The interaction of waxes with pour point depressants

Paraffin wax deposition from crude oils at low temperature is one of the serious and long-standing problems in petroleum industry. Addition of pour point depressants (PPD) has been proved to be an efficient way to inhibit wax deposition. The influence of PPD on wax precipitation at low temperature was investigated. The amount and composition of wax precipitated from paraffin solutions with and without PPD at different temperatures were studied by high speed centrifuge and gas chromatography (GC), respectively. The interactions between waxes and PPD were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed that PPD do not completely prevent the wax from precipitating, but just shift the precipitation toward a lower temperature. This conclusion was identified from the analysis of the amount and composition of precipitated wax as well as the transition temperatures and energies of wax. It was shown that this effect is due to the structure of wax is partly transformed from orthorhombic into hexagonal form by PPD.     

Molecular dynamics simulation guiding the improvement of EVA-type pour point depressant

Addition of pour point depressants (PPDs) has been proved to be an efficient way to inhibit wax deposition of diesel fuels. However, the complexity of the oil is far beyond current commercial PPD products. So far it mainly depends on syntheses of numerous candidate compounds followed by repeating experimental measurements in order to improve the efficiency of PPDs. In this article, molecular dynamic simulation was successfully used to investigate the interaction between crystal planes of wax and EVA, as well as its derivatives with different branches, based on the model of wax. Side chain effects on adsorption energy and equilibrium adsorption conformations were studied under different kind and number of branches. It was concluded that side chains introduced by propylene were benefit to the affinity between the EVA-type molecules and alkanes in the wax plane, comparing with those branches introduced by butylenes. MD simulation calculations indicated that EVAP with one branch adjacent to the VA group would be a better PPD additive than EVA in diesel fuels, which has been proved in our experimental measurements. Therefore, the MD simulation is a promising method not only for exploring the interaction mechanism in polymer system, but also for directing the design of new candidates of PPD.     

DFT and MM calculation: the performance mechanism of pour point depressants study

Adding pour point depressants (PPDs) to lower the cold filter plugging point (CFPP) of oils has been widely used as the most valuable way in the world. To develop the new type of PPDs according to the oils of different kinds, many researchers have tried to study the performance mechanism of PPDs with different methods. In this article, we have carried out this study with density function theory and molecular mechanics calculation methods. From the results of different systems, we have found that: (1) Alkane molecule is non-polar but the methyl groups on the chain ends have higher electronegativity than all the methylene groups. (2) The EVA (copolymer of ethylene and vinyl acetate) molecule is divided into segments by the polar groups, and the segments are composed of carbon chains, while at the joint points of the segments are ester groups. Calculation results show that the non-polar parts of EVA molecule have good affinity to the adjacent alkane molecules. The rigidity of the carbon bonds neighboring to ester groups is enhanced by the introduction of ester groups, which can also help the next segments to get into the next crystal units and accelerate the growth rate of the planes perpendicular to (001) plane. (3) The alkane molecules absorbed on the PPD molecules can be bent, and the bending conformation brings steric hindrance effect to the molecules to deposit on the surface near the PPD molecules. The relatively higher electronegativity of the methyl groups, which are bent out of the crystal units, can also bring more repulsion effect to the alkane molecules to deposit. This helps to restrict the high growing velocity of (001) plane and results in the uniformity growing rate in three dimensions. (4) If we want to get the good performance properties of PPDs, the carbon number should be a little lower than the mean carbon number of the wax crystals. Then the acetate percent of EVA molecules should be around 30% and the concrete value should be determined according to the oils used.     

Studies of thermal polymerization of vegetable oils with a differential scanning calorimeter

Vegetable oils are often thermally polymerized to provide a vehicle for printing inks and paints. The formations of isomerization, and the intra- and intermolecular bonds involved in the thermal process are crucial in designing a product with the appropriate characteristics. It was found, with a differential scanning calorimeter, that the thermal polymerization of various vegetable oils could be activated at lower temperatures under a dry-air purge and/or in the presence of metallic catalysts. The Diels-Alder reaction and the formation of intermolecular bonds in alkali-refined soybean oil under a dry-air purge could be activated at 99 and 161°C in the presence of metallic catalysts, compared with 231 and over 300°C in the absence of metallic catalysts, respectively. The energies needed to activate the Diels-Alder reaction and to form intermolecular bonds were calculated, and is in good agreement with available data. The hardness test of baked vegetable-oil systems was also implemented to qualitatively determine the degree of cross-linking.     

