Fractionation of pitches by molecular weight using continuous and semibatch dense-gas extraction

A countercurrent, multistage, dense-gas extraction technique with reflux was investigated for the fractionation of carbonaceous pitches. Two modes of operation were investigated: continuous-stripping and semibatch operation. For example, continuous stripping with dense-gas toluene in the supercritical state, a positive column temperature gradient from 330 to 380 °C, and a pressure of 49 bar was used to strip the monomer and dimer species from an A-240 petroleum pitch feed, yielding a high molecular weight (mol wt) bottoms product rich in trimer and higher oligomers. Afterwards, semibatch operation was used with supercritical, dense-gas toluene, a temperature gradient of 330 to 380 °C, and pressures from 84 to 111 bar to fractionate the above bottoms product, yielding a trimer-rich overhead (average mol wt (M_w) = 800) and a tetramer and higher residue with M_w ∼ 1000. Considering the two operations as a unit, a combined selectivity factor of ∼350 was obtained. Not only is this at least an order of magnitude better than what can in principle be accomplished by conventional, single-stage solvent extraction, but such extraction is inapplicable to our system because of the insolubility of the pitch fractions of interest in typical liquid solvents. Matrix-assisted, laser desorption/ionization time-of-flight mass spectrometry (MALDI) was used to verify that separation was indeed occurring by mol wt and to study the relationship between the M_w, softening point, and C/H ratio of the fractions produced.     

Measurement of through-plane effective thermal conductivity and contact resistance in PEM fuel cell diffusion media

An experimental study was performed to determine the through-plane thermal conductivity of various gas diffusion layer materials and thermal contact resistance between the gas diffusion layer (GDL) materials and an electrolytic iron surface as a function of compression load and PTFE content at 70 °C. The effective thermal conductivity of commercially available SpectraCarb untreated GDL was found to vary from 0.26 to 0.7 W/(m °C) as the compression load was increased from 0.7 to 13.8 bar. The contact resistance was reduced from 2.4×10⁻⁴ m²°C/W at 0.7 bar to 0.6×10⁻⁴ m²°C/W at 13.8 bar. The PTFE coating seemed to enhance the effective thermal conductivity at low compression loads and degrade effective thermal conductivity at higher compression loads. The presence of microporous layer and PTFE on SolviCore diffusion material reduced the effective thermal conductivity and increased thermal contact resistance as compared with the pure carbon fibers. The effective thermal conductivity was measured to be 0.25 W/(m °C) and 0.52 W/(m °C) at 70 °C, respectively at 0.7 and 13.8 bar for 30%-coated SolviCore GDL with microporous layer. The corresponding thermal contact resistance reduced from 3.6×10⁻⁴ m²°C/W at 0.7 bar to 0.9×10⁻⁴ m²°C/W at 13.8 bar. All GDL materials studied showed non-linear deformation under compression loads. The thermal properties characterized should be useful to help modelers accurately predict the temperature distribution in a fuel cell.     

Preparation and filtration testing of diatomite filtering layer by acid leaching

Ceramic membrane filter consisting of the filtration layer obtained from natural diatomite particles (finer than 50 μm) by coating onto a large porosity support made of quartz-based materials was fabricated. The coating was achieved by pressure filtration at 5 bar and later sintering applied at 600 °C. The sintered product was leached by the hot acid solution (5 M HCl; 75 °C) for 1 h. The characteristic skeletal structure of diatomite (fine microscopic pores) could be obtained without deforming the structural integrity of coating. Filtration response of the filter was tested in dead-end and periodic pressure filtration modes. The filtered particles were of calcite (finer than 1.5 μm) obtained from a marble factory wastewater stream. The diatomite leaching increased the filtration capacity of the filter media more than two times. The filtrate has high clarity (0.1 NTU turbidity). The coating maintained structural stability during a filtration process performed at 5 bar and backflushing of 4 bar.     

Supercritical carbon dioxide extraction of oil from Mexican chia seed (Salvia hispanica L.): Characterization and process optimization

Supercritical carbon dioxide (SC-CO₂) was employed to extract oil rich in omega-3 fatty acids (FAs) from chia seeds, and the physicochemical properties of the oil were determined. A central composite rotatable design was used to analyze the impact of temperature (40 °C, 60 °C and 80 °C), pressure (250 bar, 350 bar and 450 bar) and time (60 min, 150 min and 240 min) on oil extraction yield, and a response surface methodology (RSM) was applied. The extraction time and pressure had the greatest effects on oil. The highest oil yield was 92.8% after 300 min of extraction time at 450 bar. The FA composition varied depending on operating conditions but had a high content of α-linolenic acid (44.4-63.4%) and linoleic acid (19.6-35.0%). The rheological evaluation of the oils indicated a Newtonian behavior. The viscosity of the oil decreased with the increase in temperature following an Arrhenius-type relationship.     

