Electrochemical test device and method for rapidly evaluating corrosion inhibitor performance and application

Abstract

The invention provides an electrochemical test method and an electrochemical test device for rapidly evaluating the performance of a corrosion inhibitor, and belongs to the field of corrosion prevention of petrochemical engineering processes. The device comprises a reaction kettle, wherein the reaction kettle comprises a kettle body and a kettle cover; the kettle cover is connected with a reference electrode and a counter electrode, a working electrode fixing shaft is mounted on the kettle cover, the end part of one end, positioned in the kettle body, of the working electrode fixing shaft is connected with a working electrode, and a stirring paddle is arranged on the working electrode fixing shaft and positioned above the working electrode; an exhaust pipe and a gas inlet pipe are further arranged on the kettle cover, one end of the gas inlet pipe extends into the kettle body and is close to the bottom, and the other end of the gas inlet pipe is connected with an H2S gas inlet branch pipe, a CO2 gas inlet branch pipe, an N2 gas inlet branch pipe and a corrosion inhibitor branch pipe through branch pipelines. According to the invention, different medium flow rates can be simulated, and an accurate and efficient dynamic evaluation method is realized; and the corrosion inhibitor is prevented from overflowing or entering the branch pipe through the exhaust pipe when the pressure in the kettle body is too high, so that the accuracy and high efficiency of a test result are ensured.

Description

Technical Field

[0001] This invention belongs to the field of corrosion prevention in petrochemical processes, specifically relating to an electrochemical testing device, method, and application for rapidly evaluating the performance of corrosion inhibitors. Background Technology

[0002] With the increasing proportion of high-sulfur and high-chlorine crude oil processed, refining systems, including atmospheric and vacuum distillation units and secondary processing units such as catalytic cracking and hydrocracking, are facing unprecedented corrosion challenges. Sulfides and chlorides in crude oil decompose or hydrolyze during distillation, and residue oil and wax oil react with H2 during hydrotreating, generating large amounts of H2S and HCl. These, along with organic acids and water in the feedstock, cause severe corrosion to equipment and pipelines. Furthermore, with the continuous increase in global natural gas demand, the development of natural gas resources has become an inevitable trend in energy development. Most oil and gas fields contain high levels of H2S and CO2, exhibiting strong corrosiveness, posing a significant challenge to purification units and gathering and transmission pipelines.

[0003] Corrosion inhibitors, as chemical additives that require small dosages, are low in cost, have rapid effects, and are widely applicable, are extensively used in internal corrosion protection in oil refining and oil and gas field systems. However, corrosion inhibitors are highly specific to corrosive environments, and factors affecting their effectiveness include the oil and gas environment, the composition of the corrosive medium, temperature, pressure, the flow state of the medium, and the performance of the corrosion inhibitor itself. Therefore, it is particularly important to quickly, economically, and efficiently select the best corrosion inhibitor suitable for specific operating conditions.

[0004] Traditional methods for evaluating corrosion inhibitors involve immersion testing, calculating the corrosion rate based on the mass loss of the metal sample, and then comparing the corrosion rates obtained from inhibitor-added tests and blank tests to determine the inhibition rate. A drawback of this method is its long testing cycle, typically seven days. Electrochemical testing methods effectively address this issue. This method accelerates the corrosion process, completing the test in a shorter time. The electrochemical inhibition rate is calculated using the corrosion current density measured in inhibitor-added and blank tests, which helps compare the performance of different corrosion inhibitors and determine the optimal concentration for inhibitor application.

[0005] Chinese patent publication CN112345437A discloses a method and apparatus for evaluating corrosion inhibitors at the top of atmospheric and vacuum distillation towers. This method employs a pre-filming method, where different test pieces are pre-filmed with different corrosion inhibitors. The corrosion rate is calculated based on the weight loss of the pre-filmed test pieces after corrosion, and then compared with the corrosion rate of un-filmed test pieces to determine the inhibition rate of different inhibitors. While this method can simultaneously evaluate multiple corrosion inhibitors in the same test, improving efficiency, it has drawbacks. It does not realistically simulate the actual operation of a production unit where corrosion inhibitors are added. Furthermore, immersing multiple pre-filmed test pieces in the same corrosive medium may cause cross-contamination, interfering with the objectivity and accuracy of the test.

