Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

Round 1

Reviewer 1 Report

The present manuscript fulfills the criteria and quality of the Hydrogen. However, the quality of Abstract, Introduction, Results and discussion, and Conclusion sections are need to revise. It could be taken into consideration for publishing in the Hydrogen after those revisions are made in an appropriate way. The detailed comments are listed below.

1. The Hydrogen is paying more and more attention to the quality of articles, especially originality and innovation. The innovation of the work is indistinct. The authors should state the innovation of the article more clearly and fully in manuscript.

2. A review article is more than just a literature review. It should be a bird's eye view to the vast literature existing on the subject so that the main ideas can be summarized. Unfortunately, this article seems no comprehensive knowledge of the topic. Thus, I strongly recommend the authors to carefully revise this manuscript.

3. The quality of Abstract, Introduction, and Conclusion sections are not good. I strongly recommend the authors to carefully revise these sections.

4. This review can be improved for development and recent achievements in plastic and tyres waste pyrolysis, and highlights the major issues, solutions and prospects.

5.  More classic and related references should be mentioned.

6. Finally, there are some grammar mistakes and confusing sentences in the manuscript. The authors need to be corrected. Thorough editing by at least one person with extensive experience in this area is required.

Author Response

Hydrogen
Manuscript ID: hydrogen-1656241
Title:  Plastic and waste tyres pyrolysis focused on hydrogen production- a review
The manuscript was revised carefully and improved so much according to reviewers' suggestions. The scientific insights are expressed well in the revised submission.

1. Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
(x) Moderate English changes required
( ) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

Comments and Suggestions for Authors

The present manuscript fulfills the criteria and quality of the Hydrogen. However, the quality of Abstract, Introduction, Results and discussion, and Conclusion sections are need to revise. It could be taken into consideration for publishing in the Hydrogen after those revisions are made in an appropriate way. The detailed comments are listed below.

1. The Hydrogen is paying more and more attention to the quality of articles, especially originality and innovation. The innovation of the work is indistinct. The authors should state the innovation of the article more clearly and fully in manuscript.

Response: Thank You very much for pointing weakness. Innovations are more clearly highlighted in all sections of manuscript.

2. A review article is more than just a literature review. It should be a bird's eye view to the vast literature existing on the subject so that the main ideas can be summarized. Unfortunately, this article seems no comprehensive knowledge of the topic. Thus, I strongly recommend the authors to carefully revise this manuscript.

Response: Thank You very much for remark. The manuscript was extended according to request.

3. The quality of Abstract, Introduction, and Conclusion sections are not good. I strongly recommend the authors to carefully revise these sections.

Response: Thank You very much for advice. Abstract was corrected to ‘In the review were compared hydrogen production from waste by pyrolysis and bioprocesses. In contrast, pyrolysis feed was limited to plastic and tire wastes unlikely utilized by biological decomposition methods. Recent risks of pyrolysis as pollution emission during heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses like dark fermentation. Many pyrolysis reactors are adapted for plastic pyrolysis after waste tyres promising investigation experiences. Pyrolysis can transfer these wastes to other petroleum products for reuse or energy carrier, like hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method of smart polymers, including semi-conductive polymers.. Pyrolysis is less expensive than gasification and requires less energy demand with a lower emission of hazardous pollutants. Short-time utilization of these wastes without emission of metals to the environment can be solved using pyrolysis. Plastic wastes after pyrolysis produced even 20 times more hydrogen than dark fermentation from 1 kg of waste. Plastic and tyres waste pyrolysis development and recent achievements were summarized in the research.’

