JP2000273475A - Gas hydrate stabilizer and gas hydrate stabilization method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas hydrate stabilizer capable of shifting the production conditions for a gas hydrate such as of methane to higher temperature and lower pressure side, and of improving handleability thereof, by mainly including a high-molecular compound having a specific structural unit in the molecule. SOLUTION: This gas hydrate stabilizer consists mainly of a polymer having pref. 0.01 to 80 mol% of a structural unit represented by the formula [R1 to R3 are each H or a 1-2C alkyl; Sp1 is O, a 1-16C alkyl, a (substituted)nitrogen- containing functional group, or the like; X is a 3-10C straight-chain or a branched-type group each containing one or more of O and/or N atoms, or a heterocyclic group; (n) is >=1], wherein, the structural unit copolymerizable with the polymer is of a water-soluble monomer such as N-(meth)acrylamide, and a gas hydrate is pref. stabilized by adding 0.01 to 30 wt.% of this gas hydrate stabilizer to free water in the system capable of producing the gas hydrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing a gas hydrate which shifts the conditions for producing a gas hydrate such as a hydrocarbon gas such as methane, carbon dioxide gas or carbon disulfide gas to a high temperature and low pressure side. It relates to a stabilizer.

[0002]

2. Description of the Related Art An aqueous medium in which gas molecules of various hydrocarbons such as carbon dioxide, methane, and ethane are dissolved is placed at a specific temperature and pressure to dissolve the dissolved gas molecules in ice surrounding water molecules. It is known that crystals of gas, ie, gas hydrate (clathrate hydrate), are produced. This gas hydrate is often generated during the extraction and transportation of crude oil and natural gas, and causes clogging of pipelines and the like, which is a major problem in the safe continuous operation of crude oil and natural gas transport pipelines.

[0003] On the other hand, gas hydrate is known to exist naturally under high pressure and low temperature conditions. For example, gas hydrate is under permafrost in cold regions such as Siberia and Canada, or
Huge amounts of methane gas hydrate have been found in large areas of the ocean floor deeper than several hundred meters.

[0004] Natural gas has recently attracted particular attention as an energy source that emits less carbon dioxide, nitrogen oxides and sulfur oxides, which are one of the causes of environmental pollution. Natural gas is often transported as liquefied natural gas (LNG), which is usually liquid at an extremely low temperature of -162 ° C. However, a device for achieving this cryogenic state and a special tanker for transporting liquefied natural gas in a cryogenic state are required, and the transportation and storage of the tank requires too much initial cost. is there. In recent years, attention has been paid to a technology utilizing a hydrate of natural gas as one of the means for solving the difficulty of the transportation. This is for the ultimate purpose of allowing natural gas hydrate to be handled under conditions where normal gas hydrate is generated, that is, conditions that are milder than high-pressure and low-temperature conditions, ideally at normal temperature and normal pressure. is there.

[0005] Japanese Patent Application Laid-Open No. 4-316955 proposes a method for promoting gas hydrate formation by using an aliphatic amine. This gas hydrate production method using aliphatic amines seems to be easy to handle natural gas as such, but aliphatic amines are corrosive, and when natural gas is extracted from gas hydrate, There was a problem of mixing in natural gas due to its vapor pressure.

Japanese Patent Application Laid-Open No. Hei 6-17069 discloses that a cyclic compound having an alcohol group having 2 to 6 carbon atoms or the like is used so that the methane hydrate formation condition of about 3 MPa at 0 ° C. There is a report that the pressure can be reduced to as low as 0.2 MPa.

[0007] The additives used in these methods are generally low molecular weight compounds, so that when gas hydrate is decomposed to take out natural gas or the like, there is a problem that the additive is necessarily mixed into the gas due to the vapor pressure. there were.

