Application of nitrogen-based blowing agents as an additive in pyrolysis of cellulose

Pyrolysis of cellulose mixed with blowing agent additives containing high nitrogen content has been investigated in this work. The additives used are dicyandiamide (DCD), 5-aminotetrazole (5AT) and 5-phenyl-1H-tetrazole (5PT), in concentrations of 0.25, 0.50, 1.0, 2.0 and 4.0% (weight). Blowing agents are of particular interest as a cellulose pyrolysis additive for two reasons: as a first case, if these additives and their decomposition products are chemically inert with respect to cellulose pyrolysis reactions, then they can serve to enhance the ejection of high-molecular weight aerosols from the liquid intermediate phase that is known to form during pyrolysis; as a second case, if these additives are not chemically inert, then the reactions between blowing agent decomposition products (e.g., NH3 and HN3) can provide a pathway by which nitrogen-doped carbonaceous char structures can be readily produced. Pyrolysis studies were carried out using thermogravimetric analysis and analytical Py-GC/MS of the pure compounds (DCD, SAT, 5PT) and mixtures with cellulose, as well as proximate/ultimate analyses of the resulting chars from slow pyrolysis. Experiments showed that there is a reactive interaction between the additives and cellulose during pyrolysis, leading to greater char yields. Analysis of slow pyrolysis chars showed that DCD is promising for producing biochar with higher nitrogen content. This was attributed to the evolution of ammonia from DCD and due to its thermal decomposition occurring in a temperature range coincident with that of cellulose pyrolysis reactions.