U.S. patent application number 10/712707 was filed with the patent office on 2005-05-19 for preparation of polyether alcohols.
Invention is credited to Baum, Eva, Harre, Kathrin, Ostrowski, Thomas, Ruppel, Raimund.
Application Number | 20050107643 10/712707 |
Document ID | / |
Family ID | 34573601 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050107643 |
Kind Code |
A1 |
Ostrowski, Thomas ; et
al. |
May 19, 2005 |
Preparation of polyether alcohols
Abstract
The invention relates to a process for the continuous
preparation of polyether alcohols by reaction of alkylene oxides
with H-functional starter substances in the presence of DMC
catalysts, which comprises, at the beginning of the process a)
firstly placing initial charge material and DMC catalyst in a
reactor, b) metering in alkylene oxide so that the metering rate
which is maintained for continuous operation of the reactor is
reached in a time of from 100 to 3 000 seconds, c) metering in
starter substance during or after step b) so that the metering rate
which is maintained for continuous operation of the reactor is
reached in a time of from 5 to 500 seconds, d) after the fill level
in the reactor which is desired for continuous operation of the
reactor has been reached, taking product off continuously from the
reactor while at the same time metering in starter substance and
alkylene oxides in such an amount that the fill level in the
reactor remains constant and metering in DMC catalyst so that the
catalyst concentration necessary for continuous operation of the
reactor is maintained in the reactor.
Inventors: |
Ostrowski, Thomas;
(Mannheim, DE) ; Ruppel, Raimund; (Dresden,
DE) ; Baum, Eva; (Schwarzheide, DE) ; Harre,
Kathrin; (Dresden, DE) |
Correspondence
Address: |
BASF AKTIENGESELLSCHAFT
CARL-BOSCH STRASSE 38, 67056 LUDWIGSHAFEN
LUDWIGSHAFEN
69056
DE
|
Family ID: |
34573601 |
Appl. No.: |
10/712707 |
Filed: |
November 13, 2003 |
Current U.S.
Class: |
568/679 |
Current CPC
Class: |
C08G 65/2663 20130101;
C08G 65/2696 20130101; C08G 18/4866 20130101 |
Class at
Publication: |
568/679 |
International
Class: |
C07C 043/11 |
Claims
We claim:
1. A process for the continuous preparation of polyether alcohols
by reaction of alkylene oxides with H-functional starter substances
in the presence of DMC catalysts, which comprises, at the beginning
of the process a) firstly placing initial charge material and DMC
catalyst in a reactor, b) metering in alkylene oxide so that the
metering rate which is maintained for continuous operation of the
reactor is reached in a time of from 100 to 3 000 seconds, c)
metering in starter substance during or after step b) so that the
metering rate which is maintained for continuous operation of the
reactor is reached in a time of from 5 to 500 seconds, d) after the
fill level in the reactor which is desired for continuous operation
of the reactor has been reached, taking product off continuously
from the reactor while at the same time metering in starter
substance and alkylene oxides in such an amount that the fill level
in the reactor remains constant and metering in DMC catalyst so
that the catalyst concentration necessary for continuous operation
of the reactor is maintained in the reactor.
2. A process as claimed in claim 1, wherein inert solvents or
H-functional compounds are used as initial charge material.
3. A process as claimed in claim 1, wherein monofunctional or
polyfunctional alcohols are used as initial charge material.
4. A process as claimed in claim 1, wherein polyfunctional reaction
products of alcohols with alkylene oxides having a molecular weight
of greater than 300 g/mol are used as initial charge material.
5. A process as claimed in claim 1, wherein the polyether alcohol
which is the end product of the process is used as initial charge
material.
6. A process as claimed in claim 1, wherein monofunctional or
polyfunctional alcohols having a molecular weight of from 62 to 400
g/mol are used as starter substance.
7. A process as claimed in claim 1, wherein propylene oxide,
butylene oxide, ethylene oxide or a mixture of at least two of the
alkylene oxides mentioned is used as alkylene oxide.
8. A process as claimed in claim 1, wherein propylene oxide or a
mixture of propylene oxide and ethylene oxide is used as alkylene
oxide.
