Amine-based CO2 capture technology development from the beginning of 2013-a review

Effect of Extended Aging and Oxidation on Linear Poly(propylenimine)-Mesoporous Silica Composites for CO2 Capture from Simulated Air and Flue Gas Streams

Physical aging or degradation of amine-containing polymers and supported amine adsorbents is a critical issue that could limit the practical application of such materials for CO₂ capture. However, to date, there is a scarcity of studies that evaluate the long-term stability of amine-based sorbents without the exclusive use of accelerated aging tests. Here, we demonstrate that extended aging (∼2 years) of linear poly(propylenimine) (LPPI) confined in mesoporous silica (SBA-15) supports does not drastically impact the CO₂ adsorption performance under simulated flue gas (10% CO₂) and direct air capture (DAC, 400 ppm CO₂) conditions, although the behavior of the aged sorbents and polymers in the two CO₂ concentration regimes differs. The sorbents made with aged LPPI have modestly decreased CO₂ uptake performance (≲20% lower) compared to the fresh polymers, with overall good CO₂ cycling performance. The data indicate that only slow degradation occurs under the deployed ambient storage conditions. Even after extended aging, the LPPI-based sorbents preserved their ability to display stable temperature-swing cycling performance. In parallel, the impact of blending LPPI polymers of different number-average molecular weights, M_n, is evaluated, seeking to understand its impact on adsorbent performance. The results demonstrate that the blends of two M_n aged LPPI give similar CO₂ adsorption performance to adsorbents made from a single-M_n LPPI, suggesting that molecular weight will not negatively impact adsorbent performance in the studied M_n range. After an accelerated oxidation experiment, the aged LPPI sorbents retained a larger portion of the samples' original performance when cycling under simulated flue gas conditions than under DAC conditions. However, in each case, the oxidized sorbents could be cycled repeatedly with consistent uptake performance. Overall, these first of their kind extended aging tests suggest that LPPI-based amine adsorbents offer promise for long-term, stable use in carbon capture applications.

The volume expansion effect of amine during CO2 adsorption process: An experimental study combined with theoretical calculations

The volume expansion effect of amine supported on mesoporous silica during CO₂ adsorption process was found for the first time through well-designed experiments and was further confirmed by theoretical calculations. It was found that the residual pore volume of mesocellular silica foam (MCF) based solid amine sorbent (tetraethylenepentamine (TEPA) supported on MCF) gradually decreased with the increase of CO₂ uptake. Moreover, the surface area, the average diameters of window and cell of MCF show a similar changing trend. This is due to the volume expansion effect of TEPA during CO₂ adsorption process, i.e., the total volume of reaction products of TEPA and CO₂ is larger than that of pure TEPA. The products are very sticky and almost lose the liquidity totally even at 80 °C. The sticky products and the volume expansion effect may increase the mass transfer resistance and are not beneficial to higher CO₂ uptakes especially for solid amine sorbent with higher amine loading due to the decrease of pore size and the residual pore volume. DFT calculations based on simple models also indicate that the total volume of the generated products is much larger than that of unreacted amine, further confirming the volume expansion effect of amine during CO₂ adsorption process. DFT calculations also indicate that the volume is even doubled in the presence of moisture. The volume expansion effect of solid amine sorbent found in this study may help to design the sorbent with high CO₂ capture performance and less the mass transfer resistance.

Accelerated Formation Kinetics of a Multicomponent Metal-Organic Framework Derived from Preferential Site Occupancy

Metal-organic frameworks (MOFs) are typically synthesized via solvothermal reactions, whose reaction kinetics might be a bottleneck in the scaled-up manufacturing of these materials. Herein, we show that asymmetric cationic site occupancy within a mixed-metal citrate-based MOF-KM₃(C₆H₄O₇)(C₆H₅O₇)·xH₂O (M = Co, Zn), also known as UTSA-16-can be exploited for improved formation kinetics. Using this strategy, mixed-metal UTSA-16 can be crystallized under significantly milder conditions relative to the parent Co-based one, paving the way for the mass production of this promising material.

