Influence of biomass pretreatment on upgrading of bio-oil: Comparison of dry and hydrothermal torrefaction

Experimental strategy for the preparation of adsorbent materials from torrefied palm kernel shell oriented to CO2 capture

In this study, an experimental strategy to obtain biochar and activated carbon from torrefied palm kernel shell as an efficient material for CO2 removal was evaluated. Biochar was obtained by slow pyrolysis of palm kernel shell at different temperatures (350 °C, 550 °C, and 700 °C) and previously torrefied palm kernel shell at different temperatures (220 °C, 250 °C, and 280 °C). Subsequently, activated carbons were prepared by physical activation with CO2 from previously obtained biochar samples. The CO2 adsorption capacity was measured using TGA. The experimental results showed that there is a correlation between the change in the O/C and H/C ratios and the functional groups -OH and C=O observed via FTIR in the obtained char, indicating that both dehydration and deoxygenation reactions occur during torrefaction; this favors the deoxygenation reactions and makes them faster through CO2 liberation during the pyrolysis process. The microporous surface area shows a significant increase with higher pyrolysis temperatures, as a product of the continuous carbonization reactions, allowing more active sites for CO2 removal. Pyrolysis temperature is a key factor in CO2 adsorption capacity, leading to a CO2 adsorption capacity of up to 75 mg/gCO2 for biochar obtained at 700 °C from non-torrefied palm kernel shell (Char700). Activated carbon obtained from torrefied palm kernel shell at 280 °C (T280-CHAR700-AC) exhibited the highest CO2 adsorption capacity (101.9 mg/gCO2). Oxygen-containing functional groups have a direct impact on CO2 adsorption performance due to electron interactions between CO2 and these functional groups. These findings could provide a new experimental approach for obtaining optimal adsorbent materials exclusively derived from thermochemical conversion processes.

An overview of torrefied bioresource briquettes: quality-influencing parameters, enhancement through torrefaction and applications

In recent years, the need for clean, viable and sustainable source of alternative fuel is on the rampage in the global space due to the challenges posed by human factors including fossil induced emissions, fuel shortage and its ever-rising prices. These challenges are the major reason to utilize alternative source of energy such as lignocellulosic biomass as domestic and industrial feedstock. However, biomass in their raw form is problematic for application, hence, a dire need for torrefaction pre-treatment is required. The torrefaction option could ameliorate biomass limitations such as low heating value, high volatile matter, low bulk density, hygroscopic and combustion behaviour, low energy density and its fibrous nature. The torrefied product in powder form could cause air pollution and make utilization, handling, transportation, and storage challenging, hence, densification into product of higher density briquettes. This paper therefore provides an overview on the performance of torrefied briquettes from agricultural wastes. The review discusses biomass and their constituents, torrefaction pre-treatment, briquetting of torrefied biomass, the parameters influencing the quality, behaviour and applications of torrefied briquettes, and way forward in the briquetting sector in the developing world.

Conversion of cotton textile waste to clean solid fuel via surfactant-assisted hydrothermal carbonization: Mechanisms and combustion behaviors

The cotton textile was an abundant energy resource while was otherwise treated as waste. In this work, surfactants were used as catalysts in the hydrothermal carbonization (HTC) to transform cotton textile waste (CTW) into clean solid fuel. Furthermore, the conversion mechanisms of hydrothermal products during surfactant-assisted HTC were preliminarily proposed. The results showed that Span 80 and sodium dodecylbenzenesulfonate facilitated the transformation of CTW into bio-oil, while Tween 80 was more conducive to the development of pseudo-lignin, which endowed hydrochars higher energy density and updated the fuel quality and combustion behavior. Therefore, the research presented an effective method to convert CTW to clean solid fuel through the HTC treatment combining with surfactants.

