JPH047336B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to methacrylic acid alkyl esters (hereinafter referred to as
(also referred to as MAE) relates to a method for separating and recovering useful components such as methacrylamide from components discharged from the manufacturing process.

MAE uses methacrylamide (hereinafter also referred to as MAM) or methacrylic acid (hereinafter also referred to as MAA) as a lower aliphatic alcohol (hereinafter referred to as ROH).
) is reacted in the presence of sulfuric acid to esterify it.

The lower aliphatic alcohols mentioned here include alcohols having about 1 to 6 carbon atoms, such as methanol, ethanol, isopropanol, normal propanol, isobutanol, normal butanol, pentanol, and hexanol.

The esterification reaction is usually carried out at a reaction temperature of 60°C to 150°C.
°C, and the reaction time (residence time in the case of continuous reaction) is about 30 to 240 minutes, but the esterification reaction solution produced in this way does not contain the desired product.
MAE and most of the unreacted raw material as well as MAM
A part of the sulfuric acid is separated by prescribed operations such as distillation, extraction, and stripping, and the separated residual liquid is used as a waste liquid containing a high concentration of sulfuric acid and ammonium bisulfate (hereinafter referred to as waste sulfuric acid liquid) from the esterification process. be discharged.

A common method for treating such waste sulfuric acid solution is to neutralize the waste sulfuric acid solution with ammonia in a treatment tank called an ammonium sulfate saturation tank to form ammonium sulfate (ammonium sulfate), and then heat and concentrate and crystallize it to recover it as a by-product ammonium sulfate. It is something to do. (Instead of neutralization with ammonia, it is of course possible to neutralize with other inexpensively available alkalis, such as caustic soda, caustic potash, milk of lime, etc. In that case, mirabilite, gypsum, etc. are produced as by-products. ) However, the above waste sulfuric acid solution usually contains MAM,
Although it contains several percent of unreacted raw materials such as MAA and ROH, most of these components are denatured into tar-like components and produced as by-products during the neutralization, heating, concentration, and crystallization treatment of the waste sulfuric acid solution. It adheres to ammonium sulfate crystals and is discharged.

However, by-products such as ammonium sulfate mixed with such tar-like substances not only have low commercial value, but also useful unreacted components such as MAM and MAA are denatured into tar-like substances and cannot be recovered. MAE, the target substance, is lost as it is.
It is also unfavorable from the viewpoint of improving unit consumption.

As a result of intensive studies in view of the above points, the present invention, etc. has been developed by carrying out the above-mentioned neutralization heating concentration in such a way that water vapor is effectively generated from inside the waste sulfuric acid liquid layer, thereby generating water vapor that generates these unreacted useful substances. By performing an appropriate stripping operation (diffusion operation) in conjunction with this process, it can be taken out of the system without turning it into tar, and by applying appropriate means, it can be recovered with a high yield. They discovered this and completed the present invention.

That is, the present invention provides (1) a method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify the methacrylic acid alkyl ester, which is discharged from the esterification step; When the waste liquid containing sulfuric acid (hereinafter referred to as waste sulfuric acid liquid) is neutralized and concentrated with an alkali and recovered as sulfate, water vapor is effectively generated from inside the waste sulfuric acid liquid layer to neutralize the waste liquid.・The unreacted methacrylamide and/or methacrylic acid in the waste sulfuric acid solution is separated from the waste sulfuric acid solution by entraining it with the generated water vapor, and the water vapor exhaust gas is
The separated methacrylamide and/or methacrylic acid is absorbed into the water and/or alkaline aqueous solution and recovered by contacting with water and/or an aqueous alkaline solution under conditions that allow it to be treated as a substantially non-condensable gas. A method for recovering active ingredients from exhaust gas (hereinafter referred to as invention 1).

