JP2010070579A - Method for producing acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing acrylic acid at a high yield while preventing polymerization and retaining purification conditions of acrylic acid within a prescribed range. <P>SOLUTION: Acrylic acid is produced at a high yield while preventing formation of a polymer of acrylic acid, by using a single reactor. The concentration of propylene in a mixed gas introduced into a step for obtaining acrolein from propylene and the concentration of water in the mixed gas are 7-15 vol.% and 0-6 vol.%, respectively; the obtained acrylic acid-containing gas is collected by an acrylic acid-collecting column through introduction of a collection solvent into the column in the mass flow rate of 0.1-1.5 times that of the propylene introduced to the first reaction zone; and the concentration of water in the bottom liquid of the column is 1-25 mass%, thereby reducing complexity in the next step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to acrylic acid using a reactor in which a high concentration of propylene is used as a raw material, and a first reaction zone and a second reaction zone are formed by dividing a single reaction tube by at least one perforated tube plate. The present invention relates to a method for producing acrylic acid in a high yield in which the water concentration of the containing solution is improved to 1 to 25% by mass and polymerization in the subsequent steps is prevented.

  Acrylic acid is used for acrylic fiber copolymers or as an adhesive as an adhesive, and is also used as a paint, fiber processing, leather, building material, etc., and its demand is expanding. For this reason, it is common to produce by a catalytic gas phase oxidation reaction such as propylene that enables mass production using inexpensive raw materials. In the catalytic gas phase oxidation reaction, since there is a possibility that it belongs to the explosion range due to the blending of molecular oxygen used in the oxidation reaction, it is common to supply the raw material gas in the range of about 4 to 7% by volume. In order to improve this, it is preferable to use a high-concentration source gas, and various improvements have been made.

  For example, Patent Document 1 includes a plurality of reaction tubes having two reaction zones filled with a reaction composition containing more than 7% by volume of propylene, molecular oxygen, water vapor, and an inert gas in the balance, and a catalyst. It describes a method for producing acrylic acid from propylene by supplying it to a reactor. When the mixed product gas obtained by the catalytic gas phase oxidation reaction is introduced into the absorber to obtain an aqueous acrylic acid solution, unreacted propylene, unreacted acrolein and acrylic acid remain in the absorber exhaust gas. When the exhaust gas is circulated and used, the volume of the inert gas flowing through the absorber is increased, so that a load is generated at the top of the absorber, the collection efficiency is lowered, and the yield of acrylic acid is lowered. On the other hand, when the exhaust gas is not circulated and used, water vapor is used as a dilution gas, so the moisture content in the gas flowing through the absorber changes depending on the moisture, so that the selectivity, addition rate, and catalytic activity in the oxidation reaction change. Changes. In the above publication, propylene having a higher concentration than before is used in a single reactor system, the amount of exhaust gas required for dilution is reduced, and the load on the absorber is reduced.

  In addition, after collection of the acrylic acid-containing gas, purification steps such as dehydration of the collection solvent and a separation step of contained low-boiling substances and high-boiling substances are performed.

JP 2000-103761 A

  However, acrylic acid is an easily polymerizable compound. When a high-concentration raw material gas is used to increase productivity, an acrylic acid polymer is easily generated in the collection step of acrylic acid and the subsequent purification step. Become. For this reason, in various purification towers, acrylic acid is produced while adjusting the distillation pressure, temperature, amount of feed liquid, etc. to prevent the occurrence of polymerization, but changes in each condition affect other conditions, so that Control is not easy. For example, when the concentration of the bottom liquid of the collection tower is changed and the acrylic acid concentration is lowered, if the distillation conditions with a high acrylic acid concentration are maintained, an acrylic acid polymer is generated in the distillation tower, and the operation is stopped due to blockage. However, the quality may be lowered or the yield may be lowered due to the presence of the polymer.

  The acrylic acid purification process uses distillation columns called dehydration towers, low-boiler separation towers, high-boiler separation towers, etc., and a series of purification treatments by connecting multiple distillation towers with different functions. Is often done. Therefore, the change in the composition of the bottom liquid of a certain distillation column also requires the purification conditions to be changed after the next step, which makes it more difficult to control the purification step.

  On the other hand, the solution and exhaust gas discharged from the acrylic acid production process may contain raw material compounds, product compounds, and other useful compounds, and the production yield can be improved if recycled in the production process. However, since the composition of the exhaust gas also changes according to changes in the distillation conditions and the generation of the polymer proceeds in a chain, the distillation conditions are kept constant particularly in the acrylic acid production method including recycling of the exhaust gas. This is a very difficult situation.

  In the acrylic acid production process using propylene as a raw material, the present inventor uses high-concentration propylene gas to increase the productivity of acrylic acid when the conditions from the catalytic gas phase oxidation reaction to the acrylic acid collection process are limited to a specific range. Has been found, and the operation in the purification process can be simplified, and the present invention has been completed.

  In particular, when the water concentration of the acrylic acid collection tower bottom liquid is limited to 1 to 25% by mass, it is possible to effectively prevent generation of a polymer in the subsequent steps. Such control can be achieved by adjusting the amount of collected liquid. Moreover, if the range is further controlled within a range of 1 to 25% by mass, the control range of the distillation conditions after the next step can be narrowed, and the loss fluctuation of acrylic acid from the collection tower and waste water is minimized. On the other hand, operational stability after the next process including wastewater treatment facilities can be secured.

  In particular, by adjusting the collection concentration by changing the amount of the collection solution in the collection tower, acrylic acid can be collected at a high concentration without changing the amount of water from the top of the collection tower. It has been found that when the exhaust gas is recycled and used, it is excellent in that the production conditions can be stabilized.

  According to the present invention, in the acrylic acid production process using propylene as a raw material, the first reaction zone and the second reaction zone are contacted using a reactor in which a single reaction tube is divided by at least one perforated tube plate. By limiting the conditions in the acrylic acid collection step from the gas phase oxidation reaction to a specific range, acrylic acid can be produced with high productivity using a high-concentration propylene gas, and the operation in the purification step can be simplified.

  In particular, when the water concentration of the acrylic acid collection tower bottom liquid is limited to 1 to 25% by mass, the processing of the next step can be simplified.

  Also, if the amount of the collection solution in the collection tower is changed, acrylic acid can be collected at a high concentration without changing the amount of water from the top of the collection tower. In particular, the collection tower exhaust gas is recycled for use. When it does, it is excellent at the point which can stabilize manufacturing conditions.

It is a flow sheet which shows a part of acrylic acid manufacturing process using one reactor (single reactor) with which the 1st reaction zone and the 2nd reaction zone were partitioned off with the perforated tube board.

In the first aspect of the present invention, a mixed gas containing propylene and molecular oxygen is introduced into a first reaction zone filled with a complex oxide catalyst containing molybdenum and bismuth as essential components, and propylene is oxidized to contain acrolein. Gas is obtained, and the acrolein-containing gas is obtained by introducing the acrolein-containing gas into a second reaction zone formed by filling a complex oxide catalyst containing molybdenum and vanadium as essential components. In the method for producing acrylic acid comprising the step of introducing into an acid collection tower and bringing into contact with a collection solvent to obtain an acrylic acid-containing solution,
(A) the first reaction zone and the second reaction zone are formed by dividing a single reaction tube with at least one perforated tube plate;
(B) The propylene concentration of the mixed gas introduced into the first reaction zone is 7 to 15% by volume, and the water concentration in the mixed gas is 0 to 6% by volume;
(C) introducing a collection solvent having a mass flow rate of 0.1 to 1.5 times the mass flow rate of propylene introduced into the first reaction zone into the acrylic acid collection tower; and (d) capturing the acrylic acid. The acrylic acid-containing solution collected by the collecting tower has a water concentration of 1 to 25% by mass at the bottom of the collecting tower.

