Production method of environment-friendly tetrachloroethane

Abstract

The invention discloses a production method of environment-friendly tetrachloroethane, which relates to the technical field of chemical synthesis, and comprises the following steps: acetylene pretreatment: deep purification is carried out through alkaline washing and an MCM-41 nano adsorbent; chlorination reaction: catalyzing acetylene and chlorine to react at the temperature of 80-120 DEG C and the pressure of 0.05-0.1 MPa by adopting C4-C8 alkyl substituted imidazole ionic liquid as a reaction medium; multi-stage rectification: a normal pressure-reduced pressure rectification combined process is adopted; tail gas treatment: the pollutants are enriched by using amino-functionalized ionic liquid, the pollutants are recycled after reduced pressure distillation and anion exchange column regeneration, and the recovery rate of the ionic liquid is greater than or equal to 95%; wastewater treatment: the microbial fuel cell system realizes efficient removal of COD (Chemical Oxygen Demand). Through the design of the ionic liquid, the product purity and the production efficiency are remarkably improved, the energy consumption is reduced, and greenization and high efficiency of tetrachloroethane production are promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and particularly to a production method of environmentally friendly tetrachloroethane. Background Art

[0002] The traditional production process of tetrachloroethane uses the carbide hydrolysis method to produce acetylene. After simple purification, it reacts with chlorine under the catalysis of ferric trichloride. There are the following defects: 1. Low raw material utilization rate: incomplete purification of acetylene leads to impurities participating in side reactions, low raw material conversion rate, and low product purity; 2. Energy consumption and pollution problems are prominent: the reaction needs to be carried out at normal pressure of 90 - 120 °C, with high energy consumption; the tail gas contains harmful gases such as Cl2 and HCl, and the COD of the wastewater is as high as 1000 - 1500 mg / L. It is difficult to meet the standards by traditional treatment methods and cannot meet the strict requirements of environmentally friendly products.

[0003] In view of this, this application is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method of environmentally friendly tetrachloroethane to solve the problems mentioned in the above background art.

[0005] To solve the above technical problems, a production method of environmentally friendly tetrachloroethane provided by the present invention includes the following steps: S1 Acetylene pretreatment: Pass the acetylene gas containing hydrogen sulfide (H2S ≤ 100 ppm) and phosphine (PH3 ≤ 50 ppm) through an alkaline solution washing tower (packing specific surface area ≥ 200 m 2 / m 3 , liquid-gas ratio 1:5 - 10), and control the sulfide content in the washed gas ≤ 1 ppm and the phosphine content ≤ 0.5 ppm; further pass through a purification tower filled with MCM-41 nanoporous material adsorbent (specific surface area 800 - 1200 m 2 / g, pore diameter 2 - 50 nm), and contact at a flow rate of 0.5 - 1.5 m 3 / h for 30 - 60 minutes at 25 - 35 °C and 0.1 - 0.2 MPa to obtain acetylene with a purity ≥ 99.5%; S2 Chlorination reaction: In a C4 - C8 alkyl-substituted imidazole-based ionic liquid (cationic substituent carbon chain length is 4 - 8, anion is one or more of hexafluorophosphate, tetrafluoroborate, bis(trifluoromethanesulfonyl)imide, accounting for 10% - 30% of the total volume of the reactor), introduce the purified acetylene and chlorine, with a molar ratio of 1:4 - 6, and react at 80 - 120 °C and 0.05 - 0.1 MPa for 20 - 40 minutes to generate crude tetrachloroethane; S3 Multi-stage rectification and purification; S4 Tail gas treatment and ionic liquid closed-loop regeneration: S41 Pollutant Enrichment: Tail gas containing ≤100 ppm of Cl2 and ≤500 ppm of HCl is introduced into an ionic liquid absorption tower with amino functional groups (packing specific surface area ≥250 m 2 / m 3 , with a gas-liquid ratio of 1:10 - 15), a spraying rate of 5 - 15 L / h, and an absorption temperature of 40 - 60 °C. The ionic liquid with amino functional groups is obtained by grafting amino functional groups at 60 - 80 °C to the ionic liquid discharged after the S2 reaction through preliminary filtration by adding 3-aminopropyltrimethoxysilane (accounting for 5% - 10% of the ionic liquid mass); S42 Multi-stage Regeneration Process: Vacuum Distillation: The ion liquid saturated with absorption is distilled at 80 - 100 °C and a vacuum degree of -0.09 MPa to remove gaseous pollutants such as HCl and Cl2; Functional Group Removal: The amino functional groups are removed through an anion exchange column (packed with quaternary ammonium resin, resin bed height 1 - 1.5 m, flow rate 5 - 10 BV / h, eluent is 1 mol / L potassium chloride solution) to make the amino residue concentration in the ionic liquid ≤50 ppm and the anion purity ≥99%; Impurity Filtration: After filtration through a 0.1 μm microporous membrane, 70% - 90% of the regenerated ionic liquid is returned to the S2 step for recycling, and 10% - 30% is diverted to the S41 step for tail gas absorption.

