Heat Of Desorption Research Articles

Calorimetric approach to understand pH and salt influence on the adsorption mechanism of lysozyme to a traditional cation exchanger

Built upon our interest in illustrating the complexity of protein adsorption onto chromatographic supports and to understand the rule of nonspecific interactions in the ion exchange adsorption process, a traditional model system (lysozyme – carboxymethyl cellulose) was used to determine the charge influence during biomolecule adsorption. Flow microcalorimetry (FMC) was exploit as a dynamic technique that provides adsorption and desorption heat signals for a specific system, permitting an improved understanding of the driving forces and mechanisms involved during the interaction. For this purpose, measurements were made at pH 8 at both absence and presence of salt (NaCl 50 mM) and compared with previous studies performed at pH 5. Distinct FMC profiles were observed regarding pH. For most of the experiments, two exothermic heat signals are observed at pH 8 while at pH 5 one endothermic and one exothermic peak are shown. This difference was justified with a less energy demanding for desolvation at pH 8. Lysozyme adsorption was shown to be a multi-step process involving desolvation, primary protein adsorption and secondary adsorption after reorientation with distinct contributions to the overall energy. At pH 8, the exothermic contribution to the adsorption process is lower compared to pH 5, which is justified by the lower charge density that lysozyme presents at pH 8 compared to pH 5.

Rate-based simulation and techno-economic analysis of coal-fired power plants with aqueous ammonia carbon capture

Ammonia is a promising solvent for the chemical absorption of carbon dioxide owing to its characteristics of low toxicity, low degradation, low cost, and low heat of desorption. The present work evaluates the energy and economic performances of the aqueous ammonia technology applied to a coal-fired power plant. First, the kinetics of absorption are characterized in the Aspen Plus software and are calibrated against the experimental data from the Munmorah pilot plant. Then, the validated model is used for sizing the full-scale plant columns and for simulating the overall capture plant. After determining the sizes of the plant components and their energy consumptions, the capture plant is integrated with the coal-fired power plant, and the economic analysis is assessed with both retrofitted and green-field approaches as described in reports from the European Benchmarking Task Force and the United States National Energy Technology Laboratory, respectively. The novelties presented here are the new approach in the absorption reactions implemented in the rate-based model, which changes the dependency of the ammonia concentration in the absorption process, as well as the full economic analysis with both retrofitted and green-field assumptions, which enable a sound comparison of the outcomes. The results with the retrofitted approach compared with the monoethanolamine case of the European Benchmarking Task Force report returned higher electric efficiency (36.3% versus 33.50%), lower levelized cost of electricity (87.66 €/MWhel versus 92.27 €/MWhel), and lower cost of carbon dioxide avoided (47.03 €/tonCO2 versus 51.62 €/tonCO2). The results using the green-field approach compared against the Cansolv case of the National Energy Technology Laboratory report returned higher electric efficiency (33.06% versus 32.50%), lower cost of electricity (124.3 $/MWhel versus 133.2 $/MWhel) and lower cost of carbon dioxide avoided (66.5 $/tonCO2 versus 75.25 $/tonCO2). In both comparisons, aqueous ammonia had appreciably better performance than the ammine reference cases.

The determination of isosteric heats of sorption of leather: Experimental and mathematical investigations

Knowledge of sorption isotherms of leather products is necessary to control rehydration/dehydration and storage processes and it is valuable tool for prediction of the stability and shelf life of products but the impact of the controlled climate on moisture sorption isotherms of leather remains unclear. The aim of this work is to predict moisture desorption isotherms of leather of bovine variety. The static gravimetric method was used to determine sorption isotherms at four temperatures (30, 40, 50 and 60 °C) and the equilibrium moisture content of leather samples was measured within the range of 5–90% relative. All the curves exhibited type II behavior, according to Brunauer’s classification. Equilibrium moisture contents are observed to drop as the temperature is enhanced. Many models available in the literature were used to describe the experimental data. The agreement between experimental and calculated sorption isotherms is seen to be satisfactory (correlation coefficients from 0.93 to 0.99). Furthermore, DENT model is found to be the most appropriate for describing the relationship between the equilibrium moisture content, the water activity and temperature. On the other hand, the isosteric heats of desorption were determined from sorption isotherms and then correlated with corresponding equilibrium moisture contents. Besides, the isosteric heats of desorption decreased continuously with increasing of the equilibrium moisture content.

