JP2009242285A - Method for producing acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for obtaining acrylic acid by separating it from an acrylic acid aqueous solution without distilling acrylic acid in a system where water exists. <P>SOLUTION: Acrylic acid is extracted from an acrylic acid aqueous solution by using as an extracting solvent a water-insoluble solvent comprising as a main ingredient a water-insoluble aromatic compound having a boiling point lower than the boiling point of acrylic acid, and evaporating the extracting solvent from the resultant extract liquid by distillation thereby to separate acrylic acid. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for producing acrylic acid, and more particularly to a method for producing acrylic acid including extraction of acrylic acid with an organic solvent and distillation for removing the organic solvent from the obtained extract.

  As a method for producing acrylic acid, an acrylic acid-containing gas produced by a gas phase catalytic oxidation reaction using propane, propylene or acrolein as a raw material is collected in a collection solvent such as water, and acrylic acid is obtained from the resulting acrylic acid aqueous solution. A method for separating an acid and purifying the separated acrylic acid by distillation under reduced pressure is generally known.

  As a method for producing such acrylic acid, for example, acrylic acid is extracted from an aqueous acrylic acid solution using a solvent containing an azeotropic hydrocarbon with acetic acid and an ester for increasing the extraction efficiency of acrylic acid as an extraction solvent. A method including a step and a step of dehydrating the obtained extract by distillation (see, for example, Non-Patent Document 1), and esters, ketones, alcohols, ethers having lower boiling points than acrylic acid, and In a step of extracting acrylic acid from an aqueous acrylic acid solution using one or more solvents of hydrocarbons as an extraction solvent, a step of distilling the obtained extract to separate the extraction solvent and acrylic acid, and an extraction step A method (for example, refer to Non-Patent Document 2) including a step of recovering the extraction solvent from the extraction residual liquid (aqueous phase) by distillation is known.

Thus, as a conventional method for producing acrylic acid, a method is known in which an extract containing water that can be dehydrated in the distillation after the extraction step is used for the distillation.
Eizo Omori, “Acrylic acid and its polymer [I]”, 3rd edition, Shosodo Co., Ltd., April 28, 1978, p. 13 Edited by The Petroleum Society of Japan, “New Petrochemical Process”, first edition, Koshobo, Inc., September 25, 1986, p. 193

  The present invention provides a method for producing acrylic acid that does not include a distillation step for dehydration of an acrylic acid component extracted from an aqueous acrylic acid solution.

  The present invention further provides a method for producing acrylic acid, in which one or both of the extraction efficiency in the acrylic acid extraction step and the distillation efficiency in the subsequent distillation step is further enhanced.

  In the production of acrylic acid, acrylic acid in an acrylic acid-containing gas generated by a gas phase catalytic oxidation reaction is generally collected by an aqueous medium mainly composed of water. Therefore, in the production of acrylic acid, acrylic acid tends to coexist with water.

However, the present inventors have found that when acrylic acid is subjected to distillation in the presence of water, acrylic acid is likely to be polymerized, and the resulting polymerized product can cause contamination and blockage of acrylic acid production facilities. It has been found that by extracting acrylic acid from an aqueous solution of acrylic acid using a water-insoluble solvent mainly composed of a water-soluble aromatic compound as an extraction solvent, the polymerization of acrylic acid in the production of acrylic acid is suppressed, Furthermore, it has been found that by using a specific non-aromatic compound in combination with the extraction solvent, the distillation efficiency in distillation for separating the extraction solvent from the extract can be improved, and the present invention has been completed.

  That is, the present invention includes an extraction step in which an acrylic acid aqueous solution containing acrylic acid and water is brought into contact with an extraction solvent to extract acrylic acid, and the resulting extract is distilled to evaporate the extraction solvent from the extract. A method of using a water-insoluble solvent, which contains a water-insoluble aromatic compound having a boiling point lower than that of acrylic acid as a main component, as the extraction solvent, in a method for producing acrylic acid including a solvent separation step for separating. To do.

  The present invention also provides the above method, wherein the water-insoluble aromatic compound is one or more selected from the group consisting of benzene, toluene, and xylene.

  Further, in the present invention, the water-insoluble solvent contains the water-insoluble aromatic compound and a non-aromatic compound of 25% by mass or less having a boiling point lower than that of acrylic acid, and the solvent separation The method of using the condensate of the extraction solvent vapor separated in the step as the extraction solvent in the extraction step is provided.

  The present invention also provides the above method, wherein the water-insoluble solvent contains 5 to 25% by mass of the non-aromatic compound.

  The present invention also provides the above method, wherein the non-aromatic compound is one or more selected from the group consisting of n-hexane, 1-hexene, cyclohexane, hexadiene, heptane, and heptene.

  In the extraction process for extracting acrylic acid from an aqueous acrylic acid solution with an extraction solvent, the present invention uses a water-insoluble solvent mainly composed of a water-insoluble aromatic compound as the extraction solvent. As a result, an acrylic acid is prevented from being subjected to distillation in the presence of water in the subsequent distillation. Therefore, compared to the conventional acrylic acid production method in which acrylic acid is subjected to distillation in the presence of water, the obstacle of the acrylic acid production facility due to the acrylic acid polymer is further suppressed, and acrylic acid can be used for a long time. It can be manufactured stably and continuously.

