CO Impurities Research Articles

CO2-based reconfigurable enhanced oil recovery using the oxy-fuel-fired boilers: Thermal and flow properties

This work presents first-of-a-kind results on the enhanced oil recovery (EOR) by CO2 stream of oxy-fuel-fired circulating fluidized bed (CFB) boilers for Constant Furnace Size Scenario and Constant Thermal Power Scenario. The CO2 flow rate, the associated impurities and the furnace thermal properties are investigated. The total mass flow rate of the EOR gas in Constant Furnace Size Scenario for the oxy-fuel case of 70% O2 concentration becomes more than 2.6 times of the one with 29% O2 concentration. The oxy-fuel CFB usage for EOR offers the opportunity of reconfigurable manufacturing system (RMS) where the CO2 production capacity is flexible to market demand. While the increased CO2 mass flow rates at elevated O2 concentrations is in favor of Constant Furnace Size Scenario, the mass flow rates of the impurities of O2, CO and H2O also increase leading to higher costs for gas cleaning before sending the CO2 stream for EOR injection. The relatively low outgoing CO level in addition to considerably lower furnace CO maxima compared to the other scenario are merits of Constant Thermal Power Scenario.

Experimental studies on the poisoning properties of a low-plateau hydrogen storage alloy LaNi4.3Al0.7 against CO impurities

Metal hydride (MH) material can be used for effective separation of hydrogen from gas mixture. However, some impurities in the feedstock gas may cause the poisoning of the material and hence failure of the MH-based hydrogen separation system. In this paper, the hydrogen storage alloy LaNi4.3Al0.7, which has low-plateau pressure and was supposed to be used for hydrogen separation from the semi-coke oven gas, was tested in the atmosphere with relatively high concentration of CO impurities (∼0.1%v/v) by cycling experiments. Interestingly, the hydrogen storage capacity of the material shows quite mild decline during contact with CO at the temperature of 363 K or higher, and relatively fast kinetics can be kept, highlighting its application potential for hydrogen separation on a variety of occasions.

Investigating PSA, VSA, and TSA methods in SMR unit of refineries for hydrogen production with fuel cell specification

Abstract In this paper a robust and reliable process is proposed for purification of hydrogen from syngas to approach to the specification of fuel cell application (H2 purity >99.99, CO impurity 99.99%) and minimum CO content of 0.2 ppm, with appropriate recovery and productivity. Among the studied processes, PSA re-pressurized with feed had limited ability to achieve fuel cell hydrogen specification whereas PSA re-pressurized with product could achieve these specifications; however the low recovery of the process made it unreliable from economical point of view. Considering high H2 purity and acceptable recovery, TSA would be the appropriate process, but its low productivity is a great imperfection. Considering the purity of hydrogen, energy consumption and capital cost, VSA would be the most superior process compared with the other cyclic processes. At the optimal point of view, for a feed with 75mol% H2, VSA has resulted productivity of 148 mol H2/(kgads⋅day) with 940 kJ/kgH2product electrical energy consumption whereas TSA has resulted only 86 mol H2/(kgads day) productivity, with 420 kJ/kgH2product, electrical energy and 45.2 MJ/kgH2product heating energy consumption.

Iridium-Catalyzed Continuous Hydrogen Generation from Formic Acid and Its Subsequent Utilization in a Fuel Cell: Toward a Carbon Neutral Chemical Energy Storage

This study represents a notable step toward a potentially carbon neutral energy storage solution based on formic acid as a hydrogen/energy carrier. A catalytic system derived from IrCl3 and 1,3-bis(2′-pyridyl-imino)-isoindoline (IndH) in the presence of aqueous sodium formate showed high selectivity and robustness for hydrogen generation from formic acid (FA) at 90–100 °C under both high and moderate pressure conditions suppressing the formation of CO impurity. Being a solid substance, the catalyst can be recovered by a simple filtration, if necessary. Furthermore, addition of neat formic acid is sufficient to reuse the catalyst and maintain a constant flow of H2 and CO2 mixture and the stable performance of a coupled fuel cell. The easy to recycle catalyst did not show any loss of activity after 20 days of continuous use, and similar activity was observed even a year after the original preparation. The reactor for formic acid decomposition provided a one to one ratio of a H2/CO2 mixture that was coupled ...

