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Simultaneous removal of asphaltenes and water from water-in-bitumen emulsion II. Application feasibility Yingxian Zhao , Feng Wei Ningbo Institute of Technology, Zhejiang University, Ningbo, Zhejiang 315100, PR China ARTICLE INFO ABSTRACT Article history: Received 4 April 2007 Received in revised form 10 March 2008 Accepted 24 March 2008 Application feasibility of the accelerated deasphaltening process for simultaneous removal of asphaltenes and water from a water-in-bitumen emulsion has been examined with a pilot plant having capacity of 1.590 m3/day. The solvent (n-pentane) was injected into the emulsion from three locations with progressively increasing temperature from 423 K. The first solvent injection precipitated the asphaltenes in bitumen, the second broke the emulsion and facilitated the phase separation, and the third extracted the oil that remained in heavy asphaltenes/water phase. The effects of operation parameters such as temperature, solvent/ bitumen ratio, feed rate and feedstock composition on the quality of DAO (Deasphaltening oil) were investigated. The DAO with the yield of ~80 wt.% and asphaltene content of b 0.5 wt.% was produced under optimal operating conditions, and the residual product was a porous solids containing 38% sulfur, 47% nitrogen, 64% MCR, and 85% metals (nickel and vanadium) of the bitumen. For a real application in oil industry, other important aspects including energy efficiency, solvent recovery and water purification have been discussed. © 2008 Elsevier B.V. All rights reserved. Keywords: Removal Asphaltenes Water-in-bitumen emulsion n-pentane Pilot study 1. Introduction The supply of crude oil has been diminishing, and the price is soaring. Refiners have to use heavier crude as a low price substitute, and cut deeper into the bottom of the barrel to maximize the yield and produce more high-value vacuum gas oil [1,2]. Heavier crude generally contain a large part of residue fraction with high concentrations of contaminants (asphal- tenes, metals, etc.) that is responsible for much of coke- forming tendency and hydroprocessing catalyst deactivation [3]. To improve the performance of heavier crude or bitumen upgrading processes, the prior removal of these contaminants by paraffinic treatment has been under investigation [46]. However, the commercial processes of bitumen decontamina- tion such as ROSE (Resid Oil Supercritical Extraction) [4] operate under severe conditions and have difficulty to deal with feedstock containing water and solids. With a continual decline of conventional oil reserves, the oil sands become an alternative resource of heavy crude. Commercial oil sand processes such as CHWE (Clark Hot Water Extraction) [7,8] extract bitumen from mined oil sands by a flotation process, producing a froth which is a typical emulsion of water-in-bitumen with solids (clays) [9]. To meet pipeline and downstream processes specifications, the water and solids have to be removed from the froth. Since bitumen is very viscous and has the density close to 1, a complete separation of water and solids from bitumen would not be possible without adding a diluent to reduce the density and viscosity of oil phase. The commercial oil sand operations in Syncrude and Suncor use naphthas for bitumen froth treat- ment [10,11], while the operation in Shell Albian Oilsands uses aliphatic solvent for the treatment [12,13]. The prime concerns in these commercial bitumen froth treatments are to remove water and clays without emphasizing the removal of asphal- FUEL PROCESSING TECHNOLOGY 89 (2008) 941 948 Corresponding author. Tel.: +86 574 88229566; fax: +86 574 88229037. Corresponding author. Tel.: +86 574 88229566; fax: +86 574 88229037. E-mail address: [email protected] (Y. Zhao). 0378-3820/$ see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2008.03.010 available at www.sciencedirect.com www.elsevier.com/locate/fuproc

Simultaneous removal of asphaltenes and water from water-in-bitumen emulsion: II. Application feasibility

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Simultaneous removal of asphaltenes and water fromwater-in-bitumen emulsionII. Application feasibilityYingxian Zhao⁎, Feng WeiNingbo Institute of Technology, Zhejiang University, Ningbo, Zhejiang 315100, PR China

A R T I C L E I N F O

⁎ Corresponding author. Tel.: +86 574 8822956⁎ Corresponding author. Tel.: +86 574 8822956E-mail address: [email protected] (Y. Zhao

0378-3820/$ – see front matter © 2008 Elsevidoi:10.1016/j.fuproc.2008.03.010

A B S T R A C T

Article history:Received 4 April 2007Received in revised form10 March 2008Accepted 24 March 2008

