Process for the preparation of polyether polyols

Details Process for the preparation of polyether polyols Process for the preparation of polyether polyols

2002-02-19

2004-08-17

Cooney, Jr., John M. (Department: 1711)

Compositions

Compositions containing a single chemical reactant or plural...

Organic reactant

C252S182270, C521S170000, C521S174000, C568S613000, C568S619000, C568S620000, C568S621000

Reexamination Certificate

active

06776925

ABSTRACT:

The invention relates to an improved process for the preparation of polyether polyols in the presence of double-metal cyanide (“DMC”) catalysts by polyaddition of alkylene oxides to starter compounds having active hydrogen atoms.
Polyether polyols are typically prepared industrially by polyaddition of alkylene oxides to polyfunctional starter compounds such as, for example, alcohols, acids, or amines with base catalysis (for example KOH) (see, for example, Gum, Riese & Ulrich (ed.): “Reaction Polymers”, Hanser Verlag, Munich, 1992, pp. 75-96). Following completion of the polyaddition, the basic catalyst must be removed from the polyether polyol in a very elaborate process, for example, by neutralization, distillation and filtration. Moreover, polyether polyols prepared by base catalysis have the disadvantage that as chain length increases, the number of monofunctional polyethers terminating in double bonds (so-called “mono-ols”) increases constantly, lowering functionality.
The polyether polyols obtained may be utilized for the production of polyurethanes (for example elastomers, foams, coatings), particularly, for the production of flexible polyurethane foams. Flexible foams offer a low resistance to compressive stress and are open-celled, air-permeable and reversibly deformable. Slabstock foams and molded foams are distinctive products (see, for example, Kunststoffhandbuch [Manual of Plastics], Vol. 7, 3rd Edition, Hanser Verlag, Munich, 1993, pp. 193-252). Slabstock foams are produced in a continuous or discontinuous process as semi-finished products and are then cut to size and shape appropriate to the application (for example, upholstered furniture, mattresses). Molded foams, on the other hand, are produced in a discontinuous process in which the foam bodies are obtained directly in the desired shape (by expansion to fill a corresponding mold).
DMC catalysts for the preparation of polyether polyols are known. (See, for example, U.S. Pat. Nos. 3,404,109, 3,829,505, 3,941,849 and 5,158,922). The use of these DMC catalysts for the preparation of polyether polyols brings about a reduction in the monofunctional polyether (mono-ol) content, by comparison with the conventional preparation of polyether polyols with basic catalysts. Improved DMC catalysts, such as are described, for example, in EP-A 700 949, EP-A 761 708, WO 97/40086, WO 98/16310, DE-A 197 45 120, DE-A 197 57 574 or DE-A 198 102 269, additionally possess exceptionally high activity and enable polyether polyols to be prepared at a very low catalyst concentration (25 ppm or less), making separation of the catalyst from the polyol unnecessary.
Polyether polyols obtained with DMC catalysis may lead to applications-related technical problems in the production of polyurethane foam, in particular, for flexible polyurethane foams, for example, causing foam destabilization (increased susceptibility to collapse) or increased coarseness of cell size. DMC-catalyzed polyether polyols are not, therefore, in all cases able to replace corresponding base-catalyzed polyols in flexible polyurethane foam applications without adaptation of the formulation.
It has now been found that polyether polyols prepared in whole or in part with DMC catalysis possess markedly improved foaming properties in the production of polyurethane foams if the polyether polyol is guided through a suitable mixing unit during the DMC-catalyzed polyaddition of alkylene oxides to starter compounds having active hydrogen atoms.
The present invention relates to an improved process for the preparation of polyether polyols, wherein the polyether polyol is prepared in whole or in part by DMC-catalyzed polyaddition of alkylene oxides to starter compounds having active hydrogen atoms wherein the polyether polyol is guided through a suitable mixing unit during the DMC-catalyzed polyaddition. The present invention also relates to the use of polyether polyols produced from the present invention for the production of polyurethane foam, in particular, flexible polyurethane foams.
