Phenolic synthetic tanning agent without bisphenol substance as well as preparation method and application of phenolic synthetic tanning agent

Abstract

The invention discloses a bisphenol-substance-free phenolic synthetic tanning agent as well as a preparation method and application thereof, and relates to the technical field of tanning. According to the phenolic synthetic tanning agent, at least one of the R group and the X group is selected from an amide structure containing a sulfonic acid group, so that the hydrophilicity and the tanning effect of the synthetic tanning agent are better, substances such as bisphenol S and bisphenol F which have risks to the environment and health are not contained, and the tanning agent is green, environmentally friendly, safe, healthy and suitable for industrial production. And the tanned leather product has better softness, fullness and light resistance, and has better application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of tanning technology, in particular to a phenolic synthetic tanning agent without bisphenol substances, a preparation method and application thereof. BACKGROUND

[0002] Tanning agents are a class of chemicals that can chemically and physically bind to collagen (mainly derived from rawhide or leather), making its structure stable, thus giving it the key characteristics of becoming useful leather. The process of reacting with rawhide to transform it into leather is called preliminary tanning, which is the most core and foundation process in leather manufacturing. The process of re-tanning the preliminary tanned leather to improve its performance is called re-tanning. Without tanning, rawhide will dry and harden, and be easily damaged by water, and cannot become comfortable, beautiful and durable leather.

[0003] Synthetic tanning agents using phenol as a starting material are key materials in the leather manufacturing process, which can give leather excellent properties such as softness, fullness and light resistance. Since its inception a century ago, synthetic tanning agents have evolved with the development of tanning technology, from the first phenolic synthetic tanning agent to the second generation product with urea co-condensation, and then to the more light-resistant sulfone synthetic tanning agent, with gradually improved tanning performance.

[0004] However, the water solubility of synthetic tanning agents usually depends on the phenol sulfonic acid or naphthalene sulfonic acid groups introduced by sulfonation, which involves high-temperature concentrated sulfuric acid / fuming sulfuric acid sulfonation, a dangerous process that needs to be closely monitored. In addition, the problem of residual phenolic monomers (such as phenol, bisphenol S and bisphenol F, etc.) in synthetic tanning agents is increasingly prominent. These residues not only involve health risks, but also can harm the environment. Currently, the residual amount of bisphenol S in sulfone synthetic tanning agents on the market is as high as 1-6%, and the content of free phenol, bisphenol F and bisphenol S in phenolic synthetic tanning agents also varies greatly, with some values far exceeding the regulatory proposal (such as the EU REACH proposal limiting bisphenol to 200 ppm). These residual phenolic monomers are attracting widespread attention in the global leather industry, and regulatory agencies are discussing stricter limit standards. Therefore, although the preparation method of traditional synthetic tanning agents is economical and practical, it has obvious defects in environmental and health risks, and new technical means are urgently needed to reduce or eliminate these potential risks.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a phenolic synthetic tanning agent without bisphenol substances, a preparation method and application thereof.

[0007] The present application is realized as follows: In a first aspect, the present application provides a phenolic synthetic tanning agent without bisphenol substances, comprising a structure as shown in formula (I): Formula (I).

[0008] wherein R is selected from or or .

[0009] X is selected from -H or .

[0010] M is selected from any one of H, Na or NH4.

[0011] n is an integer greater than or equal to 2.

[0012] and at least one of the R group and the X group is selected from an amide structure containing a sulfonic acid group.

[0013] In a second aspect, the present application provides a preparation method of the phenolic synthetic tanning agent according to any one of the preceding embodiments, comprising: reacting an amide compound containing a carbon-carbon double bond with a sulfite to obtain an intermediate; mixing the intermediate with a phenolic compound; adding formaldehyde under a first acidic environment to perform a polycondensation reaction; and adjusting the reaction system to a second acidic environment after the reaction is completed.

[0014] The pH of the first acidic environment is less than 2, and the pH of the second acidic environment is 3-5.

[0015] In a third aspect, the present application provides an application of the phenolic synthetic tanning agent according to any one of the preceding embodiments or prepared by the preparation method according to any one of the preceding embodiments in leather tanning.

[0016] The present application has the following beneficial effects: The present application provides a phenolic synthetic tanning agent without bisphenol substances, a preparation method and an application thereof. The phenolic synthetic tanning agent provided by the present application does not contain bisphenol S and bisphenol F and other substances that are harmful to the environment and health. The tanning agent is green, safe and healthy. The leather product obtained by tanning has good softness, fullness and light resistance, and has good application value. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be clearly and completely described below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0018] The features and performances of the present application are further described in detail below in combination with embodiments.

[0019] In a first aspect, the present application provides a phenolic synthetic tanning agent without bisphenol substances, comprising a structure as shown in formula (I): Formula (I).

[0020] wherein R is selected from or or .

[0021] X is selected from -H or .

