Microwave plasma torches driven by surface wave applied for hydrogen production

A microwave (2.45 GHz) Ar plasma torch at atmospheric pressure has been applied for hydrogen production from the decomposition of alcohols (methanol and ethanol). The hydrogen yield dependence on the gas fluxes and the microwave input power has been investigated both in Ar and Ar + water plasma environments. Mass and FTIR spectroscopy have been used to detect the molecular hydrogen produced and the H₂O, CO₂ and CO molecules in the exhaust gas stream. Nearly 100% decomposition of methanol molecules was achieved in the Ar plasma torch. It was further found that the H₂ yield increases significantly when water is added into the Ar/methanol/ethanol mixtures. Moreover, optical emission spectroscopy has been applied to determine the gas temperature, the electron density and the radiative species present in the plasma torch. The results clearly show that this device provides an efficient plasma environment for hydrogen production.     

Plasma steam methane reforming (PSMR) using a microwave torch for commercial-scale distributed hydrogen production

Although large-scale hydrogen production through conventional steam methane reforming (SMR) is available at an affordable cost, there is a shortage of hydrogen pipeline infrastructure between production plants and fueling stations in most places where hydrogen is needed. Due to the difficulties of transporting and storing hydrogen, onsite hydrogen production plants are desirable. Microwave plasma torch-based methods are among the most promising approaches to achieving this goal.The plasma steam methane reforming (PSMR) method discussed here has many benefits, including a high energy yield, a small carbon footprint, real-time fueling because of the short start-up time (<10 min), and the absence of expensive metal-based catalysts. Methane reforming and water gas shift reaction (WGSR) co-occur in the method advanced without a separate WGSR to achieve a high H₂ yield.This study examines an experimental investigation of commercial-scale hydrogen production through PSMR utilizing a microwave torch system. The optimum results obtained showed that the hydrogen production rate was 2247 [g(H₂)/h], and energy yield was 70 [g(H₂)/kWh] of the absorbed microwave power. An assessment of the results indicated a similar trend to that of simulated data (ASPEN Plus). The experimental results presented in this paper demonstrate the potential of a catalyst-free PSMR for commercial-scale hydrogen production.     

Hydrogen production by direct injection of ethanol microdroplets into nitrogen microwave plasma flame

Liquid ethanol introduced as microdroplets into the tip of microwave nitrogen plasma, operating at 2.45 GHz under atmospheric pressure, has been investigated. Injection of ethanol outside the region of plasma generation eliminated a problem of soot formation at that region, which was responsible for short reactor lifetime. Using liquid ethanol allows to save energy needed for vaporization. Hydrogen, carbon monoxide and solid carbon were the main outlet products. Other products detected with gas chromatography were CH₄, C₂H₄ and C₂H₂. The best results concerning hydrogen production were as follows: concentration in the outlet gas up to 28%, production rate up to 1043 L/h, energy yield up to 209 L per kWh of microwave power, and were obtained for liquid C₂H₅OH flow rate of 3.7 L/h. A numerical 0D model was used to determine contributions of chemical reactions in formation of measured gaseous products. Simplified model involving only radical reactions without any ions and electrons predicts final concentrations of main compounds quite well for microwave power up to 4 kW.     

Atmospheric pressure microwave plasma source for hydrogen production

Nowadays hydrogen is considered as a clean energy carrier and fuel of the future. That is why the interest in production and storage of hydrogen is still increasing. One of the promising technology is using microwave plasma for hydrogen production. In this study we propose two types of an atmospheric pressure microwave plasma source (MPS) for hydrogen production via methane conversion. The first one was a nozzleless waveguide-supplied coaxial-line-based. The second one was a nozzleless waveguide-supplied metal-cylinder-based. They can be operated with microwave frequency of 2.45 GHz and power up to a few kW with a high gas flow rates (up to several thousands l/h). We present experimental results concerning electrical properties of the MPS, plasma visualization, spectroscopic diagnostics and hydrogen production. The experiment was carried out with methane flow rate up to 12,000 l/h. An additional nitrogen or carbon dioxide swirl flow was used. The absorbed microwave power was up to 5000 W. Our experiments show that MPSs presented in this paper have a high potential for hydrogen production via hydrocarbon conversion.     

