Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~lSZ677
~CKGROUND OF TIIE INV~NTION
It is well known that many polymeric materials may
: be dissolved in, or dispersed on essentially the molecular
level so as to orm a gel, with appropriate liquid vehicles
providecl that there is a high mutual compatibility between
: the polymeric material and the liquid vehicle. Dissolution
or gel formation is typically accomplished by contacting the
polymer and vehicle at ambient to relatively elevated temp-
eratures. It is generally accepted in the art that an
increase in temperature will speed dissolution of the polymer
as will an increase in surface area as by comminution of the
polymer into relatively small particles. Often, dissolution
is accomplished by refluxing boiling vehicle or solvent over
polymer particles.
Polyisobutylene, for example, is recognized to be
soluble in hydrocarbon solvents such as kerosene and the
like as is shown in U. S. Patent No. 3,215,154 but its rate
of dissolution is slow. Patentees teach heating the polymer-
solvent mixture so as to increase the speed of dissolution
and also reconunend shredding or grindinc~ the polymer to a
uarticle size of 40 mesh or finer. Even with use of these
: techniclues, a nurnber of hours arc rcquirecl to fully clissolvc
the polymer in the solvent.
~ ecause many polymeric materials are relatively
soft and resilient, they are cxtremely difficult and often
im~ossible to comminute by conventional grinding techniques.
I.ven a~ter comminution, the so-formecl particlcs tcnd to
stick ancl clump to~ether thus ne~atin~ the practical effect
of such comminution.
52677
.
It is also known to comminute relatively non-
brittle materials, including rubbery polymers such as poly-
isobutylene, by cooling the materials below their embrittlement
temperature using refrigerants. A cryogenic comminution
system for such purposes is described in U. S. Patent No.
3,771,729.
Polymeric materials dissolved or dispersed in
liquid vehicles find use in a number of different applications.
One such general application includes film forming as by
casting, spraying, brushing or otherwise applying the polymer
solution to a surface. The liquid vehicle is then removed,
usually by evaporation, to leave a polymer film upon the
surface. Cast films may be dense, in which case they are
used as intrusion barriers or they may be somewhat porous
and be used as breathing films or separation membranes.
Sprayed or brushed films are most often applied as barrier
films. Polymer solutions may also be used to form fibers by
spinniny, extrusion, or similar techniques. In film or
fiber forming applications, it is generally advantageous to
utilize a relatively conccntrated solution of polymer in the
liquid vehicle. Many commercial adhesives are also concentrated
polymeric solutions.
There are a number of specialized uses for relatively
dilute solutions of particular polymers in solvents. One
such specialized use that has been the subject of extensive
research is tlle r~duction of riction in liquids flowing
througll conùuiLs or A ro ~Ind oh ~ ec t s .
.:i
~1 5Z677
~ y~rodynamics theory and practice demonstrate that
the drag or friction caused by flowing liquid in a conduit
increases the energy requirements to transport that liquid.
This fact is particularly noticeable in the transportation
or movement of hydrocarbons in pipelines as energy requirements
increase as the square of the flow. It is recognized that
increasing pum~ing power for flow augmentation can exceed
conduit pressure limitations with accompanying deleterious
effects. The pressure drop in a pipeline as liquids are
pumped therethrough is a manifestation of this drag or
friction.
Various means have been tried to reduce the un-
desirable effects of friction mentioned above. The addition
of friction-reducing agents is described, for example, in
U.S. Patents ~los. 3,215,154i 3,682,187; 3,687,148; and
3,910,856. I~owever, little success has been obtained by
such additives because of the high cost or unavailability of
the additive; the cost of effectively adding the additive to
the hydrocarbons and dissolution therein, which may require
many hours; the incompatibility of the additive with the
subse~uent use of the hydrocarbons; or the like. Thus, U.S.
Patent No. 3,215,154 describes, to reduce Eriction, intermjx-
ing with li~uid hydrocarbons certain polyisobutylene resins
as shredded, pulverized or ~round solids, preferably of a
particle size no greater than 40 U.S. standard screen scale.
Natural rubber is also described as operable, but not as
efEectivc as polyisobutylene resin. The ratc of solution of
the polyisobutyl~ne is describcd as slow; in what is described
as an eEtcctive embodiment, polyisobutylenc of 10-20 U.S.
~LlS2~o77`
standard screcn scale particle size required stirring for
two hours, with the necessity of an additional time required
or complete solution. To decrease the time for dissolving
the resin, as is described in the pate3lt, the hydrocarbons
can be heated up to about 200~F. ~lso, the preparation of
. shredded, pulverized or ground polyisobutylene by usual
means for subsequent dissolution causes degradation of the
polymer; i.e., causes a reduction of molecular weight in
some of the polymer molecules through shearing action and
the heat generated thereby. Since it is known that friction
reduction is dependent on long chain polymer molecules of
relatively high molecular weight, such prior methods of
shredding, pulverizing or grinding causes a reduction of the
effectiveness of the polyisobutylene or other long chain
polymers. Furthermore, the particles so prepared, when in
contact with each other prior to introduction into the
li~uid hydrocarbons tend immediately to conglomerate into
large masses, especially as fresh surfaces contact other
fresh surfaces. rrhe tough, strongly adhered polyisobutylene
mass dissolves in hyclrocarbon liquids only with difficulty
ancl slowly, as above described. In fact, the stirring
action over the long timc rccluired to dissolvc a ~olyisobutylcne
; mass causes additional shearing and degraclation of the
polymer molecules to the detriment of its friction-reducing
properties.
