JPS60326B2 - Method for producing pentaerythritol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing pentaerythritol.

More specifically, a pentaerythritol crystallization solution containing bentaerythritol and sodium formate is added with caustic soda to separate sodium formate, and then this is recycled as a part of the reaction stock solution. This invention relates to an improved method for manufacturing toll. When acetaldehyde and formaldehyde are reacted in an aqueous solution of caustic soda, equimolar amounts of sodium formate are produced.

This sodium formate needs to be advantageously separated from pentaerythritol, and the reaction solution is generally concentrated and cooled to form a solid form of pentaerythritol with a low sodium formate content and a liquid form with a high sodium formate content. It is separated into pentaerythritol concentrated mother liquor. Solid pentaerythritol can be made into highly pure pentaerythritol crystals with a little purification, but pure pentaerythritol crystals can be obtained from liquid pentaerythritol concentrated mother liquor containing a large amount of sodium formate. It is not easy to separate them, and on the other hand, it is extremely uneconomical to dispose of these concentrated mother liquors as they are. Therefore, various methods have been proposed for recovering pentaerythritol from concentrated mother liquor. One such method is to add caustic soda to a strong base that has a common ion with the formate cation, such as sodium formate;
A method in which a formate such as sodium formate is crystallized and separated, and the recovered aqueous solution containing pentaerythritol and a strong base such as caustic soda is recycled as a raw material for pentaerythritol synthesis (Japanese Patent Publication No. 46-18008 No.) is known.

Formate, like pentaerythritol, dissolves extremely well in water, but when a common ion compound is added as in the method described above, sodium formate has the property of precipitating with high purity due to the salting out effect of the common ion. This method is industrially extremely useful.

However, although this method is industrially useful, the inventors have discovered that when the recovered solution is repeatedly used as a raw material for pentaerythritol synthesis, the following disadvantageous phenomenon occurs. Ta.

That is, in the alkaline aqueous solution that is recycled as a raw material for bentaerythritol synthesis, pentaerythritol formals, which are extremely thick and crystallized, are accumulated and increased compared to pentaerythritol.

Therefore, pentaerythritol formals not only reduce the yield of pentaerythritol as a by-product during the synthesis reaction of bentaerythritol, but also tend to form fine crystals themselves and are present in large amounts in aqueous solutions. In this case, it has the property of making the pentaerythritol crystals finer and lowering the crystallization rate of pentaerythritol, resulting in a significant deterioration in product purity. Further, pentaerythritol formals are converted into reticular pentaerythritol formals having a high average degree of polymerization by repeatedly circulating a large amount of pentaerythritol to the synthesis process, thereby further promoting the above-mentioned phenomenon. Representative compounds of pentaerythritol formals include bis-pentaerythritol and pentaerythritol monocyclic formal, which can be decomposed by various methods to produce pentaerythritol. Are known.

One specific method is to heat-treat an aqueous solution containing pentaerythritol formals in the presence of a strong acid such as sulfuric acid or hydrochloric acid at the boiling point of normal pressure to decompose pentaerythritol formals. U.S. Patent No. 2978514
Known by the number.

However, in this method, it is necessary to suppress the side reaction between the strong acid used and the pentaerythritol produced, so it is necessary to decompose at a relatively low temperature of 95 to 10,500 ℃, and therefore the decomposition rate is slow. It has the disadvantage of being slow. Another specific method is a method of decomposing pentaerythritol formals by heat treatment at a high temperature of 150 to 30,000 in the presence of a silica-based petroleum cracking catalyst, which is known from U.S. Pat. No. 2,939,887. There is. However, this method has the disadvantage that the operation is complicated because it uses a solid catalyst. As another specific method, pentaerythritol formal is produced by specifically selecting conditions that produce a large amount of pentaerythritol formal, and then under harsh conditions such as pH 3 to 4 and temperature 150 to 200 qo. A method of decomposition is known by Mochiko Sho 39-18107. However, this method has disadvantages in that it requires a large amount of pH regulator and the equipment cost is high due to problems such as corrosion of the equipment material. One object of the present invention is to add caustic soda to an aqueous solution containing bentaerythritol and sodium formate to crystallize and separate sodium formate, and then use the separated liquid as a part of the reaction stock solution to circulate pentaerythritol. An object of the present invention is to provide a method for easily converting pentaerythritol into pentaerythritol by decomposing accumulated pentaerythritol formals under advantageous conditions.

