Control of n-alkanes crystallization by ethylene–vinyl acetate copolymers

SiO2-Based Nanofluids for the Inhibition of Wax Precipitation in Production Pipelines

Wax deposition in high-wax (waxy) crude oil has been an important challenge in the oil and gas industry due to the repercussions in flow assurance during oil extraction and transportation. However, the nanotechnology has emerged as a potential solution for the optimization of conventional wax removal and/or inhibition processes due to its exceptional performance in the alteration of wax morphology and co-crystallization behavior. In this sense, this study aims to study the performance of two commercial wax inhibitor treatments (WT1 and WT2) on the wax formation and crystallization due to the addition of SiO2 nanoparticles. Differential scanning calorimetry experiments and cold finger tests were carried out to study the effect of the WT on wax appearance temperature (WAT) and the wax inhibition efficiency (WIE) in a scenario with an initial temperature difference. In the first stage, the behavior of both WT in the inhibition of wax deposition was achieved, ranging in the concentration of the WT in the waxy crude (WC) oil from 5000 to 50,000 mg·L-1. Then, NanoWT was prepared by the addition of SiO2 nanoparticles on WT1 and WT2 for concentrations between 1000 and 500 mg·L-1, and the performance of the prepared NanoWT was studied at the best concentration of WIT in the absence of nanoparticles. Finally, the role of the nanofluid concentration in wax inhibition was accomplished for the best NanoWT. Selected NanoWT with nanoparticle dosage of 100 mg·L-1 added to WC oil at 5000 mg·L-1 displays reductions in WAT and WIE of 15.3 and 71.6 for NanoWT1 and -2.2 and 42.5% for NanoWT2. In flow loop experiments for the crude oil at temperatures above (30 °C) and below (16 °C), the WAT value indicates an increase of 8.3 times the pressure drops when the crude oil is flowing at a temperature below the WAT value. Therefore, when NanoWT1 is added to the crude oil, a reduction of 31.8% was found in the pressure drop in comparison with the scenario below the WAT value, ensuring the flow assurance in the pipeline in an unfavorable environment. Based on the pressure-drop method, a reduction greater than 5% in the wax deposit thickness confirms the wax deposition inhibitory character of the designed NanoWT.

Insights into Flow Improving for Waxy Crude Oil Doped with EVA/SiO2 Nanohybrids

Nanohybrid materials can significantly inhibit wax deposition and improve the fluidity of crude oil. However, the mechanisms behind wax resolving, crystal modification, and flow improving are still unclear owing to the complexity of crude oil. Here, we compared the effect of ethylene vinyl acetate (EVA) and nanohybrids composed of EVA and SiO₂ nanoparticles on wax crystallization and rheological behavior of Shengli waxy oil. Differential scanning calorimetry results indicate that SiO₂ nanoparticles boost the efficiency of EVA for reducing the wax appearance temperature of waxy crude oil. Thermo X-ray diffraction characterization demonstrates that EVA/SiO₂ nanohybrids cut down the crystal index of waxes, with the grain size of crystal cells decreased in (006) and (200) but increased in (110) cross sections. Polarized optical microscopy imaging reveals that EVA can modify the morphology of wax crystals to suppress the formation of wax gel, and nanohybrids serve as nucleuses to adsorb asphaltenes and resins, restraining the appearance of wax crystals. The rheological test shows that nanohybrids outperform EVA in decreasing the viscosity, inflection point, and yield stress of waxy crude oil. These findings help the understanding of flow improving by nanohybrid materials and offer guidelines for designing the new generation of wax inhibitors for safe transportation and flow assurance of waxy crude oil.

Synthesis of crystallizable poly(behenyl methacrylate)-based block and statistical copolymers and their performance as wax crystal modifiers

Behenyl methacrylate-based diblock and statistical copolymers are evaluated as additives for the crystal habit modification of a model wax (n-octacosane) in n-dodecane. The statistical copolymers more strongly influence the wax crystal morphology.

Wax Formation Mechanisms, Wax Chemical Inhibitors and Factors Affecting Chemical Inhibition

When crude oil is extracted out of a subterranean reservoir at high temperature and pressure, it is usually transported via a pipeline, where the crude oil experiences radical changes in its physical and chemical properties, instigating numerous complications. Among the various flow assurance problems, wax deposition and build up are among the most commonly found. However, the accurate mechanism of wax deposition is still unclear and is widely debated among researchers. The mechanism under multiphase conditions is also an ambiguity. This review covers the six wax deposition mechanisms, the challenges in multiphase flow conditions, the latest types of chemical inhibitor, and a summary of factors governing chemical inhibitor performance.

