DE1667212C3 - Process for reactivating alkali-activated palladium catalysts - Google Patents

Description

The invention relates to a process for reactivating palladium catalysts which are used in the production of unsaturated esters, in particular vinyl acetate _a5, from ethylene, oxygen and acetic acid

The production of vinyl acetate from ethylene and acetic acid by catalytic oxidation with oxygen takes place either in liquid phase or in vapor phase. Palladium is used as a catalyst, among other things used, but its use gives rise to problems. It is true that the vinyl acetate yield has been achieved Activation of the palladium with sodium acetate increases, but the activity of the catalyst still decreases very quickly in technical operation. So in BE-PS 66 465 a lifetime of the Pd catalyst named after only 40 hours.

Numerous proposals have become known about the stability and service life of the catalyst to increase. Recently it was found that the addition of gold increases the service life and durability of the catalyst is increased significantly and the vinyl acetate yield is also increased. The amount of gold in Catalyst can range from about 5 to 80 percent by total weight of the metals and is preferably about 5 to 20% by weight. The Pd or the Pd-Au catalyst can be used on a carrier Before it is used, it is usually prepared by adding a small amount of an alkali or alkaline earth metal preactivated with an organic or inorganic acid. But despite all these measures In the synthesis of unsaturated esters, there has been a significant drop in catalyst activity can not be avoided for longer periods of use. The exact reason for this loss of activity is Although not fully understood, it is believed that there are inorganic or organic impurities of the starting material on the catalyst and this with metallic, from corrosion products poison originating impurities. Regardless of what the reason for such a loss of catalyst activity, this phenomenon is ruled out for a large-scale Proceedings.

The invention is therefore based on the object to develop a simple and economic process in order to reactivate in vinyl acetate ^ _{Ejner NJCH (oxidierendcn w} AESS _n s alkaJisehen solution, but in this method is the treatment of catalysts in which The anthraquinone process had been used for the production of hydrogen peroxide

are, however, of those at the V; ⁿ ^ ^ac ^ ^thers ' ^ellun 8 _so different that no conclusions about the subject matter of the invention can be drawn from this state of the art. ^o ^ P ^ ° ^ J ^ers tellung reactivating spent catalysts with particular flussigern ammonia, quite apart from the fact that remain with the erhndungsgemaßen Reaklivierung small amounts of the alkali used for Reaktiyicrung Erdalkal.salze or on the catalyst. In the process of the invention it is also technically important that the necessary duration of the reactivation treatment can be checked optically with the greatest simplicity. - Even the preactivation with alkali or alkaline earth acetate solutions mentioned at the outset, which takes place before the first use of the Pd catalyst, did not suggest the process of the invention, because the problems of contamination and deactivation only arise during use.

The reactivation treatment according to the invention is generally carried out at ambient temperature and pressure. The effluent from the initial washing treatment is quite dark in color and treatment is generally continued until the effluent is either substantially colorless or a very light gray color. When the catalyst layer is soaked in the alkali solution, the soaking is carried out for about ¹ A to 4 hours, preferably about one to one hour. After the treatment has ended, the liquid is allowed to run off the catalyst layer and the water is evaporated at an elevated temperature in the range from about 60 to 200 ° C. in a stream of an inert gas such as nitrogen or argon. The used catalyst layer can also be prewashed with deionized or distilled water before the above reactivation treatment is applied. The method according to the invention also includes the use of other treatments, e.g. B. washing with organic or inorganic solvents or solutions, before reactivation is not off.

The alkaline component of the reactivation activation can be the same alkali or earth

solution is an alkali or alkaline earth salt of an organic alkali compound as used for reactivation

nic acid, an alkali or alkaline earth metal hydroxide

or a mixture of these. The particularly valuable Estersynthese is generally conducted at a have the alkali metal or Erdalkalisalzc of 5 Ü temperature between about 350 ° C and vorschwachen organic carboxylic acids with ■> 's zugsw.ise of about 50 to 250 ° C and at pressures of 18 Carbon atoms proved. In various cases in the range from about 1 to 105 atm and preferably in cases it has also proven to be advantageous to carry out the salt of the organic acid when preparing the alkali at a pressure in the range from about 1 to 18 atm. For the reactivation, however, “if the solution is an alkali or alkaline earth hydroxide 10, neither the temperature nor the pressure conditions have to be mixed in. One can also choose the alkali or earth crucial.

