Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR PREPARING POLYETHER POLYOLS AND POLYOLS PREPARED THEREWITH
This invention relates to a process for preparing polyether
polyols. This invention particularly relates to a process for
preparing polyether polyols which are useful for preparing rigid
polyurethane foams.
Polyether polyols are useful for preparing polyurethane
products. It is known to use polyether polyols in processes for
preparing polyurethane products such as flexible foam, rigid foam,
elastomers and sealants. Of these, rigid polyurethane foams are an
important product having both insulative and structural uses.
U.S. Patent No. 4,332,936 to Nodelman discloses preparing
polyether polyols which are described as being particularly suitable
for the production of rigid polyurethane foams. Therein, it is
disclosed to mix or dissolve a multifunctional hydroxy initiator, such
as sucrose, with dimethylformamide prior to reacting the initiator
with an alkylene oxide in the presence of an amine catalyst.
U.S. Patent No. 5,030,758 and No. 5,141,968, both to Dietrich,
et al., disclose preparing polyether polyols using amine catalysts.
These references are directed to aromatic amine initiated polyols.
It would be desirable in the art of preparing polyether polyols
useful for preparing rigid polyurethane foams to prepare the polyols
using a process which could be used at high temperatures. It would
also be desirable in the art to prepare polyols using a process which
includes using a catalyst with high reactivity. Additionally, it
would be desirable in the art to prepare polyols using a process
wherein the catalyst has high reactivity at high temperatures. It
would also be desirable to prepare polyether polyols in a finished
polyether polyol diluent under conditions of imidazole catalysis which
is characterized by reaction of initiators and by non-reaction of
diluent with alkylene oxides.
In one aspect, the present invention is a process for preparing
a polyether polyol comprising admixing an initiator with an alkylene
oxide in the presence of an imidazole catalyst under high temperature
alkoxylation conditions sufficient to prepare a rigid polyether polyol
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with the proviso that when an aromatic amine initiator is used,
alkoxylation is done at a temperature greater than 125°C.
In another aspect, the present invention is a polyether polyol
prepared by a process comprising admixing an initiator with an
alkylene oxide in the presence of an imidazole catalyst under high
temperature alkoxylation conditions sufficient to prepare a rigid
polyether polyol with the proviso that when an aromatic amine
initiator is used, alkoxylation is done at a temperature greater than
125°C.
In one embodiment, the present invention is a process for
preparing rigid polyether polyols in the presence of an imidazole
catalyst. For the purposes of the present invention, an imidazole
catalyst is any compound having the general formula:
Y
N3 C
~N-X
Z.
wherein X, Y, Z, and Z' are hydrogen, methyl groups, ethyl groups, or
phenyl groups in combination to include: imidazole, N-methylimidazole,
2-methylimidazole, 4-methylimidazole, 2-ethylimidazole, 2-ethyl-4-
methylimidazole, N-phenylimidazole, 2-phenylimidazole, and 4-phenyl-
imidazole. Combinations of these compounds can be used and are also
referred to herein as imidazole catalysts.
In the process of the present invention, a polyol is prepared
by admixing an initiator with an alkylene oxide in the presence of an
imidazole catalyst. Initiators are starting materials useful for
preparing polyols characterized in that they include at least 2 active
hydrogen containing groups. For the purposes of the present
invention, an active hydrogen containing group is any group having a
hydrogen which can react with an alkylene oxide in the presence of an
imidazole catalyst. Preferably the active hydrogen containing group
is an amino or hydroxy group. The active hydrogen containing group
can be on an aliphatic or aromatic molecule. For example, the
initiators useful with the process of the present invention can be an
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aliphatic alcohol or amine having at least two active hydrogens
containing groups. In the alternative, the initiators useful with the
process of the present invention can be an aromatic diamine or
polyamine.
Initiators useful with the present invention include water,
organic dicarboxylic acids, such as succinic acid, adipic acid,
phthalic acid and terephthalic acid, aliphatic and aromatic,
unsubstituted or N-mono-, N,N- and N,N'-dialkyl-substituted diamines
having from 1 to 4 carbon atoms in the alkyl moiety, such as
unsubstituted or mono- or dialkyl-substituted ethylenediamine,
diethylenetriamine, triethylenetetramine, 1,3-propylenediamine,
1,3- and 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and
1,6-hexamethylenediamine, phenylenediamines, 2,3-, 2,4- and 2,6-
tolylenediamine and 4,4'-,2,4'- and 2,2'-diaminodiphenylmethane.