Torrefaction at 200 °C of Pubescens Pretreated with AlCl3 Aqueous Solution at Room Temperature

Metal salt soaking-torrefaction conversion technology was investigated. It was found that AlCl₃ pretreatment of pubescens favored observably the yield of liquid and small-molecular products in torrefaction via changing the composition and structure of the raw material. The maximum conversion of pretreated samples, washed (PSW) and Y _liquid were 15.5 and 10.8 wt % (with 0.26 wt % monosaccharides, 0.26 wt % carboxylic acids, 0.38 wt % furan compounds, and 1.28 wt % phenols), where 20.4 wt % hemicellulose, 22.9 wt % cellulose, and 5.7 wt % lignin were converted, respectively. However, for pretreated samples (PS), the maximum conversion and Y _liquid reached 44.2 and 32.1 wt %, respectively, along with 96.0 wt % hemicellulose and 31.8 wt % cellulose converted, yielding 2.39 wt % monosaccharides, 5.14 wt % carboxylic acids, 2.60 wt % furan compounds and 10.52 wt % phenols, indicating obvious catalytic effects of residual AlCl₃ on the decomposition of the three major components in torrefaction. Two-dimensional HSQC and electrospray ionization mass spectrometry (ESI-MS) characterizations further confirmed the dominant formation of oligomers derived from holocellulose, lignin, and cross-linkage involving the lignin-carbohydrate complex, indicating that the catalytic thermal cleavage of β-O-4, C-O-C, β-β, 5-5, 4-O-5, C_α-C_β, and α-O-4 linkages by aluminum species in the samples benefited the yield of liquid as well as monophenols.

The influence of torrefaction on pyrolysed biomass: The relationship of bio-oil composition with the torrefaction severity

In this study, three types of biomass were torrefied at different times (0.5, 1, 1.5 h) and temperature (200, 240, 280, 320 °C), which were further pyrolyzed at 550 °C after torrefaction. CEI (carbon element index), which was established based on the carbon content of the torrefied biomass, was chosen as an indicator for reflecting torrefaction severity. The results showed that there was a curvilinear relationship between CEI and the physicochemical characteristics, energy recovery of torrefied biomass, which obtained an average goodness of fit was higher than 0.93. Moreover, the goodness of fit between CEI and pyrolysis carbon and bio-oil yield was higher than 0.95 and 0.91, respectively. Especially, the bio-oil composition and CEI were fitted by a quadratic function (y = a + bx + cx²). Based on the function, the yield of phenols could be predicted based on the CEI value, which would benefit for the preparation of higher quality bio-oil directionally.

High yield self-nitrogen-oxygen doped hydrochar derived from microalgae carbonization in bio-oil: Properties and potential applications

In this work, the high yield self-N-O doped hydrochar had been prepared through the hydrothermal carbonization of microalgae in the aqueous bio-oil. The effects of temperature, residence time and the ratio of Chlorella and bio-oil on the solid yield were investigated. The results showed that the hydrochar had excellent thermal stability and abundant nitrogen and oxide functional groups, its solid yield reached 199.33%. After activated by KOH at high temperature, the hydrochar was transformed into a porous carbon material with high nitrogen content. The porous carbon showed high CO₂ absorption of 5.57 mmol/g at 0 °C and 1 bar. It also exhibited a high specific capacitance of 216.6F/g at 0.2 A/g and a good electrochemical stability with 88% capacitance retention after consecutive 5000 cycles.

Co-pyrolysis of microalgae with low-density polyethylene (LDPE) for deoxygenation and denitrification

To upgrade the algae pyrolytic oil, the influence of algae components on co-pyrolysis with LDPE were studied, with Spirulina platensis (SP), Nannochloropsis sp. (NS) and Enteromorpha Prolifera (EP) as typical algae samples, as they are enriched with proteins, lipids and carbohydrate, respectively, especially, the N and O transformation behavior during the co-pyrolysis was studied in depth. During co-pyrolysis, the interaction on products depended on the components of algae. EP and SP were prior to form CO₂, rather than CO. For pyrolytic oil, co-pyrolysis effectively inhibited the formation of N- and O-compounds, but promoted the generation of long-chain alcohol and formic/acetic ester. And the obvious decrease of N and O content in co-pyrolytic oil was observed. However, the rich lipids in NS resulted in the improvement of N yield in pyrolytic oil during co-pyrolysis.

