Commercial xylene (CAS 1330-20-7) is supplied as mixed xylene and as isolated ortho-, meta-, and para-isomers. Mixed xylene has a distillation range of 137 °C to 143 °C at 101.3 kPa, a closed-cup flash point near 25 °C, and a density of approximately 0.86 g/cm³ at 15.6 °C. The freezing points of the separated isomers are 13.2 °C for p-xylene, -25.2 °C for o-xylene, and -47.9 °C for m-xylene. This record set is maintained as Xylene Suppliers by Grade and Region: A Verified Source Directory, where entries are classified by nitration grade, p-xylene feedstock, reagent grade, and industrial solvent grade, and then by production route, terminal location, and documentary verification.

Directory entries are not commercial rankings. Each entry is admitted only after site identification, grade specification review, and confirmation of transport mode. The term “verified” is restricted to records with a supplier site declaration, documentary evidence that the production route is consistent with the nominated grade, and a scope-appropriate quality system certificate. Because trace sulfur, olefinic material, and high-boiling C9+ aromatics vary with crude slate and reformer severity, a nominal grade assignment alone does not qualify a source. The directory therefore marks which suppliers provide trace impurity profiles by ASTM D2360 or a producer-defined equivalent. Suppliers that submit bulk assays without impurity data are retained as unverified trade records rather than verified-source entries.

Xylene enters the supply chain as a coproduct from catalytic reforming, steam-cracker pyrolysis gasoline, and toluene disproportionation. Each route has a different ratio of ortho-, meta-, and para-isomers, and the non-aromatic content depends on extraction efficiency. Suppliers listed in the directory are mapped to one of these routes because a shift from reformate-derived xylene to pyrolysis gasoline-derived xylene can change C8 paraffin carryover even if the grade name remains unchanged. A seller listing only “naphtha-derived” is not given the same verification status as one that identifies the unit source.

Physical property data used in the directory are obtained from the latest safety data sheet and certified technical data sheets. The flash point places mixed xylene in flammable liquid storage classifications under NFPA 30 and transport classifications under 49 CFR in the United States. The directory does not repeat full regulatory text; it records the applicable classification from the supplier document set and notes the loading temperature range.

What Verification Metrics Define a Qualified Xylene Supplier by Grade?

Supplier qualification for nitration grade xylene is anchored to ASTM D843, which sets pass/fail requirements for acid wash color, copper strip corrosion, sulfur compound content, and distillation range. A shipment that fails acid wash color cannot be reclassified as nitration grade without selective hydrogenation or clay treatment that reduces the unsaturated species contributing to the acid wash failure. Production sites that run a hydrotreater or clay treater upstream of the final splitter can maintain acceptable acid wash stability; sites that rely on blending alone may show batch-to-batch variance. The directory records the presence or absence of that treating step because it is a stronger predictor of grade stability than a single certificate of analysis.

Selective hydrogenation of pyrolysis gasoline-derived C8 streams is typically performed over nickel-molybdenum catalyst, with hydrogen partial pressure set by the bromine index of the feed. The objective is to remove dienes and styrenics that polymerize in the acid wash test and in downstream nitration reactors. In the directory, a verified record includes whether the hydrogenation step is present and whether the catalyst changeout schedule is recent enough to prevent breakthrough. Published data for complete catalyst aging profiles across all regional suppliers is limited.

p-Xylene feedstock verification uses ASTM D5211 as the baseline reference. The grade is not defined by a single xylene purity value alone; m-xylene, o-xylene, ethylbenzene, and non-aromatic contents are critical because they control downstream separation and oxidation performance. The catalytic reformate C8 fraction contains p-xylene near 23 wt% to 24 wt% of the xylene isomers before separation. A supplier that declares only mixed xylene purity does not produce a p-xylene feedstock record in the directory. For reagent grade material, the current ACS Reagent Chemicals monograph is used, with limits applied to residue after evaporation, water, acidity, sulfur compounds, and assay. Industrial solvent grade is producer-specified and is accepted only when the supplier provides a sales specification covering distillation range, flash point, benzene content, and evaporation residue.

