JP2813026B2 - Purification method of alkanesulfonic acid alkali salt - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for purifying an alkali alkanesulfonic acid salt, and more specifically, to remove methanol and water from an alkali alkanesulfonic acid salt containing methanol and water by evaporation. To obtain highly purified alkali salts of alkanesulfonic acids.

[Prior art] Alkanesulfonate, which is a surfactant having strong detergency and excellent biodegradability, is generally prepared by reacting sulfur dioxide and oxygen on normal paraffin under irradiation of ultraviolet rays to form a photosulfonic acid. It is produced by neutralizing the obtained alkanesulfonic acid with an alkali. However, this photo-sulfonation reaction is for preventing coloration of products and suppressing the production of polysulfonic acid.
The reaction rate is set low, and the reaction product is obtained as a mixture containing unreacted normal paraffin, by-product sulfuric acid, water, and dissolved sulfur dioxide in addition to alkanesulfonic acid.

Therefore, these unreacted substances and by-products must be separated and removed before the alkanesulfonic acid is neutralized to obtain the alkanesulfonic acid alkali salt.

The sulfur dioxide is removed by heating or blowing oxygen or nitrogen gas.

Sulfuric acid by-produced becomes an alkali sulfate during neutralization of alkanesulfonic acid, consumes a large amount of alkali for neutralization, and the generated alkali sulfate is used as an alkanesulfonic acid, which is a target substance, at the time of separation. Alkaline salts are entrained to cause loss or require a great deal of equipment and labor for recovery. Therefore, they are usually removed as much as possible prior to neutralization.

To remove unreacted normal paraffin, for example, first add water to the sulfonation reaction product to separate the undissolved paraffin, and then add methanol, which is a polar organic solvent that does not mix with hydrocarbons, to this residue. This can be performed by forming a normal paraffin layer and an aqueous methanol solution layer containing alkanesulfonic acid and sulfuric acid, and separating alkanesulfonic acid and sulfuric acid as extracted raffinate. It is widely known that such a method using methanol as an extractant is an inexpensive and easy method for removing and recovering normal paraffin.

The mixture thus obtained by removing the unreacted substances and by-products still contains a considerable amount of sulfuric acid, a solvent such as methanol used for separating normal paraffin, water and a trace amount of normal paraffin.

An alkali metal such as caustic soda was added to the mixture, and from the neutralized mixture obtained by neutralization, the precipitated alkali sulfate was removed by filtration or centrifugation, and the obtained filtrate was purified to obtain the desired product. An alkanesulfonic acid alkali salt is obtained.

The neutralized mixture from which the alkali sulfate has been removed contains methanol, water and a trace amount of residual normal paraffin used as the extraction solvent. Usually, an evaporator is used as a means for removing these volatile impurities and concentrating the alkali alkanesulfonic acid salt.

For example, JP-B-46-8968 and JP-A-52-139019 employ a means of concentration for removing residual methanol and the like in the final step of producing an alkali salt of an alkanesulfonic acid. JP-A-59-148857 discloses that a mixture obtained by separating and removing unreacted substances and by-products is neutralized to remove alkali sulfates, and then an evaporator preheated to 130 ° C. Although a purification method for treating is proposed, in the embodiment, methanol is removed as much as possible at a temperature at which water does not evaporate (90 ° C.) in the first-stage evaporator, and then the second-stage evaporator is used. A method of evaporating the remaining methanol and water at a high temperature of about 180 ° C. and further purifying it by means of so-called steam stripping in which superheated steam is blown is exemplified.

However, in these methods, as the removal of methanol progresses, foaming becomes severe, and finally the evaporator is filled with foam and separation becomes impossible. To avoid such troubles, thin film evaporators are often used, but thin film evaporators are expensive and consume large amounts of energy.
It is not efficient to perform this methanol-water evaporation using only a thin film evaporator. In addition, residual methanol is 100ppm
An efficient industrial purification method for highly purified alkanesulfonic acid alkali salts such as the following has not been found yet.

