Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1993-09-10
1995-07-25
McCarthy, Neil
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210737, 210748, 210774, 252330, 252346, 252348, C02F 136, C02F 148, B01D 1705
Patent
active
054359201
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of separating emulsions, dispersions or the like in a floating organic and an aqueous phase.
The invention is capable of use for all emulsions, suspensions and dispersions, such as arise in the partial de-ratting (fat removal) production of food stuffs, in waste water from the production and treatment of dyes and lacquers, the manufacture of leather and textiles, as well as in the pharmaceutical and cosmetic industries.
Oil-in-water emulsions are employed in metal machining as combined coolants and lubricants. In such a use the stability of these emulsions represents an important criterion for their usefulness. Mostly compositions of anionic and non-ionic tensides serve as the emulsifying agents. In the course of use foreign materials such as dirt and bacteria enter the emulsions, altering their characteristics and rendering them unusable. After which the emulsion must be passed for re-treatment.
Herein most cases attempts are made by separating the emulsion into an oil phase and a water phase, to reduce the quantity to be re-treated. In the separation one can distinguish basically between physical methods (adsorption), thermal methods (combustion, heating, vapourising), chemical methods (acid separation, salt separation, separation by organic polymers), electro-chemical methods (formation of hydroxides of multi-valent metals from sacrificial anodes) and mechanical methods (centrifuging, flotation, filtering through membranes).
Of these methods, some are excluded with regard to their possible employment for the separation of the emulsion of the very stable coolant/lubricant currently in use in the machining of metals. Amongst these are physical methods such as adsorption as well as mechanical methods of centrifuging and flotation. Amongst the thermal methods only vaporisation is found to be capable of use, but it is not practical because of the very high energy requirements and the incrustation problems which arise, whereas in the case of stable emulsions, simple heating does not lead to separation. Combustion is impossible on account of the resulting "steam distillation".
The separation of emulsions by the use of acids or salts does not succeed with all emulsions. Quite apart from the costs involved for the chemicals required, a chief disadvantage is the high salt content arising in the waste water on neutralisation. It is true that the waste water situation is found to be free of problems when the chemical separation of the emulsions is performed by means of very expensive polyelectrolytes.
A modification of the chemical methods is represented by the electro-chemical methods, in which emulsion-separating hydroxide flakes or precipitates are produced by the anodic solution of multi-valent metals, chiefly iron and aluminium. By this process, which is also really expensive, contamination of the waste water by salts is largely avoided. All the same a drawback is the quantity of aqueous sludges produced.
In recent times electrical methods have been proposed, but their usefulness in practice has still not been tested.
Amongst the mechanical methods the filtration by membranes has become established in recent years. Whilst without auxiliary means a filtrate which is capable of use is produced, the retained portion can however only be concentrated to an oil content of about 40%.
It is the aim of the present invention to find a method by which the spent coolant/lubricant, but also other emulsions, dispersions and suspensions, can be separated in an environmentally acceptable manner, with minimum outlay on auxiliary means, and can be recycled for further use.
This problem is solved according to the invention in that the emulsion, which apart from auxiliary means comprises substantially oil, water and an anionic emulsifier or a combination of emulsifiers of anionic and non-ionic tensides, is either saturated with carbon dioxide under pressure or exposed to water containing carbonic acid and is separated by subsequent slow heating and/or cooling into an organic and an aqueous phase.
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