WO2013125307A1 - A method for producing a synthesis gas with low amounts of hydrogen cyanide - Google Patents

A method for producing a synthesis gas with low amounts of hydrogen cyanide Download PDF

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Publication number
WO2013125307A1
WO2013125307A1 PCT/JP2013/051939 JP2013051939W WO2013125307A1 WO 2013125307 A1 WO2013125307 A1 WO 2013125307A1 JP 2013051939 W JP2013051939 W JP 2013051939W WO 2013125307 A1 WO2013125307 A1 WO 2013125307A1
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Prior art keywords
synthesis gas
catalyst
gas
hydrogen
temperature
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PCT/JP2013/051939
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French (fr)
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Satoshi Terai
Takahiro Yanagawa
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Toyo Engineering Corporation
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Publication of WO2013125307A1 publication Critical patent/WO2013125307A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/50—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
    • C01B3/56—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids
    • C01B3/58—Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification by contacting with solids; Regeneration of used solids including a catalytic reaction
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10K—PURIFYING OR MODIFYING THE CHEMICAL COMPOSITION OF COMBUSTIBLE GASES CONTAINING CARBON MONOXIDE
    • C10K1/00—Purifying combustible gases containing carbon monoxide
    • C10K1/002—Removal of contaminants
    • C10K1/003—Removal of contaminants of acid contaminants, e.g. acid gas removal
    • C10K1/006—Hydrogen cyanide
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10K—PURIFYING OR MODIFYING THE CHEMICAL COMPOSITION OF COMBUSTIBLE GASES CONTAINING CARBON MONOXIDE
    • C10K1/00—Purifying combustible gases containing carbon monoxide
    • C10K1/34—Purifying combustible gases containing carbon monoxide by catalytic conversion of impurities to more readily removable materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2256/00—Main component in the product gas stream after treatment
    • B01D2256/16—Hydrogen
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/406—Ammonia
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/80—Water
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0405—Purification by membrane separation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435—Catalytic purification
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06—Integration with other chemical processes
    • C01B2203/062—Hydrocarbon production, e.g. Fischer-Tropsch process

Definitions

  • the present invention relates to a method for producing a synthesis gas containing hydrogen and carbon monoxide, which can be used as a wide variety of reactants.
  • a synthesis gas containing hydrogen and carbon monoxide has been commonly used as a feedstock gas for Fischer-Tropsch synthesis (FT synthesis) or the like.
  • the synthesis gas has been produced by using natural gas or the like, and through the application of steam reforming process and has also been known to contain hydrogen and carbon monoxide, as well as hydrogen cyanide and ammonia derived from a nitrogen component present in the natural gas.
  • EP 0 229 407 Al discloses a method for scrubbing the hydrogen cyanide contained in the synthesis gas with a basic aqueous solution and removing it.
  • EP 0 629 684 Al discloses a method for causing an alkali metal compound to absorb the hydrogen cyanide present in the synthesis gas obtained by a partial oxidation process and to remove it.
  • US 4,769,224 A discloses an invention which provides a method for reducing a content of hydrogen cyanide to less than 10 ppm by the hydrolysis using a titanium dioxide-containing silica catalyst.
  • US 2010/0204533 Al discloses a method for decomposing the hydrogen cyanide into ammonia, through the use of a zinc oxide catalyst, at a temperature of 100 to 240 °C, and then removing the resulting ammonia through an ion-exchange membrane to thereby produce the synthesis gas containing ammonia of less than 5 ppb and hydrogen cyanide of less than 10 ppb.
  • US 5, 968, 465 A discloses a method for producing a synthesis gas, including hydrolyzing hydrogen cyanide by using a Mo/Ti/Al 2 0 3 catalyst previously-treated with high-pressure hydrogen, and then combining scrubbing and solid-phase adsorption techniques to produce the synthesis gas containing ammonia and hydrogen cyanide in a total content of less than 10 ppb.
  • US 6,063,349 A discloses an invention which provides a method for decomposing hydrogen cyanide using a catalyst including a combination of a carrier (Ti0 2 , Hf oxide, Zr oxide or a mixture thereof) and a metal oxide (an oxide of Zn, Mo, Nb or a mixture thereof) at a temperature of 140 to 177°C.
