Showing papers on "Pyrolysis published in 2000"

Catalytic graphitization of carbon aerogels by transition metals

Abstract: Carbon aerogels and Cr-, Fe-, Co-, and Ni-containing carbon aerogels were obtained by pyrolysis, at temperatures between 500 and 1800 °C, of the corresponding aerogels prepared by the sol−gel metho...

Photoresist‐Derived Carbon for Microelectromechanical Systems and Electrochemical Applications

Abstract: Photopatterned resists pyrolyzed at different temperatures and different ambient atmospheres can be used as a carbonaceous material for microelectromechanical systems. Carbon films were prepared by pyrolysis of photoresists at temperatures ranging from 600 to 1100°C. The carbon films were characterized by several analytical techniques, viz., profilometry, thermogravimetric analysis. four-point probe measurements, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. In addition, cyclic voltammetry was performed on the carbon film electrodes, and the carbon films were compared to glassy carbon (GC for their electrochemical behavior. Electron-transfer rate constants for the benchmark Fe(CN) 3-/4- 6 and Ru(NH 3 ) 3+/2+ 6 redox systems increased with increasing heat-treatment temperature and approached those observed on GC following-treatment at 1100°C. The pyrolyzed films have low capacitance and background current, approximately one-fourth of that observed on GC. The oxygenicarbon atomic ratio determined from XPS was low (∼1% for I 100°C pretreatment), and increased more slowly upon exposure to air than that for GC treated under identical conditions. Pyrolysis of photoresist films permits photolithographic fabrication of carbon electrode devices, and also appears to yield a carbon film with a smooth surface and unusual surface chemistry.

Attainment of the Theoretical Yield of Carbon from Biomass

Abstract: Previous work has shown that very high yields of charcoal are obtained when pyrolysis of the biomass feedstock is conducted at elevated pressure in a closed vessel, wherein the pyrolytic vapors are held captive and in contact with the solid products of pyrolysis In this paper, we show that, for some biomass species, the yield of carbon produced by this process effectively attains the theoretical value predicted to exist when thermochemical equilibrium is realized Various agricultural wastes (eg, kukui nut, macadamia nut, and pecan shells) and tropical species (eg, eucalyptus, leucaena, and bamboo) offer higher yields of carbon than the hardwoods traditionally employed by industry in the US and Europe Moreover, the yields of carbon from oat and rice hulls and from sunflower seed hulls are nearly as high as the yields of carbon from hardwoods There is a correlation between the yield of carbon and the acid-insoluble lignin content of the feed Charcoal briquettes made from agricultural wastes and lump charcoal from tropical species are promising sources of renewable carbon for use in the smelting of metal ores

Catalyst Evaluation for Catalytic Biomass Pyrolysis

Abstract: Commercial catalysts, including zeolites (HZSM-5), fluid catalytic cracking (FCC) catalysts, transition metal catalysts (Fe/Cr), and aluminas, were successfully evaluated in a fixed bed catalytic reactor using a mixture of model compounds to simulate biomass flash pyrolysis vapors. Successful criteria including the stability index (SI), the water generation (WG), and the loss of organics (LO) were introduced to monitor the effect of catalysts and ascertain major changes in the obtained liquid product composition. SI being a measure of the effective carbonyls reduction after catalytic cracking reached 100% in the case of HZSM-5 catalysts, leading to the selective production of aromatic hydrocarbons. Transition metal catalysts (Fe/Cr) lead to the selective production of phenol and light phenolics. Comparable trends were obtained using solid biomass in the catalytic fixed bed reactor.

