U.S. patent application number 13/391057 was filed with the patent office on 2012-06-14 for process for preparing polyester alcohols.
This patent application is currently assigned to BASF SE. Invention is credited to Marine Boudou, Lionel Gehringer, Elke Guetlich-Hauk, Ulrike Mahn, Ulrich Mueller, Veronika Wloka.
Application Number | 20120149862 13/391057 |
Document ID | / |
Family ID | 42711161 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120149862 |
Kind Code |
A1 |
Gehringer; Lionel ; et
al. |
June 14, 2012 |
PROCESS FOR PREPARING POLYESTER ALCOHOLS
Abstract
The invention relates to a process for preparing polyester
alcohols by catalytic reaction of at least one at least
polyfunctional carboxylic acid with at least one polyfunctional
alcohol and/or by catalytic ring-opening polymerization of cyclic
esters in the presence of catalysts, wherein a zeolite is used as
catalyst.
Inventors: |
Gehringer; Lionel;
(Schaffhouse-pres-Seltz, FR) ; Wloka; Veronika;
(Mannheim, DE) ; Mueller; Ulrich; (Neustadt,
DE) ; Boudou; Marine; (Mannheim, DE) ; Mahn;
Ulrike; (Mannheim, DE) ; Guetlich-Hauk; Elke;
(Lambsheim, DE) |
Assignee: |
BASF SE
Ludwigshafen
DE
|
Family ID: |
42711161 |
Appl. No.: |
13/391057 |
Filed: |
August 16, 2010 |
PCT Filed: |
August 16, 2010 |
PCT NO: |
PCT/EP2010/061895 |
371 Date: |
February 17, 2012 |
Current U.S.
Class: |
528/81 ;
560/198 |
Current CPC
Class: |
C08G 63/12 20130101;
C08G 18/4238 20130101; C08G 63/87 20130101; B01J 29/89 20130101;
C08G 63/823 20130101; C07C 67/08 20130101; C08G 63/06 20130101 |
Class at
Publication: |
528/81 ;
560/198 |
International
Class: |
C08G 18/32 20060101
C08G018/32; C07C 69/34 20060101 C07C069/34 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2009 |
EP |
09168315.1 |
Claims
1. A process for preparing polyester alcohols, comprising (i)
catalytically reacting at least one polyfunctional carboxylic acid
with at least one polyfunctional alcohol, (ii) catalytic
ring-opening polymerizing of a cyclic ester, or both (i) and (ii),
in the presence of a titanium zeolite catalyst, to obtain a
polyester alcohol.
2. The process according to claim 1, wherein the titanium zeolite
catalyst has a structure selected from the group consisting of a
MFI structure, a MOR structure, a BEA structure, a MWW structure, a
RRO structure, a LEV structure, a FER structure, a MEL structure,
and a MFI/MEL mixed structure.
3. The process according to claim 1, wherein the titanium zeolite
catalyst has a structure selected from the group consisting of a
MFI structure, a MEL structure and a MFI/MEL mixed structure.
4. The process according to claim 1, wherein the reacting, the
polymerizing, or both, are performed in their entirety in the
presence of the titanium zeolite catalyst.
5. The process according to claim 1, wherein the titanium zeolite
catalyst is in a form of a fixed bed.
6. The process according to claim 1, wherein the titanium zeolite
catalyst is in a form of a powder.
7. The process according to claim 1, comprising: a) first reacting
at least one dicarboxylic acid with at least one polyhydroxyl
compound to obtain at least one base polyester alcohol, b) second
reacting the at least one base polyester alcohol, or optionally a
mixture of the at least one base polyester alcohol and a further
polyhydroxyl compound, in the presence of a titanium zeolite
catalyst.
8. The process according to claim 7, wherein the first reacting is
performed in the presence of an esterification catalyst.
9. The process according to claim 8, wherein the esterification
catalyst is selected from the group consisting of a toluenesulfonic
acid and a metal-organic compound.
10. The process according to claim 9, wherein the metal-organic
compound comprises titanium or tin.
11. The process according to claim 9, wherein the metal-organic
compound is at least one selected from the group consisting of
titanium tetrabutoxide, tin (II) octoate, dibutyltin laurate, and
tin chloride.
12. The process according to claim 7, wherein the second reacting
is performed continuously.
13. A method of producing polyurethanes, comprising reacting the
polyester alcohol of claim 1 with an isocyanate.
14. The process of claim 1, comprising (i) catalytically reacting
at least one polyfunctional carboxylic acid with at least one
polyfunctional alcohol in the presence of a titanium zeolite
catalyst.
15. The process of claim 1, comprising (ii) catalytic ring-opening
polymerizing of a cyclic ester in the presence of a titanium
zeolite catalyst.
16. The process of claim 15, wherein the cyclic ester is
.epsilon.-caprolactone.
17. The process of claim 6, wherein the titanium zeolite catalyst
is present in an amount of 0.001 to 1% by weight, based on the
weight of the polyester alcohol.
18. The process of claim 6, wherein the titanium zeolite catalyst
is present in an amount of 0.15 to 0.25% by weight, based on the
weight of the polyester alcohol.
19. The process of claim 7, wherein the at least one base polyester
alcohol and the further polyhydroxyl compound together have a water
content of less than 0.1% by weight.
20. The process of claim 7, wherein the at least one base polyester
alcohol and the further polyhydroxyl compound together have a water
content of less than 0.01% by weight.
Description
[0001] The invention relates to a process for preparing polyester
alcohols and also to the use of these polyester alcohols for
producing polyurethanes.
[0002] The preparation of polyester alcohols and the use of such
products in polyurethane chemistry have been known for a long time
and been widely described. These products are usually prepared by
polycondensation reactions of polybasic carboxylic acids and/or
carboxylic acid derivatives with polyhydric alcohols or polyols.
