Thermogravimetric experiments based prediction of biomass pyrolysis behavior: A comparison of typical machine learning regression models in Scikit-learn

A variety of machine learning (ML) models have been extensively utilized in predicting biomass pyrolysis owing to their prowess in deciphering complex non-linear relationships between inputs and outputs, but there is still a lack of consensus on the optimal methods. This study elaborates on the development, optimization, and evaluation of three ML methodologies, namely, artificial neural networks, random forest (RF), and support vector machines, aimed to determine the optimal model for accurate prediction of biomass pyrolysis behavior using thermogravimetric data. This work assesses the utility of thermal data derived from these models in the computation of kinetic and thermodynamic parameters, alongside an analysis of their statistical performance. Eventually, the RF model exhibits superior physical interpretability and the least discrepancy in predicting kinetic and thermodynamic parameters. Furthermore, a feature importance analysis conducted within the RF model framework quantitatively reveals that temperature and heating rate account for 98.5 % and 1.5 %, respectively.

Biomass directional pyrolysis based on element economy to produce high-quality fuels, chemicals, carbon materials - A review

Biomass is regarded as the only carbon-containing renewable energy source and has performed an increasingly important role in the gradual substitution of conventional fossil energy, which also contributes to the goals of carbon neutrality. In the past decade, the academic field has paid much greater attention to the development of biomass pyrolysis technologies. However, most biomass conversion technologies mainly derive from the fossil fuel industry, and it must be noticed that the large element component difference between biomass and traditional fossil fuels. Thus, it's necessary to develop biomass directional pyrolysis technology based on the unique element distribution of biomass for realizing enrichment target element (i.e., element economy). This article provides a broad review of biomass directional pyrolysis to produce high-quality fuels, chemicals, and carbon materials based on element economy. The C (carbon) element economy of biomass pyrolysis is realized by the production of high-performance carbon materials from different carbon sources. For efficient H (hydrogen) element utilization, high-value hydrocarbons could be obtained by the co-pyrolysis or catalytic pyrolysis of biomass and cheap hydrogen source. For improving the O (oxygen) element economy, different from the traditional hydrodeoxygenation (HDO) process, the high content of O in biomass would also become an advantage because biomass is an appropriate raw material for producing oxygenated liquid additives. Based on the N (nitrogen) element economy, the recent studies on preparing N-containing chemicals (or N-rich carbon materials) are reviewed. Moreover, the feasibility of the biomass poly-generation industrialization and the suitable process for different types of target products are also mentioned. Moreover, the enviro-economic assessment of representative biomass pyrolysis technologies is analyzed. Finally, the brief challenges and perspectives of biomass pyrolysis are provided.

Machine learning assisted predicting and engineering specific surface area and total pore volume of biochar

Biochar produced from pyrolysis of biomass is a platform porous carbon material that have been widely used in many areas. Specific surface area (SSA) and total pore volume (TPV) are decisive to biochar application in hydrogen uptake, CO₂ adsorption, and organic pollutant removal, etc. Engineering biochar by traditional experimental methods is time-consuming and laborious. Machine learning (ML) was used to effectively aid the prediction and engineering of biochar properties. The prediction of biochar yield, SSA, and TPV was achieved via random forest (RF) and gradient boosting regression (GBR) with test R² of 0.89-0.94. ML model interpretation indicates pyrolysis temperature, biomass ash, and volatile matter were the most important features to the three targets. Pyrolysis parameters and biomass mixing ratios for biochar production were optimized via three-target GBR model, and the optimum schemes to obtain high SSA and TPV were experimentally verified, indicating the great potential of ML for biochar engineering.

Machine learning prediction of pyrolytic products of lignocellulosic biomass based on physicochemical characteristics and pyrolysis conditions

This study predicts pyrolytic product yields via machine learning algorithms from biomass physicochemical characteristics and pyrolysis conditions. Random forest (RF), gradient boosting decision tree (GBDT), eXtreme Gradient Boosting (XGBoost), and Adaptive Boost (Adaboost) algorithms are comparatively analyzed. Among these algorithms, the RF algorithm is the best modeling algorithm and performs best in predicting the bio-oil yield and performs well in predicting biochar and pyrolytic gas yields. The moisture content, carbon content, and final heating temperature are the most important factors in predicting pyrolysis product yields, and biomass characteristics are more important than pyrolysis conditions. Furthermore, the carbon content positively affects the bio-oil yield and negatively affects the biochar yield, and the final temperature positively affects the pyrolytic gas yield and negatively affects the biochar yield. This work provides new insight for controlling the yields of pyrolytic products via the RF algorithm, which can facilitate the process optimization in engineering applications.

