Effects Of Pyrolysis Atmosphere Research Articles

Suppression of polycyclic aromatic hydrocarbon formation during pyrolytic production of lignin-based biochar via nitrogen and boron co-doping

Polycyclic aromatic hydrocarbons are toxic byproducts of biochar production. The effects of pyrolysis atmosphere (i.e., N2 and CO2) and temperature (i.e., 300–900 °C) and element doping (i.e., N, B, O, and S) on the production of sixteen high priority polycyclic aromatic hydrocarbons in lignin-based biochar was investigated. N2 atmosphere at 300 °C produced the highest total polycyclic aromatic hydrocarbon content (1698 ± 50 ng/g). Polycyclic aromatic hydrocarbon formation decreased with increase in temperature (31 ± 15 ng/g at 900 °C). CO2 atmosphere significantly decreased yield of polycyclic aromatic hydrocarbons. The effects of heteroatom doping on polycyclic aromatic hydrocarbon formation were investigated for the first time in the pyrolysis synthesis of lignin-based biochar. N-, B-, O, N–B-, and N–S-doping of biochar reduced polycyclic aromatic hydrocarbon formation by 90, 85, 87, 97, and 89%, respectively. Results bring new insights into the role of heteroatom-doping and pyrolysis conditions in controlling polycyclic aromatic hydrocarbon formation in biochars.

Effect of Pyrolysis Atmosphere on Syngas from Waste Biomasses

Effect of Pyrolysis Atmosphere on Syngas from Waste Biomasses

Effect of Pyrolysis Atmosphere on the Gasification of Waste Tire Char

The aim of the study is to assess the influence of the atmosphere during pyrolysis on the course of CO2 gasification of a tire waste char. Two approaches were used: the pyrolysis step was carried out in an inert atmosphere of argon (I) or in an atmosphere of carbon dioxide (II). The examinations were carried out in non-isothermal conditions using a Rubotherm DynTherm thermobalance in the temperature range of 20–1100 °C and three heating rates: 5, 10 and 15 K/min. Based on the results of the gasification examinations, the TG (Thermogravimetry) and DTG (Derivative Thermogravimetry) curves were developed and the kinetic parameters were calculated using the KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. Additionally, the CO2 gasification of tire chars reaction order (n), was evaluated, and the kinetic parameters were calculated with the use of Coats and Redfern method. Tire waste char obtained in an argon atmosphere was characterized by lower reactivity, which was reflected in shift of conversion and DTG curves to higher temperatures and higher mean values of activation energy. A variability of activation energy values with the progress of the reaction was observed. For char obtained in an argon atmosphere, the activation energy varied in the range of 191.1–277.2 kJ/mol and, for a char obtained in an atmosphere of CO2, in the range of 148.0–284.8 kJ/mol. The highest activation energy values were observed at the beginning of the gasification process and the lowest for the conversion degree 0.5–0.7.

Sulfur and Nitrogen Release From Co-Pyrolysis of Coal and Biomass Under Oxidative and Non-Oxidative Conditions

Abstract This is an investigation on the effects of pyrolysis atmosphere on the conversion of biomass/coal blends to chars and volatile matter, and on the release of sulfur and nitrogen to the gas phase. Pulverized corn straw and lignite coal were co-pyrolyzed either in an inert carrier gas (N2) or in oxidative gases consisting of 3–7% O2 and 13–17% CO2 in a balance of 80% N2. The process occurred at temperatures in the range of 300–900 °C, under 1 atm, and lasted for 20 min. The results showed that the solid-phase conversion of coal/biomass blends ranged from 30 to 60%, increasing with increasing temperature. Increasing oxygen concentration under oxidative atmospheres promoted the solid-phase conversion at 500–900 °C, more than under the inert atmosphere, but had no discernible effect at lower temperatures (300–400 °C). Under the inert atmosphere, the co-pyrolysis of coal and biomass exhibited a synergistic effect, which promoted the transformation of solid feedstock into the gas phase or tar. To the contrary, under the oxidative atmospheres, the co-pyrolysis inhibited the evolution of volatile matter. Sulfur compounds, COS and SO2, were mainly released at temperatures in the range of 300–700 °C. Higher amounts of SO2 were released under the oxidative atmosphere, and the co-pyrolysis of coal and biomass promoted the release of COS. As for the transformation and release of nitrogen, NH3 and HCN were mainly released in the temperature range of 600–900 °C and more HCN was converted into NH3 under inert atmospheres. The effects of the oxygen content in the atmosphere on conventional gas species (CO, CH4, C2H6, and HCl) released from coal/biomass blends were also recorded.

