Intensification of Nitrobenzaldehydes Synthesis from Benzyl Alcohol in a Microreactor

Abstract

A one-step process to produce 2- and 3-nitrobenzaldehyde isomers starting from benzyl alcohol in aqueous mixed nitric and sulfuric acid was developed as an inherently safe continuous flow process in a microreactor. The previously published kinetic model was validated in a microreactor and used to optimize operating conditions in silico to attain the desired product distribution. The molar fractions of nitric and sulfuric acids were increased up to 0.35, 0.45, and temperature to 68 °C, which was impossible to do under batch conditions. Experiments under continuous flow conditions have shown that yields of about 42% and 96% for the ortho- and the meta- isomers, respectively, can be achieved

Ternary HNO3–H2SO4–H2O Mixtures: A Simplified Approach for the Calculation of the Equilibrium Composition

“…The red circles represent the mixtures investigated by Albright et al 19 in which the nitronium ion concentration is measurable by Raman spectroscopy. Under the conditions represented by the green triangles, a slow nitration of benzaldehyde was reported 29 in accordance with the concentration of nitronium ion lower than the limit of detection by Raman spectroscopy. 34 The orange squares are representative of highly diluted nitrating mixtures under which no nitration or very slow nitration of organic substrates occurs.…”

“…Nitronium Ion Concentrations. All of the investigated mixtures reported in the literature 19 together with some of the experimental conditions adopted in this work and previous investigations 13,29 are shown in Figure 1. The red circles represent the mixtures investigated by Albright et al 19 in which the nitronium ion concentration is measurable by Raman spectroscopy.…”

“…The previously reported nitronium ion concentration modeling, not taking into account the nonideality of the system, fails in calculating very low nitronium ions concentrations, too. However, most nitration kinetic models reported in the literature are based on experimental data obtained with mixtures (namely standard mixed acid) of N% and S% of ∼15.6% and 30%, respectively, which corresponds to a weight percentage composition of 20 wt % HNO 3 , 60 wt % H 2 SO 4 , and 20 wt % H 2 O. ,− Under these conditions, even though nitration processes still occur, no nitronium ion quantification is possible by Raman analysis since the nitronium ion concentration is present at levels lower than the limits of detection and quantification and the eqs – are not accurate. To overcome this problem, a semiempirical function has been proposed, namely H R function. , According to this theory following the equilibrium it is possible to evaluate [NO 2 + ] by eq where the activities are expressed in mol·L –1 , together with the molar concentrations of the species in square brackets.…”

“…In addition, the calculated concentrations of the other species are not supported by any experimental measurements. In fact, most of the kinetic experimental investigations on nitration reactions have been carried out under those less acidic conditions for safety reasons. ,− Moreover, in some industrial processes, the thermal power generated by the exothermic reactions is controlled by working under less acidic conditions. The problem of the calculation of low concentrations of nitronium ion (less than 40 mmol·L –1 ) in mixed acid was addressed following different approaches, ,,, since it is impossible to quantify them by Raman analyses .…”

Separation of Pb(II) Ion with Tetraacetic Acid Derivative of Calix[4]arene by Using Droplet-based Microreactor System

“…The microreactor system has some merits, such as the large surface area per unit volume [17], short diffusion distance for the heterogeneous reaction [18], a reduced amount of reagent [19] and portable analysis [20]. Because of these, the microreactor has been widely applied in protein crystallization [21], organic synthesis [22] and solvent extraction [23]. In our previous work, the precious metal recovery with calix [4]arene derivatives by using the microreactor system was investigated.…”