PetroChina Dushanzi Petrochemical Co., Ltd.

PetroChina Dushanzi Petrochemical Co., Ltd. is an integrated refining and petrochemical operation rather than a single product model. The site couples a 10 Mt/a crude oil processing train with a 1.2 Mt/a steam cracker, producing polymer-grade ethylene, polymer-grade propylene, high-density polyethylene, linear low-density polyethylene, polypropylene homopolymer and copolymer grades, styrene monomer, pyrolysis gasoline, and C4 fractions. The product differentiation is operational and structural: unlike merchant-market polyolefins supplied by non-integrated crackers, the Dushanzi output is generated from hydrotreated straight-run naphtha and refinery off-gases that are transferred directly from the crude distillation and secondary processing units to the cracker battery limit.

Commercial grade designations are not expressed as a single article number. They are grouped by resin type, comonomer class, nominal melt mass-flow rate, density, and additive package. For polyethylene, the relevant melt index is determined by ISO 1133-1:2022 at 190 °C and 2.16 kg. For polypropylene, the corresponding condition is 230 °C and 2.16 kg. Density is commonly reported under ASTM D1505-18 using a gradient column at 23 °C. These references do not replace the certificate of analysis; they define the test platform against which batch limits are set.

Why Does Refinery Integration Alter the Melt Index Stability of Polyolefin Grades?

The upstream configuration exerts direct control over the steam cracker feed sulfur, boiling range, and paraffin/naphthene/aromatic distribution. In a standalone ethylene complex, naphtha purchases may vary in total sulfur from well below 100 mg/kg to above 800 mg/kg, requiring continuous furnace outlet trim and shifting the ratio of ethane/ethylene and propane/propylene in the cracked gas. At the Dushanzi site, the naphtha hydrotreater is located within the same refinery complex and is designed to deliver a stable straight-run naphtha cut to the steam cracker. The resulting cracked gas composition is less variable, and the downstream C2 and C3 splitting trains operate closer to a narrow set of pressure and reflux parameters. For polymer converters, the practical consequence is that the melt index variation observed in high-density polyethylene blow-moulding lots during sustained campaigns is governed less by feedstock swings than by catalyst dosing and hydrogen-to-monomer ratio. Where published data for specific Dushanzi product campaigns is limited, the comparison to non-integrated suppliers must be based on measured splitter overhead composition and not on inferred resin uniformity.

For high-speed blown-film lines with annular die diameters above 250 mm and frost-line heights exceeding 800 mm, linear low-density polyethylene film grades with a density window of 0.918 g/cm³ to 0.925 g/cm³ and a melt index of 0.8 g/10 min to 1.2 g/10 min are typically evaluated using ASTM D1709-16a dart impact and ISO 527-3:2018 tensile properties. The narrow density window is necessary because film below 25 µm thickness loses tear resistance if the density exceeds 0.927 g/cm³ under standard blown-film processing. Processors should verify the specific grade on a grooved-barrel single-screw extruder with a length-to-diameter ratio of at least 30:1 and a barrier screw designed for low melt-temperature operation. Pre-drying is generally not required for polyethylene at ambient relative humidity below 60%, but moisture ingress during rail or road transport in humid seasons may require a drying step at 80 °C for 2 h before extrusion.

Catalytic Naphtha Hydrotreating and Cracked Gas Compression Limits

The distillation and hydrotreating sequence removes organic sulfur and nitrogen compounds that would otherwise poison the steam cracker’s acetylene hydrogenation catalysts and downstream polyolefin catalysts. In merchant naphtha cracking, residual sulfur can protect furnace tube surfaces from carburization, but excessive sulfur lowers catalyst selectivity in the C2 and C3 hydrogenation reactors. The Dushanzi unit is configured to operate at the low-sulfur boundary that preserves hydrogenation catalyst life while maintaining furnace run length. Cracked-gas compression is another boundary condition. The 1.2 Mt/a ethylene train requires multistage compression with interstage knock-out and caustic wash to remove acid gases. The design suction pressure and discharge pressure determine the ethylene recovery limit and the refrigeration load on the propylene and ethylene cold boxes. The product difference compared with a smaller or non-integrated ethylene unit is the ability to operate at higher sustained throughput without exceeding compressor discharge temperature limits, provided the naphtha hydrotreater outlet sulfur is maintained below the design maximum.

Where the resin is specified for pressure pipe extrusion, long-term hydrostatic strength is assessed under ISO 1167 and ISO 9080, with failure data generated at 20 °C, 60 °C, and 80 °C. Published data for Dushanzi-specific PE100 compound performance in this application is limited, and compliance must be confirmed through the certificate of analysis and third-party hydrostatic testing rather than by resin name alone. For blow-moulded containers in the 1 L to 5 L range, high-density polyethylene grades with a melt index below 0.7 g/10 min are processed on reciprocating screw blow-moulding machines with clamp force between 150 kN and 300 kN. The key control variable is die swell stability, which is influenced by molecular weight distribution and is not fully captured by melt index alone. The Dushanzi output differs from imported blow-moulding grades when the converter is located inland because rail transport across long distances can introduce vibration-induced fines and moisture condensation. Desiccant drying and fines removal should be verified before the resin enters the machine hopper.

