Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02304201 2000-03-15
WO 99/14577= PCT/CA98/00871
ANALYZER FOR TEMPERATURE SENSITIVE COLLOIDAL MIXTURES
Field of the Invention
This invention relates to the application of ultraviolet-visible light
measurements for the
determination of colloidal substances in a liquid sample. More particularly,
the invention
relates to the application of light absorption and/or scattering measurements
for
determining a property of colloidal substances that undergo a temperature
dependent
phase transition.
Background of the Invention
Papermaker's demands for high speed and efficiency, flexible manufacturing,
stringent
quality standards, and environmental compatibility coupled with new
developments in
on-line process control are driving the development of new sensor technology
for the
paper machine wet-end. The need for better means for providing wet-end
chemistry
control is emphasized by recent reports that only 10% of the world's 150
newsprint paper
machines operate at above 88% efficiency and over 60 % operate under in the
low
efficiency range of below 82.5%. (Mardon, J., Chinn, G. P., O'Blenes, G.,
Robertson, G.,
Tkacz, A. Pulp and Paper Canada, Vol. 99 No. 5 pp. 43-46. (1998).
William E. Scott addressed problems related to wet-end chemistry control.
Principles of
Wet End Chemistry. Tappi Press, Atlanta, 1996. p 3. "Deposits and scale
usually arise
from out-of-control wet end chemistry. Typical examples include chemical
additive
overdosing, charge imbalances, chemical incompatibility and the shifting of
chemical
equilibria. All of these phenomena can lead to the formation of precipitates
or colloidal
aggregates that produce deposits and scale. While there are numerous
approaches to
treating the symptoms of deposits the best approach is to determine what is
out of control
and fix it."
Although variations in the composition and quantity of dissolved solids can
lead to
problems throughout the paper mill it is particularly important at the wet-end
of the paper
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machine where the colloidal chemistry must be tuned for optimal machine
performance.
It is important to gain knowledge and understanding of the relationship
between
measurements at both the point of origin (pulp mills, bleaching points) and
the point of
impact (headbox, press-section of the paper machine).
The measurement and characterization of colloidal particles distributed in a
liquid stream
is an important function in the control of industrial processes involving
heterogeneous
mixtures. Examples of such processes include pulping and papermaking, water
treatment,
brewing and food processing, chemical synthesis and manufacturing. Although
numerous
methods are available to characterize colloid size and concentration, methods
to measure
the amount of different colloids components mixed together or to rapidly
evaluate the
temperature stability of the colloid suspension are not readily available.
Measurements relating the intensity and angular dependence of scattered or
absorbed
light to the total concentration or size distribution of colloids are
available in numerous
forms. Instruments for characterizing the amount of colloidal particles that
rely on
scattering (nepholometry) and attenuation (turbidimetry) are commercially
available in
laboratory, hand-held and on-line instruments. On line turbidimeters relate a
ratio of light
detected in line and at an angle to a source to a turbidity value in Jackson
or NTU units.
Silveston, U.S. Patent No. 4,999,514 taught methods for controlling the
intensity of the
light source to provide a turbidimeter that operates over a broad range of
particle
concentrations. Kubisiak and Wilson (U.S. Patent No. 5,331,177) describe a
analog to
digital turbitimeter apparatus that provides a measure of the change in
turbidity over time.
Other, more sophisticated, methods involving the analysis of the time and
spatial
dependence of light attenuation and scattering may provide information on
particle size
distributions as taught by Strickland et (U.S. Patent No. 5,576,827 and the
patents
referenced therein). Instrumentation specifically designed for measuring
particle and
fiber size distributions in low consistency (<%) pulp suspensions by analysis
of the time
and spatial variation of scattered or absorbed light includes the BTG (British
Technology
Group) RET-5300 Retention Monitoring System. This instrument employs methods
taught by Lundqvist; Pettersson and Fladda U.S. Patent No. 4,318,180. The
available
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instruments do not have a means to differentiate concentrations of similarly
sized
colloidal pitch particles from colloidal clay particles.
In the area of pulp and paper manufacture the maintenance of a level of
stability and
removal of colloidal pitch is an important objective in the wet-end chemistry
programs.
Deposition leading to poor paper machine efficiency is a costly problem that
is addressed
through numerous strategies involving pulp processing or chemical addition.
Polymer,
clay and talc additives are used to prevent pitch accumulation that may lead
to deposition
and fouling of pulp processing and papermaking equipment. For example, Cutts
taught
one method for controlling pitch using micro-particle bentonite addition with
cationic
polymer flocculation, U.S. Patent No. 5,676,796. Another combination of using
kaolin
as inorganic colloid and poly(diallyldimethyl-ammonium chloride) cationic
polymer has
been taught by Lamar; Pratt; Weber and Roeder (U.S. Patent No. 4,964,955).
Alternatively, Dreisbach and Barton taught (U.S. Patent No. 5,266,166) a
method of
preventing pitch deposits by the addition of nonionic polymeric dispersing
agent. A
physical process for reducing wood resin pitch from wood process water
employing a
centrifuge has been taught by Allen and Lapointe (U.S. Patent No. 5,468,396).
