Heat Of Sorption Research Articles

A Unified Model for Gas Transfer in Nanopores of Shale-Gas Reservoirs: Coupling Pore Diffusion and Surface Diffusion

SummaryA model for gas transfer in nanopores is the basis for accurate numerical simulation, which has important implications for economic development of shale-gas reservoirs (SGRs). The gas-transfer mechanism in SGRs is significantly different from that of conventional gas reservoirs, which is mainly caused by the nanoscale phenomena and organic matter as a medium of gas sourcing and storage. The gas-transfer mechanism includes bulk-gas transfer and adsorption-gas surface diffusion in nanopores of SGRs, where the bulk-gas-transfer mechanism includes continuous flow, slip flow, and Knudsen diffusion. First, a model for bulk-gas transfer in nanopores was established, which was dependent on slip flow and Knudsen diffusion. The total gas flux in the bulk phase is not a simple sum of slip-flow flux and Knudsen-diffusion flux but a weighted sum on the basis of corresponding contributions. The weighted factors are primarily controlled by the mutual interaction between slip flow and Knudsen diffusion, which is determined by probabilities between gas molecules colliding with each other and colliding with nanopore surface in this newly proposed model. Second, a model for adsorbed-gas surface diffusion in nanopores was established, which was modeled after the Hwang and Kammermeyer (1966) model and considered the effect of gas coverage under a high-pressure condition. Finally, with the combination of these two models, a unified model for gas transport in nanopores of SGRs was established, and this model was validated through molecular simulation and experimental data. Results show that:Slip flow makes a great contribution to gas transfer under the condition of meso/macropores (pore radius greater than 2 nm) and high pressure. Knudsen diffusion makes an important contribution to gas transfer under the condition of macropores (pore radius greater than 50 nm) and less than 1 MPa in pressure, whereas it can be ignored in other cases. A surface-diffusion coefficient is comparable with a pore-diffusion coefficient, and gas transfer is always dominated by surface diffusion over all the ranges of pressure in micropores (pore radius ≤ 2 nm). Surface-diffusion contribution decreases with an increase in pore size, isosteric sorption heat, pressure, and temperature in SGRs.

Removal of Arsenic (III) from natural contaminated water using magnetic nanocomposite: kinetics and isotherm studies

The application of newly synthesized Fe3O4/TiO2–SiO2 that is modified with zinc (FTSZ) as a sorbent, for the removal of arsenic from contaminated water has been investigated in the present study. SEM, FTIR, XRD, BET, Zeta potential sizer (ξ) analyses are used to determine the sorbent characterization. The effect of the operational parameters such as initial pH, initial concentration, and the contact time were studied. In addition, the equilibrium behavior of FTSZ in As(III) removal was investigated in the temperature range of 20–40 °C. The results showed that the equilibrium data were fitted well with Langmuir than Freundlich isotherm model. The maximum monolayer adsorption capacity estimated by Langmuir isotherm was 24.010 mg g−1. Thermodynamic parameters, ∆H°, ∆S° and ∆G° were also calculated from graphical interpretation of the experimental data. Standard heats of sorption (∆H°) were found to be endothermic and ∆S° values were calculated to be positive for the sorption of As(III) onto the adsorbent.

Effect of kinetics on the thermal performance of a sorption heat storage reactor

To reach high solar fractions for solar thermal energy in the built environment, long-term heat storage is required to overcome the seasonal mismatch. A promising method for long term heat storage is to use thermochemical materials, TCMs. In this research, a lab-scale test thermochemical heat storage system is tested experimentally and modeled numerically. Water-zeolite 13X is used as the working pair in an open packed bed reactor. The purpose of this study is to understand the effects of the kinetic parameters for the adsorption of water vapor on zeolite 13X (2mm spherical beads), on the thermal performance of a sorption heat storage packed bed reactor. A mathematical model is developed incorporating the kinetics model and the isotherm curves and including the heat losses from the side wall of the reactor, and is validated by comparing the calculated temperature profiles with experimental ones from a lab-scale test setup. The numerical and experimental results are used to calculate the heat fluxes in the reactor and are compared to evaluate the thermal performance of the reactor. With the validated model, a parameter study is carried out into the effect of the reaction kinetics and the gas flow rate on thermal performance of a thermochemical heat storage reactor under full scale normal operating conditions. From this work, predictions of the thermal dynamics of an adsorption bed on reactor scale can be achieved, which can and will be used for further studies on the design and optimization of a thermochemical heat storage system.

