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A TERM PAPER ON ALKYLATION, ITS PRODUCTS AND OPTIMAL CONDITIONS FOR PRODUCTION
PRESENTED BY
GROUP 2 GAS ENGINEERING
U2005/3070211-221
DEPARTMENT OF PETROLEUM AND GAS ENGINEERING (GAS OPTION)
FACULTY OF ENGINEERING
UNIVERSITY OF PORT HARCOURT
COURSE TITLE: CATALYSIS & FUEL SYNTHESIS
COURSE CODE: GNG 507.1
COUSRE LECTURER: DR. OGBONNA JOEL
APRIL, 2010
ABSTRACTAlkylation is a chemical process which has found widespread use in various industries
spread across the various sectors of the global economy. Especially of concern to
students in the Energy industry is the usage of alkylation in the petroleum refining
industry. In the petroleum industry, a chemical process in which an olefin (ethylene,
propylene, and so forth) and a hydrocarbon, usually 2-methylpropane, are combined to
produce a higher-molecular-weight and higher-carbon-number product. The product
has a higher octane rating and is used to improve the quality of gasoline-range fuels.
Alkylation, which was first commercialized in 1938, experienced a lot of growth in
the 1940’s as a result of high demand for high-octane fuels for fighter jets during
world war 2. Its current main application is in the production of unleaded
automotive gasoline. This paper intends to talk on the process itself, its products and
the optimum conditions required for maximum production.
ii
DEDICATIONThis work is dedicated to the almighty God for his numerous kindness towards
me.
iii
ACKNOWLEDGEMENTThe efforts of all members of group two who in one way or the other helped in bringing to completion this work are all appreciated.
iv
TABLE OF CONTENTS
Table of ContentsABSTRACT.............................................................................................................................................. ii
DEDICATION.......................................................................................................................................... iii
ACKNOWLEDGEMENT........................................................................................................................... iv
TABLE OF CONTENTS.............................................................................................................................v
CHAPTER 1..........................................................................................................................................1
CHAPTER 2..........................................................................................................................................5
CHAPTER 3........................................................................................................................................10
v
CHAPTER 1
Alkylation is a process in which one or more alkyl groups are substituted for
hydrogen atoms in an organic compound or the transfer of an alkyl group from
one molecule to another. The alkyl group may be transferred as an alkyl carbocation,
a free radical, a carbanion or acarbene.
Alkyl groups range from single carbon compounds such as methyl groups to much
longer chains of hydrocarbons, and are probably the most common type of organic
molecule. Alkylation is of great importance both in cell biology and in industrial
processes such as petroleum refining.
There are several different types of alkylation. These types are classified based on the
character of the alkylating agent. The two broad types of Alkylating Agents are the
Nucleophilic Alkylating Agent and the Electrophilic Alkylating Agents.
Nucleophilic alkylating agents deliver the equivalent of an alkyl anion (carbanion).
Examples include the use of organometallic compounds such as Grignard
(organomagnesium), organolithium, organocopper, and organosodium reagents. These
compounds typically can add to an electron-deficient carbon atom such as at
a carbonyl group. Nucleophilic alkylating agents can also displace halidesubstituents
on a carbon atom. In the presence of catalysts, they also alkylate alkyl and aryl
halides, as exemplified by Suzuki couplings.
1
Electrophilic alkylating agents deliver the equivalent of an alkyl cation. Examples
include the use of alkyl halides with a Lewis acid catalyst to
alkylate aromaticsubstrates in Friedel-Crafts reactions. Alkyl halides can also react
directly withamines to form C-N bonds; the same holds true for other nucleophiles
such as alcohols, carboxylic acids, thiols, etc.
Electrophilic, soluble alkylating agents are often very toxic, due to their ability to
alkylate DNA. They should be handled with proper PPE. This mechanism of toxicity
is also responsible for the ability of some alkylating agents to perform as anti-cancer
drugs in the form of alkylating antineoplastic agents, and also as chemical
weaponssuch as mustard gas. Alkylated DNA either does not coil or uncoil properly,
or cannot be processed by information-decoding enzymes. This results in cytotoxicity
with the effects of inhibition the growth of the cell, initiation of programmed cell
deathor apoptosis. However, mutations are also triggered,
including carcinogenicmutations, explaining the higher incidence of cancer after
exposure.
Alcohols and phenols can be alkylated to give alkyl ethers:
R-OH + R'-X → R-O-R' + H-X
The produced acid HX is removed with a base, or, alternatively, the alcohol is
deprotonated first to give an alkoxide or phenoxide. For example, dimethyl
sulfatealkylates the sodium salt of phenol to give anisole, the methyl ether of
phenol. The dimethyl sulfate is dealkylated to sodium methylsulfate.[3]
Ph-O– Na+ + Me2SO4 → Ph-O-Me + Na+ MeSO4–
2
On the contrary, the alkylation of amines introduces the problem that the
alkylation of an amine makes it more nucleophilic. Thus, when an
electrophilic alkylating agent is introduced to a primary amine, it will
preferentially alkylate all the way to a quaternary ammonium cation.
