Por si puedes sacar algo de aquí. Parece que el proceso de fabricación no es sencillo.
1. Raw materials for the manufacture of alkyl polyglycosides
1.1 Fatty alcohols
Fatty alcohols can be obtained either from petrochemical sources (synthetic
fatty alcohols) or from natural, renewable resources, such as fats and oils (natural
fatty alcohols). Fatty alcohol blends are used in the alkyl polyglycoside
synthesis to build up the hydrophobic part of the molecule. The natural fatty
alcohols are obtained after transesterification and fractionation of fats and oils (triglycerides), leading to the corresponding fatty acid methyl esters, and subsequent
hydrogenation. Depending on the desired alkyl chain length of the
fatty alcohol, the main feedstocks are oils and fats of the following composition:
coconut or palm kernel oil for the C,,,,, range and tallow, palm or rapeseed oil
for the C,,,,, fatty alcohols.
1.2 Carbohydrate source
The hydrophilic part of the alkyl polyglycoside molecule is derived from a
carbohydrate. Based on starch from corn, wheat or potatoes, both polymeric
and monomeric carbohydrates are suitable as raw materials for the production
of alkyl polyglycosides. Polymeric carbohydrates include, for example, starch
or glucose syrups with low degradation levels while monomeric carbohydrates
can be any of the various forms in which glucose is available, for example waterfree
glucose, glucose monohydrate (dextrose) or highly degraded glucose syrup.
Raw material choice influences not only raw material costs, but also production
costs. Generally speaking, raw material costs increase in the order starddglucose
syrup/glucose monohydrate/water-free glucose whereas plant equipment
requirements and hence production costs decrease in the same order.
3. Synthesis processes for the production of alkyl polyglycosides
Basically, all processes for the reaction of carbohydrates to alkyl polyglycosides
by the Fischer synthesis can be attributed to two process variants, namely direct
synthesis and the transacetalization process. In either case, the reaction can be
carried out in batches or continuously.
Direct synthesis is simpler from the equipment point of view [6-81. In this
case, the carbohydrate reacts directly with the fatty alcohol to form the required
long-chain alkyl polyglycoside. The carbohydrate used is often dried before the
actual reaction (for example to remove the crystal-water in case of glucose
monohydrate = dextrose). This drying step minimizes side reactions which take
place in the presence of water.
In the direct synthesis, monomeric solid glucose types are used as fineparticle
solids. Since the reaction is a heterogeneous solid/liquid reaction, the
solid has to be thoroughly suspended in the alcohol.
Highly degraded glucose syrup (DE> 96; DE = dextrose equivalents) can
react in a modified direct synthesis. The use of a second solvent and/or emulsifiers
(for example alkyl polyglycoside) provides for a stable fine-droplet dispersion
between alcohol and glucose syrup "3,101.
The two-stage transacetalization process involves more equipment than the
direct synthesis. In the first stage, the carbohydrate reacts with a short-chain
alcohol (for example n-butanol or propylene glycol) and optionally depolymerizes.
In the second stage, the short-chain alkyl glycoside is transacetalized with a
relatively long-chain alcohol (C,,,,,-OH) to form the required alkyl polyglycoside.
If the molar ratios of carbohydrate to alcohol are identical, the oligomer
distribution obtained in the transacetalization process is basically the same as in
the direct synthesis.
The transacetalization process is applied if oligo- and polyglycoses (for example
starch, syrups with a low DE value) are used [111. The necessary depolymerization
of these starting materials requires temperatures of > 140 "C. Depending
on the alcohol used, this can create correspondingly higher pressures
which impose more stringent demands on equipment and can lead to higher
plant cost.
Generally, and given the same capacity, the transacetalization process results
in higher plant cost than the direct synthesis. Besides the two reaction stages,
additional storage facilities and, optionally, working-up facilities for the shortchain
alcohol have to be provided. Alkyl polyglycosides have to be subjected to
additional or more elaborate refining on account of specific impurities in the
starch (for example proteins). In a simplified transacetalization process, syrups
with a high glucose content (DE > 960/0) or solid glucose types can react with
short-chain alcohols under normal pressure 112-161. Continues processes have
been developed on this basis [141.
