Light Aromatics Research Articles

Converting mixed plastics into mesoporous hollow carbon spheres with controllable diameter

Upcycling waste plastics into high value-added carbon nanomaterials has been a hot topic due to ever-increasing generation of waste plastics, however, little attention has been paid to valuable hollow carbon spheres (HCSs). Herein, uniform mesoporous HCSs with controllable diameter and high surface area were efficiently prepared through the carbonization of mixed plastics consisting of polypropylene, polyethylene and polystyrene under the combined catalysis of organically-modified montmorillonite (OMMT)/Co3O4 at 700°C. The morphology, microstructure, phase structure, textural property, surface element composition and thermal stability of HCSs were investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, N2 sorption, X-ray photoelectron spectroscopy and thermal gravimetric analysis. The effects of OMMT on the dispersion of Co3O4 in the mixed plastics and the degradation of mixed plastics were studied. It was found that OMMT not only promoted the dispersion of Co3O4 in the mixed plastics, which favored to control the diameter of HCSs, but also promoted the degradation of mixed plastics into light hydrocarbons and aromatics, which facilitated the growth of HCSs. Finally, a possible mechanism was proposed to explain the growth of uniform HCSs with controllable diameter. This facile method provides a novel potential way to convert waste plastics into valuable HCSs, which can be used as catalyst support, adsorbent, storage medium and template for the synthesis of other useful hollow materials, etc.

The origin of abnormally high benzene in light hydrocarbons associated with the gas from the Kuqa depression in the Tarim Basin, China

The chemical and carbon isotopic compositions of C1–C3 and C6–C7 light hydrocarbons were analyzed in 14 natural gas samples from the Kela 2, Dabei and Dina 2 gas fields in the Kuqa depression of the Tarim Basin. The relative content of light aromatic compounds (benzene and toluene) in C6–C7 light hydrocarbons is very high, with benzene as the main peak in the gas chromatogram. The relative content of aromatic compounds generally amounts to over 30% of the C6–C7 light hydrocarbons, especially in the Kela 2 gas field where light aromatics comprise more than 70% of the C6–C7 light hydrocarbons. Compared with 255 coal derived gas samples in many other sedimentary basins in China, an abnormal distribution of hydrocarbon composition is observed in the study area. In order to investigate this abnormal distribution, light hydrocarbon yields generated from low maturity coals at different pyrolysis temperatures were simulated quantitatively. The results showed that the yield of light aromatic compounds (benzene and toluene) gradually increases with increasing pyrolysis temperature. Furthermore, the relative content of aromatic hydrocarbons generated from coal samples at high temperatures, similar to an instantaneous accumulation mode under geologic conditions, can amount to 90% of C6–C7 light hydrocarbons, while that of aromatic hydrocarbons generated cumulatively at high temperatures, similar to a cumulative accumulation mode in natural geologic bodies, and is no more than 46.6%. These phenomena have not yet been reported in the literature. By combining these data with carbon isotopic data for natural gas components, it is proposed that an abnormal distribution of aromatic hydrocarbons in gases from the Kuqa depression may imply that the Kela 2 gas field was mainly formed by instantaneous gas accumulation, while the Dabei and Dina 2 gas fields were largely formed by cumulative gas accumulations.

Rape straw as a source of bio-oil via vacuum pyrolysis: Optimization of bio-oil yield using orthogonal design method and characterization of bio-oil

Rape straw from China rural area was treated by vacuum pyrolysis for bio-oil preparation. The orthogonal design method was employed to minimize the number of experiments. The effects of the factors including pyrolysis temperature, reactor pressure, heating rate and holding time on bio-oil yield were analyzed. The optimal conditions were obtained by using SPSS Statistics 20.0 (IBM, USA) and Matlab 7.12.0 (MathWorks, USA). Furthermore, the physicochemical properties of the bio-oil obtained at optimal conditions were evaluated. The composition was examined using gas chromatograph/mass spectroscopy (GC/MS). The thermo-gravimetric analysis (TGA) of the bio-oil was investigated within N2 and O2, respectively. The results showed that the order of the effects of the factors on bio-oil yield was heating rate>pyrolysis temperature>reactor pressure>holding time. Heating rate and pyrolysis temperature had a significant interaction. Optimal conditions were obtained at pyrolysis temperature of 495.5°C, heating rate of 19.4°C/min, reactor pressure of 5.0kPa and holding time of 50min. Confirmation runs gave 43.15% and 43.44% of bio-oil yield compared to 43.62% of predicted value. The water content, carbon residue, density, pH value, dynamic viscosity and higher heat value of bio-oil were 34.20%, 4.03, 1.14g/cm3, 2.22, 4.28mm2/s and 18.72MJ/kg, respectively. Polymerization in the condensation process contributed to the higher average molecular weight distribution than pyrolysis vapors. Light aromatics (mainly including light phenols) were the dominant component for the bio-oil, which contributed to the relatively low polydispersity with a value of 1.25. The direct liquefaction bio-oil was unstable and corrosive due to the high reactivity of carbonyl extensively existing in acids, aldehydes and ketones. High oxygen content made the behavior of decomposition in O2 be similar to that in N2 before 450°C. Further study on upgrading of the bio-oil should be performed to make it become an alternative fuel.

