Influence of Structural Variations of Demulsifiers on their Performance

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Influence of Structural Variations of Demulsifiers on their Performance Ishpinder Kailey* and Xianhua Feng

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Baker Hughes, 7020 45th Street, Leduc, Alberta, Canada T9E 7E7 ABSTRACT: Chemical demulsification is the most widely used method for breaking water-in-diluted bitumen emulsions in oil sands processing. In this work, the properties and performance of six samples of ethylene oxide (EO)propylene oxide (PO) block copolymer demulsifiers from two families were investigated. The demulsifiers were characterized by their relative solubility number (RSN), EO content, PO content, and molecular weight (MW). The results showed that the performance of the demulsifiers is correlated to the starting base compound, EO content, PO content, RSN, MW, degree of cross-linking, interfacial tension (IFT), yield stress of underflow, and bitumen loss. Demulsifiers with higher MW and more EO−PO branching had higher dehydration efficiencies when the EO content was varied from 0% to 40% at constant PO content. An increase in MW by cross-linking EO−PO copolymers improved the dehydration efficiency. In this work, an appropriate rheological method was developed to correlate the properties of the demulsifiers with the properties of the underflow. The yield stress of the underflow, including settled solids, water, and the rag layer, increased with increasing RSN value and dosage of demulsifier. At high dosages, the yield stress values were high because of an increased number of aggregates, which, in turn, restricted underflow. An increase in the RSN value of the demulsifiers led to more bitumen loss to the underflow, which increased the size of the aggregates present in the underflow, resulting in increased immobility and constriction and higher yield stress.

1. INTRODUCTION Bitumen can be liberated from oil sands by the flotation process wherein oil sands are washed with hot water under alkaline conditions. Bitumen attaches to air bubbles and rises to the top of the flotation vessel in the form of bitumen froth. The bitumen froth typically consists of 60 wt % bitumen, 30 wt % water, and 10 wt % solids. Further removal of water and solids from the bitumen froth is achieved by diluting the froth with naphtha or paraffinic solvents. In the paraffinic froth treatment process, a paraffinic solvent-to-bitumen ratio greater than 2 is used to dilute the froth and precipitate asphaltenes.1 During solvent addition, water droplets and fine solids agglomerate with the precipitated asphaltenes, which settle quickly, producing clean bitumen with a total water and solids content of less than 0.1 wt %.2−5 On the other hand, in the naphthabased froth treatment, a solvent-to-bitumen ratio of 0.6−0.75 is used, and the diluted bitumen product typically contains about 2−5 wt % water and 0.3−1 wt % solids.6 Residual solids in the diluted bitumen product are primarily dispersed clay particles, whereas the residual water exists as emulsified water droplets with diameters of around 5 μm.6,7 The stability of the water-in-oil emulsions is attributed to the presence of surface-active materials, such as asphaltenes, resins, naphthenic acids, and clays. These materials form a rigid interfacial film at the oil/water interface that inhibits the coalescence of emulsified water droplets.8−14 Removal of residual water and solids from the diluted bitumen product is critical, as the chloride ions present in water cause corrosion issues and the solids cause fouling problems within the downstream refining infrastructure.15 Further complications in naphtha-based froth treatment can occur as a result of the buildup of material at the oil/water interface.16,17 The interfacial layer, also known as the rag layer, is a mixture of flocculated water droplets and complex © 2012 American Chemical Society

