KR20120023300A - Disulfonate type promoter for formation of natural gas hydrate - Google Patents

Abstract

PURPOSE: A disulfonate type promoter for formation of natural gas hydrate is provided to easily control the generation rate by controlling concentration to water, and to have large storage ability of gas hydrate. CONSTITUTION: A disulfonate type promoter for formation of natural gas hydrate is an anionic multi-chain type disulfonate type surfactant in chemical formula 1. In chemical formula 1, R^1 and R^2 is same or different each other, selected from saturated of unsaturated C1-30 linear or branched alkyl group. The alkyl is able to be substituted to fluorine atom or aromatic ring. M is selected from alkali metal, and n is the integer of 0-6. The manufacturing method of the natural gas hydrate comprises a step of hydrating natural gas in solution which contains 5-150 ppm of the promoter.

Description

Disulfonate type promoter for formation of Natural gas hydrate

The present invention relates to a disulfonate-based accelerator for producing natural gas hydrate, and more particularly, to a multi-chain disulfonate-based surfactant having two or three hydrophobic groups and two sulfonate groups in one molecule. Natural Gas Hydrate) is used as a promoter in the reaction to produce.

Natural gas has abundant reserves, generates less pollution-causing substances such as hydrocarbons, nitrogen oxides, and carbon dioxide during combustion, and has a high octane number and a wide combustion limit, making it a fuel of excellent stability, economy, and eco-friendliness. Natural gas is increasing its application mainly in the automotive industry. Natural gas is classified into compressed natural gas (CNG), liquefied natural gas (LNG) and adsorptive natural gas (ANG), depending on the type of use. CNG has the disadvantage that it needs a high pressure storage container that can withstand up to 200 atmospheres of filling pressure and there is a high risk of explosion, and LNG needs to maintain -162 ℃ ultra low temperature conditions for storage. There is a disadvantage in that it takes a lot of cost, and ANG has a disadvantage in that it is difficult to be commercialized due to the high price of the adsorbent and low storage efficiency.

In recent years, GTS (Gas To Solid) technology for hydrating natural gas and converting it into a solid has been actively studied as a natural gas transport and storage technology. Natural gas hydrate is a solid compound formed by physically combining a low molecular weight gas, which is an object molecule, and a water molecule, which is a main molecule, under conditions of low temperature and high pressure. Natural Gas Hydrate (NGH) is also called 'Methane Hydrate' because its main component is methane. Natural gas hydrate (NGH) has the advantage of being stored and transported in solid form under relatively mild conditions of -15 ° C to -20 ° C, whereas Liquified Natural Gas (NGH) requires a cryogenic system of -160 ° C or higher.

While natural gas hydrate (NGH) is commercially useful, the hydrate manufacturing technology developed to date has been applied due to the problem of increasing the volume of NGH and the increase in volume due to the presence of unreacted interstitial water. This is being limited. Accordingly, there is a need for the development of high density and high acceleration NGH production promoters capable of producing high density NGH at high production rates.

Although studies have been made on the use of organic surfactants as promoters for the production of NGH, there is no research on systematic surfactant application. The process using the surfactant, ① the rate of NGH production is fast, ② NGH particles are self-packing (self-packing) by agglomeration with each other, ③ has the advantage of minimizing the unreacted material. Dupont is launching a low dosage hydrate inhibitor (LDHI) product, but there are no reports of commercialization of surfactants as NGH production accelerators.

NGH production promoters can be broadly classified into 1) kinetic promoters that affect the rate of NGH production and 2) thermodynamic promoters that affect the temperature and pressure conditions of NGH production. Dynamic accelerators can be divided into organic accelerators and inorganic accelerators. In addition, studies on inorganic accelerators, particularly nano accelerators, have been reported to have latent heat dissipation effects and solubility enhancement of object molecules. This situation requires verification. As organic promoters, research on surfactants has been mainly focused.

