United States Patent: 4189371

 

We have many times documented the fact that any Hydrogen needed for the hydrogenation of Coal, in processes designed to convert Coal into liquid and gaseous hydrocarbons, can be produced from the co- and by-products of the Coal conversion itself, via a number of techniques that can be integrated into a complete Coal liquefaction and gasification industrial process.

 

Two Exxon scientists verify and more fully explain that fact in the United States Patent we enclose herein.

The full Disclosure is somewhat lengthy and complicated, so we reproduce, as forewords to our more complete excerpts, some passages that help to illustrate the concept; as follows:

 

"The effluent from liquefaction reactor ... contains gaseous liquefaction products such as carbon monoxide, carbon dioxide, ammonia, hydrogen, hydrogen sulfide, methane, ethane, ethylene, propane, propylene and the like, unreacted hydrogen from the feed slurry, light liquids, and heavier liquefaction products ... . (The) reactor effluent is separated ... (and) ... passed to downstream units where the ammonia, hydrogen and acid gases are separated from the low molecular weight gaseous hydrocarbons, which are recovered as valuable by-products. Some of these light hydrocarbons, such as methane and ethane, may be steam reformed to produce hydrogen that can be recycled where needed in the process."

 

And:

 

"It will be apparent ... that the invention provides an improved process for converting coal into a hydrogenated liquid product. The process results in an increased yield of hydrogenated liquid product, a decrease in the amount of high molecular weight bottoms produced, and a reduction in the amount of hydrogen consumed."

 

There is "a reduction in the amount of" externally-supplied "hydrogen consumed" since the integrated process devised by Exxon produces all, or nearly all, of the Hydrogen it needs internally.

 

There is at least one other specific advantage to this particular Exxon Coal conversion process, as well, which confirms earlier of our reports, and which we attempt to emphasize, following excerpts from:

 

"United States Patent 4,189,371 - Multiple-stage Hydrogen-donor Coal Liquefaction

 

Date: February, 1980

 

Inventors: Peter Maa and Lonnie Vernon, Texas

 

Assignee: Exxon Research and Engineering Company, NJ

 

Abstract: An increased yield of hydrogenated liquid product is obtained from coal by treating the feed coal with a hydrogen-donor solvent and hydrogen-containing gas in a first coal liquefaction reactor to produce a liquefaction effluent; separating the liquefaction effluent into a vaporous stream and a liquid stream, the liquid stream consisting of a low molecular weight liquid fraction and a high molecular weight liquid fraction; removing a sufficient amount of the low molecular weight liquid fraction from the high molecular weight liquid fraction to form a heavy bottoms stream containing less than about 50 weight percent of the low molecular weight liquid fraction based on the weight of the high molecular weight liquid fraction; treating the heavy bottoms stream with additional fresh hydrogen-donor solvent and hydrogen-containing gas in a second coal liquefaction reactor; separating the second liquefaction reactor product into a vaporous fraction and a liquid fraction, and recovering hydrogenated liquid products from the vaporous and liquid fractions. If desired the high molecular weight constituents in the liquid fraction from the second liquefaction reactor may be further treated with fresh hydrogen-donor solvent and hydrogen-containing gas in a third coal liquefaction reactor. Hydrogen-donor solvent may be produced in the process by catalytically hydrogenating at least a portion of the liquid product from each liquefaction reactor, recovering a liquid fraction from the products of the catalytic hydrogenation, and separating a hydrogen-donor solvent from the liquid fraction.

 

Claims: A multiple-stage hydrogen-donor liquefaction process for producing liquid hydrocarbons from coal or similar liquefiable carbonaceous solids which comprises ... contacting said carbonaceous solids with a first stream of hydrogen-donor solvent and a hydrogen-containing gas under liquefaction conditions in a first liquefaction zone to produce a liquefaction effluent (and) separating said liquefaction effluent into a vaporous stream and a liquid stream (and) separating a sufficient amount of ...  low molecular weight liquid fraction from (the) liquid fraction to form a heavy bottoms stream (and) contacting said heavy bottoms stream with a second stream of hydrogen-donor solvent and a hydrogen-containing gas under liquefaction conditions in a second liquefaction zone; separating the effluent from said liquefaction zone into a vaporous fraction and a liquid fraction; and recovering liquid hydrocarbonaceous products from said vaporous and said liquid fractions.

