CO Clean-up Research Articles

Investigation of a methanol processing system comprising of a steam reformer and two preferential oxidation reactors for fuel cells

Methanol steam reforming is able to produce hydrogen-rich syngas onsite for fuel cells and avoids the problems of hydrogen storage. Nevertheless, CO in the reformate needs to be further removed to ppm level before it can be fed into proton exchange membrane fuel cells. In this study, a methanol processing system consisting of a methanol reformer and two-stage preferential oxidation reactors is developed. The hydrogen production performance and scalability of the reformer are experimentally investigated under various operating conditions. The methanol reformer system shows stable methanol conversion rate and linearly increased H2 flow rate as the number of repeating unit increases. Methanol conversion rate of 96.8% with CO concentration of 1.78% are achieved in the scaled-up system. CO cleanup ability of the two-stage preferential oxidation reactors is experimentally investigated based on the reformate compositions by varying the operating temperature and O2 to CO ratios. The results demonstrate that the developed CO cleanup train can decrease the CO concentration from 1.6% to below 10 ppm, which meets the requirement of the fuel cell. Finally, stability of the integrated methanol processing system is tested for 180 h operation.

Methane Steam Reforming on the Pt/CeO2 Catalyst: Effect of Daily Start-Up and Shut-Down on Long-Term Stability of the Catalyst

An environmentally friendly auxiliary power unit requires catalysts operating in the cyclic mode, producing H2 at a steady rate with high CO2 selectivity and minimum CO clean-up. Here, 1% Pt/CeO2 catalyst was synthesized using the solution combustion synthesis method and investigated toward methane steam reforming reaction. Preliminary tests were performed by varying the steam-to-carbon ratio (S/C), gas hourly space velocity (GHSV), and time-on-stream (TOS). The catalyst showed near-equilibrium CH4 conversion and high H2 concentration (75% dry basis, N2-free) obtained at S/C = 2.8 and GHSV = 24 000 h–1. The catalytic activity was stable after 25 cycles of start-up and shut-down operations, equivalent to 150 h of TOS. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques were used to characterize either the fresh and aged catalyst after 150 h of TOS.

The influence of CO, CO2 and H2O on selective CO methanation over Ni(Cl)/CeO2 catalyst: On the way to formic acid derived CO-free hydrogen

For the first time the influence of CO, CO2 and H2O content on the performance of chlorinated NiCeO2 catalyst in selective or preferential CO methanation was studied systematically. It was shown that the rate of CO methanation over Ni(Cl)/CeO2 increases with the increasing H2 concentration, is independent of CO2 concentration and decreases with increasing CO and H2O concentrations; the rate of CO2 methanation is weakly sensitive to H2 and CO2 concentrations and decreases with increasing CO and H2O concentrations. High catalyst selectivity was attributed to Ni surface blockage by strongly adsorbed CO molecules and ceria surface blockage by Cl, which both inhibit CO2 hydrogenation.For the first time, selective CO methanation over Ni(Cl)/CeO2 was studied for deep CO removal from formic acid derived hydrogen-rich gases characterized by high CO2 (40–50 vol%), low CO (30–1000 ppm) content and trace amounts of water. Composite Ni(Cl)/CeO2-η-Al2O3/FeCrAl wire mesh catalyst was demonstrated to be effective for this process at temperatures of 180–220°С, selectivity 30–70%, WHSV up to 200 L (STP)/(g∙h). The catalyst provides high process productivity, low pressure drop, uniform temperature distribution, and appears highly promising for the development of a compact CO cleanup reactor. Selective CO methanation was concluded to be a convenient way to CO-free hydrogen produced by formic acid decomposition.

