Showing papers in "Energy & Fuels in 1999"
TL;DR: In this article, physical and chemical characteristics of bio-oils relevant to fuel applications as well as some low-cost methods for improvement of these properties are discussed, and the authors also provide bio-oil specifications proposed by some industrial users.
Abstract: Biomass pyrolysis oils have potential to be used as a fuel oil substitute. Combustion tests have shown that the oils burn efficiently in standard or slightly modified boilers and engines with rates similar to those for commercial fuels. However, these tests also identified several challenges in bio-oils applications resulting from their properties. The oils have heating values of only 40−50% of that for hydrocarbon fuels. They have a high water content that is detrimental for ignition. Organic acids in the oils are corrosive to common construction materials. Solids (char) can block injectors or erode turbine blades. Over time, reactivity of some components in the oils leads to formation of larger molecules that results in high viscosity and in slower combustion. This paper discusses physical and chemical characteristics of bio-oils relevant to fuel applications as well as some low-cost methods for improvement of these properties. It also provides bio-oil specifications proposed by some industrial users an...
731 citations
TL;DR: In this article, a variety of global kinetic models are reviewed, including first-order, nth-order and sequential models as well as models having Gaussian, Weibull, and discrete activation-energy distributions.
Abstract: A variety of global kinetic models are reviewed, including first-order, nth-order, nucleation, and sequential models as well as models having Gaussian, Weibull, and discrete activation-energy distributions. The important characteristics of these various models are outlined, with guidance in how to select the correct model. Some of the models have similar characteristics, and the parameter relationships among similar models are discussed. The comparison includes the relationship between conversion-dependent parameters determined by modified Friedman and Coats−Redfern isoconversion methods and reactivity distribution parameters determined by nonlinear regression of rate or fraction-reacted profiles. A new method for deriving discrete activation-energy distribution parameters having ln(A) = a + bE is also presented. Data accuracy requirements are discussed briefly. Kinetic analyses are given for a variety of materials, including synthetic polymers (polyethylene, polystyrene, polydimethylenenaphthalene, polys...
500 citations
TL;DR: In this article, the pyrolysis of mixed-plastic waste has been proposed as a means of recycling to produce petrochemical feedstock, and the interaction of the main plastic types in plastic mixtures is significant in predicting the likely yield and composition of products from different plastic mixture.
Abstract: The pyrolysis of mixed-plastic waste has been proposed as a means of recycling to produce petrochemical feedstock. The interaction of the main plastic types in plastic mixtures is significant in predicting the likely yield and composition of products from different plastic mixtures. The six main plastics in municipal solid waste are high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), and poly(ethylene terephthalate) (PET). Each of the plastics was pyrolyzed individually in a fixed-bed reactor heated at 25 °C min-1 to a final temperature of 700 °C. Polystyrene was then mixed with each of the other five plastics in a ratio of 1:1 and pyrolyzed in the fixed-bed reactor under the same pyrolysis conditions. The yield and composition of the derived oil/wax and gases was determined. The main gases produced from the individual plastics were hydrogen, methane, ethane, ethene, propane, propene, butane, and butene and for the PET plasti...
276 citations
TL;DR: Leaching of inorganic materials has recently been shown to substantially improve the combustion properties of biomass fuels, especially straw but including other herbaceous and woody fuels as discussed by the authors, and it has been shown that leaching with water removes large fractions of alkali metals (typically > 80% of potassium and sodium) and chlorine (>90%).
Abstract: Leaching of inorganic materials has recently been shown to substantially improve the combustion properties of biomass fuels, especially straw but including other herbaceous and woody fuels. Leaching with water removes large fractions of alkali metals (typically >80% of potassium and sodium) and chlorine (>90%). Smaller fractions of sulfur and phosphorus are also removed. Alkali metals are heavily involved in ash fouling and slagging in combustion and thermal gasification systems. Chlorine is a facilitator of alkali volatilization, and contributes to corrosion and air pollution. The presence of these elements has reduced or eliminated the use of certain biomass fuels in many combustion applications, even where such use might provide significant environmental benefits. Leaching could mitigate the undesirable effects of biomass ash in thermal systems. Reported here for the first time are comparative studies of volatile inorganic species evolving from leached and unleached biomass fuels during thermal convers...
