CN114570437B

CN114570437B - Method for removing sulfur in catalyst for moving bed propane dehydrogenation

Info

Publication number: CN114570437B
Application number: CN202011401309.3A
Authority: CN
Inventors: 王春明; 刘昌呈; 马爱增
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2023-07-14
Anticipated expiration: 2040-12-02
Also published as: CN114570437A

Abstract

A process for removing sulfur from a catalyst used in moving bed propane dehydrogenation comprising the steps of: (1) The method comprises the steps of (1) leading propane into a reaction zone of a moving bed to contact with a propane dehydrogenation catalyst, carrying out propane dehydrogenation reaction at 580-650 ℃, leading a sulfur-containing spent catalyst flowing out of the reaction zone into a regeneration zone, carrying out scorching and oxychlorination to obtain a regenerated catalyst, (2) feeding the regenerated catalyst into a reduction zone, leading hydrogen containing 0.02-0.8% by volume of water vapor into the reduction zone, carrying out reduction and desulfurization on the regenerated catalyst at 500-600 ℃. The method can effectively remove sulfate radical in the catalyst and improve the reaction performance of the catalyst.

Description

Method for removing sulfur in catalyst for moving bed propane dehydrogenation

Technical Field

The invention relates to a desulfurization method of a sulfur-containing catalyst, in particular to a method for removing sulfur in a catalyst used for dehydrogenation of moving bed propane.

Background

Propylene is an important basic organic chemical raw material and is widely applied to the production of various chemical products such as polypropylene, acetone, acrylic acid, acrylonitrile, propylene oxide and the like. Currently, propylene supplies are mainly derived from the byproducts of catalytic cracking processes in the naphtha cracking to ethylene and petroleum refining. Since the 90 s of the last century, the demand for propylene has been increasing, and the conventional propylene production process has not been able to meet the demand for propylene in the chemical industry, so that some alternative process technologies have been developed rapidly, in which the process for producing propylene by dehydrogenation of propane is developed rapidly, and in which the moving bed propane dehydrogenation process using a platinum-based noble metal catalyst is dominant.

The catalyst adopted in the moving bed propane dehydrogenation process is a platinum-containing noble metal catalyst, alumina is used as a carrier, and in order to ensure that the catalyst has good fluidity, the catalyst needs to be made into pellets, the particle size of the pellets is usually 1.2-2.5 mm, and the pellets continuously flow in a reaction zone and a regeneration zone in the process operation process. The propane in the reactor is dehydrogenated to generate propylene under the action of the catalyst, the catalyst is deactivated in the reactor due to carbon deposition and the like, the deactivated catalyst is conveyed to the regenerator, the deactivated catalyst in the regenerator is subjected to a burning regeneration process and then enters the reducer for reduction again, so that the performance of the catalyst is recovered, and the reduced catalyst continuously enters the reactor for catalytic reaction.

In the moving bed propane dehydrogenation process, the reaction is usually carried out at a high temperature of above 600 ℃, so that carbon deposition caused by iron and chromium contained in the metal wall of the reactor is avoided in order to maintain the normal operation of the reaction, sulfur injection is required to passivate the wall, a certain amount of sulfur-containing compounds such as dimethyl disulfide (DMDS) are added into propane raw materials, and the injected sulfur reacts with the metal wall to generate metal sulfides, so that the occurrence of carbon deposition reaction catalyzed by the wall is prevented. However, the injected sulfur can be adsorbed on the catalyst besides reacting with the metal wall of the reactor, and the sulfur can be oxidized into sulfate radical in the oxygen-containing atmosphere after the high-temperature burning process in the regeneration process, thereby influencing the performance of the catalyst. When a large amount of sulfate is present in the catalyst, the catalyst performance is greatly reduced even through activation reduction, which is considered to be related to the presence of sulfate preventing effective dispersion of platinum. In general, sulfur adsorbed on the catalyst can be removed by hot hydrodesulfurization, i.e., treating the catalyst with high temperature hydrogen. However, it has been found in laboratory studies and engineering practice that it is difficult to effectively remove sulfur from the catalyst using a hot hydrodesulfurization process. Apesteguia et al have found that sulfate on platinum-containing alumina catalysts can be reduced to H under hot hydrogen reduction conditions at 500 DEG C ₂ S, but H is generated ₂ S is readily re-adsorbed onto the catalyst (Journal of Catalysis, vol.106, 73-84).

