Differential Fixed-bed Reactor Research Articles

Development of a kinetic model for CO2 methanation over a commercial Ni/SiO 2 catalyst in a differential reactor

Development of a kinetic model for CO2 methanation over a commercial nickel catalyst was performed to consider pathways of CO2 conversion via Sabatier and RWGS reactions. H2/CO2 ratio in the feed gas composition was varied at the stoichiometry of the Sabatier reaction assuming a fictitious CO2 conversion of 0 to 0.7. Non-stochiometric gas feeding and the addition of product gases, i.e., methane and steam, were also considered to examine reaction orders and inhibition effects. The kinetic tests were carried out at 300–350 °C and 0.1–0.9 MPa. GHSV corresponded to 37,494 h−1. The stable activity was achieved by forcibly stressing the catalyst under the equilibria at 500 °C for 35 h. The kinetic measurements were conducted at an isothermal differential fixed bed reactor in the absence of heat and mass transport limitations. The methanation reaction was first fitted with the power law and LH approaches by considering the Sabatier reaction. Then, the RWGS reaction was added to consider CO formation using the power law models. The results showed a better fitting of experimental observations by using the LH expression with the formation of formyl as RDS and the power law model with inhibiting influence of water.

Catalytic Dry Reforming and Cracking of Ethylene for Carbon Nanofilaments and Hydrogen Production Using a Catalyst Derived from a Mining Residue

In this study, iron-rich mining residue (UGSO) was used as a support to prepare a new Ni-based catalyst via a solid-state reaction protocol. Ni-UGSO with different Ni weight percentages wt.% (5, 10, and 13) were tested for C2H4 dry reforming (DR) and catalytic cracking (CC) after activation with H2. The reactions were conducted in a differential fixed-bed reactor at 550–750 °C and standard atmospheric pressure, using 0.5 g of catalyst. Pure gases were fed at a molar ratio of C2H4/CO2 = 3 for the DR reaction and C2H4/Ar = 3 for the CC reaction. The flow rate is defined by a GHSV = 4800 mLSTP/h.gcat. The catalyst performance is evaluated by calculating the C2H4 conversion as well as carbon and H2 yields. All fresh, activated, and spent catalysts, as well as deposited carbon, were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), transmission electron microscopy (TEM), temperature programmed reduction (TPR), and thermogravimetric analysis (TGA). The results so far show that the highest carbon and H2 yields are obtained with Ni-UGSO 13% at 750 °C for the CC reaction and at 650 °C for the DR reaction. The deposited carbon was found to be filamentous and of various sizes (i.e., diameters and lengths). The analyses of the results show that iron is responsible for the growth of carbon nanofilaments (CNF) and nickel is responsible for the split of C–C bonds. In terms of conversion and yield efficiencies, the performance of the catalytic formulations tested is proven at least equivalent to other Ni-based catalyst performances described by the literature.

Kinetics of CO2 hydrogenation to methanol over silica supported intermetallic Ga3Ni5 catalyst in a continuous differential fixed bed reactor

The methanol synthesis from CO2 hydrogenation is seen as a potential reaction for alternate fuel production as well as environmental clean-up. In this study, kinetics of methanol synthesis from CO2 hydrogenation has been investigated over Ga3Ni5/SiO2 catalyst. The catalyst was characterized by XRD, TEM-EDX, SEM, and ICP-MS techniques. The influence of different reaction variables like H2/CO2 ratio (3–9), temperature (423–523 K), and W/FAo (26.54 × 103 to 79.62 × 103kg.s/kmolCO2) was studied at atmospheric pressure in a differential plug flow (PFR) fixed bed reactor. Two Langmuir-Hinshelwood models with different adsorption terms (competitive and non-competitive) were developed for methanol synthesis and reverse water gas shift (RWGS) reaction using the experimental data. Model discrimination by statistical analysis combined with physio-chemical constraints revealed that the competitive model is the best kinetic model. The model results revealed that the reactants, reaction intermediates, and products adsorb competitively over the same active sites on Ga3Ni5 surface. It was also found that the formate hydrogenation is the rate determining step for methanol synthesis with adsorbed atomic H2 and CO2 as the most abundant reaction intermediates. The kinetic model results were found consistent with the reported literature.

