Production of Acetaldehyde via Oxidative Dehydrogenation of Ethanol in a Chemical Looping Setup.

Abstract

A novel chemical looping (CL) process was demonstrated to produce acetaldehyde (AA) via oxidative dehydrogenation (ODH) of ethanol. Here, the ODH of ethanol takes place in the absence of a gaseous oxygen stream; instead, oxygen is supplied from a metal oxide, an active support for an ODH catalyst. The support material reduces as the reaction takes place and needs to be regenerated in air in a separate step, resulting in a CL process. Here, strontium ferrite perovskite (SrFeO3-δ) was used as the active support, with both silver and copper as the ODH catalysts. The performance of Ag/SrFeO3-δ and Cu/SrFeO3-δ was investigated in a packed bed reactor, operated at temperatures from 200 to 270 °C and a gas hourly space velocity of 9600 h-1. The CL capability to produce AA was then compared to the performance of bare SrFeO3-δ (no catalysts) and materials comprising a catalyst on an inert support, Cu or Ag on Al2O3. The Ag/Al2O3 catalyst was completely inactive in the absence of air, confirming that oxygen supplied from the support is required to oxidize ethanol to AA and water, while Cu/Al2O3 gradually got covered in coke, indicating cracking of ethanol. The bare SrFeO3-δ achieved a similar selectivity to AA as Ag/SrFeO3-δ but at a greatly reduced activity. For the best performing catalyst, Ag/SrFeO3-δ, the obtained selectivity to AA reached 92-98% at yields of up to 70%, comparable to the incumbent Veba-Chemie process for ethanol ODH, but at around 250 °C lower temperature. The CL-ODH setup was operated at high effective production times (i.e., the time spent producing AA to the time spent regenerating SrFeO3-δ). In the investigated configuration with 2 g of the CLC catalyst and 200 mL/min feed flowrate ∼5.8 vol % ethanol, only three reactors would be required for the pseudo-continuous production of AA via CL-ODH.