WO1996035653A1

WO1996035653A1 - Promotion of 1,2-dichloroethane pyrolysis with chloral and/or chloral hydrate

Info

Publication number: WO1996035653A1
Application number: PCT/US1996/006344
Authority: WO
Inventors: John C. Crano; Charles R. Wiedrich; Tommy G. Taylor; Randall M. Hall; John A. Hart
Original assignee: Ppg Industries, Inc.
Priority date: 1995-05-08
Filing date: 1996-05-06
Publication date: 1996-11-14

Abstract

Chloral and/or chloral hydrate is an effective promoter for the pyrolysis of 1,2-dichloroethane to produce vinyl chloride. It often also serves to reduce the concurrent production of monovinylacetylene which is an undesirable by-product.

Description

PROMOTION OF 1,2-DICHLOROETHANE PYROLYSIS WITH CHLORAL AND/OR CHLORAL HYDRATE

This application is a continuation-in-part of Application Serial No. 08/436,937, filed May 8\ 1995.

It is well known that chloroethene [CAS 75-01-4] , also known as vinyl chloride and as VC1, can be produced by the pyrolysis of 1,2-dichloroethane [CAS 107-06-2], which is also known as ethylene dichloride and as EDC. See, for example, United States Patents Nos. 4,590,318;4,584,420; and 3,655,787.

EDC may be produced by several different processes, but commercial production is most often accomplished by oxyhydrochlorination (often called oxychlorination) in which ethylene, hydrogen chloride, and oxygen are reacted in the presence of a Deacon catalyst. However, in the production of EDC by this oxyhydrochlorination route, the crude product stream from the reactor is typically contaminated by trichloroacetaldehyde [CAS 75-87-6] , also known as chloral, and/or by 2,2,2-trichloro-l,1-ethanediol [CAS 302-17-0], also known as chloral hydrate. If the chloral and/or chloral hydrate is allowed to remain in the crude EDC composition, its presence eventually gives rise to corrosive conditions that can damage equipment. Corrosion can be reduced by constructing the equipment of corrosion resistant materials such as tantalum or glass, but the capital expenditures for such equipment are very high. The usual practice in the industry has therefore been to remove the chloral and/or chloral hydrate early in the EDC purification process. See, for example, United States Patents No. 3,378,587; 3,488,398; 3,996,300; 4,151,212; and 4, 172, 099. When EDC is pyrolyzed to produce VCl, various materials have been added in small amounts to promote the pyrolysis reaction. The promoter is added to the EDC feedstock before the feedstock is introduced to the pyrolysis furnace or it is added to the gaseous reaction mixture at one or more points within the furnace. During the pyrolysis, the promoter is usually substantially consumed.

The present invention is based on the discovery that chloral and/or chloral hydrate is effective as a pyrolysis promoter. Accordingly, in the process wherein

1,2-dichloroethane is pyrolyzed in a pyrolysis zone to produce vinyl chloride, the invention is the improvement comprising conducting the pyrolysis in the presence of a pyrolysis- promoting amount of promoter selected from the group consisting of chloral, chloral hydrate, and a mixture thereof. A pyrolysis-promoting amount of promoter is an amount of promoter which results in an increase in the yield of vinyl chloride based on 1,2-dichloroethane, as compared with the yield of vinyl chloride produced in the absence of the promoter under otherwise substantially identical conditions. The pyrolysis-promoting amount of promoter may vary widely. Usually, however, the promoter and the 1,2-dichloroethane are introduced to the pyrolysis zone at a weight ratio of promoter to 1,2-dichloroethane in the range of from 0.00001:1 to 0.01:1. Often the weight ratio is in the range of from 0.0001:1 to 0.001:1. From 0.0002:1 to 0.0008:1 is preferred.

It has also been discovered that conducting the pyrolysis of 1,2-dichloroethane in the presence of chloral and/or chloral hydrate often serves to reduce the concurrent production of l-buten-3-yne, also known as monovinylacetylene [CAS 689-97-4] , which is an undesirable by-product. Accordingly, in the process wherein 1,2-dichloroethane is pyrolyzed in a pyrolysis zone to produce vinyl chloride containing by-product monovinylacetylene, another embodiment of the invention is the improvement comprising conducting the pyrolysis in the presence of a monovinylacetylene-reducing amount of promoter selected from the group consisting of chloral, chloral hydrate, and a mixture thereof.

