U.S. patent application number 14/035199 was filed with the patent office on 2014-01-23 for regenerable adsorption unit.
This patent application is currently assigned to Nano-Porous Solutions Limited. The applicant listed for this patent is Nano-Porous Solutions Limited. Invention is credited to Semali Priyanthi PERERA, Chin-Chih TAI.
Application Number | 20140020560 14/035199 |
Document ID | / |
Family ID | 38008430 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140020560 |
Kind Code |
A1 |
PERERA; Semali Priyanthi ;
et al. |
January 23, 2014 |
REGENERABLE ADSORPTION UNIT
Abstract
An adsorption unit comprising an adsorbent hollow fibre in which
the fibre includes an active component and means for transmitting
heat.
Inventors: |
PERERA; Semali Priyanthi;
(Bath, GB) ; TAI; Chin-Chih; (Taiwan, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nano-Porous Solutions Limited |
Gateshead |
|
GB |
|
|
Assignee: |
Nano-Porous Solutions
Limited
Gateshead
GB
|
Family ID: |
38008430 |
Appl. No.: |
14/035199 |
Filed: |
September 24, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12530576 |
Sep 9, 2009 |
8540810 |
|
|
PCT/GB2008/000907 |
Mar 14, 2008 |
|
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|
14035199 |
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Current U.S.
Class: |
96/126 ;
96/146 |
Current CPC
Class: |
Y02C 10/08 20130101;
B01J 20/28014 20130101; B01D 2259/40096 20130101; B01D 2257/504
20130101; B01D 2257/708 20130101; B01D 2253/108 20130101; B01J
20/3441 20130101; B01D 53/02 20130101; B01D 53/0438 20130101; Y02C
20/40 20200801; B01J 20/28023 20130101; B01D 2253/202 20130101 |
Class at
Publication: |
96/126 ;
96/146 |
International
Class: |
B01D 53/04 20060101
B01D053/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2007 |
GB |
0704934.9 |
Claims
1-31. (canceled)
32. A multi-layer hollow fibre comprising: an internal layer
comprising an organic polymer; and an inorganic adsorbent; an
external layer comprising an electrically conductive component.
33. The hollow fibre of claim 32, wherein the organic polymer is
selected from the group consisting of PESF, polysulfone,
polyvinylidenefluoride (PVDF), polyethylene, polypropylene,
poly(phenylene oxide), polymethylmethacrylate, poly(vinyl
chloride), Polysulfone, Poly(ether sulfone), Poly(vinylidene
fluoride), Polyacrylonitrile, Cellulose acetate, Polymide
Poly(ether imide), Polyamide (aromatic), Polyimide, Poly(ether
imide) and poly(vinyl alcohol) co-polymers of Polylactide (PLA) and
Polyglycolide (PGA), Polycaprolactone (PCL) and Poly(ethylene
terephathalate) (PET).
34. The hollow fibre of claim 32, wherein the adsorbent is selected
from silicalite ZSM5, MCM41, MCM48, a silica adsorbent, an
activated carbon powder, an ion exchange resin, and a combination
of two or mere thereof.
35. The hollow fibre of claim 32, wherein the electrically
conductive component is selected from the group consisting of
silver, a metal powder, carbon, a conducting polymer, conducting
cement, a semiconductor material, and a combination of two or more
thereof.
36. The hollow fibre of claim 32, wherein the fibre has a
flexibility of greater than 5.degree. bending angle from the
midpoint of the fibre.
37. The hollow fibre of claim 35, wherein the electrically
conductive component comprises a conductive polymer.
38. The hollow fibre of claim 37, wherein the electrically
conductive component further comprises a conductive powder.
39. The hollow fibre of claim 38, wherein the conductive powder is
selected from active carbon, carbon black, copper powder, and a
combination of two or more thereof.
40. The hollow fibre of claim 32, wherein the outer diameter of the
fibre is from 400 microns to 2.5 cm.
41. The hollow fibre of claim 32, wherein the fibre has a
mechanical strength of greater than 200 g force at a crosshead
speed of 1.0 mm/sec for a fibre with an effective surface porosity
(.epsilon./q.sup.2) of 0.1-0.2, as calculated from Knudsen flow
method.
42. The hollow fibre of claim 32, wherein the fibre has an area to
volume ratio greater than 1000 m.sup.2/m.sup.3.
43. The hollow fibre of claim 32, wherein the inorganic adsorbent
is a zeolite.
44. The fibre of claim 32, wherein the external layer further
comprises an additive selected from polyvinyl alcohol, polyvinyl
pyrrolidone, polyacrylic acid, calcium chloride, fumed silica and a
combination of two or more thereof.
45. The fibre of claim 32, wherein the fibre is substantially
defect free.
46. The fibre of claim 32, wherein the fibre has a graded pore
structure.
47. A gas adsorption unit comprising a plurality of fibred
according to claim 32.
48. The gas adsorption unit of claim 47, wherein the plurality of
fibres are grouped together in a bundle.
49. The gas adsorption unit of claim 48, wherein the bundle of
fibres is coated with an electrically conductive paste.
50. The gas adsorption unit of claim 49, further comprising a wire
wrapped around the bundle of fibres.
51. The gas adsorption unit of claim 47, further comprising a
housing.
Description
[0001] The present invention is directed towards the preparation
and use of regenerable adsorption units and in particular
regenerable hollow fibres and electrically regenerable fibres.
[0002] The range of regenerable adsorption units provided by the
present invention may be very useful to many process industries.
