Modeling, Simulation and Bifurcation Analysis of a Mutating Autocatalytic Reaction

In this paper, we present a conceptual model for autocatalytic reactions in which the autocatalyst undergoes a mutation process in a continuous stirred tank reactor. Three cases with different mutation coefficient (a) have been considered. The analysis of these cases shows the importance of this parameter and the qualitative and quantitative differences in the resulting bifurcation diagrams. Generally speaking, selectivity towards main product increases with decreasing substrate conversion. Co-existence of a mushroom and an isola has been determined for one of the cases. The isola portion is a low main product yield solution and is to be avoided. Keywords: Autocatalytic reactions, mutation, bifurcation, selectivit

On mutating autocatalytic reactions in a CSTR. I: Multiplicity of steady states

A conceptual model describing a mutating autocatalytic reaction in a continuous stirred tank reactor is analyzed. The mutant is assumed to compete with the original autocatalyst. The phenomenon of multiplicity of steady states is determined through the application of singularity theory. A mutant-containing feed and a mutant-free feed cases were considered. Eleven regions for the first case and at least 25 regions for the second case of qualitatively different bifurcation behavior were determined using only conditions for isola and hystersis variety. More subregions were identified when applying the double limit variety conditions. The maximum number of steady states which was found for the first case was five whereas the second case showed regions of seven steady states. The yield distribution of the main product and the mutant was briefly discussed for some cases.

Modeling, Simulation and Bifurcation Analysis of a Mutating Autocatalytic Reaction

In this paper, we present a conceptual model for autocatalytic reactions in which the autocatalyst undergoes a mutation process in a continuous stirred tank reactor. Three cases with different mutation coefficient (a) have been considered. The analysis of these cases shows the importance of this parameter and the qualitative and quantitative differences in the resulting bifurcation diagrams. Generally speaking, selectivity towards main product increases with decreasing substrate conversion. Co-existence of a mushroom and an isola has been determined for one of the cases. The isola portion is a low main product yield solution and is to be avoided. Keywords: Autocatalytic reactions, mutation, bifurcation, selectivit

Simulation and Optimization of Industrial FCC Units Using a 4-Lump Kinetic Model

Most of the previous work on the simulation and the bifurcation behavior of industrial FCC units involved a 3-lump kinetic model with coke and light hydrocarbon gases contributing one of the lumps with the ratio between them computed empirically from industrial data. In this study a 4-lump kinetic model is incorporated. This permits the calculation of the rate of coke formation thus decreasing the degree of empiricism in the model. The data from six different industrial units is used in the simulation. It was found that the model results are in good agreement with the corresponding plant data. The model predicts that the units are operated at the statically stable high temperature steady state whereas the use of the 3-lump kinetic model in previous work predicted that the units operate at the middle unstable steady state. This shows the importance of the structure of the kinetic model used for the determination of the stability characteristics of these important industrial units. The model is used to find the optimum operating conditions and the optimum performance is compared with the industrial performance

Simulation and optimization of industrial FCC units using a 4-lump kinetic model

Most of the previous work on the simulation and the bifurcation behavior of industrial FCC units involved a 3-lump kinetic model with coke and light hydrocarbon gases contributing one of the lumps with the ratio between them computed empirically ITom industrial data. In this study a 4-lump kinetic model is incorporated. This permits the calculation of the rate of coke formation thus decreasing the degree of empiricism in the model. The data ITom six different industrial units is used in the simulation. It was found that the model results are in good agreement with the corresponding plant data. The model predicts that the units are operated at the statically stable high temperature steady state whereas the use ofthe 3-lump kinetic model in previous work predicted that the units operate at the middle unstable steady state. This shows the importance of the structure of the kinetic model used for the determination of the stability characteristics of these important industrial units. The model is used to find the optimum operating conditions and the optimum performance is compared with the industrial performance

Improved regulatory control of industrial gas phase ethylene polymerization reactors

Chemical Engineering Department, King Saud University.This paper investigates the application of two techniques to improve the PI control performance when implemented to stabilize the operation of gas phase polyethylene reactors around optimal operating point which is open-loop unstable. The first technique deals with improving the performance of SISO control loop through employing on-line adaptive tuning strategy. The purpose of the tuning strategy is to force the closed-loop response to fit inside desired time-domain specification envelope by automatically adapting the PI setting values. The second technique deals with improving the MIMO control performance by simple selection of proper control structure design. The objective of the proposed control design is to avoid the procedure of screening various control structure candidates. Moreover, since there are more inputs than outputs, split-range configuration is used to utilize all available manipulated variables. This configuration allow for tight control. Simulation results demonstrated the success of the proposed methods to provide better regulatory control performance when compared to what have been reported in earlier work

