Hydrochloric Acid Production Capacity in China: Chlor-Alkali, EDC and Recovery Plants is best evaluated as a system of molar chlorine carriers rather than a single installed vessel count. Published industry surveys place Chinese chlor-alkali caustic soda capacity at 40–47 million tonnes per year, which establishes a corresponding chlorine and hydrogen envelope for synthetic acid. Integrated chlor-alkali sites can divert chlorine to hydrogen-chlorine synthesis, while EDC-based vinyl chloride operations release HCl as a cracking by-product, and recovery plants regenerate acid from spent pickle liquor, chlorinated solvent residues, or titanium dioxide chloride-process wastes. The resulting merchant supply is therefore a residual of electrochemical chlorine demand, vinyl-chain balancing, and waste-acid regeneration economics. Capacity estimates based only on absorption trains overstate availability if chlorine is committed to other chlorination products or if oxychlorination units consume by-product HCl at rates above cracking generation.

What Limits Hydrogen-Chlorine Synthesis Capacity in the Chlor-Alkali Sector?

In dedicated synthesis units, dried chlorine and hydrogen are combined in a graphite or fused-silica burner where flame temperature reaches 2,200–2,500°C. The resulting HCl gas is cooled in graphite or tantalum heat exchangers and then absorbed in a falling-film or packed-tower graphite absorber to produce 31–35 wt% acid. The capacity-limiting unit is usually the absorber and recirculating acid cooling loop, not the burner. Heat of absorption must be rejected through graphite block heat exchangers; recirculation rates are set by the allowable acid temperature rise. When cooling water temperature exceeds 32°C, the vapour pressure of HCl over the acid increases, and tailgas scrubber loading rises. Industrial reports from chlor-alkali units indicate that demister and tailgas scrubber fouling by ferric chloride and silica can reduce effective absorption capacity by 10–20% if dilution water hardness remains above 150 mg/L as CaCO₃. The synthesis step is also sensitive to chlorine moisture; upstream sulfuric acid drying towers are typically specified to maintain water below 50 ppm by mass, because wet chlorine forms hypochlorous acid and accelerates graphite attack.

Quality control follows GB/T 320-2006 for synthetic hydrochloric acid, with ASTM E224-16 used for total acidity and total chlorine verification in export-oriented shipments. Synthetic acid typically carries lower organic content than by-product or recovered acid, but iron contamination remains dependent on storage and transfer materials. Rubber-lined steel storage tanks with PTFE or PVDF internals are standard; these materials are selected because concentrated hydrochloric acid at 31–35 wt% has a pH below 0 and creates hydrogen-induced corrosion risks in carbon steel. Published data for specific burner capacity across Chinese chlor-alkali hubs is limited, but industry surveys indicate that the largest integrated sites operate multiple synthesis units with individual HCl gas capacities in the range of 50–150 tonnes/day, depending on hydrogen and chlorine availability.

EDC-based vinyl chains complicate HCl capacity accounting because the cracking furnace generates HCl and the oxychlorination reactor consumes it. In ethylene-based vinyl chloride production, 1,2-dichloroethane is pyrolyzed at 500–550°C with single-pass conversion held to 50–60% to suppress coke and acetylene formation. The hot cracked gas contains VCM, unreacted EDC, and HCl; after quench, anhydrous HCl is separated by distillation and either routed to oxychlorination or absorbed into water. Balanced vinyl plants typically maintain a near-stoichiometric HCl balance, leaving little by-product acid for merchant sale. Unbalanced or partially balanced plants, particularly those that source EDC externally, can release substantial acid quantities. Chinese vinyl capacity has been reported in public trade journals in the range of 25–30 million tonnes per year, although the share using ethylene-based EDC cracking rather than acetylene-based direct chlorination determines how much HCl by-product capacity is structurally available. Acetylene-based vinyl chloride actually consumes HCl, so regional HCl balances are route-dependent. The HCl released from EDC cracking is typically unsaturated with respect to merchant-grade quality because it contains vinyl chloride, 1,2-dichloroethane, and chlorinated organic impurities that must be stripped and adsorbed before water absorption.