emulsions stabilized by a small fraction of asphaltenes, resins, sodium naphthenate, and fine solids. This material builds up over time and can grow thick enough to overflow into either the diluted bitumen or the tailing stream. If it enters the diluted bitumen stream, it increases the amount of water and solids, which can result in corrosion and fouling problems in downstream processes. If it enters the tailing stream, it potentially reduces the bitumen recovery. Either way, a large rag layer can eventually shut down the process. The mechanisms involved in rag-layer formation and accumulation are not yet completely understood. There are two possible reasons for this: First, the collection of undisturbed rag-layer samples from industrial equipment such as centrifuges and inclined-plate settlers is extremely difficult. Second, the generation of a rag layer in the laboratory is difficult because rag-layer formation takes place during continuous operations. Saadatmand et al. investigated the mechanisms of rag-layer formation17 and found that the volume of the rag layer depends on the type of diluent and oil sands froth quality. The rag layer formed in paraffinic solvents was found to be more compact than that formed in naphtha. Also, low-grade oil sands gave larger volumes of a rag layer because of the presence of fine solids. To meet downstream fluid specifications, water and solids in naphtha-diluted bitumen are usually removed using a combination of mechanical means and chemical treatment with demulsifiers. Chemical demulsification is a cost-effective, convenient, quick, and efficient method for breaking water-inReceived: Revised: Accepted: Published: 785

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water, and 10 wt % solids. The bitumen sample used in the IFT measurements was Syncrude vacuum distillation feed bitumen. ACS-grade toluene was purchased from Fisher Scientific. Ethylene glycol dimethyl ether used for determination of RSN values was high-performance-liquid-chromatographygrade, purchased from Sigma-Aldrich, and used as received. Deionized (DI) water was used in all IFT measurements. 2.2. Demulsifiers. The EO−PO copolymer demulsifiers were synthesized in the Baker Hughes Evan Ginn Research & Development Center in Sugar Land, TX. They were synthesized by reacting base compound A or B first with PO and then with EO. The functionalities in base compounds A and B were 3 and 5, respectively. By varying the amounts of PO and EO, demulsifiers with different hydrophobicities were obtained. In this work, three A-series and three B-series compounds were prepared and studied. Within each series, the amount of PO in the PO block was constant, however, the EO content was varied from 0% to 40%, as shown in Table 1. The size of the PO block was increased from one series to the next to give a larger molecular weight. The MWs of the EO−PO copolymers are included in Table 1.

oil emulsions in the petroleum industry. The function of the demulsifier is to alter the interfacial properties and to displace the asphaltenic-stabilized emulsion film from the oil/water interface. Amphiphilic block copolymers, which contain hydrophilic ethylene oxide (EO) and hydrophobic propylene oxide (PO) blocks, are widely used as demulsifiers for the removal of water from naphtha-diluted bitumen. Numerous attempts have been made to correlate demulsifier characteristics such as hydrophile−lipophile balance (HLB),18−22 relative solubility number (RSN),23,24 chemical composition (EO and PO numbers),20,23−25 and oil/water interfacial tension (IFT)23 with performance. The HLB concept, first introduced by Griffin,26 is an important parameter for characterizing nonionic surfactants. Because HLB is difficult to determine experimentally, RSN is used to characterize HLB. Wu et al. found linear correlations between RSN and HLB for different surfactant families.18 Like HLB, RSN is directly related to the EO−PO composition of a demulsifier. A linear correlation has been established between RSN values and EO numbers for demulsifier families having the same hydroxyl equivalent number (OHEQ).23 The higher the RSN value, the greater the hydrophilicity of the surfactant. In froth treatment, the industry is always on the lookout for demulsifiers that act as effective oil dehydrators, minimize raglayer formation, and reduce solvent/bitumen loss to tailings. Although the correlation between demulsifier characteristics and performance has been extensively investigated, studies showing the influence of structural variations of demulsifiers on the rag layer and underflow have never been reported.18−26 Because of technical difficulties in generating and collecting undisturbed rag-layer samples in batch experiments, preference has been given to collecting undisturbed samples of underflow in the laboratory. To understand the influence of structural variations of demulsifiers on the underflow structure, an appropriate rheological method was developed by which demulsifiers can be characterized quantitatively by measuring the yield stress of the underflow. The underflow, which comprises water, solids, and the rag layer, was created in the laboratory to simulate the commercial tailings for the purpose of research and might not represent accurately the underflow produced during industrial operations. This study represents the first effort to investigate the influence of structural variations of demulsifiers on the yield stress of the underflow and bitumen loss in the naphtha-based froth treatment process. To achieve this purpose, six samples of EO−PO copolymer demulsifiers were synthesized with two different base compounds (A and B) by varying the molecular weight (MW) and percentage of EO gradually to give 0−40% EO in each finished product. The objective of the study was to investigate the correlation between dehydration efficiency and demulsifier characteristics, such as chemical composition (i.e., EO content, PO content, degree of cross-linking, starting base compound, number of EO−PO branches, and MW), HLB, RSN, IFT, and effect on the underflow by measuring the yield stress and composition of the underflow. The results provide an improved understanding of the correlation between demulsifier characteristics and demulsifier performance.

