Thermoresponsive Starch Nanoparticles for the Extraction of Bitumen from Oil Sands

Round 1

Reviewer 1 Report

The manuscript "Thermoresponsive Starch Nanoparticles for the Extraction of Bitumen from Oil Sands" is interesting from the approach to explore the effect of certain polymeric structures on the bitumen extraction form sand. Nevertheless, some key points need to be reviewed as follows:

a) The Table 3 shows the extraction efficiency and it is clear the influence of  DS and presence of polymeric entity on it. However, it is also clear that toluene has a big influence and the extraction efficiency with polymer (78%) is not the real one because it is the obtained in presence of toluene, which must be subtracted.  

b) Table 3. It is also important consider an experiment without toluene, just in presence of salt and/or polymer.

c) Figure 10, please explain why lower content of SNP-g-PMEO₂MA gives higher extraction efficiency.

d) In the case of the recycling experiments, were they carried out in a closed system and/or how the toluene evaporation is considered?

e) The conclusions must be shorter and conclusive not descriptive as actually they are written.

Author Response

The manuscript "Thermoresponsive Starch Nanoparticles for the Extraction of Bitumen from Oil Sands" is interesting from the approach to explore the effect of certain polymeric structures on the bitumen extraction form sand. Nevertheless, some key points need to be reviewed as follows:

1. a) The Table 3 shows the extraction efficiency and it is clear the influence of  DS and presence of polymeric entity on it. However, it is also clear that toluene has a big influence and the extraction efficiency with polymer (78%) is not the real one because it is the obtained in presence of toluene, which must be subtracted. 

Toluene clearly plays a significant role in extracting bitumen from the oil sands. This has been addressed in the manuscript. However, while all the oil extraction experiments presented in Table 3 were performed with the addition of toluene, that solvent was evaporated from the samples before weighing, so the toluene does not need to be subtracted from the results (in other words, the results in Table 3 are “real” or net bitumen extraction values). When comparing Trials #1, 4 and 5, it is clear that the higher extraction efficiencies achieved were not because of the toluene used in these experiments (60 mg) but rather because of the polymer additive.

3. b) Table 3. It is also important consider an experiment without toluene, just in presence of salt and/or polymer.

This has been tested by us and by Yang et al., and a co-solvent such as toluene was found to be essential to extract significant amounts of bitumen from tar sands. It was indeed found that even in the presence of the modified SNP additive and NaCl, lowering the amount of toluene used led to a steady decrease in extraction efficiency. One example of this has been added in the Discussion (page 17, line 608), for which the extraction efficiency dropped to 12% when only 25 mg of toluene was used. The addition of toluene appears important to decrease the viscosity of the bitumen phase, and to promote interactions between the hydrophobic PMEO₂MA chains and the bitumen above the LCAT.

1. c) Figure 10, please explain why lower content of SNP-g-PMEO₂MA gives higher extraction efficiency.

We assume that the Reviewer is referring to the PMEO₂MA content of the modified SNPs, since the additive concentration used in all the experiments was the same in Figure 10 (15 mg additive). In that respect, the caption may have been confusing since it was stated that 15 mg (as opposed to 15 mL) of water was used in the experiments; that mistake has been corrected. The main purpose of Figure 10 is to demonstrate that both the PMEO₂MA content and the structure (branching functionality) of the additives influence the extraction efficiency. It seems reasonable that a suitable hydrophilic-lipophilic balance (HLB) would be essential for the efficient extraction of bitumen from oil sands. Beyond temperature, the HLB of the additives is obviously controlled by factors such as the weight fraction of PMEO₂MA, but also by the degree of substitution (DS) of the SNP substrates. The effect of the latter parameter should be more subtle, in that a higher DS substrate produces a larger number of shorter PMEO₂MA chains, making the structure of the modified SNPs more rigid, and decreasing the ability of the hydrophilic SNP core to interact with the aqueous phase. On the other hand, if the additives are “too” hydrophilic, they would have weaker interactions with the bitumen droplets, again limiting their extraction efficiency. By considering these opposing effects, it can be rationalized that SNP-g-PMEO₂MA (15 wt%, DS 0.022) performed best at bitumen extraction. This is the essence of the discussion in Section 3.8.2 concerning the influence of composition and structure of the additives.

1. d) In the case of the recycling experiments, were they carried out in a closed system and/or how the toluene evaporation is considered?