Catalytic Cracking of Glycerol to Fine Chemicals over Equilibrium Fluid Catalytic Cracking Catalyst

Effective conversion of glycerol into fuels and chemicals is an emerging field in terms economic viability of first generation bio- fuels development. In the present work the refinery fluid catalytic cracking (FCC) process is used to convert the biomass -derived glycerol into possible fine chemicals through a series of reactions like dehydration, cracking and hydrogen transfer. The catalytic cracking of biomass–derived glycerol have been carried out using industrially available fluid catalytic cracking equilibrium catalyst (E-CAT) in an advanced cracking evaluation (ACE-R) FCC unit for temperatures ranging from 350 to 550°C. The catalyst-to-oil (C/O) ratio was kept constant at 5wt.%. At higher temperatures (430-550°C) 100% glycerol conversion and 50% of acetaldehyde yield was obtained with E-CAT. The maximum yield of acrolein was found to be 7.61% at 430°C temperature; whereas the yield of acetaldehyde was increased with increase in temperature and it was higher at 550°C. The gas and liquid products have been analyzed using gas chromatography (GC) and nuclear magnetic resonance (NMR) spectroscopy techniques, respectively. Carbon dioxide produced in the regeneration process was analyzed using infrared (IR) spectroscopy. Further in the liquid product, in addition to acetaldehyde and acrolein, light olefins and aromatics were also found.

Striking Influence about HZSM-5 Content and Nickel Catalyst on Catalytic Carbonization of Polypropylene and Polyethylene into Carbon Nanomaterials

A one-pot approach was established to effectively convert polypropylene (PP) and linear low density polyethylene (LLDPE) into carbon nanomaterials (CNMs) including cup-stacked carbon nanotubes and carbon nanofibers under the combined catalysis of HZSM-5/NiO or HZSM-5/Ni2O3 at 700 degrees C. The effects of HZSM-5 content, a nickel catalyst, and the carbon precursor on the morphology, microstructure, phase structure, and thermal stability of CNMs were investigated with scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, and thermal gravimetric analysis. The effect of HZSM-5 content on the degradation products of PP and LLDPE was analyzed by gas chromatography and gas chromatography mass spectrometry. With increasing HZSM-5 content, the yields of light hydrocarbons and aromatics increased due to proton acid sites on the surface of HZSM-5 catalyzing cracking of PP or LLDPE degradation products. This one-pot approach provides a novel potential way to largely transform mixed waste polyolefin into high value-added CNMs.

Green River Oil Shale Pyrolysis: Semi-Open Conditions

Oil shale is a petroleum source rock that has not undergone the natural processes required to convert its organic matter to oil and gas. However, oil shale kerogen can be converted artificially to liquid and gaseous hydrocarbons by pyrolysis. Heating oil shale in place (in situ) has a number of operational, economic, and environmental advantages over surface retorts, particularly when the shale is too deep to mine. This work describes experiments conducted at temperatures and pressures appropriate to commercially viable in situ pyrolysis. The data are needed to construct models to plan, interpret, and optimize field experiments and commercial operations. The experiments also provide insights into the chemical compositions of the native state shale and all the products of pyrolysis—hydrocarbon and nonhydrocarbon gases, oil, bitumen, remaining pyrolyzable kerogen, residual organic matter, and inorganic matter—as functions of thermal maturation. Numerous studies of Green River oil shale pyrolysis have been published over the years. Most of these have focused on the richest interval, the Mahogany (R-7) zone and have been performed in either open (atmospheric pressure) or closed (bomb) apparatus. The new elements of this work are as follows: (1) samples were taken from the deepest of the kerogen-rich layers of the Green River Formation, the mineralogically distinct R-1 zone; (2) experiments were performed under semi-open (controlled pressure) conditions. The data generated are therefore appropriate input to models used in conjunction with in situ controlled-pressure production tests of R-1 shale. In agreement with previous work, this investigation finds that processing shale at relatively low temperatures, for longer times, and at moderately elevated pressures, reduces yields but improves product quality relative to surface retort methods. The composition of the produced oil is generally uniform over the course of artificial maturation. It has a high H/C ratio and is predominantly composed of saturates and light aromatics, which are desirable for refinery operations. The oil has little sulfur, which is mostly in thiophene-containing moieties. Extracted bitumen has a high polar content, and its H/C ratio decreases as a result of oil and gas generation during maturation. Produced gas is rich in natural gas liquids.

