JPS58118540A - Recovery of unsaturated carboxylic acid - Google Patents

Abstract

PURPOSE:To recover the carboxylic acid remaining in waste sulfuric acid discharged from the esterification process of an unsaturated carboxylic acid with an alcohol using sulfuric acid as a catalyst, by esterifying the remaining carboxylic acid, and extracting the carboxylic acid and the ester with a hydrophobic organic solvent after the esterification step or before and after the step. CONSTITUTION:In the ester preparation process (P), a hydrophobic organic solvent and an unsaturated carboxylic acid are charged to the first stage reactor 7, and an aqueous solution of sulfuric acid and excess alcohol are charged to the final reactor 5 to carry out the esterification reaction. The crude ester composed mainly of the hydrophobic organic solvent and the ester is obtained from the final separator 19, and waste sulfuric acid is discharged from the first separator 21. The waste sulfuric acid is fed to the top of the extraction column 9, and the major part of the ester and a part of the carboxylic acid are extracted with the hydrophobic organic solvent supplied through the line 11. The extract is introduced into the reactor 13 to esterify the major part of the carboxylic acid in the waste sulfuric acid, and extracted in the extraction column 16 in the same manner as the above. The extract liquid is recycled through the line 11 to the extraction column 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses sulfuric acid as a catalyst to produce
Production of unsaturated carboxylic acid esters (hereinafter simply referred to as "esters") by esterifying I (hereinafter simply referred to as "carboxylic vinegar") with lower alcohols (hereinafter simply referred to as "alcohols"). The present invention relates to a method for recovering carboxylic acid from waste sulfuric acid produced in .

In the esterification reaction of carboxylic acids, sulfur is used as a catalyst.
I am well aware of the use of I. Esterification reaction: It is an equilibrium reaction, and it is also well known that the rate of y-emission of carbon fibers is improved by adding more than an equivalent amount of alcohol. It can be said to be a method of conversion.

Thus, in the polymerization ff1i in which carboxylic acid was esterified under the conditions of alcohol [111] using IFII as a catalyst, vermilion Reactions include alcohol, carbonic acid, sulfuric acid, etc. A possible method for separating the ester and carboxylic acid from such a reaction solution is extraction using a hydrophobic organic solvent as an extractant. As in the case of esterification of methacrylate, which is described in Japanese Unexamined Patent Publication No. 53-21114, it is possible to simultaneously carry out esterification and separation by supplying an s1 solvent as a Km agent to the esterification reactor. There are also industrially advantageous methods.

According to the studies of the present inventors, separation of the esters from the esterification reaction solution t and others can be relatively easily carried out by an extraction method using a hydrophobic organic solvent as an extractant. Due to its relatively high compatibility with sulfuric acid and am, sulfuric acid cannot be extracted by extraction with a hydrophobic organic solvent, and a considerable amount of carbonyl is present in the waste sulfuric acid. On the other hand, since alcohol has higher compatibility with water and WI than carboxylic acid, most of it remains in the waste i*acid. Therefore, this waste W! Disposing of lactic acid as it is will not only cause pollution but also be undesirable in terms of resource utilization, so we will recover as much of the useful components as possible from the waste and use it as needed. Depending on the situation, it is preferable to recycle and reuse after distillation and concentration. Examples of useful c components here include alcohols, esters, carboxylic acids, etc. Among these, alcohol Fi can be separated from the crushed IF d to a volume i by distillation. Ester is also distilled and waste sulfur 11:r.
It is also possible to separate from F! However, since ester is often counted as an azeotrope with alcohol in -#, it is economically advantageous to extract it with a hydrophobic organic solvent and recover it before distilling the alcohol. It is. However, carboxylic acids have a high lung temperature and are highly polymerizable, so it is difficult to separate them by distillation.On the other hand, simple extraction using a hydrophobic S-containing solvent is insufficient due to the 13 reasons. cannot be separated and recovered.

