Two-Dimensional Modeling of the Oxidative Coupling of Methane in a Fixed Bed Reactor: A Comparison among Different Catalysts

A proposed two-dimensional model of the oxidative coupling of methane (OCM) to C2 hydrocarbons (e.g., C2H4 and C2H6) in a fixed bed reactor operated under isothermal and non-isothermal conditions is described which can provide more accurate predictions of experimental data than the simplified one-dimensional model. The model includes a set of partial differential equations of the continuity, mass transfer and energy balance equations. The performance of the OCM using different catalysts was assessed in terms of CH4 conversion, C2 selectivity and C2 yield with respect to key operating parameters, such as feed temperature (973-1173 K), CH4/O2 ratio (3.4–7.5) and gas hour space velocity (GHSV) (18000-30000 h-1). The simulation results indicated that the Na-W-Mn/SiO2 catalyst exhibits the best performance among all of the catalysts. The C2 yield were 20.16% and 20.00% for non-isothermal and isothermal modes respectively which the OCM reactor is operated at a CH4/O2 ratio of 3.4, a feed temperature of 1073 K and a GHSV of 9720 h-1. An increase in the operating temperature increases the CH4 conversion but decreases the C2 selectivity. However, the effects of the CH4/O2 ratio and the GHSV exhibit an opposite trend to that of the operating temperature.A proposed two-dimensional model of the oxidative coupling of methane (OCM) to C2 hydrocarbons (e.g., C2H4 and C2H6) in a fixed bed reactor operated under isothermal and non-isothermal conditions is described which can provide more accurate predictions of experimental data than the simplified one-dimensional model. The model includes a set of partial differential equations of the continuity, mass transfer and energy balance equations. The performance of the OCM using different catalysts was assessed in terms of CH4 conversion, C2 selectivity and C2 yield with respect to key operating parameters, such as feed temperature (973 - 1173 K), CH4/O2 ratio (3.4 – 7.5) and gas hour space velocity (GHSV) (18000 - 30000 h-1). The simulation results indicated that the Na-W-Mn/SiO2 catalyst exhibits the best performance among all of the catalysts. The C2 yield were 20.16% and 20.00% for non-isothermal and isothermal modes respectively which the OCM reactor is operated at a CH4/O2 ratio of 3.4, a feed temperature of 1073 K and a GHSV of 9720 h-1. An increase in the operating temperature increases the CH4 conversion but decreases the C2 selectivity. However, the effects of the CH4/O2 ratio and the GHSV exhibit an opposite trend to that of the operating temperature

Electronic and Ionic Conductivities Enhancement of Zinc Anode for Flexible Printed Zinc-Air Battery

Zinc-air battery is considered a promising candidate for future energy applications due to its high energy density, safety and low cost. However, poor battery performance and low efficiency of zinc utilization, resulted from passivation effect of the zinc anode, is a major challenge. Thus, in this work, investigation of electronic and ionic conductivities enhancement of the zinc anode for flexible printed zinc-air battery has been carried out. The anode was made from a zinc-based ink, prepared from a mixture of zinc and zinc oxide particles. Carbon black, sodium silicate (Na2SiO3) and bismuth oxide (Bi2O3) were investigated for implementation on the anode. The results showed that performance of the battery increased when carbon black was introduced into the anode as the presence of carbon black improved electronic conductivity of the anode. Again, the battery performed better when Bi2O3 orNa2SiO3 was introduced due to the formation of solid electrolyte interface (SEI) on the anode. The SEI inhibits passivation of zinc active surfaces and provides effective electrolyte access. The battery with Bi2O3 provided the best performance. The highest performance was observed when Bi2O3 content reached 26wt.%. No significant improvement was observed whenBi2O3 concentration increased higher than 26 wt.%.Zinc-air battery is considered a promising candidate for future energy applications due to its high energy density, safety and low cost. However, poor battery performance and low efficiency of zinc utilization, resulted from passivation effect of the zinc anode, is a major challenge. Thus, in this work, investigation of electronic and ionic conductivities enhancement of the zinc anode for flexible printed zinc-air battery has been carried out. The anode was made from a zinc-based ink, prepared from a mixture of zinc and zinc oxide particles. Carbon black, sodium silicate (Na2SiO3) and bismuth oxide (Bi2O3) were investigated for implementation on the anode. The results showed that performance of the battery increased when carbon black was introduced into the anode as the presence of carbon black improved electronic conductivity of the anode. Again, the battery performed better when Bi2O3 or Na2SiO3 was introduced due to the formation of solid electrolyte interface (SEI) on the anode. The SEI inhibits passivation of zinc active surfaces and provides effective electrolyte access. The battery with Bi2O3 provided the best performance. The highest performance was observed when Bi2O3 content reached 26 wt.%. No significant improvement was observed when Bi2O3 concentration increased higher than 26 wt.%

