Reaction properties, fine chemical

The remarkable and singular properties shown by hierarchical zeolites have brought about potential catalytic applications for these materials in numerous reactions, especially those wherein steric or diffusion limitations are encountered. Table 8.3 summarizes the literature dealing with the application of hierarchical zeolites in a variety of reactions (oil refining and petrochemical reactions, and fine chemicals reactions). 

Figure 7 illustrates the use of HPGPC to aid a resin chemist in developing an in-house isocyanate crosslinker for a powder coating system. Isocyanate crosslinker X-02 gave desired properties and is considered the standard. At the early stage of the development, resin X-03 was initially made. By changing the types of reactants, molar ratio of reactants and reaction conditions, resin X-36 was the next iteration in the resin synthesis process. Finally, X-36 was fine-tuned to produce X-38 which matched X-02 in both its chemical reaction properties and its MWD. 

A particular shape of reactor, its specific internals, arrangements made because of special properties and/or behaviour of the reaction mixture, etc. are used as criteria to qualify a reactor. In fine chemicals manufacture two main groups of cylindrical reactors are in common use, viz. stirred-tank reactors with a small aspect ratio, and column reactors with a relatively large aspect ratio. Both types can be equipped with specific internals depending on process requirements. Researchers and designers are well acquainted with these reactors. A tendency to duplicate known equipment usually wins when considering the choice of reactor for a particular process. As a consequence, more and more stirred-tank reactors and column reactors are in use. 

Industrial applications of zeolites cover a broad range of technological processes from oil upgrading, via petrochemical transformations up to synthesis of fine chemicals [1,2]. These processes clearly benefit from zeolite well-defined microporous structures providing a possibility of reaction control via shape selectivity [3,4] and acidity [5]. Catalytic reactions, namely transformations of aromatic hydrocarbons via alkylation, isomerization, disproportionation and transalkylation [2], are not only of industrial importance but can also be used to assess the structural features of zeolites [6] especially when combined with the investigation of their acidic properties [7]. A high diversity of zeolitic structures provides us with the opportunity to correlate the acidity, activity and selectivity of different structural types of zeolites. 

Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites. 

A typical probe reaction for estimating catalytic properties in selective hydrogenations is the hydrogenation of cinnamaldehyde. This molecule contains both a C=C and a C=0 double bond, thus the formation of hydrocinnamaldehyde and/or cinnamyl alcohol by reduction of the one or the other, or the formation of phenyl propanol in the case of complete reduction may indicate the potential of the catalyst for other fine chemical transformations. Indeed, this reaction was one of the first to be tested by CNT-supported catalysts [120]. Noble metals show a high activity in this reaction and... 

The unique properties of zeolites and other micro- or mesoporous solids that may favour their application to fine chemical synthesis are (1) the compatibility between the size and shape of their channels or cavities with the size of the reactants and/or products (generally referred to as molecular shape selectivity) that may direct the reaction away from the thermodynamically favoured route (2) the occurrence of confinement effects increasing the concentration of reactants near the catalytic sites and (3) the ability to tune their catalytic properties (acidic, basic, or other) via various treatments as described in this Volume. 

The wide range of desired functionalities on the surface of catalysts that includes, for example, strong acid sites for cracking reaction, mild acid-base pairs for the synthesis of fine chemicals, redox properties for oxidation reactions, or metal nanoparticles for hydrogenation or electrochemical applications seems to complicate the derivation of general rules with respect to catalyst synthesis. It is, however, accepted without controversy that good catalysts feature the following characteristics ... 

At the basis of the application of zeolites in fine chemicals reactions is the rich variety of catalytic functions with which zeolites can be endowed. Bronsted acidity, Lewis acidity and metallic functions are well known from classical bifunctional chemistry but for specific reactions, unusual sites, e.g. Lewis acid Ti4+ centres, have been introduced into zeolites. Moreover, zeolites can acquire more or less weakly basic properties metal complexes can be entrapped in zeolite pores or cavities, and enantioselective reactions have been performed by decorating the zeolite surface with chiral modifiers. 

Metal oxide species with acid or basic properties as efficient catalysts for alkylation and related reactions have been discussed in Section 5.2. An alternative approach is based on reactions of covalent metal-to-carbon (M-C) bonds. Transition metals are well-suited for this task, as they form directional bonds using hybrid orbitals, and undergo low-energy electron promotion and transfer processes. There are now many industrial processes involving transition metal-catalyzed carbon-carbon bond formation (for example, carbonylation, metathesis, and polymerization reactions, see Chapters 4, 6 and 7, respectively). In sections 5.3-5.4 we deal with other C-C bond forming reactions that can lead to fine chemicals (see Chapter 1). 

Silicon carbide, SiC (i), and silicon nitride, Si3N4 (2), have been known for some time. Their properties, especially their high thermal and chemical stability, their hardness, and their high strength, have led to useful applications for both of these materials. The conventional methods for the preparation of SiC and SiaN4, the high-temperature reaction of fine-grade sand and coke (with additions of sawdust and NaCl) in an electric furnace (the... 

---