JP2011102248A - Method of producing acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing acrylic acid by the gas-phase catalytic oxidation of acrolein, capable of stably producing acrylic acid at a high yield for a long period of time. <P>SOLUTION: Upon packing reaction tubes of a fixed bed reactor of a heat exchanging type with a catalyst comprising molybdenum and vanadium as essential components for use in carrying out the gas phase oxidation of acrolein in the presence of molecular oxygen or a gas comprising molecular oxygen, a packing density of the catalyst charged into the respective reaction tubes is 0.90 g/cm<SP>3</SP>or higher and the surface area of the catalyst charged per unit volume is 2,000 to 6,000 m<SP>2</SP>/L (liter). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a process for producing acrylic acid by catalytic gas phase oxidation of acrolein.

  Acrylic acid is industrially important as a raw material for various synthetic resins, paints, and plasticizers, and is currently produced on a scale of several million tons / year worldwide. In recent years, the importance has increased as a raw material for water-absorbent resins, and the demand has further increased, and further improvement in the yield of acrylic acid is desired on an industrial scale.

  As an industrial process for acrylic acid, the first stage reaction is mainly acrolein by catalytic vapor phase oxidation of propylene, and the second stage reaction is contact of acrolein obtained by the first stage reaction. A two-stage oxidation method in which acrylic acid is formed by gas phase oxidation is most common. In the process of producing acrylic acid from acrolein, which is the second stage reaction in such a two-stage oxidation method, the catalyst performance such as the yield and life of acrylic acid is not always sufficient, and the performance is improved. For each purpose, various companies have studied and various proposals have been made.

  For example, a catalyst composed of molybdenum, vanadium, and tungsten (Patent Document 1), a catalyst composed of molybdenum, vanadium, copper, tungsten, and chromium (Patent Document 2), a catalyst composed of molybdenum and vanadium (Patent Document 3), molybdenum, vanadium, A catalyst composed of copper and at least one element of antimony or germanium (Patent Document 4) is disclosed.

Japanese Examined Patent Publication No. 44-12129 Japanese Patent Publication No.49-11371 Japanese Patent Publication No. 50-25914 JP-A-52-85091

  However, all of the above-described techniques still leave room for improvement in terms of the yield of the target acrylic acid, catalyst life, and the like from an industrial scale.

  Thus, an object of the present invention is to provide a method for producing acrylic acid stably in a high yield over a long period of time in a method for producing acrylic acid by catalytic gas phase oxidation of acrolein.

  Those skilled in the art will naturally recognize that the greater the amount of catalyst used in the reaction and the greater the surface area of the catalyst packed per unit volume, the better for catalyst performance and catalyst life.

  However, in a reaction accompanied by heat generation such as an oxidation reaction such as acrolein, a local abnormal heat generation portion (hereinafter referred to as “hot spot portion”) is generated, and the catalyst is pulverized, disintegrated or disintegrated during a long-term reaction. Spattering and sublimation of the constituent components from the catalyst occur, and the catalyst performance and catalyst life tend to be reduced, and the amount of catalyst charged in one reaction tube increases, that is, the packing density of the catalyst is high. The tendency becomes stronger. On the other hand, if the amount of catalyst charged in one reaction tube is small, the contact efficiency with the reaction gas decreases, so that sufficient activity cannot be obtained, and the catalyst performance is likely to deteriorate over time, etc. It is not preferable in terms of catalyst performance and catalyst life. The same problem occurs with respect to the surface area of the packed catalyst.

  As a result of intensive studies on the catalyst filling method in view of the above problems, the inventors have determined that the catalyst packing density and the surface area due to the catalyst per unit volume are specific when the catalyst is packed in the fixed bed heat exchange reactor. It has been found that by filling the catalyst so as to fall within the range, acrylic acid can be produced stably and with a high yield for a long period of time, leading to the present invention.

  According to the present invention, in a method for producing acrylic acid by catalytic gas phase oxidation of acrolein, it becomes possible to produce acrylic acid stably in a high yield over a long period of time.

  Hereinafter, although the manufacturing method of acrylic acid concerning this invention is demonstrated in detail, the range of this invention is not restrained by these description, and changes suitably in the range which does not impair the meaning of this invention except the following illustrations. And can be implemented.