1~ 52677
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SUMMARY OF THE INVENTION
The present invention provides a process for very
rapidly dissolving, or dispersing on essentially a molecular
level, certain types of polymeric materials in compatible
liquid vehicles. Dissolution is accomplished by comminuting
the polymeric material at cryogenic temperatures and
thereafter admixing the comminuted material, preferably still
at cryogenic temperature, to the liquid vehicle. The
temperature of the liquid vehicle at the time of admixing is
not critical except that it must be at a temperature
substantially above its pour point. Ambient to slightly
elevated liquid temperatures are preferred.
One specific embodiment of the present invention
provides a process for introducing a long chain polymeric
friction-reducing additive, such as polyisobutylene, into
liquid hydrocarbons wherein the additive is not degraded
significantly prior to the introduction and wherein
dissolution is accomplished rapidly. The invention provides
for cryogenic comminuting of the additive and introducing the
additive as discrete particles, preferable at cryogenic
temperature, into hydrocarbon liquids for rapid dissolution.
Figure 1 of the drawing is a simplified illustration of
an embodiment of the invention showing the cryogenic
comminuting of polyisobutylene, the addition of discrete
particles of polyisobutylene at cryogenic temperature to
liquid hydrocarbons for dissolution therein, and subsequent
introduction of the hydrocarbons containing dissolved
polyisobutylene into a pipeline transporting a main stream of
liquid hydrocarbons.
Figure 2 depicts a typical electron spin resonance plot
obtained by analysis of a cryogenically comminuted polymer
maintained at cold temperatures.
DESCRIPTION OF THE INVENTION
It has been found that certain polymeric materials may
be very rapidly dissolved in compatible liquid vehicles at
relatively high concentration provided that certain critera
are met. The polymeric materials must be cryogenically
ll~Z677
-- 7
comminuted and maintained in a surface active state until
admixed with the liquid vehicle. Dissolution of the polymer
in the liquid vehicle upon admixing is extremely rapid;
essentially instantaneous in many instances.
The term "polymeric materials" as used herein includes
both natural and synthetic linear thermoplastic polymers.
Such polymers may vary in molecular weight from a few thousand
to 10,000,000 or more; may be crystalline or amorphous,
atactic or isotactic, homopolymers or heteropolymers, provided
that no significant degree of crosslinking is present. A
minor amount of crosslinking can be tolerated in certain low
molecular weight polymers. Exemplary polymer systems useful
in the practice of this invention include the hydrocarbon
polymers in general, especially the rubbery hydrocarbon
polymers such as polyisobutylene; acrylic and other acetal
film forming polymers such as the acrylic and vinyl resins as
well as esters of cellulose, halogenated polymers such as the
polyvinyl and polyvinlidene halides, polyethers, nitriles,
polyamides, polyimides, polyesters, silicones, sulfones,
certain polyurethanes, polysulfides, and also including
polyvinyl acetate, polyvinyl butyrate, polyvinyl carbazole as
well as copolymers and terpolymers containing portions of
these, in part; fiber forming polymers including nylons and
polyesters and membrane forming polymers such as aramid and
ionomer polymers.
Appropriate polymeric materials are dissolved in
compatible liquid vehicles by practice of this invention.
The term "dissolved" as used herein includes dispersion of the
polymeric material on essentially the molecular level within
the liquid vehicle as in the formation of a gel. Whether
truly dissolved or dispersed as a gel, the admixtures of
polymer and vehicle are characterized as being essentially
infinitely dilutable blends or systems.
Compatible liquid vehicles include all of those
non-aqueous liquids in which the polymeric materials can be
dispersed at the molecular level. In general, a liquid
vehicle compatible with a particular polymer must be capable
~15267~
of dissolving that polymer, at least to some degree, by
conventional disso~ution techniques. In no case is water an
appropriate or compatible liquid vehicle because the polymer
systems useful in this invention are essentially insoluble in
water and because water neutralizes or tends to destroy the
surface active properties of the cryogenically comminuted
polymer particles. The limits of solubility of polymer in
vehicle, of course, vary as in conventional systems but in
most cases the dissolution method of this invention allows
preparation of much more concentrated polymer solutions than
are readily attainable by conventional methods.
As may be readily appreciated, not all liquid vehicles
are compatible with all polymers. Exemplary polymer-liquid
vehicle systems useful in the practice of this invention
include hydrocarbon polymers dissolved in aromatic and
aliphatic hydrocarbon liquids; acrylic resins including the
polymers or copolymers of acrylic acid, methacrylic acid,
esters or these acids or acrylonitrile dissolved in aromatic
hydrocarbons, chlorinated hydrocarbons, esters and ketones;
halogenated polymers including the polyvinyl and
polyvinylidene halides dissolved in chlorinated hydrocarbons
and nylons dissolved in phenols and lower aliphatic alcohols.
