Microwave-Assisted PUF Aminolysis: Experimental Validation, Scaling Process Assessment and LCA Evaluation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The manuscript compares polyurethane foam (wastes) microwave-assisted aminolysis from small to large scales. The small scale (1L reactor) is investigated experimentally at 225°C -with tris(2-aminoethyl)amine-, while the large scale is modelized.  

The paper deals more with processes, process and chemical engineering rather than chemistry and foams. Although not a specialist of processes, I wonder if the technique applies to PU virgin foams or PU’s in general. Can you say something about aminolysis of neat (dense) PU in the same conditions, or even PU foams (not recycled) ?

 how pure is the PU waste (if known)? does it contain several PU’s ? Provide elements about the PUF : composition, origin, blend or not, crushed or not, etc.

The choice of figures is logical. But the number and occurence of each figure is not correct, because the figures in experimental section and those in results’ section have the same numbers ?

The main result is to show that the products obtained after 30min yield around 40% of polyols used to make the initial PUF. Thus, it is a recovery of a part of the initial monomers, which is good.

Questions arise for a large scale : « will the yield be the same ?; is the temperature of 225°C attainable at a larger scale ? (energy need); is microwave a large scale solution ? . One thing is not clear for me about temperature, is 225°C the material temperature of PUF under microwave or the set temperature of reactor ? Precise.

tris(2-aminoethyl)amine, i.e. TREN, is a quite toxic compound, not very compatible with a green process ?

authors say For instance, it was proven that the recycled polyol resulting from aminolysis is fully hydroxyl functionalized analogue of the corresponding virgin polyol [14], whereas acidolysis-derived recycled polyols show different end-group functionalities, e.g. hydroxyl, aromatic amine originating from incomplete urethane group degradation and carboxyl as a consequence of esterification side reaction between carboxyl groups of adipic acid and hydroxyl groups of the polyol [11,15]. Depending on the end use of such polyols, these functionalities may play a critical role. In case the recycled polyols aim to be employed as raw materials for the production of PU foam (PUF), it was found that these carboxyl functional groups may influence the relative kinetic of cross-linking and foaming reactions, potentially resulting in closed-cell morphology and deteriorated properties of PUFs synthesized from acidolysis-derived recycled polyol [15]. Does it apply to your PUF ? in such a case, the composition of PU is known, do you have information about the chemical composition of PUF ?

what is the chemical argument to say that the recycled polyols out of MW-aminolysis are undistinguishable 16 from virgin polyols ?

in figure 5 title, maybe precise what is TDA, EA,

overall comment : major revisons, manuscript can be improved, but it is worth submitting

Author Response

Please, see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The reviewed work is devoted to the development of a technological process for the depolymerization of polyurethane after its use. The authors are absolutely fair in speaking about the huge volume of PU formed after the use of various products made from it. Therefore, the problem of recycling used PU is urgent and important from various positions. The authors propose a scheme of the technological process and the results of its laboratory testing. The scientific basis of the study does not raise objections. This part of the work is performed at a sufficiently high level using modern methods of analysis.

Further, the authors propose calculations and a layout for scaling up the laboratory scheme, which is important for further implementation of the obtained scientific results.According to all technological parameters, this is a fully qualified and promising study.

At the same time, the economic side of the problem raises certain questions. The main ones are formulated in the following comments

Comments.

1. Why did you choose PEEK for the chamber?Are you sure that microwave radiation will not affect PEEK and thus the process inside the chamber?
2. I believe that Fig. 2 is quite obvious and does not further clarify the essence of the work.Therefore, I propose to exclude it.
3. Arguments discussed in lines 67-70are serious enough to exclude this variant of PU destruction.Why do the authors further consider it as a possible possibility of the process?  Isn't price the deciding factor?
4. It would be important to provide a quantitative comparison of cost of the different methods of PU depolymerization taking into account the post-processing steps.
5. Table 1. The accuracy of the values ​​given in the second line is somewhat exaggerated and is not needed for engineering calculations, for which an accuracy of 1% is quite satisfactory.
6. What are the requirements for the quality (purification) of water used in the technological cycle?
7. If we consider the prospects for industrial application of the PU depolymerization process under discussion and take into account the extremely large volumes of the product used, it would be appropriate to discuss the transition from a periodic to a continuous process. It would be desirable to reflect in the article what the authors think about this.
8. What is the quality (purity) of the final products and can they be directly involved in the technological process without further purification?
9. Table 5. Data in the table are given with high accuracy.In reality there will certainly be deviations from the given values.Could the authors estimate possible errors in the given figures?
10. The authors provide calculations for a setup that is 300 times larger than the laboratory prototype.This is a very bold simulation.Does such a larger setup actually exist and what is the correspondence between the calculated and actual experimental results?

Author Response

Please, see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

accept

Reviewer 2 Report

Comments and Suggestions for Authors

I accept the authors' answers to my comments and believe that they are satisfactory