JP2011224537A - Catalyst for dehydrating glycerin, method of producing acrolein using the catalyst, method of producing acrylic acid, and method of producing hydrophilic resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for dehydrating glycerin, capable of stably producing acrolein for a long period of time while reducing the amount of byproducts produced, a method of producing acrolein using the catalyst, a method of producing acrylic acid, and a method of producing a hydrophilic resin.SOLUTION: The catalyst for dehydrating glycerin includes boron phosphate wherein the molar ratio of phosphorus (P) relative to boron (B), i.e., P/B is 1.02 or greater and not greater than 2. The method of producing acrolein comprises dehydrating glycerin in the presence of the catalyst. The method of producing acrylic acid comprises oxidizing the acrolein. The method of producing a hydrophilic resin comprises polymerizing a monomer component containing the acrylic acid.

Description

  The present invention relates to a catalyst used in a dehydration reaction of glycerol, a method for producing acrolein using this catalyst, a method for producing acrylic acid using the obtained acrolein as a raw material, and hydrophilicity obtained using the obtained acrylic acid as a raw material. The present invention relates to a resin manufacturing method and the like.

  Biodiesel produced from vegetable oil is attracting attention not only as a substitute for fossil fuels but also because it emits less carbon dioxide, and demand is expected to increase. When this biodiesel is produced, glycerin is produced as a by-product, so it is necessary to make effective use of it.

  One example of effective utilization of glycerin is a method of producing acrolein using glycerin as a raw material. For example, Patent Documents 1 to 3 disclose a method for producing acrolein using a glycerol dehydration catalyst containing a boron phosphate salt.

International Publication No. 2007/119528 Pamphlet JP 2008-307521 A JP 2009-263284 A

The conventional glycerol dehydration catalyst usually contains a boron phosphate salt (BPO ₄ ) having a molar ratio P / B of phosphorus (P) and boron (B) of 1. The present inventors have found that these glycerin dehydration catalysts exhibit a relatively high acrolein selectivity, but carbon-like substances are precipitated in a long-term reaction, resulting in a high pressure loss during the reaction. The acrolein selectivity is about 70% and is still insufficient; propionaldehyde is produced as a by-product, and propionaldehyde passes through acrylic acid from acrolein and absorbs a water-absorbing polymer (SAP). Hereinafter referred to as “water-absorbing resin”), it becomes a odor-causing substance (propionic acid) in the production.

  Under such circumstances, the problem to be solved by the present invention is to provide a glycerol dehydration catalyst capable of stably producing acrolein over a long period of time while reducing the amount of by-products generated, and to use this catalyst. Another object is to provide a method for producing acrolein.

  As a result of various studies, the inventors have made a molar ratio of phosphorus (P) and boron (B) in the boron phosphate salt in producing acrolein using a glycerol dehydration catalyst containing the boron phosphate salt. By adjusting P / B within a predetermined range, it was found that acrolein can be stably produced over a long period of time while reducing the amount of by-products generated, and the present invention was completed.

  That is, the present invention is a glycerol dehydration catalyst containing a boron phosphate salt, wherein the molar ratio P / B of phosphorus (P) to boron (B) in the boron phosphate salt is 1.02 or more, 2 A glycerol dehydration catalyst characterized by the following is provided. In this catalyst, the molar ratio P / B of phosphorus (P) to boron (B) in the boron phosphate salt is preferably 1.05 or more and 1.5 or less.

  The present invention also provides a method for producing acrolein by dehydrating glycerin in the presence of a catalyst, wherein the catalyst is a glycerol dehydrating catalyst as described above. . In this production method, glycerin is preferably dehydrated by a gas phase reaction in which a reaction gas containing glycerin gas and a catalyst are brought into contact with each other.

  Furthermore, the present invention is a method for producing acrolein by dehydrating glycerin in the presence of a catalyst, and then oxidizing the obtained acrolein to produce acrylic acid, wherein the catalyst is used for dehydrating glycerin as described above. Provided is a method for producing acrylic acid, which is a catalyst.

  Furthermore, in the present invention, glycerol is dehydrated in the presence of a catalyst to produce acrolein, then the obtained acrolein is oxidized to produce acrylic acid, and the resulting monomer component containing acrylic acid is polymerized. Thus, there is provided a method for producing a hydrophilic resin, wherein the catalyst is a glycerol dehydration catalyst as described above. In this production method, examples of the hydrophilic resin include a water-absorbing resin and a water-soluble resin. This production method is particularly useful for the production of water-absorbent resins because the amount of propionaldehyde generated as a odor-causing substance (propionic acid) in the production process is reduced among the by-products.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst for glycerol dehydration which can manufacture acrolein stably over a long period of time can be provided, reducing the generation amount of a by-product. If this catalyst is used, acrolein can be produced stably and continuously in a high yield by a dehydration reaction of glycerin.

≪Glycerin dehydration catalyst≫
The catalyst for dehydrating glycerol of the present invention (hereinafter sometimes referred to as “the catalyst of the present invention”) is a catalyst for dehydrating glycerin containing a boron phosphate salt, and the phosphorus (P) in the boron phosphate salt and The molar ratio P / B with boron (B) is 1.02 or more and 2 or less. In addition, molar ratio P / B means the value computed from the preparation amount of the raw material compound used when preparing a boron phosphate salt.

  In the catalyst of the present invention, the molar ratio P / B between phosphorus (P) and boron (B) in the boron phosphate salt is usually 1.02 or more and 2 or less, preferably 1.05 or more and 1.5 or less. It is. If the molar ratio P / B deviates from the proper range, that is, if the molar ratio P / B is too small or too large, a carbonaceous material is precipitated in a long-term reaction, for example, pressure loss during the reaction. May increase and it may be difficult to continue the reaction. Also, for example, the acrolein selectivity may decrease.

  The boron phosphate salt contained in the catalyst of the present invention is not particularly limited as long as the molar ratio P / B is within a predetermined range, and the boron phosphate having a molar ratio P / B within the predetermined range. A salt may be used alone or in combination of two or more.

  The boron phosphate salt preferably has a crystal structure. When the boron phosphate salt has a crystal structure, adhesion of the carbonaceous substance to the boron phosphate salt, which causes a decrease in the activity of the catalyst, is suppressed even in continuous dehydration reaction of glycerol. The crystal structure of the boron phosphate salt is not particularly limited, and examples thereof include tetragonal crystals and cristobalite crystals.

