Exothermic reactions sections

Exothermic reaction (Section 8.3) A reaction for which the enthalpy change (AH0) is negative. 

Exothermic reaction (Section 6.4) A reaction in which the energy of the products is lower than the energy of the reactants. In an exothermic reaction, energy is released and the A//° is a negative value. 

Exothermic reaction (Section 3.8A) A reaction that evolves heat. For an exothermic reaction, A7/° is negative. 

Exothermic reaction (Section 1.6) A reaction in which the bonds in the products are lower energy than those in the starting materials. In an exothermic reaction, the product is more stable than the starting meerial. 

Prepare a solution containing about 100 g, of potassium hypochlorite from commercial calcium hypochlorite ( H.T.H. ) as detailed under -Dimethylacrylic Acid, Section 111,142, Note 1, and place it in a 1500 ml. three-necked flask provided with a thermometer, a mechanical stirrer and a reflux condenser. Warm the solution to 55° and add through the condenser 85 g, of p-acetonaphthalene (methyl p-naphthyl ketone) (1). Stir the mixture vigorously and, after the exothermic reaction commences, maintain the temperature at 60-70° by frequent cooling in an ice bath until the temperature no longer tends to rise (ca. 30 minutes). Stir the mixture for a further 30 minutes, and destroy the excess of hypochlorite completely by adding a solution of 25 g. of sodium bisulphite in 100 ml. of water make sure that no hypochlorite remains by testing the solution with acidified potassium iodide solution. Cool the solution, transfer the reaction mixture to a 2-litre beaker and cautiously acidify with 100 ml. of concentrated hydrochloric acid. Filter the crude acid at the pump. 

Reasonable procedures for manufacturing resoles and novolacs are presented in subsequent sections. These procedures utilize the a concept known in the industry as programmed formaldehyde addition to avoid the problems mentioned above as well as aiding in control of the exothermic reactions resulting from the manufacture of the desired phenol-aldehyde products. These reactions are also extremely exothermic. 

It is generally desirable to minimize the diameter of a tubular reactor, because the leak rate in case of a tube failure is proportional to its cross-sectional area. For exothermic reactions, heat transfer will also be more efficient with a smaller tubular reactor. However, these advantages must be balanced against the higher pressure drop due to flow through smaller reactor tubes. 

Figure 11.4-2 shows process flows for an HF alkylation unit. The three sections are 1) reaction, 2). settling and 3) fractionation. In the reaction section isobutane feed is mixed with the olefin feed (usually propylene and butylene) in approximately a 10 or 15 to 1 ratio. In the presence of the HF acid catalyst the olefins react to form alkylate for gasoline blending. The exothermic reaction requires water cooling. The hydrocarbon/HF mixture goes to the settling... 

As can be seen in Fig. 5, exothermic reactions observed even at room temperature for Li, A.Ni02, especially with x > 0.75, with an organic electrolyte may give some problems in designing high-volume lithium-ion batteries with LiNi02. In this section a possible haystack-type reaction,... 

The curve marked ion-dipole is based on the classical cross-section corresponding to trajectories which lead to intimate encounters (9, 13). The measured cross-sections differ more dramatically from the predictions of this theory than previously measured cross-sections for exothermic reactions (7). The fast fall-off of the cross-section at high energy is quite close to the theoretical prediction (E 5 5) (2) based on the assumption of a direct, impulsive collision and calculation of the probability that two particles out of three will stick together. The meaning of this is not clear, however, since neither the relative masses of the particles nor the energy is consistent with this theoretical assumption. This behavior is, however, probably understandable in terms of competition of different exit channels on the basis of available phase space (24). 

The curves in Figure 5.2 are typical of exothermic reactions in batch or tubular reactors. The temperature overshoots the wall temperature. This phenomenon is called an exotherm. The exotherm is moderate in Example 5.2 but becomes larger and perhaps uncontrollable upon scaleup. Ways of managing an exotherm during scaleup are discussed in Section 5.3. 

