Applied Energy 161 (2016) 41–47 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Phase change amino acid salt separates into CO2-rich and CO2-lean phases upon interacting with CO2 Xianfeng Wang a,b,c,d, Novruz G. Akhmedov e, David Hopkinson d, James Hoffman d, Yuhua Duan d, ⇑ Adefemi Egbebi f, Kevin Resnik f, Bingyun Li a,d, a Biomaterials, Bioengineering & Nanotechnology Laboratory, Department of Orthopaedics, School of Medicine, West Virginia University, Morgantown, WV 26506, United States b State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China c Key Laboratory of Textile Science & Technology, Ministry of Education, College of Textiles, Donghua University, Shanghai 201620, China d National Energy Technology Laboratory-Regional University Alliance (NETL-RUA), Morgantown, WV 26506, United States e Department of Chemistry, West Virginia University, Morgantown, WV 26506, United States f URS, Pittsburgh, PA 15236, United States highlights graphical abstract Innovative phase change amino acid salt solvent is developed for CO2 capture. Amino acid salt solution is turned into aCO2-rich phase and a CO2-lean phase upon simple bubbling with CO2. The developed solvent captures the most CO2 (90%) in the CO2-rich phase. NMR spectroscopy was used to identify the species in the solution. article info abstract Article history: Concerns over global climate change have led to strong research emphasis worldwide on reducing the Received 29 July 2015 emission of greenhouse gases like CO2. One avenue for carbon emission reduction is using CO2 capture Received in revised form 1 September 2015 and storage from industrial sources. Having low toxicity and low vapor pressure and being resistant to Accepted 26 September 2015 oxidation, natural amino acids could be a better choice over current carbon capture materials. In this study, we pioneered a unique phase change amino acid salt solvent concept in which amino acid salt solution was turned into a CO2-rich phase and a CO2-lean phase upon simple bubbling with CO2 and most Keywords: importantly, this solution captured the most CO (90%) in the CO -rich phase. Bicarbonate was found to CO capture 2 2 2 be dominant in the CO -rich phase, which had a high CO loading capacity and good regenerability and Phase change solvent 2 2 ⇑ Corresponding author at: Biomaterials, Bioengineering & Nanotechnology Laboratory, Department of Orthopaedics, School of Medicine, West Virginia University, Morgantown, WV 26506-9196, United States. National Energy Technology Laboratory-Regional University Alliance, Morgantown, WV 26506-9196, United States. Tel.: +1 304 293 1075; fax: +1 304 293 7070. E-mail address: [email protected] (B. Li). URL: http://medicine.hsc.wvu.edu/ortho-bli/ (B. Li). http://dx.doi.org/10.1016/j.apenergy.2015.09.094 0306-2619/Ó 2015 Elsevier Ltd. All rights reserved. 42 X. Wang et al. / Applied Energy 161 (2016) 41–47 Amino acid salt cycling properties. Such a phase change amino acid salt solvent may provide unique solutions for indus- CO -lean phase 2 tries to reduce CO2 and other harmful emissions. CO2-rich phase Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction self-concentrating process to form a CO2-lean phase and a CO2-rich phase. The CO2-lean phase could be reused and the CO2-rich phase Currently, over 85% of the global energy demand is being sup- could be regenerated. ported by the burning of fossil fuels, which release large quantities of carbon dioxide (CO2) into the atmosphere [1–4]. Thus, intensive 2. Materials and methods research on CO2 capture and storage is being conducted to mitigate CO2 emission which is found to be a major contributor to global cli- 2.1. Materials mate change [5–9]. Significant progress has been made but unfor- tunately, none of the current carbon capture and sequestration L-alanine (Ala, P98%), L-arginine (Arg, P98%), L-lysine (Lys, methodologies can meet the overall fossil energy performance P98%), L-serine (Ser, P99%), L-aspartic acid (Asp, P98%), and goals set by the U.S. Department of Energy of a 90% CO2 capture sodium hydroxide (NaOH, P98%) were purchased from Sigma- rate with 95% CO purity at a cost of electricity 30% less than base- 2 Aldrich. Deuterium oxide (D2O, 99.9%) and tetramethylammonium line capture approaches [10]. The state-of-the-art technology for chloride (P98%), used for nuclear magnetic resonance (NMR) mea- CO capture is solvent absorption in which an aqueous solution 2 surements, were also obtained from Sigma-Aldrich. CO2 and N2 of alkanolamine serving as an absorbent reacts chemically with gases from Airgas, Inc. were used as received. Amino acid salt solu- CO2 to form soluble carbamates and/or bicarbonates [11]. This pro- tions were prepared by adding amino acids and NaOH [e.g. Ala cess has