Sorption Energy Research Articles

Structure, the energy, sorption and biological properties of chiral salts of chitosan with l- and d-ascorbic acid

The influence of l- and d-ascorbic acid diastereomers on the structure, supramolecular ordering, energy, sorption and biological properties of heterochiral (D–L) and homochiral (D–D) salt complexes of chitosan (d-glucan)–acid was studied. The thermal effect of dissolving chitosan in l-ascorbic acid and the protonation degree of (D–L)-salts were lower than those in the medium of the d-isomer. Homochiral (D–D) salts, in contrast to heterochiral (D–L) ones, are distinguished by a more developed system of intermolecular and intramolecular contacts, a more ordered and equilibrium supramolecular organization of macrochains, a higher crystallinity degree, and a smaller amount of crystallization water. The sorption isotherms of chiral salts were approximated by the thermal equation of sorption and the superposition of the Langmuir and Flory–Huggins isotherms. Significant differences were found in the limiting value and energy of sorption, the constant of adsorption equilibrium, the limiting sorption capacity of the localized mode of water, and the Gibbs mixing energy. Biotesting on non-vascular (Scenedesmus quadricauda) and vascular eukaryotes (Linum usitatissimum) revealed the growth-stimulating effect of the D–D salts. The obtained results confirm our hypothesis of the homochiral salt complexes d-glucan–d-ascorbic acid best corresponding to the principles of the functional organization of biological objects.

Characterization and transport properties of ceramic filler incorporated natural rubber composites

AbstractCrystalline glass–ceramic fillers were prepared from calcium carbonate, silica, alumina, and calcium fluoride by heating and subsequent quenching in cold water. The fillers were incorporated into natural rubber (1,4‐cis‐polyisoprene) and the filled rubber composites were crosslinked with sulfur in the presence of different rubber additives. The unfilled and filled rubber composites were characterized. The transport properties of benzene, toluene, and p‐xylene (BTX) through the rubber composites were studied in terms of sorption, diffusion, permeation, and mass transfer coefficients. The effect of the ceramic fillers on the mechanical, thermal and transport properties were studied. The sorption data at different temperatures were used for calculating activation energy of diffusion, permeation, free energy, and enthalpy of sorption. The BTX remained in the liquid state within the composite matrix as evident from negative ΔS. The diffusion coefficient (D) and mass transfer coefficient (kmtc) of BTX decreased with the increase in filler loading. Accordingly, for the transport of BTX the unfilled rubber showed a D (D × 107 cm2/s) and mass transfer coefficient (kmtc × 104 cm/s) of 5.67/3.97/2.96 and 7.71/7.08/7.04, respectively which decreased to 5.06/2.95/2.57 and 7.53/6.95/6.90, respectively for the composite containing 50 wt.% ceramic filler.

Elimination of Arsenic Using Sorbents Derived from Chitosan and Iron Oxides, Applying Factorial Designs

Arsenic is highly toxic, affecting millions of people in many regions of the world. That is why developing economic and efficient technologies is imperative to eliminate it. Sorption techniques are attractive as efficient and inexpensive sorbents can be used. Chitosan is an abundant, naturally occurring, biodegradable, low-cost biopolymer that can be combined with metal oxide to enhance its removability. This work aimed to synthesize a new chitosan–magnetite-based sorbent for arsenic removal. The synthesized sorbent does not present pores, and when using FT-IR, functional groups of the chitosan and the presence of As(V) in the sorbent treated with arsenic were identified. The synthesized magnetite was characterized using XRD spectroscopy. Application of the central composite design model showed that 0.22 g of the sorbent at pH 6.0 could remove 27.6% of As(V). Kinetic data, fitted with the pseudo-first and -second order models, indicated an ion exchange sorption and activation energy of 28.1–31.4 kJ mol−1. The isotherms were fitted with the Langmuir model, indicating favorable monolayer adsorption with high affinity. The sorption energy calculated using Dubinin Radushkevich, 9.60–8.80 kJ mol−1, confirms a sorption mechanism mediated by ion exchange. The thermodynamic parameters of the process were ΔG° (−21.7/−19.7 kJ mol−1), ΔH°(16.7 kJ mol−1) and ΔS°(123.3 J mol−1 K−1).

