WO1996015983A1 - Hydrogen cyanide gas production - Google Patents

Hydrogen cyanide gas production Download PDF

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Publication number
WO1996015983A1
WO1996015983A1 PCT/GB1995/002733 GB9502733W WO9615983A1 WO 1996015983 A1 WO1996015983 A1 WO 1996015983A1 GB 9502733 W GB9502733 W GB 9502733W WO 9615983 A1 WO9615983 A1 WO 9615983A1
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WO
WIPO (PCT)
Prior art keywords
conduit
electrically conductive
reactor
reactor according
sidewall
Prior art date
Application number
PCT/GB1995/002733
Other languages
French (fr)
Inventor
Cornelius Johannes Welgemoed
Original Assignee
Quadro Chemicals (Proprietary) Limited
Dyer, Alison, Margaret
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Quadro Chemicals (Proprietary) Limited, Dyer, Alison, Margaret filed Critical Quadro Chemicals (Proprietary) Limited
Priority to AU38785/95A priority Critical patent/AU3878595A/en
Publication of WO1996015983A1 publication Critical patent/WO1996015983A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C3/00—Cyanogen; Compounds thereof
    • C01C3/02—Preparation, separation or purification of hydrogen cyanide
    • C01C3/0208—Preparation in gaseous phase
    • C01C3/0229—Preparation in gaseous phase from hydrocarbons and ammonia in the absence of oxygen, e.g. HMA-process
    • C01C3/0233—Preparation in gaseous phase from hydrocarbons and ammonia in the absence of oxygen, e.g. HMA-process making use of fluidised beds, e.g. the Shawinigan-process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
    • B01J19/087—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electric or magnetic energy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/24—Stationary reactors without moving elements inside
    • B01J19/2415—Tubular reactors
    • B01J19/2425—Tubular reactors in parallel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/00049—Controlling or regulating processes
    • B01J2219/00051—Controlling the temperature
    • B01J2219/00132—Controlling the temperature using electric heating or cooling elements
    • B01J2219/00135—Electric resistance heaters

Definitions

  • THIS invention relates to hydrogen cyanide gas production.
  • Hydrogen cyanide gas is produced by reacting, endothermically, a saturated hydrocarbon, typically methane, and ammonia.
  • the most common production process is the Andrussow process in which air is added to methane and ammonia and this is reacted over a platinum-based catalyst.
  • the quantity of air added is such that the partial combustion of reactants provides sufficient energy for the heat of reaction required as well as to preheat the reactants to the required operating temperature, typically 850°C
  • Another process for producing hydrogen cyanide gas is to use the Degussa process.
  • the energy required is supplied by a fired furnace, with the reactants contained in platinum lined refractory tubes within the furnace.
  • Yet another process for producing hydrogen cyanide gas is the Shawinigan process.
  • the energy required is provided by electrical energy via a fluidised bed of carbon particles.
  • the absence of a catalyst in this process means that the reaction must be carried out at a very high temperature, at around 1450oC.
  • the Andrussow process is the simplest, and therefore the most common, it suffers from the disadvantage of producing a relatively low concentration hydrogen cyanide gas stream. Also, it only works effectively with methane as the hydrocarbon source. Although the other processes produce hydrogen cyanide gas in higher concentrations, and also operate relatively efficiently with other saturated hydrocarbons as the carbon source for the reaction, they are relatively complex processes which are expensive to carry out.
  • a reactor for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprises a conduit into which the reactants can be introduced, the reactor operatively being associated with a source of electrical power and the conduit having a sidewall containing or being associated with an electrically conductive material, or having an electrically conductive element passing through it, so that when a flow of electrical current is passed through the sidewall or through the element or through the electrically conductive material, or is induced therein, heat is generated therein which is convected or radiated to the reactants to promote a reaction between them.
  • a flow of electrical current is induced to flow in the sidewall or electrically conductive material or element within each conduit.
  • the reactor may comprise a plurality of separate conduits.
  • each conduit may contain or comprise graphite.
  • the inner surface of each conduit may be coated with a layer of another electrically conductive material, typically platinum or a platinised catalyst.
  • the sidewall may also comprise a composite material comprising a refractory material, such as silicone carbide, and a conductive layer.
  • a refractory material such as silicone carbide
  • the inner surface of each conduit may be coated with the conductive layer.
  • the layer may comprise platinum or a platinised catalyst.
