Arwahuzefa

HYDROFLUORIC ACID PROCESSES

There are two commercial alkylation processes using hydrofluoric acid as the

catalyst. They are designed and licensed by Phillips Petroleum Company and

UOP. The basic flow scheme is the same for both the Phillips and the UOP processes

Both the olefin and isobutane feeds are dehydrated by passing the feedstocks

through a solid bed desiccant unit. Good dehydration is essential to minimize

potential corrosion of process equipment which results from addition of

water to hydrofluoric acid.

After dehydration the olefin and isobutane feeds are mixed with hydrofluoric

acid at sufficient pressure to maintain all components in the liquid phase.

The reaction mixture is allowed to settle into two liquid layers. The acid has a

higher density than the hydrocarbon mixture and is withdrawn from the bottom

of the settler and passed through a cooler to remove the heat gained from the

exothermic reaction. The acid is then recycled and mixed with more fresh feed,

thus completing the acid circuit.

A small slip-stream of acid is withdrawn from the settler and fed to an acid

rerun column to remove dissolved water and polymerized hydrocarbons. The acid

rerun column contains about five trays and operates at 150 psig (1034 kPa) [3].

The overhead product from the rerun column is clear hydrofluoric acid which is

condensed and returned to the system.

The bottom product from the rerun column is a mixture of tar and an HF–

water . These components are separated in a tar settler (not shown on

the flow diagram). The tar is used for fuel and the HF–water mixture is neutralized

with lime or caustic. This rerun operation is necessary to maintain the activity

of the hydrofluoric acid catalyst.

The hydrocarbon layer removed from the top of the acid settler is a mixture

of propane, isobutane, normal butane, and alkylate along with small amounts

of hydrofluoric acid. These components are separated by fractionation and the

isobutane is recycled to...