Synthesis Gas and Zinc Production in a Noncatalytic Packed‐Bed Reactor

A noncatalytic packed‐bed reactor has been constructed for management of the reduction of ZnO by methane, which leads to co‐production of synthesis gas and zinc. The reactor consisted of a simple vertical pipe filled with ZnO pellets. These pellets underwent reaction with a pure methane flow. Experimental tests were conducted in the temperature range 860–995 °C at atmospheric pressure in an electrically heated reactor. The results showed complete chemical conversion of methane to synthesis gas in the aforementioned temperature range. In addition, analysis of the product solids indicated that the collected solids in the outlet of the reactor were entirely zinc. The maximum methane flow rates (149–744 mL min^–1) were adjusted to ensure complete chemical conversion of methane. These adjustments were performed for different bed heights at various operating temperatures. Analysis of the product gases revealed high quality synthesis gas production without the influence of methane cracking or other undesired side reactions in the experimental tests. Finally, the governing partial differential equations of the reactor modeling were solved by the finite element method. Consequently, the gaseous profiles along the reactor and the breakthrough curves were predicted and compared with the experimental tests.     

Tomography images to analyze the deformation of the cavern in the continuous‐flow mixing of non‐Newtonian fluids

Tomography, an efficient nonintrusive technique, was employed to visualize the flow in continuous‐flow mixing and to measure the cavern volume (V_c) in batch mixing. This study has demonstrated an efficient method for flow visualization in the continuous‐flow mixing of opaque fluids using two‐dimensional (2‐D) and 3‐D tomograms. The main objective of this study was to explore the effects of four inlet‐outlet configurations, fluid rheology (0.5–1.5% xanthan gum concentration), high‐velocity jet (0.317–1.660 m s^?1), and feed flow rate (5.3 × 10^?5?2.36 × 10^?4 m³ s^?1) on the deformation of the cavern. Dynamic tests were also performed to estimate the fully mixed volume (V_{fully mixed}) for the RT, A310, and 3AM impellers in a continuous‐flow mixing system, and it was found that V_{fully mixed} was greater than V_c. Incorporating the findings of this study into the design criteria will minimize the extent of nonideal flows in the continuous‐flow mixing of complex fluids and eventually improve the quality of end‐products. © 2013 American Institute of Chemical Engineers AIChE J, 60: 315–331, 2014     

Mathematical modeling of polyethylene terephthalate pyrolysis in a spouted bed

A model has been developed for pyrolysis of polyethylene terephthalate (PET) in a spouted bed reactor based on the conservation equations for heat, mass, and momentum transports. A spouted bed has been constructed and the kinetic parameters have been obtained within the temperature range of 723–833 K, using two particle size ranges, (0.1–1.0) × 10^?3 and (1.0–3.0) × 10^?3 m. The model' predictions for the radial distributions of temperature and concentration confirm the excellent mixing of particles. Thus, spouted beds are appropriate equipments for performing kinetic studies of PET pyrolysis. The inlet gas temperature and the mass of PET highly affect PET conversion. The amount of inert particles has a negligible effect on the conversion and it can be reduced as far as a stable spouting is preserved. The gas flow suffices to eliminate the external heat and mass‐transfer limitations. It can be reduced to the minimum value to decrease the energy consumption. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1900–1911, 2015     

A new ionic liquids‐based monolithic column for determination of caffeine and theophylline

The present study has concentrated on finding a new stationary phase in liquid chromatography. To improve the selectivity of monolithic column, a new ionic liquids–based (ILs‐based) monolithic column (150 × 4.6 mm i.d.) is synthesized. Characteristic and evaluation of monolithic column are investigated by field emission‐scanning electron microscopy (FE‐SEM) and determination of caffeine and theophylline in high performance liquid chromatography (HPLC). FE‐SEM images show that this monolithic column has a porosity structure. At the condition of mobile phase was 0.06 mol L^?1 Na₂HPO₄ (pH 9.0) and flow rate was 0.7 mL min^?1, a good linear relationship was demonstrated when the concentrations of caffeine and theophylline were in the range of 0.1–60.0 μg mL^?1. These two compounds can obtain better resolution on the ILs‐based monolithic column than non‐ILs monolithic column, and the recoveries ranged from 97.40% to 108.00% and the interday and intraday relative standard deviations were less than 5%. The HPLC method, developed in this study, was proved to be acceptable for drugs assay, and this ILs‐based monolithic column as the stationary phase was a potential tool for future HPLC separation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Performance of silicon‐carbide foams as supports for Pd‐based methane combustion catalysts

