JPH1150069A - Purification of natural gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify natural gas by bringing it into contact with a combination of silver-free zeolite with silver-contg. A-type zeolite allow water, sulfur compounds and mercury therein to be efficiently adsorbed to the zeolite combina tion and remove them as impurities. SOLUTION: (A) Natural gas is brought into contact with (B) a combination of (I) at least one kind of silver-free zeolite with (2) silver-contg. A-type zeolite (pref. sodium A-type zeolite) to remove water, sulfur compounds and mercury from the component A, thus purifying the natural gas A; wherein the volume ratio (1)/(2) is pref. (60:40) to (10:90), more pref. (50:50) to (30:70). The method for the above contact is pref. as follows: for example, a packing column is packed with the component B, and the component A is allowed to flow through the packed component B at 5-60 deg.C at a linear gas velocity of 0.01-0.5 m/s under a pressure of 0.1-10 MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying natural gas by removing impurities in natural gas, and more particularly to a method for removing water, sulfur compounds and mercury contained in natural gas by adsorption. The present invention relates to a method for purifying natural gas using an agent.

[0002]

2. Description of the Related Art Conventionally, natural gas has been used in many fields. In particular, Japan imports a large amount of liquefied natural gas (LNG) and uses most of it as fuel for power generation. By liquefying natural gas, its volume can be made compact and mass transportation is possible.

[0003] The problem in liquefying natural gas is that
It is a matter of how to remove impurities in natural gas efficiently by a simple operation and purify it. In particular, water, carbon dioxide and sulfur compounds, and heavy metals, especially mercury, have become problems as impurities. For example, if water or carbon dioxide is contained in natural gas, it freezes in the cryogenic step of liquefying natural gas and damages equipment, and even if trace amounts of mercury are present, they are used as cryogenic equipment. This has been a major problem because it reacts with the aluminum heat exchanger and damages the heat exchanger.

[0004] As techniques for removing these water and harmful mercury, US Pat. No. 4,874,525 and US Pat.
No. 7 discloses a method of using silver-containing zeolite (hereinafter referred to as "silver-containing zeolite") to remove trace amounts of mercury and water contained in hydrocarbon gases such as naphtha cracked gas and natural gas. Proposed.

However, according to the study of the present inventors, when a sulfur compound is contained in these gases, not only the purity thereof is lowered but also the above-mentioned silver-containing A-type zeolite adsorbent, especially silver-containing potassium It has become clear that the adsorption performance of A-type (A-3) zeolite and silver-containing sodium A-type (A-4) zeolite is reduced. That is,
When the adsorption / regeneration operation for removing mercury and water from natural gas containing a low concentration of sulfur compounds using silver-containing zeolite A is repeated, the mercury removal performance of silver-containing zeolite A is extremely reduced. It was found to occur. Although the cause of the decrease in the mercury removal performance is not clear, the sulfur compound in the gas is adsorbed on the silver-containing A-type zeolite, and is not desorbed during regeneration. As a result, the adsorption rate of the silver-containing A-type zeolite to mercury is reduced. It is presumed that the mercury removal performance was reduced due to adverse effects.

[0006] On the other hand, various adsorbents and removal methods have been proposed for removing sulfur compounds in gas.
For example, to remove sulfur compounds in natural gas or synthesis gas produced by steam reforming, use an amine organic base compound such as ethanolamine or an alkaline aqueous solution such as hot potassium carbonate when the concentration of the sulfur compound is high. Many methods have been proposed, such as adsorption and removal using a metal oxide or metal sulfide such as activated carbon, zeolite, or ZnO when the concentration is low.

However, in the conventional method, when water and mercury contained in natural gas are simultaneously removed by using a silver-containing A-type zeolite adsorbent, a method for suppressing a decrease in performance of the adsorbent due to a sulfur compound. Was not previously proposed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to remove water and mercury from natural gas simultaneously and economically and efficiently by a simple operation. A method for purifying natural gas by suppressing the performance of the adsorbent used in purifying gas by the sulfur compound in natural gas and removing impurities such as water, sulfur compound and mercury. Is to provide.

