JPH0428040B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields NGLs (natural gas condensate) recovered from natural gas contain mercury, which can reach tens to hundreds of ppb depending on the production area, and can cause amalgam corrosion of aluminum used as equipment material. When NGL is used as a chemical raw material, the catalyst is poisoned and causes deterioration. The present invention relates to a method for removing mercury from such liquid hydrocarbons containing mercury. Conventional technology Generally, mercury removal methods 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. On the other hand, as a method for removing mercury using metal sulfide,
For example, a method using copper sulfide (Japanese Patent Application Laid-Open No. 52-76284)
There is a method using polysulfides of metals such as copper, nickel, iron, and cobalt. The former method is said to be able to remove mercury from gases or liquids, but as a specific example, mercury is mostly methane, contains almost no C ₅ ⁺ components, and contains 19 μg/m ³ of mercury.
The main target is natural gas that contains only a small amount of mercury, and its effects on liquid components that contain a large amount of _C5 or higher fractions, such as natural gas condensate or naphtha fraction, or those that contain high concentrations of mercury are not clear. Furthermore, the latter method does not mention the adsorption effect of elements other than elemental mercury. The present inventors have proposed a method for efficiently removing mercury from natural gas condensate by eliminating the above-mentioned drawbacks. We proposed a method characterized by bringing the metal into contact with an adsorbent containing sulfides of the metals mentioned above. (Patent Application No. 62-286469) Compared to conventional methods, this method can remove mercury from liquids mainly composed of hydrocarbons, such as natural gas condensate, and can be operated at room temperature and pressure. Furthermore, since it is possible to use waste catalysts containing molybdenum sulfide, such as hydrodesulfurization catalysts, as an adsorbent, it is an extremely excellent method that can save costs and exhibits particularly high adsorption capacity for elemental mercury. was discovered. However, in addition to elemental mercury, natural gas condensate contains mercury that is difficult to adsorb (possibly ionic mercury), and the above mercury removal method using the metal sulfide does not work well for these mercury. The adsorption capacity could not be said to be sufficient. Ionic mercury present in water can be removed by, for example, activated carbon or aluminum powder, but these are not effective in removing mercury from NGLs. Problems to be Solved by the Invention An object of the present invention is to provide a method for removing mercury from liquid hydrocarbon containing mercury with high efficiency. Means for Solving the Problems The method for removing mercury according to the present invention is to remove liquid hydrocarbon containing mercury from the following formula: MM′S (where M and M′ are the same or different, hydrogen, alkali metal or and (2) contacting with an adsorbent containing one or more sulfides of heavy metals. In other words, the sulfur compound represented by the formula MM′S (hereinafter sometimes referred to as sulfur compound ()) reacts with ionic mercury to produce solid, poorly soluble mercury (estimated to be mercury sulfide). Not only is it easy to separate from liquid hydrocarbons, but it is also adsorbed by heavy metal sulfides in the same way as elemental mercury. In the end, it was discovered that mercury, which exists in different types, can be efficiently removed by combining the above two steps. 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 sulfur compound () used in the present invention is a compound in which two identical or different hydrogen, alkali metal, or ammonium groups are bonded to a sulfur atom, for example,
Examples include H ₂ S, Na ₂ S, NaHS, K ₂ S, KHS, (NH ₄ ) ₂ S, and particularly preferred are hydrogen sulfide and sodium sulfide. Hydrogen sulfide can be blown directly into the liquid hydrocarbon containing mercury in gaseous form, but it can also be brought into contact with the target liquid as an aqueous solution. Other sodium sulfide etc. are used as an aqueous solution. Examples of the heavy metal sulfide used as an adsorbent in the present invention include sulfides of molybdenum, tungsten, vanadium, copper, etc., and sulfides of two or more of these metals. Sulfides containing vanadium are preferred. The heavy metal sulfide adsorbent can be used alone, but it may also be supported on a carrier.
Particulate materials such as silica, alumina, silica-alumina, zeolite, ceramic, glass, resin, and activated carbon can be used as the carrier, 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 wt% 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, or vanadium compounds as they are, or by mixing them with a supporting material, and then subjecting them to sulfide 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 production 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. The step of treating a liquid hydrocarbon containing mercury with a sulfur compound () and the step of contacting it with a heavy metal sulfide adsorbent may be performed simultaneously or sequentially. For sequential processing, the order can be chosen arbitrarily. However, when hydrogen sulfide is used as a post-process, HgS does not dissolve in the H ₂ S aqueous solution, so a separation step for the generated HgS is required. On the other hand, if simultaneous treatment or a method in which adsorbent treatment is performed as a subsequent process is used, the generated HgS will be adsorbed by heavy metal sulfide along with elemental mercury. Alternatively, it is preferable that the adsorbent treatment be performed as a post-process. On the other hand, when treated with sodium sulfide aqueous solution,
Since HgS dissolves in sodium sulfide aqueous solution,
Easily separated by liquid phase separation. Therefore, the order of sequential processing can be arbitrarily selected. When removing mercury from mercury-containing hydrocarbons, the ^amount of sulfur compounds () used is ¹⁰
Double equivalents are also sufficient. In addition, the processing time is several minutes to several tens of minutes, usually about 5 to 10 minutes, and the temperature is room temperature.
The pressure should be normal pressure. The contact treatment temperature with the adsorbent is preferably 200°C or less. 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 liquid hydrocarbon with the adsorbent is arbitrary, a fixed bed flow system is particularly preferred. Continuous operation is possible by adopting a fixed bed flow system. The present invention will be specifically explained below using Examples. Preliminary Test 1 2% H ₂ S gas (residual H ₂ ) was blown into 200 ml of Indonesian NGL containing 350 ppb of mercury (in terms of single substance) for 10 minutes, and the mixture was left to stand to measure changes in mercury concentration over time. The results are shown in Table 1.

