Mixed N-alkanes Research Articles

Solution crystallisation of single and mixed n-alkanes, within the homologous series C16 to C23 from representative hydrocarbon fuel solvents

Solution crystallisation of single and mixed n-alkanes, within the homologous series C16 to C23 from representative hydrocarbon fuel solvents

Using an optimized relative response factor database to simplify a pyrolyzer/thermal desorption-gas chromatography-mass spectrometry method of screening for phthalate esters, polybrominated diphenyl ethers, and polybrominated biphenyls in polymers

The international analytical standard IEC 62321–3–3 describes a method for the screening analysis of phthalate esters, polybrominated diphenyl ethers (PBDEs), and polybrominated biphenyls (PBBs) in polymers by pyrolyzer/thermal desorption-gas chromatography-mass spectrometry (Py/TD-GC/MS). The IEC 62321–3–3 method uses a database of relative response factors (RRFs) (calculated by dividing the response factor (RF) for a target compound by the RF value for a substitute compound (SC) selected from among all target compounds) to quantitate each targeted analyte. A drawback of this method is that a separate RRF database must be created from expensive standard solutions that contain each targeted compound for each instrument, which is a labor-intensive task. In this study, we have developed a “ready-to-use” RRF database that can be used on multiple different instruments. This method eliminates the need to create an RRF database for each instrument and greatly simplifies the screening workflow described in the IEC 62321–3–3 standard. Because it only requires a mixed n-alkane solution and polymer reference materials, which are generally easy to procure and easy to use, the method is highly convenient and suitable for general-purpose use. Assigning tetra-BDE, penta-BDE, deca-BDE, or deca-BB as the SC for each PBDE and PBB analyte allowed the variance in RRFs between instruments to be reduced to a degree suitable for screening analysis. When this method was applied, recovery rates of individual PBDEs and PBBs remained within the range of 74–130 % over an extended period of 54 months. Simultaneous analysis of phthalate esters, PBDEs, and PBBs in various polymer reference materials was also performed with the optimized method on four different instruments and recovery rates of each targeted compound were evaluated. The recovery rates for each phthalate ester, total PBDEs, and total PBBs were within the range of around 100 ± 30 % for all tested samples.

Interactive effects of dual short-chain n-alkanes on removal performances and microbial responses of biotrickling filters

Enhanced biotrickling filtration at the presence of surfactants could be competitive in treatment of waste gas streams polluted by hydrophobic volatile organic compounds (VOCs) such as light hydrocarbons, while few such reports are available. Herein, biotrickling filters (BTFs) were applied to investigate the removal performances for binary-component n-alkanes (n ≤ 6) at the presence of sodium dodecyl benzene sulfonate (SDBS), and the microbial responses were also examined. Interestingly, results showed that the existence of shorter chain n-alkanes promoted the removal of longer chain n-alkanes, as the elimination capacities (EC) of BTF for n-hexane increased by 44 ± 1.2 % when there was methane in incoming gas stream. While the presence of longer chain n-alkanes antagonistically affected shorter chain n-alkane removal, as EC for methane decreased by 65 ± 8.1 % at the presence of n-hexane. Additionally, the presence of SDBS improved the mixed n-alkane removal. EC of the BTF with 15 mg/L SDBS for mixed propane and n-hexane reached 55 ± 1.4 and 31 ± 0.5 g/m3·h respectively, which increased by 90 ± 4.6 % and 47 ± 0.9 % compared with those without SDBS. The richness of Bacillus and Sporosarcina was improved in the BTF fed with SDBS. Moreover, the presence of SDBS improved the content of hydrophobic proteins and the activity of fluorescent substances inextracellular polymeric substances. Also, both the activities of ATPase and the antioxidant capacity of microbial cells exhibited higher than that when SDBS was not added. These data could lead to a better understanding and more reasonable design of biotrickling filtration to remove n-alkanes from waste gas streams of refinery wastewater treatment plants.

Effect of porous carbon on thermal and physical properties of composite pure alkane/expanded vermiculite phase change energy storage materials

Nine kinds of mixed N-alkanes with different proportions were prepared by mixed eutectic method. A set of ratios with enthalpy values up to 289.8 J/g were selected for encapsulated PCM. Using potato starch solution with a concentration of 30 % as porous carbon source, the heat transfer capacity of expanded vermiculite was enhanced by modification between expanded vermiculite channels, and matrix coated phase change material was prepared. SEM images show that the PCM are successfully adsorbed in the pores. The latent heat and temperature of phase change in the melting and solidification process are 208.1 J/g and 21.2 °C, 203.11 J/g and −3.4 °C, respectively. FT-IR, XRD, TGA and thermal cycling test results show that phase change energy storage particles have good thermal performance. Therefore, the prepared materials have excellent properties.