BACKGROUND: Cellular foam materials are a new type of catalyst support that provides improved mass and heat transport characteristics and similar pressure drops to other well‐established structured supports such as monoliths. RESULTS: A Pd‐based catalyst has been prepared using a moderate surface area (25 m² g^?1) β‐SiC foam support without further washcoating. The stability of this catalyst has been tested for methane combustion at lean conditions, showing a small decrease of activity during the first 10 h followed by stable performance. Characterization of fresh and aged catalyst shows no significant changes. The influence of the most important reaction conditions, such as reactor loading (0.25–1 g), temperature (300–550 °C) and inlet methane concentration (833 and 1724 ppm), was studied in a fixed‐bed reactor. The results were fitted to three kinetic models: Mars‐van Krevelen; Langmuir‐Hinselwood; power‐law kinetics. CONCLUSIONS: The Pd/β‐SiC foam catalyst, prepared without the previous addition of a washcoating has been demonstrated to be stable for the combustion of methane‐air lean mixtures. A Mars‐van Krevelen kinetic model provides the best fit to the results obtained. Copyright © 2011 Society of Chemical Industry     

Residence time distribution in a single‐phase rotor–stator spinning disk reactor

A reactor model for the single‐phase rotor–stator spinning disk reactor based on residence time distribution measurements is described. For the experimental validation of the model, the axial clearance between the rotor and both stators is varied from 1.0 × 10^?3 to 3.0 × 10^?3 m, the rotational disk speed is varied from 50 to 2000 RPM, and the volumetric flow rate is varied from 7.5 × 10^?6 to 22.5 × 10^?6 m³ s^?1. Tracer injection experiments show that the residence time distribution can be described by a plug flow model in combination with 2–3 ideally stirred tanks‐in‐series. The resulting reactor model is explained with the effect of turbulence, the formation of Von Kármán and Bödewadt boundary layers, and the effect of the volumetric flow rate. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2686–2693, 2013     

A robust mixed‐conducting multichannel hollow fiber membrane reactor

To accelerate the commercial application of mixed‐conducting membrane reactor for catalytic reaction processes, a robust mixed‐conducting multichannel hollow fiber (MCMHF) membrane reactor was constructed and characterized in this work. The MCMHF membrane based on reduction‐tolerant and CO₂‐stable SrFe_0.8Nb_0.2O_3‐δ (SFN) oxide not only possesses a good mechanical strength but also has a high oxygen permeation flux under air/He gradient, which is about four times that of SFN disk membrane. When partial oxidation of methane (POM) was performed in the MCMHF membrane reactor, excellent reaction performance (oxygen flux of 19.2 mL min^?1 cm^?2, hydrogen production rate of 54.7 mL min^?1 cm^?2, methane conversion of 94.6% and the CO selectivity of 99%) was achieved at 1173 K. And also, the MCMHF membrane reactor for POM reaction was operated stably for 120 h without obvious degradation of reaction performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2592–2599, 2015     

Stable equilibrium shift of methane steam reforming in membrane reactors with hydrogen‐selective silica membranes

