JP3819419B2 - Method for recovering methacrolein and methanol - Google Patents

Description

  The present invention relates to a method for recovering methacrolein and methanol from a mixed liquid composed of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol.

  In recent years, intensive research has been conducted on a new method for producing methyl methacrylate at once by reacting methacrolein, methanol and molecular oxygen (hereinafter referred to as direct meta method). In this method, the reaction is carried out using an excess of methanol relative to methacrolein, so the reaction solution is unreacted methacrolein and unreacted methanol, the reaction product methyl methacrylate, the reaction by-products water and methacrylic acid. Obtained as a mixed solution. In the direct meta method, since the reaction is carried out in the presence of excess methanol, it is essential from an economic point of view to recover and recycle unreacted methanol.

  The following proposal is made about the method of collect | recovering unreacted methacrolein and unreacted methanol from the reaction liquid in a direct meta method. In JP-A-58-157740, a mixed liquid comprising methacrolein, methanol, methyl methacrylate, and water obtained by the direct meta method is applied to the first distillation column, and unreacted methacrolein is first added to the unreacted methacrolein. It is recovered from the distillation tower concentration section and recycled as a mixed solution of reaction methanol and reaction product methyl methacrylate. However, in this first distillation column, only about 20% of the unreacted methanol supplied to the distillation column is recovered as a mixed liquid with methacrolein. The remaining unreacted methanol is obtained from the bottom of the distillation column as a mixture of the reaction product methyl methacrylate and water. The second and subsequent distillation towers are used to separate and recover the reaction product methyl methacrylate and unreacted methanol from the bottom liquid of the tower, to obtain the target product methyl methacrylate and unreacted. Methanol is collected and recycled.

  Furthermore, a method for separating and recovering unreacted methanol and the target methyl methacrylate from the tower bottom liquid which is a mixture of the unreacted methanol, methyl methacrylate and water is disclosed in JP-A-57-9740. JP-A-58-180457, JP-A-2-17150, and the like. That is, a specific saturated hydrocarbon and methanol are azeotroped in a distillation column, or a specific saturated hydrocarbon and methanol and water are azeotroped in a distillation column, and an azeotropic mixture from the column top and methyl methacrylate from the column bottom. A method for obtaining a mixture of water or methyl methacrylate has been proposed.

  Certainly, it is possible to recover methacrolein and methanol by these methods, but it is necessary to combine other separation operations in addition to the distillation operation in three convenient distillation columns, and the process is long. In addition, the distillation tower that separates and recovers methanol and methyl methacrylate, which is an azeotropic system, is difficult to perform a stable distillation operation, and there is a problem in the industrial implementation of the direct meta method.

In addition, since methacrolein, methacrylic acid, and methyl methacrylate are easily polymerized, when the mixed solution is separated, if the process becomes long as in the method described in JP-A No. 58-157740, it polymerizes. In addition, the loss of methacrolein, methacrylic acid, and methyl methacrylate increases, and these polymers and high-boiling substances adhere to the columns, nozzles, and reboilers of the distillation tower, hindering long-term continuous operation of the equipment. It was also the cause of coming.
JP 58-157740 A JP-A-57-9740 JP 58-180457 JP-A-2-17150

  The present invention recovers methacrolein and methanol from a mixed liquid consisting of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol in one distillation column, and a polymer of methacrolein, methacrylic acid, and methyl methacrylate. Another object of the present invention is to provide a method for recovering methacrolein and methanol that suppresses the production of high-boiling substances and reduces the loss of methacrolein and methyl methacrylate and enables long-term continuous operation.

  As a result of diligent research in view of such circumstances, the inventors of the present invention obtained a mixed liquid of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol, which is a reaction liquid obtained by the direct meta method, in the middle of the distillation column. In the distillation tower concentration section, methacrolein and methanol are azeotroped, then the remaining methanol is azeotroped with a part of the reaction product methyl methacrylate, and methanol and methacrolein are simultaneously removed. When recovered as a mixed liquid with methyl methacrylate, methanol and methacrolein can be recovered in one distillation column without greatly reducing the amount of methyl methacrylate in the bottom liquid. When methacrolein and methanol are separated and recovered at the same time, it is surprising that when only methacrolein is azeotropically separated from methanol. Than also found that high boilers and polymers produced in the distillation column collecting unit area and the column bottom is considerably reduced, and completed the present invention.

