Introduction to Green Chemistry

JAMES H. CLARK

Green Chemistry Centre of Excellence, University of York, York, UK, YO10 3HW

1.1 Introduction

This brief chapter provides readers who are unfamiliar with 'green technology' with a broad understanding of 'green principles' to better appreciate the social, economic and technical context that necessitate the development of alternative food processing techniques, that reduce energy requirements and/or organic 'chemical' solvent use. Life-cycle analysis is also introduced as a key concept in evaluating the sustainability of any green technology that uses alternative fuels, or reduces energy use, relative to established technology. The issue of biofuels is explored and supercritical extraction briefly discussed as an example of green transformation.

Developing alternative technologies and products are essential to move the food industry, and other industries, towards sustainable processing and to reduce commercial energy use and thereby responsibly preserve local and global environments. This activity is called Green Chemistry, Green Engineering or Sustainable Design and requires input from various scientific, engineering, technological, environmental, economic and legal disciplines. It is influenced by multiple drivers which affect the creation of new green technologies, which are outlined in Figure 1.1.

Green chemistry/technology involves the sustainable manipulation of chemicals and materials to value-added products, and therefore involves both new processes and products. The principles of green chemistry were first outlined in the 1990's. However, it can also be considered as simply a means of maximizing the efficient use of resources and achieving cost savings, while minimizing negative human and environmental impact (Figure 1.2). Green chemistry requires new, low environment impact technologies to reduce energy use, facilitate greater use of catalysis and environmentally benign processing and avoidance of harmful organic solvents. Furthermore, it also involves reducing the number of processing steps in industrial manufacturing to obtain the same products in fewer processing steps with less energy and waste materials.

Green engineering thus requires the application of fundamental engineering concepts and practices to reduce the environmental impact of current manufacturing practices. The United States Environmental Protection Agency describes this as the design, commercialization and use of processes and products that are economically feasible to implement, while minimizing pollution production and human/environmental risk by incorporating the principles of process optimization, life cycle assessment and the environmental economics of processing.

Sustainable design differs from a conventional approach by including a consideration of the environmental impact on local and global ecosystems. The 'three pillars of sustainable development' have been described as society, ecology and environment, often referred to as the triple bottom line of true process sustainability (Figure 1.3). This eco-efficient tool developed by the world's largest chemical company, BASF, integrates these pillars and quantifies the most sustainable processes by including the health and safety costs. Ecological impacts are evaluated by life cycle assessment by considering land use, raw material consumption, atmospheric emissions and water-borne pollutants.

The situation is made more complex by resource allocation as described by the food versus fuel debate, or as more correctly stated the food verses fuel versus feed versus chemicals issue, which stimulated discussion regarding the use of agricultural land. However, this debate is often oversimplified, as will now be considered. As oil reserves are used and the demand from a growing population increases we may experience conflict in the use of resources. The use of oil imported for chemicals plastic production and transport fuels is non-sustainable and could have a serious negative environmental and societal impact if a more efficient use of energy and greater use of alternative renewable fuels from agriculture, and other resources, is not realized. However, the food versus fuel debate has increased awareness of the direct and indirect cost of crop production. Therefore, the environmental footprint of corn production for bioethanol must include the impact of agrichemicals used to manage the land and the cost of using more land to grow the food crops that the non-food use of corn has displaced. However, there is an overall benefit if displacing a largely exported food crop from a region resulted in more locally produced food being consumed. It is also important to take into account the environmental benefits of not using petroleum, including the avoidance of environmental damage at oil extraction sites. This potential for environmental damage will become greater as efforts are made to obtain less accessible petroleum sources, such as in deep water marine environments sources in the Gulf of Mexico, the Mediterranean Sea and the Canadian tar sands. The environmental cost of oil use in food production should also include the carbon footprint developed by food production that uses oil as an energy source at various life cycle stages. Nevertheless, there may be certain biofuel crops that can grow on land not suitable for non-food or non-feed crops, and therefore do not compete with food crops. Jatropha is an example of a biodiesel feedstock which can be grown on poor quality land. Sugar cane, which is grown in excess of local food needs, can be used for bioethanol production, thereby reducing oil use and supporting the local economy. Although sugars are readily converted to bioethanol, there is a much greater volume of lignocellulose from food and forestry production and processing which is a potential source of renewable carbon (Figure 1.4). Lignocellulose represents a second generation biofuel source, but there are significant technical challenges in cellulose conversion to bioethanol fuel that are currently being addressed.

Reducing the global environmental burden is not feasible by...