GB1604076A

GB1604076A - Recovery of a salt mixture from a gas

Info

Publication number: GB1604076A
Application number: GB2125378A
Authority: GB
Original assignee: Lummus Co
Current assignee: CB&I Technology Inc
Priority date: 1978-01-18
Filing date: 1978-05-22
Publication date: 1981-12-02

Description

(54) IMPROVEMENTS IN OR RELATING TO THE RECOVERY OF A SALT MIXTURE FROM A GAS (71) We, THE LUMMUS COMPANY, of 1515 Broad Street, Bloomfield, New Jersey 07003, United States of America, a Company organized and existing under the Laws of the State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the recovery of a salt mixture from a gas and more particularly to the removal of salts from the effluent stream from a molten salt reactor.

In many processes, a molten salt mixture containing the higher and lower valent chlorides of a multivalent metal is employed as a reactant and/or catalyst for a chemical conversion. Thus, for example, a molten salt mixture containing the higher and lower valent chlorides of a multivalent metal such as copper is employed for the production of a chlorinated hydrocarbon. In such a process, a hydrocarbon such as ethane is contacted with the salt mixture to produce chlorinated product. In such a process, a small amount of the molten salt mixture is vaporised and leaves the reaction chamber. with the gaseous effluent stream, and such vaporised salt mixture is generally removed from the effluent stream by direct contact with an aqueous hydrogen chloride stream.

There is a need for an improvement in the means of separating such vaporised molten salts from the effluent stream.

According to this invention, there is provided a process for recovering a salt mixture from a gas produced in a reaction zone employing a molten salt mixture containing cuprous chloride and cupric chloride, the process comprising: (a) withdrawing from the reaction zone a gas containing reaction product and vaporised molten salt mixture, the vaporised molten salt mixture comprising cuprous and cupric chloride; (b) contacting the said gas with solid particles, the solid particles being at a temperature at which at least some of the vaporised molten salt mixture condenses from the gas onto the solid particles, the gas contacting being such that solid fines comprising cuprous chloride and cupric chloride are attrited from the solid particles in equilibrium with the said condensation; (c) separating the gas, containing the solid fines, from the solid particles; (d) separating at least some of the solid fines from the gas; (e) recycling at least some of the solid fines to the reaction zone; (f) cooling the solid particles to maintain them at a temperature at which vaporised molten salt mixture condenses from the gas; and (g) employing the cooled solid particles in step (b).

Preferably, the gas withdrawn from the reaction zone is substantially free of water.

The solid particles employed for condensing the vaporised salt mixture from the gas may be any one of a wide variety of particles which do not adversely affect the components in the gas. Representative examples of such particles include: sand, glass beads, ceramics, metals, metal salts and, in particular, copper and copper salts.

The contacting between the solid particles and the gas, containing vaporised salt mixture, may be effected by adding the solid particles to the gaseous effluent in a dilute phase transport reactor or by passing the gaseous effluent through a bed of the particles preferably as fluidized bed. The particles are maintained at a temperature at which the vaporized salt mixture condenses onto the solid particles, with such temperature being one at which the vaporised salt mixture is condensed as a solid onto the particles.

Conveniently, the solid particles employed for condensing the vaporised salt mixture are maintained at a temperature of 250"F to 550"F, and preferably at a temperature of 350'F to 500"F.

The bed of particles may be conveniently maintained at the required temperature by indirect heat transfer for example by employing a heat exchange coil within the bed or by employing a jacketed vessel. A wide variety of heat transfer fluids may be employed for maintaining the bed of particles at the desired temperature, but the heat transfer fluid is preferably water to generate steam at a medium pressure. Thus, by the use of a cooling coil containing water, heat present in the gas may be conveninetly recovered byShe generation of steam.

In the embodiment whem solid particles are added to the gas, the solid particles are then separated from the gas and cooled ibr re-use in the contacting with the gas. Tie particles may be cooled by indirect beat transfer, for example by cooling the parties in a separate vessel by the use of a beat exchange coil in a bed of the particles Or by employing a jacketed vessel. Heat may be suitably recovered, for example by tile gener- ation of steam.

