U.S. patent application number 10/183793 was filed with the patent office on 2004-01-01 for apparatus using solid perm-selective membranes in multiple groups for simultaneous recovery of specified products from a fluid mixture.
Invention is credited to Colling, Craig W., Huff, George A. JR..
Application Number | 20040000513 10/183793 |
Document ID | / |
Family ID | 30002678 |
Filed Date | 2004-01-01 |
United States Patent
Application |
20040000513 |
Kind Code |
A1 |
Colling, Craig W. ; et
al. |
January 1, 2004 |
Apparatus using solid perm-selective membranes in multiple groups
for simultaneous recovery of specified products from a fluid
mixture
Abstract
Apparatus is disclosed for economical separation of fluid
mixtures. Broadly, apparatus of the invention comprises modules
using solid perm-selective membranes. More particularly, the
invention relates to a plurality of membrane modules disposed in a
first product group, a second product group, and optionally one or
more intermediate group. Apparatus of the invention with the
membrane modules in multiple groups is beneficially useful for
simultaneous recovery of a very pure permeate product and a desired
non-permeate product from a mixture containing organic
compounds.
Inventors: |
Colling, Craig W.;
(Warrenville, IL) ; Huff, George A. JR.;
(Naperville, IL) |
Correspondence
Address: |
CAROL WILSON
BP AMERICA INC.
MAIL CODE 5 EAST
4101 WINFIELD ROAD
WARRENVILLE
IL
60555
US
|
Family ID: |
30002678 |
Appl. No.: |
10/183793 |
Filed: |
June 27, 2002 |
Current U.S.
Class: |
210/323.1 ;
210/321.6 |
Current CPC
Class: |
B01D 53/226 20130101;
B01D 53/225 20130101; C01B 3/503 20130101; Y02P 20/10 20151101;
C01B 2203/048 20130101; Y02P 20/125 20151101; B01D 61/00 20130101;
C01B 2203/0405 20130101 |
Class at
Publication: |
210/323.1 ;
210/321.6 |
International
Class: |
B01D 063/00 |
Claims
That which is claimed is:
1. Apparatus using perm-selective membranes in multiple groups for
simultaneous recovery of a very pure permeate product and a desired
non-permeate product from a fluid mixture of compounds, which
apparatus comprises (1-A) a plurality of membrane modules disposed
in a first product group, one or more intermediate group, and a
second product group, each module comprising a solid perm-selective
membrane which under a suitable differential of a driving force
exhibits a permeability of at least 0.1 Barrer, a channel having at
least one inlet and one outlet for flow of fluid in contact with
one side of a membrane, and contiguous with the opposite side
thereof a permeate chamber having at least one outlet for flow of
permeate, (1-B) means for distribution of a fluid feedstock into
the channel inlets of at least a portion of the intermediate group
of modules, (1-C) means for collection of permeate effluent from
the chamber outlets of at least a portion of the intermediate group
of modules and distribution of this intermediate permeate into the
channel inlets of the first product group modules, (1-D) means for
collection of a permeate product effluent from the chamber outlets
of the first product group of modules, (1-E) means for collection
of non-permeate effluent from the channel outlets of the first
product modules and distribution thereof into the channel inlets of
at least a portion of the intermediate group of modules, (1-F)
means for collection of non-permeate from the channel outlets of
the intermediate group of modules and distribution of this
intermediate non-permeate into the channel inlets of the second
product group modules, and (1-G) means for collection of a
non-permeate product effluent from the channel outlets of the
second product group of modules.
2. Apparatus using perm-selective membranes in multiple groups for
simultaneous recovery of a very pure permeate product and a desired
non-permeate product from a fluid mixture of compounds, which
apparatus comprises (2-A) a plurality of membrane modules disposed
in a first product group, one or more intermediate group, and a
second product group, each module comprising a solid perm-selective
membrane which under a suitable differential of a driving force
exhibits a permeability of at least 0.1 Barrer, a channel having at
least one inlet and one outlet for flow of fluid in contact with
one side of a membrane, and contiguous with the opposite side
thereof a permeate chamber having at least one outlet for flow of
permeate, (2-B) means for distribution of a fluid feedstock into
the channel inlets of at least a portion of the intermediate group
of modules, (2-C) means for collection of permeate effluent from
the chamber outlets of at least a portion of the intermediate group
of modules and distribution of this intermediate permeate into the
channel inlets of the first product group modules, (2-D) means for
collection of a permeate product effluent from the chamber outlets
of the first product group of modules, (2-E) means for collection
of non-permeate effluent from the channel outlets of the first
product modules and distribution thereof into the channel inlets of
at least a portion of the intermediate group of modules, (2-F)
means for collection of non-permeate from the channel outlets of
the intermediate group of modules and distribution of this
intermediate non-permeate into the channel inlets of the second
product group modules, (2-G) means for collection of a non-permeate
product effluent from the channel outlets of the second product
group of modules, and (2-H) means for collection of permeate
effluent from the chamber outlets of the second product modules and
distribution thereof into the channel inlets of the first product
of modules.
3. The apparatus according to claim 1 wherein the membrane modules
in the second product group have membranes of lower selectivity
than membranes in at least one of the other groups.
4. The apparatus according to claim 1 wherein the membrane modules
in the second product group have membranes of lower selectivity
than membranes in the other groups.
5. The apparatus according to claim 1 wherein the membrane modules
in at least a portion of the intermediate group have membranes of
higher selectivity than membranes in at least one of the other
groups.
6. The apparatus according to claim 1 wherein the membrane modules
in at least a portion of the intermediate group have membranes of
higher selectivity than membranes in the other groups.
7. The apparatus according to claim 1 wherein the membrane modules
in the first product group have membranes of higher selectivity
than membranes in at least one of the other groups.
8. The apparatus according to claim 1 wherein the membrane modules
in the first product group have membranes of higher selectivity
than membranes in the other groups.
