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Modeling, simulation and evaluation of biogas upgrading using aqueous choline chloride/urea
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. College of Chemical Engineering, Nanjing Tech University, Nanjing.ORCID-id: 0000-0002-0453-0450
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.ORCID-id: 0000-0002-0200-9960
College of Chemical Engineering, Nanjing Tech University, Nanjing .
Vise andre og tillknytning
2017 (engelsk)Inngår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 229, nr 1, s. 1269-1283Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Biogas has been considered as an alternative renewable energy, and raw biogas needs to be upgraded in order to be used as vehicle fuels or injected into the natural gas grid. In this work, the conceptual process for biogas upgrading using aqueous choline chloride (ChCl)/urea (1:2 on a molar basis) was developed, simulated and evaluated based on the commercialized software Aspen Plus. Reliable thermophysical properties and phase equilibria are prerequisite for carrying out process simulation. In order to carry out the process simulation, the thermophysical properties of ChCl/Urea (1:2) and its aqueous solutions as well as the phase equilibria of gas-ChCl/Urea (1:2), ChCl/Urea (1:2)-H2O and gas-ChCl/Urea (1:2)-H2O were surveyed and evaluated. After evaluation, the consistent experimental data of these thermophysical properties were fitted to the models embedded in Aspen Plus. The properties needed but without available experimental results were predicted theoretically. The Non-Random Two-Liquid model and the Redlich-Kwong equation (NRTL-RK) model were used to describe the phase equilibria. The equilibrium approach was used for process simulation. Sensitivity analysis was conducted to determine the reasonable operating parameters. With a set of reasonable operating conditions, the effects of ChCl/Urea (1:2) content on the total energy utilization, the diameters and pressure drops of absorber and desorber as well as the environmental assessment of the process were studied. The simulation results showed that, with the addition of ChCl/Urea (1:2), the total energy utilization decreased by 16% compared to the process with pure water, and the diameters of both absorber and desorber decreased with increasing content of ChCl/Urea (1:2). The process using aqueous ChCl/Urea (1:2) was more environmentally benign than that with pure water. Therefore, aqueous ChCl/Urea (1:2) is a promising solvent for biogas upgrading.

sted, utgiver, år, opplag, sider
Elsevier, 2017. Vol. 229, nr 1, s. 1269-1283
Emneord [en]
Aqueous choline chloride/urea, Thermodynamic modeling, Process simulation, Biogas upgrading
HSV kategori
Forskningsprogram
Energiteknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-63249DOI: 10.1016/j.apenergy.2017.03.059ISI: 000449891500098Scopus ID: 2-s2.0-85018938965OAI: oai:DiVA.org:ltu-63249DiVA, id: diva2:1093199
Merknad

Validerad;2018;Nivå 2;2018-12-03 (inah)

Tilgjengelig fra: 2017-05-05 Laget: 2017-05-05 Sist oppdatert: 2019-09-13bibliografisk kontrollert
Inngår i avhandling
1. Development of low-cost ionic liquids based technology for CO2 separation
Åpne denne publikasjonen i ny fane eller vindu >>Development of low-cost ionic liquids based technology for CO2 separation
2019 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
Alternativ tittel[sv]
CO2-separation med ny lågkostnads-teknik baserad på Joniska lösningar
Abstract [en]

CO2 separation plays an important role to mitigate the CO2 emissions due to burning of fossil fuels, and it is also of importance in biofuel production (e.g. biogas upgrading and bio-syngas purification and conditioning). The solvent-based absorption is the state-of-art technology for CO2 separation, where various solvents, e.g. amine solutions, Selexol (i.e. dimethyl ethers of polyethylene glycol), and propylene carbonate, have been introduced. However, these solvent-based technologies meet challenges such as high solvent degradation, high corrosion rate to equipment, high construction cost, high energy demand for solvent regeneration and high solvent make-up rate. Therefore, the development of novel solvents to overcome the challenges of the currently available solvents is essential.

Recently, ionic liquids (ILs) have gained great interest as new potential solvents for CO2 separation, mainly due to their very low vapor pressure and relatively high CO2 solubility. In addition, ILs have lower corrosive characteristic, lower degradation rate and lower energy requirement for solvent regeneration compared with the conventional organic solvents. However, the main challenge of the application of ILs is their higher viscosity than the conventional solvents, which can be solved by adding co-solvents such as water.

The overall objective of this thesis work was to develop low-cost IL based technologies for CO2 separation. To achieve this objective, the deep eutectic solvent (DES) of choline chloride (ChCl)/Urea with molar ratio 1:2 as a new type of IL was selected as an absorbent and H2O was used as co-solvent for CO2 separation from biogas. The conceptual process was developed and simulated based on Aspen Plus, and the effect of water content on the performance of ChCl/Urea for CO2 separation was evaluated. It was found that the optimal proportion of aqueous ChCl/Urea was around 50 wt% (percentage by weight) of water with the lowest energy usage and environmental effect.

The performance of aqueous ChCl/Urea was further compared with the commercial organic solvents in this thesis work. The rate-based process simulation was carried out to compare the energy usage and the cost for CO2 separation from biogas. It was found that aqueous ChCl/Urea achieved the lowest cost and energy usage compared with other commercial solvents except propylene carbonate. The performance comparison proved that CO2 solubility, selectivity and viscosity were three important parameters which can be used as criteria in the development of novel physical solvents for CO2 separation.

ILs with acetate anions normally show high CO2 solubility and selectivity, and the ILs with alkylmorpholinium as cations have low toxicity leading to lower environmental effect. Therefore, in this thesis work, a series of N-alkyl-N-methylmorpholinium-based ILs with acetate as counterpart anion were investigated, and water was added as co-solvent to adjust the viscosity. The CO2 solubility in these aqueous ILs was measured at different temperatures and pressures. It was found that the increase of alkyl chain length in the cation led to an increase of CO2 solubility of the ILs with the same anion. Aqueous N-butyl-N-methylmorpholinium acetate ([Bmmorp][OAc]) had the highest CO2 solubility, and it was selected to further carry out thermodynamic modeling and process simulation. The energy usage and the size of equipment of using aqueous [Bmmorp][OAc], aqueous ChCl/Urea, water, Selexol, and propylene carbonate for CO2 separation from biogas were compared. It was found that this novel IL mixing with water had better performance, that is, with lower energy usage and smaller size of equipment than the other solvents. This result suggests that using this aqueous [Bmmorp][OAc] has the potential to decrease the cost of CO2 separation.

sted, utgiver, år, opplag, sider
Luleå: Luleå University of Technology, 2019
Serie
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
HSV kategori
Forskningsprogram
Energiteknik
Identifikatorer
urn:nbn:se:ltu:diva-72567 (URN)978-91-7790-300-0 (ISBN)978-91-7790-301-7 (ISBN)
Presentation
2019-04-05, E632, Luleå tekniska universitet, Luleå, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2019-01-16 Laget: 2019-01-15 Sist oppdatert: 2019-10-01bibliografisk kontrollert

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