Mesophase Content Research Articles

Mesophase formation behavior in petroleum residues

Mesophase pitch is an important starting material for making a wide spectrum of industrial and advanced carbon products. It is produced by pyrolysis of petroleum residues. In this work, mesophase formation behavior in petroleum residues was studied to prepare environmentally- benign mesophase pitches, and the composition of petroleum residues and its influence on the mesophase formation was investigated. Two petroleum residues, i.e., clarified oil s (CLO-1, CLO-2) obtained from fluid catalytic cracking units of different Indian petroleum refineries, were taken as feed stocks. A third petroleum residue, aromatic extract (AE), was produced by extraction of one of the CLO-1 by using N-methyl pyrrolidone solvent. These petroleum residues were thermally treated at 380°C to examine their mesophase formation behavior. Mesophase pitches produced as a result of thermal treatment were characterized physico-chemically, as well as by instrumental techniques such as Fourier-transform infrared spectroscopy, nuclear magnetic resonance, X-ray diffraction and thermogravimetry/derivative thermogravimetry. Thermal treatment of these petroleum residues led to formation of a liquid-crystalline phase (mesophase). The mesophase formation behavior in the petroleum residues was analyzed by optical microscopy. Mesophase pitch prepared from CLO-2 exhibited the highest mesophase content (53 vol%) as compared to other mesophase pitches prepared from CLO-1 and AE.

Reinforced and Ultraviolet Resistant Silks from Silkworms Fed with Titanium Dioxide Nanoparticles

As the perfect combination of strength and luster, silkworm silks have been widely used in many fields but still need improvements. This paper demonstrates an in vivo uptake of titanium dioxide (TiO2) nanoparticles by silkworms, leading to the direct production of intrinsically modified silk. The nanoparticles can be easily incorporated into the silk gland of silkworm by using this method due to the interactions between TiO2 and silk fibroin molecules. Infrared spectra indicate that TiO2 nanoparticles confine the conformation transition of silk fibroin from random coil/α-helix to β-sheet. Results of synchrotron radiation wide-angle X-ray diffraction and small-angle X-ray scattering suggest that modified silks have lower crystallinity, higher mesophase content, and higher Herman’s orientation functions of crystalline region and mesophase region than control group. The breaking strength and elongation at break of the modified silk can be improved up to 548 ± 33 MPa and 16.7 ± 0.8%, respectively, by adding 1...

Very high methane uptake on activated carbons prepared from mesophase pitch: A compromise between microporosity and bulk density

Two petroleum residues were pyrolyzed under two different conditions to obtain pitches with low or high mesophase content. The effect of the KOH: precursor ratio and the activation temperature on the packing density and porous texture of the carbons have been studied and optimized. Activated carbons combining high micropore volume (>1cm3/g) and high packing density (0.7g/cm3) have been successfully prepared. Regarding excess methane adsorption capacities, the best results (160cm3 (STP)/cm3 at 25°C and 3.5MPa) were obtained using the pitch with the higher content of the more organized mesophase, activated at relatively low temperature (700°C), with a medium KOH: precursor ratio (3:1). Some of the activated carbons exhibit enhanced adsorption capacity at high pressure, giving values as high as 175cm3 (STP)/cm3 at 25°C and 5MPa and 200cm3 (STP)/cm3 at 25°C and 10MPa (the same amount as in an empty cylinder but at half of the pressure), indicating a contribution of large micropores and narrow mesopores to adsorption at high pressure. The density of methane in pores between 1 and 2.5nm at pressure up to 10MPa was estimated to understand their contribution to the total adsorption capacity.

