Application Description The Impact Of Poor Quality Olefin Feedstocks The Importance Of Alky Unit Pre-treatment Typical Process Conditions VULCAN VIG Catalyst Morphology Selective Hydrogenation of Acetylenes and Alkenes Alkylation Reaction Chemistry ALKYLATION CHEMISTRY AND PROCESS VARIABLES What Are VULCAN Processes FIXED BED PROCESSES Advantages Dis-Advantages VULCAN UltraPurification Guards VULCAN UltraPurification Impurities VULCAN Sulfur Guards VULCAN Guards - Prediction Of Sulfur In Feed Basic HDS Reactions Mechanisms for DBT desulfurization Relative Reactivities of Three benzothiophene molecules

1. Gerard B. Hawkins
Managing Director

2.  The aim of the alkylation unit is to produce high RON alkylates
 Alkylates are important in the refinery gasoline pool. They are
richer in branched chain high octane blending components than
either reformate or isomerate
 Alkylation refers to the reaction between low MR olefins and
isoparaffins
 eg. n-butene + isobutane dimethyl hexanes
 Alky units are therefore located downstream of FCC units
 The quality of the alkylate produced depends on the olefin
feedstock:
Isobutylene > butenes > propene > pentanes

3.  Most refiners use mono-olefin butene from the FCC as their
feedstock into the alky unit
 Di-olefins in the alky feed present problems to the refiner
and require pre-treatment
 Di-olefin spec to the alky unit is 100 ppmW
 Excessive di-olefin leads to greater acid consumption
Increased acid consumption is a serious problem to refiners,
resulting in greater costs to the refiner and increasing
governmental/environmental pressure

5.  Alky unit pre-treatment technology is catalyst based
 FCC feed [containing di-olefin] over VULCAN VIG Series
Pd/Al2O3
 Most desirable product is but-2-ene
 Historically ratio of but-2-ene to but-1-ene has been 3 to 4
 Catalyst selectivity improvements mean today ratios are at 10
to 12
 Directionally, ratios must improve for the sake of the gasoline
pool
 The role of the catalyst should be:
a]To selectively hydrogenate feed to the alky
b]To isomerize feed to the alky

6.  Temperature 40oC
 Pressure 160 psi
 Feed Flow-rate 32 m3/hr
 Feed density 0.55 Kg/L
 Volume 7 m3
 LHSV 4.6

8. Acetylenes may be reduced to olefins or
alkanes under mild reaction conditions (20 to
100ºC, 1 to 10 atmospheres H2 pressure) in
the presence of other reducible functional
groups.
Note: Palladium and platinum are the
preferred catalytic metals for these
reactions. Palladium is the most selective
metal for conversion of acetylenes to
olefins.
Selective Hydrogenation
of Acetylenes and Alkenes

9. Olefins are easily reduced to alkanes.
Platinum group metals exhibit the following general order of
activity:
Pd > Rh > Pt >> Ru.
Strained olefins are reduced more easily than unstrained
olefins; exocyclic double bonds are reduced more easily than
endocyclic double bonds.
In molecules containing more than one double bond, the least
hindered bond generally will be reduced preferentially.
Selective Hydrogenation
of Acetylenes and Alkenes

10. A complication in the
hydrogenation of alkenes
can be double bond
migration and cis-trans
isomerization.
Selective Hydrogenation
of Acetylenes and Alkenes
The tendency of the platinum group metals to promote these reactions
during hydrogenation is as follows:
Pd > Rh > Ru > Pt.

11. Double bond migration and cis-trans isomerization tend to be
faster than olefin hydrogenation with palladium catalysts.
Isomerization is impeded by conditions that minimize catalyst
acidity and increase hydrogen availability at the catalyst surface
(i.e. increased pressure and agitation, lower catalyst and/or metal
loadings, and catalysts of low intrinsic activity).
Platinum is useful when double bond migration is to be avoided.
Selective Hydrogenation
of Acetylenes and Alkenes

12. Palladium: 5% Pd/C
5% Pd/CaCO3
Platinum: 5% Pt/C
Rhodium: 5% Rh/C
Ruthenium: 5% Ru/C
Recommended VULCAN VIG Series PGM Catalysts:
Selective Hydrogenation
of Acetylenes and Alkenes

14. The alkylation of isobutane
with light olefins is an acid-
catalyzed reaction that
follows well-known
Carbo-cation chemistry.
A general representation
of the reaction mechanism
is shown in Figure 1.

15. The initial C4 carbo-cation
is formed by the
Protonation of a light
olefin on the solid
catalyst surface.
The second step, often
Referred to as isobutane
activation, is the reaction
(alkylation) of an olefin with
this C4 carbo-cation on the
catalyst surface and the
subsequent hydride
abstraction from isobutane
by the resulting C8 carbo-cation.