  • An electrically conductive collar which is electrically connected to an electrical power supply, may surround each conduit.
  • a coil of electrically conductive material which is electrically connected to an electrical power supply, may surround each conduit.
  • Each conduit preferably comprises an elongated tube having a larger space defined in its central portion than at at least one of its ends.
  • the reactor may comprise a solid body, which may be a block of graphite, with a plurality of conduits defined therein.
  • the conduits may be elongated channels defined in the block of graphite.
  • An electrically conductive collar which is electrically connected to an electrical power supply may surround the body.
  • a coil of electrically conductive material which is electrically connected to an electrical power supply, may surround the body.
  • thermocouple may be disposed within each conduit to indicate the temperature of the reactants within each conduit.
  • the reactants preferably comprise a saturated hydrocarbon, such as methane, and ammonia.
  • a process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen- containing reactant comprises the steps of: introducing the reactants into a conduit having a sidewall containing or being associated with an electrically conductive material or having an electrically conductive element passing through it; passing an electrical current through the sidewall or through the element or through the electrically conductive material, or inducing a flow of electrical current therein; and using heat generated by resistance to the current in the sidewall or the element or the electrically conductive material, and convected or radiated into the conduit, to promote a reaction between the reactants.
  • a process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-based reactant comprises the steps of: introducing the reactants into a conduit; and exposing the reactants to radiated or convected heat produced by resistance to electrical current passing through a path in or near the conduit to promote a reaction between the reactants.
  • a plant for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen- containing reactant comprises a storage facility for the saturated hydrocarbon reactant and a storage facility for the nitrogen-containing reactant, a reactor according to the invention in fluid communication with the storage facilities and an electrical power source associated with the reactor.
  • the plant may also comprise a cooler for cooling a hydrogen cyanide gas stream produced in the reactor and an absorber for entraining and/or absorbing the hydrogen cyanide gas stream into a water or alkaline stream for transportation.
  • Figure 1 is a schematic section through a reactor of the invention.
  • Figure 2 is a schematic representation of a plant of the invention.
  • the reactor of the invention is compact and efficient and enables electrical energy to be used to provide the heat for producing hydrogen cyanide gas from methane, or a higher saturated hydrocarbon, and ammonia. Because the heat generated is used efficiently, the reactor may be used without a platinum catalyst to generate hydrogen cyanide gas.
  • the reactor in one form thereof, is a block of graphite into which a number of holes have been drilled. These holes constitute conduits or tubes into which the methane and ammonia, or other suitable reactants, can be introduced.
  • the graphite is electrically conductive but has a high electrical resistance. Thus, an electrical current passed through the graphite, and thus through the sidewalls of the conduits, will generate heat. This heat is then radiated and/or convected into the conduits and supplies the heat of reaction required to promote the reaction between the methane and ammonia to produce hydrogen cyanide gas.
  • An alternative, efficient way of causing an electrical current to flow in the sidewalls of the conduits or tubes, instead of connecting a source of electrical power directly to the conduits or tubes, is to induce an electrical current to flow in the sidewall or graphite block, which will generate heat.
  • the reactor is of a simpler design and is less costly.
  • the current is induced to flow in the sidewall or graphite block under the influence of a high frequency alternating magnetic field produced by a high frequency electrical current flowing in a coil which surrounds either the graphite block or the tubes.
  • the advantage of this arrangement therefore is that the coil is not in direct contact with the graphite block or the conduits and by varying the position and/or size of the coil, the electrical current, and thus the electrical heat generated, can be concentrated in a narrow band near the centre of the tubes, i.e. in the hot or reaction zone discussed in more detail below.
  • the advantage is particularly noticeable in a multi-tube reactor.
  • the reactors can also be formed by a number of coextensive tubes made from graphite or from some other material.
  • a reactor is illustrated in Figure 1. It has been found that any material, or any composite material, that can stand up to the operating conditions and provide a resistance path for the electrical current can be used to form the conduits or tubes.
  • a suitable composite material is a non- conducting refractory material, such as silicone carbide or ceramic or alumina, which includes a conductive layer.
  • the conductive layer may be the platinum catalyst itself.
  • the reactor 10, illustrated in Figure 1 consists of an insulated furnace chamber 12.
  • the furnace chamber 12 contains a number of conduits, in the form of a graphite tubes 14.
  • These graphite tubes 14 are arranged in nests of three. A single nest of three is shown in Figure 1.