267 citations
TL;DR: In this paper, the authors investigated the production of hydrogen by catalytic steam reforming of model compounds of biomass fast-pyrolysis oil (bio-oil) using two commercial nickel-based catalysts for steam reforming naphtha.
Abstract: We investigated the production of hydrogen by the catalytic steam reforming of model compounds of biomass fast-pyrolysis oil (bio-oil). Acetic acid, m-cresol, dibenzyl ether, glucose, xylose, and sucrose were reformed using two commercial nickel-based catalysts for steam reforming naphtha. The experiments were conducted at a methane-equivalent gas hourly space velocity (GC1HSV) from 500 to 11790 h-1. Steam-to-carbon ratios (S/C) of 3 and 6 and catalyst temperatures from 550 to 810 °C were selected. Rapid coking of the catalyst was observed during acetic acid reforming at temperatures lower than 650 °C. Acetic acid, m-cresol, and dibenzyl ether were completely converted to hydrogen and carbon oxides above this temperature, and hydrogen yields ranged from 70 to 90% of the stoichiometric potential, depending on the feedstock and reforming conditions. Sugars were difficult to reform because they readily decomposed through pyrolysis in the freeboard of the reactor. This led to the formation of char and gases b...
244 citations
TL;DR: The evolution of high-energy density fuels over the past three decades is briefly described in this article, where two novel ultra-high energy density fuels, one naturally occurring and one synthetic, have emerged; these fuels, which are both composed of compact hydrocarbon molecules, have energy contents or heating values significantly greater than that of currently used standard missile fuel JP-10 (up to 160k Btu/gal (447K MJ/m3) vs 1417 K Btu /gal (396K MJ /m3)) In addition, these fuels also exhibit superior low-
Abstract: The evolution of high-energy density fuels over the past three decades is briefly described This period can be characterized by exceedingly slow progress and notable lack of success toward the development of practical, economically viable fuel systems Recently, two novel ultrahigh-energy density fuels, one naturally occurring and one synthetic, have emerged; these fuels, which are both composed of compact hydrocarbon molecules, have energy contents or heating values significantly greater than that of currently used standard missile fuel JP-10 (up to 160K Btu/gal (447K MJ/m3) vs 1417K Btu/gal (396K MJ/m3)) In addition, these fuels also exhibit superior low-temperature, viscometric, flash-point, and other properties that are desired and, indeed, required for practical fuels Initial research and development of these fuels are described, and their chemistries, properties, and, in the case of the naturally occurring fuel, engine test results are provided
242 citations
TL;DR: In this paper, the conformation of an asphaltene molecule of the Athabasca sand oil was calculated through molecular mechanics, and molecular aggregates formed with the asphalte and with nine resins from the same oil, and with n-octane and toluene, were also studied.
Abstract: The conformation of lowest energy of an asphaltene molecule of the Athabasca sand oil was calculated through molecular mechanics. The molecule has a complex globular shape with small internal cavities. This shape resulted mostly from the existence of polymethylene bridges connecting the aromatic regions. Molecular aggregates formed with the asphaltene and with nine resins from the same oil, and with n-octane and toluene, were also studied. The resins showed higher affinities for the asphaltene than toluene and n-octane and also exhibited a noticeable selectivity for some of the external sites of the asphaltene. This selectivity based on the molecular recognition of the site depends on the fit between the resins and the site of the asphaltene. The selectivity explains why resins of one oil may not solubilize asphaltenes from other crudes. An analysis of the changes in the enthalpic and entropic contributions to the free energy showed that both contributions should be considered when the stability of the as...
233 citations
TL;DR: In this article, the carbonation rate of 15−20 μm, nonporous, calcium oxide crystals has been studied over a temperature range of 550−1100 °C and a CO2 pressure range of 1−11.7 atm.
Abstract: The carbonation rate of 15−20 μm, nonporous, calcium oxide crystals has been studied over a temperature range of 550−1100 °C and a CO2 pressure range of 1−11.7 atm. At temperatures greater than 600 °C, the carbonation rate decreases more rapidly with time than would be expected from diffusion through a uniform product layer and the activation energy is initially low but increases with conversion. The product layer consists of crystalline grains, and these product layer grains grow by coalescence from less than one μm diameter to the approximate dimension of the particle. The carbonation rate can be described by a model where CO2 pressure-independent grain boundary diffusion and diffusion through the carbonate crystals act in parallel. The relative importance of bulk diffusion through the product layer crystals increases with time relative to transport through the grain boundaries and has an effective activation energy of 57 kcal/mol. Diffusion through the crystal boundaries has low activation energy and l...