  Increasing the concentration of propylene gas is effective for increasing the production yield, but it is also necessary to increase the oxygen concentration at the same time, and the reaction heat generated is not sufficiently absorbed and the control of the reaction is difficult. In some cases, a stable catalytic gas phase oxidation reaction cannot be achieved. In such a case, for example, by measuring the explosion range under the assumed operating condition and introducing a dilution gas such as propane that narrows the range within the explosion range, the range can be avoided. At the same time, limiting the water concentration of the acrylic acid-containing solution that has collected acrylic acid to 1 to 25% by mass prevents the collection tower and the generation of the polymer after the next step, and reduces the purification operation after the next step. I found out that I can do it. In the present invention, “purification” includes distillation, stripping, crystallization, extraction, absorption, partial condensation and the like.

  Here, “distillation” is a method of heating a solution to its boiling point to separate volatile components contained therein, and “emission” is a method of supplying an emitted gas and transferring a target substance in a liquid phase to a gas phase. , "Crystallization" is a method for separating the target product as crystals, "extraction" is a method for separating the target product by dissolving it in a solvent, and "absorption" is a method for separating the target product in the gas phase or liquid phase. A method of separating by contact with a liquid or a solid, and “fractionation”, respectively, mean a method of condensing a part of a gas or vapor to separate a target product. In the present invention, the low boiling point substance means a substance having a lower boiling point than acrylic acid in the standard state, and the high boiling point substance means a substance having a higher boiling point than acrylic acid in the standard state. Hereinafter, the present invention will be described in detail.

  In the present invention, propylene is introduced into a first reaction zone filled with a complex oxide catalyst containing molybdenum and bismuth as essential components, propylene is oxidized to obtain an acrolein-containing gas, and molybdenum and vanadium as essential components. The acrolein-containing gas is introduced into a second reaction zone filled with the composite oxide catalyst to obtain an acrylic acid-containing gas.

  The reactor is not particularly limited as long as a catalytic gas phase oxidation reaction can be performed, but a multitubular reactor can be preferably used in terms of excellent reaction efficiency. The reaction tube material, dimensions and number, distribution of tubes and any known reaction tubes possible may be used. In the present invention, a reactor in which the first reaction zone and the second reaction zone are formed by dividing a single reaction tube by at least one perforated tube plate (hereinafter also referred to as “single reactor”). It is characterized in that it is used. The first reaction is a step of oxidizing propylene to mainly acrolein, and the second reaction is a step of oxidizing acrolein to acrylic acid. As the oxidation catalyst to be filled, molybdenum for oxidizing propylene to obtain acrolein and a composite oxidation catalyst (i) having bismuth as essential components in the first reaction zone, and molybdenum for oxidizing acrolein to obtain acrylic acid And a composite oxide catalyst (ii) containing vanadium as an essential component is charged into the second reaction zone.

  An example of an embodiment of the present invention using a single reactor in which a first reaction zone and a second reaction zone are partitioned by a perforated tube sheet will be described with reference to FIG. In FIG. 1, 1 is propylene, 2 is water vapor, 3 is air, 10 is a reactor, 11 is a reaction tube, 12 is a composite oxide catalyst (i), 13 is a composite oxide catalyst (ii), and 15 is perforated. Tube plate, 20 is an acrylic acid-containing gas, 23 is a heat exchanger, 30 is a collection tower, 31 is a packed bed, 32 is a disperser, 33 is a collection solvent, 34 is a cooler, 35 is an acrylic acid-containing solution, Reference numeral 36 denotes exhaust gas, 40 denotes a dehydration tower, 41 denotes a distillate gas, 42 denotes a solvent phase, 43 denotes a water phase, 50 denotes a next step, 60 denotes waste gas, 71 denotes a heat exchanger, and 72 denotes a flow rate adjusting device.

  First, propylene 1 which is a raw material gas is supplied to the reactor 10 together with water vapor 2 and air 3 containing molecular oxygen. In the reactor 10, a reaction tube 11 is filled with a composite oxide catalyst (i) 12 and a composite oxide catalyst (ii) 13 as oxidation catalysts, and propylene is oxidized by the catalyst (i) to obtain acrolein. Then, acrolein is oxidized by the catalyst (ii) to obtain an acrylic acid-containing gas 20. Next, the acrylic acid-containing gas 20 is introduced into the acrylic acid collection tower 30 and collected by the collection solvent 33. A tower bottom liquid is made into acrylic acid containing solution 35, a part is cooled with the cooler 34, it is made to circulate to the acrylic acid collection tower 30, and a part is introduce | transduced into the dehydration tower 40, and a dehydration process is performed. After the distillate gas 41 is condensed by a condenser disposed at the top of the dehydration tower 40, the condensate is separated into a solvent phase 42 and an aqueous phase 43. The solvent phase 42 may be circulated through the dehydration tower 40, and the aqueous phase 43 may be used as the collection solvent 33. The bottom liquid of the dehydration tower is supplied to the next step 50 and further purified such as separation of low-boiling substances and high-boiling substances. Further, all of the exhaust gas 36 from the collection tower 30 may be treated as the waste gas 60, but a part of the exhaust gas 36 is recycled to the reactor 10 by the blower 4 as a recycle gas, and only the remainder is disposed of the waste gas 60. Can also be processed.

In the present invention, the composite oxide catalyst (i) used in the first reaction zone may contain molybdenum and bismuth, but preferably has the general formula Mo _a -B _{i b} -Fe _c -A _d -B _{e. -C f -D g -O x (Mo} , Bi, Fe represent molybdenum, represents bismuth and iron, a represents a least one element selected from the group consisting of nickel and cobalt, B is selected from alkali metals and thallium Represents at least one element, C represents at least one element selected from the group consisting of phosphorus, niobium, manganese, cerium, tellurium, tungsten, antimony and lead; D represents silicon, aluminum, zirconium and titanium; At least one element selected from the group consisting of O, oxygen represents a, b, c, d, e, f, g and x Represents the atomic ratios of Mo, Bi, Fe, A, B, C, D and O, respectively, where a = 12, b = 0.1-10, c = 0.1-10, d = 2 -20, e = 0.001-5, f = 0-5, g = 0-30, and x is a value determined by the oxidation state of each element).

As the composite oxide catalyst (ii), but may be one containing molybdenum and vanadium, preferably of the general formula _{Mo a -V b -W c -Cu d} -A e -B f -C g -O _x (Mo is molybdenum, V is vanadium, W is tungsten, Cu is copper, A is at least one element selected from antimony, bismuth, tin, niobium, cobalt, iron, nickel and chromium, and B is an alkali metal. And at least one element selected from alkaline earth metals, C represents at least one element selected from silicon, aluminum, zirconium and titanium, O represents oxygen, a, b, c, d , E, f, g, and x represent the atomic ratio of Mo, V, W, Cu, A, B, C, and O, respectively, and when a = 12, b = 2-14, c = 0 to 12, d = 0.1 to 5, e = 0 to 5, f = 0 to 5, g = 0 to 20, and x is a value determined by the oxidation state of each element) Can be illustrated.

  The preparation method of the catalyst used in the present invention and the mixing molding method are not particularly limited, and generally used methods and raw materials can be employed. Also, the shape of the catalyst is not particularly limited, and it can be spherical, columnar, cylindrical, etc., and the molding method can be support molding, extrusion molding, tableting molding, etc. A form in which these catalyst substances are supported is also useful.