Universality analysis of the reaction pathway and product distribution in C5-C10 n-alkanes pyrolysis

Hydrocarbons pyrolysis was of great significance for light olefins production. In this work, the pyrolysis of C5-C10 n-alkanes and n-alkane mixtures was studied at 650–800 °C under atmosphere to explore the universality of reaction pathway and product distribution. It was found that an increase of chain length and reaction temperature promoted pyrolysis activity, and the acceleration effect caused by increasing chain length was more noticeable at low temperature. An increase of chain length enhanced 1-hexene, 1,3-butadiene, cyclohexene and benzene formation, inhibited methane, ethane, propene and butenes formation, while hardly affected ethene and propane formation. Since the feedstock included both pure and mixed n-alkanes, the achieved regularity seemed universal for C5-C10 n-alkane pyrolysis. Based on the free radical mechanism and product distribution, the reaction network was proposed and discussed for C5-C10 n-alkanes pyrolysis. Although an increase of chain length promoted the pyrolysis activity in n-alkanes pyrolysis, it inhibited the cracking depth and light olefins formation. Fortunately, the negative effect of chain length on light olefins production was avoidable by tailoring reaction temperature.

Solution Crystallisation of Single and Mixed N-Alkanes, within the Homologous Series C16 to C23 from Representative Hydrocarbon Fuel Solvents

Solution Crystallisation of Single and Mixed N-Alkanes, within the Homologous Series C16 to C23 from Representative Hydrocarbon Fuel Solvents

Molecular dynamics simulations of two-phase flow of n-alkanes with water in quartz nanopores

Nanopore networks comprising shale reservoirs exhibit special behaviors in two-phase flow. We use molecular dynamics simulations (MD) to explore the single n-alkanes (nC3-nC10)-water and mixed n-alkanes (nC3, nC6, and nC10)-water flow mechanisms in the confined nanopores of quartz. The results reveal that water molecules form four adsorbed layers near the wall, showing greater viscosity than the bulk water. For single n-alkanes cases, in the n-alkanes-water interface regions (AWIR), n-alkanes molecules tend to be parallel to the pore wall, and the tendency is more pronounced for longer n-alkanes, resulting in a decrease of AWIR width. Moreover, we observed typical liquid–liquid slip in AWIR. Ignoring the slip velocity can underestimate the flow rate of n-alkanes more than 20%. Under the driving force, the bulk n-alkanes exhibit distinct different velocity distributions due to viscosity differences. However, the total fluid velocity distributions in AWIR are quite the same, showing an apparent viscosity independent of the type of n-alkanes and pore size. For mixed n-alkanes, the velocity distribution and apparent viscosity are still the same as single n-alkanes cases due to the unchanged structure of the molecules in AWIR. Our study could provide an in-depth understanding of the oil–water two-phase flow in nanopores, especially the influence of carbon chain length on oil–water interface properties.

Assessment of Aliphatic Hydrocarbons in Sediments of Shatt Al-Arab River, Southern Iraq, North East Arabian Gulf

Shatt Al-Arab River is one of the important rivers for water supply, industry and irrigation in Basrah City, south of Iraq. It's also supply drinking water to users in the region. Despite the significance of this river, there is a lack of previous studies dealing with petroleum pollution especially for geochemical studies of organic matter in the river sediments using molecular tracer methods. Therefore, the identification and quantification of petroleum hydrocarbons in this river at the elemental and molecular levels will be of the utmost interest. Sediments were analyzed in nine Shatt Al-Arab River stations. Texture was silty clay or silty sand. TOC and TN ranged from 0.39-0.90 and 0.02-0.16%. OM varied from 17.43-34.36 µg g-1 dw, representing 0.27-0.87% of TOC. AHs ranged from 3.19-10.27 µg g-1 dw and constituted 16.07-29.88% of OM. Total n-alkanes concentrations ranged from 0.08-42.58 µg g-1 dw with carbon numbers from C11-C34 were identified. N-alkanes content was relatively moderate compared to sites contaminated with oil worldwide. Dominance of even carbon number n-alkanes (C11-C20) with CPI and LMW/HMW values close to unity, indicated to oil-related n-alkanes. This was verified by the values of U/R (1.27-2.45), pri/phy (0.82-1.00), C17/pri (0.70-1.94) and C18/phy (0.95-1.56) ratios and the presence of UCM. Biogenic contributions were detected within the n-alkanes distribution of C17-C31 and CPI and LMW/HMW values of <1 that mainly related to terrestrial plants, phytoplankton, algae and bacteria sources, confirmed by TAR (0.79-2.15) and C31/C19 ratio (0.28-1.62) values. However, the contribution from biogenic hydrocarbons is overshadowed by petroleum origin n-alkanes. This was obvious by the presence of UCM. PCA showed concordant results with n-alkanes ratios indicating mixed n-alkanes sources in sediments. Hopanes and steranes in sediments displayed similar signatures that were characteristic of mature organic matter contribution from oil contaminations.

