Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-03-05
2001-03-06
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S096000, C095S230000
Reexamination Certificate
active
06197091
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of ozone, and more particularly to the production of ozone by ozonizing oxygen and recycling unreacted oxygen to the ozone generator.
BACKGROUND OF THE INVENTION
Ozone is a very useful agent for destroying harmful or undesirable chemical compounds and microbiological agents found in fluids such as drinking water, aqueous sewage, air and waste gases, etc. It accomplishes this by, for example, oxidizing such chemical compounds to harmless or less undesirable compounds and oxidizing or lysing the microbiological agents, thereby destroying them. Ozone is generally produced on a commercial scale by subjecting substantially pure oxygen to a high voltage discharge, which causes some of the oxygen to be converted to ozone. Conventional ozone generators produce a product stream containing about 10% by weight ozone, which is satisfactory for many ozone applications. However, because the efficiency of some industrial ozone-based processes, such as waste water treatment and pulp and paper bleaching operations, is directly proportional to the concentration of ozone in the treatment gas fed to the processes, there is a demand for equipment that can produce ozone product gases which contain higher ozone concentrations than do currently available ozone gas products. In response to this demand, equipment manufacturers have made improvements in ozone generators which make it possible to make ozone product gas containing up to about 14% by weight ozone. However, the improved ozone generators are considerably more costly to operate than are earlier ozone generators, since the improved generators consume significantly more power than do the earlier generators.
Waste water treatment and paper and pulp plant operators would like to have available ozone generating equipment that can produce ozone gas products containing up to 20% by weight or more ozone, but equipment having such capability is not currently available. Furthermore, even if such equipment were available, it would be prohibitively expensive to operate because of the very high power consumption that would be required to produce ozone gas of this quality.
Because of the continuing need for product gas containing high concentrations of ozone, techniques other than increasing the effectiveness of ozone generators per se have been investigated. For example, attempts have been made to increase the ozone concentration of generated ozone-oxygen gas mixtures by removing oxygen from the gas stream. One procedure that has been tried involves subjecting the gas stream to adsorptive separation. Ozone is generally more strongly adsorbed by adsorbent materials than is oxygen and thus it can be readily separated from oxygen by adsorption-based processes. However the sorbed ozone component cannot be recovered from the adsorption equipment until the adsorbent regeneration phase of the separation process. Since ozone is highly unstable, it is difficult or impossible to recover the ozone product stream from the adsorption equipment without some decomposition of the ozone. A further complication of ozone-oxygen adsorptive separation processes is the fact that some adsorbents actually catalyze the decomposition of ozone.
The present invention provides an efficient and effective method of increasing the ozone concentration of generated ozone-oxygen gas mixtures without significantly raising the cost of producing the gas mixtures. It accomplishes this by ozonizing a stream of oxygen to produce an ozone-oxygen mixture, then separating ozone from oxygen using an ozone-selective membrane, and finally recycling nonpermeated oxygen to the ozone generator. Additional advantages provided by the invention are that the size of downstream equipment can be reduced, and the efficiency of fluid treatment processes is enhanced by use of the ozone-enriched product gas of the invention in fluid treatment processes.
U.S. Pat. No. 5,507,957 discloses an ozone generating system in which oxygen is separated from air in an adsorption vessel and the separated oxygen is subjected to ozonization to produce an ozone-containing stream, which is recycled to the adsorption vessel. Ozone in the recycle stream is adsorbed by a preliminary bed of adsorbent and the oxygen contained in the recycle stream, passes through the preliminary adsorbent and is recycled to the ozonizer. The ozone is recovered during the adsorbent regeneration step.
U.S. Pat. No. 5,756,054 discloses an ozone generating system in which liquid oxygen from a cryogenic oxygen source is subjected to ozonization to produce an ozone-containing product gas, ozone is separated from the product gas by condensation and the gaseous oxygen fraction is recycled to the cryogenic oxygen source.
Shanbhag et al., “Membrane-Based Ozonization of Organic Compounds”, Ind. Eng. Chem. Res., vol. 37, 1998, pp. 4388-4398 describes the ozonation of water which contains organic pollutants by contacting a silicone membrane with an ozone-oxygen gas mixture. Ozone from the gas mixture passes through the membrane and contacts the pollutant-containing water on the permeate side of the membrane.
SUMMARY OF THE INVENTION
The system of the invention comprises an ozone generator and a fluid treatment unit which contains an ozone-permeable membrane. Oxygen is fed into the ozone generator to produce an ozone-containing gas. The ozone-containing gas is introduced into the feed side of the fluid treatment unit wherein some or all of the ozone contained in the gas permeates through the membrane. The oxygen-enriched gas that remains in the feed side of the membrane after depletion of ozone is optionally purified and recycled to the ozone generator as supplemental feed. In a preferred embodiment, a liquid or gas fluid stream which contains ozone-reactive substances is passed through the permeate side of the gas separator. Ozone passing through the membrane mixes with the impurity-containing liquid or gas and oxidizes the impurities to harmless or easily removable components.
Specifically, in a first broad embodiment, the invention comprises a process comprising the steps:
(a) passing an oxygen-containing gas through an ozone generator, thereby producing a gaseous product comprising ozone and oxygen;
(b) introducing the gaseous product into the feed zone of gas separation means comprising a feed zone and a permeate zone separated by at least one ozone-permeable membrane, thereby permeating an ozone-enriched stream through the membrane and into the permeate zone, and producing an oxygen-enriched stream in the feed zone; and
(c) recycling the oxygen-enriched stream to the ozone generator.
In a preferred embodiment the oxygen-containing gas is oxygen-enriched air or substantially pure oxygen. In a more preferred embodiment, the oxygen-containing gas is substantially pure oxygen.
According to another preferred embodiment, the process further comprises introducing a fluid stream into the permeate zone. In this preferred embodiment the fluid stream may contain one or more ozone-reactive substances.
In another preferred embodiment, the fluid stream is a liquid stream. In a more preferred embodiment, the fluid stream is an aqueous stream. In this preferred embodiment, the one or more ozone-reactive substances generally comprise organic compounds, microbiological agents or mixtures thereof. In one aspect of this preferred embodiment, the ozone-enriched stream enters the permeate zone in a manner such that it nondispersively mixes with the liquid stream in the permeate zone. In another aspect of this embodiment, the total pressure in the permeate zone is at least as great as the total pressure in the feed zone. The liquid stream may be an aqueous stream. The aqueous stream may be drinking water or wastewater. The aqueous stream may contain one or more ozone-reactive substances comprising organic compounds, microbiological agents or mixtures thereof.
In another preferred embodiment, the fluid stream is a gaseous stream. In this preferred embodiment, the oxygen partial pressure in the permeate zone is preferabl
Ferrell Robert James
Ji Wenchang
Sadkowski Piotr J.
Neida Philip H. Von
Pace Salvatore P.
Spitzer Robert H.
The BOC Group Inc.
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