Abstract
Biomass-derived ethylene glycol (EG) contains 1,2-propanediol (PDO) and 1,2-butanediol (BDO), and the elimination of PDO and BDO via dehydration reactions leads to EG loss due to acetalization. For the improvement of EG recovery, the selective inhibition of acetalization reaction on ion-exchange-modified H-Beta zeolite was investigated. In batch reactions, over Li2CO3-treated zeolite with ion-exchange ratio of 15 %, the selectivity to acetals declined from 74 % (untreated) to 24 %. In continuous reactions, acetalization and oligomerization were obviously suppressed, and the zeolite stability was improved. EG consumption was reduced by half in both batch and continuous reactions. Microcalorimetry, NH3-TPD, PYIR, and FTIR results demonstrated that the strong Brønsted acid sites (Si(OH)Al) with NH3 adsorption heat ≥ 158 kJ/mol were responsible for the dehydration reactions, while Brønsted (excluding silanol group) and EFAl Lewis acid sites catalyzed the acetalization and oligomerization reactions. The activation barrier of acetalization between PDO and propanal was increased from 31.1 to 85.9 kJ/mol after the ion exchange, while that of PDO dehydration to propanal was almost kept constant (70–75 kJ/mol). Weak and moderate acid sites were removed by ion exchange, so acetalization and oligomerization were suppressed without evidently inhibiting dehydration reactions.
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