Educational Modules on the Power-to-Gas ... - ACS Publications

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Educational Modules on the Power-to-Gas Concept Demonstrate a Path to Renewable Energy Futures Isabel Rubner,*,† Ashton J. Berry,*,‡ Theodor Grofe,† and Marco Oetken† †

J. Chem. Educ. Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/10/19. For personal use only.

Institut für Chemie, Physik, Technik und ihre Didaktiken, Pädagogische Hochschule Freiburg, Kunzenweg 21, 79117 Freiburg, Germany ‡ University of Seychelles, Anse Royale, Mahé, Seychelles ABSTRACT: A significant challenge for the global community is the increasing demand for clean and renewable energy technologies. However, a lack of knowledge of these technologies threatens to impede their adoption. The development of cheap, effective, and easy-to-use chemical and electrochemical storage technologies is crucial if countries are to move away from fossil fuel electricity production. In this paper, we describe simple classroom-based learning systems that can be used to demonstrate the power-to-gas concept and its ability to greatly enhance the practicability and sustainability of other renewable energy systems. Most renewable energy systems can only produce energy sporadically and at specific locations; however, the power-to-gas concept uses hydrogen, obtained by electrolysis, to produce methane via the Sabatier reaction. We also demonstrate how this “dream reaction”through the use of renewable energies such as solar and windcan produce industrially and energetically desirable methane from hydrogen and carbon dioxide. The power-to-gas concept can be easily replicated in both educational and informal settings to encourage more grassroots and scholastic interest in the development of these vital technologies. KEYWORDS: General Public, First-Year Undergraduate/General, Demonstrations, Hands-On Learning/Manipulatives, Applications of Chemistry, Mechanisms of Reactions, Electrolytic/Galvanic Cells/Potentials, Gas Chromatography, Green Chemistry, Hydrogen Bonding, Water/Water Chemistry

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INTRODUCTION

Together these factors have the potential to provide communities of various scales, locations, and stages of economic development, with a roadmap by which their transition away from nonrenewable energy sources can be achieved.14 This is as true for developed countries as it is for developing countries, with both designing and investing in renewable energy technologies at a rapid rate.16,17 A range of organizations within government, nongovernment, research, education, industry, and business sectors are investing significantly in these technologies.18 However, the limited knowledge and fluency of community members on the function and application of current and future renewable energy technologies is often a barrier impeding their acceptance, integration, and use.19 This educational shortfall needs to be addressed if the dangerous consequences of climate change are to be avoided.20,21 Thus, it is essential to embed the importance and use of renewable energy technologies, such as the power-to-gas concept, into the educational systems globally.22 In this paper, we describe the power-to-gas concept and its relevance to educational facilities and other capacity-building stakeholders, such as government agencies and conservation groups. To do this, we provide an example experiment of Sabatier’s reaction. Incorporation of this experiment into existing science education curriculum provides current and future generations with the capacity to develop and implement

The transition to renewable energies is a very important subject throughout the world.1 The goal of this “energy transition” is to enable current and future generations to sustainably move toward energy grids that are based on renewable energies.2,3 Enabling this transition requires introducing students to renewable energy technologies.4 It also requires cross-disciplinary cooperation from those involved in the fields of electromagnetism, thermodynamics, logistics, and education.5 International collaborations are also needed between external experts and local stakeholders to build human resource capacity and awareness.6 Given this cooperation, renewable energy sources could replace nonrenewable energy sources (fossil fuels, nuclear fuels, etc.) and thereby effectively reduce carbon dioxide emissions while conferring additional environmental benefits.7 However, renewable energy technologies can carry with them a critical drawback: many of these technologies are intermittent, only producing energy when the wind blows or when the sun shines.8−10 This presents significant challenges for maintaining load balance to ensure power network stability and reliability.11 Therefore, the success of this transition to renewables globally depends on two interdependent factors: (i) the additional use of energy production and storage technologies that increase the cost-effectiveness, reliability, and convenience of renewable energy production12−14 and (ii) the use of existing educational programs to raise awareness of the issues surrounding energy security and the technical capacity needed to adopt and maintain readily available renewable energy technologies.15 © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: November 13, 2017 Revised: November 30, 2018

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DOI: 10.1021/acs.jchemed.7b00865 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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Figure 1. Left panel: Educational materials/equipment demonstrating the production of hydrogen using a solar panel to power the electrolysis of water. Right panel: Educational materials/equipment demonstrating the production of hydrogen using a wind turbine to power the electrolysis of water.