Catalyzing mesophase formation by transition metals

In this work, environmentally-benign mesophase pitches were prepared from feed stocks obtained from two different petroleum refinery processes namely ‘clarified oil’ (CLO) from fluid catalytic cracking (FCC) unit of Fuel Block and ‘heavy extract’ (HE) from solvent extraction unit of Lube Block by giving thermal treatment at 370°C. The effect of thermal treatment and role of transition metal catalysts on development of mesophase in petroleum feed stocks have been discussed in this paper. Mesophase formation behavior in the feed stocks and microstructures of mesophase pitches produced were investigated by optical microscopic imaging. It was observed that mesophase formation in the feed stocks was slow under the influence of thermal soaking only. The addition of divalent transition metal salts of cobalt and nickel during thermal soaking accelerates the mesophase formation in pitches. The addition of 3wt% of cobalt catalyst enhanced the mesophase content (MC) from below countable limit (BCL) to 16vol% in CLO pitch and from 10 to 40vol% in HE pitch and also reduced thermal soaking time in both the cases. The 3wt% of nickel catalyst also showed similar behaviour and enhanced the mesophase content (MC) from below countable limit (BCL) to 13vol% in CLO pitch and from 10 to 18vol% in HE pitch in shorter thermal soaking time. The study further revealed that cobalt catalyst exhibited greater catalytic activity for mesophase formation than nickel catalyst. These catalysts also help to increase the yield of mesophase pitches. Pitch yield in case of uncatalysed pitch CLO-0-0 is 11.88wt% which increases to 16.22wt% (CLO-Co-3) and 15.08wt% (CLO-Ni-3), whereas in case of heavy extract pitch yield increases from 24.41wt% (HE-0-0) to 24.79wt% (HE-Co-3) and 26.16wt% (HE-Ni-3) by the addition of Co and Ni catalysts. The effect of transition metal catalysts on mesophase pitch properties such as elemental analyses (CHNS), softening point (SP), coking value (CV), toluene insolubles (TI) and quinoline insolubles (QI) have also been studied. The mesophase pitches were also characterized using NMR spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy, X-ray diffraction (XRD) and thermogravimetric analyses (TG/DTG).

Formation and properties of polypropylene/stearic acid composite fibers

This paper refers to the formation and properties of polypropylene/stearic acid (PP/SA) composite fibers. For the investigation, commercial metallocene-catalyzed PP polymer and SA were used. The fibers were produced in laboratory conditions using the single screw spin draw device. The textile-mechanical properties, surface composition, morphology and supermolecular structure of as-spun fibers were studied. Moreover, the nonisothermal crystallization of the PP/SA blend and melting behavior of fibers were analyzed. In the investigation Fourier transform infrared–attenuated total reflectance, scanning electron microscopy, differential scanning calorimetry and wide-angle X-ray analytical methods were used. The research showed that the PP/SA blend has lower viscosity compared to the pure polymer and that during the PP crystallization phase, separation is induced. SA delays crystallization of PP, and interaction between SA and PP is observed. The as-spun PP/SA fibers have higher linear density, higher elongation at break and slightly lower tenacity compared to fibers produced from pure PP. The fibers contain a structure with high content of mesophase. During fiber formation, SA migrates towards the fiber surface and forms droplets located beneath the surface of the fiber or crystallizes outside in the form of flake-like crystals.

Low shear rheological behaviour of two-phase mesophase pitch

The low shear rate rheology of two phase mesophase pitches derived from coal tar pitch has been investigated. Particulate quinoline insolubles (QI) stabilised the mesophase spheres against coalescence. Viscosity measurements over the range 10–106Pas were made at appropriate temperature ranges. Increasing shear thinning behaviour was evident with increasing mesophase content. At low mesophase contents the dominant effect on the near Newtonian viscosity was temperature but at higher contents it was the shear rate; temperature dependence declined to near zero. The data indicated that agglomeration could be occurring at intermediate mesophase volume fractions, 0.2–0.3. The Krieger–Dougherty function and its emulsion analogue indicated that in this region the mesophase pitch emulsions actually behaved like ‘hard’ sphere systems and the effective volume fraction was estimated as a function of shear rate illustrating the change in extent of agglomeration. At the higher volume fractions approaching the maximum packing fraction, which could only be measured at higher temperatures, the shear thinning behaviour changed in character and it is considered that this is possibly due to shear induced deformation and breakup of dispersed drops in the shear field.

