Sorption and recovery of heavy oils using carbonized fir fibers and recycling

Fibers extracted from fir trees (Abis sachalinensis Fr. Schm) and carbonized at either 380 or 900°C were found to have a high performance for sorption, recovery and recycling of heavy oils, even the viscous ones. Sorption capacity showed strong dependence on bulk density of carbonized fibers, suggesting the importance of the space formed among entangled fibers: 60-80 g/g for bulk density of ca. 6 kg/m³ and 10-20 g/g for density of ca. 40 kg/m³. The sorption capacity of carbonized fir fibers for a less viscous heavy oil was almost comparable to that of exfoliated graphite which was also reported to have high capacity. For viscous oil, however, carbonized fir fibers had higher sorption capacities than exfoliated graphite, particularly when the bulk densities are high. Less viscous heavy oil could be recovered by simple filtration under suction and the fibers could be reused for the sorption of oil, although the sorption capacity decreased with recycling. Their recycling performance was also strongly dependent on their bulk density: the sorption capacity of 6 kg/m³ fibers after the eighth cycle became less than 60% from that of the first cycle, but for 35 kg/m³ fibers it was more than 90%. Viscous oil could be recovered only by washing with n-hexane and also with less viscous oil. After washing the fir fibers could be reused for the sorption of oil.     

Sorption and recovery of heavy oils using exfoliated graphite Part IV: Discussion of high oil sorption of exfoliated graphite

The correlation between sorption capacity for heavy oil with a viscosity of 0.004 kg/m s and pore volume measured by a mercury porosimeter was studied on exfoliated graphite samples with different bulk densities. Pore volume measured by using the conventional dilatometer (N-type cell), which gives information on the pore size from 0.004 to 4 μm, was too low to explain the sorption capacity measured. However, pore volume measured by a special dilatometer (U-type cell) for large pore sizes up to 600 μm was very closed to sorption capacity. Pore volume measured by this U-type cell showed a linear relation to sorption capacity of exfoliated graphite samples, of which the slope was the same value as the density of heavy oil used (860 kg/m³). Therefore, large pores, which are reasonably assumed to be inter-particle pores among entangled worm-like particles of exfoliated graphite, were responsible for the large sorption capacity of heavy oils. Intra-particle pores inside and cleavage-like pores on the surface of worm-like particles were assumed to assist the capillary pumping of heavy oil.     

Oil sorption and recovery by using vertically aligned carbon nanotubes

We used carbon nanotubes as oil adsorbents and evaluated recycling performance by squeezing method. The sorption capacity of 3 mm long vertically aligned carbon nanotubes is almost 6.9 times higher than that of agglomerated carbon nanotubes due to the existence of large-sized macropores. Compared with exfoliated graphite (41 g/g), aligned carbon nanotubes exhibit higher sorption capacity (69 g/g) and better recycling performance due to their unique mechanical strength and excellent rebound resilience properties at high strains.     

Recovery of heavy oil from contaminated sand by using exfoliated graphite

Heavy oil was recovered from contaminated sand through capillary suction into exfoliated graphite with differentpacked densities by using model sands, alumina powders, with different particle sizes. For efficient recovery it was important to have an appropriate combination of average size of sand particles and packed density of exfoliated graphite. Pumping of heavy oil into exfoliated graphite occurs as a balance in an attracting capillary force between exfoliated graphite and sand, the former being stronger than the latter because of the hydrophobic nature of the surface of graphite.     

Small angle X-ray scattering from voids within fibers during the stabilization and carbonization stages

Five kinds of commercial carbon fibers heat-treated at various temperatures were adopted to investigate the scattering from voids within the fibers by small angle X-ray scattering (SAXS), since the voids produced during stabilization and carbonized processes provide unfavorable influence on mechanical properties of the carbon fibers. The theoretical calculation was carried out for SAXS by assuming ellipsoidal voids with different shapes. In this model system, the long axis of all ellipsoidal voids on the two-dimensional plane was assumed to be oriented predominantly with respect to the machine direction but the center of gravity of each void are assumed to be arranged in the transverse direction assuring one-dimensional lattice. To analyze inter-particle interference effect from ellipsoidal voids, the function H₁(y) proposed by Hoseman was introduced to represent the probability of finding the nearest-neighbor void at a displacement vector. In comparison with observed and calculated SAXS patterns, the inter-particle interference effect was observed for the fibers carbonized at 1200-1700 °C but the effect disappeared with further heat-treatment at 3000 °C. Namely, the scattering from the fiber heat-treated at 3000 °C, which is so-called graphite fiber, showed no inter-particle interference effect. Namely, void distribution of high modulus carbon fiber with graphite crystallites was different from that of high strength carbon fiber with turbostratic structures.     

