This is to certify that I am responsible for the work submitted in this project, that the original work is my own, except as specified in the references and acknowledgments, and that the original work contained herein is not undertaken by unspecified sources or persons or not done. . In this project, the equilibrium phase of methane hydrate is measured in the presence of ionic liquid as hydrate inhibitor. Ionic liquid is chosen because of its dual function inhibitors that can give thermodynamic and kinetic inhibition effects.
In contrast to conventional thermodynamic inhibitors such as methanol and ethanol, ionic liquid is needed in a low dosage and is an environmentally friendly solvent [2]. The progress of this ionic liquid towards the methane hydrate equilibrium phase boundary has been studied using the hydrate study system (HYDREVAL). The equilibrium phase of methane hydrate in the presence of [BMIM]-Br is compared with other hydrate inhibitors from previous studies such as methanol and [EMIM]-Cl.
In the presence of [BMIM]-Br, a temperature shift of the methane hydrate equilibrium phase occurs. Praise be to God that by His will and given strength I was able to complete this final project which proved to be really beneficial for me.
INTRODUCTION
- Background of Study
- Problem Statement
- Objective
- Scope of Study
- Relevancy and Feasibility of Project
The common application of hydrate inhibitor is also applied in guaranteeing the flow to remove gas hydrate blockage, which will improve the oil transportation through the pipeline. There are not many applications of hydrate inhibitor used for production of methane hydrate from natural reservoir hydrate deposits. There are several factors leading to the study of hydrate inhibitors on the phase equilibrium of gas hydrate.
To remove the hydrate blockage inside the pipeline, conventional hydrate inhibitor is used to dissociate the gas hydrate structure. In other words, the gas hydrate structure is disturbed in the presence of hydrate inhibitor. However, the study of hydrate inhibitor for gas hydrate extraction is still ongoing [1].
Thus, the use of a hydrate inhibitor may be one of the possible methods for use in gas recovery from hydrate deposits. Conventional hydrate inhibitors such as methanol, monoethylene glycol (MEG) and diethylene glycol (DEG) are known as high dose hydrate inhibitors (HDHI).
LITERATURE REVIEW
Methane Hydrate
For marine cases, gas hydrate is stable in water depth of 1200 m, while in permafrost cases, methane hydrate is seen stable in water 200 m and above. The gas hydrate stability zone temperature in deep-water marine environments ranges from 0 °C to 17 °C, where in permafrost environments the methane hydrate stability zone temperature ranges from -20 °C to 15 °C. In this research, the main interest is in the phase boundary of deep water marine environments.
To produce methane gas from methane hydrate deposition at this environment, the phase boundary of methane hydrate must be shifted to a lower temperature. Methane hydrate can only be found in specific zone where the pressure and temperature conditions are well known. Outside the stability zone, methane hydrate exists as free gas or gas dissolved in pore water at pressure-temperature conditions and it is estimated that 99% of gas hydrate is formed in marine sediments [1].
During the cooling process from point A to B, the hydrates begin to form, and when the hydrate is fully formed, there is a sudden drop in pressure (point B) due to the gas filling inside the hydrate former. Methane hydrate is fully formed when the methane gas filled the hydrate generator and there is no pressure drop (point C). Methane gas is released from the hydrate generator at this point and pressure began to build.
The equilibrium temperature and pressure are measured at point D, where the intersection of the hydrate formation line and the dissociation line met.
Extraction Methods
Conventional hydrate inhibitors such as methanol, ethanol and glycol are injected into the sediment beds at a certain pressure to lower the hydrate formation temperature leading to dissociation. The problem with conventional hydrate inhibitor is that this inhibitor is needed in large doses.
Ionic Liquid
The ionic liquid can shift the equilibrium temperature of methane hydrate to a lower temperature, thus promoting the hydrate-free zone. Studies on the effect of ionic liquid concentration on the dissociation curve are shown in Figure 7. In this study, the effectiveness of ionic liquids and their mixtures in inhibiting the formation of methane hydrate is investigated [11].
From the research, the higher concentration of [EMIM]-Cl shows a significant temperature shift compared to the lower concentration. The sample with 40 wt % [EMIM]-Cl shifted the methane hydrate dissolution curve to a much lower temperature compared to the sample with 5 wt % [EMIM]-Cl. The ionic liquid can also act as a kinetic inhibitor where it delays hydrate formation.
The common equipment used to study the dual function inhibitor properties of ionic liquids uses the high-pressure micro-differential scanning calorimeter (μDSC). From the above figure, [EMIM]- has the longest induction time compared to others, whereby blank samples give the shortest induction time. This proved that ionic liquids can also act as kinetic inhibitor as well as thermodynamic inhibitor.
