Torrefaction Process Research Articles

Upgrading agro-pellets by torrefaction and co-pelletization process using food waste as a pellet binder

This work presents a study on the properties of upgraded agro-pellets produced by torrefaction and co-pelletization process, where starch-rich food waste was used as a pellet binder. The impact of blending coal cutting waste (CCW), torrefaction pre-treatment and the use of starch binder on the mechanical properties of agro-pellets were examined. The resulting physical properties of agro-pellets were significantly improved. Thermal decomposition of corn straw (CS) can be divided into three stages. Co-pelleting with a small amount of CCW promote the combustion of CS showing an improved thermodynamic characteristic of torrefied corn straw (TCS). Torrefaction reduces the difference of heat distribution, improving the adaptability of pellet fuel in operation. Both co-pelletization and torrefaction processes lead to reduced concentrations of NOx and SO2, increased calorific value of fuel and elevated CO2 emission per unit mass, which are conducive to pollutants reduction and thermodynamic qualities of agro-pellets. Moreover, life cycle assessment (LCA) analysis indicated that more energy input was required for co-pelletization and torrefaction pre-treatment, consequently leading to an enhanced energy return ratio.

Analisis Karakteristik Biomassa Cangkang Kelapa Dan Kulit Mete Melalui Proses Torefaksi

In the face of the depletion of fossil fuels, alternative fuels such as biomass are needed. However, biomass has a fairly low calorific value and several other disadvantages compared to petroleum. Therefore, a new breakthrough is needed to correct these weaknesses, one of which is the Torrefaction process. The purpose of this study was to determine the effect of torrefaction of coconut shell and cashew shell biomass on the physical and chemical properties of the material. This research was conducted using coconut shells and cashew shells. The results of this study indicate that the calorific value of coconut shells and cashew shells after torrefaction is 5115,297-5147,021 cal/gr. The water content in coconut shells is 2.718% and the value of water content in cashew shells is 2.397%, the ash content of coconut shells is 6.853% and the value of cashew shell ash content is 6.600%, the value of volatile levels of coconut shells is 14.885% and the value of volatile levels of cashew shells of 14.557% and the value of fixed carbon content of coconut shell is 75.574% and the value of fixed carbon content of cashew shell is 76.447%. Keywords : Biomass, coconut shell, cashewnut shell, torrefaction

PENGUJIAN SISTEM TOREFAKSI KAYU JATI MENGGUNAKAN MICROWAVE

Torrefaction is a heat treatment of raw biomass to obtain a fuel that is more stable, has a high energy density and higher brittleness and is easy to grind. The purpose of this study is to determine changes in physical properties, calorific value of water absorption resistance (hydrophobic) in teak wood after the torrefaction process in the microwave. The method used in this study is an experimental method using a microwave heater equipped with measuring instruments such as a digital thermometer, and digital scales. The biomass material used was finished wood cut with sample sizes of Model 1 (cube 3 x 3 cm), Model 2 (rectangular 7 x 3 x 3 cm), and Model 3 (cylindrical tube 7 x 3 cm). Each material was put in a microwave depth for torrefaction for 15, 25, 35 minutes. The results showed that the model 2 sample experienced the largest mass change of 80.95%, followed by model 3 with a mass change of 76.47% and Model 1 which experienced a mass change of 70%. The longer you experience electromagnetic wave radiation in the microwave, the greater the mass change and the lower the water absorption Keywords: Torrefaction, teak wood, microwave, calorific value, moisture content

Physicochemical Properties of Biochar Produced from Goldenrod Plants.

Torrefaction is one of the methods of thermal treatment of biomass, which allows obtaining a product of better quality in the form of biochar. The aim of the paper was to analyze the possibility of using goldenrod (Solidago canadensis, Solidago gigantea) for the production of biochar. The torrefaction process involved the vegetative and generative parts as well as the whole plant at temperatures of 250 °C and 275 °C, for 3 h. Next, the physicochemical properties of the raw material and biochar were determined, namely moisture content, ash content, volatile matter content, calorific value, and heat of combustion. The bulk density of raw biomass and biochar was also determined. It was found that after biomass torrefaction, the ash content, calorific value, and heat of combustion increased, while volatile matter content decreased. It has been observed that in both the case of raw biomass and biochar, the plant species and the sampled parts have a significant impact on the ash content, volatile matter content, calorific value, and heat of combustion.

