Steam Reforming of Oxygenated Hydrocarbons for Hydrogen Production

摘要

Hydrogen is widely used in petrochemical industries as a feedstock for the production of other chemicals and is considered as economical and environmentally safe for industrial use. However, the existing production of hydrogen from natural gas steam reforming is not sustainable due to the depleting feedstock of natural gas. One of the proposed strategies to overcome this issue is to utilise oxygenated hydrocarbons derived from biomass sources that have undergone similar reforming. In this doctoral research, it is of interest to see whether the selected oxygenates, i.e. ethanol, ethylene glycol, propylene glycol and glycerol, are able to be co-fed with natural gas in a steam reforming process in the future. It is also aimed to determine whether a cost-effective catalyst can be used to produce high yields of hydrogen from these oxygenates. In addition, this catalyst is hoped to be stable for long operational hours. For the purpose of this doctoral research, simulation studies and experimental work were carried out to investigate the thermodynamic properties of the steam reforming reaction of ethanol to glycerol homologues and the catalytic activity of Ca doped Ni/Al2O3 catalyst to the respective process. The simulation studies involved thermodynamic equilibrium analysis using the Gibbs energy minimisation method via Aspen-HYSYS. It was discovered that ethanol and ethylene glycol might produce high hydrogen yield since both hydrocarbons have two carbon atoms, hence the reactions are not as complex as propylene glycol and glycerol. The experimental studies were conducted for all four oxygenates using a commercially available catalyst, known as Hi-FUEL R110 (Hi-FUEL). The main purpose of these experimental studies was to investigate the reaction feasibility and make comparisons against the simulations. The catalyst used for these experiments consisted of nickel (18 wt. %), calcium (12 wt. %) and alumina. Hi-FUEL was tested with variable parametric studies in glycerol steam reforming (effect of space-time, reaction temperature, steam partial pressure) to identify the intermediates produced in the reaction, and, eventually, to understand the reaction pathway of glycerol reforming via this particular catalyst. Some other catalysts were also prepared (xCa/Al2O3 and 15 wt. % Ni on xCa/Al2O3) and characterised. These catalysts were tested for glycerol steam reforming, together with another commercial catalyst of Ni/Al2O3 to validate the reactions involved in the Hi-FUEL catalyst and to further optimise the calcium doped nickel/alumina catalyst for the high selectivity of hydrogen. The spent catalysts were analysed to quantify any coke formed on the surface of the catalyst. This work revealed that a high hydrogen yield and selectivity could be achieved over a Ca doped Ni/Al2O3 catalyst in comparison to the typical Ni/Al2O3 catalyst. However, a high CO yield was produced with an increasing Ca/Ni ratio due to the hydrogenolysis reaction. It should be highlighted that hydrogenolysis was found to be favourable under the influence and presence of calcium. The coke formed was mainly from CO as its precursor, which, in turn, produced amorphous and filamentous carbons that are not only easily regenerated but would not easily deactivate the catalyst. Due to the discovery of value added chemicals as the intermediates from this study and their reaction pathways, it is recommended that the Ca doped Ni/Al2O3 catalyst be tested in the aqueous phase reforming as part of the integrated bio-refinery concept in the future.