Physicochemical and structural characterisation of oil palm trunks (OPT) hydrochar made via wet torrefaction

This study evaluates the effect of wet torrefaction of OPT under autogenous pressures at 3 different relatively low temperatures (i.e. 180, 200, and 220 oC) and extended residence times (i.e. 3, 6, 9, 12, 18, 24, 48, and 72 h) on the hydrochar's physical, chemical, and structural properties. Logarithmic-like increase of HHV profile was observed at the highest temperature of 220 oC, in which a plateau was reached at 24 h. Between temperature and residence time, temperature gave a more significant influence on the characteristics of the produced biochar. The HHV of the biomass sample increases from 16.4 MJ kg−1 in raw OPT to the highest HHV of 26.9 MJ kg−1 when torrefied at 220 oC for 72 h. Van Krevelen analysis shows dehydration was the primary reaction pathway that occurred during wet torrefaction of OPT at 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h. Decarboxylation dominates the reaction when temperature and residence time was increased to 220 oC for 24 h, respectively. Further increasing the residence time to 48 and 72 h at 220 oC promotes demethylation as the dominant reaction. FTIR analysis reveals that most hemicellulose and parts of cellulose decomposed when OPT was subjected to lower temperature and/or residence time (i.e. 180 oC for 24 h, 200 oC for 24 h, 220 oC for 6 h, and 220 oC for 12 h). However, increasing temperature to 220 oC and beyond 24 h resulted in carbon-rich and lignin-dense hydrochar, which was observed in powder XRD results where graphite nitrate peak at 2θ of 7.4o appears. Morphology analysis reveals that most of the hemicellulose and cellulose-rich parenchyma was removed when subjected to wet torrefaction at 220 oC for 24 h. The formation of microspheres from the repolymerisation of 5-HMF was observed in large quantities in OPT hydrochar treated at 220 oC for 72 h. Inorganic elemental analysis shows that wet torrefaction of OPT effectively removes K and Cl from the biomass. The removal of K increased with increased temperature, which may partially resolve the corrosion problems in combustion reactions related to silicate deposition. OPT hydrochar from WT under autogenous condition and relatively low temperature exhibits much more improved fuel properties compared to raw OPT

Thermal degradation behavior and kinetic modeling of green solvents-delignified biomass: a sustainable biomass-to-energy approach

The vast amount of empty fruit bunches (EFBs), which are generated in line with the huge production of crude palm oil in Malaysia, poses significant threats to the environment. In this sense, low-transition-temperature-mixtures (LTTMs) have been recognized as promising green solvents for the pretreatment of biomass as they are of low cost, easy to prepare, and environmental friendly with high delignification selectivity, which also improve the thermal degradation and hydrolysis performance of biomass. The delignification efficiency of LTTMs synthesized from malic acid-sucrose-water was investigated under various pretreatment temperatures, and the optimum temperature was identified to be 90°C. The delignified EFBs were applied in thermogravimetric analysis in order to study the effect of heating rates on their pyrolytic behaviors. Based on the differential thermogravimetric curves, the peaks of the maximum degradation temperature were moved to higher values with increasing heating rates. Iso-conversional Kissinger-Akahira-Sunose (KAS) model was applied in the kinetic modeling of the pyrolysis of delignified EFBs. The estimated activation energy for the untreated EFBs varied within the range of 42.27–254.16 kJ mol−1 while for the delignified EFBs were within the range of 57.73–262.12 kJ mol−1. This showed that the EFBs attained higher molecular stability after pretreatment using the LTTMs

Thermogravimetric analysis of face mask waste: Kinetic analysis via iso-conversional methods