Design and experimental study of a small scale adsorption desalinator

Adsorption desalinators produce potable water from seawater using low-grade heat at 50–90 °C. The technology has been proven using several experimental systems, but their sizes are too large to allow efficient further development by testing novel adsorption materials and components. In this study, we introduce the world’s most compact adsorption desalinator with a bed size of 0.2 kg silica gel. The system achieves a Specific Daily Water Production of 7.7 kgwater per kgsilica-gel and day. The performance is comparable to the best performing system to date proving that the downscaling is not detrimental. Moreover, the tests demonstrate the benefits of simple heat integration between the adsorber beds, which reduces energy consumption by 25% and increases the Performance Ratio to 0.6. The importance of heat integration is further highlighted in an unprecedented thermal response experiment, which evaluates the partition of energy input in terms of sensible heat and heat of desorption.

Energy storage analysis of CO2 in MOF-74 and UIO-66 nanoparticles: A molecular simulation study

Adding porous nanoparticles into fluid can modify the energy storage properties of working fluid in the thermodynamic cycles. The adsorption capacity and thermal energy storage of CO2 in MOF-74 and UIO-66 at different temperatures and pressures are investigated in this paper via molecular simulations. The results denote that the adsorption of CO2 in the two studied metal organic frameworks (MOFs) differ from each other due to the different structures. The adsorption capacity of CO2 in MOF-74 is larger than that in UIO-66. However, the desorption heat of CO2 in MOF-74 is lower than that in UIO-66. Also, UIO-66 impacts more than MOF-74 on the thermal energy storage property of CO2.

Water sorption properties, diffusion and kinetics of zeolite NaX modified by ion-exchange and salt impregnation

Zeolite NaX is one of the most popular water sorption materials for dehumidification, thermal energy storage and sorption cooling. In this paper, zeolite NaX is modified by magnesium chloride to achieve ion-exchange (zeolite NaMgX) and salt impregnation (zeolite NaX/MgCl2) with the aim of improving water sorption capacity and thermal performance. The pore structure, desorption heat, water equilibrium sorption property, adsorption kinetics and cycling stability of zeolite NaX, NaMgX and NaX/MgCl2 were studied to evaluate their potential for sorption application. Experimental results show the zeolite NaMgX has stronger hydrophilic and can improve the water sorption capacity from 0.17 g/g to 0.20 g/g at 2500 Pa. The zeolite NaX/MgCl2 with 12.6 wt% salt confined inside the meso-/macro-pore, can improve the water sorption capacity from 0.17 g/g to 0.26 g/g with sorption heat of 842 J/g. The sorption rate of zeolite NaX/MgCl2 is much lower than that of pure zeolite NaX, while zeolite NaMgX has a slight lower sorption rate than pure zeolite NaX. The diffusivity of zeolite NaX is in the range of 8.03 × 10−10–1.97 × 10−9 m2/s at 1000–2500 Pa, while zeolite NaMgX and zeolite NaX/MgCl2 have diffusivities in the range of 5.22 × 10−10–1.73 × 10−9 m2/s and 3.76 × 10−10–9.87 × 10−10 m2/s respectively. The diffusivities of different zeolite samples increase with temperature which can be described by activated energy factor, and the relation between diffusivity and pressure is strongly coupled with the equilibrium equation. The modified zeolites have good thermal stabilities and no obvious uptake loss after ten adsorption-desorption cycles, making them feasible, scalable and economical for sorption thermal energy storage and cooling applications.

