Technology

Historical Context

The UOP HF alkylation process has a rich development history spanning over eight decades. The foundational HF alkylation technology was developed in UOP laboratories during the late 1930s and early 1940s, initially for producing high-octane aviation fuels from butylenes and isobutane. By the mid-1950s, the increasing demand for sophisticated high-performance automotive engines drove refiners to expand gasoline production while improving motor fuel quality.​

The HF alkylation process gained significant momentum by the early 1960s, virtually displacing motor fuel polymerization units for new installations. The technology's importance further increased in the 2000s due to the scheduled phase-out of MTBE and increased emphasis on low-sulfur gasoline production. UOP's reactor and distillation systems evolved through decades of pilot-plant evaluation, engineering development, and commercial operation, resulting in the present concepts in alkylation technology.​

The AlkyPlus™ process represents UOP's enhanced alkylation technology, incorporating decades of experience with more than 210 licensed alkylation units worldwide. This advanced process solution builds upon UOP's traditional HF alkylation foundation while integrating modern safety features and process improvements developed through extensive R&D efforts.

Technology Summary and Chemistry

The AlkyPlus process catalytically combines C₃-C₅ olefins with isobutane to produce motor fuel alkylate in the presence of modified HF catalyst system with ReVAP™ technology, providing enhanced safety characteristics compared to conventional HF systems. The modified catalyst includes proprietary additives that suppress vapor pressure and reduce aerosol formation potential during accidental releases. 

The alkylation reaction mechanism proceeds via the classic carbenium ion pathway, involving initiation, propagation, and isomerization steps.​ The alkylation reactions follow a carbenium ion mechanism with several key steps:​

• Initiation: Generation of tertiary butyl cations that initiate the alkylation reaction chain. HF acid protonates olefins to form carbenium ions.​
• Propagation: Tertiary butyl cations react with olefins to form larger carbenium ions, which then abstract hydride from isobutane molecules, generating isoparaffins and regenerating tertiary butyl cations.​
• Isomerization: Critical for producing high octane quality, particularly from 1-butene feeds. The isomerization of 1-butene to 2-butene reduces dimethylhexane production (RON 55-76) and increases trimethylpentane formation.​
• Hydrogen Transfer: Most pronounced with propylene feeds, this reaction produces butylene and propane, with the butylene subsequently alkylating to form trimethylpentane.​

Secondary reactions such as hydrogen transfer, polymerization, isomerization, and destructive alkylation also occur, resulting in formation of secondary products both lighter and heavier than primary products.

Detailed Process Description with Processing Steps

The AlkyPlus process follows the proven UOP isothermal reactor design with several enhancements. The process consists of six main sections:​

1. Feed Treating Section
   • Alkylation feedstock (C3, C4, C5 olefins or mixtures) undergo treating to remove sulfur and water​
   • Feed drying systems remove water to prevent catalyst degradation​
   • Optional oxygenate removal unit (ORU) for processing MTBE/TAME raffinates​
   • Selective hydrogenation option for butylene feedstock to reduce catalyst regeneration requirements​
      
2. Enhanced Isothermal Reactor System
   • Reactor Design: Enhanced isothermal reactor designed to minimize catalyst inventory while ensuring efficient hydrocarbon-acid contacting​
   • Temperature Control: Continuous heat removal in the reaction zone reduces peak temperatures and enhances product selectivity​
   • Mixing System: Efficient dispersion of hydrocarbon feed with acid catalyst through specially designed feed distributors​
   • Heat Exchange: Effective heat transfer utilizing available cooling water supply​
   • Operating Conditions:
     • Temperature: Cooling water temperature (typically 35-45°C)​
     • Pressure: Moderate pressure operation​
     • Isobutane to olefin ratio: Optimized for maximum alkylate quality​
     • Acid inventory: Minimized through high heat-transfer rates and efficient circulation
        
3. Separation and Settling
   • Acid-hydrocarbon separation in settling vessels​
   • Gravity separation with settled acid returned to reactor through catalyst cooler​
   • Hydrocarbon phase containing propane, recycled isobutane, normal butane, and alkylate sent to fractionation​
      
4. Product Separation and Treatment
   • Main Fractionator: Separates hydrocarbon products into distinct streams​
   • Isostripper: Recovers high-purity isobutane for recycle​
   • HF Stripper: Removes HF from product streams​
   • Propane Recovery: High-purity propane through HF stripper, defluorinator, and KOH treatment​
   • Product Treatment: Defluorination and KOH treatment for all products​
      
