JPH10175915A - Recovery of lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically and advantageously separate an aqueous phase from an oily phase without causing environmental pollution and enable the efficient recovery of lead at a high recovery efficiency of an effective organic component by adding a substance capable of generating a specific anion to a hydrous crude carboxylic acid ester solution containing the lead. SOLUTION: (B) An acid or a compound capable of generating sulfate ions or phosphate ions (e.g. sulfuric acid or phosphoric acid) in (A) a carboxylic acid ester solution prepared by reacting an aldehyde and an alcohol with oxygen by using a catalyst containing lead is added to the component A to keep the pH on the side of the aqueous phase when separated into two oily and aqueous phases at <=6. The lead is extracted or precipitated and transferred to the side of the aqueous phase. A water-soluble organic substance in the aqueous phase is transferred to the oily phase and the aqueous phase is separated from the oily phases. (C) The pH of the aqueous phase is then regulated to >=7 in the presence of iron ions based on an iron compound such as an iron sulfate or an iron phosphate to generate an iron hydroxide. Thereby, the lead is coprecipitated, separated and recovered from the aqueous phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a corresponding carboxylic acid ester by reacting an aldehyde, an alcohol and oxygen using a lead-containing catalyst. The present invention relates to a method for efficiently recovering trace amounts of lead ions and lead compounds, and efficiently recovering useful carboxylic acids and organic compounds by-produced in the reaction system.

[0002]

2. Description of the Related Art Conventionally, there is known a technique for producing a carboxylic acid ester by reacting an aldehyde with an alcohol in the presence of oxygen. For example, JP-B-57-35856,
JP-B-57-35857, JP-B-57-35859
JP-B-58-4704 and JP-B-62-7902 disclose the technology, and describe the superiority of the performance of a catalyst containing palladium and lead. However, these technical disclosures mainly focus on the composition and performance of the catalyst used in the reaction, the method of recovering useful by-products generated by side reactions, and the trace amounts that partially exfoliate or elute from the catalyst. There is no disclosure of a method for recovering lead ions or lead compounds.

[0003] The carboxylic acid generated by the reaction of water and aldehyde generated by the main reaction, even in small amounts, can be efficiently recovered if it can be efficiently recovered. In recent years, the importance of environmentally friendly industrial processes has been
It is an essential requirement to establish a technology that almost completely recovers the lead leaked from the catalyst used in the present reaction system into the reaction product system by peeling or elution and prevents the lead from leaking out of the process system.

Many techniques for recovering lead have been disclosed. For example, Japanese Patent Publication No. 54-22430,
JP-B-56-41646, JP-B-59-1090,
JP-B-2-4353, JP-A-60-48139, JP-A-49-9857, JP-A-52-91707, JP-A-58-68643, JP-A-4-505569,
It is reported in JP-A-6-500822 and JP-B-7-100135.

[0005] Further, a lead separation technique is described as one of the analysis methods in an analytical chemistry handbook published by Maruzen Co., Ltd. However, when these conventional lead recovery technologies are employed in the present reaction system, even if lead can be recovered efficiently, expensive heavy metal adsorbents and organic chelating agents are required, When lead is desorbed from the chelating agent and recycled, it is economically unsuitable and has a practical problem.

[0006] Also, simply because the solubility product of lead sulfide is small, a compound that generates sulfide ions is added to a compound system having a double bond to recover a trace amount of lead ions and lead compounds that coexist. When used for removal, there is a disadvantage that the polymerization reaction is easily accelerated. From the reaction product system, not only can the desired carboxylic acid ester be efficiently recovered, but also useful by-products can be efficiently recovered, and lead leaked into the reaction system can be easily and economically recovered. It has been strongly desired to realize a technique for almost completely recovering wastewater.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides an economical and environmentally safe method for industrially synthesizing a corresponding carboxylic acid ester by reacting an aldehyde, an alcohol and oxygen using a lead-containing catalyst. An object of the present invention is to provide a method which is excellent in terms of efficiency and simultaneously satisfies both an efficient method for recovering an active ingredient and a method for recovering lead.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have reacted aldehyde, alcohol and oxygen using a catalyst containing lead, and In synthesizing an acid ester, oil-water separation is promoted by adding an acid and / or a compound capable of generating a sulfate ion or a phosphate ion or both ions to a crude carboxylate solution containing water, whereby oil-water separation is promoted. It has been found that useful organic components are more concentrated, and that lead ions and lead compounds are almost completely extracted or precipitated and concentrated in the aqueous phase.