R-NH2 → R-NH-R' → R-N(R')2 → R-N(R')3+ (alkylating agent omitted for
clarity)
If the quaternary ammonium is not the desired product, more circuitious
routes such as reductive amination are necessary.
Electrophilic alkylation is often highly toxic, due to its ability to alkylate the bases of
DNA. This is of very serious importance in cell biology as DNA which has been
subject to alkylation either does not coil or uncoil properly, or cannot be decoded.
This property is taken advantage of by alkylating antineoplastic agents, which are
used in chemotherapy to attack the DNA of cancer cells. A less scrupulous use of
these agents is as mustard gas poisons.
One specialized type of alkylation is methylation, in which the one carbon methyl
group replaces a hydrogen atom. In cells, this reaction is mediated by enzymes and
frequently targets DNA or proteins. Humans have hundreds of different methylation
reactions that take place. They frequently cause a change in a reaction, such as the
activation of gene expression or enzyme activity. Methylation can be a way of
regulating the inheritance of genes outside of the usual method of DNA inheritance;
this is known as epigenesist.
3
4
CHAPTER 2
ALKYLATION IN OIL REFINING
Figure 1 Schematic Showing Alkylation in the Petroleum Refining Process
In a standard oil refinery process, isobutane is alkylated with low-molecular-weight
alkenes (primarily a mixture of propylene and butylene) in the presence of a strong
acid catalyst, either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to
as a sulfuric acid alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU).
Refinery workers may simply refer to it as the alkyl or alkyl unit. The catalyst
5
protonates the alkenes (propylene, butylene) to produce reactive carbocations, which
alkylate isobutane. The reaction is carried out at mild temperatures (0 and 30 °C) in a
two-phase reaction. It is important to keep a high ratio of isobutane to alkene at the
point of reaction to prevent side reactions which produces a lower octane product, so
the plants have a high recycle of isobutane back to feed. The phases separate
spontaneously, so the acid phase is vigorously mixed with the hydrocarbon phase to
create sufficient contact surface.
The product is called alkylate and is composed of a mixture of high-octane, branched-
chain paraffinic hydrocarbons (mostly isopentane and isooctane). Alkylate is a
premium gasoline blending stock because it has exceptional antiknock properties and
is clean burning. Alkylate is also a key component of avgas. The octane number of the
alkylate depends mainly upon the kind of alkenes used and upon operating conditions.
For example, isooctane results from combining butylene with isobutane and has an
octane rating of 100 by definition.
The octane number of the gasoline depends on the compounds used and operating
conditions. An octane rating of 100 would be gasoline comprised entirely of
isooctane, a compound that is added to unleaded gasolines to prevent knocking. It is
possible for a fuel to have a rating higher than 100, since isooctane is not the most
knock-resistant fuel available.
There are other products in the alkylate, so the octane rating will vary accordingly.
6
Since crude oil generally contains only 10 to 40 percent of hydrocarbon constituents
in the gasoline range, refineries use a fluid catalytic cracking process to convert high
molecular weight hydrocarbons into smaller and more volatile compounds, which are
then converted into liquid gasoline-size hydrocarbons. Alkylation processes transform
low molecular-weight alkenes and iso-paraffin molecules into larger iso-paraffins with
a high octane number.
Combining cracking, polymerization, and alkylation can result in a gasoline yield
representing 70 percent of the starting crude oil. More advanced processes, such as
cyclicization of paraffins and dehydrogenation of naphthenes forming aromatic
hydrocarbons in a catalytic reformer, have also been developed to increase the octane
rating of gasoline. Modern refinery operation can be shifted to produce almost any
fuel type with specified performance criteria from a single crude feedstock.
In the entire range of refinery processes, alkylation is a very important process that
enhances the yield of high-octane gasoline. However, not all refineries have an
alkylation plant. The oil and gas journal annual survey of worldwide refining
capacities for January 2007 lists many countries with no alkylation plants at their
refineries.
Refineries examine whether it makes sense economically to install alkylation units.
Alkylation units are complex, with substantial economy of scale. In addition to a
suitable quantity of feedstock, the price spread between the value of alkylate product
and alternate feedstock disposition value must be large enough to justify the
installation. Alternative outlets for refinery alklylation feedstocks include sales as
7
Liquified Petroleum Gas (LPG), blending of C4 streams directly into gasoline and
feedstocks for chemical plants. Local market conditions vary widely between plants.
Variation in the Reid Vapour Pressure) RVP specification for gasoline between
countries and between seasons dramatically impacts the amount of butane streams that
can be blended directly into gasoline. The transportation of specific types of LPG
streams can be expensive so local disparities in economic conditions are often not
fully mitigated by cross market movements of alkylation feedstocks.
The availability of a suitable catalyst is also an important factor in deciding whether to
build an alkylation plant. If sulfuric acid is used, significant volumes are needed.