Thermodynamic and kinetic properties of NH3-K2CO3-CO2-H2O system for carbon capture applications

An innovative solvent based on the quaternary system CO2-NH3-K2CO3-H2O is reported and characterized in terms of its thermodynamic properties and rate of CO2 absorption. Thermodynamic properties of the solvent such as vapor-liquid equilibrium, solid-liquid equilibrium, and the heat of desorption were modelled with the Extended UNIQUAC thermodynamic model. The kinetics of CO2 absorption in the solvent were studied experimentally with a wetted wall column set-up. The absorption rate was investigated with respect to temperature, ammonia concentration, potassium carbonate concentration, and CO2 loading, under the typical operating conditions of a capture plant. Globally, the solvent has a number of interesting properties for CO2 capture applications. Indeed, adding K2CO3 to the ammonia solvent reduced both the ammonia slip and the heat of desorption. Experimental analysis showed that the kinetics of absorption were mainly influenced by the reaction between free ammonia and CO2. Hence, the overall mass transfer coefficient decreased when increasing the K2CO3 content of the solvent.

HPLC QUANTIFICATION OF LACTOPEROXIDASE IN THERAPEUTIC DAIRY WASTE ENRICHED BY BUBBLESEPARATION

Objective: The objective of this study was to enrich therapeutic proteins and remove pollutants from dairy wastewater for establishing foam fractionation as a lucrative unit operation.
 Methods: Dairy wastewater collected from dairy industry was processed to fat-free dried protein waste mass diluted to 1-liter feed by distilled water in different concentrations and foam fractionated by sodium dodecyl sulphate (surfactant) to enriched proteins extract (foamate) in a foam fractionator. Foamate were analysed to quantify total proteins and lacto peroxidase respectively. The efficiency was evaluated by varying parameters like pH, initial waste and ionic concentrations, the waste-surfactant mass ratio of feed and flow rate of gas (N2) through feed solution by several experiments. Heat of desorption (λ) and mass transfer coefficient (K) were determined as indicators of adsorptive bubble separation to foam phase governed by Gibb’s equation of adsorption isotherm.
 Results: The process was optimized at pH 5.5, initial feed concentration 500μg/ml, waste–surfactant mass ratio (1.5:1), gas flow rate (350 ml/min) and ionic concentration 0.1 gram-mole of NaCL per litre of feed with enrichment factor (49.09), percent recovery (98.18%) observed in foamate. One natural preservative specifically lactoperoxidase was quantified by RP-HPLC analysis as 0.49% (w/w) of total proteins at optimal condition. Heat of desorption(λ), mass transfer coefficient(K)were determined 3140cal/mol and 12.68* 10-9 mol/cal/cm2/s respectively at pH 8.5, initial feed concentration 500μg/ml and gas flow rate 350 ml/min.
 Conclusion: The method may be a useful unit operation for recovery of biomolecules and removal of toxic pollutants from industrial wastewater for coming days.

Study on the moisture adsorption isotherms and different forms of water for lignite after hydrothermal and thermal upgrading

Lignite has a high moisture content and needs to be dewatered before use. However, dewatered lignite will readily reabsorb moisture due to its unique physicochemical structure. In this work, a typical Chinese lignite was hydrothermally upgraded at 150–300 °C and thermally upgraded at 200–500 °C before analysing its moisture readsorption properties. The modified Brunauer, Emmett and Teller (BET) model was applied to analyse the moisture adsorption isotherms of lignite. Different forms of water were determined by thermogravimetry coupled with differential scanning calorimetry (TGA-DSC). With increasing upgrading temperature, the primary and secondary adsorption contents of lignite decreased constantly for both hydrothermal and thermal upgrading. At the same upgrading temperature, hydrothermal upgrading was more effective in lowering the primary and secondary adsorption contents. Three forms of water were distinguished in lignite. The sequence of desorption heat was molecular water > capillary water > free water, while the sequence of water content was free water > molecular water > capillary water. With increasing upgrading temperature, the free water content first increased slightly and then decreased significantly, while the capillary water content and molecular water content decreased continuously. Hydrothermal upgrading was more effective than thermal upgrading in inhibiting the moisture readsorption of lignite.

