Temperature Swing Adsorption Research Articles

Computational Selection of High-Performing Covalent Organic Frameworks for Adsorption and Membrane-Based CO2/H2 Separation.

Covalent organic frameworks (COFs) have high potential in gas separation technologies because of their porous structures, large surface areas, and good stabilities. The number of synthesized COFs already reached several hundreds, but only a handful of materials were tested as adsorbents and/or membranes. We used a high-throughput computational screening approach to uncover adsorption-based and membrane-based CO2/H2 separation potentials of 288 COFs, representing the highest number of experimentally synthesized COFs studied to date for precombustion CO2 capture. Grand canonical Monte Carlo (GCMC) simulations were performed to assess CO2/H2 mixture separation performances of COFs for five different cyclic adsorption processes: pressure swing adsorption, vacuum swing adsorption, temperature swing adsorption (TSA), pressure−temperature swing adsorption (PTSA), and vacuum−temperature swing adsorption (VTSA). The results showed that many COFs outperform traditional zeolites in terms of CO2 selectivities and working capacities and PTSA is the best process leading to the highest adsorbent performance scores. Combining GCMC and molecular dynamics (MD) simulations, CO2 and H2 permeabilities and selectivities of COF membranes were calculated. The majority of COF membranes surpass Robeson’s upper bound because of their higher H2 permeabilities compared to polymers, indicating that the usage of COFs has enormous potential to replace current materials in membrane-based H2/CO2 separation processes. Performance analysis based on the structural properties showed that COFs with narrow pores [the largest cavity diameter (LCD) < 15 Å] and low porosities (ϕ < 0.75) are the top adsorbents for selective separation of CO2 from H2, whereas materials with large pores (LCD > 20 Å) and high porosities (ϕ > 0.85) are generally the best COF membranes for selective separation of H2 from CO2. These results will help to speed up the engineering of new COFs with desired structural properties to achieve high-performance CO2/H2 separations.

Effects of bed aging on temperature signals from fixed-bed adsorbers during industrial operation

The capacity of adsorber beds used in industrial-scale temperature-swing adsorption diminishes over time due to bed aging. Here, we present industrial data on the temperature signals from fixed-bed adsorbers using activated carbon designed to remove benzene and other impurities from the gas produced in biomass gasification. The aging of the adsorber beds proceeds due to irreversible adsorption of trace species and manifests itself via two simultaneous effects: a decrease in the availability of active adsorption sites over time and an increase in the overall thermal mass of the bed. Both effects tend to dampen the temperature response of the beds during operation, implying that they are easily confounded. Model descriptions of bed aging should account for both effects.

Developing an adsorption-based gas cleaning system for a dual fluidized bed gasification process

Biomass has the potential to make a major contribution to a renewable future economy. If biomass is gasified, a wide variety of products (e.g., bulk chemicals, hydrogen, methane, alcohols, diesel) can be produced. In each of these processes, gas cleaning is crucial. Impurities in the gas can cause catalyst poisoning, pipe plugging, unstable or poisoned end products, or harm the environment. Aromatic compounds (e.g., benzene, naphthalene, pyrene), in particular, have a huge impact on stable operation of syngas processes. The removal of these compounds can be accomplished by wet, dry, or hot gas cleaning methods. Wet gas cleaning methods tend to produce huge amounts of wastewater, which needs to be treated separately. Hot gas cleaning methods provide a clean gas but are often cost intensive due to the high operating temperatures and catalysts used in the system. Another approach is dry or semi-dry gas cleaning methods, including absorption and adsorption on solid matter. In this work, special focus was laid on adsorption-based gas cleaning for syngas applications. Adsorption and desorption test runs were carried out under laboratory conditions using a model gas with aromatic impurities. Adsorption isotherms, as well as dynamics, were measured with a multi-compound model gas. Based on these results, a temperature swing adsorption process was designed and tested under laboratory conditions, showing the possibility of replacing conventional wet gas cleaning with a semi-dry gas cleaning approach.

