Lucio Rizzuti

Photocatalytic ammonia synthesis in a fluidised bed reactor

Abstract Photocatalytic ammonia synthesis was successfully performed in a fluidised reactor of parallel-wall configuration by irradiating iron-doped titanium dioxide with near ultraviolet light. The catalyst was prepared in such a way that good quality of fluidisation could be obtained. Mixing the catalyst with γ-alumina was found to affect the fluidisation behaviour. Ammonia production was increased when the catalyst was suitably fluidised because of enhanced utilisation of light energy. Quantum efficiencies of more than 10% have been reached. The parallel-wall reactor configuration was found to give higher energy conversion than a cylindrical one [1a].

Conversion of solar energy to chemical energy by photoassisted processes—II. Influence of the iron content on the activity of doped titanium dioxide catalysts for ammonia photoproduction

Abstract One of the new approaches of the energy problems concerning the chemical processes is the use of energy sources not yet exploited. The possibility of using in situ the products of water photodecomposition over oxide catalysts has recently received more attention. This paper reports the results of a study devoted to the ammonia photoproduction from nitrogen and water over catalysts made up of titanium and iron oxides supported on γ-alumina. A fluidized bed laboratory reactor, with radial irradiation by a high pressure mercury lamp, was used for the experiments at 120°C and atmospheric pressure. The main result is that ammonia was produced in all the experiments. A reaction mechanism has been proposed in which the photogeneration of electron-hole pairs and their separation have been considered to be the determining steps of the overall reaction with respect to the photoassisted ammonia synthesis.

Conversion of solar energy to chemical energy by photoassisted processes—I. Preliminary results on ammonia production over doped titanium dioxide catalysts in a fluidized bed reactor

Abstract A development of the water photoelectrolysis phenomenon was studied. An elliptical-reflector chamber was used to irradiate, in the near-UV region, a catalyst fluidized in a laboratory reactor. Various titanium oxide-iron oxide catalysts, supported on γ-alumina, were prepared and tested. The reactant used was a nitrogen-water mixture at atmospheric pressure and the temperature of the reactor was kept constant at 80°C. The main result was the production of ammonia over all the catalysts used. A reaction mechanism is hypothesized and the role of the irradiation and of the water is discussed. An assessment of the photoassisted heterogeneous reactors is also reported.

Ozone absorption in alkaline solutions

Abstract Using a packed column, the rate of ozone absorption into KOH aqueous solutions has been measured. The pH range was 8.5–13.5 and the temperature varied from 18 to 27°C. Independent measurements of CO 2 absorption into buffer solutions containing KAsO 2 were used to determine the interfacial area. The results can be interpreted on the basis of a first order reaction in both O 3 and OH − .

The pH dependence of the ozone absorption kinetics in aqueous phenol solutions

Abstract Using a wetted wall laboratory absorber, the rate of ozone absorption in aqueous phenol solutions has been measured in the pH range 1.75–12. The phenol concentration was varied in a wide range (7–800 ppM) and the ozone partial pressure over a six-fold range. The temperature and the liquid The results were interpreted by assuming that the rate determining step of a reaction sequence is different in acid and basic solutions.

The measurement of light transmission through an irradiated fluidised bed

Abstract The transmission of light through an irradiated fluidised bed with vertical flat walls containing catalytic particles has been experimentally studied. The amount of light transmitted through the reactor was measured at different levels by a photocell. The experimental variables studied included: (i) gas flow rate, varying from 2 to more than 10 times that required for minimum fluidisation; (ii) mean particle size, ranging from 0.138 to 0.275 mm; and (iii) internal bed thickness from 2.1 to 4.9 mm. The effect of the reflectance of the particles was also examined. Results show that the amount of light transmitted through a flat fluidised bed is low. The average transmitted light has been satisfactorily correlated

Kinetics of carbon dioxide absorption into catalysed potassium carbonate solutions

Abstract Carbon dioxide was absorbed in potassium carbonate-bicarbonate buffer solutions. Some of these solutions contained arsenious ion as catalyst. The experiments were performed in a wetted wall absorber, in conditions of stagnant gas phase and at constant temperature, with the aim of elucidating the influence of the carboante ion concentration on the catalytic process. A kinetic equation was obtained, that was critically compared with the experimental data published previously by various investigators.

Bubble phase voidage and dense phase voidage in thin two-dimensional fluidized beds

Abstract Bubble phase and dense phase voidages have been studied in a series of thin two-dimensional fluidized beds using a light transmission technique. It is proposed to divide the bubble phase voidage into a “visible” and an “invisible” portion with respect to light transmission. The variation of visible bubble phase voidage with bed thickness follows a logarithmic relationship. The analysis is especially relevant for the design of fluidized photoreactors. The effects of flow rate, particle size and bed thickness on bubble phase voidage have been examined. Average dense phase voidage, which varies with flow rate and particle size was found to exceed that at minimum fluidization in many cases. The present results show that variable dense phase porosity found in three-dimensional fluidized beds is also present in flat fluidized photoreactors.

Seawater Desalination for Freshwater Production

In the last decades more and more countries have experienced water scarcity problems, thus pointing at alternative non-conventional sources of fresh water. Seawater desalination has proven to be a reliable and economically sustainable water resource since the second half of the 20th Century. A number of well proven technologies already exist, with advantages and disadvantages making each of them more suitable in specific sites. Moreover, quite recently, coupling the use of renewable energy to the production of fresh water from seawater results in novel technologies, able to minimise the environmental impact that desalination processes can create due to their intense energy consumptions.

The influence of the liquid viscosity on the effective interfacial area in packed columns

Abstract The effective interfacial area for chemical absorption of a laboratory packed column was determined at five values of the liquid kinematic viscosity in the range 0.9 × 10 −2 −1.55 × 10 −2 cm 2 /s, using two chemical systems. The measurements have been made at various liquid flow rates. All the data can be satisfactorily correlated by an equation which indicates that the liquid viscosity has a significant influence on the effective interfacial area, even larger than that of the liquid flow rate.