HU212447B - Process for producing catalysts usable for the production of alkenyl alkanoates - Google Patents

Abstract

The present invention relates to a process for the preparation of catalysts for the preparation of alkenyl alkanoates from alkene, alkanoic acid and oxygen-containing gas. The most important characteristic of the catalysts is that their sodium content does not exceed 0.3% by weight, this low sodium content allows increasing the activity of the catalyst. In the preparation of the catalyst according to the invention, the reduction of the sodium content is achieved by washing out the sodium ions in the preparation of the catalyst by treatment with water or an aqueous solution containing potassium. EN 212 447 B Scope of the description: 10 pages (including 1 sheet)

Description

The present invention relates to the preparation of Pd / Au sodium-reduced catalysts which are useful in the preparation of alkenyl alkanoates starting from alkenes, alkanoic acids and oxygen-containing gases.

The preparation of catalysts for the preparation of alkenyl alkanoates (hereinafter alkenyl alkanoate catalysts) is known. For example, U.S. Patent 4,048,096 (Bisset) discloses the preparation of a catalyst having a specific activity of at least 83 g vinyl acetate per g of given metal and determined at 150 ° C. The vinyl acetate catalyst of the above-mentioned patent essentially consists of: (1) a catalyst support having a particle size of 37 mm and a pore volume of 0.2-1.5 ml / g, and a 10% by weight aqueous suspension of the catalyst support. pH value between 3 and 9, (2) a palladium-gold alloy distributed over the catalyst support surface layer, less than 0.5 mm from the support surface, and the amount of palladium in the alloy 1-5 g / l catalyst, gold content is 0.5-2.25 g / l catalyst, and (3) 5-6 g / l alkali metal acetate / l catalyst. Palladium is described in the catalyst as the active catalyst metal and as the gold catalyst promoter.

The above patent also describes a process for the preparation of the catalyst. Like Kronig et al., In this process, the metal salt is precipitated on the support surface of the catalyst. The procedure consists of the following steps:

(1) impregnating the catalyst support with an aqueous solution of a water-soluble palladium and gold compound, (2) precipitating the water-soluble palladium and a gold compound on the catalyst surface by contacting the impregnated catalyst support with a compound (preferably sodium metasilicate) reacting with a water-insoluble palladium and gold compound to form a water-insoluble palladium and gold compound, (3) converting the resulting water-insoluble palladium and gold compound into metal palladium and gold by treatment with a reducing agent, (4) ) drying the catalyst (see, for example, Example I), (6) impregnating the catalyst with an alkali metal acetate promoter (e.g., potassium promoter), and (7) drying the catalyst.

According to the above patent, a novel feature of the process is the distribution of palladium and gold in the form of an alloy on the catalyst support surface layer which is less than 0.5 mm of the support surface. The impregnation step is carried out with an aqueous solution of palladium and gold and the volume of the solution has an absorption capacity of ca. 95-100%. The precipitation step in the process is carried out by soaking the wet catalyst support with an alkali metal silicate solution containing an amount of an alkali metal silicate such that after contacting the catalyst support for 12-24 hours, the pH of the solution is 5. , Should be between 5-9.5.

The above patent does not mention the sodium content of the catalysts. Example 1 describes that the activity of the example catalyst is 560 g of vinyl acetate per liter of catalyst over 1 hour. In the following example (ΠΙ), two catalysts were prepared as described in Example 1 of the above patent and had a sodium content of 0.32 and 0.28% by weight and an activity of 551 and 538 g of vinyl acetate per 11 catalysts per hour. .

However, despite the known procedures, it is necessary to further increase the activity of alkenyl alkanoate catalysts.

Accordingly, the present invention relates to the preparation of improved catalysts for the preparation of alkenyl alkanoates from alkenes, alkanoic acids and oxygen-containing gas. The catalyst of the present invention contains palladium, gold, and potassium promoters and is characterized by reduced sodium content which results in increased catalyst activity. In the present invention, the reduced sodium content is provided by washing the catalyst with water or an aqueous solution of the potassium promoter after impregnation with the potassium promoter.