Many other polymer-compatible liquid vehicle systems will be
readily apparent to those skilled in the art.
Practice of this invention requires first that the
polymeric material be cryogenically comminuted. By this is
meant comminuting at very low temperatures, say below
100F. and preferably at about 100F. below the embrittlement
temperature of the polymeric material being comminuted. The
use of liquid nitrogen, which boils at -321F., as the
cryogenic refrigerant is preferred, and U. S. Patent No.
3,771,729 describes a cryogenic comminution system for soft or
resilient materials, including polyisobutylene, which has a
brittlement temperature of about -100F. and which gives
excellent results in the present process but other cryogenic
refrigerants may be used, including for example liquefied
carbon dioxide, liquefied air in some instances, liquefied
.
.
~lS2677
g
halogenated hydrocarbons and liquefied noble gases including
helium and argon.
After cryogenically comminuting the polymer to form
smaller discrete particles, sized such that they will pass
through a No. lO U.S. standard screen, and preferably through
a No. 40 U.S. standard screen, the polymer particles are
introduced into and admixed with the liquid vehicle preferably
while still at cryogenic, or near cryogenic, temperatures.
The temperature of the liquid vehicle upon admixture with the
polymer particles is not critical. It is important, however,
that the liquid vehicle be at a temperature sufficiently above
its pour point to withstand the cooling effect of the mixing
process and remain at a temperature above the pour point. The
cooling effect is insignificant when the desired
concentrations of polymer particles are less than about 1%.
Ambient to slightly elevated liquid vehicle temperatures are
preferred.
It is preferred in the practice of this invention that
the polymer particles be maintained at cold temperatures,
below the embrittlement temperature of the polymer, until
introduced into the liquid vehicle. Fresh polymer surfaces,
particularly fresh surfaces of rubbery polymers, tend to stick
together and conglomerate into clumps at temperatures above
the embrittlement temperature. So long as the particles are
maintained below the embrittlement temperature, and preferably
below a temperature of about - 100F., they will not
conglomerate on contact, and they are maintained below this
temperature until introduced into the liquid vehicle which
gives advantages as hereinafter described. Good results are
obtained so long as cryogenic temperature is maintained until
particle introduction as discrete particles into the liquid,
as by free fall therein, is assured. During introduction of
the particles, the liquid vehicle should be kept in motion so
as to minimize particle contact before immersion in the
liquid. Creation of the liquid motion should be such as to
not cause unacceptable degradation of the polymer. Mechanical
agitation as with a stirrer is suitable, with the agitation
being mild but sufficient to prevent contact of particles
X
~2677
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while on the surface thereof. A tangential entry of the
liquid causing circular flow of the hydrocarbons in the
dissolution vessel can be used with good results. Motion
produced by introducing a gas inert to the system, such as
nitrogen, carbon dioxide, methane, natural gas or flue gas
below the surface of the liquid vehicle also gives good
results.
As above stated, maintaining the polymer particles at
cryogenic temperature until their introduction into the liquid
vehicle is preferred and gives excellent results in the rapid
dissolution of the particles in the liquid, the dissolution
being so rapid it is not attributable solely to increased
surface area. While the reason for such rapid dissolution is
not known with certainty and it is not desired to be limited
by theoretical considerations, it is believed that cryogenic
comminuting is a fracturing of the particles primarily along
molecular boundaries so that the molecular weights of the
molecules are not appreciably reduced; the resulting particles
have active sites on their edges, corners and surfaces,
whereby high energy surfaces are generated. Such high energy
surfaces are believed to assist in the dissolution of the
particles in the liquid vehicle, and maintaining cryogenic
temperature is effective to preserve the high surface energy
of the particles until introduction into the liquid.
The existence of high energy sites on the comminuted
polymer particles has been experimentally verified by means of
electron spin resonance analysis of cryogenically comminuted
polymer samples. Figure 2 depicts a typical curve obtained by
such analysis. Signal intensity is plotted against magnetic
field strength (or radio frequency) in the manner
illustrated. In the data presented as Figure 2, a
cryogenically comminuted polyisobutylene sample was subjected
to electron spin resonance analysis at a temperature of
-176C. Liquid nitrogen was used as the cryogenic refrigerant
and the polymer sample was maintained at cryogenic
temperatures after comminution and until the analysis was
complete.
~1~;2677
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The curve obtained as shown in Figure 2 demonstrates the
presence of free radicals in the polymer particles. The most
likely locus of those free radicals is the particle surfaces
as this is where fracturing occurred. As the polymer
particles warm, the concentration of free radicals tends to
decrease and will eventually disappear probably by reaction
with atmospheric oxygen, water vapor or other active
compounds. In the presence of water, the effective electron
charge would be greatly reduced or neutralized by reaction
with a proton from water or the electron charge might be
shielded by a coulomb dipole interaction.