  In the present invention, the propylene concentration of the mixed gas introduced into the first reaction zone is 7 to 15% by volume, more preferably 8 to 12% by volume, and particularly preferably 8 to 10% by volume. If it is less than 7% by volume, the production efficiency may decrease and the collected acrylic acid concentration may decrease. On the other hand, if it exceeds 15% by volume, there is a risk of entering the combustion range of the reactor, increasing the risk.

  The water concentration of the mixed gas supplied to the first reaction zone is 0 to 10% by volume, more preferably 0 to 7% by volume, and particularly preferably 0 to 6% by volume. Since all the moisture used is transferred to the collection tower, if the water concentration exceeds 10% by volume, the water concentration of the bottom liquid of the collection tower rises, which is disadvantageous. On the other hand, if the water concentration of the bottom liquid of the collection tower is to be kept low, the collection efficiency in the collection tower will be lowered, and the polymerizability in the collection tower and the top pipe of the collection tower may be increased. It turns out. The collection efficiency (%) is 100 × ((AAin) when the amount of acrylic acid introduced into the collection tower is AAin and the amount of acrylic acid discharged from the top of the collection tower is AAout. -AAout) / AAin). According to the present invention, by controlling the water concentration to 10% by volume or less, the collection efficiency of acrylic acid in the collection tower can be 95% or more, preferably 96% or more.

  It is necessary to mix molecular oxygen with the mixed gas, and propylene: molecular oxygen (volume ratio) is in the range of 1: 1.0 to 2.0. Air is advantageously used as the molecular oxygen supply source, but oxygen-enriched air or pure oxygen can be used if necessary.

  Other components of the mixed gas include nitrogen, carbon dioxide, and other inert gases, and the exhaust gas 36 discharged from the collection tower 30 may be recycled and used. In that case, the amount of water vapor, the amount of molecular oxygen required for the mixed gas, and the amount of other inert gases can be adjusted by the amount of recycled gas.

In the first reaction zone, a mixed gas having the above composition is supplied to catalyst (i) 1 m ^{3 at} a space velocity of 500 to 3000 h ⁻¹ (STP) when the reaction pressure is in the range of normal pressure to 0.5 MPa. . The reaction temperature is controlled to 250 to 450 ° C, more preferably 300 to 380 ° C.

The acrolein-containing gas discharged from the first reaction zone is introduced as it is into the second reaction zone. The acrolein-containing gas supplied to the second reaction zone is a mixed gas with respect to catalyst (ii) 1 m ³ , the reaction pressure is in the range of normal pressure to 0.5 MPa, and the space velocity is 300 to 5,000 hr ⁻¹ (STP). The reaction temperature is 200 to 400 ° C, preferably 220 to 380 ° C. The water concentration of the mixed gas supplied to the first reaction zone can be measured by gas chromatography, Karl Fischer method, hygrometer, etc., and the water concentration of the mixed gas may be directly measured. The water concentration of each gas introduced into the reaction zone may be measured and calculated from them.

  The acrylic acid-containing gas 20 obtained by the catalytic gas phase oxidation reaction has a temperature of 200 to 350 ° C., and preferably is cooled to 100 to 300 ° C., particularly 130 to 270 ° C. before being supplied to the collection tower 30. As such a heat exchanger 23, a known heat exchanger can be used. This cooling is necessary to ensure that the temperature of the reaction gas mixture does not drop below its dew point. Of course, if the reaction gas is already in an appropriate temperature range, cooling is unnecessary.

  In the present invention, the acrylic acid-containing gas 20 is supplied to the collection tower 30 and collected by the collection solvent 33. The acrylic acid-containing gas 20 guided to the collection tower 30 generally contains 10 to 30% by mass of acrylic acid, 0.2 to 5% by mass of acetic acid, and 5 to 15% by mass of water. As collection conditions including the gas component composition of the reaction gas, the composition of the collection solvent, the collection temperature, etc., the water concentration of the acrylic acid-containing solution 35 in the bottom liquid of the acrylic acid collection tower is 1 to 45% by mass. Any condition may be used. The water concentration of the column bottom liquid is more preferably 1 to 25% by mass, and particularly preferably 1 to 20% by mass. It is difficult to make the water concentration below 1% by mass, and the loss of acrylic acid increases, which is disadvantageous. On the other hand, if it exceeds 45 mass%, it is necessary to increase the size of equipment such as a distillation tower in the subsequent steps, which is disadvantageous because the amount of dehydrated liquid and the amount of waste water are also increased. Furthermore, since acrylic acid is most highly polymerizable when the mixing mass ratio with water is about 1: 1, a polymer is likely to be generated in the collection tower and subsequent steps. In addition, when dehydration is performed by azeotropic distillation as shown in the figure, polymerization is caused by an increase in the partial concentration of water in the dehydration tower 40, and a polymer is easily generated. That is, in order to dehydrate the water contained in the acrylic acid-containing solution 35, an azeotropic dehydration process with the addition of an azeotropic solvent is generally performed. If the water concentration exceeds 45% by mass, a hydrophobic azeotrope is performed. The oil-water phase separation becomes remarkable between the dehydrated solvent and water, and the dispersion of the polymerization inhibitor is biased, so that acrylic acid is easily polymerized.

  As the acrylic acid collection tower 30, a publicly known tower such as a plate tower, a packed tower, a wet wall tower, a spray tower or the like can be used. However, the acrylic acid concentration contained in the acrylic acid-containing gas to be treated is high. In order to effectively prevent polymerization in the column, a plate column or packed column is preferred.

  For example, in the case of a packed tower, a packing having a relatively high collection efficiency of acrylic acid is provided on the upstream side of the flow in the tower of the collecting solution, and a packing having a relatively low polymerization ability of acrylic acid is provided on the downstream side. Preferably, objects and / or shelves are installed. In addition, relatively high (low) means that the performance is higher (lower) than others when a plurality of fillers are used. In addition, the packing having a relatively low polymerization ability means a packing having a lower polymerization ability compared to the remaining filler when a plurality of packings are packed in the acrylic acid collection tower. Usually, the upper part of the acrylic acid collection tower is the upstream side in order to bring the collection solvent and the acrylic acid-containing gas into countercurrent contact, and the downstream side corresponds to the bottom side of the acrylic acid collection tower. Among packings and shelves that are acrylic acid collection tower interiors, gauze type regular packing is the highest in the collection efficiency of general towers, sheet type regular packing, irregular packing, grid type regular packing The product is in the order of goods and shelves, but some of the shelves with high performance are equivalent to sheet-type regular packing and irregular packing. On the other hand, with respect to the ease of polymerization of acrylic acid or the like, the gauze type regular packing is the highest, and the order is sheet type regular packing, irregular packing, grid type regular packing, and shelf. Therefore, for example, if the collection efficiency is increased and the gauze type regular packing is used, the gauze type regular packing is easy to polymerize the treated product, so that a polymerization problem occurs, and the long-term operation becomes impossible. For example, when a grid type regular packing is used, an excessively high tower height is required to obtain a predetermined efficiency because the collection efficiency is low. Therefore, the gauze-type regular packing is selected on the upstream side of the flow in the liquid column containing the solvent, and the sheet-type regular packing, irregular packing, grid-type regular packing, and shelf are selected on the downstream side. Further, by using at least one kind of sheet-type regular packing and / or irregular packing, it is possible to satisfy both of the polymerization preventing ability and the collection efficiency and to perform a long-term stable operation. For gauze type regular packing, Sulzer Packing (Sumitomo Heavy Industries, Ltd.), Techno Pack (Mitsui & Co.), MC Pack (Mitsubishi Chemical Engineering), etc. Heavy machinery industry), Techno pack (Mitsui & Co.), MC pack (Mitsubishi Chemical Engineering), etc. For grid type regular packing, Flexi grid (Coke), etc. For irregular packing, Raschig ring, polling Shelf trays, valve trays, bubble cap trays, baffle trays, dual flow trays, super flack trays, ripple trays, jet trays, etc. Further, among irregular packings, cascade mini-rings and IMTP, which are flat packings, can be filled almost regularly, which is preferable because of excellent polymerization preventing ability and high collection efficiency.