Assessment of agricultural waste biochars for remediation of degraded water-soil environment: Dissolved organic carbon release and immobilization of impurities in one- or two-adsorbate systems

This paper presents a method of agricultural waste management - the production of two biochars (BC) from potato and raspberry stems. It defines the potential of these materials for remediation of degraded water and soil environments. The performed study included analyses of BC physicochemistry, dissolved organic carbon (DOC) release and ability to immobilize copper (Cu), tetracycline (TC) and carboxin (CB) in one- and two-adsorbate systems. The BCs were obtained with pyrolysis at 600 °C for 30 min in a nitrogen atmosphere. Their DOC was predominantly constituted of substances with large molecular weights and high aromaticity, meaning that both BCs can be safely applied as soil additives. Potato-biochar (P-BC) had a more developed surface than raspberry-biochar (R-BC). The specific surface area (S_BET) of P-BC was 122 m²/g, whilst of R-BC was 87 m²/g. As a result, the efficiency of impurity adsorption in the one-adsorbate systems was higher for P-BC (61.75% for Cu, 73.84% for TC, and 54.43% for CB). In the two-adsorbate systems, organic impurities improved the immobilization of heavy metal ions on BCs. The efficiency of Cu adsorption on P-BC when TC was present was 88.29%. Desorption of Cu from BC was highest using HCl, whilst that of TC and CB was highest using NaOH. Maximum desorption was observed in a two-adsorbate system with TC + CB (up to 63.6% for TC). These results confirmed that potato and raspberry stems can be used to produce highly effective BCs with large application potential, especially for remediation of degraded soils and polluted waters.

Spectral characteristics of dissolved organic carbon (DOC) derived from biomass pyrolysis: Biochar-derived DOC versus smoke-derived DOC, and their differences from natural DOC

Biochar-derived dissolved organic carbon (BDOC) and smoke-derived dissolved organic carbon (SDOC) are two different biomass-pyrogenic DOCs. They inevitably enter soil and water, then potentially pose different impacts on the chemistry of these media. This study systemically investigated the emissions and spectral characteristics of BDOC and SDOC as well as their differences from natural DOC. The results showed that the emission of SDOC was 1-3 orders of magnitude greater than that of BDOC after biomass pyrolysis. UV-vis spectra indicated that BDOC had higher aromaticity and molecular weight as well as lower polarity than SDOC. The two-dimensional correlation infrared spectrum (2D-PCIS) matrix indicated that BDOC contained more chemical groups with stronger temperature-dependence than SDOC. Fluorescence EEM-PARAFAC analysis showed that BDOC was dominated by macromolecular humic-like substances, while SDOC was primarily composed of small molecules of aromatic protein/polyphenols-like compounds. The fluorescence indicators including humification index (HIX) (0.08-0.76) and biological index (BIX) (1.18-1.72) of SDOC were significantly different from those of BDOC (HIX: 1.64-12.68, and BIX: 0.17-1.62). The higher BIX and more small molecules of aromatic protein/polyphenols-like compounds indicated SDOC had potentially higher bioavailability and turnover rate in the environment than BDOC. Furthermore, the UV-vis spectral indicator (S_275-295) and fluorescence spectral indicators (HIX, and BIX) of BDOC were equivalent to those of natural DOC, whereas these indicators of SDOC were significantly different from those of natural DOC. This study demonstrated that BDOC and SDOC had significantly different components and properties and they might present different environmental behaviors and effects.

Fast pyrolysis characteristics and its mechanism of corn stover over iron oxide via quick infrared heating

The harm done to the environment by fossil fuels was serious, and it is urgent to find effective methods and adopt carbon-neutral feedstock to prevent further environmental damage. An innovative infrared heating reactor was developed for the generation of high-yield bio-oil and cleaner pyrolysis gases. This work was devoted to exploring the fast pyrolysis characteristics and its mechanism of corn stover over the iron oxide in a novel infrared heating (IH) reactor and a traditional electric heating (EH) reactor. In the IH reactor, the bio-oil yield increased initially and then decreased with increasing pyrolysis temperature, reaching a maximum yield of 29 wt% at 600 °C. The yield of pyrolysis bio-oil and water decreased as the reusability number rose, whereas the char yield increased. Bio-oil yields decreased less from R0 to R3 and the catalyst was more effective in IH. IH produced more char and gas but considerably less water than EH, and its bio-oil had fewer phenols. Raman spectroscopy demonstrated that the aromatic structure of biochar increased as the pyrolysis temperature increased. Cellulose and hemicellulose can be completely cleaved at lower temperatures in IH. In addition, Fe₂O₃ catalysts have shown the advantages of low cost, efficient cycling, and long action time. Infrared heating coupled with iron oxide catalyst shows the potential to increase bio-oil yield and is more promising for industrial production than EH.

Visual experimental study on the effect of heat exchange area on the evolution of biomass pyrolysis vapors in a vertical indirect condensing field

The effect of heat exchange area on the componential evolutions of biomass pyrolysis vapors was visualized through an innovative combining method of bio-oil composition inversion and function fitting. As the maximal diameter of condenser at 340 K increased from 35 mm to 55 mm, the fitted heat maps showed that the recovery of organics increased in the top of condenser and remained steady in the bottom, whereas the water recovery only increased in the top but decreased in the bottom. The recovery proportion of furfural and phenolic compounds increased by 20-40% with unvaried water recovery, and the content enrichment of high value-added components increased by 30-45% at 37 wt% of bio-oil yield. Heat exchange area exhibited a finer regulation effect on the condensation of pyrolysis vapors than traditional condensing adjustment methods, which first provided a remarkable promotion for the recovery and enrichment of organic components without improving water recovery.