  In the present invention, a water-insoluble aromatic compound containing a water-insoluble aromatic compound and 25% by mass or less of a non-aromatic compound is used as the extraction solvent. The amount of acrylic acid mixed into the condensate by azeotropy with the extraction solvent can be further reduced as compared with the case of using only the extraction solvent. Therefore, in the present invention, the use of the water-insoluble solvent containing a water-insoluble aromatic compound and a water-insoluble aromatic compound as an extraction solvent further reduces the distillation reflux ratio in the solvent separation step, thereby reducing the distillation efficiency. Is more effective from the viewpoint of increasing

  Further, in the present invention, the concentration of acrylic acid in the condensate when the condensate in the distillation in the solvent separation process is reused as the extraction solvent is lower than when only the water-insoluble aromatic compound is used as the extraction solvent. From the above, the use of the water-insoluble solvent containing a water-insoluble aromatic compound and a water-insoluble aromatic compound as the extraction solvent means that the extraction efficiency of acrylic acid in the extraction process when the condensate is reused as the extraction solvent Is more effective from the viewpoint of increasing

  In the present invention, the use of a solvent containing 5 to 25 mass% of the non-aromatic compound as the water-insoluble solvent reduces the amount of acrylic acid mixed into the condensed liquid by azeotropy with the extraction solvent. Is even more effective.

  The method for producing acrylic acid according to the present invention comprises an extraction step in which an acrylic acid aqueous solution containing acrylic acid and water is brought into contact with an extraction solvent to extract acrylic acid, and the resulting extract is distilled and extracted from the extract. A solvent separation step of evaporating and separating the solvent.

  In the extraction step, a water-insoluble solvent containing a water-insoluble aromatic compound having a boiling point lower than that of acrylic acid as a main component is used as the extraction solvent. The water-insoluble solvent is a solvent having a water solubility at 20 ° C. of 1.5% by mass or less. The water solubility of the water-insoluble solvent at 20 ° C. is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, from the viewpoint of suppressing mixing of water into the extract. .

  The water-insoluble solvent contains a water-insoluble aromatic compound as a main component. The water-insoluble solvent may contain components other than the water-insoluble aromatic compound, but from the viewpoint of sufficiently obtaining the action of extracting acrylic acid and water-insoluble, the water-insoluble aromatic compound is most often used. Contains a lot. The water-insolubility of the water-insoluble solvent can be adjusted by, for example, the content of a water-insoluble aromatic compound described later.

  The water-insoluble aromatic compound has a boiling point lower than that of acrylic acid. From the viewpoint of sufficiently separating the extraction solvent by distillation in the solvent separation step, the boiling point of the water-insoluble aromatic compound is preferably 140 ° C. or less, more preferably 130 ° C. or less at normal pressure, and 120 ° C. More preferably, it is as follows. The lower limit of the boiling point of the water-insoluble aromatic compound is not particularly limited, but it is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, from the viewpoint of suppressing discharge from the system due to the distillation. More preferably, the temperature is 100 ° C. or higher.

  The water-insoluble aromatic compound is a solvent having a water solubility at 20 ° C. of 1.5% by mass or less. The water solubility of the water-insoluble aromatic compound at 20 ° C. is preferably 1.0% by mass or less, and preferably 0.5% by mass or less, from the viewpoint of suppressing the mixing of water into the extract. More preferred.

  The content of the water-insoluble aromatic compound in the water-insoluble solvent is preferably 60% by mass or more from the viewpoint of sufficiently extracting acrylic acid and suppressing the mixing of water into the extract. More preferably, the content is at least 80% by mass, and even more preferably at least 80% by mass. The water-insoluble aromatic compound may be one kind or two or more kinds.

  Examples of the water-insoluble aromatic compound include benzene, toluene, xylene, ethylbenzene, and mesitylene. The water-insoluble aromatic compound is preferably at least one selected from the group consisting of benzene, toluene, and xylene.

  The water-insoluble solvent preferably further contains a non-aromatic compound having a boiling point lower than that of acrylic acid from the viewpoint of reducing the concentration of acrylic acid in the condensate in the solvent separation step. The boiling point of the non-aromatic compound is preferably 140 ° C. or lower at normal pressure, more preferably 130 ° C. or lower, and 115 ° C. or lower from the viewpoint of sufficiently separating the extraction solvent by distillation in the solvent separation step. More preferably. The lower limit of the boiling point of the non-aromatic compound is not particularly limited, but is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, from the viewpoint of suppressing discharge from the system due to the distillation. More preferably, the temperature is higher than or equal to ° C.

The non-aromatic compound is preferably water-insoluble from the viewpoint of suppressing the mixing of water into the extract. For example, the water solubility of the non-aromatic compound at 20 ° C. is 1.5% by mass or less. It is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less.