Steam gasification of biomass in a conical spouted bed reactor with olivine and γ-alumina as primary catalysts

Olivine and γ-alumina have been used as primary catalysts for tar elimination in the continuous steam gasification of pine wood sawdust in a bench-scale plant provided with a conical spouted bed reactor. A comparison of the performance of each catalyst with that observed for a bed made up of inert silica sand shows that both catalysts have a significant activity for tar cracking/reforming, given that the amount of tar obtained by operating with beds of inert sand is reduced by 79% and 84% when olivine and γ-alumina are used, respectively. The tar cracking reduces selectively the content of light and heavy PAHs, giving way to an increase in the concentration of light aromatics. Furthermore, both catalysts cause a positive effect on the gas composition by slightly enhancing the water–gas shift and reforming reactions.

Influence of reaction conditions on bio-oil production from pyrolysis of construction waste wood

The pyrolysis characteristics of construction waste wood were investigated for conversion into renewable liquid fuels. The activation energy of pyrolysis derived from thermogravimetric analysis increased gradually with temperature, from 149.41 kJ/mol to 590.22 kJ/mol, as the decomposition of cellulose and hemicellulose was completed and only lignin remained to be decomposed slowly. The yield and properties of pyrolysis oil were studied using two types of reactors, a batch reactor and a fluidized-bed reactor, for a temperature range of 400–550 °C. While both reactors revealed the maximum oil yield at 500 °C, the fluidized-bed reactor consistently gave larger and less temperature-dependent oil yields than the batch reactor. This type of reactor also reduced the moisture content of the oil and improved the oil quality by minimizing the secondary condensation and dehydration. The oil from the fluidized-bed reactor resulted in a larger phenolic content than from the batch reactor, indicating more effective decomposition of lignin. The catalytic pyrolysis over HZSM-5 in the batch reactor increased the proportion of light phenolics and aromatics, which was helpful in upgrading the oil quality.

Catalytic conversion of C4 fraction for the production of light olefins and aromatics

The catalytic conversion of the C4 fraction from a fluid catalytic cracking (FCC) unit over a commercial FCC equilibrium catalyst was investigated using a confined fluidized bed reactor system. Butenes were easier to convert than butanes, and 1-butene was the easiest to convert among the butene isomers. The ethene and propene yields increased with increased reaction temperature and decreased with increased weight hourly space velocity (WHSV). The formation of propene involved two successive steps: butene dimerization and large hydrocarbon cracking. Aromatics were formed by the aromatization of the intermediate large olefins. A mechanism parameter RCA was proposed to describe the relative function of the cracking reaction to the aromatization reaction. RCA increased with increased reaction temperature and decreased with increased WHSV. The cracking reaction predominates on the aromatization reaction at high reaction temperatures.

Secondary organic aerosol formation from idling gasoline passenger vehicle emissions investigated in a smog chamber

Abstract. Gasoline vehicles have recently been pointed out as potentially the main source of anthropogenic secondary organic aerosol (SOA) in megacities. However, there is a lack of laboratory studies to systematically investigate SOA formation in real-world exhaust. In this study, SOA formation from pure aromatic precursors, idling and cold start gasoline exhaust from three passenger vehicles (EURO2–EURO4) were investigated with photo-oxidation experiments in a 6 m3 smog chamber. The experiments were carried out down to atmospherically relevant organic aerosol mass concentrations. The characterization instruments included a high-resolution aerosol mass spectrometer and a proton transfer mass spectrometer. It was found that gasoline exhaust readily forms SOA with a signature aerosol mass spectrum similar to the oxidized organic aerosol that commonly dominates the organic aerosol mass spectra downwind of urban areas. After a cumulative OH exposure of ~5 × 106 cm−3 h, the formed SOA was 1–2 orders of magnitude higher than the primary OA emissions. The SOA mass spectrum from a relevant mixture of traditional light aromatic precursors gave f43 (mass fraction at m/z = 43), approximately two times higher than to the gasoline SOA. However O : C and H : C ratios were similar for the two cases. Classical C6–C9 light aromatic precursors were responsible for up to 60% of the formed SOA, which is significantly higher than for diesel exhaust. Important candidates for additional precursors are higher-order aromatic compounds such as C10 and C11 light aromatics, naphthalene and methyl-naphthalenes. We conclude that approaches using only light aromatic precursors give an incomplete picture of the magnitude of SOA formation and the SOA composition from gasoline exhaust.

