Optimization of bio-ethanol autothermal reforming and carbon monoxide removal processes

Experimental investigation of bio-ethanol autothermal reforming (ATR) and water-gas shift (WGS) processes for hydrogen production and regression analysis of the data is performed in the study. The main goal was to obtain regression relations between the most critical dependent variables such as hydrogen, carbon monoxide and methane content in the reformate gas and independent factors such as air-to-fuel ratio (λ), steam-to-carbon ratio (S/C), inlet temperature of reactants into reforming process (T_ATRin), pressure (p) and temperature (T_ATR) in the ATR reactor from the experimental data. Purpose of the regression models is to provide optimum values of the process factors that give the maximum amount of hydrogen. The experimental ATR system consisted of an evaporator, an ATR reactor and a one-stage WGS reactor. Empirical relations between hydrogen, carbon monoxide, methane content and the controlling parameters downstream of the ATR reactor are shown in the work. The optimization results show that within the considered range of the process factors the maximum hydrogen concentration of 42 dry vol. % and yield of 3.8 mol mol⁻¹ of ethanol downstream of the ATR reactor can be achieved at S/C = 2.5, λ = 0.20-0.23, p = 0.4 bar, T_ATRin = 230 °C, T_ATR = 640 °C.     

Reactor concept for improved heat integration in autothermal methanol reforming

With regard to mobile applications, the autothermal methanol reforming process as hydrogen source for PEM-fuel cells has advantages compared to the externally heated steam reforming reaction in terms of control and transient behaviour. However, thermal (hot-spot) control of the autothermal process turns out to be the key issue for scale-up in order to ensure selectivity, catalyst stability and process safety. Therefore, a novel reactor concept based on flow redirection around catalytically coated plates has been developed. It shows a low pressure drop, improves heat integration and solves the scale-up problem of autothermal processes like autothermal methanol reforming. These improvements have been shown in experiments using Cu/Zn/_Al2O3$\mathrm{Cu}/\mathrm{Zn}/{\mathrm{Al}}_2{\mathrm{O}}_3$ as catalyst.     

Efficiency of a pilot-plant for the autothermal reforming of biogas

A grid of hydrogen refuelling stations comparable to gasoline is essential for improving the individual transport based on fuel cell technology. To avoid transport and storage problems with hydrogen, small-scale hydrogen production plants are required. During the project BioRobur a pilot-plant with a hydrogen output of 50 Nm³/h was constructed and investigated. The plant is based on the autothermal reforming of biogas with a noble metal catalyst. All required reactants are stored or produced at the plant side. The purification of the synthetic gas is not considered.Within the article the plant efficiency and the cold gas efficiency were measured at different temperatures, oxygen to carbon ratios and gas hourly space velocities. Additionally the workload of the pilot-plant was varied, showing a highly reliable operation for a workload of at least 20%. Furthermore, the hydrogen production costs of the pilot-plant were compared with other common technologies, like electrolysis and steam reforming.     

A CFD model of autothermal reforming

A numerical model based on computational fluid dynamics (CFD) was developed and validated to simulate the performance of a catalytic monolith reformer for the production of hydrogen that could be used in fuel cell systems. The whole reactor was modeled as porous media for the process of autothermal reforming with n-hexadecane feed. CFD results provided an adequate match to experimental data from literature with respect to temperature and the mole fractions of H₂, CO₂ and CO products. The percentage difference between each experimental measurement of the mole fraction of hydrogen and the corresponding CFD prediction was less than 16.8%. It was found that the thermal conductivity of the solid catalyst substrate affected the temperature profile in the reactor, but its effect on product hydrogen concentration was negligible. The calculated reforming efficiency based on hydrogen decreased by 11.8% as power input was increased from 1.7 to 8.4 kW.     