Investigation on the fuel quality and hydrophobicity of upgraded rice husk derived from various inert and oxidative torrefaction conditions

Torrefaction is a promising approach which could optimize the behavior of biomass effectively. In this research, a typical and abundant agricultural by-product rice husk was employed for clarifying the correlation between upgradation condition and the fuel quality of upgraded sample. Rice husk were torrefied in inert and oxidative atmospheres (O2: 0, 6, 10 and 21 vol%) at three temperatures (493, 543 and 573 K). After undergoing various torrefaction processes, the torrefied samples were analyzed by elemental analysis, componential determination, fiber component identification, Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), pore structure identification, contact angle characterization and moisture re-absorption test. The results illustrated that the additional oxidizing atoms could participate in the optimization of surface physiochemical property of rice husk particles during torrefaction process. Oxygen deficient torrefaction expressed a tendency to increase the heating value and the fixed carbon content in torrefied samples significantly. The minimum hydrophilic groups remained on the surface of rice husk sample pretreated in 6 vol% O2, and the specific surface area of upgraded sample torrefied in 6 vol% O2 at 573 K was the maximum. The contact angle results were consistent with that of moisture re-absorption tests, implying that increasing torrefaction severity appropriately was beneficial to optimizing the surface behavior and hydrophobicity of upgraded rice husk. Torrefaction of rice husk performed in 6 vol% O2 at 573 K was the optimum condition in this study.

Upgrading Characteristics of Empty Fruit Bunch Biopellet with Addition of Bintaro Fruit as Co-firing

The low density of mass and energy are the main reason for the underutilization of great potential of Empty Fruit Bunch (EFB) as a raw material of alternative and renewable fuels. The using of bintaro fruit as co-firing and treatment of torrefaction – densification processes were believed to increase the density of mass and energy of the EFB biopellet. This study aims to determine the effect of residence time, compaction pressure, and addition of bintaro fruit to the characteristics of EFB biopellet according to ISO 17225-6 standards. Biopellet manufacture was carried out two processes sequence, namely the torrefaction process and the densification process. The torrefaction process was carried out at 275oC with residence time variations 30, 45, and 60 minutes. The densification process was carried out without binder with compaction pressure variations 30, 40, and 50 bar. The addition of bintaro fruit was intended as co-firing of EFB at a ratio 70:30. The best characteristics of biopellet were obtained under conditions of 60 minutes residence time and 50 bar compaction pressures with 3.00% of moisture content, 7.90% of ash content, 8.70% of volatile content, 80.40% of fixed carbon content, 4719.59 cal/gr of heating value, and 1.28 gr/cm3 of density. Characteristics of moisture content and volatile content decreased while ash content, fixed carbon content, and heating value increased with increasing residence time. Characteristics of density increased with increasing compaction pressure. Characteristics of proximate and heating value increased while density properties of biopellet decreased with the addition of bintaro fruit as co-firing.

Comparison of Characteristics of Poultry Litter Pellets Obtained by the Processes of Dry and Wet Torrefaction

Torrefaction is a technology for the preliminary thermochemical treatment of biomass in order to improve its fuel characteristics. The aim of this work is to conduct comparative studies and select the optimal operating conditions of fluidized bed torrefaction for the processing of poultry litter (PL) into an environmentally friendly fuel. PL torrefaction was evaluated according to three different process configurations: (1) torrefaction of PL pellets in a fixed bed in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT1, NT2 and NT3); (2) torrefaction of PL pellets in a fluidized bed of quartz sand in a nitrogen medium at temperatures of 250 °C, 300 °C and 350 °C (NT4, NT5 and NT6); and (3) torrefaction of PL pellets in a fluidized bed of quartz sand in an environment of superheated steam at temperatures of 250 °C, 300 °C and 350 °C (ST1, ST2 and ST3). The duration of the torrefaction process in all experiments was determined by the time required for completion of CO2, CO, H2, and CH4 release from the treated biomass samples. The gas analyzer (Vario Plus Syngaz) was used to measure the concentration of these gases. The torrefaction process began from the moment of loading the PL sample into the reactor, which was heated to the required temperature. After the start of the torrefaction process, the concentration of CO2, CO, H2, and CH4 in the gases leaving the reactor initially increased and, subsequently, dropped sharply, indicating the completion of the torrefaction process. The chemical composition of the obtained biochar was studied, and it was found that the biochar contained approximately equal amounts of oxygen, carbon, nitrogen, hydrogen and ash, regardless of the torrefaction method. Furthermore, the biogas yield of the liquid condensate, obtained from the cooling of superheated steam used in the torrefaction process, was evaluated. The results highlight the efficiency of fluidized bed torrefaction, as well as the performance of superheated steam as a fluidization medium.

