Contents lists available at ScienceDirect Chemical Engineering & Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep Process intensification using a spiral capillary microreactor for continuous flow synthesis of performic acid and it’s kinetic study Yadagiri Maralla, Shirish Sonawane ⁎ Department of Chemical Engineering, National Institute of Technology, Warangal, Telangana, 506004, India ARTICLE INFO Keywords: Formic acid Spiral capillary microreactor Performic acid Homogeneous catalyst Sulfuric acid and synthesis Continuous synthesis ABSTRACT The continuous production of performic acid is getting significant importance due to it’s versatile oxidizing properties in various applications such as in the food, oil and chemical industries. In this work, an attempt has been made for synthesis of performic acid in a continuous flow microreator in polytetrafluoroethylene spiral capillary microreactor (PSCMR) with and without homogeneous catalyst. The effect of catalyst concentration, hydrogen peroxide concentration, temperature and radius of curvature on formation of perfomic acid was studied. The maximum conversion of FA was obtained within 6 min at 30 °C and 4 mol% catalyst. The maximum PFA was obtained (5.175 mol/L) when the reaction was performed in spiral capillary microreactor having 13.25 mm radius of curvature (Number of turns = 21). However, in the radius of curvature of 18.25 mm (Number of turns = 15) and 23.25 mm (Number of turns = 12) of the PSCMR gave 3.393 mol/L and 3.105 mol/L of PFA respectively at residence time of 9 min. Based on the kinetic equations and experimental data, the kinetic constants were determined. Thus, the average rate constants for forward and backward reaction are 0.0097 and 0.04354 L/(mol min) respectively. Based on the kinetic data, it was found that the activation energies of PFA synthesis and hydrolysis were 31.716 and 13.701 kJ/mol respectively. 1. Introduction Performic acid (PFA) is an organic compound with low molecular weight and it falls under the family of the peroxycarboxylic acids (RCOOOH). PFA is environmentally friendly and commonly used in chemical, paper, textile, medical and food industries for bleaching, chemical processing and disinfection due to it’s high oxidization property [1]. The PFA is very effective oxidizer and decompose at temperature above 40 °C [1]. Performic acid is a strong oxidiser compared to peroxyacetic acid and hydrogen peroxide, which makes the PFA a more popular oxidizing agent. The performic acid is a very versatile epoxidizing agent for epoxidation of unsaturated oil [2–6]. Generally, the epoxidation of the vegetable oil is catalyzed using mineral acids (H 2 SO 4 ) along with the performic acid. The PFA is used in the epoxidation of soybean or other vegetable oils in the presence of catalytic amount of a mineral acid sush as H 2 SO 4 [6,7–12]. The PFA is simply prepared by the reaction between formic acid and in contact with a hydrogen peroxide in the absence or in the presence of a catalytic amount of a mineral acid such as H 3 PO 4 or H 2 SO 4 [13]. The chemical reaction is as reported below as shown in Scheme (1). ⇌ HCOOH(A) + H O (B) HCOOOH(C) + H O(W) 2 2 k k 2 2 1 (1) The formation of PFA is extremely exothermic in nature (△H= -55.50 kcal/mol). The forward reaction is known as “perhy- drolysis” and the backward reaction is known as “hydrolysis”. Some of the reports have shown that hydrogen peroxide is stable below 100 °C in an acid environment, while PFA is susceptible to decompose even at room temperature in contact with impurities like metal [13–18]. Microstructured reactors have attained considerable attention in academia and industry as they provide large specific surface area with improved mass and heat transfer. The continuous synthesis processes based on microstructured reactors are expected to enhance their role in large scale production of chemicals. Recently, microstructured reactors have found place for many hazardous/exothermic reactions such as chlorinations, brominations, fluorinations, nitrations, oxidations as there is better control over the rate of reaction compared to conven- tional batch reactors [19,20,40]. Researchers very often studied planar structures of microreactors to get overall advantage in terms of mixing, mass and heat transfer in continuous synthesis. Mixing, mass and heat transfer in the micro- structured reactor is goverend by the laminar flow. The perturbation of the laminar flow supports to increase the diffusion in the https://doi.org/10.1016/j.cep.2018.01.009 Received 2 November 2017; Received in revised form 23 December 2017; Accepted 10 January 2018 ⁎ Corresponding author: +91-870-2462626 E-mail address: shirish@nitw.ac.in (S. Sonawane). Chemical Engineering & Processing: Process Intensification 125 (2018) 67–73 Available online 11 January 2018 0255-2701/ © 2018 Elsevier B.V. All rights reserved. T