US3697608A

US3697608A - Dechlorination process

Info

Publication number: US3697608A
Application number: US764642A
Authority: US
Inventors: Harold Edward Bellis
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1968-10-02
Filing date: 1968-10-02
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10

Abstract

A dechlorination process which comprises contacting halogenated hydrocarbons with a melt comprising iron chloride and/or copper chloride, and alkali metal chloride(s). This process utilizes a reduced melt, i.e., a melt containing ferrous and/or cuprous chlorides, to dechlorinate; various process parameters are controlled to provide desired product selectivity. In addition, the dechlorination process may be carried out simultaneously with chlorination or dehydrochlorination reactions.

Description

United States Patent Bellis [451 Oct. 10, 1972 [54] DECHLORINATION PROCESS 3,260,761 7/ 1966 Burrus et a1 ..260/654 R [72] Inventor: Harald gdyard Bellis, North Tona- FOREIGN PATENTS 0R APPLICATIONS wan a, 891,272 3/1962 Great Britain ..260/656 R Asslgneei (in 118 Nemollls and 951,497 3/1964 Great Britain ..260/654 D pany, Wilmington, Del. 1,050,540 12/1966 Great Britain ..260/654 D [22] Flled: 1968 Primary ExaminerLeon Zitver [21] Appl. No.: 764,642 Assistant Examiner.loseph A. Boska AttorneyJohn J. Klocko, Ill [52] US. Cl. .,260/653.5, 260/650 R, 260/654 D,

260/654 R, 260/656 R, 260/658 R, 260/659 [57] ABSIRACT R, 260/663 A dechlorination process which comprises contacting 51 1 1m. 01 ..C07c 21/18 halogenated hydrocarbons with a melt comprising iron [58] Field of Search ..260/654 D, 653.5, 654 R chloride and/or pp chloride, and alkali metal ch1oride(s). This process utilizes a reduced melt, i.e., a [56] References Cited melt containing ferrous and/or cuprous chlorides, to dechlorinate; various process parameters are con- UNITED STATES PATENTS trolled to provide desired product selectivity. In addition, the dechlorination process may be carried out 2,034,292 3/1936 Grebe et a1. ..260/654 H l 1 I 2,140,548 12/1938 Reilly ..260/654 D chlmnam dehydmch 2,697,124 12/1954 Mantell ..260/653.3 2,704,775 3/1955 Clark ..260/653.3 11 Claims, No Drawings DECIILORINATION PROCESS BACKGROUND OF THE INVENTION Dechlorination of halogenated hydrocarbons has been widely studied; several dechlorination processes have been disclosed in the literature. These dechlorination processes can be combined with hydrochlorinating processes to produce desirable products. For example, a typical method for the production of perchloroethylene and trichloroethylene from carbon tetrachloride and hexachloroethane, involves hydrochlorinating and dechlorinating, is described in US. Pat. No. 3,260,761.

There is a need for a versatile dechlorination process which can be readily controlled and adapted to most commercial applications. Moreover, a dechlorination process which can also simultaneously chlorinate would be of great commercial importance. The novel process of this invention has been developed to fulfill the needs and deficiencies of prior processes.

SUMMARY OF THE INVENTION This invention relates to a dechlorination process which comprises contacting C to C halogenated hydrocarbon(s) containing at least two chlorine atoms wherein at least one chlorine atom is on each of two adjacent carbon atoms, at a temperature within the range of lC.-600C., with a melt comprising (1) a chloride selected from the group consisting of iron chloride, copper chloride and mixtures thereof and (2) ..alkali metal chloride(s), whereby said halogenated hydrocarbon is dechlorinated by the melt, wherein:

a. At least 50 mole percent of the iron chloride is maintained as ferrous chloride when component (1) consists solely of iron chloride, at least 20 mole percent of the copper chloride is maintained as cuprous chloride when component (l) consists solely of copper chloride, and at least 20 mole percent of the copper chloride is maintained as cuprous chloride when component (1) consists of a mixture of iron chloride and copper chloride; and

b. the alkali metal chloride is selected from the group consisting of sodium chloride, potassium chloride, lithium chloride and mixtures thereof.

