Kinetics and Vapour-Liquid Equilibrium of CO2 absorption in aqueous benzyl amine solutions

In view of the increasing global warming associated with the use of fossil fuels, the emissions of CO2 must be strongly reduced. Especially at large scale point sources (e.g. power plants) CO2 capture plants are being installed, planned or considered. Typically, aqueous amine based solutions (mostly MonoEthanol Amine (MEA)) are used to capture around 80-90% of the CO2 in the flue gas. This means that flue gas leaving the stack still contains 5000-10000 ppm.

Another trend is the recent development of technologies for the removal of CO2 from ambient air, so-called Direct Air Capture (DAC). In these DAC processes CO2 is recovered from air at 0.04% CO2 (420 ppm), using often amines impregnated or attached to a solid sorbents. Due to the low CO2 concentration the energy required per ton CO2 removed are relatively high. One of the most succesful sorbents, Lewatit VPOC 1065, uses polystyrene-based particles, with benzyl amine (BZA) as functional side groups reacting with the CO2 in air. Apparently, BZA can react quickly and reversibly with CO2 at low partial pressures.

Considering this, it makes sense to improve the (designs for-) CO2 removal processes at flue gas stacks, such that the outlet conditions are no longer 5000-10000 ppm, but rather ca. 400 ppm. This is called Deep Removal of CO2 from flue gas. In that way, less DAC installations are needed, which saves both capital investment as well as energy (per ton CO2 captured). Therefore, there is a need to study and compare the kinetics for CO2 absorption for both MEA and BZA under the relevant conditions for deep removal. Whereas for MEA some experimental work under these conditions is already done, for BZA no data is yet available.

Objective: Determining the kinetics and VLE between CO2 and Benzyl Amine (in aqueous solution) at relevant CO2 partial pressures of 20-500 Pa (200- 5000 ppm) for absorption temperatures (in the range of 15-45°C).

This research will initially focus on the kinetics for aqueous BZA solutions, using a stirred cell apparatus. By letting equilibrium to be reached in the experiments also Vapor-Liquid equilibrium data is obtained. If time allows, in an more explorative part of the work, it will be tested how mixtures of BZA and MEA will behave and/or if the kinetics can also be determined for the BZA groups, which are covalently bound to the polymer backbone of the Lewatit particles.

Measurement technique

In a so-called stirred cell contactor, a well-mixed gas and liquid phase are contacted. In the gas loop between stirred cell (gas phase) and CO2 analyser a known amount of CO2 is injected. After CO2 injection, the concentration is monitored as function of time.

From the gas phase CO2 is absorbed through the (well-known geometric) interfacial area. The (chemical enhanced) absorption flux (in mol CO2 absorbed per m2 interface per second) can be related to the intrinsic reaction kinetics, provided the experiments are carried out under the right conditions (e.g. for the pseudo-first order reaction regime).

Anticipated activities

Literature study on the CO2 – benzylamine (in water) system (kinetics, equilibrium, solubility etc.)
Introduction to measurement technique; absorption of CO2 in water and into MEA solutions
Design and carry out experiments for kinetics of BZA with CO2 (at e.g. 25 and 40°C, using 200-5000 ppm CO2)
Using an available stirred cell apparatus
Reporting

This project is related to the LNG-Zero project. In the context of maritime industry, the International Marine Organization (IMO) is targeting to reduce the emissions at least by 50% (or cut down 85% of the current emission per ship) [1]. To abide to IMO targets, a R&D program LNG Zero is initiated in Netherlands targeting net-zero carbon emission technologies (i.e. < 400 ppm) in the LNG carriers. In addition to capture on-board, the CO2 needs to be stored in an energy efficient way on-board. At the University of Twente (PhD project J. Ganesan), the deep removal of CO2 and its integration with the bulk removal step for onboard application is studied.

Contact info:

Daily supervisor:
Jayaram Ganesan - g.ganesan@utwente.nl

Supervisor:
Wim Brilman - d.w.f.brilman@utwente.nl