Effect of Pyrolysis Atmosphere and Electrolyte pH on the Oxygen Reduction Activity, Stability and Spectroscopic Signature of FeNx Moieties in Fe-N-C Catalysts

Two Fe-N-C catalysts comprising only atomically-dispersed FeNx moieties were prepared, differing only in the fact that the second catalyst (Fe0.5-NH3) was obtained by subjecting the first one (Fe0.5-Ar) to a short pyrolysis in ammonia. While the initial ORR activity in acid medium in rotating disk electrode is similar for both catalysts, the activity in alkaline medium is significantly higher for Fe0.5-NH3. Time-resolved Fe dissolution reveals a circa 10 times enhanced Fe leaching rate in acidic electrolyte for Fe0.5-NH3 relative to Fe0.5-Ar. Furthermore, for the former, the leaching rate is strongly enhanced when the electrochemical potential is in the range 0.75–0.3 V vs. RHE. This may explain the reduced stability of ammonia-pyrolyzed Fe-N-C catalysts in operating PEMFCs. In alkaline medium in contrast, Fe0.5-NH3 is more active and more stable, with minimized Fe leaching during electrochemical operation in load-cycling mode. Operando X-ray absorption spectroscopy measurements in alkaline electrolyte reveals similar trends of the XANES and EXAFS spectra as a function of the electrochemical potential for both catalysts, but the magnitude of change is much less for Fe0.5-NH3, as evidenced by a Δμ analysis. This is interpreted as a lower average oxidation state of FeNx moieties in Fe0.5-NH3 at open circuit potential.

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

The influence of a CO2 or N2-based atmosphere on the porous structure and microstructure of the chars obtained from the slow devolatilization (10°C/min) of two coals of different rank (Semi-Anthracite (SA) and High Volatile Bituminous type C (HVBC)) and different particle size distribution was studied. Physicochemical characterization (ultimate and proximate analysis), structural and morphological characterization by Raman spectroscopy, FE-SEM, BET surface area, and volume and diameter microporous by CO2 adsorption measurements were carried out for all the chars. It was found that the kinetic parameters, the physicochemical properties, and reactivity of the chars are different, depending on the pyrolysis atmosphere. It was also determined that for char from SA coal with particle size greater than 0.7mm, the BET surface area increases when the atmosphere is enriched in CO2. This effect appears to be promoted by the interaction of different processes such as intraparticle side reactions (softening, nucleation and coalescence of bubbles, crosslinking, among others), differences in the thermal diffusivity of N2 and CO2, and the reactive effects of the latter. Additionally, tests of oxidative reactivity of chars showed that the char formed in a CO2 atmosphere is more reactive than that formed in N2. With the results of Raman analysis and kinetic parameters quantified, it was concluded that the reaction atmosphere determined the degree of ordering achieved by the char structure and that the thermo-diffusive properties of the reaction atmosphere promoted structural differences in the char even at low heating rates.

The effect of pyrolysis atmosphere on bio-oil yields and structure

ABSTRACTA food industry waste, almond shell, was pyrolyzed under three different environment static, nitrogen, and steam to produce bio-oil and its derivatives. The oil yield obtained at pyrolysis temperature of 600°C was 24.23% in a static atmosphere, whereas it increased to 27.25% and 33.05% in nitrogen and steam atmospheres, respectively. The bio-oil obtained under steam atmosphere is very efficient due to the production of high liquid and gas yields. Moreover, co-feeding steam during the pyrolysis altered the bio-oil structure by increasing the aliphatics and reducing the asphaltenes. Moreover, steam treatment also increases H/C and heating value of bio-oils. According to the obtained results, steam pyrolysis is an alternative option for future applications in refineries.

Effects of Pyrolysis Atmosphere and Temperature on Coal Char Characteristics and Gasification Reactivity

AbstractCoal chars are usually produced under complex atmospheres in industrial production. However, most of the research about char characteristics and gasification reactivity uses the coal char samples prepared under an inert atmosphere. In this study, the influences of the pyrolysis atmosphere and temperature on coal char characteristics and gasification reactivity were investigated. A Shanxi bituminous coal was pyrolyzed in a bubbling fluidized bed to produce char samples. A mixture of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) was used as simulated pyrolysis gas (SPG). The coal was pyrolyzed in the SPG and N2 atmospheres, respectively. SEM, Raman spectroscopy, and FTIR spectroscopy were used to study the influences of the pyrolysis atmosphere and temperature on the coal char characteristics. The char–H2O and char–CO2 gasification reactivities were measured by using a modified thermogravimetric analysis (TGA) system. The experimental results indicate that the SPG atmosphere has no obvious influence on the coal char morphology, but it has significant influences on the carbon structures and surface chemical groups. The SPG char samples have lower gasification reactivity. The disproportionation reaction of CO, the decomposition reaction of CH4, and the loss of oxygen‐containing structures induced by H2 lead to a higher‐ordered degree of char, and the graphite generated from the disproportionation reaction and the decomposition reaction can decrease the specific surface area of the coal char. These two reasons result in the lower gasification reactivity of SPG char.

