Review Reports - Liquid–Liquid Equilibrium Behavior of Ternary Systems Comprising Biodiesel + Glycerol and Triglyceride + Methanol: Experimental Data and Modeling

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study focuses on investigating the liquid-liquid equilibrium (LLE) of a ternary system consisting of waste oil biodiesel, methanol, and glycerin. The purpose of this investigation is to enhance the precision and efficiency of separation and purification processes in the biodiesel production industry. The LLE experiments were conducted under atmospheric pressure at three specific temperatures: 303.15 K, 313.15 K, and 323.15 K. The results of the study revealed that the presence of lower methanol content in the system led to nearly immiscible phases of biodiesel and glycerol, facilitating their separation. Conversely, increasing methanol content resulted in a gradual increase in the mutual solubility of biodiesel and glycerol. The following comments need to be addressed before publication.

1. What is the purpose of conducting the phase equilibrium study for the ternary system of waste oil biodiesel + methanol + glycerin?

2. Rearrange the sections 2 and 3. Results have to be presented after the Methodology section.

3. The background of UNIQUAC and NRTL models needs to be explored.

4. Describe the methodology used to correlate the ternary liquid-liquid equilibrium data with the NRTL and UNIQUAC activity coefficient models.

5. Methodology can be illustrated with graphical images and experimental needs to be presented.

6. The reviewers are unable to find Table S1.

7. The following paper can be referred to in the manuscript.

i) https://doi.org/10.47852/bonviewAAES32021761

8. What are the potential industrial applications or implications of the findings from this study?

9. The old references can be replaced with the latest references.

Comments on the Quality of English Language

Moderate editing of the English language is required

Author Response

Dear Sir/Madam,

Thank you very much for your comments and useful suggestions on structure and technical factor of our manuscript. We have modified the manuscript accordingly, and the detailed corrections are listed below step by step:

Reviewer # 1:

What is the purpose of conducting the phase equilibrium study for the ternary system of waste oil biodiesel + methanol + glycerin?
After the transesterification reaction, the main components in the system are biodiesel, methanol, and glycerol. Glycerol is a kind of product with economic value, but the existence of glycerol in biodiesel reduces the quality of biodiesel. According to the European biodiesel standard of EN 14214, The maximum allowable free glycerol value is 0.02 wt. %. Therefore, the purification step after transesterification reaction is very important. Therefore，studying the solubility of by-product glycerol with biodiesel and methanol is helpful to understand the distribution of glycerol in the system. In the manuscript，By adjustment the concentration of methanol, it is easy to separate main components of biodiesel and glycerin.

Rearrange the sections 2 and 3. Results have to be presented after the Methodology section.

Thangs to the reviewer's advice, but the format of the catalysts is the section of results in the first of the Methodology section.

The background of UNIQUAC and NRTL models needs to be explored.

Thanks to the reviewer's advice, In the manuscript, the background of UNIQUAC and NRTL models have been add to the introduction section. The details are as follows: for biodiesel phase equilibrium systems, the UNIQUAC and NRTL models, both derivatives of the Wilson model, are the most frequently utilized. These models are applicable to similar systems, specifically for calculating and predicting liquid-liquid phase equilibria, including systems composed of ketones, alcohols, ethers, nitriles, and lipids, as well as miscible systems with water, sulfur, and halides. The NRTL model, noted for its simplicity, incorporates a non-random parameter which is typically considered independent of both temperature and solution composition, but is determined by the type of solution, as a characteristic parameter of the solution. The specific selection of the solution value directly affects the fitting effect of the NRTL equation. In comparison, the UNIQUAC model is more complex. It is more theoretical, involves more parameters, but its range of applicability is broader. Specifically, in terms of volume fractions, the UNIQUAC equation considers the effects of planarity and three-dimensionality; it also introduces lattice coordination numbers (similar to those of solids), molecular contact numbers, and other parameters.

Describe the methodology used to correlatec with the NRTL and UNIQUAC activity coefficient models.

In the manuscript, the analysis methodology of the phase equilibrium study for the ternary system of waste oil biodiesel + methanol + glycerin was the chemical process simulation software of Aspen Plus. In the Aspen Plus software, we use the data regression model, then the liquid-liquid equilibrium of waste oil biodiesel + methanol + glycerin was calculated and simulated by using the NRTL activity coefficient model and the UNIQUAC activity coefficient model. This is the methodology of the phase equilibrium study in the manuscript.

