CATALYSIS AND CATALYST DISPERSION IN COAL-LIQUEFACTION

The Bergius process for the hydroliquefaction of coal has an 80-year history. This selective review attempts to trace the role of catalysis, and especially of catalyst dispersion, in this process. The metals commonly used in liquefaction catalysts, iron, molybdenum, and tin, were discovered and utilized in large-scale plants in Germany and England well before World War II. The usefulness of achieving high dispersion, and therefore high interfacial contact of catalyst with coal, coal-derived liquids, and hydrogen, was demonstrated in autoclave and pilot plant experiments during the early 1950s. Research since then has followed several themes. Although impregnation of catalyst an coal was recognized early as one method of achieving high dispersion, the cost of impregnation led to studies of other methods. Use of oil-soluble catalyst precursors (typically organometallics) without impregnation, and methods for generating particulate catalysts of high surface area, have been pursued with success, at least bn a research scale. Although iron remains the catalyst metal of choice because of cost and availability, the effectiveness of well-dispersed molybdenum at low concentrations has led to much research on precursors based on that metal, and on possible recovery sad recycle of the catalyst. Interest also remains in determining the chemical fate of precursors, and bn rising catalysis as a tool in further understanding the complex mechanism of liquefaction.