A method for producing environmentally friendly tetrachloroethane

Abstract

The present invention discloses a method for producing environmentally friendly tetrachloroethane, which relates to the field of chemical synthesis technology. The method comprises acetylene pretreatment: deep purification by alkaline washing and MCM-41 nano-adsorbent; chlorination reaction: using C4-C8 alkyl-substituted imidazole ionic liquid as the reaction medium, catalyzing the reaction of acetylene and chlorine at 80-120°C and 0.05-0.1MPa; multi-stage distillation: using a combined atmospheric-vacuum distillation process; tail gas treatment: using amino-functionalized ionic liquid to enrich pollutants, which are then recycled after vacuum distillation and anion exchange column regeneration, with an ionic liquid recovery rate of ≥95%; and wastewater treatment: a microbial fuel cell system achieves efficient COD removal. The present invention significantly improves product purity and production efficiency, reduces energy consumption, and promotes the green and efficient production of tetrachloroethane through ionic liquid design.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a method for producing environmentally friendly tetrachloroethane. Background Art

[0002] The traditional tetrachloroethane production process uses calcium carbide hydrolysis to produce acetylene, which is then reacted with chlorine under the catalysis of ferric chloride after simple purification. This process has the following defects: 1. Low raw material utilization: Incomplete purification of acetylene leads to impurities participating in side reactions, low raw material conversion rate, and low product purity; 2. Prominent energy consumption and pollution problems: The reaction needs to be carried out at 90-120℃ and normal pressure, which consumes a lot of energy; the tail gas contains harmful gases such as Cl2 and HCl, and the COD of the wastewater is as high as 1000-1500mg / L. Traditional treatment methods are difficult to meet the standards and cannot meet the stringent requirements of environmentally friendly products.

[0003] In view of this, this application is hereby filed. Summary of the Invention

[0004] The object of the present invention is to provide a method for producing environmentally friendly tetrachloroethane to solve the problems mentioned in the above background technology.

[0005] To solve the above technical problems, the present invention provides a method for producing environmentally friendly tetrachloroethane, comprising the following steps:

[0006] S1 Acetylene pretreatment: The acetylene gas containing hydrogen sulfide (H2S≤100ppm) and phosphine (PH3≤50ppm) is passed through an alkaline solution washing tower (filler specific surface area ≥200m 2 / m 3 , liquid-gas ratio 1:5-10), control the sulfide content in the gas after washing to ≤1ppm, and the phosphine content to ≤0.5ppm; further fill the MCM-41 nanoporous material adsorbent (specific surface area 800-1200m 2 / g, pore size 2-50nm) purification tower, at 25-35℃, 0.1-0.2MPa, with a flow rate of 0.5-1.5m 3 / h flow rate for 30-60 minutes to obtain acetylene with a purity of ≥99.5%;

[0007] S2 chlorination reaction: Purified acetylene and chlorine are introduced into a C4-C8 alkyl-substituted imidazole ionic liquid (the carbon chain length of the cation substituent is 4-8, and the anion is one or more of hexafluorophosphate, tetrafluoroborate, and bistrifluoromethanesulfonyl imide salt, accounting for 10%-30% of the total volume of the reactor) at a molar ratio of 1:4-6. The reaction is carried out at 80-120°C and 0.05-0.1 MPa for 20-40 minutes to produce crude tetrachloroethane;

[0008] S3 multi-stage distillation purification;

[0009] S4 tail gas treatment and ionic liquid closed-loop regeneration:

[0010] S41 pollutant enrichment: The tail gas containing Cl2≤100ppm and HCl≤500ppm is passed into an ionic liquid absorption tower containing amino functional groups (with a filler specific surface area of ≥250m 2 / m 3 , gas-liquid ratio 1:10-15), spray volume 5-15L / h, absorption temperature 40-60°C, the amino-functional ionic liquid is prepared by preliminarily filtering the ionic liquid discharged after the S2 reaction and then adding 3-aminopropyltrimethoxysilane (5%-10% by mass of the ionic liquid) to graft the amino functional group at 60-80°C;

[0011] S42 multi-stage regeneration process:

[0012] Vacuum distillation: The absorbed saturated ionic liquid is distilled at 80-100°C and vacuum degree -0.09MPa to remove gaseous pollutants such as HCl and Cl2;

[0013] Functional group removal: Remove amino functional groups through an anion exchange column (filled with quaternary ammonium resin, resin bed height 1-1.5m, flow rate 5-10BV / h, eluent 1mol / L potassium chloride solution) to make the residual amino concentration in the ionic liquid ≤50ppm and the anion purity ≥99%;

[0014] Impurity filtration: After filtration through a 0.1 μm microporous membrane, 70%-90% of the regenerated ionic liquid is returned to step S2 for recycling, and 10%-30% is diverted to step S41 for tail gas absorption.