Thermal reduction-desorption of cadmium from contaminated soil by a biomass co-pyrolysis process

Thermal desorption is one of the methods commonly used for the remediation of contaminated soil. However, its suitability for the treatment of widespread Cd-contaminated soil was seldom investigated, because the desorption of Cd was found to be difficult, even at a high heating temperature. In the present study, a biomass co-pyrolysis (BCP) method is proposed for the thermal treatment of Cd-contaminated soil. The results showed that, when the mixture of biomass and contaminated soil was pyrolyzed at ~550 ^oC, the gaseous pyrolytic products (such as CO and hydrocarbon gases) from the biomass could chemically reduce the Cd(II) into volatile Cd⁰, thereby allowing the evaporation of vaporized Cd⁰ from the soil within a short operating time. The BCP method can achieve a highly efficient removal of Cd from the soil samples spiked with a large amount of Cd(II). The remediated soil, containing the remaining biochars, showed a good regreening potential and a significant decrease in Cd bioavailability. It also showed a good performance for the remediation of field soils from four contaminated sites (>92% removal efficiencies), and one of the treated soils could even meet the Cd screening level of agricultural land of China.

Sustainable remediation of hazardous environmental pollutants using biochar-based nanohybrid materials

Biochar is a well-known carbon material with diversified functionalities and excellent physicochemical characteristics with high wastewater treatment potential. This review aims to summarize recent advancements in the development of biochar and biochar-based nanohybrid materials as a potential tool for the removal of harmful organic compounds such as synthetic dyes/effluents. The formation of biochar using pyrolysis of renewable feedstocks and their applications in various industries are explained hereafter. The characteristics and construction of biochar-based hybrid materials are explained in detail. Diversity of feedstocks, including municipal wastes, industrial byproducts, agricultural, and forestry residues, endows different biochar types with a wide structural variety. The production of cost-effective biochar drives the interest in manipulating biochars and induces desire functionality using nanoscale reinforcements. Various types of biochars, such as magnetic biochar, layered nanomaterial coated biochar, nanometallic oxide composites, chemically and physically functionalized biochar, have been produced. With the aid of nanomaterial, hybrid biochar exhibits a high potential to remove toxic contaminants. Depending upon biochar type, dyes/effluents can be removed via different mechanisms, including the Fenton process, photocatalytic degradation, π-π interaction, electrostatic interaction, and physical adsorption. In conclusion, desired physicochemical features, and tunable surface properties of biochar present high potential material in removing organic dyes and other effluents. The blended biochar with different materials/nanomaterials endows broader development and multi-functional opportunities for treating dyes/effluents.

Machine learning prediction of pyrolytic gas yield and compositions with feature reduction methods: Effects of pyrolysis conditions and biomass characteristics

This study aimed to utilize machine learning algorithems combined with feature reduction for predicting pyrolytic gas yield and compositions based on pyrolysis conditions and biomass characteristics. To this end, random forest (RF) and support vector machine (SVM) was introduced and compared. The results suggested that six features were adequate to accurately forecast (R² > 0.85, RMSE < 5.7%) the yield while the compositions only required three. Moreover, the profound information behind the models was extracted. The relative contribution of pyrolysis conditions was higher than that of biomass characteristics for yield (55%), CO₂ (73%), and H₂ (81%), which was inverse for CO (12%) and CH₄ (38%). Furthermore, partial dependence analysis quantified the effects of both reduced features and their interactions exerted on pyrolysis process. This study provided references for pyrolytic gas production and upgrading in a more convenient manner with fewer features and extended the knowledge into the biomass pyrolysis process.

Comparison of linear and nonlinear function to describe and predict componential evolution of biomass pyrolysis vapors during condensation in a tubular indirect heat exchanger

A novel experimental method based on the combination of bio-oil composition inversion and function fitting was purposed and verified for describing the componential evolution curves during the liquefaction of biomass pyrolysis vapors. The evolution curves of representative condensable components were fitted by linear and Slogistic function in the short, middle and long three condensing fields. Linear function exhibited a significant effectiveness for the description and prediction of low-boiling water and furfural and the relative deviations were no more than 5% between actual values in long condenser and predictive values from the elongation of curves in short and middle condensers. For high-boiling phenolic compounds, linear function failed to fit their evolutions in long condenser but Slogistic fitting remained effective despite the relative deviation increasing to about 10%. This investigation provided a unique and effective prediction method for the vapor evolution in industrial shell and tube heat exchanger according to laboratory-scale experiment.

Multi-distribution activation energy model on slow pyrolysis of cellulose and lignin in TGA/DSC

Developing a kinetic model to analyze the multi-step reaction of biomass pyrolysis is pivotal to elucidate the mechanism of the pyrolysis. For this purpose, a model-fitting method such as multi-distribution the Distributed Activation Energy Model (DAEM) is one of the most reliable methods. DAEM with 4 different distribution functions of Gaussian, Logarithmic, Gumbel, and Cauchy was utilized to characterize the pyrolysis of cellulose and lignin during Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC) instrumentation. By comparing Derivative Thermogravimetry (DTG) and DSC profiles, determination of pseudo-components can be done more accurately. A kinetics analysis on the pyrolysis of cellulose with a single Gaussian distribution DAEM yielded a single activation energy of 178 kJ mol⁻¹ with a narrow standard deviation. This result was justified by a single and dominant endothermic peak followed by minor exothermic peaks in the DSC result. For lignin pyrolysis, the presence of multiple peaks is characterized by four pseudo-components in DAEM with activation energies of 157, 174, 194, and 200 kJ mol⁻¹. These pseudo-components were confirmed by the DSC result which indicated the occurrences of two exothermic peaks with two lesser exothermic or possibly endothermic peaks at the same temperature range. These findings imply the importance of DSC to support a kinetics study of thermogravimetric pyrolysis.

