Quantification and Analysis of Carbon Deposition on Catalytic Oxygen Carriers for the Oxidative Coupling of Methane

Abstract

The current commercial method of obtaining ethylene, a highly valuable product, through steam cracking is highly process and energy intensive. An alternative way to obtain ethylene is through the direct conversion of natural gas to ethylene in a one step process through oxidative coupling of methane (OCM). A chemical looping scheme is an attractive mode of operation for OCM because of the enhanced selectivity towards ethylene made possible by a catalytic oxygen carrier (COC). However, a major concern for this process is carbon deposition, or “coking”, which deactivates the COC by blocking active sites. Coking may be prominent in a OCM system, as the reactor is operated with limited supply of oxygen. Solid carbon compounds form and collect in the catalyst bed and are difficult to directly measure because they are not present in the reactor gas outlet. The goal of this project is to identify and quantify solid carbon formation using analytical techniques and to determine effects of carbon deposition on the performance of our COC for OCM. To quantify the solid carbon formation, COC samples were run for different time periods in the fixed bed reactor and analyzed using a carbon analyzer. After preliminary tests, carbon was detected on both fresh and used COC. Evaluating the amount of carbon deposition and the existence of other carbon compounds is the first step in learning how they form and a step toward reducing the amount of side reactions to increase the yield of ethylene in our system. This is also helpful in indicating the upper reaction time limit for our system before coking occurs.