Sustainable production of acetaldehyde from lactic acid over the magnesium aluminate spinel

Abstract

Magnesium aluminate spinel was prepared with co-precipitation method by varying Mg, Al precursors, Mg/Al molar ratios and calcination temperatures. The as-prepared magnesium aluminate spinel was characterized by nitrogen adsorption–desorption, XRD, FT-IR, NH3-TPD, CO2-TPD and SEM, and were employed to catalyse the vapour-phase decarbonylation of lactic acid (LA) to produce acetaldehyde. Among Mg, Al precursors investigated in our experiment, overwhelming majority can be easily transformed into spinel under high temperatures, which offered highly efficient catalytic performance for decarbonylation of LA to acetaldehyde. Mg/Al molar ratios had a significant influence for this reaction. Under high Mg/Al molar ratios, the catalyst displayed low selectivity to acetaldehyde and high selectivity to propionic acid due to strong alkalinity on its surface. Decreasing Mg/Al molar ratios favoured to acetaldehyde selectivity. Calcination temperatures evidently affected to form spinel structure. With enhancing calcination temperatures, it favoured to the formation of magnesium aluminate spinels, displaying a high crystallinity. Meanwhile, the catalytic performances became better with an increase of calcination temperatures. Accordingly, magnesium aluminate spinel was thought as active species for decarbonylation of LA to acetaldehyde. With further increase of calcination temperatures, the structure of magnesium aluminate spinel was destroyed. At the same time, the catalytic performance also drastically decreased. These results can further confirm the spinel as active species. Under the optimal reaction conditions, LA was almost converted and the selectivity of acetaldehyde achieved 87.5% over the magnesium aluminate spinel with Mg/Al molar ratio = 1:2 at calcination temperature of 1000 °C.