Another aspect of this invention also involves the simultaneous chlorination and/or hydrochlorination of unsaturated hydrocarbons and dechlorination of vicinal chlorohydrocarbons.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred process of this invention involves dechlorinating pentachloroethane to trichloroethylene.

2. The variable valence metals (copper and iron) must be present in the reduced form, e.g., cuprous and ferrous.

3. The proportions of cuprouszcupric and/or ferrous:ferric are critical.

4. Alkali metal chloride(s) must be present in the melt.

The first requirement is directed to dechlorinating with a melt and/or by means of a melt (molten salts). The dechlorination reaction takes place between the melt and halogenated hydrocarbon gas. It is the melt itself which does the dechlorinating in the process of this invention and not any other liquid or gaseous additives. Dechlorinating with a melt provides uniform dechlorination rate. There is no agglomeration of catalyst particles as in a fluidized bed. More complete dechlorination rates are available due to the presence of massive amounts of the dechlorinating composition in the melt. In short, the melt dechlorination process of this invention provides a more effective means for dechlorinating.

The second requirement is that the variable valence metals which are utilized must be present at least par,- tially in the reduced form. The terminology reduced form is intended to designate the lower valence state of the metal. For example, in the case of iron and copper, the reduced forms are ferrous chloride and cuprous chloride while the oxidized forms are ferric chloride and cupric chloride. The reduced forms of these metals readily accept chlorine and, therefore, dechlorinate the chlorinated hydrocarbons. This can be illustrated by the following equation:

FeCl 15 C1 FeCl Many variable valence metal chlorides may be used, including the chlorides of iron, copper, mercury, manganese and chromium. The preferred chlorides are the chlorides of iron and copper; these are critical to this invention.

The third requirement, and probably the most important requirement, relates to the proportions of cuprous and/or ferrous chloride. Ideally, all cuprous chloride or all ferrous chloride could be used since a melt containing 100 percent of the reduced form of these chlorides would be a very strong dechlorinating melt. Therefore, the upper limit is 100 percent ferrous chloride and/or 100 percent cuprous chloride. The lower limit or the minimum amount of ferrous or cuprous chloride is set by the point at which chlorination by the melt starts to become significant. In other words, when the melt is giving up more chlorine than it is accepting, there is not enough of the reduced chlorides present. Generally, at least 50 mole percent of the iron chloride is the sole dechlorinating agent; when copper chloride is the. sole dechlorinating agent, at least 20 mole percent of the copper chloride must be maintained as cuprous ferrous chloride and/or cuprous chloride, to depress the volatility of the iron and copper chlorides at operat- MCI FeCl k C1, MFeCl,

chloride is utilized, a mixture of KCl and LiCl should also be utilized to obtain optimum results.

The temperature at which the melt dechlorination process of this invention is carried out is generally within the range of lOC.-600C. The temperature range is dependent upon the metal chloride salt mixture which is utilized and the desired product. The temv pera-ture must be adjusted so that the melt does not chlorinate rather than dechlorinate. A preferred temperature range is 250C.450C.

The pressure employed in the dechlorination process can vary considerably and be as high as 50 atmospheres. A pressure within the range of l-l0 atmospheres is preferred. The pressure utilized is restricted by materials of construction and the problems of handling the melt at the high operating temperatures of this invention.

,The halogenated hydrocarbons suitable for the dechlorination reactions described herein include C to C halogenated hydrocarbons containing at least two chlorine atomswherein at least one chlorine atom is on each of two adjacent carbon atoms, i.e., vicinal chlorides. .These include the chlorinated derivatives of ethane, propane, the butanes, ethylene, propylene, the butylenes, butadiene, isopropene, benzene, toluene, oxylene, styrene, etc. Of particular importance are the chlorinated ethylene derivatives such as ethylene n dichloride, 1,1,2-trichloroethane, symmetrical tetrachloroethane, pentachloroethane, hexachloroethane, l ,2-dichlorocyclohexane and dichlorobenzene. It is preferred that the carbon atoms, which have chlorine present thereon, be saturated.

- Other mixed halogenated compounds can also be used;

for example, symmetrical tetrafluorodichloroethane can be dechlorinated to symmetrical tetrafluoroethane. Additionally, mixtures of the vicinal chlorides can be used as the. starting materials.

