JP2009215562A - Method for producing gas hydrate and decomposition inhibitor for gas hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique improving storage property of a gas hydrate and suppressing decomposition of the gas hydrate during transportation, storing or the like. <P>SOLUTION: One or more substances are selected, for example, from the following (a) and (b) as substances having gas hydrate decomposition suppressing properties in the method for producing the gas hydrate by a reaction of a raw material water and a gas hydrate forming substance under the gas hydrate generating condition. In the substances (a) and (b), (a) represents one or more ions selected from a group composed of a chlorine ion (Cl<SP>-</SP>), a fluorine ion (F<SP>-</SP>), a bromine ion (Br<SP>-</SP>), an iodine ion (I<SP>-</SP>), a sodium ion (Na<SP>+</SP>), a potassium ion (K<SP>+</SP>), a lithium ion (Li<SP>+</SP>), a calcium ion (Ca<SP>2+</SP>), a magnesium ion (Mg<SP>2+</SP>) and an ammonium ion (NH<SB>4</SB><SP>+</SP>); and (b) represents one or more metals selected from a group composed of zinc, iron and manganese, or their ions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention improves gas hydrate which is a clathrate hydrate of a gas hydrate-forming substance such as natural gas, methane gas, carbon dioxide gas and water, a method for producing the gas hydrate, and storage stability of the gas hydrate. It relates to a decomposition inhibitor.

  Gas hydrate is an ice-like solid substance composed of water molecules and gas hydrate-forming substance molecules, and the inclusion water has a structure in which gas hydrate-forming substance molecules are incorporated inside a cage-like structure formed by water molecules. It is a Japanese product. This gas hydrate is generated by reacting water and a gas hydrate forming substance under a predetermined pressure and temperature, and is changed into water and a gas hydrate forming substance by changing the pressure and / or temperature. Dissociate. In addition, since gas hydrate has properties such as high gas occlusion, high generation / dissociation heat and high pressure generation due to small temperature changes, and selectivity of hydrated molecules, for example, natural gas, etc. Research is being conducted to use it for various purposes such as transport and storage means, heat storage systems, actuators, and gas separation and recovery.

  For example, as an advantage of transferring and storing natural gas by hydrated, the equilibrium temperature condition of natural gas hydrate (hereinafter sometimes referred to as “NGH”) under atmospheric pressure is about −80 ° C. (pure methane Therefore, it is possible to transfer and store liquefied natural gas (LNG), which has been put into practical use, under a much milder temperature condition than the transfer and storage temperature (-163 ° C.) under atmospheric pressure.・ It is expected that the durability and heat insulation of storage facilities can be greatly simplified. Here, it is considered that NGH is transferred and stored in the form of slurry, powder, pellets, compacted blocks, etc. after the gas hydrate is produced.

  The temperature at which the gas hydrate is transferred and stored is set to a temperature as close to 0 ° C. as possible, considering the advantages over the above-mentioned liquefied natural gas (LNG) and economics such as equipment costs and operating costs. It is desirable. However, there is a problem that the decomposition amount of the gas hydrate increases as the temperature increases. For example, when NGH is stored under conditions of atmospheric pressure and −20 ° C., about 80% or more of conventional NGH is decomposed in two weeks. When the decomposition amount of the gas hydrate increases, the amount of stored gas per unit weight of the gas hydrate transferred and stored decreases, leading to a decrease in the efficiency of transfer and storage. And in order to maintain the efficiency of transfer and storage, it is necessary to attach a recovery gas recovery device, a tank, a rehydration device, etc. to the transfer facility and storage facility, which increases facility costs and operation costs. Will be a factor.

  Regarding the stabilization of gas hydrates during transport and storage processes, proposals have been made to suggest that the storage and transport capacity of gas hydrates can be increased by using water stabilizers (for example, Patent Document 1). ). However, Patent Document 1 does not specifically describe what kind of substance the “water stabilizer” is, and is merely a mere idea.

  As described above, in order to stably transport and store the gas hydrate in the form of slurry, powder, pellets, compacted blocks, etc., it is necessary to reduce the decomposition of the gas hydrate as much as possible.

  The subject of this invention is providing the technique which improves the preservability of gas hydrate and suppresses decomposition | disassembly of gas hydrate at the time of transfer, storage, etc.