Practical acid trains on EDC crackers use a chilled water condenser followed by a demister and activated carbon guard bed. Without the carbon bed, total organic carbon in the resulting acid can remain above 50 mg/L, which renders the stream unsuitable for food-contact or pharmaceutical uses. With guard bed treatment, residual TOC is commonly controlled below 5 mg/L. Iron can enter from corrosion of carbon steel headers upstream of the acid absorber; operators often specify PTFE-lined or impregnated graphite downstream of the first condensation stage to keep acid iron below 0.0001 wt% where merchant sale is targeted.

Spent Acid Regeneration and Azeotropic Distillation Constraints

Recovery plants process spent hydrochloric acid streams with free HCl concentrations as low as 5–15 wt% from steel pickling, TiO₂ chloride-process wastes, or chlorinated solvent purification. Spray roasters and fluidized-bed regenerators convert metal chlorides to metal oxides and HCl gas at 500–900°C. The recovered gas is passed through dry cyclones and venturi scrubbers to remove particulate iron oxide before entering absorption. If weak liquid acid is upgraded by simple atmospheric distillation, the hydrochloric acid-water azeotrope at approximately 20.2 wt% HCl at 1 atm limits distillate concentration; a single atmospheric column cannot produce 31–33 wt% merchant acid from weak feed. Alternatively, spray-roaster gas can be absorbed to higher strengths, but single-stage venturi absorbers with high quench water often produce 18–20 wt% acid because of water balance restrictions. Extractive distillation agents such as calcium chloride or sulfuric acid are required to break the azeotrope and reach 31–33 wt% when distillation is used. This extractive step adds column height, reboiler duty, and agent recovery overhead, and is often the economic bottleneck for recovered merchant acid in China.

Feed impurities control recovery plant capacity more directly than acid concentration. Iron chloride in steel pickle liquor can be 150–250 g/L, and the spray roaster must operate above the hydrolysis temperature of FeCl₂ while avoiding sticky iron oxide deposits on the roaster walls. Published operating data from regeneration suppliers indicate that unplanned shutdowns from oxide build-up can reduce annual effective capacity by 5–15% compared with nameplate. Acid recovered from TiO₂ chloride wastes contains metal chlorides and silica; these require venturi scrubbing and mist elimination with 99% or higher droplet removal to protect downstream graphite absorber internals.

When By-Product Acid Is Upgraded for Reagent or Low-Iron Applications

Merchant acid from EDC and recovery routes can be upgraded by oxidation of free chlorine with sulfur dioxide, sulfide precipitation of heavy metals, and filtration through 0.5–1.0 µm PTFE membrane filters. The order of unit operations is critical because chlorine stripping before metal precipitation prevents re-oxidation of iron. Typical upgraded by-product acid contains total organic carbon below 10 mg/L, iron below 0.0001 wt%, and turbidity below 1 NTU. Compliance is verified using ASTM E224-16 for total acidity and specific ion methods for trace metals. Reagent-grade material requires additional redistillation or sub-boiling distillation in quartz or PTFE equipment; this capacity is small because Chinese merchant demand for reagent acid is structurally distinct from industrial volumes.

Without upgrading, by-product acid can be used in steel pickling, pH adjustment, or regeneration but cannot be blended into synthetic acid sold under GB/T 320-2006 without violating grade-specific limits. The standard defines grades by residue on ignition, iron, sulfate, and free chlorine content. Blenders that mix synthetic and recovered acid must document that each final lot meets the same grade tests. Published data for the exact share of upgraded by-product acid in China's merchant market is limited, but trade flows indicate that coastal provinces with dense EDC/VCM and TiO₂ capacity have lower merchant synthetic acid premiums than inland regions with dedicated chlor-alkali synthesis.

