Laboratory of Separation and Reaction

Laboratory of Separation and Reaction Engineering, Associate Laboratory LSRE/LCM, Department of Chemical Engineering, Faculty of Engineering University of Porto, Porto, Portugal... 

This chapter concerns the most important reactive separation processes reactive absorption, reactive distillation, and reactive extraction. These operations combining the separation and reaction steps inside a single column are advantageous as compared to traditional unit operations. The three considered processes are similar and at the same time very different. Therefore, their common modeling basis is discussed and their peculiarities are illustrated with a number of industrially relevant case studies. The theoretical description is supported by the results of laboratory-, pilot-, and industrial-scale experimental investigations. Both steady-state and dynamic issues are treated in addition, the design of column internals is addressed. 

The identification of the first transuranium elements was by chemical means. In the early 1960s physical techniques were developed which allowed for detection of nuclei with lifetimes of less than one second at high sensitivity. A further improvement of the physical methods was obtained with the development of recoil separators and large area position sensitive detectors. As a prime example for such instruments, we will describe the velocity filter SHIP (Separator for Heavy-Ion reaction Products) and its detector system, which were developed at the UNILAC. The principle of separation and detection techniques used in the other laboratories is comparable. 

Nevertheless, there are still justifiable and legal reasons to carry out such opaations in the laboratory when hazards can be reduced safely. Neutralizatiorr, oxidation, reductiorr, and various otho" chemical conversions as well as physical methods of separation and concentration can be applied prudently to many laboratory-scale mixed wastes. However, the dual character of the hazard, chemical and radioactive, requires that additional precautions be exercised. Treatment for the chemical hazard must not create a radioactivity risk for personnel or the environment. For example, vapors or aerosols from a reaction, distillation, or evaporation must not lead to escape of unsafe levels of radioactive materials into the atmosphere. Fume hoods appropriate for such operations should be designed to trap any radioactive effluent. When mixed waste is made chemically safe for disposal into the sanitary sewer, the laboratory must ensure that the radioactivity hazard is below the standards set by the publicly owned treatment works (POTW). Several examples for reducing the hazard of mixed waste are described below ... 

Dichloroacetic acid is produced in the laboratory by the reaction of chloral hydrate [302-17-0] with sodium cyanide (31). It has been manufactured by the chlorination of acetic and chloroacetic acids (32), reduction of trichloroacetic acid (33), hydrolysis of pentachloroethane [76-01-7] (34), and hydrolysis of dichloroacetyl chloride. Due to similar boiling points, the separation of dichloroacetic acid from chloroacetic acid is not practical by conventional distillation. However, this separation has been accompHshed by the addition of a eotropeforming hydrocarbons such as bromoben2ene (35) or by distillation of the methyl or ethyl ester. 

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.)... 

High-pressure liquid chromatography (HPLC) is used to separate and purify the products of laboratory reactions. 

Caution This reaction involves highly toxic cyanide salts. It may be carried out safely, however, if prudent laboratory procedures are practiced. In particular, cyanide residues should be collected and disposed of separately (Note 1), and the entire sequence should be perform,ed in an efficient hood. 

---