Equilibrium shifts of methane steam reforming in membrane reactors consisting of either tetramethoxysilane‐derived amorphous hydrogen‐selective silica membrane and rhodium catalysts, or hexamethyldisiloxane‐derived membrane and nickel catalysts is experimentally demonstrated. The hexamethyldisiloxane‐derived silica membrane showed stable permeance as high as 8 × 10^?8 mol m^?2 s^?1 Pa^?1 of H₂ after exposure to 76 kPa of vapor pressure at 773 K for 60 h, which was a much better performance than that from the tetramethoxysilane‐derived silica membrane. Furthermore, the better silica membrane also maintained selectivity of H₂/N₂ as high as 10³ under the above hydrothermal conditions. The degree of the equilibrium shifts under various feedrate and pressure conditions coincided with the order of H₂ permeance. In addition, the equilibrium shift of methane steam reforming was stable for 30 h with an S/C ratio of 2.5 at 773 K using a membrane reactor integrated with hexamethyldisiloxane‐derived membrane and nickel catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Estimation of mid‐distillates production rate in a low temperature Fischer–Tropsch process

BACKGROUND: The Fischer–Tropsch process is the most important path for converting natural gas to high quality liquid hydrocarbons. Low temperature Fischer–Tropsch synthesis in slurry bubble column reactors with cobalt‐based catalysts is used for mid‐distillates production. RESULTS: In this work the slurry bubble column reactor was simulated by applying the two‐bubble class mathematical model. In addition, the effect of operating parameters on synthesis gas conversion was studied. The distribution of products was also predicted from the simulation framework. CONCLUSIONS: The effect of synthesis gas inlet velocity on mid‐distillates production rate was studied in the present work. A maximum production rate for mid‐distillates of about 23 kg s^?1 was predicted from the simulation program. Copyright © 2011 Society of Chemical Industry     

Microwave assisted flow synthesis: Coupling of electromagnetic and hydrodynamic phenomena

This article describes the results of a modeling study performed to understand the microwave heating process in continuous‐flow reactors. It demonstrates the influence of liquid velocity profiles on temperature and microwave energy dissipation in a microwave integrated milli reactor‐heat exchanger. Horizontal cocurrent flow of a strong microwave absorbing reaction mixture (ethanol + acetic acid, molar ratio 5:1) and a microwave transparent coolant (toluene) was established in a Teflon supported quartz tube (i.d.: 3 × 10^?3 m and o.d.: 4 × 10^?3 m) and shell (i.d.: 7 × 10^?3 m and o.d.: 9 × 10^?3 m), respectively. Modeling showed that the temperature rise of the highly microwave absorbing reaction mixture was up to four times higher in the almost stagnant liquid at the reactor walls than in the bulk liquid. The coolant flow was ineffective in controlling the outlet reaction mixture temperature. However, at high flow rates it limits the overheating of the stagnant liquid film of the reaction mixture at the reactor walls. It was also found that the stagnant layer around a fiber optic temperature probe, when inserted from the direction of the flow, resulted in much higher temperatures than the bulk liquid. This was not the case when the probe was inserted from the opposite direction. The experimental validations of these modeling results proved that the temperature profiles depend more on the reaction mixture velocity profiles than on the microwave energy dissipation/electric field intensity. Thus, in flow synthesis, particularly where a focused microwave field is applied over a small tubular flow reactor, it is very important to understand the large (direct/indirect) influence of reactor internals on the microwave heating process. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3824–3832, 2014     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

ABSTRACT

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10–20% of solids was dried at different inlet air temperatures (120–160°C), air flow rate of 0.19 kg dry air s^?1 and different feed rates (1.4 ? 4.2 × 10^?4 kg dry solids s^?1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

Dynamic modeling and simulations of the behavior of a fixed‐bed reactor‐exchanger used for CO2 methanation

A multidimensional heterogeneous and dynamic model of a fixed‐bed heat exchanger reactor used for CO₂ methanation has been developed in this work that is based on mass, energy and momentum balances in the gas phase and mass and energy balances for the catalyst phase. The dynamic behavior of this reactor is simulated for transient variations in inlet gas temperature, cooling temperature, gas inlet flow rate, and outlet pressure. Simulation results showed that wrong‐way behaviors can occur for any abrupt temperature changes. Conversely, temperature ramp changes enable to attenuate and even fade the wrong‐way behavior. Traveling hot spots appear only when the change of an operating condition shifts the reactor from an ignited steady state to a non‐ignited one. Inlet gas flow rate variations reveal overshoots and undershoots of the reactor maximum temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 468–480, 2018     

