Hydrocarbon synthesis process

Abstract

(b) removing carbon dioxide from the synthesis gas in a carbon dioxide removal unit to produce a carbon dioxide stream and a purified synthesis gas comprising hydrogen and carbon monoxide; and (c) synthesizing a mixture of hydrocarbons from the purified synthesis gas in a Fischer-Tropsch hydrocarbon synthesis unit while co-producing an FT water stream, wherein: (i) at least a portion of the FT water stream is fed to an electrolysis unit to provide an oxygen stream and a hydrogen stream which are fed to the synthesis gas production unit; (ii) at least a portion of the carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolysis unit are fed to a reverse water gas shift unit to produce a carbon monoxide stream; and (iii) at least a portion of the carbon monoxide stream from the reverse water gas shift unit is fed to the Fischer-Tropsch hydrocarbon synthesis unit.

Description

Technical Field

[0001] The present invention relates to a process for synthesizing hydrocarbons from synthesis gas containing hydrogen and carbon monoxide.

[0002] Processes for synthesizing hydrocarbons from synthesis gas are known. For example, U.S. Patent No. 9,163,180 discloses a process for the conversion of carbonaceous materials to a fuel base by a hybrid route that combines direct fluidized bed liquefaction and gasification followed by Fischer-Tropsch synthesis, including a hydrogen production step from non-fossil resources and a reverse water gas shift reaction step. Electrolysis is used as a hydrogen source for liquefaction, reverse water gas reaction, and Fischer-Tropsch synthesis. U.S. Patent Application Publication No. 2014 / 288,195 discloses a process for thermochemically converting a carbonaceous feedstock, such as biomass, into synthesis gas mainly containing hydrogen and carbon monoxide, the process comprising the following steps: (a) oxy-combustion of the carbonaceous feedstock to generate electrical and heat co-generation; (b) high-temperature electrolysis of water using the heat generated in step (a); (c) a reverse water gas shift reaction starting from the carbon dioxide generated in step (a) and the hydrogen generated in step (b).

[0003] The inventors have recognized that the process efficiency is increased by using the water by-product of Fischer-Tropsch synthesis in an electrolysis unit connected to a reverse water gas shift unit and a Fischer-Tropsch synthesis unit.

[0004] Accordingly, the present invention provides a hydrocarbon synthesis process comprising: (a) a step of producing synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide from feedstock in a synthesis gas production unit; (b) a step of removing carbon dioxide from the synthesis gas in a carbon dioxide removal unit to produce a carbon dioxide stream and purified synthesis gas containing hydrogen and carbon monoxide; and (c) a step of synthesizing a hydrocarbon mixture from the purified synthesis gas in a Fischer-Tropsch hydrocarbon synthesis unit while co-producing an FT water stream, wherein (i) at least a portion of the FT water stream is supplied to an electrolytic unit to provide an oxygen stream and a hydrogen stream to be supplied to the synthesis gas production unit; (ii) at least a portion of the carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream produced by the electrolytic unit are supplied to a reverse water-gas shift unit to produce a carbon monoxide stream; and (iii) at least a portion of the carbon monoxide stream from the reverse water-gas shift unit is supplied to the Fischer-Tropsch hydrocarbon synthesis unit.

[0005] The present invention further comprises a system for carrying out a process, the system comprising: (a) a synthesis gas generation unit for producing synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide from a supply raw material; (b) a carbon dioxide removal unit connected to the synthesis gas generation unit for removing carbon dioxide from the synthesis gas and producing a carbon dioxide stream and purified synthesis gas containing hydrogen and carbon monoxide; and (c) a Fischer-Tropsch hydrocarbon synthesis unit connected to the carbon dioxide removal unit for synthesizing a mixture of hydrocarbons from the purified synthesis gas while co-producing an FT water stream, wherein (i) an electrolytic unit is connected to the Fischer-Tropsch hydrocarbon synthesis unit. (ii) A reverse water-gas shift unit is connected to a carbon dioxide removal unit and an electrolytic unit and is configured to generate an oxygen stream and a hydrogen stream, supplied from the carbon dioxide removal unit along with at least a portion of the carbon dioxide stream and a portion of the hydrogen stream generated by the electrolytic unit, and is configured to generate a carbon monoxide stream, and (iii) a Fischer-Tropsch hydrocarbon synthesis unit is connected to the reverse water-gas shift unit and receives at least a portion of the carbon monoxide stream.

[0006] In this invention, carbon dioxide recovered from synthesis gas by a carbon dioxide removal unit is combined with hydrogen from an FT water electrolysis unit and used in a reverse water-gas shift unit to produce additional carbon monoxide, which is sent to Fischer-Tropsch synthesis to increase hydrocarbon product yield. The FT water electrolysis may conveniently use electricity from renewable sources such as solar, wind, or tidal power. By using renewable electricity, the overall carbon intensity of the process can be negative, resulting in overall negative carbon dioxide emissions. This also avoids the need for carbon capture and storage. Overall, the process of this invention helps maximize the production of liquid fuel from feedstock and reduce carbon dioxide emissions.

[0007] In the process of the present invention, the feedstock supplied to the process may preferably include gaseous feedstock such as natural gas or associated gas, or solid feedstock such as coal, biomass, municipal solid waste, or equivalent materials containing abiogenic carbon. Therefore, the feedstock may include coal, biomass, algae, solid hydrocarbon waste, industrial polymers, organic waste, and / or household plastics. These feedstocks may be used individually or as mixtures of two or more in the same or different proportions. The feedstocks may also include a portion of the effluent resulting from Fischer-Tropsch synthesis or from the gasification of the feedstocks. Liquid feedstocks obtained from oil and / or oil refining, and products obtained from the thermochemical or hydrothermal conversion of these feedstocks may also be used. The present invention provides a remarkable synergistic effect when synthesis gas is produced from coal, municipal solid waste, or equivalent materials and biomass feedstocks, and the natural hydrogen to carbon monoxide ratio is typically lower than the 2:1 ratio required for efficient Fischer-Tropsch synthesis. Particularly preferred feedstocks are biomass, municipal solid waste, or equivalent materials containing abiogenic carbon, or mixtures thereof.

