Hydrofluoric Acid (HF) Alkylation Units

Olefins (C3-C4) from the FCC unit are combined with isobutane (i-C4) and are first treated with a mol sieve bed to remove water. Concentrated HF is then mixed in and fed to the reactor. The alkylation reaction is a result of combining the olefins with the isobutane to form the alkylate product consisting of high octane value products which are later blended into the gasoline pool.


The HF and alkylate product are separated by a settler and the HF is recovered for re-use in the reactor. The reactor hydrocarbons are separated by the main fractionator where the isobutane is recycled to the reactor, alkylate is drawn off the bottom and an n-butane product stream is separated and treated with caustic (KOH).


Most of the overheads consist of HF acid fumes and propane gas.  They are then cooled and the HF is separated. Propane is further treated through the propane splitter to remove any dissolved HF and finally treated with alumina to remove fluorinated organics, and then caustic (KOH) to neutralize any remaining acid. Effective separation is a critical component of an efficient, reliable and safe H2SO4 alkylation process. 


Refinery Needs


  • Equipment reliability and minimized corrosion to meet 4-6 year refinery turn around schedule
  • Meet product specs for high octane value alkylate and caustic free propane and n-butane
  • Low acid makeup costs by minimizing acid dilution from wet feedstocks
  • Maintain high levels of safety by avoiding any equipment failures that could lead to fugitive emissions of HF


HF Alkylation Challenges and Solutions


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Meeting product specifications due to bed fouling and associated channeling
  • Improve refinery productivity and product specifications by removal of water from the olefin and isobutane hydrocarbon feed streams and by removing any carryover caustic in the propane and n-butane streams.
  • Free water will reduce the life of the mol sieve dryers and potentially lead to HF dilution
High efficiency AquaSep® XS and PhaseSep® EL liquid/liquid coalescers reliably meet ‘clear and bright’ product specification and sodium levels downstream
Protecting fractionator towers from corrosion and plugging. KO pots, mesh pads and cyclonic devices may not effectively remove emulsified water, caustic or acid droplets and fine solids.
  • Improve protection of main fractionator/isobutane stripper and propane stripper.
High efficiency PhaseSep® EL Liquid/Liquid coalescers reliably remove HF acid carryover from the acid settler  and is made with Hastelloy  hardware to withstand severe HF service.
Control acid makeup costs
  • Ensure reliability of molecular sieve dryers
High efficiency AquaSep XS or PhaseSep ® EL  Liquid/Liqud coalescers remove free water that can overload sieves, allowing acid dilution



HF Alkylation Process Flow Diagram

Key Application/Filter Recommendations (other applications not shown)


ApplicationPall ProductCustomer Benefits
1, 3, 5, 7, 9. Pre-filtration prior to liquid/liquid coalescerUltipleat® High Flow or Profile® Coreless PPS filterLower operating costs by improving the life of the liquid/liquid coalescer
2. Feed water (or caustic) removalAquaSep XS liquid/liquid coalescerPrevent dilution of HF acid catalyst and potential for corrosion–extend mol sieve life
4. Water removal from propanePhaseSep® EL liquid/liquid coalescersEnsure propane meets purity spec/prevent dilution of KOH
6. Water removal from n-butanePhaseSep® EL liquid/liquid coalescersEnsure n-butane meets purity spec/prevent dilution of KOH
8. HF acid removal after reactor HF acid settlerPhaseSep® EL liquid/liquid coalescersReduce corrosion and potential fouling of trays in the isobutane stripper
10. Water removal from olefin regenerant from mol sievePhaseSep® EL liquid/liquid coalescersAllow re-use of olefin
For fast track upgrades, NO CAPEX:Pall-Fit filter and coalescer retrofitsEnable a move to Pall quality without changing your existing filter housing
Pall filter and coalescer housing rentalsEnable a technology upgrade for rapid problem resolution.


To learn more about our Liquid/Liquid Coalescers, watch our short video below or contact one of our experts on the form provided.


Video - How Pall coalescers help effective liquid separation and particle removal


For more information on improving the efficiency of your processes, contact our team of filtration experts.

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