  The content of the non-aromatic compound is sufficient to extract acrylic acid with a non-water-soluble solvent and reduce the concentration of acrylic acid in the condensate in the solvent separation step, with respect to the whole water-insoluble solvent. It is preferably 25% by mass or less, more preferably 5 to 25% by mass, and further preferably 10 to 20% by mass. The upper limit of the content of the non-aromatic compound can be determined from the viewpoint of extraction efficiency of acrylic acid, and the lower limit of the content of the non-aromatic compound is in distillation of acrylic acid and a water-insoluble aromatic compound. It can be determined from the viewpoint of separation efficiency. The non-aromatic compound may be one type or two or more types.

  Examples of the non-aromatic compound include n-hexane, 1-hexene, cyclohexane, hexadiene, heptane, and heptene. The non-aromatic compound is preferably a saturated or unsaturated hydrocarbon having 5 to 7 carbon atoms, and more preferably an aliphatic hydrocarbon. Examples of such non-aromatic compounds include n-hexane and 1-hexene.

  Specific examples of the water-insoluble solvent include, for example, toluene, a toluene-n-hexane solution containing 10% by mass of n-hexane in toluene, and a toluene-1-hexene solution containing 10% by mass of 1-hexene in toluene. Toluene-cyclohexane solution containing 10% by mass of cyclohexane in toluene, toluene-hexadiene solution containing 10% by mass of hexadiene in toluene, toluene-heptane solution containing 10% by mass of heptane in toluene, and 10% of heptene in toluene % Toluene-heptene solution.

  The concentration of acrylic acid in the aqueous acrylic acid solution is preferably 20 to 90% by mass, more preferably 30 to 80% by mass, and still more preferably 50 to 70% by mass. As such an acrylic acid aqueous solution, an acrylic acid aqueous solution obtained in a collection step of collecting acrylic acid in an aqueous medium from a reaction product gas by a gas phase catalytic oxidation reaction such as propane in the production of acrylic acid is used. Examples thereof include a mixture of acrylic acid and water, and a mixture of water component and acrylic acid discharged and recovered in the process of producing acrylic acid. As the water component, for example, extracted residual water in the extraction step can be mentioned.

  The said extraction process can be performed using the normal extraction apparatus used for liquid-liquid contact extraction. The extraction device is preferably an extraction device having a theoretical plate number of 5 or more from the viewpoint of sufficiently bringing the aqueous acrylic acid solution and the water-insoluble solvent into contact with each other. As such an extraction device, for example, as disclosed in JP-A-2002-58903, a cylindrical portion, a drive shaft that is disposed in the cylindrical portion and can reciprocate in the axial direction of the cylindrical portion, and the axial direction A reciprocating plate countercurrent extraction device having a plurality of perforated plates that are fixed to the drive shaft side by side and a drive unit that reciprocates the drive shaft in the axial direction can be used.

  The temperature of the acrylic acid aqueous solution in the extraction step is preferably 5 to 80 ° C, more preferably 10 to 60 ° C, and further preferably 20 to 50 ° C. Moreover, it is preferable that the temperature of the water-insoluble solvent in an extraction process is 5-80 degreeC, It is more preferable that it is 10-60 degreeC, It is further more preferable that it is 20-50 degreeC. Furthermore, the ratio of the supply amount of the water-insoluble solvent to the aqueous acrylic acid solution in the extraction step is preferably 1 to 5, more preferably 1 to 3.5, and 1.2 to 2.5. More preferably.

The solvent separation step can be performed under a condition that the extraction solvent is evaporated by distillation under reduced pressure using a distillation apparatus usually used in the production of acrylic acid, and acrylic acid is obtained as a bottoms. In the solvent separation step, acrylic acid can be obtained as a liquid descending the rectifying column in the distillation apparatus or as a bottoms.

  As the distillation apparatus, for example, a rectification column, a reboiler for heating and evaporating the bottom liquid of the rectification column, and a condenser for condensing the vapor discharged from the top of the rectification column were obtained. Examples thereof include an apparatus having a receiver for containing condensate, a vacuum device for reducing the pressure in the rectifying column, and a polymerization inhibitor supplying device for supplying a polymerization inhibitor into the rectifying column.

  One or both of a tray and a packing can be accommodated in the rectification column. One or both of regular packing and irregular packing can be used for the packing. Examples of the tray include a bubble bell tray, a perforated plate tray, a valve tray, a super flash tray, a max flux tray, and a dual flow tray. Examples of the regular packing include a Sulzer Pack manufactured by Sruzer Brothers Co., Ltd., Sumitomo Sulzer Packing manufactured by Sumitomo Heavy Industries, Ltd., Mera Pack manufactured by Sumitomo Heavy Industries, Ltd., and Glitch Co., Ltd. Gem Pack, Monz Pack manufactured by Monz Co., Ltd. Good Roll Packing manufactured by Tokyo Special Wire Mesh Co., Ltd., Honeycomb Pack manufactured by NGK Co., Ltd., Impulse Packing manufactured by Nagaoka Co., Ltd., and Mitsubishi Chemical Engineering Co., Ltd. MC packs made by the manufacturer are listed. Examples of the irregular packing include an interlock saddle manufactured by Norton Co., Ltd., a terrarette manufactured by Nippon Steel Chemicals Co., Ltd., a pole ring manufactured by BASF Co., Ltd., and a cascade mini-manufactured manufactured by Mass Transfer Co., Ltd. Examples include rings and flexi rings made by JGC Corporation.