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that natural gas containing low concentrations of water, sulfur compounds and mercury can be converted into a silver-containing zeolite and a silver-free zeolite (hereinafter, referred to as zeolite). (Referred to as "silver-free zeolite"), it was found that water, sulfur compounds and mercury in natural gas can be efficiently adsorbed and removed, and natural gas can be purified, thereby completing the present invention. Reached.

Hereinafter, the present invention will be described in detail.

The method of the present invention is characterized by using two types of zeolites, a silver-containing zeolite A and a silver-free zeolite.

The zeolite used in the method of the present invention is a natural or synthetic aluminosilicate having crystallinity. The synthetic product can be produced by a known method. It can be produced by adding an appropriate amount of alkali to both a solution of an acid salt as an Al source and a solution of a silicic acid salt as a Si source and subjecting them to heat treatment or the like.

Among them, the silver-containing A-type zeolite includes:
The zeolite serving as the base material may be any type A zeolite, and among them, potassium A type zeolite (hereinafter referred to as “KA type zeolite”), sodium A type zeolite (hereinafter referred to as “NaA type zeolite”) or calcium A type zeolite. (Hereinafter referred to as “CaA-type zeolite”), and NaA-type zeolite is preferably used because it has excellent removal efficiency, particularly excellent mercury removal efficiency, and has versatility such as easy production and low cost. Can be The zeolite serving as the base material of these silver-containing A-type zeolites can be used alone or as a mixture of two or more.

As the silver-free zeolite, A-type zeolite, X-type zeolite or Y-type zeolite is preferably used from the viewpoint of the adsorption rate for sulfur compounds contained in natural gas. Further, among these, when the sulfur compound has a relatively small molecular diameter such as hydrogen sulfide or COS, CaA-type zeolite, sodium X-type zeolite (hereinafter, referred to as “NaX-type zeolite”) or sodium Y-type zeolite (hereinafter, “ NaY-type zeolite) or a sulfur compound having a relatively large molecular diameter such as methyl mercaptan, NaX-type zeolite or NaY-type zeolite is preferably used from the viewpoint of its adsorption rate. These silver-free zeolites can be used alone or in combination of two or more.

It is an embodiment of the present invention to remove impurities in natural gas by combining one or more kinds of silver-free zeolites and silver-containing A-type zeolites. The A-type zeolite and the silver-free zeolite can be used not only in a layer-separated or layer-separated manner, but also in a mixed state, that is, a mixture of the silver-containing zeolite A and the silver-free zeolite. further,
When both are used in a layer separation or layer division, it is more preferable that the silver-free zeolite is installed on the upstream side of the silver-containing A-type zeolite, that is, on the supply inlet side of the natural gas for removing impurities. This is because sulfur compounds in natural gas are mainly adsorbed and removed by silver-free zeolites, and silver-containing zeolites, which are mainly involved in mercury adsorption, are suppressed from being reduced in their adsorption rate by sulfur compounds. It is. As a method of layer separation or layer division, the silver-free zeolite and the silver-containing A-type zeolite may be filled without substantially intermingling, and furthermore, any of the boundary portion of the zeolite to be combined, the supply inlet side, and the outlet side Alternatively, an appropriate amount of wire netting, glass wool, or the like may be laid on all of them, or in the case of a large-scale implementation, an alumina ball or the like may be filled in addition to the wire netting.

The ratio of the silver-containing A-type zeolite and the silver-free zeolite depends on the content of mercury and sulfur compounds in the natural gas to be treated, but based on the volume of the zeolite, the silver-free zeolite: silver-containing zeolite A-type zeolite = 60:
A range of 40 to 10:90 is preferable, and a range of 50: 5
The range of 0 to 30:70 is particularly preferred. Outside of this range, the removal of mercury and sulfur compounds in natural gas may be insufficient.

