Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1987-07-29
1989-07-11
Hruskoci, Peter
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210641, 210651, 2101952, 21032169, 21032189, 210425, B01D 1301
Patent
active
048469769
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to the treatment of emulsions particularly those containing an anionic surface active agent or detergent.
For the sake of convenience, the invention will be described in relation to the separation of oil from maritime oil emulsions. However, it is to be understood that the invention is not limited thereto as it may be used to treat other emulsions such as those occuring in oil production as well as industrial cooling and cutting solutions and laundry and car wash wastes.
BACKGROUND ART
Maritime oil emulsions are usually present in ballast tanks and bilges of ships. Various proposals have been put forward for separating the water from the oil and if the residual water is to be reused or disposed of in sewers or waterways, the degree of oil removal must be such that the residual water contains less than 10 parts per million of hydrocarbon oil.
The "Oil/Water Separation State-of-the-Art" publication prepared for Industrial Environment Research Laboratories in Cincinnati, Ohio by Rutgers State University, New Brunswick, N.J., United States Department of Commerce National Technical Information Service P.B. - 280755 is a thorough review of the problem and of updated separation procedures.
Few known procedures are successful when the oil emulsion is stabilised by a detergent especially when the maximum allowable oil content of the separated water is 10 parts per million. Complex chemical, physical and biological methods, often all three in sequence, are needed if the water must also meet rigid environmental specifications for detergents.
Oil/water/detergent blends are found in ship bilges and ballast tanks. The detergent can enter the ship system from deck cleaners, oil dispersers, laundry wastes, fire foams and deliberate addition to aid cleaning of oil storage tanks. Moreover, a detergent is an essential ingredient of industrial cutting and cooling emulsions and associated rinsing liquors, used to repair marine engines.
In all these uses, the detergent concentration and the chemical nature of the detergent are very variable due to sporadic need or uncontrolled dilution with fresh or salt water.
Ship requirements indicate the need for an on-board system so that water, substantially free of oil, but still containing biodegradable detergents can be released at sea, rather than be brought to shore where dockside water often cannot accept the detergents and other soluble contaminants which may arise from chemical and biological attack on the oil in the bilges. For example, poisonous hydrogen sulphide may be formed and, if so, needs immediate removal along with other soluble biological products while still at sea.
Recently, ultra-filtration has been used with limited success for these detergent stabilised emulsions. In principle, the oil is retained by its inability to flow through the very fine hydrophilic pores of the ultra-filter membrane whilst water passes under quite low pressure. The oil retention is by a combination of geometry and surface tension. The oil breakthrough pressure, P, is given by: ##EQU1## where: s is the oil/aqueous continuous phase interfacial tension, port wall,
Detergents lower the oil/aqueous interfacial tension s and cause breakthrough of oil at even low pressures. The interaction is complex since the detergent forms micellar structures with itself and with the oil. The critical micellar concentration depends on surfactant composition, on pH, on salts and on temperature. Special problems of anionic detergents in sea water are detailed later.
A major problem with all oil/water ultrafilters arises because they are used in the "cross-flow" mode--that is, the feed flows across the ultrafilter where some water permeates, but most of the emulsion (now richer in oil) returns to the feed. Thus, the feed oil concentration continuously rises which always reduces permeation rate but this is not the worst effect. Most ultrafilters also show some rejection of soluble anionic detergent so that the detergent concentration also rises rapidly in the diminishing
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Hruskoci Peter
Memtec Limited
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