Article

The Hy-C process (thermal decomposition of natural gas) potentially the lowest cost source of hydrogen with the least CO2 emission

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Abstract

The abundance of natural gas as a natural resource and its high hydrogen content make it a prime feedstock candidate for a low cost supply of hydrogen. The thermal decomposition of natural gas by methane decomposition produces carbon and hydrogen. Conventional steam reforming of natural gas produces CO2 and hydrogen and requires more process energy. Methane decomposition produces the least amount of greenhouse gas CO2 emissions per unit of hydrogen and can be totally eliminated when the carbon produced is sequestered or sold as a material.

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... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. ...
... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. These various methods are at different levels of maturity. ...
... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. These various methods are at different levels of maturity. ...
Article
Full-text available
The adoption of new environmentally responsible technologies, as well as, energy efficiency improvements in equipment and processes help to reduce CO2 rate emission into the atmosphere, contributing in delaying the consequences of intensive use of fossil fuels. For more effective actions, it is necessary to make the transition from the fossil-based to the renewable source economy. In this context, hydrogen fuel has a special role as clean vector of energy. Hydrogen has the potential to be decisive in mitigating greenhouse gas emissions, but fossil fuels high profitability due to global energy dependency actually drives the global economy. While renewable energy sources are not worldwide fully established, new technologies should be developed and used for the recovery of energetic streams nowadays wasted, to decarbonize hydrocarbons and to improve systems efficiency creating a path that can help nations and industries in the needed energy economy transition. Hydrogen gas can be generated by various methods from different sources such as coal and water. Currently, almost all of the hydrogen production is for industrial purpose and comes from the Steam Reforming, while the use of hydrogen in fuel cells is only incipient. The article analysis the plasma pyrolysis of hydrocarbons as a decarbonization option to contribute as a step towards hydrogen economy. It presents the Carbon Black and Hydrogen Process (CB&H Process) as an alternative option for hydrogen generation at large scale facility, suitable for supplying large amounts of high-purity carbon in elemental form. CB&H Process refers to a plant with hydrogen thermal plasma reactor able to decompose Hydrocarbons (HC's) into Hydrogen (H2) and Carbon Black (CB), a cleaner technology than its competing processes, capable of generating two products with high added value. Considering the Brazilian context in which more than 80% of the generated electricity comes from renewable sources, the use of electricity as one of the inputs in the process does not compromise the objective of reducing greenhouse gas emissions. It is important to consider that the use of renewable energy to produce two products derived from fossil fuels in a clean way represents integration of technologies into a more efficient system and an arrangement that contributes to the transition from fossil fuels to renewables. The economic viability of the CB&H process as a hydrogen generation unit (centralized) for refining applications also depends on the cost of hydrogen production by competing processes. Steam Methane Reforming (SMR) is a widespread method that produces twice the amount of hydrogen generated by natural gas plasma pyrolysis, but it emits CO2 gas and consumes water, while CB&H process produces solid carbon. For this reason, the paper seeks the carbon production cost by plasma pyrolysis as a breakeven point for large-scale hydrogen generation without water consumption and carbon dioxide emissions.
... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. ...
... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. These various methods are at different levels of maturity. ...
... For the occurrence of methane decomposition reaction (Equation (2)) and considering 20% inefficiency, an energy consumption of only 5.3% of the higher heating value of the methane combustion is necessary [12]. The energy to the pyrolysis process of NG can be supplied in several ways, for example: through the partial combustion of NG itself [12,13], by combustion of part of the hydrogen generated [12], by combustion of part of the carbon produced [12e16], by electrical heating [18,19] or even solar furnaces [20,40,57] and using electricity to forming plasmas. These various methods are at different levels of maturity. ...
Poster
Full-text available
Analysis about Carbon Black and Hydrogen Process (CB&H Process)-a SINTEF/KVAERNER technology-as alternative option for Hydrogen generation at large scale facility without consumption of water and CO 2 emissions and proper to supply large quantities of high pureness carbon at elemental form. CB&H Process refers a plant with thermal plasma reactor to decompose Hydrocarbons (HC's) into Hydrogen(H 2) and Carbon Black (CB).
... [3] [4]. C) " Decarbonisation " , in which the carbon of the fuel is removed prior to combustion, and the fuel heating value is transferred to hydrogen [5] [6]. ...
... [3,4]. C) " Decarbonisation " , in which the carbon of the fuel is removed prior to combustion, and the fuel heating value is transferred to hydrogen [5,6]. These concepts have been compared in several papers [e.g. ...
... PROCESS DESCRIPTIONFigure 1 shows the process configuration of case 2. Selected stream data is presented inTable 1. The hydrogen-rich reformed gas is combusted in a gas turbine (GT), which is integrated with the decarbonisation process [5]. A model of the gas turbine type GE9351FA from General Electric was used in the simulations. ...
Article
A concept for capturing and sequestering CO 2 from a natural gas fired combined cycle power plant is presented. The present approach is to decarbonise the fuel prior to combustion by reforming natural gas, producing a hydrogen-rich fuel. The reforming process consists of an air-blown pressurised auto-thermal reformer that produces a gas containing H 2 , CO and a small fraction of CH 4 as combustible components. The gas is then led through a water gas shift reactor, where the equilibrium of CO and H 2 O is shifted towards CO 2 and H 2 . The CO 2 is then captured from the resulting gas by chemical absorption. The gas turbine of this system is then fed with a fuel gas containing approximately 50% H 2 . In order to achieve acceptable level of fuel-to-electricity conversion efficiency, this kind of process is attractive because of the possibility of process integration between the combined cycle and the reforming process. A comparison is made between a "standard" combined cycle and the current process with CO 2 -removal. This study also comprise an investigation of using a lower pressure level in the reforming section than in the gas turbine combustor and the impact of reduced steam/carbon ratio in the main reformer.
... Hydrogen is a clean energy carrier whose combustion results only in the formation of water, thus avoiding the production of CO x and other contaminants and pollutants [1]. However, hydrogen cannot be found in a free state in our planet, so it must be produced from other compounds (such as, hydrocarbons, biomass, and water), which requires the external supply of energy. ...
