Biogas Upgrading by Capturing CO2 in Non-aqueous Phase

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Biogas upgrading by capturing CO2 into nonaqueous phase-changing diamine solutions Mengna Tao, Jinzhe Gao, Pei Zhang, Wei Zhang, Qing Liu, Yi He, and Yao Shi Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 25 May 2017 Downloaded from http://pubs.acs.org on June 1, 2017

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Biogas upgrading by capturing CO2 into non-aqueous phase-changing diamine solutions Mengna Tao1, Jinzhe Gao1, Pei Zhang1, Wei Zhang1, Qing Liu2, Yi He1 and Yao Shi1,* 1. Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, China 2. College of Chemical Engineering, Nanjing Tech University, Nanjing, China

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Abstract Ethanol solutions of diamine, ethylenediamine (EDA) or piperazine (PZ), were found to be able to produce a solid precipitate after the absorption of CO2, respectively. The precipitate was identified to be a mixture of monocarbamate and dicarbamate. The details of the reactions between CO2 and diamine were examined. Results show that EDA-ethanol solutions exhibit higher capacity and faster rate for CO2 absorption than PZ-ethanol solutions do. As a comparison, the kinetics of CO2 absorption with diamine-water solutions were also tested. It was found that the overall average absorption rate of CO2 in EDA-ethanol solutions is almost double of that in EDA-water solutions. Moreover, results show that EDA-carbamate has a decomposition temperature of ~90°C and requires a regeneration energy 25.6% less than

traditional monoethanolamine

(MEA)

solutions,

which

suggests

that

EDA-ethanol solutions is promising to be used as cost-effective absorbents for CO2 capture.


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1 Introduction Biogas, as one of the renewable, sustainable, and environmentally friendly energy resource, has been increasingly used as a substitute for natural gas1, 2 in response to global warming. Raw biogas often contains a significant amount of impurities, including 15~40vol% carbon dioxide3. Therefore, it needs to be upgraded to increase its heat value4 by removing CO2 before it can be used for many potential applications. There are several technologies which are currently been used to remove CO2 from biogas, such as chemical and physical absorption5, 6, adsorption7, 8, membrane separations9, 10 and cryogenic separation11, 12. Among these technologies, chemical absorption using aqueous monoethanolamine (MEA) solutions with thermal regeneration of the solvent is often considered as a benchmark technology for CO2 capture13. However, this technology has a major drawback due to the high energy penalty for the regeneration of aqueous alkanolamine-based solutions14. To tackle this problem, extensive efforts have been made to develop advanced absorbents. A new breed of systems, based on so called phase-changing absorbents, is promising in reducing the energy consumption for regeneration drastically and has received much attention as an alternative option. Several aqueous amine systems have been explored so that a suitable liquid-liquid phase separation system can be found. The IFP (French institute of Petroleum) Energies nouvelles15 proposed an aqueous absorbent called DMXTM which can form two immiscible liquid phases after CO2 absorption. The CO2 capture system based on this absorbent can have a specific reboiler duty as low as 2.1GJ/t CO2. Xu et al.16


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studied the aqueous solution of 2M 1, 4-Diaminobutane (BDA) and 4M 2-(diethylamino)-ethanol (DEEA). After CO2 absorption, the solution forms an upper phase and a lower one, which have a volume ratio of 21.79/78.21 with nearly 97% of the absorbed CO2 concentrated in the lower phase and a total loading of 0.51 mol CO2 / mol amine. A similar study was conducted by Pinto and coworkers17, 18. They used a blend of 5M DEEA and 2M 3-(methylamino)-propylamine (MAPA), which also separates into two phases after CO2 absorption. The CO2 rich phase gives a CO2 pressure of ~4 bar higher than the benchmark 30wt% MEA solutions at the desorption test, showing a promising regeneration ability. In another study, Lu and coworkers19 examined a

series of ternary A-B-H2O systems which turns into two phases after

CO2 absorption, where component A is a polyamine which functions as an absorption accelerator while component B is N,N-dimethylcyclohexylamine (DMCA) or DEEA that serves as a regeneration promoter. In addition, they suggested that the more amine groups polyamines contain, the better absorption and desorption performance the absorbents exhibit. Amines in non-aqueous systems have also been tested for CO2 capture recently. For instance, Hasib-ur-Rahman et al.20, 21 employed an emulsion of diethanolamine (DEA) and room-temperature ionic liquid (RTIL). The emulsion can absorb CO2 up to the stoichiometric maximum of DEA through the precipitation of CO2-absorbed product, which enables easy separation and promises a cost-effective regeneration. Nevertheless, due to the high viscosity of ionic liquid, the absorption rate of CO2 was slow as it took nearly 6 hours to achieve absorption equilibrium. In previous work22,


