Method for producing liquid hydrocarbons from synthesis gas

Abstract

A process for producing liquid hydrocarbons from synthesis gas, the process comprising: providing synthesis gas comprising hydrogen cyanide and sulfur compounds; separating the synthesis gas containing hydrogen cyanide and sulfur compounds into a first synthesis gas portion and a second synthesis gas portion; passing the mixture of the first syngas portion and steam through a water gas shift reaction chamber to provide a first syngas portion rich in hydrogen; combining the hydrogen-rich first syngas portion with the second syngas portion to provide a combined syngas; passing the combined syngas through a hydrolysis reaction chamber containing a titanium dioxide catalyst to convert at least a portion of the hydrogen cyanide in the combined syngas to ammonia to provide an ammonia rich, hydrogen cyanide depleted syngas; introducing the ammonia-rich hydrogen cyanide-depleted synthesis gas into a first scrubber and contacting the ammonia-rich hydrogen cyanide-depleted synthesis gas with a first scrubbing liquid, whereby at least a portion of the ammonia contained in the ammonia-rich, hydrogen cyanide-depleted syngas is retained in the first scrubbing liquid to form an ammonia-depleted, hydrogen cyanide-depleted syngas; passing the ammonia-depleted, hydrogen cyanide-depleted syngas through a carbon dioxide removal unit to form a carbon dioxide-depleted syngas; passing the carbon dioxide-depleted syngas to a reaction chamber containing a zinc oxide material to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas to ammonia and adsorb residual sulfur compounds present in the carbon dioxide-depleted syngas to provide an ammonia-rich, hydrogen cyanide-depleted desulfurized syngas; introducing the ammonia-rich and hydrogen cyanide-depleted desulfurized synthesis gas into a second scrubber, and contacting the ammonia-rich and hydrogen cyanide-depleted desulfurized synthesis gas with a second washing liquid, whereby at least a portion of the ammonia contained in the ammonia-rich, hydrogen cyanide-depleted desulfurized syngas is retained in the second scrubbing liquid to form an ammonia-depleted, hydrogen cyanide-depleted desulfurized syngas; and passing the ammonia-depleted, hydrogen cyanide-depleted desulfurized syngas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product.

Description

Technical Field

[0001] This invention relates to a method for producing liquid hydrocarbons from syngas. Background Technology

[0002] The Fischer-Tropsch process is a series of chemical reactions that convert a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions occur in the presence of a metal catalyst, typically at temperatures ranging from 150°C to 300°C and pressures from one atmosphere to tens of atmospheres. The Fischer-Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally possessing the formula (C... n H 2n+2 A more useful reaction is the following to produce alkanes:

[0003]

[0004] Where n can be 1 to 100 or higher. The formation of methane (n=1) is undesirable. Most of the alkanes produced tend to be straight-chain, suitable for upgrading to produce middle distillate fuels such as diesel and jet fuel. In addition to alkanes, the competing reactions also produce small amounts of alkenes, as well as alcohols and other oxidized hydrocarbons. Water, produced co-existingly, is a byproduct and is separated from the products of the Fischer-Tropsch reaction. Since the standard enthalpy of reaction (ΔH) is... The Fischer-Tropsch reaction involving CO is a highly exothermic reaction.

[0005] The syngas feedstock for a Fischer-Tropsch unit can be derived from a variety of feedstocks; for example, natural gas via steam reforming and / or autothermal reforming, municipal solid waste and biomass via high-temperature gasification, or carbon dioxide and hydrogen via reverse water-gas shift. The syngas produced by these processes typically contains ppm levels of hydrogen cyanide and ammonia, which deactivate the Fischer-Tropsch catalyst, and therefore ideally, hydrogen cyanide and ammonia must be removed to single-digit ppb levels. To remove these substances from the syngas, hydrogen cyanide is typically converted to ammonia via hydrolysis, and then the ammonia is removed using a wet scrubber. Obtaining ppb levels of ammonia is technically challenging.

[0006] Syngas can also contain many different sulfur compounds, including carbonyl sulfide (carbonyl sulfide), thiols (RSH), and hydrogen sulfide (H2S). Sulfur compounds are poisons for Fischer-Tropsch catalysts. Carbonyl sulfide is a particular problem because it is not easily removed by adsorption, and therefore it has been found that hydrolysis to hydrogen sulfide is necessary for its efficient removal from syngas.

[0007] US9422492B2 relates to an integrated process for producing liquid hydrocarbons. Syngas is split in two, one half undergoing a water-gas shift reaction, while the other half undergoes catalytic hydrolysis to hydrolyze HCN and COS, and then the mixtures are recombined. The recombined syngas is then scrubbed and treated for acidic gases before being fed into a Fischer-Tropsch reactor. This process is complex and requires a separate water source for the water-gas shift and hydrolysis steps. US10518210B2 and EP3546053B1 relate to gas purification units in which syngas undergoes an HCN hydrolysis step, followed by a COS hydrolysis step, and then gas purification and desulfurization steps. The aim of these documents is to provide gas purification units and methods that can effectively reduce the carbonyl sulfide concentration in the gas to be treated, even when the concentration is high. Such methods will not be able to reduce the HCN content in the final syngas to less than 10 ppbv, especially without the use of a large volume of hydrolysis catalyst, and therefore the purified syngas will be susceptible to poisoning of the Fischer-Tropsch catalyst.

