WO2014099568A1

WO2014099568A1 - Enhanced methane control for andrussow process

Info

Publication number: WO2014099568A1
Application number: PCT/US2013/074538
Authority: WO
Inventors: John C. Caton
Original assignee: INVISTA TECHNOLOGIES Sarl; Invista Technologies SARL USA
Current assignee: INVISTA TECHNOLOGIES Sarl; Invista Technologies SARL USA
Priority date: 2012-12-18
Filing date: 2013-12-12
Publication date: 2014-06-26
Anticipated expiration: 2015-06-18
Also published as: TW201438999A; CN103864105B; TWI519477B; CN103864105A; HK1199001A1

Abstract

The present invention relates to a process for producing hydrogen cyanide and more particularly, to a process for producing a crude hydrogen cyanide product comprising from 0.05 to 1 vol.% methane. The present invention also relates to a reactor for producing a crude hydrogen cyanide product having a catalyst bed that is supported by an annular shelf that provides a pass-through area of at least 90% of the area of the cross-sectional area of the reactor and the annular shelf substantially prevents catalyst bed bypass. The present invention also relates to a crude hydrogen cyanide product comprising from 0.05 to 1 vol.% methane.

Description

ENHANCED METHANE CONTROL FOR ANDRUSSOW PROCESS

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. App. No. 61/738,623, filed December 18, 2012, the entire contents and disclosures of which are incorporated herein.

FIELD OF THE INVENTION

[0002] The present invention relates to a process for producing hydrogen cyanide. More particularly, the invention relates to a process for producing hydrogen cyanide at enhanced levels of productivity and yield by using a controlled feedstock composition to control the amount of methane in the crude hydrogen cyanide product.

BACKGROUND OF THE INVENTION

[0003] Conventionally, hydrogen cyanide ("HCN") is produced on an industrial scale according to either the Andrussow process or the BMA process. (See e.g., Ullman's Encyclopedia of Industrial Chemistry, Volume A8, Weinheim 1987, pages 161-163). For example, in the Andrussow process, HCN can be commercially produced by reacting ammonia with a methane-containing gas and an oxygen-containing gas at elevated temperatures in a reactor in the presence of a suitable catalyst (U.S. Patent Nos. 1,934,838 and 6,596,251). Sulfur compounds and higher homologues of methane may have an effect on the parameters of oxidative ammonolysis of methane. See, e.g., Trusov, Effect of Sulfur Compounds and Higher Homologues of Methane on Hydrogen Cyanide Production by the Andrussow Method, Russian J. Applied Chemistry, 74:10 (2001), pp. 1693-1697). Unreacted ammonia is separated from HCN by contacting the reactor effluent gas stream with an aqueous solution of ammonium phosphate in an ammonia absorber. The separated ammonia is purified and concentrated for recycle to HCN conversion. HCN is recovered from the treated reactor effluent gas stream typically by absorption into water. The recovered HCN may be treated with further refining steps to produce purified HCN. Clean Development Mechanism Project Design Document Form (CDM PDD, Version 3), 2006, schematically explains the Andrussow HCN production process. Purified HCN can be used in hydrocyanation, such as hydrocyanation of an olefin-containing group, or such as hydrocyanation of 1,3 -butadiene and pentenenitrile, which can be used in the manufacture of adiponitrile ("ADN"). In the BMA process, HCN is synthesized from methane and ammonia in the substantial absence of oxygen and in the presence of a platinum catalyst, resulting in the production of HCN, hydrogen, nitrogen, residual ammonia, and residual methane. (See e.g., Oilman's Encyclopedia of Industrial Chemistry, Volume A8, Weinheim 1987, pages 161-163). Commercial operators require process safety management to handle the hazardous properties of hydrogen cyanide. (See Maxwell et al. Assuring process safety in the transfer of hydrogen cyanide manufacturing technology, JHazMat 142 (2007), 677-684). Additionally, emissions of HCN production processes from production facilities may be subject to regulations, which may affect the economics of HCN manufacturing. (See Crump, Economic Impact Analysis For The Proposed Cyanide Manufacturing NESHAP, EPA, May 2000).

[0004] Existing HCN production processes suffer from a variety of issues, including losses of productivity in producing HCN and inefficiencies in residual ammonia recovery and recycling.

SUMMARY OF THE INVENTION

[0005] In one embodiment, the present invention is directed to a process for producing hydrogen cyanide comprising forming a ternary gas mixture comprising a methane-containing gas, an ammonia-containing gas, and an oxygen-containing gas; contacting the ternary gas mixture with a catalyst bed in a reactor to form a crude hydrogen cyanide product, wherein the catalyst bed is supported by an annular shelf that provides a pass-through area that is at least 90% of the area of the cross-sectional area of the reactor and the annular shelf substantially prevents catalyst bed bypass of the ternary gas mixture or a component thereof; and controlling a flow rate of at least one of the methane-containing gas, the ammonia-containing gas, or the oxygen-containing gas to maintain a methane concentration in the crude hydrogen cyanide product from 0.05 to 1 vol.%. The methane-containing gas, the ammonia-containing gas, and the oxygen-containing gas may be combined in a mixing vessel upstream of the reactor to form the ternary gas mixture. The oxygen-containing gas may comprise greater than 21 vol.% oxygen, e.g., at least 80 vol.% oxygen. The ternary gas mixture may comprise at least 25 vol.% oxygen. The molar ratio of ammonia-to-oxygen in the ternary gas mixture may be from 1.2 to 1.6. The molar ratio of methane-to-oxygen in the ternary gas mixture may be from 1 to 1.25. The process may further comprise separating the crude hydrogen cyanide product, wherein the separation comprises: removing residual ammonia from the crude hydrogen cyanide product to provide a hydrogen cyanide product; separating the hydrogen cyanide product to form an off-gas stream and a hydrogen cyanide stream; and purifying the hydrogen cyanide stream to form a finished hydrogen cyanide product. The hydrogen cyanide stream may comprise less than 0.25 vol.% acetonitrile or less than 0.15 vol.% acetonitrile.

[0006] In a second embodiment, the present invention is directed to a crude hydrogen cyanide product produced in a process for making hydrogen cyanide, wherein the crude hydrogen cyanide product comprises hydrogen cyanide and from 0.05 to 1 vol.% methane, e.g., from 0.05 to 0.55 vol.%) or from 0.2 to 0.3 vol.% methane.

[0007] In a third embodiment, the present invention is directed to a reaction assembly for preparing hydrogen cyanide in a reaction assembly, the reaction assembly comprising: at least one inlet port for a ternary gas mixture; a catalyst support assembly comprising an annular shelf that provides a pass-through area that is at least 90%> of the area of the cross-sectional area of the reactor; a catalyst bed supported by the catalyst support assembly, wherein the annular shelf substantially prevents catalyst bed bypass of the ternary gas mixture or a component thereof; and at least one outlet port for a crude hydrogen cyanide product; wherein the ternary gas mixture comprises a methane-containing gas, an ammonia-containing gas, and an oxygen-containing gas; wherein the ternary gas mixture is fed to the at least one inlet port, and is passed over the catalyst bed; and wherein a flow rate of at least one of the methane-containing gas, the ammonia- containing gas, or the oxygen-containing gas is controlled to maintain a methane concentration in the crude hydrogen cyanide product from 0.05 to 1 vol.%, e.g., from 0.05 to 0.55 vol.% or from 0.2 to 0.3 vol.%) methane. The catalyst support assembly may comprise a perforated plate that allows the passage of gas. The catalyst support assembly may be disposed substantially adjacent to a lower surface of the catalyst bed. The catalyst support assembly may further comprise a shelf substantially parallel to and extending beyond the catalyst bed size. The shelf may comprise a ceramic material.

