ENVIRONMENTALLY, CO2 REMOVAL IN FORM OF CO2 HYDRATE IN THE OCEAN IS ONE POSSIBILITY OF REDUCING THE ATMOSPHERIC CONCENTRATIONS OF THIS GREENHOUSE GAS AND ASSIST IN DIMINISHING GLOBAL WARMING. CONSIDERING THE IMPORTANCE OF CO2 HYDRATES, THIS PAPER FOCUSES ON MOLECULAR DYNAMICS (MD) SIMULATIONS OF STRUCTURE I CO2 HYDRATE. THE GOAL IS TO STUDY THE STABILITY OF THE CLATHRATE AT DIFFERENT TEMPERATURES. FOR ACHIEVING THIS PURPOSE, ENERGETIC AND STRUCTURAL PROPERTIES ARE CALCULATED. EQUILIBRIUM MD SIMULATIONS ARE CARRIED OUT TO STUDY THE PROPERTIES OF FULLY OCCUPIED CO2 CLATHRATE-HYDRATE AT 260, 270, 280, AND 290 K USING CVFF FORCE FIELD. A MIXTURE OF WATER AND CO2 PLACED IN A CUBIC CELL IS USED AS A MODEL SYSTEM TO SIMULATE THE CO2 CLATHRATE HYDRATE AT 5 MPA DURING TOTAL SIMULATION TIME OF 200 PS. THE CELL PARAMETERS, STABLIZATION ENERGIES AS WELL AS RADIAL DISTRIBUTION FUNCTIONS ARE COMPUTED. THE OBTAINED RESULTS AT DIFFERENT TEMPERATURES INDICATE THE HYDRATE STABLILITY AT LOW TEMPERATURES UP TO 280 K. MOREOVER, STABLIZATION ENERGY OUTCOMES REVEALS THAT CO2 HYDRATE IS MORE STABLE THAN THE EMPTY CLATHRATE.

IN THIS STUDY,MOLECULAR DYNAMIC SIMULATIONS HAVE BEEN SERVED TO INVESTIGATE THE PROPERTIES OF METHANE HYDRATE. MSD AND SELF-DIFFUSION COEFFICIENT OF SYSTEM CONTAINING METHANE AND WATER MOLECULES HAVE BEEN DETERMINED AT 275 K AND HIGH PRESSURES (6- 15MPA). THE RESULTS HAVE SHOWN THAT MSD AND SELFDIFFUSION COEFFICIENTOF MOLECULES ARE SENSITIVE TO THE TEMPERATURE AND PRESSURE OF SYSTEM, SO THAT BOTH OF THEM DECREASES DUE TO INCREASING THE PRESSURE. ...

WE PERFORMED MOLECULAR DYNAMICS SIMULATION FOR POLAR AND NONPOLAR GUEST MOLECULES IN STRUCTURE   I CLATHRATE HYDRATE. WE SIMULATED TMO AS GUEST IN SI HYDRATE AND COMPARED WITH CYCLOBUTANE MOLECULE WHICH THESE TWO GUESTS ARE ISOELECTRIC AND HAVE SIMILAR MASSES BUT ARE DIFFERENT DIPOLE MOMENT AND   HYDROGEN BONDS ABILITY. WE SHOWED SNAPSHOTS OF A LARGE SI CLATHRATE HYDRATE CAGE WITH A TMO GUEST MOLECULE AT 225 K. TO DETERMINE THE ABILITY OF THE WATER MODEL WE INVESTIGATED THE RADIAL DISTRIBUTION FUNCTION FOR VARIOUS GUEST SPECIES WITH FOUR POINT CHARGES TIP4P/ICE AND SPC/E WATER POTENTIAL AT DIFFERENT TEMPERATURE AND ATMOSPHERE PRESSURE. FOR CONSIDERING DIFFERENT DYNAMICS OF POLAR AND NONPOLAR GUEST MOLECULES IN THE CLATHRATE HYDRATE WE CALCULATED VELOCITY AUTOCORRELATION FUNCTION (VACF) AND FOURIER TRANSFORMATION FROM VACF FUNCTIONS WITH TIP4P/ICE AND SPC/E WATER MODEL AT 250 K. ...

