Process for producing methacrolein and methacrylic acid

Abstract: The present invention provides a process for producing methacrolein and methacrylic acid by subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether to gas phase catalytic oxidation with molecular oxygen or a molecular oxygen-containing gas using a fixed bed multi-tubular reactor. The process is characterized by the following (α), (β) and (γ). (α) There are used, as catalysts, compound oxides represented by the following general formula (I) Mo a W b Bi c Fe d A e B f C g D h E i O x (in the formula, Mo represents molybdenum, W represents tungsten, Bi represents bismuth, Fe represents iron, A represents at least one element selected from nickel and cobalt, B represents at least one element selected from alkali metals and thallium, C represents at least one element selected from alkaline earth metals, D represents at least one element selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic and zinc, E represents at least one element selected from silicon, aluminum, titanium and zirconium, and O represents oxygen; a, b, c, d, e, f, g, h, i and x represent the numbers of atoms of Mo, W, Bi, Fe, A, B, C, D, E and O, respectively; when a is 12, b = 0-10, c = 0.1-20, d = 0.1-20, e = 2-20, f = 0-10, g = 0-10, h = 0-4, i = 0-30 and x = a value determined by the oxidation states of individual elements). (β) Each reaction tube has a plurality of reaction zones formed by dividing the catalyst layer in the reaction tube into two or more portions in the axial direction of the tube. (γ) The plurality of reaction zones are filled with catalysts shown in the above (α) having different activities, prepared by varying the types and/or amounts of the elements constituting the A group, B group, C group, D group and E group in the general formula (I) and/or with catalysts shown in the above (α) having different activities, prepared by varying the amount of at least one element of W, Bi and Fe in the general formula (I), in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the outlet.

Description: The present invention relates to a process for producing methacrolein and methacrylic acid by using, as a starting material, at least one compound selected from isobutylene, t-butanol (tertiary butanol) and methyl t-butyl ether (methyl tertiary butyl ether) and subjecting the starting material to gas phase catalytic oxidation with molecular oxygen or a molecular oxygen-containing gas. A number of proposals have'been made on the catalyst used in production of methacrolein and methacrylic acid by the high-temperature gas phase catalytic oxidation of isobutylene and/or t-butanol. These proposals relate mainly to the selection of the components constituting the catalyst and their ratio. DE-OS 33 08 625 discloses a catalytic composition corresponding to the general formula W 6 Mo a V b P c Cu d As e Sb f X g Y h O x wherein X represents K, Rb and/or Cs, Y represents Nb, Fe, Mn, Sn, Li, Na, Sr, Rh, Ce, Ti and/or Cr, a = 2.0 to <6, b = 0 to 3, c = 0.1 to 3, d = 0.01 to 1, e = 0 to 1, f = 0 to 2, g = 0.01 to 3, h = 0 to 1, x represents the number of oxygen atoms required to saturate the valence of the components of said catalytic composition. EP-A-0 102 641 relates to a catalyst for manufacturing methacrolein by the vapor phase oxidation of isobutylene or tertiary butanol, said catalyst having the composition represented by the following formula Mo a W b Bi c Fe d A e B f C g D h O x wherein A represents at least one element selected from the group consisting of nickel and cobalt, B represents at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium, C represents at least one element selected from the group consisting of phosphorus, tellurium, antimony, tin, cerum, lead, niobium, manganese and zinc, D represents at least one element selected from the group consisting of silicon, aluminium, zirconium and titanium, a, b, c, d, e, f, g, h and x respectively represent the atomic ratios of Mo, W, Bi, Fe, A, B, C, D, and O, and when a is fixed at 12, b is from 0 to 10, c is from 0.1 to 10, d is from 0.1 to 20, e is from 2 to 20, f is from 0 to 10, g is from 0 to 4, h is from 0 to 30 and x is a number determined by the atomic valences of the individual elements, and being molded in the shape of a hollow cylinder having an outside diameter of 3.0 to 10.0 mm, an inside diameter 0.1 to 0.7 times the outside diameter and a length 0.5 to 2.0 times the outside diameter. The above oxidation reaction is a highly exothermic reaction. Therefore, in the reaction, heat build-up in the catalyst layer is large; particularly in the abnormally hot areas called "hot spots", product yield is low due to an excessive oxidation reaction and, moreover, deterioration of catalyst takes place owing to a high thermal load and catalyst life is influenced greatly. Accordingly, heat build-up in hot spots is a serious problem in the industrial practice of the above oxidation reaction. This heat build-up in hot spots tends to be striking particularly when the concentration of material gas is made higher or the space velocity is made larger (such reaction conditions are hereinafter referred to as "high-load reaction conditions" in some cases) in order to enhance the productivity; as a result, the reaction conditions of the oxidation reaction are considerably restricted currently. Hence, minimization of heat build-up in hot spots is very important for industrial production of methacrolein and methacrylic acid at high yields as well as for reduction of catalyst deterioration and resultant stable operation over a long period. Prevention of heat build-up in hot spots is particularly important in molybdenum-based catalysts because the molybdenum component causes easy sublimation. Various proposals have hitherto been made in order to suppress heat build-up in hot spots. For example, Japanese Patent Publication No. 36740/1987 proposes the use of a ring-shaped catalyst. The document describes that the change of catalyst shape from spherical or columnar shape to ring shape in the molded catalyst conventionally used for oxidation of isobutylene or t-butanol can suppress heat build-up in hot spots and accordingly an excessive oxidation reaction, and is very effective for the improvement of product yield. This method certainly has an effect of reducing the thermal load for catalyst, but gives no sufficient results under high-load reaction conditions, in particular. Also, a method in which catalysts of different activities are filled in a plurality of reaction zones formed by dividing the catalyst layer of reactor and in which an oxidation reaction is carried out in the reaction zones, is known in Japanese Patent Publication No. 38331/1988 for production of, for example, acrolein and acrylic acid from propylene. GB-A-2 044 764 relates to a process for producing acrolein and acrylic acid by vapour-phase catalytic oxidation of propylene using a multi-tubular, fixed-bed reaction vessel, which is characterized by a) the use, as a reaction catalyst, of a composite oxide catalyst represented by the formula: Mo a Bi b Fe c A d B e C f D g Si h O x , wherein: A is at least one element selected from Co, Ni, and Mg; B is at least one element selected from P, B, and As; C is at least one element selected from Li, Na, and Mn; D is at least one element selected from K, Rb, Cs and Tl, b is 0.4 to 7, c is from 0.1 to 4, d is from 2 to 10, e is from 0 to 2, f is from 0 to 2, g is from 0 to 2, and h is from 0 to 60, and x is a number satisfying the valences of the elements other than oxygen when a is 12; and b) an arrangement of the catalyst in each reaction tube wherein the catalyst is packed in the tube in a plurality of divided sections disposed successively in the tube axial direction to form the bed and respectively having activities which have been so controlled by varying the composition of the Component D or/and the quantity (or quantities) of the element (or elements) thereof that the activities increase from the tube inlet towards the tube outlet. FR-A-2 114 414 relates to a process for the preparation of acrylic acid using catalysts of different activities. Said catalysts are prepared by diluting the catalytically active catalysts with an inert compound so as to reduce the activity of the catalytically active composition. GB-PS 1 529 384 relates to the oxidation of propylene and isobutylene to obtain the corresponding unsaturated aldehydes and acids. This document teaches to use two catalysts having different physical forms. The first catalyst is a coated catalyst, and the second catalyst consists essentially of the catalytic material. Further, Japanese Laid-Open Patent Publication No. 127013/1976 discloses the use of a combination of a supported catalyst and a molded catalyst essentially of the same composition for production of unsaturated aldehydes and acids from propylene and isobutylene. The document shows, in Examples, specific cases of producing acrolein and acrylic acid from propylene, but discloses no specific case of producing methacrolein and methacrylicacid from isobutylene. Therefore, it is difficult to evaluate the effect of the above technique on the production of methacrolein and methacrylic acid from isobutylene. In the reaction for producing methacrolein and methacrylic acid by subjecting isobutylene, t-butanol or methyl t-butyl ether to gas phase catalytic oxidation, all of these starting materials have a methyl group at the α-position unlike propylene; accordingly, there occur many side reactions caused by the presence of methyl group, such as parallel reactions, successive reactions and the like, producing a number of by-products in large amounts. For example, the heat generated in the reaction for producing methacrolein and methacrylic acid from isobutylene is larger than that for producing acrolein and acrylic acid from propylene; this aggravates the heat build-up in catalyst layer and promotes the formation of by-products by side reactions. Further, methacrolein is unstable as compared with acrolein and easily gives rise to so-called "post-reactions" such as autoxidation and the like, worsening the product yield. As described above, the reaction for producing methacrolein and methacrylic acid by oxidation of isobutylene, t-butanol or methyl t-butyl ether is complex as compared with the