Torrefaction Pretreatment Research Articles

Catalytic pyrolysis of corn stalk for the production of aromatics: The effects of wet torrefaction and Zn/Ni-HZSM-5 on pyrolysis behavior

The pyrolysis of corn stalk (CS) was carried out to investigate the effect of wet torrefaction (WT) pre-treatment and Zn/Ni-HZSM-5 on the production of bio-oil characteristics. The synergy between WT and the loaded metal catalyst was also analyzed. The oxygen content of the CS was reduced from 50.5% to 40.8% with WT, and hemicellulose was almost removed. WT pretreatment also significantly reduced the oxygenated compounds of bio-oil and increased the selectivity of phenols, aromatics, and anhydro-sugars. The addition of catalyst improved the deoxygenation, oligomerization, and aromatization during pyrolysis. The loading of Zn and Ni could optimize the pyrolysis reaction path and increased the relative content of monocyclic aromatics (MAHs) from 3.58% to 9.67% and 6.44% during the pyrolysis of CS-WT, respectively, and bimetallic catalyst further enhanced the relative content of MAHs to 11.1%. The relative content of aromatics below C9 was higher than other groups (14.8%). Thus, the WT pretreatment of raw materials and synergistic effect of catalysts can jointly optimize the biomass pyrolysis reaction.

The Thermochemical Conversion of Municipal Solid Waste by Torrefaction Process

In this work, the thermochemical properties of municipal solid waste (MSW) are studied using the torrefaction process as the main method for investigation. Torrefaction experiments were carried out using an electric laboratory furnace, at temperatures of 200, 250, and 300 °C. The residence time was set to 90 min. Proximate and ultimate analysis were performed on the torrefied MSW samples and compared with the properties of the raw MSW samples. In addition, the thermal properties of the obtained torrefied MSW samples were evaluated by thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). The following could be stated: the obtained results showed that mass and energy yields (MY and EY, respectively) decrease with increasing when torrefaction temperature, while the heating values (HHV) increased under the same conditions (from 24.3 to 25.1 MJ/kg). Elemental analysis showed an increase in carbon content (C), from 45.7 ± 0.9 to 52.8 ± 1.05 wt.%, and decrease in oxygen content (O), from 45.6 ± 0.9 to 39.5 ± 0.8 wt.%, when torrefaction temperature is increased, which is consistent with the general definition of the torrefaction process. In addition, enhancement factors (EFs) and fuel ratios (FRs) were calculated, which ranged from 1.00 to 1.02 and 0.16 to 0.23, respectively. Some anomalies were observed during the thermal analysis, which are assumed to be related to the composition of the selected MSW. This study therefore shows that torrefaction pretreatment can improve the physicochemical properties of raw MSW to a level comparable to coal, and could contribute to a better understanding of the conversion of MSW into a valuable, solid biofuel.

Combination of torrefaction and catalytic fast pyrolysis for aromatic hydrocarbon production from herbaceous medicine waste

The combination of torrefaction pretreatment and catalytic pyrolysis of herbaceous medicine waste (HMW) was performed. The effects of torrefaction, pyrolysis temperature, SiO2/Al2O3 atomic ratio (SAR) and catalyst-to-feedstock (C/F) ratio on the distribution of aromatic hydrocarbons (AHs) was investigated. The formation of coke and its effects on the catalytic performance of the catalyst were evaluated. The results demonstrated that zeolite can effectively convert the torrefied HMW into AHs. The liquid products were dominated by monocyclic aromatic hydrocarbons (MAHs), in which toluene and xylene were formed preferentially over other aromatics. The total content of benzene, toluene, ethylbenzene, p-xylene, and naphthalene (BTEXN) reached 49.23–76.31%. Temperature, SAR and C/F ratio exhibit a greater influence on AHs formation than the torrefaction agents. A higher pyrolysis temperature and C/F ratio can inhibit coke formation, while higher SAR is beneficial to coke formation. The catalyst with a lower SAR yield more AHs and less coke. Coke was initially formed on the surface of the catalyst at low temperature, but it was more likely to form in the pores of the catalyst at high temperatures. The results show that the combination of torrefaction and catalytic pyrolysis is a potential approach for converting HMW into valuable bio-oils.

