Commercial Kinetic Hydrate Inhibitor Research Articles

Kinetic Gas Hydrate Inhibition by Alternating Dipeptoids with Optimal Size and Shape N-Substituents.

Current commercial kinetic hydrate inhibitors (KHIs) are all based on water-soluble polymers with amphiphilic alkylamide or lactam groups. The size and shape of the hydrophobic moiety are known to be critical for optimum KHI performance. Proteins and peptides represent an environmentally friendly alternative, especially as bioengineering could be used to manufacture a product predetermined to have optimum KHI performance. Here, we explore a new series of polymers that are alternating dipeptoids where one of the peptide links originates from glycine. The dipeptoids contain n-propyl groups on the nitrogen atom and varying size and shape alkyl side chains on the neighboring carbon atom. Experiments were carried out in high-pressure steel rocking cells using the slow constant cooling (SCC) test method (1 °C/h) and a synthetic natural gas mixture. All the dipeptoids showed good KHI performance with the best result being for that with a glycine-N-propylleucine repeating unit (Poly iC4-Pr), which has pendant iso-butyl groups on the carbon atom. It exhibited the same KHI performance as poly(N-vinyl caprolactam). Dipeptoids with smaller or longer alkyl groups than iso-butyl gave worse performance. It is conjectured that the iso-butyl group is the optimal carbon length for this polymer class. In addition, the end-branching maximizes the van der Waals interaction with open cavities on growing hydrate particles, which must occur without loss of hydrogen-bonding from the neighboring peptide linkage for optimum KHI performance. Thus, the study provides further evidence for the premise that good KHI molecules must contain multiple amphiphilic groups (often as polymers) with optimal size and shape hydrophobic groups adjacent to strong hydrogen bonding groups. The solvent, n-butyl glycol ether, was shown to be a synergist for Poly iC4-Pr, lowering the onset temperature of hydrate formation in SSC tests relative to the polymer alone.

Hydrate formation and deposition behaviors with kinetic inhibitors under pseudo multiphase flow

With the successful application of kinetic hydrate inhibitors (KHIs) on hydrate plug prevention, there is a growing trend towards the development of affordable and environmentally friendly KHIs for solving challenges of high cost and inadequate biodegradability from their commercial KHIs. Therefore, further evaluation on the inhibitory effect of the developing inhibitors is needed under multiphase flow conditions. In this study, a high-pressure, fully visible rocking cell were used to simulate the multiphase transportation and both commercial KHIs and environmentally friendly KHIs were considered. Under the flow conditions of 60 % liquid loading and 20 % water cut, the results demonstrated that PVCap showed excellent inhibition performance with no hydrate formation at concentrations of 0.5 wt%, 0.2 wt% and 0.1 wt%. Although pectin exhibited certain inhibitory effect on hydrate growth rate and formation quantity, but it demonstrated a strong promoting effect on hydrate nucleation opportunities and rates. However, sodium alginate, which shares similar hydrate inhibition characteristics with pectin, exerted significantly promotional effects in terms of induction time, growth rate, and water conversion. Furthermore, the addition of pectin and sodium alginate led to the formation of hydrate balls in several test runs, resulting in complete pipeline blockage. Another noteworthy discovery was the relationship between the growth rate and final water conversion of hydrates, which exhibited an initial increase followed by a decrease, while the induction time exhibits an inverse trend, as the flow velocity increased.

Improved Gas Hydrate Kinetic Inhibition for 5-Methyl-3-vinyl-2-oxazolidinone Copolymers and Synergists.