The
teachings of this invention review the sources and problems associated with
wood resin in
paper mills and provide further information on physical methods of reducing
pitch in pulp
and paper process waters.
Chemical and physical methods of controlling pitch may be monitored by
turbidity or
Zeta or streaming potential or charge measurements. Although surface charge or
total
charge are important measures of the colloidal stability these measurements do
not
distinguish colloidal pitch from other, less problematic colloids such as
added clay.
Furthermore, turbidity may provide a means of evaluating the total amount of
colloidal
substance, but pitch colloids are not normally distinguished from other
colloids in a
turbidity measurement. Typically no instrumental means are employed to
supervise
chemical methods of controlling pitch. Despite the high cost of chemical
treatment
programs and the potential downtime caused by over or under dosing, chemical
methods
of controlling pitch are often invariant over time and substantial swings in
wet-end
chemistry.
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There is no colloidal pitch measurement available on-line. The accepted
laboratory
method of pitch analysis using microscopy was taught by Allen (Allen, L. H.,
Trans. Tech
Sect. CPPA 3(2):32 (1977)). This procedure is time consuming, as it has not
yet been
successfully automated by computerized image analysis techniques. An
instrumental
method employing a laser beam to count particles flowing through a capillary
has been
described by Eisenlauer; Hom; Ditter; Eipel; (U.S. Patent No. 4,752,131). The
laser
method, known as a pitch counter, requires expensive and specialized
instrumentation
that is not easily adopted to analysis in an industrial setting.
It is an object of the invention to provide a method of identifying and
measuring a
characteristic of a colloidal mixture.
It is a further object of this invention to provide a method and means for the
rapid
determination of an amount of colloidal pitch.
Polychromatic light passed through a colloid sample and detected at an array
of
wavelengths is a complicated function of the light absorption of the liquid,
the light
absorption of the particles, the light emission by fluorescence from dissolved
or colloidal
components and the scattering that may deflect light away from or towards the
detector.
The scattering of particles in the range of 0.1-10 times the wavelength of
light (Mie
scattering) is a complicated function of wavelength, particle size,
concentration, and
refractive index of the particles and of the medium. Hence when the absorption
of the
colloidal particles is examined we are looking at both scattering and the UV
absorbance
of the particles. The wavelength dependence will be a function of the color of
the
particles, and also the size of the particles. Mie-scattering theory may be
solved to back
out the particle size distribution from the wavelength dependence of
absorption or
scattering for a pure or well-characterized substance. But the theory and the
calculations
are complex and they are certainly can not be directly applied to analyzing
heterogeneous
industrial or pulp and paper colloids. The measurements described in this
invention
provide a means to empirically identify and measure a property related to the
particle
size, composition, and concentration of a colloidal mixture.
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Summary of the Invention
In accordance with the invention there is provided a method for identifying
and
measuring a characteristic of a colloidal mixture comprising the steps of:
irradiating at-least a first portion of the colloidal mixture with light in an
ultraviolet-visible region at a first temperature and obtaining a first
measurement of a first
wavelength within the ultraviolet-visible region, said first measurement for
obtaining a
measure of one of an absorption, emission and scattering of the first
wavelength when
said colloidal mixture is irradiated with the light;
waiting for the temperature of the colloidal mixture to change;
irradiating at least a second portion of the colloidal mixture with light in
an
ultraviolet-visible region at a second different temperature and obtaining a
second
measurement of the first wavelength within the ultraviolet-visible region;
said second
measurement for obtaining a measure of one of an absorption, emission and
scattering of
the first wavelength when said colloidal mixture is irradiated with the light;
and
determining the characteristic of the colloidal mixture from a relationship
including the first measurement and the second measurement.
In accordance with the invention there is further provided a method for
identifying and
measuring a characteristic of a colloidal mixture comprising the steps of
irradiating at least a first portion of the colloidal mixture with light in an
ultraviolet-visible region at a first temperature and obtaining at least a
first measurement
of a first and a second wavelength within the ultraviolet-visible region, said
first
measurement for obtaining one of an absorption, emission and scattering of the
first
wavelength when said colloidal mixture is irradiated with the light;
waiting for the temperature of the colloidal mixture to change;
irradiating at least a second portion of the colloidal mixture with light in
an
ultraviolet-visible region at a second different temperature and obtaining at
least a second
measurement of the first and the second wavelength within the ultraviolet-
visible region,
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said second measurement for obtaining one of an absorption, emission and
scattering of
the second wavelength when said colloidal mixture is irradiated with the
light; and
determining the characteristic of the colloidal mixture from a relationship
including a ratio of the at least first and second measurement.
