The present invention relates to a catalytic process for converting perchloroethylene to trichloroethylene. German Patent Publication DE 3804265A is exemplary of the known art, and describes a method for preparing trichloroethylene from hydrogen and perchloroethylene over a carrier catalyst of an activated charcoal carrier, copper in an elemental or chemically- -bonded (compound) form, rhodium in an elemental or chemically-bonded form, and an organic phosphine or phosphite promoter. A provisional specification is referenced in this publication which purportedly describes a method for preparing trichloroethylene from hydrogen and perchloroethylene, in which the catalyst uses an activated charcoal carrier, copper metal or a copper compound, and elemental palladium, ruthenium or rhodium or a compound thereof.

Canadian Patent No. 1,119,203 is similar to the DE 3804265A reference in describing the conversion of perchloroethylene to trichloroethylene via a catalyst including an activated carbon carrier, copper metal or a copper compound, one or more of the palladium, ruthenium or rhodium metals or compounds thereof, and optionally, an alkali metal compound as a promoter. Earlier processes for converting perchloroethylene to trichloroethylene in the presence of copper salts on alumina, and including activation by alkali metal salts are also described.

The present invention provides for the catalytic conversion of perchloroethylene to trichloroethylene in a commercially substantial proportion (that is, at a yield (defined as the product of the conversion rate of perchloroethylene and the selectivity to trichloroethylene, on a hydrogen chloride- and hydrogen-free basis) of at least 10 percent, but more preferably at least 20 percent, and most preferably at least 30 percent), in which perchloroethylene is reacted with hydrogen in the presence of a catalyst including a selected Group IB metal or metals in an elemental or compound form with one or more Group VIII metals inclusive of platinum or iridium, also in an elemental or compound form, on a support.

Preferred catalysts will, however, consist essentially of one or more Group IB metals, one or more Group VIII metals inclusive of platinum or iridium, and an additional promoter material from Groups IVB, VA or IVA, or from the organic phosphine, phosphite or phosphonium salt or alkali metal compounds on a support. More preferably, the catalysts employed in the processes of the present invention will consist of one or more Group IB metals with one or more Group VIII metals inclusive of platinum or iridium and a promoter material from Groups IVB, VA or IVA, or from the organic phosphine, phosphite or phosphonium salt or alkali metal compounds on a support.

Preferred catalysts will comprise (with the promoter material) platinum in elemental or compound form as a Group VIII metal and copper in elemental or compound form

as a Group IB metal. More preferably, the Group IB and Group VIII metals will consist substantially entirely of platinum and copper in their elemental or compound forms, and a most preferred catalyst will employ only platinum and copper in their elemental or compound forms as the Group IB and Group VIII metals, together with the promoter material which advantageously may be tin in an elemental or compound form.

In terms of the amounts of platinum, copper and tin employed in these most preferred catalysts, preferably platinum comprises from 0.01 to 5.0 percent by weight of the catalyst as calculated on an elemental basis, copper comprises from 0.5 to 20 percent by weight of the catalyst (also on an elemental basis), and the tin promoter in elemental or compound form comprises from 0.01 to lO percent by weight of the catalyst, with the support being any of the conventionally employed supports but preferably being carbon or silica, and especially being a carbon support having a specific surface area of at least 200 m ² /g.

More preferably, the catalyst includes from 0.02 to 3.0 percent by weight of platinum, from 1 to 15 percent by weight of copper and from 0.02 to 0.75 percent by weight of tin, and the carbon support has a specific surface area of at least 500 m2/g.

Most preferably, the catalyst includes from 0.04 to 1.0 percent by weight of platinum, from 4 to 12 percent by weight of copper and from 0.1 to 0.6 weight percent of tin, and the carbon support has a specific surface area of at least 800 m2/g. A presently-preferred carbon support is Calgon's wood-based WSIV Special activated carbon (Calgon Carbon Corporation), having a published or advertised specific surface area of 1400 m /g and a pore volume of 1.25 cubic centimeters per gram.