In order to solve the above-described problem, the gas hydrate according to the first aspect of the present invention is a method for producing gas hydrate by reacting raw material water and a gas hydrate-forming substance under conditions for producing gas hydrate. In the present invention, gas hydrate is produced in the presence of a substance having a gas hydrate decomposition inhibiting action.
According to this feature, gas hydrate is produced in the presence of substances that have an effect of inhibiting decomposition of gas hydrate, thereby producing gas hydrate with excellent self-preserving effect and low decomposition during transportation and storage. it can. Therefore, the gas hydrate produced by this method is excellent in transfer and storage efficiency, and for example, it is possible to omit or simplify the equipment for rehydrating cracked gas.

  The method for producing a gas hydrate according to the second aspect of the present invention is a method for producing a gas hydrate by reacting a raw material water and a gas hydrate-forming substance under a gas hydrate production condition. It is characterized in that a substance having a gas hydrate decomposition inhibitory action and / or a substance that generates the substance in water is added to water. According to this feature, the same effect as the first aspect can be obtained.

  The method for producing a gas hydrate according to the third aspect of the present invention is the method according to the first aspect or the second aspect, wherein the substance having an action of inhibiting the decomposition of the gas hydrate is an ion in which an electrolyte is dissociated in a solution. It is characterized by being. According to this feature, the same effect as the first aspect or the second aspect can be obtained.

  The method for producing a gas hydrate according to a fourth aspect of the present invention is the method according to the third aspect, wherein the ions are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium ( Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), fluorine (F), chlorine (Cl), bromine (Br), iodine (I), carbon ( C), sulfur (S), nitrogen (N), oxygen (O), boron (B), phosphorus (P), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), cadmium ( Cd), aluminum (Al), silicon (Si), tin (Sn), lead (Pb), vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co) and nickel (Ni) Selected from Characterized in that it is intended to include one or more elements as a component. According to this feature, the same effect as the first aspect or the second aspect can be obtained.

The method for producing a gas hydrate according to a fifth aspect of the present invention is the method according to the first aspect or the second aspect, wherein the substance having an action of inhibiting the decomposition of the gas hydrate is a and / or b: a: Chlorine ion (Cl ⁻ ), fluorine ion (F ⁻ ), bromine ion (Br ⁻ ), iodine ion (I ⁻ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), lithium ion (Li ⁺ ) , One selected from the group consisting of calcium ions (Ca ²⁺ ), magnesium ions (Mg ²⁺ ), carbonate ions (CO ₃ ²⁻ ), phosphate ions (PO ₄ ³⁻ ), and ammonium ions (NH ₄ ⁺ ), 2 or more types of ions; b: 1 type selected from the group consisting of zinc, iron and manganese, or two or more types of metals, or ions of the metal Wherein the or two or more substances.

  According to this feature, by using one or more ions or metals selected from the range a and b as the substance having a gas hydrate decomposition inhibitory effect, the self-preserving property is excellent, and the decomposition amount is low. Less gas hydrate can be produced.

  The gas hydrate according to the sixth aspect of the present invention is characterized in that the electrolyte contains ions dissociated in the solution.

  According to this gas hydrate invention, the electrolyte contains ions dissociated in the solution, so that the gas hydrate is excellent in self-preserving properties and has a small amount of decomposition during transportation and storage. In addition, in this embodiment, “containing” includes a state contained in the crystal and a state existing around the gas hydrate in an inseparable state from the gas hydrate particles.

  The gas hydrate according to a seventh aspect of the present invention is the gas hydrate according to the sixth aspect, wherein the ions are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), Beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), fluorine (F), chlorine (Cl), bromine (Br), iodine (I), carbon (C), Sulfur (S), nitrogen (N), oxygen (O), boron (B), phosphorus (P), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), cadmium (Cd), Selected from the group consisting of aluminum (Al), silicon (Si), tin (Sn), lead (Pb), vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co) and nickel (Ni) 1 type Others characterized in that it is intended to include as a component of two or more elements. According to this feature, the same effect as that of the sixth aspect can be obtained.

