Cleaning solution for stainless steel equipment for producing g4 grade solvent and use thereof

Abstract

This invention relates to a cleaning fluid for stainless steel equipment, particularly a cleaning fluid for stainless steel equipment used in the production of G4-grade solvents. The above technical solution uses only four common acids—acetic acid, oxalic acid, nitric acid, and phosphoric acid—and deionized water in a specific ratio to obtain the cleaning fluid for stainless steel equipment used in the production of G4-grade solvents. Using the cleaning fluid provided by this invention to clean stainless steel equipment before use allows soluble metal ions to dissolve sufficiently in advance, thus preventing excessive metal ion precipitation during the production, processing, storage, and use of solvents (controlling the metal ion precipitation to less than 100 ppt), ensuring that the metal ion content of the product meets the requirements and reaches the G4 grade. By using the cleaning fluid of this invention for stainless steel equipment used in the production of G4-grade solvents, production efficiency and quality can be greatly improved, while production costs and energy consumption can be reduced.

Description

Technical Field

[0001] This invention relates to a cleaning fluid for stainless steel equipment, and more particularly to a cleaning fluid for stainless steel equipment used in the production of G4 grade solvents. Background Technology

[0002] G4 grade solvents are high-purity organic solvents with low evaporation rates, characterized by low volatility, low toxicity, and low corrosiveness. Therefore, they are widely used in precision cleaning, surface treatment, and electronic chemicals. The specific composition of G4 grade solvents may vary depending on the manufacturer and the intended use, but they are typically a mixture containing various organic compounds. These compounds may include alcohols, ketones, esters, aromatic compounds, etc., but they all have high boiling points and low vapor pressures. G4 grade solvents can be used for precision cleaning and surface treatment to remove oxides, grease, and other contaminants from metal surfaces to ensure the quality and performance of electronic components and semiconductors. Therefore, G4 grade solvents play a vital role in the electronics and semiconductor manufacturing industry.

[0003] The semiconductor industry has extremely high requirements for metal ions. The concentration of metal ions in commonly used solvents generally needs to reach the ppt level. Therefore, during processing, storage, and use, the equipment used to produce solvents must have extremely low leaching of metal ions and impurity particles.

[0004] Semiconductor manufacturing often requires the use of large amounts of organic solvents for cleaning, and these solvents have particularly high requirements for the metal ions they contain, typically at the ppt level. However, some organic solvents used in semiconductors have high boiling points and are used in large quantities, such as PMA and NMP. The distillation process requires steam heating, necessitating negative pressure and high temperatures. Fluoroplastic equipment cannot meet the strength requirements, as it may detach or deform at high temperatures, limiting its use to smaller devices. Stainless steel equipment has suitable strength, but metal ions inevitably dissolve during distillation. Existing cleaning solutions often fail to effectively dissolve these soluble metal ions beforehand, resulting in excessive metal ion precipitation during production on the cleaned stainless steel equipment. This prevents the product from meeting the G4 solvent requirements of semiconductor chemicals, impacting product quality. Summary of the Invention

[0005] In view of the above problems, this application provides a cleaning solution and a method for cleaning stainless steel equipment used in the production of G4 grade solvents, in order to thoroughly clean the stainless steel distillation equipment to a clean state, so that when solvent distillation is performed, the stainless steel distillation equipment will no longer precipitate metal ions, or the precipitated metal ions will be very small, less than 100 ppt, and will not adversely affect the quality of the produced G4 grade solvent products.

[0006] To achieve the above objectives, the inventors provide a cleaning fluid for stainless steel equipment used in the production of G4 grade solvents, comprising, by mass percentage:

[0007] Acetic acid 0.0% to 6.0%;

[0008] Oxalic acid 0.0% to 6.0%;

[0009] Nitric acid 0.0% to 6.0%;

[0010] Phosphoric acid 0.0% to 6.0%;

[0011] The rest is deionized water.

