Thermoresponsive Starch Nanoparticles for the Extraction of Bitumen from Oil Sands

Abstract

Starch nanoparticles (SNPs) useful for the extraction of bitumen from oil sands were obtained by modification with thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PMEO2MA) segments through RAFT (Reversible Addition–Fragmentation chain Transfer) grafting. Since PMEO2MA exhibits a Lower Critical Aggregation Temperature (LCAT), the polymer-grafted SNPs are amphiphilic above the LCAT of the thermoresponsive polymer and can interact efficiently with bitumen in the oil sands, facilitating its extraction. The PMEO2MA-grafted SNPs form micellar aggregates that remain dispersed in water but can shuttle the bitumen component out of the sand and silt mixture in the extraction process above the LCAT. Upon cooling, the hydrophobic PMEO2MA domains become hydrophilic again and the grafted SNPs remain in the water phase, while the extracted oil floats on the aqueous phase and can be skimmed off. The aqueous polymer solution may be reused in other extraction cycles. Extraction by tumbling of the oil-water-SNP mixtures in vials at 45 °C reached over 80% efficiency. The synthetic methods used provide easy control over the characteristics of the grafted SNPs (number and length of grafted PMEO2MA segments), and therefore over their hydrophilic-lipophilic balance (HLB). The SNP-g-PMEO2MA samples were characterized by 1H NMR, UV-visible spectroscopy and dynamic light scattering analysis, and the grafted PMEO2MA chains were cleaved from the starch substrates for analysis by gel permeation chromatography.