Hydrogen adsorption on KOH activated carbons from mesophase pitch containing Si, B, Ti or Fe

Different activated carbons with large micropore volume (0.78-0.99 cm³/g) have been prepared by KOH activation of mesophase pitch obtained by co-pyrolysis of a petroleum residue and small amounts of different compounds, triphenylsilane, borane pyridine complex, tetrabutyl orthotitanate or ferrocene. During the preparation, the Ti introduced in the petroleum residue concentrate into the activated carbon, whereas some loss of Si and Fe occurs. The compounds modify the size of mesophase structure formed during the co-pyrolysis process, as well as the apparent height of lamelae stack, L_c, both having an important effect in the development of the porosity of the activated carbon. However, there is a scarce influence of all heteroatoms in the adsorption capacity of H₂ at −196 °C and at 25 °C, which seems to be mainly influenced by the volume and size of micropores of the activated carbon. Only the activated carbon containing Fe adsorbs a higher amount of hydrogen at 25 °C and 10 MPa than the expected one according to its micropore volume.     

Fischer-Tropsch catalyst testing in a continuous bench-scale coal gasification system

A bench-scale oxygen-blown fluid-bed gasifier was coupled to a modular fixed-bed Fischer-Tropsch (FT) reactor system for testing an FT catalyst under syngas. Various blends of subbituminous coal, torrefied biomass, and untreated biomass were gasified at 22 bar absolute, 800°-860 °C, and 4 kg/h. Syngas exiting the fluid bed passed through a cyclone, candle filter, and sulfur sorbent to reduce fine particulate and H₂S to levels well below 1 ppmv. The syngas was cooled to condense out moisture and volatiles and then reheated to temperatures required for FT synthesis. The clean syngas then flowed into the FT reactor with a 5:1 ratio of recycled FT product gas-to-fresh syngas feed. A 70% overall conversion of CO and H₂ was achieved at 269 °C and 18.9 bar over an iron-based catalyst supported on gamma-alumina pellets.     

Continuous extraction of glycerol acetates from their mixture using supercritical carbon dioxide

Supercritical carbon dioxide was used for partially selective extraction of triacetin from a mixture of triacetin, diacetin, and monoacetin with a molar ratio of 1:2:1. The extraction was carried out in two stages. In the first stage, a central composite design was used to optimize the four variables of pressure, temperature, liquid CO₂ flow rate, and extraction time at three levels using a semi-continuous, supercritical carbon dioxide extraction setup. The composition of the extract under the predicted optimum conditions (i.e., 109 bar, 56 °C, 0.86 mL min⁻¹, and 61 min) was about 69% triacetin accompanied by only 30% diacetin and no detectable monoacetin. In the second stage, the effect of the two factors, pressure (100, 109, and 140 bar) and liquid CO₂ flow rates of 0.86 and 1.5 mL min⁻¹ measured at average laboratory temperature (27 °C) and pressure (0.89 bar), were studied using a continuous, supercritical carbon dioxide fractionation setup equipped with a glass-bead packed column kept under a thermal gradient of 56-70 °C. The experimental design was organized as a 3 × 2 general factorial design. Under the best conditions (i.e., 140 bar and 1.5 mL min⁻¹), the extraction yield of triacetin and diacetin were 41.8 and 3.0%, respectively, without any detectable monoacetin as verified by GC-FID.     

Controlling the Oligomeric Composition of Carbon-Fiber Precursors by Dense-Gas Extraction

Dense-gas extraction of M-50 petroleum pitch with the solvent toluene was carried out in a continuous, countercurrent-flow, packed column at temperatures from 330° to 380°C, pressures from 42 to 84 bar, and a solvent-to-pitch ratio of 5:1. Both one- and two-column configurations were used to fractionate raw pitches into top and bottom cuts of controlled oligomeric distribution. Using matrix-assisted laser desorption–ionization mass spectroscopy for absolute molecular weight determination, the effect of changes in pitch oligomeric distribution on both the softening point and the degree of anisotropy (i.e., isotropic–mesophase equilibrium) was established. For example, pitch fractions rich in dimer and trimer species, and with essentially all monomer removed, exhibit the anisotropic microstructure typically found in precursors for high-performance carbon fibers.     