[0006] Furthermore, in the S1, the MCM-41 nanoporous material adsorbent has a specific surface area of 800 - 1200 m 2 / g and a pore diameter of 2 - 50 nm.

[0007] Furthermore, in the S2, the C4 - C8 alkyl-substituted imidazole ionic liquids include one or more of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0008] Furthermore, in the S3, after the reaction product is condensed by a shell-and-tube condenser (heat transfer area 20 - 50 m 2 , with the cooling medium temperature of -10 - 10 °C), it is successively subjected to atmospheric distillation (top temperature 120 - 130 °C, number of trays 30 - 50) and vacuum distillation (top pressure 10 - 30 kPa, top temperature 80 - 90 °C, number of trays 20 - 40) to obtain a tetrachloroethane product with a purity ≥99.8%.

[0009] Furthermore, in the S3, the atmospheric distillation column uses valve trays with a tray efficiency ≥60%; the vacuum distillation column uses structured packing with an equivalent plate height ≤0.3 m.

[0010] Further, it also includes S5 wastewater treatment: introducing production wastewater with COD ≤ 500 mg / L into the microbial fuel cell system, controlling the wastewater flow rate at 1 - 3 m 3 / h, with the effective volume of the anode chamber being 5 - 10 m 3 , and oxidizing organic pollutants at 30 - 35 °C using a microbial flora mainly composed of Bacillus (accounting for 70% - 90% of the total microorganisms, with a concentration of 1×10 8 -3×10 8 CFU / mL), with the COD removal rate of the wastewater ≥ 85%.

[0011] Further, the cathode of the microbial fuel cell system uses a platinum-carbon electrode, and the ratio of the electrode area to the effective volume of the anode chamber is 0.1 - 0.3 m 2 / m 3 .

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High-purity products: Through double purification by alkaline washing and MCM-41 nano adsorbent, the purity of acetylene reaches ≥ 99.5%. Combining atmospheric pressure - vacuum multi-stage rectification with precise temperature control, the purity of tetrachloroethane is ≥ 99.8%, far exceeding the traditional process, meeting the requirements of high-purity halogenated hydrocarbons in high-end fields such as semiconductors and pharmaceuticals, and reducing impurity interference.

[0013] 2. Green and environmentally friendly: Amino / thiol ionic liquid absorbs tail gas pollutants, with a regeneration recovery rate ≥ 95% and no secondary pollution. The microbial fuel cell treats wastewater, with a COD removal rate ≥ 85%, achieving the up-to-standard discharge of tail gas and wastewater and energy recovery.

