Hydrogen Production in Catalytic Membrane Reactors Based on Porous Ceramic Converters

Round 1

Reviewer 1 Report

The authors reported the development of membrane-catalytic methods for obtaining purified hydrogen of various degrees of purity. The porous ceramic catalytic converters were prepared using self-propagating high-temperature synthesis. These converters were suitable for high-speed steam reforming processes and direct hydrogenation of carbon monoxide contained in synthesis gas. Although this work is preliminary for practical application, this work provides various details for developing better porous membrane reactors, which can be used for solid-oxide fuel cell application. In addition, this work nicely presents multiple factors of the membrane reaction, which can be helpful in the development of a new type of reactor. Therefore, I recommend acceptance of this manuscript after minor revision.

 

1)     The authors want to check the organization of the manuscript and typos. For example, there are unrequired words ("c 2022" in front of the authors' names).

2)     Although the authors provide a perspective of this work, the attachment on the solid oxide fuel cell for hydrogen generation, there are many other factors than the generation of high purity hydrogen. The authors may want to indicate and explain the factors.

3)     How is the performance of the presented system compared to the ex-works or commercially available counterpart? The authors may want to compare the proposed method to the other counterpart.

 

Author Response

Reviewer 1, comment 1: It is necessary to check the manuscript in order to correct typographical errors. So, for example, one extra character is printed before the names of the authors.

Authors: We agree with the comment. The check has been carried out. The typos found have been corrected.

 

Reviewer 1, comment 2: Although the authors have proposed a practical application of the results of their work in conjunction with solid oxide fuel cells, there are also many other uses for ultrapure hydrogen. The authors could point them out as well.

Authors: In our work, we used synthesis gas rather than ultrapure hydrogen to power SOFCs. We designated ultrapure hydrogen as one of the most important products obtained using a hybrid membrane reactor, but in practice it has not been used anywhere. Nevertheless, we fully agree with the honorable reviewer that ultrapure hydrogen has a wide range of applications and, in addition to energy, is also needed in the organic synthesis of highly pure substances, both for large-tonnage purposes and for fine chemical synthesis.

 

Reviewer 1, comment 3: What is the productivity of the presented system compared to industrial or commercially available counterparts?

Authors: Nowadays such converters are not used in the chemical industry, however, we can use as the closest commercially available laboratory examples perovskite hollow fiber membranes and ceramic mesoporous membranes of the Pall Exekia Membralox type. Comparing them we can highlight several noticeable advantages such as:

• Wide converters modification methods range with various catalytic components, both directly during their production by self-propagating high-temperature synthesis and by surface modification of an already prepared converter using the sol-gel method.
• A wide range of practical applications in various chemical reactions and organic synthesis processes including such important ones as oxidative, steam and carbon dioxide reforming, dehydration, hydrogenation and dehydrogenation.
• Ability to work at temperatures over 1000 °C.
• High porosity of the converter (40% or more) and large pore diameter (1-3 µm) provide high gas permeability, which makes it possible to work with reagent flows over 150 l/h. This ensures high productivity in terms of synthesis gas (more than 120,000 l/h*dm³) in reforming processes.
• Converters provide hydrogen productivity of more than 1.4 l/h*cm² while well-known commercial counterparts do not exceed 0.01 l/h*cm².

Reviewer 2 Report

1. At lines 69-87 in page 2, are there any references related with this hybrid catalytic membrane reactor?  

2. From the introduction, there is no comment for purpose of this paper. You need to explain the contents of ref(32) and its application to this paper.

3. For further understanding of the main reaction, equation (8) should be moved to introduction or abstract.

 

4. You need to explain the catalytic membrane reactor or membrane-catalytic methods more precisely for further understanding of your system.  

5. At line 11 in page 1, direct hydrogenation of carbon monoxide →

direct hydrogenation of carbon monoxide with water.  

6. Abstract should be modified for better understanding.

Author Response

Reviewer 2, comment 1: In lines 69-87 on page 2, the hybrid catalytic membrane reactor is mentioned for the first time but the authors do not give any literary references to it, why?

 Authors: We do not agree with the comment of the honorable reviewer. The fact is that this publication is partly devoted to the development of such a reactor so we do not give references to it in the literary sources in the text.

 

Reviewer 2, comment 2: The introduction does not explain the objective of this paper. You need to explain the content of ref(32) and its usage in this article.

Authors: We do not agree with these comments of the honorable reviewer. Firstly, the goal of our work is to develop original porous ceramic catalytic converters for reforming and selective hydrogenation of carbon monoxide, as well as continuous membrane hydrogen extraction from the reactor during the production of synthesis gas in the processes of carbon dioxide, steam, and carbon dioxide-steam reforming of organic substrates.  This is literally stated in the last paragraph of the introduction to our article. Secondly, reference 32 is given in order to not repeat the description of the catalytic coatings applying by the sol-gel method in the text of this article which is vast.

 

Reviewer 2, comment 3: For better understanding, reaction (8) should be moved to the introduction or abstract.

Authors: We do not agree with the comment of the honorable reviewer. The fact is that our article is equally devoted to various processes for producing synthesis gas and hydrogen using catalytic converters but not specifically to the reaction of steam reforming of carbon monoxide. The section of results and discussions begins with it, and it includes other equally important reactions also given in the text.

 

Reviewer 2, comment 4: You need to be more specific about the catalytic membrane reactor and catalytic membrane methods in order to understand your system better.

