Distribution Of Paraffins Research Articles

Occurrence and fate of atmospheric short/medium chain chlorinated paraffins: Size distribution and inhalation exposure

Chlorinated paraffins (CPs) are intricate industrial compounds synthesized through alkane chlorination. Researches on the size distribution of short-chain (SCCPs) and medium-chain chlorinated paraffins (MCCPs) in atmospheric particulate matter (PM) are limited. Here, we conducted a thorough investigation on the size-dependent distribution characteristics, deposition behavior in respiratory tract, and health risks associated with CPs in atmospheric PM. The concentration of SCCPs in atmospheric particulate matter (PM10) was much higher than MCCPs, with concentration ranges of 2.53–31.8 and 1.07–4.62 ng m−3, respectively. Concentrations of CPs increase with decreasing PM size, peaking at aerodynamic diameters (Dp) < 0.49 μm. Physicochemical properties influence the distribution of CP homologs in PM. Those with lower vapor pressure, higher octanol-air and octanol-water partition coefficients tended to accumulate in PM with larger geometric mean diameters. Most of the inhaled CPs in PM deposited in the upper airways, with a small amount in the trachea and alveolar regions. The estimated daily intakes values were highest when Dp < 0.49 μm. Particle size is an essential determinant for the deposition of inhaled CPs in PM and should be considered in health risk assessments.

Seasonal variation of short-, medium- and long-chain chlorinated paraffin distribution in Belgian indoor dust

Chlorinated paraffins (CPs) are high production volume plasticizers and flame retardants, which have exhibited bioaccumulative and toxic properties. CPs may be released from treated consumer goods and bind with indoor dust, leading to human exposure via unintentional dust ingestion. In this study, the concentrations and homologue distribution of CPs were measured in 50 indoor dust samples collected in paired winter and summer sampling campaigns from 25 homes in Flanders, Belgium. Short-, medium- and long-chain CPs (SCCPs (C10-13), MCCPs (C14-17) and LCCPs (C18-20), respectively) were each detected in all Belgian indoor dust samples with overall median concentrations of 6.1 µg/g (range 0.61 to 120 µg/g), 45 µg/g (range 4.5 to 520 µg/g) and 4.5 µg/g (range 0.3 to 50 µg/g), respectively. Concentrations were significantly higher in the winter samples than summer for each of the three groups (p < 0.05). LCCPs homologues ranging from C21-32 were also detected in dust samples and accounted for approximately half of the LCCP relative abundance based on instrumental peak area, although a lack of appropriate analytical standards prevented quantification of these homologues. While clear sources of CP contamination in dust could not be identified, significant associations between concentrations of ∑SCCPs, ∑MCCPs and ∑LCCPs (C18-20) (p < 0.05) suggested the combined application within materials or products in homes. Based on typical exposure scenarios, estimated daily intake of ∑CPs (C10-20) for adults and toddlers were 14 and 270 ng/kg bw/day, respectively, though margin of exposure assessments for SCCPs and MCCPs indicated that adverse health effects were unlikely for all exposure scenarios. This study presents the first evidence of seasonal variation in the levels and distribution for each of the SCCP, MCCP and LCCP classes in indoor dust and highlights the urgent need for appropriate analytical standards for LCCP quantification.

Production and characterization of novel EPDM/NBR panels with paraffin for potential thermal energy storage applications

Innovative panels suitable for the thermal management of closed systems with potential applications for buildings have been produced combining an Ethylene-Propylene Diene Monomer (EPDM) rubber with a paraffin wax having a melting temperature of 28 °C. The compounded material was confined in a Nitrile Butadiene Rubber (NBR) envelope that impeded any paraffin leakage. According to differential scanning calorimetry, the effective thermal energy efficiency of the PCM (PCMeff) in the panel, was 37 wt% with a melting enthalpy of about 100 J/g. The homogeneous distribution of paraffin within the elastomeric matrix was verified both through scanning electron microscopy and through temperature monitoring of the panel’s surface during heating/cooling cycles, performed by an infrared camera. It was also observed that the thermal conductivity of the panels was the same above or below the melting point of paraffin with values of about 0.15 W/m·K. Shore A hardness tests revealed the dependence on the temperature due to the presence of paraffin that acted as softener above its melting point and as hardener below. The evaluation of the thermal energy storage performance of the panels was verified by monitoring the internal temperature of testing boxes (310x310x310 mm3) insulated with these elastomeric panels during heating/cooling cycles performed in a temperature interval from 16 to 31 °C (typical summer conditions in Trento, Italy). The presence of paraffin within the elastomeric panels allowed to keep the internal temperature of the box always lower than 27 °C, with a delay of the peak temperature of about 1 h with respect to a reference non-insulated box. The results of testing boxes have been confirmed after 15 months, showing the reproducibility and the stability of the assembled lab configuration.