Preparation and pervaporation performance of chitosan-poly(methacrylic acid) polyelectrolyte complex membranes for dehydration of 1,4-dioxane

Polyelectrolyte complex (PEC) membranes composed of chitosan (CS) and poly(methacrylic acid) (PMAA) were prepared by mixing the polymer solutions in different ratios. The chemical interaction and crystallinity of the resulting PEC membranes were respectively analyzed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD). Differential scanning calorimetry (DSC) was used to characterize the thermal properties of the membranes. The membranes thus obtained were subjected to pervaporation (PV) separation of water-dioxane mixtures. Among the PEC membranes, membrane containing 30 wt% ratio of PMAA (M-3) exhibited the highest separation selectivity of 840 with a flux of 12.07 × 10−2 kg/m2h at 30°C at 15 wt% of water in the feed. By the incorporation of NaY zeolite into PEC up to 5 wt%, we have been able to overcome the trade-off phenomenon existing between flux and selectivity in PV process. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The resulting activation energy values obtained for water permeation (Epw) are much lower than those of dioxane permeation (Epo), suggesting that the developed membranes have higher separation efficiency for water-dioxane system. Based on the heat of sorption (ΔHs) values, the mode of sorption was discussed. POLYM. ENG. SCI., 56:715–724, 2016. © 2016 Society of Plastics Engineers

Sorption charateristics of methane among various rank coals: impact of moisture

Enhanced coalbed methane (ECBM) in deep coal seams is being actively investigated around the world. Since the in situ coal seams are always saturated with water, methane sorption behavior on coal in the presence of water can help accurately assess the amount of recoverable methane. Thus, methane sorption isotherms have been measured on a high-rank anthracite, a low-volatile bituminous, a middle-volatile bituminous and a high-volatile bituminous coal with the manometric technology at 30 °C under six different moisture contents. The Dubinin–Astakhov (D–A) equation was used to fit the experimental sorption isotherm data. In all cases, the moisturized coals exhibited lower sorption capacity than the corresponding dry materials and moisture has a significant effect on CH4 sorption capacity. The maximum sorption capacity, V 0, displays a linear decline with the moisture content for the Changcun and Malan samples, but it is nonlinear for the other two coal samples. The net heat of CH4 sorption, βE, is also reduced by the presence of water, but varies only slightly between a relatively small span of about 8.8 and 10.0 kJ mol−1 for the dry samples studied, despite the difference in coal rank. In addition, the maximum sorption capacity of CH4 in dry coals presents the typical “U-shape” trend with coal rank. Moisture has a greater impact on the sorption capacity in low-rank coals than that in high-rank coals. The mechanisms responsible for the effect of moisture on CH4 sorption among various rank coals are also presented. The pore-blocking effect is the main influencing factor for high-rank anthracite, whereas, the competition sorption is dominant for low-rank coals.

Sorption equilibrium moisture and isosteric heat of adsorption of Chinese dried wheat noodles

