H₂ SO₄ Alkylation

Process Description

Olefins (C3-C4) from the FCC unit are combined with isobutane (i-C4). Concentrated Sulfuric Acid (H₂ SO₄) is then mixed in and fed to the reactor that is operated with refrigeration to minimize the formation of by-products. 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 acid and alkylate products are separated by a settler, and the acid 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 from the bottom, and an n-butane product stream is separated from a side stream.


The light ends of the process fluids are used in the refrigeration loop and a side stream is passed through a propane stripper to recover propane. Effective separation is a critical component of an efficient, reliable, and safe sulfuric acid 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
  • 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 acid emissions


Production Challenge/Pall Solution


Challenge Solution
Meet product specifications.

Improve refinery productivity and product specifications by removal of water from the olefin and isobutane hydrocarbon reactor feed streams and by removing any carryover caustic in the propane.


Protect fractionator towers from corrosion & plugging.

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


  • High-efficiency PhaseSep® EL Liquid/Liquid coalescers reliably remove caustic from the feed to the main fractionator / isobutane stripper and to the propane stripper tower to prevent corrosion and fouling of the internal trays.
Control acid makeup costs.

Ensure the high sulfuric acid strength is maintained.






Key Application/Filter Recommendations (other applications not shown)


Diagram number Application Pall Product Customer Benefits
1,3,5 Pre-filtration prior to liquid/liquid coalescer

Ultipleat® High Flow filter

Profile® Coreless PPS

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


2 Feed/isobutane recycle stream water removal AquaSep XS (or PhaseSep® EL liquid/liquid coalescer )

Prevent dilution of acid catalyst and potential for corrosion and poor product yields


4 Caustic removal from feed to propane stripper PhaseSep® EL Liquid/Liquid coalescers

Reduce corrosion in propane stripper and meet propane quality spec


6 Caustic removal from feed to main fractionator/isobutane stripper PhaseSep® EL Liquid/Liquid coalescers

Reduce corrosion in main fractionator and meet butane and alkylate purity specs




For fast track upgrades, NO CAPEX:


Pall 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

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

PDF version of this page



Let’s find the right solution, together.

Let’s connect. We want to share our innovative filtration solutions with you today. Contact our knowledgeable subject matter experts for information on how we can help. Thank you and we look forward to assisting you shortly.