A resourceful treatment process for VOCs-containing waste gas in perfume production

Abstract

This invention relates to the field of chemical waste gas treatment technology, and discloses a resource-based treatment process for VOCs-containing waste gas in fragrance production. S1, closed-loop collection of waste gas: VOCs-containing waste gas obtained during the synthetic oakmoss production process is introduced into a pretreatment adsorption tank via a pipeline. The tank is filled with modified alumina adsorbent to obtain pretreated waste gas. S2, the pretreated waste gas is introduced into an adsorption purification tower, which is filled with silica gel adsorbent and molecular sieve adsorbent to obtain purified waste gas. S3, the purified waste gas is condensed through a brine circulation system, the primary condensate is collected, and the remaining tail gas is introduced into a deep condenser. The deep condensation process yields secondary condensate, and the uncondensed tail gas enters the tail gas purification system. S4, the primary and secondary condensates are mixed and fed into a continuous atmospheric distillation column for separation and purification. Methanol is collected at the top of the column, and toluene is separated at the bottom. Methanol and toluene are fed into the upstream synthetic oakmoss production line, and the remaining tail gas enters the tail gas purification system.

Description

Technical Field

[0001] This invention relates to the field of chemical waste gas treatment technology, specifically to a resource-based treatment process for VOCs-containing waste gas in fragrance production. Background Technology

[0002] In the field of fragrance and fine chemical synthesis, especially in the production of products such as synthetic oakmoss, large amounts of organic solvents are often used. Typical processes include methylation, alkali-catalyzed condensation, cyclization, aromatization, and refining. These processes typically require methanol as the reaction solvent and heat-carrying medium, and toluene for extraction. During production, high-temperature vacuum distillation and solvent removal operations generate large amounts of volatile organic compounds (VOCs) containing methanol, toluene, and other trace impurities. Existing treatment methods usually employ a closed collection system to collect exhaust gases from workshop vents and storage tank breather valves. After flame-arresting and pressure-stabilizing pretreatment, the gases enter a multi-stage indirect condensation and liquefaction unit for solvent recovery. Subsequently, they are purified through a crude solvent buffer homogenization and continuous precision distillation purification unit. Finally, the refined solvent is returned to the production system for reuse, while the uncondensed exhaust gases are discharged through a terminal purification system.

[0003] However, in the existing technology, for such complex mixed waste gas containing alkaline droplets, solid dust, trace organic colloids and free acidic impurities, the existing treatment processes are difficult to achieve efficient separation and high-purity recovery of high-value organic components such as methanol and toluene while ensuring that the subsequent condensation equipment does not scale and the distillation system is not contaminated. This results in limited resource utilization and a heavy end-of-pipe treatment load.

[0004] Based on this, this application provides a resource-based treatment process for VOCs-containing waste gas in fragrance production. Summary of the Invention

[0005] Technical problems to be solved

[0006] This application provides a resource-based treatment process for VOCs-containing waste gas in fragrance production, which can solve the environmental pollution and resource waste caused by VOCs-containing waste gas emissions during fragrance production, especially addressing the technical challenge of efficiently recovering and utilizing organic waste gas, mainly methanol and supplemented by toluene, generated in the synthetic oakmoss process.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This application provides a resource recovery process for VOCs-containing waste gas in fragrance production, specifically including the following steps:

[0010] S1. Closed-loop collection of waste gas: The VOC-containing waste gas obtained during the production of synthetic oak moss is introduced into the pretreatment adsorption tank through a pipeline. The tank is filled with modified alumina adsorbent to obtain pretreated waste gas.

[0011] S2. The pretreated waste gas is introduced into the adsorption purification tower, which is filled with silica gel adsorbent and molecular sieve adsorbent to obtain purified waste gas.

[0012] S3. The purified exhaust gas is condensed by salt water circulation, the primary condensate is collected and the remaining tail gas is introduced into the deep condenser. A cascade refrigeration unit is used to provide a cold source. The deep condensation process yields secondary condensate, and the uncondensed tail gas enters the tail gas purification system.

[0013] S4. The primary and secondary condensates are mixed and fed into a continuous atmospheric distillation column for separation and purification. Methanol is collected from the top of the column, and toluene is separated from the bottom of the column. Methanol and toluene are fed into the upstream synthetic rubber production, and the remaining tail gas enters the tail gas purification system.