The mechanism of NGH generation by surfactants is as follows: 1) As the binding force of water molecules is weakened, the object molecules (e.g. natural gas) can be easily moved into the aqueous phase, so that the gas dissolution rate at the gas-water interface Or 2) as the surfactant forms a micelle structure, the object gas easily collects in the lipophilic tail and then migrates into an aqueous solution, resulting in an increase in gas dissolution rate at the gas-water interface. It is being analyzed. Kalogerakis et al. (EPE International symposium on oil field chemistry, (1993) 375) reported that a surfactant known as a hydrate formation inhibitor promotes hydrate formation at certain concentrations. Karaaslan et al. (Energy & Fuels, 14 (2000) 1103) had a large effect on the promotion of linear alkylbenzene sulfonic acid (LABSA) when anionic, cationic and nonionic surfactants were added during NGH production. It was reported that the production promoting effect favored hydrate formation of the sI structure over the sII structure (J. Pet. Sci. Eng., 35 (2002) 49). Zhong et al. (Chem. Eng. Sci, 55 (2000) 4177) found that sodium dodecyl sulfate (SDS) increased the rate of ethane hydrate production by more than 700 times above 242 ppm, the critical micelle concentration (CMC). Reported. Han et al. (4th International conference on natural gas hydrates, (2002) 1036) studied the effect of SDS on hydrate preparation of natural gas containing 90% of methane, and reported that the optimum SDS concentration was 300 ppm. Link et al. (Fluid Phase Equilib., 211 (2003) 1) reported that up to about 97% of the theoretical maximum storage capacity could be achieved using SDS as an accelerator. Gou et al. (4th International conference on natural gas hydrates, (2002) 1040) reported that calcium hypochlorite shortens the induction time for methane hydrate formation and increases hydrate storage capacity. Sun et al. (Energ. Conv. Manag., 44 (2003) 2733) apply SDS as anionic, dodecyl polysaccharide glycoside as aionic, and cyclopentane to hydrate the natural gas containing 92% methane. When reported, the anionic system has a greater promoting effect than the nonionic system, and cyclopentane reduces the hydrate generation induction time but decreases storage capacity. Gnanendran et al. (J. Pet. Sci. Eng., 40 (2003) 37) reported that para-toluic acid acts as a hydrate promoter and the optimum concentration is 3.5 g / L. Zhang et al. (Fuel, 83 (2004) 2115) reported the effect of alkylpolyglycosides, SDS and potassium oxalate monohydrates on enhancing NGH production rates and storage capacity. Ganji et al. (Fuel 86 (2007 434) report that anionic SDS and linear alkylbenzenesulfonate (LABS), cationic cetyltrimethylammonium bromide (CTAB) and nonionic epoxidized nonylphenol (ENP) promote the effects of NGH production. Reported.

According to the above results, all of the single-chain surfactant was used to maximize the promoting effect of NGH production. However, a single-chain surfactant having one hydrophobic group and a hydrophilic group is limited in its simple form and has structural limitations in performance. For example, if the carbon number of the alkyl chain, which is a hydrophobic group, is increased to improve micelle formation ability, solubility in water may be lowered. As an alternative to solve these problems of surfactants, attention is focused on multichain-type surfactants having two or more hydrophilic moieties and two or more hydrophobic chains in one molecule. It's going on.

