Tubular Reactor System Research Articles

Passivity-based control of the phthalic anhydride fixed-bed reactor

The control of tubular fixed-bed reactors with highly exothermic reactions is approached from a passivity-based control perspective. The proposed controller solves dynamic tracking of the reactor exit conversion and stabilization of the reactor temperature by exploiting the passivity properties of the process. The model-based control structure proposed in this paper provides a suitable framework for developing the passivity-based control law and the state predictor. The integrated controller is designed and its performance in the face of parameter variation and model uncertainty is tested by numerical simulation. Digital simulation on an industrial phthalic anhydride fixed-bed reactor shows that the proposed control scheme can give satisfactory dynamic tracking ability and disturbance rejection performance, which is robust in the presence of process variation and model uncertainty. This paper provides a basic insight into the characterization and solution of control problems that are particular to tubular fixed-bed reactor systems and constitutes the application of passivity-based control theory to complex chemical processes.

Highly reliable 64-channel sequential and parallel tubular reactor system for high-throughput screening of heterogeneous catalysts

Highly reliable 64-channel sequential and parallel tubular reactor for high-throughput screening of heterogeneous catalysts is constructed with stainless steel. In order to have a uniform flow rate at each channel, 64 capillaries are placed between the outlet of multiport valve and the inlet of each reactor. Flow rate can be controlled within ±1.5%. Flow distribution can be easily adjusted for sequential and parallel mode of operation. The reactor diameter is too big to have a uniform temperature distribution. Hence, the reactor body is separated into three radial zones and controlled independently with nine thermocouples. Temperature accuracy is ±0.5°C at 300°C and ±1°C at 500°C in sequential mode, while it is ±2.5°C in the range of 250–500°C in parallel mode. The temperature, flow rate, reaction sequence, and product analysis are controlled by LABVIEW™ software and monitored simultaneously with displaying a live graph. The accuracy in the conversion is ±2% at the level of 73% conversion when all reactors are loaded with same amount of catalyst. A quaternary catalyst library of 56 samples composed of Pt, Cu, Fe, and Co supported on AlSBA-15 (SBA-15 substituted with Al) are evaluated in the selective catalytic reduction of NO at various temperatures with our system. The most active compositions are rapidly screened at various temperatures.

Tubular Reactor Synthesis of Doped Nanostructured Titanium Dioxide and Its Enhanced Activation by Coronas and Soft X-rays

An aerosol tubular reactor system to synthesize nanostructured vanadium-doped titanium dioxide particles is described. The resultant particle size distributions, crystal phases, and morphology and distribution of dopant are established as a function of the operating conditions. The addition of the dopant promotes sintering and an increase in the primary particle size. Downstream of the furnace, a corona-soft X-ray reactor is used to demonstrate the effectiveness in degradation of toluene. An improvement in the degradation rates is observed when soft X-ray irradiation is used in conjunction with the corona. Addition of the V-dopant enhanced the photodegradation of toluene.

Kinetics of dibenzylether hydrothermolysis in supercritical water

AbstractThe kinetics of dibenzylether (DBE) hydrothermolysis in hot compressed water has been investigated in a continuous tubular reactor system at a pressure from 225 to 362 bar, temperature from 325 to 390°C, and a constant water load of ΘW = 100 molwater/molDBE. Thermal scission of DBE yielded equimolar amounts of benzaldehyde and toluene; the rate constant in supercritical water decreased with water density showing that the volume of activation was positive, as expected for an unimolecular scission reaction. Benzyl alcohol was produced by DBE reversible hydrolysis catalyzed by free protons from water dissociation. Density and dielectric constant of water decreased the rates of hydrolysis and DBE formation, which means that the transition state complex has a positive volume of activation, and a lower dipolar moment than the reactants. As the dielectric constant raises the reaction rates are lowered, but the equilibrium shifts toward the formation of benzyl alcohol, which is more polar than DBE. The low dipole moment of the transition state complex was further supported by the negative effect of the ionic strength on the rate constant for DBE hydrolysis. © 2005 American Institute of Chemical Engineers AIChE J, 51: 971–981, 2005