SUMMARY OF THE INVENTION The present invention relates to a process for the preparation of catalysts of increased activity for the preparation of alkenylalkanoates from alkenes, alkanoic acid and oxygen-containing gas by impregnating palladium, gold and a potassium promoter, which is a potassium alkanoate or by adding and drying the compound by washing the resulting catalyst with water or an aqueous solution containing potassium promoter in a further step, and recovering the resulting reduced sodium catalyst in a known manner.

For example, the process of the present invention utilizes a catalyst (Bissot catalyst) as disclosed in USP 4,048,096. This is the following

a) to g), the sodium content of the resulting catalyst according to the invention is reduced by washing with water or washing with an aqueous solution containing potassium promoter.

Thus, the process of the invention is carried out, for example, as follows:

a) impregnating the carrier particles with an aqueous solution of a water-soluble palladium and gold compound,

b) precipitating the water-soluble palladium and gold compound on the surface of the carrier particles with a co-precipitant,

c) reducing the precipitated water-insoluble palladium and gold compound to a metal palladium and metal gold using a reducing agent on the surface of the particles; and

d) washing the impregnated support with water,

e) drying the impregnated substrate,

f) impregnating the carrier particles with a potassium promoter,

g) drying the substrate so impregnated when

A dried catalyst containing sodium is obtained due to the presence of sodium in the materials used in steps a) to f), followed by

h) washing the dried catalyst with water or an aqueous solution containing a potassium promoter to reduce the amount of sodium in the catalyst and thereby increase the activity of the catalyst, and

i) drying the catalyst.

In the practice of the process of the invention, it is preferable to use the aqueous solution containing the potassium promoter in step h) to avoid a decrease in the concentration of the potassium promoter introduced by impregnation in step f). However, an undesirable decrease in promoter concentration can occur if water is used in step h). However, if water is used in step h) and the promoter concentration is thereby undesirably reduced, step i) may be followed by step j), which is followed by a second potassium promoter impregnation followed by step k) which is a third drying step. operation. In some cases, the first potassium promoter impregnation step f) may be used in excess of the potassium promoter to ensure that the product of step i) contains the appropriate amount of potassium promoter even after the aqueous wash step h). The latter case eliminates the need for operation steps j) and k).

Without wishing to be bound by theory, it is believed that in the Bissot catalyst preparation steps, the potassium promoter removes at least a portion of the sodium bound to the ion exchange sites on the catalyst support. The starting materials used in the Bissot process, especially the precipitant, are the source of sodium. Although the potassium promoter displaces sodium, it remains sodium in the catalyst prepared by the Bissot process, which is a contaminant that reduces activity. In the process of the present invention, the displaced sodium is easily removed from the catalyst by a simple wash with water or an aqueous solution containing the potassium promoter (step h). Prior to displacement by the potassium promoter, sodium cannot be effectively removed from the catalyst in a single wash (i.e., step d) in step f) because sodium is too tightly bound to the support. However, step d) is effective for removing unbound impurities such as chlorides and excess reagents left over from steps a) to c).

BRIEF DESCRIPTION OF THE DRAWING FIG

Figure 1 illustrates the expected effect of sodium content on the performance of vinyl acetate catalysts of the present invention.

A preferred embodiment of the process of the invention

The carrier used in the process of the present invention is a solid particulate material which is capable of exchanging anions and can be impregnated with palladium, gold and potassium promoters, and under inert conditions used in the preparation of alkenyl alkanoates such as particulate silica, aluminum. oxide and silica / alumina. Preferably, silica is used. The specific surface area of the carrier is preferably 100 to 800 m ² / g.

The water-soluble palladium and gold compounds of the present invention may be any water-soluble palladium or gold compound, such as:

palladium (II) chloride, sodium tetrachloropalladium (II) (Na ₂ PdCl ₄ ), palladium (II) nitrate, palladium (II) sulfate, gold (III) chloride, or gold (III) acid (HAuCl ₄ ). The volume of the solution used for impregnation preferably corresponds to 95-100%, preferably 98-99%, of the pore volume of the carrier.