Table 1. Structural Information on EO−PO Demulsifiers Used in This Work base compound

sample name

molecular weight

A

A1 A2 A3 B1 B2 B3

2400−3500 3600−5500 4800−7200 4000−6700 6000−10000 8000−13500

B

2.3. Demulsification Tests. The jar tests were designed to evaluate the demulsifier performance in inclined-plate settlers and settling tanks. These tests simulate the current settling operation in the industry. The jar tests were conducted on fresh froth samples from industry and used to determine the dehydration efficiency of the demulsifiers. To mimic the real system, fresh bitumen froth from industry was used. Note that the same batch of bitumen froth was used for all of the jar tests completed. The bitumen froth was homogenized by mechanical stirring at 1050 rpm at 80 °C for 3 h in a baffled stainless steel beaker with a water jacket. The homogenized froth was collected from the bottom of the beaker and placed in a set of numbered jars. Based on the mass of froth in each jar, the amount of naphtha required to give a naphtha-to-bitumen ratio of 0.7 was weighed into another set of numbered jars and dosed at 50 ppm with demulsifier. Two undosed “blank” jar tests were performed as controls in each set of experiments. The froth and naphtha jars were transferred to a water bath at 80 °C. After 30 min, the naphtha jars were shaken for 1 min on a horizontal shaker at high speed, and the contents were then added to the respective froth jars. The mixed samples were allowed to settle at 80 °C for 15 min and then shaken for 6 min on a horizontal shaker at high speed. After being shaken, the jars were transferred to a water bath at 80 °C, and their contents were allowed to settle. Oil samples were taken at one-third of the height from the surface at 10 and 30 min from each jar, and the water content was determined by Karl Fischer titration. The average water content in the two blank tests was used as a baseline. The dehydration efficiency of each demulsifier was evaluated by the water removal percentage calculated from

2. MATERIALS AND METHODS 2.1. Materials. Bitumen froth and naphtha were obtained from oil sands producers in Alberta, Canada. The composition of the froth samples was analyzed by a Dean−Stark extraction method and averaged approximately 60 wt % bitumen, 30 wt % 786

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(Wo − Wd) × 100 Wo

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thimble and then repeatedly extracted with toluene under reflux. The solids remained in the thimble, and the water was collected in the side trap. The absolute amount of bitumen was determined by a filter paper method, whereas the absolute weights of water and solids were determined by weighing. The solvent content was determined by mass balance.

(1)

