Characterization of Char from Pyrolysis of Chlorogenic Acid

Pyrolysis of chlorogenic acid was studied under varying conditions of temperature and reaction environment. The objective was to study the effect of pyrolysis conditions on the composition of the solid residue, i.e., char. Runs were made at atmospheric pressure under oxidative and non-oxidative (inert) atmospheres and at temperatures ranging from 250 to 750 °C. The characterization of char was done in terms of its elemental composition and surface area, and by Fourier transform infrared (FTIR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The surface morphology of char was studied by scanning electron microscopy (SEM). The char yield in non-oxidative runs decreased from 80% at 250 °C to 20% above 550 °C. In oxidative runs, the char was completely oxidized at 550 °C. The surface area of char increased with temperature to a maximum of 196 m2/g at 650 °C. SEM analysis indicated that the pyrolysis of chlorogenic acid first formed a melt followed by formation of varying structures that decomposed rapidly at high temperatures. The H/C and O/C ratios of the char decreased as the temperature increased. NMR analysis showed that the resonance bands corresponding to carbonyl groups mostly disappeared above 350 °C and the phenolic groups became almost totally absent in 650 °C char. The aromatic character of char was enhanced with increasing temperature. FTIR studies indicated a gradual decrease in the intensities of OH and CO stretches at high temperatures. At 750 °C, most bands disappeared, resulting in a char that was mainly an aromatic polymer of carbon atoms. The oxidative pyrolysis enhanced mainly the surface area at the expense of char yield. The results are consistent with the analysis of the evolved gases.