[0008] In a fourth embodiment, the present invention is directed to a process for controlling methane content in a crude hydrogen cyanide product, comprising: providing a ternary gas mixture comprising a methane-containing gas, an ammonia-containing gas, and an oxygen- containing gas, to at least one inlet port of a reactor; contacting the ternary gas mixture with a catalyst in the reactor to form a crude hydrogen cyanide product; wherein the catalyst is supported on an annular shelf that provides a pass-through area that is at least 90%> of the area of the cross-sectional area of the reactor and the annular shelf substantially prevents catalyst bed bypass of the ternary gas mixture or a component thereof; measuring methane content in the crude hydrogen cyanide product; and adjusting the molar ratio of at least one of ammonia to oxygen, ammonia to methane, or methane to oxygen, to provide a crude hydrogen cyanide product comprising from 0.05 to 1 vol.% methane, or from 0.05 to 0.55 vol.% methane or from 0.2 to 0.3 vol.% methane.

[0009] In a fifth embodiment, the present invention is directed to at least one inlet port for a ternary gas mixture; a catalyst bed; a catalyst support assembly for supporting the catalyst bed, wherein the catalyst support assembly comprising a perforated plate and a shelf substantially parallel to and extending beyond the catalyst bed size, wherein the shelf comprises a ceramic material; and at least one outlet port for a crude hydrogen cyanide product, wherein the reactor assembly is operated under conditions effective to produce the crude hydrogen cyanide product comprising from 0.05 to 1 vol.% methane, or from 0.05 to 0.55 vol.% methane. The ternary gas mixture may comprise a methane-containing gas, an ammonia-containing gas and an oxygen- containing gas. The shelf may be in contact with reactor walls of the reaction assembly. The catalyst bed may be a porous structure, wire gauze, pellet, tablet, monolith, foam, impregnated coating or wash coating. The catalyst bed may be a wire mesh platinum/rhodium alloy or platinum/iridium alloy. The shelf may be impermeable to gases. The shelf and perforated plate may be parallel. The reaction assembly may further comprise a flame arrestor that is upstream of the catalyst bed, wherein the flame arrestor is a refractory ceramic material.

[0010] In a sixth embodiment, the present invention is directed to a reaction assembly for preparing hydrogen cyanide, the reaction assembly comprising a reactor comprising: at least one inlet port for a ternary gas mixture; a catalyst support assembly; a catalyst bed supported by the catalyst support assembly; and at least one outlet port for a crude hydrogen cyanide product; wherein the ternary gas mixture comprises a methane-containing gas, an ammonia-containing gas, and an oxygen-containing gas; wherein the ternary gas mixture is fed to the at least one inlet port, and is passed over the catalyst bed; and wherein the reactor is operated under conditions effective to produce the crude hydrogen cyanide product comprising from 0.05 to 1 vol.% methane or from 0.05 to 0.55 vol.% methane.

[0011] The catalyst support assembly may comprise a perforated plate. The catalyst support assembly may be disposed substantially adjacent to a lower surface of the catalyst bed. The catalyst support assembly may further comprise a shelf substantially parallel to and extending beyond the catalyst bed size. The shelf may comprise a ceramic material. The catalyst bed may be a porous structure, wire gauze, tablet, pellet, monolith, foam, impregnated coating, or wash coating. The catalyst bed may be a wire mesh platinum/rhodium alloy or platinum/iridium alloy. The shelf may be impermeable to gases. The shelf and perforated plate may be in the same plane. The reaction assembly may further comprise a flame arrestor that is upstream of the catalyst bed, wherein the flame arrestor is a refractory ceramic material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a simplified schematic flow diagram of an HCN synthesis system according to an embodiment of the present invention.

[0013] FIGS. 2A and 2B are a cross-section view of a catalyst bed on a catalyst support assembly comprising a shelf according to an embodiment of the present invention.

[0014] FIG. 3 is a chart showing nitrile formation as a function of methane content in the crude hydrogen cyanide product.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, group of elements, components, and/or groups thereof.

[0016] Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, as well as equivalents, and additional subject matter not recited. Further, whenever a composition, a group of elements, process or method steps, or any other expression is preceded by the transitional phrase "comprising," "including," or "containing," it is understood that it is also contemplated herein the same composition, group of elements, process or method steps or any other expression with transitional phrases "consisting essentially of," "consisting of," or "selected from the group of consisting of," preceding the recitation of the composition, the group of elements, process or method steps or any other expression.

[0017] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims, if applicable, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments described herein were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. Accordingly, while the invention has been described in terms of embodiments, those of skill in the art will recognize that the invention can be practiced with modifications and in the spirit and scope of the appended claims.

[0018] Reference will now be made in detail to certain disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that they are not intended to limit the disclosed subject matter to those claims. On the contrary, the disclosed subject matter is intended to cover all alternatives, modifications, and equivalents, which can be included within the scope of the presently disclosed subject matter as defined by the claims.

[0019] In the Andrussow process for forming HCN, methane, ammonia and oxygen raw materials are reacted at temperatures above 1000°C in the presence of a catalyst to produce a crude hydrogen cyanide product comprising HCN, hydrogen, carbon monoxide, carbon dioxide, nitrogen, residual ammonia, residual methane, and water. These components, i.e., the raw materials, are provided to the reactor as a ternary gas mixture comprising an oxygen-containing gas, an ammonia-containing gas and a methane-containing gas. The catalyst is typically a wire mesh platinum/rhodium alloy or a wire mesh platinum/iridium alloy. The catalyst bed may be woven or knitted. Other catalyst compositions can be used and include, but are not limited to, a platinum group metal, platinum group metal alloy, supported platinum group metal or supported platinum group metal alloy. Other catalyst configurations can also be used and include, but are not limited to, porous structures, wire gauze, tablets, pellets, monoliths, foams, impregnated coatings, and wash coatings. Natural gas is typically used as the source of methane, while air, oxygen-enriched air, or pure oxygen can be used as the source of oxygen. The ternary gas mixture is passed over a catalyst to form a crude hydrogen cyanide product. The crude hydrogen cyanide product is then separated to recover HCN.

