Shift Reaction Research Articles

A membrane-assisted hydrogen and carbon oxides separation from flare gas and recovery to a commercial methanol reactor

The push to control the greenhouse gas emissions is motivated by environmental regulations. For the aim to be achieved, the suggestion of eliminating or at least reducing gas flaring is currently taken under environment. In this regard, a new configuration for flare gas treatment is proposed in this study. This configuration is aimed to collect H2 and CO2 from flare gas, simultaneously. The collected components would be sent to the methanol synthesis reactor in the upstream section. The proposed configuration is made up of a multi-step membrane-assisted separation unit. In order to clarify what lies behind the idea, we proposed a mathematical formulation which is composed of conservation equations and kinetic rate equations is developed. H2 and CO2 elimination in the first step followed by a membrane-assisted water gas shift reactor for catalytic CO conversion and H2 recovery in tandem, and removing the remaining CO2 in the supplementary step is investigated numerically. The collected H2/CO2 mixture is aimed to recover into the upstream methanol synthesis reactor. The obtained results reveal that by utilizing such a strategy, about 2500 kmol/day CO2 (almost 98% of total input) is eliminated from the flare gas stream. Moreover, by considering the converted CO, about 4050 kmol/day CO2 is recovered to the methanol reactor. As a whole, 0.68% enhancement in the methanol generation and the reduction of about 4050 kmol/day flare gas pollutants are achieved in tandem when 98% N2 and 92.9% CH4 is separated the from purge gas.

Process development for integrated coal gasification solid oxide fuel cells hybrid power plants – Investigations on solid oxide fuel cells/gas turbine hybrid power plants run on clean coal gas

On the road to sustainable generation of electricity, the efficiency of fossil-fuel power plants and CO2 emissions must be increased and decreased respectively. Integrated coal gasification solid oxide fuel cell hybrid power plants have the potential to achieve high power plant efficiencies and enable opportunities for the efficient capture of CO2. The investigation of such power plants is the subject of this publication. The developed systems are based on conventional integrated coal gasification combined cycle technology and integrated with solid oxide fuel cells preceding the combined cycle process. The state of development of the selected solid oxide fuel cell technology is similar to that of integrated coal gasification combined cycles. Along with the base case, several other concepts with and without CO2 capture are developed using various process technologies. Fundamental system and sensitivity analyses are performed using simplified sub-processes to obtain general statements and trends as well as to calculate optimal boundary conditions for the overall systems. The simulations show that the preparation of process gas using a water gas shift reactor before entering the solid oxide fuel cells is beneficial for the overall efficiency. If a CO2 capture process is included, 11–16% lower net efficiencies are achieved. The level of specific CO2 emissions is significantly influenced by the net efficiency of the power plants and the portion of carbon bound as CO2 at the beginning of the CO2 capture process. Here, the combination of CO2 capture and water gas shift reactor upstream of the solid oxide fuel cells is the preferred concept regarding efficiency and CO2 emissions.

Operational safety of an ammonia process network via model predictive control

Process safety is a crucial issue in the area of process systems engineering as accident prevention is a top priority in process operations. Operational safety needs to be directly incorporated into control system design to handle disturbances in the process. Motivated by the above considerations, this paper presents a practical application simulating multiple model predictive controllers within a multi-unit ammonia process, all of which integrate safety constraints of the process within their design. Specifically, catalytic deactivation in the shift reactor is a common and problematic disturbance that may trigger reaction thermal runaway in the methanator. Two controllers designed with the objective of improving operational safety are implemented on the ammonia plant under catalyst deactivation. Aspen Plus is a commercial process simulation software which is integrated with Matlab to run a closed-loop simulation for the ammonia process. The results demonstrate that under suitable design of the controllers, desirable closed-loop performance is achieved with high temperature extremities avoided during operation.

