Safe optimization of 2-octanol oxidation and vinyl acetate emulsion polymerization

In this work the possibility to develop reliable optimization procedures, particularly suitable for full plant exothermic semibatch processes operated in the isoperibolic temperature control mode, has been investigated. It has been found that a general optimization procedure could be developed by using a particular curve, called topological curve, resulting from the numerical solution of the ordinary differential equation system describing the process dynamics. Such a curve exhibits a series of inversion points that represent, physically, transitions between different system thermal behaviour regions. The optimization procedure based on the analysis of the topological curve uses the QFS inversion as a boundary beyond which the optimum operating conditions can be searched accounting for reacting mixture thermal stability and desired productivity constraints. Experimental temperature vs. time data spring from laboratory studies of two different potentially runaway systems (the nitric acid oxidation of 2-octanol to 2-octanone and the free radical emulsion homopolymerization of vinyl acetate) have been modelled to demonstrate that the topological criterion for the QFS detection is independent of all the thermodynamic and process variables control equations used to describe the system. Such a result suggests that this approach could be safely used to optimize even processes operated at the full plant scale

Criteri topologici per l'ottimizzazione sicura di reazioni potenzialmente fuggitive

In this work, optimization procedures, particurarly suitable for potentially runaway reactions carried out in indirectly cooled semibatch reactors operated in isoperibolic temperature control mode, have been developed. Such optimization procedures based on a particular criterion, referred to as "topological", in order tio select a set of operating conditions which is able of ensuring both process thermochemical stability and high productivity and selectivity with respect the desired product. This topological approach has been validated both experimentally and theoretically by studing kinetic schemes characterized by different complexity degrees. As an example, the relevant case study of the free radical emulsion polymerization of vinyl acetate has been analyzed and reported

Thermochemical stability: A comparison between experimental and predicted data

The first step to be performed during the development of a new industrial process should be the assessment of all hazards associated to the involved compounds. Particularly, the knowledge of all substances thermochemical parameters is a primary feature for such a hazard evaluation. CHETAH (CHEmical Thermodynamic And Hazard evaluation) is a prediction software suitable for calculating potential hazards of chemicals, mixtures or a single reaction that, using only the structure of the involved molecules and Benson's group contribution method, is able to calculate heats of formation, entropies, Gibbs free energies and reaction enthalpies. Because of its ability to predict the potential hazards of a material or mixture, CHETAH is part of the so-called \u201cdesktop methods\u201d for early stage chemical safety analysis. In this work, CHETAH software has been used to compile a complete risk database reporting heats of decomposition and Energy Release Potential (ERP) for 342 common use chemicals. These compounds have been gathered into classes depending on their functional groups and similarities in their thermal behavior. Calculated decomposition enthalpies for each of the compounds have also been compared with experimental data obtained with either thermoanalytic or calorimetric techniques (Differential Scanning Calorimeter \u2013 DSC \u2013 and Accelerating Rate Calorimeter \u2013 ARC)

Experimental design of topological curves to safely optimize highly exothermic complex reacting systems

Strongly exothermic solution homopolymerizations are a class of chain reactions particularly di\ufb03cult to be optimized from both a safety and a productivity viewpoint. Particularly, lots of side undesired reactions (e.g., backbiting, propagation of tertiary radicals, chain transfer to monomer or solvent, etc.), which a\ufb00ect the selectivity with respect to the desired product, and relevant mass and heat transfer problems, due to the increasing system viscosity, take place during such syntheses. Under these unavoidable operating conditions, it is di\ufb03cult to employ theoretical procedures that are able to safely optimize the analyzed process, because the development of a reliable mathematical model is often not a\ufb00ordable or too time-consuming. In this work, it is shown that the topological criterion theory and its related optimization procedure can be used to optimize experimentally (through a dedicated set of isoperibolic reaction calorimetry tests) a complex reacting system even if its reaction scheme and all information about the kinetics are not available

On the divergence criterion for runaway detection: Application to complex controlled systems

It is well-known that, for certain values of the operative parameters influencing the dynamic behavior of a chemical reactor, a phenomenon known as thermal runaway (that is, a loss of the reactor temperature control) may arise. Such a situation can be really dangerous because above a certain threshold temperature value unwanted side reactions or, worse, decompositions of the reacting mixture may be triggered evolving high amounts of flammable or toxic gases that can cause reactor pressurization and, eventually, its explosion. For this reason, since the beginning of the previous century a number of studies concerning the prediction of the so called runaway boundaries has been carried out. In this work, a modified version of the divergence criterion for runaway detection, originally developed by Zald\uedvar and co-workers, is presented. Such a modified divergence criterion is capable of treating whatever type of complex controlled reacting system (taking into account not only temperature control but also dosing strategies) and its reliability has been demonstrated for isoperibolic semibatch reactors using literature experimental data concerning the nitration of 4-Chlorobenzotrifluoride in mixed acids and the nitric acid oxidation of 2-octanol to 2-octanone and further carboxylic acids

Short-cut methods for the characterization of waste biomass feedstocks for energy production

A method based on thermal analysis techniques was used for the estimation of waste biomass feedstock composition with respect to the main macrocomponents. The method is based on the analysis of thermogravimetric (TG) data obtained for the biomass sample and for the macrocomponents in reference pyrolysis conditions. The method is particularly suitable to quantify the biomass content of a waste feedstock for energy production and to provide information on biomass composition. The coupling of thermogravimetry with Fourier Tranform Infrared (FTIR) analysis of evolved gases was used to provide further data for a more detailed characterization of waste biomass feedstocks, yielding specific data on volatile products released in experimental conditions typical of conventional pyrolysis processes