Method for producing liquid hydrocarbons from synthesis gas

Abstract

1. A method for producing liquid hydrocarbons from a synthesis gas, comprising: providing a hydrogen cyanide-containing synthesis gas; splitting the hydrogen cyanide-containing synthesis gas into a first synthesis gas portion and a second synthesis gas portion; passing a mixture of the first synthesis gas portion and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first synthesis gas portion; mixing the hydrogen-rich first synthesis gas portion with the second synthesis gas portion to provide a mixed synthesis gas; passing the mixed synthesis gas through a first hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the mixed synthesis gas to ammonia to provide a first ammonia-rich hydrogen cyanide-depleted synthesis gas; passing the first ammonia-rich hydrogen cyanide-depleted synthesis gas through a first scrubber and contacting the first ammonia-rich hydrogen cyanide-depleted synthesis gas with a first scrubber liquor, whereby at least a portion of the ammonia contained in the first ammonia-rich hydrogen cyanide-depleted synthesis gas is retained in the first scrubber liquor to provide a first ammonia-depleted synthesis gas. forming a hydrogen cyanide-depleted syngas; passing the first 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 through a second hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas to ammonia to provide a second ammonia-rich hydrogen cyanide-depleted syngas; passing the second ammonia-rich hydrogen cyanide-depleted syngas through a second scrubber to contact the second ammonia-rich hydrogen cyanide-depleted syngas with a second scrubber liquor, whereby at least a portion of the ammonia contained in the second ammonia-rich hydrogen cyanide-depleted syngas is retained in the second scrubber liquor to form a second ammonia-depleted hydrogen cyanide-depleted syngas; and passing the second ammonia-depleted hydrogen cyanide-depleted syngas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product.

Description

[Technical field]

[0001] The present invention relates to a method for producing liquid hydrocarbons from synthesis gas. [Background technology]

[0002] The Fischer-Tropsch process is a set of chemical reactions that convert a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions take place in the presence of a metal catalyst, typically at temperatures between 150 and 300 °C and pressures ranging from one to several tens of atmospheres. The Fischer-Tropsch process ideally involves the reaction of the following reaction product: n H 2n+2 ), a series of chemical reactions that produce various hydrocarbons with different alkane groups. The more useful reactions produce alkanes as follows: (2n+1)H2+n CO→C n H 2n+2 +n H2O (where n can be 1 to 100, or even higher). Formation of methane (n=1) is undesirable. Most of the alkanes produced tend to be straight chain and suitable for being upgraded to produce middle distillate fuels such as diesel and jet fuel. In addition to alkane formation, competing reactions result in small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons. By-product water is a by-product that is separated from the product of the Fischer-Tropsch reaction. The Fischer-Tropsch reaction is highly exothermic, with a standard enthalpy of reaction (ΔH) of -165 kJ / mol CO total.

[0003] The synthesis gas (syngas) feed to a Fischer-Tropsch unit can be derived from many feedstocks, for example, natural gas by steam and / or autothermal reforming, municipal solid waste and biomass by high-temperature gasification, or carbon dioxide and hydrogen by reverse water gas shift. The synthesis gas produced by these processes typically contains ppm levels of hydrogen cyanide and ammonia that deactivate the Fischer-Tropsch catalyst, therefore ideally hydrogen cyanide and ammonia are removed to single digit ppb levels. To remove these species from the synthesis gas, hydrogen cyanide is typically converted to ammonia via hydrolysis, and the ammonia is then removed using wet scrubbers. Achieving ppb levels of ammonia is technically challenging.

[0004] US Patent No. 9422492 (B2) relates to an integrated process for the production of liquid hydrocarbons. The synthesis gas is split in two, one half is subjected to a water-gas shift reaction and the other half is subjected to catalytic hydrolysis to hydrolyze HCN and COS before being recombined. The recombined synthesis gas is then subjected to scrubbing and acid gas removal before being sent to the Fischer-Tropsch reaction chamber. This method is complex and requires separate water sources for the water-gas shift and hydrolysis steps. US Patent No. 10518210 (B2) and European Patent No. 3546053 (B1) relate to gas purification units in which the synthesis gas is subjected to an HCN hydrolysis step, followed by a COS hydrolysis step, followed by a gas washing and desulfurization step. The aim of these documents is to provide a gas purification unit and a gas purification method that can effectively reduce the carbonyl sulfide concentration in the treated gas, even when the concentration of carbonyl sulfide in the treated gas is high. Such methods cannot reduce the HCN content in the final syngas to below 10 ppbv, especially without using large amounts of hydrolysis catalyst, and the purified syngas is therefore prone to poisoning the Fischer-Tropsch catalyst.

