U.S. patent application number 12/437349 was filed with the patent office on 2010-05-13 for inverse fluidization for purifying fluid streams.
This patent application is currently assigned to NEW JERSEY INSTITUTE OF TECHNOLOGY. Invention is credited to Robert Pfeffer, Jose Quevedo.
Application Number | 20100116746 12/437349 |
Document ID | / |
Family ID | 39283930 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100116746 |
Kind Code |
A1 |
Pfeffer; Robert ; et
al. |
May 13, 2010 |
Inverse Fluidization for Purifying Fluid Streams
Abstract
A method for removing a contaminant from a fluid system
comprises contacting the fluid system with an inversely fluidized
material, for example a particulate aerogel, thereby removing at
least a portion of the contaminant from the fluid system. The
method can be used to remove oil or other organic materials from
wastewater streams. It can be conducted in a fluidized bed, which
includes nanoporous particles and a fluidizing medium, wherein the
nanoporous particles have a density lower than that of the
fluidizing medium.
Inventors: |
Pfeffer; Robert;
(Scottsdale, AZ) ; Quevedo; Jose; (Brick,
NJ) |
Correspondence
Address: |
HOUSTON ELISEEVA
4 MILITIA DRIVE, SUITE 4
LEXINGTON
MA
02421
US
|
Assignee: |
NEW JERSEY INSTITUTE OF
TECHNOLOGY
Newark
NJ
|
Family ID: |
39283930 |
Appl. No.: |
12/437349 |
Filed: |
May 7, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US2007/084070 |
Nov 8, 2007 |
|
|
|
12437349 |
|
|
|
|
60865259 |
Nov 10, 2006 |
|
|
|
Current U.S.
Class: |
210/661 ;
210/263; 210/691 |
Current CPC
Class: |
B01J 20/28047 20130101;
C02F 1/24 20130101; B01D 15/02 20130101; C02F 2101/32 20130101;
C02F 2101/30 20130101; C02F 1/281 20130101; B01J 20/2808 20130101;
C02F 9/00 20130101 |
Class at
Publication: |
210/661 ;
210/263; 210/691 |
International
Class: |
C02F 1/28 20060101
C02F001/28; B01D 15/02 20060101 B01D015/02; B01D 17/022 20060101
B01D017/022; B01J 20/06 20060101 B01J020/06 |
Claims
1. A method for removing a contaminant from a fluid system, the
method comprising contacting the fluid system with an inversely
fluidized nanoporous metal oxide material, thereby removing at
least a portion of the contaminant from the fluid system.
2. The method of claim 1, wherein the fluid system is a liquid
system.
3. The method of claim 2, wherein the fluid system is
wastewater.
4. The method of claim 1, wherein the fluid system includes a
supercritical fluid.
5. The method of claim 1, wherein the contaminant is an organic
material.
6. The method of claim 1, wherein the contaminant is an oil.
7. The method of claim 1, wherein the nanoporous metal oxide
material is an aerogel.
8. The method of claim 1, wherein the nanoporous metal oxide
material is a particulate aerogel material.
9. The method of claim 8, wherein the aerogel has a particles size
larger than about 0.5 mm.
10. The method of claim 1, wherein the nanoporous metal oxide
material is hydrophobic.
11. The method of claim 1, wherein the nanoporous metal oxide
material is an oxide of a metal selected from the group consisting
of silicon, aluminum, zirconium, titanium, hafnium, vanadium,
yttrium and any combination thereof.
12. The method of claim 1, wherein the method is conducted in an
inverse fluidization bed.
13. A purification process, wherein the process includes the method
of claim 1.
14. A fluidized bed comprising nanoporous metal oxide particles and
a fluidizing medium, wherein the nanoporous metal oxide particles
have a density lower than that of the fluidizing medium.
15. The fluidized bed of claim 14, wherein the nanoporous metal
oxide particles are aerogel particles.
16. A purification system, wherein the system includes the
fluidized bed of claim 14.
17. A method for purifying a fluid system, the method comprising:
a. directing the fluid system to an inverse fluidized bed
comprising a nanoporous metal oxide material having a density lower
than the density of the fluid system; and b. contacting the fluid
system with the nanoporous metal oxide material, thereby removing
contaminants from the fluid system to obtain a purified fluid.
18. The method of claim 17, wherein the contaminant is an organic
material and the fluid system is a wastewater stream.
19. The method of claim 17, wherein the nanoporous metal oxide
material is a particulate aerogel.
20. The method of claim 19, wherein the aerogel is a hydrophobic
silica aerogel.
21. The method of claim 17, wherein the nanoporous metal oxide is
an oxide of a metal selected from the group consisting of silicon,
aluminum, zirconium, titanium, hafnium, vanadium, yttrium and any
combination thereof
22. The method of claim 17, wherein a difference between the
density of the fluid system and that of the nanoporous metal oxide
material is at least about 0.1 g/cm.sup.3.
23. A purification process, wherein the process includes the method
of claim 17.
24. A method for removing an oil from an aqueous system, the method
comprising contacting the aqueous system with an inversely
fluidized hydrophobic material, wherein the hydrophobic material
includes a nanoporous metal oxide, thereby removing at least a
portion of the oil from the aqueous system.
25. A purification process, wherein the process includes the method
of claim 24.