In addition, since lead ions and lead compounds can be almost completely removed from the oil phase by this operation, in the case of a carboxylic acid ester having a double bond, the oil phase is heated and distilled to obtain a purified carboxylic acid ester. Has been found to be advantageous in that the formation of a polymer is suppressed. On the other hand, since most of the form of lead precipitated and concentrated on the aqueous phase side is lead sulfate and / or lead phosphate, separation and recovery are easy. These lead sulfates and / or
Alternatively, since lead phosphate is precipitated, the concentration of lead ions remaining and dissolved in the aqueous phase is also reduced, and the lead ions are easily recovered and removed from the aqueous phase by using the co-precipitation action using iron hydroxide. Found that it is possible. The present inventors have completed the present invention based on these findings.

That is, according to the present invention, when an aldehyde, an alcohol and oxygen are reacted using a catalyst containing lead to produce a corresponding carboxylic acid ester, the lead contained in a crude carboxylic acid ester solution containing water is used. In the method of removing ions and lead compounds, an acid and / or a compound capable of generating a sulfate ion or a phosphate ion, or both ions in a crude carboxylic acid ester solution, or a mixture thereof is added to the crude carboxylic acid ester solution And the water phase side p when oil-water two layers are separated
While maintaining H at 6 or less, lead ions or lead compounds were extracted or precipitated and moved to the aqueous phase side, water-soluble organic substances in the aqueous phase were moved to the oil phase, and the aqueous phase and the oil phase were further separated. Thereafter, the pH of the aqueous phase is adjusted to 7 or more in the presence of iron ions to generate hydroxides of iron, and lead ions and lead compounds are collected by coprecipitation and separation from the aqueous phase.

Hereinafter, the present invention will be described in detail. The composition of the catalyst for reacting aldehyde, alcohol and oxygen is not particularly limited as long as it contains lead, but from the viewpoint of the reaction characteristics, it contains palladium in addition to lead, and the atom of palladium and lead Catalysts having a composition with a ratio Pd / Pb in the range of 0.1 to 10 are preferred. As a different element besides palladium and lead, for example, mercury, thallium, bismuth,
Tellurium, nickel, chromium, cobalt, indium, tantalum, copper, zinc, zirconium, hafnium, tungsten, manganese, silver, rhenium, antimony, tin,
The present recovery method can be applied to a catalyst containing rhodium, ruthenium, iridium, platinum, gold, titanium, aluminum, boron, silicon, or the like. The present recovery method can also be applied to a catalyst in which a catalyst component is supported on activated carbon, silica, alumina, silica alumina, zeolite, magnesia, magnesium hydroxide, titania, calcium carbonate, or the like.

The aldehyde to be used includes, for example, aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and isobutyraldehyde;
It is possible to use aliphatic α- and β-unsaturated aldehydes such as acrolene, methachlorene and crotonaldehyde; aromatic aldehydes such as benzaldehyde, benzylaldehyde and phthalaldehyde; and derivatives thereof. Of course, these aldehyde compounds can be used alone or as a mixture of any two or more.

The alcohols used include, for example, aliphatic saturated alcohols such as methanol, ethanol, isopropanol and octanol; ethylene glycol
Diols such as butanediol and allyl alcohol
And unsaturated aliphatic alcohols such as methallyl alcohol
And aromatic alcohols such as benzyl alcohol and phenols. Of course, these alcohol compounds can be used alone or as a mixture of any two or more. In particular, it is preferable to use industrially useful alcohols having 8 or less carbon atoms.

The acid and / or compound capable of generating sulfate ion or phosphate ion, or both ions, to be added to the crude carboxylic acid ester solution include, for example, sulfuric acid, hydrogen sulfate compound, sulfate or an aqueous solution thereof; phosphoric acid, phosphoric acid It is possible to use monohydrogen compounds, dihydrogen phosphate compounds, phosphates or their aqueous solutions. Of course, these acids and compounds can be used alone or in any mixture, but it is necessary to keep the pH of the aqueous phase at 6 or less during use, preferably in the range of pH 0.5 to pH 4. Good to keep. When the pH exceeds 6, there arises a problem that a useful carboxylic acid, for example, methacrylic acid or the like is hardly concentrated in the oil phase.