9. A process as claimed in claim 1, wherein the low molecular
weight starter is heated to from 50 to 130.degree. C. before being
metered into the reactor.
10. A process as claimed in claim 1, wherein the reactor is filled
to a fill level of from 20 to 80% in step a).
11. A process as claimed in claim 1, wherein the concentration of
the DMC catalyst at the beginning of the reaction is in the range
from 50 to 500 ppm.
Description
[0001] The present invention relates to a process for preparing
polyether alcohols using multimetal cyanide compounds as
catalysts.
[0002] Polyether alcohols are important starting materials in the
production of polyurethanes. They are usually prepared by catalytic
addition of lower alkylene oxides, in particular ethylene oxide
and/or propylene oxide, onto H-functional starters.
[0003] Catalysts used are usually soluble basic metal hydroxides or
salts, with potassium hydroxide having the greatest industrial
importance. A disadvantage of the use of potassium hydroxide as
catalyst is, in particular, that formation of unsaturated
by-products occurs in the preparation of high molecular weight
polyether alcohols and these by-products reduce the functionality
of the polyether alcohols and have a very adverse effect in the
production of polyurethanes.
[0004] To reduce the content of unsaturated components in the
polyether alcohols and increase the reaction rate in the addition
reaction of propylene oxide, it has been proposed that multimetal
cyanide compounds, preferably double metal cyanide compounds, in
particular zinc hexacyanometalates, be used as catalysts. These
catalysts are frequently also referred to as DMC catalysts. There
is a large number of publications in which such compounds are
described.
[0005] The polyether alcohols prepared using multimetal cyanide
compounds have a very low content of unsaturated constituents. A
further advantage of the use of multimetal cyanide compounds as
catalysts is the significantly increased space-time yield in the
addition reaction of the alkylene oxides.
[0006] The preparation of polyetherols using DMC technology can be
carried out both in batch processes and in continuous
processes.
[0007] Continuous processes for preparing polyether alcohols using
DMC catalysts are known. Thus, DD 203 735 describes a process for
the continuous preparation of polyether alcohols using DMC
catalysts, in which a starter substance containing an activated DMC
catalyst is metered continuously into a tube reactor, alkylene
oxide is added one or more times along the tube reactor and the
finished polyether alcohol is taken off continuously at the end of
the reactor. In this process, the activated starter substance has
to be produced in a separate process step in another reactor.
[0008] DD 203 734 describes a process for preparing low molecular
weight alkylene oxide addition products containing an activated DMC
catalyst. In this process, the catalyst is firstly activated by
means of alkylene oxide and, after the reaction has started,
alkylene oxide and low molecular weight alcohol are metered into
the reactor until the desired molecular weight has been
reached.
[0009] WO 97/29146 describes a process for preparing polyether
alcohols using DMC catalysts, in which the addition of alkylene
oxides onto the H-functional starter substance is started in a
reactor and further starter substance and alkylene oxide are
metered continuously into this reacting mixture. The finished
polyether alcohol is taken from the reactor after the addition
reaction.
[0010] WO 98/03571 describes a process for the continuous
preparation of polyether alcohols using DMC catalysts. Here,
starter substance and alkylene oxide are fed continuously into a
continuously operating reactor and the finished polyether alcohol
is taken off continuously.
[0011] In all cases, it is difficult to start the reaction and
establish steady-state conditions in the reactor owing to the
strongly exothermic nature of the reaction.
[0012] As starter substances, it is possible to use either alcohols
or alkoxylates of alcohols. In the case of low molecular weight
alcohols such as glycerol, trimethylolpropane, propylene glycol,
dipropylene glycol, ethylene glycol, diethylene glycol, sorbitol,
tridecanol-N, poisoning of the catalyst by the low molecular weight
starters can occur in the initial phase of the reaction. If
relatively high molecular weight starters are used, in particular
those having molar masses above 300 g/mol, damage to the catalyst
can likewise occur, especially as a result of thermal stress during
the commencement of the reaction.