  The catalyst of the present invention may be a supported catalyst in which a boron phosphate salt is supported on a carrier. Usable carriers include, for example, inorganic oxides and composite oxides such as silica, alumina, titania and zirconia; crystalline metallosilicates such as zeolite; metals and alloys such as stainless steel and aluminum; inorganic substances such as activated carbon and silicon carbide And so on. The shape of the catalyst is not particularly limited, and examples thereof include a spherical shape, a column shape, a ring shape, a bowl shape, a honeycomb shape, and a sponge shape.

  The catalyst of this invention should just contain the boron phosphate salt whose molar ratio P / B exists in the predetermined | prescribed range as an active ingredient, and it is not specifically limited except that. In addition, since the more active components contained in the catalyst, the more suitable for industrial production of acrolein, the content of boron phosphate in the catalyst of the present invention is the case where boron phosphate is used as an unsupported catalyst. Is preferably 5 to 100% by mass, more preferably 20% by mass or more, and still more preferably 40% by mass or more with respect to 100% by mass of the catalyst. On the other hand, when boron phosphate is used as a carrier-type catalyst, it is preferably 0.01 to 70% by mass, more preferably 1 to 60% by mass, and further preferably 5 to 50% with respect to 100% by mass of the catalyst. % By mass.

≪Manufacture of glycerol dehydration catalyst≫
The catalyst for dehydrating glycerin of the present invention contains a boron phosphate salt having a molar ratio P / B of phosphorus (P) and boron (B) within a predetermined range.

  The boron phosphate salt can be prepared by a conventionally known catalyst preparation method such as a concentration method, a precipitation method, a coprecipitation method, a sol-gel method, or a hydrothermal synthesis method. The concentration method is a method of dehydrating and concentrating an aqueous solution of the raw material compound, and is preferable in terms of easy control of the catalyst composition.

As a suitable preparation method of the boron phosphate salt, for example, H ₃ BO ₃ , HBO ₃ , H ₄ B ₂ O ₄ , H ₃ BO ₂ , H ₃ BO, (NH ₄ ) ₂ O.5B ₂ O _3. One or more boron compounds selected from 8H ₂ O and the like, and H ₃ PO ₂ , H ₃ PO ₃ , H ₃ PO ₄ , H ₂ P ₂ O ₇ , H ₅ P ₃ O ₁₀ , H ₆ One or more phosphorus selected from phosphoric acid such as P ₄ O ₁₀ , phosphate such as (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) H ₂ PO ₄ Examples include a method of dehydrating an aqueous solution prepared from an acid compound to obtain a solid. The amount of the boron compound and phosphate compound used may be appropriately adjusted so that the molar ratio P / B of phosphorus (P) and boron (B) in the boron phosphate salt is within a predetermined range, and is particularly limited. It is not something.

  In order to obtain a boron phosphate salt having a crystal structure, a solid obtained by dehydrating a solution prepared from a raw material compound may be fired. In general, the higher the firing temperature and the longer the firing time, the more crystallization tends to proceed. The firing conditions are not particularly limited as long as there is no extreme change in the crystal structure. For example, the firing conditions are 500 to 1500 ° C. for 3 to 15 hours, preferably 600 to 1400 ° C. for 3 to 10 hours in an air atmosphere. More preferably, it may be fired at 700 to 1200 ° C. for 3 to 5 hours.

  In one embodiment, the catalyst of the present invention is a glycerol dehydration catalyst containing a boron phosphate salt, wherein the molar ratio P / B of phosphorus (P) to boron (B) in the boron phosphate salt is 1. It is manufactured by dehydrating an aqueous solution prepared from a boron compound and a phosphoric acid compound in a charge amount of 0.02 or more and 2 or less to obtain a solid, and then firing the solid.

  When the boron phosphate salt is supported on the carrier, for example, an impregnation method in which the carrier is impregnated with a solution containing the raw material compound of the boron phosphate salt and heated; the boron phosphate salt is precipitated in the solution containing the carrier Alternatively, a precipitation method in which a carrier is added to a solution in which a boron phosphate salt is precipitated; a kneading method in which the boron phosphate salt is mixed with the carrier;

  By the above method, a glycerol dehydration catalyst can be produced. The produced catalyst for dehydration of glycerin is useful as a catalyst used for dehydration reaction of glycerin. Therefore, the glycerol dehydration catalyst of the present invention can naturally be used in a method for producing acrolein by a glycerol dehydration reaction.

≪Acrolein production method≫
The method for producing acrolein according to the present invention (hereinafter sometimes referred to as “the production method of the present invention”) is a method for producing acrolein by dehydrating glycerol in the presence of a catalyst, wherein the catalyst is as described above. It is a novel glycerol dehydration catalyst.

  The production method of the present invention includes, for example, a gas phase in which a reaction gas containing glycerin gas is brought into contact with a catalyst in a reactor arbitrarily selected from a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, and the like. Acrolein is produced by a dehydration reaction. The production method of the present invention is not limited to a gas phase dehydration reaction in which a reaction gas containing glycerin gas is brought into contact with a catalyst, but a liquid phase dehydration reaction in which a glycerin solution is brought into contact with a catalyst is applied. You can also. In the latter case, the liquid phase dehydration reaction is performed by combining a fixed bed and a distillation column, a method combining a stirring tank and a distillation tower, a method using a single-stage stirring tank, a method using a multi-stage stirring tank, and a multi-stage type. These can be carried out by various conventionally known methods such as a method using a distillation column and a method combining these. These methods may be either batch type or continuous type, but are usually carried out continuously.

  Below, the manufacturing method of acrolein using the vapor phase dehydration reaction excellent in the industrial productivity of acrolein will be described as an example.

  The reaction gas may be a gas composed only of glycerin, and may contain a gas inert to the dehydration reaction of glycerin in order to adjust the glycerin concentration in the reaction gas. Examples of the inert gas include water vapor, nitrogen gas, carbon dioxide gas, and air. The concentration of glycerin in the reaction gas is usually 0.1 to 100 mol%, preferably 1 mol% or more, and more preferably 5 mol% or more in order to produce acrolein economically and efficiently. .

Since the catalyst of the present invention is a glycerol dehydration catalyst having a high acrolein selectivity, acrolein can be obtained in a high yield even if the flow rate of the reaction gas is set large. The flow rate of the reaction gas is usually 50 to 20000 hr ⁻¹ , preferably 10000 hr ⁻¹ or less when expressed in terms of gas space velocity (GHSV) per unit volume of the catalyst, and acrolein is produced economically and with high efficiency. For this reason, it is more preferably 4000 hr ⁻¹ or less.

  The reaction temperature is usually 200 to 500 ° C, preferably 250 to 450 ° C, more preferably 300 to 400 ° C.

