Mixed Xylene Supplier in China: Technical Data, Grades and Export Terms

Commercial mixed xylene, identified by CAS 1330-20-7 and EINECS 215-535-7, is a process-dependent aromatic hydrocarbon blend containing ortho-xylene, meta-xylene, para-xylene, and ethylbenzene. Chinese production streams typically originate from catalytic reforming, steam cracking of heavy liquid feedstocks, or toluene disproportionation. The material is not a single isomer but a mixture whose technical acceptability hinges on distillation interval, isomer distribution, non-aromatic burden, and sulphur level rather than total xylene concentration alone. A CoA generated against GB/T 3407-2010, ASTM D843, or a buyer-specific appendix should therefore be read as a method-bound statement of process output, not a universal quality declaration.

What Parameters Appear on a Certificate of Analysis and Which Are Usually Negotiated Separately?

A buyer-facing certificate of analysis issued in China typically maps to several reference methods. Density is commonly reported by ASTM D4052; distillation by ASTM D850; acid wash colour by ASTM D848; sulphur by ASTM D4045 or ASTM D4294; and trace impurities by gas chromatography. The most frequently negotiated parameters are not total aromatics but bromine index, sulphur method designation, and the ethylbenzene ceiling. These three items create downstream risk because they are not automatically included in a basic solvent-grade CoA. At trace sulphur levels below 1 mg/kg, interlaboratory variability becomes significant; a buyer should request the method detection limit and measurement uncertainty rather than treating a single reported value as absolute.

When total aromatics is treated as the only severity indicator, a batch with 99.0 wt% total aromatics can still fail downstream isomerisation if the ethylbenzene fraction exceeds the process design threshold, often specified between 15 wt% and 25 wt%. In solvent thinning, that same batch may pass. Chinese grade designations such as 3 °C mixed xylene and 5 °C mixed xylene under GB/T 3407-2010 encode distillation interval width rather than isomer purity; the 3 °C material carries a tighter boiling range and is generally associated with lower non-aromatic carryover. Published data for direct correspondence between distillation interval width and specific isomer ratio is limited, because reformer severity, extraction efficiency, and toluene disproportionation feed produce independent compositional shifts.

Nitration-Grade and Solvent-Grade Xylene Impose Different Sulphur and Acid Wash Limits

In nitration-grade material, an acid wash colour above 2 on the ASTM D848 scale indicates sufficient reactive olefinic or low-molecular-weight polymer precursor burden to cause yield loss or unstable intermediates. Solvent-grade products may permit acid wash values up to 4 or 5, but this is not a universal acceptance rule. Buyers using mixed xylene in polyurethane solvents or unsaturated polyester dilution should fix bromine index not higher than 10 mg Br₂/100 g by ASTM D1492 or equivalent. A CoA that lists only distillation range and density does not establish the olefinic impurity burden, and this gap is the most common source of batch rejection in downstream synthesis.

For p-xylene extraction or ortho-xylene separation, mixed xylene must be evaluated by high-resolution gas chromatography, typically ASTM D2306 or UOP 744. The critical values are the mass fractions of para-xylene, meta-xylene, ortho-xylene, and ethylbenzene, because separation economics depend on the feed isomer distribution rather than total C8 aromatics. A heavier para-xylene fraction reduces extraction costs; an elevated ethylbenzene fraction, frequently in the 15–25 wt% range, lowers para-xylene feed value and may require a separate dealkylation or isomerisation step. A 60 m capillary column with flame ionisation detection is the practical minimum for baseline separation of ethylbenzene, para-xylene, and meta-xylene; ortho-xylene elution requires adequate temperature programming. Consequently, refinery-to-refinery variance is more important than grade name.