The condensed vaporized salt mixture is attrited as fines from the surface Of the particles and carried into the gas steam.

Such attrited solid salt mixture fines can be removed from the gas stream by any one of a wide variety of gas-solid separation t niques, such as filtration. The attrition I- reaches an equilibrium with the deposiin rate of the vaporised salt mixture on the cooled particles, and removal of parties which have overgrown in size as a result of the coating Of salt mixture is not reqilid.

Thus, in an equilibrium state, vaporized salt mixture is removed from the gas one the particles, with solid fines of the salt mixture being returned to the gas for subsequent removal for example by filtration.

It is advantageous to employ solid particles which are either copper or a copper salt which is present in the reaction zone (i.e.

cuprous chloride and/or cupric chloride), because this permits periodic return of at least some of the particles, coated with condensed vaporised salt mixture, to the reaction zone, should this be desired.

In the case where the particles cannot be directly returned to the reaction zone, condensed salt can be easily removed from the particles in a separate operation, such as by washing the particles with water or aqueous hydrogen chloride to dissolve the salt, with the salt solution then being returned to the reaction zone.

The molten salt mixture, contaiing the higher and lower valent chlorides of copper, can be employed in a wide variety of systems, and as a result the present invention is applicable to a wide variety of processes.

Thus, for example, molten salts employing the higher and lower valent chlorides of copper can be employed for the production of chlorinated hydrocarbons. In such systems, the salt mixture can be contacted with a hydrocarbon either in the presence or ab- sence of chlorine and/or hydrogen chloride, and the salt mixture may include or exclude the corresponding oxychloride. Such processes are described, for example, in U.S.

Patents Nos. 3,557,229; 3,879,480; 3,879,482; 3,865,886; 4,107,122; and 4,119,705. Simi larly, molten salts containing the higher and lower valent chlorides of a multivalent metal hive also Icen employed for dehydrogena 6oa prozssu, as described, for example in Tut5. Patent No.3,637,5; for the production of aIcohdls, as described in U.S. Patent No.

3,745,t93; for dealkylation, as described in U.S. Patent No. 3,536,773; for effecting coupling as described in U.S. 3,947,489; for oxidation as described in U.S. 3,641,157 and U.S. 3,947,489; for oxidation as described in US. 3,641,157 and U.S. 3,869,518; and for the production of nitriles, as described in U.S. Patent No. 3,865,238. The molten salt mixture can also he employed for the production of chlorine, in which case chlorine is slipped from a molten salt mixtuTe containing the higher and lower valent chlorides of a multivalent metal, resulting in a reduction in the higher valent content of such a salt mixture. Such a process is described, for example, in U.S. Patent Specification No.

4,119,705.

A process in accordance with the present invention may be employed in any one of the hereinabove-noted processes, when the molten salt mixture comprises cuprous and cupric chloride.

In order that the invention may be more readily understood and so that further fea tures thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings, in which: FIGURE I is a simplified schematic flow diagram of one embodiment of the present invention; and FIGURE 2 is a simplified schematic flow diagram of another embodiment of the present invention.

The present invention will be particularly described with respect to embodiments for the production of a chlorinated hydrocarbon; however, it is to be understood the scope of the invention is .not to be limited to these particular specific embodiments in that the present invention is applicable to the use of molten salt mixtures for the production of other than chlorinated hydrocarbons.

Referring to Figure 1, a hydrocarbon feed in line 10 is introduced into a chlorination reactor, schematically generally indicated as 11, wherein the hydrocarbon feed is contacted with a molten salt mixture containing the higher and lower valent chlorides of copper, and preferably also a melting point depressant, such as potassium chloride, which mixture is introduced into reactor 11 through line 12. As a result of the contact between the hydrocarbon and molten salt mixture, chlorination is effected to produce a chlorinated hydrocarbon.

