Subsurface Upgrading of Heavy Oils via Solvent Deasphalting Using

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Subsurface Upgrading of Heavy Oils via Solvent Deasphalting using Asphaltene Precipitants. Preparative Separations and Mechanism of Asphaltene Precipitation using Benzoyl Peroxide as Precipitant Estrella Rogel, Janie Vien, Harris Morazan, Francisco A Lopez-Linares, Jacqulene Lang, Ian Benson, Lante Antonio Carbognani Ortega, and Cesar Ovalles Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01588 • Publication Date (Web): 20 Jul 2017 Downloaded from http://pubs.acs.org on July 23, 2017

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July 18th, 2017 To be Submitted to Energy & Fuel

Subsurface Upgrading of Heavy Oils via Solvent Deasphalting using Asphaltene Precipitants. Preparative Separations and Mechanism of Asphaltene Precipitation using Benzoyl Peroxide as Precipitant

Estrella Rogel1, Janie Vien1, Harris Morazan1, Francisco Lopez-Linares1, Jacqulene Lang,1, Ian Benson2, Lante Antonio Carbognani Ortega,3 and Cesar Ovalles*1

1

Petroleum & Material Characterization Chevron Energy Technology Co. 100 Chevron Way, Richmond, CA 94802. USA 2

Reservoir and Petroleum Engineering Dept. Chevron Energy Technology Co 1500 Louisiana St, Houston, TX 77002. USA 3

*

To

Chemical and Petroleum Engineering Dept., Schulich School of Engineering University of Calgary, 2500 Univ. Dr. NW. Calgary, AB. T2N 1N4. Canada

whom

correspondence

should

be

addressed.

Telephone:

(510)-242-2991.

E-mail: [email protected]

ACS Paragon Plus Environment

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Abstract Subsurface upgrading of heavy oil via solvent deasphalting has been reported previously under laboratory and field conditions. However, these processes require a relatively high solvent-to-oil ratio (SvOR >1:1 v/v) to induce subsurface asphaltene precipitation, increase oil production, and upgrade crude oil in situ. In our previous work, lab experiments demonstrated that asphaltene precipitants reduce the SvOR (~30 to 50 vol. %) for subsurface upgrading at initial reservoir conditions and when heat is also applied. In this work, the preparative separations were carried out using benzoyl peroxide (BP), Fe2O3 and NiO nanoparticles as asphaltene precipitants for Venezuelan and Canadian heavy crude oils. Initial experiments showed that BP is the most effective additive, producing an increase of ~21 wt.% in the asphaltene content for a 2500 mg/kg dosage. Preparative separations at 5:1 w/w ratio and 50°C showed that the order of activity as asphaltene precipitants is BP > NiO > Fe2O3. In the presence of nickel and iron-containing precipitants, most of these metals are found in the asphaltenes indicating that the nanoparticles are acting as nucleation sites. Spectroscopic and mechanistic studies using BP as precipitant suggest a free radical mechanism that involves the thermally initiated homolytic cleavage of BP, follow by abstraction of a hydrogen atom from the asphaltenes or maltenes to produce free radical species. In the termination steps, the latter species react with each other to generate new asphaltene species that are not present the original crude oils.


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1. INTRODUCTION Subsurface upgrading of heavy oil via solvent deasphalting (SSU-SDA) has been reported previously under laboratory and field conditions.1-6 The main advantage of these processes is that they do not require external energy sources because they are operated at reservoir temperature or in the presence of a warm solvent. Specifically, VAPEX involves the injection of solvent vapor (typical light hydrocarbons in the C3 to C5 range) into an upper horizontal well in a conventional SAGD configuration pair.7-9 The solvent dissolves into the viscous oil making it mobile enough to drain downward to the production well. Laboratory experiments have shown that asphaltene precipitates in-situ which results in a 6-7°API increase in produced oil quality. The VAPEX process was field tested at the Dovap site in Canada. Its design consisted of one cold-start up well pair and one hot-start-up well pair. Unfortunately, the cold start–up well pair suffered from a lack of communication and failed to give the expected results. In the hot test, the transition from SAGD to VAPEX was unsuccessful, and oil production fell to less than 150 BBLD. However, upgrading from 10.5°API to 12°API was observed in both tests with a reduction in the percentages of asphaltenes from ~17 to ~1-5 wt.%. Unfortunately, the project was discontinued in 2008 due to poor oil recovery.7-9 In 2002, PDVSA was issued a US patent for the underground injection of a light solvent at reservoir conditions to generate upgraded crude oils from heavy crude oil reservoirs (1:1 v/v) to induce subsurface asphaltene precipitation, increase oil production, and to upgrade crude oil in situ. Also, these processes need to recycle the solvent to improve the economic prospects. Therefore, costly surface facilities are required. In this order of ideas, the use of additives that can act as asphaltene precipitants to reduce the SvOR represents a feasible alternative to decrease capital and operating expenditures and improve the economic benefits of the process.