Although none of the patents describes the amount of these additives used, since these additives are low-molecular-weight substances, they are inevitably present in a large amount, that is, to such an extent that the conditions for hydrate formation are equilibrium shifted. Need to be added.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to shift the conditions for producing gas hydrates such as hydrocarbon gas such as methane, carbon dioxide gas, or carbon disulfide gas to higher temperature and lower pressure side, An object of the present invention is to provide a polymer as a stabilizer, which is used in a small amount and has a large effect, and a method for stabilizing gas hydrate using the polymer.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a polymer having an effect of stabilizing gas hydrate and a method of stabilizing gas hydrate using the same. It was found that the use of a water-soluble polymer was effective, and a method for stabilizing gas hydrate using the same was also found.

That is, the present invention resides in a gas hydrate stabilizer and a gas hydrate stabilization method mainly comprising a polymer compound having a structural unit represented by the following general formula (1) in the molecule.

Embedded image (Wherein, R ₁ , R ₂ and R ₃ each independently represent a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and Sp ₁ represents an oxygen atom or a linear or branched chain having 1 to 16 carbon atoms. Alkyl group; carbonyl; ester; ether, carbonate, thioester, amide, urethane, or a nitrogen-containing functional group in which a hydrogen atom on the nitrogen atom may be substituted by an alkyl group having 1 or 2 carbon atoms; ether; thioether; It contains one or more functional groups selected from urea, imine, or a nitrogen atom in which a hydrogen atom on the nitrogen atom may be substituted with an alkyl group having 1 or 2 carbon atoms. X represents a linear or branched group having at least one oxygen atom and / or at least one nitrogen atom and having 3 to 10 carbon atoms; The polymer compound used in the present invention is a copolymer in which the proportion of the general formula (1) is 0.01 to 80 mol%, and the general formula (1) The gas hydrate stabilizer is characterized in that the comonomer copolymerizable with the unit (1) is a water-soluble monomer.

In addition, the present invention is characterized in that the gas hydrate stabilizer is added to a system capable of producing gas hydrate, and the stabilizer is dissolved in water and / or a solvent miscible with water. And a method of adding the stabilizer to the free water in the system capable of generating a gas hydrate.
This is a method for stabilizing gas hydrate, characterized by adding about 30% by mass.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The following general formula (1) in the polymer used in the present invention:

Embedded image (Wherein R ₁ , R ₂ and R ₃ each independently represent a hydrogen atom or an alkyl group having 1 or 2 carbon atoms;
p ₁ is an oxygen atom or a linear or branched alkyl group having 1 to 16 carbon atoms; carbonyl; ester;
Carbonate, thioester, amide, urethane, or a nitrogen-containing functional group in which a hydrogen atom on the nitrogen atom may be substituted by an alkyl group having 1 or 2 carbon atoms; ether; thioether; urea, imine, or a nitrogen atom thereof The above hydrogen atom represents a functional group comprising one or more functional groups selected from nitrogen atoms which may be substituted with an alkyl group having 1 or 2 carbon atoms, and X represents an oxygen atom And / or represents a linear or branched group having 3 to 10 carbon atoms and / or a heterocyclic group containing at least one nitrogen atom, and n represents an integer of 1 or more. The structural unit represented by ()) includes tetrahydrofurfuryl (meth) acrylate, β-methacryloyloxy-β-methyl-δ-valerolactone (meth) acrylate, β-methacryloyloxy-γ-butyrolactone (meth) acryle G, β-methacryloyloxy-
β-methyl-γ-butyrolactone (meth) acryle
, Α-methacryloyloxy-γ-butyrolactone (meth) acrylate, glycerin carbonate (meth) acrylate, 1,3-dioxan-2-one-5
-Yl (meth) acrylate, 4,4-dimethyl-1,
Examples thereof include 3-dioxan-2-one (meth) acrylate and tetrahydrofurfuryl (meth) acrylamide.

In the polymer compound containing the general formula (1), the structural unit represented by the general formula (1) is 0.0
The range of 1 to 80 mol% is used as a gas hydrate stabilizer having a structural unit containing at least one group copolymerizable with the general formula (1).