Description
RELATED APPLICATIONS
[0001] This application is a Continuation of International
Application Number PCT/US2007/084070, filed on Nov. 8, 2007,
designating the United States, which claims the benefit under 35
USC 119(e) of U.S. Provisional Application No. 60/865,259, filed on
Nov. 10, 2006. Both applications are incorporated herein by
reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] Existing methods for oil removal are based on techniques
such as filtration, gravity separation, biological treatment
methods, and induced floatation. Other approaches include API
(American Petroleum Institute) separators, developed for handling
refinery wastewaters, dissolved air flotation oil-water separators,
induced air flotation oil-water separators, carbon adsorption and
ultrafiltration treatments.
[0003] One existing technique employs a coalescing medium, such as,
for instance, that supplied by Lantec Products (www.lantecp.com)
under the name of HD Q-PAC. In a specific application for removing
oil from storm water in a power plant, a unit using HD Q-PAC
material was designed to handle 1900 gallons per minute (gpm) of
water with an oil concentration of 4250 milligrams/liter
(mg/l).
[0004] A coalescing system is also supplied by Pall Corporation of
East Hills, N.Y. under the name of AquaSep.RTM. Plus. In the Pall
AquaSep Plus Liquid/Liquid Separation System with Coalescer in a
Horizontal Housing, illustrated in FIG. 2 of Pall Corporation Data
Sheet GAS-4105g, available at www.pall.com, coalescer elements are
stacked horizontally on top of a separator element. The purpose is
to ensure equally distributed flow through the separators. After
the separator elements, a settling zone is provided for the
separation of the two liquid phases. The pressure drop through this
system is 2 pounds per square inch differential (psid) when new and
it has to be replaced when the pressure drop reaches 15 psid.
[0005] Many water treatment methods, such as, for instance, reverse
osmosis or ultrafiltration, require pre-treatment of the
contaminated water, adding to overall wastewater treatment
costs.
[0006] While filtration generally provides good oil removal,
capacity and energy consumption have to be considered when
designing filtration systems. Since filter media have a given
permeability, determining the resistance of the medium for
contaminated water flowing through it, this property, commonly
monitored by the pressure drop across the filter material,
generally increases as the filter becomes saturated with
contaminants. As a result, either the amount of water passing
through the filter has to be reduced or the pumping power has to be
increased leading to a reduction in efficiency from an energy
standpoint.
[0007] The most commonly used material for removing organic
compounds from liquids and gases is activated carbon. Activated
carbon is highly porous and thus provides large internal surfaces
for adsorbed molecules to reside. However, purification methods
based on adsorption by activated carbon as well as other
purification techniques such as reverse osmosis and ultrafiltration
strongly depend on temperature and their removal capacities and/or
efficiencies may be affected under operating temperatures higher
than ambient.
[0008] Organoclays such as bentonite modified with quaternary amine
cations, also can be used to remove oil from water and they are
particularly suitable for removal of large organic molecules of low
solubility. One of these clay-based products is sold by Biomin Inc.
(www.biomininc.com) under the name of OilSorb.TM.. In many cases, a
packed bed of organoclay granules is used before the activated
carbon to improve its adsorption efficiency, since activated carbon
can quickly be blinded by oils that clog its porous surface.
[0009] U.S. Pat. No. 6,709,600 B2 issued to Hrubesh et al. on Mar.
23, 2004, the teachings of which are incorporated herein by
reference in their entirety, discloses adsorption capacity of
hydrophobic silica aerogel for toluene, cyclohexane,
trichloroethylene and ethanol from aqueous solutions.
SUMMARY OF THE INVENTION
[0010] A need continues to exist, therefore, for methods and
devices effective in removing oil or other organic materials from
water and the invention generally relates to a method and apparatus
for purifying a fluid phase system such as a wastewater stream.
[0011] In one embodiment, the invention is directed to a method for
removing a contaminant, e.g., an oil, from a fluid system. The
method comprises contacting the fluid system with an inversely
fluidized material, thereby removing at least a portion of the
contaminant from the fluid system. In specific aspects, the
inversely fluidized material is a porous material, preferably a
nanoporous material, e.g., aerogel particles. In other aspects, the
inversely fluidized material is hydrophobic.
[0012] In another embodiment, the invention is directed to a method
for purifying a fluid system. The method comprises directing the
fluid system to an inverse fluidized bed which includes a material,
e.g., a porous material such as aerogel particles, having a density
lower than the density of the fluid system; and contacting the
fluid system with the material, thereby removing contaminants from
the fluid phase system to obtain a purified fluid.
[0013] In yet another embodiment, the invention is directed to a
method for removing an oil from an aqueous system. The method
includes contacting the aqueous system with an inversely fluidized
hydrophobic material, thereby removing at least a portion of the
oil from the aqueous system.
[0014] In a further embodiment, the invention is directed to a
fluidized bed which includes nanoporous particles and a fluidizing
medium, wherein the nanoporous particles have a density that is
lower than that of the fluidizing medium.
[0015] The invention is useful in purifying waste or other fluid
streams such as discharged or recycled in refineries, manufacturing
or processing facility, and in many other instances. The inverse
fluidization method and apparatus disclosed herein are flexible and
can remove contaminants in a broad size of droplets, for instance
they can remove droplets larger than 5 microns. Thus practicing the
invention can replace or can be used in conjunction with a system
such as the AquaSep Plus Liquid/Liquid Separation System with
Coalescer in a Horizontal Housing discussed above and/or one or
more techniques illustrated, for instance, in FIG. 1.