Another object of the present invention is to control the amount of pentaerythritol formals that adversely affect the crystal refractive index and crystal type in the crystallization of pentaerythritol crystals. It is an object of the present invention to provide a method for increasing the purity of pentaerythritol crystals while keeping the crystal form of pentaerythritol stable and facilitating operations such as crystal separation.

According to the method of the present invention, caustic soda is added to an aqueous solution containing pentaerythritol and sodium formate to crystallize and separate sodium formate, and then the separated liquid is recycled as a part of the reaction stock solution. In the method for producing toll, at least a part of the reaction solution containing bentaerythritol formals has a pH in the range of 4.5 to 5.5 and 12
After heat treatment in a temperature range of 0 to 17,000 °C and a time in a range of 20 to 180 minutes, pentaerythritol is crystallized and separated, and then caustic soda is added to the separated liquid containing pentaerythritol and sodium formate to form sodium formate. By crystallization separation, pentaerythritol formals can be easily decomposed to advantageously produce pentaerythritol.

Furthermore, according to the method of the present invention, the content of pentaerythritol formals in the liquid when pentaerythritol is crystallized and separated is defined as the bound formaldehyde concentration.3. weight% of
Crystals of pentaerythritol can be obtained advantageously by the following procedure.

Reaction conditions for reacting acetaldehyde and formaldehyde to form pentaerythritol in the method of the present invention, namely reaction temperature, reaction time, molar ratio of formaldehyde to 1 mol of acetaldehyde, molar ratio of water to 1 mol of acetaldehyde, and molar ratio of water to 1 mol of acetaldehyde. As for the conditions such as the molar ratio of caustic soda, normally employed conditions are used.

However, in the method of the present invention, pentaerythritol is crystallized and separated from the reaction solution, and then caustic soda is added to an aqueous solution containing pentaerythritol and sodium formate to crystallize and separate sodium formate. The resulting separated solution containing excess caustic soda is recycled as a part of the reaction stock solution.

The separated liquid that is recycled usually contains, in addition to excess caustic soda, sodium formate, bentaerythritol, bentaerythritol formal, polybentaerythritol, and the like. The reaction solution containing the above-mentioned separated solution and obtained by the reaction of newly supplied formaldehyde and acetaldehyde contains recycled impurities and pentaerythritol in addition to the newly produced pentaerythritol. It contains a large excess of unreacted formaldehyde along with newly formed impurities such as lythritol formals. Excess unreacted formaldehyde contained in this reaction solution is usually first removed by employing a pressure distillation method or the like.

In the method of the present invention, for example, pentaerythritol formals contained in the reaction liquid are thermally decomposed in the closed bottom part of the pressure distillation tower or in another dan-shaped vessel installed from the bottom part of the pressure distillation tower. However, it is essential to then crystallize and separate the pentaerythritol.

Thermal decomposition of pentaerythritol formals contained in the reaction solution can be carried out by lowering the pH of the treatment solution to 4 prior to heat treatment.
．． 5 to 5.5 and processing at a temperature range of 120 to 170 oo and a time range of 20 to 180 minutes.

As mentioned above, the pH range adopted in the thermal decomposition of pentaerythritol formals can be arbitrarily selected within the range of 4.5 to 5.5, but if the pH is higher than 5.5, the decomposition efficiency is extremely poor. However, this method is not economical because it causes problems such as an increase in the amount of formic acid used and an expensive material for the equipment.