... An attractive alternative to produce hydrogen is the decomposition of methane (DeCH 4 ) according to the following reaction [3][4][5]: CH 4 (g)→C (s) + 2 H 2 (g) ΔH 0 = 75.6 kJ⋅mol − 1 (1) As in this process carbon is extracted from methane in solid form, it is possible to produce H 2 with high purity and without greenhouse gases (GHG) emissions. In addition, a variety of applications have been proposed for the carbonaceous product, including soil amendment, building and construction material and the manufacture of nanostructured carbonaceous solids, such as carbon nanotubes and nanofibers, with advanced properties. ...
Article
Methane decomposition (DeCH4) over solid catalysts is an interesting route for the production of hydrogen free of CO2 emissions. Moreover, it could lead to a negative carbon balance if biogas/biomethane is used as feedstock. However, it is limited by the huge amounts of carbon that are deposited over the catalyst causing its deactivation and hindering its regeneration, which makes necessary the development of low-cost and durable catalytic systems. This work reports the use of different silica materials fully produced from rice husk, i.e. without incorporating any external phase or component, as DeCH4 catalysts. The highest catalytic activity has been found for the silica samples showing large BET surface area and amorphous nature. These properties favor the generation of the actual DeCH4 active sites (-Si-C- species), shortening the induction time detected at the beginning of the reaction tests. The nano-silica materials produced from acid-washed rice husk exhibit a remarkable resistance against deactivation, affording an almost constant reaction rate at long times on stream. This fact is assigned to the presence of large mesopores that facilitate the growth of the carbons deposits towards the outer part of the catalyst particles. The results here reported show the great potential of rice husk-derived nano-silica to overcome several of the most relevant limitations that currently exist for the commercial deployment of hydrogen production by catalytic DeCH4, as a consequence of the low cost and durable activity of these sustainable materials.
... C) "Decarbonisation", in which the carbon of the fuel is removed prior to combustion, and the fuel heating value is transferred to hydrogen. This concept can be applied both for natural gas by combining reforming, a water gas shift reaction and CO 2 removal process (Moru, 1992;Anon, 1992;Steinberg, 1995;Gaudernack and Lynum, 1997;IEA, 1998;Audus et al., 1999), and in a similar manner also for coal where gasification replaces the reforming process (Pruschek et al., 1995;Meratla, 1997;Chiesa, 1999). ...
... Selected stream data is presented in Table 1. The hydrogen-rich reformed gas is combusted in a gas turbine (GT), which is integrated with the decarbonisation process (Moru, 1992;Anon, 1992;Steinberg, 1995;Gaudernack and Lynum, 1997;IEA, 1998;Audus et al., 1999). A model of the gas turbine type GE9351FA from General Electric was used in the simulations. ...
Article
Full-text available
A concept for capturing and sequestering CO2 from a natural gas fired combined cycle power plant is presented. The present approach is to decarbonise the fuel prior to combustion by reforming natural gas, producing a hydrogen-rich fuel. The reforming process consists of an air-blown pressurised auto-thermal reformer that produces a gas containing H2, CO and a small fraction of CH4 as combustible components. The gas is then led through a water gas shift reactor, where the equilibrium of CO and H2O is shifted towards CO2 and H2. The CO2 is then captured from the resulting gas by chemical absorption. The gas turbine of this system is then fed with a fuel gas containing approximately 50% H2. In order to achieve acceptable level of fuel-to-electricity conversion efficiency, this kind of process is attractive because of the possibility of process integration between the combined cycle and the reforming process. A comparison is made between a “standard” combined cycle and the current process with CO2-removal. This study also comprise an investigation of using a lower pressure level in the reforming section than in the gas turbine combustor and the impact of reduced steam/carbon ratio in the main reformer. The impact on gas turbine operation because of massive air bleed and the use of a hydrogen rich fuel is discussed.
... C) Decarbonisation which comprise an autothermal reforming reactor (ATR) with air-blown catalytic partial oxidation of natural gas, water-shift reactors and a high pressure CO 2 removal process based on chemical absorption. The hydrogen-rich reformed gas is combusted in a gas turbine CC, which is integrated (air, steam) with the decarbonisation process [5,8,9]. There is also integration between the power plant and the reforming process with respect to preheating of feed streams in the reformer. ...
... The reaction in Eq. (7) supplies the heat required for the reaction given in Eq. (8). The natural gas feed is desulphurised and prereformed before the ATR reactor (at about 500 °C). ...
Article
Full-text available
Three concepts for collecting CO2 from natural gas fired combined gas/steam turbine power plants are evaluated and compared in this paper: A) Separation of CO2 from exhaust gas coming from a standard gas turbine power plant, using chemical absorption by amine solutions. B) Gas Turbine combined cycle using a semi-closed gas turbine with a near to stoichiometric combustion with oxygen from an air separation unit as oxidising agent, producing CO2 and water vapour as the combustion products. The gas turbine working fluid is mainly CO2 . C) Decarbonisation which comprise an autothermal reforming reactor (ATR) with air-blown catalytic partial oxidation of gas natural gas, a water-shift reaction and a high pressure CO2 removal process. The hydrogen-rich reformed fuel gas is combusted in a gas turbine Combined Cycle (CC), which is integrated (air, steam and heat) with the decarbonisation process. A novel method of comparing power plant concepts including CO2 removal is presented. Instead of using extensive thermodynamic calculations for these concepts, reaction equations for conservation of molecular species together with specific energy consumption numbers for the different process sections are used to characterise the concepts with respect to fuel-to- electricity conversion efficiency. With a combined gas/steam turbine power plant giving 58% total fuel-to-electricity conversion efficiencies (no CO2 removal), calculations for the concepts with CO2 removal including CO2 compression gave: A: 49.6%, B: 47.2% and C: 45.3%. The mechanisms leading to a reduced efficiency for the concepts A-C compared to combined gas/steam turbine with no removal of CO2, are discussed and quantified.
... Since electricity can be obtained cleanly (for example: wind and solar energy), special attention becomes the clean processing of feedstock materials, such as fossil hydrocarbons and biomasses to generate in a clean way, fuel gases, liquids fuels, chemicals, and electricity. The most effective way to CO2-free hydrogen production from fossil fuels is through the pyrolysis of hydrocarbon molecules [4]. This reaction is expressed in Equation (1). ...