Application feasibility of the accelerated deasphaltening process for simultaneous removal ofasphaltenes and water from a water-in-bitumen emulsion has been examined with a pilotplant having capacity of 1.590m3/day. The solvent (n-pentane)was injected into the emulsionfrom three locations with progressively increasing temperature from 423 K. The first solventinjection precipitated the asphaltenes in bitumen, the second broke the emulsion andfacilitated the phase separation, and the third extracted the oil that remained in heavyasphaltenes/water phase. The effects of operation parameters such as temperature, solvent/bitumen ratio, feed rate and feedstock composition on the quality of DAO (Deasphaltening oil)were investigated. TheDAOwith theyieldof ~80wt.%andasphaltenecontent ofb0.5wt.%wasproduced under optimal operating conditions, and the residual product was a porous solidscontaining 38% sulfur, 47% nitrogen, 64% MCR, and 85% metals (nickel and vanadium) of thebitumen. For a real application in oil industry, other important aspects including energyefficiency, solvent recovery and water purification have been discussed.

© 2008 Elsevier B.V. All rights reserved.

Keywords:RemovalAsphaltenesWater-in-bitumen emulsionn-pentanePilot study

1. Introduction

The supply of crude oil has been diminishing, and the price issoaring. Refiners have to use heavier crude as a low pricesubstitute, and cut deeper into the bottom of the barrel tomaximize the yield and produce more high-value vacuum gasoil [1,2]. Heavier crude generally contain a large part of residuefraction with high concentrations of contaminants (asphal-tenes, metals, etc.) that is responsible for much of coke-forming tendency and hydroprocessing catalyst deactivation[3]. To improve the performance of heavier crude or bitumenupgrading processes, the prior removal of these contaminantsby paraffinic treatment has been under investigation [4–6].However, the commercial processes of bitumen decontamina-tion such as ROSE (Resid Oil Supercritical Extraction) [4]operate under severe conditions and have difficulty to dealwith feedstock containing water and solids.

6; fax: +86 574 88229037.6; fax: +86 574 88229037.).

er B.V. All rights reserved

With a continual decline of conventional oil reserves, theoil sands become an alternative resource of heavy crude.Commercial oil sand processes such as CHWE (Clark HotWater Extraction) [7,8] extract bitumen from mined oil sandsby a flotation process, producing a froth which is a typicalemulsion of water-in-bitumen with solids (clays) [9]. To meetpipeline and downstream processes specifications, the waterand solids have to be removed from the froth. Since bitumen isvery viscous and has the density close to 1, a completeseparation of water and solids from bitumen would not bepossible without adding a diluent to reduce the density andviscosity of oil phase. The commercial oil sand operations inSyncrude and Suncor use naphthas for bitumen froth treat-ment [10,11], while the operation in Shell Albian Oilsands usesaliphatic solvent for the treatment [12,13]. The prime concernsin these commercial bitumen froth treatments are to removewater and clays without emphasizing the removal of asphal-

.

942 F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 9 4 1 – 9 4 8

tenes from bitumen. Economically, however, the simulta-neous removal of asphaltenes and water from bitumen frothcould be more beneficial to oil sand industries. Extensiveresearch studies showed that the nature and amount ofsolvents have significant impacts on the performance oftreatment processes and the properties of bitumen products[14–16]. There is a critical solvent/bitumen (S/B) ratio coincid-ing with the onset of asphaltene precipitation. The critical S/Bratio (volume) increases with increasing solvent aromaticity,and is ~1.8 for a paraffinic diluent [17] and ~4 for naphtha [18].

During the last several years, the efforts have beenmade todevelop a modified process of accelerated deasphaltening.The goal of this process is to produce high quality middlecrude by fast removal of water and asphaltenes simulta-neously from the water-in-bitumen emulsion through paraf-finic solvent treatment. The scientific fundamentals of theaccelerated deasphaltening technology have been demon-strated in the previous study with a bench-scale unit [19]. Inwhere, the results showed that asphaltenes–water interactionwas advantageous to the process, the solvency and tempera-ture played important roles in improving the operationperformance, and the simultaneous removal of 98+% asphal-tenes and 99.9+% water from the water-in-bitumen emulsionwas achieved with n-pentane/bitumen ratio ≥3.0 (volume) at423–453 K. Based on the previous bench-scale experimentalinvestigation, a follow-up study for application feasibility ofthis technology has been conducted with a pilot plant, givingthe technical data for designing a commercial plant. Here, wepresent the detailed results of this pilot plant study.