Conventionally known synthesis method of the two-chain anionic surfactant is to react diglycidyl ether by reacting relatively short α, ω type diols such as ethylene glycol and epichlorohydrin in the presence of a phase transfer catalyst and a base in a one step process. After synthesis, a long-chain alcohol and diglycidyl ether are reacted under a metal catalyst (sodium, potassium, etc.) in a two-step process to obtain a di-chain diol compound, followed by anion to two 2 ° hydroxy groups in the presence of a basic catalyst. It was a way of introducing a sex hydrophilic group. In the one step process of this known method reported by M. Okahara et al., Α, ω type diols and epichlorohydrin are reacted in the presence of an aqueous alkali metal hydroxide solution and a phase transfer catalyst, thereby simultaneously performing an addition reaction and a cyclization reaction. ? It has been reported that diglycidyl ether can be obtained with a yield of 89% ( Synthesis , 649 (1984)). However, due to the presence of alkali, complex side reactions such as ring-opening reaction of the produced epoxy group or addition of alcohol to the resulting glycidyl ether occur, resulting in oligomers, polymers, etc. There was a drawback that the yield of the dil ether is lowered, and in particular, the shorter the distance between the two 2 ° hydroxyl group has a disadvantage that the yield is significantly lowered. On the other hand, in the two-step process, 2 mol of long-chain alcohol is dissolved in a suitable solvent, an alkoxy salt is formed by using sodium or potassium metal, and then reacted with 1 mole of diglycidyl ether produced in the first step to make it into a target molecule. Two-chain diol compounds having two hydrophobic groups and two 2 ° hydroxy groups were obtained at the same time. By using this, a two-chain anionic surfactant compound was obtained by introducing an anionic submerging group into two 2 ° hydroxy groups in the presence of a basic catalyst. ( J. Jpn. Oil Chem. Soc. , 40, 473 (1991)). The two-chain anionic surfactant compounds produced through this process showed unusually low surface activity of the critical micelle concentrations compared to the one-chain surfactants, but the commercialization was difficult due to the difficult manufacturing process and low yield. . Therefore, an anionic multichain-type surfactant having a very low critical micelle concentration (CMC) compared to the single-chain anionic surfactant, which shows excellent surfactant effect even at a very low concentration, is simpler than the conventional process. Through the development of a manufacturing method that can be produced with a high yield is required. In other words, it is required to develop a multi-chain-type surfactant application system that can exhibit excellent promoting ability while using a smaller amount than the conventional single-chain surfactant, which has been mainly used as an organic accelerator to increase the NGH production rate.

An object of the present invention is to provide a novel organic-based NGH production promoter that increases the production rate of NGH (Natural Gas Hydrate) and enhances the dehydration efficiency of the produced NGH.

It is an object of the present invention to provide a method for producing natural gas hydrate (NGH) by hydrating natural gas in an aqueous solution containing 5 to 150 ppm of the novel NGH production promoter described above. have.

In order to solve the above problems, the present invention is characterized by the use of an anionic multi-chain disulfonate-based surfactant represented by the formula (1) as a natural gas hydrate (NGH) production promoter.

[Formula 1]

In Formula 1, R ¹ and R ² are the same as or different from each other selected from a saturated or unsaturated C _{1 ~} C ₃₀ linear or branched alkyl group, the alkyl may be substituted with a fluorine atom or an aromatic ring, M is selected from alkali metals, where n represents an integer from 0 to 6.

Disulfonate-based accelerator of the present invention has the effect of improving the rate of production of NGH (Natural Gas Hydrate) and the dehydration efficiency of the produced NGH.

Disulfonate-based accelerator of the present invention has an excellent effect of storage capacity of NGH (Natural Gas Hydrate).

1 is a comparative graph confirming the methane production promoting effect according to the concentration of the C8 disulfonate-based promoter.
Figure 2 is a comparative graph confirming the effect of promoting methane production according to the length of the alkyl chain in the disulfonate-based accelerator of C8, C10, C12.

The present invention relates to the use of the anionic multi-chain disulfonate-based surfactant represented by the formula (1) as an NGH production promoter.

The NGH production promoter of the present invention has two to three hydrophobic groups and two sulfonate groups in one molecular structure, so that the NGH production promoting rate and dehydration efficiency can be controlled by changing these hydrophobic groups and sulfonate groups.

In the disulfonate-based accelerator represented by Formula 1, R ¹ and R ² are the same as or different from each other, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl group, n-pentyl group, i-amyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, dodecyl group, tetra Decyl group, hexadecyl group, heptadecyl group, octadecyl group or oleyl, M may be selected from sodium or potassium, and n is selected from an integer of 0-6.

In addition, in Scheme 1, a method for preparing a disulfonate-based accelerator represented by Formula 1 was briefly described, and N, N -bis (3-alkyloxy-2-hydroxypropyl) alkyl represented by Formula 2 below After reacting with an amine compound and a sultone compound represented by Formula 3, it may be prepared by a process of neutralizing with an alkali metal base.

