U.S. patent application number 16/425255 was filed with the patent office on 2019-12-19 for modification of temperature dependence of pitch viscosity for carbon article manufacture.
The applicant listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Stephen H. Brown, Eric B. Sirota, Stuart E. Smith.
Application Number | 20190382664 16/425255 |
Document ID | / |
Family ID | 67106135 |
Filed Date | 2019-12-19 |
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United States Patent
Application |
20190382664 |
Kind Code |
A1 |
Smith; Stuart E. ; et
al. |
December 19, 2019 |
MODIFICATION OF TEMPERATURE DEPENDENCE OF PITCH VISCOSITY FOR
CARBON ARTICLE MANUFACTURE
Abstract
Methods are provided for reducing or minimizing the temperature
dependence of a pitch feed or fraction for use in carbon fiber
production, such as a mesophase pitch feed or fraction or an
isotropic pitch feed or fraction. A pitch sample can be
characterized to determine a characteristic temperature and a
characteristic viscosity for the sample. One or more solvent
extraction processes can also be performed on the pitch and/or the
extract and raffinate fractions formed by the solvent
extraction(s). The resulting raffinate and extract fractions are
then used to form a modified pitch fraction with a T.sub.0 value
that is lower than the T.sub.0 value of the original pitch. The
modified pitch fraction can optionally also have a different
.eta..sub.inf value relative to the original pitch.
Inventors: |
Smith; Stuart E.; (Easton,
PA) ; Sirota; Eric B.; (Flemington, NJ) ;
Brown; Stephen H.; (Lebanon, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
|
|
Family ID: |
67106135 |
Appl. No.: |
16/425255 |
Filed: |
May 29, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62685571 |
Jun 15, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10C 3/08 20130101; C10C
3/005 20130101; D01F 9/145 20130101 |
International
Class: |
C10C 3/08 20060101
C10C003/08 |
Claims
1. A method for forming a modified pitch, comprising: performing
solvent extraction on a pitch comprising a T.sub.0 value to form an
extract comprising a first fraction of the pitch and a raffinate
comprising a second fraction of the pitch; and blending at least a
portion of the first fraction with at least a portion of the second
fraction to form a modified pitch having a modified T.sub.0 value
less than the T.sub.0 value of the pitch.
2. The method of claim 1, wherein the first fraction and the second
fraction comprise a first volume ratio, and wherein a volume ratio
comprising the at least a portion of the first fraction and the at
least a portion of the second fraction is greater than the first
volume ratio.
3. The method of claim 1, wherein the at least a portion of the
first fraction is formed from the extract without performing an
additional solvent extraction step; or wherein the at least a
portion of the second fraction is formed from the raffinate without
performing an additional solvent extraction step; or a combination
thereof.
4. The method of claim 1, wherein the at least a portion of the
second fraction is formed by a method comprising: performing a
second solvent extraction on at least a portion of the raffinate to
form a second extract comprising a third fraction of the pitch and
a second raffinate comprising a fourth fraction of the pitch, the
fourth fraction comprising the at least a portion of the second
fraction.
5. The method of claim 4, wherein the modified pitch further
comprises at least a portion of the third fraction, a volume ratio
of the at least a portion of the first fraction, the at least a
portion of the third fraction, and the at least a portion of the
fourth fraction being different from a volume ratio of the first
fraction, the third fraction and the fourth fraction in the
pitch.
6. The method of claim 4, wherein the modified pitch does not
include a portion of the third fraction.
7. The method of claim 4, wherein performing a solvent extraction
comprises performing an extraction with a first solvent, wherein
performing a second solvent extraction comprises performing an
extraction with a second solvent, and wherein the first solvent has
a solubility parameter that is different from a solubility
parameter of the second solvent by 1.0 or more.
8. The method of claim 1, wherein the at least a portion of the
first fraction is formed by a method comprising: performing a third
solvent extraction on at least a portion of the first fraction to
form a second extract comprising a fifth fraction of the pitch and
a second raffinate comprising a sixth fraction of the pitch, the
fifth fraction comprising the at least a portion of the first
fraction.
9. The method of claim 8, wherein the modified pitch further
comprises at least a portion of the fourth fraction, a volume ratio
of the at least a portion of the second fraction, the at least a
portion of the fourth fraction, and the at least a portion of the
third fraction being different from a volume ratio of the second
fraction, the fourth fraction and the third fraction in the pitch;
or wherein the modified pitch does not include a portion of the
fourth fraction.
10. The method of claim 8, wherein performing a solvent extraction
comprises performing an extraction with a first solvent, wherein
performing a third solvent extraction comprises performing an
extraction with a second solvent, and wherein the first solvent has
a solubility parameter that is different from a solubility
parameter of the second solvent by 1.0 or more.
11. The method of claim 1, wherein the pitch comprises a mesophase
pitch and wherein the modified pitch comprises a modified mesophase
pitch; or wherein the pitch comprises an isotropic pitch and
wherein the modified pitch comprises a modified isotropic
pitch.
12. The method of claim 11, wherein the mesophase pitch comprises
10 vol % or more of an optically active fraction.
13. The method of claim 1, wherein the pitch comprises a glass
transition having a width of 40.degree. C. or less; or wherein the
pitch comprises a softening point of 100.degree. C. to 300.degree.
C.; or wherein the pitch comprises a coke value of at least 50 wt.
% or more; or a combination thereof.
14. The method of claim 1, wherein the pitch comprises a viscosity
at 280.degree. C. of 20 Pa-sec or less; or wherein the pitch
comprises a T5 distillation point of 350.degree. C. or more; or
wherein the pitch comprises a T50 distillation point of 500.degree.
C. or more; or a combination thereof.
15. The method of claim 1, wherein the modified pitch comprises a
modified T.sub.0 value that is at least 5.0.degree. C. less than
the T.sub.0 value of the pitch, or wherein the modified pitch
comprises a modified .eta..sub.inf value that is greater than a
.eta..sub.inf value of the pitch, or a combination thereof.
16. A method for forming a modified pitch, comprising: performing
solvent extraction on a pitch comprising a T.sub.0 value to form an
extract comprising a first fraction of the pitch and a raffinate
comprising a second fraction of the pitch; performing a second
solvent extraction on a) at least a portion of the first fraction
or b) at least a portion of the second fraction, to form a second
extract comprising a third fraction of the pitch and a second
raffinate comprising a fourth fraction of the pitch, wherein the
second solvent extraction is performed on the at least a portion of
the first fraction, a T.sub.0 of the fourth fraction being less
than the T.sub.0 value of the pitch, the modified pitch
corresponding to at least a portion of the fourth fraction, or
wherein the second solvent extraction is performed on the at least
a portion of the second fraction, a T.sub.0 value of the third
fraction being less than the T.sub.0 value of the pitch, the
modified pitch corresponding to at least a portion of the third
fraction.
