Integrated process and system for recovering VOCs (volatile organic compounds) from synthetic leather tail gas through multi-mode phase-change condensation

Abstract

The invention relates to the technical field of synthetic leather industry, in particular to an integrated process and system for recycling VOCs from synthetic leather tail gas through multi-mode phase change condensation. The synthetic leather tail gas multi-mode phase change condensation VOCs recovery integrated process comprises the following steps: step 1, carrying out pre-condensation treatment on a mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; step 2, carrying out primary condensation treatment on the pre-condensed mixed gas phase, and converting part of DMF gas phase and a small amount of other gas phase in VOCs into liquid phase and recovering; and step 3, carrying out secondary condensation treatment on the uncondensed gas phase in the VOCs generated in the step 2, and converting the uncondensed gas phase in the VOCs into a liquid phase and recovering the liquid phase. According to the method, the recovery rate of the DMF gas phase in the VOCs is 99% or above through the multi-stage gradient condensation recovery process step, and the investment of a large amount of production cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of synthetic leather industry, and particularly relates to an integrated process and system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas. Background Art

[0002] At present, China has become the world's synthetic leather industry center. With the continuous innovation and popularization of ecological functional synthetic leathers such as water-based synthetic leather and solvent-free synthetic leather in the industry, the environmental protection of synthetic leather has been greatly improved, and its functionality has been further enriched. In addition, the export volume of synthetic leather in China is greater than the import volume, and the industry is huge. As a pillar industry in Lishui Economic and Technological Development Zone, there are currently 26 synthetic leather enterprises in the jurisdiction, and their annual output value accounts for 38% of the total industrial output value of the park. This industry has long followed an extensive development model, with prominent problems of large three-waste pollution and high energy and resource consumption, showing a significant environmental-economic imbalance. The synthetic leather industry contains organic substances such as DMF (N,N-dimethylformamide), benzene, esters, and ketones. In particular, DMF in the tail gas is a commonly used organic solvent. Due to its good solubility and high chemical stability, it is widely used in many fields. Although DMF has many advantages, relevant safety matters need to be noted during its use and storage. DMF has certain toxicity and irritation. Contact with the skin and eyes will cause irritation, and excessive inhalation will damage the respiratory system. Therefore, direct emission or simple treatment and emission of the tail gas in the synthetic leather industry will cause serious harm to the environment and human health. Recycling DMF through tail gas DMF recovery technology not only promotes the environmental protection development of the synthetic leather industry but also can generate new economic benefits from the recycled DMF.

[0003] The traditional process for treating waste gas and wastewater in synthetic leather enterprises is to absorb at room temperature through water spray and then recover by rectification. Since the batching process will generate a large amount of DMF volatilization and traditional water washing cannot effectively treat it, the DMF concentration in the spray tower will be relatively high. Moreover, a large gas velocity in the spray tower will carry a large amount of DMF into the air, polluting the environment. Secondly, through single rectification, organic solvents that are insoluble in water and have low boiling points cannot be recovered. A large amount of organic solvents volatilize into the air and water, resulting in pollution of the air and water, and the organic solvents are not recovered and utilized, causing great losses. In addition, the rectification recovery process will generate dimethylamine, which is harmful to the human body.

[0004] With the advancement of green and sustainable industries, the treatment of highly polluting synthetic leather tail gas urgently requires the top-level design of green industrial process technology. Based on this, it is necessary to design a relatively environmentally friendly and economically feasible synthetic leather tail gas process system to achieve the economic and sustainable transformation of the traditional high-energy-consuming and highly polluting water washing and spraying methods. Summary of the Invention

[0005] The object of the present invention is to provide an integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas, so as to solve the problem that the existing waste gas and wastewater treatment processes in synthetic leather enterprises cannot effectively treat the toxic volatile organic compounds in synthetic leather tail gas.