9. The apparatus according to claim 1 wherein the (1-C) means for
collection and distribution of permeate into the channel inlets of
the first product group modules comprises a compressor.
10. The apparatus according to claim 1 further comprising means for
distribution of another feedstock into the channel inlets of the
first product of modules.
11. Apparatus using perm-selective membranes in multiple groups for
simultaneous recovery of a very pure permeate product and a desired
non-permeate product from a fluid mixture of compounds, which
apparatus comprises (11-A) a plurality of membrane modules disposed
in a first product group, one or more intermediate group, and a
second product group, each module comprising a solid perm-selective
membrane which under a suitable differential of a driving force
exhibits a permeability of at least 0.1 Barrer, a channel having at
least one inlet and one outlet for flow of fluid in contact with
one side of a membrane, and contiguous with the opposite side
thereof a permeate chamber having at least one outlet for flow of
permeate, (11-B) means for distribution of a first fluid feedstock
into the channel inlets of at least a portion of the intermediate
group of modules, (11-C) means for collection of permeate effluent
from the chamber outlets of at least a portion of the intermediate
group of modules and distribution of this intermediate permeate
into the channel inlets of the first product group modules, (11-D)
means for distribution of a second fluid feedstock into the channel
inlets of the first product group of modules, (11-E) means for
collection of a permeate product effluent from the chamber outlets
of the first product group of modules, (11-F) means for collection
of non-permeate effluent from the channel outlets of the first
product modules and distribution thereof into the channel inlets of
at least a portion of the intermediate group of modules, (11-G)
means for collection of non-permeate from the channel outlets of
the intermediate group of modules and distribution of the
non-permeate into the channel inlets of the second product group
modules, (11-H) means for collection of a non-permeate product
effluent from the channel outlets of the second product group of
modules, and (11-I) means for collection of permeate effluent from
the chamber outlets of the second product modules and distribution
thereof into at least a portion of the channel inlets of the
intermediate group of modules.
12. The apparatus according to claim 11 further comprising means
for distribution of another fluid feedstock into the channel inlets
of the second product of modules.
13. The apparatus according to claim 11 wherein the membrane
modules in the second product group have membranes of lower
selectivity than membranes in at least one of the other groups.
14. The apparatus according to claim 11 wherein the membrane
modules in the second product group have membranes of lower
selectivity than membranes in the other groups.
15. The apparatus according to claim 11 wherein the membrane
modules in at least a portion of the intermediate group have
membranes of higher selectivity than membranes in at least one of
the other groups.
16. The apparatus according to claim 11 wherein the membrane
modules in at least a portion of the intermediate group have
membranes of higher selectivity than membranes in the other
groups.
17. The apparatus according to claim 11 wherein the membrane
modules in the first product group have membranes of higher
selectivity than membranes in at least one of the other groups.
18. The apparatus according to claim 11 wherein the membrane
modules in the first product group have membranes of higher
selectivity than membranes in the other groups.
19. The apparatus according to claim 11 wherein the (11-C) means
for collection and distribution of permeate into the channel inlets
of the first product group modules comprises a compressor.
20. The apparatus according to claim 11 wherein the (11-I) means
for collection and distribution of permeate into at least a portion
the channel inlets of the intermediate group modules comprises a
compressor.
Description
TECHNICAL FIELD
[0001] The present invention relates to novel apparatus for
separation of fluid mixtures. Broadly, apparatus of the invention
comprises modules using solid perm-selective membranes. More
particularly, the invention relates to a plurality of membrane
modules disposed in a first product group, a second product group,
and optionally one or more intermediate groups. Apparatus of the
invention with the membrane modules in multiple groups is
beneficially useful for simultaneous recovery of a very pure
permeate product and a desired non-permeate product from a mixture
containing organic compounds.
BACKGROUND OF THE INVENTION
[0002] Membranes useful for the separation of gaseous mixtures are
of two very different types: one is microporous while the other is
nonporous. Discovery of the basic laws governing the selectivity
for gases effusing through a microporous membrane is credited to T.
Graham. When the pore size of a microporous membrane is small
compared to the mean-free-path of non-condensable gas molecules in
the mixture, the permeate is enriched in the gas of the lower
molecular weight. Practical and theoretical enrichments achievable
by this technique are very small because the molecular weight
ratios of most gases are not very large and the concomitant
selectivities are proportional to the square roots of these ratios.
Therefore, a large number of separation stages is needed to effect
an efficient separation of a given gas from a gaseous mixture.
However, because this method of separation relies solely on mass
ratios and not chemical differences among the effusing species, it
is the only membrane based method capable of separating isotopes of
a given element. For this reason, this method was chosen to enrich
uranium in the fissionable isotope 235 for development of the
atomic bomb during World War II. However, this method of separation
is inherently expensive due to the large amount of capital
investment needed for processing a necessary large amount of gas,
stringent membrane specifications requiring high porosity and small
pore size, and high energy requirements for operation.
[0003] In nonporous membrane systems, molecules permeate through
the membrane. During permeation across the nonporous membrane,
different molecules are separated due to the differences of their
diffusivity and solubility within the membrane matrix. Not only
does molecular size influence the transport rate of each species
through the matrix but also the chemical nature of both the
permeating molecules and the polymer matrix itself. Thus,
conceptually useful separations should be attainable.
[0004] The art is replete with processes said to fabricate
membranes possessing both high selectivity and high fluxes. Without
sufficiently high fluxes the required membrane areas required would
be so large as to make the technique uneconomical. It is now well
known that numerous polymers are much more permeable to polar gases
(examples include H.sub.2O, CO.sub.2, H.sub.2S, and SO.sub.2) than
to nonpolar gases (N.sub.2, O.sub.2, and CH.sub.4), and that gases
of small molecular size (He, H.sub.2) permeate more readily through
polymers than large molecules (CO, C.sub.2H.sub.4).