A study on the porosity development for biomass based carbonaceous materials

This study deals with the structural and morphological changes occurring during pyrolysis and activation steps for the production of porous carbons from an arid-land plant Euphorbia rigida. A fixed-bed retort was used for slow pyrolysis and for further activation processes. Effect of pyrolysis atmosphere was examined at 550 °C and char yields were calculated to be 22.6, 23.1 and 17.5% under static, nitrogen and steam atmospheres respectively. Solid product obtained under static atmosphere was then impregnated with different chemicals (HCl, KOH, K2CO3, H2SO4, H3PO4, NaOH, ZnCl2) and a second thermal treatment was applied under different activation atmospheres. It was observed that the impregnation material, impregnation ratio and activation technique showed a strong influence on the yield and porous texture of the resulting carbons. On the basis of BET surface areas, most effective chemical agent was selected as K2CO3 giving a specific surface area of 1079 m2/g and microspore volume of 0.443 cm3/g. The physical–chemical properties of the chars and activated carbons were investigated by proximate and ultimate analyses, FT-IR, SEM, EDX, XRD and iodine number. In addition, surface functional groups were classified by Boehm titration method. Results suggest that chemical activation of E. rigida char produces valuable activated carbons under proper conditions.

Atmosphere influence in the pyrolysis of poly[(alkylamino)borazine] for the production of BN fibers

The effect of pyrolysis atmosphere on products deriving from poly[(alkylamino)borazine] was studied. Pyrolysis in NH 3 resulted in BN with almost no carbon content while in Ar led to BNC materials. The crystallinity of the sample obtained in NH 3 was higher than that in Ar. BN fibers with almost no carbon impurity were obtained in NH 3 and then in Ar, possessing good oxidation resistance and low dielectric constant. The superior properties of BN fibers allow them to be promising in high-temperature, microwave-transparent applications.

Synthesis and characterization of SiC and SiC/Si3N4 composite nano powders from waste material

In the present work, nano silicon carbide has been prepared by pyrolysis of rice-husk ashes as starting materials. Three rice-husk ash samples having different features were used. The first was coarse-grained rice husk ash (fired husk as is), the second was fine rice husk ash (hand-ground), while the third was ball milled one. Effect of ball milling of the starting ashes for 6h on the formation of nano SiC was investigated and compared with those prepared without milling. The particle sizes of the prepared SiC materials were affected by the milling process. The particle sizes of the obtained nano SiC from ball milled staring materials were smaller than those prepared without milling. The pyrolysis conditions, i.e. the temperature and atmosphere were optimized. The optimum firing temperature to obtain well crystalline nano SiC was 1550°C. The effect of pyrolysis atmosphere, i.e. argon, vacuum and nitrogen was also demonstrated. The pyrolysis in argon exhibited lower efficiency on the formation of SiC than vacuum; while the pyrolysis in nitrogen atmosphere led to formation of SiC/Si3N4 nanocomposite.

Effect of Pyrolysis Atmosphere on Ferroelectric Properties of Bi3.25La0.75Ti3O12 Films Prepared by Sol-Gel Method

The effect of pyrolysis atmosphere is investigated for Bi3.25La0.75 Ti3 O12 (BLT) films prepared on Pt/TiO2/SiO2/p-Si(100) substrates by sol-gel processes. The pyrolysis is carried out at 400° C for 20 min under air or O2 atmosphere and the successive anneal is performed at 700° C for 30 min under O2 atmosphere. The pyrolysis under O2 is enough for complete removal of organic species, however after pyrolysis under air, carbon and hydrogen atomic species as organic fragment are partly remained in the film. This incomplete removal of organic fragments affects the grain growth and cause more defects in the film or between interfaces during the annealing for the crystallization of BLT film. The growth direction and grain size of the BLT film is revealed to affect ferroelectric properties. The remanent polarization Pr for the BLT films of pyrolysis in O2 and air are measured to be 18.85 μC/cm2 and 12.56 μC/cm2, respectively. The defects degrade the fatigue property dramatically for the film of pyrolysis in air. It can be concluded that the pyrolysis is an important procedure to control ferroelectric properties.

Optimization of sulfur retention in ash when cocombusting high sulfur fuels and biomass fuels in a small pilot scale fluidized bed

This study deals with the structural and morphological changes occurring during pyrolysis and activation steps for the production of porous carbons from an arid-land plant Euphorbia rigida. A fixed-bed retort was used for slow pyrolysis and for further activation processes. Effect of pyrolysis atmosphere was examined at 550 °C and char yields were calculated to be 22.6, 23.1 and 17.5% under static, nitrogen and steam atmospheres respectively. Solid product obtained under static atmosphere was then impregnated with different chemicals (HCl, KOH, K2CO3, H2SO4, H3PO4, NaOH, ZnCl2) and a second thermal treatment was applied under different activation atmospheres. It was observed that the impregnation material, impregnation ratio and activation technique showed a strong influence on the yield and porous texture of the resulting carbons. On the basis of BET surface areas, most effective chemical agent was selected as K2CO3 giving a specific surface area of 1079 m2/g and microspore volume of 0.443 cm3/g. The physical–chemical properties of the chars and activated carbons were investigated by proximate and ultimate analyses, FT-IR, SEM, EDX, XRD and iodine number. In addition, surface functional groups were classified by Boehm titration method. Results suggest that chemical activation of E. rigida char produces valuable activated carbons under proper conditions.