[0006] Chinese patent publication CN114755167A discloses a device and method for rapidly and accurately evaluating the efficiency of corrosion inhibitors and analyzing corrosion rates. It employs an electrochemical method that can simultaneously test the corrosion rates of different metallic materials and can also evaluate corrosion inhibitors by adding them to the corrosive medium. This method uses a pump to add the agent into the vessel through a metal pipe. The disadvantage is that when the pressure inside the vessel is higher than atmospheric pressure, the corrosive medium may overflow into the pump or other gas lines through the injection pipe. In addition, the magnetic stirring device used at the bottom of the vessel has limited stirring force when the amount of corrosive medium is large.

[0007] Given the shortcomings of existing technologies, it is necessary to develop a dynamic evaluation method and device that can realistically simulate the operating conditions of corrosion inhibitors, is easy to operate, and has accurate and efficient testing capabilities. This will help companies improve their process corrosion protection levels and provide a guarantee for the safe and long-term operation of equipment. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and provide an electrochemical testing device, method and application for rapidly evaluating the performance of corrosion inhibitors, which can achieve accurate and efficient dynamic evaluation.

[0009] This invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides an electrochemical testing apparatus for rapidly evaluating the performance of corrosion inhibitors, comprising a reaction vessel, the reaction vessel including a vessel body and a vessel lid, the vessel body and the vessel lid being sealed together.

[0011] The reference electrode and the counter electrode are connected to the lid of the vessel via an electrode fixing bracket. A working electrode fixing shaft is installed on the lid of the vessel. The working electrode fixing shaft is connected to a working electrode at one end inside the vessel. A stirring paddle is provided on the working electrode fixing shaft and above the working electrode.

[0012] The vessel lid is also equipped with an exhaust pipe and an intake pipe. One end of the intake pipe extends into the vessel body and is located near the bottom. The other end is connected to an H2S intake branch pipe, a CO2 intake branch pipe, an N2 intake branch pipe, and a corrosion inhibitor branch pipe through a branch pipe.

[0013] A further improvement of the present invention is that:

[0014] Both the intake pipe and the exhaust pipe are equipped with shut-off valves.

[0015] A further improvement of the present invention is that:

[0016] The air inlet pipe extends into the side wall of the vessel body and has multiple small holes evenly distributed on it.

[0017] A further improvement of the present invention is that:

[0018] One end of the working electrode fixing shaft is connected to a rotary motor fixed on the vessel lid, and the other end is connected to the working electrode; and / or,

[0019] The working electrode fixing shaft is a hollow metal tube, and a signal line is installed inside the hollow metal tube. One end of the signal line is connected to the working electrode, and the other end extends out of the hollow metal tube.

[0020] A further improvement of the present invention is that:

[0021] The electrochemical testing device also includes an electrochemical workstation, wherein the working electrode, reference motor, and counter electrode are respectively connected to the corresponding terminals on the electrochemical workstation.

[0022] A further improvement of the present invention is that:

[0023] The vessel body is externally fitted with an electric heating jacket; and / or,

[0024] Thermocouples are also installed inside the vessel and are located below the liquid surface during the test.

[0025] A further improvement of the present invention is that:

[0026] The bottom of the vessel is provided with a discharge pipe, and a discharge valve is provided on the discharge pipe.

[0027] A second aspect of the present invention provides an electrochemical testing method for rapidly evaluating the performance of corrosion inhibitors, comprising:

[0028] (1) Install the working electrode, reference electrode and counter electrode on the reactor lid, add the test medium into the reactor body, seal the reactor lid and reactor body and then introduce high pressure nitrogen into the reactor body to check the airtightness of the reactor.

[0029] (2) Under the condition that the reactor is airtight, nitrogen gas is continuously introduced into the reactor to remove oxygen;

[0030] (3) Heat the vessel to the test temperature and simultaneously introduce H2S or CO2 into the vessel to the required pressure;

[0031] (4) Connect the working electrode, reference electrode and counter electrode to the corresponding terminals on the electrochemical workstation respectively;

[0032] (5) Turn on the electrochemical workstation and rotary motor, preheat, and then set the measurement parameters of the electrochemical workstation;

[0033] (6) After the natural corrosion potential of the system stabilizes, perform a potentiodynamic scan to measure the corrosion current density i of the system under blank conditions. c0 ;

[0034] (7) After the test under blank conditions is completed, the required amount of corrosion inhibitor is injected into the reactor through the corrosion inhibitor branch pipe, and the corrosion current density i of the system under the condition of adding corrosion inhibitor is measured. c1 ;

[0035] (8) The corrosion inhibition rate was calculated.

[0036] A further improvement of the present invention is that:

[0037] The corrosion inhibition rate is calculated using the following formula:

[0038]

[0039] In the formula:

[0040] η represents the electrochemical corrosion inhibition rate, in percentages.

