Reactive Extraction of Lactic Acid, Formic Acid and Acetic Acid from Aqueous Solutions with Tri-n-octylamine/1-Octanol/n-Undecane
Round 1
Reviewer 1 Report
Dear authors,
the subject of your manuscript is significant and actual. Overall you proposed an interesting manuscript.
I found a few English mistakes that must be corrected by you and some suggestions of text quality improvement are mentioned below:
- the abstract must be improved.
- Introduction: English corrections are necessary; correct position of adverbs and linking terms must be inserted in text (e.g. here, therefore, such as dilluent..)
- results and discussion:
(i) it must be deleted terms as 'equation (i)' after its mathematical formulation, it remains only '(i)' (e.g., pages 3-6; (ii) page 3 line 123 - change text as '...Physical extraction was..."not 'physical extraction were...'; (iii) page 4 line 149 change text as '...lactic acid was investigated further';
(iv) page 6 line 205, change text as '...equations (9-10) ...'' or line 211 - '...Figs. 2-4...' or '...to the calculation (equation 10) and give...), or lines 217-218 - figure 2 title - '... lactic acid (solvent with 20 wt% TOA in ....ambient pressure)'
(v) page 7 - lines 222-223 - changes in figure 3 title - '...lactic acid ( solvent with 20 wt% TOA....pressure)' and also figure 4 title, line 226 - '...lactic acid (T=25...pressure)', or line 227 - text changes as '...association related to the solvent composition...', or 238 - '...equlibrium concentrations were obtained...', or line 240 - '...the solvent in the viscosity control.'
(vi) page 8, line 243 - text correction as '...with different ratios of...', or line 254 - text correction as '...Initial acid concentrations were...'
(vii) Conclusion: line 287, text change as '...is a potential unitary operation for...', or line 297 - '...in both binary and ternary solvent systems.', or '...n-undecane decreases the solvent...'
(viii) reference 7 must be completed with identification data no of volume and issues and complete journal title.
These are a few of my suggestions for the manuscript authors.
Author Response
Dear authors,
the subject of your manuscript is significant and actual. Overall you proposed an interesting manuscript.
I found a few English mistakes that must be corrected by you and some suggestions of text quality improvement are mentioned below:
- the abstract must be improved.
We reworked the abstract to make it more attractive for readers and inserted the novelty of the work as well as the potential transfer of data to liquid membrane permeation.
- Introduction: English corrections are necessary; correct position of adverbs and linking terms must be inserted in text (e.g. here, therefore, such as diluent..)
We read thoroughly through the whole manuscript once again and we corrected the typing mistakes as well as linking terms, thanks a lot for this remark, there appeared more than just the once mentioned below.
- results and discussion:
(i) it must be deleted terms as 'equation (i)' after its mathematical formulation, it remains only '(i)' (e.g., pages 3-6;
We deleted the term equation and left in the text just the numbering as e.g. (1), the whole manuscript was revised accordingly.
(ii) page 3 line 123 - change text as '...Physical extraction was..."not 'physical extraction were...'
Thanks for reading the manuscript that accurate, we changed the text accordingly.
(iii) page 4 line 149 change text as '...lactic acid was investigated further';
We changed the text accordingly.
(iv) page 6 line 205, change text as '...equations (9-10) ...'' or line 211 - '...Figs. 2-4...' or '...to the calculation (equation 10) and give...), or lines 217-218 - figure 2 title - '... lactic acid (solvent with 20 wt% TOA in ....ambient pressure)'
The title of Figure 2, 3 and 4 were adapted accordingly.
(v) page 7 - lines 222-223 - changes in figure 3 title - '...lactic acid ( solvent with 20 wt% TOA....pressure)' and also figure 4 title, line 226 - '...lactic acid (T=25...pressure)', or line 227 - text changes as '...association related to the solvent composition...', or 238 - '...equlibrium concentrations were obtained...', or line 240 - '...the solvent in the viscosity control.'
The text and labelling of the figures was adapted accordingly.
(vi) page 8, line 243 - text correction as '...with different ratios of...', or line 254 - text correction as '...Initial acid concentrations were...'
The text and labelling of the figures was adapted accordingly.
(vii) Conclusion: line 287, text change as '...is a potential unitary operation for...', or line 297 - '...in both binary and ternary solvent systems.', or '...n-undecane decreases the solvent...'
(viii) reference 7 must be completed with identification data no of volume and issues and complete journal title.
