Leather tanning method based on gas-phase mass transfer

Abstract

The invention discloses a leather tanning method based on gas-phase mass transfer, which comprises the following steps: firstly, unhairing, liming, deliming and softening raw leather, and carrying out gradient dehydration on the softened raw leather, so that the water content of the pretreated raw leather is 9-11%, and the pretreated raw leather is prepared; and then the pretreated raw leather is placed in a closed treatment device, after a tanning agent is gasified, the tanning agent is introduced into the closed treatment device for tanning treatment, and the tanned leather is obtained. By means of the technology, the shrinkage temperature of the tanned crust leather is increased to 80-90 DEG C, it is indicated that the performance of the leather tanned through the method is remarkably improved, and it is verified that the tanning quality can be effectively improved through the method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of leather tanning, and relates to a leather tanning method based on gas phase mass transfer. BACKGROUND

[0002] Tanning is a key process for converting raw hide into high-value leather products. Through the cross-linking between tanning agent molecules and hide collagen fibers, the physical and chemical properties of leather change, improving the heat resistance, chemical resistance, enzyme stability, and physical and mechanical properties of leather. Currently, the leather industry mainly uses metal tanning, vegetable tanning, and polymer tanning technologies for processing. These methods are all carried out in a liquid environment, but these traditional tanning methods have many problems, such as: chromium tanning waste produces harmful hexavalent chromium under certain conditions; zirconium tanning is prone to "surface over-tanning" or "raw core"; aluminum tanning has low shrinkage temperature and poor water resistance, and is prone to fading (chemical bonds will break) during washing; iron tanning has color development problems; vegetable tanned leather has poor dyeing performance; and polymer tanning can make the leather grain coarse, the leather body brittle, and the leather folding resistance decrease. In addition, traditional leather tanning processes also face problems such as long tanning cycle and water pollution, which seriously restrict the development of the leather industry. Therefore, developing a new type of leather tanning technology can effectively reduce the tanning time cost and alleviate the environmental pollution caused by traditional tanning, which is of great significance to the development of the leather industry.

[0003] In the tanning process, an efficient tanning method usually needs to achieve the synergistic effect of momentum transfer, heat transfer, mass transfer, and chemical reaction (i.e., "three transfers and one reaction"). Momentum transfer is reflected in the contact process between the tanning liquid and the leather. Proper momentum transfer can ensure that the tanning liquid uniformly acts on the leather surface, promoting subsequent mass transfer. Heat transfer affects the rate and effect of tanning reactions, and temperature control is crucial for the uniformity of tanning and the quality of leather. Mass transfer is the process of tanning agent molecules diffusing from the tanning liquid into the leather and combining with the leather fibers, which directly affects the depth and firmness of tanning. Chemical reaction is the core of tanning, where tanning agents cross-link with collagen proteins in the leather, changing the structure and properties of the leather.

[0004] Some new processes have been developed in existing research to improve mass transfer and tanning effect. The most typical one is to improve the penetration efficiency of chrome tanning agent by ultrasonic assistance, which can reduce the amount of chromium and shorten the tanning time. For example, Zhang et al. [Journal of Cleaner Production, 2020, 247: 119452.] developed a rapid and clean chrome tanning method based on ultrasonic and microwave. The tanning time can be effectively shortened under the action of ultrasonic. Mengistie et al. [Ultrasonics Sonochemistry, 2016, 32: 204-212.] used ultrasonic-assisted leather processing technology for tanning, which not only has the advantages of high efficiency and environmental protection, but also can produce higher quality leather products in a shorter processing time with a lower amount of chromium. However, the existing technology still has the technical problems of long tanning time and poor quality of leather tanning. Therefore, it is urgent to develop a new type of leather tanning process to realize the efficient synergistic effect of "three transmission and one reflection", shorten the tanning time and improve the quality of leather tanning. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a leather tanning method based on gas phase mass transfer, thereby solving the technical problems of long tanning time and poor quality of leather tanning in the prior art.

