Petrochemical & Petroleum
Refining Technology
Conversion Process
(Unification)
Conversion
Change the size and/or 2. Unification (combining)
structure of hydrocarbon
molecules - alkylation & polymerization
1. Decomposition (dividing) 3. Alteration (rearranging)
- hydro, thermal & catalytic - isomerization & catalytic
cracking, coking and reforming
visbreaking
Unification
Processes to make gasoline components from materials that are too
light to otherwise be in gasoline
Cracking + Polymerization + Alkylation = Gasoline yield representing 70
percent of the starting crude oil.
Alkylation Process
Alkylation Process
Combination of low molecular weight olefins (propylene and
butylene) with an isoparaffin (isobutane) in the presence of a catalyst
(sulfuric acid or hydrofluoric acid) to form higher molecular weight
isoparaffins.
Alkylation Process
Alkylation combines the molecules of olefins produced from catalytic
cracking with those of isoparaffins in order to increase the volume and
octane of gasoline blends.
Olefins will react with isoparaffins in the presence of a highly active
catalyst, usually sulphuric acid or hydrofluoric acid (or aluminium
chloride) to create a long-branched-chain paraffinic molecule, called
alkylate (iso-octane), with exceptional anti-knock quality.
The alkylate is then separated and fractionated.
The relatively low reaction temperatures of 10°C to 16°C for sulphuric
acid, 27°C to 0°C for hydrofluoric acid (HF) and 0°C for aluminium
chloride, are controlled and maintained by refrigeration.
Alkylation Process
The product can be made to fall within the gasoline boiling range with
MON from 88-94 & RON from 94-99.
Isobutane is normally used in Alkylation process since it is has a
sufficiently high octane number and low vapor pressure to allow it to be
effectively blended directly into finished gasoline.
Process using sulfuric acid as a catalyst is much more sensitive to
temperature than HF acid process. The reaction can carry out the
reactions at 40-70oF (5-21oC) or lower thus minimize oxidation
reduction reactions.
When anhydrous HF acid is the catalyst, the temperature usually
limited to 100oF (38oC) or below.
Alkylation Process
The volume of acid employed is about equal to that of the liquid HC
charge & sufficient pressure is maintained on the system to keep the HC
& acid in the liquid state.
High isoparaffin/olefin ratios (4:1 to 15:1) are used to :
minimize side reaction polymerization (reduce by product)
to increase product octane number.
The yield, volatility & octane no. of the product is regulated by
adjusting the temperature, acid/HC ratio & isoparaffin/olefin ratio.
In practice however, the plants are operated at different conditions &
the products are somewhat different
Isoparaffin Olefins HF /H2SO4 Isoparaffins
(Isobutane) (Propylene/Butylene) (ALKYLATE)
By products:
1. Polypropylene (polymerization
of propylene) – lower product
octane & increase acid
consumption
2. Ester (reaction with H2SO4 ) –
very corrosive, require
treatment
ALKYLATE
Excellent blending
MON 90-95 component for gasoline
RON 93-98
Sulphuric Acid Alkylation
In cascade-type sulphuric acid alkylation units, feedstocks, including
propylene, butylene, and fresh isobutane, enter the reactor, where they
contact the sulphuric acid catalyst.
The reactor is divided into zones, with olefins fed through distributors
to each zone, and the sulphuric acid and isobutanes flowing over baffles
from zone to zone.
Reaction heat is removed by evaporation of isobutane.
The isobutane gas is removed from the top of the reactor, cooled and
recycled, with a portion directed to the depropanizer tower.
Residual from the reactor is settled, and the sulphuric acid is removed
from the bottom of the vessel and recirculated.
Sulphuric Acid Alkylation
Caustic and/or water scrubbers are used to remove small amounts of
acid from the process stream, which then goes to a de-isobutanizer
tower.
The debutanizer isobutane overhead is recycled, and the remaining
hydrocarbons are separated in a rerun tower and/or sent to blending.
Schematic Diagram of Sulfuric Acid Alkylation Process
Hydrofluoric Acid Alkylation
There are two types of hydrofluoric acid alkylation processes: Phillips
and UOP.
In the Phillips process, olefin and isobutane feedstock is dried and fed
to a combination reactor/settler unit.
The hydrocarbon from the settling zone is charged to the main
fractionator.
The main fractionator overhead goes to a depropanizer. Propane, with
trace amounts of hydrofluoric acid (HF), goes to an HF stripper, and is
then catalytically defluorinated, treated and sent to storage.
Isobutane is withdrawn from the main fractionator and recycled to
the reactor/settler, and alkylate from the bottom of the main
fractionator is sent to a splitter.
Schematic Diagram of Hydrofluoric Acid Alkylation Unit
Hydrofluoric Acid Alkylation
The UOP process uses two reactors with separate settlers.
Half of the dried feedstock is charged to the first reactor, along with
recycle and make-up isobutane, and then to its settler, where the acid is
recycled and the hydrocarbon charged to the second reactor.
The other half of the feedstock goes to the second reactor, with the
settler acid being recycled and the hydrocarbons charged to the main
fractionator.
Subsequent processing is similar to Phillips in that the overhead from
the main fractionator goes to a depropanizer, isobutane is recycled and
alkylate is sent to a splitter.
Alkylation Process
Important variables in alkylation unit:
1. Reaction temperature
2. Acid strength & Composition
3. Isobutane concentration
4. Olefin type (ratio of butylene/propylene)
5. Space velocity
6. Agitation
HF Alkylation Unit
Alkylation Plant
Thank You
