Patent Application
20150136650
Many different types of chemicals are produced from the processing of petroleum. However, petroleum is becoming more expensive because of increased demand in recent decades.
Therefore, attempts have been made to provide alternative sources for the starting materials for manufacturing chemicals. Attention is now being focused on producing liquid hydrocarbons from solid carbonaceous materials, such as coal, which is available in large quantities in countries such as the United States and China.
Pyrolysis of coal produces coke and coal tar. The coke-making or “coking” process consists of heating the material in closed vessels in the absence of oxygen to very high temperatures. Coke is a porous but hard residue that is mostly carbon and inorganic ash, which is used in making steel.
Coal tar is the volatile material that is driven off during heating, and it comprises a mixture of a number of hydrocarbon compounds. It can be separated to yield a variety of organic compounds, such as benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These organic compounds can be used to make numerous products, for example, dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the separation is used for paving, roofing, waterproofing, and insulation.
The products from the coal tar often contain undesirable compounds, such as mercury, which must be removed.
Thus, there is a need for improved processes for removing mercury from coal tar products.
One aspect of the invention is a process for removing mercury from a coal tar product. In one embodiment, the process includes providing a coal tar stream. The coal tar stream is contacted with a solvent in a solvent extraction zone to remove at least one product from the coal tar stream forming at least one product stream and a remainder coal tar stream, the at least one product stream containing one or more of elemental mercury, organic mercury compounds, and inorganic mercury compounds. The at least one product stream is contacted with an adsorbent material in an mercury removal zone, the adsorbent material comprising one or more adsorbents, an ion exchange resin, or mixtures thereof to remove the one or more of elemental mercury, organic mercury compounds, and inorganic mercury compounds. The remainder coal tar stream is separated into at least two fractions.
In another embodiment, the process includes providing a coal tar stream, the coal tar stream containing one or more of elemental mercury, organic mercury compounds, and inorganic mercury compounds. The coal tar stream is introduced into a catalytic distillation zone of a fractionation zone to separate the coal tar stream into at least two fractions, the catalytic distillation zone positioned above the bottoms outlet and below the first product draw of the fractionation zone, the catalytic distillation zone containing a catalyst, the organic and ionic mercury compounds reacting in the presence of the catalyst to form elemental mercury in the reactive fractionation zone. At least one of the fractions is treated to remove the elemental mercury.
In the coking oven zone 15, the coal is heated at high temperature, e.g., up to about 2,000° C. (3600° F.), in the absence of oxygen to drive off the volatile components. Coking produces a coke stream 25 and a coal tar stream 30. The coke stream 25 can be used in other processes, such as the manufacture of steel.
The coal tar stream 30 which comprises the volatile components from the coking process can be sent to an optional contaminant removal zone 35, if desired.
The contaminant removal zone 35 for removing one or more contaminants from the coal tar stream or another process stream may be located at various positions along the process depending on the impact of the particular contaminant on the product or process and the reason for the contaminant's removal, as described further below. For example, the contaminant removal zone can be positioned upstream of the separation zone 45. Some contaminants have been identified to interfere with a downstream processing step or hydrocarbon conversion process, in which case the contaminant removal zone 35 may be positioned upstream of the separation zone 45 or between the separation zone 45 and the particular downstream processing step at issue. Still other contaminants have been identified that should be removed to meet particular product specifications. Where it is desired to remove multiple contaminants from the hydrocarbon or process stream, various contaminant removal zones may be positioned at different locations along the process. In still other approaches, a contaminant removal zone may overlap or be integrated with another process within the system, in which case the contaminant may be removed during another portion of the process, including, but not limited to the separation zone or the downstream hydrocarbon conversion zone. This may be accomplished with or without modification to these particular zones, reactors or processes. While the contaminant removal zone is often positioned downstream of the hydrocarbon conversion reactor, it should be understood that the contaminant removal zone in accordance herewith may be positioned upstream of the separation zone, between the separation zone and the hydrocarbon conversion zone, or downstream of the hydrocarbon conversion zone or along other streams within the process stream, such as, for example, a carrier fluid stream, a fuel stream, an oxygen source stream, or any streams used in the systems and the processes described herein. The contaminant concentration is controlled by removing at least a portion of the contaminant from the coal tar stream 30. As used herein, the term removing may refer to actual removal, for example by adsorption, absorption, or membrane separation, or it may refer to conversion of the contaminant to a more tolerable compound, or both.
