Although supercritical fluid (SCF) technology is now widely used in extraction and purification processes (in the petrochemical, food and pharmaceuticals industries), this book is the first to address the new application of cleaning. Our objective was to provide a road map for readers who want to know whether SCF technology can meet their own processing and cleaning needs. It should be particularly help fbl to those striving to balance the requirements for a clean product and a clean environment. The interdisciplinary subject matter will appeal to scientists and engineers in all specialties ranging from materials and polymer sciences to chemistry and physics. It should also be useful to those developing new processes for other applications, and references given at the end of each chapter provide links to the wider body of SCF literature. The book is organized with topics progressing from the fundamental nature of the supercritical state, through process conditions and materials interactions, to economic considerations. Practical examples are included to show how the technology has been successfully applied. The first four chapters consider principles governing SCF processing, detailing issues such as solubility, design for clean ability, and the dynamics of particle removal. The next three chapters discuss surfactants and micro emulsions, SCF interaction with polymers, and the use of supercritical carbon dioxide (CO,)as cleaning solvent. The closing chapters focus on more practical considerations such as scaleup, equipment costs, and financial analysis. Many contributors to this book belong to the ?Joint Association for the Advancement of SCF Technology? (JUST), a consortium established to foster the development and application of SCFs. Members of JUST meet several times each year to compare results and exchange information on their research and development activities. A primary motivation for the formation of JUST was the growing worldwide need to replace ozon edepleting compounds (ODCs) and smog-forming volatile orgic compounds (VOCs) in manufacturing processes. Although aqueous cleaning has been adopted successfully for many applications, water is not a panacea and SCF technology has emerged as a leading alternative where aqueous processes cannot be used. A substance is said to be in the supercritical state when its temperature and pressure are raised above the critical point. The state is characterized by low viscosities, low surface tensions, high diffisivities and near-liquid molar volumes, resulting in rapid wetting and excellent penetration characteristics that are highly desirable for good cleaning performance. The critical point for CO, occurs at 31.3"C and 7.4 MPa, conditions readily attained with commercially available equipment. Carbon dioxide (CO,) is also inert, ozone-friendly, noncombustible, naturally occuming, inexpensive, and does not contribute to smog. Thus, for many applications, supercritical CO, will predominate as the solvent of choice. Indeed the work of most authors has been primarily concerned with CO,, although much of the discussion applies equally to many other SCFs. For over a century, the unique properties of the supercritical state have enticed scientists and engineers to explain and harness them. Yet even today, the science and technology of SCFs remains far from mature and opporhmities abound for spectacular returns on research investments. In the final analysis, our book will have met its objective if the reader is persuaded to join the quest for a deeper understanding of this intriguing field.