The Use of Taguchi Method to Determine Factors affecting the size of fine attapulgite particles generated by Rapid Expansion of Supercritical Solution with and without cosolvents

The rapid expansion of a supercritical solution (RESS) process is a promising method for the production of small, uniform and solvent-free particles of solutes. The RESS containing a non-volatile solute leads to loss of solvent power by the fast expansion of the supercritical solution through an adequate nozzle, which can cause solute precipitation. The nozzle configuration plays an important role in RESS method and has a great effect on the size and morphology of the precipitated attapulgite particles. In this work, a RESS apparatus was set up and attapulgite submicron particles were prepared successfully with the supercritical carbon dioxide. The experiments were carried out to investigate the effect of parameters such as extraction temperature (308-328K), extraction pressure (150-200 bar), spraying distance (1-5 cm) ,the nozzle configuration besides the presence of cosolvents . Taguchi method creates an orthogonal array to accommodate these requirements. The selection of a suitable orthogonal array depends on the number of control factors and their levels. In this work our experiments carried out based on L18 orthogonal array. For the Taguchi design and subsequent analysis, the software named as Qualitek-4 (version 4.82.0) was used. The RESS process could produce ultrafine spherical particles (0.09 to 2.1 μm) of attapulgite as reflected by SEM observations. However the average size of the unprocessed particles were (1-100 μm) with average of 15 μm.