[0013] If the low molecular weight alcohols are metered
continuously into the reactor, poisoning of the catalyst has to be
suppressed. This is particularly important when small amounts of
DMC catalyst are employed.
[0014] It is an object of the present invention to configure the
start-up of continuous reactors for the preparation of polyether
alcohols by addition of alkylene oxides onto H-functional starter
substances in such a way that steady-state operation of the reactor
can be established quickly without deactivation of the catalyst
occurring, even when using low catalyst concentrations.
[0015] We have found that this object is achieved by placing an
initial charge material and DMC catalyst in the reactor at the
beginning of the reaction, running alkylene oxide into this in a
defined time up to the metering rate which is maintained during
continuous operation of the reactor, after this metering rate has
been achieved or in parallel to the metered addition of alkylene
oxide, running in starter substance in a defined time up to the
metering rate which is maintained during continuous operation of
the reactor. The metered addition of the alkylene oxides and the
starter substance from the start of the reaction until the metering
rate which is maintained for continuous operation of the reactor
has been reached will hereinafter also be referred to as metering
ramp.
[0016] The present invention accordingly provides a process for the
continuous preparation of polyether alcohols by reaction of
alkylene oxides with H-functional starter substances in the
presence of DMC catalysts, which comprises, at the beginning of the
process
[0017] a) firstly placing initial charge material and DMC catalyst
in a reactor,
[0018] b) metering in alkylene oxides so that the metering rate
which is maintained for continuous operation of the reactor is
reached in a time of from 100 to 3 000 seconds,
[0019] c) metering in starter substance during or after step b) so
that the metering rate which is maintained for continuous operation
of the reactor is reached in a time of from 5 to 500 seconds,
[0020] d) after the fill level in the reactor which is desired for
continuous operation of the reactor has been reached, taking
product off continuously from the reactor while at the same time
metering in starter substance and alkylene oxides in such an amount
that the fill level in the reactor remains constant and metering in
DMC catalyst so that the catalyst concentration necessary for
continuous operation of the reactor is maintained in the
reactor.
[0021] In a further embodiment, it is also possible to meter-in
starter substance and alkylene oxides in parallel. In this case,
the same relative metering ramp is used for both streams, i.e. the
ratio of the two metered addition streams is constant.
[0022] Furthermore, it is also possible to commence metered
addition of the starter substance before the maximum metering rate
of the alkylene oxides has been reached.
[0023] The operating state of the reactor in continuous operation
will hereinafter also be referred to as steady state. A
characteristic of the steady state is that the process parameters
such as pressure and temperature and also the product properties no
longer change with time.
[0024] Initial charge materials which can be used in step a) are
inert solvents or preferably H-functional compounds. Preferred
H-functional compounds are monofunctional or polyfunctional
alcohols. In one embodiment of the process of the present
invention, the starter substances used in step c) can be employed.
Preference is given to using polyfunctional reaction products of
alcohols with alkylene oxides having a molecular weight of greater
than 300 g/mol. In a particularly preferred embodiment of the
process of the present invention, the polyether alcohol which is
the end product of the process is used as initial charge
material.
[0025] As starter substances, preference is given to using
monofunctional or polyfunctional alcohols having a molecular weight
of from 62 to 400 g/mol. These can be the same compounds as the
initial charge material or be compounds different from this.
Preference is given to using glycerol, sorbitol, ethylene glycol,
diethylene glycol, propylene glycol, dipropylene glycol and their
reaction products with alkylene oxides.
[0026] As alkylene oxides, preference is given to using propylene
oxide, butylene oxide, ethylene oxide and mixtures of at least two
of the alkylene oxides mentioned. Particular preference is given to
using propylene oxide or mixtures of propylene oxide and ethylene
oxide.
[0027] When the times to reach the metering rates in steps b) and
c) are less than those specified, damage to the catalyst occurs,
probably because of the high temperatures caused by the rapid
metered addition and consequently spontaneous reaction of the
propylene oxide. When the times specified are exceeded, it takes a
long time for conditions in the reactor under which the target
product is produced in a consistent quality to be reached, so that
out-of-specification product is obtained in the start-up phase. The
time until constant conditions have been reached in the reactor is
usually reported as the number of residence times required to reach
steady-state operation. The residence time is the quotient of
reaction volume (I) and feed rate (in I/s). The residence time thus
corresponds to the mean time for which the molecules are present in
the reactor. In the case of reactions in which the volume does not
remain constant, the residence time is based on the conditions at
the inlet of the reactor.