where Wo is the water content in the blank test and Wd is the water content in the presence of demulsifier. The results reported for each demulsifier are the averages of three measurements. 2.4. RSN Measurements. The RSNs of the demulsifiers were determined using toluene/ethylene glycol dimethyl ether (EGDE) as the RSN solvent. In this method, 1 g of demulsifier was dissolved in 30 mL of RSN solvent, and the resulting solution was then titrated with DI water until visible, persistent turbidity appeared. The end point was detected by an 888 Titrando colorimeter. The volume of the DI water in milliliters used as titrant was recorded as the RSN value. The details of the method can be found in ref 19. 2.5. IFT Measurements. The IFTs of toluene-diluted bitumen−water interfaces in the absence and presence of demulsifier were measured by the Pt/Ir du Nouy ring method using a Fisher Scientific Semiautomatic model 21 Tensiomat tensiometer. DI water was used as the aqueous phase. All measurements were performed at 20.0 ± 0.5 °C. 2.6. Underflow Preparation. Fresh bitumen froth was homogenized and collected in jars according to the procedure mentioned in section 2.3. Based on the mass of froth in the jar, the amount of naphtha required to give a naphtha-to-bitumen ratio of 0.7 was weighed into another jar. The demulsifier was added to the naphtha, and then the froth and naphtha jars were transferred to a water bath set at 80 °C. After 30 min, the naphtha jar was shaken for 1 min on a horizontal shaker at high speed, and its contents were then transferred to the froth jar. The mixed samples were allowed to settle at 80 °C for 15 min and then shaken for 6 min on a horizontal shaker at a high speed. After being shaken, the mixture was transferred into a settling column and allowed to settle at 80 °C for 1 h. The disturbances to the underflow structure were reduced by collecting underflow directly in a measuring cup connected to the bottom of the settling column. The column was allowed to cool to 30 °C after settling for 1 h at 80 °C. The supernatant, which was diluted bitumen, was discharged from the side tap of the settling column, and then the measuring cup was disconnected from the settling column for yield stress measurements. Blank tests were performed as controls in each set of experiments. 2.7. Yield Stress Measurements. An Anton Paar MCR101 rheometer with vane geometry was used for yield stress measurements. Yield stress is defined as the level of stress at which substantial deformation suddenly takes place. For underflow, the yield stress can be defined as the stress at which the structure of the underflow is broken down and the underflow is free to flow. There are numerous methods for determining the yield stress.28 In this work, the shear stress versus shear strain method was used. The vane geometry causes fewer sample disturbances, thus minimizing thixotropic breakdown; is less susceptible to artifacts arising from large particle sizes; and minimizes wall-slip effects, as yielding occurs between layers of fluid.27,28 The shear stress as a function of shear strain was determined for underflow at 50 and 200 ppm dosages. All yield stress measurements were conducted at 30 °C. The results reported are the averages of three measurements. 2.8. Composition Analysis. The composition of the underflow was determined by the Dean−Stark extraction method. Settled material was transferred to a Soxhlet extraction

3. RESULTS AND DISCUSSION 3.1. Effects of EO Content and Cross-Linking in a Demulsifier on RSN Value. Figures 1 and 2 illustrate the

Figure 1. RSN value as a function of EO content (%) for EO−PO demulsifiers from series A.

Figure 2. RSN value as a function of EO content (%) for EO−PO demulsifiers from series B.

effects of the EO content on the RSN value of the EO−PO copolymers. The results indicate that the RSN values are dependent on both the EO and PO contents of the demulsifier. It is clear that the RSN values are linearly correlated with the EO content at fixed PO content. This reveals that, at fixed PO content, the hydrophilicity of the demulsifier increases with increasing EO content. In contrast, when the EO content in the demulsifiers is kept constant and the PO content is varied, the RSN value decreases with increasing PO content from sample 1 to sample 3 in both series A and B, as shown in Figures 1 and 2. These results noticeably signify the effects of EO and PO content on the HLB of the demulsifier. An increase in EO content increases the hydrophilicity of the demulsifier, whereas an increase in PO content increases its hydrophobicity. Xu et al. reported a linear correlation between the RSN value and the EO content for surfactant families having the same hydroxyl equivalent weight.23 787

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To study the effects of cross-linking on the RSN values of the demulsifiers, some selected EO−PO demulsifiers were crosslinked with cross-linking agents, such as dicarboxylic acid or tricarboxylic acid. The purpose of cross-linking is to increase the MW of the demulsifier. The cross-linking agent reacts with the hydroxyl groups on the polymer chains and attaches chains of either the same or different chemistry (i.e., EO or PO terminus). As a result, the polymer typically becomes more hydrophobic. Figure 3 shows the effects of cross-linking on the

Figure 5. Dehydration efficiency as a function of RSN value for EO− PO demulsifiers from series B at 50 ppm dosage and 30-min residence time, for naphtha-based bitumen emulsions.

