S. C. Cardona

Tertiary recycling of polypropylene by catalytic cracking in a semibatch stirred reactor: Use of spent equilibrium FCC commercial catalyst

Abstract Catalytic cracking of polypropylene has been carried out in a semibatch stirred reactor. The influence of the nature of the cracking catalyst and the reaction conditions on conversion and selectivity has been studied. Large pore zeolites as well as amorphous and ordered silica–aluminas have been used as catalysts, in order to better study the influence of pore size (micro and meso), crystallite size and the number and strength of the active acid sites. However, it is shown that from a practical point of view, the use of spent equilibrium catalyst from FCC units can be the most adequate solution.

Kinetic study of the catalytic cracking of polypropylene in a semibatch stirred reactor

A lumped kinetic model including both thermal and catalytic cracking and catalyst decay has been developed for the cracking of polypropylene in a semibatch stirred reactor. Two decay equations in where the catalyst decay is either a function of time on stream or function of coke on catalyst have been tested. The kinetic model fits very well the experimental results and is able to simulate the process in a wide range of operating conditions.

Ozonation of hospital raw wastewaters for cytostatic compounds removal. Kinetic modelling and economic assessment of the process.

The kinetics of the ozone consumption for the pretreatment of hospital wastewater has been analysed in order to determine the reaction rate coefficients between the ozone and the readily oxidisabled organic matter and cytostatic compounds. The wastewater from a medium size hospital was treated with ozone and peroxone methodologies, varying the ozone concentration, the reaction time and the hydrogen peroxide doses. The analysis shows that there are four cytostatic compounds, i.e. irinotecan, ifosfamide, cyclophosphamide and capecitabine, detected in the wastewaters and they are completely removed with reasonably short times after the ozone treatment. Considering the reactor geometry, the gas hydrodynamics, the mass transfer of ozone from gas to liquid and the reaction of all oxidisable compounds of the wastewater it is possible to determine the chemical ozone demand, COzD, of the sample as 256mgO3L(-1) and the kinetic rate coefficient with the dissolved organic matter as 8.4M(-1)s(-1). The kinetic rate coefficient between the ozone and the cyclophosphamide is in the order of 34.7M(-1)s(-1) and higher for the other cytostatics. The direct economic cost of the treatment was evaluated considering this reaction kinetics and it is below 0.3€/m(3) under given circumstances.

Practical identifiability analysis in dynamic gas-liquid reactors Optimal experimental design for mass-transfer parameters determination

Abstract A dynamic gas–liquid transfer model without chemical reaction based on the unsteady film theory is analysed in order to confirm the possible identifiable parameters of the model from a given set of experimental data. The structural identifiability analysis of the model using the macroscopic concentrations at the gas and liquid phase shows that the identifiable parameters of the model are the gas hold-up, ɛ , the Henrys constant, H , the reciprocal of the diffusion time, D / δ 2 , and the volumetric mass-transfer coefficient, k L a . A procedure for the optimal experimental design is proposed based on the analysis of the Fisher information matrix of the model. The analysis concludes that the measure of the dynamics of the concentration just in the liquid phase leads to important systematic errors in the determination of k L a . The importance of the concentration measurement simultaneously in the gas and the liquid phase for the parameter estimation is demonstrated and discussed.

Determination and Validation of Henry’s Constant for Ozone in Phosphate Buffers Using Different Analytical Methodologies

Different procedures for measuring the concentration of ozone in aqueous buffered solutions have been reviewed for the determination of Henry’s constant at different temperatures and pH. Iodometry, indigo trisulfonate and iron (II) chemical methods were compared with the direct UV absorbance measurement of ozone at 258 nm. From these data a new value for the molar extinction coefficient of ozone is proposed as 3840 ± 109 M−1 cm−1. After the verification of the ozone analysis methods, the solubility of ozone in phosphate buffer medium was studied with in-situ absorbance direct measurements in a device with high gas-liquid transference rate, minimizing the gas desorption process on sample manipulation. The decomposition of ozone was not detected at the experimental conditions tested and, consequently, the observed solubility of ozone is constant, with the pH ranging from 2 to 7.6. The solubility of ozone was measured between 5 and 35 °C, resulting in a dimensionless solubility ratio of HB0 = 1.797 exp[0.0277·t(°C)].