[0016] The inverse fluidization described herein shows high removal
efficiency, low and constant pressure drop (when operating above
the minimum fluidization velocity), good mixing between solid
particles and the liquid phase, high capacity, and an adjustable
voidage in the fluidized bed obtained by changing the velocity of
the fluid thus changing the void fraction due to bed expansion.
[0017] From an economic standpoint, low pressure drops result in
energy costs that are more advantageous than those associated with
packed bed filters. Furthermore, in comparison to packed bed
filters which operate batch-wise, the inverse fluidization
apparatus and method of the invention can be operated in a
continuous mode, with contaminant-saturated particles being
collected downstream the column and fresh particles being added at
the top, or anywhere else along the fluidization column. Beds of
the invention can provide more homogeneity in removal of
contaminants such as oils than is seen with many packed bed
arrangements where the flow often is not well distributed
throughout the bed. The downward flow arrangement of inverse
fluidization columns described herein promotes coalescence of the
droplets of an immiscible contaminant such as oil, favoring higher
removal efficiency.
[0018] The use of materials having high hydrophobicity, high
porosity, and large surface area, such as hydrophobic silica
aerogels, is particularly well suited for the removal of immiscible
organic compounds, e.g., oils, from water. Combining the properties
of these materials with the advantageous properties of inverse
fluidization can result in large capacity and high removal
efficiency, e.g., as high as 99.9%, depending on the operating
conditions. Oil-contaminated streams can be purified to levels of 1
part per million (PPM) or lower.
[0019] While water purification methods such as reverse osmosis or
ultrafiltration require pre-treatment of the contaminated water,
inverse fluidized beds of the invention tend to be more robust,
requiring little if any pretreatment, thereby reducing overall
costs.
[0020] Furthermore, while removal efficiencies and capacities of
reverse osmosis, ultrafiltration and adsorption using activated
carbon are affected by high temperature conditions, some of the
inverse fluidization methods and beds disclosed herein can have
removal efficiency independent of changes in temperature of the
contaminated water (except for changes in contaminant concentration
due to equilibrium considerations between the contaminant and the
water at different temperatures).
[0021] The above and other features of the invention including
various novel details of construction and combinations of parts,
and other advantages, will now be more particularly described with
reference to the accompanying drawings and pointed out in the
claims. It will be understood that the particular method and device
embodying the invention are shown by way of illustration and not as
a limitation of the invention. The principles and features of this
invention may be employed in various and numerous embodiments
without departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In the accompanying drawings, reference characters refer to
the same parts throughout the different views. The drawings are not
necessarily to scale; emphasis has instead been placed upon
illustrating the principles of the invention. Of the drawings:
[0023] FIG. 1 is a schematic representation of droplet size
classification and conventional methods that can be used to remove
them.
[0024] FIG. 2A is a photograph showing oily water before contact
with a packed bed of Nanogel.RTM. particles.
[0025] FIG. 2B is a photograph showing purified water after the
oily was contacted with the packed bed of Nanogel.RTM.
particles.
[0026] FIG. 3 is a schematic diagram of inverse fluidization.
[0027] FIG. 4 is a schematic diagram of an arrangement that can be
used to conduct the method of the invention.
[0028] FIG. 5 is a plot showing the relationship between the oil
concentration in water and the Chemical Oxygen Demand (COD) as
measured by the HACH method with the Colorimeter.
[0029] FIG. 6A is a photograph of an inverse fluidized bed of
500-850 microns Nanogel.RTM. particles (sieved).
[0030] FIG. 6B is a photograph of an inverse fluidized bed of 2.3
mm Nanogel.RTM. particles (un-sieved).
[0031] FIGS. 7A through 7C are series of plots showing pressure
drop across inversely fluidized beds of translucent Nanogel.RTM.
particles as a function of fluid velocity.
[0032] FIGS. 8A through 8C are series of plots of bed expansion as
a function of fluid velocity.
[0033] FIG. 9 is a plot of concentration, measured by COD, as a
function of time upstream (straight line) and downstream (diamonds)
in an inverse fluidized bed of 56 g of Nanogel.RTM.. Bed expansion
(squares) as a function of time also is shown. The size range of
the aerogel granules was between 0.5 to 0.85 mm. The fluid velocity
was 0.0107 cm/s. Upstream oil concentration was about 450 mg of
oil/l of water.
[0034] FIG. 10 is a plot of chemical oxygen demand (COD) and
inverse fluidized bed expansion (squares) as a function of time of
108 grams of translucent Nanogel.RTM. granules with sizes between
0.5 to 0.85 mm during removal of oil from water (0.47 g of oil/kg
of water and 0.0102 m/s fluid velocity).
[0035] FIG. 11 is a plot of chemical oxygen demand (COD) and
inverse fluidized bed expansion (squares) as a function of time of
56 grams of opaque Nanogel.RTM. granules with sizes between 0.5 to
0.85 mm during removal of oil from water (0.18 g of oil/kg of water
and fluid velocity of 0.0305 m/s).