Laboratory verification of xylene is typically performed by gas chromatography with flame ionization detection for isomer and non-aromatic distribution, while water is determined by Karl Fischer titration and residue after evaporation by gravimetric method. The directory does not publish individual chromatograms, but it indicates whether the supplier’s certified laboratory holds ISO/IEC 17025 accreditation and whether the method is listed in the scope. A supplier without an accredited internal laboratory is not automatically excluded; however, the directory requires third-party lot verification for that record.

Because verification is documentary, the directory does not certify physical parcels unless line-sampling evidence is included. A nitration-grade certificate from a producer is not verified until the terminal loading record confirms that the product was not contaminated with a previous cargo. Grade switching in multiproduct aromatics plants can create off-spec parcels when p-xylene adsorption units retain desorbent in the fractionation train during a transition to mixed xylene export. The resulting mixed xylene may show a higher dry point than the user-specific limit, and a fixed distillation range in the sales specification is insufficient to detect the desorbent if the total mass is below the assay detection limit. The directory records the last grade campaign before parcel loading.

Isomer separation for p-xylene feedstock is not controlled by simple distillation; the boiling point gap between p-xylene and m-xylene is only 0.7 °C. p-Xylene instead is isolated by crystallization, which uses the 13.2 °C freezing point of p-xylene, or by simulated moving-bed adsorption such as UOP Parex or Axens Eluxyl. These units operate with a desorbent that must be fractionated and recycled. Residual desorbent carryover into a mixed xylenes stream can increase the solvent-grade dry point and create a mismatch with a user-specific distillation endpoint. The directory therefore records whether the production site alternates between p-xylene and mixed xylene campaigns, and whether the terminal provides a previous-cargo statement for each parcel.

Temperature control in p-xylene crystallization is narrow. If cooling is too rapid, the product crystal cake entrains m-xylene-rich mother liquor and the apparent purity falls below the declared specification. The directory does not obtain crystallizer operating temperatures; however, it records whether the source offers p-xylene with a documented freeze point that is verifiable against ASTM D5211. A supplier that cannot provide a stable freeze point history is not listed as a verified p-xylene feedstock source.

This separation boundary makes regional supplier choice more than price arbitrage. A large aromatics complex in Asia-Pacific may be able to switch part of its output from p-xylene to mixed xylenes during a regional polyester downturn, but transient storage-heel carryover can shift non-aromatic or heavy aromatic content. A terminal in Europe receiving the same parcel may need to store it in a fixed-roof tank with vapour recovery, and the product may fail an acid wash color check if oxygenated components are introduced during shared-line transfer. Published data for complete trace-level oxygenate distribution in every regional supply chain is limited. The directory therefore flags the largest unresolved data gap for each record rather than filling it with an estimate.

Verified Source Directory Format and Data Granularity

Each listed record contains the plant site, nominal annual capacity expressed in kilotonnes per annum, grade, production route, distillation endpoint limits, flash point, water limit, and the date of the most recent document check. The directory does not assign a composite score. Freight cost, credit exposure, tank material compatibility, and catalyst tolerance in downstream processing are procurement-specific and cannot be reduced to a common rating. A supplier listed as ISO 9001:2015 certified is included only when the certificate scope covers xylene production or storage and the registrar is identified. The directory does not accept a generic corporate certificate for a site without a matching scope.

Production route is coded rather than free text. Codes distinguish reformate-derived, pyrolysis gasoline-derived, toluene disproportionation-derived, and alternated campaigns. Coded entries allow users to filter by route without relying on ambiguous trade names. The same coding convention is used for terminal type, loading-line status, and last-cargo protocol. This coding is not a chemical purity score, but it reduces procurement error from template-style supplier self-declarations.

