JPH0524193B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] NGLs (natural gas condensate) recovered from natural gas contain mercury ranging from tens to hundreds of ppb depending on the production area, and are used as equipment materials. This causes inconveniences such as amalgam corrosion of aluminum, which is exposed to aluminum, and catalysts that are poisoned and deteriorated when NGL is used as a chemical raw material.

Since elemental mercury and inorganic mercury compounds coexist in NGL, it is necessary to remove both.
Also, since some contain organic mercury compounds, it is also necessary to remove them.

The present invention relates to a method for removing mercury from such mercury-containing liquid or gaseous hydrocarbons.

[Prior Art] Mercury removal methods generally target industrial wastewater, incinerator exhaust gas, etc., but the following two methods target natural gas.

(1) Cooling condensation method (2) Adsorption method (absorption method) The cooling condensation method is a method adopted in natural gas liquefaction plants, but it uses adiabatic expansion and is effective for removing mercury from natural gas condensate. cannot be used.

Various adsorbents have been proposed for the adsorption method, such as alumina or zeolite impregnated with silver, activated carbon or molecular sieve impregnated with potassium iodide or sulfur, and the like. However, these have problems such as being expensive, having a small adsorption capacity, and having a reduced mercury adsorption ability due to adsorption of liquid hydrocarbons.

In addition, methods for adsorbing and removing mercury using metal sulfides include a method using copper sulfide (USP 4094777; Japanese Patent Application Laid-Open No. 1983-76284) and a method using polysulfides of heavy metals such as Cu, Ni, Fe, and Co (USP 4474896). is proposed.

The former method is said to be capable of adsorbing and removing mercury in gases or liquids, but a specific example is methane containing almost no C ₅ ⁺ components and mercury at 19μ
The main target is natural gas that contains only about g/ ^m3 , and liquid components that contain a lot of _C5 or higher fractions such as natural gas condensate or naphtha fraction, as well as high concentrations of elemental mercury and inorganic mercury compounds. The effect on what it contains is not clear.

In addition, in the latter method, metal sulfides adsorb elemental mercury and organic mercury compounds well;
Inorganic mercury compounds adsorb only extremely small amounts.

The present inventors treat a liquid hydrocarbon containing mercury with a sulfur compound of the formula MM′S (M and M′ are each the same or different and represent hydrogen, an alkali metal, or an ammonium group). A method for removing mercury (Japanese Patent Application No. 183559/1983) was previously proposed, which comprises a step of contacting the mercury with an adsorbent containing one or more sulfides of heavy metals.

The sulfur compound represented by the formula MM′S reacts with inorganic mercury compounds to produce solid, poorly soluble mercury (estimated to be mercury sulfide), and each
Since it reacts with MM'S and dissolves in the aqueous solution phase, it becomes easy to separate it from liquid hydrocarbons. However, elemental mercury cannot be removed with the sulfur compound represented by the formula MM′S, so an adsorption process using heavy metal sulfides is necessary to remove mercury from hydrocarbons containing both inorganic mercury compounds and elemental mercury. need to be combined.

[Problems to be Solved by the Invention] An object of the present invention is to provide a method for removing mercury from liquid or gaseous hydrocarbons containing mercury with high efficiency. By the way, mercury here is
A general term for elemental mercury, inorganic mercury compounds, and organic mercury compounds. It also includes inorganic mercury compounds in an ionized state.

[Means for Solving the Problems] The method for removing mercury from hydrocarbons according to the present invention includes:
It is characterized in that a liquid or gaseous hydrocarbon containing mercury is brought into contact with an aqueous solution of polysulfide and then separated from the aqueous phase.

This method allows the removal of elemental mercury and inorganic mercury compounds in hydrocarbons.

Furthermore, in order to increase the removal rate of elemental mercury and inorganic mercury compounds as well as to remove organic mercury compounds, it is necessary to contact the mercury-containing liquid or gaseous hydrocarbon with an aqueous solution of polysulfide and then add an aqueous phase. and a step of contacting with an adsorbent containing one or more sulfides of heavy metals.

The liquid hydrocarbons targeted by the present invention include:
Particular mention may be made of liquid hydrocarbons obtained from natural gas or petroleum-associated gas.