  • a carrier Ti0 2 , Hf oxide, Zr oxide or a mixture thereof
  • a metal oxide an oxide of Zn, Mo, Nb or a mixture thereof
  • US 6,107,353 A discloses an invention which provides a method for contacting a synthesis gas in the presence of water vapor with a hydrogen cyanide-hydrolysis catalyst which has been previously hydro-treated at a temperature of 200 to 600°C, and then washing the resulting hydrolyzed gas with water to thereby dissolve the ammonia and hydrogen cyanide into water and remove them. It is also described that as the catalyst, one which contains oxides of Al, Mo and Ti is used, and that in an Example, the hydrogen cyanide is hydrolyzed at a temperature of about 150 to 350°C, under a pressure of about 1 to 100 bar and at a space velocity of about 5,000 to 50,000 hr -1 . [0006]
  • JP 2000-509007 A discloses an invention which provides a method for contacting a synthesis gas in the presence of water vapor with a metal oxide catalyst including the oxides of Group VI and IVB metals and aluminum oxide, and then washing the resulting synthesis gas with water to thereby remove hydrogen cyanide present in the synthesis gas.
  • JP 2010-534758 A discloses a method for producing a purified gas from a raw material gas containing H 2 S, C0 2 and HCN and/or COS, including as a step (a) "(a) contacting feed gas comprising H 2 S, C0 2 and HCN and/or COS with a HCN/COS hydrolysis sorbent in the presence of water in a HCN/COS hydrolysis unit, thereby obtaining gas deficient in HCN and/or COS;".
  • the hydrolysis sorbent preferably includes one or more oxides of a metal from Group IVB (Zr, Ti, Hf) as a hydrolysis catalyst, and at the paragraph 0020 that the step (a) is performed at a temperature in the range of from 80 to 250 °C.
  • An object of the present invention is to provide a method for producing a synthesis gas, including the step of contacting hydrogen cyanide contained in the synthesis gas with a catalyst at high temperature, wherein a concentration of hydrogen cyanide in the synthesis gas can also be reduced, furthermore, the amount of catalyst can be reduced, and the side reaction can also be suppressed.
  • the present invention provides, as means for solving the problems, a method for producing a synthesis gas, including: a first step of obtaining a synthesis gas containing hydrogen and carbon monoxide from natural gas through steam reforming process; and a second step of, within a catalyst-packed column, reacting the synthesis gas from the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing hydrogen cyanide contained in the synthesis gas to thereby obtain a synthesis gas that contains ammonia, wherein, as the catalyst, a catalyst containing zinc oxide (ZnO) is used.
  • the present invention further provides, as other means for solving the problems, a method for producing a synthesis gas, including:
  • both contents of hydrogen cyanide and ammonia present in the synthesis gas can be reduced.
  • the amount of catalyst used can be reduced due to the reaction with the catalyst at higher temperature than the conventional technology. This makes it possible to use a catalyst packed column (a container filled with catalyst) having a smaller capacity, and to reduce the burden required to install and maintain production facilities.
  • the method for producing a synthesis gas of the present invention through the use of a certain catalyst, the production of a by-product is suppressed even if causing to react at higher temperature as compared with the conventional technology, and thus the burden required in the subsequent process for separating the by-product is reduced, but a basic unit of the raw material is not decreased.
  • the catalyst used in the present invention does not require the treatment that previously activates the catalyst through the use of hydrogen or the like after loading it, it can reduce operation procedures and utilities at the time of the start-up, and costs.
  • first and second steps or the first to sixth steps according to the present invention is merely for the purpose of illustrating order of the steps, but is not intended to restrict the production method of the present invention only to the first and second steps or the first to sixth steps.
  • the present invention further includes an invention that makes two steps into one step and another invention that makes one step divided into two steps.
  • the synthesis gas containing hydrogen and carbon monoxide is obtained from a hydrocarbon such as natural gas, through the steam reforming process (See the scheme below) .
  • the first step itself is a known process, and is performed at a temperature of about 800 to about 1,000°C.
  • the synthesis gas obtained in the first step contains ammonia and hydrogen cyanide derived from nitrogen present in the feedstock.
  • the synthesis gas obtained in the preceding step is caused to react with a catalyst.
  • the pretreatment that lowers the temperature of the synthesis gas by a heat exchanger or the like becomes unnecessary, as in the case of the reaction with the catalyst at a relatively lower temperature (approximately 80 to 350°C) .
  • Catalytic reaction of the second step causes the synthesis gas obtained in the preceding step to react at a temperature of 350 to 550°C, to thereby decompose the hydrogen cyanide present in the synthesis gas, and to thereby obtain a synthesis gas that contains ammonia (see the scheme below) .
  • ammonia is mostly separated together with condensed water because ammonia is readily-soluble in the by-product water, and the removal technique including adsorption and separation by using the adsorbent can be applied to ammonia.
