Non-oxidizing mercury cleaning agent and its use

Abstract

The application discloses a non-oxidized mercury cleaning agent and application thereof. The non-oxidized mercury cleaning agent comprises the following components: (1) a dialkyldithiophosphinic acid salt; and (2) an oily solvent system; wherein the dialkyldithiophosphinic acid salt has a molecular structure as shown in formula I: in the molecular structure, R1 and R2 are the same or different and are independently selected from linear or branched C1-C6 alkyl, M represents a cation, and m is 1-4. The mercury cleaning agent has good cleaning effect, can shorten the cleaning time, can reduce the mercury content in the equipment to a safe range, can realize manual maintenance and maintenance of the equipment, can make the mercury content in the equipment reach a standard after cleaning and adhering mercury, and can achieve a mercury cleaning rate of greater than 90%. In addition, the mercury cleaning agent does not corrode the equipment, and the safety of the equipment is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mercury cleaning, in particular to a mercury cleaning agent based on a non-oxidation mechanism and application thereof. BACKGROUND

[0002] Natural gas is a mixture of hydrocarbon and non-hydrocarbon gases naturally stored in the stratum. When burned, it produces less carbon dioxide than other fossil fuels, causing lower greenhouse effect. With the global attention to air pollution, natural gas, as a clean energy, has gradually become one of the main energy sources in industrial and civil fields. The huge market demand has brought about the large-scale development of global natural gas resources. However, most of the natural gas contains trace amounts of harmful mercury, mainly in the form of elemental mercury, and a small amount in the form of alkyl mercury.

[0003] The trace amounts of elemental mercury contained in natural gas can be partially condensed in natural gas processing equipment, adhering to the inner wall and gradually increasing over time. The adhered mercury has permeability to metal equipment, and a part of the mercury can also penetrate into the interior of the equipment material, causing corrosion to the equipment material. Therefore, after a period of operation, the natural gas processing equipment needs to be overhauled to remove the mercury deposited on the inner wall of the equipment, reducing the permeation and corrosion of mercury to the equipment. In addition, due to the volatility and toxicity of mercury, during the overhaul construction, the mercury content in the equipment interior and the ambient air of the processing plant will exceed the standard, easily causing mercury poisoning of the operating personnel and bringing health risks. Therefore, it is necessary to remove the adhered mercury from the inner wall of the processing equipment and reduce the volatilization of mercury in the natural gas processing equipment during the overhaul.

[0004] The mercury adhered to the metal surface has strong force with the metal substrate, and the natural gas processing equipment does not have a stirring device to provide shear force. Therefore, it is difficult to remove the adhered mercury from the inner wall of the equipment by physical methods, and the removal is not complete. The mercury content in the equipment interior will exceed the standard, and the maintenance personnel cannot enter the equipment interior, making it difficult to complete the manual maintenance and maintenance of the equipment. The current treatment method is to use high-temperature steam to cook the equipment for a long time during the overhaul shutdown, so that the adhered mercury is volatilized to separate from the metal substrate. The mercury condenses into liquid phase in the form of mercury beads and is cleaned out of the equipment, which can reduce the content of gas-phase mercury in the equipment interior. However, due to the slow volatilization of mercury, a long time is needed for cooking, and there is a situation of incomplete cleaning. Therefore, cooking is not an efficient method, and it is necessary to develop a new method.

[0005] In recent years, chemical methods are proposed to remove mercury, and since there is no effective solvent for mercury, a common method is to use a strong oxidizing agent such as potassium permanganate to oxidize mercury into mercury oxide, and the mercury oxide has no volatility and can reduce the mercury content in the gas phase. However, when the strong oxidizing agent oxidizes elemental mercury, the metal oxide formed is relatively dense, which can prevent the oxidizing agent from penetrating into the interior, and due to the special physical properties of mercury, it usually exists in the form of mercury beads, and in the case where there is no stirring device in the natural gas treatment equipment, large mercury beads cannot be dispersed into small mercury beads, and in this case, oxidation usually occurs on the surface, and internal oxidation is difficult to occur, therefore, the method of using a strong oxidizing agent cannot completely remove elemental mercury, and the structure of the metal oxide wrapping the internal liquid mercury is easy to be damaged under external force, and mercury can still volatilize into the gas phase, which is difficult to reduce the mercury content in the gas phase in the equipment, and the problem of maintenance is still not solved, and the strong oxidizing agent reported in the literature has a high concentration, which can corrode the equipment while oxidizing elemental mercury, so it is difficult to be applied in actual treatment. SUMMARY

[0006] In view of the above technical problems and the deficiencies in the art, the present application provides a non-oxidizing mercury cleaning agent, which is particularly suitable for cleaning mercury deposited on the wall of the equipment, and can completely clean the mercury without corroding the equipment.

