Chemical Technology

     Basic Principles of Green Chemistry
     A combination of existing and new drivers makes it m...
Figure 2: Biomass as an alternative feedstock for the chemical industry          Figure 3: Lactic acid as a platform molec...
environment and rapid biodegradation to innocuous              legislation will force an increasing emphasis on products,
Figure 5: Examples of Green Chemistry in practice

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Basic Principles of Green Chemistry

  1. 1. Chemical Technology Basic Principles of Green Chemistry A combination of existing and new drivers makes it more likely that Green Chemistry will become increasingly important in the short term, and essential in the longer term. By Professor James H. Clark and Dr Paul Smith, Clean Technology Centre, Department of Chemistry, University of York Professor James Clark has an international reputation for his work in Green Chemistry and is a Founding Director of the Green Chemistry Network. He was the founding Scientific Editor of the world’s leading journal in the field, Green Chemistry, and is also an author of numerous books on the subject. He now holds the Chair of Industrial & Applied Chemistry at York University (UK), and heads the Clean Technology Centre which integrates Green Chemistry research, industrial collaboration and educational developments and issues relevant to the public understanding of science. He is also the Director of the Greenchemistry Centre of Industrial Collaboration. Professor Clark’s research interests include heterogeneous catalysis and supported reagents and the exploitation of renewable resources. He has won medals and other awards for his research from the RSC, SCI, RSA and the EU. Dr Paul Smith, BSc CChem FRSC, is currently the Commercial Manager of the Greenchemistry Centre of Industrial Collaboration based at York University (UK). He gained his first degree in Chemistry from the University of Nottingham (UK) and his PhD from the University of Cambridge (UK). His background is Chemical Development in the pharmaceutical industry, having worked for over 20 years at GlaxoSmithKline. The major focus of his work was to ensure that initial high quality supplies of potential new drug candidates were rapidly made available and that subsequent manufacturing routes would be developed in a safe, robust, efficient, cost-effective and environmentally sound manner. He also led a ‘Green Team’ which promoted Green Chemistry within the company. Green Chemistry is the universally accepted term to REACH and other new legislation is also likely to bring describe the movement towards more environmentally many consumer product related chemicals to the public’s acceptable and sustainable chemical processes and attention, and we have often seen how even the products (1). It encompasses education and promotional suggestion of a health or environmental-related problem work, as well as research and commercial application of Alternative feedstocks cleaner technologies – some old and some new (2). (minimising petrochemicals) Pre-Manufacturing Waste minimisation While Green Chemistry is widely accepted as an essential (in mining and refining) development in the way that we practice chemistry, and is Solvent substitution (avoiding VOCs) vital to sustainable development, its application has been Alternative routes/reduced fragmented and represents only a small fraction of today’s number of process steps chemical education and chemical manufacturing. However, Manufacturing Catalysis (especially heterogenisation) a combination of existing and new drivers now makes it Intensive processing more likely that it will become increasingly important in the short term, and essential in the longer term. These drivers Alternative energy sources include the increasing proportion of process costs due to Degradable packaging energy and waste, availability and cost issues for traditional Product Delivery petroleum-based feedstocks, and perhaps most significantly Precious metal catalyst (etc) rental the dramatic increase in legislation affecting chemical production, storage, use and disposal. Product Use Safer chemicals Environmentally benign chemicals In Europe, REACH (Registration, Evaluation, Biodegradable products Assessment of Chemicals) will come into force this decade and will undoubtedly be the most important End of Life Recyclable products chemicals-related legislation in living memory (3). Its ‘Benign-by-design’ effects are as yet unclear, but conservative estimates suggest that about 10% of existing chemicals will Figure 1: Application of clean technologies for Green Chemistry become restricted, prohibitively expensive or unavailable. throughout the life-cycle of a chemical product 94 Innovations in Pharmaceutical Technology
