Exergetic Analysis of DME Synthesis from CO2 and Renewable Hydrogen

Abstract

Carbon Capture and Utilization (CCU) is a viable solution to valorise the CO2 captured from industrial plants’ flue gas, thus avoiding emitting it and synthesizing products with high added value. On the other hand, using CO2 as a reactant in chemical processes is a challenging task, and a rigorous analysis of the performance is needed to evaluate the real impact of CCU technologies in terms of efficiency and environmental footprint. In this paper, the energetic performance of a DME and methanol synthesis process fed by 25% of the CO2 captured from a natural gas combined cycle (NGCC) power plant and by the green hydrogen produced through an electrolyser was evaluated. The remaining 75% of the CO2 was compressed and stored underground. The process was assessed by means of an exergetic analysis and compared to post-combustion Carbon Capture and Storage (CCS), where 100% of the CO2 captured was stored underground. Through the exergy analysis, the quality degradation of energy was quantified, and the sources of irreversibility were detected. The carbon-emitting source was a 189 MW Brayton–Joule power plant, which was mainly responsible for exergy destruction. The CCU configuration showed a higher exergy efficiency than the CCS, but higher exergy destruction per non-emitted carbon dioxide. In the DME/methanol production plant, the main contribution to exergy destruction was given by the distillation column separating the reactor outlet stream and, in particular, the top-stage condenser was found to be the component with the highest irreversibility (45% of the total). Additionally, the methanol/DME synthesis reactor destroyed a significant amount of exergy (24%). Globally, DME/methanol synthesis from CO2 and green hydrogen is feasible from an exergetic point of view, with 2.276 MJ of energy gained per 1 MJ of exergy destroyed.

New Insights on Catalytic Valorization of Carbon Dioxide by Conventional and Intensified Processes

“…They found out that total CO 2 underground storage led to exergy destruction of 1.34 MJ per kilogram of avoided carbon emissions, versus 0.13 MJ/kg for 75% CO 2 storage and 25% conversion into DME. 140 To increase DME yield, Koybasi et al investigated alternative reactor designs for a mixed CO 2 /CO reactant, including a cascade reactor system and a microchannel reactor with reactive and cooling channels. 141 Their results showed that the DME yield was higher for the microchannel reactor, notably due to the continuous cooling of the reactor by the cooling channels distributed within the reactor structure.…”

“…Most studies on DME production from CO 2 fail to reach 10% yield, a reality that still limits the industrial feasibility of this process. De Falco et al proceeded to an exergy analysis of the DME synthesis process and compared it to CO 2 underground storage to evaluate the usefulness of such an operation (exergy is the amount of work that can be done with a given amount of energy) . They found that DME synthesis resulted in higher exergy destruction (i.e., higher energy loss), but resulted in a higher exergy efficiency compared to underground storage of CO 2 .…”

“…They suggested that, to establish a balance between both these aspects, CO 2 emissions from a power plant should be split between both possible applications (underground storage and DME synthesis), with an optimal dispatch ratio to be determined in future work. They found out that total CO 2 underground storage led to exergy destruction of 1.34 MJ per kilogram of avoided carbon emissions, versus 0.13 MJ/kg for 75% CO 2 storage and 25% conversion into DME …”

“…De Falco et al proceeded to an exergy analysis of the DME synthesis process and compared it to CO 2 underground storage to evaluate the usefulness of such an operation (exergy is the amount of work that can be done with a given amount of energy). 140 They found that DME synthesis resulted in higher exergy destruction (i.e., higher energy loss), but resulted in a higher exergy efficiency compared to underground storage of CO 2 . They suggested that, to establish a balance between both these aspects, CO 2 emissions from a power plant should be split between both possible applications (underground storage and DME synthesis), with an optimal dispatch ratio to be determined in future work.…”

Recent Advances on CO2 Mitigation Technologies: On the Role of Hydrogenation Route via Green H2

“…In this regard, aside from the extensive research that has been conducted on the appropriate materials for catalyzing the respective CO 2 hydrogenation reaction, various works have assessed PtX from a techno-economic or environmental viewpoint. In general, although an overall conclusion cannot be unequivocally reached due to the casespecific nature of any such study, promising results have been obtained for PtX implementation at a wide scale range and based on a variety of CO 2 hydrogenation products, such as methanol [212][213][214], DME [215][216][217], liquid hydrocarbons [218][219][220][221][222][223][224] or light olefins [225,226]. Additionally, a comparison of these routes has been made in the recent review by Dieterich et al [202] and in the work by Atsbha et al [220].…”