reaction for producing acrolein and acrylic acid by oxidation of propylene, making it difficult to obtain intended products at high yields. Therefore, the application of the very techniques obtained in the production of acrolein, acrylic acid, etc. to the production of methacrolein and methacrylic acid has not been sufficiently effective, and further study has been necessary in order to develop a catalyst or process suitably used for production of methacrolein and methacrylic acid. An object of the present invention is to provide a process for producing methacrolein and methacrylic acid at high yields by subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether, to gas phase catalytic oxidation. Another object of the present invention is to provide a process for producing methacrolein and methacrylic acid by subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether, to gas phase catalytic oxidation, in which process heat build-up in hot spots in catalyst layer is suppressed to improve yields of methacrolein and methacrylic acid, prevent catalyst deterioration and enable long stable use of catalyst. Still another object of the present invention is to provide a process for producing methacrolein and methacrylic acid by subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether, to gas phase catalytic oxidation under high-load reaction conditions, in which process heat build-up in hot spots in catalyst layer is suppressed to improve yields of methacrolein and methacrylic acid, prevent catalyst deterioration, enable long stable use of catalyst and enhance productivity significantly. The present invention relates to a process for producing methacrolein and methacrylic acid using a fixed bed multitubular reactor, said process comprising the following steps (a) preparing as catalysts compound oxides having different activities represented by the following general formula (I) Mo a W b Bi c Fe d A e B f C g D h E i O x (in the formula, Mo represents molybdenum, W represents tungsten, Bi represents bismuth, Fe represents iron, A represents at least one element selected from nickel and cobalt, B represents at least one element selected from alkali metals and thallium, C represents at least one element selected from alkaline earth metals, D represents at least one element selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic and zinc, E represents at least one element selected from silicon, aluminum, titanium and zirconium, and O represents oxygen; a, b, c, d, e, f, g, h, i and x represent the numbers of atoms of Mo, W, Bi, Fe, A, B, C, D, E and O, respectively; when a is 12, b = 0-10, c = 0.1-20, d = 0.1-20, e = 2-20, f = 0.001-10, g = 0-10, h = 0-4, i = 0-30 and x = a value determined by the oxidation states of individual elements) by varying the amounts of the elements W, Bi or Fe in the general formula (I) and further by varying the firing temperature employed in catalyst preparation, said firing temperature being in the range of 400 to 600°C so that the firing temperature difference between any two catalysts of the plurality of catalysts becomes at least 5°C, (β) arranging the catalysts in the axial direction of the reaction tube in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the outlet, and (γ) subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether to gas phase catalytic oxidation with molecular oxygen or a molecular oxygen-containg gas. The present invention is hereinafter described in detail. The starting material used in the present invention is at least one compound selected from isobutylene, t-butanol and methyl t-butyl ether, and is subjected to a reaction ordinarily in the form of a mixed gas further containing molecular oxygen, steam and an inert gas (e.g. nitrogen, carbon dioxide). The catalysts used in the present invention are compound oxides represented by the above-mentioned general formula (I). The method for preparing the catalysts and the materials used therefor have no particular restriction, and the catalysts can be prepared by employing the method and materials generally used in the preparation of same type catalyst. In the present invention, a plurality of catalysts of different activities, each represented by the general formula (I) are prepared and filled in a particular arrangement. The firing temperature employed in catalyst preparation in the present invention is, as mentioned above, 400-600°C, preferably 450-550°C. When the firing temperature is lower than 400°C, no sufficient catalyst activity is obtained. Meanwhile, when the firing temperature is higher than 600°C, the resulting catalyst activity is low owing to the occurrence of sintering, etc. Therefore, such firing temperatures are not preferable. When the firing temperature difference is less than 5°C between any two catalysts, the resulting catalyst activity difference caused by the firing temperature difference is insufficient between these catalysts; therefore, such a firing temperature difference is not preferable. The firing temperature difference need not be unnecessarily large and is generally 5-100°C, preferably 10-70°C. At least 2 catalysts selected from the catalysts of controlled activities