Article
The biggest challenge facing the energy sector today is how to achieve a faster transition from fossil fuel economy to sustainable energy sources. Hydrogen is a clean chemical element that can be associated to high-efficiency fuel cells. However, most industrial H2 production processes are obtained from thermochemical processes that generate large amounts of CO2, such as natural gas (NG) steam reforming and coal gasification. An option to CO2-free H2 production is by water electrolysis based on renewable electricity, however it has technical-economic limitations that make its wide use difficult. This article presents a new plasma reformer as an alternative for H2 production that uses NG with CO2 or biogas as feedstock. Conversions of 90% of NG were experimentally obtained, producing H2, CO and reduced graphene oxide in a single pass through the reactor, without catalysts or heat regeneration. The Energy Conversion Efficiency of the prototype presented values close to 50%, without regard the energy of the carbonaceous nanomaterials obtained and depending on the losses between the power supply and the plasma torch. The proposed technology contributes to the transition from fossil fuel to renewable sources, suggesting the production of H2 in a decentralized way for fuel cell electric vehicles.
... The way out of the situation dating back to the landmark studies of Steinberg [29][30][31] and also Muradov [32,33] is to adopt the strategy of using fossil fuels for the production of hydrogen but to completely change the tactics. ...
Article
The insatiable—and ever-growing—demand of both the developed and the developing countries for power continues to be met largely by the carbonaceous fuels comprising coal, and the hydrocarbons natural gas and liquid petroleum. We review the properties of the chemical elements, overlaid with trends in the periodic table, which can help explain the historical—and present—dominance of hydrocarbons as fuels for power generation. However, the continued use of hydrocarbons as fuel/power sources to meet our economic and social needs is now recognized as a major driver of dangerous global environmental changes, including climate change, acid deposition, urban smog and the release of many toxic materials. This has resulted in an unprecedented interest in and focus on alternative, renewable or sustainable energy sources. A major area of interest to emerge is in hydrogen energy as a sustainable vector for our future energy needs. In that vision, the issue of hydrogen storage is now a key challenge in support of hydrogen-fuelled transportation using fuel cells. The chemistry of hydrogen is itself beautifully diverse through a variety of different types of chemical interactions and bonds forming compounds with most other elements in the periodic table. In terms of their hydrogen storage and production properties, we outline various relationships among hydride compounds and materials of the chemical elements to provide some qualitative and quantitative insights. These encompass thermodynamic and polarizing strength properties to provide such background information. We provide an overview of the fundamental nature of hydrides particularly in relation to the key operating parameters of hydrogen gravimetric storage density and the desorption/operating temperature at which the requisite amount of hydrogen is released for use in the fuel cell. While we await the global transition to a completely renewable and sustainable future, it is also necessary to seek CO 2 mitigation technologies applied to the use of fossil fuels. We review recent advances in the strategy of using hydrocarbon fossil fuels themselves as compounds for the high capacity storage and production of hydrogen without any CO 2 emissions. Based on these advances, the world may end up with a hydrogen economy completely different from the one it had expected to develop; remarkably, with ‘Green hydrogen' being derived directly from the hydrogen-stripping of fossil fuels. This article is part of the theme issue ‘Mendeleev and the periodic table'.
... With regard to environmental aspects, a method of thermal decomposition of hydrocarbons will be discovered. The fundamental method, detailed described in [1], is based on the fact that hydrocarbons like methane, will decompose into hydrogen and carbon for temperatures higher than 600°C: CH4 (g) C(s) + 2H2 (g) (1) To realize this idea, a bubble column reactor is used, that is filled with liquid tin. Via an orifice at the bottom of the reactor, methane bubbles can be introduced. ...
Conference Paper
Full-text available
The usage of hydrogen as alternative energy offers many applications, they can be found in in vehicle technology for fuel cells or as a reducing agent. Classical production methods like steam reforming generate carbon dioxide as a byproduct. In the discovered method, hydrogen is produced CO2 free by thermal decomposition of methane. To realize the production, methane is injected into a reactor that is filled with liquid tin. Inside the melt, methane bubbles will react to carbon and hydrogen. To optimize the reaction, different parameters for influencing the bubble flow will be discussed. The focus is set on the electromagnetic stirring of bubbles. A solving method is developed to simulate this effect, and will be demonstrated in parameter studies. To get a detailed view on the produced hydrogen, also a chemical calculation method is developed, that can be coupled with the electromagnetic solver and allow a validation of the model, that is presented in this article.
... With regard to environmental aspects, a method of thermal decomposition will be discovered. The fundamental method, detailed described in [1], is based on the fact that hydrocarbons, in these studies methane, will decompose into hydrogen and carbon for temperatures higher than 600°C. The idea to realize the decomposition is to inject methane with an orifice of 0,5 mm diameter into a liquid metal bubble column with a diameter of 40,6 mm. ...
... It is a well-known process which has been described by several authors, e.g. Steinberg [6] and Poirier [7] who reported hydrocarbon reactions, like those of methane, naphtha and ethanol with water (pre-vaporized by a steam generator). The reactions that occur in this process primarily produce H 2 , CO 2 , CO and CH 4 , but there is no set quantity for these compounds whose concentration depend on several factors, such as reagents concentration, temperature and pressure of the reformer, as well as the physical and chemical characteristics of the chosen catalyst. ...
Article
This work aims to investigate a biogas steam reforming prototype performance for hydrogen production by mass spectrometry and gas chromatography analyses of catalysts and products of the reform. It was found that 7.4% Ni/NiAl2O4/γ-Al2O3 with aluminate layer and 3.1% Ru/γ-Al2O3 were effective as catalysts, given that they showed high CH4 conversion, CO and H2 selectivity, resistance to carbon deposition, and low activity loss. The effect of CH4:CO2 ratio revealed that both catalysts have the same behavior. An increase in CO2 concentration resulted in a decrease in H2/CO ratio from 2.9 to 2.4 for the Ni catalyst at 850 °C, and from 3 to 2.4 for the Ru catalyst at 700 °C. In conclusion, optimal performance has been achieved in a CH4:CO2 ratio of 1.5:1. H2 yield was 60% for both catalysts at their respective operating temperature. Prototype dimensions and catalysts preparation and characterization are also presented.
... A reforma a vapor é um processo endotérmico em que o combustível reage com água na presença de catalisadores, responsáveis por aumentar a taxa de reações, resultando em uma mistura de gases contendo, em geral, hidrogênio (H2), dióxido de carbono (CO2), metano (CH4), monóxido de carbono (CO) e água (H2O) [10,11]. A eficiência de conversão está associada às propriedades físico-químicas do combustível, às condições ambientais, tais como pressão e temperatura, às condições técnicas do reformador e ao fluxo da mistura de combustível e vapor [12]. ...
