JPS59225127A - Separation of high-boiling hydrocarbon - Google Patents

Abstract

PURPOSE:To separate inexpensively and simply high-boiling hydrocarbons such as 2-4C alkyls, etc. contained in mixed light hydrocarbons such as liquefied natural gas, etc. as inclusion compounds and to use them effectively, by bringing directly the mixed light hydrocarbons into contact with water. CONSTITUTION:The mixed light hydrocarbons 1 such as liquefied natural gas (LNG), etc. is directly brought into contact with the water 4 such as seawater, etc. under pressure preferably >=1kg/cm<2>.g, high-boiling components such as ethane, butane, and propane, etc. contained in the hydrocarbon 1 are processed into the inclusion compounds(hydrate) 7, so that they are simply separated from low-boiling components using effectively physical properties of LNG and seawater, etc. without using large energy like rectification and large-scale sevices. In the process, the amount of formation of the hydrate and its composition can be adjusted by controlling the pressure, temperature and retention time of the crystallizer 3, the vaporization of LNG and the separation of the high-boiling components can be carried out simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for separating high-boiling hydrocarbons from mixed light hydrocarbons.

[Prior art]

Natural gas is a mixture of light hydrocarbons whose main component is methane (hereinafter abbreviated as OH4), but in recent years it has become impossible to consume it only in natural gas producing areas, so it has been refined, liquefied, and exported overseas. Well, our country is importing it.

The composition of this liquefied natural gas (hereinafter abbreviated as LNG) is not constant; it is ethane (hereinafter abbreviated as 02Ha), propane (hereinafter abbreviated as 03H8), and butane (hereinafter abbreviated as C4
(abbreviated as E10) etc.) are mixed.

It is conceivable to separate the high boiling point components from this LNG and use it effectively, but the "H8
, C4HIO, etc. can be separated from a mixture only by distillation.

Table 1 shows the main physical properties of each component contained in the mixed light hydrocarbon.

As is clear from Table 1, the boiling points of each hydrocarbon are slightly different, but when a mixture is formed, the shape of each hydrocarbon (especially those with long carbon chains) is not linear. They tend to curl up, and the structure is still such that other small molecules fit into the gaps between the large molecules. Therefore, the vapor-liquid equilibrium deviates from that of a single component, and it becomes necessary to consider the vapor-liquid equilibrium as a mixture, necessitating a rectification column. LNG
As the size of the bases continues to grow, it is thought that the rectification towers will also become larger. In addition, the required pressure of gas obtained by vaporizing LNG is I D H for thermal power generation.
4/cni', 3o Kg/lyl for city gas,
The pressure is extremely high at 70 h/al. Therefore, it is necessary to make the rectification column structure pressure-resistant or to take measures to prevent heat intrusion, and the distillation method is not a good idea. Therefore, it is necessary to consider methods that can replace the distillation method.

[Purpose of the invention]

An object of the present invention is to provide a method that eliminates the drawbacks of conventional methods and can inexpensively and easily separate high-boiling hydrocarbons from mixed light hydrocarbons.

[Summary of the invention]

To summarize the present invention, the present invention is an invention of a method for separating high-boiling point hydrocarbons, which involves directly contacting mixed light hydrocarbons with water under pressure, and separating the high-boiling point hydrocarbons contained therein into clathrate compounds. Separation as a percentage is a sign of separation.

FIG. 1 shows a temperature and pressure equilibrium diagram of a clathrate compound (hereinafter referred to as hydrate) of hydrocarbon and water. The arrow in FIG. 1 indicates the hydrate formation pressure. As is clear from FIG. 1, c2H6, a3H8, c4HIO, and the like have characteristics that make it easier to generate hydrate than CH4. Each hydrate has a different composition and crystal structure. Table 2 shows the composition and physical properties of the hydrate.

In this way, the hydrate generation conditions differ depending on the hydrocarbon, and the larger the carbon number (0 < 1), the easier it is to generate hydrate, so by incorporating a hydrate generation process, It becomes possible to separate hydrocarbons with long carbon chains from mixed light hydrocarbons.

That is, in the present invention, for example, LNG is injected directly into water, such as seawater, through a nozzle to simultaneously perform heat exchange and separation of hydrocarbons.

The present invention will be explained below with reference to the drawings.

That is, FIG. 2 is a schematic diagram showing the basic process of the present invention when LNG is used as the mixed light hydrocarbon, and FIG. 3 is a process diagram showing an embodiment of the present invention. In the figure, code 1 is LNG, 2 and 5 are pumps, 3 is a crystallization tank,
4 is water, 6 is vaporized gas, 7 is a liquid containing hydrate, 8
9 is a decomposition tank, 9 is a nozzle, 10 is a cracked gas, and 11 is a pipe for heating the nozzle portion. LNG 1 is pressurized by pump 2 and sent to crystallization tank 3 . Here, it comes into contact with water 4 such as seawater sent by the pump 5 to generate hydrate. During this process, LNG exchanges heat with seawater, and a portion of the LNG is vaporized and recovered from the crystallization tank as vaporized gas 6. The other part becomes hydrate, and the liquid (slurry) 7 containing hydrate is sent to a hydrate decomposition tank 8. In this process, by controlling the pressure, temperature, and residence time of the crystallization tank, it is possible to adjust the amount of hydrate produced and its composition. Separation of the high-boiling hydrocarbons contained can be carried out.

