Ethylene undergoes high-pressure radical polymerization in autoclave and tubular reactors to produce branched low-density polyethylene (LDPE). Autoclave operation typically spans 1200–3000 bar and 150–300°C. Tubular reactors run at 2000–3500 bar and 180–330°C with residence times of 30–120 s. These configurations produce different molecular weight distributions. Autoclave LDPE contains more long-chain branching. Tubular LDPE has narrower polydispersity, typically 4–7. Chain-transfer agents such as propylene or ethane are injected at 0.5–3.0 wt% of ethylene feed to control melt index. Film extrusion on 90 mm die lines with screw L/D ratios of 24:1 to 30:1 uses die gaps of 1.2–2.5 mm and blow-up ratios between 2:1 and 4:1. Melt fracture onset is observed when wall shear stress exceeds 0.14 MPa in narrow die inserts. Slip additive erucamide at 500–1000 ppm lowers film coefficient of friction but delays corona treatment surface energy increase. Linear low-density polyethylene (LLDPE) is produced in gas-phase fluidised-bed reactors with Ziegler–Natta or metallocene catalysts. Comonomer choice changes film performance. Butene-LLDPE provides lower puncture energy than hexene-LLDPE. Hexene-LLDPE at density 0.916–0.920 g/cm³ and melt index 0.5–1.0 g/10 min at 190°C and 2.16 kg is used for high-dart-impact films. Comonomer content between 5–15 wt% shifts density down to 0.940 g/cm³. Conversion of polymer powder to pellet is carried out in twin-screw compounding extruders with barrel zones at 170–240°C. Food-contact grades comply with FDA 21 CFR 177.1520 and Regulation (EU) No 10/2011 overall migration limit of 10 mg/dm².

Process stabilization and additive blend ratios are specific to terminal film use. For frozen food packaging, LLDPE with 4–8 wt% 1-hexene is coextruded with a sealant layer having a melt index of 0.5–1.0 g/10 min. For greenhouse film, the resin requires UV stabilizer systems at 0.2–0.5 wt% hindered amine and 0.1–0.3 wt% UV absorber. Light transmission is retained above 85% after 12 months exposure. Film manufacturers measure coefficient of friction according to ASTM D1894-23, dart impact according to ASTM D1709-22, and tensile properties according to ISO 527-3:2018. Blown film line audits show that output rate is limited by bubble stability rather than extruder throughput. On 90 mm dies with 2.2 mm die gap, butene-LLDPE reaches maximum stable output near 150–180 kg/h. Hexene-LLDPE maintains bubble symmetry to 180–220 kg/h because its higher melt strength resists bubble deformation. LDPE is added at 10–30 wt% to LLDPE to improve bubble stability and processability in grocery sack and stretch film lines. This blend reduces dart impact but raises web tensile strength at high draw ratios. Anti-block silica at 1000–5000 ppm increases haze and reduces coefficient of friction. Slip additive migration reaches equilibrium after 24–72 h.

What Determines Selectivity Loss in Ethylene Oxide Direct Oxidation?

Multi-tubular fixed-bed reactors perform the vapor-phase oxidation of ethylene over silver on α-alumina carriers with silver loading of 8–15 wt%. The feed composition is maintained at 20–30 mol% ethylene, 5–9 mol% oxygen, and 40–50 mol% methane ballast, with carbon dioxide and ethane in the recycle loop. Ethyl chloride moderator is metered into the reactor feed at 0.1–5 ppmv. Chloride suppresses total combustion to carbon dioxide but excessive chloride depresses conversion. Operating conditions are 230–270°C and 1.0–3.0 MPa, with gas hourly space velocity of 3000–8000 h⁻¹. Ethylene conversion is limited to 8–12% per pass to keep oxygen concentration below the flammability envelope. Selectivity to ethylene oxide is typically 75–85%. Hot-spot temperatures above 300°C initiate ethylene oxide isomerization to acetaldehyde and subsequent combustion. Each reaction tube has an inner diameter of 20–25 mm and a length of 6–12 m. Heat transfer salt circulates across the shell side to remove heat flux of 20–40 kW/m². The ethylene oxide product is absorbed in water at 1.0–2.0 MPa, stripped, and distilled to 99.9% purity.