[0006] The present application is realized by the following technical solutions: A leather tanning method based on gas phase mass transfer, comprising the following steps: S1: dehairing, liming, deliming and softening the raw leather, and gradient dehydration of the softened raw leather to make the water content of the pretreated raw leather 9%~11%, and obtain the pretreated raw leather; S2: placing the pretreated raw leather in a closed treatment device, and making the tanning agent gasify and then entering the closed treatment device for tanning treatment, and obtaining the tanned leather.

[0007] Preferably, the gradient dehydration process includes three stages of drying control: specifically, the first stage is dried at 5~40℃ to a water content of 30%~35%, the second stage is dried at 45~50℃ to a water content of 15%~20%, and the third stage is dried at 55~60℃ to a water content of 9%~11%.

[0008] Preferably, the tanning agent is gasified by using an atomizer, the working pressure of the atomizer is 0.8~1.5MPa, and the atomized particle size is ≤10μm.

[0009] Preferably, the tanning agent is at least one of chlorine, ozone, ethylene oxide and propylene oxide.

[0010] Preferably, the tanning treatment is performed for 1 to 4 hours.

[0011] Preferably, the tanning treatment is performed at a temperature of 10 to 50 degrees Celsius.

[0012] Preferably, the tanning treatment is performed at a pressure of 0.05 to 0.3 MPa.

[0013] Preferably, the flow rate of the tanning agent during the tanning treatment is 2 to 15 L / min.

[0014] Preferably, the temperature of the cavity of the closed treatment device during the tanning treatment is 20 to 65 degrees Celsius.

[0015] A tanned leather obtained by the method described above; the shrinkage temperature of the tanned leather is 80 to 90 degrees Celsius.

[0016] Compared with the prior art, the present application has the following beneficial technical effects: The present application discloses a leather tanning method based on gas phase mass transfer. First, in the pretreatment stage, through chemical reaction and physical action, non-collagen components and excess impurities in the rawhide are effectively removed, and the fiber loosening treatment is completed. At the same time, the water content of the softened hide is controlled at about 10%, and the removal of bound water helps to better open the gas diffusion channel, which is more conducive to the gas phase mass transfer, laying a foundation for subsequent efficient tanning. Compared with the traditional process, the pretreatment is more conducive to improving the tanning effect and efficiency. Second, the tanning agent is in full contact with the collagen fiber in the form of gas, realizing the uniform distribution of the tanning agent, so that the tanning agent can act on the leather fiber more comprehensively. The gas tanning agent moves quickly to the surface of the leather under the pressure gradient, forming an efficient molecular diffusion dynamics process, which speeds up the action speed of the tanning agent and the leather fiber. At the same time, the constant temperature steam promotes the swelling of the dermal layer fiber, increasing the molecular motion freedom; on the other hand, the active groups of the tanning agent react with the functional groups on the collagen fiber to form stable cross-linking action, significantly improving the physical properties and chemical stability of the leather, and improving the tanning quality. By accurately controlling the tanning agent steam conditions, the efficient synergy of "three transmission and one reaction" is realized, compared with the traditional process, the tanning cycle is shortened, and the production efficiency is improved. Through the process of the present application, the shrinkage temperature of the tanned leather increases to 80 to 90 degrees Celsius, indicating that the performance of the tanned leather is significantly improved, and the method can effectively improve the tanning quality.

[0017] Further, the gradient dehydration process includes three-stage drying control: specifically, the first stage is dried at 5-40°C to a moisture content of 30%-35%, the second stage is dried at 45-50°C to a moisture content of 15%-20%, and the third stage is dried at 55-60°C to a moisture content of 9%-11%. The three-stage gradual drying method avoids damage to the leather fibers caused by sudden temperature changes or excessive one-time drying. In the first stage at a lower temperature, the fibers are slowly dried to remove some of the moisture, allowing them to adapt; in the second stage, the temperature is appropriately increased to further dehydrate and promote the moderate loosening of the fibers; and in the third stage, the target moisture content is reached. This gradual dehydration helps to better open the gas diffusion channels, creating favorable conditions for subsequent gas-phase mass transfer tanning processes and improving tanning results. Different temperature ranges correspond to different moisture content targets, and the drying degree of each stage is precisely controlled. Compared to traditional single-temperature or arbitrary drying methods, the leather moisture content can be more efficiently and stably controlled in the ideal range (9%-11%), ensuring the consistency of the pretreatment quality and facilitating the stable progress of subsequent tanning processes.

