Imperial CollegeLondonRevised end of Lecture 2: Effective Mass Yield - EMY

EMY = mass of desired product

mass of non-benign reagentsx 100 %

Whereas atom economies and E-factors are unlikely to measure the true sustainability of a chemical reaction, EMY values do discriminate between environmentally benign and non-benign reagents.

4.I6 2 - A1

Imperial CollegeLondonGreen Metrics - the corrected slide from lecture 2

e.g. esterification of n-butanol with acetic acid

Typical procedure: 37g butanol, 60 g glacial acetic acid and 3 drops of H2SO4 are mixed together. The reaction mixture is then poured into 250 cm3 water. The organic layer is separated and washed again with water (100 cm3), saturated NaHCO3 (25 cm3) and more water (25 cm3). The crude ester is then dried over anhydrous Na2SO4 (5 g), and then distilled. Yield = 40 g (69 %).

Metric Value Greenness

yield 69 % Moderateatom economy 85 % Good (byproduct is water)E-factor 462 / 40 = 12.2 PoorEMY 40/37 x 100 = 108 % Very good

EMY indicates that thereaction is very 'green'

4.I6 2 - A2

Imperial CollegeLondonRecap of the conclusions from lecture 2

Atom efficiencies and E-factors are often useful, simple guides to the 'greenness' of reactions, but may be overly focussed on waste.

EMY values take into account the toxicity of reagents and are therefore more likely to reflect the true 'greenness' of a process.

However, EMY values require us to decide what and what is not benign!

The only true way of judging 'greenness' is by a life cycle analysis, but this is far too time consuming to be practical. We therefore use atom economies, E-factors and EMY data as simple (but imperfect) guides.

Remember Lecture 1 - "Green Chemistry is not easy!"The difficulties measuring greenness are a major reason.

4.I6 2 - A3

Imperial CollegeLondonExam style question - answer next time

Maleic anhydride may be prepared using two routes:

Oxidation of benzene:

Oxidation of but-1-ene:

The benzene oxidation route typically occurs in 65 % yield, while the but-1-ene route only gives yields of 55 %.

(a) Assuming that each reaction is performed in the gas phase only, and that no additional chemicals are required, calculate (i) the atom economy and (ii) the effective mass yield of both reactions. You should assume that O2, CO2 and H2O are not toxic.

(b) Which route would you recommend to industry? Outline the factors which might influence your decision.

4.I6 2 - A4

Imperial CollegeLondon

Lecture 3: Renewable versus Depleting Resources

or Biomass versus Petrochemicals

4.I6 Green Chemistry Lecture 3 Slide 1

4.I6 Green Chemistry

"Many of the raw materials of industry…can be obtained from annual crops grown on the farms"

Henry Ford, 1932

Imperial CollegeLondonLecture 3 - Learning Outcomes

By the end of this lecture you should be able to

• describe the concept of carbon neutrality

• describe the use of biomass as a source of renewable fuels

• explain how biomass may be used as a source of chemicals

4.I6 3 - 2

Imperial CollegeLondonMajor petrochemical building blocks

Seven major raw materials from petroleum: C2-C4 and BTXethylene propylene butenes butadienesbenzene (B) toluene (T) xylenes (X)

Each also has extensive derivative chemistry, e.g. ethylene

CH2=CH2

CH2ClCH2Cl

CH2=CHCl

CH3CHO

CH3CO2H

(CH3CO)2O

CH2=CHOAc

HOCH2CH2OH

PhCH2CH3

CH2=CHPh

CH3CH2CHO

CH3CH2CO2H

CH3CH2CH2OH

Cl2

-HCl

O2 , H2O,PdCl2

O2,AcOH,PdCl2

O2, Ag

H2O

C6H6

-H2

H2, CO

O2

O2

O2H2

CH3CH2OH

H2O

4.I6 3 - 3

Imperial CollegeLondonThe problem with petroleum? Its use as a fuel…

Definition of sustainable development: "meeting the needs of the present without compromising the ability of futuregenerations to meet their own needs" UN Bruntland Commission 1987

• non-sustainable

• adverse direct and indirect environmental effects• limited supplies (economic pressure and potential security risk)• political entanglement

But the vast majority of contemporary industrial chemistry is based on petrochemicals - in the US > 98 % of all commercial chemicals are derived from petroleum (in Europe it is > 90 %)

4.I6 3 - 4

Imperial CollegeLondonEnergy consumption

oil

gas

coal

biomass + other renewables

nuclear

hydro

Projected Global Energy Consumption to 2030

1971 1980 1990 2000 2010 2020 2030

0

5

10

15

109 tonnes of oil equivalent

• energy demands will increase and so will CO2 production

• biomass-based fuels attracting increasing attention

Source: World Energy Outlook 2005 (International Energy Authority)4.I6 3 - 5

Imperial CollegeLondonWhat is biomass?

