IEF-PCM DFT Study of Solvent-based CO_2 Capture Thermochemistry

摘要

The reduction of greenhouse gas emissions from anthropogenic activities such as power generation is proving to be a real and immediate challenge to Australia and other developed and developing nations worldwide. A potential solution to greenhouse gas emissions from fossil-fuelled combustion sources has emerged in resent years in the form of CO_2 capture and sequestration. The technologies and systems used for capture and sequestration of CO_2 have been applied in the chemical industry for processing sour gas streams for decades. Although none of the capture technologies have been specifically developed for application in coal fired power generation, they are based on various chemical and physical processes that could be implemented at the end of a fossil fuelled combustion source. These capture methods vary from absorption with amine based solvents to adsorption on substrates to separation with CO_2 selective membranes and cryogenic separation methods. Of these technologies, the most mature and widely implemented in industry is absorption with an aqueous amine based absorbent. The chemical reactions involved in CO_2 absorption and desorption by chemical absorbents such as aqueous amines are being investigated and modelled to identify and make potential improvements in efficiency. As part of a broader investigation of the properties which impart the chemical characteristics desirable for CO_2 capture, quantum chemical calculations are being used to determine (i) gas-phase heats and free energies of CO_2 capture reactions, (ii) the effects of solvation upon the CO_2 capture reaction thermochemistry and ultimately (iii) activation energies via transition states, and thus CO_2 capture kinetics. In this paper, we present the results of a polarisable-continuum model (IEF-PCM) hybrid density functional UAHF/6-31G(d)+B3LYP/6-31++G(d,p) investigation of the thermochemistry of the capture solvents ammonia, 2-amino-2-methyl-1-propanol, 2-amino-1-propanol, ethanoloamine, N-methylhydroxyethylamine, piperidine, piperazine, ethylenediamine and trishydroxymethylaminomethane. It is anticipated that computational chemistry will ultimately be used to guide the search for the ideal capture solvent.