[0028] In the initial charging of initial charge material and DMC
catalyst in step a), the reactor is preferably filled to a fill
level of from 20 to 80%. After a fill level of 100% has been
reached in the reactor during steps b) and c), the discharge
facility is opened and the fill level in the reactor is kept
constant. The catalyst concentration is kept constant by metering
in further DMC catalysts, preferably in the form of a suspension,
in particular in a polyol.
[0029] After the metering rates of the alkylene oxide and the
starter substance selected for steady-state operation have been
reached, these are usually not altered any more. The ratio of the
two metering rates of starter and alkylene oxide determines the
molar mass of the finished polyetherol. A change in this ratio
during steady-state operation of the reactor can lead to variations
in product properties. A simultaneous increase in the two metering
rates at a constant ratio of the two streams is possible in
principle.
[0030] Since the discharge of polyether alcohol from the reactor
also results in catalyst being discharged, the catalyst has to be
replaced. This is achieved by adding catalyst in parallel to the
metered-in starter and the alkylene oxide. The catalyst can be
added continuously or in portions. The catalyst can be added in
solid form or as a dispersion in the initial charge material used
in step a). A further possibility is to disperse the catalyst in
the end product. Owing to the differential catalysis observed in
the DMC-catalyzed preparation of polyols, a narrow molar mass
distribution in the end product is achieved. In principle, the
catalyst can be added as a dispersion in any H-acid or inert
solvent. It is possible to disperse the catalyst in any propoxylate
which has a lower molar mass than the target molar mass, as long as
the same starter functionality is retained; it is therefore
possible to use masterbatch catalyst suspensions by means of which
many different products can be synthesized. For typical flexible
foam applications, the use of a glycerol propoxylate having a molar
mass of 1 000 g/mol is appropriate. For the preparation of diols,
the catalyst will be dispersed in, for example, a propoxylate of
dipropylene glycol having a molar mass of 1 000 g/mol. It is also
possible to split the stream of catalyst fed in. In this case, each
substream is metered in at the beginning as described in point c).
In a particular variant of this embodiment, not all substreams of
the starter substance contain catalyst; in a preferred variant,
only one substream of the starter substance contains catalyst. This
embodiment is particularly advantageous when only an increase in
molar mass is to be achieved without the simultaneous addition of
low molecular weight starters. In the introduction of the catalyst
into the reactor, it is not necessary for the catalyst to be
activated beforehand. Activation occurs in situ in the reactor
under the conditions of steady-state operation.
[0031] The concentration of DMC catalyst at the beginning of the
reaction is usually in the range from 50 to 500 ppm. During
steady-state operation of the reactor, the catalyst concentration
in the reactor should be regulated so that the content of free
alkylene oxide in the reactor is less than 10% by weight, based on
the contents of the reactor. If this amount is exceeded, secondary
reactions can occur to an increased extent. These result, in
particular, in an increased content of very high molecular weight
components in the polyether alcohol and in an increased viscosity.
These high molecular weight components lead to a drastic
deterioration in the processing properties of the polyether
alcohols in the production of foams, and can result in them being
completely unusable. If the content of catalyst in the system is
too high, the production costs increase.
[0032] As described above, the catalyst is suspended in the end
product in a preferred embodiment of the invention. The amount of
end product to be metered in with the catalyst or separately can be
chosen at will. For example, it is possible to dilute the reacting
mixture comprising alkylene oxide, DMC catalyst and starter with
any amount of end product which, owing to the occurrence of
differential catalysis, is inert in the present reaction. However,
a high degree of dilution leads to a reduction in the space-time
yield, since in the end product is merely circulated. The
space-time yield is defined as mass of product per unit time and
reactor volume.
