Future Developments and Scientific Requirements

The production of PET is a well-known industrial process. Early patents on PET synthesis refer to the 1940s. Esterification and transesterification reactions have been investigated since the end of the 19th century. PET production plants have been optimized over the last few decades based on well-established production know-how . PET is now a commodity product with unusually rapid growth and further nearly unlimited future growth perspectives. 

However, in contrast to the production know-how , the scientific knowledge on the details of phase equilibria, kinetics, mechanisms, catalysis and mass-transport phenomena involved in polycondensation is rather unsatisfactory. Thus, engineering calculations are based on limited scientific fundamentals. Only a few high-quality papers on the details of esterification and transesterification in PET synthesis have been published in the last 45 years. The kinetic data available in the public domain are scattered over a wide range, and for some aspects the publications even offer contradicting data. 

For the solubility of TPA in prepolymer, no data are available and the polymer-solvent interaction parameter X of the Flory-Huggins relationship is not accurately known. No experimental data are available for the vapour pressures of dimer or trimer. The published values for the diffusion coefficient of EG in solid and molten PET vary by orders of magnitude. For the diffusion of water, acetaldehyde and DEG in polymer, no reliable data are available. It is not even agreed upon if the mutual diffusion coefficients depend on the polymer molecular weight or on the melt viscosity, and if they are linear or exponential functions of temperature. Molecular modelling, accompanied by the rapid growth of computer performance, will hopefully help to solve this problem in the near future. The mass-transfer mechanisms for by-products in solid PET are not established, and the dependency of the solid-state polycondensation rate on crystallinity is still a matter of assumptions. 

The efforts undertaken to describe the influence of mass transport on the overall polycondensation rate should focus on the development of a polycondensation model based on model parameters being independent of the method of parameter 

Furthermore, the environmental impact of PET production should be reduced by substituting the commonly used antimony-based catalyst for an antimony-free catalyst leg, for a titanium-based catalyst. The pollution by liquid effluents could be reduced by installing a reverse-osmosis unit on top of the glycol distillation unit for the purification of water from the esterification process. 

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Over the last 60 years criteria and methods based upon resuits of catastrophic events have been used for the design of expl facilities. The criteria and methods did not include a detailed or reliable quantitative basis for assessing the degree of protection afforded by the protective facility. Recentiy, extensive research and development programs have been undertaken to establish procedures which permit a more sound and scientifically based approach to current and future design requirements (Refs 1 to 9)... 

This chapter illustrates that the potential of scC02 for reaction engineering of homogeneous catalysis offers a great scope for possible scientific and technical innovation. This newly emerging field of catalysis research lies at the interface of molecular sciences and process engineering and its future development will require truly interdisciplinary efforts from experts in both fields. 

The 1996 Amendments to SDWA require that every 5 years US-EPA establish a list of contaminants which are known or anticipated to occur in public water systems and may require future regulations under SDWA. The list is developed with significant input from the scientific community and other interested parties. After establishing this contaminant candidate list, US-EPA identifies contaminants, which are priorities for additional research and data gathering. US-EPA uses this... 

Development studies, summarized within a distinct report on the physiochemical aspects, drug substance attributes, and finished product characteristics, become critical parts of the validation package. Such data is also valuable for future integration into a manufacturing operation. This includes the scientific rationale for formulating and bulk-handling procedures, lyophilization processing parameters, finished product analysis, and stability requirements. 

The molecular orbital calculation approaches Klamt (1993,1996) and Medven et al. (1996) developed appear to hold promise as a more "scientific" approach based on sound chemical principles. However, these approaches also require a database for development and presently appear to apply to hydrocarbons (i.e., alkanes, alkenes, and aromatic hydrocarbons) and to fairly simple oxygenated compounds. Hopefully, these molecular orbital cal-culational method will be further extended and explored in the near future. 

The term applied indicates the application-oriented objective of this work. It was an important criterion of selection not to supply merely a collection of unweighted facts and various practical examples of homogeneous catalysis. In this context applied means a selection of homogeneous catalyzed processes, which on the one hand have already arrived at industrial success (e. g., cai bonyla-tion of alcohols, hydroformylation, Wacker-Hoechst process). On the other hand, the book also includes homogeneously catalyzed reactions of which the state-of-the-art indicates commercialization in the near future. Moreover, for scientific reasons the inclusion of newer catalytic reactions or reaction principles is required, even when commercialization is not yet in sight. Both aspects are covered by the sections Applied Catalysis and Recent Developments . 

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