Studies of a fixed bed chemical looping reactor for H2 production by in-situ and operando x-ray and neutron diffraction.

Ph. D. Thesis.The purpose of this thesis focused on the investigation of the use of non-stoichiometric oxides as oxygen carrier materials for chemical looping H₂ production. It concentrated on the use of strontium doped lanthanum ferrite (La0.6Sr0.4FeO3-δ, LSF641) for the chemical looping water-gas shift reactor. Chemical looping consists of the cyclic oxidation and then reduction of a solid oxygen carrier material. This process is used to split a redox reaction into its two half reactions using the solid as an intermediate. In a water-gas shift reactor this consist of the oxidation of CO to CO2 and the reduction of H2O to H2. It was shown that theoretically such a system would achieve higher conversions than a conventional reactor; 50% when operated at 1093 K for the conventional reactor and complete conversion when operated using a suitable non-stoichiometric oxide in a chemical looping system. When studied experimentally it was found that such a system could achieve conversions of 88% for both the reduction and oxidation half cycles. The system was also shown to continue to achieve these high conversions for over 1000 cycles without noticeable degradation in product quality or oxygen carrier material. By using the thermal and chemical expansivities of LSF641 it was possible to determine its oxidation state of the LSF641 in operando. This was carried out through the use of synchrotron x-ray diffraction, this showed that how the gradient in chemical potential changed along the bed as a function of time. This was compared with the results of an equilibrium limited thermodynamic model of the system. Both the outlet gas composition and the internal chemical potential of the system were compared to experimental results and showed good agreement. This indicates that the system operates close to its thermodynamic limitations making it a worthy system for further study.EPSR

Metagenomic characterisation of the viral community of lough neagh, the largest freshwater lake in Ireland

Lough Neagh is the largest and the most economically important lake in Ireland. It is also one of the most nutrient rich amongst the world's major lakes. In this study, 16S rRNA analysis of total metagenomic DNA from the water column of Lough Neagh has revealed a high proportion of Cyanobacteria and low levels of Actinobacteria, Acidobacteria, Chloroflexi, and Firmicutes. The planktonic virome of Lough Neagh has been sequenced and 2,298,791 2×300 bp Illumina reads analysed. Comparison with previously characterised lakes demonstrates that the Lough Neagh viral community has the highest level of sequence diversity. Only about 15% of reads had homologs in the RefSeq database and tailed bacteriophages (Caudovirales) were identified as a major grouping. Within the Caudovirales, the Podoviridae and Siphoviridae were the two most dominant families (34.3% and 32.8% of the reads with sequence homology to the RefSeq database), while ssDNA bacteriophages constituted less than 1% of the virome. Putative cyanophages were found to be abundant. 66,450 viral contigs were assembled with the largest one being 58,805 bp; its existence, and that of another 34,467 bp contig, in the water column was confirmed. Analysis of the contigs confirmed the high abundance of cyanophages in the water column

Bi-metallic Ni–Fe LSF perovskite for chemical looping hydrogen application

This work introduces a novel composite bimetallic perovskite Fe 2O 3-NiO/La 0.6Sr 0.4FeO 3 as an oxygen carrier for chemical looping hydrogen production. The materials were tested in a 2-g packed bed reactor at different temperatures ranging from 500 to 900 °C and atmospheric pressure by alternating three-stage chemical looping hydrogen reactions. Fe[sbnd]Ni bimetallic interactions and La 0.6Sr 0.4FeO 3 (LSF-641) resistance to carbon deposition resulted in a stable material with only a 2% oxygen capacity drop over 20 redox cycles. The modified LSF exhibited a 20 increase in H 2 generation compared to LSF-641. These results demonstrate the effectiveness of doping Fe with Ni to generate more stable OC and the low H 2 generation of LSF coupled with its greater redox cycling. Pre- and post-experimental (SEM-EDX) characteristics showed a homogenous distribution of Ni and Fe on the surface, thus confirming high stability to metal oxide cluster formation or sign of sintering.</p

Mono-dimensional and two-dimensional models for chemical looping reforming with packed bed reactors and validation under real process conditions

Chemical looping reforming (CLR) is an emerging hydrogen/syngas production technology, integrated with CO2 capture. Packed bed reactors are widely used in the hydrogen production industry as they are preferred for high pressure operation and the mathematical modelling describing their operation is very important for their design. In this study, a one-dimensional (1-D) and a two-dimensional (2-D) model have been developed to describe the dynamic operation of chemical looping reforming processes in packed bed reactors (CLR-PB). The reactor under study (L: 400 mm ID: 35 mm) contains an axially placed thermowell (OD: 6.35 mm) to monitor the temperature across the reactor bed at 6 points and 440 g of NiO/CaAl2O4 oxygen carrier (OC). Both models have been validated presenting very good agreement with the experimental results. The comparison between modelling and experimental results has been carried out in terms of thermowell temperature and the gas composition breakthroughs, with the 2-D model capturing the thermowell temperature recordings with high accuracy, while the 1-D model delivered results that underestimated it by 2.5%. Nonetheless, the predicted average bed temperature presented a difference limited to 1% lower estimation of the 1-D to the 2-D model. The temperature difference between the bed and the thermowell has achieved a value of &gt;180 °C thus resulting also problematic in terms of safe operation if not properly considered. with temperatures during oxidation being higher even by 181 °C inside the bed, emphasizing the importance of the model in the proper design and safe operation of the reactor. The 1-D model, due to the significantly lower computation time (∼21 times faster than 2-D), has been selected to be tested against a range of operating conditions for oxidation (500–600 °C, 1–5 bar, 10–40 NLPM, 10–20% O2), reduction (600–900 °C, 1–5 bar) with H2, syngas and CH4-rich reducing agents and dry reforming (700–900 °C, 1–5 bar), delivering results with good agreement especially under high temperature conditions where solid conversion is high and under conditions which resemble the expected industrial ones