Another effect might also contribute to the rapid
dissolution of polymer particles in the liquid vehicle. Upon
introducing polymer particles at cryogenic temperature into
liquid vehicles at a much higher temperature, say ambient
temperature, the temperature of the surfaces of the particles
on contacting the liquid rapidly rises compared to the change
of temperature at the particle center so that the already
small particles may shatter, or fracture, forming even smaller
particles or fissures throughout the particles, thus further
enhancing rapid dissolution which is instantaneous for
practical considerations.
The dissolution technique of this invention offers
important advantages as compared to conventional practice.
The rapid, almost instantaneous, dissolution or dispersion of
polymers in liquids obtainable by practice of the invention
provides substantial time saving in making up solutions.
Polymer degradation during dissolution is greatly reduced or
eliminated. In many cases, much higher concentrations of
polymer in the liquid can be attained than is practical using
prior art techniques.
Polymer-liquid vehicle systems prepared by the process
of this invention are useful for forming films as in membrane
manufacture and surface coating applications. Relatively high
polymer concentrations may be used to immobilize liquids, to
lower their vapor pressure and to form composites as by adding
resiliency to a normally brittle matrix. Other uses include
~l~i;Z67~7
- 12 -
fiber formation as by spinning or extruding. Numerous other
specialized uses will be apparent to those skilled in the art.
One such specialized use, which constitutes a specific
embodiment of this invention, is in the use of certain long
chain hydrocarbon polymers as drag-reducing additives for
liquid hdrocarbons to be transported through a conduit.
Appropriate hydrocarbon polymers for this application are
rubbery or elastomeric in nature and have the ability, when
dissolved in liquid hydrocarbons, to reduce the friction
caused by flowing the hydrocarbons through a conduit.
Generally such polymers cannot be efectively ground,
pulverized or shredded into particles by usual means without
incurring severe degradation effects on drag reducing
characteristics by the lowered molecular weight resulting
from aforementioned mechanical actions and without
conglomeration of the particles on contacting each other.
These polymers have a viscosity overage molecular weight of
from 1,000,000 to about 10,000,000. Polyisobutylene is the
preferred additive of this inventive embodiment, it being
remembered that, as above defined, block polymers, natural
rubbers, other hydrocarbon polymers soluble in liquid
hydrocarbons and which have friction-reducing properties can
also be used, including for example: natural rubber; block
copolymer or polystyrene-polyisoprene-polystyrene; block
copolymer of polybutadiene-polyisoprene-polybutadiene; and the
like, such as described in the above cited patents and which
have a molecular weight of from about 500,000 to 5,000,000.
This embodiment of the invention does not depend on the
discovery of any new drag reducing agent. Rather, it
constitutes the discovery of a new process for the
introduction of certain high molecular weight hydrocarbon
polymers into liquid hydrocarbons without incurring
unacceptable amounts of polymer degradation. The polymers are
elastic or rubbery in nature and by usual processes, i.e.,
processes heretofore used, require unacceptably long times for
dissolution in liquid hydrocarbons. Such hydrocarbon
polymers, especially in the small quantities employed for drag
X
~l~Z677
- 13 -
reduction purposes, are compatible with alluses of crude oil
and fractions and products thereof so no provision need be
made for their removal or the like.
By "friction-reducing" is meant the ability of a
polymeric material such as polyisobutylene, when dissolved in
a hydrocarbon liquid, to reduce the frictional losses
experienced as the hydrocarbon liquid is transported through a
conduit, thereby reducing energy requirements and pumping
costs, and/or effectively increasing the capacity of the
pipeline using the same pumping process. This friction-
reducing effect has been described in the literature by terms
such as drag reduction, pressure loss reduction, pressure
reduction percentage, pressure loss, friction loss, turbulent
flow friction or turbulent drag reduction, and the like.
Whatever the terminology used, the practical measure of
friction reducing is the ability to obtain a greater volume of
fluid flow through a conduit using the same amount of energy
in a set time or to flow the same amount of fluid using lesser
energy in that same time period. As will be shown herein-
after, in accordance with the invention, especially goodresults are obtained at high flow rates of the liquid
hydrocarbons, i.e., under relatively turbulent conditions of
flow, although some improvements is also obtained at low flow
rates.
By "hydrocarbon liquids" which are transported through
conduits, as described herein, is meant hydrocarbons which are
liquid under usual conditions of temperature and pressure
experienced in pipelines, such as above one atmosphere
pressure and from about 0F. to 180F. Crude petroleum and
fractions thereof, including gasoline, kerosene, fuel oils,
diesel oil, lubricating oils, and residual oils illustrate
such hydrocarbon liquids, while additional examples include
isooctane, cyclohexane, toluene, xylene, and many others.
In accordance with this embodiment, cryogenic
comminuting is used to convert polyisobutylene to discrete
particles of from about 0.05 to 2mm average diameter.
Cryogenic comminuting and dissolution of the polyisobutylene
~LlS2677
- 14 -
particles in the liquid hydrocarbon are accomplished in the
manner previously described.