In accordance with another aspect of the invention there is provided, an
apparatus for
identifying and measuring a characteristic of a colloidal mixture comprising:
filtration means for substantially removing fiber from the colloidal mixture;
detecting means for obtaining a first measurement and a second measurement of
light in an ultraviolet-visible region, said first measurement for obtaining a
measure of
one of an absorption, emission and scattering of at least a first wavelength
of the light at a
first temperature when the colloidal mixture is irradiated with the light, and
said second
measurement for obtaining a measure of one of an absorption, emission and
scattering of
the first wavelength of the light at a second different temperature when the
colloidal
mixture is irradiated with the light; and
a suitably programmed processor for determining the characteristic of the
colloidal mixture from a relationship including the first and second
measurement, said
characteristic is a function of a first or second derivative of the at least
first and second
measurement.
Brief Description of the Drawings
Exemplary embodiments of the invention will now be described in accordance
with the drawings in which:
Figure 1 presents a block diagram of an on-line sensor/apparatus for colloidal
substances
as in accordance with the invention;
Figure 2 shows a detailed schematic diagram of the filtration and backflushing
unit, a
currbackflushing apparatus for the Mott Filtration system;
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Figure 3 is a timing diagram depicting the valve sequence of the filtration
and
backflushing unit;
Figure 4 presents the UV-visible spectra of dissolved sprucelpine extractives
obtained by
filtration of a colloidal mixture at 0.45 microns;
Figure 5 presents the UV-visible spectrum of dissolved and colloidal
spruce/pine
extractives at pH 5.4;
Figure 6 shows the UV-visible difference spectrum isolating the absorbance of
the
colloidal pitch;
Figure 7 shows the UV-visible spectra of dissolved and colloidal pitch at pH
5.4 and
different temperatures;
Figure 8 shows the UV-visible difference spectrum showing the difference
between the
absorbance at 20 C and 80 C ;
Figure 9 shows a comparison of UV absorbance at different temperatures
compared as
ratios;
Figure IOa presents a plot showing the temperature dependence of the UV-
visible
absorbance at two wavelengths;
Figure I Ob presents a matrix plot showing the temperature dependence of the
UV-visible
absorbance of a mixture of wood-resin dissolved and colloidal substances at pH
11;
Figure I Oc presents a plot showing the UV absorbance at 280 nm versus
temperature
showing the first derivative absorbance-temperature relationship;
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Figure 11 shows a plot depicting the concentration dependence of the slope
(dA/dT) and
intercept from a linear regression of the absorbance of a wood-resin
suspension obtained
at 500 nm and the temperature;
Figure 12 shows a UV-visible difference spectrum from TMP (thermomechanical
pulp)
white water;
Figure 13 shows a plot depicting the temperature dependence of the absorbance
of a TMP
white water at 500 nm;
Figure 14 shows UV-visible spectra of a colloidal mixture of wood-resin with
different
amounts of added clay;
Figure 15 presents a plot showing the relationship between clay concentration
in a
pitch/clay mixture and absorbance at 500 nm at two temperatures;
Figure 16 shows a 3-D plot of the UV ratio A35o/A2so versus temperature and
concentration;
Figure 17 shows a 3-D plot of UV ratios A274/A280 versus temperature and
concentration (TDS);
Figure 18 shows a 3-D plot of UV ratios A230/A500 versus temperature and
concentration (MS); and
Figure 19 shows a 3-D plot of UV ratios A250/A280 versus temperature and
concentration (TDS).
Detailed Description of the Invention
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Figure 17 shows a 3-D plot of UV ratios A274/A230 versus temperature and
concentration
(TDS);
Figure 18 shows a 3-D plot of UV ratios A230/A500 versus temperature and
concentration
(TDS); and
Figure 19 shows a-" )-D plot of UV ratios A250/A280 versus temperature and
concentration
(TDS).
Detailed Description of the Invention
The method and the apparatus in accordance with the invention provides for on-
line
measurements of colloidal substances in a liquid sample. This invention is
particularly useful
for determining or estimating the amount of colloidal substances in pulp or
paper mill
process water or effluents.
Referring now to Figure 1, a block diagram of such an on-line sensor/apparatus
for colloidal
substances is depicted. In a preferred embodiment, the apparatus in agreement
with the
invention is controlled by a computer/processor 10 for sampling, filtration,
data acquisition,
cleaning, and temperature control.
In a preferred embodiment of the invention the processor 10 has the following
characteristics.
The processor is a Computer-Micro-AllianceTM Industrial Computer with 14 slot
chassis,
300W/ fans, 14" Industrial Rackmount monitor, and software such as LabviewTM
for
WindowsTM Development System, LabviewTM PID Control Toolkit, and PC-DIO and NI-
DAQ Software. The input/output hardware used are National InstrumentsTM AT-MIO-
16XE-
50 Multifunction IO board (ISA card), National InstrumentsTM AT-A0-6; 6
channel analog
output (ISA card) (this is for the 4-20 mA output to the temperature
controller and the
Distributed Control system), NationaIInsfrumentsTM NI DIO-24; 24 channel
digital
9 AMENDED SHEET
CA 02304201 2000-03-15
input/output (ISA card). This has all the output for the valves and input for
the proximity
sensors, and an Ocean OpticsTM ADC-500 A/D board with 500 kHz sampling
frequency.