Scheme 1

In Reaction Scheme 1, R ¹ , R ² , M, and n are as defined in Formula 1, respectively.

 The manufacturing method according to Scheme 1 is specifically disclosed in Korean Patent Registration No. 960,356. The solvent used in the reaction is preferably made under a solvent that can dissolve the reactants well and facilitate the contact between the reactants, and the solvent can be used is not particularly limited, but preferably tetrahydrofuran (THF) , Diglyme (Bis (2-methoxyethyl) ether), 1,3-dioxane (1,3-dioxane) and the like can be used. The reaction can be carried out even under conditions that do not separately control the pressure, the reaction temperature is preferably in the range of reflux temperature of the solvent used, specifically 10 ℃ to 150 ℃ range.

On the other hand, the present invention is characterized by a method for producing NGH by hydrating the natural gas in the presence of a disulfonate-based accelerator represented by the formula (1). The hydration reaction of the present invention is a conventional method applied in the art, the present invention is not particularly limited to the selection of the NGH production reactor, reaction conditions, reaction raw materials and the like. In addition, the reaction of producing methane hydrate (methane hydride) using methane instead of natural gas as a reaction raw material is also included in the scope of the present invention.

The natural gas hydrate generation reaction is described in more detail as follows.

The hydrate generating reaction apparatus is composed of a reactor in which the hydrate forming reaction is performed, a heat conduction band for controlling the temperature of the liquid phase and the gas phase, a needle valve, and a control valve. When the hydrate formation reaction is started, the additional feedstock gas is supplied as much as the feedstock gas is consumed in the reactor, so that the reaction proceeds continuously. The reaction temperature is maintained at -10 ° C to 10 ° C, and the reaction pressure is maintained at a range of 1 to 6 MPa. The accelerator represented by the formula (1) is used in a concentration range of 5 to 150 ppm relative to the weight of water, when the amount is less than 5 ppm can not be expected to promote the effect by the addition, exceeding 150 ppm used too much Rather, the promoting effect may be lowered.

In addition, in the hydrate formation reaction of the present invention, in addition to the disulfonate-based accelerator represented by Formula 1, other promoters selected from anionic, cationic and nonionic surfactants having hydrate-producing ability may be further included, Is preferably maintained in the range of 1 to 50% by weight relative to the disulfonate-based accelerator represented by the formula (1).

Anionic surfactants that may additionally be included in the hydrate formation reaction include sodium dodecylsulphate (SDS), sodium dodecylbenzenesulfonate, sodium 1-octadecanesulfonate, linear alkylbenzenesulphonic acid (LABSA), and para-toluene It is at least one selected from sulfonic acids. The cationic surfactant is at least one selected from cetyltrimethylammonium bromide (CTAB) and Dehyguard Dam (DAM). The nonionic surfactant is at least one selected from epoxidized nonylphenol (ENP), dodecyl polysaccharide glycoside, and Pluoronic 123 (EO ₂₀ PO7 ₀ EO ₂₀ ). In addition, the conventional additives used in the natural gas hydrate formation reaction may be further included.

The present invention as described above will be described in more detail by the following examples, but the present invention is not limited to these examples.

Reference Example Synthesis of Disodium Salt (C8 Disulfonate) of 5,9-Dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid

3.10 g (6 mmole) of N, N' -bis (3-octyloxy-2-hydroxypropyl) methylamine and 0.28 g (12 mmole) of sodium metal were added to a reactor equipped with a stirrer, a heating device, and a cooler. After the air in the reactor was removed using a pump, nitrogen gas was charged. 50 mL of dried THF was injected and heated to about 60 ° C. while stirring. A solution of 1.47 g (12 mmole) of 1,3-propanesultone was slowly added dropwise to 10 mL of dried THF, followed by reflux for 24 hours. When the reaction was completed, 5 mL of ethanol was added to inactivate the excess sodium metal, and then concentrated by removing the solvent. The concentrate was subjected to column chromatography to give the title compound.