[0022] M is selected from any one of H, Na or NH4.

[0023] n is an integer greater than or equal to 2.

[0024] and at least one of the R group and the X group is selected from an amide structure containing a sulfonic acid group.

[0025] By using the phenolic synthetic tanning agent having the above structure, the water solubility and application performance characteristics are comparable to those of traditional phenolic synthetic tanning agents, the high-temperature sulfonation process using phenol is not used, the synthesis conditions are more moderate, the biggest benefit is to avoid the generation of substances such as bisphenol S and bisphenol F which are harmful to the environment and health, the tanning agent is green and environmentally friendly, safe and healthy, and the leather products obtained by tanning have better softness, fullness and light resistance, and have better application value.

[0026] In an optional embodiment, the theoretical mass fraction of the amide structure containing a sulfonic acid group in the structure of formula (I) is greater than or equal to 40%.

[0027] Preferably, the theoretical mass fraction of the amide structure containing a sulfonic acid group in the structure of formula (I) is 40-60%; more preferably 50-60%.

[0028] Using the amide intermediate containing a sulfonic acid group instead of the traditional phenol sulfonic acid to synthesize the phenolic synthetic tanning agent avoids the introduction of bisphenol S from the source. By controlling the content of the amide intermediate containing a sulfonic acid group, the content of bisphenol F in the synthetic tanning agent can be reduced. When the content of the amide intermediate containing a sulfonic acid group in the structure of formula (I) is 40-60%, the content of bisphenol F in the synthetic tanning agent decreases with the increase of the amount of the intermediate until it is difficult to detect; when the content of the amide intermediate containing a sulfonic acid group in the structure of formula (I) is 50-60%, the contents of bisphenol S and bisphenol F in the synthetic tanning agent are both difficult to detect.

[0029] For example, the theoretical mass fraction of the amide structure containing a sulfonic acid group in the structure of formula (I) is any one of 40%, 45%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60% or a range value composed of any two of them.

[0030] It should be noted that the above amide structure containing a sulfonic acid group can be that the R group in the structure of formula (I) is selected from and / or, the X group is selected from .

[0031] Both of the above two structures contain amide group and sulfonic acid group, which can provide excellent tanning properties for the synthetic tanning agent provided by the present application.

[0032] In an optional embodiment, the synthetic tanning agent comprises at least one of the structures as shown in formula (II)~formula (IV): Formula (II); Formula (III); Formula (IV).

[0033] It should be noted that the synthetic tanning agent prepared by the preparation method provided by the present application contains at least one of the structures as shown in formula (II)~formula (IV).

[0034] In a second aspect, the present application provides a preparation method of the phenolic synthetic tanning agent according to any one of the preceding embodiments, comprising the following steps: reacting an amide compound containing carbon-carbon double bond with sulfite to obtain an intermediate, mixing the intermediate with a phenolic compound, adding formaldehyde in a first acidic environment to perform polycondensation reaction, and adjusting the reaction system to a second acidic environment after the reaction is completed.

[0035] The pH of the first acidic environment is less than 2, and the pH of the second acidic environment is 3~5.

[0036] It should be noted that the intermediate is a hydrophilic amide intermediate containing sulfonic acid group, and in the reaction process of the intermediate, the phenolic compound and the formaldehyde, the hydrophilic amide intermediate containing sulfonic acid group is connected to the phenol, i.e. the amide structure containing sulfonic acid group in formula (I) is formed.

[0037] The preparation method provided by the present application replaces the existing phenolic sulfonic acid hydrophilic intermediate obtained by high-temperature sulfonation of phenol with concentrated sulfuric acid by preparing a hydrophilic amide intermediate containing sulfonic acid group, which directly avoids the generation of bisphenol S in the reaction process of the intermediate, and the use amount of the hydrophilic amide intermediate containing sulfonic acid group can also be controlled to avoid the generation of bisphenol F; the intermediate provided by the present application has mild reaction conditions and safe reaction process, and does not need to use phenol sulfonation process, so that the preparation process is more mild, safe and economical, and the operation is simple.

[0038] In some embodiments of the present application, the present application provides a preparation method of a phenolic synthetic tanning agent without bisphenol substance, comprising the following steps: S01, synthesizing an intermediate (a hydrophilic amide intermediate containing sulfonic acid group) Reacting an amide compound containing carbon-carbon double bond with sulfite to obtain an intermediate.

[0039] In an optional embodiment, the ratio of the molar amount of the carbon-carbon double bond in the amide compound containing a carbon-carbon double bond to the molar amount of the bisulfite in the sulfite is 1: (1~1.05), for example, can be any one of (1:1.00), (1:1.01), (1:1.02), (1:1.03), (1:1.04) or (1:1.05) or a range consisting of any two of them.