The development of rapid thermal swing, electrically regenerable
adsorption units is an important element of the introduction of new
energy saving and environmentally friendly technologies all over
the world. For example, such technology is applicable for valuable
material recovery and recycling, pollution control, gas separation,
drying, wastewater treatment, and recovery of material from waste
gases. There is an increasing need for removal and recovery of
noxious species such as carbon dioxide and other volatile organic
compounds (VOCs) from gas and/or liquid streams. The adsorbed
compound may then be desorbed electrically and optionally be
recycled (if appropriate) or removed for downstream processing and
safe disposal. The method for removing such compounds must have a
low capital and operational cost and a low environmental
impact.
[0003] The desorption of adsorbates after they have been used to
adsorb into the matrix of the fibre the selected components can be
achieved in a number of ways (temperature, vacuum and
depressurisation) but the most common is by the application of
temperature. Current techniques for maintaining the adsorption
properties of a unit generally involve the removal of the adsorbent
from the unit where the adsorption occurs and heating this to
regenerate it. This may be done, for example, in an oven passing a
heated gas stream through the adsorbent bed or using planar
heaters. This is expensive in both time (generally requires a
minimum of 24 hours at the elevated temperature) and capital and
operational cost. Having to shut the system down while the
adsorbent is removed from the unit for treatment is inefficient
Alternatively, having a twin bed system where one adsorbent bed
does the adsorption while the other undergoes regeneration
increases the inventories and the unit will be larger and
substantially less economical.
[0004] External ovens have a high capital and operational cost,
uneven temperature distribution in the bed and also take time to
heat the adsorbent materials (as well as the surrounding air) to
the necessary temperature and to cool down to ambient or operating
temperatures again. In some cases, it may not currently be
economically viable to regenerate the adsorbent and the used
material is simply removed and replaced with a new unit.
[0005] There is therefore a need for an efficient and cost
effective regenerable adsorption unit.
[0006] According to the present invention there is provided an
adsorption unit comprising a hollow fibre in which the fibre
includes an active component and means for transmitting heat. The
active component is selected to be highly sensitive and reactive to
the component or components of choice and desorbs the selected
component or components at a reasonable temperature and under low
or no vacuum or a combination of the two. The active component in
the unit will adsorb the selected component or components while the
unit is in use. When the activity drops below a pre-determined
level or after a predetermined number of cycles, the unit is
regenerated. This may be e by the direct application of heat to the
active adsorbent in the unit.
[0007] Adsorbent hollow fibres may advantageously be used as
adsorption units as they have a high surface area to volume ratio
for the adsorption to take place on, can be flexible, have a low
pressure drop for energy efficiency, have a superior kinetic
adoption preference compared to existing units, and have a
resistance to adsorption (prevent down stream equivalent and valves
blocking). In particular a bundle of adsorbent hollow fibres may be
used through which the fluid may pass. The molecules to be
separated may be adsorbed onto the walls by Van der Waals forces
and/or by molecular sieving.
[0008] The adsorbent, for example zeolites (in particular high
silica zeolites) with a range of pore sizes can simultaneously
operate as a molecular sieve and adsorb the selected component.
There is then a carbon mixed active layer which carries the current
for heating the fibre. Alternatively, the carbon fibre could act as
an adsorbent as well as providing the heating medium although this
is less preferred. In another alternative, semi-conducting powder
in a layer may act as the heating medium.
[0009] The heat may be applied by any suitable means. In one
embodiment of the invention, the means for transmitting heat is an
electrically conductive component and the heating comprises the
application of a voltage between the two ends of the fibre. The
passing of an electrical current through the fibre by means of the
conductive component results in localised heating which thereby
desorbs the active component. The application of the voltage heats
the active component more quickly than if they were placed in an
oven and the active component cools more quickly than if it had
been heated in an oven on the removal of the electric current. The
time taken for the desorption is also substantially reduced in
comparison to existing techniques as the adsorbent does not have to
be removed from the unit, taken to a heat source (e.g. oven),
heated for desorption, cooled to operating temperatures again and
fitted back into the unit before adsorption can begin again. The
regeneration may also be assisted by the counter current passing of
an inert gas, for example heated nitrogen, through the bed as a
purge.
[0010] In another embodiment, the conductive component is a
thermally conductive material and the heating of the unit comprises
the localised application of a heat source, for example by
induction. Again, the localised application of the hear close to
the active material ensures that the desorption is conducted more
quickly than when using heating in traditional packed beds. The
active material is heated up and cooled more quickly than in
traditional means.
[0011] The hollow fibre may comprise one or more layer. The layers
may all have the same composition or they may have different
compositions. The conductive material may be in each layer or it
may only be in one layer, preferably the outer layer. The hollow
fibre must be sufficiently porous for the gaseous material to be
adsorbed is able to pass through it such that the adsorbent can
react with the selected component or components. Therefore the mean
pore size in one or more layers (including the outer layer) may be
less than 5 .mu.m. For example, the mean pore size in the one or
more layers may be less than 1 .mu.m or less than 500 nm, or less
than 100 nm, or less than 10 nm.
