Ramesh K. Sharma, Jianli Yang, John W. Zondlo and Dady B. Dadyburjor
Department of Chemical Engineering, West Virginia University, PO Box 6102 Morgantown, WV
June 1998.
Abstract
Thermal and catalytic liquefactions of waste (recycled) tire and coal were studied both separately and using mixtures with different tire/coal ratios. Runs were made in a batch tubing bomb reactor at 350–425C. The effect of hydrogen pressure on the product slate was also studied. Mixtures of tire components and coal were used in order to understand the role of the tire as a solvent in co-liquefaction. In the catalytic runs, a ferric-sulfide-based catalyst impregnated in situ in the coal was used. Both the tire components and the entire tire exhibit a synergistic effect on coal conversion. The extent of synergism depends on temperature, H2 pressure and the tire/coal ratio. Experiments with coal and tire components show that the synergistic effect of tire is due to the rubber portion of the tire and not the carbon black. The synergism mainly leads to an increase in the yields of asphaltenes, which are nearly double those in the coal-only runs at 400°C. The conversion of coal increases dramatically using the catalyst, but the catalytic effect is attenuated somewhat in the presence of tire, especially at high tire/coal ratios. The data were analyzed using a consecutive reaction scheme for the liquefaction of coal to asphaltenes and thence to oil+gas, both reactions being of second order; a second-order conversion of tire to oil+gas; and an additional synergism reaction when both coal and tire are present, first-order in both coal and tire. Parallel schemes were assumed for thermal (uncatalyzed) and catalyzed reactions. The uncatalyzed liquefaction of coal has a low apparent activation energy, 36 kJ/mol, compared to those for the synergism reaction (84 kJ/mol) and the catalytic coal liquefaction (158 kJ/mol). The conversion of asphaltenes to oil+gas is relatively independent of temperature and of the presence of the catalyst. The catalyst appears to play a significant role in the conversion of coal to asphaltenes, but a negligible role in the synergism reaction."
Again, as with the other research we've cited, adding scrap auto tires to coal in a liquefaction process improves the yield of liquid fuel raw material; the practice is "synergistic". And: "the synergistic effect of tire is due to the rubber portion of the tire and not the carbon black"; a conclusion drawn by other researchers, wherein the "rubber" contributes hydrogen to the hydrogenation and liquefaction reaction, and can reduce the amount, and associated costs, of synthetic hydrogen donor solvent, such as tetralin, or others, which might otherwise be needed to hydrogenate the coal.
So effective is the addition of "rubber" to coal, that it can "increase in the yields of asphaltenes, which are nearly double those in the coal-only runs". In other words, by adding "waste" rubber to coal in a liquefaction process, we can "nearly double" the production of liquid fuel raw materials from coal.
We were careful above to use the word "rubber" parenthetically, since modern tires can be made of either natural or synthetic polymers. But, we must note that, where natural rubber tire waste would be used in a coal co-liquefaction process, such use would represent yet another route of atmospheric carbon dioxide recycling, via the initial photosynthetic production of botanical latex.
Institute of Chemistry and Chemico-Metallurgical Processes, 42 K. Marx Str., Krasnoyarsk 660049, Russia
Institute of Organic Chemistry, 44 Kasprzaka Str., Warszawa 01-224, Poland
University of Strathclyde, Thomas Graham Building, 295 Cathedral Str., Glasgow G1 1XL, UK
Abstract
Kansk-Achinsk brown coal hydrogenation and swelling in tetralin, in low molecular alcohols, in other solvents and in binary mixtures were studied. Tetralin was found to be the most effective liquefaction solvent, but methanol and ethanol were the active ones in coal swelling. Synergistic effects were observed when the mixtures of tetralin and methanol or ethanol were used for liquefaction and swelling. The effect of binary solvents was shown to be due to the ability of alcohol components to cause brown coal to swell improving the availability of the fragments of coal matter for the reactive hydrogen donor tetralin molecules."
This study confirms, first, the efficacy of the hydrogen donor solvent, tetralin, as specified by West Virginia University in their "West Virginia Process" for direct coal liquefaction.
It also demonstrates, as has other research we've cited, that ethanol, as derived from biological fermentation, serves to enhance the coal liquefaction solvent abilities of tetralin.
Unstated is the fact that ethanol can be, and most usually is, produced from the fermentation of botanical produce, i.e., purpose-grown crops, including algae, or agricultural and forestry wastes, and it's carbon content, recycled into liquid fuel, is all extracted, via photosynthesis, from the atmospheric load of carbon dioxide.
The contribution ethanol might make to overall atmospheric carbon reduction, if used for the purpose of enhancing coal liquefaction, might be relatively small. But, it could be a piece of the total environmental solution, especially when we accept the fact that our human contributions to atmospheric carbon, relative to some natural processes, such as volcanism, are relatively small. Moreover, if you recall other research we've cited, biological cellulose, another carbon-recycling botanical material, can be converted, alongside coal, into liquid fuel products in processes just like the one cited in this dispatch.
And, perhaps at this time more importantly, ethanol, by improving the efficiency of coal conversion processes, can help us to better utilize our vast coal resources in making the liquid fuels we need domestically, rather than continuing to transfer our wealth overseas to unfriendly foreign petroleum powers, and thereby continuing to impoverish our own, United States, citizens..