Since the high molecular compound represented by the general formula (1) alone is often insoluble in water, it is desirable to use a water-soluble polymer obtained by copolymerizing a water-soluble monomer. Examples of the water-soluble monomer copolymerizable with the general formula (1) include N- (meth) acrylamide, N-methyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-ethyl-N-methyl (Meth) acrylamide, N, N-diethyl (meth) acrylamide, N-
n-propyl- (meth) acrylamide, N-isopropyl- (meth) acrylamide, N, N-di-n-propyl- (meth) acrylamide, N-vinylpyrrolidone, N-vinylcaprolactam, N-isopropenylpyrrolidone, N -Isopropenylcaprolactam, N-vinylformamide, N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinyl-N-methylformamide, N-vinyl-N-propionamide,
(Meth) acryloylpyrrolidine, (meth) acryloylpiperidine, (meth) acryloylhexamethyleneimine, (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, vinyl acetate, vinyl propionate, Methyl vinyl ether, ethyl vinyl ether, 2-vinyl-2
-Oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-isopropyl-2-oxazoline, (meth) acryloylpiperidine and the like.

The monomer having the structure represented by the general formula (1) and the water-soluble monomer can be polymerized by a known method. That is, polymerization is carried out by dissolving the monomer having the structure of the general formula (1), a water-soluble monomer, and an initiator in an arbitrary solvent. Azo-based, peroxide-based,
An initiator such as a redox system may be used.

The general formula (1) in the polymer used in the present invention:
The ratio of the structural unit represented by is 0.01 to 8 as described above.
0 mol% is preferable, and more preferably 0.05 mol%.
A good range is ５０50 mol%.

The molecular weight of the polymer compound having the structural unit of the general formula (1) used as a gas hydrate stabilizer is preferably in the range of 1,000 to 500,000, more preferably in the range of 3,000 to 100,000. If the molecular weight is less than 1,000, the effect of stabilizing gas hydrate may be insufficient. If the molecular weight is more than 500,000, the viscosity of the system may be significantly increased and the solubility may be reduced, which may cause problems.

In the polymer used as a gas hydrate stabilizer, the mol% of the structural unit of the general formula (1) is 0.01%.
At the end, the potency of the stabilizer is extremely reduced. Conversely, when the mole% of the general formula (1) is 80 or more,
Even when a monomer having the structure represented by the general formula (1) is copolymerized with a polymerizable water-soluble monomer, the copolymer often becomes insoluble in water and loses its function as a gas hydrate stabilizer. .

The present invention is characterized in that the gas hydrate stabilizer thus obtained is added to a system capable of producing gas hydrate. In this case, the “system capable of generating gas hydrate” refers to, for example, J.I. Lon
g, A. Lederhos, A .; Sum, R .; Chri
stiansen, E .; D. Sloan; Prep. 7
3rd Ann. GPAConv. , 1994, pp. 1-9, refers to a system in which a substance that forms a gas hydrate is dissolved in an aqueous solvent. By placing such a system under specific pressure and temperature conditions, gas hydrate precipitates as crystals. Examples of the substance forming the gas hydrate include gases such as carbon dioxide, nitrogen, oxygen, hydrogen sulfide, argon, xenon, ethane, and propane, and liquids such as tetrahydrofuran.

In the system capable of producing gas hydrate as referred to in the present invention, an aqueous phase in which a gas such as ethane or propane is dissolved in an aqueous solvent such as water or seawater, such as a natural gas well or oil well, includes a liquefied gas. And a system in which a gas phase such as natural gas exists in the aqueous phase in a suspended or dispersed state in an oil phase such as oil or crude oil. The gas hydrate stabilization method of the present invention is a method in which the gas hydrate stabilizer is added to a system capable of producing gas hydrate. The addition method is not particularly limited, but it is particularly preferable to add it in a state of being dissolved in water and / or a solvent miscible with water.