limited to rural areas where a steady and cheap supply of manure, vegetation, and water is available.39 Large-scale industrial biogas production is also only economically viable if large volumes of inexpensive materials, such as sewage, manure, and agricultural products, can be guaranteed.40 Thus, as the power-to-gas concept is not reliant on these limiting factors, it can, when combined with, for example, photovoltaic and wind technologies, provide a feasible alternative for the production of cheap and reliable methane. The ability to produce cheap and reliable methane to support sustainable development is a key feature of the powerto-gas concept.3 The concept provides the potential to manage localized energy resources and reduce dependence on externally traded fossil fuels, which in turn contributes to improved economic stability.35 In addition to economic stability, avoiding potential habitat loss from mining and the expense of ecosystem restoration is a key benefit for countries reliant on fragile natural resources for many other aspects of their economy.41,42 For example, in many small island developing states (SIDS), tourism and fishing form the largest pillars of the economy.43 Mining activities that degrade healthy ecosystems are not compatible with these economic structures.44 Significant social benefits are also gained through the substitution of fossil fuel products for renewables.45 The substantial savings made from the reduction of diesel fuel imports may enhance the resilience of society to increasing global fossil fuel prices, and the savings made could be reinvested into other socially beneficial pursuits, such as education, healthcare, and the development of sustainable livelihoods.46 Such advancements would enable countries without significant infrastructure investment in fossil fuels to take advantage of the renewable energy revolution.47 More industrialized countries, on the other hand, need to make difficult investment decisions on how to accommodate renewable energy technologies into their existing energy systems.48 The extent of investment in fossil fuel infrastructure and resources can make it difficult for developed countries to shift away from their fossil fuel dependence while financial returns on such enormous investments have yet to be realized.49,50 The lack of investment in these potentially

sustainable social and economic development models that include renewable energy technologies and the multidisciplinary skills necessary for their application.23,24 This is particularly important in developing countries where sustainable development and livelihoods are often restricted by a lack of energy supply and security.25,26 Indeed, sustainable development would not be possible in any country without a society’s ability to increase its electricity consumption and therefore production when required.27 Thus, to ensure the eventual take-up and adoption of renewable energy technologies, greater access is required, through education, to technologies that not only are cleaner, cheaper, and reliable substitutes but also allow for continued economic growth and the alleviation of poverty.28

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BENEFITS OF RENEWABLE TECHNOLOGIES The benefits of this renewable energy transition are numerous. Many countries currently struggle with the financial burden of supplying power to their populations using traditional energy sources.26,29,30 High fuel transportation costs mean remote island nations, for example, pay some of the highest electricity production costs in the world.31 In many instances, outdated and unreliable grid systems supplied by expensive-to-operate diesel-powered generators comprise the sole source of electricity.32,33 For example, The Republic of Seychelles generates almost 100% of its electricity from heavy and light fuel oil diesel engines.34 Sole reliance on fossil fuels also results in very high sensitivity to crude oil price increases.35 As such, renewable energy technologies that reduce dependence on fossil fuels promise a more sustainable future less reliant on international energy markets.36 Methane is currently produced and used in a variety of ways as an energy source for primarily cooking, heating, and lighting.37 The production of biogas through the fermentation of vegetation and waste is one of the most popular processes.38 However, although of great value to developing countries as a viable source of energy, providing sufficient biomass and the correct temperatures for the fermentation process is not always possible. For example, the fermentation process is only feasible in areas where the system temperature can be maintained above 10 °C.12,38 Small-scale biogas production is also typically B



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Figure 2. Principle of the power-to-gas concept applied to an industry-scale production suitable for use in SIDS. Reproduced with permission from ref 67.

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stranded investments provides one of the many advantages available to emerging economies over more developed nations. As such, small island developing states, for example, are ideal locations for pilot projects in renewable technology, which could then be transferred and up-scaled for use in other parts of the world.35