The components of natural gas are inorganic gases such as nitrogen, carbon dioxide, and hydrogen sulfide, and gaseous hydrocarbons from _C1 to _C4 , _C5
Consisting of the above liquid hydrocarbons. However, depending on the production area, it often does not contain hydrogen sulfide.

Petroleum-associated gas is composed of inorganic gas components, gaseous hydrocarbons, and liquid hydrocarbons, and even heavy oil components are included as liquid hydrocarbons. It is desirable to remove components of petroleum-associated gas with a boiling point exceeding 370°C by distillation.

The polysulfide used in the present invention has the general formula
M ₂ Sx (here, x is a number of 2 or more, M represents a cation capable of forming a water-soluble polysulfide), which is brought into contact with a liquid or gaseous hydrocarbon in an aqueous solution state. After that, the hydrocarbons are separated from the aqueous phase. This treatment removes elemental mercury and inorganic mercury compounds in the hydrocarbon.

Specific examples of polysulfides include sodium polysulfide, potassium polysulfide, ammonium polysulfide, and the like.

Elemental mercury and inorganic mercury compounds in the raw materials react with these polysulfides to form poorly soluble mercury sulfide. Since poorly soluble mercury sulfide is dispersed in the aqueous phase,
Mercury is removed by separating the oil phase consisting of hydrocarbons from the aqueous phase. The amount of polysulfide necessary to convert elemental mercury or inorganic mercury compounds in the raw material into poorly soluble mercury sulfide is sufficient if the amount of S is 10 times that of Hg.

However, when a large excess of polysulfide is used relative to the mercury in the raw material, that is, when a highly concentrated polysulfide aqueous solution is used, the poorly soluble mercury sulfide becomes water-soluble dithiomercurate and dissolves in the polysulfide aqueous solution. Therefore, separation from the oil phase is complete, which is preferable.

It is preferable to use a polysulfide aqueous solution with a high concentration because a large amount of hydrocarbon can be treated continuously with the same solution.

Therefore, it is desirable that the concentration of polysulfide in the polysulfide aqueous solution be 1% by weight or more, preferably 3% by weight or more.

Contact treatment time is several minutes to several tens of minutes, usually 5 to 10 minutes.
The temperature should be normal temperature and the pressure should be normal pressure.

If the hydrocarbon does not contain organic mercury compounds, this treatment is sufficient.

However, when the raw material hydrocarbon also contains an organic mercury compound, after the above treatment, it is further brought into contact with an adsorbent containing one or more sulfides of heavy metals.

Examples of heavy metal sulfides that are adsorbents used in the present invention include sulfides of molybdenum, tungsten, vanadium, copper, etc., and sulfides of two or more of these metals. Sulfides containing are preferred.

The heavy metal sulfide can be used as it is, but it may also be supported on a carrier. Supports include silica, alumina, silica-alumina,
Particulate materials such as zeolite, ceramic, glass, resin, and activated carbon can be used, and among these, alumina is particularly preferred as the carrier.

The carrier has a large specific surface area, which improves the contact efficiency, and is therefore preferable, and is preferably 5 to 400 m ² /g, especially 100 m 2 /g.
Those having a specific surface area of ~250 m ² /g are preferred, but are not limited thereto.

When supported on a carrier, the amount of metal supported on the adsorbent is suitably 1 to 15% by weight based on the amount of metal in the form of sulfide.

The adsorbent may also contain other metal components or inorganic components.

Adsorbents are produced by using molybdenum compounds, tungsten compounds, vanadium compounds, etc. as they are, or by mixing them with a supporting material, and then subjecting them to sulfurization treatment.

For example, a molybdenum compound is impregnated into a carrier material such as alumina or kneaded with the carrier material, and after molding, it is calcined in air at 450 to 550°C for 0.1 to 2 hours, and finally sulfurized.

Examples of molybdenum compounds include ammonium paramolybdate group [(NH ₄ ) ₆ Mo ₇ O ₂₄
4H ₂ O], as a tungsten compound, ammonium tungstate group [5(NH ₄ ) ₂ O・12WO ₃・
5H ₂ O], ammonium metavanadate group [NH ₄ VO ₃ ], etc. are used as the vanadium compound.