[0014] 3. Low consumption and high efficiency: The ionic liquid catalytic reaction is carried out under mild conditions of 80 - 120 °C and 0.05 - 0.1 MPa, with the energy consumption reduced by 30% - 40%, the reaction time shortened to 20 - 40 minutes, the cost reduced by 25% - 30% due to the recycling of ionic liquid, and the production stability increased by 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flowchart of a production method of an environmentally friendly grade of tetrachloroethane. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0017] Please refer to Figure 1, the present invention provides a technical solution: a production method of environmentally friendly tetrachloroethane, including: Example 1: C4 alkyl ionic liquid; 1. Acetylene pretreatment: The crude acetylene contains 80 ppm of H2S and 35 ppm of PH3. After being treated by a NaOH scrubbing tower (liquid-gas ratio 1:6, packing specific surface area 220 m 2 / m 3 ), the sulfide is ≤0.8 ppm and PH3 is ≤0.4 ppm; It should be noted here that: in the existing industrial preparation method of acetylene, the calcium carbide method is usually adopted, which mainly generates impurity gases such as H2S and PH3. After passing through the alkaline NaOH scrubbing tower, the generated sodium sulfide and sodium phosphide are dissolved in the scrubbing liquid, H2S + 2NaOH → Na2S + 2H2O; PH3 + 3NaOH → Na3P + 3H2O.

[0018] Then, through an MCM-41 adsorption tower (specific surface area 900 m 2 / g, pore diameter 15 nm), contacting for 50 minutes at 30 °C and 0.12 MPa, the purity of acetylene reaches 99.6%.

[0019] It should be noted here that: for H2O, the residual molecules such as H2S and PH3 are adsorbed in the pores of MCM-41 and further reduced to the ppm level.

[0020] 2. Chlorination reaction: Ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate (accounting for 20% of the reactor volume); Conditions: acetylene / chlorine molar ratio 1:5, temperature 90 °C, pressure 0.07 MPa, reaction for 30 minutes; Selectivity of the crude product: 98.7%, by-product trichloroethane 1.3%.

[0021] It should be noted here that: in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, Cl2 undergoes electrophilic addition to acetylene at 80-120 °C to form tetrachloroethane. Excess Cl2 (molar ratio 4-6:1) ensures complete conversion of acetylene: C2H2 + 2Cl2 → C2H2Cl4 (formation of tetrachloroethane); The ionic liquid can provide a polar environment, promote the dissociation and reactivity of Cl2, dissolve the reactants, improve the mass transfer efficiency, be resistant to high temperatures (80-120 °C), be not easily volatile, and can be recycled.

[0022] 3. Rectification and purification: The top of the atmospheric distillation column (with 40 trays and a tray efficiency of 62%) is at 125 °C. The top pressure of the vacuum distillation column (with 30 trays and a height equivalent to one theoretical plate of 0.28 m) is 20 kPa, and the product purity is 99.9%.

[0023] It should be noted here that: 1. Condensation process: The reaction product (gaseous) is cooled to liquid through a shell-and-tube condenser. 2. Atmospheric distillation process: At the top of the column: Separate low-boiling impurities (such as HCl, Cl2, trichloroethane); at the bottom of the column: Tetrachloroethane and high-boiling impurities (such as pentachloroethane). 3. Vacuum distillation process: At the top of the column: Purify tetrachloroethane (purity ≥ 99.5%). At the bottom of the column: High-boiling impurities (such as pentachloroethane). The principle is that reducing the pressure lowers the boiling point of tetrachloroethane and avoids high-temperature decomposition. Structured packing (height equivalent to one theoretical plate ≤ 0.3 m) provides a larger mass transfer area and improves the separation efficiency.

[0024] 4. Tail gas treatment: The spraying rate of amino-grafted ionic liquid (grafting rate 6%) is 10 L / h, the absorption temperature is 50 °C, and the Cl2 in the tail gas ≤ 0.5 ppm, HCl ≤ 5 ppm; The residual amino group in the regenerated ionic liquid is 38 ppm, which is recycled to S2 for use, and the recovery rate is 97%.