Preparation of CO2 adsorbent with N1-(3-(trimethoxysilyl)propyl)-1,3-propanediamine and its performance

N1-(3-(trimethoxysilyl)propyl)-1,3-propanediamine (2NS-P), a diaminosilane having a propyl spacer between the two amino groups was successfully synthesized, and a CO2 adsorbent functionalized with 2NS-P was prepared via impregnation of it into silica. The adsorption performance and stability of 2NS-P/Kona95 were examined and compared to that of N1-(3-(trimethoxysilyl)propyl)ethane-1,2-diamine (2NS)/Kona95 having an ethyl spacer. 2NS-P/Kona95 exhibited better CO2 adsorption capacity and CO2/N efficiency. The adsorbents were subjected to ten cycles of temperature swing adsorption (TSA), demonstrating that stability of 2NS-P/Kona95 was better than that of 2NS/Kona95. The spent 2NS-P/Kona95 showed the absence of cyclic urea formation in FT-IR spectrum, explaining the better stability of 2NS-P/Kona95 than 2NS/Kona95.

Do New MOFs Perform Better for CO2 Capture and H2 Purification? Computational Screening of the Updated MOF Database.

High-throughput computational screening of metal organic frameworks (MOFs) enables the discovery of new promising materials for CO2 capture and H2 purification. The number of synthesized MOFs is increasing very rapidly, and computation-ready, experimental MOF databases are being updated. Screening the most recent MOF database is essential to identify the best performing materials among several thousands. In this work, we performed molecular simulations of the most recent MOF database and described both the adsorbent and membrane-based separation performances of 10 221 MOFs for CO2 capture and H2 purification. The best materials identified for pressure swing adsorption, vacuum swing adsorption, and temperature swing adsorption processes outperformed commercial zeolites and previously studied MOFs in terms of CO2 selectivity and adsorbent performance score. We then discussed the applicability of Ideal Adsorbed Solution Theory (IAST), effects of inaccessible local pores and catenation in the frameworks and the presence of impurities in CO2/H2 mixture on the adsorbent performance metrics of MOFs. Very large numbers of MOF membranes were found to outperform traditional polymer and porous membranes in terms of H2 permeability. Our results show that MOFs that are recently added into the updated MOF database have higher CO2/H2 separation potentials than the previously reported MOFs. MOFs with small pores were identified as potential adsorbents for selective capture of CO2 from H2, whereas MOFs with high porosities were the promising membranes for selective separation of H2 from CO2. This study reveals the importance of enriching the number of MOFs in high-throughput computational screening studies for the discovery of new promising materials for CO2/H2 separation.

Site Trials of Ventilation Air Methane Enrichment with Two-Stage Vacuum, Temperature, and Vacuum Swing Adsorption

Site trials of a two-stage vacuum, temperature, and vacuum swing adsorption (VTVSA) process using carbon fiber composites was, for the first time, carried out at an Australian coal mine to enrich ventilation air methane (VAM) in a safe manner. Four sets of tests were carried out with average inlet VAM concentrations ranging from 0.54 to 0.73 vol %, resulting in 4.34–4.94 vol % CH4 through the first stage and 27.62–35.89 vol % CH4 in the final product, which is overall a 44–63 times VAM enrichment. The average CH4 concentrations after the first stage were successfully maintained to be less than 5 vol % by regulating the initial vacuum pressure in response to the inlet VAM concentrations. The presence of CO2 in actual ventilation air, specifically the ratio of CO2 over CH4 concentrations, was found to associate with the methane recovery of the second stage, and CH4 and O2 concentrations in the final product. Compared to our previous results with simulated ventilation air, no effect of the presence of moisture in ventilation air on CH4 capture performance was found, confirming the adequacy of carbonaceous materials such as carbon fiber composites to be employed for VAM enrichment. In addition, oxygen concentrations in the final product for all tests were less than 10 vol %, enhancing the operational safety at coal mine sites.