The amount of the stabilizer to be added to the gas hydrate generating system is 0.01 to 30% by mass, more preferably 0 to 30% by mass, based on the free water in the system capable of producing gas hydrate. 0.01 to 10% by mass. When the addition amount is less than 0.01% by mass, a sufficient gas hydrate stabilizing effect is often not obtained. On the other hand, even if the addition amount is increased more than 30% by mass, not only the improvement effect of the gas hydrate stabilization corresponding to the increase in the addition amount may not be recognized, but also the viscosity of the system increases. It is not preferable because fluidity may be extremely deteriorated. Further, the stabilizing effect of the gas hydrate may decrease on the contrary.

The gas hydrate stabilizer of the present invention may be used in combination with various additives such as a rust preventive, a lubricant, a dispersant, and a corrosion inhibitor.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these ranges.

<Evaluation Method> FIG. 1 is a schematic sectional view of a gas hydrate generator used in this embodiment. In FIG. 1, the reaction high-pressure cell has a
It has a normal withstand voltage design up to 0 MPa.

This cell is provided with three internal observation windows having a diameter of 3 cm at three places, so that gas hydrate generated inside the cell can be observed. An aqueous solution in which a stabilizer is dissolved is introduced from a liquid introduction line 2, a gas is introduced from a gas introduction line 1, and the inside of the cell is pressurized. When the cell is gradually cooled to a predetermined temperature by the constant temperature bath 8, it is possible to observe how gas hydrate is generated inside the cell at a certain temperature, that is, at a certain temperature and pressure. At this time, the temperature inside the cell rises due to the generation of hydrate, and the gas pressure falls. These are observed using an in-cell thermometer 5 and an in-cell pressure gauge 6. After completion of the experiment, the inside of the cell is returned to normal pressure by opening the purge line 3, and then the inside of the cell is washed, and the next experiment operation is performed.

The determination of the stabilizing effect of the gas hydrate stabilizer of the present invention was confirmed by the following test method. That is,
After introducing an aqueous solution containing a stabilizer and methane gas into the cell by the above-mentioned method, the pressure in the cell is set to 4 MPa, and the temperature in the cell is set to 20 ° C., which is a temperature clearly higher than the gas hydrate formation equilibrium temperature at that pressure. After setting, the temperature inside the cell is gradually lowered while stirring the inside of the cell. When the methane gas hydrate starts to be generated, the pressure in the cell decreases, and at the same time, the gas hydrate generation is an exothermic reaction, so that the temperature in the cell slightly increases. The temperature in the cell when this pressure began to drop significantly was measured, and the higher the temperature, the greater the effect of the gas hydrate stabilizer. In the case of methane gas, the hydrate formation starting temperature with respect to pure water is about 3 ° C. at 4 MPa.

Example 1 A 300 ml separable flask was charged with 9.1 tetrahydrofurfuryl methacrylate.
g, 33.4 g of N-acrylamide and 150 g of methyl isobutyl ketone, followed by nitrogen bubbling to remove dissolved oxygen. Thereafter, the temperature in the flask was increased to 80 ° C., and an azo-based initiator 2,2′-
A solution prepared by dissolving 2.0 g of azobisisobutyronitrile in 8 g of methyl isobutyl ketone was added to initiate polymerization. The polymerization is carried out while stirring under a nitrogen flow.
The reaction was continued for a time. After cooling, 3 L of diethyl ether
The polymerization solution was put thereinto with stirring, and the polymer obtained as a precipitate was vacuum-dried at 70 ° C. Again polymer 20
After dissolving in 0 g of acetone, the solution was added dropwise to 3 L of n-hexane, and the polymer obtained by reprecipitation was vacuum-dried at 70 ° C. overnight. The composition of the obtained polymer was measured by 1H-NMR.
As a result, the content of tetrahydrofurfuryl methacrylate in the polymer was 9.1 mol%. Also,
As a result of measuring the molecular weight using GPC using dimethylformamide as a mobile phase, the number average molecular weight was 10,000 and the mass average molecular weight was 43,000 in terms of standard PMMA.