Methodology can be illustrated with graphical images and experimental needs to be presented.

In the manuscript, we have added the methodology of the Liquid e liquid equilibrium calculation in page 11.

The reviewers are unable to find Table S1.

This is the Table S1, which is in the supplementary material.

Table S 1

The composition and content of waste oil biodiesel.

Waste oil biodiesel	The structure	Composition(wt%)
	C14:0（Myristic acid）	1.94
	C16:0(Methyl palmitate)	16.83
Saturated fatty acid methyl ester content*/ wt%(24.12%)	C18:0（Methyl stearate）	4.94
	C20:0(Methyl xicosanoate）	0.41
	C16:1(Methanol palmitoleate）	2.03
	C18:1（Methyl oleate）	45.07
	C18:2（Methyl linoleate）	24.82
Unsaturated fatty acid methyl ester content*/ wt%(75.88%)	C18:3（Methyl linolenic acid）	1.87
	C20:1（Eicosapentaenoic acid）	1.02
	C20:2（Eicosadienoic acid）	0.49
	C20:5（Eicosapentaenoic acid）	0.56

The following paper can be referred to in the manuscript.

According to the reviewer's advice, we have added the references to the manuscript.

What are the potential industrial applications or implications of the findings from this study?

In the manuscript, the potential industrial applications of the phase equilibrium study for the ternary system of waste oil biodiesel + methanol + glycerin was as follow: increasing the dosage of biodiesel is beneficial to promoting the miscibility of glycerol and methanol. In the production system of biodiesel, the reasonable addition of biodiesel can be considered in order to improve the miscibility of the system and improve the reaction efficiency strategically. In addition, methanol plays a crucial role in achieving the target blend of biodiesel and glycerol. For the development of biodiesel separation from reactants and product mixtures, prioritizing removal methanol is as an initial step, which can promote the subsequent separation of biodiesel and glycerol. The use of UNIQUAC and NRTL models in liquid liquid phase equilibrium characterization demonstrated a commendable agreement between experimental data and calculated values for waste oil biodiesel + glycerol + methanol. Notably, the NRTL model mitigates the superior description with a maximum RSMD of 5.26%. Therefore, the potential industrial applications of the phase equilibrium study for the ternary system of waste oil biodiesel + methanol + glycerin is very important.

The old references can be replaced with the latest references.

According to the reviewer's advice, we have modified the references to the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

In manuscript “Liquid-Liquid Equilibrium Behavior of Ternary Systems Comprising Biodiesel + Glycerol and Triglyceride + Methanol: Experimental Data and Modeling,” authors describe the study of the phase equilibrium of the ternary system comprising waste oil biodiesel + glycerol + methanol, employing a liquid-liquid phase equilibrium kettle. The NRTL and UNIQUAC activation coefficient models were utilized to correlate the acquired experimental data, and subsequently obtain the corresponding simulation parameters and relative errors. I recommend the publication of this manuscript in Catalysts after an additional revision.

-Authors should incorporate the following references in order to extend the introduction and discussion parts: (a) A. A. Albuquerque, F. T.T. Ng, L. Danielski, L.Stragevitch. Fuel 271 (2020) 11768 (b) A. Barreau, I. Brunella, J.C. de Hemptinne, V. Coupard, X. Canet, F. Rivollet. Ind. Eng. Chem. Res. 49 (2010) 5800 (c) S. Doungsri, T. Sookkumnerd, A. Wongkoblap , A. Nuchitprasittichai. IOP Conf. Series: Materials Science and Engineering 273 (2017) 012008. Particularly, authors should revise the following reference: M. Mohadesi, Liquid-Liquid Equilibrium for Ternary Systems Containing Biodiesel + Glycerol + Alcohol (Ethanol or Methanol): Thermodynamic Modeling. Journal of Chemical and Petroleum Engineering 2020, 54(2): 285-295. In this article, Mohadesi describes a similar ternary system using both NRTL and UNIQUAC models, too. Authors should compare their findings with this last paper.

-In page 3, line 121, authors state that “canola oil, which was postulated primarily composed of mesonic acid…” What is the mesonic acid? Check this name.

Author Response

Reviewer # 2:

1.I recommend the publication of this manuscript in Catalysts after an additional revision.

Particularly, authors should revise the following reference: M. Mohadesi, Liquid-Liquid Equilibrium for Ternary Systems Containing Biodiesel + Glycerol + Alcohol (Ethanol or Methanol): Thermodynamic Modeling. Journal of Chemical and Petroleum Engineering 2020, 54(2): 285-295. In this article, Mohadesi describes a similar ternary system using both NRTL and UNIQUAC models, too. Authors should compare their findings with this last paper.