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we have reported that triethylenetetramine (TETA) dissolved in ethanol produces a solid precipitate after CO2 absorption. One can observe that after a period of standing, the solid precipitate goes into the lower phase without dispersed in the liquid phase. Thus, the solid-liquid phases can be easily separated by filtration or sedimentation, which are conventional even in industrial scale23. Meanwhile, both the rate and capacity of CO2 absorption with the TETA-ethanol solution were significantly higher than those with a TETA-water solution. Due to the fact that there are several amino groups in TETA, the nuclear magnetic resonance (NMR) analysis of reaction products of TETA and CO2 is greatly complicated, which hinders the further understanding of the reaction details. In order to gain more insights into the CO2 absorption with phase-changing absorbents, we examined the ethanol solutions of two simple diamines viz ethylenediamine (EDA) and piperazine (PZ).

13

C NMR analyses and TG-DSC

(thermogravimetry-differential scanning calorimetry) techniques were employed to infer the characteristics of the solid phase formed after CO2 absorption. Besides, The CO2 absorption performance of TETA and diethylenetriamine (DETA) were also measured as comparison. Meanwhile, the viscosity, CO2 solubility and diffusivity of absorbents were also investigated to obtain the reaction kinetics of CO2 and the amines. 2 Experimental section 2.1 Chemicals All chemicals in this study were of chemical pure grade and used without further


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purification. The solvents used in the absorption of CO2 were ethylenediamine (EDA), piperazine (PZ), diethylenetriamine (DETA), triethylenetetramine (TETA) and ethanol, purchased from Sinopharm Chemical Reagent Co., Ltd.

The purity of CO2,

N2 and nitrous oxide (N2O) were more than 99.99%, purchased from Jingong Specialty Gases Co., Ltd. 2.2 Experimental method A double stirred-cell reactor with a plane, horizontal gas-liquid interface was used for the absorption studies. This experimental device (inner diameter 80mm, height 155mm) was operated batchwise. Four equally spaced vertical baffles, each one-tenth of the vessel diameter in width, were attached to the internal wall of the vessel, preventing vortex formation. The reactor was immersed in a water bath to maintain the required temperature. Agitation was driven by a magnetic stirrer, and the agitation speed applied was about 250 rpm in the gas phase and 150 rpm in the liquid phase. All experimental runs were performed under atmosphere at 30°C. Non-aqueous amine (EDA, PZ, DETA, TETA) solutions were used in the concentration range 0.2M~1M, ethanol was used as solvent. The simulated biogas was absorbed into 200mL amine-ethanol solutions, and the total gas-flow rate was controlled at 110mL min-1 by using a mass flow controller. The simulated biogas comprises 35% CO2 and 65% N2. For safety reasons, N2 was used to substitute CH4 in the simulated biogas, and this substitution didn’t show observable changes to the absorption performance of CO222. The direct measurement of the CO2 absorbed was performed in a calibrated bubble meter. Each experiment was duplicated at least once under identical


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conditions. 2.3 Analysis methods The liquid-phase mass transfer coefficient was measured by means of Danckwerts plot method24, that is, to determine by using ethanol solvent absorbing pure CO2. According to the mass transfer theory and the film model approach25, the CO2 mass transfer rate into pure ethanol can be expressed as: N = − =

∙∆ ∙∙

(1)

Where N is the physical absorption rate of CO2 per unit of interfacial area (kmol m-2 s-1), is the liquid-phase mass transfer coefficient, and were CO2 concentration in the gas-liquid interface and bulk liquid, P is pressure, ∆ is the volumetric flow difference value of inlet and exit CO2 (m3 s-1), R is the ideal gas constant, A is the surface area of the gas−liquid interface (m2), and T is absorption temperature (K). Due to the use of pure CO2, the gas phase resistance can be ignored. is close to zero. Accordingly, kLA can be simplified as: ∙∆