CN1246517A discloses a method for removing sulfate radical from semi-regenerated reforming catalyst, in which hydrogen and organic chloride capable of decomposing hydrogen chloride are introduced into catalyst bed layer in reactor under the condition of 400-600 deg.C, and then introduced into reactorThe amount of the organic chloride added is 0.2-8% of the mass of the catalyst based on chlorine element, and the method can reduce sulfate radical in the catalyst to H ₂ S, desorbing and then recovering the activity of the catalyst.

CN102166534a discloses a method for removing sulfate radical from a continuous reforming catalyst, which comprises injecting an organic chloride which decomposes hydrogen chloride at a reduction temperature into a hydrogen stream entering a catalyst reduction zone under the normal operation conditions of a continuous reforming device reaction and a catalyst recycling system, and allowing the decomposed hydrogen chloride to penetrate a catalyst bed layer, wherein the injection amount of the organic chloride is 0.02-0.5 mass% of the catalyst recycling amount based on chlorine element, and the method can remove sulfate radical in the reforming catalyst under the condition that the continuous reforming device is not stopped.

Disclosure of Invention

The invention aims to provide a method for removing sulfur in a catalyst used for moving bed propane dehydrogenation, which can effectively remove sulfate radical in the catalyst and improve the reaction performance of the catalyst.

The invention provides a method for removing sulfur in a catalyst used for moving bed propane dehydrogenation, which comprises the following steps:

(1) Propane is introduced into a reaction zone of a moving bed to contact with a propane dehydrogenation catalyst, propane dehydrogenation reaction is carried out at 580-650 ℃, a sulfur-containing spent catalyst flowing out from the reaction zone enters a regeneration zone, scorching and oxychlorination are carried out to obtain a regenerated catalyst,

(2) The regenerated catalyst is sent into a reduction zone, hydrogen containing 0.02-0.8% of water vapor by volume is introduced into the reduction zone, the regenerated catalyst is reduced at 500-600 ℃, and desulfurization is carried out.

The method of the invention gives up the prior method for desulfurizing the chlorine-containing organic compounds or the hot hydrogen used in the reduction zone, and adopts the method of injecting proper amount of water into the hydrogen entering the reduction zone to remove sulfate radical in the catalyst, which has low cost, high safety and easy implementation. The method can effectively remove sulfate radical in the regenerated catalyst, improve the activity and propylene selectivity of the catalyst, improve the operation benefit of the device and prolong the operation period of the moving bed propane dehydrogenation device.

Drawings

FIG. 1 is a schematic flow chart of the method of the present invention.

Detailed Description

The moving bed propane dehydrogenation process uses a small sphere dehydrogenation catalyst, and in order to prevent too much carbon deposition on the catalyst, the catalyst continuously flows between a reaction zone and a regeneration zone, and the reaction and the regeneration are circularly carried out. The propane dehydrogenation process belongs to an endothermic reaction, and in order to maintain the reaction temperature, 3 to 4 reactors are usually arranged in a reaction zone and a heating furnace is arranged to increase the temperature of materials. In order to achieve the desired conversion of propane by dehydrogenation, the dehydrogenation is usually carried out at a high temperature of 580 to 650 ℃. At high temperature, carbon deposition on the reactor wall is often caused by the catalysis of iron or chromium in the metal wall, and the carbon deposition on the reactor wall can cause the blockage of a screen in the reactor, thereby seriously affecting the stable operation of the device. In order to suppress carbon deposition initiated by the walls of the apparatus, it is generally necessary to inject sulfur-containing compounds, such as dimethyl disulfide, into the reaction mass. The sulfide is decomposed under the high-temperature hydrogen atmosphere to generate hydrogen sulfide, and the hydrogen sulfide reacts with metal in the wall to generate metal sulfide, so that the reaction of deep dehydrogenation of the metal catalytic hydrocarbon to generate carbon deposit is inhibited.