This is for communication with the MQ-2000 spectrophotometer.
The sample tubing is shown as thick solid lines, the optical fibre is shown as
thick dashed
lines, the sequence control is shown as thin dashed lines, and the water flow
is shown as thin
solid lines. The processor 10 is connected to the sample manifold 12 for
controlling the
operation of a valve or a plurality of valves (not shown). In a preferred
embodiment, six ball
valves are actuated in sequence by the processor 10. The sample manifold 12
allows a
plurality of water or pulp slurry samples to be sampled on-line from a
process. The liquid
sample is then delivered from the sample manifold 12 to the filtration and
backflushing unit
(FBU) 14. The FBU 14 filters the liquid sample to provide a fibre-free liquid
sample and
returns the remaining sample back into the process. The operation of this FBU
14 is also
controlled by the processor 10 and is explained in more detail below, see
Figure 2.
The usefulness of the invention could be extended by extraction of liquid
samples from a
high consistency pulp slurry before final removal of the fiber in the FBU 14.
The FBU 14 delivers the fibre-free liquid sample to a sample manager and
cleaning unit
(SMCU) 16. The operation of the SMCU 16 is controlled by the processor 12. In
one mode
of operation the SMCU 16 delivers the liquid sample to a temperature
controlled dual UV
cell holder (DUVCH) 18 for obtaining a UV measurement and in another mode of
operation
it delivers a cleaning fluid to the temperature controlled DUVCH 18 for
cleaning said
DUVCH. Both, the liquid sample and the cleaning fluid are delivered to the
DUVCH 18 by
means of a pump, such as a Cole PalmerTM variable speed peristaltic pump P-
77962-10.
In a preferred embodiment, the DUVCH 18 has a SciencetechTM custom-built cell
holder and
a temperature control unit with a Peltier Effect thermoelectric heat pump.
This means that
the DUVCH allows for UV measurements to be taken at a plurality of
temperatures.
10 AMENDED SHEET
CA 02304201 2000-03-15
Alternatively, the temperature in the DUVCH 18 is controlled by a water flow
system as
shown in Figure 1. The DUVCH has 2 UV cells, one 1.0 mm flow-through quartz UV
cell
(UV region, short wavelength)and another 10.0 mm flow-through quartz UV cell
(visible
region, long wavelength). This is desired since the absorbance in the visible
region is very
low and requires a cell having a longer path length and vice versa, the
absorbance in the UV
region is very intense and a cell having a shorter path length is more
desirable. The
processor 10 controls the operation of a temperature controller 20. This
temperature
controller 20 is connected to the DUVCH 18 for controlling the temperature
therein as. One
possible temperature controller for use with this invention is a Wavelength
ElectronicsTM
Model LFI-3526 Temperature Controller.
The DUVCH 18 is connected to a UV-visible light source (UV-vis LS) 22, such as
a
Deuterium-Tungsten combination light source, and a spectrophotometer 24, such
as a Rack
Mount Ocean OpticsTM spectrometer, through optical fibre cables suitable for
good
transmission of light at 230 nm. The UV-vis LS 22 irradiates the DUVCH 18 for
obtaining a
UV measurement of the liquid sample. The spectrophotometer 24 measures the UV
light
upon passing the liquid sample. The optical system, i.e. the UV-vis LS 22 and
the
spectrophotometer 24 are controlled by a LabviewTM VI software.
The processor 10, the DUVCH 18, the temperature controller 20, the UV-vis LS
22, and the
spectrophotometer 24 are placed within a constant temperature enclosure (CTE)
26, a
Hoffmann EnclosureTM with air conditioning for temperature control. The CTE 26
prevents
the apparatus from being effected by unwanted fluctuations in the temperature.
This is done
to prevent a possible damage to the processor 10 from excessive heat or
humidity in
industrial applications, such as in pulp and paper processing, and to obtain
reproducible
results. The CTE 26 is needed as in accordance with an embodiment of the
invention
because the response of spectrophotometer detector elements varies with
temperature.
11 AME14DFD SHtt-;-
CA 02304201 2000-03-15
Exemplary Detector Specifications:
Detector: 2048-element linear silicon CCD array
CCD elements: 2048 elements @ 12.5 mm x 200 mm per element
Well depth (@600 run): 160,000 photons
Sensitivity (estimated):86 photons/count; 2.9 x 10-17 joule/count;
2.9 x 10-17 watts/count (for 1-second integration)
Effective range: 200-1100 nm
Integration time: 4 milliseconds to 60 seconds (with 500 kHz A/D card)
20 milliseconds to 60 seconds (with 100 kHz PCMCIA A/D card)
(shorter integration times available with custom electronic interface)
Exemplary Optics Specifications:
Gratings: multiple grating choices, optimized for UV, VIS or Shortwave NIR
Slits: 10, 25, 50, 100, 200 mm widths (slit height is 1000 mm); alternative
option is no slit (optical fiber is entrance aperture)
Order-sorting: single-piece, multi-bandpass detector coating for applications
from - 200-850 nm
(available only with 600-line gratings) or Schott glass longpass filters
(installed or loose)
Resolution: -0.3 nm-10.0 nm FWHM (depends on groove density of grating and
diameter
of fiber or width of slit)
Stray light: < 0.05% at 600 nm; < 0.10% at 435 nm
Fiber optic connector: SMA 905 to single-strand optical fiber (0.22 NA)
Exemplary Rack-mount Housing Specifications:
Width: 17-5/8"
Depth: 10-1/6"
Weight: -12 lb.
