U.S. patent application number 12/277206 was filed with the patent office on 2010-07-29 for nanotechnology-driven, computer-controlled, highly sustainable process for making paper and board.
Invention is credited to John G. Penniman.
Application Number | 20100186916 12/277206 |
Document ID | / |
Family ID | 42353216 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186916 |
Kind Code |
A1 |
Penniman; John G. |
July 29, 2010 |
NANOTECHNOLOGY-DRIVEN, COMPUTER-CONTROLLED, HIGHLY SUSTAINABLE
PROCESS FOR MAKING PAPER AND BOARD
Abstract
In simple form the stock comprises water, cellulose fiber,
pigment or filler, a cationic, charge-neutralizing chemical, and an
anionic nanoparticle. The process introduces stock components in
proper order, while homogenizing them towards molecular dimensions
with low surface tension catalyst and vigorous mixing. The amount
of catalyst is optimized for stock dispersion, and formation of an
azeotrope in the dryer section. A classical nanostructure is
formed. Solids exiting the press increase by as much as 6-7%; water
removal energy in the dryer section is reduced in a 40-60% range.
Homogeneity is maximized by controlling the standard deviation of a
convenient process parameter. The system is controlled at zero zeta
potential, at the specific filtration resistance level required for
maximum productivity. Chemical usage is reduced by at least an
order of magnitude. The process is highly sustainable.
Inventors: |
Penniman; John G.;
(Larchmont, NY) |
Correspondence
Address: |
LUCAS & MERCANTI, LLP
475 PARK AVENUE SOUTH, 15TH FLOOR
NEW YORK
NY
10016
US
|
Family ID: |
42353216 |
Appl. No.: |
12/277206 |
Filed: |
November 24, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60991059 |
Nov 29, 2007 |
|
|
|
Current U.S.
Class: |
162/173 |
Current CPC
Class: |
D21H 17/04 20130101;
D21H 17/60 20130101; D21H 21/10 20130101 |
Class at
Publication: |
162/173 |
International
Class: |
D21H 17/04 20060101
D21H017/04 |
Claims
1. A method for papermaking, comprising: preparing a stock of water
and pulp; adding iso-paraffin to the stock, the iso-paraffin having
a boiling point of 150.degree. C. or greater, and a surface tension
below 30 dynes/cm.sup.2. forming a web of stock on a wire mesh;
pressing the web of stock including the iso-paraffin to remove
water; and drying the pressed web of stock to form paper.
2. The method of claim 1, wherein the iso-paraffin is one or more
iso-paraffins selected from the group consisting of ISOPAR G,
ISOPAR H, ISOPAR L. ISOPAR M and ISOPAR V; produced by
Exxon-Mobil.
3. The method of claim 1, wherein the addition of iso-paraffin to
the stock is performed before the formation of the web.
4. The method of claim 1, wherein the addition of iso-paraffin to
the stock is performed on the web of the stock before the pressing
of the web.
5. The method of claim 3, wherein the addition of iso-paraffin
further comprises: forming a mixture of iso-paraffin and one or
more additives selected from the group consisting of fillers,
sizes, coloring agents, cationic chemicals, and anionic
chemicals.
6. The method of claim 5, wherein the formation of the mixture is
performed by a high shear mixer, preferably utilizing ultrasonic
energy.
7. The method of claim 5, wherein an in-line static mixer is
employed to mix the chemicals homogeneously with the stock.
8. The method of claim 7, wherein a function of homogeneity is
measured by first, for example, measuring the specific conductance,
then calculating and outputting its standard deviation, and using
this value to adjust the upstream parameters such as mixing energy
input and chemical concentration, to maximize homogeneity by
minimizing the amount of standard deviation.
9. The method of claim 4, wherein the addition of iso-paraffin is
performed by spraying iso-paraffin on the web.
10. The method of claim 7, wherein the dispersion of iso-paraffin
is created by mixing chemicals and iso-paraffin in a high shear
mixer, preferably with ultrasonic energy.
11. The method of claim 1, wherein the iso-paraffin is present in
the stock in an amount of about 0.05 to 10% by weight stock.
12. The method of claim 1, wherein the amount of iso-paraffin is
about 0.5 to 2% by weight stock.
13. The method of claim 1 further comprising: adding cationic
chemicals and anionic chemicals to the stock prior to forming a web
of the stock, wherein the anionic chemical addition point is
sufficiently downstream of the cationic chemicals that stock
homogeneity is attained prior to reaching the anionic chemical
addition point; determining the zeta potential of recirculating
stock from a headbox of a paper making apparatus.
14. The method of claim 13 wherein the cationic chemicals are added
simultaneously with adding the iso-paraffin to the stock with
appropriate cationic functional chemical additives mixed
thoroughly; and the anionic chemicals are likewise added
simultaneously, preferably with an additional increment of
iso-paraffin in the stock, with appropriate anionic chemical
additives and mixed thoroughly; and the result is an increase in
the functional chemical additive performance of at least one order
of magnitude.
15. The method of claim 14 comprising controlling the zeta
potential of stock recirculating from a headbox at zero millivolts
by use of a computer programmed to balance the feed rates of
cationic and anionic process chemicals to attain and maintain a
continuous headbox stock value of zero millivolts.
16. The method of claim 15 in which the computer is programmed to
maximize flow rates of both cationic and anionic process chemicals
while maintaining zero zeta potential in the head box, thereby
maximizing productivity.
17. A stock used for making paper comprising: water, pulp and
iso-paraffin preferably having a boiling point of 150.degree. C. or
greater and a surface tension below 30 dynes/cm.sup.2.
