This was a presentation highlighting the objectives and results of a laboratory experiment done with my group.

1. Gas Separation
Using A Membrane
A Presentation By Tianna Drew
Lab Experiment Conducted
on 09/17/2013 by
*The Dream Team*

2. Lab Objectives
• Predict the unknown selectivity of a membrane
provided in the lab using a pilot scale gas
separation unit
• Compose a graph describing the separation process
and predicting the composition of the reject flow
• Produce an Excel worksheet describing the process
that can be used by an operator when predicting
the selectivity of future membranes
• Explain what would happen if the apparatus was
reversed and why

3. Background
Why Membrane Gas Separation?
In the large scale,
membrane gas separation can:
• Reduce processing costs because there is
no energy costs from phase changes, such
as those in cryogenic distillation
• Lessens environmental footprint because
the processing plants involved are
relatively small

4. Background
What Is Membrane Gas Separation?
Separating gases from each other, such as
removing nitrogen and oxygen from air
• Based on: each gas’s distinctive physical
properties, such as diffusion rates
• Using: semi-permeable polymer membrane

5. Background
How Does The Process Work?

6. Background
Before Getting Started
Fundamental Material Balance:
Ff = FR + FP 0.21*Ff = xj*FR + ў*FP
The following equation used to predict the concentration at the permeate was formed
using the flux and flux ratio expressions:
α is the permeability that was varied for each of the following graph in order to predict
the concentrations of the reject and permeate flows.
The flow rate was to be varied, and the concentrations recorded. Based on the
experimental results, a more accurate α value was to be predicted.
Note: Assumed no pressure drop, constant temperature, and there is
atmospheric pressure at the permeate

7. Illustration
Projection of %O2
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9 10
%Recovery
%O2 Reject
α=6
α=7
α=8

8. Methods - Apparatus

9. Methods – TCD-GC
This is the machine that:
• Requires helium as a reference inert gas
• Detects the concentration of oxygen in
either the permeate and reject streams
• Is very expensive $$$

10. Discussion – Raw Data
%O2 Reject Recovery % (reject/feed)
0.9956 41.8439716
1.6167 46.9135802
2.41795 50.5494505
3.097 53.8071066
3.77625 55.6603774
4.72075 59.2274678
5.33475 60.8870968
6.18005 63.2727273
8.18305 68.5800604
9.74935 72.7272727

11. Discussion
Graphical Representation
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7 8 9 10
Recovery%
%O2 Reject

12. Discussion
Graphical Representation
0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9 10
%Recovery
%O2 Reject
α=6
α=7
α=8
EXPERIMENTAL

13. Discussion
Finding Alpha with Excel
Ft Fr Fp yp yr α
141 59 79 0.369213 0.009956 10.13
162 76 84 0.39299 0.016167 10.82
182 92 86 0.415043 0.02418 10.94
197 106 88 0.430719 0.03097 10.83
212 118 90 0.44347 0.037763 10.57
233 138 92 0.460661 0.047208 10.28
248 151 93 0.470226 0.053348 10.06
275 174 96 0.483042 0.061801 9.8
331 227 100 0.508423 0.081831 9.2
385 280 102 0.525662 0.097494 8.83
Calculated average selectivity: 10.146

14. Conclusion
It was found that the selectivity of the
membrane averaged out to 10.146
This would be a great selectivity for a
membrane; unfortunately the theoretical
value was about 8.5

15. Conclusion
Reasons for Error
• Flow rate was slow
– Higher flow rate = higher recovery
– There may have been a more accurate depiction of the
amount of oxygen
• Not enough data points
– Carry out another hour
– Collect a few more data points at higher flow rates to let
the system reach a more steady state
• Co current flow versus countercurrent flow
– Ran the calculations assuming co current flow, whereas if
they had been run assuming countercurrent, the selectivity
would be more accurate
• Ran the experiment using countercurrent apparatus

16. Summary
• Predict the selectivity of the membrane
provided
– α = 10.146
• Compose a graph that can be used in the
future predicting the compositions of the
reject flow
• Explain what would happen if the apparatus
was reversed and why
– Used countercurrent flow apparatus, the co
current apparatus would have slightly different
equations0
10
20
30
40
50
60
70
80
1 2 3 4 5 6 7 8 9 10
%Recovery
%O2 Reject
α=6
α=7
α=8

17. References
• McCabe, Smith and Harriott, 6th edition,
Chapter 26, pages 857-871
• Excel program written by Sara Sumner
• All data collected by *The Dream Team*

18. Questions?