[0008] The gaseous feedstock is preferably treated upstream of the synthesis gas production unit to remove volatile contaminants such as sulfur, mercury, or chlorine compounds, as these contaminants can poison the reforming, reverse water-gas shift, and Fischer-Tropsch catalyst. Suitable adsorbents for these contaminants are known.

[0009] The synthesis gas production unit may be any unit that converts the feedstock into synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide. Depending on the properties of the feedstock, various synthesis gas production technologies may be preferred. For example, if the feedstock is natural gas, the synthesis gas production unit preferably includes a catalytic partial oxidation unit, a non-catalytic partial oxidation unit, or a self-thermal reformer. Alternatively, if the feedstock is coal, biomass, or municipal solid waste or an equivalent containing non-biogenic carbon, the synthesis gas production unit preferably includes a gasifier. Any known gasification technology may be used. Preferably, gasification is carried out by partial oxidation, which involves burning the feedstock at a high temperature of approximately 800°C to 1600°C under substoichiometric conditions using air or oxygen to obtain raw material synthesis gas. If nitrogen-free synthesis gas is desired, this process uses oxygen produced by air distillation using conventional techniques, such as an air separation unit (ASU). Gasification produces synthesis gas and a residual fraction containing tar oil. Synthesis gas is generally a mixture of gases containing carbon monoxide, hydrogen, water vapor, and carbon dioxide. Furthermore, synthesis gas typically contains sulfur-containing, nitrogen-containing, and halogen-containing impurities. Common sulfur-containing impurities include carbonyl sulfide (COS) and hydrogen sulfide (H2S). These impurities, if present, are removed upstream of the Fischer-Tropsch hydrocarbon synthesis unit using one or more contaminant removal steps, preferably by washing (absorption), by passing the raw material synthesis gas through one or more beds of suitable adsorbents, or by a mixture thereof. Synthesis gas purification may be carried out in one or more steps before and / or after the carbon dioxide removal unit.

[0010] The synthesis gas generation unit consumes oxygen that may be supplied by the electrolysis unit. This has the advantage of reducing capital investment in the air separation plant and / or, if necessary, reducing power consumption by the air separation plant. The oxygen required for the synthesis gas generation unit preferably comes solely from the decomposition of water by electrolysis in the electrolysis unit. This has the advantage of eliminating or reducing the size of the air separation unit.

[0011] The synthesis gas recovered from the synthesis gas generation unit may be dehydrated, if necessary, by cooling it to below the dew point in one or more steps to condense any water vapor present, and then removing the condensate using one or more gas-liquid separators.

[0012] The synthesis gas contains carbon dioxide, which is removed using a carbon dioxide removal unit. Carbon dioxide removal may involve one or more containers providing a physical or reactive cleaning system, preferably a reactive cleaning system, particularly an amine cleaning system. Carbon dioxide may also be removed by a conventional acidic gas recovery unit (AGRU). This has the advantage of further removing hydrogen sulfide, which can otherwise poison downstream catalysts. In a conventional AGRU, the dehydrated synthesis gas stream is brought into contact with a stream of a suitable absorbent, such as an aqueous solution of an amine, such as monoethanolamine (MEA), methyldiethanolamine (MDEA), or dimethylethanolamine (DMEA), particularly a methyldiethanolamine (MDEA) solution, resulting in the absorption of carbon dioxide into the liquid, yielding an absorbent and a gas stream with reduced carbon dioxide content. The packed absorbent is then regenerated by heating to desorb carbon dioxide, and the regenerated absorbent is then recycled to the carbon dioxide absorption stage. The heat generated by the regeneration of the packed absorbent can be recovered from within the process. For example, a portion of the synthesis gas from the synthesis gas generation unit may be used to heat the packed absorbent, or to generate steam, and a portion of the steam may be used to heat the packed absorbent. Alternatively, the packed absorbent may be heated by heat exchange with the product stream from the Fischer-Tropsch synthesis unit. Alternatively, instead of washing with amines, cold methanol or glycol may be used, as well as amines for capturing carbon dioxide. For example, the Rectisol® process using cold methanol may be operated in two stages to remove carbonyl sulfide (COS) and hydrogen sulfide (H2S), followed by carbon dioxide. When the carbon dioxide separation process is operated as a single pressure process, i.e., when essentially the same pressure is employed in the adsorption and regeneration steps, only minimal recompression of the recycled carbon dioxide is required.

[0013] Removing carbon dioxide from synthesis gas produces purified synthesis gas containing hydrogen and carbon monoxide. Small amounts of carbon dioxide, methane, and inert gases such as nitrogen may also be present, but this is undesirable as it prevents their accumulation in the Fischer-Tropsch synthesis unit. Therefore, if desired, one or more purification units may be provided downstream of the carbon dioxide removal unit so that the purified synthesis gas consists essentially of hydrogen and carbon monoxide.

[0014] The purified synthesis gas may, if desired, be heated to the inlet temperature of the Fischer-Tropsch synthesis unit using any available heat source.

[0015] The purified synthesis gas is supplied to the Fischer-Tropsch hydrocarbon synthesis unit, which synthesizes a mixture of hydrocarbon products.

[0016] The Fischer-Tropsch hydrocarbon synthesis unit may include one or more Fischer-Tropsch reaction vessels containing Fischer-Tropsch catalysts. The Fischer-Tropsch transformation step can be carried out according to any one of the known processes, particularly using any one of the known catalysts based on iron or cobalt, and is not limited to any particular process or catalyst.

[0017] The Fischer-Tropsch process is ideally expressed by equation (C n H 2n+2 This involves a series of chemical reactions that produce various hydrocarbons having ) . More useful reactions produce alkanes as follows: [ka] [In the formula, n is typically 5 to 100 or more, and preferred products have n in the range of 10 to 20.]