Pyrolysis of sawdust in a conical spouted‐bed reactor with a HZSM‐5 catalyst

Abstract: The effect was studied of using an in-situ catalyst based on a HZSM-5 zeolite in flash pyrolysis with an inert gas (N{sub 2}) of pinus insignis sawdust in a conical spouted-bed reactor in the 400--500 C range and for a gas residence time of 50 ms. The use of the catalyst increases the yield of gases and decreases the yields of liquid and char. Likewise, the yield of CO{sub 2} decreases, whereas the yield of C{sub 4{minus}} hydrocarbons increases (15.9 wt. % at 450 C). The catalyst is efficient for partial deoxygenation of the liquid product.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part I: Properties of bio-oil and its blends with methanol and a pyrolytic aqueous phase

Abstract: The objective of this study was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a liquid fuel for gas turbine applications. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. Alkali metal content, viscosity, solid content, heating value, surface tension, moisture content and density of the bio-oil were investigated. The effect of the addition of methanol and/or a pyrolytic aqueous phase on the physicochemical properties of the bio-oils was also investigated. The pyrolytic aqueous phase is the sum of the water contained in form of moisture in the feedstock plus the water formed during biomass pyrolysis reactions. The results indicated that the bio-oil sample investigated is a valuable gas turbine fuel: it has a relatively low Na+K+Ca content (21 ppm), a low viscosity ( 5.3 cSt @90° C ), a high net heating value (32 MJ/kg, as-received basis) and a low solid content (0.34 wt%). The addition of methanol to the oil was beneficial. It was also found that the pyrolytic aqueous phase addition had no significant effect on the viscosity, but that its “flowability” effect was beneficial for other properties. A concentration of 10–15% of the aqueous phase in the bio-oil seemed to be optimal. The second phase of this study investigated the storage and thermal stability of bio-oils and their mixtures. This was carried out using a method performed in our laboratory. The results are presented in Part II of this study.

Influence of particle size on the pyrolysis of rapeseed (Brassica napus L.): fuel properties of bio-oil

Abstract: Brassica napus L. pyrolysis experiments were performed in a Heinze reactor under static atmosphere at a pyrolysis temperature of 500°C at 40°C/min of heating rate. The effect of particle size on the yields of the products was investigated. The particle size of rapeseed was varied in the range of 0.224–1.8 mm. Pyrolysis oil and char yields from rapeseed were found to be largely independent of particle size in the experimental conditions. Oil yield shows a maximum of ca 46 wt% with a particle size range of 0.85–1.8 mm. The various characteristics of pyrolysis oil obtained under these conditions were identified on the basis of standard test methods. The empirical formula of pyrolysis oil with a heating value of 38.4 MJ/kg was established as CH 1.67 O 0.12 N 0.046 . The results from the pyrolysis of rapeseed showed the potential of rapeseed as an important source of liquid hydrocarbon fuels. Rapeseed oil was also evaluated for fatty acid composition.

Pyrolysis of Sawdust in a Conical Spouted Bed Reactor. Yields and Product Composition

Abstract: The performance of original equipment provided with a conical spouted bed reactor has been studied in flash pyrolysis of sawdust with an inert gas (N2) in the 350−700 °C range and with 50 ms of average gas residence time. The effect of pyrolysis temperature on the yields of gas, liquid, and char on gas and liquid composition and on char properties has been studied. The maximum yield of liquid (corresponding to 70 wt %) is obtained at 450 °C and its composition determined by GC/MS is similar to that reported in the literature for bubbling fluidized beds. Although temperatures above 600 °C are required for the development of the char porous structure, the yield of CO2 obtained under these conditions is unacceptable.

Bio-oils obtained by vacuum pyrolysis of softwood bark as a liquid fuel for gas turbines. Part II: Stability and ageing of bio-oil and its blends with methanol and a pyrolytic aqueous phase

Abstract: This paper completes a study the ultimate objective of which was to provide background information on biomass pyrolysis oils (bio-oils) regarding their use as a gas turbine liquid fuel. The bio-oil was obtained by vacuum pyrolysis of softwood bark residues. The stability and ageing of the bio-oil and mixtures thereof were evaluated. The samples were stored at 40, 50 and 80°C for up to 168 h and at room temperature for up to one year, period after which the phase separation time, viscosity, solid and water content and average molecular weight were measured. The results indicated that the properties of the bio-oil were significantly altered when the bio-oil was heated at 80°C, but that the variations after heating at 40 and 50°C were not critical. It was found that the molecular weight increase after heating the bio-oil for one week at 80°C was equivalent to keeping the sample for one year at room temperature. The addition of aqueous phase to the bio-oil lowered its thermal stability significantly. A rapid phase separation occurred after heating at 80°C and, therefore, the total aqueous phase concentration in the bio-oil must be limited to 15%. Ageing of the raw bio-oil at room temperature resulted in a dramatic viscosity increase during the first 65 days, period after which a plateau was reached. The addition of methanol to the bio-oil was beneficial for the bio-oil properties as well as for the stability of the bio-oil and its mixtures. Methanol dissolved some structured components of the bio-oil and thus reduced the viscosity increase rate. Moreover, the addition of methanol to the bio-oil/pyrolytic aqueous phase mixtures delayed the phase separation process.

