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Revised end of Lecture 2 Effective Mass Yield -
EMY
mass of desired product
x 100
EMY
mass of non-benign reagents
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
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Green 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
Moderate atom economy 85 Good
(byproduct is water) E-factor 462 / 40
12.2 Poor EMY 40/37 x 100 108 Very good
EMY indicates that the reaction is very 'green'
4.I6 2 - A2
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Recap 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
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Exam 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
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4.I6 Green Chemistry
Lecture 3 Renewable versus Depleting Resources
or Biomass versus Petrochemicals
"Many of the raw materials of industrycan be
obtained from annual crops grown on the farms"
Henry Ford, 1932
4.I6 Green Chemistry Lecture 3 Slide 1
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Lecture 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
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Major petrochemical building blocks
Seven major raw materials from petroleum C2-C4
and BTX ethylene propylene butenes butadienes
benzene (B) toluene (T) xylenes (X)
Each also has extensive derivative chemistry,
e.g. ethylene
CH2CH2
Cl2
H2, CO
O2 , H2O, PdCl2
C6H6
CH2ClCH2Cl
CH3CH2CHO
O2, Ag
CH3CHO
PhCH2CH3
-HCl
O2
O2, AcOH, PdCl2
O2
CH2CHCl
-H2
CH3CH2CO2H
H2
O2
H2O
H2O
CH3CO2H
CH2CHPh
CH2CHOAc
CH3CH2CH2OH
HOCH2CH2OH
(CH3CO)2O
CH3CH2OH
4.I6 3 - 3
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The problem with petroleum? Its use as a fuel

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

Definition of sustainable development "meeting
the needs of the present without compromising the
ability of future generations to meet their own
needs" UN Bruntland Commission 1987
But the vast majority of contemporary industrial
chemistry is based on petrochemicals - in the US
gt 98 of all commercial chemicals are derived
from petroleum (in Europe it is gt 90 )
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Energy consumption

• energy demands will increase and so will CO2
  production
• biomass-based fuels attracting increasing
  attention

Source World Energy Outlook 2005 (International
Energy Authority)
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What 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
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But doesn't burning biomass still produce CO2?
Biomass is said to be carbon neutral, i.e. the
CO2 absorbed from the atmosphere during plant
growth is returned to it upon burning.
biomass oil natural gas Energy release on
15 45 55 combustion (GJ tonne-1)
As burning biomass is less calorific than burning
fossil fuels, alternative ways to produce energy
from it have attracted attention.
What is the difference between carbon neutrality
and carbon offsetting?
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Energy from biomass
Method employed depends on the source of biomass
(and on its water content)
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heat, CO2, H2O
combustion thermolysis (450 - 800
C) pyrolysis (1500 C) gasification (650 -
1200 C) hydrothermolysis (250 - 600
C) fermentation anaerobic digestion
charcoal, fuel, gases
So will using biomass for energy increase the
supply of renewable feedstocks?
C2H2, charcoal
CO, H2, CH4, CO2
water content
biorenewable raw materials?
charcoal, fuel, CO2
ethanol, CO2
gt 85
CH4, H2O
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Biofuels - 1. Biodiesel
Production of Biodiesel
triglyceride, main component of vegetable oil
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)7CHCH(CH2)7CO2H
) 10.1 linoleic acid (cis,cis-9,12-octadecadieno
ic acid CH3(CH2)3(CH2CHCH)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(CH2CHCH)3(CH2)7CO2H) Other sources include
soybean, rapeseed and sunflower seed.
4.I6 3 - 10
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Biodiesel 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
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But fatty acids may also be used as chemical raw
materials
1. Modification of the acid function
Wax esters (lipids)
Fatty amides
Metal carboxylates
triglyceride
ROH
NR3
-H2O
Na, Al, Zn, Mg hydroxides
Fatty acid
Nitriles
H2
H2
1-alkenes
-H2O
Amine
Fatty alcohol
ethylene oxide
RX
Sulfosuccinates (surfactants)
R4N salts
Alcohol ethoxylate (pesticides)
Na2SO3 maleic anhydride
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Fatty acids chemistry continued
2. Modification of the alkene function
short chain acids and diacids
medium chain acids and alkenes
olefin metathesis (C2H4)
ozonolysis
conjugated fatty acids (lipids)
H or NOx
base
Fatty acid
cis-trans isomers
(i) H, H2O (ii) H2
O
epoxides
diols (precursors for polyurethanes)
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Example erucic acid (C22)
brassylic acid (nylon 13,13 precursor and musks)
erucamide (slip agent)
HO2C(CH2)11CO2H
erucic acid (rapeseed)
CH3(CH2)20CO2H
CH3(CH2)20CH2OH
behenic acid (PVC antiblocking agent)
behenyl alcohol (cosmetics)
4.I6 3 - 14
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Biofuels - 2. Bioethanol
yeast
C6H12O6 2 C2H5OH
2 CO2

• 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.