Kinetic hydrate inhibitors (KHIs) are used to prevent deposits and plugging of oil and gas production flow lines by gas hydrates. The key ingredient in a KHI formulation is a water-soluble amphiphilic polymer. Recently, polymers of a new commercially available 5-ring vinylic monomer 5-methyl-3-vinyl-2-oxazolidinone (VMOX) were investigated as KHIs and shown to perform better than some commercial KHI polymers such as poly(N-vinyl pyrrolidone). This initial study using slow constant cooling (SCC) in rocking cells with a synthetic natural gas has now been expanded to further explore low molecular weight PVMOX homopolymers and VMOX copolymers as well as blends with nonpolymeric synergists. A PVMOX homopolymer with improved KHI performance was found using 3-mercaptoacetic acid as a chain transfer agent in the radical polymerization of VMOX. Among a range of copolymers, VMOX:n-butyl acrylate copolymers in particular gave good KHI performance, better than the PVMOX homopolymer. Among the potential synergists, trialkylamine oxides (alkyl = n-butyl or iso-pentyl) and tetra(n-pentyl)ammonium bromide to 2500 ppm were found to be antagonistic with PVMOX at the test concentrations while some alcohols and glycols were synergetic. The best synergist was 2,4,7,9-tetramethyl-5-decyne-4,7-diol (TMDD). For example, a mixture of 2500 ppm TMDD with 2500 ppm PVMOX (Mw 2400 g/mol) performed significantly better than 5000 ppm PVMOX. Addition of 1250 ppm TMDD to 2500 ppm VMOX:n-butyl acrylate 6:4 copolymer lowered the hydrate onset temperature in SCC tests by a further 3 °C compared to the copolymer alone giving hydrate onset at 4.2 °C.

Kinetic Hydrate Inhibition by Lambda-Carrageenan and Its Synergistic Compositions with Ethylene Glycol, 4-Methyl-1-Pentanol, Polyvinylpyrrolidone, and Polyvinylcaprolactam

For the oil and gas industry to function smoothly, it is essential to have a continuous flow of oil and gas in pipelines without interruptions caused by hydrate blockages. Kinetic hydrate inhibitors (KHIs) are becoming popular as they offer safe and effective hydrate inhibition at low dosages (0.5–2 wt % of the water content). The current commercial KHIs are synthetic and poorly biodegradable, which causes disposal concerns for environmental regulators. The lack of natural, sustainable, and biodegradable KHIs opens the scope to develop natural and biodegradable KHI alternatives. This study investigates the use of a natural and biodegradable polysaccharide, lambda carrageenan (λ-crgn), as a standalone KHI and its combinations with biodegradable solvents mono ethylene glycol and 4-methyl-1-pentanol and commercial KHI polymers (PVP and PVCap) for improved biodegradability and performance. λ-crgn is an environmentally friendly polysaccharide derived and cultivated from red seaweeds. Two variants of λ-crgn, one with a smaller mean size and a lower viscosity (LV) and one with a larger mean size and a higher viscosity (HV), are tested for hydrate inhibition. The lower molecular size/viscosity variant, λ-crgn (LV), showed similar induction times and lower hydrate growth rates compared to PVP when used as a standalone KHI. However, the high-viscosity variant did not perform as well as PVP. λ-crgn (HV or LV), when blended with commercial KHIs (PVP and PVCap), synergized and led to an increase in induction times by up to 63% and a decrease in the hydrate growth rates by 73% compared to when only the commercial KHIs were used at the exact total dosages. When λ-crgn (HV or LV) was blended with solvents 4-methyl-1-pentanol or MEG, again a significant synergy was observed, leading to the hydrate inhibition performance that was found to be at par or better than the commercial KHIs (PVP and PVCap) at the exact total dosages.

Synergistic Kinetic Hydrate Inhibition of Pectin, PVP, and PVCap with Monoethylene Glycol