The gas hydrate according to the eighth aspect of the present invention has the following a and / or b: a: chlorine ion (Cl ⁻ ), fluorine ion (F ⁻ ), bromine ion (Br ⁻ ), iodine ion (I ⁻ ), Sodium ion (Na ⁺ ), potassium ion (K ⁺ ), lithium ion (Li ⁺ ), calcium ion (Ca ²⁺ ), magnesium ion (Mg ²⁺ ), carbonate ion (CO ₃ ²⁻ ), phosphate ion ( One or more ions selected from the group consisting of PO ₄ ³⁻ ) and ammonium ions (NH ₄ ⁺ ); b: one or more metals selected from the group consisting of zinc, iron and manganese, Or one or more substances selected from the ions of the metal.

  According to this gas hydrate invention, it contains one or more ions or metals selected from the above-mentioned ranges a and b, so that it has excellent self-preserving properties and has a small amount of decomposition during transportation and storage. Hydrate. In addition, in this embodiment, “containing” includes a state contained in the crystal and a state existing around the gas hydrate in an inseparable state from the gas hydrate particles.

  The gas hydrate decomposition inhibitor according to the ninth aspect of the present invention is characterized in that the electrolyte contains ions dissociated in a solution. By using this gas hydrate decomposition inhibitor, it is possible to improve the storage stability of the gas hydrate and suppress decomposition.

  The decomposition inhibitor for gas hydrate according to a tenth aspect of the present invention is the ninth aspect, wherein the ions are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium. (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), fluorine (F), chlorine (Cl), bromine (Br), iodine (I), carbon (C), sulfur (S), nitrogen (N), oxygen (O), boron (B), phosphorus (P), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), cadmium (Cd), aluminum (Al), silicon (Si), tin (Sn), lead (Pb), vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co) and nickel (Ni) Flock Characterized in that it is intended to include one or more elements selected as a component. According to this feature, the same effect as that of the ninth aspect can be obtained.

The gas hydrate decomposition inhibitor according to the eleventh aspect of the present invention includes the following a, b, c and / or d; a: chlorine ion (Cl ⁻ ), fluorine ion (F ⁻ ), bromine ion (Br) ⁻ ), Iodine ion (I ⁻ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), lithium ion (Li ⁺ ), calcium ion (Ca ²⁺ ), magnesium ion (Mg ²⁺ ) and ammonium ion (NH ₄₎ ⁺ ) One or more ions selected from the group consisting of; b: one or more metals selected from the group consisting of zinc, iron and manganese, or ions of the metal; c: dissociation in water A substance that generates ions of the a; d: a substance that generates the metal of the b or ions of the metal in water; It is characterized by doing. By using this gas hydrate decomposition inhibitor, it is possible to improve the storage stability of the gas hydrate and suppress decomposition.

The graph which shows the time transition of the decomposition rate of the methane hydrate of Example 1 and a comparison methane hydrate. The graph drawing which shows the time transition of the decomposition rate of the methane hydrate of Example 2, and the comparison methane hydrate. The graph which shows the time transition of the decomposition rate of the methane hydrate of Example 3, and the comparison methane hydrate. The graph which shows the time transition of the decomposition rate of the methane hydrate of Example 4, and the comparison methane hydrate. The graph figure which shows the time transition of the decomposition rate of the methane hydrate of Example 5, and a comparison methane hydrate. The graph which shows the time transition of the decomposition rate of the methane hydrate of Example 6, and a comparison methane hydrate. The graph which shows the time transition of the decomposition rate of the methane hydrate of Example 7, and a comparison methane hydrate. The graph figure which shows the time transition of the decomposition rate of the methane hydrate of a reference example. The principle figure with which it uses for description of the mechanism of the self-preservation effect of natural gas hydrate.

  The method for producing a gas hydrate according to the present invention includes a raw material water, a gas hydrate-forming substance, and a substance having a gas hydrate decomposition-inhibiting action (hereinafter sometimes referred to as “decomposition-inhibiting substance”). It is carried out by reacting.

<Raw material water>
Normally, pure water or purified water that does not contain impurities that affect the production of gas hydrate is used as the raw material water for producing gas hydrate. In the present invention, a decomposition inhibiting substance can be added to such pure water or purified water, and when an appropriate amount of a decomposition inhibiting substance is contained in the raw water, it can be used as it is.

<Gas hydrate forming substance>
The type of gas hydrate in the present invention is not particularly limited. That is, the type of the gas hydrate-forming substance is not particularly limited as long as it forms a gas hydrate under predetermined pressure and temperature conditions. For example, methane, natural gas (methane as a main component, ethane, propane, butane And a substance (gas) that is a gas at normal temperature and normal pressure, such as carbon dioxide (carbon dioxide).

