Performance investigation of silica gel based consolidated composite adsorbents effective for adsorption desalination systems

Abstract

Performance of an adsorption desalination system is mostly influenced by the type of adsorbent and their thermo physical properties such as thermal stability, thermal conductivity, surface area and pore volume. Silica gel and zeolite are the most widely employed conventional adsorbents in an adsorption desalination system. But they are characterised by low thermal stability, high desorption temperature and low percentage of water productivity. These limited adsorption capabilities of conventional adsorbent lead to low system performance. The motivation of this work is to synthesis a consolidated composite adsorbent using conventional adsorbent and other highly porous material such as metal organic frame work (MoFs) for a better adsorption capability. The introduction of such materials in adsorption desalination system is expected to significantly improve the performance due to their better adsorption/desorption capacity. Present study introduces three different combination of composite adsorbents synthesised from silica gel and MOFs with poly vinyl pyrrolidine as binder. Silica gel is used as the parent adsorbent in all three combinations. Aluminium fumarate and nickel based MoFs (CPO-27Ni) are used as the secondary adsorbents. Three combination are namely, composite 1 (silica gel and CPO-27Ni MOF), composite 2 (silicagel and aluminium fumarate) and composite 3 (silica gel, CPO-27-Ni and aluminium fumarate). Surface area, pore volume, thermal stability and adsorption capacity of composite adsorbents are evaluated in this study. It is found that the composite 2 gives maximum BET surface area of 590 ± 10 m2/g with a pore volume of 0.279cc/g. It also exhibit superior adsorption capacity than other composite adsorbents. Maximum adsorption capacity of composite 2 is found to be 0.315 kg/kg of adsorbent. Performance evaluation of composite adsorbents in a single bed adsorption desalination system is also included in this study. A single bed adsorption desalination system is designed, fabricated and tested under the meteorological condition of Kollam, Kerala, India. Performance evaluation reveals that the three composite adsorbent can co generate potable water and cooling effect in the adsorption desalination system. At an evaporation temperature of 200 C, composite 2 exhibits comparatively better desalination and cooling effect. Water productivity and coefficient of performance of composite 2 is found to be 1.12 kg/kg of adsorbent and 0.315 respectively. Composite 1 and composite 3 gives moderate or more minor desalination and cooling effect in the system. The yield of adsorption desalination system using composite 2 is found to be 16% higher than that of conventional adsorbent such as silica gel. Results highlight that composite adsorbent composed of conventional adsorbent and MOF can be a potential candidate for adsorption desalination application.