216 citations
TL;DR: The structural characteristics of a pentane-insoluble asphaltene isolated from the vacuum residue of an Arabian crude mixture have been investigated by pyrolysis gas chromatography/mass spectrometrasure as mentioned in this paper.
Abstract: The structural characteristics of a pentane-insoluble asphaltene isolated from the vacuum residue of an Arabian crude mixture have been investigated by pyrolysis gas chromatography/mass spectrometr...
196 citations
TL;DR: In this paper, a low-rank coal (Loy Yang) was acid-washed and ion-exchanged with Na and Ca to prepare the H-form, Na-form and Ca-form coal samples.
Abstract: A Victorian low-rank coal (Loy Yang) was acid-washed and ion-exchanged with Na and Ca to prepare the H-form, Na-form, and Ca-form coal samples. Two more H-form samples were also prepared by rewashing the Na-form and Ca-form samples with acid. These coal samples were pyrolyzed in a wire-mesh reactor where the secondary reactions of the evolved volatiles were minimized. The ion-exchanged coal samples were found to give very different tar yields from those of the raw coal samples. While the tar yields from the pyrolysis of the raw and H-form coal samples were observed to be very sensitive to changes in heating rate, the tar yields from the Ca-form and Na-form samples showed little heating rate sensitivity. Unlike higher rank coals studied previously, the tar yields from the pyrolysis of the raw coal and the H-form coal samples at 600 °C were found to increase much more than the corresponding increases in the total volatile yields as the heating rate was increased from 1 to 2000 K s-1. Reexchanging Na in the ...
188 citations
TL;DR: In this paper, two locations for calcined dolomites (OCa) were considered: in the same gasifier bed (mixed with silica sand) or in a secondary bed downstream from the gasifier.
Abstract: Calcined dolomites (OCa.OMg) are often used for hot gas cleanup in biomass gasification processes in a fluidized bed. Two locations are envisaged for such dolomite: in the same gasifier bed (mixed with silica sand) or in a secondary bed, downstream from the gasifier. Previous results obtained under very similar circumstances are here analyzed to determine which is the best location (regarding its chemical usefulness for tar elimination) of the dolomite. Gas and tar yields and gas compositions are here given for the two locations of the dolomite, and it is made both for gasification with air and with steam−O2 mixtures. It is demonstrated how the effectiveness of the dolomite in the second reactor is only a little bit higher than for the in-bed location. This small increase in effectiveness is mainly found in gasification with H2O−O2 mixtures, there no having noticeable chemical differences (between the two locations of the dolomite) in gasification with air.
TL;DR: In this paper, the sulfation of KCl was studied in the gas and molten phase in a laminar entrained-flow reactor at 900−1100 °C with residence times of 0.24−1.22 s.
Abstract: The sulfation of KCl was studied in the gas and molten phase in a laminar entrained-flow reactor. The experiments were performed at 900−1100 °C with residence times of 0.24−1.22 s. Small, 65−125 mi...
TL;DR: In this article, a nonlinear correlation has been developed that predicts the chemical structure parameters of both U.S. and non-U.S coals generally measured by 13C NMR and often required for advanced coal deformation models.
Abstract: 13C NMR spectroscopy has been shown to be an important tool in the characterization of coal structure. Important quantitative information about the carbon skeletal structure is obtained through 13C NMR spectral analysis of coal. Solid-state 13C NMR analysis techniques have progressed beyond the mere determination of aromaticity and can now describe features such as the number of aromatic carbons per cluster and the number of attachments per aromatic cluster. These 13C NMR data have been used to better understand the complicated structure of coal, to compare structural differences in coal, tar, and char, and to model coal devolatilization. Unfortunately, due to the expense of the process, extensive 13C NMR data are not available for most coals. A nonlinear correlation has been developed that predicts the chemical structure parameters of both U.S. and non-U.S. coals generally measured by 13C NMR and often required for advanced devolatilization models. The chemical structure parameters correlated include (i)...
