The US-patented Exxon technology we report in this dispatch is closely related to another Exxon technology, patented in the very same year, by, essentially, the same team of Exxon scientists.
As earlier seen in: Exxon Converts 99% of Coal to Methane | Research & Development; which concerns:
"United States Patent 4,077,778 - Process for the Catalytic Gasification of Coal; 1978; Assignee: Exxon Research and Engineering Company, NJ; Abstract: A process for the production of synthetic natural gas from a carbon-alkali metal catalyst or alkali-metal impregnated carbonaceous feed, particularly coal";
Exxon has developed technology that would enable the conversion of virtually all of the carbon content in Coal into Methane gas.
In the very same year, basically the same team of Exxon scientists named, though in different order, as the inventors of US Patent 4,077,778, were awarded yet another US patent for a variation on such a process, one which enables the conversion of Coal into, again, essentially, Methane.
The Coal-to-Methane technology disclosed by Exxon in our subject invention herein is somewhat different than that of USP 4,077,778, however, since not all of the Carbon is transformed into Methane.
Some of the Coal is "lost" in the co-production of a certain amount of Carbon Dioxide.
But, that isn't necessarily a "bad thing"; as we attempt to explain, following excerpts from:
"United States Patent 4,094,650 - Integrated Catalytic Gasification Process
Date: June, 1978
Inventors: Kwang Koh, et. al., MI, NJ, TX
Assignee: Exxon Research and Engineering Company, NJ
Abstract: Methane and carbon dioxide are produced by reacting steam with a carbonaceous feed material at a reaction temperature between about 1000 F and about 1500 F and a reaction pressure in excess of about 100 psi in the presence of a carbon-alkali metal catalyst and equilibrium quantities of added hydrogen and carbon monoxide. The raw product gas withdrawn from the reaction zone is treated for removal of the carbon dioxide, product methane is recovered from the treated gas, and the remaining hydrogen and carbon monoxide can be recycled to supply the added hydrogen and carbon monoxide needed in the reaction zone.
Claims: A process for the production of methane from ... solid carbonaceous feed material and steam which comprises reacting said steam with said feed material to form essentially methane and carbon dioxide while suppressing the net formation of carbon monoxide and hydrogen in a reaction (which yields) steam, molecular hydrogen, carbon monoxide, carbon dioxide, and methane, and recovering methane from the withdrawn mixture.
A process ... wherein said feed material comprises coal ... .
A process ... wherein the withdrawn (product) mixture is treated for the removal of carbon dioxide, methane is recovered from the treated gas, and hydrogen and carbon monoxide contained in said treated gas are recycled to said reaction zone as said added hydrogen and carbon monoxide.
(As in somewhat similar Coal hydro-gasification technologies we've documented for you, hydrogen and carbon monoxide are specified to be added to the initial Coal gasification process; but, just as in those previously-cited technologies, the needed H2 and CO are always extracted from the product stream of the Coal gasification itself, and then recycled back into the gasification. We don't have to "go out", and, with extra expense, obtain them.)
A process ... wherein said hydrogen and said carbon monoxide contained in said treated gas are combined with steam, heated to said reaction temperature, and thereafter recycled to said reaction zone.
A process ... wherein said steam is reacted with said feed material in the substantial absence of added molecular oxygen.
(Yet again, as in many of our previous documentation's of the fact, "steam" can be included in the Coal gasification medium, as an oxidant, in place of at least some Oxygen; which technique serves to increase the production of Hydrogen, while, at the same time, minimizing not just the co-production of Carbon Dioxide, but, except for additional Hydrogen and Carbon Monoxide, anything else extraneous, as well; a point which Exxon emphasizes throughout the Disclosure.)
A process for the production of methane and carbon dioxide from coal in the substantial absence of added molecular oxygen which comprises reacting steam with coal to form essentially methane and carbon dioxide.
Description and Background: Conventional processes for the manufacture of synthetic fuels by the gasification of coal ... generally require the reaction of carbon with steam, alone or in combination with oxygen ... to produce a gas which may contain some methane but consists primarily of hydrogen and carbon monoxide. This gas is subsequently reacted with additional steam to increase the hydrogen-to-carbon monoxide ratio by means of the water-gas shift reaction. Following this, the gas is usually treated to remove carbon dioxide and sulfur compounds and then fed to a catalytic methanation unit for reaction of the carbon monoxide and hydrogen to produce methane and water. It has been shown that processes of this type can be improved by carrying out the initial gasification step in the presence of a catalyst containing an alkali metal constituent. The alkali metal accelerates the steam-carbon gasification reaction and thus permits the generation of synthesis gas at somewhat lower temperatures than would otherwise be required or alternatively permits the use of a smaller reactor than might be necessary in the absence of such a catalyst.
