Adsorption of asphaltenes from toluene on mineral surface

Abstract

Undesirable adsorption of asphaltenes on rock minerals was studied. Asphaltenes are an important component of crude oil, being also natural surfactant stabilising water/crude oil emulsions. Owing to their chemical nature, asphaltenes are able to associate, form micelles and create a surface charge at the interface. Asphaltenes may be adsorbed on rock reservoir from the organic solvents in crude oil and as an organic colloid, they can adsorb electrolyte ions from aqueous solution. In order to simulate natural conditions we used asphaltenes from local drills, toluene as solvent and several typical oxides and carbonate rock components or minerals as adsorbents. Our study included natural Brazilian quartz, dolomite, calcite and kaolin, as well as pure oxides: Fe 2 O 3 and TiO 2 . The typical shape of asphaltene adsorption isotherms was obtained for all systems studied with the characteristic 'steps' which indicate changes in the state of asphaltene molecules in the solution and at the mineral surface. Those changes are related to the asphaltene association and further formation of hemimicelles and micelles.

Adsorption of asphaltenes from toluene on typical soils of Lublin region

“…In our previous paper [31] on adsorption of asphaltenes on mineral surfaces we measured the spectra of asphaltenes in toluene in the usual absorption linearity range i.e. absorption <1.5 and concentrations below $50 ppm.…”

“…Very often adsorption of asphaltenes is described in terms of Langmuir isotherm [34,35,37], however our analysis shows that in most cases it is not possible [31]. For comparison we supply two Fig.…”

“…Because of their interfacial activity, asphaltenes are of special interest from a colloidal point of view . Asphaltenes can adsorb electrolyte ions from brine solution [28][29][30] and they may be adsorbed from organic solution on rock reservoir and soils [1,[31][32][33][34][35][36][37][38][39]. One should expect, that these adsorption processes are further complicated by the behaviour of asphaltenes in organic solutions.…”

“…Thus, their adsorption on charged mineral surfaces could be considered as adsorption of ionic surfactants. It is well known that the shape of isotherms describing surfactant adsorption process strongly depends on its critical hemimicelle concentration and critical micelle concentration (CMC) which mark the onsets of distinct isotherm regions [31,[54][55][56][57][58]. However, phenomenon of adsorption of natural, not exactly defined surfactant adsorption on not well determined adsorbents-soilsfrom non-polar and weakly polar non-aqueous solutions is largely unexplored.…”

Asphaltene adsorption on quartz sand in the presence of pre-adsorbed water

“…Asphaltenes adsorb at solid surfaces [1], essentially to produce monolayers of nanoaggregates, the latter comprising stacks of 6 asphaltene molecules, according to the Yen-Mullins aggregation model [26]; further aggregation of nanoaggregates to form clusters at sufficiently high concentrations leads to thicker adsorbed layers [27,28]. According to Adams' comprehensive review on asphaltene adsorption, by assuming 3 nm asphaltene (nano)aggregates with a density of 1200 kg/m 3 , the maximum surface coverage for an asphaltene monolayer is calculated to be 3.6 mg/m 2 [1].…”