Crystallization of Mixed Paraffin from Model Waxy Oils and the Influence of Micro-crystalline Poly(ethylene-butene) Random Copolymers

Abstract

We report rheological, microscopic, and calorimetric studies of the crystallization of long chain n-paraffins and their mixtures from model waxy oils and the effect of microcrystalline poly(ethylene-butene) (PEB) random copolymers. Optical micrographs and differential scanning calorimetry (DSC) reveal that the crystals formed from decane solutions of binary mixtures of C36 + C32 and of C32 + C28 are of mixed composition, whereas solutions of C28 + C24, C36 + C28, C32 + C24, and C36 + C24 form separate crystal phases. There is no miscibility when the difference in carbon number between two long chain n-paraffins ∆n c > 4. These findings agree with Kravchenko's prediction for crystallization of molten binary n-alkane mixtures. However, the crystallization of long chain n-paraffins from decane solution gives a stable crystal structure directly, while from the melt it tends to pass through a metastable rotator phase. Since PEB can either self-assemble into a needlelike structure or cocrystallize with long chain n-paraffins to form small thin sheets in decane, mixtures of wax and PEB formed quite complex shapes such as rodlike or shuttle-like structures, particularly for the longer paraffin chains. These structures reduce the yield stress of the cold model waxy oil as compared with the platelike crystals formed in the absence of PEB. PEB10, which has an average of 10 ethyl side groups per 100 carbon atoms in the polymer backbone, is more effective in reducing the yield stress than PEB7.5 except for the mixture C36 + C28. All the other mixtures of paraffins with PEBs show intermediate rheological properties between those of the single paraffin components.

Recent advances on mitigating wax problem using polymeric wax crystal modifier

“…Wax tends to crystallize into quite complex shape such as rod-like or shuttlelike structures under the interference of PEB. These structures can reduce the yield stress of waxy oils compared to the plate-like crystals formed in the absence of PEB (Guo et al 2004c(Guo et al , 2006Tinsley et al 2007a). In addition, they provided a kind of hydroxyl-grafted PEB polymer (PEB-OH), which seems more efficient in reducing the yield stress of asphaltene-contained crude oils than PEB which can be interpreted by the dispersion effect of the polar group (-OH) (Guo et al 2004a).…”

“…This evaluation revealed that the efficiency of PEB 7.5 in controlling the crystallization of long wax molecule (C36) is relatively greater than that of short wax molecule (C24). However, for a certain wax molecule, Guo et al (2004c) claimed that PEB 10 which has an average 10 ethyl branches per 100 backbone carbon is more active in reducing the yield stress than PEB 7.5. These experimental results suggest that the overall performance of wax crystal modifiers is dependant not only on the wax structure but also on the structure of themselves (Ashbaugh et al 2005).…”

Synthesis of poly(maleic acid alkylamide-co-α-olefin-co-styrene) and their effect on flow ability of oils

“…With the increase of the concentration of MASCs from 0 to 100 ppm, the yield stress of the model waxy oil decreased significantly. However, further increase of the MASC concentration to 200 ppm results in the enhancement of the yield stress of model waxy oil due to the "bridge effect" of extra polymers [3]. Obviously, 100 ppm (0.10 wt-%) of MASCs is the best concentration for the reduction of yield stress of model waxy oil (Fig.…”

“…The long chain paraffins and asphaltenes will precipitate and deposit at the pipe walls, reducing oil flow and even blocking the pipeline [1]. The problem becomes more serious for offshore deep-sea wells, where the temperature at the sea bed can be 4°C or lower [2,3]. To solve this problem, heating and mechanical pigging are always applied in the petroleum industry [4].…”

Effect of the amount and the composition of precipitated n-alkanes on the yield stress of wax-decane gels

“…Guo et al (2004) found that the binary C n in decane solutions have a lower yield stress than the mono-disperse C n -decane solution. Senra et al (2008Senra et al ( , 2009 found that co-crystallization inhibits the formation of a gel by developing weaknesses in the crystal structure.…”