Aquathermolysis of humic and fulvic acids: Simulation of organic matter maturation in hot thermal waters

Dissolved aromatic compounds in Hungarian thermal waters were first reported more than 10 years ago. Among the identified compounds were alkylbenzene, polyaromatic hydrocarbon and heteroaromatic homologue series. The appearance of dissolved organic compounds has been bound to a threshold temperature of similar to 80 degrees C, and their distribution is controlled by the water temperature. Relative demethylation and aromatisation were observed with increasing temperature. The origin of these compounds is not proved. Among precursor candidates are humic substances. Simulation experiments were carried out on humic and fulvic acid and on their mixture to gain information on aromatic compounds formed. The samples were heated and products were measured with GC-MS. In the presence of oxygen, increasing concentration of benzene can be observed as a function of temperature. Toluene and thiophene can be identified, other alkylbenzenes are missing. Under reductive conditions the concentration of benzene, toluene and the ratio of short to long chained aromatics generally increases in every sample as a function of temperature. Main compounds are toluene and benzene. The amount of heteroaromatic compounds increases with temperature, but their relative concentration compared to aromatic hydrocarbons decreases. At higher temperatures the proportion of pyrroles drops and S and O containing ones become dominant. The different processes (formation, aromatisation, polycondensation, relative demethylation, decomposition) occur in parallel but their relative intensities vary as a function of temperature. The effects of duration and increasing temperature are similar but not equal: both demethylation and aromatisation can be observed. (C) 2012 Elsevier Ltd. All rights reserved.