High pressure autothermal reforming in low oxygen environments

Recent interest in fuel cells has led to the conceptual design of an ocean floor, fuel cell-based, power generating station fueled by methane from natural gas seeps or from the controlled decomposition of methane hydrates. Because the dissolved oxygen concentration in deep ocean water is too low to provide adequate supplies to a fuel processor and fuel cell, oxygen must be stored onboard the generating station. A lab scale catalytic autothermal reformer capable of operating at pressures of 6–50 bar was constructed and tested. The objective of the experimental program was to maximize H₂ production per mole of O₂ supplied (H_2(out)/O_2(in)). Optimization, using oxygen-to-carbon (O₂/C) and water-to-carbon (S/C) ratios as independent variables, was conducted at three pressures using bottled O₂. Surface response methodology was employed using a 2² factorial design. Optimal points were validated using H₂O₂ as both a stored oxidizer and steam source. The optimal experimental conditions for maximizing the moles of H_2(out)/O_2(in) occurred at a S/C ratio of 3.00–3.35 and an O₂/C ratio of 0.44–0.48. When using H₂O₂ as the oxidizer, the moles of H_2(out)/O_2(in) increased ≤14%. An equilibrium model was also used to compare experimental and theoretical results.     

Performance improvement of diesel autothermal reformer by applying ultrasonic injector for effective fuel delivery

Technology for the reforming of heavy hydrocarbons, such as diesel, to supply hydrogen for fuel cell applications is very attractive and challenging due to its delicate control requirements. The slow reforming kinetics of aromatics contained in diesel, sulfur poisoning, and severe carbon deposition make it difficult to obtain long-term performance with high reforming efficiency. In addition, diesel has a critical mixing problem due to its high boiling point, which results in a fluctuation of reforming efficiency. An ultrasonic injector (UI) have been devised for effective diesel delivery. The UI can atomize diesel into droplets (∼40 μm) by using a piezoelectric transducer and consumes much less power than a heating-type vapourizer. In addition, reforming efficiencies increase by as much as 20% compared with a non-UI reformer under the same operation conditions. Therefore, it appears that effective fuel delivery is linked to the reforming kinetics on the catalyst surface. A 100-W_e, self-sustaining, diesel autothermal reformer using the UI is designed. In addition, the deactivation process of the catalyst, by carbon deposition, is investigated in detail.     

Experimental investigation on the effect of natural gas composition on performance of autothermal reforming

This paper presents experimental study on catalytic autothermal reforming (ATR) of natural gas (NG) for hydrogen (_H2${\mathrm{H}}_2$) production over sulfide nickel catalyst supported on gamma alumina. The experiments are conducted on a cylindrical reactor of 30 mm in diameter and 200 mm in length with “simulated” NG of different composition under thermal-neutral conditions and fed with different molar air to fuel ratio (A/F$A/F$) and molar water to fuel ratio (W/F)$(W/F)$. The results showed that reforming performance is significantly dependent on A/F$A/F$, W/F$W/F$ and concentration of _C2+${\mathrm{C}}_{2+}$ hydrocarbons in inlet fuel. Fuels containing higher _C2+${\mathrm{C}}_{2+}$ hydrocarbons concentration have optimum performance in terms of more _H2${\mathrm{H}}_2$ at higher A/F$A/F$ and W/F$W/F$ but lower conversion efficiency. Good performance for ATR of fuel containing 15%–20% _C2H6${\mathrm{C}}_2{\mathrm{H}}_6$ can be achieved at A/F=5–7$A/F=5–7$ and W/F=4–6$W/F=4–6$, much higher than that for optimum performance of ATR of methane (A/F=3,W/F=2–2.5$A/F=3,W/F=2–2.5$). _CO2${\mathrm{CO}}_2$ in the inlet fuel does not have significant effect on the reversed water–gas shift reaction. Its effect on reforming performance is mainly due to the dilution of inlet fuel and products.     

Recent advances in diesel autothermal reformer design

The autothermal reforming of diesel fuel is a catalytic process that runs at temperatures of 700 °C–900 °C. Long-chain hydrocarbon molecules react with steam and O₂, yielding a product gas that mainly consists of CO, CO₂, CH₄ and H₂. H₂ is essential for the operation of fuel cell systems. The Forschungszentrum Jülich has been engaged in the cooperative development of technical apparatus for this reaction to be applied in fuel cell systems over the past 15 years, together with many other research groups worldwide, and this paper deals with reactor ATR 14, which is considered the preliminary end-product of Jülich's research and development in this field. This paper briefly summarizes Jülich's earlier reactor generations and then describes the most recent improvements embodied in the ATR 14. Additionally, the experimental evaluation of the ATR 14 is presented, which demonstrates that it can be operated over a broad load range and with almost complete carbon conversion.     

