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The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen ( H 2 ) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

The catalyzed direct synthesis of hydrogen peroxide (H2O2) from hydrogen and oxygen has the potential to become a lower cost and more environmentally friendly alternative to the commercially practi...

A low-temperature process involving the formation of dry ice to separate carbon dioxide (CO2) from a CO2-containing mixture is proved to be energy efficient. An accurate prediction of the phase equilibria of the components is necessary for the development of such a process. The current work extended a model for simultaneous calculation of phase stability and flash computations for a multicomponent and multiphase system to a system involving the formation of dry ice. This study derived composition-independent correlations of solid–vapor and solid–liquid and introduced these correlations into a Gibbs energy minimization algorithm with the stability variable of phase in predicting the phase diagram of pure CO2 and the solid–fluid-phase equilibria of a methane (CH4)–CO2 binary mixture. A CO2 solid-phase equation of state (EoS) based on Gibbs free energy and a fluid-phase EoS based on Helmholtz free energy were used in this study. Experimental data were compiled for a CH4–CO2 mixture involving the solid–vapor,...

Hydrogen (H2) plays a vital role both as a reactant in petrochemical processes and as an energy carrier and storage medium. When produced from carbon-containing feed stocks, such as fossil fuels and biomass, hydrogen is typically produced as a mixture with carbon dioxide (CO2), and must be subsequently separated by the associated energy, with an invertible energy penalty. In this study, the process for the removal of carbon dioxide from CO2 - H2 mixtures by de-sublimation was analysed. This process is particularly relevant to the production of liquid hydrogen (LH2) at cryogenic temperatures, for which cooling of the H2 stream is already necessary. The solid – gas equilibrium of CO2 - H2 was studied using the Peng-Robinson equation of state which provided a wide range of operating conditions for process simulation. The de-sublimation process was compared with selected conventional separation processes, including amine-based absorption, pressure swing adsorption and membrane separation. In the scenario in which the resulting products, carbon dioxide and hydrogen, were subsequently liquefied for transportation and storage at 10 bar and −46 °C, and 1 bar and −251.8 °C, respectively. The overall energy consumption per kg of CO2 separated (MJ/kgCO2), was found to follow the order: 8.19–11.21 for monoethanolamine (MEA) absorption; 1.81–8.93 for membrane separation; 1.53–5.69 for pressure swing adsorption; and 0.81–3.35 de-sublimation process. Each process was evaluated and compared on the bases of electricity demand, cooling water usage, high-pressure steam usage, and refrigeration energy requirements. Finally, the advantages and disadvantages were discussed and the feasibility and sustainability of the processes for application in the production of liquid hydrogen were assessed.

Fischer-Tropsch Synthesis (FTS) yields a spectrum of products with carbon lengths of 1 to upwards of 100 units. In order to make use of the full spectrum of hydrocarbon fractions, particularly the heavier units, secondary processing is required. Modifying the FTS product distribution and catalyst activity in order to decrease the amount of long chain hydrocarbons (C25 +) may allow significant simplification of FTS based processes. To this end we report the results of in-situ pre-treatment of alumina supported cobalt catalysts (Co/Ru/La – Al2O3) with acetylene in a fixed-bed reactor. It is postulated that acetylene dissociation and dehydrogenation resulted in the generation of carbidic and CxHy species on the catalyst surface. The formation of these carbonaceous species on different active sites of the catalyst surface following pre-treatment also significantly altered the FTS product distribution by affecting the extent and pathway of 1-olefin secondary reactions. It is thought that these changes resulted from decreased incorporation of 1-olefins in further chain growth and a decrease in secondary hydrogenation rate. The amount of heavy hydrocarbons (waxes) produced was reduced by more than two-fold.

The methane–steam redox process is an alternative methane conversion route to high-purity hydrogen production. Using natural ilmenite as an oxygen carrier, we investigated the effect of three different pre-oxidation temperatures (800, 1000 and 1200 °C) on redox performance and stability. We found that the pre-oxidation temperature significantly altered the crystalline properties of the ilmenite sample, which subsequently affected its morphology, reducibility and redox performance. Pre-oxidation above 1000 °C caused the formation of pseudo-brookite (Fe2TiO5), while hematite (Fe2O3) was formed at 800 °C. The presence of Fe2TiO5 lowered the reduction kinetics, but improved the oxygen-transfer capacity. This resulted in the highest redox activity for the sample pre-oxidised at 1000 °C, which had a three to fourfold increase in hydrogen yield compared with samples pre-oxidised at the other temperatures. Redox activity progressively increased during the cyclic redox operation, due to an increase in surface area caused by continual pore and crack development. Hydrogen yield was sustained at double the level of the initial yield, with a purity of more than 98% over 40 redox cycles.