The introduction of sulfide not only inhibits carbon deposition on the reactor wall, but also can be adsorbed by the catalyst, and sulfur adsorbed on the catalyst is converted into sulfate radical in a high-temperature oxygen-containing environment such as scorching, oxychlorination and the like in the regeneration process, so that the unreduced regenerated catalyst contains the sulfate radical, and the content of the sulfate radical can reach 0.5 mass percent in terms of sulfur element. The existence of the sulfate radical can influence the dispersion of noble metal in the catalyst, and quicken the carbon deposition rate of the catalyst, thereby influencing the activity of the catalyst.

The method of the invention introduces hydrogen containing a certain amount of water vapor into the reduction zone of the regenerated catalyst of the moving bed propane dehydrogenation reaction device, and utilizes the gaseous water to replace hydrogen sulfide in the catalyst, which is formed by reducing and converting sulfate radical by hydrogen, thereby effectively removing the sulfate radical in the catalyst carrier, preventing the accumulation of the sulfate radical from influencing the catalyst performance and improving the regeneration performance of the catalyst.

The method (1) comprises the steps of carrying out propane dehydrogenation reaction in a reaction zone of a moving bed device and regenerating a spent catalyst obtained after the reaction.

(1) The temperature of the step of the propane dehydrogenation reaction is preferably 590-640 ℃, the pressure is preferably 0.1-0.4 MPa, the molar ratio of hydrogen to propane is preferably 0.2-1.0, and the mass space velocity of the propane is preferably 0.5-15 hours ^-1 More preferably 3 to 10 hours ^-1 。

The propane dehydrogenation catalyst preferably comprises an alumina carrier and platinum in an amount of 0.1 to 2.0 mass%, tin in an amount of 0.1 to 2.0 mass%, a group IA metal in an amount of 0.5 to 5.0 mass% and halogen in an amount of 0.3 to 5 mass% calculated on the basis of the alumina carrier. Preferably, the propane dehydrogenation catalyst has a platinum content of 0.1 to 1.0 mass%, a tin content of 0.1 to 1.0 mass%, and a halogen content of 0.3 to 3.0 mass%. The group IA metal is preferably potassium and the halogen is preferably chlorine. The bulk density of the propane dehydrogenation catalyst may be from 0.5 to 0.7g/mL.

The alumina carrier in the propane dehydrogenation catalyst is preferably theta-alumina, and the alumina carrier is in the shape of small spheres, and the particle size of the small spheres can be 1.2-2.5 mm, preferably 1.4-2.0 mm.

(1) The reaction zone may comprise 1 to 4 reactors, more than one of which are connected in series, and the catalyst flows from the upstream reactor to the downstream reactor and then flows out from the last reactor to obtain the spent catalyst. The upstream and downstream are defined according to the flow direction of the reaction materials, and the feeding end is the upstream. The spent catalyst enters a regeneration zone for burning and oxychlorination to obtain a regenerated catalyst, the regenerated catalyst enters a reduction zone for reduction, and the reduced catalyst enters a reaction zone again for reaction, and a catalyst cycle is completed. The mass rate of catalyst circulation, i.e., the mass rate of catalyst movement in the moving bed apparatus, is the mass of catalyst transferred from the reaction zone to the regeneration zone or from the regeneration zone to the reaction zone by pneumatic transfer or the like per unit time. The regeneration zone is preferably a regenerator in which the burning and oxychlorination of the spent catalyst can be accomplished sequentially from top to bottom. The reduction zone of step (2) is preferably a reduction reactor.

(1) The sulfur-containing spent catalyst flowing out of the reaction zone enters a regeneration zone for burning at 470-600 ℃, preferably 490-590 ℃, and the gas used for burning is nitrogen containing 0.1-3.0% by volume of oxygen, preferably 0.3-1.5% by volume of oxygen, and the residence time of the spent catalyst in the burning zone is preferably 1-8 hours.

The burnt catalyst is subjected to oxychlorination to redisperse the platinum in the catalyst. The oxychlorination temperature may be 470 to 570 ℃, preferably 490 to 550 ℃, the gas used for oxychlorination is chlorine-containing air, chlorine in the chlorine-containing air is derived from chlorine gas or an organic chloride capable of decomposing chlorine, the organic chloride is tetrachloroethylene or dichloroethane, and the chlorine content in the chlorine-containing air is 0.05 to 1 mass%, preferably 0.1 to 0.5 mass%. The residence time of the catalyst in the oxychlorination zone is preferably from 1 to 4 hours.