[0036] FIG. 12 is a plot of chemical oxygen demand (COD) and
inverse fluidized bed expansion (squares) as a function of time of
100 grams of opaque Nanogel.RTM. granules with sizes between 0.5 to
0.85 mm during removal of oil from water (0.18 g of oil/kg of water
and fluid velocity of 0.0305 m/s).
[0037] FIG. 13 is plot of pressure drop across the inversely
fluidized beds of aerogel during the removal of oil corresponding
to FIGS. 11 and 12. Superficial flow velocity was kept constant at
0.0305 m/s.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The invention generally relates to removing contaminants
present in a fluid system and can be carried out for health or
safety reasons, to meet environmental requirements, to clean
recyclable or discharged streams in refineries, industrial or
commercial applications, or for other reasons.
[0039] The term "fluid" generally refers to liquids, gases,
including vapors, supercritical fluids, viscous fluids and so
forth. As further described below, specific examples of fluid
systems that can be purified by practicing the invention include
liquid systems and supercritical fluid systems. In preferred
aspects, the system is an aqueous waste stream. Non-aqueous systems
including carriers such as organic media, e.g., organic solvents,
supercritical carbon dioxide and many others also can be
purified.
[0040] In addition to the fluid carrier, the system includes a
contaminant. As used herein, the term "contaminant" refers to a
material, e.g., an impurity, or combination of materials not
desired in the fluid system. In specific aspects of the invention,
the contaminant is a liquid. Examples include organic materials
e.g., oils, such as vegetable oil, animal oil, motor oil, crude
oil, synthetic oil, and other organic compounds, e.g.,
hydrocarbons, such as reagents or solvents, e.g., cyclohexane,
toluene, benzene, ethanol, trichloroethylene, and so forth.
[0041] The liquid contaminant can be miscible or immiscible in the
carrier. For instance, one or more water-miscible organic
compound(s) can be removed from an aqueous system. In other
examples, an aqueous system can include a water-immiscible
hydrocarbon.
[0042] Solid contaminants, e.g., metals, contaminants such as
inorganic materials, biological compounds, organometallics and so
forth also could be removed by practicing implementations of the
invention.
[0043] More than one type of contaminant can be removed. For
instance, a contaminant that includes a solvent, e.g., cyclohexane,
toluene, benzene, ethanol, trichloroethylene, in combination with
an oil can be removed from an aqueous system.
[0044] The particle, e.g., droplet, size of the contaminant depends
on the application. It can be, for example, in the range of from
about 1 micrometers (microns or .mu.m) to about 150 microns or as
large as several millimeters. In some embodiments, the contaminant
has a particle size, in the range of from about 1 to about 10000
microns, preferably in the range of from about 5 to about 150
microns.
[0045] To remove a contaminant, the fluid phase system is contacted
with an inversely fluidized material. Preferably, the material is
porous, e.g., microporous or nanoporous and in particulate form. As
used herein, the term "microporous" refers to materials having
pores that are about 1 micron and larger; the term "nanoporous"
refers to materials having pores that are smaller than about 1
micron, preferably less than about 0.1 microns. Pore size can be
determined by methods known in the art, such as mercury intrusion
porosimetry, or microscopy. Preferably the pores are interconnected
giving rise to open type porosity.
[0046] The porous, e.g., nanoporous material can be an oxide of a
metal, such as, for instance, silicon, aluminum, zirconium,
titanium, hafnium, vanadium, yttrium and others, and/or mixtures
thereof. In some applications, microporous materials also could be
utilized.
[0047] Materials that are particularly preferred include aerogels
and/or xerogels.
[0048] Aerogels are low density porous solids that have a gas
rather than a liquid as a dispersant. Generally, they are produced
by removing pore liquid from a wet gel. However, the drying process
can be complicated by capillary forces in the gel pores, which can
give rise to gel shrinkage or densification. In one manufacturing
approach, collapse of the three dimensional structure is
essentially eliminated by using supercritical drying. A wet gel
also can be dried using an ambient pressure, also referred to as
non-supercritical drying process. When applied, for instance, to a
silica-based wet gel, surface modification, e.g., end-capping,
carried out prior to drying, prevents permanent shrinkage in the
dried product. The gel can still shrinks during drying but springs
back recovering its former porosity.
[0049] Product referred to as "xerogel" also is obtained from wet
gels from which the liquid has been removed. The term often
designates a dry gel compressed by capillary forces during drying,
characterized by permanent changes and collapse of the solid
network.
[0050] For convenience, the term "aerogel" is used herein in a
general sense, referring to both "aerogels" and "xerogels".
[0051] Aerogels typically have low bulk densities (about 0.15
g/cm.sup.3 or less, preferably about 0.03 to 0.3 g/cm.sup.3), very
high surface areas (generally from about 300 to about 1,000 square
meter per gram (m.sup.2/g) and higher, preferably from about 600 to
about 1000 m.sup.2/g), high porosity (about 90% and greater,
preferably greater than about 95%), and a relatively large pore
volume (about 3 milliliter per gram (mL/g), preferably about 3.5
mL/g and higher). Aerogels can have a nanoporous structure with
pores smaller than 1 micron (.mu.m). Often, aerogels have a mean
pore diameter of about 20 nanometers (nm). The combination of these
properties in an amorphous structure gives the lowest thermal
conductivity values (e.g., 9 to 16 (mW)/mK at a mean temperature of
37.degree. C. and 1 atmosphere of pressure) for any coherent solid
material. Aerogels can be nearly transparent or translucent,
scattering blue light, or can be opaque.