The reduction of Fe-bearing copper slag for its use as a catalyst in carbon oxide hydrogenation to methane. A contribution to sustainable catalysis

Reduction of Fe-phases in a slag from the copper smelting process is studied for its use as a catalyst in methanation of carbon oxide (CO). This material contains 36.4 wt% Fe and the main Fe-phases in its fresh and reduced forms were identified and quantified. Chemical analysis and X-ray diffraction (XRD) for crystalline phase detection and determination of Fe dispersion were carried out. Reducibility of Fe-oxides was studied by thermal programmed reduction (TPR) under H2 at 650 and 800 °C using 0.5 and 2 h soak time. In the fresh slag, iron was found to be in the form of Fe3O4 (17.4 wt%) and fayalite, Fe2SiO4 (43.4 wt%). The composition was experimentally determined and verified by stoichiometric balances and thermogravimetric analysis (TGA). Upon reduction at 800 °C and 2 h soak time, 87 % of the Fe-phases were reduced, leaving an activated catalyst with a 35.2 % Fe0, which is the active phase for CO hydrogenation to methane. An expression was derived to determine the Fe0 concentration in the reduced slag based on the composition of the fresh slag and its reduction degree. The catalytic activity of the reduced slag during CO hydrogenation was evaluated in a fixed bed differential reactor. The selectivity to methane, at 300 °C, was 87 %, thus confirming its catalytic activity for the selected reaction.

Optimization of the synthesis technique of molybdenum sulfide catalysts supported on titania for the hydrodesulfurization of thiophene

The present work deals with the optimization of the preparation method for the synthesis of unpromoted molybdenum catalysts supported on titania. Four methodologies have been followed: equilibrium–deposition–filtration (EDF), wet impregnation (WI), dry impregnation (DI) and controlled wet impregnation (CWI). The Mo surface density of all catalysts was 3.2 Mo atoms/nm2. The catalysts were characterized using N2 adsorption, XRD, XPS and DRS. The catalysts were evaluated in the hydrodesulfurization (HDS) of thiophene, using an atmospheric differential fixed bed reactor. EDF technique provided the most active catalyst followed by that prepared by WI and then by those prepared by DI or CWI. Although the impregnation technique does not influence the structure of the catalysts at nanoscale, a suitable choice of the impregnation technique leads to the increasing contribution of supported molybdenum clusters with small size and thus with high number of the Ti–O–Mo (Ti–S–Mo) bridges per Mo atom, stabilizing highly S-deficient structures. In order to confirm the favorable influence of titania on the catalytic performance, we have synthesized by DI a Mo catalyst supported on γ-alumina with the same loading. The relatively low activity exhibited by this catalyst was attributed to the different structure of the supported molybdenum species with respect to those formed on titania and to the lower Mo dispersion.

Preparation of Coal-Based Columnar Activated Carbon for Removal of Benzene

In the paper, a series of coal-based columnar activated carbons (CCACs) for adsorption of benzene were prepared using a factorial experiment method. The CCACs prepared were characterized, and their adsorption capacities toward benzene were measured in a differential fixed-bed reactor. Besides, through a statistical method, the importance degree of preparation variables was studied, and the effects of preparation variables on benzene adsorption capacities of the CCACs were fully evaluated. It was found that pore structure of CCACs prepared was beneficial for benzene adsorption, but preparation variable in the process has little effect on the surface chemistry of CCACs prepared. Based on statistic analysis, it was revealed that among the four process variables studied for the sorbent prepared in this work, the activation temperature was found to be the most significant one for benzene adsorption capacity, next ones are the activation time and the amount of KOH, and the last one is the flow rate of water vapor and their optimal levels were 950 °C, 3.0 h, 2.5 % and 1.25 mL/g/h respectively.