Before injecting any kinetic hydrate inhibitor (KHI) into a flow line, the standard procedure is to dissolve the chemical, which is mostly a polymer, in a solvent such as water, methanol, or glycol. It is ideal if the solvent synergizes with the KHI in hydrate inhibition. In this paper, the synergy of three KHIs, poly(vinylpyrrolidone) (PVP), poly(vinyl caprolactam) (PVCap), and a natural biodegradable polymer Pectin at 0.25 wt %, is investigated with one of the common solvents monoethylene glycol at concentrations (0.5–20 wt %). The hydrate-inhibiting performance of the KHIs and their solvent blends is evaluated using an autoclave to measure the induction time (IT) and the molar hydrate growth rate, which is approximately taken equal to the molar gas consumption rate (HGR/GCR) in constant cooling rate tests and isothermal tests. The individual hydrate inhibition testing results showed that MEG alone at high dosages (up to 20 wt %) is a very poor KHI, while Pectin is a moderate KHI with performance lower than the commercial KHIs (PVP and PVCap) at similar concentrations. The hydrate growth rate of Pectin is however, lower compared to that of both PVP and PVCap. The blends of the KHIs with MEG, showed significant hydrate inhibition synergy in all of the KHI–MEG blends with increasing MEG concentration from 0.5 to 20 wt %. The synergy was maximum at 5 wt % of MEG for all the KHIs with IT enhancement of around 50% for PVP and PVCap and 200% for Pectin. Almost 30–60% reduction in HGR was observed in the blends compared to that of their individual KHI polymer HGRs. Isothermal experiments at 1.5, 6, and 8 °C were done using KHI–MEG blends to simulate possible field/subsea conditions. Among the three KHIs at 0.25 wt % blended with 5 wt % of MEG at 6 °C, PVP–MEG and Pectin–MEG blends gave an almost equal IT of 3.5 h, while the PVCap–MEG blend gave a slightly higher IT of 4.55 h. The HGR of the Pectin–MEG blend was however, the lowest (0.055 m/h) when compared to the PVP–MEG blend HGR (0.08 m/h) and the PVCap–MEG blend HGR (0.075 m/h). Similar IT but lower HGR values were found at 1.5 °C when 20 wt % of MEG with 0.25 wt % of Pectin was used. No hydrates were formed up to 6 days with 0.25 wt % of Pectin and 5 wt % of MEG at 8 °C due to a low subcooling of 1.3 °C. In summary, adding MEG to commercial KHIs such as PVP, PVCap and natural KHI Pectin increases their IT tremendously due to synergy and at the same time lowers their HGRs. As the blends of Pectin–MEG are highly biodegradable, they can be used at locations that have relatively low subcooling requirements and where biodegradability and lower hydrate growth rate are essential as they have similar ITs as that of PVP–MEG blends while lower HGRs than both PVP–MEG and PVCap–MEG blends.

Влияние желатина трески и альгината натрия на нуклеацию газовых гидратов

This work studied the effect of mixtures of fish gelatin (protein) from Atlantic cod skin and sodium alginate (polysaccharide) from brown algae on the nucleation of sII methane-propane hydrate. The rocking cell method with ramp cooling was employed to determine the supercooling required for the hydrates formation from solutions of individual polymers and their mixtures.Unlike sodium alginate, which has practically no effect on the formation of gas hydrates, the gelatin inhibitory activity was intermediate between polyvinylpyrrolidone and polyvinyl caprolactam (commercial kinetic hydrate inhibitors). In the caseof polymer blends, a slight decrease in the efficacy of gelatin at fixed content was observed as the sodium alginate concentration decreased. The results indicate the antagonism of the kinetic inhibition of methane-propane hydrate by mixtures of biological polyelectrolytes. Undoubtedly, intermolecular interactions in polysaccharide-gelatin complexes in solution affect the abilityof polymers to retard the nucleation process. A more detailed study of the kinetics of hydrate formation depending on the ratio of polymers in solution will make it possible to reveal the mechanism of their influence and to propose mixed reagentsto control the hydrate formation.

Synthesis and evaluation of poly (N-vinyl caprolactam)–co-tert-butyl acrylate as kinetic hydrate inhibitor

• A new KHI PVCap- co -TBA was synthesized and evaluated in different hydrate forming systems. • The relationship between the dosage of KHI and the inhibition performance was analyzed. • PPG was proposed as a good synergist for PVCap- co -TBA with concentration of 1.0 wt%. Low dosage kinetic hydrate inhibitors (KHIs) are a kind of alternative chemical additives to high dosage thermodynamic inhibitors for preventing gas hydrate formation in oil & gas production wells and transportation pipelines. In this paper, a new KHI, poly ( N -vinyl caprolactam)– co - tert -butyl acrylate (PVCap- co -TBA), was successfully synthesized with N -vinyl caprolactam (NVCap) and tert -butyl acrylate. The kinetic inhibition performances of PVCap- co -TBA on the formations of both structure I methane hydrate and structure II natural gas hydrate were investigated by measuring the onset times of hydrate formation under different conditions and compared with commercial KHIs such as PVP, PVCap and inhibex 501. The results indicated that PVCap- co -TBA outperformed these widely applied inhibitors for both structure I and structure II hydrates. At the same dosage of KHI, the maximum tolerable degree of subcooling under which the onset time of hydrate formation exceeded 24 hours for structure I hydrate was much lower than that for structure II hydrate. The inhibition strength increased with the increasing dosage of PVCap- co -TBA; The maximum tolerable degree of subcooling for the natural gas hydrate is more than 10 K when the dosage was higher than 0.5% (mass) while it achieved 12 K when that dosage rose to 0.75% (mass). Additionally, we found polypropylene glycol could be used as synergist at the dosage of 1.0 % (mass) or so, under which the kinetic inhibition performance of PVCap- co -TBA could be improved significantly. All evaluation results demonstrated that PVCap- co -TBA was a very promising KHI and a competitive alternative to the existing commercial KHIs.