  As the polymerization inhibitor, a polymerization inhibitor that is usually used in the production of acrylic acid can be used. For example, phenols such as hydroquinone and methoquinone as described in JP-A-2005-336141 are used. , Nitroso compound, copper salt, manganese salt, phenothiazine and the like.

  As distillation conditions in the solvent separation step, for example, the theoretical plate number of the rectification column is 5 to 20, the column top temperature of the rectification column is 10 to 80 ° C., and the column bottom temperature of the rectification column is 60 to 60 ° C. It is 110 degreeC, the conditions (reflux ratio) of the reflux liquid with respect to the distillate of the condensate obtained by distillation are 0.3-2, and the conditions that the pressure in a rectification column is 5-70 kPa (Abs). Can be mentioned.

  In the solvent separation step, the extraction solvent is discharged as vapor from the top of the rectification column. It is preferable that a part of the condensate condensed with the vapor (distillate) is reused as the extraction solvent in the extraction step. In particular, in the solvent separation step, when the distillation is performed under the same conditions, the acrylic acid in the condensate in the distillation using the water-insoluble solvent A containing the water-insoluble aromatic compound and the water-insoluble aromatic compound is used. A density | concentration becomes smaller than the density | concentration of the acrylic acid in the condensed liquid in the distillation using the water-insoluble solvent B which consists of a water-insoluble aromatic compound.

  Therefore, when the condensate is reused as the extraction solvent, the condensate of the water-insoluble solvent A can contain more acrylic acid in the extraction step than the condensate of the water-insoluble solvent B. Therefore, the water-insoluble solvent A can further improve the extraction efficiency of acrylic acid in the extraction process when the condensate is reused as the extraction solvent, compared to the water-insoluble solvent B.

  In the solvent separation step, when the concentration of acrylic acid in the condensate is set to a constant value, the reflux ratio of distillation using the water-insoluble solvent A in the solvent separation step is changed to the water-insoluble solvent B. It can be made smaller than the reflux ratio of distillation. Therefore, in the solvent separation step, the distillation using the water-insoluble solvent A can further increase the distillation efficiency as compared with the distillation using the water-insoluble solvent B.

  The method for producing acrylic acid of the present invention may further include steps other than the extraction step and the solvent separation step described above. Examples of such other steps include various steps usually performed in the production of acrylic acid, for example, a step of producing acrylic acid by a gas phase catalytic oxidation reaction of propane, propylene, or acrolein; A step of bringing an acid-containing gas into contact with an aqueous medium and collecting acrylic acid from the gas; a step of purifying acrylic acid obtained in the solvent separation step by distillation; a effluent of the solvent separation step or the purification step A step of recovering acrylic acid by thermally decomposing high-boiling substances in the medium; and a step of recovering valuable materials from the extraction residual liquid of the extraction step.

  The high boiling point is a compound having a boiling point higher than that of acrylic acid, and examples of the high boiling point include a dimer of acrylic acid and a trimer of acrylic acid. Valuables are compounds that are evaporated together with water by distillation and recovered as a condensate, and examples thereof include acrylic acid and acetic acid.

  In the production step, one or both of a multitubular reactor and a plate reactor can be used for the gas phase catalytic oxidation reaction. Examples of the multitubular reactor include a shell having a gas vent at both ends and a heat medium vent at the body, as disclosed in JP-A-2005-336085, A tube plate that divides the inside into two end portions and a body portion, and a plurality of reaction tubes that pass through the body portion in the shell and communicate with the both end portions in the shell and that are supported at both ends by the tube plate and contain the catalyst. And a reactor having a device for circulating a heat medium in the shell of the shell. As the plate reactor, for example, a partition formed by connecting a plurality of tubes having a rugby ball type cross-sectional shape at end portions of the cross-sectional shape as disclosed in Japanese Patent Application Laid-Open No. 2004-202430. And a catalyst that is held between two partitions in the reaction section, and a device that supplies a heat medium to the pipe in the partition, wherein the gaseous raw material is a pipe in the partition. And a reactor that passes through the reaction section along the direction crossing.

As the catalyst in the production step, a catalyst that can be used in a gas phase catalytic oxidation reaction in the production of acrylic acid is used. Examples of such a catalyst include a Mo—Bi composite oxide catalyst represented by the following general formula (I) and the following general formula (II) as disclosed in JP-A-2005-336085. The Mo-V type complex oxide catalyst represented by these is mentioned.
General formula (I) MoaWbBicFedAeBfCgDhEiOx
Formula (II) MoaVbWcCudXeYfOg

  In the general formula (I), A is one or both of nickel and cobalt, B is one or more elements selected from sodium, potassium, rubidium, cesium and thallium, and C is one or more selected from alkaline earth metals Wherein D is one or more elements selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic, boron and zinc, and E is one or more selected from silicon, aluminum, titanium and zirconium And O represents oxygen. In the general formula (I), a, b, c, d, e, f, g, h, i and x are Mo, W, Bi, Fe, A, B, C, D, E and Represents the atomic ratio of O. When a = 12, 0 ≦ b ≦ 10, 0 <c ≦ 10 (preferably 0.1 ≦ c ≦ 10), 0 <d ≦ 10 (preferably 0.1 ≦ d ≦ 10) 2 ≦ e ≦ 15, 0 <f ≦ 10 (preferably 0.001 ≦ f ≦ 10), 0 ≦ g ≦ 10, 0 ≦ h ≦ 4, 0 ≦ i ≦ 30, and x is each element It is a value determined by the oxidation state of.