efficiency at fixed PO content for naphtha-based bitumen emulsions. The optimal RSN range was between 12 and 17 for the three A-series samples of EO−PO demulsifiers when the EO content was varied from 0% to 40% at fixed PO content. Figure 5 shows the dehydration efficiency as a function of RSN value for EO−PO demulsifiers with base compound B. In samples B1 and B2, the dehydration efficiency increased with RSN in the RSN range studied. However, in the case of sample B3, the dehydration efficiency increased up to an RSN of 14.8 and then leveled off. Figure 5 shows that, when the RSN value of the demulsifier from sample B3 was 7.3, the dehydration efficiency after 30 min was 22.5%. Later, the dehydration efficiency increased with increasing RSN and then leveled off after an RSN value of 14.8. The RSN value of 14.8 corresponds to 30% EO. The demulsifier with 30% EO resulted in a dehydration efficiency of 63% after a residence time of 30 min. Therefore, the performance of EO−PO demulsifiers is linked to their RSN values. Wu et al. reported earlier that an optimal RSN value in terms of demulsification was observed for surfactants in the same family.29 The optimal RSN range was found to be between 15 and 21 for the B series of EO−PO demulsifiers when the EO content was varied from 0% to 40% at fixed PO content for these naphtha-based bitumen emulsions. The key observations were that the B series of EO−PO demulsifiers with five EO−PO branches provided better dehydration efficiency than the A series of EO−PO demulsifiers with three EO−PO branches. These results revealed that the higher the number of EO−PO branches in the base compound, the higher the dehydration efficiency. Among the three B-series samples, dehydration efficiencies were highest in sample 3 and lowest in sample 1. These results also indicate that, in any series, dehydration efficiency increases as the RSN value increases. Therefore, at fixed PO content, the EO content, RSN value, and dehydration efficiency are directly dependent on each other. The dehydration efficiencies of both the A and B series were in the order of sample 3 > sample 2 > sample 1, which is reverse to the trend of the RSN values. A possible reason for this trend could be the increase in MW in moving from sample 1 to sample 3. Earlier, Zaki et al. reported that demulsification efficiency is directly dependent on residence time, MW, and HLB of the demulsifier.30 Figure 6 shows the effects of cross-linking EO−PO copolymers on the dehydration efficiency of some selected

Figure 3. RSN value as a function of cross-linking for EO−PO demulsifiers. The EO content in the demulsifiers was 40%.

RSN value for some selected demulsifiers. It is clear that the RSN value decreases with increasing percentage cross-linking at fixed EO and PO content. These results indicate that the incorporation of cross-linking has a significant effect on the hydrophilic−lipophilic balance of a demulsifier. The decrease in RSN value upon cross-linking indicates that the hydrophilicity of the demulsifier is significantly reduced upon the incorporation of cross-links. 3.2. Effects of RSN and Cross-Linking in a Demulsifier on Demulsification Efficiency. The relation between dehydration efficiency and the RSNs of EO−PO demulsifiers is shown in Figures 4 and 5. Figure 4 shows the dehydration efficiency as a function of RSN for EO−PO demulsifiers with base compound A. The dehydration efficiency increased until the RSN reached values of 12.5, 13, and 14 in samples A1, A2, and A3, respectively, and then leveled off. These results indicate that there exists an optimal RSN range for dehydration

Figure 4. Dehydration efficiency in naphtha-based bitumen emulsions as a function of RSN value for EO−PO demulsifiers from series A at 50 ppm dosage and 30-min residence time. 788

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Figure 6. Dehydration efficiency in naphtha-based bitumen emulsions as a function of cross-linking for EO−PO demulsifiers. The EO content in the demulsifiers was 40%. The demulsifier dosage and residence time were 50 ppm and 30 min, respectively.

Figure 8. Dehydration efficiency as a function of MW for EO−PO demulsifiers from series B.

demulsifiers. Clearly, the introduction of cross-links results in a slight increase in the dehydration efficiency. Cross-linking increased the hydrophobicity of the EO−PO demulsifier molecules in addition to increasing MW. Also, the demulsifiers became larger upon cross-linking. These results indicate that the effects of MW on dehydration efficiency are more pronounced than those of RSN. 3.3. Effect of MW on Demulsification Efficiency. The dehydration efficiencies of both A and B series were found to be in the order sample 3 > sample 2 > sample 1, which is reverse to the trend for RSN values. One possible reason for this trend could be the increase in MW from sample 1 to sample 3. The relationship between dehydration efficiency and MW for the EO−PO demulsifiers is shown in Figures 7 and 8.

