**Kiara Capreece Premlall and David Lokhat \***

School of Engineering, University of KwaZulu-Natal, Durban 4051, South Africa; lovekiara@hotmail.co.za **\*** Correspondence: lokhat@ukzn.ac.za; Tel.: +27-031-2601-897

Received: 26 February 2020; Accepted: 27 March 2020; Published: 16 April 2020

**Abstract:** Acrylic acid, a versatile chemical intermediate, is typically manufactured via a two-step process involving the selective oxidation of propylene and acrolein. This work presents an optimized simulation on Aspen Plus® (AspenTech, Bedford, MA, USA) of the production of acrylic acid, with focus on the optimum design and operation of the reactor train, and modification for reduction in energy usage. In the propylene oxidation reactor, an inert pre-heating zone was designed to make use of the excess energy present in the exothermic process fluid and carried within the molten salt cooling fluid circuit. In the acrolein oxidation reactor, injection of cold air was used as a means to absorb the reaction heat. The optimization methodology employed aimed to minimize the total capital expenditure (i.e., equipment sizing) and operating costs (heat exchange network) for the required acrylic acid production and design constraints. The design constraints were based on the selected reaction kinetics and design heuristics for an optimum reactor design in this service from literature. Sensitivity analyses conducted on Aspen Plus® (AspenTech, Bedford, MA, USA) were used to determine both the interactions between and grouping of the critical parameters for the optimization. Elimination of the conventional fired preheater from the propylene oxidation reactor resulted in energy savings of almost 7 MW, with the reduction in cooling fluid pumping power for the acrolein oxidation reactor amounting to 5 kW.

**Keywords:** acrylic acid; propylene oxidation; multitubular reactor; optimization
