The HF Alkylation Process:
Purpose:
Converts low-molecular-weight alkenes (primarily propylene and butylene) and isobutane into high-octane alkylate, a key blending component for cleaner-burning gasoline.
Key Steps:
Feedstock Preparation:
Alkenes are typically obtained from the fluid catalytic cracking (FCC) unit.
Isobutane is often extracted from natural gas streams.
Both feedstocks are dried to remove water before entering the process.
Reaction:
The dried feedstocks are mixed with concentrated hydrofluoric acid (HF) as a catalyst.
The mixture enters a reactor where the HF acid promotes the alkylation reaction: Alkenes react with isobutane, forming branched-chain molecules with higher octane numbers.
Separation:
The product stream leaving the reactor is sent to a settler:
The HF acid, due to its high density, separates as a bottom layer and is recycled back to the reactor.
The alkylate product floats on top and is drawn off for further processing.
Fractionation:
The alkylate is sent to a distillation column:
Unreacted isobutane is separated and recycled back to the reactor.
The final alkylate product is drawn off the bottom.
Benefits of HF Alkylation:
Produces high-octane gasoline blendstock, improving engine performance and reducing emissions.
Enables efficient utilization of light hydrocarbons from other refinery processes.
Relatively high conversion efficiency.
Safety Considerations:
HF acid is a highly toxic and corrosive substance.
Stringent safety measures are crucial to prevent leaks and ensure safe operation of the unit.
Additional Points:
HF Alkylation is a mature technology, but ongoing research focuses on improving catalyst efficiency and safety aspects.
Alternative Alkylation processes using sulfuric acid (SAAU) exist, but HF offers advantages in terms of reaction rate and product quality.
Strict environmental regulations govern the emissions and handling of HF acid in these units.
Here are some resources for further exploration:
Refinery HF Alkylation: https://www.pall.com/content/dam/pall/oil-gas/literature-library/non-gated/pdf/refinery-hf-alkylation.pdf
UOP HF Alkylation Process: https://www.e-education.psu.edu/fsc432/content/uop-hf-alkylation-process