[0033] In a preferred embodiment of the process of the present
invention, the starter is heated to from 50 to 130.degree. C.,
preferably to the reaction temperature, before being metered into
the reactor. This heating becomes more advantageous, the lower the
homogenization of the reaction mixture in the reactor and the
larger the reactor. Heating of the starter is particularly
advantageous when using glycerol, sorbitol, diethylene glycol and
dipropylene glycol as starter substances. In this embodiment of the
process of the present invention, the formation of primary hydroxyl
groups at the end of the chain, which is undesirable for many
applications of the polyether alcohols, in particular the
production of slabstock foams, is suppressed. In addition,
deactivation of the catalyst is suppressed.
[0034] As reactor, it is possible to use the customary and known
continuously operated reactors. These are, in particular, flow
reactors such as loop venturi reactors, for example as described in
EP 419 419, or flow reactors having internal heat exchangers, as
described in WO 01/62826. Furthermore, it is possible to use
jet-loop reactors having internal or external heat exchangers, as
described in PCT/EP01/02033.
[0035] Particular preference is given to using continuously
operated stirred vessels, as described, for example, in WO
01/62825. The inflow and the outflow of the products are preferably
regulated by means of pumps in this embodiment.
[0036] The multimetal cyanide compounds used for preparing the
polyether alcohols employed according to the present invention are
known. They usually have the formula (I)
M.sup.1.sub.a[M.sup.2(CN).sub.b(A).sub.c].sub.d.multidot.fM.sup.1gX.sub.n.-
multidot.h(H2O).multidot.eL, (I)
[0037] where
[0038] M.sup.1 is a metal ion selected from the group consisting of
Zn.sup.2+, Fe.sup.2+, Co.sup.3+, Ni.sup.2+, Mn.sup.2+, Co.sup.2+,
Sn.sup.2+, Pb.sup.2+, Mo.sup.4+, Mo.sup.6+, Al.sup.3+, V.sup.4+,
V.sup.5+, Sr.sup.2+, W.sup.4+, W.sup.6+, Cr.sup.2+, Cr.sup.3+,
Cd.sup.2+, Hg.sup.2+, Pd.sup.2+, Pt.sup.2+, V.sup.2+, Mg.sup.2+,
Ca.sup.2+, Ba.sup.2+, Cu.sup.2+,
[0039] M.sup.2 is a metal ion selected from the group consisting of
Fe.sup.2+, Fe.sup.3+, Co.sup.2+, Co.sup.3+, Mn.sup.2+, Mn.sup.3+,
V.sup.4+, V.sup.5+, Cr.sup.2+, Cr.sup.3+, Rh.sup.3+, Ru.sup.2+,
Ir.sup.3+
[0040] and M.sup.1 and M.sup.2 are identical or different.
[0041] A is an anion selected from the group consisting of halide,
hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate,
cyanate, carboxylate, oxalate and nitrate,
[0042] X is an anion selected from the group consisting of halide,
hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate,
cyanate, carboxylate, oxalate and nitrate,
[0043] L is a water-miscible ligand selected from the group
consisting of alkyls, aldehydes, ketones, ethers, polyethers,
esters, ureas, amides, nitriles, lactones, lactams and sulfides,
and
[0044] a, b, c, d, g and n are chosen so that the compound is
electrically neutral, and
[0045] e is the coordination number of the ligand or 0,
[0046] f is a fraction or integer greater than or equal to 0,
and
[0047] h is a fraction or integer greater than or equal to 0.
[0048] These compounds are prepared by means of generally known
methods by combining the aqueous solution of a water-soluble metal
salt with the aqueous solution of a hexacyanometalate compound, in
particular a salt or an acid, hereinafter also referred to as
starting solutions, and, if desired, adding a water-soluble ligand
thereto during or after the starting solutions have been combined.
Such catalysts and their preparation are described, for example, in
EP 862,947 and DE 197,42,978.
[0049] Particularly advantageous catalysts are multimetal cyanide
compounds in whose preparation the corresponding acids are used as
cyanometalate compound.