[0007] The present application forms a ligand by dialkyldithiophosphinic acid salt and mercury, and disperses large mercury beads into fine ligand particles by the action of an oily solvent system (i.e. a non-polar organic solvent system), so that the mercury deposited on the wall of the equipment can be efficiently stripped without stirring, and the equipment can be cleaned.

[0008] In the technical scheme of the present application, the non-oxidizing mercury cleaning agent composed of dialkyldithiophosphinic acid salt and oily solvent system utilizes the formation of a coordination compound by dialkyldithiophosphinic acid salt and mercury, and uses a non-polar organic solvent as a solvent system, which can convert large mercury beads into fine ligand particles under the action of the oily solvent and the ligand, and disperse them in the oily solvent system, so that the mercury deposited on the wall can be efficiently stripped without stirring, and the mercury deposited on the wall of the equipment can be cleaned. The mercury cleaning agent and the method of flooding and soaking can remove the elemental mercury deposited on the inner wall of the natural gas treatment equipment, and will not corrode the equipment.

[0009] The present application has the characteristics of high mercury cleaning efficiency and complete removal, and can solve the problems of long mercury cleaning time, incomplete mercury cleaning and equipment corrosion in the existing mercury cleaning methods.

[0010] The cleaning agent of the present application comprises a dialkyldithiophosphinic acid salt and an oily solvent system. When cleaning mercury, the dialkyldithiophosphinic acid salt reacts rapidly with elemental mercury to form an organic metal complex under the action of a non-polar organic solvent, which can separate elemental mercury deposited on the wall surface from the wall surface in the form of an organic metal complex and disperse in the oily solvent system in the form of fine particles, thereby achieving cleaning of the mercury deposited on the wall surface, greatly reducing the mercury content in the gas phase space in the equipment, and enabling maintenance personnel to safely enter the equipment. Compared with the existing mercury cleaning agent and cleaning method, the method of the present application does not use a strong oxidant and does not corrode the equipment, and solves the problem that the oxidation method can only treat the surface of mercury beads and is difficult to oxidize the internal mercury of the mercury beads, thereby resulting in incomplete removal. The application method of the cleaning agent of the present application is simple, and the mercury cleaning can be performed in a flooding manner without a stirring device in a natural gas treatment equipment.

[0011] It should be noted that the cleaning of mercury deposited on the wall surface of the equipment is different from the removal and purification of mercury from a mercury-containing natural gas stream or mercury-containing natural gas wastewater. In the removal of mercury from a natural gas stream or natural gas wastewater, the mercury is dispersed in the gas stream or liquid stream and flows together with the fluid, and the mercury is in a free gaseous state or a liquid state. Generally, the method for removing mercury is to use an adsorbent to adsorb, a flocculant to coagulate and filter, or a substance capable of reacting with mercury to capture and filter, so as to separate the mercury from the fluid and achieve the removal of mercury. The mercury deposited on the wall surface does not have the property of free flow and has a strong force of action with the metal wall surface. The key to cleaning is to break the force of action between the mercury and the wall surface. The aforementioned methods for removing mercury from a natural gas stream or natural gas wastewater cannot break this force of action. Even if the reagent used can react with mercury, it generally only reacts on the surface and cannot penetrate into the interior, nor can it break this force of action, so it is impossible to remove the mercury from the wall surface of the equipment. These natural gas treatment equipment generally do not have a stirrer, and the shear force cannot be applied. Some use a high-pressure water gun to wash, but the structure of the equipment is complex, and the dead angle area of the inner wall of the equipment cannot be cleaned.

[0012] The present application will be described in detail below.

[0013] The present application is mainly aimed at developing a non-oxidizing cleaning agent for cleaning mercury attached to the wall surface (especially the inner wall) of the equipment. Based on the chemical properties of elemental mercury and the existing mercury cleaning process, whether it is a high-temperature steam physical treatment method or a strong oxidant chemical cleaning method, there are two main problems: 1. Low cleaning efficiency, which makes it difficult to quickly remove the attached mercury; and 2. Incomplete cleaning, which results in excessive mercury content in the equipment and prevents manual maintenance and maintenance of the equipment.

