A reducing alkali agent with a preservative effect, a preparation method and application thereof

Abstract

The present application relates to the field of water quality additive preparation, and specifically discloses a kind of alkali-reducing agent with antiseptic effect and its preparation method and application, the alkali-reducing agent comprises the following raw materials by weight: 2-3 parts of active silicon dioxide, 2-2.5 parts of corrosion and scale inhibitor, 0.8-2.5 parts of cellulose ether, 0.5-1.5 parts of ferrous sulfate, 1-1.5 parts of naphthalene sulfonate formaldehyde condensate sodium salt and 0.5-1 part of ethylenediaminetetraacetic acid.The alkali-reducing agent with antiseptic effect provided by the present application is a comprehensive performance excellent environmental protection agent for boiler, the formula is reasonable and scientific, and each component has synergistic effect, which not only effectively reduces the alkalinity of boiler water, but also plays the roles of scale prevention, corrosion prevention, steam purification and greatly reducing the blowdown amount of boiler water, and the energy saving and consumption reduction effect is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of water quality additive preparation, and specifically relates to an alkali-reducing agent with anti-corrosion properties, its preparation method, and its application. Background Technology

[0002] A steam boiler system comprises three parts: feedwater, boiler body, and steam-condensate system. After prolonged operation, severe corrosion occurs in the feedwater and steam-condensate systems. Corrosion products are introduced into the boiler, causing scaling and corrosion, posing a threat to the safe and stable operation of the boiler. Changes in the boiler water source can lead to an increase in boiler water alkalinity, especially in areas with high heat loads such as evaporator tubes. If localized overheating occurs, this area will form a concentrated alkaline zone due to the high concentration of boiler water, dissolving the protective film on the metal surface and potentially causing alkaline corrosion and stress corrosion cracking of the water-cooled wall tubes. It may also cause foaming in the boiler water, affecting steam quality. Boiler water treatment can be divided into external and internal treatment. Internal treatment mainly uses chemical agents to reduce alkalinity, adjust pH, and inhibit corrosion and scale formation in the boiler water system.

[0003] Patent application number 202010121888.X discloses a phosphorus-free composite boiler cleaning agent for low-pressure boilers and its preparation method. This invention comprises an oxygen scavenger component, a corrosion inhibitor component, a scale inhibitor component, and a pH stabilizer component, with the following weight percentages: oxygen scavenger component: 5%-20%, corrosion inhibitor component: 1%-10%, scale inhibitor component: 0.1%-10%, pH stabilizer component: 0.1%-10%, and the remainder being pure water. It is widely applicable to boilers where the makeup water is pure water, softened water, or ordinary tap water. Adding this to boiler feedwater for low-pressure steam and hot water boilers can eliminate dissolved oxygen corrosion in the feedwater and also slow down the release of scale in the boiler water. At the same time, the specific neutralizing amine component can effectively solve the corrosion problem at the condensate end, providing a one-stop water treatment solution for low-pressure boilers. It is phosphorus-free, environmentally friendly, safe and efficient. However, when various functional water treatment agents are mixed, there is still room for improvement in the synergistic effect between their components, such as the scale inhibition and alkali reduction effect. If the synergistic effect between each component can be fully utilized, the cost of boiler water treatment can be effectively reduced.

[0004] In view of this, the alkali-reducing agent with anti-corrosion properties disclosed in this invention is particularly important. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an alkalinity-reducing agent with anti-corrosion properties and its preparation method. The alkalinity-reducing agent with anti-corrosion properties provided by this invention is an environmentally friendly boiler agent with excellent comprehensive performance. Its formula is rational and scientific, with synergistic effects from its components. While effectively reducing boiler water alkalinity, it also prevents scale buildup, corrosion, purifies steam, and significantly reduces boiler blowdown, resulting in significant energy savings and reduced consumption.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The present invention provides an alkali-reducing agent with anti-corrosion properties, wherein the alkali-reducing agent comprises the following raw materials in parts by weight: 2-3 parts activated silica, 2-2.5 parts corrosion and scale inhibitor, 0.8-2.5 parts cellulose ether, 0.5-1.5 parts ferrous sulfate, 1-1.5 parts sodium naphthalenesulfonic acid formaldehyde condensate and 0.5-1 parts ethylenediaminetetraacetic acid.

