Thermodynamic Inhibitors Research Articles

Synergistic effect of salts and methanol in thermodynamic inhibition of sII gas hydrates

In this work phase equilibrium conditions for structure II (sII) gas hydrates in systems containing a mixture of salts (NaCl, KCl, CaCl2, MgCl2) and methanol have been measured using a high-pressure cell. The concentration of salts in aqueous solution (model of reservoir water) was constant in all experiments and equal to 18 wt%. Phase equilibrium conditions were determined by the isochoric method for pressures ranging from 1 to 4.7 MPa and for mass fraction of methanol from 0 to 50 wt%. The experimental data were obtained for water + salts, water + methanol, and water + salts + methanol systems. From the results obtained, it follows that 20 wt% of methanol in distilled water (DW) gives the thermodynamic shift of the hydrate decomposition temperature close to the brine one. Mixtures of 10% methanol + brine and 20% methanol + brine significantly better reduce the equilibrium temperature of hydrate dissociation compared to samples with the similar total mass fraction of inhibitor (methanol) in water (30, 40 wt%). At the pressures of more than 4 MPa combination of 20 wt% methanol + brine provide the same thermodynamic inhibition as 50 wt% of methanol in water. Thus, the synergism of the methanol + salts mixtures in the thermodynamic inhibition of sII gas hydrates has been observed. Synergism manifested itself in a greater shift of equilibrium curves to lower temperatures and higher pressures compared to systems containing only one thermodynamic hydrate inhibitor (THI). The obtained results indicate the possibility of a significant reduction in the consumption of polar organic THI for gas hydrate prevention in deposits with highly mineralized brine. However, it is necessary to take into account the possible complications associated with the precipitation of salts from solutions of water – salt(s) – polar organic THI due to the possible limited mutual solubility of the components.

MITIGATION OF METHANE HYDRATE BLOCKAGE IN SUBSEA PIPELINES USING IONIC LIQUID AS HYDRATE INHIBITOR

Gas hydrates one of a major problem in the oil and gas industry. Formation of gas hydrates causes flow assurance issues as it can plug the pipeline. The use of chemical inhibitors; kinetic hydrate inhibitors and thermodynamic hydrate inhibitors is one of the most feasible ways to solve this problem. However, the problem with thermodynamic inhibitors is that it required in a large dosage and cause environmental issues. Thus, this study emphasises on the usage of ionic liquid as an effective kinetic hydrate inhibitor. The ionic liquid is a green chemical that can be fine-tuned explicitly as a hydrate inhibitor. The aim is to study the effectiveness of 1-Ethyl-3-Methylimidazolium Tetrafluoroborate (EMIMBF4), an ionic liquid as a kinetic hydrate inhibitor at various pressure and concentration. Micro Differential Scanning Calorimeter was used to measure the induction time of methane hydrate. The performance of ionic liquid was tested in different concentration and compared to the commercial kinetic hydrate inhibitor, Polyvinylpyrrolidone (PVP). From the experimental work, it was found that EMIMBF4 shows a dynamic inhibition effect as it can delay the induction time of hydrate. EMIMBF4 shows a higher induction time at a low concentration of 0.1wt%. At the pressure of 60 bar, the effectiveness of EMIMBF4 is comparable with PVP. However, PVP shows superior kinetic inhibition effect at the pressure of 40 bar. This study indicates that an effective, green hydrate inhibitor can be developed to counter hydrate formation problems in offshore subsea pipelines in a more cost-effective and environmentally friendly
 Keywords: Methane Hydrate; Hydrate Inhibitor; Ionic Liquid; EMIMBF4; Micro DSC; pipeline blockage

Hydrate formation management simulations with anti-agglomerants and thermodynamic inhibitors in a subsea tieback