  • the graphite sidewall 16 of each tube 14 is thickened at its upper end 18 and at its bottom end 20, i.e. each tube has a thinner central sidewall thickness and thus a larger space defined in its central portion than at either of its ends. This concentrates the energy, in the form of heat generated in the tubes, in a reaction zone or hot zone 21.
  • the inner surfaces of the tubes 14 are coated with a layer 17 of platinum or a platinum catalyst to catalyse the reaction.
  • a layer 17 of platinum or a platinum catalyst to catalyse the reaction.
  • platinum or a platinum catalyst results in the reaction occurring at a lower temperature, which improves efficiency.
  • a layer of platinum will also have the effect of concentrating the electrical current, and therefore heat production, in a reaction zone within each tube 14. This further enhances the efficiency of the reactor 10.
  • Each tube 14 in a nest of three tubes is connected near its upper end 18 to one of the three electrical phases of a three phase power supply 24.
  • the power supply 24 is typically provided by a transformer with multiple tapping points to enable the power level to be adjusted in sympathy with reaction rates.
  • Each tube 14 is connected by means of a collar 15, which surrounds the relevant tube 14, outside the hot or reaction zone 21, to the power supply 24. If the reactor is formed from a solid graphite block, a collar, which is connected electrically to the power supply, surrounds the whole block.
  • the tubes 14 are also electrically delta connected at 22 to one another at their bottom ends 20.
  • Each tube 14 is provided with a thermocouple 26 to indicate the gas temperature in the reaction zone within each tube 14.
  • the furnace wall 12 also has strategically located viewing ports 28 defined therein through which the sidewall temperature of the tubes 14 can be measured with an optical pyrometer.
  • the reactants in the form of methane, or a higher saturated hydrocarbon, and ammonia are supplied to the tubes 14 by a feed manifold 30 situated adjacent the upper ends 18 of the tubes 14.
  • the hydrogen cyanide gas-containing stream produced within the reaction zone is fed out through the bottom ends 20 of the tubes 14 and is conveyed away in a cooled water manifold 32.
  • the process of the invention utilises electrical energy passed through the reactor 10 to produce hydrogen cyanide gas.
  • Use is thus made of indirect heat, generated by passing an electrical current through a relatively poorly electrically conductive, i.e. an electrically resistive material, to promote a reaction between the reactants to produce a concentrated stream of hydrogen cyanide.
  • a relatively poorly electrically conductive i.e. an electrically resistive material
  • it is safer to entrain the hydrogen cyanide produced in a water or an alkaline stream.
  • Typical alkaline streams employed are aqueous solutions of calcium oxide (CaO) or sodium hydroxide (NaOH).
  • the hydrogen cyanide can then be removed from the gas stream exiting the tubes in the reactor by absorption into water or an aqueous alkaline solution.
  • the hydrogen gas that is coproduced with the hydrogen cyanide remains and is available for use as a fuel or for other purposes.
  • a plant of the invention containing a reactor 10a with only a single tube, is illustrated schematically in Figure 2.
  • the plant contains a propane storage tank 40 and an ammonia storage tank 42.
  • a pipe 44 leads from the propane storage tank 40 to a reactor inlet 30 and a pipe 46 leads from the ammonia storage tank 42 to the inlet 30.
  • a pressure regulator and a rotameter are provided on each pipe 44 and 46 to provide measured and controlled flow rates of these reactants to the reactor 10a.
  • the reactor 10a is a variation of the reactor 10 described in Figure 1 in that it is a one tube reactor operating on a single phase electrical supply. The main reason for this is that it is a pilot reactor.
  • two concentric tubes, an inner and an outer graphite tube 8 and 6, comprise one conduit.
  • the tubes are electrically insulated from one another at their top ends while there is an electrical contact between them where the inner tube 8 ends.
  • the inner tube 8 is connected to the outer tube 6 at a point approximately two thirds along its length via a graphite collar 7, which is able to slide to accommodate differential thermal expansion.
  • all electrical contacts to the transformer 60 occur at the top of the reactor 10a.
  • the inner and outer tubes 8 and 6 are enclosed within a steel furnace wall 50 containing alumina wool insulation 52.
  • Each of the inner and outer graphite tubes 8 and 6 is electrically connected to a low voltage/high current transformer 60.
