MICROCALORIMETRY STUDY OF THE ADSORPTION OF ASPHALTENES AND ASPHALTENE MODEL COMPOUNDS AT THE LIQUID-SOLID SURFACE

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1 Rueil-Malmaison, 30 th May 2017 MICROCALORIMETRY STUDY OF THE ADSORPTION OF ASPHALTENES AND ASPHALTENE MODEL COMPOUNDS AT THE LIQUID-SOLID SURFACE Diego PRADILLA 1, Sébastien SIMON 1, Johan SJÖBLOM 1, Isabelle BEURROIES 2, Renaud DENOYEL 2, André MORGADO LOPES 2, Véronique WERNERT 2, Loïc SORBIER 3, Vincent LECOCQ 3 1 Ugelstadt Laboratory, Norwegian University of Science and Technology, Trondheim, Norway 2 Aix Marseille Université, Laboratoire MADIREL, UMR 7246 Centre de St Jérôme, Marseille 3 IFP Energies Nouvelles, Rond-point de l échangeur de Solaize BP3, Lyon

2 Problem - Asphaltene Conversion Found in the heavy cuts of crude oil defined as the fraction insoluble in normal paraffins but soluble in aromatic solvents (e.g. toluene) Catalytic conversion of asphaltenes into lighter products is essential due to the high demand in the energy industry. Challenges: - High molecular mass and polydispersity - Typically rich in heteroatoms - Tend to form aggregates and cause flow assurance problems - Can form gel-like films in liquid-liquid interfaces How to model the behavior of these complex molecules? May 30th,

3 Molecules Used Modelling asphaltene behavior Use representative asphaltene fractions extracted from crude Synthesize asphaltene model molecule C5PeC11 Extracted from Statoil dead oil 1 with n-hexane; solutions in toluene. Assumed average molecular weight: 750 [g/mol] (This assumes no aggregation) Acidic functionalization Molecular weight: [g/mol] % C % H % N % O % S C/H atomic ratio May 30th,

4 Substrates and Pretreatments Material BET surface area [m 2 ] Particle size [nm] Treatment Representative of Silica C (24h) -> Dessicated (4h) Scale deposits Calcite C (24h) -> Dessicated (4h) Limestone in reservoirs Alumina Powder C + vacuum (24h) Catalyst support Alumina Monolith C + vacuum (24h) Catalyst support Stainless Steel Pipeline Stainless Steel composition: C: 0.03 max. Mn: 2.00 max. P: max. S: 0.03 max. Si: 0.75 max. Cr: Ni: Mo: Alumina May 30th,

5 Isotherm Depletion Method Several solutions are prepared with different concentrations and are left to adsorb until equilibrium between the liquid and adsorbed phases. The supernatant s final concentration is then measured and the difference between the concentrations before and after exposure to the substrate is measured using UV spectroscopy Γ = C i C f m s S BET V May 30th,

6 Isotherm Results C5PeC11 4,5 Adsorption Isotherms of C5PeC11 Γ ads / mg.m 2 4 3,5 3 2,5 2 1,5 1 0,5 0 Silica Alumina Calcite Stainless Steel 0 0,5 1 1,5 2 2,5 C eq / g.l -1 May 30th,

7 Isotherm Results C6-Asphaltenes 2,5 Adsorption Isotherms of C6-Asphaltenes 2 Γ ads / mg.m 2 1,5 1 0,5 Silica Calcite Stainless Steel 0 0 0,5 1 1,5 2 2,5 C eq / g.l -1 May 30th,

8 Isotherm Results Comparison Both model and real fraction follow the same pattern as far as capacity: Stainless Steel > Calcite > (Alumina) > Silica Very high affinity for the model molecule, quick saturation; dampened effect on the real fraction Adsorption isotherms with more similar plateau for C6 fraction due to polydispersity of functional groups May 30th,

9 Microcalorimetry Experiments Differential microcalorimetry (Tian Calvet) Adsorbing molecules are injected in controlled doses (titration) onto a cell containing the solvent and the adsorbing substrate. The difference in heat flow against a reference cell is measured, resulting in a heat flow vs time plot May 30th,

10 Microcalorimetry Results Analysis Blank experiments (solvent in solvent) are performed to determine the heat effects of viscosity and heat gradient (due to injection) as well as the enthalpy of dilution of the stock solution in the solvent The asphaltene concentration is chosen so that the experiment is only performed in the high affinity zone of the isotherm Dilution Enthalpy / -kj.mol C / mol.kg -1 The adsorption enthalpy is calculated using the differential method (the heat measured is the energy of adsorption in a partially covered surface) and plotted against the surface concentration May 30th,

11 Microcalorimetry Results Dilution & Aggregation Asphaltenes have a tendency to form aggregates, even at lower concentrations 0-1 Using the dilution enthalpy curve and a dimer model, it is possible to determine ΔH, ΔS and K C5PeC11 Dilution Enthalpy / -kj.mol C / mol.kg -1 Results: ΔH and ΔS are both positive enthalpydriven dissociation K C5PeC11 is much higher than K d for asphaltenes (due to COOH interaction) similar ΔH to stearic acid confirms this May 30th,

12 Differential adsorption enthalpy [-kj/mol] Microcalorimetry Results C5PeC Heat of adsorption C5PeC11 Stainless Steel Silica Calcite Alumina powder Alumina monolith ,2 0,4 0,6 0,8 1 surface concentration [µmol/m 2 ] May 30th,

13 Differential adsorption enthalpy [-kj/mol] Microcalorimetry Results C6-Asphaltenes 35 Heat of Adsorption C6-Asphlatenes Calcite Stainless Steel Silica ,2 0,4 0,6 0,8 1 surface concentration [µmol/m 2 ] May 30th,

14 Microcalorimetry Results Model and real fraction follow different sequences regarding heat of adsorption: C5PeC11 Alumina (Monoliths > Powder) > Silica > Calcite > Stainless Steel C6-Asph Calcite > Silica > Stainless Steel Adsorption on different surfaces depends on different interactions: Silica/Alumina: -COOH H-bonds; Calcite: π-π stacking and dipole-dipole interactions; Stainless steel: electrostatic bonding coupled with asphaltene surface charge Steep upwards slope in the alumina samples may mean that treatment has not been fully effective due to alumina s great hydrophilicity; slopes in the C6-Asphaltenes increase, indicating strong lateral interactions, self-association and multilayer formation May 30th,

15 Conclusions and Perspectives Isotherms have been traced for the real asphaltene fraction as well as the model molecules in different representative surfaces Microcalorimetry experiments have been performed to study the adsorption of asphaltenes in several substrates. These studies led to a better comprehension of the dilution/aggregation of the model molecule as well as a thorough understanding of the solid-liquid surface interactions experienced by the different asphaltenes in the different surfaces The model molecule manages to reproduce a good portion of the average properties exhibited by a real asphaltene fraction Perspectives include refining the results obtained with alumina as well as studying the transport of the model molecule through alumina support flowpaths in order to better understand its hydrodynamic and adsorptive behavior within catalysts May 30th,

16 Thank you for your attention!