A gaseous effluent, which includes a small amount of vaporized molten salt mixture, is withdrawn from reactor 11 through line 13 and is introduced into a cooling vessel, schematically generally indicated as 14. The cooling vessel 14 contains a bed of solid particles, such as copper particles, with the bed schematically being indicated as 15. The bed is maintained in a fluidized state by introducing the gaseous effluent in line 13 at a superficial velocity to maintain such a fluidized state.

The bed 15 of solid particles is maintained at a temperature at which the vaporized salt present in the gaseous effluent in line 13 is condensed onto the bed of solid particles. For this purpose, the bed is provided with a cooling coil schematically indicated as 16, which is provided with a heat transfer cooling fluid such as water. More particularly, water is introduced into the coil 16 through line 17 and as a result of the indirect heat transfer, steam is generated from the water in coil 16. A steam water mixture is withdrawn from coil 16 through line 18 and introduced into a vapour liquid separation tank, schematically generally indicated as 19.

Steam is withdrawn from tank 19 through line 20, with water being withdrawn therefrom through line 17. Make-up water is introduced into tank 19 through line 21.

Gaseous effluent, free of vaporised salt mixture is withdrawn from cooling tank 14 through line 22 which includes a cyclone separator 23 for removing entrained particles. As a result of the contact between the gaseous effluent and the fluidized solid particles in vessel 14, portions of the salt mixture which has condensed onto the said particles are attrited from the solid particles as fines, and such fines remain in the gaseous stream subsequent to passage through the cyclone separator 23. As a result, the gaseous effluent containing such fines in line 24 is introduced into a suitable solid separation device, such as filter 25, for separating such fines from the gaseous effluent. Such fines are returned to the reactor 11 through line 26. The gaseous effluent, now free of fines, is withdrawn from filter 25 through line 27 for further processing. As hereinabove noted, attrition of the condensed salt mixture will reach equilibrium with deposition of the vaporised molten salt mixture from the gaseous effluent. Thus, additional removal of condensed salt mixture from the particles is not necessary but, if desired, solid particles, may be withdrawn from vessel 14 through line 28 for further processing to remove such condensed salt mixture. In the case where such solid particles are copper, as particularly described, the copper particles containing condensed salt mixture can be passed to the molten salt mixture storage tank whereby the recovered vaporised molten salt is returned to the system.

The molten salt mixture withdrawn from reactor 11 through line 31 is introduced into an oxidation reactor schematically indicated as 32 which includes suitable gas-liquid contacting means, schematically indicated as 33. In reactor 32, the molten salt mixture is contacted with molecular oxygen introduced through line 34 and chlorine and/or hydrogen chloride introduced through line 35 to effect addition of chlorine values to the molten salt for subsequent use in reactor 11.

As hereinabove noted, alternatively, such chlorine values in the form of chlorine can be added to reactor 11 for effecting chlorination of the hydrocarbon in the presence of the molten salt mixture.

As a further alternative, the oxidation reactor 32 may be operated in a manner such that the molten salt mixture withdrawn therefrom includes oxychloride whereby an oxychlorination reaction is effected in reactor 11.

As should be apparent, the overall invention is not limited to a specific processing scheme for employing the molten salts in that processes in accordance with the invention are generally applicable to a wide variety of processes employing molten salts in which the gaseous effluent contains vaporized molten salt mixture.

As hereinabove noted, the present invention is particularly suitable for removing vaporized molten salt mixture from a gaseous effluent in which oxygen is not present in reactor 11 either in gaseous form or in a chemically combined form such as the oxide or oxychloride, in that such effluents are free of water, and the process for separating vaporized salt mixture does not add water to the system.

a gaseous effluent is also withdrawn from reactor 32 through line 36, and if desired, vaporized molten salt mixture, if present in the effluent in line 36, can also be removed in accordance with the present invention. However, this is not shown in the drawing.

Referring now to Figure 2, which illustrates only the portion of the overall system employed for removing vaporized molten salt mixture from the gaseous effluent, a gaseous effluent, for example as described with reference to Figure 1, which includes a small amount of vaporized molten salt mixture, in line 101, is contacted with solid particles introduced through line 102, which are at a temperature at which vaporized molten salt mixture present in the gaseous effluent is condensed onto the solid particles.

