Capture of Carbon Dioxide From Sewage Sludge Pyrolysis Gases in a Fixed Bed of 13x Zeolite

Abstract

Pyrolysis gases can be upgraded through CO2 adsorption. This work shows the pyrolysis of sewage sludge in a 1 kg h−1 rotating cylinder reactor. Non-condensable gases passed through a fixed bed of 13X zeolite at 40 ◦C. Prior to processing actual pyrolysis gases, the equilibrium adsorption capacity of the 13X was evaluated with synthetic CO2 in a magnetic suspension balance to estimate Langmuir, Freundlich and Toth isotherm parameters. Afterwards, a synthetic mixture with composition similar to that of sewage pyrolysis gases was tested in a bench-scale fixed-bed adsorption column to assess both the breakthrough curves for different adsorbent masses (10, 15, and 20 g) and the saturation time of the adsorbent. The dynamic adsorption in the column was modeled as a system of partial differential equations (PDEs), which was transformed into a system of Ordinary Differential Equations (ODEs) via the Method of Lines and, then, solved using DASSL. The ODEs were used to estimate adsorption parameters such as coefficient of axial dispersion, effective diffusivity within the particle, and external coefficient of mass transfer. The synthetic gases were replaced with actual sewage sludge pyrolysis gases in the adsorption column with 13X. The breakthrough curves revealed a quick saturation of the bed by pyrolysis aerosols. Despite its short lifetime in comparison with synthetic gases, the 13X proved effective in adsorbing pyrolysis CO2.