Water content of pyrolysis oil: Comparison between Karl Fischer titration, GC/MS-corrected azeotropic distillation and H-1 NMR spectroscopy

Abstract

Pyrolysis converts biomass waste mainly into pyrolysis oil, which is a possible source of renewable energy and/or value-added chemicals. A very important characteristic of pyrolysis oil is its water content. Karl Fischer titration and azeotropic distillation by the Dean-Stark method are two common techniques for water determination. In this study, the water content is determined for several pyrolysis oil samples with a wide range in water content and/or originating from different types of biomass. The results of the conventional techniques are compared with these of a new proposed technique based on H-1 NMR spectroscopy. Azeotropic distillation turns out to be very sensitive for overestimation of the water content in case of pyrolysis oils with high amount of water soluble volatile organic compounds. Therefore, a GC/MS-correction is applied to these results. After correction, the results of the azeotropic distillation are in good agreement with these of the Karl Fischer titration. This strongly indicates that Karl Fischer titration and GC/MS corrected azeotropic distillation are free of interferences for the investigated pyrolysis oil samples, since similar results are obtained by two independent methods. The results of the H-1 NMR spectroscopy are very comparable with these of the conventional techniques for the oil samples with low and intermediate water content (<50 wt%). Only for samples with very high water content, H-1 NMR gives an underestimation in comparison with the conventional techniques. Hence, H-1 NMR spectroscopy is a possible alternative water determination technique for most pyrolysis oils. (C) 2010 Elsevier B.V. All rights reserved.