Two-film Theory Research Articles

Kinetics of formation of methane and ethane gas hydrates

An intrinsic kinetic model with only one adjustable parameter is proposed for the formation of methane and ethane gas hydrates. Experimental formation data were obtained in a semi-batch stirred tank reactor. The experiments were conducted at four temperatures from 274 to 282 K and at pressures ranging from 0.636 to 8.903 MPa. The kinetic model is based on the crystallization theory, while the two-film theory model is adopted for the interfacial mass transfer. Experiments were performed at various stirring rates to define the kinetic regime. The study reveals that the formation rate is proportional to the difference in the fugacity of the dissolved gas and the three-phase equilibrium fugacity at the experimental temperature. This difference defines the driving force which incorporates the pressure effects. The gas consumption rate is also proportional to the second moment of the particle size distribution. The rate constants indicate a very weak temperature dependence.

Kinetics of gas hydrate formation from mixtures of methane and ethane

Experimental data on the kinetics of formation of gas hydrates from three mixtures of gaseous methane and ethane are reported. the experiments were conducted in a semi-batch stirred tank reactor at temperatures from 273 to 284 K and of pressures from 0.68 to 5.60 MPa. An intrinsic kinetic model for the growth of the gas hydrate is proposed. It is extension of the model for pure component hydrate formation. The model is based on the crystallization theory coupled with the two-film theory for the gas absorption into the liquid phase. the model does not contain any adjustable parameters. The kinetic rate constants which appear in the model are those obtained previously from pure component formation data. The results indicate that the formation rate is proportional to a lienar combination of the differences in the fugacities of the dissolved gases and their three-phase equilibrium fugacities at the experimental temperature. The effect of the mixture composition is taken into account indirectly through the computation of the three-phase equilibrium conditions and of the fugacities. the total gas consumption rate is proportional to the second moment of the particle size distribution.

Toxic organics removal kinetics in overland flow land treatment

The efficiency in removing 13 trace organics from wastewater was studied on an outdoor, prototype overland flow land treatment system. More than 94% of each substance was removed at an application rate of 0.4 cm h −1 (0.12 m 3 h −1 m −1 of width). The % removals declined as application rates were increased. Removal from solution was described by first-order kinetics. A model based on the two-film theory was developed using three properties of each substance (the Henry's constant, the octanol-water partition coefficient and the molecular weight) and two system parameters (average water depth and residence time). The dependence of the removal process on temperature was consistent with the known dependence of Henry's constant and diffusivity on temperature. The model was tested on a second overland flow system.

A general model to account for the liquid/liquid kinetics of extraction of metals by organic acids

A model based on two-film theory is developed for the case of the rate of extraction of a divalent metal from an aqueous acid phase with an organic acid HR held in a second immiscible solvent phase. The model involves a reaction zone of variable thickness so that the case of reaction at an interface of molecular dimensions can be accommodated as well as the case of reaction extending into the diffusion film on the aqueous side of the interface. Four parameters are used, one involving a partition coefficient for the acid, one involving diffusivities in the films together with the two-film mass-transfer coefficients. Rate data from three techniques used in laboratory liquid/liquid contacting are fitted by the model.

Simulation of packed-bed separation processes using orthogonal collocation

The two-point boundary value problem resulting from the heat and material balance equations of a packed separation column are solved using polynomial approximation techniques. The model equations are based on the two-film theory of mass transfer. The resulting partial differential equations are first reduced to ordinary differential equations and then integrated using semi-implicit Runge-Kutta method of integration. Application of orthogonal collocation simplifies the solution of the two-point boundary value problem. For the examples studied, the algorithm is found to converge rapidly with respect to the number of collocation points used in the polynomial approximation.

スラグ-容鉄間の酸素の移行速度

The dissolution rate of oxygen into liquid iron at 1873 K was investigated by melting the iron under the FeO-CaO-SiO2 slags in the resistance or induction furnace and determining the oxygen content of iron samples taken at an appropriate time interval. The results are as follows:(1) The oxygen content in the metal increased nearly exponetially with time. The reaction rate was increased by induction stirring and was deemed to be controlled by the mass transport steps.(2) Using the two-film theory, overall mass-transfer coefficients were calculated to be 1.3∼4.3×10−3 kg/m2s for runs in the resistance furnace and 4.4∼7.6×10−3 kg/m2s in the induction furnace. The value of mass-transfer coefficient in the metal layer, km, was calculated to be 1.96×10−4 m/s from runs with liquid iron oxide slag and values of ks in the slag layer were 0.2∼3.1×10−5 m/s.(3) From these values of km and ks it was found that the resistances to the mass transport both in the metal and slag layers were the same order and the reaction was controlled by both steps.

An Analysis of the Overall Gas-Liquid Reaction Rate based on Two-Film Theory

An Analysis of the Overall Gas-Liquid Reaction Rate based on Two-Film Theory