2. Experimental section

2.1. Materials

Two water-in-bitumen emulsions (A and B) produced fromSAGDprocesseswere provided by two Canadian oil companiesheadquartering in Calgary, Alberta, Canada. The feedstocks Aand B contain 35.85 wt.% and 15.15 wt.% water respectively,determined by the standard Dean–Stark analysis. The proper-

Table 1 – Properties of feedstocks A and B

Properties Feedstock A

Water-in-bitumen emulsion Bitumen(de-watered)

Density at 288.6 K 0.9958 0.9972Viscosity at 323 K 1897Viscosity at 343 K 594 491Bitumen, wt.% 63.84Water, wt.% 35.85Solid, wt.% 0.31C5-asphaltene, wt.% 17.7C, wt.% 84.71H, wt.% 10.28N, wt.% 0.55S, wt.% 4.01Ni, mg/kg 67.4V, mg/kg 160.3MCR, wt.% 12.71

ties of the two de-watered emulsions (bitumen) were mea-sured according to ASTM methods, and presented in Table 1.

The n-pentane with purity of 99+% was purchased from acommercial supplier, and used as a diluent without anyfurther treatment.

2.2. Pilot plant operation

The pilot plant has an operation capacity of 1.590 m3 per day,and a simplified schematic flow diagram of this plant is showninFig. 1. Typically, thephase separatorV1 (inside diameter, i.d.=0.16m)was operated at ~3450 kPa and in the temperature rangeof 433–463 K, the DAO separator V2 (i.d.=0.06 m) operated at apressure slightly higher than that of V1 and at a temperaturehigher than 469.6 K (the critical temperature of n-pentane), andthe extraction separator V5 (i.d.=0.16 m) operated at the sametemperature to V1 and a pressure slightly lower than 3450 kPa.The V3 is the DAO stripper, the V4 is the solvent (n-pentane)tank, and the V6 is the asphaltene flash drum.

During a typical run, the preheated emulsion (~343 K) wascontinually fed into the unit by pump P1. The hot pure n-pentane from V2 top was injected into the emulsion at point A(Fig. 1) to reach a designed solvent to bitumen ratio (S1/B) andtemperature (T1), and then the fluid was mixed in M1. Thesecond part of impure solvent (containing some extracted oil)from V5 top was added into the diluted emulsion at point B toreach the designed S2/B and T2, and then mixed in M2 inwhere the demulsification took place. Then the mixture ofbroken emulsion and n-pentane was separated into light andheavy phases in top section of V1. The light solution of DAOand n-pentane was heated up to a higher temperature of NT2in V1, and then was delivered by pump P3 into V2, in wheremost n-pentane was separated as supercritical fluid from theDAO, and sent from V2 top back into the point A. The DAOstream was transferred from the V2 bottom into V3, in wherethe remaining solvent was stripped out of DAO and sent backto solvent tank V4, while the dry DAO product was withdrawnin V3 bottom. At the same time, the heavy stream in V1 topsection flowed down through the internal pipe to the bottomsection of V1, more fresh n-pentane was injected in point C to

Feedstock B AnalysisMethods

Water-in-bitumen emulsion Bitumen(de-watered)

1.0017 0.9997 ASTM D40522027 ASTM D445

572 515 ASTM D44584.07 Dean–Stark15.15 Dean–Stark0.78 Dean–Stark

17.8 ASTM D405584.36 ASTM D529110.10 ASTM D52910.54 ASTM D46294.13 ASTM D4294

73.9 ASTM D5708 ICP179 ASTM D5708 ICP12.99 ASTM D4530

Fig. 1 –Simplified schematic flow diagram of the pilot plant.