<Gas hydrate generation conditions>
Conditions such as temperature and pressure for generating the gas hydrate vary depending on the substance, but are known conditions. For example, in the case of methane hydrate, it can be produced under the conditions shown in the examples described later.

  For example, when the gas hydrate-forming substance is a gas, the reaction between water and the gas hydrate-forming substance is performed by forming gas hydrate at the gas-liquid interface in a contact state between water and gas.

<Degradation inhibitor>
The decomposition inhibiting substance is not particularly limited as long as it can improve the self-preserving effect of gas hydrate, but the following substances are preferable.

  Ions generated by the dissociation of the electrolyte in the solution can be suitably used as a decomposition inhibitor. Examples of the ions include ions containing as constituent elements alkali metal elements, alkaline earth metal elements, halogen elements, nonmetallic elements, metal elements (excluding the alkali metal elements and alkaline earth metal elements), and the like. Can do. Here, the “electrolyte” is not particularly limited as long as it has the above-mentioned elements as constituents, but is preferably an electrolyte that does not decompose in raw material water to generate a gaseous substance as described later.

  Examples of the alkali metal element include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and the like. Examples of the alkaline earth metal element include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Examples of the halogen element include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the like. Examples of the nonmetallic element include carbon (C), sulfur (S), nitrogen (N), oxygen (O), boron (B), and phosphorus (P). Examples of the metal element include manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), cadmium (Cd), aluminum (Al), silicon (Si), tin (Sn), Lead (Pb), vanadium (V), chromium (Cr), molybdenum (Mo), cobalt (Co), nickel (Ni), and the like can be given.

Specific examples of ions preferable as the decomposition inhibitor include the ions shown in the following a.
a: Chlorine ion (Cl ⁻ ), fluorine ion (F ⁻ ), bromine ion (Br ⁻ ), iodine ion (I ⁻ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), lithium ion (Li ⁺ ) , Ions such as calcium ion (Ca ²⁺ ), magnesium ion (Mg ²⁺ ), and ammonium ion (NH ₄ ⁺ ).

In addition, specific examples of metals and metal ions that are preferable as a decomposition inhibitor include the metals or ions shown in b below.
b: A metal such as zinc, iron, manganese, or an ion of the metal.
The above-mentioned decomposition inhibitory substances can be used alone, but can be used in combination of two or more kinds, and it is preferable to use a combination of a plurality of decomposition inhibitory substances as shown in Examples below. There is also.

  The amount (abundance, addition amount) of the decomposition inhibitory substance is contained in the raw material water in an amount of 0.1 ppm to 10000 ppm (1 wt%) in the case where the electrolyte is an ion dissociated in solution or the ion a. Preferably, it is preferably 1 ppm or more and 1000 ppm or less. In addition, in the case of the metal b or ions of the metal, it is preferable to be contained in the raw material water in an amount of 0.01 ppm to 1000 ppm (0.1 wt%), preferably 0.01 ppm to 100 ppm. .

  When an electrolyte is added to the raw water, the ions may be contained in the raw water to the same extent as described above. As will be described later, when the substances c and d are used as the decomposition inhibitor, the substances a and b may be contained in the raw water in the same amount as described above.

Incidentally, in the decomposition inhibitor is what is known as a generation inhibitor gas hydrate (e.g. Na ^+, Cl ^-, etc.) are included, usually inhibition by these are present several wt% Happens in conditions. On the other hand, since the decomposition suppressing effect by the decomposition suppressing substance acts at a remarkably low concentration level, generation inhibition does not occur or even if it occurs, the influence can be kept small. In addition, even when the concentration at which production inhibition occurs, when priority is given to the improvement of self-preserving property, it may be present beyond the above range.

  The self-preserving effect of the gas hydrate of the present invention obtained as described above is enhanced by the decomposition-suppressing substance, and the efficiency of transfer / storage under gas hydrate decomposition conditions can be improved. The pressure and temperature at the time of transportation and storage are preferably about atmospheric pressure and the temperature should be -20 ° C or more and 0 ° C or less to reduce energy consumption and equipment burden, but the gas produced in the presence of decomposition inhibitor Hydrate can also be transferred and stored under milder conditions, for example, at a temperature of about −15 ° C. under atmospheric pressure.