Melting point 156 ° C .; ESI-mass 645.3, 646.5, 647.5, 648.5; ¹ H-NMR (300 MHz, CD ₃ OD- d ₄ ) δ ppm 0.89 (t, 6H), 1.29 (b, 20H), 1.56 (m, 4H), 2.01 (m, 4H), 2.32 (s, 3H) , 2.52 (m, 4H), 2.88 (m, 4H), 3.4-3.5 (m, 10H), 3.6 (m, 4H)

Using the synthesis method of the reference example to prepare a disulfonate-based accelerator illustrated in Table 1 below.

Example: Methane Hydrate Generation

The reactor is composed of a reactor in which the hydrate formation reaction is performed, a heat conduction band, a needle valve, and a control valve that control the temperature of the liquid phase and the gas phase. The reactor is equipped with a pressure control sensor to measure the methane consumption during the formation of methane hydrate. The reactor was washed with a detergent and then washed again with distilled water and dried. The aqueous surfactant solution containing the hydride production promoter was filled into the reactor, and purging was repeated 2-3 times. As reaction conditions, the reactor internal temperature was set at 22 ° C. and the internal pressure was set at 4.0 MPa. When the temperature inside the reactor reached the set temperature, methane gas was charged to the pressure set value. After waiting for 2 minutes to stabilize the temperature of the gas unit, the hydrate formation reaction was performed with stirring. It was confirmed that the formation of the gas hydrate was terminated because there was no further gas consumption, and the experiment was terminated after the gas in the reactor was discharged. The consumption of methane gas used in the hydrate formation reaction was calculated by Equation 1 below.

[Equation 1]

n = PV / ZRT

In Equation 1, P, V and T represent the pressure, volume and temperature of the gas, R is the gas constant, Z is a compression factor obtained from the Peng Robinson equation.

Table 1 shows the compound names and abbreviations of the accelerators used in this experiment, and the concentrations of the promoters used in the reaction, respectively.

division Compound name of surfactant Abbreviation Input concentration
(ppm) Example 1 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 5 Example 2 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 10 Example 3 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 25 Example 4 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 50 Example 5 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 100 Example 6 Disodium salt of 5,9-dioctyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C8 disulfonate 150 Example 7 Disodium salt of 5,9-didecyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C10 disulfonate 50 Example 8 Disodium salt of 5,9-diododecyloxymethyl-4,10-dioxa-7-aza-7-methyl-1,13-tridecanedisulfonic acid C12 disulfonate 50 Comparative Example 1 - - - Comparative Example 2 Sodium Lauryl Sulfate SDS 250

1 and 2, graphs showing the values obtained by dividing the consumption (m) of methane gas by the reaction time under each reaction condition divided by the amount (mole) of water initially introduced are shown. Methane hydrate was produced by the number of moles of methane gas consumed. The slope of each curve represents the rate of methane hydrate production and the highest methane hydrate storage capacity at a given condition when the methane consumption reaches equilibrium. Since methane hydrate has the form of structure I, the theoretical maximum storage capacity is 0.174 (moles of consumed methane / moles of input).

1 is a graph confirming the methane production promoting effect using the C8 disulfonate as an accelerator as in Examples 1 to 6. In Examples 1 to 6 in which C8 disulfonate was used as an accelerator, the methane hydrate promoting effect was remarkably increased compared to Comparative Example 1 in which no accelerator was added. As the concentration of the C8 disulfonate promoter was increased, the methane hydrate promoting effect was increased, and the highest methane storage capacity was obtained when 50 ppm (Example 4) was added. Increasing the input concentration to 100 ppm and 150 ppm showed lower methane hydrate formation rate and storage capacity than 50 ppm. As the concentration of the C8 disulfonate promoter increases, the surface tension of the water decreases to promote the formation of methane hydrate, but the excessive addition of the surfactant decreases the hydrate formation promoting effect. This is because the surfactant molecules cover the interface of water and gas, reducing the surface area for hydrate formation, thus preventing the contact between methane molecules and water methane. This experiment shows that it is possible to change the storage efficiency of methane gas by changing the concentration of accelerator. In addition, according to the known literature, the SDS shows the best promoting ability in the production of methane hydrate and natural gas hydrate, and the concentration is about 250 ppm. Example 4 with 50 ppm of C8 disulfonate showed higher methane hydrate storage capacity even at low loading concentrations compared to 250 ppm of SDS in Comparative Example 2. Therefore, it can be seen that C8 disulfonate is an economical and process superior surfactant than the existing SDS.

