A composite green pickling material and its usage method

Abstract

A composite green pickling material and its usage method belong to the technical field of pickling materials. The raw materials include 5-15 wt% of organic sulfonic acid, 3-8 wt% of phosphoric acid, 1.9-9.6 wt% of pickling accelerator, and the balance of water. The organic sulfonic acid can provide a large amount of free hydrogen ions, while phosphoric acid utilizes its special ternary acid buffer structure, and phosphate ions slowly release free hydrogen ions to buffer the excessive free hydrogen ion concentration in the pickling material, which can control and stabilize the pickling speed of the pickling solution, is beneficial to controlling the pickling degree, can protect the base metal, avoid the corrosion of the base material, greatly extends the service life of the pickling material, can disperse free hydrogen ions more evenly, avoid the corrosion of the base material caused by the accumulation of hydrogen ions in the exposed area of the base material, does not contain volatile strong acids, has little corrosion to the environment, and is green and environmentally friendly.

Description

Technical Field

[0001] A composite green pickling material and its usage method belong to the technical field of pickling materials. Background Art

[0002] Before the downstream processing of hot-rolled substrates, it is necessary to remove the surface scale, also known as descaling. Currently, almost all descaling of hot-rolled substrates uses pickling processes with strong acids such as hydrochloric acid. Due to the inherent physical and chemical properties of hydrochloric acid, there are inevitably environmental and process problems such as large acid mist volatilization, severe over-corrosion of the substrate, and difficult regeneration of waste acid during its pickling descaling process. In view of this, scientific and technological workers have been conducting research on green alternative processes for hydrochloric acid pickling processes, mainly including two types: physical methods and chemical methods.

[0003] The physical method is the mechanical descaling process, and its descaling effect is not thorough, unable to meet the surface cleanliness requirements of subsequent processing processes. And the new chemical descaling process is restricted by the fact that its pickling speed is significantly inferior to that of the traditional hydrochloric acid pickling process.

[0004] In addition, among the existing pickling composition materials, it is difficult to achieve multiple reuse. After one pickling, hydrogen ions will be completely released. On the one hand, it causes serious waste of pickling solution for cleaning a small amount of substrates, which is not conducive to environmental protection. On the other hand, the pickling speed is difficult to control and the speed is uneven. A large number of hydrogen ions play the pickling role completely in a short time, which will cause severe corrosion of the substrate or uneven pickling on the surface of the substrate, resulting in low pickling quality; for some pickling composition materials that can be reused, generally weak acids other than hydrochloric acid, nitric acid or hydrofluoric acid are used. In addition to the fact that their pickling speeds are still uncontrollable and uneven, the pickling speeds of these pickling composition materials are all relatively low, and it is difficult to meet the pickling efficiency requirements of bulk substrates. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a composite green pickling material and its usage method with fast pickling speed, uniform pickling speed in each stage, low environmental corrosion impact, green environmental protection, and long service life.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a composite green pickling material, characterized in that the raw materials include 5 - 15 wt% of organic sulfonic acid, 3 - 8 wt% of phosphoric acid, 1.9 - 9.6 wt% of pickling accelerator, and the balance is water.

[0007] Organic sulfonic acids can provide a large number of free hydrogen ions, while phosphoric acid utilizes its special ternary acid buffer structure. The phosphate ions slowly release free hydrogen ions to buffer the excessive free hydrogen ion concentration in the pickling material, which can control and stabilize the pickling speed of the pickling solution. This is not only beneficial to controlling the pickling degree but also can protect the base metal, avoiding substrate corrosion. Moreover, the phosphate ions slowly release and buffer the control of free hydrogen ions, making the free hydrogen ion concentration more stable and the decline in pickling effect less, greatly extending the service life of the pickling material and enabling it to be reused repeatedly for a long time. With the combination of organic sulfonic acid and phosphoric acid, free hydrogen ions can be more evenly dispersed, avoiding substrate corrosion caused by the accumulation of hydrogen ions in the exposed areas of the substrate and further protecting the substrate. And phosphoric acid itself can also release hydrogen ions, which cooperate with the organic sulfonic acid with the above weight content to synergistically increase the efficiency, significantly improving the pickling speed and pickling efficiency, achieving the same pickling speed as inorganic strong acids while avoiding substrate corrosion caused by excessive concentration. Moreover, the composite green pickling material does not contain volatile strong acids, has little corrosion to the environment, and is green and environmentally friendly.