* With 8 spectrometer channels installed.
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AME Fn _,
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Exemplary Computer and Data Acquisition:
a) Computer-Micro-AllianceTM Industrial Computer with 14 slot chassis, 300W/
fans,
b) Monitor. 14" Industrial Rackmount monitor.
c) software
i) LabviewTM for Windows Development System
ii) LabviewTM PID Control Toolkit
iii) PC-DIO and NI-DAQ Software
d) input/output hardware
i) National InstrumentsTM AT-MIO-16XE-50 Multifunction IO board (ISA card)
ii) National InstrumentsTM AT-A0-6; 6 channel analog output (ISA card) (this
is for
the 4-20 mA output to the temperature controller and the Distributed Control
system)
iii) National InstrumentsTM NI DIO-24; 24 channel digital input/output (ISA
card).
(This has all the output for valves and input for the proximity sensors.)
iv) Ocean OpticsTM ADC-500. A/D board with 500 kHz sampling frequency. This is
for communication with the MQ-2000 spectrophotometer.
Now turning to Figure 2, the FBU 14 is presented in a more detailed manner.
The FBU in
Figure 2 is a backflushing apparatus for the MottTM Filtration system. The
Filtration and
backflushing unit provides a fiber-free liquid sample. The colloidal liquid is
separated from
the fiber by cross-flow filtration using a 5 or 10 micron MottTM sintered
metal filter 109.
Tangential flow through the filter 109 is greater than 20 liters/minute and
preferably >40
liters/min. The flow across the filter 109 is 10-200 ml/minute. The
backflushing unit allows
a reservoir 112 to fill with filtrate. Then the sample valve 104 is opened for
2 seconds to
deliver 1-20 ml of colloidal sample to the DUVCH 18. The sampling period is
followed by a
delay period during which the filter 109 is closed and temperature dependent
UV
measurements are made by the spectrophotometer 24 using the recently obtained
sample.
After the measuring delay the reservoir 112 is purged by opening an air valve
102 (labeled
purge air in) and backpulsing the filtrate backwards through the filter 109
for a specified
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. .
-= .
period of at least 1 second but no longer than until the filtrate reaches the
bottom proximity
sensor 106. Backpulse pressure at pressure transmitter 107 is preferably
greater than normal
pressure measured at pressure transmitter 108. The bottom proximity sensor 106
relays a
signal to the system controller/processor 10 to close the purge air valve 102
and open the
reservoir vent valve 101. At this point the filter valve 103 is opened and the
reservoir 112
fills until the top proximity sensor 105 detects the filtrate. The full sample
valve 104
immediately opens to obtain another sample of the colloid material.
The valve sequence is shown in Figure 3 which is a detailed sketch of the
operation of valves
101-104, the top proximity sensor 105, the bottom proximity sensor106, the
filtrate pressure
sensor, and the inlet pressure sensor for the various steps in a filtration
and measurement,
cycle, such as filling, sampling, measurement, and purge.
There are a number of methods of obtaining a fiber-free colloidal sample. In a
preferred
methods a sample is obtained without filtering the liquid through a pulp mat
or filter cake. It
has been found that a pulp mat will significantly change the sample.
Centrifugal methods are
ideal, but continuous solids ejecting centrifuges are expensive. A sand filter
will remove
fiber, but the backwashing cycle would have to be frequent to prevent
filtration through a
fiber mat at the top of the sand. Backwashing would have to be done with the
filtrate.
The characteristics of the FBU are as follows:
a) filters: MottTM 7000-1/2-24-5.0 or MottTM 7000-1/2-24-10.0 (10 micron)
b) valves (stainless steel):
i) 4 '/2" NPT, 24 volt solenoid, normally closed, TelktronTM
ii) 3 3/8 tubing, ball valve, pressure actuated WhiteyTM 131 SR, normally
closed,
stainless steel
iii) 1 3/8 tubing, ball valve, pressure actuated WhiteyTM 131 SR, normally
open,
stainless steel
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AMENDED SHEET
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c) sensors: i) pressure sensor 107 and 108, 0-60 psi Cole ParmerTM Instrument
Co.
