oxygen from heavy gas oil

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