[0018] Further, the tanning agent is vaporized using an atomizer, the working pressure of the atomizer is 0.8-1.5 MPa, and the atomized particle size is ≤10 μm. By atomizing the tanning agent under a specific working pressure, the tanning agent can be more fully vaporized to form fine gaseous particles. Smaller atomized particle size increases the surface area of the gaseous molecules of the tanning agent, allowing it to be more uniformly dispersed in the sealed treatment device and greatly increasing the contact area with the leather collagen fibers, thereby accelerating the tanning reaction speed and improving the tanning efficiency. Fine atomized particle size helps the tanning agent to penetrate and distribute more uniformly inside the leather, avoiding the accumulation of tanning agent particles on the surface or in local areas due to their excessive size, ensuring consistent tanning of all parts of the leather, and improving the uniformity of the overall quality of the leather.

[0019] Further, the tanning agent is at least one of chlorine gas, ozone, ethylene oxide, and propylene oxide, providing multiple tanning agent options. Single tanning agent or multiple tanning agent combinations can be flexibly selected according to different types of leather, quality requirements, and production needs. Different tanning agents have different chemical properties and tanning effects. For example, chlorine gas has strong oxidizing and sterilizing properties, ozone has high oxidizing and disinfecting ability, and ethylene oxide and propylene oxide can react with collagen fibers to form cross-linked structures. Multiple options can meet diverse leather production needs. By reasonably selecting and matching tanning agents, the advantages of various tanning agents can be combined to achieve more precise control of the physical properties and chemical stability of the leather. For example, certain tanning agent combinations may result in leather with better softness, wear resistance, or chemical corrosion resistance, improving the overall quality of the leather.

[0020] Further, the tanning treatment time is 1-4 h, in this time interval, both can ensure that the tanning agent has enough time to react with the leather collagen fiber and physical action, form a stable crosslinking structure, achieve good tanning effect; can also avoid due to tanning time too long caused by leather excessive tanning, make leather hard, brittle and other adverse phenomena occur, at the same time also help to improve production efficiency, shorten the production cycle.

[0021] Further, the tanning treatment temperature is 10-50 ℃, the suitable temperature range provides a good environment for tanning reaction. In this temperature range, both can ensure the activity of tanning agent molecules, so that they can effectively react with the functional groups on the collagen fiber; can also avoid the thermal damage of leather fiber or the rapid decomposition of tanning agent due to high temperature, ensure the stability and controllability of tanning reaction, which is beneficial to obtain high quality tanned leather.

[0022] Further, the tanning treatment pressure is 0.05-0.3 MPa, a certain pressure condition is helpful to promote the penetration of tanning agent gas into the leather, increase the diffusion power of tanning agent in the leather, so that the tanning agent can contact and react with the collagen fiber more deeply. The suitable pressure range can not only ensure enough penetration force, but also will not cause too much physical pressure to damage the leather structure, which is beneficial to improve the uniformity and depth of tanning.

[0023] Further, in the tanning treatment process, the flow of tanning agent is 2-15 L / min, accurate control of the flow of tanning agent can reasonably adjust the amount of tanning agent entering the closed treatment device according to the thickness, area of leather and tanning requirements. The suitable flow can not only ensure that the tanning agent has enough concentration on the surface and inside of the leather to maintain effective tanning reaction; can also avoid waste caused by too large flow of tanning agent or uneven tanning caused by too high local concentration, at the same time also help to control the production cost.