[0040] Preferably, the amide compound containing a carbon-carbon double bond includes acrylamide or maleamic acid derivative; the sulfite includes at least one of sodium metabisulfite, sodium sulfite and sodium bisulfite.

[0041] Preferably, the maleamic acid derivative can be prepared by reacting concentrated ammonia with maleic anhydride, for example. The maleamic acid (HOOC-CH=CH-CONH2) obtained by reacting concentrated ammonia with maleic anhydride retains a double bond in its structure, so that the maleamic acid derivative can react with the sulfite to obtain a hydrophilic amide intermediate containing a sulfonic acid group.

[0042] Preferably, the reaction temperature of the amide compound containing a carbon-carbon double bond and the sulfite is 30~60℃, and the reaction time is 2~4h.

[0043] The reason for introducing the hydrophilic amide intermediate containing a sulfonic acid group in the present application is that the traditional preparation method of synthetic tanning agent usually uses phenol and concentrated sulfuric acid to be sulfonated at 100~110℃ to generate phenol sulfonic acid, which is then copolycondensed with urea and formaldehyde. This is the preparation method that has been followed since the invention of phenolic synthetic tanning agent, and it is the most commonly used and most economical preparation method. However, with the improvement of people's environmental awareness, during the high-temperature reaction of phenol and concentrated sulfuric acid in the traditional preparation method, a certain amount of dihydroxy diphenyl sulfone (commonly known as bisphenol S) is generated. A small part of bisphenol S is polycondensed into the resin skeleton structure, and most of it remains in the final product in the form of monomer.

[0044] With the research finding that bisphenol S, similar to bisphenol A, may interfere with human hormones and be harmful to health, it has been restricted for use in many countries. In addition, the high-temperature sulfonation process of phenol and concentrated sulfuric acid in the traditional synthesis method is very dangerous.

[0045] The present application uses the reaction of the amide compound containing a carbon-carbon double bond and the sulfite, which is carried out at normal pressure and at a lower temperature (30~60℃) than the traditional method, and the reaction conditions are milder. It does not require high temperature and high pressure, nor does it use concentrated sulfuric acid. The reaction process is very safe. The method for preparing the intermediate in the present application bypasses the traditional dangerous process and avoids the generation of bisphenol S, providing a new type of intermediate with better tanning performance and water solubility. It provides a new solution for the long-term green development of leather tanning.

[0046] S02, preparing the synthetic tanning agent The intermediate obtained in S01 is mixed with a phenolic compound, and a polycondensation reaction is performed by adding formaldehyde in a first acidic environment. After the reaction is completed, the reaction system is adjusted to a second acidic environment.

[0047] The pH of the first acidic environment is less than 2, and the pH of the second acidic environment is 3-5.

[0048] After the intermediate is mixed with the phenolic compound, the pH of the reaction system is controlled to be less than 2, which is conducive to the smooth progress of the subsequent reaction. After the formaldehyde is added, the small molecules are polycondensed to form a larger network structure, i.e., the core skeleton of the synthetic tanning agent.

[0049] In an optional embodiment, the first acidic environment is adjusted by adding an acid solution, which includes any one of a sulfuric acid solution with a mass concentration less than 55% and a concentrated hydrochloric acid solution with a mass concentration less than 36.5%. The present application does not need to use an acid solution with a high concentration, so the reaction process is safer, the reaction conditions are mild, and there are fewer by-products.

[0050] In addition, the second acidic environment is adjusted by adding a base solution, which includes any one of a NaOH solution and an industrial ammonia water solution with a mass concentration of 20-25%.

[0051] Preferably, in order to avoid the generation of by-products in the synthetic tanning agent, after the polycondensation reaction is completed, the temperature of the reaction system is reduced to 45-50°C, and then the base solution is added.

[0052] In an optional embodiment, the molar ratio of the intermediate to the phenolic compound is (0.5-1.5):(1.0-2.5), which can be any one of (0.5:2.5), (1.0:2.0), (1.5:1.5), or (1.5:1.0) or a range composed of any two of the ratios.

[0053] Preferably, the phenolic compound includes at least one of phenol, alkyl phenol, salicylic acid, or p-hydroxybenzoic acid. The alkyl phenol includes methyl phenol and / or ethyl phenol. The phenolic compound is the main raw material for the synthetic tanning agent, which is used to provide the ability to bind with leather and optimize the tanning effect.

[0054] In an optional embodiment, the molar ratio of formaldehyde to the intermediate is (0.5-1.5):(1.0-2.5), which can be any one of (0.5:2.5), (1.0:2.0), (1.5:1.5), or (1.5:1.0) or a range composed of any two of the ratios.

[0055] Preferably, the system is heated to 50-60°C before the formaldehyde solution is added, and then the polycondensation reaction is performed.

[0056] Preferably, the reaction temperature of the polycondensation reaction is 70-90℃, and the reaction time is 3-4h.

