Adiabatic Reactor Research Articles

Methanation of coke oven gas over Ni-Ce/γ-Al2O3 catalyst using a tubular heat exchange reactor: Pilot-scale test and process optimization

Traditional industrial methanation of coke oven gas (COG) to produce natural gas generally requires three or more adiabatic reactors, thus resulting in a longprocess flow, rapid deactivation of catalyst and high investment cost. Herein, a new methanation process of COG (denoted as NCtSNG) over the Ni-Ce/γ-Al2O3 catalyst was proposed, wherein a tubular heat exchange reactor and an adiabatic reactor were connected in series. The pilot-scale methanation test using a single tubular heat exchange reactor was performed, and the result demonstrated that heat exchange reactor would insure a low temperature of catalyst layer (below 500 °C), which can not only improve the efficiency of the exothermic methanation but also prolong the catalyst lifetime. A reliable simulation of the NCtSNG process was then established and validated by using the commercial software Aspen Plus based on the pilot test, and the key operation parameters and conditions were optimized so as to provide significant basic data for future industrial production. It was estimated that the new NCtSNG process presents high energy efficiency of 80%, low production cost of 2.15 CNY/m3-SNG, and low CO2 emission of 0.61 kg/m3-SNG, thus showing a great superiority in market competition.

Influence of reactor temperature conditions on the recycle flow rate

Objectives. The problem of optimizing chemical flow sheets according to energy costs associated with recycling flows is at present quite relevant. The current article investigates the influence of temperature conditions on the recycle flow rate, securing the specified conversion of the recycled flow sheet “reactor – separation unit.”Methods. The study’s main method is the mathematical simulation of a recycled flow sheet based on material balance and chemical kinetics equations. This model assumes that the separation unit can form the recycle and outlet flows of any specified compositions.Results. The mathematical model recycle flows provides the full reagent conversion of recycled flow sheet depends on the reactor type and the temperature conditions in it. It was established that the dependence of the recycle flow rate on the reactor temperature for endothermic reactions has monotonously decreasing shape. The most interesting are exothermic reactions for which the dependence of the recycle flow rate on the reactor temperature curve has a minimum. It is proved that the “reactor – separation unit” system with the plug flow reactor has lower optimal recycle flow rate than the recycled system with the continuous stirred tank reactor. For the adiabatic reactor the dependence of total conversion recycle flow rate on the inlet reactor temperature was investigated. It has been proven that the optimal recycle flow rate is equal to the minimum recycle flow rate for total conversion in the “reactor – separation unit” system.Conclusions. It has been established that isothermal operation conditions are the best in terms of the recycle flow rate, securing the specified conversion for the system.

Simulation of CO2 Conversion into Methanol in Fixed-bed Reactors: Comparison of Isothermal and Adiabatic Configurations

CO2 capture and utilization (CCU) has been widely considered as a potential solution to overcome global warming. Conversion of CO2 into methanol is an interesting option to transform waste into value-added chemical while also reducing greenhouse gases emissions in the atmosphere. In this paper, utilization of CO2 into methanol was simulated using Aspen Plus software. The reaction between CO2 and H2 to produce methanol and water was carried out in a simulated fixed-bed reactor with Cu/ZnO/Al2O3 commercial catalyst, following LHHW (Langmuir – Hinshelwood – Hougen – Watson) kinetic model. Isothermal and adiabatic reactor configurations were compared under similar feed conditions and the concentration profile along the reactor was observed. The result showed that isothermal configuration converted 3.23% more CO2 and provided 16.34% higher methanol yield compared to the adiabatic reactor. Feed inlet temperature variation was applied and the effect to methanol production on both configurations was studied. The highest methanol yield for adiabatic and isothermal reactor was obtained at 200 oC and 240 oC respectively.

Activation of catalysts in commercial scale fixed-bed reactors: Dynamic modelling and guidelines for avoiding undesired temperature excursions

During the exothermic gas phase activation (e.g. reduction) or passivation (oxidation) of a catalyst in a commercial scale fixed bed, the interaction of the heat wave propagation phenomenon and the (desired) exothermic gas-solid reaction(s) may give rise to local temperature excursions way beyond the adiabatic temperature rise of the reactions. Inspired by a decoking study by Westerterp et al. (1988), a full dynamic model for generic gas-phase catalyst activation and deactivation (reduction/oxidation) in an adiabatic fixed-bed reactor was developed. Counter intuitive effects were elucidated, e.g. for cases where a lowering of the reactant concentration or the presence of a significant reactor wall heat capacity can lead to a further increase of the maximum catalyst temperature. An easy-to-use expression was derived, initially using simplifying assumptions of full rate control by external mass transfer and neglecting heat losses and reactor wall effects. This was subsequently tested on its adequacy for more general cases accounting for (1) slower reaction kinetics, (2) significant heat losses and (3) the reactor wall heat capacity. Only for the latter effect the original expression had to be adjusted. The modified expression proved to be remarkably robust and remained relevant as a simple tool to prevent local temperature excursions also for slower reaction kinetics and significant heat losses.