[0020] As described herein, the crude hydrogen cyanide product from either the Andrussow or BMA process comprises HCN, residual ammonia and residual methane. In the Andrussow process, the amount of residual methane is controlled by a number of variables, including the molar ratios of the reactants methane, ammonia and oxygen; conversion of the reactants; and reactor efficiency. Advantageously, the process may be improved by controlling the amount of methane in the crude hydrogen cyanide product. If too little methane is present in the crude hydrogen cyanide product, residual ammonia may be cracked to form nitrogen and hydrogen. If too much methane is present in the crude hydrogen cyanide product, unwanted impurities, including nitriles, e.g., acetonitrile, may form in the crude hydrogen cyanide product as it is purified to recover HCN. Nitriles may further polymerize and clog the separation process which leads to production inefficiencies. Such nitriles would have to be purged from the separation process to avoid clogging. For purposes of the present invention, the controlled amount of methane in the crude hydrogen cyanide product is between 0.05 and 1 vol.%, e.g., from 0.05 to 0.55 vol.% or from 0.2 to 0.3 vol.%. When the amount of methane in the crude hydrogen cyanide product is between 0.6 and 1 vol.%, nitrile formation is not large enough to require a purge from the separation process and thus this amount of methane may be tolerated in the crude hydrogen cyanide product. However, over time, the nitriles may polymerize and clog the separation equipment. Thus, from 0.05 to 0.55 vol.% methane, or from 0.2 to 0.3 vol.% methane is preferred when the separation equipment is run continuously or semi-continuously for at least 6 months.

[0021] In one embodiment, the present invention is thus directed to a crude hydrogen cyanide product produced in a process for making hydrogen cyanide, wherein the crude hydrogen cyanide product comprises hydrogen cyanide and from 0.05 to 1 vol.% methane, e.g., from 0.05 to 0.55 vol.%) or from 0.2 to 0.3 vol.%> methane. This crude hydrogen cyanide product composition may be independent of the process by which it is prepared, provided that the reactants comprise methane.

[0022] As described herein, there are several variables in controlling this amount of methane. The reactants used to form HCN according to the Andrussow process include ammonia, methane and oxygen, each of which is provided as a gas. The ammonia-containing gas, methane- containing gas and oxygen-containing gas are combined and mixed in a mixing vessel prior to entering the reactor via an inlet port, e.g., upstream of the reactor. One variable in controlling the amount of methane in the crude hydrogen cyanide product is the molar ratio of ammonia-to- oxygen in the ternary gas mixture. In some embodiments, the molar ratio of ammonia-to-oxygen in the ternary gas mixture is from 1.2 to 1.6. The molar ratio of methane-to-oxygen may be from 1 to 1.25. If the molar ratio of methane-to-oxygen should be adjusted, it is preferred to adjust the flow rate of methane and maintain oxygen flow rates.

[0023] Therefore, the present invention is also directed to a process of controlling the molar ratios of ammonia-to-oxygen and methane-to-oxygen. There are several considerations when adjusting a molar ratio including oxygen. This is due to flammability and detonation limits of the ternary gas mixture, especially if oxygen-enriched air, e.g., air comprising greater than 21 vol.% oxygen, e.g., at least 80 vol.% oxygen, is used as the oxygen-containing gas.

[0024] In order to accurately adjust the molar ratios of ammonia-to-oxygen and methane-to- oxygen, it is desirable to reduce or eliminate leakage of the ternary gas mixture or components thereof, e.g., of the methane-containing gas, around the catalyst bed. This leakage, also referred to as bypass, may be reduced by including an annular catalyst shelf, described herein. By reducing, e.g., substantially reducing or eliminating bypass of the methane-containing gas around the catalyst bed, the flow rate of methane in the crude hydrogen cyanide product may be controlled with more predictability than if the methane-containing gas bypasses the catalyst bed. In other words, control of methane leakage is not possible when methane can bypass the catalyst bed. The advantage of the present invention is that methane bypass around the catalyst bed can be eliminated by using an impervious annular shelf and thus, the control of methane can be adjusted by the flow rate of methane. Enhanced Oxygen Content

[0025] As described herein, the molar ratio of ammonia-to-oxygen and the molar ratio of methane-to-oxygen may be used to control the amount of methane in the crude hydrogen cyanide product. The ability to modify these ratios is based, at least in part, on the oxygen-content of the oxygen-containing gas, and thus of the ternary gas mixture.

[0026] The term "air" as used herein refers to a mixture of gases with a composition approximately identical to the native composition of gases taken from the atmosphere, generally at ground level. In some examples, air is taken from the ambient surroundings. Air has a composition that includes approximately 78 vol.% nitrogen, approximately 21 vol.% oxygen, approximately 1 vol.% argon, and approximately 0.04 vol.% carbon dioxide, as well as small amounts of other gases.

[0027] The term "oxygen-enriched air" as used herein refers to a mixture of gases with a composition comprising more oxygen than is present in air. Oxygen-enriched air has a composition including greater than 21 vol.% oxygen, less than 78 vol.% nitrogen, less than 1 vol.% argon and less than 0.04 vol.% carbon dioxide. In some embodiments, oxygen-enriched air comprises at least 28 vol.% oxygen, e.g., at least 80 vol.% oxygen, at least 95 vol.% oxygen, or at least 99 vol.% oxygen.

[0028] The formation of HCN in the Andrussow process is often represented by the following generalized reaction:

2CH₄ + 2NH₃ + 30₂ 2HCN + 6H₂0

However, it is understood that the above reaction represents a simplification of a much more complicated kinetic sequence where a portion of the hydrocarbon is first oxidized to produce the thermal energy necessary to support the endothermic synthesis of HCN from the remaining hydrocarbon and ammonia.

[0029] Three basic side reactions also occur during the synthesis of HCN:

CH₄ + H₂0 -> CO + 3H₂

2CH₄ + 30₂ 2CO + 4H₂0

4NH₃ + 30₂ -> 2N₂ + 6H₂0

In addition to the amount of nitrogen generated in the side reactions, additional nitrogen may be present in the crude product, depending on the source of oxygen. Although the prior art has suggested that oxygen-enriched air or pure oxygen can be used as the source of oxygen, the advantages of using oxygen-enriched air or pure oxygen have not been fully explored. When using air as the source of oxygen, the crude hydrogen cyanide product comprises the components of air, e.g., approximately 78 vol.% nitrogen, and the nitrogen produced in the ammonia and oxygen side reaction.

[0030] Due to the large amount of nitrogen in air, it is advantageous to use oxygen-enriched air, which contains less nitrogen than air, in the synthesis of HCN because the use of air as the source of oxygen in the production of HCN results in the synthesis being performed in the presence of a larger volume of inert gas (nitrogen) necessitating the use of larger equipment in the synthesis step and resulting in a lower concentration of HCN in the product gas. Additionally, because of the presence of the inert nitrogen, more methane is required to be combusted (when air is used, as compared to oxygen-enriched air) in order to raise the temperature of the ternary gas mixture components to a temperature at which HCN synthesis can be sustained. The crude hydrogen cyanide product contains the HCN and also by-product hydrogen, methane combustion byproducts (carbon monoxide, carbon dioxide, water), residual methane, and residual ammonia. However, when using air (i.e., approximately 21 vol.% oxygen), after separation of the HCN and recoverable ammonia from the other gaseous components, the presence of the inert nitrogen renders the residual gaseous stream with a fuel value that may be lower than desirable for energy recovery.

