Dual Bed System Research Articles

Used Ni/KIT-6 as a sacrificial catalyst for mitigating coking in lower-layer catalyst in steam reforming of acetic acid

Deactivated or coked catalyst from steam reforming may not always be treated as a solid waste, which might be potentially used as a sacrificial or protective layer of catalyst for reducing coke formation of catalyst in the lower bed in the same steam reforming process. In this study, steam reforming of acetic acid over Ni/KIT-6 at 600 °C was conducted with used Ni/KIT-6 in upper layer and freshly reduced Ni/KIT-6 in lower layer (dual-bed system). The results suggested that significantly more coke (3 to 4 times) formed on upper-layer catalyst (used or fresh catalyst) than on lower-layer fresh catalyst. The upper-layer used catalyst was more effectively than counterpart of fresh catalyst for mitigating coking in lower-layer catalysts. The in-situ IR technique suggested that carbonaceous species on the used catalyst impacted or reacted with the intermediates newly formed, generating more oxygen-containing species with functionalities like COC and CO of anhydride or ketones/aldehyde form. These oxygen-containing species could polymerize/condense and pass down to the lower bed, forming more polymeric coke of lower thermal stability. Differently, more unsaturated hydrocarbon species formed on the upper-layer fresh catalyst, making the coke of highly aromatic nature with a higher thermal stability and crystallinity. Additionally, modification of reaction intermediates with the used catalyst in upper layer also formed carbon nanotubes of irregular structures with coarse surface.

Dual-bed catalytic system comprising Al2O3 and Ba/Al2O3 with enhanced 1-octene productivity in 1-octanol dehydration for linear α-olefin production

To produce high-purity 1-octene, the dehydration of 1-octanol was performed over a dual-bed catalytic system comprising Al2O3 and Ba/Al2O3 catalysts. The influence of the catalyst weight on the activities of Al2O3 and Ba/Al2O3 single-bed systems was initially investigated at liquid hourly space velocities (LHSVs) of 7–168 h−1 at 400 °C. For the Al2O3 single-bed system, the 1-octene selectivity decreased with an increase in the catalyst weight. Although the 1-octene selectivity of Ba/Al2O3 increased owing to the anti-Saytzeff effect, its yield was limited due to a low 1-octanol conversion. The efficiency of the dual-bed catalytic system was subsequently investigated by varying the catalyst bed ratio (i.e., xAl–yBa). The 40Al-60Ba catalytic system afforded a higher conversion (95.3%) and productivity than the Ba/Al2O3 single-bed system at an LHSV of 56 h−1. Moreover, the 10Al-90Ba catalytic system with a high Ba/Al2O3 catalyst ratio exhibited a high 1-octene productivity at LHSVs of 7–28 h−1, while also yielding a high-purity product. The single-bed system exhibited a lower selectivity toward 1-octene than the dual-bed system, and after 100 h, the 10Al-90Ba dual-bed system offered a stable catalytic performance regardless of the small reductions in the 1-octene selectivity and yield.

Steering CO2 hydrogenation coupled with benzene alkylation toward ethylbenzene and propylbenzene using a dual-bed catalyst system

Utilization of CO2 as a C1 resource for the synthesis of aromatics is of great significance and is also related to carbon recycling. However, forming an ethylated or propylated side chain at the benzene ring by this strategy is difficult, and the products reported are methylated aromatics. Here, we show the first CO2 hydrogenation in tandem coupling with benzene alkylation to synthesize ethylbenzene and propylbenzene over a dual-bed system containing ZnZrOx, SAPO-34, and phosphorus-modified ZSM-5 catalysts. Controlled experiments and density functional theory studies reveal that the intermediate reactive species CHxO∗ (x = 1–3) of CO2 hydrogenation are preferentially alkylated with benzene to give methylated aromatics, rather than to form ethylated and propylated aromatics, when the three catalysts are simply mixed. By contrast, the three catalysts with rationally spatial distribution in the dual-bed system can afford 83.5% selectivity to ethylbenzene or 64.7% to propylbenzene in total aromatics without deactivation after 100 h.

