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Abstract: The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000°C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N2 physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000°C. The carbon structure shrinkage and pore narrowing occurred above 600°C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000°C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900°C. The total surface area (S total) and micropore surface area (S micro) reached maximum values of 30.94 and 21.81m2/g at 900°C and decreased slightly at higher temperatures. The influence of heating rate on S total and S micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship. [Copyright &y& Elsevier]

Abstract: The gas release properties and char structural evolution during the pyrolysis of cotton stalk were investigated. The evolution characteristics of volatile products were examined by pyrolysis–Fourier transform infrared spectroscopy (FTIR)/thermal conductivity detection (TCD) analysis (Py–FTIR/TCD). The char chemical structure and physical characteristics were investigated by means of FTIR and N2 physisorption techniques. Evolution characteristics of the main volatile products were given. The evolution of CO2 was approximately 26°C earlier than that of CO. CH4 evolution covered over a wider temperature range of 300–600°C, with a maximum at 394°C. The amount of hydroxyl, aliphatic Cfinic Cn the char decreased significantly above 250°C. The aromatization process started at ≈350°C and continued to higher temperatures, leaving the char enriched with condensed aromatic ring systems. The BET surface area increased continually with increasing temperature to reach a maximum value of 4.68m2/g at 500°C and decreased at higher temperatures. The micropore volume showed a similar behavior to the surface area, while the mesopore volume and total pore volume always increased. [Copyright &y& Elsevier]

Abstract: Pyrolysis of agricultural residues (maize stalk, rice straw and cotton straw) was studied using a thermogravimetric (TG) analyzer and a laboratory scale fixed bed coupled with Fourier transform infrared (FTIR) analyzer. Pyrolysis characteristics of three materials were discussed. The characteristic parameters were determined for the main devolatilization step. Maize stalk showed the highest thermal reactivity, followed by cotton straw and rice straw. Their pyrolysis processes underwent three consecutive stages, corresponding to the evaporation of water, the formation of primary volatiles and the subsequent release of small molecular gases. In order to further study the pyrolysis mechanisms of agricultural wastes, the release of the main volatile and gaseous products were on-line detected by FTIR spectroscopy. The results showed that the major pyrolysis gases for the three materials were similar, including CO2, CO, methane, ethane, ethylene and some organics such as methanol, formaldehyde, formic acid and acetone. HCN was the major nitrogen containing product. At higher temperatures several small molecular gases, such as CO2, CO and methane, could still be monitored. [Copyright &y& Elsevier]

Pyrolysis technology is an effective way to realize the reduction and recycling of food waste (FW), but the generation of N-containing substances has a great impact on the quality of pyrolysis products and the environment. The present study mainly focused on the effect of typical component interaction on nitrogen conversion during the pyrolysis of FW, which was investigated by TG-FTIR, GC-MS, and DFT calculation. The experimental results show that during pyrolysis at 500 ℃, compared with soybean protein pyrolysis, co-pyrolysis of soybean protein with rice starch reduces the production of NH 3 and HCN in the pyrolysis gas and reduces the production of nitriles in the pyrolysis oil, while the production of N-containing heterocycles and amides in the pyrolysis oil increases. Soybean protein and rice starch promote the immobilization of N in pyrolysis oil through Maillard reaction and produce Maillard reaction products (MRPs). MRPs can be converted to nitrogenous heterocycles by ring formation reactions, and to amides by continued cleavage, which results in the increased yields of N-containing heterocycles and amides in the pyrolysis oil. • The effect of starch and protein interaction on nitrogen conversion was studied. • The N-containing heterocycles yields in oil during co-pyrolysis of starch and protein is significantly higher. • Maillard reaction products can be converted to N-containing heterocycles through ring-forming reactions. • MRPs can be converted to amides by lysis reaction. [ABSTRACT FROM AUTHOR]

