Toluene mass transfer characterization in a biotrickling filter

Biotrickling filters (BTFs) devoted to air pollution control often present mass transfer limitations for hydrophobic volatile organic compounds (VOCs). Under such limiting conditions, BTF design and scale-up should be based on mass transfer data. A general and simple model was developed to characterize the VOC transfer by means of the overall mass transfer coefficient (KLa). The KLa values were obtained by fitting the model to experimental data of toluene absorption obtained at empty bed residence times (EBRT) from 7 to 50 s. The model fitted well the experimental data (r2 = 0.97) and the resulting KLa values ranged from 35 to 113 h−1. These values are similar to those reported in the literature for BTF despite the lower liquid recycling velocity here used (0.6 m h−1). A critical gas-to-liquid flow rate ratio (QG/QL) of 200, above which KLa was poorly increased, was observed. In addition, the individual film coefficients were estimated from the Van Krevelen and Hoftijzer correlations, which revealed that the main resistance for toluene mass transfer was in the liquid film regardless of the EBRT used. Finally, the high mass transfer potential of BTFs was confirmed by estimating the mass transfer capacity under varied operating conditions.

► A general and simple model to characterize the VOC mass transfer in biotrickling filters by means of the overall mass transfer coefficient (KLa) was developed.
► The resulting KLa values ranged from 35 to 113 h−1. A critical gas-to-liquid flow rate ratio of 200, above which KLa was poorly increased, was observed.
► The estimation of the individual film coefficients revealed that the main resistance for mass transfer was in the liquid film.
► The calculated mass transfer capacity confirmed the high mass transfer potential of biotrickling filters.