The solid particles and gaseous effluent flow through line 103 in a direct contact relationship, resulting in cooling of the gaseous effluent and condensation of vaporized molten salt mixture onto the solid particles.

The mixture of gaseous effluent and solid particles is introduced into a gas-solid separator 104 to effect separation of the solid particles having condensed salt mixture thereon from the gaseous effluent.

Gaseous effluent, free of vaporized salt mixture and containing solid fines of the salt mixture attrited from the solid particles, is withdrawn from separator 104 through line 105 and introduced into a solid separation device, such as a filter 106, for separating such fines which may be recycled to the reaction system through line 106a. The gaseous effluent, now free of fines, is withdrawn from filter 106 through line 107 for further processing.

Solid particles, having salt mixture coated thereon, are withdrawn from separator 104 through line 111 and introduced into a cooling device 112 for reducing the temperature of the solid particles. As particularly shown, the solid particles are maintained as a fluidized bed in vessel 112 by a suitable fluidizing gas introduced through line 113.

The fluidizing gas can be an appropriate recycle gas from the process.

In vessel 112, the solids are cooled in a fluidized state by indirect heat transfer with water introduced through line 114, with the water being converted to steam. A steam water mixture is withdrawn from vessel 112 through line 115 and introduced into separator 116, which is-provided with feed water through line 117. Steam is withdrawn through line 118 for processing use, with water being returned to vessel 112 through line 114 for generation of steam therefrom.

The cooled solids are withdrawn from vessel 112 through line 102 for effecting cooling of the gaseous effluent and condensing vaporized salt mixture.

The fluidizing gas is withdrawn from vessel 112 through line 121 and combined with the effluent gas in separator 104.

As described with reference to the embodiment of Figure 1, if required, overgrown solid particles may be withdrawn for further treatment to remove condensed salt mixture therefrom.

The embodiment of Figure 2 offers an advantage over the embodiment of Figure 1 in that a smaller fluidized bed vessel is required for cooling the solids in the embodiment of Figure 2. In addition, the pressure drop in the effluent cooling system is reduced.

The preferred embodiments of the present invention have been found to be particularly advantageous in that they permit effective removal of vaporized molten salts without the use of aqueous hydrogen chloride, thereby avoiding corrosion problems. Moreover, heat can be effectively recovered from the system by use of the indirect heat transfer with a suitable heat transfer fluid. Moreover, since the cooler is operated at moderate temperature and is dry, the major part of the cooler can be made of carbon steel.

WHAT WE CLAIM IS: 1. A process for recovering a salt mixture from a gas produced in a reaction zone employing a molten salt mixture containing cuprous chloride and cupric chloride, the process comprising: a. withdrawing from the reaction zone a gas containing reaction product and vaporised molten salt mixture, the vaporised molten salt mixture comprising cuprous and cupric chloride; b. contacting the said gas with solid particles, the solid particles being at a temperature at which at least some of the vaporised molten salt mixture condenses from the gas onto the solid particles, the gas contacting being such that solid fines comprising cuprous chloride and cupric chloride are attrited from the solid particles in equilibrium with the said condensation; c. separating the gas, containing the solid fines, from the solid particles; d. separating at least some of the solid fines from the gas; e. recycling at least some of the solid fines to the reaction zone; f. cooling the solid particles to maintain them at a temperature at which vaporized molten salt mixture condenses from the gas; and g. employing the cooled solid particles in step (b).

2. A process according to claim 1, wherein, in step "b" then solid particles are employed as a fluidized bed and are cooled by indirect heat transfer to a heat transfer fluid thereby to recover heat.

3. A process according to claim 1, wherein the said contacting in step "b" of the gas and the solid particles is effected by suspending the solid particles in the gas, the solid particles, after the said separation in step "c", being cooled in a fluidized bed by indirect heat transfer to a heat transfer fluid to recover heat.

