A modification of van der Wash and Platteeuw's (1959) hydrate equilibrium model which incorporates the effect of spherical asymmetry is developed. A corresponding states correlation is used to predict the deviation of Langmuir constantsDepartment of Chemical Engineering Columbia University in the City of New York from ideal values. In this model the Kihara parameters obtained from hydrate equilibrium data agree well with those obtained from virial coefficient data.Gas hydrates are crystalline solids in which water forms a hydrogen bonded lattice with large interstitial vacancies called cavities. These cavities must be partially occupied by small gas molecules such as methane, nitrogen, or propane. Although some of the cavities will always be empty, the water lattice cannot form in the absence of gas; only through the physical interaction between the encaged gas molecules and the water lattice is the hydrate structure stabilized. In recent years much effort has been devoted to modeling the conditions at whichThe prediction of phase equilibria in gas hydrate forming V T John and K D Papadopulosare prcsmtl) with the Department of C hrnricdl I ngineering hydrates will Tulane University New Orleans LA 70118The influence of temperature on crystallization and dissolution kinetics in a fluidized bed was investigated. Values of activation energies were determined and a correlation between the rate constants of secondary nucleation and of the surface integration step of crystal growth was presented.
SCOPEThe Arrhenius equation is widely used to present the effect of temperature on kinetics of overall crystal growth, of disso-lution, and of primary and secondary nucleation, despite the well-known fact that this equation is essentially valid for chemical reaction kinetics. Similarly, the driving force for terms of absolute concentration difference but not, as theoret-piotr H, Kapi,j&i is presently &the &pfimentof Chemical Engineering, wormer polyt&nic crystallization-i'e', s'persaturation-is usually expressed in Institute, Worcester, MA 01609.
Effective in situ remediation of groundwater requires the successful delivery of reactive iron particles through soil. In this paper we report the transport characteristics of nanoscale zerovalent iron entrapped in porous silica particles and prepared through an aerosol-assisted process. The entrapment of iron nanoparticles into the silica matrix prevents their aggregation while maintaining the particles' reactivity. Furthermore, the silica particles are functionalized with alkyl groups and are extremely efficient in adsorbing dissolved trichloroethylene (TCE). Because of synthesis through the aerosol route, the particles are of the optimal size range (0.1-1 microm) for mobility through sediments. Column and capillary transport experiments confirm that the particles move far more effectivelythrough model soils than commercially available uncoated nanoscale reactive iron particles. Microcapillary experiments indicate that the particles partition to the interface of TCE droplets, further enhancing their potential for dense non-aqueous-phase liquid source-zone remediation.
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