Heterogeneous structure of poly(glycolic acid) fiber studied with differential scanning calorimeter, X-ray diffraction, solid-state NMR and molecular dynamic simulation

The heterogeneous structures of poly(glycolic acid) (PGA) fibers which have been used as bio-degradable suture were studied by differential scanning calorimeter (DSC),X-ray diffraction and ¹³C solid state NMR. The ¹³C cross polarization NMR spectra without magic angle spinning of the stretched fibers observed by changing the angle between the fiber axis and the magnetic field clearly showed the heterogeneous structures which consist of three components; well-oriented, poorly-oriented and isotropic amorphous components. The local structure, distribution of the fiber axis and fraction of each component were determined quantitatively. Change in the heterogeneous structure by changing the stretching method in the sample preparation and by changing the stretching ratio was also monitored. The X-ray diffraction data of the fibers are in good agreement with the ¹³C CP NMR data. Change in the heterogeneous structures correlate with change in the thermal properties observed by DSC method. The molecular dynamic simulation showed the generation of trans conformation of PGA chain and also change in the fraction of other conformations by stretching, which supports the experimental results obtained above and gives additional structural information.     

Diesel fuels: determination of onset crystallization temperature,pour point and filter plugging point by differential scanning calorimetry. Correlation with standard test methods

Differential scanning calorimetry (d.s.c.) has been used to determine the amount of crystallized paraffins and the temperature at which crystals appear in a diesel fuel containing no additive and submitted to slow cooling (0.5 °C/min). In the temperature range −30 °C to 20 °C the percentage of crystallized paraffins was responsible for pour and filter plugging points which corresponded to 1% and 0.4% respectively. It has been shown that ASTM pour and cloud points and European filter plugging points could be obtained in a single d.s.c. experiment with better reproducibility than standard tests.     

Polymorphism of milk fat studied by differential scanning calorimetry and real-time X-ray powder diffraction

The crystallization behavior of milk fat was investigated by varying the cooling rate and by isothermal solidification at various temperatures while monitoring the formation of crystals by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). Three different polymorphic crystal forms were observed in milk fat: γ, α, and β′. The β-form, occasionally observed in previous studies, was not found. The kind of polymorph formed during crystallization of milk fat from its melted state was dependent on the cooling rate and the final temperature. Moreover, transitions between the different polymorphic forms were shown to occur upon storing or heating the milk fat. The characteristic DSC heating curve of milk fat is interpreted on the basis of the XRD measurements, and appears to be a combined effect of selective crystallization of triglycerides and polymorphism.     

Synthesis and characterization of novel pour point depressants based on maleic anhydride‐alkyl acrylates terpolymers

The (Docosanyl acrylate‐co‐(octadecyl or hexadecyl acrylate)‐co‐maleic anhydride) terpolymers were prepared using different compositions of the used alkyl acrylates (namely, 90 : 10, 70 : 30, 50 : 50, 30 : 70, and 10 : 90) (DCA‐ODA)/(MA) or (DCA‐HDA)/(MA). The efficiency of these terpolymers as pour point depressants was discussed. Two western desert waxy crude oils with different wax content were used for evaluation. Correlation between pour point depression efficiency and rheological properties were performed. Rheological parameters were also computed and discussed. It was observed that the synthesized terpolymers showed non‐Newtonian pseudoplastic relationships at different concentrations of synthesized terpolymeres with monomer feed ratios of (DCA‐ODA (1 : 1))/(MA) or (DCA‐HDA (1 : 1))/(MA) = 90/10 mole %. This ratio showed a good ability to disperse wax crystals and improve the flow behaviors of tested two crude oils even at low temperatures below their pour points. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The splitting tendency of uniaxially-oriented PET tapes investigated with nano-indentation,nano-scratch,differential scanning calorimetry,and X-ray

Earlier, various additives werescreened to improve the weavability of poly(ethylene terephthalate) (PET) tape. For predicting the weavability, three tests had been used: tensile impact strength, fibrillar versus puckered fracture and an axial folding test. This paper shows the possibility of using a simple nano-indentation method to decide on the splintering tendency of uniaxially-oriented PET tapes, as a predictor for weavability. A plasticity index derived from the nano-indentation correlated with PET tapes that were, or were not, weavable. Nano-scratches applied parallel and perpendicular to the tape also showed differences that could be correlated to the splitting tendency. While investigating these tests methods, it was observed that pure uniaxially- oriented PET tape heat set at 140°C had a non-splintering character even without additives, while polymeric additives were needed to resist splintering for the tape heat set at 240°C. Calorimetry showed no difference in heat-of-fusion implying identical crystallinity in the tapes heat set at 140°C and 240°C. However, X-ray studies revealed that the crystallites in the tape heat set at 140°C were smaller/and or imperfect, and hence there were more lateral tie-molecules that provided it the splitting resistance. Pure PET tape if heat set below 150°C may be a workable solution for weaving, thereby dispensing with the need for toughening additives.     

