US3083239A - Treatment of catalyst in the chlorination of partially chlorinated hydrocarbons - Google Patents

Description

tties Unite f This invention relates to an improved process for the production of chlorinated olefins by heating partially chlorinated hydrocarbons in the presence of chlorine. It is particularly related to the preparation of trichlorethylene and perchlorethylene from tetrachlorethane.

The preparation of chlorinated olefins by thermal pyrolysis of partially chlorinated alkanes is old and well known to the art. Furthermore, the production of perchlorethylene by heating a mixture of tetrachlorethane and chlorine alone or in the presence of a catalyst was patented by Basel and Schaefier in 1938, US. Patent 2,139,219. Perchrlorethylene is produced by the stoic'hiometrical reaction of one mol of tetrachlorethane with one mol of chlorine as indicated by the equation:

Basel and Schaeffer also disclosed the simultaneous production of trichlorethylene and perehlorethylene by heat- .ing tetrachlorethane with less than one molecular equivalent of chlorine. In these processes, the chlorethane containing reaction mixture is passed through heated or catalytic reactors in the vapor state followed by condensation and refining of the chlorinated products.

The efiiciency of these chlorethylene processes is reduced'by incomplete utilization of chlorine. This is particularly undesirable since unreacted chlorine contaminates the by-product hydrogen chloride and limits its utility. Installation of a special purification step to re move chlorine from this material is undesirable since it adds appreciably to its cost. I

Copelin et al. application S.N. 755,150, filed August 15, 1958, now US. Patent 2,957,923 (October 25, 1960) discloses a process in which tetrachlorethane and chlorine are passed through a heated open-tube reaction zone, preferably in the range 350 to 525 0, followed by an unheated zone which is packed with metal particles, such as stainless steel, nickel-chromium alloy, etc. This process improves chlorine consumption and reduces formation of high boiling reaction by-products. It has now been discovered that chlorine consumption in this process can be still further improved by subjecting nickel or nickel alloys, preferably nickel-chromium alloys, employed as a packing in the unheated secondary reactor to, a special activation treatment.

One of the objects of this invention is to improve chlorine consumption in a process for the production of chlorinatedolefins by reactionof chlorine with a partially chlorinated alkane by contacting the reacting gases with a specially activated metal packing which serves as a chlorination catalyst. An additional object is to improve chlorine consumption in a process involving the reaction of tetrachlorethane with chlorine by use of a specially activated nickel or nickel alloy catalyst. A still further object is provision of an efficient chlorination catalyst consisting of activated nickel or nickel alloy particles.

These objects are attained by treating a nickel or nickelalloy packing, used in a reactor for producing chlorinated olefins by the gas phase reaction of chlorine on partially chlorinated alkanes, to the action of an oxygen-containing gas, preferably air and preferably in combination with steam, at temperatures of 350 C. or above. The pre- ECC ferred metal packings for the process of this invention are composed of nickel or a high nickel alloy, particularly the nickel-chromium alloy known commercially as Inconel. The term high nickel alloy refers to an alloy containing not less than 70% nickel. Inconel nickelchromium alloy is reported to contain 77% nickel, 15% chromium and 7% iron. The preferred treating temperature is in the range 400 to 550 C. In general, the preferred treating procedure involves heating with steam for about one hour, gradually adding air to the steam over an approximately 30-minute period and then heating with air for three to six hours. However, it should be noted that the time and order of treatment is not critical. Also, although a combination treatment with steam and air gives unexpectedly good results, a satisfactory activation can be obtained with the use of air alone. The nickel or nickel alloy packed reactor gradually becomes contaminated with carbon and solid reaction products on use which reduces the utility of the reactor and increases the pressure drop across the reactor. Treatment with air alone or in combination with steam burns out these impurities and improves chlorine consumption in the reaction process. In this connection, it was discovered that chlorine consumption improved progressively with successive air or steam-air treatments until, under preferred conditions, consumption was approximately 100% after three or more successive treatments. Prior to the use of the activation process of this invention, maximum chlorine consumption amounted to about whereas consumptions ranging from about to quantitative can be achieved with the activated metal packing.

Oxygen is the active ingredient in the air employed in the treating process and any oxygen-containing gas may be employed provided the non-oxygen portion of the gas is an inert diluent such as nitrogen, helium, carbon dioxide, etc. Pure oxygen may be used but its use 'in the absence of an inert diluent is not recommended since, unless great care is employed in controlling temperatures and rate of addition, uncontrolled oxidation of carbon and solid chlorohydrocarbon impurities will take place. When this occurs temperatures well over 550 C. are produced and tend to produce deformation and'metal creep in the reactor. Furthermore, hydrogen chloride liberated from solid chlorohydrocarbons in the reactor may cause serious corrosion at these temperatures. Even with air, care must be used to avoid the development of high temperatures and this can best be done by the procedure involving preliminary use of steam which is gradually mixed with air. The term oxygen-containing gas as employed in connection with this invention means oxygen or any combination of oxygen and an inert gas preferably nitrogen. Steam is describedas a special oxygen diluent since its use results in an unexpected improvement in the activated packing.

