MXPA98005111A - Method for the recovery of acid acril - Google Patents

Abstract

The present invention relates to a method for recovering acrylic acid from high boiling point impurities containing dimer of acrylic acid, acrylic acid and maleic acid, with high efficiency and stability. The method is characterized in that it comprises: (1) introducing the high boiling point impurities containing acrylic acid, acrylic acid and maleic acid dimer to a column for the recovery of acrylic acid, distilling the acrylic acid through the top of the column and recovering the same, (2) introducing the liquid A of bottoms of that column for the recovery of acrylic acid to a pyrolysis tank, to decompose the acrylic acid dimer in the liquid A of bottoms, and (3) to recycle at least a part of the liquid B of funds from that pyrolysis tank to the column for the recovery of acrylic acid

Description

METHOD FOR THE RECOVERY OF ACRYLIC ACID FIELD OF THE INVENTION The present invention relates to - Tools for the recovery of acrylic acid. More particularly, the present invention relates to methods for the recovery of acrylic acid from high boiling point impurities containing dimer of acrylic acid, acrylic acid and maleic acid. Still more specifically, the present invention relates to methods for stable and efficient recovery, acrylic acid, from high boiling point impurities, which contain dimer of acrylic acid, acrylic acid and maleic acid, which are obtained as liquid from bottoms, from a column for the separation of impurities with high boiling point, in a process to produce acid : aclitlC of high purity, which comprises contacting a gas containing acrylic acid, resulting from a catalytic oxidation of the gas phase, propylene and / or acrolein with water, to trap the acrylic acid as a REF. : 27704 aqueous solution of acrylic acid, distilling said aqueous solution in the presence of an azeotropic solvent to recover crude acrylic acid, and purifying the crude acrylic acid thus obtained with a column for the separation of impurities with high boiling point.

BACKGROUND OF THE INVENTION Conventionally, the production of high purity acrylic acid, through the gas phase catalytic oxidation of propylene and / or acrolein, has been practiced by a method comprising contacting a gas containing gaseous acrylic acid, from the oxidation step , with water, to collect acrylic acid in the form of an aqueous solution of acrylic acid (collection step); extract acrylic acid from the aqueous acid solution -acrylic, using a suitable extraction solvent (extraction step); separating the solvent from the resulting extract to recover crude acrylic acid (solvent separation step); and then separating the high-boiling impurities contained therein, such as acrylic acid dimer, maleic acid and the like, from the raw acrylic acid to obtain high purity acrylic acid (purification step). The high-boiling impurities, thus separated, contain, however, in addition to acrylic acid, acrylic acid dimers and therefore it is not economical to discard them all as liquid pastes. Consequently, methods have been proposed by JP Sho 45-19281 B2, JP Sho 51-91208A, JP Sho 61-35977 B2 and JP Sho 61-36501 B2, etc. to increase the recovery ratio of acrylic acid by pyrolysis of the acrylic acid dimer in the impurities with high boiling point, to produce acrylic acid and recover it. Recently, however, instead of the solvent extraction method, described above, which uses an extraction solvent for the recovery of acrylic acid, from aqueous acrylic acid solutions, the main practice is to use methods of extraction. azeotropic separation, that is, the distillation of an aqueous solution of acrylic acid in the presence of an azeotropic solvent that forms an azeotrope with water to cause the distillation of an azeotrope of water with the solvent, on top of a separation column azeotropic and recover acrylic acid from the bottom or bottoms of the same column. Thus, the production method of high purity acrylic acid, in recent years consists of an oxidation step to produce acrylic acid through catalytic oxidation in the gas phase, of propylene and / or acrolein; a collecting step of contacting the gas containing the acrylic acid with water and collecting the acrylic acid in the form of an aqueous solution of acrylic acid; an azeotropic separation step of distilling the aqueous solution of acrylic acid in an azeotropic separation column, in the presence of an 'azerotropic solverite and recover crude acrylic acid from the bottom of said column; and a purification step to purify the crude acrylic acid. This purification step is usually carried out using a high boiling point impurity separation column, to remove impurities with high boiling point in the crude acrylic acid and optionally an acetic acid separation column to remove, in additional , acetic acid. However, in such an acrylic acid production process, using the azeotropic separation method, as described above, still the high-boiling impurities, separated in the purification step, contain, in addition to acrylic acid, acid dimer acrylic, maleic acid and the like. It is therefore desirable, to recover acrylic acid from said impurities with high boiling point, also in the production process of high purity acrylic acid, to use the azeotropic separation method. As the recovery methods, you can • Consider methods such as those described in the JP publications listed above, which have been proposed for high purity acrylic acid production processes, followed by the solvent extraction method. However, when for example the apparatus for the destructive distillation of the acrylic acid dimer, as described in JP Sho 61-36501 B2 (the first step), is used to simultaneously carry out the decomposition of the acrylic acid dimer and the distillation of the acrylic acid formed in that decomposition, as well as that which is initially contained in the impurities with high boiling point, has been found to present a problem such as that the mixture of impurities in the product acrylic acid, reduce the purity of the product.

