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

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ “This is the peer reviewed version of the following article: BaenaMoreno FM, Rodríguez-Galán M, Vega F, RamirezReina T, Vilches L, Navarrete B. Understanding the influence of the alkaline cation K+ or Na+ in the regeneration efficiency of a biogas upgrading unit. Int J Energy Res. 2019; 43: 1578–1585, which has been published in final form at https://doi.org/10.1002/er.4448 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of SelfArchived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited." 1 Understanding the Influence of the Alkaline Cation K+ or Na+ in the Regeneration Efficiency of a Biogas Upgrading Unit. Francisco M. Baena-Moreno a,b *, Mónica Rodríguez-Galán a, Fernando Vega a, T. R. Reina b, Luis F. Vilches a, Benito Navarrete a. a Chemical and Environmental Engineering Department, Technical School of Engineering, University of Seville, C/ Camino de los Descubrimientos s/n, Sevilla 41092, Spain b Department of Chemical and Process Engineering, University of Surrey, GU2 7XH Guildford, United Kingdom *Corresponding author. E-mail address: [email protected] (Francisco M. Baena-Moreno) Abstract This paper reveals a regeneration method for a carbonate compound after carbon dioxide (CO2) absorption in a biogas upgrading unit run with caustic mixtures, obtaining precipitated calcium carbonate (PCC) as valuable by-product. This process arises as an alternative to physical regeneration, which is highly energy intensive. This work provides novel insights on the regeneration efficiency of carbonates to hydroxides while also studying the influence of K+ or Na+ in the caustic CO2-trapping solution. The compared parameters were the reaction time, temperature and molar ratio. Moreover, psychochemical characterization of solids was obtained by means of Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM) images. The results indicate that regeneration efficiencies are slightly lower when potassium is used instead of sodium, but quite acceptable for both of them. The chemical characterization experiments showed the predominance of calcium carbonate. Overall, the results obtained in this study proved 2 that this process is feasible to upgrade biogas through PCC precipitation, which appears to be a promising economically viable process to synergise CCS and CCU. Keywords Carbon Capture and Utilization; Biogas Upgrading; Precipitated Calcium Carbonate; Caustic Absorption; Biomethane Production; 1. Introduction Our environment is seriously affected by climate change, carried out largely by human action. In addition, the future shortage of conventional energy sources requires greater use of renewable energy [1,2]. Within this context, biogas is one of the most promising sources of renewable energy, having increased the existing number of biogas processing plants in recent years considerably (Figure 1). Biogas is obtained through the anaerobic digestion of biomass [3]. Regarding biogas composition, it is mainly composed by methane (CH4) and carbon dioxide (CO2), in an approximate percentage of 60% and 40% respectively [4–6]. After a complete upgrading for CO2 removal, biomethane is obtained from biogas as a valuable product [7]. Biomethane uses include heat or electricity production, natural gas substitute, compressed natural gas and diesel replacement alongside liquid natural gas after a compression stage [8–10]. Due to this variety of applications, biogas upgrading technologies have been studied by multiple researchers, chemical absorption being one of the most propitious due to the high CO2 capture efficiency of this process. Solvents typically employed for this process are monoethanolamine (MEA), piperazine (PZ), sodium hydroxide (NaOH) or potassium hydroxide (KOH) [11–14]. Even though promising results have been found by the employment of amines, nowadays there are some disadvantages discussed by the 3 scientific community. Some examples are the toxicity produced by the amine degradation through the formation of nitrosamine as a potential carcinogenic compound and the high regeneration cost in the stripping step [12,15–17]. Also the use of caustic solvents requires an elevated energy consumption to regenerate the solvent via temperature increase [12,17,18]. However, NaOH and KOH present advantages of being cheaper, having a greater