Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1994-10-06
1996-11-05
Nessler, Cynthia L.
Liquid purification or separation
Processes
Ion exchange or selective sorption
210668, 210669, 210683, 210686, 210687, 210750, 210759, 210763, 210766, 210900, 210915, C02F 142
Patent
active
055714196
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of producing pure water (deionized water including ultrapure water) and, more particularly, to a method of producing ultrapure water which can greatly reduce TOC (total organic carbon) in the pure water than a conventional method.
BACKGROUND ART
I. A conventional water purifying apparatus for producing ultrapure water from raw water such as city water, well water and industrial water is composed of a pretreatment equipment, a primary pure water equipment and secondary pure water equipment. The pretreatment equipment is composed of coagulation, floatation and filtration units. The primary pure water equipment is composed of two reverse osmosis membrane units and a mixed bed ion exchange unit, or a demineralization equipment and a reverse osmosis membrane unit. The secondary pure water equipment is composed of a low pressure mercury ultraviolet oxidization unit, a demineralization equipment and an ultrafilter (ultrafiltration membrane separation device).
Either the following process (i) or (ii) is adopted. reverse osmosis membrane unit.fwdarw.second reverse osmosis membranes unit.fwdarw.mixed bed ion exchange unit.fwdarw.primary ;pure water storage tank.fwdarw.low pressure mercury ultraviolet oxidization unit.fwdarw.demineralization equipment.fwdarw.ultrafilter.fwdarw. exchange equipment [two-bed three-tower type (cation exchange tower.fwdarw.vacuum degas tower or decarbonation tower.fwdarw.anion exchange tower) or four-bed five tower type (first cation exchange tower.fwdarw.second anion exchange tower.fwdarw.vacuum degas tower or decarbonation tower.fwdarw.second cation exchange tower.fwdarw.second anion exchange tower )].fwdarw.reverse osmosis membrane unit.fwdarw.primary pure water storage tank.fwdarw.low pressure mercury ultraviolet oxidization unit.fwdarw.mixed bed ion exchange unit.fwdarw.ultrafilter.fwdarw.ultrapure water
The above deminerlization equipment comprises an anion exchange column, a mixed bed ion exchange column or an anion exchange column and a mixed bed ion exchange column which are arranged in series.
Among these units and equipments, the reverse osmosis membrane units, the demineralization equipment and the low pressure mercury ultraviolet oxidization unit reduce the TOC components in raw water by separation, adsorption, decomposition or the like.
TOC reducing-mechanisms of these units or equipmemts are as follows.
Reverse osmosis membrane unit: Raw water is filtered through a reverse osmosis membrane so as to remove ionic and colloidal TOC.
Low pressure mercury oxidization unit: TOC is decomposed into an organic acid and further into CO.sub.2 by ultraviolet of 185 nm projected from a low pressure mercury ultraviolet lamp. The organic acid produced is removed by an ion exchange resin provided at a subsequent stage. This mechanism is used especially for the decomposition of a volatile organic matter.
The ultrapure water produced by the above-described conventional pure water apparatus, however, still contains about 3 to 5 ppb of TOC.
In order to further reduce the TOC in ultrapure water, the ultrapure water may be treated by a multiplicity of stages of reverse osmosis membrane units and an increase in irradiation of a low pressure mercury ultraviolet unit be considered. It has been confirmed, however, as a result of the studies undertaken by the inventors that neither can further reduce the TOC in ultrapure water because of the following reasons.
Raw water contains a urea component as one of the TOC components. Since the urea component is nonionic, the urea component is impossible to be removed by ion exchange. The urea component is removed at a low rate by a reverse osmosis membrane separation. For example, the urea component removal rate by a high salt rejection type reverse osmosis membrane unit, which is generally used as one of the two reverse osmosis membrane units in a primary pure water purifying equipment is about 60%. In addition, urea cannot be decomposed by a low pressure mercury ultraviolet oxidization unit.
Raw
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Kurobe Hiroshi
Obata Yoshinobu
Orita Nobuhiro
Kurita Water Insustries Ltd.
Nessler Cynthia L.
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