The reference was updated accordingly.
These are a few of my suggestions for the manuscript authors.
Thank you for reading through the manuscript that exactly, we read through the manuscript also once again and corrected some typing mistakes as well as wrong singular and plural, which occurred unfortunately quite often.
Further, we reworked the abstract and the conclusion and highlighted the novelty of the work (see comments reviewer 1 and 3)
Reviewer 2 Report
Review on manuscript:
Reactive extraction of lactic acid, formic acid and acetic acid from aqueous solutions with Tri-n-octylamine/1-Octanol/n-Undecane
Major remarks:
In general, the research topic reactive extraction of lactic acid, formic acid and acetic acid from aqueous solutions with Tri-n-octylamine/1-Octanol/n-Undecane is of importance. The authors describe the influence of different solvent mixtures on extraction yield of single acids. Furthermore, the authors investigate the selectivity.
However, besides the publications already cited in the manuscript, further relevant publications related to this topic exist. These also relevant publications should be cited and considered during in the discussion part of this manuscript.
As can be seen, some of the results, especially about solvent selection given in the below named publications partly resemble the results given in this manuscript. Therefore, I deem it necessary to further specify the novelty value of this publication and differentiate between new insights and already published results.
Publication 1: Simultaneous Influence of Active and “Inert” Diluents on the Extraction of Lactic Acid by Means of Tri-n-octylamine (TOA) and Tri-iso-octylamine (TIOA) (Kyuchoukov, 2006)
Publication 2: Extraction of lactic acid using long chain amines dissolved in non-polar diluents (Yamamoto, 2011)
Publication 3: Influence of Extractant (TBP and TOA), Diluent, and Modifier on Extraction Equilibrium of Monocarboxylic Acids (Morales, 2003)
Publication 4: Extraction of Lactic Acid by Means of a Mixed Extractant (Kyuchoukov, 2001)
In addition, further information about the experimental setup/results are required. The following information should be provided for better understanding:
• The pH value of the aqueous phase after extraction equilibrium was reached as this value can be easily measured and used to verify the results (especially important for back extraction).
• The absolute amount of TOA and acids in the system before and after extraction/back extraction in organic and aqueous phase.
• The overall molar loading of TOA (nAcid/nTOA) (the n given in the results gives information about the complex if complexation takes place but does not indicate the loading of TOA).
In the introduction, it is mentioned, that the system can be used for the recovery of acids from in fermentation broths. Fermentation broths contain side components, which strongly influence the extraction system and also mostly prevent formation of a third phase. For clarification, I would like to see a short discussion why pure acid systems and prevention of a third phase is relevant for real applications.
As a conclusion, I recommend a major revision of the manuscript.
Specific remarks:
Line 66: “However, its viscosity is expected to hindrance the mass transfer at the 66 interface. Inert diluents (non-polar) like alkanes, benzene, on the other hand, provide lower 67 viscosity, but leading to a poor distribution of polar salt.” Please add citation
Line 105: These recorded masses should be shown in the results.
Line 146-149: Please add citations
Line 155: Citation source is not available online.
Line 161: Please add information about equilibrium pH for different solvent compositions
Line 167: Please refer to literature, where this result (40% TOA) has also been show for multiple extraction systems
Table 2: Please add information as asked in major review part. Please also add to the description that solvent to water ratio is 1.
Figure 6: Back extraction was not 100% successful. What is the reason for this? Not enough stripping phase, equilibrium? What is the pH after back extraction. Please elaborate.
Line 287: Liquid-liquid extraction
Author Response
In general, the research topic reactive extraction of lactic acid, formic acid and acetic acid from aqueous solutions with Tri-n-octylamine/1-Octanol/n-Undecane is of importance. The authors describe the influence of different solvent mixtures on extraction yield of single acids. Furthermore, the authors investigate the selectivity.
However, besides the publications already cited in the manuscript, further relevant publications related to this topic exist. These also relevant publications should be cited and considered during in the discussion part of this manuscript.
As can be seen, some of the results, especially about solvent selection given in the below named publications partly resemble the results given in this manuscript. Therefore, I deem it necessary to further specify the novelty value of this publication and differentiate between new insights and already published results.
