Microwave Hydrothermal Synthesis And Performance Of Chromium-modified Alu Minophosphate Molecular Sieve(CrAlPO-5) Loaded On Alu Minum Foil

The adsorption heat pump combined traditional heat pump with solid adsorbent displays the features of high efficiency,environmental protection and energy saving,which has become a research focus.Aluminum phosphate molecular sieve?AlPO-5?with the characteristics of regular pore structure,large specific surface area,S-shaped water adsorption isotherm and high hydrothermal stability has been considered as a promising candidate for the utilization in adsorption heat pump.Based on time-consuming of traditional hydrothermal synthesis process for AlPO-5,neutral skeleton and low adsorption capacity of the adsorbent,in this paper,we attempted to synthesize chromium-modified alu minophosphate?CrAlPO-5?and CrAlPO-5loaded on alu minum foil using microwave hydrothermal synthesis strategy,and mainly investgated their structures and adsorption/desorption performances.Firstly,CrAlPO-5 molecular sieve was synthesized by microwave hydrothermal method using phosphoric acid,alu minum isopropoxide and chromium nitratesodium as basic materials and triethyla mine?TEA?as template.The factors contain chromium content,TEA/P₂O₅ molar ratio,crystallization temperature and time on crystallization behavior and adsorption property of CrAlPO-5 synthesis process were systematically discussed.Then,with the same molar ratio and synthesis technology,and using CrAlPO-5 as seed crystal,CrAlPO-5 loaded on alu minum foil was in-situ synthesized.The effects of seed coating,crystallization temperature and time on performance of CrAlPO-5 were systematically discussed.The synthetic products were characterized using X-ray diffraction?XRD?,Inductively coupled plasma atomic emission spectrometry?ICP-AES?,Fourier transform infrared spectrometer?FT-IR?,Pore analysis,Scanning electron microscopy?SEM?,and their adsorption and desorption performances were evaluated by static and dynamic adsorption,Thermogravimetry?TG?and Temperature programmed desorption?TPD?.The XRD results indicated that,compared with traditional hydrothermal synthesis,microwave hydrothermal synthesis for CrAlPO-5 significantly shortened crystallization time,and AlPO-5 modified by chromium had no obvious change to the molecular sieve skeleton,but had a better crystal morphology.The optimum preparation conditions were as follow,0.03Cr₂O₃/P₂O₅ and 1.5TEA/P₂O₅ molar ratio,crystallization temperature of 200?and crystallization time of 30 min.SEM images showed that CrAlPO-5 had a regular hexagonal prism shape with about diameter of 3?m and height of 10?m.The pore analysis showed that compared with AlPO-5,CrAlPO-5 with mostly micropore had larger specific surface area and micropore volume.Static adsorption showed that the saturation adsorption capacity of CrAlPO-5 reached to 0.175 g/g,which was nearly 7%higher than that of unmodified AlPO-5.Dynamic adsorption showed that CrAlPO-5 has a typical S-type water vapor adsorption isotherm.XRD results showed CrAlPO-5 loaded on aluminum foil can be in-situ synthesized,and the adsorbent by seed coating had a better crystal morphology and thicker coating thickness?100?m?than that by no seed coating?60?m?.For good thermal conductivity of alu minum foil,the CrAlPO-5 crystallization temperature was slightly reduced?190°C?and the crystallization time was shortened?25 min?.CrAlPO-5 by seed coating had large specific surface area?198.2 m²/g?as well as excellent adsorption capacity?0.197 g/g?.TG and DTG results showed that CrAlPO-5 had a high thermal stability and low desorption temperature?72.8??.TPD analysis results revealed that CrAlPO-5s synthesized by seed coating and no seed coating had near desorption activation energy?100.7 kJ/mol and 93.87kJ/mol,respectively?.It indicates that CrAlPO-5 is one of the ideal heat pump adsorbents.