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To reduce the pollution during the pyrolysis recovery of chlorine-containing plastic waste from different sources, effects of the interaction between different plastics and polyvinyl chloride (PVC) on the transformation of chlorine at low temperature were investigated by thermogravimetry-Fourier transform infrared (TG-FTIR) and fixed-bed pyrolysis experiments. Results showed that the proportions of chlorine in chars were all <0.04 %, indicating that almost all chlorine was released after pyrolysis. However, the chlorine forms in volatiles were significantly changed with mixing different plastics. HCl production was significantly inhibited due to the addition of other plastics, while the organic chlorinated compounds (OCCs) formation was promoted, which increased the distribution of chlorine in liquid products. During PVC pyrolysis, chlorine was mainly distributed in gas (93.09 %) in the form of HCl, only a small amount of aliphatic chlorides were generated and distributed in liquid (6.89 %). After the addition of polystyrene (PS), polyethylene (PE) and polyethylene terephthalate (PET), the chlorine distribution in liquid increased to 8.86 %, 11.98 % and 25.99 %, respectively. The formation of OCCs was significantly affected by the difference in thermochemical reaction characteristics of plastics. Specifically, the production of aromatic chlorides was promoted by PS, while the generation of aliphatic chlorides and aromatic chloroesters was significantly promoted by PE and PET, respectively. Therefore, the release form of chlorine could be significantly altered by the interaction between PVC and other waste plastics, which provides a reference for the regulation of chlorine-containing pollutants in the recovery and utilization of plastic waste. [Display omitted] ● Effect of different plastics on Cl release forms during PVC pyrolysis was revealed. ● Although Cl release ratio was not affected, HCl was promoted to transform to OCCs. ● Cl distributed in liquid increased to 8.86 % (PS), 11.98 % (PE) and 25.99 % (PET) during mixed pyrolysis, respectively. ● OCCs formation was closely related to the thermochemical reaction characteristics of plastics. [ABSTRACT FROM AUTHOR]

Highlights • Volatiles of pinewood torrefied at 250 °C (PW250) was reduced by only 4% (wt). • Devolatilization and heat transfer performances of PW250 were enhanced. • PW250 contained more cellulose and higher crystallinity degree. • Pyrolysis of pinewood (PW) followed D3 model while PW250 mainly followed D1 model. Abstract Torrefaction is a promising pretreatment technology for biomass thermochemical conversion. In this study, pinewood (PW) and PW250 (torrefied at 250 °C) were prepared for pyrolysis. Torrefaction was carried out in a fixed bed reactor and the pyrolysis was studied by thermogravimetric analyzer using six different heating rates. The results showed that the content of hemicellulose in biomass decreased while cellulose and lignin increased after torrefaction. Moreover, the C-O peaks of torrefied biomass was strengthened in FTIR spectrum and the crystallinity degree was enhanced according to XRD analysis. The performance of devolatilization and heat transfer were improved for PW250 while the volatiles only decreased by only 4%. Activation energy was calculated by three iso-conversion methods. It was found that the PW followed D3 diffusion model, while the PW250 followed D1 diffusion model and tended to higher order reaction model at high conversions. In addition, the thermodynamic parameters were compared. [ABSTRACT FROM AUTHOR]

