Characterization of Tar Products from Rapid Pyrolysis of Bituminous Coals and Development of a Physically Realistic Model of Softening Coal Pyrolysis. Final Report

摘要

This report summarizes the progress made on the two primary objectives of this research: collection of time and temperature resolved chemical information on tars evolved during the rapid pyrolysis of coals; and use of the information of Item 1 to evaluate and further develop a combined mass transfer-chemical reaction model of coal pyrolysis. Data have been collected on the tars evolved from three pulverized (50 to 100 um) bituminous coals and one lignite. These data include molecular weight distributions of the tars, and chemical compositions and infrared spectra of the tars as a function of molecular weight, time, and temperature (from 300 K to 1300 K). The conclusion is reached that escape of the tars from the particles is primarily an evaporation process, but that some role of entrainment is probable. Spectral evidence suggests that ether linkages are important in high molecular weight fractions, but not low. Otherwise, the tars are quite similar in all except the highest molecular weight fractions, suggesting that it might be appropriate to view them, to a first approximation, as depolymerization fragments consisting of similar repeat units. Time resolved compositional measurements of the tars and extractable materials remaining in chars suggest that a precursor formation in the char occurs on a time scale comparable to the evaporation time scale. Secondary repolymerization reactions are characterized by higher activation energies than are the initial tar formation reactions. Numerous experimental problems are encountered in trying to obtain reliable data on molecular weight distributions of coal tars. Recommended experimental techniques are presented. A new model of coal pyrolysis is presented, incorporating the findings of this study. Appendix 1 has been entered separately into EDB and ERA. (ERA citation 11:033525)