  • a catalyst containing zinc oxide (ZnO) is used as the catalyst, and a combined use of zinc oxide (ZnO) and the other catalyst such as aluminum oxide (A1 2 0 3 ) is possible.
  • zinc oxide (ZnO) is preferably used alone as the catalyst.
  • the catalyst containing, as an active site, metal species such as Mo which are used in the conventional techniques requires activation treatment with hydrogen or the like, for example, after loaded into the catalyst packed column .
  • zinc oxide (ZnO) and aluminum oxide (AI2O3) used in the second step of the present invention do not require the activation treatment by using hydrogen or the like as described above, and thus zinc oxide and aluminum oxide are advantageous in that operation procedures and utilities at the time of the start-up, and costs can be reduced.
  • the production method of the present invention can suppress the side reaction by using a specific catalyst, even when the reaction temperature is increased, and also reduce the amount of catalyst by the increase in the reaction temperature.
  • the reaction temperature has an upper limit from the viewpoint of the prevention of material corrosion, and the reaction temperature is preferably 380 to 500°C, more preferably 400 to 450°C.
  • the gas hourly space velocity (GHSV) can be increased when causing to react through the use of the catalytst packed column.
  • typical HCN concentration in the exit gas in the first step is approximately 20 ppb to 100 ppm
  • the gas hourly space velocity (GHSV) in the catalyst packed column can be set to approximately 40, 000 to 520,000 h "1 .
  • GHSV gas hourly space velocity
  • the catalyst packed column (catalyst-packed container) used in the second step can be a conventional fixed-bed gas-solid reactor, but is not particularly limited thereto.
  • the hydrogen cyanide present in the synthesis gas obtained in the first step is decomposed and converted into an
  • ammonia-containing gas to thereby cause the decreased content of hydrogen cyanide.
  • the synthesis gas obtained through the first and second steps can be subjected to removal of the by-product water in the third and fourth steps depending on the intended use before being used directly as a synthetic raw material as is .
  • the temperature of the synthesis gas obtained in the preceding step is lowered.
  • the temperature of the synthesis gas is lowered while heat recovery is conducted, and then the second step proceeds to the next step.
  • a commonly known heat exchanger such as a shell-and-tube heat exchanger can be used, but is not particularly limited thereto.
  • water condensed from the synthesis gas and ammonia in the preceding step are separated using a gas-liquid separator.
  • gas-liquid separator for example, a gas-liquid separation tank equipped with a demister, or the like can be used, but the separator is not particularly limited thereto.
  • the hydrogen separation membrane as disclosed in, for example, JP-A 8-151410 can be used, but the hydrogen separation membrane is not particularly limited thereto.
  • Other techniques for separating hydrogen include a pressure swing adsorption process using the adsorbent, and the like, but they make operation sequences complicated.
  • the remaining ammonia is separated from the synthesis gas from which hydrogen has been separated in the preceding step.
  • the remaining ammonia which has failed to be separated in the fourth step is further adsorbed and separated by using the commonly known adsorbent such as an activated carbon or the like.
  • the synthesis gas obtained through the steps 1 to 6 can be reduced, up to less than 10 ppb, in the total content of ammonia and hydrogen cyanide.
  • the synthesis gas when used as the raw material for the FT synthesis, it would neither substantially act as catalytic poison with respect to the catalyst for the FT synthesis, such as cobalt based catalyst, nor produce adverse effects on the activity of cobalt based catalyst or the like.
  • Natural gas (inlet gas) having the following gas composition was subjected to the steam reforming process to thereby obtain the synthesis gas having the following outlet composition :
  • the gas obtained in the preceding step was fed into a reactor filled with a zinc oxide catalyst at the inlet temperature of 410°C under the pressure of 1 MPaG, and hydrogen cyanide present in it was hydrolyzed.
  • the conversion rate of hydrogen cyanide yielded 99.3%.
  • the gas hourly space velocity (GHSV) during the second step was about 72, 000 h "1 .
  • the gas in the preceding step was cooled to 43°C.
  • the gas having the ratio of H 2 /CO adjusted in the preceding step was caused to pass through an activated carbon bed, and ammonia was subjected to adsorption removal.
  • the total content of hydrogen cyanide and ammonia in the resulting synthesis gas after the completion of the sixth step was 9 ppb.
  • Example 1 the second step was not carried out, and the synthesis gas was cooled to a temperature of approximately 185°C by means of the heat exchanger in the third step before being subjected to catalysis by using the same catalyst packed column as one used in the second step of Example 1.