  The top of the acrylic acid collection tower is generally operated at atmospheric pressure or higher. The tower top pressure (gauge pressure) is 0 to 0.4 MPa, preferably 0 to 0.1 MPa, particularly 0 to 0.03 MPa. If the pressure is lower than 0 MPa (gauge pressure), a decompression device is required, which increases equipment costs and utility costs. On the other hand, if the pressure is higher than 0.4 MPa (gauge pressure), the temperature of the collection tower is reduced in order to discharge low-boiling substances from the top of the tower. This is because it needs to be considerably increased and the polymerization property in the collection tower becomes high. Moreover, as tower | column top temperature, generally it is 30-80 degreeC, It is especially preferable that it is 40-70 degreeC.

  In the present invention, the water concentration of the acrylic acid-containing solution is adjusted to a range of 1 to 25% by mass, but such an adjustment method is not limited, but can be adjusted by changing the amount of the collection solvent introduced. it can. In the present invention, the mass of 0.1 to 1.5 times, more preferably 0.2 to 1.3 times, particularly preferably 0.3 to 1.1 times the mass flow rate of propylene introduced into the first reaction zone. It is preferable to collect acrylic acid by counterflow contact with a collection solvent at a flow rate. If it is less than 0.1 times, it will be difficult to collect acrylic acid, and the amount of wetting liquid in the collection tower will decrease, causing an extreme reduction in efficiency of the collection tower. The amount of wetting liquid in the collection tower is

The wetting liquid amount is 0.2 m ³ / m ² . hr or more, more preferably 0.8 m ³ / m ² . hr or more, particularly preferably 1.0 m ³ / m ² . hr or more. On the other hand, when it exceeds 1.5 times, the water concentration in the acrylic acid-containing solution to be collected increases. In addition, if the temperature of the collection tower is increased in order to keep the water concentration in the acrylic acid-containing solution constant, a polymer is easily generated, which is disadvantageous.

  Examples of the collecting solvent to be supplied include known solvents such as water, organic acid-containing water, and high-boiling inert hydrophobic organic liquid, and these can be used alone or in combination. In the present invention, the main component of the collection solvent is preferably water. For example, the composition of the collection solvent in the acrylic acid collection tower includes 0 to 10% by mass of acrylic acid, 0 to 20% by mass of acetic acid, and 70 to 100% by mass of water.

  In addition, in order to prevent polymerization of polymerizable substances such as acrylic acid, the collection solvent includes N-oxyl compounds, phenol compounds, manganese salts such as manganese acetate, and copper dialkyldithiocarbamates such as copper dibutylthiocarbamate. It is preferable to contain at least one compound selected from the group consisting of a salt, a nitroso compound, an amine compound and phenothiazine.

  The N-oxyl compound is not particularly limited, and any N-oxyl compound that is generally known as a polymerization inhibitor for vinyl compounds can be used. Among these, 2,2,6,6-tetramethylpiperidinooxyls represented by the following formula (1):

(In the formula (1), R ¹ represents CH ₂ , CHOH, CHCH ₂ OH, CHCH ₂ CH ₂ OH, CHOCH ₂ OH, CHOCH ₂ CH ₂ OH, CHCOOH, or C═O, and R ² represents hydrogen. Atom or CH ₂ OH) is preferably used. Any N-oxyl compound can be used without particular limitation, but 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6, which can provide a good polymerization preventing effect. , 6-tetramethylpiperidinooxyl, 4,4 ′, 4 ″ -tris- (2,2,6,6-tetramethylpiperidinooxyl) phosphite may be used alone or in combination. In particular, when 2,2,6,6-tetramethylpiperidinooxyl or 4-hydroxy-2,2,6,6-tetramethylpiperidinooxyl is used as the N-oxyl compound, Even if the component does not contain a metal, it becomes a stabilizer system, so there is no risk of metal corrosion of the equipment due to the stabilizer, and the treatment of the waste liquid becomes easy.

  Representative examples of N-hydroxy-2,2,6,6-tetramethylpiperidine compounds include 1,4-dihydroxy-2,2,6,6-tetramethylpiperidine, 1-hydroxy-2,2,6, Examples thereof include 6-tetramethylpiperidine. These N-hydroxy-2,2,6,6-tetramethylpiperidine compounds can be used alone or in combination of two or more.

  Specific examples of 2,2,6,6-tetramethylpiperidine compounds include 2,2,6,6-tetramethylpiperidine, 4-hydroxy-2,2,6,6-tetramethylpiperidine and the like, One or more of these can be used. N-hydroxy-2,2,6,6-tetramethylpiperidine compound and 2,2,6,6-tetramethylpiperidine compound may be contained as impurities in commercially available N-oxyl compound products. In such cases, the use of a commercially available N-oxyl compound may be combined with N-hydroxy-2,2,6,6-tetramethylpiperidine compound or 2,2,6,6-tetramethylpiperidine compound. Will be used together.

  Examples of the phenol compound include hydroquinone and methoquinone (p-methoxyphenol). Metoquinone is particularly preferable because it has a better polymerization prevention effect than hydroquinone when used in combination with an N-oxyl compound and a phenothiazine compound. Moreover, these phenol compounds may use 2 types together.

  Examples of the phenothiazine compound include phenothiazine, bis- (α-methylbenzyl) phenothiazine, 3,7-dioctylphenothiazine, bis- (α-dimethylbenzyl) phenothiazine and the like.

  It does not restrict | limit especially as a copper salt compound, Any of an inorganic salt and an organic salt may be sufficient, and various things can be used. Examples thereof include copper dialkyldithiocarbamate, copper acetate, copper naphthenate, copper acrylate, copper sulfate, copper nitrate, and copper chloride. These copper salt compounds may be either monovalent or divalent. Among the copper salt compounds, copper dialkyldithiocarbamate is preferable from the viewpoint of effects and the like.

  Examples of copper dialkyldithiocarbamate include, for example, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate, copper dipentyldithiocarbamate, copper dihexyldithiocarbamate, copper diphenyldithiocarbamate, copper methylethyldithiocarbamate , Copper methylpropyldithiocarbamate, copper methylbutyldithiocarbamate, copper methylpentyldithiocarbamate, copper methylhexyldithiocarbamate, copper methylphenyldithiocarbamate, copper ethylpropyldithiocarbamate, copper ethylbutyldithiocarbamate, copper ethylpentyldithiocarbamate, ethylhexyl Copper dithiocarbamate, copper ethylphenyldithiocarbamate, propyl butyl Copper rudithiocarbamate, copper propylpentyldithiocarbamate, copper propylhexyldithiocarbamate, copper propylphenyldithiocarbamate, copper butylpentyldithiocarbamate, copper butylhexyldithiocarbamate, copper butylphenyldithiocarbamate, copper pentylhexyldithiocarbamate, pentylphenyldithiocarbamate Examples include copper acid, copper hexylphenyldithiocarbamate, and the like. These copper dialkyldithiocarbamates may be monovalent copper salts or divalent copper salts. Of these, copper dimethyldithiocarbamate, copper diethyldithiocarbamate and copper dibutyldithiocarbamate are preferred, and copper dibutyldithiocarbamate is particularly preferred from the standpoints of effects and availability.