[0005] Another aspect of the art is related to two-stage and/or
multi-stage membrane separation processes and apparatus for
removing a component from a fluid stream. Such systems may be
considered when a desired separation cannot be completed using
avaiable membrane materials in a single stage. Several membrane
permeator processes have been described, for example, S. Weller and
W. Steiner published one of the first articles to address aspects
of multi-stage membrane apparatus in "Engineering Aspects of Gases
Fractional Permeation Through Membranes" in Chem. Eng. Prog. 46,
585-590 (1950).
[0006] More recently, U.S. Pat. Nos. 5,256,295 and 5,256,296 in the
name of Richard W. Baker and Johannes G. Wijmans relate to membrane
separation systems having an auxiliary membrane module installed
across the pump that drives the main membrane unit, so that the
permeate streams from the main and auxiliary membrane units are
mixed and pass together through a common driving pump. The
concentration of the mixed permeate stream is said to build up by
circulating the stream through the auxiliary unit, and where the
concentration reaches a desired level, the mixed stream can be
tapped and the product stream drawn off. An auxiliary membrane
module is also described as being installed across the second stage
of the two-stage membrane separation system. The driving force for
the auxiliary module is provided by the pump or other driving unit
for the first membrane stage. The auxiliary module provides
additional treatment of the residue stream from the second membrane
stage, but is driven by the first stage driving unit. Baker and
Wijmans did not discover that the efficiency of this design can be
dramatically improved by choosing a different feed position.
Location of the feed position for multi-stage systems becomes
critical to the recovery of two products.
[0007] U.S. Pat. Nos. 5,102,432 and 5,709,732 in the name of Ravi
Prasad relate to three-stage membrane gas separation systems for
air. U.S. Pat. No. 5,102,432 is directed to production of very high
purity nitrogen by separation of air in a three stage membrane
system in which the permeate from the product stage is recycled to
the intermediate second stage and permeate from this second stage
is recycled to the feed stage with the membrane surface area being
distributed between the stages to recovery a single purified
product. U.S. Pat. No. 5,709,732 is directed to production of
purified oxygen gas (60-90% purity) from ambient air in systems of
at least three permeator stages which together use less than one
compressor per stage. In this three-stage system the permeate from
the product stage is the purified oxygen gas, the non-permeate from
the product stage is recycled to the intermediate stage (identified
as stage 1), non-permeate from this intermediate stage is recycled
to the feed stage (identified as stage 2), and the non-permeate
effluent of the feed stage is the oxygen depleted waste stream.
Only a single purified product is recovered.
[0008] More recently U.S. Pat. No. 5,873,928 in the name of Richard
A. Callahan describes a membrane process for the production of a
desired very high purity permeate gas by use of a two-stage
membrane process. A process feed gas mixture is provided to a
primary unit comprising a membrane having a relatively high
intrinsic permeability to provide an intermediate permeate gas and
a retentate by-product, and the intermediate permeate gas is
provided to a secondary membrane unit comprising a membrane having
a relatively low intrinsic permeability to produce therefrom a very
high purity permeate gas product. The non-permeate from the
secondary membrane unit is recycled with the feed gas mixture to
the primary unit.
[0009] Although Callahan claimed reduced membrane area as the
advantage of the process, the required recycle rate increased
significantly. Considering that increased recycle requires higher
compression and operating costs, little, if any, overall benefit is
suggested for this process.
[0010] An article by T. Peterson and K. Lien entitled "Design
Studies of Membrane Permeator Processes for Gas Separations" in Gas
Sep. Purif. 9, 151-169 (1995) examined the effect of using
different membrane materials at each state of a multi-stag membrane
process, for the separation of CO.sub.2 and CH.sub.4. They
concluded that the total costs of a multiple permeability membrane
system are not significantly different than those of a single
permeability membrane system.
[0011] Neither U.S. Pat. No. 5,873,928 nor the article by T.
Peterson and K. Lien considered any possibility of purity
specifications on both permeate and non-permeate products.
[0012] There is, therefore, a present need for processes and
apparatus using perm-selective membranes for simultaneous recovery
of a very pure permeate product and a desired non-permeate product,
in contrast to by-product, waste streams, in particular, processes
which do not have the above disadvantages. A further object of the
invention is to provide inexpensive processes and apparatus for the
efficient separation of chemical compounds from mixtures which are
difficult to separate, e.g., separation of propane-propylene by
fractional distillation.
[0013] Improved apparatus should provide for an integrated
sequence, carried out with streams in gas and/or liquid state,
using a suitable perm-selective membrane, preferably a solid
perm-selective membrane which under a suitable differential of a
driving force exhibits selective permeability of a desired product.
Advantageously, apparatus using perm-selective membranes for
simultaneous recovery of a very pure permeate product and a desired
non-permeate product shall avoid or minimize formation of unwanted
by-products, waste streams. Beneficially, an improved separation
apparatus shall efficiently employ perm-selective membranes having
the same or different pre-selected permeabilities, and with optimum
distribution between stages so as to efficiently produce very high
purity product.
SUMMARY OF THE INVENTION
[0014] In broad aspect, the present invention is directed to
apparatus using solid perm-selective membranes for economical
separation of fluid mixtures. More particularly, this invention
relates to apparatus comprising a plurality of membrane modules
disposed in a first product group, a second product group, and
optionally one or more intermediate groups. Advantageously
apparatus of the invention with the membrane modules in multiple
groups is employed for simultaneous recovery of a very pure
permeate product and a desired non-permeate product from a mixture
containing organic compounds.
[0015] This invention contemplates the treatment of a fluid
feedstock, e.g. various type organic materials, especially a fluid
mixture of compounds of petroleum origin. In general, the fluid
feedstock is a gaseous mixture comprising a more selectively
permeable component and a less permeable component. Apparatus of
the invention are particularly useful in processes for treatment of
a gaseous mixture comprised of a more selectively permeable alkene
component and a corresponding alkane component, e.g. the separation
of propylene from propane.