17. The method of claim 16, further comprising separating an
extract product fraction and a solvent fraction from the extract,
the extract product fraction comprising the at least a portion of
the first fraction.
18. The method of claim 16, further comprising separating a solvent
recovery fraction from the raffinate; or further comprising
separating a second solvent recovery fraction from the second
raffinate; or a combination thereof.
19. The method of claim 16, wherein performing a solvent extraction
comprises performing an extraction with a first solvent, wherein
performing a second solvent extraction comprises performing an
extraction with a second solvent, and wherein the first solvent has
a solubility parameter that is different from a solubility
parameter of the second solvent by 1.0 or more.
20. The method of claim 16, wherein the pitch comprises a mesophase
pitch and wherein the modified pitch comprises a modified mesophase
pitch.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 62/685,571 filed Jun. 15, 2018, which is
herein incorporated by reference in its entirety.
FIELD
[0002] Systems and methods are provided for modifying the
temperature dependence of pitch feedstocks, such as mesophase pitch
feedstock and/or isotropic pitch feedstocks, for use in production
of carbon fiber.
BACKGROUND
[0003] Isotropic pitch and mesophase pitch are carbon-containing
feedstocks that can be formed from residues generated during
processing of coal or petroleum feedstocks or by other methods,
such as acid catalyzed condensation of small aromatic species. As
an example, one of the fractionation products from a catalytic
cracking process or slurry hydrocracking process can be a bottoms
or "pitch" fraction. Such a pitch fraction can correspond to
isotropic pitch. For some grades of carbon fiber, isotropic pitch
can be used as an initial feedstock. For other grades, the
isotropic pitch can be exposed to thermal cracking conditions to
cause formation of an anisotropic phase. The anisotropic pitch
phase (or mesophase pitch) can be identified, for example, using
polarized light microscopy. This mesophase pitch can then be used
for carbon fiber production. Optionally, a solvent can be added to
isotropic pitch and/or mesophase pitch to modify the viscosity
prior to carbon fiber formation.
[0004] The production of carbon fiber from isotropic pitch or
mesophase pitch is typically achieved by a melt spinning process.
The pitch is heated to sufficiently high temperatures to reduce the
viscosity of the pitch, so that the heated pitch can pass through a
spinnerette. The resulting carbon fiber is then wound on a spinning
spool. However, the viscosity of many types of pitch samples is
strongly dependent on temperature. This strong temperature
dependence can cause large variations in the fiber diameter and/or
high tensile stress within the filament with small temperature
gradients during fiber formation. In order to overcome this
difficulty, conventional production of carbon fiber from pitch
requires the process to be operated within a narrow temperature
window, which can be challenging to maintain under commercial
production conditions. Additionally, difficulties in maintaining
the production process in the desired temperature window can also
limit the throughput of the produced fiber. For example, the
sensitivity of the fiber formation process to small temperature
variations can result in fiber breakage. The fiber breakage can be
caused, for example, due to loss of ability for the mesophase pitch
to flow through the spinnerette and/or due to structural weak
points in the fiber that are created by size variations and/or
tensile stress. It would be desirable to identify systems and/or
methods that can improve the ability to produce carbon fiber from
mesophase pitch.
[0005] U.S. Pat. No. 4,208,267 describes methods for forming a
mesophase pitch. An isotropic pitch sample is solvent extracted.
The extract is then exposed to elevated temperatures in the range
of 230.degree. C. to about 400.degree. C. to form a mesophase
pitch.
[0006] U.S. Pat. No. 5,643,546 describes methods for forming carbon
fiber from mesophase pitch. As part of the preparation for the
meosphase pitch, the mesophase pitch is solvent extracted using a
mixture of solvents with different solubility parameters to remove
an undesired extract portion.
[0007] U.S. Pat. No. 6,717,021 describes the addition of an
aromatic solvent as a solvating component to produce a solvated
mesophase pitch. While this route decreases the viscosity of the
material, it requires sacrificial solvent, dilutes the amount of
mesophase pitch produced and introduces volatile components which
may break the fiber during spinning.
SUMMARY
[0008] In an aspect, a method for forming a modified pitch is
provided. The method includes performing solvent extraction on a
pitch comprising a T.sub.0 value to form an extract comprising a
first fraction of the pitch and a raffinate comprising a second
fraction of the pitch. At least a portion of the first fraction can
be blended with at least a portion of the second fraction to form a
modified pitch having a modified T.sub.0 value less than the
T.sub.0 value of the pitch. For example, the modified pitch can
have a modified T.sub.0 value that is at least 5.0.degree. C. less
than the T.sub.0 value of the pitch.
[0009] In some aspects, the at least a portion of the first
fraction can be formed from the extract without performing an
additional solvent extraction step. Additionally or alternately, in
some aspects the at least a portion of the second fraction is
formed from the raffinate without performing an additional solvent
extraction step.
[0010] In some aspects, the at least a portion of the second
fraction can correspond to a portion that is formed by performing a
second solvent extraction and/or the at least a portion of the
first fraction can correspond to a portion that is formed by
performing a third solvent extraction.
[0011] In another aspect, a method for forming a modified pitch is
provided. The method includes performing solvent extraction on a
pitch comprising a T.sub.0 value to form an extract comprising a
first fraction of the pitch and a raffinate comprising a second
fraction of the pitch. A second solvent extraction is then
performed on a) at least a portion of the first fraction or b) at
least a portion of the second fraction, to form a second extract
comprising a third fraction of the pitch and a second raffinate
comprising a fourth fraction of the pitch. In some aspects, the
second solvent extraction is performed on the at least a portion of
the first fraction. In such aspects, a T.sub.0 of the fourth
fraction can be less than the T.sub.0 value of the pitch and/or the
modified pitch can correspond to at least a portion of the fourth
fraction. In some aspects, the second solvent extraction is
performed on the at least a portion of the second fraction. In such
aspects, a T.sub.0 value of the third fraction can be less than the
T.sub.0 value of the pitch and/or the modified pitch can correspond
to at least a portion of the third fraction.
[0012] In some aspects, the pitch can correspond to a mesophase
pitch and the modified pitch can correspond a modified mesophase
pitch. In some aspects, the pitch can correspond to an isotropic
pitch and the modified pitch can correspond to a modified isotropic
pitch.
BRIEF DESCRIPTION OF THE FIGURES
[0013] FIG. 1 shows an example of a process flow for forming a
modified pitch fraction from an initial pitch fraction.
[0014] FIG. 2 shows an example of fitting an Arrhenius-style
functional form to viscosity and temperature data.
[0015] FIG. 3 shows a comparison of predicted T.sub.0 and
.eta..sub.inf values (determined according to equations 3 and 4)
with measured values for various blends of two vacuum resid
fractions.
[0016] FIG. 4 shows viscosity as a function of temperature for a
hypothetical initial mesophase pitch fraction and a modified
mesophase pitch fraction.