  • the gas hourly space velocity (GHSV) during the catalysis was about 3, 800 hr _1 , and the conversion rate of hydrogen cyanide was 99.1%.
  • the total content of hydrogen cyanide and ammonia in the resulting synthesis gas after the completion of the sixth step was 10 ppb.
  • the gas hourly space velocity (GHSV) during the second step in Example 1 (catalysis process) was about 72,000 hr -1
  • the gas hourly space velocity (GHSV) during the catalysis process in Comparative Example 1 was about 3, 800 hr -1
  • a ratio of Comparative Example 1 to Example 1 resulted in about 1/19.
  • Example 1 Comparative Example 2
  • the synthesis gas obtained by the method for producing a synthesis gas of the present invention can be used as raw materials for production for the various types of synthesis reactions including the FT synthesis.
  • the synthesis gas can be used as the raw material for production for the synthesis reaction using the catalyst to which hydrogen cyanide and ammonia serve as a catalytic poison, such as a cobalt based catalyst.

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Abstract

A method for producing a synthesis gas having the reduced HCN content is provided. A method for producing a synthesis gas, including: a first step of obtaining the synthesis gas containing H2 and CO from natural gas through the steam reforming process; a second step of contacting the synthesis gas obtained by the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing HCN contained in the synthesis gas to thereby obtain the synthesis gas that contains NH3, wherein as the catalyst, a catalyst containing ZnO is used; optionally a third step of lowering the temperature of the synthesis gas; a fourth step of separating water and NH3 from the synthesis gas in which the temperature is lowered in the preceding step; a fifth step of separating H2 from the synthesis gas from which water and NH3 are separated in the preceding step; and a sixth step of further separating the remaining NH3 from the synthesis gas from which H2 is separated in the preceding step.

Description

Description
A METHOD FOR PRODUCING A SYNTHESIS GAS WITH LOW AMOUNTS OF HYDROGEN CYANIDE
Technical Field
[0001]
The present invention relates to a method for producing a synthesis gas containing hydrogen and carbon monoxide, which can be used as a wide variety of reactants.
Background Art
[0002]
A synthesis gas containing hydrogen and carbon monoxide has been commonly used as a feedstock gas for Fischer-Tropsch synthesis (FT synthesis) or the like.
The synthesis gas has been produced by using natural gas or the like, and through the application of steam reforming process and has also been known to contain hydrogen and carbon monoxide, as well as hydrogen cyanide and ammonia derived from a nitrogen component present in the natural gas.
When using such synthesis gas containing hydrogen cyanide in the FT synthesis, there is a problem in which that hydrogen cyanide and ammonia serve as a catalytic poison against a cobalt based catalyst used in the FT synthesis, to thereby cause a decrease in catalytic activity of the cobalt based catalyst. Therefore, in the production of the synthesis gas, the reduction in the contents of hydrogen cyanide and ammonia is desired .
[0003]
EP 0 229 407 Al discloses a method for scrubbing the hydrogen cyanide contained in the synthesis gas with a basic aqueous solution and removing it.
EP 0 629 684 Al discloses a method for causing an alkali metal compound to absorb the hydrogen cyanide present in the synthesis gas obtained by a partial oxidation process and to remove it.
However, these methods would be unsuitable for the raw material for the FT synthesis because the removing process is inhibited by the acid material C02 present in the synthesis gases , and the alkali metal itself also serves as the catalytic poison against the cobalt based catalyst.
[0004]
US 4,769,224 A discloses an invention which provides a method for reducing a content of hydrogen cyanide to less than 10 ppm by the hydrolysis using a titanium dioxide-containing silica catalyst.
US 2010/0204533 Al discloses a method for decomposing the hydrogen cyanide into ammonia, through the use of a zinc oxide catalyst, at a temperature of 100 to 240 °C, and then removing the resulting ammonia through an ion-exchange membrane to thereby produce the synthesis gas containing ammonia of less than 5 ppb and hydrogen cyanide of less than 10 ppb.
US 5, 968, 465 A discloses a method for producing a synthesis gas, including hydrolyzing hydrogen cyanide by using a Mo/Ti/Al203 catalyst previously-treated with high-pressure hydrogen, and then combining scrubbing and solid-phase adsorption techniques to produce the synthesis gas containing ammonia and hydrogen cyanide in a total content of less than 10 ppb.