  The pressure of the reaction gas is not particularly limited as long as glycerin does not condense, but it is usually 0.001 to 1 MPa, preferably 0.01 to 0.5 MPa, more preferably. Is 0.3 MPa or less.

  When the dehydration reaction of glycerin is continuously performed, a carbonaceous material may adhere to the surface of the catalyst and the activity of the catalyst may be reduced. In such a case, if a regeneration treatment is performed in which the catalyst and the regeneration gas are brought into contact with each other at a high temperature, the carbonaceous material adhering to the surface of the catalyst can be removed to restore the activity of the catalyst. Examples of the regeneration gas include oxidizing gases such as oxygen and oxygen-containing air. The regeneration gas may contain an inert gas such as nitrogen, carbon dioxide, and water vapor as necessary. When there is a concern about rapid heat generation due to contact between the catalyst and oxygen, it is recommended that an inert gas be included in the regeneration gas in order to suppress the rapid heat generation. The temperature of the regeneration treatment is not particularly limited as long as the carbonaceous material can be removed without thermally degrading the catalyst, but is preferably equal to or lower than the calcination temperature in the catalyst production.

  Crude acrolein obtained by the dehydration reaction of glycerin contains a by-product. Therefore, it is preferable to purify the obtained crude acrolein. Examples of by-products include phenol, 1-hydroxyacetone, allyl alcohol and the like in addition to propionaldehyde. When the crude acrolein is purified, phenol and / or 1-hydroxyacetone is mainly removed. By removing these by-products, the yield of acrylic acid in producing acrylic acid from acrolein is improved. In particular, if 1-hydroxyacetone is removed, the amount of acetic acid generated can be reduced.

Considering that the yield of acrylic acid is improved, it is considered preferable to increase the removal amount of phenol and / or 1-hydroxyacetone. Therefore, the mass ratio Ph / A between the acrolein (A) and the phenol (Ph) after purification is preferably 1.0 or less, more preferably 0.7 or less, and further preferably 0.4 or less. The mass ratio H / A of the acrolein (A) and 1-hydroxyacetone (H) after purification is preferably 0.5 or less, more preferably 0.3 or less, and still more preferably 0.1 or less. However, if the removal amount of phenol and / or 1-hydroxyacetone is increased, the loss of acrolein may increase and the purification of acrolein may become complicated. In consideration of this, the mass ratio Ph / A and the mass ratio H / A are preferably 1 × 10 ⁻⁹ or more, more preferably 1 × 10 ⁻⁷ or more, and further preferably 1 × 10 ⁻⁵ or more. .

  The boiling points of acrolein, phenol and 1-hydroxyacetone are about 53 ° C., about 182 ° C. and about 146 ° C., respectively. By utilizing this difference in boiling point, phenol and / or 1-hydroxyacetone can be removed from crude acrolein. Examples of the method include a method in which liquid crude acrolein is treated in a distillation column to fractionate acrolein having a lower boiling point than the object to be removed, and gaseous crude acrolein is treated in a coagulation tower to have a higher boiling point than acrolein. And a method of vaporizing acrolein having a boiling point lower than that of the removal target by blowing gas into the crude acrolein introduced into the evaporation tower.

  The melting points of acrolein, phenol and 1-hydroxyacetone are about -87 ° C, about 43 ° C and about -17 ° C, respectively. By utilizing this difference in melting point, phenol and / or 1-hydroxyacetone can be removed from crude acrolein. As the method, for example, a crude acrolein is cooled to remove a phenol and / or 1-hydroxyacetone precipitate.

  Propionaldehyde has a boiling point of about 48 ° C. and a melting point of about −81 ° C., and can be removed from crude acrolein using a difference in boiling point or a melting point from acrolein. Since both the boiling point difference and melting point difference are small, acrolein loss may increase. Therefore, the catalyst of the present invention is particularly useful because it can reduce the amount of propionaldehyde generated in the dehydration reaction of glycerol.

  Acrolein can be produced by the above method. The acrolein thus produced is, as already known, acrolein derivatives such as acrylic acid, 1,3-propanediol, allyl alcohol and methionine; hydrophilic resins such as polyacrylic acid and sodium polyacrylate; It is useful as a synthetic raw material. Therefore, the method for producing acrolein according to the present invention can naturally be incorporated into a method for producing an acrolein derivative or a hydrophilic resin.

≪Method for producing acrylic acid≫
The method for producing acrylic acid according to the present invention is a method for producing acrylic acid by dehydrating glycerol in the presence of a catalyst to produce acrolein, and then oxidizing the obtained acrolein, wherein the catalyst is as described above. It is a novel glycerol dehydration catalyst. That is, acrolein obtained by the method for producing acrolein according to the present invention is used as a raw material for acrylic acid.

  In the method for producing acrolein according to the present invention, when biodiesel-derived glycerin is used as a raw material, the obtained crude acrolein may be used for the production of acrylic acid without purification. , 1-hydroxyacetone, methoxyacetone, 3-methoxypropanal, and the like. These by-products cause a decrease in catalytic activity and a decrease in yield, and formic acid, acetic acid, propion in acrylic acid. Since it may cause by-products such as acid, pyruvic acid, 3-methoxypropionic acid, etc., it may be used after purification. The purification can be performed by a conventionally known method. The collected liquid obtained by using the aggregate liquid of the reaction composition or the collection solvent is subjected to a distillation method or the collection described in JP-A-2008-115103. A method using a purifier equipped with a collecting tower and a stripping tower is exemplified. When crude acrolein is not purified, impurities in acrylic acid may be removed by purifying acrylic acid in a subsequent step. It is preferable to use crude acrolein without purification in terms of simplifying the process and reducing production costs.

  To produce acrylic acid, a gas containing acrolein (hereinafter sometimes referred to as “acrolein-containing gas”) and a catalyst for oxidizing acrolein (hereinafter referred to as “acrolein oxidation catalyst”) may be used. And acrolein are preferably vapor-phase oxidized at a temperature of 200 to 400 ° C. in an oxidation reactor arbitrarily selected from a fixed bed reactor, a moving bed reactor, a fluidized bed reactor and the like. As acrolein is oxidized, propionic acid is produced from propionaldehyde. Since acrolein obtained using the catalyst of the present invention has a low propionaldehyde content, the amount of propionic acid produced is low. There are few.