mentioned above are filled into the reaction zones formed by dividing the catalyst layer of each reaction tube, in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the The methods specified by the present invention, described in detail above, i.e., the present methods for control of catalyst activity by variation of not only catalyst composition but also firing temperature have made it possible to produce methacrolein and methacrylic acid at high yields over a long period of time. The present invention is presumed to have the following functions. Control of catalyst activity is made possible by varying the chemical properties and physical properties of the catalyst. Control of catalyst activity by composition variation is believed to bring about variation of chemical properties of catalyst. Such variation gives rise to variation of catalyst adsorbability for starting material (isobutylene, t-butanol or methyl t-butyl ether), or variation of removability of products (methacrolein and methacrylic acid) from catalyst; thus, catalyst activity and selectivity are varied. Meanwhile, variation of firing temperature is believed to contribute not only to variation of chemical properties (e.g. crystalline structure, stability) of catalyst, but also to variation of physical properties (namely, specific surface area, pore volume, distribution of pore diameters) of catalyst. It is believed that variation of firing temperature has made it possible to obtain a catalyst having physical properties most suitable for an intended reaction and, as a result, attain high yields. In the reaction for producing methacrolein and methacrylic acid, a number of by-products are generated in a large amount, as mentioned previously. Hence, by preparing catalysts different in chemical properties and preferably even in physical properties, optimization of catalysts has been achieved, whereby high yields and longer catalyst life have been realized. The catalysts used in the present invention can be made into molded catalysts by an ordinary molding method such as extrusion molding method, tablet molding method or the like, or into supported catalysts by allowing an ordinary inactive carrier (e.g. silicon carbide, alumina, zirconium oxide, titanium oxide) to support a catalyst component, i.e., a compound oxide represented by the general formula (I). The types of a plurality of catalysts filled into reaction zones may be the same or different. When the number of the reaction zones is, for example, 2, it is possible to arrange a supported catalyst in a reaction zone also functioning as a material gas inlet and a molded catalyst in a reaction zone also functioning as an outlet. The shapes of the catalysts used in the present invention have no particular restriction and can be any of spherical shape, columnar shape, ring shape, etc. The use of ring-shaped catalysts, in particular, can give various advantages such as prevention of heat build-up in hot spots, increased yield, prevention of catalyst deterioration, reduced pressure loss in catalyst layer, and the like. Therefore, ring-shaped catalysts can be preferably used in the present invention. The preferable dimensions of the ring-shaped catalysts are such that the outside diameter is 3-10 mm, the length is 0.5-2 times the outside diameter, and the inside diameter (the diameter of the through-hole formed in the length direction) is 0.1-0.7 time the outside diameter. The shapes of a plurality of catalysts filled into reaction zones may be the same or different. When the number of the reaction zones is, for example, 2, good results are obtained by arranging a ring-shaped catalyst in a reaction zone also functioning as a material gas inlet and a pellet-shaped catalyst in a reaction zone also functioning as an outlet. In the present invention, the catalyst layer in each reaction tube is divided into two or more portions in the axial direction of the tube to form a plurality of reaction zones. In these reaction zones are arranged a plurality of catalysts of different activities as mentioned above, in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the outlet. That is, a catalyst of lowest activity is arranged in the reaction zone also functioning as a material gas inlet, and a catalyst of highest activity is arranged in the reaction zone also functioning as a material gas outlet. Such arrangement of a plurality of catalysts of different activities makes it possible to suppress heat build-up in hot spots and obtain intended products at high yields. The larger the number of reaction zones formed by dividing the catalyst layer, the easier is the control of temperature distribution in reaction zones. However, 2 or 3 reaction zones can sufficiently attain an intended effect industrially. The division ratio cannot be specified in a particular range because it differs by the composition, shape, etc. to be possessed by the catalyst of each reaction zone. Desirably, the division ratio is appropriately selected so that the overall activity and selectivity become optimum. The gas phase catalytic oxidation reaction of the present invention may be carried out by an ordinary single-pass method or