Chemical process nonlinearity: choose the system that typically exhibits nonlinear dynamic behavior due to temperature–rate coupling and energy balance effects.

Introduction / Context:
Nonlinearity in chemical process models often arises from reaction-rate temperature dependence (Arrhenius) and multiplicative terms in mass/energy balances. Recognizing inherently nonlinear units is essential for selecting appropriate control strategies and for safe operation near multiple steady states or thermal runaway regions.

Given Data / Assumptions:

• CSTR stands for continuous stirred-tank reactor.
• Isothermal means reactor temperature is held constant; non-isothermal couples species and energy balances.
• Reaction rates typically follow k = k0 * exp(-E/RT), introducing strong nonlinearity.

Concept / Approach:
In a non-isothermal CSTR, the energy balance links temperature to heat generation (reaction) and heat removal (cooling). Because reaction rate depends exponentially on temperature, small temperature changes strongly affect conversion, which in turn changes heat release—a feedback that creates nonlinear dynamics, possible multiple steady states, and oscillations. In contrast, an isothermal CSTR with a first-order reaction can often be linearized to an LTI form. An ideal mixer without reaction is typically linear in concentration with constant density assumptions.

Step-by-Step Solution:

Verification / Alternative check:
Phase-plane and bifurcation analyses for exothermic CSTRs show S-shaped steady-state curves and ignition/extinction points—canonical nonlinear phenomena.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming all reactors are equally nonlinear; temperature coupling is the key differentiator here.

Final Answer:
Non-isothermal CSTR