PROCESS OF METHANATION

The second phase of the power-to-gas concept overcomes the hydrogen storage issue by using the following process: hydrogen collected from the renewable-energy-based electrolysis of water is further refined by the Sabatier reaction as it reacts with carbon dioxide or carbon monoxide to form methane.63,64 Carbon dioxide essentially becomes the raw material for the synthesis of renewable energy in the form of methane rather than as an industrial waste product accelerating the extent and rate of climate change.65 Unlike hydrogen, methane requires no specialized infrastructure to be utilized in the production of energy. Methane, once purified, can be directly injected into a range of storage mechanisms, where large quantities can be kept briefly or for a very long time.53,66 Unlike hydrogen, methane can be easily stored in existing tanks, pipes, gas grids, depleted gas fields, and other underground cavities for seasonal and strategic storage. Methane can also be distributed to industries and households through the existing local gas grids.67 Paul Sabatier discovered the CO2 methanation reaction over 100 years ago in 1902,68 yet its importance continues today, having found new usefulness in energy storage systems. As the ability of a nation to manufacture its own methane could allow it to become both energetically and politically independent,69 the Sabatier reaction holds great relevance in modern times and particularly for SIDS, where imported fuels are so expensive. The benefits of the power-to-gas concept are fully realized once scaled up to an industrialized process (Figure 2). The Sabatier reaction can be expressed in these two forms:

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PRODUCTION OF HYDROGEN USING RENEWABLE ENERGY The power-to-gas concept approaches the demand for renewable energy through two consecutive gas production phases. The first phase of the power-to-gas concept condenses energy generated from a renewable source (solar, wind, hydropower, etc.) into a more convenient and storable gaseous form, such as hydrogen.51 In practice, this process is accomplished by the electrolysis of water, with a renewable energy source powering the reaction.52,53 The hydrogen generated from this electrolysis can potentially be used immediately or stored for use at another time.54,55 Figure 1 demonstrates a simple system for the renewable-energy-based electrolysis of water forming hydrogen in a classroom setting. In the example above, a solar cell is connected to an electrolyzer with cables (Figure 1, left). By exposing the solar cell to sunlight, liquid water is dissociated into hydrogen gas (negative pole) and oxygen gas (positive pole). The solar cell can also be energized to generate hydrogen using a light source. The same principle is shown with wind power (Figure 1, right), which can also power the electrolysis of water. As the demonstration progresses, the production of gas is easily visible in the tanks. At the conclusion of the experiment, students can clearly see that the amount of hydrogen is twice the amount of oxygen. The experiment clearly demonstrates the molecular formula of water. Although hydrogen has a number of advantages in that it can be used for energy generation in a variety of ways (heat source, fuel cells, etc.)56 and produces the nontoxic combustion product of water,57 it, however, diffuses easily into metals, such as steel, and results in embrittlement.58 Due to this issue, hydrogen is problematic and expensive to store; it requires specialized pressure tanks that are resistant to embrittlement and that provide safe storage.59−62

CO2 + 4H 2 F CH4 + 2H 2O ΔH = −252.9 kJ/mol

(1)

CO + 3H 2 F CH4 + H 2O ΔH = −250.2 kJ/mol C

(2) DOI: 10.1021/acs.jchemed.7b00865 J. Chem. Educ. XXXX, XXX, XXX−XXX


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PRODUCTION OF RENEWABLE ENERGY IN THE FORM OF METHANE IN THE CLASSROOM: THE PROCESS OF METHANATION Methanation reactions are typically exothermic equilibrium reactions with an appreciable activation energy, and thus the use of an appropriate catalyst (typically nickel or ruthenium) is necessary.70 Reaction temperature is also an important consideration when utilizing these reactions, and normally (depending on the choice of material used), the catalyst needs to be heated to approximately 300 °C.71 To take advantage of the equilibrium reaction, compression must be applied in order to drive the reaction toward products as predicted by Le Châtelier’s principle.53 The nature of these reactions allows this important demonstration to be reproduced with the basic equipment already found in most school settings (Figure 3).72 As a safety consideration, carbon dioxide (eq 1) is used as a reactant instead of carbon monoxide (eq 2).

the creation of more methane. Students can watch the reaction taking place by observing the reduction in overall gas volume as the reaction progresses. The following experiment provides an example that can be easily reproduced by students. Experiment 1: Sabatier’s Reaction Using a Nickel Catalyst