Effects of O2/CH4 ratio on methane catalytic combustion over Cu/γ-Al2O3 particles

Rate measurements of methane catalytic combustion over copper catalyst were investigated in a fixed bed differential reactor with different pressure ratios of O2/CH4. Three kinetic regions were defined by the influence of pressure ratios of O2/CH4 on methane catalytic combustion. And surface reaction mechanism, as well as kinetic characteristics, was also discussed. It was found that, when O2/CH4 > 2, methane reaction rate had a positive relationship with methane pressure, and the reaction parameters were: α=0.9, β=0, Ea=146.3 kJ/mol (α and β are reaction orders with respect to methane and oxygen, Ea is apparent activation energy). Coverage ratio of chemisorbed oxygen on catalyst surface approached a saturated state. When 0.1 < O2/CH4 < 2, both methane and oxygen could affect reaction rate (α=0.43, β=0.68 and Ea=99.8 kJ/mol), and chemisorbed oxygen was unable to occupy active sites completely. When 0 < O2/CH4 < 0.1, reaction rate only depended on oxygen pressure (α=0, β=1.0, Ea=60.8 kJ/mol). Chemisorbed oxygen was depleted, and unoccupied copper sites became the most abundant surface intermediates. Transition of rate-determining step was from the reaction between methane and oxygen to oxygen adsorption on catalyst surface with decreasing pressure ratio of O2/CH4.

Preparation of un-promoted molybdenum HDS catalysts supported on titania by equilibrium deposition filtration: Optimization of the preparative parameters and investigation of the promoting action of titania

The present work deals with un-promoted molybdenum hydrodesulphurization (HDS) catalysts supported on titania (anatase) which have been prepared by “Equilibrium Deposition Filtration” (EDF). The catalysts were characterized using various techniques (XRD, N2 adsoption–desorption isotherms, TPR, DRS and XPS) and evaluated at various temperatures and atmospheric pressure in a fixed bed differential reactor, using the HDS of thiophene as a probe reaction.The calcination of the carrier before its usage has been optimized. The adjustment of the impregnation parameters allowed regulating the Mo loading in the monolayer region and thus optimizing the catalytic performance. A linear decrease of the intrinsic activity with the Mo surface density and a concomitant volcano trend for the specific activity have been found.Monomer, monopodal Mo species are deposited on the anatase surface in the pH range 7.0–4.5 and polymer Mo species at pH 2. The former are transformed into tripodal ones after calcination. Thus, the monolayer capacity of the anatase surface is decreased leading to a partial association of these species into oligomer ones where the mean number of TiOMo bridges per Mo atom is lower than three. The extent of this transformation increased with the Mo surface density. The DRS, XPS and TPR results suggested that electron transfer takes place through the TiOMo bridges from the anatase surface oxygen to the Mo4d orbitals.The monomer tripodal Mo species are transformed into relatively small Mo sulphided edge clusters in tilted or perpendicular configuration bonded on the anatase surface by TiOMo and/or TiSMo bridges. The aforementioned transfer in the electronic density from the surface oxygens, and likewise from the surface sulfur, to Mo4d orbitals weakens the MoS bonds of the clusters and stabilizes S-deficient structures creating coordinative unsaturated active sites. This explains the very high intrinsic activity of these small Mo sulphided clusters.The oligomer Mo species, on the other hand, are transformed into relatively larger Mo S-deficient sulphided clusters, also with tilted or perpendicular configuration with respect to the anatase surface. The number the MoOTi and MoSTi bridges per Mo atom is smaller than that in the small Mo sulphided clusters, resulting to less coordinative unsaturated active sites per Mo atom. The above explained the aforementioned trends for the intrinsic and specific activities.

Kinetic Modeling of MTO Process Applying ZSM-5 Zeolite Modified With Phosphorus as the Reaction Catalyst

In the present study, a number of phosphorus modified HZSM-5(Si/Al = 250) zeolite as MTO catalyst were prepared and characterized by various methods. A kinetic model for MTO process over PZSM-5 catalyst was developed based on data obtained from a differential fixed bed reactor within the temperature range of 360–425°C and 1 bar pressure applying the Langmuir-Hinshelwood formulation. The kinetic parameters were evaluated from the experimental data using genetic algorithm. It was found that the predicted data from the model were well correlated with the experimental results, indicating that ethylene and propylene are primary olefins.