Surface Modifications of Nanofillers for Carbon Dioxide Separation Nanocomposite Membrane

CO2 separation is an important process for a wide spectrum of industries including petrochemical, refinery and coal-fired power plant industries. The membrane-based process is a promising operation for CO2 separation owing to its fundamental engineering and economic benefits over the conventionally used separation processes. Asymmetric polymer–inorganic nanocomposite membranes are endowed with interesting properties for gas separation processes. The presence of nanosized inorganic nanofiller has offered unprecedented opportunities to address the issues of conventionally used polymeric membranes. Surface modification of nanofillers has become an important strategy to address the shortcomings of nanocomposite membranes in terms of nanofiller agglomeration and poor dispersion and polymer–nanofiller incompatibility. In the context of CO2 gas separation, surface modification of nanofiller is also accomplished to render additional CO2 sorption capacity and facilitated transport properties. This article focuses on the current strategies employed for the surface modification of nanofillers used in the development of CO2 separation nanocomposite membranes. A review based on the recent progresses made in physical and chemical modifications of nanofiller using various techniques and modifying agents is presented. The effectiveness of each strategy and the correlation between the surface modified nanofiller and the CO2 separation performance of the resultant nanocomposite membranes are thoroughly discussed.

Phase Splitting Agent Regulated Biphasic Solvent for Efficient CO2 Capture with a Low Heat Duty

A biphasic solvent features high absorption capacity and low heat duty for CO₂ capture. Phase separation behavior is essential to cut down energy penalty. Four phase splitting agents with different hydrophobicities, such as 1,3-dimethyl-2-imidazolidinone (DMI), 1-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide, and sulfolane, were dosed to biphasic solvents, triethylenetetramine and 2-(diethylamino)ethanol. Experimental results revealed that they can tune the phase separation behavior during CO₂ absorption. Generally, under the same CO₂ loading, the volume ratio of the rich phase increased with their hydrophobicity (log P), which accounts for over 50%. Moreover, their influences on absorption capacity, kinetics, and thermodynamics were also investigated. After dosing NMP, the heat duty was decreased by 22%. Furthermore, a phase splitting agent with a positive log P was more conducive to reducing the heat duty, and one with a negative log P enhanced the absorption rate. With DMI, the absorption rate was 114% higher than that of MEA at rich loading. The ¹³C NMR analysis showed that the agents were not involved in CO₂ absorption and did not affect the reaction mechanism. Furthermore, quantum calculation was used to verify the reaction mechanism, confirming that the phase splitting agent increases the reaction equilibrium constant and makes it proceed more thoroughly.

Materials and logistics for carbon dioxide capture, storage and utilization

The efforts to curtail carbon dioxide presence in the atmosphere are a strong function of the available technologies to capture, store and usefully utilize it. Materials with adequate CO₂ sorption kinetics that are both effective and economical are of prime importance for the whole capture system to be built around. This work identifies such materials that are currently used in CO₂ adsorption beds/columns at different global locations, along with their vital operational parameters, logistics and costs. Three main classes of materials currently in use to that end are discussed in detail here, namely solid sorbents, advanced solvents membrane systems. These materials are then compared in terms of their potential CO₂ uptake, operating parameters and ease of use and implementation of the respective technology. Tabular data are appended to each technology covered with the most relevant advantages and disadvantages. With such comprehensive survey of the recent state-of-the-art materials, recommendations are also made to facilitate the selection of systems based on their CO₂ yield, price and suitability to the geographical location.

Optimization of CO2 Adsorption on Solid-Supported Amines and Thermal Regeneration Mode Comparison

For improving the CO₂ adsorption capacity of solid-supported amines, five commercial porous supports have been selected and impregnated with tetraethylenepentamine (TEPA), and their CO₂ adsorption performances have been evaluated using a fixed-bed reactor coupled with mass spectrometry. For solid-supported amines, CO₂ adsorption capacities coincide with the texture characterization of the adsorbent supports (mesoporous alumina, montmorillonite, silica gel, porous resin, MCM-41 molecular sieve), and the optimum TEPA loading amount is mainly affected by the pore volume. The mesoporous supports were found to be more conducive to uniform loading of organic amine, with more than 370 mg/g CO₂ adsorbed per unit TEPA. Other components in flue gas, especially H₂O, favor CO₂ adsorption on solid-supported amines. SO₂ inhibited the CO₂ adsorption, which was mainly attributable to the strong and irreversible binding of SO₂ on some amine sites. NO had little effect on CO₂ adsorption. Thermal stabilities of solid-supported amines have been tested based on thermogravimetry curves, and the main weight loss peak for TEPA appears at 513 K for solid-supported amines. Linear and step regeneration modes have been compared, revealing that the temperature for step regeneration is 37 K lower than that for the linear regeneration mode. Moreover, the desorption peak area for the step regeneration mode is 20% higher than that for the linear regeneration mode, indicating that the step regeneration mode can be used in practical applications, to reduce energy consumption during regeneration.

