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Natural Resources Canada team investigates solvent extraction process for oil sand bitumen; non-aqueous alternative to hot water processing with reduced environmental impacts

16 January 2012

A team of two researchers from Natural Resources Canada’s CanmetENERGY reports on a new process for solvent extraction of bitumen from mineable Athabasca oil sands (i.e., surface mining, not in situ well-based production) in a paper published in the ACS journal Energy & Fuels. Wide-scale deployment of such a non-aqueous process could mitigate some of the negative environmental impacts of the mining method of bitumen production, such as high water consumption; the resultant tailing ponds; energy consumption; and greenhouse gas emissions, they suggest.

In this process, oil sand is mixed with light hydrocarbon solvents, and the solvent–bitumen solution is separated from the mineral solids by centrifugal filtration or regular pressure filtration. The solvent left in the filtration cake is recovered by evaporation under vacuum at room temperature.

Their results show that, for both high-grade and low-grade ores, using appropriate solvent, the bitumen recovery and product quality are comparable to those from the currently used hot water extraction followed by naphtha froth treatment. The recovery of light hydrocarbon solvent is relatively easy, so this novel process has great potential to reduce solvent losses compared to existing technologies, the team suggests.

The Clark hot water extraction (CHWE) process has been applied in commercial bitumen extraction from the Athabasca oil sands for more than 40 years. However, Jiangying Wu and Tadeusz Dabros note in their paper, the water-based technology now faces numerous challenges:

  • High water consumption. 3 to 4 barrels of water are required for every barrel of bitumen produced.

  • Tailing ponds. The hot-water process generates huge tailing ponds that have serious, long-term environmental impacts.

  • Treatment challenges. If naphthenic froth treatment is utilized, bitumen product quality is low; if paraffinic froth treatment process is utilized, the asphaltenes rejection is high.

  • Energy and GHG. The high thermal capacity of water results in high energy consumption and high greenhouse gas (GHG) emissions.

Non-aqueous bitumen extraction is being investigated as an alternative to the CHWE process. By eliminating water use in bitumen extraction, all water-related issues would be resolved. For example, elimination of the fresh water draw from the Athabasca River would help preserve the ecology. The need for wet tailing ponds would be eliminated; instead, dry tailings suitable for continuous backfilling of the open pit would make it possible to reclaim the mined-out area in a much shorter period of time than is currently feasible. The non-aqueous process also has the potential to greatly improve energy efficiency and reduce GHG emissions.

—Wu and Dabros

Overall, two types of non-aqueous bitumen recovery processes have been explored, they note: pyrolysis and solvent extraction. One drawback of the pyrolysis process is the high operating temperatures required. Several solvent extraction processes have been investigated. However, Wu and Dabros note, the major problem with solvent extraction processes is that they require large amounts of solvent to form a slurry with the oil sand feed, and high-boiling-point solvents make it difficult to recover the solvent from the large volumes of sand.

Combined solvent-and-water extraction processes have also been investigated, however, “once water is introduced into the extraction process so are most of the problems associated with conventional water-based extraction.

Wu and Dabros set out to obtain bitumen recovery of more than 90 wt % and to limit solvent losses to less than 4 bbl of solvent per 1,000 bbl of extracted bitumen (0.4%). Low-boiling-point solvents were used to facilitate recovery; five different solvents were investigated at relatively low solvent-to-bitumen ratios (S/B), which is on a mass basis.

Their findings were:

  1. Cyclopentane is a good solvent for extracting bitumen from oil sand. Cyclopentane gives higher bitumen recovery than toluene. To reduce solvent cost, cyclopentane can be mixed with n-pentane.

  2. For both high-grade and low-grade ores, bitumen recovery using the investigated solvent extraction process is comparable to that of the water-based bitumen extraction process. E.g., using a three-stage extraction process, more than 95 wt % of the bitumen from high-grade ore can be recovered.

  3. The quality of solvent extracted bitumen is similar to that of bitumen from water-based extraction followed by naphtha froth treatment.

  4. Centrifugal filtration has a higher efficiency than regular pressure filtration. However, if high S/B is used, regular pressure filtration can also achieve over 90 wt % bitumen recovery.

  5. Owing to its higher bitumen recovery and low boiling point, cyclopentane is much easier to recover than toluene. For high-grade ore, solvent loss can be easily limited to less than 4 barrels per 1,000 barrels of bitumen production; for low-grade ore, this could be achieved at slightly elevated temperatures.

Resources

  • Jiangying Wu and Tadeusz Dabros (2012) Process for Solvent Extraction of Bitumen from Oil Sand. Energy & Fuels doi: 10.1021/ef201457m

January 16, 2012 in Canada, Oil sands | Permalink | Comments (9) | TrackBack (0)

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Comments

this is a very helpful resource. I would like to share this if you dont mind sir.air compressor

Im a canadian and im ashame at what primitive oil sands extraction is. This is the fault of Pierre elliot trudeau that selled this project to americans oil compagnies for no benefits for canadians except some miserable polluting jobs.

@Mike Millikin: Any mention of EROEI implications?

I'm going to read the paper tonight.

Unfortunately, this process will be used to lower cost and increase profits, not to reduce GHG and pollution.

If you dig up two bits of fossil hydrocarbon out of the ground, use one bit to produce a single bit of usable fuel then your EROI is 50% and meaningless, since you end up with one bit of fossil fuel pulled out of the ground where before you had none..

Its the same concept of wall to wheel efficiency for electric cars.. hello!, who cares when your source of electricity is solar?

Herm...the problem with using more and more energy to pull out unsustainable bits fossil fuel is that sooner or latter 100 bits will not be enough to pull out 100 bits of energy.

The solar approach is sustainable (at least for the next 5+ billion years) and technology will increase the conversion efficiency to over 50% by 2020/2030.

@AD

Are you sure it was Trudeau? I'm not saying you're wrong but I'm sure I remember both Mulroney and Chrétien trying to take credit for it.

@ ai_vin

IT was pierre elliot trudeau, He was the cleark of american wall-street speculators for canada. He nationnalized many oil compagnies with tax money then he fonded petro-canada and resale that at a loss to americans. WE now pay 30% more at the pumps for gasoline then americans for the same gas. He also had a traumatism dream about montreal airport and it costed 2 billions in the seventies for absolutly nothing because now this airport, mirabel, is not used anymore and toronto triple his size since them and here in quebec the montreal airport is just for the region and also his son changed the montreal airport name to the name of his father. Actually his son is casching tax money as a cleark in ottawa as a politician. It's not just in germany or russia or china that we witnesse an imaginary dream politician like hitler or mao or staline, canada too has some extremists.

About that 30% more expensive Canadian petrol. Tar sands are looking increasingly uncompetitive compared to Bakken. North Dakota is about to surpass Alaska in production. Halliburton is using natural gas and another company is using gelled LPG as an alternative to water fracking. Unless in situ tar sand extraction is mastered and crude output from Athabasca is improved, there will be a serious upset in Canada. Enright Co. can threaten to export as much tar sand as they want to China as they want (now that Keystone II is on hold) but until there are refineries to handle it and China can control the margins at the pump, it's no dice. I'm sure Toronta would not appreciate the Middle Kingdom managing it's finances in exchange for oil a la Liberia or for that matter, Iran.

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