One-pot catalytic synthesis of urea derivatives from alkyl ammonium carbamates using low concentrations of CO2

Dialkyl Carbonate Synthesis Using Atmospheric Pressure of CO2

Dialkyl carbonates (DRCs) are valuable compounds widely used in the industry. The synthesis of DRC from CO2 has attracted interest as an alternative to the current method, which uses phosgene. However, the reported approaches for DRC synthesis from CO2 requires high-pressure and high-concentration CO2, resulting in elevated costs associated with CO2 purification and manufacturing facilities. In this report, we present an environmentally friendly method for producing DRC from low-concentration and low-pressure CO2 via a dehydration condensation approach without the use of halogenated alkylating agents. This method involves the formation of monoalkyl carbonate [BASE-H][ROC(O)O] using a strong organic base and alcohols, tetraalkyl orthosilicates as dehydrating agents, and CeO2 as the catalyst. Using the method, 39 and 30% of diethyl carbonate yields were accomplished with only 100 and 15 vol % CO2 (CO2/N2 = 15:85) gas bubbling at atmospheric pressure, even under reaction conditions with no large excess of either CO2, alcohol, or dehydration agent.

Direct Esterification of Alkylcarbamic Acids with Alcohols over CeO2 Catalyst

Alkylcarbamic acids, which are easily produced via chemical absorption of CO2 into amines, have a great potential to be substrates for producing value-added chemicals. In this research, the esterification of various alkylcarbamic acids with alcohols into alkyl N-alkylcarbamates was demonstrated by using a heterogeneous catalyst as well as the corresponding amine additives. In the model reaction, the esterification of benzylcarbamic acid (BZA-CA) and methanol (MeOH), the target product of methyl N-benzylcarbamate was obtained in 64 % CO2 -based yield at 413 K in 12 h over a CeO2 catalyst, which also exhibited good reusability. In this catalytic system, the corresponding amine additive (i. e., benzylamine for BZA-CA) had the important role in the improvement of CO2 -moiety-based balance, allowing the precise kinetic study, in contrast to the cases without such additive. The detailed kinetic study on the target catalytic system and control systems suggested that BZA-CA underwent the esterification by MeOH directly. The current catalytic system using the combination of CeO2 catalyst and corresponding amine additive was also demonstrated to be applicable to the synthesis of alkyl N-alkylcarbamates from alkylcarbamic acids and alcohols with short, linear alkyl chains (≤C3 ).

Recent advances in direct air capture by adsorption

Significant progress has been made in direct air capture (DAC) in recent years. Evidence suggests that the large-scale deployment of DAC by adsorption would be technically feasible for gigatons of CO₂ capture annually. However, great efforts in adsorption-based DAC technologies are still required. This review provides an exhaustive description of materials development, adsorbent shaping, in situ characterization, adsorption mechanism simulation, process design, system integration, and techno-economic analysis of adsorption-based DAC over the past five years; and in terms of adsorbent development, affordable DAC adsorbents such as amine-containing porous materials with large CO₂ adsorption capacities, fast kinetics, high selectivity, and long-term stability under ultra-low CO₂ concentration and humid conditions. It is also critically important to develop efficient DAC adsorptive processes. Research and development in structured adsorbents that operate at low-temperature with excellent CO₂ adsorption capacities and kinetics, novel gas-solid contactors with low heat and mass transfer resistances, and energy-efficient regeneration methods using heat, vacuum, and steam purge is needed to commercialize adsorption-based DAC. The synergy between DAC and carbon capture technologies for point sources can help in mitigating climate change effects in the long-term. Further investigations into DAC applications in the aviation, agriculture, energy, and chemical industries are required as well. This work benefits researchers concerned about global energy and environmental issues, and delivers perspective views for further deployment of negative-emission technologies.

CeO2-Catalyzed Synthesis of 2-Imidazolidinone from Ethylenediamine Carbamate

CeO2 acted as an effective and reusable heterogeneous catalyst for the direct synthesis of 2-imidazolidinone from ethylenediamine carbamate (EDA-CA) without further addition of CO2 in the reaction system. 2-Propanol was the best solvent among the solvents tested from the viewpoint of selectivity to 2-imidazolidinone, and the use of an adequate amount of 2-propanol provided high conversion and selectivity for the reaction. This positive effect of 2-propanol on the catalytic reaction can be explained by the solubility of EDA-CA in 2-propanol under the reaction conditions and no formation of solvent-derived byproducts. This catalytic system using the combination of the CeO2 catalyst and the 2-propanol solvent provided 2-imidazolidinone in up to 83% yield on the EDA-CA basis at 413 K under Ar. The reaction conducted under Ar showed a higher reaction rate than that with pressured CO2, which clearly demonstrated the advantage of the catalytic system operated at low CO2 pressure or even without CO2.