Carbon Dioxide isn't actually being used as one of the raw materials for hydrocarbon synthesis in the Japanese technology we report herein.
It is, instead, being utilized to help clean and purify a raw material for liquefaction that consists of low-rank Coal burdened with a relatively high amount of "ash"- forming inorganic minerals.
Additional attempt at explanation follows excerpts from:
"United States Patent 4,714,543 - Method of Treating Brown Coal for Liquefaction
Date: December, 1987
Inventor: Tetsuo Matsumura, et. al., Japan
Assignee: Mitsubishi, et. al., Tokyo and Kobe
Abstract: A starting slurry composed of raw brown coal and a solvent is heated and pressurized, subjected to gas-liquid separation and dehydration and then to hydrogenation/liquefaction. The CO2 -containing gas produced in the preheating/dehydration step and/or a CO2 -containing gas supplied from outside the system is blown into the slurry in the above-mentioned preheating/dehydration step, whereby carbonate-forming metal components in the brown coal are converted to the carbonates thereof in advance. In this manner, the hydrogenation/liquefaction efficiency is improved, and stabilized long-term continuous operation is attained.
This invention relates to a method of treating brown coal for liquefaction and more particularly to an improvement in the preliminary treatment step of the brown coal liquefaction system, which improvement consists in efficiently removing moisture in raw brown coal and at the same time preventing the adhesion and accumulation of carbonates formed in the step of dehydration and/or of precipitate carbonates in the step of hydrogenation for liquefaction or effectively separating and removing such formed carbonates and the like in the step of hydrogenation for liquefaction and thereby increasing the liquefaction efficiency and the stability of continuous operation of the system.
As one of the coal liquefaction techniques, the so-called extraction-hydrogenation method is known in which coal dust is made into a slurry by mixing with a solvent ... .
(In) the brown coal liquefaction treatment, there (is the) problem ... that when a slurry, the main component of which is brown coal, is used in an extraction-hydrogenation process, a large amount of deposit forms in the preheater, reactor and/or slurry transportation pipeline (and, it is thus) necessary to prevent deposits and scales.
This invention subjects the starting slurry composed of raw brown coal and a solvent to a gas-liquid separation at an elevated temperature and increased pressure so as to effect moisture release in the form of steam, utilizing steam as a source of heat (and) blowing ... a CO2 -containing gas (which can be) supplied from the outside the system into the starting (Coal slurry) thereby positively stabilizing Ca, etc, as fine carbonate particles.
Another object of the invention is to prevent troubles in the reaction system by positively extracting such precipitate as mentioned above, particularly the formed carbonates and the like, as early as possible and thereby assuring a long-term stable operation of the brown coal liquefaction plant."
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And, again, "assuring a long-term stable operation of the brown coal liquefaction plant" can be accomplished, in part, by utilizing "a CO2 -containing gas ... from outside the system" to precipitate and remove Calcium and other, similar, metal contaminates "as fine carbonate particles".
Calcium and other metal salts are, in other words, converted into environmentally unobjectionable "limestone", or similar, and then, one way or another, precipitated or filtered out of a Coal-solvent mixture, by utilizing Carbon Dioxide that could be captured "outside the system" - at a Coal-fired power plant, perhaps. .
It is, in one aspect, actually a reversal of Coal-fired power plant flue gas scrubbing, to remove or capture Carbon Dioxide by reacting it with metal salt in a water solution to form relatively inert, environmentally unobjectionable carbonate minerals that are easily disposed of.
In this case, however, Carbon Dioxide is being used as the "scrubber" for metal salt contaminants in a starting Coal liquefaction slurry - which slurry, though not well-specified by the Japanese inventors, we presume to be based on the suspension of the "raw brown coal" in a liquid carrier derived either from the process itself; or, derived from another process, such as a Coke oven capable of producing the Anthracene and Naphthalene-type primary Coal oils that are specified by the numerous other, similar, Coal conversion technologies we have already, in previous reports, cited for you.
Seen another way, the Coal slurry can, conceptually, be used to scrub power plant exhaust emissions in a process that is beneficial both to the power plant and to the Coal conversion and liquefaction process.
Further, the Calcium-laden brown Coal specified herein would be similar, in some respects, to the low-rank rider-seam Coal and carbon-containing shale that is often found disposed of in accumulations of waste around older Coal mines, especially those mines where the Coal was destined for steel mills, and was thus cleaned to higher standards than boiler Coal.
So, Carbon Dioxide could conceivably aid, via this Japanese technology, in the clean-up and reuse of certain Coal mine refuse in the US, with the end product, via subsequent "liquefaction", being some sort of synthetic crude liquid suitable, we must presume, for further refining into liquid hydrocarbon fuel products.