Regeneration of sodium hydroxide from a biogas upgrading unit through the synthesis of precipitated calcium carbonate: An experimental influence study of reaction parameters

Abstract

This article presents a regeneration method of a sodium hydroxide (NaOH) solution from a biogas upgrading unit through calcium carbonate (CaCO3) precipitation as a valuable by-product, as an alternative to the elevated energy consumption employed via the physical regeneration process. The purpose of this work was to study the main parameters that may affect NaOH regeneration using an aqueous sodium carbonate (Na2CO3) solution and calcium hydroxide (Ca(OH)2) as reactive agent for regeneration and carbonate slurry production, in order to outperform the regeneration efficiencies reported in earlier works. Moreover, Raman spectroscopy and Scanning Electron Microscopy (SEM) were employed to characterize the solid obtained. The studied parameters were reaction time, reaction temperature, and molar ratio between Ca(OH)2 and Na2CO3. In addition, the influence of small quantities of NaOH at the beginning of the precipitation process was studied. The results indicate that regeneration efficiencies between 53%-97% can be obtained varying the main parameters mentioned above, and also both Raman spectroscopy and SEM images reveal the formation of a carbonate phase in the obtained solid. These results confirmed the technical feasibility of this biogas upgrading process through CaCO3 production.