The DMC catalysts which are suitable for the process according to the invention are known. See, for example, JP-A 4 145 123, EP-A 654 302, EP-A 700 949, EP-A 743 093, EP-A 761 708, WO 97/40086, WO 98/16310, WO 99/19062, WO 99/19063, WO 99/33562, DE-A 198 34 572, DE-A 198 34 573, DE-A 198 42 382, DE-A 198 42 383, DE-A 199 05 611, DE-A 199 06 985, DE-A 199 13 260, DE-A 199 20 937 or DE-A 199 24 672. A typical example is the high-activity DMC catalysts described in EP-A 700 949, which in addition to a DMC compound (for example zinc hexacyanocobaltate(III)) and an organic complexing ligand (for example tert.-butanol), also comprise a polyether polyol having a number average molecular weight greater than 500 g/mol.
Compounds having molecular weights of 18 to 2,000 g/mol, preferably 62 to 1,000 g/mol, and 1 to 8, preferably 2 to 6, hydroxyl groups are utilized as the starter compounds having active hydrogen atoms. Examples of such starter compounds include butanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,6-hexanediol, bisphenol A, trimethylolpropane, glycerol, pentaerythritol, sorbitol, cane sugar, degraded starch, water or so-called pre-lengthened starters.
Ethylene oxide, propylene oxide and butylene oxide as well as mixtures thereof are preferably utilized as the alkylene oxides. The polyether chains may be constructed using only one monomeric epoxide or in random or block manner using 2 or 3 different monomeric epoxides. “Ullmanns Encyclopädie der industriellen Chemie” [Ullmann's Encyclopaedia of Industrial Chemistry], Vol. A21, 1992, p.670 et seq., provides further detail.
The polyaddition may in principle be carried out by any alkoxylation process known for DMC catalysis.
For example, a conventional batch process may be utilized. In this process, an initial charge of the DMC catalyst and the starter compound is introduced into the batch reactor which is then heated to the desired temperature, after which alkylene oxide is added in a quantity sufficient to activate the catalyst. As soon as the catalyst is activated (manifested, for example, by a pressure drop in the reactor), the remaining alkylene oxide is dispensed continuously into the reactor until the desired molecular weight of the polyether polyol is reached.
A continuous process may also be employed in which a pre-activated mixture of DMC catalyst and starter compound is supplied continuously to a continuous reactor, for example a continuous stirred-tank reactor (“CSTR”) or a tubular flow reactor. Alkylene oxide is dispensed into the reactor and the product is withdrawn continuously.
The DMC-catalyzed polyaddition is, however, preferably carried out in a process in which the starter compound is dispensed-in continuously during the polyaddition. The DMC-catalyzed polyaddition with continuous dispensing of the starter may in this case take place in a batch process, as taught by WO 97/29146, or a continuous process, such as appears in WO 98/03571.
The DMC-catalyzed polyaddition may take place at pressures of from 0.0001 to 20 bar, preferably, 0.5 to 10 bar, more preferably, 1 to 6 bar. The reaction temperatures are from 20 to 200° C., preferably, 60 to 180° C., more preferably, 80 to 160° C.
The DMC catalyst concentration is generally from 0.0005 to 1 wt. %, preferably, 0.001 to 0.1 wt. %, more preferably, 0.001 to 0.01 wt. %, in relation to the quantity of polyether polyol to be prepared.
According to the invention, during the DMC-catalyzed polyaddition, the polyether polyol is guided through a zone of high energy density, such as arises, for example, in a suitable mixing unit. The structural principles of suitable mixing units for the treatment according to the invention of the polyether polyols is described below.
Suitable mixing units are distinguished by geometries which enable them to deliver a high local energy density to the product in the form of energy of flow. Since high pressures are frequently applied for this purpose, these mixing units are also kno

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