In light of the fact that natural gas hydrate is becoming more crucial nowadays in the oil and gas industry, either to prevent its formation or to improve its formation, this project is about the study of three-phase equilibria (H-Lw-V ) for methane hydrate and performance of hydrate promoters for the formation of methane hydrate. Therefore, the aim of this project is also to analyze the ability of two types of hydrate promoters to escalate methane hydrate formation. All this phase equilibrium measurement of hydrates will be done using pure water.
In this project, the main focus will be on the study of the phase behavior of methane hydrate under the influence of two hydrate promoters, namely sodium dodecyl sulfate (SDS) and tetrahydrofuran (THF). The phase equilibria for simple methane hydrate were performed as verification data that can be used as a reference to other hydrate phase equilibria consisting of methane and hydrate promoters. The importance of knowing the phase behavior of methane hydrate with promoters should be applied to practical applications where hydrate formation is desired, such as in natural gas storage and natural gas transportation.
INTRODUCTION
- Background of Study
- Problem Statement
- Objective
- Scope of Study
Then hydrate research entered a third phase in the late 1960s when solid natural gas or methane hydrate was observed as a naturally occurring component of subsurface sediments in the Messoyahka gas field in the West Siberian Basin. This is the period when scientists begin to expand the study of natural gas hydrates around the world. This law is expected to overcome environmental issues, the emerging shortage of natural gas supply and also increase dependence on foreign energy.
The importance of studying the phase equilibria of methane hydrate with propellants in pure water is as follows: (1) In the oil and natural gas industries, gas hydrates are known to be harmful materials as they can lead to "locking problems". which cause serious operational and security problems [10]. under typical conditions of low temperature and high pressure, in the pipeline, the presence of water content will come into contact with the components of oil or natural gas, which can lead to the formation of gas hydrate. Therefore, this research will focus on the identification of methane hydrate phase equilibria in order to prevent hydrate formation in oil and natural gas pipelines and overcome the plugging problem. They also showed a significant cost saving of about 24% for transporting natural gas in the form of hydrate compared to liquid natural gas [16, 20].
LITERATURE REVIEW AND THEORY
Phase Equilibrium
In addition, the phase equilibrium condition of two or more phases is represented by the phase equilibrium line in the phase diagram. From a phase diagram, scientists and engineers understand the behavior of a system for a single component or compound. Therefore, hydrate phase equilibrium measurements are very useful in the field of hydrate research and study.
The state in which liquid and vapor can both exist in equilibrium under certain temperature and pressure conditions is similar to the state in which solid and vapor can coexist without liquid being present [22]. These two processes take place in equal measure when there is no macroscopic change in the system. The similar condition also occurs in three-phase equilibria; hydrate, liquid water and vapor (H-Lw-V), where four processes take place at equal speed.
Gas Hydrate
In fact, water has four different coordination numbers and this factor will affect the size of the cages and cavities that will accommodate guest molecules to form a hydrate. Temperature and pressure depend on the guest hydrate molecules, where each guest will form a hydrate under different conditions, as shown in Figure 2.3. Although a hydrate is a compound formed from water and gas, no chemical bond exists between the host and the guest, as it binds by weak Van Der Waals forces [1].
Van der Waals interactions between the trapped gas molecule and the surrounding water cage walls stabilize and support the individual polyhedra that form the hydrate lattice and limit the translational motion of the gas molecule. Apart from above, unit cell of sI consists of 46 water molecules, which form two types of cages which are small and large. Unit cell of sII consists of 136 water molecules, which also form two types of cages; small and large.
The sH unit cell consists of 34 water molecules forming three types of cages, two of which are small of different types and one of which is large.
Hydrate Promoter
31] reported that the effect of a nonionic wetting agent on hydrate storage capacity is less pronounced compared to that of an anionic wetting agent. SDS has a potential to prevent hydrate particles from agglomerating and forming a rigid hydrate film in the liquid-gas interface that will hinder further hydrate formation. It is well known that cyclic ethers form simple hydrates with water or mixed hydrates with low molecular weight gases such as CO2, CH4 and N2 [1].
In addition, THF forms a hydrate of structure II; sII, therefore THF molecules occupy only larger cages in the hydrate lattice. 34] studied the gas hydrate formation of binary gas mixtures H2 and CH4 in the presence of 6 mol% tetrahydrofuran (THF). The result was that the presence of THF in water drastically reduced the hydrate formation pressure of pure CH4 and also of mixtures of H2 and CH4.