Therefore, at a decomposition temperature of 12p or less in the pH range of 4.5 to 5.5, the decomposition rate of pentaerythritol formals is abnormally low, and pentaerythritol formals are produced as by-products even at relatively high concentrations. It becomes impossible to maintain the decomposition rate based on the amount of pentaerythritol formals at a high level, thus reducing the purity of the product, similar to the disadvantages of the conventional methods mentioned above. On the other hand, a decomposition temperature of 170 qo or higher is not advantageous because a normal heat source cannot be used. Generally, if the above-mentioned heat treatment temperature is low, the decomposition rate can be increased by lengthening the thermal decomposition time, but the decomposition time at the above-mentioned heat treatment temperature is usually in the range of 20 to 180 minutes.

The decomposition rate when the above pentaerythritol formals are decomposed by heat treatment is the content of pentaerythritol formals in the separated liquid obtained by crystallizing bentaerythritol, that is, the separated liquid It is necessary that the bound formaldehyde concentration therein be 3.0% by weight or less.

More preferably, the concentration of bound formaldehyde in the liquid is 2. % by weight or less.

In addition, the amount of bentaerythritol formal referred to in the present invention refers to the acetal compound of bentaerythritol and formaldehyde, and the content is determined by the amount of bentaerythritol formal obtained by mixing the formaldehyde with normal sodium chromotrope. Methods, for example, Lnd. &Eng. Chem
．． Vol 17, 400-402 (1945), formaldehyde bound to bentaerythritol was analyzed, and the concentration of bound formaldehyde was expressed as the content of pentaerythritol formals. . Then, the concentration range of bound formaldehyde in the liquid is set to, for example, 2. The reason why the concentration of pentaerythritol in the separated liquid at 40 qC is kept at a relatively low concentration range of 2% by weight or less is by controlling the bound formaldehyde concentration within this range. Therefore, it is possible to maintain a high crystallization rate of pentaerythritol.

Incidentally, when the concentration of bound formaldehyde in the separated liquid is 3.0% by weight or more, the concentration of pentaerythritol in the separated liquid becomes 30% by weight or more, which significantly reduces the crystallization rate. The concentration of bound formaldehyde in this separated liquid has a large effect on the crystal form of pentaerythritol obtained. That is, when the concentration of bound formaldehyde is high, pentaerythritol crystals become fine single crystals and do not form coarse crystals, resulting in various inconveniences in the handling of the crystals and in the quality of the obtained crystals. Here, the term "flocculated crystal" refers to a large number of small crystals fused together to form a coarse crystal particle mass in the shape of a chrysanthemum or confetti, and is technically distinguished from a single crystal. Therefore, the concentration of bound formaldehyde in the separated liquid was set to 3.
When crystallized at 0% by weight or less in a regular continuous vacuum adiabatic cooling crystallizer at 4000, the crystals of bentaerythritol become coarse crystals with a particle size of 100 to 300A, and are crystallized by normal methods. Can be easily separated.

In contrast, the bound formaldehyde concentration in the separated solution was
．． When the concentration is 0% by weight or more and crystallization is performed by the method described above, the crystals of bentaerythritol become fine single crystals of 10 to 50 crystals, and their solid-liquid separation requires a great deal of effort.

As understood from the above description, the amount of pentaerythritol formals in the liquid obtained by crystallizing and separating pentaerythritol by the method of the present invention is taken as the bound formaldehyde concentration; 3. Preferably less than 2% by weight. If the amount is less than or equal to 20% by weight, the following advantages can be obtained.

