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Techno-economic analysis and performance comparison of aqueous deep eutectic solvent and other physical absorbents for biogas upgrading
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, Nanjing.ORCID iD: 0000-0002-0453-0450
State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, Nanjing.
State Key Laboratory of Material-Oriented Chemical Engineering, Nanjing Tech University, Nanjing.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0002-0200-9960
2018 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 225, p. 437-447Article in journal (Refereed) Published
Abstract [en]

Biogas has been considered as an alternative renewable energy, and CO2 removal from raw biogas (i.e. biogas upgrading) is needed for producing biomethane to be used as vehicle fuels or injected into the natural gas grid. Biogas upgrading with physical absorbents, such as water and other commercial organic solvents, is simple, efficient and with low energy requirements for regeneration. Recently, deep eutectic solvents (DESs) with nonvolatility, nonflammability and low price have been reported as promising alternatives to replace conventional physical absorbents in many research areas including biogas upgrading. However, the performances of these physical solvents including conventional physical absorbents and DES-based solvents have not been evaluated and compared with each other. In this work, the properties of 4 physical solvents (i.e. water, dimethyl ether of polyethylene glycol (DEPG), propylene carbonate (PC), and aqueous DES (AQDES)) were compared. Furthermore, a conceptual process was developed to upgrade biogas with these solvents and simulated based on Aspen Plus in order to conduct performance comparison. The simulation results of energy utilization, the amount of recirculated solvents and the diameters of absorber and desorber were analyzed and compared based on equilibrium and rate-based approaches, respectively. The simulation results based on the rate-based approach were further used to estimate the costs of biogas upgrading process with a same raw biogas capacity for comparison. Meanwhile, the specific cost of biogas upgrading process with a same size of equipment was also evaluated. The results show that the CO2 solubility, selectivity and viscosity are three more important properties, providing valuable information for developing novel physical solvents for CO2 separation. The simulation results show that the equilibrium and rate-based approaches result in different conclusions, especially when the solvent viscosity is relatively high, and the rate-based approach is preferable. Based on the simulation results from the rate-based approach, the performances of AQDES and PC are similar with a same amount of energy utilization, that is around 11% lower than water, and DEPG is inferior to water. For the case with the same gas capacity, the total annual costs of biogas upgrading process with these solvents show the following order: DEPG > AQ60wt.%DES > water > AQ50wt.%DES ≈ PC. For the case with the same size of equipment, compared to water, the total specific costs of biogas upgrading process with PC and AQ50wt.%DES decrease by about 30% and 45%, respectively, and the treated biogas capacities increase to 1.5 and 2 times, respectively. In general, both PC and AQ50wt.%DES show better performance than the other solvents. Considering that DES is an environmentally benign solvent, and the performance of DES can be greatly improved by further designing, it is more promising

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 225, p. 437-447
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-68870DOI: 10.1016/j.apenergy.2018.04.112ISI: 000438181000032Scopus ID: 2-s2.0-85046867612OAI: oai:DiVA.org:ltu-68870DiVA, id: diva2:1209670
Note

Validerad;2018;Nivå 2;2018-05-23 (andbra)

Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2019-01-15Bibliographically approved
In thesis
1. Development of low-cost ionic liquids (ILs) based technology for CO2 separation
Open this publication in new window or tab >>Development of low-cost ionic liquids (ILs) based technology for CO2 separation
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Alternative title[sv]
CO2-separation med ny lågkostnads-teknik baserad på Joniska lösningar
Abstract [en]

CO2 capture plays an important role to mitigate CO2 emissions in fossil fuel utilized processes. Meanwhile, CO2 separation is of importance to increase the efficiency of the subsequent product in biomass process, such as biogas upgrading and bio-syngas purification. Among current technologies, the absorption process, i.e. liquid sorbent-based technologies, has received much more attention and been widely studied. Currently, some solvents are available and commercialized for CO2 separation, e.g. amine solutions, Selexol (i.e. dimethyl ethers of polyethylene glycol) and etc. However, it has been reported that these solvents meet some challenges such as high volatility, corrosion, degradation, high cost, and high energy usage for solvent regeneration. Therefore, the development of novel solvents with high capacity and, meanwhile, to overcome the challenges of the currently used or available solvents is essential.

Room temperature ionic liquids (RTILs) show a great potential as alternatives of conventional organic solvents for CO2 separation due to their favorite properties such as high CO2 capacity, non-volatility, high tunability, less corrosion and low energy requirement for solvent regeneration. Therefore, using ILs can be a technology breakthrough for CO2 separation. However, the challenges of using ILs are their high viscosity and preparation cost. To overcome these problems, one way is adding co-solvents to decrease the viscosity, and the other way is to design lowly viscous ILs. In addition, the cost and “green”, i. e. environmental benignity,  are also the concerns when choosing ILs.

The properties of solvents can be used as criteria to select solvents. However, the performance of these solvents in a real process is essential before implementing into the industry but cannot be judged only by properties. Process simulation is a way to design, develop, analyze and optimize the technical process, where the models with approximations and assumptions are used to describe properties over a wide range of temperatures and pressures based on the parameters regressed from real data. Considering that ILs are new and no data or parameters are available in the databank, data determining experimentally, thermodynamic modeling of the data and then process simulating are necessary.

In this thesis, a new type of ILs, i.e. deep eutectic solvent (DES), was selected to study their performance for CO2 separation from biogas. The promising DES investigated here, i.e. choline chloride (ChCl) /Urea with molar ratio 1:2, is “green” and with high CO2 solubility. Considering the high viscosity of this DES, the effect of adding co-solvent (i.e. water) was investigated based on the equilibrium calculation in process simulation. The conclusion from this work suggests that this aqueous ChCl/Urea (1:2) is promising, and the best proportion is around 50% weight percentage of water based on the energy and environmental analysis. After that, the rate-based calculation in process simulation was adopted, and the performance comparison including energy usage and costs for CO2 capture from biogas using aqueous ChCl/Urea (1:2) and commercial organic solvents was carried out. The results show that aqueous ChCl/Urea (1:2) is a better choice and comparable with most commercial solvents except propylene carbonate by energy and economic analyses. Therefore, there is still room to develop new ILs for the enhancement of CO2 separation. Newly prepared morpholinium based ILs were investigated and tested. The one with the highest CO2 capacity was selected, and the preliminary study shows that this novel IL mixed with water has better performance than the solvents that we investigated before, that is, the novel aqueous IL is with lower energy usage and smaller size of equipment. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Chemical Engineering Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-72567 (URN)978-91-7790-300-0 (ISBN)978-91-7790-301-7 (ISBN)
Presentation
2019-04-05, E231, Luleå tekniska universitet, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2019-01-16 Created: 2019-01-15 Last updated: 2019-01-16Bibliographically approved

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Ma, ChunyanJi, Xiaoyan

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