Hydrocarbons N-alkanes Research Articles

Excretion products of algae and their occurrence in Solar Lake. Taba, Egypt

The present study aimed to investigate the nature of organic compounds liable to be released by blue-green algae (cyanobacteria) and organic compounds detected in the Solar Lake in Taba, Egypt. The liquid-liquid extraction method and liquid chromatography technique were applied for extraction, clean-up and separation of the organics. Gas chromatography/mass spectrometry (GC/MS) was used to carry out qualitative analysis. The most dominant species in the algal samples collected from Solar lake in Taba are Aphanotheca stagnina, Synechococcus aeruginosus, Oscillatoria limnetica and Microcoleus chthonoplastes. n-Alkane hydrocarbons that ranged from C12 to C25 were identified in lake water samples, most of them were derived from algal species. Several fatty acids were isolated from water samples with predominant tridecanoic acid (C13), tetradecanoic acid (C14) and hexadecanoic acid (C16). Meanwhile, the identification of fatty acids from algal suspension samples indicated the predominance of hexadecanoic acid (C16) and heptadecanoic acid (C17), with carbon number that ranged from C10 to C17. The dominant compounds were C15, C17, C17:1, C19 n-alkanes. C13, C15, C16 fatty acids, alkyl esters of propyl decanoate, esters of benzenedicarboxlate, diphenyl amine, geosmin and 2-methyl isoborneol (2-MIB) in water and in algal suspension samples were probably enough to distinguish the cyanobacterial mat community of a saline lake shore.

The characterisation and behaviour of carbonaceous material in a refractory gold bearing ore

Sulfide ore and a flotation concentrate from Fosterville contained 0.76% carbonate carbon, 0.18% native carbon and 0.20% organic carbon of which 4.5 ppm were n-alkane hydrocarbons. The concentrate yielded 0.99% native carbon, 0.28% carbonate carbon and 0.11 % organic carbon of which 19.7 ppm was n-alkane hydrocarbons. IR spectroscopy of the fulvic acid fraction of the flotation concentrate showed it to be similar to humic acid. The addition of representative levels of n-alkane hydrocarbons, carbonate carbon and humic acid to the oxidised ore indicated that these components had negligible effect on gold recovery. The addition of 0.2% native carbon decreased gold recoveries from 84.4% to 68.8% while 0.2% activated carbon reduced recovery to 3.1%. Native carbon when acidified, mimicking the environment of bacterial oxidation, resulted in recovery dropping from 84.4% to 61.0%. Gold recovery for a standard sulfide float was 92.5%. Sodium naphthalene sulfonate (SNS) was the only depressant to lower native carbon levels in the concentrates without reducing gold recovery. 275 g/t SNS depressed 45% of the native carbon and gold recovery was unchanged. Nitric acid oxidation and subsequent cyanidation of the SNS concentrates lead to overall gold recovery improving from 88.3% for a standard sulfide float to 92.0%.

Turbulence Effects on the Vaporization of Monocomponent Single Droplets

Abstract An experimental facility has been developed to study the effects of turbulence on droplet vaporization. The facility allows lo generate a zero mean velocity, isotropic and homogeneous turbulence and to vary systematically the turbulence kinetic energy. The influence of turbulence on suspended single droplets of five n-alkane hydrocarbons is investigated, by determining the average vaporization rates by image analysis techniques. The experiments have been conducted under normal pressure and temperature conditions; for all cases, the length scales of energetic turbulence eddies are larger than the initial droplet diameter. For all the investigated cases, it is found that the presence of turbulent velocity fluctuations increases the average vaporization rates compared to the stagnant case. The linear regression rate of the projected droplet surface area versus time is observed under all turbulence conditions. It is observed that droplets of the five investigated fuels respond differently to the same...

Vapor-pressure measurement of complex hydrocarbon mixtures by headspace gas chromatography

Headspace gas chromatography was used to measure the vapor pressures of single n-alkane hydrocarbons and their binary, ternary and quaternary mixtures at various temperatures in the range 38–107°C. In addition, diesel fuel, gasoline and crude oil vapor pressures were measured at 38 and 70°C. The microprocessor-controlled headspace gas chromatograph automatically thermostated the samples contained in septum-sealed glass vials to equilibrate the vapor and liquid for a pre-set period of time (usually 60 min), pressurized the vials to a pre-set pressure (at least 138 kPa gauge) by inserting a hollow needle through the septum, and sampled the vapor for a pre-set period of time (0.01 min) by allowing the pressure in the vial to drive an aliquot of the vapor ( ca. 9 μl) through the needle and onto the analytical column. Using this technique, single n-alkane hydrocarbon vapor pressures, measured by totally vaporizing μl aliquots in the vials, agreed, on the average, to within 1% with calculated values based on hydrocarbon properties. Likewise, measured total vapor pressures of the binary, ternary, and quaternary mixtures compared well with calculated values, assuming ideal behavior for the mixtures, and the measured vapor pressures of diesel fuel, gasoline, and several crude oils showed good precision and accuracy.

Bulk atmospheric deposition of hydrocarbons to lower Chesapeake Bay

Anthropogenic and biogenic hydrocarbons (HC) were continuously deposited from the atmosphere at stations in SE Virginia. The bulk deposition rate for total unresolved complex mixture (UCM) and n-alkane HC was constant at all stations during the sampling period (> 1 year). The deposition rates at the three non-urban stations was similar and averaged 69, 27 and 18 μg m −2 d −1 for total, UCM and n-alkane HC, respectively. The urban station had a higher deposition rate for total (203 μg m −2 d −1) and UCM (90 μg m −2 d −1) HC than the non-urban stations, but a similar deposition rate for n-alkanes (22 μg m −2d −1). These results indicate a regionally similar deposition rate for biogenic ( n-alkanes) and anthropogenic (UCM) HC, with a major localized input of anthropogenic HC at the urban station. Long range atmospheric transport followed by dry deposition appear to be the major processes responsible for these similar deposition rates over this geographical area.