METHODOLOGY
Research Methodology
Experimental Methodology
- Apparatus
- Materials
- Preparation of Sample
- Measurement of Hydrate Equilibrium Point
The materials used for the experiment are distilled water ( ), methane gas ( ) and 1-butyl-3-methylimidazolium bromide ([BMIM]-Br). During the mixing process, the ionic liquid powder was slowly added to the beaker and the sample was stirred using the magnetic stirrer at 600 rpm for about 1 to 2 minutes to ensure that the ionic liquid powder was completely dissolved in the distilled water. The sapphire cell was washed with distilled water and then alternately wiped for two rounds.
Afterwards, the cell was flushed with methane gas to ensure that it was air-free for about half an hour. 25 sample with desired concentration and 55 methane gas was injected into sapphire cell with the help of external pump in separate line. The methane gas was then supplied into the cell until the desired pressure was reached.
The hydrate formation in the vessel was detected by visual observation and each data was recorded for each reduced temperature.
Project Activities
- Gant Chartt
- Key Milestone
Submission of interim report FYP 1 Verification of available equipment Weeks 2 - 5 Identification of the experimental procedures Week 5.
RESULT AND DISCUSSION
Equilibrium Measurement of Methane Hydrate
As the temperature of the cell decreased from A to B, the pressure dropped due to the loss of energy from the gas in the cell (cooling process). The water molecule began to form ice when it reached the freezing point, and the methane gas began to react with the water molecule. At point B, there was a sudden drop in pressure as the ice structure trapped the methane gas as the hydrate grew.
When the heating process started at point C, the methane hydrate started to decompose as it reached the hydrate-free zone. The pressure increased rapidly from point D to E reflecting the released methane gas from the ice structure and the methane hydrate began to dissociate. The intersection of the two lines at point E indicates the hydrate equilibrium temperature and pressure of the sample.
To achieve a pressure of 60 bar, the piston in the sapphire cell was enlarged to compress the cell. For this run, BMIM]-Br was used, but the temperature set point was changed due to the pressure changes. The formation of hydrate was observed above 0°C and methane hydrate was completely formed at a temperature of 1.7°C (point C).
Hydrate Equilibrium Curve Comparison
Methanol shifts the equilibrium temperature of methane hydrate the most compared to other hydrate inhibitors. The temperature shift of methane hydrate in the presence of ionic liquid is not significant due to the limited data obtained from the measurement. The thermodynamic effect of [BMIM]-Br is not clear compared to the conventional hydrate inhibitor (methanol).
More data are needed to analyze the thermodynamic effect of ionic liquid towards the phase equilibrium of methane hydrate. Although the thermodynamic effect is not significant compared to methanol, ionic liquid shows an increase in temperature shift at 60 Bar. Further measurement should be done to confirm the effectiveness of ionic liquid at higher pressure.
CONCLUSION AND RECOMMENDATION
The samples should be tested in different pressure ranges ranging from 20 Bar to 80 Bar to observe a clear performance of the ionic liquid. Several ionic liquid concentrations can be made to observe the effect of ionic liquid concentration towards the methane hydrate equilibrium phase. If the samples are left too long, the composition of the ionic liquid and water may be affected.
The experiment on the effectiveness of the ionic liquid prepared at different time intervals can be done to investigate the effect of sample preparation time on the effectiveness of the ionic liquid. However, deionized water is more preferable to study the formation and dissolution of methane hydrate than distilled water to obtain accurate data. The temperature set point is one of the important data to be entered into the HYDREVAL software.
Improving the Performance of Gas Hydrate Kinetic Inhibitors with Polyethylene Oxide." Chemical Engineering Science. 34; Gas Hydrate Formation, Agglomeration, and Inhibition in Oil-Based Deepwater Drilling Fluids." Journal of Natural Gas Chemistry. Hydrate Formation: Considering the Effects of Pressure, Temperature, Composition and Water, Society of Petroleum Engineers.
34; Efficacy of Ionic Liquids and Their Mixtures in Inhibiting Methane Hydrate Formation." Chemical Engineering Science. A Study on the Thermodynamic Effect of [EMIM]-Cl and [OH-MIM)-Cl on the Methane Hydrate Equilibrium Line. Thermodynamic Modeling of an Ionic Liquid Aqueous Solution and Prediction of Dissociation Conditions methane hydrate in the presence of an ionic liq.
