A Simple and Rapid Method to Determine Sulfonation Degree of Lignosulfonates
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A Simple and Rapid Method to Determine Sulfonation Degree of Lignosulfonates Qi Li 1 & Meijun Zeng 1 & Duming Zhu 1 & Hongming Lou 1,2 & Yuxia Pang 1 & Kexian Qiu 1 & Jinhao Huang 1 & Xueqing Qiu 1,2
# Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Sulfonation degree is an important structural parameter of lignosulfonates which affect their water solubility, surface activity, and dispersing performance. Presently, the methods for determining sulfonation degree include elemental analysis and potentiometric titration; they have some shortcomings such as complex purification process, high equipment requirements, and time-consuming. Hence, a simple and rapid method to determine the sulfonation degree of lignosulfonates was proposed based on the electrostatic interaction between cationic surfactant (hexadecyl trimethyl ammonium bromide (CTAB)) and anionic lignosulfonates. CTAB was added and co-precipitated with lignosulfonates and then the ultraviolet absorbance of the supernatant was determined. The sulfonation degree of lignosulfonates was calculated according to the titration curve of the supernatant absorbance to the amount of CTAB. This method is applicable to lignosulfonates recovered from acid pulping as well as sulfonation products of alkali lignin. Because of the easy operation process and no purification process for lignosulfonates, this method was simple and rapid when compared to existing methods for sulfonation degree determination of lignosulfonates. Keywords Sulfonation degree determination . CTAB . Sodium lignosulfonates . Electrostatic interaction
Introduction Lignin is the second largest biomass resource in the world. Technical lignin, main byproduct of pulp and paper industry, has great application potential in various fields. Lignosulfonates contain hydrophobic aromatic backbones with alkyl side chains and hydrophilic groups such as sulfonic acid group, a carboxyl group, and phenolic hydroxyl group [1]. Lignosulfonates are mainly recovered from spent sulfite pulping liquor and prepared from sulfonation process of alkali lignin. Due to their excellent properties such as dispersing performance, viscosity reducing capacity, rheological property, and colloidal properties, lignosulfonates have been widely used in cement [2, 3], printing and dyeing [4], mining [5, 6], pesticide [7], lead-acid battery [8], coal-water slurry [9, 10],
* Hongming Lou [email protected] 1
School of Chemistry and Chemical Engineering, Guangdong Provincial Engineering Research Center for Green Fine Chemicals, South China University of Technology, Guangzhou, China
2
State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, China
and other fields [11–14]. Sulfonation degree, defined as the millimolar content of sulfonic acid in per gram of lignosulfonates, is an important structure parameter affecting many physicochemical properties of lignosulfonates such as water solubility [15, 16], dispersing performance [17], surface activity, and complexation abi
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