JPS646187B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for removing sulfate from a photo-sulfoxylation reaction mixture of paraffin, and in particular, in a reaction system substantially free of water, in contact with sodium sulfite. This invention relates to a method for removing sulfate from a reaction mixture obtained by subjecting paraffin to a photo-sulfoxylation reaction. [Prior art] In a method of photo-sulfoxidizing paraffin using sulfur dioxide and oxygen in a reaction system that is substantially free of water, colored substances adhere to the side wall of the light source of the reaction vessel and obstruct light irradiation. Therefore, as the reaction time progresses, the photo-sulfoxylation reaction hardly progresses. Therefore, when a predetermined amount of this colored substance adheres to the side wall surface of the light source, it is necessary to stop the reaction and remove the colored substance, which is inefficient and impossible to carry out the reaction continuously for a long time. For this reason, in the industrial production of alkanesulfonic acids, a method of photo-sulfoxylation in the presence of water is exclusively employed. However, this method has low reaction efficiency because water interferes with the radical chain reaction, and in addition to the alkanesulfonic acid, almost equimolar sulfuric acid is produced as a by-product, and when the sulfuric acid is separated, the alkanesulfonic acid has an odor. However, there were problems such as coloring. The present applicant has discovered that even in a reaction system in which water does not exist, the production of colored substances can be suppressed by photo-sulfoxylation in contact with sodium sulfite, and the reaction can be continued continuously. proposed a method for producing acid (patent application 1983)
-47117, 59-261880). [Problems to be solved by the invention] When paraffin is photo-sulfoxidized in contact with sodium sulfite, part of the sodium sulfite becomes sulfates such as sodium hydrogen sulfate, and sulfur dioxide is removed from the reaction mixture by degassing. During the removal process, it precipitates as crystals. Therefore, in order to keep the sulfate content in the final product low, it is necessary to remove this precipitate by solid-liquid separation, but this precipitate has a small particle size (estimated to be colloidal) and Furthermore, the particles are sticky due to the alkanesulfonic acid present in the reaction solution. For this reason, in excess of law,
At the initial stage of overtreatment, precipitates leak into the liquid, and during overtreatment, the cloth becomes clogged, making efficient filtration impossible, and furthermore, the liquid content in the overcake increases. Large amounts of cleaning solvent are required. In addition, even with the centrifugal separation method, precipitates flow out and get mixed into the separation liquid, and in order to achieve satisfactory separation, it is necessary to apply a considerable centrifugal force.In this case, the alkanesulfonic acid is considerably concentrated on the solid side. This had problems such as being uneconomical as it required collection. As a result of intensive research aimed at solving this problem, the present inventor surprisingly found that by adding a saturated or slurry aqueous solution of sodium sulfate to the reaction mixture, the particles agglomerate and crystallize to a larger size. It has also been found that stickiness of the particles is prevented, solid-liquid separation is performed extremely smoothly, and the liquid content in the cake can be kept substantially low. The present invention has been made based on the above findings, and an object of the present invention is to efficiently remove paraffin while preventing clogging of the cloth and preventing a large amount of precipitate from flowing into the separated liquid. The present invention provides a method for removing sulfate as a precipitate from a photo-sulfoxylation reaction mixture. [Means for Solving the Problems] The present invention as a means for solving the above problems involves subjecting paraffin to a photo-sulfoxylation reaction in contact with sodium sulfite in a reaction system substantially free of water. A photo-sulfoxylation reaction of paraffin, which comprises adding a saturated aqueous solution of sodium sulfate or an aqueous slurry solution of sodium sulfate to the reaction mixture to separate the solid and liquid. This is a method for removing sulfate from a mixed liquid. A reaction system substantially free of water as used in the present invention means that water is not added to the reaction system,
It does not exclude water dissolved in raw materials or water generated by reactions. The paraffin that can be used in the present invention may be any paraffin as long as it exists as a liquid in the reaction system, but if it is for the production of surfactants such as synthetic detergents, paraffin with a carbon number of 8 to 24 may be used. Paraffin is preferred. As a light source for irradiation, a lamp capable of irradiating light with a wavelength of 500 nm or less is used. The reaction temperature for this photo-sulfoxylation reaction is -20 to 200°C, taking into account the melting point or boiling point of paraffin.
The temperature is appropriately selected within the range of °C, but when using liquid paraffin at room temperature, there is no particular need to heat it. On the other hand, the higher the reaction pressure, the higher the reaction rate, which is preferable, but a range of 0 to 50 atmospheres is sufficient. Sulfur dioxide and oxygen can be used as a mixed gas, and this mixed gas can be pressurized and retained in the reactor just to replenish the consumed amount.
