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Solomon Derese (PhD)Department of Chemistry

University of Nairobisderese@uonbi.ac.ke

http://profiles.uonbi.ac.ke/sderese

Green Economy - Through Green Chemistry

ReferencesAnastas, P. T. and Warner, J. C. (1998). Green Chemistry: Theory and Practice, Oxford University, New York.Anne E. Marteel-Parrish and Martin A. Abraham (2014). Green chemistry and engineering : a pathway to sustainability, John Wiley & Sons, New Jersey.

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Contribution of Chemistry to Society

O

O OH

CH3

OAcetyl Salicylic Acid

A.S.A.90% yield

OH

O OH

Salicylic Acid

+ H3C O

O

CH3

O

Acetic anhydride

H3C H

O

Acetaldehyde

Cu(acetate)2

liquid phase50EC, 3-4 bar

+

Shawinigan(Canada)

PdCl2 / CuCl2 Wacker-HoechstProcess

H2C CH2 + 0.5Ethylene

ONaOH

Phenol

2. H2SO4

Kolbe-Schmittreaction

2. H2SO4

1. O2

Hockprocess

Cumene

+Benzene Propylene

FOSSIL FUELS:LPG, Coal, Petroleum, etc.

catalyticprocesses

thermalcracking

1. CO2

thermalcracking

liquid phaseT & P > STP

Kellogg/Monsanto

T < 90EC

O2

O2

NaOH

H2SO4

Pharmaceutical Drugs to Treat Ailments: Aspirin®

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Epichlorohydrin Epoxy resin• Structural adhesives• Structural sealants• Primer paints• Electrical insulation• Fiber reinforced plastic

composites

Bisphenol A or Brominated Bisphenol A

• Tires• Rubber hoses• Foam for seats• Caulks & sealants• Bumpers & fenders

Vinyl

• Dashboards• Electrical insulation• Vinyl tops• Floor mats

• Body side moldings• Molded armrests• Exterior & interior trim

• Upholstery • Modular window

frame units

Polyurethanes Polyisocyanates

Cl2Vinyl chloride monomer

Ethylene

Cl2

CO2

Phosgene

Cl2 Allyl chloride

Propylene BTX

The Cars we use - Organic Chemistry of the Automobile

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World chemicals sales in 2010 are valued at € 2,353 billion

5The Chemical industry is a significant contributor to world economy .

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Throughout history, chemists have discovered somerevolutionary molecules and synthetic pathways that bringnew products and technologies to society.

Production techniques have often neglected the impact ofthese materials and processes on the environment.

This has resulted in harmful effect on the biotic as well asabiotic environment.

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Unintended Negative Impact of Chemistry

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Toxic Chemicals in the Environment

SO2 NOx Heavy metals (Hg, Pb etc.)

H2SO4 NH3

NO3 Hg Pb

Toxic substances

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The industrial disaster of 1984 in Bhopal,India, was caused by the release of 40tons of methyl isocyanate gas by a UnionCarbide pesticide plant, resulting from aseries of worker errors and safety issuesthat had not been properly addressed.

Industrial Disaster Releasing Toxic Chemicals in the Environment

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Plastics Polluting the Environment

It takes more than a 1000 years for plastics to degrade!!

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Lead Poison from the Lead Battery Smelter in Owino Uhuru

“ .. the soil they walk on, the water they drink and the food they eat is contaminated by lead ….”

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This is not sustainable, leading to a new thinking/revolution

called Green Chemistry.

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Green chemistry (a term coined in 1991) is defined as “the utilization of a set of principles

that reduces or eliminates the use

or generationof hazardous substances in

the design, manufacture

and application of chemical products”

Green Chemistry is Based on Twelve (12) Principles.

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Green chemistry applies fundamental chemical principles to producechemical products that are inherently less toxic, either to humans or tothe ecosystem, than currently existing chemical products.

It is applied to any of the various elements of the chemical product lifecycle, from manufacture, to use, and ultimately to disposal.

