BACKGROUND

Coal tar is one of the liquids derived from coal. Low and mid temperature coal tar is a by-product from semi coke generation during low or mid temperature pyrolysis using young coal, such as lignite, as feed. High temperature coal tar is produced from high temperature pyrolysis of coal for the production of coke for steel industry. Another source of coal tar is the coal gasification process for synthesis gas production. Coal derived liquid can also be generated from direct coal liquefaction. Literature reports that low and mid-temperature coal tars in China have the following compositions: phenols: 20-30% (most single ring alkyl phenols); paraffins/cycloparaffin/olefins: 20-30% (CIO-30); aromatics: 20-40%; pitch: 10-15%; and others (N, S, O containing): about 5%.

Depending on the production methods and sources of coal, the composition and property of coal tar produced could vary in certain range. Phenols, paraffms/olefins, and aromatics are the major groups of components. These three groups of compounds have different functional groups. Therefore, most of their physical and chemical properties differ significantly. It would be ideal to apply appropriate processing conditions according to their unique properties in order to maintain the desire structures of some components and achieve high yield. However, this is not the case in reported inventions. Most often, coal tar is simply split into several fractions by boiling point and processed separately. This is not very helpful because the components in the three groups mentioned above usually distribute across whole boiling range of coal tar. In other words, compounds in the same boiling point fraction have different structures and properties which require corresponding suitable processing conditions.

Many commercial processes or published inventions opt to do a fractionation first, and then process the light fraction (boiling point of less than about 360-370°C) into fuels or chemicals. The heavy fraction is left out as heating fuel or asphalt. Obviously, such methods do not fully utilize coal tar and the heavy fraction is a potential source of pollution.

CN101294107B disclosed a method of producing fuels by hydroprocessing whole coal tar. In this patent, the coal tar feed is first hydrotreated to remove sulfur, nitrogen, and oxygen. Then the hydrotreated material is separated, and the heavy fraction from this stream is hydrocracked. CN101020846 A reported a similar process with different pretreatment and separation steps. Because low and mid temperature coal tars usually contain significant amount of oxygenates such as phenols, subjecting the whole coal tar to hydroprocessing has several disadvantages. First, higher value phenolic compounds will be converted to fuels which often have lower value. Second, removing the oxygen in the phenolic compounds will consume huge amount of precious hydrogen. Third, water formed from the hydrogenation has the potential to damage the catalyst and special catalyst formulations will be needed for robustness.

Some reported processes subject the whole coal tar or part of the coal tar to delayed coking. In the process disclosed in CN204151302U, some extra effort is devoted to appreciating the feed properties. Phenols are separated from coal tar first. The rest is processed with various kinds of hydrocrackings. Heavy oil from these cracking units is sent to delayed coking. As long as delayed coking is used, a certain amount of carbon in the coal tar feed which could be converted to targeted products, such as aromatics, is converted into coke.

CN101885982B described a coal tar hydroprocessing method using a heterogeneous catalyst in an ebullating bed reactor. The coal tar is split into three fractions with boiling points of lower than about 260°C, about 260 to about 370°C, and greater than about 360°C. Phenolic compounds in the boiling range lower than about 260°C are first removed. Heavy oil (boiling point higher than about 360°C) is hydrocracked in an ebullating bed reactor into light oil, which is combined with the dephenolic oil from the first fraction and the second fraction (boiling point of about 260 to about 370°C) for hydrotreating to upgrade to final fuel products. From the coal tar composition mentioned above, it can be seen that there are substantial quantities of nitrogen and sulfur compounds in addition to oxygen compounds. The issue here is that coal tar normally contains a much higher content of nitrogen and a much lower content of sulfur than petroleum oil. If the coal tar is fed to a hydrocracker without hydrotreating, these nitrogen compounds and metals in the coal tar will deactivate the hydrocracking catalyst quickly. Furthermore, the hydrocracker often requires severe reaction condition to achieve acceptable conversion, which will result in a high yield of low value light gas (C1-C4 hydrocarbons) due to non-selective cracking. Special reactor design may also be necessary to maintain stable operation.

