Novel hindered amine absorbent for CO2 capture

Available online at www.sciencedirect.com

Energy Procedia 37 (2013) 417 – 422

GHGT-11

Novel hindered amine absorbent for CO2 capture Shinji Muraia*, Yasuhiro Katoa, Yukishige Maezawaa, Takehiko Muramatsua, Satoshi Saitob b

a Toshiba Corporation, 1, Toshiba-cho, Fuchu-Shi, Tokyo, Japan Toshiba Corporation, 2-4, Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa, Japan

Abstract

We synthesized the sterically hindered amine A by an appropriate placement of alkyl groups. Quantitative 13 C NMR spectroscopy was performed on 30 wt% aqueous solution of the amine A with different amount of CO2 at 40°C. The results suggested that the amine A only formed the carbonate anion in this system. Performance evaluations of the absorbent-A containing the amine A were carried out based on their CO2 absorption rate, absorption capacity and heat of reaction measurements. The absorbent-A containing the amine A showed high absorption capacity and high absorption rate and relative low heat of reaction compared to 30 wt% MEA solution. The absorbent-A has been selected for further tests in the benchscale apparatus. We will evaluate the absorbent-A at Mikawa pilot plant (10 ton/day) owned by TOSHIBA, using the actual flue gas from Mikawa coal fired power plant in Fukuoka prefecture, Japan. © 2013 2013 The The Authors. © Authors. Published Published by by Elsevier ElsevierLtd. Ltd. Selection and/or and/or peer-review Selection peer-review under under responsibility responsibilityof ofGHGT GHGT Keywords: carbon dioxide; absorption; loading; 13C NMR; sterically hindered amine; carbamate; carbonate

1. Introduction In recent years, a greenhouse effect resulting from an increase of CO2 concentration has been pointed out as a cause of global warming phenomena. Chemical absorption using an aqueous solution of amine based absorbents is one of the most effective methods to capture CO2 [1]. So, it is essential to reduce the absorbent regeneration cost by developing novel amine based absorbents because half of the capture cost is caused by absorbent regeneration. In the previous studies, commercially available amine based absorbents were widely investigated all over the world on terms of absorption capacity and heat of reaction of CO2 and so on. A study on particularly alkanolamine having structural steric hindrance was vigorously tried as the absorbent of acid gas [2, 3]. Alkanolamine having the steric hindrance has merits that selectivity of acid gas is very high and the energy required for regeneration is small. Then, we

* Corresponding author. Tel.: +81-42-333-2780; fax: +81-42-340-8060. E-mail address: [email protected].

1876-6102 © 2013 The Authors. Published by Elsevier Ltd.

Selection and/or peer-review under responsibility of GHGT doi:10.1016/j.egypro.2013.05.126

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Shinji Murai et al. / Energy Procedia 37 (2013) 417 – 422

focused on the development of hindered amine based CO2 absorbents that have a low heat of reaction and high capacity for CO2. We synthesized the new hindered amine (amine A) and the results for the amine A was then compared with those of the conventional absorbents such as monoethanolamine (MEA), Nmethylethanolamine (MAE), N-isopropylethanolamine (IPAE) to analyse the steric effect of the different substituents on the relative reactivity of the amino nitrogen. For the development of new absorbent we thus focused on the absorbents that outperformed MEA in screening tests. The objective of solvent screening test is to deriver the candidate for further and more detailed test in a bench-scale apparatus and finally in Mikawa pilot plant. 2. Experimental 2.1 Chemicals All the amines except the amine A were purchased from Tokyo Chemical Industry Co., Ltd. and Wako Pure Chemical Industries, Ltd. and were used without further purification. The amine A was synthesised in our laboratory by the reductive amination [4]. The purity and structure of the amine A was established by GC and NMR spectroscopy, respectively. 3. Results and discussion 3.1 CO2 absorption properties To clarify the steric effect of the different substituents on the relative reactivity, the absorption capacity and the absorption rate were determined for each amine. Absorption performance was evaluated by measuring the CO2 concentration in the gas at an exit of the test tube by using an infrared gas concentration measurement device (manufactured by Shimadzu Corporation, name of article: “CGT700”). Figure 1 illustrates the experimental system for the CO2 absorption properties. A Teflon tube (inside diameter: 1.59 mm, outside diameter: 3.17 mm) of 1/8 inches was set at a gas introducing port to the amine solution in the test tube. A water solution of 50 ml (hereinafter, referred to as an absorbing liquid) was prepared by dissolving 30 mass % of each amine in water. After this absorbing liquid was filled in a test tube and heated to 40°C , mixed gas containing 10 vol% CO2 and 90vol% N2 gas was aerated at a flow rate of 500 mL/min. The CO2 concentration in the absorbing liquid was measured by using the infrared gas concentration measurement device to evaluate absorption performance. The equilibrium was determined when the CO2 analyzer indicated a constant CO2 concentration in the outlet gas. An absorption rate is obtained by differentiating the absorption capacity with respect to the absorption time.

