Methanol formation in the water gas shift reaction over copper-containing catalysts

In ammonia and hydrogen production, methanol formation takes place mainly at the low-temperature (second) WGS stage, where the gas composition, catalysts, and operating conditions are similar to those in methanol synthesis. The methanol formation reaction consumes hydrogen, an expensive gas, and causes a number of technological and environmental problems. This raises the problem of reducing the methanol formation rate. To do this, it is necessary to analyze the kinetics, thermodynamics, and technological features of methanol formation at the low-temperature shift stage. Here, we report the equilibrium methanol concentrations calculated for CO conversion under near-industrial conditions. Systematizing the relevant experimental data available from the literature, we demonstrate how methanol formation depends on WGS conditions. The methanol formation rate can be reduced by lowering the CO concentration in the feed gas and employing low-methanol catalysts. Another favorable factor for methanol reduction is the aging of the catalyst during its operation.     

High temperature electrochemical heat pump using water gas shift reaction. Part I: Theoretical considerations

A new electrochemical heat pump using a combination of an electrolytic reaction at lower temperature to absorb low grade thermal energy and a thermochemical reaction at higher temperature to produce more efficient thermal energy is proposed. At a lower temperature, an endothermic reaction which cannot occur thermochemically proceeds with electrolysis. At a higher temperature, an exothermic reaction which is the reverse of the electrolysis reaction occurs thermochemically to produce high grade thermal energy. The water gas shift reaction, CO₂(g) + H₂(g) CO(g) + H₂O(g), in molten carbonate is one possible candidate for the new electrochemical heat pump and can lead to an increase in the temperature of the thermal energy from 1100 to 1200K. A heat pump system using the shift reaction is also considered theoretically.     

A facile method for preparation of iron based catalysts for high temperature water gas shift reaction

Nanocrystalline Fe₃O₄ based catalysts with theoretical particle size of 31–78 nm were synthesized by a facile direct pyrolysis method and employed in high temperature water gas shift reaction. XRD analysis showed that this method led to obtaining the catalysts directly in the active phase with chromium and copper incorporated into magnetite lattice. The results showed that the addition of chromium significantly increases the BET surface area of the pure iron oxide from 14.87 to 35.42 m² g⁻¹. Among the catalysts evaluated, Fe–Cr–Cu catalyst revealed higher activity compared to commercial catalyst and showed high stability during 10 h time on stream.     

Sorption-enhanced water gas shift reaction by sodium-promoted calcium oxides

The water gas shift reaction was evaluated in the presence of novel carbon dioxide (CO₂) capture sorbents, both alone and with catalyst, at moderate reaction conditions (i.e., 300-600 °C and 1-11.2 atm). Experimental results showed significant improvements to carbon monoxide (CO) conversions and production of hydrogen (H₂) when CO₂ sorbents are incorporated into the water gas shift reaction. Results suggested that the performance of the sorbent is linked to the presence of a Ca(OH)₂ phase within the sorbent. Promoting calcium oxide (CaO) sorbents with sodium hydroxide (NaOH) as well as pre-treating the CaO sorbent with steam appeared to lead to formation of Ca(OH)₂, which improved CO₂ sorption capacity and WGS performance. Results suggest that an optimum amount of NaOH exists as too much leads to a lower capture capacity of the resultant sorbent. During capture, the NaOH-promoted sorbents displayed a high capture efficiency (nearly 100%) at temperatures of 300-600 °C. Results also suggest that the CaO sorbents possess catalytic properties which may augment the WGS reactivity even post-breakthrough. Furthermore, promotion of CaO by NaOH significantly reduces the regeneration temperature of the former.     

改性铝土矿为载体的Ni-Mn-K一氧化碳高温变换催化剂工业侧流试验

采用等体积浸渍法,以改性天然铝土矿为载体,工业小试生产80 L一氧化碳高温变换催化剂。在福建永安智胜合成氨厂变换工段侧流装置上,进行催化剂工业在线侧流试验。结果表明,该催化剂活性好,机械强度高,热稳定性能良好,副反应不明显,能在低汽气体积比（约0.4）条件下运行,节能效果显著。     

Study of the water gas shift reaction on Fe in a high temperature proton conducting cell

The water gas shift (WGS) reaction was studied in a double-chamber high temperature proton conducting cell (HTPC). The proton conductor was a strontia–ceria–ytterbia (SCY) disk of the form: SrCe_0.95Yb_0.05O₃₋ and the working electrode was a polycrystalline Fe film. The reaction temperature and the inlet partial pressure of CO varied between 823 and 973 K, and between 1.0 and 10.6 kPa, respectively. The inlet partial pressure of steam (P_H2O) was kept constant at 2.3 kPa. An increase in the production of H₂ was observed upon “pumping” protons away from the catalyst surface. The Faradaic efficiency (Λ) was lower than unity, indicating a sub-Faradaic effect. The highest value of rate enhancement ratio (ρ) was approximately 3.2, at T = 823 K. The proton transport number (PTN) varied between 0.45 and 1.0. An up to 99% of the produced H₂ was electrochemically separated from the reaction mixture.     