[0052] A common type of aerogel is silica-based. Aerogels based on
oxides of metals other than silicon, e.g., aluminum, zirconium,
titanium, hafnium, vanadium, yttrium and others, or mixtures
thereof can be utilized as well.
[0053] Also known are organic aerogels, e.g., resorcinol or
melamine combined with formaldehyde, dendredic polymers, and so
forth, and the invention also could be practiced using these
materials.
[0054] Suitable aerogel materials and processes for their
preparation are described, for example, in U.S. Patent Application
No. 2001/0034375 A1 to Schwertfeger et al., published on Oct. 25,
2001, the teachings of which are incorporated herein by reference
in their entirety.
[0055] In specific aspects of the invention, the material, e.g.,
aerogel, employed is hydrophobic. As used herein, the terms
"hydrophobic" and "hydrophobized" refer to partially as well as to
completely hydrophobized aerogel. The hydrophobicity of a partially
hydrophobized material such as aerogel can be further increased. In
completely hydrophobized materials, e.g., aerogels, a maximum
degree of coverage is reached and essentially all chemically
attainable groups are modified.
[0056] Hydrophobicity can be determined by methods known in the
art, such as, for example, contact angle measurements or by
methanol (MeOH) wettability. A discussion of hydrophobicity in
relation to aerogels is found in U.S. Pat. No. 6,709,600 B2 issued
to Hrubesh et al. on Mar. 23, 2004, the teachings of which are
incorporated herein by reference in their entirety.
[0057] Hydrophobic materials such as hydrophobic aerogels can be
produced by using hydrophobizing agents, e.g., silylating agents,
halogen- and in particular fluorine-containing compounds such as
fluorine-containing alkoxysilanes or alkoxysiloxanes, e.g.,
trifluoropropyltrimethoxysilane (TFPTMOS), and other hydrophobizing
compounds known in the art. Hydrophobizing agents can be used
during the formation of aerogels and/or in subsequent processing
steps, e.g., surface treatment.
[0058] Silylating compounds such as, for instance, silanes,
halosilanes, haloalkylsilanes, alkoxysilanes, alkoxyalkylsilanes,
alkoxyhalosilanes, disiloxanes, disilazanes and others are
preferred. Examples of suitable silylating agents include, but are
not limited to diethyldichlorosilane, allylmethyldichlorosilane,
ethylphenyldichlorosilane, phenylethyldiethoxysilane,
trimethylalkoxysilanes, e.g., trimethylbutoxysilane,
3,3,3-trifluoropropylmethyldichlorosilane,
symdiphenyltetramethyldisiloxane,
trivinyltrimethylcyclotrisiloxane, hexaethyldisiloxane,
pentylmethyldichlorosilane, divinyldipropoxysilane,
vinyldimethylchlorosilane, vinylmethyldichlorosilane,
vinyldimethylmethoxysilane, trimethylchlorosilane,
hexamethyldisiloxane, hexenylmethyldichlorosilane,
hexenyldimethylchlorosilane, dimethylchlorosilane,
dimethyldichorosilane, mercaptopropylmethyldimethoxysilane,
bis{3-(triethoxysilyl)propyl}tetrasulfide, hexamethyldisilazane and
combinations thereof.
[0059] The porous material can include one or more additives, such
as fibers, opacifiers, color pigments, dyes and mixtures thereof.
For instance, a nanoporous material which is a silica aerogel can
contain additives such fibers and/or one or more metals or
compounds thereof. Specific examples include aluminum, tin,
titanium, zirconium or other non-siliceous metals, and oxides
thereof. Non-limiting examples of suitable opacifiers include
carbon black, titanium dioxide, zirconium silicate, and mixtures
thereof. While any appropriate loading of opacifier may be used,
preferred loadings for the opacifier are between 1 vol. % and 50
vol. %).
[0060] The particulate porous material can be produced in granular,
pellet, bead, powder, or other particulate form and in any particle
size suitable for an intended application. For instance, the
particles can be within the range of from about 0.01 microns to
about 10.0 millimeters (mm) and preferably have a mean particle
size in the range of 0.3 to 3.0 mm.
[0061] Examples of commercially available hydrophobic aerogel
materials in particulate form are those supplied under the
tradename of Nanogel.RTM. by Cabot Corporation, Billerica, Mass.
Nanogel.RTM. granules have high surface area, are more than about
90% porous and are available in a particle size ranging, for
instance, from about 8 microns (.mu.m) to about 10 mm.
[0062] Contaminants can be removed using combinations of materials,
for instance, combinations of materials such as those disclosed in
U.S. Pat. No. 6,709,600 B2 issued to Hrubesh et al. on Mar. 23,
2004, the teachings of which are incorporated herein by reference
in their entirety. In a specific example, aerogel granules can be
used in conjunction with activated carbon to remove miscible and
immiscible hydrocarbons from water.
[0063] In one embodiment of the invention, materials described
above, and in particular hydrophobic silica aerogel, are used to
remove organic compounds from an aqueous system.
