DE2353437A1 - Ethylene oxychlorination with oxygen and hydrogen chloride - purified from acetylene by catalytic hydrogenation - Google Patents

Abstract

C2H4 oxychlorination process, by heat-dissociation of 1,2-dichloroethane to vinyl chloride and HCl, separation of HCl, purification of HCl by hydrogenation of C2H2 present using a Pt metal catalyst and catalytic reaction of purified HCl with C2H4 and O2 to 1,2-dichloroethane, takes place by effecting hydrogenation in at least 2 consecutive catalyst zones in which catalyst activity increases in prod. stream direction. Hydrogenation of C2H2 in HCl can take place at space flow velocities >5000 (7000-15000) vol. gas/vol. catalyst/hr. without C black deposition on catalyst; high flow velocities allow use of less catalyst. In 1st zone catalyst is sufficiently active to hydrogenate most of C2H2 but not active enough to decompose C2H2 under C black formation. In subsequent zone, catalyst is so active that remaining C2H2 is completely hydrogenated.

Description

BASF Aktiengesellschaft *> q γ q / q «7

Our mark ?: O.Z. 30 173 Dd / L 6700 Ludwigshafen, 2.4.10.1972

Process for the oxychlorination of ethylene

The invention relates to a process for the oxychlorination of Ethylene with oxygen and hydrogen chloride, which by catalytic Hydrogenation of acetylene has been purified.

In a large-scale process for the production of vinyl chloride takes place as an intermediate stage, an oxychlorination of ethylene instead of. The resulting 1,2-dichloroethane is thermal split into vinyl chloride and hydrogen chloride, with the hydrogen chloride is used again in the cycle for oxychlorination. In the thermal cleavage of 1,2-dichloroethane Acetylene is formed as a by-product, which, after the hydrogen chloride has been separated off, is contained in it in quantities of about 0.1 to 1 percent by volume. In the oxychlorination reaction can Acetylene react to form highly chlorinated derivatives of ethane and ethylene, which interfere with the further course of the cycle and have to be separated.

In DT-OS 1 568 679 it is proposed to remove the acetylene by hydrogenation over platinum or palladium catalysts, namely the hydrogenation should be carried out at room flow rates of about 300 to 5,000 parts by volume of gas per part of catalyst per hour (at 15, 6 ⁰ C). The low room flow velocities result from the use of catalysts with relatively low activity, which are distributed on support materials in concentrations of only 0.5 or 0.1 percent by weight. If you do not want to reduce the flow rate of the gas and thus the space-time yield of the oxychlorination reaction, you have to use this process

404/73 -2-

509820/1155

- 2 - o "z. 30 173

use a relatively large amount of catalyst in order to obtain complete hydrogenation.

On the other hand, it has been shown that when more active catalysts are used, soot deposits as a result of decomposition in the course of time of acetylene occurs, reducing its effectiveness.

The invention was therefore based on the object of providing a method for To develop oxychlorination of ethylene, in which the hydrogenation of the acetylene contained in hydrogen chloride at higher Room flow velocities as 5,000, preferably between 7,000 and 15,000, can be made without soot formation occurs at the catalyst.

It has been found that this object is achieved - if the hydrogenation is carried out in at least two successive catalyst zones in which the activity of the catalyst in Product flow direction increases.

In the first zone, the catalyst is still active enough to cause a To hydrogenate a large part of the acetylene, but not active enough to cause the acetylene to decompose with soot deposition. In the downstream zone, the catalyst is so active that it completely hydrogenates the remaining acetylene, as a result of the essential However, with a lower acetylene concentration, no decomposition occurs here either.

Since this enables high room flow velocities to be achieved, it is possible to manage with significantly less catalyst overall • than with the known process.

The process for the oxychlorination of ethylene and the cycle process described are known per se. In the DT-OS already quoted 1,568,679 describes this procedure in detail. the Oxychlorination reaction can also be carried out in fixed bed reactors in addition to fluidized bed reactors carried out, e.g. according to a method known from DT-OS 1,493,213.

509 8 2 0/1155

ORIGINAL IMSPECTED

- 3 - O.Z. 30 173

The actual hydrogenation can be carried out under the conditions under which the hydrogen chloride is present after the cleavage and separation. One, preferably at temperatures between "50 and 25Q ° C, in particular between 120 and 200 ⁰ C, and at pressures between 1 and 10 bar, the molar ratio of hydrogen to acetylene may be between 1:. Ι .1 and 6 are 1, 2 are preferably up to 4 moles of hydrogen per mole of acetylene are used. "..- .. - ■.