The rapid formation of gas hydrates in subsea tiebacks is regarded as one of the most challenging problems in flow assurance. Due to economic reasons, the hydrate controlling strategy has moved from hydrate avoidance to hydrate management. Efficient design of hydrate management techniques requires a better understanding of hydrate formation kinetics, as well as a robust transient hydrate simulation tool. In this work, we use a transient hydrate simulation tool with the ability of predicting hydrate formation in oil- and water-dominated systems simultaneously to capture complicated multiphase flow scenarios expected in oil and gas flowlines. This modeling tool can be applied to estimate hydrate formation in flowlines exhibiting both water- and oil-dominated environments at different locations, which is especially useful in modeling transient shut-in/restart operations as well as high water cut scenarios. This simulation tool can track the concentration of multiple thermodynamic inhibitors and consider the injection of anti-agglomerants through the cohesive force change between hydrate particles. This paper presents modeling results of a real black oil subsea tieback system, considering its geometry, production data and fluid properties. The hydrate formation rates and plugging risks at different water cuts, gas-oil ratios and liquid holdups were estimated both during steady state operation and shut-in/restart conditions. A hydrate blockage formed in the real field at 49 vol% water cut was successfully predicted using the transient hydrate prediction model. This simulation tool can be applied to predict the hydrate formation rate and amount under the complicated multiphase flow scenarios in oil/gas fields, and could be useful for the design and optimization of hydrate management approaches in flowlines.

Anomalous KHI-Induced dissociation of gas hydrates inside the hydrate stability zone: Experimental observations & potential mechanisms

In the past decade, the low dosage hydrate inhibitors (LDHIs) - which include kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs) - have seen increasing use for gas hydrate prevention in hydrocarbon production operations, offering significant CAPEX/OPEX advantages over traditional thermodynamic inhibitors (e.g. methanol, glycols). Typically dosed at < 2.5% in produced water, KHIs were historically considered primarily as hydrate nucleation inhibitors, although in recent years focus has shifted towards their powerful crystal growth inhibition properties. Beginning at low aqueous concentrations, KHI polymers induce a number of highly repeatable, well-defined, hydrate crystal growth inhibition (CGI) regions as a function of subcooling, varying from complete inhibition, through long induction times and reduced growth rates, to final failure/uninhibited growth. This behaviour can be used to robustly assess KHIs for field use, as we have previously demonstrated through development of the KHI CGI evaluation method, which is now used as standard by a number of laboratories. During CGI testing, it is not uncommon to observe anomalous (should be stable thermodynamically) hydrate dissociation in the presence of KHIs, although very little is understood regarding this phenomenon. In this work, we present the initial findings of experimental studies aimed at investigating this anomalous dissociation for different commercial base polymers. Results demonstrate that, in addition to inhibiting hydrate growth/nucleation, low dosages (e.g. 0.5% and 0.25%) of KHI polymers can induce partial or complete hydrate dissociation, with this process largely generic to different KHIs. However, some KHI polymers cause catastrophic hydrate growth after nucleation begins and these polymers show no ability to dissociate hydrates, so this hydrate dissociation ability is not universal to all KHI Polymers. The cause of this dissociation is unclear, although it is postulated to result from interactions between the KHI and inherent hydrate morphological and/or structural changes. In addition to improving confidence in KHI field use, findings potentially have novel applications with respect to hydrate plug remediation and gas production from naturally occurring hydrates in oceanic/permafrost sediments.

Carboxymethylcellulose sodium salt – effective “green” regent for management of calcium carbonate crystallization and nat-ural gas hydrate formation

The effect of carboxymethylcellulose sodium salt (NaCMC) with molecular masses (Mw) of 90, 250 and 700 thousand on the crystallization of CaCO3 polymorphs, their size and deposition on the surface of stainless steel from supersaturated aqueous solution at 80 ° C was studied. As a result of specific reversible adsorption, when forming crystalline nuclei formed, it is assumed that NaCMC changes the shape of the growing crystal, preferably forming vaterite — up to 95% in the presence of NaCMC with a molecular mass of 90 thousand during the in-teraction of CaCl2 and NaHCO3. In the presence of Mg2+ ions, CaCO3 is formed mainly in the form of aragonite, and the influence of the molecular mass of NaCMC is significantly reduced. It was established that NaCMC with Mw 90 and 250 thousand inhibits the aggregation and ag-glomeration of CaCO3 crystals, leading to a decrease in the average size of crystals from 24 to 10.6 and 16.5 microns, respectively. Under the action of NaCMC with a molecular mass of 700 thousand, on the contrary, an increase in the size of crystals to 37.2 μm is observed. It is shown that NaCMC with Mw 90 and 250 thousand slows down the speed and changes the conditions of gas hydrate formation, showing the properties of a thermodynamic and kinetic inhibitor with an efficiency that exceeds methanol by 300-450 times when used in the same dosages. The da-ta obtained indicate the promise of creating new “green” reagents of complex action for oil and gas production on the basis of sodium salt carboxymethylcellulose.