Infrared spectroscopic studies on the interactions of pour point depressants with asphaltene, resin and wax fractions of Bombay high crude

The mutual interactions of asphaltene, resin and wax fractions of Bombay high crude were studied using infrared spectroscopy. The results show that the resin exists as an associated moiety with intermolecular hydrogen bonds, while asphaltene has intramolecular hydrogen bonded systems. Wax is a hydrocarbon system with aromatic and aliphatic groups without any heteroatomic groups. Pour point depressants (PPDs) were found to modify the orientation of the aliphatic portion of the crude fractions and did not interact with the polar groups present in these fractions.     

Formation and transformation of hierarchical structure of β-nucleated polypropylene characterized by X-ray diffraction, differential scanning calorimetry and scanning electron microscopy

Commercial grade isotactic polypropylene has been modified with a specific β-nucleant (N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide) in two concentrations (0.03 and 0.10 wt%). Specimens for structural characterization have been prepared by injection moulding, subsequent melting and re-crystallization or solid-state drawing at 100 °C. Individual levels of hierarchical structure, including molecular orientation, have been characterized by a combination of wide angle X-ray scattering (WAXS), differential scanning calorimetry and scanning electron microscopy. Based on the analysis of the azimuthal reflections (110) and (300), the Hermans orientation functions have been calculated separately for the crystalline phases α and β. Besides the longitudinal orientation along the injection-moulding direction, β-crystallites tilted to the injection-moulding direction have been found. Upon thermal treatment the fraction of the crystalline β-phase has decreased and molecular alignment within the crystalline regions has improved. During solid-state drawing the fraction of the crystalline β-phase was markedly decreasing with increasing draw ratio, while the overall crystallinity has not changed but slightly. The experiments have also revealed a disruption of molecular alignment at the beginning of the drawing process and subsequent distinct improvement of molecular orientation along the draw direction in crystallites α and β. The Hermans orientation functions provided by the WAXS analysis have been compared with recently published data obtained with similar specimens by polarized photoacoustic spectroscopy.     

Ignition mechanism of flammable dust and dust mixtures: An insight through thermogravimetric/differential scanning calorimetry analysis

Understanding flame propagation mechanism and thermal behavior of flammable dusts is of crucial importance, since they strongly affect the flammability and explosion parameters. In a previous work, we found that the volatile point of anthraquinone/nicotinic acid mixtures can be lower than the one of the pure dusts, suggesting a synergistic effect. In this work, thermogravimetric and differential scanning calorimetry analyses of anthraquinone/niacin mixtures were carried out both in open and closed cup, to explain the observed synergistic behavior. FTIR analysis on solid residue and evolved gaseous species showed that the mixtures change compositions during the thermal treatment, without undergoing any chemical transformation. The thermal behavior of dust mixtures reveals the presence of a eutectic point, resulting in a volatiles production at lower temperature and accelerating the flame propagation.     

Structure of polyamide 6 and poly (p-benzamide) in their rod-coil-rod triblock copolymers investigated with in situ wide angle X-ray diffraction

A series of rod-coil-rod triblock copolymers containing polycaprolactam (PA6) as the coil block and poly (p-benzamide) (PBA) as the rod block were synthesized by a two-step polycondensation reaction. Proton nuclear magnetic resonance (¹H NMR), UV-vis spectrophotometry (UVS) and differential scanning calorimetry (DSC) were performed to determine the fundamental molecular structure and thermal property of copolymers. UV-vis spectrophotometry results revealed that the content of PBA homopolymer increased with the block length (number of monomer) of PBA and reached a plateau value ranging from 22 to 40 monomers of PBA. The wide angle X-ray diffraction (WAXD) measurements indicated that the crystallization of PA6 blocks was strongly suppressed due to the stretching from rods after annealed at temperature above the melting point of PA6. Only a few imperfect crystals of PA6 existed in the samples with low volume fraction of PBA. Moreover, the variation of PA6 block length hardly affected the crystallinity of PBA, which was dominantly controlled by the block length of PBA as diffusion was the control step for PBA crystallization at the annealing temperature.     

Synthesis of polymeric pour point depressants for Nada crude oil (Gujarat,India) and its impact on oil rheology

Five flow improvers have been synthesized to study rheological properties of Nada crude oil (Gujarat, India). Anhydride copolymers were prepared making use of the copolymerization of acrylates of different alkyls with maleic anhydride and the Poly (n-alkyl acrylates-co-N-hexadecylmaleimide) were prepared by the reaction of copolymer with hexadecylamine. The additives were purified and characterized by FTIR, GPC. The prepared polymeric additives shows dual function both as wax dispersants and flow improvers and all of them acts as good pour point depressants. Yield stress and the viscosity of the crude oil at different temperatures and concentrations of additives were evaluated by zero friction advanced rheometer AR-500 of TA instrument. Comparison of morphologies and structures of wax crystals or aggregates in waxy crude oils beneficiated with and without a PPD was also done by micro photographic studies which show the modification in wax crystal morphology due to additives.     