[0014] In the above technical solution, by setting up modified alumina pretreatment and molecular sieve removal of alkaline droplets, solid dust, trace organic colloids, and free acidic impurities from the waste gas, only methanol and toluene are allowed to pass through. This solves the technical problems of scale formation in subsequent condensation equipment and contamination of the distillation system caused by impurities in existing technologies. Its beneficial effect is that it significantly improves the efficiency of subsequent condensation recovery and the purity of distillation products. By utilizing the physical properties that different temperature zones correspond to different saturated vapor pressures, it achieves efficient staged liquefaction of high-concentration and low-concentration VOCs components, avoiding the problems of excessive energy consumption or incomplete condensation from a single cold source. Finally, atmospheric pressure distillation separates the recovered mixed solvent into high-purity methanol and toluene for reuse in production, forming a complete material closed loop from waste gas collection to solvent regeneration, which significantly reduces the consumption of fresh solvent and the amount of hazardous waste emissions.

[0015] Furthermore, in step S1, the modified alumina adsorbent is a phosphoric acid-activated alumina adsorbent.

[0016] Furthermore, the modified alumina adsorbent is specifically prepared by the following steps:

[0017] Prepare a 10-20 wt% phosphoric acid aqueous solution by mixing pure phosphoric acid with deionized water. Mix the solution with alumina at a liquid-to-solid ratio of 3:1 and impregnate at room temperature for 5-6 hours. After filtration, transfer the solution to a muffle furnace and heat it from room temperature to 140-160℃ at a rate of 5-10℃ / min, holding for 1-1.5 hours. Then heat it to 480-520℃ at a rate of 1-5℃ / min, holding for 3-4 hours. Afterward, allow it to cool naturally to below 100℃ before discharging. Wash the product with deionized water until the pH of the washing solution is 6-7, and then dry it to obtain the modified alumina adsorbent.

[0018] More preferably, in step S1, the modified alumina adsorbent is specifically prepared by the following steps:

[0019] Take 500g of industrial-grade γ-alumina, wash it three times with deionized water to remove surface dust, and dry it in an oven at 120℃ for 2 hours. Prepare a 15wt% phosphoric acid aqueous solution by mixing phosphoric acid and deionized water, and pour it into the alumina at a liquid-to-solid ratio of 3:1. Impregnate at room temperature for 6 hours. Filter out the impregnated alumina and transfer it to a muffle furnace. Program the temperature: increase it from room temperature to 150℃ at 5℃ / min and hold for 1 hour; then increase it to 500℃ at 3℃ / min and hold for 4 hours. Allow it to cool naturally to below 100℃ and discharge it. Wash it with deionized water until the pH of the effluent is 6-7, and dry it to obtain the modified alumina adsorbent.

[0020] In the above technical solution, γ-alumina is modified by phosphoric acid activation. During high-temperature calcination, phosphate ions react with the alumina framework to generate a stable aluminum phosphate phase, which not only enhances the density of acidic sites on the adsorbent surface but also optimizes the pore structure. Its beneficial effect is that it significantly improves the adsorbent's retention capacity and mechanical strength for polar impurities in complex waste gases, and solves the problems of poor selectivity and easy pulverization of ordinary alumina for alkaline droplets and acidic impurities. In particular, by controlling the phosphoric acid concentration to 15wt% and setting a specific programmed temperature rise curve, first raising it at a low speed to 150℃ for dehydration, and then raising it to 500℃ for crystal transformation, the modifier is uniformly loaded without damaging the carrier framework. Washing to neutrality eliminates the risk of corrosion of downstream equipment by residual free acid.

[0021] Furthermore, in step S1, the operating parameters of the pretreatment adsorption tank are ambient temperature and the liquid residence time in the column bottom is 5-8 seconds. Hot nitrogen gas at 150°C is introduced into the adsorption tank once a week to back-purge the adsorbent, carrying away desorbed impurities into the condenser for recovery. After regeneration, the adsorbent is cooled to ambient temperature and then reused.