[0008] Preferably, it further includes 1 - 5 wt% of citric acid.

[0009] Citric acid can release free citrate ions in the pickling material. The free citrate ions have a complexing effect on iron ions, can enrich and coagulate the free iron ions pickled off, reduce the free iron ion concentration in the pickling material, thereby maintaining the pickling ability of the pickling material and further stabilizing and increasing the pickling speed. And citric acid, as an organic strong acid, can also produce complementary synergistic effects with phosphoric acid, improving the pickling ability and pickling speed.

[0010] Further preferably, the raw materials include 10 wt% of organic sulfonic acid, 3 wt% of citric acid, 5 wt% of phosphoric acid, 1.9 - 9.6 wt% of pickling accelerator, and the balance is water.

[0011] With the preferred composition and concentration combination, the pickling material has the strongest pickling ability, a relatively high pickling speed, and can also ensure the protection effect on the substrate.

[0012] Preferably, the organic sulfonic acid includes one or a mixture in any proportion of methyl sulfonic acid, aminosulfonic acid, and β - naphthalenesulfonic acid.

[0013] The combination of the preferred organic sulfonic acid and phosphoric acid has a better effect, with a stronger pickling effect, a faster and more stable pickling speed.

[0014] Preferably, the pickling accelerator includes 0.2 - 1.0 wt% of activator, 1 - 5 wt% of reducing agent, 0.5 - 3 wt% of surfactant, and 0.2 - 0.6 wt% of corrosion inhibitor.

[0015] Preferably, the pickling accelerator can appropriately increase the acidity, improve the pickling speed, reduce the pickling temperature, and inhibit corrosion to protect the substrate.

[0016] More preferably, the activator includes one or a mixture of several of chlorides, fluorides, and nitrates in any proportion.

[0017] The preferred activator can improve the pickling ability of the pickling material: chlorides, fluorides, and nitrates can release Cl - , F - or NO 3 - in the pickling material. These anions combine with free hydrogen ions in the pickling material to form a small amount of inorganic strong acid, enabling the pickling material to have stronger local descaling activity. For example, it can effectively strip refractory scale, high-valent iron oxide (inert points), etc. on the substrate surface, resulting in better pickling effect and faster speed, supplementing the limit descaling ability of organic sulfonic acid and phosphoric acid, improving the pickling effect, reducing the consumption of acid, and further extending the service life of the pickling material.

[0018] More preferably, the reducing agent includes one or a mixture of several of potassium sulfite, stannous chloride, potassium bisulfite, potassium hyposulfite, and ascorbic acid in any proportion.

[0019] The strong acid anion of the activator directly strips the inert point scale and has no reducing ability. The preferred reducing agent reduces high-valent iron oxide to easily reactive low-valent iron oxide, increasing the reaction speed.

[0020] More preferably, the surfactant includes one or a mixture of several of sodium dodecylbenzenesulfonate (AAS), sodium lauryl ether sulfate (AES), fatty alcohol polyoxyethylene ether AEO-9, alkylphenol polyoxyethylene ether (OP-10 or JFC), and coconut oil amide 6501 in any proportion.

[0021] Several preferred surfactants have excellent wetting and permeability, improving the wetting and penetration of the pickling solution on the substrate and promoting the pickling process.

[0022] More preferably, the corrosion inhibitor includes 0.1 - 0.3 wt% of corrosion inhibitor I and 0.1 - 0.3 wt% of corrosion inhibitor II;

[0023] Corrosion inhibitor I includes one or a mixture of several of hexamethylenetetramine, morpholine, thiourea, and piperazine in any proportion.