Limited influence of dry deposition of semivolatile organic vapors on secondary organic aerosol formation in the urban plume

The dry deposition of volatile organic compounds (VOCs) and its impact on secondary organic aerosols (SOA) are investigated in the Mexico City plume. Gas‐phase chemistry and gas‐particle partitioning of oxygenated VOCs are modeled with the Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO‐A) from C3 to C25 alkanes, alkenes, and light aromatics. Results show that dry deposition of oxidized gases is not an efficient sink for SOA, as it removes <5% of SOA within the city's boundary layer and ~15% downwind. Dry deposition competes with the gas‐particle uptake, and only gases with fewer than ~12 carbons dry deposit while longer species partition to SOA. Because dry deposition of submicron aerosols is slow, condensation onto particles protects organic gases from deposition, thus increasing their atmospheric burden and lifetime. In the absence of this condensation, ~50% of the regionally produced mass would have been dry deposited.

Effect of moisture content on the characterization of products from the pyrolysis of sewage sludge

Sewage sludge samples with moisture contents of 0%, 31%, 47% and 80% were pyrolyzed at 1000°C in a tubular furnace to evaluate the effect of moisture content on the pyrolysis process. The evaporation of water accelerated the evolution of porosity in the solid char and hence contributed to the devolatilization of sewage sludge, leading to an increase in the gas fraction and a decrease in the solid fraction. The steam-rich atmosphere generated by the high moisture content of sewage sludge favored the steam reforming reactions of volatile compounds and the steam gasification of solid char, enhancing the production of hydrogen rich fuel gas. A saturation value was also observed for the steam involved in the gasification and reforming reactions. GC–MS analysis showed that the increase of moisture content not only promoted the reduction of the species in the tar, but also improved the production of light aromatics, as a result, the toxic effect of tar decreased considerably. The decrease in the peak areas of organic functional groups of solid char demonstrated that the participation of steam promoted the ejection of volatile matters of sewage sludge during the pyrolysis process.

Synthesis, characterization and growth mechanism of mesoporous hollow carbon nanospheres by catalytic carbonization of polystyrene

Mesoporous hollow carbon nanospheres (HCNs) were synthesized through the carbonization of polystyrene (PS) under the combined catalysis of organically-modified montmorillonite (OMMT)/cobalt catalyst at 700°C. The morphology, microstructure, phase structure, textural property and surface composition of the obtained mesoporous HCNs were investigated by field-emission scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, N2 sorption and X-ray photoelectron spectroscopy. It was found that OMMT not only promoted the dispersion of cobalt catalyst in the PS matrix but also affected the degradation of PS into light hydrocarbons and aromatics. The lattice oxygen of the cobalt catalyst facilitated the decomposition of light hydrocarbons and aromatics into atomic carbon during the formation of the mesoporous HCNs. A possible mechanism was proposed to explain the growth of mesoporous HCNs through the carbonization of PS under the combined catalysis of OMMT/cobalt catalyst. More importantly, this approach also offers a new potential way to transform waste polymer materials into mesoporous HCNs, which may be used as catalyst supports, adsorbents, storage media and templates for the synthesis of other useful hollow materials.

Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes

For the first time, cup-stacked carbon nanotubes (CS-CNTs) with high quality were efficiently synthesized by a one-pot approach through the carbonization of polypropylene (PP) under the combined catalysis of organically-modified montmorillonite (OMMT)/NiO. The effects of the added amount of OMMT on the yield, morphology, microstructure, phase structure and thermal stability of carbon nanomaterials (including CS-CNTs and carbon nanofibers (CNFs)) were fully investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. Furthermore, the effects of OMMT on the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles before the growth of CS-CNTs and CNFs were analyzed by gas chromatography, gas chromatography–mass spectrometry and HRTEM. It was found that after adding a low amount of OMMT, a relatively large amount of light hydrocarbons and a small amount of aromatics were produced during the degradation of PP, which promoted the coalescence and reconstruction of NiO nanoparticles into rhombic shape. Subsequently, the reshaped NiO catalysts catalyzed the light hydrocarbons and aromatics into long, straight and smooth-surface CS-CNTs with narrow length and diameter distributions. This approach offers a new potential way to largely transform waste polymer materials into valuable CS-CNTs.