theoretical CO2 capture capacity and their availability in the industry market [19]. Figure 1. Number of biogas processing plants and total installed capacity [8,20]. For this reason, previously an alternative path for solvent regeneration was proposed by our group [13], which resulted to be much less energy intensive and economically attractive due to the production of a valuable by-product. A general scheme of the process can be seen in Figure 2. In brief, NaOH was employed as a CO2 capture agent to form sodium carbonate (Na2CO3), according to reaction (1). In order to make the process economically appealing, a regeneration of Na2CO3 via chemical reaction with calcium hydroxide (Ca(OH)2) was chosen to generate precipitated calcium carbonate 0 4000 8000 12000 16000 20000 Number of plants 2010 2011 2012 2013 2014 2015 2016 0 2000 4000 6000 8000 10000 Year Total installed capacity (MW) 4 (PCC) (reaction (2)). PCC is demanded as raw material in several applications, such as for example in paper industry, polymers applications and as a neutralizer in healthcare [21–23]. 2𝑁𝑎𝑂𝐻(𝑎𝑞) + 𝐶𝑂2(𝑔)→ +𝑁𝑎2𝐶𝑂3 + 𝐻2𝑂 (1) 𝑁𝑎2𝐶𝑂3 (𝑎𝑞)+ 𝐶𝑎(𝑂𝐻)2(𝑠) → 2𝑁𝑎𝑂𝐻(𝑎𝑞)+ 𝐶𝑎𝐶𝑂3 (𝑠) (2) High regeneration efficiencies as promising results for further investigations were achieved. Since KOH was proven to have improved CO2 absorption compared to NaOH [24,25], in this paper a characterization of regeneration efficiencies in a precipitation reactor for this novel method is presented. Hence, in this work novelty data regarding the comparison between both cations is presented, which have not been found in the literature. For the collection of these inputs, the purpose of this study was to analyze the differences between regeneration efficiencies and psychochemical composition of both NaOH and KOH, with the intention to investigate the effect of potassium ion in comparison with sodium. Potassium ion may have an enhancement effect into the regeneration efficiencies, as well as in the purity of final PCC. The chemical reaction carried out if reflected by reaction (3). 𝐾2𝐶𝑂3 (𝑎𝑞)+ 𝐶𝑎(𝑂𝐻)2(𝑠) → 2𝐾𝑂𝐻(𝑎𝑞)+ 𝐶𝑎𝐶𝑂3 (𝑠) (3) 5 Figure 2. Bio-waste to PCC production and biogas upgrading process. The key variables studied were the reaction time, the reaction temperature, and the molar ratio between Ca(OH)2 and K2CO3 (R), since these variables were proved to have an effect on the reaction rate [13,26,27]. Inasmuch as in the previous work [13] an exhaustive characterization of these reaction parameters was done. However, in this paper a selected number of tests were chosen to investigate the potassium ion effect. 2. Materials and Methods 2.1 Materials PanReac-AppliChem supplied the reagents employed in this work (Ca(OH)2, Na2CO3, K2CO3, CaCO3) in a pure-pharma grade (99% purity). 2.2 Regeneration experiments 6 The methodology was explained in detail in [13]. Firstly, both the carbonate aqueous solution and hydroxide slurry were prepared. Secondly, a 600 mL beaker was chosen as reactor to carry out the lab scale batch precipitation experiments, under the conditions that can be found in Table 1. Once the reaction time was finished, the solution was quickly filtered and separated for chemical analysis. The solid obtained was dried during one day at 105°C. After this time, the samples were weighed to obtain the PCC grams precipitated. The main result were considered on the KOH regeneration efficiency, which is defined as follows: 𝐾𝑂𝐻 𝑟𝑒𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 (%)= 𝑃𝐶𝐶 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 (𝑔) × 2 × 𝑃𝑀𝐾𝑂𝐻 𝑃𝑀𝐶𝑎𝐶𝑂3 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝐾𝑂𝐻 𝑡𝑜 𝑟𝑒𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑒 (𝑔) × 100 The maximum KOH to be regenerated can be obtained stochiometrically from K2CO3 initial concentration. The reaction carried out at 50°C, with a molar ratio Ca/K2CO3 of 1.2 mol and a reaction time of 30 minutes was selected as a reference experiment [13,27]. The concentration of the aqueous solution was fixed in 20g/100mL since it is an expectable value after chemical absorption of KOH [27,28]. On the other hand the Ca(OH)2 solution concentration was calculated stoichiometrically for each experiment accordingly with the molar ratio. Table 1. Matrix of experiments done in this study. EXPERIMENT CARBONATE TO REGENERATE TIME (MIN) TEMPERATURE (ºC) MOLAR RATIO (R) 1 Na2CO3 30 50 1.2 2 Na2CO3 15 50 1.2 3 