Compare isothermal and non-isothermal reactor operation.

Isothermal: constant temperature throughout reactor, simplifies kinetic analysis, requires heat exchange to maintain temperature, achievable in well-stirred or thin tubular reactors with high heat transfer. Non-isothermal: temperature varies with position/time, represents most industrial fixed bed reactors, coupling of mass and energy balances, adiabatic is limiting case. Non-isothermal design more complex but realistic. Hot spots in fixed beds can cause sintering or runaway. Temperature profile optimization important for selectivity and catalyst life.