and (2) a method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify it, containing the sulfuric acid discharged from the esterification step. When the waste liquid (hereinafter referred to as waste sulfuric acid liquid) is neutralized and concentrated with an alkali and recovered as sulfate, the neutralization and concentration are carried out in such a way that water vapor is effectively generated from inside the waste sulfuric acid liquid layer. As a result, unreacted methacrylamide and/or methacrylic acid and lower aliphatic alcohols in the waste sulfuric acid solution are separated from the waste sulfuric acid solution by entraining them with the generated water vapor, and the water vapor exhaust gas is substantially non-condensed. Contact with water and/or alkaline aqueous solution under conditions that allow it to be treated as a condensed gas, perform a gas absorption operation, absorb methacrylamide and/or methacrylic acid into the water and/or alkaline aqueous solution, recover it, and use it in the esterification process. In addition to being recycled and recovered as methacrylic acid ester, 20 to 60% of the condensed components are first partially condensed in the presence of an inert gas to remove them from the water vapor exhaust gas after the above absorption treatment. A method for recovering active ingredients from exhaust gas (hereinafter referred to as (referred to as invention 2).

exists in

Hereinafter, the constituent elements of the present invention will be explained in detail while being broken down.

First, invention 1 will be explained.

In the present invention, when the waste liquid containing sulfuric acid (waste sulfuric acid liquid) discharged from the esterification process during MAE production is neutralized and concentrated with an alkali and recovered as sulfate, the neutralization and concentration are This is done so that water vapor is effectively generated from inside the waste sulfuric acid liquid layer.

Various methods can be adopted for this purpose, but for example, ammonia gas for neutralization is introduced into the lower part of the ammonium sulfate saturation tank, and the neutralization reaction is mainly caused in this part, and the heat generated causes water vapor to be removed from the inside of the liquid layer. A large amount of water vapor may be generated, or a heating tube (heating coil) may be inserted into the layer and a stirrer may be provided to generate water vapor from the inside by stirring vigorously at the same time as heating.

As another method, the neutralization may be carried out while blowing steam into the waste sulfuric acid solution, and the heating and stirring may be performed mainly by the steam. Of course, some of these means can also be used in combination.

In addition, when adopting the steam blowing method, the flow rate of the steam blowing is not particularly limited, but
50~ per ^10m3 /hr of waste sulfuric acid solution to be normally treated
Approximately 500m ³ /hr is appropriate. The temperature at that time is approximately 100 to 125°C. The time of the blowing treatment (in the case of treatment by continuous reaction, this is the residence time of the waste sulfuric acid solution in the treatment tank) may vary depending on the flow rate of steam blown, the treatment temperature, etc.
Usually 0.5 to 3.0 hours is sufficient.

By doing so, unreacted substances in the waste liquid are removed.
MAM and/or MAA are removed from the system along with the generated water vapor and separated from the waste sulfuric acid solution. That is, by applying a stripping operation using water vapor, MAM, etc. in the waste sulfuric acid solution is quickly separated from the system without turning it into tar.

A further preferred embodiment is to simultaneously blow in an inert gas to the active ingredient to be recovered when steam is blown in as described above.

The inert gas referred to here is the gas that should be recovered.
It means a non-condensable gas that does not react with useful components such as MAM. Such inert gases include nitrogen,
Examples include oxygen, air, helium, neon, argon, methane, carbon dioxide, etc., but air is preferred from the viewpoint of ease of handling.

The amount of the inert gas blown is not particularly specified, but it is usually 1 for the water vapor in the exhaust gas (mainly composed of water vapor and inert gas) after the dispersion operation.
It is desirable to have a capacity ratio of about 10%. Under such operating conditions, components with boiling points higher than water can also be stripped and removed from the waste sulfuric acid solution into the gas phase in high yields.

The water vapor exhaust gas obtained in this way (usually 100
~110℃, discharged at normal pressure), however,
The active ingredient recovered in a large amount of water vapor
Since it contains MAM, etc. at an extremely thin concentration of 0.5 to 2% (by weight), in order to use it effectively, MAM,
It is necessary to separate MAA and ROH.

In this case, the method that would normally be adopted is to first condense the entire amount of the steam-based exhaust gas to obtain a dilute aqueous solution of MAM or the like, and then distill and concentrate this again. However, it should be noted here that the target components to be recovered, MAM and MAA (and in some cases ROH as well), have a higher boiling point than water.
These remain in the can of the distillation column, and most of the water is distilled out from the top of the column. In other words, if such an operation is adopted, a huge amount of energy will be applied to recover a small amount of the active ingredient, and a large amount of water vapor will be cooled and condensed, which will then be heated and evaporated again. This would have to be an extremely irrational operation that is completely unacceptable.