Therefore, there is a need for improved processes for treating coal derived liquids.

BRIEF DESCRIPTION OF THE DRAWING

The Figure illustrates one embodiment of the process of the present invention.

SUMMARY AND DETAILED DESCRIPTION

The present process is designed to separate the components in coal derived liquids, such as coal tar, into three groups according to their polarity and molecular structure besides boiling point. The appropriate conditions are then applied to process these groups in order to maximize the yield of chemicals (phenols, aromatics) and/or transportation fuels (gasoline, diesel, etc.) and catalyst life while minimizing the consumption of hydrogen, lowering the severity of reaction conditions, and simplifying operations.

As used herein, the term “naphtha” means hydrocarbon compounds having an initial boiling point (IBP) of about 35°C and a final boiling point (FBP) of about 200°C at atmospheric pressure, and containing between about 4 and about 11 carbon atoms. As used herein, the term “diesel” means hydrocarbon compounds having boiling points between about 200°C (392°F) and about 350°C (662°F) at atmospheric pressure, and containing between about 9 and about 25 carbon atoms.

As used herein, the term “heavy compounds” means hydrocarbon compounds having boiling points above about 350°C (662°F) at atmospheric pressure, and containing more than about 25 carbon atoms.

As used herein, the term “zone” means an area including one or more equipment items and/or one or more sub-zones. Equipment items can include, but are not limited to, one or more reactors or reactor vessels, separation vessels, distillation towers, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones.

As used herein, the term “about” means within 10% of the specified value, or within 5%, or within 1%.

One aspect of the invention is a process for processing coal derived liquid. In one embodiment, the process comprises: separating a coal derived liquid feed stream into a polar stream comprising polar compounds and a non-polar stream comprising non-polar compounds; fractionating the polar stream in a first fractionation zone into a first stream comprising components having boiling points lower than or equal to a specified temperature and a second stream comprising components having boiling points higher than the specified temperature; and separating the first stream into a phenolic stream comprising phenols and a non- phenolic stream comprising hydrocarbons.

In some embodiments, separating the coal derived liquid feed stream comprises separating the coal derived liquid feed stream by one or more of extraction, absorption, extractive distillation, crystallization, or membrane separation.

In some embodiments, separating the first stream comprises: washing the first stream with a base to obtain an aqueous stream containing phenolic salt and the non-phenolic stream; neutralizing the aqueous stream with an acid; and separating the neutralized aqueous stream into the phenolic stream and a second aqueous stream containing a salt formed by the base and the acid.

In some embodiments, the process further comprises: hydroprocessing the non-phenolic stream in a first hydroprocessing zone to form a hydroprocessed non-phenolic stream; and fractionating the hydroprocessed non-phenolic stream in a second fractionation zone into at least one of: a naphtha stream comprising naphtha, a diesel stream comprising diesel, or a heavy stream comprising heavy compounds.

In some embodiments, the process further comprises at least one of: passing the naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; passing the diesel stream to a diesel pool; or recycling the heavy stream to a hydrocracking zone.

In some embodiments, the process further comprises: passing the naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; and recycling an aromatic complex recycle stream comprising heavy compounds with 11 and more carbons from the aromatics complex to a hydrocracking zone.

In some embodiments, the process further comprises: hydrotreating and hydrocracking the second stream in a second hydroprocessing zone to form a hydroprocessed second stream; and fractionating the hydroprocessed second stream in a third fractionation zone into at least one of: a naphtha stream comprising naphtha, a diesel stream comprising diesel, or a heavy stream comprising heavy compounds.

In some embodiments, the process further comprises at least one of: passing the naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; passing the diesel stream to a diesel pool; or recycling the heavy stream to a hydrocracking zone.

In some embodiments, the process further comprises: passing the naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; and recycling an aromatic complex recycle stream comprising heavy compounds with 11 and more carbons from the aromatics complex to a hydrocracking zone in the second hydroprocessing zone. In some embodiments, the process further comprises: hydrotreating the non-polar stream.