[0012] The cleaning solution provided by this invention comprises acetic acid, oxalic acid, nitric acid, and phosphoric acid. Under certain mixing ratios, these components can chemically react with metal ions, thereby effectively dissolving soluble metal ions. Specifically, acetic acid, oxalic acid, nitric acid, and phosphoric acid are acidic and can undergo acid-base reactions with metal ions. These chemical reactions promote the dissolution of metal ions, thus reducing the metal ion content in the stainless steel equipment after cleaning. Furthermore, the deionized water, which constitutes a larger proportion of the cleaning solution, does not chemically react with metal ions but acts as a diluent, making the concentration of the cleaning solution more uniform and further promoting the dissolution of metal ions. Therefore, this cleaning solution can effectively dissolve soluble metal ions in advance, reducing the metal ion content in the stainless steel equipment after cleaning and improving the quality and efficiency of the production process.

[0013] Preferably, the cleaning solution for the stainless steel equipment used to produce G4 grade solvent comprises, by weight percentage:

[0014] Acetic acid 0.0% to 3.0%;

[0015] Oxalic acid 0.0% to 3.0%;

[0016] Nitric acid 0.5% to 5.0%;

[0017] Phosphoric acid 0.0% to 3.0%;

[0018] The rest is deionized water.

[0019] In a second aspect of the invention, the inventors provide a method for preparing a cleaning fluid for stainless steel equipment used in the production of G4 grade solvents, comprising the following steps:

[0020] Based on the total mass percentage of the cleaning solution used for producing G4 grade solvents in stainless steel equipment, 0.0% to 6.0% acetic acid, 0.0% to 6.0% oxalic acid, 0.0% to 6.0% nitric acid, and 0.0% to 6.0% phosphoric acid are added to deionized water.

[0021] It is evident that the preparation method of the cleaning fluid for stainless steel equipment used in the production of G4 grade solvent provided by this invention is simple and the raw materials are readily available.

[0022] Thirdly, the present invention provides a method for cleaning stainless steel equipment using the cleaning fluid for producing G4 grade solvents as described in the first aspect of the present invention, comprising the following steps:

[0023] First cleaning: Fill the stainless steel equipment with the cleaning solution for producing G4 grade solvent, let the cleaning solution stand in the stainless steel equipment and fully wet all parts of the stainless steel equipment to obtain the first cleaning solution.

[0024] Second cleaning: Detect metal ions and determine whether to continue cleaning. If the metal ion content of the first cleaning solution is >2000 ppt, replace it with a new cleaning solution for the stainless steel equipment used to produce G4 grade solvent and perform the first cleaning again. If the metal ion content of the first cleaning solution is 1000 ppt to 2000 ppt, let it stand for 3-5 hours, and then mark the cleaning solution in the stainless steel equipment as the first cleaning solution. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by more than 5%, repeat the second cleaning step. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by less than 5%, the cleaning is complete.

[0025] The method for cleaning stainless steel equipment provided by this invention has simple operation steps, convenient and accurate result judgment, and is easy to implement.

[0026] Furthermore, the stainless steel equipment includes stainless steel distillation equipment, stainless steel storage tanks, and stainless steel transport tanks. The method provided by this invention is applicable to stainless steel equipment involved in the processing, storage, and use of wet electronic chemicals in the semiconductor industry, effectively improving the product quality of organic solvents.

[0027] In a preferred embodiment of the present invention, when the stainless steel equipment is a stainless steel distillation equipment, the first cleaning step, which involves allowing the cleaning solution of the stainless steel equipment used to produce G4 grade solvent to stand in the stainless steel equipment, is changed to: filling the complete set of stainless steel distillation equipment with the cleaning solution of the stainless steel equipment used to produce G4 grade solvent and circulating it using a circulation pump.