Thank you for this comment, we read through the papers and added them in the discussion part as follows:
Publication 1: Simultaneous Influence of Active and “Inert” Diluents on the Extraction of Lactic Acid by Means of Tri-n-octylamine (TOA) and Tri-iso-octylamine (TIOA) (Kyuchoukov, 2006)
….., Kyuchoukpv et al obtained comparable results when a similar solvent composition consisting of TOA:1-octanol diluted in dodecane was used for the extraction of lactic acid.[33]. As expected from results gained in the physical extraction, the diluent does not influence the phase equilibrium when reactive extraction is concerned.
Publication 2: Extraction of lactic acid using long chain amines dissolved in non-polar diluents (Yamamoto, 2011)
Yamamoto [34] et al reported the improvement of the extraction ability of lactic acid by adding decanol as modifier into di-n-octylamine (DOA). They reported the tendency of third phase formation when a non-polar diluent is used. Prevention of the third phase formation was ensured by setting the volume fraction of the modifier > 10% when using solvent composting of di-n-octylamine (DOA). Secondary and tertiary amines behave differently in terms of emulsion formation, also in the present work we saw the formation of a stable third phase for all experiments having a TOA concentration ≥ 40 wt% .
Publication 3: Influence of Extractant (TBP and TOA), Diluent, and Modifier on Extraction Equilibrium of Monocarboxylic Acids (Morales, 2003)
This result is consistent with the study of Morales et al [40]. They investigated the extraction of the single mono-carboxylic acids by using TOA in decanol and dodecane and suggested a more step process for the selective acid extraction with an appropriate solvent composition.
Publication 4: Extraction of Lactic Acid by Means of a Mixed Extractant (Kyuchoukov, 2001)
TOA has been reported to extract the non-dissociated form of the mono-carboxylic acid when the pH < pKa [37]
In addition, further information about the experimental setup/results are required. The following information should be provided for better understanding:
• The pH value of the aqueous phase after extraction equilibrium was reached as this value can be easily measured and used to verify the results (especially important for back extraction).
We added the information of equilibrium pH for the extraction in Table 2. As the equilibrium concentration during the extraction is low also the amount of the stripped acids is low, which lead to a stable pH for the back-extraction, which was 12.2. We added is as follows in the discussion:
The degree of back-extraction by mean of basic property depends on the equilibrium pH of the aqueous solution [41]. The present study used a concentration of 1 mol/L NaHCO3, which leads to a pH value of 12.2, the pH remained the same also in equilibrium. However, for the back-extraction from multiple acids laden solvent, this topic need to be further studied.
• The absolute amount of TOA and acids in the system before and after extraction/back extraction in organic and aqueous phase.
TOA has negligible solubility in the aqueous phase and is hence assumed to be zero. Further, with the possibilities at the Institute we are not able to selectively detect TOA in the aqueous phase.
The concentration of the acid in the solvent phase in equilibrium for the extraction is given in Table 2. The concentrations of the stripped acid from a multiple acids solution are reported in term of back-extraction efficiency in Fig 6.
• The overall molar loading of TOA (nAcid/nTOA) (the n given in the results gives information about the complex if complexation takes place but does not indicate the loading of TOA).
The loading ration expresses the ratio of acid concentration in the solvent phase to the solvent concentration, the data show that the loading ratio increases with decreasing TOA concentration and increases with increasing acid concentration. Further, we added the loading of the solvent in Table 2.
In the introduction, it is mentioned, that the system can be used for the recovery of acids from in fermentation broths. Fermentation broths contain side components, which strongly influence the extraction system and also mostly prevent formation of a third phase. For clarification, I would like to see a short discussion why pure acid systems and prevention of a third phase is relevant for real applications.
Actually cell debris and alike do not prevent but do facilitate a third phase formation and are able to stabilize the so-called crud. We inserted a literature citation that discusses this when extracting valuables from a fermentation broth and further a second literature citation where liquid membrane permeation is discussed as potential technique for the emulsion/crud prevention.
In the introduction we added the following:
However, in-situ extraction of valuables from a fermentation broth is in general accompanied with third phase respectively crud formation, which prevents the use of conventional extraction process therefore. [17] Supported liquid membrane permeation showed to be effective for the purpose of emulsion prevention in highly emulsion tending systems and can help to overcome the drawback of emulsion /crud formation when bio-based process streams are targeted [18].
To ensure that no crud formation occur and hence the phase equilibria data are measured correctly, pure substances are used in the present study.
As a conclusion, I recommend a major revision of the manuscript.