Mention may be made by way of example of Kunststoffhandbuch, volume
VII, Polyurethane, Carl-Hanser-Verlag, Munich 1.sup.st edition
1966, edited by Dr. R Vieweg and Dr. A. Hochtlen, and also 2.sup.nd
edition 1983 and the 3rd revised edition 1993, edited by Dr. G.
Oertel. It is also known that polyester alcohols can be prepared by
polycondensation reactions of .omega.-hydroxycarboxylic acid or by
ring-opening polymerization of cyclic esters, known as
lactones.
[0003] However, it is also possible to process polyester scrap and
in particular polyethylene terephthalate (PET) or polybutylene
terephthalate (PBT) scrap. A whole range of processes is known and
has been described for this purpose. The basis of some processes is
the conversion of the polyester into a diester of terephthalic
acid, e.g. dimethyl terephthalate. DE-A 1003714 and U.S. Pat. No.
5,051,528 describe such transesterifications using methanol and
transesterification catalysts.
[0004] The use of these polyester alcohols for, in particular,
producing polyurethanes, hereinafter also referred to as PURs, in
particular flexible PUR foam, rigid PUR foam and other cellular or
noncellular PUR materials requires a specific choice of starting
materials and the polycondensation technology to be carried out. To
produce polyurethane, it is particularly important that the
polyester alcohols used have a low acid number (see Ullmann's
Encyclopedia, Electronic Release, Wiley-VCH-Verlag GmbH, Weinheim,
2000 under the keyword "polyesters", paragraph 2.3 "Quality
Specifications and Testing"). The acid number should be as small as
possible since the terminal acid groups react more slowly with
diisocyanates than do terminal hydroxyl groups. Polyester alcohols
having high acid numbers therefore lead to a lower molecular weight
buildup during the reaction of polyester alcohols with isocyanates
to form polyurethane.
[0005] A further problem with the use of polyester alcohols having
high acid numbers for the polyurethane reaction is that amide
formation with liberation of carbon dioxide occurs in the reaction
of the numerous terminal acid groups with isocyanates. The gaseous
carbon dioxide can then lead to undesirable bubble formation.
Furthermore, free carboxyl groups impair the catalysis in the
polyurethane reaction and also the stability of the resulting
polyurethanes to hydrolysis.
[0006] The known polycondensation technology for preparing
polyester alcohols is the use of polyfunctional aromatic and/or
aliphatic carboxylic acids or anhydrides thereof and bifunctional,
trifunctional and/or higher-functional alcohols, in particular
glycols, which are reacted with one another at temperatures of, in
particular, 150-280.degree. C. under atmospheric pressure and/or a
slight vacuum in the presence of catalysts with removal of the
water of reaction. The customary technology is described, for
example, in DE-A-2904184 and comprises combining the reaction
components at the beginning of the synthesis with a suitable
catalyst while simultaneously increasing the temperature and
reducing the pressure. The temperatures and the reduced pressure
are then changed further during the course of the synthesis. The
polycondensation reactions can be carried out either in the
presence or absence of a solvent.
[0007] A disadvantage is the fact that by-products are frequently
formed in the polycondensation reaction at high temperatures.
Furthermore, the high-temperature polycondensations have to take
place with exclusion of water in order to avoid the reverse
reaction. This is generally achieved by carrying out the
condensation under reduced pressure, under an inert gas atmosphere
or in the presence of an entrainer gas to effect complete removal
of the water.
[0008] A further disadvantage of these polycondensations at high
temperatures is that they proceed relatively slowly. To accelerate
the polycondensation reaction at high temperatures, esterification
catalysts are therefore frequently used. Classical esterification
catalysts employed are, for example, iron, cadmium, cobalt, lead,
zinc, zirconium, hafnium, aluminum, antimony, magnesium, titanium
and tin catalysts in the form of metals, metal oxides or metal
salts, or acids, e.g. sulfuric acid, p-toluenesulfonic acid, or
bases, e.g. potassium hydroxide or sodium methoxide.
[0009] These esterification catalysts are homogeneous and generally
remain in the polyester alcohol after completion of the reaction. A
disadvantage here is that the esterification catalysts remaining in
the polyester alcohol may interfere in the resistance of the
polyester alcohols produced to hydrolysis and also in the later
conversion of these polyester alcohols into the polyurethane.
[0010] Furthermore, the presence of the homogeneous catalysts in
the polyester alcohol can lead to discoloration.
[0011] To overcome this disadvantage, WO 2006/100231 describes a
process for preparing polyester alcohols in which enzymes are used
as catalysts. The preparation or transesterification of polyester
alcohols by means of enzymes can be carried out batchwise or
continuously. In the continuous process, the catalyst is preferably
present in immobilized form, with the reaction preferably being
carried out in a flow reactor.
[0012] However, the high-temperature polycondensations and the
enzymatically catalyzed polycondensations for preparing polyester
alcohols both have the disadvantage that the preparation of
polyester alcohols is carried out by means of condensation
reactions in plants for which a complicated periphery is necessary.
The classical high-temperature polycondensation and also the
enzymatic polycondensation require facilities on the reactor for
the metered addition of liquids and/or solids. Water has to be
removed from the reaction mixture under reduced pressure, by
introduction of an inert gas or by means of an entrainer
distillation. In addition, the water has to be separated off from
the diols by distillation, since these have to remain in the
reaction mixture as reaction partners for the acid component. The
separation of water and diols is generally effected by means of a
distillation column. Apparatuses for generating reduced pressure,
e.g. pumps, for separating diols and water, e.g. distillation
columns, or for introducing an inert gas stream incur high capital
costs. In addition, particularly in the case of the
high-temperature condensation, facilities for producing
temperatures inside the reactor of 160-270.degree. C. are
necessary.
[0013] Disadvantages of enzymatic catalysts are their high price
and the adverse effect on the odor and the color of the resulting
polyester alcohols. Furthermore, detachment of the enzymes from
their support can occur.
