Showing papers on "Chemical reactor published in 1992"

Optimal Grade Transitions in a Gas Phase Polyethylene Reactor

Abstract: Using gas-phase technology many grades of polyethylene can be produced in a single reactor. For a series of three polyethylene products, model-based dynamic optimization is used to determine optimal grade changeover policies. Optimal manipulated variable profiles are determined for hydrogen and butene feed rates, reactor temperature setpoint, gas bleed flow, catalyst feed rate, and bed level setpoint. It is shown that large transitions in melt index are hampered by slow hydrogen dynamics, and that the time required for such a transition can be reduced by manipulating the temperature setpoint and the bleed stream flow. Reduction of the bed level and catalyst feed rates during changeovers can significantly reduce the quantity of off-specification polymer produced. It is demonstrated that melt index and density are not sufficient to characterize the properties of polymer produced during grade transitions, and that the shape of the cumulative copolymer composition distribution is very sensitive to the grade changeover policy used. Optimal transition policies should not be implemented without feedback control. Disturbances and model mismatch can result in product property trajectories which deviate significantly from the nominal optimal trajectory.

Propagation failure in arrays of coupled bistable chemical reactors

Abstract: We consider a one-dimensional array of coupled stirred tank reactors. Each reactor operates with the bistable chlorite-iodide reaction. The reaction admits two stable steady sites (A and B). At time zero, all reactors are at steady state A except the first reactor which is at steady state B. Provided the coupling (exchange rate) between each reactor is sufficiently large, a propagating wave joining A to B is initiated. We determine the speed of the front and show that it fails to propagate if the exchange rate is below a nonzero value. In addition, we investigate the time history of the front and identify three distinct stages. First, we note a boundary layer regime corresponding to the end of the front and the approach to the final uniform steady state. We explain all three stages by analyzing a simple model

Targeting strategies for the synthesis and energy integration of nonisothermal reactor networks

Abstract: A constructive approach for the synthesis of nonisothermal reactor network is presented based on a targeting methodology. We determine a bound or target on a performance index for a given nonisothermal reacting system. The targeting model is based on mixing between different reacting environments and is formulated as a dynamic optimization problem, where the temperature, the feed distribution function, and an exit flow distribution function are the control profiles. In addition, the solution procedure is based on successive generation of reactor extensions that improve the target. Each reactor extension corresponds to the solution of a small nonlinear program; this procedure is repeated until no extensions that improve the objective function are generated. This technique ensures that only the simplest required model is solved. Having developed a general reactor targeting scheme, we also propose a new framework for integrating this scheme with an energy targeting approach. By discretizing the temperature profiles and allowing for heating or cooling profiles within the reactor, a combined representation for reactor and energy targeting is obtained. This model turns out to be a nondifferentiable nonlinear program, and novel smoothing techniques are presented for solution. Results on a typical process flowsheet optimization problem indicate significant increases in profit can be achieved by considering the reaction and energy synthesis schemes simultaneously

