SULFUR-DIOXIDE CONTROL BY REACTIVE PHOTOGRAFTED MEMBRANES IMMOBILIZING HIGH SURFACE-AREA CALCIUM-OXIDE

The effects of temperature (313-423 K), of feed SO2 concentration (985-2200 ppm (v/v)), of pore size (0.04-1.9-mu-m) and of surface area (11-39 m2 g-1) of CaO sorbent on the reactivity of composite membranes, immobilizing 30 wt.% of sorbent in an epoxy-diacrylate resin matrix photografted onto cellulose, towards SO2, have been studied at constant flow rate (1.85 cm min-1) and pressure (1 bar gauge). Moisture in the test gas was kept constant, by saturation with water at 343 K. With high surface area CaO and at the dew point temperature the % of SO2 captured was always greater than 50%, approaching 95-98 % at 313 K where capillary condensation of water vapour occurred. In the lower temperature range, the presence of liquid water in the membrane pores slackens gas diffusion, enhances SO2 solubility and consequently favours reactivity. The dependency of sorption rate on temperature and on pore size allows us to find experimental conditions, in which to operate with a sorption efficiency significantly lower than unity, but with an equally satisfactory overall yield, in a multistage membrane process, provided high surface area sorbents are used, and membranes immobilizing these sorbents are manufactured by a technique, such as photografting, able to maintain this surface area almost entirely active.