[0005] The present invention aims to address at least some of the problems associated with the prior art, or at least to provide a commercially acceptable alternative solution. Summary of the Invention

[0006] A first aspect of the present disclosure is a method for producing liquid hydrocarbons from synthesis gas, comprising: Providing a hydrogen cyanide-containing synthesis gas; splitting a hydrogen cyanide-containing synthesis gas into a first synthesis gas portion and a second synthesis gas portion; passing a mixture of the first syngas portion and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas portion; mixing a first hydrogen-rich syngas portion with a second syngas portion to provide a mixed syngas; passing the mixed syngas through a first hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the mixed syngas to ammonia to provide a first ammonia-rich hydrogen cyanide-depleted syngas; passing the first ammonia-rich hydrogen cyanide-depleted syngas through a first scrubber and contacting the first ammonia-rich hydrogen cyanide-depleted syngas with a first scrubber liquor, whereby at least a portion of the ammonia contained in the first ammonia-rich hydrogen cyanide-depleted syngas is retained in the first scrubber liquor to form a first ammonia-depleted hydrogen cyanide-depleted syngas; passing the first 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 through a second hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas to ammonia to provide a second ammonia-rich hydrogen cyanide-depleted syngas; passing the second ammonia-rich hydrogen cyanide-depleted syngas through a second scrubber and contacting the second ammonia-rich hydrogen cyanide-depleted syngas with a second scrubber liquor, whereby at least a portion of the ammonia contained in the second ammonia-rich hydrogen cyanide-depleted syngas is retained in the second scrubber liquor to form a second ammonia-depleted hydrogen cyanide-depleted syngas; and passing the second ammonia-depleted hydrogen cyanide-depleted synthesis gas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a flow diagram of an exemplary method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] In a first aspect, the present disclosure provides a method for producing liquid hydrocarbons from a synthesis gas, comprising: Providing a hydrogen cyanide-containing synthesis gas; splitting a hydrogen cyanide-containing synthesis gas into a first synthesis gas portion and a second synthesis gas portion; passing a mixture of the first syngas portion and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas portion; mixing a first hydrogen-rich syngas portion with a second syngas portion to provide a mixed syngas; passing the mixed syngas through a first hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the mixed syngas to ammonia to provide a first ammonia-rich hydrogen cyanide-depleted syngas; passing the first ammonia-rich hydrogen cyanide-depleted syngas through a first scrubber and contacting the first ammonia-rich hydrogen cyanide-depleted syngas with a first scrubber liquor, whereby at least a portion of the ammonia contained in the first ammonia-rich hydrogen cyanide-depleted syngas is retained in the first scrubber liquor to form a first ammonia-depleted hydrogen cyanide-depleted syngas; passing the first 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 through a second hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas to ammonia to provide a second ammonia-rich hydrogen cyanide-depleted syngas; passing the second ammonia-rich hydrogen cyanide-depleted syngas through a second scrubber and contacting the second ammonia-rich hydrogen cyanide-depleted syngas with a second scrubber liquor, whereby at least a portion of the ammonia contained in the second ammonia-rich hydrogen cyanide-depleted syngas is retained in the second scrubber liquor to form a second ammonia-depleted hydrogen cyanide-depleted syngas; and passing the second ammonia-depleted hydrogen cyanide-depleted synthesis gas through a Fischer-Tropsch reaction chamber to produce a liquid hydrocarbon product.

[0009] Each aspect or embodiment defined in this specification may be combined with any other aspect(s) or embodiment(s) unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature(s) indicated as being preferred or advantageous.

[0010] Advantageously, in contrast to conventional methods, the methods of the present invention may be simpler and / or more efficient.

[0011] In contrast to the method described in US Pat. No. 9,422,492 (B2), the method of the present invention comprises mixing a first hydrogen-rich syngas portion with a second syngas portion to provide a mixed syngas, and then passing the mixed syngas through a first hydrolysis reaction chamber. In other words, the method of the present invention performs hydrolysis on the entire syngas, i.e., on both the first syngas portion subjected to the water-gas shift reaction and the second syngas portion bypassing the water-gas shift reaction chamber. The catalyst in the water-gas shift reaction chamber typically hydrolyzes HCN and COS present in the syngas. Thus, in conventional methods such as those described in US Pat. No. 9,422,492 (B2), hydrolysis is typically performed only on the portion of the syngas that is not subjected to the water-gas shift reaction, since the other portion of HCN has already been hydrolyzed in the water-gas shift reaction chamber. However, the inventors of the present invention have surprisingly found that by remixing the two streams before feeding into the first hydrolysis reaction chamber, it is possible to take advantage of the excess steam added to the water-gas shift reactor to drive the hydrolysis reaction towards equilibrium. Specifically, by performing hydrolysis on a mixed syngas, it is possible to avoid the need to add a separate preheater and a separate 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. Thus, in contrast to conventional methods, the method of the present invention can be simpler and / or use less water.

