A method for reducing acid corrosion in a posm process

Abstract

The present application relates to the technical field of petroleum chemical industry, and particularly relates to a method for reducing acid corrosion in a POSM process, comprising the following steps: step S1, pretreatment: residual polyethylbenzene oil in an ethylbenzene unit is transported to the inlet of a heavy oil cooler of a dehydration reactor through a modified 316L stainless steel pipeline, the pipeline is subjected to internal surface passivation treatment and gradient wall thickness design, the wall thickness of a key corrosion section is 8 mm, the wall thickness of the remaining sections is 5 mm, the nominal diameter of the pipeline is DN50, the design pressure is 1.0 MPa, a double ball valve, a reverse shower valve, a check valve and a pressure transmitter are sequentially arranged on the pipeline; step S2, concentration regulation: a PTSA concentration-viscosity double-parameter detector and a thermocouple temperature sensor are arranged on the outlet pipeline of the dehydration reactor. The present application solves the problem of high-temperature acid corrosion in the POSM process, effectively prolongs the service life of equipment, effectively reduces the occurrence of pipe blockage, and is suitable for existing production lines through the measures of concentration regulation, composite neutralization, strong corrosion prevention and real-time monitoring.

Description

Technical Field

[0001] This invention relates to the field of petrochemical technology, and in particular to a method for reducing acid corrosion in the POSM process. Background Technology

[0002] In the POSM process, the dehydration reactor uses PTSA as a catalyst. After the reaction, the concentration of PTSA remaining in the heavy oil reaches 60-100 ppm, which is highly corrosive at 170-185℃. This leads to corrosion in downstream coolers and pipelines, affecting the service life of the equipment and significantly increasing maintenance costs.

[0003] The existing technology has the following problems in practical use:

[0004] Using the simple dilution method requires 5-8% of the heavy oil production as dilution medium, resulting in an increase in energy consumption of 12-15%, and the PTSA concentration is affected by fluctuations in operating conditions.

[0005] Inorganic base neutralization easily produces insoluble sulfonates, which tend to deposit at pipe bends and heat exchanger tube bundles, eventually leading to blockage.

[0006] Conventional organophosphorus corrosion inhibitors have poor oil solubility and are prone to agglomeration in high-temperature heavy oil environments, resulting in weak adhesion of the corrosion inhibitor film.

[0007] To address the above issues, we propose a method for reducing acid corrosion in the POSM process. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for reducing acid corrosion in the POSM process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for reducing acid corrosion in a POSM process includes the following steps:

[0011] Step S1, Pretreatment: The residual ethylbenzene oil in the ethylbenzene unit is transported to the inlet of the heavy oil cooler of the dehydration reactor through a modified 316L stainless steel pipeline. The pipeline adopts internal surface passivation treatment and gradient wall thickness design. The wall thickness of the critical corrosion section is 8mm, and the wall thickness of the remaining sections is 5mm. The nominal diameter of the pipeline is DN50, the design pressure is 1.0MPa, and a double ball valve, a backflow valve, a check valve and a pressure transmitter are installed on the pipeline in sequence.

[0012] Step S2, Concentration Control: A PTSA concentration-viscosity dual-parameter detector and a thermocouple temperature sensor are installed on the heavy oil outlet pipeline of the dehydration reactor. The polyethylbenzene residual oil flow rate Q2 is dynamically adjusted by the PLC control system according to an adaptive adjustment model. The model is as follows:

[0013] Q2=Q1・ρ1・(C1-C 2，target )・(μ1 / μ0) / (C 2，target ・ρ2)

[0014] Where Q1 is the heavy oil flow rate discharged from the dehydration reactor, and Q2 is the polyethylbenzene residual oil flow rate to be adjusted, with an adjustment range of 1.8-4.5m. 3 / h, ρ1 is the density of the heavy oil in the dehydration reactor, ρ2 is the density of the polyethylbenzene residual oil, ρ2=880kg / m³ 3 C1 represents the real-time concentration of PTSA in heavy oil, C 2，target The target control concentration is 50±5ppm, μ0 is the reference viscosity, μ0=90mPa・s, and μ1 is the real-time heavy oil viscosity;