18. The stock of claim 14 further comprising: one or more additives
selected from the group consisting of fillers, sizes, coloring
agents, cationic and anionic chemicals, including functional
chemical additives and process chemical additives.
19. The stock of claim 16 wherein the iso-paraffin is one or more
iso-paraffins selected from the group consisting of ISOPAR G,
ISOPAR H, ISOPAR L. ISOPAR M and ISOPAR V.
20. The stock of claim 16 wherein the iso-paraffin is present in an
amount of about 0.05 to 2% by weight stock, and serves to improve
water removal on the wet end and in the press section, thereby
increasing energy efficiency.
21. The stock of claim 16 wherein the iso-paraffin is present in an
amount of about 2.0 to 20% by weight of stock, and serves
additionally to greatly improve dryer energy efficiency, reducing
it by upwards of 50%.
22. The finished product of claim 16 which is re-processed as
"broke", wherein the addition of a cationic charge neutralizing
chemical, such as a polydadmac, disperses the product particles to
the original primary composition, such as fibers, fillers and
fines, making the broke easy to re-process and the product highly
sustainable.
Description
[0001] This application is a submission to take priority on the
provisional patent application, number 60/991059 dated Nov. 29,
2007.
FIELD OF THE INVENTION
[0002] This invention relates to the paper making process, and more
specifically, paper, tissue, towel and board.
BACKGROUND OF THE INVENTION
[0003] The paper making process can be divided into four portions,
a stock preparation portion, a wet end portion, a press portion,
and a dry end portion. The stock preparation portion provides
equipment and working space for collecting and preparing the pulp,
chemicals and other additives. The wet end portion entails
formation of stock from water, pulp and chemical additives such as
fillers, sizes, coloring agents, and cationic chemicals and anionic
chemicals which adjust the zeta potential of the stock; control
retention and drainage; and control formation of a web of stock on
a wire mesh, and optimize physical properties of the finished
product for its intended use. The press portion entails pressing
the web of stock, supported on a continuous strip of felt, in a
series of roller pairs to remove water from the web. The dry end
portion entails drying the pressed web on steam-heated drier
rollers to further remove water and produce a paper product. Water
is recovered from the web forming step, the pressing step and the
drying step, and is recycled.
[0004] A key failure that the inventor has identified in the paper
making process is the lack of homogeneity of the stock. Increasing
stock homogeneity in the wet end will result in enhanced process
cost efficiency, and a significant increase in performance of the
finished product.
[0005] Additionally, one of the problems faced in the paper making
process is the removal of water during the pressing and drying
steps. There is a need to increase the efficiency of water removal
from the web in the last three steps, wet end, pressing and
drying.
[0006] Finally, lack of computer control results in what we have
termed "gratuitous chemical consumption." Because on-line
measurement is not used to control functional chemical additive
usage, and because of the inherent variabilities of the wet end
papermaking process, chemical usage has a strong tendency to creep
up, to ensure that performance reaches at least the prescribed
minimum. Excess consumption can easily reach an order of magnitude.
Control of the head box zeta potential at zero millivolts can
immediately eliminate this excess consumption, and additionally
provide unprecedented uniformity of quality at the highest quality
level and lowest raw material usage.
SUMMARY OF THE INVENTION
[0007] It has been discovered that the homogeneity of the stock can
be improved; cost efficiency of chemicals can be improved; and that
the efficiency of water removal from the web can be increased by
the addition of a synthetic isoparaffinic petroleum hydrocarbon to
the stock.
[0008] Additionally, it has been discovered that by measuring the
zeta potential of the recirculating stock from the web forming
step; and by adding cationic chemicals such as a
charge-neutralizing chemical plus cationic functional chemicals to
enhance physical properties, followed by mixing to homogeneity; and
in a second step, adding a sufficient amount of anionic
nanoparticle, plus any anionic functional chemicals that may be
needed to improve physical properties, in amount sufficient to
obtain a zeta potential of zero in the stock, increases the
retention cellulose fines, fillers and of the various chemicals
added to the stock; maximizes drainage of the water from the web as
well as provides increased formation and strength of the formed
paper.
[0009] Broadly, the present invention can be defined as a paper
making process, comprising: [0010] preparing a stock comprising
water and pulp; [0011] mixing synthetic iso-paraffinic petroleum
hydrocarbon with cationic chemicals and adding to the stock, the
iso-paraffin having a boiling point of 150.degree. C. or greater,
[0012] in two stages, the first with cationic chemicals; [0013]
pre-mixing the cationic chemicals and hydrocarbon;
[0014] applying high positive displacement pump pressure, up to
5000 Ibs per square inch or more; [0015] circulating the mixture
under high pressure through a high shear mixer, preferably of an
ultrasonic nature; [0016] injecting the ultrasonicated mixture into
the stock at a 90 degree angle to the direction of wet end machine
flow; [0017] further mixing the ultrasonicated mixture with the
stock, using in-line static mixers well known to those skilled in
the art; [0018] measuring the specific conductance of the flowing
stock, calculating and outputting the standard deviation as a
function of homogeneity; [0019] adjusting the upstream parameters
such as positive displacement pump pressure, ultrasonication energy
and chemical concentration, respectively, so as to maintain
homogeneity at an appropriate level; [0020] followed by a second
stage of iso-paraffin mixed with anionic chemicals which is a
mirror image of the first stage, except that after an appropriate
level of homogeneity is reached on start-up, the flow rates of
cationic and anionic chemicals are balanced to obtain zero zeta
potential.