Effect of processing variables on the thermal and physical properties of poly(L-lactide) spun bond fabrics

In this paper, the influence of the take-up velocity ( Vt–u) of fibers on the molecular ordering and ά – α form transition of polylactide (PLA) non-woven fabrics during their manufacturing by spun-bonding is described. Non-woven samples were studied by wide-angle X-ray diffraction, differential scanning calorimetry and Fourier transform infrared spectroscopy. In addition, the physical and mechanical properties of the non-woven fabrics were determined. The results are discussed in terms of the structural changes of the PLA and the meso-phase content during the spun-bonded non-woven fabric forming process. This technological process includes preliminary molecular ordering of the PLA fibers in a downstream spinning block and crystallization on a calender system at a temperature higher than the glass transition. The molecular ordering of the investigated PLA fabric samples under different technological conditions was observed as follows: creation of the meso-phase and a disorder-to-order phase transition (ά to α form) during heating to approximately 110℃ and an increase in the degree of crystallinity for take-up velocities higher than 1400 m/min. The structural changes of the PLA explain the observed changes in the physical and mechanical properties of the non-woven fabrics obtained under different technological conditions.

Preparation and characterization of high surface area activated carbons from co-pyrolysis product of coal-tar pitch and rosin

Co-pyrolysis product of coal-tar pitch and rosin was used as a precursor to prepare high surface area activated carbons (ACs) by KOH activation. The influences of AC precursor origin, KOH/AC precursor weight ratio and activation time on the pore characteristics of the ACs were investigated, and meanwhile their electrochemical performance was studied. The results show that adding rosin results in a decrease in the C/H atomic ratio of AC precursor as well as a significant increase in its mesophase content, which favors the porosity development in ACs during KOH activation. The effect of adding rosin on the porosity characteristics of the ACs can be illustrated by increases in the BET surface area from 1846 to 2847m2/g and the total pore volume from 1.09 to 1.57cm3/g. In addition, the ACs possess good electrochemical performance, as indicated by that they have a maximum specific capacitance of 203F/g and exhibit good rectangular-shaped I–V curves in cyclic voltammetry.

Preparation of high metal content nanoporous carbon

Activated carbons with high metal content have been prepared by the pyrolysis of ethylene tar with dissolved metal acetylacetonates (Ti, V, Fe, Co, Ni and Cu) and subsequent activation with KOH of the pitch obtained in pyrolysis. These metal compounds decompose during the pyrolysis of ethylene tar yielding metal nanoparticles formed by metal and/or oxide which are homogeneously distributed in the pitch and remain in the activated carbon, so that the concentration of metal is, in most cases, 4–5 times higher than in the pristine ethylene tar. Since KOH is an effective activating agent, all activated carbons combine a high porosity development with a high metal content. In some of the carbons, such as P2FeA (3.3% Fe, pore volume 1.84cm3/g, BET surface area 3270m2/g), there is even an increase in the pore volume when compared to the activated carbon prepared in the same way without metal, in spite of the fact that the metal increases the weight of carbon without contributing to the adsorptive capacity. It seems that iron, on the one hand modifies the pyrolysis to give a pitch with larger mesophase content and on the other hand it locally catalyzes carbon gasification with the CO2 produced along the synthesis of the carbon. In addition to its influence on activation, iron promotes the formation of graphitic carbon fibers.

Influence of the calender temperature on the crystallization behaviors of polylactide spun-bonded non-woven fabrics

In this paper the influence of calender temperature on the crystallization behavior of polylactide (PLA) non-woven fabrics during their manufacturing by the spun-bonding technique is described. Non-woven samples were studied by wide-angle X-ray diffraction, differential scanning calorimetry and birefringence. In addition, physical–mechanical properties of the non-woven fabrics were determined. The results are discussed in terms of structural changes of PLA and meso-phase content during the calendering process in the temperature range 70–130℃. The rebuilding of the supermolecular structure of the investigated samples of PLA fabrics under the influence of increasing calender temperature is observed in terms of the disorder-to-order phase transition (ά to α form) during heating around 110℃, and increased degree of crystallinity up to 100℃. The presented structural rebuild of PLA explains observed changes of physical–mechanical properties of the non-woven fabrics obtained at different calendering temperatures. During calendering above 100℃, thermal degradation of PLA occurs at the point of contact between the non-woven fabrics and the calender rollers.