The decontaminated coal tar stream 36 from the contaminant removal zone 35 is sent to a solvent extraction zone 37.
In the solvent extraction process, a solvent stream 38 is introduced into the solvent extraction zone 37 and contacts the decontaminated coal tar stream 36. At least one product 39 containing one or more of elemental mercury, organic mercury compounds, and inorganic mercury compounds is removed from the decontaminated coal tar stream 36.
The solvents used in the solvent extraction process can include, but are not limited to, supercritical fluids, ionic liquids, polar solvents, and combinations thereof.
Supercritical fluids are substances at a temperature and pressure above the critical point, where distinct liquid and gas phases do not exist. They have properties of both liquids and vapors. Suitable supercritical fluids include, but are not limited to, supercritical carbon dioxide, supercritical ammonia, supercritical ethane, supercritical propane, supercritical butane, and supercritical water.
Ionic liquids are non-aqueous, organic salts composed of ions where the positive ion is charge balanced with a negative ion. These materials have low melting points, often below 100° C., undetectable vapor pressure, and good chemical and thermal stability. The cationic charge of the salt is localized over hetero atoms, such as nitrogen, phosphorous, sulfur, arsenic, boron, antimony, and aluminum, and the anions may be any inorganic, organic, or organometallic species. Suitable ionic liquids include, but are not limited to, imidazolium-based ionic liquids, pyrrolidinium-based ionic liquids, pyridinium-based ionic liquids, sulphonium-based ionic liquids, phosphonium-based ionic liquids, ammonium-based and caprolactam-based ionic liquids, and combinations thereof.
Suitable polar solvents include, but are not limited to, pyridine, N-methyl pyrrolidone, methylene chloride, benzyl alcohol, formamide, dimethylformamide, dimethylsulfoxide, dimethylsuccinate, dimethyladipate, dimethylglutarate, propylene carbonate, methyl soyate, ethyl lactate, tripropylene glycol (mono)methyl ether 1,3-dioxolane, and combinations thereof.
Alternatively, the extraction/adsorption zone described in U.S. application Ser. No. 61/905,898, entitled Process for Removing a Product from Coal Tar, filed Nov. 19, 2013 (Attorney Docket No. H0042311), which is incorporated herein by reference, could be used in place of the solvent extraction zone 37, if desired.
The products 39 from the solvent extraction process include, but are not limited to, hydrocarbons that distill in the range of approximately 0° C. to 350° C. Depending upon the solvent used, the predominant functional groups may be heterocyclic aromatic, naphthenic or paraffinic, and may be ionic or neutral, acidic, or basic.
The product(s) 39 containing the elemental mercury, organic mercury compounds, and inorganic mercury compounds is sent to a separation zone 110 where a solvent stream 120 is separated from the product 115 containing the elemental mercury, organic mercury compounds, and inorganic mercury compounds. The solvent stream 120 can be recycled to the solvent extraction zone 37, if desired.
When organic mercury compounds are present, the product(s) 115 can be sent to an optional conversion zone 125 where the organic mercury compounds are converted to elemental mercury or inorganic mercury compounds. Suitable conversion processes include, but are not limited to, catalytic or thermal decomposition, catalytic reaction with hydrogen, reduction by transfer hydrogenation, precipitation with sulfide sources or elemental sulfur, and oxidation followed by reduction.
In one embodiment, the product(s) 115 containing the elemental mercury, organic mercury compounds, and inorganic mercury compounds is subjected to hydroprocessing to convert the organic mercury compounds to inorganic or elemental mercury, followed by passage through a multi-layer bed for removal of more than one type of contaminant. Other contaminants may also be converted to a form that is more easily removed by adsorption.
