Energy & Fuels 1998, 12, 1245-1255
1245
Two-Stage Catalytic Coliquefaction of Coal and Waste Tire R. K. Sharma, D. Tian, J. W. Zondlo, and D. B. Dadyburjor* Department of Chemical Engineering, West Virginia University Morgantown, West Virginia 26506-6102 Received March 30, 1998
Two-stage catalytic liquefaction of coal and waste tire was studied using two bituminous coals, Blind Canyon and Illinois No. 6, and a sub-bituminous coal, Wyodak. The tire sample was a mixture of waste, recycled tires. In the first stage, the tire was liquefied separately at 350 or 400 °C under N2 or H2 to obtain tire oil. In the second stage, each coal was liquefied, in turn, with tire oil at 350-450 °C and 1000 psi of H2 (cold) using various tire-oil/coal ratios. A few second-stage runs were carried out with coal and vacuum-pyrolized tire oil obtained from a commercial source. Some of the second-stage runs were catalytic. For these, a ferric-sulfidebased catalyst was impregnated in situ in the coal. In general, the use of tire oil shows an improvement in coal conversion. In the absence of catalyst, the effects are similar with tire oils prepared under different conditions. With the catalyst, the increase upon adding tire oil is greatest when the tire oil is prepared at 400 °C in a hydrogen atmosphere. A synergistic effect can be quantified by adding to the conversion (or oil yield) for catalyst plus coal the increase in conversion (or oil yield) observed when tire oil is added to coal in the absence of catalyst and comparing this number to the conversion (or oil yield) when the feed is coal plus tire oil plus catalyst. In general, the improvements are most pronounced at the higher temperatures of the second stage and at higher ratios of tire oil to coal. For all three coals, the effects of tire oil are greater than those due to the whole tire in single-stage coliquefaction, especially with a catalyst present at high tire-oil/coal ratios. A kinetic analysis shows that the thermal reactions of coal and tire oil have lower activation energies in the second stage of two-stage liquefaction compared to those in singlestage liquefaction. A similar effect is noted for the catalytic reactions, at least for the bituminous coals. This indicates that two-stage liquefaction is beneficial, particularly at mild temperatures in the second stage. Further, the activation energies for the synergistic rate constants are higher for the catalytic reactions than for the thermal reactions, indicating that diffusion effects in the coal may be important in the noncatalytic processes.
Introduction The disposal of more than 200 million automotive tires annually in the United States is a major environmental problem since the tires do not degrade easily and are unsuitable for disposal in landfills. Farcasiu and Smith1 suggested coliquefaction of tires with coal as an alternative to tire disposal in landfills. Typically, the rubber from a tire contains about 35 wt % styrenebutadiene rubber (SBR), 8 wt % polybutadiene rubber (PBR), 20 wt % aromatic oil, and 33 wt % carbon-black, in addition to small quantities of zinc oxide, sulfur, and other unspecified miscellaneous components.1 When the tire rubber is subjected to liquefaction conditions, the organic portion is converted to tire oil, with carbonblack remaining as an unreacted residue. The presence of tire also has a synergistic effect on coal conversion, i.e., the overall conversion of coal plus tire by coliquefaction is greater than the sum of the individual conversions of coal and tire when they are liquefied * To whom correspondence should be addressed. Phone: (304) 2932111 ext 411. Fax: (304) 293-4139. E-mail
[email protected]. (1) Farcasiu, M.; Smith, C. M. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1992, 37, 472-477.
separately.2-4 The synergism is governed by the nature of the coal as well as by the conditions of liquefaction.5 The synergistic effect of the tire could be due to several factors. One of these is the presence of polyaromatic hydrocarbons produced during liquefaction. Williams and Taylor6 reported that tire oil obtained from pyrolysis of waste tires contains polyaromatic hydrocarbons. According to Whitehurst et al.7 and McMillen et al.,8 the presence of polyaromatic hydrocarbons enhances the conversion of coal. Second, the tire oil may act as a hydrogen shuttler for coal liquefaction.9 Third, the beneficial effect of the tire could also be due to (2) Liu, Z.; Zondlo, J. W.; Dadyburjor, D. B. Energy Fuels 1995, 9, 673-679. (3) Tang, Y.; Curtis, C. W. Fuel Process. Technol. 1996, 46, 195215. (4) Orr, E. C.; Burghard, J. A.; Tuntawiroon, W.; Anderson, L. L.; Eyring, E. M. Fuel Process. Technol. 1996, 47, 245-259. (5) Sharma, R. K.; Zondlo, J. W.; Dadyburjor, D. B. Energy Fuels 1998, 12, 589-597. (6) Williams, P. T.; Taylor, D. T. Fuel 1993, 72, 1469-1474. (7) Whitehurst, D. D.; Mitchell, T. D.; Farcasiu, M. Coal Liquefaction; Academic Press: New York, 1980. (8) McMillen, D. F.; Malhotra, R.; Tse, D. S.; Nigenda, S. E. Fuel 1989, 68 (3), 380-386. (9) Badger, M. W.; Harrison, G.; Ross, A. B. Prepr. Pap.sAm. Chem. Soc., Div. Pet. Chem. 1994, 39, 438.
10.1021/ef980059f CCC: $15.00 © 1998 American Chemical Society Published on Web 09/02/1998
1246 Energy & Fuels, Vol. 12, No. 6, 1998
Sharma et al.
Table 1. Proximate and Ultimate Analyses of Coal, Tire, HTO-400, and PTO-650 sample
H2O (%)
DECS-6 DECS-24 DECS-26 tire HTO-400a PTO-650b
1.8
a
0.4 0.1 18.0
ash (% dry)
volatile matter (% daf)
fixed carbon (% daf)
C (% daf)
H (% daf)
N (% daf)
S (% daf)
O (by diff) (% daf)
6.3 14.1 6.3 8.1 0.2 0.3
49.0 41.8 45.8 71.0 98.7 92.6
51.0 58.2 54.2 29.0 1.3 7.4
81.9 77.2 74.1 79.7 86.5 90.2
6.3 4.9 4.6 7.5 10.7 10.5
1.5 1.3 1.1
