Physicochemical comparison of precipitated calcium carbonate for different configurations of a biogas upgrading unit

Abstract

BACKGROUND: This paper presents a physicochemical comparison of the solid products obtained from two alternative processes that recycle waste sodium carbonate (Na 2 CO 3 ) solution, which is produced following the absorption of CO 2 in a biogas upgrading unit. Chemical regeneration processes offer an attractive alternative to the energetically demanding standard physical methods. In the first process, sodium hydroxide (NaOH) is regenerated as a precipitate from the chemical reaction of Na 2 CO 3 with calcium hydroxide (Ca(OH) 2 ). The second process shows a path to obtain a valuable sodium chloride (NaCl) and calcium carbonate (CaCO 3 ) rich brine from calcium chloride (CaCl 2 ) acting as a precipitant agent. In both processes, precipitated calcium carbonate (PCC) is obtained as the most valuable by-product, but with varying properties owing to the different origin. RESULTS: The purpose of this work is to analyze physicochemically both variations of PCCs obtained and examine the differences between these solid samples in order to determine which method produces more desirable characteristics in the final product.To this end, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed as characterization methods. The results reflect that both PCCs have a calcite crystal structure, or morph, being as both PCC products originate from CaCl 2 that is more similar to commercial calcium carbonate calcite. CONCLUSION: These results confirmed that a pure CaCO 3 valuable by-product can be obtained from a biogas upgrading unit with several industrial applications.

Advances in research project IBUMECO2: project and process description, methodology, and goals expected

“…The experimental procedure that will be used in this project is defined considering the results obtained in previous works of this research group in which precipitation reactions were studied in-depth. [16][17][18][19][43][44][45] In fact, the main conclusions from these previous works are: (1) a wide range of precipitation efficiencies (62-93%) can be obtained; (2) temperature has no remarkable influence on the precipitation efficiency, while molar ratio and reaction time are key factors to tune the precipitation efficiency;…”

“…Previous studies evaluating CO 2 capture in biogas at room temperature with NaOH solutions suggest a capture efficiency of up to 90% using 2.5 M NaOH concentrations in packing towers with variable L/G ratios between 10 and 14. [16][17][18][19]43,44 r Conceptual feasibility of the integrated process in a circular economy context using different membrane technologies and physical-chemical conditioning processes. 47 r Previous studies performed by the research team about Na 2 CO 3 reaction with CaCl 2 suggest precipitation of CaCO 3 efficiencies of 75-80% with a product quality of commercial calcite.…”

“…47 r Previous studies performed by the research team about Na 2 CO 3 reaction with CaCl 2 suggest precipitation of CaCO 3 efficiencies of 75-80% with a product quality of commercial calcite. [16][17][18][19]43,44 r Conceptual feasibility of the transformation of NaCl solutions to streams of HCl and NaOH by means of a BMED operation with membranes and commercial electrolyzers. 38 r The needs for energy sources in the different scenarios could conceptually be addressed with renewable energy or waste thermal energy from the biogas production facilities.…”

“…The hypotheses that serve as starting point are as follows: Capacity to characterize the behavior of different improved absorption systems for CO 2 capture from biogas. Previous studies evaluating CO 2 capture in biogas at room temperature with NaOH solutions suggest a capture efficiency of up to 90% using 2.5 M NaOH concentrations in packing towers with variable L/G ratios between 10 and 14 16–19,43,44 Conceptual feasibility of the integrated process in a circular economy context using different membrane technologies and physical‐chemical conditioning processes 47 …”

“…In this section, the experimental plan of the project to address the technological improvements and the process integration pursued as explained above is discussed. The experimental procedure that will be used in this project is defined considering the results obtained in previous works of this research group in which precipitation reactions were studied in‐depth 16–19,43–45 . In fact, the main conclusions from these previous works are: (1) a wide range of precipitation efficiencies (62–93%) can be obtained; (2) temperature has no remarkable influence on the precipitation efficiency, while molar ratio and reaction time are key factors to tune the precipitation efficiency; (3) commercial purity calcite can be precipitated as a high added‐value product; (4) the profitability of some potential process schemes suggest that the process can reach profitable scenarios, from a theoretically evaluated perspective.…”