Utilisation of the binders prepared from coal tar pitch and phenolic resins for the production metallurgical quality briquettes from coke breeze and the study of their high temperature carbonization behaviour

To reduce the cost of the formed coke briquettes which can be used as a substitute fuel to the metallurgical coke for the blast furnace from the coke breeze alternative binders and their blends were used. The high temperature behavior was investigated. The binders tested were: the nitrogen blown, air blown coal tar pitch and the blend of air blown coal tar pitch with the phenolic resins blends. The phenolic resin blends were prepared by mixing equal amount of resole and novalac. From the results, nitrogen blowing resulted in the weakest briquettes. The air blowing procedure should be preferred in place of nitrogen blowing for this purpose. When the air blown coal tar pitch was used alone as a binder, the briquettes must be cured at 200 °C for 2 h, then carbonized at a temperature above 670 °C. Since it requires higher temperature at carbonization stage, using air blown coal tar pitch alone as a binder was not economical. Therefore, the briquettes were prepared from the blended binder, containing air blown coal tar pitch and phenolic resins blend. The optimum amount of air blown coal tar pitch was found to be 50% w/w in the blended binder. Curing the briquettes at 200 °C for 2 h was found to be sufficient for producing strong briquettes with a tensile strength of 50.45 MN/m². When these cured briquettes were carbonized at temperatures 470 °C, 670 °C and 950 °C, their strength were increasing continuously, reaching to 71.85 MN/m² at the carbonization temperature of 950 °C. These briquettes can be used as a substitute for the metallurgical coke after curing; the process might not require un-economical high temperature carbonization stage.     

Influence of heat and pressure treatment on the rheological behavior of petroleum pitches

Pitch rheological properties are extremely important during the manufacturing process of carbon materials, in mesophase formation, and with regard to the final properties of the carbon products. In this work, pitch samples have been prepared from three different FCC decant oils by heat-treatment, under 0.9 MPa pressure, in a reactor at 390 °C, 410 °C, and 430 °C. These samples were analyzed in a rotational rheometer using a parallel-plate sensor. The rheometric softening points matched the results obtained using conventional equipment and exponential relationships were found to exist between these softening points and the pitch cosity when the former approached 180 °C. The quinoline-insoluble content (QI) has been shown to be more important in increasing the pitch viscosity than the toluene-insoluble content (TI). Oscillatory rheometry analysis has shown that an elastic response is not always found in creep and recovery tests, even when the elastic modulus G′ is dominant over the viscous modulus G′′. Pitch elasticity was found to be independent of the mesophase, and this pitch property was either only observed when the cross-over point occurred at very high frequencies or did not occur at all within the frequency range studied.     

Direct liquefaction of vitrinite concentrates obtained by column flotation

In this paper, direct liquefaction of vitrinite maceral concentrates was studied. Coals from Cerrejon and Jagua collieries (Colombia, South America) were used. Vitrinite concentrates were obtained by column flotation at pH 7, air velocity of 1.4 cm/s and frother concentration of 4 ml of frother/kg of coal. Digestion runs were made at 380, 400 and 420 °C and ratios tetraline/coal (S/C) of 2/1, 2.5/1 and 3/1. Liquefaction time was 30 min. For all runs, tetraline was the hydrogen donor solvent. Feed and vitrinite concentrates were liquefied in order to compare their conversion, product distribution and oils selectivity. It was observed that, in general, conversion rates obtained from vitrinite concentrates were higher than those obtained from feed coal. The results showed that conversion tend to increase with temperature as well as the S/C ratio. Product distribution showed that both oils and gas fractions tend to increase with temperature and S/C ratio, whereas residues have a contrary behaviour.     

Preparation of highly crystalline carbon nanofibers from pitch/polymer blend

High crystalline carbon nanofibers were prepared by using polymer blend technique. Naphthalene-based mesophase pitch (AR pitch) was dispersed finely in polymethylpentene matrix, spun by using a melt-blown spinning machine, stabilized at 160 °C in an oxygen atmosphere and carbonized at 900 °C in a nitrogen atmosphere. Bundles of the carbon nanofibers with ca. 100 nm in diameter were obtained after removal of polymethylpentene at the carbonization process. No impurity carbon was observed. The carbon nanofibers consisted of fine carbon crystallites with preferred orientation along the fiber axis. After heating to 3000 °C, the carbon crystallites grew drastically to have an interlayer spacing of 0.3367 nm and a crystallite thickness of 56.9 nm, respectively, with remarkable improvement of the preferred orientation of the crystallites. Advantages and disadvantages of the present method were discussed briefly.     