Wu et al. found that the EO−PO copolymers with MWs of 7500−15000 Da were most effective in dewatering diluted bitumen-in-water emulsions.29 They reported that the maximum dehydration efficiency with low-MW nonionic surfactants such as sorbitan esters, polyoxyethylene sorbitan esters, polyoxyethylene fatty alcohol ethers, and polyoxyethylene alkylphenol ethers was only 20% at their optimal dosage. The results reported in Figure 8 indicate that the demulsification efficiency was highest when the MWs were in the range mentioned by Wu et al.29 Furthermore, diffusivity/transport through the continuous phase (oil) is a critical aspect of performance of demulsifier. The water-in-diluted bitumen emulsion is an oil-continuous emulsion, and a high-HLB demulsifier might conceivably have trouble getting to the dispersed phase. Caution should be taken in selecting demulsifiers for waterin-oil emulsions, as the MW and HLB have significant impacts on the optimal dehydration efficiencies.19,21−23 In general, lowmolecular-weight polymeric demulsifiers exhibit high interfacial activities and adsorb irreversibly at the oil/water interface, causing film rupture and coalescence of the water droplets.34 High-molecular-weight polymeric demulsifiers are more effective in flocculating water droplets, thereby destabilizing emulsions.35 An increase in the molecular weight of the demulsifier can increase the flocculation of water droplets, thereby increasing the dehydration efficiency. Also, an increase in molecular weight can influence the interaction of the demulsifier with the asphaltene-stabilized film at the oil−water interface. 3.4. Effect of RSN on IFT. To correlate the performance of EO−PO demulsifiers with their interfacial activity, the IFT between water and bitumen diluted with toluene was measured in the absence and presence of demulsifiers. The relationships between dehydration efficiency, IFT, and RSN of the EO−PO copolymer demulsifiers with base compounds A and B are shown in Figures 9 and 10, respectively. It is evident that the dehydration efficiency increases whereas IFT decreases as the RSN increases in the A3 and B3 demulsifier samples. Therefore, the best demulsifier resulted in the lowest IFT and the highest dehydration efficiency at a 50 ppm dosage. Similar results were obtained for all other demulsifiers in series A and B. Many researchers have attempted to correlate demulsification performance with IFT and EO and PO numbers. Bhardwaj and Hartland reported that the effective partition of demulsifier decreased IFT and improved demulsification efficiency through

Figure 7. Dehydration efficiency as a function of MW for EO−PO demulsifiers from series A.

These results indicate that dehydration efficiency increases with increasing MW. The MW of sample 3 is highest and that of sample 1 is lowest for both the A and B series. This explains the increase in dehydration efficiency from sample 1 to sample 3 in the two series of EO−PO demulsifiers.31 Numerous researchers have studied the correlation between the MWs of demulsifiers and their associated efficiencies and have been able to establish a direct relationship.29,31,32 Shetty et al. investigated the effect of demulsifiers with varying HLB and MW on the destabilization of water-in-oil emulsions.33 They concluded that the demulsification efficiency of demulsifiers improves with a high HLB number and a low MW. However, 789

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Figure 11. Shear stress as a function of shear strain for underflow in the absence and presence of EO−PO demulsifiers from sample A3. The dosage of demulsifier was 200 ppm based on the mass of bitumen. The legend shows the RSN values of A3 demulsifiers.

