U.S. patent application number 11/377745 was filed with the patent office on 2006-07-20 for method of monitoring membrane cleaning processes.
Invention is credited to Bosco P. Ho, John E. Hoots, E. H. Kelle Zeiher.
Application Number | 20060157090 11/377745 |
Document ID | / |
Family ID | 32680155 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157090 |
Kind Code |
A1 |
Zeiher; E. H. Kelle ; et
al. |
July 20, 2006 |
Method of monitoring membrane cleaning processes
Abstract
Methods and systems for monitoring and/or controlling the
cleaning of membrane separation systems or processes are provided.
The present invention utilizes measurable amounts of inert
fluorescent tracer(s) added to a membrane cleaning process stream
to evaluate and/or control the removal of contaminants and/or
impurities during cleaning. The methods and systems of the present
invention can be utilized in a variety of different industrial
applications including raw water processing and waste water
processing.
Inventors: |
Zeiher; E. H. Kelle;
(Naperville, IL) ; Ho; Bosco P.; (Wheaton, IL)
; Hoots; John E.; (St. Charles, IL) |
Correspondence
Address: |
NALCO COMPANY
1601 W. DIEHL ROAD
NAPERVILLE
IL
60563-1198
US
|
Family ID: |
32680155 |
Appl. No.: |
11/377745 |
Filed: |
March 16, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10108694 |
Mar 28, 2002 |
|
|
|
11377745 |
Mar 16, 2006 |
|
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Current U.S.
Class: |
134/56R ;
134/22.1 |
Current CPC
Class: |
B01D 61/12 20130101;
B01D 65/02 20130101; C02F 1/44 20130101; B01D 2321/168 20130101;
C02F 2303/16 20130101 |
Class at
Publication: |
134/056.00R ;
134/022.1 |
International
Class: |
B08B 9/00 20060101
B08B009/00; B08B 3/00 20060101 B08B003/00 |
Claims
1. A cleaning system capable of cleaning a membrane separation
system adapted for use in an industrial process comprising: an
inert fluorescent tracer and a cleaning solution added to the
membrane separation system during cleaning; a detection device
capable of fluorometrically measuring an amount of the inert
fluorescent tracer ranging from about 5 ppt to about 1000 ppm
during cleaning of the membrane separation system wherein the
detection device is capable of producing a signal indicative of the
amount of inert tracer that is measured; and a controller capable
of processing the signal to monitor the cleaning of the membrane
separation system.
2. The cleaning system of claim 1 wherein the membrane separation
system is adapted for use in an industrial process selected from
the group consisting of raw water processes, waste water processes,
industrial water processes, municipal water treatment, food and
beverage processes, pharmaceutical processes, electronic
manufacturing, utility operations, pulp and paper processes, mining
and mineral processes, transportation-related processes, textile
processes, plating and metal working processes, laundry and
cleaning processes, leather and tanning processes, and paint
processes.
3. The cleaning system of claim 1 wherein the membrane separation
system performs a membrane separation process selected from the
group consisting of a cross-flow membrane separation process and a
dead-end flow membrane separation process.
4. The cleaning system of claim 3 wherein the membrane separation
process is selected from the group consisting of reverse osmosis,
ultrafiltration, microfiltration, nanofiltration, electrodialysis,
electrodeionization, pervaporation, membrane extraction, membrane
distillation, membrane stripping, membrane aeration and
combinations thereof.
5. The method of claim 1 wherein the cleaning system is capable of
monitoring at least one parameter specific to cleaning the membrane
separation system selected from the group consisting of a
concentration of the cleaning solution, a concentration of a
treatment chemical, a hold-up volume of the membrane separation
system and combinations thereof.
6. The method of claim 5 wherein the cleaning system monitors a
dilution effect on the concentration of the cleaning solution
during the circulation step due to the hold-up volume.
7. The method of claim 5 wherein the cleaning system monitors the
removal of the cleaning solution during the rinsing step.
8. The method of claim 1 wherein the controller controllably
adjusts cleaning of The membrane separation system based on the
measurable amount of the inert fluorescent tracer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/108,694, which was filed on Mar. 28,
2002.
FIELD OF THE INVENTION
[0002] This invention relates generally to membrane cleaning and,
more particularly, to methods for monitoring and/or controlling the
cleaning of membrane separation systems.
BACKGROUND OF THE INVENTION
[0003] Membrane separation, which uses a selective membrane, is a
fairly recent addition to the industrial separation technology for
processing of liquid streams, such as water purification. In
membrane separation, constituents of the influent typically pass
through the membrane as a result of a driving force(s) in one
effluent stream, thus leaving behind some portion of the original
constituents in a second stream. Membrane separations commonly used
for water purification or other liquid processing include
microfiltration (MF), ultrafiltration (UF), nanofiltration (NF),
reverse osmosis (RO), electrodialysis, electrodeionization,
pervaporation, membrane extraction, membrane distillation, membrane
stripping, membrane aeration, and other processes. The driving
force of the separation depends on the type of the membrane
separation. Pressure-driven membrane filtration, also known as
membrane filtration, includes microfiltration, ultrafiltration,
nanofiltration and reverse osmosis, and uses pressure as a driving
force, whereas the electrical driving force is used in
electrodialysis and electrodeionization. Historically, membrane
separation processes or systems were not considered cost effective
for water treatment due to the adverse impacts that membrane
scaling, membrane fouling, membrane degradation and the like had on
the efficiency of removing solutes from aqueous water streams.
However, advancements in technology have now made membrane
separation a more commercially viable technology for treating
aqueous feed streams suitable for use in industrial processes.
[0004] During membrane separation, deposits of scale and foulants
on the membrane can adversely impact the performance of the
membrane. For example, in membrane filtration such foulants and
scales can decrease the permeate flow for a given driving force,
lowering the permeate quality (purity), increasing energy consumed
to maintain a given permeate flow or the like. This can necessitate
the cleaning of the membrane separation system in order to remove
the scalants, foulants and the like from the membrane separation
system. Thus, the performance of the membrane system in use can be
enhanced.
[0005] In general, the membrane cleaning process includes adding a
suitable cleaning agent and circulating it within the membrane
separation system. In this regard, the cleaning agent acts to
remove scalants, foulants or the like that have deposited on
surfaces of the membrane system, including the membrane itself.
After the membrane system has been washed with the cleaning agent,
the system is then, in general, flushed or rinsed to remove the
cleaning agent along with other impurities that may remain in the
system.
[0006] Membrane cleaning processes usually consist of removing the
membrane system from service, rinsing the membrane system
(membranes, housings and associated piping) with high quality
(preferably permeate quality) water, preparing a cleaning solution
by adding the cleaner to a specified volume of permeate quality
water, heating the cleaning solution, circulating the cleaning
solution at low pressure through the membranes and back into the
clean-in-place (CIP) tank thereby displacing the rinse water and
diluting the cleaning solutions. The cleaning process further
consists of alternately circulating the cleaning solution through
the membrane system and soaking the membrane system in the cleaning
solution. During the process the system may be rinsed and fresh
cleaning solution applied as needed. Finally the system is rinsed
with permeate quality water and either subjected to a second
cleaning or placed back in service.
[0007] Typically, the membrane cleaning process is maintained by
evaluating a variety of different process conditions, particularly
the pH of the system during cleaning. However, this type of
monitoring is not very specific and/or selective to, for example,
the concentration of the cleaning agent during cleaning. In this
regard, fluctuations in the amount of cleaning agent may not be
effectively identified. Thus, the amount of cleaning agent may not
be effectively monitored and thereby controlled in order to enhance
the performance of the cleaning process.