Chemical reactor technology for environmentally safe reactors and products

Abstract: Preface H.I. de Lasa. I: Fuels of the Future and Changing Fuel Needs. How should Environmentally Benign Gasolines be Formulated? A. Ravella. Oxygenates as Gasoline Blending Components G.L. Harting, H. Shannon. Engineering of Fluidized Catalytic Crackers D. King. Scientific Aspects of Novel Catalysts for FCC A.W. Peters, W-C Cheng, T.G. Roberie. Novel Techniques for FCC Catalyst Selection and Kinetic Modelling H.I. de Lasa, D.W. Kraemer. Mixing Patterns in a Novel Riser Simulator A. Pekediz, D.W. Kramer, J. Chabot, H.I. de Lasa. Chemical Aspects of Clean Fuels Production P.H. Schipper, A.V. Sapre, Q.N. Le. II: Alternative Sources. Evaluation of Direct Methane Conversion Processes J.C.W. Kuo. Engineering Aspects of the Conversion of Natural Gas into Middle Distillates M.M.G. Senden, S.T. Sie, M.F.M. Post, J. Ansorge. Steam Reforming Opportunities and Limits of the Technology J. Rostrup-Nielsen, I. Dybkjaer, L.J. Christiansen. Oxidative Coupling of Methane for the Utilization of Natural Gas M. Baerns. Dysprosium Oxide for Oxidative Coupling of Methane O. Altin, I. Onal, T. Dogammau, J.B. Butt. Ultrapyrolysis of Heavy Oils: Reaction Kinetics and Reactor Technology F. Berruti, L.A. Behie. Bubble Column Reactors: Some Recent Developments M.P. Dudukovic, N. Devanathan. Strategies for Low Emissions from Circulating Fluidized Bed Boilers F. Berruti, R. Wong. Kinetic Modeling of Complex Processes. Thermal Cracking and Catalytic Hydrocracking G.F. Froment. Engineering of Hydrotreating Processes P. Trambouze. III: Emission Control, Chemical Reactor Safety and Engineering. Thermal Sensitivity and Runaway in Chemical Reacting Systems G. Cao, M.Morbidelli, A. Varma. Kinetics of Capture of Sulfur Dioxide and Applications to Flue Gas Desulfurization G. Dogu, T. Dogu. Removal of SO2 with Lime Slurry in a Spray Dryer G. Dogu, G. Olmez, T. Dogu. Engineering Aspects of Recirculating Fluidised Bed Combustion C. Brereton, J.R. Grace, C.J. Lim, J. Zhu. Application of a Monte Carlo Method to the Solid Flow Pattern Visualization in CFB B.P.A. Grandjean, J. Chaouki. Modelling Catalytic Monoliths for Automobile Emission Control J.P. Leclerc, D. Schweich. Photocatalytic Processes for Destruction of Organic Water Contaminants E. Pelizzetti, C. Minero, E. Pramauro. Heterogeneous Photocatalytic Degradation of the Cationic Surfactants Cetyldimethylbenzylammonium Chloride and Cetylpyridinium Chloride I. Poulios, A. Avranas. Progress in the Development of Chlorofluorcarbon (CFC) Alternatives J.J. Lerou, L.E. Manzer. Index.

Chemical reactors for gas-liquid systems

Abstract: Classification of gas-liquid reactors mass transfer with chemical or biochemical reaction flow of phases in gas-liquid reactors decisive design characteristics of gas-liquid reactors criteria for reactor type selection hydrodynamics and mass transfer in three-phase systems dynamic behaviour of gas-liquid reactors calculation of gas-liquid reactors.

Experimental investigation of an atmospheric-open cyclone solar reactor for solid-gas thermochemical reactions

Abstract: This paper reports that a solar receiver-reactor has been designed to conduct solid-gas chemical reactions, using concentrated solar radiation as the energy source of high-temperature process heat. It consists of a conical cyclone gas-particle separator that has been modified to let concentrated solar energy enter the cavity through a windowless (atmospheric-open) aperture. It combines the advantages of cavity receivers and volumetric reactors, and permits continuous mode of operation. A small-scale prototype reactor to conduct the thermal decomposition of calcium carbonate at 1300 K was experimentally investigated in a solar furnace. Its thermal performance was evaluated. The mean energy absorption efficiency, based on the optically measured power incident on the receiver aperture, was 43 percent. Reaction products showed high degree of calcination.

Synthesis of gram quantities of C60 by plasma discharge in a modified round-bottomed flask. Key parameters for yield optimization and purification

Abstract: Described is the fabrication of a plasma discharge reactor constructed from a 1-L round-bottomed flask that allows for the preparation of gram quantities of C[sub 60] in an 8-h period. The modified reactor design (1) is inexpensive, (2) required almost no machining, (3) has highthru-put, (4) affords high yields of fullerenes, (5) allows one to have near-continuous feed of graphite rods, and (6) permits control over four major reaction parameters important for the clean formation of fullerenes. The four major reaction parameters necessary to control for the high yield of fullerenes are the absolute pressure, the rate of helium gas flow through the reactor, the current level of the arc as determined by the setting on the arc welding unit, and the arc gap maintained by monitoring the current on a clip-on digital AC current meter. Since the apparatus described can allow for easy adjustment of all four major reaction parameters, this design could also be used to study the changes in fulleroid content based on parameter modification. Also detailed is the efficacy of a procedure for the purification of the crude fullerene mixtures using activated charcoal as a chromatographic stationary phase. 2 refs., 3 figs.