It is contemplated that the process of the present invention can be conducted in the gas phase or the liquid phase (in a batchwise or in a continuous mode), with a gas phase process however being presently preferred. The pressure under which the reaction is conducted in the gas phase process preferably ranges from atmospheric pressure to 1500 psig (10.3 Pa (gauge)), more preferably ranges from 15 psig (0.10 Pa (gauge)) to 500 psig (3.4 Pa (gauge)), and most preferably ranges from 30 psig (0.21 Pa (gauge)) to 300 psig (2.1 Pa (gauge)). The temperature will preferably be from 100 deg. C. to 350 deg. C, more preferably will be from 160 deg. C. to 280 deg. C, and most preferably will be from 180 deg. C. to 250 deg. C. Preferred residence times will be from 0.25 seconds to 180 seconds, more preferably will be from 30 seconds to 120 seconds, and most preferably will be from 50 seconds to 100 seconds. Hydrogen to perchloroethylene molar feed ratios will preferably be from 0.1 : 1 to 100: 1. More preferably, the hydrogen to perchloroethylene molar feed ratios will be from 0.3: 1 to 10: 1 , and most preferably from 0.5: 1 to 3.0: 1. Hydrogen chloride is preferably employed in the feed to reduce coking and catalyst deactivation rates. In this regard, the rate of conversion loss will preferably be no more than about 0.03 percent per hour, and more preferably will be no more than about 0.01 percent per hour.

Illustrative Examples

The present invention is more particularly illustrated by the examples which follow hereafter. Examples 1-6: Experimental Apparatus and Procedure For each of the Examples below, liquid perchloroethylene was pumped via a piston pump through 1/16th inch (1.6 mm) (O.D.) nickel tubing to a Monel'" alloy (Huntington Alloys, Inco Alloys International, Inc.) gas sample cylinder packed with glass beads (unless specifically noted, all fittings and tubing were of Monel'" alloy). The 1/16th inch tubing extended to the center of the sample cylinder, with the sample cylinder being heated to a vaporization temperature of 110 degrees Celsius by electrical heattracing. A thermocouple was used to monitor the skin temperature ofthe sample cylinder.

The flow of the hydrogen feed stream was controlled by a pre-calibrated mass flow controller. The desired flow of hydrogen was passed through the heated sample cylinder, where mixing of the gaseous perchloroethylene and hydrogen occurred. The mixed gases were then passed into a charged Monel" tubular reactor (0.50 in. (1.27 cm.) O.D., 21 inches (53.3 cm.) in length) heated by ceramic lined electric elements to a desired reaction temperature.

The various catalysts whose preparations are detailed below (20.0 cubic centimeters per charge) had been charged into the reactor between 3 mm glass beads, and placed in the middle of the reactor. The charged catalysts were thereafter dried under a flow of nitrogen for one hour at 130 degrees Celsius, and then reduced under a 5: 1 molar ratio of flowing nitrogen and hydrogen. In reducing a given charge of catalyst, the temperature was ramped up from 130 to 220 degrees Celsius at 3 degrees per minute, and then held at 220 degrees for a total reducing cycle time of about 2 hours.

Upon reaction over a given catalyst charge of the mixed hydrogen and perchloroethylene at a prescribed reaction temperature, a liquid hourly space velocity (LHSV) of 0.075 (LHSV = volume liquid perchloroethylene fed per hour per packed bed volume of catalyst), a residence time of 47.7 seconds and a hydrogen to perchloroethylene molar feed ratio of 1.5: 1 , the effluent from the reactor was passed to a gas sampling valve, which provided gaseous aliquots for online gas chromatographic analysis in a Hewlett-Packard Model 5790 gas chromatograph (Hewlett-Packard Company) equipped with a thermal conductivity detector. Individual components of the reactor effluent/product stream were separated by a 30 meter by 0.53 millimeter (I.D.), 5 percent phenyl, 95 percent methyl silicone/fused silica column. Response factors were conventionally determined by injections of gravimetrically- -prepared standards of the individual reaction products. These response factors were applied in conjunction with individual peak areas and the total mols of all reaction products to determine the mol percents of individual components in the reactor effluent, and the selectivity to individual reaction products on a hydrogen- and hydrogen chloride-free basis. Perchloroethylene conversion was also determined on a hydrogen- and hydrogen chloride-free

basis, and catalyst productivity for each given catalyst was calculated by dividing the number of kilograms of trichloroethylene produced per hour by the cubic meters of catalyst used to produce the trichloroethylene. Example 1 For this example, a catalyst was prepared and evaluated which consisted of 0.1 percent by weight on an elemental basis of platinum and 10 percent by weight of copper on a carbon support. This catalyst was compared to a catalyst consisting of 0.1 percent by weight of tin and 10 percent by weight of copper on the same carbon support.