[0015] Furthermore, in said S1, the MCM-41 nanoporous material adsorbent has a specific surface area of 800-1200m 2 / g, pore size 2-50nm.

[0016] Furthermore, in S2, the C4-C8 alkyl-substituted imidazole ionic liquid includes one or more of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0017] Furthermore, in said S3, the reaction product is passed through a shell and tube condenser (heat exchange area 20-50m 2 , cooling medium temperature -10-10 ℃) after condensation, followed by atmospheric distillation (tower top temperature 120-130 ℃, tower plate number 30-50) and vacuum distillation (tower top pressure 10-30 kPa, tower top temperature 80-90 ℃, tower plate number 20-40) to obtain tetrachloroethane product with a purity of ≥99.8%.

[0018] Furthermore, in S3, the atmospheric distillation tower uses a floating valve tray, and the tray efficiency is ≥60%; the vacuum distillation tower uses a structured packing, and the plate height is ≤0.3m.

[0019] Furthermore, it also includes S5 wastewater treatment: introducing production wastewater containing COD ≤ 500mg / L into the microbial fuel cell system, controlling the wastewater flow rate to 1-3m 3 / h, effective volume of anode chamber 5-10m 3 At 30-35℃, the main microorganisms were Bacillus (accounting for 70%-90% of the total microorganisms, with a concentration of 1×10 8 -3×10 8 CFU / mL) of microbial flora oxidizes organic pollutants, and the wastewater COD removal rate is ≥85%.

[0020] Furthermore, the cathode of the microbial fuel cell system adopts a platinum-carbon electrode, and the ratio of the electrode area to the effective volume of the anode chamber is 0.1-0.3m 2 / m 3 .

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. High-Purity Products: Through dual purification using alkaline washing and MCM-41 nano-adsorbent, acetylene purity reaches ≥99.5%. Multi-stage distillation under atmospheric and vacuum conditions combined with precise temperature control achieves a purity of ≥99.8% for tetrachloroethane, far exceeding conventional processes. This process meets the demand for high-purity halogenated hydrocarbons in high-end fields such as semiconductors and pharmaceuticals, while minimizing impurity interference.

[0023] 2. Environmentally friendly: Amino / thiol ionic liquids absorb tail gas pollutants, with a regeneration recovery rate of ≥95% and no secondary pollution. Microbial fuel cells treat wastewater with a COD removal rate of ≥85%, achieving standard tail gas and wastewater discharge and energy recovery.

[0024] 3. Low consumption and high efficiency: The ionic liquid catalytic reaction is carried out under mild conditions of 80-120℃ and 0.05-0.1MPa, reducing energy consumption by 30%-40%, shortening the reaction time to 20-40 minutes, reducing costs by 25%-30% through ionic liquid circulation, and improving production stability by 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a flow chart of a method for producing environmentally friendly tetrachloroethane. DETAILED DESCRIPTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] See also Figure 1 The present invention provides a technical solution: a method for producing environmentally friendly tetrachloroethane, comprising:

[0028] Example 1: C4 alkyl ionic liquid;

[0029] 1. Acetylene pretreatment:

[0030] The crude acetylene contains H2S80ppm and PH335ppm, and is washed by a NaOH washing tower (liquid-gas ratio 1:6, filler specific surface area 220m 2 / m 3 ) After treatment, sulfide ≤ 0.8ppm, PH3 ≤ 0.4ppm;

[0031] It should be noted that the existing industrial preparation method of acetylene usually adopts the calcium carbide method, which mainly produces H2S and PH3 impurity gases. After passing through the alkaline NaOH scrubber, the sodium sulfide and sodium phosphide produced are dissolved in the scrubbing liquid.

[0032] H2S+2NaOH→Na2S+2H2O;

[0033] PH3+3NaOH→Na3P+3H2O.

[0034] Then pass through MCM-41 adsorption tower (specific surface area 900m 2 / g, pore size 15nm), and contact time of 50 minutes at 30℃ and 0.12MPa, the acetylene purity reached 99.6%.

[0035] It should be noted here that H2O, residual H2S, PH3 and other molecules are adsorbed in the pores of MCM-41, further reducing to the ppm level.