Physical activation of biomass with H 2 O or CO 2 is an important method for producing activated carbon (AC). Activation of biomass with CO 2 or H 2 O follows varied mechanisms and the use of mixed CO 2 /H 2 O might show potential synergistic effects for creating pores. This was investigated by activation of lignin-derived biochar with H 2 O, CO 2 and their mixture. The results demonstrated that H 2 O as an activator was much more effective than CO 2 for generation of pores (804.1 m2g−1 versus 516.1 m2g−1in CO 2), especially mesopores (40% versus 14% in CO 2). This was achieved via enhancing cracking/gasification reactions of the biochar with H 2 O. The synergistic effect of CO 2 and H 2 O for activation of the lignin-derived biochar was insignificant as cracking/gasification reactions were not enhanced, leading to remarkably lower specific surface area of the AC (674.8 m2g−1) than that with H 2 O as an activator alone. Competitive adsorption of CO 2 and H 2 O existed and preferable adsorption of CO 2 hindered deoxygenation of the biochar with H 2 O. The in-situ IR characterization indicated that CO 2 presence suppressed decarbonylation reactions, retaining more oxygen species in form of C O, while it was the opposite in H 2 O. Additionally, activation with H 2 O formed numerous round-shape dents on surface of activated carbon, while the activation with CO 2 formed the characteristic round edges. The AC activated with H 2 O showed superior capability for adsorption of phenol than that activated with CO 2 or mixed H 2 O/CO 2. [Display omitted] • H 2 O is more effective than CO 2 for cracking, forming less activated carbon (AC). • Synergistic effect of CO 2 /H 2 O is insignificant as creating pores are not enhanced via cracking. • Competitive while preferable adsorption of CO 2 hinders activation with H 2 O. • CO 2 is not as active as H 2 O for cracking of C O in intermediates and for creating pores. • AC activated with H 2 O is superior for adsorbing phenol. [ABSTRACT FROM AUTHOR]

Understanding the complexity of thermal degradation characteristics, kinetic behavior, and thermodynamic parameters is pertinent for the efficient design and process optimization of large-scale conversion systems. Comparative assessment of pyrolysis characteristics and thermodynamic parameters of corn cobs (CC), peanut shells (PS) and sugarcane bagasse (SB) are investigated using high heating rates (100–1000 ℃/min) TGA results. Despite the effect of the heating rate increase on the degradation process of individual samples, increasing heating rates affect pyrolysis characteristics due to compositional differences. With increasing heating rates, the comprehensive pyrolysis index increased sporadically for CC (2.54–44.09 ×104%2/min2 ℃3) and PS (1.36–31.13 ×104%2/min2 ℃3), indicating easier release of volatiles at higher pyrolysis heating rates. The pyrolysis stability index (R w), which relates to thermal degradation stability, presented an increasing trend (CC>PS>SB) with a heating rate increase (≥106%). Kinetic parameters estimated using model-free methods showed that the activation energies of CC and PS were significantly lower than that of SB. Comparative evaluation of fractional conversions and kinetic parameters using traditional and modified parallel models showed that the double random pore model (DRPM) fitted the best for simulating the experimental results at higher heating rates than other models. The change in Gibbs free energy (ΔG) trend for PS and SB showed a deviation, suggesting reaction difficulties due to higher temperature demands. • High heating rates TGA analysis is performed for corncob, peanut shell and bagasse. • Corncob presented the best pyrolysis stability index with a heating rate increase. • Model-free methods and modified parallel models were used for kinetic studies. • The double random pore model is best suited for simulating the experiment results. • Thermodynamic parameters were comparatively studied from the kinetic results. [ABSTRACT FROM AUTHOR]

Highlights • Cokes generated at slow heating rates are imporous with smooth surface. • The radical concentration of cokes reaches highest at 600 °C then decreases rapidly. • Interactions among bio-oil components bring the O-functional groups into the coke. • The cokes are more condensed with bigger aromatic rings at high temperatures. Abstract Coke can be formed once the bio-oil was heated, even at very low temperatures, causing almost always serious problems in the upgrading and direct utilization of bio-oil. To minimize the negative impacts from coke formation, the key point is to fully understand the formation and evolution of coke during the thermal treatment of bio-oil. Thus, in this study, the cokes formed from the pyrolysis of bio-oil at different temperatures (300–800 °C) and heating rates were characterized by using a range of advanced analytical instruments. The evolution of cokes (e.g. morphology, elemental composition, chemical structure and concentration of radicals) with increasing temperature and heating rate was traced. The results show that the cokes generated at slow heating rates are imporous with smooth surface but porous at high temperatures and fast heating rates. The radical concentration of the cokes reaches the highest level at 600 °C, then decreases rapidly with further increasing temperature to form more free radicals, which promote the condensation reaction of aromatic systems to form larger ring structures of the coke at high temperatures, with lower H/C and O/C ratios. The O-containing functional groups could be brought into the coke via the interactions between light and heavy components of bio-oil. [ABSTRACT FROM AUTHOR]

