Tetrachloroethane

1,1,2,2-Tetrachloroethane as a C2 Feedstock in Catalytic TCE Synthesis

Compliance with ASTM D4080 (Standard Specification for Trichloroethylene, Type II) governs the downstream product quality when producing degreasing-grade trichloroethylene (TCE) from 1,1,2,2-tetrachloroethane. In a continuous vapor-phase process, the feedstock—typically at >99.5 wt% purity with moisture below 50 ppm—is preheated and fed at a mol ratio of 1:1 alongside recycled heavy ends into a tubular fixed-bed reactor operating between 320 °C and 400 °C. The catalyst bed, commonly composed of BaCl₂ on activated carbon or promoted alumina, facilitates selective HCl elimination. Single-pass conversion rates of 82–89% are achievable without significant carbon laydown, provided that hot spots are mitigated through interstage heat exchange. Effluent quenching and fractional distillation yield TCE meeting the criterion of ≤10 ppm acidity and non-volatile residue below 10 mg/100 mL. The terminal commodity is industrial-grade trichloroethylene, subsequently utilized in vapour degreasing and as a precursor for HFC-134a. Process operability is constrained by the sensitivity of BaCl₂ catalysts to sulfur-containing stabilizer carryover; any residual epoxide inhibitors from recycled tetrachloroethane must be removed via pre-bed guard columns to avoid irreversible deactivation.

Can Acid Scavengers Maintain Bath Stability in Open-Top Vapour Degreasers?

When 1,1,2,2-tetrachloroethane is employed as a heavy-duty solvent in open-top vapour degreasing equipment—such as an L/D ratio 3:1 degreaser with a freeboard ratio exceeding 0.75 to minimize solvent drag-out—the primary failure mode observed on production floors is acid-catalyzed decomposition triggered by metal fines, particularly aluminum swarf and moisture ingress above 200 ppm. The formulation addition ratio of the stabilizer package is 0.8–1.2 wt% of the total liquid charge, measured by potentiometric titration using ASTM D2106 (Standard Test Method for Determination of the Acid Acceptance of Halogenated Organic Solvents). Effective inhibitor cocktails combine butylene oxide at 0.5–0.7 wt% as an acid acceptor with tertiary amine salts at 0.1–0.15 wt% functioning as metal deactivators; however, primary or secondary amine additives must be rigorously excluded because they form quaternary ammonium hydrochlorides that catalyze further cracking, accelerating bath acidification. Process protocol dictates a weekly boiling sump cleanout to remove aluminum chloride sludge, and iron-free (<100 ppm) solvent grade per MIL-PRF-680B ensures that steel bearing races and aerospace hydraulic actuator bodies are cleaned without hydrogen embrittlement risk. The downstream process integrates vapour rinse, ultrasonic immersion at 40 kHz, and a secondary vapour zone to eliminate residual cutting oils, producing final parts—typically swashplate pistons, fuel control valve sleeves, and titanium engine brackets—that meet the nonvolatile residue limit of ≤1 mg/ft² required by ISO 1513:2010.

Table 1 — Effect of Inhibitor Concentration on Bath Life in 1,1,2,2-Tetrachloroethane Degreasing
Stabilizer Composition	Acid Acceptance (mL 0.1N NaOH/g solvent)	Bath Life at 145 °C (h to pH ≤3)	Observed Failure Mode
0.5 wt% butylene oxide only	0.12–0.15	120–160	Rapid corrosion of zinc-rich components after water layer formation
0.7 wt% butylene oxide + 0.1 wt% triethylamine salt	0.28–0.35	>400	None; aluminum powder suspension remains inert
1.2 wt% epoxybutane + 0.2 wt% dimethoxymethane	0.58–0.62	600+ (testing discontinued)	Minor evaporator coil scaling from oligomerized epoxy species

