Liquid gel breaker for fracturing fluid and preparation method thereof

Abstract

The invention discloses a liquid gel breaker for fracturing fluid and a preparation method thereof, and belongs to the technical field of oilfield chemistry, the liquid gel breaker comprises the following raw materials by weight: 15-20 parts of an oxidant, 0.5-1 part of a complexing stabilizer, 3-5 parts of an ion equilibrium inhibitor, and 0.01-0.02 part of a strong acid. The liquid gel breaker provided by the invention is more uniformly mixed with a fracturing fluid when being added, the gel breaking effect is more thorough, the retention rate of the effective content of an oxidizing agent is higher after long-time storage, and a gel breaking experiment can be continued. The technical problems that a liquid gel breaker is poor in storage effect and cannot be subjected to gel breaking after being placed for a period of time are solved, meanwhile, the continuity of on-site addition of the gel breaker is ensured, and the problem that an existing solid gel breaker is inconvenient to use is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a liquid breaker for fracturing fluid and a preparation method thereof. Background Art

[0002] In the fracturing construction of oil and gas wells, the use of gel breakers is crucial. The main function of the gel breaker is to reduce the viscosity of the fracturing fluid after the fracturing fluid completes its task of carrying the proppant into the crack, so that it can be smoothly discharged from the ground, thereby providing a smooth channel for the flow of oil and gas. At present, oxidized solid gel breakers are widely used due to their efficient gel breaking ability.

[0003] However, as a hazardous chemical, oxidized solid breakers require special handling during storage and transportation to avoid safety risks. Especially during construction in high temperature seasons, oxidized solid breakers are piled up on the surface of the sand mixer, posing a risk of combustion. In addition, with the expansion of the scale of oil and gas well development, the amount of fracturing fluid used is huge. The traditional method of manually adding solid powder breakers is not only time-consuming and labor-intensive, but also has the problem of uneven feeding. Human factors may also affect the effect of fracturing and breaking. In order to solve the above problems, it has become a trend to liquefy oxidized solid breakers and configure them into solutions for use. However, as advanced oxides, oxidized solid breakers have active chemical properties and strong oxidizing properties, and are particularly sensitive to temperature, humidity, pH value, and transition metal ions such as iron, manganese, and copper. These factors may accelerate the decomposition of oxidized solid breakers and affect their stability and use effects.

[0004] During the water treatment process, the water may contain a small amount of transition metal ions such as Fe 2+ , Cu 2+ , Mn 2+ The oxidized solid breaker can be activated by electron transfer or redox reaction, further accelerating its decomposition. This will not only accelerate the decomposition of the oxidized solid breaker, but also consume some free radicals, reducing the efficiency of the breaker. Therefore, how to improve the stability of the oxidized solid breaker during storage, transportation and use, and reduce the decomposition caused by environmental factors and metal ions, is a key issue that needs to be solved in the current technical field. Summary of the invention

[0005] The present invention relates to a liquid breaker for fracturing fluid and a preparation method thereof, which is prepared by using an oxidant, a complex stabilizer, an ion balance inhibitor and a strong acid in a temperature range of 45°C to 110°C. When used at a temperature of 20°C to 45°C, a reducing agent is added to form the liquid breaker. The liquid breaker composition is highly efficient and stable and can be stored for a long time.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A liquid degelling agent for fracturing fluid comprises the following raw materials in parts by weight: 15-20 parts of an oxidant, 0.5-1 parts of a complex stabilizer, 3-5 parts of an ion balance inhibitor, and 0.01-0.02 parts of a strong acid.

[0008] Preferably, the oxidant includes one or more of a persulfate oxidant, a bromate oxidant, and a periodate oxidant.

[0009] Preferably, the persulfate oxidant includes one or more of sodium persulfate, potassium persulfate, and ammonium persulfate; the bromate oxidant includes one or both of sodium bromate and potassium bromate; and the periodate oxidant includes one or more of sodium periodate, potassium periodate, and barium periodate.

[0010] Preferably, the persulfate oxidant is sodium persulfate; the bromate oxidant is sodium bromate; and the periodate oxidant is one or both of sodium periodate and potassium periodate.

[0011] Preferably, the complex stabilizer includes one or more of sodium hexametaphosphate, potassium hexametaphosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium ethylenediaminetetramethylenephosphonate, heptathiodium diethylenetriaminepenta(methylenephosphonate), pentasodium diethylenetriaminepenta(methylenephosphonate), pentasodium aminotrimethylenephosphonate, and potassium aminotrimethylenephosphonate.

[0012] Preferably, the complex stabilizer is one of sodium hexametaphosphate or pentasodium diethylenetriamine penta(methylenephosphonic acid).