Introduction added part was ‘Microbial electrochemical cells are suitable for utilization of ammonia due to their low voltage potential of just 0.06 V but not from water 1.17 higher about 0.93 V above MEC maximal voltage [37]. The conversion of feed is high and 32 m³ /m³ MEC d^-1 [38,39]. Biological decompositions cannot utilize plastic wastes and thus cannot solve serious plastic and waste tire problems. Problems of pyrolysis are finding a proper catalyst optimally from waste, while biological methods have unique enzymes that already exist in organisms. Catalysts can work on wide ranges of temperature while enzymes in narrow ones (usually below 55℃), limiting operational potential and causing unable to degrade polymers of high activation energy (usually obtained by high temperatures). The pyrolysis reactions are decompositions, fast, allowing desired conversion but highly consuming energy [40] in comparison to biological reactions requiring enzymes working on special conditions: need special substrates of concentration range contrary to pyrolysis, sometimes light (in the case of photofermentation) or special sequential preparation of bacterial seed) [41]. Pyrolysis has higher conversion requiring usual changes of catalytical layer (more than enzymes in biological cases), fulfilling the high demand of energy and high strength material to construct reactors more expensive than bioprocesses but requiring less space for obtaining a similar production rate [42]. The pandemic demand for the rapid solution of removal of safety protection wastes caused an increase in interest in the pyrolysis of plastic wastes [43–45]’.

Pyrolysis can utilize every type of waste with the production of hydrogen contrary to some other types of utilization

Conclusion

This review illustrated situations when pyrolysis has more advantages than bioprocess and reverse cases. In the case of artificial material waste like plastic or waste tires, the biological processes are hopeless while pyrolysis can be a helpful method of overcoming the problem of those wastes.. Plastics and tyres can be utilized by pyrolysis rapidly with transfers of other desired products or energy carriers. The pyrolysis process reduces every kind of organic waste, producing a broader variety of products than fermentation but is more energy-demanding. Pyrolysis requires separations of metals in plastics and tyres to avoid the emission of toxic compounds and expensive catalysts. The development of pyrolysis needs to overcome the production of products or energy with equipment size, conditions, high energy demands, and economic aspects. Pyrolysis of plastics permits a reduction of conventional material uses for the production of polymers, especially smart or conductive, and organic nanomaterials are approached more commonly in building a new sustainable living model suitable for a comfortable life of 7 billion people in the world without environmental damage. Hydrogen production by pyrolysis of plastic is even 64% more efficient than from tyres. Pyrolysis is more feasible in controlling and modeling than bioprocesses. Plastic waste pyrolysis obtained even 20 times more hydrogen from 1 kg of waste than dark fermentation. Waste tires pyrolysis methods can obtain even 14 times more hydrogen than the biological approach. Both wastes pyrolysis are an efficient and fast method of hydrogen production in comparison to other biological methods. The hydrogen production by pyrolysis require much less space than production using bioproccesses.

4. This review can be improved for development and recent achievements in plastic and tyres waste pyrolysis, and highlights the major issues, solutions and prospects.

Response: Thank you very much for inquiry. The manuscript was extended and even was added new section :’ Hydrogen is considered the fuel of the future and pyrolysis of plastic and tires is a method of increasing this demand. The demand growth is bound with implementing more feasible storage solution as hydride including ammonia allow development of conversion of wastes. According to Rasul et al [150] most promising is ammonia’s easy-storable, feasible accumulation of hydrogen produced from pyrolysis and bioprocesses. Pyrolysis of plastic wastes and tires produces ashes that can be a source of materials for nanotechnology with widespread application. The process allows the production of materials for photovoltaics, conjugated polymers (lowering their high price) that are more efficient in light absorption than silicon materials[151,152]. Pyrolysis requires little space and can be more mobile than bioprocesses. Therefore feasible pyrolysis mobile reactors could be applied to utilize local plastic wastes in dispersed environments, for example, pathways in national parks to transform hazardous wastes[107,153]. The method would be applicable if membrane technology allows for ‘catching’ poisonous or hazardous gases and separating them into fine gases. Pyrolysis developed faster in recent times due to the decrease of construction prices even six times in 25 years [110,154]. According to Fivga[155], the promising biofuel potential of plastic and waste tires pyrolysis are feasible for the production of aviation fuels.

Smart proportions of pyrolysis reactors would make them suitable for use on ships or other vehicles. These compatible designs would allow for the profitable elimination of plastic islands on oceans [156] and seas that requires immediate utilization to avoid rapid contamination of seas with plastic and reduce heavy metals pollution of the environment’.

5. More classic and related references should be mentioned.

Thank You very much for your remark and wide explanation. More references were mentioned.

