HK1199001A1 - Enhanced methane control for andrussow process - Google Patents

Description

Enhanced methane control for the Andrussow process

Cross Reference to Related Applications

This application claims priority to U.S. application 61/738,623 filed on 12/18/2012, the entire contents and disclosure of which are incorporated herein.

Technical Field

The present invention relates to a process for the production of hydrogen cyanide. More particularly, the present invention relates to a process for producing hydrogen cyanide in enhanced levels of yield and production by controlling the amount of methane in the crude hydrogen cyanide product through the use of a controlled feed composition.

Background

Traditionally, Hydrogen Cyanide (HCN) is produced on an industrial scale by the Andrussow process or the BMA process (see, for example, Ullman's Encyclopedia of Industrial Chemistry, Volume A8, Weinheim1987, P.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. Pat. nos. 1,934,838 and 6,596,251). Sulfur compounds and higher homologues of methane may affect the parameters of oxidative ammonolysis of methane. See, for example, Trosov, Effect of sulfurr Compounds and Higher homologues of Methane on hybridoma 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 stream with an aqueous ammonium phosphate solution in an ammonia absorber. The separated ammonia is purified and concentrated for recycle to the conversion of HCN. HCN is typically recovered from the treated reactor effluent stream by absorption into water. The recovered HCN can be treated by a further refining step to produce purified HCN. The document Clean Development process design document Form (CDM PDD, Version3),2006 graphically explains the Andrussow HCN manufacturing process. The purified HCN can be used in hydrocyanation reactions, such as hydrocyanation of alkene-containing groups or hydrocyanation of 1, 3-butadiene and pentenenitriles, which can be used to produce 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, with the result that HCN, hydrogen, nitrogen, residual ammonia, and residual methane are produced (see, e.g., Ullman's encyclopedia of Industrial Chemistry, Volume A8, Weinheim1987, P161-163). Commercial operators require process safety management to control the hazardous nature of hydrogen cyanide (see Maxwell et al, assay process in the transfer of hydrogen cyanide manufacturing technology, JHazMat142 (2007), 677-. In addition, emissions from production facilities in HCN manufacturing processes may comply with regulations, which may affect the economics of HCN production. (see Crump, eco practical impact analysis For The deployed Cyanide Manufacturing neshapap, EPA, 5 months 2000).

Existing HCN production processes suffer from various problems including lost production in the production of HCN and inefficient recovery and recycle of residual ammonia.

Disclosure of Invention

In one embodiment, the invention relates 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 three-way 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 support that provides a pass-through zone having an area of at least 90% of the cross-sectional area of the reactor and the annular support substantially prevents catalyst bed bypass of the three-way gas mixture or components thereof; and controlling the flow rate of at least one of the methane-containing gas, ammonia-containing gas, and oxygen-containing gas to maintain the methane concentration in the crude hydrogen cyanide product at 0.05 to 1 vol%. The methane-containing gas, ammonia-containing gas, and oxygen-containing gas may be combined in a mixing vessel upstream of the reactor to form a ternary gas mixture. The oxygen-containing gas may comprise more than 21 vol% oxygen, such as at least 80 vol% oxygen. The ternary gas mixture contains at least 25% by volume of oxygen. The molar ratio of ammonia to oxygen in the ternary gas mixture may be in the range of 1.2 to 1.6. The molar ratio of methane to oxygen in the ternary gas mixture may be in the range of 1 to 1.25. The process can further comprise separating the crude hydrogen cyanide product, wherein the separating 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 final hydrogen cyanide product. The hydrogen cyanide stream may comprise less than 0.25 vol% acetonitrile or less than 0.15 vol% acetonitrile.

In a second embodiment, the invention relates to a crude hydrogen cyanide product produced in a process for the preparation of hydrogen cyanide, wherein the crude hydrogen cyanide product comprises hydrogen cyanide and 0.05 to 1 vol% methane, such as 0.05 to 0.55 vol% or 0.2 to 0.3 vol% methane.

In a third embodiment, the present invention relates to a reaction apparatus for producing hydrogen cyanide in a reaction apparatus comprising: at least one inlet for a ternary gas mixture; a catalyst support assembly comprising an annular support providing a pass-through zone having an area of at least 90% of the cross-sectional area of the reactor; a catalyst bed supported by the catalyst support assembly, wherein the annular support substantially prevents catalyst bed bypass flow of the three-way gas mixture or component thereof; and at least one outlet 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 passed into the at least one inlet and through the catalyst bed; and wherein the flow rate of at least one of the methane-containing gas, ammonia-containing gas, and oxygen-containing gas is controlled to maintain the methane concentration in the crude hydrogen cyanide product at from 0.05 to 1 volume percent, such as from 0.05 to 0.55 volume percent, or from 0.2 to 0.3 volume percent methane. The catalyst support assembly may include a perforated plate to allow passage of gas. The catalyst support assembly may be disposed substantially adjacent to the lower surface of the catalyst bed. The catalyst support assembly may further comprise a support substantially parallel to the catalyst bed and extending beyond the dimensions of the catalyst bed. The stent may comprise a ceramic material.

In a fourth embodiment, the present invention is directed to a process for controlling the methane content of crude hydrogen cyanide 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 of a reactor; contacting the three-way gas mixture with a catalyst in a reactor to form a crude hydrogen cyanide product; wherein the catalyst is supported by an annular support which provides a pass-through zone having an area of at least 90% of the cross-sectional area of the reactor and which substantially prevents catalyst bed by-pass flow of the three-way gas mixture or component thereof; measuring the methane content in the crude hydrogen cyanide product; and adjusting at least one of the molar ratio of ammonia to oxygen, the molar ratio of ammonia to methane, or the molar ratio of methane to oxygen to provide a crude hydrogen cyanide product comprising 0.05 to 0.1 vol%, or 0.05 to 0.55 vol%, or 0.2 to 0.3 vol% methane.