In the general formula (II), X is one or more elements selected from Mg, Ca, Sr and Ba, Y is Ti, Zr, Ce, Cr, Mn, Fe, Co, Ni, Zn, Nb, Sn, Sb , Pb and Bi, O represents oxygen. In the general formula (II), a and b
, C, d, e, f and g represent the atomic ratios of Mo, V, W, Cu, X, Y and O, respectively, and when a = 12, 2 ≦ b ≦ 14, 0 ≦ c ≦ 12 0 <d ≦ 6, 0 ≦ e ≦ 3, 0 ≦ f ≦ 3, and g is a numerical value determined by the oxidation state of each element. Is mentioned.

  Other steps such as the collection step, the purification step, the acrylic acid recovery step, and the valuable material recovery step can be performed using the distillation apparatus or the rectification column.

  In the method for producing acrylic acid according to the present invention, for example, as shown in FIG. 1, collection is performed by collecting acrylic acid from a reaction gas by bringing a reaction gas containing acrylic acid generated in a reactor into contact with an aqueous medium. An extraction tower 2 for extracting acrylic acid into the extraction solvent by bringing the acrylic acid aqueous solution produced in the tower 1 and the collection tower 1 into contact with the extraction solvent; It can carry out by the installation which has the solvent separation tower 3 isolate | separated into acrylic acid. The facility includes a valuable material separation device that separates a valuable material from the extracted residue discharged from the bottom of the extraction tower 2, and pyrolyzes high-boilers in the bottoms of the solvent separation tower 3 to remove the bottoms. You may have further the thermal decomposition apparatus which collect | recovers acrylic acids from a liquid.

  As the collection tower 1 and the solvent separation tower 3, for example, a plate tower is used. For the extraction tower 2, for example, the reciprocating plate type countercurrent extraction device is used.

  The reaction gas obtained in the reactor is supplied to the collection tower 1 from the bottom of the tower and comes into contact with the aqueous medium supplied from the top of the collection tower 1 in the collection tower 1. By this contact, the acrylic acid in the reaction gas is dissolved and collected in the aqueous medium, and the generated aqueous acrylic acid solution is discharged from the bottom of the collection tower 1. Moreover, the reaction gas after acrylic acid is collected is discharged from the top of the collection tower 1 as exhaust gas.

  The obtained aqueous acrylic acid solution is supplied to the extraction tower 2 from the top of the extraction tower 2 and becomes a droplet state by the vertical movement of the perforated plate in the extraction tower 2. It contacts with the extraction solvent supplied to the extraction tower 2 from the bottom part of 2 towers. As the extraction solvent, for example, a water-insoluble solvent containing toluene as a main component is used. By this contact, acrylic acid in the aqueous acrylic acid solution is extracted into the extraction solvent, and the produced extract is discharged from the top of the extraction tower 2. Further, the acrylic acid aqueous solution extracted from the acrylic acid and lowered to the bottom of the extraction tower 2 is discharged from the bottom of the extraction tower 2 as a residual extraction liquid.

  The obtained extract is supplied to the solvent separation tower 3 from the middle or lower part of the solvent separation tower 3 and distilled under reduced pressure. Since the obtained extract contains almost no water, vacuum distillation is performed in a system in which acrylic acid is present but water is not present. For this reason, in the solvent separation column 3, generation | occurrence | production of the polymer of acrylic acid is prevented and vacuum distillation is performed stably for a long period of time. By this vacuum distillation, the vapor of the extraction solvent in the extract is discharged from the top of the solvent separation tower 3. Further, a part of the descending liquid in the recovery section in the solvent separation tower 3 is discharged from the solvent separation tower 3 as product acrylic acid. Further, a part of the bottom liquid of the solvent separation tower 3 is discharged from the bottom of the solvent separation tower 3 as a bottoms.

  More specifically, as shown in FIG. 2, the extracted solvent vapor discharged from the top of the solvent separation tower 3 is cooled by a condenser 4 to become a condensate. A part of the condensate obtained is returned to the upper part of the solvent separation tower 3 as a reflux liquid, and the rest is supplied as a distillate to the bottom of the extraction tower 2 and reused as an extraction solvent. A part of the bottom liquid of the solvent separation tower 3 is heated by the reboiler 5 and returned to the bottom of the solvent separation tower 3, and the rest is withdrawn as a bottoms. This liquid may be supplied to the thermal decomposition apparatus to recover valuable materials.

