Pyrolysis of textile wastes: I. Kinetics and yields

Thermal behavior of textile waste was studied by thermogravimetry at different heating rates and also by semi-batch pyrolysis. It was shown that the onset temperature of mass loss is within 104–156 °C and the final reaction temperature is within 423–500 °C. The average mass loss is 89.5%. There are three DTG peaks located at the temperature ranges of 135–309, 276–394 and 374–500 °C, respectively. The first two might be associated with either with decomposition of the hemicellulose and cellulose or with different processes of cellulose decomposition. The third peak is possibly associated to a synthetic polymer. At a temperature of 460 °C, the expected amount of volatiles of this waste is within 85–89%. The kinetic parameters of the individual degradation processes were determined by using a parallel model. Their dependence on the heating rate was also established. The pyrolysis rate is considered as the sum of the three reaction rates. The pyrolysis in a batch reactor at 700 °C and nitrogen flow of 60 ml/min produces 72 wt.% of oil, 13.5 wt.% of gas and 12.5 wt.% of char. The kinetic parameters of the first peak do not vary with heating rate, while those of the second and the third peak increase and decrease, respectively, with an increasing heating rate, proving the existence of complex reaction mechanisms for both cases.     

The fate of As, Pb, Cd, Cr and Mn in a coal during pyrolysis

Transformation of As, Pb, Cd, Cr, and Mn in Chinese Datong coal during pyrolysis was studied. Experiments were carried out in a fixed-bed quartz reactor with a heating rate of 20 °C min⁻¹. Effects of the final temperature (300–1000 °C) and atmosphere (N₂ and H₂ at 0.1 MPa) were examined. Chemical form distribution of the elements in the coal and coal-derived chars (obtained at 1000 °C under N₂ and H₂) was investigated. As, Pb, Cr, Cd, and Mn in the coal and the chars were classified into five chemical forms (ion exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and in the residue) by a sequential dissolution method. Results show that As, Pb, and Cd are more volatile and tend to enrich in the volatile phase in the pyrolysis. Cr and Mn are relative non-volatile and tend to enrich in the solid phase. H₂ atmosphere promotes the release of the elements. The elements in all the five chemical forms undergo transformation in pyrolysis, and As, Pb, Cr and Cd show similar behavior.     

Changes in commercial wood charcoals by thermal treatments

As a continuation of a recent study of commercial wood charcoals as far as their potential production of carbon adsorbents is concerned, we have studied the influence of the final heating temperature (T) as carbonization variable in the range 250–1000 °C on the yield and on the characteristics of granular chars prepared from two very different charcoals: a holm-oak charcoal manufactured by partial combustion in a charcoal kiln and an eucalyptus charcoal industrially manufactured in a continuous furnace. Our study also includes the changes produced in both charcoals heated at 250 °C in air for 24 h, and their influences on the adsorption of water vapour at 25 °C. The samples were characterized by thermogravimetry, chemical analyses, Fourier transform infrared spectroscopy, densimetric measurements and mercury porosimetry. T affects the char yield, the chemical composition and the porosity of each char series differently. In particular, the total open pore volumes (to helium) of the starting charcoals, 0.475 and 1.044 cm³ g⁻¹, increase to 0.872 and 1.293 cm³ g⁻¹ heating up to 1000 and 500 °C, respectively. The changes by carbonization are mainly due to devolatilization; moreover, a moderate structural shrinkage occurs heating the eucalyptus charcoal at T > 500 °C. Concerning the air treatments, the yields do not present a significant difference; carbonyl groups are formed and the resulting pore structures depend on the starting charcoals. Water adsorption is larger for the eucalyptus carbons (approximately type V isotherms) than for the holm-oak carbons (type II isotherms).     

Theoretical prediction of product distribution of the pyrolysis of high density polyethylene

The main objective of this work is the formulation and development of a model that predicts the product distribution obtained in the pyrolysis of polyethylene. In order to do this a mechanistic model has been developed based on a radical mechanism. This model uses a small number of elementary kinetic steps, including initiation, β-scission, H-abstraction, aromatization and radical combination. The mechanism allows the prediction of the compounds obtained during the pyrolysis. Given the great number of species considered, the simulation of the pyrolysis process requires the solution of complex systems of ordinary differential equations. The results obtained have been validated with experimental results obtained in a free fall installation in which the pyrolysis process has been studied at different temperatures (500–1000 °C) and residence times (0.52–2.07 s).     