Tandem Hydrodeoxygenation Catalyst System for Hydrocarbons Production from Simulated Bio-oil: Effect of C–C Coupling Catalysts

Research in the sustainable conversion of biomass to fuels and chemicals is a necessity for the reduction of the carbon footprint in transport energy. Herein, we demonstrate an efficient tandem catalyst to selectively convert (simulated) bio-oil to hydrocarbons with enhanced C4+ fuel yield in a fixed bed reactor of a small pilot plant. The tandem catalytic system is a multifunctional dual bed system; carbon coupling catalysts (0.2 wt % X-TiO2(X: Ru, Pd, Au) at the upper layer and hydro-deoxygenation (Ru-MoFeP/Al2O3) at the bottom layer in a single fixed bed reactor. The upper-bed catalysts facilitated the carbon coupling reaction of C2–C4 light oxygenates and significantly reduced the light gases yield (C1–C5) to ca. 40% and increased the organic (C4+) phase ca. 15%. The analysis of the organic phase suggests that among the screened upstream catalysts, 0.2 wt % Ru/TiO2||Ru-MoFeP/Al2O3 recorded the optimum activity. The coupled light oxygenates (acetone) alkylated with the phenolic compounds and sequentially hydro-deoxygenated to yield higher C4+ hydrocarbons. This versatile tandem catalytic approach has a potential application in the emerging biorefinery concept.

Lean NOx Removal by a Bifunctional (EtOH + NH3) Mixture Dedicated to (Ag/Al2O3 + NH3-SCR) Dual-Bed Catalytic System: Comparison Between WO3/CeZrO2 and Cu–FER as NH3-SCR Catalyst

In a previous study, a drastic enhancement of the NOx conversion in EtOH-SCR process was achieved by means of ammonia and ethanol co-feeding over Ag/Al2O3 catalyst to avoid the NO2/NOx ratio dependency of conventional implemented urea-SCR technology. The ammonia activation was mainly attributed to the availability of hydrogen H* species resulting from EtOH dehydrogenation, which promoted the H2 assisted NH3-SCR over Ag/Al2O3. Additional conversion gain was reached with a dual-bed configuration in which a NH3-SCR catalyst (WO3/CexZr1−xO2) was added downstream to the silver-based sample (Ag/Al2O3 + NH3-SCR catalyst). This study deals with the influence of the SCR catalyst formulation on the catalytic performances of the dual-bed system. Oxide-based sample (WO3/CexZr1−xO2) and exchanged copper zeolite (Cu2.5–FER) were selected as model NH3-SCR catalysts. Results shows that WO3/CexZr1−xO2 in more appropriate in dual-bed configuration for (EtOH + NH3)-SCR process because ammonia and ethanol (or its by-products) strongly interacted together on Cu2.5–FER.

Use of a Dual-Bed System for Producing Diesel Fuel from a Mixture of Straight-Run Diesel and Rapeseed Oil over Sulfide Catalysts

A dual-bed catalytic system including MoS2/Al2O3 and Co–MoS2/Al2O3 catalysts is proposed for the process of production of diesel fuel with the sulfur content of less than 10 ppm from a straight-run diesel fraction containing 10–45 wt % rapeseed oil. The conversion of rapeseed oil to alkanes proceeds in the MoS2/Al2O3 catalyst bed via the route of “direct” hydrodeoxygenation without the formation of carbon oxides, and the hydrodesulfurization of the diesel fraction occurs in the bed of the Co–MoS2/Al2O3 hydrotreating catalyst. Using this system provides an increase in the yield of diesel fuel and a decrease in the formation of greenhouse gases in comparison with conventional Co(Ni)–MoS2/Al2O3 catalysts.

Dual bed catalyst system for oxidative dehydrogenation of mixed-butenes: a synergistic mechanism

Oxidative dehydrogenation (ODH) of mono and mixed-butenes to 1,3-butadiene (BD) was conducted using individual and dual bed catalyst systems, consisting of ZnFe2O4, Co9Fe3Bi1Mo12O51 or both. The dual bed catalyst system gave improved catalytic performance. A mechanism based on synergy between the catalysts is proposed to explain the improved overall butene conversion. The proportion of the reactants differed between the catalyst beds in the dual bed system, making better use of the catalytic activity of the second bed. The existence of all butene isomers inhibited isomerization, leading to a higher proportion of ODH reactions and thus improved the conversion of butene and the yield of BD. The packing sequences and the volume ratio of the catalysts in the bed were optimized. The results indicated that the sequence with ZnFe2O4 on top and a catalyst packing ratio of between 4:6 and 6:4 led to better activity.