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There are several reports that have used precipitants and/or “anti-solvents” to enhance the efficiency of refinery based solvent deasphalting processes. Examples using carbon dioxide and hydrogen sulfide,13 methanol,14 isopropanol,15 silicon dioxide and silicate-containing compounds,16 alkyl, alkyl aryl alkoxylates and alkyl aryl sulfonates,17 alkoxylates of alkylphenol formaldehyde resins,18 ionic liquids,19 acetone, and ethyl acetate,20 alkyl and aryl ether,21 hexane, coal, methyl-pyrrolidinone,22 and sodium dodecyl sulfonate and cetyl pyridinium chloride23 have been disclosed. Moreira and coworkers found that polycardanol induced asphaltene precipitation whereas its monomer is an effective inhibitor.24 Pillon reported that poly(maleic anhydride-1octadecene) is an effective asphaltene precipitant.25 Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the interaction between the asphaltene and the polymer occurs via hydrogen bonding.25 Chang and Fogler studied interactions between asphaltenes and poly (octadecene maleicanhydride) (POM).26 At low POM-to-asphaltene weight ratio (less than 4), the authors found that POM strongly associated with asphaltenes in the solution which resulted in the heterocoagulation between asphaltenes and polymer.26 Lima and coworkers studied polycardanol or sulfonated polystyrene as flocculants for asphaltene dispersions. The results indicate that, at low concentrations, both sets of polymers behave as flocculants and dispersants at higher concentrations.27 Kelland describes the theory of flocculants and presents several examples of cationic, anionic, and nonionic polymers that have the possibility to behave as asphaltenes flocculants or precipitants.28 A potential application of asphaltene precipitants is depicted in Fig. 1.29-30 As shown, these additives can be mixed with the solvent and injected into the reservoir to induce subsurface asphaltene precipitation at reservoir conditions and to reduce the solvent-to-oil ratio. The process


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can be carried out using vertical and horizontal wells, or in SAGD configuration to generate an upgraded crude oil. The asphaltene precipitants are not expected to be recovered because they remain associated with the asphaltenes downhole. Also, Fig. 1 shows a solvent recovery unit to improve the economic prospect of the process.29-30 Insert Fig. 1 In our previous work, a lab-scale proof-of-concept on the use of asphaltene precipitants was presented.29-30 Benzoyl peroxide, 4-vinyl pyridine methacrylate, 4-vinyl phenol methacrylate, Poly(maleic anhydride), and Fe2O3 and NiO nanoparticles were evaluated as asphaltene precipitants by optical microscopy and by the increments measured in the asphaltene contents of crude oils. The percentages of increase of asphaltenes were measured by using the on-column filtration method,31 and around ~20% w/w of increase in asphaltene content was observed in comparison with the case without the additive.29-30 The results indicated that it is possible to save at least ~30 to 50 vol. % of the solvent by using asphaltene precipitant additives. In this work, the effect of temperature and preparative separations were carried out for benzoyl peroxide (BP), Fe2O3 and NiO nanoparticles as asphaltene precipitants for Venezuelan and Canadian heavy crude oils. Formally BP is a free radial initiator but in this work it behaves also as an asphaltene precipitant. Spectroscopic and mechanistic studies were also performed to understand the asphaltene precipitation process using BP as precipitant.