Figure 3 shows both synthesis routes for alkyl polyglycosides.
4. Requirements for the industrial production of water-soluble alkyl polyglycosides
The requirements for or rather the design of alkyl polyglycoside production
plants based on the Fischer synthesis are critically determined by the carbohydrate
types used and by the chain length of the alcohol used. It is intended here
to describe first the production of water-soluble alkyl polyglycosides on the
basis of octanol/decanol (C,,,,-OH) and dodecanol/tetradecanol (C,,,,,-OH).
Alkyl polyglycosides which, for a given DP, are insoluble in water on account
of the alcohol used (number of C atoms in the alkyl chain 2 16) are dealt with
separately (see 5. in this chapter).
Under the conditions of the acid-catalyzed syntheses of alkyl polyglycoside,
secondary products, such as polydextrose [17,181, ethers and colored impurities,
are formed. Polydextroses are substances of undefined structure which are
formed in the course of the synthesis through the polymerization of glycoses.
The type and concentration of the substances formed by secondary reactions are
dependent on process parameters, such as temperature, pressure, reaction time,
catalyst, etc. One of the problems addressed by development work on industrial
alkyl polyglycoside production over recent years was to minimize this synthesis-
related formation of secondary products.
Generally, the production of alkyl polyglycosides based on short-chain
alcohols (C,,,,-OH) and with a low DP (large alcohol excess) presents the fewest
problems. Fewer secondary products are formed with the increasing excess of
alcohol in the reaction stage. The thermal stress and formation of pyrolysis
products during removal of the excess alcohol are reduced.
The Fischer glycosidation may be described as a process in which, in a first
step, the dextrose reacts relatively quickly and an oligomer equilibrium is
reached. This step is followed by slow degradation of the alkyl polyglycoside.
In the course of the degradation, which consists of dealkylation and polymerization
steps, the thermodynamically more stable polydextrose is formed substantially
irreversibly in increasing concentrations. Reaction mixtures which
have exceeded an optimal reaction time may be described as over-reacted. If the
reaction is terminated too early, the resulting reaction mixture contains a significant
amount of residual dextrose.
The loss of alkyl polyglycoside active substance in the reaction mixture
correlates well with the formation of polydextrose, the reaction mixture in the
case of over-reacted systems gradually becoming heterogeneous again through
precipitating polydextrose. Accordingly, product quality and product yield are
critically influenced by the time at which the reaction is terminated. Starting
with solid dextrose, alkyl polyglycosides low in secondary products are obtained,
providing other polar constituents (polydextrose) are filtered off to gether with the remaining carbohydrate from a reaction mixture which has not
fully reacted [19,201.
In an optimized process, the concentration of secondary products formed by
etherification remains relatively low (depending on the reaction temperature
and time, the type and concentration of catalyst, etc.). Figure 4 shows the typical
course of a direct reaction of dextrose and fatty alcohol (C,,,,,-OH).
In the Fischer glycosidation, the reaction parameters temperature and pressure
are closely related. To produce an alkyl polyglycoside low in secondary
products, pressure and temperature have to be adapted to one another and
carefully controlled.
Low reaction temperatures (<1 00 “C)in the acetalization lead to alkyl polyglycosides
low in secondary products. However, low temperatures result in
relatively long reaction times (depending on the chain length of the alcohol) and
low specific reactor efficiencies. Relatively high reaction temperatures (> 100 “C,
typically 110-120 “C) can lead to changes in color of the carbohydrates. By
removing the lower-boiling reaction products (water in the direct synthesis,
short-chain alcohols in the transacetalization process) from the reaction mixture,
the acetalization equilibrium is shifted to the product side. If a relatively
large amount of water is produced per unit of time, for example by high reaction
temperatures, provision has to be made for the effective removal of this water from the reaction mixture. This minimizes secondary reactions (particularly the
formation of polydextrose) which take place in the presence of water. The
evaporation efficiency of a reaction stage depends not only on pressure, but also
on temperature and on the design of the reactor (stirrer, heat-exchange area,
evaporation area, etc.). Typical reaction pressures in the transacetalization and
direct synthesis variants are between 20 and 100 mbar.