Hydrogen storage in MXenes: Controlled adjustment of sorption by interlayer distance and transition metal elements

MXene is an attractive solid-state material for high-capacity, secure hydrogen storage under ambient conditions. Controlled adjustment of hydrogen sorption in MXene is essential to improve the storage capability and reversibility at room temperature. This study employed first-principles calculations to investigate the hydrogen sorption properties of multilayered MXenes at the electron level. The strong physical adsorption (Kubas type) of hydrogen was observed in MXene. The interlayer distance and the transition metal elements of MXenes allowed adjustment of the sorption energy of hydrogen. The narrow interlayer space benefited the adsorption of hydrogen molecules, instead of hydrogen atoms. Group 4B elements enhanced the chemical absorption, while Hf2C and Ta2C MXenes possessed relatively strong physical adsorption of hydrogen molecules. Furthermore, the density of states, d-band center, and electron density difference were used to reveal the electronic properties of MXene-hydrogen system.

Coupled sorptive and oxidative antimony(III) removal by iron-modified biochar: Mechanisms of electron-donating capacity and reactive Fe species

Sorption and oxidation are two potential pathways for the decontamination of trivalent antimony (Sb(III))-bearing water, using iron (Fe)-modified biochar (FeBC). Here we investigated the sorption and oxidation behavior of FeBC for Sb(III) in aqueous solutions. Results revealed that Sb(III) removal by FeBC was significantly improved showing the maximum Sb(III) sorption (64.0 mg g−1). Density functional theory (DFT) calculations indicated that magnetite (Fe3O4) in FeBC offered a sorption energy of −0.22 eV, which is 5 times that of non-modified biochar. With the addition of peroxymonosulfate (PMS), the sorption of Sb(III) on FeBC was 7 times higher than that on BC, indicating the sorption capacity of FeBC for Sb(III) could be substantially increased by adding oxidizing agents. Electrochemical analysis showed that Fe modification imparted FeBC higher electron-donating capacity than that of BC (0.045 v. s. 0.023 mmol e− (g biochar)−1), which might be the reason for the strong Sb(III) oxidation (63.6%) on the surface of FeBC. This study provides new information that is key for the development of effective biochar-based composite materials for the removal of Sb(III) from drinking water and wastewater. The findings from this study have important implications for protecting human health and agriculture.

SORPTION OF SCANDUIUM AND YTTRIUM COMPOUNDS BY ZIRCONIA-SILICA NANOSORBENT

Physical and chemical regularities of sorption extraction of scandium and yttrium compounds from (0.1–2.5)∙10-4 M aqueous solutions by zirconium-silica nanosorbent with specific surface area of 900-1000 m2/g, pore radius of 3.5-7, 6 nm and with a ZrO2 content of 29% have been established. It is shown that the studied sorbent efficiently (>99%) removes scandium and yttrium at pH 8 – 10 (Sc) and pH 9 – 10.5 (Y) and at sorbent consumption of 0.4 g/dm3. The time to reach sorption equilibrium is 240 min (Sc) and 210 min (Y). Modeling of scandium and yttrium sorption kinetics by Boyd’s external diffusion and internal diffusion models shows that sorption takes place in a mixed diffusion mode. The values of sorption rate constants (0.018 min-1 Sc, 0.033 min-1 Y), external mass transfer constants (4.74 ∙ 10-8 m/min Sc, 8.51 ∙ 10-8 m/min Y) and internal diffusion rate constants (0.0099 min-1 Sc, 0.0093 min-1 Y) have been calculated. It is established that the kinetics of sorption follows the pseudo-second-order model. It is shown that the sorption isotherms of both investigated metals are described by Freundlich, Frumkin-Fowler-Guggenheim and Dubinin-Radushkevich models. The constants of sorption isotherm models, characteristic energy of sorption (10.79 kJ/mol Sc, 9.58 kJ/mol Y), ΔG0 of sorption (-32.82 kJ/mol Sc, -30.77 kJ/mol Y) are calculated. The results of calculations indicate a significant affinity of scandium and yttrium compounds for this sorbent, spontaneous nature of the process and mixed nature of sorption with a predominance of chemisorption, a significant contribution of ion exchange to the sorption mechanism.

