Interactions Between n-Butanol/Propionic Acid and Humic Acid Studied by NMR Spectroscopy

Abstract

The Fischer-Tropsch process produces liquid fuels. However, the process also yields Fischer-Tropsch wastewater, an acidic and corrosive byproduct enriched with various water-soluble oxygen-containing compounds such as alcohols, aldehydes, ketones and carboxylic acids, demanding careful treatment before discharge. Herein, the interactions between n-butanol and propionic acid, two main components in Fischer-Tropsch wastewater, and humic acid (HA) were studied with nuclear magnetic resonance (NMR) techniques. One-dimensional 1H chemical shift titration and 1H relaxation time measurements showed that: the peak width of both n-butanol and propionic acid broadened with increasing HA concentration, while the 1H chemical shift was unaltered for n-butanol, but moved to high field for propionic acid. The 1H spin-lattice and spin-spin relaxation time of n-butanol and propionic acid decreased and the 1H correlation time increased with increasing HA concentration. The interactions between HA and n-butanol were enhanced by increasing the HA concentration, but less affected by solution pH. While, the interactions between HA (20 mg/mL) and propionic acid were promoted by increasing the HA concentration and decreasing the solution pH value. It also appeared that the HA concentration plays a decisive role in the interaction. The study demonstrated that using HA for treatment of Fischer-Tropsch wastewater has a great potential in industrial applications owing to its simplicity and low price.

Keywords

• liquid-state nmr
• adsorption
• fischer-tropsch wastewater
• humic acid
• n-butanol
• propionic acid