The Evaluation of Torrefaction Efficiency for Lignocellulosic Materials Combined with Mixed Solid Wastes

The paper presents the results of research aimed at evaluating the possibility of using selected biomass wastes to produce solid biofuels. In this work, the thermochemical properties of two lignocellulosic biomasses, namely, miscantshus (Miscanthus × Giganteus) and hops (Humulus lupulus), and non-lignocellulosic biomass, namely, municipal solid waste, and their mixtures (micanthus + municipal solid waste and hops + municipal solid waste) were studied using the torrefaction process as the main method for investigation. The effects of various torrefaction temperatures (250, 300, and 350 °C) and times (30 and 60 min) were evaluated. Proximate and ultimate analyses were performed on the torrefied samples. The following can be stated: as the torrefaction temperature and time increased, mass and energy yields decreased while the higher heating values (HHVs) and fuel ratios (FRs) increased, together with carbon contents (C). In addition, energy on return investment (EROI) was studied; the maximum EROI of 28 was achieved for MSW biochar at 250 °C for 30 min. The results of studying greenhouse gas emissions (GHGs) showed a reduction of around 88% when using torrefied biochar as a substitute for coal. In sum, this study shows that torrefaction pre-treatment can improve the physicochemical properties of raw biomasses to a level comparable with coal, and could be helpful in better understanding the conversion of those biomasses into a valuable, solid biofuel.

Effect of Torrefaction on the Physiochemical Properties of White Spruce Sawdust for Biofuel Production

Torrefaction pretreatment is a mild form of pyrolysis that has the potential to produce a high-quality raw material for making biofuel that serves as a replacement for coal in the bioenergy industry. Microwave-assisted torrefaction was conducted on white spruce sawdust (WSS) at temperatures of 200 °C, 250 °C, and 300 °C and retention times of 5 min, 7 min, and 9 min in an inert environment. The torrefaction process produces a solid carbon, commonly known as biochar, and condensable (torrefaction liquid (TL)) and non-condensable gases. In this study, torrefaction characteristics were investigated to observe its effects on the thermal and physiochemical properties of the pellets produced. During the torrefaction process, a significant mass loss associated with the decomposition of hemicellulose was observed. The hemicellulose content drastically reduced to approximately 1.8% and the cellulose content was reduced by approximately 10%, while the lignin gained approximately 35% as the severity increased. This led to an improvement in the higher heating value (HHV), hydrophobicity, bulk, particle density, pellet dimensional stability, and pellet density. However, the pellet tensile strength decreased as the torrefaction severity increased. Pellet tensile strength is a critical indicator of biomass pellets that expresses the force required to crush or damage a pellet. Therefore, to enhance the tensile strength of the pellets, the introduction of a binder was necessary. Torrefaction liquid and sawdust were used as additives at different proportions during pelletization. The addition of binders (torrefaction liquid and sawdust) to the pellet formulation increased the tensile strength of the torrefied WSS by approximately 50%. The OH groups in the biomass break down to a limited degree due to dehydration. This hinders the formation of H bonds, thereby increasing the chances that the pretreated biomass will become hydrophobic. The SEM graphs showed that the torrefied WSS pellets demonstrated more firmly glued surfaces with fewer pores spaces when set side by side with the raw pellets. The thermogravimetric analysis conducted showed that the torrefaction of WSS slightly reduced its thermal stability.

Effects of oxidative torrefaction on the physicochemical properties and pyrolysis products of hemicellulose in bamboo processing residues