[0024] Further, in the tanning treatment process, the temperature of the cavity of the closed treatment device is 20-65 ℃, maintaining the cavity of the closed treatment device in a suitable temperature range provides a stable thermal environment for the whole tanning process. This temperature range is helpful to maintain the gaseous state and activity of tanning agent, promote the heat and mass transfer synergy effect between tanning agent and leather fiber, so that the tanning reaction can be carried out efficiently and stably, further improve the tanning quality and uniformity of leather. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0026] Figure 1 Actual photos of the un-tanned leather (left) and the tanned leather (right) prepared according to the steps of Example 4; Figure 2 Shrinkage temperature of the un-tanned leather and the tanned leather prepared according to the steps of Example 4. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to understand the features and effects of the present application, the following will make a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings understood by those skilled in the art of the present application, and in case of conflict, the definition in the specification shall prevail.

[0028] Theories or mechanisms described and disclosed herein, whether correct or wrong, should not limit the scope of the present application in any way, i.e., the content of the present application can be implemented without being limited by any specific theory or mechanism.

[0029] In this document, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents and concentrations, are only for the sake of brevity and convenience. Therefore, the description of numerical ranges or percentage ranges should be considered to have covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0030] In this document, unless otherwise specified, "comprise", "include", "contain", "have", or similar words cover the meaning of "consist of" and "consist essentially of", for example, "A comprises a" covers the meaning of "A comprises a and other" and "A only comprises a".

[0031] In this document, in order to make the description simple, all possible combinations of various technical features in each embodiment or example are not described. Therefore, as long as the combinations of technical features do not conflict, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope disclosed in the specification.

[0032] The present application provides a leather tanning method based on gas phase mass transfer, the steps are as follows: Step one, hide pretreatment: The raw leather is dehaired, limed, delimed and softened to obtain pretreated raw leather; and the pretreated raw leather is gradiently dehydrated to make the water content of the pretreated raw leather 9% to 11%; Specifically, in the leather-making pretreatment stage, the conventional pretreatment process is first implemented, including key processes such as dehairing, liming, deliming and softening. Then, the gradient dehydration technology is adopted to realize accurate control of the water content through stage-by-stage temperature control drying, and finally the water content of the raw leather substrate is stabilized at 9% to 11%, creating conditions for subsequent tanning processes.

[0033] The raw leather is cowhide, sheepskin, goat skin or rabbit skin; The dehairing process specifically uses sodium sulfide and lime water to prepare a dehairing solution, which is used to remove hair and surface tissues from the rawhide to obtain barehide with smooth grain.

[0034] The liming process specifically involves soaking the dehaired hide in a lime-containing suspension to promote collagen fiber loosening through alkali swelling, providing necessary conditions for tanning and subsequent operations.

[0035] The deliming process specifically removes all lime and alkali from the barehide through water washing or acid treatment to restore the original color of the leather.

[0036] The softening process specifically uses trypsin or other proteases to treat the delimed barehide to further loosen the collagen fibers. It plays a very important role in determining the softness, fullness, elasticity, good air permeability, extensibility, and smooth and delicate hand feeling of the finished leather.

[0037] The gradient dehydration process includes three stages of drying control: specifically, the first stage is dried at 5 to 40℃ to a water content of 30% to 35%, the second stage is dried at 45 to 50℃ to a water content of 15% to 20%, and the third stage is dried at 55 to 60℃ to a water content of 9% to 11%.

[0038] Step two, steam tanning process: The pretreated and softened hide needs to be placed in a closed steam treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 10 to 50℃, the steam pressure to 0.05 to 0.3 MPa, and the steam flow to 2 to 15 L / min, and the steam tanning time to 1 to 4 hours. The tanning agent solution is converted into a gaseous carrier by an atomizer, and then distributed uniformly in space through a flow guide structure to achieve efficient tanning of the leather. When the tanning agent is vaporized using the atomizer, the working pressure of the atomizer is 0.8 to 1.5 MPa, and the atomized particle size is ≤10 μm.

[0039] Step three, post-tanning treatment: After the completion of the steam tanning process, the shrinkage temperature and performance of the tanned raw leather are detected, and the steam treatment device is provided with a steam recovery circulation system, so that the tanning agent gas which does not fully participate in the reaction after being steamed can be returned to the treatment device through the recovery circulation system for recycling by increasing the cavity temperature.