US 6,063,349 A discloses an invention which provides a method for decomposing hydrogen cyanide using a catalyst including a combination of a carrier (Ti02, Hf oxide, Zr oxide or a mixture thereof) and a metal oxide (an oxide of Zn, Mo, Nb or a mixture thereof) at a temperature of 140 to 177°C.
[0005]
US 6,107,353 A discloses an invention which provides a method for contacting a synthesis gas in the presence of water vapor with a hydrogen cyanide-hydrolysis catalyst which has been previously hydro-treated at a temperature of 200 to 600°C, and then washing the resulting hydrolyzed gas with water to thereby dissolve the ammonia and hydrogen cyanide into water and remove them. It is also described that as the catalyst, one which contains oxides of Al, Mo and Ti is used, and that in an Example, the hydrogen cyanide is hydrolyzed at a temperature of about 150 to 350°C, under a pressure of about 1 to 100 bar and at a space velocity of about 5,000 to 50,000 hr-1. [0006]
JP 2000-509007 A (WO-A 97/39979) discloses an invention which provides a method for contacting a synthesis gas in the presence of water vapor with a metal oxide catalyst including the oxides of Group VI and IVB metals and aluminum oxide, and then washing the resulting synthesis gas with water to thereby remove hydrogen cyanide present in the synthesis gas.
[0007]
JP 2010-534758 A (WO-A 2009/016139) discloses a method for producing a purified gas from a raw material gas containing H2S, C02 and HCN and/or COS, including as a step (a) "(a) contacting feed gas comprising H2S, C02 and HCN and/or COS with a HCN/COS hydrolysis sorbent in the presence of water in a HCN/COS hydrolysis unit, thereby obtaining gas deficient in HCN and/or COS;". It is also disclosed at the paragraph 0018 that the hydrolysis sorbent preferably includes one or more oxides of a metal from Group IVB (Zr, Ti, Hf) as a hydrolysis catalyst, and at the paragraph 0020 that the step (a) is performed at a temperature in the range of from 80 to 250 °C.
Disclosure of the Invention
[0008]
In a method for hydrolyzing the hydrogen cyanide present in the synthesis gas by using the catalyst, there have been carried out some methods for reacting them at a relatively low temperature (to the extent of 80 to 350°C) for the purpose of suppressing both of a CO shift reaction and the production of a by-product caused by a side reaction.
However, these methods have had a problem of requiring large amounts of the catalyst due to the lower reaction rate.
In contrast, there is a problem in which when the reaction temperature is increased, the production amount of the by-product is increased due to the generation of the side reaction. Especially, when in the case of the Mo catalyst, there has been a problem in which an activation of the FT synthesis is caused in the higher temperature range of 300°C or more, to thereby result in the formation of a wax or the like as the by-product.
[0009]
An object of the present invention is to provide a method for producing a synthesis gas, including the step of contacting hydrogen cyanide contained in the synthesis gas with a catalyst at high temperature, wherein a concentration of hydrogen cyanide in the synthesis gas can also be reduced, furthermore, the amount of catalyst can be reduced, and the side reaction can also be suppressed.
[0010]
The present invention provides, as means for solving the problems, a method for producing a synthesis gas, including: a first step of obtaining a synthesis gas containing hydrogen and carbon monoxide from natural gas through steam reforming process; and a second step of, within a catalyst-packed column, reacting the synthesis gas from the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing hydrogen cyanide contained in the synthesis gas to thereby obtain a synthesis gas that contains ammonia, wherein, as the catalyst, a catalyst containing zinc oxide (ZnO) is used.
[0011]
The present invention further provides, as other means for solving the problems, a method for producing a synthesis gas, including:
a first step of obtaining a synthesis gas containing hydrogen and carbon monoxide from natural gas through steam reforming process;
a second step of, within a catalyst-packed column, contacting the synthesis gas from the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing the hydrogen cyanide contained in the synthesis gas to thereby obtain a synthesis gas that contains ammonia, wherein, as the catalyst, a catalyst containing zinc oxide (ZnO) is used; a third step of lowering the temperature of the synthesis gas obtained by the preceding step;
a fourth step of separating water and ammonia from the synthesis gas in which the temperature is lowered in the preceding step;
a fifth step of separating hydrogen from the synthesis gas from which water and ammonia are separated in the preceding step; and
a sixth step of further separating the remaining ammonia from the synthesis gas from which hydrogen is separated in the preceding step.
[0012]
According to the method for producing a synthesis gas of the present invention, both contents of hydrogen cyanide and ammonia present in the synthesis gas can be reduced.