Reaction of Hydrogen Chloride Gas with Sodium Carbonate and Its Deep Removal in a Fixed-Bed Reactor

The chloridization rates of sodium hydrogen carbonate calcines were determined using both a differential fixed-bed reactor and an integral fixed-bed, flow-through reactor at ambient pressure and a temperature of 500 °C. In the course of the reaction with hydrogen chloride gas, monoclinic or hexagonal Na2CO3 was transformed into cubic NaCl. The expansion of the volume of the solid phase, because of the reaction, was described by means of a simple structural model. The reacted solids remained quite porous (∼29%), having decreased from an initial porosity of 45%. Up to advanced stages of the reaction, the rate-decaying behavior of the chloridization reaction can be approximated by first-order kinetics as a function of either the solids conversion or the elapsed time of reaction. The reaction between hydrogen chloride gas and the Na2CO3-based sorbents is rapid, and a high degree of sorbent utilization can be attained. The unsteady-state sorption of hydrogen chloride gas in a column packed with reactant solids...

Fischer–Tropsch synthesis on cobalt–manganese nanocatalyst: studies on rate equations and operation conditions

In this research, an active Co–Mn/TiO2 catalyst was prepared by co-precipitation method for synthesis of light olefins in Fischer–Tropsch synthesis. After studying the effects of using optimized operating conditions on catalyst performance, the kinetic of experimental study was performed in a differential fixed-bed micro reactor. The effect of a range of operating variables such as the pressure, temperature, and H2/CO molar feed ratio on the catalytic performance of precipitated catalyst were investigated. It was found that the best operating conditions are H2/CO = 2/1, T = 270 °C, and P = 3 bar. Power-law equations have been fitted with experimental data in terms of the hydrogen and carbon monoxide partial pressure for the CO conversion rate and production rates for each product. The activation energies for the carbon monoxide conversion and methane production were determined to be 30.71 and 42.37 kJ/mol, respectively.

Investigation into the kinetics of pressurized steam gasification of chars with different coal ranks

The steam gasification of coal chars derived from three different ranks of typical Chinese coals was studied in a pressurized fixed-bed differential reactor at elevated pressure (up to 2.0 MPa). Three mathematical models [volumetric model (VM), grain model (GM), and random pore model (RPM)] for the gasification kinetics of different chars were validated, through which the kinetic parameters were obtained and discussed. The results show that the evolution trend of the coal char gasification rate with carbon conversion differs from coal ranks and has little change with pressure and temperature. The pressurized gasification process of the Shenmu sub-bituminous coal char (SM char) and the Jingcheng anthracite char (JC char) can be well-predicted by the RPM, while that of the Huolinhe lignite char can be better described by the VM. The pressure has little effect on the options of the reaction kinetic models for the three chars. The kinetic parameter E is almost a constant independent of pressure, while k0 changes with pressure, and it seems that k0 would be almost a constant over 1.0 MPa for SM and JC chars. The reaction order decreases with increasing the total system pressure and differs from different coal types.

Oxygen Reactivity of Devolatilized Diesel Engine Particulates from Conventional and Biodiesel Fuels

This study reports measurements of the oxygen reactivity of diesel engine particulates generated with a range of conventional and biodiesel fuel blends. Particulate samples were collected from a modern light-duty diesel engine and then devolatilized at 650 °C under argon. Reaction rates of the remaining fixed carbon component with oxygen were measured in a differential fixed-bed reactor. Global Arrhenius kinetic parameters were determined from the measured reaction rates. Surface area measurements were also made in situ during particle burnout and revealed fuel-dependent differences in burning mode. An empirical function for correlating the variation of surface area with burnout is proposed based on these observations. When the observed reaction rates are normalized to the local active carbon surface area (which varied with fuel type and degree of burnout), it is possible to identify a single global Arrhenius activation energy of 113 ± 6 kJ/mol.

