Chemistry of hydrocarbon compounds – Hydrate or production thereof
Reexamination Certificate
2000-03-14
2003-11-25
Johnson, Jerry D. (Department: 1764)
Chemistry of hydrocarbon compounds
Hydrate or production thereof
C422S198000, C422S199000, C422S200000, C422S201000, C422S203000, C422S205000, C422S224000, C422S225000, C422S231000, C422S234000
Reexamination Certificate
active
06653516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a production method in which highly concentrated hydrate is produced efficiently by reacting hydrate producing substance, such as methane with water, and a device which is suitable for carrying out the same.
This application is based on Japanese Patent Applications Nos. Hei 11-69291 and Hei 11-69294, the contents of which are incorporated herein by reference.
2. Description of the Related Art
It is well known that a large amount of natural gas components, such as methane etc. are presented as hydrates under the ground of cold districts. The hydrates are existed stably at low temperatures and high pressures; therefore, they are anticipated to be natural gas sources for the next generation. In particular, a hydrate comprising methane (below simply denotes methane hydrate) is one kind of clathrate compound in which a methane molecule is situated into a cluster comprising water molecules stereoscopically positioned. The distance between methane molecules in the hydrate clusters is shorter than the distance between methane molecules in a gas cylinder under high pressure. That is, the methane molecules in a hydrate state are situated closely. Therefore, it is anticipated that to storage and transport methane in a methane hydrate state. In addition, the reaction between methane and water has a reversible equilibrium, and generates a large amount of hydration heat. Therefore, applications of a methane hydrate for a heat storage material, refrigerator, heat pump, etc. are currently being investigated.
As described above, many applications of the methane hydrate are anticipated, and therefore an investigation of synthesizing methane hydrate with a high efficiently is carried out, in addition to depending on the natural resources. However, in general, the pressure at which the methane hydrate is stabilized at 15° C. is 100 kg/cm
2
or greater. That is, methane hydrate is stabilized under conditions of low temperatures and high pressure; therefore, it is difficult to handle the methane hydrate. The handling the methane hydrate under such conditions is difficult. In order to solve the problem, many kinds of stabilizers for shifting the formation equilibrium conditions of the methane hydrate to the conditions of high temperatures and low pressures, have been investigated. As a result, it has been discovered that for example, aliphatic amines such as isobuthyl amine, isopropyl amine, etc. (Japanese Patent Publication, Second Publication No. Sho 53-1508 (Koukoku)), 1-3-dioxysolane, cyclobutanone, tetrahydrofuran, cyclopentanone, acetone, etc. (Seiichi Yokoi and others, Nippon Kagaku Bulletin, 1993 (4), page 378 to 394) are useful as stabilizers.
The production method in which hydrate is produced by spraying water into a gaseous phase of ethane which is one of the hydrate producing substance, thereby contacting ethane and water with a large contact area, has been suggested (INTERNATIONAL CONFERENCE ON NATURAL GAS HYDRATES (JUN. 2-6, 1996 TOULOUSE FRANCE).
In general, a device shown in
FIG. 9
, for example, has been used to produce methane hydrate using the above-mentioned production method. In
FIG. 9
, the synthesis device for methane hydrate comprises a pressure vessel
150
equipped with an aqueous phase injection pipe
151
, a methane gas injection pipe
152
, an outlet
153
, and an agitator
154
. The pressure vessel
150
is put into a thermostatic bath
155
. Furthermore, the synthesis device comprises thermometers for measuring temperatures T
1
and T
2
in a gaseous phase and an aqueous phase in the pressure vessel
150
, a pressure meter for measuring pressure P in the pressure vessel
150
, an instrument for measuring a rotational frequency R of the agitator
154
, and a thermometer for measuring temperature T
3
in the thermostatic bath
155
.
In order to synthesize the methane hydrate using the synthesis device, for example, an air in the pressure vessel
150
is expelled by introducing a methane gas in the pressure vessel
150
from the methane gas injection pipe
152
. Then, an aqueous solution containing the stabilizer having a desired concentration is introduced into the pressure vessel
150
from the aqueous phase injection pipe
151
as an aqueous phase. The temperature of the aqueous phase in the pressure vessel
150
is set at the desired temperature by the thermostatic bath
155
. Methane gas is introduced into the pressure vessel
150
from the methane gas injection pipe
152
while stirring with the agitator
154
until the pressure in the pressure vessel
150
reaches a desired pressure. When the stirring is carried out keeping these conditions, a hydration reaction occurs, and the pressure P in the pressure vessel
150
decreases. In addition, the temperature T
2
of the aqueous phase rises due to a heat of hydration. The synthesis device is left alone until the temperatures T
1
and T
2
of the gaseous phase and the aqueous phase which are enclosed by the thermostatic bath
155
are substantially equal, while the pressure P in the pressure vessel
150
is adjusted by exhausting a part of the methane gas from the outlet
153
, if necessary. Then, methane hydrate having a formation equilibrium pressure P at the temperature T
2
can be obtained.
However, the conventional methane hydrate production method using the production device shown in
FIG. 9
has following problems. The reaction between methane and water is carried out due to an absorption of methane gas into the aqueous phase at a gas-liquid interface. As shown in
FIG. 10
, the density of the methane hydrate MH produced by the reaction is smaller than the density of water (the theoretical density of methane hydrate is 0.915 g/cm
2
). Therefore, the methane hydrate MH comes near the surface of a liquid phase (aqueous phase) L, and forms a methane hydrate layer. The adsorption of methane M at the surface between a gaseous phase G and a liquid phase is prevented by the methane hydrate layer. In addition, the viscosity of the liquid phase L increases, depending on the production degree of the methane hydrate, and the stirring effect of the liquid phase L is insufficient. Consequently, it is difficult to produce the methane hydrate having a high concentration.
In addition, the concentration of the methane hydrate in the liquid phase L increases, depending on an amount of methane gas injected from the methane gas injection pipe
152
. However, the ratio of water to the methane gas, which remains in the liquid phase L decreases, while the reaction is carried out. Then, the reaction reaches an equilibrium, and the hydration reaction does not proceeded. Therefore, from this point of view, it is also difficult to produce methane hydrate having a high concentration.
Furthermore, the period from the introduction of the aqueous solution into the pressure vessel
150
to the end of hydration reaction between the aqueous solution and the methane gas, is long. Namely, a long period to fix the temperature T
2
of the aqueous solution at a desired temperature by the thermostatic bath
155
, is necessary. Therefore, the production efficiency of the methane hydrate is low.
Water particles contact ethane with a large contact area in the production method in which water is sprayed in an ethane gaseous phase. However, there is the possibility that the produced hydrate adhering the surface on especially large water particle like an epidermis. The water particles enclosed by the, hydrate does not react with the ethane gas. From this point of view, there is still room for improvement of the production efficiency of the hydrate. In addition much time is necessary to reduce the temperature of the sprayed water into the reaction vessel to the temperature required to produce the hydrate. Therefore, there is also still room for improvement of the production efficiency of the hydrate.
Therefore, an object of the present invention is to provide a production method for hydrates in which the hydrate producing substance and water are reacted efficiently a
Fujimoto Tetsuro
Kimura Takahiro
Kondo Yuichi
Yoshikawa Kozo
Johnson Jerry D.
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ridley Basia
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