Induction time of Methane Hydrate formation in the presence of electrolyte solutions of sodium chloride and sodium sulfate

Transcription

1 nd National Iranian Conference on Gas Hydrate (NICGH) Semnan University Induction time of Methane Hydrate formation in the presence of electrolyte solutions of sodium chloride and sodium sulfate M.Manteghian*,H.Ahmadi Department of Chemical Engineering, arbiat Modares University, *Corresponding Author s manteghi@modares.ac.ir Abstract Devising methods to prevent hydrate formation is of the important issues in natural gas industry. Since a great deal of money is annually spent on using hydrate inhibitors, identification of new inhibitors with higher degrees of efficacy is economically justifiable. Bearing in mind the significant role of hydrate inhibitors in prevention of natural gas pipelines getting blocked, the present study attempts to investigate two compounds of NaCl and NaSO as inhibitors of hydrate methane s formation so as to respond to what is the inhibitive kinetic impact of electrolyte compounds of NaCl and NaSO on the formation of methane hydrate? o do so, this study measures the induction time of methane hydrate crystals in the presence of electrolyte solutions of NaCl and NaSO and compares the results obtained with the state lacking such inhibitors. Keywords : Electrolyte Solutions, Induction ime, Methane Hydrate, Sodium Chloride, Sodium Sulfate. Research Highlight Induction time of methane hydrate formation in the absence and in the presence of inhibitors of sodium chloride and sodium sulfate was recorded. Both electrolytes reveal an inhibitive impact on hydrate formation he effect of sodium chloride is outperforms that of sodium sulfate.

2 Induction time of Methane Hydrate formation. Introduction Gas hydrate is a compound, which is formed in the presence of water and the guest molecule under the condition of low temperature and high pressure. After being formed, this stable and tough compound leads to creation of a blockage in natural gas pipelines []. In 8 Devi, an English chemist, for the first time found out the formation of gas chloral hydrate while cooling an aqueous solution of chlorine in the temperature of degrees centigrade []. In 9, Homer and Schmitt found that the hydrate formed created a blockage in gas pipelines. henceforth, Diatom and Frost were of the early scientists who conducted and reported on empirical experiments on hydrate formation [,]. More serious studies on these molecules were carried out regarding their crystal structure, properties, and formation conditions as well as ways to inhibit their formation[]. o examine kinetic conditions of hydrate formation, Dimo Kashchieva and Abbas Firoozadib investigated correlation of oversaturation with crystal growth and induction time []. Velocity of hydrate growth has been modeled by several researchers through measuring the velocity of gas consumption at the time of hydrate formation [5]. In addition, various crystallization-based kinetic models have been proposed to predict hydrate formation conditions; however, validity of these models requires the relevant data on the particle size distribution (PSD) of the gas hydrate []. Methods to inhibit hydrate formation were classified as the following[7]: pressure control, temperature control, removing the water existing within the fluid, direct electrical heating system (DEHS), water injection method, cold flow method and injection of inhibitors.[8] Among the methods proposed for inhibition of hydrate formation, the most scientific one is the fourth method i.e. injection of inhibitors [9]. Chemical hydrate inhibitors are classified into three categories: thermodynamic, kinetic and anti-conglomerate inhibitors []. Inhibitors of the second and third types recently have drawn a great deal of attention because even little injection of them is capable of inhibiting hydrate formation. However, thermodynamic inhibitors (HIs) postpone hydrate formation via changing thermo-dynamic equilibrium condition. When added to the fluid, HIs change its chemical potential and drive the curve of thermo-dynamic equilibrium towards a lower temperature and a higher pressure []. Kinetic inhibitors do not displace thermal and pressure equilibrium conditions of hydrate formation, rather they slow down the growth velocity of hydrate formation for a certain time period [,,]. his type of inhibitors usually consists of polymer molecules of low molecular weights that have strong interaction with the active area of hydrate formation and, within the low density of.5%, slow down the speed of hydrate formation for a certain time period, and consequently delay crystallization []. Rather than affecting thermo-dynamics or growth velocity of hydrate crystals, Anti-cluster inhibitors prevent the formed hydrate crystals from getting together, combining and creating conglomerates and lumps. Of KHIs, we can point to poly vinyl Pyrrolidone, poly vinyl Caprolactam, and some qudri-aluminum compounds. hese chemicals are injected to the system in the form of the solution of low density (about %). herefore, their consumption is much less than that of thermo-dynamic inhibitors. In the recent years, industrial utilization of these chemicals has been observed [8]. he present study makes efforts to investigate the impact of NaCl and NaSO electrolytes on the inhibition of gas methane hydrate s formation; therefore, a laboratory unit is used to conduct the relevant experiments. Next section deals with the laboratory unit, methods and materials.