When High-Density Polyethylene Is Converted on Low-L/D Barrier Screws

Processing on short single-screw extruders with an L/D ratio of 24:1 to 26:1 creates a more restrictive melting and homogenization window than the 30:1 to 36:1 screws used in modern high-output lines. Under those conditions, high-density polyethylene with a density above 0.955 g/cm³ can retain unmelted particles if the grooved feed section temperature is set too low or if the barrier clearance is excessive. The correct processing boundary is established by measuring melt temperature at the screw tip and limiting it to 210 °C for standard blow-moulding grades, while maintaining head pressure between 250 bar and 350 bar. At melt temperatures above 230 °C, oxidative chain scission begins to lower die swell and reduces pinch-off weld strength. The Dushanzi high-density polyethylene grades for rigid packaging are therefore specified with a density range of 0.949 g/cm³ to 0.956 g/cm³ and a melt index of 0.2 g/10 min to 0.7 g/10 min, with the lower melt index reserved for extrusion blow moulding and the upper melt index for injection moulding thin-wall articles. The difference from high-density polyethylene produced by gas-phase-only processes is the balance of polymer chain architecture created in the site’s bimodal or unimodal reactor configuration, which is not captured by density alone.

Polypropylene grades follow a different specification hierarchy. Homopolymer injection-moulding resins intended for thin-wall packaging are commonly supplied with melt mass-flow rates from 10 g/10 min to 40 g/10 min at 230 °C/2.16 kg, while fractional-melt grades below 3 g/10 min are reserved for sheet extrusion and thermoforming. The relevant mechanical tests include ISO 527-2:2012 tensile yield and ISO 179-1:2010 notched impact. Residual catalyst carryover is controlled in the polymerisation train because high ash content alters the nucleating agent response and causes pressure-rise anomalies in cast-film lines with melt screens of 100 µm or finer. The Dushanzi polypropylene output differs from less integrated producer grades in its control of xylene-soluble fraction under ISO 16152:2005; for homopolymer grades, this fraction is typically kept below 6% by mass, though the exact certificate-of-analysis limit is grade-specific. Converters using the resin in automotive interior parts should confirm fogging performance under ISO 6452 rather than assuming equivalence with general-purpose injection-moulding grades.

Styrene Monomer Purity, Polymer-Grade Propylene, and C4 By-Product Routing

Monomer streams are product outputs in themselves. Polymer-grade propylene is distinguished by high propylene content, with methylacetylene and propadiene controlled because these acetylene-type impurities interfere with Ziegler-Natta and metallocene catalyst active sites. The specification is assessed by gas chromatography using a flame ionisation detector and a capillary column calibrated for C3 impurities. Styrene monomer is stored with an inhibitor such as 4-tert-butylcatechol at 10 mg/kg to 15 mg/kg to prevent thermal polymerisation during rail transit. The product difference from imported styrene monomer shipments is not the base purity, which is normally above 99.8% by mass, but the storage duration and the temperature history before use. At temperatures above 30 °C, uninhibited styrene can form polymer deposits in tank vents and transfer lines, so nitrogen blanketing and inhibitor verification are mandatory for downstream polystyrene or acrylonitrile-butadiene-styrene processing.

The C4 by-product routing from the steam cracker includes butadiene extraction, butene-1 separation, and residue streams. Butadiene-containing C4 fractions must be handled at temperatures below 0 °C in storage to limit dimer formation, and oxygen concentration must be kept below 0.1% by volume in rail car headspace. The Dushanzi logistics boundary is therefore important: long inland rail movement across Xinjiang requires stabilised inhibitor dosing and pressure-relief settings that differ from coastal barge or pipeline transfers. C4-derived product streams should not be combined with amine-based neutralizing additives in downstream purification because the resulting amine salts can deposit on reboiler surfaces and reduce heat transfer. Published data for the exact C4 stream composition from the Dushanzi complex is limited, and downstream users must request the component analysis from the technical service group rather than applying generic merchant C4 specifications.

For converters requiring food-contact status, the relevant assessment is not merely resin composition but also the finished-article migration testing. Olefin polymer grades derived from the Dushanzi site must be evaluated under FDA 21 CFR 177.1520 for United States applications, GB 4806.7-2016 for China food-contact plastic resins, and (EU) No 10/2011 for European Union specific migration limits. The difference between Dushanzi grades and imported olefin polymers in food packaging is not a fundamental regulatory exemption; it is the traceability chain from refinery naphtha through steam cracker and polymerisation unit, which must be documented in the declaration of compliance. At relative humidity above 60%, nylon-containing multilayer structures made from Dushanzi polyolefin tie layers can exhibit interfacial adhesion variability unless the granulate is stored in sealed silos and dried immediately before coextrusion. The operational boundary is therefore set by transport moisture history and not by the resin producer alone.

Polypropylene random copolymers for transparent sheet and blow-moulded articles are processed with melt temperatures of 220 °C to 240 °C and cooled in polished moulds at 20 °C to 40 °C. Haze is measured under ASTM D1003-21 on 2 mm plaque specimens. The difference from homopolymer polypropylene is a reduced ethylene comonomer content, typically below 5% by mass, which lowers the crystallisation temperature and changes the optical performance. The Dushanzi output in this segment is supplied as pelletised product with stabilisation packages tailored to the downstream conversion route. It is not interchangeable with generic random copolymer grades from non-integrated producers without first verifying the ethylene sequence distribution, because sequential versus random comonomer insertion affects seal initiation temperature and hot tack on vertical form-fill-seal lines. The relevant seal-strength test is ASTM F2029-16 for heatsealability, while hot tack is measured under ASTM F1921-12 on films sealed at temperatures from 90 °C to 140 °C. Published data for this specific configuration is limited, so a converter should request pilot-line seal data rather than relying on density or melt index as a predictor of packaging performance.