  The acrolein oxidation catalyst is not particularly limited as long as it is a conventionally known acrolein oxidation catalyst used for producing acrylic acid by catalytic gas phase oxidation of acrolein using molecular oxygen or a molecular oxygen-containing gas. Although it is not a thing, For example, the mixture and composite oxide of metal oxides, such as iron oxide, molybdenum oxide, titanium oxide, vanadium oxide, tungsten oxide, antimony oxide, tin oxide, and copper oxide, are mentioned. Of these catalysts, a molybdenum-vanadium catalyst mainly composed of molybdenum and vanadium is particularly suitable. In addition, in the catalyst for acrolein oxidation, a mixture or composite oxide of the above metal oxides is supported on a carrier (for example, inorganic oxides such as silica, alumina, zirconia, composite oxides, inorganic substances such as silicon carbide). A supported catalyst may also be used.

  The amount of oxygen added to the acrolein-containing gas used in the production of acrylic acid needs to be set as appropriate because the acrolein combustion may occur and there is a risk of explosion if there is too much oxygen.

  A gaseous product containing crude acrylic acid is obtained by the gas phase oxidation reaction of acrolein. The gaseous matter is liquefied by cooling condensation, solvent collection, etc., and if necessary, the water and the collection solvent contained in the liquefied product are removed by a conventionally known method (for example, distillation), followed by a crystallization operation. By applying, high-purity acrylic acid can be obtained.

  The crude acrylic acid obtained by the oxidation reaction of acrolein contains propionic acid as a by-product. The content of propionic acid in the crude acrylic acid is relatively small because the catalyst of the present invention is used in the production stage of acrolein which is a raw material of acrylic acid. However, when producing a water-absorbing resin from acrylic acid, it is preferable to remove propionic acid from crude acrylic acid because propionic acid causes odor. Therefore, crude acrylic acid is purified to remove propionic acid.

  The boiling points of acrylic acid and propionic acid are both about 141 ° C. Therefore, it is difficult to remove propionic acid from crude acrylic acid using the difference in boiling point. In contrast, the melting points of acrylic acid and propionic acid are about 12 ° C. and about −21 ° C., respectively. Therefore, it is easy to remove propionic acid from crude acrylic acid using the difference in melting point. That is, in order to remove propionic acid from the crude acrylic acid, crystallization operation may be performed on the crude acrylic acid. Specifically, the crude acrylic acid may be cooled to recover the acrylic acid that precipitates before propionic acid. In this case, the cooling temperature of the crude acrylic acid is preferably −18 ° C. to 10 ° C., more preferably 4 ° C. or less, and further preferably 0 ° C. or less. In addition, when crude acrylic acid contains impurities other than propionic acid such as acetic acid, acrolein, and water, these impurities are removed by a conventionally known method such as distillation, and then propionic acid is removed by crystallization operation. It is preferable to do.

  The crystallization operation is not particularly limited as long as the propionic acid can be separated from the crude acrylic acid. For example, JP-A-9-227445 and JP-A-2002-519402 This can be done using the methods described.

  The crystallization operation is a process of obtaining purified acrylic acid by supplying crude acrylic acid to a crystallizer and causing it to crystallize. The crystallization method may be a conventionally known crystallization method and is not particularly limited. For example, the crystallization may be performed using a continuous or batch crystallization apparatus. It can be carried out in stages or in two or more stages. The obtained acrylic acid crystals can be further purified by washing, sweating, or the like, if necessary, to obtain purified acrylic acid with higher purity.

  Examples of the continuous crystallizer include a crystallizer in which a crystallization part, a solid-liquid separation part and a crystal purification part are integrated (for example, a BMC (Backmixing Column Crystallizer) apparatus manufactured by Nippon Steel Chemical Co., Ltd., Tsukishima Continuous melt purification system manufactured by Kikai Co., Ltd., crystallization unit (eg, CDC (Cooling Disk Crystallizer) device manufactured by GMF GOUDA), solid-liquid separation unit (eg, centrifuge, belt filter) and crystal purification unit ( For example, a crystallizer combined with KCP (Kureha Crystal Purifier) manufactured by Kureha Techno Engineering Co., Ltd. can be used.

  As the batch crystallization apparatus, for example, a layer crystallization apparatus (dynamic crystallization apparatus) manufactured by Sulzer Chemtech, a static crystallization apparatus manufactured by BEFS PROKEM, or the like can be used.

  Dynamic crystallization is, for example, a tubular crystallizer equipped with a temperature control mechanism for performing crystallization, sweating and melting, a tank for collecting the mother liquor after sweating, and supplying crude acrylic acid to the crystallizer. This is a method in which crystallization is performed using a dynamic crystallization apparatus that includes a circulation pump and can transfer crude acrylic acid from the reservoir provided at the lower part of the crystallizer to the upper part of the crystallizer with a circulation pump. Static crystallization is, for example, a tubular crystallizer equipped with a temperature control mechanism for crystallization, sweating, and melting, and a crystallizer having an extraction valve at the bottom and a mother liquor after sweating are collected. The crystallization is performed by using a static crystallization apparatus including a tank that performs the crystallization.

  Specifically, crude acrylic acid is introduced into the crystallizer as a liquid phase, and acrylic acid in the liquid phase is solidified and generated on the cooling surface (tube wall surface). Immediately after the mass of the solid phase generated on the cooling surface is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, based on the mass of the crude acrylic acid introduced into the crystallizer, the liquid The phase is discharged from the crystallizer and the solid and liquid phases are separated. The liquid phase may be discharged by either a pumping method (dynamic crystallization) or a discharging method from a crystallizer (static crystallization). On the other hand, after the solid phase is taken out from the crystallizer, purification such as washing and sweating may be performed in order to further improve the purity.

  When dynamic crystallization or static crystallization is performed in multiple stages, it can be advantageously carried out by adopting the countercurrent principle. At this time, the acrylic acid crystallized in each stage is separated from the residual mother liquor and supplied to the stage where acrylic acid having higher purity is generated. On the other hand, the residual mother liquor is fed to the stage where acrylic acid with lower purity is produced.

  In dynamic crystallization, if the purity of acrylic acid is low, crystallization becomes difficult, but in static crystallization, the time for the residual mother liquor to contact the cooling surface is longer than in dynamic crystallization, In addition, since the influence of temperature is easily transmitted, crystallization is easy even if the purity of acrylic acid is lowered. Therefore, in order to improve the recovery rate of acrylic acid, the final residual mother liquor in dynamic crystallization may be subjected to static crystallization and further crystallization may be performed.

  The number of crystallization stages required depends on the degree of purity required, but the number of stages required to obtain high purity acrylic acid is usually 1 to 6 purification steps (dynamic crystallization). The stripping step (dynamic crystallization and / or static crystallization) is usually 0 to 5 times, preferably 0 to 3 times, preferably 2 to 5 times, more preferably 2 to 4 times. In general, all stages where acrylic acid having a higher purity than the crude acrylic acid supplied is obtained are purification stages and all other stages are stripping stages. The stripping step is performed to recover acrylic acid contained in the residual mother liquor from the purification step. Note that the stripping step is not necessarily provided. For example, when the low boiling point component is separated from the residual mother liquor of the crystallizer using a distillation column, the stripping step may be omitted.