[0014] DE 10 2008 004 343 describes a process for preparing
polyester alcohols, in which multimetal cyanide catalysts, also
referred to as DMC catalysts, are used as heterogeneous catalysts.
Such catalysts are known and are frequently used as catalysts for
preparing polyether alcohols by addition of alkylene oxides onto
compounds having reactive hydrogen atoms. In the preparation of
polyester alcohols, it has been found that DMC catalysts are not
very suitable since their catalytic activity is unsatisfactory and
no homogeneous products are obtained.
[0015] EP 1679322 describes a process for preparing polyesters by
reacting polyfunctional alcohols with polyfunctional carboxylic
acids. Metal silicates are used as catalysts. The products
described in this document are not polyester alcohols but rather
thermoplastic products. The use of the catalysts mentioned is said
to make the preparation of products having a very high molecular
weight easier. Furthermore, the behavior in the thermoplastic
processing of the products and the mechanical properties of the end
products are said to be improved; in particular, the tendency for
the products to be thermally degraded during processing is said to
be reduced.
[0016] It was an object of the present invention to develop a
process for the catalytic preparation of polyester alcohols using
heterogeneous catalysts, which is simple and inexpensive. The
process should lead to colorless and catalyst-free products which
can be used without complicated work-up for producing
polyurethanes. Furthermore, it should also be possible to use the
catalyst as a fixed bed.
[0017] The object has surprisingly been able to be achieved by
using a zeolite as catalyst for the preparation of the polyester
alcohols.
[0018] The invention accordingly provides a process for preparing
polyester alcohols by catalytic reaction of at least one
polyfunctional carboxylic acid with at least one polyfunctional
alcohol and/or by catalytic ring-opening polymerization of cyclic
esters, preferably lactones, in particular .epsilon.-caprolactone,
in the presence of catalysts, wherein a zeolite is used as
catalyst.
[0019] In an embodiment of the process of the invention, the entire
reaction of the monomers to form the polyester alcohol is carried
out using zeolites.
[0020] However, it is also possible to carry out only part of the
reaction using zeolites. The remaining part of the reaction can be
carried out in the absence of catalysts or using other
esterification catalysts.
[0021] Zeolites are, as is known, crystalline aluminosilicates
having ordered channel and cage structures whose pore openings are
in the micropore range. According to IUPAC, micropores are pores
whose diameters are smaller than 2 nm. The framework of such
zeolites is made up of SiO.sub.4 and AlO.sub.4 tetrahedra which are
joined via common oxygen bridges. In an analogous way, there are
aluminophosphates made up of Pa.sub.s and AlO.sub.4 tetrahedra,
known as AIPOs, MeAPOs, MeAPSOs having a structure analogous to
zeolites, and likewise metal imidazolates, known as ZIFs, having a
structure analogous to zeolites. These materials which are
analogous to zeolites are all included within the scope of the
present invention. An overview of known structures may be found,
for example, in Ch. Baerlocher, W. M. Meier, D. H. Olson, "Atlas of
Zeolite Framework Types", 5th ed. Elsevier, 2001.
[0022] Zeolites which do not comprise any aluminum and in which
titanium as Ti(IV) partly replaces the Si(IV) in the silicate
lattice are also known. These titanium zeolites, in particular
those having a crystal structure of the MFI type, and possible ways
of preparing them are described, for example, in EP-A 311 983 or
EP-A 405 978. Apart from silicon and titanium, such materials can
also comprise additional elements such as aluminum, zirconium,
germanium, tin, iron, cobalt, nickel, gallium, boron or small
amounts of fluorine.
[0023] As zeolites, preference is given to using ones comprising
titanium, hereinafter referred to as titanium zeolites. The term
titanium zeolite thus refers to a material which comprises small
amounts of titanium in addition to silicon oxide and incorporated
in a zeolite structure.
[0024] Preferred titanium zeolites are those having pentasil units
in the structure, e.g. MFI, MEL, BEA, MOR, MWW structure, in
particular the types which can be assigned
X-ray-crystallographically to the MFI, MOR, BEA, MWW, RRO, LEV, FER
structure, in particular to the MFI structure, MEL structure or
MFI/MEL mixed structure. Zeolites of this type are described, for
example, in "Atlas of Zeolite Framework Types", Ch. Baerlocher, W.
M. Meier, D. H. Olson, 5th ed. Elsevier, 2001.
[0025] The titanium zeolites mentioned are usually prepared by
reacting an aqueous mixture of an SiO.sub.2 source, a titanium
source such as titanium dioxide or titanium alkoxide and a
nitrogen-comprising organic template for forming this structure,
e.g. tetrapropylammonium hydroxide, optionally with addition of
alkali metal compounds, in a pressure vessel at elevated
temperature for a period ranging from a few hours to some days,
forming the crystalline product. This is separated off, e.g.
filtered off, washed, dried and calcined at elevated temperature to
remove the organic nitrogen base. In the catalysts according to the
invention for preparing polyester alcohols, the molar ratio of
titanium to the sum of silicon plus titanium is generally in the
range from 0.01:1 to 0.1:1. In the powder obtained in this way, the
titanium is at least partly present in alternate four-fold,
five-fold or six-fold coordination within the zeolite framework. It
is known that titanium zeolites having the MFI structure can be
identified by a particular X-ray diffraction pattern and also by a
framework vibration band in the infrared (IR) region at about 960
cm.sup.-1 and thus differ from alkali metal titanates or
crystalline and amorphous TiO.sub.2 phases.
[0026] The titanium zeolites prepared in this way can be used in
the form of powders, spray-dried agglomerates or shaped bodies such
as extrudates, crushed material, rings, hollow cylinders, spheres
or pellets. As shaping process, it is in principle possible to use
all methods for appropriate shaping as are generally customary for
catalysts. Preference is given to processes in which shaping is
effected by extrusion in customary extruders, for example to form
extrudates having a diameter of usually from 1 to 10 mm, in
particular from 2 to 5 mm. If binders and/or auxiliaries are
required, a mixing or kneading process advantageously precedes
extrusion. If appropriate, a calcination step is carried out after
extrusion. The extrudates obtained are optionally comminuted,
preferably to form granules or crushed material having a particle
diameter of from 0.1 to 5 mm, in particular from 0.5 to 2 mm.