[0057] Preferably, the concentration of formaldehyde in the formaldehyde solution is 35-40%, for example, it can be any one of 35%, 36%, 37%, 38%, 39% or 40% or a range value composed of any two of them. Controlling the formaldehyde concentration in the above range is beneficial to control the progress of the polycondensation reaction, and further control the structure of the synthetic tanning agent.

[0058] In the traditional synthesis process, during the polycondensation of formaldehyde, two phenol molecules are connected by a -CH2- group, resulting in the generation of by-products such as bisphenol F, which is caused by the high activity of the raw materials and the less barrier in the system at the initial stage of the reaction, so that the molecules can quickly contact the reaction, resulting in the generation of by-products. However, the present application introduces a new intermediate which has a negatively charged sulfonic acid group (-SO3 - ), which is easy to attract the positive part, and secondly, its amide group (-NH2) is more easily reacted with formaldehyde, and it is also water-soluble and diffuses faster in the system, so it has more opportunities to contact with the reactants. Therefore, the activity of the hydrophilic amide intermediate containing a sulfonic acid group provided by the present application is higher.

[0059] When formaldehyde is added, it will not preferentially react with phenol to generate bisphenol F, but will be quickly captured by the hydrophilic amide intermediate containing a sulfonic acid group and undergo polycondensation reaction. The hydrophilic amide intermediate containing a sulfonic acid group acts as a high-activity target, firmly grasping the formaldehyde and guiding it to form the backbone structure of the synthetic tanning agent, greatly avoiding the generation of harmful by-products such as bisphenol F. In addition, the polycondensation reaction conditions of the present application are mild, the reaction temperature is 70-90℃, and the reaction process is not harsh, which is also not conducive to the occurrence of complex side reactions.

[0060] S03, secondary polycondensation Further, according to different tanning requirements, urea can also be added after the polycondensation reaction of phenol, intermediate and formaldehyde is completed for secondary polycondensation.

[0061] The purpose of the secondary polycondensation is to increase the molecular weight of the synthetic tanning agent by using urea and formaldehyde for polycondensation for some products that require higher molecular weight of the tanning agent. Moreover, since the phenol, intermediate and formaldehyde have been polycondensed to form macromolecular polymers before the secondary polycondensation, and the amount of the intermediate added is high, the opportunity for the mutual reaction of phenol is further suppressed. Therefore, when urea is added for secondary polycondensation, these macromolecular compounds act as a barrier, avoiding the generation of bisphenol F while reducing the cost of the synthetic tanning agent.

[0062] It should be noted that during the process of adding urea for secondary polycondensation, if the amount of formaldehyde added is insufficient, a small amount of formaldehyde can be added, and the molar ratio of formaldehyde to urea is 1:(0.8-1.2).

[0063] Preferably, the molar ratio of urea to intermediate is (0.01-1.0):(1.0). It can be understood that if the molecular weight of the synthetic tanning agent obtained by the S02 step reaction meets the tanning requirements, the amount of urea added can also be 0.

[0064] It should be noted that if secondary polycondensation is not required, the base solution can be added to adjust the pH value of the system after the phenol, intermediate and formaldehyde polycondensation reaction is completed to obtain the synthetic tanning agent product; if urea is required to be added for secondary polycondensation, urea (formaldehyde can be selectively added) is directly added for secondary polycondensation after the polycondensation reaction of phenol, intermediate and formaldehyde is completed, and then the pH value of the system is adjusted to 3-5 after the secondary polycondensation reaction is completed.

[0065] The synthetic tanning agent provided by the present application has extremely high similarity in structure to traditional phenolic synthetic tanning agents, and has an amide structure, active phenolic hydroxyl groups and hydrophilic sulfonic acid groups, which can ensure that the synthetic tanning agent has a basic filling effect as a leather retanning agent and endows the leather with a compact, full and soft hand feeling. Meanwhile, the preparation method provided by the present application brings water solubility through the sulfonic acid group of the intermediate, replaces the traditional process of bringing water solubility through phenol sulfonation, and is safer in the reaction process without high-temperature sulfonation; meanwhile, the introduction of bisphenol S and bisphenol F in the reaction process can be avoided, the tanning agent is green, safe and healthy, and greatly meets the tanning effect and environmental protection requirements of the leather tanning process.

[0066] In a third aspect, the present application provides a phenolic synthetic tanning agent as in any of the preceding embodiments or a phenolic synthetic tanning agent prepared by the preparation method as in any of the preceding embodiments for use in leather tanning.

[0067] The synthetic tanning agent provided by the present application can be applied to raw hide tanning and / or chrome tanned leather retanning, and is especially suitable for the retanning process of chrome tanned leather, and can significantly improve the fullness, inside compactness and softness of the leather.

[0068] When the synthetic tanning agent provided by the present application is applied to raw hide tanning, it is used as the main active ingredient in the leather tanning agent; when the synthetic tanning agent provided by the present application is applied to chrome tanned leather retanning, it is used as the main active ingredient in the retanning filler.

