Biomaterials for CO2 Harvesting: From Regulatory Functions to Wet Scrubbing Applications

CS2/CO2 Utilization Using Mukaiyama Reagent as a (Thio)carbonylating Promoter: A Proof-of-Concept Study

We report on the reaction of ethylene-terminated heteroatoms (C₂X; X = N, O, and S) with CS₂/CO₂ using Mukaiyama reagent (2-chloro-1-methylpyridinium iodide, CMPI) as a promoter for the preparation of imidazolidin-2-one, oxazolidin-2-one, 1,3-dioxolan-2-one, 1,3-dithiolan-2-one, and their thione counterparts at ambient temperature and pressure. Spectroscopic measurements, viz., ¹H/¹³C nuclear magnetic resonance (NMR) and ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy methods verified the reaction of CS₂/CO₂ with the ethylene-based substrates and subsequently the formation of cyclic products. The experimental data indicated the formation of the enol-form of imidazolidin-2-one and oxazolidin-2-one, while the keto-form was obtained for their thione correspondents. Furthermore, density functional theory calculations revealed the stability of the keto- over the enol-form for all reactions and pointed out the solvent effect in stabilizing the latter.

In situ activation of green sorbents for CO2 capture upon end group backbiting

Thermolysis of a urethane end group was observed as a first time phenomenon during activation. This unzipping mechanism revealed a new amine tethering point producing a diamine-terminated oligourea ([10]-OU), acting as a green sorbent for CO₂ capturing. The oligomer backbites its end group to form propylene carbonate (PC), as proved by in situ TGA-MS, which can reflect the polymer performance by maximizing its capturing capacity. Cross polarization magic angle spinning (CP-MAS) NMR spectroscopy verified the formation of the proven ionic carbamate (1:2 mechanism) with a chemical shift at 161.7 ppm due to activation desorption at higher temperatures, viz., 100 °C (in vacuo) accompanied with bicarbonate ions (1:1 mechanism) with a peak centered at 164.9 ppm. Fortunately, the amines formed from in situ thermolysis explain the abnormal behavior (carbamates versus bicarbonates) of the prepared sample. Finally, ex situ ATR-FTIR proved the decomposition of urethanes, which can be confirmed by the disappearance of the pre-assigned peak centered at 1691 cm^-1. DFT calculations supported the thermolysis of the urethane end group at elevated temperatures, and provided structural insights into the formed products.

Chemisorption of CO2 by diamine-tetraamido macrocyclic motifs: a theoretical study

Although alkanolamines have been systematically utilized for CO2 capture, intensive research efforts are still required to ultimately design more efficient CO2 sorbents with appropriate sorption characteristics. In this article, we have explored a series of diamine-tetraamido macrocyclic molecules with different organic linkers, namely, pyridine, phenylene, pyrrole, furan, and thiophene, for the titled purpose using quantum chemical calculations. The optimized structures of the sequestration reaction revealed the formation of a carbamate anion within the macrocyclic cavity that was stabilized through several intramolecular interactions compared to parent amines. The reaction thermodynamics indicated that the macrocyclic compounds with pyridine, pyrrole and furan can effectively capture CO2. The results highlight the potential application of macrocyclic structures as efficient CO2 capturing agents.

Mechanistic insights on CO2 utilization using sustainable catalysis

Caffeinium halides were used to catalyse the cycloaddition of CO2 to form cyclic carbonates. The reaction intermediates were isolated and characterized experimentally. The reaction mechanism has been confirmed by DFT calculations.

Activation of β-diketones for CO2 capture and utilization

β-Diketones are used for CO2 sequestration and utilization which was made possible due to their dual Brønsted acid/Lewis base character upon activation using a superbase,1,8-diazabicyclo[5.4.0]undec-7-ene or zinc bromide, respectively.

Cross-linked, porous imidazolium-based poly(ionic liquid)s for CO2 capture and utilisation

A series of micro/meso porous imidazolium poly(ionic liquid)s for CO2 capture and utilization is reported. They show moderate sorption capacity under RTP conditions, and good catalytic activity towards the cycloaddition of CO2 and epoxides to synthesize cyclic carbonates.

