KR930007410B1 - Dehydrogenation catalyst - Google Patents

Abstract

No content.

Description

Dehydrogenation Catalyst

The present invention relates to a dehydrogenation catalyst. More specifically, the present invention is useful in the process for preparing styrene by dehydrogenation of ethylbenzene in the presence of steam and is good even when the molar ratio of steam to ethylbenzene (hereinafter referred to as the "steam to oil ratio") is low. It relates to a magnesium oxide-containing dehydrogenation catalyst capable of producing styrene in yield.

Currently, styrene is produced on an industrial scale by dehydrogenation of ethylbenzene in the presence of steam. Conventional dehydrogenation reactions using industrial catalysts have been carried out in large quantities of steam with a steam to oil ratio of greater than 12. The reason for supplying steam is; (1) lowering the partial pressure of styrene so that the reaction proceeds advantageously at equilibrium; (2) removing the carbonaceous material precipitated on the catalyst surface during the reaction with dehydrogenation by an aqueous gas reaction; (3) The use of steam as a heat source.

Recently, efforts have been made to reduce steam consumption, that is, to reduce the steam to oil ratio, in terms of energy saving.

Lowering the steam-to-oil ratio has the advantage of reducing the cost of styrene. On the negative side, however, it promotes the production of carbonaceous materials at dehydrogenation temperatures of 500-700 ° C. Therefore, carbonaceous material tends to precipitate on the catalyst, and when the steam to oil ratio is 12 or less, there is a difficulty that deterioration of the catalyst activity occurs to a considerable extent in the conventional industrial catalyst.

Conventional industrial catalysts usually consist of iron oxides, cocatalysts (such as chromium or cerium) and alkali or alkaline earth metal compounds. Alkali or alkaline earth metal compounds are mixed for the purpose of promoting the water gas reaction and removing the carbonaceous material that precipitates on the catalyst. Generally speaking, potassium, rubidium or cesium are effective. But for economic reasons potassium is most commonly used. The content of the alkali metal or alkaline earth metal compound is described, for example, in Japanese Patent Publication No. 19864/1968, Japanese Patent Publication No. 7889/1977, 94295/1978, 129190/1978 or 129191/1978. When the alkali metal compound is used alone, the amount of use is usually 30% by weight or less. Japanese Laid-Open Patent Publication No. 25134/1972 describes a catalyst in which the total amount of potassium and calcium compounds is 24% by weight or less as a catalyst containing potassium as the alkali metal and calcium as the alkaline earth metal. In addition, dehydrogenation catalysts such as Phillips 1490 and Standard 1707 used in the past contained 30 to 45% by weight and 72.4% by weight of magnesium oxide as carriers for iron oxide as the main active ingredients, respectively.

As described above, in the conventional industrial catalyst, the content of alkali metal or alkaline earth metal compound applied as a promoter for water gas reaction is 30% by weight or less, thereby depositing carbonaceous material when the steam to oil ratio is 12 or less. Tends to increase and catalytic activity decreases and decreases. A method for preventing the deterioration of catalyst activity at low steam to oil ratios, with respect to the iron-chromium-potassium catalyst as a typical dehydrogenation catalyst, to promote the water gas reaction and to easily remove the carbonaceous material deposited on the catalyst. Methods of increasing the potassium content and calcining iron oxide at high temperatures above 800 ° C. are known to prevent the formation of the carbonaceous material itself.

However, catalysts containing a large amount of potassium tend to absorb moisture due to the very strong hygroscopicity of potassium when left in the air, thus reducing the strength of the formed catalyst pellets and dehydrogenation of potassium depending on the reaction conditions. It tends to move gradually into the interior of the pellets, or potassium is likely to move out of the catalyst pellets. As a result, catalyst pellets tend to shrink or crush during dehydrogenation reactions, which may cause various problems due to a change in catalyst size or a decrease in catalyst strength.

On the other hand, catalysts prepared by calcining iron oxide at high temperatures can produce by-products such as toluene or benzene, thus exhibiting low selectivity for styrene and having a lower steam-to-oil ratio of about 6 levels.

Japanese Patent Application Publication No. 90102/1979 discloses a catalyst containing vanadium oxide and alkali metal oxide as a cocatalyst on a spinel of MgFe _1.9 Cr _0.1 O ₄ or MnFe _1.5 Cr _0.5 O ₄ at a steam to oil ratio of 6 to 12. It is described that can be used. However, making such catalysts is difficult or cumbersome and also requires high temperatures for calcination. Therefore, it is difficult to use such a catalyst as an industrial catalyst.