New approach for kinetic parameters determination for hydrothermal oxidation reaction

The purpose of this study is to test Runge–Kutta algorithm to obtain reliable kinetic parameters for the hydrothermal oxidation of organic compounds. A tubular reactor system was used to carry out the oxidation of several model compounds: acetic acid, methanol and phenol. All experiments were performed in isothermal conditions in a temperature range varying from 250 to 500 °C and at a constant pressure of 25 MPa. Three different methods, namely pseudo-first-order kinetics, multiple linear regression and Runge–Kutta algorithm, were used to determine the kinetic parameters. Results obtained by these different methods were similar, so that Runge–Kutta algorithm was validate for the determination of kinetic parameters. In contrast with the pseudo-first-order kinetics and the multi linear regression, Runge–Kutta algorithm was more convenient for the kinetic parameter determination starting from experiments performed at the laboratory scale or in industrial scale pilot plant facilities.

Chemical Processing in High-Pressure Aqueous Environments. 7. Process Development for Catalytic Gasification of Wet Biomass Feedstocks

Through the use of a metal catalyst, gasification of wet biomass can be accomplished with high levels of carbon conversion to gas at relatively low temperature (350 °C). In a pressurized-water environment (20 MPa), near-total conversion of the organic structure of biomass to gases has been achieved in the presence of a ruthenium metal catalyst. The process is essentially steam reforming, as there is no added oxidizer or reagent other than water. In addition, the gas produced is a medium heating value gas due to the synthesis of high levels of methane, as dictated by thermodynamic equilibrium. While good gas production was demonstrated, biomass trace components caused some processing difficulties in the fixed catalyst bed tubular reactor system used for the catalytic gasification process. Results are described for tests using both bench-scale and scaled-up reactor systems.

Dynamic Comparison of Alternative Tubular Reactor Systems

Direct quantitative comparisons of the dynamic controllability of four alternative tubular reactor systems are given in this paper. An exothermic, irreversible gas-phase reaction, A + B → C, is carried out in a packed-bed tubular reactor in a process that includes reaction, separation, feed preheating, and gas recycle. The four alternative tubular reactor designs are (1) a single-stage adiabatic reactor, (2) multistage adiabatic reactors with interstage cooling, (3) multistage adiabatic reactors with cold-shot cooling, and (4) a single-stage cooled reactor. All of the adiabatic systems are open-loop unstable (exhibit limit-cycle behavior) because of the sensitivity of the first reactor, which propagates thermal waves through the system. The cooled reactor system is open-loop stable for base-case parameters. The single-stage adiabatic reactor and the multistage adiabatic reactor system with intermediate cooling are closed-loop stable. However, the optimal seven-bed multistage adiabatic reactor system with cold-shot cooling is closed-loop unstable because of the severe disturbances generated by manipulating cold-shot flows. If the number of beds is reduced to three, the system is closed-loop stable. The cooled reactor is the most controllable.

Effect of steam on coking in the non-catalytic pyrolysis of naphtha components

Coking has presented difficulties in reactions including pyrolysis and steam has been added to reduce coking. In this study, the effect of steam on coking in the pyrolysis of naphtha components was studied thermody- namically and experimentally for non-catalytic tubular reactor systems. The qualitative relations between these two thermodynamic and experimental studies were established. In both studies coking was reduced as the steam ratio increased. However, experimental studies indicated that the reduction was more effective for smaller values of the ratio, leading to an effective ratio of about 0.5, and that weak coking still occurred for the ratio greater than the thermody- namic zero-coke ratio. C9 0.5-1.5 1-15 0.2-1.0 0C10 0.2-0.5 0.5-0.7