943F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 9 4 1 – 9 4 8

reach a designed overall solvent to bitumen ratio (S3/B), strongmixing was generated by the contra-current flow and moretime was provided to extract the oil attached to asphalteneand water. Then the stream was transferred into V5 topsection, in where the solvent with the extracted oil wasseparated from water and asphaltenes and recycled by pumpP2 from V5 top back to the point B. The heavy mixture ofasphaltenes/water with the remaining solvent flowed downthrough the internal pipe into V5 bottom section, recycled bypump P5, and went through the depressurization valve intoasphaltene flash drum V6. Once the pressure droppedsuddenly (adiabatic depressurization), the solvent trappedinto asphaltenes/water was evaporated and sent from the V6top back to V4, while asphaltene particles were solidified dueto the temperature drop and flowed with water out of the V6bottom. Finally, the free water was easily filtered out of theasphaltenic solids, and the adsorbed water could be dried outof the solids if necessary.

For a continual operation, the S2/B resulted from S3/Bsubtracting S1/B. A number of runs were conducted forinvestigating the effects of parameters S1/B, S2/B, T1, T2 andT3 on the performance.

2.3. Analysis

Thematerial balance was examined for each run, and productyields were determined based on themass of dry bitumen (de-watered emulsion) used during an operation. The properties ofdry DAO liquid product (n-pentane free) and dry asphaltenicsolid product (water free) were determined according to thestandard ASTM methods. Since small changes in the densityof oils are significant, the petroleum industry uses the APIscale. A higher specific gravity (density) value corresponds to a

lower ° API value. For example, a heavy material with thespecific gravity larger than 1.0761 could have a negative APIvalue.

3. Results and discussion

3.1. DAO products

The DAO liquid products are obtained after asphaltenic solidand water have been removed from a water-in-bitumenemulsion. The quality of a DAO sample is defined by itsproperties such as density, viscosity, asphaltene and MCRcontents. Among these related properties, asphaltene contentis an important index to the quality. For a DAO liquidacceptable to a conventional refining process, its asphaltenecontent should be less than 1%, at least. The results in thispilot plant study have shown that there were variousoperation parameters affecting the quality of DAO.

3.1.1. Effects of temperature on the DAO qualityThe effects of the second solvent injection temperature T2 (atpoint B in Fig. 1) and phase separation temperature T3 (in V1) onthe DAO properties were investigated, and the data in Table 2summarized the analytical results of six DAO samples fromdifferent runswithvarying temperatureusing thesamefeedstock(A), feed rate (2.12×10−2m3/h), overall S/B ratio (3.5), and duration(8 h). Also, for all the six runs, the first part of the solvent wasinjectedat theoptimal temperatureof423K (T1 atpointAofFig. 1),according to the previous investigationwith the bench-scale unit[19]. For the runof injecting the secondpart of the solvent at 433K(T2) and separating the phases at 438 K (T3), the DAO productsampleT-1containsasphaltenesof1.7wt.%,MCRof7.0wt.% ,and

Table 2 – Effects of operating temperatures on the quality of DAO products

Operating temperature DAO sample code and analysis Massbalance

T1, K T2, K T3, K Code Gravity, API Viscosity, cSt at 323 K C5-asphaltene, wt.% MCR, wt.% Yield, vol.%

422 433 438 T-1 14.1 716 1.7 7.0 82.4 99.4%423 438 443 T-2 14.9 521 1.4 6.6 80.9 99.1%422 438 453 T-3 15.1 295 1.3 6.4 81.6 100.1%423 443 453 T-4 15.3 240 0.8 6.2 80.8 99.8%424 443 458 T-5 15.6 220 0.6 6.2 79.9 99.3%423 443 463 T-6 16.1 193 0.3 6.0 81.0 100.3%

Feed: Feedstock A.Feed rate: 2.12×10−2 m3/h.S/B ratio (vol): S1/B: 1.6±0.1; S2/B 1.9±0.1; S3/B (i.e. overall S/B): 3.5±0.1.Duration: 8 h.

944 F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 9 4 1 – 9 4 8

has the API gravity of 14.1 and viscosity of 716 cSt at 323 K,indicating a poor quality. With increasing T2 to 438 K and T3 to443K further to 453K, thequality ofDAOsamplesT-2andT-3wasimproved, but theasphaltenecontent in the twosampleswasstilllarger than 1 wt.%. As the T2 increased to 443 K the asphaltenecontent in theDAOsampleT-4wassignificantly reducedto0.8wt.%, and the asphaltene contents in the DAO samples T-5 and T-6were further reduced to 0.6 and 0.3 wt.% as the T3 increased to458 K and 463 K. The viscosity and MCR content of the DAOsamples show a similar change to asphaltene content withtemperature.