According to the reviewer's advice, we have added the references to the manuscript. Meantime, we have compared the finding of the Mohadesi's describes and this manuscript.

In page 3, line 121, authors state that “canola oil, which was postulated primarily composed of mesonic acid…” What is the mesonic acid? Check this name.

According to the reviewer's advice, we have check the name of mesonic acid and modified it to erucic acid.

Reviewer 3 Report

Comments and Suggestions for Authors

The article “Liquid-Liquid Equilibrium Behavior of Ternary Systems Comprising Biodiesel + Glycerol and Triglyceride + Methanol: Experimental Data and Modeling” is devoted to the study of mutual solubility in a system of waste oil biodiesel + methanol + glycerin. This topic is very relevant for modern ecology. However, the article needs to be better structured and clearly describe the methodology and logic of the experiments. The article may be published after major changes have been made.

Supplementary 1. I would like to ask for clarification on the second column. What does the entry C18:0 mean? C18 is the length of the carbon chain. What does “0” mean?

Entry “Saturated fatty acid methyl ester content*/mol%”. The meaning of the “*” sign is not given.

It is necessary to provide a description of all devices used - name of the device, manufacturer and year of manufacture.

How many times was each experiment performed? What is the error of the experiments and by what method was it determined?

In the abstract, the authors say they investigated one liquid-liquid ternary system. In conclusion, it is indicated that two such systems have been studied. It is necessary to eliminate the contradiction.

The reference list must be checked for compliance with the journal rules. The names of the first 10 authors must be given.

Line 276. The word “Uncertainty” must be written with a small letter. The same should be corrected throughout the article.

The word “methyl” means a radical. Since the authors of the article are not talking about a single radical, such a notation is incorrect.

Why were syringes used to separate the phases rather than separatory funnels?

Is 5 hours enough to completely remove the methanol from the mixture?

Please provide a complete list and chemical composition of the 11 oils that were studied.

Figures 3-5. The experimental points do not fit well into one line. It is necessary to conduct more experiments and obtain more points.

The authors write that at high temperatures, modeling is difficult due to the volatility of methanol. Why were these particular temperatures chosen for the study?

Figure 8. Poor quality.

Comments on the Quality of English Language

The proposals are very cumbersome. The text is difficult to understand.

Author Response

Reviewer # 3:

Supplementary 1. I would like to ask for clarification on the second column. What does the entry C18:0 mean? C18 is the length of the carbon chain. What does “0” mean? Entry “Saturated fatty acid methyl ester content*/mol%”. The meaning of the “*” sign is not given.

In Table S1, the C18:0 mean the methyl stearate. Yes, C18 is the length of the carbon chain. The 0 mean the unsaturated double bond of 0. Thank you for the reviewer's advice, we have given the saturated/ unsaturated fatty acid methyl ester content in Table S1.

It is necessary to provide a description of all devices used - name of the device, manufacturer and year of manufacture.

According to the reviewer's advice, we have added of all devices used and manufacturer on the Materials and Methods

How many times was each experiment performed? What is the error of the experiments and by what method was it determined?

The system of each component is sampled 3 times, and the triangle phase diagram is drawn by taking the average values of the initial component and the upper and lower components of the solution.

In the abstract, the authors say they investigated one liquid-liquid ternary system. In conclusion, it is indicated that two such systems have been studied. It is necessary to eliminate the contradiction.

I am sorry for the reviewer's misunderstanding. In the manuscript, we have one liquid-liquid ternary system of biodiesel +methanol+glycerol. According to the reviewer's advice, we have modified the conclusion.

The reference list must be checked for compliance with the journal rules. The names of the first 10 authors must be given.

We modified the format of the references in accordance with the requirements of the journal.

Line 276. The word “Uncertainty” must be written with a small letter. The same should be corrected throughout the article.

According to the reviewer's advice, we have modified the word “Uncertainty” to “uncertainty”。

The word “methyl” means a radical. Since the authors of the article are not talking about a single radical, such a notation is incorrect.

In previous the biodiesel's article, the compositions of biodiesel were methyl oleate, methyl linoleate, et al. Methyl is usually, it is no need to modified.

Why were syringes used to separate the phases rather than separatory funnels?

