PROCEDE D'OBTENTION DE MELANGES D'OLIGOGLYCEROLS A FORTE TENEUR EN DIGLYCEROLS

PROCESS FOR THE PRODUCTION OF OLIGOGLYCEROL MIXTURES OF HIGH DIGLYCEROL CONTENT

Abrégé anglais

D 9261
Abstract
Oligoglycerol mixtures of high diglycerol content can
be obtained by condensation of glycerol in the presence of
silicate compounds, continuous removal of the water of
condensation from the reaction mixture and termination of
the reaction when the quantity of water theoretically
required for the formation of diglycerol has been sepa-
rated.

Revendications

D 9261 6
CLAIMS
1. A process for the production of Oligoglycerol mixtures
of high diglycerol content, characterised in the glycerol
is condensed in the presence of silicate compounds, the
water of condensation is continuously removed from the
reaction mixture and the reaction is terminated when the
quantity of water theoretically required for the formation
of diglycerol has been separated off.
2. A process as claimed in claim 1, characterized in that
amorphous alkali silicates corresponding to formula (I)
(SiO2)m(M2O)n (I)
in which M is lithium, sodium or potassium and m and n are
whole or broken numbers of greater than O,
are used as the silicate compounds.
3. A process as claimed in claim 1, characterized in that
crystalline alkali disilicates corresponding to formula
(II)
(SiO2)m(M2O)n(H2O)x (II)
in which M is lithium, sodium or potassium, m is a whole or
broken number of greater than 0, n is 1 and x is O or an
integer of 1 to 20,
are used as the silicate compounds.
4. A process as claimed in at least one of claims 1 to 3,
characterized in that silicate compounds corresponding to
formula (I) or (II), in which M is sodium, are used.
5. A process as claimed in at least one of claims 1 to 4,
characterized in that silicate compounds corresponding to
formula (I) or (II), of which the modulus is 1.9 to 4, are
used.
6. A process as claimed in at least one of claims 1 to 5,
characterized in that the silicate compounds are used in

D 9261 7
the form of aqueous solutions having solids contents of 1
to 80% by weight , based on the silicate compound.
7. A process as claimed in at least one claims 1 to 6
characterized in that the silicate compounds are used in
quantities if 1 to 10% by weight, based on the glycerol.
8. A process as claimed in at least one of claims 1 to 6,
characterized in that the condensation reaction is carried
out at temperatures of 200 to 260°C.

Description

HENKE~ XGaA
Dr. Fb/49
12th Septamber 1990 ~9 1~ 8 7
Patent Application
D 9261
A process ~or t~q proau~tio~ o~ oligogly¢-rol m~Ytures of
high ~iglycerol cont~nt
This invention relates to a process for the production
of oligoglycerol mixtures of high diglycerol content by
condensation of glycerol in the presence of silicate com-
pounds A
Diglycerol has acquired considerable significance as
a starting material for the production of fatty acid
esters. Fatty acid esters are used as emulsifiers in the
food industry and in cosmetics and in various industrial
applications, for example as lubricants or stabilizers for
PVC tJ. A~. Oil. Chem. 80c. 66, 153 tl989)1.
Diglycerol is generally produced from glycerol by
reaction with glycidol tFetta, 8ei~a~, Anstri¢hm~tt., 88
101 (1986)1 or epichlorohydrin l~P-A-0 333 984]. However,
the reaction is not selective, in addition to which glyci-
dol and epichlorohydrin are difficult to handle and call
for strict works safety measures.
Alternatively, glycerol may be condensed in the
presence of alkali bases. However, it is only possible in
this way to obtain mixtures which, in addition to diglycer-
ol, also contain higher homologs and by no means negligible
quantities of unreacted glycerol.
Since the diglycerol has to be removed from these
mixtures by distillation, which is extremely time-consuming
and energy-intensive, the problem addressed by the present
invention was to provide an improved process by which

D 9261 22 ~ 916 8 7
oligoglycerol mixtures of high diglycerol content could be
obtained.
The present in~ention relates to a process for the
production of oligoglycerol mixture~ of high diglycerol
content, characterized in that glycerol is condensed in the
presence of silicate compounds, the water of condensation
is continuously removed from the reaction mixture and the
reaction is terminated when the quantity of water theoret-
ically required for the formation of diglycerol has been
separated off.
In the following, silicate compounds are understood to
be
a) amorphous alkali silicates corresponding to formula
(r)
t8io2)~(M2o)n ~I)
in which M is lithium, sodium or potassium and m and
Z0 n are whole or broken numbers of greater than 0,
and
b) crystalline alkali disilicates corresponding to
formula (II)
(8io2)~lM2o)~HzO)s (II)
in which M and m are as defined above, n is 1 and x is
0 or an integer of 1 to 20.
The amorphous alkali silicates are the glass-like,
water-soluble salts of silicic acid solidified from the
melt. Their production is described, for example, in
~OMPP~8 Chem~e L~xikon, 8th ~dition, Verlag Fr~nckh-Ro~os,
8tuttgart, Vol. 6, p~ge ~593. Both alkali silicates having
a low Si02 : M2O or m:n ratio ("basic" waterqlasses) and