a recycle method. The oxidation reaction can be effected under the conditions generally employed in similar reactions. For example, a starting material, i.e. a mixed gas consisting of 1-10% by volume of at least one compound selected from isobutylene, t-butanol and methyl t-butyl ether, 3-20% by volume of molecular oxygen, 0-60% by volume of steam, 20-80% by volume of an inert gas (e.g. nitrogen, carbon dioxide), etc. is introduced into the above-mentioned reaction zones at a temperature range of 250-450°C at a pressure of normal pressure to 1.013 MPa (10 atm.) at a space velocity (SV) of 300-5,000 hr -1 (STP). In the present process, as compared with conventional processes, particularly excellent results can be obtained under high-load reaction conditions employed for higher productivity, for example, under the conditions of higher material concentration or higher space velocity. In the present invention, various meritorious effects such as mentioned below can be obtained by filling a plurality of particular molybdenum-based catalysts of different activities into a plurality of reaction zones formed by dividing the catalyst layer in each reaction tube, in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the outlet. (a) Methacrolein and methacrylic acid can be obtained at high yields. (b) Heat build-up in hot spots can be suppressed effectively. (c) The excessive oxidation reaction in hot spots can be prevented, and intended methacrolein and methacrylic acid can be obtained at high yields. (d) Catalyst deterioration due to thermal load can be prevented and stable use of catalyst over long period is possible. (e) Intended methacrolein and methacrylic acid can be obtained at high yields even under high-load reaction conditions (e.g. high material concentration, high space velocity). As a result, significantly increased productivity can be obtained. Further, the following effect can additionally be obtained by the use of ring-shaped catalyst. (f) Pressure loss in catalyst layer is reduced, whereby electricity consumption can be lowered. Thus, the process of the present invention is very useful for industrial production of methacrolein and methacrylic acid.

Claims: A process for producing methacrolein and methacrylic acid using a fixed bed multitubular reactor, said process comprising the following steps (α) preparing as catalysts compound oxides having different activities represented by the following general formula (I) Mo a W b Bi c Fe d A e B f C g D h E i O x (in the formula, Mo represents molybdenum, W represents tungsten, Bi represents bismuth, Fe represents iron, A represents at least one element selected from nickel and cobalt, B represents at least one element selected from alkali metals and thallium, C represents at least one element selected from alkaline earth metals, D represents at least one element selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic and zinc, E represents at least one element selected from silicon, aluminum, titanium and zirconium, and O represents oxygen; a, b, c, d, e, f, g, h, i and x represent the numbers of atoms of Mo, W, Bi, Fe, A, B, C, D, E and O, respectively; when a is 12, b = 0-10, c = 0.1-20, d = 0.1-20, e = 2-20, f = 0.001-10, g = 0-10, h = 0-4, i = 0-30 and x = a value determined by the oxidation states of individual elements) by varying the amounts of the elements W, Bi or Fe in the general formula (I) and further by varying the firing temperature employed in catalyst preparation, said firing temperature being in the range of 400 to 600°C so that the firing temperature difference between any two catalysts of the plurality of catalysts becomes at least 5°C, (β) arranging the catalysts in the axial direction of the reaction tube in such a way that the activity of filled catalyst becomes higher as a material gas proceeds from the inlet to the outlet, and (γ) subjecting at least one material selected from isobutylene, t-butanol and methyl t-butyl ether to gas phase catalytic oxidation with molecular oxygen or a molecular oxygen-containg gas. The process for producing methacrolein and methacrylic acid according to claim 1, which uses catalysts of the general formula (I) (wherein when a is 12, b = 0-10, c = 0.1-10, d = 0.1-20, e = 2-20, f = 0.001-10, g = 0-10, h = 0-4, i = 0-30 and x = a value determined by the oxidation states of individual elements). The process for producing methacrolein and methacrylic acid according to any of claims 1 to 2, wherein the number of the reaction zones is 2 or 3. The process for producing methacrolein and methacrylic acid according to any of claims 1 to 3, wherein the catalysts are ring-shaped catalysts with a through-hole in the length direction, having an outside diameter of 3-10 mm, a length of 0.5-2 times the outside diameter and an inside diameter (the diameter of the through-hole) of 0.1-0.7 times the outside diameter.

Inventors: AOKI YUKIO, KURIMOTO IKUO, OHNO SHIGERU, ONODERA HIDEO, AOKI, YUKIO, KURIMOTO, IKUO, OHNO, SHIGERU, ONODERA, HIDEO
Applicants: NIPPON CATALYTIC CHEM IND, NIPPON SHOKUBAI CO., LTD.
Application year: 1990
Main classification: C07C27
IPC codes: C07C57, C07C45, B01J27, B01J23, B01J8, C07C51