[0008] In some embodiments of the present invention, the preparation steps of the activated silica are as follows:

[0009] Add 10-30 wt% inorganic alkaline solution and silicon dioxide to a reactor, stir until homogeneous, then add a coupling agent, and calcine at 120-170°C for 1-3 hours to obtain the active silicon dioxide.

[0010] Preferably, the preparation steps of the activated silica are as follows:

[0011] Add 20 wt% inorganic alkaline solution and silicon dioxide to the reactor, stir evenly, add coupling agent, and calcine at 145℃ for 2 hours to obtain the active silicon dioxide.

[0012] In some embodiments of the present invention, the mass ratio of the inorganic alkaline solution to silicon dioxide is (0.5-1):1.

[0013] Preferably, the mass ratio of the inorganic alkaline solution to silicon dioxide is 0.75:1.

[0014] Preferably, the inorganic alkaline solution is a 20 wt% sodium hydroxide solution.

[0015] In some embodiments of the present invention, the mass ratio of the coupling agent to silicon dioxide is (0.05 to 0.1):1.

[0016] Preferably, the mass ratio of the coupling agent to silica is 0.075:1.

[0017] Preferably, the coupling agent is hexadecyltrimethoxysilane.

[0018] In some embodiments of the present invention, the particle size of the silicon dioxide is 20 to 100 mesh.

[0019] This invention modifies silica with a specific particle size using a coupling agent and organically modifies its surface to increase its compatibility with the organic components in the alkali reducing agent. When added to the alkali reducing agent system, it can accelerate the reaction with inorganic alkali to form silicates. By utilizing its binding effect on impurities such as iron oxide and manganese oxide, it can prevent pipeline corrosion by forming insoluble precipitates.

[0020] In some embodiments of the present invention, the corrosion and scale inhibitor is a phosphonocarboxylic acid copolymer with a number average molecular weight of 2000 to 4000.

[0021] The applicant selected carboxylic acid polymers containing phosphonoyl groups with a number average molecular weight of 2000-4000 and added them to the alkali reduction agent system. This activated the -PO(OH)2 and -COOH groups in their molecular structure, thereby disrupting the lattice structure and normal growth model of scale particles, causing the scale particles to desorb from the metal surface. This effectively enhanced the scale inhibition and dispersing properties of the carboxylic acid polymers while improving the corrosion inhibition performance of the alkali reduction agent system.

[0022] In some embodiments of the present invention, octadecanoic acid is also added to the alkali-reducing agent.

[0023] In some embodiments of the present invention, the mass ratio of the corrosion and scale inhibitor to octadecanoic acid is 1:(0.06-0.13).

[0024] Preferably, the mass ratio of the corrosion and scale inhibitor to octadecanoic acid is 1:0.09.

[0025] The applicant reduced the surface tension of the system solution by adding a specific proportion of octadecanoic acid, which increased the dispersion stability of the system and the solubility of other components. At the same time, it was unexpectedly found that by further adjusting the mass ratio of surfactant to corrosion and scale inhibitor, the scale inhibition effect of the alkali reduction agent system was significantly improved. The possible reason is that the surfactant can promote the dissociation of the corrosion and scale inhibitor into -COOH groups to a certain extent, thus exerting an excellent synergistic scale inhibition effect. On the other hand, it also reduces the amount of corrosion and scale inhibitor added, thereby reducing water treatment costs.

[0026] Another aspect of the present invention provides a method for preparing an alkali-reducing agent with anti-corrosion properties, comprising the following steps:

[0027] The active silica, corrosion and scale inhibitor, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate, and ethylenediaminetetraacetic acid are mixed sequentially and stirred evenly to obtain the alkali reducing agent.

[0028] In another aspect, the present invention provides the application of the alkali-reducing agent in a low-pressure steam boiler.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The alkali-reducing agent with anti-corrosion function provided by the present invention is an environmentally friendly agent for boilers with excellent comprehensive performance. The formula is reasonable and scientific, and the components work together to enhance the effect. While effectively reducing the alkalinity of boiler water, it also plays a role in preventing scale, corrosion, purifying steam, and greatly reducing the amount of boiler water discharge, resulting in significant energy saving and consumption reduction.

[0031] (2) This invention modifies silica with a specific particle size by coupling agent and organically modifies its surface to increase its compatibility with the organic components in the alkali reducing agent. When it is added to the alkali reducing agent system, on the one hand, it accelerates the reaction with inorganic base to generate silicate; on the other hand, it utilizes its binding effect on impurities such as iron oxide and manganese oxide to form insoluble precipitates and thus play the role of preventing pipeline corrosion.