That is, the present invention provides: When recovering methacrolein and methanol from a mixed solution consisting of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol, the mixed solution is first supplied to the middle part of the distillation column, and the mixture is supplied from the supply site to From the concentrated part up to the top, methacrolein and methanol are simultaneously recovered as a mixture with methyl methacrylate, while from the bottom of the distillation column, a mixture consisting of methyl methacrylate, water and methacrylic acid substantially free of methacrolein and methanol. A process for recovering methacrolein and methanol, characterized in that
2. A liquid obtained by a reaction in which a mixed liquid composed of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol is methyl methacrylate by oxidatively esterifying methacrolein with an oxygen-containing gas in the presence of a catalyst. The method for recovering methacrolein and methanol as described in 1 above.

  In the present invention, as mentioned above, methacrolein and methanol are separated and recovered at the same time, so that methacrolein and methanol can be recovered in a simple and short process of only one distillation column. In addition, the loss due to polymerization of methacrolein or methyl methacrylate and high boiling point substances is suppressed, and long-term continuous operation is enabled. In addition, since a mixture of methyl methacrylate, water, and methacrylic acid substantially free of methacrolein and methanol is obtained as the bottom liquid, in the direct meta method, isolation of the target methyl methacrylate is achieved. This also has the advantage that it becomes easier.

Hereinafter, the present invention will be described in detail.
In the present invention, when a mixed liquid consisting of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol is supplied to the middle part of the distillation column, and when recovering methacrolein and methanol, the mixed liquid supply part of the distillation column In the concentrating section between the top of the column and the top of the column, methacrolein and methanol are azeotroped from the mixed solution, and then the remaining methanol is azeotroped with methyl methacrylate. Extract as a mixture with methyl. At this time, by operating the distillation column so that it does not substantially contain methacrolein and methanol in the methyl methacrylate, water, and methacrylic acid mixed liquid obtained from the bottom of the distillation column, Rain and methanol are simultaneously extracted and recovered from the concentration section of the distillation tower as a mixture with methyl methacrylate. Specific examples include a method of controlling the amount of steam cooked so that the temperature of the specific intermediate stage of the recovery unit is several degrees lower than the bottom of the tower compared to the bottom temperature of the distillation tower. For example, in Example 1, the temperature of the sixth stage is made 2.6 degrees lower than the bottom of a 45-stage plate column. Here, the concentration section of the distillation tower is between the mixed liquid supply site of the distillation tower and the top of the tower as described above, and the recovery section of the distillation tower is between the mixed liquid supply section of the distillation tower and the bottom of the tower. .

  The high boiling point product produced in the distillation column recovery area and the bottom of the present invention is mainly methacrolein, which is the most easily polymerized in a mixed liquid of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol. An oligomer derived from methacrolein having a molecular weight of 300 or less and a reaction product of methyl methacrylate produced by reaction with methacrylic acid or methyl methacrylate, and a polymer is a reactant having a molecular weight of 2000 or more.

  In the mixed liquid of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol of the present invention, in addition to methacrolein, methanol, methyl methacrylate, water, methacrylic acid, a small amount of by-product high-boiling substances There are also polymers. As described above, this high-boiling product or polymer is mainly a reaction product of methacrolein and methacrylic acid, methacrolein and methyl methacrylate, and methyl methacrylate.

  Methanol is known to behave as a poor solvent for the polymer in methyl methacrylate. If the methanol coexisting with methyl methacrylate is reduced in the distillation column recovery section, the methacrylic acid flowing down in the recovery section of the distillation tower is reduced. Since the solubility of the polymer of methyl acid increases, it can be speculated that the degree of adhesion of the polymer to the columns, walls, nozzles, etc. of the distillation column can be reduced, but as in the method of the present invention, It is an effect that was not expected at all that methacrolein and methanol were collected at the same time, and the amount of high-boiling products and polymerized products was significantly reduced by reducing the amount of methanol in the recovered liquid.