mass flow controller

mass flow CO2 meter sensor Dimroth condenser

CO2 in N2

100m䌌 test tube

heater water bath magnetic stirrer

Figure 1. Illustration of laboratory experimental system

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㪇㪅㪇㪈㪇㪇㪅㪇㪇㪏㪇㪅㪇㪇㪍㪇㪅㪇㪇㪋㪇㪅㪇㪇㪉㪇㪅㪇㪇㪇㪇

㪇㪅㪉 Amine A

㪇㪅㪋㪣㫆㪸㪻㫀㫅㪾㩷㩿㫄㫆㫃㪆㫄㫆㫃㪀 IPAE

MAE

㪇㪅㪍

㪇㪅㪏 MEA

Figure 2. Absorption rate versus amount of CO2 absorbed at 40°C Figure 2 demonstrates that the result of saturated CO2 loading and absorption rates of MEA, MAE, IPAE and amine A at 40°C, respectively. Figure1 clearly shows that the absorption rates of MAE, IPAE, the amine A are higher than that of MEA. It is observed that the rate for amine A was slightly higher than IPAE. The amine A shows a good CO2 absorption capacity as IPAE. These results provided clear trends on the structural effects of alkanolamine. Methyl group was found to be suitable functional group for the enhancement of initial absorption rate, but decreased CO2 capacity [5]. An increase in steric hindrance for alkyl groups mostly decreases the absorption rate but increases the capacity. 3.2 Quantitative 13C NMR The quantitative 13C NMR provides speciation information and is useful in the calculation of the mole percentage of each species relative to the total amine concentration [6, 7]. 13C NMR spectral was obtained using a JEOL GSX-270 with a capillary sealed DMSO-d6 as an external standard at 25°C. To obtain quantitative spectra, the inverse gate decoupling technique was used with a delay of 30 s, a pulse width of 8.4Ǵs. The samples containing different amount of dissolved CO2 in 30 wt㧑 aqueous amine are prepared by changing the absorption time. The absorption of CO2 at 40°C clearly shows their speciation through 13CNMR spectra. Due to the fast exchange of protons, it was not possible to distinguish signals of carbonate anion and bicarbonate anion, and signals of unprotonated and protonated amines from NMR spectra [8]. The results are shown in Figure 3. MEA only formed the carbamate anion at lower CO2 molar loading and then converted partially to bicarbonate anion. In MAE, MAE also formed the carbamate anion and this intermediate converted to bicarbonate anion faster than MEA. The amount of the carbamate anion is almost the same as that of the carbonate anion. In IPAE, IPAE mainly formed the carbonate anion with a slight amount of carbamate anion during the CO2 absorption. In amine A, the amount of the carbonate anion increased with the increase in the loading from 0 to 0.75 mol CO2/mol CO2 and no carbamate anion was observed in the solution even at loading of 0.75 mol CO2/mol CO2.