[0012] After being passed through the first hydrolysis reaction chamber and the first scrubber, the synthesis gas is then passed through a second hydrolysis reaction chamber and a second scrubber. Due to reaction kinetics, the hydrolysis of hydrogen cyanide is difficult to complete, especially without the use of a large catalyst bed. In addition, it is usually not possible for a scrubber to remove all of the ammonia contained in the synthesis gas. The inventors have surprisingly found that by using a second scrubber followed by a second hydrolysis reaction chamber, the hydrogen cyanide content of the synthesis gas can be reduced to ppb levels, e.g., below 10 ppbv. As a result, the poisoning of the downstream Fischer-Tropsch catalyst is reduced. Compared to conventional processes such as those described in EP 3546053(B1) and US 10518210(B2), such low levels can be achieved with a lower total volume of hydrolysis catalyst, i.e., the total volume of catalyst in the first hydrolysis reaction chamber and the second hydrolysis reaction chamber. As a result, the process is more economical and the size of the plant implementing the process can be reduced.

[0013] As used herein, the term "liquid hydrocarbon" may include species formed from carbon and hydrogen that are liquid at room temperature and pressure. Hydrocarbons typically include alkanes and may contain from 5 to 100 or more carbon atoms per molecule.

[0014] The term "syngas" or "synthesis gas" as used herein may encompass a gas mixture containing hydrogen and carbon monoxide. In the method of the present invention, the first synthesis gas contains carbon monoxide (i.e., CO), hydrogen (i.e., molecular hydrogen H2) and hydrogen cyanide (i.e., HCN). The synthesis gas may contain other gases, such as water, methane, ammonia, carbon dioxide (i.e., CO2), and sulfur-containing gases, such as hydrogen sulfide (i.e., H2S), as well as solid species, such as dust and coke. Synthesis gas is typically produced from the gasification of carbonaceous materials. In the present invention, the synthesis gas is preferably produced by gasification of biomass and / or municipal waste. While these may be more ecologically sustainable carbon sources than fossil fuels, they have issues with contaminants that need to be removed to very low levels so as not to poison the Fischer-Tropsch catalyst. The composition of the synthesis gas varies depending on its production method and the starting materials used.

[0015] The method includes passing a mixture of a first syngas portion and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas portion. Water-gas shift reaction chambers are known in the art. Steam is preferably provided in excess to drive the reaction toward equilibrium. Additionally, the excess steam may be used in a subsequent hydrolysis step.

[0016] The method includes passing a first ammonia-rich hydrogen cyanide-depleted syngas through a first scrubber and passing a second ammonia-rich hydrogen cyanide-depleted syngas through a second scrubber. Scrubbers and scrubber liquors 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 scrubber liquor, for example, by using trays, structured packing, or random packing.

[0017] The method includes passing the first ammonia-depleted hydrogen cyanide-depleted syngas through a carbon dioxide removal unit to form a carbon dioxide-depleted syngas. This can make the method more efficient since the reduced volume of inert gas reduces the energy required to perform any heating or cooling steps. The carbon dioxide removal unit may employ physical absorption, for example, using chilled methanol (e.g., Rectisol®), and / or chemical absorption, for example, using an amine-based system. Such methods may also remove some hydrogen cyanide from the syngas.

[0018] The second ammonia-depleted and hydrogen cyanide-depleted synthesis gas is passed through a Fischer-Tropsch reaction chamber, which are known in the art.

[0019] The liquid hydrocarbon products preferably comprise alkanes, more preferably alkanes having from 5 to 100 or more carbon atoms. Such hydrocarbon products can be particularly desirable as fuel sources. Furthermore, the cobalt catalysts typically used to produce such hydrocarbon products can be particularly susceptible to poisoning by hydrogen cyanide.

[0020] Providing a hydrogen cyanide-containing synthesis gas preferably involves the gasification of biomass and / or municipal waste. Gasification of coal is less preferred. Biomass and municipal waste are becoming more widely available and synthesis gas produced from these species may be particularly suitable for the production of liquid hydrocarbons. In addition, such synthesis gas typically contains hydrogen cyanide as an impurity. Gasification is a technique known in the art. During gasification, biomass and / or municipal waste and / or coal are blown with oxygen and steam (water vapor) while also being heated (and possibly pressurized). It is essential that the oxidant supplied is insufficient for complete oxidation (combustion) of the fuel. During the mentioned reactions, 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 the gasification for use in other steps of the method.

[0021] The ratio of the hydrogen-rich first syngas portion to the second syngas portion is preferably controlled to provide a molar ratio of hydrogen to carbon monoxide in the mixed syngas of 1.5 to 2.5, preferably 1.8 to 2.2. Such a ratio can result in nearly complete conversion of carbon monoxide in the Fischer-Tropsch reaction chamber.