Conference Paper
Full-text available
Atualmente a necessidade de reduzir as emissões de poluentes e obedecer às normas ambientais, principalmente no setor automotivo, tem contribuído para a busca de novas tecnologias mais eficientes e menos poluentes. As melhorias causadas nesse setor impactam diretamente o meio ambiente e a utilização de fontes energéticas. Nesse contexto, a busca por combustíveis alternativos, o hidrogênio é um combustível de queima limpa e que pode ser produzido a partir de fontes renováveis de energia, como o etanol, butanol e metanol. O etanol apresenta vantagens como o fácil manuseio, transporte, armazenamento, baixa toxidade e volatilidade, além ser facilmente obtido a partir de diferentes biomassas. A produção de hidrogênio a partir do etanol pode ser realizada a partir de diferentes técnicas, tais como a reforma a vapor, oxidação parcial (gaseificação) e a reforma autotérmica. Esse trabalho é direcionado para uma revisão de literatura da reforma a vapor de etanol, apresentando diversos estudos relacionados a essa área e a sua viabilidade.
... The CH 4 conversion value reached (50% approx.) with exLDH-I at 550 C under this conditions is close to the thermodynamic limit [32]. Consequently, the reaction temperature in the isothermal test must be increased in order to raise the H 2 production towards higher values. ...
Article
The catalytic study of the Ni-catalysts based on Ni/Mg/Al mixed oxides from hydrotalcite-like compounds (ex-LDH) shows a particular behaviour in the methane decomposition reaction. While deactivation of the catalyst occurs in the presence of methane within the range of temperature 600–700 °C, a subsequent and spontaneous “auto-regeneration” of the catalyst is observed above and below this temperature range. Increasing reaction temperature above 700 °C or decreasing it below 600 °C allows recover completely catalytic activity of the deactivated catalyst. This catalyst “auto-regeneration” process is an absolutely reversible process. XPS results of the spent catalysts suggest that the origin of this behaviour is a reversible change in the nature of the carbon deposit as a function of temperature. Consequently, the kinetic control of the carbon formation avoids the catalyst deactivation, and allows to reach the thermodynamic limit of the hydrogen produced.
... Hydrogen is currently produced by steam reforming (SR) of the methane contained in natural gas, which involves the production of CO and CO 2. Different clean techniques have been proposed for the hydrogen manufacturing from fossil fuels, as it is the case of employing the carbon capture and storage systems (CCS) for treating the exhaust gases in SR[1]. Other clean alternative is the hydrogen production by methane decomposition (CH 4 $ 2H 2 þ C), that produces 2 moles of hydrogen per mole of methane, as well as solid carbon as by-product[2]. This reaction is endothermic and has to be carried out at temperatures above 1200 C to achieve a high production yield. ...
Article
Methane decomposition to yield hydrogen and carbon (CH4⇆2H2+C) is one of the cleanest alternatives, free of CO2 emissions, for producing hydrogen from fossil fuels. This reaction can be catalyzed by metals, although they suffer a fast deactivation process, or by carbonaceous materials, which present the advantage of producing the catalyst from the carbon obtained in the reaction. In this work, the environmental performance of methane decomposition catalyzed by carbonaceous catalysts has been evaluated through Life Cycle Assessment tools, comparing it to other decomposition processes and steam methane reforming coupled to carbon capture systems. The results obtained showed that the decomposition using the autogenerated carbonaceous as catalyst is the best option when reaction conversions higher than 65% are attained. These were confirmed by 2015 and 2030 forecastings. Moreover, its environmental performance is highly increased when the produced carbon is used in other commercial applications. Thus, for a methane conversion of 70%, the application of 50% of the produced carbon would lead to a virtually zero-emissions process.
... Currently, world hydrogen production is around 5 Â 10 6 N m 3 , 96% of which is derived from fossil fuels [1] with net negative energy gain. Production of hydrogen, for example, by methane-steam reforming at best yields 2.95 mol H 2 per mole of methane, with a negative net energy gain of À16 MJ/kg of H 2 ; production by electrolysis of water using electricity generated by a natural gas-fired combined cycle power plant at best yields 1.37 mol H 2 per mole of methane, with a negative net energy gain of À172 MJ/kg of H 2 [2]. If hydrogen is to be widely accepted as a sustainable substitute for fossil fuels, it has to be produced from renewable feedstock other than the fossil fuels it is intended to replace via processes with a net positive energy gain. ...
Article
Full-text available
Most dark fermentation (DF) studies had resorted to above-ambient temperatures to maximize hydrogen yield, without due consideration of the net energy gain. In this study, literature data on fermentative hydrogen production from glucose, sucrose, and organic wastes were compiled to evaluate the benefit of higher fermentation temperatures in terms of net energy gain. This evaluation showed that the improvement in hydrogen yield at higher temperatures is not justified as the net energy gain not only declined with increase of temperature, but also was mostly negative when the fermentation temperature exceeded 25 °C. To maximize the net energy gain of DF, the following two options for recovering additional energy from the end products and to determine the optimal fermentation temperature were evaluated: methane production via anaerobic digestion (AD); and direct electricity production via microbial fuel cells (MFC). Based on net energy gain, it is concluded that DF has to be operated at near-ambient temperatures for the net energy gain to be positive; and DF + MFC can result in higher net energy gain at any temperature than DF or DF + AD.
... It is therefore more appropriate with regard to environmental concerns, and also simplifies the overall process. Comparison between these two technologies shows that pyrolysis is an appropriate method for hydrogen production and an attractive alternative to the established reforming process [19,20]. In order to produce a reasonable amount of hydrogen, thermal decomposition of natural gas is performed either at high temperatures [20,21] or with a catalyst [22][23][24]. ...