2. EXPERIMENTAL SECTION 2.1. Materials and Methods. All solvents were HPLC grade and were used without further purification. Benzoyl peroxide was purchased from Fisher (reagent grade) and used as received.


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Nickel(II) oxide nanopowder ( No additive (13.3 wt.%) > Fe2O3 (10.5 wt.%)

(2)

Insert Fig. 6 As seen, benzoyl peroxide continues to be the most active precipitant with an increase of ~15% in asphaltene content with respect to the case without additive. This value is higher than the amount of BP added, so its effect was studied further. At C7/heavy oil ratio of 10:1, the NiO nanoparticles yielded a higher amount of asphaltenes (18.2 wt.%) than BP (17.5 wt.%) indicating that both compounds are effective to increase asphaltene precipitation. Overall, nickel oxide nanoparticles are more active as asphaltene precipitant than the iron oxide counterparts. This order of activity toward asphaltene precipitant agrees with the asphaltene adsorption experiments reported by Nassar et al.41 The effect of the concentration of benzoyl peroxide in the weight percentage of asphaltenes and in the viscosity of the deasphalted oil (DAO) is shown in Fig. 7. These preparative separations were run using heptane/Venezuelan heavy crude oil = 5/1 (vol./w) at 50°C. Consistent with the on-column filtration method (Fig. 4),31 the amount of recovered asphaltenes increased from ~13 wt.% to ~18% when the concentration of BP increased to 4.8 wt.% (Fig. 7,


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black Trace). As expected, the higher amount of asphaltene precipitated led to viscosity reduction of the DAO from ~3200 cSt to ~1500 cSt (Fig. 7, red trace). These results are consistent with the known effect of asphaltenes on the viscosity of heavy crude oils42-43 and showed the potentiality of using asphaltene precipitants to reduce the viscosity of the DAO during heavy oil production. Insert Fig. 7 To further demonstrate the effect of asphaltene precipitants, preparative separations were carried out using a C7/Canadian crude oil ratio of 5:1 in the presence of 1.0 wt.% of benzoyl peroxide and nickel oxide at 50°C (Fig. 8). Consistent with the results using a Venezuelan crude oil (Fig. 6), the amount of precipitated asphaltenes increased 7% and 2%, respectively. Thus, these two materials are effective asphaltene precipitants for the two heavy crude oils studied in this work. Insert Fig. 8 3.4. Elemental Analysis. In the absence and presence of asphaltene precipitants, maltene and asphaltene fractions preparatively separated from the Venezuelan and Canadian heavy crudes were characterized by elemental analysis (Tables 1 and 2, respectively). Regardless of the presence or not of the asphaltene precipitant, maltenes showed H/C molar ratios of 1.53-1.60 whereas the asphaltenes H/C are in the 1.27-1.33 range for both studied heavy crudes (Table 1 and 2). Similar results were obtained for sulfur, i.e. maltene sulfur contents were in the 3.7-4.0 wt.% range whereas asphaltenes are 4.8-5.0%, in the presence or not of the additives. As reported,40 asphaltenes have higher hydrogen deficiency and more heteroatom content than maltenes, and in this case, the presence of the precipitant does not seem to influence their composition.


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As previously reported, V and Ni have the tendency to concentrated in the asphaltene fractions (Table 1).40 The vanadium concentration found in the asphaltenes are in the 1440-1570 mg/kg range whereas for the maltenes the values are 280-300 mg/kg. Similar results are observed for the Ni content for the no-additives (Table 1, Exp. 1) and benzoyl peroxide cases (Table 1, Exp. 2). However, in the presence of NiO nanoparticles (Table 1, Exp. 3) most of the Ni is found in the asphaltenes (~5% or 50,000 mg/kg). Same results are observed for the Fe2O3 nanoparticles (Table 1, Exp. 4). A small concentration of Fe was detected in maltenes (29 mg/kg), and most of the metals were measured in the asphaltene fraction (~3% or 30,000 mg/kg). These results indicated that NiO and Fe2O3 nanoparticles are acting as nucleation sites (agglomerants) so that higher asphaltene contents are found in the presence of these two precipitants (see Fig. 3 and 6). These results are consistent with the asphaltene adsorption experiments reported in the literature.41 Next, we focused our attention on studying the mechanism of action of benzoyl peroxide. 3.5. Asphaltene Solubility Profile and Spectroscopic Characterization. Asphaltene samples coming from the preparative separations in the absence and presence of benzoyl peroxide as precipitant were characterized by the solubility profile method34 (Fig. 9). As seen, two signals are observed corresponding to lower (~14.5 min) and higher (~16 min) solubility parameter asphaltenes.34 The results of the reaction with BP (red trace) showed an increase in the peak corresponding to the latter in comparison with the no-additive sample (black trace). This finding indicates that material with higher solubility parameter is generated by the reaction with the asphaltene precipitant (BP). Insert Fig. 9


