Micro-structured ZSM-11 catalyst on stainless-steel microfibers for improving glycerol dehydration to acrolein

Abstract

Glycerol is a byproduct from the biodiesel manufacturing. Glycerol dehydration into more valuable acrolein is desirable and essential since it improves the economics of the biodiesel production and offers a sustainable route to replace the market favorite chemical from petroleum process. Zeolites with the dominant and uniform Brønsted acid sites have been widely used in glycerol dehydration since Brønsted acid sites are flexible and interacting with the center hydroxyl of glycerol toward acrolein production. In this research, microstructured ZSM-11 catalysts have been developed by direct growth of zeolite crystals on a macroscopic three-dimensional (3D) network of sinter-locked stainless steel microfibers. It showed remarkable stability and acrolein selectivity improvement compared to conventional ZSM-11 zeolite, due to the short residence time to limit the secondary reactions and enhanced mass transfer to minimize the coke formation. The acidity of zeolites has been optimized via tuning the SiO2/Al2O3 ratios in a wide range from 78 to 283. The highest glycerol conversions and acrolein selectivity were observed over the catalyst with a SiO2/Al2O3 molar ratio of 131. A higher temperature of 300 °C was necessary to achieve better catalytic conversion and improve the acrolein formation. At the high flow of carrier gas, the coke formation was suppressed due to the enhanced diffusion of large products out of the zeolite pores.