[0022] In this invention, by limiting the residence time of the waste gas in the pretreatment adsorption tank to 5-8 seconds, a high gas throughput can be maintained while ensuring sufficient gas-solid contact to remove large particulate dust and some polar impurities. This solves the problems of incomplete purification due to too short a residence time or bulky equipment due to too long a residence time. Its beneficial effect is that it achieves a balance between pretreatment efficiency and economy. Combined with periodic regeneration using 150°C hot nitrogen, the adsorbed organic matter is desorbed and carried out by heating and purging with inert gas in an oxygen-free environment. This avoids the adsorbent sintering and deactivation caused by high-temperature oxidation and effectively restores the microporous structure of the adsorbent, thus extending the service life of the adsorbent.

[0023] Further, in step S2, the molecular sieve adsorbent is a silica gel-molecular sieve composite adsorbent, specifically prepared by the following steps: Take 300g of coarse-pore silica gel, impregnate it with a 1-3wt% silane coupling agent ethanol solution at a liquid-to-solid ratio of 2:1 for 2 hours, filter it, dry it in an oven at 150℃ for 3 hours, activate it in a muffle furnace at 300℃ for 2 hours, and cool it for later use; Take 200g of hydrogen-form ZSM-5 molecular sieve, impregnate it in a 0.1mol / L copper nitrate solution at a liquid-to-solid ratio of 4:1, stir it at room temperature for 4 hours; filter it, dry it at 120℃ for 4 hours, and calcine it in a muffle furnace at 550℃ for 5 hours to obtain Cu / ZSM-5 molecular sieve; in the adsorption purification tower, the middle is separated by a stainless steel wire mesh.

[0024] This technical solution prepares two adsorbents: hydrophobically modified silica gel and copper ion-exchange molecular sieves, separated by a stainless steel mesh. The lower silica gel layer preferentially adsorbs moisture and macromolecular colloids, while the upper molecular sieve layer specifically adsorbs methanol and toluene. This design effectively solves the problems of poor adsorption performance of single adsorbents in humid environments and low adsorption capacity for aromatic hydrocarbons, achieving staged purification and improving the purification effect. By adding a silane coupling agent to hydrophobically modify the silica gel, its surface water absorption capacity is reduced, decreasing the occupation of active sites by water vapor. Copper ion exchange constructs Lewis acid centers within the molecular sieve channels, enhancing the adsorption capacity for π-electron-containing compounds such as toluene, thereby improving the adsorption capacity and purification effect.

[0025] Furthermore, in the filling process, the lower layer is filled with silica gel adsorbent, accounting for 60% of the total filling layer height; the upper layer is filled with molecular sieve adsorbent, accounting for 40% of the total filling layer height.

[0026] In this invention, silica gel and molecular sieves are packed in a reverse density gradient. The waste gas first passes through the large-pore silica gel adsorbent to filter out most impurities, and then enters the microporous molecular sieve adsorbent for fine adsorption. This solves the problems of rapid adsorption bed penetration and uneven pressure drop. The advantages are: full utilization of expensive molecular sieves and prevention of large-molecule contamination; 60% silica gel adsorbent provides sufficient dirt-holding capacity, ensuring stable pressure drop during long-term system operation; and 40% molecular sieve adsorbent enables deep removal of target VOCs, while also effectively controlling costs.

[0027] Furthermore, in step S2, the operating parameters of the adsorption purification tower are: ambient temperature, liquid residence time in the tower bottom is 12-15s, and adsorbent activation temperature is 180℃.

[0028] In the above technical solution, by extending the residence time of the liquid in the bottom of the adsorption purification tower to 12-15s, the kinetic characteristics of the slow diffusion rate within the micropores of the molecular sieve are adapted, ensuring that methanol and toluene molecules have sufficient time to enter the pores and be adsorbed. This solves the problem of outlet concentration fluctuation caused by mass transfer resistance, and its beneficial effect is to significantly improve the purity and stability of the purified gas. At the same time, setting 180℃ as the activation and regeneration temperature of the molecular sieve adsorbent is effective in overcoming the van der Waals forces between organic matter and adsorbent to achieve complete desorption, while being lower than the sintering temperature of the molecular sieve adsorbent and the structural collapse temperature of silica gel, thus achieving the best match between regeneration efficiency and material thermal stability.

[0029] Furthermore, in step S3, the brine circulation condensation specifically uses ethylene glycol low-temperature brine heat exchange medium, with the following operating parameters: heat exchange medium temperature -15℃, exhaust gas inlet temperature 60~75℃, condenser wall temperature stably controlled at -12~-15℃, and exhaust gas residence time in the condenser bottom liquid 8~10s.