A rapid and efficient method to prepare exfoliated graphite by microwave irradiation

Exfoliated graphite materials had been rapidly and efficiently prepared by microwave irradiation in a short time (about 4 min including 3 min mixing and 1 min microwave irradiation). The promotion of the intercalation by microwave irradiation was proven by X-ray diffraction. With increasing content of oxidant and intercalation agent, the expanded volume of exfoliated graphite increased at first and then decreased. When the weight ratio of natural graphite and nitric acid to potassium permanganate was set at 1:2:1, the expanded volume of exfoliated graphite reached the maximum value (312 mL/g) and sorption capacity of this exfoliated graphite was 56 g of engine oil and 32 g of kerosene per 1 g of exfoliated graphite.     

Preparation of Carbonized Kapok Fiber/Reduced Graphene Oxide Aerogel for Oil-Water Separation

A carbonized composite aerogel was fabricated based on kapok fibers (KFs) and graphene oxide (GO) through hydrothermal and carbonizing reactions. The as-prepared carbonized kapok fiber/reduced graphene oxide (CKF/RGO) aerogel exhibited special features including light weight, fire resistance, stable structure, hydrophobicity, and oleophilicity. The wettability of the KF/GO aerogel was transformed to hydrophobicity after carbonization, which provided the CKF/RGO aerogel with a distinct ability for oil-water separation. The CKF/RGO aerogel was able to adsorb oil liquids up to 110 times of its own weight. The sorption capacity of the CKF/RGO aerogel was still higher than 90 % of the initial sorption capacity after eleven sorption-combustion cycles of n-hexane solvent.     

Hollow carbon beads fabricated by phase inversion method for efficient oil sorption

Hollow carbon beads of around 3.0 mm in diameter were prepared by a simple phase inversion method and subsequent carbonisation. Due to the low density and hydrophobic property, the hollow carbon beads were floatable on water. Different organic solvents and oils were used to study the oil sorption properties of the carbon beads. Their toluene sorption capacity was as high as 55% of their own volume. For long-chain oil like motor oil, the hollow carbon beads still adsorbed 40% of their volume. In addition, the hollow carbon beads could be refreshed by heat treatment, and the oil sorption capacity remained the same after being recycled five times. This work provides a facile and low-cost method for preparing highly efficient carbon-based sorbents for oil spill clean-up.     

Superhydrophobic and photothermal sponge for effective oil/water separation and solar-assisted recovery of viscous oil

With the occurrence of offshore oil spills, the recovery of viscous oil continues to be a significant issue. The multi-functional sponge with superhydrophobic, absorption of high viscosity oil is an effective approach to settle this problem. In this work, the melamine-formaldehyde (MF) sponge was the backbone and doped with polydopamine (PDA) to mimic mussels. Subsequently, candle soot nanoparticles (CS) and polydimethylsiloxane (PDMS) were applied to modify the MF sponge into a superhydrophobic sponge (P-CS-PDA@MF) (WCA = 153.56°). The P-CS-PDA@MF sponge showed good absorption properties for many oils and organic solvents (33.87–78.90 times of its own weight). In addition, the P-CS-PDA@MF sponge also showed outstanding chemical stability, low density (0.013 g/cm³), emulsion-breaking ability and flame retardancy. More interestingly, the P-CS-PDA@MF sponge showed superior photothermal conversion capability, the temperature of it increased to approximately 91°C within 100 s under simulated sunlight from room temperature (about 25°C), and the sorption capacity of viscous oils was significantly increased. Moreover, the P-CS-PDA@MF sponge exhibited a high efficiency (over 97%) for separating viscous oils/water mixtures with the aid of sunlight. This versatile and efficient multifunctional P-CS-PDA@MF sponge via a simple and low-cost way shows promising prospect in oily wastewater treatment and water ecosystem remediation.     

