side hóa học xanh phan thanh sơn nam

GREEN CHEMISTRY
Dr Nam T. S. Phan
Faculty of Chemical Engineering
HCMC University of Technology
Office: room 211, B2 Building
Phone: 38647256 ext. 5681
Email:
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Chapter 2:

CATALYSIS AND
GREEN CHEMISTRY

Why is catalysis important in making industrial
processes more efficient and economically profitable?

• Catalytic reagents reduce the energy of the
transition state, thereby reducing the energy
input required for a process
• Catalysts are required in small quantities
• The regeneration and reversibility of catalysts
are good for green processes
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No
catalyst

With

catalyst

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With catalyst: Less energy, less toxic reagents, less waste
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E factor
• E factor: The actual amount of waste produced in
the process (everything but the desired product
except water) / kg of product
• A higher E factor Æ more waste Æ greater
negative environmental effect
• Generally, the E factor increases dramatically on
going from bulk to fine chemicals, and then
pharmaceuticals Å multi-step syntheses +
stoichiometric reagents rather than catalysts for
the latter
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For example:

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Where is the waste from?
• Waste generated in the manufacture of organic
compounds consists primarily of inorganic salts
• Consequence of the use of stoichiometric
inorganic reagents
• For examples: Stoichiometric reductions with
metals (Na, Mg, Zn, Fe) and metal hydride
reagents (LiAlH4, NaBH4)
• Oxidation with KMnO4, CrO3 / H2SO4
• Sulfonations, nitrations, halogenations,
diazotizations and Friedel-Crafts acylations,
employing stoichiometric amounts of mineral
acids (H2SO4, HF, H3PO4) and Lewis acids (AlCl3,
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ZnCl2, BF3)


Solution to reduce waste?
• Substitution of classical stoichiometric
methodologies with cleaner catalytic alternatives
Catalyst

Stoichiometric
reagents

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Atom efficiency / economy

No
catalyst

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Atom efficiency / economy

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Classical aromatic chemistry

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Non-classical aromatic chemistry

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Two ways to hydroquinone
10 kg waste (MnSO4, FeCl2, NaCl, Na2SO4) / kg

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< 1kg waste / kg


Supported catalyst

Solid supports: polymer or silica

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Homogeneous Catalysts
•
•
•
•
•
•

High selectivity
Wide range available
High Cost
Catalyst Stability
Recycle Problem
Limited industrially

Heterogeneous Catalysts
•
•
•
•
•
•
•

Low Selectivity
Difficult to Functionalize
Ill-defined catalytic species
Limited Range of Reactions
Problems of Leaching
Ease of Recycle
Preferred Industrially

The ‘Holy Grail’: Immobilize a homogeneous
catalyst on an inert support to combine selectivity
with processability

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Using solid catalyst

Catalyst
separation by
filtration /
centrifugation

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Using solid catalyst

Reused catalyst

• Less waste

• Less energy consumed
• More possibility to recycle and
reuse
• Cleaner product

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Using homogeneous catalyst

Catalyst separation by column
chromatography / distillation / extraction

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Using homogeneous catalyst
• More waste
• More energy
consumed
• Less possibility to
recycle and reuse
• Product
contaminated with
toxic metals
• More toxic solvents
involved

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Homogeneous Friedel-Crafts acylation

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Heterogeneous Friedel-Crafts acylation

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Homogeneous synthesis of 2,6dichlorobenzonitrile

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Heterogeneous synthesis of 2,6dichlorobenzonitrile – less waste

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