[0050] The multimetal cyanide compounds preferably have a
crystalline structure. Their particle size is preferably in the
range from 0.1 to 100 .mu.m. A particular advantage of crystalline
DMC catalysts, in particular ones which have been prepared using
cyanometalic acids, is their higher catalytic activity. In this
way, the preparation of the polyether alcohols can be carried out
using a smaller amount of catalyst. The amount used in this case
usually corresponds to the amount of multimetal cyanide compounds
in the finished polyether alcohol. The costly separation of the
multimetal cyanide compounds from the polyether alcohol after the
preparation can thus be dispensed with. However, it is also
possible to use a larger amount of multimetal cyanide compounds and
to reduce the amount of the multimetal cyanide compound in the
polyol after the synthesis of the polyether alcohol to such an
extent that the polyether alcohol contains the amount of multimetal
cyanide compounds desired for further processing.
[0051] The multimetal cyanide compounds are preferably used in the
form of suspensions in organic compounds, preferably alcohols. In
the process of the present invention, it is possible to disperse
the catalyst either in an intermediate or in the end product of the
synthesis. The catalyst suspension should have a concentration of
from 0.5 to 10%.
[0052] The polyether alcohols are prepared, as indicated above, by
adding alkylene oxides onto H-functional starter substances in the
presence of the catalysts described.
[0053] Low molecular weight starter substances used are
H-functional compounds. In particular, alcohols having a
functionality of from 1 to 8, preferably from 2 to 8, are used. To
prepare polyether alcohols used for flexible polyurethane foams,
starter substances used are, in particular, alcohols having a
functionality of from 2 to 4, in particular 2 or 3. Examples are
ethylene glycol, propylene glycol, glycerol, trimethylolpropane,
pentaerythritol. In the addition reaction of alkylene oxides by
means of DMC catalysts, it is advantageous to use the reaction
products of the alcohols mentioned with alkylene oxides, in
particular propylene oxide, together with or in place of the
respective alcohols. Such compounds preferably have a molar mass up
to 500 g/mol. The addition reaction of the alkylene oxides in the
preparation of these reaction products can be carried out using any
catalysts, for example basic or Lewis-acid catalysts; basic
catalysts are separated off by appropriate methods (e.g.
crystallization or adsorption) after the synthesis. The polyether
alcohols for the production of flexible polyurethane foams usually
have a hydroxyl number in the range from 20 to 100 mg KOH/g.
[0054] The addition reaction of the alkylene oxides in the
preparation of the polyether alcohols used for the process of the
present invention can be carried out by known methods. Thus, it is
possible for the polyether alcohols to contain only one alkylene
oxide. When using a plurality of alkylene oxides, it is possible
for them to be added on in blocks by introducing the alkylene
oxides individually in succession or to be added on randomly by
introducing the alkylene oxides together. It is also possible to
incorporate both blocks and random sections into the polyether
chain in the preparation of the polyether alcohols.
[0055] In the preparation of flexible polyurethane slabstock foams,
preference is given to using polyether alcohols having a high
content of secondary hydroxyl groups and a content of ethylene
oxide units in the polyether chain of not more than 30% by weight,
based on the weight of the polyether alcohol. These polyether
alcohols preferably have a propylene oxide block at the end of the
chain. For the preparation of flexible polyurethane molded foams,
use is made of, in particular, polyether alcohols having a high
content of primary hydroxyl groups and an ethylene oxide end block
in an amount of <20% by weight, based on the weight of the
polyether alcohol.
[0056] The addition reaction of the alkylene oxides is carried out
under the conditions customary for this purpose, at temperatures in
the range from 60 to 180.degree. C., preferably from 90 to
150.degree. C., in particular from 100 to 140.degree. C., and
pressures in the range from 0 to 20 bar, preferably in the range
from 0 to 10 bar and in particular in the range from 0 to 5 bar.
The mixture of starter substance/dispersing polyol and DMC catalyst
can, according to the teachings of WO 98/52689, be pretreated by
stripping before commencement of the alkoxylation.
[0057] After the addition reaction of the alkylene oxides is
complete, the polyether alcohol is worked up by means of customary
methods by removing the unreacted alkylene oxides and volatile
constituents, usually by distillation, steam stripping or gas
stripping and/or other deodorization methods. If necessary, a
filtration can be carried out.