The effects of water on the pyrolysis and gasification characteristics of coal water slurry (CWS) and pulverized coals with different ranks have been studied in the present work. Rapid pyrolysis characteristics (i.e. char yield, char structure evolution) of raw carbonaceous materials with varied water contents were investigated by using a high frequency furnace at 800–1200 °C. Moreover, gasification characteristics of the pyrolysis char were studied by using a thermogravimetric analyzer (TGA). The results indicate that at the pyrolysis temperature of 800 °C, the char yield of Wu-ran-cha-bu (WRCB) lignite slightly decreased with increasing the water content from 2.1 wt.% to 13.98 wt.%, while that of Yun-nan (YN) lignite showed a more significant decrease with increasing water content from 2.2 wt.% to 11.54 wt.%. This could be attributed to a higher coal reactivity of YN lignite than that of WRCB lignite. When the pyrolysis temperature was at or above 1000 °C, due to more significant in-situ coal-steam interactions, a lower char yield of both the pulverized lignites were observed with increasing water content from 2 wt.% to above 10 wt.%. CWS char presented a higher graphitization degree than pulverized coal char. The carbon microcrystalline structure factors (i.e. L 002 /d 002 value) of pyrolysis char increased with coal rank, which might reflect the variation trend of the graphitization degree from low rank coal to high rank coal. During the rapid heat treatment processes, the water evaporation and the in-situ steam-char gasification were favorable for void formation for both pulverized coals with high water contents and CWS. Notably, during the gasification processes of three different rank coals at 1200 °C, a more significant inhibition effect of residual ash on CWS char was observed compared to the pulverized parent coal char with high carbon conversion (x > 0.9). [ABSTRACT FROM AUTHOR]

Rapid pyrolysis characteristics of three different rank coals and two petroleum cokes were investigated using a drop tube furnace. Moreover, gasification characteristics of char samples were studied in an in-situ heating stage. The results showed that H 2 and CO were the main gaseous pyrolysis products of coal samples. The relative content of H 2 and CO increased with increasing pyrolysis temperature. The volume fraction of H 2 in syngas increased with increasing coal rank, whereas that of CO showed the contrary trend. Anthracite and petroleum cokes (Petcoke 1 and Petcoke 2) exhibited a great similarity in gas release characteristics. There was a maximum value for the specific surface area and graphitization degree of char samples with increasing pyrolysis temperature. The results of in-situ heating stage experiments indicated that the most of char particles reacted with CO 2 in the shrinking particle mode at the initial stage. Char samples of petcokes and anthracite were similar in slow consumption of particle skeleton during gasification. Interestingly, petcokes demonstrated particle migration, residual agglomeration, and rapid consumption at the later reaction stage. The variation trend of the area shrinkage ratio of char samples was well verified by the TGA results. [ABSTRACT FROM AUTHOR]

• Effects of pyrolysis temperature, residence time and atmosphere were investigated. • Release of AAEMs was associated with char structure evolution in rapid pyrolysis. • CO 2 promoted Na release in early stage and Ca and Mg release in late stage. The release law of alkali and alkaline earth metals (AAEMs) during coal pyrolysis is crucial for controlling scaling, corrosion and slagging in the utilization of high AAEMs coal. To approximate entrained-flow bed gasification process, a free-falling reactor was used for coal pyrolysis to study the release characteristics of AAEMs in nascent char. Effects of pyrolysis temperature, residence time and atmosphere were investigated. The cumulative release of Na, Ca and Mg at 1100 °C was 68.0%, 47.5% and 69.8%, respectively. As pyrolysis temperature increased from 900 °C to 1100 °C, the release of Na, Ca and Mg increased by 7.0 %, 3.5% and 5.3%, respectively. The cumulative release of AAEMs increased with the pyrolysis residence time, but the release rate decreased significantly in middle and late stages. The promoted thermal decomposition of functional groups by CO 2 resulted in a lower char yield. CO 2 promoted Na release in early stage and Ca and Mg release in late stage. Furthermore, release of AAEMs was associated with char structure evolution in rapid pyrolysis. The presence of CO 2 , high temperature and prolonged residence time led to enhanced particle fragmentation, increased surface cracks, and intensified thermal decomposition of functional groups, resulting in the migration of AAEMs in carbon matrix to char surface and the release of AAEMs organically bound to carbon matrix. [ABSTRACT FROM AUTHOR]

