U.S. patent application number 14/468758 was filed with the patent office on 2014-12-11 for gas hydrates with a high capacity and high formation rate promoted by biosurfactants.
This patent application is currently assigned to THE TEXAS STATE UNIVERSITY-SAN MARCOS. The applicant listed for this patent is Luyi Sun, Weixing Wang. Invention is credited to Luyi Sun, Weixing Wang.
Application Number | 20140363361 14/468758 |
Document ID | / |
Family ID | 49083235 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140363361 |
Kind Code |
A1 |
Wang; Weixing ; et
al. |
December 11, 2014 |
GAS HYDRATES WITH A HIGH CAPACITY AND HIGH FORMATION RATE PROMOTED
BY BIOSURFACTANTS
Abstract
The disclosure provides an LS methane hydrate containing a
plurality of methane hydrate crystals and lignosulfonate. The
disclosure also provides a method of making an LS methane hydrate
by combining methane gas, liquid or solid water, and LS at
controlled temperature and starting pressure for a time sufficient
to form LS methane hydrate. The disclosure further provides a
method of producing energy from an LS methane hydrate by providing
an LS methane hydrate directly to a combustion chamber, whereby
methane in the methane hydrate and LS are converted to energy in
the combustion chamber and water in the methane hydrate is
converted to steam. The disclosure additionally provides a method
of releasing methane from an LS methane hydrate by heating an LS
methane hydrate.
Inventors: |
Wang; Weixing; (Guangzhou,
CN) ; Sun; Luyi; (Pearland, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wang; Weixing
Sun; Luyi |
Guangzhou
Pearland |
TX |
CN
US |
|
|
Assignee: |
THE TEXAS STATE UNIVERSITY-SAN
MARCOS
San Marcos
TX
|
Family ID: |
49083235 |
Appl. No.: |
14/468758 |
Filed: |
August 26, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US2013/028007 |
Feb 27, 2013 |
|
|
|
14468758 |
|
|
|
|
61634351 |
Feb 28, 2012 |
|
|
|
Current U.S.
Class: |
423/262 ;
423/351; 423/437.1; 423/563; 423/579; 423/658.2; 570/134;
585/15 |
Current CPC
Class: |
C10L 2230/00 20130101;
C10L 2200/0263 20130101; C10L 3/108 20130101 |
Class at
Publication: |
423/262 ; 585/15;
423/351; 423/437.1; 423/563; 423/579; 423/658.2; 570/134 |
International
Class: |
C10L 3/10 20060101
C10L003/10 |
Claims
1. A lignosulfonate (LS) gas hydrate comprising: a plurality of gas
hydrate crystals; and LS.
2. The LS gas hydrate of claim 1, wherein the gas comprises
methane.
3. The LS gas hydrate of claim 1, wherein the gas comprises
CO.sub.2 (carbon dioxide), H.sub.2 (hydrogen gas), O.sub.2 (oxygen
gas), N.sub.2 (nitrogen gas), H.sub.25 (hydrogen sulfide), Ar
(argon gas), Kr (krypton gas), Xe (xenon gas), a higher hydrocarbon
gas, or a fluorocarbon gas.
4. The LS gas hydrate of claim 1, comprising at least 0.1 wt %
LS.
5. The LS gas hydrate of claim 1, comprising at least 0.5 wt %
LS.
6. The LS gas hydrate of claim 1, comprising as much as 5.0 wt %
LS.
7. The LS gas hydrate of claim 1, comprising as much as 2.0 wt %
LS.
8. The LS gas hydrate of claim 1, wherein the LS gas hydrate has an
actual gas volumetric storage capacity of at least 80 v/v.
9. The LS gas hydrate of claim 1, wherein the LS gas hydrate has an
actual gas volumetric storage capacity of at least 160 v/v.
10. The LS gas hydrate of claim 1, wherein the LS gas hydrate has
an actual gas storage capacity of at least 180 v/v.
11. The LS gas hydrate of claim 1, wherein the LS comprises a
lignosulfonate salt.
12. The LS gas hydrate of claim 11, wherein the lignosulfonate salt
is selected from the group consisting of lignosulfonates with any
cations, such as calcium lignosulfonate (Ca-LS), sodium
lignosulfonate (Na-LS), potassium lignosulfonate (K-LS), and any
combinations thereof.