Recent Advances in the Chemistry of Metal Carbamates

Following a related review dating back to 2003, the present review discusses in detail the various synthetic, structural and reactivity aspects of metal species containing one or more carbamato ligands, representing a large family of compounds across all the periodic table. A preliminary overview is provided on the reactivity of carbon dioxide with amines, and emphasis is given to recent findings concerning applications in various fields.

Experimental Study on Postcombustion Systems Including a Hollow Fiber Membrane and a Packed Column

In this work, a comprehensive lab-scale carbon capture installation was established to study the separation performances of CO₂/N₂ systems for the postcombustion technology. Four kinds of mono-/two-stage carbon capture methods containing membrane separation and chemical absorption processes were investigated. The result shows that the CO₂ capture performance of the one-stage membrane separation method (Memb) exhibits a profitable CO₂ removal efficiency but defective CO₂ concentration, while the one-stage chemical absorption method (Chem) indicates both CO₂ removal efficiency and CO₂ purity of more than 95.0% but suffers a regeneration heat of at least 2.7 MJ/t CO₂. The CO₂ purity of the two-stage membrane separation method (Memb-Memb) is 46.2% higher than the Memb method because of the additional membrane pretreatment. Two-stage methods have a superior gas recovery efficiency of over 99.0%, which is dramatically higher than the homogeneous Memb method. In addition, the investigation on the hybrid chemical absorption-membrane separation method (Memb-Chem) provides an alternative approach to reduce the mass transfer and solve the problems caused by an unequal mass flow distribution.

CO2 coupling with epoxides catalysed by using one-pot synthesised, in situ activated zinc ascorbate under ambient conditions

An in situ generated zinc ascorbate pre-catalyst for cyclic carbonate (CC) synthesis via CO₂ coupling with epoxides under ambient conditions was reported. Spectroscopic measurements indicated that CO₂ was inserted into the zinc ascorbate complex through the formation of an activated zinc carbonate catalyst upon abstracting the enediol protons with sodium hydride. The aliphatic diols were not activated under the applied conditions and did not interfere with either the process of cycloaddition or CO₂ activation. The catalyst was active against different terminal epoxides, with a conversion of 75 and 85%, when propylene oxide and styrene oxide were used at 20 and 50 °C, respectively under 1 atm CO₂ for 17 h, which was considered a good advancement for heterogeneous based catalysis. Moreover, green chemistry principles were applied to ultimately end up with more ecofriendly approaches for the synthesis of CC following a simple balloon technique. Herein, we used zinc as a sustainable metal, together with ascorbic acid as a bio-renewable material in addition to CO₂ as a renewable feed-stock. Furthermore, waste prevention was achieved using the reaction side product, viz., NaBr as a co-catalyst.

The eternal battle to combat global warming: (thio)urea as a CO2 wet scrubbing agent

(Thio)Urea scaffolds are best known for their importance as intermediates in organic synthesis. In this work, a mechanistic study of the reaction between urea (U), (2-hydroxyethyl)urea (U-EtOH) and thiourea (tU)/NaH in DMSO with CO2 was carried out. While both U/tU reacted with CO2via a 1 : 2 mechanism through the formation of the keto (thio)carbamide-carboxylate adducts (k-U/tU-CO2- Na+), U-EtOH gave mixed CO2-adducts composed of organic carbonate and carbamide-carboxylate moieties (Na+-CO2-U-Et-OCO2- Na+). Moreover, we recorded for the first time, a new type of bond, namely sodium carbamimidothiocarbonate (e-tU-SCO2- Na+), upon bubbling CO2 in the DMSO solution of tU due to the persistence of the enol form (e-tU) and the better nucleophilicity of sulfur over nitrogen focal points. The reaction mechanisms were proven by 1D and 2D nuclear magnetic resonance (NMR) and ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopies. The stability of these bonds was studied following the changes in 1H-NMR as a function of temperature, which indicated the reversibility of these reactions. Furthermore, the proposed mechanisms were explored theoretically via density functional theory (DFT) calculations by analyzing the energetics of the anticipated products.

CO2 activation through C–N, C–O and C–C bond formation

CO₂ fixation reactions have been explored using different organic substrates upon activation with a superbase.