[0008] This invention seeks to solve at least some of the problems associated with the prior art or to provide at least commercially acceptable alternative solutions. Summary of the Invention

[0009] One aspect of this disclosure relates to a method for producing liquid hydrocarbons from syngas, the method comprising:

[0010] Provides synthesis gas containing hydrogen cyanide and sulfur compounds;

[0011] The syngas containing hydrogen cyanide and sulfur compounds is divided into a first syngas portion and a second syngas portion.

[0012] The mixture of the first syngas component and steam is passed through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas component;

[0013] The first syngas portion rich in hydrogen is combined with the second syngas portion to provide combined syngas;

[0014] The combined syngas is passed through a hydrolysis reaction chamber containing a titanium dioxide catalyst to convert at least a portion of the hydrogen cyanide in the combined syngas into ammonia to provide ammonia-rich, hydrogen cyanide-depleted syngas.

[0015] The ammonia- and hydrogen cyanide-depleted syngas is passed into a first scrubber and brought into contact with a first scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the first scrubbing liquid to form an ammonia-depleted and hydrogen cyanide-depleted syngas.

[0016] The ammonia- and hydrogen cyanide-depleted syngas is passed through a carbon dioxide removal unit to form carbon dioxide-depleted syngas.

[0017] The carbon dioxide-depleted syngas is passed into a reaction chamber containing zinc oxide material to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas into ammonia and adsorb residual sulfur compounds present in the carbon dioxide-depleted syngas, so as to provide ammonia-rich, hydrogen cyanide-depleted desulfurized syngas.

[0018] The ammonia- and hydrogen cyanide-depleted desulfurized syngas is passed into a second scrubber and brought into contact with a second scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the second scrubbing liquid to form an ammonia- and hydrogen cyanide-depleted desulfurized syngas; and

[0019] The desulfurized syngas, which is depleted of ammonia and hydrogen cyanide, is passed through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products. Attached Figure Description

[0020] Figure 1 A flowchart of an exemplary method according to the present invention is shown. Detailed Implementation

[0021] In a first aspect, this disclosure relates to a method for producing liquid hydrocarbons from syngas, the method comprising:

[0022] Provides synthesis gas containing hydrogen cyanide and sulfur compounds;

[0023] The syngas containing hydrogen cyanide and sulfur compounds is divided into a first syngas portion and a second syngas portion.

[0024] The mixture of the first syngas component and steam is passed through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas component;

[0025] The first syngas portion rich in hydrogen is combined with the second syngas portion to provide combined syngas;

[0026] The combined syngas is passed through a hydrolysis reaction chamber containing a titanium dioxide catalyst to convert at least a portion of the hydrogen cyanide in the combined syngas into ammonia to provide ammonia-rich, hydrogen cyanide-depleted syngas.

[0027] The ammonia- and hydrogen cyanide-depleted syngas is passed into a first scrubber and brought into contact with a first scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the first scrubbing liquid to form an ammonia-depleted and hydrogen cyanide-depleted syngas.

[0028] The ammonia- and hydrogen cyanide-depleted syngas is passed through a carbon dioxide removal unit to form carbon dioxide-depleted syngas.

[0029] The carbon dioxide-depleted syngas is passed into a reaction chamber containing zinc oxide material to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas into ammonia and adsorb residual sulfur compounds present in the carbon dioxide-depleted syngas, so as to provide ammonia-rich, hydrogen cyanide-depleted desulfurized syngas.

[0030] The ammonia- and hydrogen cyanide-depleted desulfurized syngas is passed into a second scrubber and brought into contact with a second scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the second scrubbing liquid to form an ammonia- and hydrogen cyanide-depleted desulfurized syngas; and

[0031] The desulfurized syngas, which is depleted of ammonia and hydrogen cyanide, is passed through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products.

[0032] Unless expressly indicated otherwise, each aspect or embodiment as defined herein may be combined with any other aspect or embodiment. Specifically, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0033] Advantageously, the method of the present invention can be simpler and / or more efficient compared to conventional methods.