High-fidelity and rapid cellular-level Mueller matrix imaging for tissue identification with unstained sections

Mueller matrix polarimetry is regarded as a promising technique in the field of biomedicine, especially for pathological diagnosis. However, the current studies on Mueller imaging of pathological sections are all at the tissue-level, and the cellular-level polarization information is difficult to obtain. To overcome this challenge, we first propose a cellular-level Mueller matrix imaging method for accurate quantitative identification of tissues in this study. Benefiting from the significant birefringent behavior of paraffin in unstained sections, the proposed method can locate the paraffin distribution areas of retardance images by involving Otsu's algorithm. Then, the real cellular-level polarization information (e.g., depolarization) is acquired. The efficiency of the proposed method was demonstrated on unstained rat tissue samples. The results showed that the obtained depolarization images are highly consistent with the stained microscopic images in terms of the morphology and arrangement of the tissues at cellular level. Finally, this method was preliminarily applied to the detection of human lung cancer tissue section, effectively realizing the quantitative differentiation of normal, inflamed, and malignant areas in unstained section. This study provides a possible approach for the rapid and accurate diagnosis of cancer.

Material Decomposition in Low-Energy Micro-CT Using a Dual-Threshold Photon Counting X-Ray Detector

Material decomposition in computed tomography is a method for differentiation and quantification of materials in a sample and it utilizes the energy dependence of the linear attenuation coefficient. In this study, a post-image reconstruction material decomposition method is constructed for a low-energy micro-CT setup using a photon counting x-ray detector. The low photon energy range (4–11 keV) allows for K-edge contrast separation of naturally occurring materials in organic tissue without the need of additional contrast agents. The decomposition method was verified using a phantom and its capability to decompose biomedical samples was evaluated with paraffin embedded human atherosclerotic plaques. Commonly, the necessary dual energy data for material decomposition is obtained by manipulating the emitted x-ray spectrum from the source. With the photon counting detector, this data was obtained by acquiring two energy window images on each side of the K-edge of one material in the sample. The samples were decomposed into three materials based on attenuation values in manually selected regions. The method shows a successful decomposition of the verification phantom and a distinct distribution of iron, calcium and paraffin in the atherosclerotic plaque samples. Though the decompositions are affected by beam hardening and ring artifacts, the method shows potential for spectral evaluation of biomedical samples.

Spatial distribution of lipids modulated by phase separation in emulsified films and the effects on structure-function relationships

The aim of this work was to develop a novel strategy to modulate the spatial distribution of paraffin in emulsified films via tuning phase separation behaviors among zein/gelatin (ZG) matrix, and to elucidate their structure-function relationships. Three phase separation behaviors within ZG matrix, namely, the zein-dominated, gelatin-dominated and ZG-macro phase separation, were developed. When the ZG matrix was tuned to ZG-macro or gelatin-dominated phase separation, the successive or partial bilayer films can be developed due to the spatial distribution of paraffin as the floating layer. While, when zein-dominated phase separation was created, paraffin uniformly distributed as dispersed phase, forming films with monolayer structure. Surface distribution of paraffin, detected by AFM, revealed that distinct interactions between paraffin and zein or gelatin drove the distribution pattern. The bilayer structure more effectively enhanced water barrier properties of films and performed preferable mechanical properties but at the expense of optical properties, whereas the release property of oregano essential oil and tea polyphenol was dominated by the chemistry nature of film matrixes rather than the spatial distribution. This study adds new knowledges to the rational design of emulsified films by tuning the spatial distribution of lipids.

Influence of Heavy Organics Composition on Wax Properties and Flow Behavior of Waxy Crude Oils

Paraffinic crude oils are desirable because of their high content of saturated hydrocarbons but may present handling challenges due to crystallization of high molecular weight paraffin at low temperatures. The prediction of wax properties and behavior of waxy crude oil is important in order to adopt appropriate mitigative measures to forestall flow assurance problems associated with wax crystallization and deposition. Accurate predictive models are limited mainly by the sheer complexity of crude oil composition. Result of analysis of saturates, aromatics, resins and asphaltene content of crude oils (SARA) has been used as a simple tool to predict and interpret crude oil properties and behavior but has been found inadequate in predicting wax instability. In this paper, we report on the use of SARA analysis and paraffin distribution data to interpret the wax properties and flow behavior of Niger-Delta crude oils. The crude oil properties determined include wax content, asphaltene and resin content by gravimetry, pour point, wax appearance temperature by cross-polarized microscopy and paraffin carbon number distribution of whole oil and wax precipitate by GC-FID. Asphaltene and resin content were found to influence the oil pour point, while saturates content, paraffin carbon number of crystallizing waxes and wax content control its low-temperature flow properties.