Thus, green chemistry may be applied to the production of a particularchemical to minimize the hazard associated with its use, or it may focuson the manufacture of the chemical to minimize the environmentalconsequences of the by-products or the synthesis, or it may equally welllook into the development of more environmentally friendly alternativesto a specific chemical. Regardless, green chemistry seeks to reduce thehazard associated with chemical species.

How

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2. Atom Economy 3.Less Hazardous Chemical Syntheses

4. Designing Safer Chemicals 5. Safer Solvents and Auxiliaries

6. Design for Energy Efficiency 7. Use of Renewable Feedstock

8. Reduce Derivatives 9. Catalysis

12. Inherently Safer Chemistry for Accident Prevention

11. Real-time analysis for Pollution Prevention

10. Design for Degradation

1. Prevention The Twelve (12) Principles of Green Chemistry

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• It is better to prevent waste than to treat or clean up waste after ithas been created.

• Prevention starts by avoiding the use or generation of hazardoussubstances. If hazardous materials are not produced, then treatmentand disposal are not required.

• Moreover, extraordinary safety measures needed for themanufacture of hazardous materials are not required, making thegreen product less costly to produce and easier to use.

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1. Prevention

Prevent rather than treat

Ozone depleting ChloroFluoroCarbons(CFCs) or flammable hydrocarbons had beenused as a blowing agent in the productionof polystyrene foam.Dow Chemical discovered that supercriticalcarbon dioxide, which is neither ozone-depleting nor flammable, could be used as aneffective blowing agent, and, because thecarbon dioxide they use is sourced from otherindustries where it as a waste product, itsimpact on the human-induced greenhouseeffect is negligible.

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Replacing Ozone Depleting CFCs

• Synthetic methods should be designed to maximize the incorporationof all materials used in the process into the final product.

• Atom economy is a measure of how much of the reactants are actuallyincorporated into the products.

• Atom economy is an essential tool in measuring how much waste isbeing produced.

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2. Atom Economy

Maximize use of materials – atom economy

퐴푡표푚푒푐표푛표푚푦 = ∑ x 100%

A + B P + Waste

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Epoxidation of Styrene

Molecular Weight 104.15 172.56 120.15

퐴푡표푚푒푐표푛표푚푦 = ∑ x 100% = .

. .= 43.4%

Assuming 100% yield, the atom economy of the reaction is 43.4 % and66.6% of the product is waste. An alternative method that avoids theproduction of waste should be designed.

Waste

• Wherever practicable, synthetic methods should be designed to useand generate substances that possess little or no toxicity to humanhealth and the environment.

• The use of hazardous chemicals is linked to risk of harm. Risk can bewritten as the product of exposure and hazard.

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3. Less Hazardous Chemical Syntheses

Avoid hazardous materials (reagents, starting materials and solvents) and products or by-products

푹풊풔풌 = 푬풙풑풐풔풖풓풆풙푯풂풛풂풓풅

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Synthesis of Polycarbonates

Advantages Polycarbonate synthesized without phosgene Solid state process, eliminates use of CH2Cl2 higher-quality polycarbonates

Polycarbonate

Disadvantagesphosgene is highly toxic, corrosiverequires large amount of CH2Cl2

polycarbonate contaminated with Cl impurities

Diphenylcarbonate

Phosgene

• Chemical products should be designed to achieve their desiredfunction while minimizing their toxicity.

• Many chemicals are multifunctional, with a specific portion of themolecule providing the desired function while another portion of themolecule might impart some undesirable toxicity characteristics.

• Careful analysis of a selected chemical can elicit which elements of themolecule provide the desired and undesired functions.

• By redesigning the molecule, the functionality related to the toxiceffect can then be avoided, minimized, or totally suppressed, while thefunctionality providing the desired activity is retained.

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4. Designing Safer Chemicals

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Solberg Co., a leading global maker of the foams, addressed the issue bydesigning a halogen-free foaming liquid concentrates in whichhalogenated materials are replaced by an environmentally benign blendof biobased surfactants and complex carbohydrates. The foams arebiodegradable, completely falling apart after six weeks.

