VAPOR–LIQUID EQUILIBRIA OF MIXTURES CONTAINING n-DECANE, CARBON DIOXIDE AND ARGON USING MOLECULAR SIMULATION TECHNIQUES (GIBBS ENSEMBLE MONTE CARLO SIMULATION)

 Abstract

 

The CO2–hydrocarbons systems is common in oil and gas industry as a geological fluid. CO2 plays a vital role in biological processes namely photosynthesis, respiration, and actively participates in the carbon cycle. However, the time gradient of carbon dioxide concentration in the atmosphere has become a major global concern. The environmental challenges associated with the control and management of anthropogenic emissions of greenhouse gases have been the focal point of society, industry, and scientific community. This linear molecule has continued to gain increased research focus due to its perceived effects which contributes to atmospheric concentration and epileptic climate change.

 

However, CO2 captured from power stations, reutilization, and subsequent storage (CCS) (long-term containment) into deep geological formations is a viable option  to mitigate global warming. The storage of CO2 in a proper characterised geological reservoir has the potential and propensity to reduce the amount of carbon dioxide being vented in the atmosphere, and also to stall global warming pending when more sustainable, efficient, and environmentally friendly source of fuel (energy) will fully be implemented in the near future. Is not enough to store CO2, because it is necessary before CO2 is stored we need to develop tool(s) to understand and monitor the phase behavior of the stored CO2 in the reservoir. Hence, the thermodynamics properties of CO2 mixtures are essential in a broad range of temperature, pressure, and compositions to gain full understanding and operations of CCS systems and its phase equilibrium will tremendously assist in storage.  

To this end, experiment is very difficult under reservoir conditions so there is a call for accurate and predictive method by employing molecular simulations to model the equilibrium between CO2 in contact with decane, in the presence of argon that acts as subsurface fluid tracers.

Table of Contents

List of Figures..................................................................................................4

List of Tables....................................................................................................5

Nomenclature...................................................................................................6

Abstract............................................................................................................7

Declaration.......................................................................................................8

Copyright Statement.......................................................................................8

Dedication.........................................................................................................9

Acknowledgements........................................................................................10

Chapter 1........................................................................................................11

1.1 Introduction.......................................................................................11

1.2 Geological Sequestration....................................................................14

1.3 Noble Gases........................................................................................14

1.4 Dissertation Structure.........................................................................15

Chapter 2........................................................................................................16

2.0 Literature Review...............................................................................16

2.1 Force Field Development....................................................................17

2.2 Intermolecular Interactions.................................................................17

2.2.1 Van der Waals interactions...........................................................18

2.2.2 Combining Rules..........................................................................20

2.2.3 Electrostatic Interactions..............................................................21

2.3 Intramolecular Interactions.................................................................22

2.3.1 Bond Stretching............................................................................22

2.3.2 Bond Angle Bending (1–3 Bonded Interactions).........................23

2.3.3 Torsional Rotation Terms.............................................................24

2.3.4 1–4 Bonded Interactions...............................................................25

2.4 Parameterization of Force Field..........................................................26

2.5 Empirical Parameterization.................................................................26

2.5.1 Intermolecular Interactions...........................................................27

2.5.2 Intramolecular Interactions...........................................................27

2.6 Force Field Families...........................................................................27

2.6.1 Transferable Force Fields ……….….………………………..........28

2.6.1.1   TraPPE Force Field …………………...…………………..….. 29

2.6.1.2  EPM2 Force Field Model……………………..……….………...33

2.6.1.3   Force Fields Comparison…………………….………………….35

2.7   Molecular Simulation Techniques…………………………………...36

Chapter 3........................................................................................................38

3.0 Methodology.......................................................................................38

3.1    The Gibbs ensemble technique............................................................38

3.2 Perturbations Moves...........................................................................40

3.2.1 Particle displacements..................................................................40

3.2.2    Volume rearrangement in the constant NPT ensemble.................41

3.2.3    Particle Interchange.......................................................................42

3.3     Generalization to a constant-pressure ensemble.................................44

3.4     Size of the Configurational Space......................................................45

Chapter 4........................................................................................................46

4.0   Simulation Details, Results and Discussion.........................................46

4.1   Computer program used.......................................................................46

4.2   Simulation details.................................................................................46

  4.2.1 Single-Components Vapor–liquid Coexistence Curves (VLCCs).......46

  4.3   Results and Discussion..........................................................................50

  4.3.1Phase Behavior of Pure Components; test of simulation Software. 4.4VLCC for Binary and Ternary mixtures................................................54

  4.5 The effects of Gases Solubility as a function of Temperature………....62

Chapter 5........................................................................................................63

5.0   Conclusion and Recommendation........................................................63

5.1   Conclusion............................................................................................63

5.2   Recommendation..................................................................................64

References......................................................................................................65