The surge of face mask waste in response to the global pandemic has proven to be a liability to the environment. Microfibers from plastic constituents of the face mask would cause microplastic pollution in the water bodies. Fortunately, these waste could be converted into renewable source of energy via thermochemical method, i.e. pyrolysis. However, the studies on the thermal decomposition of face masks and their kinetic mechanisms are not well-established. The aim of this paper focuses on the prospects of pyrolysis at low to high heating rates ranging from 10 °C min-1 to 100 °C min-1, to cater for the slow pyrolysis and fast pyrolysis modes. Following this, the thermal degradation behaviour of the face mask waste was studied via thermogravimetric analysis which determined the single peak temperature degradation range at 218 to 424 °C at 10 °C min-1, and maximum degradation rate was determined at 172.51 wt.% min-1 at 520 °C, with heating rate of 100 °C min-1. Flynn-Wall-Ozawa (FWO) and Starink method was employed to determine the average activation energy and average pre-exponential factor of the pyrolysis process of face mask waste. i.e., 41.31 kJ mol-1 and 0.9965, 10.43 kJ mol-1 and 0.9901 for FWO and Starink method, respectively

An experimental and modelling study on torrefaction and gasification of oil palm biomass

Palm oil is one of the most consumed vegetable oils in the world to date. Malaysia being the second largest exporter of palm oil generates large amount of agricultural waste from the oil palm sector. Oil palm biomass is organic and easily renewable feedstock, and has high energy content. With the constant supply of oil palm biomass from processing mills, its utilization will add economic value to the agricultural activities. Despite its advantages, certain inherent characteristics of oil palm biomass such as high moisture content, low density, and rapid iodegradation, which make its direct application in energy sector challenging. Hence torrefaction is proposed in this project as the potential pre-treatment step for oil palm biomass for gasification. This experimental and modelling-based study investigates the torrefaction of oil palm biomass followed by the application of the torrefied chars in gasification. The study focused on empty fruit bunches (EFB), mesocarp fibers (MF) and palm shells (PS). Comprehensive analysis was undertaken including the liquid and gaseous products from oil palm biomass torrefaction. The results showed that torrefaction improved both the physical and energetic characteristics of the biomass. Close examination through micrographs coupled with the thermogravimetric data showed that the fibrous EFB and MF underwent earlier and higher decomposition than the rigid PS. The presence of furan and phenolic compounds in the liquid fraction indicates that lignin and cellulose decomposition is initiated during torrefaction of oil palm biomass. Characterization results indicate that the reaction for oil palm biomass torrefaction mechanism is closely associated to the organic matrix of the biomass. A comparison between model-free isoconversional approach and 2-step consecutive model for torrefaction process indicates that the oil palm biomass can be better predicted with the latter model. The oil palm chars generated were examined in a laboratory scale fixed bed gasification reactor under CO2 and steam environment where the compositional changes in the gaseous product during gasification were examined on-line using Micro Gas Chromatography (Micro-GC). The H2/CO molar ratio for CO2 gasification of torrefied oil palm biomass was found to be below 1, hence more suitable for chemical synthesis. In steam gasification of the torrefied chars, this ratio is in the range of 2-5 indicating potential for liquid fuels synthesis. Kinetic analysis was performed on the gasification of torrefied and untorrefied oil palm biomass using thermogravimetic analyser (TGA). The thermal decomposition of the biomass was examined with five models including Shrinking Core Model (SCM), Volume Reaction Model (VRM), Modified Volume Reaction Model (MVRM), Random Pore Model (RPM) and Modified Random Pore Model (MRPM). The results from the gasification study indicate that the Modified Random Pore Model gave the best prediction without excessive mathematical complexities. The activation energy for the gasification of torrefied PS was in the range of 15.29 kJ/mol to 35.25 kJ/mol while untorrefied PS was 80.07 kJ/mol. This reduced activation energy for gasification can be related to the enhanced morphology and pore structure after torrefaction. Further to this, mass and energy balance was undertaken to examine the energy requirement of the torrefaction and gasification process. Results showed that torrefaction enhanced the energy content of syngas from all three oil palm biomasses. The torrefaction of 10 metric tons oil palm biomass requires about 2217-9645 MJ in the torrefier and this may be self-sustaining with the recovery of heat energy from the combustion of volatiles. Thermodynamic equilibrium model was used for the prediction of the gasification process. The model assumes the process to be adiabatic, and thus heat transfer is negligible. Among the three oil palm biomasses studied, PS showed the highest potential as biofuel source as it has the highest energy content after torrefaction and lowest energy requirement for pre-treatment. The results from this project serve to fill the knowledge gap and ultimately provide a clearer picture for the application of torrefaction of oil palm biomass