Ethylene glycol purification is sensitive to acidic by-products. Residual acetic acid and carbon dioxide are removed in an activated carbon bed and a demineralizer. Glycol quality for polyester-grade monoethylene glycol requires UV absorbance below 0.10 at 220 nm, aldehyde content below 5 ppm, and iron below 0.1 ppm. Hydrolysis to monoethylene glycol uses a water-to-ethylene oxide molar ratio of 20:1, 190–200°C, and 2.0 MPa. The product split is approximately 88–92% monoethylene glycol, 7–10% diethylene glycol, and 1–2% triethylene glycol. Glycol analysis follows ASTM E202-18 for water content and acidity. The ethylene glycol product is used in polyester fibre and PET resin polymerization, antifreeze formulations under ASTM D3306-20, and de-icing fluid under SAE AMS 1424. Monoethylene glycol distillation is conducted under vacuum at 160–180°C bottom temperature to avoid thermal degradation. This purification sequence supplies PET resin plants where ethylene glycol reacts with purified terephthalic acid at 250–270°C and 0.3–0.5 MPa.

Balanced oxychlorination converts recovered hydrogen chloride back into ethylene dichloride (EDC), closing the chlorine loop in vinyl chloride monomer (VCM) production. Direct chlorination of ethylene and chlorine in liquid EDC uses ferric chloride at 50–70°C and 0.2–0.5 MPa. The ethylene-to-chlorine molar ratio is held at 1.00:1.02 to avoid chlorine breakthrough. Oxygen-based oxychlorination over copper chloride on alumina operates at 220–240°C and 0.3–0.6 MPa, with a molar feed ratio of ethylene to hydrogen chloride to oxygen of 1.0:2.0:0.5. Crude EDC from both routes is washed, dried, and distilled to 99.5–99.9% purity before cracking. Thermal dehydrochlorination of EDC takes place in fired tubular coils at coil outlet temperatures of 480–530°C and residence times of 8–20 s. Conversion per pass is 50–60%. VCM selectivity is 95–98%. Coke deposition on the coil wall accelerates when outlet temperature exceeds 530°C and reduces run length between decoking cycles. Heat flux is held at 60–90 kW/m² in the radiant section. VCM is purified by distillation to 99.98% minimum before storage, with inhibitor added to prevent polymer formation.

Suspension polymerization of VCM uses polyvinyl alcohol dispersant systems at 55–65°C, producing polyvinyl chloride (PVC) with K-values of 57–70. PVC resin particle morphology is controlled by suspension stabiliser concentration and agitator tip speed. Typical reactor agitator tip speed is 2.0–3.5 m/s. Stirring rate and dispersant level determine resin grain size and plasticizer absorption. K-value is correlated with molecular weight and is measured by dilute solution viscosity under ISO 1628-2. Pipe-grade PVC with K-value 65–68 is extruded on counter-rotating twin-screw lines with L/D 30:1 and barrel temperatures of 160–190°C. The extruder must avoid stagnation zones because HCl elimination accelerates when stock temperature exceeds 200°C. Finished pipe is tested for impact resistance under ISO 1452-2:2009. Residual VCM in resin and fabricated articles is controlled under REACH Annex XVII entry 47 and EU Regulation 10/2011 specific migration limit of 0.01 mg/kg.

When Ethylbenzene Dehydrogenation Steam-to-Oil Ratios Fall Below 1.1, Catalytic Cycle Times Shorten

Ethylene alkylates benzene in liquid-phase reactors using zeolite-based catalysts. Operating conditions are 150–250°C and 3.0–4.0 MPa. The benzene-to-ethylene molar feed ratio is held between 6:1 and 10:1 to minimize polyethylbenzene formation. Ethylbenzene (EB) distillate purity is typically 99.8% or higher. Catalytic dehydrogenation of EB to styrene monomer is carried out in adiabatic radial-flow reactors over iron oxide-potassium oxide promoted with cerium oxide. Inlet temperature is 600–650°C, and outlet pressure is 0.04–0.1 MPa absolute. Steam is co-fed at a mass ratio of 1.0–1.5 steam to EB. The steam dilutes EB partial pressure, supplies reaction heat, and suppresses coke. When the steam-to-oil ratio drops below 1.1, carbon deposition accelerates and catalyst cycle times shorten from 18–24 months to under 12 months. EB conversion per pass is 60–70% with styrene selectivity of 90–95%. Condensation and vacuum distillation isolate styrene at 99.9% minimum purity with 10–15 ppm 4-tert-butylcatechol inhibitor.

