Mechanism Of Char Formation Research Articles

Hydrothermal carbonization of distiller’s grains

Wet distiller’s grains are intermediate byproducts of ethanol manufacture that have high moisture contents and require significant energy for drying and conversion into dry distiller’s grains. Hydrothermal carbonization was investigated as a wet process to provide alternative products, and chars were obtained in moderate yield that possessed high heats of combustion. The mechanism of char formation was also investigated employing constituent materials representative of the chemical composition of distiller’s grains. Char formation was discovered to chiefly involve carbohydrates (other than cellulose) and proteins. A surprising discovery was that triacylglycerides and fatty acids created under the reaction conditions did not contribute to char yield and were adsorbed onto the chars and could be easily extracted.

Char Formation Mechanism in Supercritical Water Gasification Process: A Study of Model Compounds

Char is one of the undesirable products in the supercritical water gasification of biomass, causing a reduction in carbon gasification efficiency. 5-HMF (5-hydroxymethylfurfural) is believed to be an intermediate in the char formation pathway. In this Article, the rate of formation of char particles obtained from experiments using glucose (a biomass model compound) was compared to that from experiments using 5-HMF (Chuntanapum and Matsumura, 2009). The glucose experiments were conducted in a temperature range of 300−400 °C, at 25 MPa, and for a residence time up to 70 s. The initial concentration of glucose was varied from 1.5 to 3 wt % (i.e., 0.083 to 0.167 M). Glucose was found to produce char particles 2 orders of magnitude faster than 5-HMF feedstock. The copresence of the other glucose decomposition products is thought to cause the difference in the char formation mechanism (i.e., the side reaction between 5-HMF and the other decomposition products) from that of 5-HMF alone. FT-IR and Raman spectroscopy of the solid products was carried out.

Platinum nanoparticle intercalated montmorillonite to enhance the char formation of polyamide 6 nanocomposites

Organically modified montmorillonite (OMT) was used to disperse catalytically active Pt nanoparticles that influence the char formation processes of polyamide 6 (PA6). The Pt nanoparticles of varying particle size are generated in organically modified montmorillonite (Pt–OMTs) which are subsequently melt blended with PA6. The average particle size of Pt nanoparticles ranges from 9.2 to 21.6 nm as found by X-ray diffraction and field emission scanning electron microscopy. The char formation mechanism is studied by thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG–IR). Infrared spectroscopy on the residue reveals the formation of unsaturated hydrocarbons during decomposition of PA6 nanocomposite which are crosslinked into a highly conjugated structure.

Flame retardation and char formation mechanism of intumescent flame retarded polypropylene composites containing melamine phosphate and pentaerythritol phosphate

The flame retardation of polypropylene (PP) composites containing melamine phosphate (MP) and pentaerythritol phosphate (PEPA) was characterized by cone calorimeter. The formation mechanism of the char obtained from the combustion of the composites after cone calorimeter testing was studied by scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman diffusion. Results demonstrated that the PP composite containing MP and PEPA showed good flame retardancy. It had been found that the intumescent char could be principally divided into three parts, i.e. outer, middle and inner char layer, according to their different structures and components.

Synergistic effect of ammonium polyphosphate and layered double hydroxide on flame retardant properties of poly(vinyl alcohol)

A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1–1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.

Char-forming mechanism of a novel polymeric flame retardant with char agent

A novel phosphorus-containing compound, poly(2-hydroxy propylene spirocyclic pentaerythritol bisphosphonate) (PPPBP) has been proved to be an excellent flame retardant for polyethylene terephthalate (PET) fabrics. In order to understand its flame retardant mode, FT-IR and XPS are used to investigate the char-forming mechanism of PPPBP. FT-IR spectra results show that with the increase of temperature, P–O–C group of PPPBP breaks down gradually, and species containing C C double bond appear. XPS spectra indicate that PPPBP produces phosphoric or polyphosphoric acid during thermo-decomposition. In the high temperature range (>400 °C), C C and phosphorus-containing complexes become the major components of the charred residue of PPPBP. Data of XPS and FT-IR spectra give positive evidence that PPPBP yields high amount of carbonaceous chars by producing phosphoric or polyphosphoric acid, which inhibit the oxidation of carbon atoms, and simultaneously impel the formation of carbon and species containing carbon double bond with outstanding heat resistance.