Article
In this paper, the homogeneous decomposition of methane and ethane is modeled in a well stirred flow reactor. The kinetics of this process is represented by a reaction mechanism of 242 reactions and 75 species, based on a mechanism developed for hydrocarbon combustion and soot formation. It is shown that this model correctly predicts the hydrogen yield from pyrolysis in a temperature range of 600–1600 °C, and pressure range of 0.1–10 atm. Furthermore, the effect of temperature, pressure and residence time on the amount of hydrogen produced from the decomposition of methane, ethane, natural gas, and a mixture of methane and argon is studied. The model predicts that the use of ethane or its addition to methane increases the speed of hydrogen production at low temperatures and pressures. The addition of a noble gas like argon also increases the yield of hydrogen at high pressures.
... (C) Decarbonization, which comprises a pre-reformer and an air-blown autothermal reforming reactor (ATR) for natural gas, water-shift reactors and a high-pressure CO capture process based on chemical absorption. The 2 hydrogen-rich resulting gas is combusted in a gas turbine CC, which is integrated with the decarbonization process (Hendriks and Blok, 1992;Steinberg, 1994;IEA Report PH2y19, 1998). Air from the gas turbine compressor exit is fed to the ATR. ...
Article
Three concepts for capturing CO2 from natural gas-fired combined gas/steam turbine power plants are evaluated and compared in this paper: (A) separation of CO2 from exhaust gas coming from a standard gas turbine power plant, using chemical absorption by amine solutions. (B) Gas turbine combined cycle (CC) using a semi-closed gas turbine with near to stoichiometric combustion using oxygen from an air separation unit as an oxidizing agent. This produces CO2 and water vapour as the combustion products. The gas turbine working fluid is mainly CO2. (C) Decarbonization, which comprises an autothermal reforming reactor with air-blown catalytic partial oxidation of gas natural gas, a water-shift reaction and a high-pressure CO2 capture process. The hydrogen-rich reformed fuel gas is combusted in a gas turbine CC, which is integrated (air, steam and heat) with the decarbonization process. A novel method is presented that compares power plant concepts including CO2. Instead of using extensive thermodynamic calculations for these concepts, reaction equations for the conservation of molecular species together with specific energy consumption numbers for the different process sections are used to characterize the concepts with respect to fuel-to-electricity conversion efficiency. With a combined gas/steam turbine power plant giving 58% total fuel-to-electricity conversion efficiencies (no CO2 capture), calculations for the concepts with CO2 capture including CO2 compression gave: (A) 49.6%; (B) 47.2%; and (C) 45.3%. The mechanisms leading to a reduced efficiency for concepts A–C are discussed and quantified and compared to combined gas/steam turbine with no capture of CO2.
... This type of methane cracking is called thermocatalytic decomposition of methane (TCM). TCM has been widely reported in the literature345678910111213141516171819 since early 1960s and the catalysts being studied in this process consist mainly of transition metals such as Ni, Co, and Fe. Catalysts based on Ni and Fe have shown to be the most effective . ...
Article
The paper presents the results of the investigation into the development of a robust catalyst for hydrogen production by thermocatalytic decomposition (TCD) of methane. In this paper, we present the results of the development and utilization of an iron-based catalyst for TCD. The effect of catalyst preparation methodology on the activity and robustness of the catalysts is reported. The catalyst was synthesized from magnetite by reduction in the presence of a reducing gas (methane or hydrogen) using a fixed-bed flow reactor at atmospheric pressures and temperatures ranging from 800 to 900 °C. Reduction under methane was found to synthesize a catalyst with the desired properties and smallest preparation time (2 h). The main advantages of these catalysts identified were: their ability to completely decompose methane (as compared to a maximum of 81% by other catalysts) and to maintain high reactivity for a long period of time (more than 75 h). The catalyst was characterized by SEM, TEM, BET, XRD and particle size analysis. TPR was employed to evaluate the activity of the catalysts, to investigate the various mechanisms of methane decomposition reaction for the catalysts and estimate the kinetic parameters by topochemical model postulated by Avrami–Erofeyev. The estimated kinetic parameters from the analysis of this data are presented. Carbon nanofibers were formed as a co-product of the methane decomposition reactions.
... For the case of HECAM, we envision a large CVDC production facility combined with thermal decomposition system. Methane thermal decomposition has been proposed for the production of hydrogen, with carbon black nanopowder as a byproduct [9]. Other processes include catalytic decomposition [10], plasma decomposition [11], decomposition over carbon catalysts in fixed and spouted beds [12] and fluidized beds [13]. ...
Article
Full-text available
Fossil fuels can be considered as hydrogen ores for CO2-free energy, and carbon ores for carbon construction materials. This paper discusses methods for extraction of hydrogen from fossil fuels without carbon oxidation, with co-production of high value solid carbon material products.
... Thermocatalytic decomposition of methane has become an attractive alternative for hydrogen production. In this process, methane is transformed into solid carbon and hydrogen, which implies that the latter is free of CO/CO 2 emissions, while moderate energy consumptions are required [2]. Although metal catalysts exhibit high activities, they are rapidly deactivated by carbon depositions [3]. ...
... It is an endothermic process, requiring 18 kcal/mol. Methane thermal decomposition has been proposed for the production of hydrogen, with carbon black nanopowder as a byproduct (Steinberg, 1996). Other processes include catalytic decomposition (Shah et al., 2001), plasma decomposition (Gaudermark and Lynum, 1996), etc. Simple carbon black is not the only possible product. ...
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Hydrocarbon fossil fuels can be considered as hydrogen ores for CO2-free energy, and carbon ores for carbonaceous construction materials. Hydrogen fuel can be extracted from fossil fuels by decarbonization, and used as an energy resource. The carbon byproduct can be used as a versatile construction material. Carbon materials would sequester carbon, and replace CO2-generating steel and concrete. Approximate comparison of the global consumption of energy and construction materials suggests a rough mass balance of energy and materials markets. The cost of foregoing the carbon energy content as a fuel can be easily offset by the value of the carbon-based construction material. The nature and properties of carbon materials and conventional infrastructural materials are compared.
Article
The most viable technology for production of ultra-pure hydrogen (>99.99%), required for fuel cells, is steam methane reforming (SMR) coupled with pressure vacuum swing adsorption (PVSA). A PVSA process with a two-layer bed of activated carbon (AC)/zeolite 5A for ultra-pure hydrogen production from syngas was developed and simulated with the aim of exploring the effect of impurities on energy intensity of the process. The simulated concentration profiles showed that CH4 was removed by the first half of the AC layer, CO2 and CO were mostly removed by the end of that layer, but zeolite 5A (the second layer) could not completely remove the remaining N2. Further, the effect of the N2 on performance of the PVSA process was demonstrated by simulating purification of two feeds with 3.1 and 1.1 vol% N2, respectively. The 2% drop in N2 concentration in the syngas feed resulted in decreased energy consumption of the PVSA process from 940 kJ/kg to 430 kJ/kg H2, while H2 recovery increased from 47% to 55%. Therefore, the presence of N2 has a very large impact on recovery and energy intensity of the ultra-pure hydrogen production process, and development of adsorbents with better N2 removal performance is required.