Torrefaction and Densification of Wood Sawdust for Bioenergy Applications

In this study, wood sawdust as waste residue from wood processing mills was pretreated using torrefaction to improve fuel properties and densified to facilitate transportation. Sawdust was torrefied in a fixed bed reactor using inside temperatures (IT) of 230, 260 and 290 °C for 15, 30 and 45 min, residence time. Due to the low calorific value of the treatments, the outside temperature (OT) of the fixed bed reactor was used instead for a fixed duration of 45 min, which resulted in an increase in energy value by 40% for the most severe conditions. The mechanical strength of the pellets was enhanced by adding 20% binder (steam-treated spruce sawdust) to biochar, which improved the pellet tensile strength by 50%. Liquid by-products from the torrefaction process contained furfural and acetic acid, which can be separated for commercial uses. Thermochemical analysis showed better fuel properties of OT torrefied samples such as high fixed carbon (52%), low volatiles (41%) and lower oxygen contents (27%) compared to IT torrefied samples (18, 77 and 43%, respectively). Low moisture uptake of torrefied pellets compared to raw pellets, along with other attributes such as renewability, make them competent substitutes to fossil-based energy carriers such as coal.

Characteristics of the Main- and Side-Stream Products of Microwave Assisted Torrefaction of Lignocellulosic Biomass of Different Origination

In this paper, the yields and composition of solid and condensable products that were obtained by microwave-assisted torrefaction of softwood, wheat straw, and peat fuel pellets, defined as main- and side-stream torrefaction products, were studied. The torrefaction process, at temperatures varied in the range of 200–300 °C, was performed using a laboratory-scale torrefactor of original construction. Water-enriched fractions were distilled off from condensable products to isolate tar fractions, the fuel characteristics of which were compared with those of solid fractions. Py-GC/MS/FID, GC/MS/FID, thermal analysis, elemental analysis, and wet chemistry methods were used to characterize the main- and side-stream torrefaction products, with a focus on their valorization according to the biorefinery approach. The simultaneous development of the destruction and condensation processes in lignocarbohydrate complexes during microwave treatment leads to an increase in the relative portion of aromatic compounds in torrefied biomass, increasing the higher heating value (HHV) of the solid fractions. The increase up to 60% of the heat amount that was liberated due to the thermal oxidative conversion of solid fractions vs. that of the non-treated ones was established by DSC tests. The heat that was liberated by the combustion of the tar fractions was much lower than that of solid fractions, which was explained by the composition of tars, influencing their thermal conversion.

Calorific Characteristics of Larch (Larix decidua) and Oak (Quercus robur) Pellets Realized from Native and Torrefied Sawdust

This research aimed to evaluate the calorific characteristics of two biomasses from larch and oak sawdust in the form of native or torrefied pellets. Some calorific features of these two kinds of biomasses, such as ash content, higher and lower calorific values, calorific density and many others were highlighted, allowing for a comparison between oak and larch torrefied/not torrefied pellets. Installations and methods used for the process of torrefaction and for highlighting some of the calorific features were also evaluated. As a result of experiments, it was demonstrated that the larch and oak pellets were different in terms of density, but that after thermal treatment, the calorific values of both increased considerably. The investigations evidenced some increases in calorific value, up to 15.8%, for both the larch and oak sawdust/pellets. One of the main conclusions of this research was that, even though the role of biomass has diminished considerably in the last few decades, its role as a sustainable fuel remains relevant. Its use will become more widespread when the world’s population understands that fossil fuels are depletable and that they must be replaced by renewable fuels such as biomass.