In addition, according to the method for producing a synthesis gas of the present invention, the amount of catalyst used can be reduced due to the reaction with the catalyst at higher temperature than the conventional technology. This makes it possible to use a catalyst packed column (a container filled with catalyst) having a smaller capacity, and to reduce the burden required to install and maintain production facilities.
Furthermore, according to the method for producing a synthesis gas of the present invention, through the use of a certain catalyst, the production of a by-product is suppressed even if causing to react at higher temperature as compared with the conventional technology, and thus the burden required in the subsequent process for separating the by-product is reduced, but a basic unit of the raw material is not decreased.
Moreover, since the catalyst used in the present invention does not require the treatment that previously activates the catalyst through the use of hydrogen or the like after loading it, it can reduce operation procedures and utilities at the time of the start-up, and costs.
Embodiments for Carrying Out the Invention
[0013]
Hereinafter, the method for producing a synthesis gas of the present invention will be described for each step. Note that the first and second steps or the first to sixth steps according to the present invention is merely for the purpose of illustrating order of the steps, but is not intended to restrict the production method of the present invention only to the first and second steps or the first to sixth steps.
Furthermore, the present invention further includes an invention that makes two steps into one step and another invention that makes one step divided into two steps.
[0014]
<First step>
In the first step, the synthesis gas containing hydrogen and carbon monoxide is obtained from a hydrocarbon such as natural gas, through the steam reforming process (See the scheme below) .
The first step itself is a known process, and is performed at a temperature of about 800 to about 1,000°C. The synthesis gas obtained in the first step contains ammonia and hydrogen cyanide derived from nitrogen present in the feedstock.
[0015] CH4+H20 3H2+ CO
H20+CO ^5r H2 + CO
[0016]
<Second step>
In the second step, within a catalyst packed column, the synthesis gas obtained in the preceding step is caused to react with a catalyst.
In the method of the present invention, since the synthesis gas is caused to react with the catalyst at high temperature in the second step, the pretreatment that lowers the temperature of the synthesis gas by a heat exchanger or the like becomes unnecessary, as in the case of the reaction with the catalyst at a relatively lower temperature (approximately 80 to 350°C) .
Note that, even if the first step is carried out at about 800 to about 1,000°C, in the process of transferring the synthesis gas from one reactor in the first step to another reactor in the second step, heat recovery is usually performed on a waste heat recovery boiler to the extent of approximately
500°C or less, and it is possible to transfer the synthesis gas directly to the second step without addition of any cooling processes downstream.
[0017]
Catalytic reaction of the second step causes the synthesis gas obtained in the preceding step to react at a temperature of 350 to 550°C, to thereby decompose the hydrogen cyanide present in the synthesis gas, and to thereby obtain a synthesis gas that contains ammonia (see the scheme below) .
Although it is difficult to adsorb the hydrogen cyanide through the use of a adsorbent and remove it, ammonia is mostly separated together with condensed water because ammonia is readily-soluble in the by-product water, and the removal technique including adsorption and separation by using the adsorbent can be applied to ammonia.
[0018]
HCN+H20 CO+NH3
HCN+3H2 ^ NH3 + CH4
[0019]
In the second step, a catalyst containing zinc oxide (ZnO) is used as the catalyst, and a combined use of zinc oxide (ZnO) and the other catalyst such as aluminum oxide (A1203) is possible.
In the second step, zinc oxide (ZnO) is preferably used alone as the catalyst.
The catalyst containing, as an active site, metal species such as Mo which are used in the conventional techniques requires activation treatment with hydrogen or the like, for example, after loaded into the catalyst packed column . However, zinc oxide (ZnO) and aluminum oxide (AI2O3) used in the second step of the present invention do not require the activation treatment by using hydrogen or the like as described above, and thus zinc oxide and aluminum oxide are advantageous in that operation procedures and utilities at the time of the start-up, and costs can be reduced.
The production method of the present invention can suppress the side reaction by using a specific catalyst, even when the reaction temperature is increased, and also reduce the amount of catalyst by the increase in the reaction temperature.
In the second step, although the higher the reaction temperature with the catalyst is, the smaller the amount of catalyst required can be, the reaction temperature has an upper limit from the viewpoint of the prevention of material corrosion, and the reaction temperature is preferably 380 to 500°C, more preferably 400 to 450°C.
[0020]
Since the second step allows the amount of catalyst used therein to be decreased as compared with one used in the conventional techniques, the gas hourly space velocity (GHSV) can be increased when causing to react through the use of the catalytst packed column. Although typical HCN concentration in the exit gas in the first step is approximately 20 ppb to 100 ppm, in the present invention, the gas hourly space velocity (GHSV) in the catalyst packed column (container filled with catalyst) can be set to approximately 40, 000 to 520,000 h"1.