Alternatively, it may be allowed to flow through the reaction solution. This gas mixture has a molar ratio of sulfur dioxide to oxygen of 1 to 1.
1000, preferably 2 to 100 can be used. Generally, the photo-sulfoxylation reaction is carried out in a vertical reactor in which a cylindrical light source is installed vertically and the paraffin liquid can be retained around it, or in a horizontal reactor in which the light source is installed horizontally in the paraffin liquid. Any of these can be used, and sulfur dioxide and oxygen gas are separately introduced into the paraffin liquid from the lower part of these reactors via a dispersion plate and reacted. In this case, it is preferable that the gas after the contact can be at least partially recycled. This photo-sulfoxylation reaction is carried out in contact with sodium sulfite, which is
There is no particular problem in using either anhydrous or one containing water of crystallization. In addition, powder, pellets,
It may be used in either flake or flake form; however, when it is added to the reaction system, it is preferably in the form of a powder, and when it is used in a column, it is preferably in the form of pellets or flakes. Contacting with sodium sulfite means bringing the reaction solution into contact with sodium sulfite.Sodium sulfite may be directly added to the reaction solution and brought into contact with it, or a portion of the reaction solution may be extracted from the reaction system and sodium sulfite may be added to the reaction solution. Alternatively, it may be brought into contact with and returned to the reaction system. When adding sodium sulfite to the reaction system,
Sodium sulfite may be added to the paraffin in advance before introducing it into the reactor, or it may be added directly to the reaction solution in the reactor. The amount of addition and supply at this time is preferably 10% by weight to 100% by weight based on the paraffin consumed by the reaction. If it is less than 10% by weight, it is not possible to sufficiently suppress the adhesion of the colored substance to the wall surface of the light source, and the photo-sulfoxylation reaction cannot be carried out continuously for a long time, which is not preferable. The larger the amount of sodium sulfite added, the longer it will be possible to suppress the adhesion of colored substances, but even if it exceeds 100% by weight based on the paraffin consumed in the reaction, a significant increase in the suppressing effect is not observed. Therefore, it is economical to keep the content to 100% by weight or less. Note that the reaction solution in which sodium sulfite is dispersed becomes a suspension in the reactor, but if the addition amount is less than 10% by weight based on the amount of solution in the reactor, the reaction rate may decrease due to light scattering, etc. No particular decrease was observed. In addition, in the present invention, a column is filled with sodium sulfite, and a part of the reaction liquid is extracted from the reactor and passed through the column, whereby the reaction liquid and sodium sulfite are brought into contact and dissolved. You may also adopt a method of returning it. in this case,
A short contact time between the sodium sulfite and the reaction solution is sufficient. This is because sodium sulfite has the ability to decompose and remove substances that cause the formation of colored substances by dissolving it in the reaction solution, and the dissolution rate of sodium sulfite is extremely fast, so the contact time is particularly high. This is so that it does not become rate-limiting. In this case, the amount of the reaction liquid extracted from the reactor and circulated to the column is preferably 0.01 to 1 vol%/sec of the reaction liquid in the reactor. If it is less than 0.01vol%/sec, it will not be possible to effectively prevent the formation of colored substances, and if it is less than 1vol%/sec, it will not be possible to effectively prevent the formation of colored substances.
Even if it is more than sec, no significant improvement in effectiveness is observed and it is not economical. As the reaction progresses, sodium sulfite dissolves in the reaction solution and flows out of the column, but the formation of colored substances can be effectively prevented by replenishing the column in an amount commensurate with the consumed sodium sulfite. can. After the photo-sulfoxylation reaction is completed, sulfur dioxide is degassed by depressurizing the reaction mixture taken out from the reaction system, heating it, and blowing in a degassing gas such as oxygen gas, so that the sulfur dioxide is substantially dissolved in the reaction mixture. Sulfates such as sodium hydrogen sulfate, which can be considered to have been contaminated, precipitate. In this case, the pH of the reaction mixture is adjusted by adding an alkali such as sodium hydroxide to the remaining sulfate radicals, if necessary. The sulfate is removed from the reaction mixture containing the precipitated sulfate by solid-liquid separation. At this time, the reaction mixture is a saturated aqueous solution of sodium sulfate, or preferably an aqueous slurry solution containing 40% by weight or less of solids. Add and mix. In this case, the amount of the aqueous solution added is preferably 0.1 to 10% by weight based on the reaction mixture. If it is less than 0.1% by weight, solid-liquid separation cannot be performed smoothly, making it difficult to achieve the object of the present invention. On the other hand, if less than 10% by weight is added, a considerable amount of sodium sulfate will be mixed into the final product, which is not preferable. In addition, using a saturated aqueous solution or a slurry aqueous solution is possible while ensuring the amount of added sodium sulfate.
