Plasticity, agglomeration and volatiles secondary reactions in coal pyrolysis. Final technical progress report

Initial softening of the coal is by physical melting of an estimated 25% by weight of the coal. Up to 40% by weight of the coal is further converted to liquids by pyrolytic bond breaking. These liquids can condense or polymerize to give higher molecular weight liquids and solids, and crack to give gas and coke, or escape from the coal particle to give tar. The result is that the liquid weight averaged molecular weight can increase from 570 to above 800, and then decrease to around 600. Experimental viscosity and intraparticle liquid formation/depletion data are described by a global model that accounts for melting, generation and depletion of the liquid, and volatiles formation. The kinetic parameters find quantitative application in modeling coal particle agglomeration and swelling behavior under rapid heating conditions. Predictions of models here developed are in qualitative accord with literature data on swelling. The homogeneous secondary reactions of tar appear to be well-described by a model which includes three ''lumps'' of high, medium, and low reactivity. These lumps imply the existence in tar of three broad classes of bond strengths. Analysis of the data on tar and other products allowed identification of many of the bonds inmore » each group. In general, the homogeneous secondary reactions involve cracking at the periphery of aromatic rings, which remain largely intact, leading to lower molecular weight tars and light products (gases, light oils). The conversion of aromatic rings results in a direct relationship between the fractions of aromatic carbon or aromatic hydrogen and the tar conversion, allowing the determination of kinetic parameters from analytical measurements on surviving tar. 40 refs., 54 figs., 4 tabs.« less