The platinum/copper catalyst was prepared by first dissolving 12.732 grams of CuCI ₂ (Aldrich Chemical Co., Inc., Catalog No. 22-201-1, 97 percent purity, containing approximately 0.46 percent of sodium, 0.13 percent of zinc, 380 parts per million of iron, 120 parts per million of sulfur, 120 parts per million of phosphorus and 500 parts per million of calcium as impurities) in 80.00 mL of distilled and deionized water. 60.15 grams of Calgon's wood-based WSIV Special activated carbon (Calgon Carbon Corporation, having a published or advertised specific surface area of 1400 m2/g and a pore volume of 1.25 cubic centimeters per gram) were added to the CuCI ₂ solution, and the flask was agitated rapidly to evenly coat the carbon carrier with the CuCI ₂ solution. The impregnated carrier was then dried in an evaporating dish in air at ambient temperatures for 18 hours. Thereafter, the carbon carrier was further air-dried in an oven at 120 degrees Celsius for 2 hours. An aqueous H ₂ PtCl6 stock solution was then prepared by dissolving 1.342 grams of H ₂ PtCI ₆ XH ₂ 0 (J. T. Baker, Inc., Baker Analyzed Grade, 37.5 percent platinum) in 50.00 mL of distilled, deionized water. 1.000 grams of this solution were placed in a 50 mL Erienmeyer flask and diluted with 7.00 grams of distilled, deionized water. 9.98 grams of the dried, copper- impregnated carbon carrier were then added to the flask, and the flask agitated to evenly coat the carbon with the aqueous H ₂ PtCl6 stock solution. The resulting catalyst was then dried in an evaporating dish in air at ambient temperatures for 18 hours, and further air-dried in an oven at 120 degrees Celsius for 2 hours.

The tin/copper catalyst was prepared for comparison by dissolving 0.0329 grams of Sn(C6Hs) (Aldrich Chemical Co., Inc.) in 20.00 grams of perchloroethylene in a 50 mL Erienmeyer flask. 9.14 grams of the previously-dried, copper-impregnated carbon material were then added to the flask with swirling to evenly coat the carbon with the Sn(CeHs) solution. The catalyst was air-dried, again, in an evaporating dish for 18 hours at ambient temperatures, and then dried for 2 hours at 120 degrees Celsius.

After charging, drying under a nitrogen purge and reduction, evaluations were conducted of single charges of the platinum/copper and tin/copper catalysts at several temperatures. The results of these evaluations are provided below in Table 1, and show a trichloroethylene yield for the platinum/copper catalyst at 220 degrees Celsius of 74.3 percent ((80.12 x 92.7)/100), for example.

TABLE 1

a = TCE = trichloroethylene

Example 2

For this example a supported platinum/tin/copper catalyst was prepared, having 0.10 percent by weight on an elemental basis of platinum, 0.37 percent by weight of tin, and 10.0 percent by weight of copper deposited on the same carbon carrier employed in Example 1. 0.122 grams of Sn(C6Hs) was dissolved in 48.69 grams of perchloroethylene in a 125 mL Erienmeyer flask. 17.23 grams of the previously-dried platinum/copper catalyst were added to the flask with swirling to coat the solution onto the carbon support, and the resulting catalyst was air-dried at ambient temperatures for 18 hours, then at 120 degrees Celsius for 2 hours.

A single charge of this catalyst was placed in the reactor, dried under nitrogen, reduced and then evaluated at several reaction temperatures but otherwise under the same overall conditions as in Example 1, with the results shown in Table 2:

TABLE 2

Productivity

Catalyst Other (kq/m3 ιr) 0.1 PtJ0.37Sn/10Cu//C 30.4 65.6 76.8 0.7b 78.4

a = TCE = trichloroethylene b = Vinyl Chloride

Tables 1 and 2 taken together demonstrate a higher perchloroethylene conversion for the tin-promoted platinum/copper catalyst, as compared to a like platinum/copper catalyst which does not include a promoter material. Example 3

A supported platinum/copper catalyst containing 0.044 percent by weight (on an elemental basis) of platinum and lO.O percent by weight of copper was prepared and evaluated in this example. The preparation, charging, drying and reduction of this catalyst were accomplished as in Example 1, with accommodations for the diminished platinum level. The o results of the evaluation of a single charge of this catalyst at several temperatures are as shown in Table 3 below:

5

0

5

0

5

TABLE 3

Productivity

Other

14.4 33.6 49.6 59.2 1.0b 67.2

a = TCE = trichloroethylene b = Vinyl Chloride

Example 4

A supported platinum/copper catalyst was prepared, charged, dried, reduced and evaluated as in Example 3, but for the use in the present example of a starting CuCI ₂ salt which was 99.999 percent pure as opposed to the 97 percent purity salt of Example 3.