  • a current is supplied from the transformer 60, controlled by a controller 61, directly to the sidewalls of each of the inner and outer tubes to generate heat within the tubes to provide the heat of reaction required to generate hydrogen cyanide gas within the tubes.
  • a platinum layer can be disposed or deposited within the inner tube to catalyse the reaction.
  • the hot zone temperature is maintained at 1200oC during the reaction by controlling power addition.
  • the operating temperature within the tubes is monitored by three thermocouples, one in the top end of the tubes, one in the bottom end of the tubes and one near the central, hot or reaction zone of the tubes.
  • the exit manifold 63 from the tubes is coiled and passes through a water bath 65 to cool the hydrogen cyanide gas stream.
  • a pipe containing the hydrogen cyanide gas stream is then connected to two absorbers 64 and 66, in series.
  • Each absorber consists of three plates with a plurality of 25 x 10 mm diameter holes drilled in them. The three plates are placed 150 mm apart within a pipe having a diameter of 100 mm.
  • a stream of lime slurry is circulated through each absorber at a flow rate of about 10 litres per minutes fed through the top of each absorber.
  • the hydrogen cyanide gas stream enters at the bottom of the absorber and passes, in a counter current arrangement, through the lime slurry.
  • a calcium cyanide solution is produced by the reaction of the hydrogen cyanide contained in the gas stream and the lime or calcium hydroxide.
  • the absorbers are placed directly above lime slurry storage tanks (not shown) for ease of operation. Sufficient lime slurry can be stored in the storage tank for 12 hours continuous operation of the plant.
  • the design of the reactor and process of the invention allows for the use of electrical energy, at relatively low capital and operating costs, to generate hydrogen cyanide gas. Further, the design of reactor facilitates the establishment of self contained units in movable skid-mounted frames which can be used to generate cyanide at a site where it will be consumed, and in relatively small quantities. This flexibility avoids incurring the economy of scale penalties inherent in the existing processes. Another benefit of matching hydrogen cyanide supply with demand is that safety is improved because cyanide does not have to be moved by road to the site of consumption and also does not have to be stored in large quantities as cyanide or a cyanide solution.
  • a wide range of saturated hydrocarbon feed stocks for example ethane, propane or butane or a mixture thereof, may be used in the reactor and process of the invention to generate hydrogen cyanide gas.
  • Hydrogen cyanide gas production plants utilising the reactor and/or method of the invention can therefore be erected in locations that do not have access to natural gas or methane.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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Abstract

A reactor for producing hydrogen cyanide gas, a plant containing the reactor, and a process of producing hydrogen cyanide gas using the reactor are described. The reactor comprises a number of conduits in the form of tubes (14) which is made of graphite or other relatively poorly electrically conductive material. Each conduit is connected to a source of electrical power so that when a flow of electrical current is passed through the sidewall of the conduit, or an electrical current is induced to flow therein, heat is generated within the conduit which is convected or radiated to the reactants to promote a reaction between them.

Description

HYDROGEN CYANIDE GAS PRODUCTION
BACKGROUND OF THE INVENTION
THIS invention relates to hydrogen cyanide gas production.
The advantages of on-site hydrogen cyanide gas (HCN) production for use in metals recovery processes are discussed in co-pending South African Patent Application No. 94/0281. Hydrogen cyanide gas is produced by reacting, endothermically, a saturated hydrocarbon, typically methane, and ammonia.
The most common production process is the Andrussow process in which air is added to methane and ammonia and this is reacted over a platinum-based catalyst. The quantity of air added is such that the partial combustion of reactants provides sufficient energy for the heat of reaction required as well as to preheat the reactants to the required operating temperature, typically 850°C
Another process for producing hydrogen cyanide gas is to use the Degussa process. In this process the energy required is supplied by a fired furnace, with the reactants contained in platinum lined refractory tubes within the furnace.
Yet another process for producing hydrogen cyanide gas is the Shawinigan process. In this process, the energy required is provided by electrical energy via a fluidised bed of carbon particles. The absence of a catalyst in this process means that the reaction must be carried out at a very high temperature, at around 1450ºC.
Although the Andrussow process is the simplest, and therefore the most common, it suffers from the disadvantage of producing a relatively low concentration hydrogen cyanide gas stream. Also, it only works effectively with methane as the hydrocarbon source. Although the other processes produce hydrogen cyanide gas in higher concentrations, and also operate relatively efficiently with other saturated hydrocarbons as the carbon source for the reaction, they are relatively complex processes which are expensive to carry out.
