Steady-state Nonisothermal reactor Design Part I CSTRs with Heat Exchange. PFRs with Heat Exchange.

Non Isothermal Process Most reactions are not carried out isothermally Focus is then on heat effects in chemical reactors Basic design equation such as rate laws, stoichiometric relationships used for isothermal reactor design are valid for non-isothermal reactors The major difference is method of evaluating the temperature effect e.g. length of PFR, or heat is removed from a CSTR

Non Isothermal Process So what additional information is needed to design non-isothermal reactors ? Example: For the following reaction A → B Calculate the reactor volume necessary for 70% conversion Note: The reaction is exothermic, reactor is operated adiabatically. So temperature increases with conversion down the length of reactor

Non Isothermal Process Solution: Mole Balance (design equation) Rate Law (Arrhenius equation) k = f(T)

Non Isothermal Process Stoichiometry (liquid phase), v = vo Combining and cancelling the entering concentration CA0=0

Non Isothermal Process The final equation We require a relationship which relates X and T, T and V to solve the above equation The energy balance will provide the relationship

Non Isothermal Process Energy Balance we need appropriate energy balance to relate temperature and conversion or reaction rate For adiabatic reaction we have So we have all equations needed to solve the conversion and temperature profile

The Energy Balances We know that for a closed system, the energy balance is For open (continuous) flow system where mass crosses the system boundaries

The Energy Balances The energy balance of the case of only one species entering and leaving becomes

The Energy Balances The unsteady-state energy balance for an open well-mixed system that has n species, entering and leaving the system at their respective molar flow rates Fi (moles of i per time) and their respective energy Ei (joules per mole of i)

The Energy Balances Evaluating work term W is separated into flow work (W) or other work (Ws) Ws is shaft work and produce such stirrer in CSTR or turbine in PFR Flow work is the work necessary to get the mass into and out of the system J/s

The Energy Balances Combining the energy balance term derived earlier and work term we get We know that In chemical reactor these energies are often negligible as compared to enthalpy, heat transfer and work term J/mol

The Energy Balances Enthalpy in case of into and out of the system can be expressed as the sum of the net internal energy carried into (or out of) the system by mass flow plus the flow work Combining we get We can also write

The Energy Balances Adiabatic (Q=0) CSTR, PFR, Batch or PBR. The relationship between conversion, XEB and temperature for Ws = 0, constant CPi and ∆CP = 0 For an exothermic reaction