Treatment of Spent Caustic Using Immobilized Ionic Liquids

A Master of Science thesis in Chemical Engineering by Nihal Yasir Ahmed entitled, “Treatment of Spent Caustic Using Immobilized Ionic Liquids”, submitted in April 2022. Thesis advisor is Dr. Taleb Ibrahim. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).

Abstract

Treatment of spent caustic (SC) streams from refineries and petrochemical industries is not only complicated, but also very expensive, owing to the presence of hazardous substances, high pH levels, varying waste compositions, and the need to adhere to environmental regulations. Hydrophobic ionic liquids were investigated in a previous study for their ability to treat SC with removal efficiencies of more than 99% being achieved. However, the effective regeneration of the ionic liquids, necessary for the process to be industrially viable, was not successfully achieved. To overcome this problem, modifying the surface of nanomaterials with ionic liquids is proposed. These altered materials were utilized as adsorbents for the treatment of SC. They represent a simple, high potential, easy to regenerate, and an environmentally friendly alternative to the conventional treatment technologies. Zeolite-alginate beads loaded with trihexyltetradecylphosphonium bromide (IL) were prepared and investigated to determine its efficiency towards the treatment of SC in batch adsorption experiments. FTIR, TGA, SEM and EDX techniques were utilized to determine the physicochemical parameters of the beads. The FTIR analysis revealed that the ionic liquid was efficiently absorbed into the zeolite-alginate composite. The effect of different parameters such as pH, contact time, initial concentration and temperature on the treatment of SC by the beads, was examined. Results, demonstrated that the maximum adsorption capacity on the prepared composite occurred at pH 2, contact time of 2 hours and at 25 °C with a value of 45.88 mg/g and a removal efficiency of 93%. The pseudo-second order model explained the adsorption kinetics effectively, and the Freundlich isotherm model provided the greatest fit to the experimental data. Regeneration studies revealed that the beads could be employed for SC treatment for over four successive adsorption cycles with no significant reduction in adsorption effectiveness. The beads were also employed to investigate continuous fixed-bed adsorption of SC, as well as the effect of SC flowrate and adsorbent’s column bed height. The results were fitted to different adsorption models and it was found that the adsorption of phenol from SC streams best fit the Clark’s model.