The Effect of Nonionic Surfactants on the Kinetics of Methane Hydrate Formation in Multiphase System

Gas hydrate inhibitors have proven to be the most feasible approach to controlling hydrate formation in flow assurance operational facilities. Due to the unsatisfactory performance of the traditional inhibitors, novel effective inhibitors are needed to replace the existing ones for safe operations within constrained budgets. This work presents experimental and modeling studies on the effects of nonionic surfactants as kinetic hydrate inhibitors. The kinetic methane hydrate inhibition impact of Tween-20, Tween-40, Tween-80, Span-20, Span-40, and Span-80 solutions was tested in a 1:1 mixture of a water and oil multiphase system at a concentration of 1.0% (v/v) and 2.0% (v/v), using a high-pressure autoclave cell at 8.70 MPa and 274.15 K. The results showed that Tween-80 effectively delays the hydrate nucleation time at 2.5% (v/v) by 868.1% compared to the blank sample. Tween-80 is more effective than PVP (a commercial kinetic hydrate inhibitor) in delaying the hydrate nucleation time. The adopted models could predict the methane hydrate induction time and rate of hydrate formation in an acceptable range with an APE of less than 6%. The findings in this study are useful for safely transporting hydrocarbons in multiphase oil systems with fewer hydrate plug threats.

High-throughput sapphire reaction system: A new experimental apparatus to evaluate hydrate kinetic inhibitors with high efficiency

Kinetic hydrate inhibitors (KHIs) are one of the most promising methods to overcome the hydrate blockage issues in the oil and gas production and transportation pipelines, but the development and screening of KHIs is generally inefficient by the traditional high-pressure experimental equipment. This work proposed a new high-throughput sapphire reaction system that can efficiently evaluate the inhibition effects of KHIs by characterizing hydrate nucleation under desired conditions. The crucial experimental process parameters were initially optimized including the appropriate cooling and gas loading method, sample filling ratio and the number of repetitions. The inhibition effects of four commercial KHIs (Inhibex 501, Luvicap EG, VC 713 and PVP) were investigated by measuring the onset time for hydrate formation, which were found to be sensitive with the varying concentration and subcooling degree. The ranking order of the inhibition capacity for these KHIs was consistent with that obtained from the traditional high-pressure stirred reaction system and also with the previous researches, indicating the high reliability for this new experimental equipment. Overall results proposed a potential step-by-step KHI screening procedure by the combined application of the new high-throughput sapphire reaction system, traditional stirred reaction system and flow loop, where the high-throughput sapphire reaction system would play a significant role in promoting the efficiency.

N-Vinyl Caprolactam/Maleic-Based Copolymers as Kinetic Hydrate Inhibitors: The Effect of Internal Hydrogen Bonding

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines, but they are some of the most expensive oilfield production chemicals. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups. Usually, in commercial KHI polymers, the hydrophilic part of these groups is the amide group. In addition, KHI polymers are often incompatible with film-forming corrosion inhibitors. Therefore, we sought to find cheaper but effective KHIs that could also act as a flow line corrosion inhibitor. Continuing earlier work from our group with maleic-based polymers, we have now explored maleic acid/N-vinyl caprolactam (MAcid/VCap) copolymers to introduce VCap, a well-known KHI monomer, together with the cheaper MA monomer. KHI performance screening tests were conducted under high pressure with a structure II-forming natural gas mixture in steel rocking cells using the slow (1 °C/h) constant-cooling test method. Surprisingly, the MAcid/VCap copolymer showed very poor KHI efficacy. GFN2-xTB molecular dynamics simulations revealed that MAcid/VCap exhibits intra-hydrogen bond networks that trap the polymer morphology in the globular form. In this scenario, the caprolactam ring is encapsulated inside the polymer structure due to the intra-hydrogen bonds and the hydrophobic interactions that minimize its ability to interact with the hydrate surfaces, which significantly reduces the MAcid/VCap kinetic inhibition performance. However, the polymer in such globular forms still displays an important amount of its carboxylic groups exposed to water, which explains the water solubility. In contrast to MAcid/VCap copolymers, maleimide derivatives with dibutylamino end groups were effective KHIs and even better with dibutylamine oxide end groups. A terpolymer of MA/VCap reacted with N,N-dibutylaminopropylamine followed by subsequent oxidation of the end groups to dibutylamine oxide and gave the best performance of any maleic-based polymer reported to date. The combination of caprolactam and dibutylamine oxide groups can be thought of as synergism within the same polymer, akin to the excellent synergy of the separate molecules, tributylamine oxide and PVCap.