[0017] FIG. 5 shows the derivative with respect to temperature for
the viscosity versus temperature data in FIG. 4.
DETAILED DESCRIPTION
[0018] In various aspects, systems and methods are provided for
reducing or minimizing the temperature dependence of a pitch feed
or fraction for use in carbon fiber production, such as a mesophase
pitch feed or fraction or an isotropic pitch feed or fraction.
Initially, a mesophase pitch sample (or more generally a pitch
sample) can be characterized to determine a characteristic
temperature and a characteristic viscosity for the sample. Examples
of characteristic values for a pitch fraction are the asymptotic
values of viscosity at infinite temperature (.eta..sub.inf) and the
finite temperature at which the viscosity diverges (T.sub.0). In
addition to determining a characteristic temperature and a
characteristic viscosity, one or more solvent extraction processes
can be performed on the pitch and/or the extract and raffinate
fractions formed by the solvent extraction(s). The resulting
raffinate and extract fractions are then used to form a modified
pitch fraction with a T.sub.0 value that is lower than the T.sub.0
value of the original pitch. The modified pitch fraction can also
have a different .eta..sub.inf value relative to the original
pitch. By reducing the T.sub.0 value, the temperature dependence of
the viscosity for the modified pitch is reduced relative to the
initial pitch fraction. Reducing the temperature dependence of the
viscosity can reduce or relax the temperature constraints that are
needed for producing a desired carbon fiber product from the pitch.
Optionally, the blend of extract(s) and raffinate(s) can be
selected to both reduce the T.sub.0 value and increase the
.eta..sub.inf value. Reducing the T.sub.0 value of a mesophase
pitch fraction and/or other pitch fraction can also tend to cause a
reduction in the viscosity. Selecting a blend of extract(s) and
raffinate(s) that increases .eta..sub.inf can offset some of the
decrease in viscosity due to lowering the T.sub.0 value.
[0019] In some aspects, the modified pitch fraction (such as a
modified mesophase pitch fraction) can have a T.sub.0 value that is
less than the T.sub.0 of the initial pitch by at least 5.degree.
C., or at least 10.degree. C., or at least 15.degree. C., such as
down to 40.degree. C. less or possibly still lower. Additionally or
alternately, the modified (mesophase) pitch fraction can have a
.eta..sub.inf value that is greater than the .eta..sub.inf of the
initial pitch by 0.001 Pa-sec or more, or 0.002 Pa-sec or more, or
0.003 Pa-sec or more, such as up to 0.01 Pa-sec or possibly still
greater.
[0020] In some aspects, a modified pitch fraction can be formed by
performing successive solvent extractions, but without re-blending
of the products from the solvent extractions. In such aspects, the
successive solvent extractions can be used to form a "heart cut" of
the original pitch fraction with a reduced T.sub.0 value. For
example, successive solvent extractions can be used to form a
modified pitch fraction where the highest solubility parameter
components and lowest solubility parameter components in the
initial pitch fraction are reduced or minimized. This can be
achieved, for example, by performing a solvent extraction on a
pitch sample to form an initial extract and an initial raffinate.
If the desired portion of the pitch is in the initial extract, a
second extraction can be performed using a second solvent, with the
second solvent selected so that the desired portion of the pitch is
part of the second raffinate. Alternatively, if the desired portion
of the pitch is in the initial raffinate, a second extraction can
be performed so that the desired portion of the pitch is part of
the second extract.
[0021] In some optional aspects, a test amount of carbon fiber may
be made from a pitch sample prior to separation and/or blending to
form a modified pitch. In such aspects, the T.sub.0 and values for
the pitch fraction can be determined before or after forming the
carbon fiber product. If the temperature dependence of the pitch
fraction (such as a mesophase pitch fraction) results in carbon
fiber product with undesirable properties, then solvent extraction
and blending can be performed to make a modified pitch fraction.
For example, for carbon fiber in a green state (i.e., as it leaves
the spinnerette and prior to any additional heating or pyrolyzing
to make a final carbon fiber product), if carbon fiber made from
the pitch has a variation in diameter of 10% or more, or 15% or
more, or 20% or more, due to a temperature variation across the
fiber during production (i.e., across the face of a spinnerette) of
4.0.degree. C. or less, or 3.5.degree. C. or less, or 3.0.degree.
C. or less, then solvent extraction and blending of the resulting
extract(s) and raffinate(s) can be performed to make a modified
pitch fraction.
[0022] Production of carbon fiber represents a potentially high
value end use for isotropic pitch and/or mesophase pitch fractions.
Unfortunately, the viscosity of many pitch fractions has a strong
dependence on temperature in the temperature ranges suitable for
carbon fiber formation. This can cause a variety of problems during
manufacture of carbon fiber, such as inconsistent product quality
and breaking of the fiber during the spinning process. While
addition of solvents to the pitch can potentially reduce the
temperature dependence of the viscosity, such solvents can also
dilute the pitch and/or increase the likelihood of breaking the
fiber during the spinning process. In various aspects, the methods
described herein allow an improved pitch fraction to be formed
without requiring the addition of a solvent that remain in the
improved pitch fraction. Instead, the solvents used for the
extraction process(es) to form the improved pitch fraction can be
recovered and used again to perform subsequent extractions.
[0023] In this discussion, some pitch fractions are described using
volume ratios of blending components. In some aspects, volume
ratios are provided between pairs of blending components in a
fraction. Additionally or alternately, when three or more blending
components are used to form a mesophase pitch fraction, volume
ratios of three or more components may be used, such as a three
component ratio in the form of "X:Y:Z".
[0024] In this discussion, the solvating power of a potential
solvent for use in solvent extraction can be defined based on the
Hildebrand solubility parameter. The Hildebrand solubility
parameter is defined as
.delta. = ( .DELTA. H v RT V ) 0.5 ( 1 ) ##EQU00001##
[0025] In Equation (1), .DELTA.H.sub.v is the heat of vaporization
of the solvent, R is the molar gas constant, T is the temperature
in Kelvin, and V is the molar volume. In this discussion,
solubility parameter values are based on use of SI units for
expressing the quantities in Equation (1). The units for the
solubility parameter correspond to (MPa).sup.0.5. Some values for
the solubility parameter for representative solvents include:
isopentane--13.5; n-pentane--14.4; n-hexane--14.9; n-heptane--15.3;
cyclohexane--16.8; toluene--18.3; pyridine--21.7; quinoline--22.4;
methylene chloride--20.2; and tetrahydrofuran--18.5. Values for the
solubility parameter can be found in various on-line or printed
references, such as the Material Properties Tables available
on-line from "Knovel Solvents--A Properties Database", or in tables
of solubility parameters in references such as the Adhesives
Technology Handbook, 3.sup.rd Edition (Ebnesajjadz et al.,
2014).
