Hydrogenation, fine chemical synthesis

GAS - LIQUID - SOLID REACTORS FOR HYDROGENATION IN FINE CHEMICALS SYNTHESIS... 

The three themes of the symposium selective hydrogenation, selective oxidation and acid-base catalysis were introduced by four plenary lectures and two invited communications. A panel concerned with the future of zeolites and other shape-selective materials for fine chemical synthesis was conducted by specialists in the field D. Barthomeuf (University of Paris 6), E. Derouane (University of Namur), L. Forni (University of Milan), M. Gubelmann (Rhone-Poulenc, St Fons), W. Hoelderich (BASF, Ludwigshafen) and G. Perot (University of Poitiers). An exhibition of equipment was held during the symposium on October 3 and 4. Over 20 firms exhibited equipment, chemicals and catalysts which were of interest to researchers involved with the synthesis of functional compounds by heterogeneous catalysis. 

Heterogeneous copper catalysts prepared with the chemisorption-hydrolysis technique are effective systems for hydrogen transfer reactions, namely carbonyl reduction, alcohol dehydrogenation and racemization, and allylic alcohol isomerization. Practical concerns argue for the use of these catalysts for synthetic purposes because of their remarkable performance in terms of selectivity and productivity, which are basic features for the application of heterogeneous catalysts to fine chemicals synthesis. Moreover, in all these reactions the use of these materials allows a simple, safe, and clean protocol. 

Dialkyl oxalates are of great interest as solvents, as C2 building blocks in fine chemicals synthesis and as intermediates in the manufacture of oxamide, which serves as a fertilizer mainly in the cultivation of rice. Hydrogenation of dimethyl oxalate was extensively studied at the beginning of the 1980s, when Ube (Japan) and Union Carbide searched jointly for an alternative route to the base chemical ethylene glycol, independent of natural mineral-oil resources [51, 70, 71]. 

Three-phase catalytic membrane reactor systems, in our opinion, show significant promise, for near term application to hydrogenation reactions for fine chemicals synthesis. These reactions generally require mild operating conditions which will place less stringent requirements on the available and future commercial membranes. 

Catalytic liquid phase semihydrogenation of acetylenes is an important industrial and laboratory reaction, especially in fine chemical synthesis [1]. The use of supported metal catalysts for this selective hydrogenation readily facilitates the separation of organic products from the catalyst. However, liquid phase reactions with supported catalysts tend towards mass transport limitation [2] and, therefore, the support particles should be between 1 and 10 pm in size this avoids transport limitations and separation problems. With support particles of this size high temperature reduction in a flow of H2 gas is very difficult and to avoid this step it is possible to prepare supported metal particles by decomposing organometallic compounds under mild conditions [3-5]. 

Efficient analysis plays a cracial role in chemical process industry. It should provide timely, precise and accurate measurements of the process parameters. For fine chemicals synthesis it usually means that extent of reaction in a batch reactor should be effectively determined. Although gas chromatography is a very reliable tool for accurate determination in sitosterol hydrogenation, rather cumbersome analytical procedure calls for another more fast way to monitor progress of the reaction. 

Catalytic behaviors of solid base catalysts for fine chemicals synthesis as well as the fundamental reactions are described. The reactions included are double bond isomerization of olefins, addition of hydrogen and amines to conjugated dienes, dehydration, dehydrogenation, reduction, alkylation, aldol addition and condensation, Wittig-Horner and Knoevenagel reactions, dehydrocyclodimerization, and ring transformation. The characteristic features of different types of solid base catalysts, zeolites, metal oxides, solid superbases and non metal-oxides, are summarized. 

Oxidative carbonylation of alcohols in the presence of CO provides an economically viable route to dialkyl carbonates and/or oxalates (Eqs. (8.4) and (8.5)), both of which have important industrial applications. Dialkyl carbonates (e.g., dimethyl carbonate, propylene carbonate) are excellent solvents for a variety of organic substances [14]. Dialkyl oxalates have utility as solvents, C2 building blocks in fine chemicals synthesis, and intermediates in the manufacture of oxamide (as a fertilizer) [15]. Hydrogenation of dialkyl oxalates provides an alternative route to ethylene glycol that is independent of oil-derived resources [15,16]. 

This review shows that transferring Nature s principle of homogeneously soluble macromolecular catalysts to hydrogenations in fine chemicals synthesis leads to astonishing new results. There has been a clear trend since the mid 1990s in the direction of the synthesis and application of such biomimetic catalysts, especially in reductions utilizing borane or molecular hydrogen as reduction equivalents. 

Jenck, J.F. (1991) Gas-liquid-solid reactors for hydrogenation in fine chemicals synthesis. In M. Guisnet et al. (Ed.) Heterogeneous Catalysis and Fine Chemicals II, Elsevier, Amsterdam. 

Most of the reported microstructured gas-liquid-solid reactors concern catalytic hydrogenations (Table 8.2). This is because hydrogenation reactions represent about 20% of all the reaction steps in a typical fine chemical synthesis. Catalytic hydrogenations are fast and highly exothermic reactions. Consequently, reactor performance and product selectivity are strongly influenced by mass transfer, and heat evacuation is an important issue. Both problems may be overcome using microstructured devices. 

In the following section, methods for the fabrication and deposition of Pd-based and zeolite MMs are discussed, as well as applications in (de) hydrogenation, SR, WGS, partial oxidation (POx) reactions and fine chemical synthesis. The research on Pd-based MMRs for hydrogen separation, purification and production (by dehydrogenation, SR and WGS reactions) has been selected as a case study, as significant research and, therefore, much information can be found in the literature on this field. 

A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport Large surface-to-volume ratios of microreactors would greatly benefit chemical... 

Fine chemicals synthesis via catalytic hydrogenation is an important route in chemical industry. In addition, because of the insolubility of many hydrogenation... 

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