Upgrading of bio-oil from palm empty fruit bunch fibre with non-acidic oxides via catalytic intermediate pyrolysis

In response to the concerns regarding environmental pollution and energy security, renewable energy has been perceived as a solution. As liquid fuel is the most consumed form of energy in the world, much attention has been paid to pyrolysis for the production of bio-oil. Bio-oil may be derived from biomass and is a potential fuel supplement and source of chemicals. However, lignocellulosic biomass-derived bio-oil is generally highly acidic and highly oxygenated than crude oil. Consequently, the bio-oil is unstable and has a comparatively low energy density. Hence, bio-oil has to be upgraded in order to use directly as fuel and other applications. One of the upgrading methods is catalytic pyrolysis using non-acidic oxides. The current project investigated the effects of calcium oxide (CaO), magnesium oxide (MgO), and zinc oxide (ZnO) on the upgrading of palm empty fruit bunch fibre (EFBF)-derived bio-oil. Apart from that, cellulose was used as feed to study the effects of the oxides on lignocellulosic biomass at its simplest form upon intermediate pyrolysis. The possible reaction pathways involved upon the utilization of the oxides were also summarized. Thermogravimetric studies revealed that the addition of MgO and ZnO did not affect the degradation behaviour of both cellulose and EFBF. However, because CaO is prone to adsorb moisture and carbon dioxide (CO2), an additional weight loss stage was observed. Even though the oxides did not affect the activation energy and mechanism of EFBF devolatilization, the amount of volatiles released reduced due to the restriction posed by the oxides. Despite the catalytic effects posed by the oxides, the reaction of the oxides with CO2 and water categorizes CaO, MgO, and ZnO as catalytic additives, rather than catalysts. Based on the results obtained when cellulose was used as feed, the reaction pathways involved in the catalytic upgrading of bio-oil were compiled. Nevertheless, upon comparing the results of the results with literature, it was concluded that the results may be used as a reference of the reactions involved during catalytic pyrolysis of biomass but it may not exactly reflect the absolute effects of the oxides on the physical properties of all bio-oils. All three oxides showed evidence in enhancing the physical properties of cellulose and EFBF-derived bio-oil, in terms of reducing the amounts of acids and oxygenated compounds. However, the oxides reacted with carbon dioxide (CO2) and water. Hence, the oxides may be considered as catalytic additives rather than as catalysts. Among the three oxides, CaO exhibited the best performance in the matter of reducing the acidity for both cellulose and EFBF-derived bio-oils, without affecting the bio-oil yield substantially. CaO also showed potential in stabilizing the EFBF-derived bio-oil without influencing the surface structure of the bio-oil