Investigation of the chemical exergy of torrefied biomass from raw biomass by means of machine learning

Torrefaction is one of the most important pretreatment processes to improve the quality of biomass as fuel and overcome its disadvantages. Predicting the chemical exergy of torrefied biomass is essential for evaluating and optimizing the performance of biocoal-based power plants. Therefore, the authors report on a wide range of research that has been conducted to accurately measure the chemical exergy of solid fuels. Nowadays, many researchers are working on computational methods to reduce the number of actions in experimental research. However, until now, researchers have not presented a model that predicts the chemical exergy of torrefied biomass considering the experimental conditions. This study is novel in two ways: first, the exergy of torrefied material was calculated using parameters of torrefaction conditions prior to the torrefaction process. Second, the developed model ANN predicts the chemical exergy of torrefied material directly from the results of proximate analysis of raw biomass samples. Statistical performance indicators show that the predictive capacity of the ANN model is satisfactory. The R2 value was greater than 0.92 for training and 0.79 for testing, while the MAPE value was less than 4% for both training and testing.

Beyond pretreatment: Oriented valorization of biomass into platform chemicals via torrefaction mediated by acid-base balance

Torrefaction has been usually considered as an efficient pretreatment method for improving the fuel properties of biomass, such as heating value, hydrophobicity, and grindability. Herein, it is found that oriented torrefaction mediated by acid-base balance is an efficient method capable of achieving selective valorization of biomass into levoglucosan. The effects of different types of exogenous acids and their loading amounts on the torrefaction behaviors of pine at 300 °C were systematically investigated. It is demonstrated that 0.4% H3PO4 and 0.4% H2SO4 loading can sharply improve the yield of levoglucosan from 3.5 to their respective maximum values of 52.9 and 63.6% during the torrefaction of pine at 300 °C, whereas HCOOH, CH3CHOOH, HCl, and HNO3 loading cannot significantly improve the yield of levoglucosan, indicating that the anions of exogenous acids are of great importance for achieving oriented torrefaction. The optimal loading amount of H2SO4 or H3PO4 for achieving oriented torrefaction of biomass is equal to the inherent alkali and alkaline earth metals (AAEM) content of biomass divided by its cellulose content. It is inferred that the exogenous acid-inherent AAEM balance is the key to achieving oriented torrefaction of biomass into levoglucosan. Exogenous H2SO4/H3PO4 could serve as acidic catalysts for achieving low-temperature activation of cellulose into levoglucosan, and inherent AAEM could act as basic inhibitors for suppressing dehydration reactions to form levoglucosenone. The pyrolysis kinetic analysis shows that 0.4% H3PO4 loading can promote the activation energy for the pyrolysis of pine. These findings provide theoretical guidelines for further understanding and developing the oriented torrefaction process of biomass mediated by acid-base balance.

Multi-Step Recycling of BF Slag Heat via Biomass for CO2 Mitigation

Iron- and steelmaking processes create slags, valuable by-products. Industrial utilisation of slag as a lower-value secondary mineral source has been established for decades. Slag heat recovery is an ongoing research topic and has the potential to maximise energy efficiency in iron and steel production. Heat recuperation aims to tap the unused thermal recycling potential of molten slags. This short communication expands the concept for the utilisation of recovered heat for producing torrefied biomass and biogas. The torrefaction process is linked with slag heat recovery and via the BASE method with enhanced blast furnace operation. Such a combination reduces CO2 emissions significantly in ironmaking processes. Assuming a coke consumption of 350 kg coke per tonne of hot metal and replacing it with 5% torrefied biomass injected as PC with an additional 100 m3/tHM biogas injection, the BF’s CO2 emission related to the coke can be lowered by 7.9% to 108 kg/tHM. In such a manner, the recovered slag heat can directly contribute to CO2-footprint reduction and improve the circular economy and metallurgical sustainability.

Improvement of Biocoal Quality from Empty Oil Palm Fruit Bunches by Using Peat Water to Reducing Potassium Content and Torrefaction at 300°C to Increasing Heating Value

Consumption of fossil energy continues to increase and therefore fossil energy reserves are decreasing, thus the switchover of using fossil energy into new and renewable energy is necessary. Biomass especially from oil palm empty fruit bunches is one of potential resource as new and renewable energy that can mixture with coal as fuel for power plant. However, biomass from oil palm empty fruit bunches has several weaknesses as fuel; it is containing of high potassium content and low heating value. Potassium content will react with oxygen and resulting potassium oxide (K2O) in the furnace of boiler and it can cause the fouling and slagging at the tubes and walls of boiler. Washing with flowing peat water is one of method that used to reduce potassium content in empty oil palm fruit bunches and torrefaction at 300C is a method is use to increase the heating value of biomass from empty oil palm fruit bunches. This research resulted the potassium, potassium oxide content is 5% and 3.7% respectively by flowing peat water at 5 lpm for 60 minutes, and the heating value of biomass by torrefaction process at 300C for 30 minute was obtain at 28742.17 kJ/kg.