[0012] The hollow fibre may be organic and comprise a polymer, an
additive, an adsorbent material and an electrically conductive
material. The polymer may be selected from the group consisting of
polysulfone (PSF), polyvinylidenefluoride (PVDF)), polyethylene,
polypropylene, poly(phenylene oxide), polyacrylonitrile,
polymethylmethacrylate, poly(vinyl chloride), Poly ether sulfone
(PESF), Cellulose acetate, Polyamide (aromatic), Polyimide,
Poly(ether imide) and poly(vinyl alcohol), co-polymers of
Polylactide (PLA) and Polyglycolide (PGA), Polycaprolactone (PCL)
and Poly(ethylene terephathalate) (PET) or any polymer that
dissolves in the solvents. In preparation, the fibre may have a
temperature pre-treatment, for example, at about 200.degree. C., to
remove any trapped polymer solvents and moisture and to allow
access to the adsorbent particles.
[0013] The additive may be present to improve transport properties
and may be selected from poly (vinyl alcohol), polyvinyl
pyrrolidone (PVP) polyacrylic acid (PAA), calcium chloride and
fumed silica.
[0014] The adsorbent may be a zeolite, for example a high silica
zeolite such as silicalite and ZSM5, or other molecular sieve
materials such as MCM41, MCM48, silica adsorbents or activated
carbon powders, or ion exchange resins.
[0015] The hollow fibre may be inorganic and comprise an inorganic
powder, a binder, an adsorptive component or reactive component and
an electrically conductive component. The inorganic powder may be
selected from the group consisting of ceramics, adsorbents and ion
exchange resins. The ceramic may be selected from the group
consisting of aluminium oxide bentonite, silica, hydroxyapatite or
mixtures thereof The binder may be selected from lead bisilicate
frit, fine standard borax fit, bentonite and Hyplas. The inorganic
fibres are produced by using a polymer, a binder and an adsorptive
or reactive component such as a zeolite or ion exchange resin. The
fibre is fired to burn the polymer and to partially melt the binder
to hold the adsorbent or reactive particles in the structure. The
firing temperature should be below the melting temperature of the
adsorbent to avoid any loss of activity, for example at less than
700.degree. C.
[0016] The electrically conductive component may be selected from
the group consisting of silver, metal powder (e.g. copper), carbon,
conducting polymers, conducting cement, semiconductor materials and
combinations thereof. For example, the conducting layer may
comprise one or more of polyaniline, carbon black, activated
charcoal, copper powder, polyaniline composite with 10-30% (for
example 15-25% or 20%) carbon black and silver conductive
paste.
[0017] The inorganic adsorbent fibre may have a flexibility of
greater than 5.degree. bending angle from the mid point of the
fibre, preferably greater than 10.degree., 20.degree. or
30.degree.. The bending angle of fibres produced according to the
present invention was measured by taking a 20 cm length of the
inorganic fibre, mounting this on two rods, one at each end, and
one of the rods was moved, downwards at a speed of 2 cm/min until
the fibre snapped. The angle of flex (bending angle) was then
measured between the mid point of the fibre in the horizontal
position to the end point where the fibre snapped.
[0018] The inorganic adsorbent hollow fibre may have a mechanical
strength (load) of greater than 200 g force at a crosshead speed of
1.0 mm/min for a sample which has an effective surface porosity of
1000-3000 (.epsilon./q.sup.2 calculated from Knudsen flow method).
Optionally the load at breaking point is greater than 250 g force
or greater than 300 g force. A preferred range is 250-800 g, more
preferably is 300-700 g force and most preferred 400-650 g.
Increased mechanical strength may be obtained by producing multiple
layer fibres. Particularly preferred are double or triple or
quadruple layer fibres. Double layer fibres are stronger than
single layer fibres and triple layer fibres are mechanically
substantially stronger than double layer fibres.
[0019] A further advantage to the production of double or triple or
quadruple layer fibres fin addition to the substantially increased
mechanical strength) is that the fibres are largely defect free.
With two or three layers of the same composition, any defects in
one layer are extremely unlikely to be mirrored by a similar defect
in the next layer. The net effect is that there are no pin holes in
the fibre produced and it can therefore be used as an efficient
porous layer or membrane. This benefit is present for both
inorganic adsorbent fibres and for adsorbent polymeric fibres. It
is also possible to produce fibres with a graded pore structure
which may improve the filtration properties.
[0020] Further, it is possible to have different compositions in
the two or more layers. It is therefore possible to produce a fibre
where each layer is tailored towards a particular property. For
example, the inner layer may be of a composition to provide a
particular strength to the fibre, but the outer layer may be
constructed, to provide the necessary heat transfer means to enable
the adsorbent to be desorbed. Other layers may have properties to
adsorb different components or have a particularly small pore size
for sieving or filtration purposes etc. Each layer could be
constructed from powders which are electrically conducting. This
allows the manufacture of a low resistance fibre with low
resistance in each layer and consequently a low voltage requirement
for heating.
[0021] The porous hollow fibre optionally has a surface area to
volume ratio greater than 1,000 The area to volume ratio may be in
the range 1,000-10,000 m.sup.2/m.sup.3, preferably 1,000-6,000
m.sup.2/m.sup.3, and most preferably 2,000-4,000
m.sup.2/m.sup.3.
[0022] The adsorbent hollow fibre optionally includes a high
percentage of adsorbent material. According to one embodiment,
there is at least 65% adsorbent material, preferably at least 75%
and more preferably at least 80% or 90%. The adsorbent material may
be a silicalite, preferably a zeolite and more preferably a high
silica zeolite, silica, carbon or ion exchange resin. Including a
zeolite in the composition restricts the operating temperature
range for the drying and firing (if present) processes. Zeolites
lose their functionality if subjected to temperatures of greater
than approximately 700-750.degree. C.