Experimental investigation on a thermochemical seasonal sorption energy storage battery utilizing MgSO4-H2O.

Thermochemical sorption energy storage (TSES) is the most recent thermal energy storage technology and has been proposed as a promising solution to reduce the mismatch between the energy supply and demand by storing energy for months in form of chemical bonds and restore it in form of synthesis chemical reaction. Compared with sensible/latent thermal energy processes, TSES system has major advantages, including a high energy storage capacity/density and the possibility of long-term energy retention with negligible heat loss. Therefore, a solid-gas thermochemical sorption battery is established and investigated utilizing a composite working pair of MgSO4-H2O based on room temperature expanded graphite (RTEG), treated with sulfuric acid (H2SO4) and ammonium persulfate ((NH4)2S2O8) as a porous additive. The experimental results showed that energy storage density and sorption efficiency increase with the increment of charging temperature or decreasing of discharging temperature at a certain ambient temperature. Under experimental conditions, energy density ranged from 31.7 to 908.8 kJ/kg (corresponding to volume energy density from 11.7 to 335.8 MJ/m3), while sorption energy efficiency ranged from 28.3 to 79.1%. The highest values were obtained when charging, condensation, and discharging temperatures were 95, 20, and 15 °C, respectively. The maximum thermal efficiency was 21.1% at charging/discharging temperature of 95/15 °C with sensible to sorption heat ratio of 3:1.

Stearic Acid and CeO2 Nanoparticles Co-functionalized Cotton Fabric with Enhanced UV-Block, Self-Cleaning, Water-Repellent, and Antibacterial Properties.

Superhydrophobic cotton fabrics with multifunctional features are highly desired in domestic and outdoor applications. However, the short coating longevity and hazardous reagents significantly reduce their commercial-scale applications. Herein, we introduce CeO2 nanoparticles and stearic acid (SA) to develop a fluorine-free, durable superhydrophobic cotton fabric that mimics the lotus effect. The pristine cotton fabric is treated with APTES-functionalized CeO2 nanoparticles by immersion followed by a dip and drying treatment with a 2% myristic acid solution. This sequential process creates a stable superhydrophobic cotton fabric (SA/CeO2-cotton fabric) with a water contact angle of 158° and a water sliding angle of 5°. The results are attributed to the combined effect of CeO2 nanoparticles and stearic acid that enhances surface roughness and reduces surface sorption energy. APTES facilitates the durable attachment of CeO2 nanoparticles and stearic acid to the cotton fabric. The modified cotton fabric is characterized by advanced analytical tools, demonstrating enhanced superhydrophobicity, self-cleaning, and antiwater absorption properties. Additionally, it exhibits remarkable UV-blocking (UPF 542) and antibacterial properties. The designed superhydrophobic cotton fabric unveils good mechanical, thermal, and chemical durability. The proposed strategy is simple, green, and economical and can be used commercially for functional fabric preparation.

Atomic Ru coordinated by channel ammonia in V-doped tungsten bronze for highly efficient hydrogen-evolution reaction

Regulation of the atomic distribution is crucial for the development of atomically dispersed electrocatalysts. In this study, atomic Ru coordinated by channel ammonia in V-doped tungsten bronze (Ru/V-NHWO, Ru 0.44 wt%, V 0.45 wt%) was used as a high-performance catalyst for the hydrogen evolution reaction (HER), demonstrating remarkable mass activity in a wide pH range. Atomic Ru with a regulated spatial distribution and electronic structure was achieved owing to its unique coordination with the ammonia species in the hexagonal channels of V-NHWO. V doping in NHWO led to enhanced intrinsic activity and conductivity. Theoretical calculations revealed that the multichannel, vertically integrated Ru sites in the V-doped channels, as well as the coexisting Ru sites without multichannels or V-doping, improved the free energy of water dissociation and hydrogen sorption, which boosted the HER activity. Our study paves a new way for constructing atomically dispersed materials with a regulated spatial distribution for diverse applications.