Hydrocarbons to be transported should contain from about
to 400 ppm (parts of additive per million parts of
hydrocarbons by weight), and preferably when using
polyisobutylene, the amount is advantageously in the range of
from about 20 ppm to about lOOppm. The amount to use in a
given system will largely depend on the overall
characteristics of the system, including for example the
conduit length, diameter, internal finish, type of pumps,
etc. and the particular additive used and the hydrocarbon or
hydrocarbons to be transported, and can readily be
determined. The introduction of the required amount of
additive into the hydrocarbon liquid main flow can be
accomplished by several convenient methods:
(a) Dissolution of the additive into a mixing tank
continuously filled with a drag stream of the
hydrocarbon liquid and repumped back at an appropriate
flow rate into the main stream of flow.
(b) Dissolution of the additive into fixed batches of
the liquid to form a high concentration therein, on the
order of 5% to 10%, and then adding this concentrate in
appropriate amounts into the main flow of the liquid in
order to achieve the desired accelerated flow rate or
decreased pressure or both. This concentrate method
permits preparation and storage at one site for
subsequent transportation and use at other sites.
(c) Collecting the comminuted particles into cryogenic
containers having liquid nitrogen therein and maintained
so that the ratio of additive particles to liquid
nitrogen is between about 1:1 and 1:4. The resultant
slurry of liquid nitrogen and additive particles can be
maintained for an extended time period or transported in
cryogenic vessels to using sites. In use, this slurry
is introduced into an appropriately sized mixing tank,
being continuously filled with a drag stream hydrocarbon
liquid, and as in method (a), repumped back at an
~l~;Z677
- lS -
appropriate flow rate into the main stream of liquid
hydrocarbon flow. The mixing tank should be maintained
at atmosphere pressure by suitable venting to permit
escape of vaporized nitrogen gas.
The hydrocarbon liquid for use in any of the above
methods is advantageously the same as the liquid hydrocarbon
to be transported, but other hydrocarbon liquids, for example
gasoline, cyclohexane or diesel fuel, can be used as the
concentrate solvent for introduction into different
hydrocarbon liquids, such as crude oil.
Figure l of the drawing is one simplistic illustration
of a preferred embodiment of the invention. Referring to
Figure l, a polyisobutylene slab l is introduced into area 2
bounded by hood 4. Such a slab may be, for example, from l/4
to l/2 inch in thickness and from say one to three feet wide,
with the length being such as to give convenient operation.
Liquified nitrogen, stored in tank 5, is passed via lines 6
and 8 to elongated spray header 9. Spray header 9 has
discharge ports lO spaced along its length so that liquid
nitrogen is injected into space 2 adjacent to polyisobutylene
slab 1. Slab 1, cryogenically cooled, is conveyed to chopper
ll where it is converted into particles l9 of an average
diameter of about l/4 inch. The particles, while being kept
at cryogenic temperature by liquid nitrogen injection into
space 2 via lines 6 and 3, and spray header 7 having discharge
ports 13, drop into space 12 enclosed by housing 14 containing
screw conveyor 15. Conveyor 15 is rotated by driver means 16
so that blades 18 convey particles l9 from chopper ll to
impact mill 20. During passage through space 12, the
particles are maintained at cryogenic temperature by liquid
nitogen introduced via lines 6 and 23 and through spray header
21 having discharge ports 22. Particles 19 are thus
maintained at cryogenic temperature from their formation by
chopper 11 to their introduction into impact mill 20. Impact
mill 20 is illustrated as being a high-speed rotating hammer
type enclosed by hood 17, but other impact comminution means
may be used, such as ball mills or rod mills. In impact mill
~C
:~Si2677
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20, particles 19 ar comminuted to powder particles 24 having a
particle diameter which will pass through a U.S. standard
screen size of about No. 20. Particles 19 are maintained at
cryogenic temperature during their comminution to powder
particles 24, and particles 24 are also so maintained by
liquid nitrogen introduced via lines 6 and 25 and spray header
26 having ports 28 after their formation until contact with
liquid surface 30.
Particles 24 fall on hydrocarbon liquid surface 30, with
the body of hydrocarbon liquids 31 being maintained in tank 32
equipped with stirrer 34 having driving means 35. Stirrer 34
is operated at a speed sufficient only to present a fresh
surface to particles 24 to prevent conglomeration thereof on
the surface. Dissolution of particles 24 in hydrocarbon 31
appears very rapid, instantaneous for practical purposes, so
that the average residence time of hydrocarbons in tank 32 is
not critical. A residence time of from say 1 to 20 minutes
appears adequate and from 1 to about 5 minutes is preferred.
Because of this short residence time and because of the large
amount of liquid hydrocarbons compared to the amount of added
polyisobutylene particles, the temperature of hydrocarbons 31
is not appreciably lowered, although some lowering would not
be harmful.
The main body of hydrocarbons, using crude as an
example, flows through pipeline 40, being driven by pump 41,
flow being in the direction shown by arrow 42. A portion of
crude passing through pipeline 40 is passed via line 44 into
tank 32 wherein polyisobutylene is dissolved therein. Via
line 45, crude containing dissolved polyisobutylene is passed
into surge tank 46 so that an adequate supply for introduction
to pipe]ine 40 via line 48 is assured. Mild agitation means,
shown as propeller 49, may be supplied to insure substantially
complete dissolution of the polyisobutylene if desired.