[0015] Step S3, Compound Neutralization: 1.5m downstream of the mixing point, inject 50wt% triethanolamine aqueous solution and 10wt% diethanolamine aqueous solution sequentially through a two-stage metering pump and an SK-type static mixer. The molar ratio of triethanolamine to PTSA is 0.3-0.4, and the molar ratio of diethanolamine to PTSA is 0.05-0.1.

[0016] Step S4, anchoring corrosion inhibition: At 2.0m downstream of the secondary neutral point, hydrophobic modified HEDP-isooctyl ester is injected through a pulsed dual-fluid atomizing injector and SX-type static mixer II. Its molar ratio with PTSA is controlled by C1.

[0017] Step S5: Real-time monitoring: A corrosion probe and a neutral salt precipitation monitor are installed at the cooler outlet. When the corrosion rate is >0.04mm / a or salt precipitation is detected, the PLC automatically starts to adjust the dilution flow rate, neutralizing agent dosage, and corrosion inhibitor molar ratio.

[0018] In a preferred embodiment of this application, in step S1, the inner surface passivation treatment of the modified 316L stainless steel pipeline is to soak it in a mixed solution of 5% nitric acid and 2% hydrofluoric acid for 15-20 minutes, and the passivation film thickness is ≥3μm.

[0019] As a preferred technical solution of this application, in step S2, the PTSA concentration-viscosity dual-parameter detector has a PTSA detection accuracy of ±1ppm, a response time of ≤8s, a viscosity detection range of 50-200mPa・s, and an accuracy of ±2mPa・s.

[0020] When C1 > 75 ppm or μ1 > 130 mPa·s, the PLC automatically increases Q2 and triggers a first-level warning; when C1 > 80 ppm, Q2 is locked at its upper limit of 4.5 mPa·s. 3 / h and the amount of neutralizing agent added is increased by 30%.

[0021] As a preferred technical solution of this application, in step S3, the mixing uniformity of the SK-type static mixer is set to 97%; the pKa of triethanolamine is 7.8, the pKa of diethanolamine is 8.9, the solubility of the generated mixed neutral salt at 100℃ is ≥55g / L, and the decomposition rate at 150℃ for 30 days is ≤1.2%.

[0022] As a preferred technical solution of this application, in step S4, the preparation process of the hydrophobically modified HEDP-isooctyl ester includes the following steps:

[0023] (1) Raw material ratio: Hydroxyethylidene diphosphonic acid with a purity of ≥98% and isooctyl alcohol with a purity of ≥99% are mixed at a molar ratio of 1:2.4, and 0.8% of the total mass of p-toluenesulfonic acid + 0.2% of methylbenzenesulfonic acid composite catalyst are added;

[0024] (2) Esterification reaction: under nitrogen protection, the reaction was carried out at 148-152℃ and 350r / min for 5h with stirring.

[0025] (3) De-alcoholization purification: vacuum distillation at 125-130℃ with a vacuum degree of -0.095MPa;

[0026] (4) Hydrophobic modification: Add 1.5% of γ-aminopropyltriethoxysilane by mass of the raw materials and react at 80°C for 1 hour;

[0027] (5) Neutralization and purification: Add triethylamine, with a molar ratio of triethylamine to residual acid catalyst of 1.1:1, and adjust pH to 6.8-7.2.

[0028] As a preferred technical solution of this application, the core performance of the hydrophobically modified HEDP-isooctyl ester is as follows:

[0029] Oil solubility ≥35g / L at 100℃, corrosion inhibition rate ≥90% at 150℃ and 50ppm PTSA system, chelated Fe 3+ The stability constant logK≥26.5, and the corrosion inhibitor film did not peel off after 180 days of continuous operation at 180℃.