Model 68001, 4-20 mA output
ii) proximity sensor 105 and 106, DwyerTM capacitive proximity switch model
PSC20103
Colloidal components are normally measured by turbidity or light-scattering
techniques to
give an overall composition or amount of colloidal components. However,
colloidal
substances include inorganic colloids, such as clays, insoluble salts (CaSO4),
or fillers, and
organic colloids, such as pitch. Prior art techniques cannot readily
distinguish between these
two classes of colloidal matter. Various forms of turbidity measurements,
light scattering,
and electrokinetic separation are used to measure a quantity of colloidal
particles. Using
hydrodynamic, electrokinetic separation or advanced light scattering
techniques some
information can be obtained about the particle size distribution. These
methods are not
suitable to distinguish chemically between the different types of particles.
The method and
the apparatus in accordance with the invention allow to empirically identify
and measure a
property related to the size, composition, and concentration of a colloidal
mixture.
It should be recognized that pitch is a generic term and the composition of an
individual pitch
particle may vary from relatively pure mixtures of fresh resin and fatty acids
to
heterogeneous agglomerations of wood extractives, wood-derived lignin and
hemicellulose,
salt, cationic polymer and filler particle. The degree that temperature will
alter the equilibria
between colloidal pitch and dissolved substances is a complicated function of
solution
conditions and the composition of the pitch particle. For example, our
laboratory tests have
shown that temperature changes on the same mixture at different pH values
produce a
different Dabsorbanc relationship. Furthermore, it has been reported that
Otemperature
hemicellulose components may stabilize wood colloidal resin (Sundberg, K;
Thornton, J.;
Holmbom, B.; and Ekman, R. Journal of Pulp and Paper Science Vol. 22 Number 7,
1996,
Pp J226-J230. Effects of wood polysaccharides on the stability of colloidal
wood resin). We
have found, however,.- that variatiows-of-pH, and-ionic strength that
typically occur in a pulp
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4. Defining an relative amount of colloidal pitch as a function of a
concentration
determined by the dA/dT method and the concentration determined by the total
absorbance or turbidity at a given temperature; and
5. A.system that has been characterized is simply analyzed following steps 2,
3 and 4.
And, in accordance with an embodiment of the invention, the steps in the
identification of
a transition temperature or a metastable mixture include:
1. Identification of a suitable wavelengths for the analysis by identifying a
region with
maximum and minimum change in absorbance with respect to temperature;
2. Measurement of the dA/dT, and d2A/dT2 to determine the point of the minimum
rate
of change in the slope. The point at which d2A/dT2 is zero is the temperature
that is
characteristic of the phase change;
3. Plot of the ratio of the absorbance at two wavelengths representing maximum
and
minimum values in the difference or ratio spectra obtained comparison of the
absorbance
at one temperature from the absorbance at another temperature. This plot
provides a
means to emphasize the change in the optical properties of the colloid
relative to the
composition of the mixture as a whole. A change in the slope of this plot
indicates the
initiation or termination of a phase transition.
For example, a t-butyl ether extract of wood resin is obtained by successive
extraction of
a sample of white water obtained from a spruce/pine thermomechanical pulp
mill. The
extract is concentrated and then the resin is redispersed in pH 4.85 acetic
acid aqueous
buffer by sonication. A stock mixture of the dissolved and colloidal wood
resin is diluted
with buffer to six different concentrations. The UV-visible absorbance spectra
of the
colloidal mixture are obtained directly from these mixtures at room
temperature and are
presented in Figure 5. The colloidal mixtures of different concentrations are
filtered with
a 0.45 micron syringe filter to obtain solutions of dissolved wood resin and
their UV-
visible spectra are shown in Figure 4. The signal from dissolved and colloidal
matter
followed the expected linear relationship with concentration. The attenuation
of the
signal due to the colloidal substance alone is obtained by subtraction of the
signal from
the filtered and unfiltered samples. An example for this is presented in
Figure 6. In this
example, the signal above 350 rim is taken to primarily represent turbidity or
attenuation
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of the light due to the Mie scattering of the particles. The peaks at 230 and
280 nm
indicate that the chromophore containing wood extractives in the colloidal
particles
adsorbs light.
The temperature dependence of wood resin colloidal mixtures were characterized
at
different pH values, ionic strengths values, and with different amounts of
clay relative to
pitch. An example of the temperature dependence of the UV-visible spectrum of
wood
resin colloid mixtures is shown in Figure 7. The wavelength dependence of the
temperature variation of the UV-visible spectrum can be examined as a
difference or a
ratio of the spectra taken at two wavelengths as shown in Figure 8 or Figure
9. Both
methods show a similar pattern. In the UV region the changes due to a decrease
in
scattering are compensated by an increase in the UV absorbance. This is likely
due to the
greater absorbance of the dissolved materials compared to the colloidal
materials.
