Microgravimetric and Amperometric Sensor Coated With Room Temperature Ionic Liquid to Enhance Butanol Isomers Gas Separation

Biobutanol is a promising candidate as the biofuel of the future. Four isomers exist, of which 1-butanol, isobutanol, and 2-butanol are the most promising candidates for biobutanol production. However, sensing isomers are slightly challenging due to the same molecular formula and molar mass. In this study, a sensor array system was built, which consists of three microgravimetric and three amperometric sensors coated with three room temperature ionic liquids (RTILs) with different pairs of cation and anion combinations, i.e., 1-ethyl-3-methylimidazolium acetate ([EMIM] [Ac]), 1-butyl-3-methylimidazolium bromide ([BMIM][Br]), and 1-hexyl-3-methylimidazolium chloride ([HMIM][Cl]). In the microgravimetric sensor, quartz crystal microbalance (QCM) coated with different sensing films was used to gain selectivity. In addition, the interdigitated electrode (IDA) was selected where a microdroplet of RTIL was used for the electrolytes to substitute for the conventional bulky amperometric sensor. The different mechanisms of the two sensor types are expected to enhance the separation power among butanol isomers. The reproducibility and the concentration dependency were also studied to explore the sensor characteristics. A typical statistic parameter, Wilks’ lambda, was used to calculate the discrimination power numerically from different sensor combinations. According to the numerical result, the lowest Wilks’ lambda with the numerical value of 4.82 $\times \,\,10^{{-{8}}}$ , where the separation among butanol isomers was enhanced, was achieved from two types of sensor combinations, i.e., QCM with three sensing films and amperometric sensor with the electrolyte of [EMIM][Ac].