This is to reduce the amount of water added and to prevent sulfate from leaking into the separated liquid. Moreover, although sodium sulfate easily makes a supersaturated aqueous solution, it goes without saying that the saturated aqueous solution referred to in the present invention includes this supersaturated aqueous solution. This saturated or slurry aqueous solution of sodium sulfate may be added before the deaeration operation or after the sulfate is precipitated by deaeration. By adding this aqueous solution, the sulfate, which is presumed to be in the form of a fine colloid, coagulates or grows into crystals, prevents the particles from becoming sticky, and makes solid-liquid separation extremely easy. For solid-liquid separation, pressurization, reduced pressure, centrifugation, centrifugation, gravity sedimentation, or the like can be suitably employed. In the case of pressurized, reduced pressure, or centrifugal filtration, it is particularly preferable to add an aqueous slurry solution of sodium sulfate to the reaction mixture, since the sodium sulfate crystals can act as an assisting agent and significantly improve the overrate. In this case, the concentration of sodium sulfate supplied as a solid is 0.1% by weight based on the reaction mixture.
The content is preferably 5% by weight or less. If it is less than 0.1% by weight, the function as a super-aid will decrease, and if it is less than 5% by weight.
This is because even with the above, no significant improvement in the effect as a super-aiding agent is observed and it is not economical. In this case, water or a saturated aqueous solution of sodium sulfate may be added to the reaction mixture first, and powdered sodium sulfate or a slurry of sodium sulfate in an organic solvent may be added at some point as a body feed super-aid. Needless to say, it's a good thing. After the sulfate has been separated, paraffin is separated and removed from the reaction solution by a known method such as extraction with water or an aqueous solution of a lower alcohol, and then neutralized with an alkali such as sodium hydroxide, and extracted with the extraction solvent, etc. By removing the , it is commercialized as an alkanesulfonate. Examples (Experimental Examples 1 to 5) While circulating the reaction solution at a rate of 50 c.c./sec between a photoreactor packed with 7700 g of normal pentadecane and a column initially packed with 400 g of sodium sulfite, the reaction solution was irradiated with light. A mixed gas of oxygen and sulfur dioxide (weight ratio 1:6) was blown in at 900 ml/sec to react for 1 hour to obtain a reaction mixture containing 7.4% by weight of n-pentadecanesulfonic acid and 2.7% by weight of sodium hydrogen sulfate. To 600 g of this reaction mixture was added a saturated aqueous solution of sodium sulfate in the amount shown in Table 1, and further added powder crystals of anhydrous sodium sulfate in the amount shown in Table 1, and after removing sulfur dioxide by blowing air, The mixture was vacuum-filtered using an aspirator using glass fiber paper with a diameter of 95 mm and a pore size of 0.8 μ. The results are shown in Table 1. (Comparative Experimental Example 1) Reaction mixture obtained in the same manner as the above experimental example
Add 10g of commercially available diatomaceous earth additive to 600g,
After blowing air to remove sulfur dioxide gas, diameter 95
Glass fiber paper with a pore size of 0.8 μm and a pore size of 0.8 μm was precoated with 10 g of a commercially available diatomaceous earth filtering aid, and then filtered under reduced pressure using an aspirator. The results are also shown in Table 1. (Comparative Experimental Example 2) Reaction mixture obtained in the same manner as the above experimental example
After blowing air into 600g to remove sulfur dioxide gas,
Using glass fiber paper with a diameter of 95 mm and a pore size of 0.8 μm, the mixture was evacuated using an aspirator. As a result, clogging occurred when approximately 100 g of liquid was obtained, and subsequent over-operation was virtually impossible.

[Table] [Effects of the Invention] The method of the present invention as described above is characterized in that when a photosulfonation reaction is carried out in the presence of sodium sulfite, which suppresses the production of colored substances, a saturated or slurry of sodium sulfate is added to the reaction mixture. By adding an aqueous solution of sulfate to perform solid-liquid separation, the resulting sulfate particles can be agglomerated and crystal-grown, and the particles are prevented from becoming sticky and clogging of the cloth is less likely to occur. This method has the special effect of being able to efficiently separate sulfate without a large overrate being obtained, and without leaking a large amount of sulfate into the separation liquid.

Claims (1)

[Claims] 1 In a method for removing sulfate from a reaction mixture obtained by photo-sulfoxidizing paraffin in contact with sodium sulfite in a reaction system substantially free of water, sodium sulfate is added to the reaction mixture. A method for removing sulfate from a paraffin photo-sulfoxylation reaction mixture, which comprises adding a saturated aqueous solution or a slurry aqueous solution of sodium sulfate to perform solid-liquid separation.