绿色化学与化工导论Chapter 1 introduction

1、Chapter 1 IntroductionJAMES H. CLARK 1.1 ChemistryPast, Present and Future 1.2 The Costs of Waste1.3 The Greening of Chemistry Sustainable development, Cleaner production, Atom economy, E factor, Principles of Green Chemistry, Life-cycle assessment 1.1 ChemistryPast, Present and Future Chemical prod

2、ucts make an invaluable contribution to the quality of our lives and play a fundamental role in almost every aspect of modern society. Pharmaceuticals products In twentieth century, World population: from 1.6 to 6 billion, Life expectancy: almost 60%Crop protection and growth enhancement chemicals T

3、he enormous populations demand western levelsThe public image of the chemical industry has badly deteriorated in the last ten years . . .In some of the major centres of chemicals manufacturing more people gave positive than negative views, but for many European countries the ratio of unfavourable to

4、 favourable views was alarmingly high.1.1 ChemistryPast, Present and Future Figure 1.1 Trends in the favourability to the chemical industry of the general public (smoothed plots) (based on MORI Opinion Poll figures in the period 19802000).In the UK, a steady decline in public perception of the chemi

5、cals industries over many years is clearly evident. It is especially disturbing to analyse the survey data more closely and to note that the 1624 year age group has the lowest opinion of the chemicals industries. 1.1 ChemistryPast, Present and FutureFigure 1.2 Trend in the number of applications to

6、study chemistry in UK universities (source: UCAS Universities and Colleges Admissions Services ).At present, the poor image of chemistry is adversely affecting demand. In the UK, the number of applicants to read chemistry at university has been falling steadily for several years The number of applic

7、ants to read chemical engineering is even more alarming (1000 in the year 2000 in the UK) View of twentieth century chemical manufacturing (1) Start with a petroleum-based feedstock.(2) Dissolve it in a solvent.(3) Add a reagent.(4) React to form an intermediate chemical.(5) Repeat (2)(4) several ti

8、mes until the final product is obtained; discard all waste and spent reagent; recycle solvent where economically viable.(6) Transport the product worldwide, often for long-term storage.(7) Release the product into the ecosystem without proper evaluation of its long-term effects.The recipe for the tw

9、enty-first century (1) Design the molecule to have minimal impact on the environment (short residence time, biodegradable).(2) Manufacture from a renewable feedstock (e.g. carbohydrate).(3) Use a long-life catalyst.(4) Use no solvent or a totally recyclable benign solvent.(5) Use the smallest possib

10、le number of steps in the synthesis.(6) Manufacture the product as required and as close as possible to where it is required.We must train the new generation of chemists to think of the environmental, social and economic factors in chemicals manufacturing.1.2 The Costs of Waste In the mid-1990s in t

11、he USA, for example, only about 300 or so of the 75000 commercial substances in use were classified as hazardous. Compliance with existing environmental laws will cost new EU member states well over 10 billion; a similar amount is spent each year in the USA to treat and dispose of waste. Cost of was

12、te can easily amount to 40% of the overall production costs for a typical speciality chemical product.Production costsFigure 1.3 Production costs for speciality chemicals.Breakdown of Typical Speciality Chemical Manufacturing CostWasteMaterialsLabourCapital DepreciationEnergy & UtilitiesCost of

13、Waste BreakdownMaterialsTreatment &DisposalCapitalDepreciationLabourThe Costs of WasteFigure 1.4 The costs of waste.1.3 The Greening of Chemistry Figure 1.5 Options for waste management within a chemical manufacturing process.Hierarchy of waste management techniquesPrevention, by far the most de

14、sirable optionRecycling, the next most favourable optionDisposal, the least desirable optionCleaner production: The continuous application of an integrated preventative environmental strategy to processes and products to reduce risks to humans and the environment. For production processes, cleaner p

15、roduction includes conserving raw materials, and reducing the quality and toxicity of all emissions and wastes before they leave a process.Atom economyTable 1.1 Atom accounts for a typical partial oxidation reaction using chromateElementFateAtom utilisationCProduct(s)Up to 100%HProduct(s) + waste ac

16、id100%CrChromium waste0%NaSalt waste0%SSalt waste (after acid neutralisation)0%OProduct(s) + waste100%Atom economy: how many atoms of the starting material are converted to useful products and how many to waste. A typical oxidation reaction: an alcohol a carboxylic acidchromium (VI) as the stoichiom

17、etric oxidant Environmental factor It is used to quantify the effects of production process to the environmentIdea: All other compounds formed other than the target product are considered to be WASTE.Atom Economy and environmental effectsWhere does the waste come from?E=The amount of wasteThe amount

18、 of target productThe more waste formed The more serious the pollutionIf the atom Utilization=100%E=0Environmental factorEnvironmental factorTable 1.2 Relative efficiencies of different chemicals manufacturing sectors Areas traditionally thought of as being dirty (oil refining & bulk chemical pr

19、oduction) are relatively clean - they need to be since margins per Kg are low. Newer industries with higher profit margins and employing more complex chemistry produce much more waste relatively. Industry sectorProduct tonnage By-product weight / product weightOil Refining106 - 1080.1Bulk Chemicals1

20、04 - 1061 - 5Fine Chemicals102 - 1045 50+Pharmaceuticals10 - 10325 - 100+Environmental quotient (EQ) E-Environmental factorQ-The extent of hazardousness of the waste to the environment obtained from the performance of the waste in the environment.EQEQThe E factor just gives the ratio of the waste an

21、d the target product.But the environmental pollution is strongly associated with the harmful performance of the waste.Energy EfficiencyTable 1.3 Global lost work in major chemical processesProcessTheoretical work potential (kJmol-1 final product)Raw materialsFinal productaThermodynamic efficiency (%

22、)Natural gas + air methanol113671763Natural gas + air hydrogen40923658Ammonia (from natural gas + air) nitric acid995434Copper ore copper15371309Bauxite aluminium470388819a Excludes any steam credit.Energy efficiency via lost work Biomass utilisationFigure 1.6 Biomass utilisation in 2040.Biomass uti

23、lisationTable 1.4 From fossil to greenEnergy sourcePercentage of energy sources1990a2040bOil3817Coal2018Gas1614Biomass1619Hydro55Nuclear56Solar 14Wind7Based on an energy consumption of a 3.51020J; b 11021J.We seek to satisfy our need and not our greed life-cycle assessmentThe life-cycle of a product can be considered as:Pre-manufacturing (materials acquisition)Manufacturing (processing and formulation)Product delivery (packaging and distribution)Product useEnd of (first) lifeWe can no longer afford single-use products.life