Article
Current methods of hydrogen production from methane generate more than 5 kg of CO2 for every 1 kg of hydrogen. Methane pyrolysis on conventional solid heterogeneous catalysts produces hydrogen without CO2, but the carbon coproduct poisons the catalyst. This can be avoided by using a molten metal alloy catalyst. We present here a study of methane pyrolysis using mixtures of molten Cu-Bi alloys as the catalyst. We find that molten Cu-Bi is an active catalyst, even though pure molten Bi and Cu are not. Surface tension measurements and constanterature ab initio molecular dynamics simulations indicate that the surface is enriched in Bi and that the catalytic activity is correlated with the concentration of Bi at the surface. Bader charge analysis indicates that bismuth donates charge to copper. In the most stable configuration of dissociated methane on these liquid surfaces, CH3 binds to a bismuth surface atom and H to Cu. The energy barriers for the dissociative adsorption of methane, calculated using the nudged elastic band (NEB) method, are between 2.5 and 2.6 eV, depending on the binding site on the surface of the Cu45Bi55 alloy. The computed barriers are in rough agreement with the experimental apparent activation energy of 2.3 eV.
Article
A solar-thermal aerosol flow reactor has been constructed, installed and tested at the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL). "Proof-of-concept" experiments were successfully carried out for the dissociation of methane to produce hydrogen and carbon black. Approximately 90% dissociation of methane was achieved in a 25-mm diameter quartz reaction tube illuminated with a solar flux of 2400 kW/m2 (or suns). Preliminary economics for a 1,000,000 kg/yr solar-thermal hydrogen plant were evaluated using a discount cash flow analysis that required a 15% Internal Rate of Return (IRR). If either product is the sole source of revenue, the required selling price for hydrogen was $27/MBtu ($0.092/kWhr or $25.6/GJ) and for carbon black it was $0.55/lb ($1.21/kg). If both products are sold, and carbon black is sold for $0.35/lb ($0.77/kg), the required selling price for hydrogen was $10/MBtu ($9.47/GJ or $0.034/kWhr). Both the experimental and economic results are very encouraging and support further work to address the technical issues and to develop the process.
Article
In this work, a theoretical analysis is carried out to predict the thermal decomposition of methane to hydrogen and carbon black occurring in a fluid-wall aerosol flow reactor. The mathematical formulation takes into account that the involved physical properties in the thermal decomposition process are temperature-dependent. The governing equations (mass, momentum, energy and species conservation) were nondimensionalized and simplified in order to be solved numerically. We show that the maximum conversion of methane to hydrogen occurs for a well-defined reactor length, which can be found in dimensionless form, as a characteristic Damkholer number. This dimensionless parameter represents the competition between residence to reactive times and for the present formulation is an eigenvalue of the problem. In addition, the numerical results show that considering thermal-dependent properties modify the evolution of the thermal decomposition process in a substantial manner.
Article
Non-oxidative decomposition of natural gas to COx-free hydrogen production over commercial nickel-molybdate hydrotreating catalysts with different Ni loading from 5 to 40wt% were studied at 700 °C. The catalysts were characterized by XRD, BET, TEM, Raman spectroscopy and TG-DTA analysis. The catalytic decomposition activities showed that a tremendous hydrogen production (∼90%) was obtained over 20–40wt%Ni/Mo–Al2O3 catalysts. Moreover, all catalysts exhibited excellent durability up to 9 h with stable catalytic activity toward H2 production. Although the increase of Ni content reduces the catalyst surface area, the H2 productivity and longevity increases with increased Ni content, i.e., the catalytic decomposition activity primarily depends on the active Ni sites which overcompensates the surface deficiencies. TEM, TGA and XRD data of used catalysts indicated that a higher thermal stability and graphitization degree of multi-walled carbon nanotubes were obtained on all Ni containing catalysts. Higher metal loading produced carbon nanofibers beside CNTs due to increment of particle size and long reaction time.
Article
The feasibility of an alternative CO2 mitigation system and a methanol production process is investigated. The Carnol system has three components: (i) a coal-fired power plant supplying flue gas CO2, (ii) a process which converts the CO2 in the presence of He from natural gas to methanol, (iii) use of methanol as a fuel component in the automotive sector. For the methanol production process alone, up to 100% CO2 emission reduction can be achieved; for the entire system, up to 65% CO2 emission reduction can be obtained. The Carnol system is technically feasible and economically competitive with alternative CO2-disposal systems for coal-fired power plants. The Carnol process is estimated to be economically attractive compared to the current market price of methanol, especially if credit can be taken for carbon as a marketable coproduct.
Article
The reaction kinetics of methane decomposition to yield hydrogen and carbon has been investigated comparing different types of carbonaceous catalysts: two ordered mesoporous carbons (CMK-3 and CMK-5) and two commercial carbon blacks (CB-bp and CB-v). The evolution of the reaction rate along the time has been analyzed concluding that it is governed by different and opposite events: reduction of active sites by carbon deposition, autocatalytic effects of the carbon deposits and pore blockage and diffusional constraints. A relatively simple kinetic model has been developed that fits quite well the experimental reaction rate curves in spite of the complexity of the involved phenomena.Both CMK carbons, and particularly CMK-5, present the highest initial reaction rates and the longest stability at long reaction times. In these materials, a part of the active sites remains accessible, since the carbon deposits formed from methane are capable of growing through the catalyst mesopores toward the outer part of the particles. The activation energies calculated from the initial reaction rates follow the sequence CMK-3 < CMK-5 < CB-bp < CB-v, whereas in all cases the reaction order was estimated to be 0.5 with respect to the methane partial pressure.