Kinetic modeling of high pressure autothermal reforming

Previously a lab scale catalytic autothermal reformer (ATR) capable of operating at pressures from 6 to 50 bar was constructed and tested. The objective of the experimental program was to maximize H₂ production per mole of O₂ supplied (H_2(out)/O_2(in)). In this companion paper a 1-D, heterogeneous, numerical model is developed and tested for simulating the high pressure ATR. The effects of molar steam to carbon (S/C) and oxygen to carbon (O₂/C) ratios are studied and optimal operating conditions are identified for three system operating pressures; 6, 28 and 50 bar. Experimental optimal conditions and model results are compared and found to be in close agreement. The optimal conditions, however, predicted by the model at pressures of 28 and 50 bar have higher S/C ratios and produce higher H_2(out)/O_2(in) yields than the experimentally determined optimums. A sensitivity analysis consisting of 9 model parameters is also performed. The model is most sensitive to the activation energy of the two steam reforming reactions used in the model and the operating parameter O₂/C.     

Hydrogen production by autothermal reforming of LPG for PEM fuel cell applications

Indirect partial oxidation, or oxidative steam reforming, tests of a bimetallic Pt–Ni catalyst supported on δ$\delta$-alumina were conducted in propane–n  -butane mixtures (LPG) used as feed. _H2${\mathrm{H}}_2$ production activity and _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity were investigated in response to different S/C, C/_O2$\mathrm{C}/{\mathrm{O}}_2$ and W/F ratios. It was confirmed that higher steam content in the reactant stream increases both the activity and the _H2/CO${\mathrm{H}}_2/\mathrm{CO}$ selectivity of the process. Low residence times created a positive impact on catalyst activity not only for hydrogen but also for carbon monoxide production due to the increased amount of fresh hydrocarbon in the feed stream. Hence, the highest selectivity level was obtained at intermediate residence times. The response of the system to C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratio was found to depend on the available steam content due to the complex nature of IPOX. The Pt–Ni catalyst was very prone to catalyst deactivation at low S/C ratios accompanied by high C/_O2$\mathrm{C}/{\mathrm{O}}_2$ ratios, but this problem was not encountered at high S/C ratios. A comparison of catalyst performance for different propane-to-n-butane ratios in the LPG feed indicated that the Pt–Ni catalyst has slightly better activity and selectivity at higher n-butane contents at the expense of becoming more sensitive to coke deposition.     

Comparison of steam and autothermal reforming of methanol using a packed-bed low-cost copper catalyst

Small-scale reformers for hydrogen production via steam and autothermal reforming of hydrocarbon feedstocks can be a solution to the lack of hydrogen distribution infrastructure. A packed-bed reactor is one possible design for such purpose. However, the two reforming processes of steam and autothermal methods have different characteristics, thus they have different and often opposite design requirements. In implementing control strategy for small-scale reformers, understanding the overall chemical reactions and the reactor physical properties becomes essential. This paper presents some inherent features of a packed-bed reactor that can both improve and/or degrade the performance of a packed-bed reactor with both reforming modes.The high thermal resistance of the packed bed is disadvantageous to steam reforming (SR), but it is beneficial to the autothermal reforming (ATR) mode with appropriate reactor geometry. The low catalyst utilization in steam reforming can help to prevent the unconverted fuel leaving the reactor during transient by allowing briefly for higher reactant fuel flow rates. In this study, experiments were performed using three reactor geometries to illustrate these properties and a discussion is presented on how to take advantages of these properties in reactor design.     