4. A process according to claim 2 or 3 wherein the heat transfer fluid is water.

5. A process according to claim 2 or 3, wherein the fluidized solid particles are maintained at a temperature from 250 F to 550' F.

6. A process according to claim 5 wherein the said temperature is from 350 F to 500' F.

7. A process according to any one of claims 1 to 4, wherein the gas withdrawn from the reaction zone is substantially free of water.

8. A process according to any one of the preceding claims wherein the solid particles comprise one or more of copper, cuprous chloride and cupric chloride.

9. A process according to claim 8 wherein at least some of the solid particles containing condensed salt mixture are periodically introduced into the reaction zone.

10. A process according to Claim 1 and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mixture and containing solid fines of the salt mixture attrited from the solid particles, is withdrawn from separator 104 through line 105 and introduced into a solid separation device, such as a filter 106, for separating such fines which may be recycled to the reaction system through line 106a. The gaseous effluent, now free of fines, is withdrawn from filter 106 through line 107 for further processing. Solid particles, having salt mixture coated thereon, are withdrawn from separator 104 through line 111 and introduced into a cooling device 112 for reducing the temperature of the solid particles. As particularly shown, the solid particles are maintained as a fluidized bed in vessel 112 by a suitable fluidizing gas introduced through line 113. The fluidizing gas can be an appropriate recycle gas from the process. In vessel 112, the solids are cooled in a fluidized state by indirect heat transfer with water introduced through line 114, with the water being converted to steam. A steam water mixture is withdrawn from vessel 112 through line 115 and introduced into separator 116, which is-provided with feed water through line 117. Steam is withdrawn through line 118 for processing use, with water being returned to vessel 112 through line 114 for generation of steam therefrom. The cooled solids are withdrawn from vessel 112 through line 102 for effecting cooling of the gaseous effluent and condensing vaporized salt mixture. The fluidizing gas is withdrawn from vessel 112 through line 121 and combined with the effluent gas in separator 104. As described with reference to the embodiment of Figure 1, if required, overgrown solid particles may be withdrawn for further treatment to remove condensed salt mixture therefrom. The embodiment of Figure 2 offers an advantage over the embodiment of Figure 1 in that a smaller fluidized bed vessel is required for cooling the solids in the embodiment of Figure 2. In addition, the pressure drop in the effluent cooling system is reduced. The preferred embodiments of the present invention have been found to be particularly advantageous in that they permit effective removal of vaporized molten salts without the use of aqueous hydrogen chloride, thereby avoiding corrosion problems. Moreover, heat can be effectively recovered from the system by use of the indirect heat transfer with a suitable heat transfer fluid. Moreover, since the cooler is operated at moderate temperature and is dry, the major part of the cooler can be made of carbon steel. WHAT WE CLAIM IS:

1. A process for recovering a salt mixture from a gas produced in a reaction zone employing a molten salt mixture containing cuprous chloride and cupric chloride, the process comprising: a. withdrawing from the reaction zone a gas containing reaction product and vaporised molten salt mixture, the vaporised molten salt mixture comprising cuprous and cupric chloride; b. contacting the said gas with solid particles, the solid particles being at a temperature at which at least some of the vaporised molten salt mixture condenses from the gas onto the solid particles, the gas contacting being such that solid fines comprising cuprous chloride and cupric chloride are attrited from the solid particles in equilibrium with the said condensation; c. separating the gas, containing the solid fines, from the solid particles; d. separating at least some of the solid fines from the gas; e. recycling at least some of the solid fines to the reaction zone; f. cooling the solid particles to maintain them at a temperature at which vaporized molten salt mixture condenses from the gas; and g. employing the cooled solid particles in step (b).

10. A process according to Claim 1 and

substantially as herein described with reference to Figure 10 of the accompanying drawings.

11. A process according to Claim 1 and substantially as herein described with reference to Figure 2 of the accompanying drawings.

12. An effluent, substantially free of vaporized salt, whenever produced by a process according to any one of the preceding claims.

13. A salt mixture whenever recovered by a process according to any one of claims 1 to .11.