[0013] Preferably, the ion balance inhibitor comprises one or both of sodium sulfate or potassium sulfate.

[0014] Preferably, the ion balance inhibitor is sodium sulfate.

[0015] Preferably, the strong acid includes one of hydrochloric acid, formic acid and phosphoric acid.

[0016] Preferably, the strong acid is hydrochloric acid with a concentration of 99.8%.

[0017] The present invention also provides a method for preparing the liquid breaker, comprising the following steps:

[0018] Dissolve the oxidant in deionized water, stir until the oxidant is completely dissolved, add the ion balance inhibitor, mix evenly, slowly add the complex stabilizer, stir at 300-450rpm / min for 3-5min, stir and add strong acid to adjust the pH to 3-4 to obtain a liquid breaker.

[0019] The present invention also provides the use of the liquid breaker for fracturing fluid in fracturing fluid in oil field.

[0020] Preferably, when the temperature of the oilfield fracturing fluid is 20-45°C, 1.25-1.5 parts of reducing agent are added to the liquid breaker for the fracturing fluid, and when the temperature of the oilfield fracturing fluid is 45-110°C, no reducing agent is added.

[0021] Preferably, the reducing agent includes one or more of sodium sulfite, potassium sulfite, sodium bisulfite, and potassium bisulfite.

[0022] Preferably, the reducing agent is sodium sulfite.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] In view of the problems of poor long-term stability, easy and rapid decomposition, inability to store, transport and add materials for a long time and the like of the current oxidizing degumming agents, the present invention provides a highly efficient and stable liquid degumming agent, which solves the problem that the oxidizing solid degumming agent contacts transition metal ions after mixing with water, thereby accelerating the decomposition and consumption of free radicals, and introduces a complex stabilizer to make it chelate with the transition metal ions, slowing down the generation of anions by the oxidizing solid degumming agent in water, and introduces an ion balance inhibitor to perform ion suppression, while changing the pH value in the aqueous solution, so that the degumming performance can be exerted in the best acidic environment.

[0025] At 20℃-110℃, the liquid breaker is more evenly mixed with the fracturing fluid when added to the feed, and the debonding effect is more thorough. After long-term storage, the retention rate of the effective content of the oxidized solid breaker is high, and the debonding experiment can be continued. This solves the technical problem that the liquid breaker has poor storage effect and cannot be debonded after being placed for a period of time, while ensuring the continuity of the on-site debonding agent addition and solving the problem of the inconvenience of using the existing solid debonding agent.

[0026] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further illustrated by the following embodiments.

[0028] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0029] In the present invention, unless otherwise specified, other test materials and instruments and equipment are conventional test materials in the art and can be purchased through commercial channels.

[0030] Unless otherwise specified, the "parts" described in the present invention are all based on mass parts.

[0031] Example 1 This example provides a liquid breaker suitable for 45°C-110°C.

[0032] Dissolve 20 parts of sodium persulfate in 74 parts of deionized water, stir until the sodium persulfate crystals are completely dissolved, add 5 parts of sodium sulfate, mix evenly, slowly add 1 part of sodium hexametaphosphate, stir at 300 rpm / min for 3 minutes; add 0.01 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0033] At 70° C., the retention rates of the liquid breaker provided in Example 1 on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day were measured. The test method was as follows:

[0034] Take 10.0mL of liquid breaker solution into an iodine volumetric flask with a pipette, add 20mL of water and 4g (accurate to 0.01g) of KI according to the national standard GB / T 655-2011 "Chemical Reagent Ammonium Persulfate", shake well, place in the dark for 30min, then add 2mL of 36% acetic acid, titrate with 0.1mol / L standard sodium thiosulfate solution, add 3mL of starch indicator solution near the end point and continue to titrate until the blue color of the solution disappears, and record the volume V1 of the consumed 0.1mol / L sodium thiosulfate standard solution. Perform a blank test under the same experimental conditions and record the volume V2 of the consumed sodium thiosulfate standard solution.

[0035] The effective content is calculated using the following formula:

[0036]

[0037] Where:

[0038] n—effective content (anhydrous), %;

[0039] V1—the volume of sodium thiosulfate standard solution consumed, mL;

[0040] V2—the volume of sodium thiosulfate standard solution consumed in the blank test, mL;

[0041] c—concentration of sodium thiosulfate standard titration solution, mol / L;

[0042] M—the numerical value of the molar mass of sodium persulfate is 114.1, in grams per mole (g / mol);

[0043] m—sample mass, g;

[0044] The retention rate η of sodium persulfate was calculated by the added sodium persulfate content (m) and the remaining effective content (n).

