Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-03-11
2003-09-16
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S495000, C528S110000, C502S183000, C502S226000
Reexamination Certificate
active
06620908
ABSTRACT:
BACKGROUND OF INVENTION
Ortho-alkylated hydroxyaromatic compounds are useful for a variety of purposes. For example, ortho-cresol is a useful disinfectant and wood preservative. It is often prepared by the vapor-phase reaction of a phenol with methanol. In another alkylation reaction, ortho-cresol and phenol can both be converted into 2,6-xylenol. This xylenol monomer can be polymerized to form poly(2,6-dimethyl-1,4-phenylene) ether, which is the primary component in certain high-performance thermoplastic products.
The alkylated hydroxyaromatic compounds are usually prepared by the alkylation of the precursor hydroxyaromatic compound with a primary or secondary alcohol. The alkylation must be carried out in the presence of a suitable catalyst, such as a magnesium-based compound. U.S. Pat. Nos. 4,554,267; 4,201,880; and 3,446,856 describe the use of magnesium oxide for this purpose.
A great deal of attention has been paid to optimizing the performance of magnesium-based catalysts in an industrial setting. Usually, it is very important for the catalyst to have high activity, i.e., it must have as long an active life as possible. Moreover, the catalyst must have very good ortho-selectivity. Many of the ortho-alkylation catalysts used in the past produced a high proportion of para-alkylated products of marginal utility.
As an illustration, the alkylation of phenol with methanol in the presence of a magnesium oxide catalyst yields ortho-cresol (o-cresol) and 2,6-xylenol, which are desirable products. However, the alkylation reaction may also produce substantial amounts of para-substituted compounds, such as para-cresol (p-cresol); 2,4-xylenol, and mesitol (2,4,6-trimethylphenol). In some end use applications, these para-substituted compounds are much less useful than the corresponding compounds containing unsubstituted para positions. For example, polyphenylene ethers prepared from such compounds lack the desired properties obtained when the starting material is primarily 2,6-xylenol.
Selectivity and activity are related to the characteristics of the ortho-alkylation catalyst, and to the manner in which it is prepared. In the above-mentioned U.S. Pat. No. 4,554,267 (Chambers et al), a magnesium-based catalyst is prepared with a slurry process, using selected amounts of a copper salt as a promoter. In the process, the magnesium reagent and an aqueous solution of the copper salt are combined to form a magnesium-containing solid phase, which includes uniform, well-dispersed copper. The solid phase is dried, shaped, and calcined. The catalyst system is then used in the alkylation reaction of phenol and methanol. The reaction produces relatively high levels of the desirable 2,6-xylenol product. Moreover, the “selectivity” of the catalyst system, i.e., the ratio of 2,6-xylenol yield to the combined yield of 2,4-xylenol and mesitol, is also quite high, as is the overall yield of 2,6-xylenol.
It is clear that a catalyst composition like that described in the patent of Chambers et al is very useful and effective for alkylation reactions. Moreover, the slurry process used to prepare such a catalyst can be efficiently carried out in some situations.
However, there are drawbacks associated with the slurry process in other situations—especially in a large-scale production setting. For example, the “liquid”-related steps, which involve pre-blending of a copper compound with a magnesium compound, usually require mixing and holding tanks, recirculation piping, and specialized drying systems. Storage of the dried magnesium oxide/copper product (sometimes referred to as a “matrix”) may also be required, prior to blending and shaping steps. These operations and the related equipment represent a considerable investment in time and expense (e.g., energy costs), and may therefore lower productivity in a commercial venue. Furthermore, use of the slurry process can sometimes introduce metal and halogen-based contaminants into the catalyst, via the water supply.
It should therefore be apparent that improved methods for alkylating hydroxyaromatic compounds would be welcome in the art. The improvements may advantageously depend on the catalyst systems used in the alkylation reaction. Thus, enhanced techniques for preparing the catalyst would also be very desirable. Any new process related to alkylation or catalyst preparation should provide significant advantages in one or more of the following aspects: catalyst selectivity, catalyst activity, product yield, cost savings, and overall productivity. Moreover, use of the new processes should result in products (e.g., 2,6-xylenol) which possess substantially all of the desirable characteristics of products made by prior art methods.
TECHNICAL FIELD
This invention relates generally to alkylation catalysts. More particularly, it is directed to a method for making 2,6-xylenol.
SUMMARY OF INVENTION
In response to the needs of the prior art, an improved method for preparing a solid catalyst composition has been discovered. The method comprises dry-blending at least one filler with a magnesium reagent which yields magnesium oxide upon calcination, thereby forming a blended product. The level of chlorides in the magnesium reagent is less than about 250 ppm, and the level of calcium in the magnesium reagent is less than about 2500 ppm. In some preferred embodiments, the level of chlorides in the magnesium reagent is less than about 125 ppm, and the level of calcium in the magnesium reagent is less than about 1000 ppm.
The filler is usually polyphenylene ether, graphite, or a mixture thereof, and is present in an amount up to about 20% by weight. Dry-blending in this process is carried out in the absence of a promoter, e.g., a copper promoter. In preferred embodiments, the catalyst composition is vacuum-deaerated after dry-blending. Other processing steps are often undertaken, e.g., sieving, milling, compressing, and then forming the catalyst into a desired shape, such as a pellet. The shaped catalyst is usually calcined before use.
Another embodiment of the invention is directed to a method for selectively alkylating at least one hydroxyaromatic compound, to form a desired product, such as 2,6-xylenol. In this method, the solid catalyst is prepared as mentioned above, and calcined. A hydroxyaromatic compound such as phenol is then reacted with an alkyl alcohol such as methanol, in the presence of the catalyst, to form the alkylated product.
A process for preparing a polyphenylene ether resin constitutes another embodiment of this invention. In this process, the magnesium-based alkylation catalyst is prepared and calcined as set forth below, and is used to form a 2,6-alkyl-disubstituted phenolic compound. The 2,6-alkyl-disubstituted phenolic compound is then oxidatively coupled in the presence of a suitable polymerization catalyst, to form the polyphenylene ether resin. Resins prepared by this process can be blended with one or more other materials, such as alkenyl aromatic resins, elastomers, polyamides, and combinations thereof.
Still another embodiment of this invention is directed to a catalyst composition, comprising a magnesium reagent and at least one filler, wherein the level of chlorides in the magnesium reagent is less than about 250 ppm, and the level of calcium in the magnesium reagent is less than about 2500 ppm.
Other details regarding the various embodiments of this invention are provided below.
DETAILED DESCRIPTION
As mentioned above, a magnesium reagent is the primary component of the catalyst composition. Any magnesium reagent which yields magnesium oxide can be used. The preferred reagents are magnesium oxide, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, and mixtures of any of the foregoing. The magnesium reagent is in the form of a powder. The average particle size for the powder is usually in the range of about 5 microns to about 50 microns.
There often appears to be a difference in reagent particle shape for the present invention, as compared to reagent particles of the prior art. For example, substantially all of the partic
Devanathan Narsi
Watson Beth A.
General Electric Comapany
Truong Duc
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