In the present invention, when the catalyst is filled in each reaction tube of the fixed bed heat exchange reactor, it is necessary to adjust the packing density and surface area of the catalyst to be filled in each reaction tube within a specific range. Specifically, the packing density of the catalyst packed in each reaction tube of the fixed-bed heat exchange reactor is 0.90 g / cm ³ or more, preferably in the range of 1.00~1.60g / cm ^3, and the catalyst The catalyst is packed so that the surface area per liter (liter) is in the range of 2,000 to 6,000 m ² , more preferably 2,100 to 4,000 m ² . When the packing density and surface area of the catalyst are less than the above ranges, the contact efficiency between the catalyst and the reaction gas is lowered, so that sufficient activity cannot be obtained, the yield of acrylic acid is low, and the catalyst is likely to deteriorate with time. Life is short. On the other hand, when the packing density and the surface area of the catalyst packed in the reaction tube are larger than the above ranges, the pressure loss increases, the running cost of the blower and the like increases, and the sequential reaction increases. Yield is low. Further, as described above, it is disadvantageous in terms of local catalyst deterioration due to the generation of a hot spot portion.

The packing density of the catalyst packed in the reaction tube and the surface area per 1 L (liter) of the catalyst in the present invention are calculated by the following equations.
Packing density (g / cm ³ )
= Mass of catalyst charged in reaction tube (g) / capacity of catalyst charged in reaction tube (cm ³ )
here,
Capacity of the catalyst filled in the reaction tube (cm ³ )
= Packed bed length of catalyst packed in reaction tube × ((reaction tube inner diameter / 2) ² × circumference ratio)
And
Surface area (m ² ) = packing density (g / cm ³ ) × specific surface area (m ² / g) × 1,000 (cm ³ )
The packing density is determined as follows.

  The specific surface area can be measured using an apparatus such as a BET specific surface area meter generally used for this type of measurement.

The catalyst used in the present invention is a catalyst having molybdenum and vanadium as essential components as catalyst components, and the following general formula (1)
_{Mo 12 V a A b B c} C d D e O z (1)
(Where Mo is molybdenum, V is vanadium, A is niobium and / or tungsten, B is at least one element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, and bismuth, C represents at least one element selected from the group consisting of tin, antimony and tellurium, D represents at least one element selected from titanium, aluminum, silicon and zirconium, O represents oxygen, and a, b, c, d, e, and z represent atomic ratios of V, A, B, C, D, and O, respectively, a = 1 to 14, b = 0 to 12, c = 0 to 10, d = 0 to 6, e = 0 to 40, and z is a numerical value determined by the oxidation state of each element).

  The above-described catalyst can be prepared by a method generally used for preparing this type of catalyst, and an example is shown below.

  As raw materials for catalytically active components, oxides, hydroxides, ammonium salts, nitrates, carbonates, sulfates, organic acid salts, etc. of each component element, their aqueous solutions, sols, etc., or multiple elements The compound or the like is mixed with water to form an aqueous solution or an aqueous slurry (hereinafter referred to as “starting raw material mixture”).

  Next, if necessary, the obtained starting material mixture is dried by various methods such as heating and decompression to obtain a catalyst precursor. As a drying method by heating, for example, a powdered catalyst precursor can be obtained using a spray dryer, a drum dryer or the like, or heated in an air stream using a box-type dryer, a tunnel-type dryer or the like. Block or flake catalyst precursors can also be obtained. Alternatively, a method of once concentrating the starting raw material mixture and evaporating to dryness to obtain a cake-like solid and further subjecting the solid to the above heat treatment can also be employed. As a drying method by reduced pressure, for example, a block or powdery catalyst precursor can be obtained using a vacuum dryer.

  The obtained dried product is sent to a subsequent molding step through a pulverization step and a classification step for obtaining a powder having an appropriate particle size as required. The particle size of the catalyst precursor powder is not particularly limited, but is preferably 500 μm or less in terms of excellent moldability.

  As a method for molding the catalyst, a method of molding the catalyst precursor or a mixture of the catalyst precursor and a powdery inert carrier into a certain shape by an extrusion molding method or a tableting molding method, a constant catalyst component is used. There is a supporting method of supporting on an arbitrary inert carrier having the following shape.

  In the case of an extrusion molding method or a tableting molding method, the shape is not particularly limited, and may be any shape such as a spherical shape, a cylindrical shape, a ring shape, and an indeterminate shape. Of course, in the case of a spherical shape, it does not need to be a true sphere, and may be substantially spherical, and the same applies to a cylindrical shape and a ring shape.

  As the loading method, for example, an evaporation to dryness method in which a starting inert liquid mixture or an aqueous slurry is applied to or adhered to a desired inert carrier having a certain shape while being heated or dried while being dried and supported. Alternatively, it can be produced according to a granulation method in which the catalyst precursor is supported in powder form on an inert carrier. Among these, the centrifugal fluid coating method described in JP-A No. 64-85139, the rolling granulation method described in JP-A No. 8-29997, and the rocking mixer method described in JP-A No. 2004-136267 are used. Thus, a granulation method of supporting on an inert carrier is preferable.

