Universal Phase Transformation Mechanism and Substituted Alkyl Length and Number Effect for the Preparation of Overbased Detergents Based on Calcium Alkylbenzene Sulfonates

Overbased calcium sulfonate is one of the largest commercially produced nanomaterials; the phase transformation mechanism involved in the key process of carbonation reaction for overbased detergent preparation has not yet been fully understood. Following our previous investigation based on the heavy alkylbenzene sulfonate (HABS) surfactant of industrial byproduct, two commercial products with well-defined chemical compositions and structures, long-chain alkylbenzene sulfonate (LCABS) and comparative short-chain linear alkylbenzene sulfonate (SLABS), are employed in this study as model surfactants for further mechanism study of this pivotal process by the combination of analytical techniques such as potentiometric titration, DLS, TEM, FTIR, and XRD. It has been demonstrated that amorphous calcium carbonate (ACC) is a prerequisite for the preserving and stabilization of the alkaline reserve, especially under thermal work environment. The phase transformation from ACC to crystalline vaterite polymorph rather than calcite has been unambiguously confirmed as a universal mechanism for all the alkylbenzene sulfonate based systems. Furthermore, the length and number of alkyl tails of alkylbenzene sulfonate surfactants exhibit a strong influence on characteristics of detergent products. The LCABS with long-chain alkyl substituents or HABS with dialkyl substituents plays an important role not only in inhibiting the agglomeration process, but also in protecting the metastable inorganic cores from fusion to avoid phase transformation. Such understanding should be of crucial importance for guiding the preparation of overbased detergents and greases. In addition, the study on the influence of the molar ratio of calcium oxide in the total alkaline calcium salts and the dosage of surfactant LCABS, promoter methanol, and catalyst anhydrous calcium chloride help to determine the suitable work window for detergent production, and moreover, the water content provides a handle for better understanding the reaction process and achieving good quality control for detergent manufacturing.