  Regardless of whether dynamic crystallization or static crystallization is employed, the acrylic acid crystals obtained by the crystallization operation may be used as they are, or if necessary, such as washing and sweating. It may be a product after purification. On the other hand, the residual mother liquor discharged in the crystallization operation may be taken out of the system.

  By the above method, acrylic acid can be produced. The acrylic acid thus produced is useful as a raw material for the synthesis of acrylic acid derivatives such as acrylic acid esters; hydrophilic resins such as polyacrylic acid and sodium polyacrylate; Therefore, the method for producing acrylic acid according to the present invention can naturally be incorporated into a method for producing an acrylic acid derivative or a hydrophilic resin.

≪Method for producing hydrophilic resin≫
In the method for producing a hydrophilic resin according to the present invention, acrolein is produced by dehydrating glycerin in the presence of a catalyst, and then the obtained acrolein is oxidized to produce acrylic acid. A method for producing a hydrophilic resin by polymerizing body components, wherein the catalyst is a glycerol dehydration catalyst as described above. That is, acrylic acid obtained by the method for producing acrylic acid according to the present invention is used as a raw material for hydrophilic resins such as water-absorbing resins and water-soluble resins.

  However, acrylic acid obtained by the method for producing acrylic acid using glycerin as a raw material is more organic than formic acid, acetic acid, propionic acid, etc., compared with acrylic acid obtained by the method for producing acrylic acid using propylene as a raw material. It contains a lot of acid impurities, and these impurities may cause odor and coloring of the hydrophilic resin. It is therefore important to purify the resulting acrylic acid. Of the impurities contained in acrylic acid, propionic acid has a boiling point close to that of acrylic acid, so that if the content is large, purification of acrylic acid by distillation becomes difficult. Therefore, acrylic acid from which propionic acid has been removed by purification by crystallization is preferably used in the method for producing a hydrophilic resin according to the present invention.

  When the acrylic acid obtained by the method for producing acrylic acid according to the present invention is used as a raw material for producing a hydrophilic resin such as a water-absorbing resin or a water-soluble resin, the polymerization reaction is easily controlled, and the obtained hydrophilic The quality of the functional resin is stabilized, and various performances such as water absorption performance and dispersion performance of inorganic materials are improved.

  In the case of producing a water-absorbing resin, for example, acrylic acid and / or a salt thereof obtained by the method for producing acrylic acid according to the present invention is used as a main component of monomer component (preferably 70 mol% or more, more preferably 90 mol% or more), and a crosslinking agent of about 0.001 to 5 mol% (value for acrylic acid) and a radical polymerization initiator of about 0.001 to 2 mol% (value for monomer component). After water-crosslinking polymerization, the water-absorbent resin is obtained by drying and pulverizing.

  Here, the water-absorbent resin is a water-swellable water-insoluble polyacrylic acid having a cross-linked structure, and absorbs pure water or physiological saline 3 times or more, preferably 10 to 1000 times its own weight. It means polyacrylic acid that forms a water-insoluble hydrogel having a water-soluble component (water-soluble content) of preferably 25% by mass or less, more preferably 10% by mass or less. Specific examples of such water-absorbing resins and methods for measuring physical properties are disclosed in, for example, US Pat. Nos. 6,107,358, 6,174,978, 6,241,928, and the like. .

  Further, from the viewpoint of improving productivity, preferable production methods include, for example, US Pat. Nos. 6,867,269, 6,906,159, 7,091,253, and International Publication No. 01. / 038402 pamphlet, International Publication No. 2006/034806 pamphlet and the like.

  A series of processes for producing a water-absorbing resin by neutralization, polymerization, drying and the like using acrylic acid as a raw material is as follows, for example.

  Part of the acrylic acid obtained by the method for producing acrylic acid according to the present invention is supplied to the water-absorbent resin production process via a line. In the production process of the water absorbent resin, acrylic acid is introduced into the neutralization step, the polymerization step, and the drying step, and a desired treatment is performed to produce the water absorbent resin. For the purpose of improving various physical properties, a desired treatment may be performed. For example, a crosslinking step may be interposed during or after the polymerization.

  The neutralization step is an optional step. For example, a method of mixing a predetermined amount of a basic substance powder or aqueous solution with acrylic acid or polyacrylic acid (salt) is exemplified. It may be employed and is not particularly limited. The neutralization step may be performed either before or after polymerization, or may be performed both before and after polymerization. As a basic substance used for neutralization of acrylic acid or polyacrylic acid (salt), for example, a conventionally known basic substance such as a carbonic acid (hydrogen) salt, an alkali metal hydroxide, ammonia, an organic amine or the like is appropriately used. Use it. Moreover, the neutralization rate of polyacrylic acid is not specifically limited, What is necessary is just to adjust so that it may become arbitrary neutralization rates (for example, arbitrary values in the range of 30-100 mol%).

  The polymerization method in the polymerization step is not particularly limited, and a conventionally known polymerization method such as polymerization with a radical polymerization initiator, radiation polymerization, polymerization by irradiation with an electron beam or active energy ray, ultraviolet polymerization with a photosensitizer, etc. May be used. Various conditions such as a polymerization initiator and polymerization conditions can be arbitrarily selected. Of course, if necessary, conventionally known additives such as a crosslinking agent and other monomers, and further a water-soluble chain transfer agent and a hydrophilic polymer may be added.

  Examples of the polymerization using a radical polymerization initiator include an aqueous solution polymerization method and a reverse phase suspension polymerization method. Here, the aqueous solution polymerization method is a method of polymerizing acrylic acid in an aqueous acrylic acid solution without using a dispersion solvent or the like. For example, US Pat. Nos. 4,625,001 and 4,873,299 No. 4,286,082, 4,973,632, 4,985,518, 5,124,416, 5,250,640, 5,264,495, No. 5,145,906, No. 5,380,808 and the like, and European Patent Publication Nos. 0 811 636, 0 955 086, 0 922 717 and the like. The reverse phase suspension polymerization method is a method of polymerizing acrylic acid in an aqueous acrylic acid solution in a state where the aqueous acrylic acid solution is suspended in a hydrophobic organic solvent. For example, US Pat. No. 093,776, No. 4,367,323, No. 4,446,261, No. 4,683,274, No. 5,244,735 and the like.