[0028] In some preferred embodiments, a circulating pump is used to fill the stainless steel distillation unit with the cleaning fluid from the stainless steel equipment used to produce G4 grade solvents and circulate it for 3-5 hours.

[0029] Fourthly, the present invention provides a stainless steel device, which is cleaned using the method described in the third aspect of the present invention.

[0030] In a preferred embodiment, the organic solvent product produced under process conditions of temperature 30–230°C and absolute pressure 0–200 kPa contains less than 100 ppt of metal ions.

[0031] Unlike existing technologies, the above-mentioned technical solution uses only four common acids—acetic acid, oxalic acid, nitric acid, and phosphoric acid—and deionized water in a specific ratio to prepare a cleaning solution for stainless steel equipment used in the production of G4-grade solvents, filling a technological gap in cleaning solutions for G4-grade solvent stainless steel production equipment. Using the cleaning solution provided by this invention to clean stainless steel equipment before use allows soluble metal ions to dissolve fully in advance, thus preventing excessive metal ion precipitation during production, processing, storage, and use of solvents in the cleaned stainless steel equipment (controlling the metal ion precipitation to less than 100 ppt), ensuring that the metal ions in the product meet the requirements and reach the G4 grade. By using the cleaning solution of this invention for stainless steel equipment used in the production of G4-grade solvents, production efficiency and quality can be greatly improved, while reducing production costs and energy consumption. Therefore, the cleaning solution of this invention for stainless steel equipment used in the production of G4-grade solvents has broad application prospects and promotional value.

[0032] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the description and drawings, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and drawings of this application. Attached Figure Description

[0033] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of this application and other related content, and should not be considered as limitations on this application.

[0034] In the accompanying drawings of the instruction manual:

[0035] Figure 1 This invention provides a specific method for cleaning stainless steel distillation equipment using the cleaning solution provided by the present invention. Detailed Implementation

[0036] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0037] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0038] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0039] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0040] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0041] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0042] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0043] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0044] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0045] The lower the metal impurity content and the smaller the particle size of wet electronic chemicals, the more suitable they are for use in more advanced wafer fabrication processes. Therefore, the core indicator for wet electronic chemicals is "purity." To classify wet electronic chemicals according to purity, SEMI standards and national standards are typically used for grading. The SEMI standard, developed by Semiconductor Equipment and Materials International (SEMI), classifies wet electronic chemicals into five levels: G1-G5. G1 level wet electronic chemicals are suitable for processes with >1.2µm metal impurities, <1000ug / L metal impurities, and <1.0µm particle size; while G5 level wet electronic chemicals are suitable for processes with <0.09µm metal impurities, <0.01ug / L metal impurities, and even smaller particle size. This invention focuses only on the metal ion index in G4 level wet electronic chemicals, which is also the most difficult to control. Currently, considering the requirements of high temperature and high pressure, equipment for processing, storing, and distilling organic solvents for semiconductors is mostly made of stainless steel. However, stainless steel equipment often results in the leaching of metal ions, making the products unable to meet the requirements of semiconductor chemicals. Thus, the inventors explored and obtained the technical solution of this invention through production practice.

[0046] Unless otherwise specified, the acetic acid, oxalic acid, nitric acid, phosphoric acid, and other reagents used in this invention are all commercially available high-grade chemical reagents.

[0047] In this invention, unless otherwise specified, all instruments and equipment used are familiar to those skilled in the art. Unless otherwise specified, all English abbreviations refer to conventional terms for reagents or instruments familiar to those skilled in the art.

[0048] In this invention, unless otherwise specified, the metal ion content is determined using an Agilent Technologies 7900 inductively coupled plasma mass spectrometer (ICP-MS) and its standard operating procedures, which are well known to those skilled in the art.

[0049] The term "NMP" is short for N-methylpyrrolidone; the term "PMA" is short for propylene glycol methyl ether acetate.

