JPS6121611B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and purifying diglycerin from a mixture of glycerin, triglycerin, tetraglycerin, and further polyglycerin. Diglycerin is a tetrahydric alcohol that can perform various reactions such as esterification and etherification using its four hydroxyl groups, and is used as an organic synthetic drug,
Widely used in emulsifiers, antifoaming agents, paint resins, polyurethanes, polyesters, etc. Diglycerin is produced as a by-product during glycerin production or by dehydration condensation of glycerin. However, in any case, diglycerin is obtained as a mixture with glycerin, triglycerin, tetraglycerin, and even higher polyglycerin, and it is necessary to separate and purify this mixture. Conventionally, diglycerin has been purified by batch simple distillation under reduced pressure. First, glycerin and diglycerin fractions are distilled from a mixture, and then this distillate is subjected to batch simple distillation again. The glycerin fraction was distilled off to obtain diglycerin as a bottom liquid. However, in this method, the residence time in the evaporator becomes long, so side reactions occur, such as decomposition into acrolein, water, etc., conversion into cyclic substances (mainly dioxanes), or glycerin undergoes a condensation reaction and changes to polyglycerin with a large number of carbon atoms, making it impossible to purify and recover diglycerin in a good yield. Moreover, the diglycerin obtained is highly colored, and in order to increase its commercial value, it is necessary to decolorize it using activated carbon, ion exchange resin, or the like. As described above, industrial production has many drawbacks. The inventors of the present invention have conducted extensive research in order to overcome the above-mentioned drawbacks. First, we focused on the fact that side reactions can be suppressed by adopting continuous flash evaporation rather than batch-type single distillation in order to process substances in a short time at the lowest possible temperature using this type of distillation. The following two methods can be considered for separating and purifying diglycerin from a mixture of glycerin, triglycerin, tetraglycerin, and even higher polyglycerin using continuous flash evaporation under reduced pressure. That is, there is a method (method A) in which glycerin and the like are first distilled out through first-stage flash evaporation, and then the bottom liquid is subjected to second-stage flash evaporation again to obtain diglycerin as the top liquid (method A). This is a method (Method B) in which glycerin, diglycerin, etc. are distilled out as a top liquid in the first stage flash evaporation, and then glycerin, etc. are distilled out again in a second stage flash evaporation to obtain diglycerin as a bottom liquid. . However, the former method (Method A) had the disadvantage that by-products produced by side reactions in the second flash evaporation step were mixed into the diglycerin. Furthermore, in the case of the latter (Method B), in addition to the former, diglycerin is obtained as a bottom liquid, which has the disadvantage of severe coloring. Furthermore, since flash evaporation is performed twice in both cases, there is a lot of waste in terms of energy and equipment. Next, in consideration of the above-mentioned facts, the present inventors further advanced their research and succeeded in developing an excellent method for purifying diglycerin that can achieve the objective. That is, in the present invention, when separating and purifying diglycerin from a mixture of glycerin, triglycerin, tetraglycerin, and further polyglycerin, etc., the mixture is subjected to flash evaporation under reduced pressure of 10 Torr or less, and the corresponding vapor pressure is reduced. The present invention provides a method for purifying diglycerin, which is characterized in that diglycerin is obtained as a condensate by partial condensation at a temperature within a temperature range from the dew point of diglycerin to a temperature 100° C. lower than this dew point. In the present invention, the pressure on the evaporation surface must be 10 Torr or less, preferably 5 Torr or less.
When the temperature exceeds 10 Torr, the evaporation temperature becomes high, causing a side reaction of diglycerin, reducing the recovery rate and making the heat transfer surface more contaminated. Further, the heating medium temperature is selected from about 270° C. or lower, and is appropriately determined by experiment based on the charging rate, vapor pressure, evaporation capacity, etc. The flash evaporator used in the present invention is preferably of a type having a short residence time, such as a rising thin film type evaporator or a falling thin film type evaporator. moreover,
A rotating scraper type evaporator, such as the Turba-Film type, is also effective in promoting heat transfer. Further, when using a falling film type evaporator, the charged liquid may be evaporated by single passage, but forced circulation is also possible. The steam generated by flash evaporation is introduced into a multi-tube or double-tube heat exchanger and is partially condensed, yielding diglycerin as a condensate. The decomposition temperature is suitably within the temperature range from the dew point of diglycerin at the corresponding vapor pressure to a temperature 100° C. lower than this dew point. For example, 120℃~220℃ at 5Torr, preferably
The temperature is between 120°C and 170°C. If the temperature is lower than 120°C, the concentration of glycerin in the diglycerin will be high, and if it exceeds 220°C, the diglycerin in the flash vapor will not be sufficiently condensed. Although such a dephlegmator may be installed separately from the evaporator, it is preferable to incorporate it into the upper part of the evaporator from the viewpoint of reducing pressure loss in the piping. The vapor that is not condensed in the dephlegmator is led to another heat exchanger, where it is completely condensed and recovered as a low-boiling liquid. Although any liquid containing diglycerin can be used as the charging liquid to be used in the present invention, distillation residue of crude glycerin is usually used. In this way, if the present invention is carried out, diglycerin can be efficiently obtained from a mixture of glycerin, triglycerin, tetraglycerin, and even more polyglycerin in one step of flash evaporation, which is easy in terms of equipment. Therefore, less energy is required for separation and purification.
Moreover, it has the advantage that side reactions are suppressed and the diglycerin obtained has a high yield and good quality such as purity and coloring, so it has great industrial utility value. Next, the present invention will be specifically explained with reference to Examples. In addition, samples such as charging solution, low-boiling solution, purified diglycerin, and tower bottom solution were each added with acetic anhydride and pyridine, heated under reflux for 2 hours to perform acetylation, and then analyzed by gas chromatography. . Moisture content was also analyzed by Karl Fischer titration. Example 1 Inner diameter 23 with a built-in condenser for partial condensation in the upper part
240 g/hr of diglycerin crude liquid was charged into a stainless steel falling film evaporator with a length of 500 mm and a Torr rate of 240 g/hr.
Flash evaporation was carried out under reduced pressure. A heating medium at 250°C was circulated through a jacket attached to the outside of the evaporation tube, and the vapor was fractionated to a temperature of 125°C at the outlet of the condenser to obtain purified diglycerin. The condenser outlet vapor was led to another condenser where it was completely condensed and recovered as a low-boiling liquid. The results are shown in Table 1. Example 2 The same procedure as in Example 1 was carried out, except that diglycerin crude liquid was charged at 400 g/hr, and the tower bottom liquid was withdrawn in fixed amounts while being forcedly circulated at 4000 ml/hr.
At this time, the heating medium temperature was 252°C, and the steam temperature at the condenser outlet was 130°C. The results are shown in Table 1. Example 3 The treatment was carried out in the same manner as in Example 1, except that the crude diglycerin solution was changed, it was charged at 300 g/hr, and the treatment was carried out under a reduced pressure of 5 Torr. At this time, the heating medium temperature is 260
℃, and the steam temperature at the condenser outlet was 150℃. The results are shown in Table 1.