From the economic consideration, however, operating V1at 453 K (T3) may not be a bad choice although the best qualityof DAO could be obtained at or over 463 K, because a veryhigher operating temperature could cause water evaporation.

3.1.2. Effects of S/B ratio on the DAO qualityTable 3 presents the quality data of DAO samples producedfrom six runs using feedstock (A) at the same feed rate(2.12 × 10− 2 m3/h), the same operating temperatures(T1=423 K, T2=443 K, T3=453 K), and the different S/B ratios.For those four runs operating at the same overall solvent-to-bitumen ratio (S3/B) of 3.5 with increasing S1/B ratio from 1.6 to2.2 (decreasing S2/B ratio from 1.9 to 1.3), the run with S1/B=1.8and S2/B=1.7 produced theDAO sample (S-2) having the lowestasphaltene content of 0.3 wt.%, while the run with a lower S1/B(1.6) and a higher S2/B (1.9), the asphaltene content in the DAOsample (S-1) was 0.8 wt.%, indicating that a few asphaltenes

Table 3 – Effect of n-pentane to bitumen (S/B) ratio on the quali

S/B ratio (volume) DAO

S1/B S2/B S3/B Code Gravity, API Viscosity, cSt at

1.6 1.9 3.5 S-1a 15.3 2401.8 1.7 3.5 S-2 15.9 2012.0 1.5 3.5 S-3 15.2 2512.2 1.3 3.5 S-4 14.8 5631.8 1.4 3.2 S-5 14.9 4721.8 2.0 3.8 S-6 15.8 213

Feed: Feedstock A.Rate: 2.12×10−2 m3/h.Temperature: T1: 423±1 K; T2: 443±1 K; T3: 453±1 K.Mass balance: 100±1%.Duration: 8 h.a The same DAO sample as T-4 in Table 2.

may have not precipitated yet before the second solventinjection (S2/B) to break the emulsion. Meanwhile, increasingthe S1/B from 1.8 to 2.0 to 2.2 and decreasing the S2/Baccordingly, the asphaltene content in the DAO increasedfrom 0.3 wt.% (S-2) to 1.0 wt.% (S-3) to 1.5 wt.% (S-4), indicatingpre-mature breaking of the emulsion due to an over injectionof the first solvent (S1). The pre-mature breaking of anemulsion reduced the surface area of water droplets availableto the interactionwith asphaltene particles, and thus harmingthe separation of asphaltene particles together with waterfrom the DAO-solvent solution.

On the other hand, reducing the overall S/B (or S3/B) ratio from3.5 to 3.2 significantly increased the asphaltene content in theDAO from0.3 (S-2) to 1.4wt.% (S-5), while increasing theS3/B from3.5 to 3.8 only cause an insignificant variation in the asphaltenecontent (from0.3wt.% inS-2 to0.4wt.%inS-6).Theseresults showthat there exists an optimal S3/B ratio in the range 3.2–3.5 for thetargeting asphaltene content of b1 wt.% in DAO. Below the S3/Bratio of 3.2 the asphaltene content in DAO is over the targetedvalue, while above the S3/B of 3.5 the asphaltene content is notgoing to be further reduced significantly.

3.1.3. Effects of feed rate on the DAO qualityInvestigating the effects of feed rate on the DAO quality anddetermining the maximum superficial velocity of streams tothe targeted quality could define the guidelines for design-ing pipe sizes, pump capacities, vessel diameters, etc. Fig. 2and Table 4 present the analytical data of DAO samples

ty of DAO products

sample code and analysis

323 K C5-asphaltene, wt.% MCR, wt.% Yield, vol.%

0.8 6.2 80.80.3 6.1 80.71.0 6.3 79.81.5 6.7 80.11.4 6.4 80.30.4 6.1 80.5

Fig. 2 –Asphaltene content in DAO as a function of feed rate.Feedstock A; S1/B: 1.8±0.1, S2/B: 1.7±0.1, S3/B: 3.5±0.1; T1: 423±1 K, T2: 443±1 K, T3: 453±1 K; 8 h.

Fig. 3 –Asphaltenecontent ofDAOfromfeedstocksAandBasafunctionof feed rate (operationconditionsasshown inTable5).S1/B: 1.8±0.1, S2/B: 1.7±0.1, S3/B: 3.5±0.1; T1: 423±1 K; T2: 443±1 K; T3: 453±1 K; 8 h.

