Low-boiling-point vocs gas treatment method and treatment equipment based on chlor-alkali process

Abstract

This invention discloses a method and equipment for treating low-boiling-point VOCs gas based on a chlor-alkali process. The method includes: passing waste gas containing VOCs into an adsorption tank containing an adsorbent, where the VOCs are adsorbed; desorbing the VOCs adsorbed by the adsorbent into a condenser using nitrogen stripping, balancing the gas pressure, and recovering the condensable VOCs; adding sodium chloride solution to a chlor-alkali generator, electrolyzing the sodium chloride solution to generate chlorine gas and sodium hydroxide solution; passing a mixture of uncondensed VOCs gas and nitrogen into a photochlorination reactor, introducing chlorine gas, where the chlorine reacts with the VOCs gas to generate chlorinated compounds; passing the chlorinated compounds into a hot alkaline water reactor containing sodium hydroxide solution, where the chlorinated compounds react with sodium hydroxide to generate alcohol and sodium chloride, and recovering the alcohol and sodium chloride. The method and equipment for treating low-boiling-point VOCs gas based on a chlor-alkali process provided by this invention achieve high-efficiency, high-quality, and low-energy-consumption recovery and treatment of VOCs gas.

Description

Technical Field

[0001] This invention relates to VOCs gas treatment methods, and particularly to a method and equipment for treating low-boiling-point VOCs gas based on a chlor-alkali process. Background Technology

[0002] Volatile organic compounds (VOCs) refer to organic compounds with a saturated vapor pressure greater than 70 Pa at room temperature and a boiling point below 260 °C at normal pressure, or all organic compounds with a vapor pressure greater than or equal to 10 Pa at 20 °C and corresponding volatility.

[0003] Currently, low-concentration, fugitive VOC emissions in the petrochemical industry mainly originate from volatile emissions from collection and transportation workshops, oil and gas storage breather valves, and centralized pollutant treatment points. The collection of low-concentration VOCs generates large airflow volumes, reducing the residence time of VOCs in various treatment stages, which is a detrimental factor to VOCs gas control.

[0004] Conventional methods for treating VOCs include absorption, adsorption, membrane separation, regenerative thermal oxidative combustion (RTO), regenerative catalytic oxidation (RCO), and biodegradation. Absorption is inexpensive, but certain VOC components require specific solvents. While adsorption offers good short-term results, the adsorbent needs frequent replacement, easily generating solid waste. Membrane treatment has limited capacity and high cost. For low-concentration, high-volume VOCs, RTO or RCO processes require supplemental fuel gas or energy to maintain the reaction temperature, resulting in high investment or operating costs. Biodegradation has lower energy consumption and is suitable for low-concentration VOCs, but it is no longer applicable to highly toxic or large-volume VOCs.

[0005] Currently, for VOCs gases with low boiling points, low concentrations, large volumes, and complex compositions, such as those used in petrochemical industries, single treatment technologies are insufficient to meet the treatment requirements. Therefore, combined processes are increasingly being adopted to achieve VOCs emission standards. Known combined processes include "adsorption-desorption + condensation," "adsorption-desorption + catalytic oxidation," "absorption + condensation," "absorption + distillation," and "membrane separation + condensation (or catalytic oxidation)." However, these combined processes all have issues in terms of economics and technical reliability.

[0006] With the introduction of the national "dual carbon" policy, destructive methods such as oxidative degradation easily generate large amounts of greenhouse gases, failing to meet national carbon emission standards. Under the "dual carbon" policy, more and more companies are adopting the relatively inexpensive and efficient "adsorption-desorption + condensation" combined process. However, a significant portion of petrochemical VOCs are C1-C4 components, which are difficult to recover using condensation methods, or require cryogenic processes for complete recovery, consuming substantial energy and significantly increasing the cost of VOCs recovery processes.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to provide a method for treating low-boiling-point VOCs gas based on chlor-alkali process, which can treat VOCs gas with high efficiency, high quality and low energy consumption.

[0009] To achieve the above objectives, the present invention provides a method for treating low-boiling-point VOCs gas based on chlor-alkali process, comprising the following steps:

[0010] S1. Pass the waste gas containing VOCs into an adsorption tank containing an adsorbent, and the VOCs are adsorbed by the adsorbent.

[0011] S2. The VOCs gas adsorbed by the adsorbent is desorbed into the condenser by nitrogen stripping, and nitrogen is introduced to balance the pressure and recover the condensable VOCs gas.