Headspace Solid‐Phase Microextraction (HS‐SPME) for the Determination of Benzene,Toluene, Ethylbenzene,and Xylenes (BTEX) in Foundry Molding Sand

Abstract

The use of headspace solid‐phase microextraction (HS‐SPME) to determine benzene, toluene, ethylbenzene, and xylenes (BTEX) in foundry molding sand, specifically a “green sand” (clay‐bonded sand) was investigated. The BTEX extraction was conducted using a 75 µM Carboxen‐polydimethylsiloxane (CAR‐PDMS) fiber, which was suspended above 10 g of sample. The SPME fiber was desorbed in a gas chromatograph injector port (280°C for 1 min) and the analytes were characterized by mass spectrometry. The effects of extraction time and temperature, water content, and clay and bituminous coal percentage on HS‐SPME of BTEX were investigated. Because green sands contain bentonite clay and carbonaceous material such as crushed bituminous coal, a matrix effect was observed. The detection limits for BTEX were determined to be ≤0.18 ng g^?1 of green sand.     

Flash pyrolysis of Silopi asphaltite in a free-fall reactor under vacuum

Flash pyrolysis experiments on asphaltite samples were performed in a free-fall reactor under vacuum to determine the effects of pyrolysis temperature, feed rate and particle size. Maximum liquid yield of 13 wt.% was obtained in free-fall reactor under vacuum when the pyrolysis temperature was 700 °C, feed rate was 0.4 g min⁻¹ and particle sizes were between 0.075 and 0.250 mm. The liquid products obtained at various pyrolysis conditions were analyzed by gas chromatography/mass spectrometer (GC/MS) and liquid products were classified as following: C5–C10, C11–C15, C16–C20 and C20+. The amount of saturated hydrocarbons decreased while the amount of unsaturated hydrocarbons increased with increase of temperature. While percent of C5–C10 unsaturated hydrocarbons continuously increased with increase of temperature, the percent of C11–C15 unsaturated hydrocarbons increased up to 750 °C and then started to diminish. Functional group analysis of solid residue was carried out using Fourier transform infrared spectrometry (FT-IR). The proximate analysis of solid residue indicated that percent of fixed carbon and ash increased with temperature.     

Zirconia-supported phosphotungstic acid as catalyst for alkylation of phenol with benzyl alcohol

The liquid-phase alkylation of phenol with benzyl alcohol was carried out using zirconia-supported phosphotungstic acid (PTA) as catalyst. The catalysts with different PTA loadings (5–20 wt.% calcined at 750 °C) and calcination temperature (15 wt.% calcined from 650 to 850 °C) were prepared and characterized by ³¹P MAS NMR and FT-IR pyridine adsorption spectroscopy. The catalyst with optimum PTA loading (15%) and calcination temperature (750 °C) was prepared in different solvents. ³¹P MAS NMR spectra of the catalysts showed two types of phosphorous species, one is the Keggin unit and the other is the decomposition product of PTA and the relative amount of each depends on PTA loading, calcination temperature and the solvent used for the catalyst preparation. The catalysts with 15% PTA on zirconia calcined at 750 °C showed the highest Brönsted acidity. At 130 °C and phenol/benzyl alcohol molar ratio of 2 (time, 1 h), the most active catalyst, 15% PTA calcined at 750 °C gave 98% benzyl alcohol conversion with 83% benzyl phenol selectivity.     

Production of liquid fuels and chemicals from pyrolysis of Bangladeshi bicycle/rickshaw tire wastes

Tire wastes in the form of used bicycle/rickshaw tires available in Bangladesh were pyrolyzed in a fixed-bed fire-tube heating reactor under different pyrolysis conditions to determine the role of final temperature, sweeping gas flow rate and feed size on the product yields and liquid product composition. Final temperature range studied was between 375 and 575 °C and the highest liquid product yield was obtained at 475 °C. Liquid products obtained under the most suitable conditions were characterized by elemental analyses, FT-IR, ¹H NMR and GC–MS techniques. The results show that it is possible to obtain liquid products that are comparable to petroleum fuels and valuable chemical feedstock from bicycle/rickshaw tire wastes if the pyrolysis conditions are chosen accordingly.     

Measurement of glass transition temperature by mechanical (DMTA), thermal (DSC and MDSC), water diffusion and density methods: A comparison study

Glass transition measured by DMTA from the change in slope in storage modulus was 55 °C, which was 10.5 °C lower than the value measured by tan δ peak. Initial glass transition measured by DSC, increased exponentially and reached a constant value of 55 °C at or higher heating rate of 30 °C/min. Transition temperature, measured by MDSC, remained constant up to heating rate 15 °C/min and then decreased. The glass transition values determined from reversible heat flow was 60 °C. The break in diffusivity and density (i.e. volume) was observed at 50 °C below the glass transition temperature measured by thermal and mechanical methods.     

