Dynamical adsorption and temperature-programmed desorption of VOCs (toluene, butyl acetate and butanol) on activated carbons

The elimination of solvent vapors from paint shop atmospheres and their recovery for possible re-use is a current environmental requirement. We have studied the dynamical adsorption at 23 °C of typical car paint solvents, i.e. toluene, butylacetate and butanol, on two microporous activated carbons, and the thermal regeneration of these carbons with hot air at 150 °C. A sequence of seven adsorption-desorption cycles with a mixture of these solvents left the carbons with some textural changes but the adsorption capacity remained virtually unaffected. Heavy volatile compounds, proceeding from the possibly unstabilized binder, are eliminated in the course of the first adsorption-desorption runs. Differential scanning calorimetry applied to the desorption in argon of pure solvents showed that the desorption enthalpies ΔH_des are close to, or slightly larger than, the evaporation enthalpies ΔH_vap except for butanol, which exhibited a particularly high ΔH_des value. Temperature-programmed desorption experiments, obtained with carbon samples heated in a helium flow containing oxygen traces, evidenced the desorption of numerous oxidation products. This finding may have consequences for hot air regeneration processes.