[0012] S3. Add sodium chloride solution into the chlor-alkali generator and electrolyze the sodium chloride solution to generate chlorine gas and sodium hydroxide solution;

[0013] S4. The uncondensed VOCs gas and nitrogen gas mixture from step S2 is introduced into the photochlorination reactor, and the chlorine gas generated in step S3 is introduced, so that the chlorine gas reacts with the VOCs gas to generate chlorinated products. During the reaction, nitrogen gas is introduced to balance the gas pressure in the photochlorination reactor.

[0014] S5. Pass the chlorinated compound into a hot alkaline water reactor and add the sodium hydroxide solution generated in step S3. The chlorinated compound reacts with the sodium hydroxide to produce an alcohol and sodium chloride.

[0015] In one or more embodiments, step S2 includes: evacuating the condenser, and then connecting the condenser to the adsorption tank in step S1; introducing nitrogen into the adsorption tank, where the nitrogen removes VOCs from the adsorbent and purges the VOCs into the condenser for condensation, and after condensation, the VOCs are discharged from the bottom of the condenser; during the VOCs condensation process, nitrogen is introduced into the condenser to balance the gas pressure inside the condenser.

[0016] In one or more embodiments, step S3 includes: adding sodium chloride solution to a chlor-alkali generator, electrolyzing the sodium chloride solution to generate chlorine gas, sodium hydroxide solution and hydrogen gas, directly recovering the hydrogen gas, providing the chlorine gas to the photochlorination reactor, and providing the sodium hydroxide solution to the hot alkaline water reactor.

[0017] In one or more embodiments, step S4 includes: evacuating the photochlorination reactor, transferring the uncondensed VOCs and nitrogen mixture from the condenser in step S2 to the photochlorination reactor; introducing chlorine gas generated in the chlor-alkali generator into the photochlorination reactor, where the chlorine gas reacts with the VOCs gas to generate chlorinated compounds, and during the reaction, introducing nitrogen gas into the photochlorination reactor to balance the gas pressure inside the photochlorination reactor.

[0018] In one or more embodiments, step S5 includes: conveying the chlorinated compound in the photochlorination reactor from the bottom of the hot alkaline water reactor into the hot alkaline water reactor; adding sodium hydroxide solution into the hot alkaline water reactor; heating the hot alkaline water reactor to 90~100°C to allow the chlorinated compound to react with sodium hydroxide to produce alcohol and sodium chloride, wherein the alcohol produced includes light alcohol and oil phase alcohol; and continuously injecting VOCs gas from the top of the hot alkaline water reactor to the bottom of the hot alkaline water reactor using a gas pump until the chloride ion concentration in the solution no longer increases.

[0019] In one or more embodiments, step S5 further includes: when the pH of the solution in the hot alkaline water reactor in step S5 is ≤11, 50% of the solution is removed and transported to an evaporator for evaporation. After evaporation, a concentrated solution of sodium chloride containing sodium hydroxide is obtained. The concentrated solution is then transported to a chlor-alkali generator for electrolysis to generate chlorine gas and sodium hydroxide.

[0020] In one or more embodiments, the low-boiling-point VOCs gas treatment method based on the chlor-alkali process further includes step S6: connecting the top of the hot alkaline water reactor to a condenser, and then connecting the condenser to the adsorption tank in step S1; the light alcohol and unreacted VOCs generated in the hot alkaline water reactor overflow from the top of the hot alkaline water reactor into the condenser, the light alcohol is condensed and flows out from the bottom of the condenser for recovery, and the unreacted VOCs flow back into the adsorption tank for secondary treatment; the water-insoluble oil phase alcohol generated in the hot alkaline water reactor is discharged from the hot alkaline water reactor by a water pump for recovery; and the crystalline sodium chloride and the solid residue remaining after the reaction generated in the hot alkaline water reactor are recovered by a filter.

[0021] In one or more embodiments, the crystalline sodium chloride recovered in step S6 can be used in the chlor-alkali generator in step S3 to electrolyze and generate chlorine gas and sodium hydroxide.