In a fifth embodiment, the present invention relates to at least one inlet for a three-way gas mixture, a catalyst bed, a catalyst support assembly for supporting the catalyst bed, and at least one outlet for a crude hydrogen cyanide product, wherein the catalyst support assembly comprises an apertured plate and a shelf substantially parallel to the catalyst bed and extending beyond the dimensions of the catalyst bed, wherein the shelf comprises a ceramic material; wherein the reactor unit is operated under conditions conducive to the production of a crude hydrogen cyanide product containing from 0.05 to 1 volume% methane or from 0.05 to 0.55 volume% methane. The ternary gas mixture may comprise a methane-containing gas, an ammonia-containing gas and an oxygen-containing gas. The holder may be in contact with a reactor wall of the reactor apparatus. The catalyst bed may be a porous structure, a wire mesh, a sphere, a sheet, a block, a foam, a dip coating, or a wash coating. The catalyst bed may be a wire mesh platinum/rhodium alloy or a platinum/iridium alloy. The support may be impermeable to air. The holder and the apertured plate may be parallel. The reactor apparatus may further comprise a flame arrestor upstream of the catalyst bed, wherein the flame arrestor is a refractory ceramic material.

In a sixth embodiment, the present invention relates to a reaction apparatus for the production of hydrogen cyanide, comprising: at least one inlet for a ternary gas mixture, a catalyst support assembly, a catalyst bed supported by the catalyst support assembly, and at least one outlet 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 introduced into the at least one inlet and passed through the catalyst bed, and wherein the reactor is operated under conditions conducive to producing a crude hydrogen cyanide product containing 0.05 to 1% by volume methane or 0.05 to 0.55% by volume methane.

The catalyst support assembly may contain an apertured plate. The catalyst support assembly may be disposed substantially adjacent to the lower surface of the catalyst bed. The catalyst support assembly may further comprise a support substantially parallel to the catalyst bed and extending beyond the dimensions of the catalyst bed. The scaffold may comprise a ceramic material. The catalyst bed may be a porous structure, a wire mesh, a sheet, a sphere, a block, a foam, a dip coating, or a wash coating. The catalyst bed may be a wire mesh platinum/rhodium alloy or a platinum/iridium alloy. The support may be impermeable to air. The holder and the apertured plate may be in the same plane. The reactor apparatus may further comprise a flame arrestor upstream of the catalyst bed, wherein the flame arrestor is a refractory ceramic material.

Drawings

Fig. 1 is a schematic flow diagram of an HCN synthesis system according to an embodiment of the present invention.

Fig. 2A and 2B are cross-sectional views of a catalyst bed on a catalyst support assembly including a support according to one embodiment of the present invention.

FIG. 3 is a graph showing nitrile formation as a function of methane content in the crude hydrogen cyanide product.

Detailed Description

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" 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, elements, components, and/or groups thereof.

Words such as "comprising," "including," "having," "containing," or "involving," and variations thereof, are to be understood broadly and encompass the listed subject matter as well as equivalents, as well as additional subject matter not listed. Additionally, when a component, a group of components, a process or method step, or any other expression is introduced by the transitional phrase "comprising," "including," or "containing," it is understood that the same component, group of components, process or method step, or any other expression having the transitional phrase "consisting essentially of …," "consisting of …," or "selected from the group consisting of …" prior to the recitation of that component, group of components, process or method step, or any other expression is also contemplated herein.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if applicable, 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 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 skilled in the art will recognize that the invention can be practiced with modification and within the spirit and scope of the appended claims.

Reference will now be made in detail to the specific disclosed subject matter. Although the disclosed subject matter will be described in conjunction with the recited 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 covers all alternatives, modifications, and equivalents as may be included within the scope of the disclosed subject matter as defined by the appended claims.

In the Andrussow process for forming HCN, methane, ammonia, and oxygen feedstocks are reacted at temperatures above about 1000 ℃ in the presence of a catalyst to produce a crude hydrogen cyanide product containing HCN, hydrogen, carbon monoxide, carbon dioxide, nitrogen, residual ammonia, residual methane, and water. These components, such as the feedstock, 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 platinum/rhodium or platinum/iridium gauze alloy. The catalyst bed may be made by weaving or braiding. Other catalyst components may be used including, but not limited to, platinum group metals, platinum group metal alloys, supported platinum group metals, or supported platinum group metal alloys. Other catalyst configurations may also be used, including but not limited to porous structures, screens, tablets, spheres, blocks, foams, dip coatings, and wash coatings. Natural gas is typically used as the feed for methane, and air, oxygen-enriched air or pure oxygen is used as the oxygen source. The three-way 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.

As described herein, the crude hydrogen cyanide product from either the Andrussow process or the BMA process comprises HCN, residual ammonia, and residual oxygen. In the Andrussow process, the residual methane content is controlled by several variables, including the mole ratio of the reactants methane, ammonia and oxygen, the conversion of the reactants, and the efficiency of the reaction. Advantageously, the process can 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, the residual ammonia may crack to form nitrogen and hydrogen. If too much methane is present in the crude hydrogen cyanide product, undesirable impurities, including nitriles such as acetonitrile, may be formed in the crude hydrogen cyanide product when purifying the crude hydrogen cyanide product to recover HCN. The nitrile may be further polymerized and interfere with the separation process, thereby causing insufficient production efficiency. The nitrile will have to be discharged from the separation process to avoid clogging. For the purposes of the present invention, the controlled methane content of the crude hydrogen cyanide product is between 0.05 and 1% by volume, such as 0.05 to 0.55% by volume or 0.2 to 0.3% by volume. When the methane content in the crude hydrogen cyanide product is between 0.6 and 1% by volume, the amount of nitriles formed is not sufficient to require its removal in the separation process, and therefore is acceptable in the crude hydrogen cyanide product. However, over time, these nitriles can polymerize and clog the separation equipment. Thus, when the separation apparatus is operated continuously or semi-continuously for at least 6 months, it is preferred that the methane content is in the range of from 0.05 to 0.55 volume% or from 0.2 to 0.3 volume%.

Accordingly, in one embodiment, the invention relates to a crude hydrogen cyanide product produced in a process for the preparation of hydrogen cyanide, wherein the crude hydrogen cyanide product comprises hydrogen cyanide and 0.05 to 1 vol% methane, such as 0.05 to 0.55 vol% or 0.2 to 0.3 vol% methane. The crude hydrogen cyanide product composition may be independent of its method of preparation, so long as the reactants contain methane.