Selection of optimum chromium oxide-based catalysts for propane oxidehydrogenation

Propane oxidative dehydrogenation has been studied at 350-500°C, 1.0 bar and feed flow rate of 75 cm3/min over several supported chromium oxide-based catalysts. Effects of various chromium loadings, different supports, catalyst precursors and reaction conditions were investigated in an attempt to select an optimum catalyst for the reaction. Chromium oxides of different loadings ranging from 0.1 to 20 wt.% on γ-Al2O3 were tested. At 450°C, 10 wt.% loading exhibited propane conversion of 19%. γ-Al2O3 gave the best performance when MgO, TiO2, SiO2 and γ-Al2O3 were tested as supports. As a precursor, Cr(NO3)3•9H2O exhibited the best results compared with K2Cr2O7, CaCr2O7, Na2Cr2O7, Cr2SO4•12H2O and CrO3. Effects of reaction temperatures and feed compositions were also evaluated on a 10 wt.% Cr-Al-O catalyst. The maximum selectivity to propene obtained was 61% while the yield was 18%. The 10 wt.% Cr-Al-O catalyst was characterized by X-ray diffraction patterns (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) which confirmed the presence of both Cr3+ and Cr6+ in the calcined catalyst and, also, the predominance of Cr3+ in the spent catalyst..

Oxidehydrogenation of propane over Mn-P-O catalyst: Effects of oxygen partial pressure

Manganese phosphate catalyst was prepared and tested for the catalytic oxidative dehydrogenation of natural gas components such as propane to propylene at 1 atm and 450°-550°C. In the temperature range, the propane conversion changed from 4.1 to 40.7%, the selectivity to propylene showed insignificant change at 41%. The products obtained were propylene, ethylene, methane, CO2, and CO. Selectivity to propylene could be improved by employing low or moderate oxygen partial pressure. .King Fahd University of Petroleum and Minerals, KFUPM, Japan Petroleum Industry, JP

Oxidative dehydrogenation of propane over supported chromium-molybdenum oxides catalysts

Catalytic oxidative dehydrogenation of propane to propylene was studied on alumina-supported chromium-molybdenum oxides catalysts - 10 wt% Cr xMo(1-x)/γ-Al2O3 (where x=0-1). The catalysts are active for the reaction. Increase in the amount of molybdenum in the catalysts decreases the reducibility and changes the nature of the lattice oxygen in the catalyst as indicated by TPR and XPS data. The catalysts with lower reducibilities exhibits corresponding increase in the propylene selectivities. Alkali metals (Li, K, Cs)-doped 10 wt% Cr 0.8Mo0.2 (alkali/CrMo weight ratio of 0-0.175), shows maxima in both propane degrees of conversion and propylene yields in the ratio ranges explored. One of the catalysts (Cs/CrMo=0.125) exhibits propane conversion of 15.1% and selectivity to propylene of 64.5% at 420 °C. This is among the most promising catalysts reported for oxidative dehydrogenation of propane.

Oxidative dehydrogenation of propane over supported chromium-molybdenum oxides catalysts

Catalytic oxidative dehydrogenation of propane to propylene was studied on alumina-supported chromium-molybdenum oxides catalysts - 10 wt% Cr xMo(1-x)/γ-Al2O3 (where x=0-1). The catalysts are active for the reaction. Increase in the amount of molybdenum in the catalysts decreases the reducibility and changes the nature of the lattice oxygen in the catalyst as indicated by TPR and XPS data. The catalysts with lower reducibilities exhibits corresponding increase in the propylene selectivities. Alkali metals (Li, K, Cs)-doped 10 wt% Cr 0.8Mo0.2 (alkali/CrMo weight ratio of 0-0.175), shows maxima in both propane degrees of conversion and propylene yields in the ratio ranges explored. One of the catalysts (Cs/CrMo=0.125) exhibits propane conversion of 15.1% and selectivity to propylene of 64.5% at 420 °C. This is among the most promising catalysts reported for oxidative dehydrogenation of propane.