Pitch Feedstock and Characterization
[0026] In various aspects, isotropic pitch and/or mesophase pitch
can be used as a feedstock for formation of carbon fibers. Pitch
feedstocks can be formed from a variety of heavy oil and/or heavy
hydrocarbonaceous fractions that include a substantial portion of
aromatics. Some heavy oil fractions can be suitable without further
processing, while other fractions can be at least partially
converted to mesophase pitch feeds by heat treatment and/or
performing a limited polymerization. Suitable fractions for use as
pitch and/or for forming mesophase pitch can include, but are not
limited to, heavy oils, coal tar fractions formed during conversion
of coal to coke; bottoms fractions from fluid catalytic cracking;
steam cracker tar; pitch formed during slurry hydroconversion
and/or fixed bed hydroconversion (such as hydroconversion of heavy
oils); and/or "rock" fractions generated during solvent
deasphalting of a heavy oil. More generally, pitch fractions for
formation of carbon fiber can be formed from any of the above
sources.
[0027] Suitable pitch feesdtocks and/or mesophase pitch feedstocks
for formation of carbon fiber can be identified, for example, based
on the coke yield of the (mesophase) pitch feedstock if exposed to
pyrolysis or coking conditions. For example, suitable feedstocks
can provide a coke yield of 40 wt % or more relative to a weight of
the feedstock, or 50 wt % or more, or 75 wt % or more, or 85 wt %
or more, or 95 wt % or more, when exposed to thermal cracking
conditions that include a coking temperature of 500.degree. C. at
atmospheric pressure for 15 minutes, according to the method of
ASTM D4530.
[0028] Another way of defining a feedstock is based on the boiling
range of the feed. One option for defining a boiling range is to
use an initial boiling point for a feed and/or a final boiling
point for a feed. Another option, which in some instances may
provide a more representative description of a feed, is to
characterize a feed based on the amount of the feed that boils at
one or more temperatures. For example, a "T5" boiling point for a
feed is defined as the temperature at which 5 wt % of the feed will
boil off. Similarly, a "T95" boiling point is a temperature at 95
wt % of the feed will boil. The percentage of a feed that will boil
at a given temperature can be determined, for example, by the
method specified in ASTM D2887 (or by the method in ASTM D7169, if
ASTM D2887 is unsuitable for a particular fraction). A pitch feed
or fraction for forming carbon fiber can have a normal atmospheric
initial boiling point of about 350.degree. C. or more, or
400.degree. C. or more, and can further have a penetration range
from 20 to 500 dmm at 25.degree. C. (ASTM D-5). Alternatively, a
feed may be characterized using a T5 boiling point, such as a feed
with a T5 boiling point of 350.degree. C. or more, or 400.degree.
C. or more, or 440.degree. C. or more. Additionally or alternately,
a feed may be characterized using a T50 boiling point, such as a
feed with a T50 boiling point of 500.degree. C. or more.
[0029] For mesophase pitch fractions, other types of
characterization can be based on solubility and optical activity.
In some aspects, the optically active portion of a mesophase pitch
fraction can correspond to 10 vol % or more of the fraction, or 25
vol % or more, or 50 vol % or more. In some aspects, the amount of
quinoline-insoluble content in a mesophase pitch fraction can be 75
wt % or less, or 50 wt % or less, or 30 wt % or less, or 10 wt % or
less, such as down to substantially no quinoline-insoluble content.
Additionally or alternately, the amount of toluene-insoluble
content in a mesophase pitch fraction can be 80 wt % or less, or 60
wt % or less, or 40 wt % or less, or 30 wt % or less, such as down
to substantially no toluene-insoluble content. In some aspects, the
width of the glass transition temperature for the mesophase pitch
can be 40.degree. C. or less, as determined by differential
scanning calorimetry according to ASTM D6604 (or according to
E1356, if ASTM D6604 is unsuitable for a particular sample).
[0030] Other characteristics of suitable pitch feeds or fractions
can include, but are not limited to, softening point, metals
content, solids content (for pitch feeds formed from, for example,
coal tar), heteroatom content (S, N), and viscosity. For example,
some suitable feedstocks can have a softening point according to
ASTM D3104 of 100.degree. C. to 300.degree. C., or 150.degree. C.
to 250.degree. C. Although some feedstocks may not strictly
correspond to an asphalt or bitumen fraction, it is believed that
ASTM D3104 is suitable for characterizing pitch fractions.
Additionally or alternately, the pitch can include 200 wppm or less
of metals and/or 200 wppm or less of total nickel, vanadium and
iron. Further additionally or alternately, a pitch fraction (such
as a feed for forming carbon fiber) can have a viscosity at
280.degree. C. of 20 Pa-sec or less, or 15 Pa-sec or less.
[0031] In some aspects, a pitch feed or fraction can include 50
wppm to 1000 wppm elemental nitrogen or more (i.e., weight of
nitrogen in various nitrogen-containing compounds within the feed).
Additionally or alternately, the feed can include 500 wppm to
60,000 wppm elemental sulfur. Sulfur will usually be present as
organically bound sulfur. Examples of such sulfur compounds include
the class of heterocyclic sulfur compounds such as thiophenes,
tetrahydrothiophenes, benzothiophenes and their higher homologs and
analogs. Other organically bound sulfur compounds include
aliphatic, naphthenic, and aromatic mercaptans, sulfides, and di-
and polysulfides.
Determining Characteristic Temperature and Viscosity Values for
Mixtures
[0032] In various aspects, the T.sub.0 and .eta..sub.inf values for
a potential feed component and/or potential pitch component can be
determined based on Equation (2).
.eta. = .eta. inf e D [ ( T / T 0 ) - 1 ] ( 2 ) ##EQU00002##
[0033] In Equation (2), .eta. is the viscosity at a temperature T.
.eta..sub.inf and T.sub.0 have the definitions provided above. In
Equation (2), D is a constant that can be set based on historical
data for pitch and/or asphalt fractions. While D can vary in
practice, in Equation (2), sufficient accuracy can be achieved by
setting D to a constant value that is representative of the
.eta..sub.inf values that are typically encountered in pitch blend
and/or asphalt blend components. In this discussion, D will be set
to a constant value of 7.5. Other potential values for D could be
selected while also giving suitable results, such as a constant
value for D between about 5.0 to about 15.0, and preferably a
constant value for D between about 6.5 to about 10.5.
[0034] In Equation (2), based on the use of a constant value for D,
such as 7.5, for a given feed and/or pitch component, .eta..sub.inf
and T.sub.0 are the two values that need to be fit to experimental
data. Thus, at least two measurements of the viscosity .eta. at a
temperature T are needed to fit values to .eta..sub.inf and
T.sub.0. In practice, additional measured values can be obtained
for a given component in order to further improve the fit of
Equation (2) to the data.