Highlights • Less gases while more tar formed over acidic oxides than that over basic oxides. • Over CaO, the production of phenolic compounds was suppressed. • Coking was more significant over the basic oxides than that over the acidic oxides. • The tar from cellulose contributed more to coking than that from lignin. • Cellulose–derivatives and lignin–derivatives affect coke structures in varied ways. Abstract This study investigated the effects of the acidity/alkalinity of seven oxides (Al 2 O 3 , SiO 2 , ZnO, K 2 O, MgO, CaO, La 2 O 3) on the pyrolysis of poplar, cellulose and lignin. The results showed that the basic supports such as CaO and MgO promoted the formation of gaseous products. CO, CO 2 , and CH 4 were the main gaseous products in the pyrolysis of poplar, cellulose and lignin, and CO was formed first, followed by CO 2 and CH 4. Some H 2 was also formed from the dehydrogenation reactions over CaO with cellulose as the feedstock. The acidic oxides promoted the tar formation, while the basic oxides suppressed tar formation. The oxides like CaO could remarkably suppress the production of phenolic compounds. The coke formation over the basic oxides were also much more significant than that over the acidic oxides, and the tar from cellulose contributed more towards coking. The heating of the coke in inert gas released CO 2 , CO, H 2 , CH 4 via probably decarboxylation/decarbonylation, dehydrogenation and etc. The coke from the pyrolysis of lignin was much more stable. CaO and La 2 O 3 reacted with the CO 2 produced in pyrolysis and form the carbonates, while MgO could not. The TPO–MS characterization showed that the coke species were multiple types over CaO, and a single type over MgO. The cellulose–derivatives and the lignin–derivatives have distinct effects on the structural configuration of the coke. [ABSTRACT FROM AUTHOR]

To gain new insights into lignin pyrolysis, the synergistic development of carbon skeleton and pore networks in a wide temperature range of 200–800 °C was unraveled. The relative abundance of aromatic carbon structures increased exponentially with increasing temperature, as determined by 13C NMR deconvolution. Additionally, the g-factor type of radicals changed from O-centered (g-factor <2.0030) to C-centered (g-factor >2.0040) radicals. The evolution of the char macromolecules structure from disorder to order was principally characterized by a decrease in aromatic spacing (d 002 , 3.36→3.37 Å) an d an increase in stacking degree (L c , 7.89→8.67 Å) and aromaticity (f a , 75.19%→96.94%). f a h a s a strong negative linear correlation with d 002 (R 2 = 0.965). Ternary quadratic polynomials can relate specific surface area, total pore volume, and relative carbon content to the pore fractal dimension. The hypothesized chemical reaction networks and synergistic development of carbon skeleton and pore networks are essential for lignin effective valorization by a pyrolysis-based biorefinery strategies. [Display omitted] • The synergistic development of carbon skeleton and pore network was unraveled. • f a has a strong negative linear correlation with d 002. • Developed ternary quadratic polynomials link fractal dimension to SSA , TPV and C daf. • SSA and TPV were negatively correlated with d 002 , but positively correlated with f a. [ABSTRACT FROM AUTHOR]

A study was carried out in both inert and CO 2 atmosphere to investigate the interaction mechanism of K 2 CO 3 with graphite and coal char during the catalytic gasification of coal char. The formation of K 2 CO 3 catalytic precursors was identified by using series of different techniques. The results obtained in an inert atmosphere show that the interaction between K 2 CO 3 and carbon readily took place at low temperature. For the K 2 CO 3 loaded graphite, the intermediate of C n K clusters formed by the interactions of K 2 CO 3 with carbon prevented the evaporation of K at low temperature. At temperatures above 800 °C, however, the C n K clusters were unstable, and decomposed to release K through vaporization. On the contrary, for the K 2 CO 3 loaded demineralized coal char, due to the presence of oxygen groups, K was tightly bonded to carbon during heating, forming a complex precursor containing O and K with high thermal stability. The reaction pathway of carbon-K 2 CO 3 interactions in an inert atmosphere are proposed for both char and graphite. The results of DRIFTs experiment suggest that CO 2 is chemisorbed by the K- catalytic precursors during CO 2 gasification to form potassium phenolate species and a covalently bound carbonate group (dimethyl carbonate). It is believed that these species act as active intermediates in the gasification process. [ABSTRACT FROM AUTHOR]

