Simulation of methane conversion to syngas in a membrane reactor. Part II: Model predictions

A one-dimensional non-isothermal model was employed in the simulation of partial oxidation of methane to syngas in a dense oxygen permeation membrane reactor. The model predicts that if methane is consumed completely in the reactor, a temperature runaway occurs. The reactor inlet temperature is chosen as a major factor to demonstrate the correlativity of the reactor performance and this phenomenon. A borderline inlet temperature (BIT) is defined. Simulation results showed that when the reactor inlet temperature approaches this value, an optimized reactor performance is achieved. This temperature increases with the increase of the air flow rate and carbon space velocity. The surface exchange kinetics at the oxygen-rich side has a small effect on this temperature, while that at the oxygen-lean side has a significant effect.     

Simulation of methane conversion to syngas in a membrane reactor: Part I A model including product oxidation

A one-dimensional dense membrane reactor (DMR) model has been developed to simulate the partial oxidation of methane to syngas. A combustion–reforming mechanism was adopted and the oxidation of reforming products, i.e. H₂ and CO, was considered. The performance of the DMR and a conventional fixed-bed reactor was compared and discussed. The results show that the incorporation of the product oxidation steps has a significant effect on the simulation results of a DMR and provides a reasonable explanation of the experimental data. The model is therefore more reasonable than those ignoring the product oxidation reactions.     

Lithium insertion into manganese dioxide electrode in MnO2/Zn aqueous battery: Part I. A preliminary study

The discharge characteristics of manganese dioxide (γ-MnO₂ of electrolytic manganese dioxide (EMD) type) as a cathode material in a Zn–MnO₂ battery containing saturated aqueous LiOH electrolyte have been investigated. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. The XPS data show that a layer of insoluble material, possibly Li₂CO₃, is deposited on the cathode, creating a barrier to H₂O, thus preventing the formation of Mn hydroxides, but allowing the migration of Li ions into the MnO₂ structure. The cell could be reversibly charged with 83% of voltaic efficiency at 0.5 mA/cm² current density to a 1.9 V cutoff voltage. The percentage utilization of the cathode material during discharge was 56%.     

Hybrid concentrated photovoltaic and thermal power conversion at different spectral bands

The option to use the beam down optics of a solar tower system for large-scale and grid-connected concentrated photovoltaic (PV) cells is examined. The rationale is to use this system to split the solar spectrum. Part of the spectrum can be utilized for PV cells. For instance, but not limited to, mono-crystalline silicon cells can convert the 600–900 nm band to electricity at an efficiency of 55–60%. The rest of the spectrum remains concentrated and it can be used thermally to generate electricity in Rankine–Brayton cycles or to operate chemical processes. Two optical approaches for a large-scale system are described and analyzed. In the first concept, the hyperboloid-shaped tower reflector is used as the spectrum splitter. Its mirrors can be made of transparent fused silica glass, coated with a dielectric layer, functioning as a band-pass filter. The transmitted band reaches the upper focal zone, where an array of PV modules is placed. The location of these modules and their interconnections depend on the desirable concentration level and the uniformity of the flux distribution. The reflected band is directed to the second focal zone near the ground, where a compound parabolic concentrator is required to recover and enhance the concentration to a level depending on the operating temperature at this target. In the second approach, the total solar spectrum is reflected down by the tower reflector. Before reaching the lower focal plane, the spectrum is split and filtered. One band can be reflected and directed horizontally to a PV array and, in this case, the rest of the spectrum is transmitted to the lower focal plane. To illustrate the feasibility of these options, commercial silicon cells with antireflective coating, intended to operate under concentrated solar radiation in the range of 200–800 suns, were chosen. The results show that 6.5 MWe from the PV array and 11.1 MWe from a combined cycle can be generated starting from a solar heat input of 55.6 MW.     

Hydrogen-rich syngas production via integrated configuration of pyrolysis and air gasification processes of various algal biomass: Process simulation and evaluation using Aspen Plus software

In the present study, hydrogen-rich syngas production via integrated configuration of pyrolysis and air gasification processes of different algal biomass is investigated at relevant industrial condition. A comprehensive steady state equilibrium simulation model is developed using Aspen Plus software, to investigate and evaluate the performance of pyrolysis and air gasification processes of different algal biomass (Algal waste, Chlorella vulgaris, Rhizoclonium sp and Spirogyra). The model can be used as a predictive tool for optimization of the gasifier performance. The developed process consists of three general stages including biomass drying, pyrolysis and gasification. The model validation using reported experimental results for pyrolysis of algal biomass indicated that the predicted results are in good agreement with experimental data. The effect of various operational parameters, such as gasifier temperature, gasifier pressure and air flow rate on the gas product composition and H₂/CO was investigated by sensitivity analysis of parameters. The achieved optimal operating condition to maximize the hydrogen and carbon monoxide production as the desirable products were as follows: gasifier temperature of 600 °C, gasifier pressure of 1 atm and air flow rate of 0.01 m³/h.     

