Physical plasma for lignin valorization: comprehensive analysis of aromatic substances derived from cleavage and...

Renewable raw materials, such as lignin, seem to be the solution for the depletion of crude oil, on which the chemical industry relies. However, current methods for the extration of valuable substances use harsh reaction conditions e.g. temperatures of 100-300 °C or pressures of 1-8 MPa. Therefore, physical plasma could be an environmentally friendly option with reactions mediated in aqueous solutions, at room temperature and atmospheric pressure. No catalyst is required only electricity. Cold atmospheric-pressure plasma was used for the treatment of the lignin model compound guaiacylglycerol-ß-guaiacyl ether (a β-O-4 linkage dimer). The guaiacyl ether was transformed to radicals by reactive oxygen and nitrogen species. The favoured plasma-mediated degradation reactions involved cleavage of C_α-C_β and C_β-O bonds, resulting in quantifiable amounts of vanillin and guaiacol as main products. Degradation and synthesis mechanisms were compared with other depolymerisation processes. Furthermore, the high degree of hydroxylation mediated by plasma suggested a higher hydrophilicity. Future applications of plasma may include not only a cleavage of large polymers such as lignin to valuable compounds but also the provision of highly soluble lignin. Thus, the described plasma-mediated transformation reactions represent a first step towards the sustainable utilisation of lignin and other polymers particularly in the synthesis of platform chemicals.