Precipitation from a liquid

Sedimentation of a solid material (a precipitate) from a liquid solution in which the material is present in amounts greater than its solubility in the liquid. (Gold Book online, 1990 entry [2].)... 

Precipitation foam processes where a polymer phase is formed by polymerization or precipitation from a liquid which is later allowed to escape. 

Gallagher (1) studied the precipitation of the explosives cyclonite and nitroguanidine using high-pressure carbon dioxide as an anti-solvent to reduce solvent inclusion in the crystals. Later Chang studied the separation of p-carotene from carotene mixtures by precipitation from a liquid solution (2), as well as the purification of anthracene from crude anthracene by adding compressed CO2 (3), Carbon dioxide also proved to be a suitable anti-solvent for the fractionation of a mixture of organic acids (4) and for the formation of microparticulate particles of insulin (5). 

At low volume expansion, particles are being formed by precipitation from a liquid phase at the bottom of the precipitator. The liquid phase saturated with anti-solvent is formed as the result of vapor-liquid equilibrium at operating pressure and temperature. Under these conditions the... 

The best known examples are reactions in the liquid phase combined with evaporation of the main product, and reactions where the main product is precipitated from a liquid reaction mixture. 

A solid product is precipitated from a liquid or a gaseous reaction mixture. 

Solid products precipitated from a liquid or gaseous reaction mixture often have the form of fine particles, that have to be separated afterwards. There are many examples of precipitations from solutions, both in organic and inorganic chemistry. Such precipitations are often carried out in stirred reactors. Precipitations from gaseous mixtures are less conunon they may be carried out in tubular reactors or in fluidized bed reactors. 

As a consequence of this, from the fluid dynamic point of view, the use of solvent mixtures of EtOH and acetone caimot be used to alter the mixing behavior of the injected jet as it is case for example for using mixtures of DMSO and AC as published by De Marco et al. [18,38]. A manipulation of the final properties of SAS processed particles by either precipitating from a liquid phase, a transition phase or a single phase for the system EtOH/AC/C02 does not seem to be achievable by varying the solvent composition with respect to the jet behavior. 

Potassium heptafluorotantalate, K2TaF7, or as it is called by its commercial name K-salt, is a starting material for tantalum metal production. K-salt is produced by adding potassium fluoride, KF, or potassium chloride, KC1, to a tantalum strip solution that results from a liquid-liquid extraction process. In order to prevent hydrolysis and co-precipitation of potassium oxyfluoro-tantalate, a small excess of HF is added to the solution [24]. Another way to avoid the possible formation and co-precipitation of oxyfluoride phases is to use potassium hydrofluoride, KHF2, as a potassium-containing agent. The yield of the precipitation depends mostly on the concentration of the potassium-containing salt and is independent of the HF concentration [535]. 

In some circumstances, separation of solid from a liquid is better achieved by use of a centrifuge than by filtration, and a small, electrically driven centrifuge is a useful piece of equipment for an analytical laboratory. It may be employed for removing the mother liquor from recrystallised salts, for collecting difficultly filterable precipitates, and for the washing of certain precipitates by decantation. It is particularly useful when small quantities of solids are involved centrifuging, followed by decantation and re-centrifuging, avoids transference losses and yields the solid phase in a compact form. Another valuable application is for the separation of two immiscible phases. 

Rapping Except when liquid dispersoids are being collected or, in the case of film precipitators, when a liquid is circulated over the collecting-electrode surface (Fig. 17-72), thus continuously removing the precipitated material, the collected dust is dislodged from the... 

Figure 11J7. (a) Calculated phase diagram for Ti-Be showing liquidus for the metastable compound TiBe and (b) calculated TTT curves for the precipitation of TiBe and TiBcj from a liquid Ti-40Be (at%) alloy (Saunders er al. 1985). 

Diammino-cupric Chloride, [Cu(NII3)2]C12, is obtained by heating the higher ammino-derivatives to 150° C. or less, or by the action of ammonia on a concentrated solution of cupric chloride, when the diammine is gradually precipitated from the liquid.4... 