[0022] This invention also provides a low-boiling-point VOCs gas treatment device based on a chlor-alkali process, comprising an adsorption tank, a condenser, a photochlorination reactor, a hot alkaline water reactor, a chlor-alkali generator, a condenser, and a water pump. The adsorption tank is used to adsorb VOCs gas. The condenser is connected to the adsorption tank and is used to condense and recover VOCs gas. The chlor-alkali generator can electrolyze sodium chloride solution to generate chlorine gas and sodium hydroxide solution. The photochlorination reactor is connected to the condenser and the chlor-alkali generator, and can react VOCs gas with chlorine gas to generate chlorinated compounds. The hot alkaline water reactor is connected to the photochlorination reactor and the chlor-alkali generator, and can react the chlorinated compounds with sodium hydroxide to generate alcohols and sodium chloride. The condenser is connected to the top of the adsorption tank and the hot alkaline water reactor for recovering light alcohols in the hot alkaline water reactor. The water pump is connected to the top side wall of the hot alkaline water reactor for recovering oil-phase alcohols in the hot alkaline water reactor.

[0023] In one or more embodiments, the low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process further includes a nitrogen supply device connected to the adsorption tank, the condenser, and the photochlorination reactor.

[0024] In one or more embodiments, the low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process further includes an evaporator connected to a hot alkaline water reactor, which can evaporate the solution in the hot alkaline water reactor into a concentrated sodium chloride solution and supply the concentrated sodium chloride solution to the chlor-alkali generator.

[0025] In one or more embodiments, a VOCs concentration sensor and a pressure sensor are installed in the condenser, a chlorine concentration sensor, a pressure sensor, and a VOCs concentration sensor are installed in the photochlorination reactor, and a pH sensor and a chloride ion concentration detector are installed in the hot alkaline water reactor.

[0026] Compared with existing technologies, the low-boiling-point VOCs gas treatment method and equipment based on chlor-alkali process according to one embodiment of the present invention utilizes an adsorbent to adsorb VOCs gas, then uses a condenser to condense and recover some components of the VOCs gas, while the uncondensed VOCs gas enters a photochlorination reactor to react with chlorine gas to generate chlorinated compounds. The chlorinated compounds then enter a hot alkaline water reactor to react with sodium hydroxide to generate alcohols and sodium chloride. The light alcohols and oil-phase alcohols are then recovered using a condenser and a water pump, and the sodium chloride is recovered and recycled using filtration. This achieves high-efficiency, high-quality, and low-energy-consumption recovery and treatment of VOCs gas, reducing environmental pollution and improving economic benefits. Attached Figure Description

[0027] Figure 1 This is a flowchart of a low-boiling-point VOCs gas treatment method based on chlor-alkali process according to an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of a low-boiling-point VOCs gas treatment device based on the chlor-alkali process according to one embodiment of the present invention.

[0029] The components include: 1. Nitrogen supply equipment; 2. Adsorption tank; 3. Condensation tank; 4. Photochlorination reactor; 5. Hot alkaline water reactor; 6. Chlor-alkali generator; 7. Condenser; 8. Water pump; and 9. Evaporator. Detailed Implementation

[0030] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0031] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0032] like Figure 1 As shown in the embodiment of the present invention, a method for treating low-boiling-point VOCs gas based on chlor-alkali process includes steps S1 to S6:

[0033] In step S1, the waste gas containing VOCs is passed into an adsorption tank containing an adsorbent, and the VOCs are adsorbed by the adsorbent.

[0034] Specifically, multiple adsorption tanks can be connected in parallel on the main pipeline that transports waste gas containing VOCs. The waste gas in the main pipeline enters a single adsorption tank, where the adsorbent in the adsorption tank adsorbs the VOCs. When the adsorbent in the adsorption tank is saturated, the process switches to another adsorption tank to treat the VOCs.

[0035] It should be noted that the VOCs gas treated by the low-boiling-point VOCs gas treatment method based on the chlor-alkali process in one embodiment of the present invention is a large-volume, low-concentration VOCs gas, with a VOCs gas volume of 50~50000 m³ / h. 3 / h, concentration in the range of 40~2000 mg / m³.

[0036] In step S2, the VOCs gas adsorbed by the adsorbent is desorbed into the condenser by nitrogen stripping, and nitrogen is introduced to balance the pressure and recover the condensable VOCs gas.