Recyling of plastic wastes via pyrolysis

Abstract: Pyrolysis for the simultaneous generation of oils and gases can be convenient to obtain hydrocarbons and even to recover crude petrochemicals or to generate energy from waste plastics A Gray–King apparatus has been used to pyrolyze waste polyethylene (PE), polystyrene (PS), both separately and with different compositions Thermogravimetric analysis of waste plastics indicated the critical temperatures, which should be effective for pyrolysis The chosen heating rate was low in order to achieve higher liquid yields The results showed that waste PS yielded higher liquid, and waste PE yielded higher gaseous products The dominant liquid product of PS waste was styrene whereas for waste PE, prophenylbenzene was the dominant pyrolysis product

An experimental and modeling investigation of particle production by spray pyrolysis using a laminar flow aerosol reactor

Abstract: The influence of operating parameters on the morphology of particles prepared by spray pyrolysis was investigated using a temperature-graded laminar flow aerosol reactor Experimentally, zirconia particles were prepared by spray pyrolysis using an aqueous solution of zirconyl hydroxide chloride Hollow particles were formed if the reactor temperature was high, the temperature gradient was too large, the flow rate of carrier gas was high, and the initial solute concentration was low A numerical simulation of the pyrolysis process was developed using a combination of two previous models The simulation results compared well with the experimental results

Diesel Engine Combustion of Biomass Pyrolysis Oils

Abstract: To investigate their ignition delay and combustion behavior, experiments with two biomass pyrolysis oils and No. 2 diesel fuel were performed in a direct injection diesel engine. It was found that while the indicated thermal efficiency of both pyrolysis oils equaled that of the diesel fuel, they exhibited excessive ignition delays and required a moderate degree of combustion air preheating to ignite reliably. Despite the longer ignition delays associated with the pyrolysis oils, the cylinder pressure rise rates were significantly less than with No. 2 diesel fuel. Experimental ignition delay and heat release rates were interpreted using a phenomenological spray combustion model. Using a three parameter fit for vaporization, ignition, and combustion rate, the model showed that the longer ignition delays of the bio-oils result from slow chemistry relative to diesel fuel. The model also showed that the heat release profiles of the bio-oils are consistent with slow combustion chemistry and rapid mixing relativ...

Experimental and kinetic modeling study of the oxidation of benzene

Abstract: The oxidation of benzene under flow-reactor conditions has been studied experimentally and in terms of a detailed chemical kinetic model. The experiments were performed under plug-flow conditions, at excess air ratios ranging from close to stoichiometric to very lean. The temperature range was 900–1450 K and the residence time of the order of 150 ms. The radical pool was perturbed by means of varying the concentration of water vapor and by adding NO. Furthermore, a few experiments were conducted on pyrolysis and oxidation of phenol. Benzene oxidation is initiated at ∼1000 K; the temperature for complete oxidation depends on stoichiometry, ranging from 1100 K (very lean conditions) to 1300 K (close to stoichiometric). The water vapor level and the presence of NO have only a minor impact on the temperature regime for oxidation. The proposed chemical kinetic model was validated by comparison with the present experimental data as well as flow reactor and mixed reactor data from literature. The model provides a reasonably good description of the overall oxidation behavior of benzene over the range of conditions investigated. However, before details of the oxidation behavior can be predicted satisfactorily, a number of kinetic issues need to be resolved. These include product channels and rates for the reactions of phenyl and cyclopentadienyl with molecular oxygen as well as reaction chemistry for the oxygenated cyclic compounds formed as intermediates in the oxidation process. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 498–522, 2000