A monovinylacetylene-reducing amount of promoter is an amount of promoter which results in a decrease in the concentration of by-product monovinylacetylene appearing in the effluent from the pyrolysis zone, as compared with the concentration of by-product monovinylacetylene appearing in effluent produced in the absence of the promoter under otherwise substantially identical conditions of heat flux and mass flow. The monovinylacetylene-reducing amount of promoter may vary widely. Usually, however, the promoter and the 1,2-dichloroethane are introduced to the pyrolysis zone at a weight ratio of promoter to 1,2-dichloroethane in the range of from 0.00001:1 to 0.01:1. Often the weight ratio is in the range of from, 0.0001:1 to 0.001:1. From 0.002:1 to 0.008:1 is preferred.

The promoter and the 1,2-dichloroethane may be introduced to the pyrolysis zone as separate streams, but preferably a mixture of the promoter and the* 1,2-dichloroethane is introduced to the pyrolysis zone. When introduced separately, either or both of the materials may be introduced as either vapor, liquid, or a mixture of vapor and liquid, but it is preferred that both be introduced as vapor. Each material may be introduced to the pyrolysis zone at one or more points. When a mixture of promoter and

1,2-dichloroethane is introduced to the pyrolysis zone, the mixture may be introduced as vapor, as liquid, or as a mixture of vapor and liquid. It is preferred that the mixture be introduced as vapor. The mixture may be introduced to the pyrolysis zone at one or more points.

When a mixture of promoter and 1,2-dichloroethane is introduced to the pyrolysis zone, it is within contemplation to admix promoter with relatively pure 1,2-dichloroethane to form the mixture. It is also within contemplation to use a mixture comprising crude 1,2-dichloroethane containing at least a portion of the unseparated chloral and/or chloral hydrate coproduced during production of the 1,2-dichloroethane. Crude

1,2-dichloroethane in admixture with additional chloral and/or chloral hydrate may be used when desired. Crude 1,2-dichloroethane in admixture with additional 1,2-dichloroethane may similarly be used when desired.

The pyrolysis is conducted in the vapor phase. While it may be conducted continuously, semicontinuously, batchwise, or semibatchwise, it is usually conducted continuously. The temperatures at which the pyrolysis is conducted may vary widely, but ordinarily they are in the range of from 350°C to about 650°C. Preferably, the temperatures are in the range of from 400°C to 550°C.

The pressures at which the pyrolysis is conducted are similarly susceptible to wide variation. While the pyrolysis may be conducted at ambient atmospheric pressure or below ambient atmospheric pressure, it is ordinarily conducted at pressures above ambient atmospheric pressure. Ordinarily, the pressure is in the range of from 80 to 2000 kilopascals, gauge. Often it is in the range of from 300 to 1500 kilopascals, gauge. From 700 to 1100 kilopascals, gauge is preferred. Likewise the residence time of the reaction mixture in the pyrolysis zone may be widely varied. Generally the residence time is in the range of from 0.1 to 30 seconds. Often it is in the range of from 0.5 to 20 seconds. From 1 to 10 seconds is preferred.

Following pyrolysis, the vinyl chloride may be recovered from the reaction mixture by any of the various techniques known to the art. Quenching, fractional distillation, vaporization, and condensation are techniques which are frequently employed.

Purified vinyl chloride has a multitude of uses, but principally it is use as a monomer for producing homopolymers and copolymers.

In the illustrative examples which follow, all parts are parts by weight and all percentages are percentages by weight unless otherwise specified.

EXAMPLE 1 A reactor was fabricated from 12-millimeter external diameter Pyrex^® borosilicate glass tubing with an internal volume of 50 milliliters. The tubing, bent in a ^XU' shape, was fitted with 14/40 taper joints at both ends. Glass beads weighing from 5 to 7 grams were introduced to the reactor. An Inconel^® 600 nickel alloy coupon was inserted into each leg of the 'U' tube and allowed to rest on the glass beads. Each corrosion coupon weighed approximately 4 grams and measured approximately 85 millimeters in length. The entire reactor assembly was inserted into an electrically heated fluidized sand bath to maintain the desired temperature.

