CHAPER 1: INTRODUCTION
1.2. MATERIALS INTRODUCTION
1.2.1 Bezene
1.2.1.1 Definition of Benzene
Benzene is an organic chemical compound with the molecular formula C6H6.
The benzene molecule is composed of six carbon atoms joined in a planar ring
with one hydrogen atom attached to each. Because it contains only carbon and
hydrogen atoms, benzene is classed as a hydrocarbon.
Benzene is a colorless and highly flammable liquid with a sweet smell, and is
partially responsible for the aroma of gasoline. Benzene and its measurement
continues to be important in the field of industrial hygiene. Although benzene
is a major industrial chemical, it finds limited use in consumer items because of
its toxicity.
1.2.1.2 Uses of Benzene
Benzene is a widely used industrial chemical and is a major part of gasoline.
Some other uses of Benzene include making plastics, synthetic fibres, rubber
lubricants, dyes, resins, detergents, drugs and more.
As a solvent
Manufacturers use products which contain benzene as solvents in various
production stages and it is used in manufacturing chemical and plastic products.
A few examples include resins, synthetic products such as nylon, Styrofoam
and others. Benzene is also used in the production of asphalt that is used by
roofing and paving companies.
As an intermediate
Benzene is also used in the production of tires and rubber and it is found in
adhesives that are used to glue soles to shoes. Further chemical compounds that
are manufactured using Benzene include detergents, pesticides insecticides,
herbicides, and dyes.
In printing industry
Benzene is found in most products that are used in the printing industry. There
are products that contain this chemical and are further used especially for
cleaning printing equipment which also makes them last longer and more
functional. Additionally, ink and a variety of painting products, such as spray
paints, sealers, lacquers and stains also contain some portion of benzene. It
keeps the paints in liquid form.
As a fuel
Due to the high octane number and natural availability, Benzene is used as a
fuel by a lot of people and manufacturers. Some have used it as a gasoline
additive to help burn fuel more efficiently.
1.2.1.3 Produce Benzene
Benzene is produced from product of catalyst reforming of naphtha fraction
and Aromatic complex. Benzene is also a high value commercial products of
the plant. Benzene is exported through Marine. A large volume of benzene is
made by the hydrodemethylation (HDM). According to a report by the U.S.
Department of Energy, more than a half of produced toluene is subsequently
used in the manufacture of benzene by an HDM process. In particular, the
Houdry Detol process produces benzene by combining streams of toluene and
hydrogen.
Figue 2.1 Structure of benzene
Properties
Value
Unit
Molecule weight
78
g/mol
Specific gravity
0.879
-
Boiling point
80.1
℃
Melting point
5.5
℃
Table 2.1 Physicals properties of benzene
1.2.2 Toluene
1.2.2.1 Definition of Toluene
Toluene, also known as toluol, is a substituted aromatic hydrocarbon. It is a
colorless, water-insoluble liquid with the odor associated with paint thinners.
Toluene occurs naturally in crude oil and in the tolu tree. It is a monosubstituted benzene derivative, consisting of a methyl group (CH3) attached to
a phenyl group.
Toluene reacts as a normal aromatic hydrocarbon in electrophilic aromatic
substitution. Because the methyl group has greater electron-releasing properties
than a hydrogen atom in the same position, toluene is more reactive
than benzene toward electrophiles. Toluene is one of the most abundantly
produced
chemicals.
Toluene
is
primarily derived
from petroleum or
petrochemical processes.
1.2.2.2 Uses of Toluene
Toluene is used in making paints, paint thinners, fingernail polish, lacquers,
adhesives, and rubber and in some printing and leather tanning processes. Its
main uses are as a precursor to benzene and xylenes, as a solvent for thinners,
paints, lacquers, adhesives, and as an additive for gasoline. The toluene is an
important commercial chemical product generally used as a dilution agent of
inks and as a solvent in the production of resins, glues and oils.
Nitration
Nitration of toluene gives mono-, di-, and trinitrotoluene, all of which are
broadly in use. Dinitrotoluene is the precursor to toluene diisocyanate. It is in
use for the manufacture of polyurethane foam. Trinitrotoluene is the explosive
typically abbreviated as TNT.
Oxidation
Benzoic acid and benzaldehyde are manufactured commercially by partial
oxidation of toluene with oxygen. The catalysts include cobalt or manganese
naphthenates
Fuel
Toluene is in use as an octane booster in gasoline fuels for internal combustion
engines as well as jet fuel. It was done by drawing energy from the water in the
cooling system to heat the fuel. Toluene was found to have been illegally
mixed with petrol in fuel outlets for sale as it was meant as a standard vehicular
fuel. Toluene incurs no fuel excise tax, though other fuels are taxed at more
than 40percent. It provides a greater profit margin for fuel suppliers.
1.2.2.3 Produce Toluene
It is also produced in the process of making gasoline and other fuels from crude
oil and making coke from coal. Toluene occurs naturally in crude oil at low
levels. It is a by-product in the production of gasoline by a catalytic
reformer or ethylene cracker. Toluene is also a by-product of the production
of coke from coal. The final separation and purification are done by
the distillation or solvent extraction processes that are in use for BTX aromatics
like benzene, toluene, and xylene isomers.
Figue 2.2 Structure of toluene
Properties
Value
Unit
Molecule weight
92
g/mol
Specific gravity
0.866
-
Boiling point
110.8
℃
Melting point
-95
℃
Table 2.2 Physical properites of toluene
1.2.3 Benzene - Toluene Mixture
The mono-aromatics hydrocarbons benzene and toluene are found in oil
derivatives and are widely used in chemical industries as raw materials for
synthesis of other products. Mixing of benzene and toluene does not involve
any kind of decrease or increase in interaction forces in between molecules so
they form ideal solution.
Solutions of benzene and toluene, which have very similar molecular structures,
are ideal: any mixture of the two has a volume equal to the sum of the volumes
of the separate components, and the mixing process occurs without absorption
or evolution of heat.
The boiling point of benzene is 80.1°C and the boiling point of toluene
is 110.6°C. Since the difference in their boiling points is very little, we can
separate Benzene and Toluene by fractional distillation.
x (％ mol)
y (％ mol)
T (℃)
0
0
110.6
5
11.8
108.3
10
21.4
106.1
20
38
102.2
30
51.1
98.6
40
61.9
95.2
50
71.2
92.1
60
79
89.4
70
85.4
84.4
80
91
82.3
90
95.9
82.3
100
100
80.2
Table 2.3 Liquid (X) - Vapor (Y) composition and boiling point of
Benzene - Toluene mixture at 1atm
Figue 2.3 Vapor – liquid equilibrium curve of benzene – toluene mixture
Figue 2.4 T – xy curve of benzene – toluene mixture