Dry and Wet CO2 Capture from Milk‐Derived Microporous Carbons with Tuned Hydrophobicity

AbstractPore size distribution and surface chemistry of bio‐derived (milk) microporous dominated carbon “MDC” is synergistically tuned, allowing for promising carbon capture in a dry CO2 atmosphere and in mixed H2O–CO2. The capture capacity is attributed to the synergy of a large total surface area with an ultramicroporous and microporous texture (e.g., Stot 1889 m2 g−1, Smic 1755 m2 g−1, Sultra 1393 m2 g−1), and a high content of nitrogen and oxygen heteroatom moieties (e.g., 5 at% N, 10.5 at% O). Tailored two‐step low‐temperature pyrolysis‐chemical activation is employed to take advantage of the intrinsic properties of the precursor, allowing for this unusual textural properties‐heteroatoms combination. For example, tested at 1 bar and 295 or 273 K, MDCs adsorb up to 22.0 and 29.4 wt% CO2, respectively. MDCs are also tailored to be hydrophobic, with CO2/H2O adsorption selectivity even after prolonged cycling. Maximum working capacities of 10.8 wt% for pure CO2 and 3.5 wt% for a flue gas simulant (15% CO2, 85% N2) are measured using temperature swing adsorption with dynamic purge gases, while being minimally affected by humid conditions. This work is directly aligned with the United Nation’s Sustainable Development Goal 13, take urgent action to combat climate change and its impacts.

Continuous CO2 capture performance of K2CO3/Al2O3 sorbents in a novel two-stage integrated bubbling-transport fluidized reactor

Post-combustion CO2 capture with solid sorbents is a promising technology. The feature of temperature swing adsorption for such process requires sufficient gas-sorbent contact, sustained driving force for adsorption and adjustable sorbent circulation between reactors. This, however, is hard to fully realize by traditional single-regime fluidized reactors. In view of this, we proposed a novel two-stage integrated bubbling-transport bed reactor and examined its CO2 capture performance using K2CO3/Al2O3 sorbents. The results show that the optimal adsorption temperature ranges from 60 °C to 100 °C, much wider than that of traditional reactors. The CO2 capture efficiency increases with both sorbent circulation rate and desorption temperature. Better CO2 capture performance was observed when using air instead of CO2 as the desorption gas. Nevertheless, the difference is negligible as the desorption temperature exceeds 200 °C. Stage I is the region where CO2 adsorption mainly takes place, owing to the over-adsorption of water vapor. This limits the CO2 capture performance of the entire system. To this regard, water vapor step-feeding was carried out, acting as an in-situ activation of sorbents. It enhances the maximum CO2 capture efficiency from 87% to 96%, meanwhile showing a strong anti-interference ability for water vapor fluctuation even at a fixed total water vapor. The 24 h continuous test verifies the superiority of the present system as the CO2 capture efficiency maintains around 93% and the desorption CO2 purity keeps above 98%.

Non-equilibrium thermodynamic analysis of adsorption carbon capture: Contributors, mechanisms and verification of entropy generation

Emissions of greenhouse gases should be reduced for the slowing of global warming. Carbon capture by adsorption, which is available to retrofit of existing power plants and to integration with renewable energy, is an effective technology to reduce CO2 emissions. However, the heavy energy consumption has already become a limitation to scale-up applications. Thermodynamic research, especially entropy analysis, could quantitatively clarify the irreversible loss and provide a guidance to the energy-saving design. Considering that classical thermodynamics is powerless in the description of significant kinetic characteristics of adsorption carbon capture, non-equilibrium thermodynamics is thus required, as it could provide a detailed analysis on the contributors and mechanisms of entropy sources. In this paper, the entropy source contributors of adsorption systems, which are composed of entropy generation of 9 irreversible factors for different adsorption cycles, were derived. An entropy research framework was proposed and illustrated through a case study of vacuum temperature swing adsorption (VTSA). The results are also compared with the classical exergy method, and the difference between the results of the two methods for entropy generation is 1.97%. This paper provides a thorough research framework for detailed thermodynamic analyses of adsorption carbon capture.

Experimental comparison of regeneration methods for CO2 concentration from air using amine-based adsorbent