Figure 9. Relationship between dehydration efficiency, IFT, and RSN for demulsifiers from sample A3. The dosage of demulsifier was 50 ppm.

where yo is the yield stress of underflow in the absence of demulsifier and y is the yield stress of underflow in the presence of demulsifier. Figure 12 shows the increase in yield stress as a function of RSN value at 50 and 200 ppm for demulsifier sample A3. The

Figure 10. Relationship between dehydration efficiency, IFT, and RSN for demulsifiers from sample B3. The dosage of demulsifier was 50 ppm.

rapid adsorption of the demulsifier at the oil/water interface.36 Byoung et al. found that, as the concentration of demulsifier increased, the IFT of crude oil/water interface decreased, whereas the dehydration efficiency was improved.37 Zaki et al. found that the concentration of demulsifiers required to obtain the lowest IFT were always below those inducing the maximum demulsification efficiency.30 Although an inverse correlation was found between dehydration efficiency and IFT in this study, additional parameters other than IFT should also be considered when selecting a demulsifier. 3.5. Effect of RSN on the Yield Stress of Underflow. Figure 11 shows shear stress as a function of shear strain for underflow in the absence and presence of EO−PO demulsifiers from sample A3 at a dosage of 200 ppm based on the mass of bitumen. The mass of froth was kept constant in all of these tests. The results in Figure 11 illustrate that keeping the dosage and mass of underflow constant, the yield stress increased as the RSN value increased in sample A3. It should be noted that the molecular weight increased with the increase in RSN value in sample A3. Similar trends were obtained for all other A and B demulsifier samples. To evaluate the performance of EO−PO demulsifiers, the percentage increase in yield stress for each demulsifier was calculated from yield stress increase (%) =

(yo − y) yo

Figure 12. Relationship between yield stress increase and RSN for EO−PO demulsifiers from sample A3. The demulsifier dosage is based on the mass of bitumen.

results in Figure 12 highlight two scenarios: First, when the dosage was kept constant, the increase in yield stress increased as the RSN value increased in sample A3. Second, the increase in yield stress was directly related to the dosage. For instance, at an RSN value of 13.4 when the dosage was increased from 50 to 200 ppm, the percentage yield stress increase rose from 46.7% to 263.57%. The effect of EO−PO demulsifiers on the naphtha-based froth treatment was further evaluated by analyzing the composition of the underflow for all samples with and without application of demulsifiers with the Dean− Stark analysis. The results are presented in Table 2 for sample demulsifier A3. Note that the results in Table 2 and Figure 12 were obtained from the same batch of testing samples. The reported solvent content in Table 2 was calculated based on mass of the underflow. The precise determination of solvent content in the underflow was not accomplished in the present work. The results reported in Figure 12 and Table 2 show that, at 50 ppm, the bitumen loss to the underflow was relatively constant with increasing RSN value and showed a slight increase at high RSN. However, at 200 ppm, the bitumen loss to the underflow increased with increasing RSN value.

× 100 (2) 790

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underflow and results in an increase in aggregate immobility and constriction to flow. The bitumen loss to the underflow was comparatively higher at 200 than 50 ppm. The bitumen lost to the underflow might increase the size of the aggregates. The effect is less pronounced at 50 than 200 ppm because fewer aggregates are present at 50 ppm. At 200 ppm, the number of aggregates in the underflow is already high. Additional aggregates from the bitumen lost to the underflow results in an overall slight aggregate increase, which results in a slight increase in yield stress with an increase in RSN value.

Table 2. Composition of the Underflow in the Absence and Presence of EO−PO Demulsifiers from Sample A3 RSN blank 8.7 9.5 10.9 13.4 16.2 8.7 9.5 10.9 13.4 16.2 a

