Synthesis And Water Sorption Properties Of Aluminophosphate (AlPO4) And Silicoaluminophosphate (Sapo) Molecular Sieves

1991 ◽  
Vol 233 ◽  
Author(s):  
P. B. Malla ◽  
S. Komarneni
Keyword(s):  
Molecular Sieves ◽  
Water Sorption ◽  
Hysteresis Loops ◽  
Sorption Isotherms ◽  
Cooperative Interaction ◽  
Type I ◽  
Relative Pressure ◽  
Micropore Filling ◽  
General Expectation ◽  
Initial Adsorption

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 SAPO's exhibited Brunauer Type I isotherms with water, contrary to a general expectation of the hydrophilic microporous solids.

Water sorption on Ca-saturated clays: II. Internal and external surfaces of montmorillonite

Clay Minerals ◽  
1983 ◽  
Vol 18 (3) ◽  
pp. 289-299 ◽  
Author(s):  
E. C. Ormerod ◽  
A. C. D. Newman
Keyword(s):  
Water Sorption ◽  
Pressure Range ◽  
Sorption Isotherms ◽  
Ageing Process ◽  
Oxide Surfaces ◽  
Relative Pressure ◽  
Plot Analysis ◽  
Sorption Hysteresis ◽  
Water Sorption Isotherms

AbstractWater-sorption isotherms and interlamellar spacings were measured for Ca montmorillonite (from Redhill. UK) over the relative pressure range 1 > P/P0 > 0. By taking account of the change in interlamellar volume with relative pressure, it is shown that internal and external surfaces can be calculated by a modified t-plot analysis. The results also show that sorption on the external surfaces of the montmorillonite is quantitatively similar to that on reference oxide surfaces. Desorption-sorption hysteresis occurred and was apparently caused by an ageing process in which the interlamellar volume increased at the expense of the external surfaces.

Designing Pore-Size in Silica Gels: [H2O] – [TMOS] System

1989 ◽  
Vol 175 ◽  
Author(s):  
H. Kido ◽  
P. B. Malla ◽  
S. Komarneni
Keyword(s):  
Pore Size ◽  
Water Sorption ◽  
Gelation Time ◽  
Sorption Isotherms ◽  
Silica Gels ◽  
Type I ◽  
Microporous Silica ◽  
Molar Ratios ◽  
Type Iv ◽  
Water Sorption Isotherms

AbstractA series of microporous silica gels were synthesized by hydrolyzing tetramethylorthosilicate (TMOS) with varying amounts of water. No catalyst or alcohal was added. The gels were characterized by water sorption isotherms, the BET nitrogen surface area measurements, and differential thermal analysis. Although the gelation time for all H2O/TMOS molar ratios (R) was approximately the same (about 3 hr), the pore-size (pore diameter) and sorption capacity were found to be minimum in the R range 4.96–5.37 but increased with both increasing and decreasing R. Water sorption isotherms measured at 25°C after degassing at 200°C of gels prepared with R = 4.96–5.37 exhibited moderate Type I (Brunauer classification) isotherm which changed to intermediate between Type I and Type IV with decreasing or increasing R. These results indicated that the amount of organic or water which was not utilized in the reaction and the degree of cross-linking apparently played a role for the observed variations in pore-size or shape of water isotherms.

scholarly journals Application of Molecular Sieves for Drying Transformers Insulated with Mineral Oil, Natural Ester, or Synthetic Ester

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1719
Author(s):  
Mateusz Cybulski ◽  
Piotr Przybylek
Keyword(s):  
Molecular Sieves ◽  
Water Sorption ◽  
Sorption Isotherms ◽  
Mineral Oil ◽  
Drying Process ◽  
Insulation System ◽  
Synthetic Ester ◽  
Transformer Insulation ◽  
Natural Ester ◽  
Water Sorption Isotherms

A high level of moisture in the insulation system of power transformers is often the cause of their failure. This can be prevented by drying a transformer in its place of installation. In the article the application of molecular sieves (MS) in the drying process of the transformer insulation system was analyzed. The water sorption isotherms of 3A MS in mineral oil, natural ester, and synthetic ester at 35 °C were determined, which was not described in the literature before. An evaluation of the influence of temperature on the drying dynamics of electro-insulating liquids using MS was also carried out. The drying dynamics were tested at three temperatures, i.e., 35 °C, 50 °C, and 65 °C, which allowed to analyze the effect of temperature on a short-term or continuous drying process. The tests showed that 3A MS’s ability to adsorb water varied depending on the type of electro-insulating liquid. The determined water sorption isotherms, described by means of Langmuir adsorption model, make it possible to calculate the amount of MS needed for drying transformers with different liquid insulation. The research and analyses show the MS’s great potential for the drying of transformer insulation systems.