Biomass torrefaction: An overview on process parameters, economic and environmental aspects and recent advancements

Torrefaction is one of the pretreatment processes used to overcome the disadvantages of using biomass as a fuel such as low energy density, high moisture, and oxygen contents. The torrefaction increases energy density, hydrophobicity, and reduces grinding energy requirement of biomass. This paper provides a review of the recent advancements in the torrefaction process. The discussion will cover the environmental and economic aspects of the torrefaction process and torrefied pellets, and various applications of torrefaction products. The cost competitiveness of torrefied pellets is one of the major concern of the torrefaction process. Integrating the torrefaction with other processes makes it economically more viable than as a standalone process.

The correlation of physicochemical properties and combustion performance of hydrochar with fixed carbon index

Hydrothermal carbonization (HTC) is effective method for improving fuel properties of biomass. Investigating the relationship between the HTC severity and the physicochemical properties of hydrochar is beneficial for the large-scale utilization. The fixed carbon index (FCI) based on the hydrothermal carbonization severity is introduced to predict the physicochemical properties, pelletization and combustion performance of hydrochar. The results showed the relationship between decarbonization, dehydrogenation, deoxygenation and FCI fits exponential function. It was predicted that the hydrochar pellets with FCI = 0.15-0.45 possessed the highest bulk density (>1175 kg/m3), the lowest specific energy consumption (<16.07 kJ/kg) and the strongest radial compressive strength (>10.7Mpa). Moreover, the activation energy of hydrochar combustion in FCI (0.15-0.25) is higher (the maximum is 216 kJ/mol). The study provides based datas for predicting the fuel properties of hydrochar and obtains high quality solid fuel.

Improvement of corn stover fuel properties via hydrothermal carbonization combined with surfactant

BACKGROUND

Biomass fuel has been used to supply heat or crude materials in industry to replace the traditional fossil fuel which was one of the chief causes of climate warming. However, the large-scale utilization of biomass fuel was restricted due to the low density and high hydrophilicity of biomass, which causes the problem of transportation and storage. Therefore, pelletization of biomass was used to improve its fuel density. At present, the biomass pellet was widely used to supply heat, gas or electricity generation via gasification, which supplied clean and sustainable energy for industry. However, the energy consumption during pelletization and high hydrophilicity of pellets were still the problem for the large-scale application of biomass pellet. In this study, hydrothermal carbonization and surfactant played the role of permeation, adsorption and wetting in the solution, which was expected to improve the fuel properties and pelletization effectivity of corn stover.

RESULTS

In the article, surfactant (PEG400, Span80, SDBS) was chosen to be combined with wet torrefaction to overcome the drawbacks and improve the pelletization and combustion properties of Corn stover (CS). Especially, hydrothermal carbonization (HTC) combined with surfactant improves the yield of solid products and reduces the ash content of solid product, which was beneficial for reducing the ashes of furnace during gasification. Meanwhile, surfactant promotes the formation of pseudo-lignin and the absorption for oil with low O and high C during HTC, which improves the energy density of solid product. Furthermore, the oil in solid product plays the role of lubricant and binder, which reduces the negative effect of high energy consumption, low bulk density and weak pellets strength caused by HTC during pelletization. HTC combined with surfactant improved the hydrophobicity of pellet as well as grindability due to the modification of solid product. Moreover, surfactant combined with HTC improved the combustion characteristic of solid product such as ignition and burning temperature as well as kinetic parameters due to the bio-oil absorbed and the improvement of surface and porosity.

CONCLUSIONS

The study supplied a new, less-energy intensive and effective method to improve the pelletization and combustion properties of corn stover via hydrothermal carbonization combined with surfactant, and provided a promising alternative fuel from corn stover .

The mechanism of wet/dry torrefaction pretreatment on the pyrolysis performance of tobacco stalk

In this work, the influence of dry/wet torrefaction with additives on the pyrolysis performance was investigated. The results showed that the content of phenols and ketones (62% and 42%) was improved and the content of acids decreased from 35% to 4% due to the increase of lignin content in torrefied char. Moreover, the content of aromatic hydrocarbon reached 22%. The mechanism showed that the conversion of "CO/CO" into states of "aromatic CC/CC", the removal of hemicellulose and the formation of pseudo-lignin during wet/dry torrefaction were the key factors for the enrichment of aromatic hydrocarbon. The research supplied an effective and original method for obtaining high value aromatic chemicals from the agricultural and forestry waste via the wet/dry torrefaction pretreatment combining with pyrolysis.

