Process Routes to Valuable Carbonate Products

The most important inorganic carbonate materials, their natural resources, and the conventional process routes were listed in Section 14.1. When the goal shifts from carbonate material production to a process that reduces C02 emissions, or fixes significant amounts of C02, then different process routes are followed, mainly because the raw materials are different. 

It is important for the discussion below to distinguish between direct and indirect process routes. Direct carbonation is the simplest approach to carbonate production (or mineral carbonation see Section 14.4) and the principal approach is that a suitable feedstock-for example, serpentine or a Ca/Mg-rich solid residue-is carbonated in a single process step. For an aqueous process this means that both the extraction of metals from the feedstock and the subsequent reaction with the dissolved C02 to form carbonates takes place in the same reactor. 

on the other hand, the process of mineral carbonation is divided into several steps, it is classified as indirect carbonation. In other words, indirect carbonation means that the reactive component (usually Mg or Ca) is extracted from the feedstock (typically as oxide or hydroxide) in one step and then, in another step, it is reacted with C02 to form the desired carbonates. 

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C.i.a. Sequential Hydroarylation (Hydroalkenylation)/Cyclization. Since the cis stereochemistry of addition pushes the substituents of the acetylenic moiety to the same side of the olefinic double bond, a cyclization reaction can follow the addition step when these substituents bear suitable nucleophilic and electrophilic centers, and the whole process resembles a valuable straightforward methodology for the preparation of cyclic compounds (Scheme 20). Cyclization can occur under hydroarylation(hydroalkenylation) conditions—either before or after the substitution of the carbon-hydrogen bond for the carbon-palladium bond—or by subjecting the isolated hydroarylation(hydroalkenylation) product to suitable reaction conditions. This strategy has been employed successfully to develop new routes to various heterocycles. 

The natural oleochemicals are obtained from natural oils with the least change in the structure of the carbon chain fraction. In contrast, synthetic oleochemicals are built up from ethylene to the desired carbon chain fraction or from oxidation of petroleum waxes. Fats and oils are renewable products of nature. One can aptly call them oil from the sun where the sun s energy is biochemically converted to valuable oleochemicals via oleo-chemistry. Natural oleochemicals derived from natural fats and oils by splitting or trans-esterification, such as fatty acids, methyl esters, and glycerine are termed basic oleochemicals. Fatty alcohols and fatty amines may also be counted as basic oleochemicals, because of their importance in the manufacture of derivatives (6). Further processing of the basic oleochemicals by different routes, such as esterification, ethoxylation, sulfation, and amidation (Fig. 12.1), produces other oleochemical products, which are termed oleochemical derivatives. 

A stimulating development of urea alcoholysis has been demonstrated very recently for better AE, in an innovative integrated process that incorporates fatty ester hydrolysis to co-amino-alkanoic acids [44], Within the scope of this chapter, the most interesting step of this process is the recycling of waste alcohol, formed by the hydrolysis step, for urea alcoholysis. Dialkyl carbonate is produced together with ammonia thereafter, the ammonia is engaged in the amination reaction to obtain the amino acids. The overall process avoids the storage of NH3 that is necessary for the amination route, and transforms a waste product-the alcohol-into the valuable dialkyl carbonate. 

Other chemical routes for the direct conversion of methane into valuable chemicals, that is, CH3OH and HCHO, involve partial oxidation under specific reaction conditions [24-28]. As a general rule, these conversion processes use fuel-rich mixtures with the oxidant to minimize the extent of combustion reactions, which yield unwanted carbon oxides. Under these conditions, purely gas-phase oxidation reactions require high temperatures, which are detrimental for the control of selectivity of the desired products. Among the plethora of catalysts employed for this purpose, metal oxides — most of them transition metal oxides — are prominent. These catalyst systems are considered in this chapter. 

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