[0036] 2. Chlorination reaction:

[0037] Ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate (20% of the reactor volume);

[0038] Conditions: acetylene / chlorine molar ratio 1:5, temperature 90°C, pressure 0.07 MPa, reaction time 30 minutes;

[0039] Crude product selectivity: 98.7%, by-product trichloroethane 1.3%.

[0040] It should be noted that in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, Cl2 undergoes electrophilic addition to acetylene at 80-120°C to produce tetrachloroethane. Excess Cl2 (molar ratio 4-6:1) ensures complete conversion of acetylene:

[0041] C2H2+2Cl2→C2H2Cl4 (tetrachloroethane is produced);

[0042] Ionic liquids can provide a polar environment, promote the dissociation and reaction activity of Cl2, dissolve reactants, improve mass transfer efficiency, are resistant to high temperatures (80-120°C), are not easily volatile, and can be recycled.

[0043] 3. Distillation and purification:

[0044] The top temperature of the atmospheric distillation tower (40 plates, 62% plate efficiency) is 125°C, and the top pressure of the vacuum distillation tower (30 plates, 0.28m equal plate height) is 20kPa, and the product purity is 99.9%.

[0045] Important clarifications include: 1. Condensation: The reaction product (gaseous) is cooled to a liquid state via a shell-and-tube condenser. 2. Atmospheric distillation: At the top, low-boiling-point impurities (such as HCl, Cl₂, and trichloroethane) are separated; at the bottom, tetrachloroethane and high-boiling-point impurities (such as pentachloroethane) are separated. 3. Vacuum distillation: At the top, tetrachloroethane is refined (purity ≥ 99.5%); at the bottom, high-boiling-point impurities (such as pentachloroethane) are separated. The principle is to reduce pressure and lower the boiling point of tetrachloroethane, preventing high-temperature decomposition. Structured packing (plate height ≤ 0.3m) provides a larger mass transfer area, improving separation efficiency.

[0046] 4. Exhaust gas treatment:

[0047] The spray rate of amino-grafted ionic liquid (grafting rate 6%) is 10L / h, the absorption temperature is 50℃, and the tail gas Cl2≤0.5ppm, HCl≤5ppm;

[0048] The amino residue in the regenerated ionic liquid is 38 ppm, which is returned to S2 for recycling, with a recovery rate of 97%.

[0049] It should be noted that the S41 pollutant enrichment reaction causes Cl2 and HCl to absorb:

[0050] 2R-NH2+Cl2→RN=N-R+2HCl;

[0051] R-NH2+HCl→[R-NH3] + Cl - ;

[0052] The product is: Cl2 and HCl loaded ionic liquid: containing azo compound (RN=NR) and ammonium salt ([R-NH3] + Cl - ).

[0053] In addition: Also includes S411: HCl pre-separation:

[0054] The tail gas containing Cl2 and HCl first passes through a water scrubber, and the temperature is controlled at 20-30°C to dissolve HCl in water to form dilute hydrochloric acid (concentration of about 5%-10%). After the HCl content in the tail gas is reduced to ≤50ppm, the outlet gas of the water scrubber passes through a wire mesh demister (efficiency ≥99%, droplet residue ≤50mg / m 3 ) to remove the mist droplets; then enter the S41 ionic liquid absorption tower.

[0055] S412: Cl2 absorption:

[0056] The tail gas (mainly containing Cl2 and a small amount of HCl) after pre-separation of HCl by S411 is introduced into the amino-functionalized ionic liquid absorption tower with an absorption temperature of 40-60°C (to improve the Cl2 absorption efficiency) and a spray volume of 8-12L / h.

[0057] Then S42 multi-stage regeneration process:

[0058] (1) Reaction during vacuum distillation:

[0059] [R-NH3] + Cl - →R-NH2+HCl↑;

[0060] RN=N-R+2HCl→2R-NH2+Cl2↑;

[0061] Products include: desorbed HCl and Cl2 gases, which can be further recovered (see S43 below). Regenerated ionic liquid: restores amino functional groups.

[0062] (2) Functional group removal process: Residual amino groups are removed through an anion exchange column (e.g., a strong alkaline resin). The product is an ionic liquid with a residual amino group concentration of ≤50 ppm. Deep purification is achieved by exchanging the anion exchange resin with the amino cation.

[0063] (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% is returned to S2 for recycling, and 10%-30% is used in S41.

[0064] S43:Cl2 recovery:

[0065] The Cl2 gas (containing a small amount of HCl) removed by vacuum distillation in S42 is condensed at low temperatures (-10°C to -20°C) to liquefy and collect the Cl2. The uncondensed HCl is returned to the S411 water scrubber for recycling. The recovered liquid chlorine, with a purity of ≥99%, is vaporized and returned to the S2 chlorination reaction system.