SUMMARY OF THE INVENTION
According to the invention a reactor for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprises a conduit into which the reactants can be introduced, the reactor operatively being associated with a source of electrical power and the conduit having a sidewall containing or being associated with an electrically conductive material, or having an electrically conductive element passing through it, so that when a flow of electrical current is passed through the sidewall or through the element or through the electrically conductive material, or is induced therein, heat is generated therein which is convected or radiated to the reactants to promote a reaction between them.
Preferably, a flow of electrical current is induced to flow in the sidewall or electrically conductive material or element within each conduit.
The reactor may comprise a plurality of separate conduits.
The sidewall of each conduit may contain or comprise graphite. The inner surface of each conduit may be coated with a layer of another electrically conductive material, typically platinum or a platinised catalyst.
The sidewall may also comprise a composite material comprising a refractory material, such as silicone carbide, and a conductive layer. The inner surface of each conduit may be coated with the conductive layer. The layer may comprise platinum or a platinised catalyst.
An electrically conductive collar, which is electrically connected to an electrical power supply, may surround each conduit.
Alternatively, a coil of electrically conductive material, which is electrically connected to an electrical power supply, may surround each conduit.
Each conduit preferably comprises an elongated tube having a larger space defined in its central portion than at at least one of its ends.
The reactor may comprise a solid body, which may be a block of graphite, with a plurality of conduits defined therein. The conduits may be elongated channels defined in the block of graphite.
An electrically conductive collar, which is electrically connected to an electrical power supply may surround the body.
Alternatively, a coil of electrically conductive material, which is electrically connected to an electrical power supply, may surround the body.
A thermocouple may be disposed within each conduit to indicate the temperature of the reactants within each conduit.
The reactants preferably comprise a saturated hydrocarbon, such as methane, and ammonia.
According to another aspect of the invention a process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen- containing reactant comprises the steps of: introducing the reactants into a conduit having a sidewall containing or being associated with an electrically conductive material or having an electrically conductive element passing through it; passing an electrical current through the sidewall or through the element or through the electrically conductive material, or inducing a flow of electrical current therein; and using heat generated by resistance to the current in the sidewall or the element or the electrically conductive material, and convected or radiated into the conduit, to promote a reaction between the reactants.
According to another aspect of the invention a process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-based reactant comprises the steps of: introducing the reactants into a conduit; and exposing the reactants to radiated or convected heat produced by resistance to electrical current passing through a path in or near the conduit to promote a reaction between the reactants.
According to another aspect of the invention a plant for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen- containing reactant comprises a storage facility for the saturated hydrocarbon reactant and a storage facility for the nitrogen-containing reactant, a reactor according to the invention in fluid communication with the storage facilities and an electrical power source associated with the reactor. The plant may also comprise a cooler for cooling a hydrogen cyanide gas stream produced in the reactor and an absorber for entraining and/or absorbing the hydrogen cyanide gas stream into a water or alkaline stream for transportation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic section through a reactor of the invention; and
Figure 2 is a schematic representation of a plant of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The reactor of the invention is compact and efficient and enables electrical energy to be used to provide the heat for producing hydrogen cyanide gas from methane, or a higher saturated hydrocarbon, and ammonia. Because the heat generated is used efficiently, the reactor may be used without a platinum catalyst to generate hydrogen cyanide gas.
The reactor, in one form thereof, is a block of graphite into which a number of holes have been drilled. These holes constitute conduits or tubes into which the methane and ammonia, or other suitable reactants, can be introduced. The graphite is electrically conductive but has a high electrical resistance. Thus, an electrical current passed through the graphite, and thus through the sidewalls of the conduits, will generate heat. This heat is then radiated and/or convected into the conduits and supplies the heat of reaction required to promote the reaction between the methane and ammonia to produce hydrogen cyanide gas.
An alternative, efficient way of causing an electrical current to flow in the sidewalls of the conduits or tubes, instead of connecting a source of electrical power directly to the conduits or tubes, is to induce an electrical current to flow in the sidewall or graphite block, which will generate heat. As there is no need for direct electrical contact between the power source and the conduits or tubes, the reactor is of a simpler design and is less costly. The current is induced to flow in the sidewall or graphite block under the influence of a high frequency alternating magnetic field produced by a high frequency electrical current flowing in a coil which surrounds either the graphite block or the tubes. The advantage of this arrangement therefore is that the coil is not in direct contact with the graphite block or the conduits and by varying the position and/or size of the coil, the electrical current, and thus the electrical heat generated, can be concentrated in a narrow band near the centre of the tubes, i.e. in the hot or reaction zone discussed in more detail below. The advantage is particularly noticeable in a multi-tube reactor.
