Nitration of nitrobenzene at high‐concentrations of sulfuric acid: Mass transfer and kinetic aspects

Abstract

This article reports studies on mass transfer and kinetics of nitration of nitrobenzene at high concentrations of sulfuric acid in a batch reactor at different temperatures. The effects of concentration of sulfuric acid, speed of stirring, and temperature on mass transfer coefficient were investigated. The kinetics of nitration under homogenized conditions was studied at different sulfuric acid concentrations at these temperatures. The reaction rate constants were determined. The variation of rate constant with sulfuric acid concentration was explained by the M c function. The activation energies of the reactions were determined from the Arrhenius plots. The regimes of the reactions were determined using the values of the mass transfer coefficients and the reaction rate constants. A model was developed for simultaneous mass transfer and chemical reaction in the aqueous phase. The yields of the three isomers of dinitrobenzene were determined, and the variation of isomer distribution with sulfuric acid concentration and temperature was analyzed. This work demonstrates that more than 90% conversion of nitrobenzene is possible at high-sulfuric acid concentrations resulting in high yield of the product even at moderate temperatures and at low speeds of stirring.

Determination of the kinetics of chlorobenzene nitration using a homogeneously continuous microflow

“…The value of k * increases with increasing temperature, and the value of n remains essentially unchanged. n is a specific thermodynamic parameter that is characteristic of different aromatic compounds, which is consistent with the conclusions reported in other studies 18,21,28 . The reaction rate parameters based on NO 2 + could decouple the H 2 SO 4 concentration from the reaction rate constant.…”

“…Numerous related studies 21,27,28 have shown that the rate of nitration is strongly related to the concentration of sulfuric acid. Within a certain range, the higher the concentration of sulfuric acid is, the faster the rate of aromatic nitration.…”

“…. Under homogeneous conditions, the reaction rate of CB nitration can be described by the following equation 28 : By integrating Equations () and (), we obtain: Therefore, a plot of versus residence time ( t ) should be a straight line passing through the origin with a slope equal to . The value of k obs can be calculated from the slope.…”

“…Therefore, it is necessary to study the rate constant based on NO 2 + . Extensive studies 3,13,28 have shown that the rate‐determining step for homogeneous aromatic nitration in mixed acids is the attack of nitrate ions on the aromatics, and the reaction rate can be expressed by the concentration of CB and NO 2 + as follows: where is the observed rate constant expressed for NO 2 + , and is the NO 2 + concentration.…”

The intensification of rapid reactions for multiphase systems in a microchannel reactor by packing microparticles

“…The conversion of NT first increased with the increasing of reaction temperature and then decreased, and the highest conversion was obtained at 340.2 K. The interaction between NT molecules and NO þ 2 ions increased with an increase in reaction temperature. The mass transfer rate of NT also increased and the reaction rate with the increase of temperature, as reported by Rahaman et al 28 However, NO þ 2 ions concentration decreased with an increase in temperature according to the reports by Edwards et al 29 The generation of NO þ 2 ions is through the catalysis of sulfuric acid, and the reaction is exothermic reaction. Therefore, the conversion would decrease as the reaction temperature reached a certain values in the nitration process of NT.…”