[0041] i c0 The corrosion current density in the blank system is given in A / cm². 2 ;

[0042] i c1 The corrosion current density of the corrosion inhibitor system is expressed in A / cm². 2 .

[0043] A third aspect of the present invention is the application of the electrochemical testing apparatus for rapidly evaluating the performance of corrosion inhibitors, as described above, in evaluating the performance of corrosion inhibitors.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] In this invention, by setting a stirring paddle on the fixed shaft of the working electrode and above the working electrode, the influence of factors such as the diffusion layer can be reduced or eliminated, ensuring the accuracy of the test results. On the other hand, by adjusting the stirring speed, different medium flow rates can be simulated to achieve a dynamic evaluation method that is accurate and efficient in testing.

[0046] In this invention, shut-off valves are installed on both the inlet and outlet pipes. These valves open when ventilation is needed and close when it is not needed to prevent the corrosion inhibitor from overflowing through the outlet pipe or entering the branch pipes through the inlet pipe when the pressure inside the reactor is too high, thus ensuring the accuracy and efficiency of the test results. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of an electrochemical testing device for rapidly evaluating corrosion inhibitors in an embodiment of the present invention;

[0048] Figure 2a A schematic diagram of a stirring impeller;

[0049] Figure 2bThis is a schematic diagram of the second structure of the stirring paddle;

[0050] Figure 2c This is a schematic diagram of the third type of stirring impeller structure.

[0051] In the diagram, 1. Reactor body, 2. Reactor lid, 3. Reference electrode, 4. Counter electrode, 5. Working electrode fixing shaft, 6. Working electrode, 7. Stirring paddle, 8. Exhaust pipe, 9. Inlet pipe, 10. H2S inlet branch pipe, 11. CO2 inlet branch pipe, 12. N2 inlet branch pipe, 13. Corrosion inhibitor branch pipe, 14. Rotary motor, 15. Shut-off valve, 16. Feed valve, 17. Electrochemical workstation, 18. Electric heating mantle, 19. Thermocouple, 20. Discharge valve. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to the accompanying drawings:

[0053]

Example 1

[0054] like Figure 1 As shown, this embodiment of the invention provides an electrochemical testing apparatus for rapidly evaluating corrosion inhibitors, including a high-pressure reactor. The reactor includes a reactor body 1 and a reactor lid 2, which are sealed together.

[0055] A reference electrode 3 and a counter electrode 4 are connected to the lid 2 via an electrode fixing bracket. A working electrode fixing shaft 5 is installed on the lid 2. A working electrode 6 is connected to one end of the working electrode fixing shaft 5 located inside the body 1. A stirring paddle 7 is provided on the working electrode fixing shaft 5 and above the working electrode 6.

[0056] The vessel lid 2 is also equipped with an exhaust pipe 8 and an air inlet pipe 9. One end of the air inlet pipe 9 extends into the vessel body 1 and is located near the bottom, so that the air inlet pipe is below the liquid surface during the test. The other end is connected to the H2S air inlet branch pipe 10, CO2 air inlet branch pipe 11, N2 air inlet branch pipe 12 and corrosion inhibitor branch pipe 13 through branch pipes.

[0057] In this invention, by setting a stirring paddle 7 on the fixed shaft 5 of the working electrode and above the working electrode 6, the influence of factors such as the diffusion layer can be reduced or eliminated, ensuring the accuracy of the test results. On the other hand, by adjusting the stirring speed, different medium flow rates can be simulated to achieve a dynamic evaluation method that is accurate and efficient in testing.

[0058]

Example 2

[0059] One end of the working electrode fixing shaft 5 is connected to the rotary motor 14 fixed on the lid 2, and the other end is connected to the working electrode 6. When the rotary motor 14 rotates, it drives the working electrode fixing shaft 5 to rotate, which in turn drives the working electrode 6 to rotate.

[0060] The working electrode fixing shaft 5 is a hollow metal tube. A signal line is installed inside the hollow metal tube. One end of the signal line is connected to the working electrode 6, and the other end extends out of the hollow metal tube. An external thread is provided on the lower wall of the hollow metal tube to achieve connection with the working electrode 6.

[0061] A stirring paddle 7 is mounted on the fixed shaft 5 of the working electrode and positioned above the working electrode 6. During the test, the stirring paddle is below the liquid surface, which can reduce or eliminate the influence of factors such as the diffusion layer, ensuring the accuracy of the test results. Furthermore, different medium flow velocities can be simulated by adjusting the stirring speed, thus achieving an accurate and efficient dynamic evaluation method. The stirring paddle 7 can be... Figure 2a , Figure 2b and Figure 2c The shape can also be any other existing shape of stirring paddle, as long as it can achieve the purpose of this invention, which will not be elaborated here.