[0066] 5. Wastewater treatment:

[0067] Wastewater COD450mg / L, flow rate 2m 3 / h, anode chamber volume 7m 3 , microbial concentration 2×10 8 CFU / mL, COD removal rate was 85.5%.

[0068] In each step, 1: Chemical washing and physical adsorption remove sulfur and phosphorus impurities from acetylene. 2: Ionic liquid catalyzes the chlorination reaction to produce the target product. 3: Multi-stage distillation utilizes boiling point differences to purify the product. S4: Ionic liquid cyclic absorption and regeneration treats the exhaust gas to achieve resource recovery. 5: Microbial fuel cells degrade organic matter in the wastewater and simultaneously recover electricity. Through the synergistic effects of chemical reaction, physical separation, and biodegradation, each step achieves efficient production and environmentally friendly treatment of tetrachloroethane.

[0069] Example 2: C6 alkyl ionic liquid, high selectivity process;

[0070] 1. Key adjustments:

[0071] Ionic liquid: 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (25%);

[0072] Reaction conditions: molar ratio 1:4.5, temperature 80°C, pressure 0.06 MPa, reaction time 40 minutes;

[0073] The selectivity was increased to 99.1% (by-products were reduced to 0.9%).

[0074] 2. Regeneration process:

[0075] The flow rate of the anion exchange column was 6 BV / h, the amino residue was 42 ppm, and the intensity of the amino peak in the infrared spectrum was reduced by 91%.

[0076] 3. Product purity: 99.8%, verifying the optimization effect of C6 alkyl on the reaction pathway.

[0077] Example 3: C8 alkyl ionic liquid, high temperature and high pressure conditions;

[0078] 1. Extreme condition test:

[0079] Ionic liquid: 1-octyl-3-methylimidazolium tetrafluoroborate (30%);

[0080] Conditions: temperature 120°C, pressure 1.0 MPa, molar ratio 1:6, reaction time 20 minutes;

[0081] The crude product selectivity was 97.5%, verifying the feasibility of the upper temperature / pressure limit.

[0082] 2. Exhaust gas treatment:

[0083] The ionic liquid with a grafting rate of 10% absorbed the tail gas at 60°C, and the Cl2 residual was 0.8ppm (reaching the standard).

[0084] 3. Regeneration efficiency: amino residue 48ppm, anion purity 99%, selectivity decreased by 1.2% after circulation (acceptable range).

[0085] Example 4: Low ratio circulation of ionic liquid;

[0086] 1. Process adjustment: 85% of the regenerated ionic liquid was returned to S2, and 15% was diverted to S41; after 10 consecutive cycles, the monitored selectivity dropped from 98.9% to 98.1% (impurity accumulation effect).

[0087] 2. Self-repair mechanism: Deep regeneration is automatically initiated in the 11th cycle (extending the vacuum distillation time to 40 minutes), and the selectivity is restored to 98.7%.

[0088] Example 5: Wastewater high load impact condition;

[0089] 1. Forced degradation conditions: wastewater COD suddenly increases to 800mg / L (exceeding the upper limit of 500mg / L), flow rate 3m 3 / h; anode chamber volume 5m 3 , microbial concentration 1×10 8 CFU / mL (lower limit).

[0090] 2. Treatment effect:

[0091] The COD removal rate was 78% in the first run (not up to standard), but the system automatically added bacteria (the concentration rose to 2×10 8 CFU / mL), and the removal rate recovered to 85.2% after 48 hours, verifying the robustness of the process.

[0092] As shown in Table 1 below:

[0093]

[0094] Table 1: Comparative table of example data.

[0095] Process Validation and Data:

[0096] 1. Ionic Liquid Structural Characterization (Example 1):

[0097] NMR: imidazole ring proton peaks δ = 7.22ppm, 7.38ppm, consistent with the 7.0-7.5ppm range;

[0098] FTIR: imidazole ring stretching vibration 1580 cm -1 , and 1570-1620cm -1 consistent.

[0099] 2. Purity test of regenerated ionic liquid:

[0100] After regeneration in Example 2, the anion purity was 99.3%, and the amino residue was 42 ppm, meeting the requirement of "≤50 ppm".

[0101] 3. Equipment operating parameters:

[0102] The efficiency of the floating valve tray of the atmospheric distillation tower is 65% (≥60%), and the height of the equal tray of the vacuum distillation tower is 0.25m (≤0.3m).