[0034] Contrary to the method described in US9422492B2, the method of the present invention comprises combining a hydrogen-rich syngas portion with a syngas portion to provide combined syngas, and then passing the combined syngas through a hydrolysis chamber. In other words, the method of the present invention hydrolyzes the entire syngas (both the portion undergoing the water-gas shift reaction and the portion bypassing the water-gas shift reaction chamber). The catalyst in the water-gas shift reaction chamber typically hydrolyzes hydrogen cyanide (HCN) and carbonyl sulfide (COS) present in the syngas. Therefore, in conventional methods (such as those described in US9422492B2), hydrolysis typically occurs only in the portion of the syngas that has not yet undergone the water-gas shift reaction, since the HCN in the other portions has already been hydrolyzed in the water-gas shift reaction chamber. However, the inventors of the present invention have surprisingly discovered that recombining the two feed streams before feeding them into the hydrolysis chamber can drive the hydrolysis reaction to equilibrium using excess steam added to the water-gas shift reactor. Specifically, hydrolyzing the combined syngas avoids the need to add a separate preheater and another steam or water addition line to the hydrolysis bed to process only the second syngas portion, i.e., the portion of the syngas that bypasses the water-gas shift. Therefore, the method of the present invention can be simpler and / or use less water compared to conventional methods.

[0035] Titanium dioxide catalysts can also at least partially convert carbonyl sulfide present in syngas into hydrogen sulfide, thereby providing syngas that is rich in ammonia and depleted in hydrogen cyanide, and rich in carbonyl sulfide.

[0036] The applicants have discovered that the use of titanium dioxide catalysts in the hydrolysis reaction chamber allows for lower operating temperatures and a smaller bulk hydrolysis bed size.

[0037] After being passed through the hydrolysis reaction chamber and the first scrubber, the syngas is then passed into a reaction chamber containing zinc oxide material, typically a particulate zinc oxide adsorbent suitable for capturing hydrogen sulfide (H2S) formed by the hydrolysis of COS. The inventors have surprisingly found that the use of zinc oxide material is remarkably effective in the hydrolysis and / or hydrogenation of residual hydrogen cyanide and carbonyl sulfides in the syngas. Therefore, the zinc oxide material adsorbent can be used to simultaneously hydrolyze and / or hydrogenate these residual contaminants under reaction conditions. The resulting process simplification reduces the capital and operating costs of separate upstream refining hydrolysis catalyst beds and associated heat exchangers. Consequently, the method is more economical and allows for a reduction in the size of the equipment used to perform the method.

[0038] As used herein, the term "liquid hydrocarbon" can encompass substances formed from carbon and hydrogen that are liquid at room temperature and pressure. Hydrocarbons typically include alkanes and may contain 5 to 100 or more carbon atoms per molecule.

[0039] As used herein, the term "syngas" or "synthesis gas" may encompass a gaseous mixture containing hydrogen and carbon monoxide. In the method of the present invention, the first syngas comprises carbon monoxide (i.e., CO), hydrogen (i.e., molecular hydrogen H2), hydrogen cyanide (i.e., HCN), and sulfur compounds, such as hydrogen sulfide (i.e., H2S) and / or carbonyl sulfide (i.e., COS). Syngas may contain other gases, such as, for example, water, methane, ammonia, carbon dioxide (i.e., CO2), and solid substances, such as, for example, dust and coke. Syngas is typically produced by the gasification of carbonaceous materials. In the present invention, syngas is preferably formed by the gasification of biomass and / or municipal waste. While these may be more ecologically sustainable carbon sources than fossil fuels, they present the problem of pollutants that need to be removed to very low levels to avoid poisoning the Fischer-Tropsch catalyst. The composition of the syngas will vary depending on its production method and the starting materials used.

[0040] The method involves passing a mixture of a first syngas fraction and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas fraction. Water-gas shift reaction chambers are known in the art. An acid shift catalyst or other sulfur-resistant water-gas shift catalyst is preferably used to catalyze the water-gas shift reaction. Excess steam is preferably provided to drive the reaction to equilibrium. Furthermore, the excess steam can be used in a subsequent hydrolysis step.

[0041] This method involves passing ammonia- and hydrogen cyanide-depleted syngas into a first scrubber, and ammonia- and hydrogen cyanide-depleted desulfurized syngas into a second scrubber. Scrubbers and scrubbing liquids are known in the art. Ammonia removal efficiency can be improved by increasing the residence time in the scrubber or by increasing the surface area of ​​the scrubbing liquid using, for example, trays, structured packing, or random packing.

[0042] This method involves passing ammonia- and hydrogen cyanide-depleted syngas through a carbon dioxide removal unit to form carbon dioxide-depleted syngas. This makes the method more efficient because reducing the volume of inert gas reduces the energy required for any heating or cooling steps. The carbon dioxide removal unit can employ physical absorption using, for example, cooled methanol (e.g., Rectisol®) and / or chemical absorption using, for example, amine-based systems. Such methods can also remove some hydrogen cyanide from the syngas.

[0043] The desulfurized synthesis gas, which is depleted of ammonia and hydrogen cyanide, passes through a Fischer-Tropsch reaction chamber. The Fischer-Tropsch reaction chamber is known in the art.

[0044] The liquid hydrocarbon products preferably comprise alkanes, more preferably alkanes having 5 to 100 or more carbon atoms. Such hydrocarbon products may be particularly desirable as fuel sources. Furthermore, cobalt catalysts typically used in the production of such hydrocarbon products may be particularly susceptible to poisoning by hydrogen cyanide.