The hydrogenation is carried out with hydrogen, if necessary with inert diluents such as methane, or nitrogen, can be diluted.

Platinum metals are used as catalysts, preferably Palladium, used as metals, as oxides or as salts can be. They are generally distributed on conventional carrier materials, e.g. on silicon dioxide, silica gel, aluminum trioxide, Silicon carbide, carbon or on silicates, e.g. molecular sieves. The carriers can be in the form of spheres, tablets or in the form of granules in bulk. One can also Use monoliths. The particle size of the catalyst can vary within very wide limits.

The essence of the invention is to be seen in the fact that the hydrogenation is carried out in at least two successive catalyst zones in which the activity of the catalyst increases in the direction of the product flow. In the simplest case, these are two catalyst zones. It is preferable to work in three zones, but you can also arrange more zones one behind the other. The first, least active zone, in which the majority of the ethylene is hydrogenated, should preferably make up at least 50 % of the total catalyst volume.

The relative activity of the catalyst in the various Zones can be determined by comparing catalyst efficiency; for example, by changing the degree of hydrogenation of the ace- " tylens, the sole application of the respective Catalyst zones is achieved. It is preferred to do the activities

■■ ". '. ■ -. -4-509820 / 1155

- 4 - O.Z. 30 173 *

235343?

so graded ,, that in the first zone at least 30, preferably at least 50 %, but less than 90 % of the acetylene is hydrogenated, and that. after the last catalyst zone, the acetylene is at least 95 % hydrogenated, preferably more than 99%.

There are different ways of producing catalysts with different activities. The easiest way to do this is to use different concentrations of catalyst on the support material. So for example it is advantageous to keep in the first catalyst zone, the concentration of PaIadium below 0.1 fo, and then to increase it in the last zone to over 0.2%. Another possibility is to modify the active surface of the catalyst, for example by post-treating the catalyst support at different temperatures.

Finally, you can also add inhibitors to the catalyst, which then also suppress the formation of soot. So it has proven to be useful to use small amounts in the first zone Add zinc, preferably as an oxide. Chromium, copper, silver, gold, iron, rhodium or ruthenium also act as inhibitors.

example
The following catalysts were used:

a) 0.02 % palladium and 0.01 % zinc oxide on a silica support, inner surface 125 m ² / g, pore volume 0.9 ccm / g,

b) 0.5 % palladium on aluminum oxide support, inner surface 250 m ² / g, pore volume 0.6 ccm / g,

c) 1 % palladium and 0.2 % zinc oxide on aluminum oxide support, inner surface 225 m ^ / g, pore volume 0.6 ccm / g.

These catalysts were poured into a pipe with a diameter of 26 mm one after the other in the order 400 mm a), 400 mm b) and 200 mm c). The tube was preheated to about 160 ° C. 170 ⁰ C hot hydrogen chloride from the 1,2-dichloroethane cleavage, the 0.2

5 0 9820/1155

ORIGINAL INSPECTED

Percent by volume of acetylene was mixed with 2 mol of hydrogen per mole of acetylene "and forced through the pipe at 8 atmospheres with a space velocity of 11,000 liters of gas per 1 catalyst and hour. After the treatment, the gas contained 0.11 percent by volume of acetylene, 0.15 percent by volume ethylene and 0.12 % ethane. The hydrogen chloride was then reacted with air and ethylene to give chloroethane . The reaction was operated continuously for several weeks without any noticeable soot deposition on the hydrogenation catalyst.

509820/1155

Claims (1)

- 6 - O ₀ line 30 Claim Process for the oxychlorination of ethylene by thermal cleavage of 1,2-dichloroethane into vinyl chloride and hydrogen chloride , separation of the hydrogen chloride, purification of the hydrogen chloride by hydrogenating the acetylene contained therein with a catalyst based on a platinum metal and catalytic conversion of the purified hydrogen chloride with ethylene and oxygen 1,2-dichloroethane, characterized in that the hydrogenation is carried out in at least two successive catalyst zones in which the activity of the catalyst increases in the direction of the product flow. BASF Aktiengesellschaft 508820/1 155