<Decomposition inhibitor>
The decomposition inhibiting substance (an ion obtained by dissociating an electrolyte in a solution, the a ion, the b metal or the ion) can be used as a decomposition inhibitor for gas hydrate. Moreover, the substance which produces | generates a decomposition inhibitor in water can also be used as a decomposition inhibitor of gas hydrate. Here, as the “substance that generates a decomposition-inhibiting substance in water”, for example, c: a substance that dissociates in water to generate ions of the a, d: generates the metal of b or ions of the metal in water. Substances and the like can be mentioned, and among these, electrolytes are preferably included.

Examples of the “substance that dissociates in water to generate the ion a” of c include sodium chloride, calcium chloride, magnesium chloride, sodium fluoride, calcium bromide, ammonia, and the like. Examples of the “substance that generates the metal b or ions of the metal in water” include iron chloride (FeCl ₂ ), zinc chloride (ZnCl ₂ ), manganese chloride (MnCl ₂ ), and the like. .

  These decomposition inhibitors are preferably added to the gas hydrate raw water or the like so as to have the amount described above. By using a decomposition inhibitor, the self-preserving property of the gas hydrate can be improved.

[Action]
It is known that gas hydrate has an effect of suppressing decomposition, called a self-preserving effect (self-preservation effect), at a temperature equal to or higher than the equilibrium temperature. This self-preserving effect has many unexplained points, but the following explanation is given (Hiroshi Kaneko, Journal of the Japan Institute of Shipbuilding No. 842, p38-48).

  FIG. 9 is a drawing schematically showing a cross section of gas hydrate particles. When the gas hydrate 50 [FIG. 9A] generated at low temperature and high pressure is subjected to decomposition conditions such as atmospheric pressure, partial decomposition starts from the surface, the gas hydrate-forming substance gasifies, and the water film 51 Covers the surface of the gas hydrate [FIG. When heat is taken away by the decomposition of the gas hydrate on the surface, the water film 51 on the surface of the gas hydrate becomes an ice film 52 and covers the surface of the gas hydrate [FIG. When the ice film 52 grows to a certain thickness or more, heat exchange between the internal gas hydrate and the outside is interrupted, and the internal gas hydrate is stabilized even under decomposition conditions such as atmospheric pressure. That is, the ice film 52 has a mechanical strength that resists the pressure of the gas hydrate to be decomposed (gasified), so that the gas hydrate is stabilized and further decomposition is suppressed. Self-preserving effect is considered to occur.

  The present invention has been made based on the knowledge that by generating gas hydrate in the presence of a decomposition inhibitor, the self-preserving effect is improved and the stability of the gas hydrate is increased. Some of the decomposition inhibitors have been pointed out to have an effect of inhibiting the formation of gas hydrate, but it is completely unexpected that these have the property of improving the self-preservation effect. It is a result. Although the mechanism of action by which the decomposition inhibitor improves self-preserving properties has not yet been elucidated, a rational explanation is possible by considering the following.

Among the above-mentioned decomposition inhibiting substances, substances such as chlorine ions (Cl ⁻ ), fluorine ions (F ⁻ ), and ammonium ions (NH ₄ ⁺ ) are replaced with water molecules of ice crystals and a small amount to lattice points in the ice crystals. (For example, “Basic Snow and Ice Laboratory: Structure and Crystal of Snow and Ice”: Kiichi Maeno, Masami Fukuda). Although there are no reports on the replacement of these substances with water molecules in crystals of gas hydrate cage structure, it is presumed that they enter crystals as in the case of ice. When these substances enter into the crystal, a crystal defect occurs at the lattice point where the substance enters.

  In general, in the field of metal materials, it is known that when there are various defects in a crystal, if the number of defects is small, the transition movement of the crystal is inhibited and the strength is increased. In the case of ice and gas hydrates, there are no reports of lattice defects affecting ice strength or gas hydrate strength. However, as in the case of metals, the above substances can be found at the lattice points of ice and gas hydrates. It is speculated that it enters, causes lattice defects, and increases the mechanical strength of ice and gas hydrate.

  In addition, decomposition inhibitors other than the above ions do not enter the gas hydrate cage structure or ice crystal directly as lattice points, but impurities in the gas hydrate crystal grain boundaries and ice crystal grain boundaries. It is presumed to exist as. It is speculated that the impurities present in these crystals also have an effect of inhibiting the crystal transition and increasing the mechanical strength of ice and gas hydrate.