Experimental study on the composition evolution and selective separation of biomass pyrolysis vapors in the four-staged indirect heat exchangers

This study was devoted to proposing an effective experimental method based on bio-oil composition inversion for understanding biomass pyrolysis vapor evolution in four-staged condensers. The effective length of each condenser was 200 mm. The evolution curves and heat maps of condensable vapors in the whole multi-staged condensing field were provided by Logistics model fitting. With changing condition from "365-345-325-305" to "345-325-305-285", the condensing efficiency of the first condenser increased by 100% but that of the third condenser decreased by 80%. Under condition "365-345-325-305", the largest recovery rate of water was observed at 400 mm away from multi-staged condensing field entrance while that of eugenol was observed at 50 mm away from the entrance, which explained that water was primarily recovered by the second and third condensers whereas eugenol was recovered by the first condenser, and verified the remarkable effect of fractional condensation on the separation of water and high-boiling phenols.

An overview on engineering the surface area and porosity of biochar

Surface area and porosity are important physical properties of biochar, playing a crucial role in many biochar applications, such as wastewater treatment and soil remediation. The production of engineered biochar with highly porous structure and large surface area has received extensive attention. This paper comprehensively reviewed the effects of biomass and pyrolysis parameters on the surface area and porosity of biochar. The composition of biomass feedstock and pyrolysis temperature are the major influencing factors. It is suggested that the lignocellulosic biomass is an outstanding candidate, wood and woody biomass in particular. Besides, moderate temperatures (400-700 °C) are suitable for the development of the pore structure. Further improvement can be implemented by additional treatments. Activation is the most widely used and effective way to promote biochar surface area and porosity, especially the chemical activation. Enhancement can also be achieved by using other treatment methods, such as carbonaceous materials coating, ball milling, and templating. Future research should focus on upgrading or developing treatment technology to achieve enhanced functionality and porous structure of biochar simultaneously.

Biomass pyrolysis with alkaline-earth-metal additive for co-production of bio-oil and biochar-based soil amendment

The alkaline-earth-metal (AEM) has a good performance on modification of both bio-oil and biochar during biomass pyrolysis. In this work, the pyrolysis of rice husk (RH) in the presence of CaO, CaCO₃, MgO and MgCO₃ was comparatively studied for selecting an appropriate AEM additive to balance the qualities of pyrolytic products. Pyrolysis of RH with the AEM additives could decrease the acids content and increase the hydrocarbons content in bio-oil. Compared with the Ca-additives (i.e., CaO, CaCO₃), the Mg-additives (i.e., MgO, MgCO₃) were more beneficial for enhancing the hydrocarbons production. The addition of biochar to soil can significantly enhance the water retention. RHC-MgCO₃ had a maximum water retention capacity, while RHC-MgO had a minimum water retention capacity due to its lowest specific surface area. Additionally, the Mg-modified biochar had a much higher nutrient (i.e., K⁺, PO₄^3-) adsorption capacity. In particular, RHC-MgO with a lowest specific surface area had a highest PO₄^3- adsorption capacity, which was evidenced by the adsorption of PO₄^3- onto biochar mainly controlled by the chemisorption process. PO₄^3- adsorbed in the RHC-MgO released rapidly indicating its low PO₄^3- retention capacity. In general, MgCO₃ would be an appropriate candidate that is used in pyrolysis of biomass for co-production of bio-oil and biochar composite with high capacities of water/nutrient adsorption and retention for soil amendment.

Preparation of biochar as a coating material for biochar-coated urea

Biochar was used as a coating material for slow release urea. However, influence of biochar performance on preparing biochar-coated urea (BCU) and nitrogen release characteristics is rarely reported. In this study, total of 24 biochars were prepared and characterized from six biomass residues (rice straw, chicken manure, vinasse, Phyllostachys pubescens, Arundo donax and sugarcane bagasse) at four pyrolysis temperatures (400-700 °C). Grey correlation analysis (GCA) was used to select biochar as a coating material for BCU based on biochar performance indicators. The feasibility (BCU formability) for preparing BCU and characteristics of nitrogen release in BCU based on hydrostatic dissolution test and soil column leaching experiment were evaluated. Biochar prepared at low pyrolysis temperature was not suitable as a coating material for BCU due to low specific surface area. Biochars derived from pyrolysis of Phyllostachys pubescens (B_P6), vinasse (B_V6) and rice straw (B_R6) at 600 °C were selected as coating materials for BCU based on grey correlation analysis (GCA). The adhesion of biochar to urea surface was related to biomass type that preparing biochar. B_V6 was recommended for use as coating material for BCU because the feasibility of the biochars followed the order B_R6 > B_V6 > B_P6, and the practicality of the biochars followed the order B_P6 > B_V6 > B_R6. The findings suggest that biochar with a high specific surface area, hydrophilic oxygen-containing functional groups and low pH is a suitable material for BCU.

