A three-dimensional radiation model coupled with two-dimensional mass balances for the intervening chemical species is solved for the photochemical chlorination of ethane. The analysis was carried out using the full mechanistic kinetic sequence and employing polychromatic radiation for a process conducted in a tubular reactor placed inside an elliptical reflector.Theoretical predictions were compared with bench-scale experiments 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 chlorination. 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.