[0030] In the above technical solution, by using ethylene glycol low-temperature brine as the heat exchange medium and precisely controlling the wall temperature at -12~-15℃, and utilizing the characteristic that the saturated vapor pressure of methanol and toluene drops sharply at this temperature, the liquefaction and recovery of most organic vapors are achieved. This solves the problem that conventional water cooling cannot condense low-boiling-point components or that cryogenics consumes too much energy. Its beneficial effect is that a high primary recovery rate is achieved with low energy consumption. In particular, controlling the inlet temperature of the exhaust gas at 60~75℃ and combining it with a residence time of 8~10s for the liquid in the tower bottom ensures that the gaseous material has sufficient heat transfer temperature difference and phase change time in the condenser, avoiding entrainment losses caused by excessive flow rate or icing blockage caused by excessively low temperature.

[0031] Furthermore, in step S3, the deep condensation is carried out at a condensation operating temperature of -40°C, with the heat exchange wall surface maintained at a constant temperature of -38 to -40°C, and the liquid residence time in the gaseous material tower bottom being 10 to 12 seconds.

[0032] In this invention, by introducing a cascade refrigeration unit to further reduce the condensation temperature to -40℃ and controlling the wall temperature to be constant at -38~-40℃, it is possible to capture the low-concentration, low-partial-pressure methanol and toluene vapors remaining after the first-stage condensation, thereby solving the problem that the VOCs concentration in the tail gas of the single-stage condensation is still high and difficult to meet emission standards. Its beneficial effect is that it greatly reduces the load on the end tail gas treatment system; by appropriately extending the liquid residence time in the tower bottom to 10~12s, it compensates for the mass transfer resistance caused by the increase in gas viscosity and the decrease in diffusion coefficient under low temperature environment, ensuring the full liquefaction of trace organic components, and demonstrating the synergy between deep purification and energy efficiency control.

[0033] Furthermore, in step S4, the distillation is carried out at atmospheric pressure; the reboiler heating temperature is 95~105℃, the top temperature is 64~65℃; the reflux ratio is controlled at 2.5:1, and the liquid residence time of the material in the reboiler of the distillation column is 30~40 minutes.

[0034] In this invention, by strictly controlling the column top temperature at 64-65℃ (close to the boiling point of methanol) and the column bottom temperature at 95-105℃ (below the boiling point of toluene but sufficient to vaporize it) under normal pressure, and using a reflux ratio of 2.5:1, efficient separation is achieved by utilizing the difference in volatility between methanol and toluene. This solves the technical problems of incomplete separation of mixed solvents and substandard reuse quality. Its beneficial effects include the stable acquisition of methanol with a purity ≥98.8% and toluene with a purity ≥99.0%, meeting the stringent requirements for synthetic oakmoss production. The 30-40 min residence time of the liquid in the column bottom ensures sufficient contact and equilibrium between the vapor and liquid phases, avoiding cross-contamination of components caused by insufficient separation stages.

[0035] Furthermore, in steps S3 and S4, the exhaust gas purification includes activated carbon adsorption and catalytic combustion steps. The catalytic combustion is carried out using a precious metal platinum-based honeycomb catalyst, with a catalyst activation temperature of 220°C, a catalytic combustion operating temperature of 240~260°C, and a space velocity of 8000 h⁻¹. -1 .

[0036] In the above technical solution, activated carbon is used to smooth airflow fluctuations and enrich trace organic matter. Then, at a relatively low temperature of 240-260℃, the highly active platinum catalyst completely oxidizes the organic matter into carbon dioxide and water, thus solving the problems of excessive direct emissions of trace VOCs and high energy consumption in traditional incineration. Its beneficial effects include achieving near-zero emissions of exhaust gas and energy recovery; among which, 8000h -1 The high space velocity design indicates that the catalyst has extremely high processing capacity per unit volume. Combined with the activation temperature of 220°C, it ensures rapid system start-up and maintains high conversion efficiency over a wide load range.

[0037] Beneficial technical effects

[0038] This application provides a resource-based treatment process for VOCs-containing waste gas in fragrance production. The process involves sequentially introducing the VOCs-containing waste gas into a pretreatment adsorption tank filled with modified alumina adsorbent and an adsorption purification tower filled with molecular sieve adsorbent for multi-stage purification. This effectively removes alkaline droplets, solid dust, trace amounts of organic colloids, and free acidic impurities from the waste gas, thereby obtaining high-purity purified waste gas and avoiding scaling in subsequent condensation equipment and contamination of the distillation system.