DESCRIPTION OF THE INVENTION It has been discovered that the problem has its cause in the maleic acid contained in the impurities with high boiling point. He "Maleic acid is separated and substantially eliminated completely, in the solvent extraction step, in the processes that use the solvent extraction method and therefore the resulting crude acrylic acid does not remain, but in the processes that use the azeotropic separation method remains in the raw acrylic acid and is mixed with the high boiling point impurities separated in the purification of this crude acrylic acid in a small percentage proportion.That maleic acid was distilled with acrylic acid in the apparatus for the destructive distillation of acrylic acid dimer, mentioned above.When the distillate is recirculated towards a previous step, for example, towards a column for the separation of impurities with high boiling point, in the step of purification, with the perspective to recover acrylic acid from there, the maleic acid is dragged by the distilled and condensed, at the bottom of the column a separation of impurities with high boiling point, to eventually mix with the acrylic acid product, reducing the purity; of the last . Also the maleic acid changes to fu aric acid in the acrylic acid recovery step from the high boiling impurities containing dimers of acrylic acid, acrylic acid and maleic acid, that fumaric acid precipitates in that recovery step for interfere with the stable operation. Accordingly, then, the object of the present invention is to solve the aforementioned problem, that is, to provide a method for efficiently and stably recovering acrylic acid from high boiling point impurities containing acrylic acid dimer , acrylic acid and maleic acid, in particular, the impurities with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid, as obtained as liquid from bottoms of a column of separation of impurities with high point of boiling, in a process to produce acrylic acid using the azeotropic separation method. It has been discovered that the objective Above, mentioned can be carried out by means of the use of an apparatus for the recovery of acrylic acid, and of an apparatus for the decomposition of a day of acrylic acid, instead of the above-mentioned apparatus, for the destructive distillation (the first step) of the acrylic acid dimer. More specifically, it has been discovered that acrylic acid can be efficiently recovered from high-boiling impurities, without reducing the purity of the acrylic acid product, by introducing said high-boiling impurities into an acid recovery column. Acrylic (which is preferably a distillation column equipped with a thin film vaporizer), in which to separate maieic acid and extract it from the bottom of the column and recover acrylic acid from the maleic acid cohort remarkably reduced, from the top from the column; introducing the bottom liquid containing the dimer of acrylic acid, acrylic acid and maleic acid, into a pyrolysis tank, wherein the acrylic acid dimer is pyrolyzed; and then recirculating a portion of the decomposition product to the acrylic acid recovery column, Thus, according to the present invention, there is provided a method for the recovery of acrylic acid, which is characterized in that it comprises, in the recovery of acrylic acid, from impurities with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid. (1) introduce those impurities with high boiling point, containing dimer of acrylic acid, acrylic acid and maleic acid, to an acrylic acid recovery column, and recovering acrylic acid as it is distilled from the top of the coil, (2) introducing liquid A from bottoms of the acrylic acid recovery column, to a pyrolysis tank for decomposing the acrylic acid dimer found in liquid A from bottoms, and then (3) recirculating at least a part of the liquid gone B from bottoms of the pyrolysis tank, to the acrylic acid recovery column (when the acrylic acid recovery column consists of a thin film vaporizer and a distillation column, in either or both). According to the present invention, there is further provided a method for the recovery of acrylic acid, as an improvement of an acrylic acid recovery method, comprising contacting a gas containing acrylic acid, obtained through catalytic oxidation. in gaseous phase of propylene and / or acrolein with water to trap the acrylic acid in the form of its aqueous solution, distill that aqueous solution of acrylic acid in an azeotropic separation column in the presence of an azeotropic solvent, and purify the acrylic acid crude oil obtained from the bottom of the azeotropic separation column, in a separation column of high boiling impurities, this improvement includes the recovery of acrylic acid from liquid bottoms of that separation column of impurities with high point boiling (that is, impurities with a high boiling point that "conti eien dimer of acrylic acid, acrylic acid and maleic acid), which is characterized by (1) introducing those impurities with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid, to a column for recovery of acrylic acid, composed of a distillation column equipped with a thin-film vaporizer, where the distillation is carried out under conditions of 10 to 100 mm Hg and at a bottom temperature of the column, from 60 to 120 ° C, distill Acrylic acid through the top of the column and recover it; (2) introduce liquid A from the bottoms of the thin film vaporizer, to a pyrolysis tank, whereupon the acrylic acid dimer found in the liquid A of funds, at temperatures of 120 to 220 C; and then (3) recirculating at least a portion of the liquid B from bottoms of the pyrolysis tank, to the thin film vaporizer and / or to the distillation column, at a ratio of 1 to 20 times, by volume, with respect to the "high boiling impurities containing dimer of acrylic acid, acrylic acid and maleic acid, high boiling point impurities containing dimer of acrylic acid, acrylic