13. A method of making a lignosulfonate (LS) gas hydrate comprising
combining gas, liquid or solid water, and LS at controlled
temperature and starting pressure for a time sufficient to form LS
gas hydrate.
14. The method claim 13, wherein the gas comprises methane.
15. The method claim 13, wherein the gas comprises CO.sub.2 (carbon
dioxide), H.sub.2 (hydrogen gas), O.sub.2 (oxygen gas), N.sub.2
(nitrogen gas), H.sub.2S (hydrogen sulfide), Ar (argon gas), Kr
(krypton gas), Xe (xenon gas), a higher hydrocarbon gas, or a
fluorocarbon gas.
16. The method of claim 13, wherein the time sufficient is 30
minutes or less.
17. The method of claim 13, wherein the time sufficient is the
amount of time to form LS gas hydrate containing substantially all
of its actual gas volumetric storage capacity.
18. The method of claim 17, wherein the time sufficient is 1000
minutes or less.
19. The method of claim 13, comprising combining 0.1 wt % LS.
20. The method of claim 13, comprising combining 0.5 wt % LS.
21. The method of claim 13, comprising combining as much as 5.0 wt
% LS.
22. The method of claim 13, wherein the LS gas hydrate has an
actual gas storage capacity of at least 80 v/v.
23. The method of claim 13, wherein the LS gas hydrate has an
actual gas storage capacity of at least 160 v/v.
24. The method of claim 13, wherein the LS comprises a
lignosulfonate salt.
25. The method of claim 24, wherein the lignosulfonate salt is
selected from the group consisting of lignosulfonate with any
cations or their combinations.
26. A method of producing energy from a lignosulfonate (LS)
combustible gas hydrate comprising providing an LS combustible gas
hydrate directly to a combustion chamber, whereby combustible gas
in the combustible gas hydrate and LS are converted to energy in
the combustion chamber and water in the combustible gas hydrate is
converted to steam.
27. The method of claim 26, wherein the combustible gas comprises
methane.
28. A method of releasing gas from a lignosulfonate (LS) gas
hydrate comprising heating an LS gas hydrate to at least 0.degree.
C.
29. The method of claim 28, wherein the gas comprises methane.
30. The method of claim 28, wherein the gas comprises CO.sub.2
(carbon dioxide), H.sub.2 (hydrogen gas), O.sub.2 (oxygen gas),
N.sub.2 (nitrogen gas), H.sub.2S (hydrogen sulfide), Ar (argon
gas), Kr (krypton gas), Xe (xenon gas), a higher hydrocarbon gas,
or a fluorocarbon gas.
Description
PRIORITY CLAIM
[0001] The present application is a continuation of International
Patent Application No. PCT/US2013/028007 filed Feb. 27, 2013; which
claims priority to U.S. Provisional Patent Application Ser. No.
61/634,351 filed Feb. 28, 2012 titled "High Capacity Methane
Hydrates Based on Bio-promoters," and which are incorporated by
reference herein in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to gas hydrates containing
lignosulfonate (LS) (referred to as LS methane hydrates herein) and
methods of forming LS gas hydrates using a lignosulfonate
promoter.
BACKGROUND
[0003] Gas hydrates, also known as gas clathrates, are
non-stoichiometric, crystalline inclusion compounds. In these
compounds water forms a hydrogen bonded crystal lattice with
polyhedral cavities. Gas is trapped within these cavities. When the
crystal lattice is disrupted, for example by raising the
temperature of the gas hydrate, the gas is released, leaving behind
water.
[0004] Because of their ability to trap gasses, gas hydrates may be
used to separate, capture, store, or transport gasses. Gas hydrate
forms of methane, carbon dioxide and hydrogen have been prepared
and used for these purposes. Natural gas contains primarily
methane, making methane hydrates a promising way to store and
transport natural gas.
[0005] Using current technology, methane hydrates have a low actual
methane volumetric storage capacity that does not approach the
target of 180 v/v Standard Temperature and Pressure (STP) methane
proposed by the United States Department of Energy. Additionally,
the methane hydrate is formed very slowly because it involves a
gas-solid or gas-liquid interfacial interaction. This, along with
the low storage capacity, limits the commercial use of methane
hydrates. A variety of methods have been developed to increase the
interfacial contact between liquid water or solid ice and methane
gas to enhance gas hydrate formation. These include the application
of high pressure, vigorous mixing, use of ground ice particles, use
of surfactants, such as sodium dodecyl sulfate (SDS), use of
supports, such as silica, and the use of high surface area
emulsion-templated polymers.
