Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Organic
Reexamination Certificate
1999-03-26
2001-03-27
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Organic
C204S524000, C204S533000
Reexamination Certificate
active
06207039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to processes for recovering onium hydroxides or onium salts from solutions containing onium compounds using electrochemical ion exchange techniques. In particular, the invention relates to processes for recovering one of onium hydroxides and onium salts from solutions containing onium hydroxides and/or onium salts using an electrochemical cell including at least one compartment containing an ion exchange material.
2. Description of the Related Art
Onium hydroxides, such as quaternary ammonium hydroxides including tetramethylammonium hydroxide (TMAH) and tetraethylammonium hydroxide (TEAH), are strong organic bases that have been known for many years. Quaternary ammonium hydroxides have found a variety of uses including use in zeolite manufacture and polymer manufacture. Aqueous solutions of quaternary ammonium hydroxides, particularly TMAH solutions, have also been used extensively as a developer for photoresists in printed circuit board and microelectronic chip fabrication. For a variety of reasons, it is desirable to minimize the overall amount of developer used in printed circuit board and microelectronic chip fabrication. One way to minimize the overall amount of hydroxide developer is to reuse the waste developer. Reusing developer reduces the amount lost and decreases disposal problems.
Waste developer contains impurities including ionic impurities and nonionic impurities. Ionic impurities include various metal cations such as sodium, potassium, zinc, nickel, aluminum, copper and calcium; and anions such as halides, nitrates, nitrites, carbonates, carboxylates, sulfates. Nonionic impurities include photoresists, surfactants, amines and numerous other organic molecules. Waste developer also contains relatively low concentrations of the hydroxide developer. Accordingly, there remains a continuing need to effectively recover hydroxide developer in a useable form so that it may be reused thereby minimizing the overall amount of developer used in printed circuit board and microelectronic chip fabrication.
U.S. Pat. No. 4,714,530 (Hale et al) describes an electrolytic process for preparing high purity quaternary ammonium hydroxides which utilizes a cell containing a catholyte compartment and an anolyte compartment separated by a cation-exchange membrane. The process comprises charging an aqueous solution of a quaternary ammonium hydroxide to the anolyte compartment, adding water to the catholyte compartment, and passing a direct current through the electrolysis cell to produce a higher purity quaternary ammonium hydroxide in the catholyte compartment which is subsequently recovered. The '530 patent also describes an improvement which comprises heating the quaternary ammonium hydroxide at an elevated temperature prior to charging the hydroxide to the anolyte compartment of the electrolytic cell.
U.S. Pat. No. 4,938,854 (Sharifian et al) also describes an electrolytic process for purifying quaternary ammonium hydroxides by lowering the latent halide content. The electrolytic cell may be divided into an anolyte compartment and a catholyte compartment by a divider which may be an anion or cation selective membrane. The cathode in the catholyte compartment comprises zinc, cadmium, tin, lead, copper or titanium, or alloys thereof, mercury or mercury amalgam.
Japanese Kokai Patent No. 60-131985 (1985) (Takahashi et al) describes a method of manufacturing a high purity quaternary ammonium hydroxide in an electrolysis cell which is divided into an anode chamber and a cathode chamber by a cation exchange membrane. A quaternary ammonium hydroxide solution containing impurities is charged to the anode chamber and a direct current is supplied between two electrodes after water has been charged to the cathode chamber. Purified quaternary ammonium hydroxide is obtained from the cathode chamber. The purified quaternary ammonium hydroxide contains reduced amounts of alkali metals, alkaline earth metals, anions, etc.
U.S. Pat. Nos. 5,439,564 and 5,545,309 (Shimizu et al) relate to methods of processing waste liquid containing an organic quaternary ammonium hydroxide by contacting the waste liquid with a cation-exchanging material, eluting organic quaternary ammonium cations from the cation-exchanging material, and electrolyzing the eluate in a two chamber electrolytic cell equipped with an anode, cathode and cation-exchanging membrane. Organic quaternary ammonium hydroxide is obtained from the cathode chamber of the electrolytic cell.
SUMMARY OF THE INVENTION
In one embodiment, the present invention relates to a process for recovering one of an onium hydroxide and an onium salt from a solution containing an onium compound involving the steps of charging the solution containing the onium compound to an electrochemical cell comprising at least two compartments, a cathode, an anode, and a divider, wherein at least one compartment comprises an ion exchange material; passing a current through the electrochemical cell whereby the onium hydroxide or the onium salt is produced; and recovering the onium hydroxide or the onium salt from the electrochemical cell.
In another embodiment, the present invention relates to a process for recovering one of an onium hydroxide and an onium salt from a solution containing an onium compound involving the steps of charging the solution containing the onium compound to an electrochemical cell comprising at least two compartments, a cathode, an anode, and a cation selective membrane, wherein at least one compartment comprises a cation exchange material; passing a current through the electrochemical cell whereby the onium hydroxide or the onium salt is produced; and recovering the onium hydroxide or the onium salt from the electrochemical cell.
In yet another embodiment, the present invention relates to a process for recovering a quaternary ammonium hydroxide from a solution containing a quaternary ammonium compound involving the steps of charging the solution containing the quaternary ammonium compound to an electrochemical cell comprising at least two compartments, a cathode, an anode, and a cation selective membrane, wherein at least one compartment comprises an ion exchange material; passing a current through the electrochemical cell whereby the quaternary ammonium hydroxide is regenerated; and recovering the quaternary ammonium hydroxide from the electrochemical cell.
As a result of the processes of the claimed invention, solutions of onium hydroxides can be obtained in which the concentration and purity is increased. Recycling spent solutions of onium hydroxides provides not only cost savings, but also environmental benefits by eliminating the need for synthesizing new hydroxide compound solutions and associated expensive purification processes and reducing the toxicity of waste solution effluents. An increased amount of water can be recovered after onium hydroxides are removed from solution. The relatively high concentration and purity of onium hydroxide solutions obtainable via the present invention can effectively be used in numerous applications where onium hydroxide solutions are required. Also as a result of the processes of the claimed invention, solutions of onium salts can be obtained in which the concentration and purity is increased.
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International Search Report mailed Jul. 1, 1999 for PCT Patent Application Serial No. PCT/US99/07672.
Hulme David R.
Moulton Roger D.
Gorgos Kathryn
Parsons Thomas H
Renner Otto Boisselle & Sklar
Sachem, Inc.
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