Clariant launches CATOFIN 311, a propane dehydrogenation catalyst

A co-fed process combining propane dehydrogenation (PDH) with selective hydrogen combustion (SHC) is proposed, simulated, and optimized. The co-fed process uses adiabatic moving bed radial flow reactors as PDH reactors and adiabatic fixed bed reactors as SHC reactors. This co-fed process is proven to be very advantageous over the Oleflex process in some aspects, showing a propylene yield 6.0-46.1% higher and saving 2.86-7.24 × 106 kJ per ton of propylene under different operating conditions. These advantages are attributed to the utilization of SHC reactors: they consume some hydrogen in the process, which shifts the reaction equilibrium towards propylene; they also provide much heat to drive the highly endothermic PDH reaction. For the co-fed process, a feed temperature of 873 K, a total pressure of 1 bar, and using four PDH reactors are preferable; the optimal oxygen input is significantly affected by feed temperature and number of PDH reactors. Besides, under these preferable conditions, a SHC catalyst should have a minimum hydrogen combustion selectivity of 60.4% to reproduce and exceed the Oleflex efficiency. This work should provide useful guidelines for the development of co-fed processes for propane dehydrogenation.

Analysis and optimization of a methanol reactor with the adsorption of carbon monoxide and water

Methanol is generally produced in adiabatic or Lurgi type catalytic reactors from syngas or pure carbon dioxide and hydrogen. In this research, an innovative methanol reactor is analyzed and optimized, because sorbents for the capture of carbon monoxide and water are used. In particular, zeolite molecular sieves having high SiO2/Al2O3 are used to capture carbon monoxide while zeolites 4A are implemented to adsorb water molecules. No sorbents for the capture of carbon monoxide are suggested before. In this system, the two reactions in methanol production are both favored, then it is possible to increase the methanol yield, reducing the outlet reaction temperature, compared to a traditional adiabatic reactor. An ANOVA analysis and a response surface methodology are also developed. Results show that the capture fraction is the most important factor with the aim to improve the methanol yield and to reduce the reaction temperature. Optimal operating conditions are found in order to have a nearly-isothermal system (493 K) maximizing the methanol yield (37%): the capture fraction, recycle of gases, inlet temperature and reaction pressure must be respectively equal to 80%, 79.7%, 493.32 K and 55 bar. In the future work, an experimental reactor can be realized to verify the obtained results.

Process simulation and optimization of propane dehydrogenation combined with selective hydrogen combustion

A co-fed process combining propane dehydrogenation (PDH) with selective hydrogen combustion (SHC) is proposed, simulated, and optimized. The co-fed process uses adiabatic moving bed radial flow reactors as PDH reactors and adiabatic fixed bed reactors as SHC reactors. This co-fed process is proven to be very advantageous over the Oleflex process in some aspects, showing a propylene yield 6.0-46.1% higher and saving 2.86-7.24 × 106 kJ per ton of propylene under different operating conditions. These advantages are attributed to the utilization of SHC reactors: they consume some hydrogen in the process, which shifts the reaction equilibrium towards propylene; they also provide much heat to drive the highly endothermic PDH reaction. For the co-fed process, a feed temperature of 873 K, a total pressure of 1 bar, and using four PDH reactors are preferable; the optimal oxygen input is significantly affected by feed temperature and number of PDH reactors. Besides, under these preferable conditions, a SHC catalyst should have a minimum hydrogen combustion selectivity of 60.4% to reproduce and exceed the Oleflex efficiency. This work should provide useful guidelines for the development of co-fed processes for propane dehydrogenation.