What is the leanest stream to sustain a nonadiabatic loop reactor: Analysis and methane combustion experiments

While previous studies experimentally demonstrated that loop reactor (LR) can be sustained with a lean feed (using ethylene combustion) and have analyzed the single‐reaction adiabatic case, this work analyzes the effects of heat loss and of reactor size to determine the leanest stream (expressed in terms of adiabatic temperature rise ΔT_lim) that will sustain the operation. For an adiabatic infinitely long reactor ΔT_lim→0 while for a finite reactor ΔT_lim scales as (1 + Pe/4)^?1 where Pe = Luρc_pf/k, and heat loss increases this limit by (β/Pe)^1/2. Thus, a good design of a LR will aim to decrease conductivity (k) and radial heat‐transfer coefficient (β) while increasing throughput (u) and reactor length. This article is also the first experimental demonstration of auto‐thermal operation in a LR for catalytic abatement of low‐concentration of methane, showing the leanest stream to be of 8000 ppm vs. 33,000 ppm in a once‐through reactor. Experimental combustion results of methane and of ethylene are compared with model predictions. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2030–2042, 2017     

A novel porous‐dense dual‐layer composite membrane reactor with long‐term stability

A porous‐dense dual‐layer composite membrane reactor was proposed. The dual‐layer composite membrane composed of dense 0.5 wt % Nb₂O₅‐doped SrCo_0.8Fe_0.2O_3‐δ (SCFNb) layer and porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3‐δ (BSFM) layer was prepared. The stability of SCFNb membrane reactor was improved significantly by the porous‐dense dual‐layer design philosophy. The porous BSFM surface‐coating layer can effectively reduce the corrosion of the reducing atmosphere to the membrane, whereas the dense SCFNb layer permeated oxygen effectively. Compared with single‐layer dense SCFNb membrane reactor, no degradation of performance was observed in the dual‐layer membrane reactor under partial oxidation of methane during continuously operating for 1500 h at 850°C. At 900°C, oxygen flux of 18.6 mL (STP: Standard Temperature and Pressure) cm^?2 min^?1, hydrogen production of 53.67 mL (STP) cm^?2 min^?1, CH₄ conversion of 99.34% and CO selectivity of about 94% were achieved. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4355–4363, 2013     

Elimination of chlorobenzene vapors from air in a compost‐based biofilter

In this work, the removal of monochlorobenzene (CB) vapors from air was studied, for the first time, in a non‐inoculated, laboratory‐scale, aerobic biofilter. The influence of three parameters on the bioprocess has been evaluated: the rate of nitrogen supplied to the bed, the inlet concentration of CB, and the flow rate. The CB inlet concentration was varied between 0.3 and 3.2 g m^?3, at a constant flow rate of 1.0 m³ h^?1. Removal rates of greater than 90% were achieved for CB inlet concentrations of up to 1.2 g m^?3. Then the flow rate was varied from 0.5 to 3.0 m³ h^?1 with a constant inlet concentration (1.2 g m^?3). Maximum elimination capacities (70 g m^?3 h^?1) were reached for contact times of greater than 60 s. The study of varying flow rates also permitted evaluation of a first order macrokinetic constant (1.1 × 10^?2 s^?1) for the CB biodegradation. Finally, the optimum nitrogen input value was found to lie between 0.3 and 0.4 g N h^?1 and gave rise to elimination capacities as high as 70 g m^?3 h^?1 for an inlet load of near 80 g m^?3 h^?1. Copyright © 2003 Society of Chemical Industry     

Ammonia decomposition in catalytic membrane reactors: Simulation and experimental studies