Three-phase-boundary Pt in a self-supported MoPt2-MoNi4/Mo2C heterojunction electrocatalyst for highly efficient pH-universal hydrogen evolution reaction

Design of high-performance Pt-based electrocatalysts is significant for hydrogen production through water splitting at pH-universal conditions but still challenging. Herein, the MoPt2-MoNi4/Mo2C three-phase heterojunction is fabricated via simply pyrolyzing hydrothermally resultant Mo-Ni precursor with subsequent galvanic Pt replacement process. It exhibits remarkable and stable hydrogen evolution reaction (HER) performance with impressive mass activity and low overpotential of 53, 77 and 46 mV at the current density of 100 mA cm−2 in alkaline, neutral and acidic media, respectively. Density functional theory calculations illustrate that there are multiple types of Pt sites in the phase of MoPt2 in such three-phase heterojunction, while only the Pt atoms located in the three-phase boundary not only process optimal electronic structure modulated by MoNi4/Mo2C, but also act as highly-active sites for HER. Moreover, downshifted d-band center of Pt triggered by the construction of three-phase MoPt2-MoNi4/Mo2C heterojunction, which regulating the free energy of reactive intermediates sorption and thereby accelerating the entire HER process. This work provides some constructive suggestions to design highly efficient Pt-based heterostructured electrocatalysts towards HER.

Removal of Fe(III)/Al(III)/Mg(II) by phosphonic group functionalized resin in wet-process phosphoric acid: Mechanism and intrinsic selectivity.

The removal of iron ions (Fe(III)), aluminum ions (Al(III)), and magnesium ions (Mg(II)) in phosphoric acid (H3PO4) solution is vital for the production of H3PO4 and supply of phosphate fertilizer. However, the mechanism and intrinsic selectivity for removal of Fe(III), Al(III), and Mg(II) from wet-process phosphoric acid (WPA) by phosphonic group (-PO3H2) functionalized MTS9500 are still unclear. In this work, the removal mechanisms were determined via combined analysis of FT-IR, XPS, molecular dynamics (MD), and quantum chemistry (QC) simulations based on density functional theory (DFT). The metal-removal kinetics and isotherms were further studied to confirm the removal mechanisms. The results indicate that Fe(III), Al(III), and Mg(II) interact with the -PO3H2 functional groups in MTS9500 resin with sorption energies of -126.22 kJ·mol-1, -42.82 kJ·mol-1, and -12.94 kJ·mol-1, respectively. Moreover, the intrinsic selectivities of the resin for Fe(III), Al(III), and Mg(II) removal were quantified by the selectivity coefficient (Si/j). The SFe(III)/Al(III), SFe(III)/Mg(II) and SAl(III)/Mg(II)are 18.2, 55.1 and 3.02, respectively. This work replenishes sorption theory that can be used in the recycling of electronic waste treatment acid, sewage treatments, hydrometallurgy, and purification of WPA in industry.

Contaminant retention affected by controlled and uncontrolled pH for fly ash-bentonite composites used as landfill liner material

Contaminant retention characteristics of clay-based composites as affected by pH needs to be quantified for its design, functionality, and performance as a landfill liner material. The efficacy of four fly ash (FA) in bentonite-fly ash (B-FA) mixes was investigated for its lead (Pb2+) retention characteristics under controlled pH (pH = 5) and realistic uncontrolled pH conditions anticipated in the landfill liners. B-FA mixes with 30%, 50%, and 70% FA amendment, bentonite-sand (B–S) mixes, and parent materials were tested by batch sorption tests. Under uncontrolled pH conditions, the retention capacity of all parent materials and mixes was higher than the controlled pH condition due to significant precipitation reaction and complexation associated with pH. Beyond 1000 mg.L-1 initial concentration, B-FA mixes constituting FA with inherent pH > 10.5 were the most efficacious adsorbents. Under both pH conditions, the metal retention capacity of B-FA mixes was higher than that of conventional B-sand mixes. All results were analytically substantiated by detailed FESEM micrographs, XRD, and EDX spectra of samples before and after sorption. The Freundlich and Langmuir nonlinear retention model parameters indicate that the uncontrolled pH condition results in nonlinear sorption, the higher energy of sorption, and stronger interactive bonds between Pb2+ ions and sorbent.