Biomass is all organic (living and dead) material on the planet. More realistically, the biomass that we shall consider in this lecture is made up of:

• agricultural residues

• food processing wastes

• livestock production wastes

• municipal solid waste

• wood waste

Chemical composition

Cellulose - Sugars / Starches

Hemicellulose

Lignin

4.I6 3 - 6

Imperial CollegeLondonBut doesn't burning biomass still produce CO2?

(CH2O)n + n O2 n CO2 + n H2O

Biomass is said to be carbon neutral, i.e. the CO2 absorbed from the atmosphereduring plant growth is returned to it upon burning.

biomass oil natural gas

Energy release on 15 45 55combustion (GJ tonne-1)

As burning biomass is less calorific than burning fossil fuels, alternative ways toproduce energy from it have attracted attention.

What is the difference between carbon neutrality and carbon offsetting?

4.I6 3 - 7

Imperial CollegeLondonEnergy from biomass

Method employed depends on the source of biomass (and on its water content)

combustion

thermolysis(450 - 800 °C)

pyrolysis(1500 °C)

gasification(650 - 1200 °C)

hydrothermolysis(250 - 600 °C)

fermentation

anaerobicdigestion

wat

er

con

ten

t

15 %

> 85 %

heat, CO2, H2O

charcoal,fuel, gases

C2H2, charcoal

CO, H2, CH4, CO2

charcoal,fuel, CO2

ethanol, CO2

CH4, H2O

biorenewableraw materials?

So will using biomass for energy increase the supply of renewable feedstocks?

4.I6 3 - 8

Imperial CollegeLondonBiofuels - 1. Biodiesel

Production of Biodiesel

triglyceride, main component of vegetable oil

fatty acid ester,biodiesel

e.g. palm oil based triglycerides contain:

42.8 % palmitic acid (1-hexadecanoic acid; CH3(CH2)14CO2H)

40.5 % oleic acid (cis-9-octadecenoic acid; CH3(CH2)7CH=CH(CH2)7CO2H)

10.1 % linoleic acid (cis,cis-9,12-octadecadienoic acid; CH3(CH2)3(CH2CH=CH)2(CH2)7CO2H)

4.5 % stearic acid (1-octadecanoic acid; CH3(CH2)14CO2H)

0.2 % linolenic acid (cis,cis,cis-9,12,15-octadecatrienoic acid; CH3(CH2CH=CH)3(CH2)7CO2H)

Other sources include soybean, rapeseed and sunflower seed.

4.I6 3 - 10

Imperial CollegeLondonBiodiesel: pros and cons

Advantages:• GM can increase oil yield (some sunflower seeds contain 92% oleic acid)

• Bacteria could be even more productive

• Wide range of oils tolerated (even waste chip-shop oil can be recycled in this way)

• Carbon neutral fuel source (in theory) and biodegradable

• Glycerin by-product

Disadvantages:• Land use (maximum biodiesel fraction of car fuel market in the UK ≈ 5 %)

• Higher viscosity than normal diesel (unreliable in cold weather)

• To keep costs low the transesterification step must be fast - catalyst is often NaOH which also causes saponification (ester hydrolysed to Na salt of fatty acid), which necessitates lengthy separation procedures.