[Problems to be Solved by the Invention] The present invention solves such problems, and requires complicated facilities and equipment for evaporating and removing methanol, moisture, and the like from alkanesulfonic acid alkali salts containing methanol, moisture, and a small amount of unreacted paraffin. An object of the present invention is to efficiently obtain a highly purified alkali alkanesulfonic acid salt without using a technique.

[Means for Solving the Problems] As a result of diligent research, the present inventors have divided the evaporation process into two stages of a forced circulation evaporator having a spray nozzle for breaking bubbles and a thin film evaporator. The inventors have found that the above object can be achieved by setting the concentration of methanol and water in the concentrated liquid discharged from the one-stage forced circulation evaporator to a specific concentration, and completed the present invention.

That is, the present invention relates to a method for purifying an alkali alkanesulfonic acid salt by evaporating and removing methanol and water from an aqueous methanol solution of an alkali alkanesulfonic acid salt. Using a forced circulation evaporator having a concentration of methanol, while maintaining the methanol concentration of the resulting concentrated alkanesulfonic acid salt solution at 5.0% or less and the water concentration at 30% by weight or more, and then evaporating the concentrated solution in a thin film. This is a method for purifying an alkali salt of an alkanesulfonic acid, which comprises evaporating and concentrating in an apparatus.

The aqueous methanol solution of the alkanesulfonic acid alkali salt before the evaporation purification contains a small amount of normal paraffin, sodium sulfate, sodium sulfite, etc. in addition to methanol and water. The present invention provides highly purified alkali salts of alkanesulfonic acids by evaporating and removing methanol, water and normal paraffin among these impurities with high efficiency.

FIG. 1 shows an example of the flow of the present invention. The aqueous methanol solution of the alkanesulfonic acid alkali salt supplied from the supply line (1) is heated to about 95 to 105 ° C. by a heating device (2) such as a heat exchanger, and is forced into a forced circulation evaporator (3). )
Supplied to

The forced circulation evaporator has an internal spray nozzle for foam breaking (3a)
Use the one with The evaporator feed is sprayed from the spray nozzle onto the concentrated liquid surface below in a shower form, evaporating some of the volatile components to promote gas-liquid separation, and crushing the foam generated on the liquid surface with the spray liquid, Prevent growth. A spray nozzle having a spray tip can be used as the spray nozzle. However, even when a simple flash nozzle is used to process a feed containing an appropriate amount of a component to be vaporized into the evaporator, the same spray nozzle as the chip is used. A state can be obtained, which is advantageous for clogging and pressure loss, and can be suitably used.

When the forced circulation evaporator is used in the present invention, methanol and water contained in the aqueous methanol solution of the alkanesulfonic acid alkali salt are evaporated and vaporized according to the temperature and pressure conditions in the apparatus. Is discharged from the top of the device, and the concentrated aqueous methanol solution of the alkali alkanesulfonic acid salt collects at the bottom of the device and is withdrawn from the bottom. The concentrated liquid that accumulates in the lower part of the liquid becomes foamed intensely as the methanol decreases, and a layer of foam is formed on the surface of the liquid and grows.The alkane sulfone is sprayed downward from the spray nozzle provided on the horizontal surface of the vapor part. Aqueous methanol solution of acid alkali salt is sprayed and directly hits the foam formed on the surface of the concentrate while evaporating water and methanol, so the foam on the liquid surface is beaten and crushed, maintaining normal vapor can do.

The heating temperature in the forced circulation evaporator depends on the operating pressure of the evaporator, and is in the range of 95 to 105 ° C under normal pressure conditions, but the residual methanol concentration is 5.0% by weight or less and the residual water concentration is 30% by weight or more. Control.

A part of the concentrated liquid extracted from the bottom part returns to the raw material supply line (1) of the aqueous methanol solution of the alkanesulfonic acid alkali salt via the line (4), and is again forced through the heating device. And the remainder of the concentrate is fed via line (5) to a second stage evaporator, the thin film evaporator (6). Thus, even in the evaporative concentration step involving foaming, by using such a forced circulation evaporator, it is possible to send a concentrated liquid in which methanol is reduced to a desired content or less to a thin film evaporator while suppressing foaming. .