[0018] Generally, the following distinctions are made: high temperature (320-350°C): Fischer-Tropsch processes operated with iron-based catalysts, and "low temperature" (220-240°C): Fischer-Tropsch processes operated with iron or cobalt-based catalysts. Cobalt-based catalysts typically work well with a hydrogen-to-carbon monoxide molar ratio in the feed gas of about 2, often 1.8-2.5, preferably around 2.15. When the Fischer-Tropsch catalyst is iron-based, a hydrogen-to-carbon monoxide molar ratio of 0.8-2, generally 1.2-1.8, may be used. Therefore, those skilled in the art may select the most suitable Fischer-Tropsch synthesis catalyst for the process depending on the available feedstock. Cobalt catalysts may be preferred due to their lower CO2 selectivity, which reduces the size and cost of the Fischer-Tropsch synthesis unit and increases the efficiency of the process for producing hydrocarbon products.

[0019] The feed gas for Fischer-Tropsch synthesis comprises purified synthesis gas, which can have a hydrogen-to-carbon monoxide molar ratio in the range of 1.6 to 2.5:1, and at least a portion, preferably all, of the carbon monoxide produced by the reverse water-gas shift unit. Therefore, for optimal process performance, it may be necessary to supplement the feed gas for Fischer-Tropsch synthesis with a portion of the hydrogen from the electrolytic unit to achieve the desired ratio. The optimal hydrogen-to-carbon monoxide molar ratio in the feed gas for cobalt-catalyzed Fischer-Tropsch synthesis is about 2:15. Therefore, in some embodiments, a portion of the hydrogen stream from the electrolytic unit may be supplied to the Fischer-Tropsch hydrocarbon synthesis unit.

[0020] The Fischer-Tropsch reaction may be carried out in a continuous or batch process using one or more reactors, such as a fixed-bed reactor, slurry-phase reactor, bubble column reactor, loop reactor, or fluidized-bed reactor. This process may be operated at pressures in the range of 0.1 to 10 MPa and temperatures in the range of 170 to 350°C. For continuous operation, the gas-to-space velocity (GHSV) is 1,000 to 25,000 hours. -1This is within the range. In the Fischer-Tropsch hydrocarbon synthesis unit, the feed gas is catalytically converted into oxygen-containing products and essentially linear hydrocarbons in gaseous, liquid, or solid form. These products are generally free of heteroatom impurities and are substantially or negligibly free of aromatics, naphthenes, and more generally, rings (especially in the case of cobalt catalysts). The Fischer-Tropsch synthesis is preferably operated to produce hydrocarbons with a carbon chain length ≥ 5.

[0021] Unreacted gas recovered from the Fischer-Tropsch hydrocarbon synthesis unit may be circulated through a loop within the unit to one or more Fischer-Tropsch reactors to increase efficiency. To prevent the accumulation of inert gas, the purge may be removed from the loop as Fischer-Tropsch tail gas. The tail gas typically contains small amounts of methane and C2-C10 hydrocarbons, but nevertheless, these are valuable carbon sources. Therefore, in some embodiments, tail gas containing one or more of methane, ethane, propane, butane, and C5-C10 hydrocarbons can be recovered from the Fischer-Tropsch hydrocarbon synthesis unit and supplied to a synthesis gas production unit, or subjected to a separate reforming step such as pre-reforming to form a hydrogen-containing reformed tail gas. The reformed tail gas may be supplied to the Fischer-Tropsch hydrocarbon synthesis unit and / or a reverse water-gas shift unit. Hydrogen recovered from the tail gas or reformed tail gas may be used in a hydrogenation unit. The tail gas may also be subjected to a carbon dioxide removal step by supplying it to a carbon dioxide removal unit, if desired.

[0022] Preferably, the Fischer-Tropsch synthesis is carried out using one or more fixed-bed reactors, i.e., reaction vessels having a catalyst bed fixed in a vessel through which purified synthesis gas passes. Any Fischer-Tropsch catalyst can be used, but cobalt-based Fischer-Tropsch catalysts are preferred over iron-based catalysts due to their lower carbon dioxide selectivity. Suitable cobalt Fischer-Tropsch catalysts are known, but preferred catalysts in this process contain 9-20% by weight of Co supported on a suitable support material. Accordingly, suitable catalysts include aggregates, pellets, or extruded materials containing metal oxides such as alumina, zinc oxide, titania, or silica, or mixtures thereof, on which a catalytically active metal, preferably cobalt, is deposited. In a particularly preferred configuration, the Fischer-Tropsch catalyst is used in combination with a catalyst support suitable for use in a tubular Fischer-Tropsch reactor, where the catalyst-containing catalyst support is placed in one or more tubes that are cooled by circulating a coolant such as water under pressure. "Catalyst carrier" means a catalyst container, for example, in the form of a cup or can, configured to allow gases and / or liquids to enter and exit the carrier and flow through a bed of catalyst or catalyst precursors placed within the carrier. Any suitable catalyst carrier may be used. In one configuration, the catalyst carrier is one described in International Publication 2011 / 048361, the contents of which are incorporated herein by reference. In another configuration, the catalyst carrier may include a catalyst monolith, such as that disclosed in International Publication 2012 / 136971, the contents of which are also incorporated herein by reference. In yet another configuration, the catalyst carrier may be one disclosed in International Publication 2016 / 050520, the contents of which are also incorporated herein by reference. In a preferred embodiment, the Fischer-Tropsch hydrocarbon synthesis unit includes a tubular reactor in which a catalyst carrier containing a Fischer-Tropsch catalyst is placed in one or more tubes cooled by a cooling medium.

[0023] The above Fischer-Tropsch reaction produces FT water as a by-product of the reaction. This FT water is separated from the hydrocarbon mixture produced by the Fischer-Tropsch reaction in a Fischer-Tropsch hydrocarbon synthesis unit. The separation may conveniently be effected using one or more gas-liquid or liquid-liquid separators.

[0024] In this process, at least a portion of the FT water stream is supplied to an electrolysis unit to provide an oxygen stream. The FT water may be treated upstream of the electrolysis unit to remove contaminants that may interfere with the operation of the electrolysis unit.