[0064] A qualitative assessment regarding the performance
Nanogel.RTM. particles in purifying an oil-water mixture is shown
in the photographs (FIG. 2A and FIG. 2B), where FIG. 2A shows oily
water before contact with a packed bed of Nanogel.RTM. particles
and FIG. 2B shows purified water after the oily water was contacted
with the packed bed of Nanogel.RTM. particles.
[0065] A comparison of the adsorption capacity of an hydrophobic
silica aerogel and that of a granulated activated carbon is
provided in TABLE 1 of U.S. Pat. No. 6,709,600 B2 issued to Hrubesh
et al. on Mar. 23, 2004, the teachings of which are incorporated
herein by reference in their entirety.
[0066] Aerogel and/or other materials that have a density lower
than that of the fluid phase system being purified can remove
contaminants by inverse fluidization, a process in which solid
particles are dispersed in a fluid, when the density of the
particulate material is less than the density of the fluid.
[0067] Preferably, the difference between the density of the
fluidizing fluid, e.g., a wastewater stream being purified, and the
solid material employed to effect the purification is at least
about 0.1 g/cm.sup.3. For a water-based system, the solid material
used preferably has a density that is less than about 0.8
g/cm.sup.3, more preferably a density that is less than about 0.1
g/cm.sup.3. In specific examples, the material has a density within
the range of from about 0.01 to about 0.8 g/cm.sup.3.
[0068] Shown in FIG. 3 is a schematic diagram of liquid solid
inverse fluidization. As seen in FIG. 3, the liquid flow,
represented by arrows L is in the direction of gravity, downwards,
and the bed expands from the top of the column 20 towards the
bottom. Full fluidization of the bed is reached when there is a
balance between the forces acting on the particles, e.g., particle
22, specifically: drag (arrow D), gravity (arrow G), and buoyancy
(arrow B), forces at the minimum fluidization velocity.
[0069] Particles fluidize when buoyant force is overcome by the
forces of drag and gravity, as shown in the equations below:
[0070] Buoyancy force: F.sub.B=(.rho..sub.l-.rho..sub.p)V.sub.pg
(.rho., density; V.sub.p, volume of granule; g, gravity
acceleration; subscripts: l=liquid, p=granule)
[0071] Gravity force: F.sub.g=.rho..sub.pV.sub.pg
[0072] Drag force:
F D = 1 2 C D .rho. g U mf 2 ( .pi. 4 ) d p 2 ##EQU00001##
(U.sub.mf, minimum fluidization velocity; C.sub.d, drag
coefficient; d.sub.p, granule diameter)
[0073] Inverse fluidization can be conducted in a housing, e.g.,
column, which can be constructed from a suitable material such as a
plastic material, e.g., acrylic, glass, metal, e.g., aluminum,
steel, or from another suitable material. In one example, a
fluidization bed includes nanoporous material having a density
lower than that of the fluidizing medium.
[0074] In preferred embodiments, the inverse fluidization apparatus
of the invention is configured for continuous operation. Since with
time solid, e.g. aerogel, particles saturated with contaminant
become heavy, they can be collected downstream of the fluidized bed
system. Fresh particles can be added at the top or anywhere else
along the fluidization column.
[0075] In general, the size of granules used in the inverse
fluidized beds of the invention can depend on factors such as
specific application, height of the fluidized bed and so forth. For
instance, if a design requires a bed that is relatively short,
e.g., a few feet, then a small granule size e.g., less than 1 mm,
may be preferred. Larger particle sizes can be used in taller
fluidized bed. While small granules provide better removal
efficiency they also tend to require operation at low superficial
velocities. In a specific example employing aerogel material, the
aerogel particle size is greater than 0.5 mm. For instance, the
particle size can be, but is not limited to be within the range of
from about 0.5 to about 2.3 mm. Larger aerogel particles, e.g., 10
mm, also can be used, for instance in scale-up applications, and/or
when using larger fluid velocities. Smaller particle sizes also can
be selected.
[0076] Inverse fluidization employing a material such an aerogel
can be operated at a temperature that allows for the existence of
the liquid phase. In case of water, from 32.degree. F. up to close
to 212.degree. F., preferably in the range of from about 40.degree.
F. to about 150.degree. F.
[0077] Practicing aspects of the invention can purify oil bearing
waste water streams to a level of 1 PPM or lower.
[0078] Inverse fluidization can be used in combination with other
purification techniques and/or devices, for example with packed bed
filters, regular fluidized beds, coalescing elements, API
separators, ultrafiltration systems, reverse osmosis, activated
carbon adsorbers and so forth. Systems and processes can be
designed to include a bed and/or method such as described
herein.
[0079] For instance, in one example, inverse fluidization of
aerogel particles is combined with one or more other techniques for
purifying fluid streams that contain contaminants having relatively
large droplet sizes. In another example, inverse fluidization of
aerogel particles is used upstream of an activated carbon filter to
remove water-miscible or water-immiscible hydrocarbons from water.
In yet another example, a fluid stream, e.g., wastewater,
containing solid as well as liquid, e.g., oil, contaminants is
purified by removing solid contaminants using a suitable technique,
optionally followed by a technique suitable for removal of larger
droplets, followed by an inverse fluidization process or apparatus
such as described herein for removing remaining droplets, to
produce a purified stream.
[0080] The invention is further illustrated by the following
non-limiting examples.