acid and maleic acid, to which reference is made herein, they mean a mixture containing at least 20 weight percent acrylic acid dimer, at least 20 weight percent acrylic acid and 3 to 10 weight percent maleic acid.The mixture may also contain other substances with high point of boiling, such as trimers of acrylic acid The method of this invention is used with particular convenience to recover acrylic acid from impurities with high boiling point, which contain, in addition, more than the dimer of acrylic acid, acrylic acid, and 5 to 10% by weight of maleic acid. A typical example of such high-boiling impurities, which contain dimer of acrylic acid, acrylic acid and maleic acid, is a bottom liquid, obtained when carrying out the process comprising contacting a gas containing acrylic acid, "resulting from catalytic gas-phase oxidation of propylene and / or acrolein, with water, to trap the acrylic acid in the form of an aqueous solution of acrylic acid, distill the aqueous solution in the presence of an azeotropic solvent, if necessary purify the resulting crude acrylic acid with another distillation column and then introduce the acrylic acid to a high boiling point impurity separation column.The bottom liquid is obtained from the high boiling impurity separation column. the specific composition of the liquid can not be defined in a general way, since it differs depending on the operating conditions selected for each of the steps of the process, for example, the bottom liquid may consist of 20 to 65% by weight of acrylic acid , from 30 to 60% by weight of acrylic acid dimer, from 5 to 15% by weight of polymerization inhibitor (e.g., hydroquinone) ona), from 3 to 10% by weight of maleic acid, and other substances with high boiling point. The method of the present invention basically comprises the following steps: (1) "a step of introducing impurities with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid, which are removed from the column of separation of impurities with high boiling point, and which are sent to a column of recovery of acrylic acid (distillation column), where the acrylic acid contained in the impurities with high boiling point is distilled, by the upper part of the column and the same is recovered, (2) a removal step of a liquid A of bottoms, of the part of bottoms of the acrylic acid recovery column (thin film vaporizer), the bottom liquid A contains dimer of acrylic acid, acrylic acid and maleic acid, introducing liquid A from bottoms to a tank of pyrolysis to decompose the acrylic acid dimer and form acrylic acid, and (3) a step of recirculating at least a part of the liquid B from bottoms of the pyrolysis tank, towards the lumna for the recovery of acrylic acid (distillation column and / or thin film vaporizer), means by which the dimer of acrylic acid obtained through the pyrolysis of the pyrolysis is recovered in the upper part of the column. dimer of acrylic acid contained in liquid B background s. The column for the recovery of acrylic acid, to be used in the present invention, is not subject to particular limitations, as long as it is capable of distilling high-boiling impurities containing dimer of acrylic acid, acrylic acid and maleic acid. Whereas, because the high-boiling impurities obtained as a bottom liquid, from a column for the separation of impurities with a high boiling point, in the acrylic acid production process, mentioned above, have a high viscosity, the use of a distillation column equipped with a thin film vaporizer, as a column for the recovery of acrylic acid, is preferred for the treatment of such impurities with high boiling point. Next, the present invention is explained in more detail, with reference to a modality in which a "bottom liquid from a high boiling impurity separation column, which is used for purification purposes in the acrylic acid recovery process, by means of azeotropic distillation of the product of catalytic oxidation in gas phase, of propylene and / or acrolein, it is used as the high boiling point impurities, which contain the dimer of acrylic acid, acrylic acid and maleic acid, and a distillation column equipped with a thin film vaporizer, is used as the column for the Acrylic acid recovery Fig. 1 is a flow diagram showing a working mode of the method of the present invention, high boiling point impurities containing dimer of acrylic acid, acrylic acid, maleic acid, etc. , which are obtained from the part of bottoms of a separation column 1 for impurities with high boiling point, are introduced to a column of d styling 2 equipped with a thin film vaporizer 3, where the acrylic acid is distilled and recovered. The maleic acid content of acrylic acid • Distilled, on that occasion it is markedly reduced, and varies from 0 to 3% by weight, preferably from 0 to 1% by weight. Thus the recovered acrylic acid is normally recirculated to a preceding step, for example, a purification step, more specifically, to column 1 for the separation of impurities with high boiling point, to provide acrylic acid product. This is desirable to select the design and operating conditions of the distillation column 2 as well as to perform the aforementioned separation of the maleic acid with high efficiency. Specifically, a tower of plates with a theoretical plate number (s) varying from 1 to 5, preferably from 1 to 3, and having a porous plate (s) is conveniently used as the distillation column 2. of double flow. In addition, it is desirable to carry out the distillation operation under a reduced pressure, preferably under a pressure of 10 to 100 mm Hg, and under conditions such that the bottom temperature of the distillation column 2 is not greater than 120 C, preferably that is within '60 to 120' range. When the bottom temperature of the column is too high, the precipitate, which is considered to be attributable to maleic acid, is formed to give safe operations through difficult extended periods.