Mathematical modeling of regeneration of coked Cr-Mg catalyst in fixed bed reactors

On the base of two-dimensional (bed length and pellet radius coordinates) two-temperature (gas and catalyst phases) mathematical model the coked CrF3/MgF2 catalyst regeneration process in the adiabatic reactor of gas-phase perchloroethylene hydrofluorination to pentafluoroethane (Freon 125) is studied. The parameters of the mathematical model such as coke burning rate constant, temperature of the coke burning beginning T* (ignition point), heat of the reaction and activation energy were determined from experiments in lab-scale reactor and from the thermal analysis data. The influence of process parameters, e.g. oxygen and coke concentrations, initial gas and catalyst temperatures and pellet size was investigated. The simulation was carried out under conditions of low oxygen concentration (oxygen shortage) and showed that if the inlet gas temperature Tgo is lower than initial catalyst temperature Tp0 (Tgo<Tp0, Tpo≥T*), the coke burning occurs only near the outer surface of catalyst pellet, because the bed is “cooled” by the inlet gas flow. This leads to the dramatic rise of temperature in a narrow “peak burning wave” and to an unexpected bed overheating that exceeds the adiabatic heating. This effect was not discussed in publications but was detected in industrial reactor during the coked chromium–magnesium catalyst regeneration. This result is very significant for industrial applications since it helps to avoid the catalyst overheating and the following catalyst activity decreasing during the regeneration.

Comparison of the method of variation of parameters to semi-analytical methods for solving nonlinear boundary value problems in engineering

AbstractSolutions to nonlinear boundary value problems modelling physical phenomena in engineering applications have traditionally been approximated using numerical methods. More recently, several semi-analytical methods have been developed and used extensively in diverse engineering applications. This work compares the method of variation of parameters to semi-analytical methods for solving nonlinear boundary value problems arising in engineering. The accuracy and efficiency of the method of variation of parameters are compared to those of two widely used semi-analytical methods, the Adomian decomposition method and the differential transformation method, for three practical engineering boundary value problems: (1) the deflection of a cantilevered beam with a concentrated load, (2) an adiabatic tubular chemical reactor which processes an irreversible exothermal reaction, and (3) the electrohydrodynamic flow of a fluid in an ion drag configuration in a circular cylinder conduit. The accuracy and convergence of each method is investigated using the error remainder function. The method of variation of parameters is significantly more efficient than both the semi-analytical methods and traditional numerical methods while maintaining comparable accuracy. Unlike the semi-analytical methods, the efficiency of variation of parameters is independent of the nonlinearity. Variation of parameters is shown to be an attractive alternative to semi-analytical methods and traditional numerical methods for solving boundary value problems encountered in engineering applications in which solution efficiency is important.

CO2 Methanation in Microstructured Reactors – Catalyst Development and Process Design

AbstractThe sulfur tolerance of mono‐ and bimetallic ruthenium catalysts for CO2 hydrogenation was investigated in microchannel reactors. H2S was selected as a model compound. It was found that a Ru/CeO2 catalyst deactivates rapidly. Ni was a much better additive to improve the catalyst stability compared to Rh and serves as a sulfur trap. The influence of the support was evaluated showing that a SiO2‐supported catalyst has a higher stability and better selectivity compared to CeO2 and TiO2. A plant concept was developed comprising two‐step methanation with a first adiabatic reactor stage followed by a plate heat‐exchanger reactor with integrated cooling which allows more than 97 % CO2 conversion. A pilot plant will be put into operation in connection with a biogas plant and an electrolyser of 50 kW power consumption.

Thermal Deactivation of Rh/α-Al2O3 in the Catalytic Partial Oxidation of Iso-Octane: Effect of Flow Rate

Catalytic partial oxidation (CPO) of logistic fuels is a promising technology for the small-scale and on-board production of syngas (H2 and CO). Rh coated monoliths can be used as catalysts that, due to Rh high activity, allow the use of reduced reactor volumes (with contact time in the order of milliseconds) and the achievement of high syngas yield. As the CPO process is globally exothermic, it can be operated in adiabatic reactors. The reaction mechanism of the CPO process involves the superposition of exothermic and endothermic reactions at the catalyst inlet. Thus, a hot spot temperature is formed, which may lead to catalyst deactivation via sintering. In this work, the effect of the flow rate on the overall performance of a CPO-reformer has been studied, using iso-octane as model fuel. The focus has been on thermal behavior. The experimental investigation consisted of iC8-CPO tests at varying total flow rates from 5 to 15 NL/min, wherein axially resolved temperature and composition measurements were performed. The increase of flow rate resulted in a progressive increase of the hot spot temperature, with partial loss of activity in the entry zone of the monolith (as evidenced by repeated reference tests of CH4-CPO); conversely, the adiabatic character of the reformer improved. A detailed modelling analysis provided the means for the interpretation of the observed results. The temperature hot spot can be limited by acting on the operating conditions of the process. However, a tradeoff is required between the stability of the catalyst and the achievement of high performances (syngas yield, reactants conversion, and reactor adiabaticity).