  Examples of the inert carrier include alumina, silica, silica-alumina, titania, magnesia, steatite, cordierite, silica-magnesia, silicon carbide, silicon nitride, zeolite, and the like. When used in the supporting method, the shape is not particularly limited, and known shapes such as a spherical shape, a cylindrical shape, and a ring shape can be used.

  In the molding step, a molding aid or binder for improving moldability, a pore forming agent for forming appropriate pores in the catalyst, or the like can be used. Specific examples include organic compounds such as ethylene glycol, glycerin, propionic acid, maleic acid, benzyl alcohol, propyl alcohol, butyl alcohol or phenols, water, nitric acid, ammonium nitrate, and ammonium carbonate.

  In addition, for the purpose of improving the mechanical strength of the catalyst, reinforcing agents such as ceramic fibers, glass fibers, silicon carbide, and silicon nitride can be used. The reinforcing agent may be added to the starting raw material mixture or may be blended with the catalyst precursor.

  The molded body or carrier obtained in the molding process is sent to the subsequent firing process. The firing temperature is 300 ° C to 500 ° C, preferably 350 ° C to 450 ° C, more preferably 370 ° C to 430 ° C, and the firing time is preferably 1 to 10 hours. The firing atmosphere may be an oxidizing atmosphere, but a molecular oxygen-containing gas atmosphere is preferable, and it is particularly preferable to perform the firing step under the flow of the molecular oxygen-containing gas. Air is suitably used as the molecular oxygen-containing gas.

  In addition, there is no restriction | limiting in particular as a baking furnace used by a baking process, What is necessary is just to use the box-type baking furnace or tunnel type baking furnace etc. which are generally used.

  In order to make the packing density and surface area of the catalyst packed in each reaction tube of the fixed bed heat exchange reactor in the present invention fall within the above range, the physical properties of the catalyst to be packed, particularly the density, specific surface area, etc. are set. It is necessary to control, and adjustment of conditions during catalyst preparation is particularly important.

  Specifically, a method for controlling the amount of the molding auxiliary, binder, pore forming agent, and reinforcing agent used in the molding step described above, a method for controlling the compression pressure (compression pressure) when tableting molding, Etc. can be mentioned. It is also possible to control the particle diameter of the catalyst with respect to the inner diameter of the reaction tube filled with the catalyst so that it falls within the above range. Of course, these may be combined.

  The reactor used for producing acrylic acid by catalytic gas phase oxidation of acrolein with molecular oxygen or a molecular oxygen-containing gas in the present invention is not particularly limited as long as it is a fixed bed reactor. A fixed bed multitubular reactor is preferred. The inner diameter of the reaction tube is usually 15 to 50 mm, more preferably 20 to 40 mm, and still more preferably 22 to 38 mm.

  Each reaction tube of the fixed bed multi-tubular reactor does not necessarily need to be filled with a single catalyst, but the packing density of the catalyst filled in each reaction tube and the surface area of the catalyst filled per unit volume are not limited. As long as it is within the specific range of the invention, it is possible to fill a plurality of conventionally known catalysts so as to form layers (hereinafter referred to as “reaction zones”). For example, a method of filling a plurality of catalysts having different occupied volumes as disclosed in JP-A-9-241209 so that the occupied volume decreases from the raw material gas inlet side to the outlet side, or JP-A-7-10802. A method of filling a plurality of catalysts having different loading rates such as from the raw material gas inlet side to the outlet side so as to increase the loading rate, or a part of the catalyst as in Japanese Patent Publication No. 2008-528883 A method of diluting with a simple carrier or a combination of these may be employed. At this time, the number of reaction zones is appropriately determined depending on the reaction conditions and the scale of the reactor. However, if the number of reaction zones is too large, problems such as complicated packing of the catalyst may occur. About 2-6 is desirable.

The reaction conditions in the present invention are not particularly limited, and any conditions generally used for this type of reaction can be used. For example, the raw material gas is 1-15% by volume, preferably 4-12% by volume acrolein, 0.5-25% by volume, preferably 2-20% by volume molecular oxygen, 0-30% by volume, preferably 0 A mixed gas consisting of ˜25% by volume of water vapor and the balance consisting of an inert gas such as nitrogen at a temperature of 200 to 400 ° C. under a pressure of 0.1 to 1.0 MPa and 300 to 5,000 Hr ⁻¹ (STP). What is necessary is just to contact a catalyst with space velocity.