[0006] In order to solve the above problems, the technical solution of an integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention is as follows: An integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas, comprising the following steps: Step 1, performing pre-condensation treatment on the mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; Step 2, performing primary condensation treatment on the pre-condensed mixed gas phase, and converting a part of the DMF gas phase and a small amount of other gas phases in the VOCs into a liquid phase and recovering them; Step 3, performing secondary condensation treatment on the uncondensed gas phase in the VOCs generated in Step 2, and converting the uncondensed gas phase in the VOCs into a liquid phase and recovering it.

[0007] Preferably, after Step 3, the integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas further comprises: Circulating the mixed gas phase in Step 3 to Step 2 and using it as a cooling medium for primary condensation treatment.

[0008] Preferably, in the mixed gas phase, the mass fraction of VOCs in the mixed gas phase is 1.2 - 1.4%.

[0009] Preferably, the temperature of the pre-condensation treatment is 30 - 35 °C, the temperature of the primary condensation treatment is 5 - -20 °C, and the temperature of the secondary condensation treatment is -30 - -45 °C.

[0010] Preferably, in Step 1, before the pre-condensation treatment, the temperature of the mixed gas phase is 70 - 80 °C.

[0011] Preferably, after the primary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is 80 - 85%; after the secondary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is more than 99%.

[0012] Preferably, before Step 1, the integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas further comprises: Passing air through the synthetic leather slurry under the action of an oven, and releasing the VOCs in the synthetic leather slurry to form a mixed gas phase with air.

[0013] Preferably, the temperature in the oven is 150 - 160 °C.

[0014] The present invention also provides an integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas, based on the above-mentioned integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas. The technical solution adopted is as follows: An integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas, comprising: A pre-condensation treatment module, configured to perform pre-condensation treatment on the mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; A primary condensation treatment module, connected to the pre-condensation treatment module, configured to perform primary condensation treatment on the pre-condensed mixed gas phase, and convert a part of the DMF gas phase and a small amount of other gas phases in the VOCs into a liquid phase for recovery; A secondary condensation treatment module, connected to the primary condensation treatment module, configured to perform secondary condensation treatment on the uncondensed gas phase in the VOCs generated by the primary condensation treatment module, and convert the uncondensed gas phase in the VOCs into a liquid phase for recovery.

[0015] Preferably, the integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas further comprises a circulation module, which is connected to the secondary condensation treatment module and connected to the primary condensation treatment module, and is configured to circulate the mixed gas phase in the secondary condensation treatment module to the primary condensation treatment module for use as a cooling medium for the primary condensation treatment.

[0016] Compared with the prior art, the integrated process and system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas in the present application first subject the mixed gas phase to pre-condensation treatment to reduce its temperature when entering the primary condensation treatment, prevent adverse effects caused by sudden temperature changes, and reduce the subsequent condensation energy consumption; through the primary condensation treatment, a part of the DMF gas phase and a small amount of other gas phases in the VOCs are first partially phase-changed and captured and converted into a liquid phase for recovery; through the secondary condensation treatment, the remaining DMF gas phase and other gas phases in the VOCs are again phase-changed and captured and converted into a liquid phase for recovery. The present application realizes a recovery rate of more than 99% for the DMF gas phase in the VOCs through the multi-stage gradient condensation recovery process steps of pre-condensation treatment, primary condensation treatment, and secondary condensation treatment, and can also recover other gas phases in the VOCs, and the recovery rate of other gas phases can reach more than 70%. The recovered volatile organic compounds can be further returned to the synthetic leather production process line for recycling as diluents, saving a large amount of production cost input. At the same time, the integrated process and system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas in the present application significantly improves the green environmental friendliness of the synthetic leather industry. While promoting the long-term stable operation of the synthetic leather industry, on the one hand, it greatly reduces the emissions of volatile organic poisons, and on the other hand, it greatly utilizes the recovered organic matter for recycling as diluents in the synthetic leather industry, improving the economy of the system while reducing emissions.

