http://www.anl.gov/PCS/acsfuel/preprint%20archive/Files/21_5_SAN%20FRANCISCO_08-76_0078.pdf
As we have from time to time reported in our posts, the efficient liquefaction of Coal, into raw materials suitable for refining into hydrocarbon fuels, necessitates the hydrogenation, the "hydrotreating", of primarily carbonaceous compounds derived from Coal.
In direct Coal liquefaction processes, the additional hydrogenation can be accomplished by a Hydrogen donor solvent, as in WVU's "West Virginia Process", which, as we have documented, utilizes the chemical "tetralin" to effect liquefaction and hydrogenation.
Other researchers, working with indirect Coal liquefaction processes, wherein Coal is first converted into a synthesis gas, "syngas", which is subsequently condensed via catalysis into liquid hydrocarbons, have experimented with both steam and additional syngas to effect hydrogenation.
Herein, scientists at the Pittsburgh, PA, Energy Research Center, confirm that additional syngas, combined with steam and specific catalysts, can not only effectively hydrogenate syngas, but can do so more effectively than pure Hydrogen, as could be obtained, at much higher expense, from the electrolysis of water.
Comment follows excerpts from:
"CATALYTIC LIQUEFACTION OF COAL
Yuan C. Fu and Rand F. Batchelder
Pittsburgh,PA, Energy Research Center;U. S. Energy Research and Development Administration
INTRODUCTION
Most catalytic liquefaction processes for producing low-sulfur liquid fuel from coal use large amounts of hydrogen which will have to be produced at high cost. In our previous work, we reported our attempt to use low-cost syngas to hydrotreat coal in the presence of added water, vehicle, and cobalt molybdate-sodium
carbonate catalyst. Catalytic coal liquefaction using syngas reduces the capital. Iand operating costs by eliminating shift converters and purifying systems needed for the liquefaction process using hydrogen. New catalysts have been prepared and tested with syngas to promote liquefaction and desulfurization as well as
water-gas shift conversion. Cobalt molybdate catalyst impregnated with alkali metal compounds, such as potassium carbonate, sodium carbonate, and potassium acetate, exhibited good activities for these reactions.
The liquefaction of coal by syngas, like that by hydrogen, appears to proceed via production of asphaltene and conversion of the asphaltene to oil. Because of the important effect of asphaltenes on the viscosity of the product oil, the progress of asphaltene formation and asphaltene conversion during the coal liquefaction has been investigated, and some observations on the chemistry of asphaltenes are presented here.
EXPERIMENTAL
The liquefaction of coal was studied in a magnetically-stirred autoclave. ... For coal hydrotreating by syngas, the cobalt molybdate catalyst was impregnated with alkali metal compounds, such as potassium carbonate, sodium carbonate, and potassium acetate. Coal (used was) Kentucky Bituminous and West Virginia Bituminous.
Hydrotreating of Coal.
New catalysts were prepared and tested with syngas for coal liquefaction. Catalysts were cobalt molybdate impregnated with alkali metal compounds such as potassium carbonate, sodium carbonate, and potassium acetate.
The asphaltene and the sulfur contents of the oil products obtained in the syngas and H2 runs are comparable. Under these conditions, the syngas usage was in the range of 3,900 to 4,700 scf per barrel of oil as compared to the H2 usage of 4,700 to 5,500 scf per barrel when pure H was used.
Formation of Asphaltene.
The coal liquefaction by syngas, like that by H2, proceeds via production of asphaltene. The decrease in the asphaltene formation with the increase in the syngas consumption ... indicates that the asphaltene formed
is converted to oil under further hydrotreating. ... We also found that the viscosity of the oil product correlates well with its asphaltene content, regardless of the reaction temperature and time.
Because of the important effect of the amount and the type of asphaltene on the property of the liquefied product, studies were conducted on the formation of asphaltene and oil during the progress of coal liquefaction. Kentucky bituminous coal was liquefied ... in both syngas and H2 systems.
It is interesting to note that, under similar liquefaction conditions, molecular weight (number average) of the asphaltene formed under syngas is lower than that of the asphaltene formed under H2.
CONCLUSIONS
Liquefaction of high sulfur bituminous coal at 3,000 psi under syngas in the presence of steam, recycle vehicle, and cobalt molybdate catalyst impregnated with potassium carbonate gives high coal conversions and oil yields at 400 to 450 C. The asphaltene, the sulfur content, and the viscosity of the oil products decrease with increasing consumption of syngas, and the syngas consumption increases with
increasing reaction temperature and residence time. When syngas is used in place of hydrogen in coal liquefaction, the rate of asphaltene conversion to oil is slower but asphaltenes formed have molecules of smaller sizes.
A catalytic coal liquefaction process using syngas gives high thermal efficiency and reduces the capital and operating costs by eliminating shift converters and purifying systems."
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First, "shift converters and purifying systems" refer to what would be needed to generate pure Hydrogen for the hydrogenation reactions.
They, and their associated higher costs, are not needed. In fact, if we understand all of this correctly, the use of syngas, with added steam, does a better job of hydrogenating coal-derived syngas than pure Hydrogen, as indicated by "Liquefaction of ... coal ... under syngas in the presence of steam ... gives high coal conversions and oil yields"; and, "When syngas is used in place of hydrogen in coal liquefaction, the rate of asphaltene conversion to oil is slower but asphaltenes formed have molecules of smaller sizes."
Our presumption, relative to the second statement above, is that, although the conversion is slower, the smaller molecules formed are more amenable to further processing; i.e., they're easier to refine into desired hydrocarbon compounds, with associated efficiencies and cost savings.
So, by using Coal-derived synthesis gas enriched with steam and appropriate catalysts, raw syngas can be hydrogenated to better effect and at less cost than by using pure Hydrogen.
That is, we would think, an important refinement in, and an advance in our understanding of, indirect Coal liquefaction technology that both improves hydrocarbon yields and reduces costs.
This refinement of Coal liquefaction technology was attained more than thirty years ago, through the expenditure of our US taxes, in Pittsburgh, Pennsylvania. Why have those of us tax-paying US citizens resident in the Coal Country surrounding Pittsburgh not yet heard of, or benefited from, in the ensuing three decades, this technological advancement in the utilization of Coal?