Use alkali hydroxide alone or with an alkali The catalysts to be reactivated can all-

Lischen, the hydroxide-containing solution in common in the vinylation of alkenes with 2 to

bond with another alkaline solution in 18 carbon atoms, e.g. ethylene, propylene,

reactivate successive levels. As preferred 15 butene-1, butene-2, isobutylene, octadecene-1, pentene-2,

added alkaline constituents have sodium, pentene-3, for the production of the corresponding un-

Lithium and potassium salts or hydroxides have been shown to be used in saturated esters. Further examples

and in particular one works with sodium salts. for suitable unsaturated hydrocarbons

such as sodium acetate, borate, phosphate and tartrate, butadiene, styrene, p-chlorostyrene, allyl acetate, AHyI-

as well as sodium hydroxide and mixtures of benzene, ethyl acrylate and 1,5-hexadiene, as well

the same. Mixtures of one or more of these compounds.

In general, reactivation salts are suitable, the organic acid of which is used in the process

aqueous solutions have a pH of about 7 according to the invention, preferably acetic acid

or have their ionization constant set below 10 "'. You can also use other acids

located. As anions, for. B. citrate, acetate, borate, 25 work, e.g. B. ant, chloroacetic, phenyl acetic,

Phosphate, tartrate, benzoate, aluminate and the propion, isobutter, benzoin, 4-methylbenzoe,

same can be used. Halides are said to be lauric, paimitic, stearic acid and their mixtures

be avoided because they adversely affect the synthesis. The reaction formed by the organic acid

in fl uence. tion participant can have the formula R'COOH,

The concentration of the alkali or alkaline earth salt 30 wherein R 'is hydrogen or a substituted or

or hydroxides in the alkaline solution can be unsubstituted, branched or straight-chain, ali-

over a broad range from about 0.25 to phatic, cycloaliphatic, or aromatic

30% by weight vary and is preferably about the remainder with about 1 to 17 carbon atoms, preferably

0.25 to 10%. The amount of alkali 1 to 10 carbon atoms used in the molecule is also

ical solution is not critical and may vary from 35 points.

about 0.1 to 10 1/350 g of catalyst range. Preferential reactivation according to the invention is wise however, one works with about 1 liter of one passed by terminating the synthesis and using TemlO% Alkali salt or alkali hydroxide solution to temperature and pressure to ambient conditions, before-35Og Catalyst. preferably about 20 to 100 ° C and about 0 to 1 atm,

The use of palladium metal or a 40 lowers it. Then one of the two above is combined Working methods removed from palladium and gold metal. You can holding catalyst is used in the preparation of reaction device with the alkaline solution Vinyl acetate preferred. flood and this in the reactor for about 15 to 60 minutes,

The catalysts can be impregnated on an inert carrier, preferably for about 15 to 30 minutes

ger can be used. You can leave the catalyst 45, then essentially all free liquid

also on the wall of the reaction device, let it run off and repeat the treatment,

Separate glass beads etc. or place it in a vortex until the required amount of alkaline solution

layer or in a mixture with inert solids has been used or until the withdrawn liquid

clogging of the reaction device is essentially colorless or very

prevention. The light straw color is particularly good. According to the other way of working

the obtained when the catalyst is on an inert, the alkaline solution is continuous or inter-

Carrier is applied. As carriers are in particular pumped through the catalyst layer until

their aluminum oxide or mixtures of barium, the above conditions are achieved. the

Strontium or calcium carbonates with silicon- general teaching of the invention, however, consists in

dioxide-alumina preferred. 55 the treatment of impaired or impaired

In the ester synthesis need in general needed! Catalyst with an alkaline solution only catalytic amounts of the catalysts used for reactivation to technically acceptable to become. The total metal content of the catalyst values, and neither the special method of the zucann from about 0.1 to 5% by weight of the inert contacting of the catalyst with the alkaline The carrier is sufficient and is preferably about 0.5 60 solution and the explanation of the catalyst reaction 2% by weight activation are crucial for the invention.

The catalyst can, as discussed above, be The reactivated catalyst can after use with a smaller amount of an alkali treatment with the alkaline solution of a final or alkaline earth hydroxide or salt of an organic wash with distilled or deionized water or inorganic. Acid are preactivated. 65 ser. The amount of activator treated in this way can range from about 20 to the delte catalyst by flushing with 100,000 of the total weight of the metal and an inert gas, ζ. B. nitrogen, in the case of is preferably about 50 to 250 ^u / ₀ . Dried temperatures used for the pre-ester synthesis.