[0040] The application discloses a leather tanning method based on gas phase mass transfer, which can effectively remove non-collagen components and excess impurities in rawhide and complete fiber loosening treatment through chemical reaction and physical action in the pretreatment stage, and the water content of the softened hide is controlled at about 10%, wherein, the removal of combined water helps to better open the gas diffusion channel, so that the gas phase mass transfer is more conducive to be carried out and better tanning effect is obtained. In addition, the gaseous carrier is uniformly distributed in space through the flow guide structure, so as to ensure sufficient contact with collagen fibers. The gaseous tanning agent quickly moves to the leather surface under the pressure gradient to form an efficient molecular diffusion dynamics process. In this process, the heat transfer and mass transfer produce a synergistic effect: on the one hand, the constant temperature steam promotes the expansion of the dermis layer fibers and increases the molecular movement freedom; on the other hand, the active groups of the tanning agent react with the functional groups on the collagen fibers to form stable cross-linking action. In addition, the steam which does not fully participate in the tanning process enters the recovery circulation system, which can further improve the processing efficiency and avoid unnecessary waste and environmental pollution.

[0041] Therefore, the method realizes the efficient synergy of "three transmissions and one reaction" by accurately controlling the steam conditions, i.e., the flow of the tanning agent, improves the quality and uniformity of leather tanning, and significantly improves the physical properties and chemical stability of the leather. Compared with the traditional process, the tanning cycle is shortened, and the production efficiency is improved. In addition, the use amount of the tanning agent is reduced and recycled, and the environmental pollution is reduced, so the method has good environmental benefits.

[0042] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content taught by the application, and these equivalent forms also fall within the scope defined by the appended claims of the application.

[0043] In the following examples, conventional instruments and equipment in the art are used. In the following examples, the experimental methods not specified in the specific conditions are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturer. In the following examples, various raw materials are used, unless otherwise specified, conventional commercially available products are used, and the specifications are conventional specifications in the art. In the specification of the application and the following examples, unless otherwise specified, "%" means weight percent, "parts" means weight parts, and the ratio means weight ratio.

[0044] Example 1 A gas phase mass transfer based leather tanning method, comprising the following steps: Step one: First, the raw hide is subjected to a pretreatment process including key procedures such as unhairing, liming, deliming and softening. Then, gradient dehydration technology is used to achieve accurate control of the moisture content by stage temperature control drying, and finally the moisture content of the raw hide substrate is stabilized at about 10%, preparing for the subsequent tanning.

[0045] Step two: The pretreated raw hide is placed in a special steam (ozone) treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 10 ℃, the steam pressure to 0.2 MPa, and the steam flow to 5 L / min. The steam tanning time is 1.5 h, and the tanning agent solution is converted into a gaseous carrier by an atomizer for tanning.

[0046] Step three: After tanning, the tanned leather is tested for shrinkage temperature and performance.

[0047] After testing, the shrinkage temperature of the tanned raw hide reaches 82℃, the tensile strength and tear strength both meet the relevant standards, and the leather has good softness. In addition, the ozone gas that does not fully participate in the reaction after tanning is returned to the treatment device for recycling after evaporation through a recycling system.

[0048] Example 2 A gas phase mass transfer based leather tanning method, comprising the following steps: Step one: In the pretreatment stage of leather making, the raw cotton sheep hide is first subjected to a pretreatment process including key procedures such as unhairing, liming, deliming and softening. Then, gradient dehydration technology is used to achieve accurate control of the moisture content by stage temperature control drying, and finally the moisture content of the raw hide substrate is stabilized at about 10%, preparing for the subsequent tanning.

[0049] Step two: The pretreated raw cotton sheep hide is placed in a special steam (chlorine) treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 15 ℃, the steam pressure to 0.3 MPa, and the steam flow to 10 L / min. The steam tanning time is 1 h, and the tanning agent solution is converted into a gaseous carrier by an atomizer for tanning.