In another embodiment, the product(s) 115 containing the elemental mercury, organic mercury compounds, and inorganic mercury compounds is subjected to thermal processing at a temperature from about 100° C. to about 900° C. in accordance with the teachings found in U.S. Pat. No. 5,510,565 incorporated herein in its entirety. Organic mercury and other impurities are broken down to a form that is easier to remove by adsorption.
Alternatively, the separation zone 110 can be located after the conversion zone 125, if desired. However, the separation zone 110 is desirably positioned before the conversion zone 125 because removing the solvent first would result in less material being processed in the conversion zone 125.
The effluent 130 from the conversion zone 125 comprising the product(s) containing the elemental mercury, inorganic mercury compounds (whether original or converted organic mercury compounds (if present)), and any unconverted organic mercury compounds is sent to a mercury removal zone 135. The effluent 130 is contacted with an adsorbent material in the mercury removal zone 135 to remove the elemental mercury and inorganic mercury compounds (whether original or converted organic mercury compounds (if present)). A stream 140 of elemental mercury and inorganic mercury compounds is removed from the mercury removal zone 135 and further treated and/or recovered, if desired. The product(s) 145 with a reduced mercury level is then recovered.
The elemental mercury and inorganic mercury compounds may be removed by adsorption, typically with transition metal sulfides, such as copper sulfide, or sulfur on activated carbon, activated aluminas, silica gel or molecular sieves. In addition, supported noble metals such as silver, palladium or platinum on molecular sieves or aluminas can be used. Certain zeolite/alumina hybrid adsorbents may also be used. The zeolites that can be used include, but are not limited to, faujasites (13X, CaX, NaY, CaY, ZnX), chabazites, clinoptilolites and LTA (3A, 4A, 5A) zeolites. Other adsorbents may be used including transition metals (such as, copper, lead, antimony, manganese) oxides and carbonates in hydrocarbon streams that may contain sulfur compounds to convert the metals to a sulfide form that is active for mercury removal.
Another type of layer for mercury removal that is effective in the practice of the present invention is sulfides of transition metals, such as copper, silver, gold, lead, antimony and manganese.
Ion exchange materials may be used to remove mercury compounds. Ion exchange materials include, but are not limited to, ion exchange resins and inorganic ion exchange materials. The ion exchange material can be an anionic exchange material or a cationic exchange material. One suitable adsorbent is an ion exchange resin that contains chemically bound sulfide groups.
In some cases when the product(s) also contain H2S or organic sulfur compounds, the oxide or carbonate forms of the metals may be used to sulfide the metal in the adsorbent bed insitu and make it active for mercury removal. This method of mercury scavenging may be used effectively for simultaneous removal of sulfur compounds and mercury.
In some case, the adsorbent is sulfur or a metal sulfide on an activated carbon support or an activated alumina support or other supports, such as clays, to bind the active reagents for mercury removal in the form of beads or pellets.
In some embodiments, at least two products 39 are removed from the decontaminated coal tar stream 36. The first product can be removed using a first solvent, and then the second product can removed using a second solvent, if desired.
The decontaminated coal tar feed 40 with at least one product removed is sent to a separation zone 45 where it is separated into two or more fractions. Coal tar comprises a complex mixture of heterocyclic aromatic compounds and their derivatives with a wide range of boiling points. The number of fractions and the components in the various fractions can be varied as is well known in the art. A typical separation process involves separating the coal tar into four to six streams. For example, there can be a fraction comprising NH3, CO, and light hydrocarbons, a light oil fraction with boiling points between 0° C. and 180° C., a middle oil fraction with boiling points between 180° C. to 230° C., a heavy oil fraction with boiling points between 230 to 270° C., an anthracene oil fraction with boiling points between 270° C. to 350° C., and pitch.
