(90c) Denitrogenation of Pyridine with Acetic Acid As Hydrogen Source Under Catalytic Hydrothermal Gasification Environment

Biofuel production from microalgae via hydrothermal liquefaction (HTL) produces wastewater with high organic (COD: 40 ~ 100 g/L) and nitrogen content (TN: 15g/L). The majority of nitrogen from the biomass remains in the post-HTL wastewater (PHWW). The most commonly identified chemical compounds in the PHWW are volatile fatty acids (VFAs) and cyclic amines such as pyridines. Pyridines, due to the aromaticity, are chemically stable, and they are also identified as cytotoxicity-inducing chemicals that inhibit the growth of microalgae even in 1% PHWW dilution, when the PHWW is reused as a nutrient source. Hydrodenitrogenation is an effective way to convert the pyridines into inorganic form as ammonia, or organic form as amides, which are better forms of nitrogen for biomass growth, as well as to mitigate the toxicity. Thus it is a beneficial to investigate an effective process of hydrodenitrogenation for recycling the HTL wastewater in large quantity without much dilution needed.

The first step of hydrodenitrogenation of pyridine is hydrogenation of pyridines to its piperidine form, followed by ring-opening and then C-C bond cleavage for ammonia/amine and small hydrocarbon production. Conventional hydrodenitrogenation requires hydrogen gas at high pressure to realize this series of conversions. Due to the large quantity of VFAs in the PHWW, and that VFAs have been extensively studied as model compounds for high hydrogen production in catalytic gasification conditions, it is possible to use VFAs as hydrogen precursor in the hydrodenitrogenation process without apply hydrogen gas.

In this study, acetic acid and pyridine are chosen as model compounds to evaluate the feasibility of using VFA as hydrogen source for hydrodenitrogenation of pyridine. Denitrogenation/gasification will be carried out under 500C reaction temperature, 60 min reaction time, which is previously discovered optimal operation condition for PHWW gasification. Denitrogenation efficiency and gasification yield under different pyridine to acetic acid ratio will be evaluated. Possible reaction pathway, and reaction kinetics will be discussed.