The following embodiments serve to further explain the invention.

example 1

A) In a 2.5 X 91.4 cm reaction device for Production of vinyl acetate from acetic acid, ethylene and oxygen in the vapor phase were 340 g with Sodium acetate preactivated Pd-on-aluminum oxide catalyst used. After 500 hours of use decreased in the temperature range from 143 to 152 ° C and pressure range from 2.5 to 6.0 atm the rate of formation of vinyl acetate from 7 to 2 kg / kg Pd / hour.

For reactivation, 1 liter of 10% aqueous sodium acetate solution was then passed through the catalyst layer passed in 5-200 ml aliquots. 200 ml of the solution were from the Shift held. The layer was then dried under a stream of nitrogen at 135 "C. After With a short synthesis time, the rate of formation rose from 2 to 7.5 kg vinyl acetate / kg Pd / hour.

B) After 270 hours of operation at 146 ° C. and 6.0 atm, the rate of formation decreased from 7.5 to 4.7 kg vinyl acetate / kg Pd / hour. away. By repeating the reactivation of A, the formation rate became to 13 kg vinyl acetate / kg Pd / Sld. elevated.

Example 2

In a 2.5 × 76.2 cm reaction device for generating vinyl acetate from ethylene, oxygen and acetic acid in the vapor phase, 113 g of a Pd / Au-aluminum oxide catalyst preactivated with sodium metaborate were used. After 350 hours of operation at 125 ° C., 3.5 ata and a feed ratio of ethylene to O ₂ to acetic acid (C ₂ H ₄ ZCH ₃ COOH) of 9: 1/2, the rate of vinyl acetate formation fell from the initial value of 9.0 kg vinyl acetate / kg Pd / hour to a value of 6.5 to 7.0 The material supply was interrupted at this point, and the catalyst layer was cooled to 60 to 80 ° C. with an argon flush, whereupon the layer was treated with an aqueous solution of 10 V _n Na., B., O ₄ · 8 H ₂ O + 0.25 <■ / “NaOH. The washing solution was pumped into the reactor outlet for washing at 8 to 10 ml / min, while the washing solution which ran off was collected at the reactor inlet. A total of 1 liter of washing solution was used and the layer was left to soak for 30 minutes before the last 100 ml were pumped in. The layer was finally dried under a stream of argon. After a short conditioning, the rate of formation rose to 8.5 kg vinyl acetate / kg Pd / hour.

Example 3

Catalysts contaminated with tars during vinyl acetate production (2% Pd, 0.3 ¹ Vo Au on aluminum oxide as a carrier) were regenerated as follows. 12 g items of the reduced activity catalyst were placed in glass tubes 1.9 cm in outer diameter, bedded on glass wool and covered with the washing solution according to the table, allowed to stand for 15 minutes and then washed at room temperature by periodically removing 10 to 20 ml of solution from the tube bottom were removed while fresh solution was added at the top. Washing was continued until the effluent was clear or a very light straw color. After the washing process had ended and the catalyst layers had run off, nitrogen at a temperature of up to about 140 ° C. was passed through to remove excess water. To determine the activity in the dry state in the vinyl acetate synthesis, a mixture of 15% O., in C ₀ H ₄ , in acetic acid was ^{saturated at 70 0} C, at 1.5 1 / hour. passed over 10 g of the catalyst kept at 140 ° C. in each case.

attempt Washing method (12 g catalyst)
Washing solution volume time
Hours. Millimoles of vinyl acetate
per hour with 10 g
catalyst
2 hours 24 hours 5.5 A. none 4.6 6.2 B. 5 «/ oCH ₃ COONa 160 2 4.8 7.2 O) (a) 5% CH ₃ COONa
(b) 4VoCH ₃ COONa 150
150 2 6.4 8.0 D ² ) (a) 5 "/ 0CH ₃ COONa
(b) 5% / β NaOH
(c) 5% CH ₃ COONa 60
120
50 2 7.5 8.0 E. 2% NaOH 200 3 6.3

') Washing with (a) and (b) successively;

Wash (b) with a mixture of sodium acetate and NaOH. ² ) Wash with (a), (b) and (c) in succession.