The process of this invention involves providing good contact between the halogenated hydrocarbon gas and the; melt. The gas can be distributed in the melt or the melt can be distributed in the gas (e.g spraying melt intov gas). The melt can be the continuous phase or the discontinuous phase. Also, the melt maybe dispersed on a supportand used in a fluidized bed. A very effective and preferred method that may be used is to disperse the gas in the body of the melt. The dispersal may be effected by forcing the gas, in the form of fine bubbles, to ascend through the melt, by any known means. Typical means include porous plates, or porous thimbles, a suitable bubbling apparatus or a sparger. A stirring apparatus may also be used. Several stages may be used, with the gas being dispersed into the melt at different positions in the apparatus, while the melt is passed continuously from one stage to anotherrlt is an essential requirement that the halogenated hydrocarbon gas be dispersed and finely distributed throughout the melt to provide good contact between the gas and the melt when good reaction rates are desired. The size or fineness of the bubbles also has an effect on the reaction rate. The dechlorination reaction rate increases directly with an increase in the fineness of the halogenated hydrocarbon gas bubbles, an increase in the amount of agitation utilized to disperse the.

halogenated hydrocarbon gas in the melt, or any increased overall contact of the halogenated hydrocarbon gas with the melt. However, the scope of this invention is not intended to be limited to any particular dispersing mechanisms. Comparatively speaking, if slower reaction rates and dechlorination rates can be tolerated, there is no necessity for a thorough dispersion of the halogenated hydrocarbon gas in the liquid melt as is required in the preferred embodiment of the invention.

The process of this invention can be carried'out as follows: The required amounts of each metal salt, in solid form, are mixed together to obtain even distribution of the respective salts in the salt mixture. This'salt mixture is added to a reaction vessel and heated to a temperature within the range of l00C.-600C. whereby a melt of the salt mixture is obtained. Then the halogenated hydrocarbon is fed to the reaction vessel through any appropriate inlet means. It is a matter of choice and designing skill to decide whether the halogenated hydrocarbon enters through the side, top. or bottom of the reaction vessel. It is preferred, however, that the halogenated hydrocarbon enter the reaction vessel through the bottom to give the chlorinated hydrocarbon a longer contact time with the melt. The halogenated hydrocarbon is dechlorinated and the dechlorinated reaction products begin to vaporize and rise to the top of the reaction vessel. An outlet is provided, usually at the top of the reaction vessel, where the reaction products can be drawn off; a condensation system, and possibly a scrubber system, could also be provided to recover and/or recycle any halogenated hydrocarbon which has not been dechlorinated.

The above-described is essentially a batch-type process; when the oxidation level of the iron and/or copper becomes too high, this batch process would not dechlorinate .but would be chlorinating instead. The batch process would have to be stopped in order to reduce the melt to a suitable dechlorinating level. Reduction of the melt can be accomplished by passing through the melt a material which readily accepts chlorine, such as hydrogen, acetylene, ethylene, vinyl chloride or vinylidene chloride. A suitable batch operation can be carried out by alternating between dechlorinating and reducing the melt. For example, an olefin can be fed to the reactive melt to accept chlorine and thus reduce the melt to a dechlorinating level.

Alternatively, a continuous process can also be operated whereby the melt is continually dechlorinating a halogenated hydrocarbon, being reduced and/or recycled and another hydrocarbon (chlorine acceptor) is being chlorinated. The proportions of the halogenated hydrocarbon and the chlorine acceptor must be adjusted to balance the rate of dechlorination and the rate of chlorination. The continuous process of this invention can be operated as either a single stage operation or a multi-stage operation.

The invention is illustrated by the following examples. In the examples and elsewhere in the specification, unless indicated otherwise, all parts, proportions and percentages of materials or components are in mole percent, based on the moles of melt.

