JP4074455B2 - Method for producing (meth) acrylic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing purified (meth) acrylic acid from a reaction product gas containing (meth) acrylic acid obtained by a gas phase catalytic oxidation reaction, through each step of collection, preliminary purification and purification. It is. In particular, the present invention relates to a method for recovering methacrylic acid purified from (meth) acrylic acid in a reaction product gas with high yield. In the present specification, (meth) acrylic acid means acrylic acid and methacrylic acid.
[0002]
[Prior art]
As a method for producing (meth) acrylic acid, there is a method of hydrolyzing a corresponding nitrile compound, but at present, a gas phase catalytic oxidation method of a corresponding hydrocarbon, that is, propylene or isobutylene is mainly performed. Recently, a gas phase catalytic oxidation method using a corresponding alkane as a raw material instead of olefin has been studied.
[0003]
In the production of (meth) acrylic acid by the gas phase catalytic oxidation method, first, a reaction product gas containing (meth) acrylic acid is brought into contact with an absorbing solvent, usually water, and (meth) acrylic acid in the gas is converted to (meth). Collect as an acrylic acid solution. In this solution, in addition to (meth) acrylic acid, various impurities by-produced during gas phase catalytic oxidation, for example, in the case of acrylic acid, acetic acid, maleic acid, acrolein, furfural, benzaldehyde, acetone, etc. are also included. It is. A number of methods for recovering purified (meth) acrylic acid from this (meth) acrylic acid solution have been proposed, but the mainstream is the absorption solvent from the (meth) acrylic acid solution in the preliminary purification step And a part of the impurities are removed to obtain crude (meth) acrylic acid substantially composed of (meth) acrylic acid and its dimer and other heavy components, which are then purified in a purification step to obtain a desired quality. It is a method to make a product.
[0004]
Since (meth) acrylic acid is a substance that is easily polymerized, it is generally practiced to contain a polymerization inhibitor in the absorbing solvent. In addition, a polymerization inhibitor is added as necessary in the preliminary purification step and the purification step. As the polymerization inhibitor, various organic or inorganic compounds such as gaseous substances such as oxygen are known. Usually, oxygen and an organic or inorganic compound are often used in combination.
[0005]
[Problems to be solved by the invention]
When using an organic or inorganic compound as a polymerization inhibitor, these compounds are generally used as a solution. For example, in Japanese Patent Laid-Open No. 10-17524, an aqueous acetic acid solution obtained by distilling off water from a (meth) acrylic acid solution by a dehydration distillation in a pre-purification step is used as a polymerization inhibitor such as copper carbonate or copper hydroxide. The use of a solution prepared by dissolving a copper compound and hydroquinone is described. Although the polymerization inhibitor solution obtained by this method has excellent performance, the acetic acid component to be removed in the pre-purification step is brought into the system, which increases the purification load in the pre-purification step. There is. Therefore, the present invention intends to provide a method for producing (meth) acrylic acid free from such problems.
[0006]
[Means for Solving the Problems]
According to the present invention, a reaction product gas containing (meth) acrylic acid obtained by a gas phase catalytic oxidation reaction is brought into contact with an aqueous absorbing liquid, and (meth) acrylic acid in the gas is absorbed into the absorbing liquid. Collecting step, removing the absorbing solution and impurities from the resulting (meth) acrylic acid solution to obtain crude (meth) acrylic acid, and distilling (meth) acrylic acid by vacuum distillation When (meth) acrylic acid is produced through each step of the purification process for obtaining (meth) acrylic acid purified from crude (meth) acrylic acid by purification treatment, (meth) acrylic is generated in the vacuum source of the purification process. acid using a waste water containing a polymerization inhibitor solution was prepared by feeding subjected it to the absorption step after step, without introducing impurities to increase the purification load in the system, (meth) acrylic acid Yield of It can be improved.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, vapor phase catalytic oxidation and subsequent prepurification may be carried out by a conventional method. For example, in the case of acrylic acid, a one-stage oxidation method in which propylene is directly oxidized to acrylic acid and a two-stage oxidation method in which propylene is first oxidized to acrolein and acrolein is oxidized to acrylic acid are known. It can also be. A gas containing acrylic acid generated by vapor phase contact oxidation is brought into contact with water to recover acrylic acid as an aqueous acrylic acid solution, from which water, acetic acid and other impurities are removed by preliminary purification to obtain crude acrylic acid. These collection and preliminary purification steps may be carried out in accordance with conventional methods. For example, after dehydrating by azeotropic distillation, acetic acid and other low-boiling components can be removed by further distillation. The purity of the crude (meth) acrylic acid thus obtained is usually at least 85% by weight and in many cases 90% by weight. As a matter of course, a higher purity of the crude (meth) acrylic acid is preferable. Impurities contained in the crude (meth) acrylic acid are dimers of (meth) acrylic acid and other heavy components, and low-boiling components are substantially not contained.