[0008] Accordingly, a need exists to monitor and/or control the
cleaning of membrane separation systems where conventional
monitoring techniques lack the sensitivity, selectivity and/or
accuracy necessary to adequately monitor one or more process
parameters specific to the cleaning of membranes or systems in
order to adequately evaluate the performance of the same.
SUMMARY OF THE INVENTION
[0009] The present invention provides methods and systems for
monitoring and/or controlling the cleaning of membrane separation
systems. In this regard, the detection of inert fluorescent tracers
is utilized to evaluate and/or control a number of different
process parameters unique to the cleaning of membrane separation,
such as operational parameters, chemical parameters, mechanical
parameters, the like and combinations thereof. The inert
fluorescent tracer monitoring technique of the present invention
can be performed with a high degree of sensitivity and selectivity
with respect to the monitoring of process parameters specific to
the cleaning of a membrane separation system. In this regard, the
methods and systems of the present invention can be effectively
utilized to optimize the performance of cleaning and, thus enhance
the performance of the membrane separation process. Examples of
such optimized performance include longer times between membrane
cleanings, longer membrane life, verification of treatment chemical
in the system, ability to operate at optimal recovery, and
decreased energy costs due to better control of scaling, fouling
and other system parameters.
[0010] To this end, in an embodiment of the present invention, a
method of monitoring a cleaning process capable of cleaning a
membrane separation system is provided. The method includes the
steps of providing an inert fluorescent tracer and a cleaning
solution; adding the inert fluorescent tracer and the cleaning
solution to the membrane separation system; providing a fluorometer
to detect the fluorescent signal of the inert fluorescent tracer in
the membrane separation system; and using the fluorometer to
determine an amount of the inert fluorescent tracer in the membrane
separation system during the cleaning process.
[0011] In another embodiment, a method of cleaning a membrane
separation system including a membrane capable of removing
impurities from a feed stream is provided. The method includes the
steps of providing an inert fluorescent tracer and a cleaning
solution; flushing the membrane separation system; adding the inert
fluorescent tracer and the cleaning solution to the membrane
separation system; circulating the inert fluorescent tracer and the
cleaning solution in the membrane separation system; rinsing the
membrane separation system; providing a fluorometer to detect the
fluorescent signal of the inert fluorescent tracer in the membrane
separation system; using the fluorometer to measure an amount of
the inert fluorescent tracer ranging from about 5 parts per
trillion ("ppt") to about 1000 parts per million ("ppm"); and
evaluating at least one process parameter specific to cleaning
based on the amount of the inert fluorescent tracer that is
measured.
[0012] In yet another embodiment, a cleaning system capable of
cleaning a membrane separation system adapted for use in an
industrial process is provided. The cleaning system includes an
inert fluorescent tracer and a cleaning solution added to the
membrane separation system during cleaning; a detection device
capable of fluorometrically measuring an amount of the inert
fluorescent tracer ranging from about 5 ppt to about 1000 ppm
during cleaning of the membrane separation system wherein the
detection device is capable of producing a signal indicative of the
amount of inert tracer that is measured; and a controller capable
of processing the signal to monitor cleaning of the membrane
separation system.
[0013] It is, therefore, an advantage of the present invention to
provide methods and systems that utilize inert fluorescent tracers
to monitor and/or control the cleaning of membrane separation
processes or systems.
[0014] Another advantage of the present invention is to provide
methods and systems that utilize measurable amounts of inert
tracers to improve the operational efficiency of the cleaning of
membrane separation processes or systems.
[0015] A further advantage of the present invention is to provide
methods and systems for monitoring parameters specific to the
cleaning of membrane separation processes with selectivity,
specificity and accuracy based on measurable amounts of inert
tracers added during cleaning.
[0016] Yet another advantage of the present invention is to provide
methods and systems for monitoring and/or controlling the cleaning
of membrane separation processes adaptable for use in industrial
water systems.
[0017] Still further an advantage of the present invention is to
provide an improved performance specific to the cleaning of
membrane separation processes or systems that utilize cross-flow
and/or dead-end flow separation to remove impurities from a variety
of suitable feed streams.
[0018] The benefits of this invention include the accurate
determination of the system volume of a membrane separation system
including the housings and associated piping, the accurate dosing
of cleaning chemicals during system cleaning, and the assessment of
rinse times for the system.
[0019] Additional features and advantages of the present invention
are described in, and will be apparent in, the detailed description
of the presently preferred embodiments.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0020] The present invention provides methods and systems for
monitoring and/or controlling the cleaning of membrane separation
systems. More specifically, the methods and systems of the present
invention can monitor and/or control the cleaning of membrane
separation systems based on measurable amounts of inert fluorescent
tracers which have been added during cleaning.
[0021] The methods and systems of the present invention can include
a variety of different and suitable components, process steps,
operating conditions and the like, for monitoring and/or
controlling the cleaning of membrane separation processes or
systems. In an embodiment, the membrane separation process of the
present invention includes cross-flow and dead-end flow processes.
During cross-flow processes, the feed stream can be treated in a
flow direction that is substantially parallel to the membrane of
the separation system. With respect to dead-end flow separation
processes, the feed stream can be treated in a flow direction that
is substantially perpendicular to the membrane of the separation
system.
[0022] It should be appreciated that the present invention can be
utilized with respect to a number of different types of membrane
separation processes including, for example, cross flow processes,
dead-end flow processes, reverse osmosis, ultrafiltration,
microfiltration, nanofiltration, electrodialysis,
electrodeionization, pervaporation, membrane extraction, membrane
distillation, membrane stripping, membrane aeration and the like or
combinations thereof. Reverse osmosis, ultrafiltration,
microfiltration and nanofiltration are the preferred membrane
separation processes.
[0023] In reverse osmosis, the feed stream is typically processed
under cross flow conditions. In this regard, the feed stream flows
substantially parallel to the membrane surface such that only a
portion of the feed stream diffuses through the membrane as
permeate. The cross flow rate is routinely high in order to provide
a scouring action that lessens membrane surface fouling. This can
also decrease concentration polarization effects (e.g.,
concentration of solutes in the reduced-turbulence boundary layer
at the membrane surface, which can increase the osmotic pressure at
the membrane and thus can reduce permeate flow). The concentration
polarization effects can inhibit the feed stream water from passing
through the membrane as permeate, thus decreasing the recovery
ratio, e.g., the ratio of permeate to applied feed stream. A
recycle loop(s) may be employed to maintain a high flow rate across
the membrane surface.
[0024] Reverse osmosis processes can employ a variety of different
types of membranes. Such commercial membrane element types include,
without limitation, hollow fiber membrane elements, tubular
membrane elements, spiral-wound membrane elements, plate and frame
membrane elements, and the like, some of which are described in
more detail in "The Nalco Water Handbook," Second Edition, Frank N.
Kemmer ed., McGraw-Hill Book Company, New York, N.Y., 1988,
incorporated hereinto, particularly Chapter 15 entitled "Membrane
Separation". It should be appreciated that a single membrane
element may be used in a given membrane filtration system, but a
number of membrane elements can also be used depending on the
industrial application.
[0025] A typical reverse osmosis system is described as an example
of membrane filtration and more generally membrane separation.