The scorching and oxychlorination of the catalyst may be carried out in the same regenerator, the pressure of which may be between 0.08 and 0.3MPa, preferably between 0.1 and 0.2MPa. The catalyst after oxychlorination can be conveyed to the reduction zone after being cooled.

(1) The sulfur content in the regenerated catalyst described in the step may be 0.05 to 0.5 mass% based on the carrier, and further may be 0.1 to 0.5 mass%. The sulfur in the regenerated catalyst is the sulfur element contained in sulfate radical.

The method (2) comprises the steps of reducing the regenerated catalyst and removing sulfur in the catalyst in the reduction process. (2) The water content in the hydrogen gas of the aqueous gas in the step is preferably 0.1 to 0.6% by volume. The ratio of the mass rate of the water gas introduced into the reduction zone to the mass rate of the catalyst circulation is 0.02 to 2.0%, preferably 0.05 to 1.0%.

Preferably, the mass ratio of the amount of water gas fed to the reduction zone per hour in step (2) to the sulfur content of the catalyst fed to the reduction zone per hour is from 0.5 to 2, preferably from 0.6 to 1.5.

(2) The volume ratio of the hydrogen gas of the water-containing gas which is introduced into the reduction zone to the catalyst of the reduction zone in the step is 200 to 1000 hours ^-1 Preferably 400 to 1000 hours ^-1 . The temperature of the hydrogen gas containing water vapor may be 550 to 600 ℃, preferably 560 to 590 ℃.

(2) The residence time of the regenerated catalyst in the reduction zone is from 1 to 6 hours, preferably from 1 to 4 hours. The reduction temperature is preferably 510 to 570 ℃, and the pressure is 0.1 to 0.5MPa, preferably 0.1 to 0.4MPa.

The process according to the invention is described in detail below with reference to the accompanying drawings.

In fig. 1, propane enters a reactor 1 of a moving bed through a pipeline 8, a propane dehydrogenation catalyst flows in the reactor 1, and is contacted with propane to carry out propane dehydrogenation reaction, and a reaction product flows out of the reactor 1 through a pipeline 9 to carry out subsequent separation treatment to obtain propylene. The spent catalyst flows out of the reactor 1, enters the first lifter 2 through the catalyst discharging pipe 10, enters the hopper 3 through the lifting pipe 12 under the action of lifting gas entering through the pipe 11, and enters the regenerator 4 through the catalyst discharging pipe 13, and in the regenerator 4, the burning and oxychlorination of the spent catalyst are sequentially completed from top to bottom to obtain the regenerated catalyst. Regenerated catalyst enters the second riser 5 via a feed line 14 and enters the reduction reactor 6 via a riser line 16 under the influence of lift gas from line 15. The heated hydrogen is mixed with water from a pipeline 17 through a pipeline 19, the water is gasified after being heated to form mixed gas with hot hydrogen, the mixed gas is hydrogen containing water, the hydrogen enters a reduction reactor 6 from the lower part, the regenerated catalyst is reduced, sulfate radicals in the regenerated catalyst are removed, the reduced catalyst enters the reactor 1 again through a discharging pipe 7, the gas obtained after reduction is discharged from the upper part of the reduction reactor 6 through a pipeline 18 and enters a drying unit and a desulfurization unit of the device for treatment, and the water and sulfur in the hydrogen are removed for reuse (not shown in the figure).

The invention is further illustrated by the following examples, but is not limited thereto.

In the examples and the comparative examples, sulfur content and carbon content in the catalyst were measured by using a carbon-sulfur meter, the sample was dried at 110 to 120 ℃ for 2 hours, then placed in a dryer to cool to room temperature, the sample was placed in a crucible to be weighed, metallic iron was added as a fluxing agent, and then the crucible was placed in a high-frequency induction furnace, and oxygen was introduced to burn at 1200 ℃. Generated CO ₂ 、SO ₂ The gas is absorbed by an infrared absorption cell of an instrument to obtain an infrared spectrumThe carbon content and sulfur content were measured by infrared spectroscopy.

Example 1

(1) Propane dehydrogenation reaction is carried out

100g of propane dehydrogenation catalyst A is taken, the carrier of the catalyst A is small spherical theta-alumina, the particle size is 1.4-2.0 mm, the bulk density is 0.63g/mL, and the catalyst A contains 0.30 mass percent of platinum, 0.50 mass percent of tin, 1.3 mass percent of potassium and 1.3 mass percent of chlorine based on the carrier.