Thermodynamic analysis of hydrogen production from glycerol autothermal reforming

In this work, thermodynamics was applied to investigate the glycerol autothermal reforming to generate hydrogen for fuel cell application. Equilibrium calculations employing the Gibbs free energy minimization were performed in a wide range of temperature (700–1000 K), steam to glycerol ratio (1–12) and oxygen to glycerol ratio (0.0–3.0). Results show that the most favorable conditions for hydrogen production are achieved with the temperatures, steam to glycerol ratios and oxygen to glycerol ratios of 900–1000 K, 9–12 and 0.0–0.4, respectively. Further, it is demonstrated that thermoneutral conditions (steam to glycerol ratio 9–12) can be obtained at oxygen to glycerol ratios of around 0.36 (at 900 K) and 0.38–0.39 (at 1000 K). Under these thermoneutral conditions, the maximum number of moles of hydrogen produced are 5.62 (900 K) and 5.43 (1000 K) with a steam to glycerol ratio of 12. Also, it should be noted that methane and carbon formation can be effectively eliminated.     

Hydrogen production by autothermal reforming of methane over NiPd catalysts: Effect of support composition and preparation mode

NiPd/Ce_0.5Zr_0.5O₂/Al₂O₃ and NiPd/La₂O₃/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts were prepared by incipient wetness co-impregnation method or sequential impregnation method for autothermal reforming of methane (ATR of CH₄). The influence of the preparation mode, Ce_0.5Zr_0.5O₂ and La₂O₃ additives on the physicochemical properties of NiPd supported catalysts and the effect on their activity to produce hydrogen by ATR of CH₄ were investigated. Characterization of fresh and spent Ni-based catalysts by X-ray fluorescence spectroscopy, N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were performed. It was demonstrated that support composition determines NiO dispersion as well as reducibility of Ni species through different strength of Ni-support interaction. The preparation method modifies the phase composition and catalyst ability for reduction. The catalyst evolution under reaction conditions was studied. The NiO (∼15 nm) and NiPd alloy (∼18 nm) phases were observed in the spent catalysts. It was found that the Ni^o/NiO ratio can be regulated by support composition and preparation mode of catalysts. It is demonstrated that studied catalysts provide high methane conversion of 90–100%, CO yield of 55–85% and H₂ yield of 55–75% in ATR of CH₄ at 750–950 °C. The optimal composition and preparation method of catalyst were selected. The best ATR of CH₄ performance is provided by 10 Ni_0.5Pd/10Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst prepared by Pd/Ni sequential impregnation method that can be associated with peculiarity of NiPd particles structure and the optimal ratio between NiO species with different ability for reduction.     

Durability of a Ni based monolithic catalyst in the autothermal reforming of biogas

A Ni based catalyst supported on a cordierite monolithic substrate was applied to the autothermal reforming (ATR) of biogas to produce hydrogen. When the feed rates of oxygen and steam were constant, the Steam/CH₄ (S/CH₄) and O₂/CH₄ ratios changed because of an increase or decrease in the methane concentration of the biogas. The concentration of methane in the biogas fluctuates roughly between 35% and 65% according to factors such as the properties or amount of the waste. Therefore, the effect of S/CH₄ and O₂/CH₄ ratios on catalyst durability was confirmed by using actual biogas, which was produced by anaerobic fermentation of biomass at the biogasification bench-scale plant in Kyoto. Reforming reactions were carried out at ratios of S/CH₄ = 0–4, O₂/CH₄ = 0.5 and at S/CH₄ = 2, O₂/CH₄ = 0.6. The S/CH₄ range of 0–2.0 and the O₂/CH₄ range of 0.5–0.6 had no effect on the catalyst durability and a S/CH₄ ratio of more than 3.0 led to decreased catalytic performance.     