While it is not contemplated nor necessary that the
descibed system be gas tight, it is desirable to provide
nitrogen vent 50 to conduct the gas away from the vicinity of
operation. It will be understood that, wherever possible,
~152677
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thermal insulation such as foamed rubber, foamed polyurethane
or asbestos is used to coat hoods, mechanisms and conduit
exteriors, especially liquid nitrogen tank 5 and conduits such
as 6, 25, 8, 3, and 23, hoods 4 and 17, housing 14 and impact
mill 20. It will be further understood that the crude oil in
tank 32 or surge tank 46 may be heated to assist dissolution.
However, as has been found, with preferred materials, this is
not necessary. In no event should temperature be allowed to
approach the decomposition temperature of the additive and, in
the case of polyisobutylene, should be maintained below about
200F. at all times. The use of ambient temperature in tanks
32 and 46 is preferred.
Appropriate controls such as valve means 60, 61, 62, 63,
and 64, the use and functions of which will be apparent to
those skilled in the art, are not shown; it is contemplated
that computer means to maintain temperature and flow rates of
polyisobutylene, nitrogen and liquid hydrocarbons will be
employed.
In a preferred embodiment of the invention, chopper 11
enclosed in hood 4 is positioned directly over impact mill 20
so that particles 19, at cryogenic temperature, fall by
gravity directly into the mill for comminuting into particles
24. This eliminates the need for screw conveyor 15 and
related apparatus and the temperature control afforded thereby
can be made up by appropriate regulation of liquid nitrogen
introduction into space 2.
EXAMPLES
The following examples illustrate the process of the
invention which, however, is not to be construed as limited
thereby.
Example ~:
Commercially available polyisobutylene having an
intrinsic viscosity (deciliters per gram) of from 5.56 to
7.23, a molecular weight determined by the viscosity averaging
method using the viscosity of a solution in isooctane at
20C. of 4,700,000 and a viscosity (poise) at 20C. of 1.5 x
1012, was cryogenically comminuted to particles sizes capable
Z~;77
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of passing through a No. 30 U. S. standard screen. Liquid
nitrogen was used to obtain and maintain cryogenic temperature
during comminution. The so-prepared particles were kept at
cryogenic temperature using liquid nitrogen for a short time
of less than about 30 minutes, after which the combination of
liquid nitrogen and particles as a slurry were added by
gravity flow to a commercially purchased diesel fuel.
Conglomeration of the particles, observed to some extent on
the surface of the diesel fuel, was completely prevented by
mild propeller induced swirling action to present a fresh
solvent surface to the falling particles. Approximately 712
pounds of the cryogenically ground polyisobutylene particles
were added to 5,600 gallons of the diesel fuel to make a 1.8
percent by weight solution. A mild propeller induced swirling
action was used to insure the presentation of a fresh solvent
surface to the falling particles. The diesel fuel was at
ambient temperature, which was about 70F.
The concentrate of polyisobutylene in diesel fuel was
used for drag reduction (friction reduction) in transporting
North Slope Crude through a 14 inch outside diameter pipeline
for a distance of 27,867 feet. The pipeline wall thickness
was 0.250 inches. Means for pressure determinat~on were
located at the start and end of the pipeline, and a positive
displacement meter was located immediately prior to the point
of introduction of the polyisobutylene concentrate. A
positive displacement screw pump driven by a variable speed
electric motor was used for injecting the polyisobutylene
concentrate into the pipeline.
Flow-pressure drop correlation for the untreated crude
was first obtained by noting pressure guage readings at
various flow rates. The polyisobutylene concentrate was then
injected at various concentrations and pressure readings noted
for each oil flow rate. Injections of the concentrate were
such as to give a polyisobutylene concentrate into the main
stream of crude of approximately 10 ppm, 20 ppm, 50 ppm, and
finally 75ppm and readings were obtained for different flow
rates varying in steps of 500 bbl/hr. After each change in
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the amount of concentrate added, the system was allowed to
stabilize for each change in flow rate of the crude; this
required approximately one hour after each change. From these
data a pressure drop due to friction at various flow rates was
obtained for untreated crude after correcting for elevation
difference at pressure points for calibration and comparison
to the data obtained during the injection of the
polyisobutylene concentrate. Data were recorded after steady
state conditions had been achieved in each instance.
Table I shows the results obtained.