Application of the Perturbed-Chain SAFT to Phase Equilibria in the Fischer–Tropsch Synthesis

As an alternative route to produce liquid fuels, Fischer–Tropsch synthesis (FTS) has received considerable attention. Phase equilibria have been one of the key issues in the design and operation of not only an FTS reactor, but also relevant downstream processing, e.g., stepwise condensation of FTS products, wastewater treatment, and the recovery of α-olefins. These issues are extremely complex due to a wide spectrum of FTS products and the presence of noncondensable gas, nonpolar components, associating components, and highly polar components. To address these issues, the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) was evaluated using phase equilibrium data of binary and ternary mixtures containing water, alcohols, hydrocarbons, and noncondensable gases. The parameter values are available via a three-step parametrization strategy established in our previous work [Zheng et al. Ind. Eng. Chem. Res. 2018, 57, 3014]. A couple of popular benchmark models, namely the Soave–Redlich–Kwong (SRK) EoS with the modified Huron–Vidal second-order mixing rule (SRK/MHV2) and the predictive SRK (PSRK) EoS, were selected for comparison to put the performance of the PC-SAFT EoS into perspective. It was found that the PC-SAFT EoS gives reliable correlations/predictions in all the studied cases, whereas the other two models fail to do so. The three models were also employed to simulate hot and cold traps where the stepwise condensation of the reactor effluent occurs. It was found that all three models yield satisfactory results for the paraffin distribution of the liquid stream leaving the hot trap, while the SRK/MHV2 and PSRK models are less accurate for the olefin distribution, particularly at high temperature. It was also found that all three models are capable of predicting the composition of the two liquid streams (namely organic and aqueous) leaving the cold trap except that the SRK/MHV2 model fails to accurately reproduce the distribution of alcohols in the two liquid streams. This study advocates the practical use of the PC-SAFT EoS by its application to a complex, industrially important FTS process and a comprehensive evaluation, together with the two popular benchmark models.

Technology Focus: Oilfield Chemistry (September 2018)

Technology Focus The last 3 years have seen an unprecedented increase in paraffin-related challenges in the world of production chemistry. The industry is producing more-challenging crude oil as the production of light, sweet, and easy-to-treat crude declines. The new crudes coming on stream contain more-complex combinations of paraffinic components. We are aware of the bimodal distribution of paraffin displayed nicely in high-temperature gas chromatography of, for example, Eagle Ford crude oil, which shows a double peak distribution of paraffin. Some of the more-recent publications highlighted are using more-advanced analytical techniques to characterize crude oil because heavier paraffin components are not detectable by classical methods. Characterization using techniques such as nuclear magnetic resonance and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry are detecting paraffin chains in excess of C100 and determining a trimodal distribution of paraffin in crude oil that is difficult to treat using today’s technology, thus requiring a change in approach and thinking for the production chemist. Such crudes are being developed today—crude oils from some of the more extreme shale plays around the world such as the Montney formation in British Colombia, Canada; Vaca Muerta in Argentina; East African crude oils of Uganda, Chad, and Kenya; and crude oils in the Far East such as those in Indonesia and Vietnam. The current chemical technology begins to reach its limit of functionality in a crude oil that contains paraffin chains of C75+ in length. The featured papers give some insights into the work under way to elucidate the structure performance relationships between inhibitors and crude oils containing these higher paraffinic species. Much work remains in order to develop more-effective solutions and strategies for these incredibly challenging and highly paraffinic crude oils. The featured papers summarize some of the state-of-the-art techniques to determine the true nature of paraffin deposition from these bi- and trimodal crude oils as well as advanced techniques to truly characterize and treat produced fluids and recovered solids samples. Readers are encouraged to research the recommended additional reading and take some time to delve into the references contained in these papers. This literature contains an extensive review of the history and current state of the art in paraffin science for the oilfield chemist and engineer. Recommended additional reading at OnePetro: www.onepetro.org. OTC 27855 Work Flow To Evaluate Wax-Deposition Risk Along Subsea Production Systems by O. Coronado, Genesis, et al. OTC 28714 Cold-Finger Benchmarking Study for Paraffin-Inhibitor Selection by Yun Peng, Shell, et al. SPE 187252 Investigating the Performance of Paraffin Inhibitors Under Different Operating Conditions by Anshul Dubey, The University of Tulsa, et al.