In addition, pancreatic sulfur vinegar is subjected to a sulfuric acid concentration process for reuse, and since its offshore point is higher than water, it is distributed to the sulfuric acid distillation column $E section for sulfur reactor III. Wl
If carboxylic acid remains in the chamber, its high polymerizability causes clogging of the chamber V with polymerized PS and polymerization products in the rIE section of the distillation column for sulfuric acid concentration. VIm it stinks! It was strongly desired to recover as much carboxylic acid as possible from the waste Wf culm before processing it into the condensation culm.

In addition, in the recovery of carboxylic acid by extraction as described above, it is also possible to increase the amount of hydrophobic organic solvent supplied to the extraction process to improve the overall extraction ability, thereby increasing the recovery rate of carboxylic acid. Although it is possible, in this case, the energy cost for separating the hydrophobic organic solvent and the carboxylic acid will increase needlessly, and the capacity of the extraction equipment will need to be increased, which will increase the equipment cost. (return cost) will increase significantly.

As a result of our investigation into the recovery of carboxylic acids from waste sulfuric acid from the above-mentioned viewpoints, the present inventors found that: ■ The extraction of esters from waste sulfuric acid using a hydrophobic organic solvent is effective for the recovery of carboxylic acids from waste sulfuric acid.
725. Based on these findings, we discovered that if the ester in the gem is removed, the carboxylic acid easily reacts with excess alcohol, and the ester is produced relatively quickly. As a result, the present invention was completed.

That is, the present invention deals with waste i! produced in the production of ester Cw, which is carried out by reacting a carboxylic acid having 3 or tlj4 carbon atoms with an alcohol using itgi as a catalyst. Carvone tit in acid with high recovery rate! It is a method that can be advantageously recovered and is characterized by carrying out the following steps (a) - (b) - (@) or steps (b) - (e). At the point.

(1) A step of extracting and recovering the carboxylic acid and ester contained in the waste WI using a hydrophobic organic solvent. (b) A step of esterifying the carboxylic acid remaining in the waste with alcohol to produce an ester. (e) A step of bringing the reaction solution obtained in step (b) into contact with a hydrophobic organic solvent to extract and recover carboxylic acid and ester. From the reaction solution esterified with the tilFWI catalyst, most of the ester and carboxyl-
The tortoise shells, except for , are similar in composition and are a mixture of main K ilF, acids, water, alcohols, and small amounts of esters and carboxylic acids. Carbon 11 is here! The number of carbon atoms is 3 F! Specific examples include rAKFi, acrylic acid, and methacrylic acid 111f4.

In the present invention, the step (b) of reacting the carboxylic acid remaining in the waste sulfuric acid with alcohol to esterify it is essential, or the alcohol used in this process is preferably t- Specific examples include KFi, methanol, ethanol, and furohanol. And the waste WIllI which is the object of the present invention
In the preparation of esters giving rise to - the esterification reaction is carried out under conditions of alcohol excess, thus step (b)
) If the waste sulfuric acid used in step (b) contains a sufficient amount of IC/alcohol, it is not possible to newly supply alcohol to perform the KFi step (b)! It is. However, in the production of ester 0, under conditions where the alcohol is equivalent to or less than the carboxylic acid, or when the alcohol is less than the carboxylic acid.
On the other hand, it is extremely effective if the esterification reaction is carried out under extremely excessive conditions (in which case it is necessary to separately supply alcohol when carrying out step (b)).

In order to improve the recovery rate of carboxylic acid, it is preferable that the waste via to be subjected to step (b)K contains alcohol in a molar ratio of 10 or more to the remaining carboxylic acid.

The reaction temperature of the esterification reaction in the above step (b) is usually 30 to 100°C, preferably 40 to 70°C. If the reaction temperature is too low, the reaction rate will be low; if the reaction temperature is too high, polymerization of esters and carboxylic acids may occur, and corrosion of the coating by the polishing acid may occur, resulting in the formation of other adhesives. The reaction time of this esterification reaction is usually 0.5
It is preferably 1 to 6 hours. However, if the reaction time is too long, the polymerization of esters and carboxylic acids will proceed, and the reactor will need to be increased in size. The SFi type reactor is not particularly limited and may be a so-called seed reactor, but since it does not require strict concentration control or vigorous stirring, it can be used, for example, in a tank or a column used in step (a) or tj (e). It is also possible to substitute a part of the reactor as a reactor. In principle, in step (b) above, the extraction and recovery process using a hydrophobic organic solvent as an extractant, that is, step (a) and step (e). It will be done. The hydrophobic organic solvent used here may be one or a mixture of two or more selected from aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons having a boiling point of θ to 250°C. Specific examples include butane, pentane, hexane, heptane, nonane, octane, decane,
Examples include cyclopentane, cyclohexane, methylcyclohexane, propylcyclohexane, benzene, toluene, ethylbenzene, xylene, and cumene.