Authors: We do not agree with the comment of the honorable reviewer. We have been conducting research in the field of catalytic processes carried out in porous media for more than 15 years. During this long time, we have published a large amount of material on this topic (articles, patents, monographs, abstracts of conferences, dissertations), a small part of which is cited in this manuscript. If necessary, it is possible to get known with them separately. Repetition of the material already presented will only increase the size of the article many times over.

 

Reviewer 2, comment 5: On page 1, line 11, the phrase "direct hydrogenation of carbon monoxide" should be replaced by "direct hydrogenation of carbon monoxide with water". Authors:  We agree with the comment of the honorable reviewer. The error has been corrected.

 

Reviewer 2, comment 6: The annotation to the article should be changed for better understanding.

Authors: We do not agree with the comment of the honorable reviewer. In our opinion, the annotation briefly outlines the main points of the relevant scientific information proposed for publication. Unfortunately, with such a formulation of the question, we do not really understand what exactly the honorable reviewer wants to see in the abstract that could improve its understanding.

Reviewer 3 Report

Dear authors, please find attached my comments to the manuscript

Comments for author File: Comments.pdf

Author Response

Reviewer 3, comment 1:

Introduction

• Which is the novelty of the paper. There are other works investigating similar aspects (which should be cited here, like 10.1016/j.cattod.2005.11.001 and 10.1007/s11244-008-9129-5), and it is not clear to me the original contribution of the present manuscript
• The state of the art on catalytic membrane reactors should be provided (like 10.3390/catal11060691)
• In my opinion, it is worth citing also aqueous phase reforming process, which is similar to steam reforming, but presents several advantages, it has been proposed also for feeding fuel cells, it carries out the water gas shift in the same reactor and it was studied into similar systems (10.1016/j.cattod.2020.04.024, 10.1016/j.cattod.2021.06.002, 10.1002/cssc.201301324)

 

Authors: We agree with the comment. Recommended articles are cited in the text. The originality of the manuscript proposed for publication lies in the development of catalytically active materials of a new type. And also in the possibility of their use in various processes for producing hydrogen-containing gas of various degrees of purity.

Reviewer 3, comment 2: Equation 5 raises questions both in terms of dimension (are you sure the units are seconds?) and in terms of meaning (why are you specifying the contact time of a single connection?)

	(5)

 

Authors: Answer to the first part of the question: This formula is correct for determining the contact time, with the clarification that it takes into account not the total volume of the catalytic layer, as is traditionally done in the case of using bulk catalysts, but only the working volume of the porous medium, in the calculation of which the porosity of the material is taken into account. This is done because, in the case of a converter, the contact time is determined by the internal volume of open channels, which, in turn, is calculated through the geometric volume of the working area of ​​the tubular converter, that is, through the volume of the cylinder multiplied by the porosity of the converter. As it is known the contact time (or in other words, the residence time of the reaction mixture in the reactor) is calculated by the formula:

where V is the volume of the reactor, and w is the flow rate of the reaction mixture. The ratio of temperatures and pressures, interpreted through the universal gas law,

is necessary to take into account the effect of thermal expansion of the reaction gas under the conditions of the reaction.

Answer to the second part of the question: We define the contact time of the reaction mixture fed into the reactor but not of the connection. Apparently, there is an incorrect translation of the term itself in the caption to the formula. We will correct this inaccuracy.

 

Reviewer 3, comment 3: The chemical equation (8) in the text would be more commonly referred to as "water gas shift reaction" rather than carbon monoxide steam reforming.

Authors: We agree with the comment and will correct it.

 

Reviewer 3, comment 4: Have you characterized the converter in terms of active site distribution, catalytic material deposition efficiency, etc.? In fact, the differences observed in Figure 4 could be attributed to such phenomena.

Authors: We have carried out extensive structural studies of our converters in the context of your question. These studies have previously been published in our papers, links to some of which are given in the text. However, studies specifically of the samples presented in Fig. 4, were not made by us. Nevertheless, based on the structural data on catalytic systems of other compositions and drawing an analogy with these in view of the similarity of synthesis methods, we can agree with the conclusions made by honorable reviewer with the only clarification that the distribution of active centers over the surface depends on the natural features of the materials used as well as converters preparation methods.

 

Reviewer 3, comment 5: Have you determined the stability of the membrane?

Authors: Yes, stability in laboratory tests in various processes was determined many times by us. Studies have shown that during the experimental session, which lasted about 50 hours, our converters do not lose their activity. Beyond this time, no determination was done. However, the possibility of oxidative regeneration of converters with air oxygen makes it possible to effectively remove carbon deposits from the surface of the catalytic material if necessary.

 

Reviewer 3, comment 6: It might be useful to present a figure similar to Fig. 6 showing the effect of hydrogen removal in the membrane mode on the conversion of ethanol during its reforming.

Authors: This figure is not necessary since in the traditional mode without hydrogen removal the conversion of ethanol under process conditions is already 100%. The membrane mode makes it possible to extract ultrapure hydrogen from the reaction zone but it cannot affect the conversion of the substrate in any way.

 

Reviewer 3, comment 7: For each type of processed raw material, the degree of hydrogen purity is always indicated by the authors as 99.9999%? This aspect should be made clearer as it is not clear from the presented results.

Authors: The fact is that the purity of ultrapure hydrogen is determined by the structural properties of the palladium-ruthenium membrane used to remove it, and not by the type of raw material being processed. For this very reason, the purity of hydrogen in processes with its extraction through the membrane is always the same.

Author Response File: Author Response.pdf