Reverse osmosis uses mainly spiral wound elements or modules, which
are constructed by winding layers of semi-porous membranes with
feed spacers and permeate water carriers around a central
perforated permeate collection tube. Typically, the modules are
sealed with tape and/or fiberglass over-wrap. The resulting
construction has one channel which can receive an inlet flow. The
inlet stream flows longitudinally along the membrane module and
exits the other end as a concentrate stream. Within the module,
water passes through the semi-porous membrane and is trapped in a
permeate channel which flows to a central collection tube. From
this tube it flows out of a designated channel and is
collected.
[0026] In practice, membrane modules are stacked together, end to
end, with inter-connectors joining the permeate tubes of the first
module to the permeate tube of the second module, and so on. These
membrane module stacks are housed in pressure vessels. Within the
pressure vessel feed water passes into the first module in the
stack, which removes a portion of the water as permeate water. The
concentrate stream from the first membrane becomes the feed stream
of the second membrane and so on down the stack. The permeate
streams from all of the membranes in the stack are collected in the
joined permeate tubes. Only the feed stream entering the first
module, the combined permeate stream and the final concentrate
stream from the last module in the stack are commonly
monitored.
[0027] Within most reverse osmosis systems, pressure vessels are
arranged in either "stages" or "passes." In a staged membrane
system, the combined concentrate streams from a bank of pressure
vessels are directed to a second bank of pressure vessels where
they become the feed stream for the second stage. Commonly systems
have 2 to 3 stages with successively fewer pressure vessels in each
stage. For example, a system may contain 4 pressure vessels in a
first stage, the concentrate streams of which feed 2 pressure
vessels in a second stage, the concentrate streams of which in turn
feed 1 pressure vessel in the third stage. This is designated as a
"4:2:1" array. In a staged membrane configuration, the combined
permeate streams from all pressure vessels in all stages are
collected and used without further membrane treatment. Multi-stage
systems are used when large volumes of purified water are required,
for example for boiler feed water. The permeate streams from the
membrane system may be further purified by ion exchange or other
means.
[0028] In a multi-pass system, the permeate streams from each bank
of pressure vessels are collected and used as the feed to the
subsequent banks of pressure vessels. The concentrate streams from
all pressure vessels are combined without further membrane
treatment of each individual stream. Multi-pass systems are used
when very high purity water is required, for example in the
microelectronics or pharmaceutical industries.
[0029] It should be clear from the above examples that the
concentrate stream of one stage of an RO system can be the feed
stream of another stage. Likewise the permeate stream of a single
pass of a multi-pass system may be the feed stream of a subsequent
pass. A challenge in monitoring systems such as the reverse osmosis
examples cited above is that there are a limited number of places
where sampling and monitoring can occur, namely the feed, permeate
and concentrate streams. In some, but not all, systems
"inter-stage" sampling points allow sampling/monitoring of the
first stage concentrate/second stage feed stream. Similar
inter-pass sample points may be available on multi-pass systems as
well.
[0030] In contrast to cross-flow filtration membrane separation
processes, conventional filtration of suspended solids can be
conducted by passing a feed fluid through a filter media or
membrane in a substantially perpendicular direction. This
effectively creates one exit stream during the service cycle.
Periodically, the filter is backwashed by passing a clean fluid in
a direction opposite to the feed, generating a backwash effluent
containing species that have been retained by the filter. Thus
conventional filtration produces a feed stream, a purified stream
and a backwash stream. This type of membrane separation is
typically referred to as dead-end flow separation and is typically
limited to the separation of suspended particles greater than about
one micron in size.
[0031] Cross-flow filtration techniques, on the other hand, can be
used for removing smaller particles (generally about one micron in
size or less), colloids and dissolved solutes. Such types of
cross-flow membrane separation systems can include, for example,
reverse osmosis, microfiltration, ultrafiltration, nanofiltration,
electrodialysis or the like. Reverse osmosis can remove even low
molecular weight dissolved species that are at least about 0.0001
to about 0.001 microns in minimum diameter, including, for example,
ionic and nonionic species, low molecular weight molecules,
water-soluble macromolecules or polymers, suspended solids,
colloids, and such substances as bacteria and viruses.
[0032] In this regard, reverse osmosis is often used commercially
to treat water that has a moderate to high (e.g., 500 ppm or
greater) total dissolved solids ("TDS") content. Typically on order
of from about 2 percent to about 5 percent of the TDS of a feed
stream will pass through the membrane. Thus, in general the
permeate may not be entirely free of solutes. In this regard, the
TDS of reverse osmosis permeates may be too high for some
industrial applications, such as use as makeup water for high
pressure boilers. Therefore, reverse osmosis systems and other like
membrane separation systems are frequently used prior to and in
combination with an ion exchange process or other suitable process
to reduce the TDS loading on the resin and to decrease the amount
of hazardous material used and stored for resin regeneration, such
as acids and sodium hydroxide.
[0033] Applicants have surprisingly discovered that a number of
different process parameters specific to the cleaning of membrane
separation, including, for example, operational parameters,
chemical parameters, mechanical parameters, concentration of the
cleaning solution, concentration of the treatment product including
an anti-scalant, an anti-foulant, a biocide and mixtures thereof,
the hold-up volume of the membrane separation system, like
parameters and combinations thereof can be evaluated with a high
degree of selectivity, specificity and accuracy such that the
performance of the cleaning process and thus the membrane
separation process can be effectively optimized.
[0034] It should be appreciated that the process parameters
specific to the cleaning of membranes can vary greatly with respect
to process parameters specific to the cleaning of other water
systems. Based on these differences, a number of different factors
and considerations must necessarily be taken into account when
developing and/or implementing monitoring and/or controlling
programs with respect to the cleaning of membrane separation
systems as compared to the cleaning of the other water treatment
processes. In this regard, inert fluorescent tracer monitoring as
applied to cleaning membrane separation systems can vary greatly as
applied to other water treatment systems.
[0035] As previously discussed, the methods and systems of the
present invention employ inert fluorescent tracers to monitor
and/or control the cleaning of membrane separation systems. In this
regard, the amount of inert tracers measured during cleaning can be
utilized as an indicator to monitor and/or control cleaning such
that the performance of such systems can be optimized.
[0036] The term "inert," as used herein refers to an inert
fluorescent tracer that is not appreciably or significantly
affected by any other chemistry in the system, or by the other
system parameters such as pH, temperature, ionic strength, redox
potential, microbiological activity or biocide concentration. To
quantify what is meant by "not appreciably or significantly
affected", this statement means that an inert fluorescent compound
has no more than a 10% change in its fluorescent signal, under
severe conditions normally encountered in industrial water systems.
Severe conditions normally encountered in industrial water systems
are known to people of ordinary skill in the art of industrial
water systems.
[0037] It should be appreciated that a variety of different and
suitable inert tracers can be utilized in any suitable amount,
number and application. For example, a single tracer can be used to
evaluate a number of different membrane cleaning process
parameters. However, the present invention can include the use of a
number of different tracers each functioning as tracers for
separate monitoring applications. In an embodiment, inert
fluorescent tracer monitoring of the present invention can be
conducted on a singular, intermittent or semi-continuous basis, and
preferably the concentration determination of the tracer is
conducted on-site to provide a rapid real-time determination.