Lithium and potassium silicates or hydroxides are used in the process of the invention. The precipitant is preferably used in an aqueous solution which

1.6-1.8 molar excess of precipitant. The volume of this solution is preferably such that it covers the carrier.

The reducing agent to be used in the process of the invention may be, for example, a hydrazine, ethylene, formaldehyde, hydrogen or sodium borohydride. The reducing agent is preferably used in the form of an aqueous solution containing a molar excess of 50: 1, preferably 10: 1. When hydrogen is used as the reducing agent, it is usually necessary to heat the catalyst to 100-300 ° C to complete the reduction.

The potassium promoter used in the process of the invention is, for example, potassium alkanoates or any potassium compound that is converted to potassium alkanoate during the reaction to form the alkenyl alkanoate (i.e., ethylene, alkanoic acid and oxygen-containing gas). Preferred potassium compounds are, for example, potassium acetate, hydrogen, carbonate, nitrate and, when a stable carrier is used, potassium hydroxide. The promoter is preferably used in the form of an aqueous solution.

The washing steps d) and h) of the process according to the invention can be carried out batchwise or continuously. Continuous washing is generally more effective, but not always applicable to a large scale catalyst production process. For continuous washing, the wash fluid is slowly and continuously passed through the catalyst over a specified period of time (e.g., 8 to 24 hours). For batch washing, the catalyst is contacted with the wash liquid, and the resulting mixture is allowed to stand, for example, for 0.5 to 2 hours, and then the liquid and catalyst are separated. There are often more washes than batch wash, for example

2-10, preferably 4-6 washes may be required. The temperature is generally 20-80 ° C and the volume ratio of wash liquid to catalyst is 2-1 to 1001 for both intermittent and continuous washings.

Step h) of the process of the invention wherein a

The catalyst is washed with water or an aqueous solution containing the potassium promoter, different from the impregnation step of the prior art with potassium promoter. Such prior art impregnation steps are carried out using the initial wetting method or decantation method. In the initial wetting process (see, for example, Example 5 of British Patent No. 1,215,210), the catalyst is contacted with a minimum amount of aqueous potassium promoter solution to fill the pores of the support and impregnate with the desired amount of potassium promoter, and then evaporate the water. In this method, sodium cannot be removed from the catalyst. In the decantation process, the catalyst is immersed (preferably dry) in an aqueous potassium promoter solution in a volume greater than that used in the initial wetting technique. After the pores are saturated, the excess solution is decanted and the catalyst is dried. Here, only one immersion and one decanting operation are performed and the contact time is relatively short. Consequently, a minimal amount of sodium can be removed from the catalyst by decantation. The decantation process for a wet catalyst is described, for example, in Example 9 of U.S. Patent No. 3,743,607 to Sennewald et al.

In the process according to the invention, the drying step of steps e), g), i) or k) may be carried out in any known manner. An example is the drying step of drying in flowing air at 40-120 'for 10-30 hours.

The following examples further illustrate the process of the present invention. Abbreviations have the following meaning:

Carrier I: Silica beads having an average diameter of 5-6 mm and a sodium content of 0.1% by weight. The beads have a specific surface area of 150200 m ² / g and a pore volume of 0.6-0.7 mm / g. The carrier I contains SiOH groups capable of cation exchange, manufactured by Sud Chemie AG under the designation KA-160.

STY *: Space Time Yield (measure of catalyst activity in units of vinyl acetate / liter catalyst per hour).

% Selectivity *: Selectivity is calculated as: Selectivity = 100 x (mole of vinyl acetate) / mole of vinyl acetate + 1/2 x CO ₂ mole).

AA Analysis: Atomic Adsorption Spectroscopy ICP: Inductively Coupled Plasma Optical Emission Spectrometry g VA / 1 cat / hour: amount of vinyl acetate produced per hour per catalyst.

* means: all activity and selectivity values given in the following examples refer to the activity and selectivity values determined 24 hours after completion of the oxygen addition according to the given catalyst assay.