When the pH is adjusted by using only the acid or compound to be added to the above-mentioned crude carboxylic acid ester solution, if a pH of 6 or less cannot be achieved, hydrochloric acid, nitric acid, acid salt, carboxylic acid and the like can be used in combination. . PH of the aqueous phase is 6
The use of a hydrogen sulfate compound, a sulfate salt, a monohydrogen phosphate compound, a dihydrogen phosphate compound, a phosphate salt or an aqueous solution thereof as an acid or a compound to be added to the crude carboxylic acid ester solution while keeping the oil or water separation is described below. Is effective in clarifying the separation of the oil-water interface.

When the alkali metal compound used for adjusting the pH is previously contained in the crude carboxylic acid ester in order to stabilize the carboxylic acid ester synthesis reaction system, the alkali metal ion derived from the alkali metal compound is used. Since the aqueous phase is extracted by the use of sulfuric acid and / or phosphoric acid, the same effect as when the above-mentioned sulfate or phosphate is used can be obtained. In such a case, it is only necessary to use sulfuric acid and / or phosphoric acid as the acid or compound to be added to the crude carboxylic acid ester solution.

When an acid and / or compound capable of generating sulfate ions or phosphate ions, or both ions, is added to the crude carboxylate solution, the amount added is based on the total amount of lead contained in the crude carboxylate solution. In addition, it is necessary to add one or more equivalents of the acid and / or compound. For example, in the case of sulfuric acid, it is necessary to add at least an equimolar number to the total lead amount, and to add phosphoric acid, at least 0.67 mol number. When the acid or compound to be added to the crude carboxylic acid ester solution is used as an aqueous solution, it is preferable that the acid or the compound be concentrated as much as possible to minimize the introduction of water into the system.

The temperature condition for adding the sulfate ion or the phosphate ion or an acid and / or compound capable of generating both ions to the crude carboxylate solution is preferably in the range from the freezing point to 150 ° C., and more preferably from 10 ° C. to 100 ° C. Is more preferable. The pressure conditions are under reduced pressure, under atmospheric pressure,
Any condition under pressure may be used. In a system containing a compound having a double bond, hydroquinone,
It is effective to have methoxyquinone and other polymerization inhibitors in the system.

As described above, by adding an acid and / or a compound capable of generating a sulfate ion or a phosphate ion or both ions to the crude carboxylic acid ester solution and maintaining the pH at 6 or less, the crude carboxylic acid ester solution is prepared. Can be more easily separated into two layers, lead ions or lead compounds can be extracted or precipitated and moved to the aqueous phase side, and water-soluble organic substances in the aqueous phase can be moved to the oil phase.

The precipitate precipitated in the aqueous phase may be recovered at this time, but in view of simplification of the process, a method of separating and recovering the precipitate together with a coprecipitate described later is preferable. In the present invention, further, by coexisting iron ions in the obtained aqueous phase, by utilizing the coprecipitation of iron hydroxide,
A trace amount of lead ions remaining and dissolved in the aqueous phase can be removed.

As a method for coexisting iron ions in the aqueous phase, a compound capable of generating iron ions or a solution thereof may be used as the acid and / or compound to be added to the above-mentioned crude carboxylate solution. A compound capable of generating iron ions or a solution thereof may be added only to the aqueous phase after oil-water separation, but the latter method capable of avoiding the entry of iron ions into the oil phase is preferable.

The iron compound to be used is a water-soluble iron compound such as iron sulfate, iron phosphate, iron nitrate, iron chloride, iron carboxylate, iron oxalate, iron citrate and iron tartrate. You don't need to stick to it. An iron compound may be used directly, or an aqueous solution of an iron compound may be used. The amount of iron present in the aqueous phase may be at least one equivalent, preferably 2 to 10 equivalents, of the lead dissolved in the aqueous phase.

In order to generate iron hydroxide in the aqueous phase and to co-precipitate the trace amount of lead ions and lead compounds that remain and dissolve, a basic aqueous solution is additionally added only to the aqueous phase containing iron ions. The pH needs to be 7 or higher. Preferably pH
The pH is preferably adjusted to a range of 8 to 12, and the basic aqueous solution used is preferably an alkali hydroxide or an aqueous ammonia solution. As the pH is increased, iron hydroxide is generated, and lead ions and compounds can be co-precipitated.