Torrefaction performance of camellia shell under pyrolysis gas atmosphere

In order to complete using the pyrolysis gas and heat from biomass routine pyrolysis, the camellia shell was torrefied under PG atmosphere. And the chemical and physical properties of torrefied char obtained under N₂ and pyrolysis gas were compared as well as the pyrolysis and combustion performance. Moreover, in order to investigate the mechanism of pyrolysis gas torrefaction, the influence of each composition such as H₂, CO₂ and CH₄ in pyrolysis gas on the torrefaction performance was also been studied. The results show pyrolysis gas improves the volatile matter content and heat value of the torrefied char. Moreover, pyrolysis gas promotes the degradation of cellulose and hemicellulose. Chemical structure is different for torrefied char under pyrolysis gas and N₂ atmosphere. And each composition in pyrolysis gas plays synergy role to the severity of torrefied char. The combustion kinetic of torrefied char were calculated using the Friedman method and the Ozawa-Flynn-Wall method.

Effect of surfactant on hydrothermal carbonization of coconut shell

The effect of surfactant on the hydrothermal carbonization performance and pseudo-lignin formation were investigated. Especially, the fuel properties and combustion characteristics of hydrochar and solid product were determined. Furthermore, the mechanism of surfactant acted in hydrothermal carbonization was also identified in this article. The results showed that surfactant improved the content of solid products, lignin, heavy bio-oil (HBO), H₂ and CO. Moreover, sodium dodecylbenzenesulfonate promoted the increase of the surface area of hydrochar from 4.93 to 41.43 m²/g. The mechanism showed surfactant formed water/oil film around the hydrochar to prevent HBO from leaving the pore or surface of hydrochar and promoted the condensation and polymerization of 5-hydroxymethylfurfura (5-HMF) with hydroxymethylfurfura (HMF) to form pseudo-lignin. The HBO and pseudo-lignin were beneficial for improving integrated combustion characteristic index (SN) during combustion. The article provides a new method to promote hydrothermal carbonization (HTC) for obtaining high value hydrochar as fuels.

Progress of using biochar as a catalyst in thermal conversion of biomass

Biochar is a solid residual produced from the thermochemical conversion of lignocellulosic biomass via pyrolysis or gasification. It is abundantly available and has a unique structure as well as multiple functionalities. This makes biochar a potential candidate for use as a catalyst or support in catalytic reactions relating to biomass conversion such as catalytic pyrolysis, gasification, esterification of bio-oil, tar reforming, hydrothermal treatments and upgrading of bio-oil. Although numerous studies have been conducted on the potential use of biochar in various catalysis reactions, information on the overall overview and evaluation of the feasibilities of its use, especially in biomass-related conversions, is still limited. This study reviews the state-of-the-art for the production of biochar catalyst as well as its application as a catalyst or support for catalysts in producing biofuel or syngas from biomass. Special attention is given to the reaction pathway of reactants over the surface of biochar and the potential application of biochar in commercial applications. The prospects and challenges for the application of biochar as catalysts for the thermal conversion of biomass are also proposed.

Effect of torrefaction on rice straw physicochemical characteristics and particulate matter emission behavior during combustion

In this work, the effects of different torrefaction temperatures and durations on the physicochemical properties of rice straw (RS), and the emission characteristic of PM₁₀ (particulate matter with aerodynamic diameters of ≤10 µm) during torrefied RS combustion, were investigated. Results indicate that the release of Cl and K, and decomposition of the organic matrix demonstrated a promoting effect during torrefaction. However, the removal of Cl and K did not reduce the emission of PM₁. The emission concentration of PM₁ and PM_1-10 generated from torrefied RS was enhanced, and the yields of PM_1-10 was much higher than those of PM₁. The concentrations of K and Cl in PM_1-10 increased with torrefaction temperature, combined with the microstructure, indicating that the torrefaction pretreatment promoted the heterogeneous condensation of KCl vapour to form PM_1-10.