  In the present invention, by simultaneously recovering methacrolein and methanol, as described above, the amount of high-boiling product and polymer can be significantly reduced, and the solubility of the polymer is also increased. In addition, it was possible to eliminate the fact that the polymer or the polymer adhered to the shelf, wall, nozzle, reboiler or the like of the distillation tower and hindered long-term continuous operation of the apparatus. In addition, the loss of methacrolein and methyl methacrylate separated and discarded as high-boiling products and polymers can be significantly reduced. Furthermore, the fact that the separation between the methyl methacrylate layer and the aqueous layer in the tower bottom liquid is hindered by high boiling point substances or polymerized substances has been remarkably improved.

  In the present invention, a mixed liquid of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol is supplied to the middle part of the distillation column. The middle part of the distillation column is located between the bottom and the top of the distillation column, and substantially eliminates methacrolein and methanol from a mixed solution of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol. It suffices if there are recovery sections with the number of stages necessary for reduction so as not to be contained at the bottom of the column, and it is usually determined appropriately depending on conditions such as the type of distillation column and distillation efficiency.

  The composition ratio of the mixed liquid of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol that can be used in the present invention is 1 part of methanol relative to 100 parts by weight of the total amount of methacrolein, methanol, and methyl methacrylate. -80 parts by weight, methacrolein is 2-70 parts by weight, and methyl methacrylate is 1-97 parts by weight. In the mixed solution, when the total amount of methacrolein and methyl methacrylate is small, methanol cannot be recovered, and conversely, when the amount of methanol is small and methanol required for azeotropy with methacrolein is insufficient, Methacrolein cannot be recovered.

  Also, when the mixed solution is a reaction solution obtained by the direct meta method, the composition of the reaction solution varies depending on the reaction supply methacrolein / methanol composition and the conversion rate, the reaction supply methacrolein / methanol ratio is small, and the conversion rate is low. In some cases, the total amount of unreacted methacrolein and produced methyl methacrylate is so small that methanol cannot be recovered. Conversely, when the reaction feed methacrolein / methanol ratio is large and the conversion is high, the amount of methanol required for azeotropy with unreacted methacrolein is insufficient, and methacrolein cannot be recovered. From these facts, in the present invention, 15 to 75 parts by weight of methanol, 5 to 55 parts by weight of methacrolein, and 5 to 5 parts of methyl methacrylate with respect to 100 parts by weight of the total amount of methacrolein, methanol and methyl methacrylate. A reaction solution in the range of 60 parts by weight can be used. Preferably, methanol is 15 to 55 parts by weight, methacrolein is 5 to 40 parts by weight, and methyl methacrylate is 20 to 60 parts by weight.

  The type of the distillation column used in the present invention is not particularly limited, and can be used in either a plate column or a packed column. In the present invention, methacrolein, methyl methacrylate, and methacrylic acid, which are easily polymerizable substances, are separated by distillation. Therefore, a tower type having a structure that is difficult to block with a high-boiling substance or a polymer, or a structure that easily removes the plug is preferable. . In particular, it is preferable to use a plate column because the lower part of the recovery part is likely to be clogged due to the formation or concentration of high-boiling substances or polymers. Specifically, in the case of a plate tower, a sieve tray, a cascade tray, a turbo grid tray, a ripple tray, etc., and in the case of a packed tower, regular packing such as a melapack and a thruzer pack can be used.

  In the present invention, the distillation operation is performed so that methacrolein and methanol in the mixed solution supplied to the distillation column are not substantially contained in the column bottom solution. Preferably, the concentration of methacrolein contained in the bottom liquid of the distillation column is 5000 ppm or less, more preferably 3000 ppm or less, still more preferably 2000 ppm or less, particularly preferably 1000 ppm or less, and methanol is preferably 5000 ppm or less, more preferably 4000 ppm. Hereinafter, the distillation operation is more preferably performed to 2000 ppm or less. Although the tower bottom operating temperature varies depending on the distillation operation pressure and liquid composition, it must be lower in order to suppress the loss of polymer and high boiling point formation loss derived from methyl methacrylate and methacrylic acid, which are easily polymerizable substances. Is preferred. However, when the temperature is 40 to 60 ° C. or lower, depending on the distillation operation pressure, a refrigerant such as brine is required for enlargement of the distillation column or condensation at the top of the column. It is not preferable. Usually, the bottom temperature of the distillation column is 70 to 100 ° C., preferably 70 to 85 ° C., and the pressure is preferably about 500 Torr to 2 atm.

