Feedstock conversion capacity for tetrafluoroethylene derived from chloroform through chlorodifluoromethane is fixed by the interaction of liquid-phase fluorination and gas-phase pyrolysis. The overall stoichiometry is CHCl₃ + 2 HF → CHClF₂ + 2 HCl and 2 CHClF₂ → C₂F₄ + 2 HCl, giving a theoretical TFE mass yield of 0.419 kg per kg of pure chloroform when both stages are complete. In practice, the nameplate capacity of an integrated plant is governed by the fluorination reactor throughput, the pyrolysis furnace tube volume, the quench and acid absorption train pressure drop, and the cryogenic distillation recycle purity. The liquid-phase chloroform fluorination step is carried out in a stirred, corrosion-resistant vessel with a fluoropolymer lining or a high-nickel alloy such as Hastelloy C-276, operating with a slight excess of anhydrous hydrogen fluoride and antimony pentachloride catalyst. Reactor temperatures are commonly maintained between 60 °C and 110 °C, while the pressure is held in the 0.6 MPa to 1.5 MPa range to keep hydrogen fluoride in the liquid phase and permit reflux of chlorodifluoromethane. Heat is removed through an external circulation loop with a graphite or silicon carbide exchanger, and the crude product is fed to a distillation column for separation of HCl and excess HF. The actual capacity is reduced by catalyst deactivation from water ingress, organic residue accumulation, and antimony carryover, each of which lowers fluorination yield below the stoichiometric limit. A representative mass balance using conservative industrial assumptions is obtained from the expression C_TFE = F_CHCl3 × x_CHCl3 × 0.419 × Y_R22 × R_R22 × S_TFE × R_TFE × f_operating, where F_CHCl3 is the chloroform feed rate, x_CHCl3 is chloroform purity, Y_R22 is fluorination yield, R_R22 is R22 recovery after drying, S_TFE is selectivity to TFE in pyrolysis, R_TFE is TFE recovery after distillation, and f_operating is the annual operating factor. For a chloroform feed of 20,000 t/a at 99.8 wt% purity, 98% fluorination yield, 98% R22 recovery, 95% TFE selectivity, 98% TFE recovery, and 0.95 operating factor, the calculated effective capacity is approximately 7,090 t/a of TFE. This figure illustrates the cumulative loss structure; published data for any specific integrated configuration is limited because most industrial facilities do not disclose per-pass pyrolysis conversion together with recycle recovery.

How Does Per-Pass R22 Conversion Affect Tetrafluoroethylene Capacity?

In a steam-diluted tubular pyrolysis furnace, chlorodifluoromethane is cracked at temperatures between 650 °C and 850 °C with residence times from 0.02 s to 0.5 s, producing TFE and HCl by the reaction 2 CHClF₂ → C₂F₄ + 2 HCl. Per-pass R22 conversion is deliberately limited to the 25% to 35% range in many operations because higher conversion increases the rate of TFE decomposition to carbon, CF₄, and unsaturated byproducts such as hexafluoropropylene and perfluoroisobutylene. The unconverted R22 is recovered in the downstream distillation train and recycled to the furnace, so annual capacity is not determined solely by per-pass conversion but by the product of per-pass conversion, selectivity, and recovery. Selectivity to TFE at 30% per-pass conversion is commonly reported in the 90% to 95% range under steam dilution; as conversion is raised above 35%, selectivity can fall below 85% because of secondary reactions and coke deposition on the tube wall. The volumetric capacity of the furnace is governed by the tube inside diameter, total heated length, and allowable heat flux, with industrial radiant-section tubes in the 50 mm to 150 mm nominal bore range and fired lengths of 8 m to 20 m per pass. The tube skin temperature is constrained by creep and carburization limits, typically 1,000 °C for high-nickel alloys, while the process gas outlet temperature is kept below 850 °C. Because the pyrolysis reaction is highly endothermic, heat transfer and residence time distribution in the radiant coil determine the maximum chloroform-based capacity rather than the fluorination section alone.

