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Catalytic Hydrogenation of Aromatic Nitro Compounds Steve Hallam, Process Safety, Supply Chain, Pharmaceutical Development, Ch i Ph ti l D l t Macclesfield, UK
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•The reduction of aromatic nitro compounds using
Introduction
0, X i ’a n catalyst and hydrogen is a commonly used reaction within the chemical industry.
C P 201•
The reaction is potentially hazardous as problems can arise from a number of different sources.
c t n a m e
h o p S T P o r p r o j e a l W o r k s a r t m e n t t e r n a t i o n D e p 3r d I n
Going to look at :•
Hazards related to Starting Materials
Going to look at :-0, X i ’a n •Hazards due to hydrogen, solvents, catalysts and nitro starting
compounds C P 201p
•
Hazards due to Hydrogenation Reaction
c t n a m e
h o p S T P •Hazards due to Desired Reaction (heat generation and
thermal instability)
o r p r o j e a l W o r k s •
Hazards due to Formation of Unstable Intermediates (formation of hydroxylamines)
a r t m e n t t e r n a t i o n •
Incident (Du Pont, USA)
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Hydrogen has a very low ignition energy and mixtures
Hydrogen, Catalysts & Solvents
0, X i ’a n •Hydrogen has a very low ignition energy and mixtures in air are explosive over a large range of concentrations.
C P 201co ce t at o s •Hydrogenation catalysts are pyrophoric when in contact with air.
c t n a m e
h o p S T P •Hydrogenation reactions are often run in organic
solvents. Hazards associated with flammability are
o r p r o j e a l W o r k s y therefore present.
•
The hazards associated with hydrogen,
a r t m e n t t e r n a t i o n hydrogenation catalysts and solvents will be dealt with in Mark’s presentation.
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Aromatic Nitro Compounds
0, X i ’a n •Aromatic nitro compounds have high heats of
decomposition, typically of the order of 2000kJ/mol.C P 201•
The decomposition reactions are usually fast.
•There is evidence to show that the thermal stability of c t n a m e
h o p S T P aromatic nitro compounds is reduced in the presence of catalysts.
o r p r o j e a l W o r k s •It is essential that the thermal stability of the starting nitro compound is determined.Wh thi i k t t li it b a r t m e n t t e r n a t i o n •
When this is known an upper temperature limit can be set.
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Hazards due to Hydrogenation Reaction
Th t l ti d ti f ti it d
Heat of Reaction
0, X i ’a n •The catalytic reduction of aromatic nitro compounds is very exothermic.
Th h t f ti i t i ll d 550kJ/l C P 201•The heat of reaction is typically around -550kJ/mol of nitro compound.
Th t ti l th f i t f th ti f c t n a m e
h o p S T P •The potential therefore exists for the generation of very large temperature rises.
The m ltiphase reaction mi t re is affected b mass o r p r o j e a l W o r k s •The multiphase reaction mixture is affected by mass transfer and, in most cases, is easy to control.The rate of reaction can be controlled by mixing
a r t m e n t t e r n a t i o n •
reaction between pvp and aminoThe rate of reaction can be controlled by mixing intensity, hydrogen pressure and amount of catalyst.
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