[0039] This invention utilizes a stepped cooling method combining brine circulating condensation and cascade refrigeration for deep condensation. Based on the liquefaction characteristics of methanol and toluene vapors at different temperature ranges, most organic components are condensed and recovered as primary and secondary condensates, significantly reducing the concentration of pollutants in the gas phase. The mixed condensate is then fed into a continuous atmospheric distillation column. By controlling the temperature at the top and bottom of the column and the reflux ratio, efficient separation is achieved using the difference in volatility between methanol and toluene, resulting in high-purity methanol and toluene that are returned to the upstream production system for reuse. Uncondensed tail gas is treated harmlessly through a tail gas purification system. This effectively solves the problems of inefficient separation and recovery of high-value solvents in complex VOCs waste gas and low resource utilization rates, achieving closed-loop material flow, significantly reducing fresh solvent consumption and hazardous waste emissions, and improving the stability, reliability, and economic benefits of the process operation. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a process flow diagram of the resource utilization treatment process for VOCs-containing waste gas in fragrance production according to the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The raw materials used in the embodiments of this invention are as follows:

[0044] γ-alumina: Guangdong Yuanxin Chemical, 20-40 mesh;

[0045] Phosphoric acid: analytical grade;

[0046] Coarse-porous silica gel, Qingdao Ocean Chemical, coarse-porous spherical silica gel, type C, particle size 4-6mm;

[0047] Silane coupling agent: KH-550;

[0048] Hydrogen-type ZSM-5 molecular sieve: Nankai University Catalyst Factory, silicon-to-aluminum ratio 50, model NKZ-50A;

[0049] Copper nitrate: Sinopharm Group, analytical grade;

[0050] The waste gas from the synthetic oak moss production process is taken from the desolventing vent of the synthesis workshop. Its main components are methanol, toluene, and trace impurities. The activated carbon after adsorption saturation in the tail gas purification system is treated as hazardous waste and disposed of by a qualified unit. The treated tail gas is then discharged through a 15-meter-high exhaust stack.

[0051] Example 1

[0052] A resource recovery process for VOCs-containing waste gas in fragrance production, specifically including the following steps:

[0053] S1. The VOC-containing waste gas obtained during the production of synthetic oak moss is introduced into the pretreatment adsorption tank through a pipeline. The inlet temperature is 50℃. The tank is filled with modified alumina adsorbent to obtain pretreated waste gas. The modified alumina adsorbent is prepared by mixing pure phosphoric acid and deionized water to make a 15wt% phosphoric acid aqueous solution. It is mixed with alumina at a liquid-solid ratio of 3:1 and impregnated at room temperature for 6 hours. After filtration, it is transferred to a muffle furnace and heated to 150℃ at 5℃ / min and held for 1 hour. Then it is heated to 500℃ at 3℃ / min and held for 4 hours. It is then cooled naturally to below 100℃ and discharged. It is washed with deionized water until pH=6~7 and dried to obtain the pretreated waste gas. The operating parameters of the pretreatment adsorption tank are room temperature and the residence time of the waste gas in the liquid in the bottom of the tank is 6 seconds.

[0054] S2. The pretreated waste gas is introduced into the adsorption purification tower. The lower layer of the adsorption purification tower is filled with silica gel adsorbent, and the upper layer is filled with molecular sieve adsorbent. The silica gel adsorbent is prepared by impregnating coarse-porous silica gel with a 2wt% silane coupling agent ethanol solution for 2 hours, filtering and drying, and then activating it at 300℃ for 2 hours. The molecular sieve adsorbent is prepared by impregnating hydrogen-form ZSM-5 molecular sieve in a 0.1mol / L copper nitrate solution, stirring at room temperature for 4 hours, filtering and drying, and then calcining at 550℃ for 5 hours. The silica gel adsorbent accounts for 60% of the total packing layer, and the molecular sieve adsorbent accounts for 40% of the total packing layer. The operating parameters of the adsorption purification tower are room temperature and the residence time of the waste gas in the liquid in the tower bottom is 13 seconds, resulting in purified waste gas. After adsorption saturation, hot nitrogen gas at 150℃ is introduced for back purging for 2-3 hours. The desorbed organic matter is condensed and recovered. The regenerated adsorbent is cooled to room temperature and put back into use.