Torrefaction pretreatment is applied to improve the fuel quality of biomass. However, in industrial production, oxygen can be unintentionally involved in the torrefaction process due to insufficient airtightness of the torrefaction reaction equipment or the presence of voids in the biomass particles. In this study, hemicellulose was extracted from the bamboo processing residue and was used as raw material for torrefaction experiment. We mainly studied the effects of oxidative torrefaction on physical and chemical properties of torrefied hemicellulose and the distribution of pyrolysis products under different oxygen concentrations and torrefaction temperatures. Results showed that a lower torrefaction temperature (200 °C) yielded solid products with higher HHV even when the oxygen concentration was increased to 15%. With a 5% oxygen concentration, a higher torrefaction temperature can apparently reduce the oxygen and hydrogen contents, and decrease atomic O/C and H/C ratios in torrefied hemicellulose. In terms of the pyrolysis products, at torrefaction temperature of 230 °C and 5% oxygen concentration, pyrolysis products had the lowest acid (7.85%) and the highest ester (6.32%) contents, indicating the highest quality of chemical compounds. A higher oxygen concentration of 5% was beneficial for the formation of alcohols in pyrolysis products. The highest content of furans (34.75%) in the pyrolysis products was achieved after torrefaction pretreatment at 260 °C and 5% oxygen concentration. The production of phenolics compounds favored lower temperature of 200 °C and 0% oxygen concentration in torrefaction pretreatment. This work provides a new avenue to improve the quality of pyrolysis products of biomass through oxidative torrefaction. Effects of oxidative torrefaction on the physicochemical properties and pyrolysis products distributions of hemicellulose derived from bamboo processing residues. • Effects of oxidative torrefaction on hemicellulose properties were investigated. • Hemicellulose underwent dehydrogenation, and deoxygenation, and less extent decarbonization during torrefaction. • Torrefaction pretreatment of hemicellulose at 230 °C and 5% oxygen concentration favored high-value pyrolysis products.

Potential of pretreated palm kernel shell on pyrolysis

The impact of pretreatment on palm kernel shell (PKS) with torrefaction for the possibility of pyrolysis is discussed in this study. PKS samples were torrefied at different holding times of 30 and 60 minutes at temperatures of 200, 225, 250, 275, and 300 °C. In a fixed-bed reactor with a constant nitrogen flow rate of 500 ml/min, torrefaction pretreatment was carried out. The elemental composition, mass, and energy yield, as well as proximate analysis, were all performed on the pretreated PKS. The optimised pretreated PKS was pyrolyzed next at a temperature of 400 to 550 °C in a fixed-bed reactor. The outcomes demonstrated that the pretreated PKS had a significant mass and energy yield at a temperature of 250 °C and a holding time of 30 min. PKS’s calorific value and carbon content both rose after pretreatment. However, the oxygen and moisture content decreased for pretreated PKS. The maximum bio-oil production of 58% was achieved during the pyrolysis of pretreated PKS at a temperature of 500 °C. At higher temperature of 550 °C, the bio-oil decreased due to secondary cracking reaction. Consequently, the pretreated PKS has greater potential as effective feedstock for successive proses particularly pyrolysis for bio-oil production.

Parametric studies on hydrothermal gasification of biomass pellets using Box-Behnken experimental design to produce fuel gas and hydrochar

This study involves optimization of H2-rich fuel gas yield from canola hull pellet via supercritical water gasification at variable temperatures (375–575 °C), biomass-to-water ratio (1:5–1:20) and residence time (10–60 min). The optimization study was accomplished using the Box-Behnken Design approach based on response surface methodology. The temperature was the most important process parameter for H2 yield followed by biomass-to-water ratio and residence time. The highest H2 (3.43 mol/kg) was obtained at 575 °C in 45 min with a biomass-to-water ratio of 1:20. A comparative evaluation of gas yield was performed for oat hull pellets and torrefied pellets at optimum gasification conditions. Torrefaction pretreatment of pellets significantly enhanced the fuel gas yield and gas composition. H2 yield decreased in the following order: torrefied canola hull + mustard meal pellets (4.6 mol/kg) > canola hull + mustard meal pellets (3.3 mol/kg) > torrefied oat hull + mustard meal pellets (3.3 mol/kg) > oat hull + mustard meal pellets (3.1 mol/kg). Hydrochar produced at higher gasification temperatures had greater levels of carbon, thermal stability, alkalinity and structural deformity.

