United States
Environmental Protection
Agency
EPA/540/F-94/503
May 1994
&EPA
SUPERFUND INNOmTIVE
TECHNOLOGY EVALUATION
Emerging Technology Bulletin
Volatile Organic Compound Removal from Air Streams by
Membranes Separation
Membrane Technology and Research, Inc.
Technology Description: This membrane separation tech-
nology developed by Membrane Technology and Research (MTR),
Incorporated, is designed to remove volatile organic compounds
(VOCs) from contaminated air streams. In the process, organic
vapor-laden air contacts one side of a membrane that is perme-
able to organic vapors but relatively impermeable to air. A partial
vacuum, applied to the other side, draws the organic vapor
through the membrane. The permeate vapor is then compressed
and condensed to recover the organic fraction. The purified
airstream is removed on the feed side.
The MTR membrane unit is a spirally-wound module comprised
of a perforated pipe bound within the wound membrane and
spacers. Feed gas flows between the membrane leaves, with
the preferentially permeable component spiralling inward to con-
nect in the central permeate collection pipe. The remainder of
the feed flows across the membrane surface and exits as the
residue.
In the membrane separation system pilot unit, VOCs in a com-
pressed air stream enter the first of two membrane stages (Fig-
ure 1). This first stage concentrates most of the VOCs into the
permeate stream. The permeate is recompressed and con-
densed, normally producing only water from the atmosphere. The
bleed stream leaving the condenser enters the second mem-
brane stage reducing the VOC content to a concentration close
to that of the first stage. The permeate from this stage is concen-
trated enough with VOCs to allow for its condensation. The
bleed stream from this condenser is recirculated back to the
second stage membrane unit. In its entirety, the system sepa-
rates the VOC-laden air stream into a VOC-depleted stream and
condensed liquid VOC.
Waste Applicability: The MTR membrane separation pro-
cess is geared towards removing VOCs from air streams com-
monly produced in the vacuum extraction of VOCs from soils or
by the air stripping VOCs from contaminated surface water, as
well as air streams from manufacturing operations using sol-
vents. The system produces the recovered VOCs as a liquid
from the final condenser. The process adapts to meet capacity
and separation requirements of a particular situation by arranging
the membrane modules in parallel and/or series flow.
Test Results: The MTR membrane pilot system was operated
with perchloroethylene (C2CI4 or Perc) and with a mixture of
hexane isomers and i-octane as typical contaminants be used in
the system to evaluate the system performance. Nine runs with
Figure 1. Two-stage membrane process.
Compressor
First
membrane stage
Air
Vent
Codenser
Codenser
Condensed
liquids
the Perc were used to determine the effects of inlet flow rate and
inlet concentration. Based on varying the inlet concentration
from 43 to 99 parts per million (ppmv) the overall perchloroethyl-
ene removal is approximately 90% and is relatively insensitive to
the entering concentration. The flow rate was varied from 24.1 to
27.6 scfm along with the changing concentration, but the small
range over which it was varied showed no statistically determin-
able effect. The system was compared to another study in which
inlet flowrate was an isolated variable. This other study showed
about a 17% decrease in the removal efficiency for an increase
from 7 to 28 scfm. Nine runs with varying permeate pressures
(i.e., vacuum) on each of the stages were also run with Perc.
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The data from these runs showed that it is advantageous to
operate a membrane system at the lowest attainable permeate
pressure. Also determined, the selectivity of the MTR vapor
separation membranes increases significantly with decreasing
temperature for most organic vapors
Six runs of the hexane isomer and i-octane mixture were carried
out, showing that typically 88 to 91% of these hydrocarbons
were removed even with an inlet concentration varied between
350 and 1540 ppm (Table 1).
Thirteen VaporSep systems are now operating on industrial
process streams to recover a variety of VOCs, including CFCs,
HCFCs, and vinyl chloride monomer. In partnership with a sup-
plier of hospital sterilizer equipment, MTR has applied the tech-
nology to the treatment of sterilizer emissions. Another system is
being demonstrated on an off-gass stream containing carbon
tetrachloride and chloroform generated by a soil-venting opera-
tion.
A paper describing VaporSep technology and its applications is
available.
Table 1. Two-Stage Treatment of Hexanes and i-Octane
Feed rate
(scfm)
25.8
29.7
30.8
27.4
31.4
29.3
Hexane
890
400
660
180
640
350
Feed (ppm)
i-Octane
650
250
520
170
480
230
Residue
Hexane
74
46
74
20
78
37
(ppm)
i-Octane
65
30
59
20
58
28
Total
Hydrocarbon
removal(%)
91
88
89
89
88
89
For Further Information:
EPA Project Manager:
Paul dePercin
U.S. EPA Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, Ohio 45268
(513) 569-7797
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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EPA/540/F-94/503
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