Equilibrium moisture content (EMC) data for dried wheat noodles of ten Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C. Five models were fitted to the sorption data, namely the modified Chung Pfost equation (MCPE), modified Henderson equation (MHE), modified Guggenheim Anderson deBoer equation (MGAB), modified Oswin equation (MOE), and a polynomial equation. The best fitting equations were MGAB and the polynomial equation. At a constant ERH, the EMC decreased with increasing temperature, despite the minor effect of temperature on the sorption isotherms of dried noodles. Initially, the isosteric heats of adsorption for dried wheat noodles decrease rapidly with increasing sample moisture content (m.c.); however, after the moisture content is more than 15% of the dry basis (d.b.), they decrease slowly with increasing m.c. The heat of vaporization of Chinese dried wheat noodles approaches the latent heat of pure water at a moisture content of ∼20% d.b., which is ∼2500 kJ/kg. The isosteric heats of sorption of Chinese dried noodles predicted by MCPE and MHE models at lower temperatures were higher than those at higher temperatures. When the equilibrium relative humidity (ERH) is 60%, the safe-storage moisture content of Chinese dried wheat noodles are 11.74% and 11.57% d.b. at 25 °C and 35 °C, respectively. Among ten varieties of dried wheat noodles, the egg-flavoured noodle had the highest onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of gelatinization, but the golden-silk egg noodles had the highest peak enthalpy of gelatinization. The gelatinization To, Tp, and Tc of golden-silk egg noodles were the lowest. Most of the ten varieties of dried wheat noodles demonstrated similar thermal properties and hygroscopic behaviour.

Moisture Adsorption Characteristics of Sandesh Powder

Sorption studies were carried out for sandesh powder at 10, 20 and 40 o C to determine its moisture adsorption characteristics. The adsorption curves obtained were observed to follow a sigmoid shape and corresponds to type II, with a definite inversion due to the temperature effect above 0.79 water activity. The GAB, BET and Caurie isotherm models were attempted to describe the experimental data and were found to give the best fit between experimental and predicted values as indicated by R 2 values. Monolayer moisture content was calculated using the BET and GAB model. Caurie model was used to compute the properties of sorbed water viz., monolayer water, number of adsorbed monolayer, density, and surface area of adsorption in sandesh powder. The net isosteric heat of sorption of water in sandesh powder estimated using Clausius-Clapeyron equation at different moisture contents indicated its strong dependence on moisture content.

Adsorption Studies of Radish Leaf Powder

Radish leaves ( Raphanus sativus ) powder fractions was subjected to moisture adsorption isotherms at different isothermal temperature conditions from 15-45°C with an equal interval of 10°C. The sorption data obtained in gravimetric static method under 0.11–0.90 water activity conditions were subjected for sorption isotherms and found to be typical sigmoid trend. Experimental data were assessed for the applicability in the prediction through sorption models fitting and found that Polynomial and GAB equations performed well over all fitted models in describing equilibrium moisture content – equilibrium relative humidity (EMC–ERH) relationships for shelf stable dehydrated radish leaf powder, over the entire range of temperatures condition under study. The net isosteric heat of sorption, differential entropy and free energy were determined at different temperatures and their dependence was seen with respect to equilibrium moisture content.

Water Sorption Isotherm of Pea Starch Edible Films and Prediction Models.

The moisture sorption isotherm of pea starch films prepared with various glycerol contents as plasticizer was investigated at different storage relative humidities (11%–96% RH) and at 5 ± 1, 15 ± 1, 25 ± 1 and 40 ± 1 °C by using gravimetric method. The results showed that the equilibrium moisture content of all films increased substantially above aw = 0.6. Films plasticized with glycerol, under all temperatures and RH conditions (11%–96%), adsorbed more moisture resulting in higher equilibrium moisture contents. Reduction of the temperature enhanced the equilibrium moisture content and monolayer water of the films. The obtained experimental data were fitted to different models including two-parameter equations (Oswin, Henderson, Brunauer–Emmitt–Teller (BET), Flory–Huggins, and Iglesias–Chirife), three-parameter equations Guggenhiem–Anderson–deBoer (GAB), Ferro–Fontan, and Lewicki) and a four-parameter equation (Peleg). The three-parameter Lewicki model was found to be the best-fitted model for representing the experimental data within the studied temperatures and whole range of relative humidities (11%–98%). Addition of glycerol increased the net isosteric heat of moisture sorption of pea starch film. The results provide important information with estimating of stability and functional characteristics of the films in various environments.

