 PONNALA SWATHI-B130896CH
 RAHUL CR-B130746CH
 REGHURAM V-B130245CH
CONTENTS

Raw Materials

Chemical Reactions

Properties

Flow Chart

Process descriptions

Engineering Problems

Alternate Process for Productions
RAW MATERIALS (HYDRODEALKYLATION )

Hydrodealkylation is the named process for the conversion of
toluene to benzene through reaction with hydrogen gas .
The principal raw materials for the process are obviously:
TOLUENE
HYDROGEN

Note: The above process can be used for preparing naphtha from
alkyl naphthalenes.
CHEMICAL REACTIONS

Toluene adds hydrogen gas to produce benzene
and methane.
2C6H5CH3 + H2 --------------> C6H6 + CH4

Dimethyl benzenes undergo similar reactions with
2 moles of hydrogen.
C6H4(CH3)2 + 2H2-------------> C6H6+2CH4
Properties of benzene

Molar mass : 78.11g/mole

Appearance: It is a colourless liquid with an odour
similar to that of most gasoline compounds.

Density: 0.8765 g/ cu.cm

Melting point: 278.68K

Boiling point:353.2K

Solubility: Soluble in chloroform, alcohols and
organic solvents.
Flow chart:
PROCESS DESCRIPTION:

Hydrodealkylation of toluene can be operated under
catalytic or thermal conditions. Catalytic process requires
milder conditions of 600-650oC and lower pressures
whereas the thermal process requires temperatures above
800oC.

Toluene is mixed with heavier aromatics or paraffins from
the benzene fractionation column.

The make up gas rich in hydrogen is compressed with
recycle gas and mixed with the liquid toluene stream.

The combined feed is then preheated using heat
exchange and then into a fired preheater before being
charged into the reactor.

The reactor effluents are cooled by heat exchange
and then by water before being sent to a separator.

The liquid and gas components are separated here.
The gas containing methane and remaining hydrogen
is either used directly as fuel or as a source of
methane.

The liquid is then sent to a stripping column where
residual gases are also removed.

The gas free liquid is then sent into the fractionator
where benzene is separated out.
Engineering Problems:

Reactor design: Catalytic processes were first utilised first
,operating at 600-650oC and pressure 35-40 atms.
Economic balances in yield include residence
time,temperature and reaction rates.Comparitive yields
were obtained at higher temperatures and pressures.

Hydrogen problems: The use of hydrogen requires
explosion-proof plant construction and its use at high
reaction conditions need use of chrome steel to avoid
embrittlement.
Other processes



Catalytic Reforming: Catalytic reforming involves
the dehydrogenation of naphthenes to aromatics,
or the isomerization of alkyl naphthenes and the
dehydrogenation of them.
Toluene disproportionation: Alkylated aromatics are
trans alkylated to produce benzene and alkylated
benzenes.
Pyrolysis gasoline distillation to remove benzene
and diolefins.
USES OF BENZENE

Benzene is mainly used as intermediate to make
their chemicals, most important of which include
cumene, ethyl benzene and cyclohexane.

It finds extensive use in producing precursors for
plastics, resins, rubber, pesticides, explosive
lubricant, detergents and fibres.
EXPOSURE AND HEALTH HAZARDS
• Benzene increases the risk of cancer and other illnesses, also
causing bone marrow failure ,aplastic anaemia, acute leukaemia
and related diseases in substantial amounts.
• It targets liver, kidney,lung,heart and the brain and can cause
DNA strand breaks.

Vapours from products that contain benzene such as
glues,paints,furniture,detergents etc. can also be a source of
exposure.

Exposure of the general population to benzene occurs while
breathing ,the major sources being tobacco smoke and
automobile service stations .

Certain batches of soft drinks manufactured across various
parts of the world have been found to contain benzene levels
above the limits prescribed by the world health organisation.
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