Sorption Cycles Research Articles

Introduction of chemically bonded zirconium oxide in CaO-based high-temperature CO2 sorbents for enhanced cyclic sorption

In this study, ZrO2 is introduced in a new form to reduce sintering and enhance the cyclic stability of CaO-based sorbents. Such a material has potential for high-temperature CO2 capture applications. Two Zr-modified CaO materials having a Ca/Zr molar ratio of 30 are prepared using the solid-state and citrate sol-gel methods. The solid-state method yields a physical mixture of CaO and ZrO2, while the citrate sol-gel method induces chemical bonding between ZrO2 and the CaO surface to form CaZrO3. The CO2 sorption uptake was significantly increased in both unmodified CaO and ZrO2-containing CaO [77.3 wt% (17.6 mol kg−1) and 73.2 wt% (16.6 mol kg−1), respectively, at 650 °C and 1 bar] when the citrate sol-gel method was used. The CaO having the chemically bonded ZrO2 reveals significantly enhanced cyclic stabilities, with an extremely high CO2 sorption uptake of 70.5 wt% (16.0 mol kg−1) on average during 10 cycles. On the other hand, the CaO containing the physically mixed ZrO2 reveals an average cyclic CO2 sorption uptake of only 37.2 wt% (8.5 mol kg−1). The chemically bonded ZrO2 is expected to be well scattered on the CaO surface and effectively cover the sorbent, resulting in the reduction of thermal sintering. In addition to cyclic stability, CO2 sorption kinetics of CaO-based sorbents can be enhanced through the citrate sol-gel method, which is resulted from the significantly reduced size of CaO particles.

GRAMS: A general framework describing adsorption, reaction and sorption-enhanced reaction processes

We present a generalized reaction-adsorption modeling and simulation (GRAMS) framework that captures both reaction and adsorption dynamics in columns with solid catalysts, porous adsorbents or both. It is based on a 1-dimensional, pseudo-homogeneous, non-isothermal, non-adiabatic and non-isobaric model that is extensively validated using experimental data from literature for different adsorption-reaction systems. For demonstrating the capabilities of the high-fidelity framework, simulations are performed for several configurations of a packed-column system containing (i) pure catalyst as in a fixed bed reactor, (ii) pure adsorbent as in a multi-step pressure swing adsorption (PSA) process, (iii) homogeneously-distributed uniform mixture of adsorbent and catalyst as in a cyclic sorption enhanced reaction process (SERP), and (iv) heterogeneously-compartmentalized adsorbent and catalyst as in a layered SERP. The model predictions show good agreement with experimental observations for sorption-enhanced steam methane reforming (SE-SMR), sorption-enhanced water gas shift reaction (SE-WGSR), PSA processes and conventional SMR. The framework is also used for evaluating the performance of a novel process with integrated SE-SMR and reverse water gas shift reaction (RWGSR) for direct natural-gas-to-syngas conversion. GRAMS is implemented such that it can be used for optimal design and intensification of novel, modular and multi-functional processes by combining multiple phenomena within a single unit.

Catalyst-TiO(OH)2 could drastically reduce the energy consumption of CO2 capture

Implementing Paris Climate Accord is inhibited by the high energy consumption of the state-of-the-art CO2 capture technologies due to the notoriously slow kinetics in CO2 desorption step of CO2 capture. To address the challenge, here we report that nanostructured TiO(OH)2 as a catalyst is capable of drastically increasing the rates of CO2 desorption from spent monoethanolamine (MEA) by over 4500%. This discovery makes CO2 capture successful at much lower temperatures, which not only dramatically reduces energy consumption but also amine losses and prevents emission of carcinogenic amine-decomposition byproducts. The catalytic effect of TiO(OH)2 is observed with Raman characterization. The stabilities of the catalyst and MEA are confirmed with 50 cyclic CO2 sorption and sorption. A possible mechanism is proposed for the TiO(OH)2-catalyzed CO2 capture. TiO(OH)2 could be a key to the future success of Paris Climat e Accord.

