JPH0446182B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for producing styrene by dehydrogenating ethylbenzene using a catalyst in the presence of water vapor, by using a catalyst to which magnesium carbonate or/and calcium carbonate is added.
The present invention relates to a catalyst that maintains a high yield of styrene even when the molar ratio of steam/ethylbenzene (hereinafter referred to as steam ratio) is low. Currently, styrene is industrially produced by dehydrogenating ethylbenzene in the presence of steam, but conventional industrial catalysts are used in the presence of a large amount of steam, that is, at a steam ratio of 12 or more. is normally done. In this case, the reason for supplying and using steam is to lower the partial pressure of styrene and make the reaction more favorable in terms of equilibrium. These include removing carbonaceous matter deposited on the catalyst surface during the reaction through a water gas reaction, and further using it as a heat source. In recent years, there has been a trend to reduce the amount of water vapor, that is, to lower the steam ratio, from the perspective of energy conservation. However, while lowering the steam ratio has the advantage of lowering the production cost of styrene, at the dehydrogenation temperature of 500 to 700°C, carbonaceous substances are easily generated and accumulate on the catalyst. Conventional industrial catalysts have the disadvantage that if the steam ratio is lower than 12, the catalyst activity deteriorates significantly and cannot be used. That is, conventional industrial catalysts typically contain iron oxide-
Cocatalysts (e.g. chromium, cerium, etc.) - consisting of alkali or alkaline earth compounds, in which the alkali or alkaline earth compounds are used to promote water gas reactions and remove carbon deposits on the catalyst. has been added. Among them, potassium, rubidium, and cesium are considered to be good, but potassium is most commonly used from an economical standpoint. The content of alkali or alkaline earth compounds is determined by Japanese Patent Publication No. 19864-1986 and Japanese Patent Publication No. 52
−7889, 53−94295, 53−129190, 53−
As shown in Publication No. 129191, etc., the amount of alkali compounds alone is usually 30% or less. In addition, a catalyst containing potassium as an alkali metal and calcium as an alkaline earth metal was disclosed in JP-A-47-
As shown in Japanese Patent No. 25134, the total amount of both is 24% or less in this catalyst. In addition, dehydrogenation catalysts such as Phillips 1490 and Standard 1707 that were used industrially in the past contained 30 to 45% magnesia, an alkaline earth metal oxide, or
Although it contains 72.4%, it is used as a carrier for iron oxide, which is the main active ingredient, and does not have the function of promoting water gas reactions.About 30% potassium carbonate is used to promote water gas reactions. It's just added. As mentioned above, in conventional industrial catalysts, the content of alkali or alkaline earth compounds added as promoters of water gas reactions is at most 30%.
As a result, when the steam ratio was lower than 12, the amount of carbonaceous precipitates increased, the activity decreased, and it was common for the product to eventually become deactivated. As a method of preventing deterioration of catalyst activity at low steam ratios, in iron-chromium-potassium catalysts, which are a typical composition of dehydrogenation catalysts, increasing the potassium content accelerates the water gas reaction rate. Two methods are known: one method is to quickly remove the carbonaceous material deposited on the catalyst, and the other method is to suppress the formation of carbonaceous material itself by firing iron oxide at a high temperature of 800°C or higher. However, because of its strong hygroscopicity, containing a large amount of potassium may cause the catalyst pellet to contain moisture and reduce its strength if left in the air.
Depending on the reaction conditions during the dehydrogenation reaction, potassium is gradually eliminated from the catalyst, so if this amount is large, it can cause various troubles. Furthermore, when iron oxide is fired at a high temperature, toluene, benzene, etc., which are by-products, are easily generated, and the selectivity for styrene is poor, and the lower limit of the steam ratio is also limited to 6th place. Furthermore, as described in Japanese Patent Application Laid-Open No. 54-90102, a catalyst in which MgFe _1.9 Cr _0.1 O ₄ spinel contains an alkali metal oxide and vanadium oxide as a promoter can be used at a steam ratio of 6 to 12. However, it is considered difficult to use as an industrial catalyst because the catalyst preparation involves many steps, is difficult, and requires high firing temperatures. Other than iron-chromium-potassium catalysts, iron-based catalysts disclosed in JP-A-49-120887 and JP-A-49-120888 are currently industrially used catalysts.
There is a cerium-molybdenum-potassium catalyst.
Although these are characterized by high styrene selectivity, the content of potassium compounds must be increased to around 40% in order to be used at low steam ratios, so the hygroscopicity of potassium and its migration during the reaction are important. There is no way you can avoid these shortcomings. Ultimately, it can be said that none of the conventionally known industrial catalysts has a sufficient styrene yield and activity stability with a low steam ratio of 12 or less. However, the present inventors have found that by adding magnesium carbonate or/and calcium carbonate to an iron-chromium-potassium catalyst or an iron-cerium-molybdenum-potassium catalyst, the steam ratio can be increased.