A 100-milliliter feedstock reservoir was connected to a positive displacement metering pump. The pump outlet was connected to a set of two tees, one for introduction of a nitrogen stream, the other for introduction of an oxygen stream. Each stream was separately metered by a dedicated rotameter, with flow control provided by individual metering valves. One-quarter inch (6.35 millimeters) outside diameter stainless steel tubing was utilized to convey the feeds to the 'ϋ' tube reactor inlet. The reactor outlet was connected to a length of glass tubing fitted with a tee equipped with a Teflon^® polytetrafluoroethylene stopcock and rubber septum. This was used for acquiring samples for analysis to follow the reaction. The glass tubing was connected to a condenser chilled to -17°C by a recirculating methanol/water solution. A 100-milliliter reservoir equipped with a bottom Teflon^® polytetrafluoroethylene stopcock was attached to the condenser for collection of condensed material. The condenser outlet for non-condensables was connected via Bev-A-Line^® tubing to a scrubber containing 20% NaOH aqueous solution for neutralization of HC1. The outlet of the scrubber was connected by latex tubing to a wet test meter. The outlet from the wet test meter discharged to a hood.

In conducting a run, the fluidized bath was turned on and brought to 500°C. Feedstock was charged to the feedstock reservoir. The circulation of condenser coolant was begun and the condenser was allowed to stabilize at -17°C. The feed pump was then started and feed material was metered to the reactor. During pyrolysis of the 1,2-dichloroethane, nitrogen and oxygen were not introduced through their respective tees. Ten-milliliter samples of reactor effluent were removed through the septum periodically and each sample was transferred to an evacuated glass bottle containing 2 grams of Na₂HP0₄-7H₂0 to neutralize the HC1 present in the sample. The samples were analyzed by gas chromatographic analysis to determine the yield of VC1. In this way, the yield of VCl based on EDC was calculated at several different times during a run. At the end of the run the yields so obtained were averaged and the standard deviation was calculated. As a rough check, the wet test meter measured the volume of gas leaving the scrubber during the run.

After each pyrolysis run, the apparatus was cooled and purged with nitrogen overnight. The outlet line from the reactor was then disconnected from the condenser and connected to a set of three bulbs in series. The first bulb contained magnesium perchlorate, and the following two each containing a mixture of sodium hydroxide-coated silica (Ascarite® II absorbent; Arthur H. Thomas Co.) and magnesium perchlorate. The purpose of the third bulb was to prevent back-diffusion of C0₂ and water vapor from the atmosphere which might adversely affect the results. After accurately weighing the second bulb, it was replaced in the line. Heating of the bath was begun, and a source of oxygen admitted to the reactor at approximately 75 milliliters/minute. (20°C, 1 atmosphere, absolute) . The temperature of the fluidized sand bath was brought to 500°C over 1 hr. 40 minutes, and held for about 20 minutes . During this time the portions of the glass reactor above the level of the fluid bed were heated with a torch to burn off the remaining carbon. The second bulb was again weighed, and the weight difference due to C0₂ absorption was used to calculate the milligrams of carbon formed during the pyrolysis run. Carbon formation was also calculated in terms of parts carbon formed per million parts of VCl produced, by weight ("ppm/VCl") . The results showing the effect of chloral as a pyrolysis promoter are presented in Table 1 and those showing the effect on carbon formation are presented in Table 2. __________

Effect of Chloral on Vinyl Chloride Yield

Run Addit: Lve Duration, Average Number VCl Yield, hr Flow Rate, of Data percent mL/min Points

1 None 29.4 0.391 8 31.6 ± 3.7

2 None 28.9 0.396 9 28.6 ± 8.5

3 None 30.1 0.381 11 39.6 ± 3.1

4 Chloral,

300 ppm 30 0.42 10 49.1 + 2.8

___________

Effect of Chloral on Carbon Formation

Run Addit;ive Formation mg ppm/VCl

1 None 8.8 51.3 2 None 16.3 104 3 None 17.8 83.2

Chloral, 300 ppm 14.7 54.2

The data show that chloral effectively promoted the pyrolysis of 1,2-dichloroethane to produce vinyl chloride.

