In-Situ Monitoring of Paraffin Wax Crystal Formation and Growth

The crude oil temperature in the hot flow regime is higher than the wax appearance temperature (WAT), whereas it is lower than the WAT in the cold flow regime. Under the cold flow regime, heavier paraffins in the crude oil precipitate out as crystals, resulting in a solid-liquid suspension. A new approach is presented for scrutinizing the wax crystal structure and crystal growth kinetics, during the cooling of prepared multicomponent wax-solvent mixtures from above the WAT to below the pour point temperature. The time-resolved microscale structural attributes, such as the onset of nucleation, crystal size distribution, precipitated paraffin wax volume fraction, and fractal dimension, are compared under various cooling rates ranging from 0.05 to 6 degrees C min(-1) via laser scanning confocal microscopy. At faster cooling rates, a larger number of crystals were formed, but with a smaller average crystal size. Volume fraction and crystal size were higher at lower cooling rates, but with slower crystal growth kinetics, while the fractal dimension converged to the same value at the final temperature irrespective of the cooling rate. These findings are important for understanding crystal formation and solid deposition from "waxy" mixtures in pipelines.