The rising carbon dioxide (CO2) emissions across the globe, and the resulting
negative impact on the environment, have become the focus of a multitude of scientific
studies in recent times. Despite the recent technological advancements in the
scientific area of carbon capture, reducing and managing CO2 emissions has
persisted as a huge challenge to researchers working in this area of research.
Conventional carbon capture typically uses amine absorption methods/processes,
and while the latest technologies indicate an enhancement of conventional CO2
absorption methods, there is a necessity to investigate options to replace the currently
used sorbents with more benign alternatives.
This work investigates the viability of using deep eutectic solvents (DESs) from a
specific DES system, as novel absorbents for carbon capture absorption processes.
The study was divided into two parts, firstly, mixtures/DESs composed of choline
chloride (ChCl) and levulinic acid (LvAc) were prepared at different compositions and fully characterised. Secondly, the performance of the prepared compositions in terms
of CO2 absorption and desorption, was assessed at different operational conditions.
To ensure the suitability of these sorbents for carbon capture processes, the prepared
DESs were extensively characterised to identify their nature. ChCl:LvAc DESs were
described in terms of their physicochemical properties, including their density,
viscosity, thermal stability, and chemical fingerprint (FTIR spectra). These properties
have been compared to those of other DESs that have been described in literature.
It was essential to identify the nature of ChCl:LvAc mixtures before jumping to the
application domain. For the first time in the literature, the phase behaviour plot (solidliquid equilibrium) of binary mixtures of choline chloride and levulinic acid was
developed and described. According to the phase behaviour plot, ChCl:LvAc mixtures
can only be defined as DESs when the mole percentage of levulinic acid (HBD) is
equal or higher than 66.7%.
ChCl:LvAc DESs were found to be highly thermally stable at temperatures up to 196
⁰C. The density and viscosity of the characterised DESs decrease with increasing
temperature. These figures make ChCl:LvAc DESs suitable for many engineering
applications including carbon capture processes.
The corrosivity of the prepared ChCl:LvAc DESs was found to be lower by 92% as
compared to the corrosivity of monoethanolamine under the same conditions. The
corrosivity of ChCl:LvAc DESs increases with the concentration of levulinic acid,
stirring speed, and CO2 concentration, simultaneously, and decreases with increasing
the water content in the system.
The CO2 absorption capacity of ChCl:LvAc DESs was measured at different
conditions using a vapour–liquid equilibrium rig. The experimental results showed that
the CO2 absorption capacity of the ChCl:LvAc DESs is strongly affected by the
operating pressure and stirring speed, moderately affected by the temperature, and
minimally affected by the Hydrogen bond donor (HBD): Hydrogen bond acceptor
(HBD) molar ratio as well as water content.
A maximum CO2 absorption capacity of 1.58 moles of CO2 per kg of DES (1.58 mol
kg-1
) was measured at 25 °C, 6 bar and stirring speed of 250 rpm for a DES with
HBA:HBD molar ratio of 1:3 and a water/HBA molar ratio (water content) of 2.5. The
regeneration of the DESs was performed at different temperatures, and an optimal
regeneration temperature of 60 °C was obtained. All DESs exhibited good recyclability
and moderate CO2/N2 selectivity, with a maximum selectivity value of 5.63 obtained
for a mixture of gases containing 50% CO2 and 50% N2.
| Date of Award | 19 Sept 2024 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Vitor Magueijo (Supervisor) & Sudipta Roy (Supervisor) |
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