Waxy gels with asphaltenes 1 - Characterization of precipitation, gelation, network strength and morphology

A model with 3-10wt% multi-component wax containing 85wt% n-paraffins ranging from C20-C48 was tested with 0-0.2wt% asphaltenes. Differential scanning calorimetry was used to identify the precipitation temperature, and a controlled-stress rheometer examined the gelation temperature and yield strength of the gel. Microscopy was also used to examine the morphology of the waxy gel. Results show that addition of asphaltenes depressed the precipitation and gelation temperatures. Yield stress tests and microscopic examination showed two distinct types of behavior. At high asphaltene concentration and/or low wax concentration, addition of asphaltenes greatly reduced crystal size and significantly reduce yield stress, much like a polymer additive for "wax inhibition." However, when both asphaltene concentration was low (0.1 wt% or less) and when wax concentration was high, there was little effect on microstructure. In such cases the yield stress was unaffected or even greater than the waxy sample with no asphaltenes. Furthermore, oscillatory stress ramps on this first type of waxy gel (i.e. with larger asphaltene concentrations) show two plateaus during break-down of the network, indicating that two types of network connections exist. Explanations for this behavior are discussed along with the effects wax and asphaltene solubility.