Hydrogen Production | Steam Methane Reforming (Part 1)

In the previous article, I have illustrated the importance of hydrogen for big companies and governments. In this article, I would like to bring a piece of information about its production.

Due to the transition of energy from fossil fuels, hydrogen offers a good supply of energy in the future. Therefore, it is essential to find out how we can generate this fuel. Hydrogen with high energy density was described as helpful in leading the spacecraft and rockets by NASA.

Producing hydrogen has several manners, which can be listed as below:

• Steam Methane Reforming
• Coal gasification
• Electrolysis
• Biomass gasification
• Thermochemical water splitting
• Bio-hydrogen production
• Direct/Indirect bio-photolysis
• Photo/Dark fermentation
• Bio-catalyzed electrolysis

We will discuss all the methods as mentioned earlier. In this article, we will discuss the first method, steam methane reforming, and the rest will be in future articles.

Steam methane reforming

Natural gas is not something new, but something that most people heard about it related to fossil fuels. Describing how natural gas is made is out of our aim in this article. This method can be considered the main method utilized in the 21st century; it can be realized when we inform that roughly 96% of the United States hydrogen production is produced by this method. Nearly 50% of the worldwide need for hydrogen (the estimation is 55 x 106 tons/year) is obtained from natural gas.

Natural gas mainly comprises methane (CH4) can be blended with steam using thermal processes such as steam methane reforming and partial oxidation to generate hydrogen. Here, the temperature of the steam is high (about 700C to 1000C) with a pressure of (3–25bar) to react with methane (CH4) when a catalyst exists.

Two fairly extreme conditions in the steam reforming process are listed below:

1. Reducing gas production involves primary steam reforming at low pressure and high temperature (roughly 50psi and more than 1800F) and a low steam-to-hydrocarbon feed ratio.
2. Substitute natural gas production that demands the highest pressure (as much as possible), the lowest steam-to-carbon ratio (moles of steam/carbon atom in the feedstock) likely, and the lowest temperature (as low as possible)

At the moment, converting natural gas to hydrogen is performing in a conventional reformer (CR) that is followed by a water-gas shift (WGS) reactor (temperature: high, pressure: low) and equipment to separate and purify H2 (pressure swing adsorption (PSA), preferential oxidation reactor (PrOx), …).

A schematic view can be illustrated as below:

Figure 1. Scheme of the conventional multi-stages process for hydrogen production by Methane Steam Reforming.

Methane and steam are provided to the conventional reformer (CR), where three reactions (Eq. 1–3) are performing under extreme conditions (temperature and pressure) over Ni-based catalysts.

Eq1. CH4+H2O — > CO+3H2

ΔH298K = 206 kJ/mol

Eq2. CH4+2H2O — > CO2+4H2

ΔH298K = 165 kJ/mol

Eq3. CH+H2O — > CO2+H2

ΔH298K = -41 kJ/mol

A hydrogen-rich gas mixture with significant CO content is generated in this process. Therefore, two WGS reactors serialized in a series are utilized to decrease the reformed stream’s CO content (Eq. 3) and increase the hydrogen content simultaneously.

NB. Due to methane being the main content of natural gas, it is prevalent to use methane instead in methane steam reforming (MSR).

Methane steam reforming kinetic

In the past, the research on MSR reaction used to be focused on the preparation of catalyst and the process analysis; however, both the kinetics and the mechanism of reaction were ignored, alongside the consequence of the scarcity of information. Thus, recently, several attempts have been realized with the intent to propose coherent reaction mechanisms and kinetic data.

For example, one of the first precise studies on MSR kinetics was performed by Temkin et al. [1]. In this study, they managed the experimental tests on nickel foil at atmospheric pressure and by altering temperature from 470 to 900C. Particularly, they explored that at the highest temperature, the reaction followed a first-order equation, and on the other side, at a lower temperature, a lag in the rate of H2 formation was detected.

This article summarised the importance of hydrogen as the future fuel during the energy transition. Also, a review of hydrogen production and its methods was given, and finally, the most widespread technique which is obtained widely explained briefly. Other methodologies and techniques contents will be prepared soon.

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1. Temkin, M., The kinetics of some industrial heterogeneous catalytic reactions, in Advances in Catalysis. 1979, Elsevier. p. 173–291.