Coal extraction - Patent 4521291
As we have been reporting, primary Coal tars, or oils, such as anthracene and naphthalene, sometimes referred to as polyaromatic hydrocarbons (PAH's), once extracted from Coal, can be processed and then utilized to hydrogenate, to help liquefy, additional raw Coal.
That fact is affirmed, and documented, herein by our own United States Government, as embodied in the US Patent Office, in their issuance, to inventors in the United Kingdom, of the US Patent enclosed via the above link; and, as excerpted following:
"Coal Extraction - United States Patent 4521291
Date: June, 1985
Inventors: James Clarke, Geoffrey Kimber, et. al.; Great Britain
Assignee: Coal Industry Limited; London
Abstract: Coal is extracted using a mixed solvent which includes a substantially aromatic component and a substantially naphthenic component, at a temperature of 400° to 500° C. Although neither component is an especially good solvent for coal by itself, the use of mixed solvent gives greater flexibility to the process and offers efficiency gains.
Claims:
1. A method of extracting coal at a temperature of 400 to 500 C. in the absence of added hydrogen and using a liquid solvent, comprising the use of a solvent which is a mixture consisting essentially of an aromatic polycyclic hydrocarbon which contains three- and/or four-ring molecules and has a minimum boiling point of 270 C. and at least 25% by weight of the aromatic component of a naphthenic polycyclic high boiling hydrocarbon.
2. A method as claimed in claim 1, wherein the naphthenic hydrocarbon contains predominantly two- and/or three-ring molecules and has a cut point in the range 180 to 300 C.
3. A method of extracting coal in which a recycle solvent is used, comprising the extraction of coal at a temperature of from 400 to 500 C. using a solvent comprising a hydrogenated recycle solvent under conditions at which the solvent remains in the liquid phase, and in the absence of added hydrogen, in an extraction step to form an extract, removing from the extract by distillation an aromatic polycyclic oil boiling within the range 270 to 360 C. and containing three- and/or four-ring molecules, transferring at least a portion of the remainder of the liquid extract which does not contain any substantial amount of solids to a hydrocracker and subjecting said portion to hydrocracking therein to form a hydrogenated and hydrocracked product, removing from said hydrogenated and hydrocracked product an oil boiling in the range 180 to 300 C. which consists of a major proportion of naphthenic polycyclic hydrocarbons, and admixing at least a portion thereof with at least a portion of said aromatic oil to form a recycle solvent containing at least 25% by weight of the naphthenic component, based on the aromatic oil.
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Description:
This invention concerns improvements in coal extraction using liquid solvents, more particularly it concerns coal extraction using liquid hydrogen donor solvents.
In the extraction of coal, there have been many proposals to add hydrogen during the dissolution step. This may be done by the use of a hydrogen donor solvent, which is a well-known class of materials capable of donating hydrogen during dissolution to the coal moieties produced by thermal bond cleavage in the coal; the most favoured solvents of this class are hydroaromatics. In an extraction process using a hydrogen donor solvent, the solvent itself loses hydrogen and has to be constantly replaced and/or regenerated. It is envisaged that in the hydrogen donor extraction of coal without the presence of gaseous hydrogen in the extraction vessel, the residual solvent and any part of the product having the same characteristics will be hydrogenated at a later stage in the process, possibly in a general hydrogenation or hydrocracking of the liquid products from the extraction step, and the resulting hydrogen donor solvent will be recycled to the extraction step. The liquid products comprise a wide range of materials, including high boiling point materials which it is desirable to convert into low-boiling higher--value liquids having a lower molecular weight. Therefore, in such a process, the hydrogenation/hydrocracking conditions are chosen to give an acceptable compromise between production of recycle solvent which is hydroaromatic but not completely saturated, and the production of the desired high value low-boiling products.
Our studies of coal extraction have led to the consideration of the correction of a situation in which the process solent is overhydrogenated, to yield naphthenic-type materials which are not such good solvents as hydroaromatics. Such over-hydrogenation might occur because of equipment malfunction or because of deliberate or inadvertant alteration of the process conditions, and it has been observed on a pilot plant which uses recycled hydrogen donor solvent that the composition changes and the extraction ability deteriorates. In an attempt to cure this, we have discovered a method of coal extraction which offers a surprising and economically significant improvement in the yields obtainable.
