A zyxw fedc ONM prioriDesign of a Photoreactor for the Chlorination of Ethane A three-dimensional radiation model coupled with two-dimensional mass balances for the intervening chemical species is solved for the photochemical chlorination zyxwvuts A of ethane. The analysis was carried out using the full mechanistic kinetic sequence and employing polychro- matic radiation for a process conducted in a tubular reactor placed inside an elliptical reflector. Theoretical predictions were compared with bench-scale experi- ments and showed excellent agreement. Using the validated model, computational experiments were conducted to explore the influence of reactor design and operational parameters upon the degree of chlorina- tion. Dichlorination reactions were also added to the kinetic model to analyze reactor behavior from the viewpoint of selectivity. The a priori design method described can be applied from first principles and requires no experimentally adjustable parameters. zyxwvu HGFED M. A. Claril, H. A. Irazoqui, A. E. Cassano lnstituto de Desarrollo Tecnolbgico para la Industria Quirnica, Universidad Nacional del Litoral and Consejo Nacional de lnvestigaciones Cientificas y Tecnicas Santa Fe, 3000 Argentina introduction A zyxwvutsrqp A method proposed for the design of a photoreactor may ascertain its quality by producing good results even in the pres- ence of the three following operating situations: 1. Prediction of reactor behavior for multiple-step or chain reactions 2. Modeling of a reactor with a rather complex radiation field 3. Inclusion of heterogeneities in the reacting system, for instance, in a gas-liquid reaction zyxwvuts In this work we develop an zyxwvutsr A a zyxwvuts HGFEDC priori design of a reactor for a homogeneous photochemical chain reaction, in a system with an elliptical reflector, thus addressing the first two problems. The third difficulty was dealt with in a separate work (Alfano, 1984). To achieve the scope indicated in situation 1 we studied the gas-phase photochemical monochlorination of ethane in a tubu- lar cylindrical reactor. To provide the conditions for a decisive answer with respect to situation 2 we chose a difficult setup to model: a cylindrical reflector of elliptical cross section with a tubular lamp located at one of its focal axes and the reactor tube at the other axis. This is perhaps the most practical tubular reac- tor system for laboratory and bench-scale work in continuous, single-phase experiments, although in many cases its applicabil- ity to large-scale purposes may be questioned. Success in mod ing its radiation field should provide the necessary confidenc extend the methodology to simpler situations. The system, known as an elliptical photoreactor, is show schematically in Figure 1. For a chain reaction it has never before been strictly modeled from first principles without use of experimentally adjustable parameters. On the other hand, it has been extensively used in experimental work since the e studies of Baginsky (1951). We may cite, for example, Huff an Walker (1962), Cassano and Smith (1966, 1967), Jacob an Dranoff (1969), Matsuura et al. (1969), Boval and Smith (1970), Matsuura and Smith (1970), Harada et al. (1971), Zolner and Williams (1972), Williams and Yen (1973), and Williams (l976), to mention only a few applications. A good radiation model is always necessary because the ra of reaction of the first step (initiation), in any single-phot activated photochemical reaction is proportional to the local vol- umetric rate of energy absorption (LVREA), as was shown by Irazoqui et al. (1976). The LVREA is proportional to the radia- tion energy flux density, which is a local property of the rad tion field inside the photoreactor. In any practical reactor t field is necessarily strongly nonuniform. This nonuniformity due to the attenuation produced by the radiation absorption reactants (and sometimes inerts and products) and the geom 366 March 1988 Vol. 34, No. 3 AIChE Journal