However, in the present invention, as described above,
A large amount of water vapor exhaust gas containing extremely low concentrations of MAM, etc. (0.5 to 2% at most) (in some cases, some inert gas such as air may be mixed in as mentioned above) is The gas absorption operation is carried out by bringing it into contact with water/alkaline aqueous solution under conditions that allow it to be treated as a non-condensable gas.

What I would like to draw attention to here is that this gas absorption operation itself is a well-known operation in chemical engineering, but in both cases, carbon dioxide or hydrogen sulfide, etc. in a non-condensable gas such as air is It absorbs by contacting with an aqueous solution of amine or the like, and the idea of carrying out an operation in which water vapor, which is an easily condensable gas, is brought into contact with an aqueous absorption liquid as in the present invention can be said to be truly unprecedented.

The conditions defined in the present invention under which steam-based exhaust gas can be treated as a substantially non-condensable gas are as follows:
Condensation of its condensable components, especially water vapor, is 5% or less,
Preferably, it means a state in which the content is kept within a range of 2% or less. The conditions depend on the amount of inert gas mixed in with the water vapor, but usually the gas-liquid contact system is at least
This is achieved by maintaining the temperature at 98°C or higher. For this, for example, the water vapor gas to be treated must be
Introduced into the system while maintaining the temperature at 115°C, preferably around 110°C, and also the absorption liquid described below at 70°C or higher, preferably 80°C.
It is desirable to supply the product heated to the above temperature.

Although physical absorption using water as the absorption liquid in the present invention is sufficient to achieve the objective, in order to achieve an even higher effect,
It is more desirable to carry out the reaction and absorption using an aqueous alkaline solution. As such alkali, any one such as caustic soda, caustic potash, soda carbonate, potash carbonate, etc. can be used.

In this case, it is preferable to control the pH of the absorption liquid obtained by absorbing MAM and/or MAA to be maintained in the range of 7 to 10, particularly around 8.
If the pH is less than 7, MAM etc. will not be absorbed sufficiently, and if it exceeds 10, no further improvement in the absorption effect can be expected. For example, in the case of caustic soda, glauber's salt (as a by-product) increases, which is undesirable because it reduces its commercial value.

The amount of water or alkaline aqueous solution supplied from the outside for absorption (naturally, this is approximately equal to the amount of water or alkaline aqueous solution extracted in a steady state) can be controlled within the range that achieves the purpose of the present invention. It is desirable that the amount of carbon dioxide is as low as 1% to 10% by weight of the condensable component (mostly water vapor) of the steam-based exhaust gas.

As described above, the water vapor entrained in the discharged water vapor
MAM and MAA are recovered as an aqueous solution by contact absorption with an alkaline aqueous solution, etc., and since the operation is carried out under conditions where the water vapor system can be treated as a substantially non-condensable gas, the MAM thus obtained can be recovered as an aqueous solution.
Since the aqueous solution is very concentrated, it can be recycled as it is to the esterification process and recovered as MAE.

As the device for carrying out the gas-liquid contact operation of the present invention, any known device for carrying out gas-liquid mass transfer operation, which is a unit operation, such as a packed column, plate column, spray column, etc., may be adopted. be able to. In addition, when a packed column is used, the packing material can be a Laschihilander, a ball ring, a burl saddle ring, a McMahon ring, a telleret ring, a hedgehog ring, or the like.

Furthermore, as mentioned above, in the present invention, it is desirable to use as small an amount of the absorption liquid as possible in order to maintain the water balance when reusing it in the esterification process. L/G) may become too small, making it difficult to ensure efficient gas-liquid contacting operations within the gas-liquid contacting device. In such cases, a large flow rate of absorption liquid should be circulated within the device to supply a sufficiently large amount of absorption liquid to the middle section of the tower to ensure good gas-liquid contact with the steam-based exhaust gas rising from below. At the same time, a method is adopted in which a portion of the circulating absorption liquid is extracted from the bottom of the tower, while fresh (uncirculated) absorption liquid is supplied from the top of the tower, completely absorbing the active ingredients that could not be absorbed at the bottom of the tower. It is preferable to do so.