The reduction activities and mechanisms of cobalt-based catalysts are of great interest to industry and researchers, due to their applications in Fischer–Tropsch synthesis. Here, we investigated the reduction of alumina‐supported cobalt catalysts by hydrogen using temperature-programmed reduction. We propose a five-step reduction mechanism that incorporates both amorphous and crystalline Co3O4, and includes the interaction between CoO and the Al2O3 support. Based on our proposed mechanism, we developed a kinetic model of the reduction process. The modelling results of catalysts promoted with ruthenium and lanthanum in contrast with un-promoted catalyst clearly show that the promoter improves reducibility of the catalyst. The effect of Co3O4 crystallinity was also investigated by the reduction of fresh in comparison of pre-oxidised catalyst. We conclude that high crystallinity significantly increases the difficulty of reducing Co3O4. The interaction between CoO and Al2O3 under reduction conditions to form CoAl2O4 was quantitatively simulated. The kinetic modelling confirms that the support plays an important role in catalyst reduction via the interaction between the catalyst and the support. Those kinetic modelling results are supported by in situ X-ray diffraction studies of the reduction process.

The roles of Na, Mn, W and silica, and the synergistic effects between each metal in the Mn-Na2WO4/SiO2 catalyst have been investigated for oxidative coupling of methane (OCM). The crystallisation of amorphous silica during calcination at 900°C was promoted primarily by Na, but Mn and W also facilitated this process. The interaction between Na and Mn tended to increase the extent of conversion of Mn3O4 to Mn2O3. The formation of Na2WO4 was dependent on the order in which Na and W were introduced to the catalyst. The impregnation of W before Na resulted in the formation of Na2WO4, but this did not occur when the impregnation order was reversed. MnWO4 formed in all cases where Mn and W were introduced into the silica support, regardless of the impregnation order; however, the formation of MnWO4 was inhibited in the presence of Na. Of the prepared samples in which a single metal oxide was introduced to silica, only Mn/SiO2 showed OCM activity with significant oxygen conversion, thus demonstrating the important role that Mn plays in promoting oxygen transfer in the reaction. The impregnation order of W and Na is critical for catalyst performance. The active site, which involves a combination of Na-Si-W-O, can be formed in situ when distorted WO42- interacts with silica during the crystallisation process facilitated by Na. This can only occur if the impregnation of W occurs before Na addition, or if the two components are introduced simultaneously.

Chemical looping combustion (CLC) offers a low emission route for fossil fuel-based power generation. In this study, a compact fully looped chemical looping reactor was developed in-house, and operated continuously with a Victorian brown coal as fuel and an Australian ilmenite as oxygen carrier at 940–980 °C and atmospheric pressure for 36 h. The study found that the CLC performance increased with increasing operation time. The CO2/CO molar ratio, used to evaluate the CLC reaction degree, increased from 2.3 to 8.9 over the 36 h of operation. Specifically, this paper provides a comprehensive study and evaluation of the ilmenite characteristics on morphology changes and ash interaction, due to the continuous operation. No noticeable effect by ash interaction on the CLC performance or operation was observed during the continuous operation. The characterisation results revealed a clear segregation of iron species from the iron‑titanium matrix, its migration to and enrichment over the particle surfaces. Hematite (Fe2O3) formation became more pronounced while pores developed internal and external of the ilmenite particles. These changes are believed to improve the carrier reactivity, and so the CLC performance, but also to weaken the mechanical strength of the carrier, promoting particle attrition and leading to its loss by elutriation.

Phase transformations of two types of iron-based oxides (iron ore and industrial-grade ilmenite) were studied using synchrotron powder diffraction of the samples processed in reducing and oxidizing atmospheres at 1173 K (900 °C) and 1223 K (950 °C), respectively. In iron ore oxidation, the disappearance of the wustite and fayalite phases was followed by hematite growth and a decrease of the magnetite phase. The magnetite phase was partially recovered by treatment in a reducing atmosphere. Ilmenite oxidation initiated decomposition of the ilmenite phase with rapid growth of hematite and gradual growth of the pseudobrookite phase. In a reducing atmosphere, ilmenite was gradually recovered from pseudobrookite with a relatively fast initial decrease in rutile and hematite content. Under reducing conditions, there was interaction of iron ore with magnesio-ferrites in iron ore–ash mixture and interaction of ilmenite with silica by the formation of fayalite.