  Manganese salt compounds include manganese dialkyldithiocarbamate (the alkyl group may be methyl, ethyl, propyl, or butyl, which may be the same or different), manganese diphenyldithiocarbamate, manganese formate, manganese acetate, octane Manganese acid, manganese naphthenate, manganese permanganate, manganese salts of ethylenediaminetetraacetic acid, and the like can be used, and one or more of these can be used.

  In the present invention, it is preferable to contain one or more compounds selected from the group consisting of N-oxyl compounds, phenol compounds, manganese salts, copper salts of dialkyldithiocarbamic acid, nitroso compounds, amine compounds and phenothiazines. Even when two or more of these compounds are used in combination, an equivalent or higher polymerization preventing effect can be obtained.

  The amount of the polymerization inhibitor used is appropriately adjusted according to the operating conditions, and is not particularly limited. However, the total amount of the polymerization inhibitor used is preferably 3 to 3500 ppm (mass basis) based on the mass of acrylic acid in the reaction gas to be collected. The preferred amount of each polymerization inhibitor used is 1 to 500 ppm for the N-oxyl compound relative to the mass of acrylic acid in the reaction gas, and 1 for the manganese salt compound or copper salt compound relative to the mass of acrylic acid in the reaction gas. -200 ppm, 1-500 ppm for nitroso compounds, 1-500 ppm for phenol compounds, 1-500 ppm for phenothiazine compounds.

  Furthermore, although the supply place and administration method for preventing polymerization are not particularly limited, it is preferably supplied from the top of the acrylic acid collection tower. Further, when the polymerization inhibitor is supplied after being mixed with a solvent in advance, it is effective because the polymerization inhibitor is uniformly dispersed in the acrylic acid collection tower. It is preferable to use a collection solvent or acrylic acid as the solvent, and it is economical to reuse the collection solvent separated by the purification tower.

  In this invention, there is no restriction | limiting regarding the purification method after an acrylic acid collection process. The present invention is intended to improve the collection efficiency by limiting the water concentration of the acrylic acid collection tower bottom liquid to a specific range, and to stabilize the subsequent steps, and is limited to a specific purification method. Because it is not something.

  In general, a low-boiling point substance separation step, a high-boiling point substance separation step, and other purification steps are performed after the dehydration treatment. In the present invention, any conventionally known purification method may be combined. Therefore, after the azeotropic dehydration, the low-boiling substances may be removed, and then the high-boiling substances may be removed, and then the acrylic acid and acetic acid having an approximate boiling point may be separated. Acrylic acid may be purified by appropriately combining crystallization, extraction, absorption, and partial condensation.

In the second aspect of the present invention, a mixed gas containing propylene and molecular oxygen is introduced into a first reaction zone filled with a complex oxide catalyst containing molybdenum and bismuth as essential components, and propylene is oxidized to contain acrolein. Gas is obtained, and the acrolein-containing gas is obtained by introducing the acrolein-containing gas into a second reaction zone formed by filling a complex oxide catalyst containing molybdenum and vanadium as essential components. In the method for producing acrylic acid comprising the step of introducing into an acid collection tower and bringing into contact with a collection solvent to obtain an acrylic acid-containing solution,
(A) forming the first reaction zone and the second reaction zone by dividing a single reaction tube with at least one perforated tube plate;
(B) The propylene concentration of the mixed gas introduced into the first reaction zone is 7 to 15% by volume, the water concentration in the mixed gas is 0 to 6% by volume,
(C) introducing a mass flow rate of 0.1 to 1.5 times the mass flow rate of propylene introduced into the first reaction zone into the acrylic acid collection tower; and
(D) A method for producing acrylic acid, characterized in that the water concentration at the bottom of the collection tower of the acrylic acid-containing solution obtained in the acrylic acid collection tower is 1 to 25% by mass depending on the amount of the collection solvent introduced. It is.

  The difference from the first invention resides in that the requirement (d) above, that is, the water concentration of the acrylic acid-containing solution is 1 to 25% by mass, is controlled by controlling the amount of the collection solvent introduced. Other requirements are the same as those of the first invention.

  Since the exhaust gas 36 from the collection tower 30 contains the amount of heat generated by the catalytic gas phase oxidation reaction, water vapor, unreacted propylene, acrolein, inert gas, and the like, it is heated by the heat exchanger 71 as shown in FIG. Then, after adjusting the flow rate to the optimum range with the flow rate adjusting device 72, it can be mixed with the air 3 and supplied to the first reactor 10 for reuse. However, the exhaust gas composition is likely to fluctuate depending on the temperature at the top of the collection tower, and the change in water content is particularly large. In the present application, it is necessary to limit the amount of water vapor contained in the mixed gas to a range of 0 to 6% by mass, and changing the tower top temperature to vary the amount of water contained in the exhaust gas from the top of the tower Not only is this disadvantageous in limiting the amount of water vapor contained, but when the tower top temperature is increased, acrylic acid polymers are likely to be generated in the collection tower. On the other hand, when the amount of collected solvent is changed, the change in the amount of moisture in the acrylic acid-containing gas can be adjusted by changing the amount of collected solvent, and the amount of moisture in the gas 36 discharged from the top of the tower. Fluctuations can be suppressed. Specifically, as in the first invention, the mass flow rate of propylene introduced into the first reaction zone is 0.1 to 1.5 times, more preferably 0.2 to 1.3 times, and particularly preferably 0. It is preferable to collect acrylic acid by countercurrent contact with a collecting solvent having a mass flow rate of 3 to 1.1 times.

  Note that “depending on the amount of the collection solvent introduced” means that the water concentration is controlled within the range of 1 to 45% by mass, and even within the range of 1 to 25% by mass, the concentration further varies within a certain range. There are two ways to suppress this. The significance of the former is as explained in the first invention. On the other hand, the latter meaning is that the fluctuation in the composition of the bottom of the tower is reduced upstream of the production process of the acrylic acid collection tower, and therefore the fluctuation in the downstream can be efficiently suppressed. In the production of acrylic acid, in addition to the above-described acrylic acid collection process and dehydration process, a number of processes such as a low-boiling substance separation process, a high-boiling substance separation process, and other purification processes are continuously performed. If the water content of the acid collection tower bottom liquid fluctuates, the amount of dehydrated solvent used in the dehydration process in the next step, the temperature and pressure in the dehydration tower, the amount of polymerization inhibitor used, the recovered solvent phase 42 and The amount of water phase 43 recycled changes from time to time. As a result, the acrylic acid concentration in the bottom liquid of the dehydration tower and the amount of the polymerization inhibitor to be used are changed, and the subsequent high-boiling substance separation conditions are also changed. Such fluctuations in conditions lead to the generation of acrylic acid polymer in the purification process and cause a reduction in product quality. Therefore, in the present invention, upstream of such a series of steps, the water concentration of the acrylic acid-containing solution is limited to a predetermined range, and the processing in the downstream steps is simplified, and at the same time, fluctuations are suppressed and the degree of purification is reduced. Highly decided to produce acrylic acid.

  In addition, in order to further control the water concentration of the acrylic acid-containing solution to a certain range within the range of 1 to 25% by mass, for example, within the range of 20 ± 1% by mass, the water concentration of the bottom liquid of the collection tower is measured, What is necessary is just to change the introduction amount of a collection solvent based on the value. As a method for measuring the water concentration of the collection tower bottom liquid, there are a method for obtaining from a change in the electric conductivity of the tower bottom liquid, a method for obtaining from neutralization titration, etc. in addition to gas chromatography, Karl Fischer method and the like.

