Kinetics of water adsorption in microporous aluminophosphate layers for regenerative heat exchangers (original) (raw)
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MRS Proceedings, 1991
ABSTRACTAluminophosphate (AlPO4–5, AlPO4–11, AlPO4–17, AlPO4–20) and silicoaluminophosphate (SAPO-5, SAPO- 11, SAPO-17, SAPO-20) molecular sieves of varying pore sizes (3–8 Å) were synthesized and their water adsorption and desorption properties were studied. Water sorption isotherms of AlPO4 molecular sieves were characterized by unusual isotherm shapes, that is, little or no initial adsorption followed by extreme adsorption leading to volume filling by hydrogen bonding and cooperative interaction in micropores, apparently due to the nonpolar nature of pore surfaces coupled with weak (reversible upon evacuation) chemisorption of water, and hysteresis loops extending to very low pressures. Although micropore filling in AlPO2's and isostructural SAPO's was completed almost at the same relative pressure (p/po), SAPO's exhibited less extreme adsorption isotherms as a result of their slightly more polar nature of pore surfaces compared to AlPO4's. Neither AlPO4apos;s nor...
Challenging offers of material science for adsorption heat transformation: A review
Applied Thermal Engineering, 2013
Booming progress in the materials science offers a huge choice of novel porous solids which may be used for adsorption transformation of low temperature heat. This communication gives an overview of original and literature data on several classes of materials potentially promising for this important application, namely, metalaluminophosphates (AlPOs, SAPOs, MeAPOs), metal-organic frameworks (MIL, ISE, etc.), ordered porous solids (MCM, SBA, etc.), porous carbons and various composites (SWSs, AlPO-Al foil). For the SWS composites, we briefly considered the recent trends in their developing, namely, usage of host matrices with uniform pore dimensions and binary salt systems. We hope that this review will give new impulses to target-oriented research on the novel adsorbents for AHT and may also be beneficial for further consolidating international activities in materials science and heat transformation applications.
Synthesis and Characterization of Nanocrystalline Alumino-phosphate AlPO 4-11 Molecular Sieves
2017
Aluminophosphates molecular sieves (AlPO4-11) were synthesized by hydrothermal reaction method. The syntheses were carried out using sealed stainless autoclave. Investigations of the effect of crystallization temperature, ratio of template to phosphoric pentoxide (R/P2O5), pH adjustment of gel solution and other parameters were studied. Characterization of products were carried out using powder X-ray diffraction (XRD), atomic force spectroscopy (AFM), Fourier transform infrared (FTIR), N2 adsorption-desorption BET surface, thermogravemetry (TGA) and scanning electron spectroscopy (SEM). The XRD patterns revealed that the AEL structure is obtained with high crystallinity for AlPO4-11 at crystallization temperature 190 o C. Type of template (R) and ratio of (R/P2O5) showed a great influence on XRD patterns and nano-level of particle size and optimum ratio of 1.1 was established for (R/P2O5) for AlPO4-11. AFM results showed that a nano-level has been got of 95 nm. Mapo-11 synthesized w...
Synthesis novel aluminophosphate molecular sieves at atmospheric pressure
Current World Environment, 2006
Novel small pore aluminophosphates molecular sieves AlPO 4-Atm1, AlPO 4-Atm2 and AlPO 4-Atm3 have been synthesized using hexamethyleneimine template at atmospheric pressure (373K) for the first time. Gel composition Al 2 O 3 : P 2 O 5 : 1.16HEM: 45H 2 O was taken as the standard one which gives AlPO 4-Atm12. Change in water molar ratio to 67.5 gives AlPO 4-Atm2. On changing the aluminium source from catapal B to aluminium isopropoxide in same molar gel composition gives AlPO 4-Atm3. All the materials were characterized by XRD, SEM, TG/DTA, C & N analysis, FT-IR and MASNMR analysis. Elemental analysis shows that Al and P are in equal molar composition. XRD analysis shows that the synthesized samples are highly crystalline and new. SEM shows the morphology change with structure. TG/DTA analysis reveals the presence of maximum four stage elimination of templates. Carbon and nitrogen analysis gives the amount of template present in the sample. 27 Al MASNMR shows the presence of single type tetrahedrally coordinated aluminium atoms in AlPO 4-Atm1. 31 P MASNMR of the same sample shows the presence of two type of tetrahedrally coordinated phosphorous atoms.
Adsorption, 2019
Six samples from the TMPS family of mesoporous silica nano-materials from Taiyo Kagaku Co., Ltd. were studied for their potential as a medium for the adsorption thermal energy storage. Selected specimens are distinguished by their pore size from 1.9 to 4.1 nm and aluminium doping. As the adsorbate for the adsorption pair was selected water with the most advantageous properties of high latent heat and safe chemical properties. The tested materials doped with aluminium show high affinity towards the selected adsorbate and high uptakes. The theoretical storage energy density of the materials spans from 700 to 1700 kJ kg −1 based on the adsorption heat. The storage capacity depends mostly on the pore volume and partially on the pore size. The theoretical estimation shows the temperature gain of the adsorption potential as high as T = 23 • C for the material TMPS-1.5A with the smallest pore diameter and aluminium doping and as low as T = 6 • C for the TMPS-4R with the biggest pore diameter and without aluminium doping.