Instead of being a single block of graphite, the reactors can also be formed by a number of coextensive tubes made from graphite or from some other material. Such a reactor is illustrated in Figure 1. It has been found that any material, or any composite material, that can stand up to the operating conditions and provide a resistance path for the electrical current can be used to form the conduits or tubes. A suitable composite material is a non- conducting refractory material, such as silicone carbide or ceramic or alumina, which includes a conductive layer. The conductive layer may be the platinum catalyst itself.
The reactor 10, illustrated in Figure 1, consists of an insulated furnace chamber 12. The furnace chamber 12 contains a number of conduits, in the form of a graphite tubes 14. These graphite tubes 14 are arranged in nests of three. A single nest of three is shown in Figure 1. The graphite sidewall 16 of each tube 14 is thickened at its upper end 18 and at its bottom end 20, i.e. each tube has a thinner central sidewall thickness and thus a larger space defined in its central portion than at either of its ends. This concentrates the energy, in the form of heat generated in the tubes, in a reaction zone or hot zone 21.
The inner surfaces of the tubes 14 are coated with a layer 17 of platinum or a platinum catalyst to catalyse the reaction. Although it is possible to perform the reaction without the use of platinum or a platinum catalyst, the use of platinum or a platinum catalyst results in the reaction occurring at a lower temperature, which improves efficiency. A layer of platinum will also have the effect of concentrating the electrical current, and therefore heat production, in a reaction zone within each tube 14. This further enhances the efficiency of the reactor 10.
Each tube 14 in a nest of three tubes is connected near its upper end 18 to one of the three electrical phases of a three phase power supply 24. This enables three phase alternating current to be employed, which is the most versatile power source. The power supply 24 is typically provided by a transformer with multiple tapping points to enable the power level to be adjusted in sympathy with reaction rates. Each tube 14 is connected by means of a collar 15, which surrounds the relevant tube 14, outside the hot or reaction zone 21, to the power supply 24. If the reactor is formed from a solid graphite block, a collar, which is connected electrically to the power supply, surrounds the whole block. The tubes 14 are also electrically delta connected at 22 to one another at their bottom ends 20.
Each tube 14 is provided with a thermocouple 26 to indicate the gas temperature in the reaction zone within each tube 14. The furnace wall 12 also has strategically located viewing ports 28 defined therein through which the sidewall temperature of the tubes 14 can be measured with an optical pyrometer.
The reactants in the form of methane, or a higher saturated hydrocarbon, and ammonia are supplied to the tubes 14 by a feed manifold 30 situated adjacent the upper ends 18 of the tubes 14. The hydrogen cyanide gas-containing stream produced within the reaction zone is fed out through the bottom ends 20 of the tubes 14 and is conveyed away in a cooled water manifold 32.
The process of the invention utilises electrical energy passed through the reactor 10 to produce hydrogen cyanide gas. Use is thus made of indirect heat, generated by passing an electrical current through a relatively poorly electrically conductive, i.e. an electrically resistive material, to promote a reaction between the reactants to produce a concentrated stream of hydrogen cyanide. Because of the reactivity and toxicity of the cyanide ion, it is safer to entrain the hydrogen cyanide produced in a water or an alkaline stream. Typical alkaline streams employed are aqueous solutions of calcium oxide (CaO) or sodium hydroxide (NaOH). The hydrogen cyanide can then be removed from the gas stream exiting the tubes in the reactor by absorption into water or an aqueous alkaline solution. The hydrogen gas that is coproduced with the hydrogen cyanide remains and is available for use as a fuel or for other purposes.
A plant of the invention, containing a reactor 10a with only a single tube, is illustrated schematically in Figure 2. The plant contains a propane storage tank 40 and an ammonia storage tank 42. A pipe 44 leads from the propane storage tank 40 to a reactor inlet 30 and a pipe 46 leads from the ammonia storage tank 42 to the inlet 30. A pressure regulator and a rotameter are provided on each pipe 44 and 46 to provide measured and controlled flow rates of these reactants to the reactor 10a.
