Technology Description: This membrane separation technology 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 permeable 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 connect 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 compressed air stream enter the first of two membrane stages (Figure 1). This first stage concentrates most of the VOCs into the

permeate stream. The permeate is recompressed and condensed, normally producing only water from the atmosphere. The

bleed stream leaving the condenser enters the second membrane stage reducing the VOC content to a concentration close

to that of the first stage. The permeate from this stage is concentrated 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 separates the VOC-laden air stream into a VOC-depleted stream and

condensed liquid VOC.

Waste Applicability: The MTR membrane separation process is geared towards removing VOCs from air streams commonly 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 solvents. 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 (C2Cl4

 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

EPA/540/F-94/503

May 1994

Emerging Technology Bulletin

Volatile Organic Compound Removal from Air Streams by

Membranes Separation

Membrane Technology and Research, Inc.

United States

Environmental Protection

Agency

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 perchloroethylene 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 determinable 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.

Air

Compressor First

membrane stage

Vent

Metering

pump

Vacuum

pump

Codenser

Condensed

liquids

Second

membrane stage

Vacuum

pump

Codenser

Condensed

liquids

Figure 1. Two-stage membrane process.
BULK RATE

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EPA

PERMIT No. G-35

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/540/F-94/503

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 supplier of hospital sterilizer equipment, MTR has applied the technology 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 operation.

A paper describing VaporSep technology and its applications is

available.

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

Feed rate Feed (ppm) Residue (ppm) Total

(scfm) Hydrocarbon

Hexane i-Octane Hexane i-Octane removal(%)

25.8 890 650 74 65 91

29.7 400 250 46 30 88

30.8 660 520 74 59 89

27.4 180 170 20 20 89

31.4 640 480 78 58 88

29.3 350 230 37 28 89

Table 1. Two-Stage Treatment of Hexanes and i-Octane