The thin film vaporizer 3 is not subject to critical limitations, and any of those conventional vaporizers used as film vaporizers can be used. The bottom liquid A, collected in the thin film vaporizer 3 is introduced to a pyrolysis tank 4 seated in the subsequent one, where the acrylic acid dimer is thermally decomposed and converted to acrylic acid. The pyrolysis tank 4 is not subject to critical limitations, but any of them can be used appropriately for thermal decomposition of acrylic acid dimers, which is found in the bottom liquid A, to produce acrylic acid. The pyrolysis temperature in the pyrolysis tank 4 normally varies from 120 to 220 ° C, particularly, it is convenient to "Pirolis from 120 to 160" JC. Generally it can not be defined that the residence time (tank capacity of 1 isis / quantity of the liquid A of funds) varies depending on the pyrolysis temperature, although a residence time of about 20 to 50 hours is normally required. . When the pyrolysis is carried out at very high temperature and for a short time, undesirable decomposition reactions, polymerization and the like may occur. The acrylic acid dimer is thermally decomposed in the pyrolysis tank 4. For the purpose of recovering acrylic acid from the decomposition product, at least a portion of the liquids B from bottoms of the pyrolysis tank 4 is recirculated to the thin film vaporizer 3 through the indicated route with solid lines, in the figure , and / or to the distillation column 2 through the indicated route with dashed line in the same figure. The waste is discharged as waste liquid. To make efficient the recovery of acrylic acid in the liquid B of funds, "increases the recirculated amount of liquid B from bottoms towards the thin film vaporizer and / or towards the distillation column 2, which is usually from 1 to 20 times by weight, preferably from 3 to 20 times by weight, than that from high-boiling impurities containing dimer of acrylic acid, acrylic acid and maleic acid Although bottom liquid B can be recirculated to column 1 for the separation of high-boiling impurities, it exposes to cause concentrations of maleic acid in the part of the bottoms of column 1 for the separation of impurities with high boiling point and precipitates in certain occasions.Therefore it is preferred to recirculate the liquid B from bottoms towards the thin film vaporizer 3 and / or towards the distillation column 2. The acrylic acid recovered from the top of the distillation column 2 is normally recirculated to a preceding step, for example, to a step of purification, more specifically to column 1 for the separation of impurities with high boiling point, and is recovered as the final product 'Consists of acrylic acid. The acrylic acid recovered from the top of the distillation column 2 contains only very small amounts of maleic acid and therefore the concentration of the maleic acid in the purification step is not present and the purity of the acrylic acid product is not reduced. In addition, most of the maleic acid is separated and removed as waste liquid and therefore problems occur due to the formation of precipitate attributable to it. Hereinafter, the present invention is explained in more detail, with reference to a working example.