EXAMPLES
[0081] The aerogel employed was Nanogel.RTM. obtained from Cabot
Corporation, Billerica, Mass. Two of the granule sizes used were:
(A) 2.3 mm sieved granules having a particle size range between 1.7
and 2.3 mm; and (B) 500-850 .mu.m, sieved granules. Experiments
also were conducted using un-sieved 2.3 mm granules, which included
granules in the range of 0.5 up to 2.3 mm. Translucent
specifications are labeled herein as TLD and opaque specifications
as OGD. Numbers following the TLD and OGD specifications are
particle size descriptors.
[0082] A schematic diagram of the experimental setup including an
inverse fluidization bed, in which, as discussed above,
contaminated water flows downwards inside the column, is shown in
FIG. 4.
[0083] Shown in FIG. 4 is an apparatus 40 including inverse
fluidization column 42, water supply 44, metering pump 46, static
mixer 48, sampling points 52 and 54, filter 56, drain 58, flow
meters 62 and 64 and pressure gauge 66.
[0084] During operations, flow meters 62 and 64, one provided for
low range flows and the other for larger flows, measured flow of
water. Oil, as well as any other immiscible liquid or solution,
were added to the water in a controlled manner by metering pump 46.
The added oil or solution was mixed with the water by passage
through static mixer 48. The pressure in the system was measured at
this point (by pressure gauge 56) and was kept constant during the
entire experiment, and also for different runs. The pressure drop
across the bed was measured by a differential pressure transmitter
with a range of 0 to 2 psid.
[0085] Generally, a sample of the oil-contaminated water was drawn
for analysis, e.g., at sampling point 52, before entering
fluidization column 42. A second sample of water was taken after
passing through the inverse fluidized bed, e.g., at sampling point
54.
[0086] Both samples were analyzed for either oil or hydrocarbon
content by using a colorimeter (HACH). For oil analysis, the COD
(chemical oxygen demand) method was used since it was found to be
strong enough to digest the mixture of immiscible oil and water.
The COD is a measured property, which is proportional to the
concentration of oil in water as shown in FIG. 5. A HACH test for
Chemical Oxygen Demand (COD), developed by Hach Company of
Loveland, Colo., can be conducted in about 3 hours.
EXAMPLE 1
[0087] Different amounts of granules of Nanogel.RTM. were inversely
fluidized in order to study inverse fluidization characteristics of
this material. FIG. 6A is a photograph of inverse fluidized bed of
500-850 microns Nanogel.RTM. particles (sieved). FIG. 6B is a
photograph of inverse fluidized bed of 2.3 mm Nanogel.RTM.
particles (un-sieved).
[0088] The inversely fluidized bed pressure drop and bed expansion
data were collected as a function of fluid velocity; these data are
shown in FIGS. 7A through 7C and 8A through 8C, respectively. The
data show typical behavior of liquid-solid fluidized beds
characterized by a proportional increase in the bed pressure drop
at fluid velocities below minimum fluidization velocity, a pressure
drop plateau during full fluidization, a minimum fluidization
velocity dependant on particle size, a pressure drop dependant on
the amount of particles and a bed expansion that starts at the
minimum fluidization velocity.
[0089] FIGS. 7A, 7B and 7C indicate that the pressure drop will
depend on the amount of powder that is inversely fluidized. This
behavior is quite different from that typically observed in a
packed bed where a large pressure drop is obtained even with a
small amount of granules when there is a large liquid flow passing
through it. For filter beds, a maximum differential pressure drop
of 10 psid generally is acceptable during operation; a higher
pressure drop leads to excessive energy costs.
[0090] As can be seen in FIGS. 8A, 8B and 8C, the bed starts to
expand at full fluidization, which occurs at fluid velocity values
larger than the minimum fluidization velocity (shown by the
arrows). The increase in bed height means that the void fraction of
the fluidized bed, which has strong effects on the contaminant
removal rate, is increasing. The voidage of the bed preferably is
adjusted in order to expose each individual Nanogel.RTM. particle
to the contaminant, e.g., oil in the water, but without allowing
oil droplets to pass through the fluidized bed, a condition that
can occur at high fluid velocities and large values of the void
fraction for relatively short beds.
[0091] Also, due to the mixing of particles during fluidization,
the oil will be adsorbed more homogenously in an inverse fluidized
bed than in a packed bed where, in some cases, the flow is not well
distributed within the void volume of the bed.
EXAMPLE 2
[0092] Removal of oil from water was studied by injecting oil with
a metering pump using an arrangement such as shown in FIG. 4. The
oil was mixed with the water by using an in-line static mixer.
Water samples, before and after the inverse fluidized bed, were
taken for chemical oxygen demand (COD) analysis. COD concentration
was found by using the HACH colorimetric method. In these
experiments, since oil was added to tap water, the chemical oxygen
demand (COD) was roughly proportional to the oil concentration in
the water as shown in FIG. 5. Therefore COD levels were used as a
reference of oil concentration.
[0093] In one case, 56 grams of Nanogel.RTM. granules with sizes
from 500 to 850 microns were used to adsorb oil from water. The
flow velocity was about 1.07 cm/s. The concentration of oil
upstream the fluidized bed was about 450 mg of oil/l of water.
[0094] As shown in FIG. 9, the inverse fluidized bed of
Nanogel.RTM. is very effective in removing oil from water. There
was at least a one order of magnitude reduction in COD
concentration which implies a more than 90% removal rate; other
experiments have shown removal efficiencies of 99%, and higher.