  2. 2. Figure 2: Biomass as an alternative feedstock for the chemical industry Figure 3: Lactic acid as a platform molecule OH Corn starch Glucose Petroleum CO2H Biomass Platform Molecules CO2H O OH Chemical Plastics OH Products O n O O can result in media-induced public alarm and over- imidazolium tetrafluoroborate (BMiMBF4) (10). Numerous reaction by retailers. Social as well as environmental and examples of their use in the research literature are economic drivers will force change in chemical available, many of which also involve catalysis (Figure 4). manufacturing which will require a shift in emphasis on chemistry research and education. This is being Some reactions can be carried out in the absence of solvent encouraged by a number of organisations (4). and are often accelerated using microwave activation – a methodology which shows considerable promise for the GREEN CHEMISTRY IN THEORY future, especially with the availability of commercial reactors including continuous flow systems. A number of The principles of Green Chemistry should be applied other novel reactor technologies – often based on intensive at all stages in the life-cycle of a chemical product, and processing such as microreactors – are also expected to key technologies have been identified to help achieve become increasingly important. For example, we have this (Figure 1). recently described catalytic microreactors and catalytic spinning disc reactors (12) for high-throughput, safer and Over 90% of organic chemicals in current use are more flexible chemical processing, which combines state- derived from petroleum. A truly sustainable industry will of-the-art reactor technology with the latest examples of require a shift towards renewable feedstocks (5). Biomass heterogeneous catalysis using mesoporous solid supports can be better utilised in chemical manufacturing especially useful for liquid phase organic reactions. both to provide building blocks and (close to) final products (Figure 2). The ‘platform molecule’ concept is At the product end of the life-cycle, ‘benign by design’ particularly interesting since it provides a range of useful has an especially important significance since the synthetic intermediates which are both more functional product should not cause harm to its users nor harm the and more valuable than conventional petroleum-based environment when it is released. While maximising feedstocks, and also simple enough to allow us to build reusability and recyclability of component parts are up a wide range of important products. One example of important goals, some inevitably does get into the this is lactic acid which is readily derived from the fermentation of corn starch (Figure 3) (6). Figure 4: Examples of non-VOC solvent-based organic reactions Much of the Green Chemistry research effort and most Zn, NH4Cl, water of the good case studies of Green Chemistry at work are PhNO2 PhNH2 associated with chemical manufacturing (7). The substitution of volatile organic solvents is an important + CO + H2 Rh/scCO2 target for almost all chemical manufacturers – both in CO2R OHC CO2R reactions and in work-ups and product purifications (2). A number of alternative reaction solvents have been O H proposed, including water (8), volatile supercritical CO2 OH alcohol (9) which is easily removed by a drop in pressure, + H2 dehydrogenase/ BMiMBF4 R R and non-volatile ionic liquids such as butylmethyl Innovations in Pharmaceutical Technology 95
  3. 3. environment and rapid biodegradation to innocuous legislation will force an increasing emphasis on products, breakdown species is the final green chemistry goal in the but it is also important that these in turn are manufactured product’s life-cycle. by green chemical methods – and that the advantages offered by Green Chemistry can be quantified. Legislation GREEN CHEMISTRY IN PRACTICE or supply-chain pressures may persuade a company that the use of a chlorinated organic solvent is undesirable, but how There are now enough examples of Green Chemistry at can it select a genuinely ‘greener’ alternative? How can a work in commercial processes that we can illustrate its company add environmental data to simple cost and application across the product life-cycle (Figure 5) (2, 7). production factors when comparing routes to a particular We must not, however, get complacent at these successes compound? Can the environmental advantages of using a since they only represent step-change improvements in a renewable feedstock compared with a petrochemical be tiny fraction of industrial chemistry worldwide. quantified? In order to make Green Chemistry happen, we need to see the concept mature from an almost We continue to use diminishing, polluting and philosophical belief that it is the ‘right thing to do’, to one increasingly expensive fossil feedstocks for most chemical which can give hard, reliable data to prove its merits. manufacturing. Hazardous reagents – including aluminium chloride and chromates along with volatile These needs, together with a ‘reality check’, have led to organic compounds such as dichloromethane – continue the emergence of Green Chemistry related metrics. The to dominate chemical processing. Products continue to ultimate metric can be considered to be life-cycle be designed based on cost and effort with little assessment (LCA) (16), but full LCA studies for any consideration given to fate. particular chemical product are difficult and time- consuming. Nonetheless, we should always ‘think LCA’ – We must continue to innovate and design new processes if only qualitatively – whenever we