Evaluation of Pyrolysis Reactivity, Kinetics, and Gasification Reactivity of Corn Cobs after Torrefaction Pretreatment

To reveal the effect of torrefaction pretreatment on pyrolysis and gasification reactivity of biomass, corn cob was first subjected to torrefaction pretreatment in a fixed-bed reactor at various reaction temperatures. The pyrolysis reactivity, kinetics, and gasification reactivity of torrefied corn cob were systematically assessed by various methods, proving that torrefaction pretreatment has a substantial influence on the physicochemical properties of corn cobs. The O/C and H/C molar ratios of corn cobs considerably drop with the increasing torrefaction temperature, and their higher heat-ing value (HHV) and energy density rise as well. It is found that torrefaction improves the pyrolysis reactivity of corn cobs because hemicellulose degradation is more severe than cellulose degradation during torrefaction, resulting in an increase in the percentage of cellulose in torrefied corn cobs. However, the severe depolymerization, polycondensation, and carbonization reaction during torre-faction of corn cobs at 280–300 °C can lead to a significant decline in the pyrolysis reactivity of corn cobs. Torrefaction pretreatment increases the pyrolysis activation energy of corn cobs, in addition to decreasing the char gasification reactivity of corn cob. The average char gasification reactivity of corn cobs drops when torrefaction severity increases. The passivation of active sites on the char surface may cause condensation and carbonation reactions of corn cobs during torrefaction. These findings provide new sights into the reasonable design of efficient torrefaction methods for appli-cation prior to pyrolysis and gasification of biomass.

Enhancement of the production of bio-aromatics from bamboo pyrolysis: Wet torrefaction pretreatment coupled with catalytic fast pyrolysis

Light aromatics are important organic building blocks in the chemical industry which can be produced by catalytic fast pyrolysis (CFP) of biomass. In this work, wet torrefaction pretreatment (WTP) was employed to improve the quality of bamboo by synergistic effect of deoxygenation and demineralization. Then, CFP was employed to produce bio-aromatics by using zeolite (e.g. HZSM-5, HY, Al-MCM-41, and USY) as catalyst. Results showed that WTP temperature (180–260 °C) had more significant influence on the mass yields of torrefied products compared to WTP duration (30–150 min). The maximum deoxygenation rate was 49.36% at WTP conditions of 260 °C and 150 min, and the maximum demineralization rate followed the order of 96.29% (K) > 94.54% (Na) > 90.33% (Mg) > 89.22% (Ca). Among the five types of zeolite catalyst tested, HZSM-5 (25) was the best catalyst to obtain bio-aromatics due to its unique pore size and reasonable acidity. The maximum yield of aromatics (25.46 ×107 a.u./mg) was obtained at the WTP temperature of 220 °C, biomass-to-catalyst ratio of 3:1, and CFP temperature of 850 °C. Toluene was the more favored monocyclic aromatic hydrocarbon formed during CFP compared to xylene and benzene.

Simulation and Optimization of Lignocellulosic Biomass Wet- and Dry-Torrefaction Process for Energy, Fuels and Materials Production: A Review

This review deals with the simulation and optimization of the dry- and wet-torrefaction processes of lignocellulosic biomass. The torrefaction pretreatment regards the production of enhanced biofuels and other materials. Dry torrefaction is a mild pyrolytic treatment method under an oxidative or non-oxidative atmosphere and can improve lignocellulosic biomass solid residue heating properties by reducing its oxygen content. Wet torrefaction usually uses pure water in an autoclave and is also known as hydrothermal carbonization, hydrothermal torrefaction, hot water extraction, autohydrolysis, hydrothermolysis, hot compressed water treatment, water hydrolysis, aqueous fractionation, aqueous liquefaction or solvolysis/aquasolv, or pressure cooking. In the case of treatment with acid aquatic solutions, wet torrefaction is called acid-catalyzed wet torrefaction. Wet torrefaction produces fermentable monosaccharides and oligosaccharides as well as solid residue with enhanced higher heating value. The simulation and optimization of dry- and wet-torrefaction processes are usually achieved using kinetic/thermodynamic/thermochemical models, severity factors, response surface methodology models, artificial neural networks, multilayer perceptron neural networks, multivariate adaptive regression splines, mixed integer linear programming, Taguchi experimental design, particle swarm optimization, a model-free isoconversional approach, dynamic simulation modeling, and commercial simulation software. Simulation of the torrefaction process facilitates the optimization of the pretreatment conditions.

Valorization of forestry residues by thermal methods. The effect of temperature on gradual degradation of structural components in bark from silver fir (Abies alba Mill.)

