Preparation of polyglycerols

Description,

Process for the preparation of polyglycerols

The present invention relates to a process for the preparation of polyglycerols which are low in cyclic components by reacting glycerol with chlorohydrins at elevated temperature.

US Patent 2,520,670 discloses a process for the preparation of polyglycerols in which glycerol is reacted with glycerol a-monochlorohydrin in the presence of concentrated alkali at elevated temperature to form a mixture of polyglycerols. This process has the disadvantage of a relatively long reaction duration and that the reaction mixture must be worked up using lower aliphatic alcohols when the reaction is complete.

Details on the polyglycerol yields achieved and an their cyclic component content are not given.

The object of the present invention was therefore to find a process in which polyglycerols are obtained in good yields and with an only small content of cyclic components. In this process, it should at the same time be unnecessary to isolate the intermediates (chlorohydrin/ether mixture) and, for environmental-protection reasons, to avoid work-up of the end products by treatmeat with organic solvents.

It has now been found according to the invention that this object is achieved by a process in which glycerol or diglycerol or a higher polyglycerol is reacted with epichlorohydrin (instead of chlorohydrin) at temperatures of from 90 to 170°C, preferably 120°C to 150°C, in a molar ratio between glycerol or diglycerol or higher polyglycerol and epichlorohydrin of from 5 : 1 to 1 ! 3, an alkaline medium, preferably an alkaline aqueous solution, is added at a temperature of from 50°C to 120°C, preferably 80°C to 95°C, to the unseparated reaction mixture obtained, corresponding to the organically bound chlorine content of the reaction mixture, water is added, the reaction mixture is desalinated via one or more cation exchangers and subsequently using anion exchangers, water is removed by distillation, and the glycerol/ polyglycerol mixture is separated into glycerol, diglycerol and higher polyglycerols by fractional distills־־ tion.

According to an advantageous embodiment of the invention, the reaction mixture is diluted to an approximately 70 - 40% strength by weight, preferably 60 - 50% strength by weight, solution by addition of water and desalinated via a combination of strongly acidic cation exchangers and subsequently slightly basic anion exchangers at temperatures of from 30°C to 80°C, preferably 40°C to 60°C.

According to a preferred embodiment, an alkaline alkali metal carbonate solution, preferably a concentrated sodium carbonate solution, is added to the unseparated reaction mixture from the reaction of epichlorohydrin with glycerol, diglycerol or a higher polyglycerol.

The alkaline alkali metal carbonate solution is advantageously added to the unseparated reaction mixture from the reaction of epichlorohydrin with glycerol, diglycerol or a higher polyglycerol in an equivalent ratio between alkali metal carbonate and the organically bound chlorine content of from 1 : 1 to 1.2 : 1, preferably 1.05 : 1 to 1.1 : 1.

The pH of the reaction mixture is expediently adjusted to the range 7.0 ־to 11.5, preferably 8 to 11, by addition of the alkaline aqueous solution.

According to a further embodiment, the reaction mixture is cooled to room temperature, and the majority of the salt precipitated is separated off, preferably filtered off.

If necessary, the desired composition of the polyglycerol mixture can be varied according to the invention by varying the molar ratio between glycerol and epichlorohydrin and by using diglycerol or higher polyglycerols instead of glycerol.

Thus, in order to increase the diglycerol proportion, the molar ratio between glycerol and epichlorohydrin is 4 : 1 to 2.5 : 1, according to an embodiment.

According to a further embodiment, in order to increase the polyglycerol proportion produced in addition to diglycerol, the molar ratio between glycerol and/or diglycerol and epichlorohydrin is 2.49 : 1 to 0.5 : 1, preferably 1.8 : 1 to 0.4 : 1.

According to another embodiment, the alkaline alkali metal carbonate solution is added in a slight excess to the unseparated reaction mixture from the reaction of epichlorohydrin with glycerol, diglycerol or a higher polyglycerol, and this excess is neutralized when the reaction is complete.

Hydrochloric acid is preferably employed for the neutralization, but it is also possible to use other mineral acids or acid cation exchangers.

It has furthermore been determined according to the invention that the change in the molar ratio is accompanied by a change in the reaction time. It has been shown that, with respect to the reaction time, and the minimum cyclic component content desired in the crude polyglycerol mixture, that a molar ratio between glycerol and/or diglycerol and epichlorohydrin of from 2.5 to 1.0 : 1 has proven particularly suitable.

The regeneration of the cation exchanger composition in the cation exchangers is preferably carried out by means of cocurrent or combined cocurrent regeneration.

According to a preferred embodiment, the salts are washed out after the regeneration. When the washingout process is complete, the polyglycerol-containing, preferably diglycerol-containing solution is passed through the ion exchanger, and the polyglycerol-containing, preferably diglycerol-containing solution leaving the anion exchanger is recycled until a polyglycerol content, preferably a diglycerol content, of 20% by weight is achieved, preferably until a polyglycerol content, preferably a diglycerol content, of 15% by weight is achieved, and is co-used to prepare the 70 40% strength by weight, preferably 60 - 50% strength by weight, polyglycerol-containing, preferably diglycerolcontaining starting solution.

The polyglycerol-containing, preferably diglycerol-containing solution is preferably passed through the ion exchangers under an excess pressure.

In this case, the polyglycerol-containing, preferably diglycerol-containing solution is passed through the ion exchangers, i.e. through one or more cation exchangers and at least one anion exchanger, under a pressure of 1.1 - 10 bar, preferably 2-6 bar. Valves are installed at one or more points in the line or in the ion exchangers in order to control and maintain the pressure.

In this case, the polyglycerol-containing, preferably diglycerol-containing solution is expediently passed through the ion exchangers at a flow rate of from 0.5 m/h to 15 m/h, preferably 1 m/h to 5 m/h.

