Silane functionalization on zeolite 13X surface for direct steam generation in a solid sorption heat pump

Abstract

High-temperature steam has been directly generated from hot water based on a solid sorption heat pump system by employing silane functionalized zeolite 13X (XS). The adsorbent is prepared by a liquid phase grafting method to modify functional groups on the zeolite surface with a silane coupling agent. The static water contact angle (WCA) and surface functional groups are analyzed by optical contact angle measuring instruments and Fourier transform infrared spectroscopy (FTIR), respectively. Analytical results confirm the successful preparation of surface hydrophobic zeolite. The water adsorption capacity of XS is slightly less than that of 13X, while the overall adsorption heat remains almost constant. Dry air at 130 °C is utilized for the regeneration of the wet zeolite in cyclic experiments. Steam at 207 °C is generated from input hot water at 72 °C in a packed bed filled with XS-25 (zeolite 13X functionalized by a saline solution concentration of 25%). The thermal response during the steam generation process is accelerated by utilizing XS. The mass of steam product does not change during the generation with XS, whereas cyclic time is shortened. Moreover, XS facilitates the regeneration process by decreasing the heat demand for the removal of free water. System evaluation results show that a higher Sp (steam productivity) is obtained for XS than that for zeolite 13X. COPh (coefficient of performance for heating) and SHP (specific heating power) are elevated by 23.6% and 5.7% for XS compared with those for zeolite 13X, respectively.