[0045]

[0046] Where:

[0047] η—retention rate, %;

[0048] n—effective content, %;

[0049] m—content of added sodium persulfate, %;

[0050] The results are shown in Table 1.

[0051] Table 1 Liquid breaker retention rate (%)

[0052] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 1 100％ 98.79％ 96.04％ 93.83％ 89.88％

[0053] Example 2 This example provides a liquid breaker suitable for 45°C-110°C.

[0054] Dissolve 20 parts of sodium bromate in 76 parts of deionized water, stir until the sodium bromate crystals are completely dissolved, add 3 parts of sodium sulfate, mix evenly, slowly add 1 part of diethylenetriamine pentasodium methylenephosphonate, stir at 300 rpm / min for 3 minutes, add 0.02 parts of 99.8% hydrochloric acid to adjust the pH to 3, and obtain a liquid breaker.

[0055] At 70° C., the retention rates of the liquid breaker provided in Example 2 on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day were measured. The test method was as follows:

[0056] Take 25.00mL of liquid breaker solution into an iodine volumetric flask with a pipette, add 2g of potassium iodide and 5mL of hydrochloric acid solution according to the chemical industry standard "HG / T 2766-2011 Industrial Sodium Bromate", and shake well. Add water to seal the bottle, place it in a dark place for 5 minutes, add 150mL of water below 10℃, and titrate with 0.1mol / L sodium thiosulfate standard titration solution until the solution turns light yellow. Record the volume V of the consumed 0.1mol / L sodium thiosulfate standard solution, add 3mL of starch indicator solution, and continue to titrate the solution until it is colorless. Keep it for 30s to be the end point. At the same time, perform a blank test. Except for not adding the sample to the blank test solution, the types and amounts of other reagents added are the same as those of the test solution. Record the volume V0 of the consumed 0.1mol / L sodium thiosulfate standard solution.

[0057] The content of sodium bromate is calculated as the mass fraction w1 of sodium bromate (sodium bromate), and the value is expressed in %, and the formula is as follows:

[0058]

[0059] Where:

[0060] n—effective content (anhydrous), %;

[0061] V is the volume of sodium thiosulfate standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0062] V0—the volume of sodium thiosulfate standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0063] c—the numerical value of the exact concentration of the sodium thiosulfate standard titration solution, in moles per liter (mol / L);

[0064] m—the numerical value of the sample mass, in grams (g);

[0065] M—the numerical value of the molar mass of sodium bromate (1 / 6 sodium bromate), in grams per mole (g / mol) (M=25.15);

[0066] The retention rate η of sodium bromate is calculated by calculating the added sodium bromate (m) and the remaining effective content (n).

[0067]

[0068] Where:

[0069] η—retention rate, %;

[0070] n—effective content, %;

[0071] m—content of added sodium bromate, %;

[0072] The results are shown in Table 2.

[0073] Table 2 Liquid breaker retention rate (%)

[0074] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 2 100％ 98.56％ 97.37％ 94.74％ 90.13％

[0075] Example 3 This example provides a liquid breaker suitable for 45°C-110°C.

[0076] Dissolve 20 parts of sodium periodate in 74.5 parts of deionized water, stir until the sodium periodate crystals are completely dissolved, add 5 parts of sodium sulfate, mix evenly, slowly add 0.5 parts of sodium hexametaphosphate, stir at 300 rpm / min for 3 minutes; add 0.01 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0077] At 70° C., the retention rates of the liquid breaker provided in Example 3 on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day were measured. The test method is as follows:

[0078] Take 25.00mL of liquid breaker solution into an iodine volumetric flask with a pipette, add 30mL of water, 3g of potassium iodide and 5mL of hydrochloric acid solution according to the article "TS41-152-00 Sodium Periodate Test Operation Procedure", stopper, shake well, place in a dark place for 5min, add 100mL of water (not exceeding 10°C), titrate with 0.1mol / L sodium thiosulfate standard solution, record the volume V of 0.1mol / L sodium thiosulfate standard solution consumed, add 3mL of starch indicator solution when approaching the end point, and continue to titrate until the blue color disappears: At the same time, perform a blank test with the same type and amount of other reagents added as the test solution, and record the volume V0 of 0.1mol / L sodium thiosulfate standard solution consumed.

[0079]

[0080] Where:

[0081] n—effective content (anhydrous), %;

[0082] V is the volume of sodium thiosulfate standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0083] V0—the volume of sodium thiosulfate standard titration solution consumed by titrating the test solution, in milliliters (mL);

[0084] c—the numerical value of the exact concentration of the sodium thiosulfate standard titration solution, in moles per liter (mol / L);

[0085] m—the numerical value of the sample mass, in grams (g);

[0086] The retention rate η of sodium bromate was calculated by calculating the added sodium periodate (m) and the remaining effective content (n).