Verified-source status expires after 12 months unless the supplier records are revalidated. A producer that changes feedstock crude slate or brings a new reformate splitter online may alter its impurity profile without changing the grade designation. The directory therefore records the date of the last technical audit and the date of the last loading protocol review. A purchaser may require a more recent audit, but the directory itself does not replace a site visit.

Documentary verification differs by region. European suppliers are checked against EC No 1907/2006 REACH registration data, and the directory records the EC number and registration number only if they appear on the safety data sheet and can be located in ECHA public dossiers. North American suppliers are checked under 49 CFR hazardous materials shipping papers and current ISO 9001:2015 certificates. Asia-Pacific supplier records include GHS SDS language coverage, port-storage fire safety permits, and local emergency-response codes. Middle East records are checked against terminal operating procedures and nitrogen blanketing logs where high ambient temperatures require low oxygen headspace.

Storage and terminal handling fields are not filled with default text. Closed-top nitrogen-blanketed tanks are indicated where the daily maximum ambient temperature exceeds 40 °C or where benzene vapour pressure would place emissions above the permitted limit. Floating-roof tanks for large mixed xylene pools are common in Asia-Pacific terminals, while fixed-roof tanks with vapour recovery are typical in Europe. A supplier loaded from a floating-roof tank may show clearer water phase separation after heavy rain than a fixed-roof tank, and water above the nominated limit can interfere with downstream esterification or analytical blank preparation. The directory records the tank type only when the terminal confirms it in writing.

The directory also flags whether the terminal can load marine vessels, railcars, ISO tank containers, or tank trucks. A geographically close source without marine loading is not useful for a polyester-chain buyer requiring coastal parcel sizes. Bulk lot sizes are recorded as 1,000 t to 5,000 t for coastal shipments and 20 t to 25 t for ISO tank containers, although actual parcel size depends on berth depth, draft restrictions, and product temperature at the loading point. Merchant supply is distinguished from captive supply because a captive producer that only exports occasional surplus material may not have the same loading capability as a merchant supplier with continuous export operations.

When Port Logistics Constrain Regional Supplier Choice

Xylene suppliers in the Middle East and Asia-Pacific may offer lower fob cargoes, but supplier qualification includes logistics constraints that are absent from a standard specification. A marine terminal that cannot maintain p-xylene at or above 13.2 °C during winter discharge in Northern Europe will cause solidification in transfer lines. A terminal that does not provide dedicated xylene lines may introduce residual pyrolysis gasoline or reformate components, altering the acid wash color for nitration grade. The directory records dedicated-line status only when the terminal operator confirms it in writing. If a terminal blends two grades to meet a vessel volume requirement, the blending event is recorded because it may shift non-aromatic content above the declared grade limit.

For p-xylene feedstock shipments to terephthalic acid units, loading-line residue and tank heels are operational boundaries. A shared C8 aromatics tank may accumulate heavy aromatics over repeated parcels. The directory requires the supplier to state the C9+ aromatic limit; if the limit is not declared, the record is marked with a data gap. A downstream oxidation unit using a cobalt-manganese-bromine catalyst system can accept a limited heavy-aromatic load, but excessive C9+ material raises solvent recovery maintenance and heat-transfer fouling risk. The directory does not set that limit for the buyer; it records only whether the supplier disclosed it in writing.

Loading operations at a Middle East marine terminal are recorded with nitrogen-blanketed tank vapour spaces where ambient temperatures exceed 40 °C. Line sampling, rather than tank sampling, is the only verification point that represents the transferred parcel. A sample drawn from the tank before loading may understate water content because settled water remains below a fixed sampling nozzle. The directory therefore indicates whether the supplier uses continuous line sampling during loading or batch sampling after the first 15 min of transfer. A record that lacks this field is not downgraded as a trade listing, but it is excluded from the verified-source category until the loading protocol is supplied.