Low Regeneration Temperature Research Articles

Durability and fire-hazardous-risk evaluation of unique phase separation solvent using high-boiling-point amine and ether

Durability and fire hazard risk evaluations were conducted to determine the process feasibility of a unique phase separation solvent with a low regeneration temperature (90 °C) consisting of an amine, ether, and a small amount of water. The results are as follows. I) The amine degradation rate of the phase separation solvent was determined to be less than 1/10 of that of monoethanolamine, which was attributed to the high oxidative resistance and low regeneration temperature of the former. II) The composition of the gas that formed in the absorber was completely out of the combustible range during the treatment of 6% oxygen-containing gas on a dry basis. Therefore, we believe that this phase separation solvent is applicable to the treatment of exhaust gas from coal-fired thermal power plants and can realize stable operation with a small amount of amine required for replenishment.

SO2 capture by 2-pyridineethanol through the formation of a zwitterionic liquid.

In this work, we report the SO2 capture by 2-pyridineethanol (2-PyEtOH). 2-PyEtOH exhibits a high SO2 capacity, up to 1.16 g SO2 per g solvent at 1.0 atm. The effect of temperature and pressure on the SO2 absorption by 2-PyEtOH is investigated. It is found that 2-PyEtOH can capture 0.57 g SO2 per g solvent even at a low SO2 partial pressure of 0.10 atm. Interestingly, the absorbed SO2 by 2-PyEtOH can be released at a low temperature of 50 °C, suggesting that 2-PyEtOH not only has a high capacity but also exhibits a regeneration process of low energy cost. Moreover, 2-PyEtOH also exhibits an excellent reversibility. The NMR and FTIR studies disclose that SO2 reacts with the -OH group of 2-PyEtOH, resulting in the formation of a zwitterionic sulfite. We believe that the findings of this work will be very useful for the design of efficient absorbents for SO2 capture.

Review on nanoporous inorganic desiccant materials in the context of application in rotary dehumidifiers

Desiccants play a major role in dehumidifiers operated using desiccant wheels. Performance improvement of desiccant wheels is mostly depending on the desiccants. Good desiccant materials should have high adsorption capacity and low regeneration temperature. Researchers in the past have made several attempts to review desiccant materials that possess good adsorption capacities and low regeneration temperature but not many have reviewed the class of nanoporous inorganic desiccant materials. This class of desiccants covers three novel types – Aluminosilicate zeolites, Aluminophosphate-based molecular sieves, and Aerogels. Detail review of nanoporous inorganic desiccants is presented in this paper in the context of the applicability of desiccants in the dehumidifiers operated using desiccant wheels. Authors have attempted to cover a work of researchers who have synthesized and utilized this novel class of desiccants for dehumidification. It is important to note that nanoporous inorganic desiccants have high adsorption capacity than conventional desiccants such as Silica-gel, activated carbon, zeolites, etc., and also, it possesses regeneration temperatures in the range of 50 to 90 °C which can be easy to achieve using low-grade energy or waste heat.

Thermodynamic exploration of two-stage vacuum-pressure swing adsorption for carbon dioxide capture

Adsorption technology is recognised as a promising CO2 capture method due to its characteristics of low regeneration temperature. Analysis model based on carbon pump concept could be used to reveal thermal performance of various carbon capture technologies. However, the concept still has a large gap to become a comprehensive theory. This paper aims to evaluate thermodynamic performance of two-stage vacuum-pressure swing adsorption (VPSA) from a new definition of single-stage VPSA cycle. Energy consumption and exergy efficiency of VPSA cycles are evaluated and compared. Results indicate that introduction of the second stage can significantly elevate the concentration of product gas with less energy input increase. Also, energy consumption decreases from 114.53 kJ mol−1 to 28.23 kJ mol−1 when initial concentration of CO2 rises from 15% to 75%. However, there is a maximum value of exergy efficiency, 7.01% when initial concentration is 45%. Non-discharged CO2 molecules remained in the void of bed after evacuation process will significantly influence the concentration of product gas. The final concentration of product gas achieves the minimum of 91.90% when concentration differences are both 10% at two stages. One remarkable fact is that a new definition of VPSA cycle may be more feasible for thermal analysis in real applications.

