Accelerated Solvent Extraction for Bitumen Extraction from Oil Sands Aaron Kettle and Paul Voelker Thermo Fisher Scientific, Sunnyvale, CA, USA

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Executive Summary The accelerated solvent extraction technique shows potential to replace Soxhlet-Dean Stark Extraction (SDSE) as the industry standard for bitumen extraction from oil sands. Bitumen is a sticky, black and highly viscous liquid or semi-solid form of petroleum. These two extraction techniques were compared for the extraction of bitumen, solids, and water from oil sands. In each instance, the accelerated solvent extraction technique produced equivalent performance to Soxhlet-Dean Stark extraction. Accelerated solvent extraction technique uses considerably less time and solvent per sample and has the potential to revolutionize bitumen extraction from oil sands in the heavy crude oil industry.

IntroductionThe oil sands are large deposits of bitumen (heavy crude oil). The largest deposit is located in northeastern Alberta, Canada. There is an estimated 1.7 to 2.5 trillion barrels of oil in the Alberta oil sands, approximately 40% of world wide heavy oil deposits (other oil sand deposits include Venezuela, SW Texas, and Utah).1,2 According to a 2013 report by the Canadian Association of Petroleum Producers, Canadian crude oil production is predicted to grow at a compounded annual growth rate of nearly 7% from 2015 to 2020.

The oils sands extraction process is composed of an extraction step and a characterization step. The first step is the extraction with heated toluene into three components; bitumen, solids content (sand & clay), and water (Figure 1).

An area of particular analytical interest is quantifying the fines (fine clay particles <44 microns) in the residual solid content following bitumen extraction. The problem is the fines containing residual bitumen from the extraction process are found in ground water and creating environmental concerns by polluting it with toxic chemicals. As a result, there is a growing need for conducting a mass balance analysis, i.e., gravimetrically measuring all the material before and after extraction to account for all the oil sand components.

KeywordsAccelerated Solvent Extraction, ASE, Bitumen, Oil Sands, Soxhlet-Dean Stark Extraction

Asphaltene

H2OBitumenSolids Content

Oil Sands

ExtractionToulene

Characterization

CoolingConcentrated & Dried

BenzenePentane Insoluble

Toulene Insoluble

Figure 1. Oil Sands composition.

2 The second step is the characterization of bitumen to determine the asphaltene content (tar residue that is either rejected, or converted to low value products) in the bitumen. Asphaltene is a low value added product present in the bitumen. The higher the asphaltene content, the lower the value of the bitumen. Drilled core samples are used to determine which area contains the lowest asphaltene content.4 For more information visit the Petroleum Technology Alliance Canada (PTAC) website at http://www.ptac.org/projects/59.

The Soxhlet-Dean Stark Extraction and accelerated solvent extraction techniques are shown to be effectively the same when extracting bitumen, solids, and water content from oil sands. The difference between the two techniques is that the accelerated solvent extraction technique introduces a pressure component which, when combined with heat, enables the extraction process to occur in about one-tenth the time. This White Paper discusses both extraction techniques and provides a comparison of the extraction efficiency for extraction bitumen, solids, and water content from oil sands.

Extraction Techniques for Bitumen in Oil SandsSoxhlet-Dean Stark Extraction (SDSE) The Soxhlet-Dean Stark Extraction (SDSE) is recognized standard for bitumen extraction and is used to measure the water content in oil sands. This technique applies heat to a volatile organic solvent (e.g. toluene) and brings the solvent to its boiling point. Vapors from the solvent rise to the top of the apparatus and into a condenser that forces the solvent into a liquid state. The liquid solvent to drip down into a thimble that contains the oil sands sample. The bitumen in the oil sand dissolves when the warm solvent hits the thimble and overflow occurs. This allows the bitumen containing solvent to drip down the side arm of the system and back into the boiling flask at the bottom on the apparatus. The Soxhlet extraction procedure typically requires substantial amounts of time (4–48 hours per sample) and solvent (200–500 mL per sample).

Accelerated Solvent Extraction TechniqueThe accelerated solvent extraction technique uses elevated temperatures and pressure to extract compounds from solid and semi-solid matrices. Bitumen can also be extracted using the accelerated solvent extraction technique by loading the oil sands sample into a stainless steel extraction cell and subjecting it to hot toluene at elevated pressure.

A static cycle is used to remove the bitumen from the oil sand and dissolve it into the toluene. Once the static cycle is complete, a static valve is opened and the solvent containing the bitumen is collected into a collection vial. The accelerated solvent extraction technique is fully automated and does not require an analyst to be present during the extractions. Up to 24 samples can be loaded onto the system and run overnight without analyst intervention. The accelerated solvent extraction technique uses less time (0.2–0.3 hours per sample) and solvent (15–45 mL per sample). A schematic of the Acceleration Solvent Extraction process is shown in Figure 2.