[0050] Example 1

[0051] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 4.0% nitric acid, and 3.0% phosphoric acid, and 87% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0052] Example 2

[0053] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% oxalic acid, 6.0% nitric acid, and 3.0% phosphoric acid, and 88% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0054] Example 3

[0055] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 6.0% nitric acid, and 3.0% phosphoric acid, and 88% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0056] Example 4

[0057] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 6.0% nitric acid, and 88% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0058] Example 5

[0059] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 0.5% acetic acid, 0.5% oxalic acid, 6.0% nitric acid, and 1.0% phosphoric acid, and 92% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0060] Example 6

[0061] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 3.0% nitric acid, and 3.0% phosphoric acid, and 88% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0062] Example 7

[0063] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 5.0% nitric acid, and 3.0% phosphoric acid, and 86% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0064] Example 8

[0065] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 1.0% nitric acid, and 3.0% phosphoric acid, and 90% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0066] Example 9

[0067] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 2.0% nitric acid, and 3.0% phosphoric acid, and 89% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0068] Example 10

[0069] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 6.0% acetic acid, 1.0% oxalic acid, 3.0% nitric acid, and 1.0% phosphoric acid, and 89% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0070] Example 11

[0071] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 1.0% acetic acid, 1.0% oxalic acid, 5.0% nitric acid, and 3.0% phosphoric acid, and 90% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0072] Example 12

[0073] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 3.0% acetic acid, 3.0% oxalic acid, 0.5% nitric acid, and 3.0% phosphoric acid, and 89.5% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0074] Example 13

[0075] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 6.0% nitric acid and 2.0% acetic acid, and 92% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0076] Example 14

[0077] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 6.0% nitric acid and 2.0% oxalic acid, and 92% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0078] Example 15

[0079] A cleaning solution for stainless steel equipment used in the production of G4 grade solvents comprises, by mass percentage: 6.0% nitric acid, 2.0% phosphoric acid, and 92% deionized water. The reagents are added to the deionized water according to the above proportions and mixed thoroughly.

[0080] Example 16

[0081] For the method of cleaning stainless steel distillation equipment with cleaning fluid used for producing G4 grade solvents, please refer to [reference needed]. Figure 1 The operation process shown includes the following steps:

[0082] Step 1: After installing the stainless steel distillation equipment, fill the complete distillation equipment with the cleaning solution for producing G4 grade solvents prepared in Examples 1-15 above, and circulate it for 5 hours. Then, take a sample from the sampling port and detect the metal ions in the circulating liquid using an inductively coupled plasma mass spectrometer (ICP-MS). If the metal ion count is >2000 ppt, replace it with a new cleaning solution for producing G4 grade solvents.

[0083] Step 2: Using a new cleaning solution from the stainless steel equipment used to produce G4 grade solvent, repeat Step 1, taking a sample to test for metal ions. If the metal ion concentration is greater than 2000 ppt, repeat Step 1. If the metal ion concentration is between 1000 and 2000 ppt, continue circulating for 5 hours and then test again, determining whether the increase in metal ion concentration has increased (considering detection error, a metal ion concentration exceeding 5% is considered an increase). If there is no increase, the cleaning is complete; if the increase exceeds 5%, repeat Step 2. Repeat the above steps until the metal ion concentration no longer increases, indicating that the cleaning is complete.

[0084] Example 17

[0085] A method for cleaning stainless steel storage equipment with a cleaning solution used for producing G4 grade solvents, specifically including the following steps:

[0086] First cleaning: Fill a stainless steel storage tank with the cleaning solution for the stainless steel equipment used to produce G4 grade solvents, let it stand for 5 hours to obtain the first cleaning solution.

[0087] Second cleaning: Detect the metal ion content of the first cleaning solution. If the metal ion content of the first cleaning solution is >2000 ppt, replace it with a new cleaning solution for the stainless steel equipment used to produce G4 grade solvent and let it stand for 5 hours again. If the metal ion content of the first cleaning solution is 1000 ppt to 2000 ppt, continue to let it stand for 5 hours, take a sample to detect the metal ion content, and label the cleaning solution in the stainless steel storage tank as the first cleaning solution. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by 5% or more, repeat the second cleaning step. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by less than 5%, the cleaning is complete.