Turing patterns in a simple gel reactor

Abstract: We introduce a very simple open two-dimensional gel reactor for studying chemical patterns that arise in reaction-diffusion systems. The reactor consists of a thin disk-shaped layer of polyvinyl alcohol gel with one face in direct contact with a well-stirred flow reactor containing reactants of the chlorite-iodide-malonic acid system; the other face of the gel is in contact with a piece of transparent plexiglass. We have used this reactor to study the transition from a uniform state to a hexagonal pattern; for other concentrations, striped patterns were observed. The wavelength of these structures is greater than the thickness of the gel layer, which indicates that the patterns are two-dimensional (a single layer). This reactor provides a promising new tool for studying chemical patterns since the diffusion time of reactants into and out of the gel can be made small compared to the total residence time in the stirred flow reactor. This feature facilitates the comparison between theory and experiment since the chemical concentrations leading to pattern formation are close to those in the stirred flow reactor and hence can be directly measured. Pattern formation in reaction-diffusi on systems has attracted the interest of experimentalists and theorists alike during the last few decades. Until recently experimental work centered on spatio-temporal patterns in closed systems. Typically, a thin layer of reactive solution was placed in a petri dish and patterns such as spiral waves and target patterns were observed. However, since these appeared in a closed system, they were only short-lived transients. Several open chemical reactor designs have been introduced in order to allow the study of chemical patterns at conditions maintained far from equilibrium. Most of these designs employ an inert gel reaction medium in which convection is suppressed; such a reactor has been called a CFUR (continuous flow unstirred reactor), in analogy with the acronym CSTR used for continuous flow stirred tank reactors. In 1987 Noszticzius et al. [1] used a CFUR with an annular gel that was fed at the inner and outer rims to study traveling waves in the Belousov-Zhaboti nskii (BZ) reaction. Another CFUR design consists of a thin gel layer that is sandwiched between two thin porous glass plates [2]. The face of each porous glass plate opposite to the gel is in contact with a stirred

Catalytic chemical reaction assembly

Abstract: A catalytic chemical reactor of a sandwiched configuration is described. The reactor has at least one plate with a major surface and two minor ends opposite one another across the major surface. A plurality of reaction chambers are present in the plate, parallel to one another and the major surface, extending from one of the minor ends to the other. The reactor additionally comprises at least one heating panel adjacent and parallel to the flat plate. The plates may be configured in modular pairs with a heating panel in between each pair. The reactor is particularly adapted to produce organic chemicals, such as acrolein, in significant, but moderate quantities. Additionally, the reactor is of such a size that it is readily portable. Unusually, the reactor plates, or at least their inner surfaces, may be made from materials such as aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof.

Isobutane dehydrogenation kinetics determination in a modified berty gradientless reactor

Abstract: A standard Berty gradientless reactor, designed to operate at temperatures up to 350 [degrees]C and pressures between 3 and 35 bar, has been successfully modified for operation up top 600[degrees]C and at atmospheric pressure without appreciable interparticle transport resistance. The reactor is used to establish the kinetics of the catalytic dehydrogenation of isobutane at 530-570 [degrees]C and 1 bar, using a concentration-control system to decouple the effects of concentration and activity on reaction rate. In this paper single-site LHHW model is found to provide a good fit to initial rate data. Catalyst deactivation data are also presented for dehydrogenation and coking reactions.

NOx Sensitivities for Gas Turbine Engines Operated on Lean-Premixed Combustion and Conventional Diffusion Flames