Fischer–Tropsch synthesis: Development of kinetic expression for a sol–gel Fe–Ni/Al2O3 catalyst

In this experimental study, a kinetic model has been developed for Fischer–Tropsch synthesis reactions by using sol–gel technique and Fe/Ni/Al2O3 as the catalyst (40% Fe/60% Ni/40wt.%Al2O3) in a differential fixed-bed micro reactor assuming no internal or external diffusion. Operating conditions of the reactor were as follows: total pressure 1–12atm ; Temperature 220–260°C; H2/CO feed ratio 1.5–2; gas hourly space velocity 2100–7000cm3(STP)/h/gcat and conversions of 6–37% of hydrogen and 7–21% of carbon monoxide. Mass transfer limitations were investigated by changing synthesis gas velocity in reactors which differ in size. Based on the hypothesis that water inhibits the intrinsic Fischer–Tropsch (FT) reaction rate in the iron-FT synthesis, all rate expressions in this study were in inverse ratio to number of vacant sites and CO and water content. The obtained data in this study were checked using “complete form of Langmuir–Hinshelwood–Hougan–Watson (LHHW)” which has been proposed by Van der Laan and Botes. The kinetic parameters were determined using Levenberg–Marquardt (LM) method. The activation energy and heat of adsorption of CO and water were 103.81, −56.82 and −25.62kJ/mol, respectively.

Effect of Carbon Dioxide on the Sulfation of High Surface Area CaCO3 at High Temperatures

Flue gas produced from coal combustion contains CO2, O2, and H2O in addition to SO2. The effects of these components, especially CO2, on the sulfation of a high surface area CaCO3 (73 m2/g) were studied using a differential fixed-bed reactor under conditions simulating the conventional and O2/CO2 coal combustion atmospheres. The initial sulfation rate and ultimate (1 h) conversion for CaCO3 increased as the SO2 concentration (1000–5000 ppm) and reaction temperature (750–950 °C) increased, decreased as the CO2 concentration (0–95%) increased, and was independent of O2 (5–20%) and H2O (0–10%) concentrations. Sulfation at temperatures and CO2 concentrations where CaCO3 can decompose gave higher conversions than the direct sulfation of CaCO3. CO2 impeded the sulfation of CaCO3 by inhibiting or delaying the decomposition of CaCO3 and enhancing the sintering of CaCO3 and CaO. Under the conditions where CaCO3 cannot be formed, CO2 had little effect on the sulfation of CaO; however, under the conditions where CaC...

The synthesis of hydrocarbons and oxygenates during CO hydrogenation on CoCuZnO catalysts: Analysis at the site level using multiproduct SSITKA

This paper addresses the effect of component interaction in CoCuZnO catalysts on oxygenate synthesis during CO hydrogenation. Formation of the various products was investigated for the first time using in-situ multiproduct SSITKA. CO hydrogenation was carried out in a fixed-bed differential reactor at 250°C and 1.8atm. Reaction results indicate that the activities for all products decrease with the combination of Co with Cu, possibly, based on SSITKA results, due to partial blockage of the Co surface by Cu. ZnO alone, on the other hand, seems to serve primarily as a support for Co but may increase slightly the intrinsic activities for higher oxygenates. The effects of Cu and ZnO on Co, however, were not additive. The Co–Cu–ZnO combination resulted in a synergy that greatly increased selectivities for higher oxygenates by significantly decreasing the ability for hydrocarbon formation. Interestingly, the rate of synthesis for C2 oxygenates on Co/CuZnO was identical to that on Co/Al2O3 (considered by most to be only a hydrocarbon synthesis catalyst)—but without the high production rate of hydrocarbons.