The amount of the above-mentioned hydrophobic organic solvent used is usually 0.05 to 5.0, preferably 0.3 to 5.0, based on the weight ratio of the liquid to be extracted.
It is 1.0. If the amount of hydrophobic organic solvent C is small, the carboxylic acid and ester group will be low, and conversely if it is too large, the hydrophobic organic solvent will be 6 minutes 111 times 16
costs will increase. Extraction 1: The operating temperature is usually 15-100°C, preferably 30-70°C.

If this temperature is set to an excessively low temperature, the cooling and heating costs for cooling will increase, which is disadvantageous in terms of production efficiency.On the other hand, if the temperature is set to a high temperature all at once, the extraction efficiency will decrease, resulting in the formation of esters and carboxylic acids. Yield decreases.

The extraction equipment used here may be any commonly used extraction equipment, but it is preferable that the hydrophobic organic solvent and waste sulfuric acid flow in countercurrent flow (preferably something that can be touched, such as a Raschig ring, etc.). A t-packed column, a tray column type extraction W@, etc. can be preferably used.

In the present invention, in principle, the esterification step (step (
A total of two extraction steps are performed before and after step b)), but the hydrophobic organic solvent used as the extracting agent does not need to be supplied to each separately, and the extract obtained in one extraction step is It can also be supplied as extraction IP 1 in the extraction process of how to use it.It can be supplied as extracting IP1 in the extraction process.
By doing this, it is possible to reduce the total amount of hydrophobic organic solvent L:r', thereby reducing the energy cost for recovering the hydrophobic organic solvent by 6L. .

In the present invention, there is usually a step (compilation) at the distance of step (b).
By carrying out K, it is possible to perform step (b) and this KM < step (@ n) to yield carvone! If the polymerized KFi has a very small ester content, for example, 0.5 wt. Extract, process (
In the esterification of b), the main purpose is to shift the chemical equilibrium of the system in a direction where esterification is suppressed. Therefore, the ester content of pSS is small and the carboxylic acid in the waste acid is esterified. If there is a situation where it can be done,
Step (b) can be carried out immediately, and the content of carboxylic acid in the finally obtained waste sulfuric acid can be maintained.

In addition, after performing the recovery treatment according to the present invention, the conversion rate of carboxylic acid can be improved by repeating the esterification in step (b) and the extraction in step (e). C. It is effective depending on the reaction, but the ester reaction in step (b) occurs relatively quickly, and the extraction rate of ester in step (C) is high, so -#t
cFi,■#(b) and step (c) are performed only once,
Carboxylic acid can be recovered with a sufficiently high recovery rate.

As described above, the main feature of the present invention is that carvone*t in waste sulfuric acid, which is difficult to recover by extraction alone with a hydrophobic organic solvent, is recovered by converting it into an easily recoverable ester. . Since the method of the present invention is carried out incidentally to the ester production process, there is no need to recover carvone in its original form, and recovery in the form of ester ultimately increases the yield of ester. It will also improve. Moreover, if you want to obtain the same recovery rate by recovering the carboxylic acid as an ester, which is more difficult to recover than by recovering it in the form of the carboxylic acid,
The amount of hydrophobic organic solvent used as an extractant can be significantly reduced, and therefore the hydrophobic organic solvent can be separated and recovered.
It has the advantage of reducing the energy cost of W to 11 and making it possible to fish.

Next, preferred embodiments of the present invention will be described using the drawings.

