HPTLC and UV spectroscopy as innovative methods for biomass gasification tars analysis

Abstract

The present work investigates the potential of two analytical tools to ensure rapid and affordable analysis of tar, produced during biomass gasification. On one hand, high performance thin layer chromatography (HPTLC) provides quantitative and qualitative information on tar composition and on the other, UV spectroscopy allows rapid quantitative total polycyclic aromatic hydrocarbon (PAHs) determination.An original separation method, based on HPTLC coupled with UV and fluorescence detection, enables the resolution of non-volatile hydrocarbons into families from two to five aromatic rings, with a difference between condensed and non-condensed structures. The method uses a two-stage migration with ethyl acetate/n-hexane and n-hexane on RP-plates, at −23°C. HPTLC is also used for tar quantification, by means of standard addition method after merging all the aromatic compounds in one peak.Thereafter, two approaches are proposed for UV quantification: the first, UV direct quantification, consists in determining the absorbance and concentration of a reference sample, which permits to calculate unknown tar concentration. The second, based on UV spectra deconvolution (UVSD), calculates tar concentration by UV deconvolution of selected standard spectra without the need of reference samples. Both approaches were applied on thirty-seven samples formed in three gasifiers, a Bubbling Fluidized Bed (BFB), an Internal Circulating Bubbling Fluidized Bed (ICBFB) and a Circulating Fluidized Bed (CFB).All the methods applied show a good agreement between the results obtained and the concentration of tar determined by HPLC/UV, the reference method.