Investigations into Pyrolysis of Spent Biomass
Creators: name: ., Ramandeep Kaur
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400499
subject: Chemical engineering not elsewhere classified

description: After essential oil extraction, the solid residues are generated post-distillation, and these residues are either landfilled or burned. Estimations suggest that the essential oil industries generate large amounts of residues worldwide. These residues are also considered as lignocellulosic biomass because of their plant-based origin; thus, these have a huge potential to act as renewable sources for producing value-added products. Effective utilisation of residual biomass will not only solve the problem of its disposal but can also provide an alternative to fossil-based energy and chemicals. Replacing petroleum-derived chemicals with biomass-derived alternatives is crucial for sustaining the growth of the chemical industry. The research work in the thesis is focused on the pyrolysis of spent biomass. This research analyses the properties of spent and residual biomass, as well as its pyrolysis products (biochar and bio-oil). Various types of residual biomass, including Eucalyptus, Mentha, Palmarosa, Citronella, Lemongrass, Tagetes minuta, and Cashew wastes, are considered in this thesis. We conducted both lab-scale and analytical (Py-GC/MS) flash pyrolysis. Feedstock properties were initially studied using compositional, ultimate, and proximate analysis. Then, thermogravimetric analysis was carried out to understand the mass loss profile of biomass over a wide range of temperatures. Based on the mass loss profile, lab-scale pyrolysis was carried out at different temperatures, forming bio-oil, biochar, and gaseous products. Flash pyrolysis of feedstock was carried out using Py-GC/MS at a high heating rate of 20 °C/ms, which provides insight into the breaking of biomass. Furthermore, comparative studies carried out revealed that biomass composition and its properties significantly affect the physico-chemical properties of bio-oil and biochar. Due to its porous and carbonaceous nature, biochar can be used for different applications such as adsorbent, energy storage, and soil amendment. Characterisation of bio-oil revealed the presence of a wide range of functionalities, which include phenolics, carbonyls, furans, nitrogen-containing compounds, alcohols, hydrocarbons, and ethers. These results indicate the need to enhance the concentration and selectivity of major components, such as phenolics, to use in different applications, such as phenolic resins. Therefore, catalytic pyrolysis of biomass was carried out in metal oxides, including Al2O3, Nb2O5, CaO, CeO2, and ZrO2. Maximum phenolic compounds were detected in GC-MS when Al2O3 catalysts were used. It was concluded that varying metal oxides' properties lead to different selective compounds' formation. Further, the possibilities of forming of hydrocarbons were also investigated via flash hydro pyrolysis, and the effect of varying hydrogen pressure was also studied. It was found that Al2O3 catalysts significantly enhanced the production of aliphatic hydrocarbons up to 78.4 area% at a hydrogen pressure of 10 bars. Moreover, efforts were made to explore biosolids-derived biochar catalysts (Carbo-catalysts). These carbo-catalysts demonstrated that a high content of phenolics (69.73 area%) and hydrocarbons (13.74 area%) could be obtained over H3PO4-activated carbo-catalyst compared to KOH-activated and non-activated carbo-catalyst at optimised pyrolysis temperature, i.e., 400 °C.