[0017] After step 3, the integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas further includes: Circulate the mixed gas phase in step 3 back to step 2 and use it as the cooling medium for primary condensation treatment. After secondary condensation treatment, most of the volatile organic compounds are condensed into a liquid phase for separation. At this time, the cryogenic cooling capacity carried by the mixed gas phase is recycled back to the primary condensation treatment to further condense the mixed gas phase before it enters the secondary condensation treatment after pre-condensation treatment, thereby reducing the cold capacity requirement for subsequent secondary condensation treatment and achieving the effect of recycling air resources, further reducing the cost of synthetic leather tail gas purification.

[0018] In the mixed gas phase, the mass fraction of VOCs in the mixed gas phase is 1.2 - 1.4%, which can ensure the maximum recovery treatment of volatile organic compounds in VOCs and the recycling of air simultaneously.

[0019] The temperature of the pre-condensation treatment is 30 - 35°C, the temperature of the primary condensation treatment is 5 - -20°C, and the temperature of the secondary condensation treatment is -30 - -45°C, which can maximize the effect of each stage of condensation, and then achieve the cascade condensation separation and recovery of volatile organic compounds in VOCs.

[0020] Before step 1, the integrated process for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas further includes: Pass air through the synthetic leather slurry under the action of an oven to release the VOCs in the synthetic leather slurry and form a mixed gas phase with the air. This is mainly to volatilize the volatile organic compounds in the synthetic leather slurry and be carried away by the introduced purge air, and form a mixed gas phase with the air.

[0021] The temperature in the oven is 150 - 160°C to ensure that all the volatile organic compounds in the synthetic leather slurry are volatilized. Description of the Drawings

[0022] Figure 1 is a schematic diagram of the system for treating synthetic leather tail gas by the traditional water washing and spraying method; Figure 2 is a schematic diagram of a structure of the integrated system for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention; Figure 3 is another schematic diagram of a structure of the integrated system for multimodal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention; In the figure, 1. Oven, 2. Fan, 3. Spray tower, 4. Rectifying tower, 5. Adsorption tower, 6. Pre-cooler, 7. Primary condenser, 8. Secondary condenser. Detailed Embodiments

[0023] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation of the present application.

[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned accompanying drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0025] The schematic diagram of the system for treating synthetic leather tail gas by the traditional water washing and spraying method in the prior art is as Figure 1 shown. Specifically, the synthetic leather slurry is baked at a high temperature in the oven 1, and volatile organic compounds (VOCs) are released at a high temperature and are swept away by the air introduced into the oven 1, forming a mixed gas phase of VOCs and air; the fan 2 sends the mixed gas phase into the spray tower 3 for water washing, and part of the VOCs is dissolved in water to form waste liquid and then sent into the rectification tower 4, and the VOCs that are not dissolved in water evaporate with the water, and the VOCs that are not dissolved in water still need to be further desorbed through the adsorption tower 5; the wastewater separates the VOCs in the wastewater through rectification in the rectification tower 4, and then realizes the recovery of DMF. The above process consumes a large amount of water, and the treatment of the formed wastewater and waste gas is difficult and has poor effects. 95% of the wastewater is water and 5% is organic poisons, and the subsequent treatment is difficult, resulting in serious environmental pollution and not meeting the requirements of implementing low-carbon and green chemical industry.

[0026] In view of the problems existing in the above-mentioned prior art, the present application provides an integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas.

[0027] A detailed description will be given of an integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas provided by the present application.

[0028] Specific embodiment 1 of the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention: Referring to Figure 2 , an integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas includes the following steps: Step 1, perform pre-condensation treatment on the mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; Step 2, perform primary condensation treatment on the pre-condensed mixed gas phase, and part of the DMF gas phase and a small amount of other gas phases in the VOCs are transformed into the liquid phase and recovered; Step 3, perform secondary condensation treatment on the uncondensed gas phase in the VOCs generated in Step 2, and the uncondensed gas phase in the VOCs is transformed into the liquid phase and recovered.