We reworked the abstract and the conclusion and added the novelty/highlights of the manuscript. Further, we read through the manuscript once again and increased the quality by removing typing mistakes and singular/plural mistakes as well as connecting words.
The addition of the mentioned literature and the added literature concerning crud formation and prevention makes the manuscript better readable and highlights/novelty is added accordingly.
Specific remarks:
Line 66: “However, its viscosity is expected to hindrance the mass transfer at the 66 interface. Inert diluents (non-polar) like alkanes, benzene, on the other hand, provide lower 67 viscosity, but leading to a poor distribution of polar salt.” Please add citation
Citation number 25 was added (Wasewar, K.L.; Keshav, A.; Seema. Physical extraction of propionic acid. Int. J. Res. Rev. Appl. Sci. 2010, 3, 290–302.)
Line 105: These recorded masses should be shown in the results.
Data for the masses are unfortunately not available.
Line 146-149: Please add citations
Citations 22, 30 and 31 are inserted/added:
22 Udachan, I.S.; Sahoo, A.K. A studyof parameters affecting the solvent extraction of lactic acid from fermentation broth. Braz. J. Chem. Eng 2014, 31, 821–827.;
30 Labbaci, A.; Kyuchoukov, G.; Albet, J.; Molinier, J. Detailed investigation of lactic acid extraction with tributylphosphate dissolved in dodecane. J. Chem. Eng. Data 2010, 55, 228–233;
31 Thakre, N.; Prajapati, A.K.; Mahapatra, S.P.; Kumar, A.; Khapre, A.; Pal, D. Modeling and Optimization of Reactive Extraction of Citric Acid. J. Chem. Eng. Data 2016, 61, 2614–262
Line 155: Citation source is not available online.
This citation was deleted as it was a poster within a symposium, but we added the following:
.. outcome of a previous study, we found that above that concentration third phase formation occurs.
Line 161: Please add information about equilibrium pH for different solvent compositions
We added the pH value in Table 2
Line 167: Please refer to literature, where this result (40% TOA) has also been show for multiple extraction systems
Citation was added (Nr. 33: Kyuchoukov, G.; Labbaci, A.; Albet, J.; Molinier, J. Simultaneous influence of active and “Inert” diluents on the extraction of lactic acid by means of Tri-n-octylamine (TOA) and Tri-wo-octylamine (TIOA). Ind. Eng. Chem. Res. 2006, 45, 503–510.)
Table 2: Please add information as asked in major review part. Please also add to the description that solvent to water ratio is 1.
The ratio was entered in the labelling of the table and the data are inserted as asked in the major review part.
Figure 6: Back extraction was not 100% successful. What is the reason for this? Not enough stripping phase, equilibrium? What is the pH after back extraction. Please elaborate.
See major comment and answer above.
Line 287: Liquid-liquid extraction
Thanks for reading the manuscript that exactly we checked the whole manuscript once again for typing mistakes and adapted it accordingly.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
This paper describes the reactive extraction of organic acids with TOA. Experimental methods and analysis of experimental results are clear and no problem. However, conventinal approach seems to be only applied to new solvent system. Author should emphasizes the novelty of this study in Introduction and Conclusion.
Author Response
This paper describes the reactive extraction of organic acids with TOA. Experimental methods and analysis of experimental results are clear and no problem. However, conventional approach seems to be only applied to new solvent system. Author should emphasizes the novelty of this study in Introduction and Conclusion.
We reworked the abstracted and inserted highlights especially there, further we implemented as suggested by reviewer two a few more literature citations, which enhance the quality of the manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
In general, the research topic reactive extraction of lactic acid, formic acid and acetic acid from aqueous the extraction of lactic, formic and acetic acid in mixtures thereof is of industrial importance. The authors describe the influence of different solvent mixtures on extraction yields.
All comments of the first review are considered in the actual version. Please find below some minor remarks:
Line 182: Typo: Kyuchoukpv -> Kyouchoukov
Table 2: Please define m_HA_in and m_HA_aq.
Table 3: Please add a definition for Z in the title.
Author Response
All comments of the first review are considered in the actual version. Please find below some minor remarks:
Line 182: Typo: Kyuchoukpv -> Kyouchoukov
- the typing mistake was corrected accordingly
Table 2: Please define m_HA_in and m_HA_aq.
- the nomencalture is given from line 347 on, m, HA and in and aq are defined there.
Table 3: Please add a definition for Z in the title.
- also Z is defined in the nomencalture from line 347 on.
