Note: Descriptions are shown in the official language in which they were submitted.
D 9315 PCT / 03.07.91 2095933
A ~tabilized sur~actant paste
This invention relates to a water-based surfactant
paste stabilized against ~icrobial infestation, the surfac-
tant in particular essentially oonsis,tiny of a nonionic
sur~actant of the alkyl glycoside type. The invention also
relates to a process for the production of the surfactant
paste.
The surfactants pre~ent in modern detergents and
cosmetic cleansing preparations have to ~atisfy stringent
requirements in regard to biological degradability. Such
surfactants are often marketed in the form o~ water-based
preparations which, despite a high surfactant concentra-
tion, are preferably still pumpable or pourable. By virtue
of their ready biodegradability, these water-based mixtures
are readily infested by such microbes as bacteria and
fungi, so that the quality and, in particular, stability in
storage of the surfactant mixtures can be adversely af-
fected. Although there are a number of useful antimicro-
bial agents which prevent ~icrobial infestation and guaran-
tee adequate s~ahili~y in storage, the use of preserva-
tives, such as glutaraldehyde or benzoic acid for example,is not without technical problems. Thus, there is a danger
tha~ the presence of such preservatives may cause dis-
coloration of ~he surfactant paste during storage. On the
oth~r hand, the presence of preservatives is not accepted
by the next user for all applications of the surfactant
pastes.
It has now been found that water-based surfactant
pastes protected against microbial infestation can have
excellent stability in storage, even in ~he abs~nce o~ the
usual preserva~ives, providing measures are tak~n to ensure
that certain i~purities are not pre~ent during their
~ormulation.
2~9~933
D 9315 PCT 2
These requirements are satisfied by a water-ba~ed
surfactant paste containing 30 to 70% by weight of a
surfactant stable in alkaline medium, more particularly a
nonionic surfactant of the alkyl glycoside type, charac-
s terized in that the paste is substantially fr~ frombleachable colour bodies and precursors thereof which lead to
discoloration in alkaline medium and is substantially free
from secondary products and residues which reduce the pH
value during storage by alkali consumption and in that the
paste has a pH value of at least 11, preferably in the
range from 11 to 12.5 and, more preferably, o~ at least
11.5 through the presence of added alkaline substances.
It has surprisingly been found that, even after
storage for several months at 40 to 50DC, the product
according to the invention is stable in color and is free
from microbial infestation and, hence, does not require
additional chemical stabilization.
Surfactants stable in alkaline medium are understood
to be surface-active compounds, such as alkoxylated long-
chain alcohols, more particularly fatty alcohol ethoxy-
lates, including compounds containing closed terminal
groups, surfactants such as alkylether carboxylic acids,
fatty alcohol sul~ates and ether sulfates, alkanesulfonates
and, in particular, surfactants of which the hydrophilic
part derives from carbohydrate compounds. Surfactants of
the alkyl glycoside type are particularly preferred. Sur-
~actants of this type are understood to be mixtures of
alkyl monoglycosides and alkyl oligoglycosides of the type
obtained in the acid-catalyzed reaction of sugars and
alkanols.
The particularly preferred alkyl glycosides are
nonionic surfactants of the type known, for example, fro~
US-PSS 3,547,828 and 3,839,318. PrQduction processes for
particularly light-colored and color-stable alkyl glyco
sides are descri~ed in European p~tent applications EP O
,.
D 9315 PCT 3 2~9~933
301 298 A1, EP U 362 671 A1 and EP 0 357 969 A1. The a1kY1
COmPOnent O~ the a1kY1 glycosides generally consist~ of
aliphatic residues containing 8 to 24 and, more particular-
ly, 8 to 18 carbon atoms. The corresponding ~atty alkyl
radicals obtainabls ~rom fats as renewable ra~ ~ ~ls by
way of the fattv alcohols are particularly preferred.