Volatile-char interactions during biomass pyrolysis: Cleavage of C-C bond in a β-5 lignin model dimer by amino-modified graphitized carbon nanotube

This study investigated the interactions between volatile and char during biomass pyrolysis at 400 °C, employing a β-5 lignin dimer and amino-modified graphitized carbon nanotube (CNT-NH₂) as their models, respectively. The results demonstrated that both -NH₂ and its carrier (CNT) facilitated the conversion of the β-5 dimer, which significantly increased from 9.7% (blank run), to 61.6% (with CNT), and to 96.6% (with CNT-NH₂). CNT mainly favored the breakage of C-O bond in the feedstock to produce dimers with a yield of 55.5%, while CNT-NH₂ promoted the cleavage of both C-O and C-C bonds to yield monomers with a yield up to 63.4%. Such significant changes in the pyrolysis behaviors of the β-5 lignin dimer after the introduction of CNT-NH₂ were considered to be mainly caused by hydrogen-bond formations between -NH₂ and the dimeric feedstock/products, in addition to the π-π stacking between CNT and aromatic rings.

Experimental study on composition evolution of biomass pyrolysis vapors with condensing temperature in a vertical tubular condenser

The experiments on bio-oil recovery in a vertical tubular condenser with two flumes were conducted for speculating the componential distribution of walnut shell pyrolysis vapors during condensation. Bio-oil elements and functional groups from different locations of condenser were compared with each other. Aromatic H and H in phenolic OH were concentrated in the top and middle bio-oil and their percentage were improved with increasing water bath temperature. Ten representative compounds in bio-oil were chosen for quantitative analysis. As water bath temperature increased from 273 K to 353 K, the recovered water decreased by 85% whereas the guaiacol and its derivatives (guaiacols) merely decreased by 40%. Vapor distributions of water, acetic acid, furfural and guaiacols were simulated by the back analysis of bio-oil components. According to the simulated results, tubular condenser can be properly lengthened for promoting the recovery of specific components at high water bath temperatures.

Synergetic effect of magnesium citrate and temperature on the product characteristics of waste lotus seedpod pyrolysis

To understand the synergetic effect of magnesium citrate (MC) and temperature on biomass pyrolysis, co-pyrolysis of lotus seedpod (LS) and MC was carried out in a fixed bed reactor. With the addition of MC, CO2 become the dominate composition in gas (55.83-90.75 vol%). And with temperature increasing, the main components in bio-oil converted from carboxylic acid to phenols and aromatics. Meanwhile, the mesoporous carbon was formed, with the BET specific surface area up to 514.66 m2/g, and pore diameter mainly focused at 3-8 nm. For the catalytic effect, the secondary cracking of pyrolytic volatiles (acetic acid and anhydrosugar) was inhibited, therefore the gas releasing was inhibited below 550 °C. However, at higher temperature, MgO catalysts favored the reduction of acids and deoxygenation via ketonization and aldol condensation reactions. The formed MgO as a template and the catalysis of MgO during co-pyrolysis contributed to the mesoporous structure of solid char.

High-temperature dielectric properties and pyrolysis reduction characteristics of different biomass-pyrolusite mixtures in microwave field

Exploring the dielectric properties of mineral-biomass mixtures is fundamental to the coupled application with biomass pyrolysis and microwave technology to mineral reduction. In this work, the microwave dielectric properties of five pyrolusite-biomass mixtures were measured by resonant cavity perturbation technique and the pyrolysis reduction characteristics were systematically investigated, including poplar, pine, ageratina adenophora, rapeseed shell and walnut shell. Results indicated that the dielectric properties commonalities of five mixtures with temperature represented by increasing firstly, dropping intensely and finally rising slightly, with excellent responsiveness to microwaves; which the change trend was mainly attributed to the crystal transformation of amorphous MnO₂ and pyrolusite reduction reactions by biomass pyrolysis. Meanwhile, the heating characteristics successfully matched the dielectric properties of the mixtures, and the pyrolusite reduction process by biomass can be divided into two stages: biomass pyrolysis and pyrolusite reduction. The work highlights the universal feasibility of the novel coupled method for mineral reduction.

Microwave pyrolysis of walnut shell for reduction process of low-grade pyrolusite

Replacing fossil energy by utilizing biomass as carbon source to convert metal oxides has meaning for reduction of minerals. Microwave pyrolysis of walnut shell for reduction process of low-grade pyrolusite was proposed. Thermogravimetric analysis indicated biomass pyrolysis process for reduction of pyrolusite was divided into four phases identified by temperatures: dehydration stage (<150 °C), pre-pyrolysis stage (150 °C-290 °C), curing decomposition stage (290 °C-480 °C) and carbonization stage (>480 °C), and manganese recovery reached 92.01% at 650 °C for 30 min with 18% walnut shell. The strongest preferential orientation of MnO was appeared, with good crystalline structure and no MnO₂ and FeO peaks detected. The product surface became loose and porous with numerous cracks, pits and holes, and molten granules were interconnected and stacked with regular shape. The methods propose new idea of selective reduction of pyrolusite based on biomass pyrolysis by microwave heating.