Kinetic study on the hydrodesulfurization reaction of thiophene by water gas shift reaction

The in-situ hydrodesulfurization (HDS) reaction of thiophene was performed by using hydrogen which was generated by a water gas shift reaction (WGSR) in a same catalyst bed. The catalyst used was commercial CoMo/γ-Al₂O₃ and it was used after presulfiding. The activity in the conversion of thiophene by using hydrogen generated in-situ from a WGSR was inferior to that by the pure hydrogen. The lower efficiency in the in-situ HDS with WGSR was attributed to water, carbon monoxide and carbon dioxide which were mixed after WGSR. The following rate equation, which was revised from that of Satterfield, was proposed for this in-situ HDS reaction of thiophene with WGSR to explain the observed phenomena.     

Pulse-response TAP studies of the reverse water–gas shift reaction over a Pt/CeO2 catalyst

The temporal analysis of products (TAP) technique was successfully applied for the first time to investigate the reverse water–gas shift (RWGS) reaction over a 2% Pt/CeO₂ catalyst. The adsorption/desorption rate constants for CO₂ and H₂ were determined in separate TAP pulse-response experiments, and the number of H-containing exchangeable species was determined using D₂ multipulse TAP experiments. This number is similar to the amount of active sites observed in previous SSITKA experiments. The CO production in the RWGS reaction was studied in a TAP experiment using separate (sequential) and simultaneous pulsing of CO₂ and H₂. A small yield of CO was observed when CO₂ was pulsed alone over the reduced catalyst, whereas a much higher CO yield was observed when CO₂ and H₂ were pulsed consecutively. The maximum CO yield was observed when the CO₂ pulse was followed by a H₂ pulse with only a short (1 s) delay. Based on these findings, we conclude that an associative reaction mechanism dominates the RWGS reaction under these experimental conditions. The rate constants for several elementary steps can be determined from the TAP data. In addition, using a difference in the time scale of the separate reaction steps identified in the TAP experiments, it is possible to distinguish a number of possible reaction pathways.     

Catalyst effectiveness in low-temperature water—gas shift reaction

A procedure has been developed for a priori prediction of intraparticle diffusion effects in low temperature water—gas shift reaction. Use is made of transport characteristics of the Cu/ZnO/A1₂O₃ pelleted catalyst determined independently by combination of diffusion and permeation results obtained under nonreactive conditions. The porous medium is described by the mean transport pore model and diffusional behaviour of the multicomponent reaction mixture by a modified Stefan-Maxwell equation. Using data from kinetic region obtained at 200°C, it was possible to predict the performance of a bench-scale reactor packed with pelleted catalyst at 200°C and 220°C satisfactorily.     

CFD analysis of low temperature water gas shift reactor

In the design of water gas shift reactors, the performance of catalysts is not known a priori and hence having a general kinetic expression will be of much help. Computational Fluid Dynamic study was carried out to investigate the performance of a packed bed reactor for different feed compositions using five commonly used types of macro kinetic models. User Defined Functions were developed for the reaction rate to predict the CO conversion in the reactor. The effects of temperature and time factor on CO conversion were studied. The Langmuir-Hinshelwood model gave the best prediction for H₂ rich mixtures. The Temkin model was better for higher CO concentrations, whereas the other models gave large deviations for the fixed bed reactor.     

改性铝土矿负载Ni-Mn-K一氧化碳高温变换催化剂的研究

以改性后铝土矿石为载体,采用两步浸渍法,制备Ni-Mn-K一氧化碳高温变换催化剂。采用活性评价、低温N₂吸附、XRD和TPR等表征方法,考察催化剂的结构和性能。结果表明,改性后的铝土矿本身具有一定的变换活性,用该载体负载多组分制得的催化剂具有较好的变换活性。XRD和TPR结果表明,催化剂中具有明显的晶相NiO和K₂CO₃的特征衍射峰, MnO₂与铝土矿载体中的Fe₃O₂和SiO₂形成非晶态复合氧化物。比表面积和孔容减小主要因负载引起,负载活性组分后使耗氢量增大,还原峰温降低。     

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique

The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H₂ chemisorption measurements.     