VA: vinyl acetate

KOAc: potassium acetate EtOAc: ethyl acetate NaOAc: Sodium acetate %: g: crowd% gram ml: milliliter mm: millimeter

Process for the preparation of a catalyst

A. 15 g of carrier I are mixed with 0.258 g of Na ₂ PdCl ₄ (35.86% Pd) and 0.094 g of HAuCl ₄ (48.94% Au) in 9 ml of deionized water. The resulting mixture is stirred gently until the moisture is absorbed onto the support and then allowed to stand in a sealed flask at room temperature for 1 hour to allow the palladium and gold salts to impregnate. The wet catalyst is then covered with either 0.236 g of sodium hydroxide dissolved in 28 ml of water or 0.873 g of sodium metasilicate (Na ₂ SiO ₃ ) dissolved in 28 ml of water as the precipitant. After stirring for a few seconds, the mixture is allowed to stand for 23 hours at room temperature without stirring and the liquid is covered with a solid which precipitates water-insoluble palladium and gold on the surface of the support. Palladium and gold are then reduced to metal palladium and metal gold by the addition of 1 g of 85% hydrazine hydrate by stirring for a few seconds and then standing at room temperature for 23 hours. The supernatant liquid is then separated from the catalyst by decantation and the catalyst is rinsed four times with water to remove a small amount of metal residue. The catalyst is then thoroughly rinsed by column washing or batch washing as described below. The catalyst is then dried on a stainless steel sieve at 60 flowing air for 2024 hours. The catalyst is then tested for potassium by AA analysis. The catalyst is then impregnated with the desired amount of acetate in aqueous solution according to the impregnation method described above. The impregnated catalyst is then dried at 60 'for 20-24 hours. The prior art Bissot process (i.e., steps a) to g) mentioned above is completed at this point. However, process B of the present invention further comprises steps h) and i) and, if desired, steps j) and k), which are described below:

B. The palladium, gold, sodium and potassium contents of the finished catalyst are determined by ICP analysis. In each case, the sodium and potassium contents were even determined by AA analysis for greater accuracy.

C. Unless otherwise noted, the above procedure is used to prepare the catalysts in each of the following examples, and if the quality of the support is different, the amount of starting material A is varied accordingly.

D. Each of the catalysts prepared in this example is shell-impregnated, i.e., substantially palladium and gold present in a 0.5 mm layer on the surface of the beads.

HU 212 447 Β

Catalyst wash operation

Wash and re-wash the catalyst for approx. It is carried out on a 3 cm x 60 cm glass chromatography column with a Teflon stopcock. Generally, 15 g of catalyst is added to the column which is then filled with water. The stopcock is set so that the column is approx. 1 L of water should flow at room temperature for 24 hours. The excess liquid is then sucked off from the column and the catalyst is removed and dried as described above.

Catalyst test method

Catalyst (2.5 g 5-6 mm spherical beads)

Mixed with 10.5 ml of 0.5 mm glass bead, the mixture was uniformly distributed at both ends of a 316 stainless steel U-tube reactor. The reactor outer diameter is approx. 0.9 cm and length approx. 14.5 cm. Ethylene was passed through the reactor at 151 ml / min and the catalyst was heated to 150 ° C in an oven and the system was cooled to ca. 792 x 10 ³ Pa overpressure. After the system was held for 1.5 hours under these conditions, acetic acid vapors were added to the ethylene and the mixture was passed through the catalyst for 45 minutes. Air is then added to the feed gas and the rate is increased slowly over 45 minutes until the total flow rate is 105 ml / min. The catalyst is then allowed to stabilize for 2 hours before data collection begins. The final gas composition is as follows: ethylene: acetic acid: oxygen: nitrogen = 52.9: 10.7: 7.7: 28.7, the total gas velocity is 3800 / hour and the liquid acetic acid has an approx. 1 hour. The product obtained is analyzed by gas chromatography. In several experiments, the reproducibility of the microreactor is approx. ± 10 STY units.