[0021] The remainder of the process comprises: [0022] forming a web
of stock on a wire mesh; [0023] pressing the web of stock to remove
water; [0024] and drying the pressed web of stock to form
paper.
[0025] A unique advantage of this aspect of the invention is that
productivity can be maximized by increasing the flow rates of both
the cationic and anionic components in tandem, while maintaining
zero zeta potential. Maximum productivity may thereby be achieved,
subject only to mechanical limitations such as machine speed.
[0026] Preferably, the synthetic petroleum iso-paraffinic
hydrocarbon is one or more iso-paraffins selected from the group
consisting of ISOPAR G, ISOPAR H, ISOPAR K, ISOPAR L, ISOPAR M, and
ISOPAR V. Each iso-paraffin is a fluid at room temperature and
pressure.
[0027] The addition of iso-paraffin to the stock is accomplished by
adding the isoparaffin to the stock on the wet end, prior to web
formation. It is preferred that the iso-paraffin is added to the
stock prior to formation of the web and more preferably the
iso-paraffin is added to the stock as a mixture with the
conventional chemical additives and homogenized down to molecular
dimensions with high shear mixing such as ultrasonic energy; in the
first instance combined with cationic chemicals, and in the second
instance, after homogeneity is achieved, with anionic chemicals,
followed again by homogenizing with ultrasonic energy.
[0028] It is preferred that high shear mixing, such as that
available from an ultrasonic generator, is used to disperse the
mixture of iso-paraffinic hydrocarbon and chemicals. Alternatively,
the dispersion of iso-paraffin is sprayed onto the web as it moves
to the presses; and the energy of pressing is used to generate the
necessary shear force to obtain molecular dispersion and
homogeneity. This option, however, decisively the maintenance of
zeta potential at zero millivolts, and is otherwise
uncontrollable.
[0029] Preferably, the addition of the iso-paraffin comprises:
[0030] mixing iso-paraffin and one or more additives selected from
the group consisting of cationic process additives, such as
charge-neutralizing chemicals; and cationic-compatible functional
additives such as fillers, sizes, and coloring agents, using a high
shear mixer such as an ultrasonic generator to form a homogeneous
mixture; and in a succeeding step [0031] mixing iso-paraffin and
one or more additives selected from the group consisting of anionic
process additives, such as the nanoparticles smectite (termed
"bentonite" by the paper industry) or such as colloidal silica;
[0032] followed by anionic-compatible functional additives such as
optical brightening agents; [0033] followed by homogenization of
the anionic components; and finally adding the mixture to the stock
prior to formation of a homogeneous web of stock on the wire
mesh.
[0034] The low surface tension iso-paraffin serves two purposes. On
the wet end, in low concentration levels, from about 0.1 to 2% of
stock, it efficiently facilitates the dispersion of chemical
aggregates into molecular dimensions. The precise amount of
iso-paraffin that is used for chemical dispersion purposes depends
upon the continuous reading of a surface tension sensor of the
currently prevailing conditions, and is the minimum amount required
to provide the lowest surface tension This greatly enhances the
cost-efficiency of the chemicals, reducing chemical usage by one or
2 orders of magnitude. It also reduces water re-wetting in the
press section, increasing press section water removal efficiency
significantly.
[0035] The iso-paraffin azeotropes efficiently with water. When
added at levels on the wet end, up to about 10% of stock, it
greatly reduces the energy required for drying. The total energy
cost reduction can exceed 50%.
[0036] The process of the present invention is more preferably
implemented using the following steps: [0037] determining the zeta
potential of recirculated stock from the downstream leg of the
headbox; and adding both cationic chemicals and anionic chemicals
to the stock in separate increments, each also comprising the
addition of iso-paraffin, and mixing each to homogeneity using
ultrasonic energy, prior to injection into the stock stream under
high pressure at a 90 degree angle to stock flow, followed by
static in-line mixing; and followed in turn by sensing the specific
conductance, or any other appropriate physical property parameter,
calculating and outputting the standard deviation as a function of
homogeneity; and automatically by computer, adjusting upstream
conditions such as injection pressure and ultrasonication energy or
high shear energy and chemical concentration, to maintain the most
appropriate level of homogeneity; and finally making a closed loop
computer controlled adjustment to obtain a zeta potential of
zero.
[0038] The addition of the cationic and anionic chemicals must be
done at separate times and at two separate addition points to allow
them to act on the stock independently of one another, and not to
prematurely react with each other. They are thereby enabled to form
a co-valent lattice-like nanoflocculation structure which maximizes
filler and fiber retention while permitting maximum water removal,
optimum formation, maximum strength and physical properties.
[0039] Preferably, the cationic chemicals are added simultaneously
with the isoparaffin to the stock as the first addition; and after
attaining homogeneity the anionic chemicals are also simultaneously
added to the stock with the second addition of iso-paraffin.
[0040] The present invention further entails a novel stock
composition comprising: water, pulp, and an iso-paraffin having a
boiling point of 150.degree. C. or greater, and a surface tension
below 30 dynes/cm.sup.2.
[0041] The stock can further include process chemicals that
comprise the process termed microparticulate by the industry. It
typically includes a charge-neutralizing cationic component plus a
nanoparticle; and whatever functional chemical additives are
conventionally used to realize necessary product performance
objectives, including one or more conventional additives selected
from the group consisting of fillers, sizes, coloring agents,
strength additives, optical brightening agents, cationic chemicals
and anionic chemicals.
Nanotechnology
[0042] What magic is bringing forth these miracles? A nanometer,
one billionth of a meter, is the size measure of nanotechnology. It
is the most precise (and perhaps the least useful)
characterization; not dissimilar from using billions and trillions
of dollars to discuss economics with those whose purchases are
principally at the food market and gas station.