[0030] As a preferred technical solution of this application, in step S4, the atomized particle size of the pulsed dual-fluid atomizing injector is ≤40μm, the injection pressure is 0.35MPa, and the pulse frequency is 5Hz.

[0031] The mixing uniformity setting value for the SX-type static mixer II is 98%;

[0032] The molar ratio of corrosion inhibitor to PTSA is controlled as follows:

[0033] When C1 > 60 ppm, the molar ratio is 0.2;

[0034] When 40ppm < C1 ≤ 60ppm, the molar ratio is 0.15;

[0035] When C1 ≤ 40 ppm, the molar ratio is 0.1.

[0036] As a preferred technical solution of this application, in step S5, the detection accuracy of the corrosion probe is ±0.001mm / a;

[0037] The automatic control measures of PLC are as follows:

[0038] a) Increase Q2 traffic by 10%;

[0039] b. Increase the dosage of diethanolamine by 20%;

[0040] C. Increase the molar ratio of hydrophobically modified HEDP-isooctyl ester to PTSA to 0.05.

[0041] The beneficial effects of this invention are as follows:

[0042] The PTSA concentration-viscosity dual-parameter adaptive adjustment model is adopted, and the 90-day concentration standard deviation is ≤1.0ppm, which is 74.4% lower than the existing technology. At the same time, the dilution flow rate is dynamically matched, which reduces energy consumption by 25% compared with the simple dilution method and avoids heavy oil production loss.

[0043] The combined neutralization method using triethanolamine and diethanolamine produces a mixed neutralized salt with high solubility and a significantly reduced decomposition rate, effectively reducing the risk of salt deposition and blockage. The neutralization efficiency is 21.4% higher than that of single neutralization, and there is no risk of secondary corrosion.

[0044] The modified HEDP-isooctyl ester preparation process effectively improves oil solubility and corrosion inhibition rate, and significantly reduces pipeline corrosion rate.

[0045] The equipment maintenance cycle has been significantly extended, and the annual maintenance cost has been effectively reduced; the modification cost is low and it is highly compatible with existing processes, making it of great value for promotion.

[0046] This invention solves the problem of high-temperature acid corrosion in the POSM process. Through measures such as concentration control, compound neutralization, strong corrosion protection, and real-time monitoring, it effectively extends equipment life, extends maintenance cycle, reduces maintenance costs, effectively reduces pipe blockage, has low energy consumption, and is compatible with existing production lines. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0048] Example

[0049] I. Experimental Materials and Equipment

[0050] Modified 316L stainless steel pipeline: nominal diameter DN50, critical corrosion section wall thickness 8mm, other sections 5mm, inner surface passivated by immersion in 5% nitric acid + 2% hydrofluoric acid mixed solution for 18min, passivation film thickness 3.2μm;

[0051] The pipeline is equipped with a double ball valve, a backflow valve, an H71H-16C type check valve, and a Rosemount 3051 type pressure transmitter.

[0052] Testing equipment:

[0053] The SPC-8000 PTSA concentration-viscosity dual-parameter analyzer has a PTSA detection accuracy of ±1ppm and a response time of 7s; the viscosity detection range is 50-200mPa·s with an accuracy of ±2mPa·s.

[0054] PT100 thermocouple temperature sensor, measurement accuracy ±0.5℃;

[0055] Siemens S7-1500 PLC control system;

[0056] CORRATER® 600 etching probe, accuracy ±0.001mm / a;

[0057] MSS-200 Neutralization Salt Precipitation Monitor;

[0058] Chemical reagents:

[0059] 50wt% triethanolamine aqueous solution, pKa=7.8;

[0060] 10wt% diethanolamine aqueous solution, pKa=8.9;

[0061] Self-made hydrophobically modified HEDP-isooctyl ester.

[0062] Experimental steps:

[0063] Step S1: Connect the polyethylbenzene residual oil from the outlet of the ethylbenzene unit heat exchanger to the inlet of the heavy oil cooler of the dehydration reactor through a modified 316L stainless steel pipeline, and complete the pipeline pressure test. Hold the pressure at 1.5MPa for 30 minutes without leakage.