945F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 9 4 1 – 9 4 8

from five different runs using feedstock A with varying feedrate. The asphaltene contents in the DAO kept below thelevel of 0.5 wt.% as the feed rate increased from 1.06×10−2

to 3.03×10−2 m3/h, increased to 0.8 wt.% at the feed rate of3.63×10−2 m3/h, and jumped to 1.6 wt.% with increasing thefeed rate from 3.63×10−2 to 4.54×10−2 m3/h, indicating asignificant deterioration of the DAO quality. The density,viscosity and MCR content of DAO showed the similarchange tendency to asphaltene content as feed rateincreased (Table 4). Thus, it is clear that the maximumallowable feed rate for targeting the asphaltene content ofb1 wt.% in DAO is about 3.79×10−2 m3/h.

3.1.4. Effects of the water in feedstock on the DAO qualityThe water-in-bitumen emulsion A contains water of35.85 wt.%, while the emulsion B contains water of15.15 wt.%, as presented in Table 1. The pilot plant testsshowed that the water content in feedstock has significantimpact on the quality of DAO products. As shown in Fig. 3,the DAO samples produced from the feedstock B containmuch higher asphaltene content than the DAO from the

Table 4 – Effect of feed rate on the quality of DAO products

Samplecode

Feed rate

m3/h Gravity, API Viscosity, cSt at 323

R-1 1.06×10-2 15.8 212R-2a 2.12×10-2 15.9 201R-3 3.18×10-2 15.7 223R-4 3.63×10-2 15.6 248R-5 4.54×10-2 14.8 612

Feed: Feedstock A.S/B ratio (vol): S1/B: 1.8±0.1; S2/B: 1.7±0.1; S3/B: 3.5±0.1.Temperature: T1: 423±1 K; T2: 443±1 K; T3: 453±1 K.Mass balance: 100±1%.Duration: 8 h.a The same DAO sample as S-2 in Table 3.

feedstock A under the same operation conditions. As thefeed rate was increased from 1.06×10−2 to 3.03×10−2 m3/h,the DAO from the feedstock A has a stable and lowasphaltene content of b 0.5 wt.%, while the asphaltenecontent of DAO from the feedstock B increases from ~1 wt.%to ~2 wt.%. For a feed rate of 3.79×10−2 m3/h, the DAO fromthe feedstock B contains ~2.4 wt.% asphaltenes, in compar-ison to ~0.8 wt.% for the DAO from the feedstock A, that isdifferent by a factor of three. Therefore, there is no doubtthat the water in emulsion feedstock did facilitate theremoval of asphaltenes from bitumen and improve thequality of DAO product. The analysis of gravity, viscosityand MCR of DAO product samples supports this conclusion(Table 5).

The full course and mechanism how the emulsified waterfacilitates the removal of asphaltenes from bitumen are notfully understood yet at moment, but the interaction betweenthe emulsified water droplets and the precipitated asphalteneparticles appears to be an important factor. The real control-ling parameter should be the surface area of emulsified waterdroplets instead of its weight percent. Therefore, there may be

DAO analysis

K C5-asphaltene, wt.% MCR, wt.% Yield, vol.%

0.3 6.0 80.90.3 6.1 80.70.4 6.1 80.80.8 6.3 80.61.6 6.7 80.4

Table 5 – Effect of water in feedstock on the quality of DAO products

Feedstock DAO sample code and analysis

Type Water, wt.% Rate, m3/h Code Gravity, API Viscosity, cSt at 323 K C5-asphaltene, wt.% MCR, wt.% Yield, vol.%

A 35.85 1.06×10-2 F-1a 15.8 212 0.3 6.0 80.9A 35.85 2.12×10-2 F-2a 15.9 201 0.3 6.1 80.7A 35.85 3.63×10-2 F-3a 15.7 248 0.8 6.3 80.6B 15.15 1.06×10-2 F-4 14.5 592 1.1 6.8 79.7B 15.15 2.12×10-2 F-5 14.4 753 1.8 7.1 79.4B 15.15 3.63×10-2 F-6 13.9 831 2.4 7.8 78.9

aThe same samples as R-1, R-2, and R-4 in Table 4.S/B ratio (vol): S1/B: 1.8±0.1; S2/B: 1.7±0.1; S3/B: 3.5±0.1.Temperature: T1: 423±1 K; T2: 443±1 K; T3: 453±1 K.Mass balance: 100±1%.Duration: 8 h.