[0029] In this embodiment, in the mixed gas phase, the mass fraction of VOCs in the mixed gas phase is 1.2 - 1.4%. The main components of VOCs are N, N-dimethylformamide (DMF), toluene, methyl acetate, and methyl ethyl ketone. DMF is a high-boiling organic compound with a boiling point of 153 °C; toluene, methyl acetate, and methyl ethyl ketone are medium- and low-boiling organic compounds. The boiling point of toluene is 110.6 °C, the boiling point of methyl acetate is 56.8 °C, and the boiling point of methyl ethyl ketone is 80 °C. The mixed gas phase formed by VOCs and air undergoes pre-condensation treatment to reduce the temperature of the mixed gas phase entering the primary condensation treatment; when entering the primary condensation treatment, since DMF in the VOCs is a high-boiling organic compound, it is preferentially condensed into the liquid phase for separation at this time, and a small amount of low-boiling organic compounds such as toluene, methyl acetate, and methyl ethyl ketone are condensed into the liquid phase for separation. After the primary condensation treatment, part of the high-boiling DMF gas phase and a small amount of the medium- and low-boiling toluene, methyl acetate, and methyl ethyl ketone gas phases in the VOCs are transformed into the liquid phase and recovered; after the secondary condensation treatment, the remaining DMF gas phase and toluene, methyl acetate, and methyl ethyl ketone in the VOCs are transformed into the liquid phase, and at this time the liquid phase is recovered.

[0030] In the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas in Example 1, due to the multi-stage cascade cryogenic separation and recovery of the synthetic leather tail gas, the organic poisons in the synthetic leather tail gas are significantly reduced. However, the finally purified tail gas carries a certain amount of cold energy at a certain temperature, and direct emission will also cause serious waste of cold energy. Therefore, the present invention further designs a process and system for coupling the recovery of VOCs from synthetic leather tail gas through multi-stage gradient condensation to make full use of the surplus energy of the pre-condensation and two-stage condensation purification processes. The following will be described in detail in conjunction with the embodiments of the present invention.

[0031] Specific Example 2 of the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention: Based on the above technical concept of the present invention, or on the basis of the specific embodiments of the present invention introduced above, the following provides another embodiment.

[0032] Please refer to Figure 3 , on the basis of Example 1, after Step 3, the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas further includes: The mixed gas phase in step 3 is recycled to step 2 and used as the cooling medium for the primary condensation treatment. After the secondary condensation treatment of the mixed gas phase, most of the VOCs are recovered. At this time, the condensed mixed gas phase is mainly air, and the mixed gas phase can be recycled to the primary condensation treatment as the cooling medium. At this time, the primary condensation treatment has two functions: one is to condense part of the DMF gas phase and a small amount of other gas phases in the VOCs, and the other is to recover and utilize the cold energy of the low-temperature mixed gas phase in the downstream secondary condensation treatment as the cooling medium for the primary condensation treatment, reduce the demand for additional cold energy, reduce the energy consumption in the secondary condensation treatment, and improve the system energy efficiency.

[0033] In this embodiment, before the pre-condensation treatment, the temperature of the mixed gas phase is 70 - 80 °C. The temperature of the pre-condensation treatment is 30 - 35 °C, and the temperature of the primary condensation treatment is 5 - -20 °C. After the primary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is 80 - 85%; the temperature of the secondary condensation treatment is -30 - -45 °C. After the secondary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is above 99%. At the same time, the recovery rates of toluene, methyl acetate, and methyl ethyl ketone are above 70%. At this time, the main component in the mixed gas phase after the secondary condensation treatment is air, and the temperature of the mixed gas phase is -30 - -45 °C. Recycling it back to the primary condensation treatment as the cooling medium can fully save the system's cold energy. The high-grade cold energy carried by the air can be used for the primary condensation treatment. Therefore, recycling this gas stream back to the primary condensation treatment as the cold energy source for the primary condensation treatment saves more than 70 kW·h of the system's energy consumption.

