Asphaltene Precipitation From Bitumen Diluted With n-Alkanes
Bibliographic record
Abstract
Introduction Some heavy oil and bitumen production processes involve the precipitation of asphaltenes upon the addition of a paraffinic diluent. For example, in a new oil sands process, a paraffin solvent is used to treat the froth generated in bitumen extraction. The recently proposed VAPEX process is also based on a paraffinic solvent. To optimize these processes, data is required on asphaltene precipitation from heavy oils or bitumens diluted with n-alkanes. In this work, the onset and amount of asphaltene precipitation from Athabasca bitumen were investigated in a PVT cell using three different methods over a range of temperatures and pressures. Results are presented for the precipitation of asphaltenes from the bitumen diluted with nalkanes, including n-heptane, n-pentane, n-butane, and propane. Experimental Chemicals and Materials Two batches of Athabasca coker feed bitumen were obtained from Syncrude Canada Ltd. This oil sand bitumen had been processed to remove water and solids, such as sand and clays, and was ready for upgrading. Table 1 shows the SARA analysis of the two samples. n-Heptane and npentane were obtained from Aldrich Chemical Company and were 99%+ pure. n-butane and propane were obtained from Praxair and were 99.5% pure. PVT Experiments A mercury-free PVT cell was used to study the effect of pressure and temperature on asphaltene precipitation for bitumen-alkane systems. The cell capacity is approximately 100 cm3 and a typical sample size was 35 cm3. The precipitation experiments in the PVT cell were performed using three different methods: the "premixing method", the "heating method", and the "bench-top method". Premixing Method The development and testing of the premixing method is described in detail elsewhere 1,2 and is outlined below. The bitumen was premixed with solvent at a low solvent-to bitumen ratio to reduce viscosity sufficiently to flow the bitumen. The premixed solvent-to-bitumen ratios were 0.51, 0.32, and 0.24 wt/wt for n-heptane, n-pentane, and n-butane, respectively. The bitumen and solvent were premixed in a sample cylinder, sonicated, and shaken for 2 hours for the nheptane- bitumen mixture and for 10 hours for the other bitumen-solvent mixtures. The final solvent-to-bitumen ratio was determined from the mass of solvent in the bitumen plus the mass of solvent initially charged into the cell. Note that a potential source of error is that the premixed bitumen/solvent mixture may not be homogeneous. If the mixture is not homogeneous, the solvent-to-bitumen ratio of the sample displaced into the PVT cell may not be the same as the ratio in the sample cylinder. Before charging the PVT cell, it was first evacuated using a vacuum pump for 10–15 minutes. The PVT cell was then filled with the required volume of solvent. The connecting lines were drained and evacuated once again and the required volume of premixed solvent and bitumen was added to the cell. The contents of the cell were mixed continuously with a magnetic stirrer for 23 hours. The sample was then displaced from the PVT cell to a modified sample bomb.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".