Table 6 – Properties of the asphaltenic solids

Solids from feedstockA

Solids fromfeedstock B

Yield, wt.% inbitumen

19.7 20.5

Bulk density,kg/m3

644.5 648.2

True density,kg/m3

1148.6 1139.4

R&B softeningpoint, K

449 435

Oil content,wt.%

10.40 11.29

Ash, wt.% 0.40 1.11C5-asphaltene,wt.%

89.2 87.6

MCR, wt.% 41.69 40.48S, wt.% 7.76 7.70N, wt.% 1.31 1.24Ni, mg/kg 292.8 306.4V, mg/kg 694.3 747.5

S/B ratio (vol): S1/B: 1.8±0.1; S2/B: 1.7±0.1; S3/B: 3.5±0.1.Temperature: T1: 423±1 K; T2: 443±1 K; T3: 453±1 K.Mass balance: 100±1%.Duration: 24 h.

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a minimum requirement to the surface area of water droplets,depending on the asphaltene content in bitumen and thetargeted asphaltene reduction.

3.2. Asphaltenic solids

Dry asphaltenic solids are produced after the water and tracesolvent have been removed from the heavy stream in thisaccelerated deasphaltening process, and the solids containhigh concentrations of asphaltenes, sulfur, nitrogen, metalsand carbon residue. Once the asphaltenic solids are removedfrom bitumen, the resulting DAO can be used as premiumcrude and processed by conventional refinery processes. Inthis pilot plant study, the production and properties of theasphaltenic solids from the water-in-bitumen emulsion havebeen investigated and analyzed.

3.2.1. Solidification and dryingThe routine solvent-deasphalting technologies such as ROSEupgrade water-free residue to liquid fuels plus hot-asphaltenefluid as by-product, which is difficult to be further treated. Oneunique aspect of this accelerated deasphaltening technologyis able to separate the asphaltenes as solids from water-in-bitumen emulsion with a simple and energy-efficient way,well demonstrated in this pilot plant investigation. As shownin Fig. 1, the hot stream of asphaltenes/water with somesolvent was delivered from V5 bottom into vessel V6 with asudden pressure drop. Thermodynamically, this process couldbe approximate as an adiabatic depressurization that reducesthe enthalpy of system. Once depressurized, the trace solventin the stream was quickly evaporated, the temperaturereduced, asphaltenes solidified and suspended in water.However, the significant evaporation of water with solventshould be avoided during the depressurization.

The free water was filtered out of the suspension ofasphaltenic solid–water. The adsorbed water in the solidscould be removed by air dry. The final dry solid was a porousmaterial that is easy to handle and good for further processing.

3.2.2. PropertiesThe properties of two representative asphaltenic solids (dry)produced from feedstocks A and B with the pilot plantoperations under typical conditions are presented in Table 6.As expected, the contents of sulfur, nitrogen, micro carbon

residue, nickel and vanadium in the asphaltenic solid aremuchhigher than those in the feed bitumen (Table 1). In fact, theasphaltenic solid fraction of ~20 wt.% in bitumen contains 38%sulfur, 47% nitrogen, 64% MCR, and 85% nickel or vanadium ofthe bitumen. The porous solids have the bulk density of~0.64×103 kg/m3 and the true density of ~1.14×103 kg/m3.

It should be noticed that these solids are not pure C5-asphaltenes because they still contain 10–11 wt.% oils,equivalent to ~2% of bitumen. The additional analysis hasshown that the oils in the solids mainly consist of polyaro-matics that have strong interaction with asphaltenes. There-fore, it is impossible to completely eliminate the trace oilsfrom the asphaltenic solids in this pilot plant operation, but itis possible to further reduce the amount of trace oil in thesolids by optimizing operation conditions.

3.2.3. UtilizationThe utilization of the asphaltenic solids has been considered fortechnical justification and economical evaluation. Potentially,

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they could be used as solid oil feed for ultrapyrolysis or otherhydrocarbon processing, and also be used as a solid fuel forpower plants or cement production. Suggestions on theindustrial-scale utilization of the asphaltenic solids will berecommended elsewhere in future.

