Efficient solid reducing agent CaO/SiO2 hybrid composite for hydrogen fluoride elimination

Abstract

An advanced solid reducing agent, i.e., a CaO/SiO2 composite has been optimized to improve the hydrogen fluoride (HF; a green house gas) elimination in semiconductor-based industrial applications. To avoid the Ca(OH)2 formation and enhance the HF removal efficiency of CaO, the hydrophobic properties of silica (SiO2) have used as a catalyst materials to enhance the stability of CaO/SiO2 solid reducing agent in the present investigation. The novel composite structure based on CaO/SiO2 was prepared using various concentrations of hydrophobic nano-silica sol and Ca(OH)2. The composite was characterized by contact angle goniometry, thermogravimetry analysis, and scanning electron microscopy. The water contact angle of the CaO/SiO2 composites significantly increased with increasing SiO2 content. In particular, angles of 61.6°, 73.7°, 84.8°, and 84.9° were obtained for SiO2 concentrations of 20, 40, 60, and 80 wt.%, respectively. These results suggest that the hydrophobic nature of the composites was improved with the addition of 60 and 80 wt.% of SiO2. Moreover, the surface properties were measured using the nitrogen Brunauer-Emmett-Teller method for obtaining the weight ratios (wt.%) and calcinations times. The determined specific surface areas (SSAs) were 16.19, 27.25, 32.86, and 40.56 m2/g for 80:20, 60:40, 40:60, and 20:80 CaO/SiO2 composites, respectively. From the water contact angle and SSA analysis, the optimum hydrophobic nature of CaO/SiO2 composites for HF removal was achieved at a weight ratio of 40:60 (Ca(OH)2/SiO2) at the calcination temperature of 650 °C. The perfluorinated compound (PFC) removal rate is 80 and 88% for a common regenerative catalytic system (RCS) catalyst and the CaO/SiO2 reaction-enhanced (RE)-RCS catalyst, respectively. In addition, higher amount of HF elimination is successfully achieved using CaO/SiO2 solid reducing agent. During the RE-RCS process, SiO2 acts as a catalyst to prevent the formation of Ca(OH)2 when CaO is exposed to water.