[0038] An inert tracer must be transportable with the water of the
membrane cleaning process and thus substantially, if not wholly,
water-soluble therein at the concentration it is used, under the
temperature and pressure conditions specific and unique to membrane
cleaning. In other words, an inert tracer displays properties
similar to a solute of the membrane separation process or system
which is being cleaned. In an embodiment, it is preferred that the
inert tracer of the present invention meet the following
criteria:
[0039] 1. Not be adsorbed by the membrane in any appreciable
amount;
[0040] 2. Not degrade the membrane or otherwise hinder its
performance or alter its composition;
[0041] 3. Be detectable on a continuous or semi-continuous basis
and susceptible to concentration measurements that are accurate,
repeatable and capable of being performed on any suitable process
stream during cleaning;
[0042] 4. Be substantially foreign to the chemical species that are
normally present during the cleaning of membrane separation systems
in which the inert tracer(s) may be used;
[0043] 5. Be substantially impervious to interference from, or
biasing by, the chemical species that are normally present during
cleaning of membrane separation systems in which the inert
tracer(s) may be used;
[0044] 6. Be substantially impervious to any of its own potential
specific or selective losses during cleaning of membrane separation
systems;
[0045] 7. Be compatible with all treatment agents employed in the
water of the membrane separation systems in which the inert
tracer(s) may be used, and thus in no way reduce the efficacy
thereof;
[0046] 8. Be compatible with all components of its formulation;
and
[0047] 9. Be relatively nontoxic and environmentally safe, not only
within the environs during the cleaning of the membrane separation
system in which it may be used, but also upon discharge
therefrom.
[0048] It should be appreciated that the amount of inert tracer to
be added during cleaning of the membrane separation system that is
effective without being grossly excessive can vary with respect to
a variety of factors including, without limitation, the monitoring
method selected, the extent of background interference associated
with the selected monitoring method, the magnitude of the expected
inert tracer(s) concentration in the cleaning process stream, the
monitoring mode (such as, an on-line continuous monitoring mode),
and other similar factors. In an embodiment, the dosage of an inert
tracer added during membrane cleaning includes an amount that is at
least sufficient to provide a measurable concentration of at least
about 5 ppt, and preferably at least about 1 parts per billion
("ppb") or about 5 ppb or higher, such as, up to about 100 ppm or
about 200 ppm, or even as high as about 1000 ppm in any suitable
process stream during cleaning. In an embodiment, the amount of
tracer ranges from about 5 ppt to about 1000 ppm, preferably from
about 1 ppb to about 50 ppm, more preferably from about 5 ppb to
about 50 ppb.
[0049] In an embodiment, the inert tracer can be added during
cleaning of the membrane separation system as a component of a
formulation, rather than as a separate component, such as a dry
solid or neat liquid. The inert tracer formulation or product may
include an aqueous solution or other substantially homogeneous
mixture that disperses with reasonable rapidity during cleaning of
the membrane separation system to which it is added. In this
regard, the inert tracer's concentration may be correlated to the
concentration of a product. In an embodiment, the product or
formulation can include any suitable cleaning agent (as discussed
below) which is added to clean the membrane.
[0050] A variety of different and suitable types of compounds can
be utilized as inert fluorescent tracers. In an embodiment, the
inert fluorescent compounds can include, for example, the following
compounds: [0051] 3,6-acridinediamine, N,N,N',N'-tetramethyl-,
monohydrochloride, also known as Acridine Orange (CAS Registry No.
65-61-2), [0052] 2-anthracenesulfonic acid sodium salt (CAS
Registry No. 16106-40-4), [0053] 1,5-anthracenedisulfonic acid (CAS
Registry No. 61736-91-2) and salts thereof, [0054]
2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and
salts thereof, [0055] 1,8-anthracenedisulfonic acid (CAS Registry
No. 61736-92-3) and salts thereof, [0056]
anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol, 16,17-dimethoxy-,
bis(hydrogen sulfate), disodium salt, also known as Anthrasol Green
IBA (CAS Registry No. 2538-84-3, aka Solubilized Vat Dye), [0057]
bathophenanthrolinedisulfonic acid disodium salt (CAS Registry No.
52746-49-3), [0058] amino 2,5-benzene disulfonic acid (CAS Registry
No. 41184-20-7), [0059] 2-(4-aminophenyl)-6-methylbenzothiazole
(CAS Registry No. 92-36-4), [0060]
2-(4-aminophenyl)-6-methylbenzothiazole (CAS Registry No. 92-36-4),
[0061] 1H-benz[de]isoquinoline-5-sulfonic acid,
6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt,
also known as Brilliant Acid Yellow 8G (CAS Registry No. 2391-30-2,
aka Lissamine Yellow FF, Acid Yellow 7), [0062] phenoxazin-5-ium,
1-(aminocarbonyl)-7-(diethylamino)-3,4-dihydroxy-, chloride, also
known as Celestine Blue (CAS Registry No. 1562-90-9), [0063]
benzo[a]phenoxazin-7-ium, 5,9-diamino-, acetate, also known as
cresyl violet acetate (CAS Registry No. 10510-54-0), [0064]
4-dibenzofuransulfonic acid (CAS Registry No. 42137-76-8), [0065]
3-dibenzofuransulfonic acid (CAS Registry No. 215189-98-3), [0066]
1-ethylquinaldinium iodide (CAS Registry No. 606-53-3), [0067]
fluorescein (CAS Registry No. 2321-07-5), [0068] fluorescein,
sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73,
Uranine), [0069] Keyfluor White ST (CAS Registry No. 144470-48-4,
aka Flu. Bright 28), [0070] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophen-
yl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known
as Keyfluor White CN (CAS Registry No. 16470-24-9), [0071] C.I.
Fluorescent Brightener 230, also known as Leucophor BSB (CAS
Registry No. 68444-86-0), [0072] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophen-
yl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known
as Leucophor BMB (CAS Registry No. 16470-24-9, aka Leucophor U,
Flu. Bright. 290), [0073] 9,9'-biacridinium, 10,10'-dimethyl-,
dinitrate, also known as Lucigenin (CAS Registry No. 2315-97-1, aka
bis-N-methylacridinium nitrate), [0074]
1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)--
D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No.
83-88-5), [0075] mono-, di-, or tri-sulfonated napthalenes,
including but not limited to [0076] 1,5-naphthalenedisulfonic acid,
disodium salt (hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA
hydrate), [0077] 2-amino-1-naphthalenesulfonic acid (CAS Registry
No. 81-16-3), [0078] 5-amino-2-naphthalenesulfonic acid (CAS
Registry No. 119-79-9), [0079]
4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No.
90-51-7), [0080] 6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS
Registry No. 116-63-2), [0081] 7-amino-1,3-naphthalenesulfonic
acid, potassium salt (CAS Registry No. 79873-35-1), [0082]
4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No.
90-20-0), [0083] 5-dimethylamino-1-naphthalenesulfonic acid (CAS
Registry No. 4272-77-9), [0084] 1-amino-4-naphthalene sulfonic acid
(CAS Registry No. 84-86-6), [0085] 1-amino-7-naphthalene sulfonic
acid (CAS Registry No. 119-28-8), and [0086]
2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS Registry
No. 2666-06-0), [0087] 3,4,9,10-perylenetetracarboxylic acid (CAS
Registry No. 81-32-3), [0088] C.I. Fluorescent Brightener 191, also
known as Phorwite CL (CAS Registry No. 12270-53-0), [0089] C.I.
Fluorescent Brightener 200, also known as Phorwite BKL (CAS
Registry No. 61968-72-7), [0090] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,
dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No.