The autothermal reforming of oxymethylenether from the power-to-fuel process

Synthetic energy carriers that are not based on crude oil or natural gas can contribute to the transcending of fossil-based sources of energy in the future. A contemporary example is the organic substance, oxymethylenether (OME_n), which consists of hydrogen, carbon, and oxygen. It is reported in the literature that OME_n suppresses the formation of harmful NO_x and soot and reduces CO₂ emissions during the combustion process in internal combustion engines due to its high oxygen content. For the investigation presented in this paper, the use of OME_n was transferred to the autothermal reforming (ATR) process, which is normally conducted using pure diesel fuel or kerosene in order to produce a hydrogen-rich reformate gas to operate fuel cell systems. Different mixtures of OME_n and Ultimate diesel fuel were fed into Jülich's ATR 14 at a steady state. Thereby, approved reaction conditions from former ATR diesel fuel experiments with respect to O₂/C and H₂O/C molar ratios (0.47 and 1.9, respectively) and temperatures of the educts were applied. It was observed that the addition of OME_n to Ultimate diesel fuel resulted in stable temperatures at characteristic positions within ATR 14 and had a positive effect on the quality of the ATR product gas (reformate). For instance, the concentration of the undesired byproducts ethene and benzene decreased from 800 ppmv to the range of roughly 230 ppmv and from some 130 ppmv to less than 40 ppmv, respectively, when the mass fraction of OME_n in the OME_n/Ultimate diesel mixture was increased from 0% to 30%.     

Thermodynamic analysis of hydrogen production by autothermal reforming of ethanol

Ethanol steam reforming (ESR) is a strong endothermic reaction and ideally it only produces hydrogen and carbon dioxide.     

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.     

Rapid start-up strategy of 1 kWe diesel reformer by solid oxide fuel cell integration

A rapid start-up strategy of a diesel reformer for on-board fuel cell applications was developed by fuel cell integration. With the integration with metal-supported solid oxide fuel cell which has high thermal shock resistance, a simpler and faster start-up protocol of the diesel reformer was obtained compared to that of the independent reformer setup without considering fuel cell integration. A reformer without fuel cell integration showed unstable reactor temperatures during the start-up process, which affects the reforming catalyst durability. By utilizing waste heat from the fuel cell stack, steam required at the diesel autothermal reforming could be stably provided during the start-up process. The developed diesel reformer was thermally sustainable after the initial heat-up process. As a result, the overall start-up time of the reformer after the diesel supply was reduced to 9 min from the diesel supply compared to 22 min without fuel cell integration.     

A review on reforming bio-ethanol for hydrogen production

Bio-ethanol is a prosperous renewable energy carrier mainly produced from biomass fermentation. Reforming of bio-ethanol provides a promising method for hydrogen production from renewable resources. Besides operating conditions, the use of catalysts plays a crucial role in hydrogen production through ethanol reforming. Rh and Ni are so far the best and the most commonly used catalysts for ethanol steam reforming towards hydrogen production. The selection of proper support for catalyst and the methods of catalyst preparation significantly affect the activity of catalysts. In terms of hydrogen production and long-term stability, MgO, ZnO, _CeO2${\mathrm{CeO}}_2$, and _La2O3${\mathrm{La}}_2{\mathrm{O}}_3$ are suitable supports for Rh and Ni due to their basic characteristics, which favor ethanol dehydrogenation but inhibit dehydration. As Rh and Ni are inactive for water gas shift reaction (WGSR), the development of bimetallic catalysts, alloy catalysts, and double-bed reactors is promising to enhance hydrogen production and long-term catalyst stability. Autothermal reforming of bio-ethanol has the advantages of lesser external heat input and long-term stability. Its overall efficiency needs to be further enhanced, as part of the ethanol feedstock is used to provide low-grade thermal energy. Development of millisecond-contact time reactor provides a low-cost and effective way to reform bio-ethanol and hydrocarbons for fuel upgrading. Despite its early R&D stage, bio-ethanol reforming for hydrogen production shows promises for its future fuel cell applications.     

Thermodynamic analysis and heat integration for hydrogen production from bio-butanol for SOFC application: Steam reforming vs. autothermal reforming

Thermodynamic analysis of hydrogen production by steam reforming and autothermal reforming of bio-butanol was investigated for solid oxide fuel cell applications. The effects of reformer operating conditions, e.g., reformer temperature, steam to carbon molar ratio, and oxygen to carbon molar ratio, were investigated with the objective to maximize hydrogen production and to reduce utility requirements of the process and based on which favorable conditions of reformer were proposed. Process flow diagram for steam reforming and autothermal reforming integrated with solid oxide fuel cell was developed. Heat integration with pinch analysis method was carried out for both the processes at favorable reformer conditions. Power generation, electrical efficiency, useful energy for co-generation application, and utility requirements for both the processes were compared.