Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-08-25
2003-12-30
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S689000, C210S690000
Reexamination Certificate
active
06669850
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a purification process for removing impurities from a solution that is subsequently used for example in the fabrication of photoreceptors.
BACKGROUND OF THE INVENTION
Various polymers are used in bulk in forming the layers of a photoreceptor. Examples of polycarbonates, polycarbazoles, polyarylates, and copolyesters that are suitable for use in photoreceptors are discussed in Mishra et al., U.S. Pat. No. 5,607,802 and Bergfjord, Sr. et al., U.S. Pat. No. 5,686,215, the disclosures of which are totally incorporated herein by reference.
These polymers are sometimes contaminated with trace impurities that adversely affect the electrical characteristics of the resulting photoreceptors. The contaminated materials must then be discarded, returned to the supplier, or used for non-critical layers such as the anticurl layer. Sometimes, the trace impurities cannot be identified, or if amenable to identification, the identification process may be costly. Thus, there is a need, which the present invention addresses, for a relatively inexpensive process to purify those polymers that are used in fabricating a photoreceptor. Of course, the polymers described herein can be used for other purposes and in embodiments of the present invention, these polymers as well as the instant purification process are not limited to the field of photoreceptors.
The present purification process involves the use of an adsorbent such as alumina or magnesium sulfate. A number of known uses of alumina and magnesium sulfate are described in “Reagents for Organic Synthesis,” Louis F. Fieser and Mary Fieser, John Wiley and Sons, New York (1967), pp.19, 20 and 634.
A conventional purification technique is disclosed in Sando et al., U.S. Pat. No. 5,180,497.
SUMMARY OF THE INVENTION
The present invention is accomplished in embodiments by providing a purification process comprising: contacting a contaminated composition comprised of an optional fluid, a polymer, and an impurity with an adsorbent composition including an adsorbent, wherein the adsorbent is selected from the group consisting of an alumina and a magnesium sulfate, wherein a portion of the impurity binds to the adsorbent, wherein the polymer is a polycarbonate, a carbazole, a polyarylate, or a copolyester having the formula
where n is the degree of polymerization.
DETAILED DESCRIPTION
The present purification process involves contacting the contaminated composition with the adsorbent composition. In one embodiment, the contaminated composition is passed through a column packed with the adsorbent composition where at least a portion of the impurity binds to the adsorbent in the column. After passing through the column, the purified solution is substantially or totally free of any impurity. Anhydrous magnesium sulfate was obtained as a fine powder from Fisher Scientific Company with the catalog number M65-500. Neutral alumina (activity 1) was obtained 29 from Aldrich Chemical Company (catalog number
19,997-4
) with a reported mesh size of 150 (58 Angstroms), a surface area of 155 meters
2
per gram, and with a pH 7.0 (+/−0.5) as an aqueous dispersion. Similarly, activated acidic alumina (Aldrich, catalog number 19,996-6) with a pH 4.5 (+/−0.5) as an aqueous dispersion, and activated basic alumina (Aldrich catalog number 19,944-3) with a pH 9.5 (+/−0.5) as an aqueous dispersion, were obtained with comparable mesh size and surface areas. Alternatively, suitable Woelm acidic and basic aluminas were obtained from ICN Pharmaceuticals, Inc., Life Sciences Group, 26201 Miles Road, Cleveland, Ohio 44128, or Waters Associates, 61 Fountain St., Farmington, Mass. 01701. The use of a column is preferred with the alumina.
Using any of the purification processes described herein, the contaminated composition contacts the adsorbent composition for a time effective for binding a significant portion of the impurity to the adsorbent, preferably at least about 30 minutes, more preferably at least about 4 hours, and especially for a time ranging from about 4 hours to about 16 hours. An optional vacuum may be applied to the contaminated composition during the purification process.
In another embodiment, one forms a slurry of the contaminated composition and the adsorbent composition, thereby resulting in a liquid portion and a solids portion in the slurry, and then separating the liquid portion from the solids portion by for example centrifuging or filtering. At least a portion of the impurity binds to the adsorbent where the impurity and the adsorbent are found in the solids portion. After separation of the liquid portion from the solids portion of the slurry, the liquid portion is substantially or totally free of any impurity.
In embodiments of the present invention, either the contaminated composition, the adsorbent composition, or both may contain a fluid. The fluid in the contaminated composition may be the same or different from the fluid in the adsorbent composition. The fluid in the contaminated composition is preferably a solvent for the polymer such as one or more of the organic liquids described herein. The fluids for the contaminated composition and the adsorbent composition may be an organic liquid such as chlorinated liquids like 1,1,2,2-tetrachloroethane, methylene chloride, and monochlorobenzene; toluene; tetrahydrofuran; polar aprotic liquids such as dimethyl formamide, dimethylacetamide, N-methylpyrrolidinone, and dimethylsulfoxide; water; or mixtures thereof. The preferred fluid for the adsorbent composition is water; magnesium sulfate is soluble in the water, whereas alumina is generally insoluble in water and in many other liquids. The fluid in the adsorbent composition may be a solvent for the polymer.
The contaminated composition may be composed entirely of the polymer and the impurity. If a fluid is present, the amount of polymer in the contaminated composition ranges for example from about 1 to about 50 weight percent, preferably from about 5 to about 20 weight percent, based on the weight of the contaminated composition.
The adsorbent composition may be composed entirely of the adsorbent. If a fluid is present, the amount of adsorbent in the adsorbent composition ranges for example from about 10 to about 95 weight percent, preferably from about 20 to about 70 weight percent, based on the weight of the adsorbent composition.
The anhydrous magnesium sulfate used was a fine powder and was used as received from Fisher Scientific. Because impurity levels are so low (parts per million or less), it is not known how much adsorbent is actually required. Typically, between about 50 and 100 weight percent magnesium sulfate, based on the weight of resin in solution, was used. However, the most important factor in the removal of the impurity is the time of contact between the adsorbent and the polymer in solution. For example, when polycarbonate (50 grams), contaminated with about 10 parts per million of polyethylene oxide (PEO, Scientific Polymer Products catalog number 491, with 7,000 molecular weight), at 10 weight percent solids in methylene chloride, was stirred with 50 grams of magnesium sulfate for about 10 minutes and then the dispersion was rapidly filtered through a sintered glass funnel, the PEO contaminant was not removed, as determined by xerographic testing of photoreceptor devices made with the material. When the same experiment was repeated except that the magnesium sulfate treatment time with the polymer solution was extended to 4 hours, the PEO impurity was completely removed as determined by xerographic testing. Thus, about 10 minutes contact between the magnesium sulfate and the polymer solution may be inadequate, whereas about four hours contact, and preferably about 16 hours contact, was satisfactory to remove all the PEO impurity (to less than 1 part per billion). The slurry method is preferred for the magnesium sulfate for adsorptive filtration and removal of impurities. The magnesium sulfate contained not only polyethylene oxide but also trace amounts of othe
Carmichael Kathleen M.
Crandall Raymond K.
Fuller Timothy J.
Kaplan Samuel
Maty David J.
Cintins Ivars
Soong Zosan S.
Xerox Corporation
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