Concealed risk in catalytic processes: How weather can initiate a catastrophe in an ethylbenzene-producing tower

Abstract

In a Taiwanese chemical processing plant producing ethylbenzene, an unexpected thermal runaway reaction occurred in an alkylation tower during shutdown, causing approximately 7500 kg of catalyst to be wasted. Prior risk assessments failed to identify the responsible hazard vectors. The thermal runaway occurred despite all former appropriate operating procedures being strictly followed. To identify the root cause of this incident, the generation and dissemination of the thermal source were tested and simulated using thermal analysis methods and a prototype tower. The results showed that water adsorption could provide heat to the catalyst bed, even at temperatures exceeding 350 °C, which is the temperature required for the oxidation of hydrocarbon adsorbates. High humidity caused by Typhoon Lionrock was a critical factor contributing to the incident, which was not anticipated by the plant engineers. Humidity within the air inlet supplied the abundant adsorption heat required to increase the bed temperature. This resulted in thermal runaway due to heavy oxidation of the large number of adsorbates. This study proposes a safer strategy that involves passing humid N2 through the catalyst tower to prevent the oxidation of hydrocarbon adsorbates, thereby removing the adsorption heat. The purpose of this study was to reveal hazards concealed in the catalyst system. If a catalyst has a noticeable adsorption heat that, at a given temperature, can induce spontaneous oxidation or decomposition of the adsorbates with a possible thermal runaway reaction. This paper interprets past failures as lessons and proposes solutions that can be used by those in the chemical manufacturing industry to avert such incidents in the future.