The interaction between Fischer–Tropsch wastewater and humic acid: A NMR study of butanol isomers

Fischer–Tropsch wastewater (FTW), co-produced with hydrocarbons in Fischer–Tropsch process, is usually rich in water-soluble oxygenates, e.g. carboxylic acids, alcohols and aldehydes. Purification of FTW is crucial for achieving effective resource utilization and environmental concerns. The adsorption of FTW by humic acid (HA) has been studied via NMR. Butanol isomers, n-butanol (n-BuOH), sec-butanol (s-BuOH), iso-butanol (i-BuOH) and tert-butanol (t-BuOH), were used as model compounds of water soluble organic constituent for FTW. The interaction between HA and BuOHs was evaluated based on the NMR study. Lack of chemical shift change and broadening of peak width were observed with successive HA addition, 1 H spin-lattice and spin-spin relaxation time of BuOHs decrease and 1 H correction time increased. Association percentage to HA, association constants and Gibbs free energies for BuOHs were calculated. The adsorption efficiency of BuOHs decreased in the order: s-BuOH > n-BuOH > i-BuOH > t-BuOH. The effects of HA concentration and solution pH value on the interaction were examined, and the interaction is favored by increasing HA concentration, but less dependent on solution pH value. The studied process is effective for treating FTW and has a great potential for industrial applications due to its simplicity and low price.