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.

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DEDICATIONThis work is dedicated to the almighty God for his numerous kindness towards

me.

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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.

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TABLE OF CONTENTS

Table of ContentsABSTRACT.............................................................................................................................................. ii

DEDICATION.......................................................................................................................................... iii

ACKNOWLEDGEMENT........................................................................................................................... iv

TABLE OF CONTENTS.............................................................................................................................v

CHAPTER 1..........................................................................................................................................1

CHAPTER 2..........................................................................................................................................5

CHAPTER 3........................................................................................................................................10

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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.

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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–

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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.

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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

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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.

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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

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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

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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.

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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.

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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

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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

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Figure 4 Typical Yields of the HF process

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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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