Extract ready

Cell loading

Static extraction 0 to 99

Purge with 1–2nitrogen

Rinse with 0.5fresh solvent

cycle

dynamic extraction

static extraction

Fill, heat, (min)equilibrate 5 to 9

Pump

Solvent Solvent Solvent

ReliefValve

OvenExtraction Cell

Static Valve

Collection Bottle

MixingValve

Figure 2. Example of a workflow using the accelerated solvent extraction technique.

3Comparison of Soxhlet-Dean Stark to ASESince the accelerated solvent extraction technique uses less time and solvent to extract bitumen, its effectiveness compared to the Soxhlet-Dean Stark technique to evaluate the accelerated solvent extraction technique being an effective replacement. The extraction efficiency for both techniques were compared by extracting bitumen, solids, and water from three grades of oil sands.

Bitumen ContentBitumen was extracted from oil sands using toluene with both extraction techniques. The bitumen in solution was concentrated using a rapid vacuum concentrator. Both extraction techniques were evaluated on the basis of the weight of bitumen extracted from oil sands (Table 1). A weight concentration per mass of oil sand sample (w/w) % was obtained. Three grades of oil sands were evaluated to demonstrate the scope of the technique, and in each instance, the accelerated solvent extraction technique produced equivalent performance to the Soxhlet-Dean Stark extraction.

Oil Sands Grade Accelerated Solvent Extraction Technique (w/w) %

Soxhlet-Dean Stark Extraction Technique (w/w) %

Low 5.76 +/- 0.08 5.57 +/- 0.19

Medium 10.25 +/- 0.26 10.16 +/- 0.39

High 12.62 +/- 0.15 12.27 +/- 0.10

Table 1. ASE vs SDSE for bitumen extraction from Oil Sands.

Solids Content The solids content in oil sands was also evaluated following extraction of bitumen using the accelerated solvent extraction technique and the Soxhlet-Dean Stark extraction. The solids content were obtained by measuring the weight of the oil sands following the extraction in the same three grades (Table 2). In each instance, the accelerated solvent extraction technique produced results equivalent to the Soxhlet-Dean Stark extraction.

Table 2. Accelerated Solvent Extraction Technique vs Soxhlet-Dean Stark Extraction Technique for solids content determination in Oil Sands.

Oil Sands Grade Accelerated Solvent Extraction Technique (w/w) %

Soxhlet-Dean Stark Extraction Technique (w/w) %

Low 88.16 +/- 0.24 88.52 +/- 0.19

Medium 84.81 +/- 0.18 85.28 +/- 0.23

High 85.06 +/- 0.21 85.60 +/- 0.66

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Water ContentThe accelerated solvent extraction technique and the Soxhlet-Dean Stark technique were also compared on the ability to remove water from oil sand samples. Water content estimates for each technique were determined using the difference between the weight of the total oil sands samples (100%) and the sum of the solids (S%) and bitumen (B%) content. As shown in Table 3, the accelerated solvent extraction technique was able to generate results equivalent to the Soxhlet-Dean Stark extraction.

ConclusionThe accelerated solvent extraction technique was able to demonstrate equivalency to the Soxhlet-Dean Stark extraction for bitumen in oil sands.3 Additionally, this extraction technique was able to produce equivalent performance to the Soxhlet-Dean Stark extraction for solids and water content. The accelerated solvent extraction technique uses substantially less time and solvent than Soxhlet-Dean Stark and may serve as a replacement as the industry standard for bitumen extraction from oil sands.

References1. Energy Minerals Division, a Division of the American Association of Petrolum Geoloists. Oil

Sands. [Online] http://emd.aapg.org/technical_areas/oil_sands.cfm (accessed March 20, 2014).

2. Investopedia. Oil Stands. [Online] http://www.investopedia.com/terms/o/oilsand.asp (accessed March 20, 2014).

3. Mercier.P. Comparison of oil sands OWS analyses and bitumen properties obtained by acceler-ated solvent extraction versus Soxhlet-Dean and Stark extraction techniques. Presented at the Oil Sands Conference, University of Alberta, Edmonton, Canada, 2011.

4. Petroleum Technology Alliance Canada (PTAC). Oil Sands. [Online] http://www.ptac.org/projects/59 (accessed March 27, 2014).

Oil Sands GradeAccelerated Solvent Extraction

Technique 100% - B% - S% (w/w) %

Soxhlet-Dean Stark Extraction Technique 100% - B% - S%

(w/w) %

Low 6.08 +/- 0.25 5.91 +/- 0.20

Medium 4.94 +/- 0/17 4.56 +/- 0.37

High 2.32 +/- 0.30 2.13 +/- 0.69

Table 3. Accelerated Solvent Extraction Technique vs Soxhlet-Dean Stark Extraction Technique for water content determination in Oil Sands.