As described herein, there are several variables that control the amount of methane. According to the Andrussow process, the reactants used for the formation of HCN include ammonia, methane and oxygen, each of which is provided in gaseous form. The ammonia-containing gas, the methane-containing gas and the oxygen-containing gas are combined and mixed in a mixing vessel before entering the reactor through the inlet, e.g. upstream of the reactor. One variable that controls the amount of methane in the crude hydrogen cyanide product is the molar ratio of ammonia to oxygen in the tertiary 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 1-1.25. If it is desired to adjust the molar ratio of methane to oxygen, it is preferred to adjust the flow rate of methane and maintain the flow rate of oxygen.

Thus, the present invention also relates to a method of controlling the molar ratio of ammonia to oxygen and methane to oxygen. There are several considerations when adjusting the molar ratio including oxygen. This is due to the flammability and explosion limits of the ternary gas mixture, especially if oxygen-enriched air is used as the oxygen-containing gas, e.g. air containing more than 21% by volume of oxygen, e.g. air containing at least 80% by volume of oxygen is used as the oxygen-containing gas.

In order to accurately adjust the molar ratio of ammonia to oxygen and methane to oxygen, it is desirable to reduce or eliminate leakage of the three-way gas mixture and its components, for example, leakage of methane-containing gas around the catalyst bed. Such leakage, also referred to as by-pass flow, may be reduced by including an annular catalyst support as described herein. By reducing, e.g., substantially reducing or eliminating, the by-pass flow of methane-containing gas around the catalyst bed, it is possible to more predictably control the flow rate of methane in the crude hydrogen cyanide product than if the methane-containing gas by-passes the catalyst bed. In other words, when methane can bypass the catalyst bed, control of methane slip is not possible. The advantage of the present invention is that by using an annular support that is impermeable to gas, a by-pass flow of methane around the catalyst bed can be eliminated, thus allowing methane to be controlled by adjusting the flow rate of methane.

Enhancing oxygen content

The molar ratio of ammonia to oxygen and the molar ratio of methane to oxygen can be used to control the amount of methane in the crude hydrogen cyanide product, as described herein. The method of adjusting these ratios is based at least in part on the oxygen content of the oxygen-containing gas, and thus also the ternary gas mixture.

The term "air" as used herein refers to a gas mixture having a composition that is approximately the same as the original composition of gas taken from the atmosphere (typically at the surface). In some examples, the air is taken from the ambient environment. Air has a composition comprising about 78% by volume of nitrogen, about 21% by volume of oxygen, about 1% by volume of argon and about 0.04% by volume of carbon dioxide, as well as small amounts of other gases.

The term "oxygen-enriched air" as used herein refers to a gas mixture whose composition contains more oxygen than is present in air. The oxygen-enriched air has a composition comprising greater than 21% by volume oxygen, less than 78% by volume nitrogen, less than 1% by volume argon and less than 0.04% by volume carbon dioxide. In some embodiments, the oxygen-enriched air comprises at least 28% oxygen by volume, such as at least 80% oxygen by volume, such as at least 95% oxygen by volume, or at least 99% oxygen by volume.

The formation of HCN in the Andrussow process is generally expressed as the following general reaction:

2CH₄+2NH₃+3O₂→2HCN+6H₂O

it will be appreciated, however, that the above reaction represents a simplification of a more complex kinetic process in which a portion of the hydrocarbon is first oxidized to produce the necessary thermal energy to support the endothermic synthesis of HCN from the remaining hydrocarbon and ammonia.

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

CH₄+H₂O→CO+3H₂

2CH₄+3O₂→2CO+4H₂O

4NH₃+3O₂→2N₂+6H₂O

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 it is suggested in the prior art that oxygen-enriched air or pure oxygen can be used as the oxygen source, the advantages of using oxygen-enriched air or pure oxygen are not fully exploited. When air is used as the source of oxygen, the crude hydrogen cyanide product contains components of air, such as about 78% by volume nitrogen, and nitrogen gas is produced in the side reaction of ammonia and oxygen.

The use of oxygen-enriched air, which is less than air containing nitrogen, in the synthesis of HCN is advantageous due to the large amount of nitrogen in air, because the use of air as an oxygen source in the production of HCN results in the synthesis being carried out in large amounts of inert gas (nitrogen), which requires the use of large equipment in the synthesis step, and results in low concentrations of HCN in the product gas. In addition, due to the presence of inert nitrogen, more methane (when air is used, as compared to oxygen-enriched air) needs to be combusted in order to raise the temperature of the ternary gas mixture components to a temperature that can sustain HCN synthesis. The crude hydrogen cyanide product comprises HCN and also comprises by-product hydrogen, methane combustion by-products (carbon monoxide, carbon dioxide, water), residual methane, and residual ammonia. However, when air (e.g., about 21% by volume oxygen) is used, the presence of inert nitrogen gas after separation of HCN and recoverable ammonia from other gaseous components may result in a residual gas stream with combustion values that are lower than desirable for energy recovery.

Thus, the use of oxygen-enriched air or pure oxygen instead of air in the production of HCN can provide several benefits, including an increase in the conversion of natural gas to HCN with a concomitant reduction in the size of the process equipment. Thus, the use of oxygen-enriched air or pure oxygen can reduce the size of the reactor by reducing the inert compounds entering the synthesis process and reduce at least one component of the downstream gas treatment equipment. 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.