=

∙∙

=

∙∆

(2)

∙∙

Here H is the henry’s constant of CO2 in ethanol (kPa m3 kmol-1). The enhancement factor (E) reflects the effect of chemical reaction on the flux of mass transfer, defined as the ratio of molar flux with chemical reaction to that without it (NA/N), is described as follows: =

=

(3)

∙

Here NA is the chemical absorption rate of CO2 per unit of interfacial area (kmol m-2


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s-1), which can be calculated by the equation (1) as long as change the absorption solvent form pure ethanol to amine solutions. The decomposition behavior of the solid phase was carried out using TG-DSC analyzer (TA instrument SDT-Q600). The analysis was conducted using a heating rate of 10°C per minute under a pure N2 atmosphere. 13C NMR technique was employed at room temperature with a Bruker Avance III DMX 500 spectrometer to confirm the nature of the solid phase. 3 Results and discussion 3.1 Physical properties of amine-ethanol solutions Both the diffusivity and solubility of CO2 in the liquid phase are essential to the kinetic measurements. The N2O analogy has been used to approximate these properties due to the chemical reaction. Herein, we measured the solubility of N2O in pure ethanol (

,"#$%&'( ,

kmol m-3) and ethanol solutions of amines (

kmol m-3). The physical absorption of CO2 in pure ethanol (

,%)&" ,

,"#$%&'( ,

kmol m-3)

was also studied and then the values of CO2 solubility in amine solution (

,%)&" ,

kmol m-3) were calculated as follows, *,+,-. */ ,+,-.

* ,.01+-23

=*

(4)

/ ,.01+-23

The CO2 diffusion coefficient in ethanol, 4 ,"#$%&'( (m2 s-1), was determined by means of the Wilk expression26: 4 ,"#$%&'( = 7.4 ∙ 10: ∙

; ∙ ?, ∙@=.A

(5)

where Mm is the molecular weight of ethanol (kg kmol-1), B) is the solvent viscosity (kg m-1 s-1), T is the temperature (K), C is the dimensionless association factor for


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the solvent and Vb (m-3 kmol-1) is the molar volume of the solute in the normal boiling point. The recommended value for C in ethanol is 1.5. The molar volume of CO2 in the normal boiling point is 34 ∙ 10E FE FGH I . The CO2 diffusion coefficient in the amine solution, 4,%)&" FJ K I , using ethanol as a solvent were determined by applying equation27: 4 ,%)&" = 4 ,"#$%&'( [

?,.01+-23 N.: ] ?,+,-.

(6)

where B,"#$%&'( and B,%)&" are the dynamic viscosities of the pure ethanol and the ethanol amine solution, separately. The viscosity of different amine ethanol solutions was measured by using an ubbelohde viscometer. The viscosity, CO2 solubility and diffusivity of a series of diamine-ethanol solutions under atmosphere at 30°C were obtained and listed in Table. 1. Ethanol solutions of TETA and DETA were included for comparison, as well. With the increasing of the amine concentration (0.2M~1.0M), the viscosity of amine-ethanol solutions in Table 1 gets larger. Correspondingly, the diffusivity of CO2 decreases significantly. The solubility of CO2 decreases, as well. However, within the experimental concentration, the change in the solubility is rather small, all solutions decreased less than 0.0092 kmol/m3. In addition, the solubility of CO2 in ethanol was measured to be ~0.0964 kmol/m3, which is almost two times larger than that in water28. 3.2 Characterization of Products after CO2 absorption Similar to TETA-ethanol solutions, the capture of CO2 with ethanol solutions of EDA or PZ results in the precipitates of carbamate, as illustrated in Fig. 1. To


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understand the partitioning of CO2 between phases after absorption by the diamine-ethanol solution, the amounts of CO2 chemically absorbed in the two phases were determined by titration with HCl. It was found that all the chemically absorbed CO2 were captured in the solid phase, and there is only physically absorbed CO2 in the liquid phase, which was determined by CO2 solubility in ethanol. As the amine concentration ranged from 0.2M to 0.6M, the CO2 ratio in the solid phase of EDA-ethanol solution increased rapidly from 65.5% to 84.7%. With respect to PZ-ethanol solution, it’s 45.6%~82.5%. With the increasing of the amine concentration, the amount of chemically absorbed CO2 increases while CO2 solubility remain unchanged, thus the CO2 ratio in the solid phase increases as well. To characterize the constituents of the precipitates, we performed