EXAMPLE 1 Into a glass reactor containing 2 liters of a melt of 20 moles FeCl 20 moles KCl and 4 moles CuCl was passed pentachloroethane at the rate of 2 cc./minute. The melt was mechanically stirred at 1,200 r.p.m. at a temperature of 375C., under atmospheric pressure. Approximately 80 mole percent of the pentachloroethane fed was converted to a chlorohydrocarbon mixture containing (in mole percent) 66 percent trichloroethylene, 26 percent perchloroethylene and 3 percent dichloroethylenes as the major products. Thus, a high proportion of the feed was dechlorinated.

EXAMPLE 2 Into a glass reactor containing 2 liters of a melt of 5 moles CuCl, moles CuCl and moles KCl was passed tetrachloroethane at the rate of 2 cc./minute. The melt was mechanically stirred at 1,200 r.p.m. at a temperature of 390C., under atmospheric pressure. Approximately 75 mole percent of the tetrachloroethane fed was converted to a chlorohydrocarbon mixture containing 61 percent dichloroethylenes and 31 percent trichloroethylene as the major products. The process was stopped when the melt reached an oxidation level of 65 percent.

Another important aspect of this invention is a process which simultaneously dechlorinates and chlorinates. For example, along with the chlorinated hydrocarbon, achlorine acceptor (e.g., an olefin) can be introduced into the melt. While the chlorinated hydrocarbon is being dechlorinated, the olefin can be chlorinated. A careful control and choice of conditions, temperature, stirring and feed rate must be maintained to achieve the desired dechlorination-chlorination reactions. The most critical factor, of course, is the oxidation level of the melt. The theoretical oxidation level would be 50 mole percent of ferrous chloride and 50 mole percent ferric chloride. However, various oxidation levels can be utilized to achieve the desired results.

The chlorine acceptor, i.e., the material which is to be chlorinated, can be any C to C unsaturated hydrocarbons, their incompletely chlorinated derivatives, and hydrogen. Nonaromatic hydrocarbons are preferred although the aromatics are operable. Typical of these compounds are acetylene, ethylene, vinyl chloride, vinylidene chloride, etc. The following examples are illustrative of the simultaneous dechlorinationchlorination process.

EXAMPLE 3 cent perchloroethylene, 7 percent 1,1 ,2- trichloroethane and 2 percent pentachloroethane. There was complete conversion of the hexachloroethane to perchloroethylene while 43 percent of the dichloroethylene was converted to higher chlorinated hydrocarbons.

EXAMPLE 4 Into a glass reactor containing 2 liters of a melt of 2 moles FeCl 8 moles FeCl CuCl, 5 moles CuCl, 16 moles KCL and 5 moles A1Cl was passed 1,1,2- trichloroethane at the cc./minute. of 3 cc./minute. The melt was mechanically stirred at the rate of 1,000 r.p.m. at a temperature of 400C., under atmospheric pressure. The product contained 3 percent 1,1,2- trichloroethane, 14 percent vinyl chloride, 68 percent dichloroethylene, 14 percent trichloroethylene and 1 percent perchloroethylene. This represented a 97 percent conversion of the 1,1,2-trichloroethane fed. There was a good balance between dechlorination and chlorination; the melt oxidation level was stable under these conditions.

EXAMPLE 5 Into a glass reactor containing 2 liters of a melt of 10 moles CuCl, 10 moles FeCl and 24 moles KCl were passed a feed stream containing 50 percent pentachloroethane and 50 percent vinyl chloride at the rates of 2 cc./minute and 0.5 liter/minute, respectively. The melt was mechanically stirred at 1,200 r.p.m. at the temperature of 375C., under atmospheric pressure. The major products were (mole percent) 4 percent pentachloroethane, 36 percent trichloroethylene, 4 percent perchloroethylene, 8 percent vinyl chloride, 32 percent l,1,2-trichloroethane and 8 percent dichloroethylene. This process produced a percent conversion of pentachloroethane to a product consisting of 91 percent trichloroethylene and 9 percent perchloroethylene, while there was an 80 percent conversion of the vinyl to a product consisting of 80 percent 1,l,2-trichloroethane and 20 percent dichloroethylene.

