Preparing polyether polyols with DMC catalysts

Details Preparing polyether polyols with DMC catalysts Preparing polyether polyols with DMC catalysts

1999-12-15

2002-03-19

Lovering, Richard D. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C525S403000, C528S412000, C568S623000

Reexamination Certificate

active

06359101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing polyether polyols, which are useful for making polyurethane foams, elastomers, sealants, coatings, and adhesives. In particular, the invention relates to specific process improvements for preparing polyether polyols that employ a double metal cyanide (DMC) catalyst. These improvements include using the combination of specific low molecular weight polyether polyols as starters for an epoxide polymerization reaction along with specific reaction conditions and impurity levels to achieve the initiation of those low molecular weight starters.
2. Brief Description of the Art
Polyoxypropylene polyols made with double metal cyanide catalysts (DMC) were first produced by General Tire in the 1960s. In contrast to earlier polyol-making processes that were based on KOH catalysts, this technology leads to polyols with significantly reduced unsaturation and consequently essentially “true” functionality. Also, much higher molecular weight polyols may be produced. Furthermore, double metal cyanide complexes are highly active catalysts that enable the preparation of polyether polyols having narrow molecular weight distributions and very low unsaturation (i.e., low monol content) even at high molecular weights. Recent improvements have resulted in DMC catalysts that have exceptional activity. See, for example, U.S. Pat. No. 5,470,813.
Even though DMC catalysts for the production of polyols have been known since the 1960s, commercialization of polyols made from these catalysts is a recent phenomenon, and most commercial polyether polyols are still produced with potassium hydroxide catalysts. The inherent process limitation that requires the use of “higher molecular weight” starters to produce these products is one of the reasons for the delayed commercial availability of DMC polyols. Conventional polyol starters, e.g., water, propylene glycol, glycerin, trimethylolpropane, and the like, do not readily initiate DMC-catalyzed epoxide polymerizations. The starters required for DMC catalysts in these early processes must be of a moderate molecular weight (~400 Da) and also be produced beforehand with KOH catalysts. These higher molecular weight polyol starters are disadvantageous since they must be synthesized separately (e.g., from glycerin, propylene oxide, and KOH) using a dedicated reactor. In addition, the KOH catalyst must be removed from the starter polyol before it is used as an initiator for a DMC-catalyzed polyol preparation because even traces of basic substances often deactivate DMC catalysts. Typically, the polyol starter and DMC catalyst are charged to a reactor and heated with a small amount of epoxide, the catalyst becomes active, and the remaining epoxide is added continuously to the reactor to complete the polymerization.
To avoid this problem, Olin developed a patented process, (see U.S. Pat. No. 5,391,722), in which a Lewis acid catalyst was used either separately or in situ with a DMC catalyst to eliminate the need for a separate base catalyzed treated precursor. Similarly, ARCO was later issued two U.S. patents (U.S. Pat. Nos. 5,679,764 and 5,773,525) in which the solid Lewis acid catalyst MgO was used to initiate the polymerization of low molecular weight starters and then the solid catalyst was filtered off and DMC polymerization initiated. And even more recently, Bayer (see World Patent Application WO99/54383A1) described another process similar to the Olin process using perfluoroalkyl sulfonates of Group III metals with more active DMC catalysts.
A significant improvement in the DMC catalyst art was developed by ARCO with a continuous process using low molecular weight starters. This continuous process is described in ARCO patents (U.S. Pat. Nos. 5,689,012 and 5,777,177), World Patent Application WO 99/14258A1 and U.S. Pat. No. 5,919,988, which disclose that once a DMC polymerization has been initiated with higher or moderate molecular weight starters, additional PO and very low molecular weight starter such as water, propylene glycol, glycerin, trimethylol propane, and the like can be fed into the reactor along with more PO and catalyst to produce polyols in a continuous manner. In a typical batch process for making polyols using either KOH or a DMC catalyst, all of the polyol starter is charged initially to the reactor. When KOH is used as the catalyst, it is well understood by those skilled in the art that continuous addition of the starter (usually a low molecular weight polyol such as glycerin or propylene glycol) with the epoxide will produce polyols having broader molecular weight distributions compared with products made by charging all of the starter initially. This is true because the rate of alkoxylation with KOH is substantially independent of polyol molecular weight. If low molecular weight species are constantly being introduced, the molecular weight distribution will broaden.
One consequence of charging all of the starter initially as in a typical batch polyether polyol synthesis is that reactors must often be used inefficiently. For example, to make a 4000 mol. wt. polyoxypropylene diol (4K diol) from a 2000 mol. wt. polyoxypropylene diol (2K diol) “starter”, the reactor will be almost half full at the start of the reaction; for example to make 50 gallons of product, we would start with 25 gallons of 2K diol starter (the build ratio for this process is 2). The “build ratio” is defined as the weight of polyol produced over the total weight of starter charged. A valuable process would overcome such “build ratio” limitations, and would permit efficient use of reactors regardless of the molecular weight of the starter or the product sought. For example, it would be valuable to have the option to charge a 50 gallon reactor with only 5 gallons of 2K diol starter, and still make 50 gallons of 4K diol product (build ratio is 10).
The ARCO continuous process allows a DMC catalyst to be used with a conventional starter such as propylene glycol or glycerin. In this process, the starter is added continuously, while conventional processes for making DMC-catalyzed polyols, all of the starter to be used is charged to the reactor at the start of the polymerization, and then oxide is fed continuously until the reaction is complete. Thus, the ARCO continuous process has several advantages. First, unlike other DMC-catalyzed polyol preparations, the process effectively uses water or a low molecular weight polyol as a starter. Previously, these starters were generally avoided because of sluggish initiation properties. Second, because water or a low molecular weight polyol can be used as a starter, the process eliminates the need to synthesize a costly higher molecular weight polyol starter by KOH catalysts in a separate, dedicated reactor. Third, the process overcomes the problem of reactor fouling by polyol gel formation that accompanies the use of DMC catalysts. Fourth, the ARCO process makes efficient use of reactors and overcomes many build-ratio limitations. Fifth, the ARCO process unexpectedly produces polyether polyols that have narrow molecular weight distributions, which are desirable for good polyurethane physical properties. Although the prior art teaches to avoid continuous addition of starters, ARCO found that continuous addition of starter, in the case of a DMC-catalyzed polyol synthesis, does not give polyols with broad molecular weight distributions.
In these ARCO continuous process patents, the continuously added starter is preferably water or a low molecular weight polyol. Low molecular weight polyols as defined in these end-uses have 1 or more hydroxyl groups and number average molecular weights less than about 300. Suitable low molecular weight polyols include, for example, glycerin, propylene glycol, dipropylene glycol, ethylene glycol, trimethylolpropane, sucrose, sorbitol, tripropylene glycol, and the like, and mixtures thereof. The starter can also be a polyol having a number average molecular weight greater than about 300 and less than the number avera

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