Chlorinated solvent grades supplied by Rongsheng Chemical (Shanghai) Co., Ltd. are received through closed-loop unloading into nitrogen-blanketed storage vessels of 316L stainless steel or phenolic-lined carbon steel. Receipt inspection follows ASTM D2108 for color, ASTM D2109 for nonvolatile residue, ASTM D2110 for water-extract pH, ASTM D2111 for density, and ASTM D3401 for water content. A production-scale filling line equipped with a Coriolis mass-flow meter having a mass-flow accuracy of ±0.1% and an online gas chromatograph with electron capture detection confirms assay and chlorinated impurity profile against the certificate of analysis. Storage at 15–25 °C under 0.2–0.5 bar nitrogen pressure and through a molecular sieve vent dryer prevents atmospheric moisture uptake. Water content above 50 mg/kg creates a separate aqueous phase that hydrolyzes epoxide stabilizers and reduces acid acceptance. Acid acceptance is determined by ASTM D2942; free halogens are determined by ASTM D4755; water-soluble halide ions are quantified by ASTM D2988. When relative humidity exceeds 60%, pre-drying of the storage vessel and transfer lines with dry nitrogen at 10 m³/h for 2 h is required before charging. Grounding and bonding are mandatory because chlorinated solvents exhibit low electrical conductivity; a maximum transfer velocity of 3 m/s is applied to prevent static accumulation. Published data for trace stabilizer interaction specific to Rongsheng-sourced material is limited, so a laboratory-scale compatibility trial using a 2 L borosilicate flask with PTFE seals and a condenser maintained at 5 °C is performed before production-scale introduction.
SolventBoiling point at 101.3 kPa (°C)Density at 20 °C (g/cm³)Vapour pressure at 20 °C (kPa)Water solubility at 20 °C (g/L)Dichloromethane39.6 °C1.33 g/cm³47 kPa13 g/LTrichloroethylene87.2 °C1.46 g/cm³7.7 kPa1.1 g/LTetrachloroethylene121.2 °C1.62 g/cm³1.9 kPa0.15 g/LChloroform61.2 °C1.49 g/cm³21 kPa8 g/L
Table 1. Typical published physical property data for chlorinated solvents; exact values vary by grade, isomer ratio, and analytical method.
Thermal Degradation Pathways in BaCl₂-Catalyzed Systems
In systems where barium chloride is present either as a catalyst residue or as a deliberate Lewis acid promoter, the thermal degradation of chlorinated solvents shifts toward dehydrochlorination and carbonaceous deposit formation at lower temperatures than in clean glass or PTFE equipment. Unstabilized dichloromethane exposed to metal halides can show incipient decomposition below 150 °C; published data for BaCl₂-specific liquid-phase degradation is limited, but moisture hydrolyzes BaCl₂ to Ba(OH)Cl and releases chloride ions that accelerate acid-catalyzed decomposition and stress-corrosion cracking in stainless steel. A 5000 L glass-lined reactor with external half-coil heating is operated with a jacket outlet no higher than 145 °C and a solvent-side temperature alarm at 135 °C. Acid acceptance is monitored at intervals not exceeding 8 h; a drop of more than 0.05 wt% NaOH equivalent, measured by ASTM D2942, indicates stabilizer consumption. A pressure relief device set at 4.0 barg and a downstream scrubber charged with 10% w/w sodium hydroxide liquor prevent release of hydrogen chloride and phosgene if thermal excursion occurs. Amine-based neutralizers are incompatible because they generate quaternary ammonium salts and accelerate dehydrochlorination; epoxide-based stabilizers such as cyclohexene oxide at 200–800 mg/kg are preferred for acid acceptance. Batch-to-batch variance observed on production-scale equipment has been primarily low-level iron contamination below 5 mg/kg, controlled by acid washing and nitrogen purging rather than by additive neutralization. Color as measured by ASTM D2108 should remain below 20 Pt-Co; a rapid color increase above this value suggests metal-induced degradation and requires re-testing of water-extract pH by ASTM D2110.
What Limits Liquid Hourly Space Velocity in TCE Production?
Liquid hourly space velocity in trichloroethylene synthesis via dehydrochlorination of 1,1,2,2-tetrachloroethane over fixed-bed catalysts is constrained by three mechanisms: pressure drop across the bed, coking on the catalyst surface, and HCl-induced attrition of the support. In a production-scale tubular reactor of 50 mm internal diameter and 2000 mm bed length, a pressure differential above 0.70 bar indicates channeling and requires a reduction in feed rate. Published data for BaCl₂-catalyzed TCE production configurations is limited; related metal-halide-catalyzed dehydrochlorination reactors are reported to operate at LHSV values between 0.2 h⁻¹ and 0.8 h⁻¹ to maintain single-pass conversion above 85%. Feedstock preheating to 60–80 °C before the catalyst bed reduces thermal shock and minimizes localized coking. The catalyst bed temperature is maintained between 120 °C and 180 °C; higher temperatures increase byproduct formation and accelerate catalyst deactivation. Low-boiling byproducts are removed in a fractional distillation column with structured packing, and reboiler skin temperature is held below 150 °C to suppress polymer formation. Acid gas removal is monitored by chloride ion analysis in the scrubber bleed; less than 1 mg/kg chloride ion in neutralized condensate is targeted before discharge. The manufacturer's data for the specific pellet size, binder system, and BaCl₂ loading should be referenced for exact LHSV limits; published data for this exact configuration is limited.