[0025] It should be noted here that: In S41, pollutants are enriched and react to absorb Cl2 and HCl: 2R-NH2 + Cl2 → R-N=N-R + 2HCl; R-NH2 + HCl → [R-NH3] + Cl - ; The products are: ionic liquids loaded with Cl2 and HCl: containing azo compounds (R-N=N-R) and ammonium salts ([R-NH3] + Cl - ).

[0026] In addition: It also includes S411: HCl pre-separation: The tail gas containing Cl2 and HCl is first passed through a water scrubber, controlling the temperature at 20 - 30 °C, so that HCl dissolves in water to form dilute hydrochloric acid (concentration about 5% - 10%). After the HCl content in the tail gas drops to ≤ 50 ppm; the gas at the outlet of the water scrubber passes through a wire mesh demister (efficiency ≥ 99%, liquid droplet residue ≤ 50 mg / m 3 ) to remove foggy water droplets; and then enters the S41 ionic liquid absorption tower.

[0027] S412: Cl2 absorption: The tail gas (mainly containing Cl2 and a small amount of HCl) after pre-separating HCl in S411 is introduced into the ionic liquid absorption tower functionalized with amino groups, with an absorption temperature of 40 - 60 °C (to improve the Cl2 absorption efficiency) and a spraying rate of 8 - 12 L / h.

[0028] Subsequent S42 multi-stage regeneration process: (1) Reaction in vacuum distillation: [R-NH3] + Cl - →R-NH2 + HCl↑; R-N=N-R + 2HCl → 2R-NH2 + Cl2↑; The products include: desorbed HCl and Cl2 gas, which can be further recycled (as follows in S43). Regenerated ionic liquid: The amino functional group is restored.

[0029] (2) Functional group removal process: Residual amino groups are removed through an anion exchange column (such as strongly basic resin). The product is: ionic liquid with amino residue concentration ≤ 50 ppm. Through the exchange between the anion exchange resin and amino cations, deep purification is achieved.

[0030] (3) Impurity filtration process: Mechanical impurities (such as catalyst particles) are filtered through a 0.1 μm microporous filter membrane. The product is: pure ionic liquid, 70% - 90% of which is returned to S2 for recycling, and 10% - 30% is used for S41.

[0031] S43: Cl2 recovery: The Cl2 gas (containing a small amount of HCl) removed by vacuum distillation in S42 is liquefied and collected through low-temperature condensation (-10°C to -20°C), and the uncondensed HCl is returned to the S411 water washing tower for recycling treatment. The purity of the recovered liquid chlorine is ≥ 99%, and after gasification, it is returned to the S2 chlorination reaction system.

[0032] 5. Wastewater treatment: The COD of the wastewater is 450 mg / L, the flow rate is 2 m 3 / h, the volume of the anode chamber is 7 m 3 , the microbial concentration is 2×10 8 CFU / mL, and the COD removal rate is 85.5%.

[0033] In each step: 1. Chemical washing + physical adsorption are used to remove sulfur and phosphorus impurities in acetylene. 2. Ionic liquid catalyzes the chlorination reaction to produce the target product. 3. Multi-stage rectification is used to purify the product by utilizing the boiling point difference. S4: Ionic liquid cycle absorption-regeneration is used to treat the tail gas to achieve resource recovery. 5. Microbial fuel cells degrade organic matter in wastewater while recovering electrical energy. Through the synergistic effects of chemical reactions, physical separation, and biodegradation in each step, the efficient production and environmental protection treatment of tetrachloroethane are achieved.

[0034] Example 2: C6 alkyl ionic liquid, high selectivity process; 1. Key adjustments: Ionic liquid: 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (accounting for 25%); Reaction conditions: molar ratio 1:4.5, temperature 80 °C, pressure 0.06 MPa, reaction for 40 minutes; Selectivity increased to 99.1% (by-products reduced to 0.9%).

[0035] 2. Regeneration process: Flow rate of anion exchange column is 6 BV / h, amino residue is 42 ppm, and the intensity of amino peak in infrared spectrum is reduced by 91%.

