Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-07-05
2004-01-06
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C422S198000
Reexamination Certificate
active
06673972
ABSTRACT:
The present invention relates to a process for the preparation of polyetherpolyols.
Polyetherpolyols are provided in large amounts, in particular for the preparation of polyurethane foams. In the known preparation processes, polyetherpolyols are prepared as a rule from alkylene oxides in the presence of a short-chain initiator using different catalysts, such as bases, hydrophobized double-layer hydroxides, acidic or Lewis acid systems, organometallic compounds or multimetal cyanide complexes.
Heterogeneous multimetal cyanide complex catalysts are highly selective and active catalysts which are suitable in particular for the preparation of flexible foam polyetherpolyols, in which a high molecular weight has to be achieved and in which long oxalkylation times are required. By using multimetal cyanide complex catalysts, the production costs can be reduced and at the same time high-quality polyetherpolyol, which can be further processed to give low-odor and hence high-quality polyurethane foams, can be obtained. It is known from the literature that secondary reactions which may lead to the formation of odor substances and unsaturated components scarcely occur.
However, the high activity has the result that the heat of reaction cannot be removed in conventional reactors. If the polyetherpolyol preparation catalyzed via a multimetal cyanide complex is carried out in standard stirred kettles, the metering rates of alkylene oxide are limited by the heat removal capacity of the heat exchanger.
U.S. Pat. No. 5,811,595 proposes an ideally mixed reactor having one or two heat exchangers, the polyetherpolyol being fed into the circulation stream of the heat exchanger and the ethylene oxide into the reactor. Mixing of the ethylene oxide with the liquid phase is achieved by means of a nozzle.
The high circulation rate required for maintaining the high heat removal capacity and the danger of mechanical damage to the heterogeneous catalyst by the pump are disadvantageous in this process. Moreover, the highly reactive ethylene oxide is introduced into the reactor in which, owing to the cooling coils used, in particular at low degrees of filling, and owing to the small exchange area, the heat removal is very poor. Overheating due to the high reaction rate can occur, resulting in damage to the product. This may be reinforced by the poor mixing in the reactor.
EP-A-0 850 954 describes a process in which the reaction takes place in the gas space above the reaction liquid. The polyetherpolyol is circulated via a heat exchanger by means of a pump and is fed in through nozzles. This results in a large liquid surface. At the same time, ethylene oxide and polyetherpolyol are metered in via nozzles. The large surface results in good mass transfer and hence high reaction rates.
Owing to the high reaction rate which can be achieved using this process, local excess temperatures in the individual droplets are to be expected, which in turn result in damage to the product. Here too, the high circulation rate required for heat removal is not unproblematic for the heterogeneously dispersed multimetal cyanide complex catalyst, and the danger of damage cannot be ruled out.
The artificially enlarged gas phase furthermore constitutes a potential danger, in particular in the case of the ethoxylation, since free alkylene oxide is present in the gas phase. Ethylene oxide tends toward gas phase decomposition, which may lead to bursting of the reactor. On the other hand, when the polyetherpolyol or ethylene oxide is passed into the liquid, rapid reaction of the alkylene oxide is likely owing to the active multimetal cyanide complex.
EP-A-0 419 419 proposes a jet loop reactor, i.e. a reactor having internal loop flow and external pumped circulation, for alkoxylation of alcohols having a low functionality with ethylene oxide. However, the high reaction temperatures of 165° C. and the low functionalities result in low viscosities of the reaction mixture.
It is an object of the present invention to provide a process employing simple apparatus for the preparation of polyetherpolyols in the presence of multimetal cyanide complex catalysts with improvement of the space-time yield and avoidance of local overheating and hence a higher degree of secondary reactions, thus ensuring a high product quality.
We have found that this object is achieved by a process for the preparation of polyetherpolyols by reacting diols or polyols with ethylene oxide, propylene oxide, butylene oxide or a mixture thereof in the presence of a multimetal cyanide complex catalyst.
In the invention, the reaction is carried out in a reactor of upright cylindrical design, comprising a jet nozzle which is arranged in the upper reactor region and is directed downward and via which the starting materials and the reaction mixture are fed in, and comprising a take-off, preferably in the lower reactor region, via which the reaction mixture is fed back to the jet nozzle in an external circulation by means of a pump via an equilibration container, comprising a concentric guide tube which extends over the total length of the reactor, except for the reactor ends, and comprising a heat exchanger integrated in the annular space.
The vertical, upright cylindrical reactor described in EP-A-0 419 419 was developed in particular for low-viscosity liquid reaction mixtures, i.e. for liquids which have a viscosity substantially below 10 mPa·s under reaction conditions.
In comparison, the inventors of the present process have surprisingly found that the reactor type disclosed in EP-A-0 419 419 can also be used for more highly viscous reaction media, such as the polyetherpolyols of the present invention. As a rule, polyetherpolyols have high viscosities, approximately in the range from 80 to 1500 mPa·s at room temperature and still above 20 mPa·s, frequently above 100 mPa·s, under reaction conditions (from about 100 to 130° C.). It is known that the boundary layer between heat exchanger and reaction mixture increases with increasing viscosity, with the result that the heat can be removed more and more poorly. According to the novel process, in spite of the high viscosity, it was surprisingly possible to achieve sufficient heat removal, so that high alkylene oxide metering rates could be realized, resulting in an improved space-time yield and hence higher productivity and good product quality. Local excess temperatures which might lead to damage to the product were avoided.
Moreover, in the reaction procedure with external pump circulation, deposition of catalyst in the external pump circulation and damage to the catalyst by the pump would have been expected, with the result that the reaction would be slowed down since, owing to the low catalyst concentrations of less than 500 ppm used, even small losses of catalyst could lead to a considerable loss of activity. Furthermore, owing to the external pump circulation, a shift in the molecular weight distribution would have been expected since part of the product always remains in the external circulation. Contrary to expectation, the disadvantages mentioned were not observed and, on the contrary, a product having low dispersity of the molar mass distribution, i.e. having excellent product quality, was obtained.
In reactors equipped with heat exchanger plates, there is the danger that heterogeneous catalyst will settle in corners, angles and other areas with insufficient flow and consequently would no longer be available for the catalytic reaction or would be available only to an insufficient extent. This problem is not quite so critical at relatively high catalyst concentrations because a catalyst loss in this case does not have an extreme effect on the quality of the catalysis and of the products. On the other hand, at low catalyst concentrations, for example 100 ppm or less, the loss of available catalyst of the order of magnitude of only a few 10 ppm constitutes a dramatic absolute loss of catalyst material and hence of catalyst activity. The consequence is substantially poorer product quality, broader molecular weight distributio
Bauer Stephan
Grosch Georg Heinrich
Harre Kathrin
Müller Jörn
Ostrowski Thomas
BASF - Aktiengesellschaft
Borrego Fernando A.
Keys Rosalynd
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