JP2005187598A - METHOD FOR PRODUCING alpha-SULFOFATTY ACID ALKYL ESTER SALT - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an α-sulfofatty acid alkyl ester salt with high long-term storage stability by suppressing forming substance(s) contributing to pH drop by a simpler means. <P>SOLUTION: The method for producing the α-sulfofatty acid alkyl ester salt comprises the step of contacting the corresponding fatty acid alkyl ester with a sulfonating gas to form a sulfonated reaction product, the step of adding water to the sulfonated reaction product followed by heating and the step of neutralizing a reaction product obtained through the preceding step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an α-sulfo fatty acid alkyl ester salt.

α-Sulfo fatty acid alkyl ester salts have been conventionally used as surfactants, but their performance as detergents is highly evaluated because they have particularly high detergency, good biodegradability and little impact on the environment. ing.
The α-sulfo fatty acid alkyl ester salt is obtained by bringing a fatty acid alkyl ester into contact with a sulfonated gas for sulfonation to produce an α-sulfo fatty acid alkyl ester and neutralizing it.

The sulfonation mechanism of fatty acid alkyl esters is described in Smith and Stirton: JAOCS vol. 44, p. 2, p. 105, Gelnhausen, Kurle (1984); Yoshimura: As illustrated in Oil Chemistry (JJOCS), 41, 10 (1992), the following reaction scheme explains.
That is, when a fatty acid alkyl ester is brought into contact with a sulfonated gas, as shown in the following reaction formula, SO ₃ is first inserted into the alkoxy group part of the ester, and an SO ₃ monomolecular adduct (hereinafter referred to as “single molecule addition”). Body)). Next, SO ₃ is further introduced into the α-position of the single molecule adduct to produce an SO ₃ bimolecular adduct (hereinafter referred to as “bimolecular adduct”). Thereafter, SO ₃ inserted into the alkoxy group moiety is eliminated to produce α-sulfo fatty acid alkyl ester.

In this reaction scheme, the reaction proceeds rapidly until the bimolecular adduct formation step, but the reaction rate is very slow in the step of producing α-sulfo fatty acid alkyl ester from the bimolecular adduct. For this reason, a sulfonated gas such as SO ₃ gas that reacts with the fatty acid alkyl ester theoretically in an equimolar amount is actually used in excess of the equimolar amount to improve the reaction rate, or a bimolecular adduct. After the reaction has progressed to the production stage, an aging step is provided to promote the elimination of SO ₃ . When an aging step is provided, an α-sulfo fatty acid alkyl ester salt can be obtained by neutralizing with an alkali after the aging step.
Since the α-sulfo fatty acid alkyl ester salt thus obtained solidifies when left at room temperature, it is usually stored at a temperature of 60 to 80 ° C.

However, when stored for a long time in a warmed state, an alkyl sulfate salt (R ¹ SO ₃ M: where R ¹ represents an alkyl group and M represents a base) contained as a by-product of the α-sulfo fatty acid alkyl ester salt. Due to the decomposition, a phenomenon occurs in which the pH value of the solution containing the α-sulfo fatty acid alkyl ester salt decreases with time.
The α-sulfo fatty acid alkyl ester salt causes hydrolysis of the ester bond under conditions other than the neutral region having a pH value of 5 to 8, and produces a by-product of the α-sulfo fatty acid di-salt having the following structure. Bring.
This α-sulfo fatty acid di-salt is not only poorly soluble in water but also inferior in surface activity, so that it is not preferable to be present in an aqueous α-sulfo fatty acid alkyl ester salt solution used as a cleaning material.