That is, one of them is that the crystal grain size of pentaerythritol obtained by crystallization separation is large, so that solid-liquid separation of the crystals is easy, and the separation operation is simplified. Another reason is that since the concentration of pentaerythritol in the liquid obtained by crystallizing and separating pentaerythritol is low, the crystallization rate is high and the solution viscosity of the separated liquid can be kept low, which makes it easier to handle the separated liquid. becomes easier. Another reason is that since the concentration of pentaerythritol in the separated liquid is low, it is possible to increase the crystallization rate of sodium formate, and the operation in the crystallization process is facilitated. Furthermore, it is clearly possible to increase the reaction yield of pentaerythritol, and the purity of the pentaerythritol product can also be improved. As described above, it is possible to improve the economic efficiency of producing pentaerythritol. Conventionally, it has been known that as a means for increasing the decomposition rate of bentaerythritol formals, it is advantageous to keep the pH of the treatment liquid as low as possible.
However, in this method, since the processing solution contains a large amount of sodium formate, a large amount of formic acid is required due to its buffering effect. On the other hand, in the case of the method of the present invention,
P
A small amount of formic acid added for H adjustment is sufficient, and SUS316 or SUS314, which is ordinary fusen steel, is sufficient.
It is also possible to use . In addition, the method of the present invention continuously decomposes and removes the pentaerythritol formals that are created without accumulating them in high concentrations, so there is no problem with the formation of pentaerythritol microcrystals or a decrease in the crystallization rate. Since the bentayrythritol formals can be converted into pentaerythritol, the overall yield of bentayrythritol is increased by 2 to 3% compared to the conventional method, and the purity of the obtained product is also higher than that of the conventional method. 2 to 2.5 compared to the method
% can be increased.

The production of the above-mentioned high-purity pentaerythritol in high yield by the method of the present invention is an achievement that could not be achieved by the conventional method of simply circulating the sodium formate separated liquid. . In addition, in the method of the present invention, in which sodium hydroxide is added to the crystallized separation liquid containing bentaerythritol and sodium formate to separate sodium formate, and then the sodium formate is recycled and used as a stock solution in the reaction process, all or A portion is heat-treated in a pH range of 4.5 to 5.5 and a temperature range of 120 to 17 psi, and then pentaerythritol is separated as crystals, and then caustic soda is added to the separated liquid, or
Alternatively, without heat-treating the reaction solution, pentaerythritol is separated, and then caustic soda is added to the separated solution to separate sodium formate, which is further recycled and then subjected to a heat treatment to separate pentaerythritol as crystals. An intermittent heat treatment method may also be used in which caustic soda is then added to the separated liquid. When using the latter method, the reaction solution can maintain a relatively high concentration of pentaerythritol formals,
Therefore, since the initial concentration is high, the decomposition rate can be maintained at a high level, and acid decomposition can be carried out under relatively mild conditions. Therefore, even if the decomposition rate of pentaerythritol formals based on the passed liquid is low, the decomposition rate based on the amount of pentaerythritol formals created in the reaction process can be maintained at a high level. To aid in understanding the method of the present invention, a representative flow is illustrated with reference to FIG. Pentaerythritol reactor 2 is supplied with acetaldehyde and formaldehyde aqueous solutions from conduit 1 and sodium formate crystallization furnace solution through conduit 13, and the reaction liquid in reactor 2 is supplied through conduit 3 to pressurized distillation column 4.
formaldehyde is distilled off through conduit 5 as an aqueous solution. The residual liquid from crabbing is adjusted to pH at the bottom of the tower or in a separate container.
The pentaerythritol formals contained therein are decomposed and passed through the conduit 6 to concentrate, crystallize and separate the pentaerythritol. In step 7, pentaerythritol crystals are finally separated into an aqueous solution containing pentaerythritol and sodium formate. Caustic soda is introduced into the extractor 10 and added through the conduit 11, and the crystallized sodium formate is separated from the discharge pipe 12, and the separation furnace liquid is recycled through the conduit 13 to the reaction process as a part of the reaction stock solution. Next, the present invention will be further explained by giving examples.

'Examples 1 to 3 30 (by weight) was placed in a tubular reactor equipped with a Takaazusa mixer and a cooler built into the flow shown in Figure 1.
% formaldehyde aqueous solution 30.3k9/day, 98 (weight)% acetaldehyde 1.7k9/day, 20 (weight)
Sodium formate crystallization solution containing % caustic soda 9.1k9/
(containing 0.11k9/day of bound formaldehyde) and 15k9/day of distilled water and held at 3500 for 2 hours.

