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Imperial College London

Imperial College London. Revised end of Lecture 2: Effective Mass Yield - EMY. mass of desired product. x 100 %. EMY =. mass of non-benign reagents.

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Imperial College London

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  1. Imperial College London 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

  2. Imperial College London 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

  3. Imperial College London 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

  4. Imperial College London 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

  5. Imperial College London 4.I6 Green Chemistry Lecture 3: Renewable versus Depleting Resources or Biomass versus Petrochemicals "Many of the raw materials of industry…can be obtained from annual crops grown on the farms" Henry Ford, 1932 4.I6 Green Chemistry Lecture 3 Slide 1

  6. Imperial College London 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

  7. Imperial College London 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 CH2=CH2 Cl2 H2, CO O2 , H2O, PdCl2 C6H6 CH2ClCH2Cl CH3CH2CHO O2, Ag CH3CHO PhCH2CH3 -HCl O2 O2, AcOH, PdCl2 O2 CH2=CHCl -H2 CH3CH2CO2H H2 O2 H2O H2O CH3CO2H CH2=CHPh CH2=CHOAc CH3CH2CH2OH HOCH2CH2OH (CH3CO)2O CH3CH2OH 4.I6 3 - 3

  8. Imperial College London 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 > 98 % of all commercial chemicals are derived from petroleum (in Europe it is > 90 %) 4.I6 3 - 4

  9. Projected Global Energy Consumption to 2030 15 109 tonnes of oil equivalent oil 10 gas biomass + other renewables coal 5 nuclear 0 hydro 1971 1980 1990 2000 2010 2020 2030 Imperial College London 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) 4.I6 3 - 5

  10. Imperial College London 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 4.I6 3 - 6

  11. (CH2O)n + n O2 n CO2 + n H2O Imperial College London 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? 4.I6 3 - 7

  12. Imperial College London Energy from biomass Method employed depends on the source of biomass (and on its water content) 15 % 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 > 85 % CH4, H2O 4.I6 3 - 8

  13. fatty acid ester, biodiesel Imperial College London 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)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

  14. Imperial College London 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

  15. Imperial College London But fatty acids may also be used as chemical raw materials 1. Modification of the acid function Wax esters (lipids) Metal carboxylates triglyceride Fatty amides 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 4.I6 3 - 12

  16. Imperial College London 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) base H+ or NOx Fatty acid cis-trans isomers (i) H+, H2O (ii) H2 [O] epoxides diols (precursors for polyurethanes) 4.I6 3 - 13

  17. Imperial College London 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

  18. Imperial College London 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 < 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

  19. Imperial College London 12 major sugar derived chemicals 1,4-diacids, e.g succinic acid 3-hydroxypropionic acid 2,5-furandicarboxylic acid aspartic acid glucaric acid glutamic acid levulinic acid 3-hydroxybutyrolactone itaconic acid xylitol sorbitol glycerol 4.I6 3 - 16

  20. Imperial College London Each has extensive derivative chemistry, e.g. levulinic acid c-valerolactone 2-methyl THF cellulose solvent, fuel oxygenate solvent H2SO4 > 200°C acrylic acid glucose 1,4-pentanediol monomer 200°C polyester precursor 5-amino levulinic acid levulinate esters -HCO2H herbicide biodiesel additive diphenolic acid acetyl acrylic acid monomer levulinic acid bisphenol A substitute 4.I6 3 - 17

  21. Imperial College London The difference between petrochemicals and biomass chemicals? Slide 3 Slide 17 Hydrocarbon-based chemistry Carbohydrate-based chemistry The major difference is oxygen content 4.I6 3 - 18

  22. Imperial College London 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 4.I6 3 - 19

  23. Biomass CO + H2 Imperial College London Existing Syn-gas technology polyethylene aldehydes acids alcohols esters ethers CO, H2 -H2O oligomers C2H4 EtOH O2 + Ag ethylene oxide H2O + Rh catalyst N2 Fischer Tropsch NH3 Gasoline 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 - 20

  24. Imperial College London 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

  25. Imperial College London 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 4.I6 3 - 21

  26. Imperial College London 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) 4.I6 3 - 22

  27. Imperial College London 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) polylactic acid, PLA lactide oligomers 4.I6 3 - 23

  28. Imperial College London 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 4.I6 3 - 24

  29. Biomass CO + H2 Imperial College London Approach 4: The Syn-gas economy polyethylene aldehydes acids alcohols esters ethers CO, H2 -H2O oligomers C2H4 EtOH O2 + Ag monomers ethylene oxide H2O + Rh catalyst polymers N2 Fischer Tropsch NH3 Gasoline 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

  30. Imperial College London 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). 4.I6 3 - 26

  31. Imperial College London 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 4.I6 3 - 27

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