The pH of the solution has been lowered, that is, the α-sulfo fatty acid alkyl ester salt under acidic conditions is hydrolyzed and stored as a by-product when it is stored for a long time. Therefore, in order to suppress the by-production of α-sulfo fatty acid di-salt, it is conceivable to reduce the alkyl sulfate that is a causative substance of the pH decrease.
Some techniques for reducing alkyl sulfates have been proposed for some time, although they are not intended to suppress the decrease in pH.
For example, in Patent Document 1, the reaction solution after the sulfonation reaction is aged under reduced pressure to remove surplus SO ₃ , thereby suppressing the production of by-products such as alkyl sulfate salt and sulfate, resulting in improved physical properties. It is described that there was an effect.
And in patent document 2, as a result of removing alkyl sulfate by using apparatuses, such as a thin film evaporator, for the reaction liquid after sulfonation, it was described that it was effective in odor improvement.
Japanese Patent Laid-Open No. 58-157762 JP 07-247259 A

  However, the methods described in Patent Documents 1 and 2 are not intended to suppress a decrease in pH of a solution containing an α-sulfo fatty acid alkyl ester salt as described above. Furthermore, in order to reduce the alkyl sulfate, it is necessary to add equipment such as a decompression equipment and an evaporator, which complicates the process and is not always satisfactory.

  The object of the present invention is to solve the above-mentioned problems in the prior art. That is, an object of the present invention is to provide an α-sulfo fatty acid alkyl ester salt that suppresses the production of a causative agent of pH reduction by a simpler method and has excellent long-term storage stability.

As a result of intensive studies, the present inventors have suppressed the decrease in pH of a solution containing an α-sulfo fatty acid alkyl ester salt by mixing water with the reaction liquid after sulfonation of the fatty acid alkyl ester and performing heat aging. I found out that I can do it.
That is, the first method for producing an α-sulfo fatty acid alkyl ester salt of the present invention includes a sulfonation step of bringing a fatty acid alkyl ester into contact with a sulfonation gas to obtain a sulfonation reaction product, and a sulfonation reaction product. It has the water addition process which adds and heats water, and the neutralization process which neutralizes the reaction product obtained through a water addition process, It is characterized by the above-mentioned.

  The second method for producing an α-sulfo fatty acid alkyl ester salt includes a sulfonation step in which a fatty acid alkyl ester is brought into contact with a sulfonation gas to obtain a sulfonation reaction product, and a lower alkyl alcohol is added to the sulfonation reaction product. It has an esterification step, a water addition step of adding water to the reaction product of the esterification step and heating, and a neutralization step of neutralizing the reaction product obtained through the water addition step .

  The amount of water added in the water addition step is preferably 0.5 to 5% by mass with respect to the sulfonation reaction product.

In the water addition step, it is preferable to further add a lower alkyl alcohol. Here, it is preferable that the addition amount of a lower alkyl alcohol is 2-5 mass% with respect to a sulfonation reaction product.
Moreover, it is preferable to perform a water addition process on 50-100 degreeC temperature conditions, and it is still more preferable to carry out on 80-90 degreeC temperature conditions.
In the water addition step, aging is preferably performed for 10 minutes or more after adding water, and aging is preferably performed for 2 to 4 hours.

  According to the production method of the present invention, it is possible to provide an α-sulfo fatty acid alkyl ester salt excellent in long-term storage stability by suppressing the generation of a causative substance of pH reduction by a simpler method.

In the production method of the present invention, preferably, the following steps (A) to (E) are sequentially performed to obtain an α-sulfo fatty acid alkyl ester salt.
(A) A sulfonation step, which is a step of bringing a fatty acid alkyl ester into contact with a sulfonation gas to obtain a sulfonation reaction product.
(B) An esterification step of esterifying with a lower alkyl alcohol (hereinafter referred to as “lower alcohol”) in order to suppress by-products.
(C) A water addition step of adding water and heating to remove the alkyl sulfate.
(D) A neutralization step of obtaining an α-sulfo fatty acid alkyl ester salt from the α-sulfo fatty acid alkyl ester by neutralization with an alkali.
(E) A bleaching step of bleaching the obtained α-sulfo fatty acid alkyl ester salt.
Here, the (B) esterification step can be omitted. When (B) the esterification step is performed, the (B) esterification step may be performed simultaneously with the (C) water addition step or (C) after the water addition step, but is a by-product. In order to suppress the production of α-sulfo fatty acid di-salt and to satisfactorily inhibit the production of the causative substance of the pH decrease, it is preferable to perform the (B) esterification step before the (C) water addition step.
The (E) bleaching step can be simplified or omitted depending on the color tone of the α-sulfo fatty acid alkyl ester obtained in the (A) sulfonation step. (E) When performing a bleaching process, it is preferable to carry out after the (D) neutralization process. Hereinafter, each step will be described in detail.