[0025] Separation of the FT water from the product mixture produced in the FT reaction stage enables recovery of the hydrocarbon product mixture. The gaseous hydrocarbons may be recovered for sale or recycled to the process, for example, as part of the Fischer-Tropsch tail gas or as a feedstock to a syngas production unit together with the Fischer-Tropsch tail gas. The liquid hydrocarbons may be recovered for sale or subjected to quality improvement to provide more valuable hydrocarbon products. Thus, the Fischer-Tropsch hydrocarbon synthesis unit preferably produces one or more hydrocarbon streams including, but not limited to, molten hydrocarbon wax and / or light hydrocarbon condensate that are liquid at ambient temperature.

[0026] The hydrocarbon products synthesized in the Fischer-Tropsch hydrocarbon synthesis unit can be used directly, for example, to produce base oils, or can be processed later to produce other products. The processing may be in a central processing or upgrading facility.

[0027] Preferably, the Fischer-Tropsch hydrocarbon synthesis unit is operated to produce a molten hydrocarbon wax liquid, which is subjected to a quality improvement process in a hydrotreating unit to produce a liquid fuel. Thus, in some embodiments, at least a portion, preferably all, of the liquid hydrocarbon mixture obtained from Fischer-Tropsch synthesis may be supplied as a feedstock to a hydrotreating unit in the presence of hydrogen. The hydrotreating unit may perform various conversions such as hydroisomerization, hydrogenation, hydrodeoxygenation, and / or hydrocracking using one or more vessels containing a suitable catalyst. Hydrogen is required in the hydrotreating unit. This may be provided by various sources, but preferably is provided by an electrolysis unit to minimize carbon dioxide emissions from the process. Thus, in some embodiments, a portion of the hydrogen stream from the electrolysis unit may be supplied to the hydrotreating unit.

[0028] The hydrotreating unit can be operated at a temperature of generally 200 to 450 °C, preferably 250 to 45 ℃, more preferably 300 to 450 °C, most preferably 320 to 420 °C; a pressure of 0.2 to 15 MPa, preferably 0.5 to 10 MPa, more preferably 1 to 9 MPa; 0.1 to 10 h -1 , preferably 0.2 to 7 h -1 , more preferably 0.5 to 5.0 h -1 of liquid hourly space velocity, and the hydrogen content may be 100 to 2000 liters of H2 per liter of feedstock, preferably 150 to 1500 liters of H2 per liter of feedstock.

[0029] The hydrotreating stage may preferably be carried out under conditions such that the conversion rate per pass of a product having a boiling point of 370 °C or higher to a product having a boiling point of less than 370 °C is more than 40 wt%, more preferably at least 50 wt%, thereby obtaining middle distillates (gas oil and kerosene) having good low temperature properties (pour point, freezing point) sufficient to meet the specifications effective for this type of fuel.

[0030] The catalysts used at this stage are known. For example, hydrogen isomerization and hydrocracking can be carried out using any one of the known catalysts and following any one of the known processes, and are not limited to a specific process or catalyst. Most catalysts suitable for hydrogen isomerization / hydrocracking are of the bifunctional type, combining an acidic functional group and a hydrogenating functional group. The acidic functional group is generally a high specific surface area (generally 150-800 m²) exhibiting surface acidity, such as halogenated (especially chlorinated or fluorinated) alumina, phosphorus-containing alumina, a combination of boron oxide and aluminum oxide, or silica / alumina. 2 The hydrogenation function is generally provided by one or more metals from Group VIII of the periodic table, such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum, or by a combination of at least one metal from Group VI and at least one metal from Group VIII, such as chromium, molybdenum, and tungsten. Most conventional hydrogenocrack catalysts consist of a weakly acidic support such as silica / alumina. These systems are typically used to produce middle distillates of very good quality. Many catalysts on the hydrogenocrack market are silica / alumina based in combination with metals from Group VIII. These systems have very good selectivity for middle distillates, and the products formed are of good quality. According to one preferred embodiment, the hydrogenation isomerization / hydrocracking catalyst comprises at least one hydrogenation-dehydrogenation element selected from Group VIII noble metals, preferably platinum and / or palladium, and at least one amorphous refractory oxide support, preferably silica / alumina.

[0031] Hydrocarbon products recovered from the hydrotreatment unit may be supplied to a separation unit to recover valuable hydrocarbon products. The separation unit may include one or more atmospheric distillation columns for separating (C1-C4) gas, naphtha fraction, at least one kerosene and / or diesel fraction, and then a heavy fraction, and optionally one or more vacuum distillation columns. The heavy fraction generally exhibits an initial boiling point of at least 350°C, preferably above 370°C. This fraction is advantageously recycled back to the hydrotreatment unit. It may also be advantageous to recycle a portion of the kerosene and / or diesel fuel back to the hydrotreatment unit. The diesel and kerosene fractions may or may not be recovered separately, and the cut points may be adjusted to produce the desired hydrocarbon products.

[0032] The naphtha fraction may be separated into a light naphtha fraction (C5-C6), which is preferably subjected to isomerization to produce gasoline, and a heavy naphtha fraction (C7-180°C), which is preferably subjected to catalytic reforming to produce reformed oil. Subsequently, the effluents from isomerization and reforming may be mixed to form gasoline that meets the specifications. The hydrogen generated during catalytic reforming is preferably recycled to a hydrogenation unit. To adjust the hydrogen-to-carbon monoxide ratio in the Fischer-Tropsch synthesis, hydrogen generated by catalytic reforming or feedstock supplied to a reverse water-gas shift unit may be used.

[0033] In the present invention, carbon dioxide recovered from synthesis gas using a carbon dioxide removal unit is converted to carbon monoxide by subjecting it to a reverse water-gas shift reaction in a reverse water-gas shift unit, which includes a reverse water-gas shift vessel containing a reverse water-gas shift catalyst. A preferred reverse water-gas shift unit includes a burner and a self-heating reverse water-gas shift vessel containing a fixed bed of a reverse water-gas shift catalyst. The burner is supplied with a carbon dioxide-containing gas and an oxygen stream, which burns hydrogen and a portion of any hydrocarbons present in the carbon dioxide-containing gas, thereby generating heat for an endothermic reverse water-gas shift reaction.