[0062] The working electrode 6 is a cylinder with a diameter of (10±0.2) mm and a height of (15±0.2) mm. An internally threaded hole is provided on the upper end face of the cylinder for connection with the working electrode fixing shaft. A working surface with an area of ​​1 cm² is provided on the lower end face. 2 More preferably, the sides of the cylinder and the inside of the internal threaded hole are coated with epoxy resin to provide insulation.

[0063]

Example 3

[0064] Both the inlet pipe 9 and the outlet pipe 8 are equipped with shut-off valves 15, which open when ventilation is needed and close when not needed, to prevent the corrosion inhibitor from overflowing through the outlet pipe 8 or entering the branch pipes through the inlet pipe 9 when the pressure inside the reactor is too high, thus ensuring the accuracy and efficiency of the test results.

[0065] Feed valves 16 are respectively installed on the H2S inlet branch pipe 10, CO2 inlet branch pipe 11, N2 inlet branch pipe 12 and corrosion inhibitor branch pipe 13.

[0066] Preferably, the side wall of the end of the air inlet pipe 9 that extends into the vessel body 1 is uniformly provided with a plurality of small holes (not shown in the figure). During the test, the part of the air inlet pipe with small holes is completely below the liquid surface. Moreover, in this invention, both gas intake and corrosion inhibitor injection are carried out through the air inlet pipe 9 into the vessel body 1, ensuring that the gas can be quickly absorbed and balanced in the corrosive medium, and the corrosion inhibitor can be quickly and evenly diffused in the corrosive medium.

[0067]

Example 4

[0068] The electrochemical testing device of the present invention also includes an electrochemical workstation 17, wherein the working electrode 6, the reference motor 3 and the counter electrode 4 are respectively connected to the corresponding terminals on the electrochemical workstation 17 via signal lines to collect data during the test.

[0069] An electric heating jacket 18 is provided on the outside of the vessel body 1. The electric heating jacket 18 is used to heat the corrosive medium during the test so that it reaches the temperature required for the test.

[0070] Thermocouple 19 is also installed inside the vessel body 1, and is located below the liquid surface during the test, for monitoring the temperature of the corrosive medium during the test.

[0071] The bottom of the vessel body 1 is equipped with a discharge pipe, and a discharge valve 20 is installed on the discharge pipe.

[0072]

Example 5

[0073] This invention also provides an electrochemical testing method for rapidly evaluating corrosion inhibitors, comprising:

[0074] (1) Install the working electrode 6, the high temperature and high pressure reference electrode 3 and the counter electrode 4 on the high temperature and high pressure reactor cover 2, add the test medium into the reactor body 1, seal the reactor cover 2, and then introduce high pressure nitrogen into the reactor body 1 to check the airtightness of the reactor.

[0075] (2) Under the condition that the reactor is airtight, nitrogen gas is continuously introduced into the reactor to remove oxygen;

[0076] (3) Use electric heating jacket 18 to heat the vessel 1 to the test temperature, and at the same time introduce H2S or CO2 or other gases and mixed gases into the vessel 1 to the required pressure. If the pressure is lower than the total pressure required for the test, add nitrogen to increase the pressure to the set pressure.

[0077] (4) Connect the working electrode 6, the reference electrode 3 and the counter electrode 4 to the corresponding terminals on the electrochemical workstation 17 respectively;

[0078] (5) Turn on the electrochemical workstation 17 and the rotary motor 14 to preheat;

[0079] (6) Set the measurement parameters of the electrochemical workstation 17: scan amplitude is Ec±150mV, scan rate is 0.166mV / s, and delay time is 6s;

[0080] (7) After the natural corrosion potential of the system stabilizes (Ec fluctuation does not exceed ±1mV within 5 min), perform a potentiodynamic scan to measure the corrosion current density i of the system under blank conditions. c0 ;

[0081] (8) After the test under blank conditions is completed, inject the required amount of corrosion inhibitor into the reactor through the corrosion inhibitor branch pipe;

[0082] (9) Repeat step (7) to complete the corrosion current density i of the system under the condition of adding corrosion inhibitor. c1 Measurement;

[0083] (10) The electrochemical corrosion inhibition rate is calculated using the following formula:

[0084]

[0085] In the formula:

[0086] η represents the electrochemical corrosion inhibition rate, in percentages.

[0087] i c0 The corrosion current density in the blank system is given in A / cm². 2 ;

[0088] i c1 The corrosion current density of the corrosion inhibitor system is expressed in A / cm². 2 .

