Experimental Evaluation of Hydrotreated Vegetable Oils as Novel Feedstocks for Steam-Cracking Process

Round 1

Reviewer 1 Report

Hydrotreated vegetable oils was mixture and there are many compounds in them. Based on these objects, it is difficult to achieve some valuable rules when process coefficients are not enough. It was suggested that the goals and portions are presented clearly in abstract. 

Author Response

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Reviewer 2 Report

I have read with interest the paper of Karaba and co-workers on the steam creaker of hydrogenated vegetable oils. The focus of the paper well fits within the scope of the journal. The paper is well-written but some aspect should be addressed before publication. Below, the authors may find the main comments of the reviewer.

• Table 1/3: What “Simdis” means? Please, explain.
• Why the sulphur content increases after hydrogenation?
• Why steam-creaking is carried out at 400 kPa? Usually, lower partial pressure are adopted.
• Line 153: what is “carrier-gas”? steam or nitrogen?
• What is the residence time?
• Usually quenching of the reactor out-stream is carried out at industrial scale. Have the authors considered this aspect? It should be mentioned.
• Table 3: please provide isomers distribution

Author Response

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Reviewer 3 Report

This paper deals with hydrotreated vegetable oils (HVOs) as a feedstock for experiments of pyrolysis, to produce added-value molecules. Description of procedures concerning experiments and data elaborations must be improved. The focus of the paper must be stated more clearly, starting from the title (see my comment 3). Results are presented quite well, even though the discussion is mainly descriptive; nonetheless, summarized results may be useful for researchers committed to the field of HVO pyrolysis. I suggest the publication with minor revisions, recommended in the following list:

1 – The usage of the English language needs some minor revisions

2 – I have a general concern about the conceived process. Is the cracking of a refined product such as HVO/Green-diesel (e.g., involving efforts of catalytic reactions) justified in comparison to the cracking of raw vegetable oils? Please, comment on the manuscript.

3 – The authors stated indifferently they are studying either “pyrolysis” of HVOs or “steam-cracking” of HVOs, but this generates a misunderstanding from my point of view (e.g., what named as steam-cracking at relatively high temperatures may be considered steam gasification, while pyrolysis is a thermal decomposition in absence of any oxidant, and water is an oxidant). So, it is not clear to me what occurred in the experimental apparatus Shimadzu Pyr-4A: pyrolysis (as just defined) or a reaction with steam? Please, clarify in the manuscript and modify the title of the paper, if needed. Reaction conditions and conduction of Shimadzu Pyr-4A should be described with strongly greater detail in section 2.2.

4 – Tables 1, 2, 3. A Symbols and Abbreviation section at the end of the paper should be added, in order to define extensively quantities listed in those Tables, so helping those readers who are not fully in the field of oils characterization (e.g., what Simdis means? … and so on). Elemental analyses are shown in wt.% or else?

5 – Figure 1, 2, Error bars are multiples of standard deviations, confidence intervals, ranges, …? Please clarify in figures’ captions. “Y” symbol is not defined. This confirms the need for a Symbols and Abbreviation section, also considering the intensive use of acronyms for the different feedstocks

6 – Figure 3. x-axis goes from 0 to 1, labels states wt.%. Is 0-1 interval a fraction to be substituted by 0-100%?

7 – Section 3.1. The word “yield” is used quite often to comment on experimental results. Considering that this word may be very misleading in chemical engineering, I strongly urge the authors to define what they mean by “yield” in section 2, with a specific equation.

8 – Some further details about economic analysis (methods, equations) may improve the manuscript, maybe by a dedicated subsection in Section 2

Author Response

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Round 2

Reviewer 1 Report

The manuscript can be published based on the previous revision.

Author Response

We appreciate the reviewer's warm words and the time invested by the reviewer in the review process of our manuscript.

Reviewer 2 Report

The authors have given reasonable answers, but the manuscript still requires information about steam-to-feedstock ratio, as the carrier is nitrogen. 

Author Response

The reviewer asks for the steam-to-feed ratio, but there is no mention of the dilution of feed by steam in our manuscript. In our experimental method, the sample is injected into the reactor as one short pulse (into the nitrogen flow) and continues to the reactor undiluted with plug flow. Therefore, there is no feed dilution by inert (nitrogen) [doi.org/10.1016/j.jaap.2009.12.006]. 
This might be our mistake that the reviewer could not deduce that the feed is undiluted. Therefore, we slightly reformulated the experiment description to avoid any similar misunderstandings (lines 166-168):

... The injected sample is vaporized and passes through the reactor (plug flow) as an undiluted pulse of the reaction mixture.  Pyrolysis products are then carried into the analytical system in the flow of carrier gas (nitrogen)...