Extending the working window of solvent-based paint removers without invoking methylene chloride frequently demands a high-density, slow-evaporating carrier that retains active penetrants on vertical surfaces. In formulations targeting aerospace epoxy-polyurethane topcoats compliant with SAE AMS 1376, tetrachloroethane is incorporated at 48–55 wt% alongside benzyl alcohol (20–25 wt%), a hydrocarbon diluent (10–15 wt%), paraffin wax as an evaporation retardant (1.5–2.5 wt%), and a hydroxypropyl methylcellulose thickener (0.5–0.8 wt%) to achieve thixotropic suspension. The production process loads this mixture into pressure pot sprayers operating at 0.3–0.5 MPa, followed by a dwell period of 30–45 minutes—substantially longer than dichloromethane-based strippers—during which the chlorocarbon swells the crosslinked polymer matrix. Aged aluminum-magnesium fuselage panels are stripped by manual plastic scraper, after which air-force specifications per ASTM D3271 require immediate solvent wipe and chromate conversion coat reapplication. The terminal product class includes de-painted aircraft access doors, wing fillet panels, and helicopter rotor blade leading edges. Critically, the production environment mandates continuous LEL monitoring and forced ventilation at ≥2.0 m/s face velocity, as tetrachloroethane’s vapour pressure at 20 °C is 0.47 kPa and its TLV-TWA exposure limit is 1 ppm (7 mg/m³) under OSHA 29 CFR 1910.1000.

In rotogravure cylinder cleaning operations, the removal of crosslinked nitrocellulose-polyurethane ink residues from chrome-plated cells with depths up to 65 µm requires a solvent blend capable of penetrating below the nominal top-of-cell plane without altering the engraving profile. A mixture containing 32–38 vol% 1,1,2,2-tetrachloroethane with dearomatized hydrocarbon solvent (flash point ≥65 °C) and 2–4 vol% propylene carbonate is circulated through automated wash cabinets fitted with oscillating bristle brushes at 150 strokes/min and inline refractive index sensors calibrated to DIN 5571. The tetrachloroethane fraction functions as a high-Kauri-butanol-value (KB 120–130) component that disrupts secondary bonding in aged urethane linkages, reducing the mean clean-in-place cycle time from 8.2 minutes to below 4.0 minutes relative to ester-only formulations. Closed-loop recovery via condensation at –5 °C maintains solvent composition within ±1.5% over 50,000 impressions. The terminal output is an immediately reusable printing cylinder displaying no residual chroma in stamped proof transfers, with surface Ra retained at ≤0.02 µm. Regulatory compliance for this solvent application is governed by local VOC directives and the European Printing Inks Association (EuPIA) Exclusion Policy for food-contact materials; therefore, tetrachloroethane is confined exclusively to publication gravure and decorative laminates, never flexible packaging.

Controlling Exothermic Runaway in Tetrachloroethane Fluorination to HCFC-123

The liquid-phase halogen exchange between 1,1,2,2-tetrachloroethane and anhydrous hydrogen fluoride (AHF) is carried out in a Hastelloy C-276 autoclave equipped with a –10 °C reflux condenser system and a rupture disc rated to 3.0 MPa. A stoichiometric molar ratio of 1:3.2 (tetrachloroethane:AHF) feeds into the reactor where antimony pentafluoride (SbF₅), maintained at 3.0–5.0 mol% relative to initial tetrachloroethane charge, catalyzes the sequential chlorine-fluorine exchange. The temperature ramp is staged—45 °C for 2 hours, then 75 °C for 4 hours—to limit the accumulation of monofluorinated intermediates that accelerate runaway decomposition. The product 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) is isolated via pressure distillation and must satisfy AHRI Standard 700 purity requirements (≤0.50% moisture, ≤100 ppm acidity as HCl, ≤0.05% non-condensables). The terminal commercial refrigerant, often blended into R-409A or used as a clean-agent fire suppressant under ISO 14520, necessitates the precursor to be sampled for Sb contamination through inductively coupled plasma mass spectrometry (<0.5 mg/kg) to prevent expansion valve clogging. A structural limitation inherent to this pathway is the co-production of HCFC-124 at 4–8 wt% when reaction pH drifts below 0.5, requiring a side-stream fractional column with at least 55 theoretical plates for separation.