[0006] SDS has been proven to significantly increase the rate of
methane hydrate formation, but SDS and most other surfactants are
formed using non-renewable petrochemical feedstock, making them
commercially and environmentally undesirable.
[0007] Accordingly, new materials and methods to increase the
formation rate of methane hydrate and the capacity are needed.
SUMMARY
[0008] The disclosure provides an LS gas hydrate containing a
plurality of gas hydrate crystals and lignosulfonate.
[0009] The disclosure also provides a method of making an LS gas
hydrate by combining gas, liquid or solid water, and LS at
controlled temperature and starting pressure for a time sufficient
to form LS gas hydrate.
[0010] The disclosure further provides a method of producing energy
from an LS combustible gas hydrate by providing an LS combustible
gas hydrate directly to a combustion chamber, whereby the
combustible gas in the combustible gas hydrate and LS are converted
to energy in the combustion chamber and water in the combustible
gas hydrate is converted to steam.
[0011] The disclosure additionally provides a method of releasing
gas from an LS gas hydrate by heating an LS gas hydrate to at least
0.degree. C. or a lower temperature able to allow release.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The current specification contains color drawings. Copies of
these drawings may be obtained from the USPTO. A more complete
understanding of the present embodiments and advantages thereof may
be acquired by referring to the following description taken in
conjunction with the accompanying drawings, which depict
embodiments of the present disclosure, and in which like numbers
refer to similar components, and in which:
[0013] FIG. 1 is a graph showing the methane uptake kinetics in a
Ca-LS aqueous solution of various concentrations at 273.2 K and a
starting pressure of 9.5 MPa;
[0014] FIG. 2A shows the interior of reaction vessel walls in the
presence of 0.50 wt % Ca-LS methane hydrate;
[0015] FIG. 2B shows the interior of reaction vessel walls in the
presence of 0.50 wt % Na-LS methane hydrate;
[0016] FIG. 3 is a graph showing the methane uptake kinetics in a
0.50 wt % Na-LS or K-LS aqueous solution at 273.2 K and a starting
pressure of 9.5 MPa;
[0017] FIG. 4 is a graph showing pressure-temperature dependence
during cooling and heating under methane pressure of (A) bulk
water, or (B) 0.50 wt % Ca-LS aqueous solution (temperature ramp:
4.0 K/h).
[0018] FIG. 5 is a graph show pressure-temperature dependence
during multiple cycles of cooling and heating under methane
pressure of 0.50 wt % Ca-LS aqueous solution (temperature ramp: 4.0
K/h).
[0019] FIG. 6 illustrates a methane hydrate formation system;
T=temperature; P=pressure.
DETAILED DESCRIPTION
[0020] The present disclosure relates to LS gas hydrates and
methods of forming LS gas hydrates using a lignosulfonate promoter.
Gas hydrates may include any of the following gasses: CH.sub.4
(methane), CO.sub.2 (carbon dioxide), H.sub.2 (hydrogen gas),
O.sub.2 (oxygen gas), N.sub.2 (nitrogen gas), H.sub.2S (hydrogen
sulfide), Ar (argon gas), Kr (krypton gas), Xe (xenon gas), higher
hydrocarbon gasses, fluorocarbon gasses, and the like. Methane
hydrates are described as example embodiments herein, but it will
be understood by one of ordinary skill in the art that other
gasses, such as those indicated above, may be used in place of
methane to obtain a similar product which, depending on the gas,
may be usable in similar manners.
[0021] Methane hydrates are non-stoichiometric methane-water
crystals in which the water forms a hydrogen bonded crystal lattice
with methane trapped in polyhedral cavities. Although there are at
least three known methane hydrate structures, all share the common
characteristic of trapping methane in such cavities. As a result,
methane hydrates look similar to ice. Methane hydrate crystals
containing their full capacity of methane have the chemical formula
CH.sub.4.5.75H.sub.2O. In practice, the ratio of water to methane
depends on the storage capacity of the particular hydrate crystal.
In LS methane hydrates, the LS may be trapped within crystals,
forming aberrations therein, or it may be largely confined to the
exterior of the crystals.
