Patent Application
20080072476
Not Applicable
Not Applicable
1. Field of Invention
This invention relates to a method of obtaining and refining coal liquids and incorporating them in transportation fuels that also contain alcohols.
2. Description of the Prior Art
Ethanol is used as a transportation fuel worldwide, often as a substitute for gasoline. In the US, a number of processes have been used to create ethanol. The main sources have been the fermentation of agricultural products such as corn, switchgrass, etc. However, ethanol is generally not compatible with certain polymeric seal materials, due to the low content of aromatic liquids.
Coal derived fuels are of interest due to the possible future lack of availability of petroleum products, and the rising cost of petroleum on world markets. Coal is inexpensive and widely available in North America. However, coal derived liquids are generally too aromatic and have slow kinetics resulting in significant pollution. Furthermore, aromatic coal liquids often are poorly soluble in gasoline and become tarry in the presence of gasoline. For these reasons coal liquids have not supplanted petroleum as the fuel source of choice for automotives and many other applications.
Alcohols, such as ethanol and others can also be considered as alternative fuels. Alcohols burn cleanly due to their excellent combustion kinetics. However, the lack of aromaticity of alcohol results in compatibility problems with polymer seals. These seals are generally designed to swell in the presence of aromatic liquids. The result is a tighter seal. Another issue is that alcohols have a lower energy density (i.e., joules per kg) than gasoline. Alcohols can be obtained from a number of processes including biomass processes as well as fossil fuel processes. Generally, however, alcohols are more expensive than liquids derived from petroleum or coal.
In Golubkov et al. U.S. Pat. No. 7,014,688 it was disclosed that motor fuels can be created with reduced levels of pollutants by combining two types of organic compounds. One of the organic compounds contains at least four types of oxygen-containing functional groups. The method of '688 disclosed results in diesel, gas-turbine fuel and turbojet engine fuel, but not gasoline. The present invention specifically includes gasoline fuels. In addition, the present invention can use a single alcohol, such as ethanol or methanol. The alcohol can be considered to be a single functional group as opposed to at least four types of oxygen-containing functional groups in '668. Also the coal derived hydrocarbon fraction is separate from this function.
U.S. Pat. No. 6,712,866 teaches that hydrocarbon gas, present in coal mines and known as coal gas, can be liquefied and dissolved in alcohol with the aid of a co-solvent. The present invention utilizes heavier hydrocarbons without the aid of a co-solvent. The present invention also uses coal liquids which are not coal gas liquids. The resulting fuel of the '866 patent has zero aromatic content, whereas the coal liquids in the present invention have significant aromatic content.
The present invention provides for the use of coal liquid fuels as an alternative to gasoline and other fuels. The coal liquids can be obtained by distilling a solvent extraction of coal. In addition, the steps of delayed coking, hydrothermal cracking, hydrodelalkylation, and catalytic cracking and other refining techniques can be used to break down molecules in the coal liquids and convert aromatic molecules to aliphatic molecules.
Another aspect of the present invention is the use of the coal liquids as a replacement for petroleum to make a gasoline substitute similar to Ethanol-85. The coal liquid gasoline substitute is comprised of about 85% ethanol and about 15% coal-derived counterparts.
A further aspect of the present invention is the blending of coal liquids in alcohol to create a motor fuel with a high octane rating. The coal liquids are highly soluble in alcohol and the combustion efficiency of ethanol enhances combustion of the coal liquids and thus minimizes the emission of aromatic partially-combusted hydrocarbons in the exhaust.
It is an object of the present invention to provide for methods of treating coal liquids to create a more aliphatic and less aromatic liquid.
It is a further object of the present invention to provide a method of solvent extraction for coal liquids to be processed for use as a petroleum replacement in a coal liquid gasoline substitute.
Another aspect of this invention is the use of Fischer-Tropsch liquids in place of the alcohol, while using direct-liquefied coal liquids as blending agents. The resulting fuel may be used as gasoline, jet fuel, diesel fuel, home heating oil or other liquid fuel.