Paraffin solubility curves of diesel fuels from thermodynamic model adjusted through experimental DSC thermograms

DSC and wax solubility curves were measured for two diesel fuel samples. Compositional profiles were also measured for the solubility curve points. The paraffin distributions of the samples were determined and the non-paraffinic components were lumped into pseudocomponents. The liquid phase was modeled using the Peng-Robinson equation of state with the classical van der Waals mixing rule. For the solid phase, the modified UNIQUAC model was employed. The models were fitted to the DSC data by tuning only four multipliers acting on the molecular weights, boiling and critical temperatures of the pseudocomponents as well as on the paraffins’ pair interaction energies from the UNIQUAC model. Then the model is used to predict wax appearance temperature, amount and composition of solid deposit as a function of temperature during cooling. Excellent results were obtained for the two samples analyzed. This way, the methodology developed is able to predict adequately the formation of solid paraffin from diesel fuels.

Numerical and Experimental Studies on the Heat Transfer Performance of Copper Foam Filled with Paraffin

Abstract: The pore-scale numerical works on the effective thermal conductivity and melting process of copper foam filled with paraffin, and a phase-change material (PCM) with low thermal conductivity, were conducted by utilizing the two-dimensional (2D) hexahedron Calmidi-Mahajan (C-M) model and the three-dimensional (3D) dodecahedron Boomsma-Poulikakos (B-P) model. The unidirectional heat transfer experiment was established to investigate the effective thermal conductivity of the composite. The simulation results of the effective thermal conductivity of the composite in 2D C-M model were 6.93, 5.41, 4.22 and 2.75 W/(m·K), for porosity of 93%, 95%, 96% and 98% respectively, while the effective thermal conductivity of the composite in 3D B-P model were 7.07, 5.24, 3.07 and 1.22 W/(m·K). The simulated results were in agreement with the experimental data obtained for the composite. It was found that the copper foam can effectively enhance the thermal conductivity of the paraffin, i.e., the smaller the porosity of copper foam, the higher the effective thermal conductivity of the composite. In addition, the Fluent Solidification/Melting model was applied to numerically investigate the melting process of the paraffin in the pore. Lastly, the solid–liquid interface development, completely melted time and temperature field distribution of paraffin in the pore of copper foam were also discussed.

Lu Plot and Yao Plot: Models To Analyze Product Distribution of Long-Term Gas-Phase Fischer–Tropsch Synthesis Experimental Data on an Iron Catalyst

Fischer–Tropsch synthesis (FTS) is a catalyzed chemical reaction in which synthesis gas (H2 + CO) is converted to clean fuels and chemicals. In addition to the classical Anderson–Schulz–Flory (ASF) model, two new models, namely, Yao and Lu models, are presented to show the FTS product distribution using the experimental data obtained in three fixed-bed reactors [each loaded with 1 g of the same iron-based catalyst and reduced with syngas (CO/H2), H2, and CO] over a wide range of FTS conditions. In the first approach, we plotted P(n + 1)/O(n + 1) versus Pn/On with carbon number n = 2–5, which is called Yao’s plot. The results showed that, although the P/O ratios are strongly dependent upon the process conditions, such as reduction agents, flow rates, pressures, etc., the plots of P(n + 1)/O(n + 1) against Pn/On yielded a nearly linear relationship, although with different gradients for all three reactors. These results indicate that the olefin and paraffin distributions are not independent. The current data, including the effect of the reducing agents on the catalyst performance, widen the range of the application of the Yao plot. Just like the classical ASF distribution model, this model has some deviations, especially for n = 2. The second plot, referred to as the Lu plot, depicts the relationship between normalized mole fractions of On, On + 1, and Pn. These plots show how the equilibrium points migrate with changes in the experimental conditions. These equilibrium point migrations seem to be due to changes in the CO conversion. Using the same normalized mole fraction concept, novel plots of CnH2n + 1, CnH2n, and Cn + 1H2(n + 1), that is, paraffin n, olefin n, and paraffin n + 1, when n = 2, 3, and 4, are plotted.