ZIF-8-Nanocrystalline Zirconosilicate Integrated Porous Material for the Activation and Utilization of CO2 in Insertion Reactions

The conversion of CO₂ to useful chemicals, especially to atom economical products, is the best approach to utilize an excess of CO₂ present in the atmosphere. In this study, a metal-organic framework (ZIF-8) is integrated with nanocrystalline zirconosilicate zeolite to develop an integrated porous catalyst for CO₂ insertion reactions. The catalyst exhibits excellent activity for the CO₂ insertion reaction of epoxide to produce cyclic carbonate in neat condition without the addition of any co-catalyst. The catalyst is stable and recyclable during the cyclic carbonate synthesis. Further, the catalyst also exhibits very good activity in another CO₂ insertion reaction to produce quinazoline-2,4(1H, 3H)-dione.

The Use of Conductive Polymers Embedded Macro Porous Pei and Ionic Liquid Form of Pei Cryogels for Potential Conductometric Sensor Application to CO2

Polyethyleneimine (PEI) cryogels with interconnected superporous morphology were synthesized via the cryopolymerization technique. Then, conductive polymers, poly(Aniline) (PANi), poly(Pyrrole) (PPy), and poly(Thiophene) (PTh) were prepared within these PEI cryogels. Then, the conductive polymer embedding PEI composites’ characterization was carried morphologically using scanning electron microscope (SEM) by means of Fourier Transform Infrared Radiation (FT-IR) spectrometer, and by means of electrical conductivity measurements using an electrometer. Among all the prepared cryogel conductive polymer composites, the highest value in terms of conductivity was determined for PEI/PANi cryogel composites with 4.80 × 10−3 S.cm−1. Afterward, to prepare polymeric ionic liquid (PIL) forms of PEI and PEI/PANi composites. To assess the effect of anions on the conductivities of the prepared composites, PEI-based cryogels were anion ex-changed after protonation with HCl by treatment of aqueous solutions of sodium dicyanamide (Na+[N(CN)2]−), ammonium hexafluorophosphate (NH4+[PF6]−), sodium tetrafluoroborate (Na+[BF4]−), and potassium thiocyanate (K+[SCN]−), separately. Furthermore, PEI-based cryogel composites and their PIL forms were tested as a sensor for CO2 gas. The higher conductivity changes were observed on bare PEI cryogel and PEI+[BF4]− PIL cryogels with 1000-fold decrease on conductivity upon 240 min CO2 exposure. The sensitivity and recovery percent of bare PEI and PEI+[BF4]− PIL cryogels were shown almost the same with a two-fold decrease in the presence of 0.009 mole of CO2 gas, and approximately 30% recovery after the fifth consecutive reuse.

Role of absorber and desorber units and operational conditions for N-nitrosamine formation during amine-based carbon capture

The formation of carcinogenic N-nitrosamines from reactions between solvent amines and flue gas NO_x is an important concern for the application of amine-based processes to capture CO₂ post-combustion. Using an advanced test rig with interconnected absorber and desorber units, we evaluated the importance for N-nitrosamine formation of the desorber relative to the absorber, and any synergism between the two units. Variations in desorber temperature and in flue gas composition indicated that N-nitrosamine formation from fresh monoethanolamine (MEA) occurred predominantly in the absorber. N-nitrosamine formation was driven by high NO₂ and O₂ flue gas concentrations, although NO also contributed. In contrast, N-nitrosamine formation from piperazine (PZ) was driven by reactions with nitrite in the heated desorber, and accelerated concurrent with nitrite accumulation. A complementary experiment simulating aged MEA solvent (high nitrite, 1.5% sarcosine as a proxy of secondary amine degradation products) suggested the desorber becomes an order of magnitude more important than the absorber for N-nitrosamine formation. For fresh MEA solvent, increasing the desorber temperature from 110 °C to 130 °C promoted thermal decomposition of N-nitrosamines, reducing N-nitrosamine accumulation rates two-fold. Compared to the test rig, the prevailing practice of using separate absorber columns and autoclave-like treatments to mimic desorber units predicted the direction, but underestimated the magnitude of N-nitrosamine formation. Because N-nitrosamine accumulation rates are the net result of competing formation and thermal decomposition processes, use of continuously cycling test rigs may be necessary to understand the impacts of different operating conditions.