52237-03-3), [0091] benzenesulfonic acid,
5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium
salt, also known as Pylaklor White S-15A (CAS Registry No.
6416-68-8), [0092] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium
salt (CAS Registry No. 59572-10-0), [0093] pyranine, (CAS Registry
No. 6358-69-6, aka 8-hydroxy-1,3,6-pyrenetrisulfonic acid,
trisodium salt), [0094] quinoline (CAS Registry No. 91-22-5),
[0095] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as
Rhodalux (CAS Registry No. 550-82-3), [0096] xanthylium,
9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium
salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),
[0097] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride,
also known as Safranine O (CAS Registry No. 477-73-6), [0098] C.I.
Fluorescent Brightener 235, also known as Sandoz CW (CAS Registry
No. 56509-06-9), [0099] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophen-
yl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known
as Sandoz CD (CAS Registry No. 16470-24-9, aka Flu. Bright. 220),
[0100] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1-
,3,5-triazin-2-yl]amino]-, disodium salt, also known as Sandoz
TH-40 (CAS Registry No. 32694-95-4), [0101] xanthylium,
3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt, sodium
salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1,
aka Acid Red 52), [0102] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(ph-
enylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as
Tinopal 5BM-GX (CAS Registry No. 169762-28-1), [0103] Tinopol DCS
(CAS Registry No. 205265-33-4), [0104] benzenesulfonic acid,
2,2'-([1,1'-biphenyl]-4,4'-diyldi-2,1-ethenediyl)bis-, disodium
salt also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),
[0105] benzenesulfonic acid,
5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium
salt, also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),
[0106] 7-benzothiazolesulfonic acid,
2,2'-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium
salt, also known as Titan Yellow (CAS Registry No. 1829-00-1, aka
Thiazole Yellow G), and [0107] all ammonium, potassium and sodium
salts thereof, and all like agents and suitable mixtures
thereof.
[0108] Preferred tracers include: [0109]
1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)--
D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No.
83-88-5), [0110] fluorescein (CAS Registry No. 2321-07-5), [0111]
fluorescein, sodium salt (CAS Registry No. 518-47-8, aka Acid
Yellow 73, Uranine), [0112] 2-anthracenesulfonic acid sodium salt
(CAS Registry No. 16106-40-4), [0113] 1,5-anthracenedisulfonic acid
(CAS Registry No. 61736-91-2) and salts thereof, [0114]
2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) and
salts thereof, [0115] 1,8-anthracenedisulfonic acid (CAS Registry
No. 61736-92-3) and salts thereof, [0116] mono-, di-, or
tri-sulfonated napthalenes, including but not limited to [0117]
1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CAS
Registry No. 1655-29-4, aka 1,5-NDSA hydrate), [0118]
2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),
[0119] 5-amino-2-naphthalenesulfonic acid (CAS Registry No.
119-79-9), [0120] 4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS
Registry No. 90-51-7), [0121]
6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No.
116-63-2), [0122] 7-amino-1,3-naphthalenesulfonic acid, potassium
salt (CAS Registry No. 79873-35-1), [0123]
4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS Registry No.
90-20-0), [0124] 5-dimethylamino-1-naphthalenesulfonic acid (CAS
Registry No. 4272-77-9), [0125] 1-amino-4-naphthalene sulfonic acid
(CAS Registry No. 84-86-6), [0126] 1-amino-7-naphthalene sulfonic
acid (CAS Registry No. 119-28-8), and [0127]
2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS Registry
No. 2666-06-0), [0128] 3,4,9,10-perylenetetracarboxylic acid (CAS
Registry No. 81-32-3), [0129] C.I. Fluorescent Brightener 191, also
known as, Phorwite CL (CAS Registry No. 12270-53-0), [0130] C.I.
Fluorescent Brightener 200, also known as Phorwite BKL (CAS
Registry No. 61968-72-7), [0131] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,
dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No.
52237-03-3), [0132] benzenesulfonic acid,
5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium
salt, also known as Pylaklor White S-15A (CAS Registry No.
6416-68-8), [0133] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium
salt (CAS Registry No. 59572-10-0), [0134] pyranine, (CAS Registry
No. 6358-69-6, aka 8-hydroxy-1,3,6-pyrenetrisulfonic acid,
trisodium salt), [0135] quinoline (CAS Registry No. 91-22-5),
[0136] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as
Rhodalux (CAS Registry No. 550-82-3), [0137] xanthylium,
9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium
salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8),
[0138] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride,
also known as Safranine O (CAS Registry No. 477-73-6), [0139] C.I.
Fluorescent Brightener 235, also known as Sandoz CW (CAS Registry
No. 56509-06-9), [0140] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophen-
yl)amino]-1,3,5-triazin-2-yl]amino]-, tetrasodium salt, also known
as Sandoz CD (CAS Registry No. 16470-24-9, aka Flu. Bright. 220),
[0141] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1-
,3,5-triazin-2-yl]amino]-, disodium salt, also known as Sandoz
TH-40 (CAS Registry No. 32694-95-4), [0142] xanthylium,
3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, inner salt, sodium
salt, also known as Sulforhodamine B (CAS Registry No. 3520-42-1,
aka Acid Red 52), [0143] benzenesulfonic acid,
2,2'-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(ph-
enylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt, also known as
Tinopal 5BM-GX (CAS Registry No. 169762-28-1), [0144] Tinopol DCS
(CAS Registry No. 205265-33-4), [0145] benzenesulfonic acid,
2,2'-([1,1'-biphenyl]-4,4'-diyldi-2,1-ethenediyl)bis-, disodium
salt, also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),
[0146] benzenesulfonic acid,
5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium
salt, also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),
[0147] 7-benzothiazolesulfonic acid,
2,2'-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium
salt, also known as Titan Yellow (CAS Registry No. 1829-00-1, aka
Thiazole Yellow G), and [0148] all ammonium, potassium and sodium
salts thereof, and all like agents and suitable mixtures
thereof.
[0149] The most preferred fluorescent inert tracers of the present
invention include 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt
(CAS Registry No. 59572-10-0); 1,5-naphthalenedisulfonic acid
disodium salt (hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA
hydrate); xanthylium,
9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium
salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8);
1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)--
D-ribitol, also known as Riboflavin or Vitamin B2 (CAS Registry No.
83-88-5); fluorescein (CAS Registry No. 2321-07-5); fluorescein,
sodium salt (CAS Registry No. 518-47-8, aka Acid Yellow 73,
Uranine); 2-anthracenesulfonic acid sodium salt (CAS Registry No.
16106-404); 1,5-anthracenedisulfonic acid (CAS Registry No.
61736-91-2) and salts thereof; 2,6-anthracenedisulfonic acid (CAS
Registry No. 61736-95-6) and salts thereof;
1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) and
salts thereof; and mixtures thereof. The fluorescent tracers listed
above are commercially available from a variety of different
chemical supply companies.
[0150] In addition to the tracers listed above, those skilled in
the art will recognize that salts using alternate counter ions may
be used. Thus, for example, anionic tracers which have Na.sup.+ as
a counter ion could also be used in forms where the counter ion is
chosen from the list of: K.sup.+, Li.sup.+, NH.sub.4.sup.+,
Ca.sup.+2, Mg.sup.+2 or other appropriate counter ions. In the same
way, cationic tracers may have a variety of counter ions, for
example: Cl.sup.-, SO.sub.4.sup.-2, PO.sub.4.sup.-3,
HPO.sub.4.sup.-2; H.sub.2PO.sub.4.sup.-; CO.sub.3.sup.-2;
HCO.sub.3.sup.-; or other appropriate counter ions.