[0031] Therefore, the use of oxygen-enriched air or pure oxygen instead of air in the production of HCN provides several benefits, including an increase in the conversion of natural gas to HCN and a concomitant reduction in the size of process equipment. Thus, the use of oxygen-enriched air or pure oxygen reduces the size of the reactor and at least one component of the downstream gas handling equipment through the reduction of inert compounds entering the synthesis process. The use of oxygen-enriched air or pure oxygen also reduces the energy consumption required to heat the oxygen-containing feed gas to reaction temperature.

[0032] It has been found that both productivity and production efficiency of HCN can be significantly improved, while maintaining stable operation, in part, by providing an oxygen- containing gas sufficiently enriched in oxygen and by adjusting the molar ratio of ammonia-to- methane to a sufficiently high level. In one embodiment, the oxygen-containing gas contains greater than 21 vol.% oxygen, e.g., at least 80 vol.% oxygen, at least 95 vol.% oxygen, or at least 99 vol.% oxygen the molar ratio of ammonia-to-oxygen in the ternary gas mixture is in the range from 1.3 to 1.5, e.g., from 1.3 to 1.4, and the molar ratio of ammonia-to-methane in the ternary gas mixture is in the range from 1.1 to 1.45. In another embodiment, the ternary gas mixture comprises at least 25 vol.% oxygen, the molar ratio of ammonia-to-oxygen is from 1.2 to 1.6, a molar ratio of ammonia-to-methane is from 1 to 1.5, e.g., from 1.1 to 1.45, and a molar ratio of methane-to-oxygen is from 1 to 1.25, e.g., from 1.05 to 1.15. For example, a ternary gas mixture may have a molar ratio of ammonia-to-oxygen of 1.3 and methane-to-oxygen 1.2. In another exemplary embodiment, the ternary gas mixture may have a molar ratio of ammonia-to-oxygen of 1.5 and methane-to-oxygen 1.15. The oxygen concentration may vary depending on these molar ratios.

[0033] The amount of oxygen present in the ternary gas mixture is controlled by flammability limits. Certain combinations of air, methane and ammonia are flammable and will therefore propagate a flame following ignition. A mixture of air, methane and ammonia will burn if the gas composition lies between the upper and lower flammability limits. Mixtures of air, methane and ammonia outside of this region are typically not flammable. The use of oxygen-enriched air changes the concentration of combustibles in the ternary gas mixture. Increasing the oxygen content in the oxygen-containing gas feed stream significantly broadens the flammable range. For example, a mixture containing 45 vol.% air and 55 vol.% methane is considered very fuel- rich and is not flammable, whereas a mixture containing 45 vol.% oxygen and 55 vol.% methane is flammable.

[0034] An additional concern is the detonation limit. For example, at atmospheric pressure and room temperature, a gas mixture containing 60 vol.% oxygen, 20 vol.% methane and 20 vol.% ammonia can detonate.

[0035] Thus, while the use of oxygen-enriched air in the production of HCN has been found to be advantageous, the enrichment of air with oxygen necessarily leads to a change in the concentration of combustibles in the ternary gas mixture and such a change in the concentration of combustibles increases the upper flammability limit of the ternary gas mixture fed to the reactor. Deflagration and detonation of the ternary gas mixture is, therefore, sensitive to the oxygen concentration. The term "deflagration" as used herein refers to a combustion wave propagating at subsonic velocity relative to the unburned gas immediately ahead of the flame. "Detonation," on the other hand, refers to a combustion wave propagating at supersonic velocity relative to the unburned gas immediately ahead of the flame. Deflagrations typically result in modest pressure rise whereas detonations can lead to extraordinary pressure rise.

[0036] While others have suggested the use of oxygen-enriched air for increasing HCN production capacity, they typically avoid operating in the flammable region. See U.S. Pat. Nos. 5,882,618; 6,491,876 and 6,656,442, the entireties of which are incorporated herein by reference. In the present invention, the oxygen-enriched air or pure oxygen feed is controlled to form a ternary gas mixture within the flammable region, but not within the detonable region. Thus, in some embodiments, the ternary gas mixture comprises at least 25 vol.% oxygen, e.g., at least 28 vol.% oxygen. In some embodiments, the ternary gas mixture comprises from 25 to 32 vol.% oxygen, e.g., from 26 to 30 vol.% oxygen.

Methane-Containing Gas Preparation

[0037] As would be understood by one of ordinary skill in the art, the source of the methane may vary and may be obtained from renewable sources such as landfills, farms, biogas from fermentation, or from fossil fuels such as natural gas, oil accompanying gases, coal gas, and gas hydrates as further described in VN Parmon, "Source of Methane for Sustainable Development", pages 273-284, and in Derouane, eds. Sustainable Strategies for the Upgrading of Natural Gas: Fundamentals, Challenges, and Opportunities (2003). For purposes of the present invention, the methane purity and the consistent composition of the methane-containing source is of significance.

[0038] Natural gas, one source of the methane for the methane-containing stream, is an impure state of methane. That is, natural gas is a substantially methane-containing gas that can be used to provide the carbon element of the HCN produced in the process of the present invention. However, in addition to methane, natural gas may contain contaminants such as hydrogen sulfide, carbon dioxide, nitrogen, water, and higher molecular weight hydrocarbons, such as ethane, propane, butane, pentane, and higher hydrocarbons. These higher molecular weight hydrocarbons are referred to herein as "C2+ hydrocarbons." C2+ hydrocarbons may be removed from natural gas using a variety of methods, including hydrocarbon separation. The hydrocarbon separation may be conducted using the adsorbing process or the cryogenic expansion process. The adsorbing process may be used to focus on the removal on C3+ hydrocarbons while the cryogenic expansion process may be used to focus on the removal of ethane while also removing C3+ hydrocarbons.

[0039] Natural gas composition can vary significantly from source to source. The composition of natural gas provided by pipeline can also change significantly over time and even over short time spans as sources are taken on and off of the pipeline. Such variation in composition, especially with regard to the presence of and amount of C2+ hydrocarbons, leads to difficulty in sustaining optimum and stable process performance. The presence of C2+ hydrocarbons in the natural gas composition is especially troublesome due to 1) their higher heating value than methane, 2) their deactivating effect on the catalyst in the HCN reactor, especially C3+ hydrocarbons, and 3) side reactions that may form higher nitriles, e.g., acetonitrile, acrylonitrile and propionitrile. The sensitivity of the HCN synthesis process to variations in and large amounts of C2+ hydrocarbons becomes more severe as inert loading is reduced through oxygen enrichment of the oxygen-containing gas.

[0040] Thus, the methane-containing gas may be treated to comprise less than 1 vol.% C2+ hydrocarbons, e.g., less than 5000 mpm, less than 1000 mpm, less than 150 mpm or that is substantially free of C2+ hydrocarbons. "Substantially free of C2+ hydrocarbons" includes from 0 to 100 mpm C2+ hydrocarbons. Tins methane-containing stream may also be referred to herein as "purified natural gas." In some embodiments, the methane-containing stream is substantially free of contaminants. Additionally, the methane-containing stream may be substantially anhydrous.