[0058] The DMC catalyst can remain in the polyether alcohol. When
the amount of DMC catalyst used in the preparation of the polyether
alcohols is too high, the excess can be removed from the polyether
alcohol after the reaction. This can be carried out using the
customary and known methods of purification of polyether alcohols,
for example filtration, which may be in the form of a deep bed
filtration or a membrane filtration, or sedimentation, for example
by means of centrifugation.
[0059] The polyether alcohols prepared in this way are, as
described above, preferably used as starting materials for the
production of flexible polyurethane foams.
[0060] The invention is illustrated by the following examples.
EXAMPLE 1.1 (COMPARISON)
[0061] A reactor having a total capacity of 1.3 liters and equipped
with an anchor stirrer and jacket cooling was used. The temperature
was regulated via a water circuit, with the reactor temperature
being measured at the bottom of the reactor. HPLC pumps were used
for metering in alkylene oxides, starter and DMC suspension. The
concentration of free propylene oxide was measured using an IR-ATR
probe from Mettler-Toledo (ReactIR) which had previously been
calibrated for the present system. The absolute deviations in the
determination of the concentration of free propylene oxide were
about .+-.1%.
[0062] The reactor was firstly charged with 500 g of a propoxylate
of dipropylene glycol having a mean molar mass of 1 000 g/mol in
which 200 ppm of DMC catalyst according to the teachings of the
patent EP 862 947, prepared as moist filter cake with subsequent
drying to constant mass at 100.degree. C. and 13 mbar, were
dispersed. The reactor was heated to 115.degree. C. and at the same
time the stirrer was switched on, with the stirrer speed being
chosen so that an energy input of 2.0 kW/m.sup.3 was achieved
during the entire reaction time. Propylene oxide, further
propoxylate of dipropylene glycol which had a molar mass of 1 000
g/mol and functioned as starter in the present case, and DMC
catalyst suspension (DMC concentration: .delta. 000 ppm in a
propoxylate having a molar mass of 1 000 g/mol) were subsequently
metered in simultaneously. The metering rate of the propylene oxide
was increased from 0 to 7.5 g/min over 5 s; the metering rate of
the propoxylate of dipropylene glycol was increased from 0 to 2.3
g/min over 5 s and that of the catalyst suspension was increased
from 0 to 0.2 g/min over 5 s. After 1 000 g of product were present
in the reactor, as indicated by monitoring via the weighing signals
of the starting materials metered in, the product discharge valve
was opened and a stream of 10 g/min was taken off in a controlled
fashion. The mean residence time in the reactor system was
accordingly (1 000 ml/10 ml/min)=100 min on the assumption of a
density of the reaction mixture of 1 g/ml.
[0063] In this example, an increase in the molar mass from 1 000 to
4 000 g/mol was achieved. It was observed that large temperature
peaks up to 150.degree. C. occur during the reaction, and severe
regulation fluctuations likewise occurred. Concentrations of free
propylene oxide of up to 25% were reached in the reactor.
[0064] Samples were taken from the product stream every 100 minutes
for a period of 2 500 minutes (=41 h). The mean OH number of the
products was 28.84 mg KOH/g, corresponding to a molecular weight of
about 4 000 g/mol. After 20 residence times (i.e. 33 h), the
product viscosity was largely constant and was in the range from
813 to 835 mPas at 25.degree. C.
[0065] It may be assumed that the causes of the high viscosity are
damage to the catalyst due to the temperature peaks and also the
difficulty of regulating this system. Since the unruly reaction
still occurred after 20 residence times, permanent damage occurred
even to the freshly introduced catalyst, presumably because of the
temperature fluctuations.
EXAMPLE 1.2 (COMPARISON)
[0066] The procedure of example 1.1 was repeated, but the time to
reach the metering rate for propylene oxide, propoxylate of
dipropylene glycol and catalyst was in each case 7 200 seconds.
[0067] The maximum temperature was 116.degree. C.
[0068] The concentration of free propylene oxide in the reactor was
less than 1%, determined by means of ATR-IR measurements.
