Aluminium-chromealuminium-pillared clay and its characterization

ALUMINUM-, CHROMEALUMINUM-PILLARED CLAY AND ITS CHARACTERIZATION (PhD. Thesis) Fatma AKINCI TOMUL GAZI UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY March 2000 ABSTRACT The need for solids having controlled pore structure in industry leads an increase in studies related with the production of new materials in parallel to the improvements of the pore structure of the naturally existing materials. Pillared layered clays are obtained by introducing bulky pillar agents into the natural layers of the clays and fixing of them to the structure with heat effects. The solid chosen for production, pillar agent and production conditions have rather important effects on the product quality. While the host mineral necessarily having the expanding cage structure, swelling property and high cation exchange capacity, the chosen pillar agent must have suitable properties to supply thermal stability and the desired pore structure related with the application areas. In this study, pillared layered clay production was carried out with bentonite clay minerals Hançılı Yellow (HY), Hançılı Green (HG) and Hançılı White (HW) from Hançılı region using aluminum and chromealuminum-metal complexes as pillar agent. In order to compare the suitability of these minerals for the production, the production with Texas Ca-montmorillonite (STx-1) and WyomingNa-montmorillonite (SWy-2) standard clay minerals were also carried out. The effects of clay kinds, pre-satu ration type and duration, the pillar agent preparing method and calcination temperature on product quality were investigated. Al-pillared layered clay having basal spacing varying between 15,73 Â and 18,80 A and BET surface area changing between 157 m2/g and 312 m2/g were obtained at 300°C with unsaturated, sodium and calcium pre-saturated HY, HG, HW, SWy-2 and STx-1 clay minerals. The decrease in basal spacing and surface area values were observed depending on the increase in calcination temperature. Calcium pre-satu ration yielded an increase in thermal stability of product, compared with sodium-saturated and unsaturated clay minerals. Decrease in basal spacing and surface area values were observed with increasing in pre-satu ration time. The effect of base/metal ratio in pillar solution on product quality were also investigated, for unsaturated, sodium and calcium pre-saturated clay samples and it was observed that, basal spacing value increased from 1 5,73 Â to 1 9,34 A by increased the OH/AI ratio from 1,0 to 2,5. The increasing of base/metal ratio caused an increase in the basal spacing and the surface area values it also brought out the preserved structure stability against the heat effects. The increase in basal spacing from 16,38 A to 18,14 A at 300°C, and the structure stability were observed by increasing pillar agent aging temperature from 30°C to 75°C. It was concluded that, for OH/AI ratio of 2,5, aluminum pillar agents were aged at 60°C temperature and 18 hours, time suitable ion-exchange period was, 4 hours for the homogeneous distribution of the pillar agents between the clay layers. The uniform distribution of pillar agents between clay layers were observed, in the studies carried out with the standard clay minerals. The effects of pillar solution preparation and clay solution-pillar solution mixing operation on product quality were investigated with two different methods usingVI different clay minerals in the Al-pillared clay production. The basal spacing and BET surface area values for the products obtained from calcium pre-saturated HY clay mineral, for the pillar agents prepared from high temperature-high metal concentration and low temperature-low metal concentration were 17,98 Â and 213 m2/g; 18,80 Â and 118 m2/g respectively. It was observed that, structure stability was preserved against temperature increase, in the second method in which ion exchange time was increased. In CrAI-pillared layered clay product, basal spacing and BET surface area values were increased with an increase in Al/Cr ratio. It was also seen that, the structure stability against thermal effect was preserved with an increase in this ratio. The products obtained with increased Al/Cr ratio showed similar behavior with Al-pillared layered clay product. Science Code Key Words Page Number Adviser : 603.02.01 : Montmorillonite, pillared layered clay, pillar agent, basal spacing, BET surface area, characterization :228 : Doç. Dr. F. Suna BALCI