A study of Fischer-Tropsch synthesis: Product distribution of the light hydrocarbons

The olefin (O) to paraffin (P) ratio is important in Fischer-Tropsch synthesis (FTS) and there is some disagreement as to how important diffusion, re-adsorption of olefins or other rate based phenomena are in determining this. We measured the performance of a cobalt catalyst for nearly 3000h time on stream. During this period there was first the initial unsteady state behaviour as the catalyst settled in, then we changed the temperature, the catalyst deactivated and finally we flushed the reactor with N2 and then resumed reaction to see if this would disturb the performance of the catalyst.We plotted the data in the standard formats typically used, but we also plotted the data in two other ways. The first way, which we refer to as the Yao plot, is a plot of Pn+1/On+1 versus Pn/On where for us n is a carbon number from n=2–5 as we only measure the lower hydrocarbons. We find that the data lies on two straight lines, one for n=2 and the other for n>2. What is important is that these straight lines hold during the settling in period, the change in temperature, the deactivation of the catalyst and even after the catalyst had been flushed with nitrogen. The olefin and paraffin distributions are thus dependent and cannot be changed independently. This result could imply that the product distribution might be determined by some sort of reaction equilibrium among some species (we refer to this as quasi-reaction equilibrium) or vapour–liquid equilibrium (VLE), or a combination of the two factors.The second plot, which we refer to as the Lu plot, is a plot of the relationship between normalised mole fractions of On, On+1 and Pn. These plots have previously been used in distillation and reactive distillation and the behaviour that is seen for the FT system indicates that there is a stable equilibrium point and perturbations to the reactor cause the measured data to make a step change away from this point and that over time the points move back to the stable point. This behaviour is strongly suggestive of a reactive distillation map with a stable point. This is found in for example systems with reversible reactions.Our findings suggest that equilibrium processes, such as VLE and reversible reactions, may be contributing to the observed behaviour in FT and that we perhaps should not rely solely on rate based processes, such as kinetics and diffusion, in trying to understand the behaviour of FT.

Temperature Dependent Behavior of Oil Dispersion System in Bulk and on the Metal Surface

This article focuses on the temperature dependent behavior of oil dispersion systems containing high amount of paraffins. In particular the properties of oils in bulk and during the contact with metal surface were evaluated by methods of rheoviscometry, thermal analysis, differential scanning calorimetry, gravimetry, polarization microscopy, gas chromatography and chemical analysis. Analysis of rheological parameters of oil, morphology of paraffin crystals, and thermal properties at temperature interval between 0÷90 0 С allowed to determine the transition temperature of oil dispersion system from the molecular to free-dispersal and bounded-dispersal states. It was established that the indicated parameters depend on oil composition, molecular-mass distribution of paraffins, curing temperature and cooling rate. Contacting of high paraffinic oils with steel surface leads to formation of asphaltene-resin-paraffin deposition (ARPD). The quantity, structure, composition and adhesiveness of ARPD depends on oil composition and gradient of temperature between heated oil and cooled metal surface. In case of temperature gradient is more than 30 0 С the solid and high adhesive depositions are formed. Their structure is enriched by long chain high-melting paraffins. In case of temperature gradient is less than 20 0 С, amorphous and easy removable depositions are formed. Their structures are enriched by mechanical admixtures, water, resin, asphaltene and low-melting short chain paraffins. Key words: High-paraffinic oil; Oil dispersion system; Asphaltene-resin-paraffin depositions; Wax appearance temperature; Heat treatment

Fischer–Tropsch Synthesis: Branched Paraffin Distribution for Potassium Promoted Iron Catalysts

Iron Fischer–Tropsch catalysts with varying amounts of K (0, 2, 4, 6, 10 wt%) were utilized. Except possibly for the 10 wt% catalyst, the amount of the iso-alkanes produced was essentially constant for carbon numbers from 4 to 23. Iso-alkanes accounted for about 13–15 % of the hydrocarbon products that were produced. The 2- and 3-methyl isomers were present at about two times the amount of the other methyl isomers for each carbon number. Mechanisms to account for the branching were considered but a satisfactory one could not be found.