Biomass Gasification Integrated with Chemical Looping System for Hydrogen and Power. Coproduction Process – Thermodynamic and Techno‐Economic Assessment

AbstractThree biomass gasification‐based hydrogen and power coproduction processes are modeled with Aspen Plus. Case 1 is the conventional biomass gasification coupled with a shift reactor, cases 2 and 3 involve integration of biomass gasification with iron‐based and calcium‐based chemical looping systems. The effects of important process parameters on the performance indicators such as hydrogen yield and efficiencies are evaluated by sensitivity analyses. These parameters include gasification temperature, molar ratios of steam to biomass in the gasifier, Fe2O3 to syngas in the fuel reactor, Fe/FeO to steam in the steam reactor, CaO to CO, and steam to CO in the carbonator. The energy and exergy balance distributions for the above three cases are comprehensively discussed and compared. Furthermore, techno‐economic assessments are performed to evaluate the three cases in terms of capital cost, operating cost, and leveled cost of energy.

Process analysis of hydrogen production from biomass gasification in fluidized bed reactor with different separation systems

Gasification is one of the most effective and studied methods for producing energy and fuels from biomass as different biomass feedstock can be handled, with the generation of syngas consisting of H2, CO, and CH4, which can be used for several applications. In this study, the gasification of hazelnut shells (biomass) within a circulating bubbling fluidized bed gasifier was analyzed for the first time through a quasi-equilibrium approach developed in the Aspen Plus environment and used to validate and improve an existing bubbling fluidized bed gasifier model. The gasification unit was integrated with a water-gas shift (WGS) reactor to increase the hydrogen content in the outlet stream and with a pressure swing adsorption (PSA) unit for hydrogen separation. The amount of dry H2 obtained out of the gasifier was 31.3 mol%, and this value increased to 47.5 mol% after the WGS reaction. The simulation results were compared and validated against experimental data reported in the literature. The process model was then modified by replacing the PSA unit with a palladium membrane separation module. The final results of the present work allowed comparison of the effects of the two conditioning systems, PSA and palladium membrane, indicating a comparative increase in the hydrogen recovery ratio of 28.9% with the palladium membrane relative to the PSA configuration.

Modeling and analysis of hydrogen production in steam methane reforming (SMR) process

Hydrogen is one a gas that demands continue to grow across many industries. Due to the growth for this gas the means of producing it and the ability to supply this demand is of great importance. As a result of this, steam methane reforming is a process of high significance as it is one of the most economically and popular means of producing hydrogen. The value of this process is tremendous as it is able to provide up to 48% of global demands, with this only predicted to increase. Therefore, the understanding of what occurs during this process and the steps that it experiences must be understood to ensure that an efficient system is created.Steam methane reforming operates by converting the hydrocarbons located in methane into hydrogen and COx. This process will generally occur over two different stages, a reformer stage, before going into a water-gas shift reactor. After these main processes occur the product produced may undergo purification to remove any containments and ensuring that the hydrogen is at the industry standard. To help investigate this process and how various stages affect others it can be modeled through software such as Unisim which allows modifications to be made and analyzed the effect this had on the system, allowing a potential more efficient system to be designed which will help meet the growing demand.

A numerical investigation on H2 separation by a conical palladium membrane

Separation of hydrogen gas from the outlet of water-gas shift reactor via palladium membrane was simulated with a two-dimensional computational fluid dynamic model. To study the influence of the geometry of membrane on the separation of hydrogen, four various membrane modules with cylindrical shells and cone tubes were considered. The results showed that the conical membrane module with upper and bottom diameters of 2 mm and 16 mm can potentially have the highest average flux across the other studied cases. To investigate the effect of flow pattern, four various flow patterns were applied to the model and it was found that the counter-current flow pattern has the highest flux across the membrane for the case in which the cross section is reduced along with the length of the membrane. The results also indicated that the change in the cross section of the membrane module can prevent the intensification of the concentration polarization index within the membrane.

Analysis of Membrane Reactors for Integrated Coupling of Oxidative and Thermal Dehydrogenation of Propane

AbstractThis study presents strategies capable to intensify the thermal dehydrogenation of propane (TDH) using integrated reactor concepts. An inert packed bed membrane reactor for distributed dosing of oxygen to realize the oxidative dehydrogenation (ODH) was studied and compared to a reactor with catalytically active membrane. The latter concept allows to combine TDH and ODH in one apparatus to overcome the chemical equilibrium by in situ conversion of the by‐product H2using O2or in a reverse water‐gas shift reaction by CO2. If CO2is used as active sweep gas the reactor offered better performance regarding yield and selectivity. Strategies for further thermal integration are discussed.

