Experimentally Calculated Study of the Effectiveness on the Process of Non-Catalytic Synthesis of Biodiesel in Reactors of Various Type

Round 1

Reviewer 1 Report

This work deals with the production of biodiesel under non-catalytic conditions, using two reaction systems (continuous and batch). A theoretical model is proposed and a satisfactory correlation is obtained between the experimental and calculated values. The work is interesting, although the following questions should be addressed to clarify the information provided in this manuscript:

1. After removing glycerol and methanol from the reaction mixture, before recycling, using a continuous reactor, the performance of FAME hardly improves, or even decreases (Table 2). However, it increases under batch conditions (Table 3). An explanation of the behavior in the continuous reactor should be given.
2. The values of Q and n for entry 15 in Table 2 should be reviewed. It is noted that entries 15 and 16 can be compared, but these different values do not allow it.
3. The asterisk (*, time after reaching set temperature, according to the footnote) does not appear in Table 3 (perhaps it means residence time).
4. (Table 3, entries 7, 8, and 9) How do the authors explain the decrease in FAME yield when using a 15: 1 methanol: oil molar ratio?
5. What is the effect of the methanol: oil molar ratio at 220ºC on the FAME yield? Is it similar to that observed at 230ºC?
6. Figure 6 needs to be changed because, in the current format, it is difficult to distinguish experimental and calculated values.
7. It would be interesting to include information on the existence of a monophasic or biphasic system in each of the experimental conditions reported in this study.
8. There are not many studies that work in subcritical conditions of methanol for the production of biodiesel, but it would be very useful for readers to provide comparative data focused on the kinetics of the non-catalyzed transesterification process, both at high reaction temperature and under pressure, including supercritical conditions.
9. In the present work, a refined edible rapeseed oil is used as raw material, and it is well known that the use of edible oil for biodiesel production should be avoided. Do the authors have information on the influence of the presence of water and / or free fatty acids (FFA) on the performance of FAME, under the experimental conditions used?
10. Some information on the quality of the biodiesel obtained must be included, as well as some evaluation of the economic costs of both biodiesel production processes.
11. What is the  method used for the separation of the oil and glycerol phases?

Therefore, all these points should be clarified before recommending the publication of this manuscript.

Author Response

Good afternoon!
We are sending you responses to comments and questions on our work.

Best regards,

team of authors.

Author Response File: Author Response.docx

Reviewer 2 Report

In my opinion, the article was well written howerew some tecnical aspect should be improved. In particular, the use of unrefined oils in this kind of systems, is an aspect that is necessary to valuate to increase the global impactor of the work presented. 

Author Response

Good afternoon!

In response to your`s suggestion we can propose to change the title 4. Conclusions to the title 4. Conclusions and outlook with following text:

"The most basic problem in the catalytic production of biodiesel is the disposal of the so-called "glycerin layer", the processing of which is more expensive than the production of biodiesel itself. In carrying out the process of obtaining biodiesel in sub critical methanol, glycerin is obtained with high quality (Table 1), so-called "dynamite" glycerol. For simplification and cost reduction process is advantageously carried out in two steps: preparation of a 80% FAME and selecting pure glycerol, vacuum distillation of the oil layer with selection pure biodiesel and returning the remainder of the reaction mass in a cycle. Dosed supply of methanol to the reactor will reduce the pressure in the reactor to several megapascals. The introduction of the vacuum distillation stage into the technology for producing biodiesel in subcritical methanol more than justifies the costs of both the recovery of glycerin in the catalytic process and the costs of the metal-intensive process of a conventional non-catalytic process with a pressure of tens of megapascals, a temperature of hundreds of degrees Celsius, and recovery of a tenfold excess of methanol."

Best regard,

team of authors.

Round 2

Reviewer 1 Report

The authors have made an important effort to adequately answer most of questions raised in the revision process. This has allowed to improve and clarify the information provided in the manuscript, and I could recommend its publication.