[0022] The first syngas portion preferably comprises 50-60% by volume of hydrogen cyanide-containing syngas, and the second syngas portion preferably comprises 40-50% by volume of hydrogen cyanide-containing syngas, such values ​​being based on typical syngas compositions and can provide the preferred ratios of hydrogen to carbon monoxide in the mixed syngas described above.

[0023] The first syngas portion is preferably heated to a temperature of between 200°C and 400°C, preferably by adding steam (more preferably superheated steam) to the first syngas portion, prior to being passed through the water-gas shift reaction chamber. Lower temperatures may result in undesirably slow reaction rates. Higher temperatures may result in hydrogen formation, which is thermodynamically less favorable.

[0024] The water gas shift reaction chamber preferably contains a catalyst comprising supported cobalt oxide and molybdenum oxide. Such a catalyst may be particularly suitable for catalyzing the water gas shift reaction, may provide favorable reaction rates, and / or may allow the use of lower temperatures.

[0025] The hydrolysis in the first and / or second hydrolysis reaction chambers is preferably carried out at a temperature above 100° C., more preferably between 150° C. and 300° C. Lower temperatures may result in undesirably low levels of hydrolysis. Higher temperatures may increase the energy costs of the process without significant improvement in hydrogen cyanide conversion.

[0026] The hydrolysis in the first and / or second hydrolysis reaction chamber is preferably carried out using an alumina catalyst, more preferably an activated alumina catalyst, which may provide particularly high conversion rates and / or allow operation at advantageously low temperatures.

[0027] Following hydrolysis, the first and / or second ammonia-rich hydrogen cyanide-depleted synthesis gases are preferably cooled, more preferably to a temperature of 40° C. or less, even more preferably to ambient temperature, before contacting the first and / or second scrubber.

[0028] The present invention includes passing the first ammonia-rich hydrogen cyanide-depleted syngas through a first scrubber and contacting the first ammonia-rich hydrogen cyanide-depleted syngas with a first scrubber liquor, whereby at least a portion of the ammonia contained in the first ammonia-rich hydrogen cyanide-depleted syngas is retained in the first scrubber liquor to form a first ammonia-depleted hydrogen cyanide-depleted syngas. The scrubber liquor in the first scrubber is preferably water, which may be boiler feed water or service water supply, or water condensate recovered from the process and optionally purified. The scrubber liquor of the first scrubber may also contain by-product water recovered from the FT reaction chamber. The first scrubber is upstream of the carbon dioxide removal unit. If desired, the carbon dioxide removal unit may include a water wash step to remove ammonia present in the syngas before scrubbing with a carbon dioxide absorbent to remove carbon dioxide from the first ammonia-depleted hydrogen cyanide-depleted syngas.

[0029] The synthesis gas may further comprise ammonia, which is a common impurity in synthesis gas. The method of the present invention is particularly suitable for use with synthesis gas containing ammonia in view of the high ammonia removal capacity of the scrubber liquor.

[0030] The hydrogen cyanide-containing synthesis gas may contain carbonyl sulfide, and preferably at least a portion of the carbonyl sulfide is hydrolyzed to hydrogen sulfide in the first and / or second hydrolysis reaction chamber. Preferably, the carbon dioxide removal unit through which the first ammonia-depleted, hydrogen cyanide-depleted synthesis gas is passed is an acid gas removal unit which removes carbon dioxide and optionally hydrogen sulfide and hydrogen cyanide from the first ammonia-depleted, hydrogen cyanide-depleted synthesis gas prior to passing the first ammonia-depleted, hydrogen cyanide-depleted synthesis gas to the second hydrolysis reaction chamber.

[0031] The second ammonia-rich hydrogen cyanide-depleted synthesis gas preferably contains less than 10 ppbv hydrogen cyanide. Such low levels of hydrogen cyanide may result in particularly low levels of poisoning of the Fischer-Tropsch catalyst.

[0032] The second ammonia-depleted hydrogen cyanide-depleted synthesis gas preferably contains less than 10 ppbv ammonia. Such low levels of hydrogen cyanide may result in particularly low levels of poisoning of the Fischer-Tropsch catalyst.

[0033] The temperature of the Fischer-Tropsch reaction chamber is preferably between 150°C and 300°C. Lower temperatures may result in undesirably low levels of liquid hydrocarbons being produced. Higher temperatures may increase the energy costs of the process without significantly increasing the levels of liquid hydrocarbons produced.

[0034] Passing the second ammonia-depleted and hydrogen cyanide-depleted syngas through a Fischer-Tropsch reaction chamber to produce the liquid hydrocarbon product preferably comprises contacting the second ammonia-depleted and hydrogen cyanide-depleted syngas with a catalyst comprising a metal selected from cobalt, iron, or ruthenium. Such catalysts are particularly effective in catalyzing the Fischer-Tropsch reaction and / or allow the reaction to proceed at advantageously low temperatures and / or in high yields.