[0037] Specifically, the condenser needs to be evacuated beforehand using a vacuum pump, and then connected to the adsorption tank in step S1. Nitrogen gas is introduced into both the adsorption tank and the condenser. The nitrogen in the adsorption tank removes VOCs from the adsorbent and purges the VOCs into the condenser for condensation at a temperature of 0-4°C. After condensation, the VOCs are discharged from the bottom of the condenser, while uncondensed VOCs remain stored inside. The nitrogen introduced into the adsorption tank is used to balance the pressure inside the condenser.

[0038] In the above steps, the gas pressure in the condenser should be controlled to be ≤0.2MPa.

[0039] In step S3, sodium chloride solution is added to the chlor-alkali generator, and the sodium chloride solution is electrolyzed to generate chlorine gas and sodium hydroxide solution.

[0040] Specifically, in one embodiment, a chlor-alkali generator is connected to a chlorination reactor and a hot alkaline water reactor. A sodium chloride solution is added to the chlor-alkali generator, and the sodium chloride solution is electrolyzed to generate chlorine gas, sodium hydroxide solution, and hydrogen gas. The hydrogen gas is directly recovered, while the chlorine gas and sodium hydroxide solution are used in subsequent steps.

[0041] In step S4, the uncondensed VOCs gas and nitrogen mixture from step S2 is introduced into the photochlorination reactor, and the chlorine gas generated in step S3 is introduced, so that the chlorine gas reacts with the VOCs gas to generate chlorinated products. During the reaction, nitrogen gas is introduced to balance the gas pressure in the photochlorination reactor.

[0042] Specifically, the photochlorination reactor is pre-evacuated using a vacuum pump. The evacuated reactor is then connected to a condenser, and the uncondensed VOCs and nitrogen mixture in the condenser is transferred into the photochlorination reactor. Chlorine gas generated in the chlor-alkali generator in step S3 is introduced into the photochlorination reactor, causing it to react with the VOCs to form chlorinated compounds. Nitrogen gas is introduced into the photochlorination reactor during the reaction to balance the pressure within the reactor.

[0043] In the above steps, the photochlorination reactor contains a mixture of VOCs and nitrogen, with nitrogen comprising 25-75% of the gas. The pressure inside the reactor is ≤0.5 MPa. The chlorine gas flow rate is 70-90% of the VOCs gaseous amount, and VOCs should be in excess after the reaction. The reaction time is determined by the chlorine content; the reaction ends when the chlorine concentration drops to 0, which can be measured by a chlorine concentration sensor. The reaction temperature inside the photochlorination reactor is maintained at 20-40°C, and the light intensity of the light source is 50-300 Lux.

[0044] In step S5, the chlorinated compound is passed into a hot alkaline water reactor, and the sodium hydroxide solution generated in step S3 is added. The chlorinated compound reacts with the sodium hydroxide to produce an alcohol and sodium chloride.

[0045] The bottom of the hot alkaline water reactor is connected to the photochlorination reactor, allowing the chlorides from the photochlorination reactor to be transferred from the bottom of the hot alkaline water reactor into it. Sodium hydroxide solution is added to the hot alkaline water reactor, which is then heated to 90-100°C, causing the chlorides to react with the sodium hydroxide to produce alcohols and sodium chloride. A gas pump continuously injects VOCs gas from the top of the hot alkaline water reactor to the bottom until the chloride ion concentration in the solution no longer increases, ensuring that the VOCs gas fully reacts with the sodium hydroxide.

[0046] In the above steps, a chloride ion concentration detector can be installed inside the hot alkaline water reactor to detect the chloride ion concentration in real time, helping staff determine whether the reaction in the hot alkaline water reactor has stopped.

[0047] Similarly, in step S5, a pH sensor can be installed inside the hot alkaline water reactor to detect the pH value of the solution in the reactor. When the pH of the solution in the hot alkaline water reactor is ≤11, 50% of the solution is removed and transported to an evaporator for evaporation. After evaporation, a concentrated solution of sodium chloride containing sodium hydroxide is obtained. The concentrated solution is then transported to the chlor-alkali generator in step S3 for electrolysis to generate chlorine gas and sodium hydroxide.

[0048] In the above steps, the liquid level in the hot alkaline water reactor is 60-70% of the height of the hot alkaline water reactor.

[0049] In step S6, the alcohol and sodium chloride are recovered, and the recovered sodium chloride can be used in the chlor-alkali generator in step S3.