[0035] One option for obtaining viscosity values at different
temperature for a component sample is to obtain viscosity values at
different temperatures. Preferably, the viscosity values obtained
for a component can be obtained using a single measurement device,
so that any systematic errors in the measurement will be the same
for all measured values on a component. Alternatively, other types
of devices for measuring a kinematic viscosity at a temperature can
be used to generate a plurality of viscosity values .eta. at a
plurality of temperatures T. An example of a suitable measurement
method can be ASTM D4402. It is noted that ASTM D4402 is directed
to measurements at up to 260.degree. C. If measurements at higher
temperatures are desirable, an alternative method suitable for
higher temperature measurement can be used instead.
[0036] With regard to selecting temperatures for obtaining
viscosity values, several factors can be considered. For isotropic
pitch samples, the viscosity values for a component can be obtained
at temperatures where the component behaves as a Newtonian fluid.
For instances where the pitch exhibits non-Newtonian behavior, the
viscosity can be obtained by extrapolating to zero shear. For
potential feed fractions and/or pitch samples that have a high
hardness value, it may be necessary to measure the viscosity at
higher temperatures, such as at least about 130.degree. C., or at
least about 150.degree. C., or at least about 200.degree. C., or at
least about 250.degree. C., or at least about 300.degree. C., or at
least about 350.degree. C. Another factor can be to have at least
two data points within the set of data for fitting the
.eta..sub.inf and T.sub.0 values that are at least about 10.degree.
C. apart. If the temperatures for all of the viscosity values in
the data set are grouped too closely together, the quality of the
parameter fit may be reduced.
[0037] After obtaining two or more viscosity and temperature data
point pairs for a potential feed and/or pitch component (such as a
mesophase pitch component), the .eta..sub.inf and T.sub.0 can be
calculated by fitting the data points to the functional form shown
in Equation (2). This process can be repeated for each desired
pitch component that is to be included in a pitch blend.
Additionally or alternately, the .eta..sub.inf and T.sub.0 values
for one or more pitch components in a blend can be determined based
on fitting Equation (2) to previously obtained or published data
for a component. This previously obtained or published data can
correspond to viscosity and temperature values as described above,
or the prior data can correspond to other data that allows for
calculation of a viscosity at a plurality of temperatures.
[0038] One variation on the model is that the glass transition
temperature (T.sub.g) for a group of components to be used in a
feed and/or pitch can be used in place of T.sub.0 if desired. The
procedure for fitting measured data to Equation (2) and subsequent
use of the T.sub.g and .eta..sub.inf values is otherwise
similar.
Predicting Pitch Properties Based on Blend Components
[0039] Based on T.sub.0 and .eta..sub.inf values for a plurality of
components, the T.sub.0 and .eta..sub.inf value for a resulting
blend of components can be determined. An advantage of using
T.sub.0 and .eta..sub.inf to characterize the components of a pitch
blend is that the values can be used in a weighted average to
determine the T.sub.0 and .eta..sub.inf value for the resulting
blend. In particular, the T.sub.0 value of a blend of components
can be determined by Equation (3). The .eta..sub.inf value of a
blend of components can similarly be determined by Equation
(4).
T 0 = i .phi. i T 0 , i ( 3 ) ln .eta. inf = i .phi. i ln .eta. inf
, i ( 4 ) ##EQU00003##
[0040] In Equations (3) and (4), O.sub.i corresponds to the volume
percent of component "i" in a blend. As shown in Equations (3) and
(4), the T.sub.0 values can be combined as a weighted average of
the T.sub.0 values of the components, while the .eta..sub.inf
values can be combined as a weighted average of a log of the
.eta..sub.inf values of the components.
Modification of Pitch Fractions
[0041] In various aspects, a modified pitch fraction (such as a
modified mesophase pitch fraction) can be formed by 1) performing
one or more solvent extractions on an initial (mesophase) pitch
fraction to form one or more raffinates and one or more extracts;
and 2) combining portions of the resulting raffinates and extracts
to form a modified (mesophase) pitch fraction having lower T.sub.0
values than the initial pitch fraction.
[0042] In some aspects, a modified pitch fraction can be formed
using a single solvent extraction stage. In such aspects, an
initial pitch fraction is solvent extracted using a suitable
solvent to form an extract and a raffinate. The extract
substantially corresponds to the portion of the initial pitch
fraction that is soluble in the solvent, along with the solvent,
while the raffinate substantially corresponds to a portion of the
initial pitch fraction that is insoluble in the solvent. Of course,
due to practical limitations, the extract may include some
insoluble components and the raffinate may include some soluble
components, but these can be reduced or minimized to a desired
level based on the design and the operating conditions of the
solvent extractor. Due to such practical limitations, the extract
can be referred to as including a majority of the components from
the feed to the extraction stage that are soluble in the solvent,
while the raffinate can be referred to as including a majority of
the components from the feed to the extraction stage that are
insoluble in the solvent.
[0043] In other aspects, more than one solvent extraction can be
performed. For example, after performing a first solvent
extraction, the raffinate from the first extraction stage can be
exposed to a second solvent under solvent extraction conditions.
The second solvent can have a sufficiently higher solubility
parameter value than the first solvent, so that the second solvent
is effective for solvating a portion of the raffinate. This process
can be repeated as many times as desired to form a plurality of
extracts and a final raffinate. Additionally or alternately, the
extract from the first extraction stage could be selected for
additional solvent extraction steps using solvents with a lower
solubility parameter. In this type of aspect, it may be desirable
to remove the first solvent from the extract prior to exposing the
remaining portion of the extract to the second solvent. In this
type of aspect, the second solvent can have a lower solvating power
than the first solvent. This process can be repeated as many times
as desired to form a plurality of raffinates and a final extract.
More generally, in still other aspects, a combination of extraction
stages can be used to form a plurality of extracts and a plurality
of raffinates. In such aspects, various combinations of using
solvents with various solubility parameters can be used to create
desired extract fractions and/or raffinate fractions.
[0044] A wide variety of solvents are suitable for use in a solvent
extraction stage. Typically, suitable solvents can have a T5 to T95
boiling range of 50.degree. C. to 300.degree. C. Examples of
suitable solvents include, but are not limited to, C.sub.2-C.sub.10
paraffins; single ring aromatics such as toluene, xylene, and
ethylbenzene; multi-ring aromatics, such as naphthalene and
anthracene; aromatics including a heteroatom such as pyridine;
other heteroatom compounds such as tetrahydrofuran; heavy naphtha,
kerosene, and/or light diesel fractions; and other hydrocarbon or
hydrocarbon-like fractions having a suitable boiling range.
Combinations of the above solvents may also be used in order to
achieve a desired solubility parameter. In some aspects, a paraffin
such as hexane or heptane may be included as a co-solvent to modify
the solubility parameter of a solvent mixture. References herein to
a solubility parameter are references to the Hildebrand solubility
parameter expressed in SI units, as defined above.
[0045] In aspects where multiple extractions are performed to form
a plurality of extracts and/or raffinates, a first solvent (or a
solvent from a prior extraction stage) can have a solubility
parameter that differs from a second solvent (or a solvent from a
later extraction stage) by 2.0 or more, or 4.0 or more.
