Secondary nucleation of two fast growth systems in a mixed suspension crystallizer: Magnesium sulfate and citric acid water systems

Abstract

MICHAEL E. PRUDlCHA solid/liquid separation process based on the transfer of hydrophobic coated mineral particles from a hydrocarbon to an aqueous phase is described. This process could be used, for example, to remove mineral matter from coal derived liquids in order to meet fuel specifications. A model system which involves hydrophobic, asphaltic, coated mineral matter particles in a model liquid, xylene, was used in conjunction with the mechanistic studies. The mineral matter distribution coefficient to the aqueous phase decreases rather than increases with time in batch experiments. Five asymptotic models based on the fate of the surface active chemical at long time are investigated. Included were adsorption on the mineral matter particle, adsorption at the oil/water interface, distribution of the surfactant to the aqueous phase, complete detergency, and partial detergency. Experimental data on the influence of surfactant concentration, contact time, water/oil ratio, and shear are consistent only with the partial detergency model. SCOPEAn extractive method is presented for the transfer of solid particles from one liquid stream to another. The process is based on the surface characteristics of the particle. Albertsson (1958, 1971) and Raghavan and Fuerstenau (1975) have previously demonstrated this process. This paper deals with the case where the particles are naturally wet by the original stream due to an acquired carbonaceous matter coating.An experimental system consisting of an oil phase (xylene), an aqueous phase (pH adjusted water), and composite particles is studied. A composite particle consists of a mineral matter core which is surrounded by a hydrophobic layer. The composite particles are obtained from a coal derived liquid. Particle removal from coal derived liquids is a potential application of this process. A surface active agent is used in order to promote particle transfer from the oil phase to the aqueous phase. The surfactant can function either by adsorbing onto the particle surface, making it hydrophilic, or by removing the hydrophobic coating (detergency), thereby exposing the more hydrophilic mineral matter surface. The liquid phases have been chosen so that the surface properties of the composite particles will dominate the experimental system.Five mechanistic models based on the fate of surfactant at long time are proposed. These include adsorption onto the composite particle, adsorption at the oil/water interface, distribution of the surfactant to the aqueous phase, complete detergency of the hydrophobic layer, and partial detergency. These models are compared with data from batch experiments in which mixing time, mixing speed, surfactant concentration, and water/oil ratio are varied. The asymptotic models permit an unambiguous interpretation of the qualitative parameter dependences.

Synergetic effects of temperature and magnetic field on the aragonite and calcite growth

“…This is probably true because more aragonite would be formed by nucleation at a higher temperature, as reported by Wray and Daniels (1957). Nevertheless, the temperature effects were observed for other systems without changing the crystal morphology, such as potassium alum (Wu et al, 1991;Rousseau and Woo, 1980) and citric acid (Sikdar and Randolph, 1976). Thus, the temperature might have dual effects on the growth of aragonite seeds.…”

“…Nevertheless, almost all of the clusters existing in the supersaturated solution were transformed into those available for aragonite growth under magnetizing for a long period of time. At higher temperatures, the clusters adsorbed on the crystal surface were more active in causing a higher surface-integration rate, just like the systems of potassium alum and citric acid (Sikdar and Randolph, 1976;Wu et al, 1991). For the case without the treatment of magnetic field, none of the clusters were available for aragonite growth at room temperature.…”

Estimation of crystallization kinetics from batch cooling experiments

“…Experimental results range from 1.8 to 7.82 and several studies report h=2-2.5 (Garside and Shah, 1980). However, Sikdar and Randolph (1976) found that the stirring rate did not effect the nucleation rate of citric acid and magnesium sulfate, and it has been reported (Mullin and Leci, 1972;Wang et al, 1981) that the influence of agitation on citric acid nucleation vanishes at increasing rotations per minute. A low order of dependence may reflect regeneration or survival limitation of the nucleation process.…”

Nucleation and growth rates of ammonium chloride in organic media: Development of an on‐line measurement technique

“…The on-line measurement of crystal growth and nucleation rates in a mixed suspension, mixed product removal (MSMPR) crystallizer has proved to be a versatile tool for studying nucleation/growth rate kinetics while directly observing the mechanisms underlying such kinetics (for example, Randolph and Cise, 1972;Sikdar and Randolph, 1976). Most previously studied systems are characterized by relatively high solubilities, low supersaturation, and the dominance of secondary nucleation.…”

“…The on-line sampling technique used previously in similar studies (Randolph and Cise, 1972;Sikdar and Randolph, 1976) was implemented in this study. However, the capability of on-line regression of semilog popu-Iation data to the theoretical MSMPR form was added utilizing the system shown schematically in Figure 2.…”