Quality verification for merchant-grade material relies on the following test matrix.

Resin Cracking, Not Acid Corrosion, Limits Graphite Recovery Columns

Impregnated graphite used in reboilers, columns, and absorbers has a maximum service temperature that depends on resin type. Phenolic-impregnated graphite is generally rated for continuous exposure up to 160–180°C in hydrochloric acid service, while PTFE-impregnated graphite can withstand higher excursions but at increased permeation risk. In recovery columns handling 20–33 wt% HCl, vapour-phase HCl permeates microporous graphite if the resin fill is incomplete. Operators report that repeated thermal cycling between 30°C and 120°C causes resin cracking at nozzle joints, which then allows acid to contact carbon steel backing plates. The failure mode is localized iron chloride formation, which accelerates further corrosion and reduces column capacity. Published design data for graphite equipment in Chinese recovery plants is limited, but supplier bulletins specify that steam-heated graphite reboilers should maintain steam pressure below 0.6 MPa to avoid resin degradation. This operational boundary limits reboiler duty and therefore restricts the concentration rate of recovered acid.

Ceramic and tantalum components are used where graphite is insufficient. Tantalum bayonet heaters tolerate concentrated acid but are sensitive to fluorides and to hydrogen embrittlement at temperatures above 150°C. In spent acid from titanium dioxide chloride processes, residual fluoride can exceed 10 mg/L, making tantalum unsuitable unless upstream silica precipitation removes fluoride. The capacity of such recovery plants is thus set by impurity-selective materials compatibility rather than by acid strength.

Capacity utilization in Chinese hydrochloric acid supply is not uniform across routes. Chlor-alkali synthetic acid units typically run at higher rates when chlorine derivative markets are weak, because hydrogen-chlorine synthesis can absorb surplus chlorine and hydrogen that would otherwise force electrolyzer load cuts. By contrast, EDC-based by-product acid is inelastic to HCl demand because cracking rates are set by vinyl chloride economics. Recovery plant utilization follows waste acid availability and local effluent pricing. Industry surveys indicate that effective utilization of merchant HCl capacity can range from 60–90% depending on regional chlorine balance and regeneration economics. This asymmetry explains why published nominal capacity figures often diverge from actual merchant acid supply in East China, where EDC and TiO₂ recovery dominate, versus North China, where chlor-alkali integration is more common.

Published data for precise route-specific capacity shares in China is limited. Available trade statistics and project announcements suggest that chlor-alkali-derived synthesis remains the largest flexible source, EDC by-product acid is the largest olefin-chain by-product source, and recovery plants are the most feedstock-constrained source. The technical assessment of any individual plant therefore requires confirmation of upstream chlorine balance, vinyl-chain route, and waste-acid contract composition before a nominal HCl capacity can be treated as merchant availability.

Storage and distribution of 31–35 wt% hydrochloric acid require lined carbon steel, fiberglass-reinforced plastic, or high-density polyethylene. At 20°C, concentrated acid exerts a partial pressure of HCl in the range of 1–2 kPa, so fixed-roof tanks are vented through caustic scrubbers. Local emission rules in Chinese coastal industrial parks commonly require ≥95% HCl removal from storage vent streams. Long-term storage of acid from recovery plants without post-filtration can deposit iron oxides and silica on tank floors, reducing usable volume and increasing tank cleaning frequency. Published data for precise storage losses in Chinese plants is limited, but inventory audits typically show 0.5–2% annual loss from venting and transfer when scrubber systems are not optimized. Transfer lines for merchant acid use PTFE-lined steel or PVDF pipe; carbon steel is limited to dry HCl gas service because liquid acid at concentrations above 15 wt% causes rapid hydrogen-induced corrosion. The operational boundary for recovered acid in carbon steel is therefore a concentration and moisture threshold, not merely a temperature limit.