Differential Heat Of Sorption Research Articles

ＣＯ２地中貯留への取組 収着熱測定および｀１´Ｈ‐ＮＭＲ横緩和時間測定による石炭‐ＣＯ２収着の解明

CO2 sorption on coal was estimated by two experiments, one is heat of sorption measurement and the other is 1H-NMR measurement. In the heat of sorption measurement, differential heat of sorption (qd) was compared with the calculated one. Measured qd was same value with calculated one at low pressure. It decreased gradually with pressure and became lower than the calculated one. Since it couldn't be explained by the theory based on physisorption, it is estimated that the coal-CO2 system could not be explained by only simple physisorption.In 1H-NMR measurement, spin-spin relaxation time (T2) and composition fractions of L1, L2 and G were measured. Composition fractions and T2 of L1 increased with CO2 gas pressure. Furthermore, the correlation was observed between volume increments and dissolution amount at over 10 atm. It indicates that part of CO2 sorption capacity was used to coal relaxation.

Thermodynamics of water sorption in clay

Experimental data on desorption isotherms of three types of clay at different temperatures (40, 50 and 60°C) were determined using a static method. The results were fitted by the famous Guggenheim-Anderson-deBoer (GAB) model. The thermodynamic functions, differential heat of sorption, net integral enthalpy and entropy, were evaluated at several moisture contents. Heat of sorption decreased with the moisture content and the trend became asymptotic as the moisture content of 0.01 (d.b.) was approached.

A desorption calorimetric method for use at high water activities

This paper presents a microcalorimetric technique to simultaneously measure water activity and enthalpy of mixing (differential heat of sorption) as functions of composition at high water activities. The instrument consists of a sorption vessel in a double twin microcalorimeter. A sample at high water activity is placed in one chamber of the vessel and an unsaturated salt solution is injected into another chamber. A tube connects the chambers and diffusion will cause the water in the sample to be desorbed and condensed in the salt solution. As the rate of diffusion is high when the sample is at high water activity it is possible to make detailed studies of phenomena taking place at high water activity. The method has been tested on the system dimethyldodecylamine oxide (DDAO)–water.

A desorption calorimetric method for use at high water activities

This paper presents a microcalorimetric technique to simultaneously measure water activity and enthalpy of mixing (differential heat of sorption) as functions of composition at high water activities. The instrument consists of a sorption vessel in a double twin microcalorimeter. A sample at high water activity is placed in one chamber of the vessel and an unsaturated salt solution is injected into another chamber. A tube connects the chambers and diffusion will cause the water in the sample to be desorbed and condensed in the salt solution. As the rate of diffusion is high when the sample is at high water activity it is possible to make detailed studies of phenomena taking place at high water activity. The method has been tested on the system dimethyldodecylamine oxide (DDAO)–water.

Moisture Sorption and the Degree of Starch Polymer Degradation on Flours of Popped and Malted Sorghum (Sorghum bicolor)

Moisture sorption characteristics of flours from malted and popped sorghum (MSF and PSF) were investigated based on results of moisture sorption isotherms at 25 °C and 35 °C and differential heat of sorption. The polymer degradation of flour samples was also investigated. The moisture content for optimum stability of flour samples from popped and malted sorghum lies between 4·6–7·0% under conditions that stimulated distribution and marketing of the products. No marked difference existed between the moisture–starch-binding behaviours of PSF and MSF. Higher polymer degradation was observed in the malted sample than in the popped sample.

THERMODYNAMICS OF MOISTURE SORPTION IN ALFALFA PELLETS

ABSTRACT Experimental data on sorption isotherms of alfalfa pellets were used to determine the thermodynamic functions (differential heat of sorption, spreading pressure, net integral enthalpy and entropy) of the pellets. The thermodynamic functions were then utilized in modeling the specific heats of pellets as a function of moisture content. The estimated values of the thermodynamic functions at different moisture contents confirmed the results of an earlier study on the influence of moisture sorption on the physical integrity of the pellets. The changes in the thermodynamic properties and physical integrity were prominent when the moisture of the pellets were between 0.10 and 0.12 (mass fraction basis). Using the differential heat of sorption, it was determined that alfalfa pellets have higher affinity for moisture uptake when compared to wheat and lentils. The specific heat of the solids of alfalfa pellets had a parabolic relationship with moisture whereas the specific heat of water fraction increased linearly with moisture content of the pellets.

