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Refinery HF Alkylation

Ensure your Alkylation unit operates reliably, with minimum corrosion, low acid consumption, and on spec products.

HF Alkylation

Process Description

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 Hydrofluoric Acid (HF) is then mixed in and fed to the reactor. The alkylation reaction takes place combining the olefins with the isobutane to form the alkylate product which consists of high octane value products that are later blended into the gasoline pool. The hydrocarbons leaving the reactor mostly consist of alkylate, unreacted isobutane, n-butane, and propane.


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).


The overheads consist mostly of HF acid fumes and propane gas. The overheads are then cooled and the HF 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/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


Production Challenge/Pall Solution





Meet 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® liquid/liquid coalescers reliably meet ‘clear and bright’ product specification and sodium levels downstream





Protect fractionator towers from corrosion & plugging



Improve protection of main fractionator/isobutane stripper and propane stripper.


  • KO pots, mesh pads and cyclonic devices may not effectively remove emulsified water, caustic or acid droplets and fine solids
  • High efficiency PhaseSep X 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.




HF Alkylation process diagram


Key Application/Filter Recommendations (other applications not shown)



1, 3, 5, 7, 9.

Pre-filtration prior to liquid/liquid coalescer

Customer Benefits


Lower operating costs by improving the life of the liquid/liquid coalescer


Feed water (or caustic) removal


AquaSep XS (or PhaseSep) liquid/liquid coalescer 


Prevent dilution of HF acid catalyst and potential for corrosion–extend mol sieve life


Water removal from propane


Ensure propane meets purity spec/prevent dilution of KOH


Water removal from n-butane


Ensure n-butane meets purity spec/prevent dilution of KOH


HF acid removal after reactor HF acid settler


Reduce corrosion and potential fouling of trays in the isobutane stripper


Water removal from olefin regenerant from mol sieve


Allow re-use of olefin



For fast track upgrades, NO CAPEX:


Pall-Fit filter and coalescer retrofits enable a move to Pall quality without change to your existing filter housing


Pall filter and coalescer housing rentals enable a technology upgrade for rapid problem resolution



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