[0027] Suitable binders are in principle all compounds used for
such purposes; preference is given to compounds, in particular
oxides, of silicon, aluminum, boron, phosphorus, zirconium and/or
titanium or else clays, e.g. montmorillonites, kaolins or
bentonites or other zeolites. Silicon dioxide, which can be
introduced as silica sol or in the form of tetraalkoxysilanes in
the shaping step, is of particular interest as binder. As
auxiliaries for the consolidating shaping processes, mention may be
made by way of example of extrusion aids; a customary extrusion aid
is methylcellulose. Such agents are generally completely burnt in a
subsequent calcination step.
[0028] The catalysts processed to form shaped bodies comprise up to
50% by weight of binder, based on the total mass of the catalyst,
with preferred binder contents being from 0.1 to 30% by weight,
particularly preferably from 2 to 25% by weight.
[0029] The catalysts are generally activated by means of elevated
temperature, preferably from 100 to 800.degree. C., particularly
preferably from 200 to 600.degree. C., and other conditions known
to those skilled in the art before use. In many cases, the
catalysts can be regenerated by reaction with air, lean air, i.e. a
mixture of nitrogen and oxygen having a proportion of oxygen which
is less than that of air, or by extraction or rinsing with organic
solvents or water.
[0030] When used as powder, the catalysts are preferably used in an
amount of from 0.001 to 1% by weight, based on the weight of the
polyester alcohol. The amount of catalyst is preferably in the
range from 0.15 to 0.25% by weight, based on the weight of the
polyester alcohol.
[0031] After the reaction, the catalyst is removed from the
product. This is preferably carried out by means of filtration.
[0032] After purification, the polyester alcohol usually comprises
less than 1 ppm of titanium and less than 100 ppm of silicon,
preferably less than 0.5 ppm of titanium and 50 ppm of silicon,
particularly preferably less than 0.2 ppm of titanium and 20 ppm of
silicon, and in particular less than 0.1 ppm of titanium and 10 ppm
of silicon.
[0033] The catalyst which has separated off can be reused for the
process. Here, it can be freed of adhering polyester alcohol before
reuse.
[0034] In principle, the catalyst could also be left in the
polyester alcohol but this is not preferred since it can lead to
problems in the further processing to form polyurethanes, in
particular thermoplastic polyurethanes (TPUs).
[0035] The conversion of the starting materials into the polyester
alcohol in the presence of the catalysts described is carried out
under the conditions customary for this purpose.
[0036] The preparation of the polyester alcohols is, as described,
preferably carried out by reaction of polyfunctional carboxylic
acids with polyfunctional alcohols.
[0037] The preparation of the polyester alcohols can be carried out
in one or two stages. In the single-stage process, the
esterification of the carboxylic acids and alcohols is carried out
during the entire reaction and the finished polyester alcohol is
then taken off. In the two-stage reaction, a polyester alcohol is
prepared in a first stage a) and this is reacted with further
carboxylic acids and alcohols or with a polyester alcohol in a
second stage b).
[0038] The entire reaction or part of the reaction can be carried
out using zeolite catalysts. In the two-stage reaction, one stage
can be carried out using a zeolite catalyst and the other can be
carried out using another catalyst. If this procedure is employed,
the second stage is preferably carried out using a zeolite
catalyst.
[0039] The polyester alcohols prepared by the process of the
invention have, depending on the desired application, a hydroxyl
number in the range from 20 to 400 mg KOH/g. The hydroxyl number of
polyester alcohols used for producing flexible polyurethane foams
and cellular or thermoplastic polyurethane elastomers is preferably
in the range from 20 to 250 mg KOH/g. Polyester alcohols for use in
rigid polyurethane foams preferably have a hydroxyl number above
100 mg KOH/g, in particular in the range from 100 to 400 mg
KOH/g.
[0040] As polyfunctional carboxylic acids, use is usually made of
dicarboxylic acids such as aliphatic dicarboxylic acids, preferably
succinic acid, glutaric acid, adipic acid, suberic acid, azelaic
acid, sebacic acid, decanedicarboxylic acid, maleic acid fumaric
acid, or other aliphatic dicarboxylic acids, or aromatic
dicarboxylic acids such as phthalic acid, isophthalic acid or
terephthalic acid. The dicarboxylic acids can be used either
individually or in admixture with one another. In place of or in
admixture with the dicarboxylic acids, it is also possible to use
the corresponding dicarboxylic acid derivatives, e.g. dicarboxylic
esters of alcohols having from 1 to 4 carbon atoms or anhydrides
thereof, for example phthalic anhydride.
[0041] Suitable polyhydroxyl compounds are all at least dihydric
alcohols, but preferably diol components such as ethylene glycol,
diethylene glycol, 1,3-propanediol, 1,2-propanediol, dipropylene
glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,
1,10-decanediol, neopentyl glycol, 2-methyl-1,3-propanediol,
3-methyl-1,5-pentanediol. To increase the functionality of the
polyester alcohols, trifunctional or higher-functional alcohols can
also be used. Examples of such alcohols are glycerol,
trimethylolpropane and pentaerythritol. It is also possible to use
oligomeric or polymeric products having at least two hydroxyl
groups. Examples of such products are polytetrahydrofuran,
polylactones, polyglycerol, polyetherols, polyesterol or
.alpha.-.omega.-dihydroxypolybutadiene.
[0042] To prepare the polyester alcohols, the organic
polycarboxylic acids and/or derivatives and polyhydric alcohols are
preferably polycondensed in a molar ratio of 1:1-2.1, preferably
1:1.05-1.9.
