BIO-OIL AND BIOGAS FROM THE PYROLYSIS OF SEWAGE SLUDGE, AND NON-ISOTHERMAL DEGRADATION ON USY ZEOLITE

Abstract

This paper examines the pyrolyzation of sewage sludge using a bench scale reactor and the characterization of its products. Non-isothermal degradation via thermogravimetry was used to estimate activation energy of regular and catalytic degradation under inert atmosphere. The pyrolysis reactor, a rotating cylinder coupled to a gas-washing column with a centrifuge at the top, was used to condensate pyrolysis vapors. The experimental procedure was divided into two parts: (I) pyrolysis of a sewage sludge guided by a 23 experimental design with center point, at temperatures of 520, 560, and 600 °C; inert flow rates of 3, 4.5, and 6 L h-1; centrifugation rotation frequencies of 20, 23, and 26 Hz; under a constant biomass flow rate of 408 g h-1; (II) determination of the activation energy of thermal degradation, with and without the USY zeolite catalyst, using an isoconversional analysis of integration. For the later, three heating rates were tested: 5, 10, and 20 °C min-1. The bio-oil obtained in the bench-scale pyrolysis reactor had the following characteristics: pH from 6.0 to 8.1, density from 1.0 to 1.1 g mL-1, solid contents from 0.7 to 0.8%, and higher heating values from 17.4 to 18.4 MJ kg-1. The bio-oil consisted mostly of aliphatic and monoaromatic hydrocarbons, substituted aromatics, polyaromatic hydrocarbons, long amides, and amines. The components found in the gas phase were: H2, CO, CO2, CH4, C2, C3, C4, C5, and C6. The syngas maximum content was 59.2%. Results from the thermal analysis showed that the USY was effective in decreasing the thermal degradation activation energy. Near the temperature when the pyrolysis occurred, the activation energy dropped from 78.5 to 62.6 kJ mol-1, and the conversion was 80%. The average values observed for the activation energy with and without catalyst, at conversions from 40 to 80%, were 103.9 and 155.0 kJ mol-1, respectively, which indicates that the USY zeolite successfully enabled a new pathway for the sewage sludge’s thermal degradation.