https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:42625 Wed 31 Aug 2022 15:54:21 AEST ]]> 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:46161 2 absorption rates in ammonia-based absorbents via addition of fast reacting primary/secondary amines are of great interest. In this work, a new substituted cyclic amine 4-aminomethyltetrahydropyran (4-AMTHP) was blended with aqueous ammonia to increase its reactivity toward CO₂. Stopped-flow spectrophotometry was employed to investigate the underlying reaction mechanism between dissolved CO₂(aq) and a series of blended NH₃/4-AMTHP solutions under homogeneous conditions. A comprehensive chemical model describing the blended 4-AMTHP–NH₃–CO₂–H₂O system, which involves a total of 11 kinetic reactions and 15 species, has been developed and further evaluated to explore the experimental kinetic and CO₂ mass transfer data measured from a bench-scale wetted-wall column. From the resulting data, it was demonstrated here that the addition of a small quantity of ∼0.3 M 4-AMTHP into the 3 M NH₃/0.9 M CO₂ solution can effectively increase the kinetic reactivity during CO₂ absorption into aqueous ammonia solutions, resulting in a ∼50% increase in mass transfer.]]> Wed 07 Dec 2022 14:17:24 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:49925 9.0 (k7 = 6.99 × 103 M–1·s–1). Below this pH, the formation of protonated monocarbamic acid (DMEDACOOH2) via the pathway involving DMEDAH+ and CO2(aq) becomes active and contributes to the kinetics despite the 107-fold decrease in the rate constant between the two pathways. 1H and 13C NMR spectra as a function of decreasing pH (increasing HCl concentration) at 25.0 °C have been evaluated here to confirm the protonation events in DMEDA. Calculations of the respective DMEDA nitrogen partial charges have also been undertaken to support the NMR protonation study. A comparison of the DMEDA kinetic constants with the corresponding data for piperazine (PZ) reveals that despite the larger basicity of DMEDA, the enhanced and superior kinetic performance of PZ with CO2(aq) above its predicted Bronsted reactivity is not observed in DMEDA.]]> Thu 15 Jun 2023 11:34:48 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 ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:17212 Sat 24 Mar 2018 07:59:17 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:19716 Sat 24 Mar 2018 07:53:45 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:3267 Sat 24 Mar 2018 07:21:22 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:36515 Mon 25 May 2020 14:00:47 AEST ]]>