This study reports the conversion of carbon dioxide (CO2) by ceria (CeO2)-zirconia (ZrO2) composites with various ZrO2 contents (0, 20, 50, 80 and 100 %). The modification introduced by ZrO2 altered the structural properties of the ceria samples, affecting their reducibility and subsequent activity to convert CO2. The characterisation results showed a clear relationship between the structural properties of the materials and the activity for CO2 conversion. The addition of ZrO2 was effective to improve a close interaction between CeO2 and ZrO2 and induced the formation of structural defects that further promoted oxygen transport and facilitated the creation of oxygen vacancies that were critical for CO2 conversion. All samples investigated were found to be effective in converting CO2 into carbon monoxide (CO) at 450 °C, and the addition of ZrO2 was also found to be effective in improving the thermal resistance and stabilising the crystalline structure of the samples especially when the ZrO2 content was > 50 %. When the content of ZrO2 controlled between 50 % and 80 %, the onset temperature for CO2 conversion was found to be 285 °C, which was about 80 °C lower than that required for the sample without ZrO2 modification. Thus, modifying CeO2 by ZrO2 was effective to prevent both the textural and structural alteration of the samples under a high temperature environment as well as cyclic redox operations, resulting in a constant and high degree of CO2 conversion into CO.

This study reports the effects of oxidative-reductive (OR) treatment on 10 wt% Co/Al 2 O 3 and 0.25 wt% Ru-10 wt% Co/Al 2 O 3 catalysts. Temperature-programmed analysis revealed that the cobalt in both catalysts became more reducible with increase number of OR treatment. A reduction–oxidation–reduction treatment increased Co surface area and dispersion of the Ru-Co/Al 2 O 3 catalyst from 7.6 to 10.1 m 2 /g and from 14.9% to 17.3%, respectively. The treatment also increased the CO conversion from 21% to 36% and accompanied a small increase in CH 4 selectivity in Fischer–Tropsch synthesis experiments. However, the effect of OR treatment on the Co/Al 2 O 3 catalysts was insignificant.

The effects of ceria loading (0.1–6.0 wt%) on the properties of Li/MgO catalysts and on their activities for oxidative coupling of methane (OCM) were studied. The catalysts were characterised by surface area measurement, XRD, XPS, SEM and CO 2 temperature programmed desorption. The catalyst activity study suggested that the addition of 0.5–1.0 wt% ceria improved the methane conversion of Li/MgO catalyst significantly at reaction temperatures below 800 °C with little change in C 2 selectivity compared to un-promoted Li/MgO. Further increases in ceria loading resulted in lower methane conversion and C 2 selectivity. The CH 4 conversion was related to the surface distribution of O − and O 2− on the catalysts. An increase in reaction temperature beyond 800 °C or a decrease in CH 4 :O 2 ratio from 7:1 to 3:1 imparted negative effects on the methane conversion and C 2 selectivity of the ceria (0.5 wt%) doped Li/MgO catalyst. All ceria doped catalysts did not show any methane coupling activity in the absence of gaseous oxygen, suggesting that they were ineffective to work with alternate feeds of CH 4 and O 2 (redox) mode. Based on the OCM activity and characterisation results, a new pathway that describes the formation of active sites through the electron transfer between Ce 4+ /Ce 3+ and Li/MgO was proposed to help explain the improved OCM activity by using ceria doped Li/MgO catalysts.

The redox performance of pure iron oxide (Fe2O3) and iron oxide modified with ceria (CeO2) and/or zirconia (ZrO2) as an oxygen carrier was investigated for hydrogen (H2) production through a methane–steam redox process. The addition of both CeO2 and ZrO2 were found to be a more effective modification of Fe2O3 than the addition CeO2 or ZrO2 alone. It was found that the reducibility of Fe2O3 was enhanced by CeO2 and the thermal stability of Fe2O3 was improved by ZrO2. These results, therefore, led to the conclusion of the synergistic effect in the Fe2O3-CeO2-ZrO2 mixed oxide. As a result, both the redox activity and the thermal stability were significantly improved, and increases in H2 yield and purity could be maintained by the modification. The redox temperature was found to have a significant effect on redox performance. The production of H2 was considerably improved when the redox temperature was increased from 650 to 750 °C. The ZrO2 concentration in Fe2O3-CeO2-ZrO2 mixed oxide samples was also found to influence performance with the highest H2 yield observed at a ZrO2 concentration of 75 wt.%. Although all materials tested showed a reduction in surface area in the first redox cycle, the change in surface area in subsequent cycles was found to be smaller and the yield of H2 could be maintained at a constant level over a longer period for the mixed oxide containing 75 wt.% ZrO2.