Article
Hydrogen production by methane cracking over a bed of different coal chars has been studied using a fixed bed reactor system operating at atmospheric pressure and 1123K. The chars were prepared by pyrolysing four parent coals of different ranks, namely, Jincheng anthracite, Binxian bituminous coal, Xiaolongtan lignite and Shengli lignite, in nitrogen in the same fixed bed reactor operating at different pyrolysis temperatures and times. Hydrogen was the only gas-phase product detected with a GC during methane cracking. Both methane conversion and hydrogen yield decreased with increasing time on stream and pyrolysis temperature. The lower the coal rank, the greater the catalytic effect of the char. While the Shengli lignite char achieved the highest methane conversion and hydrogen yield in methane cracking amongst all chars prepared at pyrolysis temperature of 1173K for 30min, a higher catalytic activity was observed for the Xiaolongtan lignite char prepared at 973K, indicating the importance of the nature of char surfaces. The catalytic activity of the coal chars were reduced by the carbon deposition. The coal chars had legible faces and sharp apertures before being subjected to methane cracking. The surfaces and pores of coal chars were covered with carbon deposits produced by methane cracking as evident in the SEM images. The results of BET surfaces areas of the coal chars revealed that the presence of micropores in the chars was not an exclusive reason for the catalytic effect of the chars in methane cracking.
Article
To reduce the emission of CO2 into the atmosphere, two schemes are proposed. The first one is a coal-fired MHD-steam combined power generation system where coal is burned with oxygen rather than air, the obtained high temperature is utilized for the MHD generator and the CO2 is liquefied and recovered. The cycle efficiency with CO2 recovery is estimated to be 45.3% (HHV). Another scheme is a combination of liquid fuel production and MHD-steam combined system, where the CARNOL processes of methanol production are used to reduce CO2 emission from sectors where collection of CO2 is otherwise impossible, such as highly dispersed heat engines and small scale fuel users. The carbon produced from the CARNOL processes is used as a fuel for the MHD-steam combined cycle, and CO2 is liquefied and recovered. 56.2 kg/sec of methanol is produced while the net power delivered to the grid is 370.7 MW, 42.2 kg/sec of CH4 is consumed.
Article
Studies of methane decomposition were performed over nickel alumina catalysts modified with magnesia. The catalysts were obtained by the co-precipitation method. The properties of catalysts were investigated by the temperature programmed reduction (TPR) and hydrogen desorption (TPD) methods. Methane decomposition was studied by the thermogravimetric and transient temperature programmed reaction methods. The nature of carbon deposits formed under different reaction conditions was investigated by the temperature programmed oxidation method (TPO) and high resolution transmission electron microscopy (HRTEM). An introduction of magnesium to the preparation mixture of catalysts led to the formation of smaller nickel crystallites with stronger adsorption sites. It was found out that the activity of catalysts and the properties of carbon deposits were related to the catalysts composition and the reaction temperature. Carbon filaments with fishbone-like packed graphitic layers were formed at 500°C, while the multi-walled nanotubes were observed after reaction performed at 700°C. The increase of magnesium content led to the increase of the rate of methane decomposition at the initial stages of the reaction. Deactivation of the catalysts was related to the insufficient removal of carbon species from the surface of nickel crystallites and the formation of stable, graphitic carbon deposits covering the surface of metal.
Article
In the present work, Ni and NiCu catalysts have been prepared by the fusion method using different textural promoters, and their performances in catalytic methane decomposition have been studied in a thermobalance tester at different operating temperatures. The nickel crystal domain sizes, as determined from their respective powder XRD patterns, have been correlated with the catalyst performance measured by the carbon deposition rate and the amount of accumulated carbon at the end of the test. The best performances were for those catalysts showing nickel domain sizes after reaction tests in the range of 10–20nm, the lowest domain sizes achieved with the fusion method, indicating that lower nickel particle size leads to better catalytic performance in the methane decomposition reaction. Ni/MgO catalysts doped with copper had the best performances in terms of carbon accumulation capacity (40g/gcat at 600°C). The effect of copper on the catalyst performance, however, is highly dependent on the textural promoter used. The morphology and structural properties of carbon deposited after the reaction tests revealed by XRD and TEM of different catalysts are also presented.
Article
A solar-thermal aerosol flow reactor has been constructed, installed, and tested with the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL). Experiments were successfully carried out for the dissociation of methane to produce hydrogen and carbon black and for the dry reforming of methane with carbon dioxide to form syngas (hydrogen and carbon monoxide). Approximately 90% dissociation of methane was achieved in a 25-mm diameter quartz reaction tube illuminated with a solar flux of 2400 kW/m2 (or suns). The carbon black produced was amorphous and had a particle size of 20 to 40 nm. Approximately 70% conversion was achieved for dry reforming using a solar flux of 2000 kW/m2. The experimental results for both processes are very encouraging and support further work to address the technical issues and to develop the processes.
Article
Thermo-catalytic decomposition of methane over different carbonaceous materials has been studied using a thermobalance by monitoring the mass gain (the amount of carbon deposited) with time. A kinetic study has been carried out using one carbon black, BP2000, and an activated carbon, CG Norit, to compare the behaviour of two carbon samples of different origin/nature as catalysts for this process. The reaction order of the carbon growth over CG Norit and BP2000 catalysts may be practically said to be 0.5. The activation energies over these catalysts were 141 and 238 kJ/mol, respectively. Methane decomposition reaction over carbon catalysts seems to be controlled by two simultaneous processes: first, decrease in methane decomposition rate due to the blocking of catalytic active sites by the carbon species deposited, and secondly, an increase in methane decomposition rate due to the formation of catalytically active carbon species produced from methane.
Article
Methane decomposition offers an interesting route for the CO2-free hydrogen production. The use of carbon catalysts, in addition to lowering the reaction temperature, presents a number of advantages, such as low cost, possibility of operating under autocatalytic conditions and feasibility of using the produced carbons in non-energy applications. In this work, a novel class of carbonaceous materials, having an ordered mesoporous structure (CMK-3 and CMK-5), has been checked as catalysts for methane decomposition, the results obtained being compared to those corresponding to a carbon black sample (CB-bp) and two activated carbons, presenting micro- (AC-mic) and mesoporosity (AC-mes), respectively. Ordered mesoporous carbons, and especially CMK-5, possess a remarkable activity and stability for the hydrogen production through that reaction. Under both temperature programmed and isothermal experiments, CMK-5 has shown to be a superior catalyst for methane decomposition than the AC-mic and CB-bp materials. Likewise, the catalytic activity of CMK-5 is superior to that of AC-mes in spite of the presence of mesoporosity and a high surface area in the latter. The remarkable stability of the CMK-5 catalyst is demonstrated by the high amount of carbon deposits that can be formed on this sample. This result has been assigned to the growth of the carbon deposits from methane decomposition towards the outer part of the catalyst particles, avoiding the blockage of the uniform mesopores present in CMK-5. Thus, up to 25 g of carbon deposits have been formed per gram of CMK-5, while the latter still retains a significant catalytic activity.