Abstract: Pine sawdust catalytic steam gasification has been studied in a fluidized bed at a relatively low temperature, 700 °C. The Ni−Al catalyst used was prepared by coprecipitation and calcined at 750 °C for 3 h. The influence of the catalyst weight/biomass flow rate (W/mb) and steam/biomass (S/B) ratios on the product distribution and on the quality of the gas product obtained was analyzed. An increase of the W/mb ratio increases the total gas, H2, CO, and CO2 yields, while CH4 and C2 yields decrease. An increase of the S/B ratio increases H2 and CO2 yields while CO and CH4 yields decrease. This fact can be explained by steam reforming and water-gas shift reactions. The increase of the S/B ratio also has a positive effect on the life of the catalyst. The gas composition and gas yields at initial time have also been studied. For W/mb ratios > 0.5 h, the gas composition at initial time is similar to that for thermodynamic equilibrium for different S/B ratios. The influence of the S/B ratio on gas yield at initia...
TL;DR: In this paper, a simple relationship exists between the onset of precipitation and the refractive index of the mixture in which precipitation is first observed, which can be used to quantify the ability of a crude oil to disperse its asphaltene fraction.
Abstract: Despite the complexity of asphaltene chemistry, a simple relationship exists between the onset of precipitation and the refractive index of the mixture in which precipitation is first observed. Separation of asphaltenes from oil is a colloidal phenomenon. Because aggregation and separation of the asphaltenes are primarily dependent on the magnitude of van der Waals forces between nonpolar species, the mixture refractive index can be used to quantify the ability of a crude oil to disperse its asphaltene fraction. In some crude oils, asphaltenes are very close to the onset of precipitation, while in other oils, the asphaltenes are relatively stable. The value of the refractive index of an oil sample and the refractive index at which precipitation is first observed are distinctive properties of each crude oil. The difference between these two values is a measure of the stability of the asphaltenes in their respective crude oils. Mixture refractive index correctly predicts the onset of asphaltene precipitatio...
TL;DR: In this article, the molecular structure of Athabasca asphaltene is discussed in light of new results on aromatic-attached appendages derived from ruthenium-ions-catalyzed oxidation (RICO).
Abstract: After some general comments on the concept of asphaltene, outstanding problems relating to the molecular structure of Athabasca asphaltene are discussed in light of new results on aromatic-attached appendages derived from ruthenium-ions-catalyzed oxidation (RICO). Detected were homologous series of α-branched C1−C4 n-alkyl side chains up to C30−C40 in an aggregate amount of ∼10% of the n-alkyl side chains, C15−C20 regular isoprenoids, C20−C28 cheilanthanes, C27−C32 hopanes, C27−C29 steranes, C21−C24 pregnanes, and a number of branched hydrocarbons giving hydroxy carboxylic acids. The nature and distribution of these aromatic-attached biomarkers are similar but not identical to those reported to be attached to the asphaltene via a sulfide bridge. They may have originated from secondary biotic sources and became incorporated into the asphaltene via a Friedel−Crafts-type reaction. Additional, previously not considered reactions in the RICO of asphaltene are described, and aspects of the analytical procedures...
TL;DR: In this paper, seven commercial nickel-based catalysts for steam reforming of light hydrocarbons and of heavier polycyclic aromatic compounds were tested for tar removal in a flue gas from an atmospheric fluidized bed biomass gasifier, using air as the gasifying agent.
Abstract: Seven different commercial nickel-based catalysts for steam reforming of light hydrocarbons and of heavier hydrocarbons were tested for tar removal in a flue gas from an atmospheric fluidized bed biomass gasifier, using air as the gasifying agent. The catalysts were provided by BASF AG, ICI-Katalco, Haldor Topsoe a/s, and United Catalyst Inc. The facility used is a small pilot plant, and the catalytic reactor operates in full flow with a real gasification gas. A guard bed with a calcined dolomite is used to decrease the tar content at the inlet of the catalytic bed to a level below 2 g/m3n. The variables studied include the temperature (730−850 °C) of the catalytic bed, gas residence time, steam content in the flue gas, and composition of the reacting atmosphere. All catalysts for steam reforming of naphthas provide a similar and very high activity. Values of the apparent activation energy and preexponential factor are given and analyzed for the most active catalysts. The catalyst life is also studied. No...