[0043] The single-stage preparation of the polyester alcohols or
reaction step a) of the two-stage preparation of the polyester
alcohols is, as described, carried out by reaction of the
polyfunctional carboxylic acids with the polyfunctional alcohols
with removal of water. Process step a) is preferably carried out
using a stirred tank reactor provided with agitator and
distillation column. This apparatus is generally a closed system
and can generally be evacuated by means of a vacuum pump. The
starting materials are heated while stirring and preferably with
exclusion of air (e.g. in a nitrogen atmosphere or under reduced
pressure). The water formed in the polycondensation is preferably
distilled off at a low pressure or a continuously decreasing
pressure (see Batchwise Vacuum-Melt-Verfahren, Houben-Weyl 14/2,
2).
[0044] The reaction temperature is preferably in the range from 160
to 280.degree. C. The pressure is gradually reduced during the
course of the reaction, and the final pressure is preferably below
200 mbar. At this pressure, the reaction is continued to the
desired degree of conversion.
[0045] In a single-stage process, the entire reaction can
preferably be carried out using zeolite catalysts. It is also
possible to use different catalysts during the course of the
reaction, but this embodiment is not preferred. The polyester
alcohols prepared by the single-stage process usually have the
above-described hydroxyl numbers and acid numbers of less than 2 mg
KOH/g.
[0046] In the two-stage preparation of the polyester alcohols, the
reaction products of step a) preferably have a number average
molecular weight in the range from 200 g/mol to 10 000 g/mol,
particularly preferably in the range 500-5000 g/mol.
[0047] The acid numbers of the base polyester alcohols prepared in
step a) are preferably less than 10 g KOH/kg, more preferably less
than 5 g KOH/kg, in particular less than 2 g KOH/kg. The acid
number serves as a measure of the content of free organic acids in
the polyesterol. The acid number is determined by the number of mg
of KOH (or g of KOH) consumed in the neutralization of 1 g (or 1
kg) of the sample.
[0048] The functionality of the base polyester alcohols prepared in
step a) is, depending on the raw materials used, preferably in the
range from .gtoreq.1.9 to 4.0, more preferably in the range from
2.0 to 3.0.
[0049] As described, step a) can be carried out using zeolite
catalysts. However, it is also possible to work without catalysts
or preferably using customary esterification catalysts. Examples of
customary esterification catalysts are preferably metal-organic
compounds such as titanium tetrabutoxide, tin dioctoate or
dibutyltin dilaurate, an acid such as sulfuric acid,
p-toluenesulfonic acid or a base such as potassium hydroxide or
sodium methoxide. These esterification catalysts are generally
homogeneous and generally remain in the polyester alcohol after
completion of the reaction. The reaction is carried out at
160-280.degree. C., preferably 200-260.degree. C.
[0050] The second process step (step b)) of the two-stage process
is preferably carried out exclusively by means of zeolite
catalysts. The reaction carried out in step b) is either [0051] 1.
transesterification catalyzed by means of zeolite catalysts without
additional glycolysis, [0052] 2. glycolysis catalyzed by means of
zeolite catalysts without additional transesterification or [0053]
3. a mixed reaction comprising transesterification catalyzed by
means of zeolite catalysts and glycolysis or alcoholysis catalyzed
by means of zeolite catalysts.
[0054] In the transesterification catalyzed by means of zeolite
catalysts, (see No. 1), two or more base polyester alcohols from
step a) are admixed with a sufficient amount of zeolite catalysts,
but in this case no additional polyfunctional polyhydroxy compound
(diols, glycols) is added. This leads to formation of a new
polyesterol which in the ideal case is a random copolymer of the
monomers of all base polyester alcohols used.
[0055] In the glycolysis catalyzed by means of zeolite catalysts,
only one base polyester alcohol from step a) is reacted with one or
more polyhydroxy compounds, preferably diols or polyols, and a
suitable amount of zeolite catalyst. In this case, the mean
molecular weight of the base polyester alcohol is generally reduced
by glycolysis or by alcoholysis of part of the ester bonds.
[0056] As an alternative, a mixed reaction comprising a
transesterification catalyzed by means of zeolite catalysts and a
glycolysis or alcoholysis catalyzed by means of zeolite catalysts
can also take place in process step b). Here, a mixture of at least
two base polyester alcohols from step a) and at least one
polyfunctional polyhydroxy compound, preferably diols or polyols,
with a suitable amount of the zeolite catalyst is reacted. The
change in the mean molecular weight or in the other materials
parameters of the base polyester alcohols, e.g. viscosity, acid
number or melting point, in this variant of process step b) depends
on the components used in the particular case, in particular on the
type and amount of the base polyester alcohols used and on the type
and amount of the polyhydroxy compounds used.
[0057] The properties of the end product from step b) likewise
depend on whether the transesterification or glycolysis according
to step b) has proceeded to completion. The completeness of the
transesterification or glycolysis according to step b) in turn
depends on the reaction time, with long reaction times resulting in
complete transesterification or glycolysis. The reaction times for
the transesterification step b) are preferably chosen so that the
polyester alcohols finally obtained have very similar properties to
polyester alcohols prepared by the classical single-stage
high-temperature polycondensation process. The reaction time for
the transesterification or glycolysis according to step b) can be
from 1 to 36 hours, preferably from 2 to 24 hours.
[0058] The reaction in process step b) can, like that in process
step a), be carried out in the presence of a solvent or in the
absence of a solvent (reaction "in bulk").
[0059] If the reaction in process step b) is carried out in the
presence of a solvent, it is possible to use all known suitable
solvents, in particular the solvents toluene, dioxane, hexane,
tetrahydrofuran, cyclohexane, xylene, dimethyl sulfoxide,
dimethylformamide, N-methylpyrrolidone, chloroform. The choice of
solvent depends in the particular case on the starting materials
used, (the base polyester alcohols and the polyhydroxy compounds)
and in particular on their solubility properties. However, the
reaction of process step b) in the presence of a solvent has the
disadvantage that it comprises additional process substeps, namely
dissolution of the at least one base polyester alcohol in the
solvent and removal of the solvent after the reaction. Furthermore,
the dissolution of the at least one base polyester alcohol in the
solvent can, depending on the hydrophobicity of the base polyester
alcohol, be problematical and may decrease the yield.