[0034] The reverse water-gas shift reaction can also be expressed as follows: [ka]

[0035] This reaction consumes hydrogen, and since synthesis gas production units generally do not produce more hydrogen than is needed for Fischer-Tropsch synthesis, an additional hydrogen source is required. In this invention, this is provided by the electrolysis of FT water, which is produced as a byproduct of Fischer-Tropsch synthesis. Alternatively, one or more additional hydrogen sources may be used. The additional hydrogen source may be generated by steam reforming at least a portion of the Fischer-Tropsch tail gas and / or gaseous hydrocarbons recovered from the Fischer-Tropsch hydrocarbon synthesis unit. This can be done using an adiabatic steam reformer or pre-reformer, a conventional combustion steam reformer, a self-heating reformer, a small reformer or gas-heated reformer, or any combination thereof.

[0036] The reverse water-gas shift unit enables the conversion of carbon into liquid hydrocarbons via the Fischer-Tropsch reaction while simultaneously reducing carbon dioxide emissions, thereby improving carbon yield.

[0037] The product gas stream from the reverse water-gas shift unit contains water vapor. The water may be recovered, for example, by cooling the product gas stream below its dew point and separating the condensate using one or more conventional gas-liquid separators. The condensed water may, if desired, be recycled at least partially to an electrolytic unit to generate additional hydrogen for the process. Thus, in some embodiments, the water stream produced by the reverse water-gas shift unit, or the water stream recovered from the reverse water-gas shift unit, may be supplied to an electrolytic unit.

[0038] The product gas stream from the reverse water-gas shift unit may contain unreacted carbon dioxide, which is preferably removed before the carbon monoxide-containing gas is supplied to the Fischer-Tropsch synthesis unit. The carbon dioxide may be removed from the reverse water-gas shift effluent using any suitable absorbent, such as those described above for the carbon dioxide removal unit. Alternatively, the carbon dioxide may be separated by a membrane separation unit. In some embodiments, the carbon dioxide may be removed from the reverse water-gas shift product gas stream by returning it to a carbon dioxide removal unit connected to a synthesis gas generation unit that supplies the synthesis gas. Alternatively, a separate, dedicated carbon dioxide removal unit may be provided to remove carbon dioxide only from the product gas stream recovered from the reverse water-gas shift reactor. If a liquid absorbent is used, this may have the additional advantage of removing carbon dioxide, in addition to at least some water, from the product gas.

[0039] The reverse water-gas shift reaction is accelerated by high temperature and may be carried out under temperature and pressure conditions similar to those for synthesis. The pressure may be, for example, 0.1 to 8 MPa, preferably 1 to 4 MPa, and the temperature at the outlet of the reverse water-gas shift reactor may be 750 to 2000°C, preferably 800 to 1800°C, more preferably 850 to 1600°C. The catalyst may be any suitable transition metal oxide catalyst, such as a catalyst based on nickel oxide, iron oxide, or chromium oxide, but other catalysts provided as reverse water-gas shift catalysts may also be used. Operating under these conditions makes it possible to adjust the hydrogen-to-carbon monoxide molar ratio to a value close to that desired for Fischer-Tropsch synthesis, while limiting the content of unconverted methane and unconverted carbon dioxide.

[0040] To generate a high temperature suitable for efficient operation of the reverse water-gas shift unit, the carbon dioxide stream may be heated, for example, electrically using renewable energy, by heat exchange with a suitable fluid, or in a combustion heater. In a preferred embodiment, the carbon dioxide stream and the hydrogen stream may be heated in the combustion section of the reverse water-gas shift unit by burning portions of the carbon dioxide and hydrogen-containing streams with an oxidizer. Combustion consumes some of the hydrogen. An excess of hydrogen exceeding a molar ratio of 1:1 is preferably present in the feed gas. Using hydrogen-to-carbon dioxide molar ratios in the range of 1.5 to 7.5:1, a reverse water-gas shift gas with the desired H2:CO ratio for Fischer-Tropsch synthesis can be produced. Methane or another fuel may be included in the feed gas if desired. In some embodiments, the Fischer-Tropsch tail gas may be supplied directly to the reverse water-gas shift unit, or, preferably, the Fischer-Tropsch tail gas may be subjected to a pre-reforming step, in which case it is subjected to adiabatic steam reforming on a nickel catalyst to convert the higher hydrocarbons present in the tail gas to methane, and the pre-reformed Fischer-Tropsch tail gas is supplied to the reverse water-gas shift unit. Combustion may take place in an upstream combustion chamber or combustion zone within the reverse water-gas shift vessel, upstream of the bed of the reverse water-gas shift catalyst located within the reverse water-gas shift reaction vessel. Combustion may be carried out non-catalyzably or catalytically on a suitable oxidation catalyst such as a platinum-containing catalyst. The oxidizer is preferably pure oxygen, for example, >98 volume% O2, because this minimizes inert substances in the downstream Fischer-Tropsch synthesis. This oxygen may be conveniently provided by an electrolytic unit. Thus, in some embodiments, the oxygen stream provided by the electrolytic unit may be used to burn a portion of the supply gas, which contains carbon dioxide and hydrogen, supplied to the reverse water-gas shift unit, thereby raising the temperature of the supply gas.

[0041] Hydrogen and oxygen for the process are produced using an electrolytic unit supplied with FT water recovered from a Fischer-Tropsch hydrocarbon synthesis unit. The electrolytic unit typically includes one or more electrolytic cells operating according to the following general formula: [ka]

[0042] Electrolysis is a process that chemically decomposes water under the action of an electric current to obtain oxygen and hydrogen. Industrial electrolysis is generally carried out at temperatures below 200°C. If desired, FT water may be combined with potassium hydroxide, the concentration of which may vary as a function of temperature (typically from 25% by weight at 80°C to 40% by weight at 160°C). Potassium hydroxide is preferred over sodium hydroxide for its superior conductivity at essentially equivalent temperature levels. Alternatively, polymer electrode membrane electrolytic cells may be used. Alternatively, high-temperature electrolysis may be used in the process. High-temperature electrolysis is operated at high temperatures (700-900°C) and under reduced pressure. High-temperature electrolysis is more efficient than processes at ambient temperature because part of the energy required for the reaction is provided via heat, which is often cheaper than electricity, and the electrolytic reaction has better yields at high temperatures.

