Continuous precipitation

Using the following assumptions, the SFM will be applied to continuous precipitation (Zauner and Jones, 2000b) ... 

Attarian, C., Baker, C.G. and Svrcek, W.Y., 1976. pH control of a continuous precipitator. Canadian Journal of Chemical Engineering, 54, 606-611. 

Chakraborty, D. and Bhatia, S.K., 1996a. Fomiation and aggregation of polymorphs in continuous precipitation. 1. Mathematical modelling. Industrial and Engineering Chemistry Research, 35, 1985-1994. 

Hostomsky, J. and Jones, A.G., 1991. Calcium carbonate crystallization kinetics, agglomeration and fomi during continuous precipitation from solution. Journal of Physics D Applied Physics, 24, 165-170. 

The structures and phase transformations observed in steels have been dealt with in some detail not only because of the great practical importance of steels, but also because reactions similar to those occurring in steels are also observed in many other alloy systems. In particular, diifusionless transformations (austenite -> martensite), continuous precipitation (austenite -> pearlite) and discontinuous precipitation (austenite -> bainite and tempering of martensite) are fairly common in other alloy systems. 

Perhaps the most challenging reactor design problem is the design of the continuous precipitation polymerization reactor. Although several patents (45,46,47) are concerned with this problem, the topic has been generally neglected in the reactor-... 

However, since virtually no published data are available on the mechanism of continuous particle formation and growth, particlarly under the influence of mechanical agitation, continuous precipitation polymerization remains a vast engineering wilderness waiting for experimental and theoretical explorations. 

On the other hand, very little is known about the mechanism of continuous precipitation polymerization. In particular, the mechanism of continuous particle formation and growth and the effects of starvation feeding on reaction rate and copolymer composition are areas of particular interest. 

Fig. 1 shows the reactor setup used for continuous precipitation of lanthanum phosphate. A tube made of silicone rubber was used as a reactor. The inner diameter of the reactor tube... 

Polysaccharide formation may be endocellular, exocellular or capsular. The polysaccharide is usually a normal metabolic product, frequently a major product. Isolation and purification of a bacterial polysaccharide generally involve continued precipitations from a buffered solution, together with electrodialysis or ultrafiltration. 

Calcitic oolite A pavement of calcitic ooids formed by continuing precipitation of calcium carbonate between the calcitic ooids. 

Precipitation of the coating from aqueous solutions onto the suspended Ti02 particles. Batch processes in stirred tanks are preferred various compounds are deposited one after the other under optimum conditions. There is a very extensive patent literature on this subject. Continuous precipitation is sometimes used in mixing lines or cascades of stirred tanks. Coatings of widely differing compounds are produced in a variety of sequences. The most common are oxides, oxide hydrates, silicates, and/or phosphates of titanium, zirconium, silicon, and aluminum. For special applications, boron, tin, zinc, cerium, manganese, antimony, or vanadium compounds can be used [2.40], [2.41],... 

Copolymers Prepared with Benzene. Copolymers prepared with benzene (0.25 part) or small quantities of dichloroethane (<0.25 part) show continuous precipitation above n = 10. For polymerization with benzene, vinyl chloride content of the fraction is always about 51-53.5% compared with a mean value of 52.4 for the sample. How can we explain this ... 

Concerning aggregation kinetics and stabilization it was found in case of barium sulfate that barium ions adsorb more readily than sulfate ions [11], Thus, increasing the ratio R of barium to sulfate ions in the educt composition and thereby increasing the excess of barium ions after precipitation leads to high surface potentials and stabilization. Fig. 5 shows measured particle size distributions of continuously precipitated barium sulfate, measured based on quasi-elastic fight scattering (UPA 150 by Microtrac) within 3 min after pie-... 

Oxygen liberation is thought to be initiated by the presence of a large quantity of sulphate ions in the solution. In order to prevent an unduly high concentration of sulphate ions during electrolysis a low concentration level is maintained by their continuous precipitation by means of barium chloride. 

Hitt, J., et al. (2002), Nanoparticles of poorly water soluble drugs made via a continuous precipitation process, in Proceedings, American Association of Pharmaceutical Scientists, annual meeting, Toronto. 