In addition, the method of contacting water and/or alkaline aqueous solution as an absorbing liquid with steam-based gas may be either countercurrent operation or cocurrent operation, and may be a liquid one-pass type (non-circulation type), liquid circulation type, or a combination thereof. can also be adopted. As mentioned above, the aqueous alkaline solution, etc. may be supplied at the top of the tower in the case of a one-pass system, but in the case of a circulation system, the uncirculated absorption liquid is supplied to the top of the tower, and the circulating liquid is supplied to the circulating liquid section in the middle stage. You can also do that. In this case, these fluctuations can be effectively dealt with by adjusting the flow rate ratio of uncirculated liquid and circulating liquid according to the composition ratio of MAM and MAA contained in the steam gas system.

Furthermore, it is also possible to use a plurality of contact towers having different absorption liquid compositions connected in series. The various factors mentioned above affect the exhaust steam system to be treated.
The most effective contact method can be determined by selecting and employing the optimal combination of operating conditions after considering these equilibrium and absorption relationships according to the MAM and MAA composition ratios.

As described above, in the present invention, the gas absorption operation is performed under conditions in which water vapor exhaust gas can be treated as a substantially condensable gas.
Since MAA etc. can be obtained as a sufficiently high concentration liquid,
When this is reused, it can be used as is without any pretreatment such as concentration. For example, as a reuse method, this absorption liquid can be recycled to the esterification process and recovered as MAE, but even in such a case, the water balance of the esterification process can be carried out as it is without disturbing the water balance in any way. This is because the esterification reaction is a reversible reaction, so if a large amount of water is introduced into the system, the MAE produced may decompose and return to MAA.

In addition, even if the aqueous alkali solution absorption liquid is circulated to the esterification process, the small amount of alkali is easily neutralized by the excess sulfuric acid present in the reaction system of the esterification process, so there is no effect on the esterification reaction itself. There will be no impact.

Although MAM and MAA are originally polymerizable components, it was found that when handled under such alkaline conditions, no tendency for polymerization was observed.

Next, invention 2 will be explained.

Invention 2 is to recover not only MAA and/or MAA but also lower aliphatic alcohol (ROH).

Regarding the constituent elements of the first half of Invention 2, the same as described in Invention 1 is applicable. However, the water vapor that accompanies the exhaust gas generated from processing waste sulfuric acid solution
Unlike MAM, ROH is not substantially recovered in the gas absorption operation using the alkaline absorption liquid in Invention 1, so the water vapor exhaust gas discharged from the gas-liquid contact device still contains a considerable amount of the alcohol. -ing

In the present invention, first, 20
~60%, preferably 45-60%, is preliminarily removed by condensation in the presence of an inert gas.

The volume ratio of inert gas to condensable components is 1 to 1.
Although it is necessary to make the alcohol present at 10%, when performing the partial condensation in this way, by making the specified amount of inert gas exist, the apparent alcohol This results in a significant increase in the equilibrium water vapor pressure of the alcohol, and most of the alcohol (more than 85%) passes through to the next condensation operation without being condensed.

Conversely, since the alcohol concentration in the preliminarily condensed water vapor is extremely low, even if this condensed water is disposed of without being collected,
The loss of alcohol is small and therefore
Since the COD value is low, the burden of wastewater treatment is extremely small.

The inert gas used here and the water vapor exhaust gas from which MAM, etc. have been removed may be mixed, for example, in the pipe on the way from the gas-liquid contact tower to the pre-condensation tower, or in the pre-condensation tower. You can mix it with Moreover, as a more preferable and easy means, it is also possible to blow an inert gas together with the steam in the first step of blowing steam into the waste sulfuric acid solution and mix it at this stage.

As the device for carrying out the preliminary condensation operation, a multi-tube type, spiral type, or double-tube type condensing heat exchanger (condenser), which is commonly used for condensing steam, is suitably used.