Catalytic valorization of glycerol to hydrogen and syngas

Glycerol, a byproduct derived from the production of biodiesel, is currently in an oversupply crisis worldwide. One approach to alleviate this problem is to transform glycerol into valuable chemicals such as hydrogen and syngas. Pyrolysis, steam reforming, partial oxidation, autothermal reforming, and aqueous-phase reforming are promising routes for the catalytic conversion of glycerol. However, certain challenges are still limiting their development. Recent advances in catalyst design, reactor engineering, and theoretical chemistry have enabled us to understand glycerol valorization on macro- and microscopic scales, and may help overcome existing thresholds. With the synergistic efforts of these tools, glycerol may no longer be a burden, but a valuable resource of hydrogen and syngas in the near future.     

Low temperature conversion of syngas to ethanol in liquid phase over Fe modified CuZn catalyst: The promoting effect of Fe

Fe modified CuZn catalysts were prepared and first used for the low temperature ethanol synthesis from syngas in liquid phase. Fe greatly enhanced the CO dissociative adsorption and promoted the formation of C₂₊ alcohols. The role of Fe was dependent on the catalyst preparation method. The co-precipitation method enhanced the interaction between Fe and other components, which could control the CO dissociative desorption to terminate the carbon chain growth of alcohols at ethanol. The wetness impregnation method benefited the dispersion of iron species and the synthesis of methanol and butanol. As a result, the co-precipitation method prepared Fe modified CuZn catalyst with spinel structure exhibited excellent catalytic performance for the low temperature syngas hydrogenation to ethanol in liquid phase with an ethanol selectivity of 40.9%.     

Laminar burning velocities and flame stability analysis of syngas mixtures at sub-atmospheric pressures

The effects of low pressure on the laminar burning velocity and flame stability of H₂/CO mixtures and equimolar H₂/CO mixtures diluted with N₂ and CO₂ were studied experimentally and theoretically. Experiments were conducted at real sub-atmospheric conditions in three places located at high altitudes 500 m.a.s.l. (0.947 atm), 1550 m.a.s.l. (0.838 atm), and 2300 m.a.s.l. (0.767 atm). Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. The behavior of the laminar burning velocity at low pressures depends on the equivalence ratio considered; it decreases at lean and very rich equivalence ratios when pressure is increased. However, a contrary behavior was obtained at equivalence ratios corresponding to the highest values of the laminar burning velocity, where it increases as pressure increases. Numerical calculations were also conducted using a detailed reaction mechanism, and these do not reproduce the behavior obtained experimentally; a sensitivity analysis was carried out to examine the differences found. At lean equivalence ratios, flame instabilities were observed for all the syngas mixtures. The range of equivalence ratios where flames are stable increases at lower pressures. This behavior is due to the increase of the flame thickness, which considerably reduces the hydrodynamic instabilities in the flame front.     

Biomass-derived syngas production via gasification process and its catalytic conversion into fuels by Fischer Tropsch synthesis: A review

The Fischer–Tropsch (FT) synthesis has been investigated over decades as an alternative route to obtain synthetic fuels from synthesis gas. FT is a high-performance synthesis based on metallic catalysis, mainly using ruthenium, cobalt and iron catalysts, which converts syngas in hydrocarbons and chemical precursors. This work presents a review on the aspects of the syngas production from biomass gasification and its subsequent conversion into fuels through the Fischer-Tropsch synthesis. The usage of biomass, including lignocellulosic residues, as a raw material in the gasification process. Biosyngas is highlighted as a synthetic fuel source to replace nonrenewable, conventional fossil fuels. Lignocellulosic material must be considered a low-cost feedstock to the liquid biofuel production on a large scale. Studies on syngas cleaning to attain the purity required by the FT process is revised. Recent understanding of reaction kinetics and thermodynamics has contributed to increasing the FT performance and economic viability. This paper includes also the debate on main catalysts, industrial process requirements, and chemical reaction kinetics and mechanisms of Fischer–Tropsch synthesis.     

Electrochemical and structural characteristics of metal oxide-coated lithium manganese oxide (spinel type): Part I. In the range of 2.5–4.2 V

The electrochemical and structural characteristics of the metal oxide-coated spinel were investigated in the range of 2.5–4.2 V. Metal oxide coating on commercial spinel powder (LiMn_2−xM_xO₄, M=Zr, Nikki, Japan) was carried out using the sol–gel method. Al₂O₃/(PtO_x or CuO_x)-coated spinel exhibited improved cyclability compared to bare spinel. Impedance analysis results indicated that electrochemical resistance value was not consistent with cycle performance. The improved cycle performance of metal oxide-coated spinel may be due to formation of a new Li₂Mn₄O₉, Li₂MnO₃ phase, which is expected to have stability to phase transition (Jahn–Teller distortion).     