[0023] The outer diameter of the fibres produced can be 400
.mu.m-2.5 cm depending on the diameter of the spinneret used to
produce the fibres and the number of layers used. Therefore,
lightweight and compact adsorption units or membranes can be made
using a single hollow fibre or a cluster of narrower adsorbent
fibres as appropriate. The hollow fibres are nanoporous or
microporous and can be tailored to exhibit significant adsorption
capacity, gas fluxes, bending strength (flexibility) and bursting
pressure (7-15 bar). The properties of the fibre can be tailored to
individual situations.
[0024] Flexible hollow fibres are much more resistant to stresses
caused during installation, operation and service, and because they
can be much smaller in diameter and thus the surface area to volume
ratio is much larger, bundles of such fibres can process a great
deal more gas/liquid than existing tubular membranes or adsorption
units (and thus are far more economical).
[0025] If different compositions are used for the different layers,
then it may be possible to have a selective porous layer which can
absorb different compounds at different rates. It is also possible
to have one layer present for one property (for example, increased
strength) and another layer for another property (for example,
selectivity towards a particular molecule or compound).
[0026] The invention may be put into practice in a number of ways
and a number of embodiments are shown here by way of example with
reference to the following figures, in which:
[0027] FIGS. 1a and 1b show triple layer fibres according to the
present invention;
[0028] FIGS. 2a, 2b and 2c show SEMs of the individual layers of
the triple layer fibre shown in FIG. 1;
[0029] FIGS. 3a, 3b and 3c show an arrangement of a bundle of
triple layer fibres;
[0030] FIG. 4 shows the response of triple layer fibres to
different voltage inputs;
[0031] FIG. 5 shows the heating and cooling cycle of triple layer
fibres;
[0032] FIG. 6 shows the adsorption performance of the triple layer
fibres;
[0033] FIG. 7 shows the desorption performance of the triple layer
fibres;
[0034] FIG. 8 shows a double layer fibre according to the present
invention;
[0035] FIGS. 9a and 9b show SEMs of the individual layers of the
double layer fibre shown in FIG. 8;
[0036] FIGS. 10a and 10b show an arrangement of a bundle of double
layer fibres;
[0037] FIG. 11 shows the heating curve of a double layer fibre as
it reaches steady state;
[0038] FIG. 12 shows the steady state heating and cooling cycles of
the double layer fibres;
[0039] FIG. 13 shows the adsorption performance of the double,
layer fibres;
[0040] FIG. 14 shows the desorption performance of the double layer
fibres;
[0041] FIG. 15 shows the adsorption performance of a double layer
fibre; and
[0042] FIG. 16 shows the temperature profiles of double layer
fibres for examples 5 to 10 for a range of applied voltages.
TRIPLE LAYER FIBRES
[0043] A polymeric three layer conductive adsorbent hollow fibre
was produced in accordance with the details below and tested.
[0044] Materials
[0045] Adsorbents used to demonstrate and exemplify the invention:
[0046] 4A zeolites (particle size 5 .mu.m) [0047] 13X zeolites
(particle size used 5 .mu.m).
[0048] Main polymer for the examples: [0049] Polyethersulfone (PESO
(from Ameco Performance, USA) with a glass transition temperature
(Tg) of up to 230.degree. C.-250.degree. C. was used as a common
polymer in all the spinning dopes.
[0050] Materials for outer conducting layer: [0051] Polyaniline
(emeraldine base, MW 65,000), (Aldrich, UK), conductive polymer
with the Tg up to 300.degree. C. [0052] Carbon black (metal basic,
fine powder) (Alfa Aesar, UK). [0053] Activated charcoal (<40
micrometer) (Fluka, UK). [0054] Copper powder (metal basic, <10
.mu.m) (Alfa Aesar, UK) [0055] Polyaniline (emeraldine salt),
composite 20 wt % on carbon black (Aldrich, UK). [0056] Silver
conducting adhesive paste (Alfa Aesar, UK). [0057] Semiconductor
materials
[0058] Preparation of spinning dopes: First layer dope and second
layer dope
[0059] The required quantity of organic solvent (NMP) was poured
into a 250 ml wide-neck bottle and then the desired quantity of
polymer (PESF) was slowly added. The mixture was stirred on a
rotary pump to form the polymer solution. After the clear polymer
solution was formed, a required amount of adsorbent (4A and 13X)
was added into the polymer solution slowly. The mixture was stirred
by an IKA.RTM. WERKE stirrer at a speed between 500-1000 rpm for
2-4 days to ensure that the adsorbent powder was dispersed
uniformly in the polymer solution. Finally, the mixture was put
back on a roller to degas and form the uniform spinning dope.
[0060] The spinning dope of conductive layer was prepared from
required quantity of NMP and the desired quantity of conductive
polymer (polyaniline). The mixture was filtered through a 100 .mu.m
Nylon filter in order to remove the non-dissolved polyaniline. The
desired quantity of second polymer (PESF) was then added into
solution. The mixture was put on the roller to form the polymer
solution. After the clear polymer solution was formed, the required
amounts of finely divided conductive powder (for example, active
carbon, carbon black and copper powder) were slowly added to the
polymer solution.
[0061] Detailed procedure for the preparation of the first spinning
dope which forms a first (inside) layer in the fibre: [0062] 1.
