Oral questions

Pagina 1

Oral questions 1)Ethylene oxide: processes, catalysis, mechanisms of reaction, reactor, process plant. General thermodynamics and kinetics questions about random processes. Reazione bilanciata con valore del deltaH, effetti della temperatura sulla selettività, ragionamento sulla struttura del catalizzatore e sulle limitazioni diffusive (perché alfa allumina e perché uso uno strato sottile), schema dell'impianto, temperature e pressioni usate. Ethylene oxide is a very reactive gas, due to its strongly tensionated ring. Its main uses are to produce Et-glycol and Amines or polymers. In the past, it was produced via HidroClorination of Etilene: this is a 2 step process which involves first the reaction of etilene and gaseus cloro (in water solution) to give OH-Et-Cl and wasted HCl, and then the saponification reaction with Ca(OH)2 to give the desired product, water and the wasted salt CaCl2. This reaction was very exothermic, corrosive and had many sideproducts in stechiometric amounts. For this reasons, nowadays, it is produced by selective catalytic oxidation of Et by Ag. As a partial oxidation, is very exothermic and led to total combustion as side reaction, both of reagent and product. In order to increase the selectivity (around 70%) the operating condition are managed: low T (250°C), high p (30bar), to favour the TD. Moreover, inibitors and inerts are added; and the Ag catalyst is supported on a alfa-Al2O3 support, with large pores, in order to reduce diffusion problems and control thereaction time (<1s). In this way we can also reduce runaway reactions risk, which can develop when T increase due to the decreasing of combustion Ea. For the mechanism, there are 2 different proposal: the 1st starts with non-dissociative adsorption of O2 on the Ag catalyst, which then…