The invention is illustrated by the following experimental examples in which variously treated reactor pack- .ings were studied under substantially the same conditions. In these experiments, a mixture of tetrachlorethane and chlorine vapors containing approximately 10% by weight chlorine were passed through a heated cracking furnace followed by a packed reactor. In the cracking furnace the gases passed through 92" of diameter nickel-chromium alloy Inconel tubes. The packed reactor consisted of about 192" of 1" nickel-chromium alloy Inconel pipe. The cracking furnace was maintained at a temperature of approximately 440 to 460 C. whereas the temperature of the packed reactor ranged from about 350 to 370 C. The feed gas was passed through the reactor system at a rate of about 12 grams per minute.

XAMPLE 1 In this example, the packed reactor was filled with clean A" Inconel nickel-chromium alloy Raschig rings. A series of chlorine-tetrachlorethane reactions were then carried out in the cracker-packed reactor system as previously described. These chlorination reactions ranged in length from about to 6 hours with production of perchlorethylene and trichlorethylene as the principal products. Unreacted chlorine was determined at intervals of 1.5 to 2 hours throughout the reaction period by measuring the iodine liberated from a potassium iodide solution through which the total product gas had been bubbled for a two-minute period. Following each chlorination reaction, the packing was subjected to a heat treatment with air or air plus steam. In Table I, the percent chlorine con- .sumptions and the packing treatments preceding each re action are summarized.

Table I Packing Treatment Percent Reac- Chlorine Consumption tion ,No.

No. Time, Temp. Gas Individual Averhrs. degrees a Tests age None 8887-87-83 86 1 8 4.50 Air 95-878387 88 2 4 450-500 Air 92-83-79 85 3 5 500 Air 98999698 96 4 6 450 Air+ 100-100-100 100 Steam Preceding Reaction No. 5, the air-steam treatment of the packing comprised /2 hour air treatment, 1 /2 hours air plus steam and 4 hours air alone, all at 450 C. It should be noted that this treatment even at a 50 lower temperature than the previous air treatment made it possible to achieve quantitative chlorine consumption.

EXAMPLE 2 This example was identical to Example 1 except that the packed reactor contained nickel rings cut from A diameter tubing. In addition, the first chlorination reaction was carried out in two approximately 6-hour periods on consecutive days with air passing through the reactor as it cooled down and warmed up. The second chlorination ran for a complete 10 hours while the last two were given the usual 5- to 6-hour period.

In the ease of nickel, more treatments are required before the activation begins to take efiect than in the case of the Inconel nickel-chromium alloy of Example 1. However, it will be noted that after three treatments the chlorine consumption ranged from 94-96% in the first 3 to 4 hours as indicated by the first two chlorine consumption tests which as previously stated were made after intervals of 1.5 to 2.0 hours of operation.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

I claim:

1. In a process for the production of chlorinated ethylenes by reaction of chlorine with tetrachlorethane, the step for improving chlorine consumption comprising contacting the reacting gases with a packing consisting of particles of metal selected from the group consisting of nickel and high nickel alloys which packing has been subjected to at least three successive treatments with an oxygen-containing gas at a temperature over 350 C.

2. In a process for the production of chlorinated ethylenes by reaction of chlorine with tetrachlorethane in the presence of a packing of particles of metal selected from 'the group consisting of nickel and high nickel alloys, the steps for improving chlorine consumption comprising at least three periodic treatments of said packing with air at a temperature in the range 350 C. to 550 C.

3. In a process for the production of chlorinated ethylenes by reaction of chlorine with tetrachlorethane in the presence of a packing of particles of metal selected from the group consisting of nickel and high nickel alloys, the steps for improving chlorine consumption comprising at least three periodic treatments of said packing with air and steam at a temperature in the range 350 to 550 C.

4. In a process for the production of chlorinated ethylenes by reaction of chlorine with tetrachlorethane in the presence of a packing consisting of a nickel-chromium alloy consisting by weight of approximately 77% nickel, 15%, chromium, and 7% iron, the steps for improving chlorine consumption comprising at least three periodic treatments of said packing with an oxygen-containing gas 'at a temperature in the range 350 C. to 550 C.

5. The process of claim 4 in which the packing is treated with an oxygen-containing gas and steam.

6. In a process for the production of chlorinated ethylenes by passing a mixture of tetrachlorethane and chlorine containing approximately 10% by weight chlorine through a heated furnace followed by a reactor containing a packing of metal selected from the group consisting of nickel and high nickel alloys, the steps for improving chlorine consumption comprising at least three periodic treatments of said packing with air at a temperature in the range 350 C. to 550 C.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A PROCESS FOR THE PRODUCTION OF CHLORINATED ETHYLENES BY REACTION OF CHLORINE WITH TETRACHLORETHANE, THE STEP FOR IMPROVING CHLORINE CONSUMPTION COMPRISING CONTEACTING THE REACTING GASES WITH A PACKING CONSISTING OF PARTICLES OF METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND HIGH NICKEL ALLOYS WHICH PACKING HAS BEEN SUBJECTED TO AT LEAST THREE SUCCESSIVE TREATMENTS WITH AN OXYGEN-CONTAINING GAS AT A TEMPERATURE OVER 350*C.