We use an Aspen model of the separation chain downstream of the steam cracker to investigate the reaction and flow conditions around which polymer fouling occurs, and study the dissolved oxygen concentrations in the distillation column of interest. The debutanizer column is downstream of a depropanizer, so the feed is a C4+ mixture. The biggest component is butadiene, but it also contains benzene, cyclopentadiene, and other compounds. We modify the Aspen model from our previous work and introduce various oxygen concentrations to the debutanizer feed, up to that it contains an air-saturated level of dissolved oxygen as an upper bound. Since we weren't able to find experimental data for oxygen solubility in butadiene, we approximate it using the saturated concentration of O 2 in benzene (1.9 mol of O 2 per m 3 of benzene) .