Example 1

A. Comparison

One important step in the preparation of alkenyl alkanoate catalysts is aqueous washing, in which known liberated chlorides and starting materials are removed. At laboratory scale, catalysts are generally washed on a column for 20-24 hours with 60-80 mL / g of catalyst water. On a practical and economically large scale (e.g., semi-scale), the formulations are washed intermittently for a much shorter period of time using much less water. Catalysts produced in large scale equipment have been found to be less active than catalysts produced in laboratory equipment. It is hypothesized that the difference in activity is due to less efficient washing in large-scale equipment.

Table 1 compares the performance of laboratory scale catalysts with that of large scale plant catalysts obtained by the Bissot method. In particular, each catalyst was subjected to the catalyst preparation procedure described above using sodium metasilicate as the precipitant, except that the starting material was increased according to the size of the plant and except that the washing operations were different. In the case of laboratory scale production, the column washing process was used, and in the case of large scale production, the batch washing process was used. In the case of large-scale production, 801 semi-industrial plants and 260 1 large-scale plants were used. Catalysts produced in large-scale equipment generally contain 5 to 10% more palladium by weight than laboratory-scale catalysts, while large-scale catalysts have STY values of ca. 5-10% by weight.

Table I

Activity of catalysts produced in laboratory and industrial scale

Comparative catalyst STY (a) Spec.Akt. (C) Laboratory Pd% % Au (c) 1-1 571 (3) 197.0 0.516 0.198 1-2 546 (3) 188.5 0.516 0.208 1-3 543 191.6 0,505 0.198 1-4 556 (2) 181.9 .510 0,200 1-5 547 194.4 0,500 0,190 1-6 567 198.0 .510 0,200 average 555 191.9 Running High I-7 (d) 521 165.4 0.558 0.231 I-8 (d) 532 (2) 172.0 0.554 0.248 I-9 (d) 534 (2) 172.7 .553 0.238 I-10 (d) 521 (2) 168.5 0.552 0.237 1-11 (0 495 (6) 163.0 0.543 0.214 1-12 (e) 484 156.5 .553 .223 I-13 (e) 485 156.9 0.554 0.222 I-14 (e) 528 173.9 0.589 .226 1-15 (e) 525 172.8 .568 0.217 I-16 (e) 468 154.1 .536 0,204 I-17 (e) 489 (2) 155.5 0.562 0.213 I-18 (e) 520 165.1 0.564 0.212 I-19 (e) 479 149.6 .568 0.203 average 497 160.6

(a) STY = Space Time yield, g VA / 1 cat / hr, numbers in parentheses represent number of parallels (b) spec. activity, g VA / g Pd / hr, (ej% w / w Pd and Au IPC, (d) 80 liters small farm., (e) 260 liters large farm small.

HU 212 447 B

B. Process of the Invention The data summarized in Table I indicate that the catalysts produced on a large scale are less active than those obtained on a laboratory scale. To determine whether this lower activity is caused by unsatisfactory washing, four catalysts were prepared in large-scale equipment (see 1-7,1-9,1-12 and 1-17 in Table I) for the purpose of this invention. step a) was repeatedly washed by the column washing process and then dried by step i) according to the invention. A fifth catalyst, prepared in a laboratory scale according to the catalyst preparation method and the batch wash method, was repeatedly washed according to step h) of the process according to the invention and then dried according to step i) of the process according to the invention. Each of the five re-washed and re-dried catalysts was then impregnated again with 5% potassium acetate according to step j) of the process of the invention, assuming that the previously added potassium acetate was removed during the repeated wash and the samples were dried again according to step k). The results obtained are summarized in Table I and these results show that repeated washing increased the activity by 5-10% in each case.