Coconut shell (CS) can be efficiently utilized by coupling hydrothermal carbonization (HTC) pretreatment with pyrolysis to meet the goal of global green development. In-situ Raman spectroscopy and thermogravimetric analyzer (TGA) were adopted to investigate the structural evolutions and reaction kinetics characteristics of hydrochar during the pyrolysis process. According to the results, the intensity of peak D and peak G in Raman spectrum decreased with increasing hydrothermal degree. Mild HTC treatment (≤200 °C) led to an increase in I D /I G , indicating the formation of large aromatic rings through small ring condensation. In contrast, severe HTC treatment (≥220 °C) reduced the I D /I G ratio, indicating an increased polycondensation of aromatic compounds and a higher degree of aromatization, resulting in larger molecules sizes. The spectral area below 400 °C reduced with increasing pyrolysis temperature due to the reduction of oxygen-containing functional groups and thermal radiation. Above 400 °C, the total area remains stable as the Raman spectrum scattering ability increases due to char formation and aromatization reactions. HTC-200 exhibited an increase in I D /I G from 0.54 to 0.72 and I D /I (Me + Ke + GL) from 0.58 to 0.68 with increasing pyrolysis temperatures. The activation energy during pyrolysis ranged from 194.50 to 238.34 kJ/mol for CS and 217.51–259.51 kJ/mol for HTC-200. Hydrothermal carbonization had a significant effect on pyrolysis behavior of hydrochar, as it was found that the mild HTC hydrochar followed D-type diffusion models when conversion rate was less than 0.65, and transitioned to higher reaction order in the late-stage of pyrolysis. [Display omitted] • Carbon structure in pyrolysis of coconut shell hydrochar is characterized in-situ. • A thorough evaluation of the pyrolysis kinetic was performed by model-free method. • Mild hydrochar changed from diffusion to higher reaction order model in pyrolysis. • Improved hydrochar properties showed high potential of HTC for alternative energy. [ABSTRACT FROM AUTHOR]

In this study, corn straw and rice husk were hydrothermally carbonized at 180 °C and 240 °C. The effect of hydrothermal carbonization on the biomass/hydrochar characteristics, fate of heavy metals such as As, Cr, Pb, Ti, Cd, Zn, Fe, Cu, and Ni, global reactivity of the pyrolysis and gasification of biomass and hydrochar were investigated in a thermogravimetric analyzer, followed by kinetic modeling and reactivity prediction. Results showed that hydrothermal carbonization temperature 180 °C is more suitable for producing solid fuel in terms of low heavy metals content. Higher hydrothermal carbonization temperature (240 °C) decreased O/C content and improved various characteristics of the hydrochar such as coalification degree, carbon content, higher heating value and the specific surface area. While hydrothermal carbonization conducted at lower temperature of 180 °C, was advantageous for obtaining higher energy yield efficiency and hydrochar yield. The gasification reactivity of hydrochar was more sensitive to the heating rate than the pyrolysis process. The activation energy (E a) of the pyrolysis process varied significantly with conversion, whereas the gasification activation energy changes were insignificant. Based on the reactivity prediction, the hydrothermal carbonization effect on corn straw and rice husk was almost similar. The hydrochar generated under severe hydrothermal carbonization temperature (240 °C) showed higher thermal stability during pyrolysis in comparison with gasification. Compared with the gasification of rice husk hydrochar, hydrochar gasification of corn straw had lower E a , hence requires less energy to produce syngas. The results of this research imply that biomass hydrochar is a suitable alternative option to produce pulverized solid fuel. [Display omitted] • Gasification and pyrolysis of Agriculture residues-derived hydrochars were performed. • HTC improved coalification degree and carbon content and higher heating value. • 180 °C provided a higher hydrochar and energy yields with lower HMs content. • Changes of E a variation during pyrolysis and gasification by HTC were compared. • Gasification reactivity of CS was more sensitive to HTC temperature than that of RH. [ABSTRACT FROM AUTHOR]

