Ultra-violet Treatment as a Strategy for Destruction of Degradation Products from Amine Based Post Combustion CO2 Capture

AbstractThe amine-based post-combustion capture (PCC) of CO2 is an option being considered for the reduction of anthropogenic CO2 emissions. PCC plants will be attached or retro-fitted to fossil-fuel fired power generating infrastructure (i.e. large stationary point sources) during the transition to renewable energy, which is expected to take place over several decades. Despite being an established technology widely used to remove CO2 from small scale-commercial process such as natural gas sweetening, there are many challenges that must be overcome before large scale implementation of the process can be realised. Some of these challenges include:•Reducing plant capital costs•Reducing the energy required for solvent regeneration/release of captured CO•Reducing solvent degradation in the presence of O2 and other flue gas contaminants, such as NOx and SOx,and•Reducing and understanding the environmental impact i.e. the potential of solvents and solvent degradation products to be released into the environment through off-gases, leaks or spills, and any associated impact this might have.Several recent research articles1-3 have highlighted the propensity of amine-based solvents to undergo certain chemical transformations, both in the condensed and aqueous phases, which produce harmful materials such as nitrosamines and nitramines. The formation and emission of nitrosated amines from the PCC process has not been fully investigated, although it is now the focus of some research agencies in Europe and Australasia. Nitrosamine formation mechanisms are presented in relation to the post- combustion capture of CO2 with aqueous amine solvents. The relative merits of nitrosamine mitigation strategies are also discussed. In particular the susceptibility of several nitrosamines to UV destruction is explored; the results are compared with TD-DFT results which predict excitation energies with good accuracy. The rate of destruction versus UV wavelength is also discussed, with a view to understanding which electronic transition facilitates decompositio

Predicting emissions of trace metals from coal combustion

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Simulation of enthalpy and capacity of CO₂ absorption by aqueous amine systems

A model has been developed to predict the CO₂ capacity of amine-based solvent systems as well as the enthalpy associated with absorption/desorption. This model can be used to accurately predict the behavior of well-characterized solvent systems under a range of different conditions. Alternatively, the model can be used to estimate the properties of less well-defined systems as part of an initial rapid screening procedure. Investigation into the effects of varying amine basicity and degree of carbamate formation indicates that there is considerable room for improvement on the standard MEA (monoethanolamine) system in terms of both capture capacity and enthalpy of CO₂ desorption

An ATR-FTIR study on the effect of molecular structural variations on the CO₂ absorption characteristics of Heterocyclic Amines: part II

This paper reports on an ATR-FTIR spectroscopic investigation of the CO₂ absorption characteristics of a series of heterocyclic diamines: hexahydropyrimidine (HHPY), 2-methyl and 2,2-dimethylhexahydropyrimidine (MHHPY and DMHHPY), hexahydropyridazine (HHPZ), piperazine (PZ) and 2,5- and 2,6-dimethylpiperazine (2,6-DMPZ and 2,5-DMPZ). By using in situ ATR-FTIR the structure–activity relationship of the reaction between heterocyclic diamines and CO₂ is probed. PZ forms a hydrolysis-resistant carbamate derivative, while HHPY forms a more labile carbamate species with increased susceptibility to hydrolysis, particularly at higher CO₂ loadings (>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

An FTIR spectroscopic study on the effect of molecular structural variations on the CO₂ absorption characteristics of heterocyclic amines

Herein, the reaction between CO₂ 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

NPI emission estimation techniques? Getting it better for fossil fuelled electricity generators

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