[0050] Specifically, the top of the hot alkaline water reactor can be connected to a condenser, and the condenser can then be connected to the adsorption tank in step S1. The cooling temperature of the condenser is controlled at 0~4°C. In this way, the light alcohol and unreacted VOCs generated in the hot alkaline water reactor can overflow from the top of the reactor into the condenser. The light alcohol is condensed and flows out from the bottom of the condenser for recovery, while the unreacted VOCs flow back into the adsorption tank for secondary treatment according to the treatment methods in steps S1-S5.

[0051] For the water-insoluble oil phase alcohol generated in the hot alkaline water reactor, a visible telescopic pipe can be installed on the top of the hot alkaline water reactor and connected to a water pump. The water pump can then be used to recover the water-insoluble oil phase alcohol generated in the hot alkaline water reactor.

[0052] The crystalline sodium chloride generated in the hot alkaline water reactor and the solid residue remaining after the reaction can be directly filtered and recovered using a filter.

[0053] In the above steps, the recovered crystalline sodium chloride can be used in the chlor-alkali generator in step S3 to electrolyze and generate chlorine gas and sodium hydroxide.

[0054] like Figure 2 As shown in the figure, a low-boiling-point VOCs gas treatment device based on chlor-alkali process according to an embodiment of the present invention includes an adsorption tank 2, a condenser tank 3, a photochlorination reactor 4, a hot alkaline water reactor 5, a chlor-alkali generator 6, a condenser 7, and a water pump 8. The adsorption tank 2 is used to adsorb VOCs gas. The condenser tank 3 is connected to the adsorption tank 2 and is used to condense and recover VOCs gas. The chlor-alkali generator 6 can electrolyze sodium chloride solution to generate chlorine gas and sodium hydroxide solution. The photochlorination reactor 4 is connected to the condenser tank 3 and the chlor-alkali generator 6, and can react VOCs gas with chlorine gas to generate chlorinated compounds. The hot alkaline water reactor 5 is connected to the photochlorination reactor 4 and the chlor-alkali generator 6, and can react the chlorinated compounds with sodium hydroxide to generate alcohols and sodium chloride. The condenser 7 is connected to the top of the adsorption tank 2 and the hot alkaline water reactor 5, and is used to recover light alcohols in the hot alkaline water reactor 5. The water pump 8 is connected to the top side wall of the hot alkaline water reactor 5, and is used to recover oil-phase alcohols in the hot alkaline water reactor 5.

[0055] The low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process described above adsorbs VOCs gas through an adsorption tank 2, condenses and recovers some components of the VOCs gas using a condenser tank 3, and the uncondensed VOCs gas enters a photochlorination reactor 4 to react with chlorine gas to generate chlorinated products. The chlorinated products then enter a hot alkaline water reactor 5 to react with sodium hydroxide to generate alcohol and sodium chloride. The light alcohol and oil phase alcohol are then recovered using a condenser 7 and a water pump 8, and the sodium chloride in the hot alkaline water reactor 5 is recovered by filtration.

[0056] In one embodiment, the low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process further includes a nitrogen supply device 1, which is connected to the adsorption tank 2, the condenser 3, and the photochlorination reactor 4. The nitrogen supply device 1 can supply nitrogen to the adsorption tank 2, the condenser 3, and the photochlorination reactor 4 to purge the VOCs gas in the adsorption tank 2 and to balance the gas pressure in the condenser 3 and the photochlorination reactor 4.

[0057] like Figure 2 As shown, in one embodiment, the low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process further includes an evaporator 9, which is connected to a hot alkaline water reactor 5 and can evaporate the solution in the hot alkaline water reactor 5 into a concentrated sodium chloride solution, and provide the concentrated sodium chloride solution to the chlor-alkali generator 6.

[0058] In one embodiment, a VOCs concentration sensor and a pressure sensor are installed inside the condenser tank 3 to detect the VOCs gas concentration and internal pressure within the condenser tank 3. A chlorine concentration sensor, a pressure sensor, and a VOCs concentration sensor are installed inside the photochlorination reactor 4. The chlorine concentration sensor can detect the chlorine concentration inside the photochlorination reactor 4 in real time; when the chlorine concentration is 0, it indicates that the reaction inside the chlorination reactor 4 has ended. It can also detect the VOCs gas concentration and pressure inside the photochlorination reactor 4 in real time. A pH sensor and a chloride ion concentration detector are installed inside the hot alkaline water reactor 5. The pH sensor can detect the pH value of the solution inside the hot alkaline water reactor 5 to determine whether evaporation and concentration of the solution inside the hot alkaline water reactor 5 is necessary. The chloride ion concentration detector can determine whether the reaction inside the hot alkaline water reactor 5 has ended.