[0087]

[0088] Where:

[0089] η—retention rate, %;

[0090] n—effective content, %;

[0091] m—content of sodium periodate added, %;

[0092] The results are shown in Table 3.

[0093] Table 3 Liquid breaker retention rate (%)

[0094] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 3 100％ 98.84％ 97.15％ 94.90％ 88.68％

[0095] Example 4 This example provides a liquid breaker suitable for 45°C-110°C.

[0096] Dissolve 10 parts of sodium persulfate and 10 parts of sodium bromate in 75 parts of deionized water, stir until the sodium persulfate and sodium bromate are completely dissolved, add 4 parts of sodium sulfate, mix evenly, slowly add 1 part of diethylenetriamine pentasodium methylenephosphonate, stir at 300 rpm / min for 3 minutes; add 0.02 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0097] At 70°C, the method for determining the effective content of sodium persulfate and sodium bromate in Examples 1 and 2 was combined to test the retention rates of the liquid breaker on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day, respectively. The results are shown in Table 4.

[0098] Table 4 Liquid breaker retention rate (%)

[0099] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 4 100％ 98.61％ 96.89％ 94.39％ 87.11％

[0100] Example 5 This example provides a liquid breaker suitable for 45°C-110°C.

[0101] Dissolve 15 parts of sodium persulfate and 5 parts of sodium bromate in 76 parts of deionized water, stir until the sodium persulfate and sodium bromate are completely dissolved, add 3 parts of sodium sulfate, mix evenly, slowly add 1 part of diethylenetriamine pentasodium methylenephosphonate, stir at 300 rpm / min for 3 minutes; add 0.02 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0102] At 70°C, the method for determining the effective content of sodium persulfate and sodium bromate in Examples 1 and 2 was combined to test the retention rates of the liquid breaker on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day, respectively. The results are shown in Table 5.

[0103] Table 5 Liquid breaker retention rate (%)

[0104] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 5 100％ 98.53％ 94.15％ 93.56％ 87.91％

[0105] Example 6 This example provides a liquid breaker suitable for 45°C-110°C.

[0106] Dissolve 10 parts of sodium persulfate and 10 parts of sodium periodate in 76.5 parts of deionized water, stir until the sodium persulfate and sodium periodate crystals are completely dissolved, add 2.5 parts of sodium sulfate, mix evenly, slowly add 1 part of diethylenetriamine pentasodium methylenephosphonate and stir at 300 rpm / min for 3 minutes; add 0.02 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0107] At 70°C, the method for determining the effective content of sodium persulfate and sodium periodate in Examples 1 and 3 was combined to test the retention rates of the liquid breaker provided in Example 6 on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day, respectively. The results are shown in Table 6.

[0108] Table 6 Liquid breaker retention rate (%)

[0109] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 6 100％ 97.89 95.86 93.27 88.34

[0110] Example 7 This example provides a liquid breaker suitable for 20°C-45°C.

[0111] Dissolve 20 parts of sodium persulfate in 75 parts of deionized water, stir until the sodium persulfate crystals are completely dissolved, add 5 parts of sodium sulfate, mix evenly, slowly add 1 part of sodium hexametaphosphate, stir at 300 rpm / min for 3 minutes; add 0.01 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0112] At 30°C, 1.5 parts of sodium sulfite was slowly added during use, and the retention rates of the liquid breaker provided in Example 7 on the 1st day, 10th day, 20th day, 30th day and 45th day were tested in combination with the method for determining the effective content of sodium persulfate in Example 1. The results are shown in Table 7.

[0113] Table 7 Liquid breaker retention rate (%)

[0114] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 7 100％ 97.93 96.12 93.94 87.65

[0115] Example 8 This example provides a liquid breaker suitable for 20°C-45°C.

[0116] Dissolve 10 parts of sodium persulfate and 10 parts of sodium bromate in 75 parts of deionized water, stir until the sodium persulfate and sodium bromate are completely dissolved, add 5 parts of sodium sulfate, mix evenly, slowly add 1 part of sodium hexametaphosphate, stir at 300 rpm / min for 3 minutes; add 0.02 parts of 99.8% hydrochloric acid to adjust the pH to 3 to obtain a liquid breaker.

[0117] At 30°C, 1.5 parts of sodium sulfite was slowly added during use, and the method for determining the effective content of sodium persulfate and sodium periodate in Examples 1 and 3 was combined to test the retention rates of the liquid breaker provided in Example 8 on the 1st day, the 10th day, the 20th day, the 30th day, and the 45th day, respectively. The results are shown in Table 8.