  Acrylic acid obtained by the first or second invention is supplied to a polyacrylic acid (salt) production process to produce polyacrylic acid (salt), and the resulting polyacrylic acid (salt) is used for further water absorption. Resin etc. can be manufactured. That is, the third of the present invention is a method for producing polyacrylic acid, characterized in that acrylic acid obtained by the above method is used.

  As a polyacrylic acid (salt) production process, polyacrylic acid (salt) can be produced by sequentially introducing the acrylic acid into a neutralization process, a polymerization process, a drying process, and a cooling process and performing desired treatments. it can. When acrylic acid is not neutralized, polyacrylic acid is obtained, and the neutralization step is optional. In addition, a desired treatment may be performed for the purpose of improving various physical properties. For example, a crosslinking step may be interposed during or after polymerization.

  The neutralization step is an optional addition step. For example, a method of mixing a predetermined amount of a basic substance powder or aqueous solution with acrylic acid or the obtained polyacrylic acid (salt) is exemplified. There is no particular limitation as long as it is adopted. The neutralization step may be performed either before polymerization (neutralization with monomers), during polymerization, or after polymerization (neutralization with gel), or both before and after polymerization. In the illustrated example, the step of performing polymerization after neutralization is shown. However, when neutralization is performed after polymerization, the configuration of the apparatus may be appropriately changed in accordance with the steps. The polymerization apparatus and the neutralization apparatus may be the same apparatus or different apparatuses.

  As a basic substance used for neutralization of acrylic acid, for example, a known basic substance such as a carbonate (hydrogen) salt, an alkali metal hydroxide, ammonia, or an organic amine may be appropriately used. Moreover, it does not specifically limit about the neutralization rate of acrylic acid, What is necessary is just to adjust so that it may become arbitrary arbitrary neutralization rates, for example, 30-100 mol%, Preferably it is 50-80 mol%. In addition, when it is necessary to remove the reaction heat at the time of neutralization, it may be introduced into any cooling means, for example, a cooling device such as an optional chilled water tower. At this time, the liquid supplied via the line 4a is used. It is desirable to use a cooling medium as the refrigerant because the cooling cost can be reduced.

  If necessary, the acrylate solution is introduced into the polymerization step after neutralization, but the polymerization method in this step is not particularly limited, and in the case of using a radical polymerization initiator, radiation polymerization, electron beam polymerization, photosensitizer. A well-known polymerization method such as ultraviolet polymerization by the method may be used. In the polymerization step, acrylic acid is neutralized as necessary, preferably at least 10 mass%, more preferably at least 20 mass%, preferably at most 80 mass%, more preferably at most 70 mass%. It is desirable to polymerize as an acrylic acid (salt) aqueous solution.

  In the present invention, various conditions such as a polymerization initiator and polymerization conditions can be arbitrarily selected. A known additive such as a water-soluble chain transfer agent or a hydrophilic polymer may be added if necessary. Moreover, what is necessary is just to use arbitrary containers and apparatuses for a superposition | polymerization process, and if it is a normally used superposition | polymerization apparatus, it will not specifically limit.

  The polyacrylic acid (salt) after polymerization is usually a hydrogel polymer and is further subjected to a drying step in order to remove moisture. The drying method is not particularly limited and may be appropriately dried at a desired drying temperature, preferably 70 to 230 ° C., using a known drying apparatus such as a hot air dryer, a fluidized bed dryer, a drum dryer, or a nauter dryer. That's fine. As the heat medium supplied to the drying process, steam discharged in the acrylic acid production process, particularly reaction heat obtained from a catalytic gas phase oxidizer can be used.

  At the time of drying, a hydrogel of polyacrylic acid (salt), that is, a water-containing polymer is heated and dried using various dryers. For example, the drying may be performed by bringing the heat transfer surface obtained by heating the heat transfer surface of the dryer with water vapor into contact with the hydrogel using a heat transfer type dryer such as a drum dryer or a paddle dryer. From the viewpoint of reduction and drying efficiency, it is desirable to carry out hot-air heat-drying in which the hydrogel is brought into direct contact with water vapor. That is, a gas containing water vapor, preferably a dew point of 50 ° C. or higher, more preferably 60 ° C. or higher, preferably 90 ° C. or lower, more preferably 80 ° C. or lower, and a temperature of preferably 100 ° C. or higher, More preferably, the hydrogel is dried with hot air at 150 ° C. or higher, preferably 200 ° C. or lower, more preferably 180 ° C. or lower, to reduce the residual monomer and improve the water absorption capacity of polyacrylic acid (salt). It is desirable because it can be planned. The drying time may be appropriately selected from 1 minute to 3 hours, preferably 5 minutes to 1 hour.

  Since the polyacrylic acid (salt) obtained through the drying step is discharged at a high temperature, it is desirable to cool it to a desired temperature, for example, room temperature to 90 ° C, preferably 40 ° C to 80 ° C, in the cooling step. Although it does not limit as a method of cooling polyacrylic acid (salt), for example, you may blow cold air or introduce | transduce into cooling devices, such as arbitrary refrigerators.

  The polyacrylic acid (salt) obtained by cooling to the desired temperature may be used as it is, and further granulated and pulverized into the desired shape, and various additives such as reducing agents, fragrances, and binders are further added. For example, it can be used for various purposes.

  In the present invention, it is preferable to cool the dried polyacrylic acid (salt). For example, when the hydrogel is subdivided into about 1 to several millimeters and dried, the polyacrylic acid (salt) after drying is about 1 to several millimeters of dry particles, and depending on the drying method, it is usually dried The dried particles later are aggregates. Therefore, the dried polyacrylic acid (salt) is pulverized or further classified as necessary to obtain a polyacrylic acid (salt) powder, for example, a weight average particle diameter of 10 to 1000 μm, preferably 100 to 800 μm, and further if necessary. When various modifiers such as aqueous solution of surface cross-linking agent, granulating binder, deodorant, etc. are added to the powder, applying the cooling process only improves the grinding efficiency and sharpens the particle size distribution. In addition, since various modifiers and the like can be uniformly added to the powder, various physical properties of the water-absorbent resin, such as absorption capacity under pressure, can be improved while suppressing variations between the powders.

  Hereinafter, examples of the present invention will be described in detail.

(Reference Example 1) Preparation of Catalyst A molybdenum-bismuth catalyst was prepared as a catalyst for the first reaction zone in accordance with the description in Example 1 of JP-A No. 2000-325795. This is designated as catalyst (I). Further, a molybdenum-vanadium catalyst was prepared as a catalyst for the second reaction zone according to the description in Example 1 of JP-A-8-206504. This is referred to as catalyst (II).

Example 1
A reaction tube with a heat medium circulation jacket having an inner diameter of 25 mm and a length of 7,000 mm is provided with a perforated tube plate with a thickness of 75 mm that divides the heat medium jacket up and down at a position of 3,500 mm from the bottom of the jacket. In the reaction zone (lower part corresponds to the first reaction zone and upper part corresponds to the second reaction zone) in which the lower heating medium can be circulated and the temperature of each heating medium can be controlled, from the lower part to the upper part of the reaction tube (1) Only ceramic balls having an average diameter of 5 mm, (2) Mixture obtained by mixing catalyst balls (I) and ceramic balls having an average diameter of 5 mm in a volume ratio of 70:30, (3) Only catalyst (I) ( 4) A stainless steel Raschig ring having an outer diameter of 5 mm, an inner diameter of 4.5 mm, and a length of 6 mm. (5) A mixture in which catalyst (II) and ceramic balls having an average diameter of 5 mm are mixed at a volume ratio of 75:25. (6) in the order of only the catalyst (II), each length was packed 250mm, 700mm, 2,300mm, 500mm, 600mm, so that 1,900Mm.

