CATALYST SYSTEM FOR PREPARING PROPYLENE OXIDE

Abstract

A catalytic system containing a titanium zeolite of structure type MWW optionally containing zinc and containing at least one of an inorganic potassium salt and an organic potassium salt is provided. The catalyst system is useful in the preparation of propylene oxide.

Claims

1-27. (canceled)

28. A catalytic system comprising: a titanium zeolite of structure type MWW optionally comprising zinc: and a potassium salt, wherein the potassium salt comprises at least one selected from the group consisting of an inorganic potassium salt, and an organic potassium salt.

29. The catalytic system according to claim 28, wherein the potassium salt comprises an inorganic potassium salt which is selected from the group consisting of potassium hydroxide, potassium chloride and potassium nitrate.

30. The catalytic system of claim 28, wherein a content of titanium, calculated as elemental titanium, is from 0.1 to 5 weight %, based on the total weight of the titanium zeolite of framework structure type MWW.

31-32. (canceled)

33. A continuous process for the preparation of propylene oxide, comprising: acetonitrile as solvent; hydrogen peroxide as epoxida.tion agent, and the catalytic system of claim 28.

34-35. (canceled)

36. The catalytic system according to claim 28, wherein the potassium salt comprises an organic potassium salt which is selected from the group consisting of potassium formate, potassium acetate, potassium carbonate, and potassium hydrogen carbonate.

37. The catalytic system of claim 28, wherein the titanium zeolite of structure type MWW comprises zinc and a content of t he zinc, calculated as elemental zinc, is from 0.1 to 5 weight %, based on the total weight of the titanium zeolite of framework structure type MWW.

Description

EXAMPLES

Potassium Salts as Additives

Example 1

[0387] In a first run, potassium dihydrogen phosphate was dissolved in the third stream, the aqueous hydrogen peroxide solution described above in Reference Example 1. The concentration of the potassium dihydrogen phosphate was chosen so that the molar ratio of potassium relative to the hydrogen peroxide in the liquid feed stream was 13010.sup.6:1. In particular, the concentration of the potassium dihydrogen phosphate in the liquid feed stream was 130 micromol per mol hydrogen peroxide. The epoxdation reaction was carried out as described above in Reference Example 1.

[0388] After a certain time on stream the reaction was stopped. At this point in time, the hydrogen peroxide conversion had reached a value of 90%. Since for this additive and this catalytic system, comprising a ZnTiMWW catalyst and potassium dihydrogen phosphate, excellent propylene oxide selectivities were observed, this system was set as reference system for all other systems below.

Examples 2 to 6

[0389] Since the use of potassium dihydrogen phosphate as additive led to such good results, the following examples and comparative examples were carried out by starting the continuous epoxidation reaction with potassium dihydrogen phosphate as additive. Then, the reaction was continued until the hydrogen peroxide conversion reached a value of 90%.

[0390] At this point in time, the addition of potassium dihydrogen phosphate via the third stream described in Reference Example 1 was stopped and other potassium salts were used instead as indicated in Table 1 below.

[0391] For every potassium salt used, the concentration of the salt was chosen so that the potassium concentration in the liquid feed stream passed to the epoxidation reactor remained at the value of example 1 (molar ratio of potassium relative to the hydrogen peroxide in the liquid feed stream 13010.sup.6:1).

[0392] For every system, the epoxidation reaction was continued until, after a first deviation of the hydrogen peroxide conversion, this conversion reached the value of 90% again, i.e. the value at which the additive had already been changed from potassium dihydrogen phosphate to another additive. At a point, when this value of 90% conversion could be kept constant for 48 hours without changing the reaction parameters, the epoxidation reaction was stopped.

[0393] The deactivation rate was then determined as the difference in the reaction temperature (delta Tr) divided by the period of time (delta t). The difference in the reaction temperature is defined as the reaction temperature at the end of the epoxidation reaction (i.e. the reaction temperature at which the hydrogen peroxide conversion had reached the value of 90% and could be kept constant for another 48 hours without any further parameter changes within the system after having replaced potassium dihydrogen phosphate by the new additive) minus the reaction temperature at the point in time where potassium dihydrogen phosphate had been used as additive, the hydrogen conversion had reached the value of 90% and potassium dihydrogen phosphate had been replaced. The period of time (delta t) is defined by the time on stream from the change in additive until the end of the epoxidation reaction, i.e. the period of time during which the epoxidiation reaction was carried out in the presence of the additive replacing potassium dihydrogen phosphate.