[0118] Table 8 Liquid breaker retention rate (%)

[0119] Serial number Day 1 Day 10 Day 20 Day 30 Day 45 Example 8 100％ 98.26 96.47 94.14 88.48

[0120] It can be seen that the overall addition of different amounts of stabilizers, ion balance agents and strong acids can slow down the decomposition rate of sodium persulfate after dissolving in water, and form a stable complex to prevent transition metal ions from catalyzing the decomposition of sodium persulfate, sodium bromate and sodium periodate. After long-term storage, the liquid gel breaker of the present invention has a high retention rate of sodium persulfate, sodium bromate and sodium periodate, and the gel breaking experiment can be continued.

[0121] The effect of the breaker provided in the above-mentioned Examples 1-8 was verified by the following test. Test method: 100 ml of the commonly used polymer emulsion thickener fracturing fluid in oil fields was taken and placed in a breaker bottle, and 0.04% of the liquid breaker prepared in Examples 1-8 after storage for 45 days was added in sequence, and after sealing, the fracturing fluid with the liquid breaker prepared in Examples 1-6 was placed in a 70°C oven for constant temperature reaction for 12 hours, and the fracturing fluid with the liquid breaker prepared in Examples 7-8 was placed in a 30°C oven for constant temperature reaction for 12 hours. After the above reaction was completed, the viscosity of the breaker was measured, and the test results are shown in Table 9 below.

[0122] Table 9 Results of the liquid breaker test for Examples 1-8

[0123] sample Viscosity of degelling liquid mPa·s Gel breaking situation Example 1 3.421 Complete gel breaking Example 2 4.452 Complete gel breaking Example 3 3.875 Complete gel breaking Example 4 3.542 Complete gel breaking Example 5 4.678 Complete gel breaking Example 6 3.875 Complete gel breaking Example 7 3.542 Complete gel breaking Example 8 4.876 Complete gel breaking

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A liquid breaker for fracturing fluid, characterized in that: The invention comprises the following raw materials in parts by weight: 15-20 parts of an oxidant, 0.5-1 parts of a complex stabilizer, 3-5 parts of an ion balance inhibitor, and 0.01-0.02 parts of a strong acid.

2. A liquid breaker for fracturing fluid according to claim 1, characterized in that: The oxidant includes one or more of a persulfate oxidant, a bromate oxidant, and a periodate oxidant.

3. A liquid breaker for fracturing fluid according to claim 2, characterized in that: The persulfate oxidant includes one or more of sodium persulfate, potassium persulfate, and ammonium persulfate; the bromate oxidant includes one or both of sodium bromate and potassium bromate; and the periodate oxidant includes one or more of sodium periodate, potassium periodate, and barium periodate.

4. The liquid breaker for fracturing fluid according to claim 1, characterized in that: The complex stabilizer includes one or more of sodium hexametaphosphate, potassium hexametaphosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium ethylenediaminetetramethylenephosphonate, heptasodium diethylenetriaminepenta(methylenephosphonate), pentasodium diethylenetriaminepenta(methylenephosphonate), pentasodium aminotrimethylenephosphonate, and potassium aminotrimethylenephosphonate.

5. The liquid breaker for fracturing fluid according to claim 1, characterized in that: The ion balance inhibitor includes one or both of sodium sulfate and potassium sulfate.

6. The liquid breaker for fracturing fluid according to claim 1, characterized in that: The strong acid includes one of hydrochloric acid, formic acid and phosphoric acid.

7. A method for preparing a liquid breaker for fracturing fluid according to any one of claims 1 to 6, characterized in that: The following steps are involved: Dissolve the oxidant in deionized water, stir until the oxidant is completely dissolved, add the ion balance inhibitor, mix evenly, slowly add the complex stabilizer, stir at 300-450rpm / min for 3-5min, stir and add strong acid to adjust the pH to 3-4 to obtain a liquid breaker.

8. Use of the liquid breaker for fracturing fluid according to any one of claims 1 to 6 in fracturing fluid in oil fields.

9. The use according to claim 8, characterized in that: When the temperature of the oilfield fracturing fluid is 20-45°C, 1.25-1.5 parts of reducing agent are added to the liquid breaker for fracturing fluid, and when the temperature of the oilfield fracturing fluid is 45-110°C, no reducing agent is added.

10. The use according to claim 9, characterized in that: The reducing agent includes one or more of sodium sulfite, potassium sulfite, sodium bisulfite, and potassium bisulfite.

Images