Technology

The Neste NEXPAO™ technology is a process for producing high-quality polyalphaolefin (PAO) synthetic base oils from 1-decene feedstock. The original PAO process of Neste in commercial operation at Neste's Beringen facility (1991-2011) used catalytic distillation with solid acid catalysts. The advanced NEXPAO technology (2021-present) described in this article features Neste's innovative cone reactor design with BF₃/alcohol homogeneous catalysts combined with advanced catalyst recovery systems, and is currently being implemented at CSPC China's 50,000 tpy facility.

Process Description

Feed Preparation and Storage

• Primary feed: 1-Decene (C₁₀H₂₀), minimum 98% purity
• Impurity limits: <100 ppm total impurities including peroxides, oxygen, sulfur, nitrogen compounds, acetylenic compounds
• Storage: Ambient temperature with nitrogen blanket to prevent oxidation and polymerization
• Feed treatment: Molecular sieve drying and trace contaminant removal before reactor feed

Oligomerization Section

Cone Reactor Design:

The centerpiece of NEXPAO technology is Neste's patented cone reactor featuring:

• Unique geometry: Cross-sectional area decreases from top (large diameter) to bottom (small diameter)
• Self-mixing: Cone shape eliminates need for external mixing equipment through natural circulation
• Materials: Stainless steel construction for BF₃ compatibility
• Volume: Sized for 5-40 minute residence time at design capacity
• Cooling system: External heat exchangers with thermal oil circulation
• Capacity flexibility: Operates efficiently at 60-100% capacity with constant residence time
• Temperature control: Extensive external cooling loop maintains isothermal conditions
• Recycle pump: High-capacity circulation pump (180-300 m³/h)

Operating Conditions:

• Temperature: 30°C (optimized for maximum conversion rate and selectivity)
• Pressure: Moderate pressure (40-60 psig estimated)
• Residence time: 5-40 minutes total, with 90-95% recycle providing optimal contact time
• Conversion: >95% 1-decene conversion per pass through reactor system

Catalyst System:

• Primary catalyst: Boron trifluoride (BF₃) gas
• Co-catalyst: n-Butanol (preferred) forming liquid BF₃/alcohol complex
• Catalyst loading: 1 mol-% BF₃/n-butanol complex relative to fresh feed
• Mechanism: Cationic oligomerization producing statistical distribution of dimers, trimers, tetramers, pentamers

Product Distribution:

• Dimers (C₂₀): 15-25%
• Trimers (C₃₀): 40-50% (markedly peaked for PAO 4 optimization)
• Tetramers (C₄₀): 25-35%
• Pentamers+ (C₅₀+): 5-15%

Catalyst Recovery Section

Flash Separation:

• Flash separator: Low-pressure vessel designed for BF₃ vapor handling
• Flash conditions: 0.1-2 psia to vaporize BF₃ from product stream
• BF₃ recovery: Up to 80% recovery efficiency at optimal conditions
• Temperature: Ambient to 50°C to maintain BF₃ vapor pressure

Catalyst Recycling:

• Vapor treatment: Counter-current absorption column using fresh n-butanol
• Catalyst reformation: Reformed BF₃/alcohol complex recycled to reactor
• Economic benefit: 39-47% improvement in catalyst efficiency vs once-through operation
• Purge stream: Small purge to prevent accumulation of catalyst deactivators

Unreacted Monomer Recovery:

• Separation: Flash overhead contains unreacted 1-decene
• Recycle: High-purity 1-decene recycled to reactor feed
• Efficiency: >99% monomer recovery minimizing feedstock losses

Product Separation and Hydrogenation

Primary Fractionation:

• Feed: Crude oligomer product from catalyst recovery
• Separation: Distillation into two fractions based on viscosity
  • Light fraction: ≤5 cSt (primarily PAO 2 + PAO 4)
  • Heavy fraction: >5 cSt (primarily PAO 6 + PAO 8)

Hydrogenation Units

• Reactor design: Fixed-bed reactors with downflow operation
• Catalyst loading: 50-100 m³ catalyst per reactor
• Pressure rating: Designed for 10 MPa operating pressure
• Temperature control: Multi-zone heating with inter-bed cooling

