Novel synthetic CaO-based sorbents for carbon dioxide (CO2) capture in sorption-enhanced steam reforming (SESR) were prepared by the co-precipitation method. Magnesium oxide (MgO) and cerium oxide (CeO2) were mixed with calcium oxide (CaO) in different molar percentages in order to obtain the optimum percentage, which provide high CO2 uptake capacity and cyclic stability. The TGA results for CO2 uptake, revealed that for the molar ratio of CaO, MgO and CeO2 of (6:2:1) and (4:2:1), the sorbents had CO2 capture capacity of 29 and 25 wt.%, respectively. The fresh sorbents were characterized using X-ray diffraction, mercury porosimetry, N2 physisorption and scanning electron microscopy. It was found that the sorbents with higher CO2 uptake capacities had relatively high porous surface structure with porosity percentage (>66%). Modelling of CO2 uptake kinetics showed that JMA (Johnson-Mehl-Avrami) fits best the first and second stages except for the molar ratio of CaO, MgO and CeO2 of (4:2:1) sample where, surface chemisorption (SC) fits the initial stage and JMA fits the second stage. While the contracting volume model (CV2/3) fits the final stages of all the studied sorbents. The stability of sorbents at high temperatures was examined over multiple cycles of carbonation/de-carbonation reactions. After 45 cycles, the sample with a molar ratio of CaO, MgO and CeO2 of (6:2:1) remained as high as 25 wt.% (0.43g CO2 /1g CaO) with only 25% decrease from its CO2 uptake capacity as a fresh sample. Therefore, the latter sample was selected to be mixed with iron oxide catalyst and used for the SESR. The study of ethanol steam reforming employing an iron oxide as a catalyst, with and without in-situ CO2 removal, has been investigated. The results confirmed that iron oxide exhibited catalytic activity for hydrogen (H2) production from ethanol steam reforming/decomposition reactions. Furthermore, the CaO-based sorbent had sucessfully decrease the amount of CO2 produced during ethanol reforming reaction up to 70 min of reaction time. Ethanol reformation with in-situ CO2 removal was investigated at 550-700 °C. The maximum H2 yield achieved was 3.5 mol (H2) /mol (EtOH) at 600°C. GC results revealed that there was no evidence of CO and C across the studied temperature range. The results showed an enhancement in reaction reactivity by increasing the gas hourly space velocities (GHSVs). The amount of H2 produced remained stable within 10 cycles, which is equivalent to 30 hours of reaction time.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:692721 |
| Date | January 2016 |
| Creators | Elfaki, Hind Omer Elsheikh |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/31789/ |
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