(A) Sulfonation step (A) The sulfonation step is a step in which the fatty acid alkyl ester is sulfonated by contacting with a sulfonate gas. In addition to the α-sulfo fatty acid alkyl ester which is the main product of the sulfonation reaction, the sulfonation reaction product obtained in this (A) sulfonation step is usually a bimolecular adduct, alkyl sulfate, etc. as a by-product. Will be included.
The sulfonation step includes a sulfonation reaction step in which a fatty acid alkyl ester and a sulfonation gas are brought into contact with each other, and an aging step in which the mixture is kept at a suitable temperature for a certain period of time in order to promote elimination of SO ₃ from the bimolecular adduct. It is preferable in order to reduce by-products in the sulfonation process.
Here, a monomolecular adduct and a bimolecular adduct are obtained by the sulfonation reaction step, and the elimination of SO ₃ from the bimolecular adduct is promoted by the aging step.
If the aging step is insufficient and the bimolecular adduct remains, an α-sulfo fatty acid disulfide such as α-sulfo fatty acid disoda as a by-product in the neutralization step performed after the aging step, for example, sodium hydroxide. A salt is formed. Since such a by-product is inferior in detergency and water solubility and does not contribute to the performance as a cleaning agent, it is desirable to reduce the bimolecular adduct by performing the aging step.

Examples of the sulfonation gas used in the sulfonation reaction step include SO ₃ gas and fuming sulfuric acid, but SO ₃ gas is preferably used.
The SO ₃ gas is usually used with an inert gas such as dehumidified air or nitrogen, preferably diluted to a concentration of 3 to 30% by volume. The SO ₃ gas is preferably used in a proportion of 1.0 to 2.0 mol, more preferably 1.1 to 1.5 mol, relative to 1.0 mol of the fatty acid alkyl ester to be sulfonated. If the amount is less than 1.0 times mol, the sulfonation reaction does not proceed sufficiently. If the amount exceeds 2.0 times mol, the sulfonation reaction becomes more extreme and coloring due to local heat may become significant. This is not preferable in terms of obtaining a light product.

As the fatty acid alkyl ester, a fatty acid alkyl ester represented by the following general formula (I) (hereinafter referred to as “fatty acid alkyl ester (I)”) is preferably used.
R ¹ CH ₂ COOR ² (I)
(In the formula, R ¹ represents a linear or branched alkyl group or alkenyl group having 6 to 24 carbon atoms, and R ² represents a linear or branched alkyl group having 1 to 6 carbon atoms.)
As the fatty acid alkyl ester, a saturated fatty acid alkyl ester is preferably used. Fatty acid alkyl esters are derived from animal fats derived from beef tallow, fish oil, lanolin, etc., derived from vegetable fats derived from palm oil, palm oil, soybean oil, etc., derived from the oxo method of α-olefins Any of the synthetic fatty acid-derived alkyl esters may be used and is not particularly limited.
Specifically, methyl dodecanoate, ethyl or propyl; tetradecanoate methyl, ethyl or propyl; methyl palmitate, ethyl or propyl; stearate methyl, ethyl or propyl; hydrogenated beef tallow fatty acid methyl, ethyl or propyl; hydrogenated fish oil fatty acid methyl , Ethyl or propyl; coconut oil fatty acid methyl, ethyl or propyl; palm oil fatty acid methyl, ethyl or propyl; palm kernel oil fatty acid methyl, ethyl or propyl, and the like. A mixture of more than one species can be used.