Note that, the GHSV (gas hourly space velocity) refers to a ratio of catalyst volume (m3) to raw material gas flow rate (Nm3/hr) in terms of the normal condition (0°C, 1 atm) , and can be obtained by the following equation. GHSV (hr_1) = flow rate of raw material gas (NmVhr) / catalyst volume (m3)
[0021]
The catalyst packed column (catalyst-packed container) used in the second step can be a conventional fixed-bed gas-solid reactor, but is not particularly limited thereto.
[0022]
In the synthesis gas obtained through the second step, the hydrogen cyanide present in the synthesis gas obtained in the first step is decomposed and converted into an
ammonia-containing gas, to thereby cause the decreased content of hydrogen cyanide.
Therefore, the synthesis gas obtained through the first and second steps can be subjected to removal of the by-product water in the third and fourth steps depending on the intended use before being used directly as a synthetic raw material as is .
[0023]
<Third step>
In the third step, the temperature of the synthesis gas obtained in the preceding step is lowered.
Since in the second step of the present invention, the catalytic reaction is carried out at higher temperature than the conventional techniques, in the third step, the temperature of the synthesis gas is lowered while heat recovery is conducted, and then the second step proceeds to the next step. In the third step, a commonly known heat exchanger such as a shell-and-tube heat exchanger can be used, but is not particularly limited thereto.
[0024]
<Fourth step>
Then, in the fourth step, water and ammonia are separated from the synthesis gas the temperature of which is lowered in the preceding step. Note that the third to fourth steps can be combined into one step.
In the fourth step, water condensed from the synthesis gas and ammonia in the preceding step are separated using a gas-liquid separator.
As the gas-liquid separator, for example, a gas-liquid separation tank equipped with a demister, or the like can be used, but the separator is not particularly limited thereto.
[0025]
<Fifth step>
Next, in the fifth step, hydrogen is separated from the synthesis gas from which water and ammonia are separated in the preceding step.
In the fifth step, hydrogen is selectively separated using a hydrogen separation membrane.
As the hydrogen separation membrane, the hydrogen separation membrane as disclosed in, for example, JP-A 8-151410 can be used, but the hydrogen separation membrane is not particularly limited thereto. Other techniques for separating hydrogen include a pressure swing adsorption process using the adsorbent, and the like, but they make operation sequences complicated.
[0026]
<Sixth step>
After that, in the sixth step, the remaining ammonia is separated from the synthesis gas from which hydrogen has been separated in the preceding step.
In the sixth step, the remaining ammonia which has failed to be separated in the fourth step is further adsorbed and separated by using the commonly known adsorbent such as an activated carbon or the like.
[0027]
The synthesis gas obtained through the steps 1 to 6 can be reduced, up to less than 10 ppb, in the total content of ammonia and hydrogen cyanide.
If the synthesis gas has reduced contents to such extent, when used as the raw material for the FT synthesis, it would neither substantially act as catalytic poison with respect to the catalyst for the FT synthesis, such as cobalt based catalyst, nor produce adverse effects on the activity of cobalt based catalyst or the like.
Furthermore, since the synthesis gas obtained through the first to sixth steps can adjust the molar ratio of hydrogen to carbon monoxide to H2/C0= approximately 2/1, it is suitable for the raw material for the FT synthesis. Examples
[0028]
Example 1
(First step)
Natural gas (inlet gas) having the following gas composition was subjected to the steam reforming process to thereby obtain the synthesis gas having the following outlet composition :
Inlet gas composition: CH4=82.5%, C2H6=6.0%, C3H8=0.5%, CO2=1.0%, N2=10%;
Outlet gas composition: CH4=1.2%, 00=11.7%, C02=5.2%, H2=53.9%, N2=1.9%, H2O=26.0%, NH3=403 ppm, HCN=1.5 ppm.
(Second step)
The gas obtained in the preceding step was fed into a reactor filled with a zinc oxide catalyst at the inlet temperature of 410°C under the pressure of 1 MPaG, and hydrogen cyanide present in it was hydrolyzed. The conversion rate of hydrogen cyanide yielded 99.3%.
The gas hourly space velocity (GHSV) during the second step was about 72, 000 h"1.
(Third step)
The gas in the preceding step was cooled to 43°C.
(Fourth step)
The water condensed in the preceding step was separated and removed by a gas-liquid separator. (Fifth step)
The gas in the preceding step was flown to a hydrogen separation membrane and the gas composition was adjusted so as to be a ratio of H2/CO = 2/1.
