A Study on Characteristics of Quaternary Ammonium Salts in Electrosynthesis of Adiponitrile

• Main Authors: Fang-YiChen, 陳芳毅
• Other Authors: Ming-Chang Yang
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/5g3wqp

碩士 === 國立成功大學 === 化學工程學系 === 106 === Recently, with the increment of the needs of nylon, the demands of the key raw material, adiponitrile (ADN), also increase, whose production technology has been controlled by developed countries. In Taiwan, ADN strongly relies on the import from foreigner countries now, so the researches of synthesis of ADN are much important obviously. Electrosynthesis of ADN from acrylonitrile (AN) is a one-step reaction, and the toxicity of acrylonitrile is low. Therefore, the production technology is developed and researched comparatively easier. In this study, the influences of each component in the existing electrolyte on the electrode surface behavior during the reduction reaction were investigated with Electrochemical Impedance Spectroscopy. And the adsorption characteristics of quaternary ammonium salts (QASs) with different carbon chain lengths and added concentrations were investigated. Finally, the ADN was electrosynthesized in an stirring batch cell without diaphragm to investigate the effect of carbon chain lengths and concentrations of QASs on the selectivity and current efficiency of ADN. The results of batch reaction were used to estimate the selectivity and current efficiency of ADN under continuous reaction conditions. The results showed that AN, QASs and ADN did be adsorbed on the surface of the electrode; ethylenediaminetetraacetic acid (EDTA) did not. The QASs with different carbon chain length have different adsorption characteristics, and the adsorption layers of MBAP and TBAP can maintain the adsorption layer structure over a wider range of potentials. It is calculated that the longer the carbon chain in QAS, the more the number of average adsorption layers on the electrode surface, and that increasing the concentration of the QASs increased the adsorption amount on the electrode surface. With low organic concentration in an electrolyte, the QAS with longer carbon chain decreased hydrogen evolution reduction current more significantly probably because of larger number of adsorption layers and higher hydrophobicity. Furthermore, probably because the QAS with longer carbon chain had stronger lipophilicity and larger ion diameter to form larger interspacing in the adsorption layer, AN was easier to diffuse to electrode surface for reduction reaction. The effect was most significant with TBAP. Increasing the concentration of the QASs from 20 mM to 40 mM enhanced the decrease in hydrogen evolution reaction current, and probably then increased the concentration of AN on the electrode surface, thereby effectively promoted the reduction reaction of AN. Higher concentration of TPAH was most effectively. The results of electrosynthesis in batch reactor showed that the QAS with longer carbon chain gave higher selectivity and current efficiency of ADN. Increasing the concentration of the QASs increased the selectivity of ADN or trimer, and decreased the selectivity of propionitrile significantly. When adding 20 mM TBAP, there is the highest ADN selectivity and ADN current efficiency. The estimation for a continuous reaction condition from the batch reactor reaction showed that the ADN selectivity and current efficiency were 78.3 % and 75.5 % respectively with 20 mM MBAP; the ADN selectivity and current efficiency were 85.4 % and 83.7 % respectively with 20 mM TBAP.