Steady-State Economic Comparison of Alternative Tubular Reactor Systems

This paper presents a comparison of the steady-state economics of alternative tubular reactor systems. These alternative designs use different tubular reactor configurations including single adiabatic, multistage adiabatic with interstage cooling, multistage adiabatic with cold-shot cooling, single cooled, multistage cooled with interstage cooling, and multistage cooled with cold-shot cooling. The design considers the entire plantwide process: reactor(s), heat exchangers, gas recycle compressor, preheat furnace, condenser, and separator. The chemistry is the exothermic, irreversible, solid catalytic, gas-phase reaction A + B → C, which is carried out in a packed-bed tubular reactor. The economic objective function is total annual cost, which includes annual capital cost (reactor, catalyst, compressor, and heat exchangers) and energy cost (compressor work and furnace fuel). Design and optimization procedures are developed for each alternative design. Optimum operating conditions and equipment sizes are determined. The effect of catalyst cost on the steady-state design is considered. The steady-state design results indicate that the single cooled reactor configuration is the best from the standpoint of steady-state economics.

Selective oxidation of propylene to acetone by molecular oxygen over M x/2 H 5− x[PMo 10V 2O 40]/HMS (M=Cu 2+, Co 2+, Ni 2+)

The transition metal salts (Cu 2+, Co 2+ and Ni 2+) of 10-molybdo-2-vanadophosphoric acid (H 5[PMo 10V 2O 40]) were supported on hexagonal mesoporous silica (HMS), and the resultant materials were used as catalysts for the selective oxidation of propylene to acetone by molecular oxygen. CuH 3[PMo 10V 2O 40]/HMS showed a high selectivity for acetone of 84.2% at 17.8% propylene conversion in a tubular fixed-bed reactor system under atmospheric pressure at 423 K. The high yield of acetone over CuH 3[PMo 10V 2O 40]/HMS at 423 K resulted from the proper acidity and oxidation ability of the heteropoly compound, the nature (acid property, redox property, etc.) of the Cu 2+ counter-ion, the high surface area of the HMS support and the proper reaction temperature for the propylene oxidation.

Nonlinear Control of a Reduced-Order Tubular Reactor System

This article deals with the output regulation of distributed reacting systems with a single manipulated variable. Since the coil apparatus for heat removal can be conditionally adopted, the finite difference-based nonlinear model as a class of approximate control systems can be established. Through use of the non-distributed feedback linearization strategy and the successive Lyapunov function design, synthesis of the dynamic feedback controller can ensure asymptotic output regulation. From the practical viewpoint, an extended observer-based control scheme based on the similar Lyapunov-based linearization algorithm is developed. Simulations clearly demonstrate that the proposed control methodologies can achieve good tracking Performance and are robust against the presence of measurement errors and model mismatch.

Difference-based Nonlinear Control Designs of a Reduced-order Tubular Reactor System.

This article deals with output regulation of an exothermic tubular reactor system. Based on model order reduction and a specified coil apparatus for heat removal, a finite difference-based nonlinear model with single manipulated input can be developed. Under the difference-based feedback linearization strategy associated with Lyapunov stability analysis, the developed low-order state/output feedback controllers can induce asymptotic output regulation. Moreover, the output feedback control scheme together with anti-windup compensation can reduce the controller saturation and provide satisfactory control performance. Simulations clearly demonstrate that the proposed control methodologies with a fast coil flow rate condition can recover the desired temperature performance, and that they are also robust against the presence of unstructured modeling errors.

Design of Cooled Tubular Reactor Systems

Tubular reactors in which exothermic reactions take place sometimes are operated adiabatically and sometimes are cooled. Adiabatic operation makes reactor design easier because tube geometry can be selected simply on the basis of pressure drop considerations. Steady-state temperature profiles in adiabatic reactors increase monotonically. The design of cooled tubular reactors, however, involves complex tradeoffs between tube geometry, pressure drop, and heat-transfer area. Temperature profiles typically exhibit a peak at some axial position. This paper considers the impact of these interacting parameters on the optimum steady-state economic design of the entire plantwide process. The system studied has an exothermic, irreversible, gas-phase reaction A + B → C occurring inside the tubes of a packed plug-flow tubular reactor. Steam is generated on the shell side to remove heat. The process consists of a reactor, feed-effluent heat exchanger, furnace, partial condenser, separator, and recycle compressor. Pressure drop through the reactor is important because of compression costs of the gas recycle and is reduced by using large-diameter tubes because of the smaller velocities. Heat removal is also important in cooled reactors and is improved by using small-diameter tubes because of their larger heat-transfer area-to-volume ratio. This paper presents a design methodology for considering all these complex tradeoffs. After specifying a reasonable tube length and fixing the maximum peak temperature, the two design degrees of freedom chosen are tube diameter and reactor pressure drop. The economic objective function is to minimize the total annual cost of the process: the annual capital cost of the reactor, catalyst, compressor, heat exchanger, and furnace; and the operating cost of the compressor and furnace. The method calculates the optimum tube diameter, reactor pressure drop, amount of catalyst, coolant temperature, number of tubes; and recycle flow rate. Results show that optimum designs of systems with small specific reaction rates feature large reactors and large recycle flow rates, which dictate the use of larger tube diameters and smaller pressure drops over the reactor. As specific reaction rates increase, reactor size and recycle flows decrease, which leads to optimum designs with smaller tube diameters and larger reactor pressure drops.

