Gaseous by-products

It will be noted that the by-products are both gaseous. In practice, a slight excess over the theoretical quantity (20-75 per cent.) of thionyl chloride is used some of this is volatilised with the gaseous by-products and the remainder is easily removed by fractional distillation (thionyl chloride has b.p. 77°). 

The epitaxy reactor is a specialized variant of the tubular reactor in which gas-phase precursors are produced and transported to a heated surface where thin crystalline films and gaseous by-products are produced by further reaction on the surface. Similar to this chemical vapor deposition (CVE)) are physical vapor depositions (PVE)) and molecular beam generated deposits. Reactor details are critical to assuring uniform, impurity-free deposits and numerous designs have evolved (Fig. 22) (89). 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

In general, the reaction can be performed between 0-60°C with the majority of the reactions being run at room temperature. The reactivity of the hydrazones with either the acyl or tosyl leaving group with thionyl chloride depends on the substrate. However, the acylated hydrazones generally provide gaseous by-products where as the tosyl chloride reaction products have to be separated from the reaction mixture. 

The use of silylated monomers is an interesting alternative method of aromatic polyester synthesis since the silylated gaseous by-products cannot participate in the reverse reaction, shifting polyesterification toward polymer formation. Reactions between silyl esters and acetates (Scheme 2.23) and reactions between silyl ethers and acid chlorides (Scheme 2.24) have been applied to the synthesis of linear265-267 and hyperbranched wholly aromatic polyesters202,268 269 (see Section 2.4.5.2.2). 

Gaseous by-products of the reaction are diffused away from the surface, through the boundary layer. 

In general, the pressure of a reaction system can increase for three reasons (1) evaporation of low boiling chemicals, (2) formation of gaseous by-products as a result of the desired reaction, and (3) production of gases as a consequence of undesired reactions or decompositions. For normal operations, it is imperative to know how deviations in operating conditions affect the gas production. Further, the effect of increased pressure on the reaction rate must be determined to avoid uncontrollable pressure increases in confined systems. 

In the post-treatment of films or fibers, fluorine-containing gas is continuously injected into the reactor and gaseous by-products are removed. The other type of reactor for posttreatment is the batch process reactor, which consists of a suitably sized vacuum chamber provided with means of evacuation and injection. 

An alternative means of generating a polyimide foam with pore sizes in the nanometer regime has been developed [80-90]. This approach involves the use of block copolymers composed of a high temperature, high Tg polymer and a second component which can undergo clean thermal decomposition with the evolution of gaseous by-products to foam a closed-cell, porous structure (Fig. 7). 

The carbonylation of MeOH catalysed by Ir and Mel can also be operated at lower reactor ]H20] and higher ]MeOAc] than the original Monsanto process and without issues of catalyst stability. Commercially acceptable rates can be achieved at lower ]MeI] concentrations by using promoters such as carbonyl iodide complexes of Ru and Os or covalent iodides such as Inij or Znl2 ]9]. Ionic iodide salts are potent poisons for the Ir catalysed reaction ]11]. In contrast with the Rh catalysed systems, CH4 and not H2 is co-produced as a gaseous by-product (Eq. (8)). 

For most practical coating processes, the monomer flows into a plasma reactor with a continuous glow discharge, and is wholly or partially consumed in the conversion to plasma polymer. In such a setup, gaseous by-products and unconverted monomer are continuously pumped out of the reactor. 

In chemical vapor deposition (CVD) complex shaped surfaces can be coated with homogeneous layers, especially when carried out at low pressure (LPCVD, low pressure chemical vapor deposition) (review Ref. [410]). A gas reacts with the heated substrate surface to give a solid coating and gaseous by-products which have to be removed continously. Layer thicknesses created by chemical vapor deposition are usually in the order 5-10 pm.. In cases where it is necessary to keep the temperature low, a plasma can stimulate the surface reaction in plasma enhanced chemical vapor deposition (PECVD). 

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