13

C NMR

analysis. Results in Fig. 2 show that there are two peaks in the range of 160ppm~165ppm for either EDA-carbamate or PZ-carbamate. Peaks in this range suggest the existence of carbonyl in carbamates. Because either EDA or PZ has two homotopic nitrogen atoms, there must be two types of carbamates for each individual precipitate. The two types of carbamates are the products of the following reactions29: CO2 + 2H2N·R·NH2 +H3N·R·NH2 + H2N·R·NH·COO-

(7)

2CO2 + 2H2N·R·NH2 +H3N·R2·NH3+ + -OOC·NH·R·NH·COO-

(8)

Therefore, the 13C NMR analysis demonstrates that the precipitate of the EDA-ethanol solution or the PZ-ethanol solution is a mixture of monocarbamate and dicarbamate. The three peaks ranging from 38ppm to 41ppm in Fig. 2(a) corresponds to three types of carbon atoms labeled with C1, C2, and C3 in Fig. 3. This is close to the chemical


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shifts of the two carbon atoms in EDA at 45ppm30. Similarly, the three peaks within a range of 41ppm to 44ppm in Fig. 2(b) corresponds to three types of carbon atoms labeled with C1’, C2’, and C3’ in Fig. 3. Carbamate regeneration was carried out using TG-DSC analyzer. Fig. 4 shows that the decomposition of both EDA-carbamate and PZ-carbamate commences at ~90°C, which is close to the decomposition temperature of TETA-carbamate22. The integral of heat flow in Fig. 4 gives the energy required for the regeneration of carbamates (instrumental error±15%), which is approximately 2.9 GJ/t CO2 and 3.1 GJ/t CO2 for EDA-carbamate and PZ-carbamate, respectively. Although the energy is larger than the regeneration energy for MEA-carbamate31, which is 1.71 GJ/t CO2, the overall energy for the regeneration of EDA-carbamate and PZ-carbamate is even 25.6% and 20.5% lower than that for the regeneration of MEA-carbamate aqueous solution32, as there is no need to heat up the liquid phase after the absorption of CO2. Moreover, when comparing with the PZ aqueous solution, whose reboiler duty is 3.4GJ/t CO233, the energy required for regeneration of EDA-carbamate is 14.7% lower. 3.3 CO2 absorption kinetics and capacities in ethanol solutions The CO2 absorption rate and capacity of diamine-ethanol solutions were measured in the double stirred-cell reactor at 30°C. The TETA, DETA ethanol solutions were also examined as comparison. Results in Fig. 5 show that EDA-ethanol solutions have a much higher absorption rate of CO2 than PZ-ethanol solutions in all the concentration used in this study. At a relatively low concentration of 0.2M, the EDA-ethanol solution has slower absorption rate of CO2 than TETA or DETA ethanol


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solutions in whole absorption processes. However, at higher concentrations, for instance, 0.4M or 0.6M, EDA-ethanol solutions have an initial absorption rate of CO2 comparable to TETA or DETA ethanol solutions. However, the absorption rates for EDA-ethanol solutions decrease significantly after passing a certain time. The absorption kinetics of CO2 for PZ-ethanol solutions is quite different from other amine-ethanol solutions. The initial absorption rate of CO2 for PZ-ethanol solutions drops dramatically soon after the absorption process. This could be due to the lower Lewis basicity of the secondary amino group in PZ, which also leads to lower affinity with the carbon atom in CO2 because of the slight steric hindrance created by the methyl group on nitrogen34. Fig. 6 shows the capacity of CO2 absorption for EDA, TETA, DETA, and PZ-ethanol solutions. As EDA and PZ contain less amine groups than TETA or DETA, their capacities for CO2 capture in ethanol solutions are also smaller than the latter. There are slight decreases in the loading capacity of CO2 absorption with increasing amine concentrations for EDA, TETA, and DETA ethanol solutions. This might be attributed to the higher mass transfer resistance caused by the higher viscosity of the solutions. The influence of CO2 partial pressure on the absorption rate was investigated at a constant amine concentration of 0.2M. The agitation speed in the gas phase was kept at 250 rpm to minimize the mass transfer resistance of gas phase. Fig. 7 shows a linear relationship between the absorption rate and partial pressure of CO2, where all of the four curves have a slope of one for each amine-ethanol solutions. This suggests that the order of reaction between amine and CO2 in ethanol solutions is one, which is in