Coordinated Phosphate Method. In this method of treatment, no free caustic is maintained in the boiler water. Fig. 10 shows the phosphate concentration versus die resulting pH when trisodium phosphate is dissolved in water. Recent laboratory tests show that the crystals which precipitate from a concentrated solution of trisodium phosphate at elevated temperatures contain disodium phosphate and that the supernatant liquid is rich in sodium hydroxide. The sodium hydroxide can destroy the magnetite protective film on boiler surfaces. To assure that no free caustic is present, a boiler-water phosphate concentration thal corresponds Lo a sodium-lo-phosphate mole-ratio of 2.6 is recommended above 1000 psi (68 atm), as... 

The methods most commonly used for preparing catalysts are precipitation (Section A 2 1 3) and impregnation (Section A 2 2 1 1) In both of them, the catalyti cally active material is transferred from a liquid phase, usually an aqueous solution, to a solid By contrast, other catalysts are obtained from solid precursors Solid state reactions, namely solid-to-solid reactions in which both the starting material (the catalyst precursor) and the catalyst are solids, offer convenient methods to prepare several industrial catalysts, especially those con taming two or more metallic elements or their oxides The reason of the conspicuous efficiency of these methods to prepare phases containing two or several metallic elements is due to special features of solid-state reactions, compared to liquid-to-solid or gas-to-solid reactions This section briefly outlines these peculiarities and presents the most frequent types of solid-state processes used in preparing catalysts... 

Samples were taken from the precipitated bottom phase, the solvent phase, and the C02 vapour phase. The sampling procedure for the bottom phase depended on whether the precipitate was a liquid (triglyceride oil), solid (lecithin) or a mixture of both components. Samples of liquid bottom phase were withdrawn from valves V3 and V16 positioned at the base of the view cell, with valve VI shut. Valves V5, V6 and V2 were opened to ensure constant pressure inside the view cell during sampling. Samples of solid lecithin were recovered by first removing the solvent phase under pressure as above, followed by depressurization, and then solvent washing of the apparatus. Lecithin was retained on a filter placed above valve V3. For mixtures of lecithin and Soya oil, the two sampling procedures were combined. The Soya oil was first removed under pressure, followed by the solvent phase. The apparatus was then depressurized and solvent washed. Samples of the solvent phase at pressure were also taken via valve V4 and collection vessel CV3, to measure the C02 content, and the concentration of solute still in solution. 

A polymer/monomer (polymer/repeat-unit or polymer/macrocycle) switch may become of practical importance where a polymer decorated with certain groups has specific size-dependent properties that the monomeric units do not have. The modulation of the conversion between polymeric and monomeric (or macrocyclic) states would also result in the modulation of these properties. Moreover, such size switches, represented by polymerization/depolymerization processes that operate under the control of external events, are examples of environmentally-friendly recyclable polymers (reduction of waste treatment). As well, if the polymer has low solubility and the polymer/monomer switch can work in spite of this, then it becomes possible to reversibly generate a precipitating (solid) polymeric material from a liquid solution of monomer. 

Precipitation is usually understood as obtaining a solid from a liquid solution. In the production of precipitated catalysts, the first step is the mixing of two or more solutions or suspensions of materials, causing the precipitation of an amorphous or crystalline precipitate or gel. The wet solid is converted to the finished catalyst by filtration, washing, drying, forming, calcination and activation. Adjusting production conditions can vary cristallinity, particle size, porosity, and composition of the precipitate or gel. 

If the dye has been precipitated from a hot solution, it is usually desirable to filter and wash at higher temperatures also filtration is more rapid under these conditions, and the impurities are held in solution more completely. It is necessary to cool before filtration only if precipitation is incomplete in the hot solution. Washing is done with a salt solution corresponding in salt concentration and temperature to the mixture filtered. More complete removal of by-product dyes may be achieved if some soda solution is added to the wash liquid. If the product is still insulficiently freed from by-products, it must be purified by reprecipitation. For this purpose, the dye is dissolved in hot water, the solution is filtered if necessary and then salted out using about the same temperature and salt concentration as in the first precipitation. 

Polymers that form from the liquid phase may remain dissolved in the remaining monomer or solvent, or they may precipitate. Sometimes beads are formed and remain in suspension sometimes emulsions form. In some processes solid polymers precipitate from a fluidized gas phase. 

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