[0041] Using purified natural gas to obtain the methane-containing gas to produce HCN increases the catalyst life and yield of HCN. In particular, utilizing the purified natural gas stream stabilizes the remaining composition at a consistent level to allow downstream HCN synthesis to be optimized, and enables the use of highly enriched or pure oxygen feed streams by mitigating large temperature excursions in the HCN synthesis step that are typically related to variation in higher hydrocarbon content and which are detrimental to optimum yield and operability, such as catalyst damage, interlock, and loss of uptime. Using the purified natural gas also minimizes formation of higher nitriles and minimizes the associated yield losses of HCN during removal of nitriles. In addition, use of the purified natural gas as the source of the methane-containing gas minimizes variability in the feed stock by stabilizing the carbon and hydrogen content as well as the fuel values and thereby stabilizes the entire HCN synthesis system allowing for the determination and control of methane-to-oxygen and ammonia-to- oxygen ratios for stable operation and more efficient HCN yield. Further, using the purified natural gas minimizes related temperature spikes and resulting catalyst and catalyst bed damage.

Ammonia-Containing Gas Preparation

[0042] Prior to being mixed with the oxygen-containing gas and the methane-containing gas, the ammonia-containing gas source may be subject to treatment. This processing may include removing contaminants, such as water, oil, and iron (Fe), from the ammonia-containing gas source. Contaminants in the ammonia-containing gas can reduce catalyst life which results in poor reaction yields and earlier replacement. The processing may include using processing equipment, such as vaporizers, and filters, to provide a treated ammonia-containing gas.

[0043] For example, commercially available liquid ammonia can be processed in a vaporizer to provide a partially purified ammonia vapor stream and a first liquid stream containing water, iron, iron particulate and other nonvolatile impurities. An ammonia separator, such as an ammonia demister, can be used to separate the impurities and any liquid present in the partially purified ammonia vapor stream to produce the treated ammonia-containing gas (a substantially pure ammonia vapor stream) and a second liquid stream containing entrained impurities and any liquid ammonia present in the partially purified ammonia vapor stream.

[0044] In one embodiment, the first liquid stream containing water, iron, iron particulate and other nonvolatile impurities is fed to a second vaporizer where a portion of the liquid stream is vaporized to create a second partially purified ammonia vapor stream and a second, more concentrated, liquid stream containing water, iron, iron particulate and other nonvolatile impurities which can be further treated as a purge or waste stream. The second partially purified ammonia vapor stream can be fed to the ammonia separator. In another embodiment, the second, more concentrated, liquid stream containing water, iron, iron particulate and other nonvolatile impurities is fed to a third vaporizer to further reduce the ammonia content before treating this stream as a purge or waste stream.

[0045] Foaming in the vaporizers can limit the vaporization rate of ammonia and decrease the purity of the ammonia vapor produced. Foaming is generally retarded by the introduction of an antifoaming agent into the vaporizers directly or into the vaporizer feed streams. The antifoaming agents belong to a broad class of polymeric materials and solutions that are capable of eliminating or significantly reducing the ability of a liquid and/or liquid and gas mixture to foam. Antifoaming agents inhibit the formation of bubbles in an agitated liquid by reducing the surface tension of the solutions. Examples of antifoaming agents include silicones, organic phosphates, and alcohols. In one embodiment, a sufficient amount of antifoaming agent is added to the ammonia-containing gas to maintain an antifoaming agent concentration from 2 to 20 mpm in the ammonia-containing gas. A non-limiting example of an antifoaming agent is Unichem 7923 manufactured by Unichem of Hobbs, NM. The processing of the ammonia- containing gas source may also include a filter system for removing micro particulates in order to prevent poisoning of the catalyst in the reactor. The filter system can be a single filter or a plurality of filters.

HCN Reactor

[0046] The present invention also relates to a reactor assembly 106 that may be used to produce a crude hydrogen cyanide product 107 comprising from 0.05 to 1 vol.% methane, e.g., from 0.05 to 0.55 vol.% or from 0.2 to 0.3 vol.% methane. Reactor assembly 106 comprises a mixing section 155 for introducing and mixing reactant gases to form a thoroughly mixed ternary gas mixture 105 that is introduced to reacting section 157. Reacting section 157 comprises at least one inlet port 160 for the ternary gas mixture 105, a catalyst support assembly 161, a catalyst bed 162 supported by the catalyst support assembly, and at least one outlet port 163 for the crude hydrogen cyanide product 107. As described here, controlling reactor efficiency is one variable in controlling methane content in the crude hydrogen cyanide product.

[0047] As described herein, one way to control the reactor efficiency is to provide a catalyst support assembly. As shown in FIG. 2A, the catalyst support assembly may be disposed substantially adjacent to a lower surface 164 of the catalyst bed 162, and is configured such that the catalyst bed 162 rests on and is supported by the catalyst support assembly. The catalyst support assembly comprises a perforated (e.g., monolith or ceramic foam) plate 170 and a shelf 171, e.g., an annular shelf. Annular shelf 171 may extend outwardly from the internal wall 165 of the reacting section 157 and a uniform distance. Annular shelf 171 travels along the circumference of the reacting section 157. Plate 170 may be in the same plane as annular shelf 171. Perforated plate 170 allows the passage of gases. Annular shelf 171 is solid and impermeable to gases. Annular shelf 171 is substantially parallel to the catalyst bed 162 and is in contact with the reactor walls 165. In some embodiments, the annular shelf 171 is comprised of ceramic and is an integral part of the reactor. In some embodiments, annular shelf 171 is comprised of the same materials as the reactor. Annular shelf 171 is configured to allow a pass- through area to allow the crude hydrogen cyanide product formed from the ternary gas mixture to contact the catalyst bed to fonn the crude hydrogen cyanide product. The crude hydrogen cyanide product may contain components of the ternary gas, e.g., methane, oxygen and/or ammonia. The pass-through area, which is permeable to gases, may be at least 85% of the cross- sectional area of the reactor, e.g., at least 90%, depending on the anticipated amount of catalyst shrinkage and desired HCN yield. In terms of ranges, the pass-through area may be from 85% to 95%, e.g., from 90 to 95%. For example, if the reactor has a 137.16 cm internal diameter and catalyst diameter shrinkage is assumed to be between 0.64 cm and 1.26 cm over time, annular shelf 171 may extend from 2.54 cm to 3.18 cm from the reactor wall. Larger extensions into the reactor may reduce the pass-through area to less than 85%) and reduce productivity. Small annular walls with a larger pass-through area of greater than 95%> also face problems if the catalyst shrinks more than anticipated or shifts in the reactor. In general, the catalyst shrinkage may occur at least partially on startup and then remain in the shrunken fonn over the reactor running time. In addition, extending the shelf further from the reactor wall reduces the frequency that the reactor is taken off-line to replace the catalyst bed but also may increase the pressure drop across the reactor, thus decreasing HCN yield.