In the distillate, for example, when toluene is used as the extraction solvent, acrylic acid having a concentration of several thousand ppm is azeotropically contained. For example, when a mixed solvent of 20% by mass of n-hexane and toluene is used as the extraction solvent, the concentration of acrylic acid mixed into the distillate by azeotropic distillation is higher than that when the extraction solvent is only toluene. It becomes about 2/3. For this reason, when the mixed solvent is used as an extraction solvent, the concentration of acrylic acid in the distillate is kept below a certain value even when the reflux ratio is lowered, compared with the case where an extraction solvent containing only toluene is used. be able to. Or, when the mixed solvent is used as an extraction solvent, the concentration of acrylic acid in the distillate should be reduced by several thousand ppm without increasing the reflux ratio, compared with the case where an extraction solvent containing only toluene is used. Therefore, the extraction efficiency of acrylic acid in the extraction process when such a distillate is reused as the extraction solvent can be further enhanced. Or, when the mixed solvent is used, both of these effects can be achieved by adjusting the reflux ratio.

  A part of the extraction liquid discharged from the bottom of the extraction tower 2 is reused as an aqueous medium supplied to the top of the collection tower 1. Further, a part of the extraction residual liquid may be supplied to the valuable material separation device to collect the valuable material.

  Although not shown in FIG. 1, for example, the bottoms discharged from the bottom of the solvent separation tower 3 and supplied to the thermal decomposition apparatus are heated by the thermal decomposition apparatus, and the acrylic acid in the bottoms is discharged. A polymer of acrylic acid such as a monomer is decomposed by heat, and acrylic acid generated by the decomposition is discharged from the top of the thermal decomposition apparatus. The obtained acrylic acid component is supplied to the extract supplied to the solvent separation tower 3 and used as a raw material liquid in the solvent separation step. The tower bottom liquid of the thermal decomposition apparatus is discharged out of the system as a high boiling point component (Heavy End).

  Moreover, the manufacturing method of acrylic acid of this invention can be performed with the installation shown in FIG. This equipment is the same as the equipment shown in FIG. 1 except that it has a solvent separation tower 6 instead of the solvent separation tower 3 and further has a purification tower 7.

  In the solvent separation tower 6, the extract is supplied to the solvent separation tower 6 from the middle or lower part of the solvent separation tower 6 and distilled under reduced pressure. By this vacuum distillation, the vapor of the extraction solvent in the extract is discharged from the top of the solvent separation tower 6. In addition, acrylic acid in the extract is discharged from the bottom of the solvent separation tower 3 as a bottoms. Also in the solvent separation tower 6, the vapor of the extraction solvent discharged from the top of the solvent separation tower 6 is cooled by a condenser to become a condensate, and a part of the obtained condensate is used as a reflux liquid based on a desired reflux ratio. The solvent is returned to the upper part of the solvent separation tower 3, and the remainder is supplied as a distillate to the bottom of the extraction tower 2 and reused as the extraction solvent. The bottoms of the solvent separation tower 6 is supplied to the purification tower 7 as an acrylic acid component.

  The acrylic acid component supplied to the purification tower 7 is supplied from the upper part of the purification tower 7 to the purification tower 7 and distilled under reduced pressure. By this vacuum distillation, low-boiling substances having a boiling point lower than the boiling point of acrylic acid in the acrylic acid component are evaporated and discharged from the top of the purification tower 7, and acrylic acid in the acrylic acid component passes through the purification tower 7. By descending and discharging a part of the liquid descending the purification tower 7 in the recovery section of the purification tower 7, product acrylic acid is obtained.

  According to the above-mentioned method for producing acrylic acid, an extract containing almost no water can be obtained by using a water-insoluble solvent mainly composed of a water-insoluble aromatic compound such as toluene as the extraction solvent. Since water is not included in the distillation in the system containing acrylic acid in the steps after the extraction step, polymerization of acrylic acid due to distillation in the presence of water can be prevented, and the production of acrylic acid can be stabilized for a long time. Can be done.

Further, according to the above-mentioned method for producing acrylic acid, when a water-insoluble mixed solvent of a water-insoluble aromatic compound and a non-aromatic compound such as n-hexane is used as an extraction solvent, only the water-insoluble aromatic compound is used. The concentration of acrylic acid in the condensate in the distillation in the solvent separation step can be reduced as compared with the case of using this extraction solvent. Therefore, when a set value of the concentration of acrylic acid in the condensate is provided, the distillation efficiency can be increased by lowering the reflux ratio in the distillation as compared with the case where an extraction solvent containing only a water-insoluble aromatic compound is used. Alternatively, the extraction efficiency when the distillate is reused as the extraction solvent can be increased, or both of them can be increased.

[Examination of distillation efficiency]
A toluene solution containing 5,000 ppm by mass of acrylic acid was distilled under reduced pressure under the condition of a pressure of 100 mmHg, and the concentration of acrylic acid in the condensate when the total amount of the condensate was refluxed was measured. The mass was ppm. The toluene solution was distilled under reduced pressure at a pressure of 200 mmHg, and the concentration of acrylic acid in the distillate when the total amount of the condensate was refluxed was 7,000 ppm by mass.