(Note that this technology "permits the generation of synthesis gas at somewhat lower temperatures than would otherwise be required", which implies that not as much Coal needs to be completely combusted, with consequent formation of CO2, to attain the temperature required by this Exxon gasification process.)
The methanation reaction is conventionally carried out in the presence of a catalyst containing iron, nickel or cobalt as the principal constituent. Although catalysts of this type are reasonably effective, experience has shown that most such catalysts are highly sensitive to sulfur compounds and are quickly poisoned. To avoid this, the synthesis gas fed to the methanation unit may be treated to remove organic and inorganic constituents containing sulfur. This is generally done by first scrubbing the gas stream with a solvent such as monoethanolamine to eliminate most of the hydrogen sulfide, mercaptans, and the like and then removing the last traces of these impurities by adsorption on reduced zinc oxide or a similar adsorbent. Periodic regeneration of the methanation catalyst by treatment with hydrogen is generally required. These gas feed purification and catalyst regeneration steps are expensive. Moreover, the overall program is costly because of the large quantities of heat required in order to sustain the steam-carbon reaction, the large losses of low level exothermic heat of reaction from the water-gas shift and methanation reactions, and the substantial investment in equipment necessary to carry out the individual steps of the process.
To avoid difficulties of the type described above, it has been proposed that the steam-carbon reaction be used for the generation of a synthesis gas containing hydrogen and that the water-gas shift and methanation steps be eliminated by reacting the hydrogen thus produced with elemental carbon to form methane. It is known that the gasification of carbon with steam is an endothermic reaction and that the hydrogenation of carbon to form methane is exothermic. The heat liberated by the exothermic reaction of hydrogen with carbon to produce one mole of methane is about 83% of that necessary to generate the corresponding quantity of hydrogen by the endothermic reaction of steam with carbon. It has therefore been suggested that these two reactions be integrated to obtain an overall process ... ."
(Again, in concordance with other, similar Coal conversion technologies we have reported, at least 80% of the energy needed by the process can be generated by the process itself.)
Summary: This invention provides a substantially thermoneutral, hydrogen-balanced process for the generation of methane by the reaction of steam with coal ... in the presence of recycle hydrogen and carbon monoxide which largely avoids the difficulties (of), and has pronounced advantages over, processes suggested in the past.
In accordance with the invention, it has now been found that methane gas of essentially pipeline quality can be generated by reacting steam with a carbonaceous feed material in the presence of a carbon-alkali metal catalyst and equilibrium quantities of added hydrogen and carbon monoxide ... .
(Which "added hydrogen and carbon monoxide", again, are generated, and are recycled from, within the overall Coal gasification process itself. There is no need for additional expense to obtain them.)
The resulting raw product gas, an equilibrium mixture at reaction temperature, is withdrawn from the gasification zone, carbon dioxide is removed, and methane is recovered from the gas stream.
The remaining hydrogen and carbon monoxide, present in the raw gas in equilibrium concentrations, can be recycled to the catalytic gasification zone to supply the added hydrogen and monoxide required.
(It) will be noted that hydrogen is neither consumed nor produced in this overall system. Aside from the contaminants formed from sulfur and nitrogen in the coal, the reaction products are essentially methane and carbon dioxide.
Raw Product Gas Composition: % - CO 7.1; CO2 14.3; H2 23.0; H2O 31.2; CH4 22.8 (plus traces of Ammonia, H2S, etc.)"
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In the very lengthy full Disclosure, Exxon seems to stipulate that some quantities of the hydrocarbons "ethylene" and "propylene" can also be produced, in addition to or instead of, primarily, Methane, CH4.
That might be one reason for the co-production of Carbon Dioxide, relative to the related Exxon technology disclosed in the above-referenced "United States Patent 4,077,778".
There might, too, be considerations involving thermal and energy efficiencies; and, the process of our subject, "USP 4,094,650", might, in fact, supply more of it's own energy requirements, with the resultant excretion of a little more Carbon Dioxide.
However, the mix of products in the equation we reproduced at the conclusion of our excerpts as an example, is just one of the several possibilities provided by Exxon, based on various suggested ratios of starting feeds.
We excerpted it specifically to make note of a few items that should be of interest.
First, the relative proportions of Carbon Monoxide (CO - 7.1%) and Hydrogen (H2 - 14.3%) are intriguing. Such a balance of the two gases, based on our understanding, might be very well-suited for further catalytic processing, via the Fischer-Tropsch technique, and it's related derivatives, to form liquid hydrocarbons.
But, we don't know what the trade-offs would be, relative to recycling those gases, as Exxon stipulates, back into the Coal gasification process to influence the mix of products generated by that gasification.