[0035] The scrubber liquor of at least the second scrubber is suitably water, and preferably includes by-product water. In a preferred embodiment, liquid hydrocarbon products and by-product water are produced by passing the second ammonia-depleted hydrogen cyanide-depleted synthesis gas through a Fischer-Tropsch reaction chamber, and at least the second scrubber liquor includes by-product water recovered from the Fischer-Tropsch reaction chamber. The by-product water may be separated from the products recovered from the Fischer-Tropsch reaction chamber using conventional separation equipment.

[0036] The hydrocarbon products from the Fischer-Tropsch reaction chamber may be separated from by-product water and unreacted gases and then converted to liquid hydrocarbon fuels, for example by hydrocracking.

[0037] Furthermore, the by-product water contains dissolved carbon dioxide from the synthesis gas and from the carbon dioxide produced as a by-product in the Fischer-Tropsch reaction chamber. The ammonia removal capacity of the scrubber liquor can be improved by the presence of carbon dioxide. It is therefore easier to reduce the ammonia and hydrogen cyanide content of the synthesis gas to single digit ppb levels. As a result, the poisoning of the Fischer-Tropsch catalyst is further reduced, which means that the process is more efficient as the Fischer-Tropsch catalyst does not have to be regenerated or replaced less regularly. Furthermore, it is possible to avoid the use of hydrogen cyanide and ammonia absorption beds just before the Fischer-Tropsch reaction chamber, thereby resulting in a more simplified process compared to conventional processes. The use of by-product water, rather than having to use another water source such as boiler feed water or demineralized water, simplifies the process and reduces operating costs. Furthermore, since the by-product water is recovered from the Fischer-Tropsch reaction chamber, the water is poison-free. Therefore, the risk of introducing poisons that could deactivate the catalyst is reduced over comparable processes using other scrubber liquor sources. The use of by-product water recovered from the Fischer-Tropsch reaction chamber in the second scrubber liquor ensures that additional Fischer-Tropsch catalyst poisons that may be present in other water streams, such as boiler feedwater, where chemicals are added, are not introduced into the system.

[0038] The scrubber liquor, preferably the second scrubber liquor, may contain at least 0.01 mol / L of carbon dioxide, more preferably at least 0.02 mol / L of carbon dioxide. Such a concentration of carbon dioxide may result in a particularly high ammonia removal capacity of the scrubber liquor.

[0039] In a preferred embodiment, the scrubber liquor, in particular the second scrubber liquor, is saturated with carbon dioxide under the temperature and pressure conditions of the scrubber.

[0040] If the hydrogen cyanide-containing synthesis gas further comprises particulate matter entrained therein, preferably upstream of the water-gas shift reaction chamber, more preferably as a first purification step, the hydrogen cyanide-containing synthesis gas is passed through a particulate filter. The particulate filter may comprise a high temperature high porosity inert filtration medium, such as shaped pellets of high purity alumina. A commercially available example of a suitable filter medium is Dypor™ 607, which can operate within a temperature range from ambient to 500° C., preferably 60-200° C.

[0041] If the hydrogen cyanide-containing synthesis gas further comprises hydrogen halide compounds, the hydrogen cyanide-containing synthesis gas is passed through a bed of hydrogen halide adsorbent, preferably upstream of the water-gas shift reaction chamber, more preferably downstream of the particulate filter. The first synthesis gas portion is preferably passed through a bed of hydrogen halide adsorbent upstream of the water-gas shift reaction chamber. The placement of the hydrogen halide adsorbent immediately after the particulate filter reduces the corrosivity of the synthesis gas to high temperature sulfidation, which is accelerated in the presence of halides. This allows the use of lower cost materials of construction in 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 in a temperature range from ambient to 400°C, preferably from 120 to 300°C.

[0042] If the hydrogen cyanide-containing synthesis gas further contains mercury, preferably upstream of the first scrubber and downstream of the first hydrolysis reaction chamber, the first ammonia-rich hydrogen cyanide-depleted synthesis gas is passed through a bed of mercury sorbent. Mercury is a common impurity in synthesis gas, particularly synthesis gas produced using gasification. Removal of mercury can reduce poisoning of downstream Fischer-Tropsch catalysts. The mercury sorbent preferably comprises sulfided activated carbon. The mercury sorbent preferably operates at a temperature of about 20°C above the dew point, i.e. about 60°C.