In order to facilitate the sulfurization treatment and improve the mercury adsorption ability, it is preferable to add a trace amount of a cobalt or nickel compound during the adsorbent manufacturing process. The amount of cobalt or nickel added is preferably 0.1 to 5% by weight based on the adsorbent.

A mixed gas of hydrogen and hydrogen sulfide is used to sulfurize the adsorbent. Hydrogen sulfide is preferably used in a concentration range of 0.1 to 10 vol%. The temperature required for sulfurization is
The temperature is 200-450°C, preferably 300-400°C.

As the adsorbent, a molybdenum-based catalyst used for desulfurization treatment of kerosene, vacuum gas oil (VGO), etc. can be used as a hydrodesulfurization catalyst. This molybdenum-based catalyst that has been sulfurized or a waste catalyst that has deteriorated after being used for a certain period of time (sulfurized) can effectively adsorb mercury contained in liquid hydrocarbons. Therefore, the use of waste catalyst as an adsorbent is very advantageous because the manufacturing cost of the adsorbent can be significantly reduced.

A step in which a liquid or gaseous hydrocarbon containing mercury is brought into contact with an aqueous solution of polysulfide and then separated from the aqueous phase, and a step in which it is brought into contact with an adsorbent containing one or more sulfides of heavy metals. Simultaneous processing or sequential processing may be used. For sequential processing, the order can be chosen arbitrarily.

The contact treatment temperature with the adsorbent is preferably 200°C or lower. If the temperature exceeds 200℃, problems such as mercury dissipating from the adsorbent, evaporation of hydrocarbons, and cracking occur.

Although the method of contacting the mercury-containing hydrocarbon and the adsorbent is arbitrary, it is preferable to adopt a fixed bed flow system since continuous operation is possible.

The present invention will be specifically explained below using Examples.

Example 1 (Removal of elemental mercury in liquid) Elemental mercury was dissolved in naphtha as a model liquid.
A material with Hg = 520 ppb was prepared and used as a raw material.

100 ml of 5% Na ₂ S ₄ aqueous solution was mixed with 100 ml of this raw material, and the mixture was stirred with a shaker to measure the relationship between shaking time and mercury removal rate. For the analysis of mercury, a Nippon Instruments Mercury SP-3 analyzer was used.

The results are shown in Figure 1 along with other examples. 1st
In the figure, the horizontal axis represents treatment time (minutes), and the vertical axis represents mercury removal rate (%). As shown by the circle in the figure, almost 100% of elemental mercury was removed in 5 minutes.

Furthermore, when 100 ml of 1% Na ₂ S ₄ aqueous solution was used, almost 100% of elemental mercury could be removed in 20 minutes, as shown by the ● mark in the figure.

Comparative Example 1 FIG. 1 shows the results of an experiment conducted in the same manner as in Example 1, except that a 5% Na ₂ S aqueous solution was used. ◇ in the diagram
As indicated by the mark, the removal rate did not reach 100% even after 60 minutes.

In this example, Na ₂ S also appears to have the ability to remove elemental mercury, but Na ₂ S solutions usually have a
This contains 1000ppm Na ₂ S _x
It is presumed that Na ₂ S _x reacted.

[Reference Example] In order to investigate whether Na ₂ S ₄ is also effective against organic mercury compounds, Example 1 was prepared using naphtha with 500 ppb diethylmercury dissolved as a raw material.
The removal rate was determined in the same manner as above. Even after shaking for 60 minutes, the removal rate was 0-5%. That is, organic mercury compounds cannot be removed with Na ₂ S ₄ .

The oil phase after shaking for 60 minutes was separated and added with 7% by weight of molybdenum and 2% by weight of cobalt as adsorbents.
Add 0.1g of Co・Mo sulfide/Al ₂ O ₃ including weight%
After stirring for 30 minutes, the mercury in the oil phase was reduced to 3 ppb.

Example 2 (Removal of elemental mercury in liquid) The same test as in Example 1 was conducted except that a 5% K ₂ S ₄ aqueous solution was used instead of the 5% Na ₂ S ₄ aqueous solution. Ten
After shaking for a minute, the mercury concentration in the oil phase was measured.
Almost 100% had been removed.

