Salting effect of tetraalkylammonium salts on the cloudingthermodynamic functions of aqueous butanol system

Biobutanol, the primary four-carbon alcohol produced based on fermentation processes, hasbeen considered a renewable energy source to reduce the emission of greenhouse gases and airpollutants [۱]. Moreover, ۱-butanol, having complete miscibility with organic solvents and partialmiscibility with H۲O, is widely used as a solvent (purely or in mixed solvent systems) in a varietyof chemical and industrial processes [۲]. Investigating the salting effects of different solutes on theclouding (liquid-liquid demixing) phase diagram of ۱-butanol/water mixed solvent systemsprovides valuable information for extracting biobutanol from fermentation broth or optimumdesigning of separation processes involving alcohol-based aqueous biphasic systems [۳]. Thiswork focused on the salting effect of a wide range of tetraalkylammonium salts, includingtetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide,tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium hydrogensulfate, dodecyltrimethylammonium bromide, and cetyltrimethylammonium bromide on thewater-solubility of ۱-butanol. The effects of anion type, cation alkyl chain length, andconcentration of the salts on the thermodynamic quantities of the clouding process have beenscrutinized in a wide temperature range (۲۸۳.۱-۳۵۳.۱ K). The values obtained for the relativecontribution of enthalpy and entropy to the clouding Gibbs free energy demonstrate that theclouding process of ۱-butanol in aqueous solutions of tetraalkylammonium salts with smallerhydrocarbon portion is entropy-driven. However, the clouding process for ۱-butanol in aqueoussolutions of tetraalkylammonium salts with longer hydrocarbon chains, especially at highertemperatures and higher salt concentrations, is often enthalpy-driven.

کلیدواژه ها:

Clouding diagram ، Butanol ، Tetraalkylammonium salts ، Salting effect