Other suitable initiator molecules useful with the present invention
include alkanolamines, for example, ethanolamine, N-methyl- and N-
ethyl-ethanolamine, dialkanolamines, for example, diethanolamine, N-
methyl- and N-ethyl-diethanolamine, and trialkanolamines, for example,
triethanolamine, and ammonia.
Preferably, initiators used with the present invention are the
polyhydric alcohols, in particular dihydric and/or trihydric alcohols,
such as ethanediol, nonyl phenol, bisphenol-A, bisphenol-F, novolak
phenolic resins, mannich base polyols derived from phenol or alkyl
phenol reacted with formaldehyde and diethanol or dipropanolamine
(mannich bases), propylene glycol, dipropylene glycol, 1,4-butanediol,
1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol,
sorbitol, alpha methyl glucoside and sucrose. For purposes of the
present invention, water is a dihydric alcohol because the reaction
product of water and an alkoxide is a dihydric alcohol. More
preferably, the initiators used with present invention are glycerine,
water, sucrose and mixtures thereof.
Initiators useful with the present invention can also be
aikoxylation products of the above listed initiator molecules. For
example,- in one preferred embodiment, an initiator useful with the
present invention is a propoxylated or ethoxylated ethylene glycol.
Another example of a similar useful initiator is a propoxylated or
ethoxylated glycerin. Still another example of a similar useful
initiator is a propoxylated or ethoxylated propylene glycol.
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Mixtures of initiators can be used with the present invention
and are also preferred. Examples~of mixed initiators include mixtures
such as: sucrose and water; glycerin and sorbitol; propylene glycol
and sucrose; and ethylene glycol and sucrose. More preferably, the
initiators used with the present invention are propoxylated mixed
initiators. Most preferably, the initiator used with the present
invention is a propoxylated mixture of sucrose and glycerin.
In the process of the present invention, a polyol is prepared by
admixing an initiator with an alkylene oxide in the presence of an
imidazole catalyst. The alkylene oxides which can be used with the
present invention include any which are useful in preparing polyether
polyols. Preferably, the alkylene oxide has from 2 to 8 carbons.
More preferably, the alkylene oxide has from 2 to 4 carbons. Most
preferably, the alkylene oxide is ethylene oxide, propylene oxide,
butylene oxide and mixtures thereof.
The polyols prepared by the process of the present invention can
be used in any application where a similar conventional polyol could
be used, but are particularly useful in preparing rigid polyurethane
foams. Polyols useful for preparing rigid polyurethane foams
typically have: an OH functionality of from 2 to 8; an OH number of
from 200 to 2000; and a molecular weight of from 62 to 2000. These
ranges represent the typical reaction products resulting from the
alkoxylation of initiators such as water which has a low OH
functionality of 2 and initiators such as sucrose which has a high OH
functionality of 8. The present invention also contemplates the
alkoxylation of initiators having intermediate functionalities as well
as mixtures of initiators.
Preferably the polyols of the present invention have an average
functionality of from 2 to 8, an OH number of from 200 to 800, and a
molecular weight of from 150 to 2,900. More preferably, the polyols
of the present invention have an average functionality of from 3 to 8,
an OH number of from 200 to 600, and a molecular weight of from 300 to
2,400. Most preferably, the polyols of the present invention have an
average functionality of from 4 to 8, an OH number of from 300 to 600,
and a molecular weight of from 350 to 1,600.
In the process of the present invention, a reaction of an
initiator and alkylene oxide is done in the presence of an imidazole
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catalyst. Preferably, from 0.0001 parts to 0.01 parts of imidazole
catalyst are used. Most preferably 0.001 parts of an imidazole
catalyst are used. Parts of catalyst are calculated by dividing the
weight of imidazole catalyst used by the total weight of product made
and diluent present in the reactor.
The reaction of an initiator and an alkylene oxide are done in
the process of the present invention under high temperature
alkoxylation conditions sufficient to prepare a polyether polyol. The
art of preparing conventional polyether poiyols by conventional
processes is well known to those of ordinary skill in the art of
preparing polyols. The high temperature alkoxylation conditions of
the present invention substantially the same except the temperatures
at which the alkoxylation are done is at from 100°C to near but not at
the decomposition or discoloration point of the polyol. These
conditions include a pressure of from 10 psig (69 kPa) to 100 psig
(690 kPa) and a temperature of from 100°C to 150°C. More
preferably
the high temperature alkoxylation conditions are a pressure of from 30
psig (206 kPa) to 80 psig (551 kPa). Even more preferably, the
temperature of the high temperature alkoxylation conditions is from
120°C to 150°C. Most preferably, the temperature of the high
temperature alkoxylation conditions is from 130°C to 145°C. When
the
process of the present invention is used to prepare polyols from
formulations including aromatic amine initiators, the alkoxylation is
done at a temperature of greater than 125°C.