In the step of producing waste sulfuric acid to which the present invention is applied, esters are synthesized by esterifying carboxylic acids and alcohols in a carp medium of W, and most of the esters and carboxylic acids contained in reaction J are The step in which waste sulfuric acid is recovered by separating the sulfuric acid from the sulfuric acid is not particularly limited, but will be described by way of example as an esterg) I&l production process carried out by the method described in Japanese Patent Application Laid-Open No. 53-21114 KII.

The first WJK produced PFi ester, and the JF had 13 complete mixing tank reactors 5. Fi, 7 are connected in series to these reactors 5, 6, 7 through separators 19, 20, 21, respectively, and OII aqueous organic solvent and OII aqueous organic solvent as the reaction medium are supplied from the first stage reactor 7, KFi tube 1. Carboxylic acid is supplied, and the final stage glue reactor 5 is supplied with an io'* aqueous solution as a catalyst and excess alcohol through a pipe 2, and each reactor 5.6.
In step 7, the reactant gII supplied with Fi is brought into contact with the countercurrent and repulsed, and the resulting reaction liquid is transferred to the 111F reactor 19.20.
．． 21, it is separated into a phase mainly composed of crushed water, water, and alcohol, and a phase mainly composed of carboxylic acid, ester, and a hydrophobic organic solvent. A crude ester mainly composed of a synthetic organic solvent and ester is obtained, and waste sulfuric acid is obtained from the tube 4 of the first stage III reactor 21. In the present invention, this waste IS is treated as follows to recover carboxylic acid.

That is, the waste sulfur from the pipe 4 is cooled in the heat exchanger 8 as necessary, and then transferred to the top of the extraction tower 9! ! ! supplied to,
Down the tower via tube 11! Most of the esters and a part of the carboxylic acid in the waste sulfuric acid are extracted by the extractant mainly composed of a hydrophobic Ill-containing solvent. The extract from the top of the extraction tower 9 is discharged through a pipe 10 and sent to a separation step (not shown) for each component.From a pipe 12 at the bottom of the extraction tower 9, most of the ester The waste sulfuric acid from which all of the carbons have been removed is extracted, and if necessary, the temperature is raised using a heat exchanger or the like, and then the sulfuric acid is supplied to the esterification reactor 13.

Waste sulfur supplied here! As most of the c-ester was removed in the extraction column 9, the chemical equilibrium shifted in the direction of promoting esterification, and the waste that was supplied to the reactor 13 was 1IIF
Most of the carboxylic acids in the reactor react with the excess alcohol to form esters.If the alcohol content supplied to the reactor 13 is low, the pipe 22 and It is preferable that 1IIK of dialcohol is supplied to adjust the amount of alcohol to 11 carvone in molar ratio of 10 or more.

The reaction liquid ii@14 is extracted from the reactor 13, and after being cooled by a heat exchanger 15 as necessary, it is transferred to an extraction column 16.
Most of the esters and a part of the carboxylic acid are extracted by the hydrophobic organic solvent that is supplied to the extraction column 16 via the pipe 17. The extract containing an organic solvent as a main component is supplied to the extraction column 9 as an extractant through a pipe lit. A tube 18 at the bottom of the extraction column 16 then yields waste containing almost no ester and carboxylic acid, which is usually sent to a sulfuric acid concentration step.

In the above, the hydrophobic organic solvents supplied to the tubes 1 and 17 may be of the same type as K14, but they are preferably the same. Also, reactor 5e 6a
7 or polymerized KF with low reaction temperature in reactor 13
i. Heat exchanger A8 or heat exchanger 15 may not be necessary.In the example shown in Fig. 1, an independent glue reactor 13 was used, but as shown in Fig. 2, the reactor 13 is connected to an extraction tower. A device integrated into the tower of 9* may be used, or the 3rd v! As shown in JK, extraction towers 9 and 16 are integrated, and the volume of the central part of the tower is increased to form reactor 1.
A device having the function of 3 may also be used. Also, the volume of the extraction towers 9 and 16 may be increased to increase the capacity of the extraction towers 9 and 16 during retention. It is also possible to make various changes to the structure, such as increasing the length of the reaction time or advancing the reaction while performing extraction, and all such changes are included in the present invention as long as they do not depart from the spirit of the present invention. Ru.

