• Energy Research

During the course of this study, beech wood, flax shives and the three biomass components: cellulose, hemicellulose and lignin, were pyrolysed at 450 °C, 500 °C, 550 °C and 600 °C. The liquid bio-oil samples recovered in each case were analysed through gas chromatography-mass spectrometry (GC–MS) and gas chromatography-flame ionisation detection (GC-FID) to identify and quantify the different molecules present. Then, principal component analysis (PCA) was used to visualise the global trend of the data. It was found that in most cases, carboxylic acids were the dominating chemical group present. Deeper analysis of the results also showed that by increasing the pyrolytic temperature, the production of some chemical groups, like carboxylic acids, was enhanced while that of other groups, like sugars and furans, was diminished. Examination of the pyrolytic liquid products from the different biomass components helped to determine the provenance of each molecule family. These results allowed to see that the formation or degradation of specific chemical families did in fact follow about the same trend as that for xylan, used as a proxy for hemicellulose, at the different pyrolytic temperatures. A quick glance at the oxygen content of the bio-oils also showed an increasing trend with pyrolytic temperature.

Lignocellulosic biomass and waste, such as plastics, represent an abundant resource today, and they can be converted thermo-chemically into energy in a refinery. Existing research works on catalytic and non-catalytic pyrolysis performed in thermally-heated reactors have been reviewed in this text, along with those performed in microwave-heated ones. Thermally-heated reactors, albeit being the most commonly used, present various drawbacks such as superficial heating, high thermal inertia and slow response times. That is why microwave-assisted pyrolysis (MAP) appears to be a very promising technology, even if the process does present some technical drawbacks as well such as the formation of hot spots. The different types of catalysts used during the process and their impacts have also been examined in the text. More specifically, studies conducted in fluidised bed reactors (FBR) have been detailed and their advantages and drawbacks discussed. Finally, future prospects of MAP have been briefly presented.

Anaerobic digestion is a promising method of organic waste valorisation, particularly for fish farm waste, which has experienced a high growth rate in recent years. The literature contains predictive mathematical models that have been developed by various authors, allowing the prediction of the composition of bio-gas production from organic waste. In general, Monod’s kinetic expression is the basis for describing the enzymatic reaction rates for anaerobic digestion. In this work, several parameters are taken into account, such as temperature, cell growth inhibition, and other operating parameters, and systems of differential equations coupling the kinetics and stoichiometry for bio-reactions are applied to better describe the dynamics. Because of the high number of initial parameters that need to be defined for the anaerobic digester, the use of this model requires significant resources and a long calculation time. For this reason, a global sensitivity analysis (GSA) is applied to this predictive model based on the Sobol index method, in order to identify the most influential key parameters and the interactions between them. For the digestion of fish waste, it is observed that the key parameters influencing methane production are the lipid concentration of the waste, temperature, and hydraulic retention time (HRT).

Abstract This study presents a detailed analysis of the liquid and gaseous pyrolytic products of the three principal components of biomass (cellulose, hemicellulose and lignin) using two different catalysts (HZSM-5 and its iron-modification, Fe-HZSM-5). The experiments were conducted in a semi-batch reactor under the same operating conditions for all feed materials. The results allow the determination of the provenance of aromatic compounds, which are essential components of bio-oil to be used as a bio-fuel. Transformation schemes have been proposed for each biomass component so as to better comprehend the formation of these aromatic compounds. BET specific surface area, BJH pore size distribution and FT-IR technologies have been used to characterise the catalysts, while gas chromatography-mass spectrometry (GC–MS), flame ionisation detection (GC-FID) and thermal conductivity detection (GC-TCD) were used to examine the liquid and gaseous pyrolytic products. It was firstly found that HZSM-5 favoured the decarbonylation route (production of CO), whilst Fe-HZSM-5 favoured the decarboxylation one (production of CO2) for the same feed. Then, a competition was seen to arise from the presence of the catalysts: the chemical family present in majority in the oils was the one converted by the catalysts, rather than one single family. Finally, from the transformation schemes, it was seen that even though both catalysts boosted the aromatics production, HZSM-5 produced more aromatics than its iron-modification. It was also observed that HZSM-5 formed more phenols, and hence, more coke, than Fe-HZSM-5.

Thermogravimetric analysis was employed to investigate the combustion characteristics of flax shives, beech wood, hemicellulose, cellulose, lignin, and their chars. The chars were prepared from raw materials in a fixed-bed reactor at 850 °C. In this study, the thermal behavior based on characteristic temperatures (ignition, maximum, and final temperatures), burnout time and maximum rate was investigated. The kinetic parameters for the combustion of different materials were determined based on the Coats-Redfern approach. The results of our study revealed that the combustion of pure pseudo-components behaved differently from that of biomass. Indeed, principal component analysis showed that the thermal behavior of both biomasses was generally similar to that of pure hemicellulose. However, pure cellulose and lignin showed different behaviors compared to flax shives, beech wood, and hemicellulose. Hemicellulose and cellulose chars had almost the same behaviors, while being different from biomass and lignin chars. Despite the difference between flax shives and beech wood, they showed almost the same thermal characteristics and apparent activation energies. Also, the combustion of the hemicellulose and cellulose chars showed that they have almost the same structure. Their overall thermal and kinetic behavior remained between that of biomass and lignin.

Anaerobic digestion is a promising method of organic waste valorisation, particularly for fish farm waste, which has experienced a high growth rate in recent years. The literature contains predictive mathematical models that have been developed by various authors, allowing the prediction of the composition of bio-gas production from organic waste. In general, Monod’s kinetic expression is the basis for describing the enzymatic reaction rates for anaerobic digestion. In this work, several parameters are taken into account, such as temperature, cell growth inhibition, and other operating parameters, and systems of differential equations coupling the kinetics and stoichiometry for bio-reactions are applied to better describe the dynamics. Because of the high number of initial parameters that need to be defined for the anaerobic digester, the use of this model requires significant resources and a long calculation time. For this reason, a global sensitivity analysis (GSA) is applied to this predictive model based on the Sobol index method, in order to identify the most influential key parameters and the interactions between them. For the digestion of fish waste, it is observed that the key parameters influencing methane production are the lipid concentration of the waste, temperature, and hydraulic retention time (HRT).