  As a reaction raw material gas, not only a mixed gas composed of acrolein, oxygen and an inert gas, but also an acrolein-containing mixed gas obtained by a dehydration reaction of glycerol or an oxidation reaction of propane and / or propylene can be used. In addition, air or oxygen can be added to the mixed gas as necessary.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Hereinafter, for convenience, “parts by mass” may be simply referred to as “parts”.

The acrolein conversion rate and acrylic acid yield were determined by the following equations.
Acrolein conversion [mol%]
= (Mole number of reacted acrolein) / (Mole number of supplied acrolein) × 100
Acrylic acid yield [mol%]
= (Number of moles of acrylic acid produced) / (number of moles of acrolein supplied) × 100
[Measurement of specific surface area of catalyst]
The specific surface area of the catalyst was measured using a Macsorb model-1210 manufactured by Mountec Co., Ltd. as a BET specific surface area meter.
[Catalyst Production Example 1: Preparation of Catalyst (1)]
While heating and stirring 2000 parts of ion-exchanged water, 350 parts of ammonium paramolybdate, 116 parts of ammonium metavanadate, and 44.6 parts of ammonium paratungstate were dissolved therein. Separately, 87.8 parts of cupric nitrate and 12 parts of antimony trioxide were added while heating and stirring 200 parts of ion-exchanged water. The two liquids obtained were mixed to obtain a suspension. This suspension was evaporated to dryness to obtain a cake-like solid. The obtained solid was dried and pulverized to 500 μm or less to obtain catalyst precursor powder. 1,200 parts by mass of a spherical carrier made of silica-alumina with an average particle diameter of 5 mm is put into a centrifugal fluidized coating apparatus, and then a catalyst precursor powder together with a 15% by mass ammonium nitrate aqueous solution is fed as a binder while passing hot air at 90 ° C. And supported on a carrier. The obtained carrier was calcined at 400 ° C. for 6 hours in an air atmosphere to prepare a catalyst (1). The loading ratio of the catalyst (1) was about 32% by mass, and the composition of the metal elements excluding the carrier and oxygen was as follows in terms of atomic ratio.
Catalyst _{(1) Mo 12 V 6 W} 1 Cu 2.2 Sb 0.5
The loading rate was determined by the following formula.
Loading rate (mass%) =
[(Mass of catalyst after calcination (g) −Mass of carrier used) / Mass of carrier used (g)] × 100
It was 2.3 m < ² > / g when the specific surface area of the catalyst (1) was measured.
[Catalyst Production Examples 2 to 7: Preparation of Catalysts (2) to (7)]
The same procedure as in Catalyst Production Example 1 was carried out except that the particle size of the support was changed as shown in Table 1. The results of measuring the specific surface area of each catalyst are also shown in Table 1.

<Examples 1 to 6 and Comparative Example 1>
[Oxidation reaction]
Each of the catalysts (1) to (7) was packed into a stainless steel reaction tube having an inner diameter of 25 mmφ so that the packed bed length of the catalyst was 2000 mm. Table 2 shows the packing density of each of the catalysts (1) to (7) and the surface area of the packed catalyst. A mixed gas of 5% by volume of acrolein, 6% by volume of oxygen, 25% by volume of water vapor, and 64% by volume of inert gas such as nitrogen was introduced into the reaction tube at a space velocity of 1500 Hr ⁻¹ , and an oxidation reaction was performed at a reaction temperature of 260 ° C. Went. The oxidation reaction was continued for 4000 hours while appropriately changing the reaction temperature. The results are also shown in Table 2.

Claims (2)

When filling a reaction tube of a fixed bed heat exchange reactor with a catalyst having molybdenum and vanadium as essential components used in catalytic gas phase oxidation of acrolein in the presence of molecular oxygen or a molecular oxygen-containing gas, The packing density of the catalyst filled in each reaction tube is set to 0.90 g / cm ³ or more and the surface area of the catalyst filled per unit volume is set to 2,000 to 6,000 m ² / L (liter). A process for producing acrylic acid, characterized in that The method for producing acrylic acid according to claim 1, wherein the catalyst containing molybdenum and vanadium as essential components is represented by the following general formula (1).
_{Mo 12 V a A b B c} C d D e O z (1)
(Where Mo is molybdenum, V is vanadium, A is niobium and / or tungsten, B is at least one element selected from the group consisting of chromium, manganese, iron, cobalt, nickel, copper, zinc, and bismuth, C represents at least one element selected from the group consisting of tin, antimony and tellurium, D represents at least one element selected from titanium, aluminum, silicon and zirconium, O represents oxygen, and a, b, c, d, e, and z represent atomic ratios of V, A, B, C, D, and O, respectively, a = 1 to 14, b = 0 to 12, c = 0 to 10, d = 0 to 6, e = 0 to 40, and z is a numerical value determined by the oxidation state of each element)