(67b) Amine-Functionalized Hierarchical Zeolites for Carbon Dioxide Capture

Maryam Khaleel^*, Anna
Tuneu Pujolras, Issam Ismail, Georgios
Karanikolos, Lourdes F. Vega, Fèlix Llovell.

*E-mail: maryam.khaleel@ku.ac.ae

Abstract

One of the greatest challenges we
are facing in the 21^st century is our ability to provide sustainable
energy sources to meet the demands for quality of life and economic growth. As
most of the energy today is provided from fossil fuels, huge amounts of CO₂
and other greenhouse gases are emitted to the atmosphere, with negative effects
on the environment. Depletion of fossil fuels and their associated
environmental pollution lead scientists to the pursuit of renewable energy
sources and clean energy. However, reducing dependency on fossil fuels is a
major challenge for most economically advanced countries. To make fossil fuels
clean, efficient, reliable and scalable technologies for CO₂ capture
from large sources should be developed to control CO₂ emission in
the short-medium term. Although some technologies for carbon capture are
available in the market they still suffer from some limitations to be fully
implemented at large scale.

Conventional
CO₂ removal using aqueous alkanolamine solutions is energy
intensive. This lead researchers to investigate various solid adsorbents for
selective CO₂ removal at low pressure ranges while requiring less
energy for regeneration compared to alkanoamine solutions [1]. Various porous
solids were tested for post-combustion CO₂ capture including
activated carbon [2], zeolites [3] and metal–organic frameworks (MOFs) [4]. 
Solid materials grafted or impregnated with amines were also studied to further
increase the CO₂ binding strength and hence CO₂ uptake
[5, 6]. Of particular interest are amine grafted zeolites that combine strong CO₂
capturing zeolite micropores with the chemical binding of CO₂ with
amines [7]. Hierarchical zeolites, combining zeolite micropores and mesoporous
domains, show increased surface area and pore volume compared to conventional
zeolites. Functionalizing the mesoporous domains in such materials with amines
can result in high CO₂ uptake because both the active sites of the
zeolite and the amine groups in the mesopore space can simultaneously capture CO₂.
However, there are very few studies of amine grafted hierarchical zeolites and
the latter were prepared using expensive organics [7].

In this
work we study the performance of amine grafted hierarchical zeolites, prepared
from inorganic (i.e. inexpensive) routes, in CO₂ capture. A series
of zeolites with varying textural properties are synthesized and grafted with
different amines and their performance is tested for CO₂ adsorption. Synthesized materials are characterized using X-ray
Diffraction, Nitrogen Physisorption and Scanning Electron Microscopy. CO₂
uptake properties are evaluated by equilibrium gas uptake measurements to study
the effect of hierarchy on the performance of the materials. Thermogravimetric
Analysis is used to estimate the amount of amine grafted on zeolite samples and
Infrared Spectroscopy is used to study the functionality of the materials.

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