Kinetic Hydrate Inhibitors Performance Research Articles

Comparing the Kinetic Hydrate Inhibition Performance of Linear versus Branched Polymers.

Kinetic hydrate inhibitors (KHIs) are a chemical method of preventing gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation is one or more water-soluble amphiphilic polymers. Poly(N-vinyl caprolactam) (PVCap) is an unbranched polymer and a well-known industrial KHI, often used as a yardstick to compare the performance of new polymers. The effect of branching PVCap on KHI performance has been investigated by polymerizing the VCap monomer in the presence of varying amounts of trimethylolpropane triacrylate, pentaerythritol tetraacrylate, or bis-pentaerythritol hexaacrylate cross-linkers to give PVCap polymers with 3, 4, and 6 branches, respectively. If the ratio of cross-linker to VCap was too high (6:1 to 8:1), gelling and/or poor water solubility was observed, giving short polymer chains and poor KHI efficacy. For higher ratios (30:1 to 60:1), it was found that the concentration of the polymer needed to give total inhibition of structure II tetrahydrofuran hydrate crystal growth could be lowered by using tribranched rather than linear PVCap. Slow constant cooling (1 °C/h) gas hydrate experiments with a synthetic natural gas in steel rocking cells at 76 bar were also carried out. A small improvement in KHI performance was observed for one of the branched PVCaps compared with a linear PVCap. Branched and linear poly(N-isopropylmethacrylamide) (PNIPMAm) polymers were also investigated in the gas hydrate system, but there was no benefit observed when branching this polymer class.

Improved industrial induction time-based technique for evaluating kinetic hydrate inhibitors.

Kinetic hydrate inhibitor laboratory testing before field application is one of the key priorities in the oil and gas industry. The common induction-time-based technique is often used to evaluate and screen for kinetic hydrate inhibitors (KHIs). However, the main challenge relates to the stochastic nature of hydrate nucleation observed in fresh systems, which often results in scattered data on hydrate formation with unacceptable uncertainties. A much more precise KHI evaluation method, called crystal growth inhibition (CGI), provides comprehensive insights into the inhibitory behavior of a kinetic hydrate inhibitor, including both hydrate formation and decomposition. Given that industry does not require this much information, it is not feasible to expend either much time or cash on this strategy. This study aims to provide a cost-effective technique that presents maximum data accuracy and precision with relatively little time and cost expenditure. Hence, the impact of water-hydrate memory on improving the accuracy and repeatability of the results of the induction-time-based technique (IT method) was examined. First, the concept of water-hydrate memory, which contains information about how it is created, was reviewed, and then, the factors influencing it were identified and experimentally investigated, like the heating rate of hydrate dissociation and the water-hydrate memory target temperature during heating. Finally, a procedure was developed based on the background information in the earlier sections to compare the consistency of the results, originating from the conjunction of water-hydrate memory with the IT technique. The results of replications at KHI evaluation target temperatures of 12.3-12.4°C and 11.5-11.7°C showed that more repeatable data were obtained by applying water-hydrate memory, and a more conclusive decision was made in evaluating KHI performance than with an IT method. It seems that combining the IT method with water-hydrate memory, introduced as the "HME method", can lead to more definitive evaluations of KHIs. This approach is expected to gain in popularity, even surpassing the accurate but complex and time-consuming CGI method.

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.

High-Performance Kinetic Hydrate Inhibition with Poly(N-isopropyl methacrylamide) and Triisopentylamine Oxide─Surprising Concentration-Dependent Results

Kinetic hydrate inhibitors (KHIs) are mostly used to prevent the deposition of gas hydrates in gas and condensate production flow lines. The main component in a KHI formulation is a water-soluble polymer, blended with solvents and other synergists to boost the performance. The performance limit in terms of subcooling and other factors restricts the application range of KHIs. Earlier, we reported on the synergetic performance of trialkylamine oxides with polyalkyl(meth)acrylamides using high-pressure steel rocking cell experiments. In particular, blends of poly(N-isopropyl methacrylamide) (PNIPMAm) in isobutyl glycol ether (iBGE) with triisopentylamine oxide (TiPeAO) gave exceptional KHI performance, better than what we have seen for any other KHI blend so far. Therefore, it is important to evaluate the limitations of this KHI. Here, we report the results of the KHI performance of this blend in more detail. The cloud point decreased with increasing salinity (0–15 wt % NaCl), but the blend remained soluble, giving excellent KHI performance even at the highest brine concentration. We also varied the concentration of the PNIPMAm/TiPeAO blend from 250 to 5000 ppm in deionized water in KHI slow constant cooling (SCC) tests using both a natural gas mixture [synthetic natural gas (SNG)] and methane gas. A unique concentration-dependent performance was discovered, wherein the performance decreased greatly above about 1500–2000 ppm, possibly due to aggregation of the polymer and amine oxide. This was observed for SCC tests with both SNG and methane, with the phenomenon being more pronounced for methane. In addition, an unusual double pressure drop was observed in SCC tests with methane and a blend of 5000 ppm PNIPMAm and TiPeAO. This study underlines the fact that overdosing of components in a synergistic blend can sometimes lead to detrimental effects on the KHI performance.

