Note: Descriptions are shown in the official language in which they were submitted.
21 642~4
_ O.Z 4901
Process for Bleaching Alkyl Polyglycosides
The invention relates to a process for bleaching low-
moisture and low-fatty-alcohol alkyl polyglycosides using solid
oxidizing agents with thorough mixing at temperatures in the
range from 80 to 160C. The thorough mixing is performed, e.g.
in a kneader or in an extruder.
Alkyl polyglycosides are prepared from natural raw
materials and are nontoxic and readily degradable surface-
active materials. They are therefore used as detergents,
cleaning agents, emulsifiers and dispersants. However, they
only have the desired interfacial properties when the alkyl
groups have at least 8 carbon atoms. The alkyl polyglycosides
for the purposes of this invention have with the formula:
R' - C ~ Zn'
in which R' represents an unbranched or branched, saturated
or unsaturated aliphatic hydrocarbon radical having 8 to 18
carbon atoms or mixtures thereof and Zn represents a poly-
glycosyl radical having a polymerization degree n of 1.1 to
3 of hexose or pentose units or mixtures thereof.
Preference is given to alkyl polyglycosides having
alkyl radicals having 12 to 16 carbon atoms and a polyglycosyl
radical having a polymerization degree n of 1.1 to 2.
Particular preference is given tc alkyl polyglycosides having
a polyglycosyl radical in which n is 1.1 to 1.5 and very
particularly preferably n is 1.2 to 1.4. The preferred
glycosyl radical is a glucosyl radical. Alkyl polyglycosides
having long-chain alkyl groups are generally prepared by
single- or multi-stage syntheses. A single-stage preparation
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process id described inter alia in DE-A-41 01 252.
A two-stage preparation process is described, for
example in EP-A-0 306 652, according to which an n-butyl
glycoside is first prepared by glycosidation with n-butanol
and thereupon the desired long-chain alkyl polyglycoside is
prepared by transglycosidation with a long-chain alcohol.
When the reaction is complete, the alkyl polyglyco-
sides are present dissolved in long-chain alcohols. These
alcohols must then be separated off if it is desired to obtain
products completely soluble in water.
In the case of relatively high aesthetic requirements,
alkyl polyglycosides are products which must be sub~ected to a
bleaching reaction in order to obtain sufficiently light-
colcured products. This bleaching is generally carried out
using hydrogen peroxide with aqueous alkyl polyglycoside
solutions. A disadvantage in this process is the poor space-
time yields, especially if, for complete decomposition of the
residual peroxide, the aqueous alkyl polyglycoside solutions
must still be kept at elevated temperature for a relatively
long time. The product can be damaged by this, and dark colours
and decomposition products, some of which have an unpleasant
odour, occur. Moreover, there is the risk of foam development
which can no longer be controlled.
Wo 91/19723 describes a route for alkyl polyglycoside
bleaching, where the material which is virtually free of fatty
alcohol and water is kneaded at temperatures of 50 to 150C with
aqueous hydrogen peroxide and a base, e.g. sodium hydroxide
solution. The above-described disadvantages of the alkyl
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..
polyglycoside bleaching in aqueous solution no longer occur in
this bleaching method. It is a disadvantage that the bleaching
is not possible in this manner at temperatures significantly
above 100C. However, often low-fatty-alcohol and low-moisture
products can be kneaded only at temperatures above 100C.
Difficulties can further arise in the addition of sodium
hydroxide solution. A certain acidification effect during the
bleaching reaction must be compensated for by the addition of
base. Controlled addition of the sodium hydroxide solution
would only be effected at great expense, because the pH cannot
be measured directly in the melt. Addition by hand always
introduces the risk of overdosing or underdosing, as a result
of which the bleaching result would rapidly worsen.
A major object according to the present invention is
therefore to find a process which permits the oxidizing bleach-
ing in a melt without the problems described above with the
addition ¢f hydrogen peroxide and sodium hydroxide solution.
It has now been found that very good bleaching
results can be achieved even at temperatures above 100C if
solid bleaching agents such as sodium percarbonate or sodium
perbGrate are used, instead of the aqueous hydrogen peroxide
solution.
The present invention therefore provides a process
for bleaching low-moisture and low-fatty-alcohol alkyl poly-
glycosides, which is characterized in that solid oxidizing
agents are added and the bleaching is carried out at tempera-
tures of 80 to 160C with thorough mixing.
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According to the process of the present invention,
preferably temperatures of 90 to 150C are employed, and very
particularly preferably, temperatures of 100 to 140C. The
alkyl polyglycoside (APG) used is preferably the alkyl poly-
glucoside.
The substances can be incorporated withcut
difficulty into viscose APG (temperature 80-160C) using, e.g.
extruders or kneading machines, so that homogeneous products
result. An addition of alkali during bleaching is superfluous,
since when these bleaching agents are used there is no pH
decrease. The products obtained are very light in colour and
are markedly low in odour. Addition of small amounts of water
before bleaching can further improve the result. The content
of water can be 0 to 10% by weight, but it is preferably
between 0 and 5%. The fatty alcohol content in the alkyl
polyglycoside subjected to bleaching is 0 to 10% by weight,
preferably 0 to 5%, values of 0 to 2.5% being very particularly
preferred. The fatty alcohol is typically a fatty alcohol
having 8 to 18 carbon atoms.
For better understanding the present invention, an
example is described hereinunder. However, it should never be
considered that the present invention is limited to the
example.
Example
Solid APG containing about 15% fatty alcohol and
about 4.5% water is molten in 500 g portions at a temperature
of 95C. A solution of 50% of this APG in demineralized water
has aniodine colour number of 52 and a pH value of 7.2.
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.
An extruder with a capacity of 600 milliliters, as
being used for test extrusion purposes of plastic material, is
heated to 95C. The APG melt is filled in in 100 g portions.
On 100 g of molten APG a 1,5 g portion of solid sodium perborate
is added. The extrusion speed is regulated to about 2.5 kg an
hour. The mixture is extruded on a running belt for cooling
down, so that a line of solid APG with a crGsscut of 8 milli-
meters in diameter is resulting.
The solid APG is collected and dissolved in warm
demineralized water, using a water APG weight ratio of 1:1.
The resulting APG solution is nearly odourless and has an
iodine colour number of 2.3. The measured pH value of the
solution is 7.7.
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