The invention relates to the ability to make a gasoline substitute similar to Ethanol-85, composed of about 85% ethanol and about 15% petroleum, with the petroleum components replaced with coal-derived counterparts. Coal derived is the use of any source of coal such as coal tar, liquefied coal, or other coal liquids. Coal liquids are much more soluble in ethanol than in gasoline and ethanol is clean burning which helps to prevent unburned aromatic hydrocarbons from persisting in the exhaust. This result is due to the combustion efficiency of ethanol which minimizes the emission of aromatic partially-combusted hydrocarbons found in the exhaust.
Coal liquids can optionally be blended with 10-95% alcohol to create a motor fuel with high octane rating and compatible combustion kinetics. In a blend, a higher percentage content of aromatic molecules can be tolerated from the coal liquids, than would be the case if coal liquids were the only component used. Coal liquids are highly soluble in alcohol. Moreover, the high energy density of coal liquids acts to increase the energy density of the blend. The aromatic content of coal liquids enables the blend to be compatible with polymer seals. In addition, although the coal liquids are inherently slow burning, they are combusted more rapidly in the presence of a combusting alcohol. Hence the combination of coal liquids and ethanol is much more favorable than either component used in its pure state or blended with gasoline alone.
Because E-85 (85% ethanol, 15% petroleum) is being introduced as a domestic US motor fuel, a coal based counterpart, CE-85 (85% ethanol, 15% coal liquids) is sought as a non-petroleum derived motor fuel. With additional processing to reduce the ratio of the number of aromatic molecules to the number of aliphatic molecules, a higher percentage of coal-derived liquids can be realized.
Coal liquids are mainly derived from the distillation of coal tar. Coal tar is produced as a byproduct of metallurgical coke production. This occurs when coal is heated in a non-oxidizing environment producing condensible vapors that can be recovered as coal tar. Coal tar distillates can be incorporated in liquid fuels directly, but generally must be made less aromatic and more aliphatic. These upgrading processes can include one or more processes chosen from the list comprising: delayed coking, hydrothermal cracking, hydrodelalkylation, hydrodesulphurization, steam cracking, catalytic cracking and distillation. The result is to break down the aromatic chains into smaller units that are also more aliphatic. Aliphatic chains are able to burn more rapidly, and are less likely to from toxic byproducts.
In addition to obtaining coal liquids from coal tar, the coal liquids of the present invention can be obtained via a direct liquefaction process in which an effective amount of hydrogen is used to enhance the solubility of an effective amount of coal in an effective amount of a carrier solvent. The solvent can then be used to dissolve coal in a manner common to one skilled in the art. The carrier solvent can be one or more of an aromatic heavy oil such as coal tar distillate, decant oil from petroleum refining, or other oil that contains compounds such as naphthalene or three-ringed aromatic molecules such as acenaphthene, phenanthrene, fluorene, anthracene or others. Insoluble solids are removed from the resultant coal solution using a separation process such as centrifugation, filtration, or any other standard separation product known to one skilled in the art. The resulting product is a liquid hydrocarbon that can be processed in much the same way as coal tar and its distillates.
A variant of the direct liquefaction process is used to produce a hydrocarbon liquid from which fuels, pitches and cokes can be derived, as shown in
The extraction yield, the mass of coal that can be dissolved in solution divided by the total mass of the input coal feedstock, can be significantly increased by hydrogenating a portion of the coal tar distillate oil or other solvent. Hydrogenation can be accomplished in the presence of a catalyst at temperatures between about 350° C. and about 550° C. and pressure of at least 700 psig, although 1500 or higher psig is preferred. A pound of catalyst can be sufficient to hydrogenate at least 1000 pounds of solvent. The catalyst can be any commercial catalyst used for hydrogenation such as nickel-molybdenum or any hydrogenation catalyst that would be recognized by one skilled within the art. The hydrogenated solvent may also be blended with non-hydrogenated solvent by any technique known to one skilled within the art. The result is less volume of liquid required in the hydrogenation process and a high extraction yield. The amount of non-hydrogenated solvent can range from zero to approximately ten times the amount of hydrogenated solvent. The blended solvent is then used to incorporate coal. It has been found that overall hydrogenation levels of the aromatic oil, after blending, of a few tenths of a percent by weight is sufficient to result in increasing the solubility of several bituminous, sub-bituminous and lignite coals to about 90% in said oil on a dry, ash-free basis. The reason for blending is to avoid the cost of hydrogenating the entire quantity of solvent. As in non-blended methods, coal is then added to the solvent at a ratio of at least one part solvent to one part coal, with a ratio of about 2.5 parts solvent to one part coal preferred in order to avoid overly high viscosity. The coal can optionally be dried and/or crushed to enhance its solubility. During digestion, the slurry of coal and solvent thus formed is then subjected to high temperature in a chemical reactor. A minimum of 350° C. is required, with 415° C. preferred. High pressure is not required, although the boiling pressure of the slurry is usually several hundred psig at this temperature. After a period of five minutes to one hour, approximately 50% to 90% of the coal is digested and dissolved in the solvent. This slurry with reduced solids content can then be filtered or centrifuged to remove the remaining insoluble matter.