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agreement with similar studies examined in aqueous amine solutions35, 36. As both physical and chemical absorption exist in the capture of CO2 with amine-ethanol solutions, the enhancement factors (E) of different amine-ethanol solutions were calculated to quantify their effects. Fig. 8 shows the enhancement factors when the concentrations of amines are in a range of 0.2M ~ 1M. For the amine-ethanol solutions examined in this work, their enhancement factors are around 3, which is close to Park’s study28 on diisopropanolamine (DIPA)-ethanol solutions. These enhancement factors are considerably smaller than those for aqueous amine solutions, which indicates that ethanol has a strong physical absorption for CO2 compared with water. 3.4 Absorption kinetics and capacities in aqueous solutions Diamine-ethanol solutions and diamine-water solutions were used for CO2 absorption at 30°C, respectively. TETA, DETA ethanol solutions and TETA, DETA water solutions were also tested as comparison. Results in Fig. 9 demonstrate that using ethanol as solvent greatly enhances the absorption of CO2 in compare with water. The capacity of CO2 absorption in EDA or PZ ethanol solutions is nearly 1.1 times of that in water solutions, similar to the relative relationship between TETA or DETA ethanol solutions and their aqueous ones. Moreover, the absorption time needed to reach equilibrium for EDA-ethanol solution is almost half of that with EDA-water solution. Therefore, EDA in ethanol solutions exhibit an overall average absorption rate of CO2 about one time higher than that in water solutions, similar to TETA or DETA does as well. Even though the absorption rate of PZ-ethanol solutions


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is relatively smaller than other amine-ethanol solutions, it is still 1.2 times as fast as PZ water solutions. 4 Conclusions In the present work, we have investigated the CO2 absorption with EDA and PZ dissolved in ethanol. Both solutions can produce a solid precipitate after absorption, which has been identified to be the mixture of monocarbamate and dicarbamate from its 13C solid state NMR spectrum. EDA-carbamates and PZ-carbamates have a similar decomposition temperature of ~90°C. The regeneration heat of EDA-carbamate and PZ-carbamate is 25.6%, 20.5% less than traditional MEA solutions, respectively. In addition, the kinetics of CO2 absorption with TETA, DETA ethanol solutons were also examined for comparison. EDA-ethanol solutions exhibit a rate of CO2 absorption comparable to TETA or DETA ethanol solutions, while PZ-ethanol solutions have the slowest rate among the four amine ethanol solutions examined in this study. As EDA and PZ contain less amine groups than TETA or DETA, the CO2 absorption capacities of EDA, PZ ethanol solutions are lower than TETA, DETA ethanol solutions. Moreover, results show that the capacity of diamine-ethanol solutions is ~1.1 times as much as that of diamine-water solutions. The overall average CO2 absorption rate of EDA-ethanol solutions is almost doubled compared to that of EDA-water solutions, while the CO2 absorption rate of PZ-ethanol solutions is only slightly enhanced than that of PZ-water solutions. Author information Corresponding Author


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*E-mail: [email protected] Acknowledgments The authors would like to thank the National Natural Science Foundation of China (grant number 21676245 and 21476191) for financial support. The authors also acknowledge the Ministry of Science and Technology of the People´s Republic of China (grant number 2014BAC22B06) and the Science and Technology Department of Zhejiang Province (grant number 2014C03025) for financial support. Reference (1) Divya, D.; Gopinath, L. R.; Christy, P. M. A review on current aspects and diverse prospects for enhancing biogas production in sustainable means. Renew Sust Energ Rev, 2015, 42, 690-699. (2) Xia, A.; Cheng, J.; Murphy, J. D. Innovation in biological production and upgrading of methane and hydrogen for use as gaseous transport biofuel. Biotechnol Adv, 2016, 34, 451-472. (3) Weiland, P. Biogas production: Current state and perspectives. Appl Microbiol Biotechnol, 2010, 85, 849-860. (4) Xu, Y. J.; Huang, Y.; Wu, B.; Zhang, X. P.; Zhang, S. J. Biogas upgrading technologies: Energetic analysis and environmental impact assessment. Chin J Chem Eng, 2015, 23, 247-254. (5) Barzagli, F.; Lai, S.; Mani, F.; Stoppioni, P. Novel non-aqueous amine solvents for biogas upgrading. Energ Fuel, 2014, 28, 5252-5258. (6) Kamopas, W.; Asanakham, A.; Kiatsiriroat, T. Absorption of CO2 in biogas with amine solution for biomethane enrichment. J Eng Sci Tech, 2016, 48, 231-241. (7) Castrillon, M. C.; Moura, K. O.; Alves, C. A.; Bastos-Neto, M.; Azevedo, D. C. S.; Hofmann, J.; Mollmer, J.; Einicke, W.-D.; Glaser, R. CO2 and H2S removal from CH4-rich streams by adsorption on activated carbons modified with K2CO3, NaOH, or Fe2O3. Energ Fuel, 2016, 30, 9596-9604.