The reactor 10a is a variation of the reactor 10 described in Figure 1 in that it is a one tube reactor operating on a single phase electrical supply. The main reason for this is that it is a pilot reactor. To obviate the need for electrical contact at the bottom end of the tube, two concentric tubes, an inner and an outer graphite tube 8 and 6, comprise one conduit. The tubes are electrically insulated from one another at their top ends while there is an electrical contact between them where the inner tube 8 ends. The inner tube 8 is connected to the outer tube 6 at a point approximately two thirds along its length via a graphite collar 7, which is able to slide to accommodate differential thermal expansion. Thus, all electrical contacts to the transformer 60 occur at the top of the reactor 10a. The inner and outer tubes 8 and 6 are enclosed within a steel furnace wall 50 containing alumina wool insulation 52.
Each of the inner and outer graphite tubes 8 and 6 is electrically connected to a low voltage/high current transformer 60. A current is supplied from the transformer 60, controlled by a controller 61, directly to the sidewalls of each of the inner and outer tubes to generate heat within the tubes to provide the heat of reaction required to generate hydrogen cyanide gas within the tubes. A platinum layer can be disposed or deposited within the inner tube to catalyse the reaction. The hot zone temperature is maintained at 1200ºC during the reaction by controlling power addition. The operating temperature within the tubes is monitored by three thermocouples, one in the top end of the tubes, one in the bottom end of the tubes and one near the central, hot or reaction zone of the tubes.
The exit manifold 63 from the tubes is coiled and passes through a water bath 65 to cool the hydrogen cyanide gas stream. A pipe containing the hydrogen cyanide gas stream is then connected to two absorbers 64 and 66, in series. Each absorber consists of three plates with a plurality of 25 x 10 mm diameter holes drilled in them. The three plates are placed 150 mm apart within a pipe having a diameter of 100 mm. A stream of lime slurry is circulated through each absorber at a flow rate of about 10 litres per minutes fed through the top of each absorber. The hydrogen cyanide gas stream enters at the bottom of the absorber and passes, in a counter current arrangement, through the lime slurry. On contact with the hydrogen cyanide gas stream, a calcium cyanide solution is produced by the reaction of the hydrogen cyanide contained in the gas stream and the lime or calcium hydroxide. The absorbers are placed directly above lime slurry storage tanks (not shown) for ease of operation. Sufficient lime slurry can be stored in the storage tank for 12 hours continuous operation of the plant.
The design of the reactor and process of the invention allows for the use of electrical energy, at relatively low capital and operating costs, to generate hydrogen cyanide gas. Further, the design of reactor facilitates the establishment of self contained units in movable skid-mounted frames which can be used to generate cyanide at a site where it will be consumed, and in relatively small quantities. This flexibility avoids incurring the economy of scale penalties inherent in the existing processes. Another benefit of matching hydrogen cyanide supply with demand is that safety is improved because cyanide does not have to be moved by road to the site of consumption and also does not have to be stored in large quantities as cyanide or a cyanide solution.
A wide range of saturated hydrocarbon feed stocks, for example ethane, propane or butane or a mixture thereof, may be used in the reactor and process of the invention to generate hydrogen cyanide gas. Hydrogen cyanide gas production plants utilising the reactor and/or method of the invention can therefore be erected in locations that do not have access to natural gas or methane.

Claims

1. A reactor for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprising a conduit into which the reactants can be introduced, the reactor operatively being associated with a source of electrical power and the conduit having a sidewall containing or being associated with an electrically conductive material, or having an electrically conductive element passing through it, so that when a flow of electrical current is passed through the sidewall or through the element or through the electrically conductive material, or is induced therein, heat is generated therein which is transmitted to the reactants to promote a reaction between them.
2. A reactor according to claim 1 , wherein a flow of electrical current is inducible in the sidewall or electrically conductive material or element within the conduit.
3. A reactor according to claim 1 or claim 2, which comprises a plurality of separate conduits.
4. A reactor according to claim 3, wherein the sidewall of each conduit contains graphite.
5. A reactor according to claim 4, wherein the sidewall of each conduit comprises graphite and wherein the inner surface of each conduit is coated with a layer of another electrically conductive material.
6. A reactor according to claim 5, wherein the other electrically conductive material is platinum or a platinised catalyst.