Waste fan blade would explosively grow with the life time of wind power machine is ended. Developing new low carbon-emission method to treat waste fan blade and achieving high resource recovery is promising. In this work, a novel photothermal pyrolysis method was developed and firstly applied to treat waste fan blade. A typical waste fan blade was cut, crushed and screened to separate base material and reinforcing fiber, whose mass ratio was 74.36:25.64. The base material was pyrolyzed at varied conditions of pyrolysis temperature, heating rate, gas flow rate respectively. The study showed that bisphenol A was significantly acquired in tars (relative contents were commonly over 40%), and its generation can be promoted by increasing pyrolysis temperature, heating rate and gas flow rare. The generation mechanism of bisphenol A was revealed during photothermal pyrolysis process: The main chain of 2,2-bis(4-glycidyloxyphenyl)propane resin in base material undergone random or chain cracking reaction to produce bisphenol A rigid skeleton, phenoxy, alkane, hydroxyl and other active groups. Bisphenol A rigid skeleton was the precursor of bisphenol A. Bisphenol A was formed after receiving hydrogen atoms, accompanied by the formation of tetrahydrofuran, 4,4-(propane-2,2-diyl)bis(methoxybenzene) and other substances. Bisphenol A undergone decomposition via secondary reactions, and it was mainly decomposed into phenol and 4-isopropylphenol, 4-isopropylphenol was then dehydrogenated to produce 4-isopropenylphenol. • Waste fan blade was firstly pyrolyzed using novel photothermal pyrolysis system. • High yield and relative content of bisphenol A was detected in pyrolytic oil. • Generation mechanism of bisphenol A during photothermal pyrolysis was revealed. [ABSTRACT FROM AUTHOR]

Pyrolysis has been demonstrated to be promising for the conversion of coal slime (CS) to fuels and high value-added chemicals, which could achieve resource utilization of CS. For the in-depth understanding of the pyrolysis mechanism of CS, in this study, the pyrolysis kinetics and pyrolytic products distribution were investigated by TG-FTIR and Py-GC/MS and compared with those of raw coal (RC). The results demonstrated that the pyrolysis of CS comprises three reaction stages, with the decomposition of volatiles as the main stage (180–680 °C). Using the master plot method, the pyrolysis kinetic mechanism of RC and CS were predicted to be f(α) = (1 – α)4.6 and f(α) = (1 – α)5.4, respectively. The enrichment of inorganic minerals significantly increased the order of the CS pyrolysis reaction, indicating that minerals play an important role in the pyrolysis chemical reaction. Compared to that of RC, the alkene content of CS pyrolysis products decreased significantly, while the contents of CO 2 and aromatics increased, indicating that the minerals in CS promote the polymerization and cyclization of alkene, as well as the formation of macrocyclic aromatic hydrocarbons in CS tar. Those consequences also determined that inorganic matter in CS considerably affects pyrolysis, which in turn affects the whole pyrolysis process and tar quality. Therefore, in this study, theoretical and practical guidance on the efficient thermochemical conversion and utilization of CS is provided. • RC and CS were comparatively pyrolized. • Minerals in ash enhance kinetics resulting in higher reaction order. • CS rich in AAEMs promoted the formation of phenol and alcohol. • Tar precursors prefer to form larger PAHs by high ash content from CS. [ABSTRACT FROM AUTHOR]

The accumulation of food waste brings several challenges to the economy and environment, its pyrolysis technology has received extensive attention. The present investigation mainly focused on the evolution of char structure and bio-oil composition during the pyrolysis process of the typical food waste, which was characterized by FT-IR, Raman, UV, and GC/MS. The experimental results show that the bio-oil has the highest yield at 400–600 ℃ and remains basically unchanged (around 40%), and decreases apparently at 700 ℃ due to the secondary thermal cracking and reforming. With the increase of temperature, the cracking of macromolecular organic matter in the food waste becomes more intense, resulting in the yield of bio-char gradually decreasing from 34.90% to 23.54% in the range of 400–700 ℃. The ratio of small aromatic ring systems to large aromatic systems (I (VR+VL+GR) /I D) in the bio-chars increases apparently with temperature, and the amounts of aromatic rings in bio-oil also increase gradually. The content and relative percentage of N-compounds are the largest in bio-oil, and the content of it reaches the maximum value at 500 ℃, while the changes in its relative percentage are slightly different, which decreases from 33.57% to 24.15% at 400–600 ℃, and then increases apparent to 40.63% at 700 ℃. Hydrocarbons are also one of the main components in bio-oil, their relative percentage decreases from 17.70% to 2.40% in the range of 400–700 ℃. In addition, Carboxylic acid, alcohols, esters, ketones, saccharides, phenols, and other substances are also contained in bio-oil, and its content has different changing trends with temperature. [Display omitted] • The maximum yields of bio-char and bio-oil are observed at 400 ℃. • The increase of temperature is beneficial to improve the aromatization degree of bio-oil. • The content of large aromatic ring system on the surface of char decreases with temperature. • N-compounds, hydrocarbons, and carboxylic acid are the main component in bio-oils. [ABSTRACT FROM AUTHOR]