Thermodynamics of Moisture Sorption by the Giant-Timber Bamboo

The thermodynamic interaction of water with giant-timber bamboo (Phyllostachys bambusoides Sieh. & Zucc.) was investigated. Thermodynamic properties were evaluated based on isosteric calculations from sorption isotherms at 20, 30, 40 and 50°C. The results show that. compared to wood, giant-timber bamboo exhibits less hygroscopicity and greater hysteresis. The differential heat of sorption. Q was found to be an exponential function of fractional moisture content, m, and decreased somewhat with increasing temperature. The relation Q s = (Q s ) o exp(-B 1 m) was considered to he reasonably adequate, but a better fit was provided by the equation Q s = A 2 + B 2 m + C 2 exp(-D 2 m) so that it was used in the calculation of the heat of wetting, W, and the integral heat of sorption, (W o - W). The differential heat of sorption at ovendry condition fell within the range observed for wood and other lignocellulosic material, The free energy, G., and the entropy, S., of sorbed water were in close agreement with those observed for wood, reconfirming the theory that definite enthalpy, free energy, and entropy changes accompany the sorption of water by lignocellulosic materials.

Estimation of Humic‐Based Sorption Enthalpies from Nonlinear Isotherm Temperature Dependence: Theoretical Development and Application to Substituted Phenylureas

AbstractThermodynamic assessments of organic chemical‐soil interactions are important for understanding various aspects of sorption phenomena, including isotherm nonlinearity. Expressions were derived here for calculating organic carbon based Freundlich nonlinear sorbed phase partial molar enthalpies (ΔH̄1) and entropies (ΔS̄1) from isotherm temperature dependence. It was shown that, in general, any changes in nonlinearity with temperature must be evaluated when estimating enthalpy effects from isotherm temperature dependence. The results were applied to nonlinear soil sorption data of three substituted phenylurea herbicides between 281 K and 297 K. The ΔH̄1 estimated at 289 K were found to range down to approximately −50 kJ mol−1, and were associated with negative ΔS̄1. Differential heats of sorption, which also include solution phase interactions, were ≈ 10 to 15 kJ mol−1 more exothermic than ΔH̄1. The ΔH̄1 were significantly less exothermic as sorbed phase concentrations increased. For diuron (1,1‐dimethyl‐3‐(3,4‐dichlorophenyl) urea), a compound that displays comparable solubility and octanol‐water partition coefficient as naphthalene, ΔH̄1 at higher concentrations were similar to values estimated for naphthalene (approximately −4 to + 10 kJ mol−1, calculated here from literature data), a nonpolar compound without polar functional groups. The data suggest that specific interactions between the phenylureas and soil organic matter moieties are dominant at low sorbed phase concentrations, but become less important relative to nonspecific London‐van der Waals forces as sorbed phase concentration increases. The urea isotherms are therefore nonlinear, with nonlinearity fundamentally related to the nature of substituted phenylurea sorbed phase interactions.

Moisture Sorption Properties of Collagens Varied in Polarity and Porous Structure by Alkali-Treatment

Moisture sorption properties of steer hide collagen fibers treated with calcium hydroxide were investigated on the basis of sorption isotherm, differential heat of sorption, entropy of moisture sorption, and applicability of isotherm equations to elucidate the difference between untreated and treated collagens in interaction with water molecules. The alkali-treatment resulted in the occurrence of new and more active sorption sites, the increases in both number of free carboxyl and void space of collagen molecules, and also the change to a more disentangled structure. The increase in moisture content and the changes in interactive force between water molecules and various sorption sites of collagens at different ranges of water activity (Aw) were attributed to the changes in number and strength of polar groups and in inner space of collagens due to alkali-treatment. Sorption characteristics of moisture on collagen could well be explained by the strength of interaction of water with collagen and the surface hydrophobicity of collagen. The Henderson and Chung and Pfost equations fitted the moisture sorption isotherms well over a wide Aw range up to 0.90. The large values of constants in the equations to the moisture sorption isotherms of collagens indicated both unstability of the collagen structure to moisture and negative electrification due to polar groups on the surface of collagen.

Calorimetric study on the state of aromatic molecules sorbed on silicalite

Differential heats of sorption have been determined calorimetrically for benzene, toluene, ethylbenzene, and p-xylene on silicate as a function of pore filling. In all cases abrupt changes in the state of the sorbed molecules are observed when the amount sorbed exceeds 1 molecule per 1/4 unit cell. While in the case of benzene, toluene, and ethylbenzene sorbate-sorbate interaction occurs only above 1 molecule per 1/4 unit cell, the sorbed p-xylene molecules interact with each other below this loading.

Sorption equilibrium of a solid desiccant felt and the effect of sorption properties on a cooled-bed desiccant cooling system

The equilibrium sorption isotherms of a silica gel matrix manufactured in the form of a desiccant felt are experimentally determined as a function of temperature and relative humidity. Using the data, the differential heat of sorption and the integral heat of wetting are calculated. These results then are used as property data in a numerical model of the nonlinear heat and mass transfer processes that occur in a cooled-bed, desiccant dehumidifier which is the principal component of a low temperature (i.e. typically 60–65°C) thermally activated desiccant cooling system. Using the numerical model, the effect of variations in the equilibrium isotherm shape and the heat of sorption on the performance of the desiccant cooling system are also documented.