Evolution of wood cell wall nanopore size distribution in the hygroscopic range

Holzforschung ◽  
2019 ◽  
Vol 73 (10) ◽  
pp. 899-910 ◽  
Author(s):  
Jingbo Shi ◽  
Stavros Avramidis
Keyword(s):  
Cell Wall ◽  
Pore Size ◽  
Size Distribution ◽  
Water Sorption ◽  
Wood Cell Wall ◽  
Sorption Isotherms ◽  
Initial Boundary ◽  
Sorption Mechanism ◽  
Micropore Filling ◽  
Pore Size Distributions

Abstract Owing to technical difficulties, experimental assessment of wood cell wall pore size distribution (PSD) in the hygroscopic range still remains challenging. Here, a “trial-and-error” approach was proposed to calculate such distribution through bridging experimental and simulated sorption isotherms presented by the authors in the past. Two main assumptions were made in the calculations, namely, the generation of new and the swelling of existing cell wall pores during water sorption. The nanopore size distribution of dried cell wall derived from the experimental CO2 gas sorption isotherms was used as the initial boundary condition. Predicted pore size distributions were assessed to be fairly reasonable by comparing them at 95% relative humidity with the PSD of fully saturated cell walls derived from the solute exclusion method. The predicted distribution was relatively wide with several major peaks evolving in the hygroscopic range. The present work also showed that confounded by a wide PSD that includes mostly micropores, the shape of the experimental sorption isotherms was not reliable in assessing the sorption mechanism. The simulations suggested an alternative water sorption mechanism for wood, i.e. micropore filling of cell wall nanopores.

WATER SORPTION ISOTHERMS OF FREEZE DRIED FISH SARDINES

2001 ◽  
Vol 19 (3-4) ◽  
pp. 673-680 ◽  
Author(s):  
S. S. Sablani ◽  
R. M. Myhara ◽  
Mahgoub ◽  
Z. H. Al-Attabi ◽  
M. M. Al-Mugheiry
Keyword(s):  
Water Sorption ◽  
Sorption Isotherms ◽  
Freeze Dried ◽  
Dried Fish ◽  
Water Sorption Isotherms

Water Sorption Isotherms of Pistachio Nuts

LWT ◽  
1996 ◽  
Vol 29 (4) ◽  
pp. 372-375 ◽  
Author(s):  
S. Yanniotis ◽  
I. Zarmboutis
Keyword(s):  
Water Sorption ◽  
Sorption Isotherms ◽  
Pistachio Nuts ◽  
Water Sorption Isotherms

Sorption of Water, Ammonia, Ethyl Chloride, and Methane on Na—X Zeolite and Associated Framework Distortion

1974 ◽  
Vol 52 (22) ◽  
pp. 3699-3706 ◽  
Author(s):  
D. L. Rimmer ◽  
R. McIntosh
Keyword(s):  
Water Sorption ◽  
Room Temperature ◽  
Sorption Isotherms ◽  
Length Change ◽  
Sorption Process ◽  
Ethyl Chloride ◽  
Two Dimensional ◽  
X Zeolite ◽  
Methane Sorption ◽  
Multilayer Formation

Length change and sorption isotherms have been determined for water, ammonia, ethyl chloride, and methane on compacted samples of zeolite NaX. Methane sorption at 0 °C and ethyl chloride sorption at −10°C were accompanied by little or no framework distortion as monitored by length change measurements; sorption of ammonia in the temperature range −50 to −70 °C produced more appreciable distortion; and water sorption at room temperature caused large changes. In each case the framework distortion was correlated with different stages in the sorption process. The sorption isotherms for the ammonia/NaX system indicated the possibility at high uptakes of two-dimensional condensation or multilayer formation. The critical temperature for two-dimensional condensation would be −70 °C.

scholarly journals Thermodynamic properties and moisture sorption isotherms of two pharmaceutical compounds

2018 ◽  
Author(s):  
Amel Zammouri ◽  
M. Ben Zid ◽  
N. Kechaou ◽  
N. Boudhrioua Mihoubi
Keyword(s):  
Experimental Data ◽  
Thermodynamic Properties ◽  
Moisture Content ◽  
Equilibrium Moisture Content ◽  
Water Sorption ◽  
Pharmaceutical Preparations ◽  
Sorption Isotherms ◽  
Integral Enthalpy ◽  
Isotherm Models ◽  
Water Sorption Isotherms

This investigation examines and compares the water sorption isotherms and the thermodynamic properties of two pharmaceutical preparations (Hypril and Azix) intended to be manufactured with the same process plant and equipment. The moisture equilibrium isotherms were determined at 50, 60 and 70 °C using a gravimetric technique. Five isotherm models were explored for their fitting to the experimental data. Azix showed sigmoid type II isotherms while Hypril showed type III isotherms according to the BET classification. All investigated models fitted well the water sorption isotherms of Hypril. By contrast, only GAB and Adam and Shove equations gave appropriate fit to the experimental data of Azix. For both formulations, the isosteric heat and the differential entropy decreased sharply with the increase of equilibrium moisture content to minimum values and thereafter remain constant. In the case of Azix, the integral enthalpy decreased with equilibrium moisture content while the integral entropy increased until reaching a constant value. Contrariwise, Hypril showed decreasing of the integral enthalpy and entropy with the equilibrium moisture content. Keywords: sorption isotherm, enthalpy, entropy, spreading pressure, pharmaceutical formulations  

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