Non-Energy Valorization of Residual Biomasses via HTC: CO2 Capture onto Activated Hydrochars
, Luca Taglieri, Alessandro Antonio Papa, Francesco Di Lauro, Zaheer Ahmad and Alberto GallifuocoRound 1
Reviewer 1 Report
The authors have presented their work quite well. The work can be accepted as it is with few minor English corrections.
Author Response
The authors thank the reviewer for his/her very positive comment. As required by the reviewers the English changes have been implemented in the revised manuscript.
Reviewer 2 Report
In the present work, the authors report the preparation of different hydrochars prepared by hydrothermal synthesis and KOH chemical activation, using silver fir sawdust as carbon precursor. The samples are only characterized using N2 adsorption-desorption isotherms and SEM images. The materials are used for the separation of CO2 for the upgrading of biogas to bio-methane by pressure swing adsorption experiments. The results obtained are compared with the literature.
In general the materials characterization development is quite weak or non-existent and, in some cases, are not applicable properly. This part should be considerably improve. Here are some of the most important aspects of this paper.
Abstract
Line 9: Actually, only two retention time were study, 0 and 120 min.
Line 11: the chemical properties of the hydrochar are not characterized. Only the textural properties and SEM images are presented in the paper.
Line 12: the textural parameters were not compared in the manuscript with traditional sorbents.
Introduction
Line 77: from the liquid of valuable platform chemicals from the liquid.
Why the authors have selected Silver fir sawdust as carbon precursor? The need of using silver fir sawdust as biomass precursor should be highlighted.
Materials and methods
How was silver fir sawdust obtained? Was it submitted to any previous conditioning treatment?
Origin and purity of all gases and liquids should be given.
Amounts of reactants and solids and concentrations of solutions have to be given
The protocol of impregnation of the hydrochar precursor with the KOH has to be completed
Line 113: Please complete details of the protocol used to characterize the porous structure of the samples and provide the corresponding bibliography when it is necessary (BET method, t method BJH method, micropore and mesopore volumens calculations). Is the hydrochar outgassed before the N2 adsorption measurement? Is the BJH method applied to the adsorption or desorption branch of the N2 isotherm?, …
The N2 adsorption-desorption isotherms should be presented in the manuscript.
Line 109: Why the CHNS characterization is not included?
Line 127; grain sized from 106 m to 355 m?
Results and discussion
The carbon yields defined as the weight of the hydrochar prepared related to weight of carbon precursor initially used, in dry basis, should be provided for the three different materials prepared.
The BET surface area values should not have decimals. The BJH method is especially suited for assessment of mesopore size distributions. However, the authors do not show the mesopore size distributions. Standard values like the micropore volume and the mesopore volume should be determined and included in the textural characterization of the samples.
Could the authors clarify what is the significance of “Volume of the pores desorption”? Instead, micropore and mesopore volume values should be provided in order to compare with other materials.
Line 181: How is the average diameter calculated? Is this a standard procedure? It should be supported by the literature.
Line 184: Its quite confusing when the authors described the SEM images as “on the left or right-hand side”. Instead, Figure 2a, 2b,2c…should be expected.
CHNS results and thermogravimetric analysis should be provided to have a better knowledge of the physicochemical properties of the hydrochars prepared.
Was all the inorganic matter removed from the hydrochar prepared after the washing step?. Which is the amount of inorganic matter that remains on the hydrochar?. How can this fact influence the adsorption properties of the materials? Have you measured TGA analysis of the samples?
Line 209: The BET specific surface area and the pore diameter is being compared with a reference sample, which sample? This part should be rewritten based on the revised textural parameters.
Line 210: In fact, the quality of the paper would be higher including the optimal retention time.
Author Response
Thank you for this comment. Authors revised the manuscript extensively, improving the readability of work.
Anyway, because they are not native speakers, the editor could suggest a further language and style editing.
All details are reported in the attached file.
Author Response File: 
Author Response.docx
Reviewer 3 Report
Dear authors,
your paper intitled "Non-energy valorization of residual biomasses via HTC: CO2 capture onto activated hydrochars" is well-written and the method is clear. Good topic to investigate. I'm suggesting to spend some words for the industry application: what are your comments about this future implementation?
Minor revision to check:
1) increase the font size for the diagrams in Figure 3;
2) #205: what is the sample size for calculating Standard deviation?
Best regards.
Author Response
Thank you for all comments, we tried to improve the general aspect of the manuscript.
Minor revision to check:
1) increase the font size for the diagrams in Figure 3;
Thank you for your comment, the font size of Figure 3 and also of Figures 4 and 5 were increased.
2) #205: what is the sample size for calculating Standard deviation?
As reported in the text line 151 of the original manuscript: “All tests were repeated for almost 5 times”. This is the sample size for standard deviation in Table 3.
Round 2
Reviewer 2 Report
The quality of the paper has improved significantly. I suggest its pubblication at Applied Sciencies journal after some minor revision.
line 195: area instead of area)
Line 203-205: This text should be removed. MA NON é 203 CHE LI VOSGLIAMO RIPORTARE COSI’ DA RISPONDERE ANCHE ALLA DOMANDA SULLA 204 GLI ELEMENTI LISCIAVIATI O MENO? SUPPLEMENTARY MATERIAL?
Author Response
Thank you for this remark. We have modified the text according to the suggestion.
The surface area and the average diameter of the pore Dav,BJH (obtained as 4·VBJHa/ABET, where VBJHa is the BJH desorption pore volume, and ABET is the BET surface area), are critical parameters for physical adsorption. In general, the higher the superficial area, the better the sorbent capacity.
The surface area and the average diameter of the pore Dav,BJH, (obtained as 4·VBJHa/ABET, where VBJHa is the BJH desorption pore volume, and ABET is the BET surface area), are critical parameters for physical adsorption. In general, the higher the superficial area, the better the sorbent capacity.
Sorry, it was a residual of previous editing work. We have dropped the sentence.
The EDSSD analysis, nor reported here, shows the Ccarbon as the main element with a distributed trace of Cchlorine, due to the HCl washing step of the activation method. MA NON é CHE LI VOSGLIAMO RIPORTARE COSI’ DA RISPONDERE ANCHE ALLA DOMANDA SULLA GLI ELEMENTI LISCIAVIATI O MENO? SUPPLEMENTARY MATERIAL?
The EDSSD analysis, nor reported here, shows the Ccarbon as the main element with a distributed trace of Cchlorine, due to the HCl washing step of the activation method.