[0045] Providing syngas containing hydrogen cyanide and sulfur compounds preferably involves the gasification of biomass and / or municipal waste. Coal gasification is less preferred. Biomass and municipal waste are becoming more widely available, and syngas produced from these materials can be particularly suitable for the production of liquid hydrocarbons. Additionally, such syngas typically contains hydrogen cyanide and sulfur compounds as impurities. Gasification is a technique known in the art. During gasification, biomass and / or municipal waste and / or coal are purged with oxygen and steam (water vapor) while also being heated (and in some cases pressurized). Importantly, the supplied oxidant is insufficient to completely oxidize (combust) the fuel. During the aforementioned reaction, oxygen and water molecules oxidize the biomass, municipal waste, and / or coal, producing a gaseous mixture of carbon dioxide, carbon monoxide, water vapor, and molecular hydrogen. Advantageously, heat can be recovered from gasification for use in other steps of the method.

[0046] Preferably, the ratio of the hydrogen-rich first syngas portion to the second syngas portion is controlled to provide a hydrogen to carbon monoxide molar ratio of 1.5 to 2.5, preferably 1.8 to 2.2, in the combined syngas. Such a ratio results in almost complete conversion of carbon monoxide in the Fischer-Tropsch reaction chamber.

[0047] The first syngas portion preferably comprises 50 to 60 vol% of syngas containing hydrogen cyanide, and the second syngas portion preferably comprises 40 to 50 vol% of syngas containing hydrogen cyanide. Based on the composition of typical syngas, such values ​​can lead to a preferred ratio of hydrogen to carbon monoxide in the combined syngas described above.

[0048] More preferably, steam (more preferably superheated steam) is added to the first syngas section before it is introduced into the water-gas shift reaction chamber, and the first syngas section is preferably heated to a temperature of 200°C to 400°C. Lower temperatures may result in unfavorable low reaction rates. Higher temperatures may cause hydrogen formation to become thermodynamically less favorable.

[0049] The water-gas shift reaction chamber preferably contains a catalyst comprising supported cobalt oxide and molybdenum oxide. Such a catalyst is particularly suitable for catalyzing water-gas shift reactions and can provide favorable reaction rates and / or enable the use of lower temperatures.

[0050] Hydrolysis in the hydrolysis reaction chamber is preferably carried out at a temperature greater than 100°C, more preferably 150°C to 300°C, and most preferably 150°C to 200°C. Lower temperatures may result in undesirable low levels of hydrolysis. Higher temperatures may increase the energy cost of the method without significantly improving the conversion rate of hydrogen cyanide.

[0051] Hydrolysis in the hydrolysis reaction chamber is carried out using a titanium dioxide catalyst. The applicant has found that titanium dioxide catalysts are superior to alumina catalysts. This catalyst can lead to particularly high conversion rates and / or enables advantageous operation at low temperatures.

[0052] After hydrolysis, the ammonia- and hydrogen cyanide-depleted syngas and the ammonia- and hydrogen cyanide-depleted desulfurized syngas are preferably cooled before contact with the first scrubber and / or the second scrubber, more preferably cooled to 40°C or lower, and even more preferably cooled to ambient temperature.

[0053] The present invention involves passing an ammonia- and hydrogen cyanide-depleted syngas into a first scrubber and contacting the ammonia- and hydrogen cyanide-depleted syngas with a first scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the first scrubbing liquid to form an ammonia- and hydrogen cyanide-depleted syngas. The scrubbing liquid in the first scrubber is preferably water, which may be boiler feedwater or utility water, or water condensate recovered from the process and optionally purified. The scrubbing liquid of the first scrubber may also contain co-generated water recovered from the FT reaction chamber. The first scrubber is upstream of a carbon dioxide removal unit. If desired, the carbon dioxide removal unit may include a water washing step to remove ammonia present in the syngas before washing with a carbon dioxide absorbent to remove carbon dioxide from the ammonia- and hydrogen cyanide-depleted syngas.

[0054] Syngas may also contain ammonia. Ammonia is a common impurity in syngas. Given the high ammonia removal capacity of the washing liquid, the method of the present invention is particularly suitable for syngas containing ammonia.

[0055] The syngas containing hydrogen cyanide may contain carbonyl sulfide, and preferably at least some of the carbonyl sulfide is hydrolyzed to hydrogen sulfide in a hydrolysis reaction chamber containing a titanium dioxide catalyst and a reaction chamber containing zinc oxide material. Preferably, the carbon dioxide removal unit introduced into the ammonia-depleted and hydrogen cyanide-depleted syngas is an acid gas removal unit that removes carbon dioxide, and optionally hydrogen sulfide and hydrogen cyanide, from the ammonia-depleted and hydrogen cyanide-depleted syngas before introducing it into the reaction chamber containing zinc oxide material.