In the first reaction zone, a mixed gas of propylene: 8.0% by volume, O ₂ : 14.4% by volume, H ₂ O: 5.0% by volume (the rest is N ₂ , propane, etc.) is added to the first reaction zone. It supplied so that space velocity might be 1,250hr < ^-1 > (STP).

  At this time, at the second reaction zone outlet pressure of 0.15 MPa (absolute pressure), the propylene conversion rate was 97 ± 0.5 mol%, and the acrolein yield was 1 ± 0.5 mol%. The reaction was continued while adjusting the heating medium temperature in each of the second reaction zones. The acrylic acid yield is 87.0 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 170 ° C. and 14 theoretical plates. In the collected water containing 1.8% by mass of acrylic acid, 5.6% by mass of acetic acid and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas to be introduced into the collection tower. Acrylic acid was collected. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 25% by mass. When the amount of water was adjusted, an acrylic acid aqueous solution having a target water concentration was obtained with the collected solvent amount / propylene mass flow rate = 0.9.

  The collection efficiency at that time was 98.3%, and no polymer was observed in the tower and in the tower top piping even after one week of operation without any increase in pressure loss in the vicinity of the collection tower. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, and it was immersed in the oil bath maintained at 95 degreeC, the time until a viscosity raises was measured, it was 11.5 hr. This increase in viscosity is related to the polymerization start time. When this is short, it means that the solution is easy to polymerize, and when it is long, it means that the solution is difficult to polymerize.

(Example 2)
The composition of the mixed gas supplied to the first reaction zone was propylene: 9.0% by volume, O ₂ : 16.2% by volume, H ₂ O: 2.9% by volume (the rest was N ₂ , propane, etc.). The reaction was performed in the same manner as in Example 1 except for the above. The acrylic acid yield is 86.5 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 168 ° C. and 14 theoretical plates is calculated. In the collected water containing 1.8% by mass of acrylic acid, 6.0% by mass of acetic acid and hydroquinone equivalent to 200% by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas to be introduced into the collection tower. Acrylic acid was collected. The acrylic acid collection tower is collected so that the top temperature is 62.9 ° C. and the top pressure is 0.11 MPa (absolute pressure) so that the water concentration in the bottom liquid of the collection tower is 21% by mass. When the amount of water was adjusted, the amount of collected solvent / propylene mass flow rate = 0.8, and an aqueous acrylic acid solution having a target water concentration was obtained.

  The collection efficiency at that time was 98.5%, and no polymer was observed in the tower and in the tower top piping even after open inspection after one week of operation without an increase in pressure loss near the collection tower. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 13.2 hr.

(Example 3)
Using the same reactor as in Example 1, from the bottom to the top of the reaction tube, (1) only ceramic balls with an average diameter of 5 mm, (2) catalyst (I) and ceramic balls with an average diameter of 5 mm have a capacity ratio of 55: 45 mixture, (3) catalyst (I) and a mixture of ceramic balls having an average diameter of 5 mm in a volume ratio of 70:30, (4) catalyst (I) only, (5) outside A stainless steel Raschig ring having a diameter of 5 mm, an inner diameter of 4.5 mm and a length of 6 mm, (6) a mixture of catalyst (II) and ceramic balls having an average diameter of 5 mm mixed in a volume ratio of 65:35, (7) catalyst ( II) and a ceramic ball having an average diameter of 5 mm mixed at a volume ratio of 80:20, and (8) each layer length is 250 mm, 500 mm, 500 mm, 2,200 mm, 500 in the order of catalyst (II) only. m, 500mm, 500mm, was packed so as to 2,000mm.

A mixed gas of propylene: 10.0% by volume, O ₂ : 18.0% by volume, H ₂ O: 0.9% by volume (the rest is N ₂ , propane, etc.) is added to the first reaction zone. It supplied so that space velocity might be 1,250hr < ^-1 > (STP).

  At this time, at the second reaction zone outlet pressure of 0.15 MPa (absolute pressure), the propylene conversion rate was 97 ± 0.5 mol%, and the acrolein yield was 1 ± 0.5 mol%. The reaction was continued while adjusting the heating medium temperature in each of the second reaction zones. The acrylic acid yield is 85.6 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 167 ° C. and the calculated theoretical number of plates is 14. Into the collected water containing 1.8% by mass of acrylic acid, 6.5% by mass of acetic acid and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas introduced into the collection tower Acrylic acid was collected. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 17% by mass. When the amount of water was adjusted, the amount of collected solvent / propylene mass flow rate = 0.7, and an aqueous acrylic acid solution having a target water concentration was obtained.

  The collection efficiency at that time was 98.6%, and no polymer was observed in the tower and in the tower top piping even after open inspection after one week without any increase in pressure loss near the collection tower. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 15.5 hr.

Example 4
The acrylic acid-containing gas obtained in Example 3 was introduced into an acrylic acid collection tower having a calculated theoretical plate number of 14 at a temperature of 167 ° C., and 1.8% by mass of acrylic acid, 7.1% by mass of acetic acid, and Acrylic acid was collected with collected water containing hydroquinone equivalent to 200 mass ppm with respect to the amount of acrylic acid in the acrylic acid-containing gas introduced into the collection tower. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 8% by mass. When the amount of water was adjusted, an acrylic acid aqueous solution having a target water concentration was obtained with the collected solvent amount / proprene mass flow rate = 0.5.

  The collection efficiency at that time was 97.5%, and even if the open inspection was performed after one week of operation without increasing the pressure loss of the collection tower, almost no polymer was found in the tower and in the tower top piping. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was made to osmose | permeate in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 18.8 hr.

(Comparative Example 1)
The same reactor and the same catalyst as in Example 1 were packed so that each layer length was 250 mm, 800 mm, 2,200 mm, 500 mm, 700 mm, and 1,800 mm.

In the first reaction zone, a mixed gas of propylene: 8.0% by volume, O ₂ : 14.4% by volume, H ₂ O: 9.6% by volume (the rest is N ₂ , propane, etc.) is added to the first reaction zone. It supplied so that space velocity might be 1,500 hr < ^-1 > (STP).

  At this time, at the second reaction zone outlet pressure of 0.15 MPa (absolute pressure), the propylene conversion rate was 97 ± 0.5 mol%, and the acrolein yield was 1 ± 0.5 mol%. The reaction was continued while adjusting the heating medium temperature in each of the second reaction zones. The acrylic acid yield after 100 hours from the start of the reaction is 86.3 mol%, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 172 ° C. and 14 theoretical plates. Into the collected water containing 1.8% by mass of acrylic acid, 3.8% by mass of acetic acid, and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas introduced into the collection tower Acrylic acid was collected. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 40% by mass. When the amount of water was adjusted, an acrylic acid aqueous solution having a target water concentration was obtained with the collected solvent amount / propylene mass flow rate = 1.1.

  The collection efficiency at that time was 98.9%, and no polymer was observed in the tower and in the tower top pipe even after open inspection after one week without any increase in pressure loss near the collection tower. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 8.2 hr.

(Comparative Example 2)
The reaction was performed in the same manner as in Example 4 except that the H ₂ O concentration in the mixed gas supplied to the first reaction zone was 7.9% by volume. The acrylic acid yield is 86.0 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 171 ° C. and 14 theoretical plates. And collected water containing 1.3% by mass of acrylic acid, 4.4% by mass of acetic acid and hydroquinone equivalent to 200% by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas to be introduced into the collection tower. Acrylic acid was collected with the collected solvent amount / propylene mass flow rate = 1.6. The top temperature of the acrylic acid collection tower at that time is 73.7 ° C., the top pressure is 0.11 MPa (absolute pressure), the water concentration in the bottom liquid of the collection tower is 25 mass%, and the collection efficiency is 97.1. When the operation was opened after one week without any increase in pressure loss in the vicinity of the collection tower, a slight amount of polymer was observed in the tower and in the tower top piping.

