Solar Pyrolysis Research Articles

Analyzing Solar Pyrolysis Process of Walnut Shells: Thermal Biomaterial Behavioral Outcomes

This paper presents a new experimental method for the thermal analysis of solar pyrolysis of walnut shells. The method consists of two types of thermal experiments: (A) the pyrolysis of walnut shells, and (B) the heating-cooling of the biochar obtained during experiment A. Nutshells are a waste product from the pecan nut industry. The state of Sonora, Mexico, produces large volumes of walnuts and their residue. Likewise, this region has a considerable solar resource. The motivation of this study is to obtain biochar - a bi-product of high commercial value used for soil enhancement - using solar energy and agro-industrial waste. In this experiment, biomass pyrolysis of 50g of nutshells was carried out inside a stainless-steel reactor heated with concentrated radiation from a solar simulator. Three different heat fluxes were used: 234, 482, and 725 W. The maximum reaction temperatures were: 382, 498, and 674 °C respectively. The composition of the pyrolysis gases (H2, CO, CO2, and CH4) was measured and the biochar obtained was characterized. Finally, the performance of the solar reactor allowed us to identify and differentiate between evaporation, pyrolysis of cellulosic material, and lignin degradation

Properties of Biochar Prepared by Solar Pyrolysis and Its Adsorption of Cu<sup>2+</sup> in Water

This study investigates the potential of biochar produced via a solar pyrolysis system and its effectiveness in removing copper (Cu<sup>2+</sup>) ions from water, presenting a sustainable and energy-efficient method for biochar production and biomass recycling. Two common agricultural and livestock wastes, corn straw and cow dung, were used as raw materials to produce biochar. These materials underwent solar pyrolysis under limited oxygen conditions to produce biochar, which was then compared to biochar produced via traditional pyrolysis. The comparison involved elemental analyses, infrared spectroscopy, scanning electron microscopy, and specific surface area and pore size analysis to highlight differences in their physical and chemical properties. Adsorption experiments were conducted to evaluate the adsorptive capacity of biochar for copper ions (Cu<sup>2+</sup>) from water, determining the optimal pH conditions and underlying adsorption mechanisms. The findings reveal that biochar produced through solar pyrolysis exhibits similar properties and Cu<sup>2+</sup> adsorption capacities to those prepared by traditional methods. Specifically, cow dung biochar demonstrated a higher adsorption capacity for Cu<sup>2+</sup> compared to corn straw biochar. The Cu<sup>2+</sup> adsorption by corn straw biochar followed the Langmuir isothermal adsorption model and pseudo-second-order kinetic equation, whereas cow dung biochar conformed to the Freundlich isothermal adsorption model and pseudo-second-order kinetic equation. By demonstrating the comparable efficacy of solar pyrolysis biochar in heavy metal adsorption, this study highlights its potential for sustainable environmental remediation and biomass utilization.

Design and performance optimization of solar pyrolysis reactor for organic impurities in waste salt

The efficient removal of organic impurities in waste salt is significant for its recycling and environmental protection. In present paper, a solar pyrolysis reactor is proposed by integrating the parabolic trough concentrator (PTC) and solar reactor (SR). The results demonstrate that organic impurities react completely in 1290.7 s, and the thermal efficiency is up to 89.90 % at the initial temperature of 293.15 K and the reactor radius of 32 mm. However, the temperature difference (ΔT) in reactor is over 110 K. Based on this, the effects of initial temperature and reactor radius on pyrolysis results are explored. To improve the uniformity of temperature distribution and pyrolysis performance, a new pitchfork-shaped fin has been designed. Compared with no fins, the ΔT and reaction time are reduced by 54.99 % and 24.36 %, and the thermal efficiency is improved by 6.47 %. In comparison to traditional star-shaped fins, the ΔT is reduced by 13.1 %. Then, to further enhance the comprehensive performance of pitchfork-shaped fins, optimization on fin structure parameters is performed and validated. After optimization, the ΔT and reaction time are further reduced by 10.27 % and 2.3 %. The present work demonstrates that the PTC-SR is feasible for the efficient removal of organic impurities in waste salts, which is significant for the recycling and utilization of waste salt.

