Catalytic Pyrolysis of Tetra Pak over Acidic Catalysts

Round 1

Reviewer 1 Report

Catalytic upgrading of Tetra Pak (TP) waste into base chemicals such as aromatics is a very interesting topic, as it aims not only to use alternative raw materials instead of oil, but also to the recovery of this waste by its conversion into valuable products. Moreover, due to the composition of TP this task is highly challenging. Thus, the work is in the scope of the journal and of interest to its readers. The study is well approached and clearly exposed, and the authors have experience in catalytic upgrading of low value products. However, the catalytic results presented in this work are discussed in a very qualitative way, and should be treated more thoroughly. Although different activity and selectivity is observed for the thermal experiments as compared to the catalytic pyrolysis, and also for the different catalysts employed, no conversion levels nor yields are presented. According to the GCMS spectra presented, and as could be expected, CO2 is one of the products formed. Which is the selectivity to CO2? And the selectivity to hydrocarbons? Within the hydrocarbon fraction, which is the selectivity to the desired aromatics? This part should be thoroughly revised, in my opinion, before the manuscript can be accepted for publication.

Additional comments and suggestions are listed below:

1. The introduction is complete and well written, with the state of the art nicely revised. However, there is a sentence in page 2, lines 72 to 76, that should be revised and rewritten, trying to avoid the repetition of several concepts.
2. The authors should briefly define the Proximate Analysis performed on the two TP samples, this would be useful for readers of different expertises. Moreover, the procedure for performing the proximate analysis should be described in section 3. Finally, in Table 1, the proximate analysis sums 101 % for TP1.
3. Regarding the TG analysis, the authors compare their TG results with those described in the literature in order to assign the different weight losses. However, they have also performed some TG analysis on mixtures of the SPE and SKP obtained by solvent separation. This could be mentioned here and reference could be made to Figure S1 besides comparing with previous publications.
4. Catalyst description and properties (Si/Al ratio, textural properties and acidity) are critical for determining their catalytic behavior. They should be presented in the results and discussion section, and not in materials and methods, as it may help both, authors and readers, to understand the catalytic results.
5. Catalytic results should be presented giving values of conversion, yields and selectivity. The amount of CO2 formed, thermally and with the different catalyst, is very important.
6. The acid catalyst used for this study are zeolites ZSM-5 (10x10x10 medium pore channel system with pore dimensions around 5.0-5.5 Å), Beta (12x12x12 large pore channel system pore dimensions around 6.5-7 Å) and MCM-41, with larger pores (2.8 nm). Due to the long chain dimensions of PE, I would not expect much of the catalytic pyrolysis to take place inside of the zeolites pores, but more probably at the external surface area (see, for instance, Cardona et al., Appl. Catal. B: Env. 2000, 25, 151-162), although probably the primary –smaller- products may further react inside of the crystalline zeolite structure. Thus, it would be interesting to include information regarding external surface area of the catalysts and/or crystal size, as crystal size can play an important role in reactions involving bulky products or reactants (see, for instance, Díaz-Rey et al., ACS Catal. 2017, 7, 6170−6178, or Gallego et al., Chem. Sci., 2017, 8, 8138). Please take this into consideration when discussing the catalytic results.
7. Diffusional problems may be and important issue in zeolites. Also deactivation of the zeolite, PE will have no problems in entering the pores of MCM-41. In fact, previous papers show better performance of MCM-41 as compared to zeolites (see for instance Van Grieken et al. J. Anal. Appl. Pyrolysis 58–59 (2001) 127–142)

Author Response

We highly appreciate your dedicated review of our manuscript. Owing to your review, the quality of our manuscript was dramatically increased compared to the first submission. Although we could not reply completely, we tried to our best to meet the requirements. Please consider the acceptance of our revised manuscript.

- Please refer to the enclosed word file!

Thank you for your support!