The temperature dependence of the UV absorbance of the extracted pitch is
plotted for
two wavelengths in Figure I Oa. The variation at the 242 nm minimum in the
difference
spectrum shown in Figure 8 and 9 amounts to less than 3% of the total
absorbance at that
wavelength. On the other hand, the variation at 500 nm is approximately 25% of
the
absorbance at that wavelength. The variation of the absorbance at 500 nm is
substantially
linear with changes in temperature ranges between 40 C and 80 C. It is within
this linear
region that two measurements provide a slope (dA/dT) that is proportional to
the
concentration of colloidal pitch. The slope (dA500 /dT) and intercept lim Abss
are
temperature--O
calculated from the temperature dependence of multiple concentrations of
colloidal pitch.
The slope (dA/dT) and the intercept plotted against the relative concentration
are shown
in Figure 11. These original results demonstrate, for the first time, that the
temperature
variation of the absorbance or turbidity of colloidal pitch is proportional to
the amount of
pitch in the mixture. The results showing the variation of the intercept with
concentration
confirm the expected result that the turbidity is a function of the colloid
concentration.
There, is a small non-linearity of the dA/dT with respect to concentration at
unusually
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high concentrations. Measurements are normally made in the concentration
region that
produces dA/dT values between 0.0 and -0.0025.
Multiple regressions fit to temperature and concentration for absorbance
measurements
made for UV data at eight representative wavelengths. Exemplary regressions
are
presented below:
A500 =0.033499 +.152465*c -.0011 80*T-.00465 1 *c2
A450=0=04060 + =195378*c -.001387*T-.004470*c2
A350=0.084676 + .674637*c -.002693*T-.006859*c2
A300=0.073323 + 1.584808*c -.002703*T-.013407*c2
A280=0.26034 + 3.054065*c -.005966*T
A274=0.22676 + 3.007551 *c -.006236*T-.019463*c2
A250=0.05867+ 2.893070*c-.003785*T-.039531*c2
A230=0.60932 + 7.328961 *c-.019106*T-.141523*c2
Multiple regression for UV absorbance at selected wavelengths for TMP white
water
pitch. The equations are a function of concentration, temperature and the
square of the
concentration. Regression correlation coefficients of >0.99 were found. The
coefficient
for the concentration squared indicates interaction between components similar
to a
second virial coefficient.
In order to make a colloid concentration measurement using this technique a
temperature
change must significantly perturb an equilibrium between dissolved and
colloidal
components. The dissolved and colloidal components must have measurably
different
properties. The material, solution conditions determine if such a change
occurs and the
temperature range and wavelength must be selected to best measure the phase
change.
The optimal wavelength is selected by choosing a maximum or minimum from the
ratio
or difference of two spectra obtained at two temperatures as shown in figures
8 and 9.
The optimal temperature range is chosen by identification of a temperature
region around
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a zero point in the second derivative of the absorbance with respect to
temperature. An
example of the method of selection of a temperature region follows.
Figure I Ob shows a matrix plot of the temperature variation of the UV
absorbance at pH
11Ø Plots A-D show a variation in the shape of the curves of the absorbance
at different
wavelengths with respect to temperature (abscissa). At this mixture there is a
relatively
complete transition between the dissolved and colloidal components. In
particular, the
slope falls off significantly at the temperature extremes for the absorbance
values at 280
nm. Plot D in figure l Ob is examined in more detail in Figure I Oc.
Inspection of the
graph indicates that two measurements made in the region between 20 C and 40 C
would
give different results than measurements made between 40 C and 60 C. The best
region
to measure the transition between the colloidal and liquid state is selected
from the region
where the slope is most constant. This occurs around the central point in the
transition
that is defined by the minimum in the first derivative function plotted in
figure 10c. This
minimum in the first derivative is the zero point in the second derivative
function that
occurs, for the data shown in figure l Oc at 50 C. Secondary zero points in
the second
derivative occur around 23 C and 74 C but these are small regions with very
small
changes in the absorbance.
The matrix plot presented in Figure I Ob provides further means for the
identification of
phase changes in colloidal mixtures. In six plots (F, G, H, J, K, M) the
absorbance at one
wavelength is plotted against another. The linear relationship in plot G shows-
that the
component which provides the dominant temperature variation contributes to
both of
these wavelengths at all temperatures. Plot H, on the other hand shows that
the relative
change absorbance is linear in two regions, but the relationship appears to
change in an
intermediate region. The relative absorbance at two wavelengths may be
captured in a
ratio as is plotted against temperature in plot E. At the simplest level the
ratio of
absorbance values provides a means to inspect the relative change in one
component with
respect to the change in another component. The linear region with little
slope in the
central portion of the plot corresponds to a temperature region where changes
in the
absorbance at 500 nm directly correspond with a change in the absorbance at
280 nm.
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Additional techniques to obtain accurate and reproducible measurements are
learned
through experience of applying these measurement techniques at a paper mill.
Trial
experiments were conducted at a paper mill using white water manually filtered
on a
Whatman 41 filter paper. This filter paper has a nominal size cut-off of
approximately 20
microns. The results are exemplified by the difference spectrum in Figure 12.
This
spectrum was obtained with a 1 mm UV cell on a Cary 1 spectrophotometer. This
spectrum shows the same minimum points as the difference spectrum in Figures 8
and 9.
