Waxy gels with asphaltenes 2 - Reduction of network strength with polymer additives

An 8wt% wax solution with 0.1wt% asphaltenes was tested with various polymer additives to examine the ability of the polymers to break down the strength of the waxy gel. The presence of crystalline domains in the polymers probed interactions with crystalline wax, while presence of polar groups sought beneficial interactions with the 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. Results show that polar domains had no significant effect upon polymer efficacy whereas the crystalline domains were essential to disrupt the strength of the gel. The best polymer of those tested, MAC Et22 - a maleic anhydride co-polymer with C22 alkyl appendages - reduce yield stresses up to 2000-fold. Other crystalline polymers induced 10 to 100-fold reductions in yield stress. In the presence of asphaltenes the polymers had negligible effect on precipitation temperature (up to 0.3°C change) and only small effects on gelation temperature (up to 4°C). The exception to this was the MAC Et22, with 1.0°C and 37°C decreases in precipitation temperature and gelation temperature, respectively, at 0.1 wt% addition of the polymer. Comparison of this polymer with a maleic anhydride co-polymer with shorter alkyl appendages, MAC 16-18 supports co-precipitation of the polymer with the wax as the dominant mechanism. Higher wax concentrations were shown to decrease the polymer efficacy in its ability to reduce precipitation temperature, gel point and yield stress, and were also shown to be more selective to the length of alkyl chain (i.e., the efficacy of the shorter C18 MAC polymers dropped off much more than the C22 polymer). Coprecipitation is identified as the key to polymer efficacy for the systems tested.