Catalytic decomposition of NH₃ with H₂‐selective microporous silica membranes for CO_x‐free hydrogen production was studied theoretically and experimentally. The simulation study shows that NH₃ conversion, H₂ yield and H₂ purity increase with the Damköhler number (Da), and their improvement is affected by the effect of H₂ extraction as well as NH₃ and N₂ permeation through the membranes. The experimental study of NH₃ decomposition was carried out in a bimodal catalytic membrane reactor (BCMR), consisting of a bimodal catalytic support and a H₂‐selective silica layer. Catalytic membranes showed H₂ permeances of 6.2–9.8 × 10^?7 mol m^?2 s^?1 Pa^?1, with H₂/NH₃ and H₂/N₂ permeance ratios of 110–200 and 200–700, respectively, at 773 K. The effect of operating conditions on membrane reactor performance with respect to NH₃ conversion, H₂ yield and H₂ purity was investigated, and the results were in agreement with those calculated by the proposed simulation model. © 2012 American Institute of Chemical Engineers AIChE J, 59: 168–179, 2013     

Chemical‐looping combustion process: Kinetics and mathematical modeling

Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO₂ and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600–800°C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900°C in both a fixed bed microreactor (WHSV = 2‐4 g CH₄/h/g oxygen carrier) and a fluid bed reactor (WHSV = 0.014‐0.14 g CH₄/h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO₂ and H₂O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H₂ yields increase, whereas the CO₂ and H₂O concentrations decrease. The kinetics parameter of the gas–solids reactions (reduction of NiO with CH₄, H₂, and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Microchannel Autothermal Reforming of Methane to Synthesis Gas

Autothermal reforming of methane to synthesis gas (CO and H₂) is studied in a microchannel reactor comprised of Pt- and Rh-based catalysts that are coated on opposite walls of the channel. The effects of operating parameters and microchannel catalyst configuration on methane conversion and CO selectivity are analyzed. The parameters considered are the residence time of the reactants (12.9–25.7 ms), reaction temperature (500–650 °C), molar steam-to-carbon (S/C = 0–3.0) and oxygen-to-carbon (O₂/C = 0.47–0.63) ratios at the inlet. Doubling the residence time leads to ca. 10 % increase in methane conversion, but has only a 4 % contribution to the CO selectivity. Higher O₂/C ratios improve extent of methane oxidation, but reduce selectivity due to CO₂ production. When the temperature is raised from 500 to 650 °C, conversion increases from 12.8 to 46.6 % and selectivity increases from 20.1 to 35.7 %. S/C ratio has the greatest effect on the outlet H₂/CO ratio, which is found to vary between 0.93 and 2.68, via the water–gas shift reaction. Comparison of the present catalyst configuration with the use of bimetallic Pt–Rh coating in the microchannel under identical conditions shows that the latter can improve conversion by 20 % and CO selectivity by 33 %.     

Digestion of pre‐treated food waste in a hybrid anaerobic solid–liquid (HASL) system

The hybrid anaerobic solid–liquid (HASL) system was developed to be used in industrial‐scale operations to minimize the amount of food waste for disposal in Singapore. Thermal pre‐treatment of food waste at 70 °C for 2 h (experiment E1) or at 150 °C for 1 h (experiment E2) facilitated the hydrolytic and acidogenic processes in the acidogenic reactor and methanogenesis in the methanogenic reactor in the HASL system. The highest dissolved chemical oxygen demands in the effluents from the acidogenic reactors were 17 575, 19 980 and 24 235 mg dm^?3 in the control with food waste without thermal pre‐treatment and experiments E1 and E2, respectively. The maximum concentrations of methanogens in the methanogenic reactor were 2.3 × 10⁷, 3.8 × 10⁷, 4.3 × 10⁷ cells cm^?3 for the control and experiments E1 and E2, respectively. However, the performances of the methanogenic phase in terms of specific activity of methanogens did not differ significantly for the control and experiments E1 and E2. Use of thermally pre‐treated food waste halved the time to produce the same quantity of methane in comparison with anaerobic digestion of fresh food waste. The fluorescent measurements of co‐enzyme F₄₂₀ and oligonucleotide probe Arc915 specifically bound (hybridized) with 16S rRNA were used for monitoring of methanogens during anaerobic digestion of food waste. There was a linear correlation between these parameters and the concentration of methanogens in the effluent from the methanogenic reactor. Copyright © 2005 Society of Chemical Industry