[0055] S3. The purified waste gas is condensed by circulating brine, using ethylene glycol low-temperature brine as the heat exchange medium. The heat exchange medium temperature is -15℃, the waste gas inlet temperature is 65℃, and the condenser wall temperature is stably controlled at -15℃. The liquid residence time of the waste gas in the condenser is 9s. The primary condensate is collected and the remaining tail gas is introduced into the deep condenser. The deep condensation working temperature is -40℃, the heat exchange wall temperature is constant at -40℃, and the liquid residence time of the gaseous material in the condenser is 11s. The deep condensation process yields secondary condensate, and the uncondensed tail gas enters the tail gas purification system.

[0056] S4. The primary and secondary condensates are mixed and fed into a continuous atmospheric distillation column for separation and purification. The distillation column has 40 trays, with the feed position at the 15th tray. The operating pressure is atmospheric pressure, the reboiler temperature is 100℃, the top temperature is 64.5℃, the reflux ratio is controlled at 2.5:1, and the liquid residence time of the material in the reboiler is 35 minutes. Methanol is collected at the top of the column, and toluene is separated from the reboiler. Methanol and toluene are fed into the upstream synthetic rubber production. The remaining tail gas enters the tail gas purification system, which uses activated carbon adsorption and catalytic combustion. The catalytic combustion is filled with a precious metal platinum-based honeycomb catalyst. The catalytic combustion operating temperature is 250℃, and the space velocity is 8000 h⁻¹. The treated gas meets the emission standards.

[0057] Example 2

[0058] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the bottom of the pretreatment adsorption tank in step S1 is adjusted from 6s to 5s, so as to obtain pretreated waste gas and continue to carry out subsequent treatment.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the bottom of the pretreatment adsorption tank in step S1 is adjusted from 6s to 8s, so as to obtain pretreated waste gas and continue to carry out subsequent treatment.

[0061] Example 4

[0062] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the bottom of the adsorption purification tower in step S2 is adjusted from 13s to 12s, while the other conditions remain unchanged.

[0063] Example 5

[0064] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the bottom of the adsorption purification tower in step S2 is adjusted from 13s to 15s, while the other conditions remain unchanged.

[0065] Example 6

[0066] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the waste gas tower of the brine circulating condenser in step S3 is adjusted from 9s to 8s, while the other conditions remain unchanged.

[0067] Example 7

[0068] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the waste gas tower of the brine circulating condenser in step S3 is adjusted from 9s to 10s, while the other conditions remain unchanged.

[0069] Example 8

[0070] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the gas phase material tower of the deep condenser in step S3 is adjusted from 11s to 10s, while the other conditions remain unchanged.

[0071] Example 9

[0072] The difference between this embodiment and Embodiment 1 is that the residence time of the liquid in the gas phase material tower of the deep condenser in step S3 is adjusted from 11s to 12s, while the other conditions remain unchanged.

[0073] Example 10

[0074] The difference between this embodiment and Embodiment 1 is that the heating temperature of the distillation column reboiler in step S4 is adjusted from 100℃ to 95℃, while the other conditions remain unchanged.

[0075] Example 11

[0076] The difference between this embodiment and Embodiment 1 is that the heating temperature of the distillation column reboiler in step S4 is adjusted from 100℃ to 105℃, while the other conditions remain unchanged.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that the original waste gas is directly subjected to two-stage condensation and distillation without adsorption pretreatment.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that step S2 uses only unmodified ordinary ZSM-5 molecular sieve, without using silica gel composite and copper modification.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that only -15°C brine condensation is used, and the -40°C deep condensation step is omitted.

[0083] Comparative Example 4

[0084] The difference between this comparative example and Example 1 is that it uses a traditional process of water spraying and activated carbon adsorption to treat the same waste gas, without solvent recovery. The specific operation is as follows: The VOC-containing waste gas obtained during the synthetic rubber moss production process is first introduced into a packed water spray tower, using tap water as the spray liquid, with a liquid-to-gas ratio controlled at 3 L / m³, and the waste gas residence time in the bottom of the tower is 2 seconds. After spraying, the wet waste gas enters a demister to remove droplets and then enters a fixed-bed activated carbon adsorption tank. The coal-based granular activated carbon used is ≥800 mg / g, and the waste gas residence time in the bottom of the adsorption tank is 1.2 seconds.

