https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:22205 0.5 mol CO₂/mol amine). HHPY exhibits similar reactivity toward CO₂ to PZ, but with improved aqueous solubility. The α-methyl-substituted MHHPY favours HCO₃− formation, but MHHPY exhibits comparable CO₂ absorption capacity to conventional amines MEA and DEA. MHHPY show improved reactivity compared to the conventional α-methyl-substituted primary amine 2-amino-2-methyl-1-propanol. DMHHPY is representative of blended amine systems, and its reactivity highlights the advantages of such systems. HHPZ is relatively unreactive towards CO₂. The CO₂ absorption capacity C_A (mol CO2/mol amine) and initial rates of absorption R_IA (mol CO₂/mol amine min⁻¹) for each reactive diamine are determined: PZ: C_A =0.92, R_IA=0.045; 2,6-DMPZ: C_A =0.86, R_IA=0.025; 2,5-DMPZ: C_A =0.88, R_IA=0.018; HHPY: C_A =0.85, R_IA=0.032; MHHPY: C_A =0.86, R_IA=0.018; DMHHPY: C_A =1.1, R_IA=0.032; and HHPZ: no reaction. Calculations at the B3LYP/6-31+G** and MP2/6-31+G** calculations show that the substitution patterns of the heterocyclic diamines affect carbamate stability, which influences hydrolysis rates.]]> Wed 11 Apr 2018 15:00:20 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34458 Tue 03 Sep 2019 18:22:25 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:12609 2 and piperidine, as well as commercially available functionalised piperidine derivatives, for example, those with methyl-, hydroxyl- and hydroxyalkyl substituents, has been investigated. The chemical reactions between CO₂ and the functionalised piperidines were followed in situ by using attenuated total reflectance (ATR) FTIR spectroscopy. The effect of structural variations on CO₂ absorption was assessed in relation to the ionic reaction products identifiable by IR spectroscopy, that is, carbamate versus bicarbonate absorbance, CO₂ absorption capacity and the mass-transfer coefficient at zero loading. On absorption of CO₂, the formation of the carbamate derivatives of the 3- and 4-hydroxyl-, 3- and 4-hydroxymethyl-, and 4-hydroxyethyl-substituted piperidines were found to be kinetically less favourable than the carbamate derivatives of piperidine and the 3- and 4-methyl-substituted piperidines. As the CO₂ loading of piperidine and the 3- and 4-methyl- and hydroxyalkyl-substituted piperidines exceeded 0.5 moles of CO₂ per mole of amine, the hydrolysis of the carbamate derivative of these amines was observed in the IR spectra collected. From the subset of amines analysed, the 2-alkyl- and 2-hydroxyalkyl-substituted piperidines were found to favour bicarbonate formation in the reaction with CO₂. Based on IR spectral data, the ability of these amines to form the carbamate derivatives was also established. Computational calculations at the B3LYP/6-31+G** and MP2/6-31+G** levels of theory were also performed to investigate the electronic/steric effects of the substituents on the reactivity (CO₂ capture performance) of different amines, as well as their carbamate structures. The theoretical results obtained for the 2-alkyl- and 2-hydroxyalkyl-substituted piperidines suggest that a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area of the nitrogen atom play a role in destabilising the carbamate derivative and increasing its susceptibility to hydrolysis. A theoretical investigation into the structure of the carbamate derivatives of these amines revealed shorter N-C bond lengths and a less-delocalised electron distribution in the carboxylate moiety.]]> Sat 24 Mar 2018 08:17:28 AEDT ]]>