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㪈㪅㪇

㪈㪅㪇

MEA

MAE 㪇㪅㪏㪚㪦㪉㩷㫄㫆㫃䋦

㪚㪦㪉㩷㫄㫆㫃䋦

㪇㪅㪏㪇㪅㪍㪇㪅㪋

㪇㪅㪍㪇㪅㪋㪇㪅㪉

㪇㪅㪉㪇㪅㪇

㪇㪅㪇㪇

㪇㪅㪉

㪇㪅㪋

㪇㪅㪍

㪇㪅㪏

㪇

㪇㪅㪉

㪚㪦㪉㩷㪣㫆㪸㪻㫀㫅㪾㩷㩿㫄㫆㫃㪆㫄㫆㫃㪀

㪇㪅㪋

㪇㪅㪍

㪈㪅㪇

㪈㪅㪇

IPAE

Amine A

㪇㪅㪏

㪇㪅㪏㪚㪦㪉㩷㫄㫆㫃䋦

㪚㪦㪉㩷㫄㫆㫃䋦

㪇㪅㪏


㪇㪅㪍㪇㪅㪋

㪇㪅㪍㪇㪅㪋㪇㪅㪉

㪇㪅㪉

㪇㪅㪇

㪇㪅㪇㪇

㪇㪅㪉

㪇㪅㪋

㪇㪅㪍

㪇㪅㪏

㪇


carbonate

㪇㪅㪉

㪇㪅㪋

㪇㪅㪍

㪇㪅㪏


carbamate

free amine

Figure 3. Plots of mole ratio of chemical species as a function of CO2 loading 3. 3 Vapor-liquid equilibrium

㪘㪹㫊㫆㫉㫇㫋㫀㫆㫅㩷㫉㪸㫋㪼㩿㫄㫆㫃㪆㫄㫆㫃㪆㫄㫀㫅㪀

As the amine A showed superior performance in the 㪇㪅㪇㪋 screening test, the absorbentA containing amine 㪇㪅㪇㪊 A was further investigated by measuring their vapour-liquid equilibrium along with both 㪇㪅㪇㪉 absorbent-B containing IPAE and 30 wt% MEA solution. Absorption performance at 㪇㪅㪇㪈 40°C was conducted in a similar manner as above. Besides, the absorbent after 㪇㪅㪇㪇 the mixed gas was absorbed at 㪇㪇㪅㪉㪇㪅㪋㪇㪅㪍㪇㪅㪏 40°C as stated above was 㪣㫆㪸㪻㫀㫅㪾㩷㩿㫄㫆㫃㪆㫄㫆㫃㪀 heated to 120°C, 10 vol% CO2 and 90 vol% N2 was aerated at a MEA Absorbent-A Absorbent-B flow rate of 100mL/min, and the CO2 concentration in the Figure 4. Absorption rate versus amount of CO2 absorbed at 40°C


absorbing liquid was measured by using the infrared gasconcentration measurement device to evaluate release performance. These temperatures are regarded as typical conditions for the chemical process. The absorption rates versus loading curves for three absorbents are shown in Figure 4. Figure 4 clearly shows that the absorption rates of absorbent-A and absorbent-B are much higher than that of 30 wt% MEA solution. Absorbent-A showed a similar behaviour to absorbent-B. The absorption rate of absorbent-A is almost the same as that of absorbent-B and the absorbent-A shows a good CO2 absorption capacity along with the absorbent-B. Table 1. Experimental results for vapour-liquid equilibrium

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㪘㫄㫀㫅㪼㩷㪘㪹㫊㫆㫉㪹㪼㫅㫋㫊㪘㪹㫊㫆㫉㪹㪼㫅㫋㪄㪘㪘㪹㫊㫆㫉㪹㪼㫅㫋㪄㪙㪤㪜㪘㩷㪊㪇㫎㫋䋦㩷㫊㫆㫃㫌㫋㫀㫆㫅 a

