Alternative Wax Removal Methods for Waste Plastic Pyrolysis

Alternative Wax Removal Methods for Waste Plastic Pyrolysis

In addition to a dedicated dewaxing tank, four main technical routes are widely used in the industry: front-end catalytic inhibition, back-end physical separation, process parameter control, and raw material/system optimization.

1. Catalytic Wax Inhibition (Reduce Wax at Source)

• Wax Reduction Catalyst (Most Common)Principle: Add molecular sieves, clay, talc powder, or special cracking catalysts during pyrolysis to break long-chain alkanes (C₂₀+) into C₅–C₁₂ light fuel fractions, suppressing wax formation at the source.Application: Batch plants mix catalyst with feedstock; continuous plants install a catalytic tower before the cooling system.Benefits: No pipe blockage, better oil quality, continuous operation; Drawback: Catalyst cost and periodic replacement.

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• Non-hydrogen Pour Point Depression CatalysisPrinciple: Hot pyrolysis oil/gas enters a depression reactor for isomerization/cracking over specialty catalysts, converting high-pour-point long-chain alkanes into low-pour-point isoalkanes.Performance: Oil pour point drops to below -15°C, eliminating the need for downstream dewaxing.

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2. Physical Separation (Back-end Dewaxing, Replace/Complement Dewaxing Tank)

• Cooling + Filtration/CentrifugationProcess: Cool pyrolysis oil to 0~-20°C to crystallize wax → plate-frame/vacuum filtration or centrifugation → dewaxed clean oil + crude wax.Features: Simple equipment, low cost; ideal for small-to-medium plants; requires a cooling system.

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• Solvent DewaxingPrinciple: Add solvents such as acetone, toluene, methanol to reduce oil viscosity and promote wax crystallization, followed by filtration; solvents are recovered and recycled.Benefits: Thorough dewaxing, high-purity wax; Drawbacks: Flammable, high cost, explosion-proof design required.

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• Scraper/Scraping Dewaxing TowerStructure: Equipped with rotary scrapers inside; wax solidifies on cooled walls and is scraped off automatically for collection, enabling continuous wax removal without shutdowns.

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3. Process & Temperature Control (Low-cost Wax Prevention)

• Full-line Tracing & InsulationPractice: Insulate and trace (steam/electric) pipes, buffer tanks, and condensers to maintain oil temperature >40°C, preventing wax condensation and adhesion.Application: Cold climates; Benefits: No equipment cost, simple & reliable; Drawback: Higher energy consumption.

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• Elevated Pyrolysis TemperatureMeasure: Increase cracking temperature from 380–420°C to 450–500°C to intensify long-chain cleavage and reduce C₂₀+ wax formation.Caution: Excessively high temperature causes coking, higher gas yield, lower oil yield—balance is critical.

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• Wax Recycle & RepyrolysisDesign: Install a wax collection tank at the reactor outlet to send condensed crude wax back to the reactor for secondary cracking into light oil.Benefits: Zero waste, higher oil yield; Drawback: Increased reactor load.

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4. Raw Material & System Optimization (Preventive Measures)

• Raw Material Sorting & PE ControlKey Point: Minimize PE (HDPE/LDPE) content (PE produces the most wax); blend more PP, PS, ABS, paper-plastic; control PE <30% to reduce wax significantly.

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• Multi-stage Condensation + Pre-interceptionConfiguration: Add 1–2 low-temperature pre-coolers before the main condenser to capture most wax upfront, protecting the main condenser from blockage.

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• Periodic Mechanical/Chemical Wax CleaningMechanical: High-pressure water jet, mechanical pipe scrapers for regular cleaning;Chemical: Circulate toluene-ethanol mixture for cleaning, achieving >85% wax dissolution.

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