  Further, a toluene-hexane solution obtained by adding n-hexane to the toluene solution so as to have a content of 20% by mass was distilled under reduced pressure under the condition of a pressure of 100 mmHg, and the distillate obtained when the total amount of the condensate was refluxed. When the density | concentration of acrylic acid in was measured, it was 2,000 ppm. In addition, a toluene-hexene solution in which 1-hexene was added to the toluene solution so as to have a content of 20% by mass was distilled under reduced pressure under the condition of a pressure of 100 mmHg, and the distillate when the total amount of the condensate was refluxed. The concentration of acrylic acid in the liquid was measured and found to be 2,000 ppm.

[Examination of extraction efficiency]
A toluene solution containing 4,500 mass ppm of acrylic acid, a toluene-hexane solution obtained by adding n-hexane to the toluene solution so that the content is 25% by mass, and a content of 25 in the toluene solution. Extraction of acrylic acid from an aqueous acrylic acid solution was performed using each toluene-hexene solution added with 1-hexene so as to be mass% as an extraction solvent, and the amount of acrylic acid extracted into the extraction solvent was measured. . A 500 mL glass flask equipped with a stirrer is used as the extraction device, and the extract and the extractant are put into this flask in a 1: 1 ratio (volume ratio), stirred, and then allowed to stand, so that the extraction temperature is 25 ° C. Liquid-liquid equilibrium measurement was performed at The results are shown in FIG.

  As is apparent from FIG. 4, the amount of acrylic acid extracted from the aqueous acrylic acid solution into the extraction solvent was higher in the order of toluene solution, toluene-hexene solution, and toluene-hexane solution. When the mass ratio of acrylic acid to water in the aqueous acrylic acid solution is mass ratio A and the mass ratio of acrylic acid to the extraction solvent of the extract is mass ratio B, the ratio of mass ratio B to mass ratio A (B / A) When the concentration of acrylic acid in the aqueous acrylic acid solution is high, for example, when the mass ratio A is 0.3, there is a maximum difference of about 0.1 between the three, but the acrylic acid in the aqueous acrylic acid solution When the concentration of is low, for example, when the mass ratio of acrylic acid to water is 0.02 or less, the difference between the three is as small as about 0.02. That is, in the extraction device, the contact between the extraction solvent and the aqueous acrylic acid solution is repeatedly performed, and the concentration of acrylic acid in the aqueous acrylic acid solution decreases with extraction, but immediately before the aqueous acrylic acid solution is discharged from the extraction device, That is, at the end of extraction, the extraction efficiency of the three parties is almost the same.

[Example 1]
Using an extraction device and a distillation device, extraction of acrylic acid from the aqueous acrylic acid solution and separation of the acrylic acid component by vacuum distillation of the resulting extract were performed.

The extraction device includes a cylindrical portion, a drive shaft that is disposed in the cylindrical portion and can reciprocate in the axial direction of the cylindrical portion, a plurality of perforated plates that are aligned with the axial direction and fixed to the drive shaft, and a drive shaft. A reciprocating plate countercurrent extraction device having a theoretical plate number of 7 and having a drive unit that reciprocates in the axial direction was used. The vacuum distillation includes a rectification column, a reboiler for heating and evaporating a part of the bottom liquid of the rectification column, a condenser for condensing the vapor discharged from the top of the rectification column, and The distillation apparatus which has the receiver which accommodates the obtained condensate, and the vacuum apparatus which decompresses the inside of a rectification column, and a part of condensate is supplied to a rectification column as a reflux liquid was used. As the rectifying column, a plate column having 30 theoretical plates was used. And the continuous operation was performed on condition of the following.

An acrylic acid aqueous solution having the following composition and a temperature of 25 ° C. was supplied from the top of the extraction apparatus to the extraction apparatus at 0.098 kg / h. In addition, a liquid having a temperature of 25 ° C., a water solubility at 20 ° C. of 0.1% by mass, and having toluene as a main component and having the following composition is extracted from the bottom of the extraction apparatus as an extraction solvent 1. The apparatus was fed at 0.229 kg / h. <Acrylic acid aqueous solution>
Acrylic acid 59 parts by weight Acetic acid 1 part by weight Water 39 parts by weight <Extraction solvent 1>
Toluene 99 parts by mass Acrylic acid 0.45 parts by mass Acetic acid 0.5 parts by mass

From the top of the extraction apparatus, Extract 1 having the following composition was discharged at 0.287 kg / h and supplied to the rectification tower of the distillation apparatus. From the bottom of the extraction apparatus, the extraction liquid 1 having the following composition was discharged at 0.039 kg / h.
<Extract 1>
Toluene 80 parts by mass Acrylic acid 20 parts by mass Acetic acid 0.4 parts by mass <Extracted liquid 1>
Water 96 parts by weight Acrylic acid 2.9 parts by weight Acetic acid 2.5 parts by weight Toluene 0.3 parts by weight

In the vacuum distillation, the tower top temperature is 57 ° C., the tower bottom temperature is 89 ° C., the tower top pressure is 16 kPa (Abs), and the reflux ratio, which is the ratio of the flow rate of the reflux liquid to the distillate, is 1. And a condition 1 in which a 5 mass% phenothiazine-containing toluene solution as a polymerization inhibitor was supplied to the rectification column at 0.001 kg / h. By this distillation under reduced pressure, an acrylic acid component having the following composition was obtained as a bottom liquid at 0.058 kg / h.
<Acrylic acid component>
Acrylic acid 98.5 parts by mass Toluene 1.5 parts by mass