The catalytic behaviour of ceria supported iron catalysts (Fe–CeO2) was investigated for methane decomposition. The Fe–CeO2 catalysts were found to be more active than catalysts based on iron alone. A catalyst composed of 60 wt.% Fe2O3 and 40 wt.% CeO2 gave optimal catalytic activity, and the highest iron metal surface area. The well-dispersed Fe state helped to maintain the active surface area for the reaction. Methane conversion increased when the reaction temperature was increased from 600 to 650 °C. Continuous formation of trace amounts of carbon monoxide was observed during the reaction due to the oxidation of carbonaceous species by high mobility lattice oxygen in the solid solution formed within the catalyst. This could minimise catalyst deactivation caused by carbon deposits and maintain catalyst activity over a longer period of time. The catalyst also produced filamentous carbon that helped to extend the catalyst life.

Coal is a heterogeneous substance and its heterogeneity is identified and characterized by variation in reflectance. The main objective of this paper is to characterize the heterogeneity of char and to correlate it with the coal reflectogram, which accounts for both rank and maceral composition effects. Chars from two density fractions in a set of coals were obtained in a Drop Tube Furnace (DTF) at 1400 °C in N 2 environment. The chars were examined under a Scanning Electron Microscope (SEM) and the morphology information was obtained from the image-processing technique. The average porosity of char changes systematically with the FMR of its parent coals (defined as the summation of each reflectance multiplied with its frequency). The char porosity increased with an increase in FMR up to a critical value around 98. With further increase in FMR, the corresponding char becomes dense. The char macro porosity distribution was found to be related to the coal reflectogram. In general, the char porosity distribution shows two peaks, which corresponds to the inertinite and vitrinite peaks in reflectogram. The intensity depends on the maceral content. The relationship between the char porosity and coal reflectance for this set of sample has been found, which is strongly dependent on the coal rank. However, these findings cannot be applied to coals with a strong maceral association (microlithotype).

Measurements of the intrinsic reactivity of chars to oxygen are increasingly being sought as an indicator of the combustion potential of fuels. The coal reflectogram has been used to characterize the chemical properties of coal and its resultant char structure. In this study, six Australian coals varying in rank were separated using density separation technique to obtain vitrinite and inertinite rich fractions. Chars were obtained from these density fraction samples in a Drop Tube Furnace (DTF) at 1673 K. The reactivity of the chars was measured non-isothermally in a Thermal Gravimetric Analysis (TGA) in the temperature range of 573–1073 K. The results suggested that with the increase in the coal rank, the maximum reactivity of chars derived from vitrinite rich fractions decreases, while the reactivity of chars derived from inertinite rich fractions decreases with the increase in the inertinite content in samples and has no obvious relationship with rank. The kinetic parameters were derived using data from non-isothermal TGA after accounting for changing in surface area with conversion. The frequency factor is found to decrease with increasing coal FMR, defined as the summation of each reflectance value multiplied by its frequency, for a constant activation energy ( E =146 kJ/mol). This suggests that the behavior of a maceral is characterized primarily by its reflectance distribution instead of the type of its parent coal.

The proximate and ultimate analyses of a coal are regarded as sufficient to describe its chemical composition, and they have been widely used for practical applications. However, coal is actually a...

The industrial production of hydrogen by reforming natural gas is well established. However, this process is energy intensive and process economics are adversely affected as scale is decreased. There are many situations where a smaller supply of hydrogen, sometimes in remote locations, is required. To this end, the steam-iron process, an originally coal-based process, has been re-considered as an alternative. Many recent investigations have shown that hydrogen (H2) can be produced when methane (CH4) is used as the feedstock under carefully controlled process conditions. The chemistry driving this chemical looping (CL) process involves the reduction of metal oxides by methane and the oxidation of lower oxidation state metal oxides with steam. This process utilises oxygen from oxide materials that are able to transfer oxygen and eliminates the need of purified oxygen for combustion. Such a system has the potential advantage of being less energy intensive than reforming processes and of being flexible enough for decentralised hydrogen production from stranded reserves of natural gas. This chapter first reviews the existing hydrogen production technologies then highlights the recent progress made on hydrogen production from small scale CL processes. The development of oxygen carrier materials will also be discussed. Finally, a preliminary economic appraisal of the CL process will be presented.

In the current work, a simplified hard templating approach is used to synthesise metal (Ag, Rh, Ir and Pt) containing structured carbon. The target metals are first introduced into the NaY zeolite template by wetness impregnation. The metals are carried in the super cages of the zeolite and subsequently embedded in the final structures after the steps of carbonisation and the template removal. Scanning electron microscopy images have confirmed that the carbon structures produced by this method retain the morphology of the original template. Transmission electron microscopy reveals the presence of dispersed metal particles in all the carbon structures produced. The metal loadings in these templated structures can reach 35 wt% without significant losses of surface areas and pore volumes. Selected carbon supported metals are tested for their catalytic activity for the methanation of carbon monoxide. The finding suggested that this method is effective in preparing metal nanoparticles for use as catalysts.