Methane dry (CO2) reforming to syngas (H2/CO) in catalytic process: From experimental study and DFT calculations

Dry reforming of methane (DRM) is a promising reaction, it could convert two greenhouse gases CO₂ and CH₄ into syngas (CO and H₂) which could provide a mixed fuel for daily life or chemical feedstock for industrial application. Transition metals were widely applied in this process, however, single component of transition metal catalysts could not meet the stability, selectivity and activity demands simultaneously. And the coke formation on the catalysts is the major barrier to the commercialization of DRM. This review presents a systematic discussion and analysis of methane dry reforming to syngas in the catalytic process from both experimental study and density functional theory (DFT) calculation based on recent research. It includes catalytic performance test of activity, selectivity and stability in DRM on monometallic and bimetallic systems, and also gives the discussion of carbon formation in the former parts. The later parts focus on CH₄ and CO₂ activation over monometal and bimetal surface using DFT simulation. The rate determining step and reaction mechanisms involved in DRM are obtained based on thermodynamic analysis and microkinetic model. In the end, we give our outlook to the design and preparation of good performance catalysts as well as further theoretical simulation and analysis in DRM. This review could provide some useful information for going into methane dry reforming from both experimental application and atomic scale.     

Operation conditions of batteries in PV applications

For a continuous energy supply of photovoltaic operated and off-grid loads, the storage of the solar generated electrical energy is necessary. About 60% of all over the world manufactured solar cells are used for such stand alone systems. In case of photovoltaic systems, mainly electrochemical battery storage systems are used.

The paper describes the requirements for batteries in solar systems. The most important storage systems, such as lead–acid, NiMH and Li-ion batteries are described in detail and further developing trends are discussed.

As it is well known that the operation conditions strongly influence the battery lifetime, this paper reviews photovoltaic operation conditions and experience in performance and lifetime in photovoltaic systems.     

Recent advances of high-efficiency single crystalline silicon solar cells in processing technologies and substrate materials

Single crystalline silicon solar cells have demonstrated high-energy conversion efficiencies up to 24.7% in a laboratory environment. One of the recent trends in high-efficiency silicon solar cells is to fabricate these cells on different silicon substrates. Some silicon wafer suppliers are also involved in such development. Another recent trend is the increased production of high-efficiency silicon cells, some of them with low-cost structures. This paper will discuss the progress at the University of New South Wales, and these trends in other organisations.     

Direct numerical simulation of ignition of syngas (H2/CO) mixtures with temperature and composition stratifications relevant to HCCI conditions

In this paper, ignition characteristics of syngas (H₂/CO) under homogeneous charge compression ignition environment have been studied using direct numerical simulation (DNS) and detailed reaction mechanism with temperature stratification. 2D DNS are performed by varying several parameters such as fuel composition, temperature fluctuation $\left(T^{\prime }\right)$ and with different temperature and composition correlations. Results show that high H₂ content syngas mixture exhibits increase in peak mean heat release rate (HRR) and decrease in spreading of mean HRR. Also, for large $T^{\prime }$, deflagration mode of ignition becomes dominant source of HRR and reduces the effects of fuel composition on peak mean HRR. On the contrary, spontaneous mode of ignition becomes dominant source of HRR and occurs more homogenously for small $T^{\prime }$, and this phenomenon becomes significant for low H₂ content syngas mixture. The effect of different correlations between temperature and composition on ignition in syngas illustrate that HRR occurs from mixed mode of deflagration and spontaneous ignition for uncorrelated cases, whereas spontaneous mode of ignition occurring homogeneously is the major source of HRR for negatively correlated cases.     

Pyrolysis-catalytic steam reforming of agricultural biomass wastes and biomass components for production of hydrogen/syngas

The pyrolysis-catalytic steam reforming of six agricultural biomass waste samples as well as the three main components of biomass was investigated in a two stage fixed bed reactor. Pyrolysis of the biomass took place in the first stage followed by catalytic steam reforming of the evolved pyrolysis gases in the second stage catalytic reactor. The waste biomass samples were, rice husk, coconut shell, sugarcane bagasse, palm kernel shell, cotton stalk and wheat straw and the biomass components were, cellulose, hemicellulose (xylan) and lignin. The catalyst used for steam reforming was a 10 wt.% nickel-based alumina catalyst (NiAl₂O₃). In addition, the thermal decomposition characteristics of the biomass wastes and biomass components were also determined using thermogravimetric analysis (TGA). The TGA results showed distinct peaks for the individual biomass components, which were also evident in the biomass waste samples reflecting the existence of the main biomass components in the biomass wastes. The results for the two-stage pyrolysis-catalytic steam reforming showed that introduction of steam and catalyst into the pyrolysis-catalytic steam reforming process significantly increased gas yield and syngas production notably hydrogen. For instance, hydrogen composition increased from 6.62 to 25.35 mmol g^?1 by introducing steam and catalyst into the pyrolysis-catalytic steam reforming of palm kernel shell. Lignin produced the most hydrogen compared to cellulose and hemicellulose at 25.25 mmol g^?1. The highest residual char production was observed with lignin which produced about 45 wt.% char, more than twice that of cellulose and hemicellulose.     