3.3. Solvent recovery and consumption

For any commercial solvent-deasphalting process, the solventrecovery efficiency is absolutely important to the economicsandsafety. In this pilot plant operation, the solvent (n-pentane)was continually recovered and recycled to different locations,as showed in Fig. 1. The majority of n-pentane was separatedas supercritical fluid on top of the DAO separator (V2) atpressures of 3490–3620 kPa and temperatures of 473–503 K,passed through a heat-exchanger and then recycled back tothe point A for the first solvent injection (S1). Such supercriticalrecovery of solvent has been demonstrated to be very effectiveand economic [20]. The small percentage of n-pentane wasstripped out in DAO stripper (V3), recycled back to the solventtank (V4). The dry DAO product (solvent free) was withdrawnfrom the bottom of V3. At the same time, the n-pentaneremaining in asphaltene/water stream was evaporated afterthe stream was delivered from the vessel V5 bottom to thevessel V6with depressurization, and sent back from the V6 topto the solvent tank (V4). Thus, only the solvent dissolved in thewater out of V1 bottom or V6 bottom has lost during theoperation. Since the solubility of solvent in water is tempera-ture dependent, the net loss of solvent could be minimized byoptimizing the process conditions. For a continual run of 24 hwith the current pilot plant under normal conditions, the netloss (consumption) of n-pentane was found to be less than0.05%which can be further reduced in a commercial operation.

3.4. Water purification

From an environmental protection point of view, waterpurification is of great importance to any commercial oilprocess dealing with a large amount of water. For thisaccelerated deasphaltening process, removal of asphaltenesandwater from awater-in-bitumen emulsion produces a lot ofwater, and hence the purification of water has to be seriouslyconsidered. During an operation of the pilot plant, free waterwas produced after breaking the emulsion, flowed out of theV1 bottom and V6 bottom (Fig. 1). Analysis of water sampleshas showed that the water of V1 bottom contains a traceamount of n-pentane but no oil or solid, and thus no need to bepurified. In fact, the solvent injected at point C of V1 generatesa good mixing with the heavy stream flowing down from theV1 top section by the contra-current contact, but the lowersection of the V1 bottom below point C keeps still and servesas water reservoir. With the smart design of the V1 andprocess, the clean water was continually withdrawn from V1bottom, while the mixture of diluted asphaltenes/oil withsome water and original clays was continually delivered fromV4 to V5 top section.

Besides the dissolved n-pentane, however, the water with-drawn from V6 bottom contained some very fine solids due tothe turbulent depressurization. It could be difficult or uneco-nomic to remove these fine solids from the water by routine

filtration or centrifugation. The better way to deal with thewater containing fines is to recycle it back to V1 bottomsection, or send to feedstock for making high water content ofwater-in-bitumen emulsion.

This pilot plant study gives a technical approval for a go-ahead application of the accelerated deasphaltening technol-ogy in oil industry. Once commercialized, this technology willprobably innovate the oil-sands processing and bitumenupgrading, produce middle crude flexible to refiners, andpotentially play an important role in the integration of oil-sands processing, bitumen upgrading and crude refining.

4. Conclusion

The pilot tests have been successfully conducted for the SAGDwater-in-bitumen emulsion which contains insignificantamount of solids (clay). Asphaltenes and water have beensimultaneously removed from the water-in-bitumen emul-sions with the pilot plant operation. DAO with the yield ofN80wt.% in bitumen and lowC5-asphaltene content of b1wt.%was continuously produced with minimum solvent consump-tion. Asphaltenes were solidified as porous materials contain-ing mostly of sulfur, nitrogen, MCR, and metals in bitumen.The produced water was self-purified in this process.

For the feedstock containing the amount of solids (clay)N10%, the current pilot plant would have a problem ofpotential pipe plugging, mainly due to the small diameter ofpipe (3/8 in.). The problem of pipe plugging could be solvedwith increasing the diameter of pipe. Therefore, the suggestedprocess should be suitable to the bitumen feedstock contain-ing a significant amount of solids.

Acknowledgements

The authors thank the National Natural Science Foundation ofChina (20673099) and the Scientific Research Fund of Ningbo(2006A610065) for the financial support of this work.

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