A review on co-pyrolysis of agriculture biomass and disposable medical face mask waste for green fuel production: recent advances and thermo-kinetic models

The Association of Southeast Asian Nations is blessed with agricultural resources, and with the growing population, it will continue to prosper, which follows the abundance of agricultural biomass. Lignocellulosic biomass attracted researchers’ interest in extracting bio-oil from these wastes. However, the resulting bio-oil has low heating values and undesirable physical properties. Hence, co-pyrolysis with plastic or polymer wastes is adopted to improve the yield and quality of the bio-oil. Furthermore, with the spread of the novel coronavirus, the surge of single-use plastic waste such as disposable medical face mask, can potentially set back the previous plastic waste reduction measures. Therefore, studies of existing technologies and techniques are referred in exploring the potential of disposable medical face mask waste as a candidate for co-pyrolysis with biomass. Process parameters, utilisation of catalysts and technologies are key factors in improving and optimising the process to achieve commercial standard of liquid fuel. Catalytic co-pyrolysis involves a series of complex mechanisms, which cannot be explained using simple iso-conversional models. Hence, advanced conversional models are introduced, followed by the evolutionary models and predictive models, which can solve the non-linear catalytic co-pyrolysis reaction kinetics. The outlook and challenges for the topic are discussed in detail

Co-pyrolysis of oil palm trunk and polypropylene: Pyrolysis oil composition and formation mechanism

Pyrolysis oil can be used as a precursor to synthesize value-added biochemicals. Co-pyrolysis of two or more feedstocks generally improves the selectivity and yield of the target compounds. In this work, oil palm trunk (OPT) was subjected to single-feed pyrolysis and co-pyrolysis with polypropylene (PP) from 500 to 700 °C. The highest pyrolysis oil yield of 26.33 wt.% was obtained from OPT at 700 °C, which mainly contributed by the lignin decomposition in OPT. Phenolics (51.77–57.78%) and oxygenates (36.31–46.99%) were the major compounds detected in the OPT-derived pyrolysis oil. The addition of PP enhanced the formation of hydrocarbons (5.19–10.22%) and decreased the contents of phenolics (34.01–41.85%) in the co-pyrolysis oil. In the case of co-pyrolysis, the intermolecular reactions between PP and OPT-derived radicals led to the formation of ketones and alcohols, which contributed to the increase of oxygenates content. The highest oil yield of 16.17 wt.% was obtained at 600 °C from co-pyrolysis, the oil of which contained mainly phenolic compounds, oxygenated compounds (i.e., ketones and furans), and hydrocarbons. These findings highlighted the potential of oil derived from the pyrolysis of OPT (single feed) and co-pyrolysis of OPT and PP (binary feed) for the production of value-added chemicals

A review on co-pyrolysis of agriculture biomass and disposable medical face mask waste for green fuel production: recent advances and thermo-kinetic models

The Association of Southeast Asian Nations is blessed with agricultural resources, and with the growing population, it will continue to prosper, which follows the abundance of agricultural biomass. Lignocellulosic biomass attracted researchers’ interest in extracting bio-oil from these wastes. However, the resulting bio-oil has low heating values and undesirable physical properties. Hence, co-pyrolysis with plastic or polymer wastes is adopted to improve the yield and quality of the bio-oil. Furthermore, with the spread of the novel coronavirus, the surge of single-use plastic waste such as disposable medical face mask, can potentially set back the previous plastic waste reduction measures. Therefore, studies of existing technologies and techniques are referred in exploring the potential of disposable medical face mask waste as a candidate for co-pyrolysis with biomass. Process parameters, utilisation of catalysts and technologies are key factors in improving and optimising the process to achieve commercial standard of liquid fuel. Catalytic co-pyrolysis involves a series of complex mechanisms, which cannot be explained using simple iso-conversional models. Hence, advanced conversional models are introduced, followed by the evolutionary models and predictive models, which can solve the non-linear catalytic co-pyrolysis reaction kinetics. The outlook and challenges for the topic are discussed in detail