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript from Prof. Kim and co-workers reported employing acid catalyst pyrolysis of Tetra Pak. I should note that this manuscript is clearly  written. However, some of the studies such as in TG and TMR-GC/MS were using a small amount of samples (1-2 mg) and readers will have doubt about the reproducibility of the results. Since the error can come from the sampling of the TP1 and TP2 (as they are mixture component and not homogenerous). Finally, I recommend acceptance of the manuscript after major revision based on the following comments:

1. Duplicate /triplicate of some experimental results (with the error bars) to support the samplings of TP1 and TP2 are the representative samples.
2. Line 54: not agree to use ‘important’ type.
3. Line 56: healthcare industry also consume many plastics.
4. Line 82: miss use of ‘such as’
5. Line 86: not clear what the relationship between ‘large amounts of solvent consumed‘ in an extraction process. Why the solvent consume? Solvent cannot be recycle?
6. Line 92: : ‘et al.’ should be in italic
7. Lines 114, 177: What made TP1 and TP2 fixed carbon contents different? Are they came from the same source? (Find the answer in line 305). However should comment this different in line 144.
8. Line125: what are BPW and KOS?
9. Line125: suggest to use ‘composition profile’ to replace ‘Physico-chemical properties’ (not observe any physical properties)
10. Lines 150 and 159: 1^st and 2^nd should use the same format for consistency.
11. Lines 330-331: not clear if 6 mg of catalysts for 2 mg of samples can be a catalytic reaction. In addition, the blank reaction with different catalyst alone should also needed to be included. As in (line 299) figure 6. The MS intensity of catalyst HZSM was decreased significantly after the 1^st pyrolysis and remain constant at 2^nd to 4^th  
12. Line:337: ‘in-situ’ should be in italic.
13. Line 360: suggest to calculate the ‘% of mass intensity decrease’ of both catalysts in order to support your argument of catalyst lifetime.

Author Response

We highly appreciate your dedicated review of our manuscript. Owing to your review, the quality of our manuscript was dramatically increased compared to the first submission. Although we could not reply completely, we tried to our best to meet the requirements. Please consider the acceptance of our revised manuscript.

- Please refer to the enclosed word file!

Thank you for your support!

 

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript is exemplary from the scientific point of view, maybe not from a practical point of view (in my opinion, the catalyst/sample mass ratios used for the different experiments are too high). It could be accepted for publication as is, if it were not for a few typos:

Line 125: I cannot understand the acronyms in table title

Line 288: actually, Figure 6 does not show results for TP-1 sample

Line 300: please check figure caption numbering

Author Response

We highly appreciate your dedicated review of our manuscript. Owing to your review, the quality of our manuscript was dramatically increased compared to the first submission. Although we could not reply completely, we tried to our best to meet the requirements. Please consider the acceptance of our revised manuscript.

- Please refer to the enclosed word file!

Thank you for your support!

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Although some of the suggestions of the Reviewer have been incorporated into the new version of the manuscript, the authors have not addressed the main weakness of the original version, the  analysis of the TMR-GC/MS results, which has not been improved. The thermal and catalytic pyrolysis is not quantified and discussed with the rigor and the thoroughness required for its publication in Catalysts. I am aware that quantification of complex mixtures such as those obtained in this work is a hard task. However, an effort should have been done in order to give an overall evaluation of the results, at least an overall product distribution taking into account CO2 and other –non-aromatic- compounds that may be formed during the catalytic tests. Carbon-based balances are very useful in cases such as this, when dealing with processes where oxygenated products and water are formed.

Regarding the characterization of the catalyst used in the work, the authors may no have access to crystal size information, but external surface area can be determined from N2 adsorption isotherms, for instance.

In my opinion, the modifications performed on the previous version of the manuscript are not sufficient, and the work is not suitable for publication.

 

Author Response

We highly appreciate your comments. Please refer to the enclosed file for the reply to the review comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript from Prof. Kim and co-workers reported employing acid catalyst pyrolysis of Tetra Pak. After author’s major revision, I recommend acceptance of the manuscript.

Author Response

We highly appreciate your dedicated review of our manuscript and final decision.