Effect of microwave plasma torch on the pyrolysis fuel oil in the presence of methane and ethane to increase hydrogen production

Pyrolysis fuel oil (PFO) processing by microwave plasma torch was developed for the production of hydrogen. The PFO cracking process was performed at atmospheric pressure in the absence of catalyst and effect of plasma gas on the production rate of hydrogen and light hydrocarbons (C₂–C₄) was evaluated. In the first step, effect of the applied power and the working gas flow rate was investigated. In the second step, the applied power and working gas rate were set to 650 W and 4000 sccm, respectively, which were provided by combining methane or ethane as 0%, 2.5%, 7.5%, and 20% with argon. By increasing the percentage of the existing methane in argon, production rate of the sum of the light hydrocarbons was increased and that of hydrogen was reduced, but it was more than the case when argon was applied alone. By increasing ethane percentage, hydrogen production and light hydrocarbon rate were increased. The best conditions of the plasma gas for producing hydrogen at the power of 650 W were obtained as 5CC PFO feed, 2500 sccm (80%) argon, and 500 sccm (20%). The hydrogen production rate in optimized conditions was 2343.16SCCM with selectivity of 84.41%. Sum of the obtained hydrocarbons in this test was 434.25 sccm. Another parameter in the present study was the feed volume processed by plasma. In this case, 5 cc, 3 cc, and 1 cc of the feed were tested when the plasma gas was 3000 sccm argon with the power of 650 W. The results showed that, by increasing the feed, the products were increased. In the processing of 5 cc feed with plasma, 896.41 sccm hydrogen and 61 sccm light hydrocarbon were produced.     

Hydrogen production from ethanol decomposition by microwave plasma TIAGO torch

This paper describes the study of molecular hydrogen production from ethanol decomposition by argon microwave TIAGO discharge in air ambiance at atmospheric pressure. In order to estimate the influence of the experimental conditions on the hydrogen production, a wide range of Ar flows, input powers and ethanol flows were tested. The simultaneous use of emission spectroscopy and mass spectrometry techniques allowed us to gain knowledge about the mechanisms which lead to the obtaining of hydrogen and other by-products (C₂H₂, C(s) …) at the plasma exit. Results showed a great capability of TIAGO discharges to withstand ethanol introduction as well as an almost complete ethanol decomposition (higher than 99.6%) with high hydrogen selectivity; argon and ethanol flows were found to be the key parameters in the by-products formation.     

Experimental validation of local thermal equilibrium in a MW plasma torch for hydrogen production

In this paper, experimental and numerical studies are made to investigate local thermal equilibrium in a microwave plasma torch at atmospheric pressure for hydrogen and carbon black production from methane dissociation. The microwave induced plasma can be operated up to 2 kW power at 2.45 GHz frequency. Methane is dissociated in argon, air or nitrogen plasma and optical emission spectroscopy is used to characterize the plasma. C₂, CN and OH ro-vibrational bands are used for rotational and vibrational temperature estimation while stark broadening of H-line is used for electron temperature calculation. Temperatures are determined at varying operating parameters of microwave power, axial gas flow rate, and methane flow rate. The rotational (heavy particle), vibrational, and electron temperatures are found to be equal to 5000 ± 500 K. The plasma is thus at local thermodynamic equilibrium.     

Hydrogen production by steam-oxidative reforming of bio-ethanol assisted by Laval nozzle arc discharge

The hydrogen production from an easily transported liquid feedstock can be an efficient alternative for fuel cells application. The steam-oxidative reforming of bio-ethanol by a novel gliding arc discharge named Laval nozzle arc discharge (LNAD) was investigated in this paper at low temperature and atmospheric pressure. The conversion efficiency and product distributions, mainly of H₂ and CO, were studied as functions of O/C ratio, S/C ratio, the ethanol flow rate and input power. The voltage–ampere (V–I) characteristic is also discussed here concerning the non-thermal plasma effect on the bio-ethanol reforming. A high conversion rate and fair H₂ yield have been achieved, 90% and 40% respectively. When the ethanol flow rate (G_ethanol) was 0.15 g s⁻¹ and S/C = 2.0, the minimum specific energy requirement of H₂ and CO were achieved at O/C = 1.4 with the specific energy input of 55.44 kJ per ethanol mole, 72.92 kJ mol⁻¹ and 80.20 kJ mol⁻¹ respectively. The optimal conditions for ethanol reforming seem to be S/C = 2.0 and O/C = 1.4–1.6, which are higher than those of the reaction's stoichiometry. This paper shows interesting results in comparison with the ethanol reforming assisted by other discharges. Compared with others, it features good conversion rate, low energy consumption and significantly reduced nitrogen oxide emission.     