[0022] LS may include any known water-soluble, anionic
polyelectrolyte polymer identified by those in the art as
lignosulfonate and salts thereof. LS has a hydrophobic lignin
backbone with hydrophilic side groups, including sulfonate,
hydroxyl, phenolic, and carboxyl groups. It may behave as a
polymeric surfactant, as demonstrated by its ability to reduce the
surface tension of water (data not shown). In specific embodiments,
it may include lignosulfonate salts with any cations (such as
calcium, potassium, sodium) and combinations thereof. LS may have
any molecular weight ranges from 1,000 to 1,000,000.
[0023] LS may be derived from any source, but in a particular
embodiment, it may be derived from the production of wood pulp
using sulfite pulping. LS is generally considered a by-product of
sulfite pulping, rendering LS from such a source both
cost-effective and environmentally friendly. Other plants
containing high amounts of lignin may be treated with sulfite to
produce LS. For example, agricultural waste, such as corn stover,
sugarcane bagasse, spoiled fodder, and grain straw, rice, wheat,
and rye straw may be treated with sulfite to produce LS. LS derived
from any plant source is renewable, unlike SDS and most other
agents currently used in the production of methane hydrates.
[0024] In one specific embodiment, an LS methane hydrate is
provided which contains at least 0.1 wt % LS, or at least 0.2 wt %
LS. In another specific embodiment, a methane hydrate is provided
which contains as much as 1 wt %, as much as 2 wt % LS or as much
as 5 wt % LS. In another specific embodiment, a methane hydrate is
provided that contains between 0.1 wt % LS and 5 wt % LS, between
0.1 wt % LS and 2 wt % LS, between 0.1 wt % LS and 1 wt % LS,
between 0.2 wt % LS and 5 wt % LS, between 0.2 wt % LS and 2 wt %
LS, or between 0.2 wt % LS and 1 wt % LS.
[0025] In another specific embodiment, an LS methane hydrate
containing LS is provided with an actual methane volumetric storage
capacity of at least 80 v/v, at least 120 v/v/, at least 140 v/v,
at least 150 v/v, at least 160 v/v, at least 170 v/v, or at least
180 v/v.
[0026] LS methane hydrates according to the present disclosure may
release methane at a temperature of 10.degree. C. or at a lower
temperature able to release methane. For example methane may be
released at 0.degree. C. at an appropriate pressure, such as of 27
bar.
[0027] The present disclosure also provides methods of producing LS
gas hydrates, such as LS methane hydrates using a LS promoter.
Generally, any available method of creating a methane hydrate may
be used, but LS may be added in the above amounts at the beginning
or at any state during hydrate formation. In a specific embodiment,
LS may be added at the beginning to achieve maximum improvements in
methane hydrate formation time. Methane hydrates may grow in a
two-phase process. During the first phase, called induction,
methane hydrate crystals begin to form. The time required for this
phase is referred to as the induction time. When the crystals reach
a certain critical radius, they grow continuously and the second
phase, called the formation phase begins. The time required for
this phase is referred to as the formation time.
[0028] In a specific embodiment LS is combined with methane gas and
liquid or solid water in a container which is adjusted to a
controlled temperature and pressure sufficient to allow a methane
hydrate to form. Fore example, a system as shown in FIG. 6 may be
used. In example embodiments, the temperature may be between
0.degree. C. and 10.degree. C. at a pressure of 5 mPa to 10 MPa. In
general, the use of a low temperature such as 0.degree. C. or
-5.degree. C. or lower and a high pressure, such as 10 MPa or 15
MPa or higher is helpful in the formation of methane hydrates.
[0029] In one specific embodiment, the induction and formation time
required to reach 90% of the final volumetric capacity of the
methane hydrate may be little as 100 minutes, 30 minutes, or even
20 minutes.
[0030] In another specific embodiment, the induction time may be as
little as 10 minutes or even 5 minutes.
[0031] In another specific embodiment, the induction and formation
time required to reach substantially full actual storage capacity
may be as little as 1000 minutes.
[0032] LS methane hydrates according to the present disclosure may
be used for any purpose for which methane hydrates are otherwise
suited. For instance, they may be used to transport and store
methane gas.
[0033] One specific embodiment provides a method of using LS
combustible has, such as methane, hydrates in energy production. In
an example of this embodiment, an LS methane hydrate according to
an embodiment of this disclosure is provided directly to an energy
production facility, such as a combustion chamber. Unlike most
current methane hydrates, in which the methane is first released
and the promoter, such as SDS, is recovered, there is no need for
pre-release of methane when using methane hydrates containing LS.