7. A reactor according to claim 6, wherein the sidewall of each conduit comprises a refractory material and wherein the inner surface of each conduit is coated with a layer of electrically conductive material.
8. A reactor according to claim 7, wherein the refractory material is silicone carbide.
9. A reactor according to claim 7 or claim 8, wherein the electrically conductive material is platinum or a platinised catalyst.
10. A reactor according to any one of claims 1 to 9, which comprises an electrically conductive collar which surround:, each conduit and which is electrically connected to an electrical power supply.
11. A reactor according to any one of claims 1 to 10, wherein each conduit is electrically delta-connected to every other conduit at adjacent ends thereof.
12. A reactor according to claim 1 or claim 2, which comprises a solid body with the conduit defined therein.
13. A reactor according to claim 12, wherein the body comprises a plurality of separate conduits defined therein.
14. A reactor according to claim 12 or claim 13, wherein the solid body comprises graphite.
15. A reactor according to any one of claims 12 to 14, which comprises an electrically conductive collar which surrounds the body and which is electrically connected to an electrical power supply.
16. A reactor according to any one of claims 1 to 11, wherein each conduit comprises an elongate tube having a larger space defined in its central portion than at at least one of its ends.
17. A reactor according to any one of claims 1 to 16, which comprises a thermocouple disposed within each conduit to indicate the temperature of the reactants within each conduit.
18. A process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprising the steps of. introducing the reactants into a conduit having a sidewall containing or being associated with an electrically conductive material or having an electrically conductive element passing through it; passing an electrical current through the sidewall or through the element or through the electrically conductive material, or inducing a flow of electrical current therein; and using heat generated by resistance to the current in the sidewall or the element or the electrically conductive material, and transmitted into the conduit, to promote a reaction between the reactants.
19. A process according to claim 18, wherein an electrical current is induced to flow in the sidewall or electrically conductive material or in the element within the conduit.
20. A process for producing hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprises the steps of: introducing the reactants into a conduit; and exposing the reactants to radiated or convected heat produced by resistance to electrical current passing through a path in or near the conduit to promote a reaction between the reactants.
21. A process according to claim 20, wherein an electrical current is induced to flow in the path.
22. A process according to any one of claims 18 to 21, wherein the reactants comprise a saturated hydrocarbon and ammonia.
23. A process according to claim 22, wherein the saturated hydrocarbon is methane, ethane, propane or butane or a mixture thereof.
24. A process according to claim 23, wherein the saturated hydrocarbon is methane.
25. A process according to any one of claims 18 to 24, wherein the hydrogen cyanide produced in each conduit is entrained and/or adsorbed in a water or alkaline stream for transportation.
26. A plant for the production of hydrogen cyanide gas from a saturated hydrocarbon reactant and a nitrogen-containing reactant comprising a storage facility for the saturated hydrocarbon reactant and a storage facility for the nitrogen-containing reactant, a reactor according to any one of claims 1 to 17 in fluid communication with the storage facilities and an electrical power source associated with the reactor.
27. A plant according to claim 26, which also comprises a cooler for cooling a hydrogen cyanide gas stream produced in the reactor and an absorber for entraining and/or absorbing the hydrogen cyanide gas stream into a water or alkaline stream for transportation.
28. A reactor substantially as herein described with reference to Figure
1 or Figure 2.
29. A process substantially as herein described with reference to Figure
2.
30. A plant substantially as herein described with reference to Figure 2.
PCT/GB1995/002733 1994-11-24 1995-11-23 Hydrogen cyanide gas production WO1996015983A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU38785/95A AU3878595A (en) 1994-11-24 1995-11-23 Hydrogen cyanide gas production

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ZA94/9334 1994-11-24
ZA949334 1994-11-24

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WO1996015983A1 true WO1996015983A1 (en) 1996-05-30

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US20210316262A1 (en) * 2018-08-31 2021-10-14 Dow Global Technologies Llc Systems and processes for improving hydrocarbon upgrading
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WO2007006398A1 (en) * 2005-06-17 2007-01-18 Exxonmobil Chemical Patents Inc. Oligomerisation of olefins with zeolite catalyst
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US12059663B2 (en) 2018-08-31 2024-08-13 Dow Global Technologies Llc Systems and processes for transferring heat using molten salt during hydrocarbon upgrading
WO2024074277A1 (en) 2022-10-07 2024-04-11 Evonik Operations Gmbh Catalytically active heating elements, production and use thereof

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