  Under the gas hydrate production conditions, the decomposition inhibiting substance is present in the ice adhering to the periphery of the gas hydrate and increases the surrounding ice strength. When the gas hydrate is subjected to mild decomposition conditions, the ice around the gas hydrate will also melt once, but when the ice film covering the gas hydrate particles [FIG. Inhibitors are also incorporated into the ice film. The presence of the decomposition inhibiting substance is considered to improve the mechanical strength of the ice film, increase the pressure resistance against the internal decomposition gas, and improve the self-preserving effect. Therefore, it is considered that the decomposition inhibitor is not limited to the above-described exemplary decomposition inhibitor, and may be any substance that can increase the mechanical strength of ice, particularly a substance that can replace water molecules as a crystal lattice.

  In addition, an explanation based on the ion effect as described below is possible as an action compatible with the above-described estimation of improvement in mechanical strength due to lattice defects in the crystal.

  In other words, the electrolyte as the decomposition inhibitor has an equal amount of charges for positive ions and negative ions. Since positive and negative ions have the property of attracting each other, the electrical properties of the gas hydrate change when these minute amounts of ions are present in or between the crystal structure of the gas hydrate. It was confirmed that the gas hydrate to which ions were added was easily charged with static electricity and the electrical properties were clearly different from those of ordinary gas hydrate. Due to the nature of ions, the electrical coupling force also acts on the hydrate structure. It is presumed that this binding force contributes to the improvement of storage stability by suppressing the release of internal gas by strengthening the cage structure of the water molecules to be included.

  EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

Example 1
Calcium chloride (CaCl ₂ , 2H ₂ O, molecular weight M = 147.02) was dissolved in 200 g of distilled water (raw water) to obtain a calcium chloride solution. This solution was placed in a stainless steel container and sealed, and then filled with methane gas (purity 99% or more) at a pressure of 8 MPa.

  The container was kept at 4 ° C., and gas hydrate was generated while stirring with a stirrer. As the methane hydrate was produced, the gas pressure decreased, so methane was supplied so that the pressure was constant.

  After the methane hydrate is produced, the container temperature is set to −20 ° C. (it may be 0 ° C. or less), the internal excess moisture is frozen, the pressure in the container is reduced to atmospheric pressure, and the produced methane hydrate is surrounded by the surroundings. It was taken out into the atmosphere at a temperature of −20 ° C.

  A gas hydrate sample was put in a container with a small hole through which cracked gas escapes, the sample weight was measured, and the decomposition rate of gas hydrate was determined from the change in weight by the following measurement method.

<Measurement of decomposition rate>
(1) Put a methane hydrate sample in a container, measure the weight of the container, and obtain the sample weight (w1).
(2) Maintain at −20 ° C., measure the weight of the sample container every predetermined time, and obtain the sample weight.
(3) After the predetermined time, the sample is completely decomposed and the weight (w2) of residual water (ice) is obtained.
(4) The hydrate conversion rate and the decomposition rate are obtained by the following equations.

  The initial hydrate conversion rate of the methane hydrate of this example was 90%. The amount of chlorine ions as a decomposition inhibitor was 100 ppm, and the amount of calcium ions was 57 ppm. The measurement result of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example is shown in FIG.

Example 2
0.016 g of sodium chloride (NaCl, molecular weight M = 58.44) was dissolved in 200 g of distilled water (raw water) to obtain a sodium chloride solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured. The amount of chlorine ions as a decomposition inhibitor was 50 ppm, and the amount of sodium ions was 32 ppm. The measurement result of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example is shown in FIG.

Example 3
0.0573 g of magnesium chloride (MgCl ₂ .6H ₂ O, molecular weight M = 203.3) was dissolved in 200 g of distilled water (raw water) to obtain a magnesium chloride solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured. The amount of chlorine ions as a decomposition inhibitor was 100 ppm, and the amount of magnesium ions was 34 ppm. The measurement result of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example is shown in FIG.

Example 4
Sodium chloride, calcium, magnesium, zinc, iron and manganese were dissolved in 200 g of distilled water (raw water) (sodium ion 20 ppm; chloride ion 20 ppm; calcium 50 ppm; magnesium 50 ppm; zinc 0.012 ppm; iron 0.08 ppm, manganese) 0.043 ppm). Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured. The measurement result of the decomposition rate of the gas hydrate (particle diameter 4 mm) of this example is shown in FIG.

