Francesco Gioia

Catalytic hydrodechlorination of 1,2,3-trichlorobenzene

Abstract Detoxification by catalytic hydrotreatment can be a valid alternative to thermal incineration for the disposal of hazardous organic waste liquids. With this aim, the hydrodechlorination of 1,2,3-trichlorobenzene on a Ni-Mo/γ-Al2O3 catalyst has been investigated experimentally and theoretically. The behaviour of this chemical in hydrotreatment is hopefully representative of that of many toxic chlorinated compounds. The experimental reaction runs were conducted in a stirred batch reactor in the presence of hydrogen, at constant pressure (pH2 = 100 bar), and using hexadecane as a reaction medium. The temperature, kept constant during each run, was varied in the range 200°C⩽T⩽350°C. The experimental results consisting of concentrations of reactant, reaction products and intermediates vs. time, permit the identification of the reaction network and its modification with temperature. The kinetic constants (and their temperature dependence) of the reactions which form the network are also determined.

Detoxification of organic waste liquids by catalytic hydrogenation

Abstract Catalytic hydrogenation is proposed here as a possible alternative to thermal incineration for the disposal of hazardous organic waste liquids. The validity of this proposal depends on the fact that the toxicity of organic liquid wastes is caused mainly by compounds containing heteroatoms in their chemical structure. Hydroprocessing, while converting these heteroatoms into easily removable inorganics, also produces non-toxic recyclable organic chemicals. The paper analyzes in detail, on the basis of the available results reported in the literature, both the chemistry and the chemical kinetics of hydrotreating of the most representative heteroatom-containing compounds. It thus provides the basic tools for the design of future detoxification plants based on hydroprocessing. Both the kinetic analysis reported here and, what is more important, the concrete realization of the proposed detoxification method are made possible by the fact that hydroprocessing is a well known technology in the petroleum and petrochemical industries.

Oil mobility in a saturated water-wetted bed of glass beads

The mobilization of an oil bank in a packed bed of glass beads saturated with an aqueous phase has been studied both theoretically and experimentally. The size of the glass beads was varied in the range between 0.5 and 5mm. Two oils (hexadecane and hexane) with viscosities different for an order of magnitude and densities smaller than that of water have been used. A few more runs have been carried out using perchloroethylene (PCE), with density greater than that of water. The interfacial tension in the aqueous phase was varied in a quite large range (0.38-39.1 dyn/cm) by adding surfactants to the water. The glass assembly made it possible to follow the evolution of the dyed oily phase by the use of a digital camera. A very simple stochastic model for describing the porous structure of the packed bed made it possible to set a criterion for determining the probability of mobilization of ganglia which are produced by the fragmentation of the oil bank. The same model permits also to estimate the probability function of the velocity of a ganglion of an assigned size.

Transient evaporation of multicomponent liquid mixtures of organic volatiles through a covering porous layer

The release into the atmosphere of volatile organic components, evaporating from a multicomponent liquid mixture covered by a porous layer, is studied theoretically and experimentally. The modelling has been developed on the basis of fundamental principles and the most appropriate approximations have been suggested by the physics of the problem. The results of the investigation indicate that in most cases, neglecting the bulk flow induced by diffusion in the Ficks equation is a good approximation. Moreover, a criterion is established which may even quantify the accuracy of this approximation. On the contrary, it is shown that the change in the liquid composition during the evaporation plays a predominant role on the predictive capability of the model. Finally, the reliability of the physical parameters reported in the literature for an accurate modelling of the process is assessed. Experiments have been conducted with an arrangement of particles of a porous rock tuff in a packed bed geometry covering a liquid mixture of volatile components. The experimental investigation has been extended to liquid mixtures of up to four components which have vapor pressures falling into a two order of magnitude range of values. The effect of the non-ideality of the liquid mixture is investigated, too. The theoretical model, very simple indeed, represents the experimental data with good accuracy, and is a reliable tool for accurately predicting the time required for the complete release of the volatiles and emission fluxes into the atmosphere.

Solvent extraction of chlorinated compounds from soils and hydrodechlorination of the extract phase

The remediation of soils contaminated with chlorinated compounds was investigated. The process consists of solvent extraction followed by catalytic hydroprocessing (hydrodechlorination) of the extract phase. A mixture of ethylacetate-acetone-water (E-A-W) was adopted as solvent in the extraction process. Tests of extraction of chlorobenzene from a model contaminated soil were carried out and the Langmuir adsorption equation was characterized. The solvent, contaminated with different chlorinated compounds was then hydrotreated with a Pd/C catalyst. The chlorinated compounds tested are: chlorobenzene, hexachlorobenzene and hexachloroethane at various initial concentrations. The reaction runs were carried out at room temperature and at a hydrogen pressure of 1bar. Hydrotreating of these compounds takes place according to a Langmuir-Hinshelwood mechanism whose kinetic parameters were determined. The experiments show that high destruction efficiencies may be reached in reasonably short times, particularly for hexachloroethane. Longer times are necessary for the aromatic compounds (chlorobenzene and hexachlorobenzene) for which the CCl bond is much stronger than that in the aliphatic compound. Time for a 95% destruction efficiency for all experimental runs was determined. A noteworthy finding is that ethylacetate and acetone do not undergo any reaction during hydrotreating. Thus the treated extract solution may be recycled inasmuch as it conserves its full extracting capacity towards chlorinated compounds. A limitation in recycling is the inhibiting effect of benzene on the HDCl rate: benzene produced by HDCl of chlorinated compounds, accumulates in the solvent mixture in the event of recycling. Simulation of the process with the recycling of the solvent was carried out, accounting for the inhibiting effect of benzene.

The release into the atmosphere of hazardous volatiles Part I. Release from porous solids imbued with a liquid mixture in which the volatiles are dissolved

Abstract An experimental and theoretical study to investigate the release of toxic volatiles from porous media is presented. Three porous media, one synthetic and the other two natural, have been selected. They were imbued in a solution containing toxic volatiles in dilute concentrations. The heavy oily medium used to hold the volatiles in the liquid phase is tetradecane. The toxic volatiles whose diffusion is studied include benzene, chlorobenzene and 1,3-dichlorobenzene. These chemicals were chosen so that a wide range of volatilities could be studied. Two different desorbers have been used. The first is a desorption chamber containing a single sphere of the porous medium. The second, more suitable for studying the diffusion of the less volatile components, has a cylindrical fixed bed geometry in which smaller porous spheres are arranged. The theoretical tools used to model the diffusion process show good accuracy in describing the experimental data.

The release into the atmosphere of hazardous volatiles Part II. Release from a slab of contaminated porous particles. The importance of free convection

Abstract The release of a volatile organic compound from a slab of porous particles imbued with an immobile oily phase containing the volatile is studied. The most important feature of the model is that it accounts for natural convection besides diffusion. The gas which fills the interparticle porosity of the contaminated slab has a composition, and thus a density, different from that of the surrounding atmosphere. Therefore, a natural convection flux may be established through the slab. The model shows that natural convection indeed plays an important role which increases with the vapor pressure of the component. For benzene it predominates the overall process.

Theoretical analysis and experimental evaluations of the behaviour of granular moist pig iron stocked in the presence of air and related hazards

Abstract The influence of the chemical, physical and geometrical properties of a stockpile of moist granular pig iron on its self-heating, due to the reaction w The mathematical model describing the mass and heat transfer inside the pile has been solved and given are, among other things, the temperature and oxy Specifically designed laboratory experiments have been conducted in order to evaluate some chemical, physical and geometrical parameters of interest. M