[0056] In this method, downstream of the carbon dioxide removal unit, the carbon dioxide-lean syngas is passed into a reaction chamber containing zinc oxide material to convert at least a portion of the hydrogen cyanide in the carbon dioxide-lean syngas into ammonia and adsorb residual sulfur compounds present in the carbon dioxide-lean syngas, thereby providing ammonia-rich, hydrogen cyanide-lean desulfurized syngas. Sulfur removal reduces poisoning of the downstream Fischer-Tropsch catalyst. The zinc oxide sulfur compound adsorbent preferably operates in a temperature range of 100°C to 230°C, preferably about 150°C. The zinc oxide material also simultaneously hydrolyzes and / or hydrogenates residual hydrogen cyanide and carbonyl sulfides present in the syngas.

[0057] The desulfurized syngas, rich in ammonia and depleted in hydrogen cyanide, preferably contains less than 10 ppbv of hydrogen cyanide. This low level of hydrogen cyanide can lead to particularly low levels of poisoning in the Fischer-Tropsch catalyst.

[0058] The preferred temperature in the Fischer-Tropsch reaction chamber is between 150°C and 300°C. Lower temperatures may result in the formation of undesirable low levels of liquid hydrocarbons. Higher temperatures may increase the energy cost of the method without a significant increase in the level of liquid hydrocarbons produced.

[0059] The desulfurized syngas, depleted of ammonia and hydrogen cyanide, is passed through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products. Preferably, this involves contacting the desulfurized syngas, depleted of ammonia and hydrogen cyanide, with a catalyst containing a metal selected from cobalt, iron, or ruthenium. Such a catalyst may be particularly effective in catalyzing the Fischer-Tropsch reaction and / or enables the reaction to proceed advantageously at low temperatures and / or in high yields.

[0060] At least the washing liquid of the second scrubber is suitably water, and preferably contains co-generated water. In a preferred embodiment, the desulfurized syngas, depleted of ammonia and hydrogen cyanide, is passed through a Fischer-Tropsch reactor to produce liquid hydrocarbon products and co-generated water; and at least a portion of the second washing liquid contains co-generated water recovered from the Fischer-Tropsch reactor. The co-generated water can be separated from the products recovered from the Fischer-Tropsch reactor using conventional separation equipment.

[0061] The hydrocarbon products from the Fischer-Tropsch reactor are separated from the water and unreacted gases produced together, and can then be converted or upgraded into liquid hydrocarbon fuels, for example, by hydrocracking.

[0062] Furthermore, the co-generated water will contain dissolved carbon dioxide from the syngas and from carbon dioxide generated as a byproduct in the Fischer-Tropsch reactor. The ammonia removal capacity of the wash liquid can be enhanced by the presence of carbon dioxide. Therefore, it is easier to reduce the ammonia and hydrogen cyanide content in the syngas to single-digit ppb levels. Consequently, poisoning of the Fischer-Tropsch catalyst is further reduced, meaning the method is more efficient as it does not require periodic regeneration or replacement of the Fischer-Tropsch catalyst. Additionally, the use of hydrogen cyanide and ammonia absorption beds just before the Fischer-Tropsch reactor can be avoided, resulting in a simpler method compared to conventional approaches. Using co-generated water, instead of another water source (such as boiler feedwater or softened water), simplifies the method and reduces operating costs. Moreover, since the co-generated water is recovered from the Fischer-Tropsch reactor, it is free of poisons. Therefore, the risk of introducing poisons that could deactivate the catalyst is reduced compared to similar processes using other wash liquid sources. Using co-generated water recovered from the Fischer-Tropsch reactor in the second wash liquid ensures that no Fischer-Tropsch catalyst poisons that may be present in other water streams (such as boiler feedwater with added chemicals) are introduced into the system.

[0063] The washing liquid, preferably the second washing liquid, may contain at least 0.01 mol / L carbon dioxide, more preferably at least 0.02 mol / L carbon dioxide. This carbon dioxide concentration can result in a high ammonia removal capacity of the washing liquid.

[0064] In a preferred embodiment, the washing liquid, especially the second washing liquid, is saturated with carbon dioxide under the temperature and pressure conditions of the washer.

[0065] In cases where the syngas containing hydrogen cyanide and sulfur compounds also contains particulate matter entrained within the hydrogen cyanide-containing syngas, the hydrogen cyanide-containing syngas is preferably passed through a particulate filter upstream of the water-gas shift reaction chamber, and more preferably as a first purification step. The particulate filter may comprise a high-temperature, high-porosity inert filter media, such as high-purity alumina shaped beads. A commercial example of a suitable filter media is Dypor™ 607, which can operate over a temperature range from ambient to 500°C, preferably from 60°C to 200°C.

[0066] In cases where the syngas containing hydrogen cyanide and sulfur compounds also contains hydrogen halide compounds, the hydrogen cyanide-containing syngas is preferably passed through a hydrogen halide adsorbent bed upstream of the water-gas shift reaction chamber, and more preferably downstream of the particulate filter. The first portion of the syngas upstream of the water-gas shift reaction chamber preferably passes through the hydrogen halide adsorbent bed. Placing the hydrogen halide adsorbent immediately after the particulate filter reduces the corrosiveness of the syngas relative to high-temperature sulfidation, which is accelerated in the presence of halides. This allows for the use of lower-cost structural materials for downstream purification and the remainder of the water-gas shift system. The hydrogen halide adsorbent preferably comprises an alkali-promoted adsorbent. The hydrogen halide adsorbent preferably operates within a temperature range of ambient temperature to 400°C, preferably 120 to 300°C.