Co-pyrolysis of microalgae and plastic: Characteristics and interaction effects

To improve the quality of the oil produced from microalgae, the co-pyrolysis of low-density polyethylene (LDPE) and Nannochloropsis sp. (NS) in a fixed bed reactor was investigated at different mixing ratios. Co-pyrolysis improved the gas yield, and the lower heating value of the gas products increased obviously with an increase in the LDPE amount. Furthermore, co-pyrolysis promoted the generation of CH₄ and C₂₊, especially C₂H₄, with the maximum C₂₊ yield (84.86 mL/g) obtained with 75% LDPE. Meanwhile, the amounts of oxygenous and nitrogenous compounds in the liquid products decreased rapidly with LDPE addition. The aliphatic hydrocarbon content of the liquid products increased from 22.63% for NS pyrolysis to 77.4% with 25% LDPE. During co-pyrolysis with LDPE, O tended to evolve as H₂O and CO (rather than as CO₂ for NS pyrolysis) and N was more likely to be released into gas products, which enhanced the quality of the pyrolysis oil.

Physicochemical characteristics and pyrolysis performance of corn stalk torrefied in aqueous ammonia by microwave heating

The physicochemical characteristics and pyrolysis performance of corn stalk (CS) torrefied in water and aqueous ammonia by microwave heating were investigated. Physicochemical characterization revealed that both microwave water torrefied CS (MCS) and microwave ammonia torrefied CS (MACS) showed low hemicellulose content, disrupted macrostructure, improved porous properties, and low ash content. MACS exhibited a significantly lower crystallinity degree of 44.34% than CS (79.55%) and MCS (89.50%). MACS also showed increased methyl/methylene groups intensity, and complete acetyl groups disrupture. Pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) revealed that compared with CS and MCS, MACS exhibited higher peak areas for ketones, aldehydes, furans and esters, and significantly lower peak areas for acids and phenols. A possible mechanism was proposed for the effects of wet torrefaction with aqueous ammonia on changes in physicochemical structure and pyrolysis behavior of corn stalk.

The influence of combined pretreatment with surfactant/ultrasonic and hydrothermal carbonization on fuel properties, pyrolysis and combustion behavior of corn stalk

The surfactant/ultrasonic combined with hydrothermal carbonization (HTC) were performed to investigate the effect on fuel properties, pyrolysis and combustion behavior of hydrochar under different condition. The results showed that the C/H and O/C ratio of corn stalk (CS) + H₂SO₄ + tween was 1.1 and 0.29, which were close to coal, and the heat value reached 28.89 MJ/kg. HTC combined with ultrasonic/surfactant realized the complete separation of lignin with cellulose and hemicellulose in CS. Ultrasonic restricted the hydrolysis of lignin under alkaline condition and pseudo-lignin formation under acidic condition. Tween inhibited the formation and deposition of "pseudo-lignin". The thermogravimetric (TG) experiments displayed the tween combined with HTC improved the pyrolysis temperature and decreased activation energy as well as the combustion ignition temperature which showed better pyrolysis and combustion characteristics. The n^th-order kinetic mode was fit with the TG datas. The mechanism of tween combined with HTC was also analyzed.

The pelletization and combustion properties of torrefied Camellia shell via dry and hydrothermal torrefaction: A comparative evaluation

The torrefaction performance and properties of torrefied CS (Camellia shell) bio-char obtained via dry and hydrothermal torrefaction have been compared as well as pyrolysis and combustion properties. And making of torrefied pellets and their properties such as pellet density, Meyer hardness, and energy consumption are also investigated. The results showed that dry torrefied bio-char had higher energy and density at 220 °C and decreased significantly with temperature, while hydrothermally prepared bio-char had stable energy and mass yield with temperature. The coalification status of hydrothermally bio-char is similar to that of sub-bituminous coal. The pellet formed from dry terrified bio-char via quart tube in 220 °C with high pellet density (1048 kg/m³) and low energy consumption (17.6 KJ/kg) in spite of low the Meyer hardness (6.8 N/mm²). As for the process kinetics, the activation energy via dry torrefection with auger showed lower activation energy 43.26 KJ/mol as well as lowest ignition temperature (290 °C), compared to hydrothermal torrefaction.