[0069] Samples were taken from the product stream every 100 minutes
for a period of 2 500 minutes. The mean OH number of the products
after 22 residence times was 28.21 mg KOH/g, corresponding to a
molecular weight of about 4 000 g/mol. The samples taken after more
than 18 residence times had a largely constant product viscosity of
about 820.+-.7 mPas at 25.degree. C.
[0070] The cause for the long time taken to reach a steady state
may be assumed to be the excessively slow activation of the
catalyst present at the beginning. It therefore took a long time to
reach the required activity.
EXAMPLE 1.3 (ACCORDING TO THE PRESENT INVENTION)
[0071] The procedure of example 1.1 was repeated, but the time to
reach the metering rate for propylene oxide, propoxylate of
dipropylene glycol and catalyst was in each case 600 seconds.
[0072] Samples were taken from the product stream every 10 minutes
for a period of 1 000 minutes. The mean OH number of the products
after 10 residence times was 28.95 mg KOH/g, corresponding to a
molecular weight of about 4 000 g/mol. After 5 residence times, the
product viscosity was largely constant and was 818.+-.8 mPas at
25.degree. C.
[0073] This example shows that the metering ramp according to the
present invention enables the steady state to be reached quickly
(after 500 minutes), so that economical operation can be
achieved.
EXAMPLE 1.4 (COMPARISON)
[0074] A reactor as in example 1.1 which was additionally provided
with metered introduction of monomeric dipropylene glycol by means
of HPLC pumps was used. The reactor was initially charged with 500
g of a propoxylate of dipropylene glycol having a mean molar mass
of 2 000 g/mol in which 300 ppm of DMC catalyst was dispersed. The
catalyst was prepared according to the teachings of EP 862 947.
After heating to 115.degree. C. and setting the stirrer power to
2.0 kW/m.sup.3, propylene oxide (metering: from 0 to 4.67 g/min in
5 s), dipropylene glycol (metering: from 0 to 0.33 g/min in 5 s),
propoxylate of dipropylene glycol having a molar mass of 2 000
g/mol (metering: from 0 to 4.7 g/min in 5 s) and DMC suspension
(concentration: 5 000 ppm, dispersed in a propoxylate of
dipropylene glycol having a molar mass of 2 000 g/mol, metering:
from 0 to 0.3 g/min in 5 s) were metered in simultaneously. After 1
000 g of reaction mixture were present in the reactor, the
discharge valve was opened and product was taken off at a rate of
10 g/min.
[0075] An unruly reaction associated with strong temperature pulses
and temporary cessation of the reaction was observed. Steady-state
operation was not achieved.
[0076] Samples were taken from the product stream every 100 minutes
up to a reaction time of 3 000 minutes. The mean OH number of the
products was 56.4 mg KOH/g, corresponding to a molecular weight of
about 2 000 g/mol. After 25 residence times, the product viscosity
was largely constant and was in the range from 324 to 344 mPas at
25.degree. C.
EXAMPLE 1.5 (COMPARISON)
[0077] The procedure of example 1.5 was repeated, but the time to
reach the metering rate for propylene oxide, dipropylene glycol,
propoxylate of dipropylene glycol and catalyst was in each case 8
000 seconds.
[0078] Samples were taken from the product stream every 100 minutes
up to a reaction time of 2 500 minutes. The mean OH number of the
products after 24 residence times was 55.2 mg KOH/g. After 23
residence times, the product viscosity was largely constant and was
333.+-.11 mPas at 25.degree. C.
EXAMPLE 1.6 (ACCORDING TO THE PRESENT INVENTION)
[0079] The procedure of example 1.5 was repeated, but the time to
reach the metering rate for propylene oxide, dipropylene glycol,
propoxylate of dipropylene glycol and catalyst was in each case 400
seconds.
[0080] Samples were taken from the product stream up to a reaction
time of 1 500 minutes.
[0081] The mean OH number of the products after 10 residence times
was 54.8 mg KOH/g. After 6 residence times, the product viscosity
was largely constant and was 331.+-.8 mPas at 25.degree. C.
* * * * *