Additionally or alternately, when multiple extraction stages are
used to form a plurality of extracts and a raffinate, in some
aspects a suitable solvent for a first stage can correspond to
pyridine or another solvent (such as a mixture of solvent
components) that has a solubility parameter of 21 or more. In such
aspects, a suitable second solvent can have a lower solubility
parameter, such as toluene or tetrahydrofuran, or possibly a
solvent where at least one component of the solvent corresponds to
a paraffin. Such second solvents can have a solubility parameter of
19.5 or less.
[0046] After forming the extract(s) and the raffinate(s), the one
or more extracts (after removal of solvent) and one or more
raffinates (optionally after removing any solvent) can be
characterized to determine a T.sub.0 and an .eta..sub.inf value for
each portion. Based on the T.sub.0 and an .eta..sub.inf values, the
extract and raffinate can be recombined in desired weight ratio(s)
to produce a modified pitch product with a lower T.sub.0 value. Any
convenient weight ratio of the various extracts and raffinates that
results in a lower T.sub.0 value can potentially be used. It is
noted that the ratio will be different from the weight ratio(s) of
the extract and raffinate that are generated based on the solvent
extraction(s).
[0047] The desired ratio of extract to raffinate can be determined
based on Equations (2) to (4) as described above. The desired ratio
can be selected, for example, to form a modified pitch fraction
having a T.sub.0 value that is lower than the T.sub.0 value of the
initial pitch fraction by 3.0.degree. C. or more, or 5.0.degree. C.
or more, or 10.degree. C. or more, or 15.degree. C. or more, such
as up to 40.degree. C. or possibly still greater. The amount of
difference in T.sub.0 in the resulting extracts and raffinates can
be determined in part based on the solubility of the one or more
solvents used to form the extracts and raffinates.
[0048] Although it is not required, the extract phase (after
removal of solvent) will typically have a lower T.sub.0 value than
the initial pitch fraction while the raffinate (after removing
solvent, if necessary) will typically have a higher T.sub.0 value.
As a result, when a single extraction is performed to form a single
raffinate and single extract, in many instances the weight ratio of
extract to raffinate in the modified mesophase pitch will be
greater than the weight ratio of the amount of extract formed
versus the amount of raffinate formed during the solvent
extraction.
[0049] In aspects where a plurality of solvent extractions are
performed, at least three fractions will be available for
recombination to form the modified mesophase pitch. The three
fractions can include the final raffinate, the final extract, and
one or more intermediate raffinates or extracts. In some aspects,
the one or more intermediate extracts can correspond to extract
fractions formed during extraction stages prior to the final stage,
with the intermediate extracts not be subjected to further solvent
extraction. In some aspects, the one or more intermediate
raffinates can correspond to raffinate fractions formed during
extraction stages prior to the final stage, with the intermediate
raffinates not be subjected to further solvent extraction.
[0050] When multiple extracts and/or raffinates are available based
on performing a plurality of solvent extractions, multiple options
are available for blending the multiple extracts and/or raffinates
to form a desired modified pitch with a reduced T.sub.0 value. In
some aspects, the composition of the modified pitch can be
described in relation to the composition of the initial pitch. The
initial pitch feed can roughly be described as a combination of the
various extracts and raffinates that are generated by performing
solvent extraction(s) on the initial feed, with weight ratios
corresponding to the resulting weights of the various raffinate and
extract fractions. When a modified pitch is formed by blending
portions of the raffinate and extract fractions, the weight ratios
for the initial feed can be compared with the weight ratios for the
modified pitch. It is noted that for the modified pitch, the value
in the weight ratio for one or more of the raffinate or extract
fractions may be "0", as it may be desirable to entirely exclude
one or more of the extract and/or raffinate fractions from the
modified pitch product.
[0051] As an example, one option can be to form a modified pitch
having weight ratios corresponding to an increased amount of the
final raffinate, an increased amount of at least one intermediate
extract, and a decreased amount of the final extract, relative to
the weight ratio of the final raffinate, intermediate extract, and
final extract in the initial feed. More generally, this can
correspond to forming a modified pitch having a weight ratio
(relative to the initial feed) corresponding to an increased amount
of one or more low solubility portions of the initial pitch (such
as the final raffinate), an increased amount of one or more high
solubility portion of the initial pitch (such as the initial
extract or another intermediate extract), and a reduced percentage
of one or more intermediate solubility portions of the initial
mesophase pitch (the final extract).
[0052] As another example, a modified pitch can have weight ratios
corresponding to an increased amount of the final extract, an
increased amount of at least one intermediate raffinate, and a
decreased amount of the final raffinate. More generally, this can
correspond to forming a modified pitch with an increased weight
percentage of a high solubility portion of the initial mesophase
pitch (such as the final extract), an increased percentage of a low
solubility portion of the initial mesophase pitch (such as the
initial raffinate or another intermediate raffinate), and a reduced
percentage of an intermediate solubility portion of the initial
mesophase pitch (the final raffinate).
[0053] As will be recognized by those of skill in the art, the
above two options can be generally understood as providing a
general strategy for forming a modified mesophase pitch having a
"dual-peak" composition, where a high solubility and low solubility
portion of the initial mesophase pitch are re-combined while
incorporating a reduced amount, such as none, of an intermediate
solubility portion of the initial mesophase pitch. This type of
"dual-peak" composition cannot be formed simply by performing a
series of extractions. Additionally, the proper combination of the
high solubility and low solubility portions, while reducing or
minimizing the amount of the intermediate solubility portion, is
enabled by an understanding of how to combine fractions while
producing a modified mesophase pitch with a reduced T.sub.0
value.
[0054] FIG. 1 shows an example of a process flow for forming a
modified mesophase pitch fraction based on performing two solvent
extractions using two solvents with different solubility
parameters. In the example process flow shown in FIG. 1, a
mesophase pitch feed 105 is passed into a solvent extractor 120,
along with a first solvent 111. This results in formation of an
extract stream 127 that includes a majority of first solvent 111
and a majority of the portions of feed 105 that are soluble in
first solvent 111. A raffinate stream 126 including a majority of
insoluble portions of feed 105 is also formed. Optionally, a
portion of extract stream 127 can undergo a separation (not shown)
to separate the first solvent from a first supplemental pitch
product 129.
[0055] The raffinate stream 126 is then exposed to a second solvent
112 in a second solvent extractor 130. The second solvent 112 can
have a higher solvency power than first solvent 111. In some
alternative aspects, if a second solvent 112 has a lower solvency
power than the first solvent 111, a portion of the extract stream
127 could be used as the input to a second solvent extractor. In
various aspects, any convenient number of solvent extractors can be
used, each with different solvents, to form a desired plurality of
raffinates and/or extracts.