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The FTIRs of the preparatively separated asphaltenes from the Venezuelan crude oil and the products of the reaction with benzoyl peroxide at different concentrations (1-4.8 wt.%) are shown in Fig. 10. As seen, bands at 3600-2500, 1694 and 710 cm-1, are produced after benzoyl peroxide addition i.e. the product from the reaction of BP with components from the oil. By comparison with the literature,44-45 they can be assigned to oxygenate compounds. Most likely, benzoates moieties attached to asphaltene molecules; thus, increasing the solubility parameter of the sample as shown by the asphaltene solubility profile (Fig. 9). Insert Fig. 10 Precedents of this behavior can be found in the literature. Tsubota et al. reported similar FTIR results (Fig. 10) after the reaction of diamond surfaces with benzoyl peroxide in various solvents (toluene, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, cyclohexane, and n-hexane).46 They proposed a mechanism that involves the abstraction of hydrogen atoms by benzoyl peroxide to form a benzoate moiety attached to the diamond surface.46 Siskin et al. reported that air oxidation increases both the asphaltene content and the polarity of the asphaltenes by increasing the organic-oxygen content of the asphaltene fraction of VR feeds.47 Similarly, Carbognani and coworkers found that the asphaltene contents increased with the oxidation time for virgin and oxidized aliquots of Cerro Negro 550°C VR.48 SARA analysis indicated that, during air oxidation, the aromatic fraction was converted into resins and the latter suffered further oxidation that gave an increment of the asphaltene contents.48 Oxidized sulfur and nitrogen containing signals were found in the asphaltene and resin fractions, as determined by XPS.49 It was reported that the presence of these species is a leading factor for their precipitation in alkane solvents.49 Polarity, as derived from the presence of oxygen functions, is one of the two most important properties for asphaltene definition as proposed a long time ago by Long.50


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Maltenes (C7-solubles), separated from the reaction of heptane/Venezuelan C. = 5:1 with BP (Table 1, Exp. 2), were further treated with 4.8% BP using the same C7/crude ratio at 50°C for 6 h. After filtration, ‘new’ asphaltenes were separated (3.4 wt.% yield) and characterized by elemental analysis, solubility profile,34 and FTIR. As shown in Table 1, exp. 5, these new species have a H/C molar ratio of 1.24 and a greater concentration of higher solubility parameter asphaltenes (Fig. 11, red trace) than the starting material (Fig. 11, black trace). Insert Fig. 11 Consistent with the spectra shown in Fig. 10, a carbonyl stretching band at 1694 cm-1 indicates the presence of oxygenated species in these ‘new’ asphaltenes (Fig. 12, red trace). As mentioned previously, this carbonyl band increased (Fig. 12, blue trace) in the benzoyl peroxide treated asphaltenes (Table 1, exp. 2). These results indicate that maltenes could be further functionalized with BP to yield additional asphaltenes with “oxygenate” species, most probably benzoate, and thus higher solubility parameter was observed (Fig. 11). Insert Fig. 12 To further confirm the presence of “oxygenate” species”, the

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C-NMR spectrum of the

asphaltenes preparatively separated from the Venezuelan crude oil and the products of the reaction with benzoyl peroxide at 4.8 wt.% was carried out and the results are shown in Fig. 13. As seen, a small signal of BP (at ~130 ppm) was observed suggesting an almost complete reaction with the asphaltenes. As reported by Ashtari et al.,52 the peaks assigned to BP (~130 ppm) and benzoic acid (~192 ppm) were found severely shifted from the values reported in the literature (163 ppm and 172.8 ppm, respectively).45 These results suggest a strong interaction of these moieties with the asphaltenes backbones.52 Insert Fig. 13