Abstract: NOx exhaust emissions for gas turbine engines with lean-premixed combustors are examined as a function of combustor pressure (P), mean residence time (τ), fuel-air equivalence ratio (φ), and inlet mixture temperature (Ti). The fuel is methane. The study is accomplished through chemical reactor modeling of the combustor, using CH4 oxidation and NOx kinetic mechanisms currently available. The NOx is formed by the Zeldovich, prompt, and nitrous oxide mechanisms.The combustor is assumed to have a uniform φ, and is modeled using two reactors in series. The first reactor is a well-stirred reactor (WSR) operating at incipient extinction. This simulates the initiation and stabilization of the combustion process. The second reactor is a plug-flow reactor (PFR), which simulates the continuation of the combustion process, and permits it to approach completion. For comparison, two variations of this baseline model are also considered. In the first variation, the combustor is modeled by extending the WSR until it fills the whole combustor, thereby eliminating the PFR. In the second variation, the WSR is eliminated, and the combustor is treated as a PFR with recycle. These two variations do not change the NOx values significantly from the results obtained using the baseline model.The pressure sensitivity of the NOx is examined. This is found to be minimum, and essentially nil, when the conditions are P = 1 to 10atm, Ti = 600K, and φ = 0.6. However, when one or more of these parameters increases above the values listed, the NOx dependence on the pressure approaches P raised to a power of 0.4-to-0.6.The source of the NOx is also examined. For the WSR operating at incipient extinction, the NOx is contributed mainly by the prompt and nitrous oxide mechanisms, with the prompt contribution increasing as φ increases. However, for the combustor as a whole, the nitrous oxide mechanism predominates over the prompt mechanism, and for φ of 0.5-to-0.6, competes strongly with the Zeldovich mechanism. For φ greater than 0.6-to-0.7, the Zeldovich mechanism is the predominant source of the NOx for the combustor as a whole.Verification of the model is based on the comparison of its output to results published recently for a methane-fired, porous-plate burner operated with variable P, φ, and Ti. The model shows agreement to these laboratory results within a factor two, with almost exact agreement occurring for the leanest and coolest cases considered. Additionally, comparison of the model to jet-stirred reactor NOx data is shown. Good agreement between the model results and the data is obtained for most of the jet-stirred reactor operating range. However, the NOx predicted by the model exhibits a stronger sensitivity on the combustion temperature than indicated by the jet-stirred reactor data.Although the emphasis of the paper is on lean-premixed combustors, NOx modeling for conventional diffusion-flame combustors is presented in order to provide a complete discussion of NOx for gas turbine engines.Copyright © 1992 by ASME

Method and apparatus for chemically altering fluids in continuous flow

Abstract: The present invention relates to a continuous flow fluid reactor for chemically altering fluids. The reactor operates on standard frequency (50 to 60 Hz) electricity. The fluid reactor contains particles that are energized by the electricity to form a corona throughout the volume of the reactor and subsequently a non-equilibrium plasma that interacts with the fluid. Particles may form a fixed bed or a fluid bed. Electricity may be provided through electrodes or through an inductive coil. Fluids include gases containing exhaust products and organic fuels requiring oxidation.

Evaluation of NOx Mechanisms for Lean, Premixed Combustion

Abstract: In this paper the formation of the oxides of nitrogen, NO{sub x}, is examined through experiments and chemical kinetic modeling for lean, premixed combustion in a laboratory, atmospheric pressure, jet-stirred reactor. The experimental conditions are as follows: fuel-air equivalence ratio ({phi}) of 0.6, temperatures of 1460 to 1730 K, and reactor loadings of 20 to 150 kg/sec-m{sup 3}-atm{sup 2}, which correspond to reactor mean residence times of 11.4 to 1.8 milliseconds. Two fuels are examined: ethylene because of its importance as a combustion intermediate, and methane, because of its importance as a component of natural gas. Besides the premixed operation, the reactor also is operated nonpremixed. For both modes, the NO{sub x} increases with decreasing loading, from abut 3-4 ppmv at the highest loading to about 11-21 ppmv at the lowest loading for the ethylene fuel. This increase in NO{sub x} occurs because a hot spot develops on centerline when the reactor is lightly loaded. Also for the lowest loading, the nonpremixed mode produces about twice as much NO{sub x} as the premixed mode, i.e., about 21 versus 11 ppmv. At the other reactor loadings, however, because of the intense mixing, the NO{sub x} levels are only slightly elevated formore » the nonpremixed mode compared to the premixed mode. Upon switching to methane fuel, the NO{sub x} decreases by about 25 percent.« less

Method of and system for producing electrical power

Abstract: A method and system for converting the chemical energy of methane to electrical energy. Methane is thermally decomposed to hydrogen and carbon in a decomposing unit at a temperature not less than about 1200° K. and at a pressure at least slightly above atmospheric pressure. Carbon and substantially pure oxygen and a cesium or potassium seed material is transmitted to a combustor which is maintained at a pressure of at least about 50 atmospheres to combust the carbon and oxygen and provide an ionized plasma having a temperature not less than about 2800° K. The ionized plasma is accelerated to a velocity not less than about 1000 m/sec and transported through an MHD generator having a magnetic field in the range of from about 4 to about 6 Tesla to generate dc power. The ionized plasma is de-accelerated and passed from the MHD generator in heat exchange relationship with the methane to heat same for decomposition and or reaction, and thereafter any cesium or potassium seed material is recovered and transported to the combustor, and the dc power from the MHD generator is converted to ac power.