As described above, the alcohol concentration in the steam exhaust gas that has passed through the pre-condensation tower without being condensed is about 1.9 times more concentrated than the gas before treatment. Subsequently, the condensed components in the steam-based exhaust gas are completely condensed (ie, total condensation) to obtain a condensate containing ROH.

(Of course, non-condensable inert gas is separated in the condensation column without being condensed.) The alcohol concentration in the condensate is extremely high because the preliminary condensation operation has been performed in advance as described above. This is received in an alcohol distillation recovery column, where water is easily separated and concentrated to at least 60% or more, preferably about 80%, and then recycled to the esterification process as it is to effectively recover the water without disrupting the water balance. It is possible.

As a device for carrying out the total condensation operation, a device similar to that used for preliminary condensation, ie, a multi-tube condenser, etc., is suitably applied.

It should be noted that the condensation operation used in Invention 2 is a simple cooling operation with almost no stages, and therefore it can be used for cooling without any thermoeconomically problematic distillation operation. It should be noted that such concentrated recovery is effected only by the energy used.

The embodiments of the present invention will be explained below with reference to Examples, but these are merely illustrative, and Patent Law 70
The technical scope of the invention stipulated in Article 1 shall not be construed as being limited by these.

Example 1 Figure 1 shows a flow sheet of the equipment used in the experiment. 10 is an ammonium sulfate saturation tank. The waste sulfuric acid solution is received in the saturation tank and neutralized with ammonia, and at 110°C, 80.0 kg/Hr of water vapor is passed from pipe 01 through the tank blow-in pipe installed at the bottom of the saturation tank.
A stripping operation was performed by blowing 511 kg/hr of air. The water vapor exhaust gas generated is MAM10.8
Kg/Hr, MAA14.0Kg/Hr, MeOH40.0Kg/Hr,
It has a composition of 4000.0 Kg/Hr of water vapor and 511.0 Kg/Hr of air, and is introduced into the gas-liquid contact tower 30 through the pipe 20 while being maintained at 110°C. The gas-liquid contact tower is a 0.9 mφ * 16.0 mL empty column with 2 inches of Rashihi Lang, respectively in the recovery section 40: 6.0 m and circulation section 50: 7.0 m.
It is filled. Approximately 7% caustic soda aqueous solution is supplied as a fresh absorption liquid at a flow rate of 171.0 Kg/Hr to the recovery section 40 at 80°C through the distribution pipe 60 at the top of the tower, and the circulating liquid 70 at the bottom of the tower is supplied through the pipe 90 by a pump 80. It was circulated and supplied to the circulation section 50 at 100°C to ensure the recovery of active ingredients such as MAM and MAA. The circulation amount is determined by the liquid/gas ratio (L/G)=
The pH of the circulating liquid 70 at the bottom of the tower was controlled to 8.0 by adjusting the caustic soda layer supplied from the top of the tower using a fresh absorption liquid.

A part of the circulating fluid that has absorbed MAM etc. is transferred to the pipe 10.
0 at a temperature of 100℃, the extracted liquid was MAM7.0Kg/Hr, MAA13.9Kg/Hr,
MeOH2.0Kg/Hr, water 196.0Kg/Hr, caustic soda
It had a composition of 13.0Kg/Hr, and could be recycled to the esterification process and recovered without any problems.

The water vapor exhaust gas that is absorbed and leaves the gas-liquid contact tower 30 is MAM3.8Kg/Hr, MAA0.1Kg/Hr,
MeOH38.0Kg/Hr, water vapor 3975.0Kg/Hr, air
It has a composition of 511.0Kg/Hr, and the pipe 1
10 into a precondensation column 120. The pre-condensation tower consists of 25.4mmφ*750 heat transfer tubes with a pitch of 50.
It is a shell tube type that is arranged in an equilateral triangle in mm.

49.4% of the total condensed components in the precondensation column 120
condensed and was removed through drain line 130 at 95°C and disposed of. The composition of the condensate is MAM3.8Kg/
Hr, MAA0.1Kg/Hr, MeOH3.8Kg/Hr, water
It has a composition of 1975.0Kg/Hr, and COD
The processing load was light.