Analysis of the Solar Pyrolysis of a Walnut Shell: Insights into the Thermal Behavior of Biomaterials

The state of Sonora, Mexico, stands as one of the leading producers of pecan nuts in the country, which are commercialized without shells, leaving behind this unused residue. Additionally, this region has abundant solar resources, as shown by its high levels of direct normal irradiance (DNI). This study contributes to research efforts aimed at achieving a synergy between concentrated solar energy technology and biomass pyrolysis processes, with the idea of using the advantages of organic waste to reduce greenhouse gas emissions and avoiding the combustion of conventional pyrolysis through the concentration of solar thermal energy. The objective of this study is to pioneer a new experimental analysis methodology in research on solar pyrolysis reactors. The two main features of this new methodology are, firstly, the comparison of temperature profiles during the heating of inert and reactive materials and, secondly, the analysis of heating rates. This facilitated a better interpretation of the observed phenomenon. The methodology encompasses two different thermal experiments: (A) the pyrolysis of pecan shells and (B) the heating–cooling process of the biochar produced in experiment (A). Additionally, an experiment involving the heating of volcanic stone is presented, which reveals the temperature profiles of an inert material and serves as a comparative reference with experiment (B). In this experimental study, 50 g of pecan shells were subjected to pyrolysis within a cylindrical stainless-steel reactor with a volume of 156 cm3, heated by concentrated radiation from a solar simulator. Three different heat fluxes were applied (234, 482, and 725 W), resulting in maximum reaction temperatures of 382, 498, and 674 °C, respectively. Pyrolysis gas analyses (H2, CO, CO2, and CH4) and characterization of the obtained biochar were conducted. The analysis of heating rates, both for biochar heating and biomass pyrolysis, facilitated the identification, differentiation, and interpretation of processes such as moisture evaporation, tar production endpoint, cellulosic material pyrolysis, and lignin degradation. This analysis proved to be a valuable tool as it revealed heating and cooling patterns that were not previously identified. The potential implications of this tool would be associated with improvements in the design and operation protocols of solar reactors.

Optimizing capacitance performance: Solar pyrolysis of lignocellulosic biomass for homogeneous porosity in carbon production

This work compares the effect of using a solar reactor against a conventional electrical furnace to obtain carbon materials by pyrolysis of a lignocellulosic precursor. The solar reactor is directly irradiated and includes modifications to improve the control of the process and the reproducibility of solar experiments. A bagasse of agave creole was selected as the lignocellulosic precursor or biomass to obtain carbon materials at temperatures of 700 °C. Comparing carbons produced by conventional and solar pyrolysis, higher crystallinity and lower hydrophilicity are evident in the former. Moreover, conventional pyrolysis tends to promote a more homogeneous porous structure in comparison to solar pyrolysis. However, within the spectrum of solar carbons produced, the morphology of biomass plays a crucial role in influencing the chemical composition and porosity properties. Specifically, the use of fibers instead of powders to produce carbons through solar pyrolysis results in a more homogeneous porosity, attributed to an enhanced volumetric absorption of solar radiation. This modification leads to a significant improvement in capacitance, increasing from 125 F/g to 175 F/g at 5 mV/s in aqueous electrolytes. The carbons from the solar furnace are reproducible, underlying the potential of the proposed process towards a sustainable alternative. To achieve a theoretical reference, the pyrolysis process was mimic trough Reactive Molecular Dynamics calculations modeling the initial structural conditions of agave biomass with its corresponding lignocellulosic components and considering analogous thermal conditions. The resulting carbon structures at the end of the simulations showed structural properties that are consistent with those observed in the pair distribution functions obtained from XRD and the pore size distribution from physisorption analyses. This combined experimental–theoretical approach offers the potential to elucidate porous carbon structures derived from pyrolysis processes powered by solar radiation . This method can help in the design and identification of lignocellulosic structures in biomass, with the resulting carbon materials suitable for energy storage applications.

A New Approach for Reduction of Greenhouse Gas Emissions from Groundwater Treatment: Biochar derived by Solar Pyrolysis

A New Approach for Reduction of Greenhouse Gas Emissions from Groundwater Treatment: Biochar derived by Solar Pyrolysis

Techno-economic analysis of a solar-driven biomass pyrolysis plant for bio-oil and biochar production

Transforming conventional biomass pyrolysis through solar-driven pyrolysis with a falling particle receiver and intermediate hybrid solution reduces costs by 21% and 32% and emissions by 27.5 and 22.3 kgCO2 GJoil−1, respectively.