[0043] The electrical energy required for hydrogen production in the electrolysis unit is preferably non-fossil fuel-based so as not to emit carbon dioxide, or neutral in terms of carbon dioxide emissions. One non-fossil fuel energy source is nuclear energy. Other energy sources that do not emit carbon dioxide, or are neutral in terms of carbon dioxide emissions, include renewable energy, such as solar energy, wind energy, tidal energy, hydroelectric power or hydropower, ocean energy sources, geothermal energy, and / or biomass. These non-fossil fuel energy sources may be used individually, or two or more may be used in equal or different proportions.

[0044] The hydrogen used in this process is preferably produced by the electrolysis of water, and the electrical energy for this is preferably supplied by renewable energy sources, particularly solar energy, wind energy, tidal energy, geothermal energy and / or biomass. This is because these energy sources are distinguished by being virtually inexhaustible, easily accessible, and producing little to no problematic waste.

[0045] The oxygen required for synthesis gas production in the synthesis gas generation unit includes oxygen produced by the electrolysis unit, and, if necessary, is supplemented by oxygen from the air separation unit. The use of oxygen produced by electrolysis allows for the depletion of the air separation unit, which was previously used to supply the oxidizer to the synthesis gas generation unit.

[0046] In the present invention, all of the oxygen recovered from the electrolysis unit may be used for synthesis gas production. However, the electrolysis unit may provide excess oxygen for export to other processes that require oxygen for combustion in the oxygen feeder and / or in the reverse water-gas shift unit, if the hydrogen requirements of the process necessitate it. The portion of oxygen produced by the electrolysis unit and supplied to the synthesis gas production unit may be in the range of 30 to 100 volume percent of the total electrolytic oxygen, and in the case of reverse water-gas shift combustion, the portion of oxygen produced by electrolysis may be in the range of 0 to 70 volume percent, preferably 10 to 50 volume percent, more preferably 10 to 25 volume percent, of the total electrolytic oxygen.

[0047] Hydrogen from the electrolysis unit is used in the process as a feed gas for the reverse water-gas shift unit. A portion of the hydrogen may also be supplied to the Fischer-Tropsch hydrocarbon synthesis unit, i.e., a portion of the hydrogen from the electrolysis unit may bypass the reverse water-gas shift unit. In addition, or instead, a portion of the hydrogen may be supplied to the hydrogenation unit. The portion of hydrogen produced by the electrolysis unit supplied to the reverse water-gas shift unit may be in the range of 30 to 100% by volume, preferably 30 to 60% by volume, more preferably 40 to 50% by volume, of the total amount of electrolyzed hydrogen. Preferably, 40 to 60% of the electrolyzed hydrogen is supplied to the Fischer-Tropsch synthesis. Optionally, 0 to 10% of the electrolyzed hydrogen may be supplied to the hydrogenation unit.

[0048] In addition to the electrolysis unit, an external hydrogen source may be used in the process, but this is not very desirable and is generally not a requirement.

[0049] As a result, the process of the present invention provides a more efficient and environmentally friendly method than conventional processes for producing valuable Fischer-Tropsch hydrocarbon products. [Brief explanation of the drawing]

[0050] The present invention will be described by reference to the accompanying drawings: [Figure 1] This is a schematic flowchart of one embodiment of the present invention.

[0051] Those skilled in the art will understand that the drawings are schematic, and that commercial plants may require additional items of equipment such as reflux drums, compressors, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, and storage tanks. Providing accessories for such equipment would not form part of the present invention and would follow conventional chemical engineering practices.

[0052] In Figure 1, municipal solid waste or equivalent feedstock is supplied via line 10 to a synthesis gas generation unit 12, which includes a gasifier supplied via line 14, and an oxygen gas stream produced in an electrolytic unit 16. In the gasifier, the feedstock reacts with oxygen at elevated temperature and pressure to produce a synthesis gas stream containing hydrogen, carbon monoxide, carbon dioxide, and water vapor. The synthesis gas generation unit may further include a separate partial oxidation or tar reforming unit downstream of the gasifier to perform the complete conversion of the feedstock into synthesis gas. The synthesis gas generation unit 12 may further include a heat exchanger for cooling the synthesis gas below its dew point and one or more gas-liquid separation vessels for recovering condensates from the synthesis gas.

[0053] The synthesis gas is sent from the synthesis gas generation unit 12 through line 18 to a carbon dioxide removal unit 20, which operates by absorption using a liquid absorbent washing system, at a suitable temperature and pressure. The washing system within the carbon dioxide removal unit produces a carbon dioxide stream and a purified synthesis gas stream containing hydrogen and carbon monoxide. Upstream of the carbon dioxide removal unit, one or more purification steps (not shown) may be used to remove unwanted contaminants such as carbonyl sulfides, hydrogen cyanide, and heavy metals, such as mercury, from the synthesis gas recovered from the synthesis gas generation unit.

[0054] A carbon dioxide stream is recovered from the carbon dioxide removal unit 20 via line 22, treated in a purification unit (not shown) to remove residual contaminants such as hydrogen sulfide if necessary, and supplied at a suitable temperature and pressure to a reverse water-gas shift unit 24, which includes a container housing a suitable transition metal oxide reverse water-gas shift catalyst. A hydrogen stream is supplied to the reverse water-gas shift unit via line 26. If the reverse water-gas shift unit includes a combustion section for preheating the feed gas, an oxygen stream may optionally be supplied from the electrolysis unit 16 via line 41. The carbon dioxide and hydrogen react on the reverse water-gas shift catalyst to produce a product gas stream containing carbon monoxide and water vapor. The reverse water-gas shift unit includes a heat exchanger downstream of the reverse water-gas shift reactor for cooling the product gas below its dew point, and one or more gas-liquid separators for separating the resulting condensates to provide a carbon monoxide-containing gas stream.