[0043] If the hydrogen cyanide-containing syngas further comprises one or more sulfur compounds, preferably upstream of the second scrubber and downstream of the second hydrolysis reaction chamber, the second ammonia-rich hydrogen cyanide-depleted syngas is passed through a bed of sulfur compound sorbent. Sulfur is a common impurity in syngas, particularly syngas produced using gasification. Removal of sulfur can reduce poisoning of downstream Fischer-Tropsch catalysts. The sulfur sorbent preferably comprises zinc oxide. The sulfur compound sorbent preferably operates in the temperature range of 100-230°C, preferably at about 150°C.

[0044] If the hydrogen cyanide-containing synthesis gas further comprises one or more arsenic compounds, preferably upstream of the second scrubber and downstream of the second hydrolysis reaction chamber, preferably downstream of the sulfur sorbent, the second ammonia-rich hydrogen cyanide-depleted synthesis gas is passed through a bed of arsenic compound sorbent. Arsenic is a common impurity in synthesis gas, particularly synthesis gas produced using gasification. Removal of arsenic can reduce poisoning of downstream Fischer-Tropsch catalysts. The arsenic compound sorbent preferably comprises copper oxide and / or zinc oxide. A commercially available example of a suitable arsenic compound sorbent is Puraspec™ 2088. The arsenic compound sorbent preferably operates in the temperature range of 100-230°C, preferably about 150°C.

[0045] The invention will now be described with reference to the following non-limiting examples. EXAMPLES

[0046] A flow diagram of an exemplary process according to the present invention is shown in Figure 1. Referring to Figure 1, in the first stage of purification, particulates are removed from the syngas 100 in particulate guard bed 1. Particulate guard bed 1 comprises a high temperature, high porosity inert filtration media. Following particulate guard bed 1, the syngas 110 passes through halide guard bed 2. Halide guard bed 2 absorbs halides from the syngas on an alkali promoted sorbent and is configured in a lead / rag arrangement to improve removal efficiency and allow for effective replacement of the lead bed before contaminants slip, given the difficulty of measuring halides to these low levels. It is located upstream of the first HCN hydrolysis bed 5, as halides are poisons to this catalyst.

[0047] The syngas 120 is then shifted to provide the optimum H2:CO molar ratio for FT synthesis (2.11-2.14 mol / mol from start of run (SOR) to end of run (EOR)). This molar ratio is controlled by a bypass 125 around the shift reactor 4, where approximately 40-50% of the total syngas is bypassed. The H2:CO molar ratio of the syngas is increased across the WGS reactor via the following reactions:

[0048] [ka]

[0049] Prior to the shift, the syngas 120 is preheated in a process exchanger (not shown). Following this, the stream is split into two separate streams, with one stream 125 bypassing the shift reactor 4. The remaining syngas is further preheated in another process exchanger (not shown) by hot product gas from the shift reactor 4. This stream is further heated to 230-320°C by the addition of superheated HP steam, which also provides the water to drive the shift reaction. The inlet temperature is generally set to keep the outlet temperature below about 550°C, meaning that typical inlet temperatures are between 200-400°C. If arsine is present in significant amounts in the syngas, the remaining syngas is first passed through a pre-shift guard bed 3 to prevent poisoning of the shift catalyst. This sacrificial pre-shift guard bed 3 may be configured in a duty / standby arrangement for on-line exchange when arsine levels are high. The syngas 130 is then fed to the main shift reactor 4. Since the shift reaction is exothermic, the hot product gas is used to raise HP steam in a shift gas boiler (not shown). Both the shift guard catalyst and the pre-shift guard catalyst are cobalt and molybdenum oxides on a high strength magnesium aluminate support.

[0050] After heat recovery in a process exchanger (not shown), the syngas 125 bypassing the shift reactor 4 is mixed with the shifted syngas to form mixed syngas 140. A bypass 125 around the shift gas boiler controls the inlet temperature to the first HCN hydrolysis bed 5 at 250°C.

[0051] In the mixed syngas 140, COS and HCN are then hydrolyzed to H2S and NH3, respectively, over activated high surface area alumina in the first HCN hydrolysis bed 5. The hydrolysis reactions are as follows:

[0052] [ka]

[0053] This produces a first hydrogen cyanide-depleted synthesis gas 150. Following hydrolysis, cooling is provided by in-process heat recovery to the boiler feed water and process gas streams in a series of heat exchangers / exchangers (not shown).

[0054] Further cooling is provided in an air cooler and a water trim cooler (not shown), which cool the syngas to 60° C. and 40° C., respectively, and condense water not consumed in the shift reaction. The condensed water is separated from the syngas 150 in a syngas knockout drum (not shown) and sent to wastewater treatment.

[0055] Following the syngas knockout drum, a mercury guard bed 6 uses sulfided activated carbon to remove mercury from the syngas 150 to the levels required for the acid gas removal unit 8 .