Article
In view of the stringent CO intolerance of the state-of-the-art proton exchange membrane (PEM) fuel cells, it is desirable to explore CO-free fuel processing alternatives. In recent years, step-wise reforming of hydrocarbons has been proposed for production of CO-free hydrogen for fuel cell applications. The decomposition of hydrocarbons (first step of the step-wise reforming process) has been extensively investigated. Both steam and air have been employed for catalyst regeneration in the second step of the process. Since, PEM is poisoned by very low (ppm) levels of CO, it is essential to eliminate even trace amounts of CO from the reformate stream. Preferential oxidation of CO (PROX) is considered to be a promising method for trace CO clean up. Related studies along with a discussion of catalytic ammonia decomposition (for applications in alkaline fuel cells) will be included in this review.
Article
A high-enthalpy source (HES) has been developed in Rennes either to heat gases up to 2000 K in local thermodynamic equilibrium (LTE) or to generate hypersonic expansions. The HES prototype has been associated with a high-resolution Bruker IFS 120 HR Fourier transform spectrometer to record emission spectra of hot gases, in LTE conditions. A series of emission spectra of methane has been obtained at 1005, 1365, 1485, 1625 and 1820 K in the pentad spectral region located around 3000 cm−1, at Doppler-limited resolution (0.02 cm−1). Spectra have been corrected for the transmission function that strongly affects the infrared radiation emitted by the hot gas. Line-integrated absorption cross sections have been extracted from the corrected spectra using an improved procedure for the calculation of the total partition function Q of methane at high temperature. This calculation included anharmonicity and rovibrational interaction effects, and was based on a multi-resolution fully converged direct partition sum. It has been shown that, as the temperature increases above 1000 K, the commonly used harmonic and rigid rotor double approximation to estimate Q leads to underestimated values.
Article
A CO2 mitigation process is developed which converts waste CO2, primarily recovered from coal-fired power plant stack gases with natural gas, to produce methanol as a liquid fuel and coproduct carbon as a materials commodity. The Carnol process chemistry consists of methane decomposition to produce hydrogen which is catalytically reacted with the recovered waste CO2 to produce methanol. The carbon is either stored or sold as a materials commodity. A process design is modelled and mass and energy balances are presented as a function of reactor pressure and temperature conditions. The Carnol process is a viable alternative to sequestering CO2 in the ocean for purposes of reducing CO2 emissions from coal burning power plants. Over 90% of the CO2 from the coal burning plant is used in the process which results in a net CO2 emission reduction of over 90% compared to that obtained for conventional methanol production by steam reforming of methane. Methanol as an alternative liquid fuel for automotive engines and for fuel cells achieves additional CO2 emission reduction benefits. The economics of the process is greatly enhanced when carbon can be sold as a materials commodity. Improvement in process design and economics should be achieved by developing a molten metal (tin) methane decomposition reactor and a liquid phase, slurry catalyst, methanol synthesis reactor directly using the solvent saturated with CO2 scrubbed from the power plant stack gases. The benefits of the process warrants its further development.
Article
Ordered mesoporous carbons have been applied, for the first time, as catalysts for hydrogen production via methane decomposition, showing higher and more stable activity than commercial carbonaceous catalysts.
Article
The reaction rate of methane decomposition using a tubular reactor having a 1 inch inside diameter with an 8 foot long heated zone was investigated in the temperature range of 700 to 900 C with pressures ranging from 28.2 to 56.1 atm. Representing the rate by a conventional model, -dC{sub CH4}/dt= k1 C{sub CH4} -k2 C{sub H2}², the rate constant k1 for methane decomposition was determined. The activation energy, 31.3 kcal/mol, calculated by an Arrhenius Plot was lower than for previously published results for methane decomposition. This result indicates that submicron particles found in the reactor adhere to the inside of the reactor and these submicron high surface area carbon particles tend to catalyze the methane decomposition. The rate constant has been found to be approximately constant at 900 C with pressure range cited above. The rate of methane decomposition increases with methane partial pressure in first-order. The rate of the methane decomposition is favored by higher temperatures and pressures while the thermochemical equilibrium of methane decomposition is favored by lower pressures. 8 refs., 7 figs., 2 tabs.
Article
A study is presented assessing the technology and economics of hydrogen production by conventional and advanced processes. Six conventional processes are assessed: (1) steam reforming of natural gas, (2) partial oxidation of residual oil, (3) gasification of coal by the Texaco process, (4) gasification of coal by the Koppers-Totzek process, (5) steam-iron process and (6) water electrolysis. The advanced processes include (1) high temperature electrolysis of steam, (2) coal gasification and electrochemical shift, (3) integrated coal gasification and high temperature electrolysis, (4) thermal cracking of natural gas and (5) the HYDROCARB thermal conversion of coal. Thermochemical water splitting, high energy nuclear radiation, plasma and solar photovoltaic-water electrolysis and by-product hydrogen from the chemical industry are also briefly discussed. It is concluded that steam reforming of methane is the most economic near-term process among the conventional processes. Processes based on conventional partial oxidation and coal gasification are two to three times more expensive than steam reforming of natural gas. New gas separation processes, such as pressure swing adsorption, improve the economics of these conventional processes. Integration of hydrogen production with other end-use processes has an influence on the overall economics of the system. The advanced high temperature electrochemical systems suffer from high electrical energy and capital cost requirements. The thermochemical and high energy water splitting techniques are inherently lower in efficiency and more costly than the thermal conversion processes. The thermal cracking of methane is potentially the lowest cost process for hydrogen production. This is followed closely by the HYDROCARB coal cracking process. To reach full potential, the thermal cracking processes depend on taking credit for the clean carbon fuel by-product. As the cost of oil and gas inevitably increases in the next several decades, emphasis will be placed on processes making use of the world's reserve of coal.