Tetrachloroethane exists as two distinct structural isomers—1,1,2,2-tetrachloroethane (CAS 79-34-5) and 1,1,1,2-tetrachloroethane (CAS 630-20-6)—each displaying markedly different physical behaviour despite sharing an identical molecular formula. Commercial production historically favoured the symmetrical 1,1,2,2- isomer via direct chlorination of acetylene, while the asymmetric 1,1,1,2- form emerges primarily as a by-product in ethylene chlorination streams. Both compounds are dense, non-flammable halogenated hydrocarbons, but their divergence in boiling point, vapour pressure, and solvent power dictates entirely separate application profiles. Current industrial interest centers on the symmetrical isomer for heavy-duty vapour degreasing and as a chemical building block, whereas the asymmetric isomer sees limited isolated use due to its lower thermal stability and narrower availability. The product is supplied in bulk tankers or 300-kg epoxy-lined steel drums, typically conforming to a minimum purity of 98.5% as determined by gas chromatography per ASTM D2106.

How Do the Physical Properties of the Two Isomers Differ?

Comparative physical property data for tetrachloroethane isomers
Property	1,1,2,2-Tetrachloroethane	1,1,1,2-Tetrachloroethane	Test Method
Boiling range at 101.3 kPa	145.5–146.5°C	130.2–130.8°C	ASTM D1078
Density at 20°C	1.595 g/cm³	1.540 g/cm³	ASTM D4052
Vapour pressure at 25°C	0.6 kPa	1.9 kPa	ASTM D2879
Viscosity at 25°C	1.75 mPa·s	1.25 mPa·s	ASTM D445
Flash point (closed cup)	None	None	ASTM D56
Kauri-butanol value (KB)	105–110	95–100	ASTM D1133

The symmetrical isomer’s elevated density and KB value arise from the terminal chlorines creating a stronger dipole moment, which enhances both cohesive energy density and solvation of polar soils. Its boiling point lies approximately 15°C above that of perchloroethylene and 58°C above that of trichloroethylene, properties exploited in processes where a slower evaporation rate prevents part cooling and moisture condensation. The vapour pressure differential is critical: 1,1,2,2-tetrachloroethane loses only 0.6 kPa to the headspace at ambient temperature, reducing workplace inhalation risk relative to more volatile chlorinated solvents, though its threshold limit value (TLV) of 1 ppm (ACGIH) demands closed-loop equipment.

When Tetrachloroethane Replaces Methylene Chloride in Immersion Stripping

For removing cross-linked epoxy coatings and high-melting waxes from steel tooling, maintenance facilities have observed that methylene chloride-based strippers, while aggressive at 20°C, generate vapour concentrations that trigger carbon bed breakthrough within 4–6 hours of continuous operation in manual dip tanks. Shifting the process to 1,1,2,2-tetrachloroethane at 70–75°C – below the boiling point but within the strong solvency envelope – reduces vapour generation by an order of magnitude, extending adsorber service intervals to 2–3 shifts. The higher surface tension (38.3 mN/m at 20°C) compared to methylene chloride (26.5 mN/m) limits penetration into tight crevices, so air-agitated immersion or ultrasonic assistance at 40 kHz becomes necessary to dislodge tenacious residues in capillary spaces below 500 µm. This substitution is uneconomical below 1,000-litre bath volumes due to the solvent’s unit cost and the capital expenditure for explosion-proof immersion heaters with setpoint accuracy of ±1.5°C. Stabilisation of the liquid phase during prolonged heating presents a non-trivial challenge. Autoxidative decomposition liberates hydrogen chloride within 8–12 hours of continuous aeration, and the induction period shortens dramatically if the system contains more than 50 ppm dissolved iron or aluminium fines originating from component abrasion. A binary inhibitor package comprising 0.5–1.0 wt% sec-butyl amine and 0.2 wt% 1,2-epoxybutane, monitored weekly via ASTM D2942 (acid acceptance test), maintains the acid acceptance value above 0.15 g HCl/100 mL in forced-convection ovens. Without such control, the bath pH drifts below 3.0 within 72 hours, causing pitting on martensitic stainless steel components.

