A Novel Photometric Technique to Detect the Onset of Asphaltene Precipitation at Low Concentrations: The Effect of Maltenes and Water

A photometer was utilized to measure the intensity of scattered light in toluene / heptane / asphaltenes mixtures. On the scattering‐intensity versus heptane‐to‐toluene ratio functions, two linear regions can be observed. The intersection of these regions determines the heptane‐to‐toluene ratio at which the precipitation of asphaltenes starts. The onset of asphaltene precipitation was determined as a function of asphaltene concentration in the presence and in the absence of maltenes as well as water. The onset is dependent on the asphaltene concentration. The presence of water promoted while the presence of maltenes inhibited the precipitation of asphaltenes.     

Residua coke formation predictability maps

The dispersed particle solution model of petroleum residua structure was used to develop predictors for pyrolytic coke formation. Coking Indexes were developed in prior years that measure how near a pyrolysis system is to coke formation during the coke formation induction period. These have been demonstrated to be universally applicable for residua regardless of the source of the material. Coking onset is coincidental with the destruction of the ordered structure and the formation of a multi-phase system. The amount of coke initially formed appears to be a function of the free solvent volume of the original residua. In the current work, three-dimensional coke make predictability maps were developed at 400, 450 and 500 °C for four residua with nominal H/C atomic ratios of 1.4. The maps relate residence time and free solvent volume to the amount of coke formed at a particular pyrolysis temperature. Coke formation reactions can be modeled with zero-order kinetics which occur in two stages. The first stage produces 22.5-27.0 wt% coke with activation energies ranging from 22,000 to 38,000 cal/mol. The second stage continues the reaction to completion, producing 58.1-63.6 wt% coke with activation energies ranging from 54,000 to 83,000 cal/mol. The activation energies correlate with the original residua free solvent volumes. The results provide a new tool for ranking residua, gauging proximity to coke formation, and predicting initial coke make tendencies.     

Analysis of lipids from cooked beef by thin-layer chromatography with flame-ionization detection

Lipids were extracted from cooked ground beef with methylene chloride/methanol (2:1). The lipids were separated on a silicic acid column, into neutral and polar fractions by elution with methylene chloride, followed by methanol. These fractions were analyzed by Iatroscan thin-layer chromatography with flame-ionization detection instrumentation on Chromarods S-III (silica gelcoated quartz rods). Comparison of cooked beef stored for 0, 4 and 7 d at 4°C indicated that storage caused a decrease in total lipids, an increase in neutral lipids and a decrease in polar lipids, specifically in phosphatidylcholine. These changes in the lipid fraction were associated with meat flavor deterioration and an increase in lipid oxidation.     

Dry column method for the quantitative extraction and simultaneous class separation of lipids from muscle tissue

A method for lipid isolation is presented that is alternative to the traditional chloroform/methanol extraction methods. This new method allows lipid isolation by solvent elution of a dry column composed of a tissue sample, anhydrous sodium sulfate, and Celite 545 diatomaceous earth groud together. To isolate total lipids, the dry column is eluted with a mixture of dichloromethane/methanol (90∶10, v/v). Alternatively, the lipids may be isolated and simultaneously separated into neutral and polar fractions by a sequential elution procedure; neutral lipids free of polar lipids are eluted first with dichloromethane, followed by elution of polar lipids with the dichloromethane/methanol (90∶10) mixture. The two dry column methods-isocratic or sequential elution-were compared with the traditional chloroform/methanol methods by gravimetric, thin layer chromatographic and phosphorus analyses. Presented in part at the AOCS 70th Annual Meeting, San Francisco, May 1979. Agricultural Research, Science and Education Administration, U.S. Department of Agriculture.     

Coal-derived asphaltenes. Relationship between chemical character and process history

The chemical character of asphaltenes isolated from coal-derived liquids and the relative ease of their catalytic and noncatalytic conversion to oil has been found to depend upon their processing history. To facilitate chemical characterization, a simple analytical method was developed for separation of the asphaltenes into three subfractions according to their relative strength of absorption on silica gel. Using this separation technique, differences in the relative content of polar molecules were found among asphaltenes of various processing histories. In general, the relative content of polar compounds in the asphaltenes decreases with increasing conversion to oil. The relative rate of conversion also declines after the asphaltene content reaches a low level. The asphaltenes remaining after long hydrotreatment are more aromatic, contain fewer polar functional groups and are of somewhat smaller molecular size than those obtained after short hydrotreatment. The initial rates of asphaltene conversion were considerably enhanced by a commercial CoMo hydrodesulfurization catalyst. The catalyst increased the conversion of the nonpolar subfraction to a greater extent than the polar subfraction.     