AlXyl radicals derived from synthetic primary alcohols,
more particularly from the so-called oxo alcohols, are al50
suitable in principle, but are less preferred in the
present case. The sugar component in the alkyl glycoside
may emanate from typical aldoses or ketoses, such as for
example glucose, fructose, mannose, galactose, talose,
gulose, allose, altrose, idose, arabinose, xylose, lyxose
and ribose. 8y virtue of the abundantly available raw
materials glucose or starch or starch degradation products,
glucose is the particularly preferred sugar component. The
average degree of oligomerization of the alkyl glycosides
present in the pastes according to the invention may assume
any value from the point of view of paste stability, i.e.
it may be in the typical range of 1.2 to 3Ø This averagP
degree of oligomexization is based on the quantity of alkyl
monoglycoside and alkyl oligoglycoside surfactant in the
alkyl glycoside product. However, it is preferred to use
alkyl glycosides in ~hich the degree of oligomerization is
distinctly below 1.5 and, more particularly, in the range
from 1.3 to 1.4, the associated fatty alkyl radical essen-
tialiy being around Cl2. Different quantitie~ of C8l0 and
CL~ 16 may be present, depending on the width of the cut.
These alkyl glycosides are distinguished by particularly
good surfactants properties. Together with water and the
alkaline substances, they represent a par~icularly prefer-
red embodiment of t~e invention. Other preferred embodi-
mel1tS are baSed On C Chain CUtS Centered around C8~10 and
arOUnd C14/1~ The fOrmer haVe VerY gOOd 5O1Ubi1iZing
35 PrOPertieS Whi1e the 1atter are suitable as wetting agents
; D 9315 PCT 4 2095933
and emulsifiers.
Tha "su~actant paste" is a paste in a viscosity range
extending from flowable to viscous. Accordingly, the
viscosities (as measured using a Hoppller viscosimeter at
40C or a Brookfiel~ ~alipath visco!simeter at 40 C/4
r.p.m.~ are in thé range from about 1,000 to 100,000.
The surfactants present in the water-based surfactant
paste, more particularly the al~yl ~lycosides, are sub
stantially free from bleachable pi~ments, pigment precur-
sors, secondary products and residues adversely affecting
color quality where these surfactants have been subjected
to a bleaching process after their production. The bleach-
ing process in question is preferably an oxidative bleach-
ing process, more particularly using hydrogen peroxide as
the oxidizing agent. This bleaching process is preferably
carried out in the presence of magnesium cations which may
enter the system either in the form of alkaline magnesium
compounds, such as the oxide, hydroxide, carbonate, or an
alcoholate to neutralize the acidic catalyst at the end of
the production process in the case of the alkyl glycosides.
However, it is also sufficient if neutralization is carried
out with typical alkalis, more particularly alkaline sodium
compounds, at the end of the surfactant production process
and water-soluble or insoluble magnesium compounds, for
example those mentioned above, are subsequently added in
such a quantity that the subsequent bleaching step takes
place in the presence of 100 to 1,000 ppm magnesium. If
steps are taken in the bleaching process to ensure that a
high pH value of at least 9 and preferably at least 10 i5
maintained, the residual peroxide content can be reduced to
values of at most S0 to 100 ppm ~2~ in the final stage of
the bleachinq process by heat treatment of the paste at 8 o
to 150 C . The oxidatively bleached products may be after-
treated with reducing agents: the pH value should not ~all
35 below ~.5 during the redu~::tiYe aftertreatment. The surfac-
.
D 9315 PCT 5 209~c~33
tant paste thus treated acquires the high pH value accord-
ing to the i~vention by compensation of th~ consu~ption o~
alkali observed during bleaching by addition of sodium
hydroxide, potassium hydroxide or sodium or po~as~ium
carbonates and adjustment of the desired pH value.
Accordingly, the present invention al50 rala~es to a
process for the production o~ the storable aqueous ~urfac-
tant paste, more particularly an alkyl glycoside paste, of
the type obtained by th~ typical production processes for
alkali-stable surfactants, more particularly alkyl glyco-
sides, after the additional bleaching with aqueous H2O2, the
bleaching process being carried out as oxidative bleaching
with H202 in the presence of magnesium compounds in alkaline
medium at pH values above pH 9 and preferably above pH 10,
characterized in that, after the residual peroxide content
has been reduced to values of at most 50 to 100 ppm H202,
the pH is adjusted to a value of at least 11, preferably in
the range from 11 to 12.5 and, more preferably, at least
ll.S by addition of alkalis, more particularly alkaline
compounds whose presence does not affect the subseguent use
of the surfactant paste or is desirable, more particularly
sodium hydroxide, potassium hydroxide or sodiu~ or potas-
sium carbonates, the water content of the pastes being
adjusted to a value in the range from 30 to 70%.
