The influence of pyrolysis conditions on the subsequent gasification of lignocellulosic chars

Prune pit chars prepared by pyrolysis at heating rates of 1 and 15°C/min to 500, 700 and 900°C were subsequently gasified by exposure to CO₂ at 900°C for various lengths of time. Gasification rate was found to be dependent on the conditions during pyrolysis: slow heating below 500°C and prolonged exposure to high temperatures (~900°C) during pyrolysis in an inert atmosphere lead to lower rate gasification. Despite differences in gasification rate, the pore structure developed for a given mass loss due to the gasification reactions was apparently independent of the char preparation conditions. Pore volume in the gasified char (expressed on an absolute basis) passed through a maximum at 40–50% burnoff, apparently due to mass loss from the exterior of the particles.     

PRODUCTION OF BIOFUEL FROM SOFT SHELL OF PISTACHIO (PISTACIA VERA L.)

Soft shell of pistachio (Pistacia vera L.) pyrolysis experiments were performed in a fixed-bed reactor to produce bio-oil. The effects of temperature, heating rate, and sweep gas (N₂) flow rates on the yields and compositions of products were investigated. Pyrolysis runs were performed using reactor temperatures between 350° and 500°C with heating rates of 15° and 50°C/min. Nitrogen flow rates varied between 50 and 200 cm³/min and mean particle size was 0.8 mm. The maximum bio-oil yield of 33.18% was obtained in a nitrogen atmosphere with nitrogen flow rate of 150 cm³/min and at 450°C pyrolysis temperature with a heating rate of 50°C/min.The elemental analysis and gross heating value of the bio-oil were determined, and then the chemical composition of the bio-oil was investigated using chromatographic and spectroscopic techniques. The chemical characterization has shown that the bio-oil obtained from soft shell of pistachio can be used as a renewable fuel and chemical feedstock.     

Spray pyrolysis synthesis of mesoporous TiO<Subscript>2</Subscript> microspheres and their post modification for improved photocatalytic activity

Mesoporous TiO₂ microspheres were prepared by spray pyrolysis for photocatalysis. Post modification of TiO₂ by heat treatment was performed to optimize its photocatalytic performance. First, spherical TiO₂ particles with mesoporous structure were synthesized at pyrolysis temperatures of 500, 600, and 700 °C. After characterization by XRD, SEM, and N₂ adsorption, a sample prepared at 500 °C was found to possess desirable properties for photocatalytic performance through post-modification. In methylene blue degradation, mesoporous TiO₂ microspheres synthesized at 500 °C outperformed other microspheres. Furthermore, samples obtained by spray pyrolysis at 500 °C were calcined at various temperatures as a post-modification process. The sample calcined at 350 °C showed improved photocatalytic activity due to optimal anatase crystallinity and surface area.     

Effect of pyrolysis pressure and heating rate on radiata pine char structure and apparent gasification reactivity

The knowledge of biomass char gasification kinetics has considerable importance in the design of advanced biomass gasifiers, some of which operate at high pressure. The char gasification kinetics themselves are influenced by char structure. In this study, the effects of pyrolysis pressure and heating rate on the char structure were investigated using scanning electron microscopy (SEM) analysis, digital cinematography, and surface area analysis. Char samples were prepared at pressures between 1 and 20 bar, temperatures ranging from 800 to 1000 °C, and heating rates between 20 and 500 °C/s. Our results indicate that pyrolysis conditions have a notable impact on the biomass char morphology. Pyrolysis pressure, in particular, was found to influence the size and the shape of char particles while high heating rates led to plastic deformation of particles (i.e. melting) resulting in smooth surfaces and large cavities. The global gasification reactivities of char samples were also determined using thermogravimetric analysis (TGA) technique. Char reactivities were found to increase with increasing pyrolysis heating rates and decreasing pyrolysis pressure.     