6. Finally, there are some grammar mistakes and confusing sentences in the manuscript. The authors need to be corrected. Thorough editing by at least one person with extensive experience in this area is required.

Thank You very much for correction. The grammar is corrected.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript "  Plastic and waste tyres pyrolysis focused on hydrogen produc-2 tion- a review" the authors state that waste tyres and plastics are a growing problem for landfills and the environment. Short-12 time utilization of these wastes without emission of metals to the environment can be solved using 13 pyrolysis. Many pyrolysis reactors are adapted for plastic pyrolysis after waste tyres promising in-14 vestigation experiences. Pyrolysis can transfer these wastes to other petroleum products for reuse 15 or energy carrier, like hydrogen. Plastic and tyres pyrolysis is an alternative method to produce 16 smart polymers, including semi-conductive polymers. These polymers are necessary for renewable 17 energy developments like photovoltaics. Recent risks and dangers of pyrolysis like pollution emis-18 sion during heat decomposition of polymers, high cost, and energy demands are described. The 19 process can reduce plastic and tyres wastes which are unutilized by bioprocessing like fermentation. 20 Pyrolysis is less expensive than gasification and requires less energy demand with a lower emission 21 of hazardous pollutants. Plastic and tyres waste pyrolysis development and recent achievements 22 are compared and summarized. The review is well written except some typo it should be corrected therefore, I recommended its publication after the corrections.

Author Response

1. The manuscript "  Plastic and waste tyres pyrolysis focused on hydrogen produc-2 tion- a review" the authors state that waste tyres and plastics are a growing problem for landfills and the environment. Short-12 time utilization of these wastes without emission of metals to the environment can be solved using 13 pyrolysis. Many pyrolysis reactors are adapted for plastic pyrolysis after waste tyres promising in-14 investigation experiences. Pyrolysis can transfer these wastes to other petroleum products for reuse 15 or energy carrier, like hydrogen. Plastic and tyres pyrolysis is an alternative method to produce 16 smart polymers, including semi-conductive polymers. These polymers are necessary for renewable 17 energy developments like photovoltaics. Recent risks and dangers of pyrolysis like pollution emis-18 sion during heat decomposition of polymers, high cost, and energy demands are described. The 19 process can reduce plastic and tyres wastes which are unutilized by bioprocessing like fermentation. 20 Pyrolysis is less expensive than gasification and requires less energy demand with a lower emission 21 of hazardous pollutants. Plastic and tyres waste pyrolysis development and recent achievements 22 are compared and summarized. The review is well written except some typo it should be corrected therefore, I recommended its publication after the corrections.

Response:  Thank you very much for the improvements. The manuscript was corrected according to the remarks.

Author Response File: Author Response.pdf

Reviewer 3 Report

This review article deals with hydrogen production from plastic-based wastes.

The discussed topic is unquestionable of potential interest to the Readers of this Journal.

However, several concerns arise once the methodological section, as well as the discussion, are considered.

In particular:

1.      The boundaries of the analysis and the main focus of the presented review should be specified and discussed

2.      The procedure implemented to select the articles to be analysed seems unclear and inadequate. Possibly, the list of keywords used at this stage may be considered as a starting point for the description of the methodology

3.      Provided information should be rationalized and connected each other to identify the main findings and prioritize the gap in knowledge

4.      The inclusion of figures to discuss the quantitative data (e.g. initial composition, production level, operative conditions) should be preferred to help the visualization process

5.      Speaking of alternative processes, schematization of a generic process plant is strongly encouraged to discuss the differences in terms of units and concepts among them.

6.      The differences between biological and chemical processes should be deeply discussed in terms of phenomenological and practical perspectives

7.      The discussion related to the decomposition pathway should be supported by an extensive review of the kinetics characterizing the chemical phenomena.

8.      Conclusions should be supported by quantitative data and observations discussed in previous sections and briefly reported in the conclusion section.