Abstract: Recently the oxyfuel combustion of coal chars having a significant impact on reducing greenhouse emissions is gradually paid extensive attention by many researchers, but only a limited number of studies have focused on its reaction mechanism. Therefore, it is important to investigate the combustion mechanism of coal chars in oxyfuel atmosphere, while random pore model (RPM) is usually recommended as a model for the comprehensive simulation of coal chars reaction. In this context, the values of structure parameter ψ in RPM were calculated based on pore structural character at various carbon conversions, and show interesting evolution phenomena keeping constant at the preceding reaction stage before increasing remarkably at the end of stage. Consequently, a new model, two-stage random pore model (TRPM), was applied to the coal chars combustion in oxyfuel atmosphere. Compared to other models such as RPM, the Struis model (Model I), the Liu model (Model II), and fractal random pore model (FRPM), it shows that two-stage random pore model was more accurate to describe coal chars combustion under oxyfuel conditions, especially at higher carbon conversions. In addition, the oxyfuel combustion process of coal chars at 1323K and 1373K were analyzed. [Copyright &y& Elsevier]

• Lignin tar components were detailedly characterized via FT-ICR MS measurement. • Experimental results and theoretical calculation were significantly combined. • The formation of two typical OPAH and SPAH during lignin pyrolysis were revealed. OPAHs and SPAHs are highly genotoxic and would largely be formed during the thermal conversion of lignin. Herein, the distribution of OPAHs and SPAHs in lignin pyrolytic tar at different temperatures is elaborated with ESI (-) FT-ICR MS and GC–MS, and the formation routes of two typical OPAH and SPAH are deeply explored via DFT. It is found that most of oxygen-containing compounds convert to phenols and their homologues such as guaiacol (a typical precursor of OPAHs) with the temperature increased. The tar prepared at high temperature contains disulfide, thiophene and thiophene homologues, which are typical precursors of SPAHs. FT-ICR-MS strongly suggests that molecular mass of OPAHs and SPAHs compounds mainly concentrates between 200 Da and 400 Da with carbon atom number from 5 to 25 and DBE from 4 to 15. Higher temperature significantly promotes deoxygenation reaction since weighted average carbon atom number and DBE of molecules increase 28.4 % and 12.9 %, while the corresponding weighted average oxygen atom number decreases from 7.21 to 5.96 with temperature rising from 500 ℃ to 900 ℃. Incorporating with DFT calculation, the pathways of OPAHs and SPAHs during lignin pyrolysis at high temperature are concluded: Guaiacol converts to 1-methoxynaphthalene via 4 methylation reactions, and butene firstly generates thiophene and then converts to methyl-benzothiophene. Among the reactions above, benzene ring and thiophene ring generation steps possess the highest energy barriers (436.74 kJ/mol and 446.33 kJ/mol), further illustrating higher temperature promotes the formation of OPAHs and SPAHs. [ABSTRACT FROM AUTHOR]

• Higher partial pressure of N 2 suppressed the decomposition of limonene during pyrolysis process. • Shorter residence time in pyrolysis suppressed the decomposition of limonene at high pressures. • The decomposition of limonene can be divided into (1) breaking initially, then cyclizing and (2) direct aromatization. Pyrolysis of waste tires is a promising way to cost-efficiently produce high value limonene, but the reaction characteristics and mechanisms of limonene under pressurized pyrolysis are unclear to date. This study aims to investigate the effects of residence time and pressure on limonene conversion during waste tire pyrolysis. The yields of limonene increased significantly with a decrease of residence time during high pressure pyrolysis. At a pressure of 1.0 MPa, the yield of limonene increases by 20 % as the residence time decreases from 60 s to 15 s, while limonene concentration in TDO (tire-derived-oil) increases to 35.10 wt.%. On the other hand, the pressure has a positive effect on limonene production. The yield of limonene at 1.0 MPa is approximately 1.7 times larger than that of 0.1 MPa at a residence time of 30 s. Based on Spearman correlation analysis, the mechanisms of limonene conversion at pressurized pyrolysis were studied. Longer residence time means limonene undergoes more secondary reactions to be degraded to aromatic rings such as xylene and trimethylbenzene. However, the higher N 2 partial pressure during pyrolysis suppressed the decomposition of limonene, producing TDO with high limonene concentration. Therefore, methods of reducing residence time and increasing pressures promote yield and concentration of limonene in the aspect of inhibiting decomposition, which provides references for improvement in limonene production by waste tire pyrolysis. [ABSTRACT FROM AUTHOR]