Valorization of Kraft Lignin of Different Molecular Weights as Surfactant Agent for the Oil Industry

After cellulose, lignin is the second most abundant biopolymer in the vegetable world. Since lignin is a natural phenolic polymer, there are a variety of potential products obtainable by its chemical modification, including surfactants. In this regard, lignin is of great interest because represent a byproduct of pulp industries for papermaking; however, this byproduct can be harnessed for obtaining aromatic derivatives of industrial interest. In this work, alkali lignin derivatives of different molecular weights were synthesized from lignin fractions from Pinus caribaea obtained by ultrafiltration. Lignin and lignin-fractions were modified with succinic anhydride (SA), and dodecyl-succinic anhydride (DSA) under microwave heating. The reaction was monitored by Fourier Transform Infrared Spectroscopy. The surface activity of lignin, and lignin-derivatives was evaluated through surface tension measurements, while the stability of suspensions and emulsions was evaluated by the volumetric separation method. The lignin fractions, and the esterified derivatives were obtained in very short reaction times (90–110 s) using a mixture of acetonitrile/ethanol. The lignin-derivatives showed higher surface activity in comparison to the neat lignin. Derivatives prepared from the lower molecular weight fraction by using DSA showed the best emulsifying properties. Lignin-derivatives also showed significant dispersing properties in comparison to a commercial dispersant (lignosulfonate). The best dispersant properties were obtained from the higher molecular weight ultrafiltered lignin fraction esterified with SA.