As an industrially used catalyst other than the iron-chromium-potassium type described above, there is an iron-cerium-molybdenum-potassium catalyst as described in Japanese Patent Laid-Open Publication No. 120887/1974 or 120888/1974. This catalyst is characterized by high styrene selectivity. However, in order to use it at a low steam to oil ratio, the potassium carbonate content must be higher than 40% by weight, which causes the catalyst to undergo structural degradation due to the hygroscopicity of potassium or the movement of potassium during the dehydrogenation reaction. Defects cannot be avoided.

Thus, there are currently no industrial catalysts available that can provide adequate stability of catalytic activity and proper styrene yield at low steam to oil ratios below 12.

The inventors have found that, for example, by mixing magnesium with an iron-chromium-potassium catalyst or an iron-cerium-molybdenum-potassium catalyst, stable catalyst activity and high yield even under dehydrogenation conditions with a low steam to oil ratio of 3.5 to 12 It has been found that a catalyst can be obtained that gives a citrate of. The present invention has been completed based on this finding.

The present invention essentially provides a dehydrogenation catalyst consisting of 9.0-35.6 weight percent potassium oxide, 1.8-8.0 weight percent magnesium oxide, a cocatalyst selected from a) and b) and the remainder consisting of iron oxides: a) Ce ₂ O ₃ 3 to 6 wt%, and MoO ₃ 0.5 to 3 wt%; b) 3 to 6 weight percent Ce ₂ O ₃ , 0.5 to 3 weight percent MoO ₃ , and 2.0 to 7.3 weight percent CaO.

According to the invention, the shaped catalyst pellets are structurally stabilized by the addition of magnesium, thus preventing degradation of the catalyst strength due to water absorption of potassium in the catalyst and at the same time decomposing the catalyst due to the movement of potassium during the dehydrogenation reaction. Can be prevented. In addition, by limiting the amount of magnesium to the level of 1.8 to 8.0% by weight as an oxide, it is possible to prevent the decrease in catalyst strength after the dehydrogenation reaction. Furthermore, the amount of potassium oxide in the catalyst can be adjusted to a level of 9.0 to 35.6% by weight which is substantially the same as the content of conventional industrial catalysts used at steam to oil ratios above 12.

To date, even catalysts having a potassium oxide content of about 35% by weight can be stabilized by calcining at a high temperature of 700 to 900 DEG C, which is known to hardly cause shrinkage or grinding during dehydrogenation. However, it is almost impossible to avoid a decrease in catalyst activity due to sintering of the catalyst by calcination or a substantial reduction in surface area.

On the other hand, the catalyst containing magnesium oxide of the present invention is structurally stable, and even when the catalyst having a potassium oxide content of about 35% by weight is calcined at a high temperature of 700 ° C or higher, the pellet structure of the catalyst does not deteriorate the catalytic activity. More stable. That is, the magnesium-containing iron-chromium-potassium catalyst having the following composition exhibits stable performance at a steam-to-oil ratio of 3.5 to 12, whereby the conversion of ethylbenzene is applied to the iron-chromium-potassium catalyst containing 40.5% by weight of potassium oxide. Higher than that obtained, and the styrene selectivity is substantially the same or higher.

Fe ₂ O ₃ 52.4 ~ 88.2% by weight,

Cr ₂ O ₃ 1-4 wt%

K ₂ O9.0 ~ 35.6 wt%

MgO1.8-8.0 wt%

(The content of each component in the composition is expressed by weight percentage of the oxide. The same principle applies to the specification described later)

Iron-chromium-potassium catalysts often undergo substantial decreases in their surface area before and after dehydrogenation (e.g., catalysts containing 40.5% by weight of potassium oxide have a surface area of about 30.5% reduction and an average pore diameter of about 10% increase). Particularly, catalysts containing at least 22.6% by weight of potassium oxide shrink 5 to 8% of the pellet size or decompose or completely break down during dehydrogenation (decomposition ratio: 100%).

On the other hand, the catalyst containing magnesium oxide of the present invention tends to increase the surface area after the reaction, and the change in the average pore diameter of the catalyst is small. Further, in the present invention, even if the catalyst contains 22.6% by weight or more of potassium oxide, the shrinkage of the catalyst pellet after the reaction is low to 4% or less, and the decomposition rate of the catalyst in boiling water is as low as 35% at most.

