Membrane Gas Separation

14.2.1
Membrane Modules 
GS membranes are formed in hollow - fi bre or spiral - wound modules and, in some applica-
tions, also in plate and frame modules. A hollow - fi bre module (Figure 14.1 a) contains a 
large number of membrane fi bres housed in a shell. Feed can be introduced on either the 
fi bre or shell side. Permeate is usually withdrawn in a co - current or counter - current 
manner, with the latter being generally more effective. Spiral - wound modules (Figure 
14.1 b) are made from fl at membrane envelopes, wrapped around a central tube. The feed 
passes along the length of the module and the permeate passes into a membrane envelope 
and then out via the central tube. Both the feed and the permeate are transported through 
the module in fl uid - conductive spacer material. Modern modules tend to contain multiple 
membranes that are all attached to the same central tube. Usually in spiral - wound mem-
brane modules, the size of the feed channel is greater than the active membrane area. In 

---

Membrane Engineering: Progress and Potentialities in Gas Separations
285
particular, the feed channel spacer is typically about 20% wider than the membrane 
envelope. This additional width may promote fl ow perpendicular to the bulk fl ow (along 
the spiral) [29] . Currently, the spiral wound modules contain around 1 – 2 m of rolled 
sheets, for 20 – 40 m 
2
of membrane area.
Each membrane module confi guration presents advantages and drawbacks. Hollow 
fi bres are the cheapest on a per square metre basis (with the highest membrane area to 
module volume ratio); however, to make very thin selective layers in hollow - fi bre form 
is harder than in fl at sheet confi guration. This implies that the permeance of hollow fi bres 
is generally lower than that of a fl at sheet membrane prepared with the same material. 
Therefore, larger membrane area is required for achieving the same separation by HF 
modules. Hollow fi bre modules also require more pre - treatments of the feed than is 
usually required by spiral wound modules for removing particles, oil residue and other 
fouling components. These factors strongly affect the cost of the hollow fi bre module 
design, therefore, currently, spiral wound modules are employed in several separations 
(e.g. in natural gas processing) particularly for those separations which cannot support 
the costs associated with the hollow fi bre modules. 
The size of the membrane modules for GS is rapidly increasing in order to follow the 
economies of scale. As reported by Baker [30] , from 1980 up to now the size of Cynara ’ s 
hollow - fi bres modules, employed for natural gas treatment, increased by a factor of 6, 
while the spiral - wound modules are increasing, with the diameter passing from 20 cm to 
30 cm (Figure 14.2 ). GS systems require membrane modules contained in high - pressure, 
code - stamped vessels. The costs of the vessels, frames and associated pipes, valves, etc. 
can be several times the cost of the membranes. Therefore, considerable reduction of costs 
can be achieved by packing larger membrane modules into fewer vessels [29] . This 
fact allows weight and footprint to be reduced. This is extremely important on offshore 
platforms and other space - constrained facilities.
A membrane GS production process can be realized assembling the membrane modules 
in several confi gurations, depending on the particular type of separation. The single - 
stage, double - stage, multi - stage with recycle constitute the main design solutions. Some 
examples are given in the following paragraphs relative to the industrial applications for 
the GS.
(a)
(b)
Housing
(shell)
Seal Bundle
in Housing
Potting
(seal)
Membrane
Perforated
permeate
collection
pipe
Residue
flow
Membrane
envelope
Permeate
spacer
Permeate
flow
Membrane
Feed
flow
Feed
spacer
Hollow
Fibers
Hollow Fiber Bundle
Figure 14.1 (a) Hollow fi bre module (image courtesy of www.medarray.com , Copyright 
(2010) Medarray); (b) Spiral - wound module (image courtesy of www.mtrinc.com , 
Copyright (2010) mtrinc)

---

286
Membrane Gas Separation
30˝
Element
16˝
12˝
5˝
Figure 14.2 Photograph showing the development of hollow - fi bre membrane modules 
at Cynara, from the fi rst 5 - inch modules of the 1980s to the 30 - inch diameter currently 
being introduced [51] (Cynara Company now part of NATCO Group, Inc.). Reprinted 
with permission from Ind. Eng. Chem. Res., Natural gas processing with membranes: an 
overview, by R. W. Baker and K. Lokhandwala, 47, 7, 2109 – 2121, Copyright (2008) 
American Chemical Society