The light oil fraction contains compounds such as benzenes, toluenes, xylenes, naphtha, coumarone-indene, dicyclopentadiene, pyridine, and picolines. The middle oil fraction contains compounds such as phenols, cresols and cresylic acids, xylenols, naphthalene, high boiling tar acids, and high boiling tar bases. The heavy oil fraction contains benzene absorbing oil and creosotes. The anthacene oil fraction contains anthracene. Pitch is the residue of the coal tar distillation containing primarily aromatic hydrocarbons and heterocyclic compounds.
As illustrated, the coal tar feed 40 is separated into gas fraction 50 containing gases such as NH3 and CO as well as light hydrocarbons, such as ethane, hydrocarbon fractions 55, 60, and 65 having different boiling point ranges, and pitch fraction 70.
Suitable separation processes include, but are not limited to fractionation, crystallization, and inclusion compound formation.
One or more of the fractions 50, 55, 60, 65, 70 can be further processed, as desired. As illustrated, fraction 60 can be sent to one or more hydrocarbon conversion zones 75, 80. For example, where hydrocarbon conversion zone 80 includes a catalyst which is sensitive to sulfur, fraction 60 can be sent to hydrocarbon conversion zone 75 for hydrotreating to remove sulfur and nitrogen. Effluent 85 is then sent to hydrocarbon conversion zone 80 for hydrocracking, for example, to produce product 90.
Suitable hydrocarbon conversion zones include, but are not limited to, hydrotreating zones, hydrocracking zones, transalkylation zones, selective hydrogenation or complete hydrogenation zones, oxidation zones, and thermal conversion zones.
Hydrotreating is a process in which hydrogen gas is contacted with a hydrocarbon stream in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. Typical hydrotreating reaction conditions include a temperature of about 290° C. (550° F.) to about 455° C. (850° F.), a pressure of about 3.4 MPa (500 psig) to about 6.2 MPa (900 psig), a liquid hourly space velocity of about 0.5 hr−1 to about 4 hr−1, and a hydrogen rate of about 168 to about 1,011 Nm3/m3 oil (1,000-6,000 scf/bbl). Typical hydrotreating catalysts include at least one Group 8 metal, preferably iron, cobalt and nickel, and at least one Group 6 metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other typical hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum.
Hydrocracking is a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. Typical hydrocracking conditions may include a temperature of about 290° C. (550° F.) to about 468° C. (875° F.), a pressure of about 3.5 MPa (500 psig) to about 20.7 MPa (3000 psig), a liquid hourly space velocity (LHSV) of about 1.0 to less than about 2.5 hr−1, and a hydrogen rate of about 421 to about 2,527 Nm3/m3 oil (2,500-15,000 scf/bbl). Typical hydrocracking catalysts include amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components, or a crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base.
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. The process typically employs a powdered catalyst having the particles suspended in a rising flow of feed hydrocarbons to form a fluidized bed. In representative processes, cracking takes place in a riser, which is a vertical or upward sloped pipe. Typically, a pre-heated feed is sprayed into the base of the riser via feed nozzles where it contacts hot fluidized catalyst and is vaporized on contact with the catalyst, and the cracking occurs converting the high molecular weight oil into lighter components including liquefied petroleum gas (LPG), gasoline, and a distillate. The catalyst-feed mixture flows upward through the riser for a short period (a few seconds), and then the mixture is separated in cyclones. The hydrocarbons are directed to a fractionator for separation into LPG, gasoline, diesel, kerosene, jet fuel, and other possible fractions. While going through the riser, the cracking catalyst is deactivated because the process is accompanied by formation of coke which deposits on the catalyst particles. Contaminated catalyst is separated from the cracked hydrocarbon vapors and is further treated with steam to remove hydrocarbon remaining in the pores of the catalyst. The catalyst is then directed into a regenerator where the coke is burned off the surface of the catalyst particles, thus restoring the catalyst's activity and providing the necessary heat for the next reaction cycle. The process of cracking is endothermic. The regenerated catalyst is then used in the new cycle. Typical FCC conditions include a temperature of about 400° C. to about 800° C., a pressure of about 0 to about 688 kPa g (about 0 to 100 psig), and contact times of about 0.1 seconds to about 1 hour. The conditions are determined based on the hydrocarbon feedstock being cracked, and the cracked products desired. Zeolite-based catalysts are commonly used in FCC reactors, as are composite catalysts which contain zeolites, silica-aluminas, alumina, and other binders.