Investigation of gas hydrate formation and inhibition in oil-water system containing model asphaltene

Gas hydrate and asphaltene are two major flow assurance issues that will cause severe plugging in the subsea transportation pipelines, but the detailed understanding of their interactions remains insufficient. Systematic experiments were performed in the present study to investigate the influence of light oil components and asphaltene on gas hydrate formation, and to evaluate the performance of commercial kinetic hydrate inhibitors (KHIs) in different oil-water systems. Results demonstrated the promotion effect of light oil on initial hydrate growth, and the inhibition effect of asphaltene particularly with the light oil solvent of toluene. The influence mechanisms of asphaltene were based on the weakening mass transfer of methane at the gas-liquid interface, and the adsorption of free methane in the bulk liquid phase, while the degree of inhibition on hydrate formation was not positively related to the total concentration of asphaltene. Results also indicated that light oil components can weaken the performance of KHIs, but the role of asphaltene was closed related to the type of KHIs and light oil solvent. The overall experimental results of gas hydrate formation in the asphaltene system are consistent with our previous molecular dynamics simulations researches. Meanwhile, it provides an implication that asphaltene may have a potential ability to help some KHIs recover their inhibition performance, and emphasizes the necessity in systematically considering the oil composition when attempting to develop and utilize KHIs in oil-water system.

Performance of Waterborne Polyurethanes in Inhibition of Gas Hydrate Formation and Corrosion: Influence of Hydrophobic Fragments.

The design of new dual-function inhibitors simultaneously preventing hydrate formation and corrosion is a relevant issue for the oil and gas industry. The structure-property relationship for a promising class of hybrid inhibitors based on waterborne polyurethanes (WPU) was studied in this work. Variation of diethanolamines differing in the size and branching of N-substituents (methyl, n-butyl, and tert-butyl), as well as the amount of these groups, allowed the structure of polymer molecules to be preset during their synthesis. To assess the hydrate and corrosion inhibition efficiency of developed reagents pressurized rocking cells, electrochemistry and weight-loss techniques were used. A distinct effect of these variables altering the hydrophobicity of obtained compounds on their target properties was revealed. Polymers with increased content of diethanolamine fragments with n- or tert-butyl as N-substituent (WPU-6 and WPU-7, respectively) worked as dual-function inhibitors, showing nearly the same efficiency as commercial ones at low concentration (0.25 wt%), with the branched one (tert-butyl; WPU-7) turning out to be more effective as a corrosion inhibitor. Commercial kinetic hydrate inhibitor Luvicap 55 W and corrosion inhibitor Armohib CI-28 were taken as reference samples. Preliminary study reveals that WPU-6 and WPU-7 polyurethanes as well as Luvicap 55 W are all poorly biodegradable compounds; BODt/CODcr (ratio of Biochemical oxygen demand and Chemical oxygen demand) value is 0.234 and 0.294 for WPU-6 and WPU-7, respectively, compared to 0.251 for commercial kinetic hydrate inhibitor Luvicap 55 W. Since the obtained polyurethanes have a bifunctional effect and operate at low enough concentrations, their employment is expected to reduce both operating costs and environmental impact.

Experimental and density functional theory computational evaluation of poly(N-vinyl caprolactam-co-butyl methacrylate) kinetic hydrate inhibitors

Natural gas hydrate inhibitor has been serving the oil and gas industry for many years. The development and search for new inhibitors remain the focus of research. In this study, the solution polymerization method was employed to prepare poly(N-vinyl caprolactam-co-butyl methacrylate) (P(VCap-BMA)), as a new kinetic hydrate inhibitor (KHI). The inhibition properties of P(VCap-BMA) were investigated by tetrahydrofuran (THF) hydrate testing and natural gas hydrate forming and compared with the commercial KHIs. The experiment showed that PVCap performed better than copolymer P(VCap-BMA). However, low doses of methanol or ethylene glycol are compounded with KHIs. The compounding inhibitors show a synergistic inhibitory effect. More interesting is the P(VCap-BMA)-methanol system has a better inhibitory effect than the PVCap-methanol system. 1% P(VCap-BMA) + 5% methanol presented the best inhibiting performance at subcooling 10.3 °C, the induction time of natural gas hydrate was 445 min. Finally, the interaction between water and several dimeric inhibitors compared by natural bond orbital (NBO) analyses and density functional theory (DFT) indicated that inhibitor molecules were able to form the hydrogen bond with the water molecules, which result in gas hydrate inhibition. These exciting properties make the P(VCap-BMA) compound hydrate inhibitor promising candidates for numerous applications in the petrochemical industry.