Modeling of an Autothermal Reactor for the Catalytic Oxidative Decomposition of H2S to H2 and Sulfur

An adiabatic fixed-bed reactor for the simultaneous production of sulfur and hydrogen by catalytic oxidative decomposition of H2S was simulated using a steady-state one-dimensional heterogeneous re...

Ethanol-to-ethylene dehydration on acid-modified ring-shaped alumina catalyst in a tubular reactor

New results of endothermic dehydration of undiluted ethanol on alumina catalyst in pilot wall-heated tubular reactor are presented. Activity and physicochemical characteristics of the proprietary acid-modified alumina (AMA) prepared by gibbsite flash calcination in TSEFLAR™ reactor were compared to the properties of commercially available alumina samples prepared by precipitation (CS1) or flash calcination of gibbsite in a flue gas (CS2). The samples differed in phase composition, which corresponds to γ-Al2O3 in CS1, mixed γ- and χ-Al2O3 in AMA and CS2; sodium content and concentration of Lewis acid sites (LAS) were different as well. Acid modification resulted in AMA catalyst with improved acidic properties and catalytic activity higher than that of CS2, despite the lower sodium content in the latter. Ethanol-to-ethylene dehydration in the wall-heated tubular reactor proceeded at the catalyst bed temperatures mainly below 385 °C, where AMA catalyst is the most active due to the highest content of strong LAS. The heat-agent temperature favors yield of ethylene rather than that of by-products. Higher linear velocity and porosity contribute to a flatter axial temperature profile in the bed; a higher average integral temperature gives a quantitative estimate. This ensures higher ethylene yield with a lower ethanol consumption even at a reduced heat-agent temperature. On the ring-shaped AMA catalyst, the greater ethylene yield, catalyst productivity and sharply reduced hydraulic resistance are reached compared to CS2 cylinders. For the first time we showed that use of AMA ring-shaped catalyst in wall-heated tubular reactor in contrast to the SynDol alumina based catalyst in adiabatic reactor can improve the catalyst productivity by 5–8 times and WHSV by 5–12 times.

Introducing a novel process to enhance the syngas conversion to methanol over Cu/ZnO/Al2O3 catalyst

In this study, a novel configuration, Adiabatic and Plate Water-cooled Reactors, which called APW is introduced as an alternative for a two stage conventional methanol process consisting of gas-cooled and water-cooled reactors. In the APW configuration, the gas-cooled reactor is replaced with two adiabatic reactors with the optimized basic design. A water-cooled reactor is like a plate heat exchanger with three sections by the different number of plates. The gas flow rate through each section is optimized, so that pressure and temperature changes along these sections are almost identical. Mathematical modeling indicates that, temperature rise within the adiabatic reactor precludes gas condensate formation, consequently improves the catalyst durability. Moreover, the small length to cross section ratio of the adiabatic bed results in low pressure drop. Also, high average temperature and low pressure drop along the adiabatic beds enhance methanol production. The proposed configuration, provides different advantages than the conventional process, e.g. low pressure drop, high cooling efficiency of the water-cooled reactor and higher H2 and CO2 conversions. The APW configuration enhances the methanol production rate 12.2% in comparison with conventional configuration. Other advantages in this configuration are, eliminating condensate formation, preventing greenhouse gas emissions and improving catalyst durability.

Optimal design of washcoated monolith catalyst for compact, heat -integrated ethanol reformers

Monolith reactors are extensively employed for adiabatic gas-solid reactions, primarily in environmental applications. They are emerging as an attractive application in catalytic reformers where hydrogen needs to be produced on-board. These uses of monoliths are based on the optimal configuration and geometry of the washcoat, i.e., the thin catalytic layer impregnated onto the inert backbone of the monolith. In this paper, we present an analysis of the influence of geometric parameters of the washcoated monolithic catalyst towards affecting the reactor performance of non-isothermal reactor operation. The reactor performance is accounted through ‘volumetric reactor activity’ which comprises of the transport-kinetic interactions under adiabatic reactor condition. The effects of different combinations of the radius of curvature and coating thickness on the reactor activity and effectiveness factor are investigated for different backbone geometries. Through this process, an optimal combination of (R, dh) for each backbone configuration is evaluated. The radius of curvature (R = 0) always gives highest reactor activity due to low mass transfer resistance obtained in corners. With the increase in washcoat loading, the reactivity increases and after a certain point, it decreases owing to the mass transfer resistance which starts dominating at beyond that point. Finally, a 3D monolith geometry is modeled, and its performance is evaluated through ethanol conversion and temperature variations while the reforming section is coupled with ethanol combustion. Parametric sensitivity analysis is also performed by varying the effective diffusivity, the reaction rate constant, reforming section inlet velocity and feed temperature.