The water vapor exhaust gas that passed through the pre-condensation tower 120 without being condensed no longer contains MAMA or MAA, MeOH34.2Kg/Hr, and water vapor 2000.0Kg/Hr.
The air has a composition of 511.0 Kg/Hr and is introduced into the total condensation column 150 through a pipe 140. The total condensation tower is of the same shell tube type as the pre-condensation tower, and has 25.4mmφ*750 heat transfer tubes arranged in an equilateral triangle with a pitch of 50mm.

All condensed components in the gas are condensed in the total condensation tower 150, MeOH 34.0Kg/Hr, water vapor 1995.8Kg/Hr.
A condensate having a composition of Hr was removed through line 160 and collected. On the other hand, non-condensable inert gas is mainly air-based and MeOH0.2Kg/
The gas had a composition of 4.2.0 Kg/Hr of water vapor and 511.0 Kg/Hr of air, and could be disposed of as a completely odorless gas through the exhaust pipe 170.

The recovered condensate is sent to a methanol distillation recovery column by a pump 180 to reduce the methanol concentration.
The methanol was distilled to 65% and then recycled to the esterification process, allowing 85% of the methanol to be recovered.

[Brief explanation of drawings]

FIG. 1 is a flow sheet diagram showing an apparatus for carrying out the present invention.

Claims (1)

[Scope of Claims] 1. A method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify the sulfuric acid discharged from the esterification step. When neutralizing and concentrating waste liquid containing sulfuric acid (hereinafter referred to as waste sulfuric acid liquid) with alkali and recovering it as sulfate, water vapor is effectively generated from inside the waste sulfuric acid liquid layer to neutralize and concentrate the waste liquid. to separate unreacted methacrylamide and/or methacrylic acid in the waste sulfuric acid solution from the waste sulfuric acid solution by entraining the generated water vapor,
The water vapor exhaust gas is brought into contact with water and/or an alkaline aqueous solution under conditions that allow it to be treated as a substantially non-condensable gas, and a gas absorption operation is performed to convert the separated methacrylamide and/or methacrylic acid into the water and/or methacrylic acid. A method for recovering active ingredients from exhaust gas, which comprises recovering active ingredients by absorption in an alkaline aqueous solution. 2. The method according to claim 1, wherein neutralization and concentration are carried out while blowing steam and/or inert gas into the waste sulfuric acid solution. 3. The method according to claim 1, wherein the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid have been separated and absorbed is recycled to an esterification step and recovered as a methacrylic acid alkyl ester. 4. The method according to claim 1, wherein the pH of the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid has been separated and absorbed is controlled to be maintained in the range of 7 to 10. 5 In a method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify the waste liquid containing the sulfuric acid discharged from the esterification process (hereinafter referred to as When the waste sulfuric acid solution is neutralized and concentrated with an alkali and recovered as sulfate, water vapor is effectively generated from inside the waste sulfuric acid solution layer. Unreacted methacrylamide and/or methacrylic acid and lower aliphatic alcohol in the liquid are entrained in the generated water vapor and separated from the waste sulfuric acid liquid, and the water vapor exhaust gas is treated as a substantially non-condensable gas. Methacrylamide and/or
Alternatively, methacrylic acid is absorbed into the water and/or alkaline aqueous solution and recovered, and then recycled to the esterification process to be recovered as methacrylic acid ester. 20 to 60 of its condensed components
% is partially condensed in the presence of an inert gas to remove it in advance, and the remaining uncondensed portion is then completely condensed to obtain a condensate containing lower aliphatic alcohol, which is then recycled to the ertelization step and reused. A method for recovering active ingredients from exhaust gas, characterized by: 6. The method according to claim 5, wherein after introducing and mixing an inert gas into the water vapor exhaust gas from which methacrylamide and the like have been removed, a partial condensation operation is performed. 7. The method according to claim 5, wherein neutralization and concentration are carried out while blowing steam and/or inert gas into the waste sulfuric acid solution. 8. The method according to claim 5, wherein the pH of the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid has been separated and absorbed is controlled to be maintained in the range of 7 to 10.