Kinetics of Coal Liquefaction at Very Short Reaction Times

摘要

Kinetics of thermal and catalyzed coal liquefaction was investigated from 10 s to as long as 60 min using a short contact time batch reactor (SCTBR). Using this reactor system avoids the problems of slow heat up and cool down associated with the massive apparatus required for running high-pressure and high-temperature reactions. Coal liquefaction conversion to tetralin-soluble products was determined by changes in ash content in the partially reacted coal relative to that of the unreacted coal. Three distinct phases in the liquefaction process were observed: a very rapid extraction followed by an induction period (i.e., a short period when the extraction is ending and the conversion appears to be stopped) and then a slower conversion of the coal structure itself. By examining the liquefaction process at very short reaction times, it is possible to separate the very rapid extraction process (representing 20-30 wt % of the total conversion) from the slower liquefaction of the coal structure itself. Most previous work has measured the overall reaction rate by studying the process to higher or complete conversion, resulting in a composite of several vastly different rate processes and confounding a valid kinetic analysis. Solvents with different hydrogen donor strengths were also shown to have a strong influence on conversion rate and molecular hydrogen consumption. Thermogravimetric analysis was used to measure the contents of volatile matter, fixed carbon, a possible precursor or intermediate to the retrograde product formation (tar and coke), and ash in the liquefaction solids as a function of liquefaction time.