Styrene is then bulk-polymerized thermally in continuous stirred-tank reactors at 120–180°C, reaching 70–80% conversion before devolatilization at 220–240°C. General-purpose polystyrene tensile yield strength is tested according to ISO 527-2:2012 with typical values of 35–60 MPa. Melt flow rate is measured by ISO 1133-1:2022 at 200°C under 5 kg. Rubber-modified high-impact polystyrene incorporates 6–10 wt% polybutadiene and requires twin-screw compounding with L/D 32:1 to control gel particle size. During bulk prepolymerization, polystyrene-grafted polybutadiene particles of 0.5–2.0 µm are generated by controlled shear at 1.0–3.0 s⁻¹. HIPS notched Izod impact under ISO 180:2019 ranges from 8–15 kJ/m², while general-purpose polystyrene usually remains below 2 kJ/m². Extrusion of styrenic sheet is run on vented single-screw extruders with L/D 30:1 and barrel zones of 180–240°C. Styrene monomer residues in food-contact polystyrene must comply with FDA 21 CFR 177.1640 and EU Regulation 10/2011 specific migration limit for styrene of 0.01 mg/kg.

Vinyl Acetate Monomer Acetoxylation over Palladium-Gold Catalysts

Acetoxylation of ethylene with acetic acid and oxygen is performed in multi-tubular fixed-bed reactors. The catalyst is palladium-gold on silica with potassium acetate promoter. Operating temperatures are 175–200°C and inlet pressure 0.6–0.8 MPa. The ethylene-to-oxygen-to-acetic acid molar feed ratio is maintained near 1.0:0.04:0.2 to stay below the oxygen flammability limit. Oxygen conversion is near 30–60%, ethylene conversion per pass 8–12%, and acetic acid conversion 15–20%. Vinyl acetate monomer (VAM) selectivity is above 90–95%. By-products include carbon dioxide, ethyl acetate, and acetaldehyde. Crude VAM is recovered by absorption in acetic acid and purified by azeotropic distillation to 99.9% purity, with hydroquinone inhibitor at 5–15 ppm.

Polymerization of VAM with ethylene produces ethylene-vinyl acetate (EVA) copolymers in high-pressure autoclave reactors at 1000–2500 bar and 150–250°C. Vinyl acetate content ranges from 5–40 wt%. Films containing 7–18 wt% vinyl acetate provide low-temperature sealability. Adhesive grades with 28–40 wt% vinyl acetate require lower compounding temperatures to prevent acetic acid evolution. Melt flow index is measured by ISO 1133-1:2022 at 190°C and 2.16 kg, with grades from 0.3–500 g/10 min. Food-contact EVA copolymers are subject to FDA 21 CFR 177.1350 and EU Regulation 10/2011, with overall migration limit 10 mg/dm². Polyvinyl acetate emulsion polymerization uses continuous stirred reactors at 70–80°C, producing wood adhesives and water-based coatings. EVA extrusion temperatures must remain below 220°C to limit acetic acid elimination. Corrosion-resistant barrel internals are specified for adhesive and encapsulant compounds. Screw designs use lower compression ratios of 2.5:1 to 3.0:1 compared with higher compression ratios for homopolymer LDPE. Film grades containing 7–12 wt% vinyl acetate are processed on blown film dies with die gaps of 0.8–1.8 mm and blow-up ratios of 2.5:1 to 3.5:1. Seal strength after jaw sealing is tested under ASTM F88/F88M-21. For photovoltaic encapsulant film, vinyl acetate content is 28–33 wt%, and gel content after peroxide crosslinking is controlled above 70%. The crosslinker is added at 0.5–1.5 wt% tert-butyl peroxide, and cure is performed at 145–160°C in a vacuum laminator.