Recent Advance on Torrefaction Valorization and Application of Biochar from Agricultural Waste for Soil Remediation

With the increase of global proportion of soil pollution and the number of areas at risk, researchers have sought to develop various pathways to repair or relieve the pollutants in soil. Among them, biochar represents one multidimensional soil amendment which has got great deal of attention on its physicochemical properties towards the removal or mitigation of contaminants in soil. A variety of agricultural wastes like straw and manure prepared from different torrefaction process have been employed as feedstock for the production of biochar, which can be applied to the contaminated soil to facilitate the growing environment for crops, and to improve soil fertility and microbial environment. In addition, the utilization of biochar for soil remediation is also considered as a process of carbon sequestration. The purpose of this review is to summarize the latest research progress in torrefaction processes and mechanism of agricultural waste, the effects of different torrefaction methods on the formation and properties of biochar were explained, coupled with the effects of process parameters. Especially, the conversion and mechanisms of biochar prepared from agricultural wastes composed mainly with lignocellulosic material were discussed, and the characteristics of biochar prepared for improving soil physical and chemical characteristics, microbial community characteristics, nutrients, and the stability and relief of soil pollutants, especially heavy metals, are compared. Finally, this work discussed the application and future technical challenges of soil remediation based on agricultural waste derived biochar.

Impact of Torrefaction and Alkali Pretreatment on Glucose Production From Wheat Straw

Highlights Glucose yield from torrefied wheat straw is improved when samples are subjected to alkaline pretreatment. Torrefaction time, temperature, and alkaline treatment all impact yields. Glucose yield from torrefied material, on a “per treated gram” basis, approaches that of raw feedstock in some cases. Optimized process and plant design could make torrefied feedstock a viable option for biofuel production. Abstract. The impact of torrefaction, alkaline pretreatment, and their combination on enzymatic hydrolysis was explored in terms of their effect on glucose yield from wheat straw. Samples were ground and torrefied at varying degrees of process severity, subjected to enzymatic hydrolysis, and analyzed for glucose yield. While glucose yield from raw biomass averaged 190.1 mg per g of dry raw biomass, the yield from torrefied samples was lower, ranging from 0.0 to 63.8 mg g-1, depending on the duration and temperature of the torrefaction process. Alkaline pretreatment increased the glucose yield of raw biomass to an average of 354.9 mg g-1. The highest glucose yield of 359.1 mg glucose g-1 was achieved for samples that were pretreated with a 1% NaOH solution. Alkaline pretreatment after torrefaction but prior to hydrolysis results in glucose yields ranging from 1.2 to 318.2 mg g-1, which are higher than the yields from torrefied-only samples but lower than those of raw, alkaline pretreated samples. When measured on a “per torrefied g” basis, yields of torrefied, alkaline pretreated samples approach those of raw biomass. These results indicate that there may be potential to use torrefaction and hydrolysis together when combined with an alkaline solution pretreatment. Keywords: Alkaline Pretreatment, Enzymatic hydrolysis, Lignocellulosic waste, Torrefaction, Wheat straw.

Influence of torrefaction on yields and characteristics of densified solid biofuel

