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.

Understanding the influence of the alkaline cation K + or Na + in the regeneration efficiency of a biogas upgrading unit

“…Once regeneration efficiencies differences have been compared, the purpose of this section is to contrast both PCCs obtained from K 2 CO 3 and Na 2 CO 3 . The analyses were carried out over the tests numbers 1 and 10 ( T = 50°C, R = 1.2, t = 30 min), which were selected as standard tests in a previous study . At the same time, these two samples were compared with commercial Ca (OH) 2 and CaCO 3 .…”

“…The methodology was explained in detail . First, both the carbonate aqueous solution and hydroxide slurry were prepared.…”

“…The maximum KOH to be regenerated can be obtained stochiometrically from K 2 CO 3 initial concentration. The reaction carried out at 50°C, with a molar ratio Ca/K 2 CO 3 of 1.2 mol and a reaction time of 30 minutes, was selected as a reference experiment . The concentration of the aqueous solution was fixed in 20 g/100 mL since it is an expectable value after chemical absorption of KOH .…”

“…Because of this variety of applications, biogas upgrading technologies have been studied by multiple researchers, chemical absorption being one of the most propitious because of the high CO 2 capture efficiency of this process. Solvents typically employed for this process are monoethanolamine (MEA), piperazine (PZ), sodium hydroxide (NaOH), or potassium hydroxide (KOH) . Even though promising results have been found by the employment of amines, nowadays there are some disadvantages discussed by the scientific community.…”

“…For this reason, previously an alternative path for solvent regeneration was proposed by our group, which resulted to be much less energy intensive and is economically attractive because of the production of a valuable by‐product. A general scheme of the process can be seen in Figure .…”