[0043] The reason is that, as particles get smaller, their
properties change. Nanoparticles are typically not described by
size, but by surface area. For example, the colloidal silica used
at the wet end has a surface area of about 600 m2/gram.
Additionally, the smaller they are, the more negative, and (for
quite different reasons) the more attracted to each other.
[0044] Please refer to FIG. 1, the graph entitled "Computer Control
of Papermaking Nanotechnology"
BRIEF DESCRIPTION OF THE DRAWING
[0045] The stock is a bleached hardwood Kraft (BHK) with
precipitated calcium carbonate (PCC) as filler. The cationic
chemical component is added first, mixed to homogeneity, and
followed by the negative nanoparticle which is also mixed to
homogeneity.
[0046] The nanotechnology papermaking example depicted is
represented by the line furthest to the right: cationic starch and
colloidal silica. The two chemicals interact electrostatically to
form a lattice work which functions to simultaneously increase both
retention and water removal, or "drainage".
[0047] It is important to know that this particular
nanoflocculation lattice work represents the most efficient
papermaking means so far discovered to simultaneously maximize
retention and water removal on the one hand, and formation on the
other. This is of great significance because retention and water
removal are paramount process objectives, and good formation is
indispensable to surface smoothness and strength.
[0048] To illustrate the significance of zero zeta potential, two
additional lines are plotted. The orange line is polyethylenimine
(PEI). It shows a sharp charge reversal at zero zeta potential,
towards re-dispersion, which results from its highly cationic
nature, and demonstrates the importance of maintaining zero zeta
potential in order to maximize retention, water removal and
strength.
[0049] The blue line is a monomeric cationic starch which, because
of its greatly reduced cationicity, manifests a more gentle
inclination change at charge reversal.
[0050] The red line represents an optimum nanotechnology
papermaking system, exhibiting the best retention and water
removal. The line extends to zero zeta potential.
[0051] Maximum retention and drainage are simultaneously achieved
by increasing both feed rates in balance, for example, that is both
the cationic starch and the colloidal silica, to maintain zero zeta
potential, until the SFR is maximized. This action also maximizes
productivity.
[0052] Among the many benefits realizable by closed loop computer
control is a calculation and output of real-time cost of each real
to the penny, and the continuous attainment of minimum cost. [0053]
forming a web of stock on a wire mesh; [0054] pressing the web of
stock to remove water; [0055] and drying the pressed web of stock
to form paper.
DEFINITIONS
[0056] Papermaking carries its own vernacular, and it is
appropriate to offer a few definitions for some of the more
esoteric expressions:
[0057] "Process Chemical Additives" are chemicals employed to
manifest or improve the papermaking process. Examples are retention
of fines and/or fillers, drainage on the wire, water removal in the
press section and/or dryer section, runnability, productivity,
up-time, etc.
[0058] "Functional Chemical Additives" are chemicals employed to
manifest or improve physical properties of the finished product.
Examples include strength, sizing, printability, brightness,
opacity, color, etc.
[0059] "Zeta Potential" refers to the on-line measurement of
electrostatic charge on the stock particulates, as assessed by the
streaming potential process, expressed in millivolts. Operating the
headbox at zero zeta potential with the nanoparticulate process,
for example cationic starch and colloidal silica, maximizes
retention of fines and fillers; creates a nanoflocculation which
enables a stronger, thinner product; and an exceptionally smooth,
uniform printing surface.
[0060] The alternative to zeta potential control, and the current
industry practice, is to use a high molecular weight "retention and
drainage aid" which creates macroflocculation, poor formation, and
degraded strength properties.
[0061] "Homogeneity" is assessed by measuring the standard
deviation of an easily measured parameter such as conductance; or
otherwise easily available parameter such as zeta potential. The
lower the standard deviation, the greater is the homogeneity.
Inspiration for this approach came to the inventor from the
well-known 6 sigma technology for quality control.
[0062] These and other aspects of the present invention may be more
fully understood by reference to the following description:
Introduction
[0063] ISOPAR is a brand name for different grades of isoparaffin,
a high purity isoparaffinic solvent which has a narrow boiling
range. ISOPAR solvents are available from ExxonMobil and are
generally sold under various letter designations. In the present
invention, the boiling of the iso-paraffin should be 150.degree. C.
or greater. This means, that ISOPAR G, H, K, L, M, and V are
suitable in the present invention. Such iso-paraffins are also
available under the name ISOZOR provided by NIHON Petrochemical and
under the trade name IP SOLVENT from Idemitsu Petrochemical. These
hydrocarbon chemicals comprise mainly aliphatic hydrocarbons,
virtually no aromatics, and have surface tensions in the range of
24 to 27 dynes/cm.sup.2 when measured at 25.degree. C. Such
hydrocarbons are considered water insoluble.
[0064] Sizes typically include hydrophobic organic molecules such
as rosin, alkenylsuccinic-anhydride (ASA), and alkyl-ketene-dimer
(AKD). Typically, the amount of size added to the stock is in the
range of 0.03 to 3 weight % based on the weight of the fiber.
[0065] Coloring agents include various dyes or pigments used to
either improve the color of the finished paper or to change the
color of the finished paper, to increase apparent whiteness or to
raise the level of brightness.
[0066] Cationic chemicals added to affect the zeta potential of the
stock, include conventional cationic chemicals used in the paper
industry such as cationic starches, cationic functional chemicals
such as alkyl-ketene dimer (AKD) and cationic scavengers such as
poly-diallyl-dimethyl-ammonium-chloride (polydadmac) and
polyamines.