Maleic and Methacrylic Homopolymers with Pendant Dibutylamine or Dibutylamine Oxide Groups as Kinetic Hydrate Inhibitors.

Kinetic hydrate inhibitors (KHIs) are applied in oil and gas fields to prevent gas hydrate formation, most often in cold subsea flow lines. The main component in industrial KHI formulations is a water-soluble polymer with many amphiphilic groups of which the hydrophilic part is most commonly the amide functional group. In the last decade, we have investigated polyamine oxides as alternatives to polyamides due to the strong hydrogen bonding of the amine oxide group. Here, we report the KHI performance of maleic and methacrylic homopolymers with dialkylamine and dialkylamine oxide pendant groups. Performance screening experiments 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. Polymers with dibutylamine groups gave much better KHI performance than polymers with dimethylamine or diethylamine groups. Polyamines formed from polymaleic anhydride reacted with 3-(dibutylamino)-1-propylamine (DBAPA) or 2-(dibutylamino)-ethanol (DBAE) gave good water solubility and good KHI performance, probably due to self-ionization between the dibutylamino and carboxylic acid groups. The lack of self-ionization for the methacryl homopolymers of DBAPA and DBAE explains why these polymers are not water-soluble. Oxidation of the maleic or methacryl polyamines to polyamine oxides gave water-soluble polymers with good compatibility with brines (0.5-7.0 wt % NaCl), but only the DBAPA-based polyamine oxides gave improved KHI performance compared to the polyamines. Poly(3-(dibutylamino oxide)-1-propyl methacrylamide) gave a similar performance to commercial N-vinyl pyrrolidone:N-vinyl caprolactam 1:1 copolymer and without a cloud point in deionized water up to +95 °C.

Oxyvinylenelactam Polymers-A New Class of Lactam-Based Kinetic Hydrate Inhibitor Polymers.

The deployment of kinetic hydrate inhibitors (KHIs) is a chemical method for the prevention of gas hydrate plugging in gas, condensate, and oil production flow lines. Polymers made using the monomer N-vinylcaprolactam (VCap) are one of the most common KHI classes. Alternative classes of polymers containing caprolactam groups are rare. Here, we present a study on oxyvinylenelactam polymers and copolymers with pendant piperidone or caprolactam groups. Low-molecular-weight homo- and copolymers were obtained. The nonrotating vinylene groups impart rigidity to the polymer backbone. Poly(oxyvinylenecaprolactam) (POVCap) was insoluble in water, but poly(oxyvinylenepiperidone) (POVPip) and OVPip:OVCap copolymers with 60+ mol % OVPip were soluble with low cloud points. KHI screening tests were carried out using the slow constant cooling method in steel rocking cells. POVPip was water soluble with no cloud point up to 95 °C but showed a poor KHI performance. In contrast, OVPip:OVCap copolymers with about 60–70 mol % OVPip were also water soluble and showed a reasonable KHI performance, better than that of poly(N-vinylpyrrolidone) but not as good as that of poly(N-vinylcaprolactam). Surprisingly, several additives known to be good synergists for VCap-based polymers showed negligible synergy or were antagonistic with the 62:38 OVPip:OVCap copolymer with regard to lowering the onset temperature of hydrate formation. However, a blend with hexabutylguanidinium chloride showed a strong effect to delay the onset of rapid hydrate formation.

Nonpolymeric Citramide-Based Kinetic Hydrate Inhibitors: Good Performance with Just Six Alkylamide Groups.