[0064] Step S2: Start the PLC control system and set C 2，target =50ppm, μ0=90mPa・s, Q2 adjustment range 1.8-4.5m 3 / h; During operation, C1 and μ1 are monitored in real time. When C1 = 81ppm, the PLC automatically adjusts Q2 to 4.5m. 3 / h, simultaneously triggering an audible and visual alarm; when C1=42ppm and μ1=85mPa・s, Q2 drops to 2.0m3 / h.

[0065] Step S3: Inject a triethanolamine aqueous solution 1.5m downstream of the mixing point using a two-stage metering pump, controlling the molar ratio of triethanolamine to PTSA to be 0.35; inject a diethanolamine aqueous solution 0.8m downstream of the first-stage neutralization point, with a molar ratio of diethanolamine to PTSA of 0.08. Mix the solutions evenly using an SK-type static mixer, achieving a mixing uniformity of 97.5%.

[0066] Step S4: At 2.0m downstream of the secondary neutralization point, hydrophobically modified HEDP-isooctyl ester is injected through a pulse-type dual-fluid atomizing injector (model WQS-50, atomized particle size 38μm, injection pressure 0.35MPa, pulse frequency 5Hz). When C1=75ppm, the molar ratio is set to 0.2; when C1=55ppm, the molar ratio is adjusted to 0.15. The mixture is then mixed by an SX-type static mixer II, with a mixing uniformity of 98.8%.

[0067] Step S5: The corrosion probe at the cooler outlet monitors the corrosion rate in real time. When the detected corrosion rate is 0.042 mm / a, the PLC automatically starts.

[0068] a. Increase Q2 traffic by 10%, from 3.2m. 3 / h increased to 3.52m 3 / h;

[0069] b. Increase the dosage of diethanolamine by 20%;

[0070] C. Increase the molar ratio of corrosion inhibitor by 0.05, from 3.2m 3 / h increased to 3.52m 3 / h;

[0071] After 30 minutes, the corrosion rate dropped to 0.037 mm / a.

[0072] Operating Results: After 18 months of continuous operation, the inlet temperature of the mixed cooler remained stable at 151-153℃, the heavy oil viscosity at 100℃ was 105-108 mPa·s, and the oil phase foaming height after 30 minutes of standing was 6-7 mm. Test Data: 90-day PTSA concentration standard deviation was 1.0 ppm, pipeline corrosion rate was 0.038 mm / a, 24-month pipeline micro-corrosion depth was 82 μm, neutralizing salt decomposition rate was 1.1%, corrosion inhibitor oil solubility was 36 g / L, and corrosion inhibition rate was 92%. The equipment operated continuously for 36 months without maintenance, showing no neutralizing salt deposition or pipeline blockage.

[0073] Comparative Example 1

[0074] Specific solution: Adopting existing technical solutions: simple dilution and conventional corrosion inhibitors;

[0075] Equipment and materials: Ordinary 316L stainless steel pipeline is used, with a fixed Q2=3.0m. 3 / h, add conventional HEDP corrosion inhibitor, the rest of the equipment is the same as in the example.

[0076] Operating procedures: Only simple dilution and corrosion inhibitor addition are retained, without dynamic concentration control, compound neutralization and interlock monitoring steps. The corrosion inhibitor is injected at a dosage of 0.2 PTSA molar ratio.

[0077] Operating results: After 9 months of continuous operation, the standard deviation of PTSA concentration was 3.9 ppm after 90 days, the pipeline corrosion rate was 0.19 mm / a, the micro-corrosion depth was 290 μm after 24 months, the heavy oil viscosity at 100℃ was 135 mPa·s, the oil solubility of the corrosion inhibitor was 19 g / L, and the corrosion inhibition rate was 56%.