[0024] Corrosion inhibitor II includes one or a mixture of several of pyridine, non-ionic imidazoline, and imidazoline quaternary ammonium salt in any proportion.

[0025] Preferably, a binary corrosion inhibitor is used, which can effectively protect the exposed surface of the substrate and reduce substrate corrosion.

[0026] The present invention also relates to a method for using a composite green pickling material, which is characterized in that: the object to be cleaned is immersed in the above composite green pickling material at 60-80°C for 3-7 minutes.

[0027] When pickling in the above composite green pickling material, a good pickling effect can be achieved only at 60-80°C, and pickling for 3-7 minutes can fully pickle the oxide layer such as surface scale, and at the same time, over-corrosion of the substrate can be avoided.

[0028] Compared with the prior art, the beneficial effects of the present invention are: as a pickling material without volatile strong acids, it has a pickling speed and pickling effect close to those of volatile strong acids, and the pickling speed is more stable, it is easier to control the pickling degree, has less corrosion to the substrate, and has a better protection effect; it is non-volatile, and the corrosion impact on the environment can be almost ignored; it has a longer service life, can be reused repeatedly for a longer time, makes full use of free hydrogen ions, saves acid consumption, and is green and environmentally friendly. Detailed implementation manners

[0029] The following further illustrates the present invention with reference to embodiments, and Embodiment 1 is the best embodiment of the present invention.

[0030] In the following embodiments and comparative examples, the hot-rolled substrates to be pickled are obtained by cutting the same section of hot-rolled plain carbon steel, and have the same oxidation degree, that is, the side surface is completely covered with metal oxides.

[0031] Embodiment 1

[0032] A composite green pickling material, the raw materials include 10 wt% of methanesulfonic acid, 3 wt% of citric acid, 5 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt corrosion inhibitor and the balance of water.

[0033] The preparation method is carried out in the order of dissolving solids first and then adding liquids, and specifically according to the following steps:

[0034] (1) According to the raw material ratio, add citric acid and activator (sodium chloride) to water, stir and dissolve until clear to obtain solution A;

[0035] (2) Add a reducing agent (potassium sulfite) and a corrosion inhibitor I (hexamethylenetetramine) to solution A in sequence, stir and dissolve until clear to obtain solution B;

[0036] (3) While stirring, slowly add organic sulfonic acid (methylsulfonic acid) and phosphoric acid to Solution B in sequence until the solution becomes clear to obtain Solution C;

[0037] (4) While stirring, slowly add surfactant (sodium lauryl polyoxyethylene ether sulfate (AES)), corrosion inhibitor II (imidazoline quaternary ammonium salt corrosion inhibitor) to Solution C, and add a trace amount of defoamer dropwise. After the solution becomes clear, it can be discharged to obtain the composite green pickling material.

[0038] A method for using the composite green pickling material, which immerses the hot-rolled substrate with surface oxidation into the obtained composite green pickling composition, and the temperature of the composite green pickling composition is 70 °C.

[0039] Immerse and wash until there is no black-gray metal oxide residue on the surface of the substrate visually, which is regarded as the end of pickling, and the pickling time is 3 min.

[0040] Example 2

[0041] A composite green pickling material, the raw materials include 13 wt% of methylsulfonic acid, 5 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt corrosion inhibitor and the balance of water.

[0042] Other conditions are the same as those in Example 1, and the usage method is the same as that in Example 1. The final pickling time is 5 min.

[0043] Example 3

[0044] A composite green pickling material, the raw materials include 13 wt% of β-naphthalenesulfonic acid, 1 wt% of citric acid, 5 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt corrosion inhibitor and the balance of water.

[0045] Other conditions are the same as those in Example 1, and the usage method is the same as that in Example 1. The final pickling time is 4 min.

[0046] Example 4

[0047] A composite green pickling material, the raw materials include 10 wt% of methylsulfonic acid, 3 wt% of citric acid, 8 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt corrosion inhibitor and the balance of water.