[0067] Anionic chemicals added to the stock include conventional
anionic nanoparticles used in the paper industry such as colloidal
silica and bentonite. The amount of anionic chemicals added to the
stock is sufficient to bring the zeta potential to zero.
[0068] The use of cationic and anionic chemicals to change the zeta
potential is disclosed in U.S. Pat. No. 5,373,229, the contents of
which are incorporated herein by reference. The '229 patent
discloses an apparatus for measuring the zeta potential and is used
in the present invention to measure the zeta potential of the
recirculating stock from the head box.
[0069] Suitably, the zeta potential sensor measures the zeta
potential and transfers the information to a computer which then
controls the addition of cationic and anionic chemicals. Zeta
potential is controlled at zero millivolts in order to maximize
quality, process efficiency and cost-efficiency of chemical
usage.
Retention and Water Removal
[0070] The process of the present invention creates a lattice-like
nano structure that enables simultaneous maximizing of retention
and formation, while simultaneously facilitating water removal.
[0071] Maximum process and physical property parameters are
achieved by precisely neutralizing the repulsive negative surface
charge, a key factor in maximizing productivity.
Papermaking Nanotechnology
[0072] The energy of conventional mixing is not sufficient to
accomplish stock homogeneity on a modern high speed paper making
machine. The present invention provides for homogeneity, and in
turn, allows for reduction of chemical usage on a magnitude of 1 to
2 orders. The benefit is very large. For example, on a large modern
high-speed machine that consume $3 per ton of a particular chemical
or $600K per year, the chemical cost can be reduced to between $60K
and $6K per year; the saving is more than $500K.
[0073] It has been found that iso-paraffin is removed from the web
in the drying section. The iso-paraffin evaporated from the web in
the dryer is collected in a conventional manner using technology
well known to those skilled in the art.
[0074] It has been found that an increased water removal of 6 to 7%
was achieved in the pressing section when iso-paraffin was added to
the stock. This in turn reduces the energy needed in the drying
section by 24 to 28%.
[0075] Furthermore, it has been found that water removal in the
drying section is improved by as much as 20% because of the
presence of iso-paraffin. In fact, a total energy savings of 50%
can be obtained with the use of iso-paraffin in the stock.
[0076] Iso-paraffin is also present in the water recovered from
press section. This is likewise recovered and recycled.
Conventional equipment operating in the conventional manner is used
to recover the iso-paraffin from the water obtained from the press
section.
[0077] It has been found that the amount of iso-paraffin that is in
the paper is so low as to be analytically undetectable, or less
than 5 ppm.
[0078] The nanotechnology-driven process accomplishes stock
homogeneity by use of a water insoluble, low surface tension,
iso-paraffin hydrocarbon catalyst, preferably with a boiling range
well above 150.degree. C., and a surface tension below 30
dynes/cm.sup.2. There are major collateral benefits. See U.S. Pat.
No. 4,684,440, issued to the present inventor.
[0079] The process creates a nano-structure on the wire that
enables simultaneous maximizing of retention and formation, while
facilitating water removal. Maximum process and physical property
parameters are achieved by precisely neutralizing the repulsive
negative surface charge, a key factor in maximizing
productivity.
[0080] The energy of conventional mixing is not sufficient to
accomplish stock homogeneity on a modern, high-speed machine, nor
does the industry practice control of the electrostatic surface
charge, or zeta potential.
[0081] Two conditions must simultaneously apply: [0082] 1. The
spreading coefficient must be increased by reducing the surface
tension from 72 dynes/cm.sup.2 down below 30 dynes/cm.sup.2. [0083]
2. The addition of ionically polar molecules must be accompanied by
computer control of the ultimate zeta potential at zero mV.
[0084] Chemical usage, both of process and functional chemical
additives, is typically reduced by 1 or 2 orders of magnitude. The
benefit is very large: on a large, modern, high speed machine that
consumes, for example, 3$/ton of a particular chemical, or
$600K/year, the chemical cost can be reduced to between $60K and
$6K/year, saving more than $500K.
[0085] The first step in the process is to add the catalyst,
premixed with chemicals, at the wet end, preferably with a positive
displacement pump, an ultrasonic generator and an in-line static
mixer, to homogenize the stock. The catalyst rapidly diffuses and
circulates throughout the entire white water system.
Food-Related Applications
[0086] The iso-paraffin catalyst is permitted for certain direct
food applications under FDA Regulation CFR 21 172.882 and 172.884,
and for certain indirect food applications under FDA Regulations 21
CFR 178.3530 and 178.3650. It is also permitted for use under FDA
Regulations 40 CFR 180.1001 (d) and (e).
Functional and Process Chemicals "Cationic", or positively charged,
process improvement and functional chemicals are added to the stock
via a positive displacement pump and a high shear mixer until the
entire system becomes positively charged, typically in a zeta
potential range of +5 to +10 mV zeta potential. See U.S. Pat. No.
5,373,229, issued to the present inventor.
[0087] A negatively charged or "anionic" nanoparticle is introduced
downstream, via a second positive displacement pump and high shear
mixer; in amount sufficient to reach a final charge of precisely
zero zeta potential. This enables maximum retention, drainage,
formation and strength to be simultaneously attained.
[0088] Following each of the two chemical addition points, a
specific conductance sensor is installed. The computer calculates
standard deviation of the two conductance sensor outputs as a
function of thoroughness of mixing, or homogeneity. Chemical
addition, booster pump and high shear mixing system parameters are
then automatically adjusted by the computer to maximize
homogeneity.