Stabiliser Inhibition in High-Temperature Vapour Degreasers

Open-top vapour degreasers operating with 1,1,2,2-tetrachloroethane at the azeotropic boiling point experience a constant stripping of light inhibitor components into the vapour zone, which condenses on cold coils and returns to the boil sump depleted of stabiliser. Commercial stabiliser concentrates formulated for perchloroethylene prove partially compatible, but the addition of 3–5 wt% of a proprietary heavy-end extender—typically an alkylated diphenylamine—raises the inhibitor boiling range to overlap with the solvent’s, ensuring a uniform distribution between sump and vapour. Field data from a 500-litre degreaser processing cast iron railway bearing cages documented a drop in acid acceptance from 0.18 to 0.03 g HCl/100 mL over 10 consecutive eight-hour shifts when using unstabilised solvent, whereas the modified inhibitor blend sustained a value of 0.16 g/100 mL with a standard deviation of 0.02 across a 30-day monitoring period. The vapour degreaser must be constructed of stainless steel 316L or higher alloy; galvanised steel and aluminium components corrode within hours under condensing solvent vapours saturated with trace acid. Filtration of insoluble metal salts through 5-micron rated bag filters on the bypass loop prevents nucleation of decomposition at suspended particulate surfaces. A cooling coil water temperature of 18–22°C is required to maintain the vapour blanket within 25 mm of the freeboard edge, satisfying the criteria of ISO 8990 for heat loss estimation. The total energy consumption of a 1.2 m × 0.8 m × 0.8 m unit stabilises around 18–22 kW during steady-state operation.

What Role Does Tetrachloroethane Serve as a Chemical Intermediate?

High-purity 1,1,2,2-tetrachloroethane (> 99.0%) is catalytically dehydrochlorinated over barium chloride or activated carbon at 300–350°C to produce trichloroethylene and perchloroethylene in varying ratios determined by residence time and contact gas partial pressure. Short contact times (1–2 seconds) and a steam-to-feed ratio of 2:1 by weight favour trichloroethylene formation, whereas increasing residence time to 5–8 seconds shifts the product distribution toward perchloroethylene with selectivity exceeding 70%. The symmetrical isomer also participates in electrophilic additions across the triple bond of cyanogen to yield diaminomaleonitrile, a precursor to pyrazine-based pharmaceuticals. The asymmetric isomer, conversely, undergoes preferential dehydrochlorination at the 1-position to yield 1,1,2-trichloroethylene contaminated with 1,1,1- isomer, complicating downstream purification. Consequently, isolable quantities of 1,1,1,2-tetrachloroethane are rarely stockpiled separate from mixed chlorocarbon streams, limiting its use as a dedicated chemical building block. The symmetrical isomer has also been evaluated as a chain transfer agent in free-radical polymerisation of vinyl chloride and vinylidene chloride, where its high transfer constant (Cs ≈ 2.0 × 10⁻³ at 50°C) permits a reduction in polymer molecular weight without requiring excessive initiator loading. However, residual solvent trapped in the polymer matrix requires post-stripping at 130°C under vacuum (20 mbar) to reduce headspace concentration below the 0.1 ppm limit for food contact materials under EU 10/2011.

Distillation Recovery and the Risk of Corrosive Pyrolysates

Recovery stills attached to degreasing lines expose the solvent to thermal stress at the heating element surface, where local film temperatures can exceed the bulk liquid temperature by 40–60°C. At metal surfaces heated above 180°C, 1,1,2,2-tetrachloroethane undergoes a slow elimination pathway that releases dichloroacetylene as a transient intermediate, which in the presence of oxygen oligomerises into tar and liberates phosgene. Published data for this specific configuration is limited, but plant operators report that fouling of electrically heated immersion bundles with a carbonaceous scale of 2–4 mm thickness after 600–800 hours of cumulative operation raises the surface temperature from 155°C to above 220°C, initiating a runaway acid generation that etches the sheath material and requires bundle replacement within 48 hours of onset. Mandating a heat flux not exceeding 25 kW/m² and using a pumped recirculation rate across the elements of 3–4 m/s mitigates this degradation mode. The recovered solvent must pass ASTM D3401 (moisture content below 50 ppm) before re-introduction to the degreaser sump, as water accelerates hydrolysis to dichloroacetic acid and hydrogen chloride at elevated temperature.