Thus, magnesium oxide has a function of stabilizing the structure of the catalyst pellets. However, if the amount of magnesium oxide exceeds 8.0% by weight, the pore volume of the catalyst is so large that there is a tendency for the catalyst (crushing loss) to occur by 20 to 40% during the polishing test after the dehydrogenation reaction. This wear loss causes catalyst crushing when a substantial force is applied to the catalyst during the reaction (eg when part of the catalyst bed flows due to excess gas flow), which is undesirable. However, when the magnesium oxide content is limited in the range of 1.8 to 8.0% by weight, the wear loss is reduced to about 15%, which is comparable to the conventional industrial catalyst, and the effect of magnesium oxide on the stabilization of the catalyst pellet structure is not lowered. And catalytic activity will be maintained. On the other hand, if the magnesium oxide content is less than 1.8% by weight, it will not be possible to obtain an adequate effect on the structure stabilization by magnesium oxide.

From the observation by X-ray diffraction, a part of magnesium oxide in the catalyst formed a solid solution in iron oxide in the form of MgFe ₂ O ₄ so that no spinel of MgFe _1.9 Cr _0.1 O ₄ was found. Magnesium-containing iron-chromium-potassium-calcium catalysts with the following composition have styrene selectivity, although the conversion of ethylbenzene at a steam to oil ratio of 3.5-12 is substantially the same as for the iron-chromium-potassium-magnesium catalyst of the present invention. This is very high.

Fe ₂ O ₃ 45.1 ~ 86.2% by weight,

Cr ₂ O ₃ 1-4 wt%

K ₂ O9.0 ~ 35.6 wt%

MgO1.8-8.0 wt%

CaO 2.0 ~ 7.3 wt%

The change in surface area and pore diameter of the catalyst before and after the dehydrogenation reaction is small, and the catalyst is structurally stable.

On the other hand, iron-cerium-molybdenum-potassium catalysts are known to have high styrene selectivity. When magnesium is added thereto to obtain a catalyst having the following composition, the catalyst exhibits stable performance at a steam to oil ratio of 6 to 12 and the conversion of ethylbenzene to iron-cerium-molybdenum containing 26.8% by weight of potassium oxide. Higher than that obtainable by the potassium catalyst, the selectivity being the same or higher.

Fe ₂ O ₃ 47.4-85.7 wt%,

Ce ₂ O ₃ 3 ~ 6 wt%

MoO ₃ 0.5 ~ 3% by weight

K ₂ O9.0 ~ 35.6 wt%

MgO1.8-8.0 wt%

Changes in surface area and pore diameter and shrinkage of catalyst pellets before and after the reaction are small. No decomposition of this catalyst pellet was observed in boiling water. Wear loss is small when compared to catalysts with more than 8.0 weight percent magnesium oxide.

The magnesium-containing iron-cerium-molybdenum-potassium-calcium catalyst with the following composition shows stable performance at a steam to oil ratio of 6 to 12, and the ethylbenzene conversion is applied to the iron-cerium-molybdenum-potassium catalyst containing 26.8% by weight of potassium oxide. It is more than you get by, and selectivity is high.

Fe ₂ O ₃ 40.1 ~ 83.7% by weight,

Ce ₂ O ₃ 3 ~ 6 wt%

MoO ₃ 0.5 ~ 3% by weight

K ₂ O9.0 ~ 35.6 wt%

MgO1.8-8.0 wt%

CaO 2.0 ~ 7.3 wt%

In addition, the magnesium-containing iron-cerium-molybdenum-potassium-chromium catalyst having the following composition exhibits stable high performance and high selectivity at a steam to oil ratio of 3.5 to 12. It is particularly characterized by high selectivity at steam to oil ratios of 6 and below, and high activity at steam to oil ratios of 6 and above.

Fe ₂ O ₃ 43.4 ~ 84.7% by weight,

Ce ₂ O ₃ 3 ~ 6 wt%

MoO ₃ 0.5 ~ 3% by weight

K ₂ O9.0 ~ 35.6 wt%

Cr ₂ O ₃ 1-4 wt%

MgO1.8-8.0 wt%

Therefore, it is apparent that the dehydrogenation catalyst of the present invention has excellent catalytic activity, selectivity and structural stability.

In addition, according to the present invention, even if the catalyst has a high content of potassium oxide, by calcination at a high temperature of 700 ℃ or more can improve the structural stability of the catalyst pellets without inhibiting the catalyst activity.

The present invention will now be described in more detail with reference to examples. The catalytic activity test was carried out by the following method unless otherwise specified.

A stainless steel reaction tube with an inner diameter of 32 mm was charged with 50 cc of extruded catalyst, and the reaction tube was heated in an electric furnace to react at a predetermined temperature.

