Valorization of cattle manure via a thermo-chemical process

Abstract

World population growth and improvements in income levels have led to an increase in the global consumption of animal-sourced proteins. However, the massive production of animal manure has resulted in significant environmental burdens, such as increasing greenhouse gas emissions, eutrophication, and water and soil contamination. As such, this study proposed a sustainable and rapid disposal platform for animal manure as a precautionary approach to attenuate the environmental burdens caused by manure. A pyrolysis process was used to convert cattle manure into value-added products with the aim of achieving both rapid volume reduction and sustainable conversion. CO2 was fed into the process to increase the green/sustainable benefits and the results were compared with pyrolysis with the addition of N2 (inert gas). Pyrolysis oil was the major product of cattle manure pyrolysis. However, because of its complicated composition, pyrolysis oil cannot be considered a beneficial product. Thus, pyrolysis oil was converted into value-added syngas (H2/CO). Under pyrolysis with an introduction of CO2, the homogeneous reaction converted the volatile compounds and CO2 into CO at ≥ 510 ˚C. However, the reaction rate leading the CO2 reactivity was insufficient. To improve CO2 reactivity, supported Ni catalyst was introduced for catalytic pyrolysis. The concentration of CO from CO2-induced pyrolysis jumped 3.5 times (42.0 wt%) when the supported Ni catalyst was loaded in comparison with catalyst free pyrolysis setup. The increase in CO generation led to a decrease in the pyrolysis oil content (benzene analogs and polycyclic aromatic hydrocarbons) because the carbon was mostly reallocated to CO. The results of this study offer a strategic means of valorizing manure into syngas by tailoring the carbon length of the pyrogenic products.