Weighed 100 gram of NMP, and poured it into a 250 ml wide-neck
bottle. [0063] 2. Weighed 20 gram of PESF, and then added it slowly
to the solvent. [0064] 3. Put the mixture on a rotary pump to form
the polymer solution. Allow 2-3 days to dissolve the PESF, [0065]
4. After the clear polymer solution was formed, the bottle was
reset in an IKA.RTM. WERKE stirrer at a speed between 500-1000 rpm.
[0066] 5. Weighed 80 gram of 13X adsorbent, and then added it
slowly into the polymer solution. Allow 1-2 days to ensure that the
adsorbent powder dispersed uniformly in the polymer solution.
[0067] 6. The mixture was put back on a rotary pump to degas and
form the uniformly spinning dope. Allow 4-7 days in order to form a
uniform spinning dope.
[0068] Detailed procedure for the preparation of second spinning
dope which forms a second (intermediate) layer in the fibre: [0069]
1. Weighed 80 gram of NMP, and poured it into a 250 ml wide-neck
bottle. [0070] 2. Weighed 20 gram of PESF, and then added it slowly
to the solvent. [0071] 3. Put the mixture on a rotary pump to form
the polymer solution. Allow 2-3 days to dissolve the PESF. [0072]
4. After the clear polymer solution was formed, the bottle was
reset in an IKA.RTM. WERKE stirrer at a speed between 500-1000 rpm.
[0073] 5. Weighed 80 gram of 4A adsorbent, and then added it slowly
into the polymer solution. Allow 1-2 days to ensure that the
adsorbent powder dispersed uniformly in the polymer solution.
[0074] 6. The mixture was put back on a rotary pump to degas and
form the uniformly spinning dope. Allow 4-7 days in order to form a
uniform spinning dope.
[0075] Detailed procedure for preparation of conducting spinning
dope (outer layer) of the fibre: [0076] 1. Weighed 160 gram of NMP
and poured it into a 250 ml wide-neck bottle. [0077] 2. Weighed 1
gram of polyaniline, and then added it slowly to the solvent.
[0078] 3. Put the mixture on a rotary pump to form the polymer
solution. Allow 1 day to dissolve the polyaniline. [0079] 4. The
mixture was filtered through the 100 .mu.m Nylon filter-paper in
order to remove the non-dissolved polyaniline. [0080] 5. Weighed 39
gram of PESF, and then added it slowly to the solvent. [0081] 6.
Put the mixture on a rotary pump to form the polymer solution.
Allow 2-3 days to dissolve the PESF. [0082] 7. After the clear
polymer solution was formed, the bottle was reset in an IKA.RTM.
WERKE stirrer at a speed between 500-1000 rpm. [0083] 8. Weigh 10
gram of carbon black, and then add it slowly into the polymer
solution. Allow 1 day to ensure that the carbon powder dispersed
uniformly in the polymer solution. [0084] 9. Weigh 10 gram of
active carbon, and then add it slowly into the polymer solution.
Allow 1 day to ensure that the carbon powder dispersed uniformly in
the polymer solution. [0085] 10. Weigh 10 gram of copper, and then
add it slowly into the polymer solution. Allow 1 day to ensure that
the carbon powder dispersed uniformly in the polymer solution.
[0086] 11. The mixture was put back on a rotary pump to degas and
form the uniformly spinning dope. Allow 4-7 days in order to form a
uniform spinning dope.
[0087] The tables below gives spinning conditions for use in the
spinnerette for the preparation of the triple layer hollow fibre
using the three spinning dopes described above. The table also
summarises the precursor mixtures compositions of three layer
fibres
TABLE-US-00001 TABLE 1 Resistance .OMEGA./(25 cm .times. Sample
Polymer/Solvent Polymer/additives Pressure 100-300 name Wt % Wt %
Supply Parameter fibres) Ex. 1 PESF/NMP PESF/13X 2 bar Boreliquid:
4 ml/min 90-15 Internal- 16/84 19/81 Air gap: 5 cm layer Roller
mixture: 25 rpm Ex. 1 PESF/NMP PESF/4A 1.5 bar Water bath:
25.degree. C. Medium- 20/80 20/80 layer Ex. 1 Polyaniline + PESF/
Polyaniline + PESF/ 1 bar External- NMP carbon layer 0.5 + 19.5/80
black + active carbon + copper 1.4 + 55.7/14.2 + 14.2 + 14.2
TABLE-US-00002 TABLE 2 Resistance .OMEGA./(25 cm .times. Sample
Polymer/Solvent Polymer/additives Pressure 100-300 name Wt % Wt %
supply Parameter fibres) Ex. 2 PESF/NMP PESF/13X 2 bar Bore 100-25
Internal- 20/80 23.8/72.2 liquid: 4 ml/min layer Air gap: 5 cm Ex.
2 PESF/NMP PESF/4A 1.5 bar Roller: 25 rpm Medium- 20/80 29.1/71.9
Water layer bath: Ex. 2 Polyaniline + PESF/NMP PESF/activated 1 bar
25.degree. C. External- 0.4 + 19.6/80 charcoal + carbon layer black
+ copper 38/19 + 14.5 + 28.5
[0088] Spinning Multi-Layer Conducting Adsorbent Hollow Fibres
[0089] The mixtures were transferred to three stainless steel
vessels and degassed by vacuum pump for 1 hour at room temperature
before the spinning process. This step was to ensure that the gas
bubbles were completely removed from the viscous polymer solution.
The tank for internal dope was pressurised to 2-3 bar using
nitrogen during the spinning process. The vessel for second layer
dope was pressurized to 1.5-2 bar using nitrogen during the
spinning process. The external layer vessel was pressurized to
0.5-1.5 bar keep this pressure below 2nd layer).