[0048] As shown in FIG. 2B, the annular shelf 171 may extend beyond the catalyst bed 162 when in a reduced form, due to catalyst shrinkage. As the lifetime of the catalyst increases, the catalyst may experience shrinkage as shown in FIG. 2B, resulting in the catalyst bed 162 no longer being in contact with the reactor walls 165. This catalyst shrinkage could allow components of the ternary gas mixture, including methane, to bypass the catalyst, resulting in increased methane content in the cmde hydrogen cyanide product. By including an annular shelf 171, this ternary gas mixture component bypass is reduced, substantially reduced, and/or eliminated. [0049] Reactor assembly 105 may also comprise a flame arrestor 180 positioned downstream of distributor plate 181, a radiation shield 182 adjacent to catalyst bed 162. Reactor vessel 106 may also comprise a heat exchanger 183, e.g., waste heat boiler, for cooling crude hydrogen cyanide product. An igniter hole (not shown) may extend through radiation shield 182 to enable an igniter to touch the upper surface of catalyst bed 162. Other ignition techniques that do not require a hole in the radiation shield may be used with embodiments of the present invention. The ignition of catalyst bed can be carried out in any manner known to those skilled in the art.

[0050] Flame arrestor 180 is spatially disposed above catalyst bed so as to provide a space therebetween. The flame arrestor quenches any upstream burning resulting from flash back within the reaction vessel. Ceramic foam may be disposed along at least a portion of an interior wall of the housing defining the internal reaction chamber and the catalyst. The ceramic foam minimizes feed gas bypass due to catalyst shrinkage when the reactor is shut down. Ceramic foam disposed above the catalyst bed functions to minimize ternary gas volume, reduce pressure drop and quench formation of radicals during operation of the reactor. Ferrules are disposed in each of the outlets of the housing and provide fluid communication between the catalyst bed and an upper portion of a waste heat boiler.

[0051] The reaction to produce HCN is conducted in the catalyst bed. Suitable catalysts for use in the catalyst bed of the Andrussow process contain Group VIII metals. The Group VIII metals include platinum, rhodium, iridium, palladium, osmium or ruthenium and the catalyst can be such metals, a mixture of such metals or alloys of two or more of such metals. A catalyst containing from 50 wt.% to 100 wt.% platinum, based on the total weight of the catalyst, is employed in many instances for the production of HCN. The catalyst must be sufficiently strong to withstand to increased velocity rates possible with using oxygen-enriched air or pure oxygen to form the ternary gas having greater than 25 vol.% oxygen. Thus, a 85/15 platinum/rhodium alloy may be used on a flat catalyst support. A 90/10 platinum/rhodium alloy may be used with a corrugated support that has an increased surface area as compared to the flat catalyst support.

Crude Hydrogen Cyanide Product Production

[0052] As is shown in FIG. 1, hydrogen cyanide production system 100, ternary gas mixture 105 comprises a methane-containing gas 102, an ammonia-containing gas 103, and an oxygen- containing gas 104. Ternary gas mixture 105 is fed to reactor assembly 106 to produce crude hydrogen cyanide product 107 comprising from 0.05 to 1 vol.% methane, e.g., from 0.05 to 0.55 vol.% or from 0.2 to 0.3 vol.% methane. Crude hydrogen cyanide product 107 is fed to ammonia absorber 110 to form an overhead HCN stream 111 and an ammonia residue stream 112.

[0053] Generally, it is desirable that unreacted ammonia, also referred to as residual ammonia, be removed from the crude hydrogen cyanide product prior to further HCN purification. Ammonia absorber 110 is provided with a sufficient number of absorption stages to obtain the desired level of separation. Standard engineering practice can determine the number of stages necessary. The crude hydrogen cyanide product 107 is introduced into the ammonia absorber 110 and the ammonia is absorbed from the crude hydrogen cyanide product 107 into a lean phosphate feed stream (not shown).

[0054] In one embodiment, the lean phosphate feed stream is an "ammonia-lean" aqueous solution comprising mono-ammonium hydrogen phosphate (NH₄H₂P0₄) and di-ammonium hydrogen phosphate ((NH₄)₂HP0₄) having an N¾ /P0₄ ^" ratio in the range from 1.2 to 1.4 and a pH from 5 to 6.1, e.g., from 5.3 to 6.0. Values for the NH₄ /P0₄ ^" ratio include only the ammonia tied up with phosphate and do not consider ammonia tied up with other compounds such as, for example, formate or oxalate. Make up phosphoric acid stream can be added to the ammonia-lean phosphate solution before the solution is fed as a lean phosphate feed stream into an ammonia absorber upper portion. Performance of the ammonia absorber 110 is controlled, at least in part, by monitoring and adjusting temperature, pH and solution density. The temperature of the lean phosphate feed stream is controlled to a temperature between 90°C and a temperature above the freezing point (sometimes referred to as the frost point which is defined herein as the saturation point, i.e., the temperature below which solids precipitation begins) of the lean phosphate feed stream, to effect the desired ammonia absorption. The crude hydrogen cyanide product 107 passes up through the ammonia absorber 110 and contacts, in a countercurrent manner, the lean phosphate feed stream flowing in a downward direction through the ammonia absorber 110. The unreacted ammonia present in the crude hydrogen cyanide product 107 is absorbed by and reacts with the "ammonia-lean" phosphate solution to form additional di- ammonium hydrogen phosphate thereby providing an "ammonia-rich" phosphate solution, which flows to the ammonia absorber lower portion. The ammonia-rich phosphate solution, having an NH₄ ⁺/P0₄ ^"3 ratio in the range from 1.5 to 2.0 (and in another embodiment in the range from 1.7 to 1.9) and a pH in the range from 6.2 to less than 7.0, is discharged from the ammonia absorber 110 as ammonia residue stream 112.

[0055] In another embodiment, the ammonia lean phosphate solution is stored in an ammonia absorber feed tank, where make up phosphoric acid stream can be added to the ammonia lean phosphate solution before it is fed as the lean phosphate feed stream into the ammonia absorber upper portion. Ammonia absorber feed tank may be heated or cooled to maintain the temperature of the ammonia lean phosphate solution at a desired temperature for ammonia absorption in the ammonia absorber 110.

[0056] In another embodiment the lean phosphate feed stream comprises an aqueous lean phosphate solution of mono-ammonium hydrogen phosphate (NH₄H₂PO₄) and di-ammonium hydrogen phosphate ((NH₄)₂HP0₄) having an NH₄ /P0₄ ^" ratio in the range of 1.2 to 1.4 and a pH from 5 to 6.1, e.g., from 5.3 to 6.0. The lean phosphate feed stream is introduced into the ammonia absorber 110 as two different streams, at different locations and at two different NH₄ ⁺/P0₄ ^"3 ratios, as more fully set forth in Carlson et al, U.S. Patent No. 3,718,731, incorporated herein in its entirety. The ammonia absorber 1 10 may utilize packing and/or trays. In one embodiment, the absorption stages in the ammonia absorber 110 are valve trays. Valve trays are well known in the art and tray designs are selected to achieve good circulation, prevent stagnant areas, and prevent polymerization and corrosion. In order to avoid polymerization, equipment is designed to minimize stagnant areas generally wherever HCN is present, such as in the ammonia absorber 110 as well as in further HCN purification areas described herein. The ammonia absorber 110 may also incorporate an entrainment separator above the top tray to minimize carryover. Entrainment separators typically include use of techniques such as reduced velocity, centrifugal separation, demisters, screens, or packing, or combinations thereof.