The use of kinetic hydrate inhibitors (KHIs) is a well-known method for preventing gas hydrate formation in oil and gas production flow lines. The main ingredient in KHI formulations is one or more polymers with amphiphilic groups. Here, we report a series of citramide-based nonpolymeric KHIs. The KHI performance of these citramide derivatives has been studied using a synthetic natural gas mixture (forming structure II hydrate as the thermodynamically preferred phase) in slow constant cooling (ca. 1 °C/h starting from 20.5 °C) high-pressure (76 bar) rocking cell experiments. Isobutyl-substituted alkyl chains in the mono/bis(trialkyl citric acid) amide derivative gave better KHI performance than n-propyl-substituted citramide derivatives. Moreover, biscitramides with six alkylamide functional groups gave better performance than the equivalent monocitramides with three alkylamide groups. A solution of 2500 ppm of bis(tributyl citric acid) amide gave an average gas hydrate onset temperature (To) of 8.4 °C compared to 8.9 °C for a low molecular weight N-vinyl pyrrolidone/N-vinyl caprolactam 1:1 copolymer. For the bis(tributyl citric acid) amide, addition of liquid hydrocarbon (n-decane) lowered further the average To value to 6.2 °C, although this is at least partly due to lowering of the hydrate equilibrium temperature. This study demonstrates that good KHI performance can be obtained from molecules with as little as six amphiphilic alkylamide groups.

Alternative Lactam-Based Kinetic Hydrate Inhibitors─Investigation of Polymers of 2-Methacrylamido-caprolactam

Kinetic hydrate inhibitors (KHIs), such as poly(N-vinylcaprolactam) (PVCap) and related copolymers, are a well-known method to help combat gas hydrate formation in oil and gas field production flow lines. The caprolactam groups in this polymer class have been shown previously to have a particularly strong interaction with hydrate surfaces, inhibiting crystal growth, but probably also gas hydrate nucleation. In an earlier study, we reported on the first alternate KHI polymer class with pendant caprolactam groups based on the 2-methacrylamido-caprolactam (2-MACap) monomer. This report builds on that study, by optimizing the best copolymers from that study and copolymerizing 2-MACap with other comonomers. KHI experiments were carried out in high-pressure steel rocking cells using a structure II-forming natural gas mixture. The KHI performance of some of these copolymers exceeded that of PVCap of similar molecular weight. In addition, the importance of the methyl group in 2-MACap for enhanced KHI performance was confirmed by making and testing polymers with 2-acrylamido-caprolactam, which has no methylated backbone. Further confirmation from 2-MACap copolymers with 1-acryloylpyrrolidine and N-methacryloylpyrrolidine, for which the latter copolymer performed best. Finally, it was shown that a series of well-known synergists for PVCap were able to give excellent KHI performance enhancement of the selected 2-MACap copolymers, although some molecules showed antagonistic effects. This could be due to unhelpful polymer–synergistic interactions or both molecules competing in the same KHI mechanistic processes.

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.

5-Methyl-3-vinyl-2-oxazolidinone–Investigations of a New Monomer for Kinetic Hydrate Inhibitor Polymers

Kinetic hydrate inhibitors (KHIs) are polymers used in a chemical method to prevent gas hydrate plugging of oil and gas production flow lines. The main ingredient in a KHI formulation is one or more water-soluble amphiphilic polymers. Several classes of KHI polymers contain pendant heterocyclic 5-rings including poly(N-vinylpyrrolidone) (PVP) and poly(2-isopropenyl-2-oxazoline) (PiPOx). Here, we present a KHI performance study on polymers based on the 5-ring vinylic monomer 5-methyl-3-vinyl-2-oxazolidinone (VMOX), which has only recently been manufactured in large quantities. Low molecular weight PVMOX homopolymers were produced in quantitative yield using radical polymerization, with or without a chain transfer agent. For example, PVMOX-2.4k (Mn = 2400 g/mol) had a cloud point at 2500 ppm of 73 °C in deionized water. The polymers were screened for KHI performance using slow constant cooling tests (1.0 °C/h) in high-pressure rocking cells with a synthetic natural gas blend. At 2500 ppm, PVMOX-2.4k gave a better performance than PVP or PiPOx at a similar molecular weight but not as good as poly(N-vinylcaprolactam) (PVCap). Isobutyl glycol ether was shown to enhance the KHI performance of PVMOX. PVMOX gave improved performance with increasing concentration but not as steep of an improvement as some of the best amide-based KHI polymers. A 1:1 copolymer of VMOX with N-vinylcaprolactam gave improved performance compared to the PVMOX homopolymer.