[0034] Specific embodiment 3 of the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas of the present invention: Based on the above technical concept of the present invention, or based on the specific embodiments of the present invention introduced above, another embodiment is provided below.

[0035] Based on embodiment 2, before step 1, the integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas further includes: The synthetic leather slurry is purged with air under the action of oven 1, and the VOCs in the synthetic leather slurry are released and form a mixed gas phase with the air. Among them, the temperature in oven 1 is 150 - 160 °C.

[0036] In this embodiment, the synthetic leather tail gas is treated by the normal and low temperature coupled condensation method. The composition of the synthetic leather tail gas is 134 kg / h of DMF, 19 kg / h each of toluene, methyl acetate and methyl ethyl ketone, and 14495 kg / h of air. At this time, the temperature of the mixed gas phase is 150 °C. The mechanical refrigeration method is adopted. The temperature of the mixed gas phase entering the pre-condensation treatment is 80 °C, the temperature of the pre-condensation treatment is 35 °C, the temperature of the first-stage condensation treatment is -24.5 °C, and the temperature of the second-stage condensation treatment is -35 °C. The cooling capacity of the first-stage condensation treatment is completely provided by the gas phase stream after the second-stage condensation treatment. After being treated by the above process, the recovery rate of DMF reaches 99.13%, the recovery rates of toluene, methyl acetate and methyl ethyl ketone are 72.37%, and the energy consumption can be reduced by 77.71 kW·h.

[0037] The present invention also provides an integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas. Based on the above-mentioned integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas, it includes: A pre-condensation treatment module for pre-condensing the mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; A first-stage condensation treatment module connected to the pre-condensation treatment module for performing first-stage condensation treatment on the pre-condensed mixed gas phase, and converting a part of the DMF gas phase and a small amount of other gas phases in the VOCs into a liquid phase and recovering them; A second-stage condensation treatment module connected to the first-stage condensation treatment module for performing second-stage condensation treatment on the uncondensed gas phase in the VOCs generated in the first-stage condensation treatment module, and converting the uncondensed gas phase in the VOCs into a liquid phase and recovering it.

[0038] Among them, the integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas further includes a circulation module, which is connected to the second-stage condensation treatment module and connected to the first-stage condensation treatment module for circulating the mixed gas phase in the second-stage condensation treatment module to the first-stage condensation treatment module and using it as a cooling medium for the first-stage condensation treatment.

[0039] The integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas further includes a preheating and volatilization module for introducing air purge under the action of oven 1 for the synthetic leather slurry, and releasing the VOCs in the synthetic leather slurry and forming a mixed gas phase with air.

[0040] Specifically, as Figure 2 and Figure 3As shown, the preheating and volatilization module is the oven 1, and the temperature in the oven 1 is 150 - 160 °C. The synthetic leather slurry and air enter the oven 1 together. Under the purging action of the air, the VOCs in the synthetic leather slurry are released and form a mixed gas phase with the air. The pre-condensation treatment module is the pre-cooler 6. The mixed gas phase is transported through the pipeline and naturally cooled to 70 - 80 °C, and then enters the pre-cooler 6. Among them, the cooling medium in the pre-cooler 6 is supplied by the normal-temperature process water circulation system, and its cooling capacity is provided by the normal-temperature process water circulation system. The primary condensation treatment module is the primary condenser 7. The cooling medium in the primary condenser 7 is the mixed gas phase circulated in the secondary condensation treatment module. The VOCs recovered by condensation are mainly DMF gas phase. The secondary condensation treatment module is the secondary condenser 8. The cooling medium in the secondary condenser 8 is the refrigerant, and its cooling capacity is supplied by the refrigerating machine. The model of the refrigerating machine is determined according to the condensation load requirement, and finally the recovery of VOCs is realized.