Evaluation of Two Methods for Measuring Vapor Sorption in Polymers

In this paper, two methods for measuring the equilibrium vapor sorption in polymers are critically compared and data on sorption of toluene, p-xylene, hexane, cyclohexane, and heptane in low density polyethylene are reported. The vapor phase calibration method (VPC) was used to measure vapor sorption at low vapor activities in air (below 0.01), and the gravimetric method was used to measure sorption over wide range of activities of pure vapors (0.1–0.9). The Flory-Huggins interaction parameter (in amorphous phase) varied between 1.00 for cyclohexane and 1.19 for toluene. The resulting confidence intervals are conjunctive, indicating that both methods provide consistent results.     

Langmuir and Langmuir‐Blodgett Asphaltene Films at Heptane‐water Interface

Monolayer characteristics of subfractions and unfractionated whole asphaltenes from Athabasca oil sands bitumen were studied at heptane‐water interface. The transferred Langmuir‐Blodgett films of asphaltenes were characterised with atomic force microscopy and contact angle measurements. Monolayers prepared from the three asphaltene samples are found to behave similarly at heptane‐water interface. The high molecular weight asphaltene monolayer is the most expanded one whereas the low molecular weight asphaltene monolayer is the most condensed one. An asphaltene monolayer behaves differently at an airwater interface to a heptane‐water interface. The presence of the bulk heptane phase renders the interfacial asphaltene monolayer more flexible as compared to that at air‐water interface.     

Fractionation and characterisation of bisphenol a polycarbonate by gel permeation chromatography

Bisphenol A polycarbonate was fractionated from methylene chloride solution by a progressive precipitation technique. The intrinsic viscosities of these fractions were obtained in methylene chloride solution and corresponded to a viscosity average molecular weight range of 2 × 10³ to 80 × 10³. The fractions were used to calibrate a gel permeation chromatograph, an experimental Q-factor of 23.8 was found. The calibration was further confirmed by membrane osmometry and light scattering experiments. The experimental viscosity data demonstrated that the Kurata-Stockmayer-Roig relationship is suited to interpret the molecular expansion of polycarbonate in methylene chloride.     

Preparation and characterization of paclitaxel from plant cell culture

The solvent treatment of paclitaxel is a convenient method for controlling the morphologies of paclitaxel. Amorphous paclitaxel was simply made by dissolving paclitaxel in methylene chloride/methanol (98/2, v/v) and in relatively non-polar solvents (t-butyl methyl ether, pentane, acetonitrile/hexane (1/2, v/v), methylene chloride, chloroform). On the other hand, dihydrated paclitaxel (paclitaxel.2H₂O) was made by dissolving paclitaxel in a special polar solvent containing a small amount of water. However, when we used only methanol, we got mixed morphologies of paclitaxel made of both the dihydrated and amorphous forms. Their physicochemical properties were investigated by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). The initial water content of amorphous paclitaxel and dihydrated paclitaxel was determined for 0.65 wt% and 5.85 wt%, respectively. The hygroscopic property of dihydrated paclitaxel was very changeable in all given humidity (15, 60, 95 RH%) during storage. Dissolution profiles for paclitaxel showed that amorphous paclitaxel measured the highest solubility in water and its solubility held most stable during the measurements. The residual solvent could be reduced to the maximum allowed value (600 ppm for methylene chloride, 3,000 ppm for methanol) of guidance for the International Conference on Harmonization (ICH) by spray drying.     

Investigations into asphaltenes in heavy crude oils. I. Effect of temperature on precipitation by alkane solvents

Precipitation of asphaltenes by alkane solvents from the Qaiyarah heavy crude oil resulted in relatively higher yields under both cooling and solvent reflux temperature conditions as compared to room temperature. Resins occlusion in the cold precipitation conditions is suggested. From detailed elemental analysis, molecular weight and spectroscopic measurements, it is suggested that at reflux temperatures a rearrangement of the asphaltene moeity takes place through molecular degradation followed by a reaction with resins to form new modified asphaltic materials. A typical light crude oil behaved differently, the asphaltene yield increasing continuously with temperature of precipitation.     

The Stability of Water‐in‐Crude and Model Oil Emulsions

The critical electric field (cef) technique has been utilized to measure the stabilities of a variety of water‐in‐model oil and petroleum emulsions. The cef method allows for a fast, reproducible, and quantitative gauge of emulsion stability. Here, we have used cef to measure the stability of water‐in‐heptane‐toluene‐asphaltene emulsions and confirmed the importance of solvation of asphaltenes and the state of asphaltene aggregation to emulsion stability. Emulsion stability increased with the concentration of soluble asphaltenes near the point of precipitation. Droplet sizes were measured with optical microscopy in order to calculate interfacial areas and film thicknesses. It was found that film thickness increased with asphaltene concentration up to the solubility limit, above which increased concentration had little effect, and cef increased with interfacial film thickness up to a monolayer coverage of asphaltene aggregates, above which film thickness had a much smaller effect. These findings were applied to a cef investigation of water‐in‐ppetroleum emulsions to develop correlations of the stability of water‐in‐ccrude oil emulsions. A strong correlation (coefficient = 0.95) was found for cef with the product of asphaltene concentration and the difference in hydrogen to carbon atomic ratios of the asphaltenes and petroleum solvent. The development of a kinetic model and its fit to experimental data revealed the effects of asphaltene chemistry, solvency, and resin concentration on the adsorption and consolidation of emulsion stabilizing interfacial films.     