We discovered that high styrene yield and stability of activity can be obtained under low steam operation of 3.5 to 12.
As a result, the amount of potassium carbonate contained in the catalyst was able to be suppressed to 15-35%, which is almost the same as the content in industrial catalysts conventionally used with a steam ratio of 12 or more, and alkali metal carbonate By setting the blending amount of salt and alkaline earth metal carbonate to 30% or more, it is possible to prevent a decrease in pellet strength due to moisture absorption of the catalyst, and also to prevent collapse of the catalyst structure due to migration of potassium during the reaction. did it. In other words, in a catalyst with a composition of Fe ₂ O ₃ 40-68% Cr ₂ O ₃ 2-5% K ₂ CO ₃ 15-35% MgCO ₃ 15-30%, which is an iron-chromium-potassium catalyst with magnesium carbonate added. It shows stable performance at steam ratios of 3.5 to 12, and the conversion rate of ethylbenzene is higher than that of iron-chromium-potassium catalysts.
It was higher than that containing 50% K ₂ CO ₃ , and the selectivity to styrene was almost the same or higher. Normally, iron-chromium-potassium catalysts show a significant decrease in surface area before and after the dehydrogenation reaction (with 50% K ₂ CO ₃ , the surface area decreases by about 30%, and the average pore diameter In contrast, with the catalyst to which magnesium carbonate (commercially available basic magnesium carbonate) was added, the surface area after reaction increased by about 20%, and the average pore diameter slightly decreased. (approximately 5%). Furthermore, using an X-ray diffraction device, it was confirmed that some of the MgCO ₃ in the catalyst was dissolved in iron oxide to form MgFe ₂ O ₄ .
No spinel MgFe _1.9 Cr _0.1 O ₄ was found. Based on the above facts, one of the effects of adding MgCO ₃ is considered to be a structural stabilizer. On the other hand, the composition of Fe ₂ O ₃ 40-68% Cr ₂ O ₃ 2-5% K ₂ CO ₃ 15-35% Ca ₂ CO ₃ 15-30% was prepared by adding calcium carbonate to an iron-chromium-potassium catalyst. Regarding the catalyst, the conversion rate of ethylbenzene at a steam ratio of 3.5 to 12 was slightly lower than that of an iron-chromium-potassium system containing 50% K ₂ CO ₃ , but the selectivity to styrene was very high. However, the stability of activity was not necessarily sufficient, and deterioration over time was observed. The reduction in surface area of this catalyst before and after the reaction is approximately 33
%, the increase in average pore size is about 30%, K ₂ CO ₃
Structural changes similar to those in 50% were observed. The above iron-chromium-potassium catalyst with magnesium carbonate added has a steam ratio of 3.5.
It has become clear that the catalyst with calcium carbonate added exhibits a stable high conversion rate in ~12 to 12%, and exhibits high selectivity.What is noteworthy in this invention is that carbonate A catalyst with a composition of both magnesium and calcium carbonate is Fe ₂ O ₃ 40-68% Cr ₂ O ₃ 2-5% K ₂ CO ₃ 15-35% MgCO ₃ 10-30% CaCO ₃ 5-10%. It shows stable performance at steam ratios of 3.5 to 12, and the conversion rate of ethylbenzene is equivalent to or higher than that of 50% K ₂ CO ₃ , and the selectivity is also high, so the yield of styrene is very high. The characteristics were shown. It was revealed that the surface area and pore diameter of this catalyst before and after the reaction changed little (the former increased by about 5%, the latter decreased by about 5%), and was structurally very stable. On the other hand, Fe ₂ O ₃ 40-64% Ce ₂ O ₃ 4-6% MoO ₃ 2-3% K ₂ CO ₃ 15-25% MgCO ₃ 15 The catalyst with a composition of ~30% shows stable performance at steam ratios of 6 to 12, and the conversion rate of ethylbenzene is the same as that of the iron-cerium-molybdenum-potassium system.
It was higher than that containing 35% K ₂ CO ₃ and the selectivity was the same or higher. Formation of MgFe ₂ O ₄ was also shown for this catalyst by X-ray diffraction. Furthermore, the changes in surface area and pore diameter before and after the reaction were small. Iron-cerium-molybdenum-potassium catalyst with magnesium carbonate and calcium carbonate added Fe ₂ O ₃ 40-64% Ce ₂ O ₃ 4-6% MoO ₃ 2-3% K ₂ CO ₃ 15-25% MgCO ₃ The catalyst with a composition of 10-30% CaCO ₃ 5-10% shows stable performance at a steam ratio of 6-12, and the conversion rate of ethylbenzene is high in the iron-cerium-molybdenum-potassium system.