[0032] (3) The corrosion-resistant alkali reducing agent provided by the present invention selects a carboxylic acid polymer containing phosphonoyl groups with a number average molecular weight of 2000 to 4000 and adds it to the alkali reducing agent system to activate the function of -PO(OH)2 groups and -COOH groups in its molecular structure, thereby effectively exerting the scale inhibition and dispersing properties of the carboxylic acid polymer while improving the corrosion inhibition performance of the alkali reducing agent system.

[0033] (4) The corrosion-resistant alkali-reducing agent provided by the present invention also contains a specific proportion of octadecanoic acid, which significantly reduces the surface tension of the system solution, increases the dispersion stability of the system, and increases the solubility of other components in the alkali-reducing agent; at the same time, by further controlling the mass ratio of the preferred surfactant and the corrosion and scale inhibitor within a certain range, the surfactant promotes the dissociation of the -COOH groups of the corrosion and scale inhibitor to a certain extent, thereby exerting a better synergistic scale inhibition effect and improving the scale inhibition effect of the alkali-reducing agent system simultaneously; on the other hand, it also reduces the amount of corrosion and scale inhibitor added, thereby reducing the cost of water treatment. Detailed Implementation

[0034] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0035] Unless otherwise specified, all reagents used below are readily available from commercial companies. Specifically, the phosphonocarboxylic acid copolymer with a number-average molecular weight of 3000 was purchased from Hubei Jiufenglong Chemical Co., Ltd.; sodium naphthalenesulfonic acid formaldehyde condensate was purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.; silica with a particle size of 60 mesh was purchased from Nangong Jiuxin New Material Technology Co., Ltd.; corrosion and scale inhibitor PO-600 was purchased from Shenzhen Derunfeng Industrial Co., Ltd.; and cellulose ether was purchased from Henan Jinshuo Technology Co., Ltd.

[0036] Preparation Example 1

[0037] The preparation steps of the first active silica are as follows:

[0038] 7.5 mL of 20 wt% sodium hydroxide solution and 10 g of silicon dioxide were added to the reactor and stirred until homogeneous. Then, 0.75 g of hexadecyltrimethoxysilane was added and calcined at 145 °C for 2 h to obtain the first active silicon dioxide.

[0039] Preparation Example 2

[0040] The preparation steps for the second type of active silica are as follows:

[0041] Add 7.5 mL of 20 wt% sodium hydroxide solution and 10 g of silicon dioxide to the reactor, stir well, then add 0.5 g of hexadecyltrimethoxysilane, and calcine at 145 °C for 2 h to obtain the second active silicon dioxide.

[0042] Preparation Example 3

[0043] The preparation steps for the third type of active silica are as follows:

[0044] 7.5 mL of 20 wt% sodium hydroxide solution and 10 g of silicon dioxide were added to the reactor and stirred until homogeneous. Then, 1.1 g of hexadecyltrimethoxysilane was added and calcined at 145 °C for 2 h to obtain the third active silicon dioxide.

[0045] Example 1

[0046] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 2.5 parts of primary active silica, 2.25 parts of phosphonocarboxylic acid copolymer, 1.7 parts of cellulose ether, 1 part of ferrous sulfate, 1.25 parts of sodium naphthalenesulfonic acid formaldehyde condensate and 0.75 parts of ethylenediaminetetraacetic acid;

[0047] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0048] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate and ethylenediaminetetraacetic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0049] Example 2

[0050] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 2 parts of primary active silica, 2 parts of phosphonocarboxylic acid copolymer, 0.5 parts of cellulose ether, 0.5 parts of ferrous sulfate, 1 part of sodium salt of naphthalenesulfonic acid formaldehyde condensate and 0.5 parts of ethylenediaminetetraacetic acid;

[0051] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0052] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate and ethylenediaminetetraacetic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0053] Example 3

[0054] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 3 parts of primary active silica, 2.5 parts of phosphonocarboxylic acid copolymer, 2.5 parts of cellulose ether, 1.5 parts of ferrous sulfate, 1.5 parts of sodium naphthalenesulfonic acid formaldehyde condensate, and 1 part of ethylenediaminetetraacetic acid.

[0055] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0056] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate and ethylenediaminetetraacetic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0057] Example 4

[0058] An alkali-reducing agent with anti-corrosion properties and its preparation method are described. The specific implementation method is the same as in Example 1, except that the first active silica is replaced by an equal amount of second active silica.