It has been found that both HCN production capacity and production efficiency can be significantly increased while maintaining stable operation, in part by providing a sufficiently oxygen-rich oxygen-containing gas 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% oxygen by volume, such as at least 80% oxygen, at least 95% oxygen, or at least 99% oxygen by volume, the molar ratio of ammonia to oxygen in the ternary gas mixture is in the range of 1.3 to 1.5, such as in the range of 1.3 to 1.4, and the molar ratio of ammonia to methane in the ternary gas mixture is in the range of 1.1 to 1.45. In another embodiment, the ternary gas mixture contains at least 25% by volume oxygen, the molar ratio of ammonia to oxygen is from 1.2 to 1.6, the molar ratio of ammonia to methane is from 1 to 1.5, such as from 1.1 to 1.45, and the molar ratio of methane to oxygen is from 1 to 1.25, such as from 1.05 to 1.15. For example, the ternary gas mixture may have a molar ratio of ammonia to oxygen of 1.3 and a molar ratio of methane to oxygen of 1.2. In another exemplary embodiment, the ternary gas mixture may have a molar ratio of ammonia to oxygen of 1.5 and a molar ratio of methane to oxygen of 1.15. Wherein the oxygen concentration may vary depending on the molar ratio.

The flammability limit is used to control the amount of oxygen present in the ternary gas mixture. Some combinations of air, methane and ammonia are flammable and will therefore propagate a flame upon ignition. If the gas composition of a mixture of air, methane and ammonia is between the upper and lower flammability limits, the mixture will combust. Mixtures of air, methane and ammonia outside this range are generally non-flammable. The use of oxygen-enriched gas can change the concentration of combustibles in the ternary gas mixture. Increasing the oxygen content of the oxygen-containing gas feed stream significantly expands the flammability range. For example, a mixture containing 45% by volume air and 55% by volume methane is considered fuel rich and non-flammable, while a mixture containing 45% by volume oxygen and 55% by volume methane is flammable.

Another problem is the explosive limit. For example, a gas mixture containing 60% by volume oxygen, 20% by volume methane, and 20% by volume ammonia can explode at atmospheric pressure and room temperature.

Thus, although the use of oxygen-enriched air was found to be advantageous in the production of HCN, oxygen-enriched air necessarily results in a change in the concentration of combustibles in the ternary gas mixture, and this change in the concentration of combustibles increases the upper flammability limit of the ternary gas mixture entering the reactor. Thus, deflagrations and explosions of the ternary gas mixture are sensitive to oxygen concentrations. As used herein, the term "deflagration" refers to a combustion wave that propagates at a subsonic velocity relative to unburned gases immediately before the flame. "explosion" refers to a combustion wave that propagates at supersonic velocity immediately before the flame relative to unburned gas. Deflagration generally results in a modest pressure increase, while explosions may result in an excessive pressure increase.

Other proposals use oxygen-rich gas for increasing HCN production, which generally avoid operating in the flammable regime. See U.S. patent nos. 5,882,618, 6,491,876, and 6,656,442, the entire contents of which are incorporated herein by reference. In the present invention, the feeding of oxygen-enriched air or pure oxygen is controlled to form a ternary gas mixture in the flammable region but not in the explosive region. Thus, in some embodiments, the ternary gas mixture contains at least 25% oxygen by volume, such as at least 28% oxygen by volume. In some embodiments, the ternary gas mixture contains 25-32 vol% oxygen, such as 26-30 vol% oxygen.

Production of methane-containing gas

As will be appreciated by those of ordinary skill in the art, the Source of methane may vary and may be derived from renewable feedstocks such as landfills, farms, biogas from fermentation, or fossil fuels such as Natural Gas, petroleum associated Gas, Gas and Gas hydrates, such as VN Parmon, "Source of methane for Sustainable Development", P.273-284 and the Sustainable strategees by Derouane Master for the upgrading of Natural Gas: Fundamentals, Challeges, and Opportunits (2003) are further described. For the purposes of the present invention, it is important that the purity of the methane and the consistent composition of the source containing the methane are consistent.

As a source of methane for methane-containing gases, natural gas is an impure state of methane. That is, natural gas is a methane-containing gas that can be substantially used to supply carbon atoms to the HCN produced in the process of the present invention. However, in addition to methane, natural gas may contain impurities such as hydrogen sulfide, carbon dioxide, nitrogen, water, and high molecular weight hydrocarbons such as ethane, propane, butanes, pentanes, and higher hydrocarbons. These high component hydrocarbons are referred to herein as "C2 + hydrocarbons. Various methods can be used to remove C2+ hydrocarbons from natural gas, including hydrocarbon separation processes. The hydrocarbon separation process may be carried out using an adsorption process or a cryogenic expansion process. The absorption process may be used primarily for the removal of C3+ hydrocarbons, while the low temperature expansion process may be used primarily for the removal of ethane, while also removing C3+ hydrocarbons.

The composition of natural gas from different sources varies significantly. The composition of the natural gas provided through the pipeline can also vary greatly over time or even over a short time span as the source is opened and closed by the pipeline. This difference in composition, particularly the presence of C2+ hydrocarbons and the amount of C2+ hydrocarbons, makes it difficult to maintain optimum and stable process performance. The presence of C2+ hydrocarbons in natural gas compositions is particularly troublesome for the following reasons: 1) its higher calorific value than methane; 2) its deactivation effect on the catalyst in the HCN reactor, especially C3+ hydrocarbons; 3) side reactions that may form higher nitriles such as acetonitrile, acrylonitrile and propionitrile. Sensitivity of the HCN synthesis process to changes in the large number of C2+ hydrocarbons is increased by the reduction in inerting load through oxygen enrichment of the oxygen-containing gas.

Thus, the methane-containing gas may be treated to contain less than 1% by volume of C2+ hydrocarbons, such as less than 5000mpm, less than 1000mpm, less than 150mpm, or substantially no C2+ hydrocarbons. "substantially free of C2+ hydrocarbons" includes C2+ hydrocarbons ranging from 0 to 100 mpm. This methane-containing stream may also be referred to as "purified natural gas". In some embodiments, the methane-containing stream is substantially free of impurities. Additionally, the methane-containing stream may be substantially anhydrous.