LS is cheap and simply burns along with the methane. Due to the low
amounts of LS in the methane hydrates, any release of sulfur
compounds is negligible. Water is vaporized and released with other
exhaust gasses.
[0034] In an alternative embodiment for using LS methane hydrates
in energy production or for other purposes in which freed methane
is used, the methane may be released from the LS methane hydrate by
heating to a temperature of at least 0.degree. C. In a more
specific embodiment, the methane may be released by heating to a
temperature of at least 10.degree. C. In general, heating to a
higher temperature results in faster methane release. The resulting
water and LS may be disposed of in essentially the same manner as
normal non-potable water due to the low amounts of LS.
EXAMPLES
[0035] The following examples are provided to further illustrate
specific embodiments of the disclosure. They are not intended to
disclose or describe each and every aspect of the disclosure in
complete detail and should be not be so interpreted. Unless
otherwise specified, designations of cells lines and compositions
are used consistently throughout these examples.
Example 1
LS Methane Hydrate Formation Kinetics
[0036] Methane hydrates containing varying concentrations of
calcium lignosulfonate (Ca-LS) as a promoter were prepared at 273.2
K and a starting pressure of 9.5 MPa. Results are shown in FIG. 1.
The optimal Ca-LS concentration was 0.5 wt %, which resulted in the
formation of an LS methane hydrate with an actual methane
volumetric storage capacity of 167 v/v, which is slightly higher
than the 163 v/v volumetric capacity typically achieved with an SDS
promoter. This volumetric capacity was substantially reached after
1000 minutes total initiation and formation time, but 90% of
volumetric capacity was reached in only 20 minutes. Additionally,
induction time was only 6 minutes.
[0037] Ca-LS at concentrations of 0.20 wt % and 1.00 wt % gave very
similar results, but with actual methane volumetric storage
capacity reduced to 166 v/v and 161 v/v, respectively. When the
concentration of Ca-LS was reduced to 0.10 wt %, LD methane hydrate
formed, but actual methane volumetric storage capacity was only 132
v/v after 1000 minutes and induction time was 150 minutes. Higher
concentrations of Ca-LS (2.0 wt % and 5.0 wt %) reduced capacity to
133 v/v and 84 v/v, respectively, but induction times remained in
the 5 to 10 minute range at these concentrations.
[0038] Overall, these results show that the induction time in
methane hydrate formation may be significantly shortened to 10
minutes or less by using at least 0.2 wt % Ca-LS or other LS. Above
0.2 wt %, the concentration of Ca-LS did not appear to
significantly affect induction time. Without limiting the invention
to a particular mechanism, this likely occurred because 0.2 wt % is
sufficient to promote nucleation of methane hydrate while
simultaneously preventing the formation of agglomerates and
allowing capillary-driven supply of the hydrate solution into the
hydrate layers.
[0039] The LS methane hydrate actual methane volumetric storage
capacity reached the maximum when Ca-LS concentration was 0.50 wt
%. Without limiting the invention to a particular mechanism, this
likely occurred because of effects of the Ca-LS. The a bulk water
system without Ca-LS, visual observations of hydrate growth in the
quiescent water-methane mixture have revealed that a rigid hydrate
film forms at the liquid/gas interface, which hinders further
hydrate formation. In contrast, in a system containing Ca-LS, the
material acts as a polymeric surfactant and aligns along the
liquid/gas interface and prevents hydrate crystals from
agglomerating and forming a film. Furthermore, hydrate nucleation
may begin at the liquid/gas interface close to the reactor wall,
where temperature is lowest. Gas hydrates may grow upward on the
wall by feeding the LS solution to the porous methane hydrates by
capillary action ash shown in FIG. 2A. At 0.50 wt %, there is
likely sufficient Ca-LS to serve this function.
[0040] The actual methane volumetric storage capacity of the
methane hydrates studied decreased at tested Ca-LS concentrations
above 0.50 wt %. Without limiting the invention to a particular
mechanism, this likely occurred because the LS polymers began to
block methane trapping into water, thereby lowering capacity.