[0085] Operate according to the process conditions of Example 1.

[0086] The processes in the examples and comparative examples are now subjected to performance tests. Specific test parameters and methods are as follows:

[0087] 1. VOCs Removal Rate Test: Gas chromatography was used. 1L gas samples were collected using airtight syringes at the inlet manifold of the waste gas treatment system and the outlet of the tail gas after secondary condensation. An Agilent 7890B gas chromatograph equipped with an FID detector was used for detection. The chromatographic column was DB-624 (30m × 0.32mm × 0.25μm), and the temperature program was: initial 50℃ held for 2 min, then increased to 150℃ at 10℃ / min and held for 2 min. The concentrations of methanol and toluene were quantified using the external standard method. Removal rate (%) = (Inlet concentration - Outlet concentration) / Inlet concentration × 100%.

[0088] 2. Solvent Purity Test: Gas chromatography was used. Condensed liquid samples were collected in sample vials at the sample outlets of the distillation column (top and bottom). The samples were analyzed using a gas chromatograph equipped with an FID detector (as above). The chromatographic column was a DB-624 (60m × 0.32mm × 1.4μm). The temperature program was: initial 40℃, held for 5 min, then increased to 200℃ at a rate of 5℃ / min, and held for 5 min. The purity of methanol and toluene was calculated using the area normalization method.

[0089] 3. Adsorbent Performance Testing: The adsorption capacity of the S2 step adsorption purification tower was determined using the static adsorption method, and the specific surface area and pore volume were determined using the BET method. 0.5 g of dried adsorbent was placed in a constant temperature chamber at 25℃ and 30% RH, exposed to a 1000 ppm toluene standard gas atmosphere (N2 equilibrium), and tested using a constant gas flow of 100 mL / min until adsorption saturation. Adsorption saturation was considered achieved when the sample mass changed by less than 0.1% of the initial mass for 30 consecutive minutes. The saturated adsorption capacity was calculated using the gravimetric method.

[0090] 4. Exhaust gas emission test: At the exhaust stack of the catalytic combustion device, the concentration of non-methane total hydrocarbons (NMHC) is measured by gas chromatograph using a gas bag sampling method according to the standard method of HJ 38-2017 "Determination of total hydrocarbons, methane and non-methane total hydrocarbons in exhaust gas from stationary sources".

[0091] The specific test results are shown in Table 1.

[0092] Table 1

[0093]

[0094] According to the data in Table 1, Comparative Example 1 lacked the pretreatment adsorption tank, allowing acidic impurities and colloids in the waste gas to directly enter the subsequent system, leading to scaling and corrosion in the distillation column. After 30 days of operation, the purity of methanol and toluene decreased, and the VOCs removal rate was also lower than in all examples, proving that impurities interfered with the overall separation efficiency. Examples 1-3 all included pretreatment. The comparison showed that the removal rate of Example 2 was slightly lower than that of Examples 1 and 3, indicating that a residence time of 6-8 seconds in the column bottom is suitable for ensuring sufficient adsorption of impurities. Too short a residence time would lead to insufficient adsorption, while too long a residence time would increase equipment investment and limit benefits. Comparative Example 2 used unmodified ordinary ZSM-5 molecular sieve. Its toluene saturated adsorption capacity was lower than that of the composite adsorbent in Example 1. After two weeks of operation, its insufficient adsorption selectivity was exposed, failing to effectively intercept aromatization byproducts, resulting in a decrease in toluene product purity and the detection of phenolic impurities. This proves the necessity of combining silica gel with Cu-modified ZSM-5. Comparative Example 3 eliminated the -40℃ deep condensation, retaining only the -15℃ primary condensation. This results in the methanol component, which still has a high saturated vapor pressure at low temperatures, not being fully liquefied and recovered. Its VOCs removal rate drops sharply, and a large amount of methanol enters the tail gas system, increasing the concentration at the catalytic combustion inlet and relatively increasing catalytic combustion energy consumption. Comparative Example 4 uses a traditional water spray and activated carbon adsorption approach, which only transfers or dilutes VOCs, resulting in a low initial removal rate and a sharp increase in tail gas concentration after activated carbon deteriorates. This process does not produce any reusable products and continuously generates hazardous waste activated carbon, leading to high and unstable operating costs.