Partial oxidation of ethanol using a non-equilibrium plasma

Partial oxidation of ethanol with air was carried out in a pulsed discharge plasma reactor at low temperature and atmospheric pressure. Effects of O₂:ethanol ratio, ethanol flow rate, and discharge current were investigated. H₂ and CO are the major products (>86%). Increases of O₂:ethanol ratio promote CO formation at the expense of C₂ hydrocarbons. H₂ selectivity and H₂ + CO selectivity are maximized at O₂:ethanol ratios of 0.3 and 0.5, respectively. Increases of feed flow rate accompanied by current increases allow the reactor to operate with high throughput. The LHV energy efficiency is increased with increasing feed flow rate, reaching 85% at high ethanol flow rates, conditions that also increase throughput. In contrast to catalytic and homogenous reactions, not all O₂ is consumed at high O₂:ethanol ratio for the low temperature plasma reaction. A radical reaction pathway of H abstraction from –OH and the α-H in ethanol to form CH₃CHO followed by C–C scission is proposed. The produced hydrogen rich gas can be potentially used in fuel cells and engines.     

Hydrogen production from ammonia by the plasma membrane reactor

A new plasma membrane reactor (PMR) was developed to efficiently produce hydrogen from NH₃ with the use of atmospheric pressure plasma and a hydrogen separation membrane. The generation of high-purity hydrogen from NH₃ was also examined. First, hydrogen gas flowing into the PMR revealed the effect of the PMR on hydrogen separation. Hydrogen separation depends on the partial pressure of hydrogen gas supplied (P_{in, H2}) and permeated (P_{out, H2}) when P_{in, H2}^0.5 − P_{out, H2}^0.5 > 0. Second, NH₃ gas flowing into the PMR revealed its hydrogen production characteristics: the maximum hydrogen conversion rate of a typical plasma reactor (PR) is 13%, whereas the PMR converted 24.4%. Hydrogen obtained by hydrogen separation was approximately 100% pure. A hydrogen generation rate of 20 mL/min was stably obtained.     

Ethanol reforming into hydrogen-rich gas applying microwave ‘tornado’-type plasma

Ethanol reforming in microwave argon plasma, operating at 2.45 GHz under atmospheric pressure and vortex gas flow has been investigated. Hydrogen, carbon monoxide and solid carbon are the main outlet products. H₂ and CO have been detected by mass spectrometry (MS) and Fourier transform infrared spectroscopy (FT-IR) whereas “black” carbon deposited at the wall has also been observed. The hydrogen yield has an average value of 98.4%, for ethanol fluxes in the range 4–15 sccm. An increase of about 32% in the energetic hydrogen mass yield has been observed as compared to laminar flow conditions.     

Biological fermentative hydrogen and ethanol production using continuous stirred tank reactor

Hydrogen and ethanol are promising biofuels and have great potential to become alternatives to fossil fuels. The influence of organic loading rates (OLRs) on the production of fermentative hydrogen and ethanol were investigated in a continuous stirred tank reactor (CSTR) from fermentation using molasses as substrate. Four OLRs were examined, ranging from 8 to 32 kg/m³·d. The H₂ and ethanol production rate in CSTR initially increased with increasing OLR (from 8 to 24 kg/m³ d). The highest H₂ production rate (12.4 mmol/h l) and ethanol production rate (20.27 mmol/h l) were obtained in CSTR both operated at OLR = 24 kg/m³ d. However, the H₂ and ethanol production rate tended to decrease with an increase of OLR to 32 kg/m³ d. The liquid fermentation products were dominated by ethanol, accounting for 31-59% of total soluble metabolities. Linear regression results show that ethanol production rate (y) and H₂ production rate (x) were proportionately correlated which can be expressed as y = 0.5431x + 1.6816 (r² = 0.7617). The total energy conversion rate based on the heat values of H₂ and ethanol was calculated to assess the overall efficiency of energy conversion rate. The best energy conversion rate was 31.23 kJ/h l, occurred at OLR = 24 kg/m³ d.     

Enhanced hydrogen-rich gas production from steam gasification of coal in a pressurized fluidized bed with CaO as a CO2 sorbent

