Fixed Bed Adsorption Of Carbon Dioxide On Modified Coconut Shell Granular Activated Carbon
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Date
2014-08
Authors
Tan, Yee Ling
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Abstract
Chemically modified adsorbent is attracting attention on its ability in carbon dioxide
capture in order to increase the adsorption capacity and enhance its characteristics
such as thermal and chemical resistance. In this research, a series of chemically
modified coconut shell granular activated carbon were prepared, characterized and
used in CO2 adsorption process in a fixed-bed adsorption system. Coconut shell
granular activated carbon was chosen due to its large surface area, its stable
properties to withstand destruct under cyclic heating and relatively low cost among
the adsorbents available in the market. Basic chemicals such as triethanolamine
(TEA), sodium hydroxide (NaOH), chitosan, 3-aminopropyl-triethoxysilane
(APTES) and polyethylenimine (PEI) were used to modify the activated carbon. Two
preparation methods were used, the impregnation method and chitosan beads
preparation method by alkali gelation. The surface properties, functional groups and
surface morphologies of the prepared adsorbents were characterized by BET, FT-IR
and SEM, respectively. The adsorption of carbon dioxide was carried out in a fixed
bed adsorption system with an online carbon dioxide analyzer to determine the
concentration of carbon dioxide in the outlet gas. The effect of operating conditions
such as gas flow rate (90-150 mL/min), adsorption temperature (35-55 °C), adsorbent
loading (depends on the density of adsorbent) and initial CO2 concentration (10-
20%) were studied. The BET results showed that the surface area decreased and the
pore characteristics changed after chemical modification. The FT-IR spectra of the
unmodified and modified samples were similar due to a small dosage of chemicals
was impregnated onto the activated carbon. The bed adsorption capacity of
unmodified activated carbon was 17.52 mg/g with adsorbent loading 3 g, adsorption
temperature 35 °C, gas flow rate 90 mL/min and 10% CO2. The highest adsorption
capacity was 81.56 mg/g, which was obtained by using chitosan-PEI-AC beads with
adsorbent loading of 0.5 g, adsorption temperature 35 °C, gas flow rate 90 mL/min
and 10% CO2. The modified sample with the best stability in the regeneration test
was 125CAC6, which decreased about 11.30% over 10 cyclic adsorption process.
The results showed that chemical modification of activated carbon gave positive
effects on the adsorption performance.
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Keywords
Modified coconut shell granular activated carbon were prepared , characterized and used in CO2 adsorption process in a fixed-bed adsorption system.