Non-Amide Polymers as Kinetic Hydrate Inhibitors-Maleic Acid/Alkyl Acrylate Copolymers and the Effect of pH on Performance.

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines. The main component in KHI formulations is a water-soluble polymer with many amphiphilic groups, usually made up of amide groups and adjacent hydrophobic groups with 3–6 carbon atoms. KHI polymers are one of the most expensive oilfield production chemicals. Therefore, methods to make cheaper but effective KHIs could improve the range of applications. Continuing earlier work from our group with maleic-based polymers, here, we explore maleic acid/alkyl acrylate copolymers as potential low-cost KHIs. Performance experiments 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. Under typical pipeline conditions of pH (4–6), the performance of the maleic acid/alkyl acrylate copolymers (alkyl = iso-propyl, iso-butyl, n-butyl, tetrahydrofurfuryl, and cyclohexyl) was poor. However, good performance was observed at very high pH (13–14) due to the thermodynamic effect from added salts in the aqueous phase and the removal of CO2 from the gas phase. A methyl maleamide/n-butyl acrylate copolymer gave very poor performance, giving evidence that direct bonding of the hydrophilic amide and C4 hydrophobic groups is needed for good KHI performance. Reaction of the maleic anhydride (MA) units in MA/alkyl acrylate 1:1 copolymers with dibutylaminopropylamine or dibutylaminoethanol gave polymers with good KHI performance, with MA/tetrahydrofurfuryl methacrylate being the best. Oxidation of the pendant dibutylamino groups to amine oxide groups improved the performance further, better than poly(N-vinyl caprolactam).

Pushing the Known Performance Envelope of Kinetic Hydrate Inhibitors─Powerful Synergy of Trialkylamine Oxides with Acrylamide-based Polymers

Poly(N-isopropyl methacrylamide) (PNIPMAm) and copolymers are a class of commercially used kinetic hydrate inhibitors (KHIs) for deployment in oil and gas field production flow lines. Here, we report improvements of the KHI performance of PNIPMAm in the presence of various alkyl amine oxide (chain lengths C3–C6)-based synergists. A structure II hydrate-forming gas mixture was used to examine the KHI performance of PNIPMAm in slow constant cooling (ca. 1 °C/h) high-pressure (76 bar) rocking cell experiments. Blends of amine oxide as a synergist with PNIPMAm extended the hold time to first-detected gas hydrate formation. The KHI performance of PNIPMAm is improved going from propyl to butyl but is even better for pentyl, isopentyl, and isohexyl substituents on the amine-N-oxide. With added isobutyl glycol ether as the solvent, a solution of 1000 ppm low-molecular-weight (4700 g/mol) PNIPMAm (20.1% solution in isobutyl glycol ether) with 1000 ppm triisopentylamine oxide (TiPeAO) gave no detectable hydrate formation down to 2 °C. The same formulation in isothermal tests at 68 bar and 4 °C in the presence of externally added liquid hydrocarbon (n-decane) giving 15.5 °C subcooling gave no catastrophic hydrate formation for 48 h. These are the some of the best results we have seen in our steel rocking cells. Good synergy of TiPeAO with polyacryloylpyrrolidine was also observed but not as good as with PNIPMAm. The study also highlights that overdosing the polymer or synergist in the blends can worsen the KHI performance, probably by unwanted interaction between the two chemicals.

Further Investigation of Solvent Synergists for Improved Performance of Poly(N-vinylcaprolactam)-Based Kinetic Hydrate Inhibitors

Poly(N-vinylcaprolactam) (PVCap) and related copolymers have been used as kinetic hydrate inhibitors (KHIs) to combat gas hydrate formation in oil and gas field production flow lines. It is known that the addition of certain solvents to the KHI polymer can enhance its ability to hinder gas hydrate formation. In an earlier study, a wide range of alcohols, glycol ethers, and ketones were investigated as synergetic solvents with PVCap. In that study, an outstanding synergetic effect was achieved by 4-methyl-1-pentanol (iHexOl). This report builds on that study by investigating iHexOl in more detail as well as some newly synthesized solvents predicted by the first study to have good synergism. Both slow constant cooling (SCC) and isothermal KHI experiments were conducted in high-pressure steel rocking cells using a structure II-forming natural gas mixture. The KHI polymer concentration, solvent concentration, and mixed solvent systems were investigated. The solvent synergist water solubility, also in brines, and partitioning to the liquid hydrocarbon phase are shown to be important factors to consider for optimizing KHI performance. Further, it was observed that the optimal molecular weight distribution for the KHI polymer when used with a solvent synergist is not the same as the optimum distribution when using the polymer alone.

