A Comparison of Computerized Chemical Models for Equilibrium Calculations in Aqueous Systems

A survey of computer programs which are currently being used to calculate the distribution of species in aqueous solutions, especially natural waters, has been made in order to 1) provide an inventory of available programs with a short description of their uses, 2) compare the consistency of their output for two given test solutions and 3) identify major weaknesses or problems encountered from their use. More than a dozen active programs which can be used for distribution of species and activity calculations for homogeneos equilibria among the major anions and cations of natural waters have been inventoried. Half of these programs can also accept several trace elements including Fe, Al, Mn, Cu, Ni, Zn, Cd, Pb, Ag, Hg, As, Ba, Sr, and B. Consistency between programs was evaluated by comparing the log of the molal concentrations of free ions and complexes for two test solutions: a hypothetical seawater analysis and a hypothetical river water analysis. Comparison of the free major ion concentrations in the river water test case shows excellent agreement for the major species. In the seawater test case there is less agreement and for both test cases the minor species commonly show orders of magnitude differences in concentrations. These differences primarily reflect differences in the thermodynamic data base of each chemical model although other factors such as activity coefficient calculations, redox assumptions, temperature corrections, alkalinity corrections and the number of complexes used all have an affect on the output

Workshop on Applications of Phase Diagrams in Metallurgy and Ceramics

A workshop was held to assess the current national and international status of phase diagram determinations and evaluations for alloys, ceramics, and semiconductors; to determine the needs and priorities, especially technological, for phase diagram determinations and evaluations; and to estimate the resources being used and potentially available for phase diagram evaluation. Highlights of the workshop, description of a new poster board design used in the poster sessions, lists of attendees and demonstrations, the program, and descriptions of the presentations are included

Carbon Dioxide, a Solvent and Synthon for Green Chemistry

Carbon dioxide is a renewable resource of carbon when we consider the reuse of existing CO2 as a carbon source for producing chemicals. The development of new applications is of major interest from the point of view of carbon dioxide sequestration and within the scope of green chemistry. For example, using CO2 instead of CO or COCl2 for chemical synthesis constitutes an attractive alternative avoiding hazardous and toxic reactants. However, it has the lowest chemical reactivity, which is a serious drawback for its transformation. Supercritical CO2 as a reaction medium offers the opportunity to replace conventional organic solvents. Its benign nature, easy handling and availability, non volatile emitting, and the relatively low critical point (Pc = 73.8 bar, Tc = 31 °C) are particularly interesting for catalytic applications in chemical synthesis, over a wide range of temperatures and pressures. The benefits of coupling catalysis and supercritical fluids are both environmental and commercial: less waste and VOCs emission, improved separation and recycling, and enhanced productivity and selectivity. The case study described in this paper concerns the reaction of carbon dioxide with alcohols to afford dialkyl carbonates with special emphasis on dimethyl carbonate. It is of significant interest because the industrial production of this class of compounds, including polycarbonates, carbamates, and polyurethanes, involves phosgene with strong concerns on environmental impact, transport, safety and waste elimination. The future of carbon dioxide in green chemistry, including supercritical applications, is highly linked to the development of basic knowledge, know-how, and tools for the design of catalyst precursors and reactors

Distillation

The purpose of this book is to offer readers important topics on the modeling, simulation, and optimization of distillation processes. The book is divided into four main sections: the first section is introduction to the topic, the second presents work related to distillation process modeling, the third deals with the modeling of phase equilibrium, one of the most important steps of distillation process modeling, and the the fourth looks at the reactive distillation process, a process that has been applied successfully to a number of applications and has been revealed as a promising strategy for a number of recent challenges