Catalysis and Catalyst Dispersion in Coal Liquefaction

Abstract

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 11. 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 on 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 on 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 and recycle of the catalyst. Interest also remains in determining the chemical fate of precursors, and on using catalysis as a tool in further understanding the complex mechanism of liquefaction.

Molybdenum Compounds

“…For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming CoðMoS 4 Þ 3À 2 Tetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (15) and the hydroliquefaction of coal (16). The intermediate forms MoOS 2À 3 , MoO 2 S 2 2À , MoO 2 S 2À 2 and MoO 3 S 2À have also been prepared (17).…”

Catalysis in Direct Coal Liquefaction

“…Several recent reviews of catalyst developments are available [9,10,[96][97][98][99][100][101][102]. Several recent reviews of catalyst developments are available [9,10,[96][97][98][99][100][101][102].…”

Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, January--March, 1995

“…It is known (7,8,9) that some precursors like metal carbonyls require the addition of sulfur for sufficient activity. There seems (10) to be consensus that the sulfides of the transition metals are more active in catalytic hydroliquefaction than their oxides. The reason for this remains unclear.…”

“…Therefore, deoxygenation during the liquefaction process would be beneficial. This goal may be attainable with the use of sulphided bimetallic catalysts dispersed onto the coal using an organometallic precursor [10,11].…”