This paper describes a solvent regeneration method unique to CO2-binding organic liquids (CO2BOLs) and other switchable ionic liquids: utilizing changes in polarity to shift the free energy of the system. The degree of CO2 loading in CO2BOLs is known to control the polarity of the solvent; conversely, polarity can be exploited as a means to control CO2 loading. In this process, a chemically inert nonpolar "antisolvent" (AS) such as hexadecane (C16) is added to aid in de-complexing CO2 from a CO2-rich CO2BOL. The addition of this polarity assist reduces the temperature required for regeneration of our most recent CO2BOL, 1-((1,3-dimethylimidazolidin-2-ylidene)amino)propan-2-ol by as much as 73 °C. The lower regeneration temperatures realized with this polarity change allow reduced solvent attrition and thermal degradation. Furthermore, the polarity assist shows considerable promise for reducing the regeneration energy of CO2BOL solvents, and separation of the CO2BOL from the AS is as simple as a cooling the mixture to promote phase separation. Based on vapor–liquid and liquid–liquid equilibrium measurements of a candidate CO2BOL with CO2, with and without an AS, we present the evidence and impacts of a polarity change on a CO2BOL. Equilibrium thermodynamic models and analysis of the system were constructed using Aspen Plus®, and forecasts of preliminary process configurations and feasibility are also presented. Lastly, projections of solvent performance for removing CO2 from a subcritical coal-fired power plant (total net power and parasitic load) are presented with and without this polarity assist and compared to the U.S. Department of Energy's Case 10 monoethanolamine baseline.
This manuscript provides a detailed analysis of a continuous-flow, bench-scale study of the CO2-binding organic liquid (CO2BOL) solvent platform with and without its polarity-swing-assisted regeneration (PSAR). This study encompassed four months of continuous-flow testing of a candidate CO2BOL with a thermal regeneration and PSAR regeneration using a decane antisolvent. In both regeneration schemes, steady-state capture of >90% CO2 was achieved using simulated flue gas at reasonable liquid/gas (L/G) ratios. Aspen Plus modeling was performed to assess process performance, compared to previous equilibrium performance projections. This paper also includes net power projections, and comparisons to DOE's Case 10 amine baseline, and comments on the viability of the CO2BOL solvent class for post-combustion CO2 capture.
The Cover Feature illustrates the approach that bridges the fundamental aspects of atomistic simulations with the design of single-components diamines for CO2 capture. The image was designed by Cortland Johnson and Vassiliki-Alexandra Glezakou of PNNL. More information can be found in the Full Paper by D. C. Cantu et al. on page 3429 in Issue 13, 2020 (DOI: 10.1002/cssc.202000724).
Pumping of fluids is universally performed by using mechanical or thermal compressors. We introduce a new solid-state molecular pumping approach induced by switching the adsorption affinity for a gas through polarization of a chromophore under an applied electric field. Mass spectrometry was used to trace refrigerant gas (difluoromethane) uptake on a chromophore-coated capacitor under applied voltage and subsequent desorption when the voltage and electrode polarization was removed, showing an exchange capacity of 0.11 mol of refrigerant/(L of chromophore). Calorimetry confirmed a reversible enthalpy change of 9 kcal/mol in the polarization-induced sorption–desorption process. The present work establishes the principle and feasibility of nonmechanical molecular pumping, which could be exploited to transport any fluid, opening numerous potential applications.
The kinetics of the absorption of CO2 into two nonaqueous CO2-binding organic liquid (CO2 BOL) solvents were measured at T=35, 45, and 55 °C with a wetted-wall column. Selected CO2 loadings were run with a so-called "first-generation" CO2 BOL, comprising an independent base and alcohol, and a "second-generation" CO2 BOL, in which the base and alcohol were conjoined. Liquid-film mass-transfer coefficient (k'g ) values for both solvents were measured to be comparable to values for monoethanolamine and piperazine aqueous solvents under a comparable driving force, in spite of far higher solution viscosities. An inverse temperature dependence of the k'g value was also observed, which suggests that the physical solubility of CO2 in organic liquids may be making CO2 mass transfer faster than expected. Aspen Plus software was used to model the kinetic data and compare the CO2 absorption behavior of nonaqueous solvents with that of aqueous solvent platforms. This work continues our development of the CO2 BOL solvents. Previous work established the thermodynamic properties related to CO2 capture. The present paper quantitatively studies the kinetics of CO2 capture and develops a rate-based model.
Natural gas purifications using chemically selective hydrogen sulfide (H2S) sorbents could be more efficient if chemical selectivity for H2S could be maintained without thermal regeneration of the sorbent. We used tertiary alkanolamines to reversibly capture H2S in the absence of water to produce hydrosulfide-based ionic liquids in high yield. These alkanolammonium hydrosulfide ionic liquids release H2S by exposure to inert gas or by mild heating. H2S can be rapidly and nearly quantitatively released at ambient temperature from the alkanolammonium hydrosulfide ionic liquids by the addition of nonpolar antisolvents, some of which naturally phase separate from the spent alkanolamine. The antisolvent-induced regeneration of the alkanolamine potentially allows an efficient H2S gas scrubbing process that is chemically selective and can be operated continuously at or near ambient temperature.