Sinterability enhancement in semicokes obtained by controlled pyrolysis of a petroleum residue

Self-sintering semicokes were prepared by pyrolysis of an aromatic petroleum residue at 460–480 °C and pressures of 0.1–1.0 MPa. The evolution of gases and thermoplasticity from resultant semicokes were monitored by TGA and TMA, respectively. Sintering behaviour of the semicokes is extremely sensitive to pyrolysis conditions which determine contents of volatile matter and binder phase. Semicokes produced at 1.0 MPa have high volatile contents with excessive plasticity. Changes of temperature and soak time, used to reduce volatile matter contents induce reductions to the plasticity and sintering. A lower pyrolysis pressure has a similar effect. Although the operational window is narrow, heat-treated compacts (2500 °C) can be made with high density (1.9 g cm⁻³) and bending strengths >75 MPa. Using high-temperature pyrolysis (460 °C) with a post-treatment at 350–400 °C eliminates light components, without decreasing sintering properties. Compacts from these powders also exhibit high density (1.9 g cm⁻³) with higher bending strengths >90 MPa, comparable or superior to mesocarbon microbeads (MCMB) obtained from the same precursor.     

Thermogravimetric analysis of aluminised E-glass fibre reinforced unsaturated polyester composites

Novel aluminised E-glass fibre reinforced unsaturated polyester composites, originally formulated for enhanced thermal and electrical shielding properties were evaluated in terms of their thermal performance. The thermal degradation of these specimens was analysed using a thermogravimetric analyser (TGA). The samples were heated from ambient temperature to 500 °C at a heating rate of 20 °C/min. All specimens were decomposed under dry nitrogen (N₂) at a flow rate of 40 ml/min to yield gases and solid char. Aluminised E-glass composites were compared alongside the unmetallised E-glass and unreinforced composite. The major weight loss occurred between 200 and 400 °C. The unreinforced polyester had a maximum weight loss, 1.25%/°C, occurring at 360 °C. For the aluminised and unmetallised E-glass composites, the maximum rate of weight loss was 0.34 and 0.55%/°C, respectively. Experimental results show the degradation of the aluminised E-glass composites obtained from TGA tests is higher compared to those of unmetallised E-glass fibre and unreinforced polyester composite. This improvement is correlated to the aluminium coating.     

Thermal solid–solid interactions and physicochemical properties of NiO/Fe2O3 system doped with K2O

The effects of calcination temperature and doping with K₂O on solid–solid interactions and physicochemical properties of NiO/Fe₂O₃ system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K₂O were 0.62, 1.23, 2.44 and 4.26. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000 °C. The catalytic activity was determined for each solid in H₂O₂ decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe₂O₃ phases detected for all solids calcined at 300 and 500 °C. Fe₂O₃ interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe₂O₄ phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K₂O-doping stimulates the ferrite formation to an extent proportional to its amount added. The stimulation effect of potassium was evidenced by following up the change in the peak height of certain diffraction lines characteristic NiO, Fe₂O₃, NiFe₂O₄ phases located at “d” spacing 2.08, 2.69 and 2.95 Å, respectively. The change of peak height of the diffraction lines at 2.95 Å as a function of firing temperature of pure and doped mixed solids enabled the calculation of the activation energy (ΔE) of the ferrite formation. The computed ΔE values were 120, 80, 49, 36 and 25 kJ mol⁻¹ for pure and variously doped solids, respectively. The decrease in ΔE value of NiFe₂O₄ formation as a function of dopant added was not only attributed to an effective increase in the mobility of reacting cations but also to the formation of potassium ferrite. The calcination temperature and doping with K₂O much affected the catalytic activity of the system under investigation.     

Characterization of surface interaction of inorganic fillers with silane coupling agents

Coupling agent (CA) can not only help filler achieve better dispersion in polymer matrix, but also improve the roughness of the composite with good rigidity at the same time. In this paper, the interaction of silane coupling agents with inorganic fillers (in our case are Mg(OH)₂ and CaCO₃) were studied by pyrolysis gas chromatography (PGC), as well as Fourier transform infrared spectroscopy. By two-step pyrolysis (first at 250 °C, then at 600 °C), physisorbed and chemisorbed silane on fillers can be distinguished. The bonded silane cannot be flash vaporized at 250 °C, it results in new peaks different from that of silane in pyrograms at 600 °C. The chemisorbed amount of silane increases with time and temperature and finally reaches a plateau. The result showed that PGC was an effective analytical tool to prove the existence of interaction between inorganic filler and CA.     

