Kinetic study on catalytic dehydration of 1,2-propanediol and 1,2-butanediol over H-Beta for bio-ethylene glycol purification

1,2-propanediol (PDO) and 1,2-butanediol (BDO) are preferentially dehydrated over the H-Beta zeolite catalyst in the presence of ethylene glycol (EG). The reaction kinetics of diol conversions over H-Beta was studied. The PDO and BDO conversions were found to follow the route of pseudo-first-order reaction (dehydration) or pseudo-second-order reaction (dehydration and acetalization), which was highly dependent on the diol/H-Beta mass ratio. At the ratios < 1, aldehydes were the dominant products from the pseudo-first-order reactions. EG dehydration rarely produced acetaldehyde but formed oligomers following pseudo-third-order kinetics. The apparent activation energies (E-a) for PDO and BDO conversions to aldehydes were lower than that of the EG oligomerization (69.9, 54.0, 99.3 kJ/mol, respectively), consistent with the reactivity order of BDO > PDO > EG as evidenced in temperature-programed reaction analysis. At the mass ratios > 16-25, acetals were the main products from the pseudo-second-order reactions, and Ea values of PDO and BDO conversions were 153.6 and 120.7 kJ/mol, respectively. The acetalization has a much lower Ea value than that of diol dehydration. The reactions of PDO conversion were first-order with respect to the H-Beta catalyst regardless of the diol/H-Beta mass ratio, indicating that the acetalization follows the Eley-Rideal mechanism