Microporous and Mesoporous Materials, 2012
A new method to describe the structures of zeolites and related open-framework crystalline solids was developed on the basis of the atom-atom distance matrix (DM). It has been mathematically proved that each such distance matrix corresponds to no more than two different (racemic) structures. For a given structure, the distance matrices for different atom-labeling schemes within a unit cell can be transformed to each other through a matrix transformation, and all these equivalent matrices correspond to the same (or the mirror) structure. A procedure was developed to standardize such representing matrices for each structure, which can be represented as a heat map, the 2-dimensional (2D) barcode or finger print of a structure. With this method, information on the connectivity of the framework atoms in the structure of zeolites or related open-framework crystalline solids was included in the heat map. The structural features of rings, channels, and cages of zeolites and related open-framework crystalline materials can also be recognized in the heat map. The inherent correlation between the structures and their heat maps is discussed. With this new method, the structure of zeolites or related open-framework crystalline solids can be studied by the well developed matrix theory, graph theory, or other mathematic tools.
Energy, 2020
An innovative adsorber plate heat exchanger (APHE), which is developed for application in adsorption heat pumps, chillers and thermal energy storage systems, is introduced. A test frame has been constructed as a representative segment of the introduced APHE for applying loose grains of AQSOA-Z02. Adsorption kinetic measurements have been carried out in a volumetric large-temperature-jump setup under typical operating conditions of adsorption processes. A transient 2-D model is developed for the tested sample inside the setup. The measured temporal uptake variations with time have been fed to the model, through which a micro-pore diffusion coefficient at infinite temperature of 2 EÀ4 [m 2 s À1 ] and an activation energy of 42.1 [kJ mol À1 ] have been estimated. A 3-D model is developed to simulate the combined heat and mass transfer inside the APHE and implemented in a commercial software. Comparing the obtained results with the literature values for an extruded aluminium adsorber heat exchanger coated with a 500 mm layer of the same adsorbent, the differential water uptake obtained after 300 s of adsorption (8.2 g/100 g) implies a sound enhancement of 310%. This result proves the great potential of the introduced APHE to remarkably enhance the performance of adsorption heat transformation appliances.
International Journal of Heat and Mass Transfer, 2003
A selective water sorbent (SWS) is a composite material consisting of a porous host matrix and a hygroscopic substance (commonly an inorganic salt) impregnated into its pores. This work presents an experimental investigation for the kinetics of water vapor sorption on two host materials; namely mesoporous silica gel and alumina in comparison with the two composites SWS-1L and SWS-1A formed by impregnating these two host matrices with CaCl 2 . Moreover, the kinetics of water vapor sorption on microporous silica gel have been also investigated. The measurements have been carried out on 3 g samples of loose pellets on an isothermal wall under three different operating conditions of sorption heat pumps. The results obtained evidence a remarkable increase in the differential water loading of both SWS-sorbents over their host materials. However, and due to the increased diffusion resistance to water sorption resulting from the salt impregnation, the kinetics of water sorption into the host matrices is faster than that into the two SWS-composites. Moreover, SWS-1L is found to be faster than SWS-1A in sorbing water vapor. The differential water loading on microporous silica is about twice that on mesoporous silica and alumina, but the sorption kinetics are a little bit slower.
Angewandte Chemie International Edition, 2010
Microporous crystalline aluminophosphates, an important class of molecular sieves, are of great interest as adsorbents, membrane materials, and heterogeneous catalysts. They are active in, for example, alkene isomerization, catalytic cracking, alkane dehydrogenation, and hydrocarbon oxidation. To expand our understanding of transport mechanisms and diffusion in microporous crystalline aluminophosphates and connect this information to their catalytic and sorption properties, scientists have performed extensive research on large crystals as model systems. For about twenty years it has been known that the properties of large crystals are severely influenced by building defects. For example, Lehman et al. elucidated the internal structure of CrAPO-5 molecular sieves by studying the intracrystalline concentration profiles of probe molecules such as methanol and water by interference and FTIR microscopy. They showed an inhomogeneous distribution of water adsorbed at low pressures in CrAPO-5 and SAPO-5 molecular sieves, attributed to structural defects in the crystals. This work was confirmed by Chmelik et al., who focused on the influence of surface and intracrystalline defects on molecular uptake.
Rapid synthesis and characterization of aluminophosphate molecular sieve: EMM-8
Materials Letters, 2008
The crystallization of microporous aluminophosphate EMM-8 has been investigated under microwave-hydrothermal (M-H) conditions. The crystallization was performed by employing pseudoboehmite and ortho-phosphoric acid as alumina and phosphorous precursors respectively, using 4-dimethylaminopyridine (4-DMAP) as a structure directing agent (SDA). The crystallized phases were characterized by means of X-ray diffraction, scanning electron microscopy (SEM), and N 2 adsorption measurement at 77 K. EMM-8 was achieved within 4 h at 453 K through the formation of AlPO-5 as an intermediate phase. The presence of AlPO-5 phase is judged from SEM studies wherein the presence of crystallization of hexagonal rods, characteristic of AlPO-5 phase is noticed.