[0059] The chlorine and sodium hydroxide used in the above embodiments are generated by electrolyzing sodium chloride solution in chlor-alkali generator 6. Part of the sodium chloride solution needs to be prepared in advance, part can be provided by sodium chloride recovered in hot alkaline water reactor 5, and part can be provided by concentrated sodium chloride solution obtained by evaporation of solution with pH≤11 in hot alkaline water reactor 5.

[0060] The following is a further explanation with reference to an embodiment. In this embodiment, VOCs gas is recovered from the oil and gas in the crude oil loading and unloading truck of the oil field. The specific steps are as follows:

[0061] 1. Adsorption of VOCs gas

[0062] Oil and gas containing VOCs are transported into an adsorption tank containing an adsorbent using pneumatic conveying equipment such as compressors. The adsorbent then adsorbs the VOCs. During the adsorption process, the airflow rate for transporting the oil and gas is controlled at 105-115 m³ / h. 3 / h, the concentration of VOCs in oil and gas is ≤872mg / m³.

[0063] 2. Preliminary condensation

[0064] A vacuum pump is used to evacuate the condenser, controlling the condensation temperature to 0-4°C. Nitrogen gas is then introduced into both the adsorption and condensation tanks. The nitrogen in the adsorption tank removes VOCs from the adsorbent and purges the VOCs into the condenser for condensation. After condensation, the VOCs are discharged from the bottom of the condenser, while uncondensed VOCs remain stored inside. Nitrogen gas is introduced into the condenser during the condensation process, maintaining the pressure within the condenser at ≤0.2 MPa.

[0065] 3. Preparation of chlorine gas and sodium hydroxide

[0066] Add 50L of 20% sodium chloride solution to the chlor-alkali generator, electrolyze the sodium chloride solution to generate chlorine gas, sodium hydroxide solution and hydrogen gas. The hydrogen gas is directly recovered, the chlorine gas is supplied to the photochlorination reactor, and the sodium hydroxide solution is supplied to the hot alkaline water reactor.

[0067] 4. Formation of chlorinated products

[0068] A mixture of uncondensed VOCs and nitrogen is introduced into a photochlorination reactor, with the light intensity controlled at 80 Lux. Chlorine gas generated by a chlor-alkali generator is then introduced, causing the chlorine to react with the VOCs to form chlorinated compounds. During the reaction, the reaction temperature inside the photochlorination reactor is maintained at 30°C. Nitrogen gas is also introduced during the reaction, ensuring that the nitrogen content inside the reactor is 50%, and the pressure inside the reactor is ≤0.5 MPa.

[0069] 5. Produces alcohol and sodium chloride.

[0070] The chlorinated compound in the photochlorination reactor is transferred from the bottom of the hot alkaline water reactor into the hot alkaline water reactor. Sodium hydroxide solution is added into the hot alkaline water reactor, and the liquid level in the hot alkaline water reactor is controlled to be 66% of the height of the hot alkaline water reactor. The hot alkaline water reactor is then heated to 95°C, so that the chlorinated compound reacts with sodium hydroxide to produce alcohol and sodium chloride.

[0071] A gas pump is used to continuously inject VOCs gas from the top of the hot alkaline water reactor to the bottom of the reactor until the chloride ion concentration in the solution no longer rises, allowing the VOCs gas to fully react with sodium hydroxide.

[0072] 6. Recover reaction products

[0073] When recovering the generated light alcohol, the cooling temperature of the condenser is controlled at 2°C. The light alcohol generated in the hot alkaline water reactor and the unreacted VOCs overflow from the top of the hot alkaline water reactor into the condenser. After the light alcohol is condensed, it flows out from the bottom of the condenser to complete the recovery. The unreacted VOCs flow back into the adsorption tank for secondary treatment.

[0074] When recovering the water-insoluble oil phase alcohol generated, the water-insoluble oil phase alcohol generated in the hot alkaline water reactor can be discharged by a water pump, thus enabling its recovery.

[0075] When recovering the generated crystalline sodium chloride and the remaining solid residue from the reaction, a filter is used for direct filtration and recovery.

