Non-ionic surfactants are considered as one of the highly utilized surfactants as they are the second largest group by volume at about 35%. Due to their low toxicity, the demand is escalating on extensive use of these amphiphilic materials for efficient, no-energy-requiring recovery of volatile organic acids (VOA). This separation process takes placed due to the cloud point of the surfactants which is referred as the temperature of the system at which two phases are formed. One of the phases is micellar-rich and the other is micellar-poor. In these micelles, the surfactant molecules are oriented in a way that the hydrophilic heads shield the hydrophobic tails from the other water molecules in the system. This assembly partitions the organic compounds through interior of the micelles which acts as the organic pseudo-phase. The goal of this study is to determine how salting-out affects the cloud point of ethoxylated non-ionic surfactants, and consequently, the VOA separation. Based on literatures, cloud point is sensitive to the presence of electrolytes and depends on the parameters hydrophile-lipophile balance (HLB) and on the number of ethylene oxide (EON) units of the surfactant. The mechanism involved upon electrolyte addition is the dehydration of micelles as salt is a water-structure maker. The salt changes the solvent structure by aggregation and formation of larger micelles. This translates into a lipophilic shift which reduces the cloud point and the surfactant HLB. As this HLB decreases, the more hydrophobic is the surfactant and can form better separation. Also, the type of salt influences the interphase mass transfer. Polyvalent cations such as Al3+ and Ca2+ are more effective in decreasing the HLB than the monovalent cations like Na+ and K+, because of their higher surface charge densities. The electrolyte capacity to reduce the cloud point is dependent as well on the hydrophilicity of the surfactant which is dictated by its ethylene oxide component. Non-ionic surfactants with higher EON value can achieve improved separation in the presence of salt. By considering these inferences, the extraction of VOA could be successfully improved.

Salting-out induced recovery of volatile organic acids using non-ionic surfactants

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