[0016] In one aspect, the invention provides apparatus using
perm-selective membranes in multiple groups for simultaneous
recovery of a very pure permeate product and a desired non-permeate
product from a fluid mixture of compounds. The apparatus comprises:
a plurality of membrane modules disposed in a first product group,
one or more intermediate groups, and a second product group, each
module comprising a solid perm-selective membrane which under a
suitable differential of a driving force exhibits a permeability of
at least 0.1 Barrer, a channel having at least one inlet and one
outlet for flow of fluid in contact with one side of a membrane,
and contiguous with the opposite side thereof a permeate chamber
having at least one outlet for flow of permeate; means for
distribution of a fluid feedstock into the channel inlets of at
least a portion of the intermediate group of modules; means for
collection of permeate effluent from the chamber outlets of at
least a portion of the intermediate group of modules and
distribution of this intermediate permeate into the channel inlets
of the first product group modules; means for collection of a
permeate product effluent from the chamber outlets of the first
product group of modules; means for collection of non-permeate
effluent from the channel outlets of the first product modules and
distribution thereof into the channel inlets of at least a portion
of the intermediate group of modules; means for collection of
non-permeate from the channel outlets of the intermediate group of
modules and distribution of this intermediate non-permeate into the
channel inlets of the second product group modules; means for
collection of a non-permeate product effluent from the channel
outlets of the second product group of modules; and means for
collection of permeate effluent from the chamber outlets of the
second product modules and distribution thereof into the channel
inlets of the first product of modules.
[0017] The means for collection and distribution of permeate into
the channel inlets of the first product group modules,
advantageously comprises a compressor and/or pump, preferably a
compressor.
[0018] Depending on the separation required to simultaneously
recover a very pure permeate product and a desired non-permeate
product from feed streams in a particular application, preferred
embodiments of the invention further comprises means for
distribution of another fluid feedstock into the channel inlets of
the first and/or second product of modules. In another preferred
embodiment of the invention, the apparatus further comprises means
for distribution of another feedstock into the channel inlets of
the first product of modules. Optionally, the apparatus may further
comprises means for distribution of a "sweep" stream into the
permeate chambers of one or more of the modules.
[0019] In another aspect, this invention provides apparatus using
perm-selective membranes in multiple groups for simultaneous
recovery of a very pure permeate product and a desired non-permeate
product from a fluid mixture of compounds in which the apparatus
comprises: a plurality of membrane modules disposed in a first
product group, one or more intermediate group, and a second product
group, each module comprising a solid perm-selective membrane which
under a suitable differential of a driving force exhibits a
permeability of at least 0.1 Barrer, a channel having at least one
inlet and one outlet for flow of fluid in contact with one side of
a membrane, and contiguous with the opposite side thereof a
permeate chamber having at least one outlet for flow of permeate;
means for distribution of a first fluid feedstock into the channel
inlets of at least a portion of the intermediate group of modules;
means for collection of permeate effluent from the chamber outlets
of at least a portion of the intermediate group of modules and
distribution of this intermediate permeate into the channel inlets
of the first product group modules; means for distribution of a
second fluid feedstock into the channel inlets of the first product
group of modules; means for collection of a permeate product
effluent from the chamber outlets of the first product group of
modules; means for collection of non-permeate effluent from the
channel outlets of the first product modules and distribution
thereof into the channel inlets of at least a portion of the
intermediate group of modules; means for collection of non-permeate
from the channel outlets of the intermediate group of modules and
distribution of the non-permeate into the channel inlets of the
second product group modules; means for collection of a
non-permeate product effluent from the channel outlets of the
second product group of modules; and means for collection of
permeate effluent from the chamber outlets of the second product
modules and distribution thereof into at least a portion of the
channel inlets of the intermediate group of modules.
[0020] Depending on the separation required to simultaneously
recover a very pure permeate product and a desired non-permeate
product from feed streams in a particular application, preferred
embodiments of the invention further comprises means for
distribution of another fluid feedstock into the channel inlets of
the second product of modules. In another preferred embodiment of
the invention, the means for collection and distribution of
permeate into the channel inlets of the first product group modules
comprises a compressor, and/or the means for collection and
distribution of permeate into at least a portion the channel inlets
of the intermediate group modules comprises a compressor.
[0021] According to the invention, the membrane modules in a group
having membranes of about the same selectivity which selectivity is
about the same or may be critically different from that of the
other group or groups. In one aspect of the invention the membrane
modules in the second product group have membranes of lower
selectivity than membranes in at least one of other group.
Preferably, the membrane modules in the second product group have
membranes of lower selectivity than membranes in the other
groups.
[0022] In another aspect of the invention the membrane modules in
at least a portion of the intermediate group have membranes of
higher selectivity than membranes in at least one of the other
groups. Advantageously, the membrane modules in the intermediate
group have membranes of a selectivity which is about 35 percent or
more higher than membranes another group, preferably at least about
50 percent higher, and more preferably at least about 100 percent
higher. Preferably, the membrane modules in at least a portion of
the intermediate group have membranes of higher selectivity than
membranes in the other groups.
[0023] In other preferred embodiments, the membrane modules in the
first product group have membranes of higher selectivity than
membranes in at least one of the other groups. More preferably the
membrane modules in the first product group have membranes of
higher selectivity than membranes in the other groups.
[0024] This invention is particularly useful towards separations
involving organic compounds, in particular compounds which are
difficult to separate by conventional means such as fractional
distillation. Typically, these include organic compounds are
chemically related as for example alkanes and alkenes of similar
carbon number.