are comparing routes and products but – just as importantly – we need to learn or considering a significant change in any product supply to more quickly adopt the new cleaner technologies if we chain. Green Chemistry metrics (17, 18) are most widely are to achieve the triple bottom line of an economically, considered when comparing chemical process routes, environmentally and socially effective industry (13). including limited – if easy-to-understand – metrics such as atom efficiency (how many atoms in the starting However, the uptake of Green Chemistry by the materials end up in the product) and attempts to pharmaceutical industry is particularly encouraging and measure overall process efficiency such as E Factors this is well illustrated by the success seen in the US (amount of waste produced per kg product). Environment Protection Agency’s (EPA) prestigious annual Presidential Green Chemistry Challenge (14). As with LCA, these metrics have to be applied with clear For example, Bristol Myers Squibb won the Alternative system boundaries, and it is interesting to note that for Synthetic Pathways Award in 2004 for the development process metrics these boundaries generally do not include of a green synthesis for the manufacture of Taxol® via feedstock sources or product fate. Energy costs and water plant cell fermentation and extraction. consumption are also normally not included, although – given the increasing concerns over both of these – it is Industry alone cannot be expected to discover and develop difficult to believe that they can be ignored for much the novel green chemistry methods and technologies that longer. We propose that process efficiency metrics such as are still needed. The good news is that, in the UK, E factor can be improved by including the CO2 equivalent university research is becoming more focused on industry’s of the energy used in the process when calculating the total needs – a good example being the recent setting-up of the waste for that process. At the product end of the life-cycle Greenchemistry Centre of Industrial Collaboration, which we are used to testing for human toxicity, but we will is based at the University of York (15). also need to pay more attention to environmental impact and, here, measures of biodegradability, environmental GREEN CHEMISTRY METRICS persistence, ozone depletion and global warming potential are all important metrics. In its short history, Green Chemistry has been heavily focused on developing new, cleaner, chemical processes Last, but not least, we are moving towards applying using the type of technologies described here. Increasing Green Chemistry metrics to feedstock issues. As we seek 96 Innovations in Pharmaceutical Technology
  4. 4. Figure 5: Examples of Green Chemistry in practice Polymer – Clay Specific processes nanocomposites as flame (e.g. Ibuprofen, cyclohexanone) retardants (electronics Biosynthesis of lactic Degradable acid (Cargill Dow) manufacturers?) Polyethylene (Symphony) PLA Green Chemistry (Cargill Dow) process metrics (GSK) Biodegradable chelant (Octel) Product Pre-manufacturing Manufacturing Product Use End of Life Delivery Clean pharmaceutical Chitin (crabshell) synthesis (several Catalyst rental based adsorbents companies) (Johnson Matthey) Supercritical (Carafiltration) carbon dioxide for hydrogenation (Thomas Swan) Solid acids in Friedel Crafts reactions (Rhodia, UOP, Contract Catalysts) ‘sustainable solutions’ to our healthcare, housing, food, 7. Lancaster M. Green Chemistry, an introductory clothes and lifestyle needs, so we must be sensitive to the text, RSC, Cambridge, 2002. long term availability of the raw materials that go into the supply chain for a product. With increasing financial 8. Tsukinoki T and Tsuzuki H (2001), Green Chemistry, 37. and legislative pressures from the feedstock and product ends, and increasing restrictions and controls on the 9. Hu Y, Chen W, Banet Osuna AM, et al. intermediate processing steps, chemistry must get greener! (2001). Chem Comm, 725. The authors can be contacted at 10. Eckstein M, Filho MV, Liese A and Kragl U and (2004). Chem Comm, 1084. References 11. Jackson T, Clark JH, Macquarrie DJ and Brophy JH (2004). Green Chemistry, 2, 6, 193. 1. Anastas PT and Warner JC. Green Chemistry; Theory and Practice, University Press, Oxford, 1998. 12. Vicevic M, Jachuck RJJ, Scott K et al. (2004). Green Chemistry, 6, 533 2. Clark JH and Macquarrie DJ. Handbook of Green Chemistry and Technology, Blackwell, Oxford, 2002. 13. Clark JH in: Green Separation Processes, A Crespo Ed. Wiley, Chichester, 2005. 3. Warhurst AM (2002). Green Chemistry, 4, G20; see also 14. chemicals/chempd/reach/explanatory-note.pdf 15. 4.;; 16. Graedel TE. Streamlined Life Cycle Assessment, Prentice Hall, New Jersey, 1998. 5. Stevens CV and Vertie RG, Eds, Renewable Resources, Wiley, Chichester, 2004. 17. Constables DJC, Curzons AD and Cunningham VL (2002). Green Chemistry, 4, 521. 6. Clark JH and Hardy JJE in: Sustainable Development in Practice, Azapagic A, Perdan S and Clift R, Eds. 18. Nüchter M, Ondruschka B, Bonrathard W and Wiley, Chichester, 2004. Gum A (2004). Green Chemistry, 6, 128. Innovations in Pharmaceutical Technology 97