Solar oil refinery: Solar-driven hybrid chemical cracking of residual oil towards efficiently upgrading fuel and abundantly generating hydrogen

There is an urgent need to shift away from the present heavy dependence on fossil fuels and embrace renewable energy sources, particularly in the context of the energy-intensive oil refining process. Built on the Solar Reactive Utilization framework, this study presents an innovative concept called the Solar Oil Refinery, applying solar energy in the energy-demanding oil refining. Herein, a solar multi-energies-driven hybrid chemical oil refining system, exemplified by residual oil cracking, has been successfully developed and formulated in solar-driven thermo-electrochemical cracking of residual oil. This integrated solar oil refining system, coupled with solar pyrolysis and electrolysis - synergistic thermo- and electrochemistry, can greatly promote the “cracking” of residual oil. Owing to the simultaneous applications of solar heat, solar electricity, and the relevant chemical reactions, the system can significantly improve solar utilization efficiency, the cracking rate and the hydrogen yield. In the operation, solar energy, co-functioning with oil, is converted into light hydrocarbon fuel with the advantage of excess hydrogen energy storage. Notably, the temperature required for solar oil cracking is considerably reduced compared with that of conventional pyrolysis, with a cracking rate of 11.2% at the initial temperature of 230 ℃. As the temperature rises, the cracking rate is elevated, reaching 45.22% at 275 ℃ and an impressive 89.85% at the typical temperature of 425 ℃, in contrast to the 44.25% achieved in conventional pyrolysis. In the conventional pyrolysis, the gas, liquid, solid products and unreacted residual oil are accounted for 3.98%, 24.57%, 15.57%, and 55.75%, respectively, but, in the solar oil cracking, the gas, liquid, solid products and residual oil improve to 13.2%, 75.1%, 1.65%, and 10.05%, respectively. This process is characterized by a substantial increase of gas and liquid phase products, coupled with a significant reduction of solid phase products and unreacted residual oil. At 425 ℃, a noteworthy increase of 10.7% in gasoline, 21.7% in diesel, and 18.13% in vacuum gas oil occurs in solar oil cracking compared to conventional pyrolysis. The presence of light hydrocarbons and oxygen-containing organic compounds are detected in both gas-phase and liquid-phase products. In solar oil cracking, the hydrogen yield has been significantly boosted to 63.0% in the combined action of the hydrolysis and electrolysis, surpassing the hydrogen yield achieved through the conventional pyrolysis. The simultaneous utilization of both solar heat and solar electricity which substantially enhances total solar utilization efficiency and the oil conversion rate, can effectively reduce the consumption of the fossil energy in petroleum industry.

Transient analysis of solar pyrolysis and hydrogen yield via interband cascade laser absorption spectroscopy of methane, acetylene, ethylene, and ethane

A mid-infrared laser absorption sensing method has been developed to measure species concentrations of four hydrocarbons and gas temperature over a range of temperatures in mixture compositions relevant to the pyrolytic decomposition of natural gas. The four measured species (methane, acetylene, ethylene, and ethane) are the most abundant hydrocarbons during the pyrolysis of natural gas, and provide a means to monitor decomposition progress and hydrogen yield through molar balance. In this work, time-division multiplexed signals of three distributed-feedback interband cascade lasers are used to make simultaneous measurements of select C-H stretch rovibrational transitions of the target hydrocarbons in the 3.00–3.34 μm range. The sensor was validated over a range of temperatures and pressures (300–1000 K, 0.03–1 atm) at relevant mixture compositions, with correction methods developed to mitigate cross-species interference. The sensor was demonstrated on a solar-thermal pyrolysis reactor, where time-resolved measurements of species mole fractions were performed across a range of insolation conditions to capture the transient response of the reactor.