- D 9261 3 2~1687
those having a high m:n ratio ("neutral" or "acidic" water-
glasses) may be used in the process according to the inven-
tion. The sio2 : M20 ratio is alRo known a~ the "modulus"
of the silicate.
The crystalline alkali disilicates are also known
substance~. They have a layer-like structure and may be
obtained, for example, by sintering of alkali waterglass or
by hydrothermal reactions tGlast-chn. ~-r., 37 19~ ~1964)].
Suitable alkali disilicates, which catalyze the autoconden-
sation of glycerol in the process according to the inven-
tion, are for example makatite (Na2Si~09 5 H2O), kenyaite
(Na2Si220~ 10 HzO) or ilerite (Na2Si~O" 9 HzO) tAmer.
Mineral. 38, 163 ~1953)].
Silicate compounds corresponding to formulae (I) and
~I~), in which M stands for sodium and x is 0 and of which
the modulus, i.e. the m:n ratio, is from 1.9 to 4 and
preferably from 1.9 to 2.5 have proved to be particularly
active catalysts in the condensation of glycerol to oligo-
glycerols of high diglycerol content~
The silicate compounds may be used as solids or even
in the form of aqueous solutions having solids contents of
1 to 80% by weight and preferably 30 to 60% by weight,
based on the silicate compound.
The silicate compounds are used in quantities of 1 to
10% by weight and preferably in quantities of 2 to 5% by
weight, based on the glycerol, in the condensation reac-
tion. The condensation of the glycerol is carried out at
temperatures of 200 to 260-C and preferably at temperatures
o~ 240 to 2SO-C.
To carry out the condensation reaction, the glycerol
and the silicate compound are initially introduced and are
heated to the reaction temperature in an inert gas atmos-
phere. T~ shift the equilibrium, the water of condensation
for~ed is removed, for example through a water separator.
The reaction is terminated when the quantity of water

D 9261 4 ~9~687
theoretically required for the formation o~ diglycerol has
been separated. I~ the catalysts are used in the form o~
aqueous solutions in the condensatlon reaction, their water
content must be taken into account when calculating the
S quantity o~ water Or condensation reguired for th~ ~orma-
tion o~ diglycerol. In general, thQ reaction time i~ 1 to
30 h and pre~erably 3 to 15 h. The catalyst may be sepa-
rated from the reaction mixture by, for example, filtration
or centrifugation. For a number of applications, this may
even be unnecessary. The diglycerol is removed from the
oligoglycerol mixture formed, for example by distillation
in a high vacuum. For a number of applications, however,
the oligoglycerol mixture~ according to the invention may
be used without further separation.
The following Examples are intended to illustrate the
invention without limiting it in any way.
~xample~
Exam~l~ 1 to 6: Comparison Example 1
G-n-ral prooedur- ~or th- pro~uction o~ oligoglycerol
miYtur-~ of hlg~ d~gly¢erol content
184 g (2 mol) glycerol (99.5% by weight) were intro-
duced into a 250 ml three-necked flask equipped with a
reflux condenser, water separator and internal thermometer
and 2 to 5% by weight of a silicate compound were added.
The reaction mixture was heated to 240-C in a nitrogen
atmosphere, the water of condensation being removed through
the water separator. The reaction was terminated after the
quantity required for the formation of diglycerol had been
separated. The composition of the oligoglycerol mixture
was determined by HPLC. Particulars of the catalysts, the
test procedure and the product compositions are shown in
Table 1. In Comparison Example Cl, potassium hydroxide was
used instead of a silicate compound.

~ 9261 5 2091~87
Table 1:
Test procedures and product compositiona
Percentages as % by weight
Ex. Catalyst Modulus SC Q~ t Gly ~i ~Li Tetra
% % h t % % %
.
1 Na silicate* 2.03 100 2.4 7 20 41 20 10
2 ~a silicate* 2.03 100 5.0 7 27 41 16 7
3 Na silicate# 2.03 55 5.0 8.5 26 40 18 8
4 Na silicate# 2.40 47 5.015 15 37 23 12
Na silicate# 3.35 36 5.025 13 37 23 12
6 ~a disilicate+ 1.94 100 3.0 8 25 42 17 7
C1 KOH - 100 2.4 7 32 29 16 9
. _ _
Legend: Modulus = ratio by weight of SiO2 to NazO
QU = quantity of catalyst used, based on gly-
cerol
SC = solids content of the catalyst
t = reaction time
Gly = glycerol
Di = diglycerol
Tri = triglycerol
~etra = tetraglycerol
* = spray-dried, amorphous
# = aqueous solution
+ - anhydrous, crystalline, ~-modification