The cation exchanger compositions and anion exchanger compositions preferably used are those which are temperature-stable to above 80°C, preferably to above 100°C.

The ion exchanger composition of the cation exchanger and/or anion exchanger is expediently covered by a sieve plate, perforated plate or a device which is arranged movably in the height direction of the ion exchanger, covers the exchanger composition and enables a uniform rate of liquid passage, and/or an inert compressed composition and/or an elastic plastic composition.

The strongly acidic cation exchanger composition and the slightly basic, anion exchanger composition preferably have an internal surface area (measured by the BET method) of greater than 25 m²/g, preferably 50 to 100 m²/g.

Working Examples:

1. Working example for the preparation of polyglycerol having a relatively high content of diglycerol:

1.474 kg (16 mol) of glycerol and 740 g (8 mol) of epichlorohydrin were introduced into a 2 1 twin-walled reactor (heating liquid: oil). The two-phase reaction mixture was heated to boiling (reflux) with stirring. After about 80 minutes, the oil flow temperature was increased to about 145°C, unreacted epichlorohydrin again refluxing. After 50 minutes at an oil flow temperature of 145°C, the latter was reduced to 140°C. It was thus possible to stop the slightly exothermic reaction and to keep the reaction temperature at 150°C. The oil flow temperature and the temperature of the reaction solution had equalized after about 50 minutes. The reaction was complete after a total of 3.25 hours.

Crude product weight: 2.205 kg ~ 1.75 1.

1.284 kg (= organically bound chlorine : 4.776 mol) of this crude chlorohydrin/ether mixture were introduced into the same reactor and warmed to 90°C.

I. 125 1 (corresponding to the organically bound chlorine content plus an excess of 5%) of a 2.23 molar sodium carbonate solution were added at 90°C over the course of 1 hour (moderate C0₂ evolution) . After a further 1.5 hours at this temperature, the heating was removed and the reaction batch was neutralized by addition of 1/2 concentrated hydrochloric acid.

Crude product weight: 2.516 kg

Final volume: about 2.15 1

The neutral reaction solution was diluted with water, the mixture was desalinated via a combination of strongly acidic cation exchangers and slightly basic anion exchanger, and the water was removed by evaporation in vacuo.

Final product weight: 1.040 kg

The product mixture had the following composition in % by weight: glycerol 43.5, cyclic diglycerol 0.9, diglycerol 38.5, cyclic triglycerol 0.4, triglycerol

II. 8, cyclic tetraglycerol 0.1, tetraglycerol 3.0, pentaglycerol 0.7, hexaglycerol 0.1.

Values obtained for the polyglycerol mixture in % by weight on changing the glycerol:epichlorohydrin molar ratio 3 : 1, 2 : 1, 1 : 1 and 1 : 2

<td></td><td> 1 : 1</td><td> 2 : 1</td><td> 3 : 1</td><td> 1 : 2</td>

<td> Glycerol</td><td> 25.4</td><td> 43.5</td><td> 53.-6</td><td> 37.2</td>

<td> Cyclic diglycerol</td><td> 1.5</td><td> 0.9</td><td> 1.2</td><td> 1.5</td>

<td> Diglycerol</td><td> 42.4</td><td> 38.5</td><td> 33.1</td><td> 41.7</td>

<td> Cyclic triglycerol</td><td> 1.0</td><td> 0.4</td><td> -</td><td> 0.8</td>

<td> Triglycerol</td><td> 19.6</td><td> 11.8</td><td> 8.4</td><td> 13.6</td>

<td> Cyclic tetraglycerol</td><td> 0.9</td><td> 0.1</td><td> 0.7</td><td> 0.5</td>

<td> Tetraglycerol</td><td> 5.7</td><td> 3.0</td><td> 1.8</td><td> 3.1</td>

<td> Pentaglycerol</td><td> 2.4</td><td> 0.7</td><td> 0.6</td><td> 1.0</td>

<td> Hexaglycerol</td><td> 0.6</td><td> 0.1</td><td> -</td><td> -</td>

. Working example for the preparation according to the invention of polyglycerol having a relatively high content of triglycerol:

664.6 g (4 mol) of diglycerol and 185 g (2 mol) of epichlorohydrin were introduced into all twin-walled reactor־ (heating liquid: oil). The two-phase reaction mixture was heated to boiling (reflux, bath temperature 130°C) with stirring. After about 1 hour, the oil flow temperature was increased to 145°C and kept at this temperature for about 2 hours.

The reaction was complete after a total of about hours.

Crude product weight: 849 g 1 0.7 ־

784.9 g ( = organically bound chlorine: 1.848 mol) of this crude chlorohydrin/ether mixture were introduced into a 2 1 twin-walled reactor and warmed to 90°C. 485 ml of a 2 molar sodium carbonate solution were added at 90°C over the course of about 45 minutes (moderate C0₂ evolution). After a further 1.5 hours at this temperature, the heating was removed and the reaction batch was neutralized by addition of 1/2 concentrated hydrochloric acid.

Crude product weight: 1.315 kg — 1.15 1

The neutral reaction solution was diluted with water, the mixture was desalinated via a combination of strongly acidic cation exchangers and slightly basic anion exchangers, and the water was removed by evaporation in vacuo.

Final product weight: 715 g.

The product mixture had the following composition in % by weight:

glycerol 4.9, cyclic diglycerol 0.1, diglycerol 50.8, cyclic triglycerol 2.1, triglycerol 25.6, cyclic tetraglycerol 0.5, tetraglycerol 4.9, pentaglycerol 6.0, hexaglycerol 3.5, heptaglycerol 0.8 and octaglycerol 0.1.