  The acrylate polymer after polymerization (namely, water-absorbing resin) is subjected to a drying step. The drying method is not particularly limited, and using a conventionally known drying means such as a hot air dryer, a fluidized bed dryer, a nauter dryer, etc., a desired drying temperature, preferably 70 to 230 ° C., What is necessary is just to dry suitably.

  The water-absorbent resin obtained through the drying step may be used as it is, or may be used after granulation / pulverization and surface cross-linking into a desired shape, and conventionally known reducing agents, perfumes, binders, etc. You may use it, after giving post-processing according to a use, such as adding an additive.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and appropriate modifications are made within a range that can meet the purpose described above and below. Any of these can be carried out and are included in the technical scope of the present invention.

  First, the manufacture example of the catalyst for glycerol dehydration is demonstrated. “%” Representing the concentration of the phosphoric acid aqueous solution means “mass%”.

≪Example of production of glycerin dehydration catalyst≫
Example 1
First, an aqueous solution of 332.17 g of 85% phosphoric acid aqueous solution and 232.52 g of distilled water was added to an aqueous solution of 169.67 g boric acid and 1567.5 g distilled water to obtain a mixed solution. The mixed solution was heated to reflux at 90 ° C. for 2 hours while stirring to obtain a colorless and transparent mixed solution.

  Subsequently, the obtained mixed solution was dehydrated and concentrated on a 60 ° C. hot water bath under a reduced pressure condition of 0.005 MPa using an evaporator. The obtained concentrate was dried at 120 ° C. for 24 hours under an air stream to obtain a solid.

  Finally, the obtained solid was fired at 1000 ° C. for 5 hours in an air atmosphere. The obtained fired product was sieved using a sieve having openings of 0.7 mm and 2.0 mm. The fired product classified in the range of 0.7 to 2.0 mm was used as a catalyst for glycerin dehydration.

<< Example 2 >>
In Example 1, an aqueous solution of 85.3% phosphoric acid aqueous solution 337.05 g and distilled water 235.93 g was added to an aqueous solution of boric acid 164.34 g and distilled water 1564.1 g, and the resulting mixed solution was used. Except for this, a glycerol dehydration catalyst was produced in the same manner as in Example 1.

Example 3
In Example 1, an aqueous solution of 345.94 g of 85% phosphoric acid solution and 242.16 g of distilled water was added to an aqueous solution of 154.61 g of boric acid and 1557.8 g of distilled water, and the resulting mixed solution was used. Except for this, a glycerol dehydration catalyst was produced in the same manner as in Example 1.

Example 4
In Example 1, an aqueous solution of 85.73 g of 85% phosphoric acid aqueous solution and 257.07 g of distilled water was added to an aqueous solution of 131.31 g of boric acid and 1542.9 g of distilled water, and the resulting mixed solution was used. Except for this, a glycerol dehydration catalyst was produced in the same manner as in Example 1.

≪Comparative example 1≫
In Example 1, an aqueous solution of 85.63 g of phosphoric acid aqueous solution and 214.42 g of distilled water was added to an aqueous solution of 197.94 g of boric acid and 1585.6 g of distilled water, and the resulting mixed solution was used. Except for this, a glycerol dehydration catalyst was produced in the same manner as in Example 1.

«Comparative example 2»
In Example 1, an aqueous solution of 326.96 g of 85% phosphoric acid and 228.87 g of distilled water was added to an aqueous solution of 175.36 g of boric acid and 1571.1 g of distilled water, and the resulting mixed solution was used. Except for this, a glycerol dehydration catalyst was produced in the same manner as in Example 1.

≪Example of acrolein production≫
Using the catalysts produced in Examples 1 to 4 and Comparative Examples 1 and 2, acrolein was produced by dehydrating glycerin by the atmospheric pressure gas phase fixed bed flow reaction mode shown below.

First, 15 mL of a catalyst was filled in a stainless steel reaction tube (inner diameter 10 mm, length 500 mm) to prepare a fixed bed reactor, and this reactor was immersed in a salt bath at 360 ° C. Thereafter, nitrogen gas was allowed to flow through the reactor at a flow rate of 62 mL / min for 30 minutes, and then a reaction gas (reaction gas composition: glycerin 27 mol%, water 34 mol) consisting of a vaporized gas of 80 mass% glycerin aqueous solution and nitrogen gas. %, Nitrogen 39 mol%) at a flow rate (GHSV) of 640 hr ⁻¹ for 3 hours.

  The effluent gas in each 30 minutes of 0.5 to 1 hour, 1.5 to 2 hours, and 2.5 to 3 hours after flowing the reaction gas through the reactor was collected by cooling and absorbing in acetonitrile. . Hereinafter, the “cooled absorption material of collected effluent gas” may be referred to as “effluent”.

  A part of the effluent was taken, and qualitative and quantitative analysis of the effluent was performed with a gas chromatography (GC) apparatus equipped with a FID in the detector. The internal standard method was adopted for quantitative analysis by GC. As a result of qualitative analysis by GC, by-products such as propionaldehyde and 1-hydroxyacetone were detected together with glycerin and acrolein. From the quantitative analysis results, glycerin conversion rate (GLY conversion rate), acrolein selectivity (ACR selectivity), propionaldehyde selectivity (PARD selectivity) and 1-hydroxyacetone selectivity (HDAC selectivity) were calculated. These calculation formulas are as follows.

GLY conversion = (1− (number of moles of glycerin in the effluent) / (number of moles of glycerin introduced into the reactor in 30 minutes)) × 100;
ACR selectivity = ((moles of acrolein) / (moles of glycerol fed into the reactor in 30 minutes)) × 100 / glycerin conversion × 100;
PALD selectivity = ((number of moles of propionaldehyde) / (number of moles of glycerin introduced into the reactor in 30 minutes)) × 100 / glycerin conversion × 100;
HDAC selectivity = (number of moles of 1-hydroxyacetone) / (number of moles of glycerin introduced into the reactor in 30 minutes)) × 100 / glycerin conversion × 100.

<Reaction result>
Table 1 shows the molar ratio P / B of each catalyst and the reaction results (data for the last 30 minutes) obtained when acrolein was produced using each catalyst. In Table 1, glycerin is abbreviated as GCR, acrolein, propionaldehyde, and 1-hydroxyacetone as ACR, PALD, and HDAC, respectively. Further, the molar ratio of the catalyst component is a value calculated from the charged amount of the raw material compound used when preparing the boron phosphate salt.