Deactivation mechanism of Ni supported on Mg-Al spinel during autothermal reforming of model biogas

Nickel supported on Mg-Al oxides was studied in the autothermal reforming (ATR) of model biogas at 700°C. Ni/Mg0.4Al2O3.4 deactivated with time on stream and the cause of deactivation was investigated and identified. Ni was readily oxidized to NiO in the presence of O2. While NiO was essentially inactive for the reforming reaction, this oxide was yet active for methane combustion. Exhaustion of the O2 supply at front of the catalyst bed enabled the remaining CH4 to be steam and dry reformed on the metallic Ni left downstream. Gradual formation of NiAl2O4 spinel was also observed, likely caused by the higher temperature prevailing in the exothermic combustion zone that favors the diffusion of nickel cations into the alumina structure. In contrast to NiO, NiAl2O4 spinel was poorly active for CH4 oxidation. The frontline associated with the formation of the NiAl2O4 spinel phase eventually reached the end of the catalyst bed, resulting in a complete loss of activity. No significant coke deposition could be evidenced here. The Ni deactivation profile was adequately fitted using a methane ATR kinetic model that included a linear decrease in the number of Ni metallic sites. Addition of Rh/Mg1.1Al2O4.1 in front of a nickel-based catalyst led to a stable activity. Using this dual-bed system, no NiAl2O4 formation was identified after reaction.

Catalytic hydro-pyrolysis of lignocellulosic biomass over dual Na2CO3/Al2O3 and Pt/Al2O3 catalysts using n-butane at ambient pressure

Hydro-pyrolysis of biomass was studied at 500°C and atmospheric pressure, applying Al2O3 supported platinum and sodium carbonate catalysts. CO chemisorption has shown that platinum particles are well dispersed in Pt/Al2O3 catalyst while they get agglomerated in Pt–Na2CO3/Al2O3. The co-impregnated or sequentially impregnated Pt–Na/Al2O3 catalysts have not shown improvement compared to either Na2CO3/Al2O3 or Pt/Al2O3 catalysts when it comes to quality of bio-oil. A dual bed system in which Na2CO3/Al2O3 and Pt/Al2O3 are packed in two consecutive beds has combined the advantages of all catalytic systems, resulting in high quality bio-oil with oxygen content 5.6wt.% and HHV 42MJkg−1. N-butane shows equivalent performance as hydrogen in hydro-pyrolysis of biomass, opening new possibility for economical hydrogen sources.

Gasification of Bituminous Coal in a Dual-Bed System at Different Air/Coal Ratios

Gasification experiments on bituminous coal at different air/coal ratios were carried out using a newly designed combined dual-fluidized-bed pyrolysis/gasification (CDBPG) system. The effect of the air/coal ratio on temperature profiles, gas composition, gas heat value, tar yield, carbon conversion, and cold gas efficiency were demonstrated in this study. In the CDBPG system, only mixing the pyrolysis gas and the gasification gas to produce fuel gas is more efficient than single-bed gasification. Tar cracking was favored by an increase in the air/coal ratio of up to 2.4 m3/kg, and this is beneficial to improve the fuel gas value. The heat value of the product gas and the cold gas efficiency were maximized at an air/coal ratio of 2.1 m3/kg.

Technoeconomic Analysis of Solar H2 Production in the Vicinity of Indian Refineries

A technoeconomic evaluation has been conducted by the US Department of Energy, for four conceptual photoelectrochemical (PEC) H2 production systems namely, single-bed particle system, dual-bed particle system, PEC planar array system and PEC tracking solar concentrator system. The present work extends the analysis to capture solar energy in the vicinity of Indian oil refineries and generate H2 at estimated costs of 42, 84, 281 and 85 in ₹/kg H2 for the four systems, respectively. This includes the capital and operating costs involved if the PEC H2 production plant is set up around these refineries. Employing PEC H2 production systems obviate the CO2 generated by conventional processes like steam reforming, and thereby earning carbon credits. Inclusion of such credits is found to increase the annual earnings of the four conceptual systems by 0.7–8% depending on the selling price of H2. The sensitivity analysis of various economic factors like payback time, H2 price, carbon credit, efficiency of the system, etc., is performed which is useful in judging economics of the venture depending on the market variations in prices or rise in efficiency of the system or variable economic constraints of the investor.

Preliminary Study on the New Dual-Bed Photocatalytic Hydrogen Production System

A new dual-bed photocatalytic hydrogen production reaction system is proposed in this paper. In this dual-bed system, one bed is photocatalytic hydrogen evolution reaction bed in which I- is oxidized into I2 by a hole and H+ is reduced to H2 by an electron, and the other is the hole-sacrificed agent regeneration bed in which I- is regenerated by reducing I2 with Cu2O. The two reaction beds are connected with two constant flow pumps to form a circulation loop. The hole-sacrificed agent I- can always be renewable by circulating the reaction solution between dual beds. The dual-bed reaction system achieves to produce hydrogen continuously, steadily and efficiently.