[0078] The cooler tube bundle showed 12 pitting corrosions, with the largest pit depth being 0.3 mm. There was also slight scaling at the pipe bends.

[0079] Comparative Example 2

[0080] Specific solution: Use dynamic dilution, single neutralization, and unmodified corrosion inhibitor;

[0081] Equipment and materials: The modified 316L stainless steel pipeline in the example is used. Step S2 is retained. In step S3, only triethanolamine is used for neutralization with a molar ratio of 0.43. In step S4, unmodified HEDP-isooctyl ester is used. The remaining operations are the same as in the example.

[0082] Operating results: After 20 months of continuous operation, the standard deviation of PTSA concentration was 1.3 ppm after 90 days, the pipeline corrosion rate was 0.065 mm / a, the micro-corrosion depth was 105 μm after 24 months, the neutral salt decomposition rate was 1.4%, the heavy oil viscosity at 100℃ was 112 mPa·s, the oil solubility of the corrosion inhibitor was 32 g / L, and the corrosion inhibition rate was 86%. A small amount of neutral salt flocculent material with a deposition thickness of 0.1 mm was found at the cooler inlet, requiring regular online cleaning.

[0083] IV. Experimental Results and Data Tables

[0084] Data statistics table (comparison of core indicators after 18 consecutive months of operation)

[0085]

[0086] V. Results Analysis

[0087] 1. Analysis of core indicators for corrosion inhibition

[0088] PTSA concentration stability: The standard deviation of concentration in the example over 90 days was only 1.0 ppm, which is 74.4% lower than that of Comparative Example 1 and 23.1% lower than that of Comparative Example 2. The core reason is that the present invention adopts adaptive adjustment of PTSA concentration and viscosity dual parameters, which realizes that when the viscosity of heavy oil increases, the dilution flow rate is automatically increased to avoid local enrichment of PTSA, and when the viscosity is low, the flow rate is reduced to reduce energy consumption, thereby achieving concentration control and energy consumption reduction.

[0089] Corrosion rate and micro-etching depth: The corrosion rate of the example was 0.038 mm / a, which was 80% lower than that of Comparative Example 1 and 41.5% lower than that of Comparative Example 2;

[0090] The micro-etching depth after 24 months was 82 μm, far lower than that of Comparative Example 1 and Comparative Example 2. This is the result of the synergistic effect of composite neutralization and hydrophobic modified corrosion inhibitor.

[0091] a. The combination of triethanolamine and diethanolamine increases the solubility of the neutralizing salt to over 55 g / L, preventing localized corrosion caused by salt precipitation;

[0092] b. The hydrophobically modified HEDP-isooctyl ester has an oil solubility of 36 g / L, which is 89.5% higher than that of conventional corrosion inhibitors. The corrosion-inhibiting film is stable for a long time at 180℃, and the corrosion inhibition rate exceeds 92%.

[0093] 2. Process Operation Stability Analysis

[0094] Oil phase properties: The viscosity of heavy oil in Example 1 at 100℃ was 106 mPa·s, which was 21.5% lower than that of Comparative Example 1; the foaming height was 6.5 mm, which was 56.7% lower than that of Comparative Example 1. This shows that the solution of the present invention does not affect the flow characteristics of heavy oil, and avoids the increase in transportation energy consumption caused by increased viscosity, or the risk of equipment cavitation caused by foaming.

[0095] Stability of neutralized salt: In the example, the decomposition rate of neutralized salt at 150°C was 1.1%, which was 21.4% lower than that of Comparative Example 2. Moreover, no salt deposition occurred after 36 months of operation. The key is that when triethanolamine and diethanolamine are amination, the pKa of diethanolamine is higher than that of triethanolamine. The mixed salt structure generated with PTSA is more stable, which solves the problem of easy decomposition and precipitation of neutralized salt at high temperature when using triethanolamine alone.

