CA2350582A1

CA2350582A1 - Catalytic dehydrodechlorination of ethylene dichloride

Info

Publication number: CA2350582A1
Application number: CA002350582A
Authority: CA
Inventors: Zhang Zongchao; Jelle J. Nieuwland
Original assignee: Individual
Current assignee: Akzo Nobel NV
Priority date: 1998-11-16
Filing date: 1999-10-26
Publication date: 2000-05-25
Also published as: AU1155800A; WO2000029359A1

Abstract

Ethylene dichloride can be dehydrodechlorinated to vinyl chloride by heating the ethylene dichloride at a temperature of not less than about 250~C in the presence of hydrogen gas and a dehydrohalogenation catalyst that comprises a noble metal on a carbon support.

Description

WO 00!29359 PCT/EP99/08160 CATALYTIC DEHYDRODECHLORINATION OF ETHYLENE DICHLORIDE
S Background of the nvention It is well known to dehydrochlorinate ethylene dichloride (also known 'as " 1,2-dichloroethane" ) thermally to form vinyl chloride. Typically, this is accomplished at temperatures of from about 500°C to about 550°C.
The art also contains certain disclosures about catalytic means to dehydrochlorinate ethylene dichloride to vinyl chloride. For example, U.S.S.R. Patent No. 2,070,551 teaches that ethylene dichloride is catalytically converted to vinyl chloride by heating at from about 280°C to about 400°C in the presence of hydrogen using a catalyst which comprises platinum or palladium on y-alumina. As illustrated by Comparative Example 2, which follows, the yield of vinyl chloride was found to vary from about 15%
to about 35% with a maximum selectivity to vinyl chloride of about 70%.
S~~mmar~of the Invention The present invention is directed to a catalytic process with good catalyst durability for the selective catalytic conversion of ethylene dichloride (EDC) to vinyl chloride (VC). The disclosed process utilizes a carbon-supported hydrogenation catalyst and also uses hydrogen during catalyst activation and reaction conditions. While it is not intuitive to have hydrogen in the feed for a dehydrochlorination reaction, the presence of hydrogen in the disclosed process allows the reaction to proceed with a relatively long catalyst life without deactivation with superior selectivity (Compare Comparative Example 2 with Examples 3 and 4, hereinbelow).
The catalyst that is employed in the process of the present invention is one that comprises a noble metal component on a carbon support. The noble metal that is selected for use is preferably selected from Groups 8-10 of the Periodic Table of the Elements, as depicted in Chemical and Engineering News, 63(5), 27 (1985). The preferred metals are platinum (Group 10) or palladium (Group 10), although ruthenium (Group 8) or rhodium (Group' 9) can also be used.
The amount of noble metal on the carbon support can range from about 0.05%, by weight of the support, to about 10%, preferably from about 0.3%
to about 3%. The support can be in any desired physical form (e.g., an extrudate or in pelleted form).
The process is carried out at elevated temperatures of over about 250°C, preferably from about 250°C to about 350°C in the presence of hydrogen, which can be present at a molar concentration with respect t0 the ethylene dichloride of from about 0.05% to about 5%, preferably from about 0.5% to about 1 %.
The claimed process involves hydrogenation conditions, meaning that the gas phase process involves the use of a hydrogenation catalyst and molecular hydrogen. It is noted that the claimed main process is not a hydrogenation reaction. However, according to the following non-binding theory, which was construed with hindsight, the hydrogenation conditions result in the selective hydrogenation of an acetylene by-product, which prevents the formation of coke from said acetylene. The reduced formation of coke is considered to be responsible for the improved catalyst life.
This invention is further illustrated by the Examples that follow.
This Example illustrates that when it is attempted to catalytically convert ethylene dichloride to vinyl chloride without the use of hydrogen during the reaction using a catalyst comprising an alumina support.

A fixed bed glass reactor with a diameter of 20 mm was used. About 100 ml (about 83 grams) of a conventional 0.5 wt% Pt/A1203 catalyst (1/8" pellets) was loaded into the reactor. The catalyst was activated with a stream of nitrogen (475 mllmin) containing 5% hydrogen gas at 300°C for five hours. The reaction was started at 300°C with an ethylene dichloride (EDC) feed rate of 0.8 ~Imin and nitrogen feed rate of 500 mllmin in the absence of hydrogen gas. The catalyst was found to rapidly deactivate from an initial conversion level of 20%.
This Example illustrates the present invention in which the reaction described in Example 1 is conducted in the presence of hydrogen.
A fresh catalyst from the same batch as described in Example'1 was used. The catalyst was activated in a stream of nitrogen (450 ml/min} and 10% hydrogen at 300°C for five hours. The reaction was performed at 280°C and 300°C, initially at an EDC feed rate of 0.72 g/min, and hydrogen concentration of from 1% to 2.4% in a total of 500 ml/min of nitrogen and hydrogen feed. The total feed rate was varied without changing the relative concentration of each component during later experiments. The EDC conversion was found to vary between 15% and 35% depending on the total feed rate and there was a maximum selectivity to vinyl chloride of about 70%. An important observation was that the catalyst showed improved stability in the presence of hydrogen during the test for about eight hours.
Fxam Ip a 3 This Example illustrates an embodiment of the invention. About 100 ml (43.5 grams) of a 0.8% PdIC catalyst ex Johnson Matthey was used. The catalyst was activated in a stream of nitrogen (450 ml/min) and 10% hydrogen at 300°C
for five hours. The reaction started at 280°C with an EDC feed rate of 0.72 glmin, and a hydrogen concentration of 0.26% in nitrogen (totaling 500 ml/min of H2 and N2). The EDC cracking level was 37% with a selectivity of 97%-100%
to VC. The catalyst was stable during the test for over six hours.
Exam In a 4 The previous test run was continued with the same catalyst at a decreased N2 and EDC feed rate and at 280°C. The EDC conversion was 60% with a selectivity of nearly 100% to VC under a EDC feed rate of 0.36 g/min and a nitrogen feed rate of 250 ml/min (0.5% Hz). The catalyst was evaluated at 280°C for about forty hours without showing signs of deactivation.
The preceding Examples are intended to only illustrate certain embodiments of the present invention and, for that reason should not be construed in a limiting sense. The scope of protection sough is set forth in the Claims that follow.

Claims

1. A process for the catalytic dehydrohalogenation of ethylene dichloride to vinyl chloride which comprises heating the ethylene dichloride in the presence of a dehydrohalogenation catalyst comprising a noble metal under hydrogenation conditions as obtained by the addition of hydrogen gas, characterized in that the noble metal dehydrohalogenation catalyst is supported by a carbon support.

2. A process as claimed in Claim 1 wherein the catalyst comprises a noble metal selected from any of Groups 8-10 of the Periodic Table of the Elements on the carbon support.

3. A process as claimed in Claim 2 wherein the noble metal is platinum.

4, A process as claimed in Claim 2 wherein the noble metal is palladium.

5. A process according to any one of the preceding claims wherein the ethylene dichloride is heated to a temperature of not less than 250°C.

6. A process according to any one of the preceding claims wherein the noble metal is present at from 0.05% to 10% by weight of the support.

7. A process according to claim 6 wherein the molar amount of hydrogen gas, based on the molar amount of ethylene dichloride, is from 0.05% to 5%.