Na2CO3 60 50 1.2 4 Na2CO3 30 30 1.2 5 Na2CO3 30 50 1.2 6 Na2CO3 30 70 1.2 7 Na2CO3 30 50 1 8 Na2CO3 30 50 1.2 9 Na2CO3 30 50 1.5 10 K2CO3 30 50 1.2 11 K2CO3 15 50 1.2 12 K2CO3 60 50 1.2 13 K2CO3 30 30 1.2 14 K2CO3 30 50 1.2 15 K2CO3 30 70 1.2 16 K2CO3 30 50 1 17 K2CO3 30 50 1.2 18 K2CO3 30 50 1.5 7 FTIR, Raman spectroscopy. XRD and SEM technique were employed for the characterization of the solid samples. A Perkin Elmer FTIR BX spectrometer was used to perform the attenuated total reflection Fourier transform infrared spectroscopy in the powders (ATR-FTIR). Background subtracted spectra of the raw and the treated samples were collected at room temperature by co-adding 32 scans at 4 cm−1 resolution in transmittance mode. Data were baseline corrected using Spectrum 5™ software. XRD analysis was completed by an X’Pert Pro PAN analytical instrument. The 2θ angle was increased by 0.05o, with a 450 time per step over a range of 10-90o. Diffraction patterns were then recorded at 40 mA and 45 kV, using Cu Kα radiation (λ=0.154 nm). Raman measurements of the powders samples were recorded using a Thermo DXR2 spectrometer equipped with a Leica DMLM microscope. A diffraction grating of 600 grooves per mm, a CCD detector, a green laser with a wavelength of 532.14 nm (maximum power 20 mW), and a 50x objective were used. The morphology of the samples were studied using SEM. This was carried out on a JSM6400 equipped with an Energy Dispersive X-ray Spectroscope (EDS) analyzer (Oxford Link) and operated at 20 KV. Reproducibility of the experiments were conducted giving as result ±2% of error. 3. Results Herein regeneration results are presented and discussed. Firstly, both NaOH and KOH regeneration efficiencies are compared under the reaction conditions indicated above. Secondly, chemical comparison between both carbonates obtained are shown by means of Raman, FTIR and XRD measurements as well as SEM images. 3.1 Regeneration efficiencies results Figures 3, 4 and 5 reveal the curves of NaOH and KOH resulting from the precipitation experiments previously identified in section 2. The left hand side of the Figures correspond to the net regeneration efficiency obtained with both caustic solutions, while 8 the right hand side indicates the regeneration efficiency differences between NaOH and KOH. Figure 3. Comparison of NaOH and KOH regeneration with time at T=50oC and R=1.2. 3.1.1 Reaction Time Variation The evolution of regeneration efficiencies during the reaction time is shown in Figure 3. Curiously, KOH regeneration efficiencies are to be lower than those of NaOH. This result is in good agreement with separated previous studies [29] and may be caused by the higher stability of K2CO3 in comparison to Na2CO3. Given these circumstances, it may be better to employ NaOH instead of KOH. However, as discussed previously, KOH was proven to be a better solvent for CO2 removal [12,30] and the differences in the regeneration stage can be overcome by increasing the reaction time. At 60 minutes, the differences between NaOH and KOH regeneration efficiencies are much lower than that at 15 minutes (1.27% vs 3.99%). In any case, an almost 4% of difference in regeneration 10 15 20 25 30 35 40 45 50 55 60 65 60 65 70 75 80 85 90 95 100 Regeneration efficiency (%) Reaction time (min) KOH NaOH 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 Differences Regeneration efficiency differences 15 Figure 9. PCC SEM from Na2CO3. Figure 10. PCC SEM from K2CO3. 4. Conclusions 16 The present paper shows an interesting method for biogas upgrading from an economical point of view. With respect to other commercial methods for biogas upgrading, this process generates bio-methane and PCC as valuable products. The process performance results are quite promising exhibiting high regeneration efficiencies (60-95%) for both tested carbonates. Generally and comparing with other previous studies in which waste were chosen as precipitating agents [27,29], our results are enhanced regarding regeneration efficiency (60-95% vs 50-60%). Thus, our process seems to be more viable from an industrial point of view. KOH regeneration efficiencies are always lower than those of NaOH, probably due to the greater stability of K2CO3. However, these are subtle differences that might be subjugated by the enhancement of operation parameters, as long as the overall economics of the process is improved. Regarding