Desorption isotherms and isosteric heat of anaerobic fermentation residues

Abstract This paper presents the equilibrium desorption isotherms and the isosteric heat of sorption of a mixture containing mechanically dewatered fermentation residue (obtained from a blend of chicken, swine and cattle manure) used in biogas plants and corn spoiled silage in a ratio of 2:1. The moisture desorption isotherms of the fermentation residue were determined at 32 °C, 40 °C and 80 °C and in the relative humidity range of 0.057 / 1 using static gravimetric method. Mathematical equations were used to analyze the desorption data of Modified Henderson, Modified Halsey, Modified Oswin, Modified Chung–Pfost and Modified GAB models. The constants of the model equations were calculated by non-linear regression analysis. The Modified Henderson model fitted to the desorption isotherm data well. Using the proposed function, the final moisture content of the material can be determined as long as it can be dried in infinite time with the drying gas in the given conditions. The isosteric heat of desorption was calculated by using the Modified Henderson model in the studied temperature range based on the Clausius–Clapeyron equation. The isosteric heat varied between 46 kJ·mol−1 and 67 kJ·mol−1 at moisture levels 1.91

Moisture Sorption Isotherms and Isosteric Heats of Sorption of High-Pressure Treated Paulownia Wood under Different Storage Conditions

Abstract. Understanding of moisture sorption isotherms (MSI) is critical for predicting the stability of wood during handling, transport, and storage. The aim of this study was to evaluate the adsorption and desorption isotherm characteristics of high-pressure (HP) treated paulownia wood and to identify the best-fitting model to describe its sorption behavior. The equilibrium moisture contents (EMCs) of HP-treated paulownia wood were obtained using a static gravimetric method under different storage conditions: three temperatures (20°C, 30°C, and 40°C) and five water activity (aw) levels (0.32 to 0.95). Results showed that HP parameters did not significantly affect the MSI trend of treated groups. Eight modified models (modified Chung-Pfost, modified Henderson, modified Oswin, modified Halsey, Chen-Clayton, Guggenheim-Anderson-de Boer (GAB), simply modified GAB, and Peleg) were fitted to the experimental data. The Chen-Clayton model (temperature-dependent) produced randomized residuals and the best prediction performance for both adsorption and desorption among all models. Net isosteric heat of adsorption and desorption decreased from 7.55 to 4.84 kJ mol-1 and from 18.1 to 12.2 kJ mol-1, respectively, with an increase in EMC from 7.5% to 10%. The isosteric temperature (Tß) was 352 K for adsorption and 335 K for desorption, between which all the adsorption and desorption reactions proceeded at the same rate. All thermodynamic functions were adequately characterized by a power law model. Keywords: Equilibrium moisture content, High-pressure treatment, Modeling, Moisture sorption isotherm, Paulownia wood, Temperature, Thermodynamic analysis.

Moisture sorption isotherms of sunflower seeds: Thermodynamic analysis

ABSTRACT The study of the thermodynamic properties provides the knowledge of the sorbent affinity by the water and the spontaneity of the sorption process, important to design drying equipment and to predict hygroscopic behavior during storage. This work aimed to determine and evaluate isotherms of hygroscopic equilibrium and thermodynamic properties for different equilibrium conditions (water contents and temperatures) in sunflower seeds, using the indirect static method. Sunflower seeds with initial water content of 0.164 (decimal, dry basis - d.b.) were used. Fifteen mathematical models were tested for hygroscopic equilibrium modeling, and the Smith model presented the best fit. It was verified that the thermodynamic properties were influenced by the water content, the integral isosteric desorption heat increased with the decrease of the equilibrium water content, ranging from 1.787 to 2.670 kJ kg-1 to 0.198 to 0.0518 (decimal, d.b.), respectively, the desorption process of the sunflower seeds was controlled by the enthalpy and the Gibbs free energy, which varied from 3.6363 to 200.1730 kJ kg-1, was positive for the temperatures studied, with increase to during the desorption process, proving to be a non-spontaneous process.