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3.6. Plausible Mechanism for Asphaltene Precipitation. For the use of benzoyl peroxide (BP) as asphaltene precipitant, a general mechanism consistent with the literature and the experimental evidences is shown in eq. 3 to 10: Initiation C6H5-COO-OOC-C6H5 2C6H5-COO•

(3)

Propagation C6H5-COO• + [Asphaltenes]-H C6H5-COOH + [Asphaltenes]•

(4)

[Asphaltenes]• + C6H5-COO-OOC-C6H5 C6H5-COO-[Asphaltenes] + C6H5-COO•

(5)

C6H5-COO• + [Maltenes]-H C6H5-COOH + [Maltenes]•

(6)

[Maltenes]• + C6H5-COO-OOC-C6H5 C6H5-COO-[Maltenes] + C6H5-COO•

(7)

Termination [Asphaltenes]• [Asphaltenes]-[Asphaltenes]

(8)

[Maltenes]• + [Asphaltenes]• [Maltenes]-[Asphaltenes]

(9)

2[Maltenes]• [Asphaltenes]

(10)

Where 2C6H5-COO•, [Asphaltenes]•, and [Maltenes]• are benzoate, asphaltene, and maltene radical species, respectively.

Eq. 3 is the thermal initiation reaction and consist of the well-known homolytic cleavage of BP to yield two benzoate radicals.51 In the propagation steps, eq. 4 corresponds to the abstraction of a hydrogen atom by the benzoate radical to generate benzoic acid and an asphaltene radical.43 In turn, the latter species reacts with BP (eq. 5) to generate benzoate-containing asphaltenes and a new benzoate radical.46-47 Similar reactions (eqs. 6 and 7) are proposed for the maltene counterparts (C7-solubles). Eq. 5 and 7 led to the presence of “oxygenated” asphaltenes (as


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shown by the higher solubility parameter, and FTIR and

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C-NMR signals) which are most

probably benzoate. Eq. 7 can explain the formation of “New Asphaltenes” by the reaction of BP with maltenes. In the termination steps (eqs. 8-10), asphaltene and maltene radicals react with each other to generate non-radical species as reported in Tables 1 and 2 and Fig. 3-4, and 6-8. Eq. 5, 7 and 810 leading to a higher asphaltene content in the presence of precipitants than that found for the original crude oil. 4. CONCLUSIONS •

Initial experiments showed that benzoyl peroxide, iron and nickel nanoparticles were effective asphaltene precipitants for Venezuelan and Canadian heavy crude oils. Benzoyl peroxide seems the most active additive and ~21 wt.% of increase in the asphaltene content was obtained.

•

In the presence of BP, percentages of increase in the amount of asphaltenes precipitated at 195°C in comparison to that at 60°C were found. This finding was attributed to the higher decomposition rate of benzoyl peroxide at a higher temperature.

•

Preparative separations at 5:1 vol./w ratio showed that the order of activity as asphaltene precipitants is BP > NiO > Fe2O3.

•

Regardless of the presence or not of precipitants, maltenes showed H/C molar ratios of 1.531.60 and sulfur contents in the 3.7-4% range whereas asphaltenes H/C ratio and sulfur content were in the 1.27-1.33 and 4.8-5%, respectively for both heavy crudes studied.

•

In the presence of NiO and Fe2O3 precipitants, most of the nickel and iron are found in the asphaltenes (~3-5% or 30,000-50,000 mg/kg) indicating that the nanoparticles are acting as nucleation sites (agglomerants) enhancing asphaltenes precipitation.


