Industrial Scale Direct Liquefaction of E. globulus Biomass
, José Condeço 1, Duarte M. Cecílio 1,2, João Bordado 1 and Margarida Mateus 1,2,*Round 1
Reviewer 1 Report
1. Page 1, line 15: In industrial scale tests, 100 %was achieved, it is not clear on how 100% is achieved. is 100 % talking about bio-oil ? or what ? please explain in detail.
2. When the HTL was carried out at 160 C at atmospheric pressure, how the liquid was in liquid state as water evaporates at 100 C ? Please explain in detail for readers understanding. Many of the HTL wxperiments were carried out in between 270-350 C, please check.
3. Please mention the Temp, Pressure, and Reaction time in Table 1.
4. Please explain the patent briefly which is mentioned in line 145.
5. If you have done the fiber analysis (cellulose, hemicellulose, and lignin), please report them. They are very useful for the readers to understand the reaction mechanism with TGA data reported in lines 230 - 246.
6. please explain the Fig 1 in detail, i.e, write the names of the each reactor, process conditions, it not clear.
7. section 2.3; standard testing method names are not mentioned, please add them.
8. Data in Tables 1 and 2 are not matching for the same feedstocks, please check and revise.
9. Lines 230 - 245: How do authors know that only these compounds are degrading in this range ? pls add references to support this explanation.
10. For Fig 4: how did you measure the catalyst loading and solvent addition during the reaction?
11. Drawing a schematic would be very helpful on the biomass is degrading to various products (bio-oils, polyols, hydrochar, and aqueous phase).
12. As hydrothermal liquefaction was used in this process, it would be good to use the biocrude term rather than bio-oil. Bio-oil is derived via pyrolysis.
13. Table 6: please add the missing data in weight loss, moisture, LHV, and density. With time why CHNSO data is not following any trend?
14. Conclusions need to be more focused on the application part of the study with industrial relevance and connection between the lab scale studies and pilot scale studies with focus on comparison of the physicochemical properties the produced bio-oils.
None
Author Response
1.Page 1, line 15: In industrial scale tests, 100 %was achieved, it is not clear on how 100% is achieved. is 100 % talking about bio-oil ? or what ? please explain in detail.
Yes. According to eq. 1 on pg 16 the conversion is referred to the mass ratio of bio-oil to biomass.
The bio-oil is removed from the reactor through a bottom valve and is filtered through two different mesh filters, which are very effective. In the liquefaction reactions presented in the manuscript, no solid particles were observed in the filter, which indicates the complete liquefaction of the biomass. This result was also confirmed by weighing the liquefied biomass recovered from the reaction and comparing it to the mass of the raw materials initially introduced into the reactor.
- When the HTL was carried out at 160 ºC at atmospheric pressure, how the liquid was in liquid state as water evaporates at 100 ºC ? Please explain in detail for readers understanding. Many of the HTL experiments were carried out in between 270-350 C, please check.
As mentioned in the introduction (pg 2, line 82) “Liquefaction can be carried out in different conditions at high temperatures (>200 °C) and pressures, as in hydrothermal upgrading – HTU, or at moderated temperatures (100 – 250 °C) and atmospheric pressure in the presence of solvent and a catalyst, as in direct liquefaction studied in this work. “ . In fact, this work describes the use of a thermochemical process that is a combination of solvolysis and thermochemical liquefaction. Furthermore, as mentioned in the text, the azeotrope observed between 2-EH and water, with a boiling point of » 99 °C, whereas the boiling point of the solvent itself is approximately 183 °C.
- Please mention the Temp, Pressure, and Reaction time in Table 1.
The relevant information was added.
- Please explain the patent briefly which is mentioned in line 145.
More information was added and it now reads: “The procedure used in the pilot reactor is presented in EP3689847, which describes a catalytic and continuous thermochemical process of biomass liquefaction that allows to produce a bio-fuel and valuable products. In this process, the biomass is transported to the reactor though a screw-conveyor where, as mentioned above, the solvent or the mixture of solvents is injected to promote the swelling of the biomass cells. Simultaneously, the preheating of the mixture is carried out through the counter-current passage of the vapours removed from the reactor. The liquefaction was carried out at atmospheric pressure and 160 °C. The biomass incrementation was 10% mass per hour.”
- If you have done the fiber analysis (cellulose, hemicellulose, and lignin), please report them. They are very useful for the readers to understand the reaction mechanism with TGA data reported in lines 230 - 246.
In line 149 of the revised manuscript (243 of the first version) it is explained: “The TGA results allowed to establish the relative composition (dry basis) in the three biopolymers of the two biomass samples (Table 2). As shown, E. globulus sawdust presents a higher content of hemicellulose and a lower content of lignin, which indicates that it should be easily liquified. “ and the bio-polymers quantification is presented in Figure 2 and Table 2.
- please explain the Fig 1 in detail, i.e, write the names of the each reactor, process conditions, it not clear.
The requested information was added in the new version of the manuscript.
