Catalytic Esterification of Pentaerythritol over a Mesoporous Composite SnCl2@HZSM-5 Catalyst

The mesoporous HZSM-5 and SnCl2@HZSM-5 mesoporous composite were prepared by two-step crystallization and wet impregnation method, respectively. The catalytic esterification performances of SnCl2, HZSM-5 and SnCl2@HZSM-5 were compared. SnCl2@HZSM-5 had the most amount of total and weak acidity, and the weakest acid strength. More total acid content was beneficial to increase pentaerythritol conversion, and the weak acid could improve the selectivity of PETS, and weak acid strength was beneficial to inhibit the formation of carbon deposits. Bronsted and Lewis acid sites were present simultaneously on the SnCl2@HZSM-5 catalyst. Moreover, some extra Bronsted acid sites were created on the SnCl2@HZSM-5 catalyst, because the interaction of SnCl2 with HZSM-5 may result in the exchange of Sn2+ with protons. Both acid sites could catalyze the esterification reaction, and the Bronsted acid site was more beneficial to increasing PETS selectivity. Therefore, SnCl2@HZSM-5 showed the highest pentaerythritol conversion, PETS selectivity and catalytic stability. The generation of coke and the leaching of Sn were the main cause of catalyst deactivation. Under the optimized process conditions: 105 degrees C, 4.7 molar ratio of stearic acid and pentaerythritol, 1.2 wt % catalyst amount and 2.5 wt % SnCl2 loading, after 3 h reaction time, the pentaerythritol conversion, PETS selectivity and yield was 99.3 %, 97.2 % and 96.5 %, respectively.