Thermal treatments are largely used for valorization of biomass resources. However, thorough knowledge on gradual degradation of chemical and structural components of biomass are still needed to allow selection of best procedures and operation conditions that lead to desired properties according to target applications. In this paper we studied thermal degradation of silver fir bark by torrefaction at 240–310 °C and pyrolysis at 550 °C. Detailed characterization of products and hierarchical clustering analysis was performed to obtain an overview on the relation between the severity of thermal treatment, the compositional and structural changes of material and the properties of final products. Hemicelluloses started to degrade around 250 °C into furans, acids and linear ketones. Part of volatile terpenes remained embedded in the unaffected lignin and cellulose. Degradation of lignin became significant around 270 °C, producing phenol derivatives, especially at higher temperatures. Cellulose was apparently not affected by torrefaction but was degraded by pyrolysis. Color gradually changed towards black with increasing temperature, O/C and H/C atomic ratios decreasing close to those of coals. Compressibility was maintained after torrefaction but was lost by pyrolysis while wettability changed to the hydrophobic side, even reaching highly hydrophobic character. Porosity increased, solids having complex structured morphology due to slow release of volatiles during torrefaction pretreatment step.

Oxidative torrefaction and torrefaction-based biorefining of biomass: a critical review

Torrefaction is a vital pretreatment technology for thermochemical biorefinery applications like pyrolysis, gasification, and liquefaction. Oxidative torrefaction, an economical version of torrefaction, has recently gained much attention in the renewable energy field. Recent literature on inert and oxidative torrefaction was critically reviewed in this work to provide necessary guidance for future research and commercial implementations. The critical performance parameters of torrefaction for thermochemical biorefinery applications, such as solid yield, energy yield, carbon enhancement, higher heating value (HHV) enhancement, and energy-mass co-benefit index (EMCI), were also analyzed. Agricultural waste, woody biomass, and microalgae were considered. The analysis reveals that woody biomass could equally benefit from oxidative or inert torrefaction. In contrast, inert torrefaction was found more suitable for agricultural wastes and microalgae. Using flue gas as the oxidative torrefaction medium and waste biomass as the feedstock could achieve a circular economy, improving the sustainability of oxidative torrefaction for thermochemical biorefineries. The significant challenges in oxidative torrefaction include high ash content in torrefied agricultural waste, the oxidative thermal runaway of fibrous biomass during torrefaction, temperature control, and scale-up in reactors. Some proposed solutions to address these challenges are combined washing and torrefaction pretreatment, balancing oxygen content, temperature, and residence time, depending on the biomass type, and recirculating torrefaction gases.

Valorisation of cotton stalk toward bio-aromatics: Effect of wet torrefaction deoxygenation and deminerization pretreatment on catalytic fast pyrolysis using Ga modified hierarchical zeolite

Wet torrefaction pretreatment (WTP) can upgrade the property of biomass by synergistic effect of deoxygenation and deminerization (e.g. K, Ca, Na, Mg). In this work, valorisation of cotton stalk (CS) was performed by using combined approaches of WTP and catalytic fast pyrolysis (CFP) to produce bio-aromatics. First, the maximum deoxygenation and deminerization rates were 53.84 % and over 90 %, respectively, at the WTP temperature of 260 °C. Second, the bifunctional catalyst of Ga modified hierarchical HZSM-5 with micro-mesopore structure allowed more oxygenates diffusing into the channel of catalyst and increased the reaction rates of deoxygenation and aromatization reactions which highly improved the yield of bio-aromatics. Third, higher CFP temperature was favored for the formation of aromatics. The yield of aromatics increased first with the raise of catalyst-to-biomass (C/B) ratio from 1:1 to 1:3, then decreased slightly at the highest C/B of 1:5. At last, the operation parameter of WTP and SS-CFP was optimized which the maximum yield of light aromatics was 1.08 × 108 a.u./mg at WTP temperature of 220 °C, biomass-to-catalyst ratio of 3:1, and CFP temperature of 850 °C.