[0057] In another embodiment, the ammonia absorber 110 is provided with packing in the ammonia absorber upper portion and a plurality of valve trays in the ammonia absorber lower portion. The packing acts to reduce and/or prevent ammonia and phosphate from escaping the ammonia absorber 110 via the overhead HCN stream 111 and thereafter entering further HCN purification areas. The packing provides additional surface area for ammonia absorption while reducing entrainment in the overhead HCN stream 111, resulting in an overall increased ammonia absorption capability. The packing employed in the ammonia absorber upper portion can be any low pressure drop, structured packing capable of performing the above disclosed function, such as 250Y FLEXIPAC^® packing marketed by Koch-Glitsch of Wichita, KS.

[0058] In a further embodiment, the temperature of the ammonia absorber 110 is maintained, at least in part, by withdrawing a portion of liquid from the ammonia absorber lower portion and circulating it through a cooler and back into ammonia absorber 110 at a point above the withdrawal point.

[0059] Overhead HCN stream 11 1 may then be directed to scrubber 120. The scrubber 120 is designed to remove substantially all of the free ammonia present in the overhead HCN stream 111 because free ammonia, (i.e. un-neutralized ammonia) will raise the pH in the remainder of the HCN purification areas, thus increasing the potential for HCN polymerization. Overhead HCN stream 111 is scrubbed with a dilute acid stream comprising sulfuric acid or phosphoric acid in scrubber 120. In some embodiments, phosphoric acid is preferred. The amount of phosphoric acid present in the dilute acid stream may depend on the amount of ammonia present in the overhead HCN stream 111. Scrubber 120 is utilized to separate overhead HCN stream 111 into overhead scrubber stream 121 and scrubber residue stream 122. Overhead scrubber stream 121 may comprise HCN, water, carbon monoxide, nitrogen, hydrogen, carbon dioxide and methane. Scrubber residue stream 122 may be returned to a lower portion of ammonia absorber 110 when phosphoric acid is used as the acid. When sulfuric acid is used as the acid, scrubber residue stream 122 may be purged (not shown).

[0060] Overhead scrubber stream 121 is then fed to HCN absorber 130 to form off-gas 131 and absorber stream 132. HCN absorber 130 is designed to remove essentially all HCN from the overhead scrubber stream 121. Off-gas 131 may be purged from the system to be burned and used as fuel. In some embodiments, when the oxygen-containing gas comprises greater than 21 vol.% oxygen, off-gas 131 may be further treated to recover hydrogen. The hydrogen may be recovered using any suitable equipment, such as a pressure swing adsorber unit. The high purity recovered hydrogen is more valuable as an ingredient than as a fuel and as such may be used as a feed stream to another process such as in the hydrogenation of adiponitrile (ADN) to 6- aminocapronitrile (ACN) and hexamethylenediamine (HMD). It should be noted that the amount of nitrogen in the off-gas will impact the economic feasibility of recovering hydrogen from the off-gases rather than burning the off-gases in a boiler. Other compositions can also impact the desirability of recovering hydrogen. For example, in the event that the HCN concentration in the off-gas 131 exceeds a predetermined maximum value, the off-gas 131 can be redirected to either the steam-generating boilers or to a flare rather than proceeding to hydrogen recovery.

[0061] Absorber stream 132 may next be directed to HCN stripper 140 to form overhead stripper stream 141 and stripper residue stream 142. Prior to entering HCN stripper 140, absorber stream 132 may be heated to a temperature from 80°C to 100°C. Absorber stream 132 includes acidified water and a minor concentration (e.g., from 2 vol.% to 8 vol.%) HCN, although the percentage of HCN can vary due to operational factors. The HCN stripper 140 removes HCN from the absorber stream 132 and feeds the HCN via a partial condenser to the HCN enricher 150, for further purification.

[0062] HCN stripper 140 can contain packing and/or trays. In one embodiment, HCN stripper 140 contains trays, such as bubble-cap trays, valve trays, or sieve trays. Bubble-cap trays, valve trays, and sieve trays are well known in the art. Tray designs are selected to achieve good vapor- liquid mass transfer and minimize stagnant zones to prevent polymerization and corrosion. Acceptable materials of construction in the HCN stripper 140 include, but are not limited to, substantially corrosion resistant metals as previously described. In one embodiment, trays are constructed of 316 stainless steel. In another embodiment, trays are constructed of Alloy 20 and titanium hardware is used.

[0063] Stripper residue stream 142 may be recycled to HCN absorber 130. Stripper residue stream 142 is substantially free of HCN. Prior to entering HCN absorber 130, stripper residue stream 142 may be cooled from a temperature of up to 120°C down to a temperature from 30°C to 65°C. Overhead stripper stream 141 contains a major amount of HCN and minor amounts of water and nitriles.

[0064] Overhead stripper stream 141 may then be introduced into HCN enricher 150 where it is separated to form HCN product 151 and enricher residue stream 152. HCN enricher 150 contains trays, such as fixed-valve trays or sieve trays. Valve trays and sieve trays are well known in the art. Tray designs are selected to achieve good vapor-liquid mass transfer and minimize stagnant zones to reduce the potential for polymerization, pluggage, and corrosion. Suitable materials of construction for the trays in HCN enricher 150 include, but are not limited to, 316 stainless steel. [0065] Enricher residue stream 152 comprises HCN, water, and other organic components including mid-boiling impurities. Enricher residue stream 152 is combined with stripper residue stream 142 and is then recycled to HCN absorber 130 so that mid-boiling impurities such as acetonitrile, propionitrile, and acrylonitrile, which could otherwise build up in the HCN stripper and enricher columns, are removed.

[0066] Nitriles such as acetonitrile, propionitrile, and acrylonitrile, as well as other mid-boiling impurities in the HCN/H₂0 system may concentrate at the lower portion of HCN enricher 150. A nitriles purge may be employed to remove mid-boiling impurities from HCN enricher 150. A buildup of nitriles causes an increase in temperature in the HCN enricher 150, which interferes with utilizing temperature to infer acceptable HCN purity and can eventually lead to fouling as well as unacceptable HCN purity. The nitriles purge can be conducted continuously or intermittently. By recycling the stream comprising the nitriles purge to HCN absorber 130, the nitriles may be removed in off-gas 131.

[0067] As described herein, without being bound by theory, it is believed that by controlling the amount of methane in the crude hydrogen cyanide product to be from 0.05 to 1 vol.%, e.g., from 0.05 to 0.55 vol.%, or 0.2 to 0.3 vol.%, the formation of nitriles is reduced. By reducing the formation of nitriles, the nitriles purge stream may be reduced, allowing for increased HCN recovery.

