Non-isothermal pyrolysis of de-oiled microalgal biomass: Kinetics and evolved gas analysis

Comparative Analysis of Energy Viability of Crop Residue from Different Corn Varieties

The valorization of agricultural residues assumes a pivotal position in the circular economy by transforming waste into a useful and environmentally friendly product, with the cultivation of corn, as one of the world's predominant crops, being crucial. This article aimed to investigate the feasibility of using residues from corn crop as biofuels, going more in-depth into determining the effect that crop variety may have on its thermal qualities. Specifically, 12 samples of corn crop residues were studied in three main groups: conventional, forage, and transgenic varieties. To achieve this, proximate and ultimate analyses, thermogravimetric analyses, and differential scanning calorimetry were conducted, along with a study of gas emissions and a statistical comparison of different varieties. From the results obtained, it is worth highlighting the low ash content in all the samples (between 5.55% and 8.42%) and high calorific values (higher than 17 MJ/kg in all cases), as well as optimal thermal results for all the samples studied in both pyrolysis and combustion processes. Significant differences were found between the different varieties; in particular, it was observed that the forage variety presented more optimal conditions for its application in both processes. This may represent a potential competitive advantage for the forage varieties.

Effects of Extraction Methods on the Thermal Stability of Extracellular Polymeric Substances-Based Biomaterials from Wastewater Sludge

Various methods for recovering extracellular polymeric substances (EPS)-based biomaterials from wastewater sludge exist. However, the relationships between extraction methods and properties of biomaterials have not been fully explored. In this study, the thermal properties, including activation energy (AE) and thermal decomposition mechanism, of EPS-based biomaterials extracted by different methods have been determined by thermogravimetric analysis integrated with the deconvolution method. Simultaneously, the chemical properties of these biomaterials, such as the extraction yield, chemical composition, and functional groups, have been monitored to clarify the influences of extraction methods. Notably, proteins and humic-like substances have been found as the major components to determine thermal stability and AE. Moreover, the physicochemical method shows significant effects on enhancing extraction yield and AE, with the NaOH and heat methods proving to be outstanding by delivering the highest AE of 300 kJ/mol and a substantial char formation of 24%. The results have demonstrated the significant impact of extraction methods on the thermal stability of EPS-based biomaterials. Moreover, this finding provides insights into the linkages between the properties of EPS-based biomaterials and extraction methods to guide the selection of appropriate extraction methods tailored to specific applications, including flame-resistant materials.

Thermodynamics, kinetics and thermal decomposition characteristics of sewage sludge during slow pyrolysis

Pyrolysis has shown great potential for sewage sludge valorisation and management by producing value-added chemicals. Although the product process yields are extensively studied, a few studies exist without consensus on the kinetic properties of sewage sludge pyrolysis. As a result, a study to investigate the thermal decomposition characteristics of Gauteng sewage sludge (GSS) at various heating rates (10, 20, and 30 °C/min), its pyrolysis kinetic parameters, reaction mechanism and thermodynamic properties was meticulously conducted. The results show that sewage sludge decomposition occurs in three stages, whereby the main decomposition (active pyrolysis) takes place at 150-570 °C. Fourier transform infrared spectroscopy (FTIR) analysis results confirm progression of thermal decomposition of GSS and drive off volatile compounds and formation of aromatic structures during TGA studies of GSS. An increase in heating rate shifts the characteristic temperatures towards higher temperatures with the highest decomposition rate of 1.10%/min.mg at 30 °C/min. The activation energies of GSS pyrolysis were calculated using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Starink methods and averaged as 225.92, 218.04 and 218.97 kJ/mol, respectively. GSS pyrolysis involves complex reaction chemistry with high reactivity whereby reactions that follow third order and three-dimensional diffusion-reaction mechanisms dominated the process. However, these mechanisms cannot be used explicitly to define the global pyrolysis kinetics due to the occurrence of multiple simultaneous reactions. The obtained thermodynamic and kinetic data will advance and amplify the design, simulation and optimisation of global energy pyrolysis units for production of value-added chemicals.

Kinetic Analysis of Algae Gasification by Distributed Activation Energy Model

Conversion of algal biomass into energy products via gasification has attracted increasing research interests. A basic understanding of the gasification kinetics of algal biomass is of fundamental importance. Distributed activation energy model (DAEM), which provides the information of energy barrier distribution during the gasification process, is a promising tool to study the kinetic process of algae gasification. In this study, DAEM model was used to investigate Chlorella vulgaris and Spirulina gasification. The activation energy of Chlorella vulgaris gasification was in the range from 370 to 650 kJ mol−1. The range of activation energy for Spirulina gasification was a bit wider, spanning from 330 to 670 kJ mol−1. The distribution of activation energy for both Chlorella vulgaris and Spirulina showed that 500 kJ mol−1 had the most components, and these components were gasified at around 300 °C. The DAEM algorithm was validated by the conversion and conversion rate from experimental measurement, demonstrating that DAEM is accurate to describe the kinetics of algal biomass gasification.