[0069] Example 1 The present embodiment provides a phenolic synthetic tanning agent without bisphenol substances, and the preparation method is as follows: S01, synthesis of intermediate (hydrophilic amide intermediate containing sulfonic acid group) A constant temperature reactor with a thermometer and a mechanical stirring device is added with 200 parts by weight of water and 110 parts by weight of sodium pyrosulfite, which is dissolved under stirring at room temperature (25℃) to obtain a sodium pyrosulfite aqueous solution.

[0070] 80 parts by weight of acrylamide was dissolved in 175 parts by weight of water to obtain an acrylamide aqueous solution. The acrylamide aqueous solution was added dropwise into the sodium metabisulfite aqueous solution at room temperature, the dropping speed was controlled to slowly increase the temperature of the system, and the temperature was not more than 60℃, and the reaction was carried out at 60℃ for 2 hours. After the reaction was completed, the temperature was lowered to obtain a hydrophilic amide intermediate containing sulfonic acid groups, denoted as a1.

[0071] The hydrophilic amide intermediate a1 containing sulfonic acid groups was a light yellow transparent liquid, and the solid content was about 33.63%.

[0072] S02, a synthetic tanning agent was prepared In a constant temperature reactor with a thermometer and a mechanical stirring device, 110 parts by weight of the intermediate a1 prepared in S01 step and 30 parts by weight of phenol were added, and the temperature was increased to 50℃ for stirring and dissolution. 10 parts by weight of 50% sulfuric acid solution was used to adjust the pH of the system to be less than 2, 36.6 parts by weight of 37wt% formaldehyde was added at one time, the temperature was increased to 70~75℃ and kept for 2 hours. Then 3.7 parts by weight of urea was added, and the temperature was kept at 70~75℃ for another 2 hours. The temperature was lowered to about 60℃, 30 wt % sodium hydroxide was added, the pH of the system was neutralized to 3~4, 1.8 parts by weight of sodium metabisulfite was added, stirred for half an hour, and then discharged to obtain a synthetic tanning agent with structures as shown in formula (II)~formula (IV).

[0073] Examples 2~6 also provided a phenolic synthetic tanning agent without bisphenolic substance, and the preparation method was similar to that of example 1, and the difference was only in the process parameters of S02 step. The different process parameters in S02 step are shown in table 1. The parameters not mentioned in table 1 are the same as those in example 1.

[0074] Table 1 Process parameters of S02 step of phenolic synthetic tanning agent without bisphenolic substance

[0075] Among them, the solid content of a1 refers to the mass ratio of intermediate a1 (solid fraction) to total raw materials (solid fraction) after converting each raw material into solid fraction; that is, the solid content of a1 = (a1 weight parts*a1 solid content) / (a1 weight parts*a1 solid content+ phenol weight parts*phenol solid content+ formaldehyde weight parts*formaldehyde solid content+ urea weight parts*urea solid content+ sodium metabisulfite weight parts*sodium metabisulfite solid content+ acid weight parts*acid solid content+ base weight parts*base solid content); the contribution of 37% formaldehyde to solid content is 0.17 (note: when formaldehyde is subjected to polycondensation, one molecule of water is lost, and only one -CH2- molecule with a molecular weight of 14 remains in the molecular skeleton, not CH2O with a molecular weight of 30. Solid content=37%*14 / 30=0.172), and the solid content of solid substance is 1.

[0076] The urea / a1 solid mass ratio refers to the mass ratio of intermediate a1 (solid parts) to total raw materials (solid parts) after the urea and intermediate a1 are converted into solid parts; that is, (urea weight parts * urea solid content) : (a1 weight parts * a1 solid content).

[0077] Example 7 The present embodiment provides a phenolic synthetic tanning agent without bisphenol substances, and the preparation method is as follows: S02, preparation of a synthetic tanning agent In a constant temperature reactor with a thermometer and a mechanical stirring device, 280 parts by weight of intermediate a1 prepared in step S01 of Example 1 and 49.1 parts by weight of phenol were added, and the temperature was raised to 50°C for stirring and dissolution. A 10 parts by weight of 50% sulfuric acid solution was used to adjust the pH of the system to less than 2, and 81.8 parts by weight of 37wt% formaldehyde was added at one time, and the temperature was raised to 70-75°C for 2 hours. Then 16 parts by weight of urea and 22 parts by weight of 37wt% formaldehyde were added, and the temperature was continuously maintained at 70-75°C for 2 hours, and the temperature was lowered to about 50°C, sodium hydroxide was added to neutralize the system pH to 3.5, 10 parts by weight of sodium pyrosulfite was added, and the system was stirred for half an hour to obtain a synthetic tanning agent with a solid content of 41.74%.