Steam gasification of a typical Chinese bituminous coal for hydrogen production in a lab-scale pressurized bubbling fluidized bed with CaO as CO₂ sorbent was performed over a pressure range of ambient pressure to 4 bar. The compositions of the product gases were analyzed and correlated to the gasification operating variables that affecting H₂ production, such as pressure (P), mole ratio of steam to carbon ([H₂O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H₂ concentration was enhanced by raising the temperature, pressure and [H₂O]/[C] under the circumstances we observed. With the presence of CaO sorbent, CO₂ in the production gas was absorbed and converted to solid CaCO₃, thus shifting the steam reforming of hydrocarbons and water gas shift reaction beyond the equilibrium restrictions and enhancing the H₂ concentration. H₂ concentration was up to 78 vol% (dry basis) under a condition of 750 °C, 4 bar, [Ca]/[C] = 1 and [H₂O]/[C] = 2, while CO₂ (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be used as a substantially excellent CO₂ sorbent for the pressurized steam gasification of bituminous coal. For the gasification process with the presence of CaO, H₂-rich syngas was yielded at far lower temperatures and pressures in comparison to the commercialized coal gasification technologies. SEM/EDX and gas sorption analyses of solid residues sampled after the gasification showed that the pore structure of the sorbent was recovered after the steam gasification process, which was attributed to the formation of Ca(OH)₂. Additionally, a coal-CaO–H₂O system was simulated with using Aspen Plus software. Calculation results showed that higher temperatures and pressures favor the H₂ production within a certain range.     

Study of the plasma and heating effect on hydrogen permeation through Pd0.60-Cu0.40 membrane in a micro-channel plate reactor

The diffusion of hydrogen through palladium and palladium-copper alloys membrane have been provided the highest hydrogen selectivity and permeance. In this study the composite Pd_0.60-Cu_0.40 wt% membrane foil with thickness 20 μm was measured in the micro-channel plate reactor (MPR) with gap length 4.5 mm. The hydrogen permeation flux was measured at atmospheric feeding pressure for 100% H₂ concentration in the temperatures range of 423–573 K under heating only and plasma-heating experiments. The plasma firing high voltage source ranges of 10–18 kV are tested. The hydrogen permeation flux and hydrogen permeability have been calculated according to Fick's and Sieverts combining laws with power exponent n-value 0.5. It was found that the maximum hydrogen flux, hydrogen permeability and Permeation rate percent of the heating only experiment at MPR heating temperature of 573 K and flow rate 0.1 l/min. In the plasma heating experiment, it was observed that the maximum hydrogen flux, hydrogen permeability, and permeation rate percent at MPR heating temperature of 573 K and plasma firing voltage of 14 kV. Also, the hydrogen permeation rate percent decreased due to the hydrogen reverse reaction even though the plasma firing voltage increased to 16 kV and 18 kV. The results also reveal that the activation energy and Pre-exponential constant factor decreased with increasing the feeding H₂ flow rate while the linear regression R² decreased with increasing H₂ feeding flow rate that in the heating only experiment, in contrast, the plasma-heating experiment showed non-linearity values. A comparison between both experiments showed the hydrogen permeation flux of the plasma-heating experiment is higher than that obtained from the heating only experiment, additionally; the plasma effect increased at low hydrogen flow rates. In contrast, the energy efficiency of heating only experiment was higher than that obtained from the plasma-heating experiment due to the total energy consumption of plasma experiment is high.     

A strategy of mid-temperature natural gas based chemical looping reforming for hydrogen production

Steam methane reforming (SMR) needs the reaction heat at a temperature above 800 °C provided by the combustion of natural gas and suffers from adverse environmental impact and the hydrogen separated from other chemicals needs extra energy penalty. In order to avoid the expensive cost and high power consumption caused by capturing CO₂ after combustion in SMR, natural gas Chemical Looping Reforming (CLR) is proposed, where the chemical looping combustion of metal oxides replaced the direct combustion of NG to convert natural gas to hydrogen and carbon dioxide. Although CO₂ can be separated with less energy penalty when combustion, CLR still require higher temperature heat for the hydrogen production and cause the poor sintering of oxygen carriers (OC). Here, we report a high-rate hydrogen production and low-energy penalty of strategy by natural gas chemical-looping process with both metallic oxide reduction and metal oxidation coupled with steam. Fe₃O₄ is employed as an oxygen carrier. Different from the common chemical looping reforming, the double side reactions of both the reduction and oxidization enable to provide the hydrogen in the range of 500–600 °C under the atmospheric pressure. Furthermore, the CO₂ is absorbed and captured with reduction reaction simultaneously.Through the thermodynamic analysis and irreversibility analysis of hydrogen production by natural gas via chemical looping reforming at atmospheric pressure, we provide a possibility of hydrogen production from methane at moderate temperature. The reported results in this paper should be viewed as optimistic due to several idealized assumptions: Considering that the chemical looping reaction is carried out at the equilibrium temperature of 500 °C, and complete CO₂ capture can be achieved. It is assumed that the unreacted methane and hydrogen are completely separated by physical adsorption. This paper may have the potential of saving the natural gas consumption required to produce 1 m³ H₂ and reducing the cost of hydrogen production.     

