Reductive pyrolysis of leonardite humic acids

Abstract

Leonardite humic acids from Kaz Daglari (Turkey) are studied by reductive pyrolysis. Sample is pyrolysed in a H-2 flow in the temperature range 250 degrees C divided by 950 degrees C. Volatiles are trapped in two ice-cooled Tenax tubes. Atmosphere Pressure-Temperature Programmed Reduction (AP-TPR) technique coupled "off-line" with thermal desorption gas chromatography - mass spectrometry (TD-GC/MS) apparatus is used to specify organic compounds in the pyrolysate. During sample thermal decomposition a broad range of species is produced. Aliphatic compounds, i.e. n-alkenes/n-alkanes, i.e. nC(6)divided by nC(14); aromatic compounds, i.e. benzene, alkylated benzenes, naphthalenes, biphenyls; oxygen containing compounds, i.e. phenols, methoxy phenols, furans, benzofurans; sulphur containing compounds, i.e. polysulphides, thiophenes and nitrogen compounds, i.e. benzonitriles, indoles and quinolines. Leonardite organic matter is rich in oxygen, where phenolic structures are the most abundant. Compounds are quantitatively interpreted. According to pyrolysis data "average" structural units of leonardite humic acids from Kaz Daglari deposit are mainly composed by 1-2 aromatic cycles, condensed or coupled. Heteroatom compounds are also admitted. Experimental data argue for sample low maturity as rests of lignin building blocks, i.e. methoxy phenols, and carbohydrate degradation products, i.e., 2-methyl-2-cyclopenten-1-one, are still present.