[0088] The steps for cleaning stainless steel reaction equipment using the cleaning solution provided by this invention are similar to those in Example 17.

[0089] Application Example 1

[0090] The stainless steel equipment cleaned by the method in Examples 16-17 was used to produce G4 grade organic solvent products. The organic solvent products produced under the process conditions of temperature 30-230℃ and absolute pressure 0-200kPa all had a metal ion content of less than 100ppt.

[0091] Application Example 2

[0092] The distillation equipment cleaned by the method in Examples 16-17 was used to produce G4 grade NMP. Two-tower continuous distillation was carried out, with the pressure of the first tower controlled at 20±1 kPa and the pressure of the second tower controlled at 10±1 kPa. Industrial grade NMP was used as raw material (10,000 ppt of raw material metal ions). After continuous distillation in the two towers, NMP product with metal ions less than 100 ppt was obtained on the second tower side. After further processing, other indicators also reached the G4 grade.

[0093] In summary, the cleaning solution for stainless steel equipment used in the production of G4 grade solvents provided by this invention can clean the equipment before use. The cleaning process allows soluble metal ions to dissolve in advance, so that excessive metal ions will not precipitate during the production of solvents after cleaning, ensuring that the metal ion content of the product meets the G4 grade qualification standard.

[0094] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A cleaning fluid for stainless steel equipment used in the production of G4 grade solvents, characterized in that, By weight percentage, including: Acetic acid 0.5% to 3.0%; Oxalic acid 0.5% to 3.0%; Nitric acid 0.5% to 5.0%; Phosphoric acid 1.0% to 3.0%; The rest is deionized water.

2. The method for preparing the cleaning fluid for stainless steel equipment used in the production of G4 grade solvent as described in claim 1, characterized in that, Includes the following steps: Based on the total mass percentage of the cleaning solution used for producing G4 grade solvents in stainless steel equipment, 0.5% to 3.0% acetic acid, 0.5% to 3.0% oxalic acid, 0.5% to 5.0% nitric acid, and 1.0% to 3.0% phosphoric acid are added to deionized water.

3. A method for cleaning stainless steel equipment using the cleaning solution for producing G4 grade solvents as described in claim 1, characterized in that, Includes the following steps: First cleaning: Fill the stainless steel equipment with the cleaning solution for producing G4 grade solvent, let the cleaning solution stand in the stainless steel equipment and fully wet all parts of the stainless steel equipment to obtain the first cleaning solution. Second cleaning: Detect metal ions and determine whether to continue cleaning. If the metal ion content of the first cleaning solution is >2000 ppt, replace it with a new cleaning solution for the stainless steel equipment used to produce G4 grade solvent and perform the first cleaning again. If the metal ion content of the first cleaning solution is 1000 ppt to 2000 ppt, let it stand for 3-5 hours, and then mark the cleaning solution in the stainless steel equipment as the first cleaning solution. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by more than 5%, repeat the second cleaning. If the metal ion content of the first cleaning solution exceeds the difference between the metal ion content of the first cleaning solution and the first cleaning solution by less than 5%, the cleaning is complete.

4. The method according to claim 3, characterized in that, The stainless steel equipment includes stainless steel distillation equipment, stainless steel storage tanks, and stainless steel transport tanks.

5. The method according to claim 4, characterized in that, When the stainless steel equipment is a stainless steel distillation equipment, in the first cleaning, the cleaning solution of the stainless steel equipment used to produce G4 grade solvent is filled into the complete stainless steel distillation equipment and circulated by a circulation pump.

6. The method according to claim 5, characterized in that, Use a circulating pump to circulate for 3-5 hours.

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