Principles and Concepts of Green Chemistry

1.1 INTRODUCTION

During the twentieth century chemistry changed for ever the way we live. Perhaps the greatest perceived benefits, to the general public, have come from the pharmaceuticals industry with developments of painkillers, antibiotics, heart drugs and, more recently, Viagra. However, it is difficult to think of an important facet of modern life which has not been transformed by products of the chemical and related industries, for example:

• Transportation – production of gasoline and diesel from petroleum, fuel additives for greater efficiency and reduced emissions, catalytic converters, plastics to reduce vehicle weight and improve energy efficiency.

• Clothing – man-made fibres such as rayon and nylon, dyes, water proofing and other surface finishing chemicals.

• Sport – advanced composite materials for tennis and squash rackets, all-weather surfaces.

• Safety – lightweight polycarbonate cycle helmets, fire-retardant furniture.

• Food – refrigerants, packaging, containers and wraps, food processing aids, preservatives.

• Medical – artificial joints, 'blood bags', anaesthetics, disinfectants, anti-cancer drugs, vaccines, dental fillings, contact lenses, contraceptives.

• Office – photocopying toner, inks, printed circuit boards, liquid-crystal displays.

• Home – material and dyes for carpets, plastics for TVs and mobile phones, CDs, video and audio tapes, paints, detergents.

• Farming – fertilizers, pesticides.

The value of the chemical industry is shown in Figure 1.1. In the UK over 450 000 people are employed by the industry (including pharmaceuticals and plastics) and the industry is manufacturing's number one exporter.

In many countries, however, the chemical industry is often viewed, by the general public, as causing more harm than good. There are several reasons for this, including general ignorance of the end use and value of the industry's products; however, a major reason is that the industry is perceived as being polluting and causing significant environmental damage. There is a certain amount of truth in this view with well-publicized disasters such as Bhopal causing both environmental damage and loss of life. As well as specific disasters, general pollution which came to the public's attention in the 1960s and 70s through eutrophication, foaming rivers, the discovery of persistent organic pollutants and the famous 'burning' Cuyahoga river, have all played a part in formulating this view of the chemical industry.

Chemists and engineers engaged in development of chemical products and processes have never set out to cause damage to the environment or human health. These have occurred largely through a lack of knowledge, especially of the longer-term effects of products entering the environment and possibly an over-reliance on procedures to ensure operations are carried out safely. The challenge for the chemical industry in the twenty-first century is to continue to provide the benefits we have come to rely on, in an economically viable manner, but without the adverse environmental side effects.

1.2 SUSTAINABLE DEVELOPMENT AND GREEN CHEMISTRY

Current thinking on sustainable development came out of a United Nations Commission on Environment and Development in 1987 (Bruntland Commission), which defined sustainable development as: '... meeting the needs of the present without compromising the ability of future generations to meet their own needs.' Although the ideals on which sustainable development is based are not new, indeed Thomas Jefferson made similar comments in 1789, the Bruntland Commission did catalyse the sustain-ability debate. Since 1987 Governments, NGOs, society in general and industry sectors have considered what sustainable development really means and how best to start to achieve it from their own standpoint. Issues that will have a significant impact on how the move towards sustainability is approached, include time-scale, likely future technology developments and population forecasts. Two of the key aspects of sustainable development from a chemicals and energy perspective are: 'how fast should we use up fossil fuels?' and 'how much "waste" or pollution can we safely release to the environment?' Whilst there are no agreed answers to these questions there is general agreement to develop more renewable forms of energy and to reduce pollution.

The Natural Step, an international movement, started in Sweden, dedicated to helping society reduce its impact on the environment has developed four system conditions for sustainability:

• Materials from the Earth's crust (e.g. heavy metals) must not systematically increase in nature.

• Persistent substances produced by society (e.g. DDT, CFCs) must not systematically increase.

• The physical basis for the Earth's productive natural cycles must not be systematically deteriorated.

• There must be fair and efficient use of resources with respect to meeting human needs.

This approach recognizes that the Earth does have a natural capacity for dealing with much of the waste and pollution which society generates; it is only when that capacity is exceeded that our lifestyle becomes unsustainable.

During the early 1990s the US Environmental Protection Agency (EPA) coined the phrase Green Chemistry 'To promote innovative chemical technologies that reduce or eliminate the use or generation of hazardous substances in the design, manufacture and use of chemical products.' Over the last 10 years Green Chemistry has gradually become recognized as both a culture and a methodology for achieving sustainability. The 12 Principles of Green Chemistry (Box 1.1) help show how this can be achieved. Many of these 12 principles, e.g. catalysis and increased use of renewable resources, are expanded on in later chapters. When looking at Green Chemistry from an industrial perspective it is important to take the costs of implementing green technology into account; from this point of view it is helpful to look at Green Chemistry as a reduction process (Figure 1.2). From this perspective it becomes obvious that through application of Green Chemistry concepts significant savings can be made, arising from reduced raw material use, lower capital expenditure, lower costs of waste treatment and disposal, etc. The fundamental challenge for the chemical industry is to continue to provide the benefits to society without overburdening or causing damage to the environment, and all this must be done at an acceptable...