[0089] The inventor did research on many machines, measuring zeta
potential standard deviation as a function of thoroughness of
mixing, or homogeneity. Machines with poor runnability,
characterized by many breaks and poor runnability, had zeta
potential standard deviations in the very high range of 4 to 5 mV.
They were often plagued by a common white water system shared with
other machines, multiple head boxes, or producing coated board made
with recycle fiber.
[0090] On the other hand, a slow 1920's machine had a standard
deviation in the range 0.5 to 1 mV, accompanied by excellent
runnability.
[0091] Conventional practice has six decisive flaws: [0092] It
fails the task of mixing to homogeneity [0093] It does not offer a
means of measuring homogeneity. [0094] It typically uses a
"retention aid", intended to create macroflocculation. [0095] In
contrast to the present invention, this usage sharply degrades
formation and strength properties, at a significantly higher cost.
[0096] It lacks the capability of appropriately measuring and
controlling electrostatic surface charge, or zeta potential. [0097]
It fails to control the process by computer, a task essential to
both process efficiency and quality uniformity. [0098] Finally, it
fails to reduce the surface tension of the water, thereby greatly
increasing the amount of energy required for its removal to
specified finished product solids content.
Zeta Potential
[0099] In the new method, an on-line zeta potential sensor is
installed on the downstream re-circulation leg of the head box.
Zeta potential, specific filtration resistance (SFR) or drainage,
specific conductance and temperature are measured and out-put to
the computer for process control purposes.
[0100] Chemical addition rates are computer controlled. The process
is optimized and at maximum efficiency when the total amount of
process chemicals is controlled at the optimum level of specific
filtration resistance (SFR). See U.S. Pat. No. 5,365,775, issued to
the present inventor. FIGS. 7 and 9 show the typically sharp,
optimum peak in SFR on addition of a cationic, charge-neutralizing
chemical, followed (after thorough mixing) by an anionic
nanoparticle.
[0101] Early laboratory investigations with a zeta potential sensor
indicated that the conventional process was optimized at a low,
positive zeta potential, typically in the range of +2 to +6 mV,
raising the question as to why it is not zero millivolts. The
reason is that, in the conventional practice, the
charge-neutralizing chemicals are initially dispersed as aggregates
and it takes time for them to unbundle. The phenomenon is familiar
to the industry as "cationic decay".
[0102] The reason why there is such a broad zeta potential range is
that, at the early date our lab experiments were executed, the time
between zeta potential measurement and making of hand sheets varied
substantially, because we had no idea that it was a major
influential factor.
[0103] The new method disperses the chemicals towards monomolecular
scale, with three benefits: cationic decay and its time dependence
are completely eliminated; chemicals become far more effective, as
reflected in the fact that the amount required can be reduced by
one or two orders of magnitude; product quality and cost-efficiency
are maximized.
[0104] Inefficiency of the conventional process was illustrated on
a coated free sheet (CFS) machine. The zeta potential was monitored
continuously for a period of months, while the level of
alkyl-ketene-dimer (AKD) sizing was measured on a sample removed
from the end of each reel. The Correlation Coefficient of zeta
potential with the AKD sizing level was high, at 0.71. However, the
absolute level of sizing was about 10.times. greater than
necessary. The data clearly indicates that lack of a means of
appropriate control of AKD feed rate invites use of a costly excess
of AKD, to ensure that a satisfactory minimum level of sizing is
achieved.
[0105] Consider that the amount of AKD sizing approximates $3/ton
of product, or $600K/year on the CFS machine on which we did the
experiment. Computer control of zeta potential would decrease AKD
purchase cost to about $60K/year. Increasing mixing efficiency to
obtain homogeneity would further reduce AKD cost to at least
$6K/year, and perhaps ultimately reach as low as $600 annually.
[0106] The annual cost difference between $600K and $6000 (or
perhaps $600) speaks volumes about the poor efficiency of the
conventional process. Internal size is the chemical chose for the
illustration of increased cost efficiency because the sizing
measurement is easily quantifiable in the laboratory. The
principle, however, applies equally to all process and functional
chemical additives.
[0107] The current, widely used, conventional means of charge
measurement is the off-line assessment of cationic demand, using a
special instrument. The cationic demand of white water is measured,
with the objective of reaching and maintaining a small negative
charge so as to avoid over-cationization. Its exceptionally poor
effectiveness was revealed in the following described
experiment.
[0108] An on-line zeta potential sensor was installed at the head
box of a large specialty groundwood machine, and the zeta potential
was continuously monitored for a period of one year. On each
working day, a cationic demand measurement was made in the lab by
the chemical supplier, and a notation simultaneously made of the
current on-line zeta potential measurement. At the end of the year,
a Correlation Coefficient calculation of zeta potential vs.
cationic demand produced the exceptionally low value of 0.17.
[0109] This experiment, and others with similar results, provides
compelling evidence that the cationic demand measurement, in global
use by the industry, is not repeatable. Even if it were repeatable,
the objective of leaving a residual negative charge is totally
incompatible with the tenets of nanoscience.
[0110] Use of cationic demand for process control has the benefit
of giving mill personnel a warm, fuzzy feeling that something
useful is going on. By any other criterion, it is
counter-productive.
[0111] The efficiency of the conventional process, on a modern
machine, is poor.
Special Properties
[0112] We have described a nanotechnology-driven, computer
controlled process that maximizes productivity, quality and
cost-efficiency. It can serve as the ideal platform for realizing
any reasonably specified special properties, for example,
stiffness.