[0089] In this invention, after completing the blank test, the required dose of corrosion inhibitor is injected into the reactor through the corrosion inhibitor branch pipe. Then, the corrosion current density of the system under the condition of adding the corrosion inhibitor is measured. This avoids interference caused by baseline drift in each blank test, resulting in higher accuracy of the measured corrosion inhibition rate. Furthermore, when selecting the optimal concentration of the corrosion inhibitor, different concentrations can be added sequentially from low to high to adjust the concentration, and the optimal concentration can be selected based on the test results.

[0090] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0091] In the description of this invention, unless otherwise stated, the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0092] The above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the technical solutions described in the specific embodiments of the present invention. Therefore, the foregoing description is only preferred and not restrictive.

Claims

1. An electrochemical testing device for rapidly evaluating the performance of corrosion inhibitors, characterized in that, Includes a reaction vessel, which includes a vessel body and a vessel lid; The reference electrode and the counter electrode are connected to the lid of the vessel via an electrode fixing bracket. A working electrode fixing shaft is installed on the lid of the vessel. The working electrode fixing shaft is connected to a working electrode at one end inside the vessel. A stirring paddle is provided on the working electrode fixing shaft and above the working electrode. The vessel lid is also equipped with an exhaust pipe and an intake pipe. One end of the intake pipe extends into the vessel body and is located near the bottom. The other end is connected to an H2S intake branch pipe, a CO2 intake branch pipe, an N2 intake branch pipe, and a corrosion inhibitor branch pipe through a branch pipe.

2. The apparatus according to claim 1, characterized in that, Both the intake pipe and the exhaust pipe are equipped with shut-off valves.

3. The apparatus according to claim 1 or 2, characterized in that, The air inlet pipe extends into the side wall of the vessel body and has multiple small holes evenly distributed on it.

4. The apparatus according to claim 1, characterized in that, One end of the working electrode fixing shaft is connected to a rotary motor fixed on the vessel lid, and the other end is connected to the working electrode; and / or, The working electrode fixing shaft is a hollow metal tube, and a signal line is installed inside the hollow metal tube. One end of the signal line is connected to the working electrode, and the other end extends out of the hollow metal tube.

5. The apparatus according to claim 1, characterized in that, The electrochemical testing device also includes an electrochemical workstation, wherein the working electrode, reference motor, and counter electrode are respectively connected to the corresponding terminals on the electrochemical workstation.

6. The apparatus according to claim 1, characterized in that, The vessel body is externally fitted with an electric heating jacket; and / or, Thermocouples are also installed inside the vessel and are located below the liquid surface during the test.

7. The apparatus according to claim 1, characterized in that, The bottom of the vessel is provided with a discharge pipe, and a discharge valve is provided on the discharge pipe.

8. An electrochemical testing method for rapidly evaluating the performance of corrosion inhibitors, characterized in that, The experiment is conducted using the electrochemical testing apparatus according to any one of claims 1-7, comprising: (1) Install the working electrode, reference electrode and counter electrode on the reactor lid, add the test medium into the reactor body, seal the reactor lid and reactor body and then introduce high pressure nitrogen into the reactor body to check the airtightness of the reactor. (2) Under the condition that the reactor is airtight, nitrogen gas is continuously introduced into the reactor to remove oxygen; (3) Heat the vessel to the test temperature and simultaneously introduce H2S or CO2 into the vessel to the required pressure; (4) Connect the working electrode, reference electrode and counter electrode to the corresponding terminals on the electrochemical workstation respectively; (5) Turn on the electrochemical workstation and rotary motor, preheat, and then set the measurement parameters of the electrochemical workstation; (6) After the natural corrosion potential of the system is stable, a potentiodynamic scan is performed to measure the corrosion current density i of the system under blank conditions c0 ; (7) After the test under blank conditions is completed, the required amount of corrosion inhibitor is injected into the reactor through the corrosion inhibitor branch pipe, and the corrosion current density i of the system under the condition of adding corrosion inhibitor is measured. c1 ; (8) The corrosion inhibition rate was calculated.

9. The method according to claim 8, characterized in that, The corrosion inhibition rate is calculated using the following formula: In the formula: η represents the electrochemical corrosion inhibition rate, in percentages. i c0 The corrosion current density in the blank system is given in A / cm². 2 ; i c1 The corrosion current density of the corrosion inhibitor system is expressed in A / cm². 2 .

10. The application of the electrochemical testing apparatus for rapidly evaluating the performance of corrosion inhibitors as described in any one of claims 1-7 in evaluating the performance of corrosion inhibitors.

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