Substantive intumescence from phosphorylated 1,3‐propanediol derivatives substituted on to cellulose

AbstractCellulose flame retarded with an ammonia‐cured, polycondensed tetrakis(hydroxymethyl)phosphonium–urea derivative (as Proban CC®, Rhodia) phosphorylated by cyclic 1,3‐propanediol phosphoryl chloride and cyclic 2,2‐diethyl‐1,3‐propanediol phosphoryl chloride can give phosphorus levels up to 6.9% (w/w). Such high levels suggest up to 35.5% yields of reaction if the free secondary amine groups present in the crosslinked flame retardant and the C(6) primary hydroxyl groups are the assumed phosphorylation sites. The presence of substituted propanediol phosphonate moieties in the fibers significantly increases char formation above 400©C and scanning electron microscopy indicates that the char has an intumescent structure. The influence of the chemical structure of the propanyl moeity to the reaction extent of the possible phosphorylation sites and the char formation mechanism during thermal pyrolysis of the modified samples are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3165–3172, 2003

Ignition of char-forming polymers at a critical mass flux

A simple model of ignition is discussed in the context of char-forming polymers. The model in question assumes that ignition occurs at a critical value of volatile mass flux from the degrading material. The char-forming mechanism chosen for the study is the simplest possible formulation preserving finite-rate kinetics—char and volatile products are formed together in a single step. This simple pyrolysis model has the advantage that the ultimate char yield is known a priori, and is in fact a parameter of the model. Results are presented and discussed for a number of cases, depending on char yield and char thermal properties. Complex ignition behaviour is exhibited by the model and practical consequences of the model predictions are discussed.

95/00137 Study on char formation mechanism from woody brown coal

95/00137 Study on char formation mechanism from woody brown coal

Cellulose pyrolysis kinetics and char formation mechanism

The pyrolysis of cellulose was studied by electrically heating in helium single strips (0.75 cm×2.5 cm) of low ash (<0.07%) predried filter paper (≈0.01 cm thick) supported inside a folded wire mesh heating element mounted in a sealed vessel. The samples were rapidly brought to a desired temperature, held there for a desired time and then rapidly cooled. Extents of conversion to volatiles, measured by weighing samples before and after experiments of known duration, were determined as a function of residence time (0.2–75,600 s), final temperature (250–1,000°C), heating rate (400–10,000°C/s), and ambient pressure (0.0005–1 atm). Pyrolysis kinetics was determined by nonisothermal techniques to account for substantial reaction occurring during sample heat-up and cool-down. All of the cellulose was converted to volatiles without char formation, except when an extended heating period at a low temperature (e.g., an hour or longer at 250°C) preceded the pyrolysis at higher temperatures. The latter procedure resulted in char yields of about 2% by weight of the original cellulose. The kinetics data are well described by a single-reaction first-order decomposition model with an activation energy of 33.4 kcal/mole and a frequency factor of 6.79×10 9 s −1 . The correlation is slightly improved by use of a multiple-reaction model based on a set of independent parallel first-order reactions represented by a Gaussian distribution of activation energies with a mean of 37.0 kcal/mole and a standard deviation of 1.1 kcal/mole. Selected experiments at reduced pressures (0.0005 atm), elevated heating rates (10,000°C/s), or both resulted in rate constants smaller than those obtained at 400°C/s and 1 atm. The results indicate that the residence time of volatile products within the pyrolyzing cellulose matrix is extremely important in determining conversion. Suggested pathways for cellulose pyrolysis that are consistent with these findings and with much of the pertinent literature involve primary decomposition to an oxygen-rich intermediate (probably levoglucosan) which then participates in three processes to extents depending on experimental conditions: (a) direct escape from the decomposing material into the ambient gas; (b) polymerization, cross-linking and cracking to form char and (c) pyrolysis to smaller volatiles some of which inhibit the char formation in (b) or autocatalyze (c). Accordingly, char is not a primary product, and the yield of char is zero for extremely short residence times of the primary products within the matrix of the decomposing material or for conditions that permit complete inhibition of char formation by secondary pyrolysis products.