Access to a suitable plant is required for the supply of fresh acid and the disposition of
spent acid. If a sulfuric acid plant must be constructed specifically to support an
alkylation unit, such construction will have a significant impact on both the initial
requirements for capital and ongoing costs of operation. Alternatively it is possible to
install a WSA Process unit to regenerate the spent acid. No drying of the gas takes
place. This means that there will be no loss of acid, no acidic waste material and no
heat is lost in process gas reheating. The selective condensation in the WSA condenser
ensures that the regenerated fresh acid will be 98% w/w even with the humid process
gas. It is possible to combine spent acid regeneration with disposal of hydrogen
sulfide by using the hydrogen sulfide as a fuel.
The second main catalyst option is hydrofluoric acid. Rates of consumption for HF
acid in alkylation plants are much lower than for sulfuric acid. HF acid plants can
process a wider range of feedstock mix with propylenes and butylenes. HF plants also
8
produce alkylate with better octane rating than sulfuric plants. However, due to the
hazardous nature of the material, HF acid is produced at very few locations and
transportation must be managed rigorously.
9
TABLE IV: 2-17. ALKYLATION PROCESS
Feedstock From Process Typical products . . . . To
Petroleum
gas
Distillation or
cracking
Unification High octane gasoline . . Blending
Olefins Cat. or hydro
cracking
n-Butane & propane . . . Stripper or blender
Isobutane Isomerization
CHAPTER 3
DIFFERENT KINDS OF ALKYLATION
Sulfuric Acid Alkylation Process.
a. In cascade type sulfuric acid (H2SO4) alkylation units, the feedstock
(propylene, butylene, amylene, and fresh isobutane) enters the reactor
and contacts the concentrated sulfuric acid catalyst (in concentrations
of 85% to 95% for good operation and to minimize corrosion). The
reactor is divided into zones, with olefins fed through distributors to
each zone, and the sulfuric acid and isobutanes flowing over baffles
from zone to zone.
b. The reactor effluent is separated into hydrocarbon and acid phases
in a settler, and the acid is returned to the reactor. The hydrocarbon
phase is hot-water washed with caustic for pH control before being
successively depropanized, deisobutanized, and debutanized. The
alkylate obtained from the deisobutanizer can then go directly to
motor-fuel blending or be rerun to produce aviation-grade blending
stock. The isobutane is recycled to the feed.
10
Figure 2 Sulfuric Acid Alkylation Process
Hydrofluoric Acid Alylation Process. Phillips and UOP are the two common
types of hydrofluoric acid alkylation processes in use. In the Phillips process,
olefin and isobutane feedstock are dried and fed to a combination
reactor/settler system. Upon leaving the reaction zone, the reactor effluent
flows to a settler (separating vessel) where the acid separates from the
hydrocarbons. The acid layer at the bottom of the separating vessel is
recycled. The top layer of hydrocarbons (hydrocarbon phase), consisting of
propane, normal butane, alkylate, and excess (recycle) isobutane, is charged
to the main fractionator, the bottom product of which is motor alkylate. The
main fractionator overhead, consisting mainly of propane, isobutane, and HF,
goes to a depropanizer. Propane with trace amount of HF goes to an HF
stripper for HF removal and is then catalytically defluorinated, treated, and
sent to storage. Isobutane is withdrawn from the main fractionator and
11
recycled to the reactor/settler, and alkylate from the bottom of the main
fractionator is sent to product blending.
The UOP process uses two reactors with separate settlers. Half of the dried
feedstock is charged to the first reactor, along with recycle and makeup
isobutane. The reactor effluent then goes to its settler, where the acid is
recycled and the hydrocarbon charged to the second reactor. The other half of
the feedstock also goes to the second reactor, with the settler acid being
recycled and the hydrocarbons charged to the main fractionator. Subsequent
processing is similar to the Phillips process. Overhead from the main
fractionator goes to a depropanizer. Isobutane is recycled to the reaction zone
and alkylate is sent to product blending.
Figure 3 Hydrogen Flouride Alkylation
12
Figure 4 Typical Yields of the HF process
13
REFERENCES
1. March Jerry; (1985). Advanced Organic Chemistry reactions, mechanisms and
structure (3rd ed.). New York: John Wiley & Sons, inc.
2. Stefanidakis, G.; Gwyn, J.E. (1993). "Alkylation". in John J.
McKetta. Chemical Processing Handbook. CRC Press. pp. 80–138.
3. G. S. Hiers and F. D. Hager (1941), "Anisole", Org. Synth.; Coll. Vol. 1: 58
4. Sulphur recovery; (2007). The Process Principles, details advances in sulphur
recovery by the WSA process. Denmark: Jens Kristen Laursen, Haldor Topsøe
A/S. Reprinted from Hydrocarbonengineering August 20075. http://www.wikipedia.com accessed 23/03/20106. http://www.eoearth.org/article/Alkylation_in_petroleum_refining accessed
21/03/2010
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