Chemical-looping gasification of corn straw with Fe-based oxygen carrier: Thermogravimetric analysis

The chemical-looping gasification kinetics of corn straw with iron-based oxygen carrier to produce syngas were studied using thermogravimetric analysis. The main reactions of corn straw based on iron-based composite oxygen carrier is divided into three stages: the pyrolysis stage (200-500 °C), the gas-solid reaction stage (500-700 °C), and the solid-solid reaction stage (700-1100 °C). The Coats-Redfern method and the Malek method were used to screen the thirty reactions. The activation energies for the most likely main reactions were estimated to be 81.6 kJ/mol (Mample single-line rule), 117.5 kJ/mol (reaction order function), and 140.9 kJ/mol (Ginstling-Brounshtein equation). The chemical-looping gasification of corn straw with Fe-based oxygen carrier involved multi-step reaction mechanisms.

Thermal degradation kinetics of sugarcane leaves (Saccharum officinarum L) using thermo-gravimetric and differential scanning calorimetric studies

Pyrolysis of sugarcane (Saccharum officinarum L) leaves (SCL) has been investigated using DTA/TGA and DSC techniques. Proximate and ultimate analyses and calorific value measurement have been carried out using standard protocols. The sugar cane leaves contain 44% cellulose, 22% hemicellulose and 17% lignin. The pyrolysis have been carried out at six heating rates varying from 5 to 40 °C/min. Analysis of the pyrolysis results has been carried using iso-conversional model free methods as well as multiple linear regression method. For the fractional conversion range of 0.05-0.95, the average apparent activation energy values evaluated from iso-conversional methods have ranged from 214.9 to 239.6 kJ/mol where as in the case of multiple linear regression analysis it has ranged from 25.06 to 57.23 kJ/mol. The multi-step reaction mechanism has been investigated using the Criado method. The results of this study are useful for the design of large scale biomass thermal conversion process.

A review on the production of nitrogen-containing compounds from microalgal biomass via pyrolysis

Nitrogen-containing compounds (NCCs) which may be produced from nitrogen-rich biomass such as microalgae, may find important biochemical and biomedical applications. This review summarizes the recent knowledge about the formation mechanism of NCCs during pyrolysis of microalgae. The key technical and biological aspects of microalgae and pyrolysis process parameters, which influence the formation of NCCs, have been analyzed. The mechanism of formation of NCCs such as indole, pyridine, amides, and nitriles during primary and secondary pyrolysis reactions are elaborated. It has been emphasized that the pyrolysis conditions and the use of catalysts had significant impacts on the yields and compositions of NCCs. The available information shows that the transformation of nitrogen and nitrogen functionalities during pyrolysis are strongly associated with the formation process of NCCs. The challenges in the development of pyrolysis technologies for the production of NCCs from microalgae are identified with future research needs identified.

Pyrolysis, kinetics analysis, thermodynamics parameters and reaction mechanism of Typha latifolia to evaluate its bioenergy potential

This work was focused on understanding the pyrolysis of Typha latifolia. Kinetics, thermodynamics parameters and pyrolysis reaction mechanism were studied using thermogravimetric data. Based on activation energies and conversion points, two regions of pyrolysis were established. Region-I occurred between the conversion rate 0.1-0.4 with peak temperatures 538K, 555K, 556K at the heating rates of 10Kmin^-1, 30Kmin^-1, and 50Kmin^-1, respectively. Similarly, the Region-II occurred between 0.4 and 0.8 with peak temperatures of 606K, 621K, 623K at same heating rates. The best model was diffusion mechanism in Region-I. In Region-II, the reaction order was shown to be 2nd and 3rd. The values of activation energy calculated using FWO and KAS methods (134-204kJmol^-1) remained same in both regions reflecting that the best reaction mechanism was predicted. Kinetics and thermodynamic parameters including E, ΔH, ΔS, ΔG shown that T. latifolia biomass is a remarkable feedstock for bioenergy.

Thermochemical conversion pathways of Kappaphycus alvarezii granules through study of kinetic models

Kappaphycus alvarezii seaweed belongs to the class of red alga (Rhodophyta). The granules obtained after recovery of "sap" (liquid plant stimulant) from freshly harvested alga is a promising biomass feedstock for energy application. Herein we report the kinetic behaviour of the granules using thermogravimetric analysis (TGA) at different heating rates in N₂ atmosphere and thermogravimetric-mass spectrometry (TG-MS) analysis. Sawdust as lignocellulosic biomass is considered for comparative study. Four different kinetic models (i) multilinear regression technique, (ii) Friedman method, (iii) Flynn-Wall-Ozawa (FWO) method and (iv) Kissinger-Akahira-Sunose (KAS) method are used to evaluate the apparent activation energy (E_a), the pre-exponential factor (A_α) and the overall reaction order (n). Maximum SO₂ peak at 300°C and 950°C (from TG-MS), indicates that slow pyrolysis at 500°C, with a packed bed lime scrubber at the outlet during temperature rise, is the best suited thermochemical pathway for energy harnessing.