Example 1 An apparatus having a configuration according to the flowchart shown in FIG. 1 was used to produce methacrylic and methanol mixed with methacrylic and methyl. That is, in the ester TiL-based P, methacrylic acid and n-hexane containing 500 p, p, m of heid p-quinone as tubes IK, tlj, and 1 reaction were added at 299 g/hr and 14 g/hr, respectively.
At the same time, methanol and an Australian aqueous solution with a concentration of 70% were added at a flow rate of 6 g/kr, and 234 g/kr each was added to pipe 2.
'B was fed at my of 235g/hr, and reactor 5.
In 6.7, an esterification reaction was carried out at a reaction temperature of 65°C and a residence time of 6 hours.As a result, 3 tubes were twisted, normal hexane was 28.4% by weight, and methyl methacrylate was 64.5% by weight. A crude ester having a composition of 6.1% by weight and 6.1% by weight of methanol and further containing ter methacrylic acid, tS, water, etc.
Obtained with 1 g/kr of II, stranded in tube 4, normal hexane 0.3% by weight, methyl methacrylate 2.5% by weight,
Methacrylate 4111.0% IIN%, methanol 23.3
A waste** was obtained with a flow rate of 403 g/hr.

The nine waste sulfuric acid thus obtained was cooled by 940"CK with cooling water in a heat exchanger 8, and then cooled to an inner diameter of 2.5 am.

403g/h in the top stage of the 20-stage rotary multi-blade temporary extraction tower 9
Extraction was carried out by supplying at a flow rate of rC and an extract containing 97% by weight of normal hexane, methyl methacrylate, etc. obtained from the top of the extraction column 16 in the lower stage of C1/J as an extractant. .

As a result, a liquid consisting of 89.1% by weight of n-hexane, 85% by weight of methyl methacrylate, and small amounts of methacrylic acid, methanol, etc. was collected from the pipe 10 at the top of extraction column 9.
It was obtained at a flow rate of 7 g/kr, and from the pipe 12 at the bottom of the extraction column 9, the main components were methanol, sulfuric acid, and water, and 0.
．． A liquid containing 6% by weight of methacrylic acid and 0.05% by weight of methyl methacrylate was obtained at a flow rate of 391 t/br and the 0IF12 liquid was heated to 6% by weight in a heat exchanger (not shown).
After heating to 0°C, it was supplied to reactor 13, and esterification of methacrylic acid was carried out at an average residence time of 2 hours and a reaction temperature of 60°C. As a result, the 63 weight bullet of methacrylic acid in the liquid from pipe 12 is esterified, and
The concentration of methacrylic acid in the reaction solution obtained in step 4 is 023
The concentration of methyl methacrylate was 0.5% by weight. The reaction solution in this tube 14 is heated to 40°C by heat exchanger 115 into water. After cooling, normal hexane is supplied to the uppermost stage of an extraction tower 16 having the same structure and capacity as the extraction tower 9, and normal hexane is supplied from the lowermost 19K Fi pipe 17.
Extraction was performed by supplying at a flow rate of hr.

As a result, 1i-11 at the top of this extraction column 16! An extract containing mainly 100 ml of liquid was obtained, and this liquid was supplied to the above-mentioned extraction column 9.

from the tube 18 at the bottom of the extraction column 16, containing 0.11% by weight methacrylic acid and 0.06% by weight methyl methacrylate,
387 g/liquid mainly composed of methanol, sulfuric acid, and water
As a result of continuous throttling operation for 48 hours at a flow rate of 0 or more, the recovery rate of methacrylic acid was 90 arcs, and 42 arcs of the recovered methacrylic acid were recovered as methyl methacrylate. .

Comparative Example 1 In the 7P-C shown in Figure 1111, reactor 1
31 heat exchange I! 15tll extraction $9 and extraction tower 1
The operation was exactly the same as in Example 1, except that an apparatus in which K.6 was connected in series was used.