Advancing biomass pyrolysis by torrefaction pretreatment: Linking the productions of bio-oil and oxygenated chemicals to torrefaction severity

Torrefaction is an efficient pretreatment method to improve the quality of biomass feedstock and resulting bio-oil. Herein, the relationships of torrefaction severity of sweet sorghum bagasse (SSB) with its physicochemical properties and resulting pyrolytic product distributions were systemically investigated. The SSB was first pretreated by torrefaction at different temperatures (230, 260, and 290 °C) with a constant residence time of 30 min, and the resulting torrefied SSB was subsequently pyrolyzed at 500 °C for the production of bio-oil. The carbon enrichment index (CEI) is used as an indicator to quantitatively reflect the torrefaction severity of SSB. The results show that the extents of decarbonization, dehydrogenation, and deoxygenation reactions of SSB increase linearly with the increase of CEI, and the extent of deoxygenation reaction is the most severe among them. Torrefaction can effectively regulate the pyrolytic production distributions of SSB, and severe torrefaction favors the formation of biochar. The productions of bio-oil and major oxygenated chemicals (e.g., ketones, carboxylic acids, and phenols) in bio-oil as the functions of CEI could be fitted well by quadratic polynomial functions. The findings can guide the rational design and optimization of the torrefaction process for improved biomass pyrolysis.

Effect of dry torrefaction pretreatment of the microwave-assisted catalytic pyrolysis of biomass using the machine learning approach

This study employs the Leave-One-Out cross-validation approach to build a machine-learning model using polynomial regression to predict pyro product yield through microwave-assisted pyrolysis of sawdust over KOH catalyst and graphite powder a susceptor. The determination of coefficient (R2) validates the developed models. All the developed models achieved a high prediction accuracy with R2 > 0.93, which signifies that the experimental values are in good agreement with the predicted one. The dependence of the catalyst loading and pretreatment temperature on dominating process parameters such as heating rate, pyrolysis temperature, susceptor thermal energy, and pyro products, namely bio-oil, biochar, and biogas, are explored. The yield of biochar is reduced; however, bio-oil and biogas are enhanced as the catalyst loading increased. On the other hand, increasing the temperature of pretreated sawdust decreased bio-oil and biogas yields while increasing biochar yields. Further, microwave conversion efficiency, and susceptor thermal energy increased with increased catalyst quantity and pretreatment temperatures of sawdust. It was observed that the average heating rate was increased by increasing the catalyst quantity while maintaining the same pyrolysis time until pretreatment temperatures of 150 °C were reached, after which the heating rate dropped due to the continuous microwave energy input to the system.

Effect of torrefaction on the evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake

Chemical looping gasification (CLG) is a novel approach to efficiently convert rapeseed cake (RC) to tunable syngas and NH3. However, the low energy density of RC seriously hinders its utilization. Meanwhile, torrefaction is an effective pretreatment for biomass upgrading. Hence, the combination of torrefaction with CLG is proposed as an alternative technology to efficiently utilize RC. In this work, the effect of torrefaction temperature on the evolution behaviors of carbon and nitrogen in CLG of RC with Ca2Fe2O5 OC was systematically investigated using TG-FTIR. Results show that torrefaction can effectively improve the physiochemical properties of RC. The torrefied RC possesses higher energy density and HHV, and lower atomic H/C and O/C ratios. Additionally, higher torrefaction temperature can facilitate the thermal degradations of N-IN and labile NP, with the productions of NH3 and HCN. During CLG, the rise of OC/Fuel mass ratio can increase the yields of the major gases (CO2, CO, CH4, NH3 and HCN), owing to both the oxidative effect of the lattice oxygen (O*) and the catalytic effects of Fe3+ and Ca2+ in OC. Moreover, torrefaction pretreatment can improve the CLG behavior of RC and the optimal torrefaction temperature is 250 °C, attributing to the improvement of fuel stability after torrefaction. Besides, torrefaction can marginally reduce the yields of the major nitrogen species (NH3 and HCN). This is ascribed to both the more stable structure of heterocyclic-N and the insufficiency of H radical in the torrefied RC compared to the raw. These findings provide a feasible guidance for the effective insight in nitrogen evolution during CLG coupled with torrefaction, and thereafter for the efficient utilization of biomass.