Effect of elastomer on crystalline transition and deformation behavior of isotactic polypropylene

The structural evolution during uniaxial tensile deformation of isotactic polypropylene (iPP) and its blend with olefin block copolymer (OBC) was comparatively investigated by in-situ synchrotron X-ray scattering. Small angle X-ray scattering showed that cavitation in iPP/OBC blend took place at a smaller strain than that in neat iPP. The reorientation of the cavities in iPP/OBC occurred at a lower strain than that in iPP as well. Wide angle X-ray scattering was applied to study the crystal-mesophase transition and the orientation process. Compared to the sharp transition in neat iPP, the mesophase formation and orientation in iPP/OBC blend proceeded gradually. The mesophase content and degree of orientation of iPP matrix in iPP/OBC blend were much lower than that in neat iPP within the investigated strain range. By the combination of scattering results and morphological observations, a deformation mechanism based on strain distribution and fracture mechanics was proposed.

Production of nanoTiC–graphite composites using Ti-doped self-sintering carbon mesophase powder

This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO2 nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC.

KOH activation of carbon materials obtained from the pyrolysis of ethylene tar at different temperatures

A complete study of the importance of the pyrolysis temperature (up to 1500°C) of a petroleum residue (ethylene tar) in the activation with KOH of the resultant pyrolysis products (covering from the own ethylene tar to pitches and well developed cokes) has been carried out. The trend in the porosity found for activated carbons is as follows: the pore volume increases with the pyrolysis temperature reaching a maximum value (1.39cm3/g) at about 460°C, just at the transition temperature between a fluid pitch and a solid coke. It is the pitch with highest mesophase content that develops the maximum porosity when activated with KOH. The amount of H2, CO and CO2 produced during the reaction of the mesophase pitch and coke with KOH has been quantified, and a trend as described for the pore volume was found with the pyrolysis temperature. Therefore, there is a relationship between the reactivity of the precursor with KOH and the porosity developed by the activated carbon. Since the reactions that produce H2 initiate at temperatures as low as 300°C, it seems that KOH is modifying the conditions under which the pyrolysis occurs, and this fact is critical in the development of porosity.

The effect of molecular composition and structure on the development of porosity in pitch-based activated carbon fibers

Seven oligomeric fractions of well-defined composition and molecular weight distribution were generated via supercritical extraction from an isotropic petroleum pitch (M-50) and used as precursors for the production of activated carbon fibers. Both isotropic and mesophase-containing fractions were produced, so that the effects of molecular order and molecular weight could be separated. Carbonization weight loss was found to gradually decrease with increasing molecular weight (and oligomeric number), with mesophase content not being a significant factor. Similar behavior was observed for activation weight loss when the precursors were isotropic; however, even modest increases in molecular order significantly retarded the activation process and resulted in dramatic drops in specific pore volume. A 100% dimer precursor fraction with an average molecular weight of 480Da produced activated carbon fibers with the highest (specific) pore volume, and the highest pore volume in the range desired for hydrogen adsorption (6–7Å). Even for isotropic precursors, decreases in pore volume with increasing molecular weight were observed. The incremental pore size distribution generated from the nitrogen adsorption data consisted of discrete peaks, which is consistent with the formation of pores by the removal of short micrographene layers, with each layer being formed from an individual oligomeric molecule.

Influence of the meso phase in high-temperature pitch on the properties of artificial graphite

A relation is established between the content of meso phase in high-temperature pitch and the condensation of coal tar used for pitch production. The influence of the meso-phase content in the high-temperature pitch on the quality of the artificial graphite produced is demonstrated.

