Preparation of adsorbents from sewage sludge pyrolytic char by carbon dioxide activation

This work focuses the valorization by CO2 activation of the sewage sludge char obtained in the fast pyrolysis in a conical spouted bed reactor at 500 °C. In order to improve the quality of the activated material for use as adsorbent, the sewage sludge char was subjected to two sequential steps of washing by using first a solution of HCl (in order to remove part of the ashes) and then a solution of Na2CO3 (to extract most of the silica remaining), thereby comparing the properties of the char washed with only HCl with that treated with both HCl and Na2CO3. The materials treated with one or two steps of washing were activated with CO2 in a fixed bed reactor at 800 °C, which allowed proving that the step of Na2CO3 washing contributes significantly to increasing the gasification rate. Furthermore, the properties of interest for use as adsorbents were greatly improved, attaining a BET surface area of 440 m2 g−1 with a notorious presence of meso and macropores for an activation time of 15 min and a burn-off value of 42%.