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:
1


Chapter 3:

SOLVENT AND GREEN
CHEMISTRY

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3


4


Solvents used in synthesis &
product separation /
purification

5

Why are reactions performed using solvents?
• To dissolve
reactants.
• To slow or
increase the rate
of reactions.
• To act as a heat
sink or heat
transfer agent.
• To prevent hot
spots and runaway reactions
6


Several solvents are volatile organic compounds
(VOCs) Æ toxic, flammable Æ environmental, health,
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and safety concerns


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9


Principle 8 of green
chemistry: Use safer
solvents and
reaction conditions:

Avoid using
solvents, separation
agents, or other
auxiliary chemicals.
If these chemicals
are necessary, use
innocuous
chemicals
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11


The best solvent is no solvent

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Advantages of solvent-free conditions
1. There is no reaction
media to collect,
dispose of, or purify and
recycle.
2. On a laboratory’s
preparative scale, there
is often no need for
specialized equipment.
3. Extensive and
expensive purification

procedures such as
chromatography can
often be avoided.

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Advantages of solvent-free conditions
4. Greater selectivity is
often observed.
5. Reaction times can be
rapid, often with increased
yields and lower energy
usage.
6. Economic considerations
are more advantageous,
since cost savings can be
associated with the lack of
solvents requiring disposal
or recycling.

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Limitations of solvent-free conditions
• Not all reactions will
work in the absence of
solvent
• Exothermic reactions
are potentially

dangerous
• If aqueous quench
and organic extraction
are performed, this
reduces green
benefits
15


Supercritical Fluids
Moves like a gas
and dissolves
things like a
liquid

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Pressure (bar)

SOLID

SUPERCRITICAL
FLUID
Critical
point
•

74
LIQUID

GAS

Triple
point •

CO2
Temperature (K)

303
17


Pressure (bar)

SOLID

SUPERCRITICAL
FLUID
Critical
point
•

74
LIQUID
Triple
point •

GAS

Temperature (K)

303
18


Pressure (bar)

SOLID
Critical
point
•

74

SUPERCRITICAL
FLUID

LIQUID
Triple
point

GAS
•

Temperature (K)

303
19

Pressure (bar)

SOLID

SUPERCRITICAL
FLUID

Critical
point
74

•
LIQUID
Triple
point •

GAS

Temperature (K)

303
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Why use sc fluids?
•
•
•
•
•

•
•
•

Increased mass transport
Gases are totally miscible
No surface tension
Excellent for infusion and
extraction
Inert and non-toxic
Inexpensive fluids
Environmentally compatible
Solvent is tuneable with
pressure
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Can sc fluids be scaled up?
• One of the biggest chemical reactions

(polythene production) is carried out under
sc conditions

• Natural products such as Caffeine and hops
extract obtained using scCO2

• Union Carbide developed a spray painting

process using scCO2 which decreases VOC
emissions by 80%

• Thomas Swan & Co Ltd have built a SCF

plant for continuous synthesis with
capacity of up to 1000 tonnes per year
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Deven Supercriticals
Pvt. Ltd offer Pilot and
Commercial scale
Supercritical Fluid (SCF)
Processing plants

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Synthesis with ScCO2

Organic and water layers are easily separated to leave clean
product, which can be directly analyzed by 1H NMR 25