//. spreadsheet

Effect of repeated washing on catalyst activity

Woman. Catalyst Rep. washing apprenticeship we STY Change% * 1 1-7 No 521 - 2 1-7 Yes 557 +7 * 3 1-9 No 534 (2) - 4 1-9 Yes 566 +6 * 5 1-12 No 484 - 6 1-12 Yes 537 +11 7 * 1-17 No 489 (2) - 8 1-17 No 524 +5 Laboratories interministerial 9 * No 508 - 10 Yes 561 +10

* comparative example

II. example

In the experiment described in Example I, it was assumed that the potassium acetate was completely removed by repeated washing according to step h) according to the invention. As a result, in these experiments, potassium acetate was repeatedly added according to step j) in an amount equal to that used in the first impregnation step. This assumption was verified by another series of experiments in which eight catalysts were tested at different potassium contents. The results of the analytical tests performed before and after repeated washing for the eight catalyst samples (catalyst ΙΙ-1-Π-8) are shown in the following section III. are summarized in Table. These analytical results show that the repeated washing step described in Example I does not actually remove the total amount of potassium acetate. AIII. The results of Table 1 show that ca. 0.9% by weight of potassium is retained on the catalyst after repeated washing, it is believed that this potassium is bound to the support by the ion-exchange mechanism.

III. spreadsheet

Repeated wash / KOAc production

Catalyst Kiin. Vol% Ism. washing Difference II-1 2.80 3.67 0.86 II-2 1.50 2.33 0.83 11-3 1.40 2.27 0.87 II-4 1.40 2.35 0.95 11-5 2.70 3.51 0.81 11-6 1.40 2.35 0.95 11-7 2.90 3.64 0.73 II-8 2.80 3.68 0.87 Avg: 0.86 % RSD (b) 8.30

(a) After repeated impregnation with KOAc in the same amount as KOAc present in the original catalyst.

b) RSD is relative standard deviation

III. example

The ΠΙ. Taking into account the findings of Table II, Table II. Two of the re-washed catalysts shown in Table II were tested before being re-applied with potassium acetate. The results obtained, which are reported below, are fully consistent with those of Table III. Table.

Washed catalyst again K% remaining

1-12 0.88

1-17 1.19

It follows that the II. In the case of the re-washed catalysts shown in Table I, the potassium content is ca. 0.8-1.2% higher than expected. A higher potassium content than the desired potassium content would have expected a decrease in catalyst activity. These data indicate that even with the observed 5-10% increase in activity, an increase in activity would be achieved with the appropriate (lower) final potassium content. This was confirmed by our experiment, which, after repeated washing, was added only with the amount of potassium that was necessary to obtain the original amount (see experiment ΙΙΙ-1-ΠΙ-7 below).

HU 212 447 Β

Comparative experiment ΙΠ-1:

2.5 g of catalyst II were tested for vinyl acetate productivity and the results were reported in Table IV. in Table. The catalyst details were repeatedly washed according to the following experiments III-2 and III-3.

Experiment ΙΠ-2:

Three grams of the catalyst from Experiment l-1 were washed three times with the column washing method and analyzed for potassium content, with a potassium content of 0.92% by weight. 15 grams of the catalyst were re-impregnated with 0.469 g of potassium acetate dissolved in 9 ml of water and plated at 60 for 18 hours. The results of the analysis and analysis of the sample are given in Annex IV. Table.

Experiments ΙΠ-3:

Experiment A-2 was performed except that four 200-200 g samples of Catalyst II were washed with 7.56 liters (2 gallons) of water for 48 hours according to the column washing procedure. According to the analysis carried out, the potassium content was 0.86% after the washing was combined. A sample (15 g) was impregnated with 0.556 g of potassium acetate in 9 ml of water and dried at 60 ° for 24 hours. The analytical and analytical results are shown in Annex IV. are summarized in Table.

Comparative experiment kísér-4:

This catalyst was prepared according to the catalyst preparation process except that the amount of palladium and gold salts in the impregnating solution and the amount of the other starting materials were selected by the method described in Table IV. yields according to Table. Evaluation was carried out according to the catalyst assay except that 0.75 g of catalyst was used. Analytical and analytical results are reported in Annex IV. Table.

Experiments ΙΠ-5:

2.75 g of the catalyst of Experiment 4-4 were washed by column washing using 500 ml of water for 24 hours. After drying, the catalyst was impregnated with an amount of potassium acetate such that ca. Ensure a potassium content of 3% in the final product. Evaluation was carried out using the catalyst assay except that 0.75 g of catalyst was used. The analytical and analytical results are reported in Annex IV. Table.