[0151] Modifications of these tracers to control molecular weight
or physical size within a desirable size range by, for example,
affixing them to an inert polymeric molecule, incorporating them
into a fluorescent microsphere or adding additional chemical
moieties in the side chains of the molecules should be obvious to
those skilled in the art. Such modifications are included
herein.
[0152] As previously discussed, the inert tracer(s) is measured or
detected to evaluate the performance during cleaning of the
membrane separation system. A determination of the presence of an
inert fluorescent tracer and the concentration thereof in any
suitable process stream during membrane cleaning can be made when
the concentration of the inert tracer in the process stream of a
membrane separation system is several parts per million or less,
even as low as parts per billion as previously discussed.
[0153] At times, it may be desired to employ a number of inert
tracers. In this regard, it may be desired to use a number of inert
tracers to monitor, for example, inert tracer-specific losses,
variances, like conditions or combinations thereof. Such separate
and distinct inert tracers can each be detected and quantified in a
single process stream despite both being inert fluorescent tracers
provided that their respective wavelengths of emission do not
interfere with one another. Thus, concurrent analyses for multiple
inert tracers is possible by selection of inert tracers that have
appropriate spectral characteristics.
[0154] The inert tracers of the present invention can be detected
by utilizing a variety of different and suitable techniques. For
example, fluorescence emission spectroscopy on a substantially
continuous basis, at least over a given time period, is one of the
preferred analytical techniques according to an embodiment of the
present invention. One method for the continuous on-stream
measuring of chemical tracers by fluorescence emission spectroscopy
and other analysis methods is described in U.S. Pat. No. 4,992,380,
B. E. Moriarty, J. J. Hickey, W. H. Hoy, J. E. Hoots and D. A.
Johnson, issued Feb. 12, 1991, incorporated hereinto by
reference.
[0155] In general, for most fluorescence emission spectroscopy
methods having a reasonable degree of practicality, it is
preferable to perform the analysis without isolating in any manner
the tracer(s). Thus, there may be some degree of background
fluorescence in the influent/feedwater and/or concentrate on which
the fluorescence analysis is conducted. This background
fluorescence may come from chemical compounds in the membrane
separation system and/or cleaning thereof that are unrelated to the
membrane separation process or system cleaning of the present
invention.
[0156] In instances where the background fluorescence is low, the
relative measurable intensities (measured against a standard
fluorescent compound at a standard concentration and assigned a
relative intensity, for instance 100) of the fluorescence of the
inert tracer versus the background can be very high, for instance a
ratio of 100/10 or 500/10 when certain combinations of excitation
and emission wavelengths are employed even at low fluorescent
compound concentrations, and such ratios would be representative of
a "relative fluorescence" (under like conditions) of respectively
10 and 50. In an embodiment, the excitation/emission wavelengths
and/or the amount of inert tracer employed are selected to provide
a relative fluorescence of at least about 5 or about 10 for the
given background fluorescence anticipated.
[0157] Examples of fluorometers that may be used in the practice of
this invention include the TRASAR.RTM. 3000 and TRASAR.RTM. 8000
fluorometers (available from Ondeo Nalco Company of Naperville,
Ill.); the Hitachi F-4500 fluorometer (available from Hitachi
through Hitachi Instruments Inc. of San Jose, Calif.); the JOBIN
YVON FluoroMax-3 "SPEX" fluorometer (available from JOBIN YVON Inc.
of Edison, N.J.); and the Gilford Fluoro-IV spectrophotometer or
the SFM 25 (available from Bio-tech Kontron through Research
Instruments International of San Diego, Calif.). It should be
appreciated that the fluorometer list is not comprehensive and is
intended only to show examples of fluorometers. Other commercially
available fluorometers and modifications thereof can also be used
in this invention.
[0158] It should be appreciated that a variety of other suitable
analytical techniques may be utilized to measure the amount of
inert tracers during cleaning of membrane separation process.
Examples of such techniques include combined HPLC-fluorescence
analysis, colorimetry analysis, ion selective electrode analysis,
transition metal analysis and the like.
[0159] For example, the combination of high-pressure liquid
chromatography ("HPLC") and fluorescence analyses of inert
fluorescent tracers can be utilized to detect measurable amounts of
the inert tracer during cleaning of the membrane separation system
of the present invention, particularly when very low levels of the
inert tracer is used or the background fluorescence encountered
would otherwise interfere with the efficacy of fluorescence
analysis. The HPLC-fluorescence analysis method allows the inert
tracer compound to be separated from the fluid matrix and then the
inert tracer concentration can be measured.
[0160] The HPLC method can also be effectively employed to separate
an inert tracer compound from a fluid matrix for the purposes of
then employing an inert tracer-detection method other than the
fluorescence analysis. An example of this type of chromatographic
technique is described in "Techniques in Liquid Chromatography", C.
F. Simpson ed., John Wiley & Sons, New York, pp. 121-122, 1982,
incorporated herein by reference, and "Standard Method For The
Examination Of Water And Wastewater", 17th Edition, American Public
Health Association, pp. 6-9 to 6-10, 1989, incorporated herein by
reference.
[0161] With respect to colorimetry analysis, colorimetry and/or
spectrophotometry may be employed to detect and/or quantify an
inert chemical tracer. Colorimetry is a determination of a chemical
specie from its ability to absorb ultraviolet or visible light.
Colorimetric analysis techniques and the equipment that may be
employed therefor are described in U.S. Pat. No. 4,992,380, B. E.
Moriarity, J. J. Hickey, W. H. Hoy, J. E. Hoots and D. A. Johnson,
issued Feb. 12, 1991, incorporated herein by reference.
[0162] With respect to ion selective electrode analysis, an ion
selective electrode may be used to determine the concentration of
an inert chemical tracer through the direct potentiometric
measurement of specific ionic tracers in aqueous systems. An
example of an ion selective electrode tracer monitoring technique
is described in U.S. Pat. No. 4,992,380, B. E. Moriarity, J. J.
Hickey, W. H. Hoy, J. E. Hoots and D. A. Johnson, issued Feb. 12,
1991, incorporated herein by reference.
[0163] It should be appreciated that analytical techniques for
detecting and/or quantifying the presence and/or concentration of a
chemical specie without isolation thereof are within an evolving
technology. In this regard, the above survey of analytical
techniques suitable for use in detecting measurable amounts of the
inert tracer during cleaning of the membrane separation system of
the present invention may presently not even be exhaustive. Thus,
analytical techniques equivalent to the above for purposes of the
present invention may likely be developed in the future.
[0164] The methods and systems of the present invention can include
a variety of different and suitable components, process steps,
operating conditions and the like, for monitoring and/or
controlling the cleaning of membrane separation systems. In an
embodiment, the membrane cleaning methods of the present invention
include the steps of providing an inert fluorescent tracer and a
cleaning solution; adding the inert fluorescent tracer and cleaning
solution to the membrane separation system; providing a fluorometer
to detect the fluorescent signal of the inert fluorescent tracer in
the membranes separation system; and using the fluorometer to
determine an amount of the inert fluorescent tracer in the membrane
separation system during the cleaning process.