9.      The inclusion of an additional section for future developments is suggested

10.  Extensive editing of English is recommended to improve the clarity and the readability of the manuscript

Author Response

1. Open Review
2. ( ) I would not like to sign my review report
   (x) I would like to sign my review report
3. English language and style
4. (x) Extensive editing of English language and style required
   ( ) Moderate English changes required
   ( ) English language and style are fine/minor spell check required
   ( ) I don't feel qualified to judge about the English language and style

5. Comments and Suggestions for Authors
6. This review article deals with hydrogen production from plastic-based wastes.

The discussed topic is unquestionable of potential interest to the Readers of this Journal. However, several concerns arise once the methodological section, as well as the discussion, are considered

7. In particular:
8. The boundaries of the analysis and the main focus of the presented review should be specified and discussed

Response: All sections were extended to highlight boundaries of the analysis

9. The procedure implemented to select the articles to be analysed seems unclear and inadequate. Possibly, the list of keywords used at this stage may be considered as a starting point for the description of the methodology

Response: Thank You very much for remark. Methodology was corrected as follows:

’The analysis selected paper due to results, an actual scientific interest of the chosen paper, and new insights presented in the research. The articles were searched by following questions in Scopus and Google Scholar: plastic waste pyrolysis, waste tires pyrolysis, hydrogen production from plastic wastes, hydrogen production from waste tires, contaminants from pyrolysis of plastic, contaminants from pyrolysis of waste tires, and assesment of hydrogen production from pyrolysis. The review is made by selection paper with data from years 1950-2022 on Scopus 5844 focusing on years 2020-2022. During this period papers included on plastic wastes pyrolysis (487 in 2020 and 477 in 2021) and 1117 papers on waste tyre pyrolysis (99 in 2020 and 123 in 2021), reviewed from September 2020 to October 2022. Both plastic and waste tyre pyrolysis was the topic of 144 papers, including 14 in 2020 and 20 in 2021. This record scientific interest in waste tyre pyrolysis is progressing into a wider interest in co-pyrolysis of plastic waste and tyres pyrolysis [57]. The increase of plastic pyrolysis is caused by a sudden increase of plastic wastes connected with COVID-19 pandemic time like masks [58]. The review is enriched with some papers on life cycle, renewable source energy, circular economy, and environmental production. Those papers provide a general view of problems and challenges that can be solved by the development of plastic and tyres pyrolysis, sample preparation, and measuring. Additionally for comparison of hydrogen production between dark fermentation and pyrolysis on chosen examples was made economic and technological comparison.

’

‘]

• Provided information should be rationalized and connected each other to identify the main findings and prioritize the gap in knowledge

Response: Thank You very much for hints. Findings of the manuscript were more highlighted and extended.

• The inclusion of figures to discuss the quantitative data (e.g. initial composition, production level, operative conditions) should be preferred to help the visualization process
• Speaking of alternative processes, schematization of a generic process plant is strongly encouraged to discuss the differences in terms of units and concepts among them.

Response: Thank You very much for correction. The Figure 1 was added was fulfilling the request.

• The differences between biological and chemical processes should be deeply discussed in terms of phenomenological and practical perspectives

Thank You very much differences were extended in sections describing introduction reactors, process conditions and conclusions

• The discussion related to the decomposition pathway should be supported by an extensive review of the kinetics characterizing the chemical phenomena.
• Thank You very much for pointing weakness. The discussion added :’ The decomposition of plastic and waste tires is simpler to control than bioprocesses. In dark fermentation, the control of process and continuity is hard due to difficulties in modelling [137] that are solved in the case of pyrolysis [138]. Pyrolysis kinetics is based on the Arrhenius equation changing depending on the material, and temperature both in plastics[127] and tires [139]. In the case of bioprocesses equations, Gompertz and logistics are special modifications of the Arrhenius equation[140]. In the biological process because of biological hydrogen production phenomena that single bacteria produce, usually as a metabolism byproduct generated periodically while continuous production can be assumed only in a numerous enough bacteria group; modeling algorithms are still in the test stage [141]. Thus phenomena can be interpreted as trigonometric dependences [142,143] or exponential [144,145]. Pyrolysis processes developed special programs and algorithms like special Aspen code suitable for predicting according to the heating values of plastic most efficient processes[123]. Waste tyres pyrolysis simulations are more factors responding to heterogeneous components mixture similar to pyrolysis of a mixture of plastics [146].