[0025] For a more complete understanding of the present invention,
reference should now be made to the embodiments illustrated in
greater detail in the accompanying drawing and described below by
way of examples of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention is hereinafter described in detail with
reference to the accompanying drawings in which are schematic flow
diagrams depicting preferred aspects of the multi-stage membrane
separation processes and apparatus of the present invention for
simultaneous recover of a very pure permeate product and a desired
non-permeate product from a fluid mixture of compounds.
[0027] FIG. 1 is schematic drawing showing an embodiment of the
present invention which includes three groups of perm-selective
membrane modules, one feedstream location and a compressor.
[0028] FIG. 2 is schematic drawing showing an embodiment of the
present invention which includes three groups of perm-selective
membrane modules, one and/or two feedstream locations and two
compressors.
GENERAL DESCRIPTION
[0029] Any solid perm-selective membrane which under a suitable
differential of a driving force exhibits a permeability and other
characteristics suitable for the desired separations may be used
according to the invention. Suitable membranes may take the form of
a homogeneous membrane, a composite membrane or an asymmetric
membrane which, for example may incorporate a gel, a solid, or a
liquid layer. Widely used polymers include silicone and natural
rubbers, cellulose acetate, polysulfones and polyimides.
[0030] Preferred membranes for use in vapor separation embodiments
of the invention are generally of two types. The first is a
composite membrane comprising a microporous support, onto which the
perm-selective layer is deposited as an ultra-thin coating.
Composite membranes are preferred when a rubbery polymer is used as
the perm-selective material. The second is an asymmetric membrane
in which the thin, dense skin of the asymmetric membrane is the
perm-selective layer. Both composite and asymmetric membranes are
known in the art. The form in which the membranes are used in the
invention is not critical. They may be used, for example, as flat
sheets or discs, coated hollow fibers, spiral-wound modules, or any
other convenient form.
[0031] The driving forces for separation of vapor components by
membrane permeation include, predominately their partial pressure
difference between the first and second sides of the membrane. The
pressure drop across the membrane can be achieved by pressurizing
the first zone, by evacuating the second zone, introducing a sweep
stream, or any combination thereof.
[0032] The membranes used in each group of modules may be of the
same type or different. Although both units may contain membranes
selective to the desired component to be separated, the
selectivities of the membranes may be different. For example, where
intermediate modules process the bulk of the fluid feedstock, these
modules may contain membranes of high flux and moderate
selectivity. The module group which deals with smaller streams, may
contain membranes of high selectivity but lower flux. Likewise the
intermediate modules may contain one type of membrane, and product
modules may contain another type, or all three groups may contain
different types. Useful embodiments are also possible using
membranes of unlike selectivities in the intermediate modules and
product modules.
[0033] Suitable types of membrane modules include the hollow-fine
fibers, capillary fibers, spiral-wound, plate-and-frame, and
tubular types. The choice of the most suitable membrane module type
for a particular membrane separation must balance a number of
factors. The principal module design parameters that enter into the
decision are limitation to specific types of membrane material,
suitability for high-pressure operation, permeate-side pressure
drop, concentration polarization fouling control, permeability of
an otional sweep stream, and last but not least costs of
manufacture.
[0034] Hollow-fiber membrane modules are used in two basic
geometries. One type is the shell-side feed design, which has been
used in hydrogen separation systems and in reverse osmosis systems.
In such a module, a loop or a closed bundle of fibers is contained
in a pressure vessel. The system is pressurized from the shell
side; permeate passes through the fiber wall and exits through the
open fiber ends. This design is easy to make and allows very large
membrane areas to be contained in an economical system. Because the
fiber wall must support considerable hydrostatic pressure, the
fibers usually have small diameters and thick walls, e.g. 100 .mu.m
to 200 .mu.m outer diameter, and typically an inner diameter of
about one-half the outer diameter.
[0035] A second type of hollow-fiber module is the bore-side feed
type. The fibers in this type of unit are open at both ends, and
the feed fluid is circulated through the bore of the fibers. To
minimize pressure drop inside the fibers, the diameters are usually
larger than those of the fine fibers used in the shell-side feed
system and are generally made by solution spinning. These so-called
capillary fibers are used in ultra-filtration, pervaporation, and
some low- to medium-pressure gas applications.
[0036] Concentration polarization is well controlled in bore-side
feed modules. The feed solution passes directly across the active
surface of the membrane, and no stagnant dead spaces are produced.
This is far from the case in shell-side feed modules in which flow
channeling and stagnant areas between fibers, which cause
significant concentration polarization problems, are difficult to
avoid. Any suspended particulate matter in the feed solution is
easily trapped in these stagnant areas, leading to irreversible
fouling of the membrane. Baffles to direct the feed flow have been
tried, but are not widely used. A more common method of minimizing
concentration polarization is to direct the feed flow normal to the
direction of the hollow fibers. This produces a cross-flow module
with relatively good flow distribution across the fiber surface.
Several membrane modules may be connected in series, so high feed
solution velocities can be used. A number of variants on this basic
design have been described, for example U.S. Pat. Nos. 3,536,611 in
the name of Filipp et al., 5,169,530 in the name of Schucker et
al., 5,352,361 in the name of Prasad et al., and 5,470,469 in the
name of Eckman which are incorporated herein by reference each in
its entirety. The greatest single advantage of hollow-fiber modules
is the ability to pack a very large membrane area into a single
module.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] In order to better communicate the present invention,
several preferred aspects of the multi-stage membrane separation
process and apparatus of the present invention for simultaneous
recovery of a very pure permeate product and a desired non-permeate
product from a fluid mixture of compounds are depicted
schematically in FIG. 1 and FIG. 2. In these preferred embodiments
of the invention, the fluid feedstock is a gaseous mixture
comprising a more selectively permeable alkene component and a
corresponding alkane component, for example propane and propene
(propylene). Other examples of light hydrocarbon compounds which
are difficult to separate by traditional separtion methods, such as
fractional distillation, are shown in Table I.