Mathematical Model for Monitoring Gas-Liquid Reactors by Means of Continuous Flow Analysis

A Global Mathematical Model, which predicts the observed signal in a detector when Continuous Flow Analysis (CFA) is used for the monitoring of ozone gas-liquid reactors, has been proposed. This model combines the description of mass transfer and kinetic processes in the reactor (based on Surface Renewal and Film Layer theories) with dispersion in the manifold of the CFA. To validate the Global Model, the reaction between ozone and a dye (blue indigo trisulfonate) in a semi-batch gas-liquid reactor monitored by CFA is investigated.

Unstationary film model for the determination of absolute gas-liquid kinetic rate constants: ozonation of Acid Red 27, Acid Orange 7, and Acid Blue 129

A method for the determination of absolute kinetic rate constants is proposed using an unstationary film model. This methodology avoids the experimental determination of parameters like the enhancement factor or the Hatta number which are usually model-dependent. The mathematical model is general for gas-liquid systems with irreversible second order reactions. An optimization procedure based on artificial neural networks is used to estimate the initial guess of the parameters and the subsequent application of Gauss-Newton algorithm for the final nonlinear parameter estimation. The model is tested with the ozonation reaction of Acid Red 27, Acid Orange 7 and Acid Blue 129. The second-order kinetic rate constants for the direct reaction with O3 are 1615 ± 93, 609 ± 83, and 49 ± 2 M−1s−1, respectively.

Dynamic optimization of a gas-liquid reactor

A dynamic gas-liquid transfer model without chemical reaction based on unsteady film theory is considered. In this case, the mathematical model presented for gas-liquid mass-transfer processes is based on mass balances of the transferred substance in both phases. The identificability property of this model is studied in order to confirm the possible identifiable parameters of the model from a given set of experimental data. For that, a different modeled of the system is given. A procedure for the identification is proposed. On the other hand, the aim of this work is to solve the quadratic optimal control problem, using an explicit representation of the model. The problem includes some results on controllability, observability and stability criteria and the relation between these properties and the parameters of the model. Using the optimal control problem we study the stability of the system and show how the choice of the weighting matrices can improve the behavior of the system but with an increase of the energy control cost.

Ozonation Kinetics of Acid Red 27 Azo Dye: A Novel Methodology Based on Artificial Neural Networks for the Determination of Dynamic Kinetic Constants in Bubble Column Reactors

A procedure for the determination of initial parameter values for quadratically convergent optimization methods is proposed using artificial neural networks coupled with a non-stationary gas-liquid reaction model. The evaluation of the regression and the mean squared error coefficients of the neural network during its training process allow the parameter sensitivity analysis of the gas-liquid model. This analysis examines how many and which parameters of the model will be available depending on the observable information of the mathematical model. Numerical simulations show the relevance of the initial values and the non-linearity of the objective function. The methodology has been applied to the study of the reaction of the azo-dye Acid Red 27 with ozone in acid media. The rate constant is in the order of (1.6 ± 0.1) 103 M−1 s−1 under the experimental conditions.

On identifiability for chemical systems from measurable variables

The dynamics of the composition of chemical species in reacting systems can be characterized by a set of autonomous differential equations derived from mass conservation principles and some elementary hypothesis related to chemical reactivity. These sets of ordinary differential equations (ODEs) are basically non-linear, their complexity grows as much increases the number of substances present in the reacting media and can be characterized by a set of phenomenological constants (kinetic rate constants) which contains all the relevant information about the physical system. The determination of these kinetic constants is critical for the design or control of chemical systems from a technological point of view but the non-linear nature of the ODEs implies that there are hidden correlations between the parameters which maybe can be revealed with a identifiability analysis.