[0014] For the treatment method of strong oxidizing agent, we found that using high concentration of strong oxidizing agent, a more dense mercury oxide layer will be formed, the penetration of oxidizing agent is more difficult, without stirring, it is difficult to destroy the mercury oxide layer, so the mercury in the internal oxidation layer still exists, when the maintenance personnel enter the equipment for operation, the oxidation layer will be destroyed, the harm of mercury still exists, and high concentration of strong oxidizing agent will also cause equipment corrosion. Therefore, in the actual treatment, this method has not been applied.

[0015] Since chemical method is an efficient cleaning method, but if strong oxidizing agent is not used, chemical method will not have the negative effect of corroding the equipment. Our idea is still to use chemical agents, which still belongs to chemical method, but the chemical agent is not a strong oxidizing agent and does not have an oxidation reaction with elemental mercury. Since mercury is a metal, we consider the idea of forming a coordination compound of mercury and organic compounds, and this coordination compound can be dissolved in water or other solvents, or the complex compound has strong interaction with the solvent and occurs with the wall separation, so as to achieve the effect of cleaning mercury.

[0016] Through molecular characteristics screening, dialkyldithiohypophosphite salt is used, which contains organic groups such as alkyl groups in its molecular structure, has certain lipophilicity, contains P and S atoms, and can form coordination compounds with metallic mercury. And because it is a neutral salt, it will not corrode the metal material of the equipment.

[0017] Elemental mercury has strong electron pushing effect, and the electron cloud density of P atom on P-S bond in the structure of dialkyldithiohypophosphite salt is greatly displaced to S atom, so that S on P-S can form coordination bond with mercury, and the coordination reaction as shown in the following formula occurs, and Hg coordination compound is formed.

[0018]

[0019] The coordination reaction is fast, and the reaction conditions are not harsh, and it can occur in aqueous or organic phase. The generated mercury coordination compound is a black substance and is insoluble in water.

[0020] In the actual elemental mercury cleaning process, since elemental mercury usually exists in the form of small droplets, the sulfur atom in the mercury cleaning agent molecule can form a coordination bond with mercury due to the existence of lone pair electrons, the sulfur atom in the mercury cleaning agent molecule is combined with mercury, and the organic group in the molecular structure surrounds the outside of the mercury bead droplet, which will form an oleophilic organic film on the surface. This layer of film has a certain strength and can protect the mercury bead from being damaged, and also has a barrier effect, so the coordination reaction only occurs on the surface of the mercury bead, and the inside is still mercury.

[0021] Although the dialkyldithiophosphinic acid salt can form a complex with mercury, the complex is not soluble in water, and the complexation only occurs on the surface of the mercury beads, while the interior is still elemental mercury, which cannot complete the cleaning of mercury. The possible reason for this phenomenon is that the dialkyldithiophosphinic acid salt actually contains an oleophilic alkyl group and a hydrophilic dithiophosphinic acid group, the dithiophosphinic acid group has a strong complexation with mercury, and the alkyl group is exposed to the water phase, but due to the non-hydrophilic nature of the alkyl group, it is repelled by the water phase, which is equivalent to pressing the complex on the surface of the mercury beads. Although using water as the solvent is the most economical in terms of cost, it cannot complete the cleaning work.

[0022] Based on the results in the aqueous phase, to complete the cleaning of mercury, the cleaning agent should be able to destroy this surface structure and reduce the mercury bead particles. According to the mechanism of action, if the solvent is changed from water to an oily solvent, the force between the alkyl group exposed to the solvent phase and the solvent phase changes from mutual repulsion to mutual attraction, and the mercury beads will become multiple small particles coated with the complexing agent. If the complexing agent is soluble in the oily solvent, it is most advantageous for mercury cleaning, even if it is not dissolved, but the large particle mercury beads are converted into fine particles distributed in the solvent system, which is very effective for the deposited mercury on the wall, and can strip the deposited mercury from the wall, achieving the purpose of cleaning. Moreover, the complexing agent is dispersed in the solvent, which can be separated from the solvent by filtration, and the solvent can be recycled.

[0023] Therefore, the present application provides a non-oxidized mercury cleaning agent, comprising the following components:

[0024] (1) dialkyldithiophosphinic acid salt;

[0025] (2) an oily solvent system;

[0026] wherein the dialkyldithiophosphinic acid salt has a molecular structure as shown in formula I:

[0027]

[0028] In the molecular structure, R1 and R2 are the same or different, and are independently selected from linear or branched C1-C6 alkyl groups, M represents a cation, and m is 1-4.