Bio-oil from olive oil industry wastes: Pyrolysis of olive residue under different conditions

Olive residues were pyrolysed in a fixed bed reactor under different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and steam velocity on the product yields and liquid product composition with a heating rate of 7 °C/min. Final temperature range studied was between 400 and 700 °C and the highest liquid product yield was obtained at 500 °C. Liquid product yield increased significantly under nitrogen and steam atmospheres. Liquid products obtained under the most suitable conditions were characterised by elemental analyses, FT-IR and ¹H-NMR. In addition, column chromatography was employed and the yields of the sub-fractions were calculated. Gas chromatography was achieved on n-pentane fractions. The results show that it is possible to obtain liquid products similar to petroleum from olive residue if the pyrolysis conditions are chosen accordingly.     

Bio-oil from olive oil industry wastes: Pyrolysis of olive residue under different conditions

Olive residues were pyrolysed in a fixed bed reactor under different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and steam velocity on the product yields and liquid product composition with a heating rate of 7 °C/min. Final temperature range studied was between 400 and 700 °C and the highest liquid product yield was obtained at 500 °C. Liquid product yield increased significantly under nitrogen and steam atmospheres. Liquid products obtained under the most suitable conditions were characterised by elemental analyses, FT-IR and ¹H-NMR. In addition, column chromatography was employed and the yields of the sub-fractions were calculated. Gas chromatography was achieved on n-pentane fractions. The results show that it is possible to obtain liquid products similar to petroleum from olive residue if the pyrolysis conditions are chosen accordingly.     

Pyrolysis of coal and iron oxides mixtures. 2. Reduction of iron oxides

The reduction of iron oxides during the pyrolysis of blends of coal and iron oxides on a laboratory scale, has been studied. The pyrolysis of blends of bituminous coal and 30 wt% of magnetite or hematite has been studied by thermogravimetry and analysis of gases, using a heating rate of 3.2 K min^?1. The state of iron in ferrocoke has been established by X-ray diffraction. A primary reduction by hydrogen and carbon monoxide of the hematite has been observed at between 400 °C and 500 °C, but hidden in thermogravimetric measurements by primary volatilization of the coal. At ≈600 °C magnetite is progressively reduced to wustite and then to iron. This reduction starts a little earlier if the heating rate is slow and the coal rank is low and progresses more rapidly when using hematite. Except for higher heating rates in the coal-magnetite blends, the reduction is complete at 1000 °C. The reductants are H₂ and CO, with production of H₂O and CO₂. When the temperature is increased the reduction by CO becomes of increasing importance, being mainly produced from the coke by the Boudouard reaction. The consumption of coke for the reduction of iron oxides is therefore more important at higher temperatures. Lignite is clearly a better reducing agent than the other coals, because of larger quantities of CO produced from the start of its pyrolysis, and the good reactivity of its char towards CO₂ and H₂O.     

Pyrolysis and thermo‐oxidative degradation of polycyclopentadiene

Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500–950°C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E_a) was obtained from an Arrhenius‐type plot using the concentration of the product ethylene (C₂) at different pyrolysis temperatures and the value was found to be 138 kJ mol⁻¹. Thermo‐oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700°C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635–641, 2000     

Value-added products from waste: Slow pyrolysis of used polyethylene-lined paper coffee cup waste

The objectives of this study were to examine how to recycle cup waste efficiently and effectively and to determine if cup waste can be converted into liquid, solid, and gas value-added products by slow pyrolysis. The characteristics and potential utilizations of the pyrolysis products were investigated. The study included the effects of temperature, heating rate, and different feedstocks. The yield of pyrolysis oil derived from cup waste increased from 42% at 400°C to 47% at 600°C, while the yield of char decreased from 26% at 400°C to approximately 20% at 600°C. Acetic acid and levoglucosan were identified as the main components of the pyrolysis oil. The char obtained at 500°C was physically activated at 900°C for 3 h with CO₂. The adsorption capacity of the activated char was investigated with model compounds, such as methyl orange, methylene blue, ibuprofen, and acetaminophen. The results showed that the adsorption capacity of the activated char was similar to that of commercial activated carbon produced from peat. The higher heating value of the produced gas stream calculated at 400°C was 19.59 MJ/Nm³. Also, conventional slow pyrolysis (CSP) and microwave-assisted pyrolysis (MAP) technologies were compared to determine the differences in terms of products yields, composition and characteristics of the pyrolysis oil, and their potential applications. The CSP yields higher liquid products than MAP. Also, the pyrolysis oil obtained from the CSP had significantly more levoglucosan and acetic acid compared to that of the MAP.     