[0050] Step three: After the completion of the steam tanning process, the shrinkage temperature and performance of the tanned raw leather are detected. The detection results show that the shrinkage temperature of the tanned cotton sheepskin reaches 75°C, the tensile strength and tear strength meet the relevant standards, and the softness of the leather is good. In addition, the chlorine gas that does not completely participate in the reaction after tanning is returned to the treatment device through the recycling system after evaporation for recycling.

[0051] Example 3 A leather tanning method based on gas phase mass transfer, comprising the following steps: Step one: In the pretreatment stage of leather making, the rabbit skin is first subjected to a pretreatment process including key processes such as unhairing, liming, deliming, and softening. Then, gradient dehydration technology is used to accurately control the water content by stage temperature control drying, and finally the water content of the raw hide substrate is stabilized at about 10%, preparing for the subsequent tanning.

[0052] Step two: The pretreated rabbit skin is placed in a special steam (ethylene oxide) treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, and the cavity temperature is adjusted to 20°C, the steam pressure is 0.15 MPa, the steam flow is 8 L / min, the steam tanning time is 2 h, and the tanning agent solution is converted into a gaseous carrier by an atomizer for tanning.

[0053] Step three: After tanning, the shrinkage temperature and performance of the tanned raw leather are detected. The detection results show that the shrinkage temperature of the tanned rabbit skin reaches 90°C, the tensile strength and tear strength meet the relevant standards, and the softness of the leather is good. In addition, the ethylene oxide that does not completely participate in the reaction after tanning is returned to the treatment device through the recycling system after evaporation for recycling.

[0054] Example 4 A leather tanning method based on gas phase mass transfer, comprising the following steps: Step one: In the pretreatment stage of leather making, the goat skin is first subjected to a pretreatment process including key processes such as unhairing, liming, deliming, and softening. Then, gradient dehydration technology is used to accurately control the water content by stage temperature control drying, and finally the water content of the raw hide substrate is stabilized at about 10%, preparing for the subsequent tanning.

[0055] Step two: The pre-processed goat skin is placed in a special steam (propylene oxide) treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 40 ℃, the steam pressure to 0.15 MPa, the steam flow rate to 10 L / min, and the steam tanning time to 1.5 h. The tanning agent solution is converted into a gaseous carrier by an atomizer for tanning.

[0056] Step three: After completing the steam tanning process, the shrunken temperature and performance of the tanned raw leather are detected. The detection shows that the shrinkage temperature of the tanned goat skin reaches 90 ℃, and the physical properties and appearance quality meet the expected requirements. In addition, the chlorine gas that does not fully participate in the reaction after tanning is recycled and reused by returning to the treatment device through the recovery circulation system.

[0057] Example 5 A leather tanning method based on gas phase mass transfer, the steps are as follows: Step one, raw skin pretreatment: First, the raw leather is subjected to a pretreatment process, including key processes such as unhairing, liming, deliming, and softening. Then, gradient dehydration technology is used to achieve precise control of the moisture content by controlling the temperature in stages. Finally, the moisture content of the raw skin substrate is stabilized at 9%, creating conditions for subsequent tanning processes.

[0058] The raw leather is cowhide; The unhairing process specifically uses a mixture of sodium sulfide and lime water to remove hair and surface tissue from the rawhide, resulting in a smooth and clean barehide.

[0059] The liming process specifically involves soaking the unhairing skin in a lime-containing suspension to promote collagen fiber loosening through alkali swelling, providing necessary conditions for tanning and subsequent operations.

[0060] The deliming process specifically involves removing all lime and alkali from the barehide through water washing or acid treatment to restore the original color of the leather.

[0061] The softening process specifically uses trypsin or other proteases to treat the delimed barehide, further loosening the collagen fibers. It plays a crucial role in determining the softness, fullness, elasticity, good air permeability, extensibility, and smooth and delicate texture of the finished leather.