Hydrodenitrogenation reaction of quinoline with nascent hydrogen generated from water gas shift reaction

The HDN of quinoline was investigated for the purpose of utilizing the hydrogen which could be generated from the water gas shift reaction (WGSR). The optimum concentration of hydrogen were produced under 1.5 of water to carbon monoxide mole ratio and 6 hr^-1 of space velocity at 390°C of temperature during WGSR over Co-Mo/γ-Al₂O₃ catalyst. The HDN reactions were compared by using the pure hydrogen and the nascent hydrogen which was produced by a WGSR. The pure hydrogen gave much higher activity in the overall HDN reaction than the nascent hydrogen. However, kinetic study on the hydrogenation, hydrogenolysis and cracking reaction steps showed that only at the cracking reaction step the nascent hydrogen gave the superiority to the pure hydrogen. This inferiority of the nascent hydrogen in overall HDN reaction could be resulted from the negative effect of water which should be accompanied during WGSR. The conversion of the HDN reaction was maximized at the water pressure of 150 kpa.     

Multiscale model based design of an energy-intensified novel adsorptive reactor process for the water gas shift reaction

In this work, an adsorptive reactor (AR) process is considered that can energetically intensify the water gas shift reaction (WGSR). To best understand AR process behavior, a multiscale, dynamic, process model is developed. This multiscale model enables the quantification of catalyst and adsorbent effectiveness factors within the reactor environment, obliviating the commonly employed assumption that these factors are constant. Simulations of the AR's alternating adsorption-reaction/desorption operation, using the proposed model, illustrate rapid convergence to a long-term periodic solution. The obtained simulation results quantify the influence of key operating conditions and design parameters (e.g., reactor temperature/pressure, W_cat/F_CO, W_ad/F_CO, F_H2O/F_CO ratios, and pellet size) on the AR's behavior. They also demonstrate, for pellet diameters used at the industrial scale, significant temporal and axial variation of the catalyst/adsorbent pellet effectiveness factors. Finally, the energetic intensification benefits of the proposed AR process over conventional WGSR packed-bed reactors are quantified.     

Temperature control of the water gas shift reaction in microstructured reactors

Microchannel reactors offer unique possibilities for temperature control of chemical reactions due to the strong coupling of channel and wall temperatures. This may be applied to all chemical reactions which require a certain temperature profile to achieve an optimum yield. For the reformation of hydrocarbons for fuel cell applications a low CO concentration of the product gas is desired. In conventional systems, this is achieved by sequentially processing the reformate through a high and low temperature water gas shift reactor because increased temperature enlarges the reaction rate while lower temperature shifts the equilibrium to the desired small CO concentrations. However, for every gas composition arising during the reaction process an optimum temperature exists at which the reaction rate is highest. We will demonstrate that this optimum temperature profile to a good approximation can be achieved in a single step WGS reactor by controlling the temperature via cooling gas flowing in counter current to the reformate. Furthermore, the effect of water addition (steam injection) is analysed for a conventional two-step adiabatic reactor system and the possible size reduction in an integrated heat-exchanger reactor under comparable conditions is validated. Finally, the effect of diffusion limitations at various channel dimensions is investigated applying a two-dimensional model which allows a trade-off between pressure drop or respective reactor size and performance when dimensioning a real system in future.     

Novel CuS hollow spheres fabricated by a novel hydrothermal method

A thioglycolic acid (TGA) assisted hydrothermal process has been developed to synthesize submicron-sized copper sulfide (CuS) hollow spheres via the reaction between copper sulfate (CuSO₄) and thioacetamide (CH₃CSNH₂). X-ray diffraction, transmission electron microscopy and scanning electron microscopy were employed to characterize the obtained product. Furthermore, the possible mechanism and the critical factors for the TGA-assisted hydrothermal synthesis of the CuS hollow spheres have been preliminarily presented.     

The effect of La on Au-ceria catalyst for water gas shift reaction

For Au-ceria catalysts prepared by deposition-precipitation method, catalytic performance of water gas shift reaction was studied in different La loadings. In the complete doping range, ceria retains with its cubic fluorite structures. BET, XRD, H₂-TPR, HRTEM studies showed that La doping can improve the activity of Au-ceria catalyst by stabilizing ceria and modifying its morphology. In addition, the test of catalyst stability evaluation also proved a better stability performance of Au-ceria catalyst can be realized by appropriate La doping.     

Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditions

A simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo‐homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H₂) supported over a porous ceramic layer. The effect of temperature, overall heat‐transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers AIChE J, 2009