Silver-containing A used in the method of the present invention
The silver raw material to be contained in the type A zeolite, which is the base material of the type zeolite, includes silver nitrate, silver acetate, silver chloride, silver sulfate,
A silver compound such as silver oxide can be exemplified, and as a method for incorporating silver into the A-type zeolite, a known method can be used, for example, an ion exchange method, an impregnation-supporting method, a kneading method, a dry mixing method, and the like. Can be applied. Further, the silver content in the zeolite A generally includes the concentration of mercury in natural gas, the gas linear velocity of natural gas, the contact time between natural gas and the zeolite used in the present invention, the contact temperature, and the silver content. Although it can be changed according to the ratio of the silver-containing A-type zeolite in the combination of the silver-containing zeolite and the silver-free zeolite, in order to remove mercury more efficiently, the mercury removal efficiency is good and the price is low. , 0.01 to 20% by weight based on the total amount of silver-containing A-type zeolite
Is more preferable, and more preferably 0.05 to 5% by weight.

Silver-containing A used in the method of the present invention
In order to use the zeolite and the zeolite containing no silver on an industrial scale, it is preferable to use the zeolite by filling it in a packed tower or the like, or to form a compact such as a granular material in order to facilitate handling. At the time of molding, it is preferable to mix the zeolite with a binder such as a clay mineral and mold, for example,
As the binder, clay minerals such as attapulgite, sepiolite, bentonite, kaolin, montmorillonite, and allophane can be used. The amount of the binder may be any amount that facilitates molding, and is usually 5 to 4 parts by weight based on 100 parts by weight of zeolite.
0 parts by weight are used. Further, two or more of these binders may be used. As for the silver-containing A-type zeolite, silver may be contained after molding the base A-type zeolite, or it may be molded after containing silver.

As the molding method, a commonly used method,
For example, methods such as extrusion molding, press molding, and rolling granulation are used. As its shape, a spherical shape, a columnar shape, a disk shape, an elliptical spherical shape, a pellet shape, and the like can be adopted, and its size is 0.5 to 5 mm in diameter, and 1 to 4 m in diameter.
Those having a size of m are preferably used, and if necessary, may be used after being classified using a sieve or the like. Here, if the size is within this range, for example, water in natural gas, sulfur compounds and mercury in a continuous flow operation can be reduced pressure resistance generated when removing,
When the molded body is too large, it is possible to avoid that the contact area with the natural gas is reduced and the removal efficiency is reduced.

The silver-containing zeolite and the silver-free zeolite used in the method of the present invention are preferably fired after being molded using a binder. As the firing temperature,
It is preferable to perform calcination at a temperature of 600 ° C. or higher and further at a temperature of 600 to 800 ° C. in an atmosphere such as air, nitrogen gas, and reducing gas. The firing time is not particularly limited, but usually about 30 minutes to 50 hours is sufficient. By this calcining operation, the strength of the zeolite can be increased, and the activation of the adsorption performance of moisture and mercury can be promoted. If the temperature deviates from the above-mentioned temperature range, these effects may be reduced.

As described above, the zeolite used in the method of the present invention (hereinafter referred to as "adsorption remover") can be prepared.

Examples of such an adsorbent-removing agent include A-3MG (trade name) and A-4MG (trade name) as silver-containing zeolites and A-5 as a silver-free zeolite from Tosoh Corporation. (CaA type) and F-9 (NaX type) are commercially available.

The adsorption remover thus prepared is
Heat treatment in a dry gas atmosphere such as hydrogen gas, hydrogen-containing gas, methane gas, methane-containing gas, etc. in order to further desorb moisture adsorbed before use after newly filling the adsorption tower to further improve adsorption efficiency Is preferred. The heating conditions are as follows: a temperature in the range of 100 to 400 ° C .;
0 hour, linear velocity of dry gas 0.01 to 0.5 m / sec,
It is preferable to heat-treat the adsorption remover using a dry gas at a pressure of 0.1 to 3 MPa.