[0078] The synthetic tanning agent provided in the present embodiment was sent to a third party institution to detect the content of bisphenol S and bisphenol F, wherein the third party institution was BUREAU VERITAS CONSUMER PRODUCTS SERVICES (GUANGZHOU) CO., LTD; the detection method was first solvent extraction, and then liquid chromatography mass spectrometry method was used for detection; the detection limit of the third party institution was bisphenol F: 1 ppm, bisphenol S: 1 ppm.

[0079] The third party inspection result of the present embodiment was that the content of bisphenol F was 1.87 ppm, and bisphenol S was not detected.

[0080] Example 8 The present embodiment provides a phenolic synthetic tanning agent without bisphenol substances, and the preparation method is as follows: S01, synthesis of intermediate (hydrophilic amide intermediate containing sulfonic acid group) In a constant temperature reactor with a thermometer and a mechanical stirring device, 100 parts by weight of 22wt% concentrated ammonia water and 80 parts by weight of water were stirred. The reactor was placed in an ice water bath for cooling, and 55 parts by weight of maleic anhydride solid was added in small batches, and the feeding speed was controlled to make the temperature in the system not exceed 40°C. After the addition was completed, the system was stirred at room temperature for 1 hour to obtain a maleic amide acid derivative reaction solution.

[0081] Sodium metabisulfite 54 parts by weight and 80 parts by weight of water were stirred and dissolved at room temperature (25°C) to obtain a sodium metabisulfite aqueous solution.

[0082] The sodium metabisulfite aqueous solution was added dropwise to the maleamic acid derivative reaction solution, the dropping speed was controlled to slowly increase the temperature of the system, and the temperature was not allowed to exceed 60°C, and the reaction was carried out at 60°C for 2 hours. After the reaction was completed, the temperature was lowered to obtain a hydrophilic amide intermediate containing a sulfonic acid group, denoted as a2.

[0083] The hydrophilic amide intermediate a2 containing a sulfonic acid group was a light yellow transparent liquid, and the solid content was about 34.96%.

[0084] S02, Synthesis of synthetic tanning agent In a constant temperature reactor with a thermometer and a mechanical stirring device, 365 parts by weight of the intermediate a2 prepared in the above S01 step and 49.1 parts by weight of phenol were added, and stirred and dissolved at 50°C. A 10 parts by weight of 50% sulfuric acid solution was used to adjust the pH of the system to less than 2, and 81.8 parts by weight of 37wt% formaldehyde was added at one time and slowly, and the temperature was raised to 70~75°C and kept for 2 hours. Then 16 parts by weight of urea and 22 parts by weight of 37wt% formaldehyde were added, and the temperature was kept at 70~75°C for another 2 hours. The temperature was lowered to about 50°C, sodium hydroxide was added to neutralize the pH of the system to 3.5, and 10 parts by weight of sodium metabisulfite was added. After stirring for half an hour, the product was discharged to obtain a synthetic tanning agent with a solid content of 49.17%.

[0085] Comparative Example 1 This comparative example provides a preparation method of a phenolic synthetic tanning agent, which comprises the following steps: S01, Preparation of phenol sulfonic acid intermediate In a constant temperature reactor with a thermometer and a mechanical stirring device, 1120 parts by weight of molten phenol was added, and 1210 parts by weight of concentrated sulfuric acid was slowly added at about 50°C. The feeding speed was controlled to ensure that the maximum reaction temperature did not exceed 105°C, and then the stirring was continued at 100~105°C for 2 hours to obtain a phenol sulfonic acid intermediate a3.

[0086] S02, Synthesis of synthetic tanning agent In a constant temperature reactor with a thermometer and a mechanical stirring device, 34 parts by weight of water, 80 parts by weight of the a3 phenol sulfonic acid intermediate obtained in the above S01 step, and 25 parts by weight of urea were added, and stirred for 30 minutes. At the same time, the reaction temperature was adjusted to 66~68°C, and then 60 parts by weight of 37% formaldehyde solution was started to be added, and the feeding speed was controlled to make the internal temperature not exceed 75°C. After the formaldehyde was added, the temperature was continued to be kept at 70~75°C for 2 hours. The temperature was lowered to 50°C, about 46 parts by weight of 32% sodium hydroxide was used to adjust the pH to about 3.5, and the product was discharged to obtain a conventional synthetic tanning agent with a solid content of 50.2%.