Frontispiece: Application of In Situ Product Crystallization and Related Techniques in Biocatalytic Processes

Biocatalytic reactions have become a potent alternative to conventional chemical catalysts for the synthesis of a wide variety of valuable organic compounds. In the Minireview on page 4871 ff. J. von Langermann et al. discuss product crystallization as a powerful technique to overcome fundamental limitations in biocatalytic reactions, with special emphasis on its use for in situ product crystallization (ISPC) to overcome unfavorable thermodynamic reaction equilibria, inhibition, and undesired reactions.

Phase Equilibrium of Methane Hydrate in Aqueous Solutions of Polyacrylamide, Xanthan Gum, and Guar Gum

The use of water-soluble polymers as natural gas hydrate inhibitors has gained interest in recent years. Variety of polymers have been studied for their kinetic performance in methane hydrate inhibition in the past; however, thermodynamic hydrate inhibition by water-soluble polymers is not fully understood and needs further investigation. This study investigates the effect of molecular weights and concentrations of aqueous solutions of various oilfield water soluble polymers on phase equilibrium of methane hydrate. Water-soluble polymers, such as polyacrylamide (PAM), xanthan gum (XG), and guar gum (GG) with two different molecular weights and varying concentrations, have been considered for the investigations. These are as follows: PAM (Mw: 1.1 × 106 g/mol, PAM-1 and 1.5 × 105 g/mol, PAM-2), XG (Mw: 6.4 × 105 g/mol, XG-1 and 2.4 × 105 g/mol, XG-2), and GG (Mw: 1.7 × 106 g/mol, GG-1 and 6 × 105 g/mol, GG-2), with varying concentrations of 100, 200, and 500 ppm each. These are referred to as high-molecular...

Reviews of gas hydrate inhibitors in gas-dominant pipelines and application of kinetic hydrate inhibitors in China

Abstract During the development and application of natural gas, hydrate plugging the pipelines is a very important issue to solve. Currently, adding thermodynamic hydrate inhibitors (THIs) and kinetic hydrate inhibitors (KHIs) in gas-dominated pipelines is a main way to prevent hydrate plugging of flow lines. This paper mainly reviews the efforts to develop THIs and KHIs in the past 20 years, compare the role of various THIs, such as methanol, ethylene glycol and electrolyte, and give the tips in using. The direction of KHIs is toward high efficiency, low toxicity, low pollution and low cost. More than a hundred inhibitors, including polymers, natural products and ionic liquids, have been synthesized in the past decade. Some of them have better performance than the current commercial KHIs. However, there are still few problems, such as the complex synthesis process, high cost and low solubility, impeding the commercialization of these inhibitors. The review also summarized some application of KHIs in China. Research of KHIs in China began late. There are no KHIs used in gas pipelines. Only a few field tests have been carried out. In the end of this paper, the field test of self-developed KHIs by China is summarized, and the guidance is given according to the application results.

Inhibitory effects of novel green inhibitors on gas hydrate formation

Abstract Natural gas hydrates easily form in pipelines, causing potential safety issues during oil and gas production and transportation. Injecting gas hydrate inhibitors is one of the most effective methods for preventing gas hydrate formation or aggregation. However, some thermodynamic hydrate inhibitors are toxic and harmful to the environment, whereas degradation of kinetic inhibitors is difficult. Therefore, environmentally friendly and easily biodegradable novel green inhibitors have been proposed and investigated. This paper provides a short but systematic review of the inhibitory performance of amino acids, antifreeze proteins, and ionic liquids. For different hydrate formation systems, the influences of the inhibitor type, structure, and concentration on the inhibitory effects are summarized. The mechanism of green inhibitors as kinetic inhibitors is also discussed. The progress described here will facilitate further developments of such green inhibitors for gas hydrate formation.