The natural gas to be used in the present invention is a gas containing methane as a main component and, after being collected from a natural gas field, absorbs a large amount of a sulfur compound, carbon dioxide, etc., into an amine organic compound, an alkaline aqueous solution, etc. Those removed by a conventional method such as a method using an agent are preferred. Even with these treatments, the natural gas still contains water close to the saturation concentration, a trace amount of hydrogen sulfide, COS, sulfur compounds such as mercaptans and disulfides, and trace amounts of mercury that cannot be removed. The concentration of water, sulfur compounds and mercury contained in such natural gas is not particularly limited, but in order to reduce the load on the adsorptive removal agent and obtain better removal efficiency, the water concentration is determined as The concentration of the sulfur compound is preferably 50 ppm or less, more preferably 20 ppm or less, based on the volume, and the mercury concentration is preferably 200 ppb or less, more preferably 100 ppb or less, based on the weight.

In the method of the present invention, when the natural gas and the adsorbing and removing agent are brought into contact with each other, the contacting conditions described below can increase the efficiency of removing water, sulfur compounds and mercury. That is, as the contact method, a fixed bed circulation method can be adopted by using a molded adsorption removal agent, and continuous operation becomes possible. The optimum conditions for the continuous flow contact system are as follows: the adsorption temperature is 5 to 60 ° C., preferably 10 to 60 ° C.
The gas linear velocity at the time of passing natural gas through the adsorption removal agent in the range of ４０40 ° C. is 0.01 to 0.5 m / sec, preferably in the range of 0.05 to 0.4 m / sec. Is preferably performed in the range of 0.1 to 10 MPa from the viewpoint of removal efficiency.

The adsorbing and removing agent which has adsorbed impurities such as water, sulfur compounds and mercury can be used in a reducing gas atmosphere, especially by using a dry reducing gas such as purified dry natural gas and the like. Flow, temperature 100 ~ 400 ℃,
The linear velocity of the dry reducing gas is 0.01 to 0.1 for 1 to 50 hours.
It can be regenerated at a pressure of 5 m / sec and a pressure in the range of atmospheric pressure to 3 MPa, and can be used repeatedly. In particular, in an adsorption tower filled with an adsorption remover, the impurities are generally adsorbed in large amounts on the natural gas inlet side during adsorption, so that the flow of reducing gas during regeneration is made opposite to that during adsorption. In addition, the inside of the adsorption tower can be prevented from being contaminated with impurities.

[0027]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to only these examples. In addition, evaluation was implemented by the method shown below.

(1) Mercury concentration The mercury concentration was determined based on the fertilizer analysis method (1982 version).
It was measured by heat decomposition-gold amalgam-cold atomic absorption spectrometry (manufactured by Nippon Instruments Co., Ltd., model: Mercury SP-3D).

(2) Silver Concentration The silver concentration in the silver-containing zeolite was measured by an ICP method (Perkin Elmer Japan, model: OPTIMA). (3) Moisture Concentration The moisture concentration was measured using a moisture meter (manufactured by Japan Panametrics, model: MMS35).

(4) Sulfur concentration The sulfur compound concentration was measured using a gas chromatograph (model: GC-16A FPD, manufactured by Shimadzu Corporation).

Example 1 Each of pulverized powders of 12 to
0.02 liter of silver-containing sodium A-type zeolite (A-4MG, silver content 0.1% by weight) manufactured by Tosoh Corporation and sodium X-type zeolite (F- 9) Filled with 0.02 liter, water and mercury removal test (repeated test of adsorption and regeneration) was performed. Also, F-9 is connected to the supply gas inlet side by A-
The layers were separated and filled through 4MG and glass wool. Methane gas, a representative component of natural gas (Sumitomo Seika Co., Ltd.)
(Purity: 99.9% by volume). Methane gas and methyl mercaptan gas (manufactured by Sumitomo Seika Co., Ltd., concentration: about 1000 ppm by volume / nitrogen) were each mixed with a line using a mass flow controller to adjust the concentration of methyl mercaptan. The mercury vapor was entrained using a part of methane gas and supplied to the adsorption column. The mercury concentration in the feed gas was adjusted by controlling the mercury vapor generation temperature and the amount of methane gas accompanying the mercury vapor. In addition, a part of the supplied methane gas was bubbled into water at room temperature, and supplied to the adsorption column together with water vapor. The concentrations of water, methyl mercaptan and mercury in the gas supplied to the adsorption column were about 2,000 ppm by volume, about 10 ppm by volume, and about ppb by weight, respectively. The gas mixture is supplied at a gas linear velocity of 0.15.
Water and mercury removal tests were performed at 20 ° C. and atmospheric pressure, fed at m / s. After the end of the 50-hour adsorption test, regeneration was performed. Regeneration is performed using methane gas at atmospheric pressure, 350
C. for 5 hours. The regeneration treatment was carried out five times, and the fresh adsorption removal test and the adsorption removal test after the regeneration treatment were carried out for 50 hours, and the mercury removal rate, residual moisture concentration and residual sulfur compound concentration in each were determined by the method described above. The results are summarized in Table 1.