A novel lung-inspired 3D-printed desiccant-coated heat exchanger for high-performance humidity management in buildings

Offering an independent humidity management method for buildings, desiccant-coated heat exchangers (DCHXs) are deemed a promising approach to improve the overall energy efficiency of air conditioning (AC) systems. State-of-the-art DCHXs, however, are bound with conventional HX topologies either providing limited desiccant-air interfacial areas or introducing excessive pressure drop penalties. Here, a novel 3D-printed DCHX concept inspired by the bronchi arrangement of a human lung is introduced to address the shortcomings inherent in existing DCHX designs. The proposed lung-inspired DCHX utilizes two intertwined bicontinuous flow networks enabling highly efficient heat and mass transfer characteristics for augmented adsorption and regeneration processes at low pressure drop penalties. While the first network evenly distributes an incoming air stream through the entire volume of the lung-inspired DCHX, the second network volumetrically splits a cooling water stream within and through the first network. Effects of various parameters including air flow rate, outdoor air humidity ratio, and regeneration temperature on dehumidification performance and energy efficiency of the proposed lung-inspired DCHX were investigated. Experimental results indicated the proposed lung-inspired 3D-printed DCHX outperforms existing DCHX systems by demonstrating an excellent balance between a high volumetric adsorption rate and a low pressure drop penalty. The volumetric adsorption rate of the proposed lung-inspired DCHX technology is 54.8 g/m3-s, a more than two-fold improvement compared with state-of-the-art DCHX systems. Additionally, the lung-inspired DCHX offers high thermal energy efficiency of 56% at a low regeneration temperature of 40 °C. Therefore, the proposed lung-inspired 3D-printed DCHX offers a new solid-desiccant-based air dehumidification pathway for next-generation high-performance AC systems.

A facile and green strategy to synthesize N/P co-doped bio-porous carbon with high yield from fungi residue for efficient VOC adsorption

This paper reports a facile and green strategy using hydrothermal treatment coupled with (NH4)3PO4 activation of fungi residue to synthesize N/P co-doped porous carbon. (NH4)3PO4 has no corrosion effect on reactor and attains high carbon yield, ca. 64.5 wt%. Hydrothermal treatment, cross-linked action by (NH4)3PO4, and low-temperature pyrolysis contribute to high carbon yield. To evaluate the economy, another index Qfr (mg/g-fr) is proposed to express the adsorption capacity based on the dosage of original fungi residue. Comparing with H3PO4 and CO(NH2)2, (NH4)3PO4 activation exhibits the highest adsorption capacity of PhH (benzene). Accordingly, its Qfr has surpassed KOH activated carbon, ca. 84.2 > 31.4 mg/g-fr. The abundant surface functional groups of N/P (7.20 and 5.54 at.%) and mesopores-dominant hierarchical pore structure contribute to its excellent adsorption performance. DFT (density functional theory) calculations demonstrate that N/P co-doped porous carbon possesses the highest adsorption binding energy, ca. −1.07 eV. Next, four types of VOC compounds with different physicochemical properties are evaluated for adsorption, i.e., PhH (84.2 mg/g-fr), DCE (dichloroethane, 128.7 mg/g-fr), MeOH (methanol, 23.7 mg/g-fr) and MTHM (methyl mercaptan, 26.0 mg/g-fr). Multi components co-adsorption, adsorption thermodynamics, and recyclability analysis are also evaluated for industrial application. Competitive adsorption still exists but the total adsorption capacity is close to or slightly lower than sole adsorption capacity. After four cycles by low-temperature regeneration, the capacity of tri-component adsorption only decreases 28.0%. Economic analysis demonstrates that the cost of (NH4)3PO4 activation is obviously lower than KOH activation and even superior to commercial activated carbon. Above all, this paper successfully exploits new approach for renewable adsorbents synthesis with facile and green strategy.