The reaction temperature in the sulfonation reaction step may be a temperature at which the fatty acid alkyl ester has fluidity. Preferably, it is a temperature range higher than the melting point of the fatty acid alkyl ester and 100 ° C. higher than the melting point, more preferably a temperature range higher than the melting point and higher than the melting point by 70 ° C.
The sulfonation method may be any sulfonation method such as a thin film type sulfonation method or a batch type sulfonation method. The batch sulfonation method is excellent in terms of the color tone of the α-sulfo fatty acid alkyl ester, and the thin film sulfonation method is excellent in terms of production cost. As the sulfonation reaction method, a tank reaction, a film reaction, a tube-type gas-liquid mixed phase reaction, or the like is used.
Although the reaction time of the sulfonation reaction step varies depending on the sulfonation method employed, it is generally preferably 5 to 120 seconds for the thin film sulfonation method and about 10 to 240 minutes for the batch sulfonation method.
After completion of the sulfonation reaction step, the bimolecular adduct is transferred to the aging step. In the aging step, the SO ₃ elimination reaction from the bimolecular adduct is promoted. The temperature of the aging step is preferably 70 to 100 ° C. If it is lower than 70 ° C., the elimination reaction does not proceed rapidly, and if it is higher than 100 ° C., the coloring may be remarkable. The time for performing the aging step is preferably in the range of 1 to 120 minutes.

Further, (A) the sulfonation step is preferably performed in the presence of a coloring inhibitor, and when the aging step is provided in the (A) sulfonation step, at least the aging step is preferably performed in the presence of the coloring inhibitor. .
Various conventionally proposed coloring inhibitors can be used. The coloring inhibitors are disclosed in, for example, JP-A-10-175940, JP-A-10-175941, JP-A-09-216863, and the like.
As the coloring inhibitor, a salt containing a monovalent metal ion (monovalent metal salt) is particularly preferable, and as the monovalent metal salt, inorganic sulfates such as sodium sulfate, potassium sulfate, and lithium sulfate are preferable.
The inorganic sulfate is not particularly limited as long as it is a powdered anhydrous salt having a monovalent metal ion. Among these, the monovalent metal ion has a monovalent metal ion disclosed in JP 09-216863 A, It is particularly preferable to use an inorganic sulfate having an average particle size of 250 μm or less. Inorganic sulfate has a high coloration suppressing effect and is inexpensive, and is a component blended in a cleaning agent, and therefore does not need to be removed from the product α-sulfo fatty acid alkyl ester salt. In addition, during the reaction, the inorganic sulfate is hardly dissolved in the reaction solution to the extent that its surface is slightly dissolved, and is dispersed in the reaction solution. Therefore, by adjusting the average particle size to 250 μm or less, the fatty acid The contact area with the alkyl ester is increased, the dispersibility is improved, and the effect of addition is further increased.
The average particle diameter of the inorganic sulfate is preferably 250 μm or less, more preferably 50 μm or less.
The addition amount of the coloring inhibitor is preferably 0.1 to 20% by mass, more preferably 2 to 10% by mass with respect to the fatty acid alkyl ester. If it is less than 0.1% by mass, the effect of addition may not be obtained.

(B) Esterification step (A) A lower alcohol is allowed to act on the sulfonation reaction product obtained in the sulfonation step to esterify by-products such as a bimolecular adduct contained in the sulfonation reaction product. By providing an esterification step, by-products can be reduced. As a specific method of esterification, a lower alcohol is added to the sulfonation reaction product.
By adding a lower alcohol, the bimolecular adduct in the sulfonated reaction product is reduced. Therefore, when performing the below-mentioned neutralization process, the production | generation of a di salt can further be suppressed.

The lower alcohol used in the esterification step is preferably one having 1 to 6 carbon atoms, but is not particularly limited. The lower alcohol is preferably used in an amount of 0.5 to 5 times mol, more preferably 0.8 to 2 times mol for the bimolecular adduct in the reaction solution. The reaction temperature is preferably 50 to 100 ° C, more preferably 50 to 90 ° C, and the reaction time is preferably 5 to 120 minutes.
As described above, the esterification step may be performed simultaneously with the water addition step, may be performed after the water addition step, or may be performed before the water addition step, but is performed before the water addition step. It is preferable.