[0067] In cases where the syngas containing hydrogen cyanide and sulfur compounds also contains mercury, the ammonia-rich, hydrogen cyanide-depleted syngas is preferably passed through a mercury adsorbent bed upstream of the first scrubber and downstream of the hydrolysis reaction chamber. Mercury is a common impurity in syngas (especially syngas produced by gasification). Removal of mercury can reduce poisoning of downstream Fischer-Tropsch catalysts. The mercury adsorbent preferably contains sulfurized activated carbon. The mercury adsorbent is preferably operated at a temperature about 20°C above the dew point (i.e., about 60°C).

[0068] When the syngas containing hydrogen cyanide and sulfur compounds further contains one or more arsenic compounds, it is preferable to pass the hydrogen cyanide-depleted desulfurized syngas through an arsenic compound adsorbent bed downstream of a reaction chamber containing zinc oxide material. Arsenic is a common impurity in syngas (especially syngas produced by gasification). Arsenic removal can reduce poisoning of downstream Fischer-Tropsch catalysts. The arsenic compound adsorbent preferably contains copper oxide and / or zinc oxide. A commercial example of a suitable arsenic compound adsorbent is Puraspec™ 2088. The arsenic compound adsorbent is preferably operated in a temperature range of 100°C to 230°C, preferably about 150°C.

[0069] The invention will now be described in conjunction with the following non-limiting embodiments.

[0070] Example

[0071] exist Figure 1A flowchart of an exemplary method according to the present invention is shown in the figure. See also Figure 1 In the first stage of purification, fine particles are removed from syngas 100 at approximately 120°C in a particulate guard bed 1. Particulate guard bed 1 contains a high-temperature, high-porosity inert filter medium. Following particulate guard bed 1, syngas 110 passes through a halide guard bed 2 at approximately 120°C. The halide guard bed 2 absorbs halides from the syngas on an alkali-promoted adsorbent and is configured in an advanced / retarded arrangement to improve removal efficiency and effectively replace the pre-bed before contaminant slippage, taking into account the difficulty in measuring the low levels of halides. This is located upstream of the HCN hydrolysis bed 5 because halides are poisons for that catalyst.

[0072] Syngas 120 is then shifted in water-gas shift (WGS) reactor 4 to provide the optimal H2:CO molar ratio for FT synthesis (2.11 mol / mol–2.14 mol / mol, run start “SOR” to run end “EOR”), controlled by bypass 125 around shift reactor 4, with approximately 40%–50% of the total syngas bypassed. The H2:CO molar ratio of the syngas is increased across the WGS reactor via the following reactions:

[0073]

[0074] Prior to the shift reaction, syngas 120 is preheated in a process heat exchanger (not shown). This stream is then split into two separate streams, one of which, 125, bypasses the shift reactor 4. The remaining syngas is further preheated in another process heat exchanger (not shown) by the hot product gas from the shift reactor 4. The stream is further heated to 230°C–320°C by adding superheated HP steam, which also provides water to drive the shift reaction. The inlet temperature is typically set to keep the outlet temperature below approximately 550°C, meaning a typical inlet temperature of 200°C–400°C. If a significant amount of arsine is present in the syngas, the remaining syngas is first fed into a pre-shift protector bed 3 at approximately 230°C–320°C to prevent poisoning of the shift catalyst. If arsine levels are high, this sacrificial pre-shift protector bed 3 can be configured in a working / standby arrangement for in-line replacement. Syngas 130 is then fed into the main shift reactor 4. The shift reaction is exothermic, and therefore the hot product gas is used to raise the HP steam in the shift gas boiler (not shown). Both the conversion and pre-conversion protection catalysts are cobalt oxide and molybdenum oxide on a high-strength magnesium aluminate support.

[0075] After heat recovery in a process heat exchanger (not shown), the syngas 125 bypassing the shift reactor 4 is combined with the shifted syngas to form a combined syngas 140. A bypass 125 around the shift gas boiler controls the inlet temperature of the HCN hydrolysis bed 5 at approximately 200°C.

[0076] In the combined syngas 140, COS and HCN are hydrolyzed to H2S and NH3, respectively, in the HCN hydrolysis bed 5 over a granular titanium dioxide catalyst. The hydrolysis reaction is as follows:

[0077]

[0078]

[0079] This produces syngas 150, which is rich in ammonia, depleted in hydrogen cyanide, and depleted in hydrogen sulfide and carbonyl sulfide. After hydrolysis, the syngas is cooled to the boiler feedwater and process gas stream through heat recovery within the process in a series of heat exchangers (not shown).