After the extraction and removal of the toluene-bitumen mixture on top of the aqueous phase, toluene was again used to remove the bitumen and water-bitumen emulsion adhered to the wall of the vial. The toluene on the surface of the aqueous phase was then carefully removed with a pipette. Residual toluene on the surface of the recycled aqueous phase was evaporated with a stream of nitrogen in a fume hood, to remove any residual toluene potentially present at the surface of the aqueous phase. This ensured that no additional toluene was introduced in the next extraction cycle, as now pointed out on page 7, line 289 of the revised manuscript.

1. e) The conclusions must be shorter and conclusive not descriptive as actually they are written.

We thank the Reviewer for the comment. The Conclusions section has been rewritten to make it more concise and conclusive.

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

The manuscript described the preparation of novel starch nanoparticles functionalized with thermos-responsive polymers. The resulted SNPs showed controlled UCST and several affecting factors were investigated. These SNPs showed a high extraction efficiency of bitumen from oil sands and can be reused for multiple times. However, the oil extraction process, especially the droplet demulsification based on SNP’s thermos-responsiveness, needs to be better illustrated.

Major:

1. What is the role of temperature-responsiveness in oil extraction?

From my understanding, SNPs will stabilize toluene and form droplets at temperatures higher than UCST, solubilizing bitumen and bring to the top of solution. The following cooling step will destabilize the droplets and accumulate the bitumen. However, the cooling step is not fully described in the manuscript. In addition, the extraction efficiency was calculated from bitumen from both top layer and the emulsion layer in the middle. Thus, I’m wondering if destabilization of emulsion droplets is working well. This is important because oil-in-water emulsion is difficult to separate. Maybe the oil extraction efficiencies from top and middle layer can be calculated separately and compared.

Since the unmodified SNPs are not thermoresponsive, we assume that the Reviewer is referring to the modified SNPs. The SNPs are made thermoresponsive by grafting PMEO₂MA chains onto them, as the PMEO₂MA chains become hydrophobic above a certain temperature and an LCAT is observed. Thus, a SNP-g-PMEO₂MA system above its LCAT should solubilize the toluene-swollen bitumen droplets and extract them from the oil sands. Upon removal from the 45 °C oven and relatively fast cooling to room temperature (below the LCAT), as stated in the Experimental Section (line 278), the bitumen droplets are destabilized and result in the formation of an oily (bitumen + toluene) layer on top of the aqueous phase containing the SNP-g-PMEO₂MA additive. We believe that the addition of 0.5 M NaCl results in further destabilization of the emulsion, as discussed on pages 17 and 18 of the manuscript. Furthermore, we accounted for the bitumen present in the middle layer (Section 2.8, line 281) and determined that on average, less than 2% of the total bitumen content was found in the middle layer.

Minor:

1. For the introduction of oil extraction or bitumen extraction methods, the manuscript includes conventional CHWE and SAGD. However, only one recent research (Ref 12) was described. It’s better to introduce more current research such as oil extraction by micelles, absorbers or membrane filtration.

We thank the reviewer for the feedback. While the CHWE and SAGD techniques are by far dominant in the oil sands industry, we also included recent papers and reviews on other research such as using micellar extraction, ionic liquids, organic solvents, absorbants and modified flotation techniques (references #12-14 added, lines 88-91) in the Introduction of the revised manuscript. The following paragraph (starting at line 92) was also expanded to include additional examples of stimulus-responsive micellar extraction systems, as these are most directly related to the thermoresponsive SNP systems being investigated.

2. For the bitumen extraction, the bitumen amount before extraction was measured using Soxhlet extraction, and the amount after extraction was also measured. I’m wondering if the mass balance of bitumen could be demonstrated.

We thank the reviewer for the suggestion. We did consider the oil extraction efficiency in terms of oil extracted/total oil content determined by Soxhlet extraction. This method would work well if the oil sand samples were cleaner. Unfortunately, the oil sands sample we received contained significant amounts of debris and small stones, which would have led to inconsistent results when calculating the overall mass balance.

3. Some details such as the calculation process of monomer conversion and polymer composition can be moved to the experimental section.

We thank the Reviewer for the suggestion. Because these calculations were made using the ¹H NMR spectra discussed in the Experimental section, we would like to keep these details in the Results and Discussion section.

Round 2

Reviewer 1 Report

Thank you for considering the reviewer's comments. 

Reviewer 2 Report

The questions are well addressed and the manuscript are significantly improved.