Study on the effect of condensing temperature of walnut shells pyrolysis vapors on the composition and properties of bio-oil

The effect of condensing temperature on composition of bio-oil obtained via fractional condensation was investigated by pyrolysis-condensation experiments of walnut shells at condensing temperatures from 290 K to 370 K. The condensing efficiency of the first stage condenser decreased from 0.59 to 0.12 with increasing temperature. Moisture of bio-oil decreased from 40% to 5%, but the C/O ratio increased from 0.50 to 1.50. Compared with contents observed at the lowest condensation temperature, the maximum content of each component increased by 50%-500%. Combined with variations in condensing efficiency and composition content, the optimum condensing temperature range for declining water in bio-oil was 340-350 K. The condensing temperature associated with the enrichment of acetic acid and furfural was 345 K. The 355 K optimum condensing temperature could be selected to achieve the maximum enrichment of guaiacol and its derivatives.

The effect of microwave drying pretreatment on dry torrefaction of agricultural biomasses

This paper examines the effect of microwave drying on biomass characteristics and subsequent dry pyrolysis and characteristics of produced biochar from rice straw, sugarcane bagasse, rice husk and cotton stalk compared to oven drying at 105 °C. Dried samples from both methods are torrefied at 250 and 300 °C with 30-minutes residence time. Drying time reached 60 times faster with microwave. The fast and violent microwave drying ruptured the biomasses' surface, releasing more volatiles and having lower crystallinity; these lowered the heating value, energy yield and elemental carbon compared to oven drying except for cotton stalk only due to its woody nature which reduced devolatilization. Sugarcane, rice husk and cotton stalk have the most promising values of elemental carbon, energy yield and heating value reaching that of the bituminous coal. Torrefied rice straw showed high crystallinity of 50.7% while sugarcane and rice husk were completely amorphous.

Catalytic performance of potassium in lignocellulosic biomass pyrolysis based on an optimized three-parallel distributed activation energy model

The pyrolysis kinetics of extractive tobacco stem and pretreated samples with different KCl impregnation ratios were investigated by the thermogravimetric experiment and an optimized three-parallel distributed activation energy model (DAEM). The significant fitting deviation for the cellulose pyrolysis and the unrealistic partial fitting curve for the hemicellulose pyrolysis were mitigated during the optimization process by applying the Avrami-Erofeev-DAEM and reducing the latent interferences. The optimized parameters with good fitting qualities (about 2%) were obtained. Furthermore, based on the experimental results (changes in reaction intensity and temperature), model calculations (differences in reaction order, activation energy, volatiles fraction, etc.), and the maximum residual error analysis (with a high catalytic reaction rate) regarding different KCl-to-biomass ratios, it was found that KCl kinetically promoted the hemicellulose pyrolysis, which can be utilized as the theoretical support for the industrial application.

Porous carbon supported nanoceria derived from one step in situ pyrolysis of Jerusalem artichoke stalk for functionalization of solution-gated graphene transistors for real-time detection of lactic acid from cancer cell metabolism

Effective detection of biomarkers for tumor cells has been the focus of attention. In this work, we have successfully fabricated a highly sensitive sensor based on solution-gated graphene transistors (SGGT) for detecting lactic acid content accumulated in tumor cells through their glycolysis metabolism. The sensing mechanism of the lactic acid sensor is attributed to electrochemical catalysis of H₂O₂ produced by the oxidation of lactic acid by lactate oxidase near the gate electrode. The key component of the sensor is the functionalization of porous carbon loaded with ceria nanoparticles derived from a novel one step in situ pyrolysis of pretreated Jerusalem artichoke stalk, which significantly improved the sensor sensitivity, i.e. a detection limit as low as 300 nM and linear range from 3 μM to 300 μM. The optimized lactic acid sensor has successfully applied to the detection of lactic acid in practical cell culture samples with high credibility. The SGGT-based lactic acid biosensor shows great potential for the application in tumor microenvironment due to its superior biocompatibility and accuracy.

Kinetic compensation effect in logistic distributed activation energy model for lignocellulosic biomass pyrolysis

The kinetic compensation effect in the logistic distributed activation energy model (DAEM) for lignocellulosic biomass pyrolysis was investigated. The sum of square error (SSE) surface tool was used to analyze two theoretically simulated logistic DAEM processes for cellulose and xylan pyrolysis. The logistic DAEM coupled with the pattern search method for parameter estimation was used to analyze the experimental data of cellulose pyrolysis. The results showed that many parameter sets of the logistic DAEM could fit the data at different heating rates very well for both simulated and experimental processes, and a perfect linear relationship between the logarithm of the frequency factor and the mean value of the activation energy distribution was found. The parameters of the logistic DAEM can be estimated by coupling the optimization method and isoconversional kinetic methods. The results would be helpful for chemical kinetic analysis using DAEM.