• 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 lt 15 ).
  Energy intensive and expensive distillation is
  therefore required.

Large amount of research now looking at the
conversion of ligninocellulosic feedstocks into
sugars
4.I6 3 - 15
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12 major sugar derived chemicals
1,4-diacids, e.g succinic acid
2,5-furandicarboxylic acid
3-hydroxypropionic acid
aspartic acid
glucaric acid
glutamic acid
levulinic acid
3-hydroxybutyrolactone
itaconic acid
xylitol
glycerol
sorbitol
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Each has extensive derivative chemistry, e.g.
levulinic acid
c-valerolactone
2-methyl THF
cellulose
solvent, fuel oxygenate
solvent
H2SO4
gt 200C
acrylic acid
glucose
1,4-pentanediol
monomer
200C
polyester precursor
5-amino levulinic acid
levulinate esters
-HCO2H
herbicide
biodiesel additive
acetyl acrylic acid
diphenolic acid
monomer
levulinic acid
bisphenol A substitute
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The difference between petrochemicals and biomass
chemicals?
Slide 3
Slide 17
Hydrocarbon-based chemistry
Carbohydrate-based chemistry
The major difference is oxygen content
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An alternative source of biomass chemicals -
Syn-gas

• Three classical routes
• Steam reforming of methane
• Shell Gasification process
• Coal gasification

1 3
1 1
1 1
1 0
In theory any hydrocarbon can be used, e.g.
toluene steam dealkylation
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Existing Syn-gas technology
polyethylene
aldehydes acids alcohols
esters ethers
-H2O
CO, H2
C2H4
oligomers
EtOH
O2 Ag
ethylene oxide
H2O Rh catalyst
N2
Fischer Tropsch
Gasoline
NH3
CO2
CH3CO2H
CO Ir / Rh cat.
HCHO
urea
MeOH
zeolite H-ZSM-5
alkanes
ROH
CO, H2
HCl
Al2O3 / Pt
urea-formaldehyde (Bakelite) resins
aromatics
acrylic acid
polymers
MeCl
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Renewable chemical feedstocks - summary

• Four approaches
• use naturally-occurring chemicals extracted
  directly from plants
• e.g. natural rubber, sucrose, vegetable oils,
  fatty acids, starch
• use chemicals extracted by a one-step
  modification of biomass
• e.g. fermentation to give lactic acid (lecture
  2), bioethanol,
• furans, levulinic acid, adipic acid,
  poly(hydroxyalkanoates)
• synthesise chemicals by multi-step conversion of
  biomass chemicals
• e.g. polylactide
• use biomass as a source of basic building blocks
  (H2, CO, CH4 etc)
• e.g. Syn-gas economy, polyethylene

The four approaches will now be exemplified using
examples from polymer chemistry.
4.I6 3 - 9
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Renewable 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
amylopectin
amylose

• Advantages of polysaccharides
• Cheap and biodegradable
• Disadvantages
• Crystalline (not plastic)
• Properties difficult to modify

e.g. cellulose
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Approach 2 one-step modification of biomass
e.g. Polyhydroxyalkanoates - PHAs
R Me poly(hydroxybutyrate) - PHB R 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)
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Approach 3 multi-step conversion of biomass
chemicals
e.g. Poly(lactic acid) - PLA
enzymatic degradation
fermentation
corn
starch
lactic acid
step-growth condensation
(-H2O)
ring-opening polymerisation
heat
(chain growth)
oligomers
lactide
polylactic acid, PLA
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Polylactide
The synthesis of PLA is now being carried out on
an industrial scale by Cargill in a distinctly
green manner
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
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Approach 4 The Syn-gas economy
polyethylene
aldehydes acids alcohols
esters ethers
-H2O
CO, H2
C2H4
oligomers
EtOH
O2 Ag
ethylene oxide
monomers
H2O Rh catalyst
polymers
N2
Fischer Tropsch
Gasoline
NH3
CO2
CH3CO2H
CO Ir / Rh cat.
HCHO
urea
MeOH
zeolite H-ZSM-5
alkanes
ROH
CO, H2
HCl
Al2O3 / Pt
urea-formaldehyde (Bakelite) resins
aromatics
acrylic acid
polymers
MeCl
4.I6 3 - 25
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Conclusions

• 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).

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Learning 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-gas and subsequent Fischer-Tropsch like
chemistry
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