Vapor-phase reactions, irreversible

Increasing the pressure of irreversible vapor-phase reactions increases the rate of reaction and hence decreases reactor volume both by decreasing the residence time required for a given reactor conversion and increasing the vapor density. In general, pressure has little effect on the rate of liquid-phase reactions. 

P8-10g The irreversible endothermic vapor-phase reaction follows an elementary rale law ... 

The numerical example is the chlorination of propylene. There are two vapor-phase, irreversible, exothermic reactions ... 

Szollosi et al. have studied MgO as a catalyst for the hydrogen-transfer reaction between methyl ketones and /-PrOH in the vapor phase [19]. It was shown that deactivation occurred as a result of condensation products formed from methyl ketones and acetone. This deactivation could be prevented by pretreatment of the catalyst with carbon tetrachloride. It was proposed that CP ions block the irreversible adsorption of ketones at Lewis-acid sites. 

Care must be present when involing a photo process in CVD. In particular, the absorption induced reaction of a vapor phase precursor molecule must be distinguished from temperature effects. Otherwise, the irreversible result is a combination of a photo-event and a pyro-event. Although substrate cooling will rule out surface mobility of atoms due to light-induced heating, care must be utilized when attributing all gas phase chemistries to purely photo events. 

Another ammonia sensor speciHcally designed for use in bioliquids is based on the evanescent wave technique and can be applied to the vapor-phase determination of ammonia above blood and serum [136]. It utilizes the ninhydrin reaction occurring in the polymer coating of the fiber, and the resulting color change is monitored by total internal reflection. The probe is applicable to clinical determinations normally carried out in the vapor phase, but works irreversibly. A linear relationship exists between absorbance and ammonia concentration in the clinically useful range of 0-4.0 pg mL. Comparison with the reference method showed a correlation coefficient of 0.92. 

ER.26 An irreversible reaction in vapor phase A R + S is carried out in an adiabatic reactor of 500 L. The reactant A is fed into the reactor with inert 50% and a volumetric flow rate of 10 mol/min with a total pressure of 40 atm, the inlet temperature is 1100 K. 

In the production of cumene from propylene, the following elementary, vapor-phase, irreversible reaction takes place ... 

The use of reactive solvents has a signiflcant advantage over physical solvents, where applicable, because normally the impurity is destroyed or altered by the reaction and does not exhibit a significant vapor pressure over the solution once absorbed. When the liquid phase reaction is irreversible and rapid, which is often the case, a countercurrent contactor is not necessary, and simple venturi or spray scrubbers can provide high efficiency. The design of such equipment is discussed in Chapter 1. 

Numerous industrial operations involve a heat transfer between a liquid phase and a gaseous phase, with an important mass transfer effect, either as desorption-evaporation or as absorption-condensation. Here are some examples reconcentration, by evaporation, of solvents, toxic industrial effluents production, by absorption, of industrial aqueous acid solutions reversible or irreversible chemical reactions (oxidation, hydrogenation, sulfonation) purification of permanent gases (air, smoke) by scrubbing of soluble vapors desorbers and absorbers for heat pumps, where these two operations occur simultaneously. 

First of all, three special cases of vapor-hquid equilibrium of binary mixtures are presented qualitatively in Fig. 5.1-2. Considered are ideal mixtures (case A ), mixtures with total miscibiUty gap in the hquid phase (case B), and mixtures with irreversible chemical reaction in the liquid phase (case C). By converrtion, the symbols X and y denote the molar fraction of the low-boiling component a in the hq-ttid and the gas phase, respectively. 

Big. 5.1-2 Vapor-liquid equilibrium of three binary mixtures (A) ideal system, (B) system with a total miscibility gap in the liquid phase, and (C) system with irreversible chemical reaction in the liquid phase... 

The second process considered in detail is a reactor that is cooled by evaporative cooling the boiling liquid in the CSTR uses the latent heat of vaporization to remove the exothermic heat of reaction. The irreversible exothermic reaction A + B -> C occurs in the liquid phase in the reactor. Figure 4 shows the process configuration. 

Consider a recycle process where an irreversible, exothermic reaction A-t-B—>X occurs in a gas phase, adiabatic tubular reactor. The process flowsheet consists of one tubular reactor, one distillation column, one vaporizer, and one furnace with two heat exchangers which was first studied by Reyes and Luyben [10] (Fig. 1). Two fresh feed streams FoAand Fob are mixed with the liquid recycle stream D and sent to a steam-heated vaporizer. According to the requirement of reaction temperature, the vapor from the vaporizer outlet stream is preheated first in a feed-effluent heat exchanger followed by a furnace to get proper reactor temperature as well as for the start-up purpose. The exothermic reaction takes place in the tubular reactor and the reactor temperature increases monotonically along the axial direction with the following inlet and outlet temperatures, Tj and Tout- The hot gas from the reaetor preheats the... 

Chemical reactions in the liquid phase are either reversible or irreversible. Typical reversible reactions are involved in the absorption of H2S into ethanolamines, or the absorption of CO2 into alkali carbonate solutions. These reversible reactions permit the resultant solution to be regenerated so that the solute can be recovered in a concentrated form. Some irreversible reactions are the absorption of NH3 into dilute acids and the absorption of CO2 into alkaline hydroxides. The solute in such absorptions is so tightly bound in the reaction product that there is no appreciable vapor pressure of solute above the liquid phase. Under these conditions, regeneration of the solute is not possible, and the reacting component in the liquid is consumed. The purpose of such a reactant is to increase the solubility of the solute in the liquid phase and/or reduce the liquid-film resistance to mass transfer. Much theoretical work has been conducted since the 1950s to study diffusion and reaction in the liquid phase [19]. To calculate the effect of the rate of chemical reaction on the mass transfer requires the prediction of physical/chemical constants of salt solutions, such as equilibrium constants, reaction velocities, solubilities, and diffusion coefficients. Often, these constants must be available at elevated temperatures and/or pressures. 

Irreversible Reaction. In this type of absorption the component being absorbed reacts with a component of the liquid phase to form reaction products that can not readily be decomposed to release the absorbate. An example is the absorption of hydrogen sulfide in iron chelate solution to form a slurry of elemental sulfur particles. The analysis of systmns involving irreversible reactions is simplified by the absence of an equilibrium vapor p>res sure of adsorbate over the solution, but becomes more complex if the irreversible reaction is not instantaneous or involves several stqis. 

With cocurrent absorbers, the highest gas purity attainable is represented by equilibrium between the product gas and the product (rich) solution. When an irreversible reaction occurs in the liquid phase, the equilibrium vapor pressure of acid gas over the solution is negligible... 

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