Here, we report a microwave-assisted catalytic pyrolysis method for directly upcycling low-density polyethylene (LDPE) into high-value H 2 and multi-walled carbon nanotubes (MWCNTs) over a porous ternary composite NiFeAl-T catalyst as a microwave absorber. Moreover, successive cycling tests further demonstrated the potential of continuously recycling plastic waste into H 2 -rich fuel and high-quality MWCNTs, ultimately achieving a high carbon yield of 70.8 wt%. [Display omitted] • The microwave-assisted catalytic pyrolysis is employed to directly upcycling LDPE into valuable H 2 and MWCNTs. • A porous ternary NiFeAl-T catalyst is synthesized using a polymer-assisted chemical solution method. • NiFeAl-450 catalyst with low calcination temperature and abundant porous structure achieves the best performance, with an H 2 yield of 60.5 mmol g L D P E - 1. Polyolefins, comprising the majority of disposable plastics, face challenges in catalytic upcycling due to their inert saturated C(sp3)-C(sp3) bonds. This work demonstrates microwave-assisted catalytic pyrolysis, demonstrating the direct conversion of low-density polyethylene (LDPE) into valuable H 2 and multi-walled carbon nanotubes (MWCNTs) over a porous ternary NiFeAl-T composite catalyst that serve as a microwave absorber. Optimizing the calcination temperature promoted metal nanoparticle dispersion, leading to enhanced catalytic performance. Specifically, lower temperatures favored metal–metal interactions, inducing porous architectures with superior microwave absorption and energy dissipation capabilities. This facilitated cleavage of C–C and C–H bonds in LDPE during microwave irradiation. An optimal NiFeAl-450 catalyst achieved a maximum H 2 yield of 60.5 mmol g L D P E - 1 , with an H 2 concentration of 85.1 vol% in gas products, alongside high-value MWCNTs. Moreover, successive recycling test displayed stable H 2 and MWCNTs yields from LDPE. This work elucidates a promising pathway for upcycling plastic waste via microwave-assisted catalytic pyrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combining wet torrefaction (WT) and pyrolysis for bioresource utilization. • Global reactivity was inhibited whereas local reactivity could be promoted by WT. • WT changed the structure and reactivity of softwood biochar significantly. • WT temperature had limited effect on AAEMs removal efficiency in biochar. • Relationship between X - T - t was determined by model-free method. This study investigated the effect of wet torrefaction (WT) on biochar property derived from softwood (PIW) and hardwood (POW) pyrolysis. The biochar gasification was performed in a thermogravimetric analyzer, followed by kinetic modelling. The biochar structure was analyzed, including inherent metals, pore structure and carbon structure. The results showed that WT affected reactivity and structure of PIW-derived biochar more than that of POW-derived biochar. The critical WT temperature determined the reactivity changes together with kinetic parameters. The WT affected the inorganic and organic component in biochar simultaneously. As results of WT, more than 70 and 50% ion-exchanged AAEMs in PIW-derived biochar and POW-derived biochar were removed. Nevertheless, the organic structure had essential effect on the gasification reactivity. More pronounced structure evolution of PIW-derived biochar was observed, including lower mesopore surface area, more graphite structure and small rings. This research provides new insights into the structure–reactivity correlation for biochar utilization. [ABSTRACT FROM AUTHOR]

• 300 °C torrefaction reduced gasification reactivity mainly in midterm and late stage. • Low-temperature torrefaction had slight effect on char gasification reactivity. • Gasification kinetics were analyzed based on the gas-solid reaction methods. • Pathways of char structure evolution changed after 800 °C pyrolysis. • Gasification reactivity decreased significantly for chars pyrolyzed after 800 °C. In this study, the effect of torrefaction on the gasification reactivity of chars from raw and torrefied biomass was investigated. Three torrefaction temperatures and four pyrolysis temperatures were taken into consideration. It was found that the severe torrefaction (300 °C) would reduce the char gasification reactivity by at least 19% according to the normalized gasification rate. Moreover, the reduction of gasification reactivity appeared after the midterm stage. The gasification reaction were further analyzed by nucleation/growth model and model-free method. The activation energy increased by ~80 kJ/mol with conversion, indicating an enhancement of the reaction resistance. Furthermore, 800 °C pyrolysis was found to be a turning point, beyond which the gasification reactivity reduced significantly. These reactivity changes were implied by the bio-char structure evolution and active alkali and alkaline earth metals (AAEMs) contents variations. The research results provide insights into the effect of torrefaction on biomass gasification. [ABSTRACT FROM AUTHOR]