[0008]
This crude (meth) acrylic acid is then further refined in a purification step to (meth) acrylic acid of the desired quality. Several purification methods have been proposed. In any method, (meth) acrylic acid purified by distillation under reduced pressure is obtained as a top distillate. Depending on the process, (meth) acrylic acid may be obtained as an intermediate overhead distillate by vacuum distillation in addition to this vacuum distillation in the purification step. As a vacuum source for these vacuum distillations, a steam ejector, a water ring vacuum pump or the like is generally used. By the way, (meth) acrylic acid corresponding to the vapor pressure at the condensation temperature flows into these vacuum sources, which cannot be condensed by the condenser of the distillation column. Therefore, (meth) acrylic acid is dissolved in the wastewater discharged from the vacuum source, such as the wastewater from the condenser of the steam ejector. However, this waste water contains almost no impurities that cause (meth) acrylic acid.
[0009]
In the present invention, this waste water is used as a solvent for dissolving the polymerization inhibitor. Thereby, (meth) acrylic acid in waste water can be recovered as a product, and the load on the purification system is not increased. As the polymerization inhibitor, various known organic and inorganic substances can be used. For example, phenolic compounds such as hydroquinone, hydroquinone monomethyl ether, pyrogallol, catechol and resorcin can be used. Also, tertiary butyl nitrooxide, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 2,2,6,6-tetramethylpiperidine-1-oxyl, 4,4 ′, 4 N-oxyl compounds such as “-tris- (2,2,6,6-tetramethylpiperidinooxyl) phosphite can also be used.
[0010]
Various metal compounds can also be used as polymerization inhibitors, but the most common are metal salts. For example, copper salts such as cupric chloride, copper acetate, copper carbonate, and copper acrylate, and manganese compounds such as manganese acetate and manganese octoate are used. In the present invention, it is preferable to use inexpensive copper carbonate or copper hydroxide. They are insoluble in water but readily dissolve in waste water from a vacuum source. This is considered to react with dissolved (meth) acrylic acid to form (meth) acrylate. The amount of the copper compound added to the waste water is arbitrary, but is usually 1 ppm by weight to 10% by weight. In addition, instead of the waste water containing (meth) acrylic acid obtained from the vacuum source of the purification process, the waste water generated in the vacuum source of the pre-purification process, for example, the vacuum source of the light boiling distillation column that removes acetic acid and other low-boiling components. Can also be used. However, in addition to (meth) acrylic acid, acetic acid is also dissolved in the wastewater, and the concentration of (meth) acrylic acid is usually low, so it is preferable to use wastewater from the vacuum source in the above-described purification process.
[0011]
The polymerization inhibitor solution prepared using waste water containing (meth) acrylic acid from a vacuum source is mainly added to an absorbing solution for collecting the reaction product gas. Thereby, the (meth) acrylic acid in the waste water of a vacuum source will be supplied to a refinement | purification system, and the yield of (meth) acrylic acid can be improved.