[0060] In a further preferred embodiment of the process, process
step b) is preferably carried out using base polyester alcohols
and, if appropriate, additional polyhydroxyl compounds which
together have a water content of less than 0.1% by weight,
preferably less than 0.05% by weight, more preferably less than
0.03% by weight, in particular less than 0.01% by weight. At higher
water contents during process step b), hydrolysis also takes place
in addition to the transesterification, so that the acid number of
the polyester alcohol would increase in an undesirable way during
step b). Carrying out step b) of the process of the invention at a
water content of less than 0.1% by weight, preferably less than
0.05% by weight, more preferably less than 0.03% by weight, in
particular less than 0.01% by weight, thus leads to the formation
of specialty polyester alcohols having a low acid number as end
products. Polyester alcohols having a low acid number are generally
more stable to hydrolysis than polyester alcohols having a high
acid number, since free acid groups catalyze the reverse reaction,
i.e. hydrolysis.
[0061] Preparation of polyester alcohols having water contents of
more than 0.1% by weight leads to polyester alcohols having an acid
number of greater than 10 mg KOH/g. However, polyester alcohols
having such high acid numbers (greater than 10 mg KOH/g) are
unsuitable or have only limited suitability for most industrial
applications, in particular for use in the production of polyester
alcohols.
[0062] Polyester alcohols also take up, depending on atmospheric
humidity and temperature, at least 0.01% by weight, but in general
at least 0.02% by weight, in some cases even more than 0.05% by
weight, of water. Depending on the degree of conversion and the
molecular weight of the base polyester alcohols used, this water
concentration is higher than the equilibrium water concentration.
If the polyester alcohol is not dried before process step b),
hydrolysis of the polyester alcohol inevitably occurs.
[0063] The water content of the base polyester alcohols used in
step b) is therefore preferably reduced by drying before the
transesterification in process step b). Any polyfunctional
polyhydroxyl compound to be used, for example the diol, is
preferably also dried before the transesterification reaction in
order to attain the abovementioned low water content in the
transesterification. Drying can be carried out by means of
customary drying methods known from the prior art, for example by
drying over molecular sieves or by means of falling film
evaporators. As an alternative, base polyester alcohols having low
water contents, preferably less than 0.1% by weight, more
preferably less than 0.05% by weight, more preferably less than
0.03% by weight, in particular less than 0.01% by weight, can also
be obtained by carrying out the reaction according to process step
a) and any temporary storage of the at least one base polyester
alcohol entirely under inert conditions, for example in an inert
gas atmosphere, preferably in a nitrogen atmosphere. In this case,
the base polyester alcohols have, from the beginning, no
opportunity of taking up relatively large amounts of water from the
environment. A separate drying step could then become
superfluous.
[0064] In a further preferred embodiment of the process, the at
least one base polyester alcohol from process step a) is therefore
temporarily stored, preferably in an inert gas atmosphere, so as to
keep the water content low before the reaction in process step b).
A mixture of two or more base polyester alcohols can then be put
together from the temporarily stored base polyester alcohols in
suitable ratios in order to obtain a particular specialty polyester
alcohol having very specific physical properties and a specific
structure after the transesterification and after any additional
glycolysis by means of polyhydroxy compounds.
[0065] The polyester alcohols prepared by the two-stage process of
the invention generally have relatively low acid numbers, viz.
preferably acid numbers of less than 3 mg of KOH per gram of
polyesterol, more preferably less than 2 mg of KOH per gram of
polyester alcohol, in particular less than 1 mg of KOH per gram of
polyester alcohol.
[0066] These low acid numbers are ensured by, in particular,
process step b) preferably being carried out at a water content of
less than 0.1% by weight, more preferably less than 0.05% by
weight, more preferably less than 0.03% by weight, in particular
less than 0.01% by weight.
[0067] As described above, the polyester alcohols can also be
prepared by ring-opening polymerization of cyclic esters,
preferably lactones, in particular .epsilon.-caprolactone. These
cyclic esters can be used either alone or in admixture with the
above-described starting materials.
[0068] To carry out process step a), it is possible to use all
reactors whose use is known for classical high-temperature
polycondensations (see Ullmann Encyclopedia (Electronic Release),
chapter: Polyesters, paragraph: Polyesters as Intermediates for
Polyurethane).
[0069] Process step b) is usually carried out in a temperature
range of 50-160.degree. C., preferably under atmospheric pressure.
The reaction is preferably carried out in an inert atmosphere with
exclusion of moisture, for example by passing nitrogen over the
reaction mixture. Process step b) is preferably carried out in a
heated stirred tank or fixed-bed reactor. The process of the
invention can be carried out batchwise, semicontinuously or
continuously.
[0070] The polyester alcohols prepared by the process of the
invention can preferably be processed by reaction with isocyanates
to form polyurethanes, e.g. rigid polyurethane foams, flexible
polyurethane foams, integral foams, for example shoe soles. A
particularly preferred field of use is the production of
thermoplastic polyurethane elastomers, also referred to as
TPUs.
[0071] Processes for producing the polyurethanes are likewise
generally known. For example, thermoplastic polyurethanes can be
produced by reacting diisocyanates with compounds having at least
two hydrogen atoms which are reactive toward isocyanate groups,
preferably bifunctional alcohols and, if appropriate, chain
extenders having a molecular weight of from 50 to 499, in the
presence or absence of catalysts and/or customary auxiliaries.