Kinetics of the degradation of aliphatic hydrocarbons by the bacteria Rhodococcus ruber and Rhodococcus erythropolis

Consumption of aliphatic hydrocarbons by the bacteria Rhodococcus ruber Ac-1513-D and Rhodococcus erythropolis Ac-1514-D grown on mixed n-alkanes and diesel fuel was studied. Consumption of diesel fuel hydrocarbons by the strains was less intense in comparison with the n-alkane mixture. The strains showed differences in growth rate and consumption of the substrates, which suggests that they possess different mechanisms of hydrocarbon uptake.

Prediction of viscosities and surface tensions of fuels using a new corresponding states model

While some properties of diesels are cheap, easy and fast to measure, such as densities, others such as surface tensions and viscosities are expensive and time consuming. A new approach that uses some basic information such as densities to predict viscosities and surface tensions is here proposed using a Corresponding states model previously developed for the accurate estimation of several thermophysical properties of pure and mixed n-alkanes. This approach is tested with good results in five petroleum distillation cuts from crudes of different sources (North Sea, Africa and Middle East).

Generalized relation between surface tension and viscosity: a study on pure and mixed n-alkanes

A generalized relation is presented to correlate liquid–vapor surface tension with viscosity, both for pure compounds and mixtures. Plots of different data sets verify that the natural logarithm of the surface tension is linear with the reciprocal viscosity, with slope-dependent on the molecular weight and constant intercept for n-alkanes with chain length greater than n-C 10H 22. For these, the value of the intercept can be related to the surface tension at the temperature of homogeneous nucleation, where the reciprocal viscosity tends to zero. The relations found for the slope and intercept of pure components are also shown to be valid for mixtures, so that only a viscosity (or surface tension) value is required to calculate a surface tension (or viscosity). Some distillation cuts from crude oils of different origins were also presented. Although the linear relation is still valid, the proposed correlations for the slope and intercept of n-alkanes cannot be used, confirming that mixing rules and family specific correlations are required for fluids containing components of different families. The results presented on this work show how bulk transport and equilibrium surface properties can be interrelated.

Isothermal Transformations in Alkane Alloys

We show that it is possible to make mixed n-alkane samples to change isothermally from the ordered crystal state (Φord) to the rotator state R. This isothermal transition has been observed in DSC and X-ray powder diffraction experiments, for all compositions in various binary systems, by maintaining mixed samples for a long time in the R state. Thermodynamic analysis of the isothermal data, which correspond to experimental EGC temperatures, results in a successful calculation of the [Φord + R] equilibrium temperatures. The thermodynamic interpretation and X-ray diffraction observations show that the phenomenon corresponds to diffusionless, or martensitic transitions, in metal alloys.

Hydroconversion of methylcyclohexane on TEOS-modified H-ZSM-5 zeolite catalysts: Production of a high-quality synthetic steamcracker feedstock

With the advent of the European Auto Oil Programme and comparable legislation in other parts of the world, the aromatics content of gasoline has to be reduced considerably. Therefore, new outlets for surplus aromatics have to be found. Mixed n-alkanes with two and more carbon atoms (C 2+- n-alkanes) represent a high-quality synthetic feedstock for steamcrackers. Thus, the hydrogenation of aromatics to cycloalkanes followed by their hydroconversion into C 2+- n-alkanes (predominantly ethane, propane and n-butane) could become a useful process option for converting surplus aromatics into a synthetic steamcracker feed. During hydroconversion of methylcyclohexane to C 2+- n-alkanes, the catalytic properties of acidic zeolite H-ZSM-5 can be remarkably improved by chemical liquid deposition of tetraethoxysilane. Thereby, the yield of the desired C 2+- n-alkanes at, e.g., 400 °C can be enhanced from around 77% to nearly 82%. Simultaneously, a drastic diminution of the concentration of external Brønsted acid sites and a significant decrease of the total concentration of Brønsted acid sites were observed by adsorption of, respectively, collidine and pyridine monitored by FTIR spectroscopy. Nitrogen adsorption experiments revealed a slight decrease of the micropore volume. These data are consistent with an extensive deactivation of the active sites on the external surface and in close proximity to the pore openings, the latter leading to pore mouth narrowing or, more likely, to partial pore mouth plugging.