The use of purified natural gas to produce HCN to produce methane-containing gas increases catalyst life and HCN production. In particular, the use of purified natural gas streams stabilizes the remaining composition at the same level in order to optimize the synthesis of downstream HCN and to enable the use of highly enriched oxygen or pure oxygen feeds by reducing large temperature excursions in the HCN synthesis step, which are typically associated with changes in the content of higher hydrocarbons and which are detrimental to optimal production and operability (e.g., catalyst damage, interlock and loss of operating time). The use of purified natural gas also minimizes the formation of higher nitriles and the associated yield loss of HCN in the removal of nitriles. In addition, using purified natural gas as the feed for the methane-containing gas minimizes feed variability by stabilizing the carbon and hydrogen content and heating value, and thereby stabilizes the overall HCN synthesis system, allowing the determination and control of optimal methane to oxygen and ammonia to oxygen molar ratios for stable operation and more efficient HCN production. Furthermore, the use of purified natural gas can minimize associated temperature spikes and resulting catalyst damage.

Preparation of ammonia-containing gas

The ammonia-containing gas source may be treated prior to mixing with the oxygen-containing gas and the methane-containing gas. The process may include removing impurities, such as water, oil, and iron (Fe), from the ammonia-containing gas source. Impurities in the ammonia-containing gas can reduce catalyst life, resulting in low reaction yields and earlier replacement. The process may include the use of treatment equipment, such as evaporators and filters, to provide a treated ammonia-containing gas.

For example, commercially available liquid ammonia can be treated in a vaporizer to provide a partially purified ammonia vapor stream and a first liquid stream containing water, iron particles, and other non-volatile impurities. An ammonia separator, such as an ammonia demister, can be used to separate impurities and all liquids present in the partially purified ammonia vapor stream to produce a treated ammonia-containing gas (a substantially pure ammonia vapor stream) and a second liquid stream containing entrained impurities and all liquids present in the partially purified ammonia vapor stream.

In one embodiment, a first liquid stream containing water, iron particles, and other non-volatile impurities is passed to a second still where a portion of the liquid stream is evaporated to produce a second partially purified ammonia vapor stream and a more concentrated second liquid stream containing water, iron particles, and other non-volatile impurities, which may be further processed as a blowdown or waste stream. The second partially purified ammonia vapor stream may be passed to an ammonia separator. In another embodiment, a more concentrated second liquid stream containing water, iron particulates, and other non-volatile impurities is passed to a third still to further reduce its ammonia content prior to treating the stream as a blowdown or waste stream.

Foaming in the still limits the distillation rate of the ammonia and reduces the purity of the ammonia vapor produced. Typically, foaming is prevented by introducing a defoamer either directly in the still or in the still feed stream. Defoamers belong to a broad class of polymeric materials and solutions that eliminate or significantly reduce the ability of liquids and/or liquid and gas mixtures to foam. By reducing the surface tension of the solution, the anti-foaming agent inhibits the formation of foam in the agitated liquid. Examples of defoaming agents include silicones, organophosphates and alcohols. In one embodiment, a sufficient amount of defoamer is added to the ammonia-containing gas 132 to maintain the concentration of defoamer in the ammonia-containing gas 132 at about 2-20 mpm. One non-limiting example of an antifoaming agent is Unichem7923, manufactured by Unichem of Hobbs, NM (new mexico). The treatment of the ammonia-containing gas source 130 may also include a filter system for removing particulates to prevent poisoning of the catalyst in the reactor 152. The filter system may be a single filter or a plurality of filters.

HCN reactor

The invention also relates to a reactor unit 106, the reactor unit 106 being adapted to produce a crude hydrogen cyanide product 107, the crude hydrogen cyanide product 107 comprising 0.05-1 vol% methane, such as comprising 0.05-0.55 or 0.2-0.3 vol% methane. Reactor assembly 106 contains a mixing element 155 for introducing and mixing the reactant gases to form a fully mixed ternary gas mixture 105 which is introduced into reaction element 157. The reaction section 157 comprises at least one inlet 160 for the three-way gas mixture 105, a catalyst support assembly 161, a catalyst bed 162 supported by the catalyst support assembly, and at least one outlet 163 for the crude hydrogen cyanide product 107. As described herein, controlling reactor efficiency is one variable in controlling the methane content of the crude hydrogen cyanide product.

One way to control the efficiency of the reactor, as described herein, 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 disposed such that the catalyst bed 162 rests on and is supported by the catalyst support assembly. The catalyst support assembly includes a foraminous plate (e.g., block or ceramic foam) 170 and a support 171, such as an annular support. The annular support 171 may extend outwardly from the inner wall 165 of the reaction member 157 at a uniform distance. The annular support 171 follows the circumference of the reaction member 157. Apertured plate 170 may be coplanar with annular support 171. The perforated plate 170 allows gas to pass through. The annular support 171 is solid and gas impermeable. The annular support 171 is substantially parallel to the catalyst bed 162 and is in contact with the reactor wall 165. In some embodiments, the toroidal support 171 is composed of ceramic and is an integral part of the reactor. In some embodiments, the toroidal support 171 is composed of the same material as the reactor. The annular support 171 can be configured to allow for a pass-through zone to allow the crude hydrogen cyanide product formed from the three-way gas mixture to contact the catalyst bed to form the crude hydrogen cyanide product. The crude hydrogen cyanide product may contain components of a ternary gas mixture, such as methane, oxygen, and/or ammonia. The gas permeable pass-through zone may comprise at least 85%, such as at least 90%, of the cross-sectional area of the reactor, depending on the expected catalyst shrinkage and the desired HCN production. The pass zone may range from 85-95%, such as from 90% to 95%. For example, if the reactor has an internal diameter of 137.16cm, and the catalyst diameter is assumed to shrink over time between 0.64cm and 1.26cm, the annular support 171 may extend from 2.54cm to 3.18cm from the reactor wall. Greater extension into the reactor reduces the pass zone to less than 85% and reduces the yield. Small annular walls with larger pass zones of greater than 95% also face problems if the catalyst shrinks more than expected or moves in the reactor. Typically, catalyst shrinkage occurs at least in part at start-up and then remains as it shrinks throughout reactor operation. In addition, extending the legs further from the reactor wall reduces the frequency of reactor shutdowns to replace the catalyst bed, but also increases the reactor pressure drop, resulting in reduced HCN production.