[0080] Further cooling is provided in an air cooler and a water temperature-controlled cooler (not shown), which cool the syngas to approximately 60°C and 40°C, respectively, and condense the water not consumed in the shift reaction. The condensate is separated from the syngas 150 in a syngas separator (not shown) and sent to effluent treatment.

[0081] After the syngas separator, the syngas is heated to 50°C in a heat exchanger (not shown) and passed into a mercury protection bed 6, which uses sulfurized activated carbon to remove mercury from the syngas 150 to the level required by the acid gas removal unit 8.

[0082] Between the mercury protection bed 6 and the acid gas removal unit 8 is a first syngas scrubber 7. Syngas 160 recovered from the mercury protection bed 6 is cooled in a first process heat exchanger (not shown), and then cooled to approximately 40°C using cooling water. Ammonia present in the gas or formed by the hydrolysis of HCN is scrubbed out of the syngas 160 using water in the first syngas scrubber 7. The first syngas scrubber 7 contains trays or packing. The syngas scrubbing water from the syngas scrubber 7 is sent to effluent treatment, and the cleaned syngas feed stream 170 is fed to the acid gas removal unit 8.

[0083] The acid gas removal unit 8 removes most of the carbon dioxide from the syngas and can be a chemical absorption unit such as an amine unit or a physical absorption system such as Rectisol® technology, which uses cooled methanol. The acid gas removal unit 8 will also reduce the levels of other contaminants.

[0084] After the acidic gases are removed, the synthesis gas 180 is heated to approximately 100°C–130°C in a process heat exchanger (not shown) using hot gas from the downstream arsine guard bed 10. After this, the synthesis gas 180 is passed through a second process heat exchanger, where it is heated to approximately 130°C–180°C using hot gas from the sulfur guard bed 9.

[0085] Using saturated HP steam, the syngas 180 is further heated to 150°C to 200°C in a sulfur-protected bed preheater (not shown). If necessary, a steam or boiler feedwater addition line (not shown) can be provided upstream of the sulfur-protected bed 9 to provide steam for hydrolyzing residual contaminants in the syngas.

[0086] Syngas 180 enters a sulfur guard bed 9, which includes a particulate zinc oxide adsorbent bed that is also effective for the hydrolysis and / or hydrogenation of residual HCN and COS in the syngas. This sulfur guard bed produces HCN-depleted desulfurized syngas 190. After cooling in a process heat exchanger (not shown), syngas 190 enters an arsine guard bed 10, which uses a copper / zinc oxide catalyst / adsorbent to adsorb arsine and produce purified syngas 200. The arsine guard bed 10 is configured in a working / standby arrangement for online replacement.

[0087] The syngas 200 is then cooled in a process heat exchanger (not shown), followed by cooling water to approximately 40°C. Ammonia present in the gas or formed by HCN hydrolysis is washed out of the syngas 200 in a second syngas scrubber 11 using water co-produced from the FT unit (not shown). The second syngas scrubber 11 contains trays or packing. The syngas scrubbing water from the second syngas scrubber 11 is sent to effluent treatment, and the cleaned syngas feed is fed to the FT unit.

[0088] The detailed description above has been provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments shown herein will be apparent to those skilled in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. A method for producing liquid hydrocarbons from syngas, the method comprising: Provides synthesis gas containing hydrogen cyanide and sulfur compounds; The synthesis gas containing hydrogen cyanide and sulfur compounds is divided into a first synthesis gas portion and a second synthesis gas portion. The mixture of the first syngas fraction and steam is passed through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas fraction. The hydrogen-rich first syngas portion is combined with the second syngas portion to provide combined syngas; The combined syngas is passed through a hydrolysis reaction chamber containing a titanium dioxide catalyst to convert at least a portion of the hydrogen cyanide in the combined syngas into ammonia to provide ammonia-rich, hydrogen cyanide-depleted syngas. The ammonia- and hydrogen cyanide-depleted syngas is passed into a first scrubber and brought into contact with a first scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the first scrubbing liquid to form an ammonia-depleted and hydrogen cyanide-depleted syngas. The syngas, which is depleted of ammonia and hydrogen cyanide, is passed through a carbon dioxide removal unit to form carbon dioxide-depleted syngas. The carbon dioxide-depleted syngas is passed into a reaction chamber containing zinc oxide material to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas into ammonia and adsorb residual sulfur compounds present in the carbon dioxide-depleted syngas, thereby providing ammonia-rich, hydrogen cyanide-depleted desulfurized syngas. The ammonia- and hydrogen cyanide-depleted desulfurized syngas is passed into a second scrubber and brought into contact with a second scrubbing liquid, thereby retaining at least a portion of the ammonia contained in the ammonia- and hydrogen cyanide-depleted syngas in the second scrubbing liquid to form ammonia- and hydrogen cyanide-depleted desulfurized syngas; and The desulfurized syngas, which is depleted of ammonia and hydrogen cyanide, is passed through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products.