[0096] Equipment compatibility: The embodiment uses modified pipelines with wall thickness adjustment and passivation treatment, with a wall thickness of 8mm in the key corrosion section. Combined with closed-loop joint monitoring, the maintenance cycle is extended from 9 months to more than 36 months, which is 3 times longer than the existing technology. This completely solves the industry pain point of frequent maintenance affecting production capacity when using POSM equipment.

[0097] 3. Economic Benefit Analysis

[0098] Direct cost savings: The annual maintenance cost of the example was reduced by 72% compared to Comparative Example 1 and by 35% compared to Comparative Example 2, mainly due to the extended maintenance cycle and reduced corrosion inhibitor consumption.

[0099] Indirect energy saving: The example uses dual-parameter dynamic dilution, which reduces dilution energy consumption by 25% compared to the simple dilution method, effectively achieving the goal of energy saving and emission reduction.

[0100] Overall Value: The modification cost of this invention is only 18% of the total cost of equipment replacement, but it achieves multiple benefits such as reduced corrosion rate, extended maintenance cycle, and reduced energy consumption, and has extremely strong industrial promotion value.

[0101] 4. Comparative Analysis of Key Defects in Example 2

[0102] Comparative Example 2 retained the dynamic dilution and modification pipeline, but lacked steps S3 and S4, which ultimately led to an increase in the neutralized salt decomposition rate and the appearance of salt flocculents at the cooler inlet, resulting in the need for cleaning in a shorter period of time.

[0103] In Comparative Example 2, the oil solubility and corrosion inhibition rate of the corrosion inhibitor were significantly lower than those in the Example, and the maintenance cycle was also shortened. Therefore, this effectively proves that the innovation of the present invention does not exist in isolation, but is a synergistic system composed of various links.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for reducing acid corrosion in a POSM process, characterized in that, Includes the following steps: Step S1, Pretreatment: The residual ethylbenzene oil in the ethylbenzene unit is transported to the inlet of the heavy oil cooler of the dehydration reactor through a modified 316L stainless steel pipeline. The pipeline adopts internal surface passivation treatment and gradient wall thickness design. The wall thickness of the critical corrosion section is 8mm, and the wall thickness of the remaining sections is 5mm. The nominal diameter of the pipeline is DN50, the design pressure is 1.0MPa, and a double ball valve, a backflow valve, a check valve and a pressure transmitter are installed on the pipeline in sequence. Step S2, Concentration Control: A PTSA concentration-viscosity dual-parameter detector and a thermocouple temperature sensor are installed on the heavy oil outlet pipeline of the dehydration reactor. The polyethylbenzene residual oil flow rate Q2 is dynamically adjusted by the PLC control system according to an adaptive adjustment model. The model is as follows: Q2=Q1・ρ1・(C1-C 2，target )・(μ1 / μ0) / (C 2，target ・p2) Where Q1 is the heavy oil flow rate discharged from the dehydration reactor, and Q2 is the polyethylbenzene residual oil flow rate to be adjusted, with an adjustment range of 1.8-4.5m. 3 / h, ρ1 is the density of the heavy oil in the dehydration reactor, ρ2 is the density of the polyethylbenzene residual oil, ρ2=880kg / m³ 3 C1 represents the real-time concentration of PTSA in heavy oil, C 2，target The target control concentration is 50±5ppm, μ0 is the reference viscosity, μ0=90mPa・s, and μ1 is the real-time heavy oil viscosity; Step S3, Compound Neutralization: 1.5m downstream of the mixing point, inject 50wt% triethanolamine aqueous solution and 10wt% diethanolamine aqueous solution sequentially through a two-stage metering pump and an SK-type static mixer. The molar ratio of triethanolamine to PTSA is 0.3-0.4, and the molar ratio of diethanolamine to PTSA is 0.05-0.

1. Step S4, anchoring corrosion inhibition: At 2.0m downstream of the secondary neutral point, hydrophobic modified HEDP-isooctyl ester is injected through a pulsed dual-fluid atomizing injector and SX-type static mixer II. Its molar ratio with PTSA is controlled by C1. Step S5: Real-time monitoring: A corrosion probe and a neutral salt precipitation monitor are installed at the cooler outlet. When the corrosion rate is >0.04mm / a or salt precipitation is detected, the PLC automatically starts to adjust the dilution flow rate, neutralizing agent dosage, and corrosion inhibitor molar ratio.