5. Acid Regeneration
   • On-site catalyst regeneration removes heavy oils (tars) from catalyst​
   • Internal acid regeneration technique minimizes acid consumption​
   • Additive recovery system for ReVAP™ components​
      
6. Neutralization Section
   • Relief-gas scrubber
   • KOH mixing tank
   • Circulating pumps
   • KOH regeneration tank

Safety and Mitigation Features

The AlkyPlus process incorporates multiple safety enhancements:​

Active Mitigation:

• Improved volatility suppression systems
• Enhanced detection and monitoring systems
• Rapid response mitigation equipment

Passive Mitigation:

• Pre-blended catalyst reducing transportation risks
• Reduced aerosol formation characteristics
• Lower catalyst inventory requirements

Technology Performance

Yields and Product Properties

The AlkyPlus process delivers competitive yields and high-quality alkylate products:​

Olefin Feed	Isobutane Consumed (vol/vol)	C5+ Alkylate Produced (vol/vol)	API Gravity	RON Clear	MON Clear	RVP (psia)
C3=	1.4	1.8	70.7	91.0	89.5	3.0
C4=	1.2	1.8	69.9	96.0	94.0	2.7
C5=	1.3	2.0	69.9	90.0	89.0	0.45

 

Alkylate Quality Characteristics

The AlkyPlus process produces alkylate with superior environmental and performance characteristics:​

• Ultra Low Sulfur: Essentially sulfur-free product
• No Aromatics: Clean-burning characteristics
• High Octane: Research octane numbers 90-96 clear
• No Olefins: Stable blending component
• Low Vapor Pressure: Assists in gasoline pool RVP control

Catalyst Efficiency:

• Catalyst consumption less than 1/200th required for sulfuric acid technologies​
• No expensive solid catalysts required​
• Simple on-site catalyst regeneration​

Operational Efficiency:

• No mechanical agitation required​
• No refrigeration equipment needed​
• No compression requirements​
• High on-stream availability through elimination of compressors and rotating equipment in reactor​

Energy Integration:

• Efficient heat transfer with cooling water utilization​
• Heat integration opportunities in fractionation section​
• Steam generation potential from reaction heat​

Process Flexibility

The AlkyPlus technology provides enhanced operational flexibility:​

• Wide range of olefin feedstocks (C₃-C₅)​
• Ability to process MTBE/TAME raffinates with appropriate pretreatment​
• Revamp capabilities for existing HF alkylation units​
• Scalable design for various capacity requirements

Commercial Experience and Process Scale

Global Market Position

UOP maintains its position as the leading licensor of alkylation technology with more than 210 licensed units worldwide. The company's alkylation portfolio has evolved to include several technology variants addressing different market needs and safety requirements.​

Technology Evolution and Deployment

The AlkyPlus process represents the latest evolution in UOP's alkylation technology development, building upon decades of commercial experience. The technology incorporates lessons learned from extensive commercial operations and addresses current industry challenges related to safety, environmental compliance, and economic optimization.​

Commercial Scale Applications:

• New grassroots installations
• Revamp projects for existing HF alkylation units requiring major modifications​
• Capacity expansion projects where full reactor/settler replacement is required​
• Units requiring enhanced safety profile competitive with alternative technologies

Implementation Considerations

Revamp Opportunities:
The AlkyPlus process solution is particularly suitable for existing HF alkylation units requiring major modifications to achieve refinery goals. The technology can be implemented when full reactor/settler replacement is required for capacity expansion, providing necessary performance upgrades coupled with reduced-risk profile.​

Project Economics:
The AlkyPlus solution remains economically attractive for alkylate production, offering competitive capital and operating costs while providing enhanced safety characteristics. The technology's ability to process various feedstocks and integrate with existing infrastructure provides additional economic benefits for refiners.

References

1. PennState College of Earth and Mineral Sciences > FSC 432: Petroleum Refining > Lesson 8: Catalytic Conversion Processes Part 2 > Alkylation > UOP HF Alkylation Process.
2. Honeywell UOP. 2016 UOP LLC Information Bulletin: UOP AlkyPlus™ Alkylation Process Solution.
3.