㪣㫆㪸㪻㫀㫅㪾㪹㫄㫆㫃㪆㫄㫆㫃㪇㪅㪈㪈㪇㪅㪇㪍㪇㪅㪉㪈

㪚㫐㪺㫃㫀㪺㩷㪚㪸㫇㪸㪺㫀㫋㫐㪺㫄㫆㫃㪆㫄㫆㫃㪇㪅㪌㪇㪇㪅㪌㪍㪇㪅㪊㪌

b

Maximum CO2 loading at 40°C, Maximum CO2 loading at 120°C,

c

Difference of CO2 loading between 40°C and 120°C

The results in table 1 show the summary of vapour liquid equilibrium characteristics for absorbent-A and absorbent-B and 30 wt% MEA solution. Both absorbent-A and absorbent-B have the large cyclic capacity compared with 30 wt% MEA solution. The cyclic capacity of the absorbent-A has 1.4 times that of 30 wt% MEA solution. 3.4 Heat of reaction Heat of reaction of the CO2 absorption for both the absorbent-A and 30 wt% MEA solution was measured with a differential reaction calorimeter “DRC” (product name, manufactured by SETRAM Company) composed of a glass reaction vessel and a reference vessel with the same shape installed in a thermostatic oven. The reaction vessel and the reference vessel were each filled with a 100 mL absorbing liquid, and 40°C constant-temperature water was circulated in jacket portions of the vessels. In this state, CO2 gas with a 50% concentration was blown to the absorbing liquid in the reaction vessel at a flow rate of 200 mL/min, a temperature increase of the liquid was continuously recorded by a thermograph until the CO2 absorption was finished, and the heat of reaction was calculated by using an overall heat transfer coefficient between the reaction vessel and the jacket water which was measured in advance. The heat of reaction for absorbent-A is smaller than that of MEA solution. The heat of reaction of the CO2 absorption for 30 wt% MEA solution and absorbent-A is 70.5 kJ/mol and 64.0 kJ/mol, respectively. In general, amine absorptions with higher absorption rates usually show higher heat of reaction, but absorbent-A has properties opposite to the 30 wt% MEA solution. 4. Conclusion We synthesized the amine A with specific steric hindrance substituent and it formed only carbonate anion in the CO2 loaded aqueous solution. It was proved that the amine A had a unique characteristic different from other amines in terms of CO2 chemical species by quantitative 13C NMR spectroscopy. The absorption rates of MAE, IPAE, the amine A were higher than that of MEA. The rate for amine A was slightly higher than IPAE. The amine A showed a good CO2 absorption capacity as IPAE. The absorbent

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containing the amine A showed higher absorption capacity and relative lower heat of reaction compared to 30 wt% MEA solution. As a result of the screening test for the absorbents, the absorbent-A has been selected for further tests in the bench-scale apparatus. We will evaluate the absorbent-A at Mikawa pilot plant (10 ton/day) owned by TOSHIBA using the actual flue gas from Mikawa coal fired power plant in Fukuoka prefecture, Japan [9]. Higher CO2 absorption capacity and relative lower heat of reaction characteristics will reduce the regeneration energy. 5. References [1] Blauwhoff, P. M. M.; Versteeg, G. F.; Van Swaaij, W. P. M. A study on the reaction between carbon dioxide and alkanolamines in aqueous solutions. Chemical Engineering Science. 1984, 39(2), 207-225 [2] Sartori, Guido; Savage, David W. Sterically hindered amines for carbon dioxide removal from gases. Industrial 㧒 Engineering Chemistry Fundamentals, 1983, 22(2), 239-249 [3] Hidetaka Yamada, Yoichi Matsuzaki, Hiromichi Okabe, Shinkichi Shimizu, Yuichi Fujioka Quantum chemical analysis of carbon dioxide absorption into aqueous solutions of moderately hindered amines. Energy Procedia, 2011, 4, 133-139 [4] Joseph E. Saavedra; Reductive alkylation of .beta.-alkanolamines with carbonyl compounds and sodium borohydride.J. Org. Chem., 1985, 50(13), 2271-3373 [5] FirozAlam Chowdhury, Hiromichi Okabe, Hidetaka Yamada, Masami Onoda, Yuichi Fujioka Synthesis and selection of hindered new amine absorbents for CO2 capture. Energy Procedia, 2011, 4, 201-208 [6] Suda, T.; Iwaki. T; Miura, T. Facile determination of dissolved species in CO2-amine-H2O system by NMR spectroscopy. Chem.Lett. 1996, 25(9), 777-778 [7] Robert J. Hook. An investigation of some sterically hindered amines as potential carbon oxide scrubbing compounds, Industrial Engineering Research, 1997, 36, 1779-1790 [8] Jakobsen, J. P.; Krane, J.; Svendsen, H. F. Liquid-phase composition determination in CO2-H2Oalkanolamine systems. Ind. Eng. Chem. Res. 2005, 44, 9894-9903 [9] Y. Ohashi, T. Ogawa, T. Suzuki; Toshiba’s pilot programme results. Carbon capture journal, 2011, 24, 2-6