Transalkylation is a chemical reaction resulting in transfer of an alkyl group from one organic compound to another. Catalysts, particularly zeolite catalysts, are often used to effect the reaction. If desired, the transalkylation catalyst may be metal stabilized using a noble metal or base metal, and may contain suitable binder or matrix material such as inorganic oxides and other suitable materials. In a transalkylation process, a polyalkylaromatic hydrocarbon feed and an aromatic hydrocarbon feed are provided to a transalkylation reaction zone. The feed is usually heated to reaction temperature and then passed through a reaction zone, which may comprise one or more individual reactors. Passage of the combined feed through the reaction zone produces an effluent stream comprising unconverted feed and product monoalkylated hydrocarbons. This effluent is normally cooled and passed to a stripping column in which substantially all C5 and lighter hydrocarbons present in the effluent are concentrated into an overhead stream and removed from the process. An aromatics-rich stream is recovered as net stripper bottoms, which is referred to as the transalkylation effluent.
The transalkylation reaction can be effected in contact with a catalytic composite in any conventional or otherwise convenient manner and may comprise a batch or continuous type of operation, with a continuous operation being preferred. The transalkylation catalyst is usefully disposed as a fixed bed in a reaction zone of a vertical tubular reactor, with the alkylaromatic feed stock charged through the bed in an upflow or downflow manner. The transalkylation zone normally operates at conditions including a temperature in the range of about 130° C. to about 540° C. The transalkylation zone is typically operated at moderately elevated pressures broadly ranging from about 100 kPa to about 10 MPa absolute. The transalkylation reaction can be effected over a wide range of space velocities. That is, volume of charge per volume of catalyst per hour; weight hourly space velocity (WHSV) generally is in the range of from about 0.1 to about 30 hr−1. The catalyst is typically selected to have relatively high stability at a high activity level.
Hydrogenation involves the addition of hydrogen to hydrogenatable hydrocarbon compounds. Alternatively hydrogen can be provided in a hydrogen-containing compound with ready available hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes, and others via a transfer hydrogenation process with or without a catalyst. The hydrogenatable hydrocarbon compounds are introduced into a hydrogenation zone and contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst in order to hydrogenate at least a portion of the hydrogenatable hydrocarbon compounds. Typical hydrogenation catalyst include Group VIB (Cr, Mo, W), Group VIIB (Mn, Tc, Re) or Group VIIIB (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) metals and combinations thereof supported on an inorganic oxide, carbide or sulfide support, including Al2O3, SiO2, SiO2—Al2O3, zeolites, non-zeolitic molecular sieves, ZrO2, TiO2, ZnO, and SiC. The catalytic hydrogenation zone may contain a fixed, ebulated or fluidized catalyst bed. This reaction zone is typically at a pressure from about 689 k Pa gauge (100 psig) to about 13790 k Pa gauge (2000 psig) with a maximum catalyst bed temperature in the range of about 177° C. (350° F.) to about 454° C. (850° F.). The liquid hourly space velocity is typically in the range from about 0.2 hr−1 to about 10 hr−1 and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m3 /m3) to about 10,000 SCFB (1778 m3 /m3).
