Liquid products chemical modification

The CSC precursor build-up has been studied after modification of the silica gel surface from the gas phase. This gas phase modification involves the deposition of one molecular layer at the time. For thicker coatings, a cyclic procedure is needed. Liquid phase modification of the silica surface may also yield valuable ceramic precursors. The precursor molecular structure and layer thickness is controlled by other parameters compared to gas phase procedures. Parameters such as reaction solvent, silane concentrations and presence of water are of primal importance. Those have been discussed in detail in chapter 9. In this chapter, the application of silica modified with aminosilanes, will be discussed. The aminopropylsilica is used as a prototype compound for the production of ceramics by liquid phase chemical surface coating. 

Reaction-extraction This technique involves chemical modification of solutes in solution in order to more easily extract them in a subsequent extraction operation. Applications generally involve modification of impurity compounds to facilitate purification of a desired product. An example is the oxygenation of sulfur-containing aromatic impurities present in fuel oil by using H2O2 and acetic acid, followed by hquid-liquid extraction into an aqueous acetonitrile solution [Shiraishi and Hirai, Energy and Fuels, 18(1), pp. 37-40 (2004) and Shiraishi et al., Ind. Eng. Chem. Res., 41, pp. 4362-4375 (2002)]. Another example involves esterification of aromatic alcohol impurities to facihtate their separation from apolar hydrocarbons by using an aqueous extractant solution [Kuzmanovid et al., Ind. Eng. Chem. Res., 43(23), pp. 7572-7580 (2004)]. 

A less frequent but nonetheless interesting problem arises in the chemical modification of liquid, or low-melting, active principles in solid prodrugs, suitable for tablet or capsule preparation. Indeed solid dosage forms are still the most widely used for the administration of medicines, as well for patient acceptability and convenience for product stability and ease of manufacture. Their preparation implies that the active principle can itself be handled as a stable solid, an objective that is usually attained by one of the following strategies formation of a salt or a molecular complex, formation of a crystalline covalent derivative, introduction of symmetry. 

The present world rcscr es of natural gas that contains mainly methane are still underutilized due to high cost of transportation. Considerable interest is therefore presently shown in the conversion of methane to transportable liquids and feedstocks in addition to its previous sole use for heating purposes by combustion. One possible new route for the utilization of methane derived from natural gas or other sources for conversion to more valuable higher hydrocarbons is the methylation of aromatic hydrocarbons. This chapter provides a general overview of the work that has been done so far on the use of methane for catalytic methylation of model aromatic compounds and for direct liquefaction of coal for the production of liquid hydrocarbons. The review is especially focused on the use of both acidic and basic zeolites in acid-catalyzed and base-catalyzed methylation reactions, respectively. The base-catalyzed methylation reaction covered in this discussion is mainly the oxidative methylation of toluene to produce ethylbenzene and styrene. This reaction has been found to occur over basic sites incorporated into zeolites by chemical modification or by changing the electronegative charge of the zeolite framework. 

More productive chemical results, which stiU harness the destructive action of ultrasound on certain bonds, can be attained when sonication is applied to biological fluids (e.g. protein solutions) en route to bionanomaterials [15], A conspicuous example can be found in sonochemically-prepared protein microspheres, in which the interplay of mechanical effects (emulsification) and chemical effects (formatiOT of transient species) is noticeable. A protein emulsion is readily created at the interface between two immiscible liquid phases, while radicals generated by water sonolysis promote disulfide bond cross-linking between cysteine residues. Surface modifications, via conjugation with monoclonal antibodies or RGD-containing peptides, can also be carried out [102, 103]. The sonochemical preparation of chitosan microspheres also exploits the intermolecular cross-linking of imine bonds from the sugar precursor [104]. 

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