3 nd National Iranian Conference on Gas Hydrate (NICGH) Semnan University. Experiment.. Laboratory Unit he laboratory unit used by the study consists of a milliliter reactor, which is cooled down with water of circulator. he gas methane is prepared from a gas capsule which is connected to the laboratory unit. he computer records rector temperature and pressure, specifically the use of sensors that are connected to the system. he laboratory unit is shown by figures and. Figure.. Laboratory unit of methane hydrate formation Figure.. Laboratory unit of methane hydrate formation.. Methodology After injecting cc of water to the reactor, Methane at two different initial pressures and 8 were injected into the system. In addition, in different conditions in the absence of inhibitors and in the presence of inhibitors of and 5% wt sodium sulfate and sodium chloride, and set the temperature at 7.5 K, the temperature and pressure drop diagrams were recorded. o investigate kinetic conditions induction time is recorded for two weight densities of % and 5% using both inhibitors of NaCl and NaSO.. Results and Discussion

4 Induction time of Methane Hydrate formation..impacts of NaCl and NaSO electrolytes on Induction ime of methane hydrate formation Pressure-emperature vs ime formation of hydrate methane in the absence of inhibitors and in the presence of inhibitors at two weight densities of % and 5 % sodium and sulfate chloride are shown by the following figures time (min) آب خالصP ( o C) Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the absence of inhibitors, the initial pressure bar and temperature 7.5 K P(%NA Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of % wt NaSO inhibitor, the initial pressure bar and temperature 7.5 K..5.5 ( o C) P(5%NASO) 8 ( o C) Figure.5. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of 5% wt NaSO inhibitor, the initial pressure bar and temperature 7.5 K.

5 nd National Iranian Conference on Gas Hydrate (NICGH) Semnan University P(%NACL) 7 5 ( o C) Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of % wt NACL inhibitor, the initial pressure bar and temperature 7.5 K P(5%NACL) 5 ( o C) Figure.7. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of 5% wt NACL inhibitor, the initial pressure bar and temperature 7.5 K P(NASO) Figure.8. Kinetic of methane hydrate formation (increase in pressure drop) in the absence of inhibitors, the initial pressure 8 bar and temperature 7.5 K ( o C)

6 Induction time of Methane Hydrate formation P(%NASO 8 ( o C) Figure.9. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of % wt NaSO inhibitor, the initial pressure 8 bar and temperature 7.5 K P(5%NASO).5(oC) Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of 5% wt NaSO inhibitor, the initial pressure 8 bar and temperature 7.5 K P(%NACL) Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of % wt NACL inhibitor, the initial pressure 8 bar and temperature 7.5 K ( o C)

