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

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Presentation on theme: "Imperial College London Revised end of Lecture 2: Effective Mass Yield - EMY EMY = mass of desired product mass of non-benign reagents x 100 % Whereas."— Presentation transcript:

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

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 H 2 SO 4 are mixed together. The reaction mixture is then poured into 250 cm 3 water. The organic layer is separated and washed again with water (100 cm 3 ), saturated NaHCO 3 (25 cm 3 ) and more water (25 cm 3 ). The crude ester is then dried over anhydrous Na 2 SO 4 (5 g), and then distilled. Yield = 40 g (69 %). MetricValueGreenness yield69 %Moderate atom economy85 %Good (byproduct is water) E-factor462 / 40 = 12.2Poor EMY40/37 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 O 2, CO 2 and H 2 O 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 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

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.I

7 Imperial College London Major petrochemical building blocks Seven major raw materials from petroleum: C 2 -C 4 and BTX ethylenepropylenebutenesbutadienes benzene (B)toluene (T)xylenes (X) Each also has extensive derivative chemistry, e.g. ethylene CH 2 =CH 2 CH 2 ClCH 2 Cl CH 2 =CHCl CH 3 CHO CH 3 CO 2 H (CH 3 CO) 2 O CH 2 =CHOAc HOCH 2 CH 2 OH PhCH 2 CH 3 CH 2 =CHPh CH 3 CH 2 CHO CH 3 CH 2 CO 2 H CH 3 CH 2 CH 2 OH Cl 2 -HCl O 2, H 2 O, PdCl 2 O 2, AcOH, PdCl 2 O 2, Ag H2OH2O C6H6C6H6 -H 2 H 2, CO O2O2 O2O2 O2O2 H2H2 CH 3 CH 2 OH H2OH2O 4.I

8 Imperial College London The problem with petroleum? Its use as a fuel… 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 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.I

9 Imperial College London Energy consumption oil gas coal biomass + other renewables nuclear hydro Projected Global Energy Consumption to tonnes of oil equivalent energy demands will increase and so will CO 2 production biomass-based fuels attracting increasing attention Source: World Energy Outlook 2005 (International Energy Authority) 4.I

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.I

11 Imperial College London But doesn't burning biomass still produce CO 2 ? (CH 2 O) n + n O 2 n CO 2 + n H 2 O Biomass is said to be carbon neutral, i.e. the CO 2 absorbed from the atmosphere during plant growth is returned to it upon burning. biomassoilnatural gas Energy release on 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.I

12 Imperial College London Energy from biomass Method employed depends on the source of biomass (and on its water content) combustion thermolysis ( °C) pyrolysis (1500 °C) gasification ( °C) hydrothermolysis ( °C) fermentation anaerobic digestion water content 15 % > 85 % heat, CO 2, H 2 O charcoal, fuel, gases C 2 H 2, charcoal CO, H 2, CH 4, CO 2 charcoal, fuel, CO 2 ethanol, CO 2 CH 4, H 2 O biorenewable raw materials? So will using biomass for energy increase the supply of renewable feedstocks? 4.I

13 Imperial College London Biofuels - 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; CH 3 (CH 2 ) 14 CO 2 H) 40.5 % oleic acid (cis-9-octadecenoic acid; CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 CO 2 H) 10.1 % linoleic acid (cis,cis-9,12-octadecadienoic acid; CH 3 (CH 2 ) 3 (CH 2 CH=CH) 2 (CH 2 ) 7 CO 2 H) 4.5 % stearic acid (1-octadecanoic acid; CH 3 (CH 2 ) 14 CO 2 H) 0.2 % linolenic acid (cis,cis,cis-9,12,15-octadecatrienoic acid; CH 3 (CH 2 CH=CH) 3 (CH 2 ) 7 CO 2 H) Other sources include soybean, rapeseed and sunflower seed. 4.I