TL;DR: In this paper, used tires were pyrolyzed in a nitrogen-purged 3 kg static bed, batch reactor, and the char was subsequently activated in an equimolar mixture of either steam and nitrogen or carbon dioxide and nitrogen.
Abstract: Used tires were pyrolyzed in a nitrogen-purged 3 kg static bed, batch reactor. The char was subsequently activated in an equimolar mixture of either steam and nitrogen or carbon dioxide and nitrogen. Activation was a two-stage process, with an initial more rapid gasification of carbonized rubber deposits followed by less rapid gasification of carbon black. The activation energy in steam was 201 kJ mol-1. The burnoff achieved by carbon dioxide under otherwise identical conditions to that of steam was on average 72% of that found when steam was used. The reactivity of acid-demineralized char in steam was around 22% less than that of raw char. It was suggested that calcium ions in the raw tire char catalyzed the gasification reactions. The tire pyrolysis temperature had an unclear influence on the rate of activation of the derived chars. The influence of particle size on the rate of activation was also investigated, and the results are discussed in terms of ash content and distribution. The outflow gas compo...
TL;DR: In this paper, a simple experimental technique, referred to as the filter drop spreading method, was used to detect the onset of flocculation quite accurately for crude oil mixtures and for mixtures of crude oils plus additives.
Abstract: Experimental results confirm that resins isolated from Boscan crude oil have a stabilizing effect on asphaltenes in Hamaca crude oil and in Boscan crude oil. A simple experimental technique, referred to as the filter drop spreading method, was used to detect the onset of flocculation quite accurately for crude oil mixtures and for mixtures of crude oils plus additives.
TL;DR: In this paper, the combustion behavior, gaseous emissions, and alkali metals released during the combustion of several biomass/coal blends were investigated using a direct sampling, molecular beam mass spectrometer (MBMS) system in conjunction with a high-temperature alumina-tube flow reactor.
Abstract: The combustion behavior, gaseous emissions, and alkali metals released during the combustion of several biomass/coal blends were investigated using a direct sampling, molecular beam mass spectrometer (MBMS) system in conjunction with a high-temperature alumina-tube flow reactor. Pittsburgh No. 8 and Eastern Kentucky coals were blended with various biomass samples such as red oak wood chips, Imperial wheat straw, and Danish wheat straw. The coal/biomass blends were 15% biomass on an energy input basis. All pure fuels and blends were subjected to combustion in 20% oxygen in helium at a furnace temperature of 1100 °C, and the products were monitored with the MBMS. The amounts of NO(g) and SO2(g) detected during the combustion of the coal/biomass blends suggested that any change was the result of diluting the nitrogen and sulfur present in the fuel blend. The amount of HCl(g) detected during the combustion of the coal/wheat straw blends was higher than expected based on the combustion results for the pure fue...
TL;DR: In this paper, the enhancement of NO reduction via a carbon-surface-catalyzed reaction such as NO + CO → 1/2N2 + CO2 was investigated.
Abstract: The enhancement of the NO/carbon reduction reactions by carbon monoxide has been demonstrated for carbons of widely varying nature (coal char, phenolic resin-derived char and graphite). The evidence supports enhancement of NO reduction via a carbon-surface-catalyzed reaction such as NO + CO → 1/2N2 + CO2. This reaction appears to be characterized by an activation energy of around 116 kJ/mol, and by zero order with respect to CO, in the range of CO pressures examined here (up to order 500 ppm). This suggests that an oxide stripping reaction, e.g., CO + C(O) → CO2 + C*, cannot be invoked in its usual form, to explain the rate enhancement. The reaction appears to be first order with respect to NO, at high temperatures and at NO concentrations of above roughly 100 ppm, but kinetic analysis is complicated by the fact that the NO−carbon reaction itself does not have a unique order at low temperatures. It is also shown that kinetic analysis can be greatly complicated in the presence of other oxidizing gases or s...
TL;DR: In this article, the corrosion of superheater tube material in straw-fired boilers was investigated in the laboratory and metal test elements of boiler tube steel (X20CRMV121 and AISI 347FG) were covered with synthetic (KCl and/or K2SO4) and real deposits, and exposed to synthetic flue gas (6 vol % O2, 12 vol % CO2, 400 ppmv HCl, 60 ppmv SO2, balance N2) in 550 °C electrically heated ovens.