Fluorinated surfactants are critical components of firefighting foams. But the surfactants come with significant health and environmental concerns because they are persistent, bioaccumulative, and toxic.

Replacement of Environmentally Unfriendly Firefighting Foam withEnvironmentally Benign Foam

• The use of auxiliary substances (e.g., solvents and separation agents)should be made unnecessary wherever possible and innocuous whenused.

• Whenever possible, reactions should be developed with theenvironmental impacts of the solvent in mind, and benign solventssuch as supercritical CO2 or water, immobilized solvents, or solventlesssystems should be considered.

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5. Safer Solvents and Auxiliaries

In the first commercial synthesis ofViagra by Pfizer, 31 L of solvents per kg ofproduct were used. The newermicrowave-mediated synthesis requiresonly 10 L of solvents per kg of product forthe production of Viagra.

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Reducing the use of Toxic Organic Solvents

Reactions without solvents

Synthesis with minimum solvents

N

NS

O

O

N

NN

HN

O

O

Viagra

• Energy requirements of chemical processes should berecognized for their environmental and economic impactsand should be minimized.

• Synthetic methods that are conducted at ambienttemperature and atmospheric pressure consume lessenergy than those that are done at high temperature andpressure.

• Use of greener source of energy should be encouraged.

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6. Design for Energy Efficiency

Sources of Energy

Non-renewable RenewableFossil fuels Biomass

Crude oilNatural gasCoal, etc

Organic wasteOil and FatsCarbohydrates, ProteinsSewage, etc

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Renewable Sources of Energy

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Renewable Sources of Energy

CH

CH2

H2C

O

O

O

C

C

C

O

R3

O

R2

O

R1

+ 3 MeOH O C

O

R2Me

O C

O

R1Me

O C

O

R3Me

CH

CH2

H2C

O

O

O

H

H

H

+KOH

Triglyceride Methanol Biodiesel Glycerol

Biodiesel from Oils and Fats (triglyceride)

Jatropha curcas

The calorific value of triglycerides is about 9 Kcal/g comparable to 11 Kcal/g offossil fuels.

A biodegradable and environmental energy you can grow !!!

The high viscosity of triglycerides does not allow them to be used as it is,however, it can be transesterified with methanol in the presence of a base toyield the less viscous biodiesel which can be used as a renewable source ofenergy.

• A raw material or feedstock should be renewable rather thandepleting whenever technically and economically practicable.

• Depleting or nonrenewable fossil resources are subject to thecriterion of time and cannot be replenished nearly as rapidly as theyare consumed.

• Renewable feedstock are biological and plant-based startingmaterials that can be replaced through their natural processes.

• The reuse and recycle of metals and other nonrenewable naturalresources must also be considered as an opportunity to minimize theconsumption of these depleting materials

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7. Use of Renewable Feedstock

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85 -90 % 10 -15 % WasteAtom economy

Use of glycerol as renewable feedstock for the chemical industry

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In 2001, 97x106 lb of glycerol were consumed for the production of skincare products (suntan lotions, cleansing wipes and cloths, creams,other cosmetics and toiletries), hair care (moisturizers andconditioners), soaps (Neutrogena, designer soaps), toothpastes andmouthwashes, etc.

Current uses of glycerol

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If biodiesel became a significant product of the oleochemical industry,capture of even a relatively small portion of the currentnonrenewable diesel market would result in a large increase in theamount of glycerol available for the marketplace.The most broad based opportunity for the effective consumption ofglycerol will arise from its use as a primary chemical building block(feedstock).

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Future uses of glycerolOnce it is recognized that a ready source of low cost glycerol isavailable from the biodiesel unit operation, glycerol could bepositioned within the biorefinery as a primary renewable buildingblock analogous to those of the petrochemical industry (methane,ethylene, BTX, etc.).As the price of glycerol drops and its availability rises, glycerol ceasesto become an “additive” for a fragmented list of small volumeproducts, and assumes a position as the starting point for theproduction of fewer, but much larger volume materials.When the cost of a chemical drops, its range of industrial utilitybroadens, and the ability to absorb the cost of additional chemicaltransformations increases.