2 is a graph confirming the effect of promoting the methane production according to the length of the carbon chain, the shorter the length of the hydrophobic carbon chain hydrate production rate was increased. Therefore, when the C8 disulfonate was added, the formation rate of methane hydrate was the fastest, and the methane gas storage amount was the best. On the other hand, when C12 disulfonate was added, the rate of hydrate formation was the slowest and the methane gas storage amount was the lowest. At the input of C10 disulfonate, the rate of methane hydrate formation was about the same as that of C8 disulfonate, but the methane storage amount was higher for C8 disulfonate. In addition, although the rate of methane hydrate formation of SDS is faster than that of C8 disulfonate, the methane storage capacity of C8 sulfonate is more than twice that of SDS. C8 disulfonate has higher CMC than C10 and C12 disulfonate but shows a high promoting effect because of its lowest surface tension in CMS. In the case of C12 disulfonate, the CMC value is the lowest, but since the surface tension value is high, the hydrate formation rate and storage degree are relatively lower than that of C8 disulfonate and C10 disulfonate. Small surface tensions cause interactions between water molecule interfaces to be weakened by the surfactant, increasing the rate of absorption of the object gas.

As described above, the natural gas hydrate (NGH) production promoter according to the present invention is a multi-chain-type surfactant used in the hydration of natural gas (Hydration) to easily control the rate of hydrate production through the concentration control on water In addition, the gas hydrate storage capacity is large, and high density NGH can be produced at a high production rate. The present invention is therefore useful in the field of transport and storage of natural gas.

Claims (8)

A natural gas hydrate (NGH) production accelerator, characterized in that the anionic multi-chain disulfonate-based surfactant represented by the formula (1):
[Formula 1]

In Formula 1, R ¹ and R ² are the same as or different from each other selected from a saturated or unsaturated C _{1 ~} C ₃₀ linear or branched alkyl group, the alkyl may be substituted with a fluorine atom or an aromatic ring, M is selected from alkali metals, where n represents an integer from 0 to 6.
The method according to claim 1,
R ¹ and R ² are the same as or different from each other, and are methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl and i-amyl groups. , n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, dodecyl group, tetradecyl group, hexadecyl group, heptadecyl group, octadecyl group Or natural gas hydrate (NGH) production promoter selected from oleyl.
The method according to claim 1,
A natural gas hydrate (NGH) production promoter, characterized in that it further comprises another promoter selected from anionic, cationic and nonionic surfactants having an ability to promote hydrate production.
The method according to claim 3,
The anionic surfactant is at least one selected from sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate, sodium 1-octadecane sulfonate, linear alkylbenzene sulfonic acid (LABSA), and para-toluene sulfonic acid. Natural gas hydrate (NGH) production promoter.
The method according to claim 3,
The cationic surfactant is natural gas hydrate (NGH) production promoter, characterized in that at least one selected from cetyltrimethylammonium bromide (CTAB), Dehyguard Dam (DAM).
The method according to claim 3,
The nonionic surfactant is natural gas hydrate (NGH) generation, characterized in that at least one selected from epoxidized nonylphenol (ENP), dodecyl polysaccharide glycoside, and Pluoronic 123 (EO ₂₀ PO7 ₀ EO ₂₀ ) accelerant.
The method for producing natural gas hydrate (NGH), characterized in that the hydration reaction (hydration) of natural gas in an aqueous solution containing 5 to 150 ppm concentration of any one of the promoter selected from claim 1 to 6.
The method according to claim 7,
The natural gas is a method for producing natural gas hydrate (NGH), characterized in that methane is contained as a main component.

Images