Downstream of the pyrolysis furnace, the cracked gas is quenched within 0.1 s to 0.5 s to below 120 °C using a venturi quench with aqueous HCl or recirculated acid. Rapid quenching preserves TFE selectivity by stopping radical decomposition pathways that would otherwise convert TFE to CF₄, C₂F₆, and polyfluorinated oligomers. The quench liquid leaving the venturi contains HCl at concentrations between 15 wt% and 25 wt%, and is transferred to an adiabatic absorber where HCl is recovered as a byproduct at commercial-grade concentration. Unabsorbed gas then passes through a water scrubber, a caustic scrubber using 5% to 10% NaOH, and a drying bed of activated alumina or molecular sieve to reduce moisture below 5 mg/kg before compression. The scrubber train is sized for the maximum chlorine throughput, and its pressure drop of 25 kPa to 60 kPa across the entire train determines the suction pressure at the cracked-gas compressor. In plants using an oil-flooded screw compressor, the interstage temperature is kept below 90 °C to avoid TFE dimerization and the lube oil is selected for low solubility of fluorinated gases. Graphite and PTFE-lined components are used in the acid area, while stainless steel 316L is limited to low-temperature, low-acid locations because chloride stress corrosion cracking occurs above 60 °C in the presence of HCl. The namesake capacity of the TFE plant is therefore reduced by any fouling of the quench venturi or the scrubber packing, because increased pressure drop limits compressor throughput and imposes a lower recycle flow of R22 to the furnace.

When Chloroform Feedstock Contains Brominated or Unsaturated Chlorocarbon Impurities

Chloroform feedstock is typically specified at 99.5 wt% minimum purity, with water below 50 mg/kg, acidity below 10 mg/kg as HCl, and nonvolatile residue below 5 mg/kg. Brominated impurities, unsaturated chlorocarbons such as trichloroethylene and perchloroethylene, and chlorinated ethanes enter the fluorination reactor and undergo side reactions that consume HF, deactivate the antimony pentachloride catalyst, and form high-boiling oligomers that deposit on the reboiler and distillation trays. The presence of 0.1 wt% trichloroethylene in chloroform can reduce the fluorination yield by several percentage points over a catalyst cycle and increase the rate of antimony carryover into the R22 distillation column. Analytical verification of feedstock quality uses GC methods such as ASTM D6806 for halogenated solvents, Karl Fischer titration per ISO 760 for water, and distillation range per ASTM D1078. The specifications below are representative for polymer-grade chlorodifluoromethane production; they are not universal, and published data for specific impurity interactions with antimony pentachloride catalyst life is limited.

Compression of cracked gas is preceded by drying to a moisture level below 5 mg/kg, because water promotes HCl corrosion and can hydrolyze fluorinated intermediates. The cracked-gas compressor is a two-stage screw or centrifugal machine with intercoolers and separators, and the discharge pressure is set by the critical conditions of the TFE distillation train, usually between 1.5 MPa and 2.5 MPa. Before distillation, a polymerization inhibitor is injected at 5 mg/kg to 50 mg/kg relative to TFE; terpene-based inhibitors such as d-limonene are used in several industrial operations, while other plants rely on low-temperature storage and continuous circulation to limit residence time. The distillation train separates HCl, R22, TFE, and heavier fluorocarbons using three or four columns. The HCl column operates at relatively low temperature with a refrigerant condenser, while the R22 recovery column returns unconverted chlorodifluoromethane to the pyrolysis furnace. The TFE product column is operated with a high-purity overhead and a bottoms stream containing hexafluoropropylene, octafluorocyclobutane, and other oligomers. The reboiler of the TFE column is a critical safety boundary because TFE can undergo exothermic dimerization if localized wall temperatures exceed approximately 200 °C in stagnant zones. The distillation column pressure is selected to keep the overhead condenser above the TFE boiling point of -76.3 °C at 101.325 kPa, usually with a refrigerant such as R22 or ammonia in a cascade. The capacity of the distillation train is therefore defined by the volumetric flow of noncondensables, the condenser heat removal at low temperature, and the recycle R22 purity. If the R22 recycle stream contains more than 1 wt% TFE or heavy ends, the pyrolysis furnace selectivity decreases because heavy ends coke the radiant tubes and TFE decomposes upon re-exposure.