Phase equilibrium measurement and modeling approach to quaternary ammonium salts with and without monoethylene glycol for carbon dioxide hydrates

This experimental work evaluates the thermodynamic hydrate inhibition behavior of three quaternary ammonium salts (QAS) namely tetra ethyl ammonium iodide (TEAI), tetra methyl ammonium bromide (TMAB) and tetraethyl ammonium bromide (TEAB) for carbon dioxide (CO2) hydrates. The Hydrate Liquid Vapor Equilibrium (HLVE) data for CO2 are evaluated through T-cycle method at different temperature (275–283 K) and pressure (2.0–3.50 MPa) conditions in the presence and absence of 5 and 10 wt% aqueous QAS and QAS + MEG solutions. Among all the considered compounds, the inhibition effect of TMAB was found to be the best in pure as well as in mixture with MEG therefore, extended further for 1 wt% also along with 5 and 10 wt%. The inhibition effect including average suppression temperature (ΔŦ) and dissociation enthalpies (ΔHdiss) for hydrate formation are also calculated for the systems taken into consideration. Additionally, a thermodynamic model offered by Dickens and Quinby-Hunt has been used for the prediction of HLVE temperatures of CO2 gas for the considered systems. The results obtained from experimental and modeling data indicate that pure QAS and their mixtures with MEG perform efficiently as thermodynamic hydrate inhibitor for CO2 gas. Therefore, the use of these compounds in thermodynamic inhibition of CO2 hydrates systems can lead towards their application in flow assurance strategies.

An in situ method on kinetics of gas hydrates

Gas hydrate formation is a high-risk and common flow assurance problem in subsea oil production plants. The modern strategies to mitigate hydrate formation have switched from thermodynamic inhibition to risk management. In this new mitigation strategy, hydrate formation is allowed as long as it does not lead to plugging of pipelines. Thus, understanding the growth kinetics of gas hydrates plays a critical role in risk management strategies. Here, we report a new accurate and in situ approach to probe the kinetics of gas hydrate formation. This approach is based on the hot-wire method, which probes the thermal properties of the medium surrounding the hot-wire. As the thermal properties of gas hydrate and its initial constituents are different, variation in these properties is used to probe kinetics of hydrate growth front. Through this in situ method, we determine kinetics of cyclopentane hydrate formation in both mixing and flow conditions. The findings show that at ambient pressure and a temperature of 1-2 °C, the hydrate formation rate under mixing condition varies between 1.9 × 10-5 and 3.9 × 10-5 kg m-2 s-1, while in flow condition, this growth rate drops to 4.5 × 10-6 kg m-2 s-1. To our knowledge, this is the first reported growth rate of cyclopentane hydrate. This in situ approach allows us to probe kinetics of hydrate formation where there is no optical access and provides a tool to rationally design risk management strategies for subsea infrastructures.

Application of novel High Molecular Weight amine donors in chiral amine synthesis facilitates integrated downstream processing and provides in situ product recovery opportunities

Abstract The immense potential of transaminase-catalyzed reactions for chiral amine synthesis is often hampered by unfavorable thermodynamic equilibrium positions and product inhibition issues. In the here presented proof of concept, we demonstrate a membrane assisted strategy for addressing these challenges. It involves a separation based on differently sized amine donor and amine product molecules. Novel High Molecular Weight (HMW) amine donors, provided in excess for thermodynamic equilibrium shifting, are successfully employed in transaminase-catalyzed reactions and are effectively retained by commercial nanofiltration membranes by a size exclusion mechanism. Retention of HMW amine donors combined with selective product removal, in batch mode, shifted the equilibrium enhancing substrate conversion by an additional 25% compared to the control reaction. Along with the potential of this approach, certain limitations were also revealed in this study. Only few of the investigated enzymes accepted the HMW donor molecules, and along with very efficient amine product removal, there was undesirable loss of ketone substrate. Therefore, a broader enzyme screening, and the selection of a selective and solvent stable membrane, is essential for better and broader applicability of the concept.

