Development of antifouling membranes using agro-industrial waste lignin for the treatment of Canada's oil sands produced water

Abstract

Steam assisted gravity drainage (SAGD) is one of the key technologies that largely contributes to the global oil and gas production. However, the sustainable growth of this technology strongly depends on the judicious management of the mass-produced process-affected water. Membrane separation, considered as an advanced treatment process, fails to efficiently treat the SAGD produced water due to inevitable fouling if the membrane is not modified accordingly. Here, we used an industrial waste derivative of lignin, sulfonated Kraft lignin (SKL), containing highly hydrophilic and negatively charged functional groups, as a bulk modifier for the fabrication of antifouling polyethersulfone (PES) membrane. SKL concentration was varied to tune the internal morphology, permeability, hydrophilicity, and surface charge of the PES membranes. The modified membrane containing the highest amount of SKL additive (3 wt%) exhibited profound enhancement in the flux recovery ratio from 52.2% to 98.2% compared to the pristine PES membrane against the complex mixture of organic pollutants in SAGD produced water. The key parameters that contributed to the enhancement of the antifouling properties of the membranes were the surface hydrophilicity and the negative surface charge. The oil contact angle increased from 132.8°±1.0° for the pristine PES membrane to 146.8°±1.0° for 3 wt% SKL-embedded membrane while its negative surface charge increased by about 3 times under the operational pH (>8) of SAGD produced water. Another distinct feature of the SKL-modified membrane was that the rejection of the organics decreased only slightly from 61.7% for the pristine membrane to 56.1% for the 3 wt% SKL-embedded membrane while the permeability and molecular weight cut-off (MWCO) increased by 43.3 LMH/psi and 144 kDa, respectively. Such a similar removal efficiency of the SKL-modified membrane to the tighter pristine PES membrane was achieved presumably due to the shielding of the hydrophobic negatively-charged foulants by the hydration barrier and the negative charges on the surface of the SKL-modified membrane.