(C) Water addition step (C) In the water addition step, when the (B) esterification step is omitted, the sulfonation reaction product obtained in the (A) sulfonation step is added to the (B) esterification step. In the case of carrying out (B), water is added to the reaction product of the esterification step and heated. Thereby, the alkyl sulfate contained in the sulfonated reaction product is decomposed. By performing the neutralization step after the alkyl sulfate in the sulfonation reaction product is decomposed, the production of the alkyl sulfate salt is suppressed.
In particular, if (B) the esterification step is performed, and (B) the esterification step is followed by (C) the water addition step, the bimolecular adduct is reduced by esterification, and the α-sulfo fatty acid alkyl ester salt is added as a secondary salt. It becomes possible to suppress the pH drop of the solution containing the α-sulfo fatty acid alkyl ester salt while preventing the production of α-sulfo fatty acid di-salt which is a living organism.

(C) It is preferable that the addition amount of the water in a water addition process is 0.5-5 mass% with respect to a sulfonation reaction product, More preferably, it is 1-3 mass%. If it is less than 0.5% by mass, it may be insufficient for the decomposition of the target alkyl sulfate, and as a result, the effect of suppressing the pH decrease of the neutralized solution obtained through the neutralization step (D) described later. May not be fully exhibited. On the other hand, when the content is more than 5% by mass, the viscosity of the reaction solution is remarkably increased and handling properties are deteriorated.
(C) 50-100 degreeC is preferable and the temperature heated in a water addition process has more preferable 80-90 degreeC. It is preferable to heat to the above preferred temperature range and hold for a certain period of time (heating and aging), and the holding time is preferably 10 minutes or more, and more preferably 2 to 4 hours.

(C) In the water addition step, it is preferable to further add a lower alcohol. When the lower alcohol is further added in this manner, the fluidity of the α-sulfo fatty acid alkyl ester is improved, which can be advantageous for transporting and storing the α-sulfo fatty acid alkyl ester.
(C) The lower alcohol used in the water addition step is preferably one having 1 to 6 carbon atoms, but is not particularly limited. The addition amount of the lower alcohol is preferably 2 to 5% by mass with respect to the sulfonation reaction product. If the amount is less than 2% by mass, the effect of improving fluidity is low. If the amount is more than 5% by mass, the amount of lower alcohol remaining in the product obtained through the neutralization step (D) described later increases. (C) When the lower alcohol is added in the water addition step, the timing of addition may be before, at the same time as, or after the time at which water is added. It is preferable to do.
Moreover, you may perform physical processing like the process using a decompression process, a thin film evaporator, etc. after the (C) water addition process. By performing the treatment, the alkyl sulfate that causes a decrease in pH of the solution containing the α-sulfo fatty acid alkyl ester salt is further reduced.

(D) Neutralization step (D) In the neutralization step, the reaction product obtained through the above (C) water addition step, containing an α-sulfo fatty acid alkyl ester and reduced byproducts such as alkyl sulfate, By neutralizing by adding an alkali, an α-sulfo fatty acid alkyl ester salt can be obtained. At this time, the reaction product obtained through the (C) water addition step may have undergone the esterification step before or after the (C) water addition step.
(C) When adding an alkali to the reaction product of a water addition process, the system which uses an alkali as aqueous solution is possible. Further, a method (dry neutralization) in which alkaline inorganic powder is directly added to the reaction product in the water addition step to obtain a reaction mixed powder is also possible.
(D) It is preferable that the neutralization step is performed in a neutral range (pH 5 to 8) of a mixed solution (neutralized solution) of a reaction product containing an α-sulfo fatty acid alkyl ester and an alkali. . In the case of strong alkalinity, the ester bond may be easily cleaved.
When alkali is used as an aqueous solution, examples of the alkali used include alkali metals, alkaline earth metals, ammonia, and ethanolamine.
The concentration of the aqueous alkali solution is preferably about 2 to 50% by mass. The neutralization temperature is preferably 30 to 140 ° C., and the neutralization time is preferably 10 to 60 minutes.
Moreover, it is preferable that the activator density | concentration (active ingredient density | concentration (AI density | concentration)) in a neutralization liquid (slurry) shall be 10-80 mass%. The activator concentration is the total concentration of the α-sulfo fatty acid alkyl ester salt and the by-product α-sulfo fatty acid di-salt.
When dry neutralization is employed, the type of alkaline inorganic powder is arbitrary, but carbonates such as sodium carbonate and potassium carbonate are preferred.
The concentration of the α-sulfo fatty acid alkyl ester salt in the reaction mixture powder is preferably 10 to 95% by mass. The neutralization temperature is preferably 10 ° C. to 80 ° C., and the neutralization time is preferably 10 to 180 minutes.

