Exothermic reactions liquid-phase

The reactions are highly exothermic. Under liquid-phase conditions at about 200°C, the overall heat of reaction is —83.7 to —104.6 kJ /mol (—20 to —25 kcal/mol) ethylene oxide reacting (324). The opening of the oxide ring is considered to occur by an ionic mechanism with a nucleophilic attack on one of the epoxide carbon atoms (325). Both acidic and basic catalysts accelerate the reactions, as does elevated temperature. The reaction kinetics and product distribution have been studied by a number of workers (326,327). 

The process considered in this section is the ideal quaternary exothermic reversible liquid-phase reaction... 

This is an exothermic, reversible, homogeneous reaction taking place in a single liquid phase. The liquid butadiene feed contains 0.5 percent normal butane as an impurity. The sulfur dioxide is essentially pure. The mole ratio of sulfur dioxide to butadiene must be kept above 1 to prevent unwanted polymerization reactions. A value of 1.2 is assumed. The temperature in the process must be kept above 65°C to prevent crystallization of the butadiene sulfone but below lOO C to prevent its decomposition. The product must contain less than 0.5 wt% butadiene and less thM 0.3 wt% sulfur dioxide. 

To 19 8 of well-agitated distilled water plus 18 g of ditertiary-butyl-ppinene oxide that was about half racemic, half d-form. The temperature was maintained at 30°C to 50°C, first with ice bath cooling and then with tap water cooling. The addition of the pinene oxide required 1 h hours. After the addition was complete and the exothermic reaction was about over, the mixture was stirred for 1 h hours at about 30°C, and then centrifuged to separate the crude sobrerol from the liquid phase consisting of oil and water. 

In the direct hydration method, the reaction could be effected either in a liquid or in a vapor-phase process. The slightly exothermic reaction evolves 51.5 KJ/mol. 

Older methods use a liquid phase process (Figure 10-11). ° New gas-phase processes operate at higher temperatures with noble metal catalysts. Using high temperatures accelerates the reaction (faster rate). The hydrogenation of benzene to cyclohexane is characterized by a highly exothermic reaction and a significant decrease in the product volume... 

The last comprehensive review of reactions between carbon-centered radicals appeared in 1973.142 Rate constants for radical-radical reactions in the liquid phase have been tabulated by Griller.14 The area has also been reviewed by Alfassi114 and Moad and Solomon.145 Radical-radical reactions arc, in general, very exothermic and activation barriers are extremely small even for highly resonance-stabilized radicals. As a consequence, reaction rate constants often approach the diffusion-controlled limit (typically -109 M 1 s"1). 

Ozone is strongly exothermic in its reactions and neat solid or liquid phases are highly explosive. 

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. 

The liquid phase hydrolysis reaction of acetic anhydride to form acetic acid is carried out in a constant volume, adiabatic batch reactor. The reaction is exothermic with the following stoichiometry... 

The existence of pulsating motion of the liquid phase within the catalyst pellet indicates that under certain conditions a steady-state regime of reaction progress can become unstable due to the exothermicity of the reaction under study. Further... 

Thermal reaction techniques enable a quantification of the influence of solvation on reactivities.1,2,19 One particular reaction which is a good example of how solvation can affect the nature of a core ion reaction site comes from a study118 of the interaction of OH with C02. The gas-phase reaction between the individual species is quite exothermic and can only take place by a three-body association mechanism. The reaction proceeds very slowly in the liquid phase and has been calculated119 to have a barrier of about 13 kcal mol-1. In biological systems, the reaction rate is enhanced by about 4 orders of magnitude through the enzyme carbonic anhydrase. Recent studies carried out in our laboratory provide detailed... 

The only difference between them is that Reaction (1) involves water in the liquid phase and Reaction (2) involves water as water vapor. Since more heat is released when H20(g) - H20(f), as shown in the adjacent diagram, Reaction (1) is more exothermic than Reaction (2). 

White phosphorus (15.5 g, 0.5 g-atom) was cut into approximately 0.1-g pieces under water, washed with acetone followed by ether, and then added in one portion to the reaction mixture. The reaction mixture consisted of 1.0 mol of phenyl lithium in 750 ml of diethyl ether. The exothermic reaction was continued by heating at reflux for 3 h. Water was then added to hydrolyze the remaining organometallic this resulted in the precipitation of a yellow solid. The solid was removed by filtration, and the two phases of the remaining liquid portion were separated. The aqueous portion was extracted with three 50-ml portions of diethyl ether, which were combined with the organic layer, dried over anhydrous sodium sulfate, and evaporated to give the product phenylphosphine in 40% yield. 

An exothermic first-order liquid-phase reaction A - R is conducted in a PFR. Determine the volume required for 90% conversion of A, if the process is adiabatic. 

For the exothermic, liquid-phase, reversible isomerization reaction, A B, taking place in... 

A batch reactor is an agitated vessel in which the reactants are precharged and which is then emptied after the reaction is completed. More frequently for exothermic reactions, only part of the reactants are charged initially, and the remaining reactants and catalysts are fed on a controlled basis this is called a semi-batch operation. For highly exothermic reactions and for two-phase (gas-liquid) reactions, loop reactors with resultant smaller volumes can be used. 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

If die semiempirical equations proposed in Reference 4 are correct, then die exothermicity of die reaction RX+R1 Y —RY+R1 X would be identical in the gaseous and liquid phases. Experience shows die assumption generally results in much poorer agreement for all-solid reactions. No such semiempirical equations for enthalpy of sublimation and its estimation appear to be available, although some cancellation is expected. 

Method 4 Na2S.9H20 (2.65 g, 11 mmol) in H20 (10 ml) is added the dibromoalkane (5 mmol) and Aliquat or TEBA-C1 (0.5 mmol) in PhH (10 ml). The initially exothermic reaction is stirred for ca. 1 h at room temperature and the organic phase is then separated, washed with H20 (2 x 20 ml), dried (MgS04), and evaporated to yield the alkene. Gaseous alkenes are collected using a gas burette ( the solvent can be omitted with liquid dihaloalkanes). 

A schematic representation of the combustion wave structure of a typical energetic material is shown in Fig. 3.9 and the heat transfer process as a function of the burning distance and temperature is shown in Fig. 3.10. In zone I (solid-phase zone or condensed-phase zone), no chemical reactions occur and the temperature increases from the initial temperature (Tq) to the decomposition temperature (T ). In zone II (condensed-phase reaction zone), in which there is a phase change from solid to liquid and/or to gas and reactive gaseous species are formed in endothermic or exothermic reactions, the temperature increases from T to the burning surface temperature (Tf In zone III (gas-phase reaction zone), in which exothermic gas-phase reactions occur, the temperature increases rapidly from Tj to the flame temperature (Tg). 

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