Transformation analysis of key liquid phase products during lignite fermentation to produce biological hydrogen

Abstract

There was little research on the changes and interconversion of organic compounds in the intermediate liquid-phase productsin the hydrogen production by anaerobic fermentation of coal. The types and concentrations of the intermediate liquid-phase products are not only related to the efficiency of coal conversion into biohydrogen, but one of the important contents of study on the generation mechanism of biohydrogen from coal. In order to study the change of key liquid phase products in the process of bio-hydrogen production from coal, the simulation experiments of bio-hydrogen production were conducted under suitable environmental conditions using lignite from Daliuta, Shaanxi province. The hydrogen concentration and key liquid phase products were measured using gas chromatography and GC–MS, respectively, to reveal its change. The results show that: (1) there is correspondence between the key liquid phase products and hydrogen yield. The saturated alkanes and cyclic hydrocarbons show a trend of first increasing, then decreasing, and finally increasing, but the changes of proteinaceous materials are just the opposite, which is correspondent to the initial stage, peak stage and terminal stage of hydrogen production, respectively. (2) The short-chain volatile fatty acids are accumulated gradually in the process of hydrogen production, and the short-chain acids of aromatic show a trend of first increasing, then decreasing, increase again and finally decreasing, which is correspondent to the different biochemical reactions, such as the release of small molecules, the utilization of microorganisms, hydrocarbon oxidation and the redegradation of macromolecule. (3) The lipids, aldehydes and ketones are the parent substances of acid production, and the changes are related to the increased acids to a certain extent. This research not only reveals the biochemical effects between gas and liquid phases, but further enriches the theory of bio-hydrogen production from coal. Keywords: Lignite, Anaerobic fermentation, Biological hydrogen, Key liquid phase products, Origin bacteria, GC–MS, Variation law, Hydrogen-generating mechanism