Ultra-selective chelating membranes for recycling of cobalt from lithium-ion spent battery effluents by electrodialysis

The recovery of valuable resources from spent effluents is critical to ensure sustainable growth and reduce commodity shortages at global levels. Spent batteries are largely untapped resources containing multiple high-value metal ions that may be harnest and resued indefinitely to develop a circular battery economy. Challenges however lay with the cost of purification and recovery strategies and the limited selectivity of existing processes. This work presents the development of selective cation exchange membranes suitable for the selective recovery of cobalt from mixtures of lithium, cobalt, and nickel from spent battery effluents. Efficient cation exchange membranes were generated by modifying poly(vinyl chloride) films with ethylene diamine followed by grafting of 5-chloro-8-hydroxyquinoline (5C8Q) chelating agents and two synthesis routes were compared including surface and bulk grafting and the membrane separation properties were benchmarked against CIMS Neosepta. Besides being stable across a pH range between 2 and 8, relevant to spent battery lixiviat, the surface grafted membranes exhibited the lowest energy of sorption in comparison to bulk membranes, which was ten times lower than that of the commercial CIMS Neosepta reference membranes. The transfer of ions from model single salt solutions across the surface grafted membranes allowed for over 60 % of cobalt recovery within 1 h, while nickel and lithium were transferred only up to 18 % and 0.2 %, respectively. In addition, the electrodialysis-based separation of multi-component solutions remained very cost-effective with cobalt ion removal amounts up to 58 %, leading to Co/Li separation factors as high as 247. This novel chelating agent strategy opens avenues for the development of highly efficient and selective membrane materials, which are able to operate in extreme pH environments and supporting ultra-selective ionic transfer.

Misinterpretation of Dubinin–Radushkevich isotherm and its implications on adsorption parameter estimates

ABSTRACT Dubinin–Radushkevich (D – R) isotherm remains one of the widely used adsorption models in solid/liquid interface. However, adsorption potential (ε), as a function of equilibrium concentration (Ce) and solubility (Cs) of adsorbate, is frequently expressed through a dimensionally inconsistent form i.e. , instead of the correct form i.e. . Although Hu and Zhang (2019) have pointed out the misinterpretation, incorrect use of isotherm however continues. All of the 10 all-time highly cited articles on D-R isotherm and 80 out of 117 articles citing the work of Hu and Zhang (2019) adopted the incorrect or ambiguous form. Only six research articles have referred source of required Cs data, i.e. literature reported value, approximated to initial adsorbate concentration, or as an additional model parameter. Modeling of D-R isotherm using datasets extracted from three selected references suggests that using the incorrect expression would have a variable impact on maximum adsorption capacity estimates. However, sorption energy would invariably be overestimated (at least 200 times) in all data sets. In the absence of any unified approach and the practical difficulty associated with ascertaining the correct Cs value, researchers are inclined to use the inconsistent model.

Electrosorption Integrated with Bipolar Membrane Water Dissociation: A Coupled Approach to Chemical-free Boron Removal.

Boron removal from aqueous solutions has long persisted as a technological challenge, accounting for a disproportionately large fraction of the chemical and energy usage in seawater desalination and other industrial processes like lithium recovery. Here, we introduce a novel electrosorption-based boron removal technology with the capability to overcome the limitations of current state-of-the-art methods. Specifically, we incorporate a bipolar membrane (BPM) between a pair of porous carbon electrodes, demonstrating a synergized BPM-electrosorption process for the first time. The ion transport and charge transfer mechanisms of the BPM-electrosorption system are thoroughly investigated, confirming that water dissociation in the BPM is highly coupled with electrosorption of anions at the anode. We then demonstrate effective boron removal by the BPM-electrosorption system and verify that the mechanism for boron removal is electrosorption, as opposed to adsorption on the carbon electrodes or in the BPM. The effect of applied voltage on the boron removal performance is then evaluated, revealing that applied potentials above ∼1.0 V result in a decline in process efficiency due to the increased prevalence of detrimental Faradaic reactions at the anode. The BPM-electrosorption system is then directly compared with flow-through electrosorption, highlighting key advantages of the process with regard to boron sorption capacity and energy consumption. Overall, the BPM-electrosorption shows promising boron removal capability, with a sorption capacity >4.5 μmol g-C-1 and a corresponding specific energy consumption of <2.5 kWh g-B-1.