[0090] A quadruple orifice spinneret with external layer
(d.sub.out/d.sub.in, 4 mm/3.2 mm), second layer
(d.sub.out/d.sub.in, 2.95 mm/2.25 mm) internal layer
(d.sub.out/d.sub.in, 2 mm/1.1 mm), and the bore diameter 0.8 mm was
used to obtain hollow fibre precursors. The air gap was kept at
5-10 cm and water was used as the internal and external coagulator
for all spinning runs. Finally, in forming the hollow fibre the
precursor was passed through a water bath to complete the
solidification process. The hollow fibre was then washed thoroughly
in a second water bath. It is very important to ensure that the
hollow fibre is not subjected to mechanical dragging throughout the
spinning process. Care was taken to ensure continuity of the
pressure and internal water support in order to avoid entrapment of
air and separation of the fibre, which would eventually result in
an unsuccessful spinning.
[0091] The hollow fibre precursors were left to soak for 3-4 days
in fresh water; this is being very important to ensure the removal
of any residual solvent. After the soaking process, the hollow
fibre precursors were dried at ambient conditions for seven days
before firing and characterization of the inorganic hollow
fibre.
[0092] FIGS. 1a and 1b show the triple layer fibre formed with the
SEMs taken at different voltages. The inner (core) layer contains
13X as the active ingredient to primarily adsorb CO.sub.2 from a
gas stream. The intermediate layer contains 4A as the active
ingredient and is present primarily to remove moisture from the gas
stream. The outer layer is the conducting layer to pass the current
through the fibre and provide localised heating of the two
adsorbents in the inner and intermediate layers and thereby to
desorb the materials.
[0093] FIGS. 2a, 2b and 2c show each of the three layers at much
higher magnification to show in more detail the structure of each
layer. FIG. 2a shows the outer conducting layer which is dominated
by the carbon and other conducting components. This has a dense
structure to enable the current to pass through the fibre but must
still have sufficient porosity to allow the gases to pass through
to the active intermediate and inner layers. FIG. 2b shows the
intermediate layer which includes the 4A zeolite and FIG. 2c shows
the inner layer including the 13X zeolite.
[0094] In one embodiment, a bundle of fibres may be grouped
together as shown, for example, in FIG. 3. In this case, the end of
the bundle of fibres may be coated with an electrically conductive
paste such as silver. This is shown more clearly in FIGS. 3b and
3c. This simplifies the electrical supply to the fibre by ensuring
that it is not necessary to have separate supplies to each fibre
but a single connection at each end. It is not essential to have an
end cap of silver or carbon and the current could alternatively be
supplied to the fibre by means of a wire wrapped round the
perimeter of the bundle of fibres which would then be conducted by
the conductor (carbon, carbon composite or semi-conductor material)
in the outer layer.
[0095] FIG. 4 shows the heating performance of a triple layer fibre
(composition as set out in table 2 above) with different power
inputs ranging from 20V AC to 50V AC. These results show the fibre
heating while the fibre is reaching steady state or optimisation.
It has been found that the fibres typically reach a steady state
and optimised performance airier approximately 10 heating and
cooling cycles. Referring to FIG. 4, as would be expected the
higher the applied voltage, the higher the temperature reached. The
heating rates of all four experiments is high and operating
temperatures may be reached quickly. Some zeolites may desorb the
adsorbed gases at temperatures as low as 60-80.degree. C. but
typically the temperature should be above 90.degree. C. for
desorption. As can clearly be seen from FIG. 4, at the application
of both 40V and 50V, the temperature of the fibre exceeds
90.degree. C. substantially within 10 minutes.
[0096] FIG. 5 shows the heating and cooling performance of a bundle
of 100 fibres (composition from table 2 above). The applied voltage
in each case is 40V AC and the resistance of the bundle is
100.OMEGA.. The net effect is a voltage range of 10 to 20V. As will
be seen from the close concordance of the three sets of results,
the fibres had substantially reached their steady state. Again, the
fibres heat up to above 90.degree. C. very quickly (less than 5
minutes) and on the removal of the applied voltage at 120 minutes
the temperature drops back to close to ambient temperatures in
about 10 minutes. These heating and cooling curves are
substantially steeper than would be achieved for fibres using the
heating techniques of the prior art (oven or flat plates).
[0097] FIG. 6 shows the adsorption performance of fibres
(composition as set out in table 1 above) once they have reached
the equilibrium state. At 0 minutes the test gas starts passing
through the fibres. For curve (a) the test gas comprises 3000 ppm
CO.sub.2 at 1 litre/min with 55% relative humidity. For curve (b)
the gas is similar but without the humidity. The fibres had been
regenerated at 180.degree. C. by application of 35V AC. The
CO.sub.2 is completely adsorbed by the fibres for just about 2
hours from the start of the gas flow. After this time, adsorption
efficiency decreases and CO.sub.2 starts to appear in the exit gas.
This is called the breakthrough point and is a first indication
that the fibres need to be regenerated.