The selectivity was higher than or equal to that containing 35% K ₂ CO ₃ . The activity test method was as follows unless otherwise specified. 50 c.c. in a stainless steel flow-through reaction tube with an inner diameter of 32 mmφ.
The reaction tube is filled with an extruded catalyst and heated electrically to carry out the reaction at a predetermined reaction temperature. The pressure is normal pressure, LHSV of ethylbenzene is 1, and the molar ratio of water vapor to ethylbenzene is 3.5 to 12 (usually 6 or 9). Here, the conversion rate of ethylbenzene (%) = Ethylbenzene concentration (%) at the catalyst layer inlet - Ethylbenzene concentration (%) at the catalyst layer outlet / Ethylbenzene concentration (%) at the catalyst layer inlet × 100 Styrene selectivity (%) = Amount of styrene produced / Amount of reacted ethylbenzene x 100 Example 1 500 g of α-ferric oxide, 32 g of chromium oxide, 320 g of potassium carbonate, and 212 g of magnesium carbonate were powder-mixed, pure water was added to this mixture, and the mixture was thoroughly kneaded using a grinder. Make into an extrudable paste. After extruding this paste into a 1/8 inch diameter,
It was dried and fired at 540°C for 6 hours. Catalyst composition Fe ₂ O ₃ 47% Cr ₂ O ₃ 3% K ₂ CO ₃ 30% MgCO ₃ 20% The results are shown in Table 1. Example 2 A product was prepared in the same manner as in Example 1 except that 131 g of magnesium carbonate and 81 g of calcium carbonate were used. Catalyst composition Fe ₂ O ₂ 47% Cr ₂ O ₃ 3% K ₂ CO ₃ 30% MgCO ₃ 12% CaCO ₃ 8% The results are shown in Table 1. Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that calcium carbonate was used instead of magnesium carbonate. The results are shown in Table 1. Comparative Example 2 Same as Example 1 except that 500 g of α-ferric oxide, 32 g of chromium oxide, and 532 g of potassium carbonate were used. Catalyst composition Fe ₂ O ₃ 47% Cr ₂ O ₃ 3% K ₂ CO ₃ 50% The results are shown in Table 1. Comparative Example 3 A sample was prepared in the same manner as in Example 1 except that strontium carbonate was used instead of magnesium carbonate. The results are shown in Table 1. Comparative Example 4 A sample was prepared in the same manner as in Example 1 except that barium carbonate was used instead of magnesium carbonate.
The results are shown in Table 1. Example 3 α-ferric oxide 500g, cerium oxide 47.6g,
Molybdenum oxide 23.8g, potassium carbonate 190.5g.
It was prepared in the same manner as in Example 1 using 190.5 g of magnesium carbonate. Catalyst composition Fe ₂ O ₃ 52.5% Ce ₂ O ₃ 5% MoO ₃ 2.5% K ₂ CO ₃ 20% MgCO ₃ 20% The results are shown in Table 1. Example 4 α-ferric oxide 500g, cerium oxide 47.6g,
Molybdenum oxide 23.8g, potassium carbonate 190.5g,
Magnesium carbonate 114.3g, calcium carbonate 76.2
It was prepared in the same manner as in Example 1 using g. Catalyst composition Fe ₂ O ₃ 52.5% Ce ₂ O ₃ 5% MoO ₃ 2.5% K ₂ CO ₃ 20% MgCO ₃ 12% CaCO ₃ 8% The results are shown in Table 1. Comparative example 5 α-ferric oxide 500g, cerium oxide 47.6g,
It was prepared in the same manner as in Example 1 using 23.8 g of molybdenum oxide and 381 g of potassium carbonate. Catalyst composition Fe ₂ O ₃ 52.5% Ce ₂ O ₃ 5% MoO ₃ 2.5% K ₂ CO ₃ 40% The results are shown in Table 1. Comparative Examples 6 and 7 Ciel 105 The results are shown in Table 1.

[Table] As shown in Table 1, the dehydrogenation catalyst according to the present invention is T
-50%, S-50%, it can be seen that the stability is excellent.

Claims (1)

[Scope of Claims] 1. In a dehydrogenation catalyst consisting of iron oxide, alkali metal carbonate, alkaline earth metal oxide, and various auxiliaries, 30% or more by weight or more than 60% by weight of the weight of the blended composition.
The following consists of alkali metal carbonates and alkaline earth metal carbonates, and the alkali metal carbonates are 50~
70% by weight, the alkaline earth metal carbonate is 50 to 30% by weight, the alkali metal carbonate is K ₂ CO ₃ , the alkaline earth metal carbonate is composed of the following a or b, and the auxiliary agent is c. or d. A catalyst for ethylbenzene dehydrogenation. a _{MgCO3 b MgCO3} 10-30% by weight and _CaCO3 5-10% by weight c _Cr2O3 2-5% by weight d _{Ce2O3 4-6} % by weight and _MoO3 2-3% by weight