Torrefaction is a mild thermal pretreatment for enhancing the combustion property of biomass to be properly applied to biomass or co-firing power plants. The present research investigated mass yields, fuel characteristics and hydrophobicity of rubber wood pellet torrefied at different temperatures and residence times. Proximate and ultimate analyses, the enhancement factor of higher heating value, energy yield, lignocellulosic components and Fourier transform infrared spectroscopy (FT-IR) of torrefied samples were performed to evaluate the influence of the process parameters and compared to those of the untreated ones. The non-condensable and condensable products were analyzed by GC and GC-MS. The results showed that the torrefaction severity index (TSI) correlated sufficiently with the properties of torrefied biomass and was more sensitive to torrefaction temperature than residence time. The increase in the TSI value resulted in an increase in heating value but a decrease in energy yield. The energy density increased by 14% at 260 °C and reached up to 35% at torrefaction temperature of 300 °C. FT-IR analysis revealed that the contents of hydroxyl and carbonyl groups appeared in torrefied wood pellets were decreased and increased, respectively, due to the torrefaction process. Furthermore, the hydrophobicity of torrefied pellets can be significantly improved as torrefaction temperature increases. The non-condensable gaseous products were mostly composed of CO2, CO, and traces of CH4. While the organic compounds found in condensable liquid products were acids, ketones, furans and phenols.

Torrefaction of Palm Kernel Shell and Petcoke Blends for Various Mixing Ratios and Temperatures

In the present study, torrefaction of palm kernel shell (PKS) and petcoke blends was performed for the production of solid biofuels with high energy density. The torrefaction process was performed for mixtures with various mixing ratios (by weight) from 90:10 to 60:40 (PKS:petcoke). For torrefaction under various temperatures of 250℃ to 300℃, the mixing ratio of 60:40 was used. Meanwhile, residence time and nitrogen flow rate were fixed at 30 minutes and 1 l/min, respectively. In general, the fixed carbon and ash contents increased, while the moisture and volatile matter contents decreased after torrefaction. It has been elucidated that mass yield is a dominant factor that affects the energy yield of torrefied mixtures rather than the higher heating value (HHV) ratio. Based on the energy yield and ultimate analysis, it was found that a higher amount of petcoke and higher temperature give better performance, thus causing the torrefied mixture to become very close to coals region in Van Krevelen diagram. In this case, the mixture with a mixing ratio of 60:40 torrefied under the temperature of 300℃ gives the best performance. It was also found that this mixture is thermally stable than the mixture torrefied at 250℃.

Pemanfaatan Air Gambut Untuk Meningkatkan Kualitas Produksi Biocoal dari Limbah Tandan Kosong Kelapa Sawit Dengan Variasi Waktu dan Temperatur Proses Torefaksi

Efforts to increase the use of new and renewable energy continue to be carried out where the one of the programs is to seek the use of mixed fuels (co firing) in fossil fuel power plants such as steam power plant. The main fuel in steam power plant mostly uses coal and the mixed fuel can be used as biomass fuel. Palm oil empty fruit bunches are one of the potentially large biomass that can be used as mixed fuel because of its abundant availability, especially in Riau Province. However, palm oil empty fruit bunches have a low heating value of combustion, so the treatment needs to be carried out in order to palm oil empty fruit bunches as biomass fuel have a high heating value. This study aims to increase the heating value of palm oil empty fruit bunches by torrefaction process so that palm oil empty fruit bunches have a high heating value and equivalent to the heating value of coal. The torrefaction process is carried out with variations in time and temperature of torrefaction, namely 30 - 60 minutes and 200 o C - 300 o C. The research carried out results in the largest heating value of 7470.59 kcal/kg at a time process of 60 minutes and a torrefaction temperature of 300 o C.

Elemental loss, enrichment, transformation and life cycle assessment of torrefied corncob

Elemental loss, enrichment, and transformation are crucial to evaluate the fuel properties of torrefied biomass, and life cycle assessment (LCA) can reflect the environmental impact of torrefaction operation. The corncob is selected as the feedstock for the exploration of fuel properties variation during the torrefaction process. The obtained result implies that torrefaction operation obviously changes the macroscopic and microscopic morphologies of torrefied corncob, and leads to a higher calorific value and bigger surface area. With the increase of torrefaction temperature and torrefaction duration, the loss of weight percentage of elemental C, H, and O occurs and is in the order of O > C > H. The relative content of elemental C gradually increases and leads to better fuel properties. The forms of elemental N and O are stable and do not change during the torrefaction process, but the form of C gradually changes from a combined state to an elemental state. These results are confirmed by Fourier transform infrared (FT-IR) spectra, contact angle detection, and thermogravimetric and derivative thermogravimetric analysis. The LCA result infers that the light torrefaction process (200 °C) possesses the lowest environmental impact, whereas the mild torrefaction condition of 250 °C appears to be the optimal choice for corncob upgrading.