The insights into chlorine doping effect on performance of ceria supported nickel catalysts for selective CO methanation

Selective CO methanation (CO-SMET) in the reformate gas, containing (vol.%): 1.0 CO, 65H2, 10H2O, 20 CO2 with He as balance, was investigated over a number of nickel-ceria catalysts: treated with NH4Cl before (Ni/CeO2(Cl*)) and after (Ni(Cl*)/CeO2) Ni deposition, prepared by Cl-containing Ni precursor (Ni(Cl)/CeO2) and Cl-free one (Ni/CeO2). The effect of residual chlorine, originating from the catalyst preparation procedures, on the activity and CO selectivity of the samples was demonstrated. It was shown that all Cl-containing Ni/CeO2 catalysts provided efficient CO cleanup. They provided the removal of CO from reformate gas to the level below 10ppm with a selectivity up to 90%. The catalyst characterization by BET, XRD, XPS, HAADF-STEM, EDX-mapping, FTIR in situ and CO chemisorption techniques revealed that the decrease in chlorine content in the order Ni(Cl)/CeO2≥Ni(Cl*)/CeO2>Ni/CeO2(Cl*) was accompanied by the increase of Ni dispersion that most likely provided high performance of Ni/CeO2(Cl*) in CO-SMET. The turnover frequencies of Ni surface atoms as well as activation energies in CO methanation were practically similar for all studied catalysts, indicating that Cl did not influence catalyst’s activity and CO methanation proceeded by similar ways over Ni surface in both Cl-free and Cl-containing samples. The advanced performance of Cl-containing catalysts was associated with the inhibition of undesirable side reaction of CO2 methanation. The chlorine doping effect was attributed to the blockage of surface Ce3+-coupled oxygen vacancy sites by CeOCl species that inhibited ceria-assisted CO2 activation and hydrogenation. The CeO2 treatment with NH4Cl before Ni deposition allows to prepare highly active and selective CO-SMET catalyst with high nickel dispersion and Cl-modified ceria surface.

Combination of preferential CO oxidation and methanation in hybrid MCR (micro-channel reactor) for CO clean-up

CO in the hydrogen stream must be reduced to extremely low levels, under 10 ppm, because the Pt electrode is detrimentally affected by residual CO in the H2 stream. Therefore removal of carbon monoxide from the H2-rich stream during fuel generation from hydrocarbons is a critical challenge, especially for PEMFC (proton exchange membrane fuel cell) applications. Herein, CO an initial concentration of 1.0 vol.% was successfully removed from a H2-rich stream to a residual level below 10 ppm, within the wide operating temperature range from 92 to 235 °C by utilizing a hybrid channel reactor comprising a micro-channel heat exchanger and mini-packed bed reactor. The mini-packed bed reactor contained two kinds of catalysts that promote preferential oxidation and methanation of CO in series. The HMCR (hybrid micro- and mini- channel reactor) offers not only ultimately safe operation but also easy scale-up and is adaptable to mass production of CO clean-up units.

Multiwalled carbon nanotube mixed matrix membranes containing amines for high pressure CO2/H2 separation

CO2-selective mixed matrix membranes capable of facilitated transport were synthesized for CO2/H2 separation at high pressures of at least1.52 MPa and high temperatures above373.15 K. A significant improvement in membrane stability was achieved by thoroughly dispersing multiwalled carbon nanotubes (MWNTs) as mechanical reinforcing fillers in a polyvinylalcohol matrix containing amines. With 2wt% MWNTs incorporated, the membrane performance, including a CO2/H2 selectivity of 43 and a CO2 permeability of 836Barrers (1 Barrer = 7.5×10−11 cm3(STP) cm/(cm2 s kPa)), showed no change for 444h (18.5 days) when operated at1.52 MPa and380.15 K. At the same conditions, the membrane containing 4wt% acid-treated MWNTs also showed good stability. The membranes synthesized in this work are the first of this kind, displaying exceptional CO2/H2 separation performance and high tolerance to feed gas at high pressures and high temperatures. Potentially, they could be used in a stand-alone membrane unit for energy-efficient precombustion carbon capture from coal-derived syngas or in conjunction with water-gas-shift reaction for CO clean-up to produce high-purity H2 for fuel cells and to simultaneously capture CO2.