[0076] The VOCs gas concentration at the treated oil and gas exhaust port in the above embodiments is <1 mg / m³. 3 The emission standards were met, and the VOCs removal rate reached 99.9%, achieving efficient and high-quality purification of VOCs. Furthermore, the power consumption in the above embodiment was 5.62 kW, while the power consumption of the traditional adsorption-desorption-cryogenic condensation process was approximately 9 kW. The energy consumption of the above embodiment was only 62.4% of that of the traditional process, achieving low-energy treatment of VOCs.

[0077] In summary, the low-boiling-point VOCs gas treatment method and equipment based on the chlor-alkali process according to an embodiment of the present invention utilizes an adsorbent to adsorb VOCs gas, then uses a condenser to condense and recover some components of the VOCs gas, while the uncondensed VOCs gas enters a photochlorination reactor to react with chlorine gas to generate chlorinated compounds. The chlorinated compounds then enter a hot alkaline water reactor to react with sodium hydroxide to generate alcohols and sodium chloride. The light alcohols and oil-phase alcohols are then recovered using a condenser and a water pump, and sodium chloride is recovered and recycled using filtration. This achieves efficient, high-quality, and low-energy treatment of VOCs gas, reducing environmental pollution and improving economic benefits.

[0078] Furthermore, in this embodiment, the raw materials for electrolyzing sodium chloride can be provided partly by the sodium chloride recovered in the hot alkaline water reactor and partly by the concentrated sodium chloride solution obtained by evaporation of the solution in the hot alkaline water reactor. This allows the sodium chloride solution to be recycled, reducing the consumption and emissions of sodium chloride solution, reducing environmental pollution, and improving economic efficiency.

[0079] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent, as taught above, that many changes and variations can be made. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for treating low-boiling VOCs gases based on a chlor-alkali process, characterized in that, include: S1. Pass the waste gas containing VOCs into an adsorption tank containing an adsorbent, and the VOCs are adsorbed by the adsorbent. S2. The VOCs gas adsorbed by the adsorbent is desorbed into the condenser by nitrogen stripping, and nitrogen is introduced to balance the pressure and recover the condensable VOCs gas. S3. Add sodium chloride solution into the chlor-alkali generator and electrolyze the sodium chloride solution to obtain chlorine gas and sodium hydroxide solution; S4. The uncondensed VOCs gas and nitrogen mixture from step S2 is introduced into the photochlorination reactor, and the chlorine gas generated in step S3 is introduced, so that the chlorine gas reacts with the VOCs gas to generate chlorinated products. During the reaction, nitrogen gas is introduced to balance the gas pressure in the photochlorination reactor. as well as S5. The chlorinated compound is passed into a hot alkaline water reactor, and the sodium hydroxide solution generated in step S3 is added. The chlorinated compound reacts with sodium hydroxide to produce an alcohol and sodium chloride.

2. The low-boiling point VOCs gas treatment method based on a chlor-alkali process according to claim 1, characterized by, Step S2 includes: The condenser is evacuated, and then connected to the adsorption tank in step S1. Nitrogen gas is introduced into the adsorption tank, where it removes VOCs gas from the adsorbent and purges the VOCs gas into a condenser for condensation. After condensation, the VOCs gas is discharged from the bottom of the condenser. Nitrogen gas is introduced into the condenser during the VOCs gas condensation process to balance the gas pressure inside the condenser.

3. The low-boiling point VOCs gas treatment method based on a chlor-alkali process according to claim 1, characterized by, Step S3 includes: Sodium chloride solution is added to the chlor-alkali generator, and the sodium chloride solution is electrolyzed to generate chlorine gas, sodium hydroxide solution and hydrogen gas. The hydrogen gas is directly recovered, the chlorine gas is supplied to the photochlorination reactor, and the sodium hydroxide solution is supplied to the hot alkaline water reactor.

4. The low-boiling point VOCs gas treatment method based on a chlor-alkali process according to claim 1, characterized by, Step S4 includes: The photochlorination reactor is evacuated to transfer the uncondensed VOCs and nitrogen mixture in the condenser tank in step S2 into the photochlorination reactor. Chlorine gas generated in the chlor-alkali generator is introduced into the photochlorination reactor. The amount of chlorine gas provided is 70% to 90% of the amount of uncondensed VOCs in the condenser. The chlorine gas reacts with the VOCs gas to generate chlorinated compounds. During the reaction, nitrogen gas is introduced into the photochlorination reactor to balance the gas pressure inside the photochlorination reactor.