Design and Control of Tubular Reactor Systems with Both Gas and Liquid Recycles

Previous studies of tubular reactor systems have explored flowsheets with either a gas recycle or a liquid recycle. In this paper, we extend this work to consider a flowsheet with two recycle streams: a large gas recycle from a separator drum and a small liquid recycle from a distillation column. Both the steady-state economics and the dynamic controllability of this dual-recycle system are compared with those of single-recycle processes. Three kinetic cases are considered: an irreversible reaction with moderate activation energy, an irreversible reaction with high activation energy, and a reversible reaction. Results demonstrate that the dual-recycle flowsheet is less expensive than the liquid-recycle system for the irreversible reaction case, particularly for the high activation energy where the total annual cost is 50% less. In the reversible reaction case, the liquid-recycle system is less expensive, because of the need for a high-purity recycle. Control structures are developed for all three flowsh...

Synthesis and characterization of nano-scale aluminum nitride produced from vapor phase

Nano-scale AlN particles were synthesized from the vapor phase using ammonia and aluminum chloride vapor as reactants. The apparatus consists of vaporization system, ammonia distributor, tubular synthesis reactor and powder collection system. The aluminum nitride nucleates and grows along the reactor length. The AlN powder produced was collected and chemically and physically characterized. For microstructural and microchemical characterization, X-ray diffractograms taken from the powder have shown the presence of primarily AlN, with traces of Al 2O 3, while the deposit removed from the reactor wall has displayed solely AlN. Van der Waal's forces and the tendency for surface energy minimization cause the particles to hold together and what the SEM, in fact, reveals are small particle aggregates. TEM observations, however, confirm the nano-scale nature of such particles with an average particle size of 30 nm. HREM imaging of individual particles indicates that most of them are single crystals, since lattice fringes run continuously along the entire length of the particle.

The fate of methane in a claus plant reaction furnace

AbstractExperimental kinetic data are reported for key side reactions occurring in the front end [i. e. the reaction furnace (RF) and the waste heat boiler (WHB)] of modified Claus plants used for sulfur recovery from the sour gases evolved in the treatment of natural gas. An extensive experimental study was conducted in a high temperature tubular reactor system for two important homogenous gas‐phase reactions. Firstly, experiments were carried out to study the oxidation of hydrogen sulfide and methane mixtures in the presence of oxygen. Secondly, the reaction between methane and sulfur dioxide was investigated experimentally. These results showed that methane was much less competitive for oxygen than hydrogen sulfide. Hence, in a partially oxidizing environment of a RF, data showed that methane reacted significantly with other major sulfur containing species, as secondary reactions, to form COS and especially CS2. This is highly problematic from an environmental point of view.