[0072] As diisocyanates, it is possible to use customary aromatic,
aliphatic, cycloaliphatic and/or araliphatic isocyanates,
preferably diisocyanates, for example diphenylmethane 2,2'-, 2,4'-
and/or 4,4'-diisocyanate (MDI), naphthylene 1,5-diisocyanate (NDI),
tolylene 2,4- and/or 2,6-diisocyanate (TDI), diphenylmethane
diisocyanate, 3,3'-dimethylbiphenyl diisocyanate,
1,2-diphenylethane diisocyanate and/or phenylene diisocyanate,
trimethylene, tetramethylene, pentamethylene, hexamethylene,
heptamethylene and/or octamethylene diisocyanate,
2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene
1,4-diisocyanate, pentamethylene 1,5-diisocyanate, butylene
1,4-diisocyanate,
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane
(isophorone diisocyanate, IPDI), 1-methylcyclohexane 2,4- and/or
2,6-diisocyanate, dicyclohexylmethane 4,4'-, 2,4'- and/or
2,2'-diisocyanate (H12MDI), 2,6-diisocyanatohexanecarboxylic
esters, 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI),
cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and/or
2,6-diisocyanate and/or dicyclohexylmethane 4,4'-, 2,4'- and
2,2'-diisocyanate, preferably diphenylmethane 2,2'-, 2,4'- and/or
4,4'-diisocyanate (MDI), naphthylene 1,5-diisocyanate (NDI),
tolylene 2,4- and/or 2,6-diisocyanate (TDI), hexamethylene
diisocyanate, dicyclohexylmethane 4,4'-, 2,4'- and/or
2,2'-diisocyanate (H12MDI), and/or IPDI, in particular 4,4'-MDI
and/or hexamethylene diisocyanate and/or H12MDI.
[0073] As compounds which are reactive toward isocyanates, use is
made of, as described above, the polyester alcohols of the
invention. In admixture with these, it is possible to use generally
known compounds which are reactive toward isocyanates, for example
polyesterols, polyetherols and/or polycarbonate diols, which are
usually summarized under the term "polyols", having molecular
weights of from 500 to 12 000 g/mol, preferably from 600 to 6000
g/mol, in particular from 800 to 4000 g/mol, and preferably an
average functionality of from 1.8 to 2.3, preferably from 1.9 to
2.2, in particular 2. Preference is given to using exclusively the
polyester alcohols of the invention as compounds which are reactive
toward isocyanates.
[0074] Compounds which are reactive toward isocyanates also include
chain extenders. As chain extenders, it is possible to use
generally known aliphatic, araliphatic, aromatic and/or
cycloaliphatic compounds having a molecular weight of from 50 to
499, preferably 2-functional compounds, for example alkanediols
having from 2 to 10 carbon atoms in the alkylene radical,
preferably 1,4-butanediol, 1,6-hexanediol, 1,3-propanediol,
1,2-ethylene glycol and/or dialkylene, trialkylene, tetraalkylene,
pentaalkylene, hexaalkylene, heptaalkylene, octaalkylene,
nonaalkylene and/or decaalkylene glycols having from 3 to 8 carbon
atoms, preferably unbranched alkanediols, in particular
1,3-propanediol, 1,4-butanediol and 1,6-hexanediol.
[0075] Catalysts which accelerate the reaction between the NCO
groups of the diisocyanates and the hydroxyl groups of formative
components are usually used. These are the customary tertiary
amines known from the prior art, e.g. triethylamine,
dimethylcyclohexylamine, N-methylmorpholine,
N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol,
diazabicyclo[2.2.2]octane and the like and in particular organic
metal compounds such as titanic esters, iron compounds such as
iron(III) acetylacetonate, tin compounds, e.g. tin diacetate, tin
dioctoate, tin dilaurate or the dialkyltin salts of aliphatic
carboxylic acids, e.g. dibutyltin diacetate, dibutyltin dilaurate
or the like. The catalysts are usually used in amounts of from
0.00001 to 0.1 part by weight per 100 parts by weight of
polyhydroxyl compound.
[0076] Apart from catalysts, customary auxiliaries can also be
added to the formative components. Examples which may be mentioned
are surface-active substances, flame retardants, nucleating agents,
lubricants and mold release agents, dyes and pigments, inhibitors,
stabilizers against hydrolysis, light, heat, oxidation or
discoloration, protective agents against microbial degradation,
inorganic and/or organic fillers, reinforcing materials and
plasticizers.
[0077] Further details regarding the abovementioned auxiliaries and
additives may be found in the specialist literature, e.g. Plastics
Additive Handbook, 5th edition, H. Zweifel, ed, Hanser Publishers,
Munich, 2001. All molecular weights mentioned in this text have the
unit [g/mol].
[0078] To adjust the hardness of the TPUs, the formative components
polyols and chain extenders can be varied within a relatively wide
molar ratio range. Molar ratios of polyols to the total chain
extenders to be used of from 10:1 to 1:10, in particular from 1:1
to 1:4, have been found to be useful, with the hardness of the TPUs
increasing with increasing content of chain extenders.
[0079] The production of the polyurethanes can be carried out
batchwise or continuously by known methods, for example using
reaction extruders or the belt process by means of the one-shot or
prepolymer process, preferably by the one-shot process. In the
prepolymer process, the components isocyanates, polyols and, if
appropriate, chain extenders, catalysts and/or auxiliaries to be
reacted can be mixed with one another either in succession or
simultaneously, with the reaction commencing immediately. In the
extruder process, the formative components isocyanates, polyols
and, if appropriate, chain extenders, catalysts and/or auxiliaries
are introduced individually or as a mixture into the extruder and
reacted at temperatures of usually from 100.degree. C. to
280.degree. C., preferably from 140.degree. C. to 250.degree. C.
The TPU obtained is extruded, cooled and pelletized.
[0080] The process of the invention has surprisingly made it
possible to reduce the reaction time required for preparing the
polyester alcohols. The polyester alcohols display improved storage
stability and a low color number. There were no disadvantages in
the processing properties and in the characteristic properties of
the polyurethanes produced using the polyester alcohols.
