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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the manufacture of polyether
polyols from polyols and alkylene oxide.
2. Background
The invention relates to a process for the manufacture of polyether polyols
by reaction between an organic compound containing 2 or more active
hydrogen atoms in the molecule and an alkylene oxide in the presence of an
amine catalyst. Such polyether polyols are suitable starting materials for
the production of polyurethanes.
As used herein the term "active hydrogen atom" means a hydrogen atom
capable of reacting according to the Zerewitinoff reaction.
It is well known to carry out the above-mentioned oxyalkylation reaction
using as catalyst an organic amine, and preferably a tertiary amine, such
as a trialkylamine. See, for example, U.S. Pat. No. 3,357,970, issued Dec.
12, 1967. However, it has been found that under such conditions the
reaction requires in many cases a comparatively long induction period,
which can be reduced by including in the reaction system a certain amount
of water but this procedure is not desirable if a high functionality
(i.e., the number of hydroxyl groups per molecule) of the resulting
product is aimed at. Other disadvantages of carrying out the oxyalkylation
reaction under the above-mentioned conditions include a rather low
reaction rate, even after the induction period, and comparatively high
alkylene oxide losses unless large catalyst quantities are used.
It has now been found that the disadvantages described above can be
circumvented by the use, as catalyst or catalyst component, of a tertiary
amine of a special structure, namely one in which at least one of the
carbon atoms attached to the nitrogen atom forms part of a non-aromatic
ring structure whilst the other carbon atoms attached to the nitrogen atom
do not form part of that ring structure.
It is perhaps useful to add that the use of such amines as catalysts in the
formation of polyurethane foams has been known for a long time. It is
therefore surprising that their catalytic activity in the oxyalkylation
reaction has not been described before.
SUMMARY OF THE INVENTION
The present invention provides a process for the manufacture of a polyether
polyol by reaction between an organic compound containing 2 or more active
hydrogen atoms in the molecule and an alkylene oxide in the presence of an
amine catalyst, characterized in that the catalyst comprises a tertiary
amine NRR'.sub.2, in which R is a cycloalkyl or cycloalkenyl group and
each R' may be an alkyl, cycloalkyl or cycloalkenyl group. In a preferred
embodiment the catalyst composes additionally a nitrogen compound
containing in the molecule at least one hydrogen atom which is capable of
reacting with alkylene oxides. The use of the above-described catalyst
provides for a short induction period and a rapid reaction rate while
minimizing alkylene oxide losses.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a process for the manufacture of a polyether
polyol by reaction between an organic compound containing 2 or more active
hydrogen atoms in the molecule and an alkylene oxide in the presence of an
amine catalyst, characterized in that the catalyst comprises a tertiary
amine NRR'.sub.2, in which R is a cycloalkyl or cycloalkenyl group and
each R' may be an alkyl, cycloalkyl or cycloalkenyl group. R has a carbon
number ranging from 3 to about 12, preferably from 3 to about 8 and R' has
a carbon number ranging from 1 to about 12, preferably from 1 to about 8.
When R' is alkyl it preferably ranges from 1 to about 8, and most
preferably from 1 to 2.
Suitable tertiary amines to be used as catalyst or catalyst component in
the process of the invention are tricycloalkylamines,
tricycloalkenylamines, N-alkyl-N,N-dicycloalkylamines and N-alkyl-N,
N-dicycloalkenylamines. Preferably a tertiary amine is used, in which R is
a cyclohexyl group and each R' is an alkyl group, such as
N-methyl-N-ethylaminocyclohexane, N-methyl-N-propylaminocyclohexane and
N,N-diethylaminocyclohexane. Particularly preferred as catalyst or
catalyst component is dimethylaminocyclohexane.
The process of the invention may be carried out using as catalyst the
tertiary amine NRR'.sub.2 as defined hereinbefore in combination with
other components, and the use of such combinations, particularly with
certain nitrogen compounds, is preferred in many cases. In a preferred
embodiment of the present process the amine catalyst also additionally
comprises a nitrogen compound containing in the molecule at least one
hydrogen atom which is capable of reacting with alkylene oxides. Suitable
nitrogen compounds are primary or secondary amines, such as dimethylamine,
diethylamine and alkylenediamines, e.g. ethylenediamine or
triethylenediamine. Other suitable nitrogen compounds include amines
containing at least one hydroxyl group in the molecule, and preferred
amines of this category are tertiary amines, such as
2-(dimethylamino)ethanol. In a particularly preferred embodiment of the
process of the invention a catalyst comprising dimethylaminocyclohexane
and 2-(dimethylamino)-ethanol is used.