  In the mixed liquid supplied to the distillation column, methacrolein is methanol, and methyl methacrylate is methanol. In the concentration section of the distillation column, azeotropic compositions (for example, methacrolein and methanol are normal pressure, boiling point 58). Methanol / methacrolein = 45.7 mol% / 54.3 mol% at ° C Methanol and methyl methacrylate at normal pressure and boiling point 64.5 ° C Methanol / methyl methacrylate = 93.4 mol% / 6.6 mol However, these values are obtained when the two components of the substance are present, and when a coexisting substance is present as in the present invention, the composition is slightly different), and an intermediate stage (feed stage and tower) of the concentration section of the distillation tower is formed. It is the stage near the middle of the top.) Or extracted from the top of the tower. When extracting from the top of the column, it is necessary to re-separate the low-boiling substances accumulated in the system and the mixture of methacrolein, methanol and methyl methacrylate contained in the extract. And the methyl methacrylate mixture is preferably withdrawn.

  Further, as described above, the azeotropic composition of methanol and methyl methacrylate is methanol / methyl methacrylate = 93.4 mol% / 6.6 mol% at normal pressure and boiling point 64.5 ° C. The amount of methyl methacrylate, which is a reaction product of the direct meta method that is entrained, is relatively small, and the methyl methacrylate obtained from the bottom liquid in the direct meta method is not greatly reduced.

  Also in the present invention, it is preferable to use 50 to 500 ppm by weight of a polymerization inhibitor in order to handle the easily polymerizable substances methacrolein, methacrylic acid and methyl methacrylate in the distillation system as described above. As a polymerization inhibitor, hydroquinone, phenothiazine and the like can be supplied from the top of the distillation column. These supplies can make the present invention more effective.

  Reduces the loss of methacrolein, methacrylic acid, and methyl methacrylate by suppressing the formation of methacrolein, methacrylic acid, methyl methacrylate polymer and high-boiling products while recovering methacrolein and methanol with one distillation column In addition, it has become possible to provide a method for recovering methacrolein and methanol that enables long-term continuous operation.

  Next, the method of the present invention will be described specifically by way of examples. In addition, the high boiling point substance and polymer amount which arise in the distillation column collection | recovery area | region and a tower bottom part are the values which measured the tower bottom liquid using GPC. GPC was manufactured by Tosoh Corporation, the column used was TSK gel G3000HHR + G2000HR, the detector used was a differential refractometer RI-8020 manufactured by the same company, and polymethyl methacrylate standard molecular weight dimer to 110000. In the present invention, since the tower bottom liquid does not contain methanol, which is a poor solvent for the polymer, if the amount of the high boiling point produced and the amount of polymer is the same, the high boiling point contained in the tower bottom liquid. And the amount of polymer should be higher than in the case of the conventional technique in which methanol is contained in the bottom liquid. That is, if the amount of high boilers and polymer in the bottom liquid is small, it can be said that the amount of high boilers and polymer generated in the distillation column recovery area and tower bottom is small. The physical quantity measurement results were used for the evaluation of the amount of high-boiling substances and polymer products produced.