Pyrolysis of human feces: Gas yield analysis and kinetic modeling

Pyrolysis of human feces renders the waste free of pathogens and is a potential method of treating fecal sludge waste collected from non-sewered systems. Slow pyrolysis experiments were conducted on human feces and the char yield and gas evolution quantified at 1-10 °C/min heating rates. Char yield ranged from 35.1 to 35.8% (dry mass basis), while the gas yield ranged from 17.2 to 29.6% (dry mass basis). The pyrolysis gases detected were CO, CO₂, CH₄, C₂H₆, and H₂. These non-condensable gases contained a higher heating value (HHV) ranging from 7.2 to 22.8 MJ/Nm³. Kinetic analysis was done by a pyrolysis reaction model free method (Isoconversional) as well as a DAEM (Distributed Activated Energy Model) method that assumes many irreversible first order reactions. Both yielded very close values for activation energy ranging from 141 kJ/mol to 409 kJ/mol, with half of the biomass conversion happening at 241.5 ± 2.9 kJ/mol. The findings of the research provide useful technical information that can guide the design of a pyrolysis system to treat fecal waste. Social acceptance and scale-up issues need to be addressed through further research.

The major parameters on biomass pyrolysis for hyperaccumulative plants--A review

Phytoextraction is one of the main phytoremediation techniques and it has often been described as a potentially feasible in situ soil decontamination method of large amounts of heavy metals, organic pollutants and explosive compounds. As this remediation technique is approaching extensive on-field experimentation and commercialization, research focus is on investigating new ways to achieve the valorisation of its by-products. Biomass pyrolysis represents a key step to numerous valorisation options and it is characterized by differential output products that are determined by the operating conditions of the process and the characteristics of the input. However, when used to valorise plants that have undergone significant metal uptake, this strategy involves some new aspects related to harvest, procedure and final product reutilization. This paper reviews the studies made on biomass pyrolysis of plants with emphasis on the differential quality and distribution of pyrolysis products in relation with the variables of the process and the metal-rich phytoextraction feedstock properties. By investigating these parameters, this survey provides indications on ways to optimize the valorisation of phytoremediation by-products through biomass pyrolysis.

Pyrolysis of rice straw with ammonium dihydrogen phosphate: Properties and gaseous potassium release characteristics during combustion of the products

The effect of ammonium dihydrogen phosphate (NH4H2PO4) on rice straw (RS) carbonization was evaluated at temperatures of 350-650°C. The carbonized products of RS with NH4H2PO4 show higher solid and energy yields, but lower higher heating values than the carbonized RS at every carbonization temperature. The optimum carbonization operation of RS with NH4H2PO4 which has a higher energy yield at a lower solid volume may be determined between 350 and 450°C, and RS with NH4H2PO4 carbonized at 450°C presents better pore properties than carbonized RS. The carbonized products of RS with NH4H2PO4 all have lower gaseous potassium release ratios than those of RS carbonized at the same temperature at combustion temperatures of 700-1000°C by retaining potassium in non-volatile phosphorus compounds with high melting points. It is an effective method for inhibiting the gaseous potassium release during combustion of the carbonized products.

Improved lignin pyrolysis for phenolics production in a bubbling bed reactor--Effect of bed materials

Lignin pyrolysis was studied in a bubbling fluidized bed reactor equipped with a fractional condensation train, using nitrogen as the fluidization gas. The effect of different bed materials (silica sand, lignin char, activated lignin char, birch bark char, and foamed glass beads) on bio-oil yield and quality was investigated for a pyrolysis temperature of 550 °C. Results how that a bed of activated lignin char is preferable to the commonly used silica sand: pyrolysis of Kraft lignin with a bed of activated lignin char not only provides a pure char product, but also a higher dry bio-oil yield (with a relative increase of 43%), lower pyrolytic water production, and better bio-oil quality. The bio-oil obtained from Kraft lignin pyrolysis with a bed of activated lignin char has a lower average molecular weight, less tar, more phenolics, and less acidity than when sand is used as bed material.

Physical and chemical characterization of waste wood derived biochars

Biochar, a solid byproduct generated during waste biomass pyrolysis or gasification in the absence (or near-absence) of oxygen, has recently garnered interest for both agricultural and environmental management purposes owing to its unique physicochemical properties. Favorable properties of biochar include its high surface area and porosity, and ability to adsorb a variety of compounds, including nutrients, organic contaminants, and some gases. Physical and chemical properties of biochars are dictated by the feedstock and production processes (pyrolysis or gasification temperature, conversion technology and pre- and post-treatment processes, if any), which vary widely across commercially produced biochars. In this study, several commercially available biochars derived from waste wood are characterized for physical and chemical properties that can signify their relevant environmental applications. Parameters characterized include: physical properties (particle size distribution, specific gravity, density, porosity, surface area), hydraulic properties (hydraulic conductivity and water holding capacity), and chemical and electrochemical properties (organic matter and organic carbon contents, pH, oxidation-reduction potential and electrical conductivity, zeta potential, carbon, nitrogen and hydrogen (CHN) elemental composition, polycyclic aromatic hydrocarbons (PAHs), heavy metals, and leachable PAHs and heavy metals). A wide range of fixed carbon (0-47.8%), volatile matter (28-74.1%), and ash contents (1.5-65.7%) were observed among tested biochars. A high variability in surface area (0.1-155.1g/m(2)) and PAH and heavy metal contents of the solid phase among commercially available biochars was also observed (0.7-83 mg kg(-1)), underscoring the importance of pre-screening biochars prior to application. Production conditions appear to dictate PAH content--with the highest PAHs observed in biochar produced via fast pyrolysis and lowest among the gasification-produced biochars.