[0062] The gradient dehydration process includes three stages of drying control: specifically, the first stage is dried at 5 ℃ to a moisture content of 30%, the second stage is dried at 45 ℃ to a moisture content of 15%, and the third stage is dried at 55 ℃ to a moisture content of 9%.

[0063] Step two, steam tanning process: The pre-processed softened hide needs to be placed in a closed steam treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 10 ℃, the steam pressure to 0.05 MPa, and the steam flow to 2 L / min, and the steam tanning time to 1 h. After the tanning agent solution is converted into a gaseous carrier by the atomizer, it is uniformly distributed in space through the flow guide structure to achieve efficient tanning of the leather. When the tanning agent is gasified by the atomizer, the working pressure of the atomizer is 0.8 MPa, and the atomized particle size is ≤10 μm.

[0064] Step three, post-tanning treatment: After completing the steam tanning process, the tanned leather is detected for shrinkage temperature and performance, etc. In addition, the steam treatment device has a steam recovery and circulation system. By increasing the cavity temperature, the tanning agent gas that does not fully participate in the reaction after tanning is returned to the treatment device for recycling through the recovery and circulation system after being steamed out.

[0065] Example 6 A leather tanning method based on gas phase mass transfer, the steps are as follows: Step one, hide pretreatment: First, the raw leather is subjected to a pretreatment process, including key processes such as unhairing, liming, deliming, and softening. Then, gradient dehydration technology is used to achieve precise control of the moisture content by controlling the temperature in stages and drying, finally stabilizing the moisture content of the raw hide substrate at 11%, creating conditions for subsequent tanning processes.

[0066] The raw leather is sheepskin; The unhairing process specifically uses a mixture of sodium sulfide and lime water to remove hair and surface tissue from the raw hide, resulting in a smooth and clean skin.

[0067] The liming process specifically involves soaking the unhairing hide in a lime-containing suspension, promoting collagen fiber loosening through alkali swelling, and providing necessary conditions for tanning and subsequent operations.

[0068] The deliming process specifically involves removing all lime and alkali from the raw hide through water washing or acid treatment to restore the original color of the leather.

[0069] The softening process specifically uses trypsin or other proteases to treat the delimed raw hide, further loosening the collagen fibers. It plays a very important role in determining the softness, fullness, elasticity, good air permeability, extensibility, and smooth and delicate feel of the finished leather.

[0070] The gradient dehydration process includes three stages of drying control: specifically, the first stage is dried at 40°C until the moisture content is 35%, the second stage is dried at 50°C until the moisture content is 20%, and the third stage is dried at 60°C until the moisture content is 11%.

[0071] Step two, steam tanning process: The pretreated softening skin needs to be placed in a closed steam treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 50°C, the steam pressure to 0.3 MPa, and the steam flow to 15 L / min, and the steam tanning time is 4 h. After the tanning agent solution is converted into a gaseous carrier by the atomizer, it is uniformly distributed in space through the flow guide structure to achieve efficient tanning of the leather. When the tanning agent is gasified using the atomizer, the working pressure of the atomizer is 1.5 MPa, and the atomized particle size is ≤10 μm.

[0072] Step three, post-tanning treatment: After completing the steam tanning process, the shrinkage temperature and performance of the tanned leather are detected. In addition, the steam treatment device has a steam recovery and circulation system. By increasing the cavity temperature, the tanning agent gas that has not fully participated in the reaction after tanning is returned to the treatment device for recycling after being steamed out through the recovery and circulation system.

[0073] Example 7 A leather tanning method based on gas phase mass transfer, the steps are as follows: Step one, raw skin pretreatment: First, the raw leather is subjected to a pretreatment process, including key processes such as unhairing, liming, deliming, and softening. Then, gradient dehydration technology is used to accurately control the moisture content through stage-by-stage temperature control drying, ultimately stabilizing the moisture content of the raw skin substrate at 10%, creating conditions for subsequent tanning processes.

[0074] The raw leather is rabbit skin; The unhairing process specifically uses a mixture of sodium sulfide and lime water to remove hair and surface tissue from the raw skin, resulting in a smooth and clean pelt.