Also, perhaps more importantly, we make note of the relative proportions of Carbon Dioxide, 14.3%, versus Methane, 22.8%, that are produced.
As seen in one of our earlier reports:
Pittsburgh 1941 CO2 + Methane = Hydrocarbon Syngas | Research & Development; concerning: "United States Patent 2,266,989 - Manufacture of a Gas from CO2 and Methane; 1941; Assignee: Koppers Company, Pittsburgh, PA; Abstract: The present invention relates to the manufacture of gases suitable for the synthesis of higher hydrocarbons or the like, said gases containing definite volumes of carbon monoxide and hydrogen in a certain proportion, by reacting on methane ... with carbon dioxide or a mixture of carbon dioxide and steam, so that the methane ... is decomposed into hydrogen and carbon monoxide. (And,) a gas in the proportion of one volume carbon monoxide to one volume hydrogen ... (i.e.,) 2CO + H2 (which) is especially suitable for the synthesis of hydrocarbons ... (can be produced) in accordance with the ... reaction: CH4 + CO2 = 2CO + H2";
we could use just a portion of the Methane that is so produced to react with all of the co-produced Carbon Dioxide; and, thereby make a product gas mixture "especially suitable for the synthesis of hydrocarbons".
And, that would still result in a net production of Methane from the process of our subject "USP 4,094,650".
Such remaining Methane could then itself be reacted with even more Carbon Dioxide, recovered from whatever handy source, perhaps a Shale Gas cleaning and compressing station. as in, for another example:
Standard Oil 1987 CO2 + CH4 = Syngas | Research & Development; wherein is detailed: "United States Patent 4,690,777 - Production of Synthesis Gas; 1987; Assignee: The Standard Oil Company, Cleveland;
Abstract: Gas mixtures containing at least hydrogen and carbon monoxide are prepared by reforming hydrocarbons in the presence of a catalyst ... to produce a product gas mixture containing carbon monoxide and hydrogen ... (and) wherein the light hydrocarbon is methane (and, wherein the) ratio of methane to carbon dioxide in the feed gas effects the ratio of carbon monoxide to hydrogen in the product gas (and, it) has been found that higher concentrations of carbon dioxide than methane in the reactant gas mixture will result in a product gas mixture containing about equal amounts of carbon monoxide and hydrogen which is generally a desirable feed ratio for Fisher-Tropsch type reactions";
wherein it's confirmed that we can use "higher concentrations of carbon dioxide than methane" to make a "gas mixture containing about equal amounts of carbon monoxide and hydrogen which is generally a desirable feed ratio for Fisher-Tropsch type reactions".
We can, in other words, "leverage" Methane to recycle a correspondingly larger amount of Carbon Dioxide in the production of a hydrocarbon synthesis gas.
And, such a fact should inspire some thought as to what can be done with the Methane remaining from the process of our subject "US Patent 4,094,650", after just a portion of the Methane produced therein is used, in a fashion similar to that, as above, of "USP 4,690,777", or, as also above, of "USP 2,266,989", to convert the Carbon Dioxide that is co-produced in our subject process into a mixture of Hydrogen and Carbon Monoxide that is "especially suitable for the synthesis of hydrocarbons".
Further, the title of "United States Patent 4,094,650 - Integrated Catalytic Gasification Process" seems related to another, earlier Exxon technology, which we reported in:
Esso/Exxon 1973 Integrated Coal Liquefaction Process | Research & Development; concerning: "United States Patent 3,726,784 - Integrated Coal Liquefaction and Hydrotreating Process; 1973; Assignee: Esso Research and Engineering Company; Abstract: A hydrotreated liquid product from coal is obtained by a process in which liquefaction and hydrotreating zones are operated at essentially the same moderate pressures".
And, upon study of the full Disclosures of each US Patent, we take the word "Integrated" in both their titles to mean that certain processing steps in the two technologies, relative to earlier, similar and precedent techniques, for converting Coal into either hydrocarbon liquids or hydrocarbon gases, can be and have been consolidated, with a resultant increase in productivity and decrease in required capital equipment investment, relative to the prior art.
The word "Integrated" can, thus, relative to that prior art, be taken to mean "more efficient".
Which, of course, begs the question:
Just how efficient do such technologies, for converting our abundant Coal and our unjustly vilified Carbon Dioxide, into seemingly desperately-needed hydrocarbon liquids and gases, have to get, before we stop accommodating Big Oil's and OPEC's economically and environmentally devastating production and business practices to get them?
We can make anything now derived from natural petroleum sources from both our abundant Coal and our some-say-too abundant Carbon Dioxide.
Why haven't we yet started doing so?