Exploring the Steady Operation of a Continuous Pilot Plant for the Di‐Nitration Reaction

• Published in: Chemical engineering & technology 2019-10, Vol.42 (10), p.2241-2251
• Main Authors: Sharma, Mrityunjay, Acharya, Roopashree B., Kulkarni, Amol A.
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Continuous flow; Continuous manufacturing; Di‐nitration; Equilibrium flow; Feature extraction; Herbicides; Laboratories; Mass transfer; Nitration; Nitric acid; Phase separation; Pilot plants; Reaction kinetics; Reactor design; Scale‐up; Steady state
• ISSN: 0930-7516; 1521-4125
• DOI: 10.1002/ceat.201900140

Continuous‐flow synthesis of the selective herbicide pendimethalin was demonstrated in both a laboratory‐scale and a pilot‐scale reactor using only concentrated nitric acid as nitrating agent. The di‐nitration reaction follows second‐order kinetics where the reaction is first order with respect to both reactant and nitric acid. The pinched‐tube reactor was chosen for pilot‐scale reactor fabrication due to its excellent mixing and mass transfer characteristics compared to a straight‐tube reactor. The estimated mass transfer coefficient showed similar nature in the laboratory‐scale and the pilot‐scale pinched‐tube reactor, ensuring similar performance at the pilot scale. Di‐nitration in continuous flow, inline quenching, extraction, and phase separation are some of the salient features of the developed pilot plant. The importance of the start‐up time for achieving steady state in the flow system at the large scale is highlighted. The highly exothermic di‐nitration reaction for pendimethalin synthesis was successfully carried out in a pilot‐scale reactor. Model equations showed that a 1/4‐inch‐diameter tube as continuous reactor provides the desired output while meeting the heat transfer requirements. The time to achieve temperature steady state was the controlling factor compared to the overall time to achieve steady state.