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Sodium hypochlorite poses explosive hazards associated with its complex reactive chemistry. The production process of sodium hypochlorite consists of a first block where the chlorine, caustic soda and hydrogen are produced in an electrolytic cell from brine and a second block where chlorination of caustic soda to form hypochlorite is carried out. This process is characterized by several hazards such as chlorine gas toxicity, explosive hazards due to the presence of hydrogen and chlorine and corrosive hazards. Loss of control of such substances has the potential to cause high-consequence low-probability events. Thus, specific safety measures have to be designed to mitigate risk. In the present work, the risk assessment of the first block of the process is performed, focusing on hydrogen risks. To this end, HAZOP analysis was performed to identify the top events. For each top event, based on properly developed fault trees, the frequency analysis was performed. Eventually, the consequence analysis was carried out by the simulation of phenomena leading to dispersion and consequent ignition of the cloud as function of the distance from the source. Simulations were performed by means of the software PHAST.

Anaerobic digestion (AD) is a promising and consolidated biological process used to treat organic solid wastes and produce biogas, recovering both energy and rich in nitrogen material (digestate) while reducing the amount of waste to be disposed. Despite the experience gained over the last years, still represent critical points for AD the efficiency as well as the reliability f the process and the safety of the biogas storage and utilization. Biogas is a mixture of different organic and inorganic gases. A lack of knowledge of proper biogas management could result into accidents due to the formation of explosive mixture both inside and outside the buildings. These relevant aspects are discussed and for each of them is provided a detailed description and a critical analysis of the modern systems used to reduce the uncertainty on the expected results and also to increase the safety of biogas production, purification and utilization.

The 2-nitrobenzaldehyde is an important intermediate currently obtained through the nitration of benzaldehyde by means of mixed acid. Unfortunately this process is characterized by poor yield in the target product coupled to considerable risks in its management due to the intrinsic hazard of the nitrations reactions. In the present investigation the production of the target mononitroderivative is studied by a chemical and kinetic point of view. The present investigations aims to clarify the behavior of the system, mixed acid and benzaldehyde, at varying the operative conditions (temperature and chemical composition of the nitrating system) to increase the yield in the product of interest and, at the same time, to reduce the risks connected to the process. © Copyright 2014, AIDIC Servizi S.r.l.

A new catalytic system, CuII (or Cu(0))/Cl-/TiO2/formic acid/UVssr , is proposed to generate hydrogen by photoreforming of formic acid. The influence of TiO2 loads and formic acid concentrations is investigated. Starting from zero-valent copper, the results indicate that, in the presence of TiO2 and formic acid, no gains in terms of hydrogen formed are observed with respect to the adoption of the subsystem Cu(0)/Cl-/UVssr. On the other hand, starting from cupric ions, a surplus of hydrogen production is recorded with respect to that obtained from this subsystem.

Poitiers (France)

Adiabatic Calorimetry is currently used to achieve a thermokinetic characterization of reactive systems in which exothermic reactions occur. The adoption of simplified assumptions makes possible the estimation of important properties of the investigated system such as kinetic parameters or the heat of reaction. Sometimes this approach can lead to major inaccuracies when safer process conditions need to be established. The use of the data recorded under adiabatic conditions does not allow to correctly asses the concentration dependence of the rate of reactions. In the present work it is demonstrated that the use of the sole adiabatic calorimetry for the decomposition of Cumene Hydroperoxide in Cumene may lead to wrong reaction kinetics resulting into erroneous safety evaluations. An approach based on combined different calorimetric techniques may result for the case study into the development of a global kinetic autocatalytic model which satisfactory simulates the system behaviour.

The problem of the formation of unwanted substances that can occur during a thermal decomposition process is studied from a toxicological point of view. Starting from available data on the concentration profile of intermediates and product recorded during the thermal decomposition of a commonly used pesticide (Ethyl Paration), the use of the program ECOSAR shows that some species are more relevant from a toxicological standpoint than the initial compound. Since it is practically impossible to completely characterize the decomposition products of all the potential dangerous chemicals handled in the chemical industry, the result of ECOSAR calculation points out the necessity of developing a new experimental protocol devoted to fulfil the "Seveso II" directive. As a first attempt to solve this problem a preliminary screening based on toxicological tests is proposed. Encouraging results are obtained on Ethyl parathion thermal decomposition.

Runaway phenomena and thermal explosions can originate during the nitration of salicylic acid by means of a nitric acid/acetic acid mixture when the thermal control is lost, mainly as a result of the formation and thermal decomposition of picric acid. The prediction of the behaviour of this system is thus of great importance in view of possible industrial applications and the need to avoid the occurrence of unwanted dangerous events. During a previous investigation a model was developed to simulate its behaviour when the starting concentration of the substrate is too low, thus, preventing the precipitation of poor soluble intermediates. In this work this model is extended to deal with more concentrated systems even in case of a solid phase separating during the process. To this purpose the previously assessed dependence of the solubility of 3-nitro and 5-nitrosalicylic acids upon temperature and nitric acid concentration is included in the model. It is assumed that when 3-nitro and 5-nitrosalicylic acids are partially suspended in the reacting medium a kinetic regime of "dissolution with reaction" is established; that is, the redissolution of these species is a fast process compared to the successive nitration to give dinitroderivatives. Good results are obtained in the comparison of the experimental data with those calculated both in isoperibolic and adiabatic conditions when the revised model is used.

The present work aims at assessing both thermodynamic and kinetic parameters of the esterification process of the (S)-carnitine, using calorimetric techniques. The use of the system acetic anhydride/nitric acid/acetic acid as esterifying agent and the explosive behaviour of nitric esters lead to safety considerations that have been investigated by hypothesizing some common process deviations. In particular, it has been investigated in adiabatic conditions both the batch addition of acetic anhydride and the effect of an initial temperature higher than those required by the process. © 2004 Elsevier B.V. All rights reserved.