High Cloud Point Polyvinylaminals as Non-Amide-Based Kinetic Gas Hydrate Inhibitors

In recent years, we have explored non-amide-based classes of kinetic hydrate inhibitor (KHI) polymers to determine if the same level of performance can be achieved as commercial KHI polymers, which...

Does the Cloud Point Temperature of a Polymer Correlate with Its Kinetic Hydrate Inhibitor Performance?

Most polymers used in commercial kinetic hydrate inhibitor (KHI) formulations show thermoresponsive behavior in aqueous solution. This means that they exhibit a cloud point (or lower critical solut...

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

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.

Evaluation of whey protein as a natural hydrate kinetic inhibitor

The toxicity of hydrate inhibitors used in the field has attracted more attention. A natural material, i.e., whey protein, was assessed to act as kinetic hydrate inhibitors (KHIs) in a sapphire cell and an autoclave equipped with particle video microscope (PVM) and focused beam reflectance measurement (FBRM) probes. The pressure dropping method was utilized to estimate the hydrate induction time, and the results demonstrate that the hydrate inhibition performance of whey protein is superior to that of the commercial KHI, polyvinylpyrrolidone. The induction time for the pure water system was found to increase linearly with the increase in the dosage of whey protein until it reached approximately 2.5 wt%. As it is usually inevasible to apply KHIs under conditions of high water contents, the feasibility of whey protein as a KHI in the (oil + water) system with and without an emulsifier of Tween 20 was evaluated. A small amount of oil was found to have no obvious influence on the induction time for the system with whey protein under the circumstances without the addition of emulsifier. When Tween 20 was added, the induction time obviously increased under the same operating conditions, which could be attributed to the emulsifier–protein interactions in aqueous solutions. The oil drops decrease and are distributed more evenly with the increasing dosage of Tween 20 under the PVM and FBRM probes measurement. Additionally, the particles decrease during the hydrate formation process. This work presents a natural KHI and gives the inhibition discipline in a high-water-content system.

A Review of Kinetic Hydrate Inhibitors from an Environmental Perspective

Kinetic hydrate inhibitors (KHIs) have been used in the upstream petroleum industry for about 25 years to prevent plugging of flow lines with gas hydrates. The main ingredients in current commercial KHI formulations are one or more water-soluble polymers which contain both hydrophobic and hydrophilic functionalities. Although the vast majority of KHIs are low in acute toxicity and bioaccumulation, very few commercial products show good biodegradability, and for that reason, there is always some concern of long-term chronic toxicity from partially degraded products if discharged into the environment. This report reviews all efforts to develop more biodegradable KHIs, and outlines the fact that some classes of so-called “green” chemicals are not necessarily readily biodegradable or low in toxicity. The review also covers methodologies to recover or destroy KHIs and reduce their discharge to the environment.

Poly(alkyl ethylene phosphonate)s: A New Class of Non-amide Kinetic Hydrate Inhibitor Polymers

All commercial kinetic hydrate inhibitor (KHI) formulations are based on polymers with amide (or imide) functional groups. In our continuing work to explore non-amide-based KHI polymers, a series of poly(alkyl ethylene phosphonate)s (PPns) has been synthesized. These polymers were investigated for their performance as KHIs in high-pressure rocking cells using a structure-II-forming gas mixture and the slow constant cooling test method over 24 h. All of the PPns gave better KHI activity than tests with no additive. However, despite several of the polymers being designed to have low cloud points, a factor that is often useful for good KHI performance, none of the PPns gave lower onset temperatures than poly(N-vinylcaprolactam), a well-known commercial KHI with a low cloud point. A random PPn copolymer with eight ethyl and eight n-hexyl groups gave a biodegradation of about 31% using the marine OECD 306 test protocol.