This document summarizes the hydrodealkylation process for converting toluene to benzene using hydrogen gas. It discusses the raw materials of toluene and hydrogen, the chemical reaction where toluene and hydrogen produce benzene and methane, properties of benzene, a flow chart of the process, descriptions of process steps including reactor design and hydrogen issues, alternative processes, uses of benzene, and health hazards of benzene exposure.

1.  PONNALA SWATHI-B130896CH
 RAHUL CR-B130746CH
 REGHURAM V-B130245CH

2. CONTENTS
 Raw Materials
 Chemical Reactions
 Properties
 Flow Chart
 Process descriptions
 Engineering Problems
 Alternate Process for Productions

3. 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.

4. 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

5. 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.

6. Flow chart:

7. 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.

8.  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.

9. 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.

10. 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.

11. 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.

12. 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.

13.  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.

14. THANK
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