Improved Exhaust System for Laboratory Work with Fluorine

Abstract

Hydrofluoric acid (HF) is a widely used chemical in laboratories as well as in the glass and ceramics industries. It is valued for its high reactivity; however, it poses significant disadvantages, including high toxicity to humans and corrosive effects on equipment. To prevent damage to laboratory and surrounding equipment as well as to ensure operator safety, an appropriate exhaust ventilation system must be used. Exhaust systems for hydrofluoric acid applications must meet stringent technical standards. Depending on the frequency of use, they may incorporate wet scrubbers, which necessitate considerable energy input and consumption of alkaline neutralizing agents and cause a substantial pressure drop. We here present an easy-to-handle alternative system based on calcium hydroxide honeycomb monoliths (HMs). We calculated and simulated the HF precipitation on the HMs based on thermodynamic data and with finite elements. We considered a liquid HF concentration of up to 50% in use within a standard laboratory fume hood. The HF concentration in the exhaust air after HMs throughflow was measured as well as the pressure drop. Theoretically and experimentally, HF was completely bound to calcium hydroxide HMs. Moreover, we find that the pressure drop in the fume hood was low compared to that of wet scrubbers. Calcium hydroxide HMs are a promising option for adsorbing HF from exhaust gas flows. From the economic viewpoint and from technical and organizational requirements, HMs offer significant benefits over wet scrubbers. Our findings can be directly implemented within experimental laboratories handling HF containing exhaust air.