Raman Spectroscopic Study of the Effect of Aqueous Salt Solutions on the Inhibition of Carbon Dioxide Gas Hydrates.

We present an experimental Raman study on the thermodynamic inhibition effect of different salts (NaCl, KCl, MgCl2, and CaCl2 from 2.5 to 11 wt %) on the formation of carbon dioxide gas hydrates. We performed the experiments in a high-pressure vessel with two phases: a water-rich phase and a CO2-rich phase. We investigated the changes the inhibitors induce in the water-rich phase before the onset of hydrate formation. This includes a study of the change in molar reaction enthalpy between strongly and weakly hydrogen-bonded water and the decrease in solubility of carbon dioxide in water. Additionally, the growth mechanisms of carbon dioxide hydrates were investigated by determining the amount of solid hydrates formed and the reaction constant. The results show that the molar reaction enthalpy, the solubility of CO2, and the amount of solid hydrates formed can be correlated with the effective mole fraction, whereas the reaction constant is not affected by the addition of salts. The decrease of the molar reaction enthalpy can be directly correlated with the equilibrium temperature of the gas hydrates.

Economic leverage affords post-combustion capture of 43% of carbon emissions: Supersonic separators for methanol hydrate inhibitor recovery from raw natural gas and CO2 drying

Offshore oil/gas productions are power intensive and CO2 emitters from gas-fired power generation. This work investigates supersonic separator as a strategy for affording post-combustion capture backed up by cost reductions. Conventional offshore gas processing usually loses thermodynamic hydrate inhibitor methanol in processing and exported gas. This work analyses a supersonic separator variant gas processing simultaneously reducing methanol losses. Such process dramatically improves gas-plant profitability via cost-reduction of methanol make-up and power-consumption, simultaneously increasing revenues from liquefied-petroleum-gas by-product. This economic leverage affords post-combustion carbon capture, including subsequent CO2 dehydration and compression for exportation of high-pressure liquid CO2. This corresponds to abate 43% of CO2 emissions boosting revenues via enhanced oil recovery. Moreover, CO2 is dehydrated via another supersonic separator operating with minimum head-loss, minimizing compression costs. Despite its much higher investment, the new process with carbon capture presents higher net value (865.63 MMUSD) than the conventional processing without carbon capture (829.31 MMUSD), being economically feasible and more environmentally adequate with cleaner natural gas production and successful CO2 management. The new process is superior in several scenarios and particularly favored by oil prices above 55 USD/bbl. Rising oil price from 40 to 100 USD/bbl, the new process net value rises 29%, whereas the conventional counterpart rises only 7.5%. In addition, as a plausible future scenario, CO2 taxation favors the new process, which always has superior economic performance, even without CO2 taxation. In summary, implementing supersonic separators in offshore natural gas processing aiming at anti-hydrate recovery and CO2 dehydration for enhanced oil recovery creates economic leverage sustaining Carbon Capture & Storage without loss of competitiveness. This result, backed up by rigorous thermodynamic simulations and economic-environmental assessments, configure an original achievement to the literature.

Equilibrium conditions of xenon hydrates in the presence of water-soluble additives of dimethyl sulfoxide, amides and amines

Equilibrium conditions of clathrate hydrates formed from xenon and aqueous solutions of dimethyl sulfoxide (DMSO), formamide, acetamide, isobutylamine and pyrrolidine were experimentally measured up to 1.0 MPa using an isochoric method. Adding DMSO, formamide and acetamide shifted the xenon hydrate equilibria toward low temperature, indicating that these additives acted as thermodynamic hydrate inhibitors. The inhibiting effects of the additives were almost as strong as those of methanol and ethylene glycol on a mole basis. In contrast, isobutylamine and pyrrolidine had promoting effects on xenon hydrate formation. The promoting effects were stronger than that of acetone but weaker than that of 1,3-dioxolane.

Application of In Situ Product Crystallization and Related Techniques in Biocatalytic Processes.