Proton Transfer from Alkane Radical Cations to Alkane Molecules: Selectivity with Respect to the Site of Proton Donation and Proton Acceptance

AbstractFor Abstract see ChemInform Abstract in Full Text.

Proton transfer from alkane radical cations to alkane molecules: selectivity with respect to the site of proton donation and proton acceptance.

Information on the donor and acceptor site selectivity in the proton transfer from n-alkane radical cations to n-alkane molecules is gathered from gamma-irradiated frozen CCl(3)F/n-alkane solutions (symmetric transfer) and mixed n-alkane crystals (asymmetric transfer) by EPR spectroscopy at 77 K and gas chromatographic analysis after melting. The proton-donor site is related very strictly to the structure of the semi-occupied molecular orbital of the parent radical cation, with proton transfer taking place from those C-H bonds that carry appreciable unpaired-electron and positive-charge density. Proton acceptance is restricted to C-H bonds at secondary carbon atoms (no proton transfer to C-C bonds nor to C-H bonds at primary carbon atoms), with a preference for the penultimate position and equal (but considerably lower) transfer to the interior sites. In mixed n-alkane crystals, additional selectivity with respect to the site of proton acceptance results from structural factors in combination with the donor site selectivity (structurally determined acceptor site selectivity).

The uptake of n-alkanes from alkane mixtures during growth of the hydrocarbon-utilizing fungus Cladosporium resinae

Cladosporium resinae growing on alkane mixtures removed n-alkanes sequentially in order of increasing molecular weight, each at about the same rate as during growth on it as single alkane. This sequence is not in order of the ability of each alkane to support growth. No alkane-specific extracellular solubilizing agent able to affect the order o metabolism could be detected during the growth of C. resinae on mixed n-alkanes, but supplementing the medium with phospholipids like those produced during growth on specific alkanes increased the rate or removal of the respective alkanes. Kinetic analysis indicated that the uptake of dodecane, hexadecane and octadecane from a mixture could be by a common mechanism, the order being determined, through competition, by the affinity of the system for each alkane.

Excess thermodynamic functions of n-alkane mixtures. Prediction and interpretation through the corresponding states principle

Using published reduction parameters for pure normal alkanes, the Prigogine corresponding states principle is extended to excess thermodynamic functions of n-alkane mixtures. All alkane segments have identical interactions (no end-effects), an assumption justified by the success of the treatment. The TCEp data of Trejo Rodriguez and Patterson (J. Chem. Soc., Faraday Trans. 2, 1982, 78, 491), for n-alkane mixtures through the composition range at 20, 40, 55 °C are given by a single reduced TCEp against T curve. Similarly, single curves against T of HE, GER and TSER represent literature HE, residual GE and residual TSE data through the composition ranges and at various temperatures for n-C6+ n-C16. The Flory and the Guggenheim–Huggins–Miller–Orr combinatorial SE approximations lead to equally successful corresponding states representations for TSER and GER. Maximum deviations from the corresponding states curves correspond to ca. 10 J mol–1 for HE, GE and TSE, and ca. 0.2 J K–1 mol–1 in CEp, indicating conformity of the excess functions with the corresponding states principle. The TCEp, HE, TSER and GER may be represented by a single Cp(T) curve for pure and mixed n-alkanes. The curve first decreases with increasing T corresponding to decreasing short-range orientational order in the liquid, then passes through a wide minimum and increases with T corresponding to an increase of free volume. The Cp function predicts all the complex temperature and composition dependences of CEp, HE, TSER and GER for a typical system, n-C6+ n-C16, as effects of orientational order and free volume. Experimental data available for numerous n-alkane systems at different temperatures are used to test the calculations of the following quantities: equimolar HE, finite concentration and infinite dilution activity coefficients (including polyethylene systems) and lower critical solution temperatures for polyethylene systems. Agreement with experiment is almost always within experimental error and is considerably better than with other predictive methods. Experimental data for the pure n-alkanes from n-C5 to polyethylene follow the corresponding states principle imperfectly, but give a Cp(T) curve which is of the same shape as that obtained from excess quantities, i.e.Cp indicates both orientational order and free volume effects. However, the magnitude of Cp is considerably greater and reasons for this difference are discussed.