[0059] Example 5

[0060] An alkali-reducing agent with anti-corrosion properties and its preparation method are described. The specific implementation method is the same as that in Example 1, except that the first active silica is replaced by an equal amount of third active silica.

[0061] Example 6

[0062] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 2.5 parts of primary active silica, 2.25 parts of phosphonocarboxylic acid copolymer, 1.7 parts of cellulose ether, 1 part of ferrous sulfate, 1.25 parts of sodium naphthalenesulfonic acid formaldehyde condensate, 0.75 parts of ethylenediaminetetraacetic acid and 0.2 parts of octadecanoic acid;

[0063] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0064] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate, ethylenediaminetetraacetic acid and octadecanoic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0065] Example 7

[0066] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 2.5 parts of primary active silica, 2.25 parts of phosphonocarboxylic acid copolymer, 1.7 parts of cellulose ether, 1 part of ferrous sulfate, 1.25 parts of sodium naphthalenesulfonic acid formaldehyde condensate, 0.75 parts of ethylenediaminetetraacetic acid and 0.11 parts of octadecanoic acid;

[0067] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0068] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate, ethylenediaminetetraacetic acid and octadecanoic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0069] Example 8

[0070] An alkali-reducing agent with anti-corrosion properties, the alkali-reducing agent comprising the following raw materials in parts by weight: 2.5 parts of primary active silica, 2.25 parts of phosphonocarboxylic acid copolymer, 1.7 parts of cellulose ether, 1 part of ferrous sulfate, 1.25 parts of sodium naphthalenesulfonic acid formaldehyde condensate, 0.75 parts of ethylenediaminetetraacetic acid and 0.34 parts of octadecanoic acid;

[0071] The preparation method of the alkali-reducing agent with anti-corrosion effect in this embodiment includes the following steps:

[0072] The first active silica, phosphonocarboxylic acid copolymer, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate, ethylenediaminetetraacetic acid and octadecanoic acid are mixed sequentially and stirred evenly to obtain an alkali-reducing agent with anti-corrosion properties.

[0073] Comparative Example 1

[0074] An alkali-reducing agent with anti-corrosion properties and its preparation method are described. The specific implementation method is the same as that in Example 6, except that the phosphonocarboxylic acid copolymer is replaced by an equal amount of corrosion and scale inhibitor PO-600.

[0075] Comparative Example 2

[0076] An alkali-reducing agent with anti-corrosion properties and its preparation method are described. The specific implementation method is the same as that in Example 6, except that the first active silica is replaced with an equal amount of silica.

[0077] Performance testing:

[0078] The alkali reducing agents prepared in the above examples and comparative examples were tested for the following properties, and the test results are shown in Table 1:

[0079] (1) Corrosion inhibition performance test: The rotating plate corrosion test method was adopted. The test water was the standard water recommended by GB18175-2000. The test piece was A3 carbon steel with a diameter of 50mm×25mm×2mm. The corrosion inhibition performance was tested: Corrosion inhibition rate (%) = (X0-X1) / X0×100%, where: X0 (mm / a) - corrosion rate of blank test piece without alkali reducing agent; X1 (mm / a) - corrosion rate of test piece with alkali reducing agent;

[0080] (2) Scale inhibition performance test: The static scale inhibition method - calcium carbonate deposition method was adopted, referring to GB / T16632-2008. The scale inhibition rate = (ρ-ρ0) / (ρ1-ρ0)×100%, where: ρ - the scale inhibition rate of the test solution after the scale inhibition test with added water treatment agent. 2+ Concentration, mg / mL; ρ0 - after the scale inhibition test of blank solution, Ca 2+ Concentration, mg / mL; ρ1 - Ca in the test solution prepared before the scale inhibition test 2+ Concentration, mg / mL.

[0081] Table 1

[0082] project Corrosion inhibition rate / % Scale inhibition rate / % Example 1 96.7 95.8 Example 2 96.3 95.5 Example 3 96.5 94.8 Example 4 94.1 93.4 Example 5 93.9 94.1 Example 6 97.8 97.1 Example 7 97.5 96.6 Example 8 97.1 96.3 Comparative Example 1 92.1 93.0 Comparative Example 2 87.5 90.2

[0083] As shown in Table 1, the alkali reducing agent prepared in Examples 1-3 of this invention is an environmentally friendly agent for boilers with excellent comprehensive performance. The formula is reasonable and scientific, and the components work synergistically to reduce the alkalinity of boiler water while playing an excellent role in corrosion inhibition and scale inhibition.