[0056] In the example shown in FIG. 1, introducing raffinate stream
126 and second solvent 112 into solvent extractor 130 results in
formation of second extract stream 137 and second raffinate stream
136. Second extract stream 137 can include a majority of the
components in raffinate stream 126 that are soluble in the second
solvent 112, while second raffinate stream 136 can include a
majority of second solvent 112 and a majority of components from
raffinate stream 126 that are insoluble in second solvent 112.
[0057] The outputs from the two solvent extraction stages 120 and
130 correspond to extract 127, extract 137, and raffinate 136. In
this type of configuration, a modified mesophase pitch fraction can
be formed by selectively combining extract 127, extract 137, and/or
raffinate 136 in a desired ratio. In the example shown in FIG. 1,
the modified mesophase pitch fraction corresponds to a combination
of (at least) a portion 143 of extract 127 and (at least) a portion
146 of raffinate 136. The unused portion of raffinate 136 can
correspond to a second supplemental pitch product 139. The portion
143 of extract 127 and the portion 146 of raffinate 136 are blended
together in a desired ratio in blending stage 140. Optionally but
preferably, at least a portion of the solvent present in portion
143 of extract 127 can be separated from the modified mesophase
pitch fraction 145 as a first separated solvent portion 141. The
first separated solvent portion 141 can be used, for example, as a
recycle stream to form part of first solvent 111. A separation 150
can also be performed on extract 137 to form a second separated
solvent portion 152 and a third supplemental pitch product 159. It
is noted that an additional portion of second solvent 112 may be
included in second raffinate stream 136. This additional portion of
second solvent 112 can be recovered as an additional solvent
portion 142 by separation as part of blending stage 140. This
additional solvent portion 142 can, for example, be combined with
second separated solvent portion 152 for recycle and use as part of
second solvent 112.
[0058] After forming a modified pitch, the modified pitch can be
used to form carbon fibers, such as by using a conventional melt
spinning process. Melt spinning for formation of carbon fiber is a
known technique. For example, the book "Carbon-Carbon Materials and
Composites" includes a chapter by D. D. Edie and R. J. Diefendorf
titled "Carbon Fiber Manufacturing." Another example is the article
"Melt Spinning Pitch-Based Carbon Fibers", Carbon, 27(5), p 647,
(1989).
Example 1--Determining Characteristic Temperature and
Characteristic Viscosity
[0059] Characteristic temperature values corresponding to T.sub.0
values and characteristic viscosities corresponding to
.eta..sub.inf values were determined for three representative
vacuum resid fractions. The dots in FIG. 2 correspond to measured
values for viscosity at various temperatures. It is noted that the
vertical axis in FIG. 2 corresponds to the log of the viscosity.
The lines in FIG. 2 correspond to fits of the measured values to
Equation (2), the Arrhenius-style equation for the
viscosity-temperature relationship as described above. As explained
in association with Equation (2), D was set to 7.5 for purposes of
fitting the curve to the data. As shown in FIG. 2, the form of
Equation (2) provides a relatively good fit for the shape of the
data for each of the vacuum resid fractions. Table 1 shows the
resulting T.sub.0 and .eta..sub.inf values determined based on the
curve fitting.
TABLE-US-00001 TABLE 1 Characteristic Temperature and Viscosity
Parameters Sample T.sub.0 (K) .eta..sub.inf (Pa*s) VR1 249.7 8.4E-5
VR2 217.6 4.2E-5 VR3 211.4 2.0E-5
[0060] Thus, Equation (2) in combination with measured viscosity
values provides a suitable method for determining a characteristic
viscosity and a characteristic temperature for a hydrocarbon or
hydrocarbon-like fraction.
Example 2--Prediction of T.sub.0 and .eta..sub.inf for Blends of
Hydrocarbon Fractions
[0061] Two additional vacuum resid fractions (VR4 and VR5) where
characterized to determine T.sub.0 and .eta..sub.inf values by
fitting viscosity versus temperature data using Equation (2).
Blends of VR4 and VR5 at various weight ratios were then formed.
The blends were also characterized (measurement of viscosity versus
temperature) to allow for calculation of T.sub.0 and .eta..sub.inf
values for each blend. Additionally, the T.sub.0 and .eta..sub.inf
values for VR4 and VR5 were used in conjunction with Equation (3)
and Equation (4) to calculate curves corresponding to T.sub.0 and
.eta..sub.inf values for blends of VR4 and VR5.
[0062] FIG. 3 shows a comparison of a) the T.sub.0 and
.eta..sub.inf values determined for each blend of VR4 and VR5 based
on measured viscosity values at various temperatures, and b) the
T.sub.0 and .eta..sub.inf curves predicted by using the T.sub.0 and
.eta..sub.inf values for VR4 and VR5 in Equation (3) and Equation
(4). As shown in FIG. 3, within reasonable experimental error, the
predicted T.sub.0 and .eta..sub.inf from Equation (3) and Equation
(4) are in good agreement with the measured values for each blend
of VR4 and VR5. This demonstrates the ability to predict the
T.sub.0 and .eta..sub.inf values of a modified mesophase pitch
fraction if the T.sub.0 and .eta..sub.inf values are known for the
individual components used to form the modified mesophase pitch
fraction.
Example 3--Blending of Extract and Raffinate to Form Modified
Mesophase Pitch
[0063] The following example is a prophetic example. In this
example it is assumed that the initial feed has T.sub.0=300 K and
.eta..sub.inf=8.times.10.sup.-5 Pa*s. The initial feed is then
separated into two streams with different T.sub.0 and
.eta..sub.inf. Stream 1 has T.sub.0=230 K and
.eta..sub.inf=8.times.10.sup.-5 Pa*s and stream 2 having
T.sub.0=315 K and .eta..sub.inf=8.times.10.sup.-5 Pa*s. Stream 1
corresponds to 18 vol % of the initial feed, while Stream 2
corresponds to 82 vol % of the initial feed. The streams were
combined in the volumetric fractions .PHI..sub.1=0.30 and
.PHI..sub.2=0.70, producing a modified product with T.sub.0=289.5 K
and .eta..sub.inf=8.times.10.sup.-5 Pa*s.
[0064] FIG. 4 show a comparison of the temperature dependence of
the viscosity for the initial feed and the modified product. In
FIG. 4, the viscosity is plotted on a log scale. As shown in FIG.
4, the modified product has a reduced temperature dependence for
all temperatures, including those temperature near 550 K to 595 K
that correspond to a desirable temperature range for production of
various widths of carbon fiber.
[0065] To further illustrate the reduced temperature dependence, a
derivative with respect to temperature was taken for the plot shown
in FIG. 4. The resulting derivative corresponds to Equation
(5).
d log(.eta.)/dT=-0.434*D*T.sub.0/(T-T.sub.0).sup.2) (5)
[0066] The T.sub.0 and .eta..sub.inf values for the initial feed
and the modified product were used in Equation 5 to show the rate
of change of viscosity as a function of temperature. This plot is
shown in FIG. 5. As shown in FIG. 5, at sufficiently high
temperatures, both the initial feed and the modified product have
relatively small temperature dependence for the viscosity, but the
modified pitch fraction has a consistently lower temperature
dependence than the feed. However, in the temperature region of
interest for formation of at least some types of carbon fiber, the
initial feed has a substantially greater temperature dependence for
the viscosity.