Example 5
0.0044 g of sodium fluoride (NaF, molecular weight M = 42) was dissolved in 200 g of distilled water (raw water) to obtain a sodium fluoride solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured. The amount of fluorine ions as a decomposition inhibitor was 10 ppm, and the amount of sodium ions was 12 ppm. The measurement result of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example is shown in FIG.

Example 6
0.03 g of calcium bromide (CaBr ₂ ) was dissolved in 200 g of distilled water (raw water) to obtain a calcium bromide solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured. The amount of bromine ions as a decomposition inhibitor was 100 ppm, and the amount of calcium ions was 50 ppm. FIG. 6 shows the measurement results of the decomposition rate of the gas hydrate (particle size 0.5 mm) of this example.

Example 7
0.088 g of ammonium sulfate [(NH ₄ ) ₂ SO ₄ ; molecular weight 132] as an electrolyte was dissolved in 200 g of distilled water (raw water) to obtain an ammonium sulfate solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

The amount of ammonium ion NH ₄ ⁺ as a decomposition inhibitor was 120 ppm, and the amount of sulfate ion SO ₄ ²⁻ was 320 ppm. FIG. 7 shows the measurement results of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example.

Comparative Examples 1-7
As a comparative example, methane hydrate was produced under the same conditions as in Examples 1 to 7, except that distilled water without adding a decomposition inhibitor was used. The measurement result of the decomposition rate of the comparative methane hydrate in the same particle size as each Example was written together in FIGS.

Example 8
0.055 g of magnesium carbonate (MgCO ₃ ; molecular weight 84) as an electrolyte was dissolved in 450 g of distilled water (raw water) to obtain a magnesium carbonate solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

The amount of carbonate ion CO ₃ ²⁻ as a decomposition inhibitor was 90 ppm, and the amount of magnesium ion Mg ²⁺ was 35 ppm. As a result of measuring the decomposition rate of the gas hydrate (particle diameter 1 mm) of this example, it was confirmed that the decomposition was suppressed as compared with the case of no addition.

Example 9
0.060 g of potassium hydrogen phosphate (K ₂ HPO ₄ ; molecular weight 133) as an electrolyte was dissolved in 200 g of distilled water (raw water) to obtain a potassium hydrogen phosphate solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

The amount of phosphate ion PO ₄ ³⁻ as a decomposition inhibitor was 200 ppm, and the amount of potassium ion K ⁺ was 80 ppm. As a result of measuring the decomposition rate of the gas hydrate of this example, it was confirmed that the decomposition was suppressed as compared with the case of no addition.

Example 10
0.140 g of lithium chloride (LiCl; molecular weight 41) as an electrolyte was dissolved in 200 g of distilled water (raw water) to obtain a lithium chloride solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

The amount of lithium ion Li ⁺ as a decomposition inhibitor was 100 ppm, and the amount of chlorine ion Cl ⁻ was 580 ppm. As a result of measuring the decomposition rate of the gas hydrate of this example, it was confirmed that the decomposition was suppressed as compared with the case of no addition.

Example 11
0.0236 g of sodium iodide (NaI; molecular weight 150) as an electrolyte was dissolved in 200 g of distilled water (raw water) to obtain a sodium iodide solution. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

The amount of iodine ion I ⁻ as a decomposition inhibitor was 100 ppm, and the amount of sodium ion Na ⁺ was 200 ppm. As a result of measuring the decomposition rate of the gas hydrate of this example, it was confirmed that the decomposition was suppressed as compared with the case of no addition.

Reference Example Sodium hypochlorite (NaClO) was dissolved in 200 g of distilled water (raw water) to give a solution having a ClO concentration of 1 ppm. Residual chlorine concentration was measured by the orthotolidine method. Methane hydrate was produced in the same manner as in Example 1 except that this solution was used, and the decomposition rate was measured.

  The measurement result of the decomposition rate of the gas hydrate (particle diameter 1 mm) of this comparative example is shown in FIG. From FIG. 8, it was confirmed that when sodium hypochlorite was added, the gas hydrate decomposition inhibitory action was not obtained, and conversely, the decomposition rate was larger than when no additive was added and the storage stability was lowered. .