In the feed pretreatment section oil and water are removed from the recovered or converted CCI2F2. The reactor type will be a multi-tubular fixed bed reactor because of the exothermic reaction (standard heat of reaction -150 kJ/mol). After the reactor the acids are selectively removed and collected as products of the reaction. In the light removal section the CFCs are condensed and the excess hydrogen is separated and recycled. The product CH2F2 is separated from the waste such as other CFCs produced and unconverted CCI2F2. The waste will be catalytically converted or incinerated. A preliminary process design has shown that such a CFC-destruction process would be both technically and economically feasible. 

The parameter p (= 7(5 ) in gas-liquid sy.stems plays the same role as V/Aex in catalytic reactions. This parameter amounts to 10-40 for a gas and liquid in film contact, and increases to lO -lO" for gas bubbles dispersed in a liquid. If the Hatta number (see section 5.4.3) is low (below I) this indicates a slow reaction, and high values of p (e.g. bubble columns) should be chosen. For instantaneous reactions Ha > 100, enhancement factor E = 10-50) a low p should be selected with a high degree of gas-phase turbulence. The sulphonation of aromatics with gaseous SO3 is an instantaneous reaction and is controlled by gas-phase mass transfer. In commercial thin-film sulphonators, the liquid reactant flows down as a thin film (low p) in contact with a highly turbulent gas stream (high ka). A thin-film reactor was chosen instead of a liquid droplet system due to the desire to remove heat generated in the liquid phase as a result of the exothermic reaction. Similar considerations are valid for liquid-liquid systems. Sometimes, practical considerations prevail over the decisions dictated from a transport-reaction analysis. Corrosive liquids should always be in the dispersed phase to reduce contact with the reactor walls. Hazardous liquids are usually dispensed to reduce their hold-up, i.e. their inventory inside the reactor. 

Note A negative sign is necessary in equation 3.24 as Qr is positive when heat is evolved by the reaction, whereas the standard enthalpy change will be negative for exothermic reactions. Qp will be negative when cooling is required (see Section 3.4). 

Exothermic Reactions of Transition Metal Ions with Hydrocarbons. Cross sections for the formation of product ions resulting from the interaction of Ni+ with n-butane are shown in Figure 6 for a range of relative kinetic energies between 0.2 and 4 eV. In contrast to the results shown in Figure 3, several products (reactions 6-8) are formed with large cross section at low energies. These cross sections decrease with... 

For T < 2.2 K, 4He can also form a superfluid film which contributes to the heat transfer. H2 can be used as exchange gas the advantage is that it can be condensed when 4He is transferred into the cryostat and does not need to be pumped. However, the orthopara conversion produces heating (see Section 2.2). 3He, with a high vapour pressure, no exothermic reactions and no superfluidity in the kelvin temperature range is the best solution except when its residual radioactivity cannot be tolerated (see Section 16.5). Examples of gas switches are reported in ref. [22-27],... 

An unusual feature of a CSTR is the possibility of multiple stationary states for a reaction with certain nonlinear kinetics (rate law) in operation at a specified T, or for an exothermic reaction which produces a difference in temperature between the inlet and outlet of the reactor, including adiabatic operation. We treat these in turn in the next two sections. 

For an endothermic, reversible reaction (such as the dehydrogenation of ethylbenzene), as also shown in Section 5.3 and illustrated in Figure 5.2(b), the rate does not exhibit a maximum with respect to T at constant /, but increases monotonically with increasing T. The rate also decreases with increasing / at constant T, as does the rate of an exothermic reaction. 

This section on protective measures discusses three elements (1) containment, (2) instrumentation and detection of a runaway, and (3) mitigation measures. For each element, examples are given to illustrate the principles discussed. This section is basically a summary of protective measures, not an exhaustive treatise. Protective measures are necessary considerations, and in fact, safety requirements, when handling reactive substances and exothermic reactions. 

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