Comparison of different regeneration options for direct air capture (DAC) has usually been limited to only consider pure CO2 production, limiting the process options to e.g. temperature-vacuum swing adsorption (TVSA) or steam-stripping. In this work, detailed experimental comparison is conducted of temperature swing adsorption (TSA/TCSA) and TVSA for DAC. Particularly, TVSA is assessed with air or inert gas purge flow (TVCSA) and without purge flow. The working capacity, regeneration specific energy requirement (SER) and adsorbent regenerability of these processes was compared. For all other studied regeneration options except TVSA without purge flow, over 85% regeneration was obtained already at 60 °C. Isobaric TSA at 60 °C had the lowest regeneration SER of 4.2 MJ/kgCO2. Coupling TSA with mild vacuum improved desorption rate and increased working capacity from 0.47 to 0.51 mmolCO2/gsorbent, requiring 7.5 MJ/kgCO2 for regeneration. Without purge flow, TVSA resulted in only 0.39 mmolCO2/gsorbent with the SER of 8.6 MJ/kgCO2 at 100 °C. Due to lower allowable regeneration temperature of 60 °C, mild vacuum TVSA with air flow also had a lower cyclic capacity decrease rate of 0.26%/cycle compared to 0.38%/cycle with TVSA without purge flow at 100 °C. However, using 100 °C with air flow in the TVSA process lead to a significant capacity decrease of 0.6%/cycle. Therefore, using either air or inert purge flow below 100 °C coupled with mild vacuum has benefits over the TVSA process with no inflow in terms of CO2 productivity, specific energy requirement and adsorbent regenerability. For utilization purposes that require low-concentration CO2, TVSA with purge flow should thus be considered as a viable regeneration option for direct air capture along with isobaric TSA.

A novel technology for liquefied synthetic natural gas production powered by renewable electricity: Process development and impact analysis on vehicular transportation

Overgeneration of wind energy conversion systems represents a grid issue, limiting the growth of renewable energy utilization. Alternative fuels utilization such as liquefied natural gas is emerging as a new market with a big potential in freight transport. In order to mitigate wind energy production curtailment, a power to liquefied synthetic natural gas process is proposed. Solid oxide electrolyser and catalytic methanation integrated system is applied to produce hydromethane. After a dehydration step in a temperature swing adsorption unit, low temperature gas upgrading techniques are applied for the first time to hydromethane mixture. Liquified synthetic natural gas is produced, meeting grid injection and endothermic engines requirements after regasification. A higher energy efficiency with respect to the application of traditional technologies is achieved. Plant configuration was optimized for internal thermal and chemical energy recovery and exploitation, achieving an overall electrical to chemical efficiency of about 50%. A case study was analyzed for the Irpinia (Italy) territory, strongly affected by wind energy overgeneration. Impact on local transport infrastructure was assessed through well-to-wheel analysis, considering the use of produced liquified synthetic natural gas in heavy duty vehicles. Greenhouse gas avoided emissions are expected to correspond to 7.1% of the vehicular emissions related to local traffic statistics for 2016.

Industrial-Scale Benzene Adsorption: Assessment of a Baseline One-Dimensional Temperature Swing Model against Online Industrial Data

Existing models for industrial gas cleaning via temperature-swing adsorption are typically validated against laboratory-scale test units, while industrial cases involve units that are significantly larger, operate with complex gas mixtures, and are cycled for long times. The extent up to which existing model formulations are applicable in industrial units is not well established. Here, we compare simulations with a baseline 1D model at an industrial scale to the online temperature data from steam-regenerated adsorbers in a 32 MW biomass gasification plant. Adsorption of benzene is described using the Dubinin–Radushkevich isotherm, and steam may condense/evaporate but not adsorb. The simulations reproduce the main trends in the industrial data, meaning that they can be used to assess dynamic properties that are not measured, such as the amounts of adsorbates and water. Additional model development is however needed to better represent the effects of complex gas mixtures and water transport and evaporation inside the beds.

Synthesis and functionalization of cauliflower-like mesoporous siliceous foam materials from oil shale waste for post-combustion carbon capture

In this work, meso-structured siliceous form materials (SFM) were synthesized from oil shale ash via a green and time-saving microemulsion templating method and modified with polyethleneimine (PEI) for post-combustion carbon capture. The effects of preparation conditions, such as P123/TMB ratio, aging temperature and pH values, on sample morphology and pore structure were studied to understand the characteristics of inorganic silica precursors. Results show that the SFMs possess 3-dimensional porous framework with a large surface area of 901.3 m3/g and a pore volume of 2.0 cm3/g. The CO2 adsorption behaviour of PEI-impregnated SFMs were investigated in terms of CO2 adsorption capacity and temperature swing adsorption (TSA) cycling stability under a simulated flue gas condition (75 °C and 15% CO2/N2). The results show that pore-expanded SFMs with 50 wt% PEI loading exhibited higher CO2 uptake (109 mg/g-adsorbent) compared to non-pore-expended materials (50 mg/g-adsorbent) and no appreciable reduction in CO2 uptake was observed in the first 10 cycles. However, the DRIFTS spectra of CO2-evacuated adsorbents revealed the presence of alkylammonium carbamates residuals and formations of urea species. This could explain the reduction in CO2 adsorption capacity after 10 cycles.