As a result, the pipe 10 at the top of the extraction tower 9 was washed, normal hexane 89.611%, methacrylic methyl 73% by weight ≦
, Methacrylic I! 1.9wt%, methanol 12wt%! I
A liquid consisting of methanol and gli! was obtained at a flow rate of 136 t/br from the tube 18 at the bottom of the extraction column 16. I
, 388 tons of liquid containing water as the main component, 0.02% by weight of methyl methacrylate, and 0.36% by weight of methacrylic acid.
/br, and in the end we were able to recover methacrylic Wi with a recovery rate of 65%, but the number of plates in the extraction column and K, which is the same as *Fi Example] of n-hexane as the extractant.
Nevertheless, it is clear that because the esterification reaction was not performed, the methacrylic alcohol recovery rate was lowered to 11 compared to Example IKJt.

Comparative Example 2 The same operation as in Comparative Example 1 was performed except that the flow rate of normal hexane supplied from the pipe 17 to the extraction column 16 was changed to 363 t/br.

As a result, the tube 10 at the top of the extraction column 9 contained 96.0% normal hexane and 2.6% methyl methacrylate.
Weight %, methacrylic acid, o*ii, methanol 0.
A liquid consisting of 4 wt. Methyl, 0.09 heavy I! 1% methacrylic! The flow rate of liquid containing l is 387 min/hr! In the end, methacrylic l! was obtained with a recovery rate of 91 da! I was able to recover it.

According to this example, almost the same recovery rate as in Example 1 was obtained, but since no esterification reaction was performed, about three times as much normal hexane as in Real 1111 was used. It is clear that a large amount of energy is required for recovery.

Example 2 Methyl acrylate (ta) was prepared using acrylic acid and methanol using exactly the same equipment as in Example 1. That is,
In the system P, tube 1 contains 251 t each of acrylic acid and normal pentane containing 500 p-pm m- of hydroquinone as a polymerization inhibitor.
/br7hi 302 g/hr when supplied at K
, Tube 2KFi methanol 2 Aqueous solution with 70% degree of penetration was supplied at a flow rate of 234 g/hr and 2301/br, respectively, and esterification was carried out in reactor 5.6.7 at a reaction temperature of 60°C and a residence time of 5 hours. React 60 As a result, tube 3, 6h normal pentane 48.11i
A crude ester having a composition of 44.5% by weight of methyl acrylate and 6.1% by weight of methanol and containing small amounts of acrylic acid, sulfuric acid, water, etc. was obtained at a flow rate of 625 g/kr.
Pipe 4, 0.3 wt% normal pentane, 2.5 wt% methyl acrylate, acrylic I! 1.011)
Arc, methanol 22.6% by weight, sulfur I% 40.8% by weight, water 32.8% by weight [392 g/k of waste sulfuric acid]
obtained at a flow rate of r.

The waste ** thus obtained is converted into cooling water through the heat exchanger 8!
While supplying the filter cooled to 1140°C to the extraction column 9, 234 °C of normal pentane was added to the pipe 17 and 1lIlsjl16.
Methyl acrylate and acrylic acid in the waste sulfuric acid were recovered by supplying at a flow rate of g/hr. Pipe 12 at the bottom of extraction column 9
The liquid obtained from
◎Reactor 13 was supplied to Reactor 13.
At the same time, esterification of the acrylic acid that was not obtained was carried out in the extraction column 9 at a residence time of 2 hours and a reaction temperature of 50'C, and the reaction liquid in the tube 14 at the bottom of the column was transferred to the heat exchanger 15. After cooling to 40℃, extract @16
Methyl acrylate and acrylic acid were recovered.

As a result, from 910 at the top of the extraction column 9, a liquid consisting of 92.61 r of normal pentane, 4.3% by weight of methyl acrylate, and small amounts of acrylic acid, methanol, etc. was obtained.
It was obtained with a fi amount of 54 g/hr. On the other hand, in the pipe 1825 at the bottom of the extraction column 16, there was 372 g of a liquid containing 0.08% by weight 9% acrylic acid and 0.01% I≦methyl acrylate, and whose main components were methanol, sulfuric acid, and water. / hr flow rate was obtained. As a result of continuous operation for 48 hours with K as described above, the recovery rate of acrylic acid was 92 times (92 times), and 27 times out of the recovered acrylic acid, 27 times were recovered as methyl acrylate. Note that the reaction rate of acrylic acid in reactor 13 was 157%.