Oxidation involves the oxidation of hydrocarbons to oxygen-containing compounds, such as aldehydes. The hydrocarbons include alkanes, alkenes, typically with carbon numbers from 2 to 15, and alkyl aromatics, Linear, branched, and cyclic alkanes and alkenes can be used. Oxygenates that are not fully oxidized to ketones or carboxylic acids can also be subjected to oxidation processes, as well as sulfur compounds that contain —S—H moieties, thiophene rings, and sulfone groups. The process is carried out by placing an oxidation catalyst in a reaction zone and contacting the feed stream which contains the desired hydrocarbons with the catalyst in the presence of oxygen. The type of reactor which can be used is any type well known in the art such as fixed-bed, moving-bed, multi-tube, CSTR, fluidized bed, etc. The feed stream can be flowed over the catalyst bed either up-flow or down-flow in the liquid, vapor, or mixed phase. In the case of a fluidized-bed, the feed stream can be flowed co-current or counter-current. In a CSTR the feed stream can be continuously added or added batch-wise. The feed stream contains the desired oxidizable species along with oxygen. Oxygen can be introduced either as pure oxygen or as air, or as liquid phase oxidants including hydrogen peroxide, organic peroxides, or peroxy-acids. The molar ratio of oxygen (O2) to substrate to be oxidized can range from about 5:1 to about 1:10. In addition to oxygen and alkane or alkene, the feed stream can also contain a diluent gas selected form nitrogen, neon, argon, helium, carbon dioxide, steam or mixtures thereof. As stated, the oxygen can be added as air which could also provide a diluent. The molar ratio of diluent gas to oxygen ranges from greater than zero to about 10:1. The catalyst and feed stream are reacted at oxidation conditions which include a temperature of about 25° C. to about 600° C., a pressure of about 101 kPa to about 5,066 kPa and a space velocity of about 100 to about 100,000 hr−1.
Thermal conversion involves heating the composition to effect the chemical change. The thermal conversion can be any suitable process, such as a delayed coking or slurry hydrocracking zone. The hydrocarbons are heated and fed into the bottom of one or more coking drums where the first stages of thermal decomposition reduce the hydrocarbons to a very heavy tar or pitch which further decomposes into solid coke. Typically, the vapors formed during the decomposition produce pores and channels in the coke through which the incoming oil from the furnace may pass. This process may continue usually until the drum is filled to a desired level with a mass of coke. The vapors formed in the process can exit the top of the coking drum and can be further processed. The resulting coke is removed from the coking drum.
Slurry hydrocracking involves combining a catalyst with the hydrocarbon stream. The slurry stream typically has a solids content of about 0.01-about 10%, by weight.
The slurry stream and the recycle gas can enter a heater. The recycle gas typically contains hydrogen, which can be once-through hydrogen optionally with no significant amount of recycled gases. Alternatively, the recycle gas can contain recycled hydrogen gas optionally with added hydrogen as the hydrogen is consumed during the one or more hydroprocessing reactions. The recycle gas may be essentially pure hydrogen or may include additives such as hydrogen sulfide or light hydrocarbons, e.g., methane and ethane. Reactive or non-reactive gases may be combined with the hydrogen introduced into the upflow tubular reactor or slurry hydrocracking reactor at the desired pressure to achieve the desired product yields. Often, slurry hydroprocessing is carried out using reactor conditions sufficient to crack at least a portion of the hydrocarbon stream to lower boiling products, such as one or more distillate hydrocarbons, naphtha, and/or C1-C4 products. Conditions in the slurry hydrocracking reactor can include a temperature of about 340° C. to about 600° C., a hydrogen partial pressure of about 3.5-about 30 MPa and a space velocity of about 0.1-about 30 volumes of the hydrocarbon stream per hour per reactor or reaction zone volume.
Generally, the catalyst for the slurry hydrocracking reactor provides a composition that is hydrophobic and resists clumping. Typically, the slurry catalyst composition can include a catalytically effective amount of one or more compounds having iron. Particularly, the one or more compounds can include at least one of an iron oxide, an iron sulfate, and an iron carbonate. Other forms of iron can include at least one of an iron sulfide, a pyrrhotite, and a pyrite. What is more, the catalyst can contain materials other than an iron, such as at least one of molybdenum, nickel, and manganese, and/or a salt, an oxide, and/or a mineral thereof. Preferably, the one or more compounds includes an iron sulfate, and more preferably, at least one of an iron sulfate monohydrate and an iron sulfate heptahydrate. Alternatively, one or more catalyst particles can include about 2-about 45%, by weight, iron oxide and about 20-about 90%, by weight, alumina. In some embodiments, the catalyst is supported. The support can be alumina, silica, titania, one or more aluminosilicates, magnesia, bauxite, coal and/or petroleum coke, for example. Such a supported catalyst can include a catalytically active metal, such as at least one of iron, molybdenum, nickel, and vanadium, as well as sulfides of one or more of these metals. Generally, the catalyst can have about 0.01-about 30%, by weight, of the catalytic active metal based on the total weight of the catalyst.