Comparative experiment ΙΠ-6:

The catalyst was prepared as described in Experiment ΙΠ-4, except that the amount of palladium and gold salts present in the impregnating solution and the amount of the other starting materials were chosen so that the amount of the catalyst was determined in Table IV. The values given in Table 1 are swallowed. Evaluation was carried out using the catalyst assay except that 0.75 g of catalyst was used. The analytical and test data are given in Annex IV. Table.

Experiments ΙΠ-7:

The catalyst of Experiment III-6 was repeatedly washed with water according to the column washing procedure. Evaluation was carried out using the catalyst assay except that 0.75 g of catalyst was used. The analytical and analytical results are reported in Annex IV. are summarized in Table.

ARC. spreadsheet

Repeated wash effect constant. For K content (a)

Small. Pd% Au% STONE- c% So% Rep. washing STY Shift% III-l * 0.55 0.22 5.8 0.45 No 565 - III-2 0.55 0.22 5.3 0.14 Yes 615 +9 III-3 0.5 0.22 5.8 0.12 No 642 +14 III-4 * 0.56 0.46 7.6 0.42 No 734 (b) - III-5 0.56 0.46 7.6 0.17 Yes 850 (b) +15 III-6 * 1.02 0.46 7.2 0.48 No 967 (b) - III-7 1.02 0.47 7.7 0.17 Yes 1141 (b) +18

a) The column washing procedure was used for both the original formulation and for repeated washing.

b) This catalyst was tested at low conversion, which explains the exceptionally high STY at this metal content.

* Comparative examples

Based on the results described above, studies were performed to determine whether other impurities may justify the effects described. ICP analytical data on the original catalysts and their re-washed samples showed a significant difference in sodium content, but no significant difference was found for other impurities.

ARC. example

To test the effect of sodium content on the activity of the catalyst, several experiments were carried out in which the sodium content was changed but the potassium content was kept constant. In another set of experiments, the sodium / potassium ratio was changed while the total molar amount of alkaline content was kept constant. The results of both sets of experiments are summarized in Table V and the results confirm that as sodium content increases, activity decreases.

In Experiment 2 of Table V, the re-washed catalyst impregnated with the same amount of sodium as the original, non-washed sample (Table V, Experiment 4) exhibited strikingly high activity values. This indicates that further harmful dirt can also be removed by repeated washing.

Table V.

Effect of Na content on catalyst performance

Small. K% So% STY Slice controversy% Constant K content and variable Na content (a) 1 2.4 0,117 642 93.1 2 2.22 0.457 609 93.5 3 2.18 0.912 540 94.1 4 2.31 0.453 563 93.4

HU 212 447 Β

Small. K% So% STY Slice% Variable Na / K constant total alkaline molar content 1 2.21 .435 616 93.6 2 1.77 0.705 584 94.0 3 0.77 1,300 501 94.2

a) The column-washed catalysts II were repeatedly impregnated with KOAc and NaOAc solutions.

(b) Samples prepared by the addition of an appropriate amount of KOAc and NaOAc to the catalyst I samples.

XXIV K ₂ SO ₄ 0.618 0.216 2.13 0.12 493 ** XX Mg (OAc) ₂ 0.573 0,225 2.39 0.17 575

* Comparative Examples ** The reaction time was not sufficient to demonstrate the efficacy of the cation exchange solution.

The catalyst compositions of the present invention

The catalyst prepared by the process of the present invention is suitable for catalyzing the reaction between the starting alkene, alkanoic acid and oxygen-containing gas in the preparation of alkenyl alkanoates. These catalysts consist of a carrier which is capable of cation exchange and impregnated with palladium and gold and with a potassium promoter and preferably having a sodium content of not more than 0.3% by weight based on the total weight of the catalyst.