An advantage of the imidazole catalysts used with the process of
the present invention when they are compared with other conventional
amine catalysts such as triethylamine, trimethylamine and
methyldiethylamine is that the imidazole catalysts have both a high
level of reactivity at conventional alkoxylation temperatures and the
reactivity of imidazole catalysts increases with temperature up to the
decomposition point for most polyols and initiators. For example,
trialkylamine catalysts begin to lose catalytic activity as
alkoxylation temperature is increased starting at about 110°C while
the imidazole catalysts continue to increase in catalytic activity
until the reaction temperature reaches at least 150°C. The ability to
use the process of the present invention at elevated temperatures
results in increased reaction rates and decreased residence time and
energy consumption for production of polyether polyols.
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Another advantage of the amine catalysts generally and the
imidazole catalysts in particular is that processes utilizing such
catalysts can be employed to alkoxylate initiators in polyol diluents
without also alkoxylating the diluents. Suitable diluents include any
polyether or polyester polyol which was prepared such that at least
two and preferably three alkylene oxides were added to each active
hydrogen of the initiator. Since the amine catalysts only catalyze
the addition of from one to three alkylene oxides per active hydrogen
group on an initiator, polyols wherein more than 2 alkylene oxide
groups have been added can be used as diluents without the polyol
reacting further with alkylene oxides. This can be an advantage,
particularly when alkoxylating solid initiators such as sucrose and
sorbitol. This is particularly an advantage when it is desired to
prepare a substantially homogenous polyol prepared from solid
initiators because a polyol which is substantially similar to the
desired product polyol can be used as a solvent for the initiator.
Polyols are often prepared by both continuos and batch
processes. In a batch process, a polyol is made by charging the
components of a formulation in one or more steps, but essentially all
of any given component is charged at one time. For example, all of
the initiator for the polyol is placed into a reactor at the start of
the reaction. That "batch" of raw materials is then taken through the
steps of making the polyol to produce a single "batch" of polyols. In
contrast, in a continuos process, the raw materials are fed into a
production unit continuously, so that the polyol is at different
stages of production at different points in the production unit. The
imidazole catalysts of the present invention can be used with either
batch or continuos processes.
The polyols prepared by the process of the present invention can
be used in the same way as are similar conventional polyols prepared
using conventional processes. For example, the polyols of the present
invention can be used as prepared or admixed with additives. Where
desirable, the polyols of the present invention can be admixed with
other types of polyols.
The following examples are provided to illustrate the present
invention. The examples are not intended to limit the scope of the
present invention and should not be so interpreted. Amounts are in
weight parts or weight percentages unless otherwise indicated.
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EXAMPLES
Example 1: A mixture of 3008 of glycerin and 0.5g of 2-ethyl-4-
methylimidazole was heated to 100°C in a 1 liter pressure vessel
equipped with a stirrer. After the vessel reaches thermal
equilibrium, 11.96g of propylene oxide were injected into the vessel.
The initial concentration of propylene oxide was measured by gas
chromatography to be 1.8 percent. After 195 minutes, the
concentration of propylene oxide was 0.04 percent.
Example 2: A mixture of 10.6 pounds (9.8Kg) of VORANOL 490* and 7.1
pounds (3.2Kg) of VORANOL 370** was added to a 20 gallon (75.7L)
pressure vessel. To this were added 0.1 pounds 45.4g) of 2-ethyl-9-
methylimidazole and 16 pounds (7.3Kg) of sucrose. The admixture was
heated and stirred under a nitrogen pad until it reaches thermal
equilibrium at 120°C. Next, 93 (19.5Kg) pounds of propylene oxide
were added at a rate of 0.11 pounds (49.9g) per minute and then the
admixture was maintained at 120°C for five hours. The final product
was analyzed for physical properties and has a viscosity of 78.7Cs at
210°F (98.8°C), a hydroxyl content of 10.73 percent, and a
Gardener
color of 13. * VORANOL 490 is a trade designation of The Dow Chemical
Company. **VORANOL 370 is a trade designation of The Dow Chemical
Company.