CO2 adsorption capacity of zeolites synthesized from coal fly ashes

Given the increase in CO2 emissions, the adsorption process using zeolites are proposed to remove this compound from combustion gases in pulverized coal power plants. Besides it, these materials can also be synthesized using coal fly ash to reconcile environmental and economic concerns. The aim of this study was to measure the adsorption capacity of zeolites synthesized from coal fly ash compared with commercial zeolites and assess their performance in temperature swing adsorption processes. Two pelletized synthetic zeolites were selected, one NaX type (SZX) and one NaA type (SZA), and two commercial zeolites, one NaX (CZX) and one NaA (CZA). Zeolites were characterized by XRF, XRD and textural analysis (BET). Adsorption capacity tests were performed by thermogravimetric analysis using similar CO2 concentrations to those found in pulverized carbon combustion gases, without moisture. Isotherms were also obtained for synthetic and commercial zeolites type X. The XRD results showed substantial similarity between the commercial and synthesized zeolites, indicating a good degree of crystallinity. The CO2 adsorption capacity at 303 K for both samples showed values similar to those reported in the literature (1.97 mmol/g for SZX and 1.37 mmol/g for SZA), demonstrating their potential in commercial applications. After five cycles, the adsorption capacity of all samples remained practically unchanged, indicating the possibility of application in TSA processes. In the adsorption tests at different temperatures and in the isotherms, adsorption capacity declined as temperature increased for both samples, being similar to benchmark commercial 13X and 4A zeolite adsorbents.

Low-pressure supersonic separator with finishing adsorption: Higher exergy efficiency in air pre-purification for cryogenic fractionation

Air fractionation in cryogenic plants demands a Pre-Purification Unit for air compression and removal of water, carbon dioxide and trace-species. The conventional Pre-Purification Unit – FULL-TSA – adopts temperature-swing adsorption (TSA) with an activated-alumina bed for dehumidification followed by a molecular-sieve bed removing carbon dioxide and trace-species. A novel scheme – SS-TSA – prescribes a Supersonic Separator abating ≈98.5% of moisture followed by a small single-bed molecular-sieve removing remaining impurities. SS-TSA-HI is a SS-TSA variant allocating compression heat for molecular-sieve regeneration. This work compares thermodynamic performances of FULL-TSA, SS-TSA and SS-TSA-HI via exergy analyses and discloses better utilization of resources. Exergy analyses are supported by HYSYS simulator running with unit-operation extensions for calculating the phase-equilibrium sound speed and simulating the supersonic separator. Since exergy rates depend on Reference Environmental Reservoirs, two Reference formalisms are employed at 1 atm and 25 °C. Reference#1 prescribes air with 60% relative humidity (the raw air feed), while Reference#2 adopts water-saturated air. It is shown that Reference#1 is appropriate for overall system analysis, while Reference#2 is better for sub-systems analysis as it dramatically lowers cooling-water exergy flows. SS-TSA has 61% less exergy losses than FULL-TSA in the purification step as the supersonic separator accomplishes bulk dehumidification drastically reducing steam and nitrogen for bed regeneration. Reference#1 exergy efficiencies of FULL-TSA, SS-TSA and SS-TSA-HI attained 57.9%, 60.0%, and 60.3%, respectively.

Environmental Assessment of a Coal Power Plant with Carbon Dioxide Capture System Based on the Activated Carbon Adsorption Process: A Case Study of the Czech Republic

The Czech Republic is introducing new technological concepts for mitigation of greenhouse gases (GHG) in coal-based energy industries. One such technology, in power plants, is post combustion CO2 capture from flue gases by activated carbon adsorption. A life cycle assessment (LCA) was used as the assessment tool to determine the environmental impacts of the chosen technology. This article focuses on a comparative LCA case study on the technology of temperature-swing adsorption of CO2 from power plant flue gases, designed for the conditions of the Czech Republic. The LCA study compares the following two alternatives: (1) a reference power unit and (2) a reference power unit with CO2 adsorption. The most significant changes are observed in the categories of climate change potential, terrestrial acidification, and particulate matter formation. The adsorption process shows rather low environmental impacts, however, the extended LCA approach shows an increase in energy demands for the process and fossil depletion as a result of coal-based national energy mix. The feasibility of the study is completed by the preliminary economical calculation of the payback period for a commercial carbon capture unit.