Hydrogen production by onboard gasoline processing – Process simulation and optimization

Fuel cell vehicles have reached the commercialization stage and hybrid vehicles are already on the road. While hydrogen storage and infrastructure remain critical issues in stand alone commercialization of the technology, researchers are developing onboard fuel processors, which can convert a variety of fuels into hydrogen to power these fuel cell vehicles. The feasibility study of a 100kW on board fuel processor based on gasoline fuel is carried out using process simulation. The steady state model has been developed with the help of Aspen HYSYS to analyze the fuel processor and total system performance. The components of the fuel processor are the fuel reforming unit, CO clean-up unit and auxiliary units. Optimization studies were carried out by analyzing the influence of various operating parameters such as oxygen to carbon ratio, steam to carbon ratio, temperature and pressure on the process equipments. From the steady state model optimization using Aspen HYSYS, an optimized reaction composition in terms of hydrogen production and carbon monoxide concentration corresponds to: oxygen to carbon ratio of 0.5 and steam to carbon ratio of 0.5. The fuel processor efficiency of 95.98% is obtained under these optimized conditions. The heat integration of the system using the composite curve, grand composite curve and utility composite curve were studied for the system. The most appropriate heat exchanger network from the generated ones was chosen and that was incorporated into the optimized flow sheet of the100kW fuel processor. A completely heat integrated 100kW fuel processor flow sheet using gasoline as fuel was thus successfully simulated and optimized.

200 W급 휴대용 연료전지 시스템의 빠른 기동 특성을 위한 수성 가스 반응기 설계

휴대용 연료전지 시스템에 사용되는 연료 개질 시스템은 수소 발생기, 산화기, 일산화탄소 제거기로 구성되어 있다. 휴대용 연료전지 시스템 설계에서 시스템의 기동 시간은 매우 중요한 설계 인자이다. 특히, WGS 반응기의 기동 시간은 리포메이트의 질을 결정하기 때문에 전체 시스템의 기동 시간에 중요한 부분을 차지한다. 본 논문에서는 과량의 일산화탄소가 포함되어 있는 리포메이트 가스를 WGS 반응기에서 산화시킴으로써 WGS 반응기를 가열하는 방법을 사용하였다. 이때 공급되는 공기는 WGS 반응기 입구에 공급되어 기동 초기에 발생되는 과량의 일산화탄소가 함유된 리포메이트 가스를 제거하므로써, 운전 중에 일산화탄소의 과잉 공급없이 안정적으로 리포메이트를 공급함으로써 기동 시간을 단축할 수 있었다. The fuel processor for the portable fuel cell includes multi-step processes consisting of hydrogen generator, heat generator and several CO clean-up stages. One of requirements of the fuel processor for portable fuel cell system is a rapid start-up time. Especially, the warm-up time for WGS reactor is crucial factors for total start-up time. In this paper, active heating protocol, which is the heating protocol of WGS reactor supplied by the oxidation of CO rich reformate in the initial stage, is used for a rapid start-up. The air stream fed to the inlet of WGS reactor rapidly oxidize the CO rich reformate in the WGS reactor. Therefore, CO concentration in reformate quickly stabilized at the desired concentration without CO surges.

A comparative study on energetic and exergetic assessment of hydrogen production from bioethanol via steam reforming, partial oxidation and auto-thermal reforming processes

Three known types of ethanol reforming processes, ethanol steam reforming (ESR), partial oxidation (POX) and auto-thermal reforming (ATR), are investigated. Favorable operating conditions are identified for each reaction system to maximize the production of hydrogen from bioethanol. Each process consists of three sections: the main reactor (ESR, POX or ATR), the CO clean-up section comprised of the water gas shift reactor and preferential CO oxidation reactor and finally, the purification section. The performances of these processes are evaluated through mass, energy and exergy analyses.The material balances show that the total amount of ethanol required to generate 1mol of hydrogen is 0.23mol for the ATR, 0.24mol for the POX and 0.25mol for the ESR. The ATR reforming process is shown to have the highest energetic efficiency, i.e., the lowest amount of energy is consumed to produce the same amount of hydrogen from ethanol. Moreover, the ATR process has the best exergetic performance, as it presents the highest ratio of exergy recovered in the hydrogen stream to the total exergy supplied to the system. For all three of the systems, the exergy destruction occurs mainly in the reformer due to the high irreversibility of the reaction.