Experiment and computational fluid dynamics simulation of in-depth system hydrodynamics in dual-bed gasifier

Dual-bed gasifier is a new gasifier system with separated combustion and gasification zones. The two-zone separation makes it possible to increase calorific value of the producer gas. In order to develop and improve the process operation, understanding of system dynamics and parameters that describe the in-depth hydrodynamics are essential. Computational fluid dynamics is a tool that can be used to explain the complex multiphase system behavior. The considered dual-bed gasifier had 3.00 m height and the maximum width diameters of riser and downcomer were 0.14 and 0.40 m, respectively. Conservation equations of mass, momentum, energy and species for each phase were solved coupling with the kinetic theory of granular flow using ANSYS FLUENT version 12.1. Here, two-dimensional simulation had been successfully determined the flow pattern and chemical reaction corresponding with actual experimental and theoretical data. The calculated results of the solid volume fraction in the riser section showed the bubbling and slugging flow patterns. The product gas composition and gas temperature inside dual-bed gasifer reflected the advantages for this type of reactor over the other conventional gasifiers. The system turbulences were firstly explored in dual-bed system which were normal Reynolds stresses and granular temperatures. For the effect of interphase exchange coefficient model, the pressure-loop using drag force model proposed by Gidaspow was in good agreement with the experiment than the ones proposed by Wen-Yu and Syamlal-O'Brien.

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry

Photoelectrochemical water splitting is a promising route for the renewable production of hydrogen fuel. This work presents the results of a technical and economic feasibility analysis conducted for four hypothetical, centralized, large-scale hydrogen production plants based on this technology. The four reactor types considered were a single bed particle suspension system, a dual bed particle suspension system, a fixed panel array, and a tracking concentrator array. The current performance of semiconductor absorbers and electrocatalysts were considered to compute reasonable solar-to-hydrogen conversion efficiencies for each of the four systems. The U.S. Department of Energy H2A model was employed to calculate the levelized cost of hydrogen output at the plant gate at 300 psi for a 10 tonne per day production scale. All capital expenditures and operating costs for the reactors and auxiliaries (compressors, control systems, etc.) were considered. The final cost varied from $1.60–$10.40 per kg H2 with the particle bed systems having lower costs than the panel-based systems. However, safety concerns due to the cogeneration of O2 and H2 in a single bed system and long molecular transport lengths in the dual bed system lead to greater uncertainty in their operation. A sensitivity analysis revealed that improvement in the solar-to-hydrogen efficiency of the panel-based systems could substantially drive down their costs. A key finding is that the production costs are consistent with the Department of Energy's targeted threshold cost of $2.00–$4.00 per kg H2 for dispensed hydrogen, demonstrating that photoelectrochemical water splitting could be a viable route for hydrogen production in the future if material performance targets can be met.

A novel dual-bed photocatalytic water splitting system for hydrogen production

A novel dual-bed system was designed to produce hydrogen through photocatalytic water splitting. The system was comprised of a photocatalytic reaction bed and a regeneration bed. Aqueous KI solution and Pt-loaded TiO 2 constituted the photocatalytic reaction bed where hydrogen was produced; meanwhile the hole scavenger iodide ion was oxidized into I 2. The effluent containing I 2 from the photocatalytic bed entered the regeneration bed and passed through a Cu 2O layer where I 2 was reduced to I −. The regeneration bed effluent was then recycled to the photocatalytic reaction bed. Since the hole scavenger KI in the photocatalytic bed was constantly kept at a high level through the continuous reduction of I 2 in the regeneration bed, steady production of hydrogen was achieved in the dual-bed system for a much longer period as compared to a single-bed system without regeneration.

DeNOx performance of Ag/Al2O3 catalyst using simulated diesel fuel–ethanol mixture as reductant

The NOx reduction activity of Ag/Al2O3 catalyst has been investigated systematically, using a mixture of simulated diesel fuel (SD) and ethanol (E) as the reductant with special interest in the low temperature deNOx performance below 350°C. The Ag loading and catalyst operating conditions such as C1/NOx and ethanol/simulated diesel fuel (E/SD) ratios have been optimized in order to achieve the maximum deNOx performance of the Ag/Al2O3 catalyst. Ammonia has been identified as the most abundant reaction intermediate over the Ag/Al2O3 catalyst under the optimized operating conditions. To further enhance the deNOx performance by utilizing the NH3 formed over the Ag/Al2O3 catalyst, a dual-bed reactor system has been employed with CuZSM5 catalyst in the rear bed consecutively following the front bed containing the Ag/Al2O3. The NOx-to-N2 conversion in this dual-bed system increased up to 85% from 275 to 450°C, mainly due to the NH3 oxidation to N2 by the CuZSM5 in the rear bed. Physicochemical characterization of the Ag/Al2O3 catalysts by UV–vis, TEM and EELS has indicated that both ionic and metallic Ag formed on the catalyst surface play important roles for the high deNOx performance of the present catalytic system; the ionic Ag including Ag+ and Agδ+ is the active reaction site for the reduction of NOx to N2, while the metallic Ag is responsible for the partial oxidation of hydrocarbons (HCs) which promotes the initiation of the HC/SCR process in the low temperature range. The optimum ionic/metallic (I/M) ratio of Ag species on Al2O3 support surface appears to be in the range of 1.4–1.7, depending upon the catalyst temperature range of interest.