Hydrogen production by radio frequency plasma stimulation in methane hydrate at atmospheric pressure

Methane hydrate, formed by injecting methane into 100 g of shaved ice at a pressure of 7 MPa and reactor temperature of 0 °C, was decomposed by applying 27.12 MHz radio frequency plasma in order to produce hydrogen. The process involved the stimulation of plasma in the methane hydrate with a variable input power at atmospheric pressure. It was observed that production of CH₄ is optimal at a slow rate of CH₄ release from the methane hydrate, as analyzed by in light of the steam methane reforming (SMR) and the methane cracking reaction (MCR) processes in accordance with the content of gas production. In comparison with the steam methane reforming (SMR), it was found that methane-cracking reaction (MCR) was dominant in conversion of CH₄ into hydrogen. An H₂ content of 55% in gas production was obtained from conversion of 40% of CH₄ at an input power of 150 W. The results clearly show that hydrogen can be directly produced from methane hydrate by the in-liquid plasma method.     

Hydrogen production from dry spirulina algae with downstream feeding in microwave plasma reactor assisted under atmospheric pressure

Advancement in the field of biomass and bioenergy has pulled in researchers to produce biofuels derived from naturally accessible feedstock by adopting diverse innovative approaches in biomass pretreatment. In this study, pyrolysis of micro algae with downstream processing of biomass from the resonator cavity under atmospheric pressure was conducted and hydrogen production produced under different microwave power was analyzed. With the increase in microwave power, the hydrogen gas yield accounted to be as twice as that at lower power, where the concentration of produced hydrogen accounts for about 30.80%, 33.20%, and 37.58% at microwave power levels of 800, 900 and 1000 W. It was also observed that no methane was produced in this study since most of the methane produced from microwave plasma conversion has reacted with CO₂ and produced CO and H₂, hence dropped in the concentration of CO₂ with decline in power intensity.     

Dissociation of H2S in non-equilibrium gliding arc “tornado” discharge

The process of hydrogen sulfide, H₂S, dissociation was studied in a non-equilibrium gliding arc “tornado” (GAT) plasma discharge. Utilizing GAT ensured uniform H₂S gas treatment in the reactor. In addition, it created a low temperature zone near the cylindrical wall of the reactor, while maintaining a high temperature zone near the reactor axis. An energy cost of 1.2 eV per H₂ molecule was achieved in this plasma system at atmospheric pressure. These results are particularly important for the oil industry, which consumes large amounts of hydrogen in oil hydro-treatment, and for gas industry because of the high H₂S content in “sour” gas.     

Comparative study of fuel gas production for SOFC from steam and supercritical-water reforming of bioethanol

Theoretical study of fuel gas (H₂ + CO) production for SOFC from bioethanol was carried out to compare performances between two reforming technologies, including steam reforming (SR) and supercritical-water reforming (SCWR). It demonstrates that the fuel gas productions are comparable among the two reforming systems; however, SCWR requires the operation at much higher temperature and pressure than SR. The maximum hydrogen yield can be obtained at 850 K, atmospheric pressure, ethanol to water molar feed ratio of 1:20 for SR system and at 1300 K, 22.1 MPa, and ethanol to water feed ratio of 1:20 for SCWR. The use of a distillation column to purify the bioethanol feed was proven to improve the fuel conversion efficiency of both systems. The analysis reveals that SCWR is a promising system for fuel production for SOFC when a gas turbine is incorporated to the system for energy recovery. Further, it is not necessary to distil bioethanol to obtain too high ethanol recovery (i.e. >90%) as higher energy consumption at the distillation column could lead to lower overall thermal efficiency.     

Hydrogen production by glycerol steam reforming with in situ hydrogen separation: A thermodynamic investigation

Thermodynamic features of hydrogen production by glycerol steam reforming with in situ hydrogen extraction have been studied with the method of Gibbs free energy minimization. The effects of pressure (1–5 atm), temperature (600–1000 K), water to glycerol ratio (WGR, 3–12) and fraction of H₂ removal (f, 0–1) on the reforming reactions and carbon formation were investigated. The results suggest separation of hydrogen in situ can substantially enhance hydrogen production from glycerol steam reforming, as 7 mol (stoichiometric value) of hydrogen can be obtained even at 600 K due to the hydrogen extraction. It is demonstrated that atmospheric pressure and a WGR of 9 are suitable for hydrogen production and the optimum temperature for glycerol steam reforming with in situ hydrogen removal is between 825 and 875 K, 100 K lower than that achieved typically without hydrogen separation. Furthermore, the detrimental influence of increasing pressure in terms of hydrogen production becomes marginal above 800 K with a high fraction of H₂ removal (i.e., f = 0.99). High temperature and WGR are favorable to inhibit carbon production.