[0075] The liming process specifically involves soaking the unhairing skin in a lime-containing suspension, promoting collagen fiber loosening through alkali swelling, providing necessary conditions for tanning and subsequent operations.

[0076] The deliming process specifically removes all lime and alkali from the pelt through water washing or acid treatment, restoring the original color of the leather.

[0077] The softening process is specifically using trypsin or other proteases to treat the de-limed raw hide to make the collagen fibers further loose. It plays a very important role in determining the softness, fullness, elasticity, good air permeability, extensibility, and smooth and delicate hand feeling of the finished leather.

[0078] The gradient dehydration process includes three-stage drying control: specifically, the first stage is drying at 25°C until the moisture content is 32%, the second stage is drying at 48°C until the moisture content is 17%, and the third stage is drying at 57°C until the moisture content is 10%.

[0079] Step two, steam tanning process: The pretreated softening hide needs to be placed in a closed steam treatment device to complete the tanning process. The device integrates a multi-parameter intelligent control system, which adjusts the cavity temperature to 25°C, the steam pressure to 0.2 MPa, and the steam flow to 10 L / min, and the steam tanning time is 2 h. After the tanning agent solution is converted into a gaseous carrier by the atomizer, it is uniformly distributed in space through the flow guide structure to achieve efficient tanning of the leather. When the tanning agent is gasified using the atomizer, the working pressure of the atomizer is 1.0 MPa, and the atomized particle size is ≤10 μm.

[0080] Step three, post-tanning treatment: After completing the steam tanning process, the shrinkage temperature and performance of the tanned leather are detected. In addition, the steam treatment device is equipped with a steam recovery and circulation system. By increasing the cavity temperature, the tanning agent gas that has not fully participated in the reaction after tanning is returned to the treatment device for recycling after being steamed out through the recovery and circulation system.

[0081] Figure 1 The actual photos of the un-tanned leather sample (left) and the tanned leather sample (right) according to the steps of Example 4 show that the color of the tanned leather sample is more uniform, the surface is smooth, and it has certain toughness and elasticity.

[0082] Figure 2 The shrinkage temperature of the un-tanned leather and the tanned leather according to the steps of Example 4 is shown in the figure. The shrinkage temperature of the un-tanned leather sample is 50~55°C, and the shrinkage temperature of the tanned leather sample increases to 80~90°C.

[0083] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A leather tanning method based on gas-phase mass transfer, characterized in that, Includes the following steps: S1: The raw leather is dehaired, soaked in ash, delimed and softened, and the softened raw leather is subjected to gradient dehydration so that the moisture content of the pretreated raw leather is 9%~11%, thus obtaining pretreated raw leather. S2: The pretreated raw leather is placed in a closed treatment device, and the tanning agent is vaporized and then introduced into the closed treatment device for tanning treatment to obtain tanned leather.

2. The leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The gradient dehydration process includes three stages of drying control: specifically, the first stage is drying at 5~40℃ to a moisture content of 30%~35%, the second stage is drying at 45~50℃ to a moisture content of 15%~20%, and the third stage is drying at 55~60℃ to a moisture content of 9%~11%.

3. The leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The tanning agent is vaporized using an atomizer. The working pressure of the atomizer is 0.8~1.5MPa, and the atomized particle size is ≤10μm.

4. The leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The tanning agent is at least one of chlorine, ozone, ethylene oxide, and propylene oxide.

5. A leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The tanning process takes 1 to 4 hours.

6. A leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The tanning process is carried out at a temperature of 10~50℃.

7. A leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, The tanning process is carried out at a pressure of 0.05~0.3 MPa.

8. A leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, During the tanning process, the flow rate of the tanning agent is 2~15 L / min.

9. A leather tanning method based on gas-phase mass transfer according to claim 1, characterized in that, During the tanning process, the temperature of the cavity of the sealed treatment device is 20~65 ℃.

10. A tanned leather, characterized in that, The tanned leather is prepared by the method described in any one of claims 1 to 8; the shrinkage temperature of the tanned leather is 80 to 90 °C.

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