Hollow fiber-based rapid temperature swing adsorption process for carbon capture from coal-fired power plants

Post-combustion carbon capture is one of the feasible methods to reduce emission of carbon dioxide (CO2) from coal-fired power plants. The biggest challenge in this technology is reduction of energy consumption. This work proposes a hollow fiber based rapid temperature swing adsorption (RTSA) method for capturing CO2 from typical coal-fired power plants. The proposed RTSA approach can shorten the operating time and using low-grade energy for regeneration of adsorption elements. In this study, the tank-in-series model is used to simulate the RTSA process including adsorption and desorption periods. A dual-column operating procedure is then used to treat the flue gas continuously from the coal-fired power plants. Main operating variables including inlet gas volume flow rate (0.1–0.2 m3/s), abandon time (0–10 s), desorption temperature (80–120 °C) on key performance factors such as discharge gas purity, capture ratio of CO2, and energy consumption per unit CO2, etc. are investigated for reducing the energy consumption. This study found that the inlet gas volume flow rate will significantly affect the capture ratio, where smaller gas volume flow rate would be beneficial to increase capture ratio. The abandon time obviously affects the purity of the captured CO2, where the longer abandon time leads to higher purity. Desorption temperature affects both the capture ratio and purity of captured CO2. The higher the desorption temperature, the greater the purity and capture ratio. For one typical basic unit with dual-column hollow fiber-based RTSA, the study found that when the inlet gas volume flow rate is 0.12 m3/s, the desorption waiting time is 7 s, and the desorption temperature is 120 °C, both the CO2 purity and capture ratio can exceed 90%. With considering the possibility of using steam in a low-pressure turbine as a source of heat required for Dual column vacuum RTSA (DC-vRTSA), the impact on the efficiency and stream data of typical coal-fired power plants are calculated. DC-vRTSA at 120 °C, 100 °C and 80 °C will reduce the efficiency of coal-fired power plants by 8.2%, 6%, and 3.4%, respectively.

Experimental Validation of a Multidimensional Model for an Indirect Temperature Swing Adsorption Unit

AbstractConventional temperature swing adsorption (TSA) is mainly applied for the removal of trace contaminants. Indirectly heated and cooled adsorbers were developed to make bulk separation economically feasible. A quasi‐continuous TSA process to remove CO2 from an N2/CO2 mixture with a pilot plant is established. The experimentally determined data are taken to validate and to adjust a 2D simulation model. For the validation, the CO2 desorption, the N2 recovery rate as well as the axial temperature profile are compared. The successful model validation can be seen in the good agreement between simulation and experimental results. Moreover, this process is able to separate high amounts of CO2 and to produce a nearly CO2‐free product stream.

Concentrated Carbon Dioxide (CO2) from Diluted Sources through Continuous Temperature Swing Adsorption (TSA)

Carbon dioxide (CO2) capture and storage (CCS) and most CO2 capture and utilization (CCU) routes require concentrated CO2 streams for efficient compression, pipeline transport, injection, or chemic...

Finite-volume method for industrial-scale temperature-swing adsorption simulations

We formulate a mathematical model for temperature-swing adsorption systems. A finite-volume method is derived for the numerical solution of the model equations. We specifically investigate the influence of the choice of spatial discretization scheme for the convective terms on the accuracy, convergence rate and general computational performance of the proposed method. The analysis is performed with the nonlinear Dubinin-Radushkevich isotherm representing benzene adsorption onto activated carbon, relevant for gas cleaning in biomass gasification.The large differences in accuracy and convergence between lower- and higher-order schemes for pure scalar advection are significantly reduced when using a non-linear isotherm. However, some of these differences re-emerge when simulating adsorption/desorption cycling. We show that the proposed model can be applied to industrial-scale systems at moderate spatial resolution and at an acceptable computational cost, provided that higher-order discretization is employed for the convective terms.