Effect of Temperature on Sorption Isotherms and Thermodynamics of Intermediate Moisture Category Indian Milk Product Cham-cham

Cham-cham, a traditional Indian milk product prepared by heat and acid coagulation of milk, has a shelf life of a few days. Its storage stability could be studied by monitoring the changes in water activity at different temperatures and humidity. Hence, moisture sorption characteristics of cham-cham were determined at three temperatures i.e., 5, 25 and 40C to obtain sorption isotherms. The data obtained were fitted to several models in which BET (Brunauer–Emmett–Teller), Modified Mizrahi and Henderson model gave best fit. From the BET equation, monolayer moisture content calculated at 5, 25 and 40C were 24.27, 15.60 and 18.25%, respectively. Density of sorbed water, number of adsorbed monolayers, percent bound water and surface area of adsorbent were calculated. The porosity of cham-cham increased with increase in temperature. The net isosteric heat of sorption decrease exponentially with increasing moisture content and enthalpy–entropy compensation theory confirmed the process to be spontaneous and enthalpy driven. Practical Applications The equilibrium moisture content, monolayer moisture content, net isosteric heat of sorption and related properties calculated can be used to represent the state of water present in cham-cham at different temperatures for physicochemical and microbiological changes. These results could successfully be utilized in predicting water activity values of cham-cham at different temperature and moisture content. The predicted water activity values may prove successful in studying and enhancing the shelf life of cham-cham by designing the production process and packaging material for cham-cham making and packaging.

Application of soy hull biomass in removal of Cr(VI) from contaminated waters. Kinetic, thermodynamic and continuous sorption studies

Soy hull was evaluated as a new material for Cr(VI) removal from aqueous solutions. Cr(VI) removal was associated to a redox mechanism, in which Cr(VI) was reduced to Cr(III) by the biomass. The redox capacity of soy hull was 1.12mmolg−1. A kinetic model that considers the redox reaction between Cr(VI) and the biomass surface was proposed. The maximum sorption capacity was 7.286mgg−1 at 20°C and pH 1.5. Activation parameters and mean free energies suggest that the sorption process follows a mechanism of chemical sorption. Thermodynamic parameters show that Cr(VI) removal was spontaneous. The isosteric heat of sorption indicated that soy hull has an energetically homogeneous surface. XPS spectra showed that chromium bound on the biomass was Cr(III). These results were confirmed by XANES and EXAFS experiments. EPR spectra showed the presence of Cr(V)-soy hull at short contact time and only a signal corresponding to Cr(III)-soy hull at long contact times. Continuous sorption data were fitted to Thomas and modified dose–response models. The bed depth service time (BDST) model was used to scale-up the continuous sorption experiments.

Experimental and numerical investigations of a zeolite 13X/water reactor for solar heat storage in buildings

This paper addresses the thermal performances of a zeolite-based open sorption heat storage system to provide thermal energy for space heating needs. The study focuses on the experimentation of a significant scale prototype using zeolite 13X/H2O as the reactive pair, and on the development of a 1D mathematical model used to predict both the charging (desorption) and the discharging (adsorption) processes occurring inside the storage unit. The experimental campaigns and the numerical results lead to some promising conclusions on the thermal performances of such a storage unit. With 40kg of zeolite, a temperature lift of 38°C on average at the outlet of each zeolite’s vessel during 8h was achieved during the discharging with an airflow inlet at 20°C, 10g/kg of dry air of specific humidity and a flow rate of 180m3/h. Some discrepancies between the experimental and simulation results were observed during both the charging and discharging tests, and were explained.

Sorption isotherms and thermodynamic properties of grated Parmesan cheese

SummaryThis study focuses on isotherms, isosteric heat of sorption and enthalpy–entropy mechanism of water sorption of grated Parmesan cheese at simulating conditions of storage and drying processes. Isotherms were determined by gravimetric method using different saturated salt solutions. Samples were submitted to different temperatures, and several models were used to fit experimental data, GAB and modified GAB being those which best represented experimental data in all temperature ranges. The isosteric heat of sorption was calculated by Clausius–Clapeyron equation, and higher values of integral isosteric sorption heat were verified for storage temperatures. Besides it, both conditions showed higher values of sorption heat corresponding to low water content. This phenomenon was supported by the enthalpy–entropy compensation study, which demonstrated a higher spontaneity of water sorption for storage temperatures, confirming that the lower the water content of food products is, the stronger the intermolecular bonds of water are.