[0041] Similar experiments were conducted using 0.50 wt % sodium
lignosulfonate (Na-LS) or potassium lignosulfonate (K-LS) during
the formation of methane hydrates at a temperature of 273.2 K and a
starting pressure of 9.5 MPa. Results are presented in FIG. 3. Both
Na-LS and K-LS showed LS methane hydrate formation kinetics similar
to those observed with Ca-LS and both produced LS methane hydrates
with high actual methane volumetric storage capacities. Na-LS
reached an actual methane volumetric storage capacity of 170 v/v in
1000 minutes total induction and formation time with 90% of
capacity being reached within 30 minutes. Induction time was 8
minutes.
[0042] FIG. 2B shows gas hydrate growth on the reaction vessel
walls in a 0.50 wt % Na-LS system.
Example 2
Cooling and Heating Behaviors of LS Methane Hydrates Systems
[0043] The behavior of LS methane hydrates systems upon cooling and
heating as well as bulk water methane hydrate systems was tested
and results are presented in FIGS. 4 and 5. As shown in FIG. 4, in
a bulk water system, the pressure-temperature (P-T) relationship of
methane approximated the ideal gas law during a continuous
cooling-heating cycle. There was no appreciable methane hydrate
formed in this system. In contrast, in a system containing 0.50 wt
% Ca-LS, clear evidence of methane hydrate formation and subsequent
dissociation was provided by the dramatic pressure drop upon
cooling and the rapid pressure rise upon heating. The observed
dissociation closely follows the phase boundary curve for structure
I methane hydrate, which suggest that the presence of Ca-LS does
not change the equilibrium pressure or thermodynamic data of
methane hydrate. This is similar to the effects seen when SDS is
used as a promoter during the formation of methane hydrate.
However, a deviation from the phase boundary curve was observed as
warming continued, suggesting that Ca-LS methane hydrate is
metastable beyond the normal P-T range, similar to dry water
methane hydrate. This stability at higher temperatures renders the
LS methane hydrate more desirable as a transport or storage
material.
[0044] Results from repeated cooling-heating cycles, shown in FIG.
5. establish that recyclability of LS methane hydrates remains
high. Recyclability allows for reuse of the LS and water to reform
methane hydrates.
Example 3
Calculations
[0045] The following calculations were used in the experiments in
Examples 1 and 2.
Calculation of Actual Methane Volumetric Storage Capacity
[0046] Actual methane volumetric storage capacity is defined in
terms of the number of volumes of methane released per unit volume
of methane hydrate at STP. Capacity was calculated relative to the
pressure change within the reaction vessel. The free space volume
of the reaction vessel was obtained by subtracting the sum volume
of methane hydrate, unreacted water, and solid LS from the total
reaction vessel volume. Taking non-ideality factors into account,
GASPAK v3.41 software (Horizon Technologies, USA) was employed to
calculate the actual methane volumetric storage capacity, according
to the temperature and pressure. It was assumed that the liquid and
gas phases within the reaction vessel were exclusively formed from
the water and methane, respectively, neglecting any dissolution of
methane into the water and mixing of any water vapor into the
methane.
Methane Hydrate Formation Systems
[0047] Kinetic experiments were carried in system 10 generally
shown in FIG. 6. 20.0 g of LS solution was placed in high pressure
stainless steel vessel 20. The temperature of the coolant was
controlled by a programmable thermal circulator (not shown). The
sample temperature in the high pressure vessel was measured using
type K thermocouple 30. The gas pressure was monitored using a High
Accuracy Gauge Pressure Transmitter (not shown). Methane was
provided from gas cylinder 40 and regulated by regulator 50.
Pressure was also controlled using vent 60. Both the thermocouple
and the pressure transmitter were connected to Digital Universal
Panel Input Meter 70, which communicated with computer 80.
[0048] Prior to each experiment, vessel 20 was purged with methane
three times to remove the air, and then was pressurized with
methane to the desired pressure at the designated temperature.
[0049] Although only exemplary embodiments of the invention are
specifically described above, it will be appreciated that
modifications and variations of these examples are possible without
departing from the spirit and intended scope of the invention.
Numeric amounts expressed herein will be understood by one of
ordinary skill in the art to include amounts that are approximately
or about those expressed. Furthermore, the term "or" as used herein
is not intended to express exclusive options (either/or) unless the
context specifically indicates that exclusivity is required; rather
"or" is intended to be inclusive (and/or).
* * * * *