In the present invention, it is necessary to adjust the impurity content of the concentrated liquid at the bottom of the forced circulation evaporator so that the residual methanol concentration is 5.0% by weight or less and the residual water concentration is 30% by weight or more.

If the residual methanol concentration exceeds 5.0% by weight, the concentration of methanol contained in the product alkanesulfonic acid alkali salt will be reduced to 100 ppm by weight or less even if it is treated in the following thin film evaporator, unless evaporation under reduced pressure is adopted. If the residual water concentration is less than 30% by weight, it is preferable to maintain the methanol concentration in the thin film evaporator at 100 ppm by weight or less and maintain the fluidity of the alkanesulfonic acid alkali salt in a thin film evaporator as described later. The concentration cannot exceed 0.5% by weight. The residual methanol concentration and the residual moisture concentration can be adjusted by controlling the bottom temperature of the forced circulation evaporator according to the operating pressure.

The thin film evaporator is a device for evaporating and concentrating the generated bubbles while destroying the generated bubbles with mechanical energy, and can be used in either a vertical type or a horizontal type. Alkanesulfonic acid alkali salt is a compound that is more stable to heat than sulfonic acid before neutralization, but in order to obtain a good hue and odorless alkali metal alkanesulfonic acid, it is necessary to heat a thin film evaporator. Preferably, the temperature is controlled at 200 ° C. or less.

In addition, in a thin film evaporator, 100
It is preferable to maintain fluidity on the order of poise for evaporation and fluid movement. For this purpose, for example, if the fluid temperature is 190 ° C., the water concentration may be set to 0.5% by weight or more.

The alkanesulfonic acid alkali salt concentrated in the thin film evaporator is withdrawn from the bottom and sent through a line (7) to be a product.

On the other hand, methanol, water and a small amount of normal paraffin evaporated and separated from the forced circulation evaporator and the thin film evaporator are supplied to the methanol distillation column (10) by lines (8) and (9).
To be rectified and separated. If these vapors are supplied to the distillation column as they are without being condensed and separated by supplying them to the distillation column, water and methanol do not form an azeotropic mixture, which is economically preferable. Normal paraffin can be easily separated into two layers and easily separated as an upper layer by extracting the bottom liquid of the distillation column and allowing it to stand. The separated methanol, water and normal paraffin can be recycled and reused again in the production process of the alkali alkanesulfonic acid salt.

EXAMPLES Example 1 atmospheric pressure, in a continuous optical reactor operating at room temperature, in the presence of water in normal paraffins C ₁₃ -C ₁₈ by the action of sulfur dioxide and oxygen, subjected to optical sulfonation reaction Was. The resulting reaction mixture was allowed to stand to form two layers, and a part of the by-product sulfuric acid was separated as a lower layer of dilute sulfuric acid. Then, the upper layer was extracted with water to separate unreacted normal paraffin, and then nitrogen gas was blown in to remove sulfur dioxide. Then, methanol is added to separate into an upper layer of normal paraffin and a lower layer composed of an aqueous methanol solution of alkarsulfonic acid and sulfuric acid. Neutralize the lower layer mixture with caustic soda,
The precipitated sodium sulfate was filtered off.

The neutralized solution from which sodium sulfate had been removed was sent to the evaporation concentration system shown in FIG. 1 for purification. First, 115 Kg / Hr of the neutralized solution was introduced into the vertical forced circulation evaporator (3) through the plate heat exchanger (2), and spray-injected by the spray nozzle (3a) toward the entire concentrated liquid surface, and the pressure was reduced to 210 Torr and 60 Torr. The methanol and water were evaporated at ° C. Of the concentrated liquid extracted from the forced circulation evaporator outlet, 47.5 kg / Hr was led to the thin film evaporator through the line (5), and the remainder was again circulated to the forced circulation evaporator. The thin film evaporator (6) was of a horizontal centrifugal type, and was continuously evaporated at 180 ° C. The combined methanol and steam from the forced circulation evaporator and the thin film evaporator were sent to a methanol distillation column (10) for rectification.

28.5Kg / Hr of molten salt of sodium alkane sulfonate was obtained from the lower part of the thin film evaporator. This molten salt contained 3.0% by weight of sodium sulfate and 0.3% by weight of normal paraffin, but was colorless and odorless.