Sorption isotherms modeling approach of rice-based instant soup mix stored under controlled temperature and humidity

Moisture sorption isotherms of rice-based instant soup mix at temperature range 15–45°C and relative humidity from 0.11 to 0.86 were determined using the standard gravimetric static method. The experimental sorption curves were fitted by five equations: Chung-Pfost, GAB, Henderson, Kuhn, and Oswin. The sorption isotherms of soup mix decreased with increasing temperature, exhibited type II behavior according to BET classification. The GAB, Henderson, Kuhn, and Oswin models were found to be the most suitable for describing the sorption curves. The isosteric heat of sorption of water was determined from the equilibrium data at different temperatures. It decreased as moisture content increased and was found to be a polynomial function of moisture content. The study has provided information and data useful in large-scale commercial production of soup and have great importance to combat the problem of protein-energy malnutrition in underdeveloped and developing countries.

Removal and Recovery of Nickel Ions from Aqueous Solutions using Bacillus Sphaericus Biomass

This paper discusses the biosorption of Ni(II) ions from aqueous solutions by Bacillus sphaericus biomass. The biosorption process was affected by the solution pH, biomass concentration, contact time, temperature and initial Ni(II) concentration respectively. The sorption kinetics and equilibrium data were described well with the pseudo-second order kinetic model and the Freundlich isotherm model. The maximum monolayer biosorption capacity value of Bacillus sphaericus biomass for Ni(II) ions was calculated at 55.55 mg/g using the Langmuir isotherm model. The thermodynamic study shows the Ni(II) biosorption was spontaneous and exothermic in nature. The change in heat of sorption (ΔHo) and the isosteric heat of sorption (ΔHr) values indicate the physical sorption as the predominant mechanism for Ni(II) biosorption. The Ni(II) ions were recovered effectively from Bacillus sphaericus biomass using 0.1 M HNO3 and can be recycled. FTIR results showed that carboxylic and amine groups of Bacillus sphaericus cells were responsible for Ni(II) binding.

Moisture sorption isotherms and heat of sorption of Algerian bay leaves (Laurus nobilis)

The moisture sorption isotherms of Algerian bay leaves (Laurus nobilis) were determined experimentally in this work. The equilibrium moisture contents of the leaves were measured at 40, 50, and 60 °C using static gravimetric method. Six mathematical models were tested to fit the experimental data of sorption isotherms and predict the hygroscopic behavior during storage or drying. Peleg model was found to be the best fitting model for describing the sorption curves. The net isosteric heat of sorption was computed from the equilibrium data at different temperatures by applying the integrated form of the Clausius-Clapeyron equation. The net isosteric heat of sorption is inversely proportional to the equilibrium moisture content and is found to be an exponential function of moisture content.

Development of novel alginate–silica hybrid membranes for pervaporation dehydration of isopropanol

Using a sol–gel technique, organic–inorganic hybrid membranes were prepared by incorporating silica precursors into alginate matrix. Alginate was used as a starting organic polymer, whereas 3-aminopropyl triethoxysilane was used as a counter cation and precursor for the development of inorganic phase. The content of silica gel was controlled by the further addition of tetraethoxysilane (TEOS). The resulting membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. After measuring the swelling data at different mass% of water, membranes were subjected for the pervaporation separation of water–isopropanol mixtures in a temperature range of 30–60 °C. The experimental results demonstrated that membrane containing 30 mass% of TEOS showed the highest separation factor of 17,253 with flux of 4.42 × 10−2 kg/m2 h at 30 °C for 5 mass% of water. Except in pure alginate membrane, the values of total flux and flux of water are found to be almost overlapping, suggesting that the developed hybrid membranes could be effectively used to break the azeotropic point of water–isopropanol mixtures. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The estimated E p and E D values were ranged between 27.84 and 32.63, and 26.98 and 31.28 kJ/mol, respectively. The positive heat of sorption (∆H s) values was observed in all the membranes, indicating that Henry’s mode of sorption is predominant.