(E) Bleaching step In the (E) bleaching step in this embodiment, by adding a bleaching agent to the solution containing the α-sulfo fatty acid alkyl ester salt obtained through the (D) neutralization step, α- The sulfo fatty acid alkyl ester salt is bleached.
As the bleaching agent, for example, hydrogen peroxide or hypochlorite can be used, and the addition amount of the bleaching agent is preferably 0.2 to 10% by mass with respect to the α-sulfo fatty acid alkyl ester salt. More preferably, it is 1-5 mass%. The bleaching temperature is preferably from 50 to 140 ° C, more preferably from 60 to 120 ° C. Further, the bleaching temperature is preferably 50 to 90 ° C. under atmospheric pressure, 50 to 135 ° C., more preferably 105 to 135 ° C. under a gauge pressure of 0.5 to 3.0 kgf / cm ² . The bleaching time is preferably 1 hour to 1 week, and can be carried out until the desired color tone is bleached.
In addition, when it is necessary to bleach the highly colored α-sulfo fatty acid alkyl ester, the (E) bleaching step may be performed before the (D) neutralization step, if necessary. (D) When bleaching before a neutralization process, it is preferable to bleach with hydrogen peroxide in presence of alkyl alcohol. As said alkyl alcohol, a C1-C6 lower alcohol is mentioned, for example, The addition amount of alcohol has preferable 2-30 mass% with respect to alpha-sulfo fatty-acid alkylester. The amount of hydrogen peroxide added is preferably 0.5 to 10% by mass with respect to the α-sulfo fatty acid alkyl ester. The bleaching temperature is preferably 100 ° C. or less, and the bleaching time is preferably 0.5 to 5 hours.
When the bleaching step is performed before the (D) neutralization step, the bleached α-sulfo fatty acid alkyl ester is sent to the (D) neutralization step together with the alkyl alcohol, in which the α-sulfo fatty acid alkyl ester salt Then, the product is separated from the alkyl alcohol-containing aqueous solution into a product.

According to the present invention, in the process for producing an α-sulfo fatty acid alkyl ester salt, water is added to the sulfonation reaction product containing the α-sulfo fatty acid alkyl ester to decompose the alkyl sulfate, thereby An α-sulfo fatty acid methyl ester salt that can suppress a decrease in pH of the aqueous α-sulfo fatty acid alkyl ester salt solution and has excellent long-term storage stability can be obtained by a simple method.
In addition, the α-sulfo fatty acid methyl ester salt obtained by the production method is less susceptible to the formation of α-sulfo fatty acid di-salt because the pH drop during storage at high temperatures is suppressed, and the device that handles this There is no fear of corroding the metal parts, and undesirable odors and changes in color tone are stably prevented.