Multi-functional oilfield production chemicals: maleic-based polymers for gas hydrate and corrosion inhibition

Several chemical problems can occur during the production of oil and gas through flow lines. This includes corrosion, scale deposition and gas hydrate plugging. Three separate chemicals may be needed to treat these issues. Kinetic hydrate inhibitors (KHIs) are used in cold oil or natural gas production flow lines to prevent the formation and plugging of the line with gas hydrates. They are often injected concomitantly with other production chemicals such as corrosion and scale inhibitors. KHIs are specific low molecular weight water-soluble polymers with amphiphilic groups formulated with synergists and solvents. However, many corrosion inhibitors (CIs) are antagonistic to the KHI polymer, severely reducing the KHI performance. It would be preferable and economic if the KHI also could act as a CI. We have explored the use of maleic-based copolymers as KHIs as well as their use as film-forming CIs. KHIs were tested using a natural gas mixture in high pressure rocking cells using the slow constant cooling test method. A terpolymer from reaction of vinyl acetate:maleic anhydride copolymer with cyclohexy lamine and 3,3-di-n-butylaminopropylamine (VA:MA-60% cHex-40% DBAPA), gave excellent performance as a KHI, better than the commercially available poly(N-vinyl caprolactam) (PVCap). CO2 corrosion inhibition was measured by Linear Polarization Resistance (LPR) in a 1 litre CO2 bubble test equipment using C1018 steel coupons. The new terpolymer gave good CO2 corrosion inhibition in 3.6 wt% brine, significantly better than PVCap, but not as good as a commercial imidazoline-based surfactant corrosion inhibitor. The terpolymer also showed good corrosion inhibition efficiency at high salinity conditions, (density 1.12 g/cm3). VA:MA-60% cHex-40% DBAPA shifted the open-circuit potential to more positive values and significantly decreased the corrosion rate.

A new investigation of polymaleamides as kinetic hydrate inhibitors – Improved performance and compatibility with high salinity brines

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flowlines. The main component in KHI formulations is a water-soluble polymer and most of these polymers are amide-based. A few polymaleamides were investigated as KHIs in the 1990 s. Since then, our knowledge of the optimal structural features for KHI polymers has improved. Here we report a more detailed KHI study on this class of polymers, demonstrating significant KHI performance enhancement. KHI experiments were conducted under high pressure with natural gas mixture in steel rocking cells using the slow (1 °C/h) constant cooling test method. The best polymaleamides gave To (av.) values at around 6.1 °C (Ca. ΔT = 14.0 °C) at the concentration of 2500 ppm. In addition, the best polymaleamides were compatible with 15 wt% (150,000 ppm) brines at up to 95 °C.

Kinetic inhibition of structure I and II hydrate using novel modified poly(N-vinylcaprolactam)s in methane-water and methane-THF-water systems

In the present study, poly(N-vinylcaprolactam)s (PVCaps) as potent kinetic hydrate inhibitors (KHIs) were synthesized to unveil their effect on the structure I (sI) and structure II (sII) hydrate nucleation and growth rate. With the aim of enhancing the KHI performance of PVCap, 3-mercaptopropionic acid, mercaptoacetic acid, and L-cysteine as chain transfer agents (CTAs) were applied to produce polymers with different end groups. The synthesized polymers were evaluated in methane-water system and methane-THF-water system. All of the modified PVCaps outperformed the non-modified PVCap in terms of cloud point temperature (Tcl) and decreasing both sI and sII hydrate growth rate. The most effective PVCap to reduce the sI growth rate was mercaptoacetic acid-modified PVCap, while mercaptopropionic acid-modified PVCap was the strongest to slow down the sII growth rate. Furthermore, the synthesized polymers acted better than commercial Luvicap EG and PVP to retard the induction time in a way that the relative inhibition power (RIP) value for PVCap was 1.5 times greater than the RIP when Luvicap EG was used, also the maximum subcooling that synthesized PVCap could tolerated, was 2.7 and 1.5 K greater than that of PVP and Luvicap EG, respectively. Besides, it was found that a blend of PVCap (MWav = 4308 g/mol) with a higher molecular weight PVCap (6900 g/mol) had the best performance to increase the RIP values to 4.07 and 22.87 on sI and sII hydrate, respectively.