2. The method for reducing acid corrosion in a POSM process according to claim 1, characterized in that, In step S1, the inner surface passivation treatment of the modified 316L stainless steel pipeline is to soak it in a mixed solution of 5% nitric acid and 2% hydrofluoric acid for 15-20 minutes, and the passivation film thickness is ≥3μm.

3. The method according to claim 1, characterized in that, In step S2, the PTSA concentration-viscosity dual-parameter detector has a PTSA detection accuracy of ±1ppm and a response time of ≤8s, and a viscosity detection range of 50-200mPa・s with an accuracy of ±2mPa・s. When C1 > 75 ppm or μ1 > 130 mPa·s, the PLC automatically increases Q2 and triggers a first-level warning; when C1 > 80 ppm, Q2 is locked at its upper limit of 4.5 mPa·s. 3 / h and the amount of neutralizing agent added is increased by 30%.

4. The method for reducing acid corrosion in a POSM process according to claim 1, characterized in that, In step S3, the mixing uniformity of the SK-type static mixer is set to 97%; the pKa of triethanolamine is 7.8, and the pKa of diethanolamine is 8.

9.

5. A method for reducing acid corrosion in a POSM process according to claim 1, characterized in that, In step S4, the preparation process of the hydrophobically modified HEDP-isooctyl ester... Includes the following steps: (1) Raw material ratio: Hydroxyethylidene diphosphonic acid with a purity of ≥98% and isooctyl alcohol with a purity of ≥99% are mixed at a molar ratio of 1:2.4, and 0.8% of the total mass of p-toluenesulfonic acid + 0.2% of methylbenzenesulfonic acid composite catalyst are added; (2) Esterification reaction: under nitrogen protection, the reaction was carried out at 148-152℃ and 350r / min for 5h with stirring. (3) De-alcoholization purification: vacuum distillation at 125-130℃ with a vacuum degree of -0.095MPa; (4) Hydrophobic modification: Add 1.5% of γ-aminopropyltriethoxysilane by mass of the raw materials and react at 80°C for 1 hour; (5) Neutralization and purification: Add triethylamine, with a molar ratio of triethylamine to residual acid catalyst of 1.1:1, and adjust pH to 6.8-7.

2.

6. A method for reducing acid corrosion in a POSM process according to claim 5, characterized in that, The core properties of the hydrophobically modified HEDP-isooctyl ester are: Oil solubility ≥35g / L at 100℃, corrosion inhibition rate ≥90% in a 50ppm PTSA system at 150℃, chelated Fe 3+ The stability constant logK≥26.5, and the corrosion inhibitor film did not peel off after 180 days of continuous operation at 180℃.

7. A method for reducing acid corrosion in a POSM process according to claim 1, characterized in that, In step S4, the atomized particle size of the pulsed dual-fluid atomizing injector is ≤40μm, the injection pressure is 0.35MPa, and the pulse frequency is 5Hz. The mixing uniformity setting value for the SX-type static mixer II is 98%; The molar ratio of corrosion inhibitor to PTSA is controlled as follows: When C1 > 60 ppm, the molar ratio is 0.2; When 40ppm < C1 ≤ 60ppm, the molar ratio is 0.15; When C1 ≤ 40 ppm, the molar ratio is 0.

1.

8. A method for reducing acid corrosion in a POSM process according to claim 1, characterized in that, In step S5, the detection accuracy of the corrosion probe is ±0.001 mm / a; The automatic control measures of PLC are as follows: a. Increase Q2 traffic by 10%; b. Increase the dosage of diethanolamine by 20%; C. Increase the molar ratio of hydrophobically modified HEDP-isooctyl ester to PTSA to 0.05.

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