Interaction of trifluoromethane (CHF3) with alkali hydroxides and carbonates

Heterogeneous reactions of trifluoromethane (CHF3) with solid alkali hydroxides and carbonates were investigated under static and dynamic conditions and at moderate temperatures. In all cases, main reaction is fluorination characterised by a complete decomposition (mineralisation) of the fluorinating agent, CHF3, and the formation of solid metal fluorides, CO, and H2O. Under specific conditions, CO and H2O may react further through the water–gas shift reaction and form solid metal carbonate. Extent of fluorination strongly depends on temperature and is dictated by the nature of the solid precursor. Alkali hydroxides, KOH, NaOH, and LiOH, are the most reactive solids that start to react with CHF3 at relatively low temperatures, 370–484 K. Onset temperatures for fluorination of corresponding carbonates are 100–150 K higher. Reactivity of the solids towards CHF3 can be correlated with their basicity. Reactions are rationalised on the basis of an acid–base type of interactions between CHF3 as a very weak CH acid and the very strong basic oxygen species in the solids. These interactions apparently play a decisive role during the initial binding of CHF3 molecule to the solid reactant, in this way enabling or facilitating other decomposition steps that finally lead to a complete destruction of the CHF3 molecule. Total decomposition of CHF3 with KOH or NaOH, achievable at relatively very low temperatures, could in some specific cases represent a possible alternative to the energy-demanding CHF3 decomposition by incineration.

Trifluoromethane (CHF3) is completely decomposed (mineralised) with alkali (Li, Na, K) hydroxides and carbonates at moderate temperatures. Activity of the solids towards CHF3 strongly depends on their basicity. It appears that acid–base interactions have a decisive role in the initial stages of the CHF3 decomposition process.Figure optionsDownload as PowerPoint slideHighlights
► CHF3 is mineralised by alkali hydroxides at 420–470 K.
► The key role of acid–base interactions in CHF3 decomposition is highlighted.
► Under specific conditions, CO is converted to solid carbonate.