Note: Descriptions are shown in the official language in which they were submitted.
- ~ULS AgTIENGESELLSCHAFT 2157 ~46 O.Z. 4862
- Patentabteilung -
Process for preparinq alkyl PolYqlycosides
The invention relates to a single-stage process for
preparing alkyl polyglycosides by acid-catalyzed reaction
of saccharides and alcohols having 8 to 20 C atoms.
Alkyl polyglycosides having C8- to C20- alkyl radicals can
be prepared in whole or in part from renewable raw
materials. The alkyl polyglycosides are becoming increas-
ingly important because of their interesting surfactant
properties with, simultaneously, very good
biodegradability. For applications in the home and in the
cosmetics sector, these products must conform with high
aesthetic demands. There is therefore interest in pro-
cesses by which alkyl polyglycosides can be prepared in
transparent aqueous solutions of attractive colour.
To prepare alkyl polyglycosides having long-chain alkyl
groups, alkyl glycosides having Cl- to C6- alkyl groups
can first be prepared by glycosidation of saccharides
with short-chain alcohols. These products are then
converted into the desired alkyl polyglycosides by
transglycosidation at elevated temperature with long-
chain alcohols. However, the products thus prepared are
of dark colour.
Reeping to defined weight ratios, and using solubilizers,
the polar saccharides can also be reacted directly with
the nonpolar long-chain alcohols to give the alkyl
polyglycosides. In this case also, without the addition
of colour improvers, dark-coloured products are obtained
if the reaction is carried out in a stirred tank.
In EP 0 077 167, a single-stage preparation process is
described in which an aldose or ketose is reacted di-
rectly with a long-chain alcohol in a molar ratio of
1 : 1.2S to 1 : 4. The reaction is carried out at low
water contents in the presence of a reducing agent.
- 2157~4~
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This single-stage process is improved in
DE-A-41 01 252 by using a large excess of alcohol and using
alkali metal hydroxide dissolved in alcohols for neutraliza-
tion. The reaction is carried out here in a stirred tank.
Furthermore, it is known that the colour quality of
the alkyl polyglycosides can be improved by measures relating
to equipment.
Thus, according to EP-A-0 482 325, in a two-stage
preparation process, the first stage, the glycosidation of
saccharides in aqueous solution with Cl- to C6- alcohols, can
be carried out in a counter-current reaction column, for
example in a bubble-cap column.
Furthermore, according to DE-A-41 16 665, the
transglycosidation, the second stage of the two-stage process,
can also be carried out in a reaction column and preferably
under counter-current flow conditions.
However, the two-stage process having two columns
connected in series is associated with a relatively high
expenditure in terms of apparatus.
It is attempted according to the present invention
to avoid the disadvantages of the prior art and to prepare
light-coloured products without addition of reducing agents
in a simple process.
Therefore, according to the invention, in a single-
stage preparation of alkyl polyglycosides, the reaction is
carried out using a tubular reactor under co-current flow
conditions.
23443-544
- 2~5754~
Suitable tubular reactors generally have a diameter
of 0.5 to 50 cm and a length of 0.5 to 50 m, where the length
is to be at least 4 times the diameter. In the simplest case
this is a heatable tube. Preferably, however, the tubular
reactor is also provided with a plurality of nozzles via
which the vacuum can be applied and water which is introduced
and formed can be taken off.
The tubular reactor can also contain chicanes and
turbulence-generating internals. The tube can be arranged
I0 horizontally, at an incline or vertically so that in the
context of this invention columns, for example bubble-cap
columns, are also considered to be tubular reactors. However,
it must be noted in this context that the reaction components
are conducted in co-current flow.
The saccharides used can be aldoses or ketoses.
Examples of these are glucose, mannose, galactose and
fructose, glucose being preferably used. The saccharides
can be used in the anhydrous state or as an aqueous syrup.
Alcohols suitable for the present process are
general monoalcohols, preferably linear primary monoalcohols
having 8 to 20 carbon atoms, for example octanol, decanol,
lauryl alcohol, myristyl alcohol, palmityl alcohol and
stearyl alcohol. Mixtures of alcohols can also be used.
Preferably, alchohols having 8 to 12 C atoms are used.
The saccharide/alcohol molar ratio is preferably in
the range from 1 : 2 to 1 : 10.
Catalysts which are suitable are mineral acids and
strong organic acids. Examples of these are sulphuric acid,
23443-544
21~7~46
- 3a -
phosphoric acid and p-toluenesulphonic acid. The catalyst is
preferably used in concentrations of 0.2 to 5 %, based on the
saccharide.
The reaction is usually carried out at a temperature
of 50 to 140C, temperatures of 70 to 130C being particularly
preferred.
At the same time, a mean residence time of 5 to 90
minutes is preferably set.
23443-544
2157~
~ - 4 - O.Z. 4862
The process is preferably carried out continuously. The
products generally have a mean degree of glycosidation of
1 to 10, mean degrees of glycosidation of 1.1 to 4 being
particularly preferably set and mean degrees of glycosi-
S dation of 1.1 to 1.4 being very particularly preferablyset.
By means of the present invention, in particular in the
case of continuous synthesis plants, the expenditure in
term~ of apparatus is greatly decreased. Owing to the
short residence times and the narrow residence time
distributions, light products of high quality are
obtained because of the low thermal stress. The products
are of light colour when their 50 % strength aqueous
solutions have iodine colour values of < 60 before the
HzO2 bleaching.
After the reaction the product is neutralized with a base
in a known manner, wheleu~o~ excess fatty alcohol is
separated off by distillation. The product is then
generally mixed with water and bleached with H2O2.
When the invention is carried out in practice, stirred
tanks can also be connected upstream or downstream of the
tubular reactor. Thus, for example, when syrup is used,
water can be removed under a low vacuum at 70 to 130C in
the stirred tank before catalyst is added and the mixture
is passed to the tubular reactor. The water can also be
stripped using inert gas. The catalyst can also already
be added to an upstream stirred tank so that in addition
to the removal of water, some of the compounds react. The
reaction mixture which has begun to react is then prefer-
ably homogenized via a mixer and passed into the tubularreactor. Downstream stirred reactors generally serve only
to increase the residence time and to complete the
reaction. Preferably, 5 to 80 %, in particular cases 10
to 60 %, of the reaction is carried out in a tubular
reactor.
~t 57~6
- - 5 - O.Z. 4862
~xample
A 25 1 stirred reactor is fed with a mixture of 14.7 kg
of fatty alcohol (66 % dodecanol, 28 % tetradecanol, 6 %
hexadecanol) and 1.8 kg of anhydrous glucose per hour. By
addition of p-toluenesulphonic acid, a catalyst concen-
tration of 0.25 per cent by weight is maintained in the
reactor. The mean residence time is 30 minutes. At an
intern~l temperature of 110C, a vacuum of 30 mbar i8
applied so that reaction water can be distilled off
rapidly. The reactor discharge still has a glucose
content of 2.1 %.
The reaction mixture is passed through a static mixer and
then through a heatable tube having an internal diameter
of 10 cm and a length of 175 cm. The reaction mixture
contains 77.6 % fatty alcohol, 12.9 % alkyl glucoside
having a mean degree of glycosidation of 1.26 and < 0.1 %
glucose.