Control of the NO–NH3 SCR Behavior of Cu-ZSM-5 by Variation of the Electronic State of Copper

The effect of NH4OH/Cu2+ in a copper-acetate solution on the properties of ion-exchanged Cu-ZSM-5 catalysts in the selective catalytic reduction of NO by NH3 (NO–NH3 SCR) has been studied. The temperature programmed desorption of ammonia (NH3-TPR) on Cu-ZSM-5 and the ammonia adsorption–desorption dynamics at 75–300 °C were studied to identify and quantify the nature of acid sites and ammonia desorption heat of Cu-ZSM-5. The Cu-ZSM-5 catalysts containing Cu-structures with extra-lattice oxygen were active in the low-temperature SCR, whereas those with isolated Cu2+ ions were active in the high-temperature SCR. It was shown that Cu-structures with extra-lattice oxygen were generated during the ion exchange of H-ZSM-5 with a water-ammonia solution of copper-acetate where the NH4OH/Cu2+ ratio was in the range of 6–15. Isolated Cu2+ ions were produced in the ion-exchange mode with the ammonia-free solution.

CO2 capture from lime kiln using AMP-DA2MP amine solvent blend: A pilot plant study

This experimental study covered pilot plant analysis of novel AMP and 1,5–diamino–2–methylpentane (DA2MP) amine solvent blend for CO2 capture from a lime kiln. The gas flow rate (F(GAS)), amine solution flow rate (F(amine)), CO2 concentration and reboiler temperature (T(REB)) were kept at 14 SLPM, 50 mL/min, 30 vol.% CO2 (N2 balance) and 120 °C respectively. The AMP concentration was kept at 2 kmol/m3 while DA2MP was varied from 1.5 kmol/m3 to 2 kmol/m3. The MEA and AMP-DA2MP comparative analysis was based on rich amine loading (αrich, mol CO2/mol amine), lean amine loading (αlean, mol CO2/mol amine), cyclic loading (CL, mol CO2/mol amine), cyclic capacity (CC, mol CO2/L–amine soln.), CO2 absorption rate (rabs, g–CO2/hr), CO2 absorption efficiency (%), regeneration energy (Qreg, GJ/tonne CO2), absorber overall average volumetric mass transfer coefficient (KGav(ave), kmol/kPa.hr. m3), desorber mass transfer coefficient (KLav, hr–1), initial amine solution utilized (Aminesoln._utilized, g-amine soln./g-CO2) and initial amine solution cost (US$/g-CO2). The influence of sensible energy (Qsen, GJ/tonne CO2), vaporization energy (Qvap, GJ/tonne CO2), and desorption heat (ΔHdes, GJ/tonne CO2) towards regeneration energy (Qreg) was also examined. Results showed that the AMP-DA2MP blend possesses higher CO2 absorption efficiency (up to 36.17%), higher KGav(ave) (up to 65.85%), higher KLav (up to 28.29%) and lower Qreg (up to 32.54%) compared to the single solvent MEA. Also, MEA possessed higher initial amine solution utilized (28.86%) and lower initial amine solution cost (28.5%) compared to the AMP-DA2MP blend. This is an initial revelation that AMP-DA2MP can provide cost-effective CO2 capture from a lime kiln.