Ion-exchange sorption of singly charged organic cations on cross-linked carboxylic cation-exchangers

1. A method is proposed for studying the sorption of organic ions on cross-linked polyelectrolytes; this is based on an analysis of the variation of the differential heat of sorption and the concentration exchange constant under alteration of the degree of filling of the sorbate with the organic ion. 2. A study has been made of the differential and integral thermodynamic functions for the sorption of Novocaine, Oleandomycin, and tetracycline on Biocarb, a carboxylic cation-exchanger. 3. Estimates of the enthalpy of sorption in these systems have been made on the basis of an electrostatic model for sorbent-sorbate interaction. Evidence indicating that this is a type of ion-ion interaction at low degree of sorbent filling has been obtained. 4. The concentration ion-exchange constant for sorption from aqueous solution increases at high degree of sorbent filling (positive cooperative effect). For sorption from methanol solution, the concentration constant and the differential heat of ion exchange remain constant over the entire range of sorbent filling by the organic ion.

Study on the Heat of Wetting of Starch

AbstractThe integral heat and the differential heat of sorption have been calculated from the heat of wetting of starch and informations related to the structure of starch and to its affinity for water are given. The relationship between the moisture content and the heats o f wetting of the starches decrease exponentially with increasing of sorption water. The heats of crystallinization of the starches of tubers and roots are lower than those of cereal starches. The crystallinity depending on the integral net heat of sorption of dry corn starch is the same as that of wheat, higher than those of sweet potato and tapioca, and lower than that of cellulose. The differential net heat of sorption shows two proportional decays according to the increasing amount of moisture.

The sorption of krypton and xenon in zeolites at high pressures and temperatures I. Chabazite

Isotherms of Kr and Xe in chabazite have been obtained for absolute sorption and for Gibbs excess sorption, in the temperature range 150 to 450 °C and at pressures up to 100 atm. Thermodynamic equilibrium constants for distribution of gas between the crystals and the gas phase, standard state concentrations and heats of sorption have been determined. At the highest pressures differences between absolute sorption and Gibbs excess sorption were large. The change of equilibrium fugacity with temperature for given absolute and Gibbs excess sorptions yielded two differential heats of sorption and two differential entropies of the sorbate. These heats, and the corresponding entropies, differed numerically and in their dependence upon amount sorbed. The thermodynamic relationship between the two heats has been derived and discussed.

Temperature and Moisture Regain Changes of Textiles During Vacuum-Steaming

A report is given of temperature and regain changes which occur during steaming of a mass of hygroscopic textile fibers held in an initially evacuated chamber. The experimental measurements for wool are compared with values of temperature and regain calculated by Nordon and Haly. Similar calculations are carried out for cotton and are compared with experimental measurements. When the initial regain of the textile is low, the temperature of the mass of fibers during steaming rose to a value considerably in excess of the steam temperature (because of the effect of heat of sorption). At higher initial regains, the fiber temperature during steaming was equal to the steam temperature. The accuracy of the theoretical calculations is discussed in terms of the accuracy of the data used, viz, sorption isotherms for wool and cotton at elevated temperatures, specific heats, and differential heats of sorption for these fibers.

11—THE HEATS OF SORPTION OF CELLULOSIC FIBRES DEDUCED FROM CALORIMETRIC MEASUREMENTS

An absorption theory of the type proposed by Peirce suggests that between the heats of wetting (qc ) of cellulosic fibres conditioned by absorption from dryness and the regain (c) to which they have been conditioned, there should be simple relationships of the form qc = q 0 exp (−αc) An analysis of published data confirms that such relationships exist and shows that the variation of α from fibre to fibre is such as to suggest real differences between the differential heats of sorption of the fibres, although it is pointed out that this does not necessarily imply differences in the energies of the cellulose–water bonds. The variation of α for the fibres studied at 25°C is described closely by an equation of the form 100α = a 0 – a 1 q 0 – a 2 q 0 2 in which the total heat of wetting (q 0 is the only variable between the fibres.

Correlation between Initial Young's Modulus and Differential Heat of Sorption at Zero Regain for Cellulosic Fibres

DERIVATIONS of the differential heat of sorption of dry textile fibres (ΔH0) from measurements of heat of wetting have yielded values which are approximately equal for the cellulosic fibres (c. 250–300 cal./gm.). This has been taken to imply that the type of reaction, that is, hydroxyl bonding with water, is similar for all cellulosic fibres, and that varying hygroscopicity is dependent on the relative amount of material within the fibre which is available for moisture sorption1–4.