  As is apparent from Table 1, when the results of Examples 1 to 4 and Comparative Example 2 are compared with the results of Comparative Example 1, the ACR selectivity is improved in the catalyst having a molar ratio P / B of 1 or more. I can confirm. Moreover, when the results of Examples 1 to 4 are compared with the results of Comparative Examples 1 and 2, it can be confirmed that the PALD selectivity is decreased in a catalyst having a molar ratio P / B larger than 1. From these facts, it is expected that by using a catalyst having a molar ratio P / B larger than 1, it is possible to stably produce acrolein while reducing the amount of by-products generated.

  Next, according to the acrolein production example described above, acrolein was continuously produced without stopping the reaction time at 3 hours, and the life of the catalyst was evaluated. The maximum evaluation time for the catalyst life was 48 hours.

Example 5
Using the catalyst produced in Example 1, the life of the catalyst was evaluated according to the above-mentioned production example of acrolein. This catalyst was able to produce acrolein continuously for 48 hours.

Example 6
Using the catalyst produced in Example 2, the lifetime of the catalyst was evaluated according to the above-described production example of acrolein. This catalyst was able to produce acrolein continuously for 48 hours.

Example 7
Using the catalyst produced in Example 4, the lifetime of the catalyst was evaluated according to the above-described production example of acrolein. This catalyst was able to produce acrolein continuously for 48 hours.

«Comparative Example 3»
Using the catalyst produced in Comparative Example 1, the life of the catalyst was evaluated according to the above-described production example of acrolein. With this catalyst, when the reaction time passed 4.7 hours, a sudden pressure drop occurred, making it impossible to produce acrolein.

<< Comparative Example 4 >>
Using the catalyst produced in Comparative Example 2, the life of the catalyst was evaluated according to the above-described production example of acrolein. With this catalyst, the pressure loss gradually increased with the lapse of the reaction time, and when a reaction time of 20 hours had passed, it became impossible to produce acrolein.

<Reaction result>
The obtained reaction results (data for 30 minutes immediately before reaching each reaction time) are shown in Table 2. In Table 2, glycerin is abbreviated as GCR, acrolein, propionaldehyde, and 1-hydroxyacetone as ACR, PALD, and HDAC, respectively. Further, the molar ratio of the catalyst component is a value calculated from the charged amount of the raw material compound used when preparing the boron phosphate salt.

  As is apparent from Table 2, when the results of Examples 5 to 7 are compared with the results of Comparative Examples 3 and 4, the time during which the reaction can be continued in a catalyst having a molar ratio P / B greater than 1 is 2 It can be confirmed that it is longer than double. From this, it is expected that acrolein can be stably produced over a long period of time by using a catalyst having a molar ratio P / B larger than 1.

≪Example of acrylic acid production≫
In the steps shown below, acrylic acid was produced from glycerin.
(1) Pre-reaction step: Glycerol was dehydrated to obtain a reaction product containing propionaldehyde and acrolein.
(2) Preliminary purification step: The reaction product obtained in (1) was purified to obtain a composition containing propionaldehyde and acrolein that can be used in the subsequent reaction.
(3) Subsequent reaction step: The composition obtained in (2) was subjected to an oxidation reaction to obtain a reaction product containing crude acrylic acid.
(4) Subsequent purification step: After the reaction product obtained in (3) was distilled to obtain crude acrylic acid, the crude acrylic acid was purified by crystallization to obtain acrylic acid.

Hereafter, each said process is demonstrated in order.
(1) First stage reaction process (First stage reaction catalyst)
The catalyst shown in Example 2 was used as the catalyst used in the previous reaction.

(Dehydration reaction)
50 mL of the above catalyst was filled in a stainless steel reaction tube (inner diameter 25 mm, length 500 mm) and prepared as a fixed bed reactor, and this reactor was placed in a 360 ° C. night bath.

A condenser was provided at the reactor outlet, and cooling water at about 4 ° C. was allowed to flow. The reaction system was depressurized to 62 kPa with a vacuum pump, and a constant vacuum apparatus was used to adjust the pressure. Thereafter, a glycerin-containing gas was circulated in the reactor. Here, as the glycerin-containing gas, a mixed gas composed of 44% by volume of glycerin and 56% by volume of water was circulated at a flow rate of gas space velocity (GHSV) 420 hr ⁻¹ . The glycerin-containing gas was intermittently supplied for 20 hours from the start of the circulation, and all the gas flowing out from the reactor was condensed with a condenser and collected in a receiver cooled with an ice bath. The weight of the recovered reaction product was 939 g, which was 99% by mass of the feedstock.

  As a result of quantitative analysis of the obtained reaction product by gas chromatography, the reaction product contained 36% by mass of acrolein, 0.3% by mass of propionaldehyde, 6.6% by mass of 1-hydroxyacetone, 45% by mass of water, heavy The mass was 12% by mass.

(2) Preliminary purification step The reaction product obtained in (1) was supplied to the thin film distillation apparatus at 0.12 kg / h and operated under conditions of normal pressure, liquid film wall temperature of 85 ° C. and blade rotation speed of 300 rpm. From the top of the column, a distillate containing 42% by mass of acrolein, 0.6% by mass of propionaldehyde, 4% by mass of 1-hydroxyacetone and 51% by mass of water (that is, a composition containing propionaldehyde and acrolein) is 0. Obtained at 11 kg / h.

(3) Second-stage reaction step (Second-stage reaction catalyst)
The oxidation catalyst used for the latter stage reaction was prepared as follows. 350 g of ammonium paramolybdate, 116 g of ammonium metavanadate, and 44.6 g of ammonium paratungstate were dissolved in 2500 mL of water with heating and stirring, and then 1.5 g of vanadium trioxide was added. Separately, 87.8 g of copper nitrate was dissolved in 750 mL of water with stirring, and then 1.2 g of cuprous oxide and 29 g of antimony trioxide were added. After mixing these two liquids, 1000 mL of a spherical α-alumina having a diameter of 3 to 5 mm as a carrier was added and evaporated to dryness with stirring to obtain a catalyst precursor. This catalyst precursor was calcined at 400 ° C. for 6 hours to prepare an oxidation catalyst for producing acrylic acid. Incidentally, supported metal composition of the oxidation catalyst for production of acrylic acid _{is Mo 12 V 6.1 W 1 Cu 2.3} Sb 1.2.