[0095] The bed height (squares) was also monitored during the
removal of oil from water by the inverse fluidized bed as shown in
FIG. 9. It can be clearly seen that the bed expands as a
consequence of the saturation of some of the Nanogel.RTM. granules
with oil. Since they become heavier, they tend to move towards the
bottom of the column, increasing the bed height of the fluidized
bed.
[0096] In addition, the adsorption capacity of the Nanogel.RTM. was
quite large since 56 grams of the material adsorbed 420 grams of
oil (as estimated by the injection of oil, 0.105 kg/h, during 4
hours). This means a 7.5 by weight ratio of oil adsorbed with
respect to the amount of Nanogel.RTM..
[0097] The pressure drop of the inversely fluidized bed was
monitored during the removal of oil from water and the maximum
pressure drop was about 700 Pa (0.1 psi), which is far below the
pressure drop of a packed bed containing a similar amount of
granules. As can be seen in FIG. 9, there is a change in slope
(inflection point) with time; the pressure drop increases as oil is
injected into the fluidizing water but then decreases as
Nanogel.RTM. granules become heavier reducing their buoyancy and
the drag force needed to fluidize them. During the process,
granules are also being entrained from the fluidization column
reducing the pressure drop even further.
EXAMPLE 3
[0098] In another case, 108 grams of Nanogel.RTM. granules with
sizes from 500 to 850 microns were used to adsorb oil from water.
The flow velocity was about 1.02 cm/s. The concentration of oil
upstream the fluidized bed was about 470 mg of oil per kg (liter)
of water.
[0099] As shown in FIG. 10, the inverse fluidized bed of
Nanogel.RTM. was very effective on removing oil from water with a
reduction in COD concentration from 1400 mg/l down to 40 mg/l,
which implies a 97% removal.
[0100] The bed height was also monitored during the removal of oil
from water by the inverse fluidized bed as also shown in FIG. 10.
It can be clearly seen that the bed reduces as a consequence of the
saturation of some of the Nanogel.RTM. granules with oil. In this
case, because of the initial taller height of the fluidized bed
(more particles were used thus increasing the initial bed height),
there was an oil concentration gradient, with more oil at the top.
This gradient makes particles at the top saturate faster than
particles at other locations in the fluidized bed. After
saturation, these particles become heavier and are entrained by the
flow leading to a reduction in the bed expansion. Thus a continuous
process can easily be designed by feeding clean granules into the
system at the top, while granules saturated with oil leave the
column at the bottom.
EXAMPLE 4
[0101] Another set of experiments was performed to find the effect
of using different amounts of fluidized granules on the oil removal
efficiency; for these experiments the U/U.sub.mf ratio was kept at
4.4, where U.sub.mf is the minimum fluidization velocity and U the
superficial fluid velocity. Adding different amounts of granules to
the column will result in different initial fluidized bed heights.
The residence time of oil droplets in tall fluidized beds (large
amount of granules) is larger when compared to short fluidized
beds. Therefore, in short fluidized beds the oil and granules will
be more homogeneously mixed much like in a Continuous Stirred Tank
Reactor (CSTR). In tall beds granules at the top of the column will
be more saturated with oil than granules at other locations in the
fluidized bed.
[0102] FIG. 11 shows the COD levels and the bed expansion of 56
grams of small aerogel granules. It can be seen that there is a
significant bed expansion from 40 to 50 cm, indicating a CSTR-type
of mixing where most of the granules saturate simultaneously. FIG.
12 shows COD levels and bed expansion for 100 grams of small
aerogel granules exposed to the same concentration of oil and
operating conditions as in the experiment using 56 grams described
in FIG. 11.
[0103] The data indicate that the bed height increases slightly at
the beginning of the experiment, but then drops off because of the
loss of saturated granules during the adsorption of oil. As
expected, the fluidized bed with the smaller amount of granules
gets saturated faster as seen by the more rapid changes in bed
height with time. It is also important to note that the COD levels
at the exit of both fluidized beds are fairly similar even though
different amounts of aerogel are used; this indicates that the
removal efficiency is independent of the height of the bed at
relatively high U/U.sub.mf ratios (e.g., U/U.sub.mf=4.4).
[0104] FIG. 13 shows the differential pressure drop across the
inverse fluidized beds described by FIG. 11 and FIG. 12 during oil
removal; as expected, the figure shows that the pressure drop is
proportional to the amount of fluidized powder in the bed. In both
cases, the pressure drop across the bed of granules does not
plateau, indicating that the granules did not fully saturate.
[0105] Generally, pressure drop observed with inverse fluidized
beds described herein is low, e.g., about 0.2 psid, and does not
build up with use. Moreover, the initial pressure drop across the
fluidized bed of granules is only dependant on the amount of
aerogels used, the density of the aerogels and the cross sectional
area of the column. As oil is added, the pressure drop increases
initially, due to the buoyancy of the oil droplets, then decreases
due to the reduction in the buoyancy of the aerogel granules as oil
is adsorbed into them increasing their weight. With Nanogel.RTM.
particles, the bed exhibits very good mixing between the aerogel
and a liquid phase system, e.g., aqueous system.
[0106] While this invention has been particularly shown and
described with references to preferred embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *
References