Recently, Charpentier et al. [36] demonstrated the synthesis of PVDF by a continuous precipitation polymerization in SCCO2, using diethyl per-oxydicarbonate (DEPDC) as an initiator. Low molecular weight polymers (Mjj<20,000 g/mol) were reported in this first work. However, subsequent research has yielded PVDF with number-average molecular weights upwards of 79,000 g/mol [51,52]. PVDF made in the continuous CO2-based system had molecular weights comparable to commercial polymers, but also exhibited unique properties not observed in PVDF made by conventional processes. 

Precipitation of the coating from aqueous solutions onto the suspended Ti02 particles. Batch processes in stirred tanks are most common various compounds are deposited one after another under specific conditions. There are hundreds of patents on this subject. Continuous precipitation is sometimes... 

Figure 8. Accumulation of rafts (arrows) at a depth of about 28 meters below Browns Room in Devils Hole. Rafts have been cemented in place by continued precipitation of mammillary calcite. Thickness of bedrock block left of the arrow is about 15 cm.

Hitt, J.E. Curtis, C.A. Eransen, K.L. Kupperblatt, G.B. Rogers, T.X. Scherzer, B.D. Svenson, S. Tucker, C.J. Wilson, D.L. Young, T.J. Nanoparticles of poorly water, soluble drugs made via a continuous precipitation process. Poster, 2002 AAPS Annual meeting, Toronto, CA. (accessed Nov 2004). 

The special feature of Burger s process is the observation that after complete consumption of the bromofurfural, the formation of difurfural continues indefinitely. Thus, after a start with bromofurfural, a continuous addition of furfural results in a continuous precipitation of solid difurfural (melting point 264.5 C), which can be removed continuously by sedimentation or filtration. By contrast, if the process is started without the bromofurfural, no difurfural is formed. 

Feasibility studies of continuous precipitation of oxalates in the OPIX process. 

Continuous Precipitation of Actinide-Lanthanide Oxalates from HLLW... 

Figure 3. Equipment flowsheet for continuous precipitation of lanthanide oxalates...

Table II. Experimental Conditions and Results of Continuous Precipitation of Lanthanide Oxalates...

Four precipitated iron-based catalysts were used. The first catalyst consisted of only iron. The other catalysts contained either added potassium, added silicon or both. The catalysts were designated in terms of the atomic ratios as lOOFe, 100Fe/3.6Si, 100Fe/0.71K and 100Fe/3.6Si/0.71K. The catalysts were prepared by continuous precipitation from iron (111) nitrate and concentrated ammonium hydroxide. For silica-containing catalysts, a colloidal suspension of tetraethyl ortho silicate was mixed with the iron nitrate solution prior to precipitation. Potassium was added to the catalysts in the form of potassium tertiary butoxide during the loading of the FTS reactor. 

Dehydration with phenyl isocyanate afforded a more homogeneous product (still a mixture of isomers) of higher vitamin A activity. The reaction was carried out by treating a solution of 33 g. of (1) in 150 ml. of purified phenyl isocyanate with 2 ml. of 1.5M ethylmagnesium bromide as catalyst and stirring the mixture at 95° for 3 hrs., during which time diphenylurea continuously precipitated (in the absence of catalyst no significant amount of diphenylurea was observed). 

Additionally, the pellicle modulates the process of mineral precipitation at the enamel surface. Saliva is supersaturated with respect to calcium and phosphate ions and provides the potential for remineralisation of the demineralised enamel surface. In the absence of the pellicle, calcium phosphate salts would continuously precipitate on the enamel surface [100]. Acidic PRPs reveal a high affinity for hydroxyapatite and are obligate components of the in vivo-formed pellicle layer [9, 10]. These pellicle proteins can act as inhibitors for surface-induced precipitation of calcium salts onto the enamel [101, 102], thus providing mineral homeostasis at the enamel-saliva interface. 

The only possibility to limit the steadily increasing back pressure caused by the continuing precipitation of silver chloride in the suppressor column was to cut off the exhausted part of the cartridge after some days of operation. 

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