Concentrated solar pyrolysis for oil palm biomass: An exploratory review within the Malaysian context

Malaysia is one of the leading producers and exporters of oil palm, and the industry contributes significantly to the growth of the national economy. Nonetheless, the consequential oil palm biomass (OPB) with a potential yield of ∼97 million tonnes annually presents both challenges and opportunities, demanding innovative waste management solutions. This paper explores the feasibility of converting OPB into valuable commodities by employing concentrated solar-driven pyrolysis. A detailed overview of the biomass produced from oil palm plantations and mills is provided, along with a discussion of the industry stakeholders and associated biomass management challenges. The pyrolysis of OPB is explored, emphasizing benefits, potential barriers, and techniques. The focus then shifts to Malaysia's solar potential, which ranges from 1470 to 1900 kWh/m2 annually. The potentials of solar pyrolysis are explored, encompassing discussions on solar concentrator types, reactors, and the distribution of solar and OPB resources throughout Malaysia. The paper then recommends Tawau in Sabah, as an ideal location for OPB solar pyrolysis, due to its solar availability (up to 1873 kWh/m2), potential OPB resources from 19 mills and 241 plantations, and supportive infrastructure. The paper proposes solar-driven pyrolysis as a sustainable solution for Malaysia's OPB management, offers insights for policy initiatives and technological innovations in optimizing OPB and solar energy utilization.

Continuous solar-thermal methane pyrolysis for hydrogen and graphite production by roll-to-roll processing

Global climate concerns have motivated the search for new approaches that can decarbonize fossil fuels to produce clean fuels and commodities at large scale. A promising approach is solar-thermal methane pyrolysis to convert natural gas into hydrogen and high-quality carbon product with virtually no CO2 emission. However, challenges in continuous methane pyrolysis include deactivation of catalyst, when present, and establishing a facile means of extracting the valuable carbon product. This work reports a scalable route to continuous solar-thermal methane pyrolysis that employs a roll-to-roll mode of operation using a fibrous carbon substrate. A high-flux solar simulator is used to mimic concentrated solar irradiation and to allow operation at temperatures as high as 1650 K, at which methane rapidly decomposes onto fibers of the porous carbon roll, collecting graphite and exhausting hydrogen and unconverted methane. The efficacy of the roll-to-roll approach for methane decomposition is demonstrated, and the technique is shown to be effective in achieving continuous processing. The roll-to-roll mechanism maintains stable and relatively high methane conversion compared to that of a stationary substrate, with enhancements in methane conversion up to a factor of 1.5. The efficacy of the roll-to-roll process is also evaluated through parametric variations of operating conditions, which include solar power (0.92 to 2.34 kW), methane inlet flow rate (25 to 2000 sccm), and pressure (0.67 to 4.67 kPa). The quality of the carbon product obtained is generally high, with Raman D/G peak ratios as low as 0.3. This work therefore establishes a highly functional baseline for continuous production of graphitic carbon and hydrogen from solar pyrolysis.

Biochar pyrolyzed with concentrated solar radiation for enhanced nitrate adsorption

Biochar has been recognized as an effective soil amendment for reducing nitrogen leaching in agriculture, but its large-scale implementation is impeded by the costly production process due to high energy requirements for thermal decomposition of feedstock. This study aimed to develop a novel pyrolysis system utilizing concentrated solar radiation to produce biochar and explore the potential of solar-pyrolyzed biochar for nitrate adsorption. Results showed that the solar-pyrolyzed biochar exhibited a maximum adsorption capacity of 35.59 mg/g for nitrate, significantly higher than two out of the three commercially available biochars in America that are selected for comparison. The Fourier-transform infrared (FTIR) analysis suggested a variety of oxygen-containing polar functional groups present in the solar-pyrolysis biochar, which enhances its affinity for nitrate and other hydrophilic ions. The X-ray diffraction (XRD) analysis revealed that the solar pyrolysis biochar was an amorphous material with a poorly crystalline, carbon-rich phase, indicating a high degree of carbonization and recalcitrance, as confirmed by Raman spectroscopy and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analysis. The porous structure of the solar-pyrolysis biochar suggested a larger specific surface area, which could benefit adsorption. Although further experiments are required to determine the stability and cost-effectiveness of a scaled-up solar-pyrolysis apparatus, these findings provide hope for a more sustainable and high-performing biochar production process in the future.

