Effect of Asphaltene Dispersants on Aggregate Size Distribution and Growth

Abstract

A crude oil system can become unstable because of changes in hydrocarbon composition, pressure, or temperature during normal production from the reservoir or during commingling with dissimilar crude oils. These changes can generate asphaltene particles that can result in significant production and refining problems. The generation of these particles is a two-step process: phase separation and asphaltene particle growth. Phase separation occurs when nanosize asphaltene particles from the crude oil precipitate and grow into large aggregates. Our study on asphaltene precipitation shows that large asphaltene particles are aggregates consisting of very small (sub-micrometer) size asphaltene particles. One mechanism to control asphaltenes is to kinetically inhibit the phase separation of asphaltenes by adding a small amount of a chemical that interferes with the phase separation processes. Another mechanism to control asphaltenes is to inhibit growth by stabilizing the colloidal suspension of the sub-micrometer asphaltene particles to significantly slow the flocculation and settling processes. Asphaltene chemical additives of known molecular structures as well as proprietary chemical blends were selected for this study. None of chemicals studied inhibited phase separation; however, some of the dispersants did slow or stop flocculation and growth. Four different analytical techniques have been used to study the effect of chemical additives on asphaltene aggregation and settling and to evaluate the effectiveness of different asphaltene chemicals in keeping asphaltene particles suspended/dispersed in crude oils. From the turbidity measurement, asphaltene dispersants can be classified into three categories based on their performance. The particle size distribution measurement showed three different types of asphaltenes: stable asphaltenes, colloidal asphaltenes, and flocculated asphaltenes, on the basis of aggregate sizes. Asphaltene dispersants can stabilize colloidal asphaltenes and slow the growth and formation of flocculated asphaltenes. These results can be used to select the best chemical treatment plan for preventing/reducing asphaltene settling and deposition.

Role of ion-pair interactions on asphaltene stabilization by alkylbenzenesulfonic acids

“…Although both DBSA and OP [2] favored the formation of filamentary asphaltene flocculates, the mechanism by which these filaments formed was very different. In addition to the strong acid-base interaction between protonated asphaltenes (i.e., AH + ) and DBS À molecules, which was in accord with previous studies [1,3,[4][5][6][7][8], an additional electrostatic attraction was found between AH + -DBS À ion pairs. The latter was responsible for (i) the formation of very large and compact asphaltene flocculates, and (ii) the binding of these flocculates in series (generating long filaments) or in parallel (generating lateral ramifications).…”

“…Asphaltene interactions with DBSA are significantly stronger than with alkylphenols since acid-base interactions are stronger than hydrogen bonding [1,3,[4][5][6][7][8]. The acidic ASO 3 H groups of DBSA can protonate the basic groups of asphaltenes containing heteroatoms such as Nitrogen.…”

“…As a result, DBSA is able to reduce the size of asphaltene aggregates to sub-micron scale [8,13], or even nanoscale [14], enhance the precipitation onset [6], and decrease the amounts precipitated [5,15]. However, it is unclear how the interactions between DBSA and asphaltenes affect the structure of asphaltenes.…”

Effective Removal of Asphaltene Deposition in Metal-Capillary Tubes

“…Strong organic acids, in particular DBSA, are found to work by attacking heteroatomic sites in asphaltene molecules Hashmi and Firoozabadi 2013). The resultant acid-base interactions along the long-chain carbon tails of DBSA form a solvation shell around the asphaltene molecules, thereby dissolving them (Leon et al 1999;Rogel and Leon 2001).…”

Method for Determining the Effectiveness of Asphaltene Antifoulants at High Temperature: Application to Residue Hydroprocessing and Comparison to the Thermal Fouling Test

“…A non-exhaustive list includes automatic titration, [23][24][25] optical microscopy, 23 dynamic turbidity, 23 particle size distribution, 23 SARA analysis, 26 Vapor Pressure Osmometry (VPO), 27 Gel Permeation Chromatography (GPC), 28 etc. These techniques are used to study the effect of inhibitors/dispersants on the precipitation onset, flocculation, settling and aggregate size distribution of asphaltenes.…”