Techno‐economic analysis of a novel hydrothermal liquefaction implementation with electrofuels for high carbon efficiency

AbstractThis study describes a techno‐economic analysis (TEA) to evaluate the feasibility of developing an electrofuel (eFUEL) system based on hydrothermal liquefaction (HTL). The system is developed to make use of the carbon in the aqueous and gas phases of an HTL process as inputs for the production of renewable transportation fuels, supplementing those from the ‘traditional’ HTL pathway. An Aspen Plus® model of the eFUEL system is developed containing a partial oxidation gasifier (POX), a reverse water gas shift (RWGS) reactor, and a Fischer–Tropsch (FT) process. The combined HTL, upgrading, and eFUEL (Electro‐HTL) system is designed with a capacity of 1000 tonne of organic matter per day as input. The electro‐HTL system increases carbon efficiency to 84.81% and the plant's fuel mass yield by 69.2% (from a yield of 27.8 to 47.0%) compared to a stand‐alone HTL and upgrading system. The TEA of the electro‐HTL system shows a minimum fuel‐selling price (MFSP) of 26.06 USD GJ−1, with a carbon efficiency of 84.91%. A sensitivity analysis is performed identifying hydrogen as the key cost influence on the MFSP. The study shows that the incorporation of the eFUEL system decreases the MFSP by 8.9% compared to the standalone HTL and upgrading system. The price generated by the electro‐HTL system is 1.5–2.2 times higher than the price of fossil gasoline. In conclusion, the study shows that the production of renewable drop‐in fuels using the electro‐HTL system is not only cost competitive with other alternative fuel processes, but also with fossil fuels. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd

The implications of choice between sour and sweet shift on process design and operation of an IGCC power plant integrated with a dual-stage selexol unit

In this study, it was sought to design and evaluate two process configurations of an Integrated Gasification Combined Cycle (IGCC) integrated with a dual-stage Selexol unit in which they differ in that one IGCC is configured with sour shift and the other is based on sweet shift. Incorporating water gas shift reactors consuming vast amount of shift steam into an IGCC involves significant alternations to the associated steam cycle, in addition to simply changing the location of the H2S removal step around the shift reactors. It turned out that the sweet shift case would require approximately 4.6 times more shift steam than the sour shift case, as the syngas after H2S removal did not have much steam in it. However, the energy penalties incurred by the carbon capture integration were estimated almost identical regardless of the choice between the sour and sweet shift. This is because the sour shift case would also undergo considerable reduction in power generation at steam cycle due to water quenching. In both shift cases, the high and low temperature shift reactors were sized using the reaction rate models reported in literature.

Life Cycle Assessment and Economic Analysis of an Innovative Biogas Membrane Reformer for Hydrogen Production

This work investigates the environmental and economic performances of a membrane reactor for hydrogen production from raw biogas. Potential benefits of the innovative technology are compared against reference hydrogen production processes based on steam (or autothermal) reforming, water gas shift reactors and a pressure swing adsorption unit. Both biogas produced by landfill and anaerobic digestion are considered to evaluate the impact of biogas composition. Starting from the thermodynamic results, the environmental analysis is carried out using environmental Life cycle assessment (LCA). Results show that the adoption of the membrane reactor increases the system efficiency by more than 20 percentage points with respect to the reference cases. LCA analysis shows that the innovative BIONICO system performs better than reference systems when biogas becomes a limiting factor for hydrogen production to satisfy market demand, as a higher biogas conversion efficiency can potentially substitute more hydrogen produced by fossil fuels (natural gas). However, when biogas is not a limiting factor for hydrogen production, the innovative system can perform either similar or worse than reference systems, as in this case impacts are largely dominated by grid electric energy demand and component use rather than conversion efficiency. Focusing on the economic results, hydrogen production cost shows lower value with respect to the reference cases (4 €/kgH2 vs 4.2 €/kgH2) at the same hydrogen delivery pressure of 20 bar. Between landfill and anaerobic digestion cases, the latter has the lower costs as a consequence of the higher methane content.

