Energy recovery in wastewater decontamination: simultaneous photocatalytic oxidation of an organic substrate and electricity generation.

The contemporary removal of organic pollutants from aqueous solution and electricity generation is studied in the present work by means of an experimental device resulting from the combination of a photocatalytic reactor and an electrochemical cell. The proposed system relies on the capability of Cu2+ ions to reduce in the presence of TiO2, (solar) UV radiations and a sacrificial organic agent. In the anodic solution of the combined photoreactor-cell, Cu0 is oxidized to Cu2+ and the latter is reduced again to the lowest oxidation state. The use of different sacrificial agents ranging from formic acid (FA) to glycerol (GLY) to glucose (GLU) is investigated along with the adoption of two different cathodes for the cell, the first based again on the couple Cu2+/Cu0 and the second on the couple O2/H2O.

Toxicity of unwanted intermediates and products formed during accidental thermal decomposition of chemicals.

The problem of the formation of unwanted substances that can occur during thermal decomposition of chemicals is studied from a toxicological point of view. Two species, ethyl parathion (a widely used pesticide) and cumene hydroperoxide (an intermediate for the industrial production of phenol and acetone), are selected for this investigation. The hazards associated to their accidental thermal decomposition are estimated on the basis of the (known) intermediates and products formed by means of a computational tool (ECOSAR programme) and assessed experimentally by means of algal bioassays. Green alga Pseudokirchneriella is used as target organism for all the toxicological assessments. The results of these tests on the samples collected during the thermal decomposition of the two studied species indicate that in the case of ethyl parathion the decomposition process gives rise to a mixture of compounds which are more toxic than the parent species. On the other hand, the decomposition of cumene hydroperoxide in cumene results into the formation of different species whose toxicity towards the adopted organism is lower than that shown by the starting compound. A procedure is proposed to ascertain when it is necessary or it is avoidable to carry out further investigations that involve the analytical resolution of mixtures resulting from the thermal decomposition process. This approach is suggested as a preliminary screening to identify the hazards associated with an accidental decomposition either of pure chemicals or of mixtures of compounds.

Batch salicylic acid nitration by nitric acid/acetic acid mixture under isothermal, isoperibolic and adiabatic conditions.

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.

Kinetic and safety assessment for salicylic acid nitration by nitric acid/acetic acid system.

The nitration process of salicylic acid for the production of the important intermediate 5-nitrosalicylic acid is studied from thermokinetic and safety points of view. Investigations carried out by considering, as process deviations, the loss of the thermal control point out the possibility of runaway phenomena due to the occurrence of polynitration reactions. Isothermal experiments are carried out in various conditions to assess the involved reaction network and reaction kinetics.