Liquid phase mononitration of chlorobenzene over WOx/ZrO2: A study of catalyst and reaction parameters

To study the effect of W concentration and activation temperature of the catalysts a series of WO_x/ZrO₂ samples with varying concentration of W (10–25 wt.%) were prepared and activated at 650/750 °C. XRD of sample shows 15 wt.% W stabilizes the tetragonal phase of zirconia up to 750 °C. Above and less than 15 wt.% shows peaks corresponding to monoclinic WO₃ and monoclinic ZrO₂, respectively. Further, the tungsten modification stabilizes the specific surface area of ZrO₂. There is an increase in the surface area observed up to 15 wt.% W, which declines on further increase in the concentration. The NH₃ TPD confirms the presence of acid sites with varying strength from the broad desorption profile. The 15 wt.% W and activated at 750 °C shows maximum acidity. The results of the nitration reaction of chlorobezene imply the 15 wt.% W and activation at 750 °C shows maximum activity. Not only yield, a better para-selectivity is also achieved with WO_x/ZrO₂ samples. Effect of activation temperature, W concentration and reaction parameters such as reaction temperature, reaction time, the presence of solvent and solvent free medium on activity and selectivity are studied in details.     

Effects of heat on physicochemical properties of whey protein-stabilised emulsions

The effect of heating has been studied for whey protein-stabilised oil-in-water emulsions (25.0% (w/w) soybean oil, 3.0% (w/w) whey protein isolate, pH 7.0). These emulsions were heated between 55 and 95 °C as a function of time and the effect on particle size distribution, adsorbed protein amount, protein conformation and rheological properties was determined. Heating the emulsions as a function of temperature for 25 min resulted in an increase of the mean diameter (d₃₂) and shear viscosity with a maximum at 75 °C. Heating of the emulsions at different temperatures as a function of time in all cases resulted in a curve with a maximum for d₃₂. A maximum increase of d₃₂ was observed after about 45 min at 75 °C and after 6–8 min at 90 °C. Similar trends were observed with viscosity measurements. Confocal scanning laser micrographs showed that after 8 min of heating at 90 °C large, loose aggregates of oil droplets were formed, while after 20 min of heating compact aggregates of two or three emulsion droplets remained. An increase of the adsorbed amount of protein was found with increasing heating temperature. Plateau values were reached after 10 min of heating at 75 °C and after 5 min of heating at 90 °C. Based on these results we concluded that in the whole process of aggregation of whey protein-stabilised emulsions an essential role is played by the non-adsorbed protein fraction, that the kinetics of the aggregation of whey protein-stabilised emulsions follow similar trends as those for heated whey protein solutions and that upon prolonged heating rearrangements take place leading to deaggregation of initially formed large, loose aggregates of emulsion droplets into smaller, more compact ones.     

Phase transformation on heating of an aged cement paste

The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 (2002) 187]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating (ΔM versus the final mass). The sorbed water (EV), escaping at 110 °C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1–2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 °C into C₂S and C₃S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 °C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation ΔM(700–800 °C) increased highly with ageing.     

Non-discriminating flash pyrolysis and thermochemolysis of heavily contaminated sediments from the Hamilton Harbor (Canada)

Analytical pyrolysis of sediments contaminated with pollutants of medium to high molecular weights (up to approximately 500 Da) is very challenging when using conventional pyrolysis systems due to discrimination of high molecular weight analytes. In the framework of this contribution, non-discriminating pyrolysis and thermochemolysis using rapid heating in a Silcosteel capillary were applied to study organic pollutants in heavily contaminated sediments taken from the Hamilton Harbor. The novel pyrolysis approach, requiring very small amounts of sample, turned out to be very useful as a rapid screening method, e.g. for risk assessment studies, proving superior to commonly used solvent extraction. Main pollutants in the sediments under study included aromatic hydrocarbons, chiefly originating from coal tar and petroleum. Polycyclic aromatic hydrocarbons (PAHs) beyond six-rings, including coronene and truxene, could be detected. Sequential tetramethyl ammonium hydroxide-induced thermochemolysis performed at 500 and 750 degrees C enabled the differentiation between organic pollutants sorbed onto the sediment matrix on the one hand, and structural moieties of the condensed polymeric humic sediment matrix along with bound residues on the other hand. Thermochemolysis at 500 degrees C removed sorbates quantitatively, leaving only bare polymeric humic matrix. Significant PAH source indicators provided evidence that the lipidic fraction sorbed onto the sediments originated from PAHs formed chiefly in coal combustion processes. The polymeric humic organic matter network of the less polluted sediment was mainly of petrogenic origin, whereas black carbon, kerogen, etc. contributed to the organic carbon of the heavily polluted sediment. Thermochemolysis at 500 degrees C was also used to study fatty acid profiles of the sediments. The fatty acid methyl ester patterns obtained for the two sites under study differed significantly, with strong indications that microbial attenuation of the pollutants at the heavily polluted site 2 was strongly suppressed.     

