Kinetic Study and Advanced Control of Bechamp Reduction of p-Nitrotoluene Process in a CSTR

Abstract

In any process control study, the first step is to develop a reliable process model. This model can then be used for process control and other process engineering tasks. Further, kinetic study is the heart of the process model of a Chemical reactor. We in this work present the experimental kinetic study of aromatic nitro reduction reaction by Bechamp process followed by a simulation study of advanced control of a continuous reactor. Bechamp process is a process for the reduction of aromatic nitro compound using zero valent iron in acidic conditions. The Bechamp process is especially more popular in the ground water treatment, where the contaminants such as nitro aromatic compounds (NACs) are converted to less harmful counterpart aromatic amines [1]. Further, the Bechamp process is also used to produce aromatic amines from their counterpart nitro compounds. Bechamp process is one of the specific requirements for most of the pharmaceutical products, which is an alternative process to catalytic hydrogenation. Usually, in the Bechamp process, by products such as p-azotoluene and p,p’-ditolylamine are also obtained along with the amine product. Kinetic study for nitro benzene and p-nitro toluene (PNT) [1] using Bechamp process has been studied earlier [2]. The latter study was conducted for the effect of rpm and temperature with 6-9 μm of iron particle. Further, they also concluded that the adsorption of the PNT on the solid surface is the limiting step, which was confirmed by Frossling Correlation [3]. Considering the high cost of such small sized iron particles, they may not be commercially useful even though the smaller particles have large surface area. Hence, it is logical to study the kinetics with coarser iron particles. We in this work have first reproduced few results reported in Popat and Padhiyar [2] in a 500 ml of batch reactor with 6-9 μm iron particles at different rpm. Further, we in this work have focused on the kinetic study of PNT reduction using Bechamp process similar to Popat [2], though with the coarser iron particles, which is commercially more applicable. Apart from the effect of iron particle size, the effect of temperature and the initial composition has also been studied on the Bechamp reduction of PNT. Chemical analysis has been carried out with Gas Chromatography (GC) to find out the compositions of various components involved in the reaction mixture. Further, Frossling correlation of mass transfer coefficient and rpm has been fitted in the current study. Since the kinetic study of PNT was not sufficient to develop a process model for the control of a reactor, we present the advanced process control study of Bechamp reduction of PNT in a continuous reactor. An advanced control algorithm, Model Predictive Control (MPC) has been used for this purpose, which has number of advantages over the conventional single loop, linear controller, namely PID controller. Before applying the MPC to a reactor, an experimental study of process dynamics and control has been presented for a popular temperature control system, namely Single Board Heater System (SBHS) as well.