Recent developments in dehydration of glycerol toward acrolein over heteropolyacids

As biodiesel production from triglyceride transesterification increases, a surplus amount of by-product glycerol is produced. The glycerol production per year in Europe has tripled within the last 10 years to 800-900 kt per year. This motivates the development of new processes for the conversion of glycerol into valuable chemicals, e.g., the transformation into acrolein. It is an attractive intermediate for acrylates, methionine, glutaraldehyde, etc. In the recent years, some researchers studied the dehydration of glycerol to acrolein over acidic bulk and supported catalysts, in particular with heteropolyacids (HPAs) as active compounds. HPAs attracted the attention due to their high Bronsted acidity and well known structures, however, they have some disadvantages such as low surface area, low thermal stability, and rapid coking leading to deactivation. To overcome these drawbacks, HPAs are often supported on oxidic carriers showing high surface areas. In addition, redox active metals are incorporated into HPAs and oxygen-containing feed is used to suppress coke formation. This review presents a summary on recent research on HPA based catalysts in the gas phase dehydration of glycerol to acrolein.