The Experimental And Theoretical Studies Of The Diffusivities Of Amino Acids In Aqueous Solution

Holographic interferometer has become a generally accepted and the most effective method today in the study of transport phenomena, it has been widely applied to precise, qualitative and quantitative measurement of various physical parameters in fluids such as velocity, temperature, concentration and density etc. with the advantages of high sensitivity and accuracy, large capacity of information, non-instructive and feasible to make instantaneous measurement and visualization in overall insight into the whole process. The molecular diffusivity in liquid phase is one of the most important dynamical parameter for describing mass transfer. Due to the lack of satisfactory theoretical model to predict liquid diffusivity, it necessitates to exploit a novel and accurate experimental technique in order to meet the need of practical utilization and validate theory. Thus the holographic interference method has been paid much attention in the field. Based on a lot of references, the developments of the determination methods, applications of holographic interferometer to determine liquid diffusivity and prediction of aqueous diffusion coefficients for organic compounds were briefly reviewed.Amino acids are used widely as nutriment and medicine, so it is virtual significance to investigate their diffusion in aqueous solution. A real-time holographic interferometer and a simulator for liquid-liquid diffusion were specially designed and constructed in order to measure liquid diffusivity in transparent fluids. The diffusivities of 0.33 KCl and 5 various concentration sucrose aqueous solution at temperature 298.15K were determined experimentally to verify the accuracy and reliability of the instrument, the determined results are at good agreement with ones in literature and validate the experimental set-up. Furthermore, the diffusion coefficients of alanine, glynine, arginine, serine, threonine, valine and isoleucine aqueous solution at 298.15K and on 5 various concentrations were measured respectively. The experimental results are analyzed and discussed. This investigation provides a fundament to profoundly study the micro diffusion behavior and mass transfer mechanism of aqueous solution of amino acid and develop theoretical model of liquid-liquid interfacial mass transfer. On the basis of Fick's law, and combining the analysis of predictive model of diffusion coefficient in literature, a new semi-empirical model was developed to predict the liquid diffusion coefficients as follow:This model includes four adjustable parameters that extend the application range of equation and improve its predictive accuracy.The equation parameter were fitted by the experimented data of seven amino acids in this paper and four ones in literature. The average deviation between model prediction values and experimental ones is below 0.5%, it shows a considerably satisfactory accuracy.