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.