(Oxidation reaction)
A stainless steel reaction tube (inner diameter 25 mm, length 500 mm) filled with 50 mL of the catalyst was prepared as a fixed bed oxidation reactor, and this reactor was placed in a night bath at 260 ° C. Thereafter, the composition obtained in (2) was supplied to the reactor. A condenser was provided at the reactor outlet, and cooling water of about 15 ° C. was allowed to flow. Here, propionaldehyde-containing gas is composed of 6.5% by volume of acrolein, 0.06% by volume of propionaldehyde, 0.45% by volume of 1-hydroxyacetone, 6% by volume of oxygen, 13% by volume of water, and 74% by volume of nitrogen. The mixed gas was circulated at a flow rate of space velocity (GHSV) 1900 hr ⁻¹ . A composition containing propionaldehyde and acrolein was intermittently supplied for 22 hours from the start of the reaction, and the gas flowing out from the reactor was condensed by a condenser and collected in a receiver cooled by an ice bath and a cold trap provided thereafter. .

  The recovered reaction product containing crude acrylic acid weighed 614 g and was 95% by mass of the feedstock. As a result of quantitative analysis by gas chromatography, the reaction product was 62% by mass of crude acrylic acid, 0.01% by mass of propionic acid, 1% by mass of formic acid, 3% by mass of acetic acid, and 34% by mass of water.

  In the production of acrylic acid using glycerin as a raw material, by-products of organic acids such as propionic acid, formic acid, and acetic acid, which are by-products, are increased, compared to the known acrylic acid production method using propylene as a raw material. I understand that

(4) Subsequent purification step The reaction product obtained in (3) is supplied to the fifth stage of the distillation column having 10 plates at 0.2 kg / h, the reflux ratio is 1, and the distillation amount from the top is 0.070 kg. Continuous distillation was carried out under the conditions of / h. As a result, crude acrylic acid having a composition of 88.1% by mass acrylic acid, 0.01% by mass propionic acid, 2.3% by mass acetic acid, 0.04% by mass formic acid, and 9.5% by mass water from the tower bottom. Was obtained at 0.130 kg / h. The crude acrylic acid is cooled to room temperature (about 15 ° C.) to −5.8 ° C. as a mother liquor to precipitate crystals, and held at the same temperature, then the crystals are separated from the liquid by suction filtration. Analysis operation was performed. After the separated crystals were melted, a part was sampled and analyzed, and the rest was cooled as a mother liquor to a temperature range of room temperature (about 15 ° C.) to 4.6 ° C. to precipitate the crystals, and kept at the same temperature. Thereafter, a crystallization operation for separating the crystals from the liquid by suction filtration was performed. A total of two crystallization operations finally yielded acrylic acid with a purity of 99.9% by mass or more. The results are shown in Table 3. In addition, the total amount of propionic acid and acetic acid was below the detection limit (1 mass ppm).

≪Example of manufacturing water-absorbing resin≫
In the production example of acrylic acid, acrylic acid containing 60 mass ppm of a polymerization inhibitor was prepared in acrylic acid having a total amount of acetic acid and propionic acid obtained by the second crystallization operation of 200 mass ppm. Separately, 75 mol% neutralization was performed by adding the above acrylic acid under cooling (liquid temperature 35 ° C.) to an aqueous NaOH solution obtained from sodium hydroxide containing 0.2 mass ppm of iron. It was. Acrylic acid and iron in water were below the detection limit. Therefore, the iron content of the monomer was calculated to be about 0.07 mass ppm.

  By dissolving 0.05 mol% of polyethylene glycol diacrylate (value relative to an aqueous sodium acrylate solution) as an internal cross-linking agent in the obtained sodium acrylate aqueous solution having a neutralization rate of 75 mol% and a concentration of 35 mass%, a simple solution was obtained. A mass component was obtained. 350 g of this monomer component was placed in a cylindrical container having a volume of 1 L, and nitrogen was blown at a rate of 2 L / min to deaerate for 20 minutes. Next, an aqueous solution of sodium persulfate 0.12 g / mol (value relative to the monomer component) and L-ascorbic acid 0.005 g / mol (value relative to the monomer component) was added under stirring with a stirrer to initiate polymerization. I let you. Stirring was stopped after the initiation of polymerization, and a standing aqueous solution polymerization was carried out. After the temperature of the monomer component showed a peak polymerization temperature of 108 ° C. after about 15 minutes (polymerization peak time), the polymerization was allowed to proceed for 30 minutes. Thereafter, the polymer was taken out from the cylindrical container to obtain a hydrogel crosslinked polymer.

  The obtained hydrogel crosslinked polymer was subdivided at 45 ° C. with a meat chopper (pore diameter: 8 mm) and then heat-dried with a hot air dryer at 170 ° C. for 20 minutes. Furthermore, a dry polymer (solid content: about 95%) is pulverized with a roll mill and classified with a JIS standard sieve to a particle size of 600 to 300 μm to obtain a polyacrylic acid water-absorbing resin (neutralization rate 75%). It was.

  The polymerizability of acrylic acid obtained by the method for producing acrylic acid according to the present invention is equivalent to the polymerizability of acrylic acid obtained by the method for producing acrylic acid using propylene as a raw material. There was no odor and the physical properties were the same.

  Since the present invention makes it possible to stably and continuously produce acrolein from glycerin in a high yield, as an important technique for achieving effective utilization of glycerin by-produced during the production of biodiesel, It contributes greatly to the spread of D-cell and the measures against global warming.

Claims (7)

  A catalyst for dehydration of glycerin containing a boron phosphate salt, wherein a molar ratio P / B of phosphorus (P) to boron (B) in the boron phosphate salt is 1.02 or more and 2 or less. A catalyst for dehydration of glycerin.   The catalyst for glycerol dehydration according to claim 1, wherein the molar ratio P / B of phosphorus (P) and boron (B) in the boron phosphate salt is 1.05 or more and 1.5 or less.   A method for producing acrolein by dehydrating glycerol in the presence of a catalyst, wherein the catalyst is the glycerol dehydrating catalyst according to claim 1 or 2.   The method for producing acrolein according to claim 3, wherein glycerol is dehydrated by a gas phase reaction in which a reaction gas containing glycerol gas is brought into contact with a catalyst.   A method for producing acrolein by dehydrating glycerin in the presence of a catalyst and then oxidizing the obtained acrolein to produce acrylic acid, wherein the catalyst is a glycerol dehydration catalyst according to claim 1 or 2. A method for producing acrylic acid, comprising:   Acrolein is produced by dehydrating glycerin in the presence of a catalyst, then the resulting acrolein is oxidized to produce acrylic acid, and the resulting monomer component containing acrylic acid is polymerized to produce a hydrophilic resin. A method for producing a hydrophilic resin, wherein the catalyst is the glycerol dehydration catalyst according to claim 1.   The method for producing a hydrophilic resin according to claim 6, wherein the hydrophilic resin is a water absorbent resin.