2. The method according to claim 1, wherein the liquid hydrocarbon product comprises alkanes.

3. The method according to any of the preceding claims, wherein the synthesis gas containing hydrogen cyanide comprises the gasification of biomass and / or municipal waste.

4. The method according to any of the preceding claims, wherein the ratio of the hydrogen-rich first syngas portion and the second syngas portion is controlled to provide a hydrogen to carbon monoxide molar ratio of 1.5 to 2.5, preferably 1.8 to 2.2, in the combined syngas.

5. The method of claim 4, wherein the first synthesis gas portion comprises 50 vol% to 60 vol% of the hydrogen cyanide-containing synthesis gas, and the second synthesis gas portion comprises 40 vol% to 50 vol% of the hydrogen cyanide-containing synthesis gas.

6. The method according to any of the preceding claims, wherein, prior to being introduced into the water-gas shift reaction chamber, the first syngas section is preferably heated to a temperature of 200°C to 400°C by adding steam to the first syngas section.

7. The method according to any of the preceding claims, wherein the water-gas shift reaction chamber comprises a catalyst containing supported cobalt oxide and molybdenum oxide.

8. The method according to any of the preceding claims, wherein the hydrolysis in the hydrolysis reaction chamber containing the titanium dioxide catalyst is carried out at a temperature greater than 100°C, preferably from 150°C to 200°C.

9. The method according to any of the preceding claims, wherein the synthesis gas further comprises ammonia.

10. The method according to any of the preceding claims, wherein the hydrogen cyanide-containing syngas comprises carbonyl sulfide, and at least some of the carbonyl sulfide is hydrolyzed into hydrogen sulfide in the hydrolysis reaction chamber to produce a hydrogen sulfide-rich, carbonyl sulfide-depleted syngas.

11. The method according to any of the preceding claims, wherein the carbon dioxide removal unit to which the ammonia-depleted, hydrogen cyanide-depleted syngas is introduced is an acid gas removal unit that removes carbon dioxide and optionally hydrogen sulfide and hydrogen cyanide from the ammonia-depleted, hydrogen cyanide-depleted syngas before introducing the ammonia-depleted, hydrogen cyanide-depleted syngas into a reaction chamber containing the zinc oxide material.

12. The method according to any of the preceding claims, wherein the ammonia-rich, hydrogen cyanide-depleted desulfurized syngas contains less than 10 ppbv of hydrogen cyanide.

13. The method according to any of the preceding claims, wherein the ammonia-depleted, hydrogen cyanide-depleted desulfurized syngas contains less than 10 ppbv of ammonia.

14. The method according to any of the preceding claims, wherein the temperature of the Fischer-Tropsch reaction chamber is from 150°C to 300°C.

15. The method according to any of the preceding claims, wherein passing the ammonia-depleted and hydrogen cyanide-depleted desulfurized syngas through a Fischer-Tropsch reactor to produce liquid hydrocarbon products comprises contacting the ammonia-depleted and hydrogen cyanide-depleted syngas with a catalyst containing cobalt, iron, or ruthenium.

16. The method according to any of the preceding claims, wherein: The ammonia-depleted and hydrogen cyanide-depleted desulfurized syngas is passed through the Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products and co-produced water; and At least the second washing liquid contains water that is co-generated and recovered from the Fischer-Tropsch reaction chamber.

17. The method of claim 15 or claim 16, wherein the co-generated water is saturated with carbon dioxide under the temperature and pressure conditions of the washer employing the co-generated water.

18. The method according to any of the preceding claims, wherein the syngas containing hydrogen cyanide and sulfur compounds further comprises particulate matter entrained in the syngas containing hydrogen cyanide and sulfur compounds, wherein the syngas containing hydrogen cyanide and sulfur compounds is passed through a particulate filter upstream of the water-gas shift reaction chamber, and preferably as a first purification step.

19. The method according to any of the preceding claims, wherein the synthesis gas containing hydrogen cyanide and sulfur compounds further comprises hydrogen halide compounds, wherein the synthesis gas containing hydrogen cyanide and sulfur compounds is passed through a hydrogen halide adsorbent bed upstream of the water-gas shift reaction chamber and preferably downstream of the particulate filter.

20. The method of claim 19, wherein the first syngas portion upstream of the water-gas shift reaction chamber is passed through a hydrogen halide adsorbent bed.

21. The method according to any of the preceding claims, wherein the syngas containing hydrogen cyanide and sulfur compounds further comprises mercury, wherein the ammonia-rich, hydrogen cyanide-depleted syngas is passed through a mercury adsorbent bed upstream of the first scrubber and downstream of the hydrolysis reaction chamber containing the titanium dioxide catalyst.

22. The method according to any of the preceding claims, wherein the syngas containing hydrogen cyanide and sulfur compounds further comprises one or more arsenic compounds, wherein the ammonia-rich, hydrogen cyanide-depleted desulfurized syngas is passed through an arsenic compound adsorbent bed upstream of the second scrubber and downstream of the reaction chamber containing zinc oxide material.

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