Influence of precipitation conditions (n-heptane or carbon dioxide gas) on the performance of asphaltene stabilizers

The destabilization of asphaltenes in crude oil mainly happens due to variations in pressure, temperature and oil composition, causing significant losses. Chemical additives that inhibit deposition of asphaltenes can be used to counteract this problem. Their effectiveness is generally evaluated by tests of the variation in stability of asphaltenes in function of adding a flocculant solvent (n-heptane). However, asphaltenes can also be destabilized by the addition of carbon dioxide gas (CO2) to petroleum. In this study, we assessed the influence of the flocculant agent (n-heptane or CO2) on the behavior of the asphaltene phases and the performance of the stabilizer molecules. The behavior of these phases was monitored by ultraviolet–visible (UV–vis) spectrometry. The results indicated that depending on the system and concentration, the additives can stabilize asphaltenes to varying degrees. In turn, CO2 was able to induce asphaltene precipitation, and at the pressures tested, no significant change was observed in this induction. Overall, the results show that the efficiency of the stabilizer additive tested is not reflected only in the test of asphaltene precipitation induced by n-heptane. In other words, there is selective action of the additive for each method of inducing precipitation.