EXAMPLE 6 Into a glass reactor containing 2 liters of a melt of 10 moles CuCl, 10 moles FeCl and 24 moles KCl were passed pentachloroethane and hydrogen at the rates of 2 ccJminute and 0.5 liter/minute, respectively. The melt was mechanically stirred at 1,200 r.p.m. at a temperature of 390C, under atmospheric pressure. Approximately 95 mole percent of the pentachloroethane fed was converted to a chlorohydrocarbon mixture containing 95 percent trichloroethylene and 4 percent perchloroethylene. The hydrogen was fully converted to hydrogen chloride. Thus, by controlling the ratio of hydrogen to pentachloroethane, the desired amount of ously trichloroethylene.

cuprous chloride can be maintained at any desirable level.

EXAMPLE 7 This example. illustrates dechlorination at a significantly lower temperature with some water present in g r.p.m. at a temperature of 190C., at atmospheric pressure.

,tachloroethane fed was converted to a chlorinated hydrocarbon Approximately 87 percent of the penmixture comprising 94 percent trichloroethylene and percent perchloroethylene.

EXAMPLE 8 Into a glass reactor containing 2 liters of a melt of 7.5 moles FeCl 7.5 moles FeCl and 15 moles KCl was passed symmetrical dichlorotetrafluoroethane at the rate of 0.5 liter/minute. The melt was mechanically stirredat 1,200 r.p.m. at a temperature of 375C., under atmospheric pressure. Approximately 35 'mole percent of the starting material was converted to 'a product comprising 98 percent tetrafluoroethylene.

in addition to the iron, copper and alkali metal chlorides, the meltcan contain inert salts such as zinc chloride, aluminum chloride, etc. Also water may be present to promote chlorination in instances where higher chlorination rates are desired.

A further aspect of this invention involves a combined hydrochlorination and dechlorination process. For example, the conversion of perchloroethylene to trichloroethylene is carried out by (l) hydrochlorinating perchloroethylene to pentachloroethane and (2) dechlorinating pentachloroethane to trichloroethylene. The hydrochlorination reaction will take place, preferably, in the presence of aluminum chloride and other metal and metalloid halides of the type known as Friedal-Crafts catalyst, although these are not necessary. This can be carried out in the melt or prior to the formation of the melt. Pentachloroethane, which is obtained from the hydrochlorination reaction, is then dechlorinated by the previously described process of this invention. 1'

The hydrochlorination and dechlorination reactions may also be carried out simultaneously in the melt system. The use of pressure is beneficial to these reactions. Thus, if aluminum chloride. is included in the melt system, both reactions may take place simultaneto produce the desired product, i.e.,

EXAMPLE 9 Into a glass reactor containing 2 liters of a melt of 10 moles CuCl, 10 moles FeCl and 24 moles KC] were I passed perchloroethylene and hydrogen chloride at the 1. A dechlorination process which comprises contacting C, to C halogenated hydrocarbon(s) containing at least two chlorine atoms wherein at least one chlorine atom is on each of two adjacent carbon atoms,

5 at a temperature within the range of l00C.-600C., with a melt comprising l) a chloride selected from the group consisting of iron chloride, copper chloride and mixtures thereof and (2) alkali metal chloride(s), whereby said halogenated hydrocarbon is dechlorinated by the melt, wherein:

a. at least 50 mole percent of the iron chloride is maintained as ferrous chloride when component (1) consists solely of iron chloride, at least 20 mole cuprous chloride when component (1) consists solely of copper chloride, and at least mole percent of the copper chloride is maintained as cuprous chloride when component (1) consists of a mixture of iron chloride and copper chloride;

2. A process in accordance with claim] wherein the halogenated hydrocarbon is pentachloroethane and the dechlorinated product comprises a mixture of trichloroethylene andperchloroethylene.

3. A process in accordance with claim 1 wherein the halogenated hydrocarbon contains at least one fluorine atom and the dechlorinated product contains at least one fluorine atom.