Additional Embodiments
Embodiment 1
[0067] A method for forming a modified pitch, comprising:
performing solvent extraction on a pitch comprising a T.sub.0 value
to form an extract comprising a first fraction of the pitch and a
raffinate comprising a second fraction of the pitch; and blending
at least a portion of the first fraction with at least a portion of
the second fraction to form a modified pitch having a modified
T.sub.0 value less than the T.sub.0 value of the pitch.
Embodiment 2
[0068] The method of Embodiment 1, wherein the first fraction and
the second fraction comprise a first volume ratio, and wherein a
volume ratio comprising the at least a portion of the first
fraction and the at least a portion of the second fraction is
greater than the first volume ratio.
Embodiment 3
[0069] The method of any of the above embodiments, wherein the at
least a portion of the first fraction is formed from the extract
without performing an additional solvent extraction step; or
wherein the at least a portion of the second fraction is formed
from the raffinate without performing an additional solvent
extraction step; or a combination thereof.
Embodiment 4
[0070] The method of Embodiment 1 or 2, wherein the at least a
portion of the second fraction is formed by a method comprising:
performing a second solvent extraction on at least a portion of the
raffinate to form a second extract comprising a third fraction of
the pitch and a second raffinate comprising a fourth fraction of
the pitch, the fourth fraction comprising the at least a portion of
the second fraction.
Embodiment 5
[0071] The method of Embodiment 4, wherein the modified pitch
further comprises at least a portion of the third fraction, a
volume ratio of the at least a portion of the first fraction, the
at least a portion of the third fraction, and the at least a
portion of the fourth fraction being different from a volume ratio
of the first fraction, the third fraction and the fourth fraction
in the pitch; or wherein the modified pitch does not include a
portion of the third fraction.
Embodiment 6
[0072] The method of Embodiment 1, 2, 4, or 5, wherein the at least
a portion of the first fraction is formed by a method comprising:
performing a third solvent extraction on at least a portion of the
first fraction to form a second extract comprising a fifth fraction
of the pitch and a second raffinate comprising a sixth fraction of
the pitch, the fifth fraction comprising the at least a portion of
the first fraction.
Embodiment 7
[0073] The method of Embodiment 6, wherein the modified pitch
further comprises at least a portion of the fourth fraction, a
volume ratio of the at least a portion of the second fraction, the
at least a portion of the fourth fraction, and the at least a
portion of the third fraction being different from a volume ratio
of the second fraction, the fourth fraction and the third fraction
in the pitch; or wherein the modified pitch does not include a
portion of the fourth fraction.
Embodiment 8
[0074] A method for forming a modified pitch, comprising:
performing solvent extraction on a pitch comprising a T.sub.0 value
to form an extract comprising a first fraction of the pitch and a
raffinate comprising a second fraction of the pitch; performing a
second solvent extraction on a) at least a portion of the first
fraction orb) at least a portion of the second fraction, to form a
second extract comprising a third fraction of the pitch and a
second raffinate comprising a fourth fraction of the pitch, wherein
the second solvent extraction is performed on the at least a
portion of the first fraction, a T.sub.0 of the fourth fraction
being less than the T.sub.0 value of the pitch, the modified pitch
corresponding to at least a portion of the fourth fraction, or
wherein the second solvent extraction is performed on the at least
a portion of the second fraction, a T.sub.0 value of the third
fraction being less than the T.sub.0 value of the pitch, the
modified pitch corresponding to at least a portion of the third
fraction.
Embodiment 9
[0075] The method of any of the above embodiments, wherein the
pitch comprises a mesophase pitch and wherein the modified pitch
comprises a modified mesophase pitch; or wherein the pitch
comprises an isotropic pitch and wherein the modified pitch
comprises a modified isotropic pitch, the mesophase pitch
optionally comprising 10 vol % or more of an optically active
fraction.
Embodiment 10
[0076] The method of any of the above embodiments, wherein the
pitch comprises a glass transition having a width of 40.degree. C.
or less; or wherein the pitch comprises a softening point of
100.degree. C. to 300.degree. C.; or wherein the pitch comprises a
coke value of at least 50 wt. % or more; or wherein the pitch
comprises a viscosity at 280.degree. C. of 20 Pa-sec or less; or
wherein the pitch comprises a T5 distillation point of 350.degree.
C. or more; or wherein the pitch comprises a T50 distillation point
of 500.degree. C. or more; or a combination of any two or more
thereof; or a combination of any three or more thereof.
Embodiment 11
[0077] The method of any of the above embodiments, further
comprising separating an extract product fraction and a solvent
fraction from the extract, the extract product fraction comprising
the at least a portion of the first fraction.
Embodiment 12
[0078] The method of any of Embodiments 4-11, further comprising
separating a solvent recovery fraction from the raffinate; or
further comprising separating a second solvent recovery fraction
from the second raffinate; or a combination thereof.
Embodiment 13
[0079] The method of any of Embodiments 4-12, wherein performing a
solvent extraction comprises performing an extraction with a first
solvent, wherein performing a second solvent extraction comprises
performing an extraction with a second solvent, and wherein the
first solvent has a solubility parameter that is different from a
solubility parameter of the second solvent by 1.0 or more, or 2.0
or more, or 4.0 or more.
Embodiment 14
[0080] The method of any of the above embodiments, wherein the
modified pitch comprises a modified T.sub.0 value that is at least
5.0.degree. C. less than the T.sub.0 value of the pitch, or at
least 10.degree. C. less; or wherein the modified pitch comprises a
modified .eta..sub.inf value that is greater than a .eta..sub.inf
value of the pitch; or a combination thereof.
Embodiment 15
[0081] A modified pitch made according to the method of any of
Embodiments 1-14.
[0082] When numerical lower limits and numerical upper limits are
listed herein, ranges from any lower limit to any upper limit are
contemplated. While the illustrative embodiments of the invention
have been described with particularity, it will be understood that
various other modifications will be apparent to and can be readily
made by those skilled in the art without departing from the spirit
and scope of the invention. Accordingly, it is not intended that
the scope of the claims appended hereto be limited to the examples
and descriptions set forth herein but rather that the claims be
construed as encompassing all the features of patentable novelty
which reside in the present invention, including all features which
would be treated as equivalents thereof by those skilled in the art
to which the invention pertains.
[0083] The present invention has been described above with
reference to numerous embodiments and specific examples. Many
variations will suggest themselves to those skilled in this art in
light of the above detailed description. All such obvious
variations are within the full intended scope of the appended
claims.
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