Sunday 4 September 2016

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

Published Date

September 2016, Vol.103:76–86, doi:10.1016/j.psep.2016.06.035

Title

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

Author

Jon Alvarez

Gartzen Lopez

Maider Amutio

Javier Bilbao

Martin Olazar^,

Department of Chemical Engineering, University of the Basque Country UPV/EHU, P.O. Box 644-E48080, Bilbao, Spain

Received 11 February 2016. Revised 7 June 2016. Accepted 27 June 2016. Available online 2 July 2016.

Highlights

•
Sewage sludge char is valorized for the production of adsorbents.
•
HCl and Na₂CO₃ sequential washing steps to extract most of the ashes.
•
Lower inorganic content favors the accessibility of CO₂ into the pores network.
•
Maximum BET surface area (440 m² g⁻¹) is attained after 15 min of activation.
•
Promising results for the viability of sewage sludge flash pyrolysis.

Abstract

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%.