[0095] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0097] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A resource-based treatment process for VOCs-containing waste gas in fragrance production, characterized in that, Specifically, the following steps are included: S1. Closed-loop collection of waste gas: The VOC-containing waste gas obtained during the production of synthetic oak moss is introduced into the pretreatment adsorption tank through a pipeline. The tank is filled with modified alumina adsorbent to obtain pretreated waste gas. S2. The pretreated waste gas is introduced into the adsorption purification tower, which is filled with silica gel adsorbent and molecular sieve adsorbent to obtain purified waste gas. S3. The purified exhaust gas is condensed by salt water circulation, the primary condensate is collected and the remaining tail gas is introduced into the deep condenser for deep condensation treatment to obtain secondary condensate, and the uncondensed tail gas enters the tail gas purification system. S4. The primary and secondary condensates are mixed and fed into a continuous atmospheric distillation column for separation and purification. Methanol is collected from the top of the column, and toluene is separated from the bottom of the column. Methanol and toluene are fed into the upstream synthetic rubber production, and the remaining tail gas enters the tail gas purification system.

2. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S1, the modified alumina adsorbent is specifically prepared by the following steps: Prepare a 10-20 wt% phosphoric acid aqueous solution by mixing pure phosphoric acid with deionized water. Mix the solution with alumina at a liquid-to-solid ratio of 3:1 and impregnate at room temperature for 5-6 hours. After filtration, transfer the solution to a muffle furnace and heat it from room temperature to 140-160℃ at a rate of 5-10℃ / min, holding for 1-1.5 hours. Then heat it to 480-520℃ at a rate of 1-5℃ / min, holding for 3-4 hours. Afterward, allow it to cool naturally to below 100℃ before discharging. Wash the product with deionized water until the pH of the washing solution is 6-7, and then dry it to obtain the modified alumina adsorbent.

3. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, The operating parameters of the above pretreatment adsorption tank are ambient temperature and the liquid residence time in the bottom of the tower is 5-8 seconds.

4. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S2, the silica gel adsorbent and molecular sieve adsorbent are specifically prepared by the following steps: Coarse-porous silica gel was impregnated with a silane coupling agent ethanol solution for 1.5-2 hours, filtered, dried, activated in a muffle furnace at 300-320℃ for 1.5-2 hours, and cooled to obtain silica gel adsorbent; hydrogen-form ZSM-5 molecular sieve was impregnated in copper nitrate solution and stirred at room temperature for 3-4 hours; filtered, dried, and calcined at 520-580℃ for 4.5-5 hours to obtain molecular sieve adsorbent.

5. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S2, the filling process involves first filling the lower layer with silica gel adsorbent, which accounts for 55-60% of the total filling layer height; and then filling the upper layer with molecular sieve adsorbent, which accounts for 40-45% of the total filling layer height.

6. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S2, the operating parameters of the adsorption purification tower are ambient temperature and the residence time of the liquid in the tower bottom is 12-15s.

7. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S3, the brine circulation condensation specifically uses ethylene glycol low-temperature brine heat exchange medium with a temperature of -12 to -15°C, an exhaust gas inlet temperature of 60 to 75°C, a stable condenser wall temperature of -12 to -15°C, and an exhaust gas residence time of 8 to 10 seconds in the condenser bottom liquid.

8. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S3, the deep condensation operates at a temperature of -38 to -40°C, maintains a constant temperature of -38 to -40°C on the heat exchange wall, and has a liquid residence time of 10 to 12 seconds in the gaseous material tower bottom.

9. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In step S4, the distillation is carried out at atmospheric pressure; the reboiler temperature is 95~105℃, the top temperature is 64~65℃; the reflux ratio is controlled at 2-3:1, and the liquid residence time of the material in the reboiler of the distillation column is 30~40 minutes.

10. The resource-based treatment process for VOCs-containing waste gas in fragrance production according to claim 1, characterized in that, In steps S3 and S4, the exhaust gas purification includes activated carbon adsorption and catalytic combustion steps. The catalytic combustion is carried out using a precious metal platinum-based honeycomb catalyst, and the catalytic combustion operating temperature is 240~260℃.

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