DMOa (ppm) 50 50 50 50 50 200 200 200 200 200

bitumen (%) 32.6 32.6 32.6 32.6 32.8 33.0 32.6 32.7 32.9 33.5 33.7

± ± ± ± ± ± ± ± ± ± ±

0.3 0.1 0.2 0.1 0.2 0.1 0.2 0.2 0.1 0.2 0.1

solids (%) 8.3 8.3 8.2 8.2 8.2 8.1 8.2 8.1 8.1 8.0 7.9

± ± ± ± ± ± ± ± ± ± ±

0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.0

water (%) 37.6 37.6 37.4 37.1 37.1 37.4 37.8 37.1 36.5 36.6 36.9

± ± ± ± ± ± ± ± ± ± ±

0.2 0.2 0.4 0.2 0.4 0.2 0.7 0.7 0.1 0.5 0.2

solvent (%) 21.5 21.5 21.7 22.1 21.9 21.5 21.4 22.1 22.5 22.0 21.6

± ± ± ± ± ± ± ± ± ± ±

0.2 0.2 0.3 0.1 0.2 0.3 0.5 0.6 0.4 0.5 0.3

4. CONCLUSIONS On the basis of the research reported herein, the following conclusions can be made: (1) The results indicate that the B series of EO−PO demulsifiers with five EO−PO branches provided better dehydration efficiency than the A series of EO−PO demulsifiers with three EO−PO branches. Higher dehydration efficiency is associated with higher branching. (2) The dehydration efficiency was found to be directly correlated with the MW of the demulsifier. An increase in the MW resulted in a higher dehydration efficiency. The MW of sample 3 was the highest and that of sample 1 was the lowest in both the A and B series. The trend of dehydration efficiencies was the same as the trend of MWs. Thus, the effect of MW on dehydration efficiency was more pronounced than the effect of the RSN. (3) The dehydration efficiency increased and the IFT decreased as the RSN increased in both the A and B series. (4) An increase in MW by cross-linking EO−PO copolymers decreased the RSN value while improving the dehydration efficiency. (5) In the present work, an appropriate rheological method was developed by which demulsifiers can be quantitatively characterized by measuring the yield stress of the underflow. The yield stress of the underflow, which includes settled solids, water, and the rag layer, increased with increasing RSN value and demulsifier dosage. At high dosage, the yield stress values were high because of the increase in the number of aggregates, which restrict the underflow. The increase in yield stress with RSN value is due to bitumen loss to the underflow. The

Demulsifier dosage based on the mass of bitumen.

Figure 13 shows the relationship between the percentage yield stress increase and the bitumen loss to the underflow as a function of RSN value at 50 ppm and 200 ppm for A3 demulsifier sample. The results reveal that the RSN value is related to the increase in yield stress and bitumen loss to underflow. Both yield stress and bitumen loss to underflow values were higher at 200 than 50 ppm. For instance, at 50 ppm, when the RSN value increased from 8.7 to 16.7, the increase in yield stress was from 11.7% to 110%, and the bitumen loss to the underflow went from 32.6% to 33%. However, at a dosage of 200 ppm, the yield stress shifted from 217% to 280%, and the bitumen loss to the underflow increased from 32.6% to 33.7% when RSN increased from 8.7 to 16.7. At an RSN value of 8.7, the yield stress increase varied from 11.7% to 217%, whereas the bitumen loss to the underflow remained constant at 32.6% when the demulsifier dosage increased from 50 to 200 ppm. A possible reason for the higher value of the yield stress increase at 200 ppm compared to 50 ppm is that, at high dosage, the underflow is more immobile because of an increase in the number of aggregates, which restricts the flow of the underflow. On the other hand, at low dosage, the values of yield stress increase are comparatively smaller because of the presence of fewer structural aggregates, which do not cause much restriction to the underflow. A possible reason for the yield stress increase with RSN value is bitumen loss to the underflow. The bitumen lost to the underflow increases the size of the aggregates present in the

Figure 13. Relationship between yield stress increase, bitumen loss to underflow, and RSN for EO−PO demulsifiers from sample A3. 791

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bitumen lost to the underflow increases the size of the aggregates present in the underflow and results in an increase in their immobility and constriction to flow.

AUTHOR INFORMATION

Corresponding Author

*Tel.: 1-780-980-5978. Fax: 1-780-980-5989. E-mail ishpinder. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the support from our colleagues in Sugar Land, TX. In particular, we thank Darryl Stepien for synthesizing the demulsifiers. We also thank Dr. Patrick Breen, Dr. Jackie Behles, and Curtis Lawton for their valuable suggestions throughout this work and Larry Sartori for his valuable feedback. This work was generously funded by Alberta Innovates Technology Futures. We thank Alberta Innovates for the funding and Baker Hughes for the permission to publish this work.

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