[0113] The nano sheet is inherently thinner and stronger. It can be
increased in bulk to increase stiffness. For example, feed rates of
both the cationic charge-neutralizing chemical and the anionic
nanoparticle can be increased in tandem, under computer control,
while holding the net charge at zero zeta potential.
[0114] The result will be a bulkier, stiffer sheet.
[0115] Strength can be increased by adding a small amount of
natural gum, plus whatever amount of cationic starch is appropriate
to the task.
Water Removal
[0116] Research utilizing the variable speed pilot plant of a felt
manufacturer, Albany International of Albany, N.Y., revealed that
hydrodynamics play an important role in operation of the press
section. At slow speed, the inventor's catalyst had little effect.
However, as the speed increased, water re-wetting was reduced. The
result, as machine speed increased, was a progressive consistency
increase up to 6 or 7% out of the press section.
[0117] The amount of catalyst that exits the machine with the
product is so low as to be undetectable, less than Sppm. Surface
tension is monitored on-line, and catalyst addition is adjusted by
software under computer control, to maintain a minimum surface
tension value, ensuring cost effectiveness. Use of the isoparafine
hydrocarbon will require effective recovery systems to eliminate
environmental concerns. Addition upstream of, or in the press
section will result in the hydrocarbon coming out in press
whitewater, vacuum pump discharges, and dryer hood exhaust. Proven
technology for removing hydrocarbon is available for all three
areas.
[0118] Iso-paraffin hydrocarbon can be removed from vacuum pump and
hood exhaust air flows with an activated carbon system. Hydrocarbon
laden air flows through a filter/cooler before entering a blower,
which forces the hydrocarbon laden air stream through an adsorber
vessel containing activated carbon. Hydrocarbon contained in the
processed air is adsorbed by the activated carbon and clean air
released to atmosphere. When an adsorber vessel becomes saturated
with hydrocarbon, the air stream is transferred to a previously
regenerated adsorber. Regeneration of the saturated adsorber than
proceeds by using steam in a direct contact thermal desorption
process or by replacing the activated carbon.
[0119] A minimum of two adsorbers is required to provide continuous
operation. Desorbed hydrocarbon can be condensed and decanted for
return to the process and reused. Recovery efficiencies of 99% are
common. The hydrocarbon not recovered in the charcoal is
replaced.
[0120] Water and iso-paraffin hydrocarbon are immiscible liquids,
and form a constant boiling azeotrope, with a lower boiling point
than either pure component. The iso-paraffine is separated in the
dryer by employing the most cost-effective of several engineering
solutions, depending on the operational scale: distillation,
fractional distillation or use of a rotary evaporator.
[0121] The two components volatilize sequentially, hydrocarbon
first, and create two liquid layers on condensation. The azeotrope
is easily broken by using a liquid-liquid separator (a decanter) to
separate the two liquid layers.
[0122] Increased water removal occurs in three different ways:
[0123] 1. At the wet end, it is enhanced by formation of an open
nanoparticulate structure which facilitates water removal on the
wire. [0124] 2. In the press section, it decreases water re-wetting
on high speed machines. Press section water removal efficiency is
increased by 6-7%. Since each 1% increase in consistency translates
to 4% in the dryer, the total press contribution can be as much as
24-28% on the dry end. [0125] 3. In the dryer section, the
attractive influence of hydrogen bonding is greatly decreased, so
that much less energy is required to volatilize water. First
section dryer efficiency is increased by as much as 20%, according
to differential scanning calorimetry and thermogravimetric
studies.
[0126] Sum total of energy saving from the three sources approaches
50% at low hydrocarbon levels. It can be increased by mixing up to
10% or more hydrocarbon, so as to increase the amount available to
azeotrope.
Fire Safety
[0127] When asked about fire safety, the supplier of iso-paraffin
hydrocarbon requested extensive data on the machine in question,
and its operation. The analysis that followed required a total of 7
pages, too extensive to fully report here. Bottom line is that the
exposure did not exceed 5% of the LEL, lower explosive limit.
[0128] The iso-paraffinic hydrocarbon used in our research was
Isopar G and the upper homologues produced by ExxonMobil. The lower
homologues are less desirable because of increased volatility and
therefore flammability.
[0129] The particular hydrocarbon is extensively consumed in the
copy process: millions of copy machines, barge loads of product,
and no reported incidents.
Sustainability
[0130] A leading retailer has embarked on a sustainability program,
initiated on Feb. 1, 2008. Instead of purchasing packaging
materials at the lowest cost, Wal-Mart is applying quite a
different set of sustainability metrics, weighted as follows:
[0131] 1. 15% is based on GHG/CO2 per ton of Production [0132] 2.
15% is based on Material Value [0133] 3. 15% is based on
Product/Package Ratio [0134] 4. 15% is based on Cube Utilization
[0135] 5. 10% is based on Transportation [0136] 6. 10% is based on
Recycled Content [0137] 7. 10% is based on Recovery Value [0138] 8.
5% is based on Renewable Energy [0139] 9. 5% is based on
Innovation
[0140] The new process goes much further than the conventional
process in meeting these criteria. The author anticipates that the
Wal-Mart initiative will lead to a sea change in the manufacture of
paper and board. This is the first time that a complex, definitive
set of specifications has been imposed on the industry.
[0141] Recognition that the manufacture of paper and board is a
scientific task, instead of an art form, is long over-due.
[0142] Re-cycling of the nanotechnology paper is easily
accomplished by adding an increment of the cationic
charge-neutralizing component used to create the nanostructure.
This breaks the lattice-work down into pieces as small as
molecules, which can be added as broke to fresh stock and easily
reincorporated as nano paper.