[Table] It seems that it takes time for the concentration to decrease, but this is because it takes time for the formed insoluble Hg compounds to settle. Example 1 2% H ₂ S gas (residual H ₂ ) was blown into Indonesian NGL containing 350 ppb of mercury (single amount) for 10 minutes, and then 7 wt % of molybdenum was added as an adsorbent.
The mercury concentration in the effluent was measured when it was fed into an adsorption tower filled with 1 g of Co.Mo sulfide/Al ₂ O ₃ containing 2 wt% cobalt at a fixed bed flow rate of 300 ml/hour for 6 hours and found to be less than 2 ppb. Preliminary Test 2 100 ml of the raw material used in Preliminary Test 1 and 100 ml of 5% sodium sulfide aqueous solution were placed in a separating funnel and mixed by shaking for 10 minutes. Next, the water layer and oil layer were separated and the mercury concentration in the oil layer was measured and found to have decreased to 60 ppb. Example 2 The same Co/Mo sulfide used in Example 1 was added to 100 ml of the oil layer obtained in Preliminary Test 2 as an adsorbent.
0.1 g of Al ₂ O ₃ was added, this was placed in a glass container with a lid, and after being gently shaken for 10 minutes, the mercury concentration in the oil layer was measured and found to be less than 1 ppb. Example 3 2% H ₂ S (residual H ₂ ) gas was blown into the raw material of Example 1 and about 2 ppm of mercury dissolved therein for 10 minutes.
300 ml/hour was supplied to an adsorption tower packed with 1 g of Al ₂ O ₃ ). When the outlet mercury concentration was measured, it was still 2.5 ppb even after 10 hours. From these results, it was found that the metal sulfide adsorbent of the present invention is effective against both insoluble mercury compounds and elemental mercury produced by H ₂ S treatment. Examples 4 to 10 The same test as in Example 2 was conducted, except that the MM'S and adsorbent shown in Table 2 were used, and the mercury concentration in the oil layer was measured. The results are shown in Table 2.

[Table] Note: All adsorbents are comparative examples of supporting γ-alumina. 1 NGL produced in Indonesia containing 350 ppb of mercury (in terms of single substance) was used as an adsorbent for the same Co.
300 in an adsorption tower filled with 1g of Mo sulfide/Al ₂ O ₃
When the mercury concentration in the effluent was measured by feeding at a rate of ml/hour, it was 4 ppb after 1 hour, but exceeded 100 ppb after 5 hours, indicating that the adsorption capacity was extremely small. In addition, elemental mercury is included under the same conditions.
When NGL was treated, almost no mercury was detected even after 50 hours. Comparative Example 2 The NGL after H ₂ S injection in Example 1 was supplied at 300 ml/hour to an adsorption tower packed with 1 g of silica.
The concentration at the outlet of the adsorption tower was 30 ppb immediately after the start of the experiment, and the ability to collect mercury compounds made insoluble by H ₂ S injection was inferior to that of metal sulfides. It turned out that it is very effective when combined with processing. Reference example: To see what types of mercury can be removed by _H2S treatment, 300 ppb each of elemental mercury, diethylmercury, mercuric chloride, and methylchloromercury were used.
It was dissolved in light naphtha and the effect of H ₂ S treatment was observed. Mercury chloride could be removed by H ₂ S treatment, but it had little effect on other substances. From this result, the type of mercury in the NGL used in Example 1 is estimated to be Hg ²⁺ . Effects of the invention Elemental mercury and ionic mercury in liquid hydrocarbons can be removed simultaneously with high efficiency. Both hydrogen sulfide and sodium sulfide treatments can be performed at room temperature and pressure, so equipment costs are low. Waste catalysts containing molybdenum sulfide, such as hydrodesulfurization catalysts, can be used as adsorbents.
You can save costs. Continuous operation is possible by adopting a fixed bed flow system.

Claims (1)

[Scope of Claims] 1 A liquid hydrocarbon containing mercury is a sulfur compound represented by 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 comprising the steps of treating with a compound and (2) contacting with an adsorbent containing one or more sulfides of heavy metals.