[0048] Other conditions are the same as those in Example 1, and the usage method is the same as that in Example 1. The final pickling time is 3 minutes.

[0049] Example 5

[0050] A composite green pickling material, based on Example 1, sodium chloride is replaced by sodium fluoride, and other conditions are the same as those in Example 1.

[0051] The usage method is the same as that in Example 1, and the final pickling time is 3 minutes.

[0052] Example 6

[0053] A composite green pickling material, based on Example 1, potassium sulfite is replaced by 5 wt% ascorbic acid, and other conditions are the same as those in Example 1.

[0054] The usage method is the same as that in Example 1, and the final pickling time is 4 minutes.

[0055] Example 7

[0056] A composite green pickling material, based on Example 1, sodium dodecyl polyoxyethylene ether sulfate (AES) is replaced by fatty alcohol polyoxyethylene ether AEO-9, and other conditions are the same as those in Example 1.

[0057] The usage method is the same as that in Example 1, and the final pickling time is 4 minutes.

[0058] Example 8

[0059] A composite green pickling material, based on Example 1, 0.2 wt% hexamethylenetetramine and 0.2 wt% imidazoline quaternary ammonium salt inhibitor are replaced by only 0.6 wt% morpholine, and other conditions are the same as those in Example 1.

[0060] The usage method is the same as that in Example 1, and the final pickling time is 4 minutes.

[0061] Comparative Example 1

[0062] A pickling material is a 13 wt% hydrochloric acid solution.

[0063] After being formulated into an acid pickling solution, it is heated to 80 °C and used to soak and wash the hot-rolled substrate with surface oxidation until there is no black-gray metal oxide residue visually on the substrate surface, which is regarded as the completion of pickling. The pickling time is 3 minutes.

[0064] Comparative Example 2

[0065] A pickling material, comprising 17 wt% of methanesulfonic acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt inhibitor, and the balance being water.

[0066] The usage method is the same as that of Example 1, and the final pickling time is 6 minutes.

[0067] Comparative Example 3

[0068] A pickling material, comprising 10 wt% of citric acid, 8 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt inhibitor, and the balance being water.

[0069] The usage method is the same as that of Example 1, and the final pickling time is 10 minutes.

[0070] Comparative Example 4

[0071] A pickling material, comprising 18 wt% of methanesulfonic acid, 3 wt% of citric acid, 5 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt inhibitor, and the balance being water.

[0072] The usage method is the same as that of Example 1, and the final pickling time is 3 minutes.

[0073] Comparative Example 5

[0074] A pickling material, comprising 18 wt% of methanesulfonic acid, 3 wt% of citric acid, 8 wt% of phosphoric acid, 0.6 wt% of sodium chloride, 3 wt% of potassium sulfite, 2 wt% of sodium lauryl polyoxyethylene ether sulfate (AES), 0.2 wt% of hexamethylenetetramine, 0.2 wt% of imidazoline quaternary ammonium salt inhibitor, and the balance being water.

[0075] The usage method is the same as that of Example 1, and the final pickling time is 2 minutes.

[0076] Performance test

[0077] In addition to the performance test of the pickling speed (time) for the above examples and comparative examples, the weight loss rate of the substrate, the acid consumption rate, and the service life of each example and comparative example were also tested.

[0078] Substrate weight loss rate: The percentage reduction in the weight of the substrate before and after the complete removal of the scale. The calculation formula is:

[0079] 。

[0080] The weight loss rate of the substrate indicates the corrosion of the substrate by acid. When there is no residual ferrous metal oxide on the surface of the substrate after pickling, the smaller the weight loss rate of the substrate, the less the substrate is corroded.

[0081] Acid consumption rate: The free acid consumed for removing the mill scale per unit area during the first use of the pickling material is measured by chemical titration of the free acid. The acid consumption rate can reflect the pickling efficiency. The smaller the acid consumption rate, the higher the pickling efficiency.