Beitrag zur analytischen Erfassung der Cholesterylfettsäureester in biologischem Material

Contribution to Analytical Determination of Cholesterol Fatty Acid Esters in Biological Material A method for analysis of cholesterol esters in biological material is described. The methodology is devided into sample preparation, lipid extraction with methylene chloride/methanol, subsequent isolation of the cholesterol ester fraction with column chromatography on water containing silica gel and the determination with nonaqueous reverse phase h.p.l.c. Each step of the procedure is discussed in detail. Finally we report about application of the method to biological samples.     

Reduced coke formation and aromaticity due to chloroperoxidase-catalyzed transformation of asphaltenes from Maya crude oil

The transformation of the porphyrin-free asphaltene fraction from a heavy Maya crude oil was catalyzed by chloroperoxidase from Caldariomyces fumago (CPO) in a ternary system with low water content of 6.3%. The total turnover number (TTN) in this system was determined for lyophilized CPO in the presence of sucrose as cryoprotector and for a covalent bioconjugate with chitosan. The covalent conjugation of CPO with chitosan increased the TTN by 10-fold. Fluorescence due to aromatic groups decreased by 24% in treated asphaltenes, indicating significant changes after the biotransformation. On the other hand, the solubility profile indicated that transformed asphaltenes are less soluble in toluene and more prone to precipitate in the presence of hexane, compared to untreated asphaltenes, which could be related to the introduction of polar atoms. Energy-dispersive X-ray spectroscopy (EDS) showed that the content of chlorine increased six-fold on an atomic basis. Finally, enzymatically transformed asphaltenes are more reactive and thus generate less coke, as evidenced by thermal degradation under nitrogen atmosphere.     

Photopolymerizable Synthons from Glycerol Derivatives

Photopolymerizable monomers based on monoglycerides were prepared by a convenient two-step procedure. The first one consists of the synthesis of highly pure monoglycerides by an organocatalyzed solvent-free route. This process was carried out by condensation of bio-sourced carboxylic acids (i.e. butyric, decanoic, undecylenic or stearic acids) with glycerol carbonate or glycidol in the presence of a quaternary ammonium salt as a catalyst. The obtained bio-based monoglycerides were modified in the second step by reaction with acryloyl and methacryloyl chloride leading to a series of new diacrylated and dimethacrylated monomers. The structures of the monoglycerides, diacrylated and dimethacrylated monomers were fully characterized by spectroscopic methods. Photopolymerization investigations monitored by infrared spectroscopy were achieved under ultraviolet radiation in the presence of a photoinitiator. The resulting cross-linked materials were analyzed by thermal gravimetric analysis, gel content determination and tests of swelling in water, ethanol and methylene chloride. Data relative to the pendulum hardness of these materials are also included.     

Use of a gas chromatograph for measurement of the rate of monomer desorption from poly (vinyl chloride) resins

Previous studies by a gravimetric technique have established that the sorption and desorption of small quantities of vinyl chloride monomer (VCM) by poly (vinyl chloride) (PVC) resin powders obeys Fickian diffusion kinetics. Consequently, the rate of sorption or desorption is very sensitive to the size and structure distribution of the resin particles and is a useful measure of these properties. To facilitate the measurement of desorption rates, an “inverse GC” technique has been developed, with the PVC powder taking the place of the usual gas Chromatograph column. The detector and electronics of the GC are used to follow the VCM content of a carrier gas stream passing through a PVC resin sample initially equilibrated to a uniform VCM content. This method yields results consistent with the gravimetric data and provides a convenient means of characterizing PVC particle structure.     