EXAMPLE 2

1,2-Dichloroethane was introduced to a gas-fired pyrolysis furnace in a commercial vinyl chloride plant. When no chloral was added and equilibrium had been established, the outlet temperature was 518°C and three analyses of the effluent showed the presence of monovinylacetylene at 4.7, 7.6, 4.3 parts per million, respectively. Chloral was thereafter concurrently introduced to the pyrolysis furnace with the 1,2-dichloroethane at a weight ratio of chloral to 1,2-dichloroethane in the range of from 0.0002:1 to 0.0005:1. The feed rate of 1,2-dichloroethane and the feed rate of the gas fuel to the pyrolysis furnace were the same as before the chloral addition. When equilibrium had been established, the outlet temperature was 501°C and three analyses of the effluent showed the presence of monovinylacetylene at 0, 0, 1.4 parts per million, respectively. Vinyl chloride production increase between 5 and 10 percent when the chloral was introduced.

Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except insofar as they are included in the accompanying claims.

Claims

CLAIMS :

1. In the process wherein 1,2-dichloroethane is pyrolyzed in a pyrolysis zone to produce vinyl chloride, the improvement comprising conducting the pyrolysis in the presence of a pyrolysis-promoting amount of promoter selected from the group consisting of chloral, chloral hydrate, or a mixture thereof.

2. The process of claim 1 wherein said promoter and said 1,2-dichloroethane are introduced to said pyrolysis zone at a weight ratio of promoter to 1,2-dichloroethane in the range of from 0.00001:1 to 0.01:1.

3. The process of claim 1 wherein a mixture of said promoter and said 1,2-dichloroethane is introduced to said pyrolysis zone.

4. The process of claim 3 wherein said promoter and said 1,2-dichloroethane are admixed to form said mixture.

5. The process of claim 3 wherein said mixture comprises crude 1,2-dichloroethane containing at least a portion of the unseparated chloral and/or chloral hydrate coproduced during production of the 1,2-dichloroethane.

6. The process of claim 1 wherein the pyrolysis is conducted at temperatures in the range of from 350°C to 650°C.

7. The process of claim 1 wherein the pyrolysis is conducted at pressures above ambient atmospheric pressure.

8. The process of claim 7 wherein said pressures are in the range of from 80 to 2000 kilopascals, gauge.

9. The method of claim 1 wherein the residence time of the reaction mixture in said pyrolysis zone is in the range of from 0.1 to 30 seconds.

10. In the process wherein l,2-dichloroethane is pyrolyzed in a pyrolysis zone to produce vinyl chloride containing by-product monovinylacetylene, the improvement comprising conducting the pyrolysis in the presence of a monovinylacetylene-reducing amount of promoter selected from the group consisting of chloral, chloral hydrate, and a mixture thereof.

11. The process of claim 10 wherein said promoter and said 1,2-dichloroethane are introduced to said pyrolysis zone at a weight ratio of promoter to 1,2-dichloroethane in the range of from 0.00001:1 to 0.01:1.

12. The process of claim 10 wherein a mixture of said promoter and said 1,2-dichloroethane is introduced to said pyrolysis zone.

13. The process of claim 12 wherein said promoter and said 1,2-dichloroethane are admixed to form said mixture.

14. The process of claim 12 wherein said mixture comprises crude 1,2-dichloroethane containing at least a portion of the unseparated chloral and/or chloral hydrate coproduced during production of the 1,2-dichloroethane.

15. The process of claim 10 wherein the pyrolysis is conducted at temperatures in the range of from 350°C to 650°C.

16. The process of claim 10 wherein the pyrolysis is conducted at pressures above ambient atmospheric pressure.

17. The process of claim 16 wherein said pressures are in the range of from 80 to 2000 kilopascals, gauge.

18. The method of claim 10 wherein the residence time of the reaction mixture in said pyrolysis zone is in the range of from 0.1 to 30 seconds.