Measurements of Decompression Wave Speed in Binary Mixtures of Carbon Dioxide and Impurities

Shock tube tests were conducted on a number of binary CO2 mixtures with N2, O2, CH4, H2, CO, and Ar impurities, from a range of initial pressures and temperatures. This paper provides examples of results from these tests. The resulting decompression wave speeds are compared with predictions made utilizing different equations of state (EOS). It was found that, for the most part (except for binaries with H2), the GERG-2008 EOS shows much better performance than the Peng–Robinson (PR) EOS. All binaries showed a very long plateau in the decompression wave speed curves. It was also shown that tangency of the fracture propagation speed curve would normally occur on the pressure plateau, and hence, the accuracy of the calculated arrest toughness for pipelines transporting these binary mixtures is highly dependent on the accuracy of the predicted plateau pressure. Again, for the most part, GERG-2008 predictions of the plateau are in good agreement with the measurements in binary mixtures with N2, O2, and CH4. An example of the determination of pipeline material toughness required to arrest ductile fracture is presented, which shows that prediction by GERG-2008 is generally more conservative and is therefore recommended. However, both GERG-2008 and PR EOS show much worse performance for the other three binaries: CO2 + H2, CO2 + CO, and CO2 + Ar, with CO2 + H2 being the worst. This is likely due to the lack of experimental data for these three binary mixtures that were used in the development of these EOS.

Growth of transition metals on cerium tungstate model catalyst layers

Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed.

Impurity effect on surface states of Bi (111) ultrathin films**Project supported by the National Basic Research Program of China (Grants Nos. 2015CB921400 and 2011CB921802) and the National Natural Science Foundation of China (Grants Nos. 11374057, 11434003, and 11421404).

The surface impurity effect on the surface-state conductivity and weak antilocalization (WAL) effect has been investigated in epitaxial Bi (111) films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.

Solid-state hydrogen sensors based on calixarene—12-phosphatotungstic acid composite electrolytes

An electrochemical system sensitive to hydrogen was studied. A composite proton conductor based on calixarene sulfonic acid and 12-phosphotungstic acid was used as a solid electrolyte membrane. The system is tolerant to CO impurities (up to 200ppm) in H2. The catalytic properties of the composite electrolyte can be described using percolation theory. Variation in the composition of the solid composite electrolyte in the investigated system allowed to adjust its properties and improve the performance of potentiometric hydrogen sensors under ambient conditions.

Influence of CO molecular impurity on the structural and thermodynamic properties of fullerite C60, in a broad range of sorption temperatures

An x-ray diffraction study of how sorption of CO gas at a pressure of 30 atm in the temperature range of 150–600 °C influences the structural characteristics of polycrystalline and single crystal fullerite C60. The sorption kinetics are studied by constructing a dependence of the lattice parameter on the time it takes for fullerite to be saturated by CO molecules. At temperatures Tsorb > 300 °C there is an observed dissociation of carbon monoxide, accompanied by the precipitation of carbon powder and the chemical interaction of atomic oxygen with C60 and CO molecules, and possibly with the carbon condensate. These processes have a strong influence on the structural characteristics of fullerite, thus creating, in part, a nonmonotonic dependence of the parameter and lattice matrix volume on the impurity saturation temperature. The concentrations of solid solutions C60(CO)x poly- and single crystal samples are determined in the physisorption range for two modes (150 and 250 °C). It is found that the CO impurity has a linear effect on the lattice parameter and the temperature of the orientational transition of fullerite C60.

