KINETICS OF ADSORPTION OF 4,4-DIMETHYL-1,3-DIOXANE FROM AQUEOUS SOLUTIONS BY SYNTHETIC ZEOLITES IN PRESENCE OF PHOSPHORIC ACID

Abstract

In this paper we studied the kinetics of adsorption of 4,4-dimethyl-1,3-dioxane by synthetic zeolites from aqueous solutions in the presence of phosphoric acid. Kinetic mechanism of DMD adsorption from aqueous solutions by synthetic zeolites were considered from the position of three kinetic models: the diffusion model (Boyd and Morris-Weber model), Lagergeren (pseudo-first order), and pseudo-second order. As sorbents we have used synthetic zeolites KA, NaA, CaA, CaX, NaX with a pore diameter of 3-9 Å. DMD (boiling point is 113-114 ºC) was synthesized from isobutylene. Chromatographic analysis was performed on Chromatec Crystal 5000.1 instrument (Russia) using columns (2.0 m in length) with silicone SE-30 (5%) stationary phase (0.16–0.20 mm, operating temperature is 50–220 °C) with nitrogen as a carrier gas. An adsorption of DMD from aqueous solutions was investigated at (75±1) °C from a limited volume under constant mixing (laboratory mechanical stirrer, 17 rps). The contact time of the solution with samples of sorbents varied from 120 to 3600 s. The DMD concentration in solution was determined by the chromatographic method (the internal standard is 4,4,5-trimethyl-1,3-dioxane). The values of the external and internal mass transfer diffusion coefficients were obtained. The effect of the size of zeolite’s pores on the contribution of the external or internal diffusion mass transfer in the process of adsorption of 4,4-dimethyl-1,3-dioxane was founded. The time of establishment of sorption equilibrium was determined. We have found that the process of adsorption of DMD by synthetic zeolites in the presence of phosphoric acid is determined by the values of the diameter of the pores. It is shown that the value of pore diameter of synthetic zeolites does not influence on the аdsorption equilibrium time of DMD. The adsorption equilibrium time for all used family zeolites is 900 s. The kinetics of adsorption of DMD on synthetic zeolites can be correctly described by a pseudo-second-order equation, which indicates the presence of sorbate (DMD) interaction with the sorbent (synthetic zeolite).