Comparison Example 3 Since the 70-C shown in Fig. 1 was used, the reactor 13 and the heat exchanger M15 were removed and the extraction tower 9 and the extraction tower 16 were connected in a static row. The same operation as in tFi Example 2 was performed.

As a result, the pipe 10 at the top of the extraction tower 9 contained 93.2% by weight of normal hentane and 3.91% by weight of methyl acrylate.
, acrylic 1111% by weight and other liquids such as methanol were obtained at a flow rate of 252 g/hr, and 1 g of the tube at the bottom of the extraction column 16 contained methanol, sulfuric acid, and water as main components, and 0.03 % by weight methyl acrylate, 0.32
A liquid containing acrylic acid of 374 g/brO was obtained at a flow rate of 374 g/brO, and acrylic acid was eventually recovered at a recovery rate of 70 times. ! ! Although it is the same as Example 42, it is clear that the recovery rate of acrylic acid is significantly lower than in Example 2 because the esterification reaction is not performed.

Example 3 5% by weight methacrylic acid, 21.5% by weight methanol, 40.2% by weight 11Fl! , 33. Ot of double p arc
・Lana Shiro. Waste 1 containing 1% by weight methyl methacrylate
The methacrylic acid was recovered in the same manner as in the previous example, except that the extraction tube was not used prior to esterification. That is, the waste W# acid was directly supplied to the reactor at a flow rate of 390 g/hr, and the average residence time was 1'l12 hours, and the reaction concentration was 5.
Esterification of methacrylic acid was carried out at 0°C, and the liquid thus obtained was supplied to the uppermost extraction column ## having exactly the same structure and capacity as extraction #16 in Example], and the lowermost stage Kij of the extraction column was
Extraction was performed by supplying normal hexane at a flow rate of 156 g/br.

As a result, the top of the extraction column contained 87.7% by weight of n-hexane, 8.3% by weight of methyl methacrylate, 2.
A crude ester consisting of 5% by weight of methacrylic acid and a small amount of methanol etc. was obtained at a flow rate of 178 g/hr, while at the bottom of the extraction column, O,OS weight - of methyl methacrylate, 0.7 A liquid containing methanol, sulfuric acid, and water as main scales and containing methacrylic acid at a flow rate of 368 g/hr was obtained.

As a result of continuous operation for 48 hours as described above, the recovery rate of methacrylate was 87%. Note that the reaction rate of methacrylic acid in the reactor was F165%.

In this way, when the content of carboxylic acid to be recovered was very small, it was possible to recover waste sulfuric acid at a high recovery rate by esterifying and extracting the waste sulfuric acid without passing through one extraction culm.

[Brief explanation of the drawing]

FIGS. 1 to 3 are 70-sheet diagrams of steps preferably used in the implementation of the present invention. 5, 6. 7.13...Reactor 9.16...
Extraction tower 19, 20, 21-... Separator

Claims (1)

[Scope of Claims] 1) A method for reducing the amount of waste produced in the production of unsaturated carboxylic acid esters by reacting unsaturated carboxylic acids with 3 or #'i4 carbon atoms with lower alcohols using sulfuric acid as a catalyst. The unsaturated carboxylic acid is subjected to the following steps (*)-(b)
-(c) or step (b)-(C). (1) Step of extracting and recovering unsaturated carboxylic acids and unsaturated carboxylic acid esters contained in waste WIt acid using a hydrophobic organic solvent (b) #Wl! (e) The reaction solution obtained in step (b) is subjected to an esterification reaction with a lower alcohol to produce an unsaturated carbon ester. , is an alcohol having 1 to 3 carbon atoms, Claim tIp1 Item f' IF +7゛ A method for recovering carbon II. Claims: Claim 1: The three-layer hydrophobic aqueous melt is at least one glue with a boiling point of 0 to 250°C (an aliphatic hydrocarbon, an alicyclic hydrocarbon, and an aromatic hydrocarbon). Or the unsaturated carboxylic acid C recovery method described in Section 2.