4.I6 3 - 11

Fatty acid

Imperial CollegeLondonBut fatty acids may also be used as chemical raw materials

1. Modification of the acid function

Wax esters (lipids)

Fatty amides

Nitriles

Amine

R4N+ salts

Fatty alcohol

Alcohol ethoxylate(pesticides)

Metal carboxylates

1-alkenes

Sulfosuccinates(surfactants)

ROH

NR3 -H2O

H2

RX

H2

ethyleneoxide

Na2SO3

maleic anhydride

-H2O

Na, Al, Zn, Mghydroxides

triglyceride

4.I6 3 - 12

Imperial CollegeLondonFatty acids chemistry continued

2. Modification of the alkene function

Fatty acid cis-trans isomers

epoxidesdiols (precursorsfor polyurethanes)

conjugated fattyacids (lipids)

medium chain acidsand alkenes

short chain acidsand diacids

olefin metathesis(C2H4)

ozonolysis

H+ or NOx

(i) H+, H2O(ii) H2

[O]

base

4.I6 3 - 13

Imperial CollegeLondonExample: erucic acid (C22)

CH3(CH2)20CO2H CH3(CH2)20CH2OH

HO2C(CH2)11CO2H

erucic acid (rapeseed)

erucamide(slip agent)

behenic acid(PVC antiblocking agent)

behenyl alcohol(cosmetics)

brassylic acid(nylon 13,13 precursor

and musks)

4.I6 3 - 14

Imperial CollegeLondonBiofuels - 2. Bioethanol

C6H12O6 2 C2H5OH + 2 CO2

yeast

Disadvantages• Of all the saccharides present in biomass, only glucose is readily fermented, lowering competitiveness and increasing waste (genetic engineering may solve this problem).

• Enzymes do not operate if the EtOH concentration is too high (typically needs to be < 15 %). Energy intensive and expensive distillation is therefore required.

Advantages• Cheap hydrated bioethanol can be used neat as a car fuel, but requires specially adapted engines. Anhydrous bioethanol must be mixed with petrol (up to 22 %) but can then be used in conventional engines.

Large amount of research now looking at the conversion of ligninocellulosic feedstocks into sugars

4.I6 3 - 15

Imperial CollegeLondon12 major sugar derived chemicals

1,4-diacids, e.g succinic acid

2,5-furandicarboxylic acid 3-hydroxypropionic acid

aspartic acid glucaric acid glutamic acid

itaconic acid levulinic acid 3-hydroxybutyrolactone

glycerol sorbitol xylitol

4.I6 3 - 16

Imperial CollegeLondonEach has extensive derivative chemistry, e.g. levulinic acid

-valerolactone 2-methyl THF

acrylic acid1,4-pentanediol

levulinate esters

acetyl acrylic acid

5-aminolevulinic acid

diphenolic acid

cellulose

H2SO4 > 200°C

glucose

200°C

-HCO2H

levulinic acid

herbicide

solvent, fuel oxygenate

monomer

bisphenol Asubstitute

biodieseladditive

polyester precursor

solvent

monomer

4.I6 3 - 17

Imperial CollegeLondonThe difference between petrochemicals and biomass chemicals?

The major difference is oxygen content

4.I6 3 - 18

Hydrocarbon-based chemistry Carbohydrate-based chemistry

Slide 3 Slide 17

Imperial CollegeLondonAn alternative source of biomass chemicals - Syn-gas

Three classical routes:

1. Steam reforming of methane

2. Shell Gasification process

3. Coal gasification

1 : 3

1 : 1

1 : 1

1 : 0

In theory any hydrocarbon can be used, e.g.

toluene steamdealkylation

4.I6 3 - 19

Imperial CollegeLondonExisting Syn-gas technology

Biomass

CO + H2 GasolineFischer Tropsch

MeOH

CH3CO2H

alkanes

aromaticsMeCl

ROH

HCHO

N2NH3

CO2

acrylicacid

urea

urea-formaldehyde(Bakelite) resins polymers

EtOHestersethers

-H2OC2H4

polyethylene

oligomersaldehydes

acidsalcohols

ethyleneoxide

O2 + Ag

H2O + Rh catalyst

CO + Ir / Rh cat.

zeolite H-ZSM-5

Al2O3 / PtHClCO, H2

CO, H2

4.I6 3 - 20

Imperial CollegeLondonRenewable chemical feedstocks - summary

Four approaches:

• use naturally-occurring chemicals extracted directly from plantse.g. natural rubber, sucrose, vegetable oils, fatty acids, starch

• use chemicals extracted by a one-step modification of biomasse.g. fermentation to give lactic acid (lecture 2), bioethanol, furans, levulinic acid, adipic acid, poly(hydroxyalkanoates)

• synthesise chemicals by multi-step conversion of biomass chemicalse.g. polylactide

• use biomass as a source of basic building blocks (H2, CO, CH4 etc)e.g. Syn-gas economy, polyethylene

4.I6 3 - 9

The four approaches will now be exemplified using examples from polymer chemistry.