TABLE I
Run Flow Velocity2 Conc P. In P. Out Drag Re-
No. Time Bbl/hr (ft/Sec. (ppm) (psig) (psig) duction %
1 1045 5364 8.4110.3 273.011.0 1.22
2 1055 5000 7.849.9 242.810.5 1.81
3 1110 4500 7.0610.7 201.0 9.7 4.23
4 1120 4000 6.2711.4 165.0 9.1 5.85
1220 5504 8.6320.9 274.812.9 5.49
6 1230 4911 7.7020.7 229.011.8 5.66
7 1240 3978 6.2420.9 169.010.5 3.29
8 1250 4444 6.9720.4 133.211.3 7.26
9 1355 5714 8.9650.0 254.414.6 19.18
1405 5240 8.2247.1 229.013.9 16.40
11 1415 4718 7.4046.9 196.813.3 15.48
12 1425 4150 6.5145.7 166.412.6 12.89
13 1435 3610 5.6645.~ 136.811.9 11.84
14 1540 5487 8.6078.5 228.016.0 23.89
1555 5070 7.9577.2 201.015.3 24.29
16 1605 4639 7.2776.7 186.014.3 18.95
17 1615 4211 6.6076.2 160.014.5 19.97
1~ 1630 3515 5.5174.8 128.813.7 15.67
Clock reading of time of day.
2Linear velocity of hydrocarbons through the pipeline.
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Runs 1 through 4 were obtained using a polyisobutylene
concentrate solution of about 10 ppm; flow rates were
progressively reduced in steps of about 500 bbl/hr., as
shown. It will be noted that the polyisobutylene was
effective in reducing drag and the effect thereon increased
with decreasing flow rate; i.e., with decreasing turbulence.
Runs 5 through 8 were performed using a concentrate of
polyisobutylene of about 20 ppm, followed with the same
procedure as for the Runs 1 through 4. It will be noted that
again the polyisobutylene is effective and effectiveness
increased with decreasing flow rate.
In Runs 9 through 13, the polyisobutylene concentrate
was increased to about 50 ppm and the procedure of Runs 1
through 4 repeated; again the flow rate was decreased by steps
of 500 bbl/hr to observe the effect on drag reduction. The
effectiveness of this concentrate is significantly above that
obtained at 10 ppm and 20 ppm, and the effectiveness decreased
with decreasing flow rate; i.e., increased with increasing
turbulence.
Runs 14 through 18 use a concentration of about 75 ppm
of polyisobutylene and again, following the same procedure, an
effectiveness of well over 20% was obtained at the higher flow
rates with the effectiveness decreasing somewhat with
decreasing flow rate.
The highest effectiveness was obtained by using a
concentration of polyisobutylene above 20 ppm, and especially
good results were obtained at relatively high flow rates of
the main body of hydrocarbons.
Example 2:
The same polyisobutylene of Example 1 was cryogenically
ground as therein described, and the particles were maintained
at cryogenic temperature until contacting with kerosene, i.e.,
with the hydrocarbons contained in the kerosene fraction of
petroleum. These hydrocarbons boil in the range of from about
310F. Mild stirring was used during contacting of the
particles with kerosene, and dissolution appeared to be
instantaneous.
~1~;i267~7
- 21 -
Sufficient concentrate was added to Sadlerochit (North
Slope) Crude Oil to give the indicated concentrations
of polyisobutylene therein
TABLE II
Concentration of Pipe Insude Drag
Polyisobutylene Diameter velocity Reduction
(ppm) (in~.-)--~~ (ft/sec) (%)
1.049 4.46 21.6
5.10 22.2
5.66 29.3
6.61 31.4
8.20 37.0
1.049 4.59 32.9
5.54 38.4
6.55 41.8
8.15 46.5
2.067 2.59 5.3
3.39 23~2
6.26 39.6
Drag reduction was very significant and greater
improvement was obtained at relatively high velocities.
Example 3:
The concentrate of polyisobutylene in diesel fuel
prepared in Example 1 was used to show drag reduction in the
pipeline tranportation of diesel fuel. The procedure of
Example 2 was followed and the following results obtained:
X
1~52f~77
- 22 -
TABLE III
Concentration ofPipe Inside Drag
PolyisobutyleneDiameter Velocity Reduction
(ppm) (in.) (ft/sec) (%)
1.049 3.0 24.0
2.3 14.8
1.9 9.6
2.1 13.9
1.5 0.8
1.3 0.0
1.6 6.4
2.1 14.6
2.5 18.5
2.7 19.6
3.2 24.5
1.6 2.1
1.8 7.4
2.067 3.0 28.2
2.3 20.2
1.9 15.1
1.7 14.6
2.1 21.7
2.5 22.7
2.7 29.5
3.2 32.9
1.3 8.8
1.6 9~4
1.8 15.1
2.0 18.9
Example 4:
A concentrate of polyisobutylene in kerosene having from
1% to 2~ by weight of the polymer was prepared for subsequent
introduction in hydrocarbons to be transported through a
conduit. Cubes of polyisobutylene measuring between about 3/8
inch and 1/2 inch, were added, while largely conglomerated, to
kerosene in a container with provision made for gentle
rotating motion. The polyisobutylene had a molecular weight
of about 4,700,000 Mv, and an amount sufficient to give the
desired concentration when completely dissolved was added.
Several batches were prepared. A mixing time of from 10 to 14
days were required before complete dissolution was obtained.
The resulting concentrations were tested by injection into a
flowing stream of additional kerosene to form a final
polyisobutylene concentration of 44 ppm, and flowing through a
copper pipe 1/2 inch internal diameter and about 150 feet in
~;2677
- 23 -
length. A reduction in friction, as determined by the
pressure drop in the pipe, was about 40%.