The embodiments of the present invention are summarized as follows.
(1) The fatty acid alkyl ester is converted into an α-sulfo fatty acid alkyl ester salt through a sulfonation step and converted into an α-sulfo fatty acid alkyl ester salt through a water addition step and a neutralization step. Here, it is preferable to provide an esterification step before the water addition step, at the same time as the water addition step, or after the water addition step, and the obtained α-sulfo fatty acid alkyl ester salt is added before the neutralization step or If necessary, it can be bleached later by a bleaching step.
(2) The sulfonation reaction product containing an α-sulfo fatty acid alkyl ester is preferably added with 0.5 to 5% by mass, more preferably 1 to 3% by mass of water, preferably 60 in the water addition step. C. to 100.degree. C., more preferably 80 to 90.degree. C. At this time, the handleability can be improved by adding preferably 2 to 5% by mass of a lower alcohol. Further, a mechanical treatment step may be provided after the water addition step.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all by description of this Example.
[Examples 1 to 4]
Palm oil was transesterified with methyl alcohol, fractionated, and hydrogenated to obtain methyl esters of saturated fatty acids having 12 (C12), C14, C16, and C18 alkyl groups, and then mixed at a mass ratio shown in Table 1. The raw material methyl ester was obtained. In a 300 mL glass reactor equipped with a stirrer, this mixed saturated fatty acid methyl ester was diluted to 8% by volume with N ₂ gas while maintaining at 80 ° C., and 1.2 times moles of SO ₃ gas (vs. mixed saturated fatty acid methyl ester) was 60 Introduced at a constant rate for 1 minute, the sulfonation reaction step was performed. After the introduction, a ripening step was performed by stirring for 40 minutes while maintaining the temperature at 80 ° C. to obtain a sulfonation reaction product containing α-sulfo fatty acid methyl ester.
Thereafter, 3% by mass of methanol was added and an esterification reaction was carried out at 80 ° C. for 30 minutes to produce α-sulfo fatty acid methyl ester.
As a water addition step, 1% by mass of water (indicated in the table as “to acid”) with respect to 100% by mass of the sulfonation reaction product is added to the obtained α-sulfo fatty acid methyl ester under the condition of pH 1 or lower. 2% by mass was added and heat aging was performed (heating aging conditions were the heating temperature and heating time shown in Table 1).
Then, it neutralized using 2% NaOH aqueous solution so that pH might be set to 7, and manufactured alpha-sulfo fatty acid methyl ester salt aqueous solution with 13% of surfactant concentration. The obtained α-sulfo fatty acid methyl ester salt aqueous solution was stored at 70 ° C., and the pH change with time was measured using a glass electrode type pH meter (“Glass electrode type hydrogen ion concentration meter HM-26S” manufactured by Toa Denpa Kogyo Co., Ltd.). ).
[Examples 5 to 7]
After the sulfonation reaction and aging in the same manner as in Examples 1 to 4, water was added in 2% by mass or 5% by mass, and at the same time methanol or ethanol in Table 2 without performing the esterification step. The mixture was added in the indicated amount and heated, and the pH change after neutralization was measured in the same manner as in Examples 1 to 3.

[Comparative Example 1]
After the sulfonation reaction and aging in the same manner as in Examples 1 to 4, neutralization was performed using an aqueous 2% NaOH solution to a pH of 7 without using an esterification reaction and a water addition step. The pH change after neutralization was measured in the same manner as in -4.
[Comparative Example 2]
After the sulfonation reaction, aging and esterification reaction were carried out in the same manner as in Examples 1 to 4, the pH change after neutralization was measured in the same manner as in Examples 1 to 4 without a water addition step.
The evaluation results are shown in Tables 1-3.

As is clear from Tables 1 and 2 above, in Comparative Examples 1 and 2 in which the water addition step was not performed, the pH dropped sharply one day after neutralization and became strongly acidic after one month. On the other hand, in the examples in which the water addition step was performed, the pH reduction from immediately after neutralization to one month later was suppressed.

Claims (4)

  Sulfonation step of contacting fatty acid alkyl ester with sulfonation gas to obtain sulfonation reaction product, water addition step of adding water to the sulfonation reaction product and heating, reaction product obtained through water addition step And a neutralizing step for neutralizing the product, a method for producing an α-sulfo fatty acid alkyl ester salt.   A sulfonation step of contacting a fatty acid alkyl ester with a sulfonation gas to obtain a sulfonation reaction product, an esterification step of adding a lower alkyl alcohol to the sulfonation reaction product, and water in the reaction product of the esterification step A method for producing an α-sulfo fatty acid alkyl ester salt, comprising: a water addition step of adding and heating, and a neutralization step of neutralizing a reaction product obtained through the water addition step.   3. The production of an α-sulfo fatty acid alkyl ester salt according to claim 1, wherein the amount of water added in the water addition step is 0.5 to 5 mass% with respect to the sulfonation reaction product. Method. The method for producing an α-sulfo fatty acid alkyl ester salt according to any one of claims 1 to 3, wherein a lower alkyl alcohol is further added in the water addition step.