Temperature dependence of gas transport and sorption in carbon molecular sieve membranes derived from four 6FDA based polyimides: Entropic selectivity evaluation

Temperature dependences of gas transport and sorption properties on four previously isothermally studied 6FDA based carbon molecular sieve (CMS) membranes: 6FDA/DETDA, 6FDA:BPDA(1:1)/DETDA, 6FDA/DETDA:DABA(3:2) and 6FDA/1,5-ND:ODA(1:1), were examined over the temperature range from 35 °C to 50 °C. The permeability, sorption and diffusivity of these materials are reported, and activation energies of permeation and diffusion as well as heats of sorption for gases CO2, CH4, O2, and N2 of these materials are compared. Permselectivity of these materials at 35 °C was probed for three gas pairs: CO2/CH4, O2/N2, and N2/CH4, and results show that diffusion selectivity is the dominant factor in providing permselectivity. Diffusion selectivity can be factored further into an energetic selectivity and an entropic selectivity. The temperature dependence of both energetic and entropic selectivity and their contributions to overall diffusion selectivity are discussed in detail in this study. All four CMS membranes showed larger than unity entropic selectivity discriminations. 6FDA/DETDA derived CMS membrane, with the most compact structure, showed the largest entropic selectivity for CO2/CH4, O2/N2, and N2/CH4 as about 7.40, 4.24, and 2.17 respectively. Analysis of the selectivity factors provides insights into the effects of polymer precursor backbone structures on key transport and sorption properties in CMS materials.

Assessment of drying temperature of sugarcane bagasse on sorption of reactive blue 5G dye

We studied the effect of drying temperature of sugarcane bagasse (SB) on sorption of reactive blue 5G (RB5G) dye to test whether SB is a suitable biosorbent for industrial dye removal. First we assessed a set of SB characteristics that could influence the sorption capacity of dried biomass. Kinetic drying of the SB biomass was measured at different drying temperatures, ranging from 30 °C to 80 °C. We used a static gravimetric method to perform equilibrium moisture sorption experiments at drying temperatures of 35–65 °C. In addition, we measured activation energy and net isosteric heat of sorption. SB biomass was characterized as a heterogeneous low-porous and hygroscopic material, with a series of functional groups on its surface. A Lewis thin-layer model best represented the kinetic drying data. In addition, moisture diffusion into the SB biomass was characterized by a rate-controlling step in the drying process. Equilibrium moisture sorption data showed the expected effects of temperature controlling the sorption capacity and a multilayer sorption process. A sigmoidal sorption isotherm data was best represented by a BET model. A high energy demand is required for moisture removal from biomass as suggested by the measured isosteric heat of moisture sorption. Drying temperature did not influence the RB5G adsorption capacity of bagasse, therefore any drying temperature in the range of 30 °C to 80 °C could be used to make this material feasible as an industrial adsorbent.

Thermodynamic and surface characterisation of 4-[4-((S)-citronellyloxy)benzoyloxy]benzoic acid thermotropic liquid crystal

ABSTRACTThe inverse gas chromatography (IGC) method was used to obtain thermodynamic and surface properties of the thermotropic liquid crystalline material, 4-[4-((S)-citronellyloxy)benzoyloxy]benzoic acid (CBB). Liquid crystal (LC) selectivity was investigated using the alcohol and acetate isomers by the IGC method at temperatures between 338.2 K and 463.2 K. The retention diagrams of n-decane, undecane, dodecane, tridecane, n-butyl acetate, iso-butyl acetate, ethylbenzene and chlorobenzene on CBB were plotted in the temperature range between 468.2 K and 493.2 K. The specific retention volume, , Flory–Huggins interaction parameter, , equation-of-state interaction parameter, , the partial molar heat of sorption, , the partial molar heat of mixing, , the molar heat of vaporization, and the weight fraction activity coefficient, , were determined.The dispersive component of the surface free energy, , of the studied adsorbent surface was estimated in the infinite dilution region. The specific free energy of adsorption, , the enthalpy of adsorption, and the entropy of adsorption, , of solvents on LC were determined. The values of were correlated with the donor and the acceptor numbers of the probes to quantify the acidic and the basic parameters of the LC surface. The values obtained for and parameters indicated an acidic character for the surface of CBB.