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.
- 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.
- High efficiency AquaSep XS or PhaseSep liquid/liquid coalescers remove free water that can overload sieves, allowing acid dilution
Key Application/Filter Recommendations (other applications not shown)
1, 3, 5, 7, 9.
Pre-filtration prior to liquid/liquid coalescer
Lower operating costs by improving the life of the liquid/liquid coalescer
Feed water (or caustic) removal
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
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