When Incoterms and Hazardous Cargo Classification Override a Lower Commercial Price

Mixed xylene exported from Chinese ports is classified as UN 1307, Xylenes, Class 3, Packing Group III. The IMDG Code applies flammable liquid packing provisions and, for bulk cargo, closed sampling and vapour control requirements. EXW or FOB pricing can appear lower per tonne, but the buyer assumes classification, documentation, and sampling liability at the point of handover. Under CFR or CIF terms, the supplier arranges freight and insurance, but the importer remains accountable for destination landing checks and product acceptance. The HS code is 2707.30; Chinese export declarations under HS 2707.3000 may require hazardous chemical inspection and an SDS conforming to GB/T 16483-2008. A CoA generated according to ASTM D843 does not automatically satisfy an importer’s obligations under REACH or destination GHS; the recipient must verify that the substance is registered for the relevant tonnage band and that the extended SDS contains exposure scenarios for solvent use and bulk transport.

Loading and transport of mixed xylene in ISO tank containers is governed by the vapour-space requirement and the need to prevent electrostatic discharge. Lined or stainless steel ISO tanks are preferred; unlined mild steel tanks are acceptable only when water content is controlled below the saturation point, because free water at the tank bottom creates interfacial rust that releases iron into the product. Nitrogen padding is not mandatory for xylene but is used when colour stability or acid wash retention is specified. Sampling during loading should follow ISO 3170 or API MPMS Chapter 8, with top, middle, and bottom samples composited before the CoA is issued.

Vapour Pressure, Peroxide Formation and Storage Tank Metallurgy

Because mixed xylene has a closed-cup flash point in the range 25–32 °C, it is classified as a flammable liquid in most jurisdictions. The vapour pressure at 20 °C of approximately 0.8–1.2 kPa means fixed-roof storage without internal floating covers will emit volatile organic compounds; API 650 tanks with internal floating roofs and rim seals are typical for large terminals. The lower explosive limit is approximately 1.1 vol% and the upper explosive limit is approximately 7.0 vol%. Auto-ignition occurs near 464 °C, but hot surfaces and static discharge should be controlled to a much lower threshold. Unlike ethers, mixed xylene does not form explosive peroxides; however, prolonged exposure to air can raise colour and acid wash values. Carbon steel is acceptable provided water content is controlled below the saturation point, but the presence of free water at tank bottoms creates interfacial rust that releases iron. Piping systems should avoid NBR or natural rubber gaskets because aromatic swelling leads to seal failure; PTFE or EPDM gaskets are normally specified. Centrifugal pumps require mechanical seals compatible with aromatic hydrocarbons; packing glands may leak at operating temperatures above 35 °C.

In thinner formulations, the evaporation rate relative to n-butyl acetate is roughly 0.7–0.8, placing mixed xylene in the medium evaporation window. High-shear dispersion equipment does not require pre-dissolution of most alkyd or acrylic resins, but dissolution temperature should remain below the flash point unless a closed reactor with inert gas is used. Paint manufacturers using high-speed dispersers must control local exhaust because the lower explosive limit is approximately 1.1 vol% in air. Viscosity adjustment in printing inks and coatings is commonly checked with ISO 2431 flow cups, while VOC content is determined by ASTM D2369. Published data for optimum addition levels in specific coating systems is limited; formulation tests are more reliable than supplier generalities.

Export Documentation Rejections Follow Method Designation Gaps, Not Low Isomer Purity

When a cargo surveyor compares discharge samples at the destination port, acceptance is determined by the exact method designation fixed in the technical appendix. If the supplier’s CoA used a different sulphur method, such as ASTM D4294 instead of ASTM D4045, the importer may reject the lot for documentation mismatch even when the actual sulphur concentration is within specification. The technical appendix should therefore specify method designations, not merely parameter limits. The table below lists the documentation set most commonly checked at discharge for mixed xylene shipments from China.

Bulk mixed xylene shipped to Southeast Asia or the Middle East often requires a cargo surveyor’s report based on ASTM D850, ASTM D4052, and a visual colour check. Discharge samples are tested against the same methods; any mismatch between the loaded sample and the shore tank sample can trigger demurrage and rejection. Chinese suppliers exporting to EU member states must ensure that the extended SDS includes exposure scenarios for solvent use and transportation; importers may ask for the REACH registration number before customs clearance. In such transactions, the first documents examined at destination are the CoA method designation, the tank cleanliness certificate, and the hazardous cargo declaration.