Linear Alpha-Olefin Chain Growth Distributions and Surface Fouling

The Shell Higher Olefin Process (SHOP) oligomerizes ethylene to linear alpha-olefins (LAOs) over a nickel-phosphine catalyst in a polar solvent. Ethylene pressure is 3–10 MPa and reaction temperature 80–120°C. Chain growth follows a Schulz-Flory distribution with a propagation-to-displacement factor alpha of 0.70–0.75. The reactor effluent contains C4 to C20+ olefins. Lighter and heavier fractions are separated by distillation. Internal olefins formed during isomerization are converted by metathesis into additional C6 and C8 fractions. Ethylene feed purity must be controlled below 1 ppmv acetylene, 1 ppmv sulfur compounds, and 0.1 ppmv water to prevent catalyst deactivation and by-product formation. 1-Hexene and 1-octene comonomers must exceed 99.5% purity for gas-phase LLDPE plants. Trace paraffins and branched olefins above 0.5 wt% degrade copolymer clarity and mechanical properties. LAO products are also hydrogenated to polyalphaolefins for synthetic lubricants. Purification columns for C6 and C8 cuts are operated with reflux ratios of 5:1 to 15:1 and bottom temperatures below 120°C to prevent thermal dimerization. Product analysis of alpha-olefin content uses ASTM D1159 for bromine number and ASTM D6352 for boiling range distribution.

Gas-phase LLDPE reactors impose strict comonomer purity because polar impurities poison Ziegler–Natta and metallocene active sites. 1-Hexene feed is specified with total alpha-olefin content above 99.5%, peroxide-forming compounds below 5 ppm, and water below 1 ppm. Oxygen ingress during tank transfer is controlled below 1 ppmv in the vapour space. When comonomer purity drops below 99.0%, catalyst productivity decreases by 10–30% and film gel count rises. The same C6 and C8 fractions are used in polyalphaolefin production via oligomerization over boron trifluoride or aluminium chloride catalysts. Polyalphaolefin kinematic viscosity at 100°C is controlled from 2–40 cSt depending on hydrogenated oligomer chain length. Testing follows ASTM D445-21 for viscosity and ASTM D2270-10(2020) for viscosity index. The main process bottleneck is polymer formation on reboiler surfaces when trace oxygen entry exceeds 1 ppmw.

Ethylene-propylene elastomer synthesis is conducted in continuous solution polymerization trains. Ethylene and propylene are copolymerized with ethylidene norbornene (ENB) in hexane using vanadium-aluminum or metallocene catalysts. Reactor temperature is held at 30–50°C and pressure at 0.5–1.5 MPa. Ethylene content is controlled between 45–75 wt%. ENB is added at 3–10 wt% to provide sulfur-curable unsaturation. Mooney viscosity ML(1+4) at 125°C ranges from 20–90. Molecular weight is moderated by hydrogen feed. Catalyst residues are removed by water washing and steam stripping. Diene loading above 10 wt% raises gel particle content and reactor fouling rates. The polymer crumb is dried and baled. Compounding uses internal mixers with ram pressure 0.5–0.8 MPa and dump temperatures of 120–150°C. Filler systems include carbon black N550 at 30–120 phr, paraffinic oil at 10–80 phr, zinc oxide 5 phr, and stearic acid 1 phr.

Peroxide cure systems with dicumyl peroxide at 2–8 phr require coagent triallyl cyanurate at 0.5–2 phr and are preferred for low compression set. Sulfur cure systems using 1.5–2.5 phr sulfur and thiuram accelerators are used where flex fatigue resistance is critical. Extrusion of weatherstrip profiles is performed on cold-feed pin barrel extruders with L/D 20:1 to 24:1 and temperature profiles of 60–90°C. Ethylene content is measured by ASTM D3900-17, ENB content by ASTM D6047-17, and cure behaviour by moving die rheometer ASTM D5289-19. EPDM sponge and dense profiles require different cure packages. Sponge compounds use azodicarbonamide blowing agent at 3–8 phr with urea activator at 1–3 phr. Dense extrusion profiles for automotive weatherseals are crosslinked in hot-air tunnels at 200–230°C for 2–5 min. Sulfur-cured EPDM exhibits a compression set of 20–35% after 22 h at 70°C under ISO 815-1:2019. Peroxide-cured compounds achieve compression set below 15% but require an inert cure atmosphere to avoid surface tack. Roofing membrane compounds use carbon black N550 and paraffinic oil to reach tensile strength above 10 MPa and elongation at break above 400% under ISO 37:2017.