Insights into sorption and molecular transport of atrazine, testosterone, and progesterone onto polyamide microplastics in different aquatic matrices

Microplastics can act as vectors of a wide class of contaminants in aquatic environments. The sorption behavior of two hormones known to cause adverse effects in biota even in low concentrations (testosterone-TTR and progesterone-PGT), and a pesticide with a high environmental persistence known as endocrine disruptor chemical (atrazine-ATZ) onto polyamide (PA) microplastics is investigated under different aquatic matrices using kinetic and isotherm experiments. The sorption equilibrium is achieved in 48 h, and the experimental results are better fitted by pseudo-2nd-order model. Langmuir isotherm better describes the sorption of the contaminants onto PA microplastics. PGT presents the highest sorption efficiency at around 90%, followed by TTR at 70% and ATZ at approximately 20%. Moreover, ATZ is the contaminant with the highest desorption efficiency (∼65%), indicating its preference for staying solubilized in water. Combining classical molecular dynamics and density functional theory calculations, the sorption energies were calculated as 12–15 kcal mol−1, 13–16 kcal mol−1, and 19–22 kcal mol−1 for PGT, TTR, and ATZ, respectively, showing that PGT needs less energy to be transferred from the solvent network to the PA surface, in agreement with experimental results. The sorption mechanism is driven by hydrogen bonds onto PA outer surface, while the electrostatic interactions dominate the PA inner surface sorption. Moreover, the sorption efficiency is statistically different between the investigated matrices, indicating that physicochemical characteristics of water systems could influence the interactions between PA-contaminant. In seawater, the phenomena of salting-out/in and competitive sorption with saline ions are observed for three contaminants. The PA-contaminant complexes are more polar and soluble than the dissociated ones, which increases the contaminant's co-transport by PA in water.

Molecular dynamics and energy distribution of methane gas adsorption in shales

This study uses simulations to explore the energy distributions involved in the adsorption of methane gas in shales. Molecular mechanics calculations were carried out using the Forcite module in BIOVIA material studio software. The critical challenge in molecular-scale simulations remains the need to improve the description of the gas adsorption prior to up-scaling to a realistic scenario. Resolving this challenge requires the implementation of multi-scale techniques that employ atomistic/molecular-level results as input. Thus, it is pertinent that the appropriate molecular data on CH4 gas interaction with shale is obtained. This study provides empirical data on CH4 sorption/adsorption in shale at the molecular level to confirm the CH4 storage potential of shales. The effect of pressure on the CH4 sorption/adsorption was also investigated. A vital aspect of this study is elucidating the energy distribution and dominant energy that controls CH4 sorption/adsorption to serve as a basis for the exploitation of CH4 in productive shales. Following the intensive simulation exercise, the average total energy of CH4 sorption varied from approximately −30 to −120 kcal/mol with increase in pressure from 500 to 2500 psi, suggesting increasing thermodynamic stability. The results indicated that van der Waals energy is the major sorption energy with values ranging from 60 to −250 kcal/mol as the sorption pressure increased, while electrostatic energy recorded the least contribution. The total adsorption energy increased from −5 to −16 kcal/mol for reservoir pressure range of 1–15 MPa. This energy distribution data confirmed the possibility of CH4 adsorption on shale under reservoir pressure conditions.