[0055] The carbon monoxide-containing gas stream recovered from the reverse water-gas shift unit 24 may contain unreacted carbon dioxide, in which case the carbon monoxide-containing gas may be supplied to the carbon dioxide removal unit 20, or preferably to a separate carbon dioxide removal unit (not shown) downstream of one or more gas-liquid separators in the reverse water-gas shift unit 24. The advantage of using a separate carbon dioxide removal unit within the reverse water-gas shift unit is that the carbon dioxide is less likely to contain contaminants, and therefore the carbon dioxide removal unit can be operated differently and / or smaller in scale and different absorbents can be used. The carbon dioxide recovered from the carbon monoxide-containing gas stream is recycled to the reverse water-gas shift reactor.

[0056] The output from a reverse water-gas shift unit, including any carbon dioxide removal process, is a carbon monoxide gas stream.

[0057] The carbon monoxide gas stream is recovered from the reverse water-gas shift unit 24 via line 28 and merges with the synthesis gas recovered from the carbon dioxide removal unit 20 via line 30 to form a combined gas mixture in line 32. If desired, the combined gas mixture may be treated in a purification unit (not shown) downstream of the carbon dioxide removal unit 20 and upstream of the Fischer-Tropsch hydrocarbon synthesis unit 38 to remove residual contaminants such as hydrogen sulfide and FT catalyst poisoning.

[0058] The combined gas mixture in line 32 may optionally be combined with a hydrogen gas stream supplied by line 34 and, if desired, at a suitable temperature and pressure, with the resulting mixture supplied to the Fischer-Tropsch hydrocarbon synthesis unit 38 via line 36 to adjust the hydrogen-to-carbon monoxide molar ratio.

[0059] The Fischer-Tropsch hydrocarbon synthesis unit 38 includes a tubular reaction vessel housing a catalyst support containing a cobalt Fischer-Tropsch catalyst arranged in several tubes within the reactor. Hydrogen and carbon monoxide react on the catalyst to form a mixture of gaseous and liquid hydrocarbons, as well as FT water as a byproduct. The hydrocarbon mixture is processed within the hydrocarbon synthesis unit 38 to separate the FT water from the gaseous and liquid hydrocarbons. The FT water is recovered from the Fischer-Tropsch hydrocarbon synthesis unit 38 and supplied to the electrolytic unit 16 via line 40.

[0060] The electrolysis unit 16 comprises one or more electrolytic cells that convert FT water 40 into oxygen and hydrogen using electrical energy provided by an electrical energy source (not shown). The oxygen produced by the electrolysis unit is supplied to the synthesis gas production unit 12 via line 14. If the combustion unit is located in the reverse water-gas shift unit, oxygen may also be supplied to the combustion unit by the electrolysis unit 16 via line 41. Excess oxygen may be sent to a separate process via an outlet line (not shown). Hydrogen is recovered from the electrolysis unit 16 via line 42. Hydrogen from line 42 is supplied to the reverse water-gas shift unit 24 via line 26. Optionally, a portion of the hydrogen in line 42 may bypass the reverse water-gas shift unit 24 and be supplied directly to the feed gas for the Fischer-Tropsch hydrocarbon synthesis unit 38 via line 34. Optionally, a portion of the hydrogen from line 42 may be supplied to the hydrogenation unit 46 via line 56.

[0061] The Fischer-Tropsch hydrocarbon synthesis unit 38 produces one or more hydrocarbon streams, including but not limited to molten hydrocarbon waxes and / or light hydrocarbon condensates, which are liquid at ambient temperature. One or more hydrocarbon products from the Fischer-Tropsch hydrocarbon synthesis unit 38 are supplied to the hydrogenation unit 46 via line 44 at a suitable temperature and pressure. The hydrogenation unit includes one or more containers housing catalysts, such as hydrogenation isomerization, hydrogenation, hydrogenation deoxygenation, and / or hydrocracking catalysts, which convert the hydrocarbon waxes or hydrocarbon condensates into one or more valuable hydrocarbon products. Hydrogen is supplied to the hydrogenation unit. Any hydrogen source may be used, but preferably, a portion of the hydrogen produced by the electrolysis unit 16 is supplied to the hydrogenation unit 46 via line 56. Valuable hydrocarbon products, such as kerosene, are recovered from the hydrogenation unit 46 via line 48.

[0062] In further embodiments, the process may be enhanced as follows:

[0063] 1. The reverse water-gas shift unit 24 produces water as a byproduct. Water or a portion thereof may be supplied from the reverse water-gas shift unit 24 to the electrolysis unit via line 52 to replenish the FT water. The FT water may also be replenished with a supplement water supply via line 54 if necessary.

[0064] 2. The Fischer-Tropsch hydrocarbon synthesis unit 38 produces gaseous hydrocarbons as part of the hydrocarbon mixture. A portion of the gaseous hydrocarbons is recovered from the Fischer-Tropsch hydrocarbon synthesis unit 38 and returned to the synthesis gas production unit 12 via line 58 as FT tail gas, where it may be used as fuel and / or subjected to steam reforming and / or partial oxidation to form a hydrogen / carbon monoxide-containing gas stream for use in the process, or merged with feedstock. Alternatively, a portion of the FT tail gas may be directly supplied to the reverse water-gas shift unit 24, or subjected to an adiabatic steam reforming (pre-reformation) process to convert higher hydrocarbons into methane, and the resulting pre-reformed gas mixture may be supplied to the reverse water-gas shift unit 24.

[0065] 3. A cryogenic air separation unit (ASU) (not shown) may be used to generate supplemental oxygen that will be supplied to the synthesis gas generation unit via line 60.