The co-precipitate obtained is filtered, centrifuged,
It can be separated and recovered from the aqueous phase by an ordinary solid-liquid separation method such as sedimentation separation, but when the coprecipitate is extremely small, filtration is simple.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples.

[0026]

EXAMPLE 1 5% by weight of palladium was added to silica gel (Carrierct 10 trade name) manufactured by Fuji Silysia Ltd. as a carrier.
Catalyst 15 supporting 5% by weight of lead and 4% by weight of magnesium
0 g was charged into a stainless steel bubble column reactor equipped with a catalyst separator having a liquid phase portion of 1.2 liters, and 34% by weight of methchlorene / methanol was added at 0.54 liter / hr, NaO
The reaction was carried out while supplying H / methanol at 0.06 liter / hr and supplying air at a temperature of 80 ° C. and a pressure of 5.03 kg / cm ² . The NaOH concentration was adjusted so that the pH of the reaction solution was from 7.0 to 7.5, and lead acetate was added with methacrylene / metachlorene so that the lead concentration in the reaction solution was 20 ppm.
It was dissolved in methanol and supplied continuously. On the other hand, the reaction was maintained while adjusting and supplying air so that the oxygen concentration at the reactor outlet was 4% by volume. When the composition of the continuously withdrawn reaction solution becomes steady, start accumulating the reaction solution at 2 ° C.
Stored refrigerated below. At this time, the conversion of methachlorene varied from 60% to 65%, and the selectivity for methyl methacrylate varied from 85% to 90%.

Since unreacted methachlorene and methanol are present in the refrigerated storage solution, continuous distillation is carried out using a distillation column packed with a Helipack, and the methachlorene and methanol are removed.
From the top of the tower. When the crude methyl methacrylate solution was continuously extracted from the bottom of the tower and allowed to stand, a solution in which two layers of oil and water were separated was obtained. When 5 kg of the crude methyl methacrylate solution was taken out with good stirring, and 150 g of concentrated sulfuric acid was added with slow stirring, it was observed that the oil-water two-layer separation time was significantly shortened and the oil-water interface became clear. Was. Further, since the water-soluble organic compound was more extracted from the water phase to the oil phase, a phenomenon in which the volume of the oil phase increased was observed. On the other hand, fine particles of lead sulfate were observed to precipitate in the aqueous phase. The pH of the aqueous phase at this time was 1.9.

Table 1 shows the results of measuring the concentrations of methyl methacrylate, methacrylic acid, methacrylene, and lead in the oil phase and the aqueous phase before and after the addition of sulfuric acid. MMA in Table 1
Is methyl methacrylate, MAA is methacrylic acid, M
acr represents methachlorene and Pb represents lead. Table 1
For the values of Comparative Example 1 in the table, MMA, MAA,
The reason why the concentration of Macr is low is that organic substances in the aqueous phase are extracted into the oil phase and the volume of the oil phase is increased. As is clear from the distribution ratios in Table 1, it is understood that MMA, MAA, and Macr are concentrated as absolute amounts in the oil phase after the addition of sulfuric acid. After the addition of sulfuric acid, the co-precipitated aqueous phase had a lead concentration of 0.1 ppm or less, and as can be seen from the distribution ratio of lead to the oil phase and aqueous phase, almost all the lead component was extracted into the aqueous phase. Or it can be seen that the precipitate has moved.

Next, the oil phase and the aqueous phase were separated by decantation, and an aqueous ferric sulfate solution was added to the aqueous phase so that the concentration of iron was 2.5 times the concentration of dissolved lead in the aqueous phase. Was added. Then, an aqueous solution of sodium hydroxide was added to adjust the pH to 9.1, and then a thickness of about 3 cm was placed in a buchner funnel.
Was passed through a diatomaceous earth layer deposited on the slag, and 500 g of an aqueous phase containing lead sulfate and a coprecipitate was filtered. The filtrate was analyzed with an ICP measuring device (JY-138 model manufactured by Rigaku Denki Group), and the amount of lead was 0.1 ppm or less. The results are shown in Table 2.