Torrefaction of low-value agro-industrial wastes using macro-TGA with GC-TCD/FID analysis: Physicochemical characterization, kinetic investigation, and evolution of non-condensable gases

Two low-value agro-industrial residues, passion fruit peel waste (PF) and pineapple peel waste (PA), were considered in this study as feedstocks to produce solid biofuels by torrefaction. The experiments were conducted in a macro-TGA with GC-TCD/FID analysis to investigate their torrefaction characteristics. The GC-TCD/FID analysis allowed quantifying the non-condensable gases, including CO, CO2, CH4 and H2. The impacts of pretreatment with torrefaction on the physicochemical properties were investigated by using proximate analysis, ultimate analysis, and calorific values. The torrefaction of PF and PA was investigated at three different temperatures (200, 250, and 300 °C) and two residence times (15 and 60 min). The torrefaction pre-treatment led to higher levels of elemental carbon, fixed carbon, HHV and energy density than in the raw biomass. Experimental results showed that the most favorable torrefaction condition for producing a solid biofuel with a high energy density is a moderate temperature of 250 °C and 15 min of residence time. Two models were applied to the torrefaction kinetics of the two agro-industrial wastes: one with the one-step method and the other with the two-step method. The two-step reaction method was the most appropriate for describing the torrefaction behavior of the two agro-industrial wastes in all conditions studied. As determined by the two-step reaction method, the torrefaction activation energies ranged from 17.9 to 199.9 kJ mol−1 for PF and 5.3–84.0 kJ mol−1 for PA. Findings from this study are potentially valuable for the design of large-scale equipment for the torrefaction of PF and PA residues.

Steam gasification of the raw and torrefied mixed typical food wastes: Effect of interactions on syngas production

In this work, rice (RI), pork (PO), and cabbage (CA) were chosen as typical food wastes to investigate the steam gasification performance of raw and torrefied mixed food wastes at 800 °C, with a focus on the effect of interactions between two components on syngas production. The results showed that there is a synergistic promotion of H2 and CO2 production when co-gasification of CA with RI or PO, mainly due to the reforming of char and volatiles were promoted by alkali and alkaline earth metallic (AAEM) in CA. In contrast, char interaction between PO and RI leads to the formation of more large aromatic carbon structures (≥6 rings), thus resulting in an inhibition effect on the major gas formation, especially for H2 and CO. Torrefaction seems to enhance the synergistic promotions of H2, CO2, and CO production for mixtures containing CA, and alleviate the inhibitory effect for mixed PI and RI. Overall, co-gasification of food waste containing high AAEM with another typical food waste is an important strategy to improve the overall gasification efficiency (CGE). Moreover, torrefaction pretreatment could both increase the CGE and promote the syngas quality, making the syngas more suitable for Fischer-Tropsch synthesis.

Solar pyrolysis of cotton stalks: Combined effects of torrefaction pretreatment and HZSM-5 zeolite on the bio-fuels upgradation

Solar pyrolysis of biomass is a novel method for bio-fuels production. In this study, cotton stalks were first subjected to solar torrefaction at 200–300 °C, and then subjected to solar catalytic pyrolysis at 550 °C. The effects of torrefaction deoxygenation pretreatment and HZSM-5 zeolite on the bio-fuels (gas, biochar, and bio-oil) upgradation was investigated. Results showed that the elements of cotton stalks removed via torrefaction follow the order of deoxygenation > dehydrogenation > decarbonization. Torrefaction pretreatment has a remarkably influence on the subsequent catalytic pyrolysis. The bio-oil and gas yields were considerably reduced while the biochar yield increased with increasing torrefaction temperature. The primary pyrolytic volatiles cracked under the HZSM-5 catalyst, followed by a series of deoxygenation and aromatization reactions to form H2O, CO2, CO, alkanes, olefins, and aromatic hydrocarbons. Consequently, the oxygen-containing functional groups were removed to generate hydrocarbons that were rich in bio-oil, meanwhile the selective yield of benzene, toluene, and xylene (BTX) increased remarkably. Moreover, the torrefaction pretreatment inhibited the formation of coke deposited on the catalyst and promoted the carbon yield in the biochar. Considering the benefits of electricity savings, the approach proposed herein is a potential way to improve the competitiveness of biomass-derived products.