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(8) Cheng, J.; Li, Y.; Hu, L.; Zhou, J.; Cen, K. CO2 adsorption performance of ionic liquid [P66614][2-Op] loaded onto molecular sieve mcm-41 compared to pure ionic liquid in biohythane/pure CO2 atmospheres. Energ Fuel, 2016, 30, 3251-3256. (9) Umaiyakunjaram, R.; Shanmugam, P. Study on submerged anaerobic membrane bioreactor (sambr) treating high suspended solids raw tannery wastewater for biogas production. Bioresour Technol, 2016, 216, 785-792. (10) Chen, X. Y.; Hoang, V.-T.; Ramirez, A. A.; Rodrigue, D.; Kaliaguine, S. Membrane gas separation technologies for biogas upgrading. Rsc Adv, 2015, 5, 24399-24448. (11) Dimaria, P. C.; Dutta, A.; Mahmud, S. Syngas purification in cryogenic packed beds using a one-dimensional pseudo-homogenous model. Energ Fuel, 2015, 29, 5028-5035. (12) Tuinier, M. J.; Annaland, M. V. S. Biogas purification using cryogenic packed-bed technology. Ind Eng Chem Res, 2012, 51, 5552-5558. (13) Svendsen, H. F.; Hessen, E. T.; Mejdell, T. Carbon dioxide capture by absorption, challenges and possibilities. Chem Eng J, 2011, 171, 718-724. (14) Rochelle, G. T. Amine scrubbing for CO2 capture. Science, 2009, 325, 1652-1654. (15) Raynal, L.; Bouillon, P. A.; Gomez, A.; Broutin, P. From mea to demixing solvents and future steps, a roadmap for lowering the cost of post-combustion carbon capture. Chem Eng J, 2011, 171, 742-752. (16) Xu, Z.; Wang, S.; Chen, C. CO2 absorption by biphasic solvents: Mixtures of 1,4-butanediamine and 2-(diethylamino)-ethanol. Int J Greenh Gas Con, 2013, 16, 107-115. (17) Pinto, D. D. D.; Knuutila, H.; Fytianos, G.; Haugen, G.; Mejdell, T.; Svendsen, H. F. CO2 post combustion capture with a phase change solvent. Pilot plant campaign. Int J Greenh Gas Con, 2014, 31, 153-164. (18) Pinto, D. D. D.; Zaidy, S. a. H.; Hartono, A.; Svendsen, H. F. Evaluation of a phase change solvent for CO2 capture: Absorption and desorption tests. Int J Greenh Gas Con, 2014, 28, 318-327.