Mathematical modelling of slow pyrolysis of segregated solid wastes in a packed-bed pyrolyser

Waste segregation is being explored as one of the potential effective ways for waste management, where wastes are separated for either recycling or energy recovery. In this paper, three segregated wastes, contaminated waste wood, cardboard and waste textile are pyrolysed in a slow-heating packed-bed reactor for the purpose of solid, liquid and gas recovery. The effect of final temperature was investigated and product yields and compositions were measured. Mathematical modelling was employed to simulate the heat, mass transfer and kinetic processes inside the reactor. Both a parallel reaction model and a function group model were used to predict the product yields as well as their compositions. Char yield of 21–34%, tar 34–46% and gas 23–43% were obtained. It is found that packed-bed pyrolysis produces 30–100% more char compared to standard TGA tests and the local heating rate across the packed-bed reactor differs remarkably from the programmed wall-heating rate and varies greatly in both time and space. Mathematical modelling suggests that wood has higher tar cracking ability than cardboard and textile wastes during pyrolysis, and the effects of mineral contents in the fuel need to be explored. CO₂, CO, tar and water are the main released species during the major stage of the pyrolysis processes which occurs between 250 and 450 °C, whereas noticeable quantity of hydrogen and light hydrocarbons is observed only at higher temperature levels and at the final stage.     

In-Situ Carbon Content Adjustment in Polysilazane Derived Amorphous SiCN Bulk Ceramics

The present paper is concerned with the in-situ carbon content adjustment in amorphous bulk silicon carbonitride (SiCN) ceramic matrices prepared by the polymer to ceramic transformation of cross-linked and compacted poly(hydridomethyl)silazane powders. Heat treatment in inert (Ar) or reactive atmosphere (ammonia, or mixed Ar/NH₃ with different volume ratio of ammonia) was used for carbon content adjustment. Isothermal annealing steps in Ar and/or mixed atmospheres at various intermediate temperatures were also included into the pyrolysis schedule (i) to adjust the final carbon content, (ii) to control outgassing of low molecular reaction products like methane or hydrogen from the matrix during polysilazane decomposition and thus (iii) to avoid cracking of the pressed polymer powders. Optimal annealing temperature for carbon content adjustment was found to be in the range between 500 and 550°C. Increasing NH₃ contents from 10 to 50 vol% in the pyrolysis atmosphere as well as enhanced transient annealing temperature and time promote carbon reduction. In contrast intermediate isothermal annealing in Ar at 500 up to 600°C results in pronounced formation of Si–C bonds and in increased carbon contents after the final pyrolysis process. Depending on the pyrolysis conditions, flawless bulk specimens with carbon contents ranging from 0·3 up to 16·2 wt% were obtained. Different possible chemical reactions are considered to explain the generation of the particular Si(C)N compositions found. ©     

Pyrolysis of polymethylsilsesquioxane

Changes of the composition and structure of various samples of polymethylsilsesquioxane (PMSQ), pyrolyzed at different temperatures under flowing nitrogen, were investigated using thermogravimetric analysis, Raman and Fourier transform infrared spectroscopies, X‐ray photoelectron spectroscopy, elemental analysis, scanning electron microscopy, and transmission electron microscopy. The center of the Si2p peak could be used to estimate the extent of the pyrolysis of PMSQ. Two temperature domains correspond to important changes in the chemical composition of PMSQ. The former (T_p < 500°C) is related to the conversion from a regular structure to an irregular structure and the latter (T_p > 500°C) is associated with the organic– ceramic conversion. During the latter pyrolysis, flowing of the molten bulk occurred and then a final solid structure was obtained. The main product of PMSQ, pyrolyzed at 900°C, is silica, as well as some amount of silicon oxycarbide and traces of amorphous carbon. Based on the above analysis and observation, a conversion process from polysilsesquioxane to a ceramic is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1077–1086, 2002     