On the other hand, with respect to the oil phase from which lead has been removed, after adding 1000 ppm of hydroquinone as a polymerization inhibitor, two distillation towers packed with Helipack were used to separate low boiling compounds and high boiling compounds from methyl methacrylate, respectively. Separation and removal in a tower yielded purified methyl methacrylate.
Generation of the polymer in both distillation columns was extremely small, and the polymerization loss of methyl methacrylate was 1% or less. Table 3 shows the recovery rates of crude methacrylic acid and purified methyl methacrylate based on the amounts of MAA and MMA contained in the crude methyl methacrylate solution.

[0031]

EXAMPLE 2 Instead of adding concentrated sulfuric acid to 5 kg of the crude methyl methacrylate solution in Example 1, 85%
The same operation as in Example 1 was performed except that phosphoric acid having a concentration of 120 g was slowly added with stirring. As a result, similar to the phenomenon observed in Example 1, a precipitation phenomenon of lead phosphate and a reduction in oil-water separation time were observed. An oil phase and an aqueous phase were separated by decantation in the same manner as in Example 1. At this time, the pH of the aqueous phase was 2.0.

After the lead phosphate precipitated in the aqueous phase was separated by filtration, an aqueous ferrous sulfate solution was added to the filtrate so that the concentration of iron was 5 times the concentration of dissolved lead in the filtrate. Thereafter, the same operation as in Example 1 was performed, and as a result, the lead concentration in the finally obtained filtrate was 0.1 ppm or less. The oil phase from which lead was removed was purified by distillation using the same distillation column as used in Example 1, and as a result, the polymerization loss of methyl methacrylate generated in the distillation process was 1% or less. .

MMA in the oil phase and the aqueous phase after the addition of phosphoric acid,
Table 1 shows the analysis values of MAA, Macr, and Pb. Table 2 shows the Pb concentration in the aqueous phase after co-precipitation using iron hydroxide. Table 2 shows the polymerization of the oil phase from which lead was removed by distillation purification. Table 3 shows the recoveries of the crude methacrylic acid and the purified methyl methacrylate based on the loss and the amounts of MAA and MMA contained in the crude methyl methacrylate solution.

[0034]

EXAMPLE 3 In Example 1, instead of adding concentrated sulfuric acid to 5 kg of the crude methyl methacrylate solution, 100 g of sodium hydrogen sulfate and 70 g of potassium dihydrogen phosphate were added.
The same operation as in Example 1 was performed, except that the saturated mixed aqueous solution at 5 ° C. was added with slow stirring. As a result, similar to the phenomenon observed in Example 1, a precipitation phenomenon of a lead compound considered to be a mixture of lead sulfate and lead phosphate and a reduction in oil-water separation time were observed. Further, sulfuric acid was added to adjust the pH to 1.8, and then the oil phase and the aqueous phase were separated by decantation in the same manner as in Example 1, and the iron concentration was 5 times the concentration of dissolved lead in the aqueous phase. An aqueous solution of ferric chloride was added to the aqueous phase to a concentration. Thereafter, the same operation as in Example 1 was performed, and as a result, the lead concentration in the finally obtained filtrate was 0.1 pp
m or less.

The oil phase from which lead was removed was purified by distillation using the distillation column used in Example 1 by the same operation. As a result, the polymerization loss of methyl methacrylate generated in the distillation process was 1% or less. Met. MMA, M in oil phase and aqueous phase after addition of sodium hydrogen sulfate and potassium dihydrogen phosphate
The analytical values of AA, Macr, and Pb are shown in Table 1, the Pb concentration in the aqueous phase after co-precipitation using iron hydroxide is shown in Table 2, and the polymerization in the distillation phase of the oil phase from which lead was removed was conducted. Table 3 shows the recoveries of the crude methacrylic acid and the purified methyl methacrylate based on the loss and the amounts of MAA and MMA contained in the crude methyl methacrylate solution.

[0036]

Example 4 Example 1 was repeated except that 150 g of concentrated sulfuric acid and 50 g of a 10% by weight ferric sulfate solution were added to 5 kg of the crude methyl methacrylate solution with slow stirring. The operation was performed. As a result, Example 1
A precipitation phenomenon of lead sulfate was observed in the same manner as the phenomenon observed in FIG. An oil phase and an aqueous phase were separated by decantation in the same manner as in Example 1. The pH of the aqueous phase at this time was 1.8.