  A reaction liquid consisting of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol obtained by a reaction of methacrylin in methanol in the presence of a catalyst to oxidatively esterify with an oxygen-containing gas to methyl methacrylate. It was fed at a rate of 633.6 g / hr from the 30th stage from the top of a tower column type distillation column equipped with a sieve tray having a diameter of 10 cm, a height of 6 m, and an actual number of 45 sieves. From the top of the column, hydroquinone was supplied so that the concentration of the polymerization inhibitor in the falling liquid in the column was 100 ppm or more. The feed solution composition was 8.5% methacrolein, 32.6% methyl methacrylate, 7.7% water, 2.2% methacrylic acid, and 49.0% methanol. The top temperature of the distillation column is 31 ° C., the bottom temperature is 84 ° C., the temperature at the sixth stage from the bottom is 81.4 ° C., and the pressure is atmospheric pressure. At this time, methacrolein is 712 ppm by weight, methanol is A tower bottom liquid of 1470 ppm by weight was obtained. A mixed liquid of methacrolein, methanol, and methyl methacrylate was extracted from the fifth stage from the top of the distillation column. In the mixture, methacrolein had a composition of 13.2% by weight and methanol of 74.7% by weight. At this time, 98.7% by weight of methacrolein fed to the distillation column and 99.8% by weight of methanol. Was recovered in one distillation column at the same time. In addition, the amount of the polymer and high boiling point in the column bottom liquid was 0.23% by weight of methyl methacrylate supplied to the distillation column.

  A distillation column having the same structure as that of Example 1 was similarly supplied with a reaction solution composed of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol having the same composition as that of Example 1. A polymerization inhibitor was also supplied from the top of the column. Although the tower bottom temperature is the same, by operating the temperature at the 6th stage from the tower bottom to 80.2 ° C. which is 1.2 ° C. lower than Example 1, methacrolein is 2655 ppm by weight and methanol is 4730 ppm by weight. A bottom liquid was obtained. From the top of the top of the distillation column, 97.8% by weight of methacrolein fed to the distillation column and 99.6% by weight of methanol are simultaneously mixed as a mixed liquid of methacrolein, methanol and methyl methacrylate. It was recovered in the distillation column. Further, the amount of the polymer and high boiling point in the column bottom liquid was 0.28% by weight of methyl methacrylate supplied to the distillation column.

<Comparative Example 1>
As in Example 1, methacrolein, methyl methacrylate, water, methacrylic acid, and methanol obtained by reaction of methacrolein in methanol in the presence of a catalyst to oxidatively esterify with oxygen-containing gas to methyl methacrylate. The reaction solution consisting of was fed to a distillation column having the same structure as in Example 1 in an amount of 683.2 g / hr. From the top of the column, hydroquinone was supplied so that the concentration of the polymerization inhibitor in the falling liquid in the column was 100 ppm or more. The feed solution composition was methacrolein 6.3% by weight, methyl methacrylate 32.4% by weight, water 7.3% by weight, methacrylic acid 2.6% by weight, and methanol 51.4% by weight. The top temperature of the distillation column was 31 ° C., the bottom temperature was 71 ° C., and the pressure was atmospheric pressure. At this time, about half of the methanol supplied to the distillation column was extracted from the bottom of the column. The methacrolein in the bottom extract was 1300 ppm by weight and methanol was 42.1% by weight. A mixed liquid of methacrolein, methanol, and methyl methacrylate was extracted from the 10th stage from the top of the distillation column. The extracted liquid mixture had a composition of 18.5% by weight of methacrolein and 70.2% by weight of methanol. At this time, 97.4% by weight of methacrolein fed to the distillation column was recovered. At the same time, only 46.1% by weight of methanol was recovered as a mixed solution from the 10th stage, and one distillation column could not recover the methanol sufficiently. Distillation separation in the next step to recover the remaining methanol Operation was necessary. Further, the amount of the polymer and high boiling point in the column bottom liquid was 0.60% by weight of the supplied methyl methacrylate.

Claims (2)

From a reaction liquid consisting of methacrolein, methyl methacrylate, water, methacrylic acid, and methanol, obtained by a reaction of methacryloline in methanol in the presence of a catalyst to oxidatively esterify with an oxygen-containing gas to methyl methacrylate. When recovering methacrolein and methanol, the reaction solution is supplied to the middle part of the distillation column, and methacrolein and methanol are simultaneously recovered as a mixture with methyl methacrylate from the concentrated part from the reaction solution supply site to the top of the column. On the other hand, a method for recovering methacrolein and methanol comprising obtaining a mixture of methyl methacrylate, water, and methacrylic acid substantially free of methacrolein and methanol from the bottom of the distillation column. The method for recovering methacrolein and methanol according to claim 1, wherein a mixture of methacrolein, methanol and methyl methacrylate is extracted from the intermediate stage of the concentration section.