Surface-Modified Multi-lumen Tubular Membranes for SAGD-Produced Water Treatment

Abstract

The extraction of bitumen from oil sands using steam-assisted gravity drainage (SAGD) produces a considerable amount of oily process water that must be recycled. Ceramic membranes are well suited for this task, but membrane fouling remains a significant barrier to their widespread application. Bituminous clays in produced water are heavily charged and interact with the charged surfaces of ceramic membranes in a way that reduces membrane performance. To address this problem, the surfaces of commercially available multi-lumen tubular ceramic membranes were chemically modified using several charge-neutral polyethylene oxide (PEO)-based organosilanes. Membranes with a pore size of 10 nm and selective layers of either γ-Al₂O₃ or TiO₂ were modified based on protocols previously used on small-scale ceramic membrane disks and challenged with SAGD-produced water. Results indicate that the modification leads to an improvement in membrane performance. Modification of γ-Al₂O₃ membranes by a 30% solution of straight-chain PEO-silane increased permeate flux by factors as high as 2.9. Modification of TiO₂ membranes also improved permeate flux. Flux recovery factors upon backflushing increased from 1.3 to 1.6. Furthermore, flux values for γ-Al₂O₃ membranes ranged between 50 and 150 Lmh and increased over time, while flux values for TiO₂ membranes ranged between 220 and 350 Lmh and declined slightly over time. This indicates that γ-Al₂O₃ is a stronger adsorbent for bituminous foulants than TiO₂, with foulants being adsorbed quickly and subsequently released during filtration and backflushing. Finally, the decline in performance when switching to a SAGD feed, with a higher pH, total organic carbon and alkalinity, was significantly less severe for modified TiO₂ membranes compared to unmodified counterparts. Based on these results, surface modification of tubular ceramic membranes with PEO-based silanes was successful in improving the rejection of bituminous foulants from the membrane surface.