Table 1 shows the concentration of each component in the newly supplied aqueous methanol solution of alkanesulfonic acid sodium salt, the concentrate at the outlet of the forced circulation evaporator and the concentrate at the outlet of the thin film evaporator. The amount of water and methanol sent to the methanol distillation column was 86.5 Kg / Hr.

Comparative Example 1 The neutralized solution obtained in Example except for sodium sulfate was evaporated and concentrated using the same forced circulation evaporator and thin film evaporator as in Example 1. However, the methanol concentration at the outlet of the forced circulation evaporator was adjusted to 5.8% by changing the evaporator tower bottom temperature. As a result, the methanol concentration at the outlet of the thin film evaporator was 160 ppm by weight, and the removal of methanol was insufficient.

Table 1 shows the concentrations of the components in the feed solution, the concentrate at the outlet of the forced circulation evaporator, and the concentrate at the outlet of the thin film evaporator.

Comparative Example 2 The neutralized solution obtained in Example except for sodium sulfate was evaporated and concentrated using the same forced circulation evaporator and thin film evaporator as in Example 1. However, the water concentration at the outlet of the forced circulation evaporator was concentrated to 25.0% by changing the evaporator tower bottom temperature. Subsequently, the concentrated liquid was led to a thin film evaporator and concentration was continued. However, the liquid had a high viscosity, lost its own weight falling property, and could not be discharged.

Table 1 shows the concentration of each component in the feed liquid and the concentrated liquid at the outlet of the forced circulation evaporator.

[Effect of the Invention] The method of the present invention uses a forced circulation evaporator and a thin film evaporator from an aqueous methanol solution of an alkanesulfonic acid alkali salt, and determines the concentration of methanol and water in the concentrate at the forced circulation evaporator outlet. Evaporating and removing methanol and water to purify the alkali alkane sulfonic acid while adjusting it to a specific range allows efficient use of highly purified alkali alkane sulfonic acid salt without using complicated equipment and technology. If the separated methanol, water and the like are rectified and separated in a distillation column in a vapor state, the methanol and water can be recycled and reused in the alkali alkanesulfonic acid production apparatus. It has a remarkable effect of being more economical.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an evaporation concentration system of an aqueous methanol solution of an alkali alkanesulfonic acid salt of the present invention. 1 ... supply line 2 ... heating device 3 ... forced circulation evaporator 3a ... spray nozzle 4 ... circulation line 5 ... concentrated liquid line 6 ... thin film evaporator 7 ... product line 8, 9 ... methanol Recovery line 10 …… Methanol distillation tower

Continuation of front page (56) References JP-A-59-148757 (JP, A) JP-A-52-139019 (JP, A) JP-A-63-126858 (JP, A) JP-B-46-8968 (JP) , B1) Practical application Microfilm (JP, U) photographing the contents of the specification and drawings attached to the application of Japanese Utility Model Application No. Sho 61-85349 (Japanese Utility Model Application No. Sho 62-199103) (58) Field surveyed (Int. . ^6, DB name) C07C 309 / 00,303 / 42 C07B 63/00

Claims (3)

(57) [Claims] 1. A method for purifying an alkali alkane sulfonic acid salt by evaporating methanol and water from an aqueous methanol solution of an alkali alkane sulfonic acid salt, comprising the steps of: Using a forced circulation evaporator having a concentration of methanol of not more than 5.0% and a concentration of water of not less than 30% by weight of the obtained concentrated solution of the alkanesulfonic acid alkali salt. A method for purifying an alkali salt of an alkanesulfonic acid, comprising concentrating the solution in an evaporator. 2. The method according to claim 1, wherein the methanol concentration of the alkali alkanesulfonic acid obtained from the thin film evaporator is 100 ppm by weight or less and the water concentration is 0.5 to 2.5% by weight. . 3. The method according to claim 1, wherein the vapor of methanol and water evaporated in the forced circulation evaporator and the thin film evaporator is led to a distillation column without being condensed, and separated and recovered into methanol and water in the distillation column. The method according to claim 1.