Sorption of CO2 and CH4 on Raw and Calcined Halloysite-Structural and Pore Characterization Study

The article presents comparative characteristics of the pore structure and sorption properties of raw halloysite (R-HAL) and after calcination (C-HAL) at the temperature of 873 K. Structural parameters were determined by optical scanning and transmission electron microscopy methods as well as by mercury porosimetry (MIP, Hg) and low-pressure nitrogen adsorption (LPNA, N₂, 77 K). The surface area parameter (LPNA) of halloysite mesopores before calcination was 54–61 m²/g. Calcining caused the pore surface to develop to 70–73 m²/g. The porosity (MIP) of halloysite after calcination increased from 29% to 46%, while the surface area within macropores increased from 43 m²/g to 54 m²/g. The total pore volume within mesopores and macropores increased almost twice after calcination. The course of CH₄ and CO₂ sorption on the halloysite was examined and sorption isotherms (0–1.5 MPa, 313 K) were determined by gravimetric method. The values of equilibrium sorption capacities increased at higher pressures. The sorption capacity of CH₄ in R-HAL was 0.18 mmol/g, while in C-HAL 0.21 mmol/g. CO₂ sorption capacities were 0.54 mmol/g and 0.63 mmol/g, respectively. Halloysite had a very high rate of sorption equilibrium. The values of the effective diffusion coefficient for methane on the tested halloysite were higher than De > 4.2 × 10⁻⁷ cm²/s while for carbon dioxide De > 3.1 × 10⁻⁷ cm²/s.

Poly(ionic liquid)-Modified Metal Organic Framework for Carbon Dioxide Adsorption

The design and synthesis of solid sorbents for effective carbon dioxide adsorption are essential for practical applications regarding carbon emissions. Herein, we report the synthesis of composite materials consisting of amine-functionalized imidazolium-type poly(ionic liquid) (PIL) and metal organic frameworks (MOFs) through complexation of amino groups and metal ions. The carbon dioxide adsorption behavior of the synthesized composite materials was evaluated using the temperature-programmed desorption (TPD) technique. Benefiting from the large surface area of metal organic frameworks and high carbon dioxide diffusivity in ionic liquid moieties, the carbon dioxide adsorption capacity of the synthesized composite material reached 19.5 cm3·g-1, which is much higher than that of pristine metal organic frameworks (3.1 cm3·g-1) under carbon dioxide partial pressure of 0.2 bar at 25 °C. The results demonstrate that the combination of functionalized poly(ionic liquid) with metal organic frameworks can be a promising solid sorbent for carbon dioxide adsorption.

Ultrathin Films of Porous Metal-Organic Polyhedra for Gas Separation

Ultrathin films of a robust Rh^II -based porous metal-organic polyhedra (MOP) have been obtained. Homogeneous and compact monolayer films (ca. 2.5 nm thick) were first formed at the air-water interface, deposited onto different substrates and characterized using spectroscopic methods, scanning transmission electron microscopy and atomic force microscopy. As a proof of concept, the gas separation performance of MOP-supported membranes has also been evaluated. Selective MOP ultrathin films (thickness ca. 60 nm) exhibit remarkable CO₂ permeance and CO₂ /N₂ selectivity, demonstrating the great combined potential of MOP and Langmuir-based techniques in separation technologies.

Conjugated porous polymers: incredibly versatile materials with far-reaching applications

This review discusses conjugated porous polymers and focuses on relating design principles and synthetic methods to key properties and applications such as (photo)catalysis, gas storage, chemical sensing, energy storage and environmental remediation.

The effect of the layer-interlayer chemistry of LDHs on developing high temperature carbon capture materials

(a) SEM image of the fresh MMOs, (b) carbonation/regeneration cycles, and (c) SEM image of the MMOs after 60 carbonation/regeneration cycles of the Ca–Al-ada LDHs.

High-performance carbon dioxide capture and storage by multi-functional sphingosine kinase inhibitors through a CO2-philic membrane

Carbon dioxide (CO₂) capture using environmentally friendly sphingosine-based materials was theoretically studied.

Rapid CO2 capture-to-mineralisation in a scalable reactor

A CO₂ mineralisation process using brine solutions with a catalyst was investigated from experimental and modelling perspectives.