Secondary organic aerosol from polycyclic aromatic hydrocarbons in Southeast Texas

Recent chamber studies show that low-volatility gas phase precursors such as polycyclic aromatic hydrocarbons (PAHs) can be a significant source of secondary organic aerosol (SOA). In this work, formation of SOA from the photo-oxidation products of PAHs is added to the SOA modeling framework of the Community Multiscale Air Quality (CMAQ) model to determine the regional distribution of SOA products from PAHs (PAH-SOA) and the contributions from sources in Southeast Texas during the Texas Air Quality Study 2006 (TexAQS 2006). Results show that PAHs released from anthropogenic sources can produce SOA mass as much as 10% of that from the traditional light aromatics or approximately 4% of total anthropogenic SOA. In areas under the influence of wildfire emissions, the amount of PAH-SOA can be as much as 50% of the SOA from light aromatics. A source-oriented modeling framework is adopted to determine the major sources of PAH-SOA by tracking the emitted PAHs and their oxidation products in the gas and aerosol phases from different sources separately. Among the eight sources (vehicles, solvent utilization, residential wood, industries, natural gas combustion, coal combustion, wildfire and other sources) that are tracked in the model, wildfire, vehicles, solvent and industries are the major sources of PAH-SOA. Coal and natural gas combustion appear to be less important in terms of their contributions to PAH-SOA.

Catalytic pyrolysis of waste rice husk over mesoporous materials

Catalytic fast pyrolysis of waste rice husk was carried out using pyrolysis-gas chromatography/mass spectrometry [Py-GC/MS]. Meso-MFI zeolite [Meso-MFI] was used as the catalyst. In addition, a 0.5-wt.% platinum [Pt] was ion-exchanged into Meso-MFI to examine the effect of Pt addition. Using a catalytic upgrading method, the activities of the catalysts were evaluated in terms of product composition and deoxygenation. The structure and acid site characteristics of the catalysts were analyzed by Brunauer-Emmett-Teller surface area measurement and NH3 temperature-programmed desorption analysis. Catalytic upgrading reduced the amount of oxygenates in the product vapor due to the cracking reaction of the catalysts. Levoglucosan, a polymeric oxygenate species, was completely decomposed without being detected. While the amount of heavy phenols was reduced by catalytic upgrading, the amount of light phenols was increased because of the catalytic cracking of heavy phenols into light phenols and aromatics. The amount of aromatics increased remarkably as a result of catalytic upgrading, which is attributed to the strong Brönsted acid sites and the shape selectivity of the Meso-MFI catalyst. The addition of Pt made the Meso-MFI catalyst even more active in deoxygenation and in the production of aromatics.

Explicit modeling of organic chemistry and secondary organic aerosol partitioning for Mexico City and its outflow plume

Abstract. The evolution of organic aerosols (OA) in Mexico City and its outflow is investigated with the nearly explicit gas phase photochemistry model GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere), wherein precursor hydrocarbons are oxidized to numerous intermediate species for which vapor pressures are computed and used to determine gas/particle partitioning in a chemical box model. Precursor emissions included observed C3-10 alkanes, alkenes, and light aromatics, as well as larger n-alkanes (up to C25) not directly observed but estimated by scaling to particulate emissions according to their volatility. Conditions were selected for comparison with observations made in March 2006 (MILAGRO). The model successfully reproduces the magnitude and diurnal shape for both primary (POA) and secondary (SOA) organic aerosols, with POA peaking in the early morning at 15–20 μg m−3, and SOA peaking at 10–15 μg m−3 during mid-day. The majority (≥75%) of the model SOA stems from reaction products of the large n-alkanes, used here as surrogates for all emitted hydrocarbons of similar volatility, with the remaining SOA originating mostly from the light aromatics. Simulated OA elemental composition reproduces observed H/C and O/C ratios reasonably well, although modeled ratios develop more slowly than observations suggest. SOA chemical composition is initially dominated by δ-hydroxy ketones and nitrates from the large alkanes, with contributions from peroxy acyl nitrates and, at later times when NOx is lower, organic hydroperoxides. The simulated plume-integrated OA mass continues to increase for several days downwind despite dilution-induced particle evaporation, since oxidation chemistry leading to SOA formation remains strong. In this model, the plume SOA burden several days downwind exceeds that leaving the city by a factor of >3. These results suggest significant regional radiative impacts of SOA.