Comparison of ion-exchange resins for efficient cobalt(II) removal from acidic streams

ABSTRACTThe ion-exchange method was applied for cobalt(II) removal from acidic streams using Lewatit MonoPlus TP 220, Purolite A 830, Lewatit SR 7, Purolite S 984, Purolite A 400 TL, Lewatit AF 5, Dowex PSR 2, and Dowex PSR 3. The effects of phase contact time, acid concentration, initial Co(II) concentration, and temperature were evaluated. The cobalt(II) desorption, ion exchanger reuse, and attenuated total reflection with the Fourier transform infrared spectroscopy, column studies were also performed. Lewatit MonoPlus TP 220 exhibits the highest sorption capacities and sorption follows the pseudo-second-order kinetics. The Freundlich model fitted the experimental data adequately. Desorption of cobalt(II) loaded is not quantitative. Sorption capacity reduction after three cycles of sorption–desorption (static method) was not observed.

Na2CO3-doped CaO-based high-temperature CO2 sorbent and its sorption kinetics

CaO-based sorbents have received much research attention for high-temperature CO2 capture because of their high theoretical sorption capacities. However, harsh conditions are needed to regenerate CaO-based sorbents, and their high CO2 sorption capacities diminish significantly in cyclic sorption procedures owing to thermal sintering effects. To solve these problems, dopant components have been applied to CaO-based sorbents. In this study, a new CaO-based sorbent containing Na2CO3 was synthesized using a precipitation method. The prepared sorbent (Na2CO3-CaO) was characterized using various analytic methods, and its CO2 sorption performance was studied using thermogravimetric analysis. Na2CO3-CaO showed high CO2 affinity above 600 °C, and its sorption/regeneration kinetics were faster than those of the conventional CaO sorbent. To investigate the CO2 sorption mechanism onto Na2CO3-CaO, the change in crystalline structure with respect to temperature was analyzed using in-situ X-ray diffraction; the results revealed that the double salt Na2Ca(CO3)2 was generated from the reaction of CO2 with CaO and Na2CO3. Kinetic models were also developed to describe the CO2 sorption behavior of Na2CO3-CaO. The results of this study advance our understanding of the effect of alkali metal carbonates on CaO-based sorbents.

Dimensional stability and hygroscopic properties of waterlogged archaeological wood treated with alkoxysilanes

Archaeological waterlogged elm wood was treated with methyltrimethoxysilane (MTMS) and (3-mercaptopropyl)trimethoxysilane (MPTES), respectively, and anti-shrink efficiency and sorption properties of the impregnated wood samples were determined. The applied impregnants stabilized wood dimensions efficiently enough, i.e. the obtained anti-shrink efficiency was 81 and 98% for MTMS- and MPTES-treated wood, respectively. Both alkoxysilanes can be considered as potential new consolidants. Hygroscopic properties of untreated and impregnated wood were investigated with the DVS experiments. The application of MTMS and MPTES reduced wood equilibrium moisture content (EMC) and sorption hysteresis e.g. hysteresis relative change was −83.7 and −73.7% for MTMS- and MPTES-treated wood, respectively. The EMC reduction was observed in the whole hygroscopic range and it was primary due to the monolayer capacity decrease to 50 and 30% of the value for untreated wood and observed for adsorption and desorption modes, respectively. The DVS experiments revealed chemical instability of the MTMS-wood system which was neutralized after the cyclic sorption. The possible scenarios of the interaction of both alkoxysilanes with wood structure were discussed.