[0087] Comparative Example 2 The present comparative example provides a preparation method of a phenolic synthetic tanning agent, comprising the following steps: In a constant temperature reactor with a thermometer and a mechanical stirring device, 43 parts by weight of water, 80 parts by weight of the a3 phenol sulfonic acid intermediate obtained in step S01 of Comparative Example 1, and 25 parts by weight of urea were added, and stirring was performed for 30 minutes while adjusting the reaction temperature to 66-68°C. Then, 60 parts by weight of a 37% formaldehyde solution was added at a controlled feeding speed so that the internal temperature did not exceed 75°C. After the formaldehyde was added, the reaction was continued at 70-75°C for 2 hours. The temperature was lowered to 50°C, and about 10 parts by weight of a 32% sodium hydroxide solution was used to adjust the pH of the system to about 2. Then, 24 parts by weight of phenol was added, and stirring was performed for 5 minutes. Then, 17 parts by weight of a 37% formaldehyde solution was added, and the reaction was continued at 70-75°C for 2 hours. The temperature was lowered to 50°C, and about 36 parts by weight of a 32% sodium hydroxide solution was used to adjust the pH of the system to 3.5. The product was discharged, and a conventional synthetic tanning agent with a solid content of 50.4% was obtained.

[0088] Comparative Example 3 The present comparative example provides a preparation method of a phenolic synthetic tanning agent, and the specific steps are similar to those of Example 1, except that the solid content of the intermediate a1 is 30%.

[0089] The scheme of the present comparative example will generate more bisphenol F and phenolic aldehyde phenol oligomers during the synthesis process, and the insufficient content of hydrophilic structures will cause poor water solubility of the product, etc., resulting in that the synthetic tanning agent cannot be used for leather tanning.

[0090] Test Example 1 The bisphenol S, bisphenol F, free phenol, and free formaldehyde in the synthetic tanning agents provided in Examples 1-8 and Comparative Examples 1-2 were detected, and the detection results are shown in Table 2.

[0091] In the detection method, bisphenol F and bisphenol S were detected by a high-performance liquid chromatograph LC2050 produced by Shimadzu, Japan; the detection limit of bisphenol F was 5 ppm, and the detection limit of bisphenol S was 5 ppm.

[0092] Free phenol and free formaldehyde were detected by a UV-visible spectrophotometer uv-1900i produced by Shimadzu, Japan; the detection limit of free phenol was 20 ppm, and the detection limit of free formaldehyde was 20 ppm.

[0093] Table 2: Impurity content in synthetic tanning agent

[0094] As can be seen from Table 2, the method of the embodiment of the present application can avoid the generation of bisphenol S, and with the increase of the addition amount of the hydrophilic amide intermediate containing sulfonic acid groups, the content of bisphenol F in the synthetic tanning agent gradually decreases until it cannot be detected. When the addition amount of the hydrophilic amide intermediate containing sulfonic acid groups reaches 50%, the contents of harmful monomers such as bisphenol F, bisphenol S, free formaldehyde and free phenol are all lower than the detection limit. Bisphenol S is detected in Comparative Examples 1 and 2, and in Comparative Example 2, in order to improve the tanning property of the synthetic tanning agent, the content of bisphenol F is increased by several times, and the use risk is increased.

[0095] Test Example 2 The phenolic synthetic tanning agents provided in Examples 4, 7 and Comparative Examples 1 and 2 were used as re-tanning agents for re-tanning of chrome tanned blue wet leather, and after the chrome tanned blue wet leather was weighed (the amount of the product used in the examples and comparative examples was calculated based on the weight of the chrome tanned blue wet leather), the specific process of re-tanning is shown in Table 3. In the process shown in Table 3, the temperature during the whole re-tanning process was maintained at 35℃.

[0096] Table 3 Re-tanning process

[0097] Note: The amount of synthetic tanning agent is calculated based on the solid content.

[0098] The tanning effect and dyeing and fatliquoring effect of the blue wet leather obtained by re-tanning were tested and judged by sensory evaluation, and the results are shown in Table 4.

[0099] Among them, the fullness and grain tightness were determined by sensory evaluation, and the score range was 1-5, with 5 being the best; the softness test was carried out by using a leather softness tester, the manufacturer was Dongguan Dazhong Instrument Co., Ltd., and the test standard was ISO 17235-2015; the xenon lamp resistance test was carried out by using a xenon lamp weathering test chamber, the equipment model was SN-80A, the manufacturer was Beijing Hengtai Fengke Test Equipment Co., Ltd., and the test standard was ISO 105-B06-2020; the ultraviolet resistance test was carried out by using an ultraviolet irradiation chamber, the equipment model was GT-7035-UB, the manufacturer was Gao Tie Detection Instrument Co., Ltd., and the test standard was HG / T 3689 ASTM D 1148-2013; the wet heat resistance test was carried out by using a constant temperature and humidity chamber GT-7005-1, the manufacturer was Gao Tie Detection Instrument Co., Ltd. of Taiwan, China, and the test standard was ISO 17228.