Influence of in Situ Steam Formation by Radio Frequency Heating on Thermodesorption of Hydrocarbons from Contaminated Soil

Thermal desorption of a wide spectrum of organic contaminants, initiated by radio frequency (RF) heating, was studied at laboratory and pilot-plant scales for an artificially contaminated soil and for an originally contaminated soil from an industrial site. Up to 100 °C, moderate desorption rates were observed for light aromatics such as toluene, chlorobenzene, and ethylbenzene. Desorption of the less volatile contaminants was greatly enhanced above 100 °C, when fast evaporation of soil-water produced steam for hydrocarbon stripping (steam-distillation, desorption rates increased by more than 1 order of magnitude). For hydrocarbons with low water solubility (e.g., aliphatic hydrocarbons), the temperature increase above 100 °C after desiccation of soil again led to a significant increase of the removal rates, thus showing the impact of hydrocarbon partial pressure. RF heating was shown to be an appropriate option for thermally enhanced soil vapor extraction, leading to efficient cleaning of contaminated soils.

Permeation of Gasoline, Diesel, Bioethanol (E85), and Biodiesel (B20) Fuels Through Six Glove Materials

Biofuels and conventional fuels differ in terms of their evaporation rates, permeation rates, and exhaust emissions, which can alter exposures of workers, especially those in the fuel refining and distribution industries. This study investigated the permeation of biofuels (bioethanol 85%, biodiesel 20%) and conventional petroleum fuels (gasoline and diesel) through gloves used in occupational settings (neoprene, nitrile, and Viton) and laboratories (latex, nitrile, and vinyl), as well as a standard reference material (neoprene sheet). Permeation rates and breakthrough times were measured using the American Society for Testing and Materials F739-99 protocol, and fuel and permeant compositions were measured by gas chromatography/mass spectrometry. In addition, we estimated exposures for three occupational scenarios and recommend chemical protective clothing suitable for use with motor fuels. Permeation rates and breakthrough times depended on the fuel-glove combination. Gasoline had the highest permeation rate among the four fuels. Bioethanol (85%) had breakthrough times that were two to three times longer than gasoline through neoprene, nitrile Sol-Vex, and the standard reference materials. Breakthrough times for biodiesel (20%) were slightly shorter than for diesel for the latex, vinyl, nitrile examination, and the standard neoprene materials. The composition of permeants differed from neat fuels, e.g., permeants were significantly enriched in the lighter aromatics including benzene. Viton was the best choice among the tested materials for the four fuels tested. Among the scenarios, fuel truck drivers had the highest uptake via inhalation based on the personal measurements available in the literature, and gasoline station attendants had highest uptake via dermal exposure if gloves were not worn. Appropriate selection and use of gloves can protect workers from dermal exposures; however, current recommendations from the National Institute for Occupational Safety and Health should be revised to account for contemporary fuel formulations that routinely contain ethanol.

Continuous pyrolysis of waste tyres in a conical spouted bed reactor

Continuous pyrolysis of scrap tyres has been carried out in a conical spouted bed reactor and the results (yields, composition of the volatile fraction and carbon black properties) have been compared with those obtained operating in batch mode in a previous study. Continuous operation in the 425–600 °C range gives way to a yield of 1.8–6.8 wt.% of gases, 44.5–55.0 wt.% of liquid fraction (C 5–C 10 range hydrocarbons, with a maximum yield of limonene of 19.3 wt.% at 425 °C), 9.2–11.5 wt.% of tar C 11 + and 33.9–35.8 wt.% of char. The main differences between the continuous and batch processes are in the yield of light aromatics, which is higher in the continuous process, and in that of the heavy liquid fraction or tar, which is higher in the batch process. These are the advantages of the continuous process, although hydrogenation of the liquid fraction is required even in this case in order to use it as fuel. The high yield of limonene, the flexibility in the operating conditions and the capacity for a continuous removal of the residual carbon black from the reactor are the advantages of conical spouted bed technology. The excellent performance of the conical spouted bed reactor for the tyre pyrolysis process is due to the solid cyclic movement, the good contact between phases, the high heating rate and the reduced residence time of the volatile products.