Amidated Cellulose Nanofibrils as Demulsifying Agents for a Natural Water-in-Heavy-Crude-Oil Emulsion

Abstract

The presence of emulsified water in heavy crude oils invariably causes processing problems and financial costs associated with an increased energy input required to handle highly viscous fluids. Thus, physical or chemical separation methods are usually applied to dehydrate crude oils before processing. Dehydration chemicals or demulsifiers are among the most widely used chemical strategies to rid heavy crude oil from water. In this work, we explore the use of amidated cellulose nanofibrils as dehydrating agents for a water-in-heavy-crude-oil emulsion. Using microcrystalline cellulose (MCC) as raw material, we extracted oxidized cellulose nanofibrils (1.25 mmol COOH/g cellulose) via ultrasound-assisted TEMPO oxidation. TEMPO-oxidized cellulose nanofibrils (TOCNs) were rendered hydrophobic through the coupling with dodecyl-and octadecylamine through one-pot amidation reactions. The introduction of C 12 and C 18 alkyl moieties on the cellulose surface was enough to promote the dispersion of the materials in toluene and increase the water contact angle (CA) from 17°for TOCN to 61°and 67°for TOCN-AMDC 12 and TOCN-AMDC 18 , respectively. HLB values of 9.6 and 9.2 for TOCN-AMDC 12 and TOCN-AMDC 18 are characteristic of dehydrating agents for w/o emulsions. Thus, the materials were tested as demulsifying agents for the disruption of a natural water-inheavy-crude-oil emulsion with a water content of 55%. Conventional tests (BSW, bottle test) showed the ability of TOCN-AMDC 12 and TOCN-AMDC 18 to effectively dehydrate the emulsions, with a water recovery up to 74%, when used at 1500 ppm in toluene as the carrier fluid. Optical microscopy and rheological analysis were performed before and after the nanofluids' application to determine the viscosity profile of the emulsion and to observe the types and sizes of water droplets in the oil phase after dehydration.

Perspectives in Nanocellulose for Crude Oil Recovery: A Minireview

“…CNF dispersibility in nonpolar phases, such as toluene, is improved after surface modification with alkyl units by amidation reactions. 119 Unmodified CNFs (1.25 mmol of COOH/g of cellulose) exhibit water CAs of 17°, which changed to 61°and 67°after introducing C12 and C18 alkyl moieties, respectively. The CA between a liquid, water in most cases, and a surface depends upon the liquid cohesive forces and the adhesive forces between the surface and the liquid at the point of contact.…”

“…Modified CNFs (1.5 wt % in toluene) with HLB values of around 9.6, characteristic of dehydrating agents for w/o emulsions, effectively broke a natural water/heavy crude oil emulsion [basic sediment and water (BSW) of 55%], allowing for water recovery up to 74%. 119 Optical microscopy (Figure 9a) shows large water droplets in the original water/heavy crude oil emulsion. After water drainage with the modified CNFs, the nonpolar phase exhibits less and smaller water droplets (panels b and c of Figure 9).…”

“…Unmodified NCs are suitable surface-active additives for emulsion inhibition, as demonstrated above; however, highly hydrophilic NCs are not very useful as demulsifiers once the water-in-crude oil emulsion is already formed as a result of dispersibility limitations in the emulsion nonpolar continuous phase. CNF dispersibility in nonpolar phases, such as toluene, is improved after surface modification with alkyl units by amidation reactions . Unmodified CNFs (1.25 mmol of COOH/g of cellulose) exhibit water CAs of 17°, which changed to 61° and 67° after introducing C12 and C18 alkyl moieties, respectively.…”

“…Hydrophobic (or oil-wet) surfaces present CA values between 90° and 180° as a result of dominant cohesive forces. Modified CNFs (1.5 wt % in toluene) with HLB values of around 9.6, characteristic of dehydrating agents for w/o emulsions, effectively broke a natural water/heavy crude oil emulsion [basic sediment and water (BSW) of 55%], allowing for water recovery up to 74% . Optical microscopy (Figure a) shows large water droplets in the original water/heavy crude oil emulsion.…”

Improvement of oil field development using enhanced oil recovery methods

“…alkali or surfactant fl ooding) [9]. In addition, when there is highly viscous heavy oil in a subterranean formation, fl ooded water tends to bypass signifi cant parts of the formation due to its mobility and low viscosity [10] This can be addressed by increasing the viscosity of the injected water, which is often achieved using materials such as water soluble or water dispersible removable polymers with high molecular weight [11]; however, adverse environmental conditions in the subterranean formation, such as high temperature and dissolved electrolytes, can cause some polymers to precipitate and/or lose their viscosity-increasing efficiency, thereby again increasing fl ood water mobility.…”