[0100] Table 4 Properties of blue wet leather

[0101] From table 4, it can be seen that the synthetic tanning agent provided by the embodiment of the present application does not contain bisphenol F and bisphenol S, the synthetic tanning agent of comparative example 1 contains 171 ppm of bisphenol S, and after the leather is retanned, 30 ppm of bisphenol S is detected in the leather, so that the synthetic tanning agent of comparative example 1 has double risks of environmental protection and health when used for treating the leather. The synthetic tanning agent of comparative example 2 contains 113 ppm of bisphenol S and 10434 ppm of bisphenol F, and after the leather is retanned, 16 ppm of bisphenol S and 925 ppm of bisphenol F are detected in the leather, so that the double risks of environmental protection and health are significantly improved.

[0102] In addition, the synthetic tanning agent provided by the embodiment of the present application has conventional hand feeling performances such as fullness, inside tightness and softness, and is slightly improved in light aging resistance compared with the conventional synthetic tanning agents (comparative examples 1 and 2), which may be caused by the fact that the relative content of phenol in the synthetic tanning agent of the present application is slightly lower than that of the conventional synthetic tanning agent, and the free phenol and residual phenol sulfonic acid residual amount are lower. It is shown that the synthetic tanning agent provided by the embodiment of the present application can realize the tanning effect equivalent to or even better than the conventional synthetic tanning agent, and can avoid the generation of bisphenol S and bisphenol F, so that the use safety of the synthetic tanning agent is significantly improved, and the preparation method of the synthetic tanning agent provided by the embodiment of the present application is simple, the reaction condition is mild, the reaction safety is improved, and the synthetic tanning agent has great commercial application value.

[0103] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A phenolic synthetic tanning agent free of bisphenolic substances, characterized in that it comprises: comprising a structure as shown in formula (I): formula (I); wherein R is selected from or ; X is selected from -H or ; M is selected from any one of H, Na or NH4; n is an integer greater than or equal to 2; and at least one of the R groups and the X groups is selected from a sulfonic acid group-containing amide structure.

2. Phenolic synthetic tanning agent according to claim 1, characterized in that, The theoretical mass fraction of the sulfonic acid group-containing amide structure in the structure of formula (I) is greater than or equal to 40%; Preferably, the theoretical mass fraction of the sulfonic acid group-containing amide structure in the structure of formula (I) is 40-60%; more preferably 50-60%.

3. The phenolic synthetic tanning agent according to claim 1, characterized in that, including at least one of the structures of formula (II)-(IV): Formula (II); Formula (III); Formula (IV).

4. A process for the preparation of a phenolic synthetic tanning agent according to any one of claims 1 to 3, characterized in that, including reacting an amide compound containing a carbon-carbon double bond with a sulfite salt to obtain an intermediate, mixing the intermediate with a phenol compound, adding formaldehyde in a first acidic environment for polycondensation reaction, adjusting the reaction system to a second acidic environment after the reaction is completed; The pH of the first acidic environment is less than 2; the pH of the second acidic environment is 3-5.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the molar amount of the carbon-carbon double bond in the amide compound containing a carbon-carbon double bond to the molar amount of the hydrogen bisulfite in the sulfite salt is 1:(1-1.05); Preferably, the amide compound containing a carbon-carbon double bond includes acrylamide or maleamic acid derivative; the sulfite salt includes at least one of sodium metabisulfite, sodium sulfite and sodium bisulfite; Preferably, the reaction temperature of the amide compound containing a carbon-carbon double bond and the sulfite salt is 30-60℃, and the reaction time is 2-4h.

6. The preparation method according to claim 4, characterized in that, The molar ratio of the intermediate to the phenol compound is (0.5-1.5):(1.0-2.5); Preferably, the phenol compound includes at least one of phenol, alkyl phenol, salicylic acid or p-hydroxybenzoic acid.

7. The production method according to claim 4 or 6, characterized by, The molar ratio of the formaldehyde to the intermediate is (0.5-1.5):(1.0-2.5); Preferably, the system is warmed to 50-60℃ and then formaldehyde solution is added, followed by polycondensation reaction. Preferably, the reaction temperature of the polycondensation reaction is 70-90℃, and the reaction time is 3-4h. Preferably, the concentration of formaldehyde in the formaldehyde solution is 35-40%.

8. The preparation method according to claim 4, characterized in that, Further including adding urea for secondary polycondensation after the polycondensation reaction of the intermediate is completed; Preferably, the molar ratio of urea to the intermediate is (0.01-1.0):(1.0).

9. The preparation method according to claim 4, characterized in that, The first acidic environment is adjusted by adding an acid solution, and the acid solution includes any one of sulfuric acid solution with a concentration less than 55% and hydrochloric acid with a concentration less than 36.5%; and / or, the second acidic environment is adjusted by adding a base solution, and the base solution includes any one of NaOH solution and industrial concentrated ammonia water with a mass concentration of 20-25%; Preferably, when the base solution is added, the temperature of the reaction system is 45-50℃.

10. Use of the phenolic synthetic tanning agent according to any one of claims 1-3 or prepared by the preparation method according to any one of claims 4-9 in leather tanning.

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