Synthesis and thermal performance of polymer precursor for ZrC ceramic

A novel ZrC preceramic precursor (PZC) was compounded via liquid phase chemical reaction without any organic solvent choosing ZrOCl₂·8H₂O and polyvinyl alcohol as Zr source and C source, respectively. The composition and structure of ZrC precursor were analysed through XRD, FT-IR, XPS and SEM. The results showed both Zr-O-C bonds and Zr-O bonds existed in the precursor. The results observed by SEM showed that many irregular particles were generated, whose particle sizes were mainly in the range of 0.2–3 μm. In addition, particle aggregation can be easily observed. Besides, the thermal property and pyrolysis process of PZC were studied. In accordance with XRD, the initial temperature of the earliest detection of ZrC in pyrolysis products of PZC was 1300 °C. Monoclinic ZrO₂ and tetragonal ZrO₂ can be observed at this temperature as well. Ulteriorly, when the pyrolysis temperature was risen up to 1500 °C, only ZrC ceramic can be found.     

The effect of inorganic additives on the formation,composition, and combustion of cellulosic char

At temperature above 300°C the glycosyl units of cellulose are simultaneously depolymerized to a tar and decomposed to a char by evolution of H₂O, CO, and CO₂. When the glycosyl units are depleted, a stable char is formed containing about 30% aliphatic and 70% aromatic components. The aliphatic component is formed first, but on further heating is converted to polycyclic aromatic structures. The chars formed at lower temperatures are more combustible because the aliphatic component of the char is highly pyrophoric and is oxidized almost at the same temperature at which it is formed (～360°C). The aromatic component, however, is less reactive and is oxidized at ～520°C. Consequently, the chars formed at higher temperatures are less combustible. It has been shown that (NH₄)₂HPO₄, which is a well-known flame retardant and smoldering inhibitor, lowers the pyrolysis temperature and increases the char yield by accelerating the decomposition reactions. This affects the composition of the intermediate chars but the final products have about the same composition irrespective of additives. (NH₄)₂HPO₄ also lowers the rate of oxidation of the aromatic component and the corresponding heat release. NaCl, which is an enhancer of smoldering combustion, has a slight stabilizing effect on pyrolysis of cellulose. It lowers the oxidation temperature of the aromatic component and dramatically increases its rate. The corresponding heat release is also increased due to complete oxidation to CO₂. The rate of oxidation calculated from the dynamic thermal analysis data is more than tripled by NaCl and significantly reduced by (NH₄)₂HPO₄.     

Coal pyrolysis at high temperatures and pressures

At high temperatures (s> 1100°C), pyrolysis of coal plays an increasingly important role in the overall coal conversion process. This Paper presents experimental data on the extent of pyrolysis of coal at 800–1600°C. In addition, the effects of the following parameters are examined: gaseous environment (N₂, CO₂ and H₂O), pressure (1–20 atm), particle size, moisture content and type of coal. Previous data on some of these parameters are non-existent. A unique TGA apparatus constructed for this work allows high heating rates (10²–10³°Cs^?1) due to the direct radiation heating. In all the gaseous environments, a plateau in per cent pyrolysis is noticed at 1200–1400°C followed by a sharp increase in the amount of pyrolysis as the temperature is raised. This is found consistent with the three-stage mechanism proposed for the evolution of volatiles. In CO₂ and steam environments, there is slightly less pyrolysis than in pure nitrogen, while considerably more pyrolysis is noted for predried coal and for smaller particle sizes. The results suggest a strong influence of secondary volatile reactions on the extent of pyrolysis. Pyrolysis in steam at 800–900°C shows an increase with pressure similar to that reported for pyrolysis in hydrogen. Finally, gasification rates of chars immediately following the pyrolysis are found to be much higher than those of chars prepared separately and then reacted. These results suggest morphological rearrangements and crystallization effects.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Up-scalable preparation of nano zirconium carbide powder in liquid polymeric precursor and its pyrolysis mechanism

