Constant pressure adiabatic reaction

The molar enthalpy depends on temperature only, i.e., AHi = Cp, AT, so that the basic energy conservation equation for constant-pressure adiabatic reaction is... 

Suppose pure ethane is fed to a continuous constant-pressure adiabatic reactor at 1273 K and pressure P(atm), the products emerge at rs(K) and / (atm), and the residence time of the reaction mixture in the reactor is large enough for the outlet stream to be considered an equilibrium mixture of ethane, ethylene, and hydrogen. 

If an exothermic reaction takes place at constant pressure adiabatically (the system does not exchange heat with the surroundings), the released heat causes an increase in temperature of the reaction products from temperature T to temperature T2. Then it holds ... 

Computed Adiabatic Reaction Temperature (CART) at constant pressure and/or volume... 

Adiabatic Reaction Temperature (T ). The concept of adiabatic or theoretical reaction temperature (T j) plays an important role in the design of chemical reactors, gas furnaces, and other process equipment to handle highly exothermic reactions such as combustion. T is defined as the final temperature attained by the reaction mixture at the completion of a chemical reaction carried out under adiabatic conditions in a closed system at constant pressure. Theoretically, this is the maximum temperature achieved by the products when stoichiometric quantities of reactants are completely converted into products in an adiabatic reactor. In general, T is a function of the initial temperature (T) of the reactants and their relative amounts as well as the presence of any nonreactive (inert) materials. T is also dependent on the extent of completion of the reaction. In actual experiments, it is very unlikely that the theoretical maximum values of T can be realized, but the calculated results do provide an idealized basis for comparison of the thermal effects resulting from exothermic reactions. Lower feed temperatures (T), presence of inerts and excess reactants, and incomplete conversion tend to reduce the value of T. The term theoretical or adiabatic flame temperature (T,, ) is preferred over T in dealing exclusively with the combustion of fuels. 

The adiabatic flame temperature is defined as the maximum possible temperature achieved by the reaction in a constant pressure process. It is usually based on the reactants initially at the standard state of 25 °C and 1 atm. From Equation (2.20), the adiabatic temperature (7 i[Pg.30]

A tubular flow reactor is used for the gas phase reaction, A => 2B, under adiabatic conditions with a constant pressure of 2 atm. Pure A is charged at 600 R. The heat of reaction is AHr = -2000 Btu/lbmol of A. Heat capacities are 20 and 15 Btu/(Ibmol)(R) for A and B and the specific rate is... 

The gas phase reaction, 2A = B, occurs in a batch reactor at a constant pressure of 5 atm under adiabatic conditions. Initially the reactor contains 2 Ibmol of pure A at 600 R. Heat... 

N2 at a constant pressure of latm and initial temperature of 1100K. Assume an adiabatic reaction with an initial concentration of CH4 of... 

The meaning of Eq. (4.35) is that the sum of the thermal and chemical energies per unit mass of the mixture is constant in the combustion zone that is, the relation between the temperature and the composition of the gas mixture is the same as that for the adiabatic behavior of the reaction at constant pressure. 

It is common to equate the strength of interaction of an acid and a base with the enthalpy of reaction. In some cases this enthalpy may be measured by direct calorimetry AH q for an adiabatic process at constant pressure. 

Suppose now that the reaction takes place adiabatically at constant pressure from an initial composition cf> and temperature To. Then the concentrations will be governed by... 

For an adiabatic combustion process at constant pressure, the enthalpy stays constant. Figure 2 shows the exergy of the reactants, e, and the exergy of the reaction products, e , after this reaction has taken place. The loss in exergy is ... 

Constant-Pressure Reaction Calorimeters. A constant-pressure calorimeter measures the change in enthalpy AH for a chemical reaction occurring in solution under constant atmospheric pressure a trivial example is the coffee-cup calorimeter, which is constructed from two nested polystyrene (Styrofoam ) cups having holes through which a thermometer and a stirring rod can be inserted. The inner cup holds the solution in which the reaction occurs, while the outer cup provides insulation. (A fancier version uses a Dewar181 vessel to approximate adiabatic conditions for the reaction.) Then... 

If the whole process is carried out at constant pressure, then all the heat generated goes into increasing the enthalpy of the products. This internally generated heat is designated as Q, where Q = n AH (heat generated by the reaction at standard state conditions), and Q = n Ai/[products] (heat absorbed by the products of the reaction, at adiabatic conditions). 

Consider the following reaction in an adiabatic, constant-pressure PFR... 

At constant pressure, AH = Qpi but, since this first step is adiabatic, (Qp)i = 0 and AH I = 0. In the second step, the system is placed in a heat reservoir at the initial temperature T. Heat flows into or out of the reservoir as the products of the reaction come to the initial temperature. 

Reactions can be classified as reversible, irreversible, parallel, and consecutive. With regard to operating conditions they are isothermal at constant volume, isothermal at constant pressure, nonisothermal, adiabatic, and polytropic. Reactions are also classified according to the phases involved ... 

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