膨胀石墨对高分子吸附的研究

本文对膨胀石墨制备方法进行了研究,以及各种方法制得的膨胀石墨对油类物质及些有机物的吸附效果进行了比较。     

Fabrication of rubber gel as oil absorbent by using water as porosity agent for oil removal

Oil pollution is a crucial issue that has adversed impact not only on the environment but also human beings. As an alternative to all conventional approaches, a porous rubber gel based on liquid natural rubber (LNR) with excellent hydrophobic and wettability properties has been developed using a simple vulcanization reaction. To determine their sorption capability, LNR gel was employed for absorption of various types of oils such as Petrol A, Petrol B, kerosene, diesel, crude oil, and olive oil. The functionality of LNR gel was characterized by Fourier transform infrared spectroscopy and the morphology of LNR gel was observed using a scanning electron microscope. By combining wettability and hydrophobicity, the LNR gel exhibited high oil sorption capacity and selectivity for oil removal from water. The LNR gel was able to absorb oils, especially the low viscosity types. Besides, it can also be reused up to 20 cycles while maintaining its oil sorption performance. The selective absorbent shows the recovery of petrol in the range of 96–99% by squeezing the oil. Thus, LNR gel has great potential as green material for cleaning up oil contaminants on a large scale. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47749.     

Preparation and characterization of graphite nanosheets from ultrasonic powdering technique

Natural flake graphite was exfoliated into exfoliated graphite via an acid intercalation procedure. The resulting exfoliated graphite was a worm-like particle composed of graphite sheets with thickness in the nanometer scale. Subjecting it to ultrasonic irradiation, the exfoliated graphite was effectively further foliated into isolated graphite nanosheets. SEM, TEM, SAD, laser counting, and BET measurements revealed that the graphite nanosheets prepared with 10 h irradiation were about 52 nm in thickness and 13 μm in diameter. FTIR examination showed that there were oxygen-containing groups presented on the surface of the exfoliated graphite. This result substantiated the statement reported in the literature that acid treatment could result in oxidization of carbon bonds on graphite surface.     

Electrochemical characterization of laser‐carbonized polyacrylonitrile nanofiber nonwovens

Porous carbon materials represent prospective materials for absorbers, filters, and electronic applications. Carbon fibers with high surface areas can be produced from polyacrylonitrile and spun as thin fibers from solution. The resulting polymer fibers are first stabilized to obtain conjugated ribbons and then carbonized to graphitic structures in a second high‐temperature step in an inert atmosphere. In this study, we investigated a previously described fast laser‐heating process that delivered fibers with a higher crystallinity and surface area compared to the thermally carbonized fibers. In a subsequent KOH‐activation step, the crystalline domains were exfoliated, and the surface of the fibers became macroporous. This led to a reduced specific surface area but a higher capacitance compared to thermally carbonized nanofibers. We report the electrochemical properties of the electrochemical cells and discuss their potential applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46398.     

Deposition mechanism of pyrolytic carbons at temperature between 800–1200 °C

The textures, growth features, microstructures and binding of carbon atoms of pyrolytic carbons prepared by chemical vapor deposition (CVD) at a temperature between 800–1200 °C on graphite substrate and carbon fibers were studied. The intermediate product phase of pyrolytic carbons was also investigated. Based on the present study a deposition model of viscous droplet was proposed in this paper. The viscous droplet here refers to all kinds of fine spheroids that are more or less viscous. The mechanism of the formation of three typical textures namely, smooth laminar, rough laminar and isotropic carbons can be satisfactorily explained by this model.     

The study on composition changes of heavy oils during steam stimulation processes

Using the heavy oils obtained from Liaohe oilfields in China, we have conducted the aquathermolysis reaction in laboratory at 240 °C. The results showed that Liaohe heavy oils have been undergoing visbreaking in the process of steam-drive and steam stimulation. After reaction with steam, the viscosity of the heavy oil was reduced by 28-42% and the amount of the saturated and aromatic hydrocarbons increased, while resin and asphaltene decreased. The gas partition chromatography showed that the accumulated amount of carbon numbers increased, after reaction, the accumulated amount of carbon numbers less than C₂₀ are 38.79-53.92%, and before reaction they are 13.30-20.92%. The results provided the basic data for heavy oil recovery by in situ catalytic method in production of heavy oil in oilfields.     