Hydrocracking of petroleum vacuum distillate containing rapeseed oil: Evaluation of diesel fuel

Hydrocracking of pure petroleum vacuum distillate and the same fraction containing 5 wt.% of rapeseed oil was carried out at 400 and 420 °C and under a hydrogen pressure of 18 MPa over commercial Ni-Mo catalyst. Reaction products were separated by distillation into kerosene, gas oil and the residue. Fuel properties of fractions suitable for diesel production were evaluated (gas oils and remixed blends of kerosene and gas oil). Gas oils obtained from co-processing showed very good fuel properties as the remixed distillates did. Gas oil obtained from co-processing at 420 °C showed also reasonable key low-temperature properties (cloud point: −23 °C, CFPP: −24 °C) similar to those of gas oil obtained from pure petroleum raw material processing.     

Experimental cloud points for polybutadiene + light solvent and polyethylene + light solvent systems at high pressure

The hydrogenation of unsaturated heavy compounds is conventionally carried out in the presence of two fluid phases, because the immiscibility in the binary subsystem ‘hydrogen + heavy substrate’ cannot be overcome by adding a standard solvent. Using a supercritical or quasicritical solvent allows the hydrogen and the unsaturated heavy substrate to dissolve into a single phase. To select the operating conditions of a supercritical reactor, it is necessary to determine the phase boundaries of the subsystems ‘solvent + hydrogen’ and ‘solvent + heavy compound’. In this work, we measured cloud points for binary systems made of polybutadiene (PB) or polyethylene (PE) and a light solvent, i.e., propane or dimethyl ether (DME) or diethyl ether (DEE). The temperature range studied was from 50 to 160 °C for ‘PB + DME’ and ‘PB + Propane’ and from 100 to 190 °C for ‘PB + DEE’ and ‘PE + DEE’. We found that in PB-containing binary systems, at the ranges of conditions of the experiments, the minimum pressure required to guarantee homogeneity, at any temperature, is below 200 bar for DEE, below 300 bar for DME and in the order of 500 bar when using propane as solvent. Our data for ‘PE + DEE’ indicate the need for a minimum pressure of about 240 bar to keep the system within a single phase. The results from this work and from the literature suggest that the use of binary solvent mixtures may be convenient to carry out the supercritical hydrogenation of PB.     

Hydrothermal reforming of bio-diesel plant waste: Products distribution and characterization

A viscous waste derived from a bio-diesel production plant, in the form of crude glycerol, was reacted under subcritical and supercritical water conditions and the product composition determined in relation to process conditions. Preliminary analysis of the original sample showed that the main constituent organic compounds were methanol (20.8 wt.%), glycerol (42.3 wt.%) and fatty acid methyl esters (33.1 wt.%). Uncatalyzed reforming experiments were carried out in a 75 ml Hastelloy-C batch reactor at temperatures between 300 °C and 450 °C and pressures between 8.5 MPa and 31 MPa. Oil/wax constituted more than 62 wt.% of the reactions products. At 300 °C, the main product was a waxy material containing mainly glycerol and fatty acid methyl esters. As the temperature increased to supercritical water conditions, low viscosity oils were produced and all of the glycerol was reacted. The oils contained mainly saturated and unsaturated fatty acid esters as well as their decomposition products. The gaseous products were carbon dioxide, hydrogen and methane and lower concentrations of carbon monoxide and C₂-C₄ hydrocarbons. No char formation was observed. However, during alkaline gasification with sodium hydroxide at 380 °C, the reaction products included a gaseous effluent containing up to 90% by volume of hydrogen, in addition to oil and significant amount of whitish solid residue (soap). Sodium hydroxide influenced the production of hydrogen via water-gas shift by the removal of carbon dioxide as sodium carbonate, but also decreased oil product possibly through saponification.     

Primary carbonization of an anisotropic ‘mesophase’ pitch compared to conventional isotropic pitch

The evolution during carbonization treatments of a 100% anisotropic pitch (pitch C) was compared to that of Ashland 240 (100% γ resins). The anisotropic pitch C results from a gas-sparge preparation leading to a composition of 93% β resins (QS-TI) and 7% γ resins (QS). It is made of a major component (QS-TI), in which droplets (100-300 nm in size) partially toluene soluble are distributed. The physicochemical, textural and microtextural evolutions of the two pitches were studied. During pitch C primary carbonization, anisotropic droplets grow by coalescence, then decompose into Brooks and Taylor mesophase spheres suspended in isotropic drops. These drops develop at the expense of the anisotropic matrix by a continuous regeneration of the small anisotropic droplets which feed the isotropic drops by diffusion process. Then inside these drops, mesophase spheres grow then coalesce and the behaviour of a conventional pitch is restored. These various molecular associations are due to absence of chemical events below 450 °C, leading to the global mass spectrum being constant. At 500 °C the material is homogeneously anisotropic though plastic, the metastable system is destroyed and the evolution of conventional pitches is recovered, i.e. above 550 °C macropores develop up to solidification at 600 °C (semi-coke stage).     