Thermal Performance of a Phase Change Material‐Based Latent Heat Thermal Storage Unit

An experimental analysis is presented to establish the thermal performance of a latent heat thermal storage (LHTS) unit. Paraffin is used as the phase change material (PCM) on the shell side of the shell and tube‐type LHTS unit while water is used as the heat transfer fluid (HTF) flowing through the inner tube. The fluid inlet temperature and the mass flow rate of HTF are varied and the temperature distribution of paraffin in the shell side is measured along the radial and axial direction during melting and solidification process. The total melting time is established for different mass flow rates and fluid inlet temperature of HTF. The motion of the solid–liquid interface of the PCM with time along axial and radial direction of the test unit is critically evaluated. The experimental results indicate that the melting front moves from top to bottom along the axial direction while the solidification front moves only in the radial direction. The total melting time of PCM increases as the mass flow rate and inlet temperature of HTF decreases. A correlation is proposed for the dimensionless melting time in terms of Reynolds number and Stefan number of HTF. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21120

Post-mortem Reperfusion of a Pig: a First Step to a New Surgical Training Model?

The purpose of this experimental study was to establish a short-term post-mortem circulation in a pig model using liquid paraffin. This study also investigated the quality of vascular perfusion in the peripheral tissues. This is the first step in the development of a new revascularized human surgical training model. This first experience was performed on the hind leg of a pig. Initial cannulation of the external iliac artery and vein was followed by connection of the arterial inflow to a heart-lung machine and using the venous outflow to flush post-mortem clots and blood. Subsequently, after connecting the venous outflow to the heart-lung machine, circulation was initiated. Circulation was established during 27min, during which the flow was constantly 130mL/min. A steady increase in inlet pressure was observed during the experiment, which finally reached a minimum value of 124mmHg. Perfusion was interrupted early due to an uncontrollable fluid leak. Afterwards, the distal hind leg was incised showing an equal distribution of paraffin. A short-term revascularization was successfully re-established under excellent conditions. Although the results are promising, further experiments are necessary to eventually perform a wide range of surgical procedures on revascularized human cadavers.

Separation and Characterization of Olefin/Paraffin in Coal Tar and Petroleum Coker Oil

We have investigated and established a preparative method of using a solid-phase extraction cartridge containing Ag+-exchange resin (Ag+-SPE) for separating olefins and paraffins in the saturate fractions of coal tar and petroleum coker oil. The successful separation of paraffins and olefins was confirmed by gas chromatography coupled with mass spectrometry (GC–MS). Proton nuclear magnetic resonance (1H NMR) spectroscopy was applied to determine the olefin structures for olefin-type distributions. None or negligible amounts of iso-α-olefins were detected by 1H NMR in the coal tar but were found significant in the coker oil. Gas chromatography coupled field ionization time-of-flight mass spectrometry (GC–FI-TOF MS) was employed to determine the molecular distribution of paraffins and olefins. With separate paraffin and olefin fractions, the differentiation between isomers, such as monocycloparaffins versus monoolefins, can be made.

Olefin pseudo-equilibrium in the Fischer–Tropsch reaction

Overall or global thermodynamic equilibrium predicts a predominately methane product for the Fischer–Tropsch (FT) reaction. Even though the FT product distribution may not be described by overall thermodynamic equilibrium, there may be aspects of it that can be described by equilibrium. We postulate that an equilibrium is set up in the FT reaction between species, i.e. between hydrocarbon or a surface precursor of chain length n and that of chain length n+1, and thus although we do not have global equilibrium, we have an approach to equilibrium between the product species. As olefins are reactive under FT reaction conditions we initially postulate that an equilibrium distribution is set up between the α-olefins or a species that leads to α-olefins.The calculated results predict that equilibrium between the species of any homologous series would results in a Flory-type distribution, where the ratio of the moles of species n to that of the moles of species n+1 would be constant. When the value of this ratio α is calculated for olefins, it is found that the experimentally measured values match those calculated and thus the measured and predicted distribution of the olefins agree. However, assuming that the alcohols or paraffin distribution approaches equilibrium, leads to calculated values of α that are not consistent with the experimental results. Therefore, there may be an equilibrium set up between species of either an olefin precursor or the olefins themselves which leads to the Flory-type distribution found in the FT reaction.

High pressure phase equilibria in methane + waxy systems. 3. Methane + a synthetic distribution of paraffin ranging from n-C 13 to n-C 22

Liquid–vapor and fluid–waxy solid phase transitions were measured under pressure on a pseudo binary system made up of methane + a waxy distribution of normal paraffins ranging from C 13 to C 22. The composition of the paraffins in the waxy fraction was defined in order to obtain an average molecular weight equal to that of pure heptadecane. Measurements were carried out up to 90 MPa by using a synthetic method on various mixtures ranging from 0 to 99% of methane. Results were compared to the phase equilibrium data of the binary system methane + heptadecane in the same conditions.