The pyrolysis of plastic or tyre is a method (see Figure 2) to return a petrochemical product as chemical raw materials, fuels, or polymer chain monomers. After pyrolysis, these wastes can regain usefulness for a human. The process design requires choosing a pyrolysis method focused on obtaining selected products. For example, when there is a design of nanomaterials production demand, ultrasonic pyrolysis should be selected[147,148], while in the case of BTX production catalytical pyrolysis [149].

8. Conclusions should be supported by quantitative data and observations discussed in previous sections and briefly reported in the conclusion section.

Response: Thank you very much for correction.  Qualitative data was added to Conclusions

• This review illustrated situations when pyrolysis has more advantages than bioprocess and reverse cases. In the case of artificial material waste like plastic or waste tires, the biological processes are hopeless while pyrolysis can be a helpful method of overcoming the problem of those wastes.. Plastics and tyres can be utilized by pyrolysis rapidly with transfers of other desired products or energy carriers. The pyrolysis process reduces every kind of organic waste, producing a broader variety of products than fermentation but is more energy-demanding. Pyrolysis requires separations of metals in plastics and tyres to avoid the emission of toxic compounds and expensive catalysts. The development of pyrolysis needs to overcome the production of products or energy with equipment size, conditions, high energy demands, and economic aspects. Pyrolysis of plastics permits a reduction of conventional material uses for the production of polymers, especially smart or conductive, and organic nanomaterials are approached more commonly in building a new sustainable living model suitable for a comfortable life of 7 billion people in the world without environmental damage. Hydrogen production by pyrolysis of plastic is even 64% more efficient than from tyres. Pyrolysis is more feasible in controlling and modeling than bioprocesses. Plastic waste pyrolysis obtained even 20 times more hydrogen from 1 kg of waste than dark fermentation. Waste tires pyrolysis methods can obtain even 14 times more hydrogen than the biological approach. Both wastes pyrolysis are an efficient and fast method of hydrogen production in comparison to other biological methods. The hydrogen production by pyrolysis require much less space than production using bioprocesses.

9. The inclusion of an additional section for future developments is suggested

Response: Future of pyrolysis processes ‘Hydrogen is considered the fuel of the future and pyrolysis of plastic and tires is a method of increasing this demand. The demand growth is bound with implementing more feasible storage solution as hydride including ammonia allow development of conversion of wastes. According to Rasul et al [150] most promising is ammonia’s easy-storable, feasible accumulation of hydrogen produced from pyrolysis and bioprocesses. Pyrolysis of plastic wastes and tires produces ashes that can be a source of materials for nanotechnology with widespread application. The process allows the production of materials for photovoltaics, conjugated polymers (lowering their high price) that are more efficient in light absorption than silicon materials[151,152]. Pyrolysis requires little space and can be more mobile than bioprocesses. Therefore feasible pyrolysis mobile reactors could be applied to utilize local plastic wastes in dispersed environments, for example, pathways in national parks to transform hazardous wastes[107,153]. The method would be applicable if membrane technology allows for ‘catching’ poisonous or hazardous gases and separating them into fine gases. Pyrolysis developed faster in recent times due to the decrease of construction prices even six times in 25 years [110,154]. According to Fivga[155], the promising biofuel potential of plastic and waste tires pyrolysis are feasible for the production of aviation fuels. Smart proportions of pyrolysis reactors would make them suitable for use on ships or other vehicles. These compatible designs would allow for the profitable elimination of plastic islands on oceans [156] and seas that requires immediate utilization to avoid rapid contamination of seas with plastic and reduce heavy metals pollution of the environment.’

• Extensive editing of English is recommended to improve the clarity and the readability of the manuscript
• Thank You very much for correction. The grammar is corrected.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have revised this article based on the reviewer's suggestion. The manuscript can be accepted.

Author Response

Thank You very much for the remarks

Reviewer 3 Report

Authors have positively addressed issues previously raised

Author Response

The language is corrected.

Thank You very much for remarks