Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Patent
1998-06-10
2000-08-29
Warden, Jill
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
516 31, 10617301, 10616282, 8190, 252 891, B01F 1700, B01F 312, C08L 126, D06M 900
Patent
active
061109789
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to pastes, slurries and dispersions of powders in liquids and has particular connection with methods for the safe handling of powdered solids, more especially during the preparation of solutions of such substances.
It is often necessary to measure and control the flow of a powdered solid into a process step. It is known that some powders, in particular those containing a high proportion of fine particles, are readily dispersible in the atmosphere and can give problems of dust formation. This may be a particular problem with toxic substances. It is also known that some powdered solids are susceptible to ignition or detonation. It is further known that some powdered solids are difficult to handle, for example when metering using a screw feeder. It may be convenient to disperse a powder in a suitable liquid to form a paste, slurry or dispersion (all such solid/liquid mixtures being on occasion referred to hereinafter as dispersions) both for ease of storage and transport and to alleviate such problems. The liquid is often and conveniently a process liquid, for example either the solvent (if it is desired to form a solution of the solid) or some other liquid required in or after the process step into which the solid is to be introduced. In other cases, an inert liquid or a volatile liquid which can subsequently be removed from the process by evaporation may be used.
Some dispersions are difficult to form, because the solid is not readily wetted by the liquid. It is known to include wetting agents in a dispersion to alleviate this difficulty. Some dispersions are unstable, in that the solid and liquid phases tend to separate on storage or when the dispersion is subjected to shearing forces, for example during pumping. It is known to include dispersing agents in a dispersion to inhibit such separation. For example, aqueous dispersions of the textile auxiliary 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAHT) which contain a dispersing agent are described by D M Lewis et al. in Journal of the Society of Dyers and Colourists, Volume 111, January/February 1995, pages 12-18.
Nevertheless, there is always the risk that such dispersions may become dried out. This may happen for example with splashes or with residues in pipes and vessels. If this occurs, then any hazards associated with handling the dry powder can recur. It is an object of the invention to provide a means of guarding against such problems.
DISCLOSURE OF INVENTION
According to the invention there is provided a method of forming a solution of a solid in a solvent, including the steps of (1) forming a dispersion which comprises (a) a liquid, (b) the solid dispersed in powder form in the liquid and (c) a polymeric binder dissolved in the liquid, and (2) mixing the dispersion with the solvent under conditions such that the powder dissolves in the solvent.
The liquid is often a volatile liquid, and dispersions based on such liquids are liable to dry out. The liquid is often of low viscosity, for example up to about 10 mPa s (10 centipoise). Mixtures of liquids may be used. For many applications, the liquid may contain a major proportion of water or consist essentially of water, and in such cases the polymeric binder is a water-soluble polymer. Many water-soluble polymeric binders suitable for use in the invention are known in the art. Examples include cellulose ethers, for example carboxymethylcellulose and alkylcelluloses, linear polysaccharides such as sodium alginate, xanthan gum and guar gum, gelatin, poly(vinyl alcohol), poly(acrylamide) and polymers based on acrylic acid. The polymeric binder may be a film-forming polymer.
The liquid may be the same substance or mixture of substances as the solvent. In such a case it will be understood that additional solvent is required in step (2) of the method of the invention. It will be appreciated that in such a case the dispersion will contain both dissolved solid and dispersed powder. Such a dispersion can readily be diluted with further solvent to form a so
REFERENCES:
patent: 4978541 (1990-12-01), Stypula et al.
patent: 5310424 (1994-05-01), Taylor
patent: 5413631 (1995-05-01), Gray et al.
Lewis et al., "Level fast dyeing of wool with nucleophilic aminoalkyl dyes and crosslinking agents. Part 1--Using a trifunctional crosslinking agent", Journal of the Society of Dyers and Colourists, vol. 111, pp. 12-18, Jan. 1995.
Graveson Ian
Philip Kevin
Ross George Russell
Towlson David Stephen
Acordis Acetate Chemicals Limited
Cole Monique T.
Warden Jill
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