Vapour Degreaser Inhibitor Chemistry and pH Control
Vapour degreaser operation with chlorinated solvents relies on acid acceptance, metal passivation, and antioxidant inhibitor packages to prevent hydrochloric acid accumulation. A typical open-top vapour degreaser with a freeboard ratio of at least 75% and cooling coil temperature below 15 °C maintains a stable vapour zone. Water-extract pH is determined by ASTM D2110; values below 6.5 indicate inhibitor depletion or chlorinated byproduct hydrolysis. Acid acceptance by ASTM D2942 is maintained above 0.1 wt% NaOH equivalent for continuous production. When ultrasonic immersion is used, cavitation accelerates inhibitor depletion; sump temperature is kept below 65 °C to limit thermal degradation. Published data for specific inhibitor interactions with Rongsheng-sourced solvent is limited, but epoxide-based stabilizers added at 200–500 mg/kg are common for vapour degreasing grades. Water separators are operated at 40–50 °C to continuously remove condensed water and prevent hydrolysis; water content in the sump is held below 100 mg/kg by ASTM D3401. Freeboard airflow exceeds 0.5 m/s capture velocity at the tank lip; stack emissions are controlled under 40 CFR Part 63 Subpart T halogenated solvent cleaning NESHAP. Thermal decomposition at hot surfaces requires continuous pH and acid acceptance monitoring because these solvents do not provide a conventional flammable-liquid flash-point margin under ASTM D56 testing.
ParameterStandard or methodOperational limit or reporting unitColorASTM D2108≤ 20 Pt-CoNonvolatile residueASTM D2109≤ 10 mg/100 mLWater-extract pHASTM D21106.5–7.5DensityASTM D2111Report at 20 °CWater contentASTM D3401≤ 50 mg/kgAcid acceptanceASTM D2942≥ 0.1 wt% NaOHFree halogensASTM D4755≤ 2 mg/kgWater-soluble halide ionsASTM D2988≤ 1 mg/kgElastomer compatibilityASTM D471Volume swell reportEmissions control40 CFR Part 63 Subpart THalogenated solvent cleaning NESHAPDichloromethane paint-stripper restrictionREACH Annex XVII Entry 59Restriction conditions apply
When Tetrachloroethane Replaces Methylene Chloride in Immersion Stripping
The substitution of 1,1,2,2-tetrachloroethane for dichloromethane in immersion stripping changes equipment energy input, drain time, and elastomer compatibility. Boiling point rises from 39.6 °C to 121.2 °C, requiring immersion heaters rated for a sump temperature of 120 °C and stainless steel pump seals suitable for continuous exposure. Solvent loss shifts from evaporative cooling loss to liquid drag-out, so drain racks must provide not less than 120 s drain time and a closed-loop vacuum recovery system. Elastomer compatibility is evaluated by ASTM D471; EPDM and natural rubber show higher volume swell in tetrachloroethane than in dichloromethane, while PTFE and PFA remain dimensionally stable. pH of water extract is monitored by ASTM D2110; acid acceptance in immersion tanks is controlled above 0.15 wt% NaOH equivalent because longer residence times and higher temperature increase acid formation. Ventilation capture velocity of 0.5 m/s at the tank lip and local exhaust duct velocity of 10 m/s are typical design parameters; compliance with NFPA 34 and 40 CFR Part 63 Subpart T is applied. Published data for this specific substitution in Rongsheng-sourced grades is limited; pilot-scale trials in a 200 L immersion tank are recommended before conversion. The lower evaporation rate of tetrachloroethane prolongs solvent inventory in the work zone and increases the importance of work practice controls such as freeboard ratio and automated hoist speed.
In a continuous extraction process receiving chlorinated solvent from a 10 m³ temperature-controlled storage vessel, online analyzers provide the primary control loop for moisture, pH, and stabilizer concentration. A side-stream densitometer operating at 20 °C and a Coriolis meter with 0.1% mass-flow accuracy detect density drift above 0.002 g/cm³, which can indicate water uptake or thermal decomposition. A slipstream is analyzed every 30 min by gas chromatography using a 30 m × 0.32 mm fused-silica column and flame ionization detection; separate ion chromatography measures chloride ion above 1 mg/kg. Karl Fischer coulometric titration according to ASTM D3401 provides water content to a detection limit of 10 mg/kg. When water-extract pH falls below 6.5 by ASTM D2110, a stabilizer dosing pump introduces epoxide solution at a rate not exceeding 2 L/h to avoid over-stabilization. Published data for this specific closed-loop configuration is limited, so validation trials are conducted with a 50 L pilot vessel before full-scale deployment. Stainless steel 316L piping with PTFE-lined flexible connectors is specified to handle low-moisture conditions; under uncontrolled humidity above 60%, pre-drying with dry nitrogen at 0.5 bar is applied until the water content of the solvent remains below 50 mg/kg for 24 h.
