The role and potential of attapulgite in catalytic pyrolysis of refinery waste activated sludge

Pyrolysis is a promising technology for the treatment of refinery waste activated sludge（r WAS）. In this study, attapulgite as a natural clay was used to enhance the pyrolysis of r WAS. The yields, characteristics of pyrolytic products, pyrolytic kinetics and mechanisms were investigated. The attapulgite improved the conversion of r WAS into non-condensable gases and pyrolytic liquids. The bio-oil quality improved and the biochar yield reduced. The average activation energy of Stage Ⅰ（230-400°C） and Stage Ⅱ（400-500°C） decreased by 36.5% and 49.7%, respectively, compared to r WAS alone. Al2 O3 and Fe2 O3 in attapulgite enhanced the dealkylation reaction and cracking of C-C bonds. The content of the gasoline(13) fraction of bio-oil doubled relative to r WAS alone. Attapulgite promoted the deoxygenation,dehydroxylation and dehydrogenation reactions of O-containing compounds, and the content of CO and CO2 in non-condensable gases increased. Addition of attapulgite（r WAS:attapulgite ratio of 1:1）decreased the O mobility from 14.6% to 12.8% relative to r WAS alone. Also, the content of saturates in biooil increased from 38.5 wt% to 47.2 wt% and the lower heating value（LHV） increased from 6.8 kcal/kg to8.4 kcal/kg. The heavy metals originally in r WAS were fixed into the pyrolytic residue and the environmental risks are low. This study demonstrates the role and potential of attapulgite in catalytic pyrolysis of r WAS with an added advantage of increased cost-effectiveness.