 

Background: This invention relates to coal liquefaction and is particularly concerned with multiple-stage hydrogen-donor coal liquefaction.


A number of different processes are being developed for the production of liquid hydrocarbons from coal.

 

Among the most promising of these are processes in which the feed coal is first contacted with a hydrogen-containing gas and a hydrogen-donor solvent ... in a liquefaction reactor and a portion of the liquid product is then catalytically hydrogenated in a solvent hydrogenation reactor to generate additional liquid products and a hydrogen-donor solvent for recycle to the liquefaction step.

 

Within the liquefaction zone, the high molecular weight constituents of the coal are cracked and hydrogenated to form lower molecular weight vapor and liquid products. The effluent from the liquefaction reactor is then separated into gases, low molecular weight liquids, and a bottoms stream containing high molecular weight liquids and unconverted mineral matter.

 

Although the process outlined above has numerous, advantages over other liquefaction processes, the limited amount of low molecular weight liquids that can be produced, the excessive quantity of high molecular weight bottoms formed and the high consumption of hydrogen, which results from the production of undesirably large quantities of gases and saturated liquids, renders the process somewhat inefficient. To make the process economically more attractive, it is desirable to further convert the bottoms into lower molecular weight liquids and to decrease the hydrogen consumption.

 

Summary: The present invention provides an improved process for the preparation of liquid products from coal or similar liquefiable carbonaceous solids ... . In accordance with the invention, it has now been found that an increased yield of hydrogenated liquid products is obtained from bituminous coal, subbituminous coal, lignite or a similar carbonaceous feed material by treating the feed coal with a hydrogen-donor solvent and hydrogen-containing gas in a first liquefaction zone to produce a liquefaction effluent; separating the liquefaction effluent into a vaporous stream and a liquid stream ... ; removing a sufficient amount of the low molecular weight liquid fraction from the high molecular weight liquid fraction to form a heavy bottoms stream (and) treating the heavy bottoms stream with additional fresh hydrogen-donor solvent and hydrogen-containing gas in a second liquefaction zone, separating the second liquefaction zone product into a vaporous fraction and a liquid fraction, and recovering hydrogenated liquid products from the vaporous and liquid fractions. 

If desired, the high molecular weight constituents in the liquid fraction from the second liquefaction zone may be separated from the low molecular weight liquids and further treated with fresh hydrogen-donor solvent and hydrogen-containing gas in a third liquefaction zone.

 

As many liquefaction zones as desired may be used to increase the overall conversion of coal into low molecular weight liquids, but it appears that two reactors is the economic optimum.

 

Preferably, hydrogen-donor solvent is produced in the process by catalytically hydrogenating at least a portion of the liquid product from each liquefaction zone, recovering a liquid fraction from the products of the catalytic hydrogenation and separating the hydrogen-donor solvent from the liquid fraction.

 

The process of the invention results in significant advantages over single-stage hydrogen-donor solvent liquefaction. The amount of coal converted into lower molecular weight liquids is substantially increased while hydrogen consumption and gas make are reduced."

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The full Disclosure is quite lengthy, detailed and complicated. The important facts, though, are represented in our excerpts.

 

The needed Hydrogen, or "hydrogen-containing gas" most often specified by Exxon, is obtained from "light hydrocarbons, such as methane and ethane" that are co-produced within the system, and which "may be steam reformed to produce hydrogen that can be recycled where needed in the process".

 

Moreover, again, the needed "hydrogen-donor solvent is produced in the process by catalytically hydrogenating at least a portion of the liquid product from each liquefaction zone".

 

Though not seemingly specified by Exxon, there also seems to be opportunity to reclaim and recycle energy within the process.

 

That is a consideration, since elevated temperatures and pressures are specified throughout the sequence of reactions.

 

And, finally, as per our introductory comments, note that, in confirmation of many of our earlier reports, the Coal liquefaction solvent is made from the Coal itself, as in: "hydrogen-donor solvent is produced in the process by catalytically hydrogenating at least a portion of the liquid product from each liquefaction zone".


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