An aqueous solution having a concentration of 0.5% by mass was prepared using this polymer, and the gas hydrate formation starting temperature was measured by the above-mentioned evaluation method. As a result, it was 15.0 ° C.

Example 2 The procedure was the same as in Example 1 except that the charged amounts of tetrahydrofurfuryl methacrylate and N-acrylamide were different.
The same operation as in Example 1 was performed to obtain a polymer which was a copolymer with acrylamide containing 5 mol% of tetrahydrofurfuryl methacrylate. The number average molecular weight of this polymer was 15,000, and the mass average molecular weight was 56,000.

An aqueous solution having a concentration of 0.5% by mass was prepared using this polymer, and the gas hydrate formation starting temperature was measured by the above-mentioned evaluation method. As a result, it was 10.1 ° C.

[0033]

According to the method of the present invention, the conditions for producing hydrates such as hydrocarbon gas such as methane, carbon dioxide gas, or carbon disulfide gas can be shifted to higher temperatures and lower pressures. The polymer of the present invention has a large function as a stabilizer having a large effect with a small amount of addition to a gas hydrate generation system, and furthermore, a method for stabilizing gas hydrate using the same is based on a hydrate generation equilibrium curve. Hydrate can be generated at a temperature higher than the temperature to be expressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an experimental apparatus for confirming a stabilizing effect of a gas hydrate stabilizer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas introduction line 2 Stabilizer-containing water introduction line 3 Purge line 4 Reaction high pressure cell 5 Reaction cell thermometer 6 Reaction cell pressure system 7 Reaction cell agitator 8 Constant temperature bath

Claims (6)

[Claims] 1. A gas hydrate stabilizer mainly comprising a polymer compound having a structural unit represented by the following general formula (1) in a molecule. Embedded image (Wherein, R ₁ , R ₂ and R ₃ each independently represent a hydrogen atom or an alkyl group having 1 or 2 carbon atoms, and Sp ₁ represents an oxygen atom or a linear or branched alkyl having 1 to 16 carbon atoms. Group; carbonyl; ester; ether, carbonate, thioester, amide, urethane, or a nitrogen-containing functional group in which a hydrogen atom on the nitrogen atom may be substituted by an alkyl group having 1 or 2 carbon atoms; ether; thioether; , Imine, or a functional group comprising one or more functional groups selected from nitrogen atoms in which a hydrogen atom on the nitrogen atom may be substituted by an alkyl group having 1 or 2 carbon atoms X represents a linear or branched group having 3 to 10 carbon atoms containing at least one oxygen atom and / or nitrogen atom, It represents a group, and n represents an integer of 1 or more.) 2. The content of the structural unit of the general formula (1) is as follows:
2. The gas hydrate stabilizer according to claim 1, wherein a polymer in the range of 0.01 to 80 mol% is used. 3. The gas hydrate stabilizer according to claim 2, wherein the copolymerizable structural unit comprises a water-soluble monomer. 4. A method for stabilizing a gas hydrate, comprising adding the gas hydrate stabilizer according to any one of claims 1 to 3 to a system capable of producing a gas hydrate. . 5. A gas hydrate which can be produced by dissolving the gas hydrate stabilizer according to any one of claims 1 to 3 in water and / or a solvent miscible with water. The method for stabilizing a gas hydrate according to claim 4, wherein the gas hydrate is added to a system. 6. The gas hydrate stabilizer according to any one of claims 1 to 3, wherein the gas hydrate stabilizer is used in an amount of 0.01 to 30% by mass based on free water in a system capable of producing gas hydrate. 6. The method for stabilizing gas hydrate according to claim 4, wherein the gas hydrate is added.