[0082] Life test: After pickling once, for the pickling materials obtained in each example and comparative example, the pickling material of the same volume is continuously used to pickle the substrate with the same degree of oxidation until it is qualified, and this is repeated until the content of Fe 2+ and Fe 3+ reaches 110 g / L or more, and the concentration of Fe 2+ and Fe 3+ is detected by ferrous ion chemical titration, and the number of pickling uses experienced by the pickling material in total is recorded as the test result.

[0083] The final test results are shown in Table 1 below.

[0084] Table 1 Test Results

[0085] 。

[0086] According to the comparison results between Example 1 and Comparative Example 1, the composite green pickling material of the present invention can achieve the pickling speed of the hydrochloric acid type pickling material, and has a smaller substrate corrosion degree, acid consumption rate and service life (higher pickling efficiency). At the same time, the corrosion degree can prove that the overall pickling degree of the composite green pickling material obtained in Example 1 is more uniform, more inclined to metal oxides, and has a better protection effect on the substrate. The comparison between Example 1 and Comparative Examples 2 and 3 can prove that there is a certain special synergistic effect between phosphoric acid and organic sulfonic acid. Phosphoric acid buffers the free hydrogen release effect of organic sulfonic acid, which can not only appropriately increase the acidity to improve the pickling speed, greatly reduce the acid consumption rate, but also fully retain the self-characteristics of organic acid to reduce the corrosion effect on the substrate. The comparison results between Example 1 and Comparative Examples 4 and 5 can prove that simply increasing the acid content in the pickling material cannot improve the pickling speed, but will cause the collapse of the buffer synergistic system of organic sulfonic acid and phosphoric acid, the acid consumption rate will rise rapidly, and then cause excessive corrosion of the substrate.

[0087] From the comparison results between Example 2 and Example 1, it can be seen that the addition of citric acid can maintain the concentration of free ferrous ions during the pickling process, and then cooperate with the ternary acid buffer structure of phosphoric acid to stabilize the concentration of free hydrogen ions in the pickling material, making the concentration of free hydrogen ions in the whole pickling process more stable, ensuring the pickling speed, and having a longer service life.

[0088] As described above, it is only the preferred embodiment of the present invention, and it is not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still belong to the protection scope of the technical solution of the present invention.

Claims

1. A composite green pickling material, characterized in that: The raw materials include 10wt% of organic sulfonic acid, 3wt% of citric acid, 5wt% of phosphoric acid, 1.9-9.6wt% of pickling accelerator and the balance of water; The pickling accelerator includes 0.2~1.0wt% of activator, 1~5wt% of reducing agent, 0.5~3wt% of surfactant and 0.2~0.6wt% of corrosion inhibitor; The surfactants include sodium dodecylbenzene sulfonate, sodium sulfate of fatty alcohol polyoxyethylene ether, , alkylphenol polyoxyethylene ether and coconut oil amide 6501, or a mixture of any proportions thereof; The corrosion inhibitor comprises 0.1-0.3wt% of corrosion inhibitor I and 0.1-0.3wt% of corrosion inhibitor II; The corrosion inhibitor I comprises one or a mixture of any proportion of hexamethylenetetramine, morpholine, thiourea and piperazine; The corrosion inhibitor II comprises one or a mixture of any proportion of pyridine, nonionic imidazoline and imidazoline quaternary ammonium salt.

2. The composite green pickling material according to claim 1, characterized in that: The organic sulfonic acid includes one or a mixture of any proportion of methanesulfonic acid, aminosulfonic acid and beta-naphthalenesulfonic acid.

3. The composite green pickling material according to claim 1, characterized in that: The activator comprises one or a mixture of any proportion of chloride salt, fluoride salt and nitrate salt.

4. The composite green pickling material according to claim 1, characterized in that: The reducing agent comprises one or a mixture of any proportion of potassium sulfite, stannous chloride, potassium hydrogen sulfite, potassium hyposulfite and ascorbic acid.

5. A method for using the composite green pickling material according to any one of claims 1 to 4, characterized in that: The object to be cleaned is immersed in the composite green pickling material at 60-80° C. for 3-7 minutes.