already been in commercial use; however, this technology (34 wt% or 4.9 mol/L), NaOH (15 wt%)] at a 1:1 molar ratio in requires an inhibitively high amount of regeneration energy, deionized water or D2O. because CO2 can only be released at quite high temperatures, owing to the strong interactions of CO2 with such absorbents 2.2. CO2 absorption/desorption [12,13]. In order to identify cost-effective approaches for CO2 capture, CO2 absorption was carried out using 100% CO2 in a 25 mL glass new materials and techniques have been studied [1,8,14–18].In impinger seating in a water bath of 313 K. Candidate solutions particular, phase change solvents, a new class of solvents, have (18 g) were loaded in the reactor and heated to 313 K. A fritted emerged and been developed into one of the most promising tech- nozzle with a special nozzle tip (170–220-lm glass frit) was used nologies for CO2 capture. Several experimental studies with absor- for CO2 bubbling, which was inserted in the bottom of the impin- bents that exhibit phase-change features during the absorption or gers. For desorption, samples were heated to 393 K for 90 min in desorption of CO2 have shown promise to reduce solvent regener- an oil bath equipped with a condenser. For absorption/desorption ation energy [19–21]. Such phase change technology removes CO2 cycling runs of phase change amino acid salt solvent, CO2 absorp- from power plant flue gases using a solvent that, when it reacts tion was also carried out using 100% CO2 in a 25 mL glass impinger with CO2, rapidly forms two distinct phases: a CO2-rich phase seating in a water bath of 313 K. The CO2-loaded phase change and a CO2-lean phase. Only the CO2-rich phase will then undergo amino acid salt solvent with precipitates was centrifuged to speed regeneration. By regenerating only the CO2-rich phase, signifi- up the phase separation of the two phases. The clear phase was cantly less energy may be needed for the whole process [22]. pipetted out for reuse in the next cycle. The CO2-rich precipitates The current phase change solvents, which often require organic in the glass impinger were heated to 393 K and maintained at this solvents [23], may form liquid–liquid phases or liquid–solid phases temperature for 90 min to release the captured CO2. The clear upon CO2 absorption. Phase change solvents that form two liquid phase pipetted out was added back to the impinger with the regen- phases after CO2 absorption include the mixed amine systems erated solution, and cooled down to 313 K for the next absorption– and DMXTM process which can be separated based on differences desorption cycle. The amounts of CO2 absorbed (i.e. mass change in density [24]. Bruder and Svendsen found that certain blends of before and after CO2 absorption) and desorbed (i.e. mass change 2-(Diethylamino)ethanol/3-(Methylamino)propylamine could before and after CO2 desorption) were determined using an analyt- form two liquid phases after CO2 absorption and the cyclic loading ical balance with an accuracy of 0.0001 g. could be significantly higher than that of monoethnolamine (MEA) [24]. Phase change solvents that form a liquid phase and a solid 2.3. Nuclear magnetic resonance (NMR) studies phase (due to precipitation during CO2 absorption) can be found in systems such as alkanolamine/ionic liquids, chilled ammonia, 1H and 13C NMR measurements were performed using Varian and triethylenetetramine/ethanol solutions. Independent of the INOVA 600 MHz to identify the species in solution and solid sam- precipitate type, the formation of a solid reaction product during ples. The samples were prepared in NMR sample tubes and D2O absorption and its removal from the solution phase by precipita- was used instead of H2O. The volumes of the solution (i.e. CO2- tion may shift the reaction equilibrium toward the production of lean phase solution and entire solution) sample and D2O were more products (carbamate or bicarbonate). 200 lL and 500 lL. The amounts of the CO2-rich phase and D2O Amino acids are of great interest as potential solvents and sor- were 100–200 mg and 700 lL. The 1H NMR spectra were obtained bents for CO2 capture because they are environmentally friendly, with a delay time (D1) of 1 s and the number of scans was 32. The are naturally present in the environment, and have low volatility 13C NMR measurements were performed with a delay time of 20 s (due to their ionic nature) [25–31]. In this study, we report, for and number of scans of 64. In the 13C NMR spectra, bicarbonate the first time, the development of phase change solvents based peak was presented at 161 ppm; Ala carbamate at 164 ppm; À on amino acid salts to convert CO2 emissions into regenerable car- + + Ala/AlaH at 18, 50, and 177 ppm; and (CH3)4N Cl at 55 ppm.