Performance of synthetic CaO-based sorbent pellets for CO2 capture and kinetic analysis

Three powdery CaO-based sorbents were synthesized respectively from calcium acetate and three different inert support precursors. Based on these sorbent powder, sorbent pellets without and with pore forming material (cellulose) were fabricated using an extrusion-spheronization method. Cyclic CO2 sorption performance of all powdery sorbents and sorbent pellets were tested in a TGA. It was found that introduction of inert supports was beneficial for enhancing the CO2 capture capacity of CaO. For sorbent powder, sintering was retarded due to high thermal stability of inert supports and good dispersion of CaO particles among inert supports, resulting in better performance of synthetic sorbent than calcined CaCO3. However, CO2 uptake of sorbent pellets deteriorated dramatically owing to damage of pore structure caused in the extrusion process. Cn and Xn was even lower than 0.1 g CO2/g sorbent and 20% for sorbent pellets during the 25th cycle. Adding cellulose was found to be effective for promoting the CO2 sorption capacity of sorbents which was mainly ascribed to enlarged specific surface area and pore volume during cellulose burning. Two kinetic models were used to understand the mechanism of the carbonation reaction and the models were proven to be feasible for analyzing the chemical reaction controlled stage and diffusion controlled stage in the carbonation process. Reaction rate constants obtained from kinetic calculation can also be used to explain the different performance between different types of sorbents.

Optimization of TiH2 content for fast and efficient hydrogen cycling of MgH2-TiH2 nanocomposites

Magnesium hydride is extensively examined as a hydrogen store due to its high hydrogen content and low cost. However, high thermodynamic stability and sluggish kinetics hinder its practical application. To overcome this last drawback, different Ti amounts (y = 0, 0.025, 0.05, 0.1, 0.2 and 0.3) were added to magnesium to form (1-y)MgH2+yTiH2 nanocomposites (NC) by reactive ball milling under hydrogen gas. Thermodynamic stability of the MgH2 phase in NCs was determined using a manometric Sieverts rig. Reversible hydrogen capacity and reaction kinetics were determined at 573 K over 20 sorption cycles under a limited reaction time of 15 min. On increasing Ti amount, reaction kinetics are enhanced both in absorption and desorption leading to a higher reversibility for hydrogen storage with the MgH2 phase. However, titanium increases the molar weight of NCs and forms irreversible titanium hydride. The highest reversible capacity (4.9 wt% H) was obtained for the lowest here studied TiH2 content (y = 0.025).

Synthesis of mesoporous triple-metal nanosorbent from layered double hydroxide as an efficient new sorbent for removal of dye from water and wastewater

In this study, co-precipitation synthesis of the mesoporous triple-metal nanosorbent from Fe, Cu, Ni layered double hydroxide (FeCuNi-LDH), on the basis of the data obtained from the TG analysis was carried out. The FTIR spectroscopy and XRD results confirm the formation of CuO, NiO and Fe2O3 nanoparticles, while the EDX analysis does not show significant variations on the surface in elemental composition. BET analysis shows that FeCuNi-280 (FeCuNi-LDH calcinated at 280 °C) with mesoporous structure, has larger surface area compared to FeCuNi-LDH and FeCuNi-550 (FeCuNi-LDH calcinated at 550 °C). The value of pHPZC of FeCuNi-280 is found to be 8.66. Obtained FeCuNi-280 material showed the ability for efficient removal of dye Reactive Blue 19 (RB19) from water, with a very high sorption capacity of 480.79 mg/g at optimal conditions: the sorbent dose of 0.6 g/dm3, stirring speed of 280 rpm and pH 2. The kinetics results of the sorption process were well fitted by pseudo-second order and Chrastil model, and the sorption isotherm was well described by Sips, Langmuir and Brouers–Sotolongo model. FeCuNi-280 was easily regenerated with aqueous solution of NaOH, and reutilization was successfully done in five sorption cycles. The present study show that easy-to-prepare, relatively inexpensive nanosorbent FeCuNi-280 is among the best sorbents for the removal of RB19 dye from water solution and wastewater from textile industry in wide range of pH.

