Effects of low-temperature catalytic pretreatments on coal structure and reactivity in liquefaction

Abstract

Low-temperature catalytic pretreatment is a promising approach to the development of an improved liquefaction process. This work is a fundamental study on effects of pretreatments on coal structure and reactivity in liquefaction. The main objectives of this project are to study the coal structural changes induced by low-temperature catalytic and thermal pretreatments by using spectroscopic techniques; and to clarify the pretreatment-induced changes in reactivity or convertibility of coals in the subsequent liquefaction. This report describes the progress of our work during the first quarterly period. Substantial progress has been made in the spectroscopic characterization of fresh and THF-extracted samples of two subbituminous coals and fresh samples of three bituminous coals using cross-polarization magic angle spinning (CPMAS) solid-state 13C NMR and pyrolysis-GC-MS techniques. CPMAS 13C NMR and pyrolysis-GC-MS provided important information on carbon distribution/functionality and molecular components/structural units, respectively, for these coal samples. Pyrolysis-GC-MS revealed that there are remarkable structural differences in structural units between the subbituminous coals and the bituminous coals. Furthermore, significant progress has been made in the pretrearments and spectroscopic characterization of catalytically and thermally pretreated as well as physically treated Wyodak subbituminous coal, and temperature-staged and temperature-programmed thermal and catalytic liquefaction of a Montana subbituminous coal. The analytical results show that both catalytic and thermal pretreatments result in some changes in coal structure. In many cases such structured changes are subtle and not easily detectable by conventional analytical methods such as FF-IR. We have detected the changes in coal macromolecular structure by using a combination of pyrolysis-GC-MS and CPMAS 13C NMR as well as FF-IR. Liquefaction data indicates that lowtemperature catalytic pretreatments enhance coal conversion and oil production. Among the two different liquefaction procedures incorporating pretreatments, temperature-programmed liquefaction of a Montana subbituminous coal using dispersed Mo catalyst has been shown to be superior to the temperature-staged liquefaction.

Effects of low-temperature catalytic pretreatments on coal structure and reactivity in liquefaction

“…'Fable 5 shows the results of the TGA experiments. Song et al, (1992d). A series of four Py/GC/MS experiments were preformed on the Adaville #1 and the Blind Canyon coals with pyrolysis temperatures starting at 310°C and increasing to 610°C at 100°C…”

“…In the first quarterly report [Song et al, 1992d], we compared the liquefaction results of samples impregnated by H20 solution (named sample I) and H20/THF solution (named sample II). Sample II showed a significant increase in total conversion and much better product distribution than sample I. lt was predictext that THF had a higher affinity to coal surface than water.…”

“…Considerable work at Penn State (Davis et al, 1986(Davis et al, , 1989Derbyshire et al, I986a, 1986bDerbyshire et al, I986a, , 1989Stansberry et al, 1987;Burgess and Schobert, 1990; Burgess et al, 1991) has demonstrated that the combination of low-temperature catalytic reaction followed by the high temperature catalytic reaction using dispersed molybdenum catalysts significantly enhanced coal conversion and oil production. More recent work in this laboratory has shown that temperature-programmed liquefaction using programmed heat-up is more effective for converting low-rank coals (Song et al, 1991b;Huang et al, 1992). Ali these results point to the beneficial effects of reactions at lower temperatures as compared to conventional high-severity processes.…”

“…Probably the catalytic pretreatment affects _e early reaction stage most significantly. The importance of, and potential problems, associated with early steps in direct liquefaction has been discussed in relation to the catalytic pretreatments in the previous report (Song et al, 1992d). Briefly, the most important issue in the early stage of coal dissolution is to suppress the retrograde reactions to produce higher yields of less refractory liquids for the down-stream catalytic upgrading.…”

Effects of low-temperature catalytic pretreatments on coal structure and reactivity in liquefaction. Technical progress report, January 1992--March 1992

“…The importance of, and potential problems, associated with early steps in direct liquefaction has been discussed in relation to the catalytic pretreatments in the previous report (Song et al, 1992c). Briefly, the most important issue in the em'ly stage of coal dissolution is to suppress the retrograde reactions to produce higher yields of less refractory liquids for the down-stream catalytic upgrading.…”