On the chemistry of the oxidative stabilization and carbonization of carbonaceous mesophase

Two mesophase samples, one derived from a coal-tar pitch (M-A) and the other from a naphthalene-based pitch (M-B), were stabilized with air in a temperature range of 200-300 °C and then carbonized to 1000 °C. Elemental analysis and FTIR spectroscopy were used to monitor the changes produced by oxygen in the chemical composition of the mesophase samples at different stages of stabilization (from 200 to 300 °C) and after carbonization of the stabilized samples (from 300 to 1000 °C). The results show that oxidative stabilization is a dehydrogenative process, where the hydrogen removed is predominantly aliphatic and the oxygen uptake is mainly in the form of C-O-C and CO groups. The more aliphatic character of M-B accelerates the stabilization process with respect to M-A. M-B shows a higher weight gain and also a greater variety of oxygen-containing functional groups. As a result, the plasticity of M-B is more affected by changes in the stabilization temperature than that of M-A. Thus, the stabilization process is easier to control in the case of M-A. On carbonization, oxygen and hydrogen are removed from the stabilized samples and the carbons generated exhibit an increase in interlayer spacing and a decrease in crystallite size as the carbonization temperature increases.     

Electrochemical synthesis of Ni-Sn alloys in molten LiCl-KCl

The electrochemical formation of Ni-Sn was investigated in molten LiCl-KCl in the temperature range 380-580 °C. Before, an electrochemical study of the Ni²⁺/Ni⁰, Sn⁴⁺/Sn²⁺ and Sn²⁺/Sn⁰ redox couples was performed by cyclic voltametry and chronopotentiometry in a wide temperature range. It had been pointed out that in the case of the Sn⁴⁺/Sn²⁺ redox couple, an insoluble compound is probably formed for T < 460 °C. For higher temperature, this compound becomes soluble and then, the shape of the cyclic voltammogram is analogue to the one usually observed when a diffusion-controlled process is involved. The diffusion coefficient values of Ni²⁺ and Sn²⁺ ions were determined. For instance, D_Ni(II) and D_Sn(II) values deduced from chronopotentiometry were about 2.1 × 10⁻⁵ and 2.7 × 10⁻⁵ cm² s⁻¹ at 440 °C, respectively. Then, Ni-Sn alloys have been formed in potentiostatic mode. The electrochemical route proposed in this paper leads to the formation of crystallized alloys with a well-defined composition depending on the operating conditions.     

Low-temperature solution combustion synthesis of high performance LiNi0.5Mn1.5O4

High-voltage LiNi_0.5Mn_1.5O₄ spinels were synthesized by a low temperature solution combustion method at 400 °C, 600 °C and 800 °C for 3 h. The phase composition, structural disordering, micro-morphologies and electrochemical properties of the products were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and constant current charge–discharge test. XRD analysis indicated that single phase LiNi_0.5Mn_1.5O₄ powders with disordered Fd-3m structures were obtained by the method at 400 °C, 600 °C and 800 °C. The crystallinity increased with increasing preparation temperatures. XRD and FTIR data indicated that the degree of structural disordering in the product prepared at 800 °C was the largest and in the product prepared at 600 °C was the least. SEM investigation demonstrated that the particle size and the crystal perfection of the products were increased with increasing temperatures. The particles of the product prepared at 600 °C with ~200 nm in size are well developed and homogeneously distributed. Charge/discharge curves and cycling performance tests at different current density indicated that the product prepared at 600 °C had the largest specific capacity and the best cycling performance, due to its high purity, high crystallinity, small particle size as well as moderate amount of Mn³⁺ ions.     

Catalytic hydroprocessing of cottonseed oil in petroleum diesel mixtures for production of renewable diesel

The conversion of the esters included in refined cottonseed oil into hydrocarbon molecules compatible with petroleum diesel, which are named renewable diesel, has been studied at conventional hydrotreatment conditions. The vegetable oil was fed in mixture with desulphurized petroleum diesel to the hydrotreater containing a conventional CoMo/Al₂O₃ hydrotreatment catalyst. Conversion of esters was determined in the temperature range of 305-345 °C, at 30 bar and for 5 h⁻¹ < WHSV < 25 h⁻¹. Catalyst deactivation was followed for a period of 450 h in operation. A simple kinetic model of ester conversion suitable for scale-up and simulation studies has been tested.