• Effect of HTC on softwood and hardwood was compared. • Model-free kinetic prediction was performed. • Cellulose structure was activated firstly and then decomposed with HTC temperature. • Pyrolysis mechanism changed from diffusion model to reaction order model. • Pore structure changed more significantly for pinewood after HTC. Hydrothermal carbonization (HTC) pretreatment is an effective method to upgrade the low quality biomass properties. In this work, the pinewood (PIW) and poplar wood (POW) were selected to study the effect of HTC (180–240 °C) on woody biomass structure and reactivity. The results showed that the slight and moderate HTC can make the cellulose structure more ordered, while the severe HTC leaded to the decomposition of cellulose structure. The mesoporous specific surface area and pore volume increased with the HTC temperature, and the pore structure of PIW was more developed than that of POW. The slight HTC had little effect on cellulose structure and the diffusion effect played the dominant role. The severe HTC increased the relative content of lignin and the pyrolysis followed the high order reaction model. The model-free method was used to determine the relationship between T - β - X , and the specific temperature T HTC / T raw was calculated. The T HTC / T raw value of PIW and POW located in the range of 0.938–1.340 and 0.924–1.422, indicating the HTC pretreatment had great effect on POW pyrolysis reactivity. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) of carbonaceous waste is an important way of energy recovery to obtain renewable fuels. Here, cow manure (CM) and industrial sludge (IS), two kinds of wastes with different properties, were pretreated by HTC at different temperatures. The elements migration and the physicochemical structural characteristics of hydrochar during HTC were evaluated. The pyrolysis and gasification performance of hydrochar was also studied. The results show that HTC treatment can significantly increase the carbon content and reduce the oxygen content of feedstocks, so as to obtain clean solid fuels with high energy densification and realize energy recovery from low value wastes. The distribution of pyrolysis products of co-hydrochar is close to that of IS due to the interaction between the components of CM and IS. The co-hydrochar has good gasification reactivity, showing obvious synergistic effect. There is multi-component interaction in the process of co-HTC due to the difference of feedstocks composition and properties between CM and IS. The abundant aliphatic and oxidized aliphatic hydrocarbons in IS may inhibit the polycondensation and aromatization of cellulose and hemicellulose hydrolysates in CM due to hydrogen supply or steric hindrance. Therefore, co-hydrochar has carbon structure and fuel properties close to that of IS hydrochar. [Display omitted] [ABSTRACT FROM AUTHOR]

Organic additives, which are generally used as binders, play an important role in pelletization technology. However, they influence the pyrolysis performance of pellets. In this study, pea starch (PS) and carboxymethyl cellulose (CMC) were added to rice straw pellets (RS) to investigate their influence on the pyrolysis performance. The results demonstrated that when PS was added, the yield of bio-oil and the proportion of CO were higher. When the temperature was higher than 600 °C, the pyrolysis of PS was complete, and the pyrolysis behavior of the pellets with PS was similar to that of the straw pellets without binders. CMC had no obvious effects on the pyrolysis of RS, but introducing Na (in form of Na 2 CO 3 in the bio-char) had apparently positive synergistic effects on the gasification of bio-char. This study could serve as a reference for selecting binders and for the industrial gasification of pellets from biomass. • Rapid pyrolysis behavior of pellet with organic binders was investigated. • Addition of starch improved the yield of bio-oil below 600 °C. • Starch is not a satisfactory pellet binder for low temperature pyrolysis. • CMC introduced sodium into char in form of Na 2 CO 3. [ABSTRACT FROM AUTHOR]