Software implementation of the dynamic model of the first stage of the reactor unit for styrene production in the MATLAB/SIMULINK environment

A mathematical description of the physicochemical processes occurring in the first stage of ethylbenzene dehydrogenation in a two-stage adiabatic continuous reactor is developed. A software implementation of the resulting model in Matlab/Simulink environment is presented, that allows to simulate the sequence and dynamics of the flow of internal processes during the equipment operation, taking into account the decrease in activity of the catalytic layer. The algorithm of functioning, structure and model of information flows of the created software, implementing a modular approach to the description of a series-parallel system of thermal, chemical processes and processes on the surface of the catalytic layer are given. The created software allows to simulate the operation of the reactor stage when process parameters change.

Dehydrogenation of Methylbutenes to Isoprene: A Comparative Mathematical Analysis of the Dehydrogenation of Methylbutenes to Isoprene in Axial and Radial Reactors

Using a mathematical model that describes the process of methylbutene dehydrogenation to isoprene, a comparative analysis of energy efficiency is performed for two upgrading variants: (1) a system of two serially arranged axial fixed-bed reactors and (2) an adiabatic fixed-bed reactor. A mathematical analysis is performed to determine the dependence of yield Y and selectivity S on quantity Q of thermal energy supplied by means of steam in each case. For the two-reactor system, the best performance characteristics (Y = 53.1% and S = 82.9%) are attained at Q = 9.0 MJ/kg and contact time t = 0.8 s. However, the best performance characteristics in the radial reactor (Y = 42.0% and S = 86.1%) are observed at Q = 7.8 MJ/kg and t = 0.8 s. It follows that the thermal energy required for the methylbutenes dehydrogenation reaction in the radial reactor is 13.0% lower than for the axial reactors.

Four computational approaches for solving a class of boundary value problems arising in chemical reactor industry

In this work the performance of four new and different approaches are presented for numerical solution of some nonlinear boundary value problems which arise in modelling a tabular adiabatic chemical reactor. Quasi-linearization and converting differential equations to integral equation techniques and derivative and integration operational matrices of Cubic B-spline wavelets via some projection methods are applied to reducing the nonlinear problem to some algebraic system. For study of effect of involved parameters in main problem and for showing the accuracy and efficiency of the introduced methods some cases of main problem are given and findings are compared with the results of alternative methods for numerical solving of this class of equations.

Energy Efficient Styrene Process: Design and Plantwide Control

The paper deals with conceptual design and simulation of an energy efficient process for manufacturing styrene by ethylbenzene dehydrogenation in adiabatic reactors using superheated steam as inert...

Complex study of the activity, stability and sulfur resistance of Pd/La2O3-CeO2-Al2O3 system as monolithic catalyst for abatement of methane

New and complex results on catalytic activity, thermal stability, effect of H2O and SO2 on the Pd/La2O3-CeO2-Al2O3 model system in methane combustion have been obtained. The catalyst characterization has been made by N2- physisorption, XRD, SEM/EDX, HRTEM, XPS, TPD, TPR and FTIR methods. The observed high activity is related to the stabilization of highly dispersed Pd4+ species, strongly interacting with the support. As it was expected, La2O3 prevented the sintering of the gamma-alumina carrier, in addition it probably contributed to avoid further agglomeration of the palladium species by the formation of La2PdO4 mixed phase. It is supposed that the most probable reason for the observed decrease in activity in the presence of water vapor of thermally aged sample is the increase in PdO/Pd – ratio above its optimum. The presence of both H2O and SO2 in the gas leads to formation of surface Al2(SO4)3, thus indicating a limited possibility to regenerate completely the catalyst. The reaction pathway over Pd/La2O3-CeO2-Al2O3 catalysts proceeds most probably through Mars–van Krevelen mechanism upon adsorption of water molecules on both oxidized and reduced sites and slow desorption of reaction products. For practical evaluation of the synthesized material, a sample of Pd/La2O3-CeO2-Al2O3 was examined as supported on stainless steel (Aluchrom VDM®) in the form of single monolithic channel. Two-dimensional heterogeneous models were used to simulate the methane combustion from laboratory scale up to pilot- and full-scale adiabatic monolithic reactors.