Introduction endothermic process

Processes An Introduction— A process that proceeds without external intervention is said to be a spontaneous process. A nonspontaneous process cannot occur without external intervention. If a process is spontaneous in one direction, then it is nonspontaneous in the reverse direction. Some spontaneous processes are exothermic, and others are endothermic, so the criterion for spontaneous change cannot be based on enthalpy changes alone. The direction of spontaneous change involves changes in another property called entropy. Entropy provides a measure of the number of ways a given quantity of energy can be dispersed, or distributed, among the particles of the system. 

Reactor heat carrier. As pointed out in Chapter 7, if adiabatic operation is not possible and it is not possible to control temperature by indirect heat transfer, then an inert material can be introduced to the reactor to increase its heat capacity flowrate (i.e. product of mass flowrate and specific heat capacity). This will reduce temperature rise for exothermic reactions or reduce temperature decrease for endothermic reactions. The introduction of an extraneous component as a heat carrier effects the recycle structure of the flowsheet. Figure 13.6a shows an example of the recycle structure for just such a process. 

In the petrochemical industry the introduction of unsaturations in hydrocarbons is mainly obtained by dehydrogenation. This kind of reaction is less suitable for the functionalization of fine chemicals, because the high temperature necessary for the endothermic reaction can lead to the decomposition of thermally unstable compounds. An alternative reaction consists in the oxidative dehydrogenation, that can be carried out at lower temperatiu es. An example of this kind of reaction is constituted by the synthesis of methacrylic add (MAA, intermediate of methylmethacrylate production) via the oxidative dehydrogenation of isobutyric add (IBA), itself obtained from isobutyraldehyde (by-product of the oxo synthesis of nbutyraldehyde from propylene). This process constitutes one of the economically most interesting routes, alternative to the acetone-cyanohydrin process, which nowadays is the predominant process for the MAA production. 

Introduction DMB leads to significant changes in processes thermo-oxidative decomposition the weight loss for copolymers is registered at lower temperatures (Fig. 2) and proceeds more intensively (Fig. 3). With the increase of temperature up to 300°C, as can be seen, the presence of DMB causes the reduction of the speed of weight loss. The speed of the smaller, more content maleic links. The endothermic peak of more than offset by a comparison with PVA, however, extends to a wider temperature field (200-350°C). 

In fact, the absolute value of the enthalpy associated with the overall process of dissolving hydrocarbons in water at 25 C, A//soiution. is an order of magnitude smaller than that of the heat of their evaporation, which is always endothermic (Table 1). This must mean that solvatation (hydration) of the hydrocarbons is exothermic and of the same order of magnitude as the heat of evaporation. It can therefore be concluded that the new bonds created in the presence of hydrocarbons (Af/cw) are enthalpically more beneficial than the hydrogen bonds between the water molecules that break down as a consequence of the introduction of a hydrocarbon chain into water... 

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