Thermochemical conversion of cellulose in polar solvent (sulfolane) into levoglucosan and other low molecular-weight substances

Pyrolysis of cellulose in sulfolane, an aprotic polar solvent, was conducted at the temperature between 200 and 330 °C. Sulfolane was used as a good solvent for levoglucosan, the major anhydromonosaccharide formed from cellulose pyrolysis, for prevention of the polymerization reaction. Cellulose was observed completely decomposed into soluble products in sulfolane within 3, 10, 60 and 480 min at 330, 280, 240 and 200 °C, respectively. The soluble products had molecular weights less than 500 after acetylation (GPC analysis) and similar product composition to that from cellulose pyrolysis under nitrogen (levoglucosan, levoglucosenone, furfural and 5-hydroxymethylfurfural by HPLC analysis). Pyrolysis of cellulose in polar solvent, which can solubilize anhydromonosaccharides, is proposed as a method for selective formation of levoglucosan and other low molecular-weight (MW) substances. As well, the cellulose pyrolysis in sulfolane did not suffer from carbonization reactions (microscopic and IR spectroscopic analysis) as did cellulose pyrolysis under nitrogen or in dioctyl phthalate (a poor solvent for levoglucosan) which gave brown/black solids. The residues obtained from the pyrolysis in sulfolane were colorless and gave similar IR spectra to that of the original cellulose. Based on these results, a ‘surface-peeling mechanism’ is proposed, and the role of the solvent in the mechanism is discussed.     

Detailed kinetic modeling of pyrolysis of tetrabromobisphenol A

The thermal degradation of 4,4′-isopropylidenebis(2,6-dibromophenol), commonly known as tetrabromobisphenol A (TBBA), was studied by means of a semi-detailed kinetic model. TBBA is a widely adopted flame retardant. It decomposes in a temperature range between 200 °C and 500 °C, forming gaseous mixtures of HBr and harmful compounds such as bromine-containing phenols, the precursors of brominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs). These thermochemical characteristics constitute a significant risk of environmental contamination right throughout TBBA's whole life cycle. A kinetic model based on about 60 components (real and lumped species and radicals) and about 900 reactions satisfactorily reproduces the main aspects of TBBA degradation and volatilization. The model was validated by comparison with several thermogravimetric analyses, both isothermal and dynamic at 10 °C/min. The vaporization of pure TBBA, the formation of hydrogen bromide and of carbonaceous residue were all correctly predicted in quantitative terms right across the entire temperature range. Compared to conventional one-step global apparent degradation models, the proposed model spans much larger operating ranges, especially in predicting the gas phase products distribution. The results are encouraging and confirm the validity of the detailed kinetic model.     

High temperature pyrolysis of novolac resin biomass composites

Composites of novolac resin (N.R.) and biomass derived from olive stones (OL.B.), in various proportions, were cured with hexamethylenetetramine (HTA) and pyrolyzed up to 900°C. The pyrolysis mechanism was monitored using TGA and gas chromatography. The pyrolysis regions, as well as important pyrolysis parameters of the materials used, were determined. Cured and pyrolyzed composites of N.R./OL.B. varied from 20/80 to 75/25, exhibiting at temperatures up to approx. 600°C lower weight losses than expected by the rule of mixtures, owing to additional cross linkages of lignin with HTA. This stabilization effect vanished during pyrolysis at higher temperatures because of the breaking of other chemical bonds, e.g. cross linkages. The release of CH₄ during the pyrolysis of OL.B. is derived from the lignin contained in OL.B. The other gases, CO, CO₂ and H₂, could be formed from celluose, hemicellulose and lignin which are the main components of OL.B. The use of N.R. in the initial mixture with OL.B. reduces the weight losses during pyrolysis compared with OL.B. alone. A heating rate of 10°C/min was necessary for the carbonization processes of OL.B. and its mixtures with N.R. in order to promote minimum weight loss of material and minimum pyrolysis time.