Aprotic heterocyclic anion ionic liquids (AHAs) are a promising new class of CO 2 absorbents, with a capacity of one mole of CO 2 chemically absorbed per mole of AHA. By tailoring the substituents on the anion, the AHA properties, in particular the enthalpy of absorption, can be tuned over a wide range. Furthermore, the entropy of absorption can be tuned by tailoring substituents on the cation. This then presents a materials design challengeWhat are the optimal AHA properties? This challenge is addressed by incorporating AHAs into a simple process model of CO 2 capture from postcombustion flue gas, and formulating the question as a type of simultaneous materials and process design problem. New absorption isotherm data is presented, over a larger pressure range than studied previously, for a few AHAs, and is used to suggest a simple thermodynamic model for CO 2 uptake, to be used in connection with the process model. The possibility of ionic liquids (ILs) that exhibit a 2:1 CO 2 uptake (two moles CO 2 per mole IL) with a cooperative binding mechanism is also considered, with absorption isotherm data for one such compound presented, together with a corresponding isotherm model. The process model is an equilibrium-based material and energy balance model, which is used to determine flow rates, heat duties, and process conditions that minimize a simple energy usage objective function. The sensitivity of this optimum with respect to various material properties and process parameters is studied, for flue gas from both pulverized coal and natural gas combined cycle power plants. The results provide materials property targets for the identification of new AHA molecules for CO 2 capture, leading to significant reductions in heat requirements relative to conventional amine technology.
Ionic
liquids (ILs) are a promising class of absorbents for next-generation
carbon-capture processes. In particular, aprotic heterocyclic anion
ILs (AHAs) have received significant attention due to their ability
to chemically absorb CO2 without a significant increase
in viscosity. The development of process modeling and mathematical
optimization approaches for AHA-based carbon-capture processes is
essential for the evaluation of economic feasibility before industrial
implementation. In this paper, we use a pseudo-transient modeling
approach that enables the robust simulation and optimization of the
large-scale process flowsheet. A Langmuir-type model that incorporates
both the chemical and physical uptake of CO2 is used to
describe the equilibrium absorption of CO2 by the IL. A
rigorous rate-based model for the absorption column is employed to
account for the effect of reversible chemical reactions on mass transfer.
The models are then used to carry out economic optimization of a prototypical
IL-based carbon-capture process. A sensitivity analysis of important
IL properties is provided, revealing the key factors that affect IL
choice. Finally, a comparison to an advanced amine-based process is
briefly discussed.
For the fabrication of a multilevel resist (MLR) based on a very thin, physical-vapor-deposited (PVD) amorphous carbon (a-C) layer, the etching characteristics of the PVD a-C layer with a SiOx hard mask were investigated in a dual-frequency superimposed capacitively coupled plasma etcher by varying the following process parameters in O2∕N2∕Ar plasmas: high-frequency/low-frequency combination (fHF∕fLF), HF/LF power ratio (PHF∕PLF), and O2 and N2 flow rates. The very thin nature of the a-C layer helps to keep the aspect ratio of the etched features low. The etch rate of the PVD a-C layer increased with decreasing fHF∕fLF combination and increasing PLF and was initially increased but then decreased with increasing N2 flow rate in O2∕N2∕Ar plasmas. The application of a 30nm PVD a-C layer in the MLR structure of ArF PR∕BARC∕SiOx∕PVD a-C∕TEOS oxide supported the possibility of using a very thin PVD a-C layer as an etch-mask layer for the TEOS-oxide layer.
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