Materials: Stands or alternatively a whiteboard (magnetic board) with clips; two 100 mL syringes (luer-lock type); three short pieces of hose; 3 or 4 three-way valves; an injection plug; quartz tube (l = 10 cm, d = 1 cm); glass wool; 2 luer-lock adapters; carbon dioxide (GHS04); hydrogen (GHS02, GHS04); nickel−zeolite (GHS02, GHS08) catalytic materials (experimental sets including the catalytic unit can be ordered online; perforated plug (bored hole 1.5 mm); micro burner (e.g., proxxon); temperature sensor (1.5 mm; e.g., Leybold Nr. 529676); and temperature indicator (e.g., Greisinger GTH 1150). Safety Information: Hydrogen is an extremely flammable gas. It may form explosive mixtures with air. The following safety precautionary codes should be referred to when carrying out these experiments: P202−P210, P271, P403, P377, and P381. Chemical dangers include the following: Heating may cause violent combustion or explosion. Reactions occur violently with air, oxygen, halogens, and strong oxidants, causing fire and an explosion hazard. Metal catalysts, such as platinum and nickel, greatly enhance these reactions. For these reasons, it is important to flush the apparatus with hydrogen before the start of the reaction to strip the oxygen out of the system. Procedure: Load the catalyst into the quartz tube (observe safety issues as detailed above). Fill both ends of the quartz pipe with glass wool, and finish the end with a piece of silicone tube and a luer-lock adapter. Build the apparatus as shown in Figure 4. A small amount (e.g., 200 mL) of hydrogen is filled from the hydrogen gas bottle into a syringe or a balloon that is closed by a three-way valve. The luer-lock adapter enables gas-tight working and creates a closed system. Please double check that the luer-lock adapter is closed correctly so that hydrogen cannot escape. Finally, introduce the 80 mL of hydrogen into one of the syringes and 20 mL of carbon dioxide into the other syringe. Afterward, mix the reactants in the apparatus by compressing the syringe contents of the first syringe into the other, so the volume of both syringes makes a total of 100 mL.

Figure 3. Catalytic unit with nickel on zeolith and glass wool at both sides.

Hydrogen and carbon dioxide are used in a 4:1 stoichiometric ratio (eq 1) in conjunction with a nickel− zeolite catalyst. Water produced as a byproduct of the reaction is absorbed by the zeolite, further pushing equilibrium toward

Figure 4. Experimental setup. Left: Scheme. Right: Photograph as attached to whiteboard.73 D



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Figure 5. Gas chromatography of the reactants and products. Blue: reactants, 80% H2, 20% CO2. Red: products, ca. 20% H2, 80% CH4. Green: 100% CH4. Dark green: 100% H2.

heat conductivity detector and the flow rate of 150 l/h (for additional information on the Kappenberg GC, see ref 74). Because heat conductivity is specific to each gas, a comparison of the product peaks to the 100% peak of the pure substance is needed. Without this comparison, accurate quantitative statements are not possible. Thus, with very basic equipment, one can generate methane gas at 80% purity, an outcome with significant application in energy production. The teaching process can now follow another examination of the reactants.

Heat the catalyst for a few seconds with the micro burner until the temperature indicator shows 300 °C. Once the temperature is reached, the gas mixture is passed through the catalyst by compressing the syringe containing the reactants with a rate of approximately 3 mL/s. Repeat this process 8−12 times while continuously heating the catalyst with the burner to maintain the temperature of 300 °C. If the catalyst gets too hot (over 600 °C), the catalytic activity will decrease because solid carbon may coat the catalyst (Bosch reaction). Observations: The total gas volume should decrease from 100 mL to approximately 20−30 mL; the formation of liquid droplets should be observed in the connecting tubes next to the quartz tube including the catalyst. Evaluation: The exothermic reaction of carbon dioxide and hydrogen yields methane and water as reaction products. The reaction is considered to be complete when the volume of the gas remains constant in the syringe and when all the product is in one syringe. The liquid formed can be identified as water through the use of water detection test (Watesmo) paper. Results: In order to identify the resulting product as methane, a gas chromatograph (GC) can be used. Three milliliters of the gas produced by the reaction can be collected using a small syringe with cannula through the injection plug that is located at the three-way valve (Figure 4, left; yellow injection plug). A small amount of the resulting product can be injected into a GC in order to identify their components. From the GC’s output (Figure 5), one can verify the change from the reactants in the Sabatier process (hydrogen and carbon dioxide) to the product (methane) and some remaining hydrogen. The hydrogen peak in the product line is clearly lower than the reactants’ line. In addition, there is a higher concentration of carbon dioxide in the reactants than in the products. These results can be further confirmed by the use of the limewater test for carbon dioxide. The successful reaction produces a negative result on this test. The GC measurements taken in this experiment (Kappenberg system) work by heat conductivity detection. The Kappenberg GC is a low-cost school GC that works with a

Experiment 2: Differentiation of the Substances on the Basis of the Combustion Enthalpy

