Conversion of water-organic solution of sodium naphtenates into naphtenic acids and alkali by electrodialysis with bipolar membranes.

Graphical abstract Highlights • The electromembrane process for production of naphthenic acids is proposed. • The BPM-C-C ED stack shows stable characteristics in the presence of naphthenate ions. • Conversion of sodium naphthenate is complicated by micelle formation in solution. • Ways to counter the negative effects of micellation are provided. Abstract The process of recovery of sodium naphtenates into naphtenic acids and sodium alkali using electrodialysis with bipolar membranes is investigated. A membrane stack of an electrodialyzer with a three-chamber unit cell in which the salt chamber is formed by two cation-exchange membranes is proposed, which eliminates the transfer of anions from the salt chamber to an adjacent alkaline and acidic one. The values of current efficiency for naphtenic acid and alkali, as well as energy consumption for the process, are determined. It is shown that the main problems with the development of electro-membrane technology for producing naphtenic acids from petroleum and petroleum products are associated with micelle formation of a mixture of naphtenic acids with sodium naphtenate in the pH = 6.5–8 range, which leads to a sharp increase in the viscosity and electrical resistance of solutions. Introduction of the cation-exchanger and sodium sulfate to the intermembrane space of naphtenthe salt chamber can significantly improve the technical and economic characteristics of the process - for example, the specific energy consumption decrease from 0.86 kW h·L−1 down 0.38 kW h·L−1, which is more than two times lower than the original three-chamber cell. At the same time, the production of naphtenic acids remains on the same level which is 17 L·m−2·h−1. [ABSTRACT FROM AUTHOR]