DE4117033A1 - Prodn. of oligo:glycerol mixts. - by condensing glycerol in presence of boron cpd. and continually removing water formed - Google Patents

Abstract

Prodn. of oligoglycerol mixts. is effected by condensing glycerol in the presence of a B cpd. while continuously removing the H20 formed. The reaction is terminated when the amt. of H20 removed corresponds to the amt. theoretically required for diglycerol formation. The process gives prods. with a higher diglycerol content than processes using alkali metal base catalysts and with a higher content of alpha, alpha-linked diglycerol than processes using silicate catalysts. The reaction is effected at 200-260 deg.C. in the presence of 1-10 wt.% Li, Na or K metaborate or Na tetraborate. USE/ADVANTAGE - Diglycerol is useful for making fatty acid esters, which are useful as food and cosmetic emulsifiers and for industrial applications, e.g. as lubricants or stabilisers for PVC.ef

Description

The invention relates to a process for the preparation of oligo glycerol mixtures by condensation of glycerol in the presence of Boron compounds.

Diglycerin has as a starting material for the production of fat Acid esters acquired great importance. Such esters find Ver use as emulsifiers in the food industry and the Cosmetics as well as in various technical applications, at For example, as lubricants or stabilizers for PVC (J.A. Oil., Chem. Soc., 66, 153 (1989)).

For the production of diglycerol is usually of glycerol with glycidol (fats, soaps, paints., 88, 101 (1986)) or epichlorohydrin (EP 03 33 984 A1). The Reaction, however, is less selective, besides, glycidol and Epichlorohydrin difficult to handle and make high demands to occupational safety.

Alternatively, glycerol in the presence of alkali bases kon be densified. Depending on whether the condensation to Linking two primary (alpha, alpha), two secondary (be ta, beta) OH functions or one primary and one secondary Hydroxyl group (alpha, beta) leads to a distinction between three  different types of condensation among which alpha, alpha-diglycerol be of special technical importance be sitting.

However, the alkaline condensation is with a series of after share tainted. In particular, only mixtures are in this way available, which in addition to diglycerol even higher homologs and not negligible amounts of unreacted glycerol The diglycerol must be distilled off from these mixtures be separated, resulting in a great deal of time and energy connected is. For this reason, the production of oligo Glycerenemischen sought, the highest possible Diglyce have rinanteil. Performing the self-condensation of glycerol in the presence of silicates as catalysts, though diglycerol-rich oligoglycerols obtained, the proportion of alpha, al However, pha-linked dimers in these mixtures is ver at the same time low.

The object of the invention was therefore to provide a method for Production of oligoglycerine mixtures to develop, free of the disadvantages described is.

The invention relates to a process for the preparation of Oligoglyceringemischen, which is characterized in that one Glycerol condensed in the presence of boron compounds, the Kon condensation water continuously removed from the reaction mixture and the reaction stops as soon as the formation of diglycerol theoretically required amount of water has been deposited.

Surprisingly, it has been found that the use of boron compounds in the Glycerinkondensation

• - Compared with alkali catalysts to Oligoglyceringemischen with a comparatively higher proportion of diglycerol and
• - Compared to silicate catalysts to Oligoglyceringemischen with a comparatively higher content of alpha, alpha-linked diglycerol

leads.

Boron compounds which are used in the context of the process according to the invention as catalysts for the Glycerinkondensation into consideration come, amorphous alkali borates are selected from the group that of lithium metaborate, sodium metaborate, sodium tetraborate and Ka liummetaborat is formed to understand. Preferably, the one Set of sodium metaborate.

The boron compounds may be used in the condensation in amounts of 1 to 10, preferably 2 to 5 wt .-% - based on the glycerol - a be set. The temperature at which the condensation of Gly cerins may be 200 to 260, preferably 240 to 250 ° C.

To carry out the condensation reaction, glycerol and Boron compound submitted and in an inert gas atmosphere on the Reaction temperature heated. To shift the balance For example, the resulting condensation water over a Separated water separator. The reaction is stopped when the amount theoretically required to form diglycerin Water has been separated. In general, the reac tion time 1 to 30, preferably 3 to 15 h. The separation of the Diglycerol from the oligoglycerol mixture formed takes place  for example by distillation in a high vacuum. For a variety however, applications of the invention may be the oligoglyce of the invention Ringemische be used without further separation.

The following examples are intended to form the subject of the invention explain it in more detail without restricting it to it.

Examples example 1

In a 250 ml three-necked flask with reflux condenser, Wasserabschei and internal thermometer 184 g (2 mol) of glycerol (99.5 wt .-% strength) were introduced and with 4.4 g (0.07 mol) of sodium metaborate (NaBO ₂ ) - corresponding to 2.4 wt .-% based on the glycerol - added. The reaction mixture was heated to 240 ° C in a nitrogen atmosphere, with the condensation water removed via the water separator. The reaction was stopped after the amount required for the formation of diglycerol had been removed. The composition of the oligoglycerol mixture was determined by HPLC.

Characteristics of the product glycerin 25% by weight diglycerol 37% by weight triglycerol 15% by weight tetraglycerol 9% by weight oligoglycerins 14% by weight

Composition of the diglycerin fraction beta, beta-diglycerol 8.9% by weight alpha, beta-diglycerol 39.1% by weight alpha, alpha-diglycerol 52.0% by weight

Comparative Example 1

Analogously to Example 1, 184 g of glycerol in the presence of 4.4 g (0.08 mol) of potassium hydroxide - corresponding to 2.4 wt .-% based on the glycerin - condenses.

Characteristics of the product glycerin 32% by weight diglycerol 29% by weight triglycerol 16% by weight tetraglycerol 9% by weight oligoglycerins 14% by weight

Composition of the diglycerin fraction beta, beta-diglycerol 1.0% by weight alpha, beta-diglycerol 25.9% by weight alpha, alpha-diglycerol 73.1% by weight

Comparative Example 2

Analogously to Example 1, 184 g of glycerol in the presence of 4.4 g (0.03 mol) of sodium silicate (Portil ^(R) AW, modulus: 2.03, Fa. Henkel KGaA) - corresponding to 2.4 wt .-% based on the glycerol - condensed kon.

Characteristics of the product glycerin 20% by weight diglycerol 41% by weight triglycerol 20% by weight tetraglycerol 10% by weight oligoglycerins 9% by weight

Composition of the diglycerin fraction beta, beta-diglycerol 22.5% by weight alpha, beta-diglycerol 48.7% by weight alpha, alpha-diglycerol 28.8% by weight

Claims (4)

1. A process for the preparation of Oligoglyceringemischen, characterized in that condensing glycerol in the presence of Borverbin applications, the condensation water continuously removed from the reaction mixture and the reaction stops, as soon as the theoretically required for the formation of diglycerol amount of water has been deposited. 2. The method according to claim 1, characterized in that as Boron compounds amorphous alkali borates selected from Grup derived from lithium metaborate, sodium metaborate, sodium tetra borate and potassium metaborate. 3. Process according to claims 1 and 2, characterized in that that the boron compounds in amounts of 1 to 10 wt .-% - based on the glycerin - uses. 4. The method according to at least one of claims 1 to 3 characterized characterized in that the condensation at temperatures of 200 to 260 ° C performs.