1TABLE I NORMAL BOILING POINT TEMPERATURES OF LIGHT HYDROCARBON
COMPOUNDS HEAVY LIGHT HYDROCARBON B.P. .degree. C. HYDROCARBON B.P.
.degree. C. Ethane -88.5 Ethene -102.4 (ethylene) Propane -42.2
Propene -47.7 (propylene) Propadiene -34.5 Propane -42.2 Butane
-0.6 Methylpropene -6.6 (isobutylene) Butane -0.6 1-Butene -6.47
(.alpha.-butylene) Butane -0.6 1,3-Butadiene -4.75 2-Butene 3.73
Butane -0.6 (.beta.-butylene) n-Butane -0.6 iso-Butane -12 1-Butene
-6.47 Methylpropene -6.6 (.alpha.-butylene) (isobutylene 2-Butene
3.73 Methylpropene -6.6 (.beta.-butylene) (isobutylene
[0038] The membrane staging configuration for a particular
separation depends on many factors. These factors include (1) the
concentration of the desired component in the feed stream; (2) the
physical and chemical properties of the components being separated;
(3) the required purity of the product streams; (4) the relative
values of the products, which determines acceptable recovery; (5)
the tradeoff between membrane capital cost and the cost of pumping
or compression; and (6) how the membrane is integrated with other
processing steps. In the separation of mixtures using membranes,
the required product recoveries and product purity must be achieved
at acceptable capital and operating costs. For multi-staged
systems, the stage configuration and operating conditions of the
individual stages must be balanced to meet the purity, recovery,
and cost requirements.
[0039] Referring now to FIG. 1, membrane modules are disposed
according to a preferred aspect of the invention in three groups
represented in the drawing by modules 120, 140 and 160. A feedstock
from a source 112 is passed through conduit 114, and, depending on
the operating conditions employed in a particular application, an
optional compressor or pump and vaporizer (not shown), into a first
zone of intermediate membrane module 140.
[0040] Permeate, comprising the more selectively permeable
component of the feedstock, e.g. alkene, is withdrawn from the
second zone of membrane module 140 and transferred to compressor
150 through conduit 144 and manifold 146. Effluent from compressor
150 is transferred into the first zone of a first product module
160 through conduit 152. Very pure permeate product is recovered
from the second zone of the first product module 160 through
conduit 164.
[0041] Non-permeate effluent, comprising the less permeable
component of the feedstock, e.g. alkane, is withdrawn from the
first zone of the first product module 160 is recycled through
conduit 162 into the first zone of intermediate membrane module
140. Non-permeate effluent, comprising the less permeable component
of the feedstock, e.g. alkane, is withdrawn from the first zone of
intermediate module 140 and transferred through conduit 142 into a
first zone of second product module 120.
[0042] A second product, the non-permeate effluent enriched in the
less permeable component of the feedstock, e.g. alkane, is
withdrawn from the first zone of second module 120 through conduit
122. A permeate gas is withdrawn from the second zone of second
product module 120 and transferred to the suction side of
compressor 150 through conduit 124 and manifold 146. Permeate from
the second product module 120 and permeate from the intermediate
module 140 are thereby mixed as they pass through the compressor,
and a single stream is transferred into the first zone of a first
product module 160 through 152.
[0043] Referring now to FIG. 2, the membrane modules are disposed
according to the invention in three groups represented in the
drawing by modules 220, 240 and 260. A first feedstock which
typically includes hydrocarbon compounds, such as a gaseous mixture
of light hydrocarbons having from 1 to about 4 carbon atoms, from
source 212, such as a steam-cracker, light-olefins upgrading unit
or another refinery operation, is passed through conduit 214 and,
depending on the operating conditions employed in a particular
application, an optional compressor and/or pump and vaporizer (not
shown), into a first zone of intermediate membrane module 240.
[0044] Permeate, comprising the more selectively permeable alkene
component of the feedstock, is withdrawn from the second zone of
membrane module 240 and transferred to the suction side of
compressor 250 through conduit 244 and, depending on the operating
conditions employed in a particular application, an optional heat
exchanger (not shown). Effluent from compressor 250 is transferred
into the first zone of a first product module 260 through conduit
252. An additional feedstock which typically has a higher
concentration of the alkene component than the first feedstock,
from a source 266 is passed through conduit 268 and, depending on
the operating conditions employed in a particular application, an
optional compressor or pump and vaporizer (not shown), and into a
first zone of the first product module 260. Very pure permeate
product is recovered from the second zone of the first product
module 260 through conduit 264.
[0045] Non-permeate effluent, comprising the less permeable alkane
component of the feedstock, is withdrawn from the first zone of the
first product module 260 is recycled through conduit 262 and
manifold 234 into the first zone of intermediate membrane module
240. Non-permeate effluent, comprising the less permeable alkane
component of the feedstock, is withdrawn from the first zone of
intermediate module 240 and transferred through conduit 242 into a
first zone of second product module 220.
[0046] A second product, the non-permeate effluent rich in the less
permeable alkane component of the feedstock, is withdrawn from the
first zone of second module 220 through conduit 222. A permeate gas
is withdrawn from the second zone of second product module 220 and
transferred to the suction side of compressor 230 through conduit
224 and, depending on the operating conditions employed in a
particular application, an optional heat exchanger (not shown).
Effluent from compressor 230 is transferred into the first zone of
a intermediate module 240 through conduit 232 and manifold 234.
[0047] In other preferred embodiments of the invention, another
fluid feedstock which advantageously has a concentration of the
alkene component of less than the first feedstock, e.g. a
steam-cracker, light-olefins upgrading unit or another refinery
operation, is passed into the first zone of the second product
module 220 thereby replacing or supplementing feedstock from source
212 and/or source 266.
EXAMPLES OF THE INVENTION
[0048] The following Examples will serve to illustrate certain
specific embodiments of the herein disclosed invention. These
Examples should not, however, be construed as limiting the scope of
the novel invention as there are many variations which may be made
thereon without departing from the spirit of the disclosed
invention, as those of skill in the art will recognize.