Example 3. A series of experiments was run where 1-methoxy-2-propanol
was reacted with propylene oxide using trimethylamine and 2-ethyl-4-
methylimidazole as catalysts. The reactions were run in a 1 liter,
stirred stainless steel pressure vessel that was heated with
electrical coil heaters to maintain temperature control. The vessel
was loaded with about 300 grams of 1-methoxy-2-propanol, closed and
then purged with nitrogen to remove oxygen. For the runs using
trimethylamine as a catalyst, 300 ml of gaseous trimethylamine
catalyst was added as a gas using a 50 ml syringe. For the runs using
2-ethyl-4-methylimidazole as a catalyst, 0.52 g of 2-ethyl-4-
methylimidazole was introduced into the pressure vessel with the 1-
methoxy-2-propanol. The vessel was then stirred and heated to the
indicated reaction temperature and about 6 g of propylene oxide was
pressured into the reaction vessel from another small pressure vessel
using nitrogen gas. Samples were taken of the liquid phase using an
attached dip tube for analysis of a) amine content, by titration,* and
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b) unreacted propylene oxide (PO) content by gas chromatography**.
The amount of PO was quantified by also including about 6 grams of
methyl tertiary butyl ether as an unreactive internal standard for gas
chromatography.
The rate of the reaction was followed by plotting the unreacted PO
concentration versus time. A plot of the In (natural log) of PO
concentration (as wt $), if linear, gives a first order rate constant
for comparison of reaction rates. For comparison between runs that
may have a different amine catalyst concentration, a second order rate
constant may be derived by division of this slope by the molar base
concentration. The Table below lists the rate data for these
reactions. Reaction rates for propoxylation vary with amine catalyst
and polyol reactant. Low equivalent weight alcohols or polyols react
faster than materials already propoxylated. It can be seen that the
rate of propoxylation decreases with reaction temperature for
trimethylamine and increases for imidazoles.
TABLE
Reactant Temp Catalyst Basicity slope rate
2MP 80C TMA 0.034 0.00410.121
2MP 90C TMA 0.032 0.00370.116
2MP 100C TMA 0.031 0.00320.103
2MP 110C TMA 0.036 0.00180.050
2MP 100C EMI 0.035 0.00430.123
2MP 120C EMI 0.010 0.00260.260
Glycerine 100C EMI 0.026 0.012 0.462
Glycerine 100C TMA 0.029 0.011 0.379
Suc-Glyc 100C EMI 0.035 0.00490.126
Suc-Glyc 130C NMI 0.0127 0.07565.953
~2MP = 1-methoxy-2-propanol
~EMI = 2-ethyl-4-methylimidazole
~NMI = N-methyiimidazole
~Suc-glyc is a polyether polyol based on 60/40 weight ratio of
sucrose/glycerine propoxylated to an OH number of 370
~basicity as milliequivalents/gram by titration
~siope g slope of plot In PO vs. time (minutes)
~rate = slope divided by base concentration as grams/equiv.-minute.
*The titration analysis of the catalyst was done by adding about 5 g
of sample to 50 ml methanol. This was titrated using a Mettler DL40
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autotitrator (Mettler DL40 is a trade designation of the Mettler
Company). The total basicity was taken as the sum of all endpoints in
the titration.
**The gas chromatography analysis was done using a 10 meter, 50 micron
internal diameter glass capillary column coated with a
polydimethylsiloxane stationary phase. The reaction vessel was also
charged with 6 grams of methyl tertiary butyl ether (MTBE) which is
used as an internal standard. By comparing peak areas of MTBE and
propylene oxide and knowing their relative response factors, it is
possible to calculate the concentration of unreacted propylene oxide
in the liquid phase.
Example 4. A polyol based on a 60/40, by weight, mixture of
sucrose/glycerine, propoxylated to an equivalent hydroxyl weight of
about 150 (specification range 10.8-11.6$ OH, viscosity 0.89 - 1.17
poise (0.089 - 0.117 Ns/m2) wass used as a reaction solvent. 468
grams of this polyol was admixed with 419 grams of sucrose and 1.82
grams of N-methylimidazole. This admixture was stirred in a 4 liter
pressure vessel which was heated to 130°C and maintained at
130~0.5°C
for the course of the reaction. 1113 grams of propylene oxide was
added using a positive displacement pump over 4.1 hours. The amount
of residual propylene oxide was measured by monitoring the reactor
pressure over the final 2 hr period. A rate constant was obtained by
plotting the natural log of pressure against time until the pressure
remains constant. The slope of this plot gives a linear first order
plot with a slope of -0.0756 per minute. Division of this value by
the catalyst concentration at the end of reaction (measured as 1040
ppm or O.OI27 milliequivalents/g)gives a second order rate constant of
5.95 g/meq.-min. The resulting product had 12.16 OH and a viscosity
of 1.05 poise (0.105 Ns/mZ) at 210°F (98.9°C).
_g_
