How does the oxidation and reduction time affect the chemical looping epoxidation of ethylene?

Abstract

<jats:title>Abstract</jats:title><jats:p>The chemical looping epoxidation (CLE) of ethylene was performed over an Ag catalyst supported on strontium ferrite perovskite (SrFeO<jats:sub>3-δ</jats:sub>). CLE consists of a reduction step in ethylene where oxygen is transferred from the support to the Ag catalyst to form ethylene oxide (EO), and a separate regeneration step, in which the support is reoxidised in air. The effect of altering the reduction and oxidation times was investigated, analysing changes in the conversion of ethylene and selectivity to EO. Experiments were conducted at 270 °C in a packed bed of Ag(15 wt.%)/SrFeO<jats:sub>3-δ</jats:sub> with a gas hourly space velocity of 9600 h<jats:sup>−1</jats:sup> and a total operation time &gt; 40 h. When the time of the reduction step was increased from 1 to 3 min, selectivity to EO only decreased by 0.4%, demonstrating that CLE can run with prolonged reduction times while maintaining high selectivity. Increased duration of the reoxidation step resulted in both selectivity and conversion increasing, but when varying the oxidation time from 10 to 15 min, the overall improvement in the performance was minimal; thus, CLE can feasibly operate at shortened oxidation times. By increasing the pressure during the oxidation step to 2.5 bar, the duration of the reoxidation step was further shortened to 5 min without impacting the CLE performance. With 1.5 min reduction and 5 min reoxidation steps, a CLE installation producing EO in a pseudo-steady manner would require 4 packed bed reactors operating in parallel. The role of Ag<jats:sub>2</jats:sub>O in the CLE process was also investigated, demonstrating that the oxide was not selective towards EO.</jats:p>