[0012]
【Example】
Gas phase contact of propylene using the apparatus shown in FIG. 1 comprising a collection tower (A), a dehydration tower (B), a light boiling removal tower (C), a purification tower (D), and a pyrolysis tower (E) The present invention will be described more specifically by taking as an example the case of obtaining purified acrylic acid from a reaction product gas containing acrylic acid obtained by an oxidation reaction. The reaction product gas is supplied to the collection tower (A), and about 0.6 kg of water is allowed to flow down from the top of the tower with respect to 1 kg of acrylic acid in the gas to absorb acrylic acid. From the collection tower (A), an acrylic acid solution containing about 1.7 kg of acrylic acid per liter of water is extracted and supplied to the dehydration tower (B). Further, a polymerization inhibitor solution is supplied to the collection tower so that the polymerization inhibitor concentration in the tower is kept constant. In the dehydration tower (B), azeotropic distillation is performed using an azeotropic agent, the gas flowing out from the top of the tower is condensed in a condenser, the condensate is stratified, and water is discharged out of the system. Return to. The bottom liquid of the dehydration tower is then supplied to the light boiling removal tower (C) and distilled under reduced pressure to distill off substantially all components having a lower boiling point than acetic acid and other acrylic acids. This distillation is usually carried out under mild pressure reduction so that acrylic acid is not distilled as much as possible. The liquid at the bottom of the light boiling removal tower (C) is supplied to the purification tower (D), and distilled and purified acrylic acid is distilled off under reduced pressure at a tower top pressure of 20 to 30 mmHg. A steam ejector is used as a vacuum source for the purification tower (D).
[0013]
The bottom liquid of the purification tower (D) is supplied to the pyrolysis tower (E), the light boiling fraction containing acrylic acid distilled from the top of the tower is supplied to the light boiling removal tower (C), and the heavy components are Discharge out of the system. In the case of producing acrylic acid purified at a production rate of 10,000 kg / Hr in the above process, cupric carbonate or acetic acid is added to the condensed water (acrylic acid concentration 10% by weight) of the steam ejector as the vacuum source of the purification tower (D). When a polymerization inhibitor solution prepared by dissolving 6000 ppm by weight of manganese and 5% by weight of hydroquinone was supplied to the collection tower (A) at 400 kg / Hr, it was 96 with respect to acrylic acid in the reaction product gas. Purified acrylic acid can be obtained with a yield of 6%. On the other hand, polymerization inhibition prepared by dissolving cupric carbonate or manganese acetate to 6000 wtppm and hydroquinone to 5 wt% in the waste water (acetic acid concentration 10 wt%) obtained from the top of the dehydration tower. When the agent solution is supplied at 400 kg / Hr, the yield of purified acrylic acid is only 96.1%.
[Brief description of the drawings]
FIG. 1 is an example of a flow sheet of an acrylic acid production process.
[Explanation of symbols]
A Collection tower B Dehydration tower C Light boiling removal tower D Purification tower E Thermal decomposition tower 1 Reaction product gas introduction pipe 2 Absorbed water introduction pipe 3 Polymerization inhibitor solution introduction pipe 4 Distilled water discharge pipe 5 Distillation light boiling substance discharge Pipe 6 Purified acrylic acid extraction pipe 7 Light boiling fraction extraction pipe 8 Heavy component extraction pipe

Claims (5)

  A reaction step of bringing a reaction product gas containing (meth) acrylic acid obtained by a gas phase catalytic oxidation reaction into contact with an aqueous absorbing solution and absorbing (meth) acrylic acid in the gas into the absorbing solution, was obtained The pre-purification step for obtaining the crude (meth) acrylic acid by removing the absorbing solution and impurities from the (meth) acrylic acid solution, and the purification process including distilling (meth) acrylic acid by distillation under reduced pressure ) When producing (meth) acrylic acid through each step of the purification process to obtain purified (meth) acrylic acid from acrylic acid, use waste water containing (meth) acrylic acid generated in the vacuum source of the purification process Preparing a polymerization inhibitor solution, supplying it to the steps after the collection step, and using at least a metal compound as the polymerization inhibitor.   The method of claim 1, wherein the vacuum source is a steam ejector.   The method according to claim 1 or 2, wherein the step after the collecting step is a collecting tower.   4. The method according to claim 1, wherein at least a copper compound is used as the polymerization inhibitor.   5. The method according to claim 1, wherein at least a metal carbonate or hydroxide is used as the polymerization inhibitor.

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