Highly efficient hydrogen generation from formic acid using a reduced graphene oxide-supported AuPd nanoparticle catalyst.

Highly dispersed AuPd alloy nanoparticles have been successfully immobilized on reduced graphene oxide (rGO) using a facile non-noble metal sacrificial method, which exhibit the highest activity at 323 K (turnover frequency, 4840 h(-1)) for hydrogen generation without CO impurity from the formic acid/sodium formate system.

Preferential Photooxidation of CO in Hydrogen across the Crystalline Face Boundary over Spheroidal ZnO Promoted by Cu Ions

The design and synthesis of nanoscale zinc oxides (ZnOs) and their applications to photocatalysis are widely explored. However, the photocatalytic controls needed to design appropriate crystalline faces and promoter sites for each catalytic reaction step using ZnO have been rarely reported. This study optimized photocatalytic hydrogen purification using the preferential oxidation (PROX) of CO impurities among nanoscale disk-like, spheroidal, and rod-like ZnO promoted by adsorbed Cu ions. Four key factors were examined: (1) the diffusion length to the surface of separated electrons and holes induced by light; (2) the crystalline face where formate was formed from CO and its stability; (3) the crystalline face where Cu ions adsorbed for trapping electrons and reducing O2; and (4) the frequency factor of “charge recombination as cations and anions” derived from photogenerated holes and electrons, respectively, at the boundary of crystalline faces. The optimal photocatalyst for hydrogen purification (CO PROX)...

C-, N-, S-, and Fe-Doped TiO2 and SrTiO3 Nanotubes for Visible-Light-Driven Photocatalytic Water Splitting: Prediction from First Principles

The ground state electronic structure and the formation energies of both TiO2 and SrTiO3 nanotubes (NTs) containing CO, NO, SO, and FeTi substitutional impurities are studied using first-principles calculations. We observe that N and S dopants in TiO2 NTs lead to an enhancement of their visible-light-driven photocatalytic response, thereby increasing their ability to split H2O molecules. The differences between the highest occupied and lowest unoccupied impurity levels inside the band gap (HOIL and LUIL, respectively) are reduced in these defective nanotubes down to 2.4 and 2.5 eV for N and S doping, respectively. The band gap of an NO+SO codoped titania nanotube is narrowed down to 2.2 eV (while preserving the proper disposition of the gap edges relatively to the reduction and oxidation potentials, so that eHOIL < ϵO2/H2O < ϵH+/H2 < ϵLUIL), thus decreasing the photon energy required for splitting of H2O molecule. For C- and Fe-doped TiO2 NTs, some impurity levels lie in the interval between both redox po...

Dynamic Modeling for the Simulation of AC Spectra for HT-PEMFC

High Temperature Polymer Electrolyte Membrane Fuel Cells, (HT-PEMFCs), offer significant advantages over low temperature operation, such as simplified water management, increased tolerance to CO poisoning and impurities and simple balance of plant [1]. Even though the operating principles of an HT-PEMFC are understood, the overall system’s behavior is determined by a number of strongly coupled processes, each proceeding at a different rate. Thus, to optimize the performance of the fuel cell, an in depth understanding of the various processes and their interactions is necessary. One of the most powerful electrochemical characterization methods is the Electrochemical Impedance Spectroscopy technique, (EIS). It is a very powerful and sensitive technique that has already become a primary diagnostic tool in PEM fuel cell research, [2, 3]. EIS can provide valuable information on the various physicochemical and electrochemical processes taking place in the Membrane Electrode Assembly, (MEA), of an HT-PEMFC. Unfortunately the behavior of many electrochemical processes, such as Hydrogen and Oxygen adsorption relaxation phenomena, (Fig. 1), and the effect they have on the performance of the fuel cell is very difficult to deduce from experimental spectra. Fig. 1 Simulated impedance spectra for H2/O2 HT-PEMFC, , (Icell = 200mA/cm2), depicting the low frequency capacitive impedance caused by the relaxation of H2 adsorption, (black) when O2 adsorption dynamics are absent for both spectra, frequency range 10mHz – 50kHz. In this study a 2-D dynamic mathematical model has been developed on the cross section of the membrane electrode assembly in order to simulate AC impedance spectra under various operational conditions. The model includes a detailed macroscopic description of the diffusion processes within the electrode, the electro-kinetic model of the chemical and electrochemical reactions within the catalytic layers as well as the charge transfer across the various parts of the MEA. The aim of the 2-D cross section simulation of the MEA is to carry out a parametric and sensitivity analysis of the various parameters that govern the various processes across the MEA. By decoupling the various processes and simulating an AC impedance spectrum, information will be extracted on the various kinetic and equilibrium constants related with the interaction of the reacting gases in the catalytic layer and the electrochemical interface.