[0032]

[Table 1]

Example 2 In place of F-9, 0.02 liter of calcium A-type zeolite (A-5, 3 mmφ pellet) manufactured by Tosoh Corporation was used in 12 to 42 meshes (the inlet was smaller than that of A-4MG). And hydrogen hydrogen sulfide gas (manufactured by Sumitomo Seika Co., Ltd., concentration: about 1000 ppm by volume / nitrogen) in place of methyl mercaptan to reduce the hydrogen sulfide concentration in the feed gas to about 15 volumes. A water and mercury removal test was performed and evaluated in the same manner as in Example 1 except that the content was set to ppm. Table 2 shows the test results.

[0034]

[Table 2]

From the results shown in Tables 1 and 2, in Examples 1 and 2, the removal efficiency of water, mercury and sulfur compounds was not changed by repeated use, and the performance of the adsorbent was maintained. I knew it was there.

COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated except that 0.04 L of A-4MG manufactured by Tosoh Corporation (silver content: 0.1% by weight, 3 mmφ pellets) was used in an amount of 12 to 42 mesh without using F-9. A water and mercury removal test was performed and evaluated in the same manner as in 1. Table 3 shows the test results.

[0037]

[Table 3]

From the results shown in Table 3, it was found that, in Comparative Example 1, the efficiency of removal of mercury was reduced due to repeated use, and the performance of the remover was reduced.

[0039]

According to the method of the present invention, water, sulfur compounds and mercury can be efficiently and economically removed from natural gas, so that natural gas can be purified and the adsorbent is regenerated. Is industrially useful because it can be used repeatedly.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C01B 39/02 C01B 39/02

Claims (6)

[Claims] 1. A method of combining one or more silver-free zeolites selected from the group consisting of A-type zeolites, X-type zeolites and Y-type zeolites with silver-containing A-type zeolites and contacting them with natural gas. A method for refining natural gas, comprising removing sulfur compounds and mercury. 2. The method for refining natural gas according to claim 1, wherein the zeolite containing no silver and the zeolite containing A-type silver are mixed and brought into contact with natural gas. 3. A silver-free zeolite and a silver-containing zeolite, wherein silver-free zeolite: silver-containing zeolite = 60: 40.
The method for purifying natural gas according to claim 1 or 2, wherein the method is used in a range of from 10 to 90 (based on volume). 4. A packed column comprising a combination of silver-free zeolite and silver-containing A-type zeolite, wherein natural gas is charged at a temperature of 5 to 60 ° C., a gas linear velocity of 0.01 to 0.5 m / sec, and a pressure of 0 The gas purification method according to any one of claims 1 to 3, wherein the gas is circulated at 1 to 10 MPa. 5. The method for purifying natural gas according to claim 4, wherein the natural gas is continuously passed through the packed tower. 6. The method according to claim 1, comprising subjecting the silver-free zeolite and the silver-containing A-type zeolite to a regeneration treatment in a reducing gas atmosphere at 100 to 400 ° C. and then contacting with natural gas.
The method for purifying natural gas according to any one of the above.