In a simplified form, as shown in fig. 2B, the toroidal support 171 may extend beyond the catalyst bed 162 as the catalyst undergoes shrinkage. As the catalyst life increases, the catalyst may shrink as shown in fig. 2B, causing the catalyst bed 162 to no longer contact the reactor walls 165. The shrinkage of the catalyst may allow components of the three-way gas mixture, including methane, to bypass the catalyst, resulting in an increase in the methane content of the crude hydrogen cyanide product. By including the annular support 171, by-pass flow of the ternary gas mixture may be reduced, substantially reduced, and/or eliminated.

The reactor apparatus 105 may also include a flame arrestor 180 downstream of the distribution plate 181, a radiation shield 182 adjacent the catalyst bed 162. The reaction vessel 106 may also include a heat exchanger 183, such as a waste heat boiler, for cooling the crude hydrogen cyanide product. Ignition holes (not shown) may extend through the radiation shield 182 to bring the igniter into contact with the upper surface of the catalyst bed 162. In some embodiments of the present invention, other ignition techniques may be used that do not require holes in the radiation shield 182. The catalyst bed may be ignited by any known method by those skilled in the art.

A flame arrestor is spatially disposed above the catalyst bed to provide a space therein. The flame arrestor may extinguish any upstream combustion within the internal reaction chamber due to back flow. The ceramic foam is disposed along at least a portion of an inner wall of the housing defining the internal reaction chamber and the catalyst. When the reactor is shut down, the ceramic foam minimizes the by-pass flow of the feed gas due to catalyst shrinkage. Ceramic foam disposed over the catalyst bed serves to minimize the volume of the three-way gas, reduce pressure drop, and inhibit the formation of free radicals during operation of the reactor. In each outlet of the housing a collar is arranged, which provides fluid communication between the catalyst bed and the upper part of the waste heat boiler.

The reaction to make HCN is carried out in a catalyst bed. Suitable catalysts for use in the catalyst bed of the Andrussow process contain a group viii metal. The group VIII metal includes platinum, rhodium, iridium, palladium, osmium or ruthenium, and the catalyst may be these metals, a mixture of these metals or an alloy of two or more of these metals. In many cases for the production of HCN, a catalyst containing 50 to 100 mass% of platinum based on the total mass of the catalyst is used. The catalyst must be strong enough to withstand the rate that may increase when oxygen-enriched air or pure oxygen is used to produce a three-way mixture containing greater than 25% oxygen by volume. Thus, 85/15 platinum/rhodium alloy may be used on a planar catalyst support. 90/10 platinum/rhodium alloy may also be used on a corrugated load having a larger surface area than a planar catalyst support.

Production of crude hydrogen cyanide product

As shown in fig. 1, in the hydrogen cyanide production system 100, the ternary gas mixture 105 comprises a methane-containing gas 102, an ammonia-containing gas 103, and an oxygen-containing gas 104. The ternary gas mixture 105 is passed to a reactor unit 106 to produce a crude hydrogen cyanide product 107, the crude hydrogen cyanide product 107 comprising from 0.05 to 1 volume% methane, such as from 0.05 to 0.55 volume% or from 0.2 to 0.3 volume% methane. The crude hydrogen cyanide product 107 is passed to an ammonia absorber 110 to form an overhead HCN stream and a residual ammonia stream 112.

Generally, it is desirable to remove unreacted ammonia (also referred to as residual ammonia) from the crude hydrogen cyanide product prior to further HCN purification. The ammonia absorber 110 is provided with a sufficient number of absorption stages to achieve the desired level of separation. Standard industry practice can determine the number of segments necessary. The crude hydrogen cyanide product 107 is introduced into an ammonia absorber 110 and ammonia is absorbed from the crude hydrogen cyanide product 107, which enters a phosphate lean feed stream (not shown).

In one embodiment, the phosphate-lean feed stream is a stream comprising a stream having NH₄ ⁺/PO₄ ³⁺The ratio is in the range of 1.2-1.4Monoammonium hydrogen phosphate (NH)₄H₂PO₄) And diammonium hydrogen phosphate ((NH)₄)₂HPO₄) And the pH of the "ammonia-lean" aqueous solution of (a) is 5-6.1, such as 5.3-6.0. NH (NH)₄ ⁺/PO₄ ³⁺Values for the ratio include only ammonia bound to phosphate, and do not consider ammonia bound to other compounds such as formate or oxalate. A make-up phosphoric acid stream may be added to the ammonia-lean phosphate solution before the solution is passed as a phosphate-lean feed stream to the upper section of the ammonia absorber. The operation of the ammonia absorber 110 is controlled, at least in part, by monitoring and adjusting the temperature, pH, and solution density. The temperature of the phosphate-lean feed stream is controlled between 90 ℃ and above the freezing point of the phosphate-lean feed stream (sometimes referred to as the frost point, which is defined herein as the saturation point, i.e., below which solids begin to settle) to achieve the desired ammonia absorption. The crude hydrogen cyanide product 107 passes upward through ammonia absorber 110 and contacts the phosphate lean feed stream flowing downward through ammonia absorber 110 in a countercurrent manner. Unreacted ammonia present in the crude hydrogen cyanide 107 is absorbed by the "ammonia lean" phosphate solution and reacts to form additional diammonium phosphate, thereby providing an "ammonia rich" phosphate solution that flows to the lower portion of the ammonia absorber. Will have NH₄ ⁺/PO₄ ³⁺An ammonia-rich phosphate solution having a ratio in the range of 1.5 to 2.0 (in another embodiment in the range of 1.7 to 1.9) and a pH in the range of 6.2 to less than 7.0 is discharged from ammonia absorber 110 as residual ammonia stream 112.