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.I

15 Fatty acid Imperial College London But fatty acids may also be used as chemical raw materials 1. Modification of the acid function Wax esters (lipids) Fatty amides Nitriles Amine R 4 N + salts Fatty alcohol Alcohol ethoxylate (pesticides) Metal carboxylates 1-alkenes Sulfosuccinates (surfactants) ROH NR 3 -H 2 O H2H2 RX H2H2 ethylene oxide Na 2 SO 3 maleic anhydride -H 2 O Na, Al, Zn, Mg hydroxides triglyceride 4.I

16 Imperial College London Fatty acids chemistry continued 2. Modification of the alkene function Fatty acid cis-trans isomers epoxides diols (precursors for polyurethanes) conjugated fatty acids (lipids) medium chain acids and alkenes short chain acids and diacids olefin metathesis (C 2 H 4 ) ozonolysis H + or NO x (i) H +, H 2 O (ii) H 2 [O] base 4.I

17 Imperial College London Example: erucic acid (C 22 ) CH 3 (CH 2 ) 20 CO 2 H CH 3 (CH 2 ) 20 CH 2 OH HO 2 C(CH 2 ) 11 CO 2 H erucic acid (rapeseed) erucamide (slip agent) behenic acid (PVC antiblocking agent) behenyl alcohol (cosmetics) brassylic acid (nylon 13,13 precursor and musks) 4.I

18 Imperial College London Biofuels - 2. Bioethanol C 6 H 12 O 6 2 C 2 H 5 OH + 2 CO 2 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.I

19 Imperial College London 12 major sugar derived chemicals 1,4-diacids, e.g succinic acid 2,5-furandicarboxylic acid 3-hydroxypropionic acid aspartic acidglucaric acidglutamic acid itaconic acid levulinic acid3-hydroxybutyrolactone glycerol sorbitol xylitol 4.I

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

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

22 Imperial College London An 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 : 0 In theory any hydrocarbon can be used, e.g. toluene steam dealkylation 4.I

23 Imperial College London Existing Syn-gas technology Biomass CO + H 2 Gasoline Fischer Tropsch MeOH CH 3 CO 2 H alkanes aromatics MeCl ROH HCHO N2N2 NH 3 CO 2 acrylic acid urea urea-formaldehyde (Bakelite) resins polymers EtOH esters ethers -H 2 O C2H4C2H4 polyethylene oligomers aldehydes acids alcohols ethylene oxide O 2 + Ag H 2 O + Rh catalyst CO + Ir / Rh cat. zeolite H-ZSM-5 Al 2 O 3 / Pt HCl CO, H 2 4.I

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 (H 2, CO, CH 4 etc) e.g. Syn-gas economy, polyethylene 4.I The four approaches will now be exemplified using examples from polymer chemistry.

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 e.g. cellulose amylose amylopectin Advantages of polysaccharides Cheap and biodegradable Disadvantages Crystalline (not plastic) Properties difficult to modify 4.I

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 N 2 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.I

27 Imperial College London Approach 3: multi-step conversion of biomass chemicals e.g. Poly(lactic acid) - PLA cornstarch lactic acid oligomerslactidepolylactic acid, PLA fermentation enzymatic degradation step-growth condensation (-H 2 O) heat ring-opening polymerisation (chain growth) 4.I

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.I

29 acrylic acid ethylene oxide C2H4C2H4 Imperial College London Approach 4: The Syn-gas economy Biomass CO + H 2 Gasoline Fischer Tropsch MeOH CH 3 CO 2 H alkanes aromatics MeCl ROH HCHO N2N2 NH 3 CO 2 urea urea-formaldehyde (Bakelite) resins polymers EtOH esters ethers -H 2 O polyethylene oligomers aldehydes acids alcohols O 2 + Ag H 2 O + Rh catalyst CO + Ir / Rh cat. zeolite H-ZSM-5 Al 2 O 3 / Pt HCl CO, H 2 monomers polymers 4.I

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 C 2 - C 4 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.I

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 CO 2 to the atmosphere. Burning fossil fuels increases atmospheric CO 2. 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.I


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