7 nd National Iranian Conference on Gas Hydrate (NICGH) Semnan University P(5%NACL) 5 5 Figure.. Kinetic of methane hydrate formation (increase in pressure drop) in the presence of 5% wt NACL inhibitor, the initial pressure 8 bar and temperature 7.5 K ( o C) According to the figures induction time for each of the different states are presented in the table. able.. Induction time of methane hydrate formation in the presence of various concentrations of inhibitors of sodium sulfate and sodium chloride Initial pressure bar Induction time (min) Initial pressure 8 bar Induction time (min) Pure water 8 Pure water % sodium sulfate % sodium sulfate 5% sodium sulfate 5 5% sodium sulfate 5 % sodium chloride % sodium chloride 9 5% sodium chloride 5% sodium chloride 5 As shown able, the highest inhibition belongs to the presence of 5% sodium chloride. In addition, it is observed that induction time is higher at the weight density of 5% than that at the weight density of %. For example, at the initial pressure of 8 bar, the induction time of the weight density of 5% equals min, whereas that of the weight density of % amounts to min. herefore, it is seen that the greater the electrolyte s density, the increase the induction time gets. However, in the same concentration of inhibitor, at higher degrees of pressure, we witness lower induction time. It is also found that sodium chloride has a greater deterrent effect than sodium sulfate on induction time of formation hydrate methane.. Conclusions he empirical data on the kinetic impact of NaCl and NaSO inhibitors on induction time of methane hydrate. Having obtained from both electrolytes, we compared them with the values of induction time at the inhibitors absence. he smallest induction time belongs to sodium sulfate of % in weight density and initial pressure 8 bar. With increasing concentrations of chloride and sodium sulfate inhibitors, inhibition and induction time increases. Highest inhibition belongs to the presence of 5% sodium chloride and sodium chloride has a greater deterrent effect than sodium sulfate on induction time of formation hydrate methane.

8 Induction time of Methane Hydrate formation References []Sloan, E. D.,Clathrate Hydrates of Natural Gases, Chem. and Indust. Syst., Marcel Decker, New York,998. []Carl R. Branan.,Rules Of humb For Chemical Engineers,Gulf Professional Publishing is an imprint of Elsevier,. [] Katz L.,Handbook of natural gas Engineering, McGraw Hill,959. [] Dimo Kashchiev, Abbas Firoozabadi, "Induction time in crystallization of gas hydrates", Journal of Crystal Growth,Vol.5,. [5] alaghat.m. R, Esmaeilzadeh.F and Fathikaljahi.J, Experimental and heoretical Investigation of Double Gas Hydrate Formation in the Presence or Absence of Kinetic Inhibitors in a Flow Mini- Loop Apparatus, Chemical Eng. echnology,vol., No. 5, 9. [] Elgibaly Ahmed * and Elkamel Ali,"Optimal Hydrate Inhibition Policies with the Aid of Neural Networks", Energy & Fuels, Vol., No.,999. [7] Pickering P. F., Edmonds B., Evaluation new chemicals and alternatives for mitigating hydrates in oil & gas production,. [8] Sørheim R., Gudmundsson J. S., ransportation of Petroleum in Subsea Pipelines A Competitive Analysis, NNU,5. [9] Shabani, Mohammad Mehdi; Rashtchian, Davood; Ghotbi, Cyrus;aghikhani, Vahid; Khayat, Ghazaleh., Prediction of Hydrate Formation for the Systems Containing Single and Mixed Electrolyte Solutions,Iran. J. Chem. Chem. Eng. Vol., No.,7. [] Sefidroodi Hamidreza, Chua PeiCheng, Kelland.MalcolmA, "HF hydrate crystal growth inhibition with small anionic organic compounds and their synergistic properties with the kinetic hydrate inhibitor poly(n-vinylcaprolactam)".chemical Engineering Science. Vol., No.,. [] Englezos, Clathrate Hydrates, Ind. Eng. Chem. Res.,Vol., 99. [] Kvenvolden, K. A.. "A primer on gas hydrate",he Future of Energy Gases. US Geological Survey Professional Paper 57, 99. [] Sloan, E.D. and Koh, C.A., Clathrate Hydrates of Natural Gases,Press Publishers,8. [] Erik M. Freer. Methane Hydrate Formation Kinetics. hesis of Master of Science in Chemical and Petroleum-Refining Engineering. Faculty and the Board of rustees of the Colorado School of Mines,.