Surface Properties of Asphaltenes by Atomic Force Microscopy

1
Surface Properties of Asphaltenes by Atomic
Force Microscopy

• Dharamdat Christendat
• NSERC Industrial Research Chair
• in Oil Sands Engineering
• Department of Chemical and Materials Engineering
• University of Alberta
• Edmonton Alberta

2
Outline

• Introduction
• Experimental Methods
• Atomic Force Microscope
• Sample Preparation
• Zetaphoremeter
• Results and Discussion
• Summary and Conclusions

3
Introduction

• What are asphaltenes and why are they
  important
• in the oil sands industries?
• Complex mixture of aliphatic and aromatics
• Responsible for emulsion formation
• and fines entrapment

4
Objective

• ? To study the interaction between
• asphaltenes and fines at molecular level.
• Atomic Force Microscope (AFM)

Silica Particle
Asphaltene Surface
5
Optical Lever for Monitoring Tip Movement in the
Atomic Force Microscope
6
SEM Micrograph of Silica Particle
6 ?m
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Sample Preparation

• Asphaltene samples were prepared from light
• Alberta crude by the addition of n-pentane
• A 11 mixture of toluene asphaltene was
• centrifuged and spin coated onto silicon
  wafer
• 5 10 ?m silica particles were glued onto
• AFM cantilever and used for force
• measurement.

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Typical Force Plots Between Substrate and AFM Tip

Tip Deflection
Piezo Displacement (nm)
9
Time Dependent Force Profile between Asphaltene
and Silica in Millipore Water
Repulsive Force
120 mins.
F/R (mN/m)
15 mins.
Attractive Force
Separation (nm)
10
pH Dependent Force Profile between Asphaltene and
Silica in 10-3 M KCl
Repulsive Force
Attractive Force
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Salt Dependent Force Profile between Asphaltene
and Silica at pH 10
10-3 M KCl
10-2 M KCl
Force (mN/m)
10-1 M KCl
Repulsive Force
Separation (nm)
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Zetaphoremeter

CCD Camera / Computer Interface
Laser Beam
Anode
Cathode
Quartz Cell
13
Zeta Potential of Si and Asphaltene Particles in
10-3 KCl Solution
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Summary

• Atomic Force Microscopy was used to study the
• interactions between asphaltene and silica
  particles
• at different pH and salt concentration.
• Zetaphoremetry was used to test for transfer of
• asphaltene molecules onto the surface of
  silica
• particles.

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Conclusions

• Surface characteristics of asphaltenes
• are time dependent in solution.
• The range and magnitude of repulsive
• surface interactions increase with pH.
• The measured forces are sensitive to the
• added salt concentration.

16
Further Work

• More experiments
• Functionalize surfaces
• Carboxylic acid
• Amine
• Hydrophobic

17
Acknowledgments

• Dr. Kunal Karan
• Dr. Thomas Abraham
• Drs. Zhenghe Xu and Jacob Masliyah
• NSERC/Syncrude Industrial Research
• Chair in Oil Sands Engineering