[Table] Comparative Example 1 (Batch type simple distillation) Example 1 was placed in a glass round bottom flask with a capacity of 2.
Pour 1600g of the diglycerin crude liquid used in , and heat it with a mantle heater under reduced pressure of 3Torr.
Batch simple distillation was performed. The distillate is fr-1, fr
- Divided into 2. At this time, the liquid temperature is fr-1, 196 to 225
°C, fr-2 was 225-268 °C. The results are shown in Table 2. Comparative Example 2 (Two-stage flash evaporation = Method B) Diglycerin crude liquid was charged at 300 g/hr into a stainless steel falling film type evaporator with an inner diameter of 23 mm and a length of 500 mm, and the first stage flash evaporation was performed under a reduced pressure of 3 Torr. Summer. A heat medium at 250°C was circulated through a jacket attached to the outside of the evaporation tube, and the generated steam was led to a condenser where it was completely condensed. Next, second-stage flash evaporation was performed in the same manner as the first-stage flash evaporation, except that the top liquid was collected and the heating medium temperature was changed to 220° C., and purified diglycerin was obtained as a bottom liquid.
The results are shown in Table 2. Comparative Example 3 (Two-stage flash evaporation=Method A) Processing was carried out in the same manner as Comparative Example 2 except for the following changes. The first stage flash evaporation was carried out at a heating medium temperature of 230° C., and a low-boiling liquid was distilled off as the top liquid.
Next, this bottom liquid is collected and the heating medium temperature is adjusted to 260°C.
A second flash evaporation was carried out at °C to obtain purified diglycerin as the top liquid. The results are shown in Table 2.

【table】

Claims (1)

[Claims] 1. When separating and purifying diglycerin from a mixture of glycerin, triglycerin, tetraglycerin, and even higher polyglycerin,
The mixture is subjected to flash evaporation under a reduced pressure of 10 Torr or less and fractionated at a temperature within the temperature range from the dew point of diglycerin at the corresponding vapor pressure to a temperature 100°C below this dew point, thereby producing diglycerin as a condensate. A method for purifying diglycerin, characterized in that it obtains diglycerin.