Where present in the particularly preferred form of
alkyl glucoside pastes, the water-based surfactant pastes
according to the invention produced in this way can be
mixed with additional surfactants otherwise made stable to
alkalis to obtain a product which contains a surfactant
mixture in compounded form which is particularly suitable
for subseguent processing or whereby the viscosity and flow
behavior of the paste during storage are promoted.
To produce the stabilized paste according to the in-
vention, the procP~s steps of peroxide bleaching, peroxide
degradation, optionally reductive aftertreatment and pH
3 3
D 9315 PCT 6
adjustment ~ay be carried out continuously or discontinu-
ously. Tha~bleaching step and the peroxide degradation
step are preferably carried out continuously, more par-
ticularly in cascades of stirrPd tanks with suitable
temperature and residence time parameters. For example,
the peroxide bleaching step is carrield out with H2O2 at
110C over an average residence time of 2 hours, which
leaves a residual peroxide value of about 300 to 600 ppm
H2O2. In the subsequent peroxide degradation step, the
mixture is kept at 120C for an average time o~ 3 hours,
leaving a residual peroxide content of 30 to 70 ppm.
E x a m p 1 e s
Example 1:
The microbially stable alkaline version was produced
from 100 kg of a reaction mixture prepared by reaction of
dodecanol with glucose in a molar ratio of 5:1. The
mixture contained approx. 27.5% alkyl glucoside and 0.2%
catalyst ~p-toluene sulfonic acid). Working up was carried
out as follows:
- The catalyst was neutralized by addition of 100 g of
S0% sodiu~ hydroxide at 90-C.
- 15 g finely divided magnesium oxide were then stirred
in.
- The mixture was concentrated by evaporation to 1%
residual fatty alcohol in a thin-layer evaporator at
1 mbar and at a heat carrier temperature o~ 200'C.
Approx. 28 kg distillation residue were obtained.
- By addition of fully deionized water, the residue was
convexted into approx. 56 kg of a water-based paste.
- The paste was then bleached for 1 hour at llO-C in a
pressure reactor by addition o~ 300 g H22 (1~000 g 30%
D 9315 PCT 7 2 0~ 3 ~3~3
~olution) and 420 g NaOH (840 g 50~ solution). Vacuu~
degassi~g left a light yellow ~product containing
approx. 350 ppm residual hydrogen ]peroxide.
- The product was thermally aftertreated for another 3
hours at 120C. The residual peroxide conten~ ~ell to
less than 50 ppm withou~ any significa~ ~ ~ e in the
color of the product.
The paste obtained had a pH value of llo5 which
remained stable after storage for 4 months at 60-C. In a
microbial infastation test with 106 bacteria and 105
fungi/g, the product produced destruction times o~ at most
3 days for bacteria and at most 14 days ~or funyi ovar the
entire storage period. ~Bacterial mixture: Staphylococcus
aureus, Enterococcus ~aecium, Escherichia coli, Enterobac-
ter aerogenes, Pseudomonas aeruginosa. Fungal mixture:
Candida albicans, Aspergillus niger, Penicillium rubrum,
Trichoderma viride).
The paste had a viscosity of 1,800 mPa.s at 40-C, as
measured in accordance with DIN 53015.
E~umpl0 2:
100 kg of a reaction mixture obtained by reaction of
qlucose with C12~ atty alcohol (75/25%) in a molar ratio
of 1:4.5, alkyl glycoside con~ent 29%, wa~ worked up as
follows:
- The catalyst (0.2% p-toluene sulfonic acid) was
neutralized with 110 g 50% sodium hydroxide.
- 20 g finely divided ~fgO were stirred inO
- Distillation was carried out as in Exa~ple 1 and
produced approx. 30 kg APG residue.
- After preparation of a 50% water-based paste, the
3S paste was ~leached for 2 hour~ a~ 105-C with addition
2~ 33
D g315 PCT 8
of 400 ~ H2O2 ~1,330 g 30% solution) and 300 g NaOH
(600 g 60% sol~tio~).
The thermal aftertreatmen~ was carried out over a
period of 6 hours at 105C, the residual peroxide
content falling to less than 50 ppm.
- The produc~ a~sed ~ y~çyQ. The pH Yalue was
adjusted to 11.8 by addition o~ another 300 g NaOH (as
600 g 50% solution).
After storage for 4 months, the product was color-
stable, the pH value remained constant at 11.8 and the
microbial sta~ility corresponded to that o~ the sample o~
Example 1. Viscosity of the paste: 2,000 mPa.s (measured
as in Example 1).
