Impacts of Sn(II) doping on the Keggin heteropolyacid-catalyzed etherification of glycerol with tert-butyl alcohol

Abstract

In this work, phosphomolybdic acid salts were synthesized exchanging their protons by the Sn(II) cations (i.e., H3-xSnx/2PMo12O40; x = 0.0, 1.0, 2.0, 3.0), and evaluated in the etherification reactions of glycerol with tert-butyl alcohol (TBA). The catalytic activity of the phosphomolybdate salts containing a variable load of Sn(II) ions was further compared to phosphotungstic and silicotungstic acid salts (i.e., H3-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 3.0 and H4-xSnx/2PW12O40; x = 0.0, 1.0, 2.0, 4.0, respectively). The integrity of the Keggin anion after the synthesis was confirmed by infrared spectroscopy analysis. Physical properties were determined through thermal analyses, powder X-Rays diffraction patterns, N2 adsorption-desorption isotherms, and scanning electron microscopy. The acidity properties were analyzed by adsorbed pyridine FT-IR spectroscopy, NH3-programmed-temperature desorption, and potentiometric titration. Among all the Sn(II) heteropoly salts tested, the Sn3PMo12O40 was the most active and selective catalyst toward glyceryl ethers. The highest activity of Sn3PMo12O40 was assigned to the greater Lewis acidity strength. Modeling, simulation, and economic analysis allowed to evaluate the viability of the process. An annual capacity of 30,000 metric tons was developed, and the process is feasible with a return on investment (ROI) of 30.7%.