In order to reduce the amount of pollution that is generated by burning fossil fuels alternative
energy sources should be explored. Hydrogen has been identified as the most promising
replacement for fossil fuels and can be produced by using the Hybrid Sulphur (HyS) cycle.
Currently the SO2/O2 separation step in the HyS process has a large amount of knock out
drums. The aim of this study was to investigate new technology to separate the SO2 and O2.
The technology that was identified and investigated was to separate the SO2 and O2 by
absorbing the SO2 into an ionic liquid.
In this study the maximum absorption, absorption rate and desorption rate of SO2 from the
ionic liquid [BMIm][MeSO4] with purities of 95% and 98% was investigated. These ionic liquid
properties were investigated for pure O2 at pressures ranging from 1.5 to 9 bar(a) and for
pure SO2 at pressures from 1.5 to 3 bar(a) at ambient temperature. Experiments were also
carried out where the composition of the feed-stream to the ionic liquid was varied with
compositions of 0, 25, 50, 75 and 100 mol% SO2 with O2 as the balance. For each of these
compositions the temperature of the ionic liquid was changed from 30oC to 60oC, in
increments of 10oC.
The absorption rate of SO2 in the ionic liquid increased when the mole percentage SO2 in the
feed stream was increased. When the temperature of the ionic liquid was decreased the
maximum amount of SO2 that the ionic liquid absorbed increased dramatically. However, the
absorption rate was not influenced by a change in the absorption temperature.
The experimental results for the maximum SO2 absorption were modelled with the Langmuir
absorption model. The model fitted the data well, with an average standard deviation of
17.07% over all the experiments. In order to determine if the absorption reaction was
endothermic or exothermic the Clausius-Clapeyron equation was used to calculate the heat
of desorption for the desorption step. The heat of desorption data indicated that the
desorption of SO2 from this ionic liquid was an endothermic reaction because the heat of
desorption values was positive. Therefore the absorption reaction was exothermic.
From the pressure-change experiments the results showed that the mole percentage of O2
gas that was absorbed into the ionic liquid was independent of the pressure of the O2 feed.On the other hand, there was a clear correlation between the mole percentage SO2 that was
absorbed into the ionic liquid and the feed pressure of the SO2. When the feed pressure of
the SO2 was increased the amount of SO2 absorbed also increased, this trend was
explained with Fick’s law.
In the study the effect of the ionic liquid purity on the SO2 absorption capacity was
investigated. The experimental results for the pressure experiments showed that the 95%
and 98% pure ionic liquid absorbed about the same amount of SO2. During the temperature
experiments the 95% pure ionic liquid absorbed more SO2 than the 98% pure ionic liquid for
all but two of the experiments. However the 95% pure ionic liquid also absorbed small
amounts of O2 at 30 and 40oC which indicated that the 95% pure ionic liquid had a lower
selectivity than the 98% pure ionic liquid. Therefore, the 95% pure ionic liquid had better SO2
absorption capabilities than the 98% pure ionic liquid.
These result showed that the 98% pure ionic liquid did not absorb more SO2 than the 95%
pure ionic liquid, but it did, however, show that the 98% pure ionic liquid had a better
selectivity towards the SO2. Hence, it can be concluded that even with the O2 that is
absorbed it would be economically more advantageous to use the less expensive 95% pure
ionic liquid rather than the expensive 98% pure ionic liquid, because the O2 would not
influence the performance of the process negatively in such low quantities. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/9100 |
| Date | January 2012 |
| Creators | Rabie, Samuel Liversage |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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