96/05850 Effect of iron catalysts on hydrogenation pathways in direct coal liquefaction

Abstract

The effect of a collnnerciany available, high surface area nanometer size iron oxide (SFIO) catalyst on the pathway by which hydrogen is added to a subbituminous coal during direct lquefaction was studied under a variety of conditions. This unique iron oxide, prepared by pyrolyzing volatilized iron carbonyl to produce a finely divided product, is characterized as y-F%03 having a surface area of -300 m'/g and particle size of 1-3 nm. Liquefying Wyodak coal in tetralin (0.5 hrs, 415 C, 2.3 tetralinldry coal, 6.89 Mpa & cold) containing 1.2 wt % Fe as SFIO resulted in an increase in o v d coal conversion (77 to 83%) with most of the increase in product being in formation of THF soluble-pentane insoluble Addhg an excess of sulfur to convext the iron to pyrrhotite funher increases conversion to 85% along with a decrease in the THF solublepentane insoluble fraction. The presence of catalyst increases the amount of hydrogen added to the product as dihydrogen (HJ relative to the amount from tetralin via the H-donor pathway. In the absence of *t, 60% was added as adding 1.2% Fe increased H2 addition to 67%; adding 3 mol Shnol Fe to 1.2% Fe further increased & addition to 82%. Introduction Through the use of various types of catalysts, high yields of distillate fuels have been pmduced in pilot plants firomlowerast subbituminous coal.' The use of high surface area, small particle catalysts has been one area that has been extensively explored in an effort to maximize yields and reduce the cost of catalyst. Fe has been of particular interest as a dispersed catalyst because of its abundance, low cost and its environmental acceptability. Various approaches have been used for preparing disposable nanometer size Fe catalysts, among which are nirmmdm ' aerosols,*a9 hydrothermal disproportionation of sulfides, and precipitation of sulfated oxyhydroxides. Highly dispersed iron particles, in various forms as oxides and oxyhydroxides, have been shown to retain their small size upon conversion to pyrrhotite under coal hydroliquefaction condition^.*^^'^ In OUT laboratory, a specially prepared Commercially available supexfine Fe oxide (SFTO) was found to have high activity for coal conversion and excellent selectivity for producing distillate product. In the study reponed hae, the activity of this catalyst for conversion of a Wyodak coal in teualin was compared with a nnich Lower surface a m Fe oxide prepared from AiusNther spray roast processing of spent acid from steel pickling.I4 The effect of these catalysts on the pathways by which hydrogen (H) is added to the coal and its products was investigated. Experimental Samples of the subbituminous coal and powdered iron oxides used at the Wilsonville Advanced Coal Liquefaction Facility in Run 263Jl4 were supplied by CONSOL, Inc. The Wyodak coal from the Black Thunder mine in Wright, Wyoming was ground to -200 mesh, M e d and stored under nitrogen at 4 C. Proximate and ultimate analyses are presented in Table I. The average moisture content measured at the beginning of each run was 21.9 f 0.72 wt % of as-received coal. Two iron oxide catalysts were used. One, a sample of SFIO provided by MACH I, Inc., King of P r U S k PA, contained 63 wt % Fe with a y-F%03 structure, average particle size of 1-3 nm, and nitrogen BET surface area of 300 t~?/g.'~ The second, from Bailey Engineers, Fairfield, AL, (IO) was 99% Fq03 with 0.35 wt % manganese oxide being the largest impurity. The material had a structure of a-FqO,, nitrogen BET surface area of 8.6 d/g , an average particle size of -140 nm, and bulk density 26 times greater than SFIO (1.37 vs. 0.052 ghl ) . Carbon black (CB) was purchased from UIC, Inc. and had a fixed carbon content of 93% with a nitrogen BET surface area of 90 m'/g. ~ u e f a c t b n eXperiments were conducted by adding 3 gratns of coal 5.4 grams of tea&, and catalyst to a 50 mL microautoclave. When used, dimethyl disulfide @MDS) was added at a ratio of 3.0 moles S per mole Fe. The reactor was sealed, pressurized with Hz to 6.89 MPa, and immersed in a fluidized sand bath set at the V@.%kd temperatun while continuously agitating at a rate of 400 cycles per minute. After the specified reaction period the microautoclave was rapidly cooled in a sand bath at room temperature. Gaseous products