Example The acrylic acid was recovered following the flow chart of Figure 1. The details of the distillation column 2, the thin film vaporizer 3 and the pyrolysis tank 4 are as follows: distillation column 2: number of plates 15, distillation column of the plates "poroscts, double flow thin film vaporizer 3: 7.5 m ~ heat transfer area, horizontal type Pyrolysis tank 4: capacity 11 rrr The high boiling point impurities containing acrylic acid, acrylic acid and maleic acid dimer, which were obtained through the gas phase catalytic oxidation step of the propylene, the capture step, the azeotropic separation step and the step of purification (column 1 of separation of impurities with high boiling point), were introduced in a central plate of the distillation column 2, with a flow magnitude of 0.7 t / h. In the distillation column 2, the thin film vaporizer 3 was adjusted in order to make the temperature at the bottom of the column 85 ° C, and the column was operated under the conditions of a pressure of 'operation of 25 mm Hg and with a reflux ratio of 0.9. The acrylic acid was recovered from the top of the column at a rate of 0.5 t / h. (Hereinafter, this acrylic acid is referred to as the recovered acrylic acid). The liquid A from bottoms of the thin film vaporizer 3 was introduced into a pyrolysis tank 4 and thermally decomposed there under conditions in which the temperature thermally under conditions in which the internal temperature of the tank was 140 ° C and a time of residence of 45 hours. A part of the resultant bottom liquid B was recirculated to the thin film vaporizer 3. The flow quantity of the recirculated liquid B was 2.8 t / h, which was 4 times the weight of the impurities with high Boiling point containing dimer of acrylic acid, acrylic acid and maleic acid. The rest was discarded as waste liquid. The compositions of the impurities with high boiling point, the acrylic acid recovered and the waste liquid were as shown in Table 1.