Synthesis of Mesoporous γ-Alumina Support for Water Composite Sorbents for Low Temperature Sorption Heat Storage

The efficiency of thermochemical heat storage is crucially determined by the performance of the sorbent used, which includes a high sorption capacity and a low regeneration temperature. The thermochemical salt hydrate– γ-alumina composite sorbents are promising materials for this application but lack systematic study of the influence of γ-alumina structural properties on the final storage performance. In this study, mesoporous γ-Al2O3 supports were prepared by solvothermal and hydrothermal synthesis containing a block copolymer (F-127) surfactant to design thermochemical CaCl2 and LiCl composite water sorbents. Altering the solvent in the synthesis has a significant effect on the structural properties of the γ-Al2O3 mesostructure, which was monitored by powder XRD, nitrogen physisorption, and SEM. Solvothermal synthesis led to a formation of mesoporous γ-Al2O3 with higher specific surface area (213 m2/g) and pore volume (0.542 g/cm3) than hydrothermal synthesis (147 m2/g; 0.414 g/cm3). The highest maximal water sorption capacity (2.87 g/g) and heat storage density (5.17 GJ/m3) was determined for W-46-LiCl containing 15 wt% LiCl for space heating, while the best storage performance in the sense of fast kinetics of sorption, without sorption hysteresis, low desorption temperature, very good cycling stability, and energy storage density of 1.26 GJ/m3 was achieved by W-46-CaCl2.

Preliminary experimental research of metal-organic frameworks (MOFs) for formaldehyde dynamic adsorption

Formaldehyde is a common emission from furniture and indoor decorations. Although the concentration of formaldehyde gas is not too high in the indoor environment, it is highly toxic and carcinogenic. The formaldehyde removal potential of a novel type of green and safe nano-porous materials, Metal-Organic Frameworks (MOFs), with a high surface-to-volume ratio, strong adsorption capacity, and low regeneration temperature was investigated. To date, researchers are mainly focusing on formaldehyde selectivity and detection using MOFs in low moisture circumstances. This study carried out a series of experiments to compare breakthrough curves of formaldehyde dynamic adsorption on MIL-100(Fe), MIL-160(Al), and aluminum fumarate with activated carbon. In experiments, the formaldehyde was evaporated from diluted formalin solution, dried to 30±5 % RH, and driven through different adsorbents by nitrogen. The results indicated that MOFs showed great potential for indoor air formaldehyde removal.

Theoretical dehumidification capacity of acorn nutshell-based activated carbon under two Asian urban cities’ ambient air condition

• Prepared activated carbon has better dehumidification performance than silica gel under humid ambient air conditions. • Prepared activated carbon can be utilized as desiccant material with a regeneration temperature of lower than 60°C. • The water isotherm shape of prepared activated carbon gives an advantage to the dehumidification performance. Indoor air humidity plays a vital role in determining occupants’ health and industrial product quality. Removing excess humidity by adsorption dehumidification is still facing a challenge in finding a suitable material with high adsorption capacity and low regeneration temperature. In this study, the theoretical dehumidification capacity of prepared acorn nutshell-based activated carbons was calculated and compared with silica gel type RD and RD-2060. The calculation was based on the outdoor air condition in two Asian capital cities: Jakarta and Tokyo. The theoretical study found that prepared activated carbon has better dehumidification performance under Jakarta conditions using regeneration temperatures of less than 60°C. Under Tokyo conditions, activated carbon shows auspicious performance during the summer season. Compared with silica gels, acorn nutshell-based activated carbon has a better dehumidification capacity to process high humidity ambient air with a lower regeneration temperature.

Heat and Mass Transfer Characteristics of a Desiccant Dehumidification System Operating by Low Regeneration Temperature

Heat and mass transfer characteristics (HMTCs), which defined the latent and sensible load, are essential for developing an effective desiccant dehumidification system (DSDHS). Therefore, the current work provides an investigation on the HMTCs, in the form of the Nusselt and Sherwood numbers. Under constant adsorption temperature of 293 K, the HMTCs were analyzed with three different regeneration temperatures of 308 K, 318 K, and 328 K. While the velocities were kept constant of 0.1 kg/s both for adsorption and regeneration processes. The DSDHS used the polymer material having the highest adsorption capacity of 0.78 kg/kg. Using the thermal and mass resistance approaches, the heat, and mass transfer coefficients were able to predict. The results show that the highest regeneration temperature revealed the most top differences between the humidity ratio inlet and outlet, which was 2.2 g/kg. The Nusselt number values, as well as Sherwood number, tend to increase with the rise of regeneration temperature. The proposed empirical correlation for predicting the HMTCs was followed by the experimental data with a maximum discrepancy of 17%. It is suggested that the properties of the interface must be carefully acquired to reduce the discrepancy between the experimental data and analytical.

