Evaluating the techno-economic potential of defossilized air-to-syngas pathways

Abstract

Defossilizing the chemical industry using air-to-chemicals processes offers a promising solution to driving down the emissions trajectory to net-zero by 2050. Syngas is a key intermediate in the chemicals industry,...

Closing the Loop: Unexamined Performance Trade-Offs of Integrating Direct Air Capture with (Bi)carbonate Electrolysis

“…To estimate the air contactor outlet composition with a changing solvent concentration, we use a verified DAC plant model from our previous work. 13 To fairly compare the mass-balance and equipment sizing results, we fix the captured CO 2 rate at 646 t-CO 2 /yr, comparable to the CO 2 capture rate of a single air contactor unit as developed by Keith and colleagues. 5 We assume constant flow rates of the air and liquid solvent inlets, unless otherwise noted.…”

“…Unfortunately, the reported total energy consumption of DAC (i.e., CO 2 capture and regeneration from air) is high, ranging from 5.50 to 9.50 GJ/t-CO 2 (i.e., from 242.1 to 418.1 kJ/mol-CO 2 ) . Because CO 2 capture is highly exothermic (eqs and ), its release from the capture solvent requires substantial regeneration energy to recover the captured CO 2 in a high-purity form and allow for the solvent to be regenerated in order to recapture fresh CO 2 . ,,, Concentrated hydroxide-based DAC processes, which capture CO 2 using hydroxides to form carbonates, requires a particularly high temperature (≥900 °C) to dissociate the metal carbonate into metal oxide and CO 2 via calcination. , This high temperature is challenging to reach via electrical energy input alone and requires a thermal energy input of 4.05 GJ/t-CO 2 (i.e., 178.2 kJ/mol-CO 2 ). ,, Comparatively, the established monoethanolamine (MEA) solvent recovery method can be performed at much milder temperatures of 80–120 °C, which can be achieved from waste heat and renewable electricity integrations. However, the MEA/CO 2 regeneration step still requires a regeneration energy input in the range of 2.00–5.50 GJ/t-CO 2 (i.e., 88.0–242.1 kJ/mol-CO 2 ). − …”

“…At these conditions and at a cell voltage of 3.3–3.5 V, we estimate the air contactor and (bi)­carbonate electrolyzer capital costs to be approximately $ 2023 582000 and $ 2023 352000–373000, respectively. These numbers are equivalent to 2.14 times the baseline contactor capital cost and 3.40–3.60 times the capital cost of a typical low-temperature CO 2 electrolyzer, , respectively (see section S.7 in the Supporting Information). Note that the (bi)­carbonate electrolyzer in this route produces CO at a low selectivity of 40%, which is likely due to the presence of both HCO 3 – and CO 3 2– species (see Figure ).…”

“…Table summarizes the operational parameters of air contactors and (bi)­carbonate electrolyzers, which include the temperature, pressure, pH of the two connecting streams (i.e., catholyte inlet/outlet or contactor inlet/outlet), and electricity consumption. Based on literature values, ,,,, the capture and conversion units are possibly compatible in terms of operational temperature and pressure. However, we find the pH values of the two connecting streams to be mostly incompatible.…”

“… 5 , 11 This high temperature is challenging to reach via electrical energy input alone and requires a thermal energy input of 4.05 GJ/t-CO 2 (i.e., 178.2 kJ/mol-CO 2 ). 5 , 12 , 13 Comparatively, the established monoethanolamine (MEA) solvent recovery method can be performed at much milder temperatures of 80–120 °C, which can be achieved from waste heat and renewable electricity integrations. However, the MEA/CO 2 regeneration step still requires a regeneration energy input in the range of 2.00–5.50 GJ/t-CO 2 (i.e., 88.0–242.1 kJ/mol-CO 2 ).…”