Cooling reactive treatment

Inherent hazard (e.g., toxicity, stability, reactivity) Cost Renewability Recyclability Size (volume) Scalability Controllability Energy (i.e., total, heating, cooling, recovery, treatment, etc.) Ease of cleaning and maintenance Safety/process safety ... 

Commercial benzene (bp 80°) and toluene (bp 111°) contain thiophene and methylthiophene as the main impurities. These impurities are more reactive than benzene or toluene in aromatic substitution reactions and therefore should be removed before using the material for reactions such as the Friedel-Crafts reaction. The thiophenes may be removed by shaking or stirring the hydrocarbon with one-tenth its volume of concentrated sulfuric acid for one-half hour. Because of the reactivity of toluene, the temperature should be maintained under 35° by occasional cooling. This treatment is, however, rarely necessary since thiophene-free benzene and toluene are commercially available at a reasonable cost. 

Toluene and xylenes are purified in the same manner as benzene however, these solvents should be kept cool (at or below room temperature) during sulfuric acid treatment due to their greater reactivity toward sulfonation. 

For stage VI, the analysis of inherent (or residual) stresses resulting from nonuniform cooling and heat treatment of final articles appears to be critical.Thus, stages IV to VI should be the subject of mathematical modelling specific to reactive processing (chemical molding processes). 

The physico-mechanical properties of aminoplasts in the articles are determined by the degree of hardening and macrostructural defects. In the cooling of the articles down to room temperature reactive groups in the polymer are still retained, but their interaction is made difficult due to the loss of mobility caused by the molecules of the reticular polymer because of the latter s vitrification. Simultaneously a nonequilibrium supramolecular structure is recorded. Heat treatment of the articles does not alter the supramolecular structure, the latter remaining invariable. Heat treatment at a temperature below the vitrification temperature may only cause either a certain additional hardening of the binder or increase the... 

The needles shown in Fig. 10-3a were subjected to this heat-cool treatment resulting in the large three-dimensional crystals shown in Fig. 10-3b. Success in growing seed crystals both prepares seed for larger batches and establishes that this compound will actuaUy grow. It is then necessary to determine if it will grow at a practical rate in the actual reactive crystallization system. 

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