Experimental assessment of reverse water gas shift integrated with chemical looping for low-carbon fuels

Chemical looping integrated with reverse water gas (CL-RWGS) shift is presented in this study using Cu-based oxygen carrier (OC) supported on Al2O3 has been used to convert the CO2 and H2 mixture stream into a syngas stream with a tailored H2 to CO ratio and relevant conditions. The results demonstrated consistent breakthrough curves during redox cycles, confirming the chemical stability of the material. In 10 consecutive cycles at 600 °C and 1 bar, bed temperatures increased by 184 °C and 132 °C across the bed during oxidation and reduction stages respectively. The cooling effects during RWGS showed a decline in solid temperatures demonstrating the effectiveness of the heat removal strategy while attaining a CO2-to-CO conversion close &gt;48%. The outlet gas maintains a H2/CO ratio above 2, confirming the material's dual role as OC and catalyst. During complete CL-RWGS cycles, varying temperature from 500 °C to 600 °C at a constant H2/CO2 molar ratio (1.3) and pressure (1 bar) reduces the H2/CO molar ratio from 3.14 to 2.35, respectively with a remarkable continuous CO2-to-CO conversion &gt; 40%. The decrease in H2/CO molar ratio with the increase in temperature is consistent with the expected results of equilibrium limited conditions. Additionally, in CL-RWGS cycles, pressure insignificantly affects product molar composition. The study showed the capability of Cu material in converting CO2 into syngas through the CL-RWGS technique

Experimental assessment of reverse water gas shift integrated with chemical looping for low-carbon fuels

Chemical looping integrated with reverse water gas (CL-RWGS) shift is presented in this study using Cu-based oxygen carrier (OC) supported on Al2O3 has been used to convert the CO2 and H2 mixture stream into a syngas stream with a tailored H2 to CO ratio and relevant conditions. The results demonstrated consistent breakthrough curves during redox cycles, confirming the chemical stability of the material. In 10 consecutive cycles at 600 °C and 1 bar, bed temperatures increased by 184 °C and 132 °C across the bed during oxidation and reduction stages respectively. The cooling effects during RWGS showed a decline in solid temperatures demonstrating the effectiveness of the heat removal strategy while attaining a CO2-to-CO conversion close &gt;48%. The outlet gas maintains a H2/CO ratio above 2, confirming the material's dual role as OC and catalyst. During complete CL-RWGS cycles, varying temperature from 500 °C to 600 °C at a constant H2/CO2 molar ratio (1.3) and pressure (1 bar) reduces the H2/CO molar ratio from 3.14 to 2.35, respectively with a remarkable continuous CO2-to-CO conversion &gt; 40%. The decrease in H2/CO molar ratio with the increase in temperature is consistent with the expected results of equilibrium limited conditions. Additionally, in CL-RWGS cycles, pressure insignificantly affects product molar composition. The study showed the capability of Cu material in converting CO2 into syngas through the CL-RWGS technique.</p

Carbon-neutral and carbon-negative chemical looping processes using glycerol and methane as feedstock

Carbon-negative and neutral methods to produce H2 and other syngas-derived chemicals are tested and demonstrated in this study through chemical looping reforming of methane or glycerol. A chemical looping reactor provides the heat required to reform the glycerol or methane while having inherent CO2 capture. This is achieved using dynamically operated packed beds. If the glycerol or methane is from a biological source this gives the system the potential for negative emissions. To evaluate the potential of this system, 500 g packed bed of oxygen carriers were cyclically reduced, oxidized, and used to carry out reforming experiments. The reforming process was tested at various pressure (1 – 9 bar) and temperature (600 – 900 °C). These conditions were tested at this scale for the first time. Complete conversion of glycerol is achievable with only small quantities of CH4 slip. The maximum H2 production was achieved at 1 bar and 700 °C producing a H2/CO ratio of 10, this lowered to 9 when the temperature was increased to 900 °C. Adding CO2 to the feed stream along with H2O allows for a H2/CO ratio suitable for the Fischer Tropsch (FT) synthesis. Chemical looping reforming of CH4 with steam was successfully demonstrated in a lab reactor setup at 1 and 5 bar for multiple cycles with CH4 conversion &gt; 99% and controlled heat losses. The temperature and concentration profiles provided identical results for consecutive cycles verifying the continuity and the feasibility of the process