PRIORITY CLAIM

The present application claims priority to United States Provisional Patent

Application Serial No. 61/634,351 filed February 28, 2012 titled "High Capacity Methane Hydrates Based on Bio-promoters," which is incorporated by reference herein in its entirety. TECHNICAL FIELD

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

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.

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.

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.

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.

Accordingly, new materials and methods to increase the formation rate of methane hydrate and the capacity are needed.

SUMMARY

The disclosure provides an LS gas hydrate containing a plurality of gas hydrate crystals and lignosulfonate.

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.

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.

The disclosure additionally provides a method of releasing gas from an LS gas hydrate by heating an LS gas hydrate to at least 0 °C or a lower temperature able to allow release.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIGURE 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; FIGURE 2A shows the interior of reaction vessel walls in the presence of 0.50 wt% Ca-LS methane hydrate;

FIGURE 2B shows the interior of reaction vessel walls in the presence of 0.50 wt% Na-LS methane hydrate;

FIGURE 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;

FIGURE 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).

FIGURE 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).

FIGURE 6 illustrates a methane hydrate formation system; T=temperature; P=pressure.

DETAILED DESCRIPTION

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 ₄ (methane), C0 ₂ (carbon dioxide), H ₂ (hydrogen gas), 0 ₂ (oxygen gas), N ₂ (nitrogen gas), H ₂ S (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.

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 ₄ ^» 5.75H ₂ 0. 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.

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. .

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.

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.

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.

LS methane hydrates according to the present disclosure may release methane at a temperature of 10 °C or at a lower temperature able to release methane. For example methane may be released at 0 °C at an appropriate pressure, such as of 27 bar.

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.

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 FIGURE 6 may be used. In example embodiments, the temperature may be between 0 °C and 10 °C at a pressure of 5 mPa to 10 MPa. In general, the use of a low temperature such as 0 °C or -5 °C or lower and a high pressure, such as 10 MPa or 15 MPa or higher is helpful lin the formation of methane hydrates.

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.

In another specific embodiment, the induction time may be as little as 10 minutes or even 5 minutes.

In another specific embodiment, the induction and formation time required to reach substantially full actual storage capacity may be as little as 1000 minutes.

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.

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.

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 °C. In a more specific embodiment, the methane may be released by heating to a temperature of at least 10°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

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

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 FIGURE 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.

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.

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.

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 FIGURE 2A. At 0.50 wt%, there is likely sufficient Ca-LS to serve this function.

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.

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 FIGURE 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.

FIGURE 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

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 FIGURES 4 and 5. As shown in FIGURE 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.

Results from repeated cooling-heating cycles, shown in FIGURE 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

The following calculations were used in the experiments in Examples 1 and 2. Calculation of Actual Methane Volumetric Storage Capacity 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

Kinetic experiments were carried in system 10 generally shown in FIGURE 7. 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.

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.

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).