[0103] Summary of the embodiments:

[0104] 1. Example 1 is a basic process verification: full process feasibility under standard parameters;

[0105] 2. Example 2 is a structural optimization verification: the effect of C6 alkyl on the selectivity improvement;

[0106] 3. Example 3 is the extreme working condition verification: the safety of the temperature / pressure upper limit;

[0107] 4. Example 4 is a cycle stability verification: impurity accumulation and self-repair ability during long-term operation;

[0108] 5. Example 5 is environmental robustness verification: treatment capacity under wastewater load impact.

[0109] In summary, the present invention has constructed a high-efficiency, low-consumption, and environmentally friendly tetrachloroethane production process through key technological innovations such as nanomaterial purification, ionic liquid catalysis, multi-stage distillation, and pollutant recycling treatment. This method not only achieves a breakthrough in product purity ≥99.8%, significantly improving raw material utilization and production stability, but also achieves environmental protection goals of tail gas pollutant removal rate ≥99% and wastewater COD removal rate ≥85% through ionic liquid closed-loop regeneration and microbial fuel cell technology, while simultaneously reducing energy consumption by 30%-40% and production costs by 25%-30%. The present invention provides a new paradigm for the green production of halogenated hydrocarbon compounds, has significant industrial application value and social benefits, and effectively promotes the sustainable development of related industries.

Claims

1. A method for producing environmentally friendly tetrachloroethane, characterized in that: The following steps are involved: S1 Acetylene pretreatment: The acetylene gas containing hydrogen sulfide and phosphine is passed through an alkaline solution washing tower; further passed through a purification tower filled with MCM-41 nanoporous material adsorbent, at 25-35 ° C, 0.1-0.2 MPa, and 0.5-1.5 m 3 / h flow rate for 30-60 minutes to obtain pretreated acetylene; S2 chlorination reaction: into a C4-C8 alkyl-substituted imidazole ionic liquid, the C4-C8 alkyl-substituted imidazole ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium tetrafluoroborate, and 1-hexyl-3-methylimidazolium bistrifluoromethanesulfonyl imide, purified acetylene and chlorine are introduced at a molar ratio of 1:4-6, and the reaction is carried out at 80-120° C. and 0.05-0.1 MPa for 20-40 minutes to produce crude tetrachloroethane; S3 multi-stage distillation purification; S4 tail gas treatment and ionic liquid closed-loop regeneration: S41 pollutant enrichment: the tail gas containing Cl2 and HCl is passed into an ionic liquid absorption tower containing amino functional groups, with a spray rate of 5-15 L / h and an absorption temperature of 40-60°C. The ionic liquid containing amino functional groups is obtained by preliminarily filtering the ionic liquid discharged after the S2 reaction and then grafting the amino functional groups with 3-aminopropyltrimethoxysilane at 60-80°C; S42 multi-stage regeneration process: Vacuum distillation: The absorbed saturated ionic liquid is distilled at 80-100°C and vacuum degree -0.09MPa to remove HCl and Cl2 gas pollutants; Functional group removal: amino functional groups are removed through anion exchange columns to make the residual amino concentration in the ionic liquid ≤50ppm; Impurity filtration: After filtration through a 0.1 μm microporous membrane, 70%-90% of the regenerated ionic liquid is returned to step S2 for recycling, and 10%-30% is diverted to step S41 for tail gas absorption.

2. The method for producing environmentally friendly tetrachloroethane according to claim 1, wherein: In S1, MCM-41 nanoporous material adsorbent has a specific surface area of 800-1200m 2 / g, pore size 2-50nm.

3. The method for producing environmentally friendly tetrachloroethane according to claim 1, wherein: In S3, the reaction product is condensed in a shell-and-tube condenser and then subjected to atmospheric distillation and vacuum distillation in sequence to obtain tetrachloroethane product.

4. The method for producing environmentally friendly tetrachloroethane according to claim 3, wherein: In S3, the atmospheric distillation tower uses floating valve trays with a tray efficiency of ≥60%; the vacuum distillation tower uses structured packing with a plate height of ≤0.3m.

5. The method for producing environmentally friendly tetrachloroethane according to claim 1, wherein: 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 to 1-3 m 3 / h, effective volume of anode chamber 5-10m 3 At 30-35℃, the microbial flora mainly composed of Bacillus is used to oxidize organic pollutants and remove COD from wastewater.

6. The method for producing environmentally friendly tetrachloroethane according to claim 5, wherein: The cathode of the microbial fuel cell system adopts a platinum-carbon electrode, and the ratio of the electrode area to the effective volume of the anode chamber is 0.1-0.3m 2 / m 3 .

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