Loading the above propane dehydrogenation catalyst into a fixed bed reactor, introducing propane, and feeding propane at 620 deg.C and 0.21MPa for 9 hr at mass space velocity ^-1 The propane dehydrogenation reaction was carried out for 50 hours at a hydrogen/propane molar ratio of 0.5. An amount of dimethyl disulfide (DMDS) was injected into the propane feed, with a mass content of sulfur in the propane feed of 90ppm, calculated as elemental sulfur. The propane dehydrogenation gave a catalyst to be regenerated containing carbon, wherein the carbon content was 2.9 mass% and the sulfur content was 0.42 mass% based on the carrier.

(2) Catalyst regeneration

The spent catalyst obtained in the step (1) was burned with nitrogen containing 0.8% by volume of oxygen at 530 ℃ for 2 hours, then tetrachloroethylene was added to the air, and oxychlorination was carried out with the obtained chlorine-containing air at 530 ℃ for 2 hours, the chlorine content in the air being 0.16% by mass, and then cooled to room temperature, to obtain a regenerated catalyst. The pressure at which the scorching and oxychlorination were carried out was 0.11MPa.

(3) Catalyst reduction

Taking 100g of the regenerated catalyst obtained in the step (2), and the volume of the regenerated catalyst was 160mL, wherein the carbon content was 0.01 mass% and the sulfur content was 0.41 mass% based on the carrier. The catalyst is placed in a fixed bed reduction reactor, the temperature is raised to 520 ℃, hydrogen containing water vapor with the temperature of 520 ℃ and the water vapor content of 0.3 volume percent is introduced, the flow rate of the hydrogen containing water vapor is 2000mL/min, the regenerated catalyst is reduced for 1 hour under the conditions of 520 ℃ and 0.11MPa, sulfur in the catalyst is removed in the reduction process, the introduced water quantity is 0.29g, and the mass rate of the introduced water is 0.29g/h. In this case, the amount of the catalyst in the reducer corresponds to a catalyst circulation mass rate of 100g/h, and the mass ratio of the amount of water gas injected into the reducer per hour to the sulfur contained in the catalyst entering the reduction reactor per hour is 0.71. Catalyst B was obtained after reduction and its sulfur content is shown in Table 1.

Example 2

100g of the regenerated catalyst described in the step (2) of example 1 was taken and reduced according to the method of step (3), except that the reduction reactor was heated to 550℃and then the regenerated catalyst was reduced by introducing hydrogen gas containing water vapor at 550℃for 1 hour, to obtain catalyst C having a sulfur content shown in Table 1.

Example 3

Taking 100g of the regenerated catalyst in the step (2) in the example 1, and reducing according to the step (3), wherein the reduction reactor is heated to 550 ℃, hydrogen with the water vapor content of 0.5 volume percent and the flow rate of 2500mL/min at 550 ℃ is introduced into the reduction reactor to reduce the regenerated catalyst for 1 hour, sulfur in the catalyst is removed in the reduction process, the introduced water amount is 0.60g, the mass rate of introduced water is 0.6g/h, and the mass ratio of the water vapor injected into the reduction reactor per hour to the sulfur contained in the catalyst entering the reduction reactor per hour is 1.47. Catalyst D was obtained after reduction and its sulfur content is shown in Table 1.

Comparative example 1

100g of the regenerated catalyst described in example 1 (2) was taken and reduced in the process of step (3) except that no water was injected into the hydrogen gas, and catalyst E was obtained after reduction, the sulfur content of which was shown in Table 1.

Comparative example 2

100g of the regenerated catalyst described in the step (2) of example 1 was taken and reduced according to the method of step (3), except that the reduction reactor was heated to 550℃and the regenerated catalyst was reduced with the introduction of hydrogen containing dichloroethane at 550℃for 1 hour, the flow rate of the hydrogen containing dichloroethane was 2500mL/min, the total amount of the injected dichloroethane was 0.5g, the corresponding chlorine injection amount was 0.36g, and catalyst F was obtained after reduction, the sulfur content of which was shown in Table 1.