Isotherms and Isosteric Heat Desorption of Hymenaea stigonocarpa Mart. Seeds

The Brazilian Cerrado is one of the most important ecosystems and due to the extractivism it is necessary to recover the degraded areas. The tree of Hymenaea stigonocarpa Mart. is used in this reforestation system, so the study of post-harvest management of the seed is necessary for the propagation. The objective of this work was to determine the isotherms and the isosteric desorption heat of Hymenaea stigonocarpa Mart. Seeds, and to test the methodology of the Akaike’s information criterion (AIC) and Schwarz’s bayesian information criterion (BIC) for the choice of the best mathematical model. Different mathematical models were fitted to the experimental data and the model that best represents the phenomenon was selected, from the statistical parameters. To obtain the equilibrium moisture content was used static method using desiccants in incubators cameras with control of relative humidity by salt solution. The Oswin Modified model obtained better results according to analyzed parameters, being this model the one selected for prediction of the hygroscopic balance of the Hymenaea stigonocarpa Mart. seeds. It was found that the higher the temperature for the same equilibrium moisture content, the higher the water activity values. The AIC and BIC methodology contributed to the choice of the best mathematical model to predict the hygroscopicity phenomenon. The isosteric heat increased with the decrease in the equilibrium moisture content requiring a greater amount of energy to remove water from the seeds.

Evaluation of the Roles of Absorber and Desorber Catalysts in the Heat Duty and Heat of CO2 Desorption from Butylethanolamine–2-Amino-2-methyl-1-propanol and Monoethanolamine–Methyldiethanolamine Solvent Blends in a Bench-Scale CO2 Capture Pilot Plant

The performance of a novel bi-blend butylethanolamine (BEA)–2-amino-2-methyl-1-propanol (AMP) solvent developed from an earlier work using a semi-batch method was validated in a bench-scale CO2 capture pilot plant in terms of its CO2 capture performance criteria compared to the benchmark 7 M monoethanolamine (MEA)–methyldiethanolamine (MDEA) solvent blend. Also, the synergistic benefits provided by placement of a solid acid catalyst (HZSM-5) in the desorber column and a solid base catalyst (K/MgO) used for the first time in the CO2 absorber column were evaluated. In addition, a process method was developed to use the pilot plant to determine, for the first time, the intrinsic heat of CO2 desorption from BEA–AMP and MEA–MDEA blends (or any solvent), without making any assumptions and/or reference to the heat of CO2 absorption. The results showed that all of the performance parameters for the novel 4 M BEA–AMP bi-blend were tremendously better than those of the 7 M MEA–MDEA bi-blend for both catalytic and n...

A comparative study of novel activated AMP using 1,5-diamino-2-methylpentane vs MEA solution for CO2 capture from gas-fired power plant

Bench-scale pilot plant study of AMP and 1,5-diamino-2-methylpentane (DA2MP) blend for CO2 capture from gas-fired power plant is investigated. The concentration of the amine blend is 2 kmol/m3 AMP-1.5 kmol/m3 DA2MP while that of single solvent MEA is 5 kmol/m3. Comparative analysis was based on CO2 absorption efficiency (%), absorber mass transfer coefficient (KGav(ave), kmol/kPa h m3), desorber mass transfer coefficient (KLav, h−1), rich amine loading (αrich, mol CO2/mol amine), lean amine loading (αlean, mol CO2/mol amine), cyclic loading (CL, mol CO2/mol amine), cyclic capacity (CC, mol CO2/L-amine soln.), CO2 absorption rate (rabs, g-CO2/h), and regeneration energy (Qreg, GJ/tonne CO2). The contribution of sensible energy (Qsen, GJ/tonne CO2), vaporization energy (Qvap, GJ/tonne CO2), and desorption heat (ΔHdes, GJ/tonne CO2) towards Qreg was also investigated. Results showed that the AMP-DA2MP blend possess higher KGav(ave) (11.66%), KLav (7.67% higher), and CO2 absorption efficiency (4.66% higher) than MEA. Also, the superior cyclic loading (51.5%) and cyclic capacity (6.7%), and lower regeneration energy (13.8% lower) was observed for the AMP-DA2MP blend. The desorption heat (ΔHdes) was the major contributor to the Qreg of both amine systems however the ΔHdes of AMP-DA2MP was 23% lower than MEA. It was noticed that though the water concentration of the amine blend (60.7 wt%) is lower than MEA (70 wt%), the vaporization energy of the amine blend was 32.9% higher than MEA. Therefore, besides the amount of water concentration, higher desorber temperature profile, amine solvent vapor pressure and boiling point also increases the vaporization energy. The results is a revelation of possible reduction in capital cost and operating costs for the AMP-DA2MP blend compared to the standard MEA.