[0165] As previously discussed, a variety of different and suitable
types and amounts of inert fluorescent tracers can be utilized. It
should be appreciated that any suitable type and amount of cleaning
agent can also be utilized. In general, the cleaning agent is
utilized to remove deposits of scalants, foulants, treatment
agents, solutes and other impurities that remain within the
membrane separation system, particularly deposits on the
membrane.
[0166] The cleaning agent can be in any suitable form, preferably
in a liquid form as applied during cleaning. The cleaning agents,
whether in dry or liquid form, are typically diluted with water to
make a cleaning solution. The types of cleaning agents may vary
depending on the application, for example, the type of membrane
that is being cleaned. In this regard, the cleaners can be added at
a pH level including a high, moderate and low level. In an
embodiment, the high pH level ranges from about 8 to about 12; the
moderate pH level ranges from about 6 to about 8; and the low pH
level ranges from about 3 to about 6.
[0167] In an embodiment, the cleaners added at high pH levels
include, for example, any suitable high pH surfactant formulations
or the like; the cleaners added at moderate pH levels include, for
example, any suitable moderate pH surfactant formulations or the
like; and the cleaners added at low pH levels include, for example,
any suitable weak organic acid or combination thereof, such as
phosphoric acid, citric acid, the like and buffered versions
thereof. Other suitable cleaning agents include, for example,
strong acids, including hydrochloric acid, which are diluted to a
suitable concentration prior to use; chelants, such as EDTA; and
biocides, preferably non-oxidizing biocides. It should be
appreciated that the cleaning agents can be added to the membrane
cleaning process in any suitable amount.
[0168] As previously discussed, the membrane cleaning process of
the present invention can include a variety and number of suitable
process steps and components. In an embodiment, the membrane
cleaning process can include the step of flushing the membrane
separation system prior to adding the inert fluorescent tracer and
the cleaning solution. The membrane separation system of the
present invention can be flushed in any suitable way, such as with
an aqueous stream of permeate quality. After flushing, the inert
tracer and cleaning solution can be added together, separately
and/or as a single formulation, to the cleaning process. Once
added, the inert tracer and cleaning solution are circulated
through the membrane separation system in any suitable way.
[0169] In an embodiment, the inert tracer and/or cleaning solution
can be added to a cleaning tank prior to addition to the membrane
separation system. The cleaning tank and/or a feed system
containing cleaning chemicals can be coupled to the membrane
separation system including the membrane housings and associated
piping in any suitable way such that cleaning can be conducted
while the membrane separation system is on-line. Alternatively, the
membrane separation system can be taken off-line and at least a
portion thereof cleaned (e.g., a single stage or pass). This method
is known as "Clean-in-Place" ("CIP"). A CIP setup typically
includes a tank for mixing the cleaner (with optional heater), a
low pressure pump, and a cartridge filter. Alternatively,
individual membrane elements can be cleaned in a single element
cleaning skid equipped with its own CIP system.
[0170] In an embodiment, the membrane cleaning process of the
present invention can include the step of rinsing the membrane
after the inert tracer and cleaning solution have been circulated
during cleaning. The rinsing step can be utilized to remove any
amount of the inert tracer, cleaning solution, membrane separation
process contaminant or impurity deposits, the like or combinations
thereof. In an embodiment, the rinsing step can include the rinsing
with an aqueous stream of permeate quality.
[0171] It should be appreciated that the membrane cleaning process
or system of the present invention can include any variety and
number of suitable other components and process steps. For example,
the membrane cleaning process of the claimed invention can include
the step of soaking the membrane separation system (e.g., the
membrane) in the solution of the cleaning agent and inert tracer
for a suitable period of time subsequent to the circulation step.
The soaking step can provide an additional level of cleaning that
can facilitate the cleaning process.
[0172] In an embodiment, the present invention includes a
controller (not shown) to monitor and/or control the performance of
the membrane separation cleaning process based on the measurable
amount of inert fluorescent tracer(s). The controller can be
configured and/or adjusted in a variety of different and suitable
ways.
[0173] For example, the controller can be coupled with a detection
device (not shown) to process a detection signal (e.g., filter
noise from the signal) in order to enhance the detection of the
inert tracer. Further, the controller can be adjusted to
communicate with other components of the membrane cleaning system.
The communication can be either hard wired (e.g., electrical
communication cable), a wireless communication (e.g., wireless RF
interface), a pneumatic interface or the like.
[0174] In an embodiment, the membrane cleaning process of the
present invention can be utilized to monitor with a high degree of
selectivity, sensitivity, responsiveness and accuracy based on the
measurable amount of inert tracer a number of different process
parameters specific to membrane cleaning. The parameters include,
for example, operational parameters; chemical parameters;
mechanical parameters; a hold-up volume of the membrane cleaning
process and its effects on the concentration of the cleaning agent;
the concentration of the cleaning agent during various stages of
cleaning; such as, initial feed, circulation, soaking and/or
rinsing; like parameters; or combinations thereof. With the
monitoring capabilities based on the inert tracer detection, the
present invention can controllably adjust a variety of different
cleaning process conditions including, for example, the dosage of
cleaning agents, rinse rates, flushing agents, the like or
combinations thereof to optimize the cleaning performance.
[0175] It should be appreciated that the fluorescent monitoring
technique of the present invention can be utilized to monitor the
level of treatment agents that may remain in the membrane
separation system. By "treatment chemicals and/or agents" is meant
without limitation treatment chemicals that enhance
membrane-separation process performance, antiscalants that
retard/prevent membrane scale deposition, antifoulants that
retard/prevent membrane fouling, biodispersants, microbial-growth
inhibiting agents, such as biocides and cleaning chemicals that
remove membrane deposits.
[0176] "Deposits" is meant herein to refer to material that forms
and/or collects on surfaces of a membrane. The "amount" or
"concentration" of inert tracer is meant herein to refer to the
concentration of the inert tracer in the specified fluid in terms
of weight of the inert tracer per unit volume of the fluid, or
weight of the inert tracer per unit weight of the fluid, or some
characteristic of the inert tracer that is proportional to its
concentration in the fluid and can be correlated to a numerical
value of the inert tracer concentration in the fluid (whether or
not that correlation conversion is calculated), and can be a value
of zero or substantially zero. Thus, the process of the present
invention includes the detection of the absence of such chemical
species, at least to the limitations of the analytical method
employed.
[0177] In an embodiment, the inert tracer selected is not a visible
dye, that is, the inert tracer is a chemical specie that does not
have a strong absorption of electromagnetic radiation in the
visible region, which extends from about 4000 Angstroms to about
7000 Angstroms (from about 400 nanometers ("nm") to about 700 nm).
Preferably the tracer is chosen from a class of materials which are
excited by absorption of light and product fluorescent light
emission, where the excitation and emission light occurs at any
point within the far ultraviolet to near infrared spectral regions
(wavelengths from 200-800 nm). The relative fluorescence intensity
of the inert tracer must be such that it is detectable in the
amounts specified by product formulations (typically 2-10 ppb as
active fluorophore when dosed into the feed water stream of a
device).
[0178] Alternatively, when the tracer dye does have strong
adsorbtions in the visible spectrum, it is used in concentrations
such that it is not detectable to the naked eye. Such embodiments
may be preferred, for instance, when a membrane's percent rejection
of the tracer is less than 100 percent, and it is desirable to
produce a permeate free of color.
[0179] In some instances, it may be preferable to chose a
fluorophore which emits visible fluorescent light when excited by
UV light. This may be preferred when visual detection and/or
photographic or other imaging of the system is desired.