Adsorption of Zinc ions by native and modified acacia bark (Acacia auriculiformis)

Modified sorption materials were produced by treating earleaf acacia (Acacia auriculiformis) bark with low-concentration (1-3%wt) sulfuric acid solutions. The sorption properties of native and modified acacia bark for zinc (II) ions were studied. Based on the values of the initial and equilibrium concentrations of zinc ions in the solution, the materials' sorption capacity (A, mmol/g) was found and adsorption isotherms were plotted. It was found that the isotherms are type I isotherms according to the IUPAC classification and describe the process of monomolecular adsorption. It was found that acacia bark treatment with H2SO4 solutions resulted in an increase in the sorption capacity of the latter with respect to zinc (II) ions due to an increase in the area of the sorption material due to the extraction of part of the biopolymers in the matrix of the sorption material into solution. This circumstance leads to an increase in the pore space of modified samples of sorption material, which is proved by a decrease in the degree of crystallinity. The thermodynamic process parameters were found using the resulting adsorption process constants of the Langmuir and Dubinin-Radushkevich models: sorption energy (E, kJ/mol) and Gibbs energy (ΔG, kJ/mol), which values indicate that the processes of zinc (II) ions adsorption by native and modified acacia bark are physical adsorption processes. The kinetics has been studied and kinetic dependences of the processes of Zn2+ ions adsorption by native and modified acacia bark have been plotted. The resulting kinetic dependences were analyzed based on the Boyd diffusion model and it was determined that in all four cases mixed adsorption occurred, that is, both external and internal diffusion are limiting.

Performance regulation characteristics of bi-halide sorbents in the thermochemical sorption system for cold/heat storage

Thermochemical sorption is a promising technology for cold and heat storage. The performance regulation characteristics of bi-halide sorbents composed of CaCl2 and MnCl2 in different mixing ratios in the sorption energy storage system are investigated and compared by simulation and experiments in this paper. The simulation results show that the bi-halide sorbent can effectively reduce the reaction hysteresis temperature difference. The output energy becomes more concentrated, the start-up time is effectively shortened, and the stability of the energy output is ameliorated as the ratio of MnCl2 increases. Moreover, the experimental results corroborate the analysis in the simulation, and the maximum average cold and heat storage capacity of 2.7 kW and 1.6 kW, and their COP of 0.32 and 0.19 are obtained when the ratio of CaCl2 and MnCl2 is 6:1. In addition, the refrigerating power becomes concentrated in the early stage of the reaction with the mixing ratio of 1:3, and the time for rising to the average refrigerating capacity is significantly shortened from 900 s to 100 s. The consistency between simulation and experiments in the regulation characteristics illustrates that the bi-halide sorbent can improve the applicability of the sorption energy storage system in practical scenarios with different requirements.

Experimental and numerical investigation of multistage sorption energy storage system

In this paper, thermal energy storage is utilized to store heat from solar energy and also use waste heat to counterbalance the demand and supply of energy. A laboratory multistage closed sorption thermal energy storage (STES) unit is designed and tested to study the performance of a cascade sorption system. The experimental unit consists of three sorbent reactors, an ammonia cycle, and an oil cycle. Composite sorbents namely, MnCl₂, CaCl₂, and Nh₄Cl are used with ammonia as sorbate. Expanded natural graphite (ENG) is mixed with sorbents to increase the thermal conductivity and improve the mass transfer performance of sorbents. Further, a computational fluid dynamic model using COMSOL Multiphysics is built to study the performance of triple, double, and single closed STES systems. For the triple experimental STES system, a charging temperature up to 155 °C is used. At Nh3 pressure of 7.5 bar, the discharging temperatures are found to be 132.9 °C, 99.1 °C, and 60.3 °C for MnCl₂-ENG , CaCl₂-ENG , and Nh₄Cl-ENG composite sorbents, respectively, while a total energy storage density (ESD) of 3474.28 kJ/kgsalt has been achieved. For a double experimental STES system, a charging temperature up to 105 °C is used. Discharging temperatures are found to be 95.3 °C and 60.1 °C for CaCl₂-ENG , and Nh₄Cl-ENG composite sorbents, respectively, and a total ESD of 2471.94 kJ/kgsalt is achieved at Nh3 pressure of 7 bar. A parametric study is carried out to study the effect of different parameters on the performance of STES system at different arrangements. Increasing the inlet oil temperature during discharge results in a reduction of total ESD. For the specified design condition, the optimum oil mass flow rate is found to be 0.04 kg/s to achieve the highest ESD.