Methods for direct contact between hydrocarbons and water include the stirring method using rotating stirring blades, the nozzle blowing method, and the wet wall method. When considering this, in a normal nozzle system, the temperature of LNG is extremely low at 1160°C, so the nozzle end face becomes clogged with water or hydrate, making continuous operation impossible.

This problem is caused by heating the nozzle part, which forms a space at the LNG spout of the nozzle 9, which has an inner wall made of a material with good thermal conductivity and an outer wall made of a material with poor thermal conductivity. This can be solved by replacing the nozzle with a nozzle having a special structure, such as by providing piping 11.

The hydrate-containing liquid led to the decomposition tank is heated under reduced pressure or (
The temperature of the leaves is raised, the hydrate is decomposed, and 10 decomposed gas is obtained.

Simple solid-liquid separation of hydrate and liquid is currently extremely difficult due to the small particle size of hydrate. However, if a solid-liquid separation means is available, it may be possible to separate the solid-liquid. In addition, fresh water can also be obtained by decomposing hydrate under reduced pressure under adiabatic conditions to convert it into ice crystals, and then separating the ice crystals.

As another embodiment of the present invention, the following method is also carried out.

Figure 1 shows the temperature of seawater that comes into contact with LNG when LNG is brought into direct contact with seawater through a nozzle under pressure.)
- If the temperature is higher than the idrate formation temperature, the generated idrate will immediately decompose and hydrocarbons will be rectified, and a portion of the heavy hydrocarbons will accumulate as a liquid in the upper part of the seawater.

In this case, by adjusting the seawater temperature, it is possible to adjust the composition of the vaporized gas, and it is also possible to omit the idrate decomposition tank.

By this method, for example, the composition is OH4:55-70.
mol%, c2a6:is ~20 mol%, C! 3H1l
: 10-15 mol%, C4HIO' 1-3 mol% L
From NG, the composition is OH4: 13-24 mol%, ○! H
6: 14-30 mol%, 03H8: 20-40 mol%
, 04HIO: 15-25 mol% liquid hydrocarbons were obtained. FIG. 4 shows a phase diagram of the liquid hydrocarbon production region for reference.

[Embodiments of the invention]

Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

Example 1 Table 3 shows the results when LNG as a mixed light hydrocarbon was blown into water under pressure to produce no-hydrate.

As is clear from this table, OH in the produced hydrate
The ratio of 4 decreases compared to LNG, and the ratio of (!31M) increases.In addition, IJG with a low OH4 content has a high hydrate formation ratio.Furthermore, as is clear from Figure 1, By increasing the precipitation pressure, the yield of hydrate can be increased.

Example 2 Hydrocarbons: CH4: 71 mol%, C2: 12 mol%, C3H8: 15 mol%, 04H1G' 2 mol%
Compress the mixed gas to 50 Kg/tyn2ψf and
blown into water at ℃. The composition of the hydrate produced is OH
4: 21 mol%, O, H6: 24 mol%, C3Hr:
48 mol%, C4H10: 7 mol%. The amount of hydrate produced at this time was 20% of the injected hydrocarbons.

〔Effect of the invention〕

As explained above, the present invention efficiently utilizes the physical properties of LNG and seawater to separate high-boiling point components and low-boiling point components without using large amounts of energy or large-scale equipment such as rectification. It has the extremely remarkable effect of being easily separable.

[Brief explanation of the drawing]

Fig. 1 is a temperature and pressure equilibrium diagram of no-idrate, Fig. 2 is a schematic diagram showing the basic steps of the present invention, Fig. 3 is a process diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing the basic steps of the present invention. The figure is a state diagram of the liquid hydrocarbon production region. 1: LNG, 2 and 5: Pump, 3: Crystallization tank, 6: Vaporized gas, 7: Liquid containing noidlate, 8: Decomposition tank, 9:
Nozzle, 10: Decomposition gas, 11: Piping for heating the nozzle part. Patent applicant: Tokyo Gas Co., Ltd. Hitachi, Ltd. Agent: Hiroki Nakamoto / Temperature (°C) Figure 2 Figure 3

Claims (1)

[Claims] 1. Bringing mixed light hydrocarbons and water into direct contact under pressure,
A method for separating high boiling point hydrocarbons, which comprises separating the high boiling point hydrocarbons contained therein as clathrate compounds. 2. The method for separating high-boiling hydrocarbons according to claim 1, wherein the mixed light hydrocarbon is liquefied natural gas. 3. The method for separating high-boiling hydrocarbons according to claim 1 or 2, wherein the pressure of the pressurization is 1:7/-.1 or more. 4. A method for separating high-boiling hydrocarbons according to any one of claims 1 to 6, wherein the water is seawater.