When this example is repeated in accordance with the
present invention, the cryogenically ground polyisobutylene
particles are contacted with mildly stirred kerosene and
substantially immediately dissolved. When tested in
additional kerosene in the same manner as above, substantially
the same friction reduction, about 40% is obtained.
Example S:
When Example 4 is repeated except that vigorous
mechanical agitation is provided to dissolve the
polyisobutylene, the effectiveness of the resulting
concentrate is decreased to about 28% reduction in friction,
believed due to a decrease in the molecular weight of the
polymer caused by the vigorous mechanical stirring.
The foregoing examples illustrate specific embodiments
of the invention. It may be noted that inconsistencies may
appear, as in Example 1 at low polyisobutylene concentration,
below about 20 ppm, when using conduits of widely different
diameters. In the preferred concentration range of above 20
ppm of polyisobutylene in the liquid hydrocarbons transported,
any such inconsistencies may be expected to disappear.
Repeating the examples according to the prior art by chopping,
grinding or shredding polyisobutylene and dissolving the so
produced particles in hydrocarbons requires hours and usually
many hours of stirring so that the shearing action degrades
the additive, and/or the application of heat to assist the
dissolution which also tends to degrade the polymer. The time
required and the degrading of the polyisobutylene make these
and comparable processes uneconomical.
When subjected to shearing conditions, polyisobutylene
will be degraded, i.e., there is a lowering of the molecular
weight, the amount being dependent upon the severity of the
conditions, as discussed in Example 5. As observed in Example
1, when used in large size conduits, degradation due to flow
is minimal. However, where pumping or other means are
employed which impart a high shearing action to polyiso-
;77
- 24 -
butylene, it may be advantageous to inject the additive into
the hydrocarbons being transported at points immediately
following such shearing means to insure excellent operation.
In accordance with the present invention, practically
instantaneous dissolution of polyisobutylene is essential so
that immediate introduction into hydrocarbons being
transported can be achieved. It is also possible to include
larger particles which do not so immediately dissolve, but
which slowly dissolve as they travel with the hydrocarbons
through the conduit so that additional protection against drag
increase at locations remote from the additive introduction is
obtained.
Example 6:
Commercially available polyethylene was cryogenically
comminuted to particles of size capable of passing through a
No. 30 U. S. standard screen. Liquid nitrogen was used to
obtain and maintain cryogenic temperature during comminution.
The so-prepared particles were maintained at cryogenic
temperature using liquid nitrogen until they were added by
gravity flow to mildly agitated toluene. A dilute solution of
polyethylene in toluene was obtained. The solution would
readily form thin, coherent and transparent films upon
evaporation of the toluene when spread on a solid surface.
Example 7:
A sample of commercially available polystyrene was
cryogenically comminuted in the manner described in Example
6. One portion of the so-prepared particles was maintained at
cryogenic temperature using liquid nitrogen until it was added
by gravity flow to mildly agitated toluene. Dissolution of
the polystyrene in the toluene was essentially instantaneous.
A second portion of the cryogenically ground polystyrene was
allowed to warm to room temperature and was thereafter added
to toluene. Dissolution of the warmed polystyrene in toluene
was observed to be much slower than was the dissolution of
polystyrene maintained at cryogenic temperature.
Example 8:
Cryogenically comminuted polyisobutylene was added as a
115Z677
- 25 -
slurry in liquid nitrogen to Sadlerochit (Alaskan North Slope)
crude oil by the method described in Example 1 to obtain
concentrations of polyisobutylene in the crude oil as high as
30 weight percent as determined by extraction analysis. The
samples containing relatively high polyisobutylene
concentrations, above about 10% to 15%, were rubbery, tacky
solids at room temperature.
The viscosity of several intermediate concentration
samples was determined by the cone and plate method using a
Weissenberg rheogoniometer at a temperature of 24C. The
viscosity, ~, was calculated from the equation:
~ = a
where a is the shear stress, and
~ is the rate of shear.
The following data were obtained:
TABLE IV
Rate of
Shear Viscosity x 10-3 (poise)
4.0 Wt. %* 7.7 Wt. 5* ~ 9.4 Wt. %*
(sec~l)
0.00886 9.15 77.4
0.0177 8.12 50.3 60.0
0.0352 5.80 35.9 50.5
0.0702 4.00 23.1 33.9
0.13~ 2.63 14.3 24.0
0.280 1.67 8.47 16.5
0.556 1.06 5.00 10.5
1.11 0.694 3.04 6.44
2.22 0.443 1.80 3.80
4.43 0.268 1.05 2.25
8.86 1.41
17.7 0.883
35.2 0.531
*Polyisobutylene incrude oil.
The viscosities listed are equilibrium values. At
intermediate shear rates a maximum appears in the stress vs.
time curves. At the higher shear rates a minimum appears in
the stress vs. time curves.
The foregoing description and Examples of the invention
are intended to be explanatory thereof, and various changes
may be made, within the scope of the following claims, without
departing from the spirit of the invention.