Performance of Membrane-Assisted Solid Oxide Fuel Cell System Fuelled by Bioethanol

The membrane separation units for bioethanol purification including pervaporation and vapor permeation are integrated with the bioethanol-fuelled solid oxide fuel cell (SOFC) system. The preliminary calculations indicate that Hydrophilic type is a suitable membrane for vapor permeation to be installed after a hydrophobic pervaporation. Based on energy self-sufficient condition and data of available pervaporation membranes, the simulation results show that the use of vapor permeation unit after the pervaporation can significantly improve the overall electrical efficiency from 10.96% for the system with pervaporation alone to 26.56%. Regarding the effect of ethanol recovery, the ethanol recovery at 75% can offer the optimal overall efficiency from the proposed purification system compared to the ethanol recovery at 31.16% for the case with the single pervaporation

Optimal Design of Biodiesel Production Process from Waste Cooking Palm Oil

AbstractA design methodology for biodiesel production from waste cooking palm oil is proposed. The proposed method is flexible to the biodiesel process using various catalyst types: alkali and acid catalyst in homogenous and heterogeneous forms, and different process: enzyme process and supercritical process. A two-step approach of hydrolysis and esterification processes is also considered. Waste cooking palm oil consists of a mixture of triglyceride (e.g., trilaurin, tripalmitin, triolein, tristearin, trilinolein and trilinolenin) and free fatty acids (e.g., lauric acid, palmitic acid, stearic acid, oleic acid, linoleic and linolenic acid). A driving force approach and thermodynamic insight are employed to design separation units (e.g., flash separator and distillation) minimizing the energy consumption. Steady-state simulations of the developed biodiesel processes are performed and economic analysis is used to find a suitable biodiesel process. The results show that based on a net present value, the heterogeneous acid catalyzed process is the best process for biodiesel production. With the design methodology, the proposed biodiesel process can save the energy requirement of 41.5%, compared with a conventional process

One input voltage and three output voltage universal biquad filters with orthogonal tune of frequency and bandwidth

This research paper contributes the one input three output voltage mode universal biquad filters with linear and electronic control of the natural frequency (w0), using two commercially available ICs, LT1228s as active device with two grounded capacitors, five resistors. The presented universal biquad filters can simultaneously provide three voltage-mode filtering functions, low-pass (LP), high-pass (HP) and band-pass (BP) without changing the circuit architecture. Furthermore, the first presented biquad filter provides low impedance at HP, BP voltage output nodes and LP, BP output voltage nodes are low impedance for the second proposed filter which is easy cascade ability with other voltage mode circuits without the employment of buffer circuits. The quality factor (Q) of both proposed filters is orthogonally adjusted from the passband voltage gain and w0. The proposed filters are simulated and experimented with commercially accessible ICs, LT1228. The simulated and experimental results demonstrate the filtering performances

Two-Dimensional Mathematical Modeling of the Oxidative Coupling of Methane in a Membrane Reactor

The oxidative coupling of methane (OCM) in a dense BSCFO membrane reactor (MR) was theoretically studied using a two-dimensional reactor model. The simulation results indicated that increasing the operating temperature results in increased CH4 conversion and decreased C2 selectivity. An increase in the methane feed flow rate lowers the CH4 conversion but increases the C2 selectivity; however, the effect of the air flow rate on the OCM membrane reactor exhibits an opposite trend. The optimum configuration of the dense BSCFO-MR to provide the best performance was 0.018 m in diameter and 0.2 m in length at a GHSV of 38904.54 h-1 and temperature of 1073 K. Under these optimal conditions, the CH4 conversion is 43.713%, the C2 selectivity is 61.352% and the C2 yield is 26.82%