[0056] Between the mercury guard bed 6 and the acid gas removal unit 8 is a first syngas wash drum 7. The syngas 160 recovered from the mercury guard bed 6 is cooled in a process exchanger (not shown) and then subsequently cooled to about 40° C. using cooling water. Ammonia present in the gas or formed by HCN hydrolysis is scrubbed from the syngas 160 using water in the first syngas wash drum 7. The first syngas wash drum 7 contains trays or packing. The syngas wash water from the syngas wash drum 7 is sent to wastewater treatment and the clean syngas stream 170 is fed to the acid gas removal unit 8.

[0057] The acid gas removal unit 8 removes most of the carbon dioxide in 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 chilled methanol. The acid gas removal unit 8 also reduces the levels of other contaminants.

[0058] After acid gas removal, the synthesis gas 180 is heated to about 100-130°C in a process exchanger (not shown) using hot gas from the downstream Arsynguard bed 11. Following this, the synthesis gas 180 passes through a second process exchanger where it is heated to about 190-210°C using hot gas from the second HCN hydrolysis bed 9.

[0059] The syngas 180 is further heated to 250° C. by an HCN hydrolysis bed preheater (not shown) using saturated HP steam. There is a boiler feedwater connection (not shown) upstream of the second HCN hydrolysis bed 9 to provide sufficient water for the hydrolysis of COS and HCN in the second HCN hydrolysis bed 9.

[0060] After cooling to 150° C. in a process exchanger (not shown), the syngas 190 enters final purification beds including a sulfur guard bed 10 containing a zinc oxide adsorbent and producing a desulfurized syngas 200, followed by an arsine guard bed 11 which adsorbs arsine using a copper / zinc oxide catalyst / adsorbent to produce purified syngas 210. The arsine guard bed 11 is configured in a duty / standby arrangement for on-line exchange.

[0061] The syngas 210 is then cooled in a process exchanger (not shown) and subsequently cooled to about 40° C. using cooling water. Ammonia, either present in the gas or formed by HCN hydrolysis, is scrubbed from the syngas 210 in the second syngas wash drum 12 using FT by-product water from a FT unit (not shown). The second syngas wash drum 12 comprises trays or packing. The syngas wash water from the second syngas wash drum 12 is sent to wastewater treatment and the clean syngas stream is fed to the FT unit.

[0062] The foregoing detailed description has been provided for purposes of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the presently preferred embodiments described herein will be apparent to those of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.

Claims

1. 1. A method for producing liquid hydrocarbons from synthesis gas, comprising the steps of: Providing a hydrogen cyanide-containing synthesis gas; splitting the hydrogen cyanide-containing synthesis gas into a first synthesis gas portion and a second synthesis gas portion; passing a mixture of the first syngas portion and steam through a water-gas shift reaction chamber to provide a hydrogen-rich first syngas portion; mixing the hydrogen-rich first syngas portion with the second syngas portion to provide a mixed syngas; passing the mixed syngas through a first hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the mixed syngas to ammonia to provide a first ammonia-rich hydrogen cyanide-depleted syngas; passing the first ammonia-rich hydrogen cyanide-depleted syngas through a first scrubber and contacting the first ammonia-rich hydrogen cyanide-depleted syngas with a first scrubber liquor, whereby at least a portion of the ammonia contained in the first ammonia-rich hydrogen cyanide-depleted syngas is retained in the first scrubber liquor to form a first ammonia-depleted hydrogen cyanide-depleted syngas; passing the first 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 through a second hydrolysis reaction chamber to convert at least a portion of the hydrogen cyanide in the carbon dioxide-depleted syngas to ammonia to provide a second ammonia-rich hydrogen cyanide-depleted syngas; passing the second ammonia-rich hydrogen cyanide-depleted syngas through a second scrubber and contacting the second ammonia-rich hydrogen cyanide-depleted syngas with a second scrubber liquor, whereby at least a portion of the ammonia contained in the second ammonia-rich hydrogen cyanide-depleted syngas is retained in the second scrubber liquor to form a second ammonia-depleted hydrogen cyanide-depleted syngas; and passing the second ammonia-depleted hydrogen cyanide-depleted synthesis gas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products.

2. The method of claim 1 , wherein the liquid hydrocarbon product comprises an alkane.

3. 3. The method of claim 1 or 2, wherein providing a hydrogen cyanide-containing synthesis gas comprises gasification of biomass and / or municipal waste.

4. 4. The method according to any one of claims 1 to 3, wherein the ratio of the first hydrogen-rich syngas portion to the second syngas portion is controlled to provide a molar ratio of hydrogen to carbon monoxide in the mixed syngas of 1.5 to 2.5, preferably 1.8 to 2.

2.

5. 5. The method of claim 4, wherein the first syngas portion comprises 50 to 60 volume percent of the hydrogen cyanide-containing syngas and the second syngas portion comprises 40 to 50 volume percent of the hydrogen cyanide-containing syngas.