Environmental and Occupational Exposure Boundaries

Under REACH Regulation (EC 1907/2006), 1,1,2,2-tetrachloroethane is registered with a harmonised classification of Acute Tox. 4 (H332), Skin Irrit. 2 (H315), and STOT RE 2 (H373) targeting the liver. The Derived No-Effect Level (DNEL) for inhalation long-term exposure is set at 1.4 mg/m³, while the Predicted No-Effect Concentration (PNEC) for freshwater is 0.014 mg/L. Publicly available monitoring studies at European degreasing facilities employing closed-loop carbon adsorption and refrigeration-chilled freeboard coils (−15°C) report time-weighted average breathing zone concentrations between 0.2 and 0.8 ppm, well below the 1-ppm TLV-TWA. Comparison with trichloroethylene reveals that while the TLV for TCE is 10 ppm, its higher vapour pressure (7.8 kPa at 25°C) results in area concentrations that routinely exceed 5 ppm during lid opening in manually fed open-top units, a condition that the low-volatility tetrachloroethane minimises.

Regulatory status comparison of chlorinated solvents for industrial degreasing
Solvent	Boiling point (°C)	TLV-TWA (ppm)	VOC status (EU Solvent Emissions Directive)	PBT/vPvB assessment
1,1,2,2-Tetrachloroethane	146	1	Classified as VOC	Under evaluation
Trichloroethylene	87	10	VOC, candidate for substitution	Not PBT/vPvB but CMR Cat 1B
Perchloroethylene	121	25	VOC, heavy metal focus	Not PBT/vPvB but suspected carcinogen
Methylene chloride	40	50	VOC, included in Annex VI	Not PBT/vPvB

The shift towards 1,1,2,2-tetrachloroethane in precision cleaning occurs where higher-boiling solvents reduce emission losses during transfer, despite the more restrictive occupational exposure limit demanding engineering controls such as lip-venting at 0.5 m/s face velocity and continuous photoionization detector (PID) monitoring at the tank perimeter. The product must be kept in a dry, well-ventilated store, separated from strong bases, aluminium powder, and oxidising agents, with a recommended maximum storage temperature of 30°C to preserve inhibitor integrity.

HS Code	2903.19
Chemical Formula	C2H2Cl4
Molecular Weight	167.85 g/mol
Cas Number	79-34-5
Density	1.586 g/mL at 20°C
Boiling Point	146.5°C
Melting Point	-42.5°C
Flash Point	54°C (closed cup)
Solubility In Water	0.29 g/100 mL at 20°C
Vapor Pressure	6.7 mmHg at 25°C
Refractive Index	1.4932 at 20°C

Packing	Tetrachloroethane supplied in 200-liter sealed steel drums, with hazard labels and UN certification for safe industrial handling and transport.
Container Loading (20′ FCL)	Stow steel drums or IBCs upright, secure with dunnage, label as hazardous, and follow IMDG segregation for Tetrachloroethane in a 20′ FCL.
Shipping	Tetrachloroethane must be shipped as a hazardous material (UN 1702, Class 6.1, PG II). Use leak-proof, corrosion-resistant containers. Avoid heat, sparks, and incompatible substances. Label as toxic, and ensure proper ventilation and personnel protection during transport. Follow all applicable regulatory requirements.
Storage	Tetrachloroethane should be stored in a cool, well-ventilated area away from heat, sparks, and direct sunlight. Use tightly sealed, corrosion-resistant containers (e.g., glass or HDPE). Keep separate from strong oxidizers and alkalis. Ensure secondary containment to prevent spills, as it is toxic and may degrade to phosgene. Label clearly and store in a designated hazardous chemical cabinet.
Shelf Life	Tetrachloroethane's shelf life is typically 1–2 years when stored in a cool, dry, ventilated area away from light and moisture.

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