Phytic acid as a biorenewable catalyst for cellulose pyrolysis to produce levoglucosenone

Abstract

Phytic acid (PA) is a cheap organophosphorus compound readily available from agricultural wastes, with the potential to serve as a biogenic source of phosphorus compounds currently derived from finite phosphate rock. Developing applications for PA is important for its industrial implementation. This study demonstrates that PA serves as an effective organocatalyst during the pyrolysis of cellulose, promoting the selective formation of the high-value platform chemical levoglucosenone (LGO). With a loading of only 0.3 wt% PA (<0.1 wt% on a phosphorus basis), the onset temperature of cellulose pyrolysis decreased by over 60 °C. A detailed analysis of the catalytic performance, mainly during slow pyrolysis, revealed that PA penetrates the cellulose particles and fibers during the heating process, forming various chemical bonds and promoting dehydration. As a result, the LGO yield, which was only 2 wt% for pure cellulose, increased to 19.6 wt% (25.0% on a carbon basis) with a loading of 0.75 wt%. Excessive loading promoted char formation. The amount of PA required to maximize the LGO yield was about two-thirds that of conventional phosphoric acid (based on phosphorus content), suggesting superior catalytic performance and lower P loadings are possible. PA also led to the selective formation of LGO in the pyrolysis of lignocellulosic biomass, though in poorer yield compared to pure cellulose. Although it was difficult to extract PA from pyrolysis char for direct reuse, this residue could, in principle, re-enter the phosphorus cycle, possibly as a fertilizer.