The results from the evaluation of a charge of this catalyst at several temperatures are shown in Table 4 as follows:

a = TCE = trichloroethylene

Tables 3 and 4 together show that a platinum/copper catalyst made from the particular 97 percent purity copper salt from Aldrich Chemical Co., Inc., yields a higher conversion of perchloroethylene than does a 99.999 percent pure salt. The precise reasons for this difference are not presently known, although it is suspected that several or perhaps all of the various trace metals in the 97 percent purity grade may act synergistically with the prevailing copper and platinum metals. Example 5

A platinum/tin/copper catalyst was prepared, charged, dried, reduced and tested in this example which contained 0.044 percent by weight of platinum, 0.023 percent by weight of tin, and 10.0 percent by weight of copper.

An aqueous H ₂ tCl6 stock solution was prepared by dissolving 2.684 grams of H ₂ PtCI ₆ XH ₂ 0 (37.5% Pt, J. T. Baker, Inc., Baker Analyzed Grade) in 100.00 mL of distilled, deionized water. 2.122 grams of the stock solution and 10.138 grams of the 97% purity CuCI ₂ Aldrich salt were placed in a 250 mL Erienmeyer flask, and diluted with swirling with 52.00 grams of distilled water. 38.27 grams of the WSIV Special activated carbon (Calgon Carbon Corp.) were added to the flask with rapid agitation. The catalyst was dried in an evaporating dish in air at ambient temperatures for 18 hours, after which the catalyst was further air-dried in an oven at 120 degrees Celsius for 2 hours. A solution of Sn(C6Hs) dissolved in C CI was prepared by dissolving 0.0352 grams of this salt in 40.00 grams of C ₂ CI in a 250 mL Erienmeyer flask. 42.69 grams of the previously dried catalyst was added to this flask with rapid agitation. The catalyst was again air-dried at ambient temperatures for 18 hours, and then in an oven at 120 degrees Celsius for 2 additional hours.

The results of the evaluation are as shown below in Table 5.

TABLE 5

Selectivity (%)

Conversion trans- cis- Productivity

Catalyst ICQ TCEa QH?Cb C ₂ H _? CI _? (kq/m3^hr) 0.044Pt/0.023Sn/10Cu//C 190 12.68 >99 11.2 200 22.54 >99 20.8 210 38.89 95.3 3.0 1.7 35.2 220 65.86 92.5 4.6 2.8 57.6

a = TCE = trichloroethylene

Example 6

A platinum/tin/copper catalyst was also prepared in this example, but a CuCI ₂ salt of 99.999 percent purity was used to start rather than a 97 percent purity salt as in Example 5. In addition, the relative amount of tin was increased substantially, from 0.023 percent by weight in the previous example, to 0.15 percent by weight on an elemental basis.

The results of testing on a charge of this catalyst at various temperatures are provided in Table 6, all other circumstances and conditions being the same as in the immediately preceding examples:

TABLE 6

Selectivity (%)

Conversion trans- cis- Productivity

Catalyst IC ^Q i%l TCEa H?Cb C?H _? CI _? (kq/m3^hr) 0.044Pt/0.15Sn/10Cu//C 190 10.71 >99 9.6 200 15.68 >99 14.4 210 23.32 >99 22.4 220 32.15 94.5 5.5 28.8

a = TCE = trichloroethylene

Comparing Tables 5 and 6, the catalyst prepared from the 97 percent purity copper salt again converted more of the perchloroethylene than the 99.999 percent pure copper salt.

While various embodiments of the processes and catalysts of the present invention have been described and/or exemplified herein, those skilled in the art will readily appreciate that numerous changes can be made thereto which are nevertheless properly considered to be within the scope or spirit of the present invention as more particularly defined by the claims below.