Although the invention is advantageous with respect to the oxyalkylation of
any organic compound containing 2 or more active hydrogen atoms in the
molecule or a mixture of such compounds, it is in many cases preferred to
use certain types thereof, for instance aliphatic amines, and in
particular hydroxyalkyl-substituted ones, such as monoethanolamine,
di-ethanolamine, or tri-ethanolamine. Another category of suitably
employed starting material (although to a certain extent overlapping the
last-mentioned category are aliphatic polyhydroxy compounds containing 2
or 3 hydroxyl groups in the molecule, such as diphenylolpropane,
trimethylolpropane and glycerol. The invention is of particular value for
the oxyalkylation of polyhydroxy compounds having a relatively high
melting point, for instance a melting point above 80.degree. C., such as
pentaerythritol, methylglucosides, mannitol, dulcitol, glucamine and
glucosamine. Particularly preferred polyhydroxy compounds used in the
process of the invention are sucrose and sorbitol, which upon conversion
with alkylene oxide yield polyether polyols which are in great demand as
starting materials for the production of rigid polyurethane foams. If
desired, mixtures of organic compounds containing 2 or more active
hydrogen atoms in the molecule may be used as starting material in the
present process, as well as mixtures of one or more of such compounds with
other organic compounds.
Alkylene oxides, which are particularly suitable for use in the process of
the invention are, for instance, ethylene oxide, propylene oxide, butylene
oxide, and/or mixtures thereof. If desired, the alkylene oxide may be
added to the reaction mixture in more than one step, whilst different
oxides may be used in each step. For example, propylene oxide may be used
as the initial reactant, whilst at a later stage ethylene oxide is
incorporated into the reaction mixture, or vice versa.
The amount of the amine catalyst used in the present invention is suitably
within the range of about 0.2 to about 10% by weight of the active
hydrogen atoms-containing compound and preferably within the range of
about 0.5 to about 5% by weight thereof.
The general conditions for the reaction between alkylene oxide and active
hydrogen atom-containing compound according to the present invention may
be selected in analogy with those described in the literature for the
alkoxylation of such compounds. Temperatures between about 50.degree. and
about 160.degree. C., preferably between about 80.degree. and about
120.degree. C., are suitably employed, whilst pressures up to about 6 bar
or more may be used. The amount of alkylene oxide to be used in the
reaction according to the present process is usually selected so as to be
sufficient for the formation of a polyether, or a mixture of polyethers,
having the desired molecular weight and functionality.
The presence of substantial amounts of water is usually avoided for the
reason as indicated hereinbefore, although a small proportion, usually no
more than about 0.2-1 mol per mol of active hydrogen atoms-containing
organic compound, of water may in some cases by advantageous to achieve a
further reduction of the induction period of the reaction, if any.
After the reaction has reached the desired stage the polyether polyol or
polyether polyols formed may be collected without further treatment or, if
desired, neutralized and/or purified, e.g. by treatment with active carbon
or natural or synthetic absorbent earths, followed by filtration. It will
be clear that numerous other substances may be added before, during and/or
after the reaction.
The polyether polyols obtained in the process of the invention show a high
reactivity with respect to isocyanates and are, as already indicated
above, particularly suitable for the production of cellular or
non-cellular polyurethanes in accordance with the general methods
described in the literature, for instance by reacting the polyether
polyols, possibly admixed with other active hydrogen atoms-containing
compounds, with organic polyisocyanates, if desired in the presence of
other substances, such as foaming agents, surface-active agents,
flame-retarding agents and other additives known in the art.
The invention will be illustrated by the following Examples which are
provided for illustration purposes only and are not to be construed as
limiting the invention.
EXAMPLE I
Two experiments were carried out, in which 2160 g of sucrose were
introduced into a stainless steel pressure reactor equipped with cooling
coils. The reactor was sealed and inert material removed by vacuum.
The amine catalyst used was mixed with an equal amount by weight of cooled
propylene oxide and introduced into the reactor. Thereafter the total
amount of 5256 g of propylene oxide admixed with 584 g of ethylene oxide
was introduced into the reactor and the time recorded.
The reaction mixture was heated to 90.degree. C. by means of an oil jacket,
and this temperature was maintained by using the cooling coils. As the
reaction proceeded the pressure dropped, indicating a decrease of the
amount of alkylene oxide present. The mixture was allowed to react until
the pressure became constant, whereupon the time was again recorded and
the difference of the two time recordings was noted as being the reaction
time.
After removing unreacted alkylene oxide by vacuum distillation the
polyether polyol so obtained was an alkyoxylated sucrose ether having a
hydroxyl value of 363 and a viscosity of 6205 cSt at 38.degree. C.
Further conditions of the experiments and the results obtained thereby are
shown in columns A and B of Table I.
EXAMPLE II
In three experiments Example I was repeated with the only exception that an
amine catalyst outside the scope of the invention was used.
Comparative data and results are given in columns C-E, inclusive, of Table
I, and clearly show that considerably longer reaction times than those of
Example I are required.
TABLE I
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Column A B C D E
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Catalyst (a)
DMAC DMAC DMAE DMAE DMAE
(b)
-- DMAE -- TPA TEA
Amount of catalyst
(a)
2.5 1.2 2.0 1.2 1.2
as % w of sucrose
(b)
-- 0.8 -- 0.8 0.8
Final absolute
0.6 0.7 1.4 1.2 1.5
pressure (bar)
Reaction 360 300 414 445 508
time (min)
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DMAC = dimethylaminocyclohexane
DMAE = 2(dimethylamino)ethanol
TPA = tripropylamine
TEA = triethylamine
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