Experimental studies of a ceramic membrane reactor for the steam/methane reaction at moderate temperatures (400-700°C)

Abstract: The Paper shows that the conversion of the steam/methane reforming reaction can be enhanced by the use of a ceramic membrane reactor. The improvements in methane conversion are in the range of 10 to 15% higher than the conversion corresponding to simple equilibrium

Improved vortex reactor system

Abstract: An improved vortex reactor system for affecting fast pyrolysis of biomass and Refuse Derived Fuel (RDF) feed materials comprising: a vortex reactor having its axis vertically disposed in relation to a jet of a horizontally disposed steam ejector that impels feed materials from a feeder and solids from a recycle loop along with a motive gas into a top part of said reactor.

A New Microwave Reactor Suitable for Organic Synthesis and Kinetics Studies.1

Abstract: A microwave unit and reaction vessel for chemical synthesis or kinetics studies is described. The Teflon reaction vessel could be operated at temperatures up to 200°C and pressures up to 10 atmospheres. It was possible to stir and directly monitor the temperature and pressure in the microwave environment. The system was demonstrated by preparing isopropyl 2,4,6-trimethylbenzoate.

Equipment Simulation of Selective Tungsten Deposition

Abstract: This paper presents the numerical modeling of a cold wall reactor for selective tungsten chemical vapor deposition. In a two dimensional simulation the mass and heat transfer equations were solved considering the five chemical species H{sub 2}, WF{sub 6}, HF, WF{sub x}, and SiF{sub y}. Detailed models for multicomponent diffusion and for the autocatalytic tungsten nucleation process were implemented. Model results are in good agreement with experimental findings. The simulations are used to study the impact of reactor design on selectivity.

A radiant flow reactor for high‐temperature reactivity studies of pulverized solids

Abstract: Our radiant two‐phase flow reactor presents several new possibilities for high‐temperature reactivity studies. Most importantly, the thermal histories of the suspension and entrainment gas can be independently regulated over wide ranges. At low suspension loadings, outlet temperatures can differ by hundreds of degrees and gas temperatures are low enough to inhibit hydrocarbon cracking chemistry, so primary products are quenched as soon as they are expelled. With coal suspensions, tars were generated with the highest H/C ratio and lowest proton aromaticity ever reported. Alternatively, particles and gas can be heated at similar rates to promote secondary chemistry by increasing particle loading. Simply by regulating the furnace temperature, arbitrary extents of conversion of coal tar into soot were observed for fixed total mass loss. Under both circumstances heat fluxes are comparable to those in large furnaces, so relevant heating rates and reaction times are accessible. Suspensions remain optically thin even for the highest loadings of technological interest because they are only 1 cm wide. Consequently, the macroscopic behavior remains firmly connected to single‐particle phenomena. Mass and elemental closures are rarely breached by more than 5% in individual runs, so interpretations are not subject to inordinate scatter in the data. The reactor is also well suited for combustion studies, as demonstrated by extents of carbon and nitrogen burnout from 50% to 100% for various gas‐stream oxygen levels.

Stirring sense in a chemical reactor

Abstract: The effect of the stirring rate and stirring sense of the bifurcation points of the oscillatory domain of the minimal bromate system in a stirred flow reactor is studied experimentallay and computationally using nonpremixed feedstreams.

Selective oxidation of n-butane to maleic anhydride; 4. Recycle reactor studies

Abstract: This paper reports on the selective oxidation of n-butane to aleic anhydride which has been modeled using recycle reactor data. Two different types of models have been tested based on the concept that V[sup 5+] is the selective site and V[sup 4+] is the nonselective site and vice versa. Recycle reactor data support the model which assumes V[sup 5+] as the selective site as the selective site and V[sup 4+] as the nonselective site. The model has been used to predict the performance of an integral reactor and tested with experimental integral reactor data.