[0084] Examples 4 and 5 changed the preparation ratio of active silica. Compared with Example 1, it can be seen that the active silica prepared by the present invention has good compatibility with the organic components in the alkali reducing agent. On the one hand, it promotes the reaction of active silica with inorganic alkali to form silicates; on the other hand, the generated silicates are used to adsorb and bind impurities such as iron oxide and manganese oxide to form insoluble precipitates. The alkali reducing, corrosion prevention and scale inhibition effects are achieved simultaneously through boiler water drainage, effectively protecting the pipelines of the boiler water system.

[0085] Example 6 added octadecanoic acid in a specific mass ratio, while Examples 7 and 8 changed the mass ratio of octadecanoic acid and corrosion and scale inhibitor. Compared with Example 1, they all showed better synergistic scale inhibition effect, but the corrosion inhibition rate and scale inhibition rate were slightly lower than the specific mass ratio. This indicates that the components of the alkali-reducing agent system specifically prepared in this invention have a better synergistic scale inhibition effect, resulting in a significant improvement in corrosion and scale inhibition effect.

[0086] In Comparative Example 1, the phosphonocarboxylic acid copolymer was replaced by an equal amount of corrosion and scale inhibitor PO-600. The corrosion and scale inhibition effect of the system was not very significant. This may be because the addition of octadecanoic acid increased the dispersion stability and solubility of other components, resulting in improved performance. In particular, the corrosion and scale inhibition effect did not decrease significantly when the amount of corrosion and scale inhibitor added was reduced. This may be because the surfactant promoted the dissociation of the -COOH groups of the corrosion and scale inhibitor to a certain extent, thus exhibiting a better synergistic scale inhibition effect. This indicates that adding the surfactant can reduce the amount of corrosion and scale inhibitor added, thereby reducing water treatment costs.

[0087] In Comparative Example 2, replacing the first active silica with an equal amount of silica affected the corrosion and scale inhibition effects of the alkali reducing agent system, especially the corrosion inhibition rate, which decreased significantly. This may be due to the deterioration of its compatibility with the organic components in the alkali reducing agent, which hinders its binding effect on impurities such as iron oxide and manganese oxide, making it difficult to effectively prevent pipeline corrosion.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An alkali-reducing agent with anti-corrosion properties, characterized in that, The alkali-reducing agent comprises the following raw materials in parts by weight: 2-3 parts activated silica, 2-2.5 parts corrosion and scale inhibitor, 0.8-2.5 parts cellulose ether, 0.5-1.5 parts ferrous sulfate, 1-1.5 parts sodium naphthalenesulfonic acid formaldehyde condensate and 0.5-1 parts ethylenediaminetetraacetic acid; The preparation steps of the activated silica are as follows: Add 10-30 wt% inorganic alkaline solution and silicon dioxide to a reactor, stir evenly, then add a coupling agent, and calcine at 120-170℃ for 1-3 hours to obtain the active silicon dioxide. The coupling agent is hexadecyltrimethoxysilane; The mass ratio of the coupling agent to silica is (0.05–0.1):1; The corrosion and scale inhibitor is a phosphonoylcarboxylic acid copolymer with a number average molecular weight of 2000-4000. The alkali-reducing agent also contains octadecanoic acid; The mass ratio of the corrosion and scale inhibitor to octadecanoic acid is 1:(0.06-0.13).

2. The alkali-reducing agent with anti-corrosion properties according to claim 1, characterized in that, The mass ratio of the inorganic alkaline solution to silicon dioxide is (0.5-1):

1.

3. The alkali-reducing agent with anti-corrosion properties according to claim 1, characterized in that, The silica has a particle size of 20–100 mesh.

4. A method for preparing an alkali-reducing agent with anti-corrosion properties as described in any one of claims 1-3, characterized in that, Includes the following steps: The active silica, corrosion and scale inhibitor, cellulose ether, ferrous sulfate, sodium salt of naphthalenesulfonic acid formaldehyde condensate, ethylenediaminetetraacetic acid and octadecanoic acid are mixed sequentially and stirred evenly to obtain the alkali reducing agent.

5. The application of the alkali reducing agent according to any one of claims 1-3 or the alkali reducing agent obtained by the preparation method of claim 4 in a low-pressure steam boiler.