B is η ie 1 4 ⁶ 5 ethylene and oxygen in the vapor phase were

110 g of a Pd / Äu- preactivated with sodium acetate

A) In a 2.5x76.2 cm reaction device on alumina catalyst at 125 to 142 ° C, for the production of vinyl acetate from acetic acid, 3.5 ata and a molar feed ratio

of C ₂ H ₄ ZCH ₃ COOH from 10:> / ₂ to 7: V * are used. After 1904 hours of use and four previous regeneration wash treatments, the catalyst was washed with a solution of 10% sodium acetate and 0.25% sodium hydroxide, for which the wash solution was poured into the water at 7 to 10 ml / min, at 60 to 80 ° C The reactor outlet was pumped in and the washing medium flowing out was collected at the reactor inlet. After 600 ml of washing solution had been consumed, with the catalyst being soaked for 30 minutes after 500 ml had been consumed, the washing medium flowing off was clear. Then the catalyst was dried in a stream of argon. After conditioning for 24 hours, the vinyl acetate formation rose from 7.5 to 3.5 kg vinyl acetate / kg Pd / hour.

B) The same catalyst was washed again after 2523 hours, the operating conditions remaining the same with the modification that the molar charge ratio of ethylene to O ₂ to acetic acid was 6: 1: 2. Washing was carried out in the same way, and after using 700 ml of washing solution and soaking the catalyst layer for 30 minutes, after 600 ml had been consumed, the washing medium flowing off was clear. After drying the layer in a stream of argon and conditioning for 16 hours, the vinyl acetate formation rose from 7.3 to 8.5 kg vinyl acetate / kg Pd / hour.

C) In another reactor unit, 108 g of a Pd / Au catalyst were a total of 309 hours, namely 88 hours with pure reagent acetic acid and 221 hours with recovered, distilled acetic acid in the feed stream at 125 to 127 ° C, 3.5 ata and one molar Charge ratio of C ₂ H ₄ O _{2 ZCH 3} COOH of 9.5 to 8.8: · / «used. After 309 hours the rate of formation fell to 16.7 kg vinyl acetate Zkg PdZStd. and the layer was washed as under A and B with 10 ⁰ Zo sodium acetate + 0.25 ⁰ Zo NaOH. After using 1 l of washing solution and soaking the layer for 30 minutes after using up 800 ml, the washing medium which ran off was clear. After the layer had been dried in a stream of argon and conditioned for 23 hours, the vinyl acetate formation rose from 6.7 to 8.0 kg vinyl acetate Zkg Pd / hour.

Example 5

113g catalyst 511 hours at a vinyl acetate-vapor-phase synthesis at 125 to 137 ° C and was used ata 3.5, were washed at 60 to 80 ° C with a solution of lO ° / o sodium acetate + 0.25 ⁰ Zo sodium hydroxide by adding 8 to 10 ml of ZMin. into the reactor outlet

ao was pumped in. The first material flowing off was very dark in color and began to flow after 100 ml to lighten something. After 1250 ml the washing medium was still colored, after which the layer was 20 minutes was left to soak. The good that ran off after the watering was a little darker than that last outflowing washing medium colored. The catalyst was now washed with a further 300 ml, whereby the washing medium cleared, but still showed some color.

After the synthesis was restarted, the formation of vinyl acetate rose from 7.1 to 9.3 kg of vinyl acetate Zkg PdZStd.

The above values show the considerable efficiency with which the reactivation takes place.

709 647/31

Claims (1)

Claim: Process for reactivating alkali-activated Pallad.umkataiysatoren for the production of vinyl acetate from ethylene, acetic acid and oxygen with aqueous-alkali agents, characterized in that the reduced activity exhibiting palladium catalyst with an aqueous solution of an alkali or alkaline earth metal salt of a weak organic carboxylic acid or with alkali or alkaline earth metal hydroxide solutions or mixtures thereof and the washing treatment continues until the washing solution flowing off is light straw-colored to colorless, and that you then incrlen Sefisr ^{in a streak of water} Gas dries. used valuable palladium catalysts to recover with little effort and without loss. . The invention is a method for of alkali activated palladium for the manufacture of vinyl acetate Acetic acid and oxygen with aqueous Mitieln, characterized in that nian "the 'cine exhibiting reduced activity Palladium catalyst with an aqueous solution of an alkali or alkaline earth salt of a weak organic carboxylic acid or with alkali or alkaline earth metal hydroxide solutions or mixtures thereof washes and the washing treatment continues until the washing solution draining off is light straw-colored to colorless is and that you then the catalyst in