- section 2.3; standard testing method names are not mentioned, please add them.
This information is now given in the manuscript.
- Data in Tables 1 and 2 are not matching for the same feedstocks, please check and revise.
We apologize for the mistake. The correction was made.
- Lines 230 - 245: How do authors know that only these compounds are degrading in this range ? pls add references to support this explanation.
The main components of lignocellulosic biomass, such as Eucalyptus bark, are cellulose, hemicellulose, and lignin. These components have distinct thermal degradation profiles, which have been extensively studied and reported in the literature.
Moisture Evaporation: The initial weight loss observed between 25 ºC and 140 ºC is commonly attributed to the evaporation of moisture, which is consistent with numerous studies on the thermal degradation of biomass.
Hemicellulose Degradation: The weight loss between 140-300 ºC is attributed to the degradation of hemicellulose. Hemicellulose is known to degrade at lower temperatures compared to cellulose and lignin, typically in the range of 150-350 ºC.
Cellulose Degradation: The weight loss observed between 300 and 420 ºC corresponds to the degradation of cellulose. Cellulose typically degrades in the range of 315-400 ºC.
Lignin Degradation: Lignin has a broader degradation range, starting from around 160 ºC and extending beyond 900 ºC, with various peaks. The weight loss observed in the fourth plateau is consistent with the degradation of lignin.
The comparison with standards, as mentioned in the manuscript, further supports these attributions. The focus on these main components is essential for understanding the feedstock's behavior, especially when considering scaling up the reaction for pilot-scale operations.
- For Fig 4: how did you measure the catalyst loading and solvent addition during the reaction?
Thank you for pointing out the need for clarity regarding our procedure. To elucidate:
We added neither solvent nor catalyst throughout the reaction, but only the biomass. This information was given in the previous version of the manuscript but, having in mind this comment of the Reviewer, we have clarified this aspect with the text: “In the laboratory tests carried out using sequential biomass additions, the solvent and the catalyst were added initially to the reactor and heated while stirring. When the reaction temperature was reached, 10% wt of biomass vs. the solvent was added to the reactor. This biomass addition was repeated hourly until the limit condition, which corresponds to the formation of a very viscous mixture impossible to stir and filtrate.”
It is important to note that during this process, we consistently extracted samples at 1-hour intervals. These hourly samples were always analysed to ensure the accuracy and reliability of the results.
- Drawing a schematic would be very helpful on the biomass is degrading to various products (bio-oils, polyols, hydrochar, and aqueous phase).
We understand this comment. In the first version of the manuscript this schematic was partially given in Figure 1 of the pilot installation. The idea was to provide a comprehensive overview of the process, showing the degradation of the biomass into the bio-oil and polyols. Nevertheless, as suggested by the Reviewer in point 6, this figure was reviewed to ensure its clarity and a legend was also added.
- As hydrothermal liquefaction was used in this process, it would be good to use the biocrude term rather than bio-oil. Bio-oil is derived via pyrolysis
The process is actually a mixture of solvolysis and thermochemical liquefaction, and due to the presence of the organic solvent we feel that the term bio-oil is adequate.
- Table 6: please add the missing data in weight loss, moisture, LHV, and density. With time why CHNSO data is not following any trend?
Some of the samples were not analysed for all variables. This information is now given in Table 6 and 7.
Concerning the bio-oil composition trend, it is worth noting that these samples were industrial samples produced in a 3 ton reactor. Therefore, only major conclusions should be taken as, for example, the similar properties of the different bio-oils. Nevertheless, when the 24h and 120h samples are compared, it is possible to observe a slight increase in the C content and decrease in the O content, which result in an increase of the heating value.
- Conclusions need to be more focused on the application part of the study with industrial relevance and connection between the lab scale studies and pilot scale studies with focus on comparison of the physicochemical properties the produced bio-oils.
In fact, too many details were given in the previous version of the conclusions. Therefore, they were shortened and the values of several properties of the bio-oils are now presented for the lab and pilot bio-oils.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The work reported is good and authors are requested to do suggested changes.
Comments for author File: Comments.pdf
Should be proofread, minor mistakes are present.
Author Response
1.Abstract is too formal, please incorporate more information regarding the results and emphasize its relative importance.
The Abstract intends to present a general overview of the work. However, bearing in mind the reviewer comment, more results were included.
- Cite references for the methodology adopted or followed.
Two references were introduced.
- Line 190: HPLC-MS Methodology, please include solvent system and program details (such as flow rate, gradient system, if any).
This information was included.
- Authors are requested to use more recently published articles for references.
We do not understand this comment. 30% of the references are newer than 2019. The number increases to 38% if we include the year 2018.
- It would provide more insights if the authors could compare the obtained results with the similar and relevant literature.
The comparison with literature results was carried out whenever possible and appropriate. Thus, for example, the FTIR, TG and bio-oil ageing results were compared with literature references.
Minor Comments
All minor comments have been addressed.
Author Response File: 
Author Response.docx