[0180] It should be appreciated that the present invention is
applicable to cleaning membranes in any suitable industries that
can employ membrane separation processes. For example, the
different types of industrial processes in which the method of the
present invention can be applied generally include raw water
processes, waste water processes, industrial water processes,
municipal water treatment, food and beverage processes,
pharmaceutical processes, electronic manufacturing, utility
operations, pulp and paper processes, mining and mineral processes,
transportation-related processes, textile processes, plating and
metal working processes, laundry and cleaning processes, leather
and tanning processes, and paint processes.
[0181] In particular, food and beverage processes can include, for
example, dairy processes relating to the production of cream,
low-fat milk, cheese, specialty milk products, protein isolates,
lactose manufacture, whey, casein, fat separation, and brine
recovery from salting cheese; uses relating to the beverage
industry including, for example, fruit juice, clarification,
concentration or deacidification, alcoholic beverage clarification,
alcohol removal for low-alcohol content beverages, process water;
and uses relating to sugar refining, vegetable protein processing,
vegetable oil production/processing, wet milling of grain, animal
processing (e.g., red meat, eggs, gelatin, fish and poultry),
reclamation of wash waters, food processing waste and the like.
[0182] Membrane cleaning is required in a variety of industrial
water applications, which include, but are not limited to, boiler
water production, process water purification and recycle/reuse,
softening of raw water, treatment of cooling water blow-down,
reclamation of water from papermaking processes, desalinization of
sea and brackish water for industrial and municipal use,
drinking/raw/surface water purification including, for example, the
use of membranes to exclude harmful micro-organisms from drinking
water, polishing of softened water, membrane bio-reactors, mining
and mineral process waters.
[0183] Examples of waste water treatment applications with respect
to the inert tracer monitoring methods of the present invention
include, for example, industrial waste water treatment, biological
waste treatment systems, removal of heavy metal contaminants,
polishing of tertiary effluent water, oily waste waters,
transportation-related processes (e.g., tank car wash water),
textile waste (e.g., dye, adhesives, size, oils for wool scouring,
fabric finishing oils), plating and metal working waste, laundries,
printing, leather and tanning, pulp and paper (e.g., color removal,
concentration of dilute spent sulfite liquor, lignin recovery,
recovery of paper coatings), chemicals (e.g., emulsions, latex,
pigments, paints, chemical reaction by-products), municipal waste
water treatment (e.g., sewage, industrial waste).
[0184] Other examples of membrane cleaning in industrial
applications include, for example, semiconductor rinse water
processes, production of water for injection, pharmaceutical water
including water used in enzyme production/recovery and product
formulation, and electro-coat paint processing.
EXAMPLES
[0185] The following examples are intended to be illustrative of
the present invention and to teach one of ordinary skill how to
make and use the invention. These examples are not intended to
limit the invention or its protection in any way.
Example 1
[0186] A test was conducted to demonstrate that the present
invention can be utilized to calculate the hold-up volume and
evaluate the dilution effects thereof with respect to a cleaner
solution based on a measurable amount of an inert tracer added
during cleaning.
[0187] A cleaning solution was prepared by adding 30 g of a
suitable cleaner (PermaClean PC-67 available from Ondeo Nalco
Company of Naperville, Ill.) to 20 L of water in order to make a
bulk cleaning solution that included about 0.15% of the cleaner by
weight. An inert tracer (1,3,6,8-pyrenetetrasulfonic acid,
tetrasodium salt (PTSA)), was added to the bulk solution.
Fluorescence measurement of the cleaning tank bulk solution (using
a Hitachi F-4500) indicated that about 128 ppb of the tracer were
present.
[0188] The cleaning solution was sent to a reverse osmosis ("RO")
membrane separation unit containing four 4-inch by 40-inch Osmonics
spiral wound composite membranes arranged in a 2:1:1 array, where
it was diluted with the standing water in the membranes, pressure
vessels and associated piping. After sufficient mixing, the cleaner
solution was sampled and found to contain 42.5 ppb of the tracer.
The volume of the RO system and associated piping was calculated as
follows: (C1)(V1)=(C2)(V2)
[0189] where C1 is the concentration of the bulk cleaning solution
before mixing; V1 is the volume of the cleaning solution before
mixing; C2 is the concentration of the cleaning solution after
mixing with the hold-up volume from the RO system; and V2 is the
final volume of the cleaning solution. The hold-up volume can be
calculated as follows: (128 ppb) (20 L)=(42.5 ppb) (total volume in
L) Total volume in L=60 L Hold-up (RO system) volume=total
volume-volume of bulk cleaning solution Hold up (RO system)
volume=60 L-20 L=40 L.
[0190] Likewise, the final concentration of the cleaning solution
may be calculated from the same equation where C1 and V1 are the
initial concentration and volume of the cleaner and V2 is the total
volume of the diluted solution (bulk cleaner plus hold-up volume of
the RO system). C2 is the final concentration of the dilute
cleaner. (20 L) (0.15%)=(60 L) (diluted cleaner concentration)
Diluted cleaner concentration=0.05%
[0191] As demonstrated, the present invention can be utilized to
calculate the hold-up volume with a high degree of accuracy and
immediacy based on the measurable amount of the inert tracer in the
cleaning system. This can be utilized to ensure that the proper
cleaner dosage is obtained after dilution effects. In this regard,
the present invention can be configured to controllably adjust the
dosage of cleaner to account for the dilution effects due to the
hold-up volume. Thus, membrane cleaning performance can be
enhanced.
Example 2
[0192] A series of tests were conducted to demonstrate that that
present invention can be utilized to determine an endpoint of
cleaning based on the monitoring of a measurable amount of an inert
fluorescent tracer(s) in the cleaning system.
[0193] In this example, a reverse osmosis system (as described
above in Example 1) was cleaned in accordance with an embodiment of
the present invention. A cleaning solution was prepared in the CIP
tank by adding 300 g PermaClean PC-99 to 20 L of RO permeate water
to make a bulk cleaning solution that included about 1.5% of
cleaner by weight. 2 mL of a solution containing approximately 0.1%
by weight of an inert tracer (1,3,6,8-pyrenetetrasulfonic acid,
tetrasodium salt (PTSA)), were added to the cleaning tank. After
circulating in the reverse osmosis system for approximately one
hour, the cleaner solution contained a measurable amount of inert
fluorescent tracer in the water. The concentration of the tracer in
the cleaning solution (measured with a Hitachi F-4500 fluorometer)
was 92 ppb. Table 1 below identifies the concentration of the
tracer in the rinsate over time. TABLE-US-00001 TABLE 1 Rinse Time
Tracer Percentage of (minutes) Concentration (ppb) Tracer Remaining
0 92 100 1 28.8 31.3 3 16.6 18.0 5 10.1 11.0 10 0.47 0.5 15
Non-detectable 0.0
[0194] As demonstrated in Table 1, the monitoring of the inert
tracer can be utilized to indicate when the rinsing stage is
complete (e.g., about 15 minutes as shown in Table 1). In this
regard, the amount of rinsate which is necessary to complete
rinsing can be optimally utilized. Thus, the performance of
membrane cleaning can be enhanced.
[0195] While the present invention is described above in connection
with preferred or illustrative embodiments, these embodiments are
not intended to be exhaustive or limiting of the invention. Rather,
the invention is intended to cover all alternatives, modifications
and equivalents included within its spirit and scope, as defined by
the appended claims.
* * * * *