Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using disinfecting or sterilizing substance
Reexamination Certificate
1999-01-12
2001-12-18
Thornton, Krisanne (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using disinfecting or sterilizing substance
C099S495000, C422S001000, C422S031000, C422S033000, C422S041000, C422S048000, C422S256000, C422S905000, C426S330000, C426S424000, C426S425000
Reexamination Certificate
active
06331272
ABSTRACT:
TECHNICAL FIELD
This invention relates to the sterilization and preservation of liquids such as liquid foods for example and more particularly to methods and apparatus for inactivating microbes and/or enzymes in liquids by exposure of the liquids to dense carbon dioxide.
BACKGROUND OF THE INVENTION
Preservation of many liquids such as juices or other liquid foods or medicines requires killing of microbes, such as bacteria, viruses and spores, in the liquid. It may also be necessary to inactivate enzymes which can catalyze undesired reactions in the liquid. Pasteurization is the most commonly used process for the purpose. Pasteurization requires heating of the liquid to temperatures which can degrade the quality of the liquid. Heating of liquid foods for example can adversely affect the taste and nutritional quality of the food.
It has heretofore been recognized that liquids can be sterilized and preserved by contacting the liquids with pressurized dense CO
2
(carbon dioxide). The process does not require heating of the liquids to damaging temperatures. Prior processes and equipment for this purpose have not been ideally suited for commercial operation.
Some prior processes are static in that the dense CO
2
and liquid are simply allowed to stand together in a pressure vessel for a period of time. The production rate of treated liquid is undesirably low. Other prior processes are dynamic in that a forced dispersion of a flow of dense CO
2
into a flow of the liquid is brought about in a column which contains conventional packing such as rashig rings or a frit. Dispersive processes of this kind increase the production rate of treated liquid by creating a greater interfacial contact area between the dense CO
2
and liquid than is present in the static processes. A still greater interface area between the liquid and dense CO
2
, in a given volume of flow, would be advantageous.
Dispersive processes of the above discussed kind are also subject to other problems. For example, emulsification of the liquid and dense CO
2
can occur necessitating further steps to break the emulsion. Processing of liquids of certain densities may not be practical as a density difference between the liquid and dense CO
2
is needed in order to separate the two. Fouling of components within the processing vessel may occur if the liquid contains suspended particulate matter.
The present invention is directed to overcoming one or more of the problems discussed above.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a method for preserving a liquid by exposure of the liquid to pressurized dense carbon dioxide. Steps in the method include directing a flow of the liquid along a liquid flow path which extends along a first surface of a porous membrane and directing a flow of the dense carbon dioxide along a carbon dioxide flow path which extends along an opposite surface of the membrane including contacting the liquid and pressurized carbon dioxide at pores in the membrane. Further steps include recirculating the flow of dense carbon dioxide through the carbon dioxide flow path while maintaining the dense carbon dioxide in the pressurized state throughout the recirculation.
In another aspect of the invention, wherein the liquid has a constituent that is soluble in dense carbon dioxide and which becomes a solute in the dense carbon dioxide during passage of the carbon dioxide along the membrane, the method includes the further steps of establishing saturation of the dense carbon dioxide with the solute and maintaining saturation of the dense carbon dioxide with the solute during the recirculation of the dense carbon dioxide.
In another aspect the invention provides apparatus for preserving liquids by exposure of the liquids to pressurized dense carbon dioxide. Components of the apparatus include a membrane contactor having a liquid flow path and a carbon dioxide flow path therein. The flow paths are separated by porous membrane having pores which enable contact of a liquid flowing in the liquid flow path with carbon dioxide flowing in the carbon dioxide flow path. A liquid pressurizing pump has an outlet communicated with the membrane contactor to direct liquid into the liquid flow path. A dense carbon dioxide recirculation pump has an inlet communicated with the membrane contactor to receive pressurized dense carbon dioxide which flows out of the carbon dioxide flow path and has an outlet through which the pressurized dense carbon dioxide is returned to the carbon dioxide flow path.
In sill another aspect of the invention, the membrane contactor has a shell and a plurality of hollow fiber porous membranes extend in a generally parallel direction within the shell. One of the liquid flow path and the carbon dioxide flow path extends through the lumen regions of the hollow fiber porous membranes and the other of the flow paths extends along exterior surfaces of the hollow fiber porous membranes.
The invention enables nondispersive contacting of flows of a liquid and dense CO
2
in which the area of contact of the two flows in a given volume is far greater than in prior static or dispersive processes. The production rate of sterilized liquid is thereby increased. Emulsion formation does not occur as dispersion of the CO
2
flow into the liquid flow is not required. It is not necessary that there be a density difference between the liquid and dense CO
2
in order to separate the two. The invention does not require components which may be subject to fouling by suspended particulates in the liquid. The process can be run continuously and isobarically thereby saving energy and equipment costs.
The invention, together with further aspects and advantages thereof, may be further understood by reference to the following description of the preferred embodiment and by reference to the accompanying drawings.
REFERENCES:
patent: 5490884 (1996-02-01), Robinson et al.
Porocrit L.L.C.
Thornton Krisanne
Zimmerman Harris
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