Hygroscopic behaviour of lignocellulosic materials: Dataset at oscillating relative humidity variations

The objective of this work is to study the hygroscopic behaviour of lignocellulosic materials used in building insulation. Five lignocellulosic materials have been studied and compared: cellulose, flax-hemp wool, low fibreboard density (LDF), Norway spruce and wheat straw. Particular attention is paid to the history of changes in relative humidity (RH). The RH trajectories were chosen to meet two objectives: i) to precisely determine the envelope curves (full adsorption and full desorption in the absence of memory effect) and ii) to quantify the memory effect in the case of partial sorption cycles, likely to occur in these materials in use. The Hailwood-Horrobin model was used to describe the envelope curves and the effect of temperature on isotherms was also modelled. The difference in hygroscopic behaviour is explained by the differences in the chemical and structural composition of the materials studied. The parameters identified in this work provide very useful information to assess the sorption behaviour of lignocellulosic materials when in use in buildings.

Constrained growth of solid amino alkyl siloxane (an organic–inorganic hybrid): The ultimate selective sorbent for CO2

Herein, we report a solid matrix of amino alkyl siloxane of porous nature with alkyl groups thoroughly distributed in the matrix by constrained growth technique; this sorbent is ideal for CO2 sorption. The sorbent exhibits higher sorption (4mmol CO2/g), and selectivity to CO2. It is enriched with voids, and exhibits adequate thermal stability. Adsorption occurred below 100°C, while desorption occurred between 100 and 200°C. When the sorbent underwent both sorption and desorption of CO2, a sharp enthalpy change was observed; such an enthalpy change is a crucial characteristic of cyclic sorption desorption (CSD).

Mechanochemical synthesis and effect of various additives on the hydrogen absorption\u2013desorption behavior of Na3AlH6

Sodium aluminum hydride has been extensively investigated for hydrogen storage applications whereas its intermediate decomposition compound Na3AlH6 received much less attention, despite having a lower dissociation pressure and a reasonable hydrogen storage capacity of 3.0 wt%. In this work, Na3AlH6 is synthesized through ball milling, starting from NaAlH4 and 2 NaH in the presence of TiCl3 catalyst precursor, and evaluated on its hydrogen sorption properties and cycle stability. Further addition of 8 mol% Al and 8 mol% activated carbon (AC) and their effect on both the hydrogen sorption properties and cycle stability have been investigated. In order to explore whether the introduction of the Al and AC additives would be more beneficial (in terms of hydrogen sorption behavior and cycle stability) after the Na3AlH6 synthesis or during its synthesis, pre-synthesized Na3AlH6-based measurements were also included in this work. TiCl3-catalyzed NaAlH4 + 2 NaH sample showed a stable reversible hydrogen storage capacity of 1.7 wt%, which was further increased to 2.1 wt% with the addition of Al-powder and activated carbon AC.

Self-activation of CaO/Ca3Al2O6 sorbents by thermally pretreated in CO2 atmosphere

CaO/Ca3Al2O6 sorbents have been proved to be a promising sorbent for CO2 sorption. However, the sorbents still suffer from low CO2 sorption capacity. In this work, self-activation was generated via thermally pretreating CaO/Ca3Al2O6 sorbents in CO2 atmosphere at various temperatures to enhance the CO2 sorption capacity of CaO/Ca3Al2O6 sorbents. Results showed that the thermally pretreated temperature plays an overwhelming role in the CO2 sorption capacity and stability of the CaO/Ca3Al2O6 sorbents. Superior CO2 sorption capacity (8.01 mmol g−1 for C9A1-650 at 500 °C) is achieved, which is 72% higher than that of C9A1 (no pretreatment sample). After 50 carbonation-calcination cycles, the CO2 sorption capacity of C9A1-650 still remained 20% higher than that of C9A1. The high CO2 sorption capacity is ascribed to the smaller CaO grain size (37.1 nm) and the higher surface area (13.1 m2 g−1), resulting from the self-activation process. Meanwhile, the CO2 cyclic sorption stability is due to the small original surface free energy. Furthermore, the C9A1-650 sorbent is employed to use in sorption enhanced methane steam reforming process. It provides a H2 concentration of 98.9% and CH4 conversion of 98.7%, presenting greatly potential in practical application.