The Implication of the Choice between Sour and Sweet Shift on Process Design and Operation of an IGCC Power Plant Integrated with a Dual-Stage Selexol Process

In this study, it was sought to design and evaluate two different process configurations of an IGCC integrated with a dual stage Selexol unit where they differ in that one is based on sour shift and the other is sweet shift (Fig. 1). Depending on the choice of the two water-gas shift reactors, the process configuration undergoes significant changes in steam cycle, syngas cooling and Selexol process, apart from the location of the H2S removal step around the shift reactor. Integrating an IGCC with a pre-combustion capture involves a significant energy penalty. The energy penalty associated with carbon capture integration was mainly due to the power plant demanding a greater heat input for running the same gas cycle. Also the syngas must undergo water-gas shift reaction (WGSR) in order to convert CO to CO2, as the ensuing separation process can capture only CO2 efficiently from the syngas. The WGSR needs a huge amount of steam. The syngas leaving the scrubber already contains some steam, as it leaves the scrubber saturated with water. However more steam has to be added to the syngas to have the water-to-CO ratio around 2, to make sure good CO conversion. The extra steam has to be sourced from the steam cycle. Adding new units of the pre-combustion capture process and CO2 compressors augments the total capital cost and the operation of the CO2 capture and compression units increases the auxiliary power consumption. In turn, the net plant efficiency of the IGCC drops significantly with the cost of electricity rising accordingly. In this study, the whole IGCC power plant was simulated by using Honeywell UniSim based on the DOE study. The IGCC simulation also include a dual-stage Selexol process for pre-combustion capture to estimate the energy consumption involved, similarly to the past researches carried out by the group. It turned out that the sweet shift would give rise to greater reduction of the net power efficiency than the sour shift (Table 1), mainly due to it requiring approximately 4.6 times more shift steam, most of which has to be sourced from the steam cycle. This substantial increase of the shift steam usage involves significant alternation to the steam cycle. From the perspective of the energy penalty, the adverse effect resulting from the need for vast shift steam outweighs the positive aspect of the AGR (Acid Gas Removal) unit of the sweet shift case spending less power. On the other hand, the sour shift catalyst (CoMo) was estimated to have a reaction rate much lower than the sweet shift catalyst (Cu-ZnO) by two orders of magnitude at the condition of the low temperature shift reactor. It was certain that the sweet shift case had to undergo significant energy penalty due to it having to source vast steam from the steam cycle. This is not only because the syngas loses almost all the steam while being cooled for H2S removal, but also it requires a steam-to-CO ratio of water-gas shift reaction greater than it would do in sour shift case. To alleviate these adverse effects, the sweet shift case was designed to generate additional LP steam by recovering the heats from the raw and shifted syngas. Also the auxiliary power expensed in the AGR unit was found to be slightly less, due to the H2S absorber also functioning as a H2S concentrator. The resultant net plant efficiencies of the two cases exhibited that the sour shift case would be more energy-efficient than the sweet shift case by 3.7% points as shown in Table 1. However, the advantage would be compromised to some extent, given that the low temperature sour shift reactor had to be sized larger than the equivalent sweet shift reactor, due to the sour shift catalysts exhibiting lower reaction rates than the sweet catalysts at the condition.

Enhanced CO selectivity for reverse water‐gas shift reaction using Ti4O7‐doped SrCe0.9Y0.1O3‐δ hollow fibre membrane reactor

AbstractReverse water‐gas shift reaction (RWGS) is important in the CO2 utilization cycle to convert carbon dioxide (CO2) and hydrogen (H2) to carbon monoxide (CO). In this work, the RWGS performance is evaluated by utilizing Ti4O7‐doped SrCe0.9Y0.1O3‐δ (SCY‐b) hollow fibre membrane reactor where H2 permeates through the SCY‐b proton conducting membrane and reacts with CO2 feed gas. Upon increasing the temperature from 750 to 950 °C, the CO yield increased from a negligible value to 14.82 %, when the sweep gas flow rate was 50 mL min−1 H2‐He (50:50 vol. ratio) and the feed gas flow rate was 100 mL min−1 CO2‐N2 (5:95 vol. ratio). The CO yield increase with the temperature increase reflects the enhanced H2 permeation flux through the SCY‐b membrane at higher temperatures. Higher CO2 concentration in the feed gas led to lower CO yield due to the higher amount of remaining CO2 in the outlet stream. The deposition of porous SCY or SCY‐b surface layer onto the hollow fibre outer circumference surface also increased H2 flux through the fibre relative to the non‐deposited one. Thermogravimetric and CO2‐temperature programmed desorption results further reveal that SCY‐b adsorbed CO2 at temperature above 500 °C due to the reaction between CO2 and SCY‐b material. Despite the formation of SrCO3 during RWGS, the SCY‐b hollow fibre membrane reactor still displayed a stable CO yield of around 14 % throughout the 6‐day continuous membrane reactor test.