Biomass solar fast pyrolysis with a biomimetic mini heliostat field and thermal receiver for nitrogen heating

Biofuels may significantly influence the world's transition from hydrocarbons to renewable energies. Pyrolysis uses thermal energy in an anaerobic ambiance to crack biomass and create biofuels (bio-oil and synthesis gas). This work reports a detailed computational study of a novel system to develop fast biomass pyrolysis with concentrated solar energy. A fluidized bed reactor was coupled to a solar thermal receiver to heat the inert fluid (nitrogen) using a biomimetic mini heliostat field which provides the required thermal energy. A detailed kinetic model for the pyrolysis of lignocellulosic biomass was solved simultaneously with a set of differential equations based on mass, momentum, and energy conservation principles. An Eulerian-Eulerian approach was considered with three phases. The computational model was compared with data reported in the literature for the fluidized bed reactor and heat transfer in the solar thermal receiver with good agreement. Concentrated solar fluxes on the receiver, nitrogen outlet temperatures, temperature contours inside the reactor, concentration contours of relevant gases, and global product percentages (Tar, Char, and Gas) are reported. The products reach an almost constant composition of Gas, Tar, and Char after 6 s of reaction, indicating the annual operational stability of the solar pyrolysis plant in terms of biofuel production.

A review on solar energy intensified biomass valorization and value-added products production: Practicability, challenges, techno economic and lifecycle assessment

Solar technology is a viable alternative which can be used in place of conventional energy sources. Conversion of biomass to valuable high-end products have also been touted as potential sources of energy which can replace conventional fossil fuel sources. The integration of solar energy in aiding the conversion of biomass to products seeks to completely transform the process into using renewable energy only, without aid of fossil fuel-based electricity. This review discusses the various applications of solar thermal energy and solar photovoltaic energy in various thermochemical processes like solar pyrolysis, hydrothermal liquefaction and gasification. The use of solar energy in production of biodiesel, bioethanol, biohydrogen and biomethane is elucidated on. The integration of all these process into a biorefinery aided by solar technology also has been briefly looked upon, with emphasis on the techno-economic analysis and life cycle analysis of the biorefineries. Finally, opportunities and challenges regarding solar technology has been elucidated with respect to the bioprocess industry.

Solar pyrolysis of algae in molten salt for capacitive carbon preparation

Pyrolysis of algae in molten carbonates driven by concentrated solar energy is proposed as an economical and environmentally friendly method to obtain capacitive carbon for supercapacitors. The effects of molten carbonates on pyrolysis process and electrochemical performance at different temperatures (800, 850 and 900 °C) are investigated. Na2CO3–K2CO3 leads to a relatively high carbon yield and superior microstructure at around 900 °C compared with other molten salts, which is beneficial for capacitive carbon production. The as-prepared carbon possesses a high specific surface area of 2009.26 m2/g and a hierarchical porous structure mainly consisting of micropores and mesopores. Moreover, it contains abundant oxygen- and nitrogen-containing functional groups, such as CO, –OH, pyrrolic–N and quaternary–N. These features play an important multiple synergy for the preparation of desirable capacitive carbon, which has a high specific capacitance of 230.2 F/g at 0.25 A/g and a capacitance retention of 75.54% at 2 A/g. This work provides a green and promising approach for the production of heteroatom-doped capacitive carbon with superior porosity and specific surface area.

Design of a Self-Management Solar Pyrolysis Packed-Bed Reactor by Coupling Thermal Energy Storage

A new packed-bed reactor coupled with thermal energy storage (TES) for solar pyrolysis of biomass is developed to overcome the shortcomings of solar energy. The numerical model of a 3.5 kW reactor is formulated by coupling heat and mass transfer balances to chemical kinetics for biomass pyrolysis. It is solved numerically by finite element techniques. The model is applied to analyze the influence of the storage component on the thermal and chemical performance of the pyrolysis process. A new criterion Y defined as the ratio of the char yield and the effective solar power input is proposed to evaluate the effectiveness of solar power input. Under different solar radiation conditions, the coupled TES reduces the solar energy consumption for the char production by over 16%. The storage component can alleviate the overheating and thermal cyclic stresses on the absorption surface. As compared to the non-TES design, the new design can decrease the temperature fluctuation on the absorption surface for over 300 K during solar intermittencies. Moreover, the latent heat in the storage component makes the pyrolysis process stable. Under short-term interruptions, the variation of char yield in the terminal temperature range of 623–673 K is as large as 34.9% in the non-TES design, and it can be decreased to 16.5% after coupling TES. This value can also be decreased from 66.8% to 17.0% under long-term interruptions by coupling the storage.