5. The low-boiling point VOCs gas treatment method based on a chlor-alkali process according to claim 1, characterized by, Step S5 includes: The chlorinated compound in the photochlorination reactor is transported from the bottom of the hot alkaline water reactor into the hot alkaline water reactor. Sodium hydroxide solution is added to the hot alkaline water reactor, and the hot alkaline water reactor is heated to 90~100°C, so that the chlorinated compound reacts with sodium hydroxide to produce alcohol and sodium chloride. The alcohol produced includes light alcohol and oil phase alcohol. A gas pump is used to continuously inject VOCs gas from the top of the hot alkaline water reactor to the bottom of the reactor until the chloride ion concentration in the solution no longer increases.

6. The method for treating low-boiling-point VOCs gas based on chlor-alkali process as described in claim 5, characterized in that, Step S5 further includes: when the pH of the solution in the hot alkaline water reactor in step S5 is ≤11, 50% of the solution is removed and transported to an evaporator for evaporation. After evaporation, a concentrated solution of sodium chloride containing sodium hydroxide is obtained. The concentrated solution is then transported to a chlor-alkali generator for electrolysis to generate chlorine gas and sodium hydroxide.

7. The method for treating low-boiling-point VOCs gas based on chlor-alkali process as described in claim 1, characterized in that, Step S5 is followed by step S6: Connect the top of the hot alkaline water reactor to the condenser, and then connect the condenser to the adsorption tank in step S1. The light alcohol and unreacted VOCs generated in the hot alkaline water reactor overflow from the top of the reactor into the condenser. The light alcohol is condensed and flows out from the bottom of the condenser to be recovered, while the unreacted VOCs flow back into the adsorption tank for secondary treatment. The water-insoluble oil phase alcohol generated in the hot alkaline water reactor is discharged from the reactor by a water pump for recycling. The crystalline sodium chloride generated in the hot alkaline water reactor and the remaining solid residue are recovered through a filter.

8. The method for treating low-boiling-point VOCs gas based on chlor-alkali process as described in claim 7, characterized in that, The crystalline sodium chloride recovered in step S6 can be used in the chlor-alkali generator in step S3 to electrolyze and generate chlorine gas and sodium hydroxide.

9. A low-boiling-point VOCs gas treatment device based on chlor-alkali process, characterized in that, include: Adsorption tank (2) is used to adsorb VOCs gas; A condenser (3) is connected to the adsorption tank (2), and the condenser (3) is used to condense and recover VOCs gas; The chlor-alkali generator (6) is capable of electrolyzing sodium chloride solution to generate chlorine gas and sodium hydroxide solution; A photochlorination reactor (4) is connected to the condenser (3) and the chlor-alkali generator (6). The photochlorination reactor (4) can react VOCs gas with chlorine gas to generate chlorinated products. A hot alkaline water reactor (5) is connected to the photochlorination reactor (4) and the chlor-alkali generator (6). The hot alkaline water reactor (5) can react the chlorinated product with sodium hydroxide to produce alcohol and sodium chloride. A condenser (7) is connected to the top of the adsorption tank (2) and the hot alkaline water reactor (5) for recovering light alcohols in the hot alkaline water reactor (5); A water pump (8) is connected to the top side wall of the hot alkaline water reactor (5) for recovering oil phase alcohols in the hot alkaline water reactor (5).

10. The low-boiling-point VOCs gas treatment equipment based on the chlor-alkali process as described in claim 9, characterized in that, It also includes a nitrogen supply device (1), which is connected to an adsorption tank (2), a condenser (3) and a photochlorination reactor (4).

11. The low-boiling-point VOCs gas treatment equipment based on chlor-alkali process as described in claim 10, characterized in that, It also includes an evaporator (9) connected to a hot alkaline water reactor (5), which can evaporate the solution in the hot alkaline water reactor (5) into a concentrated sodium chloride solution and supply the concentrated sodium chloride solution to the chlor-alkali generator (6).

12. The low-boiling-point VOCs gas treatment equipment based on chlor-alkali process as described in claim 9, characterized in that, The condenser (3) is equipped with a VOCs concentration sensor and a pressure sensor. The photochlorination reactor (4) is equipped with a chlorine concentration sensor, a pressure sensor and a VOCs concentration sensor. The hot alkaline water reactor (5) is equipped with a pH sensor and a chloride ion concentration detector.

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