Application of a Fluidized Bed Reactor in the MTO (Methanol to Olefin) Process: Preparation of Catalyst and Presentation of a Kinetic Model

Light olefins are basic raw materials for petrochemical industries and the global demand for the latter is growing. The authors investigated the conversion of methanol to light olefins in presence of acidic SAPO-34 molecular sieve as the reaction catalyst. SAPO-34 was synthesized by hydrothermal method, applying morpholine as the template. The molecular sieve was then changed into protonated form by ion exchange process with ammonium chloride at 80°C. A kinetic study was carried out within the temperature range of 375–425°C and 4 bar pressure using a differential fixed bed reactor. An appropriate kinetic model was presented and the kinetic parameters were evaluated as functions of temperature. In addition, the formation of light olefins was implemented in a fluidized bed reactor under a wide range of operating conditions. The experimental results were correlated with those predicted from a hydrodynamic model. Taguchi's experimental design method was applied to determine the optimum operating parameters of this process conducted in the fluidized bed reactor. The optimized parameters were the following: temperature = 425°C; ratio of inlet gas velocity to minimum fluidizing velocity (U0/Umf) = 7; catalyst mean particle size = 240 μm.

Preparation of SAPO-34 catalyst and presentation of a kinetic model for methanol to olefin process (MTO)

Conversion of methanol to light olefins (MTO) using acidic SAPO-34 molecular-sieve as the reaction catalyst was studied in a differential fixed bed reactor within the temperature range of 375–425 °C and under 4 bar pressure. The importance of MTO process is due to the increasing demand for light olefins in recent years. SAPO-34 was synthesized by hydrothermal method, applying morpholine as the template. The latter compound was then changed into protonated form by ion exchange method with ammonium chloride at 80 °C. A simple stoichiometric scheme has been presented for MTO. In addition a mechanism for this process based on Langmuir–Hinshelwood formulation has been put forward and the kinetic parameters have been evaluated as functions of temperature.

Relationships between oxygenate and hydrocarbon formation during CO hydrogenation on Rh/SiO 2: Use of multiproduct SSITKA

In the present research, the mechanism of C 1 and C 2 hydrocarbon and oxygenate formation during CO hydrogenation on Rh/SiO 2 were for the first time investigated in detail using multiproduct SSITKA (steady-state isotopic transient kinetic analysis). This was also the first effort to explore at the site level the relationship between similar products [e.g., EtOH (ethanol) vs. AcH (acetaldehyde)] on Rh/SiO 2. A fixed-bed differential reactor was used for CO hydrogenation and SSITKA at 250 °C and 1.8 atm. The selectivity to CH 4 was higher than any other product, but the surface reaction residence time for CH 4 formation was not the shortest among all the products. The surface reaction residence time for C 2 hydrocarbons was longer than that for any other product (C 1–C 2). Even though the selectivities to AcH and EtOH were similar, their surface reaction residence times differed significantly. Based on the SSITKA results, MeOH and CH 4 appear to be produced on completely different active sites. Moreover, C 2 hydrocarbons do not appear to be formed from adsorbed AcH. It is likely, however, that all C 2 products share at least one intermediate with CH 4, but none with MeOH. Several recently proposed pathways for EtOH and AcH formation are presented and compared to our results. The secondary reaction of AcH to form EtOH on the same sites does not appear to be a dominant pathway for EtOH formation. However, the precise mechanism for EtOH formation still needs further investigation.

Effect of SO2 on the Reaction of Calcium Hydroxide with CO2 at Low Temperatures

The flue gas generated from a coal-fired power plant contains CO2 and SO2. The effect of SO2 concentration (≤1000 ppm) on the reaction of CO2 with Ca(OH)2 was studied using a differential fixed-bed reactor under the low-temperature and humid conditions similar to those in the bag filters of a dry or semidry flue gas desulfurization (FGD) system. When both CO2 and SO2 were present, they reacted with Ca(OH)2 simultaneously to form calcium carbonate and sulfite, but part of the carbonate formed reacted further with SO2 to form sulfite. Ca(OH)2 ceased to react due to the formation of an impervious product layer. The fraction of carbonate increased significantly with decreasing SO2 concentration in the range below 500 ppm SO2, but the fraction of sulfite decreased little except in the range below 100 ppm SO2 or at a relative humidity (RH) above 70%. Both fractions of carbonate and sulfite increased markedly with increasing relative humidity and slightly with increasing temperature, but they were little affecte...