However, in this case the relative absorbance at long wavelengths is much
lower. The
difference spectrum demonstrates that the temperature change necessary to get
accurate
measurements must be at least 30 degrees C. Furthermore, a long path UV cell
(10 or 20
mm) is used to increase the accuracy of the measurements made at long
wavelengths.
Scatter in the mill data required to obtain dA/dT is shown in the Figure 13.
Figure 14 shows the spectral effects of adding multiples of a clay
concentration to a
colloidal pitch solution. The absorbance changes are nearly linear with clay
concentration and relatively monotonic with wavelength. Clay and fillers
scatter light
well and absorb little light compared to colloidal pitch.
Figure 15 shows absorbance at 500 nm for different concentrations of clay in a
colloidal
pitch mixture. The total absorbance is linear with clay concentration. The
temperature
variation, representing the constant amount of pitch, is shown by the gap
between the
absorbance at 20 C and 80 C. Although the size of the gap appears to increase
slightly at
higher clay concentrations, it is relatively constant given the dramatic range
in clay
concentrations. Normal variation in clay or filler concentration in a paper
mill is usually
no more than a factor of two. The data in Figures 14 and 15 may be used with a
measure
of the temperature dependence to first calculate the total amount of the
colloids and then
calculate the amount of colloidal pitch and finally calculate the difference
that constitutes
colloidal clay and other components that are insensitive to transitions
between the
colloidal and dissolved phases in the measured temperature range.
.30
In a paper mill situation, it is advantageous to make maximum use of carrying
capacity of
water resources and still minimize the risk of sudden or catastrophic wet-end
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events that lead to deposits and machine fouling associated with poor
efficiency and
runability. A measurement that provides the paper-maker a better means of
predicting the
sensitivity of the white water system upsets may be applied to circumvent
expensive
episodes of deposition on the paper machine. Among diverse causes of wet-end.
chemistry upsets the sudden variation in white water temperature leading to a
wet-end
upset is known among papermakers as temperature shock. A sudden change in
white
water temperature may occur when unusual quantities of fresh water are brought
into the
water system. In an embodiment, this invention provides a measure of the
susceptibility
of the water system to a temperature shock. UV ratios track critical behavior
better than
UV absorbance.
In another embodiment in agreement with the invention concentrations of
dissolved and
colloidal substances that may lead to deposition events are identified. The
intention of
the papermaker is thus to avoid a metastable state where dissolved components
may
suddenly come out with a minor fluctuation in operating conditions.
Figures 8, 9, 1Ob, and 12 all show that spectral changes occurring pitch phase
transitions
are rich sources of information about the transitions occurring. Comparing
absorbance
values at different wavelengths provides a means of comparing the amount of
one
component to another component. Examples of three-dimensional plots of
temperature,
relative dissolved and colloidal substances are provided in Figures 16 to 19.
Although for
the most part UV-visible absorbance shows linear or nearly linear
relationships with
concentration (TDS) and temperature, the use of UV ratios provides insight
into discrete
changes in the state of the dissolved and colloidal substances. Figure 16
shows the ratio
A350A2so versus temperature and concentration. The most pronounced change
exhibited
in this plot is below I mg/ml. The relative absence of slope in this graph at
high
temperatures suggests a change of state that is more discrete than the gradual
change at
low temperature. The UV ratio A330/A28o appears to be a comparison of the
contributions
of turbidity and UV absorbance. Figure 17 shows UV ratios of A274/A280 versus
temperature and concentration (TDS). At high concentrations this ratio is
essentially
constant. At low concentrations the ratio decreases. This is interpreted as a
red shift due
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to the comparative effects of solvation in water versus solvation in pitch.
Figure 18
shows UV ratios of A230/A500 versus temperature and concentration (TDS). At
high
concentrations this ratio is essentially constant. Scattering adds
proportionately to both
long and short wavelengths. At low concentrations the ratio increases as more
extractives
are UV absorbing in the dissolved state but not colloidal. Figure 19 shows UV
ratios of
A250/A280 versus temperature and concentration (TDS). At high concentrations
this
ratio is essentially constant indicating no substantial change in the
ionization. At low
concentrations the ratio increases as more extractives become ionized as they
dissolve.
At concentrations above a critical concentration the UV ratio is essentially
constant.
Ratios that are important include ratios that emphasize ionization (A250/A280,
A300/A280); solvent shifts (A300/A292) and a comparison between scattered and
UV
absorbed light (A500/A230). The absorbance at 292 nm is essentially constant
as a
function of colloidal or dissolved state.
A scan of selected wavelength ratios versus temperature and identification of
points at
which the slope changes will identify temperatures that correspond to a
transition between
dissolved and colloidal components. These temperatures may be used as guides
of the
system stability at a different temperature.
The above-described embodiments of the invention are intended to be examples
of the
present invention and numerous modifications, variations, and adaptations may
be made
to the particular embodiments of the invention without departing from the
scope and spirit
of the invention, which is defined in the claims.
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