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OHO

Glycdiol

O

OH

O

HAcrolein

Acrylic acid

O

OH

HOOH

Glycic acid

OH OH

OHOO

Tartonic acid

OHOH

1,2-Propanediol

OH1,3-Propanediol

HOOOO

OH

ClO

Epichlorohydrin

O O

O

tert-Butylethers

Glycerol would transition from its current state as an advanced intermediate orchemical end-product to utility as a starting material for a family of compounds.

Epichlorohydrin is achemical intermediate usedin the manufacture ofepoxy resins, elastomers,water treatment chemicals,polyols, pharmaceuticalproducts, etc.

1,2-Propanediol is usedin the pharmaceuticalmanufacturing as asolvent and vehicleespecially for drugsunstable or insoluble inwater. It may also beused as a stabilizingagent, plasticizer and asa preservative.

• Unnecessary derivatization (use of blocking groups,protection/deprotection, temporary modification of physical/chemicalprocesses) should be minimized or avoided if possible, because suchsteps require additional reagents and can generate waste.

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8. Reduce Derivatives

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Protection of the carbonyl group

Alkylation of alkyne

Deprotection of the carbonyl group

Protection/Deprotection in Synthesis

• Catalytic reagents are superior to stoichiometric reagents.• Catalysts increase the rates of chemical reactions but are not

consumed in the reactions. As such, a catalyst may decrease thetemperature at which a reaction can be performed economically, thussaving energy costs.

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9. Catalysis

•Chemical products should be designed so that at theend of their function they break down into innocuousdegradation products and do not persist in theenvironment.

•Some chemicals such as plastics made frompetroleum intermediates or pesticides persist in theenvironment.

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10. Design for Degradation

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Materials Designed to be Biodegradable

Made from starch like maize

Plastics made from Polydroxyalkanoates synthesized by

bacteria

• Analytical methodologies need to be further developedto allow for real-time, in-process monitoring andcontrol prior to the formation of hazardous substances.

• The monitoring of a chemical process is beneficial forseveral reasons: the formation of toxic by-products canbe detected early on and parameters can be adjustedto reduce or eliminate formation of these substances.

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11. Real-time Analysis for Pollution Prevention

• Substances and the form of a substance used in a chemicalprocess should be chosen to minimize the potential forchemical accidents, including releases, explosions, andfires.

• Toxicity, explosivity, and flammability must be part of thedesign of chemical products and processes.

• Pollution prevention relies on accident prevention tominimize the likelihood of chemicals leaking into theenvironment. However, if one uses inherently safematerials, then even in the event of a leak, there isminimal hazard. 41

12. Inherently Safer Chemistry for Accident Prevention

42The green synthesis is cheaper as well as more environment friendly.

Example: Green Synthesis of the Pain Killer Ibuprofen

• Six steps• 40% atom economy,

which implies 60% of the materials used is wasted,

• The only ‘catalyst’ in theBoots’ synthesis (AlCl3) isnot a true catalyst. In theprocess it is changed intoa hydrated form that hasto be disposed of –usually in landfill sites.

• Three steps,• 77% atom economy,• All the three steps in

the green synthesisuse catalyst (HF, Raneynickel and palladium)that are recovered andre-used.

The Boots’ synthesis (1960) The BHC synthesis (1993)

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Green chemistry is not just a way toprotect the environment by preventingpollution before its creation; it is also away to increase efficiency and reducecosts of production, an opportunity forbusinesses to lighten theirenvironmental burdens and makemoney.

reduces or eliminates the use

or generationof hazardous substances in

the design, manufacture

and application of chemical products

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ReactantReagents, Energy

Solvent

Product

By-products

+

Green chemistry is the utilization of a set of principles that

…. vital for green economy, embrace it.

Waste

Materials

Hazard

Risk

Energy

Cost

Reducing

Green Chemistry is about...