Example 2a

[0394] As shown in Table 1 below, potassium formate was found to be the most preferred additive among all potassium salts tested. Therefore, a further run was carried out in the same manner as the run according to Example 2, with the difference that potassium formate was used as additive from the very beginning of the epoxidation reaction. The deactivation rate was then determined as the difference in the reaction temperature (delta Tr) divided by the period of time (delta t). The difference in the reaction temperature is defined as the reaction temperature at the beginning of the epoxidation reaction (i.e. the reaction temperature at the beginning of the experiment was identical to the ones used in Examples 1 to 6 and Comparatives Examples 1 to 3) minus the reaction temperature at the point in time the hydrogen peroxide conversion had reached the value of 90% and could be kept constant without any further parameter changes for 48 h.

COMPARATIVE EXAMPLES

[0395] Salts Other than Potassium Salts as Additve; No Additive

Comparative Example 1

[0396] The Comparative Example 1 was carried out as Example 2. However, after the hydrogen peroxide conversion had reached a value of 90% with potassium dihydrogen phosphate as additive, the addition of potassium dihydrogen phosphate was stopped, and via the third stream described in Reference Example 1, no additive was used anymore.

Comparative Examples 2 to 3

[0397] The Comparative Examples 2 and 3 were carried out as Example 2. However, after the hydrogen peroxide conversion had reached a value of 90% with potassium dihydrogen phosphate as additive, the addition of potassium dihydrogen phosphate was stopped, and via the third stream described in Reference Example 1, the additives according to Table 1 below were used instead. Regarding Comparative Example 2, the concentration of NH.sub.4H.sub.2PO.sub.4 was identical to the concentration of KH.sub.2PO.sub.4 according to Example 1, i.e. 130 micromol per mol hydrogen peroxide. Regarding Comparative Example 3, the concentration of NaH.sub.2PO.sub.4 was identical to the concentration of KH.sub.2PO.sub.4 according to Example 1, i.e. 130 micromol per mol hydrogen peroxide.

TABLE-US-00001 TABLE 1 Results of the Examples and the Comparative Examples deactivation catalytic rate/ propylene oxide example additive system K/d selectivity/% 1 KH.sub.2PO.sub.4 ZnTiMWW .sup.0 .sup.1) 98.8 KH.sub.2PO.sub.4 2 HCOOK ZnTiMWW 1.14 98.8 HCOOK 2a .sup.2) HCOOK ZnTiMWW 2.18 99.1 HCOOK 3 K.sub.2CO.sub.3 ZnTiMWW 0.67 98.4 K.sub.2CO.sub.3 4 KHCO.sub.3 ZnTiMWW 0.48 98.7 KHCO.sub.3 5 KOH ZnTiMWW +0.13 98.4 KOH 6 KCl ZnTiMWW +0.19 98.4 KCl comp. 1 ZnTiMWW +1.23 97.1 comp. 2 NH.sub.4H.sub.2PO.sub.4 ZnTiMWW +0.83 97.8 NH.sub.4H.sub.2PO.sub.4 comp. 3 NaH.sub.2PO.sub.4 ZnTiMWW +0.58 97.4 NaH.sub.2PO.sub.4 .sup.1) reference value .sup.2) no replacement of additive; the potassium formate was used as additive from the very beginning of the epoxidation reaction

Results

[0398] Compared to the epoxidation reactions where either no additive or an additive other than a potassium salt was employed, all epoxidation reactions which were carried out with a potassium salt as additive showed higher propylene oxide selectivities at the same hydrogen peroxide selectivity of 90%. Reference is made to Table 1, showing that in all comparative examples, the propylene oxide selectivity is below or significantly below 98% whereas in the Examples, all respective values are significantly above 98% and, for potassium formate as additive, even above 99%. Thus, these reactions where potassium salts were employed as additives lead to a higher yield in propylene oxide as valuable product, and the selectivity with regard to undesired by-products or side-products is decreased.

[0399] Further, it was found that these higher propylene oxide selectivites at constant hydrogen peroxide conversion can be realized at advantageous deactivation rate. Compared to the epoxidation reaction with potassium dihydrogen phosphate as additive, the deactivation rate at the end of a run where no potassium salt was employed was at least +0.58 K/d, i.e. significantly higher than the maximum value of +0.19 K/d obtained for reactions where potassium salts were employed as additives. In this context, it is noted that a positive value indicates that compared to potassium dihydrogen phosphate, a respective additive leads to an increase in reaction temperature which in turn means that more energy has to be provided to realize a given hydrogen peroxide conversion. Therefore, a low positive value and in particular a negative value are preferred.

[0400] Therefore, on particular the organic potassium salts, represented by potassium formate, potassium carbonate and potassium hydrogen carbonate in the Examples, and the respective catalytic systems show excellent suitability for the epoxidation reaction since they all lead to a negative relative deactivation rate and, at the same time, to very high propylene oxide selectivities. Especially potassium formate was found to be of particular suitability since this additive showed the lowest relative deactivation rate and, at the same time, the highest propylene selectivity.

CITED LITERATURE

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