Transformation of nitrogen during solar pyrolysis of algae in molten salt

Molten salt pyrolysis of N-rich algae driven by concentrated solar energy is considered as an economical and environmentally friendly method to prepare N-doped value-added carbon. The transformation of nitrogen during the carbon production process by algae pyrolysis in molten Na2CO3-K2CO3 is investigated in-depth, which contributes to the utilization or treatment of nitrogen-containing products. Algae-N is mainly converted to gasN, and the gas-N yield increases as temperature rises, reaching 75.7 wt.% at 900 °C. Molten salt reduces the release temperature of all N-containing gas, captures 89.6% of HCN as CN−, and promotes the release of NH3 and NO. The char-N is dominated by pyrrole-N and quaternary-N at 800–900 °C due to the promotion of molten salt and higher temperature. The major contributors to the bio-oil-N yield are pentadecanenitrile, isoamyl cyanide, benzyl nitrile, styryl cyanide, pyrrole and indole. Nitriles and indoles are promising N-containing products in value-added carbon production, while NH3 and NO are primary pollution gas to be controlled.

Minimization of Greenhouse Gas Emissions From Groundwater Treatment Using Biochar Derived by Solar Pyrolysis in Compliance with EU Green Deal

Minimization of Greenhouse Gas Emissions From Groundwater Treatment Using Biochar Derived by Solar Pyrolysis in Compliance with EU Green Deal

Obtaining and characterizing biochar from Eichhornia crassipes using a solar pyrolysis reactor prototype

[Introduction]: Latin America has extensive wetland areas of international importance, since these wetlands preserve wildlife, acting as a source and purifier of water; protecting us from floods, droughts, and other environmental disasters. However, these wetlands are threatened by eutrophication and aquatic weeds, such as the water lily in La Presa, La Vega, Jalisco, Mexico. [Objective]: The present investigation provides an alternative for the sustainable management of the water lily (Eichhornia crassipes) by obtaining biochar and its evaluation. [Methodology]: A functional prototype of a solar pyrolysis reactor was developed, running 36 tests to pyrolyze water lily samples with 17-23% humidity, applying a 5 in Hg vacuum at different temperatures (170, 200 and 230 ºC) and residence times (120, 150, 180 and 210 min); finding the best yield of biochar by the response surface method. [Results]: The optimal conditions in the reactor were found at 170 ºC, with a residence time of 171.8 min. The biochar presented a calorific value of 17.56 MJ/kg, 20.11 % by weight of fixed carbon and 6.89 C/H (carbon-hydrogen) ratio. [Conclusions]: This proposal provides evidence for a new solar pyrolytic reactor that processes water lily to produce high calorific biochar or to fix carbon, which could be a solution to one of the effects of eutrophication.

The combined effect of solar assisted torrefaction and pyrolysis on the production of valuable chemicals obtained from water hyacinth biomass

In this study, both the torrefaction and pyrolysis of water hyacinth biomass samples were accomplished by using concentrated solar radiation. The first attempt was to prepare torrefied samples and then used those in the following pyrolysis process. The aim of preparing pretreated torrefied samples was to reduce moisture from the feedstock and make it perfect for the pyrolysis process besides improving product quality. Three different torrefied samples were prepared by pretreating at 200, 250, and 300℃. The pyrolysis operation was done by maintaining a reactor temperature of 440±10℃. Torrefaction severity had a greater influence on char yields. The char yield was found to be 27.4 wt.% for the non-torrefied sample (ST-Raw) while 42.3, 51.2, and 59.4 wt.% for torrefied samples of ST-200, ST-250, and ST-300 respectively. However, an increase in torrefaction temperature had negative consequences on bio-oil and syngas yields. The acidity of the bio-oils was greatly reduced with an increase in torrefaction temperature. The lowest acid content in ST-300 bio-oil sample was confirmed by the FTIR, and GC-MS analysis. This ensures that the torrefied bio-oils are more non-corrosive than non-torrefied bio-oils. The heating values of ST-300 bio-oils were found to be about 75% of diesel fuel. The char obtained in the pyrolysis process for all torrefied samples was of high quality and graded as peat or brown coal. Considering the characteristics of biomass, products, and method used in this study, solar pyrolysis is a promising technique to produce high-quality chemical intermediates. • The combined effect of solar torrefaction and pyrolysis on the products was investigated. • Torrefaction severity significantly increased char (27.4 to 59.4 wt.%) content. • Torrefaction severity improved the product's heating values. • Torrefaction reduced the acidity of bio-oils obtained in solar pyrolysis.