As reaction conditions, the pressure was atmospheric pressure, the liquid space velocity of ethylbenzene per hour was 1, and the steam to oil ratio was 6 or 10.

The conversion and selectivity of ethylbenzene was calculated by the following formula.

The dehydrogenation test results of each example are shown in Tables 1 and 2.

In Table 1, "temperature -50%" represents the temperature of the catalyst bed showing 50% ethylbenzene conversion, and "selectivity-50%" represents styrene selectivity at 50% ethylbenzene conversion.

In Table 2, the decomposition rate (HWT) of pellets in boiling water was calculated by the following formula after evaporating to dryness after adding about 10 g of catalyst to 50 ml of boiling water.

Changes in physical properties such as surface area, pore volume, pore diameter and pellet diameter before and after the reaction were calculated by the following formula.

The abrasion loss after the reaction was measured by putting about 10 g of the catalyst after the reaction in a horizontal cylinder, rotating for a polishing test, and sieving the pulverized catalyst with 10 sieves. The amount of catalyst remaining was measured and the abrasion loss was calculated according to the following formula.

Example 1

500 g of α-iron (III) oxide, 43 g of cerium oxide, 22 g of molybdenum oxide, 261 g of potassium carbonate and 43 g of magnesium carbonate (commercially available basic magnesium carbonate) were mixed. After pure water was added, the mixture was thoroughly mixed with a stirrer to obtain an extrudable paston. The paste was extruded to a diameter of 1/8 ", dried and calcined at 540 DEG C for 6 hours to obtain a catalyst having the following composition.

Fe ₂ O ₃ 65.7 wt%

Ce ₂ O ₃ 5.7 wt%

2.9 wt% MoO ₃

K ₂ O 23.3 wt%

MgO2.4 wt%

Dehydrogenation test data are shown in Tables 1 and 2.

Example 2

A catalyst was prepared in the same manner as in Example 1, except that 500 g of α-iron (III) oxide, 51 g of cerium oxide, 25 g of molybdenum oxide, 303 g of potassium carbonate, 51 g of magnesium carbonate, and 81 g of calcium carbonate were used.

58.9 weight% Fe ₂ O ₃ ,

Ce ₂ O ₃ 6.0% by weight

MoO ₃ 3.0 wt%

K ₂ O 24.3 wt%

MgO2.5 wt%

CaO 5.3% by weight

Dehydrogenation test data are shown in Tables 1 and 2.

Comparative Example 1

A catalyst was prepared in the same manner as in Example 1, except that 500 g of α-iron (III) oxide, 42 g of cerium oxide, 21 g of molybdenum oxide, and 277 g of potassium carbonate were used.

66.5 wt% Fe ₂ O ₃ ,

Ce ₂ O ₃ 5.6 wt%

MoO ₃ 2.8 wt%

K ₂ O 25.1 wt%

Dehydrogenation test data are shown in Tables 1 and 2.

Comparative Example 2

A catalyst was prepared in the same manner as in Example 1, except that 500 g of α-iron (III) oxide, 59 g of cerium oxide, 29 g of molybdenum oxide, 353 g of potassium carbonate, and 235 g of magnesium carbonate were used.

53.9 wt% Fe ₂ O ₃ ,

Ce ₂ O ₃ 6.3 wt%

MoO ₃ 3.2 wt%

K ₂ O25.9 wt%

MgO10.7 wt%

Dehydrogenation test data are shown in Tables 1 and 2.

Comparative Example 3

A catalyst was prepared in the same manner as in Example 1, except that 500 g of α-iron (III) oxide, 42 g of cerium oxide, 21 g of molybdenum oxide, 252 g of potassium carbonate, and 25 g of magnesium carbonate were used.

Fe ₂ O ₃ 67.1 wt%

Ce ₂ O ₃ 5.6 wt%

MoO ₃ 2.8 wt%

K ₂ O 23.0 wt%

MgO 1.4 wt%

Dehydrogenation test data are shown in Tables 1 and 2.

TABLE 1

TABLE 2

Claims (2)

As a dehydrogenation catalyst consisting of iron oxide, potassium oxide, magnesium oxide and a cocatalyst, 9.0 to 35.6 wt% of potassium oxide, 1.8 to 5.4 wt% of magnesium oxide, and 3.0 to 6.0 wt% of cerium oxide and 0.5 to 3.0 wt% of molybdenum oxide as cocatalysts A dehydrogenation catalyst containing% and the remainder consisting of iron oxide. The dehydrogenation catalyst according to claim 1, further comprising 2.0 to 7.3 wt% of calcium oxide as another cocatalyst.