TABLE 1

Example number	Catalyst numbering	Sulfur content, mass%
			1	B	0.07
2	C	0.05
			3	D	0.03
Comparative example 1	E	0.25
			Comparative example 2	F	0.15

The data in Table 1 shows that the inventive process is effective in removing sulfur from the catalyst and significantly reducing the sulfur content of the reduced catalyst compared to the comparative process.

Examples 4 to 9

The following examples evaluate catalyst reactivity.

10g of catalyst is filled in a fixed bed reactor, mixed gas of hydrogen and propane is taken as raw material, the molar ratio of the hydrogen to the propane is 0.5, and the feeding mass space velocity of the propane is 9.0 hours ^-1 The reaction temperature was 620℃and the pressure was 0.21MThe reaction was carried out under Pa for 10 hours, and during this period, the sample was taken on line at intervals of 0.5 hour for chromatographic analysis, and propane conversion and propylene selectivity were calculated. The average results of the catalysts used in each example and reacted for 10 hours are shown in Table 2.

In the table 2 of the description of the present invention,

propane conversion = 1- (propane content in product/propane content in feed)

Propylene selectivity = propane mass corresponding to propylene produced/converted propane mass

Propylene yield = mass fraction propylene in product/mass fraction propane in feed

TABLE 2

As can be seen from Table 2, the method of the present invention is used for treating the catalyst by injecting water vapor during the hydrogen reduction process, so that sulfur in the catalyst can be effectively removed, the activity and selectivity of the catalyst can be greatly improved, and a higher propylene yield can be obtained, and the catalyst performance is comparable to that of the fresh catalyst A, which indicates that the catalyst performance is well recovered.

Claims

1. A process for removing sulfur from a catalyst used in moving bed propane dehydrogenation comprising the steps of:

(1) Introducing propane into a reaction zone of a moving bed to contact with a propane dehydrogenation catalyst, carrying out propane dehydrogenation reaction at 580-650 ℃, enabling a sulfur-containing spent catalyst flowing out of the reaction zone to enter a regeneration zone, and carrying out scorching and oxychlorination to obtain a regenerated catalyst, wherein the sulfur content of the regenerated catalyst is 0.05-0.5 mass% based on a carrier,

(2) Feeding the regenerated catalyst into a reduction zone, introducing hydrogen containing 0.02-0.8% by volume of water into the reduction zone, reducing the regenerated catalyst at 500-600 ℃, desulfurizing, wherein the ratio of the mass rate of the water introduced into the reduction zone to the catalyst circulation mass rate is 0.02-2.0%, and the amount of the water introduced into the reduction zone per hour and the catalyst entering the reduction zone per hour are equalThe mass ratio of sulfur to the catalyst in the reduction zone is 0.5-2, and the volume ratio of the hydrogen of the water-containing gas introduced into the reduction zone to the catalyst in the reduction zone is 200-1000 hours ^-1 The temperature of the hydrogen containing the water vapor is 550-600 ℃, the residence time of the regenerated catalyst in the reduction zone is 1-6 hours, and the reduction temperature is 510-570 ℃.

2. The process of claim 1, wherein (1) said reaction zone comprises 1 to 4 reactors, said reactors being connected in series when more than one is present, and (2) said reduction zone is a reduction reactor.

3. The method according to claim 1, wherein (1) the scorch temperature is 470-600 ℃, and the gas used for the scorch is nitrogen containing 0.1-3.0% by volume of oxygen; the oxychlorination temperature is 470-570 ℃, and the gas used for oxychlorination is chlorine-containing air, wherein the chlorine in the chlorine-containing air is from chlorine gas or organic chloride capable of decomposing chlorine.

4. A method according to claim 3, wherein the organic chloride is tetrachloroethylene or dichloroethane, and the chlorine-containing air has a chlorine content of 0.05 to 1.0 mass%.

5. The method according to claim 1, wherein the propane dehydrogenation catalyst in the step (1) comprises an alumina carrier and platinum in an amount of 0.1 to 2.0 mass%, tin in an amount of 0.1 to 2.0 mass%, a group IA metal in an amount of 0.5 to 5.0 mass% and halogen in an amount of 0.3 to 5 mass%, based on the alumina carrier.

6. The method of claim 5 wherein the group IA metal is potassium and the halogen is chlorine.