delhi technological university

NARENDER SINGHDTU/2K14/B7/1085

de

Green solvent or also known as bio-solvent is typically an alternative to the conventional solvents

available in the market. It is an innovative idea of reducing the environmental impact resulting from the

use of solvents in chemical production.

CHARACTERISTICS OF GREEN SOLVENTS

Green solvent has a lower environmental impact compared to other conventional petroleum-based

solvents. Besides, it has a host of advantages that gives it an added boost to edge out its rivals.

Completely biodegradable

Can be recycled

Non-corrosive

Non-carcinogenic

Non-ozone depleting

Attractive solvent properties

THE NEED FOR GREEN SOLVENTS

Play a major role in many areas of technology

Provide many opportunities for improvement of environmental aspects.

Represent a very large proportion of the volatile organic compounds (VOCs) released into the

atmosphere.

£1,000 million spent on environmental technology, much of which is end of pipe equipment and

associated operating costs to clean up emissions and air.

THE VARIOUS GREEN SOLVENTS

No solvent “solventless reactions”

Super critical fluids

Water

Ionic liquids

Simplest solution

Fails on large scale – Exothermic reactions can be dangerous reactions can be dangerous

Problem in mixing – especially in case of Solids

Solvents still required for extraction, separation and purification of products.

EXAMPLE- polymerisation of propene – (Catalyst is soluble in liquid propene)

NO SOLVENT- “solventless reactions”

GREEN SOLVENTS

MAIN DISADVANTAGES OF SOLVENT-FREE SYNTHESES:

solvents are often still required during work-up (e.g. extraction)

poor heat transfer in the solid state (although this may be overcome using microwaves)

Substance at a temperature and pressure above its critical point

Diffuse through solids like a gas dissolve materials like a liquid

Suitable substitute for organic solvents

Carbon dioxide and water are the most commonly used

Supercritical fluids are intermediate between liquids and gases

SUPERCRITICAL CO 2

Similar advantages to water -Natural, cheap, plentiful (too much of it!)

Easily removed and recycled, and can be disposed of with no net increase in global CO2

No solvent effluent

ADVANTAGES DISADVANTAGES

• Non-toxic & cheaply available

• Readily removed (and recyclable)

• Non-flammable

• Low viscosity (fast diffusion)

• Good solvent of gases (e.g. H2)

• High pressure equipment is expensive

and potentially dangerous

• CO2 is a relatively poor solvent

• Reacts with strong nucleophiles (e.g.

amines)

EXAMPLE –Imine hydrogenation (20 times faster in SC-CO2 than CH2Cl2)

USES OF SUPERCRITICAL-CO 2 :

• extraction of caffeine from coffee (traditional method uses CH2Cl2)

• dry-cleaning (traditional method uses C2Cl4) & spray-painting

One of the most obvious alternatives to VOCs.

Cheap, readily available, and plentiful

Clean up of aqueous waste difficult

Useful in biphasic processes in conjunction with other solvents

SUPERCRITICAL FLUIDS

WATER AS A GREEN SOLVENT

ADVANTAGES DISADVANTAGES

Non-toxic

Cheap

Biorenewable

Non-flammable

High specific heat capacity

Removal requires distillation∴ energy intensive

Waste streams may be difficult to treat

Many reagents are water-sensitive

Generally a poor solvent for organics

EXAMPLE -geraniol isomerisation - a source of fragrances without organic solvents.

Typically consist of organic cation (often ammonium or phosphonium salt) and inorganic anion

Usually only consider IL’s which are liquid at room temperature

Great variety of structures possible

Very low vapour pressure – attractive alternative to VOCs.

Good solvents for a wide range of organic, inorganic and polymeric compounds

ADVANTAGES DISADVANTAGES

• Readily prepared

• Can act as catalysts

• Tuneable viscosity (via anion)

• Stable at high temperature

• Highly solvating

• Non-biodegradable

• Concerns over toxicity

• Synthesis often requires haloalkanes

• Product isolation often requires distillation or

extraction into an organic solvent

USES OF IONIC LIQUID

Solvents for catalysis

Metal deposition e.g. Al

Desulphurisation of oil

Lubricants & Anti-static agents

APPLICATIONS OF GREEN SOLVENTS

Replacing VOCs and Chlorinated solvents

New syntheses of ibuprofen and Zoloft.

Integrated circuit production & Getting the lead out of automobile paints.

Many new pesticides & Biodegradable polymers from renewable resources.

N N

1. Ethylmethylimidazoliumtetrafluoroborate, [emim][BF4]

•BF4-

2.Choline chloride/Zinc chlorideionic liquid

N+

Me

Me

Me

OH+

•Zn2Cl5-

IONIC LIQUIDS