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(19) Ye, Q.; Wang, X.; Lu, Y. Screening and evaluation of novel biphasic solvents for energy-efficient post-combustion CO2 capture. Int J Greenh Gas Con, 2015, 39, 205-214. (20) Hasib-Ur-Rahman, M.; Larachi, F. CO2 capture in alkanolamine-rtil blends via carbamate crystallization: Route to efficient regeneration. Environ Sci Technol, 2012, 46, 11443-11450. (21) Hasib-Ur-Rahman, M.; Siaj, M.; Larachi, F. CO2 capture in alkanolamine/room -temperature ionic liquid emulsions: A viable approach with carbamate crystallization and curbed corrosion behavior. Int J Greenh Gas Con, 2012, 6, 246-252. (22) Zheng, S. D.; Tao, M. N.; Liu, Q.; Ning, L. Q.; He, Y.; Shi, Y. Capturing CO2 into the precipitate of a phase-changing solvent after absorption. Environ Sci Technol, 2014, 48, 8905-8910. (23) Kinnarinen, T.; Golmaei, M.; Jernstrom, E.; Hakkinen, A. Separation, treatment and utilization of inorganic residues of chemical pulp mills. J Clean Prod, 2016, 133, 953-964. (24) V., D. P.; Mcneil, K. M. Absorption of carbon dioxide into aqueous amine solutions and effects of catalysis. Trans Inst Chem Eng, 1967, 45, T32-&. (25) Sharma, M. M.; Danckwerts, P. V. Chemical methods of measuring interfacial area and mass transfer coefficients in 2-fluid systems. Br Chem Eng, 1970, 15, 522-+. (26) Wilke, C. R. Estimation of liquid diffusion coefficients. Chem Eng Prog, 1949, 45, 218-224. (27) Versteeg, G. F.; Vanswaaij, W. P. M. On the kinetics between CO2 and alkanolamines both in aqueous and non-aqueous solutions .2. Tertiary-amines. Chem Eng Sci, 1988, 43, 587-591. (28) Hwang, K. S.; Park, S. W.; Park, D. W.; Oh, K. J.; Kim, S. S. Absorption of carbon dioxide into diisopropanolamine solutions of polar organic solvents. J Taiwan Inst Chem E, 2010, 41, 16-21. (29) Sada, E.; Kumazawa, H.; Han, Z. Q. Kinetics of reaction between carbon-dioxide and ethylenediamine in nonaqueous solvents. Chem Eng J Biochem Eng J, 1985, 31, 109-115.


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(30) Wang, H. L.; Kao, H. M.; Digar, M.; Wen, T. C. Ftir and solid state C-13 nmr studies on the interaction of lithium cations with polyether poly(urethane urea). Macromolecules, 2001, 34, 529-537. (31) Gao, J.; Yin, J.; Zhu, F. F.; Chen, X.; Tong, M.; Kang, W. Z.; Zhou, Y. B.; Lu, J. Orthogonal test design to optimize the operating parameters of CO2 desorption from a hybrid solvent mea-methanol in a packing stripper. J Taiwan Inst Chem E, 2016, 64, 196-202. (32) Abu-Zahra, M. R. M.; Schneiders, L. H. J.; Niederer, J. P. M.; Feron, P. H. M.; Versteeg, G. F. CO2 capture from power plants. Part i. A parametric study of the technical-performance based on monoethanolamine. Int J Greenh Gas Con, 2007, 1, 37-46. (33) Gaspar, J.; Ricardez-Sandoval, L.; Jorgensen, J. B.; Fosbol, P. L. Controllability and flexibility analysis of CO2 post-combustion capture using piperazine and mea. Int J Greenh Gas Con, 2016, 51, 276-289. (34) Kortunov, P. V.; Siskin, M.; Baugh, L. S.; Calabro, D. C. In situ nuclear magnetic resonance mechanistic studies of carbon dioxide reactions with liquid amines in aqueous systems: New insights on carbon capture reaction pathways. Energ Fuel, 2015, 29, 5919-5939. (35) Bindwal, A. B.; Vaidya, P. D.; Kenig, E. Y. Kinetics of carbon dioxide removal by aqueous diamines. Chem Eng J, 2011, 169, 144-150. (36) Salvi, A. P.; Vaidya, P. D.; Kenig, E. Y. Kinetics of carbon dioxide removal by ethylenediamine and diethylenetriamine in aqueous solutions. Can J Chem Eng, 2014, 92, 2021-2028.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table

Table 1. Physical properties of solutions and CO2/amine at 30°C Solutions TETA/Ethanol