Hydrogen storage capacity of carbon nanotubes, filaments, and vapor-grown fibers

We have studied the sorption of hydrogen by nine different carbon materials at pressures up to 11 MPa (1600 psi) and temperatures from −80 to +500°C. Our samples include graphite particles, activated carbon, graphitized PYROGRAF vapor-grown carbon fibers (VGCF), CO₂ and air-etched PYROGRAF fibers, Showa-Denko VGCF, carbon filaments grown from a FeNiCu alloy, and nanotubes from MER Corp. and Rice University. We have measured hydrogen sorption in two pieces of equipment, one up to 3.5 MPa, and one to 11 MPa. The results so far have been remarkably similar: very little hydrogen sorption. In fact, the sorption is so small that we must pay careful attention to calibration to get reliable answers. The largest sorption observed is less than 0.1 wt.% hydrogen at room temperature and 3.5 MPa. Furthermore, our efforts to activate these materials by reduction at high temperatures and pressures were also futile. These results cast serious doubts on any claims so far for room temperature hydrogen sorption in carbon materials larger than a 1 wt.%.     

Ultradispersed particles in heavy oil: Part II, sorption of H2S(g)

During steam assisted gravity drainage for heavy oil recovery aqua-thermolysis reactions take place, whereupon gaseous hydrogen sulfide, H₂S_(g), is produced. A method to capture H₂S_(g) and convert it into a chemically inactive species is deemed necessary for sustaining in-situ recovery and upgrading. Part I of the current study explored the formation and stabilization of colloidal FeOOH particles in heavy oil matrices. In this Part, we evaluate the H₂S_(g) sorption ability of these particles as well as other metal oxide/hydroxide particles. Furthermore, the effect of mixing and temperature on H₂S_(g) sorption was investigated. Results showed that the rate and capacity of H₂S_(g) sorption increased as the concentration of FeOOH increased. Mixing, on the other hand, had insignificant effect on the sorption capacity, however it improved the sorption kinetics. In addition, in-situ prepared colloidal particles showed better reactivity towards H₂S_(g) than commercial α-Fe₂O₃ nanoparticles. Temperature had an adverse effect on the H₂S_(g) sorption capacity of FeOOH. This was attributed to a change in chemical structure of FeOOH as the temperature increased. Nevertheless, in-situ prepared ZnO colloidal particles completely removed H₂S_(g) even at high temperatures.     

膨胀石墨的化学制备法和影响其质量的因素

膨胀石墨作为新型炭素密封件材料广泛用于石油、化工、电力、冶金、医药、食品、机械等行业。介绍了用化学法制备的膨胀石墨的过程中石墨的粒度、酸化液配比、pH、膨胀温度对膨胀石墨质量的影响。     

Thermophysical properties of carbon/carbon composites and physical mechanism of thermal expansion and thermal conductivity

Five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied. These were three needled carbon felts impregnated with pyrocarbons (PyC) of different microstructures, chopped fibers/resin carbon + PyC, and carbon cloth/PyC. The results show that the X-Y direction thermal expansion coefficient (CTE) is negative in the range 0-100 °C with values ranging from −0.29 to −0.85 × 10⁻⁶/K. In the range 0-900 °C, their CTE is also very low, and the CTE vs. T curves have almost the same slope. In the same temperature range composites prepared using chopped fibers show the smallest CTE values and those using the felts show the highest. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture. Their expansion is mainly caused by atomic vibration, pore shrinkage and volatilization of water. However, the PyC structure has a large effect on thermal conductivity (TC) with rough laminar PyC giving the highest value and isotropic PyC giving the lowest. All five composites have a high TC, and values in the X-Y direction (25.6-174 W/m K) are much larger than in the Z direction (3.5-50 W/m K). Heat transmission in these composites is by phonon interaction and is related to the preform and PyC structures.     

Evaluation of carbonized medium-density fiberboard for electrical applications

The conversion of wood-based fiberboard materials into crack-free, monolithic, porous hard carbons is of significant interest due to their ability to perform in a multifunctional capacity. Three varieties of carbonized medium-density fiberboard (c-MDF) were studied for electrical, mechanical, and structural properties. X-ray diffraction data suggested that the volume fraction of large turbostratic crystallites increased with carbonization temperature (T_carb). The volume fraction of large turbostratic crystallites had a positive correlation with elastic modulus and electrical conductivity. The c-MDF materials were approximately isotropic with respect to elastic modulus and exhibited increasing stiffness with increasing T_carb (up to 4.5 GPa). Between 600 and 1400 °C, the electrical resistivity of c-MDF varied by seven orders of magnitude. The electrical resistivity of the hard carbon material in c-MDF 1400 °C was found to be within about an order of magnitude of polycrystalline graphite.