Effect of Design and Kinetic Parameters on the Control of Cooled Tubular Reactor Systems

The steady-state design of cooled tubular reactor systems involves tradeoffs between reactor costs and compression costs, which are both affected by kinetic parameters and by tube geometry (diameter, length, and number). Peak temperatures occur in cooled reactors, which makes temperature control more challenging and which might necessitate the use of multiple temperature measurements along the length of the reactor. This paper considers the impact of these parameters on the dynamic controllability of the system. The exothermic, irreversible, gas-phase reaction A + B → C occurs inside the tubes of a packed tubular reactor. Steam is generated on the shell side to remove heat. The process consists of a feed−effluent heat exchanger, furnace, reactor, partial condenser, separator, and recycle compressor. Cases are explored that have different kinetic parameters (specific reaction rates and activation energies), different design parameters (tube diameters and reactant concentrations), and different control structures (number of temperature sensors). A conventional selective control scheme is used that controls the highest of several temperatures along the length of the reactor by manipulating the steam pressure in the reactor shell. Results show that dynamic controllability worsens as specific reaction rates, activation energies, and tube diameters increase and as the number of temperature sensors decreases. Designs with large reactor heat-transfer areas are easily controlled. Tube diameter has a greater impact on controllability than does reactant dilution. Reactant dilution appears to be less effective in cooled tubular reactors than in adiabatic tubular reactors.

The Effect of Ether on the Reaction Rate of MTBE Synthesis

The influence of the product on the kinetics of the MTBE synthesis reaction has been investigated. Experimental reaction rates for the MTBE synthesis reaction in the liquid phase by addition of methanol (MeOH) to isobutene (IB) were determined on the sulfonic macroporous resin Bayer K2631 at 45−90 °C for a wide range of IB, MeOH, and MTBE concentrations and operating in the differential regime in a tubular reactor system. The affinity between the bulk phase and the resin depends on the composition of the reaction medium, and it plays an important role in the catalyst activity. This effect has been implemented into the kinetic equation as a function of the resin and the medium solubility parameters. Experimental data are well described through a LHHW mechanism, the surface reaction being the limiting step. The obtained kinetic equation correctly predicted the additional experimental data obtained in a batch reactor. The apparent activation energy was estimated to be 84.31 ± 1.09 kJ/mol, and the resin solub...

Extensions of the Simultaneous Design of Gas-Phase Adiabatic Tubular Reactor Systems with Gas Recycle

Luyben studied the simultaneous design of a simple gas-phase tubular reactor system with a single feed stream and independent reactor preheating and cooling for a reversible reaction. Reyes and Luyben studied an irreversible reaction system with a reactor feed preheating system (feed-effluent heat exchanger and furnace) but assumed equimolal concentrations of reactants in the recycle gas. A simple separation was assumed in both of these studies. Reyes and Luyben recently explored systems with more realistic separation systems (a distillation column) for gas-phase tubular reactors with liquid recycle and with a dual recycle system. This paper extends this work for two cases: (1) the reversible reaction system is explored with a realistic feed preheating system and with two fresh feed streams, and (2) the irreversible reaction system is studied for nonequimolal reactant concentrations. The exothermic gas-phase reaction A + B ⇔ C occurs in an adiabatic tubular reactor. A gas recycle returns unconverted reactants from the separation section consisting of a simple separator in which product C is removed in the liquid phase and reactants A and B are recycled in the gas phase back to the reactor inlet. Optimum steady-state economic designs are shown to lead to poor dynamic responses. Slight modifications of the plant design lead to a much more easily controlled plant. In the reversible case, the additional furnace heat input leads to a better dynamic performance. In the irreversible case, a higher reactor inlet temperature improves dynamics.

A study on the development of composite membranes for the separation of organic vapors

Composite membranes were prepared by the plasma polymerization of hexamethyldisiloxane (HMDS) monomer, and the membranes were applied for the separation of volatile organic compounds (VOC) from air. A tubular type reactor system with an external coil was provided to initiate and maintain glow discharges. Through the plasma polymerization of HMDS, poly(dimethylsiloxane)-like films were prepared. The FT-IR spectra of the plasma-polymerized films were similar to that of poly(dimethylsiloxane) (PDMS). The ratio of discharge power to monomer flow rate ( W/ F) in plasma polymerization affected the permeability of penetrants. In the plasma-polymerized membranes prepared under low W/ F ratio, the permeability was mainly dependent of the condensability of VOCs and the membrane showed the high permselectivity of organic vapors over nitrogen. As the W/ F ratio increased, molecular size effect became stronger and the selectivities decreased.