THE CLASSICAL CUBIC EQUATIONS OF STATE SUCH AS THE SRK AND PR EOS GENERALLY DO NOT RESULT IN ACCURATE PREDICTION OF THE VOLUMETRIC PROPERTIES AND PHASE EQUILIBRIA OF COMPLEX MIXTURES CONTAINING HYDROGEN BONDING COMPONENTS. THIS IS PARTLY BECAUSE OF THE STRONG HYDROGEN BONDING FORCES, WHICH CANNOT BE WELL REPRESENTED BY THE AFOREMENTIONED EOSS. THE CUBIC PLUS ASSOCIATION (CPA) EOS HAS BEEN PROPOSED TO COMBINE A CUBIC EOS EXPRESSION WITH AN ASSOCIATION TERM, DERIVED FROM THE WERTHEIM THEORY AS APPLIED IN THE STATISTICAL ASSOCIATING FLUID THEORY (SAFT) FOR TAKING INTO ACCOUNT THE HYDROGEN BOND INTERACTIONS. IN THIS STUDY THE PHASE BEHAVIOR OF THE WATER + HYDROCARBONS (METHANE AND ETHANE) AND AFOREMENTIONED HYDROCARBONS + METHANOL AQUEOUS SOLUTION SYSTEMS IS MODELED. THE VAN DER WAALS AND PLATTEEUW SOLID SOLUTION THEORY IS APPLIED TO DEAL WITH THE HYDRATE PHASE AND THE CPA EOS IS USED FOR MODELING THE FLUID PHASES.THE 4C AND 2B ASSOCIATION SCHEME FOR WATER AND METHANOL IS USED, RESPECTIVELY. ACCEPTABLE AGREEMENTS ARE FOUND BETWEEN THE REPRESENTED/PREDICTED RESULTS BY THE APPLIED THERMODYNAMIC MODEL AND THE EXPERIMENTAL PHASE EQUILIBRIUM DATA OF THE PURE METHANE OR ETHANE + WATER SYSTEMS AND IN THE PRESENCE OF METHANOL AQUEOUS SOLUTION FROM THE LITERATURE.

INTRODUCTION: GAS HYDRATES ARE NON-STOICHIOMETRIC SOLID SUBSTANCES COMPOSED OF GASES INCLUDING METHANE, ETHANE, CARBON DIOXIDE AND WATER FORMED UNDER LOW TEMPERATURE AND HIGH PRESSURE CONDITIONS. THESE SUBSTANCES ARE ICE-LIKE AND OCCLUDE HIGH VOLUMES OF GASES. ...

IN THIS COMMUNICATION, WE FIRST REPORT EXPERIMENTAL HYDRATE DISSOCIATION PRESSURES FOR THE METHANE/ CARBON DIOXIDE + FURAN/ ACETONE/ 1,4-DIOXANE + WATER AND THE METHANE + TETRA N-BUTYL AMMONIUM CHLORIDE (TBAC) + WATER AS WELL AS THE METHANE /CARBON DIOXIDE + TETRA N-BUTYL AMMONIUM FLORIDE (TBAF) + WATER SYSTEMS IN THE TEMPERATURE RANGES OF (269.9 TO 303.3) K. AN ISOCHORIC PRESSURE-SEARCH METHOD WAS USED TO GENERATE THE EXPERIMENTAL DATA. THE HYDRATE DISSOCIATION DATA ARE COMPARED WITH THE CORRESPONDING LITERATURE DATA AND THE PREDICTIONS OF A PREVIOUSLY REPORTED THERMODYNAMIC MODEL AND ACCEPTABLE AGREEMENT IS OBSERVED.