[0049] General
[0050] These Examples demonstrate effects of different processing
configurations and membrane selectivities on overall process
performance for simultaneous recovery of a very pure permeate
product and a desired non-permeate product from a propane-propylene
feedstock. The examples include the results of computer
calculations, performed using commercially available chemical
process modeling programs (e.g. Aspen Plus from Aspen Technology,
Inc.) where models of membranes have been incorporated with
standard chemical process equipment models. The models of membranes
were developed by BP and based on generally accepted gas permeation
equations. (See Shindo et al., "Calculation Methods for
Multicomponent Gas Separation by Permeation," Sep. Sci. Technol.
20, 445-459 (1985), Kovvali et al., "Models and Analyses of
Membrane Gas Permeators," J. Memb. Sci. 73, 1-23 (1992), and Coker
et al., "Modeling Multicomponent Gas Separation Using Hollow-Fiber
Membrane Contactors," AIChE J. 44, 1289-1302 (1998).)
[0051] For the purposes of the present invention, the permeability
of gases through membranes is measured in "Barrer", which is
defined as 10.sup.-10 [cm.sup.3 (STP)
cm/(cm.sup.2.multidot.sec.multidot.cmHg)] and named after R. M.
Barrer. Membrane permeability is a measure of the ability of a
membrane to permeate a gas. The term "membrane selectivity" is
defined as the ratio of the permeabilities of two gases and is a
measure of the ability of a membrane to separate the two gases.
(For example, see Baker, Richard W., "Membrane Technology and
Applications", pp 290-291, McGraw-Hill, New York, 2000)
[0052] The feedstock compositions represent an industry average
composition of catalytic or pyrolysis cracker effluents. The liquid
feed was pressurized with a pump to the operating level and
vaporized before introduction into the apparatus. The permeate from
the non-permeate product and intermediate stages was compressed
from the permeate pressure to the feed pressure before introduction
to the next stage. Calculations suggested that three stage
compressors with two interstage coolers (to limit compressor
temperatures to 200-250.degree. F.) were sufficient between each
membrane stage. A cooler was used after each compressor to keep the
feed to each membrane stage at 200.degree. F. The final
non-permeate product was condensed with 100.degree. F. water after
exiting the process. The final permeate product was compressed
after exiting the process to a pressure where it could be condensed
with 100.degree. F. water (approximately 250 psia). For feedstock
and other stream compositions of the present invention, the term
"percent" is defined liquid percent by volume.
[0053] Calculations for these examples were performed using the
following parameters:
2 Feedstock Composition Propylene 70 percent Propane 30 percent
Feedstock Flow Rate 10,000 BPD.dagger. Membrane Temperature
200.degree. F. Module Feed Pressure 580 psia Module Permeate
Pressure 40 psia .dagger.BPD is barrels per day
Example 1
[0054] This example documents an aspect of the preferred embodiment
of the invention depicted in FIG. 1. Feed was supplied to modules
140 from source 112. Membrane propylene selectivity of 35 and a
propylene permeability of 1 Barrer in each of membrane modules were
used for these calculations.
[0055] Membrane area for the non-permeate product modules and the
permeate product modules were adjusted so that the final permeate
product stream 164 met Polymer-Grade Propylene (PGP) specifications
and, at the same time, the final non-permeate product steam 122 met
Liquified Petroleum Gas (LPG) specifications. Also the membrane
area for the intermediate modules 140 was adjusted to minimize the
total required compression work, which is a major cost driver. The
results of these calculations are shown in Table II. When the
membrane selectivity dropped below about 25, the flow of material
in stream 124 increased and the concentration of propylene in
stream 152 decreased so much that it was no longer possible to make
a final permeate product which met PGP specifications. At these
lower membrane selectivities, an appratus similar to that shown in
FIG. 2, where the permeate from the non-permate product stage is
directed to an intemediate stage, is required.
3TABLE II TOTAL COMPRESSION 0.051 kWh/lb of Permeate
Product.dagger. PROPYLENE MEMBRANE AREA, CONCENTRATION, MODULE
ft.sup.2 .times. 10.sup.-3 Percent Final Non-Permeate 120 5.0
Product Intermediate 410 Final Permeate Product 160 99.5
.dagger.Total is for the interstage compressor and the Permeate
Product compressor.
Example 2
[0056] This example documents an aspect of the preferred embodiment
of the invention depicted in FIG. 2 where only the feed stream from
source 212 was introduced into the apparatus, and the membrane
modules had different membrane properties. In particular, two
propylene permeability-selectivit- y pairs were used in these
calculations: propylene permeability of 2 Barrer with 15 propylene
selectivity and propylene permeability of 1 Barrer with 35
propylene selectivity.
[0057] The membrane area for the permeate product module was
adjusted so that the final permeate product met Polymer-Grade
Propylene (PGP) specifications. At the same time, the membrane area
for the final non-permeate product module was adjusted so that the
final non-permeate product met Liquefied Petroleum Gas (LPG)
specifications. Also the membrane area for the intermediate module
was adjusted to minimize the total required compression work.
4TABLE III SEPARATIONS USING MEMBRANES HAVING TWO LEVELS OF
SELECTIVITY ACCORDING TO WHICH THE MODULES ARE DISPOSED INTO THREE
GROUPS DISPOSITION EDUCTION OF MEMBRANE OF ENERGY MEMBRANE TOTAL
AREA, REQUIRED SELECTIVITY.dagger. COMPRESSION.dagger-dbl. ft.sup.2
.times. 10.sup.-3 Percent 15 - 15 - 15 0.084 510 0.0 35 - 35 - 35
0.050 675 40.5 15 - 35 - 35 0.051 607 39.3 35 - 15 - 35 0.058 684
31.0 35 - 35 - 15 0.056 701 33.3 35 - 15 - 15 0.078 978 7.1 15 - 35
- 15 0.059 537 29.8 15 - 15 - 35 0.061 528 27.4 .dagger.Disposition
in order of Non-Permeate Product Module - Intermediate Module -
Permeate Product Module. .dagger-dbl.Total is for both interstage
compressors and the final permeate product compressor, k Wh/lb
permeate product.
