Reports: DNI1053638-DNI10: Bi-Compartmental Targeting Vehicles for In-Situ Catalytic Recovery of Hydrocarbon Molecules
Ning Wu, Ph. D, Colorado School of Mines
Heavy oil is abundant in the world; however, most of it is highly viscous and difficult to extract by conventional methods. As identified recently by the Society of Petroleum Engineers, downhole delivery of nanocatalysts for in-situ conversion of heavy oil into lighter grade oil could be a game-changing technology. Unfortunately, most of the catalytic nanoparticles are not amphiphilic in nature and targeted delivery towards the oil phase through water flooding is one of the grand challenges facing the petroleum industry. The objective of this project is to build a unique type of targeting vehicle that can encapsulate catalytic nanoparticles, transport them within porous media, seek oil-water interfaces, and finally deliver them to the oil phase.
Within year one of this project, we have successfully designed, synthesized, and tested a unique type of bi-compartmental targeting vehicle that encapsulates catalytic molecules, finds and accumulates at oil-water interface, releases the catalysts towards the oil phase, and performs hydrogenation reaction of unsaturated oil. As shown in Fig. 1, the targeting vehicle is designed based on a two-compartmental polystyrene particle where one non-crosslinked compartment encapsulates the catalysts. The other compartment consists of highly crosslinked polymer. Although the vehicle is hydrophilic and dispersible in water initially, it can become amphiphilic because the non-crosslinked compartment swells in oil easily. This will enable the vehicle to transport through the aqueous phase; seek and then attach to the oil-water interface. Furthermore, the non-crosslinked compartment is designed to swell significantly and dissolve in oil eventually, which will facilitate the targeted release of catalysts into the oil phase. Fig. 2 summarize the synthetic route we have followed to make conventional polystyrene dimers and those encapsulate different kinds of active agents (e.g., fluorescent molecule Oil Red O, molecular catalysts Pd(OAc)2 and RhCl(PPh3)3). Both fluoresecent and scanning electron microscopy images in Fig. 2b and 2c show that the active agents have been selectively encapsulated in one lobe.
Fig. 1 A schematic of the bi-compartmental vehicle (colloidal dimer) targeted for delivering catalysts to oil phase underground. (a) One compartment is hydrophilic and highly crosslinked, while the other one is non-crosslinked and oil-swellable. (b) The vehicle transports through water flooding, adsorbs at the oil-water interface, and swells significantly in oil. (c) The hydrophobic compartment eventually dissolves in oil and releases catalysts for subsequent hydrogenation.We further study the behavior of the dimers in a mixture of toluene and water. As shown in Fig. 3, the dye is initially encapsulated in the non-crosslinked (larger) lobe, rendering the water phase red. Since the dimers possess a uniform distribution of sulfonate groups on their surfaces, they are well dispersed in the aqueous phase initially. They sediment to the bottom of the vial within ~1 day because of their large sizes and higher density than water. Afterwards, the uncrosslinked lobe swells significantly upon contact with a trace amount of oil in aqueous phase. The dimers then become amphiphilic, migrate towards, and accumulate at the oil-water interface. As the uncrosslinked lobe swells and eventually dissolves in oil, the encapsulated dyes are fully released. By examining the particles at the final stage, we find that the non-crosslinked lobes eventually disappear, indicating that they dissolve completely in the oil phase. We note that the dissolvability of the non-crosslinked lobe will allow potential encapsulation and release of much larger species such as catalytic nanoparticles in addition to molecular catalysts, which will be tested in future. We confirm that the oil-phase delivery of organometallic salts which can catalyze the hydrogenation of olefins can be achieved in a similar way.
Fig. 2 The synthetic route of polystyrene dimers encapsulating different molecules. (a) Synthesis of conventional polystyrene dimers. Fluorescent image shows that the negatively charged dimers absorb positively charged fluorophores (i.e., Rhodamine 6G) uniformly. (b) The fluorescent image shows selective encapsulation of Oil red O in the uncrosslinked lobe. The SEM image shows the large-field view of polymerized dimers. (c) Encapsulation of two molecular catalysts in the uncrosslinked lobe. Scale bar for all images: 2 micron.
Fig. 3 (a) Time evolution of the Oil Red O encapsulated dimers in a mixture of toluene and water. (b) When t=0, both fluorescent and bright-field microscopy images show that the dye is encapsulated in the large and non-crosslinked lobe. At t~177 hrs, the non-crosslinked lobes eventually dissolve in the oil phase. Scale bar for all images: 2 µm.
After the catalysts are delivered into the oil phase, we perform the hydrogenation reaction for three different kinds of α-olefins, i.e., styrene as a model for aromatics, octene for linear hydrocarbons, and butyl acrylate for unsaturated esters. 40 µl of olefins is each dissolved in separated vials of 2 ml toluene where the Wilkinson catalysts have already been delivered through dimers (see experimental methods for details). The mixtures are then heated to 80 °C under 2 bar of hydrogen gas. After one hour, we stop the reaction and take the oil phase for GC-mass spectrometry. We find that both styrene and octene reach 100% conversion to ethylbenzene and octane, respectively. For butyl acrylate, its conversion to butyl propionate is ~84.5%. Clearly, the high conversion rates prove that our dimer system is capable of performing oil-phase catalytic reactions by delivering the encapsulated catalysts from water to oil. Our unique approach allows the efficient encapsulation and safe transport of nanoparticles or small molecules, the specific detection of oil pockets within a reservoir, and the targeted delivery of catalysts for modifying oil properties in-situ. It is anticipated that this study will provide fundamental knowledge necessary for the development of a game-changing extraction technology of unconventional hydrocarbons. This research also allows the support of one Ph. D. student. One paper based on this research has been submitted for publication.
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