Selective Oxidation of Ethylene to Ethylene Oxide on Silver Catalysts at Industrial Conditions: Reactor Profiles, Kinetics, and Chlorine Inhibition

Ethylene oxide (EO) is an important intermediate in the chemical industry to make polymers (PET) or ethylene glycol. The latter is used as antifreeze in the coolant cycle of cars. EO is further used to sterilize medical products such as medical dressings, hypodermic syringes and surgical equipment. With a production volume of more than 30 million metric tons per year, EO synthesis is a large-scale chemical process. Making and handling EO is dangerous because EO reactors are operated at high temperatures and pressures and because EO is very toxic, carcinogenic, mutagenic, flammable and explosive in mixtures with oxygen or air.

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.

The full paper was published in Industrial & Engineering Chemistry Research (DOI 10.1021/acs.iecr.3c04345) and can be download here:


If you would like to look inside your catalytic reactor, even for dangerous reactions and under challenging conditions, do not hesitate to contact us (crt(at)tuhh(dot)de). Knowing what is happening where and when in your reactor and on the catalyst will help you to optimize your catalytic process based on knowledge which can make a difference, in particular at large production volumes in competitive markets.