Another important optimization factor is the development of selective catalysts
for the glycosidation process so that for example the formation of polydextrose
and etherification reactions can be suppressed. As already mentioned,
acetalization or transacetalization in the Fischer synthesis is catalyzed by acids.
In principle, any acids with sufficient strength are suitable for this purpose, such
as sulfuric acid, para-toluene- and alkylbenzene sulfonic acid and sulfo succinic
acid. The reaction rate is dependent on the acidity and the concentration of the
acid in the alcohol. Secondary reactions which are also catalyzed by acids, such
as the formation of polydextrose, mainly take place in the polar phase (traces of
water) of the reaction mixture and can be reduced by using hydrophobic acids
such as alkylbenzene sulfonic acids which, through the length of their alkyl
chain, mainly dissolve in the less polar phase of the reaction mixtures [21-241.
After the reaction, the acidic catalyst is neutralized by a suitable base, for
example sodium hydroxide, magnesium oxide. The neutralized reaction mixture
is a yellowish solution containing 50 to 80 O/o fatty alcohol. The high fatty
alcohol content results from the molar ratios of carbohydrate to fatty alcohol.
This ratio is adjusted to obtain a specific DP for the technical alkyl polyglycosides
and is generally between 1:2 and 1:6. Several common technical
products are specified and listed under 6. in this chapter.
The excess fatty alcohol is removed by vacuum distillation. Important boundary
conditions include:
- Residual fatty alcohol content in the product must be <1% because otherwise
solubility and odor are adversely affected.
- To minimize the formation of unwanted pyrolysis products or discoloring
components, thermal stressing and residence time of the target product must
be kept as low as possible in dependence upon the chain length of the
alcohol.
- No monoglycoside should enter the distillate because the distillate is recycled
in the reaction as pure fatty alcohol.
In case of dodecanolhetradecanol these requirements for the removal of excess
fatty alcohol are largely satisfied by multistage distillation. It is important to
note that there is a distinct increase in viscosity with decreasing fatty alcohol
content. This significantly impairs heat and mass transport in the last distillation
stage. Accordingly, thin-layer or short-path evaporators are preferred
[25,261. In these evaporators, the mechanically moved film provides for high specific evaporation efficiency and a short product residence time and at the
same time a good vacuum. The end product after distillation is an almost pure
alkyl polyglycoside which accumulates as a solid with a melting range of 70 to
150 "C. Figure 5 summarizes the main process steps for the synthesis of alkyl
polyglycosides.
One or two alcohol recycle streams accumulate in alkyl polyglycoside production
depending on the manufacturing process used: excess fatty alcohol
and-in case of the transacetalization process-the short-chain alcohol which is
almost completely recovered. These alcohols may be reused in subsequent reactions.
The need for purifying or the frequency with which purifying steps have
to be carried out depends upon the impurities accumulated in the alcohol. This
is largely dependent upon the quality of the preceding process steps (for example
reaction, alcohol removal).
After removal of the fatty alcohol, the alkyl polyglycoside active substance
is directly dissolved in water so that a highly viscous 50 to 70% alkyl polyglycoside
paste is formed. In subsequent refining steps, this paste is worked up
into a product of satisfactory quality in accordance with performance-related
requirements. These refining steps may comprise bleaching of the product, the adjustment of product characteristics, such as pH value and active substance
content, and microbial stabilization. In the patent literature, there are many
examples of reductive [271 and oxidative bleaching [28-321 and of two-stage
processes of oxidative bleaching and reductive stabilization 1331. The effort and
hence the cost involved in these process steps to obtain certain quality features,
such as color, depend on performance requirements, on the starting materials,
the DP required and the quality of the process steps.
Figure 6 illustrates an industrial production process for long-chain alkyl
polyglycosides (C,,,,, APG) via direct synthesis.
convertida en alguna cosa rara 
pero tiene que haber alguna manera de enterarse, no? 
a lo más lo que voy a perder es un euro que cuesta el coco... 