Abstract: The corrosion of superheater tube material in straw-fired boilers was investigated in the laboratory. Metal test elements of boiler tube steel (X20CRMV121 and AISI 347FG) were covered with synthetic (KCl and/or K2SO4) and real deposits, and exposed to a synthetic flue gas (6 vol % O2, 12 vol % CO2, 400 ppmv HCl, 60 ppmv SO2, balance N2) in 550 °C electrically heated ovens. Exposure times from 1 week to 5 months were used. The corrosion of the metal test elements was, in general, quite uniform, and the corrosion products consisted mainly of oxides of iron and chromium. All test elements covered with KCl suffered from minor internal attack, and some elements had severe pits with chlorine found in the pit. A dense layer of potassium sulfate and iron oxide was found adjacent to the metal oxide layers on all the metal test elements covered with a deposit containing KCl. The layer had a characteristic structure, with iron oxide threads in a dense potassium sulfate matrix. A mechanism for chlorine corrosion is s...
TL;DR: The abundantly used technique of flocculation onset titration (FT) of asphaltenes is investigated, and it is shown how additional information on AS and oil properties in terms of solubility parameters may be derived from the data obtained as mentioned in this paper.
Abstract: The abundantly used technique of flocculation onset titration (FT) of asphaltenes is investigated, and it is shown how additional information on asphaltene and oil properties in terms of solubility parameters may be derived from the data obtained. The classical ways of interpreting the results are outlined. Analysis of the effect of oil concentration on FT is shown to add information on the stability of the asphaltenes in the oil. Application to various areas of asphaltene stability related problems is shown. This includes emulsion stability by asphaltenes, change in stability by conversion, oil field deposition, segregation, and asphaltene dispersant evaluation. Recommendations are given on the performance of this type of experiment, such as on titration rates. The analyses of more than 25 different oils are reported in the present work.
TL;DR: In this article, the XAFS results showed that each type of activated carbon behaves differently with respect to sorption of mercury and other species from the synthetic flue gas (SFG).
Abstract: The sorption of mercury, as Hg0 and HgCl2, in a synthetic flue gas (SFG) by three activated carbons has been examined by XAFS spectroscopy. The three carbons consisted of a sulfur-activated carbon, an iodine-activated carbon, and an activated carbon derived from lignite. In addition to mercury, the occurrence and behavior of sulfur, chlorine, calcium, and iodine were also examined by XAFS spectroscopy. These other elements were present either as activating species on the carbons or as reactive components (SO2, HCl) in the SFG. The XAFS results showed that each type of activated carbon behaves differently with respect to sorption of mercury and other species from the SFG. For the iodine- and sulfur-activated carbons, the XAFS data confirm that it is the activating element (I or S) that forms a sorption complex with mercury. However, the activated carbon from lignite exhibited a more variable behavior that reflected the conditions of the experiments, in particular whether HCl or HgCl2 was present in the SFG...
TL;DR: The surface of bitumen particles are rendered asphaltene-like owing to the adsorption of polar, aromatic, toluene-insoluble organics as mentioned in this paper.
Abstract: Bitumen separated from Athabasca oil sands by the hot water extraction process (HWEP) contains residual salty water and inorganic solids. Because of their strong interaction with bitumen, the solids fraction has been designated bitumen associated solids, abbreviated as BS. The major constituent of BS is ultrafine, aluminosilicate, clay crystallites. There is a minor contribution from sulfur- and titanium-bearing minerals. The surfaces of BS particles are rendered asphaltene-like owing to the adsorption of polar, aromatic, toluene-insoluble organics. Most of these solids are removed when asphaltenes are precipitated during treatment of bitumen with solvents less polar in nature than the naphtha in current use. Owing to their bi-wettable surface characteristics, the BS are likely to occur in association with water droplets in the bitumen phase. These droplets, or clusters, have an asphaltene-like exterior and exist as a stable colloidal dispersion in the maltene component of bitumen. These factors explain t...
TL;DR: In this article, surface and interfacial tension in systems formed by Brazilian crude oil n-pentane insolubles (C5I) and n-heptane (C7I) in the aromatic solvents toluene, pyridine, and nitrobenzene were measured at room temperature using the ring method and employing an automatic tensiometer.