A New Spectroscopic Technique for in situ Chemical Reaction Monitoring Using Mid-Range Infrared Optical Fibers:

Abstract: A new versatile spectroscopic technique for chemical reaction monitoring using mid-range infrared optical fibers has recently been developed. Chalcogenide glass optical fibers were used to direct infrared radiation from an FT-IR spectrometer through ZnSe Cylindrical Internal Reflectance (CIR) crystals embedded within laboratory scale reactors. The utility of this technique for studying chemical systems was demonstrated by monitoring various stoichiometric reactions at ambient conditions. A laboratory-scale glass reactor fabricated with the capability to mount a CIR crystal was used as the reaction vessel. The ability of this system to monitor high-pressure and/or high-temperature chemical reactions was also demonstrated by studying the cobalt catalyzed hydroformylation of olefins. A stainless steel CIR reactor, slightly modified to allow for connections with optical fibers, was used for experiments ranging from 50 to 90°C and under 750 to 800 psi synthesis gas (H2/CO mixture). In all cases sufficient signal strength at the detector and adequate penetration into the bulk reaction medium was achieved, resulting in infrared spectra of high quality and resolution. Spectral scans of the reaction in progress allowed the accurate determination of the concentration of reactants and products as a function of time.

Fluid catalytic cracking hits 50 year mark on the run

Abstract: As we approach the fiftieth anniversary of the start-up of the first commercial fluid catalytic cracker, it seems appropriate that we examine some of the background and details of that auspicious event and how it came about. Not only was this the birth of what rapidly became the world's major refining process, but also the beginning of fluidization technology that reached outside the oil industry. This paper reports on the advantages of a fluidized bed, with or without circulation, over fixed-bed, gas/solid contacting that were quickly recognized within the chemical industry. And practical applications, particularly as a chemical reactor, were soon developed in diverse areas other than catalytic cracking. By 1956, over 500 U.S. patent applications for fluidized bed processes had been granted. By 1967, fluidized reactors were in commercial use for naphtha hydroforming, fluid coking, coal carbonization, coal coking, chemicals production iron ore reduction, roasting of sulfide ores, limestone calcination, uranium processing, and other processes. Fluidization continues today as a major component of chemical engineering technology, with a steady stream of improved understanding of this complex operation, new developments, and commercial operations.

Fixed bed chemical reactor

Abstract: A catalyst support for use in promoting oxidation reactions composed of metal particles is described. The metal particles are selected from the group of aluminum, tantalum, titanium, tungsten, niobium and mixtures thereof, where aluminum is preferred. The metal particles may have a rough diameter of from 0.02 to 10 mm. The particles may be in the form of spheres, shavings, irregular granules and the like. When the catalyst support is to be used in a tubular reactor, the ratio of the diameter of the reactor to the diameter of the catalyst may range from 1.1 to 200:1. The metal catalyst supports are inert in the reaction and give excellent uniformity in heat distribution throughout the catalyst bed. In oxidation reactions, the catalyst support may bear a metal oxide catalyst to give good results. The particulate catalyst support bearing the active catalyst may also be compressed to inhibit channelling and to help provide higher yield to the desired product. The use of perforated plates within the catalyst bed also aids heat distribution, prevention of channelling and product yield improvement.

The thermal decomposition of methane in a tubular reactor

Abstract: The reaction rate of methane decomposition using a tubular reactor having a 1 inch inside diameter with an 8 foot long heated zone was investigated in the temperature range of 700 to 900 C with pressures ranging from 28.2 to 56.1 atm. Representing the rate by a conventional model, {minus}dC{sub CH4}/dt= k1 C{sub CH4} {minus}k2 C{sub H2}{sup 2}, the rate constant k1 for methane decomposition was determined. The activation energy, 31.3 kcal/mol, calculated by an Arrhenius Plot was lower than for previously published results for methane decomposition. This result indicates that submicron particles found in the reactor adhere to the inside of the reactor and these submicron high surface area carbon particles tend to catalyze the methane decomposition. The rate constant has been found to be approximately constant at 900 C with pressure range cited above. The rate of methane decomposition increases with methane partial pressure in first-order. The rate of the methane decomposition is favored by higher temperatures and pressures while the thermochemical equilibrium of methane decomposition is favored by lower pressures. 8 refs., 7 figs., 2 tabs.