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In the presence of benzoyl peroxide and consistent with the literature and experimental

•

evidence, a free radical mechanism can be proposed that involves the thermally initiated homolytic cleavage of BP, followed by abstraction of a hydrogen atom from the asphaltenes or maltenes to produce free radical species. In the termination steps, the latter species react with each other to generate new asphaltene species that are not found in the original crude oils. Acknowledgments We thank Chevron Energy Technology Company for providing funding and the permission to publish this paper. Many thanks to Marianna Trujillo for her technical assistance in carrying out the

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C-NMR spectrum. Our appreciation to the Products &Analytical Unit and the Petroleum

and Material Characterization managements for their support. Lante Carbognani acknowledges the support and permission to publish provided by University of Calgary. References 1. Guo, K., Li, H., Yu, Z. In-Situ Heavy and Extra-Heavy Oil Recovery: A Review, Fuel 2016, 185, 886–902 and references therein. 2. Pourabdollah, K., Mokhtari, B. The VAPEX Process, from Beginning Up to Date, Fuel 2013 107, 1–33 and references therein. 3. Huc, A.-Y., Ed. Heavy Crude Oils. From Geology to Upgrading. An Overview, Technip: Paris, France, 2011; p387 and references therein. 4. Nourozieh, N., Kariznovi, M., Abedi, J. Liquid-Liquid Equilibria of Solvent/Heavy Crude Systems: In Situ Upgrading and Measurements of Physical Properties, SPE No. 152319 presented at SPE Western Regional Meeting, Bakersfield, California, USA, 21-23 March, 2012.


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5. Pathak, V., Tayfun Babadagli, T., Edmunds, N. Mechanics of Heavy-Oil and Bitumen Recovery by Hot Solvent Injection, SPE Res. Eval. Eng. 2012 15, 182-194. 6. Ovalles, C., Rogel, E., Alboudwarej, H., Inouye, A., Benson, I.P., Vaca, P., Physical and Numerical Simulations of Subsurface Upgrading using Solvent Deasphalting in a Heavy Crude Oil Reservoir SPE Res. Eval. & Eng. (SPE-183636), 2016, August, 1-15 and references therein. 7. Butler, R. M., Mokry, I. J. In-Situ Upgrading of Heavy Oils and Bitumen by Propane Deasphalting: The VAPEX Process, SPE 25452, presented at Productions Operations Symposium, Oklahoma City, USA, March 21-23 1993 and references therein. 8. Das, S. K., Vapex: An Efficient Process for the Recovery of Heavy Oil and Bitumen, SPE 50941, SPE Journal, 1998, Sept. 22. 9. Das S., Diffusion and Dispersion in the Simulation of VAPEX Process, SPE No. 97924, presented at SPE International Thermal Operation and Heavy Oil Symposium, Calgary Alberta, Nov. 1-3 2005 and references therein. 10. Vallejos, C., Vasquez, T, Siachoque, G, Layrisse, I., Process for the In Situ Upgrading of Hydrocarbons, US Patent No. 6,405,799 (2002). 11. Nenninger, J., Nenninger, E., Method and Apparatus for Stimulating Heavy Oil Production, US Patent 6,883,607 (2005). 12. Krawchuk, P. Development and Operation of the N-Solv BEST Demonstration Facility, Proceedings for the 2016 World Heavy Oil Congress, Calgary, Alberta, Canada, WHOC16 – 135. 13. Audeh, C. A., Johnson, G. C., Process for Deasphalting Hydrocarbons Oils, US Patent No. 4,191,639 (1980). 14. Rollmann, L. D., Wash, D. E., Deasphalting process, US Patent No. 4,324,651 (1982). 15. Rhoe, A., Pisani, J. A., Hamilton, G. L. Suciu, G. D. Solvent for refining of residues US Patent No. 4,592,831 (1986). 16. Ikematsu, M., Honzyo, I., Sakai, K. Process for the solvent deasphalting of asphaltenecontaining hydrocarbons US Patent No. 4,502,950 (1985).


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Table 1. Characterization of the Venezuelan heavy crude oil used in this work, and the preparatively separated maltenes, and asphaltenes in the presence of 1 wt.% precipitant compounds Exp.

1

2

3

4

5

Sample - Precipitanta

V Ni (mg/kg)h Fe (mg/kg)i (mg/kg)g

%Cb

%Hc

%Nd

H/Ce

% Sf

Venezuelan C. Feed

84.21

10.38

0.68

1.48

4.17

435

104

n-dj

Maltenes - No additive

83.27

10.84

Subsurface Upgrading of Heavy Oils via Solvent Deasphalting Using

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