Immobilizing highly catalytically active noble metal nanoparticles on reduced graphene oxide: a non-noble metal sacrificial approach.

In this work, we have developed a non-noble metal sacrificial approach for the first time to successfully immobilize highly dispersed AgPd nanoparticles on reduced graphene oxide (RGO). The Co3(BO3)2 co-precipitated with AgPd nanoparticles and subsequently sacrificed by acid etching effectively prevents the primary AgPd particles from aggregation. The resulted ultrafine AgPd nanoparticles exhibit the highest activity (turnover frequency, 2739 h(-1) at 323 K) among all the heterogeneous catalysts for the dehydrogenation of formic acid to generate hydrogen without CO impurity. The sacrificial approach opens up a new avenue for the development of high-performance metal nanocatalysts.

Water oxidation catalysis by Co(II) impurities in Co(III)4O4 cubanes.

The observed water oxidation activity of the compound class Co4O4(OAc)4(Py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water oxidation activity that has been reported for Co4O4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials and demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis.

Competition between CO2 Reduction and H2 Evolution on Transition-Metal Electrocatalysts

The well-known hydrogen evolution reaction (HER) volcano plot describes the relationship between H binding energy and the corresponding hydrogen evolution catalytic activity, which depends on the species of metal. Under CO2/CO reduction conditions or in cases where CO impurities enter electrodes, the catalyst may exist under a high coverage of coadsorbed CO. We present DFT calculations that suggest that coadsorbed CO during hydrogen evolution will weaken the binding strength between H and the catalyst surface. For metals on the right-hand side (too weak of hydrogen binding) this should lead to a suppression of the HER, as has been reported for metals such as Cu and Pt. However, for metals on the left-hand side of the volcano (too strong of hydrogen binding), this may actually enhance the kinetics of the hydrogen evolution reaction, although this effect will be countered by a decreased availability of sites for HER, which are blocked by CO. We performed experiments in Ar and CO2 environments of two representative metals that bind CO on the far right- and left-hand side of the volcano, namely, Cu and Mo (respectively). On Cu, we find that the CO2 environment suppresses HER, which is consistent with previous findings. However, on Mo we find that the CO2 environment enhances HER in the kinetically active region. This helps to explain the outstanding performance of copper in CO2 reduction and suggests that searches for high-selectivity CO2/CO reduction catalysts may benefit from focusing on the right-hand side of the HER volcano. This also suggests principles for assessing the activity of catalysts for fuel cell and electrolysis reactions in which impurities such as CO may be present.

Discussion of the influence of CO and CH4 in CO2 transport, injection, and storage for CCS technology.

