Julià Sempere

Emulsion polymerization of vinyl acetate: safe optimization of a hazardous complex process.

Fast and exothermic discontinuous emulsion polymerization processes are particularly difficult to optimize from both safety and productivity point of view because of the occurrence of side undesired reactions (e.g. chain transfer to monomer, backbiting, propagation of tertiary radicals, termination by disproportion, etc.) and the hazards of boiling phenomena and stable foam formation under atmospheric pressure. Moreover, the relevant number of loading, heating and cooling steps, required before starting the monomer addition (that is, the desired reaction), makes a strict product quality reproducibility very difficult to obtain. Under these operating conditions, it is necessary to employ a suitable combined theoretical and experimental procedure able to detect the optimum process dosing time at both the laboratory and the industrial scale. In this work, it is shown how to use the topological criterion theory together with proper adiabatic calorimeter and RC1 experimental data to safely optimize the synthesis of polyvinyl acetate through the radical emulsion polymerization of vinyl acetate by the means of an indirectly cooled isoperibolic semibatch reactor.

Detection and characterisation of water alcohol hydrates by on-line FTIR using multivariate data analysis

Abstract In the current work, several chemometric functions based on the principal component analysis (PCA) are studied in order to determine the number of absorbing species in an infrared data matrix acquired during a mixing process. Applying a target factor analysis (TFA), the concentration profiles of the chemical substances are obtained without the need for a calibration of the spectrometer. Different considerations concerning the objective function of the optimisation process have been tried. The chemical systems tested for such techniques are alcohol–water mixtures. The study is completed with calorimetric data that confirm the hypothesis of the presence of a hydrate suggested by the information from the spectra. The mathematically extracted concentration–time profile results are finally verified with traditional methods of quantitative analysis. This particular case will also confirm the validity of the experimental design, according to the rank compatibility test (RCT) for semibatch reactors proposed by our group.

Sensitivity analysis of the 2-methylpyridine N-oxidation kinetic model

A sensitivity analysis of a previously developed global kinetic model, of the N-oxidation of 2-methylpyridine, involving seven kinetic and equilibrium constants, has been performed. It has been identified how individual constants influence the power evolution profile. The conditions, which ensure measurements sensitive to all constants, are outlined. A readily applicable, simple methodology has been developed to achieve accurate evaluation of the kinetic constants involved.

Maximum temperature attainable by runaway of synthesis reaction in semibatch processes

Abstract A new scenario for the calculation of the adiabatic temperature increase for semi-batch processes is presented. In the safety assessment of chemical reactions it is necessary to determine the value of the Maximum Temperature attainable by runaway of the Synthesis Reaction for the worst case. We demonstrate that the batch scenario is not always the most dangerous way to carry out a reaction. In addition, an improvement in the calculation of the MTSR is presented in order to obtain more realistic scenarios.

Solving the seveso II prediction problem of substance generation during loss of control by Al techniques.

Abstract The European Directive 96/82/EC forces industries to know exactly what substances may be generated during loss of control of an industrial chemical process. The study must be as accurate as possible, as the design of the safety measures that will be ready in case a real loss of control occurs depends on these results. Chemical reactions under out of control conditions, follow defined but difficult to know rules, specially at high temperatures showing high molecular complexity. It seems that the application of artificial intelligence techniques will help to predict which substances are produced given an initial chemical scenario. In this paper the k -nearest algorithm and its application to this problem will be studied. A database has been developed to manage reactive information independently from the algorithm or technique of AI to be applied. The most important information of the database are relations between substances present on the initial reactive scenario and the ones detected after reaction under out of control conditions occurred. Chemical substances contained in the database have been analysed by decomposing them into Benson’s Groups, which is thought to be the most adequate level of detail to preserve chemical information while establishing relations between non-identical substances. The Shepard’s modification of k -nearest neighbor algorithm has been used for the Boolean prediction of formation of a certain substance given a reactive scenario. Results show an accuracy above 95%.

A comparison of calorimetric measurements by using different reaction calorimeters

For a great number of European safety groups, reaction calorimetry is the key technique for analysis of the main reaction in the risk assessment of chemical processes. A comparison of calorimetric studies of model reactions, the N-oxidation of two substituted pyridines with hydrogen peroxide, made by several European groups, can open the door to standardization of the methodologies used. However, the intrinsic experimental complexity of the model reactions, which included dosing at high temperature, a multiphase system and evaporation, and the different evaluation criteria, produced a considerable dispersion between the results obtained by the various groups.

Check Cards for Runaway (CCR): An Operative Tool for the Risk Assessment of Highly Reactive Systems Performed in Small-and Medium-sized Enterprises

The Check Cards for Runaway is a simple tool to evaluate quickly the safety level of a chemical plant liable to suffer a runaway reaction. It is obtained by defining all the necessary safety considerations required to design a safe process and predicting systematically all the runaway hazards. Moreover, this tool can be used even when only limited resources are available, as in the case of many small and medium-sized enterprises. The tool resulting from this project is very simple and requires only standard chemical knowledge.

Numerical simulation of fixed bed for CO 2 capture in a fossil fuel emission points by Pressure Swing Adsorption system

Abstract In many previous works, zeolites are the commercially available adsorbents mostly studied for CO 2 capture, with attention to zeolite 5A and zeolite 13X. In this study, we have modelled the adsorption equilibrium and simulated the breakthrough curves for the adsorption of carbon dioxide on Pressure Swing Adsorption (PSA) processes for CO 2 capture from a mixture with 15% CO 2 –85% N 2 (simulating dry post-combustion flue gases of a coal-fired power station) using the experimental characterization of zeolite 5A and zeolite 13X published in a recent bibliography. A model based on the Linear Driving Force (LDF) approximation for the mass balance, including energy balance and momentum, was used for the simulation of CO 2 capture in pressure swing adsorption systems. The models were described by partial differential equations (PDEs) coupled with Algebraic Equations (PDAEs) including conservation equations, models for equation of state, equilibrium, thermodynamic, and transport properties. This work was implemented and solved with Matlab™ software. We present numerical results that adequately reproduce the experimental data for the studied temperatures, suggesting that the assumptions on which the model is based on could be valid for this system and can be used to design a PSA cycle to separate CO 2 /N 2 mixtures.

Nonparametric Kinetic Methods

As all classic methods for kinetic analysis of data from thermal analysis experiments, the nonparametric kinetics method, NPK, assumes that the general expression for the reaction rate of a simple reaction is