[0098] For the wet gas, the first appearance of CO.sub.2 in the
exit gas takes places at about 140 minutes and there is then a very
rapid increase in the concentration of the CO.sub.2 in the exit gas
peaking at just under 4000 ppm after just under 1 hour. The slope
of the breakthrough curve is an indication of the efficiency of
mass transfer within the system, a sharper curve indicates a more
efficient system with lower resistance to adsorption and subsequent
desorption in regeneration. The moisture presence in the fibre
matrix seems to be improving the CO.sub.2 adsorption and solubility
in the matrix. Moisture adsorption with 4A zeolite fibres
breakthrough times are greater than 2 hours. The internal layer of
13X and the intermediate layer of 4A both adsorb CO.sub.2, however
the kinetic adsorption of CO.sub.2 onto 4A is slower and hence the
curves for adsorption on 4A would be shallower and the capacity for
CO.sub.2 would be less. This shows that two or three types of
adsorbents could be incorporated into the fibre structure either as
a mixed matrix or as a layered system to adsorb selected components
at different rates. It also shows the benefits of an open structure
with open pore macrovoids proving more efficient for both
adsorption and desorption.
[0099] FIG. 7 shows the electrical regeneration performance of the
fibres (again, composition from example 1) and in particular the
desorption of CO.sub.2 from the adsorbent. In runs (a) and (b) the
fibre was purged with a flow of nitrogen as the electrical current
is applied. In both cases the current was 35V AC and for run (a)
the purge was 200 ml/min of nitrogen and for run (b) the purge was
100 ml/min of nitrogen. In both cases it can be seen that the
adsorbent is purged of substantially all of the adsorbed CO.sub.2
within 10 minutes. For run (a) the desorption is marginally quicker
with the higher concentration of nitrogen purge.
[0100] Double Layer Fibres
[0101] The fibres were prepared in similar ways to that set out
above with a triple orifice spinnerette being used to produce the
double layer fibre. The inner layer includes the active component,
in this case 13X which is sensitive to the presence of CO2. The
composition of the double layer fibre of this example is set out in
table 3 below.
TABLE-US-00003 TABLE 3 double layer fibre Resistance in the
external layer Polymer/solvent Polymer/adsorbent .OMEGA./(25 cm
.times. 100-300 wt (%) wt (%) Fibres) Internal PESF/NMP PESF/13X
120-30 layer 20/80 22/78 External PESF + polyanille/ PESF/activated
layer NMP charcoal + carbon 19.8 + 0.2/80 black + copper 38/19 +
14.5 + 28.5
[0102] FIG. 8 shows an SEM of the double layer fibre formed. The
inner layer contains 13X as the active ingredient to primarily
adsorb CO2 from a gas stream and the outer layer is the conducting
layer to pass the current through the fibre and provide localised
heating of the adsorbent in the inner layer and thereby to desorb
the material.
[0103] FIGS. 9a and 9b show each of the layers at much higher
magnification to show in more detail the structure of each layer.
FIG. 9a shows the outer conducting layer which is dominated by the
carbon. This again has a dense structure to enable the current to
pass through the fibre but still has sufficient porosity to allow
the gases to pass through to the active inner layer. FIG. 9b shows
the inner layer which includes the 13X zeolite.
[0104] In one embodiment, a bundle of fibres such as those shown in
FIG. 10a may be grouped together as shown, for example, in FIG.
10b. In this case, the end of the bundle of fibres may be capped
with an electrically conductive cap with a conductor on the inside
which contacts all of the fibres. This simplifies the electrical
supply to the bundle of fibres by ensuring that it is not necessary
to have separate supplies to each fibre but a single connection at
each end of the overall bundle.
[0105] FIG. 11 shows the heating performance of a fibre under
cyclic heating at 40V AC input current. The initial resistance in
the fibre was 158.OMEGA. but this decreased down to a steady
118.OMEGA. after 6 heating cycles. All of the subsequent testing
was done on fibres which had reached this steady state with a
resistance of 118.OMEGA.. The graph also shows that the rate of
heating up increased as the fibre reached steady state and once at
this state the fibre rapidly increased temperature to 190.degree.
C. (without insulation) within 15 minutes and stayed at this level
while the voltage remained on.
[0106] FIG. 12 shows the steady state heating and cooling
performance of double layer fibres without the use of a purge
during the regeneration step. Again it can be seen that the fibres
rapidly heat to a temperature of 190.degree. C. (within 20 minutes)
and that this is maintained while the voltage is applied. The
voltage is switched off at 120 minutes and it an be seen that the
temperature drops away equally rapidly back down towards ambient
temperatures. Much more rapid heating to 190.degree. C. was
observed with tripling the fibre numbers (within 5 minutes). The
fibres are back at worn temperature within 20 minutes of the
voltage being stopped even without the use of a purge. With a purge
the increase and decrease in temperature may be slightly quicker as
the temperature gradient is maintained by the effective removal of
desorbed gas.
[0107] FIG. 13 shows the adsorption performance of a number of
fibres after they have already been regenerated and have reached
the steady state. The regeneration took place at 190.degree. C. as
described above. For curve (a) the regeneration took place in the
presence of a purge of 200 ml/min of nitrogen. For run (b) the
regeneration took place with a lower purge of just 100 ml/min of
nitrogen. For run (c) the regeneration took place in the absence of
a nitrogen purge but under a low atmospheric vacuum.
[0108] FIG. 14 shows the desorption performance of the fibres under
a nitrogen purge (200 ml for curve (a) and 100 ml for curve (b)) at
180.degree. C. as generated by an applied voltage of 40V AC. While
the use purges is known in existing techniques for regeneration,
the quantity of nitrogen required is of the order of 10 times as
much as may be used in the present invention. However, as indicated
above the use of a nitrogen or other gas (e.g. air) purge is not
essential in the present invention which works effectively with no
purge.