Abstract: Data on the behavior of crude oil n-pentane- and n-heptane-insoluble fractions in aromatic solvent systems were obtained. Surface and interfacial tensions in systems formed by Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in the aromatic solvents toluene, pyridine, and nitrobenzene were measured at room temperature using the ring method and employing an automatic tensiometer. The results indicated possible asphaltene aggregation as well as the probable existence of critical micelle concentrations for both C5I and C7I fractions in each of the three solvents considered. Critical micelle concentrations measured for the C5I fraction in toluene and pyridine solutions were consistently higher than those in systems containing the C7I fraction, indicating a lower association tendency in the C5I fraction. Average molecular areas for asphaltenes adsorbed at different interfaces estimated from surface tension measurements were found to be in agreement with literature values and appear...
TL;DR: In this paper, the molecular structural units of Boscan and Duri asphaltenes have been investigated in ruthenium-ion-catalyzed oxidation (RICO) and pyrolysis.
Abstract: The molecular structural units of Boscan and Duri asphaltenes have been investigated in ruthenium-ion-catalyzed oxidation (RICO) and pyrolysis. From the RICO reactions, homologous series of n-alkanoic acids (C1−C31), representing aromatic-attached n-alkyl side chains, α,ω-di-n-alkanoic acids (C4−C26), representing polymethylene bridges connecting two aromatic units, and benzenecarboxylic acids, indicating the major modes of aromatic condensations in the asphaltene molecules and the minor role of pericondensed aromatic structures in them, were detected and measured. The RICO reaction also yielded a nondistillable oxidized residue. Pyrolysis of this material after methylation yielded a homologous series of n-alkanes and n-alk-1-enes, n-alkanoic and n-alkenoic acid methyl esters, and free n-alkanoic acids with strong even-to-odd carbon preference. These products prove the presence of naphthenic-attached n-alkyl side chains and bridges, polymethylene bridges connecting aromatic to naphthenic systems, and n-al...
TL;DR: Peat char samples produced by heat treatments under an inert atmosphere of nitrogen were characterized through 13C solid-state NMR, allowing the achievement of a detailed picture of the mechanism of mechanism.
Abstract: Peat char samples produced by heat treatments under an inert atmosphere of nitrogen were characterized through 13C solid-state NMR, allowing the achievement of a detailed picture of the mechanism o...
TL;DR: In this article, a comparison between three different types of techniques to predict the bed agglomeration tendency of a FBC (fluidized-bed combustor) was performed.
Abstract: In this paper a comparison between three different types of techniques to predict the bed agglomeration tendency of a FBC (fluidized-bed combustor) was performed. The three techniques were the standard ASTM ash fusion test, a compression strength based sintering test and a lab-scale combustion test. The tests were performed on 10 different types of biomasses. The results showed significant differences in the predicted bed agglomeration temperatures depending on which technique was used. The ASTM standard ash fusion test generally showed 50−500 °C higher temperatures than the sintering tests or the lab-scale FBC combustion tests. The sintering test showed, in five cases, 20−40 °C lower sintering temperatures than what was detected as the bed agglomeration temperature with the lab-scale FBC. In two cases, a significantly lower sintering temperature than the bed agglomeration temperature was detected, and in three cases, a significantly higher sintering temperature was detected than the bed agglomeration tem...
TL;DR: A multidisciplinary approach was followed, adopting diverse gravimetric, spectrometric, and chromatographic procedures as discussed by the authors, and three groups of variables were assessed simultaneously to help in solving the problem.
Abstract: Precipitated solid phases from oil wells and storage tanks have hampered oil operations and decreased revenues in Venezuelan facilities during recent decades. Physicochemical characterization of oils and separated solids was undertaken 6 years ago to understand the phenomenon and contribute to its prediction under production conditions. A multidisciplinary approach was followed, adopting diverse gravimetric, spectrometric, and chromatographic procedures. The purpose of this contribution is to summarize some of the most relevant findings from this research. Emphasis was focused more on the analytical aspects rather than on the engineering ones. Three groups of variables were assessed simultaneously to help in solving the problem. These were (I) the intrinsic nature of crudes, (II) mineral and porous matter effects, and (III) operational variables.