The tails from the solids separation step can optionally be further processed. For example thermal processing such as thermocracking or delayed coking can liberate liquid fuels and gaseous fuels, while leaving a residue rich in carbon as well as mineral matter (ash). The liquid fraction from the separation step thus contains less than 1% solids. The liquid fraction can be distilled into at least two fractions. The lighter fraction(s) can be recycled for use as coal solvent, or optionally can be used to produce fuels and chemicals. The residue from the distillation process can be a pitch material used for applications such as binder pitch or impregnation pitch, both of which are used to make carbon composites for metals smelting applications. Alternatively, the residue from the distillation process can undergo thermal processing such as the residue can be placed in a delayed coker (also referred to as a thermocracker) or the residue can undergo catalytic cracking, thermocracking, or hydrocracking. High temperatures, typically between 400° C. and 600° C. liberate lighter molecules in the form of gas or condensible vapors, leaving behind a solid non-melting residue that is mostly carbon that can be referred to as a coke. This coke is referred to as a “green coke” in industry jargon, and can be further treated at a temperature of 1000° C. to 1400° C. to produce anode grade coke or needle grade coke. The condensed liquids can be used as liquid fuels or chemicals.
After the removal of the solid phase, the resulting coal liquid can be optionally further refined via distillation and/or other refining processes such as thermocracking, or upgrading which includes one or more of catalytic cracking, thermocracking, hydrocracking, hydrotreatment, hydrogenation, distillation and combinations of these processes to modify its properties, potentially resulting in enhanced properties for use in fuels. The resulting product is combined with a coal (lignite, sub-bituminous, or bituminous) and heated to about 350-500° C. in order to dissolve the coal. Insoluble mineral matter and fixed carbon are removed via centrifugal separation or filtration, thus resulting in a coal solution. This coal solution is distilled, resulting in a heavier fraction that can be used as a pitch or coke precursor, and a lighter fraction that can be recycled as a coal solvent or further refined for use to produce standard finished fuel products such as gasoline, diesel, aviation fuel, heating oil, etc. as a fuel or fuel additive. These further refining techniques are well known to practitioners of petroleum refining, and include catalytic cracking, thermocracking, hydrocracking, hydrotreatment, hydrogenation, distillation and combinations of these processes.
A variation of the present invention results in a gasoline, diesel or jet fuel using Fischer-Tropsch liquids in place of the alcohol, while using direct-liquefied coal liquids as blending agents for example in a blend of 85% or less Fischer Tropsch Liquids with 10% or more coal liquids and the remainder optionally being derived from petroleum. The Fischer-Tropsch process reacts methane or gasified coal with air over a catalyst to create synthesis gas, which is a mixture of carbon monoxide and hydrogen. Using another catalyst, the synthesis gas is then converted to a mixture of liquid hydrocarbons. The second catalyst is a commercial catalyst based upon iron or cobalt. The present invention does not involve the production of synthesis gas or conversion of synthesis to liquids, but instead involves producing coal liquids via mild direct liquefaction which can then be blended with Fischer-Tropsch liquids to produce a substitute kerosene or jet fuel.
These terms and specifications, including the examples, serve to describe the invention by example and not to limit the invention. It is expected that others will perceive differences, which, while differing from the forgoing, do not depart from the scope of the invention herein described and claimed. In particular, any of the function elements described herein may be replaced by any other known element having an equivalent function.
This application claims priority to provisional application No. 60/841,624 filed on Aug. 31, 2006.
| Number | Date | Country | |
|---|---|---|---|
| 60841624 | Aug 2006 | US |