Characterization and Modelling Studies of Activated Carbon Produced from Rubber-Seed Shell Using KOH for CO2 Adsorption

Global warming due to the emission of carbon dioxide (CO2) has become a serious problem in recent times. Although diverse methods have been offered, adsorption using activated carbon (AC) from agriculture waste is regarded to be the most applicable one due to numerous advantages. In this paper, the preparation of AC from rubber-seed shell (RSS), an agriculture residue through chemical activation using potassium hydroxide (KOH), was investigated. The prepared AC was characterized by nitrogen adsorption–desorption isotherms measured in Micrometrices ASAP 2020 and FESEM. The optimal activation conditions were found at an impregnation ratio of 1:2 and carbonized at a temperature of 700 °C for 120 min. Sample A6 is found to yield the largest surface area of 1129.68 m2/g with a mesoporous pore diameter of 3.46 nm, respectively. Using the static volumetric technique evaluated at 25 °C and 1.25 bar, the maximum CO2 adsorption capacity is 43.509 cm3/g. The experimental data were analyzed using several isotherm and kinetic models. Owing to the closeness of regression coefficient (R2) to unity, the Freundlich isotherm and pseudo-second kinetic model provide the best fit to the experimental data suggesting that the RSS AC prepared is an attractive source for CO2 adsorption applications.

The Surface Science of Microarray Generation-A Critical Inventory

Microarrays are powerful tools in biomedical research and have become indispensable for high-throughput multiplex analysis, especially for DNA and protein analysis. The basis for all microarray processing and fabrication is surface modification of a chip substrate and many different strategies to couple probe molecules to such substrates have been developed. We present here a critical assessment of typical biochip generation processes from a surface science point of view. While great progress has been made from a molecular biology point of view on the development of qualitative assays and impressive results have been obtained on the detection of rather low concentrations of DNA or proteins, quantitative chip-based assays are still comparably rare. We argue that lack of stable and reliable deposition chemistries has led in many cases to suboptimal quantitative reproducibility, impeded further progress in microarray development and prevented a more significant penetration of microarray technology into the diagnostic market. We suggest that surface-attached hydrogel networks might be a promising strategy to achieve highly sensitive and quantitatively reproducible microarrays.

Integrated CO2 Capture and Conversion to Formate and Methanol: Connecting Two Threads

The capture of CO₂ from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO₂ concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO₂ is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO₂, methanol and formic acid are of high interest because they can be used directly as fuels or to generate H₂ on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H₂ in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO₂ is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO₂ and H₂ using homogeneous catalysts. Importantly, several studies have combined CO₂ capture and hydrogenation, where captured CO₂ (including from air) was directly utilized to produce formate and CH₃OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO₂ capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO₂, which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO₂ is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO₂ using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO₂ capture by hydroxide bases and conversion to methanol process.

Suppression of Charge Carrier Recombination in Lead-Free Tin Halide Perovskite via Lewis Base Post-treatment

Lead-free tin perovskite solar cells (PSCs) show the most promise to replace the more toxic lead-based perovskite solar cells. However, the efficiency is significantly less than that of lead-based PSCs as a result of low open-circuit voltage. This is due to the tendency of Sn²⁺ to oxidize into Sn⁴⁺ in the presence of air together with the formation of defects and traps caused by the fast crystallization of tin perovskite materials. Here, post-treatment of the tin perovskite layer with edamine Lewis base to suppress the recombination reaction in tin halide PSCs results in efficiencies higher than 10%, which is the highest reported efficiency to date for pure tin halide PSCs. The X-ray photoelectron spectroscopy data suggest that the recombination reaction originates from the nonstoichiometric Sn:I ratio rather than the Sn⁴⁺:Sn²⁺ ratio. The amine group in edamine bonded the undercoordinated tin, passivating the dangling bonds and defects, resulting in suppressed charge carrier recombination.

The effect of CO2 loading on alkanolamine absorbents in aqueous solutions

Post-combustion carbon capture by amine scrubbing is the most frequently used process to remove CO2 from pulverized coal-fired power plants and also biogas flue gas streams. The quest for novel absorbents for CO2 capture with improved properties requires insight into the properties of the CO2-loaded mixed solutions. A comparative molecular dynamics study of the product state solutions, with chemically-bound CO2 of standard monoethanolamine (MEA) and the new alternative 4-diethylamino-2-butanol (DEAB) at various CO2-loadings yields solvent properties in good agreement with experimental data. The concentration of all post-reaction species in solution was based on experimental equilibria distributions. The data generated provide detailed insight into the properties of reactive mixed alkanolamine solutions. The liquid structure of aqueous MEA solutions undergoes only minor changes when absorbing CO2. The diffusion coefficients of all molecular species, however, decrease significantly with increasing CO2-loadings. The large hydrophobic clusters formed in the reactant state by DEAB molecules in water prior to CO2 binding significantly decrease in size and structure upon CO2 absorption. The diffusion coefficients of all components decrease with increasing CO2-loading, whereas the pre-reaction alkanolamine DEAB shows an increase in diffusion coefficient. This structural and kinetic information supports the molecular design and further development of novel compounds and provides data for a global process simulation and optimization.