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Sustainability is an essential requirement of biofuel production. The reduction of ecological impact by using renewable resources instead of fossil raw materials is a major driving force for biofuel implementation.The investigation of ethanol production systems on different scales utilizing corn as well as wheat as raw material reveals, however, a strong infl uence of the size of the plant on the environmental pressure exerted by biofuel production. Comparing different technological options at different levels of production capacity gives insights into the major factors governing ecological as well as economical performance.The trend with regard to economic performance is straightforward and well known: the higher the production capacity of a plant, the lower the costs. The picture is less clear with regard to ecological performance. Increased effi ciency of larger plants usually reduces not only the costs but also the ecological impacts. Logistical factors, however, become increasingly important, leading to situations where economy of scale and ecology of scale are in contradiction.

The 21 st century inherits stark challenges for human society: environmental degradation, global warming and shrinking fossil resources. All these problems are paired with a dramatic growth of the economy in China and India, home to 2.3 billion people. We need to make more from less and we need to do this while reducing our impact on nature by the order of magnitudes. This challenge is particularly tough for chemical engineering. This sector is on the one hand responsible for providing most of the products of daily consumption, the base for modern agriculture as well as energy carriers for power generation, transport, heating and cooling. On the other hand chemical engineering has a considerable impact on the environment, via its resource consumption, its emissions and the impact of its products. Chemical engineering will have to explore new ways in order to stay ahead of these challenges. The paper discusses some of the aspects of the changes that process engineering will face in the 21 st century as it will widen its raw material base to include more renewable resources and simultaneously reduce its environmental impact. As a result, the structure of process industry will be transformed dramatically. Existing design principles and methods will also be challenged and adapted to the new challenges of sustainable development. Given the strong impact that the challenge of sustainable development will pose to process technology engineering education will have to change accordingly. For the first time in decades, process engineers will again be faced with developing new processes rather than process optimisation. They will need to understand how to integrate processes into the ecosphere, how to set up raw material logistics and will have to deal with stake holders outside industry. The process concept will become more encompassing and include the life cycle of products. All these new skills must be taught to students today to make them fit for their carrier in the 21 st century.

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