In some processes, all or a portion of the coal feed 10 is mixed with oxygen 95 and steam 100 and reacted under heat and pressure in the gasification zone 20 to form syngas 105, which is a mixture of carbon monoxide and hydrogen. The syngas 105 can be further processed using the Fischer-Tropsch reaction to produce gasoline or using the water-gas shift reaction to produce more hydrogen.
The coal tar stream 230 which comprises the volatile components from the coking process is sent to fractionation zone 245 including a catalytic distillation zone 247. The use of a catalyst in the catalytic distillation zone 247 allows simultaneous distillation and catalytic reactions in a single contacting section or the dual functions of distillation and catalytic reaction in different sections of a common column.
The fractionation zone 245 and catalytic distillation zone 247 are operated at conditions effective to further react and fractionate the coal tar stream 230. The catalytic distillation zone 247 can operate at a wide variety of temperatures depending on the catalyst type, the presence of hydrogen, and the location of the catalytic distillation zone. For example, the temperatures can range from about 35° C. to about 320° C. The pressure can be low, for example, about 100 kPa (g) (1 bar (0) to about 300 kPa (g) (3 bar (g)).
The coal tar feed 230 is introduced to the fractionation zone 245 in the catalytic distillation zone 247 at a point below the draw for fraction 265 and above where pitch fraction 270 is removed. The catalytic distillation zone 247 extends from the coal tar feed inlet to a position below where the product draws are taken. The location for the catalytic distillation zone will be a function of the catalyst type and properties, and the presence or absence of hydrogen. More active catalysts need a lower temperature to be effective and will be located higher in the column. The length of the catalytic distillation zone is a function of the space velocity needed for complete conversion, with a more active catalyst needing less volume. No particular apparatus or arrangement is needed to retain the catalyst bed within the distillation zone and a variety of methods can be used to incorporate the bed or region of catalyst within the distillation zone. For example, catalyst may be retained between suitable packing materials or may be incorporated on to a distillation tray itself.
In one example, the catalytic distillation zone 247 contains a hydrogenation or hydrotreating catalyst, as described above. During fractionation, the coal tar stream 230 contacts the catalyst and at least a portion of the organic and ionic forms of mercury react to form elemental mercury. The reactions can take place in the liquid or vapor phase.
The elemental mercury and inorganic mercury compounds are removed from one or more streams as described above, and further treated and/or recovered, if desired. The mercury can be recovered by vacuum distillation at high temperature (typically about 600° C.), for example. The treaters can be operated in a lead-lag mode in series. When the first one is spent, flow switches to the second treater to allow for continuous protection.
As illustrated, the coal tar feed 230 is separated into gas fraction 250, hydrocarbon fractions 255, 260, and 265 having different boiling point ranges, and pitch fraction 270.
One or more of the fractions 250, 255, 260, 265, 270 can be further processed, as desired. As illustrated, fraction 260 can be sent to one or more hydrocarbon conversion zones 275, 280. Fraction 260 can be sent to hydrocarbon conversion zone 275 for hydrotreating to remove sulfur and nitrogen. Effluent 285 is then sent to hydrocarbon conversion zone 280 for hydrocracking, for example, to produce product 290.
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.
This application claims the benefit of Provisional Application Ser. No. 61/905,902 filed Nov. 19, 2013, entitled Process for Removing Mercury from a Coal Tar Product.
| Number | Date | Country | |
|---|---|---|---|
| 61905902 | Nov 2013 | US |
