Syngas Production via CO2-Mediated Melamine Pyrolysis

Abstract

Melamine is an extensively used fire retardant in various commercial products. Along with its applications, awareness about its toxicity also increases and the accelerated rate of waste generation has become a concern. This study proposes a systematic approach for the conversion of melamine into syngas. For enhanced sustainability of this process, CO2 was used as the reactive medium during pyrolysis. Before pyrolysis, melamine was examined by using thermogravimetric analysis and pyrolysis-gas chromatography. Subsequent melamine pyrolysis yielded only ammonia and condensed pyrolysates. A double-stage pyrolysis setup was used to optimize the thermal cracking of melamine. Under CO2 conditions, CO was generated although melamine lacks an inherent oxygen source. The CO evolution under the CO2 condition is attributed to the homogeneous interaction between CO2 and volatile pyrolysates. However, the slow kinetics of this homogeneous reaction hinders its complete activation. To expedite the homogeneous reaction, a Ni catalyst was introduced. The concentration of CO from catalytic pyrolysis under the CO2 condition enhanced 109 times (35 mol %) compared to double-stage pyrolysis setup. Furthermore, melamine completely transformed into gaseous pyrolysates after catalytic pyrolysis under CO2 conditions. All experimental observations highlighted that melamine pyrolysis under CO2 and a Ni catalyst could be a useful energy and chemical recovery approach.