The catalysts of the present invention are prepared according to any of the methods described above and have a palladium content of greater than 25% by weight, preferably greater than 0.5% by weight and more preferably 0.51.7% by weight based on the total weight of the catalyst. The weight ratio of gold to palladium in the catalyst according to the invention is preferably between 0.2 and 1.5, and more preferably between 0.4 and 1.2.

The catalysts of the present invention are preferably shell-impregnated catalysts and catalyst support particles having a diameter of 3 to 7 mm and a pore volume of 0.2 to 1.5 ml / g. Palladium and gold are preferably distributed in an outer layer of granules 1 mm thick. The catalyst is preferably 1.4-

3.8% by weight, more preferably 2 to 3.6% by weight of potassium due to the potassium promoter.

The catalysts of the present invention have a reduced sodium content. The catalysts preferably contain not more than 0.3% by weight of sodium based on the total weight of the catalyst. More preferably, the sodium content is not more than 0.2% and most preferably not more than 0.1% by weight. The sodium content of the catalyst depends on various factors, such as starting materials used, number of washing operations, total wash time, volume of wash solutions, and concentration of cations in the cation exchange solution.

Preparation of alkenyl alkanoates

In the preparation of alkenyl alkanoates, an alkene compound is reacted with an alkanoic acid and an oxygen containing gas in the presence of a catalytic amount of the catalysts of the invention described above. The process is preferably carried out at a temperature of 100-250 ° C, preferably 140-200 ° C, and a pressure of 103 x 10 ^{3 to} 2100 x 10 ³ Pa, more preferably 620 x 10 ³ to 1050 x 10 ³ . Preferably, the process is carried out continuously in a vapor phase.

The preparation of alkenyl alkanoates is characterized by higher catalyst activity. Typically, the catalyst activity is 5 to 25% higher (expressed as the amount of alkenyl alkanoate produced per unit time in the presence of a unit catalyst) as compared to a catalyst having the same composition but containing 0.3% to 1% by weight of sodium. Although the selectivity of the catalyst, i.e. the tendency to form alkenyl alkanoates rather than various by-products (such as carbon dioxide), is slightly worsened by decreasing sodium content, this disadvantage is substantially offset by increased catalyst activity, especially of commercial alkenyl alkanoate catalysts. sodium (for example, 1% by weight of sodium).

Preferred alkanoic acid starting materials for the preparation of alkenyl alkanoates are C2-C4, such as acetic acid, propionic acid, or butyric acid; preferred alkene starting materials also have from 2 to 4 carbon atoms, such as ethylene, propylene or n-butene. Preferably, the process provides vinyl acetate, vinyl propionate, vinyl butyrate or allyl acetate.

The alkenyl alkanoates prepared as described above are known compounds which are used for known purposes, such as vinyl acetate for the preparation of polyvinyl acetate.

Claims (8)

PATENT CLAIMS A process for the preparation of catalysts of increased activity for the preparation of alkenyl alkanoates from alkenes, alkanoic acid and oxygen-containing gas by impregnating palladium, gold and a potassium promoter, which can be converted into a potassium alkanoate or a compound thereof, into a cation exchange support. - applying and then plating, the step further comprising washing the resulting catalyst with water or an aqueous solution containing the potassium promoter and recovering the resulting reduced sodium catalyst in a known manner. 2. The method of claim 1, wherein the potassium promoter solution is an aqueous potassium acetate solution. A process according to claim 1, wherein a second impregnation step is carried out with an aqueous potassium promoter solution prior to recovering the catalyst. The process according to claim 1, wherein the impregnation with the potassium promoter utilizes a potassium promoter solution at a concentration of 5 to 8%, which is max. Provides 4% potassium content. The method of claim 1, wherein the step of washing with the potassium promoter is 5-8 The potassium promoter solution was used at a concentration of max. Provides 4% potassium content. 6. The process of claim 1, wherein the resulting catalyst has a sodium content of less than 5% by weight. The process of claim 1, wherein the resulting catalyst has a sodium content of less than 0.2% by weight. The process of claim 1, wherein the resulting catalyst has a sodium content of less than 0.1% by weight.