Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Water – sewage – or other waste water
Reexamination Certificate
1999-08-09
2001-04-17
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Water, sewage, or other waste water
C205S748000, C205S688000, C204S522000, C204S537000
Reexamination Certificate
active
06217743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for recovering organic hydroxides from waste solutions. In particular, the invention relates to a process for recovering organic hydroxides using a metal ion scavenger and an electrochemical cell.
2. Description of the Related Art
Quaternary ammonium hydroxides such as tetramethylammonium hydroxide (TMAH) and tetraethylammonium hydroxide (TEAH) are strong organic bases that have been known for many years. Such quaternary ammonium hydroxides have found a variety of uses including use as a titrant for acids in organic solvents and as a supporting electrolyte in polarography. Aqueous solutions of quaternary ammonium hydroxides, particularly TMAH solutions, have 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.
However, waste developer contains impurities including ionic impurities and nonionic impurities. Ionic impurities include cations such as sodium, potassium, zinc 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.
SUMMARY OF THE INVENTION
In one embodiment, the present invention relates to a process for recovering an onium compound from waste solutions or synthetic solutions containing the onium compound and impurities including the steps: contacting the waste solution or synthetic solution with a metal ion scavenger to remove metal ion impurities, wherein the metal ion scavenger comprises at least one of a chelating compound, a nanoporous material, and a magnetically assisted chemical separation (MACS) material; charging the waste solution or synthetic solution to an electrochemical cell containing at least two compartments, a cathode, an anode and a divider and passing a current through the cell whereby the onium compound is regenerated or produced; and recovering the onium compound from the cell.
In another embodiment, the present invention relates to a process for recovering onium hydroxide from waste solutions or synthetic solutions containing the onium hydroxide and impurities including metal ion impurities including the steps: contacting the waste solution or synthetic solution with at least one of a chelating compound, a nanoporous material, and a MACS material thereby decreasing the amount of metal ion impurities in the waste solution or synthetic solution; charging the waste solution or synthetic solution to an electrochemical cell containing at least two compartments, a cathode, an anode and a cation selective membrane and passing a current through the cell whereby onium ions pass through the cation selective membrane and onium hydroxide is regenerated or produced; and recovering the onium hydroxide from the cell.
In yet another embodiment, the present invention relates to a process for recovering an onium compound from waste solutions or synthetic solutions containing the onium compound and impurities including metal ion impurities including the steps: charging the waste solution or synthetic solution to an electrochemical cell containing at least two compartments, a cathode, an anode and a divider and passing a current through the cell whereby onium ions pass through the divider and the onium compound is regenerated or produced; recovering an onium compound solution from the cell; contacting the onium compound solution with a metal ion scavenger to remove metal ion impurities, wherein the metal ion scavenger comprises at least one of a chelating compound, a nanoporous material, and a MACS material; and recovering the onium compound.
In still yet another embodiment, the present invention relates to a process for recovering onium hydroxide from waste solutions or synthetic solutions containing the onium hydroxide and impurities including metal ion impurities including the steps: charging the waste solution or synthetic solution to an electrochemical cell containing at least two compartments, a cathode, an anode and a divider and passing a current through the cell whereby onium ions pass through the divider and onium hydroxide is regenerated or produced; recovering onium hydroxide solution from the cell; contacting the onium hydroxide solution with at least one of a chelating compound, a nanoporous material, and a MACS material to remove metal ion impurities; and recovering the onium hydroxide.
As a result of the processes of the claimed invention, recycled solutions of organic hydroxides and newly synthesized solutions of organic hydroxides and salts can be obtained in which the concentration and purity is increased. Recycling spent solutions of organic 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 organic hydroxides are removed from solution. Additionally, it is not necessary to store large amounts of chemicals. The relatively high concentration and purity of organic hydroxide solutions obtainable via the present invention can effectively be used in numerous applications where organic hydroxide solutions are required.
REFERENCES:
patent: 3402115 (1968-09-01), Campbell et al.
patent: 4714530 (1987-12-01), Hale et al.
patent: 4931155 (1990-06-01), Dutcher et al.
pa
Lang Weilian
Moulton Roger D.
Tanner Allen
Benner, Otto, Boisselle & Sklar
Gorgos Kathryn
Parsons Thomas H
Sachem, Inc.
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