Example 3 (Removal of elemental mercury in gas) Add HgCl ₂ to 100 ml of pure water to give 1 μg of Hg.
An aqueous solution was added and this was reduced to elemental mercury with stannous chloride.

Bubbling city gas (natural gas) into this,
Furthermore, the outlet gas was bubbled into 100 ml of a 5% Na ₂ S ₄ aqueous solution to absorb mercury.

After 10 minutes, the mercury in the Na ₂ S ₄ aqueous solution was measured to be µg, indicating that all the mercury entrained in the gas was
It was found that it was absorbed by Na ₂ S ₄ .

Example 4 (Treatment of inorganic mercury compounds and hydrocarbons containing elemental mercury with Na ₂ S ₄ aqueous solution) A model solution was prepared in which 200 ppb of elemental mercury and 200 ppb of mercuric chloride (as Hg) were dissolved in naphtha. 100 ml of this raw material was mixed with 100 ml of a 5% Na ₂ S ₄ aqueous solution, and the mixture was stirred using a shaker. After 10 minutes, the mixture was separated into an oil phase and an aqueous phase, and the mercury concentration in the oil phase was measured, and the mercury concentration had decreased to 2 ppb.

Example 5 (Na ₂ S _x treatment of hydrocarbons containing all elemental mercury, inorganic mercury compounds, and organic mercury compounds and combination of adsorbent) As a model liquid, 200 ppb of elemental mercury was added to naphtha,
A solution of 200 ppb of mercuric chloride (as Hg) and 200 ppb of diethylmercury (as Hg) was prepared, and 100 ml of this raw material was mixed with 100 ml of a 5% Na ₂ S ₄ aqueous solution and stirred with a shaker. After 10 minutes, the oil phase was separated into the water phase and the mercury concentration in the oil phase was measured.
The amount was 210ppb (mostly organic mercury compounds).

Next, this liquid phase contains Co/Mo sulfide containing 7% by weight of molybdenum and 2% by weight of cobalt as an adsorbent.
After adding 0.5% by weight of Al ₂ O ₃ and shaking for 60 minutes and separating the adsorbent by filtration, the mercury concentration in the filtrate was measured and found to be 6 ppb.

[Effect] The above results show that elemental mercury and inorganic mercury compounds in hydrocarbons can be removed simultaneously by treatment with an aqueous polysulfide solution. However, organic mercury compounds cannot be removed with an aqueous polysulfide solution, so for hydrocarbons containing elemental mercury, inorganic mercury compounds, and organic mercury compounds, a combination of an aqueous polysulfide solution treatment and an adsorbent is required. but
The amount of adsorbent used can be reduced compared to the case where Na ₂ S is used.

[Effects of the Invention] Elemental mercury and inorganic mercury compounds in hydrocarbons can be removed simultaneously with high efficiency.

Since both polysulfide aqueous solution treatment and adsorption treatment can be performed at room temperature and pressure, equipment costs can be reduced.

Waste catalysts containing molybdenum sulfide, such as hydrodesulfurization catalysts, can be used as adsorbents.
You can save costs.

There is no need for manpower as operations such as filtration are not required.

The amount of adsorbent used can be significantly reduced compared to conventional techniques.

[Brief explanation of the drawing]

Figure 1 shows naphtha in which elemental mercury is dissolved.
The relationship between treatment time and mercury removal rate when treated with 5% Na ₂ S ₄ aqueous solution (○ mark), 1% Na ₂ S ₄ aqueous solution (● mark), or 5% Na ₂ S ₄ aqueous solution (◇ mark) is shown. In the figure,
The horizontal axis is processing time (minutes), and the vertical axis is mercury removal rate (%).
represents.

Claims (1)

[Scope of Claims] 1. A method for removing mercury from hydrocarbons, which comprises bringing a liquid or gaseous hydrocarbon containing mercury into contact with an aqueous solution of polysulfide and then separating it from the aqueous phase. 2. A step of contacting a liquid or gaseous hydrocarbon containing mercury with an aqueous solution of polysulfide and then separating it from the aqueous phase, and a step of contacting it with an adsorbent containing one or more sulfides of heavy metals. A method for removing mercury from hydrocarbons, characterized by comprising a combination.