In a joint project by researchers at the Institute of Chemical Reaction Engineering at Hamburg University of Technology (TUHH), the BasCat team in Berlin, industrial EO researchers at the BASF headquarter in Ludwigshafen and Reacnostics in Hamburg, we used our Compact Profile Reactor (CPR) to explore what is happening inside an EO reactor and derived a kinetic model of the reaction under industrial conditions.

The reaction is carried out on a catalyst consisting of rather large silver particles on an α-Al₂O₃ support. A few ppm of small chlorinated hydrocarbons such as 1,2-dichloroethane (DCE) are added to the reactor feed to poison intentionally some of the silver surface sites by chlorine atoms, making the adsorbed oxygen species on the remaining sites more selective preventing combustion of ethylene and EO to CO₂. Oxygen and chlorine compete for the active sites on the silver surface despite four orders of magnitude different concentrations (vol% vs. ppm respectively). The DCE concentration in the reactor feed must be controlled to the decimal place because already a fraction of a ppm too much DCE might lead to a full blockage of the silver surface and shutdown of all reactions somewhere in the catalyst bed.

The CPR allows measuring highly resolved species and temperature profiles along the catalyst bed revealing what is happening where and when inside the reactor. We can show that the chlorine coverage increases from inlet to outlet of the catalyst packing due to the decreasing oxygen partial pressure. While surface chlorine is indispensable to achieve high EO selectivity, over-moderation is easily possible shutting down all reactions and leaving some of the catalyst inventory unused.