[0081] The invention is illustrated by the following examples.
EXAMPLE 1
Production of a Zeolite Extrudate
[0082] 3.0 kg of powder of a titanium zeolite were mixed in a pan
mill with 2.5 kg of Ludox.RTM. AS 40, 3.83 kg of a 33.5% strength
polystyrene dispersion, 120 g of Walocel.RTM., 40 g of polyethylene
oxide and 1000 g of water for 65 minutes. The mixture was
subsequently extruded at a pressure of 140 bar to give 1.5 mm
extrudates. The extrudates were dried at 120.degree. C. for 16
hours and subsequently calcined in air at 490.degree. C. for 5
hours. This gave 3.75 kg of extrudates having a Ti content of 1.5%
and an Si content of 44.0%.
Preparation of the Polyester Alcohols
COMPARATIVE EXAMPLE 1
[0083] 6040.1 g of adipic acid, 1406.8 g of ethylene glycol, 2042.6
g of 1,4-butanediol, 1 ppm of titanium tetrabutoxide and 5 ppm of
tin octoate were placed in a round-bottom flask having a volume of
12 liters. The mixture was heated to 180.degree. C. while stirring
and kept at this temperature for 3 hours. The water formed was
removed by distillation.
[0084] The mixture was then heated to 240.degree. C. and kept at
this temperature under a reduced pressure of 40 mbar until an acid
number of less than 1 mg KOH/g had been reached.
[0085] The colorless, liquid polyester alcohol formed had the
following characteristic properties:
[0086] Hydroxyl number: 56.5 mg KOH/g
[0087] Acid number: 0.10 mg KOH/g
[0088] Viscosity: 670 mPas at 75.degree. C.
[0089] Water content: 0.04%
[0090] Color number: 64 APHA/Hazen
[0091] Cycle time: 14 hours
[0092] Metal content of the polyester alcohol: Ti: 0.21 ppm; Sn:
1.2 ppm
COMPARATIVE EXAMPLE 2
[0093] 5301.6 g of adipic acid, 1586.4 g of 1,6-hexanediol, 2419.5
g of 1,4-butanediol and 10 ppm of tin octoate were placed in a
round-bottom flask having a volume of 12 liters. The mixture was
heated to 180.degree. C. while stirring and kept at this
temperature for 3 hours. The water formed was removed by
distillation.
[0094] The mixture was then heated to 240.degree. C. and kept at
this temperature under a reduced pressure of 40 mbar until an acid
number of less than 1 mg KOH/g had been reached.
[0095] The colorless, liquid polyester alcohol formed had the
following characteristic properties:
[0096] Hydroxyl number: 56 mg KOH/g
[0097] Acid number: 0.27 mg KOH/g
[0098] Viscosity: 690 mPas at 75.degree. C.
[0099] Water content: 0.1%
[0100] Color number: 50 APHA/Hazen
[0101] Cycle time: 11 hours
[0102] Metal content of the polyester alcohol: Sn: 2.6 ppm
EXAMPLE 1
[0103] 6040.1 g of adipic acid, 1406.8 g of ethylene glycol, 2042.6
g of 1,4-butanediol and 18.9 g of titanium zeolite catalyst were
placed in a round-bottom flask having a volume of 12 liters. The
mixture was heated to 180.degree. C. while stirring and kept at
this temperature for 3 hours. The water formed was removed by
distillation.
[0104] The mixture was then heated to 240.degree. C. and kept at
this temperature under a reduced pressure of 40 mbar until an acid
number of less than 1 mg KOH/g had been reached.
[0105] Removal of the titanium zeolite catalyst by filtration gave
a colorless, liquid polyester alcohol having the following
characteristic properties:
[0106] Hydroxyl number: 57 mg KOH/g
[0107] Acid number: 0.1 mg KOH/g
[0108] Viscosity: 660 mPas at 75.degree. C.
[0109] Water content: 0.05%
[0110] Color number: 12 APHA/Hazen
[0111] Cycle time: 10 hours
[0112] Metal content of the polyester alcohol: Ti: <0.1 ppm
EXAMPLE 2
[0113] 5301.6 g of adipic acid, 1586.4 g of 1,6-hexanediol, 2419.5
g of 1,4-butanediol and 18.6 g of titanium zeolite catalyst were
placed in a round-bottom flask having a volume of 12 liters. The
mixture was heated to 180.degree. C. while stirring and kept at
this temperature for 3 hours. The water formed was removed by
distillation.
[0114] The mixture was then heated to 240.degree. C. and kept at
this temperature under a reduced pressure of 40 mbar until an acid
number of less than 1 mg KOH/g had been reached.
[0115] Removal of the titanium zeolite catalyst by filtration gave
a colorless, liquid polyester alcohol having the following
characteristic properties:
[0116] Hydroxyl number: 56 mg KOH/g
[0117] Acid number: 0.51 mg KOH/g
[0118] Viscosity: 680 mPas at 75.degree. C.
[0119] Water content: 0.04%
[0120] Color number: 18 APHA/Hazen
[0121] Cycle time: 9 hours
[0122] Metal content of the polyester alcohol: Ti: <0.1 ppm
TABLE-US-00001 OH number Acid number Viscosity (75.degree. C.)
Color number Cycle time Polyesterol Diol (mg KOH/g) (mg KOH/g) (mPa
s) (APHA/Hazen) hours Comparative example 1 Ethylene glycol,
1,4-butanediol 56.5 0.1 670 64 14 Comparative example 2
1,4-butanediol, 1,6-hexanedlol 56 0.27 690 50 11 Example 1 Ethylene
glycol, 1,4-butanediol 57 0.1 660 12 10 Example 2 1,4-butanediol,
1,6-hexanediol 56 0.51 680 18 9
[0123] Table 1 shows that the polyesterols prepared by the process
of the invention could be prepared in a shorter cycle time and that
the polyesterols prepared by the process of the invention have
lower discoloration.
* * * * *