Correlation between feedstock SARA components and FCC product yields

Daqing, Shengli, Liaohe, Gudao, Dagang and Huabei vacuum residua were subjected to deep solvent fractionation by using the supercritical fluid extraction and fractionation, a novel separation technology recently developed by the State Key Laboratory of Heavy Oil Processing. Each residuum was fractionated to produce deasphalted oil (DAO) at four yield levels: 30, 40, 50 and 60 wt%. The saturates, aromatics, resins and asphaltenes (SARA) composition of each DAO sample was determined, indicating that the saturates and aromatic contents of DAO decreases with increased DAO yield.The DAO samples were reacted in a laboratory scale confined fluidized bed, fluid catalytic cracking (FCC) reactor. The results show that most of the gasoline yields originates from the saturate fraction of DAO. The aromatics fraction of DAO contributes to gasoline and diesel yields. Most of the coke yield is from resin fraction of DAO.Generalized empirical correlations were developed for predicting the FCC gasoline, diesel, light oil and coke yields as a function of feedstock SARA composition. These yield correlations can be used to set the upper limit of feedstock resins content for commercial FCC operations. The implications of feedstock properties on FCC products were discussed.     

Influence of asphaltenes on coke formation during the thermal cracking of different Brazilian distillation residues

This research was conducted to allow the investigation on the influence of asphaltenes on coke formation, during the thermal cracking of atmospheric distillation residues, using thermogravimetry. Asphaltenes of five refinery atmospheric distillation residues, of different API gravity Brazilian crude oils, were isolated by the IP143 methodology. The original samples and the same samples, after asphaltenes extraction, were analyzed by thermogravimetry. It was observed that the heavier the sample, the higher was the contribution of the asphaltenes to the coke formation. The extracted asphaltenes were analyzed under the same TG conditions of the atmospheric distillation residues and all asphaltenes appeared to form approximately the same amount of carbonaceous residue after the thermal cracking. Heavier and lighter atmospheric distillation residues were doped with 10%, 20% and 30% amount of asphaltenes and, again, the higher the asphaltenes amount, the higher would be the carbonaceous material formation. The same tendency was observed for both doped samples.     

The chemical nature of material released from coal-derived asphaltenes by reprecipitation and cyclohexane extraction

The yields and chemical nature of n-pentane solubles released from three coal-extract asphaltenes by reprecipitation with n-pentane and cyclohexane extraction have been investigated. With increasing concentration of n-pentane solubles in the original coal liquid, the yield of oils obtained by reprecipitation increases, as also does the tendency for their structures to resemble those of the original n-pentane solubles. No alkanes below C₄₀ were released from the asphaltenes by extraction with cyclohexane and therefore the long alkyl chains (10% of the total carbon in the lignite asphaltenes) must be bound to aromatic, carboxyl or heteroatomic groups.     

Demetallization of heavy oil through pyrolysis: A reaction kinetics analysis

By tracking the transfer of vanadium and nickel in pyrolysis products, a seven-lump reaction kinetic model for pyrolysis-based demetallization of heavy oil was established. During pyrolysis, the demetallization of heavy oil is achieved by condensing metal-rich resins and asphaltenes to coke. The condensation of oil components originally contained in heavy oil differs greatly in reaction behavior, having the activation energy between 167 and 361 kJ/mol. As the pyrolysis progresses, the newly formed heavy components show a condensation behavior close to that of the light components. Limited by high activation energy and low initial fraction, the condensation of asphaltenes to coke and the resulting removal of metals contained in asphaltenes are hindered. Meanwhile, the condensation of light components has a major contribution to coke formation. An increase in reaction temperature accelerates the demetallization, but hardly changes the yield and component distribution of liquid products at the same metal removal rate.     

Pressurized liquid extraction of polar and nonpolar lipids in corn and oats with hexane,methylene chloride,isopropanol, and ethanol

Samples of freshly ground corn kernels and freshly ground rolled oats were extracted via pressurized liquid extraction (accelerated solvent extraction) using four different organic solvents [hexane, methylene chloride (also known as dichloromethane), isopropanol, and ethanol] at two temperatures (40 and 100°C). Lipid yields varied from 2.9 to 5.9 wt% for ground corn and from 5.5 to 6.7 wt% for ground oats. With ground corn, more lipid was extracted as solvent polarity was increased, and for each individual solvent, more lipid was extracted at 100°C than at 40°C. With ground oats, the same temperature effects was observed, but the solvent polarity effect was more complex. For both corn and oats, methylene chloride extracted the highest levels of each of the nonpolar lipid classes. In general, for both corn and oats, icnreasing solvent polarity resulted in increasing yields of polar lipids, and for each solvent, more of each lipid class was extracted at 100°C, than at 40°C. Among the lipids in corn extracts, the phytosterols may be the most valuable, and total phytosterols ranged from about 0.6 wt% in the hot ethanol extracts to about 2.1 wt% in the hot hexane and methylene chloride extracts. Total phytosterols in all oat extracts were about 0.1 wt%. Digalactosyldiacylglycerol was the most abundant polar lipid in the oat extracts; its levels ranged from 1.6 wt% in the cold hexane extracts to 4.3 wt% in the hot ethanol extracts.