Use of surface modified natural zeolite (SMNZ) in pharmaceutical preparations. Part 2. A new approach for a fast functionalization of zeolite-rich carriers

Abstract

Main purpose of the research was to define an operative protocol, applicable at industrial scale, optimizing the functionalization of natural zeolites with surfactants, especially in pharmaceutical and environmental sphere. Three zeolite-rich samples from Italy (PHI_SAV), Slovakia (CLI_SK) and California (CLI_CA) were used for preparation of SMNZ. Two different protocols allowed to carry out surfactant adsorption equilibrium runs and surfactant sorption kinetics by varying different parameters: mixing speed (4000, 6000, and 8000 rpm); contact time (15 divided by 90 min) and initial surfactant concentration (from 25% to 200% of the external cation exchange capacity - ECEC) at a constant solid/liquid ratio (1 g/50 mL). Zeolite-rich materials were treated with solutions of cetylpiridinium chloride (CP-Cl). The functionalization of SMNZ was obtained by using a high-speed disperser. The amount of absorbed surfactant onto two carriers (CLI_SK and PHI_SAV) was evaluated through kinetic experiments under the following conditions: the initial CP-Cl concentration of 150% of the ECEC and a disperser speed of 8000 rpm. Results showed that after 15 min, equilibrium was attained with the adsorbed amount of about 0.14 meq/g of CP-Cl (equivalent to the ECEC of the investigated zeolitic support), confirming formation of monolayer (emi-micelle). The functionalization (micelle formation) of two samples occurred after 70 min of solid/liquid interaction with a total yield equal to 150% of the ECEC, thus indicating formation of a patchy bilayer. By contrast, CLI_CA behaves completely differently since the formation of emi-micelle was achieved only at much higher speed (18000 rpm) and not earlier than 90 min of mixing.