Process, Physicochemical Characterization and In-Vitro Assessment of Albendazole Microcrystals

Purpose: Albendazole is a poorly soluble drug which limits its oral bioavailability. The study was focussed to enhance the solubility by in-situ micronization.

Methods: Albendazole microcrystals were prepared by solvent change method using gum karaya and hupu gum as stabilizing agents and the effect of each stabilizer on the prepared microcrystals were studied. FT-IR, DSC, XRD and SEM analysis were performed as a part of characterization studies. The formulations were evaluated for micromeritics, solubility and drug release. The microcrystals that had shown optimized properties were filled into suitable capsules.

Results: The formulations showed reduction in particle size with uniform size distribution and three folds increase in drug release. The microcrystals had shown more than 100-folds increase in solubility compared to pure drug. Surface energy, enthalpy and crystalline nature of microcrystals were found to be reduced. Microcrystals containing gum karaya had shown more drug release. The filled-in capsules also showed increase in drug release rate. The solubility enhancement of albendazole microcrystals was mainly due to the surface adsorption of the stabilizing agents that led to reduction in surface energy and crystalline nature as substantiated by the DSC and XRD studies. The type of stabilizing agent had significant effect on dissolution rate. High affinity of albendazole with gum karaya led to faster drug release profiles.

Conclusion: The study proved that in-situ micronization is an effective technique to enhance the solubility and dissolution rate of poorly soluble drugs like albendazole.

How polymer additives reduce the pour point of hydrocarbon solvents containing wax crystals

We have investigated how four different pour point depressant (PPD) polymers affect the pour point transition in mixtures of a single pure wax in a solvent. We used either n-eicosane (C20), CH3(CH2)18CH3, n-tetracosane (C24), CH3(CH2)22CH3 or n-hexatriacontane (C36), CH3(CH2)34CH3 as the wax component with either n-heptane or toluene as the solvent component. For all wax-solvent combinations, the measured variation of wax solubility with temperature is well predicted by ideal solution theory. The variation of pour point temperature as a function of the overall wax concentration is quantitatively modelled using the idea that, for each overall wax concentration, the pour point occurs at a temperature at which a critical volume fraction ϕ* of wax crystals has precipitated. Close to the pour point temperature, extraction and examination of the wax crystals show they consist of polydisperse, irregularly-shaped platelets with axial ratios (h/d, where h is the plate thickness and d is the plate long dimension) in the range 0.005-0.05. It is found that the measured ϕ* values corresponding to the pour point transitions are weakly correlated with the wax crystal axial ratios (h/d) for all wax-solvent-PPD polymer combinations. These results indicate that the pour point transition occurs at a volume fraction larger than the value at which the volumes of rotation of the platelet crystals overlap, i.e., 2.5(h/d) < ϕ* < 11(h/d). PPD polymers work, in part, by increasing the wax crystal axial ratio (h/d), thereby increasing ϕ* and reducing the pour point temperature. Since the PPD's ability to modify the wax crystal shape relies on its adsorption to the crystal-solution surface, it is anticipated and observed experimentally that optimum PPD efficacy is correlated with the difference between the wax and the polymer solubility boundary temperatures. This finding and the mechanistic insight gained here provide the basis for a simple and rapid screening test to identify candidate species likely to be effective PPDs for particular wax systems.

The influence of pressure and dissolved gases in petroleum on the efficiency of wax deposition inhibitors

Evaluations of wax inhibitors carried out in laboratories are generally performed on stabilized oil samples, that is, without the presence of natural gas and at atmospheric pressure. Therefore, the effects of two important factors that influence wax solubility – the light fractions and temperature – are not considered, and the results may not reflect what really happens in production lines and facilities. This work evaluates the efficiency of two wax inhibitors based on ethylene copolymer and vinyl acetate, at four concentrations, in a sample of paraffinic oil in the presence of light fractions and under pressure. The parameter employed in the evaluation was the wax appearance temperature (WAT), or the cloud point, determined by high-pressure differential scanning calorimetry. The gas used was a mixture of eight components and the tests were run at three pressures. In general, the inhibitors had little influence on the cloud point and a pronounced effect on the pour point and viscosity. In this case it was possible to observe changes in the WAT with both wax inhibitors in the tests conducted at atmospheric pressure up to 150 bar and in the presence of the multi-component gas mixture, suggesting that one of the mechanisms through which wax deposition inhibitors work is polynucleation.