Enhanced hydrogen production in catalytic pyrolysis of sewage sludge by red mud: Thermogravimetric kinetic analysis and pyrolysis characteristics

Abstract The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe 2 O 3 , Al 2 O 3 , SiO 2 ) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe 2 O 3 and Al 2 O 3 in the RM. Adding Fe 2 O 3 or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol −1 , respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al 2 O 3 , Fe 2 O 3 or the RM could produce more gas than the addition of SiO 2 , especially at high temperatures. Fe 2 O 3 and Al 2 O 3 acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of C C and C H bonds to produce more gases. Especially, Fe 2 O 3 and Al 2 O 3 increased the H 2 yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.