Analysis on innovative resorption cycle for power and refrigeration cogeneration

A novel resorption cycle with internal heat recovery process is proposed, which is expected to further explore potentials of power and refrigeration cogeneration. Two sets of basic resorption refrigeration cycles are adopted, which are integrated with turbine/expander to realize quasi-continuous output in both half cycles. An improved cogeneration efficiency could be obtained with safety feature. Different ammonia composite sorbents with better heat and mass transfer performance are selected to investigate the overall performance when heat source temperature is in the range from 200 °C to 360 °C. It is indicated that energy efficiency for power generation is able to reach up to 0.263 at 360 °C heat source temperature while refrigeration coefficient of performance could achieve up to 1.31 at 200 °C heat source temperature. The optimal total exergy efficiency of novel resorption cogeneration cycle is as high as 0.74 by using working pair of FeCl2-CaCl2-BaCl2 at 240 °C heat source temperature. Compared with other sorption cycles for power and refrigeration cogeneration at similar heat source temperatures, the proposed resorption cycle exhibits the highest exergy efficiency, which is about 30% higher than that of water-ammonia sorption cogeneration cycle, and twice higher than that of basic resorption cogeneration cycle.

Analysis of ideal sorption compressor cycles operating with gas mixtures

Sorption-based compressors are thermally driven and because of the absence of moving parts they are vibration free, and have the potential for long life. Sorption-based compressors have been reported to operate Joule–Thomson (JT) cryogenic coolers with pure working fluids. However, using mixed refrigerants instead of pure refrigerants is attractive since that would dramatically improve the system coefficient of performance. Our on-going research aims to develop an efficient JT sorption cryocooler, operating with mixed refrigerants, and is focused on studying the characteristics of the sorption compressor cycle. This paper presents the results of an advanced numerical analysis, which is based on a previous model, and its experimental verification. The analysis relates to the ideal cycle of a sorption compressor operating with a gas mixture. Obviously, dynamics and kinetics play a major rule in a real sorption compressor cycle. However, since there are no reported gas-mixture sorption compressors and the existing experience in this field is poor, a preliminary ideal cycle analysis is considered. Satisfying agreement between the numerical and experimental results is obtained and the processes in the sorption cycle are discussed. The outcomes of the current study are the basis for the next phase in which a sorption compressor prototype will be built operating with gas mixtures.

Feasibility study of seasonal solar thermal energy storage in domestic dwellings in the UK

Seasonal solar thermal energy storage (SSTES) has been investigated widely to solve the mismatch between majority solar thermal energy in summer and majority heating demand in winter. To study the feasibility of SSTES in domestic dwellings in the UK, eight representative cities including Edinburgh, Newcastle, Belfast, Manchester, Birmingham, Cardiff, London and Plymouth have been selected in the present paper to study and compare the useful solar heat available on dwelling roofs and the heating demand of the dwellings. The heating demands of space and hot water in domestic dwellings with a range of overall heat loss coefficients (50 W/K, 150 W/K and 250 W/K) in different cities were calculated; then the useful heat obtained by the heat transfer fluid (HTF) flowing through tilted flat-plate solar collectors installed on the dwelling roof was calculated with varied HTF inlet temperature (30 °C, 40 °C and 50 °C). By comparing the available useful heat and heating demands, the critical solar collector area and storage capacity to meet 100% solar fraction have been obtained and discussed; the corresponding critical storage volume sizes using different storage technologies, including sensible heat water storage, latent heat storage and various thermochemical sorption cycles using different storage materials were estimated.