METHODOLOGY
Research Methodology
- Apparatus, Equipment and Materials
- Methodology
- Sample Preparation
- Measurement of Hydrate Equilibrium Point
The chemicals used in this work are distilled water (H2O), methane (CH4), sodium dodecyl sulfate (SDS), and tetrahydrofuran (THF). The chemical that will be used as hydrate promoters are sodium dodecyl sulfate (SDS) and tetrahydrofuran (THF), obtained from Avantis Laboratory Supply. Due to the use of promoters in different concentrations, in terms of weight percent (wt%) and parts per million (ppm), the promoters were diluted with distilled water.
The flow chart below, Figure 4.1, shows the sequence of experiments that will be performed to accomplish the objective of this project. Two experiments will be performed for THF that are at two selected concentrations of THF; 5 wt% and 7 wt. Similar to SDS, the experiments conducted using SDS will be at two different concentrations which are 300 ppm and 600 ppm.
For SDS, there are two concentrations that will be used in this study, namely 600 ppm and 300 ppm. The equation below is used to calculate the volume of 600 ppm SDS solution to be used to produce a concentration of 300 ppm SDS solution. In the meantime, V1 is the volume of stock solution that will be used to produce the desired concentration solution of V2 volume.
Then the prepared solution to be used in the test is filled in the liquid accumulator, which this liquid will later be transferred to the sapphire cell by means of the external pump. The sapphire cell was then washed with distilled water and then vacuumed alternately in two rounds. During rinsing, the stirrer was turned off to prevent solubility of methane in the aqueous solution.
Hydrate formation in the vessel was detected by visual observation and all data was recorded for each reduced temperature.
Project Activities
- Key Milestone
- Gantt Chart
Perform the verification test using pure methane with pure water - Perform the methane hydrate experiment in the presence of promoter (SDS).
RESULT AND DISCUSSION
Results and Discussions
Point D of Figure 4.1 is the hydrate equilibrium point where the equilibrium pressure obtained is 69.14 bar and the equilibrium temperature is at 8.8oC. However, at this stage hydrate does not form due to metastability. As a result of the four equilibrium measurement tests, methane hydrate phase equilibrium line is reached and comparison is made with the data from various previous literature. As shown in Figure 4.2, the H-Lw-V data indicate that the verification experiment was consistent with several previous literature reviews.
Methane hydrate equilibrium measurement experiments with both hydrate promoters were performed at the same experimental pressure for each experiment, namely 137.56 bar. Several researchers understand that the main function expected of the methane hydrate promoting agent is to improve the solubility of the hydrate-forming gas in water [17]. From this study, SDS performance has been observed and the results are plotted in Figure 4.6, which shows the effect of different SDS concentrations on the equilibrium temperature of methane hydrate at the same experimental pressure, 138.9 bar.
The lower surface tension between water and methane gas indicates that the solubility of methane gas in water is higher, thus promoting the formation of methane hydrate. The CMC of a surfactant solution depends on the temperature, pressure, and nature of the hydrate-forming gas. Based on Figure 4.6, by adding 300 ppm of SDS concentration, the equilibrium temperature increases slightly, approximately 3oC increase.
This proved that SDS gave only a small effect in terms of thermodynamic hydrate, which involved the formation and dissolution of methane hydrate, as it shifted the equilibrium temperature slightly higher. The hydrate equilibrium data for the ternary system of methane, tetrahydrofuran (THF), and water with 5% wt% and 7 wt% THF in aqueous solution are plotted and compared in Figure 4.9 with the binary system of methane and pure water. Similarly, the performance of THF in methane hydrate also showed the promotion of hydrate formation.
However, compared to SDS, THF resulted in a remarkable increase in equilibrium temperature than in the pure methane hydrate. As shown in Figure 4.9, the addition of a small amount of THF in water did have a significant effect on the hydrate-water liquid-vapor (H-Lw-V) equilibrium line by expanding the hydrate stability region to higher temperature at the same pressure. This observation confirms that the presence of tetrahydrofuran in the system increased the stability of the hydrate phase.
CONCLUSION AND RECOMMENDATION
Conclusion
Recommendation
Sloan Jr., Clathrate Hydrates of Natural Gases: Revised and Expanded, 2nd Edition, Marcel Dekker, New York, 1998. Competitive adsorption of sodium naphthenates and naturally occurring species to water-in-crude oil emulsion droplet surfaces. Effects of surfactants on hydrate formation in an unstirred gas/liquid system: an experimental study with methane and sodium alkyl sulfates.
Experimental study on the effect of increasing gas hydrate storage in a quiescent reactor. 28] Seo, Y.T.; Lee, H.: "Multiphase Hydrate Equilibria of Ternary Mixtures of Carbon Dioxide, Methane, and Water," J.