An aqueous sodium hydroxide solution is added to the aqueous phase, and p
H was adjusted to 9.8. Then, the solution was passed through a diatomaceous earth layer having a thickness of about 3 cm in a buchner funnel, and 500 g of an aqueous phase containing lead sulfate and a coprecipitate was filtered. Thereafter, the same operation as in Example 1 was performed, and as a result, the lead concentration in the finally obtained filtrate was 0.1 ppm or less. Further, using the distillation column used in Example 1 for the oil phase after removing the lead,
As a result of distillation and purification by the same operation, the polymerization loss of methyl methacrylate generated in the distillation process was 1% or less.

The analytical values of MMA, MAA, Macr, and Pb in the oil phase and the aqueous phase after the addition of the sulfuric acid and the ferric sulfate solution are shown in Table 1, and the aqueous phase after the co-precipitation treatment using iron hydroxide is shown in Table 1. Table 2 shows the Pb concentration in the crude methacrylic acid and the purified methacrylic acid based on the polymerization loss in the distillation purification process of the oil phase from which lead was removed, the amount of MAA and MMA contained in the crude methyl methacrylate solution. Table 3 shows the methyl recovery.

[0039]

Comparative Example 1 An oil phase and an aqueous phase were added to the crude methyl methacrylate solution obtained in Example 1 without adding a sulfate ion or a phosphate ion or an acid and / or compound capable of generating both ions. Was separated by decantation. At this time, the pH of the aqueous phase was 7.2.

The obtained oil phase was purified by distillation using the distillation column used in Example 1 by the same operation. As a result, the polymerization loss of methyl methacrylate generated in the distillation process became 10% or more, and a phenomenon in which a polymer was accumulated in the column was observed, and the distillation operation had to be abandoned on the way. . During the distillation purification, even if the concentration of the polymerization inhibitor was increased from 1000 ppm to 3000 ppm, the polymerization loss could not be suppressed. Generation of a polymer was confirmed not only in the bottom of each column but also in the column below the distillate supply position.

As for the aqueous phase, a ferric sulfate solution was added so that the concentration of iron was 10 times higher than that of the dissolved lead. Thereafter, the same operation as in Example 1 was performed, and as a result, the concentration of lead in the finally obtained filtrate was 2.7.
ppm was detected. Although the reason is not clear, it is considered that the co-precipitation effect of dissolved lead by iron hydroxide was reduced due to the high concentration of dissolved organic matter in the aqueous phase.

Table 1 shows the analysis values of MMA, MAA, Macr, and Pb in the oil phase and the aqueous phase after decantation, and Table 2 shows the Pb concentration in the aqueous phase after the co-precipitation treatment using iron hydroxide. In addition, the polymerization loss in the distillation purification process of the oil phase containing lead and the crude methacrylic acid based on the amount of MAA and MMA contained in the crude methyl methacrylate solution until the distillation purification was abandoned. Table 3 shows the recovery of methyl methacrylate.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

According to the present invention, not only is it possible not only to efficiently recover trace amounts of lead ions or lead compounds that are partially peeled or eluted from the catalyst, but also to produce carboxylic acid esters and by-products in the reaction system. Useful carboxylic acids and organic compounds can be efficiently recovered, and by removing lead ions and lead compounds almost completely, the target product, carboxylic acid ester, has a double bond. It is possible to provide a method for producing a carboxylic acid ester which has a high industrial practical value that can sometimes suppress a polymerization reaction and is excellent in economic efficiency.

Claims (2)

[Claims] An aldehyde, an alcohol and oxygen are reacted with a catalyst containing lead to produce a corresponding carboxylic acid ester. In a method for removing a lead compound, an acid and / or a compound capable of generating a sulfate ion or a phosphate ion, or both ions, or a mixture thereof in a crude carboxylic acid ester solution is added to the crude carboxylic acid ester solution; P on the water phase side when oil-water two layers are separated
While maintaining H at 6 or less, lead ions or lead compounds were extracted or precipitated and moved to the aqueous phase side, water-soluble organic substances in the aqueous phase were moved to the oil phase, and the aqueous phase and the oil phase were further separated. Then, a method of adjusting the pH of the aqueous phase to 7 or more in the presence of iron ions to generate iron hydroxide, and recovering lead ions and lead compounds by coprecipitation separation from the aqueous phase. 2. The lead recovery method according to claim 1, wherein the substance capable of generating sulfate ions or phosphate ions in the crude carboxylic acid ester solution is sulfuric acid or phosphoric acid.