Kinetics of short contact time coal liquefaction. Part I: Effect of operating variables

Abstract

The liquefaction kinetics of Powhatan No. 5 mine coal (Pittsburgh Seam) in the presence of SRGII recycle solvent at short contact times (<lo min) and temperature and pressure ranges of 573-723 K and 10.3-13.8 MPa is examined in a well-mixed reactor. In the initial stages of liquefaction, while overall coal conversion (tetrahydrofuran solubles) increases with temperature, oil (pentane solubles) is lost with an increase in temperature. An increase in solvent-tcxoal ratio results in an increase of conversion. The initial coal particle size distribution, total pressure, and nature of gas phase (nitrogen or hydrogen) have no significant effect on the production of any of the product of liquefaction for contact times up to 10 min. A lumped kinetic model is presented to describe the product distribution. SCOPEThe primary reactions in conversion of coal to liquid fuels in any coal-oil slurry liquefaction process are pyrolytic in nature and require high temperature to overcome the distribution of activation energies involved in the rupture of bond linkages in the macromolecular network of coal. It is known that when coal is contacted with a hydrogendonor solvent, at elevated temperatures (693-733 K), much of the coal conversion to soluble products takes place in the initial 2-5 min. Hence, the preheater in the coal liquefaction process is a critical component, as it behaves as a short contact time reactor. Recently, there has been a considerable interest in the development of a short contact time two-stage process. This paper presents a short contact time (<lo min) coal liquefaction kinetic study which is carried out in a well-mixed, 1-L semibatch autoclave reactor. The experimental data are obtained for Powhatan No. 5 mine coal at various practical ranges of temperatures, pressures, solvent-to-coal ratio, and initial coal particle size. Both nitrogen and hydrogen was used as the gas phase. The data are correlated by a lumped kinetic model which would be useful in predicting the performances of a preheater or a short contact time coal liquefaction reactor.

On the measurement of coal liquefaction kinetics

“…With due cognizance of reaction mechanism, it is possible to derive kinetic rate expressions (Abichandani et al, 1984;Cronauer et al, 1978) of coal liquefaction. Of course, the lumping technique does not prove the reaction mechanism and may not carry full information about the dynamic behaviour of the reactions.…”

“…The apparent activation energies computed in this study are comparable to those reported in Table 1, and elsewhere (cf. Abichandani et al, 1984;Douglas et al, 1982;Furlung et al, 1982;Ozum et al, 1984;Shah et al, 1978). These activation energies are generally considered to be low for thermal reactions.…”

Kinetics of Thermal and Catalytic Coal Liquefaction with Plastic-Derived Liquids as Solvent

“…Weller et al (1950Weller et al ( , 1951 first proposed essentially linear reaction pathways: coal to asphaltene, followed by asphaltene to oil. Thereafter, this simplistic series thermal reaction model was extensively developed to various combinations of series and parallel reaction pathways (Liebenberg and Potgieter, 1973;Cronauer et al, 1978;Shalabi et al, 1979;Mohan and Silla, 1981;Abichandani et al, 1982Abichandani et al, , 1984. Kinetics of catalytic coal liquefaction was further investigated by many researchers (Ruether, 1977;Gollakota et al, 1985;Pradhan et al, 1992;Suzuki, 1994).…”

A novel concept for high conversion of coal to liquids. Final report, 1 September 1988--31 August 1992

“…(2) The investment for a hydrogen production and compression facility is large, amounting in some cases to one third of the cost of the entire plant. and Mitchell, 1977;Hill, et al, 1966;Wiser, 1968;Shabtai, 1974;Foster, 1983;Foster, 1984a;b;Abichandani, 1984). Some investigators (Gorin, 1981;Shah, 1981;Whitehurst, et al, 1980 and others, 1986;Weller, 1982;Zielke andothers, 1966a, 1966b).…”