[0036] 3. Product purity: 99.8%, verifying the optimization effect of C6 alkyl group on the reaction path.

[0037] Example 3: C8 alkyl ionic liquid, high temperature and high pressure working conditions; 1. Extreme condition test: Ionic liquid: 1-octyl-3-methylimidazolium tetrafluoroborate (accounting for 30%); Conditions: temperature 120 °C, pressure 1.0 MPa, molar ratio 1:6, reaction for 20 minutes; Selectivity of crude product is 97.5%, verifying the feasibility of temperature / pressure upper limit.

[0038] 2. Tail gas treatment: Ionic liquid with grafting rate of 10% absorbs tail gas at 60 °C, and Cl2 residue is 0.8 ppm (meeting the standard).

[0039] 3. Regeneration efficiency: amino residue is 48 ppm, anion purity is 99%, and selectivity decreases by 1.2% after cycling (within the acceptable range).

[0040] Example 4: Low proportion recycling of ionic liquid; 1. Process adjustment: 85% of the regenerated ionic liquid returns to S2, and 15% is diverted to S41; continuous operation for 10 cycles, monitoring the selectivity decreases from 98.9% to 98.1% (due to impurity accumulation).

[0041] 2. Self-healing mechanism: Deep regeneration is automatically started in the 11th cycle (prolonging the vacuum distillation time to 40 minutes), and the selectivity is restored to 98.7%.

[0042] Example 5: Wastewater high load impact working conditions; 1. Forced degradation conditions: Wastewater COD suddenly increases to 800 mg / L (exceeding the upper limit of 500 mg / L), flow rate 3 m 3 / h; anode chamber volume 5 m 3 , microbial concentration 1×10 8 CFU / mL (lower limit value).

[0043] 2. Treatment effect: The COD removal rate was 78% (not up to standard) during the first run, but the system automatically added microbial agents (the concentration increased to 2×10 8 CFU / mL within 2 hours), and the removal rate recovered to 85.2% after 48 hours, verifying the process robustness.

[0044] As shown in Table 1 below:

[0045] Table 1: Comparison table of example data.

[0046] Process verification and data: 1. Structural characterization of ionic liquid (Example 1): NMR: The proton peaks of the imidazole ring are δ = 7.22 ppm and 7.38 ppm, which are within the range of 7.0 - 7.5 ppm; FTIR: The stretching vibration of the imidazole ring is 1580 cm -1 , which is consistent with 1570 - 1620 cm -1 .

[0047] 2. Purity detection of regenerated ionic liquid: After regeneration in Example 2, the purity of the anion is 99.3% and the amino residue is 42 ppm, meeting the requirement of "≤50 ppm".

[0048] 3. Equipment operation parameters: The tray efficiency of the valve tray in the atmospheric distillation column is 65% (≥60%), and the height equivalent to a theoretical plate in the vacuum distillation column is 0.25 m (≤0.3 m).

[0049] Summary of examples: 1. Example 1 is the basic process verification: the feasibility of the full process under standard parameters; 2. Example 2 is the structural optimization verification: the improvement effect of C6 alkyl on selectivity; 3. Example 3 is the extreme condition verification: the safety of the upper limits of temperature / pressure; 4. Example 4 is the cyclic stability verification: impurity accumulation and self-repair ability during long-term operation; 5. Example 5 is the environmental protection robustness verification: the treatment ability under the impact of wastewater load.

[0050] In summary, through key technological innovations such as nanomaterial purification, ionic liquid catalysis, multi-stage rectification, and pollutant recycling treatment, the present invention has constructed an efficient, low-consumption, and environmentally friendly production process for tetrachloroethane. This method not only achieves a breakthrough in product purity ≥ 99.8%, significantly improving the raw material utilization rate and production stability, but also, through ionic liquid closed-loop regeneration and microbial fuel cell technology, achieves the environmental protection goals of a tail gas pollutant removal rate ≥ 99% and a wastewater COD removal rate ≥ 85%, while reducing energy consumption by 30% - 40% and production costs by 25% - 30% simultaneously. The present invention provides a new paradigm for the green production of halogenated hydrocarbon compounds, has significant industrial application value and social benefits, and strongly promotes the sustainable development of related industries.

