Modelling of mass transfer coupling with crystallization kinetics in microscale

Abstract

a b s t r a c tMicrostructure technologies have attracted interests in chemistry, chemical engineering, and biotechnology. To investigate the mass transfer of ions and crystallization of crystals in microscale and then to explain the formation mechanism of the porous structure materials, a microscale mathematical model for mass transfer processes coupling with local reactions is proposed in which the chemical potential gradient Dm is used as the driving force to avoid the discontinuity of the kinetics equations in the micro-channels. Meanwhile, the dissolution kinetics of KCl at 298.15 K is measured to determine the dissolution rate constant k d and the average area of crystals Ac. The investigation for the fractional crystallization process of carnallite shows that the calculated mixing time versus channel width agree with the Einstein diffusion equation, which validates that the model can be used to describe the ion diffusion very well. Meanwhile, to have an accurate Dm of KCl, in the channel width of or narrower than 2.0 Â 10 À 6 m, it is enough to consider the diffusion only, while in the channel width of or wider than 2.0 Â 10 À 5 m, diffusion should be coupled with reaction. The investigation also shows the vital of the consideration of the ionic activity coefficient for the investigated systems in micron scales. Moreover, the new formation mechanism of the porous structures in the inorganic material fabrication will be proposed from the process simulation for the synthesis of porous KCl, which will provide a reference for the porous structure formation in the advanced inorganic material synthesis.

Modeling mass transfer of CO2 in brine at high pressures by chemical potential gradient

“…In this case, chemical potential gradient should be used as the driving force. Our previous work based on non-equilibrium thermodynamics [21][22][23] also reveals that it is necessary to consider the non-ideality of such complex systems.…”

Methodology of non-equilibrium thermodynamics for kinetics research of CO2 capture by ionic liquids

“…In this paper, three key scientific problems of non-equilibrium thermodynamic investigations on CO 2 absorption kinetics by ionic liquids are proposed on the basis of the non-equilibrium thermodynamic model of CO 2 absorption kinetics by ionic liquids as described in Section 2.2 and our previous linear non-equilibrium thermodynamic investigations on the dissolution and crystallization kinetics of potassium inorganic compounds [31][32][33]. These problems are shown as follows.…”

“…The non-equilibrium thermodynamic model of CO 2 absorption kinetics by ionic liquids could be investigated on the basis of the schematic diagram of CO 2 absorption kinetics process by ionic liquids shown in Figure 1 and our previous linear non-equilibrium thermodynamic investigations on the dissolution and crystallization kinetics of potassium inorganic compounds [31][32][33]. In this paper, the surface reaction rate and diffusion rate will be described using the linear non-equilibrium thermodynamic theory.…”

“…Based on our previous work of linear non-equilibrium thermodynamic investigations on the dissolution and crystallization kinetics of potassium inorganic compounds [31][32][33], in this paper, the kinetic process of CO 2 absorption by ionic liquids is assumed to comprise two steps: surface reaction and diffusion, which is shown in Figure 1. As shown in Figure 1, when CO 2 in the vapor phase and the ionic liquids are in contact, for the chemical absorption process of CO 2 by ionic liquids in the first step, the chemical reaction of CO 2 with ionic liquids takes place, which is called the surface reaction layer; for the physical absorption process of CO 2 by ionic liquids in the first step, CO 2 in the vapor phase will be transferred into the ionic liquid phase, which could also be called the assumed "surface reaction layer".…”

Modeling of specific structure crystallization coupling with dissolution

“…The positive chemical potential difference (Δ ) means that the aqueous solutions are supersaturated and crystallization may occur, the negative Δ means that the aqueous solution is unsaturated or crystal may dissolve, and the zero value of Δ means that the aqueous solution is saturated and neither crystallization nor dissolution will occur. The ion diffusion is described by the convectiondiffusion equation [21]:…”