Prediction of product distribution in fine biomass pyrolysis in fluidized beds based on proximate analysis

A predictive model was satisfactorily developed to describe the general trends of product distribution in fluidized beds of lignocellulosic biomass pyrolysis. The model was made of mass balance based on proximate analysis and an empirical relationship with operating parameters including fluidization hydrodynamics. The empirical relationships between product yields and fluidization conditions in fluidized bed pyrolyzers were derived from the data of this study and literature. The gas and char yields showed strong functions of temperature and vapor residence time in the pyrolyzer. The yields showed a good correlation with fluidization variables related with hydrodynamics and bed mixing. The predicted product yields based on the model well accorded well with the experimental data.

Role of Brønsted acid in selective production of furfural in biomass pyrolysis

In this work, the role of Brønsted acid for furfural production in biomass pyrolysis on supported sulfates catalysts was investigated. The introduction of Brønsted acid was shown to improve the degradation of polysaccharides to intermediates for furfural, which did not work well when only Lewis acids were used in the process. Experimental results showed that CuSO4/HZSM-5 catalyst exhibited the best performance for furfural (28% yield), which was much higher than individual HZSM-5 (5%) and CuSO4 (6%). The optimum reaction conditions called for the mass ratio of CuSO4/HZSM-5 to be 0.4 and the catalyst/biomass mass ratio to be 0.5. The recycled catalyst exhibited low productivity (9%). Analysis of the catalysts by Py-IR revealed that the CuSO4/HZSM-5 owned a stronger Brønsted acid intensity than HZSM-5 or the recycled CuSO4/HZSM-5. Therefore, the existence of Brønsted acid is necessary to achieve a more productive degradation of biomass for furfural.

Catalytic pyrolysis of miscanthus × giganteus in a spouted bed reactor

A conical spouted bed reactor was designed and tested for fast catalytic pyrolysis of miscanthus × giganteus over Zeolite Socony Mobil-5 (ZSM-5) catalyst, in the temperature range of 400-600 °C and catalyst to biomass ratios 1:1-5:1. The effect of operating conditions on the lumped product distribution, bio-oil selectivity and gas composition was investigated. In particular, it was shown that higher temperature favors the production of gas and bio-oil aromatics and results in lower solid and liquid yields. Higher catalyst to biomass ratios increased the gas yield, at the expense of liquid and solid products, while enhancing aromatic selectivity. The separate catalytic effects of ZSM-5 catalyst and its Al2O3 support were studied. The support contributes to increased coke/char formation, due to the uncontrolled spatial distribution and activity of its alumina sites. The presence of ZSM-5 zeolite in the catalyst enhanced the production of aromatics due to its proper pore size distribution and activity.

High quality fuel gas from biomass pyrolysis with calcium oxide

The removal of CO2 and tar in fuel gas produced by biomass thermal conversion has aroused more attention due to their adverse effects on the subsequent fuel gas application. High quality fuel gas production from sawdust pyrolysis with CaO was studied in this paper. The results of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments indicate that the mass ratio of CaO to sawdust (Ca/S) remarkably affects the behavior of sawdust pyrolysis. On the basis of Py-GC/MS results, one system of a moving bed pyrolyzer coupled with a fluid bed combustor has been developed to produce high quality fuel gas. The lower heating value (LHV) of the fuel gas was above 16MJ/Nm(3) and the content of tar was under 50mg/Nm(3), which is suitable for gas turbine application to generate electricity and heat. Therefore, this technology may be a promising route to achieve high quality fuel gas for biomass utilization.

Additives initiate selective production of chemicals from biomass pyrolysis

To improve chemicals selectivity under low temperature, a new method that involves the injection of additives into biomass pyrolysis is introduced. This method allows biomass pyrolysis to achieve high selectivity to chemicals under low temperature (300°C), while nothing was obtained in typical pyrolysis under 300°C. However, by using the new method, the first liquid drop emerged at the interval between 140°C and 240°C. Adding methanol to mushroom scrap pyrolysis obtained high selectivity to acetic acid (98.33%), while adding ethyl acetate gained selectivity to methanol (65.77%) in bagasse pyrolysis and to acetone (72.51%) in corncob pyrolysis. Apart from basic chemicals, one high value-added chemical (2,3-dihydrobenzofuran) was also detected, which obtained the highest selectivity (10.33%) in corncob pyrolysis through the addition of ethyl acetate. Comparison of HZSM-5 and CaCO3 catalysis showed that benzene emerged in the liquid because of the larger degree of cracking and hydrodeoxygenation over HZSM-5.

Reaction pathways of β-D-glucopyranose pyrolysis to syngas in hydrogen plasma: a density functional theory study

In this work, density functional theory (DFT) was employed to investigate the reaction pathways of β-D-glucopyranose for better understanding the pyrolysis mechanism of cellulose in hydrogen plasma. Many possible reactions were considered, and the reaction enthalpies and activation energies of these reactions were calculated using density functional theory (DFT) with a Gaussian method of B3LYP and basic set of 6-31G(d,p). A most possible reaction pathway was brought up. According to this reaction pathway, the main products of cellulose pyrolysis in hydrogen plasma would be syngas, and few light hydrocarbons. CO mainly comes from the decomposition of aldehyde group, while H2 mainly comes from dehydrogenation processes. Active H in plasma are found to play a very important role in many reactions, and they can remarkably lower the energies needed for reactions.