[0068] HCN product 151 contains substantially pure HCN and traces of water, e.g., less than 100 mpm or less than 10 mpm water. HCN product 151 may be used in further processes such as for hydrocyanation of an olefm-containing group, or such as hydrocyanation of 1,3-butadiene and pentenenitrile, which can be used in the manufacture of ADN.

[0069] Returning to ammonia residue stream 112, the stream may be directed to ammonia recovery zone 101, which may include further processing to purify ammonia, which may then be recycled and combined with ammonia-containing gas 103. Ammonia recovery zone 101 may comprise one or more strippers to remove HCN and acid and to separate ammonia from other impurities. Ammonia recovery zone 101 may also comprise an ammonia enricher, to further purify the ammonia. By controlling the amount of methane in the crude hydrogen cyanide product, ammonia recovery may be enhanced. Without being bound by theory, it is believed that when less than 0.05 vol.% methane is present in the crude hydrogen cyanide product 107, the residual ammonia may crack to nitrogen, thus reducing the ammonia content. It is also believed that if more than 1 vol.% methane is present in the crude hydrogen cyanide product 107, undesirable acetonitrile formation occurs downstream in the process.

[0070] Various control systems may be used to regulate the reactant gas flow. For example, flow meters that measure the flow rate, temperature, and pressure of the reactant gas feed streams and allow a control system to provide "real time" feedback of pressure- and temperature- compensated flow rates to operators and/or control devices may be used.

[0071] As will be appreciated by one skilled in the art, the foregoing functions and/or process may be embodied as a system, method or computer program product. For example, the functions and/or process may be implemented as computer-executable program instructions recorded in a computer-readable storage device that, when retrieved and executed by a computer processor, controls the computing system to perform the functions and/or process of embodiments described herein. In one embodiment, the computer system can include one or more central processing units, computer memories (e.g., read-only memory, random access memory), and data storage devices (e.g., a hard disk drive). The computer-executable instructions can be encoded using any suitable computer programming language (e.g., C++, JAVA, etc.). Accordingly, aspects of the present invention may take the form of an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects.

[0072] From the above description, it is clear that the present invention is well adapted to carry out the objects and to attain the advantages mentioned herein as well as those inherent in the presently provided disclosure. While preferred embodiments of the present invention have been described for purposes of this disclosure, it will be understood that changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the present invention.

[0073] In order that the invention disclosed herein may be more efficiently understood, the following examples are provided below. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting the invention in any manner. Example 1

[0074] A crude hydrogen cyanide product is produced according to the Andrussow process using air as the oxygen-containing gas to form the ternary gas mixture. The ternary gas mixture is passed over a catalyst bed to form the crude hydrogen cyanide product. The methane content in the crude hydrogen cyanide product is measured as the product exits the reactor assembly. As is shown in FIG. 3, as the methane concentration in the crude hydrogen cyanide product increases, the acetonitrile concentration increases. This trend of increased nitrile formation is also expected when pure oxygen is used as the feed gas instead of air.

Example 2

[0075] A crude hydrogen cyanide product is produced according to the Andrussow process using pure oxygen as the oxygen-containing gas to form a ternary gas mixture. The ternary gas mixture is formed using an ammonia-to-oxygen molar ratio of 1.3:1 and a methane-to-oxygen molar ratio of 1.2:1. The ternary gas mixture comprises 28.5 vol.% oxygen. The reactor has an internal diameter of 142.2 cm and a platinum/rhodium catalyst bed rests on a castable annular shelf that extends 2.86 cm into the reactor, allowing for 90% pass-through area of the crude hydrogen cyanide product formed by the catalyst bed. Over a continuous operating period of 150 days, the catalyst bed diameter shrinks by 0.64 to 1.26 cm and no methane bypasses the catalyst bed because the annular shelf supports the shrunken catalyst bed. The crude hydrogen cyanide product comprises from 0.2 vol.% to 0.3 vol.% methane.

Comparative Example A

[0076] The process and reactor are the same as in Example 2, except that the annular shelf extends further into the reactor, reducing the pass-through area to 85%. The pressure drop through the reactor increases by 20% as compared to Example 2, resulting in a decrease in HCN yield.

Claims

We claim:

1. A process for producing hydrogen cyanide, comprising:

forming a ternary gas mixture comprising a methane-containing gas, an ammonia- containing gas, and an oxygen-containing gas; and

contacting the ternary gas mixture with a catalyst bed in a reactor to form a crude hydrogen cyanide product, wherein the catalyst bed is supported by an annular shelf that provides a pass-through area that is at least 90% of the area of the cross-sectional area of the reactor and the annular shelf substantially prevents catalyst bed bypass of the ternary gas mixture or a component thereof into the crude hydrogen cyanide product; and

controlling a flow rate of at least one of the methane-containing gas, the ammonia- containing gas, or the oxygen-containing gas to maintain a methane concentration in the crude hydrogen cyanide product from 0.05 to 1 vol.%.

2. The process of claim 1, wherein the process comprises controlling the flow rate of the methane-containing gas.

3. The process of any of the preceding claims, wherein the annular shelf is impermeable to the ternary gas mixture.

4. The process of any of the preceding claims, wherein the crude hydrogen cyanide product comprises from 0.05 to 0.55 vol.% of methane.

5. The process of any of the preceding claims, wherein the crude hydrogen cyanide product comprises from 0.2 to 0.3 vol.% of methane.

6. The process of any of the preceding claims, wherein the methane-containing gas, the ammonia-containing gas, and the oxygen-containing gas are combined in a mixing vessel upstream of the reactor to form the ternary gas mixture.

7. The process of any of the preceding claims, wherein the oxygen-containing gas comprises greater than 21 vol.% oxygen, preferably at least 80 vol.% oxygen.

8. The process of any of the preceding claims, wherein the oxygen-containing gas comprises pure oxygen.

9. The process of any of the preceding claims, wherein the ternary gas mixture comprises at least 25 vol.% oxygen.

10. The process of any of the preceding claims, wherein the ternary gas mixture comprises from 25 vol.% to 32 vol.% oxygen.

11. The process of any of the preceding claims, wherein the molar ratio of ammonia-to- oxygen in the ternary gas mixture is between 1.2 and 1.6.

12. The process of any of the preceding claims, wherein the molar ratio of methane-to- oxygen in the ternary gas mixture is between 1 and 1.25.

13. The process of any of the preceding claims, wherein the crude hydrogen cyanide product is separated, wherein the separation comprises:

removing residual ammonia from the crude hydrogen cyanide product to provide a hydrogen cyanide product;

separating the hydrogen cyanide product to form an off-gas stream and a hydrogen cyanide stream; and

purifying the hydrogen cyanide stream to form a finished hydrogen cyanide product.

14. The process of claim 13, wherein the hydrogen cyanide stream comprises less than 0.25 vol.% acetonitrile.

15. The process of claim 13, wherein the hydrogen cyanide stream comprises less than 0.15 vol.%) acetonitrile.