the effects of the different parameters studied, it seems that temperature is the most influential factor indeed, an increase in its value from 30oC to 50oC has caused an almost 20% of improvement in the overall regeneration performance. Nevertheless, reaction time could also play a key role in the hypothetical case of an industrial plant to enhance the regeneration efficiencies. FTIR and XRD studies confirm the purity of the carbonate phase obtained in the precipitation experiments, whereas no significant differences in the morphology were detected by the employment of SEM. This however could open new research avenues since other precipitating materials could be tested to get a more valuable product. Overall, the technical feasibility of this process was demonstrated for both solvents, indicating that further research on this process is worth considering in the context of carbon capture/utilization. Future works will deal with finding new precipitating materials that can produce a more valuable final product, in order to improve the overall economy of the process. Furthermore, preliminary studies for scaling up the lab-scale work presented in this paper to a bench-scale unit will be carried out, where the economy of the process could be 17 examined more accurately. Potentially our work could be integrated with other industrial processes in the future. For instance, there is a possibility to use the carbonate solution obtained after the absorption step as draw solution in forward osmosis and then precipitating CO2 as valuable by-product [35]. Acknowledgments and Funding This work was supported by University of Seville through its V PPIT-U. Financial support for this work was also provided by the EPSRC grant EP/R512904/1 as well as the Royal Society Research Grant RSGR1180353. This work was also partially sponsored by the CO2Chem UK through the EPSRC grant EP/P026435/1. Furthermore this work was supported by EMASESA through NURECCO2 project and Corporación Tecnológica de Andalucía (CTA). References 1. IPCC (2018) Global Warming of 1.5°C. Summary for Policymakers. 2. BP Energy Economics (2018) BP Energy Outlook 2018. 2018 BP Energy Outlook. 3. Zhang, T., Yang, Y., and Xie, D. (2015) Insights into the production potential and trends of China’s rural biogas. Int. J. Energy Res. 4. Singhal, S., Agarwal, S., Arora, S., Sharma, P., and Singhal, N. (2017) Upgrading techniques for transformation of biogas to bio-CNG: a review. Int. J. Energy Res. 5. Feroldi, M., Neves, A.C., Bach, V.R., and Alves, H.J. (2016) Adsorption technology for the storage of natural gas and biomethane from biogas. Int. J. Energy Res. 18 6. Kerroum, D., Mossaab, B.L., and Hassen, M.A. (2014) Production of bio-energy from organic waste: Effect of temperature and substrate composition. Int. J. Energy Res. 7. Demirel, Y., Matzen, M., Winters, C., and Gao, X. (2015) Capturing and using CO2as feedstock with chemical looping and hydrothermal technologies. Int. J. Energy Res. 8. Kadam, R., and Panwar, N.L. (2017) Recent advancement in biogas enrichment and its applications. Renew. Sustain. Energy Rev. 9. Heyne, S., and Harvey, S. (2014) Impact of choice of CO2separation technology on thermo-economic performance of Bio-SNG production processes. Int. J. Energy Res. 10. Walker, S.B., Sun, D., Kidon, D., Siddiqui, A., Kuner, A., Fowler, M., and Simakov, D.S.A. (2018) Upgrading biogas produced at dairy farms into renewable natural gas by methanation. Int. J. Energy Res. 11. Vega, F., Cano, M., Gallego, M., Camino, S., Camino, J.A., and Navarrete, B. (2017) Evaluation of MEA 5 M performance at different CO2 concentrations of flue gas tested at a CO2 capture lab-scale plant. Energy Procedia, 114 (114), 6222–6228. 12. Leonzio, G. (2016) Upgrading of biogas to bio-methane with chemical absorption process: Simulation and environmental impact. J. Clean. Prod. 13. Baena-Moreno, F.M., Rodríguez-Galán, M., Vega, F., Reina, T.R., Vilches, L.F., and Navarrete, B. (2018) Regeneration of Sodium Hydroxide from a Biogas Upgrading Unit through the Synthesis of Precipitated Calcium Carbonate: An Experimental Influence Study of Reaction Parameters. Processes, 6 (205). 14. Zhang, F., Zhou, Y., Sun, W., Hou, S., and Yu, L. (2018) CO2 capture from 19 reheating furnace based on the sensible heat of continuous casting slabs. Int. J. Energy Res., 42 (6), 2273–2283. 