Energy & Fuels, Vol.33, No.10, 9604-9618, 2019
Experimental Investigation of the Rheology and Crystal Morphology of Model Waxy Oils under Gelling Conditions
The influence of six experimental variables (cooling rate, weight fraction of linear wax, weight fraction of branched wax, shear rate during cooling, final cooling temperature, and aging time) on the yield stress of gelled waxy oils was simultaneously investigated using an experimental design. Rheological tests were performed with systems comprising spindle oil and a blend of paraffin waxes. The waxes were characterized by differential scanning calorimetry, gas chromatography-flame ionization detection, Fourier transform infrared and C-13 NMR spectroscopy, and X-ray diffraction, pointing to predominantly linear- and branched-type wax. Also, wax crystal morphology was assessed through polarized light microscopy. Cooling rate, wax content, shear rate during cooling, final cooling temperature, and aging time were the variables analyzed. The obtained results disclosed the relative importance of these variables on the viscoelastic properties of the gelled oils. Multiple linear regression was used to propose a mathematical expression for yield stress estimation. It was also found that the storage modulus in the linear region was highly correlated with the yield stress; thus, an alternative method to estimate the yield stress was proposed. The wax network restructuring level for different aging times are also discussed, and evidence indicates that after fracture the gel is unable to rebuild its original structure. The presented information may be useful for start-up prediction and/or the feasibility of a remediation procedure aimed at helping the removal of wax plugs.