Chemical Visualization of Asphaltenes Aggregation Processes Studied in Situ with ATR-FTIR Spectroscopic Imaging and NMR Imaging

Abstract

Crude oil phase behavior and asphaltene precipitation have been studied by two complementary chemical imaging methods for the first time. ATR-FTIR spectroscopic imaging approach has revealed the chemical composition of agglomerated and precipitated asphaltenes upon dilution with a flocculant. Asphaltenes, containing oxygen and nitrogen heteroatomic functional groups, have been detected to be least stable. Aromatic abundant asphaltenes have been observed to have relatively high solubility in crude oil/heptane blends. NMR imaging approach, capable of imaging in the bulk of crude oil samples, has demonstrated that n-heptane causes aggregation which can lead to the stable suspension or to the sedimentation followed by the formation of deposits, depending on flocculant concentration. These processes have been monitored for small and large amounts of heptane added to crude oil. The data obtained by ATR-FTIR spectroscopic imaging and NMR imaging have been correlated to propose a possible link between the chemical structure of asphaltenes and a mechanism of the formation of deposits.

Determining the Kinetics of Asphaltene Adsorption from Toluene: A New Reaction–Diffusion Model

“…precipitate with the smallest volume fraction of heptane [13]. In a similar way a 11 particular subset of asphaltene structures with specific functionality may be the first to self-associate at 12 high concentration. These molecules would preferentially form nanoaggregates and clusters meaning that 13 the chemistry of the residual free monomer fraction is altered.…”

“…For initial solution concentrations of 10 0.005 to 0.05 gL⁻¹, the rate of adsorption with respect to concentration of asphaltene was first order and 11 had a rate constant of 1.17 x 10⁻³ min⁻¹. At higher concentrations of 0.2 and 0.4 gL⁻¹ the initial rate 12 constant was similar, but decreased at long adsorption times. The rate of diffusion to the outer surface of 13 the silica was found to be the rate-limiting step at initial adsorption times and it was proposed that 14 adsorbed asphaltene provided a fresh site for further adsorption.…”

“…A wide range of different experimental conditions were covered including the effect of 10 heptane/toluene ratio, flow rate and surface chemistry. It was found that the deposited mass of 11 asphaltene increased with increasing volume ratio of heptane to toluene up to the precipitation point 12 which was determined to be 76 vol% heptane. 13…”

“…Heteroatoms including 39 nitrogen, sulphur and oxygen are reported to be found in various functional groups [11]. The least stable 1 asphaltene molecules tend to contain a greater proportion of oxygen-containing groups [12]. Cooperative 2 polar and hydrogen-bonding interactions between asphaltenes are responsible for aggregation and are 3 the likely cause of fouling in pipes [13].…”

Effect of Aging on the Removal of Asphaltene Deposits with Aromatic Solvent

“…The heptane-toluene ratio used to destabilize asphaltenes has several important effects: (1) on the rate of asphaltene aggregationhow the particle size distribution evolves with time, (2) on the proportion of asphaltenes that will eventually precipitate at equilibrium and (3) on the respective chemistries of the soluble and insoluble subfractions, see Fig 1 [16,17]. Thus, when we change the heptane vol% used to destabilize asphaltenes, we may alter the properties of the deposited filmboth its morphology and its chemistry [18,19]. Previously, we have seen a mismatch between laboratory studies and observations of asphaltene deposition in the field.…”