Combustion characteristics of anode off-gas on the steam reforming performance

The combination of steam reforming and HT-PEMFC has been considered as a proper set up for the efficient hydrogen production. Recycling anode off-gas is energy-saving strategy, which leads to enhance the overall efficiency of the HT-PEMFC. Thus, the recycling effect of anode off-gas on steam-reforming performance needs to be further studied. This paper, therefore, investigated that the combustion of anode off-gas recycled impacts on the steam reformer, which consists of premixed-flame burner, steam reforming and water-gas shift reactors. The temperature rising of internal catalyst was affected by lower heating value of fuels when the distance between catalyst and burner is relatively short, while by the flow rate of fuels and the steam to carbon ratio when its distance is long. The concentration of carbon monoxide was the lowest at 180 °C of LTS temperature, while NG and AOG modes showed the highest thermal efficiency at LTS temperature of 220–300 °C and 270–350 °C, respectively. The optimum condition of thermal efficiency to maximize hydrogen production was determined by steam reforming rather than water gas shift reaction. It was confirmed that the condition to obtain the highest thermal efficiency is about 650 °C of steam reforming temperature, regardless of combustion fuel and carbon monoxide reduction. The difference of hydrogen yield between upper and lower values is up to 1.5 kW as electric energy with a variation of thermal efficiency. Hydrogen yield showed the linear proportion to the thermal efficiency of steam reformer, which needs to be further increased through proper thermal management.

Multigenerational Theoretical Study of Isoprene Peroxy Radical 1-5-Hydrogen Shift Reactions that Regenerate HO x Radicals and Produce Highly Oxidized Molecules.

A computational protocol is employed to glean new insight into the kinetics of several 1,5-hydrogen atom (H) shift reactions subsequent to first- and second-generation OH/O2 additions to isoprene. The M06-2X density functional was initially used with the Nudged Elastic Band (NEB) method to determine the potential energy surface of OH/O2 addition reactions, the 1,5-H shift reactions, and the fragmentation exit channels. The Master Equation Solver for Multi-Energy Well Reactions (MESMER) was applied to determine the rate constants for OH addition and the 1,5-H shifts. M06-2X was capable of quantifying the rate constants of OH addition to the first and second double bonds of isoprene with deviations less than 17% from the experimentally determined values. However, M06-2X underestimated the 1,5-H shift rate constants of second-generation isoprene peroxy radicals. Consequently, MN15, ωB97X-D, and CBS-QB3 methods were employed to compute average barrier heights to first- and second-generation 1,5-H shifts. In the first generation, the rate constants of H abstraction by β-(1,2) and (4,3) isoprene hydroxy-peroxy radicals from the neighboring hydroxyl group are 1.1 × 10-3 and 2.4 × 10-3 s-1, respectively. These values are determined primarily by the barrier of the H shift reaction and, to a smaller albeit nonnegligible extent, by the stability of the resulting alkoxy radical and the exit barrier leading to C-C bond dissociation. In contrast, the average second-generation rate constant of 1,5-H shifts from H-R-OH sites to the peroxy radical is 1.8 × 10-1 s-1, with tunneling playing the significant role of increasing this value relative to first-generation 1,5-H shifts. Under low NO x conditions, first-generation isoprene oxidation reactions may recycle HO x at levels ranging from 10 to 30% due in large part to 1,5-H shifts, with the recycling efficiency being sensitive to HO2 concentrations and temperature. HO x recycling is expected to increase to levels beyond 80% in second-generation reactions of oxidized isoprene species because of isoprene epoxydiol (IEPOX) formation and further 1,5-H shifts that are kinetically favorable.