[0029] Further, R1 and R2 can be independently selected from methyl, ethyl, n-propyl, n-butyl, isobutyl, t-butyl, n-pentyl, isopentyl, n-hexyl, and isohexyl.

[0030] Further, M m+ may be selected from Na + , K + , NH4 +These are water-soluble salts, and also have no corrosive. These compounds, in addition to being soluble in water, can also be soluble in some oily organic solvents.

[0031] In order to ensure a certain cleaning efficiency when mercury cleaning is carried out, the mass concentration of the dialkyldithiophosphinic acid salt in the oily solvent system can be 0.01%-50%, preferably 0.1%-10%. Too high a concentration will not improve the cleaning efficiency, and will result in increased cost, and too low a concentration will result in reduced cleaning efficiency and prolonged cleaning time.

[0032] In order to ensure that the dialkyldithiophosphinic acid salt forms a coordination compound with mercury, according to research, the pH of the non-oxidized mercury cleaning agent is preferably ≥7, and preferably >7, to maintain weak alkaline conditions.

[0033] The oily solvent system can include at least one of linear alkanes, cycloalkanes, aromatic hydrocarbons, etc.

[0034] The application further provides the use of the non-oxidized mercury cleaning agent in cleaning mercury.

[0035] The application further provides a method for cleaning mercury deposited on the wall of a device, using the non-oxidized mercury cleaning agent, and using a flooding immersion method, wherein:

[0036] The dialkyldithiophosphinic acid salt and the oily solvent system are added simultaneously; or,

[0037] The aqueous solution of the dialkyldithiophosphinic acid salt is first added for immersion, the aqueous solution is discharged after a period of immersion, and then the oily solvent system is added for immersion, and this cycle is repeated until the mercury cleaning is completed.

[0038] Further, the immersion time of the dialkyldithiophosphinic acid salt during cleaning can be greater than 0.1 hour, and is preferably 0.5-10 hours.

[0039] The mercury cleaning agent of the application can be carried out at room temperature, or can be heated, and can be carried out at a higher temperature, and increasing the temperature is beneficial to improving the cleaning efficiency.

[0040] Compared with the prior art, the mercury cleaning agent of the application has the beneficial effects that: the mercury cleaning agent of the application shows good cleaning effect, and can also shorten the cleaning time, so that the mercury content in the device is reduced to a safe range, manual maintenance and maintenance of the device can be realized, and after cleaning and mercury adhesion, the mercury content in the device reaches the standard, and the mercury cleaning rate is greater than 90%. In addition, the device is not corroded, and the safety of the device is ensured. DETAILED DESCRIPTION

[0041] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application.

[0042] Raw materials:

[0043] 1) n-hexane, cyclohexane, National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0044] 2) sodium diisobutyl dithiophosphinate, Solvay.

[0045] Experiment:

[0046] 1, Mercury deposition on the surface of the flask

[0047] Experimental process: about 1g of mercury beads was weighed and placed in a sealed container, heated at 180℃ until the mercury beads were completely volatilized, and the mercury would be deposited on the container wall, leaving it for cleaning. The mercury content in the gas phase space of the test container was tested.

[0048] Gas phase mercury content test: Mercury Analyzer Waterstar N3000.

[0049] 2, Mercury cleaning

[0050] Experimental process: Since natural gas treatment equipment usually does not have a stirrer, in order to adapt to the mercury cleaning operation of natural gas treatment equipment, the full tank soaking method was adopted. That is, the container with mercury deposition on the wall surface was filled with mercury cleaning agent, and the temperature was kept constant. After a certain time, the soaking was ended, the mercury cleaning agent was discharged, and the mercury content in the gas phase space of the container was tested. The mercury cleaning rate was calculated according to the following formula:

[0051] Mercury cleaning rate % = (mercury content before cleaning-mercury content after cleaning) / (mercury content before cleaning) x 100%

[0052] Example 1

[0053] Mercury cleaning agent: 2wt% sodium diisobutyl dithiophosphinate n-hexane solution

[0054] The mercury cleaning operation was carried out according to the foregoing mercury cleaning method, the cleaning temperature was room temperature 25℃, the soaking time was 6hr, the mercury cleaning rate was calculated, and the results are shown in Table 1.