6. 6. The method according to any one of claims 1 to 5, wherein the first syngas portion is heated to a temperature of from 200°C to 400°C, preferably by adding steam to the first syngas portion, before being passed through the water-gas shift reaction chamber.

7. The method of any one of claims 1 to 6, wherein the water gas shift reaction chamber contains a catalyst comprising supported cobalt oxide and molybdenum oxide.

8. 8. The method according to any one of claims 1 to 7, wherein the hydrolysis in the first hydrolysis reaction chamber and / or the second hydrolysis reaction chamber is carried out at a temperature above 100°C, preferably between 150°C and 300°C.

9. The method according to any one of claims 1 to 8, wherein the hydrolysis in the first hydrolysis reaction chamber and / or the second hydrolysis reaction chamber is carried out using an alumina catalyst.

10. The method of any one of claims 1 to 9, wherein the synthesis gas further comprises ammonia.

11. 11. The method of any one of claims 1 to 10, wherein the hydrogen cyanide-containing synthesis gas comprises carbonyl sulfide, and at least a portion of the carbonyl sulfide is hydrolyzed to hydrogen sulfide in the first hydrolysis reaction chamber and / or the second hydrolysis reaction chamber.

12. 12. The method of any one of claims 1 to 11, wherein the carbon dioxide removal unit through which the first ammonia-depleted, hydrogen cyanide-depleted syngas is passed is an acid gas removal unit that removes carbon dioxide and optionally hydrogen sulfide and hydrogen cyanide from the first ammonia-depleted, hydrogen cyanide-depleted syngas prior to passing the first ammonia-depleted, hydrogen cyanide-depleted syngas to the second hydrolysis reaction chamber.

13. 13. The method of any one of claims 1 to 12, wherein the second ammonia-rich hydrogen cyanide-depleted synthesis gas contains less than 10 ppbv hydrogen cyanide.

14. 14. The method of any one of claims 1 to 13, wherein the second ammonia-depleted hydrogen cyanide-depleted synthesis gas contains less than 10 ppbv ammonia.

15. The method of any one of claims 1 to 14, wherein the temperature of the Fischer-Tropsch reaction chamber is from 150°C to 300°C.

16. 16. The method of any one of claims 1 to 15, wherein passing the second ammonia-depleted hydrogen cyanide-depleted syngas through a Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products comprises contacting the second ammonia-depleted hydrogen cyanide-depleted syngas with a catalyst comprising cobalt, iron, or ruthenium.

17. passing the second ammonia-depleted and hydrogen cyanide-depleted synthesis gas into the Fischer-Tropsch reaction chamber to produce liquid hydrocarbon products and by-product water; The method of any one of claims 1 to 16, wherein at least the second scrubber liquor comprises by-product water recovered from the Fischer-Tropsch reaction chamber.

18. 18. The method of claim 16 or claim 17, wherein the by-product water is saturated with carbon dioxide under temperature and pressure conditions of the scrubber where carbon dioxide is employed.

19. 19. A method according to any one of the preceding claims, wherein the hydrogen cyanide containing synthesis gas further comprises particulate matter entrained therein, and wherein upstream of the water-gas shift reaction chamber, the hydrogen cyanide containing synthesis gas is passed through a particulate filter, preferably as a first purification step.

20. 20. The method of any one of claims 1 to 19, wherein the hydrogen cyanide-containing synthesis gas further comprises hydrogen halide compounds, and wherein upstream of the water gas shift reaction chamber, preferably downstream of a particulate filter, the hydrogen cyanide-containing synthesis gas is passed through a bed of hydrogen halide adsorbent.

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

22. 22. The method of any one of claims 1 to 21, wherein the hydrogen cyanide-containing synthesis gas further comprises mercury, and wherein upstream of the first scrubber and downstream of the first hydrolysis reaction chamber, the first ammonia-rich hydrogen cyanide-depleted synthesis gas is passed through a bed of mercury sorbent.

23. 23. The method of any one of claims 1 to 22, wherein the hydrogen cyanide-containing synthesis gas further comprises one or more sulfur compounds, and wherein upstream of the second scrubber and downstream of the second hydrolysis reaction chamber, the second ammonia-rich hydrogen cyanide-depleted synthesis gas is passed through a bed of a sulfur compound adsorbent.

24. 24. The method according to any one of claims 1 to 23, wherein the hydrogen cyanide-containing synthesis gas further comprises one or more arsenic compounds, and wherein, upstream of the second scrubber and downstream of the second hydrolysis reaction chamber, preferably downstream of a sulfur sorbent, the second ammonia-rich hydrogen cyanide-depleted synthesis gas is passed through a bed of an arsenic compound sorbent.

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