16. In liquid acid systems,
and particularly those
using sulfuric acid, key
Reactions are promoted
by the Intimate mixing of
acid with hydrocarbon
and by adequate
isobutane-to Olefin (I/O)
ratios.

17. The key process variables in alkylation are the reaction
temperature, the I/O ratio, reactant contact time with
the catalyst, and the catalyst-to-olefin (C/O) ratio.
The effect that each of these variables has on process
performance in the Alkylene process is similar to the
effect they have in conventional liquid acid
technologies:
·

18. Reaction temperature. Alkylate product quality, particularly
octane, improves as the reaction temperature is reduced.
Refrigeration is typically required to optimize alkylation
reaction conditions.
The optimum temperature is chosen by balancing the
improvement in product quality against the increased utility
consumption and capital investment for lower temperature
operation.

19. · Isobutane-to-olefin (I/O) ratio. Alkylate product quality
improves with higher I/O ratios because olefin polymerization
reactions are minimized as a result of the higher isobutane
concentration present in the second reaction step.
The result is that the alkylate product is enriched in the
higher-octane trimethylpentane isomers rather than the lower-
octane olefin oligomers. Generally, the I/O ratio determines
the capital and operating costs for the process.
Lower I/O ratios reduce these costs and improve the process
economics. The optimum I/O ratio is chosen by balancing the
improvement in product quality against the higher capital
and operating costs resulting from increasing the I/O ratio.
·

20. Catalyst-to-olefin (C/O) ratio. The ratio of active catalytic sites
to olefins is a key parameter related to catalyst activity and
stability. A higher C/O ratio results in less deactivation per
pass through the reactor.
In liquid acid systems, such as the UOP HF Alkylation
process, this ratio is expressed as the acid-to-hydrocarbon
ratio. Liquid acid alkylation units are usually operated at a
constant acid circulation rate. In solid acid alkylation units,
the additional catalyst required to maintain a high C/O ratio
must be balanced against improved catalyst stability.

21. Reactant contact time. The reactant contact time with the
catalyst has a significant impact on product quality because
undesirable secondary reactions, such as isomerization and
cracking, occur at longer contact times.
These secondary reactions act to degrade alkylate product
quality. Determining the correct contact time that will
maximize alkylate product quality, while still achieving high
olefin conversion, is critical in optimizing the process design.
·

22.  Processes to remove impurities to extremely
low concentrations
 Use of fixed bed technology, employing
catalysts, catalytic absorbents and
regenerable adsorbents

23.  Low capital cost
 Easily retrofitted
 No environmental impact
 Dispose of spent material by recycling
 Minimal operator attention
 No feed losses
 Impurities removed to ppb levels
 Flexible and robust design

24.  Only remove reactive species
 May have a high operating cost.

25. •Liquid or Gas duty
•High Capacity
•Sharp Absorption Profile
•Effective in Dry Streams

26. •Sulfur compounds
•Halogen compounds
•Organometallics
•Mercury
•Nitrogen compounds
•Unsaturated hydrocarbons
•Oxygenates

27. CAPACITY DEPENDENT ON THE NATURE OF
THE SULFUR SPECIES:
H2S FULL REMOVAL
RSH FULL REMOVAL
RSSR PARTIAL REMOVAL
THIOPHENE NO REMOVAL
THIOPHENE DOES NOT "POISON" GUARD

28. MO + H2S → MS + H2O
MO + COS → MS + CO2
2 MS + Hg → M2S + HgS

29. Cu /Zn PRODUCT:
SINCE RSH / H2S IS THE PREDOMINANT
SULFUR SPECIES FOUND IN NAPHTHA,
THE MIXED METAL OXIDE (Cu / Zn)
OFFERS THE MOST COST EFFECTIVE
GUARD.
A Ni BASED MATERIAL MAY BE REQUIRED
IN SELECTIVE CASES TO POLISH LESS
REACTIVE SULFUR SPECIES, i.e., THIOPHENE

30. VULCAN GUARDS
PREDICTION OF SULFUR IN FEED

31.  Mercaptans: RSH + H2 → RH + H2S
 Sulfides: R2S + 2H2 → 2RH + H2S
 Disulfides: (RS2) + 3H2 → 2RH + 2H2S
 Thiophenes: C4H4S + 4H2 → C4H10 + H2S
 Aromatics: ArS + 2H2 → Aromatic + H2S
(excludes ring saturation)

32. The chemical reaction mechanism essentially involves the direct
desulfurization (DSD) path and to a lesser extent the more
hydrogen consuming hydrogenation route (HYD)..