Hydrogen Production from Sorption Enhanced Biogas Steam Reforming Using Nickel-Based Catalysts

Hydrogen gas is a clean and sustainable fuel/energy carrier considered to be a possible alternative to fossil fuels. Sorption enhanced biogas steam reforming is a process which combines a CO2 adsorption unit with a hydrogen production unit. In the CO2 sorption section, CaO was selected as the adsorbent due to its high stoichiometric adsorption capacity. From the adsorption test, the highest adsorption capacity (0.2849 gCO2/gCaO) was achieved at a temperature of 873 K. Four types of bed arrangement were investigated using a feed gas with a CH4/CO2 ratio of 1.5, an S/C ratio of 3, a temperature of 873 K and at atmospheric pressure. The results indicate that the Type II system (Catalyst physical mixed with sorbent system packed in fixed bed quartz reactor, 0.8 g of 12.5 wt% Ni/Al2O3 mixed with 2 g of CaO) exhibits the highest improvement in CH4 conversion with the introduction of CO2 adsorption (93.0% and 81.7%, with and without CO2 sorption, respectively) and high purity hydrogen was produced (97.0% v/v and 62.3% v/v, with and without CO2 sorption respectively)

Model-Based Analysis of an Integrated Zinc-Air Flow Battery/Zinc Electrolyzer System

This work aims at analyzing an integrated system of a zinc-air flow battery with a zinc electrolyzer for energy storage application. For efficient utilization of inherently intermittent renewable energy sources, safe and cost-effective energy storage systems are required. A zinc-air flow battery integrated with a zinc electrolyzer shows great promise as an electricity storage system due to its high specific energy density at low cost. A mathematical model of the system was developed. The model was implemented in MATLAB and validated against experimental results. The validation of the model was verified by the agreement between the simulation and experimental polarization characteristic. The behavior and performance of the system were then examined as a function of different operating parameters: the flow rate of the electrolyte, the initial concentration of potassium hydroxide (KOH) and the initial concentration of zincate ion. These parameters significantly affected the performance of the system. The influence of the hydrogen evolution reaction (HER) on the performance of the system was investigated and discussed as it significantly affected the coulombic efficiencies of both the zinc-air flow battery and the zinc electrolyzer. Optimal KOH concentration was found to be about 6–7 M. Whilst increased KOH concentration enhanced the discharge energy of the battery, it also increased HER of both the battery and the electrolyzer. However, higher initial concentration of zincate ion reduced HER and improved the coulombic efficiency of the system. Besides, a higher flow rate of electrolyte enhanced the performance of the system especially at a high charge/discharge current by maintaining the concentration of active species in the cell. Nevertheless, the battery suffered from a higher rate of HER at a high flow rate. It was noted that the model-based analysis provided better insight into the behavioral characteristics of the system leading to an improved design and operation of the integrated system of zinc-air flow battery with the zinc electrolyzer

Molecular detection and speciation of pathogenic Leptospira spp. in blood from patients with culture-negative leptospirosis

Abstract Background Pathogenic Leptospira spp. present in the blood of patients with leptospirosis during the first week of symptoms can be detected using culture or PCR. A proportion of patients who are positive by PCR are negative by culture. Leptospira spp. are fastidious bacteria, and we hypothesized that a false-negative culture result may represent infection with a distinct bacterial subset that fail to grow in standard culture medium. Methods We evaluated our hypothesis during a prospective study of 418 consecutive patients presenting to a hospital in northeast Thailand with an acute febrile illness. Admission blood samples were taken for Leptospira culture and PCR. A single tube nested PCR that amplified a region of the rrs gene was developed and applied, amplicons sequenced and a phylogenetic tree reconstructed. Results 39/418 (9%) patients were culture-positive for Leptospira spp., and 81/418 (19%) patients were culture-negative but rrs PCR-positive. The species associated with culture-positive leptospirosis (37 L. interrogans and 2 L. borgpetersenii) were comparable to those associated with culture-negative, PCR-positive leptospirosis (76 L. interrogans, 4 L. borgpetersenii, 1 unidentified, possibly new species). Conclusion Molecular speciation failed to identify a unique bacterial subset in patients with culture-negative, PCR-positive leptospirosis. The rate of false-negative culture was high, and we speculate that antibiotic pre-treatment is the most likely explanation for this.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are