In some embodiments, the process further comprises: fractionating the hydrotreated non-polar stream in a fourth fractionation zone into at least one of: a naphtha stream comprising naphtha, a diesel stream comprising diesel, or a heavy stream comprising heavy compounds.

In some embodiments, the process further comprises at least one of: passing the naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; passing the diesel stream to a diesel pool; or hydrocracking the heavy stream and recycling the hydrocracked heavy stream to the fourth fractionation zone.

In some embodiments, the process further comprises: hydroprocessing the non-phenolic stream in a first hydroprocessing zone to form a hydroprocessed non-phenolic stream; hydrotreating and hydrocracking the second stream in a second hydroprocessing zone to form a hydroprocessed second stream; fractionating the hydroprocessed non-phenolic stream and the hydroprocessed second stream in a second fractionation zone into at least one of: a first naphtha stream comprising naphtha, a first diesel stream comprising diesel, or a first heavy stream comprising heavy compounds.

In some embodiments, the process further comprises at least one of: passing the first naphtha stream to an aromatics complex to produce one or more of benzene or xylenes; passing the first diesel stream to a diesel pool; or recycling the first heavy stream to a hydrocracking zone in the second fractionation zone.

In some embodiments, the process further comprises: hydrotreating the non-polar stream; fractionating the hydrotreated non-polar stream in a third fractionation zone into at least one of: a second naphtha stream comprising naphtha, a second diesel stream comprising diesel, or a second heavy stream comprising heavy compounds; and at least one of: passing the second naphtha stream to the aromatics complex to produce one or more of benzene or xylenes; passing the second diesel stream to the diesel pool; or hydrocracking the second heavy stream and recycling the hydrocracked heavy stream to the third fractionation zone. In some embodiments, the specified temperature is a temperature in a range of about 240°C to about 360°C. A temperature of about 240°C to about 260°C will allow recovery of most of single ring phenols, while a temperature of about 340°C to about 360°C will allow recovery of heavier phenols such as naphthols in addition to the single ring phenols.

Although the process is described below for use with coal tar for the sake of convenience, those of skill in the art will recognize that it can also be other coal derived liquids, including, but not limited to, the liquid generated by the coal liquefaction process.

The Figure illustrates one embodiment of the process 100 of the present invention.

The coal tar feed stream 105 is separated in a separator 110 into polar stream 115 comprising polar compounds, and non-polar stream 120 comprising non polar compounds. Polar stream 115 typically contains less than about 10% non-polar compounds, or less than about 5%, or less than about 1%, or less than about 0.1%. Polar compounds include, but are not limited to, phenols and aromatics. Non-polar stream 120 typically contains less than about 10% polar compounds, or less than about 5%, or less than about 1%, or less than about 0.1%. Non-polar compounds include, but are not limited to, paraffins, olefins, and cycloparaffms.

The coal tar feed stream 105 can be pretreated to remove water and ash, as is known in the art.

The separation of the coal tar feed stream 105 can be accomplished using known technologies including, but not limited to, one or more of extraction, absorption, extractive distillation, crystallization, or membrane separation.

The polar stream 115 is then fractionated in the first fractionation zone 125 into a first stream 130 comprising components having boiling points lower than or equal to a specified temperature and a second stream 135 comprising components having boiling points higher than the specified temperature. This temperature is selected to be the temperature at which the most of the desired phenols will be separated. In some embodiments, the specified temperature is in the range of about 340°C to about 360°C, or about 350°C to about 360°C, or about 340°C to about 350°C.

The first stream 130 is separated in a phenolic separation zone 140 into a phenolic stream 145 comprising phenol-containing compounds and a non-phenolic stream 150 containing non-phenolic compounds. The phenolic stream 145 typically contains less than 1% non-phenolic compounds, or less than 0.5%, or less than 0.1%. The non-phenolic stream 150 typically contains less than 10% phenolic compounds, or less than 5%, or less than 1%, or less than 0.1%. The separation of the first stream 130 into the phenolic stream 145 and non-phenolic stream 150 can be accomplished using any suitable process. Suitable processes include, but are not limited to, acid- base neutralization, liquid-liquid extraction, reactions with reagents (e.g., quaternary ammonium salts, such as 2-hydroxy-N,N,N-trimethyl-ethanaminium chloride and N,N,N-triethyl-ethanaminium chloride), crystallization, and adsorption.