Comparison of the sorption properties of natural and synthetic zeolites for the purification of aqueous solutions from cobalt: sorption of the cobalt from aqueous solutions in dynamic conditions and the quantitative determination of cobalt by the PIXE method

A methodology of quantitative determination of cobalt using the PIXE method has been developed. The method is based on the use of instant nuclear-physical analysis with the inducement of a target by a 1.6 MeV proton beam and the recording of the characteristic X-ray emission of the K-series of the cobalt. The linear relationship between the quantitative content of cobalt strontium and its X-ray emission K-shell was obtained. The sorption of cobalt by natural and synthetic zeolites from aqueous solutions in dynamic conditions has been studied. Sorption of cobalt with clinoptilolite after 80 cycles of sorption was about 60%. Sorption of cobalt after 80 cycles of sorption by zeolites NaX and NaA was 86 and 70%. Consideration was given to the influence of competing ions (sodium) on the sorption of cobalt by zeolites. The introduction of competing ions leads to a decrease in sorption of the cobalt by 25–60%, depending on the content of competing ions.

Synthesis of D2EHPA Impregnated Polymeric Beads for the Extraction of Zinc from Zinc-rich Waste Liquor

Background: Di- (2-ethyhexyl phosphoric acid), commonly known as D2EHPA, is an important extractant used for the recovery of Zn (II) from aqueous waste. The D2EHPA extractant encapsulated polymeric beads (EEPBs) were synthesized and investigated for the sorption of Zn (II) from aqueous medium. Objective: Synthesis of D2EHPA impregnated polymeric beads for the extraction of Zinc from zincrich waste liquor. Method: The beads were prepared by the phase inversion technique. Results: The amount of Zn (II) extracted was found to increase with contact time, beads weight and concentration of solution. The kinetics measurement showed that about 250 min of equilibration time was enough to remove saturation amount of Zn (II) from the solution. The sorption kinetics data fitted well in the pseudo second order model and sorption results were found to follow Langmuir sorption isotherm model. Stripping investigations carried out using different stripping agents indicated that 2M HCl is effective for stripping the Zn (II) loaded onto the synthesized beads. Conclusion: The maximum experimental capacity of the D2EHPA encapsulated beads was found to be 33.8 mg g-1 for Zn (II). The synthesized beads enabled the selective extraction of Zn (II) ions from a simulated complex waste matrix with good recyclability upto the studied 4 sorption and desorption cycles. The sorption capacity was found to be maximum at pH 5.0 and decreased significantly on either side of pH 5.0. These synthesized sorbent beads can be selectively and efficiently employed for the recovery of zinc from usual Zinc-rich waste liquor. Keywords: D2EHPA, extractant-encapsulated beads, isotherm model, Langmuir sorption, waste liquor and Zn extraction.

Positron Spectroscopy of Nanodiamonds after Hydrogen Sorption.

The structure and defects of nanodiamonds influence the hydrogen sorption capacity. Positronium can be used as a sensor for detecting places with the most efficient capture of hydrogen atoms. Hydrogenation of carbon materials was performed from gas atmosphere. The concentration of hydrogen absorbed by the sample depends on the temperature and pressure. The concentration 1.2 wt % is achieved at the temperature of 243 K and the pressure of 0.6 MPa. The hydrogen saturation of nanodiamonds changes the positron lifetime. Increase of sorption cycle numbers effects the positron lifetime, as well as the parameters of the Doppler broadening of annihilation line. The electron-positron annihilation being a sensitive method, it allows detecting the electron density fluctuation of the carbon material after hydrogen saturation.

Microscopic swelling analysis of spruce wood in sorption cycle

Depending on drying or humidification conditions, spruce wood tends respectively to shrink or swell, because of internal mechanical stresses that cause microscopic morphological changes. In the present paper, an experimental campaign is performed at the microscopic scale, in order to study the structural changes caused by relative humidity solicitations along the sorption cycle, for both early wood and latewood phases. That is why many specimens were scanned at different relative humidity levels using X-ray tomography. Relative humidity conditioning was successful by designing a specific device adapted to tomography. The obtained resolution using X-ray tomography was 3.3µm/pixel. After that, the reconstructed volumes were post-treated using adapted software to spruce wood, iMorph. Cell walls’ thicknesses and lumens’ diameters have been calculated at each humidity state. These results have given much better understanding of the localized phenomena that take place at the fiber’s scale.