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

In another embodiment, the phosphate-lean feed stream comprises a stream having NH₄ ⁺/PO₄ ³⁺Monoammonium hydrogen phosphate (NH) in a ratio in the range of 1.2-1.4₄H₂PO₄) And diammonium hydrogen phosphate ((NH)₄)₂HPO₄) And the pH of the phosphate-depleted aqueous solution is in the range of 5 to 6.1, e.g., 5.3 to 6.0. The phosphate-lean feed stream is fed as two different streams at different locations and as two different NH' s₄ ⁺/PO₄ ³⁺As more fully set forth in US patent US3,718,731 to Carlson et al, which is hereby incorporated by reference, than is incorporated into ammonia absorber 110. The ammonia absorber 110 may utilize packing and/or trays. In one embodiment, the absorption section in the ammonia absorber 110 is a valve tray. Valve trays are well known in the art, and the design of the trays can be selected to achieve good circulation, prevent stagnant zones, and prevent polymerization and corrosion. To avoid polymerization, the apparatus can be designed to minimize the residence zone where HCN is substantially present, such as in ammonia absorber 110 and in the zone where HCN is further purified as described herein. The ammonia absorber 110 may also incorporate an entrainment separator above the top tray to minimize entrainment. The entrainment separator generally includes the use of techniques such as reduced velocity, centrifugal separation, de-mister, screen or packing or combinations thereof.

In another embodiment, an ammonia absorber 110 is provided wherein the upper portion of the ammonia absorber is provided with packing and the lower portion of the ammonia absorber has a plurality of valve trays. Packing is used to reduce/prevent ammonia and phosphate from escaping from ammonia absorber 110 via overhead HCN stream 111 and then entering the region where HCN is further purified. The packing provides additional surface area for ammonia absorption while reducing entrainment in overhead HCN stream 111, resulting in an overall increase in ammonia absorption capacity. The packing used in the upper portion of the ammonia absorber can be any low pressure drop, self-contained packing capable of performing the above-described function, such as 250Y sold by Koch-Glisch of Wichita, KSAnd (4) filling.

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

Overhead HCN stream 111 can then enter scrubber 120. The scrubber is designed to remove substantially all of the free ammonia present in the overhead HCN stream 111 because the free ammonia (i.e., unneutralized ammonia) increases the pH in the remainder of the HCN purification zone, thus increasing the likelihood of 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, it is preferred to use phosphoric acid. The amount of phosphoric acid present in the diluted acid stream is dependent on the amount of ammonia present in the overhead HCN stream 111. Overhead HCN stream 111 is separated into overhead scrubber stream 121 and scrubber residue stream 122 using scrubber 120. Overhead scrubber stream 121 can comprise HCN, water, carbon monoxide, nitrogen, hydrogen, carbon dioxide, and methane. When phosphoric acid is used as the acid, scrubber residue stream 122 may be returned to the lower portion of ammonia absorber 110. When sulfuric acid is used as the acid, the scrubber residue 122 may be discharged (not shown).

The overhead scrubber stream 121 is then passed to HCN absorber 130 to form a waste gas 131 and an absorber stream 132. HCN absorber 130 is designed to remove substantially all HCN from overhead scrubber stream 121. The exhaust 131 may be exhausted from the system for combustion or use as fuel. In some embodiments, when the oxygen-containing gas comprises greater than 21 vol% oxygen, the off-gas 131 may be further treated to recover hydrogen. Any suitable apparatus may be used to recover the hydrogen, such as a pressure swing adsorption unit. The high purity recovered hydrogen is more valuable as a feedstock than as a fuel because it can 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 is noted that the amount of nitrogen in the flue gas affects the economic viability of recovering hydrogen from the flue gas, and does not affect the economic viability of combusting the flue gas in the boiler. For example, in the event that the HCN concentration in the exhaust 131 exceeds a preset maximum, the exhaust 131 may be passed to a steam generation boiler or igniter without hydrogen recovery.

Absorber stream 132 can next be passed to HCN desorber 140 to form desorber overhead stream 141 and desorber residue stream 142. Absorber stream 132 can be heated to a temperature of 80-100 c prior to entering HCN desorber 140. Absorber stream 132 comprises acidified water and a minor concentration (e.g., 2-8 vol%) of HCN, however the percentage of HCN will vary depending on operating factors. HCN desorber 140 removes HCN from absorber stream 132 and passes the HCN through a partial condenser to HCN enricher 150 for further purification.

HCN desorber 140 can contain packing and/or trays. In one embodiment, HCN desorber 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. The tray design is selected to achieve good vapor-liquid mass transfer and to minimize the stagnant zone to prevent polymerization and corrosion. Acceptable materials for construction of HCN desorber 140 include, but are not limited to, substantially corrosion-resistant metals as previously described. In one embodiment, the trays are constructed from 316 stainless steel. In another embodiment, the tray is constructed using alloy 20 and titanium hard (titanium hard).

Desorber residue stream 142 can be recycled to HCN absorber 130. The desorber residue stream 142 is substantially free of HCN. The desorber residue stream 142 is cooled from up to 120 c down to 30-65 c before entering the HCN absorber. Desorber overhead stream 141 contains a major amount of HCN and minor amounts of water and nitriles.

Desorber overhead stream 141 can then be introduced to HCN concentrator 150 where it is separated to form HCN product 151 and concentrator residue stream 152. The HCN enricher 150 comprises trays such as fixed valve trays or sieve trays. Valve trays and sieve trays are well known in the art. The tray design is selected to achieve good vapor-liquid mass transfer and to minimize stagnant zones to reduce the potential for polymerization, fouling and corrosion. Suitable materials for constructing trays in HCN concentrator 150 include, but are not limited to, 316 stainless steel.

The enricher residue stream 152 contains HCN, water and other organic components including mid-boiling impurities. The enricher residue stream 152 is combined with desorber residue stream 142 and then recycled to HCN absorber 130, thus removing mid-boiling impurities such as acetonitrile, propionitrile, and acrylonitrile that would otherwise accumulate in the HCN desorber and enricher columns.

Nitriles such as acetonitrile, propionitrile and acrylonitrile and in HCN/H₂Other mid-boiling impurities in the O system may accumulate in the lower portion of the HCN concentrator 150. Nitrile bleed can be utilized to remove mid-boiling impurities from the HCN enricher 150. The accumulation of nitriles can cause a temperature rise in the HCN concentrator 150 that can prevent the use of temperature to infer acceptable HCN purity and ultimately lead to contamination and unacceptable HCN purity. The nitrile drainage can be performed continuously or intermittently. The nitriles may be removed by removal into waste gas 131 by recycling the stream containing the nitrile bleed to HCN absorber 130.