Non-amide based zwitterionic poly(sulfobetaine methacrylate)s as kinetic hydrate inhibitors

Applying kinetic hydrate inhibitors (KHIs) to avoid the pipeline blockage caused by hydrate formation in gas and oil industry is a comparatively effective and cost-saving method. The main ingredients in most KHIs are water-soluble polymers containing repeating amide group units, placed structurally close to hydrophobic groups. In this report we have synthesized a class of non-amide polymers, zwitterionic poly(sulfobetaine methacrylate)s, and investigated them as KHIs for the first time. Results show that the best zwitterionic polymers have good KHI efficacy with the key performance parameter being the length of the alkyl chain on the monomer unit side chains. Copolymer of the zwitterionic monomers and N-isopropylmethacrylamide (NIPMAM) gave much better increase in KHI performance with increasing concentration than the zwitterionic homopolymers. This result together with other related studies suggests that strong hydrogen-bonding groups like amide or amine oxide groups are important for high KHI performance. Reasons for this are discussed.

Kinetic Hydrate Inhibition of Glycyl-valine-Based Alternating Peptoids with Tailor-Made N-Substituents

A series of alternating peptides with glycine-N-substituted valine dipeptide repeating units were synthesized. The N-substitution included methyl, ethyl, n-propyl, and hydroxyl groups. The performance of the polypeptides as kinetic hydrate inhibitors (KHIs) was evaluated in high pressure rocking cells with a synthetic natural gas mixture using the slow constant cooling method. All the polypeptides gave better KHI effect than a low molecular weight poly(N-vinylpyrrolidone). The polypeptide with N-substituted n-propyl groups, PA-Pep, performed the best, the same as a commercial poly(N-vinyl caprolactam) (PVCap) at the same concentration. The KHI performance of PA-Pep improved as the concentration of the solution was increased from 1000 to 5000 ppm. At 5000 ppm the average (10 experiments) onset temperature for hydrate formation was 9.8 °C (ca. ΔT = 10.4 °C).

Systematic Study of Polyglyoxylamides as Powerful, High-Cloud-Point Kinetic Hydrate Inhibitors

A series of polyglyoxylamides (PGAms) have been synthesized and investigated for performance as kinetic hydrate inhibitors (KHIs) in slow constant cooling high-pressure rocking cell experiments using a structure II-forming synthetic natural gas mixture at 76 bar initial pressure. We found that the KHI performance improved as the size of the alkyl pendant group was increased. The best performing PGAm, poly(pyrrolidinyl glyoxylamide) (PPyGAm-I), gave an onset temperature of 8.2 °C at 2500 ppm. The KHI performance was improved by increasing the polymer concentration or by adding the high-flash-point solvent n-butyl glycol ether (nBGE) as a synergist. For example, using 7500 ppm of PPyGAm-I, the onset temperature was lowered to 3.8 °C (giving a subcooling of 15.7 °C, compensating for the drop in pressure at To). A mixture of 2500 ppm PPyGAm-I and 7500 ppm nBGE gave an onset temperature of 5.1 °C. Combined with a high cloud point (TCl = 79 °C), this makes PPyGAm-I a strong candidate for potential industrial us...

A short review on natural gas hydrate, kinetic hydrate inhibitors and inhibitor synergists

Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations. Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from high dosing, environmental unfriendliness, corrosiveness, and economical burden. The development and use of kinetic hydrate inhibitors (KHIs), mostly polymeric compounds, with their inhibiting effects on hydrate nucleation and growth are considered an effective and economically viable chemical treatment for hydrate prevention. However, the actual performance of a KHI candidate is dependent on various factors including its chemical structure, molecular weight, spatial configuration, effective concentration, pressure and temperature, evaluation methods, use of other additives, etc. This review provides a short but systematic overview of the fundamentals of natural gas hydrates, the prevailing categories of polymeric kinetic hydrate inhibitors with proposed inhibition mechanisms, and the various synergists studied for boosting the KHI performance. Further research endeavors are in need to unveil the KHI working modes under different conditions. The conjunctive use of KHIs and synergists may facilitate the commercial application of effective KHIs to tackle the hydrate plugging problem in the oil and gas flow assurance practices.