One method involves a base wash followed by acid neutralization. In this method, the first stream 130 is washed with a base to obtain the non-phenolic stream 150 and an aqueous stream containing phenolic salts. The aqueous stream is neutralized with an acid, and separated into the phenolic stream 145 and a second aqueous stream containing the salts formed by the base and the acid.

The phenolic stream 145 can be further processed (not shown) to obtain pure phenol, cresols, xylenols, and other heavy phenols using known methods.

The non-phenolic stream 150 is hydroprocessed (hydrotreated only or hydrotreated and hydrocracked) in the first hydroprocessing zone 155 to form a hydroprocessed non-phenolic stream 160. Typical hydroprocessing conditions include a temperature in the range of about 150°C to about 510°C, a pressure of about 340 kPa(g) to about 6.9 MPa(g), LHSV of about 0.1 hr ¹ to about 30 hr ¹ , and a hydrogen gas rate of about 500 SCF/B to about 10,000 SCF/B.

The hydroprocessed non-phenolic stream 160 can be sent to the second fractionation zone 165. The second fractionation zone 165 can separate the hydroprocessed non-phenolic stream 160 into one or more of light stream 170, naphtha stream 175, diesel stream 180, and heavy stream 185. Light stream 170, which comprises compounds with boiling points below naphtha, can be further processed as desired. For example, the light stream 170 can be processed to recover hydrogen which can be recycled to first hydroprocessing zone 155. The rest of light stream 170 can be used as fuel gas or sent to an ethane cracker to produce light olefins, for example.

Naphtha stream 175 can be sent to an aromatics complex 190 for processing to produce one or more product streams 195. Product streams 195 can include one or more of a benzene stream, a xylene stream (para-xylene, meta-xylene, ortho-xylene, or combinations thereof), an ethylbenzene stream, or streams of derivatives from these compounds, such as cumene, styrene, phenol.

Diesel stream 180 can be sent to diesel pool 200.

Second stream 135 can be sent to a second hydroprocessing zone 205 to form a hydroprocessed second stream 210. The second hydroprocessing zone 205 will typically include both hydrotreating and hydrocracking, although this is not required in all situations. The hydroprocessed second stream 210 is sent to the second fractionation zone 165 and separated into one or more of light stream 170, naphtha stream 175, diesel stream 180, and heavy stream 185, as discussed previously.

Heavy stream 185 can be recycled to the hydrocracking zone in the second hydroprocessing zone 205. Alternatively, it could be sent to a stand-alone hydrocracking zone (not shown).

Aromatics complex recycle stream 215 can be recycled to the hydrocracking zone in the second hydroprocessing zone 205, the hydrocracking zone in another hydroprocessing zone, or a stand-alone hydrocracking zone.

As shown, second fractionation zone 165 receives both the hydroprocessed non-phenolic stream 160 and the hydroprocessed second stream 210. Alternatively, there could be separate fractionation zones for each stream in order to maximize specific products.

Non-polar stream 120 is sent to a hydrotreating zone 220. The hydrotreated non-polar stream 222 is sent to a third fractionation zone 225 where it is separated into one or more of light stream 227, naphtha stream 230, diesel stream 235, and heavy stream 240. Light stream 227 comprises compounds with boiling points below naphtha. It can be combined with light stream 170 and processed as described above, or processed separately, as desired.

Naphtha stream 230 can be sent to an aromatics complex 190 or another aromatics complex (not shown). Diesel stream 235 can be sent to diesel pool 200 or another diesel pool (not shown).

Heavy stream 240 can be sent to hydrocracking zone 245, and the hydrocracked heavy stream 250 can be recycled to the third fractionation zone 225.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.