This paper discusses the influence of the noncondensable impurities CO and CH4 on Carbon Capture and Storage (CCS) technology. We calculated and drew conclusions about the impact of both impurities in the CO2 on selected transport, injection, and storage parameters (pipeline pressure drop, storage capacity, etc.), whose analysis is necessary for the safe construction and operation of CO2 pipelines and for the secure long-term geological storage of anthropogenic CO2. To calculate these parameters, it is necessary to acquire data on the volumetric properties and the vapor-liquid equilibrium of the fluid being subjected to CCS. In addition to literature data, we used new experimental data, which are presented here and were obtained for five mixtures of CO2+CO with compositions characteristic of the typical emissions of the E.U. and the U.S.A. Temperatures and pressures are based on relevant CO2 pipeline and geological storage site values. From our experimental results, Peng-Robinson, PC-SAFT, and GERG Equations of State for were validated CO2+CO under the conditions of CCS. We conclude that the concentration of both impurities strongly affects the studied parameters, with CO being the most influential and problematic. The overall result of these negative effects is an increase in the difficulties, risks, and overall costs of CCS.

Can CO-Tolerant Anodes be Economically Viable for PEMFC Applications with Reformates?

Several years ago, the answer to this question was negative based on the criteria for an anode with <0.1 mg cm-2 of platinum group metals to perform similarly without and with 50 ppm CO in hydrogen proton exchange membrane fuel cells (PEMFCs). Now, with the amount of CO impurities reduced to 10 ppm in reformates, a <1% performance loss with a 1.5% air-bleed has become a reasonable target. The CO-tolerant catalyst also needs to be dissolution resistant up to 0.93 V, viz., the potential experienced at the anode during startup and shutdown of the fuel cells. We recently demonstrated our ability to simultaneously enhance activity and stability by using single crystalline Ru@Pt core-shell nanocatalysts. Here, we report that the performance target with reformates was met using bilayer-thick Ru@Pt core-shell nanocatalysts with 0.047 mg cm-2 Pt and 0.024 mg cm-2 Ru loading, supporting a positive prognosis for the economically viable use of reformates in PEMFC applications.

Effect of CO on hydrogen storage performance of KF doped 2LiNH2 + MgH2 material

(2LiNH2+MgH2) material is one of the most promising hydrogen storage materials. In applications, CO impurity in hydrogen has an effect on the hydrogen storage performance of (2LiNH2+MgH2) material. In this work, the effect of CO on the hydrogen storage properties of KF doped (2LiNH2+MgH2) material was investigated by using hydrogen containing 1mol% CO as the hydrogenation gas source. The results indicate that the hydrogen desorption capacity of the hydride decreases from 4.73wt.% to 3.88wt.% after 5 hydrogenation cycles. The decrease of the capacity is attributed to the permanent loss of the NH2 caused by the formation of Li2CN2 and KCN. Moreover, the hydrogen desorption kinetics declines obviously, and the dehydrogenation activation energy increases from 122.1kJ/mol to 132.0kJ/mol. Furthermore, it is found that the hydrogen desorption kinetics cannot be recovered to the initial level after re-milling. The main reason for these is that the catalytic effect on (Mg(NH2)2+2LiH+0.05KF) system disappears due to the transformation from KH to KCN.

CO impurities effect on LaNi4.7Al0.3 hydrogen storage alloy hydrogenation/dehydrogenation properties

LaNi4.7Al0.3 alloy was prepared by vacuum induction melting in high purity helium atmosphere, and the ingot was pulverized into 200–400 mesh powder after annealing. X-ray diffraction (XRD) and scanning electron microscopies (SEM) were utilized to study the alloy morphology and phase structure. X-ray photoelectron spectroscopy (XPS) was used for surface analysis. The poisoned alloy was tested at 30 °C in the mixture gas by thermogravimetric and differential thermal analyses (TG + DTA). The hydrogen storage properties were studied by the pressure-composition-temperature test. The activated sample was completely deactivated after only 3 hydriding/dehydriding cycles in hydrogen containing 300 ppm CO at 30 °C, but hydrogen storage capacity did not degrade when tested at 80 °C. Additionally, two different steps appeared in the absorption processes. Combined with XRD, XPS and TG + DTA results, an explanation for this phenomenon is given.