4. A process in accordance with claim 1 wherein the melt contains at least 50 percent cuprous chloride.

5. A process in accordance with claim 1 wherein the halogenated hydrocarbon is dispersed in the melt.

6. A process of simultaneously dechlorinating a chlorinated hydrocarbon and chlorinating a chlorine acceptor which comprises simultaneously contacting a C to C halogenated hydrocarbon containing at least two chlorine atoms wherein at least one chlorine atom is on each of two adjacent carbon atoms and a chlorine acceptor selected from the group consisting of hydrogen, C to C unsaturated hydrocarbons, incompletely chlorinated derivatives of C to C unsaturated hydrocarbons, and mixtures thereof, at a temperature within the range of l00C.-600C., with a melt comprising l a chloride selected from the group consisting of iron chloride, copper chloride and mixtures thereof and 2) alkali metal chloride(s), by 50 dispersing the chlorinated hydrocarbon and the chlorine acceptor in the melt, wherein:

a. at least 50 mole percent of the iron chloride is maintained as ferrous chloride when component (1 consists solely of iron chloride, at least 20 mole percent of the copper chloride is maintained asv cuprous chloride when component (1) consists solely of copper chloride, and at least 20 mole percent of the copper chloride is maintained as cuprous chloride when component (1) consists of a mixture of iron chloride and copper chloride;

7. A process in accordance with claim 6 wherein the halogenated hydrocarbon is pentachloroethane and the dechlorinated product comprises a mixture of trichloroethylene and perchloroethylene.

percent of the copper chloride is maintained as v comprising l) hydrochlorinating perchlorethylene to pentachloroethane by heating perchloroethylene with hydrogen chloride at a temperature of at least C. in the presence of a Friedel-Crafts catalyst to form pentachloroethane, and (2) dechlorinating said pentachloroethane of step 1 to trichloroethylene in accordance with the process of claim 1.

Claims

2. A process in accordance with claim 1 wherein the halogenated hydrocarbon is pentachloroethane and the dechlorinated product comprises a mixture of trichloroethylene and perchloroethylene.
3. A process in accordance with claim 1 wherein the halogenated hydrocarbon contains at least one fluorine atom and the dechlorinated product contains at least one fluorine atom.
4. A process in accordance with claim 1 wherein the melt contains at least 50 percent cuprous chloride.
5. A process in accordance with claim 1 wherein the halogenated hydrocarbon is dispersed in the melt.
6. A process of simultaneously dechlorinating a chlorinated hydrocarbon and chlorinating a chlorine acceptor which comprises simultaneously contacting a C2 to C10 halogenated hydrocarbon containing at least two chlorine atoms wherein at least one chlorine atom is on each of two adjacent carbon atoms and a chlorine acceptor selected from the group consisting of hydrogen, C2 to C10 unsaturated hydrocarbons, incompletely chlorinated derivatives of C2 to C10 unsaturated hydrocarbons, and mixtures thereof, at a temperature within the range of 100*C.-600*C., with a melt comprising (1) a chloride selected from the group consisting of iron chloride, copper chloride and mixtures thereof and (2) alkali metal chloride(s), by dispersing the chlorinated hydrocarbon and the chlorine acceptor in the melt, wherein: a. at least 50 mole percent of the iron chloride is maintained as ferrous chloride when component (1) consists solely of iron chloride, at least 20 mole percent of the copper chloride is maintained as cuprous chloride when component (1) consists solely of copper chloride, and at least 20 mole percent of the copper chloride is maintained as cuprous chloride when component (1) consists of a mixture of iron chloride and copper chloride; b. the alkali metal chloride is selected from the group consisting of sodium chloride, potassium chloride, lithium chloride and mixtures thereof.
7. A process in accordance with claim 6 wherein the halogenated hydrocarbon is pentachloroethane and the dechlorinated product comprises a mixture of trichloroethylene and perchloroethylene.
8. A process in accordance with claim 6 wherein the halogenated hydrocarbon contains at least one fluorine atom and the dechlorinated product contains at least one fluorine Atom.
9. A process in accordance with claim 6 wherein the melt contains at least 50 percent cuprous chloride.
10. A process in accordance with claim 6 wherein the halogenated hydrocarbon is dispersed in the melt.
11. A process for the production of trichloroethylne comprising (1) hydrochlorinating perchlorethylene to pentachloroethane by heating perchloroethylene with hydrogen chloride at a temperature of at least 100*C. in the presence of a Friedel-Crafts catalyst to form pentachloroethane, and (2) dechlorinating said pentachloroethane of step 1 to trichloroethylene in accordance with the process of claim 1.