Further, by distillation under reduced pressure, a distillate 1 having the following composition was obtained at 0.229 kg / h. The obtained distillate was supplied as an extraction solvent to the bottom of the extraction apparatus.
<Distillate 1>
Toluene 99 parts by mass Acetic acid 0.5 parts by mass Acrylic acid 0.45 parts by mass

The acrylic acid component was continuously produced from the aqueous acrylic acid solution for 4 hours by the above-described extraction, distillation under reduced pressure, and reuse of the distillate. After the continuous operation, the inside of the rectification column was inspected, and no acrylic acid polymer was found. The extraction efficiency of acrylic acid in this continuous operation (
([Acrylic acid amount in the lotion] − [Acrylic acid amount in the residual solution]) / [Acrylic acid amount in the lotion] × 100) was 98.1%.

[Example 2]
Except that the extraction solvent 2 having the following composition was used in place of the extraction solvent 1, extraction of acrylic acid and separation of the acrylic acid component were performed in the same manner as in Example 1. The solubility of water at 20 ° C. of the extraction solvent 2 was 0.1% by mass. Further, by using the extraction solvent 2, an extract 2a having the following composition was obtained from the top of the extraction apparatus, and a residual extraction liquid 2 having the following composition was obtained from the bottom of the extraction apparatus.
<Extraction solvent 2>
Toluene 79.2 parts by mass n-hexane 19.8 parts by mass Acrylic acid 0.3 parts by mass Acetic acid 0.5 parts by mass <Extract 2a>
Toluene 64 parts by mass Acrylic acid 20.6 parts by mass n-hexane 16 parts by mass Acetic acid 0.4 parts by mass <Extracted liquid 2>
Water 96 parts by mass Acrylic acid 2 parts by mass Acetic acid 2.5 parts by mass Toluene 0.2 parts by mass n-hexane 0.1 parts by mass

The vacuum distillation was performed under the same condition 2 as the condition 1 in Example 1. Distilled liquid 2 having the following composition was obtained at 0.229 kg / h by vacuum distillation under this condition 2. The obtained distillate 2 was supplied to the tower bottom of the extraction apparatus as an extraction solvent.
<Distillate 2>
Toluene 79.2 parts by mass n-hexane 19.8 parts by mass Acetic acid 0.5 parts by mass Acrylic acid 0.3 parts by mass

With continuous operation of the extraction and distillation under reduced pressure, the extraction solvent is replaced with the distillate 2, and thereafter, an extract 2b having the following composition is obtained at 0.229 kg / h from the top of the extractor, Feeded to the distillation apparatus.
<Extract 2b>
Toluene 64 parts by mass Acrylic acid 20.6 parts by mass n-hexane 16 parts by mass Acetic acid 0.4 parts by mass

  The acrylic acid component was continuously produced from the aqueous acrylic acid solution for 4 hours by the above-described extraction, distillation under reduced pressure, and reuse of the distillate. After the continuous operation, the inside of the rectification column was inspected, and no acrylic acid polymer was found. The extraction efficiency of acrylic acid in this continuous operation was 98.7%.

It is a figure which shows an example of the equipment used for the manufacturing method of acrylic acid of this invention. It is a figure which expands and shows the principal part of FIG. It is a figure which shows the other example of the equipment used for the manufacturing method of acrylic acid of this invention. It is a figure which shows the relationship between the density | concentration of the acrylic acid of acrylic acid aqueous solution, and the quantity of acrylic acid extracted by an extraction solvent when acrylic acid is extracted from acrylic acid aqueous solution with an extraction solvent.

Explanation of symbols

1 Collection Tower 2 Extraction Tower 3, 6 Solvent Separation Tower 4 Capacitor 5 Reboiler 7 Purification Tower

Claims (5)

An extraction step of extracting acrylic acid by bringing an aqueous solution of acrylic acid containing acrylic acid and water into contact with an extraction solvent;
In the method for producing acrylic acid, including a solvent separation step of distilling the obtained extract and evaporating the extraction solvent from the extract to separate it,
A method for producing acrylic acid, wherein a water-insoluble solvent containing a water-insoluble aromatic compound having a boiling point lower than that of acrylic acid as a main component is used as the extraction solvent.   The method for producing acrylic acid according to claim 1, wherein the water-insoluble aromatic compound is at least one selected from the group consisting of benzene, toluene, and xylene. The water-insoluble solvent contains the water-insoluble aromatic compound and 25% by mass or less of a non-aromatic compound having a boiling point lower than that of acrylic acid,
And the manufacturing method of acrylic acid of Claim 1 or 2 using the condensate of the vapor | steam of the extraction solvent isolate | separated at the said solvent separation process for the extraction solvent of the said extraction process.   The said water-insoluble solvent contains 5-25 mass% of said non-aromatic compounds, The manufacturing method of acrylic acid of Claim 3 characterized by the above-mentioned.   5. The production of acrylic acid according to claim 3, wherein the non-aromatic compound is one or more selected from the group consisting of n-hexane, 1-hexene, cyclohexane, hexadiene, heptane, and heptene. Method.

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