The present invention provides a method of extracting coal at temperature of 400° to 500° C. using a liquid solvent comprising the use of a solvent which is a mixture of a substantially aromatic polycyclic hydrocarbon which contains three and/or four-ring molecules and has minimum boiling point of 270° C. and at least 25% by weight of the aromatic component of a substantially naphthenic polycyclic high-boiling hydrocarbon. Preferably, the aromatic component boils within the range 270° to 360° C., giving predominantly three-ring species. Preferably, the naphthenic component contains predominantly two-and/or three-ring molecules and has a cut-point in the range 180° to 300° C. Although the invention has particular application to a method of extracting coal with continuous recycles of the solvent components, as will be described in more detail hereafter, it also includes the possibility of semi-continuous or intermittent operation within a process using a recycled hydrogen donor solvent, for example to correct an imbalance in the desired properties of the coal solvent. The invention offers flexibility in operation while retaining or improving on extraction efficiency. If the solvent or any component contains an undesirably high level of hydroaromatics, these can be reduced, for example by reaction with coal.
The present invention also provides a method for the extraction of coal in which a recycle solvent is used, comprising the extraction of coal at a temperature of from 400° to 500° C. using a solvent comprising a hydrogenated recycle solvent under conditions at which the solvent remains in the liquid phase, and in the absence of added gaseous hydrogen, in an extraction step, removing from the extract, by distillation, a substantially aromatic polycyclic oil boiling within the range 270° to 360° C., transferring a portion of the remaining liquid extract which does not contain any substantial amount of solids to a hydrocracking reactor, removing from the hydrogenated and hydrocracked product from the reactor an oil boiling in the range 180° to 300° C. which consists of a major proportion of substantially naphthenic polycylic hydrocarbons, and admixing at least a portion thereof with at least a portion of the substantially aromatic oil to form the solvent containing at least 25% by weight of the naphthenic component based on the aromatic oil for the extraction step.
The products from the hydrocracker are passed to a separator to remove gaseous products, including hydrocarbon gases, and are suitably fractionated to give a range of product streams including the desired naphthenic oil for recycle. The other products will include gasoline, naphtha and gas oil fractions and heavier oils boiling in the fuel oil ranges. These product streams may, after possible further processing, including further hydrogenation if necessary, and/or blending and formulation, be used for a wide range of substitute fuels including gasoline, Diesel, jet fuels and furnace oils, as well as feedstocks, such as naphtha, for chemical production, and lubricant oils. The process of the invention is extremely flexible and offers the possibility of concentrating production on one or two product streams depending upon the economics and values of the various products. "
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We'll close our excerpts here, and recap what we understand of this patented technology:
In brief: Some Coal tars can be separated from other Coal liquids after the original hydrogenation step, and prior to the remaining Coal liquids being sent downstream for further refining into "other products". Such products include "gasoline, naphtha and gas oil fractions and heavier oils boiling in the fuel oil ranges" suitable for "further processing" into "a wide range of substitute fuels including gasoline, Diesel, jet fuels and furnace oils". That separated Coal tar, the hydrogenated "naphthenic oil", will be synergistically recycled back into the process to assist in the liquefaction, the "extraction", of additional raw Coal feed.
The primary benefit might be cost savings, in that this Coal liquefaction process can be carried out in the "absence of added hydrogen".
Again, we submit this US Patent primarily to substantiate earlier of our reports, wherein the use of Coal tars and Coal oils to assist in the liquefaction of additional raw Coal was documented.
But, it is also further confirmation that the technologies, complete and well-thought out technologies, exist which would enable us to begin converting our abundant Coal into the liquid fuels we need; thus satisfying that need, and thereby freeing us from our current economic enslavement to largely unfriendly foreign oil powers and avaricious oil corporations.
Moreover, it is further confirmation that our own United States Government, as embodied in the US Patent Office, knows that such technologies exist.