Synthesis of MgO nanostructures through simple hydrogen peroxide treatment for carbon capture

The acceleration of global warming induced by uncontrolled CO2 emission has placed a potential threat to human survival and development. The unique properties of magnesium oxide (MgO) including having appropriate surface basicity, low regeneration temperature and high theoretical CO2 uptake capacity make it a promising adsorbent candidate for CO2 capture. Herein, the development and investigation of structure-activity relationships of MgO nanostructures prepared via simple hydrothermal-calcination synthesis method for CO2 capture were reported in this work. The correlation of structural characteristics and basic site properties of MgO samples were discussed by implementing a variety of analytical technologies including BET, SEM, XRD, TPD, Malvern Mastersizer and XPS. The TPD, XPS analysis as well as Claisen-Schmidt condensation reaction show that the hydrothermal-calcination process strongly reduced crystal size and transformed high, low, and moderate basic sites at different ratios for MgO samples. Particularly, MgO nanostructures with morphology of irregular tiny nanocrystals (down to ~5 nm) prepared from simple hydrogen peroxide (H2O2) treatment on commercial MgO exposed abundant moderate and strong basic sites demonstrated significantly better performance (1.04–1.73 mmol/g in a wide temperature range of 100–300 oC) than commercial MgO for CO2 capture. Recyclability of prepared MgO absorbents was also examined and a simple H2O2 regeneration method was explored. The proper correlation of structural characteristics and basic site properties of MgO samples vs their CO2 capture performance were established.

Nitrogen-rich layered carbon for adsorption of typical volatile organic compounds and low-temperature thermal regeneration

Carbon-based adsorbents with a high adsorption capacity and low price have been widely used in the removal of volatile organic compounds (VOCs), but the poor gas selectivity and reusability limit their industrial applications. In this work, disc-like nitrogen-rich porous carbon materials (HAT-Xs) were synthesized to remove typical VOCs via adsorption. By controlling the synthesis temperature from 450 to 1000 °C, the C/N ratio of the HAT-Xs increased from 1.85 to 12.56. The HAT-650 synthesized at 650 °C with the high specific surface area of 305 m2 g−1 exhibits the highest adsorption capacity of 141 mg g−1 for ethyl acetate (which is 3.2 times for that of activated carbon), and 39.4 mg g−1 for n-hexane, 48.6 mg g−1 for toluene. Kinetic studies indicated that the adsorption is physical adsorption and that the interior surface diffusion is the main rate-determining step during the adsorption progress, the interior surface diffusion rate of ethyl acetate on HAT-650 is 1.455 mg g−1 min−0.5. At the same time, the desorption and reuse tests show that HAT-650 has excellent reusability with low desorption and regeneration temperature of 120 °C, and high desorption efficiency of 95.2% and that it could be a promising ethyl acetate adsorbent for industrial applications.

Preparation and characterization of thermo-responsive composite for adsorption-based dehumidification and water harvesting

Adsorption technologies for adsorption-based dehumidification and water harvesting from the atmosphere have great potential for energy-saving and environmental protection. The key to successful utilization of these technologies is desired properties of adsorbents. However, most existing adsorbents fail to have the characteristic of both high adsorption capacity and good desorption ability under low regeneration temperature such as at 40 °C. In this work, we grafted a thermo-responsive polymer (Poly(N-isopropylacrylamide) PNIPAM) to silica gel and impregnated with lithium chloride to prepare a composite adsorbent. The adsorption capacity of this composite can reach 1.70 g g−1 at 20 °C&70%RH, and 56% of adsorbed moisture can be released within 60 min at 40 °C&10%RH. This method offers a promising route to develop high-performance thermo-responsive composite adsorbents for desiccant coated heat exchanger (DCHE)-based dehumidification and adsorption-based atmospheric water harvesting (ABAWH).