As described herein, without being bound by theory, it is believed that nitrile formation can be reduced by controlling the amount of methane in the crude hydrogen cyanide product to be in the range of 0.05 to 1 volume percent, such as 0.05 to 0.55 volume percent or 0.2 to 0.3 volume percent. By reducing the formation of nitriles, the nitrile bleed stream can be reduced, allowing for enhanced recovery of HCN.

HCN product 151 contains substantially pure HCN and trace amounts of water, such as less than 100mpm or less than 10 mpm. The HCN product 151 can be used in further processes such as for hydrocyanation of olefin-containing groups or for hydrocyanation of 1, 3-butadiene and pentenenitriles useful for making ADN.

Returning to residual ammonia stream 112, this stream may be passed directly to ammonia recovery zone 101, which may include further ammonia purification, and the resulting ammonia may then be recycled and combined with ammonia-containing gas 103. The ammonia recovery zone 101 may include one or more desorbers to remove HCN and acids and separate ammonia from other impurities. The ammonia recovery zone 101 may also include an ammonia concentrator to further purify the ammonia. By controlling the amount of methane in the crude hydrogen cyanide product, ammonia recovery can 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 will crack into nitrogen gas, thus reducing the ammonia content. It is also believed that if more than 1% by volume methane is present in the crude hydrogen cyanide product 107, undesirable formation of acetonitrile can occur downstream in the process.

Various control systems may be used to control the reactant gas flow. For example, a flow meter that measures the flow rate, temperature, and pressure of the reactant gas feed stream and allows the control system to provide "real-time" feedback of the pressure-compensated and temperature-compensated flow rates to the operator and/or control equipment may be used.

As will be appreciated by one skilled in the art, the foregoing functions and/or methods may be embodied as a system, method or computer program product. For example, the functions and/or methods may be implemented as computer-executable program instructions recorded in a computer-readable storage device that, when retrieved and executed by a computer processor, control the computer system to perform the functions and/or methods of the embodiments described above. In one embodiment, the computer system may include one or more central processing units, computer memory (e.g., read-only memory, random access memory), and data storage devices (e.g., hard disk drives). The computer-executable instructions may 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.

From the foregoing it will be seen that this invention is one well adapted to attain all the ends and advantages mentioned as well as those inherent in the disclosure. While preferred embodiments of the invention have been described for purposes of this disclosure, it will be understood that variations which are obvious to those skilled in the art and which can be made within the spirit of the invention may be made.

In order that the invention disclosed herein may be more effectively understood, the following examples are set forth. It should be understood that this example is for illustrative purposes only and should not be construed as limiting the invention in any way.

Example 1

The crude hydrogen cyanide product is produced according to the Andrussow process using air as the oxygen-containing gas to form a tertiary mixed gas. The three-way mixed gas is passed through a catalyst bed to form a crude hydrogen cyanide product. The methane content of the crude hydrogen cyanide product was measured as it exited the reactor unit. As shown in fig. 3, as the concentration of methane in the crude cyanide product increases, the concentration of acetonitrile also increases. This increased tendency to nitrile formation is also expected when pure oxygen is used as the intake gas instead of air.

Example 2

According to the Andrussow process, a tertiary gas mixture is formed using pure oxygen as the oxygen-containing gas to produce a crude hydrogen cyanide product. The ternary mixed gas was formed using a molar ratio of ammonia to oxygen of 1.3:1 and a molar ratio of methane to oxygen of 1.2: 1. The ternary mixed gas contained 28.5 vol% oxygen. The reactor had an internal diameter of 142.2cm and the platinum/rhodium catalyst bed was mounted on a cast annular support extending 2.86cm into the reactor so that the catalyst bed formed a 90% pass-through zone for the crude hydrogen cyanide product. Over 150 days of continuous operation, the catalyst bed contracted in diameter by 0.64 to 1.26cm, with no methane by-pass catalyst bed, because the annular support supported the contracted catalyst bed. The crude cyanogen cyanide product contains 0.2 to 0.3% by volume of methane.

Comparative example A

The process and reactor were the same as in example 2 except that the annular shelf extended into the reactor more and the pass through zone was reduced to 85%. The pressure drop in the reactor was increased by 20% compared to example 2, so that the production of HCN was reduced.

Claims (15)

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 three-way gas mixture with a catalyst bed in a reactor to form a crude hydrogen cyanide product, wherein the catalyst bed is supported by a ring support, the ring support providing a pass-through zone having an area of at least 90% of the cross-sectional area of the reactor, and the ring support substantially prevents catalyst bed bypass of the three-way gas mixture or components thereof from entering the crude hydrogen cyanide product; and

the flow rate of at least one of the methane-containing gas, ammonia-containing gas, and oxygen-containing gas is controlled to maintain the methane concentration in the crude hydrogen cyanide product at from 0.05 to 1 volume percent.

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

3. The method of claim 1, wherein the ternary gas mixture is impermeable to the toroidal support.

4. The process of claim 1, wherein the crude hydrogen cyanide product comprises from 0.05 to 0.55 vol% methane.

5. The process of any of claims 1-4, wherein the crude cyanogen cyanide product comprises 0.2-0.3 vol% methane.

6. The process of claim 1, wherein the methane-containing gas, ammonia-containing gas, and oxygen-containing gas are combined in a mixing vessel upstream of the reactor to form a ternary gas mixture.

7. The method according to claim 1, wherein the oxygen containing gas comprises more than 21 vol% oxygen, preferably at least 80 vol% oxygen.

8. The method of claim 1, wherein the oxygen-containing gas comprises pure oxygen.

9. The method of claim 1, wherein the ternary gas mixture comprises at least 25% oxygen by volume.

10. The method of claim 1, wherein the ternary gas mixture comprises 25-32 vol% oxygen.

11. The method of claim 1, wherein the molar ratio of ammonia to oxygen in the ternary gas mixture is between 1.2-1.6.

12. The method of claim 1, wherein the molar ratio of methane to oxygen in the ternary gas mixture is between 1-1.25.

13. The process of claim 1, wherein a crude hydrogen cyanide product is isolated, wherein the isolating comprises:

removing residual ammonia from the crude hydrogen cyanide 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 final 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.