[0055] Example 2

[0056] The same as Example 1, except that the concentration of sodium diisobutyl dithiophosphinate was 5wt%. The mercury cleaning rate of mercury was calculated, and the results are shown in Table 1.

[0057] Example 3

[0058] The same as Example 1, except that the soaking time was 8hr. The mercury cleaning rate of mercury was calculated, and the results are shown in Table 1.

[0059] Example 4

[0060] The same as Example 1 except that the temperature of the wash was 40°C. The mercury wash rate was calculated and the results are shown in Table 1.

[0061] Example 5

[0062] The same as Example 1 except that the pH of the sodium diisobutyl dithiophosphinate in n-hexane was adjusted to 9. The mercury wash rate was calculated and the results are shown in Table 1.

[0063] Example 6

[0064] The same as Example 1 except that the oily solvent system was changed from n-hexane to cyclohexane. The mercury wash rate was calculated and the results are shown in Table 1.

[0065] Table 1: Mercury Wash Results (Examples)

[0066]

[0067] Comparative Example 1

[0068] The same as Example 1 except that the solvent system was water. The mercury wash rate was calculated and the results are shown in Table 2.

[0069] Comparative Example 2

[0070] The same as Example 1 except that no sodium diisobutyl dithiophosphinate was used. The mercury wash rate was calculated and the results are shown in Table 2.

[0071] Comparative Example 3

[0072] The same as Example 1 except that the pH of the solvent system was adjusted to 3. The mercury wash rate was calculated and the results are shown in Table 2.

[0073] Comparative Example 4

[0074] The mercury deposited in the unit was treated using 120°C steam for 24 hours. The mercury wash rate was calculated and the results are shown in Table 2.

[0075] Table 2: Mercury Wash Results (Comparative Examples)

[0076] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Mercury content before washing (μg / m 3 )]]> 588 603 573 610 Mercury content after washing (pg / m 3 )]]> 528 592 565 303 Mercury removal rate (%) 10.2 1.8 1.4 50.3

[0077] It is to be understood, moreover, that the application is not limited to the particular examples described hereinabove, which are presented for illustrative purposes only and which are not intended to limit the scope of the application. Variations in the procedures described above and other uses will occur to those of ordinary skill in the art upon consideration of the application as set forth hereinabove.

Claims

1. A non-oxidizing mercury cleaning agent, characterized by, The non-oxidized mercury cleaning agent comprises the following components: (1) a dialkyldithiohypophosphite salt; (2) an oily solvent system, wherein the oily solvent system comprises at least one of a linear alkane, a cycloalkane and an aromatic hydrocarbon; wherein the dialkyldithiohypophosphite salt has a molecular structure as shown in Formula I: in the molecular structure, R1 and R2 are the same or different and are independently selected from linear or branched C1-C6 alkyl, M represents a cation, and m is 1-4; the pH of the non-oxidized mercury cleaning agent is greater than or equal to 7.

2. The non-oxidizing mercury scavenger of claim 1, wherein, R1 and R2 are independently selected from methyl, ethyl, n-propyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, n-hexyl and isohexyl.

3. The non-oxidizing mercury scavenger of claim 1, wherein, M m+ selected from Na + , K + , NH4 + .

4. The non-oxidizing mercury scavenger of claim 1, wherein, The mass concentration of the dialkyldithiohypophosphite salt in the oily solvent system is 0.01%-50%.

5. The non-oxidizing mercury scavenger of claim 4, wherein, The mass concentration of the dialkyldithiohypophosphite salt in the oily solvent system is 0.1%-10%.

6. Use of the non-oxidized mercury cleaning agent according to any one of claims 1-5 in cleaning mercury.

7. A method of cleaning mercury deposited on a wall of a device, the method comprising: The non-oxidized mercury cleaning agent according to any one of claims 1-5 is used in cleaning mercury by means of flooding immersion, and in the cleaning process: the dialkyldithiohypophosphite salt and the oily solvent system are added simultaneously; or the dialkyldithiohypophosphite salt is first added in the form of an aqueous solution for immersion, the aqueous solution is discharged after a period of immersion, and then the oily solvent system is added for immersion, and the process is repeated until the mercury cleaning is completed.

8. The method of claim 7, wherein, In the cleaning process, the immersion time of the dialkyldithiohypophosphite salt is greater than 0.1 hour.

9. The method of claim 8, wherein, In the cleaning process, the immersion time of the dialkyldithiohypophosphite salt is 0.5-10 hours.

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