Analysis of the microstructure and elemental occurrence state of residual ash-PM following DPF regeneration by injecting oxygen into non-thermal plasma

Particulate matter (PM) capture tests were carried out on clean diesel particulate filters (DPFs) under different loads (25%, 50%, 75% and 100%). DPFs were regenerated by a non-thermal plasma (NTP) injection device. Raman spectroscopy and x-ray photoelectron spectroscopy were used to investigate changes in the microstructure and element occurrence state of the sediment in DPF channel before and after regeneration. The order of the PM samples decreased before NTP treatment as the load increased; the amorphous carbon content was high, and the oxidation activity was higher. After NTP treatment, the carbon atoms at the edge of the microcrystalline structure in the ash-PM samples were oxidized, and the structure was reorganized; in addition, the amorphous carbon content decreased, and the structure was more diversified. Before NTP, the C element of PM samples was the main component, and the content of the O element was relatively low. The C element occurred in the form of C–C, C–OH, and O–C=O functional groups, and O atoms were mainly combined with C–O. After NTP, the content of Na, P, S, Ca, and other inorganic elements in ash-PM samples was prominent because C atoms were removed by NTP active substances. There were two forms of S element occurrence (SO4 2− and SO3 2−); the proportion of SO4 2− was approximately 40%, and the proportion of SO3 2− was approximately 60%. Study of the microstructure and element occurrence of the residues in the DPF channels improved our understanding of the mechanism of the low-temperature regeneration of DPF from NTP.

Amine-functionalized fumed silica for CO2 capture through particle molecular layer deposition

Solid adsorbent materials for CO2 capture have received increasing attention due to the high regenerative energy requirements and physical limitations of traditional liquid systems. Supported amines have become widely-researched materials due to their ambient adsorption capabilities and low regeneration temperatures. Here, Particle Molecular Layer Deposition (MLD) is introduced as a novel loading method for amine functionalization to improve the regeneration stability and adsorption capacity of supported amine sorbents. This paper confirms two MLD chemistries: (3-aminopropyl)triethoxysilane (APTES) and N1-(3-trimethoxysilylpropyl)diethylene triamine (TMPTA). Both precursors were deposited at 150 °C in a binary reaction with water. Adsorption capacity of the amine functional groups increased to ~0.005 mmol/m2 as the number of MLD cycles increased. Low sorbent regeneration temperatures and stable regeneration of active sites over 25 cycles were demonstrated by both the APTES and TMPTA functionalized sorbent. This is the first demonstration of an MLD process used to functionalize a sorbent for CO2 capture. This is also the first use of TMPTA for MLD.

Performance characterization and application of composite adsorbent LiCl@ACFF for moisture harvesting

Freshwater scarcity is a global threat to modern era of human society. Sorption-based atmospheric water harvesting (AWH) is prospective to provide fresh water for remote water-stressed areas lacking in water and electricity. Adsorbent material plays a vital role in such AWH systems. Here, we report a solid adsorbent synthesized by impregnating hygroscopic salt lithium chloride (LiCl) into solidified activated carbon fiber felt (ACFF modified by silica sol). Composite samples immersed with different mass concentrations of silica sol are prepared and characterized for dynamic water uptake, equilibrium water uptake, textural and thermal properties. AS5Li30 (ACFF + 5 wt% silica gel + 30 wt% LiCl) exhibits an efficient water uptake of 2.1 g/g at 25 °C and 70% relative humidity (RH). The material further demonstrates a heat storage capacity of 5456 kJ/kg. Its low regeneration temperature (< 80 °C) and good cycle stability make it feasible to be used in practical water production applications, driven by solar energy and other low-grade energy. Estimation results show that water harvesting unit can produce 1.41 gH2O/gAS5Li30 under 25 °C and 75% RH.