Low-temperature catalytic conversion of greenhouse gases (CO2 and CH4) to syngas over ceria-magnesia mixed oxide supported nickel catalysts

Running dry reforming of methane (DRM) reaction at low-temperature is highly regarded to increase thermal efficiency. However, the process requires a robust catalyst that has a strong ability to activate both CH₄ and CO₂ as well as strong resistance against deactivation at the reaction conditions. Thus, this paper examines the prospect of DRM reaction at low temperature (400–600 °C) over CeO₂–MgO supported Nickel (Ni/CeO₂–MgO) catalysts. The catalysts were synthesized and characterized by XRD, N₂ adsorption/desorption, FE-SEM, H₂-TPR, and TPD-CO₂ methods. The results revealed that Ni/CeO₂–MgO catalysts possess suitable BET specific surface, pore volume, reducibility and basic sites, typical of heterogeneous catalysts required for DRM reaction. Remarkably, the activity of the catalysts at lower temperature reaction indicates the workability of the catalysts to activate both CH₄ and CO₂ at 400 °C. Increasing Ni loading and reaction temperature has gradually increased CH₄ conversion. 20 wt% Ni/CeO₂–MgO catalyst, CH₄ conversion reached 17% at 400 °C while at 900 °C it was 97.6% with considerable stability during the time on stream. Whereas, CO₂ conversions were 18.4% and 98.9% at 400 °C and 900 °C, respectively. Additionally, a higher CO₂ conversion was obtained over the catalysts with 15 wt% Ni content when the temperature was higher than 600 °C. This is because of the balance between a high number of Ni active sites and high basicity. The characterization of the used catalyst by TGA, FE-SEM and Raman Spectroscopy confirmed the presence of amorphous carbon at lower temperature reaction and carbon nanotubes at higher temperature.     

Determination of the operating range of CO2 conversion and syngas production in dry auto-thermal reforming

A porous medium-catalyst hybrid reformer for CO₂ conversion by dry auto-thermal reforming (DATR) was investigated in this study, and its operating range was discovered. The hybrid design was used to enhance the oxidative heat release by internal heat recirculation during exothermic reaction conditions, thereby increasing the CO₂ conversion efficiency. The experimental results show that the CO₂ conversion could be enhanced with higher catalyst inlet temperatures. The examination of the operating range of DATR showed that the CO₂ conversion efficiency increased at higher reaction temperatures and CO₂/CH₄ ratios (≧1). Moreover, DATR in high temperature conditions must be carried out with high O₂/CH₄ ratios. Under these conditions of high oxygen content, CO₂ generation and reduction reactions occur simultaneously. Overall, optimal CO₂ conversion can be obtained with an O₂/CO₂ ratio of approximately 0.5. At these conditions, CO₂ conversion efficiency can reach approximately 13% without external heat addition.     

Thermodynamic equilibrium analysis of combined carbon dioxide reforming with partial oxidation of methane to syngas

The chemical equilibrium analysis on combined CH₄-reforming with CO₂ and O₂ (combined CORM–POM) has been conducted by total Gibbs energy minimization using Lagrange's undetermined multiplier method. The equilibrium compositions of the combined CORM–POM process were considerably influenced by CH₄:CO₂:O₂ feed ratios and operating temperatures. Methane oxidation reaction occurred predominantly at low temperatures, while the CO₂ conversion was strongly influenced by the O₂/CH₄ feed ratio. The addition of O₂ to the CORM process improved the CH₄ conversion, H₂ and H₂O yields and also the H₂/CO product ratio at the expense of CO₂ conversion and CO yield. Accordingly, the optimal equilibrium conditions for the CH₄:CO₂:O₂ ratio were within the range of 1:0.8:0.2–1:1:0.2 and a minimum requirement temperature of 1000 K.     

Organic heterojunction photovoltaic cells: role of functional groups in electron acceptor materials

We have fabricated and characterized some donor/acceptor type photovoltaic devices. While zinc phthalocyanine has been the donor material, a series of acceptor materials with identical backbone but different strength has been chosen. The role of function groups in acceptor material on photovoltaic device characteristics has been studied under different illumination intensities. Origin of the open-circuit voltage has been discussed considering ionization potential of donor and electron affinity of the acceptor material. Nonlinear increase of short-circuit current on light intensity has been observed and discussed in terms of conductance switching of acceptor material via electroreduction.