The absorption of CO 2 in aqueous NH 3 solutions occurs with high efficiency and loading capacity at room temperature and atmospheric pressure producing the ammonium salts of bicarbonate (HCO 32 ), carbonate (CO 3 22 ), and carbamate (NH 2 CO 2 2 ) anions. 13 C NMR spectroscopy at room temperature has been proven to be a simple and reliable method to investigate the speciation in solution of these three ionic species. Fast equilibration of HCO 3 2 /CO 3 22 anions results in a single NMR peak whose chemical shift depends on the relative concentration of the two species. A method has been developed to correlate the chemical shift of this carbon resonance to the ratio of the two anionic species. Integration of the carbamate carbon peak provided the relative amount of this species with respect to HCO 3 2 /CO 3 22 pair. No other species was detected in solution by 13 C NMR, and no solid compounds separated out under our experimental conditions. Finally, the relative amount of HCO 3 2 , CO 3 22 , and NH 2 CO 2 2 in solution have been correlated to the molar ratio between free ammonia in solution and absorbed CO 2 .

The capture of carbon dioxide by ammonia in both aqueous and non-aqueous solutions was investigated at atmospheric pressure and 273 K under different operating conditions. The CO 2 capture is fast and efficient ranging between 78 and 99%, depending on both the NH 3 concentration and the solvent nature. The precipitation of solid mixtures of ammonium bicarbonate, ammonium carbonate and ammonium carbamate occurred in ethanol-water solution. Selective precipitation of ammonium carbamate was achieved by reacting gaseous CO 2 and NH 3 in anhydrous ethanol, 1-propanol or N,N-dimethylformamide (DMF) in a flow reactor that operates in continuous. In the second step of the process, the pure ammonium carbamate is used to produce urea with good yield (up to 54% on carbamate basis) at 393-413 K in the presence of inexpensive Cu(II) and Zn(II) catalysts. The yield of urea depends on several factors including the catalyst, the reaction temperature and the reaction time. Identification and quantification of urea in the reaction mixtures was obtained by analysis of its 13 C NMR spectrum. A preliminary mechanistic interpretation of the catalytic reaction is also briefly presented and commented.

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The CO2 uptake by single 2-amino-2-methyl-1-propanol (AMP) and its blends with 2-(ethylamino)­ethanol (EMEA) or N-methyl-2,2′-iminodiethanol (MDEA) has been investigated in both aqueous and nonaqueous solutions, and compared with aqueous 2-aminoethanol (MEA), the most used sorbent in carbon capture and storage (CCS) processes. The loading capacity, the rate of absorption, and the heat of CO2 absorption have been experimentally determined for all the amine solutions. 13C NMR analysis allowed the identification of the carbonated species formed in solution and evaluation of their relative amounts. The most promising sorbents have been further tested in continuous cycles of absorption and desorption carried out in packed columns, in order to verify their CO2 (15% in N2) capture efficiency. Thanks to their good CO2 loading, high rate of reaction with CO2, and low heat of absorption, the AMP–EMEA blend solutions, both in water and in organic diluents, are good candidates for CO2 capture as an alternative to the conventional aqueous MEA solution.

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The efficiency of CO 2 uptake by the amines 2-(2-aminoethoxy)ethanol (DGA), 2-amino-2-methyl-1,3propanediol (AMPD), 2-amino-2-methyl-1-propanol (AMP), 2,2'-iminodiethanol (DEA) and 2-(butylamino)ethanol (BUMEA) has been investigated either in aqueous and in 2-(2-methoxyethoxy)ethanol (DEGMME) solutions and compared with 30% aqueous MEA. Batch experiments were carried out to measure the CO 2 loading capacity of the different amine solutions and the rate of CO 2 absorption. The 13 C analysis has been applied to identify and quantify the carbonated species in solution upon CO 2 uptake. The efficiency of CO 2 (15% in air) capture was measured in continuous cycles of absorption (40 °C) and desorption (110 °C) carried out in packed columns at room pressure. The efficiency of the aqueous absorbents is greater than 90% and overcomes that in DEGMME. The CO 2 absorption heat of aqueous BUMEA and DGA in DEGMME calculated using Gibbs-Helmholtz equation was found to be lower than that of conventional 30% aqueous MEA: the possible advantages of these systems with respect to aqueous MEA as CO 2 absorbents have been discussed. Keywordscarbon dioxide capture • heat of CO 2 reaction • alkanolamine • 13 C NMR speciation • amine carbamates

Studio dell'assorbimento e del desorbimento a bassa temperatura (80-90°C) di CO2 utilizzando AMP (2-ammino-2-metil-propanolo) in solventi non-acquos

The neat secondary amines 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol, 2-(benzylamino)ethanol and 2-(butylamino)ethanol react with CO2 at 50-60 °C and room pressure yielding liquid carbonated species without their dilution with any additional solvent. These single-component absorbents have the theoretical CO2 capture capacity of 0.50 (mol CO2/mol amine) due to the formation of the corresponding amine carbamates and protonated amines that were identified by the (13)C NMR analysis. These single-component absorbents were used for CO2 capture (15% and 40% v/v in air) in two series of different procedures: (1) batch experiments aimed at investigating the efficiency and the rate of CO2 capture; (2) continuous cycles of absorption-desorption carried out in packed columns with absorption temperatures brought at 50-60 °C and desorption temperatures at 100-120 °C at room pressure. A number of different amines and experimental setups gave CO2 capture efficiency greater than 90%. For comparison purposes, 30 wt % aqueous MEA was used for CO2 capture under the same operational conditions described for the solvent-free amines. The potential advantages of solvent-free alkanolamines over aqueous MEA in the CO2 capture process were discussed.