Energy and Exergy Analysis of Waste Heat Recovery Closed-Cycle Gas Turbine System while Operating with Different Medium

In this paper is performed energy and exergy analysis of waste heat recovery closed-cycle gas turbine system. Analyzed system can use waste heat from various main propulsors (gas turbines or internal combustion engines). Basically, the observed system operates by using CO2, what was the baseline for the analysis. It is investigated did the observed system, while retaining the same configuration, can operate with different operating mediums instead of CO2. Other observed operating mediums were Air and Helium. During the change in operating medium, pressures and temperatures in some system operating points cannot remain the same as in the process with CO2, but the intention was to perform only the necessary changes (to ensure proper operation of each system component). Obtained results show that the system, while retaining the same configuration, can operate by using different operating mediums. Energy analysis of the system shows that the whole configuration is composed to operate with CO2, because the whole system energy efficiency is much higher than in operation with Air or Helium. The energy efficiency of the whole system during operation with CO2 is 87.68%, with Air is 58.39% and operation with Helium gives energy efficiency of 49.25%. Exergy analysis of the observed system shows that the system has a good potential to operate with other mediums, because in any observed situation exergy efficiency of the whole system was higher than 50%. In this analysis the highest exergy efficiency of the whole system was obtained during operation with Air (57.76%). In the observed system, low-temperature regenerator and main turbo-compressor are detected as components which are highly influenced by the change of operating medium. Therefore, these two components should be a baseline for further improvements and system optimization.

Hygroscopic salt-modulated UiO-66: Synthesis and its open adsorption performance

Adsorption-based passive solar air water collection devices have great potential for delivering potable water to arid or desert regions of the world. Here, we synthesized the hygroscopic salt-modified UiO-66 composite adsorbents by impregnation method. In the open adsorption test, LiCl particles have high water adsorption and a large contact area with water vapor, which enhances the water adsorption performance of the composite adsorbents. Furthermore, in the regeneration temperature test, LiCl/UiO-66 showed the performance of low regeneration temperature. The hydrothermal stability of LiCl/UiO-66 was confirmed by cycle tests. The experimental results show that the solar air water collection device based on LiCl/UiO-66 composite adsorbents is a promising method to solve the problem of water shortage in arid areas.

Dynamic Simulation of Desiccant Cooling System with Simultaneously Using Solar and Ground Renewable Energies in Hot-Humid Regions

This paper presents the dynamic operation of a desiccant cooling system combined with solar and ground source energies. Solar energy is used for providing the required energy for regenerating the desiccant wheel, and the ground source heat exchanger is exploited as an air pre-cooling component. The potential of the system in providing thermal comfort is assessed in hot-humid regions. Results reveal that this system is capable of providing thermal comfort in these regions with low-grade regeneration temperatures (lower than 75 ℃). As a new perspective, the maximum value of the desiccant wheel regeneration temperature is controlled. The effect of the desiccant wheel performance and its maximum regeneration temperature is evaluated on the behavior of the system. With results, high performance desiccant wheel increases the provided thermal comfort up to 40% and the contribution of solar energy up to 14% compared with its low performance. Reducing the maximum regeneration temperature to 50 ℃, decreases the achieved thermal comfort to lower than 30%. Ground source heat exchanger enhances the thermal comfort and a specified level of that can be provided with lower regeneration temperatures. The economical assessment shows that in entirely provided thermal comfort conditions by the system, the payback period is calculated to be 8.2 years.

Design of thermo-responsive hyperbranched nanofibre-based adsorbent with high CO2 adsorption capacity and analysis of its ultra-low temperature regeneration mechanism

Thermo-responsive solid amine adsorbents are used for adsorption of CO2 in carbon capture and storage. They have a low temperature regeneration, but are incapable of high CO2 adsorption capacity because of the imbalance between the densities of the amino and thermo-responsive groups. Hence, a novel thermo-responsive hyperbranched intelligent nanofibre-based adsorbent was designed via cross-linking with a hyperbranched polyamine and a thermo-responsive intelligent nanofibre. The liquid–solid phase one-step rapid conversion used here balanced the high amino density (12.40 mmol g−1) with that of the synergistic groups (thermo-sensitive groups, 3.12 mmol g−1, and hydroxyl groups, 4.35 mmol g−1) of the adsorbent. A high-efficiency diffusion kinetics was maintained, and the conversion rate of the reactants reached 99%. An in situ variable-temperature characterisation and density functional theory (DFT) analysis were performed. The adsorbent possessed high CO2 adsorption capacity (6.23 mmol g−1) and ultra-low regeneration temperature (60 °C), the lowest regeneration temperature reported in the literature to date. These were attributed to the specialized and cooperative mechanism between amino, hydroxyl, and thermo-responsive groups of the adsorbent.