At this point of the teaching unit, it is interesting to view the reaction in terms of the energy produced during combustion (eqs 3 and 4). The examination of the reactants relating to the combustion enthalpy shows thatusing the same amounts of the gaseshydrogen delivers considerably less energy than methane: 2H 2(g) + O2 (g) → 2H 2O(l) ΔH = −286 kJ/mol H 2

(3)

CH4(g) + 2O2 (g) → CO2 (g) + 2H 2O(l) ΔH = −890 kJ/mol CH4

(4)

Materials: Two 20 mL syringes with three-way valves (and plugs); two 15 cm Heidelberger lengthening pieces; 2 injection cannulas 1.2 × 40 mm (metal tube used to inject reactants into test tubes); 2 test tubes 75 × 12 mm (Fiolax); boiling stones; micro burner; reactant mixture (80% hydrogen, 20% carbon dioxide); product mixture (p.e. 80% methane, p.e. 20% hydrogen). Procedure: Syringe 1 is filled with 20 mL of the reactant mixture; syringe 2, with 20 mL of the product mixture. The used gases are taken from the gas bottle with a syringe that is closed gas-tight by a three-way valve. One syringe is filled with carbon dioxide and another with hydrogen. From these syringes, the necessary amounts of gases are filled in the E



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hydrogen). Therefore, the combustion of the main reactant hydrogen produces less energy than the combustion of the main product methane. The presence or absence of carbon atoms affects the color of the flame. If there are no carbon atoms, as in this case, the flame is blue. With carbon atoms, the flame is yellow. Hydrogen has a high heat conductivity that causes the glowing of the cannula. The heat conductivity of methane (product) is lower. In the context of experiment 2, it can be easily demonstrated to the students that the production of methane from hydrogen allows for the manufacture of an energetically upgraded energy storage product (methane), when compared to hydrogen. Videos showing the procedure of the methanation and the combustion enthalpy of hydrogen and methane can be accessed online.75

examination syringe. The connection with the lengthening pieces is constructed as shown in Figures 6 and 7. With the

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HAZARDS Hydrogen is an extremely flammable gas. It may form explosive mixtures with air. The following safety precautionary statements76 should be referred to when carrying out these experiments: P202−P210, P271, P403, P377, and P381.

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Figure 6. Experimental setup of combustion enthalpy attached to a whiteboard.

CONCLUSION One of the most important issues facing current and future generations is the creation of renewable energy infrastructure, policies, and social norms that enable the sustainable production of energy that meets the needs of growing global populations. Incorporating the use and benefits of renewable energy technologies into educational programs is vitally important to enabling this transition from fossil-fuel-based economies. In this article, we demonstrate how the power-togas concept can be simply and effectively demonstrated in the classroom as a viable means of energy production, one that is not only economically beneficial but suggests a way to mitigate the rate of increase in atmospheric carbon dioxide. Hydrogen can be produced on-demand using photovoltaic cells as an energy source rather than fossil fuels. As an alternative to being stored, hydrogen can be produced as required and rapidly transformed to create methane. The methane can be used immediately or stored for later use in a number of ways and at a cost far less than hydrogen. Methane, in contrast to hydrogen, does not require specialized equipment or tanks and can be conveyed and stored in the same way as propane or butane. As such, the power-to-gas concept can have immediate environmental and political benefits through its incorporation into existing educational and energy networks. However, without proper training and implementation, the expertise required to use such solutions is simply out of reach. Thus, an emphasis on impactful and practical education in renewable energy technologies is fundamental to ensuring clean and sustainable energy production into the future at both local and international scales. With careful dissemination, education may prove to be the simplest route in providing solutions to complex global energy supply issues.

Figure 7. Scheme description of the experimental setup of combustion enthalpy.

luer-lock adaption, the system is gas-tight. The test tubes are filled with 0.6 mL of water (1 mL syringe used) and one boiling stone to enhance smooth boiling. It is helpful for the observation to use a black background behind the flames so that the flames can be seen more easily. The gas is pressed slowly (e.g., approximately 1 mL/s) out of the syringe and ignited. The burning gas heats the water. After completely burning the gas from the syringe, water will be observed. Observations: At the combustion of 20 mL of the reactants, the water is not boiling, but with the product gas, it is. The flame of the reactants is not visible (colorless), and the top of the cannula glows. The flame of the product gas is visible and colored yellow, and the top of the cannula is not glowing. Results: The combustion of the reactant mixture (hydrogen and carbon dioxide) supplies considerably less energy than the combustion of the product gas mixture (methane and

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Ashton J. Berry: 0000-0001-5881-7994 F



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Notes

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The authors declare no competing financial interest.

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