Preferential CO oxidation over CuO–CeO2 in excess hydrogen: Effectiveness factors of catalyst particles and temperature window for CO removal

In the preferential oxidation of CO in hydrogen mixtures (PROX), CO and H2 oxidation occur in parallel on the surface in a porous catalyst. The diffusion of the reactants into the pore structure of the catalyst can affect the catalyst performance significantly, and its effect can be accounted for in terms of the effectiveness factor. Conventional methods for estimating the effectiveness factor are not directly applicable because they have been developed for a single reaction in a catalyst particle. A novel method for a simultaneous estimation of the effectiveness factors of the two reactions was developed in this study. This method is based on the PROX kinetics over a CuO–CeO2 catalyst and is applicable to the cases where the CO oxidation can be approximated by a first-order reaction and both oxidations are zero-order reactions with respect to the O2 partial pressure. With the method, the performance of an isothermal PROX reactor was simulated to determine the effects of the feed flow rate, feed composition, reactor temperature and catalyst size on the CO clean-up.

Non-syngas direct steam reforming of methanol to hydrogen and carbon dioxide at low temperature

A non-syngas direct steam reforming route is investigated for the conversion of methanol to hydrogen and carbon dioxide over a CuZnGaO(x) catalyst at 150-200 °C. This route is in marked contrast with the conventional complex route involving steam reformation to syngas (CO/H2) at high temperature, followed by water gas shift and CO cleanup stages for hydrogen production. Here we report that high quality hydrogen and carbon dioxide can be produced in a single-step reaction over the catalyst, with no detectable CO (below detection limit of 1 ppm). This can be used to supply proton exchange membrane fuel cells for mobile applications without invoking any CO shift and cleanup stages. The working catalyst contains, on average, 3-4 nm copper particles, alongside extremely small size of copper clusters stabilized on a defective ZnGa2O4 spinel oxide surface, providing hydrogen productivity of 393.6 ml g(-1)-cat h(-1) at 150 °C.

Integrated methanol reforming and oxidation in wash-coated microreactors: A three-dimensional simulation

A microreactor consisting of two parallel channels is numerically simulated where methanol steam reforming takes place in one channel, and the required heat is supplied by methanol oxidation in the other channel. Effects of different parameters on methanol conversion, hydrogen yield and CO concentration are examined. Results from the parametric study are then used to propose conditions for high methanol conversion and hydrogen yield. A microreactor with enhanced output conditions is thus designed which is capable of producing a gas stream consisting of 74% hydrogen (dry). CO concentration in the generated synthesis gas stream is low enough to require only a PROX reactor for CO clean-up, eliminating the need for a bulky water–gas shift reactor. The produced hydrogen from an assembly of such microreactors can feed a low-power PEM fuel cell. A cluster of these microreactors would take a volume of about 91 cm 3 to feed a typical 30-watt PEM fuel cell.

Microfibrous structured catalytic packings for miniature methanol fuel processor: Methanol steam reforming and CO preferential oxidation

The microfibrous structured catalytic packings for miniature fuel processor consisting of a methanol steam reformer and a subsequent CO cleanup train has been investigated experimentally. A highly void and tailorable sinter-locked microfibrous carrier consisting of 3.5 vol% 8 μm diameter Ni-fibers is used to entrap 35 vol% 150–250 μm catalyst particulates for both methanol steam reforming (MSR) and CO preferential oxidation (PROX). We demonstrate a microfibrous entrapped Pd-ZnO/Al 2O 3 catalyst packings for high efficiency hydrogen production by the MSR reaction. The use of microfibrous entrapment technology significantly enhances the catalyst utilization efficiency by a 4-fold improvement of the weight hourly space velocity (WHSV), compared to the single Pd–ZnO/Al 2O 3 particulates as keeping the methanol conversion at >98%. The microfibrous entrapped Pt–Co/Al 2O 3 catalyst packings can drive the CO from 2% down to <50 ppm at 150 °C with O 2/CO ratio of 1 using a gas hourly space velocity (GHSV) of 32,000 h −1. Finally, a prototype fuel processor system integrating MSR reformer and CO PROX train is demonstrated as three reactors in series. Such test rig is capable of producing roughly 1700 standard cubic centimeter per minute (sccm) PEMFC-grade H 2 (equivalent to ∼163 W of electric power) in a longer-term test, in which the MSR reactor is operated at 300 °C using a methanol/water (1/1.1, mole) mixture WHSV of 9 h −1 and CO PROX reactors at 150 °C using an O 2/CO molar ratio of 1.3, respectively. In the test of this prototype system, MSR reactor delivers >97% methanol conversion throughout the entire 1200-h test; the CO cleanup train placed in line after 800-h MSR illustrates the capability to decrease the CO concentration from ∼3.5% to ∼1% at PROX-1 and then to less than 20 ppm at PROX-2 until to the end of test.