DETA/Ethanol

EDA/Ethanol

PZ/Ethanol

Ethanol

CAmine kmol/m3

µ mpa·s

CO2 Solubility kmol/m3

DCO2×109 m2s-1

0.2 0.4 0.6 0.8 1.0

1.134 1.273 1.428 1.614 1.791

0.1012 0.1005 0.0970 0.0944 0.0933

2.034 1.854 1.691 1.533 1.411

0.2 0.4 0.6 0.8 1.0

1.082 1.166 1.251 1.327 1.432

0.1012 0.0974 0.0958 0.0933 0.0920

2.112 1.990 1.881 1.793 1.688

0.2 0.4 0.6 0.8 1.0

1.053 1.089 1.116 1.158 1.178

0.0962 0.0956 0.0947 0.0912 0.0901

2.158 2.100 2.060 2.001 1.972

0.2 0.4 0.6 0.8 1.0 0

1.063 1.126 1.182 1.245 1.299 1.010

0.1020 0.1016 0.0999 0.0993 0.0993 0.0964

2.142 2.045 1.968 1.889 1.825 2.265


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figures

Figure 1. CO2 absorption with ethanol solutions of EDA (a) before CO2 absorption (b) after CO2 absorption


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

Figure 2. 13C NMR spectra of (a) EDA-carbamate and (b) PZ-carbamate


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3. Potential species in loaded ethanol solutions of EDA or PZ


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120 2 100 0

Weight(%)

80 -2 60 -4

40

0 20

-6

Weight% Heat flow

20

40

60

80

Heat Flow(w/g)

100

120

140

160

180

200

-8 220

Temperature(°C)

(a) 120 1 100 0 80

Weight(%)

-1 60 -2 40

-3

Weight% Heat flow

20

0 20

40

60

80

Heat Flow(w/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-4

100

120

140

160

180

200

-5 220

Temperature(°C)

(b) Figure 4. TG-DSC curves of (a) EDA-carbamate and (b) PZ-carbamate


Energy & Fuels

5

0.2M

4

EDA/Ethanol DETA/Ethanol TETA/Ethanol PZ/Ethanol

3

-1

2 1

-3

-2

Absorption Rate / 10 mol m s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0

0.4M

4 3 2 1 0

0.6M

4 3 2 1 0 20

40

60

80

100 120 140 160 180 200

Time / min

Figure 5. CO2 absorption rate of amine-ethanol solutions


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1.8

Absorption Load / mol CO2/ mol Amine

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.6

0.6M 0.4M 0.2M

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

EDA /Ethanol DETA/Ethanol TETA/Ethanol PZ/Ethanol

Figure 6. CO2 absorption capacity of amine-ethanol solutions


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-1

5

4

-3

-2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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3

TETA DETA EDA PZ 2 20

30

40

CO2 pressure / Mpa

Figure 7. Plots of CO2 absorption rate vs O (O measured in experiments equals to 15%, 20%, 25%, 35% in volume)


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4.0

TETA DETA EDA PZ

3.5

Enhancement factor (Ε)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

3.0

2.5

2.0 0.0

0.2

0.4

0.6

0.8

Concentration / kmol m

1.0

1.2

-3

Figure 8. Effect of amine concentration on enhancement factor (E)


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1.0

3.5 3.0

0.8

2.5 0.6

2.0 1.5

Water solution Ethanol solution

1.0

0.4 0.2

0.5 0.0

0.0 20

40

60

80

100

-1 -2 -3

1.2 4.0

5.0


-1 -3

-2


1.4

4.5

1.4

4.5 1.2 4.0 1.0

3.5 3.0

0.8

2.5 0.6

2.0 1.5


1.0

0.2 0.5 0.0 20

120

40

60

3.5

1.2

3.0 1.0 2.5 0.8 2.0


0.6 0.4

1.0

0.2

0.0

0.0 60

80

100

120

140

160

-1 -2

-1

0.5

-3

1.4

1.6

5.0


4.0

-3

-2


1.6

40

0.0 120

100

4.5

1.4

4.0 1.2 3.5 1.0

3.0

0.8

2.5 2.0

0.6

1.5


1.0

0.2

0.5 0.0

Time / min (c)

0.0 20

40

60

80

100

Time / min (d)

Figure 9. CO2 absorption rate and capacity in amine-ethanol and amine-water solutions at 30°C: (a) 0.2M EDA (b) 0.2M PZ (c) 0.2M TETA (d) 0.2M DETA.


0.4

120

140

Absorption capacity / mol CO2 /mol Amine

1.8

4.5


5.0

20

80

Time / min (b)

Time / min (a)

1.5

0.4


5.0


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Biogas Upgrading by Capturing CO2 in Non-aqueous Phase

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