This Minireview highlights the application of crystallization as a very powerful in situ product removal (ISPR) technique in biocatalytic process design. Special emphasis is placed on its use for in situ product crystallization (ISPC) to overcome unfavorable thermodynamic reaction equilibria, inhibition, and undesired reactions. The combination of these unit operations requires an interdisciplinary perspective to find a holistic solution for the underlying bioprocess intensification approach. Representative examples of successful integrated process options are selected, presented, and assessed regarding their overall productivity and applicability. In addition, parallels to the use of adsorption as a very similar technique are drawn and similarities discussed.

Effect of Fulvic Acid and Sodium Chloride on the Phase Equilibrium of Methane Hydrate in Mixed Sand–Clay Sediment

The phase equilibrium conditions for methane hydrate in mixed sand–clay sediment with the presence of fulvic acid (FA) and sodium chloride (NaCl) were measured using the multistep heating method. The experiments were conducted at the temperatures from 281.45 to 290.65 K and pressures from 6.33 to 17.39 MPa, respectively. The mixed sand–clay porous media and aqueous solutions containing 2.0, 6.0, and 10.0 wt % FA and 3.0 wt % NaCl were used. The experimental results indicate that the phase equilibrium curve of methane hydrate in mixed porous media shifts to the left side as compared to that in bulk solutions because of the capillary force and hydrophilic surfaces of porous media. FA is a thermodynamic inhibitor for methane hydrate formation as the −COO– and short alkyl substituent of FA could compete with hydrate for water molecules, and the inhibition effect of FA on methane hydrate formation is weaker as compared to 3.0 wt % NaCl under all studied concentration conditions. The phase equilibrium pressures...

Inhibitory effect of water-based drilling fluid on methane hydrate dissociation

Hydrate dissociation poses a significant problem during drilling operations in hydrate-bearing sediments. The drilling fluid is in direct contact with hydrates, and understanding its inhibitory effect on hydrate dissociation is important for stabilizing hydrates during drilling operations. In this work, an apparatus was designed for investigating hydrate dissociation in drilling fluids, and the effects of thermodynamic hydrate inhibitors (THIs), polyvinyl pyrrolidone (PVP), and soybean lecithin on hydrate dissociation were studied. The inhibitory effect of a water-based drilling fluid in the presence of the potential hydrate dissociation inhibitors was also studied. An unexpected inhibitory effect occurred with ethylene glycol (EG) at concentrations below 10 wt%, resulting from a range of factors including the dissociation driving force, and mass and heat transfers in the EG solution. PVP and lecithin reduced the hydrate dissociation rate and increased the time required for complete dissociation of hydrates. These can, therefore, be used in water-based drilling fluids to inhibit hydrate dissociation. A combination of 0.1 wt% PVP and 0.5 wt% lecithin was selected as an optimal hydrate dissociation inhibitor, considering its inhibitory effect and compatibility with the drilling fluid. Using EG at a concentration below 10 wt% as a THI instead of NaCl can also help inhibit hydrate dissociation. The findings of this work provide a basis for the development and design of drilling fluids for drilling in hydrate-bearing sediments.

Synergism of Methanol and Magnesium Chloride for Thermodynamic Inhibition of Methane Hydrate

Mixtures of magnesium chloride and MeOH were studied as mixed thermodynamic inhibitors of hydrate formation. The equilibrium P,T-conditions for methane hydrate decomposition in the presence of binary solutions H2O—MeOH and H2O—MgCl2 and ternary solutions H2O—MeOH—MgCl2 were determined using an isochoric method in a stirred autoclave. Measurements were made at pressures of 3.5-9.5 MPa; MeOH concentrations, 0-25 mass%. The salt content in the aqueous solutions was constant at 5 mass%. The results showed that mixed samples containing MeOH and MgCl2 gave the largest thermodynamic shifts of hydrate formation as compared to samples with MeOH at the same inhibitor mass fraction. The larger thermodynamic shift was related to synergism between the affects of MgCl2 and MeOH in the aqueous solution.

Thermodynamic, Adsorption and Corrosion Inhibition Studies of Mild Steel by Artemisia vulgaris Extract from Methanol as Green Corrosion Inhibitor in Acid Medium

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