Steam-Dilution Ratios and Tube Metallurgy Limits in Pyrolysis Furnaces

Steam-dilution ratios in industrial furnaces are constrained by the need to suppress coke formation without excessively increasing the furnace pressure drop and energy load. The molar ratio of steam to chlorodifluoromethane is typically set between 1.5:1 and 3.0:1; a ratio below 1.0:1 accelerates coke deposition and reduces selectivity to TFE, while a ratio above 4.0:1 increases the downstream water load and acid recovery cost. The radiant coil is commonly fabricated from centrifugally cast HP-40 modified with niobium or from Incoloy 800H, with tube skin temperatures held below 1,000 °C to limit carburization and creep. Coke formation on the inner tube wall raises the tube skin temperature at constant heat input, and periodic decoking is conducted with steam-air mixtures at 800 °C to 900 °C. The furnace capacity is reduced by the decoking downtime and by the gradual increase in pressure drop as coke narrows the effective flow area. A typical industrial furnace is arranged as a multi-pass coil with inlet mixing of preheated R22 and superheated steam, a radiant-section residence time of 0.05 s to 0.3 s, and a transfer-line exchanger that quenches the cracked gas to below 350 °C before the venturi quench. The capacity of the furnace is proportional to the total tube volume and the allowable gas density, but the maximum tube volume is limited by the tube metal temperature and the need to avoid laminar flow in the coil. Published data for specific TFE furnace metallurgy and tube life is limited, but tube life of 20,000 h to 50,000 h between replacements is often used as an engineering estimate when selecting coil thickness.

Tetrafluoroethylene autopolymerization is an Arrhenius-dependent process that becomes uncontrollable if the monomer is stored in the presence of oxygen, metal ions, or excessive heat. The monomer is therefore kept below -20 °C in some operations, but more commonly it is compressed and stored at moderate pressure with a terpene-based inhibitor concentration of 5 mg/kg to 50 mg/kg. The inhibitor must be continuously replenished because it is consumed by radical scavenging, and its concentration is monitored by GC or UV spectroscopy. Oxygen is excluded from the TFE system to below 5 ppmv because oxygen initiates peroxide formation and accelerates autopolymerization; the system is purged with nitrogen to an oxygen concentration below 0.5 vol% before maintenance. The TFE handling system is designed with pressure relief valves and rupture disks, and dead-leg lengths are minimized to less than three pipe diameters because low-velocity zones can accumulate polymer and initiate plugging. In the storage sphere or cylinder, the TFE vapor space is continuously circulated through an inhibitor-containing scrubber or a refrigerated condenser to maintain the inhibitor concentration in both liquid and vapor phases. The capacity of the TFE production plant is directly coupled to these safety constraints because storage capacity must not exceed the volume that can be inhibited and monitored; exceeding the maximum safe hold-up creates a deflagration hazard. The rated capacity of the downstream polymerization area is therefore matched to the TFE production rate and the safe storage volume, rather than to the theoretical stoichiometric output.

Hydrochloric acid recovery, hydrogen fluoride recovery, and fluorinated byproduct handling are integrated with the main TFE capacity because waste treatment bottlenecks can cap production even when the pyrolysis furnace has spare capacity. The HCl from the fluorination reactor and the pyrolysis furnace is absorbed in water to produce a 30 wt% to 35 wt% commercial acid stream, but the acid must be stripped of dissolved fluorinated organics before sale. The dilute caustic scrubber stream contains sodium fluoride, sodium chloride, and trace fluorinated anions; it is treated by precipitation with lime to remove fluoride as calcium fluoride, and the resulting sludge is dewatered in a filter press. The heavy ends from the TFE distillation column, containing hexafluoropropylene, octafluorocyclobutane, and higher oligomers, are either routed to a thermal oxidizer with a scrubbing system or reclaimed as separate fluorochemical products. The thermal oxidizer must operate at temperatures above 1,100 °C and with a residence time greater than 2 s to destroy perfluorinated compounds, and the flue gas is scrubbed with alkali to remove HF. The environmental permits for these auxiliary units often specify a maximum fluoride emission limit of 5 mg/m³ or less, and the plant capacity is constrained by the scrubber water treatment rate. Any increase in chlorodifluoromethane-based TFE capacity therefore requires a corresponding expansion of acid recovery, fluoride removal, and thermal destruction capacity, because these systems are tightly coupled to the pyrolysis selectivity and quench efficiency.