Challenges in Thermodynamics

An examination of the program of the next meeting of distillation and absorption indicates there are only a few lectures on thermodynamcis. The authors asked some important companies to give their view of the trends in thermodynamics. This plenary lecture concerns some of the remaining challenges in the thermodynamics related to distillation: data banks and locations for measuring experimental data new solvents for extractive distillation reacting systems a priori prediction of thermodynamic properties Recent theoretical advances provide benefits that should encourage engineers to switch from activity-coefficient models to equations of state. TRENDS AND CHALLENGES IN THERMODYNAMICS Vision 2020 [39] summarizes the directions of distillation and absorption. New technologies compete with distillation. Vision 2020 balances distillation and absorption as follows: "Under these conditions adsorbents might displace energy intensive cryogenic distillation and liquefaction systems and displace distillation as a separation technology in application where reflux ratios greater than 10:1 are required." About distillation itself, Vision 2020 says that " it is considered to be a mature technology and is often the separation technology of choice because of its wellunderstood nature." Are there goals achievable? Vision 2020 identifies significant barriers such as understanding of fluid flow, foaming and frothing and the lack of effective sensors for large distillation colunms. Common complaint is that there is a general lack of both sponsors and mentors in the field and that the number of international ranked experts in the field of both -thermodynamics and distillationis declining sharply. Yes, there are goals to reach but there is only one in thermodynamics: enhance relative volatilities. The assessment of the authors of this article is to show that a lot of computational work is possible with complicated but readily accessible models. We want to show that the authors of Vision 2020 have forgotten prediction of thermophysical properties. In addition we will demonstrate that the experimental problems concerning reactive distillation appear to be solved. For this conference, the authors have asked some prominent thermodynamicists from larger companies about their opinion of the role of thermodynamics in distillation. The view of a specialty company. At present and in the future, our job is to find the purification route for a complex compound from a mixture of side products. Complex means a molecule having more than one functional group and a molar mass above 100 amu. Typical distillations will be performed at about 150°C and vacuum. The purification route has to be known within a year (with 1 kg of pre-product) and the production has to be in an existing plant (multi-purpose plant). Thus we apply predictive models like COSMO-RS, Unifac(Do) to find difficult close boilers and azeotropes. The process will not run at room temperature but somewhere between 100-200°C. Both models suffer inaccuracies at this level. It would be helpful to improve the quality of the methods for higher temperatures. Also we need methods for accurate vapor pressure estimation methods that can distingish between isomers. An alternative is that analytic equipment becomes available to measure small amounts of material at a high through-put. Thermodynamics plays also an essential role in the synthesis of biomolecules at high pressure (P>50 bar, T<150°C). Especially for gases like CO2 we wish to have tools that calculate the entire phase diagram for SLE-LLE-VLLE-GLE. The view of an international chemical and pharmaceutical company We found that small errors can cause big effects in the separation equipment. Thermodynamics is the basis for understanding transport phenomena. Thermodynamics should produce predictive methods for all kinds of thermophysical properties. The view of an engineering company We are convinced that thermodynamics remains as one of the cornerstones of chemical engineering. All over the chemical engineering world, thermodynamics seems to be on the decline. That is, in part, our own fault because we have not given sufficient attention (in our courses, publications, technical meetings, etc.) to show how and why thermodynamics is important not only for conventional but also for modern (hightech) chemical engineering. Thermodynamics serves as the integrating factor for chemical engineering sciences. We complain that thermodynamics is not standardized: there are no accepted recommendations for what G-model and what EOS should be used with what parameters. There is still a lack of compatibility: h to activity coefficients, LLE to VLE, infinite dilution to finite dilution and vice versa. We would like to apply EOS but there are too many models. We miss mixture rules for density, viscosity, surface tension and heat conductivity. We find excess volumes for binary mixtures and do not know how to extrapolate to multicomponent mixtures. Universities tend to publish correlations and models restricted to special applications without testing general applicability. They do not program in the rules of CAPE. We need predictive methods for the first guess and for non-important traces of components. Real predictive methods do not pay back their implementation compared to structure-interpolating methods. In the end, we only trust measurements. We predict that the description of complex mixtures (electrolytes, polymers, special substances like formaldehyde) becomes more important. We are looking forward to activities in Germany to step into the area of biotechnology. Data banks for this kind of data are missing. We face new problems: bacteria as reactors, products, catalysts and solid products. This is a challenge for simulation programs. This lecture excludes electrolytes because they do not play an important role in distillation except for absorption where powerful methods, especially for CO2 or NH3 in water or in aqueous electrolyte solutions are available from the work of Maurer in Kaiserslautern, Germany.