SUMMARY
[0143] Implementation of the new method entails first achieving
stock homogeneity by dispersing chemicals to the molecular level.
Chemical usage can then be reduced by 1 or 2 orders of magnitude.
Precise neutralization of the repulsive negative charge is a key
step in activating and maximizing powerful intermolecular
attractive forces; it can enable an increased fine paper loading at
a (counter-intuitive) higher strength than the lower loading
level.
[0144] It will produce the highest possible quality product from
the available stock, at the highest level of productivity and
lowest feasible cost; with exceptional uniformity under computer
control.
[0145] The greatly reduced need for both chemicals and water
removal energy, and appropriate control of the production process,
leads to a thinner, stronger product, accompanied by decreased need
for landfill, resulting in higher sustainability Since the fibers
can be unlocked by adding a cationic charge-neutralizing component
that re-disperses them, re-cycling of fibers can be accomplished
many more times than with the conventional process, another major
sustainability factor.
[0146] The novel nanotechnology-driven process first homogenizes
the stock towards molecular dimensions with a small amount of low
surface tension, water insoluble, catalyst. The catalyst remains,
circulating in the white water system. It is introduced, together
with process and functional chemicals by a total of two booster
pumps, the first for cationic chemicals and the catalyst, and the
second for anionic chemicals, including an anionic nanoparticle. A
classical microparticle nanostructure is formed with commonly
available, cost-effective chemicals such as cationic starch and
colloidal silica. Zeta potential and specific filtration resistance
(SFR) are also sensed, and the zeta potential is controlled at
zero, at the total nanostructure level, (or SFR level) required for
maximum productivity. The amount of catalyst is optimized by
computer, with guidance from an on-line surface tension sensor, at
the lowest achievable surface tension. It increases water removal
on the wire; reduces press section water re-wetting on a modern,
high speed machine, increasing consistency exiting the press
section by as much as 6-7%; and reduces water removal energy in the
dryer section in the 20% range. Total energy saving from the three
sources, at a hydrocarbon level up to 2%, amounts to about a 50%
reduction in energy usage. Energy saving increases at higher
hydrocarbon levels because of thee mass action azeotropic
efficiency increase.
[0147] Homogeneity is maximized, first by measuring it as a
function of the standard deviation of data produced by two specific
conductance sensors, one installed immediately downstream of each
positive displacement pump, high shear mixer and in-line static
mixer; and secondly by making computerized adjustments to improve
it. The finished product is thinner and stronger. Because the
chemicals are reduced toward molecular dimensions by a low surface
tension catalyst, chemical usage is reduced by one to two orders of
magnitude. Actual product and process costs are calculated on a
running basis, so that the cost of each reel is available as it is
produced. The nanotechnology-driven process is highly
sustainable.
[0148] The invention can be defined in the following items: [0149]
Item 1. A microparticulate process in which a low functionality
cationic chemical such as cationic starch is added to the
negatively charged cellulose fibers in excess amount, typically to
a zeta potential of +5 or +10 mV. This is followed by addition of a
nanoparticle such as colloidal silica until the final zeta
potential is precisely zero. [0150] Item 2. A process for
manufacturing paper and board that catalytically disperses the
chemicals, fibers and fillers to obtain a homogeneous stock, down
to individual molecules of chemicals and particles of fiber and
filler. Chemical addition points are supported by a positive
displacement pump followed by a high shear mixer, preferably a
source of ultrasonic energy; inline static mixers; and homogeneity
sensors, under computer control. The first chemical addition point
injects a dilute solution or dispersion of cationic functional and
charge-neutralizing chemicals, plus catalyst. The second injects a
dilute solution or dispersion of an anionic nanoparticle plus
anionic functional chemical additives if needed. Injection is at
high speed, vertical to the flow of stock through the main stock
pipe. A nano-structure is formed, maintained at a zeta potential of
zero millivolts electrostatic charge, in order to enable maximizing
both process and physical property parameters, while minimizing
cost. The quality of homogeneity, or thoroughness of mixing, is
determined by use of a sensor to measure the specific conductance,
followed by calculation of its standard deviation. A high level of
sustainability results from a significant reduction in chemical
usage, reduced energy usage in the press and dryer sections,
increased strength at a decreased basis weight which translates to
greater recyclability of fibers, ease of re-processing broke, and
decreased landfill. Cost savings on a high speed machine can range
well into 7 dollar figures annually. [0151] Item 3. The method of
item 1 in which homogeneity of stock is obtained by effective
dispersion use of a small amount of iso-paraffin, low surface
tension hydrocarbon which acts as a catalyst to achieve chemical
and particulate homogeneity down to a molecular scale and greatly
facilitate water removal in the press and dryer sections. A larger
amount of catalyst is required, and its function in the dryer
section is to azeotrope with the water, reducing the heat of
evaporation; and displacing water as the adsorbed liquid, thereby
reducing the hydrogen bonding which normally requires an enormous
amount of energy to overcome. [0152] Item 4. The method of item 1
in which an on-line surface tension sensor is used to enable
process adjustments in order to hold surface tension at the minimum
and most efficient value. [0153] Item 5. The method of item 1 in
which standard deviation of an easily measured process parameter,
such as specific conductance, is used to assess thoroughness of
mixing, or stock homogeneity, so that adjustments to the positive
displacement pump pressure and/or high shear mixer energy input
and/or chemical additive concentration, can be made to improve it.
[0154] Item 6. The method of item 1 in which the iso-paraffin
hydrocarbon is collected for re-use.
* * * * *