Formation of polypropylene/stearic acid fibers

Polypropylene/stearic acid fibers were produced in laboratory conditions from hot homogenous blends. After formation, as-spun fibers were treated in potassium hydroxide and rinsed in water. Supermolecular structure and morphology of fibers were investigated by wide-angle X-ray scattering, FTIR, and scanning electron microscopic (SEM) methods. It was stated that by fibers' formation, thermally induced phase separation takes place. Polypropylene starts to crystallize, while liquid stearic acid is expelled out and forms drops wrapped in polymer matrix. As a result of the crystallization inside fibers the structure with high content of mesophase is formed. During crystallization, interactions between stearic acid and polypropylene are observed. As a result of alkali treatment and rinsing, drops of stearic acid are partially removed. After removal of the stearic acid from the fibers, the porous structure is formed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Isotropization, perfection and reorganization of the mesophase of isotactic polypropylene

The perfection, reorganization, and isotropization of the mesophase of isotactic polypropylene were investigated by fast scanning calorimetry (FSC). The analysis was made at different heating rates, to evaluate the isotropization temperature of the initially grown mesophase and of mesophase which has been perfected or even reorganized into crystals. Mesophase formation is paralleled by formation of a rigid–amorphous fraction which was about twice the mesophase content. While the isotropization temperature of the initially grown mesophase is controlled by the temperature of its formation, the isotropization temperature of perfected or reorganized mesophase was independent on the condition of prior formation. Absence of exothermic heat flow during heating suggests that the mesophase converted gradually into crystals due to the fast heating rate. The discussion of data includes new ideas about nucleation, growth, and perfection of the mesophase, involving nanophase to microphase and rigid–amorphous fraction to mesophase transitions.

Determining the anisotropic content in a petroleum pitch – Comparison of centrifugation and optical microscopy techniques

The anisotropic content of a pitch is one of the most important parameters for characterizing such materials. Polarized light optical microscopy is the technique most commonly employed (ASTM D 4616 standard procedure) to measure this pitch parameter. However, this standard procedure is limited to pitches with mesophase contents only up to 20%. An alternative technique for determining the anisotropic content of a pitch is high-temperature centrifugation, which can be used without limitation for pitches with up to 100% anisotropic content. In this work, the two techniques have been compared; samples of four pitches with mesophase contents lower than 20% have been analyzed by both techniques and the results have been compared. The high-temperature centrifugation technique showed good repeatability, and the results that it yielded matched those obtained from optical microscopy when the anisotropic content of the pitch was higher than around 5%. The centrifugation technique is always faster, simpler, and possibly more accurate than optical microscopy for pitches with mesophase contents higher than 20%.

New insights on the direct activation of isotropic petroleum pitch by alkaline hydroxides

The paper provides interesting evidences that a low softening point isotropic petroleum pitch can be used as a good carbon precursor for the preparation of activated carbons. The activation is carried out by KOH and/or NaOH and the resulting activated carbons present well developed porosity. Such hydroxide activations can be done directly on the pristine petroleum pitch (P) or on the pitch that has been submitted to an air stabilisation followed by a N 2 heat treatment (TAN). In general, KOH activation produces better results than NaOH, both in terms of porosity and yield, the results obtained for the activation of TAN being impressive because of the good porosity developments and high yields reached. The different treatments carried out over the petroleum pitch precursor clearly show that they significantly influence the extent of microporosity development. This is due to different changes occurring in the porous structure of the precursor as a function of the treatment carried out. The efficiency of the activation process increases as the mesophase content of the precursor decreases, as well as the mesophase formation during the activation process is avoided.

Obtenção de piches mesofásicos em dois estágios a partir de piche de petróleo

A obtenção de piches mesofásicos para a produção de fibras de carbono de alta performance foi investigada por meio de tratamento térmico de três piches de petróleo, em dois estágios em um reator com agitação magnética e capacidade de 700 g. O primeiro estágio consistiu de um pré-tratamento sob agitação e atmosfera de nitrogênio a 0,9 MPa, a 390, 410 e 430 °C, durante três horas. No segundo estágio, o tratamento térmico foi realizado por mais três horas, sob pressão atmosférica. Durante os experimentos, amostras foram recolhidas e analisadas por meio de medidas de solubilidade em tolueno e quinolina, ponto de amolecimento e o percentual de mesofase. Foi verificado que, para todos os piches produzidos, nas temperaturas de 390 e 410 °C a variação dos parâmetros físico-químicos foi muito pequena e que os tratamentos térmicos no patamar de 430 °C produziram piches com pontos de amolecimento acima de 300 °C, e percentual de mesofase próximo a 70%.