Claims

1. A production method of environmentally friendly tetrachloroethane, characterized in that: It includes the following steps: S1 Acetylene pretreatment: Pass the acetylene gas containing hydrogen sulfide and phosphine through an alkaline solution scrubbing tower; further pass it through a purification tower filled with an MCM-41 nanoporous material adsorbent, and contact it at a flow rate of 0.5-1.5 m³ / h for 30-60 minutes at 25-35 °C and 0.1-0.2 MPa to obtain pretreated acetylene; S2 Chlorination reaction: Introduce the purified acetylene and chlorine into an imidazole-based ionic liquid substituted by C4-C8 alkyl groups, with a molar ratio of 1:4-6, and react at 80-120 °C and 0.05-0.1 MPa for 20-40 minutes to produce a crude product of tetrachloroethane; S3 Multi-stage rectification and purification; S4 Tail gas treatment and ionic liquid closed-loop regeneration: S41 Pollutant enrichment: Pass the tail gas containing Cl2 and HCl into an ionic liquid absorption tower containing an amino-functionalized group, with a spraying amount of 5-15 L / h and an absorption temperature of 40-60 °C. The ionic liquid containing an amino-functionalized group is obtained by preliminarily filtering the ionic liquid discharged after the S2 reaction and grafting an amino-functionalized group by adding 3-aminopropyltrimethoxysilane at 60-80 °C; S42 Multi-stage regeneration process: Vacuum distillation: Distill the saturated ionic liquid at 80-100 °C and a vacuum degree of -0.09 MPa to remove HCl and Cl2 gas pollutants; Functional group removal: Remove the amino-functionalized group through an anion exchange column to make the amino residue concentration in the ionic liquid ≤50 ppm; Impurity filtration: After filtering through a 0.1 μm microporous filter membrane, 70%-90% of the regenerated ionic liquid returns to the S2 step for recycling, and 10%-30% is diverted to the S41 step for tail gas absorption.

2. The production method of an environment-friendly tetrachloroethane according to claim 1, characterized in that: In the above S1, the MCM-41 nanoporous material adsorbent has a specific surface area of 800-1200 m² / g and a pore diameter of 2-50 nm.

3. The production method of an environment-friendly tetrachloroethane as described in claim 1, characterized in that: In the above S2, the imidazole-based ionic liquid substituted by C4-C8 alkyl groups includes one or more of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

4. The production method of an environmentally friendly tetrachloroethane as described in claim 1, characterized in that: In the above S3, after the reaction product is condensed by a shell-and-tube condenser, atmospheric rectification and vacuum rectification are carried out in sequence to obtain a tetrachloroethane product.

5. The production method of an environmentally friendly tetrachloroethane according to claim 4, characterized in that: In the above S3, the atmospheric rectification tower uses a floating valve tray with a tray efficiency ≥60%; the vacuum rectification tower uses structured packing with a height equivalent to a theoretical plate ≤0.3 m.

6. The production method of an environment-friendly tetrachloroethane according to claim 1, characterized in that: It also includes S5 Wastewater treatment: Introduce the production wastewater with a COD ≤500 mg / L into a microbial fuel cell system, control the wastewater flow rate at 1-3 m³ / h, the effective volume of the anode chamber at 5-10 m³, and use a microbial flora mainly composed of Bacillus at 30-35 °C to oxidize organic pollutants and remove the COD of the wastewater.

7. The production method of an environment-friendly tetrachloroethane according to claim 6, characterized in that: The cathode of the above microbial fuel cell system uses a platinum-carbon electrode, and the ratio of the electrode area to the effective volume of the anode chamber is 0.1-0.3 m² / m³.

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