Nano size ZrC powder was prepared by liquid polymeric precursor method. Zirconium n-butoxide (Zr(OⁿBu)₄) and benzoylacetone (BA) were mixed directly with different molar ratios to synthesize transparent liquid zirconium carbide single-source precursors. The carbon content in the precursor could be changed by adding different amount of BA. X-ray pure ZrC was obtained when the molar ratio of BA/Zr(OⁿBu)₄ was 4.6:1. The viscosity of the precursor was very low (<8 mPa s) without the addition of solvents. Zirconium carbide powders were fabricated by the pyrolysis at 800 °C in argon and subsequent heating at various temperatures in vacuum for carbothermal reduction reaction. The pyrolysis behavior, phase composition and transformation, and microstructure of the as-fabricated ZrC powders were analyzed. The gases of CH₄, CO and CO₂ released due to decomposition and evaporation of the organic component and transformation from ZrO₂ to ZrC during pyrolysis resulted in total 60–70% mass loss. The average grain size of the synthesized X-ray pure ZrC powders was less than 30 nm. Meanwhile, the pyrolysis mechanism of nano zirconium carbide powder was deduced.     

Evaporation of pyrolysis oil: Product distribution and residue char analysis

The evaporation of pyrolysis oil was studied at varying heating rates (～1–10⁶°C/min) with surrounding temperatures up to 850°C. A total product distribution (gas, vapor, and char) was measured using two atomizers with different droplet sizes. It was shown that with very high heating rates (～10⁶°C/min) the amount of char was significantly lowered (～8%, carbon basis) compared to the maximum amount, which was produced at low heating rates using a TGA (～30%, carbon basis; heating rate 1°C/min). The char formation takes place in the 100–350°C liquid temperature range due to polymerization reactions of compounds in the pyrolysis oil. All pyrolysis oil fractions (whole oil, pyrolytic lignin, glucose and aqueous rich/lean phase) showed charring behavior. The pyrolysis oil chars age when subjected to elevated temperatures (≥700°C), show similar reactivity toward combustion and steam gasification compared with chars produced during fast pyrolysis of solid biomass. However, the structure is totally different where the pyrolysis oil char is very light and fluffy. To use the produced char in conversion processes (energy or syngas production), it will have to be anchored to a carrier. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Polymer derived silicon oxycarbide ceramic monoliths: Microstructure development and associated materials properties

Polymer derived SiOC and SiCN ceramics (PDCs) are interesting candidates for additive manufacturing techniques to develop micro sized ceramics with the highest precision. PDCs are obtained by the pyrolysis of crosslinked polymer precursors at elevated temperatures. Within this work, we are investigating PDC SiOC ceramic monoliths synthesized from liquid polysiloxane precursor crosslinked with divinylbenzene for fabrication of conductive electromechanical devices. Microstructure of the final ceramics was found to be greatly influenced by the pyrolysis temperature. Crystallization in SiOC ceramics starts above 1200?°C due to the onset of carbothermal reduction leading to the formation of SiC and SiO₂ rich phases. Microstructural characterisation using ex-situ X-ray diffraction, FTIR, Raman spectra and microscopy imaging confirms the formation of nano crystalline SiC ceramics at 1400?°C. The electrical and mechanical properties of the ceramics are found to be significantly influenced by the phase separation with samples becoming more electrically conducting but with reduced strength at 1400?°C. A maximum electrical conductivity of 10¹ S?cm^?1 is observed for the 1400?°C samples due to enhancement in the ordering of the free carbon network. Mechanical testing using the ball on 3 balls (B3B) method revealed a characteristic flexural strength of 922?MPa for 1000?°C amorphous samples and at a higher pyrolysis temperature, materials become weaker with reduced strength.