DSC and synchrotron-radiation X-ray diffraction studies on crystallization and polymorphic behavior of palm stearin in bulk and oil-in-water emulsion states

The crystallization and polymorphic behavior of palm stearin (PS) in a bulk state and in oil-in-water (O/W) emulsion droplets (average diameter, 1.7±0.3 μm) was observed by using DSC, optical microscopy, and in situ X-ray diffraction with synchrotron radiation (SR-XRD). For the bulk sample the DSC measurements revealed three main exothermic peaks at approximately 31 (large), 21 (small) and 3°C (medium) on cooling, and broad endothermic peaks at approximate −3 (small), 8, 15 to 25 (medium), and 37 and 53°C upon heating. The SR-XRD patterns taken during cooling from 60 to −5°C clarified that the DSC exothermic peaks around 31 and 3°C corresponded to crystallization of the α form of high-melting and low-melting fractions, respectively, and that the occurrence of β′ corresponded to the small exothermic peak around 21°C. The XR-XRD patterns taken during heating from −5 to 60°C demonstrated that the DSC endothermic peaks corresponded to the following transformation processes: melting of α of the low-melting fraction (−3°C), melt-mediated transformation from α to ∇′ (15–25°C), melting of β′ (36°C), and melting of β (53°C) of the high-melting fraction. As for the O/W emulsion sample, the DSC and SR-XRD measurements during the cooling and heating processes exhibited basically the same behavior as that of PS in the bulk state, except that β′ did not crystallize during the cooling process, and the temperatures of crystallization of α, melt-mediated α→β′→β transformation, and melting of β were lower in the emulsion droplets than in the bulk state.     

A differential scanning calorimetry study on the oxidation of C12-C18 saturated fatty acids and their esters

The autoxidation of lauric, myristic, palmitic, and stearic acids, their ethyl esters, and palmitic and stearic triglycerides was investigated by means of the isothermal and nonisothermal differential scanning calorimetry methods under oxygen flow. The activation energies of oxidation of all investigated compounds were similar (106.0–134.3 kJ/mol) and did not depend on length of the carbon chain. Kinetic parameters of start of the oxidation were similar for each investigated fatty acid and ester. Esterification of carboxyl group did not interfere with the reaction rate. The study showed good agreement between isothermal and nonisothermal data.     

In-situ X-ray diffraction studies and magneto-optic Kerr effect on RF sputtered thin films of BaTiO3 and Co,Nb co-doped BaTiO3

The effect of annealing on structural and magnetic properties of the RF sputtered BaTiO₃ and Co, Nb co-doped BaTiO₃ thin films on Si (001) substrates were studied. The structure of the as-deposited (amorphous) films was changed into cubic perovskite phase during the in-situ X-ray diffraction from room temperature to 900 °C. The enhancement of crystalline quality with respect to the increase of annealing temperature was observed by the in-situ XRD. The magnetic properties of the films before and after annealing were studied by the measurement of Magneto-Optic Kerr Effect (MOKE). The pure BaTiO₃ revealed a paramagnetic behavior, whereas the Co and Nb co-doped BaTiO₃ films exhibited room temperature ferromagnetism. The increase in ferromagnetic response was observed in the Co and Nb co-doped BaTiO₃ films annealed at 900 °C rather than the as-deposited film.     

BEM/PMSQ杂化降凝剂对青海含蜡原油作用效果及其机理

基于聚甲基硅倍半氧烷（PMSQ）微球良好的有机相容性与规则的微观球形形貌,将PMSQ微球与BEM降凝剂通过熔融共混制备了BEM/PMSQ杂化降凝剂。以青海含蜡原油为研究对象,通过流变实验评价了BEM/PMSQ杂化降凝剂对原油的凝点、黏弹性、黏度与屈服值的影响,利用偏光显微镜观察了加剂前后原油蜡晶形貌的变化,并与单独添加BEM降凝剂的油样进行了对比。结果表明：不加剂原油凝点27.0℃;在相同的降凝剂加量下（100 μg·g^-1）,降凝效果最好的是BEM/PMSQ 2%杂化降凝剂,可降低原油凝点19.0℃,相较于添加BEM降凝剂,进一步降凝6.0℃,降低胶凝点4.3℃,10℃时平均降黏率39.0%,G'值降低了62.0%。PMSQ微球与BEM/PMSQ杂化降凝剂在十二烷中的分散状态照片表明PMSQ微球表面吸附了BEM降凝剂,从而在原油中作为蜡晶的成核模版存在,使所形成的蜡晶结构更为紧凑,包覆更少的液态油,从而改善原油的宏观流变性。