When the reaction solution was adjusted to pH 6.0 to 6.5 with formic acid, the reaction solution contained 0.48% (by weight) of bound formaldehyde, and 0.16 k9/day of bound formaldehyde was added to Tomiyama during the reaction process. It was born. Subsequently, excess formaldehyde was distilled off under pressure, and the residual liquid was placed at the bottom of the column or in a separate container as shown in the table below, while maintaining the pH temperature and time at the values shown in the table below. A portion of the liquid collected from the outlet liquid was analyzed for monobentaerythritol content by the JIS K1510 method of quantifying it using penzaldehyde, and on the other hand, it was analyzed as pentaerythritol formals by the usual method using sodium chromotrope. Analysis of bound formaldehyde revealed that monobentaerythritol was present. 1 ~ Shigeru. It was found that the bound formaldehyde obtained in the range of 3 mol % and produced as a by-product in the reaction process was completely decomposed. Furthermore, pentaerythritol was concentrated, crystallized, and separated, and pentaerythritol crystals were found to be 1
00~300〃 coarse crystals, easily separated,
It was found that the purity of bentaerythritol was as high as 95.4 to 95.5% by weight.

At this time, the concentration of bound formaldehyde in the separated liquid was 1.2
% by weight. The separated liquid is then led to a salting out crystallizer, where caustic soda is added, and after the formic acid sodium hydroxide is separated,
It was recycled as a stock solution for some reactions. For comparison, in Comparative Examples 1 and 2, caustic soda was added to an aqueous solution containing pentaerythritol and sodium formate to crystallize and separate sodium formate, and then the separated liquid was recycled as a part of the reaction stock solution. The results of comparison with conventional methods other than the method of the present invention are shown, and the results of comparison when heat treatment is not performed in Comparative Example 3 are shown. The results of Comparative Example 2 are described for the case where heat treatment was performed under heat treatment conditions other than the heat treatment conditions of the present invention in the conventional method. Ya chicken;
Pentaerythritol was synthesized according to the flow shown in the figure.

However, 2/milk volume of the bottom liquid of the pressure distillation column was handled together with the remaining 1/3 volume after pentaerythritol formals were decomposed in a special high-temperature container. At this time, the decomposition conditions for pentaerythritol formals are at a temperature of 150°C.
, decomposition time 10 minutes, decomposition pH 4.7, reaction solution bound formaldehyde concentration 0.45% by weight, bound formaldehyde production amount 0.14 k9/day, bound formaldehyde decomposition amount 0.14 k9/day, monobentaerythritol Yield 88.3 mol%, bentaerythritol crystal grain size 1
00-300, bentaerythritol product purity 95.
A result of 5% by weight was obtained, which was a good result similar to the result of Example 1.

[Brief explanation of drawings]

FIG. 1 is an example of an apparatus suitable for carrying out the method of the present invention. 1...Acetaldehyde/formaldehyde aqueous solution supply conduit, 2...Reactor, 3...Reaction liquid conduit,
4... Pressure distiller, 5... Formaldehyde distillation tube, 6... Decomposition liquid, 7...
Bentaerythritol concentration, crystallization and separation process, 8.
...Ventaerythritol crystal discharge conduit, 9...
...Aqueous solution conduit containing bentaerythritol and sodium formate, 10...Salt crystallization separator, 11...
... Caustic soda supply pipe, 12... Sodium formate discharge pipe,
13... Sodium formate crystallization furnace liquid supply conduit. O diagram

Claims (1)

[Claims] 1 Crystallize and separate pentaerythritol from the reaction solution obtained by reacting acetaldehyde and formaldehyde in the presence of caustic soda, then add caustic soda to the crystallized separated solution containing pentaerythritol and sodium formate to crystallize sodium formate. In a method for producing pentaerythritol, in which the separated liquid containing caustic soda is recycled as a part of the reaction stock solution after separation, the reaction liquid is heated in a temperature range of 120 to 170°C at a pH of 4.5 to 5.5. Pentaerythritol is crystallized and separated after heat treatment so that the concentration of formaldehyde bonded to pentaerythritol in the separated liquid after crystallization and separation of erythritol becomes 3.0% by weight or less. Method for producing erythritol.