Efficient low temperature lean NOx reduction over Ag/Al2O3—A system approach

This study focuses on lean NOx reduction (LNR) by n-octane using silver–alumina based catalysts, with the addition of hydrogen. The work takes a system approach, where parameters such as temperature, reformate gas composition, fuel penalty and realistic monolith samples are considered. The LNR catalyst samples were prepared by impregnation and sol–gel methods and the NOx reduction performance was characterized by flow-reactor experiments, where realistic engine-out gas compositions were used. The hydrogen feed over the LNR catalyst samples was determined via data achieved by autothermal reforming experiments over a rhodium based catalyst, using real diesel as feedstock. The LNR catalyst samples generally show an enhanced NOx reduction when hydrogen is added to the gas feed. In particular, a 2wt% silver–alumina sample with the addition of minute amounts of platinum, shows a high increase in NOx reduction when hydrogen is added to the feed. The addition of CO, a potential poison in the reaction and a by-product from the reforming, did not show any significant effect on the LNR catalyst performance at the conditions used. This is beneficial, since it renders a CO clean-up step in the reformer system unneeded. Ammonia formation is discussed in terms of a possible dual-SCR system. Finally, the fuel penalty for hydrogen production and hydrocarbon addition is taken into consideration. It is found that an addition of 1000ppm H2 leads to unacceptable fuel penalties.

Hydrocarbons valorisation to cleaner fuels: H 2-rich gas production via fuel processors

This paper presents a panoramic overview of the experimental work carried out at Politecnico di Torino on the development of structured catalytic reactors for the production of H 2-rich streams from hydrocarbons, to be fed to PEM-FCs: short contact time catalytic partial oxidation (SCT-CPO) reactor for syngas production, micro-channelled reactors for syngas CO clean-up, water gas shift (WGS) and preferential oxidation (PROX). Concerning the reactor for methane SCT-CPO, 10% Ni deposited on irregular γ-Al 2O 3 particles presented the best performance (CH 4 conversion > 90%; H 2 selectivity > 95%) compared to 0.5% Rh deposited over γ-Al 2O 3 spheres. As regards the HT-WGS reaction, the best performance was obtained with the catalyst 1% Pt/(CeO 2 + TiO 2): it reached the thermodynamic equilibrium (inlet CO: 10% b.v.; WHSV = 40 Nl h −1 g cat −1) in the temperature range 450–525 °C, allowing the abatement of almost 60% of the CO present in the fed gas stream. Finally, the best performance towards CO-PROX reaction was obtained with the catalyst 1% Rh/(Al 2O 3 + 3A zeolite): it reached the complete CO conversion (inlet CO: 0.5% b.v.; WHSV = 40 Nl h −1 g cat −1; λ = 3) in the temperature range 130–160 °C, thus assuring an easy controllability of the system.

Thermodynamic analysis of ethanol processors – PEM fuel cell systems

This work presents a simulative energy efficiency analysis performed on fuel processor – PEM fuel cell systems, considering ethanol as fuel and steam reforming or autothermal reforming as processes to produce hydrogen. System analysis was performed on conventional configuration, where a classic reforming reactor is followed by a conventional CO clean-up section, constituted by water gas shift and preferential CO oxidation reactors, and on innovative configuration, where the reforming unit is coupled with an innovative highly selective hydrogen membrane. Steam to ethanol and oxygen to ethanol inlet ratios and reforming temperature are screened to identify the conditions that maximize global system efficiency. Pressure and sweep gas to ethanol inlet ratio are also considered as operative parameters in the membrane-based systems. A comparison with the results obtained when crude-ethanol is employed as fuel is also presented and discussed.

Energy efficiency of membrane-based fuel processors – PEM fuel cell systems

This work presents a simulative energy efficiency analysis performed on fuel processor – PEMFC systems, considering methane as fuel and steam reforming or autothermal reforming as processes to produce hydrogen. Computation of energy efficiency takes into account the power required by the auxiliary units, coupling of the fuel processor with the fuel cell as well as heat recovery and integration. Two system configurations were simulated and compared: an innovative configuration, based on an integrated membrane reactor directly coupled with the fuel cell, and a conventional configuration, based on a classic reforming reactor followed by a conventional CO clean-up section, constituted by water gas shift and preferential CO oxidation reactors. Reforming temperature, plant pressure, steam to methane and oxygen to methane inlet ratios were considered as process parameters. The effect of the addition of steam as sweep gas is also presented and discussed.