Comparison of Axial and Radial Water Gas Shift Reactors Based on CFD Simulation

Comparison of Axial and Radial Water Gas Shift Reactors Based on CFD Simulation

Comparative genomic analysis of Parageobacillus thermoglucosidasius strains with distinct hydrogenogenic capacities

BackgroundThe facultatively anaerobic thermophile Parageobacillus thermoglucosidasius produces hydrogen gas (H2) by coupling CO oxidation to proton reduction in the water-gas shift (WGS) reaction via a carbon monoxide dehydrogenase–hydrogenase enzyme complex. Although little is known about the hydrogenogenic capacities of different strains of this species, these organisms offer a potentially viable process for the synthesis of this alternative energy source.ResultsThe WGS-catalyzed H2 production capacities of four distinct P. thermoglucosidasius strains were determined by cultivation and gas analysis. Three strains (DSM 2542T, DSM 2543 and DSM 6285) were hydrogenogenic, while the fourth strain (DSM 21625) was not. Furthermore, in one strain (DSM 6285) H2 production commenced earlier in the cultivation than the other hydrogenogenic strains. Comparative genomic analysis of the four strains identified extensive differences in the protein complement encoded on the genomes, some of which are postulated to contribute to the different hydrogenogenic capacities of the strains. Furthermore, polymorphisms and deletions in the CODH-NiFe hydrogenase loci may also contribute towards this variable phenotype.ConclusionsDisparities in the hydrogenogenic capacities of different P. thermoglucosidasius strains were identified, which may be correlated to variability in their global proteomes and genetic differences in their CODH-NiFe hydrogenase loci. The data from this study may contribute towards an improved understanding of WGS-catalysed hydrogenogenesis by P. thermoglucosidasius.

Transition Metal‐Doped Edge‐Terminated MoS2 Superstructures as Efficient Catalysts for H2 Production

AbstractAs the most important layered transition metal dichalcogenide, molybdenum disulfide (MoS2) is applicable for simultaneous H2 production and CO elimination by water‐gas shift reaction (WGSR), while its performance is still not satisfactory. To further promote the catalytic activities of MoS2, herein a series of transition metals (M = Mn, Fe, Co, Ni, Cu, and Zn) into the column‐like superstructures with edge‐terminated MoS2 nanosheet building blocks (termed as M‐ET MoS2 SSs) is doped as the efficient catalysts for WGSR. A precise M doping into ET MoS2 SSs reveals that the M‐ET MoS2 SSs exhibit the volcano‐like activity toward WGSR as a function of specific M with the 5%Ni‐ET MoS2 SSs displaying the best average rate of 50.48 µmolH2 gcat. −1 s−1 in WGSR at 473 K, which is 4 and 13 times higher than those of the ET MoS2 SSs and commercial MoS2, respectively, and is even comparable to many noble‐metal‐based catalysts. The valence band spectra reveal that the boosted WGSR activity of 5%Ni‐ET MoS2 SSs can be ascribed to the downshift of the d‐band center relative to the Fermi level, which facilitates the H desorption to produce H2 in WGSR, showing a highly efficient and earth‐abundant catalysts for WGSR and beyond.

Solvent free, light induced 1,2-bromine shift reaction of α-bromo ketones

Photolysis of α-bromopropiophenones in acetonitrile results in formation of β-bromopropiophenones with good product selectivity, which can be coined as 1,2-Br shift reaction. The product selectivity increases when the reaction is done in neat or solid state, where only the 1,2-Br shift product is formed in some cases. The reaction is suggested to proceed by CBr bond homolysis to give a radical pair, followed by disproportionation and conjugate addition of HBr to the α,β-unsaturated ketone intermediate. When the unsaturated intermediate is stabilized by an extra conjugation, the reaction stops at the stage, in which the unsaturated ketone becomes a major product. The synthetic method described in this research fits in a category of eco-friendly organic synthesis nicely since the reaction does not use volatile organic solvents and any other additives such as acid, base or metal catalysts, etc. Besides, the method fits into perfect atom economy, which does not give any side products. The synthetic method should find much advantage over other alternative methods to obtain β-bromo carbonyl compounds.

Theoretical Study of the Formation Methane in the Reaction of Methyl Radical with Propanol-2

Theoretical Study of the Formation Methane in the Reaction of Methyl Radical with Propanol-2