TABLE 1 Unit in weight The aforementioned operation was continued for 6 months. The operation was stable and free of problems such as precipitation. The purification yield was 98%, and the decomposition rate of the acrylic acid dimer was 73.9%. As it is understood from the previous example, according to the present invention, the acrylic acid dimer can be decomposed efficiently, to increase the recovery percentage of acrylic acid In accordance with the present invention, in addition, the recovery of the acid Acrylic on the top of the acrylic acid recovery column (distillation column) contains only very small amounts of maleic acid, and when recirculated towards the purification step, causes a small accumulation of maleic acid in that step. Thus, the method is free of the risk of reducing the purity of the acrylic acid product resulting from the mixture of maleic acid with the product, Thus, according to the invention, acrylic acid can be recovered from the acid dimer acrylic with high efficiency and can produce a high purity acrylic acid., since the invention can prevent the formation of precipitate attributable to maleic acid, the operation is performed safely over prolonged periods. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is' that which. it is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (7)

1. A method for recovering acrylic acid characterized in that it comprises, by recovering acrylic acid from high boiling point impurities containing dimer of acrylic acid, acrylic acid and acid ma 1 ei co, (1) introducing those impurities with high boiling point containing dimer of acrylic acid, acrylic acid and maleic acid, to a column for the recovery of acrylic acid and recover the acrylic acid as it is removed by distillation through the top of the column, (2) introducing the liquid A of bottoms from that column for the recovery of acrylic acid to a pyrolysis tank to decompose the acrylic acid dimer in the bottom liquid A, and then, (3) to recirculate at least a part of the bottom liquid B, from the bottom tank. pyrolysis to the column for the recovery of acrylic acid.

2. A method according to claim 1, characterized in that the impurities, with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid, is a liquid of bottoms obtained from a column for the separation of impurities with high boiling point used in the process comprising contacting a gas containing acrylic acid resulting from catalytic gas phase oxidation of propylene and / or acrolein with water to trap the acrylic acid in the form of an aqueous solution of acrylic acid, distilling the aqueous solution in an azeotropic separation column in the presence of an azeotropic solvent, and purifying the resulting crude acrylic acid obtained by the bottom part of the azeotropic separation column, in the column for the separation of impurities with high boiling point.

3. A method according to claim 1 or 2, characterized in that the column for the recovery of acrylic acid is operated under reduced pressure and at a temperature in the bottom part of the column ranging from 60 to 120 ° C.

4. A method according to claim 1, 2 or 3, characterized in that the column for the recovery of acrylic acid is a distillation column equipped with a thin film vaporizer.

5. A method according to claims 1, 2, 3 or 4, characterized in that the pyrolysis temperature ranges from 120 to 220 ° C.

6. A method according to any one of claims 1 to 5, characterized in that the recirculated amount of the liquid B from bottoms from the pyrolysis tank, is from 1 to 20 times that of impurities with high boiling point which * conti e-nen dimer of acrylic acid, acrylic acid and maleic acid.

7. A method for recovering acrylic acid as an improvement of an acrylic acid recovery method comprising contacting a gas containing acrylic acid obtained through catalytic gas phase oxidation of propylene and / or acrolein with water to trap the acid acrylic in the form of its aqueous solution, distill that aqueous solution of acrylic acid in an azeotropic separation column in the presence of an azeotropic solvent, and purify the crude acrylic acid obtained by the bottom part of that azeotropic separation column, in a column for the separation of impurities with high boiling point, that improvement comprises recovering acrylic acid from those impurities with high boiling point that contain dimer of acrylic acid, acrylic acid and maleic acid as obtained from the bottoms part of the column of separation of impurities with high boiling point, the method is "car acterized because it comprises (1) introducing those high boiling impurities containing dimer of acrylic acid, acrylic acid and maleic acid, into a column for the recovery of acrylic acid, composed of a distillation column equipped with a thin film vaporizer , where the distillation is carried out under conditions of 10 to 100 mm Hg and the bottom temperature of the column ranges from 60 to 120 ° C, extracting the acrylic acid by distillation through the top of the column and recovering the same; (2) iducing the liquid A from the bottoms of the thin film vaporizer, into a pyrolysis tank, whereby the dimer of acrylic acid is decomposed in that liquid A of bottoms, at a temperature ranging from 120 to 220 ° C; and thereafter (3) recirculating at least a portion of the liquid B from bottoms of the pyrolysis tank to the distillation column and / or to the thin film vaporizer, at a ratio of 1 to 20 times in volume with respect to the impurities with a high boiling point that conti e-nen dimer of acrylic acid, acrylic acid and maleic acid.