[0109] Referring to FIGS. 13 and 14, it can be seen that adsorption
of the carbon dioxide can be achieved rapidly with all fibres and
they all provide a sharper breakthrough curve and much better
kinetic adsorption performance than existing adsorbents. This
results in reduced bed sizes and inventory. Electrical heating
under a low vacuum (ETVS) gave an improved performance when
compared to the fibres which had been regenerated with the nitrogen
purge. The electrically desorbed CO.sub.2 will be taken away by the
small purge gas flow rate while the vacuum will assist in removing
any trapped molecules within the structure. An improved adsorption
capacity is therefore shown by reference to FIG. 14. This shows
that complete desorption can be achieved within around 20 minutes
by electrical heating at 90.degree. C. with a nitrogen purge.
EXAMPLE 4
[0110] A double layer fibre made according to the composition set
out in table 4 below was made. The fibre was heated to 200.degree.
C. and was then allowed to cool with different cooling patterns.
(a) Fibre module was regenerated at 200.degree. C. with 200
ml/N.sub.2 purging. (b) Fibre module regenerated at 200.degree. C.
while vacuuming for 2 hrs without N.sub.2 purging and then cooling
for 1 hr. (c) Fibre module regenerated at 200.degree. C. while
vacuuming for 1 hrs without N.sub.2 purging and then cooling for 4
hrs. (d) Fibre module was regenerated at 200.degree. C. while
vacuuming for 1 hrs without N.sub.2 purging and then cooling for 1
hrs. (e) Fibre module was regenerated at 200.degree. C. while
vacuuming for 30 mins without N.sub.2 purging and then cooling for
1 hrs. (f) Fibre module was regenerated 200.degree. C. while
vacuuming for 20 mins without N.sub.2 purging and then cooling for
1 hrs.
TABLE-US-00004 TABLE 4 Resistance in the external layer
Polymer/solvent Polymer/adsorbent .OMEGA./(25 cm .times. 100-200 wt
(%) wt (%) Fibres) Internal PESF/NMP PESF/13X 100-60 layer 20/80
10/90 External PESF + polyanille/ PESF/activated layer NMP charcoal
+ carbon 19.8 + 0.2/80 black + copper 38/19 + 15 + 28
[0111] FIG. 15 shows the adsorption performance of the double layer
fibre and the different cycles of thermal and vacuum cycling. It is
apparent that adsorbent fibre regeneration can be successfully
achieved with vacuum while electrically heating at 200.degree. C.,
for 20-30 minutes without any purge flow. Further, the adsorption
performance of the fibre module after vacuum-thermal regeneration
is similar to thermal regeneration With heated N (for an extended
period of time). The breakthrough time is similar even if heated at
a slightly higher temperature (210.degree. C.). There is also no
substantial difference between 2 hours vacuum, 20 minutes vacuum or
heating at 210.degree. C. or 200.degree. C.
EXAMPLES 5 TO 10
[0112] Double layer fibres were made in the same way as for example
4, but with the compositions for the external layer as set out in
table 5 below. In each of examples 5 to 10 the internal layer is
20% PESF/80% 13X adsorbent by weight. FIG. 16 shows the temperature
profile for these 6 examples for different applied voltages where
the voltage ranging, from 20V to 150V AC is applied for 2 minutes.
In each case a bundle of 25 fibres is heated by application of the
voltage.
TABLE-US-00005 TABLE 5 The various compositions of fibre conductive
layer (external layer) Polymer/solvent Polymer/adsorbent resistance
Dope No Wt (%) Wt (%) additives .OMEGA./cm Example 5 PESF +
polyaniline/ PESF/activated none 80 NMP 15 + 0.5/84.5 charcoal
27.9/72.1 Example 6 PESF/NMP PESF/activated Polyaniline 193
15.3/84.7 charcoal composite 33/67 20 wt % in carbon 2 g Example 7
PESF/NMP PESF/activated Polypyrrole 196 15.3/84.7 charcoal
composite 33/67 20 wt % in carbon 2 g Example 8 PESF + polyaniline/
PESF/activated none 60 NMP 19.8 + 0.2/80 charcoal + carbon black
50/31.25 + 18.75 Example 9 PESF + polyaniline/ PESF/activated none
90 NMP 19.8 + 0.2/80 charcoal + carbon black + 4A 35.3/20.6 + 14.7
+ 29.4 Example 10 PESF + polyaniline/ PESF/semi- none 120 NMP 19.8
+ 0.2/80 conducting material 25/75
[0113] Referring to table 5 and FIG. 16, it can be seen that a
range of properties are available by varying and controlling the
resistance and conductivity properties of the fibre layer. This is
largely determined by the selection of polymer/solvent and the
presence or absence of an additive/conducting materials. The
appropriate use of such additives and the thickness of the
conducting layer can closely control the resistance and hence the
voltage and the required regeneration temperature of the fibre.
[0114] For the multilayer fibres prepared using composition set out
in an example 5 very high temperatures could be reached with a very
short space of time, in excess of 300.degree. C. in 2 minutes of
heating at an applied, voltage of about 108V AC. The conductivity
of the hollow fibre prepared from (PESF+polyaniline) and activated
charcoal with carbon black (Example 8) gives a lower resistance (60
ohm/cm) and good conductivity. It is possible to achieve
regenerable temperatures using low voltages. When the voltage
applied was up to 50VAC the temperature of hollow fibre reached at
190.degree. C. in 2 minutes.
* * * * *