Analysis of adiabatic heat and mass transfer of microporous hydrophobic hollow fiber membrane-based generator in vapor absorption refrigeration system

A microporous hydrophobic hollow fiber membrane-based generator (HFM-G) is expected to be an alternative type of generator in vapor absorption refrigeration system, which can be compact and lightweight with the enhanced heat and mass transfer. This paper pursues a comprehensive understanding of a detailed desorption mechanism of the proposed HFM-G, and suggests the feasible configuration for the practical use. A theoretical HFM-G mechanism is first introduced to gain an understanding of the adiabatic heat and mass transfer. A gas permeation test determines the nominal pore size of the membrane, which characterizes the mass transfer across the membrane. Transient experiments demonstrate the characteristics of the adiabatic desorption process on the HFM-G for wide range of feed solution concentrations under various practical operating conditions. A comparison shows that the experimental heat and mass transfer results are consistent with the theoretical values of adiabatic desorption heat and mass transfer on the HFM-G.

Thermal Energy Storage of R1234yf, R1234ze, R134a and R32/MOF-74 Nanofluids: A Molecular Simulation Study.

Thermal energy storage can be carried out by working fluid adsorbing and desorbing in porous materials. In this paper, the energy storage properties of four refrigerants, R1234yf, R1234ze, R134a and R32, with M-metal organic framework (MOF)-74 (M = Zn, Ni, Mg, Co) nanoparticles are investigated using molecular dynamics simulations and grand canonical Monte Carlo simulations. The results show that M-MOF-74 can adsorb more R32 and R134a than R1234yf and R1234ze, as the molecular structures of R32 and R134a are smaller than those of R1234yf and R1234ze. Mg-MOF-74 owns a higher adsorbability than the other MOFs. The energy storage properties of the studied refrigerants can be enhanced when the sum of thermodynamic energy change of MOF particles and the desorption heat of fluid in MOFs is larger than the enthalpy change of pure organic fluid. The R1234yf/M-MOF-74 (M = Co, Mg, Ni) nanofluid can store more energy than other refrigerants/M-MOF-74 (M = Co, Mg, Ni) nanofluid. The energy storage enhancement ratios of R1234yf, R1234ze and R134a with Mg-MOF-74 nanoparticles are higher than those of other M-MOF-74 (M = Co, Ni, Zn) materials.

Thermodynamic properties of Buriti (Mauritia flexuosa) tree gum

Abstract Moisture adsorption and desorption isotherms from buriti tree gum (BG) were obtained at different temperatures (25 to 55 °C) in a water activity range of 0.1 to 0.9. The isotherms were classified as type II. The hysteresis loop and moisture of the monolayer decreased as temperature increased and Halsey’s equation proved able to predict with good precision the product’s sorption isotherms in the conditions studied. BG’s isosteric heats of moisture adsorption and desorption were close to the latent heat of vaporization of pure water for moisture levels above 30 g/100 g db and exponentially increased below that level. The enthalpy-entropy compensation theory and the isokinetic relationship were applied and indicated that BG’s moisture adsorption and desorption processes are spontaneous. The integral sorption properties indicated that the increase in surface tension at BG’s moisture sorption sites was more representative for the desorption process.