Neste's advanced approach uses separate hydrogenation for each fraction:

• Light Fraction Hydrogenation:
  • Temperature: 130-200°C
  • Pressure: 3-5 MPa H₂
  • Catalyst: Nickel on alumina support (extruded pellets)
  • LHSV: 2-8 h⁻¹
  • Objective: Saturate double bonds while minimizing thermal stress
     
• Heavy Fraction Hydrogenation:
  • Temperature: 150-250°C
  • Pressure: 4-6 MPa H₂
  • Catalyst: Noble metal (Pd/Pt) on support for lower temperature operation
  • LHSV: 0.5-3 h⁻¹
  • Benefits: Reduced thermal degradation of higher molecular weight oligomers

Final Product Fractionation

Product Separation:

• Distillation columns: Multi-stage atmospheric and vacuum distillation columns with structured packing
• Product cuts: Precise molecular weight separation
• Blending: Fine-tuning of viscosity grades through controlled blending

Final Product Specifications:

Grade	Viscosity @ 100°C (cSt)	Viscosity @ 0°C (cSt)	Viscosity ndex	Pour Point (°C)	NOACK (%)
PAO 2	1.9 ± 0.1	5.2 ± 0.3	135 ± 5	-65	16
PAO 4	3.9 ± 0.1	17.0 ± 1.0	127 ± 3	-62	13
PAO 6	5.9 ± 0.1	31.0 ± 2.0	140 ± 5	-57	9
PAO 8	7.8 ± 0.2	46.0 ± 3.0	142 ± 5	-54	7

 

Utilities Systems

• Thermal oil system: 8,000 kW total heating capacity (modernized to electric heating)
• Cooling water: Closed-loop system with cooling towers
• Nitrogen system: For tank blanketing and process purging
• Hydrogen supply: On-battery storage with vaporization system
• Emissions control: Thermal oxidizer (3,000 kW) for process emissions

Process Block Flow Summary

Stream Flows:

• Feed: 1-Decene → Purification → Cone Reactor
• Catalyst: BF₃ + n-Butanol → Complex Formation → Reactor → Recovery → Recycle (80% recovery)
• Recycle: 90-95% reactor outlet → External cooling → Back to reactor
• Product: Crude PAO → Primary separation → Dual hydrogenation → Final fractionation → PAO grades

Key Equipment:

1. Cone Reactor: Unique geometry, no external mixing, 30°C operation
2. Flash Separator: BF₃ recovery at 0.1-2 psia
3. Dual Hydrogenation: Separate light (≤5 cSt) and heavy (>5 cSt) fraction processing
4. Multi-stage Distillation: Precise molecular weight separation

Operating Conditions:

• Oligomerization: 30°C, 5-40 min residence time, 90-95% recycle
• Hydrogenation: 130-250°C, 3-6 MPa H₂ pressure
• Product Quality: VI 127-142, Pour points -65°C to -54°C

Process Performance

Conversion and Yields

• 1-Decene conversion: >95% per pass, >99.5% overall with recycle
• Selectivity to desired oligomers: >85% (dimers through pentamers)
• Catalyst consumption: 0.5-1.0 kg BF₃ per tonne PAO product (with recovery)
• Energy consumption: 0.8-1.2 GJ per tonne PAO product

Product Quality Advantages

• Ultra-high viscosity index: Superior temperature-viscosity characteristics
• Exceptional low-temperature performance: Pour points as low as -65°C
• Low volatility: Excellent NOACK evaporation loss values
• Thermal stability: Enhanced through complete hydrogenation (bromine number <1)
• Oxidative stability: Excellent additive response and long service life

Operational Reliability

• Plant availability: >95% based on 20-year Beringen operational history
• Campaign length: >12 months between major turnarounds
• Catalyst life: 2-4 years for hydrogenation catalysts
• Environmental compliance: Zero serious incidents in commercial operation

Commercial Validation

• Original Neste's PAO technology: 20-year commercial operation (60,000 tpy Beringen plant)
• Technology transfer success: Seamless transition to Chevron Phillips Chemical
• Newest NEXPAO technology: Active liensing to CSPC China for 50,000 tpy project demonstrates continued viability

References

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