When the mixture achieved to the two-phase equilibrium, the separation can not be done by using a separatory funnels because the separation funnel needs to first remove the mixture from the thermostatic oscillator, which affects the two-phase equilibrium, so we slowly take the two phases mixture out with a syringe.

Is 5 hours enough to completely remove the methanol from the mixture?

According to the characteristics of methanol, its boiling point is 337.85 K, here we set the oven temperature of 348.15 K, at this temperature, methanol quickly volatilized as a gas. According to previous experimental results, when the mixture drying 5 h at the temperature of 348.15 K, the test of gas chromatogram shown no methanol phase. Therefore, 5 hours enough to completely remove the methanol from the mixture.

Please provide a complete list and chemical composition of the 11 oils that were studied.

Table S2 the FAME composition of biodiesel produced from different feedstock

Structure of Fatty acid methyl ester	wt%
Structure of Fatty acid methyl ester	Sunflower oil	Palm oil	Cotton seed oil	Waste oil	Seasame oil	Sunflower oil	Soybean oil	Corn oil	Canola oi	Olive oil	Salad oil
C14:0	0.06	1.44	1.28	1.94	0.19	0.14	0.19	0.06	0.33	0.00	0.10
C16:0	10.87	26.95	24.04	16.83	11.42	7.91	11.09	11.96	9.35	11.60	6.90
C18:0	5.17	6.40	4.94	4.94	5.59	5.83	5.50	3.45	3.51	1.00	0.10
C20:0	2.55	0.72	0.41	0.49	0.65	0.47	0.60	0.91	0.79	3.10	4.00
C22:0	4.84	0.21	0.00	0.40	0.64	1.21	0.69	0.27	0.49	75.00	19.00
C24:0	2.47	0.14	0.00	0	0.21	0.38	0.22	0.33	0.22	7.80	69.10
C16:1	0.16	0.42	2.15	2.03	0.22	0.19	0.26	0.29	0.44	0.60	0.30
C18:1	38.87	42.13	38.87	45.07	29.70	27.90	28.56	33.20	40.33	0.30	0.30
C20:1	1.63	0.34	0.61	1.02	0.45	0.32	0.41	0.66	3.05	0.00	0.00
C22:1	0.11	0.15	1.10	0.00	0	0	0.11	0.84	6.95	0.10	0.00
C18:2	32.09	18.20	23.32	24.82	41.30	52.96	42.95	45.8	25.25	0.00	0.00
C18:3	0.11	1.59	1.78	1.87	7.12	0.51	7.74	1.23	7.38	0.50	0.00

Figures 3-5. The experimental points do not fit well into one line. It is necessary to conduct more experiments and obtain more points.

Thank you for the reviewer's advice, according to the advice, we have re-experimental the phase equilibrium and modified the figure 3-5.

The authors write that at high temperatures, modeling is difficult due to the volatility of methanol. Why were these particular temperatures chosen for the study?

In the manuscript, the waste oil biodiesel + methanol + glycerin phase equilibrium system was conducted under the influence of atmospheric pressure at precise temperatures of 303.15 K, 313.15 K, and 323.15 K. According to the experimental results, we found at high temperature of 323.15 K, due to the the volatility of methanol, the relative accuracy of the results of the UNIQUAC and NRTL model was larger than 5% . On the transesterification reaction，the reaction temperature was usually near to 333.15 K, the high temperature of 323.15 K was near to the reaction temperature of 333.15 K, It is more advantageous to analyze the solubility of biodiesel, glycerin and methanol in industry.

13.Figure 8. Poor quality.

According to the advice, we have modified the Figure 8.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Congrats to the authors.

Comments on the Quality of English Language

Minor editing of the English language is required

Author Response

Dear Sir/Madam,

Reviewer # 1:

Minor editing of the English language is required

Thanks to the reviewer's advice, the English language has been polished.

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the authors of the article and the editorial board of the journal for their excellent work. The article has become much better. The article can be published after making minor revision.

It is necessary to provide a description of all devices used - year of manufacture.

An interesting table is given in the response to the reviewer (question 10). It probably makes sense to insert this table as a Supporting Information to the article.

Author Response

Dear Sir/Madam,

Reviewer #2:

It is necessary to provide a description of all devices used - year of manufacture.

According to the reviewer's advice, we have added year of manufacture

on the device.

An interesting table is given in the response to the reviewer (question 10). It probably makes sense to insert this table as a Supporting Information to the article.

According to the reviewer's advice, we have added the table to the supporting information.