15. Zhang, Y., Zhang, L., Wang, Y., Wang, M., Wang, Y., and Ren, S. (2015) Dissolution of surfactants in supercritical CO2with co-solvents. Chem. Eng. Res. Des., 94, 624–631. 16. Zhu, L., Chen, H., Fan, J., and Jiang, P. (2016) Thermo-economic investigation: an insight tool to analyze NGCC with calcium-looping process and with chemical-looping combustion for CO2 capture. Int. J. Energy Res., 40 (14), 1908–1924. 17. He, Q., Yu, G., Wang, W., Yan, S., Zhang, Y., and Zhao, S. (2017) Oncethrough CO2absorption for simultaneous biogas upgrading and fertilizer production. Fuel Process. Technol. 18. Jande, Y.A.C., Asif, M., Shim, S.M., and Kim, W.S. (2014) Energy minimization in monoethanolamine-based CO2capture using capacitive deionization. Int. J. Energy Res. 19. Abdeen, F.R.H., Mel, M., Jami, M.S., Ihsan, S.I., and Ismail, A.F. (2016) A review of chemical absorption of carbon dioxide for biogas upgrading. Chinese J. Chem. Eng., 24 (6), 693–702. 20. Dareioti, M.A., and Kornaros, M. (2014) Effect of hydraulic retention time (HRT) on the anaerobic co-digestion of agro-industrial wastes in a two-stage CSTR system. Bioresour. Technol., 167, 407–415. 21. Munawaroh, F., Muharrami, L.K., Triwikantoro, T., and Arifin, Z. (2018) The effect of CO2 gas flow rate on precipitated CaCO3 formed at room temperature. AIP Conf. Proc., 2014. 22. Liu, X., Jia, H.H., Zhou, J., Yong, X.Y., Wei, P., and Jiang, M. (2016) Application 20 of a Gas-Liquid Mixing Pump in Biogas Purification and the Co-production of Nano Calcium Carbonate. Energy and Fuels, 30 (11), 9947–9952. 23. Liu, X., Zhou, J., Zhang, Y., Liu, X., Chen, Y., Yong, X., Wang, S., Zheng, T., and Yuan, H. (2015) Continuous process of biogas purification and coproduction of nano calcium carbonate in multistage membrane reactors. Chem. Eng. J., 271, 223–231. 24. Mahmoudkhani, M., Heidel, K.R., Ferreira, J.C., Keith, D.W., and Cherry, R.S. (2009) Low energy packed tower and caustic recovery for direct capture of CO2 from air. Energy Procedia, 1 (1), 1535–1542. 25. He, Q., Yu, G., Yan, S., Dumée, L.F., Zhang, Y., Strezov, V., and Zhao, S. (2018) Renewable CO2 absorbent for carbon capture and biogas upgrading by membrane contactor. Sep. Purif. Technol., 194, 207–215. 26. Baciocchi, R., Costa, G., Gavasci, R., Lombardi, L., and Zingaretti, D. (2012) Regeneration of a spent alkaline solution from a biogas upgrading unit by carbonation of APC residues. Chem. Eng. J. 27. Baciocchi, R., Carnevale, E., Corti, A., Costa, G., Lombardi, L., Olivieri, T., Zanchi, L., and Zingaretti, D. (2013) Innovative process for biogas upgrading with CO2 storage: Results from pilot plant operation. Biomass and Bioenergy. 28. Baciocchi, R., Carnevale, E., Costa, G., Gavasci, R., Lombardi, L., Olivieri, T., Zanchi, L., and Zingaretti, D. (2013) Performance of a biogas upgrading process based on alkali absorption with regeneration using air pollution control residues. Waste Manag., 33 (12), 2694–2705. 29. Lombardi, L., Baciocchi, R., Carnevale, E., and Corti, A. (2012) Investigation of an innovative process for biogas up-grading – pilot plant preliminary results. Proc. ECOS 201225th Int. Conf. Effic. cost, Optim. Simul. Environ. impact 21 energy Syst. June 26-29, Perugia, Italy, 1–12. 30. Mahmoudkhani, M., and Keith, D.W. (2009) Low-energy sodium hydroxide recovery for CO2 capture from atmospheric air-Thermodynamic analysis. Int. J. Greenh. Gas Control, 3 (4), 376–384. 31. Altiner, M., and Yildirim, M. (2017) Production of precipitated calcium carbonate particles with different morphologies from dolomite ore in the presence of various hydroxide additives. Physicochem. Probl. Miner. Process. 32. Dandeu, A., Humbert, B., Carteret, C., Muhr, H., Plasari, E., and Bossoutrot, J.M. (2006) Raman spectroscopy - A powerful tool for the quantitative determination of the composition of polymorph mixtures: Application to CaCO3 polymorph mixtures. Chem. Eng. Technol. 33. Ni, M., and Ratner, B.D. (2008) Differentiating calcium carbonate polymorphs by surface analysis techniques - An XPS and TOF-SIMS study. Surf. Interface Anal. 34. Kontoyannis, C.G., and Vagenas, N. V. (2000) Calcium carbonate phase analysis using XRD and FT-Raman spectroscopy. Analyst. 35. Nematzadeh, M., Samimi, A., and Shokrollahzadeh, S. (2016) Application of sodium bicarbonate as draw solution in forward osmosis desalination: influence of temperature and linear flow velocity. Desalin. Water Treat., 57 (44), 20784– 20791.