[0058] The results of these calculations are shown in Table III.
These results show that less energy and more membrane area are
required when higher selectivity membranes are used. However these
results show the unexpected result that exactly how much less
energy is required depends on the stage in which the higher
selectivity membrane is employed. Note that using the membranes
with a propylene selectivity of 35 in the intermediate or permeate
product modules stages reduces the energy required to about 30
percent of the energy required using membranes with a propylene
selectivity of 15 in each stage while requiring an increase in
membrane area of only approximately 5 percent. Using membranes with
propylene selectivities of 35 in the intermediate and permeate
product modules requires about the same amount of energy as using
membranes with propylene selectivities of 35 in all three stages
while using approximately 10 percent less membrane area. These
results suggest that the energy and membrane area requirements can
be adjusted by using different selectivities in each stage.
Example 3
[0059] This example documents an aspect of the preferred embodiment
of the invention depicted in FIG. 2 where different feed streams
supplied from source 212 and source 266 were introduced into the
apparatus at two different locations. For clarity, membranes with
the same permeability-selectivity have been employed in each stage
of the apparatus in this example: propylene permeability of 1
Barrer with a 35 propylene selectivity. To ease comparison to the
previous examples, the same total feed rate (10,000 BPD) has been
used for these calculations and has been split evenly between
source 212 and source 266 (5,000 BPD each). As before, the membrane
area for the permeate product and non-permeate product modules were
adjusted so that the propylene and propane products met the PGP and
LPG specifications, respectively, and the membrane area for the
entermediate module was adjusted to minimize the total required
compression work. This example illustrates the effect of the
composition of the streams from sources 212 and 266 on the total
required compression work and membrane area needed to meet the PGP
and LPG specifications. The specific compositions used in this
example were selected to keep the total amount of propylene
constant (70 percent) and the same as that employed in previous
examples.
[0060] Table IV shows the results of these calculations. Recall
that in the previous example where a propylene permeability of 1
Barrer and 35 propylene selectivity was employed in each stage and
feed with 70 percent propylene was introduced only from source 212
the total required compression work was 0.050 kWh/lb of propylene
product and the total required membrane area was 675,000 ft.sup.2.
Table V shows that the required work and membrane area increases
when feed containing 70 percent propylene is introduced form
sources 212 and 266. However, Table V shows that the total work and
membrane requirements are dependent on the propylene content of the
streams from sources 212 and 266. When the propylene content from
source 266 rose above about 83 percent and the propylene content
from source 212 fell below about 57 percent, the total work and
membrane area requirements fell below those levels that would have
been needed if these streams had been mixed and introduced only to
the Intermediate stage. This example shows that depending on the
propylene content of the feed sources it may be possible to lower
the total work and membrane area required to make PGP and LPG by
introducing the feeds at more than one location.
Comparative Example A
[0061] This example is based upon the preferred embodiment of the
invention depicted in FIG. 2, except that feed streams supplied
from source 212 and source 266 were replaced with a single feed
(not shown) which was introduced into the apparatus at a different
location, i.e., into the first zone of the second product module
220. Membranes with the same permeability-selectivity have been
employed in each stage of the apparatus in this example: propylene
permeability of 1 Barrer with a 35 propylene selectivity. As
before, the membrane area for the permeate and non-permeate modules
were adjusted so that the propylene and propane products met the
PGP and LPG specifications, respectively, and the membrane area for
the intermediate module was adjusted to minimize the total required
compression work.
[0062] Table V shows that the position where the feed is introduced
greatly influences the compression and membrane area requirements
needed to meet the PGP and LPG specifications.
5TABLE IV SEPARATIONS USING TWO FEED LOCATIONS WITH MODULES
DISPOSED INTO THREE GROUPS.dagger. PROPYLENE PROPYLENE CONTENT OF
CONTENT OF MEMBRANE SOURCE212, SOURCE266, TOTAL AREA, percent
percent COMPRESSION.dagger..backsla- sh. ft.sup.2 .times. 10.sup.-3
70 70 0.069 813 65 75 0.062 770 60 80 0.055 718 55 85 0.047 656 50
90 0.040 597 .dagger.The feed rate from source 212 is 5,000 BPD and
the feed rate from source 266 is 5,000 BPD in every case.
.dagger..dagger.Total is for both interstage compressors and the
final permeate product compressor, k Wh/lb permeate product.
[0063]
6TABLE V SEPARATIONS USING ONE FEED LOCATION WITH MODULES DISPOSED
INTO THREE GROUPS AND TOTAL COMPRESSION 0.088 kWh/lb of Permeate
Product.dagger. Propylene MEMBRANE AREA, Concentration, MODULE
ft.sup.2 .times. 10.sup.-3 Percent Final Non-Permeate 1930 5.0
Intermediate 338 Final Permeate 147 99.6 .dagger.Total is for both
interstage compressors and the final permeate product compressor, k
Wh/lb permeate product.
[0064] For the purposes of the present invention, "predominantly"
is defined as more than about fifty percent. "Substantially" is
defined as occurring with sufficient frequency or being present in
such proportions as to measurably affect macroscopic properties of
an associated compound or system. Where the frequency or proportion
for such impact is not clear, substantially is to be regarded as
about twenty percent or more. The term "a feedstock consisting
essentially of" is defined as at least 95 percent of the feedstock
by volume. The term "essentially free of" is defined as absolutely
except that small variations which have no more than a negligible
effect on macroscopic qualities and final outcome are permitted,
typically up to about one percent.
* * * * *