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath maintained at 95 degreeC, and the time until a viscosity raises was measured, it was 11.6 hr.

(Comparative Example 3)
The composition of the mixed gas supplied to the first reaction zone was propylene: 6.0% by volume, O ₂ : 10.8% by volume, H ₂ O: 9.9% by volume (the rest was N ₂ , propane, etc.). The reaction was performed in the same manner as in Example 1 except for the above. The acrylic acid yield is 87.8 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 172 ° C. and 14 calculated theoretical plates. In the collected water containing 1.8% by mass of acrylic acid, 4.8% by mass of acetic acid and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas to be introduced into the collection tower. Acrylic acid was collected. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 25% by mass. When the amount of water was adjusted, the amount of collected solvent / propylene mass flow rate = 0.8, and an aqueous acrylic acid solution having a target water concentration was obtained.

  The collection efficiency at that time was 95.2%. After 5 days, the pressure loss in the vicinity of the collection tower increased, and when it was stopped and checked for opening, a considerable amount of polymer was found in the tower and in the top piping.

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 11.8 hr.

(Comparative Example 4)
The reaction was performed in the same manner as in Example 1 except that the H ₂ O concentration in the mixed gas supplied to the first reaction zone was 11.6% by volume. The acrylic acid yield is 87.4 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 173 ° C. and 14 theoretical plates. Into the collected water containing 1.8% by mass of acrylic acid, 4.1% by mass of acetic acid and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas introduced into the collection tower Acrylic acid was collected. The acrylic acid collection tower has a top temperature of 62.9 ° C. and a top pressure of 0.11 MPa (absolute pressure), so that the water concentration in the bottom liquid of the collection tower is 25% by mass. When the amount of water was adjusted, the amount of collected solvent / propylene mass flow rate = 0.8, and an aqueous acrylic acid solution having a target water concentration was obtained.

  The collection efficiency at that time was 94.9%. After 4 days, the pressure loss in the vicinity of the collection tower increased, and when it was stopped and inspected for opening, a considerable amount of polymer was found in the tower and in the top piping.

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath kept at 95 degreeC, and the time until a viscosity raises was measured, it was 11.8 hr.

(Comparative Example 5)
The reaction was performed in the same manner as in Example 1 except that the H ₂ O concentration in the mixed gas supplied to the first reaction zone was 9.6% by volume. The acrylic acid yield is 87.1 mol% after 100 hours from the start of the reaction, and the acrylic acid-containing tower is obtained by using the acrylic acid-containing gas obtained at that time at a temperature of 171 ° C. and 14 theoretical plates. Into the collected water containing 1.8% by mass of acrylic acid, 3.5% by mass of acetic acid and hydroquinone equivalent to 200 ppm by mass with respect to the amount of acrylic acid in the acrylic acid-containing gas introduced into the collection tower Acrylic acid was collected. The acrylic acid collection tower is collected so that the top temperature is 62.9 ° C. and the top pressure is 0.11 MPa (absolute pressure) so that the water concentration in the bottom liquid of the collection tower is 47% by mass. When the amount of water was adjusted, the amount of collected solvent / propylene mass flow rate = 1.5, and an aqueous acrylic acid solution having a target water concentration was obtained.

  The collection efficiency at that time was 99.0%, and no polymer was seen in the tower and in the tower top piping even after open inspection after one week without any increase in pressure loss near the collection tower. .

  Moreover, when 5 ml of obtained acrylic acid aqueous solution was put into a test tube, it was immersed in the oil bath maintained at 95 degreeC, and the time until a viscosity raises was measured, it was 6.5 hr.

1 ... propylene,
2 ... water vapor,
3 ... Air,
4 ... Blower,
10 ... reactor,
11 ... reaction tube,
12 ... Composite oxide catalyst (i),
13 Complex oxide catalyst (ii),
15 ... perforated tube sheet,
20 ... Acrylic acid-containing gas,
23 ... heat exchanger,
30 ... Collection tower,
31 ... packed bed,
32. Disperser,
33 ... Collection solvent,
34 ... cooler,
35 ... Acrylic acid-containing solution,
36 ... exhaust gas,
40 ... dehydration tower,
41 ... distillate gas,
42 ... solvent phase,
43 ... Aqueous phase,
50: Next step,
60 ... waste gas,
71 ... heat exchanger,
72: Flow rate adjusting device.

Claims (7)

A mixed gas containing propylene and molecular oxygen is introduced into a first reaction zone filled with a complex oxide catalyst containing molybdenum and bismuth as essential components, and propylene is oxidized to obtain an acrolein-containing gas. Introducing the acrolein-containing gas into a second reaction zone filled with a composite oxide catalyst containing vanadium as an essential component to obtain an acrylic acid-containing gas, introducing the acrylic acid-containing gas into an acrylic acid collection tower In the method for producing acrylic acid comprising the step of obtaining a solution containing acrylic acid by contacting with a collection solvent,
(A) the first reaction zone and the second reaction zone are formed by dividing a single reaction tube with at least one perforated tube plate;
(B) The propylene concentration of the mixed gas introduced into the first reaction zone is 7 to 15% by volume, and the water concentration in the mixed gas is 0 to 6% by volume;
(C) introducing a collection solvent having a mass flow rate of 0.1 to 1.5 times the mass flow rate of propylene introduced into the first reaction zone into the acrylic acid collection tower; and
(D) A method for producing acrylic acid, wherein the concentration of water at the bottom of the collection tower of the acrylic acid-containing solution collected by the acrylic acid collection tower is 1 to 25% by mass. The method according to claim 1, wherein the main component of the collection solvent is water. The method according to claim 1 or 2, wherein the propylene concentration in the mixed gas in step (b) is 8 to 12% by volume. The method according to any one of claims 1 to 3, wherein the water concentration of the acrylic acid-containing solution in the step (d) is 1 to 20% by mass. The water concentration in step (d) is controlled by (i) controlling the introduction of the collection solution or (ii) changing the temperature and / or pressure at the top of the acrylic acid collection tower. The method as described in any one of -4. A mixed gas containing propylene and molecular oxygen is introduced into a first reaction zone filled with a complex oxide catalyst containing molybdenum and bismuth as essential components, and propylene is oxidized to obtain an acrolein-containing gas. Introducing the acrolein-containing gas into a second reaction zone filled with a composite oxide catalyst containing vanadium as an essential component to obtain an acrylic acid-containing gas, introducing the acrylic acid-containing gas into an acrylic acid collection tower In the method for producing acrylic acid comprising the step of obtaining a solution containing acrylic acid by contacting with a collection solvent,
(A) forming the first reaction zone and the second reaction zone by dividing a single reaction tube with at least one perforated tube plate;
(B) The propylene concentration of the mixed gas introduced into the first reaction zone is 7 to 15% by volume, the water concentration in the mixed gas is 0 to 6% by volume,
(C) introducing a mass flow rate of 0.1 to 1.5 times the mass flow rate of propylene introduced into the first reaction zone into the acrylic acid collection tower; and
(D) A method for producing acrylic acid, characterized in that the water concentration at the bottom of the collection tower of the acrylic acid-containing solution obtained in the acrylic acid collection tower is 1 to 25% by mass depending on the amount of the collection solvent introduced. . A method for producing polyacrylic acid, comprising using acrylic acid obtained by the method according to claim 1.