Exerting the structural advantages of Ir-in-CeO 2 and Ir-on-CeO 2 to widen the operating temperature window for preferential CO oxidation

The activities of Ir-in-CeO 2 (Ir embedded in CeO 2) and Ir-on-CeO 2 (Ir dispersed on the surface of CeO 2) in preferential CO oxidation were comparatively studied in terms of their specific structures with different amount of surface Ir. It was found that the surface exposed Ir sites on Ir-on-CeO 2 were favorable for CO oxidation at low temperature (<100 °C). Encapsulating Ir in CeO 2 inhibited the adsorption of H 2, and also facilitated the activation of surface CeO 2 on Ir-in-CeO 2, which promised a high CO conversion at high temperature (>120 °C). Then a dual bed system with the top Ir-in-CeO 2 and the bottom Ir-on-CeO 2 was developed to widen the temperature window. This dual bed system is unique in affording a high CO conversion in a wide temperature window, from 80 to 200 °C, which is superior to single bed catalyst.

Photocatalytic overall water splitting with dual-bed system under visible light irradiation

Photocatalytic overall water splitting has been demonstrated with WO3 for oxygen producing photocatalyst (OPC), and Rh-doped SrTiO3 for hydrogen producing photocatalyst (HPC) in a simulated dual-bed system under visible light irradiation (λ ≥ 400 nm). The Fe3+/Fe2+ redox couple was chosen as the most effective electron mediator between OPC and HPC. The overall performance of the dual-bed system was limited by the low activity of HPC, and thus the activity of HPC should be increased to improve the overall performance. For overall water splitting reaction in a dual-bed system, the conduction band of OPC must be more negative than the redox potential of the electron acceptors and the valence band of HPC must be more positive than the redox potential of the electron donors.

Photocatalytic production of oxygen in a dual bed system using a reversible redox mediator on Ir-TiO2 catalyst

Photocatalytic O2 evolution by water splitting in an alkaline solution with a redox mediator was investigated in a dual bed system configuration: one bed was used for oxygen evolution and the other for hydrogen evolution. The employed photocatalyst was Ir-TiO2 and the iodate ion, KIO3, was used as a redox mediator. In order to find the optimum conditions for oxygen evolution, the effect of alkaline concentration, KIO3 concentration and the amount of Ir loading on the photocatalytic reactivity was examined in an irradiation area of 0.055 m2 reactor with a 400 W U.V. lamp. The experimentally obtained results showed that oxygen evolution depends on the concentration of the alkaline solution, the potassium iodate concentration and the amount of Ir loading.

Oxidative Dehydrogenation of C4 Raffinate-3 to 1,3-Butadiene in a Dual-bed Reaction System Comprising ZnFe2O4 and Co9Fe3Bi1Mo12O51 Catalysts: A Synergistic Effect of ZnFe2O4 and Co9Fe3Bi1Mo12O51 Catalysts

Oxidative dehydrogenation of C4 raffinate-3 to 1,3-butadiene was carried out in a dual-bed reaction system comprising ZnFe2O4 and Co9Fe3Bi1Mo12O51 catalysts in order to investigate a synergistic effect of these two catalysts. Conversion of n-butene and yield for 1,3-butiadene obtained in a dual-bed reaction system comprising ZnFe2O4 (first-bed) and Co9Fe3Bi1Mo12O51 (second-bed) were higher than those obtained in a single-bed reaction system using either ZnFe2O4 or Co9Fe3Bi1Mo12O51. 1-Butene-TPD and 2-butene-TPD measurements revealed that ZnFe2O4 catalyst retained more selective oxygen species for the reaction with 2-butene than for the reaction with 1-butene, while Co9Fe3Bi1Mo12O51 catalyst retained more selective oxygen species for the reaction with 1-butene than for the reaction with 2-butene. The synergistic effect of ZnFe2O4 (first-bed) and Co9Fe3Bi1Mo12O51 (second-bed) catalysts in the oxidative dehydrogenation of C4 raffinate-3 was attributed to the combination of high catalytic activity of ZnFe2O4 for 2-butene and high catalytic activity of Co9Fe3Bi1Mo12O51 for 1-butene.