The reason why the decomposition suppression effect is not obtained even when sodium hypochlorite is added is not clear, but is presumed as follows.
That is, sodium hypochlorite dissociates in an aqueous solution to produce hypochlorite ions (ClO ⁻ ), but these hypochlorite ions are unstable and easily decomposed, and eventually molecular oxygen is dissolved. Arise. That is, sodium hypochlorite is gradually decomposed according to the following reaction formula.

2NaClO → 2NaCl + O ₂

Similarly, release of molecular oxygen occurs in calcium hypochlorite [Ca (ClO) ₂ ].

Ca (ClO) ₂ → CaCl ₂ + O ₂

Oxygen gas generated by these reactions continues to dissipate in the process of gas hydrate formation, which may adversely affect the physical properties of the gas hydrate. Specifically, for example, gaseous oxygen is volatilized in the process of forming gas hydrate, thereby forming micropores in the gas hydrate, resulting in an increase in the surface area of the gas hydrate, It is presumed that it will be easily decomposed with changes in pressure. From this, it is considered that the electrolyte used in the present invention is preferably an electrolyte (non-gas generating electrolyte) having a property of not generating gaseous substances such as oxygen molecules in an aqueous solution. Also, when using an electrolyte such as sodium hypochlorite that can generate gaseous substances, adjust the conditions such as pH to form hydrates in a state where gas generation is unlikely to occur. Is preferred.

  From the results of the above Examples and Comparative Examples, it was shown that the methane hydrate produced in the presence of the decomposition inhibitory substance had a lower decomposition rate under the same conditions than the comparative methane hydrate. Therefore, it has been clarified that a gas hydrate having a low decomposition rate at the time of transportation and storage can be produced by producing a gas hydrate in the presence of a decomposition inhibiting substance or by adding a decomposition inhibiting substance.

[The invention's effect]
According to the method for producing a gas hydrate of the present invention, a gas hydrate having a high self-preserving effect and having a small amount of decomposition during transfer or storage can be produced.

  In addition, the gas hydrate produced by the method of the present invention is excellent in transfer and storage efficiency and has a small amount of decomposition during transfer and storage, so the equipment for rehydrating boil-off gas is omitted or simplified. it can.

More specifically, for example, in the case of NGH, the following effects (1) to (5) can be obtained.
(1) The self-preserving effect of NGH is sufficiently obtained even in a normal NGH decomposition region (for example, conditions of atmospheric pressure and −15 ° C.), and transfer and storage are possible with a small amount of gas decomposition. Accordingly, the amount of natural gas transferred and the amount of natural gas stored can be increased, and high transfer / storage efficiency is ensured.
(2) Since the transfer / storage temperature can be increased to, for example, about −15 ° C., energy required for cooling can be reduced, and equipment can be simplified.
(3) Since the transfer / storage temperature can be increased to, for example, about −15 ° C., the energy required for regasification can be reduced and the equipment can be simplified.
(4) Since the intrusion heat is reduced, the thickness of the heat insulating material (heat insulating material amount) can be reduced. Therefore, in a container having the same volume, it is possible to reduce the outer dimension, and the volume efficiency is increased.
(5) Since the amount of cracked gas can be reduced, a cracked gas recovery device and a rehydration facility are not required.

  Furthermore, the same effect as described above can be obtained by using the decomposition inhibitor of the present invention.

50 Natural gas hydrate 51 Water film 52 Ice film

Japanese Patent No. 3173611

Claims (2)

In a method for producing gas hydrate by reacting raw material water and a gas hydrate-forming substance under conditions for producing gas hydrate,
Gas hydrate is generated in the presence of a substance having a gas hydrate decomposition inhibiting action, and the substance having the gas hydrate decomposition inhibiting action is prescribed for sodium hypochlorite and / or calcium hypochlorite. A method for producing a gas hydrate, characterized by being subjected to the following treatment. In a method for producing gas hydrate by reacting raw material water and a gas hydrate-forming substance under conditions for producing gas hydrate,
A substance having a gas hydrate decomposition inhibitory action and / or a substance that produces the substance in water is added to the raw water, and the substance having a gas hydrate decomposition inhibitory action is sodium hypochlorite and A method for producing a gas hydrate, wherein the calcium hypochlorite is subjected to a predetermined treatment.

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