[0066] Furthermore, the present invention will be further illustrated by referring to the following calculation example of the flow sheet in Figure 1, in which O2 from the electrolytic unit 16 is supplied to the combustion section of the reverse water-gas shift reactor and a portion of the hydrogen from line 42 is supplied to the hydrogenation unit 46 via line 56. The flow sheet is based on 1000 kmol / h of synthesis gas from the synthesis gas production unit 12, and the final FT production, represented as "CH2", was based on the CO content to provide a final comparison. [Table 1] [Table 2]

[0067] A comparative example without the reverse water-gas shift unit 24 connected to the electrolytic unit 16 was also modeled using the same criteria. The results were as follows. [Table 3] [Table 4]

[0068] The FT product at this 301 kmol / h rate is 41% less than when an inverse water-gas shift unit is included.

Claims

1. A hydrocarbon synthesis process comprising: (a) a step of producing synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide from a supply raw material in a synthesis gas production unit; (b) a step of removing carbon dioxide from the synthesis gas in a carbon dioxide removal unit to produce a carbon dioxide stream and purified synthesis gas containing hydrogen and carbon monoxide; and (c) a step of synthesizing a hydrocarbon mixture from the purified synthesis gas in a Fischer-Tropsch hydrocarbon synthesis unit while co-producing an FT water stream, wherein (i) at least a portion of the FT water stream is supplied to an electrolytic unit and supplied to the synthesis gas production unit as an oxygen stream and water A process comprising: (ii) supplying a stream, at least a portion of the carbon dioxide stream recovered from the carbon dioxide removal unit and a portion of the hydrogen stream generated by the electrolysis unit to a reverse water-gas shift unit to generate a carbon monoxide stream, and (iii) supplying at least a portion of the carbon monoxide stream from the reverse water-gas shift unit to the Fischer-Tropsch hydrocarbon synthesis unit, which uses the oxygen stream provided by the electrolysis unit to burn a portion of the feed gas containing carbon dioxide and hydrogen supplied to the reverse water-gas shift unit to raise the temperature of the feed gas.

2. The process according to claim 1, wherein the raw material supplied includes natural gas, associated gas, coal, biomass, or municipal solid waste.

3. The process according to claim 2, wherein the raw material supplied is natural gas, and the synthesis gas production unit includes a catalytic partial oxidation unit, a non-catalytic partial oxidation unit, or a self-thermal reformer.

4. The process according to claim 2, wherein the raw material supply is coal, biomass, or municipal solid waste, and the synthesis gas production unit comprises a gasification apparatus having one or more downstream processing units selected from a partial oxidation unit, a tar reforming unit, and a refining reactor containing a refined material.

5. The process according to any one of claims 1 to 4, wherein the carbon dioxide removal unit includes a physical cleaning system or a reactive cleaning system.

6. The process according to any one of claims 1 to 5, wherein the Fischer-Tropsch hydrocarbon synthesis unit includes a tubular reactor in which a catalyst support containing a Fischer-Tropsch catalyst is arranged in one or more tubes that are cooled by a cooling medium.

7. The process according to any one of claims 1 to 6, further comprising the step (d) of improving the quality of a mixture of hydrocarbons synthesized in the Fischer-Tropsch hydrocarbon synthesis unit within a hydrogenation unit to produce a hydrocarbon product, wherein the hydrogenation unit is connected to the Fischer-Tropsch hydrocarbon synthesis unit.

8. The process according to claim 7, wherein the hydrogenation treatment unit includes one or more containers for housing a catalyst selected from a hydrogenation isomerization catalyst, a hydrogenation catalyst, a hydrogenation deoxygenation catalyst, and / or a hydrogen cracking catalyst.

9. The process according to claim 7 or 8, wherein a portion of the hydrogen stream from the electrolytic unit is supplied to the hydrogenation unit.

10. The process according to any one of claims 1 to 9, wherein the water flow generated by the reverse water-gas shift unit is supplied to the electrolysis unit.

11. The process according to any one of claims 1 to 10, wherein a portion of the hydrogen stream from the electrolytic unit is supplied to the Fischer-Tropsch hydrocarbon synthesis unit.

12. The process according to any one of claims 1 to 11, wherein the water formed in the reverse water-gas shift unit is supplied to the electrolysis unit.

13. The process according to any one of claims 1 to 12, wherein a tail gas containing one or more of methane, ethane, propane, butane, and C5-C10 hydrocarbons is recovered from the Fischer-Tropsch hydrocarbon synthesis unit and supplied to the synthesis gas production unit.

14. The process according to any one of claims 1 to 12, wherein a tail gas containing one or more of methane, ethane, propane, butane, and C5-C10 hydrocarbons is recovered from the Fischer-Tropsch hydrocarbon synthesis unit, subjected to a separate reforming step to form a hydrogen-containing reformed tail gas, and the reformed tail gas is supplied to the Fischer-Tropsch hydrocarbon synthesis unit and / or the reverse water-gas shift unit.

15. The process according to claim 7, wherein the hydrocarbon product recovered from the hydrogenation unit is supplied to a separate unit to recover C1-C4 gas, naphtha fraction, at least one kerosene and / or light oil fraction, and heavy fraction.

16. A system for carrying out the process according to any one of claims 1 to 15, comprising: (a) a synthesis gas generation unit for producing synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide from a supply raw material; (b) a carbon dioxide removal unit connected to the synthesis gas generation unit for removing carbon dioxide from the synthesis gas and producing a carbon dioxide stream and purified synthesis gas containing hydrogen and carbon monoxide; and (c) a Fischer-Tropsch hydrocarbon synthesis unit connected to the carbon dioxide removal unit for synthesizing a mixture of hydrocarbons from the purified synthesis gas while co-producing an FT water stream, wherein (i) the electrolysis unit is the Fischer-Tropsch hydrocarbon synthesis unit (ii) a reverse water-gas shift unit is connected to the carbon dioxide removal unit and the electrolysis unit and is configured to generate an oxygen stream and a hydrogen stream, supplied together with at least a portion of FT water and supplied to the synthesis gas generation unit, and (iii) the Fischer-Tropsch hydrocarbon synthesis unit is connected to the reverse water-gas shift unit and receives at least a portion of the carbon monoxide stream.

17. The system according to claim 16, further comprising a hydrogenation treatment unit connected to the Fischer-Tropsch hydrocarbon synthesis unit for improving the quality of a hydrocarbon mixture to produce a hydrocarbon product.

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