Numerical Simulation of a Two-Phase Flow for the Acrylonitrile Electrolytic Adiponitrile Process in a Vertical/Horizontal Electrolysis Cell

Jiin-Yuh Jang,Yu-Feng Gan

doi:10.3390/en11102731

Abstract

This paper investigated the effect of oxygen holdup on the current density distribution over the electrode of a vertical/horizontal electrolysis cell with a two-dimensional Eulerian–Eulerian two-phase flow model in the acrylonitrile (AN) electrolytic adiponitrile (ADN) process. The physical models consisted of a vertical/horizontal electrolysis cell 10 mm wide and 600 mm long. The electrical potential difference between the anode and cathode was fixed at 5 V, which corresponded to a uniform current density j = 0.4 A/cm2 without any bubbles released from the electrodes. The effects of different inlet electrolyte velocities (vin = 0.4, 0.6, 1.0 and 1.5 m/s) on the void fraction and the current density distributions were discussed in detail. It is shown that, for a given applied voltage, as the electrolyte velocity is increased, the gas diffusion layer thickness decreased and this resulted in the decrease of the gas void fraction and increase of the corresponding current density; for a given velocity, the current density for a vertical cell was higher than that for a horizontal cell. Furthermore, assuming the release of uniform mass flux for the oxygen results in overestimation of the total gas accumulation mass flow rate by 2.8% and 5.8% and it will also result in underestimation of the current density by 0.3% and 2.4% for a vertical cell and a horizontal cell, respectively. The results of this study can provide useful information for the design of an ADN electrolysis cell.

Highlights

Adiponitrile (NC(CH2 )4 CN, ADN) is an important chemical compound as an intermediate in the production of hexamethylenediamine (HMDA), which, in combination with adipic acid, is employed in the manufacture of nylon-6,6
The resistance of the electrolyte purpose of this paper is to investigate the effects of oxygen gas release at the anode on the void fraction, and the current density of a vertical and a horizontal electrolysis cell, respectively
The electrical potential difference between the anode and cathode was fixed at 5 V, which corresponded to a uniform current density j = 0.4 A/cm2 without any bubbles released from the electrodes

Summary

Introduction

Adiponitrile (NC(CH2 ) CN, ADN) is an important chemical compound as an intermediate in the production of hexamethylenediamine (HMDA), which, in combination with adipic acid, is employed in the manufacture of nylon-6,6. Owing to the industrial value of ADN, several methods have been developed for its synthesis. The most modern production route involves electrosynthesis starting from acrylonitrile (CH2 CHCN, AN) in an electrochemical reactor [1,2]. Cathode: 2CH2 = CHCN + 2H+ + 2e− → NC(CH2 ) CN. Synthesis reaction: 2CH2 = CHCN + H2 O → NC(CH2 ) CN + 1/2O2. The AN gets the electron, and the product ADN is formed at the cathode. As the water loses the electron, the product of oxygen gas is released at the anode. The evolved oxygen in the electrolyte makes the problem a two-phase flow and has great impact on the performance of the electrode. The major aim of this study is to investigate the effects of oxygen

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