[0041] Here, those skilled in the art can understand that the specific operations of each use step in the above-mentioned integrated system for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas have been introduced in detail in the description of a kind of integrated process for multi-modal phase change condensation recovery of VOCs from synthetic leather tail gas with reference to Figures 2 to 3 Therefore, the repeated description will be omitted.

[0042] The above is only the preferred embodiment of the present invention, and it is not intended to limit the present invention. The patent protection scope of the present invention is subject to the claims. All equivalent structural changes made by using the description and drawings of the present invention should be included in the protection scope of the present invention by the same token.

Claims

1. An integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation, characterized in that: The following steps are involved: Step 1, pre-condensing a mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; Step 2, the pre-condensed mixed gas phase is subjected to a primary condensation treatment, and part of the DMF gas phase and a small amount of other gas phases in the VOCs are converted into a liquid phase and recovered; Step 3, performing secondary condensation treatment on the uncondensed gas phase in the VOCs generated in step 2, and converting the uncondensed gas phase in the VOCs into a liquid phase and recovering it.

2. The integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 1, characterized in that: After step 3, the integrated process for recovering VOCs from synthetic leather tail gas by multimodal phase change condensation further includes: The mixed gas phase in step 3 is circulated to step 2 and used as a cooling medium for the primary condensation treatment.

3. The integrated process for recovering VOCs from synthetic leather tail gas by multimodal phase change condensation according to claim 1 or 2, characterized in that: In the mixed gas phase, the mass fraction of VOCs in the mixed gas phase is 1.2-1.4%.

4. The integrated process for recovering VOCs from synthetic leather tail gas by multimodal phase change condensation according to claim 1 or 2, characterized in that: The temperature of the pre-condensation treatment is 30-35°C, the temperature of the first-stage condensation treatment is 5--20°C, and the temperature of the second-stage condensation treatment is -30--45°C.

5. The integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 4 is characterized in that: In step 1, before the pre-condensation treatment, the temperature of the mixed gas phase is 70-80°C.

6. The integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 4, characterized in that: After the primary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is 80-85%; after the secondary condensation treatment, the recovery rate of the DMF gas phase in the VOCs is more than 99%.

7. The integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 1 or 2, characterized in that: Before step 1, the synthetic leather tail gas multimodal phase change condensation VOCs recovery integrated process also includes: The synthetic leather slurry is blown with air in the oven, and the VOCs in the synthetic leather slurry are released and form a mixed gas phase with the air.

8. The integrated process for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 7, characterized in that: The temperature in the oven is 150-160°C.

9. A synthetic leather tail gas multi-modal phase change condensation VOCs recovery integrated system, characterized in that: The integrated process for recovering VOCs by multimodal phase change condensation of synthetic leather tail gas according to any one of claims 1 to 8 comprises: A pre-condensation processing module is used to pre-condense a mixed gas phase formed by VOCs and air to obtain a pre-condensed mixed gas phase; The primary condensation processing module is connected to the pre-condensation processing module and is used to perform primary condensation processing on the pre-condensed mixed gas phase, and part of the DMF gas phase and a small amount of other gas phases in the VOCs are converted into liquid phase and recovered; The secondary condensation treatment module is connected to the primary condensation treatment module and is used to perform secondary condensation treatment on the uncondensed gas phase in the VOCs generated in the primary condensation treatment module, and the uncondensed gas phase in the VOCs is converted into a liquid phase and recovered.

10. The integrated system for recovering VOCs from synthetic leather tail gas by multi-modal phase change condensation according to claim 9, characterized in that: The synthetic leather exhaust multimodal phase change condensation VOCs recovery integrated system also includes a circulation module, which is connected to the secondary condensation treatment module and connected to the primary condensation treatment module, and is used to circulate the mixed gas phase in the secondary condensation treatment module to the primary condensation treatment module for use as a cooling medium for the primary condensation treatment.

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