(Sixth step)
The gas having the ratio of H2/CO adjusted in the preceding step was caused to pass through an activated carbon bed, and ammonia was subjected to adsorption removal.
The total content of hydrogen cyanide and ammonia in the resulting synthesis gas after the completion of the sixth step was 9 ppb.
[0029]
Comparative Example 1
In Example 1, the second step was not carried out, and the synthesis gas was cooled to a temperature of approximately 185°C by means of the heat exchanger in the third step before being subjected to catalysis by using the same catalyst packed column as one used in the second step of Example 1.
The gas hourly space velocity (GHSV) during the catalysis was about 3, 800 hr_1, and the conversion rate of hydrogen cyanide was 99.1%.
After that, the fourth to sixth steps were carried out.
The total content of hydrogen cyanide and ammonia in the resulting synthesis gas after the completion of the sixth step was 10 ppb.
[0030] Comparative Example 2
In Comparative Example 1, at the gas hourly space velocity (GHSV) of about 72, 000 hr-1 during the catalysis, the conversion rate of hydrogen cyanide was 22.0%.
[0031]
The gas hourly space velocity (GHSV) during the second step in Example 1 (catalysis process) was about 72,000 hr-1, whereas the gas hourly space velocity (GHSV) during the catalysis process in Comparative Example 1 was about 3, 800 hr-1, and thus a ratio of Comparative Example 1 to Example 1 resulted in about 1/19. The larger the gas hourly space velocity is, the smaller the amount of catalyst is required. Therefore, it was perceived that the method of Example 1 would allow for the decrease in the amount of catalyst if Example 1 is at the same processing level as Comparative Example 1.
It was perceived that, by carrying out the production method of Example 1 (especially, the production step 2), comparison between Example 1 and Comparative Example 2 allows obtaining the synthesis gas having the decreased contents of hydrogen cyanide and ammonia at higher gas hourly space velocity
(that is, by using a smaller amount of catalyst).
[0032]
The synthesis gas obtained by the method for producing a synthesis gas of the present invention can be used as raw materials for production for the various types of synthesis reactions including the FT synthesis. In particular, the synthesis gas can be used as the raw material for production for the synthesis reaction using the catalyst to which hydrogen cyanide and ammonia serve as a catalytic poison, such as a cobalt based catalyst.

Claims

Claims
1. A method for producing a synthesis gas, comprising: a first step of obtaining a synthesis gas comprising hydrogen and carbon monoxide from natural gas through steam reforming process; and
a second step of, within a catalyst-packed column, reacting the synthesis gas obtained from the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing hydrogen cyanide contained in the synthesis gas to thereby obtain a synthesis gas comprising ammonia, wherein as the catalyst, a catalyst comprising zinc oxide (ZnO) is used.
2. A method for producing a synthesis gas, comprising: a first step of obtaining a synthesis gas comprising hydrogen and carbon monoxide from natural gas through steam reforming process;
a second step of, within a catalyst-packed column, contacting the synthesis gas obtained by the preceding step with a catalyst at a temperature of 350 to 550°C and decomposing hydrogen cyanide contained in the synthesis gas to thereby obtain a synthesis gas that comprises ammonia, wherein as the catalyst, a catalyst comprising zinc oxide (ZnO) is used; a third step of lowering the temperature of the synthesis gas obtained by the preceding step;
a fourth step of separating water and ammonia from the synthesis gas in which the temperature is lowered in the preceding step;
a fifth step of separating hydrogen from the synthesis gas from which water and ammonia are separated in the preceding step; and
a sixth step of further separating the remaining ammonia from the synthesis gas from which hydrogen is separated in the preceding step.
3. The method for producing a synthesis gas according to claim 1 or 2, wherein a temperature at which the synthesis gas is contacted with the catalyst in the second step ranges from 380 to 500°C.
4. The method for producing a synthesis gas according to claim 1 or 2, wherein a temperature at which the synthesis gas is contacted with the catalyst in the second step ranges from 400 to 450°C.
5. The method for producing a synthesis gas according to any one of claims 1 to 4, wherein the catalyst used in the second step is zinc oxide (ZnO) .
6. The method for producing a synthesis gas according to any one of claims 1 to 5, wherein in the fifth step, hydrogen is separated with a hydrogen separation membrane.
PCT/JP2013/051939 2012-02-20 2013-01-23 A method for producing a synthesis gas with low amounts of hydrogen cyanide WO2013125307A1 (en)

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