Modeling Study on the Performance of an Integrated APU Fed with Hydrocarbon Fuels

The employment of H2 in fuel cell (FCs) technologies could ensure significant advantages in terms of efficiency and environmental impact, representing thus an important alternative to the conventional energy production systems. As far as the actual lack of infrastructure for H2 production, storage, and distribution is concerned, FCs fed with H2, produced by fossil fuel reforming to generate on-board vehicles at least auxiliary power, represent a valid and interesting alternative to overcome the actual unfavorable situation, waiting for further development of infrastructures. The present work deals with the analysis of a 5 kWe auxiliary power unit (APU) integrated with a fuel processor unit (FPU), based on oxidative steam reforming (OSR, with bleed air, BA) and related CO clean-up technologies, for the production of H2-rich fuel gas, which is fed to a PEM-FC stack. Using the results of a series of steady-state system simulations with Matlab/Simulink, the APU performance was analyzed in terms of FP and APU efficiency, specific power produced by the stack, and water balance, by considering different liquid hydrocarbon fuels (gasoline, light and heavy diesel) and compressed natural gas (CNG) as feed. A parametric sensitivity analysis concerning the effects of the variation of steam to carbon ratio (SCR) and the BA rate to OSR was also carried out. As the main obtained results, the APU performance in transforming the primary fuel in H2-rich gas was more efficient according to the higher H2 to carbon ratio HCR of the feedstock. In fact, the APU net efficiency decreased with the following order: methane (27.8%) > gasoline (27.0%) > light diesel (26.5%) > heavy diesel (26.0%). The parametric sensitivity analysis revealed that with small SCR decrease and bleed air rate increase it was possible to improve the APU performance.

Diesel reformer — a key component for a truck fuel cell APU

A diesel fuel processor has been developed to integrate with a high-temperature polybenzimidazole (PBI) based polymer electrolyte membrane (PEM) fuel cell, to provide power for truck auxiliary power unit (APU) applications. The fuel processor is designed to operate at low temperatures, ranging from 490 to 600°C, and convert ultra low sulfur diesel (ULSD) to C1 (CH4, CO and CO2) compounds without intermediate products. Reforming in this low temperature range is an effective approach to minimizing carbon deposition. It also produces less CO in the product; consequently the CO cleanup component is greatly simplified when the system is integrated with a PBI fuel cell that tolerates some CO. This reduction in system complexity will help lower costs while improving reliability.

Evaluating the impact of enhanced anode CO tolerance on performance of proton-exchange-membrane fuel cell systems fueled by liquid hydrocarbons

Recent advances in anode electrocatalysts for low-temperature PEM fuel cells are increasing tolerance for CO in the H 2-rich anode stream. This study explores the impact of potential improvements in CO-tolerant electrocatalysts on the system efficiency of low-temperature Nafion-based PEM fuel cell systems operating in conjunction with a hydrocarbon autothermal reformer and a preferential CO oxidation (PROx) reactor for CO clean-up. The incomplete H 2 clean-up by PROx reactors with partial CO removal can present conditions where CO-tolerant anode electrocatalysts significantly improve overall system efficiency. Empirical fuel cell performance models were based upon voltage–current characteristics from single-cell MEA tests at varying CO concentrations with new Pt–Mo alloy reformate-tolerant electrocatalysts tested in conjunction with this study. A system-level model for a liquid-fueled PEM fuel cell system with a 5 kW full power output is used to study the trade-offs between the improved performance with decreased CO concentration and the increased penalties from the air supply to the PROx reactor and associated reduction in H 2 partial pressures to the anode. As CO tolerance is increased over current state-of-the-art Pt alloy catalysts, system efficiencies improve due primarily to higher fuel cell voltages and to a lesser extent to reductions in parasitic loads. Furthermore, increasing CO tolerance of anode electrocatalysts allows for the potential for reduced system costs with minimal efficiency penalty by reducing PROx reactor size through reduced CO conversion requirements.