Imperial CollegeLondonRenewable polymers - approach 1

The four approaches to using biomass-derived feedstocks are all found in polymer chemistry.

Approach 1: use naturally-occurring chemicals extracted directly from plants

e.g. starch

e.g. cellulose

amylose

amylopectin

Advantages of polysaccharides• Cheap and biodegradable

Disadvantages• Crystalline (not plastic)• Properties difficult to modify

4.I6 3 - 21

Imperial CollegeLondonApproach 2: one-step modification of biomass

e.g. Polyhydroxyalkanoates - PHAs

R = Me: poly(hydroxybutyrate) - PHBR = Et: poly(hydroxyvalerate) - PHV

In the absence of N2 bacteria form PHAs as energy storage (just as plants produce starch).

Accumulation of PHA in rhodobacter sphaeroides

Advantages of PHAs:Desirable physical properties (PHB is similar to polypropylene) and biodegradable

Disadvantages:High cost of production and processing ($15 per kg - polyethylene costs $1 per kg)

4.I6 3 - 22

Imperial CollegeLondonApproach 3: multi-step conversion of biomass chemicals

e.g. Poly(lactic acid) - PLA

corn

OOHO

CH2OH

HO On

HOOH

Me

O

starch lactic acid

Me

O

On

oligomers

O

O

O

O

Me

Me

lactide

O

Me

O

O

O

Men

polylactic acid, PLA

fermentationenzymatic

degradation

step-growthcondensation

(-H2O)

heat

ring-openingpolymerisation

(chain growth)

4.I6 3 - 23

Imperial CollegeLondonPolylactide

The synthesis of PLA is now being carried out on an industrial scale by Cargillin a distinctly green manner…

O

O

O

O

Me

Me

O

Me

O

O

O

Men

160 °C

No solvent - reaction is a melt phase polymerisation

The industrial process is 'catalysed' by tin (II) bis(2-ethylhexanoate).

The development of other catalysts for this process is dealt with in 4I-11: 3pm Friday 2nd and Friday 9th March

4.I6 3 - 24

acrylicacid

ethyleneoxide

C2H4

Imperial CollegeLondonApproach 4: The Syn-gas economy

Biomass

CO + H2 GasolineFischer Tropsch

MeOH

CH3CO2H

alkanes

aromaticsMeCl

ROH

HCHO

N2NH3

CO2

urea

urea-formaldehyde(Bakelite) resins polymers

EtOHestersethers

-H2O

polyethylene

oligomersaldehydes

acidsalcohols

O2 + Ag

H2O + Rh catalyst

CO + Ir / Rh cat.

zeolite H-ZSM-5

Al2O3 / PtHClCO, H2

CO, H2

monomers

polymers

4.I6 3 - 25

Imperial CollegeLondonConclusions

Although entirely different, global warming and green chemistry share a common potential solution - biomass.

Biomass can be converted into fuel and into raw materials for the chemical industry in the same way that oil is currently used to produce fuel (petroleum) and petrochemicals (particularly C2 - C4 alkenes, and BTX aromatics).

Four ways biomass can be used to provide raw materials:• (i) direct use of naturally occurring compounds• (ii) one step modification of biomass• (iii) multi-step conversion of biomass• (iv) gasification of biomass to syn-gas

The use of biomass as a source of fuel fits well into existing petrochemical infrastructure.

The use of biomass as a source of raw materials requires the development of new reduction chemistry (petrochemicals use oxidation chemistry).

4.I6 3 - 26

Imperial CollegeLondonLearning outcomes revisited

By the end of this lecture you should be able to

• explain the concept of carbon neutrality

• describe the use of biomass as a source of renewable fuels

•describe the use of biomass as a source of chemicals

Burning biomass returns CO2 to the atmosphere.Burning fossil fuels increases atmospheric CO2.

Low temperature: biotechnology / fermentation to produce bioethanol.High temperature: charcoal, gases, heat etc.

Fatty acids: production of biodiesel.

Potentially most important: gasification to syn-gasand subsequent Fischer-Tropsch like chemistry

4.I6 3 - 27