Tailored Amine Oxides─Synergists, Surfactants, and Polymers for Gas Hydrate Management, a Minireview

Abstract

Low-dosage hydrate inhibitors (LDHIs) are used to prevent gas hydrates from plugging upstream gas and oil flow lines. LDHIs come in two main classes, kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs). KHIs delay the hydrate formation process, while AAs ultimately disperse any formed hydrates so that no deposits or plugs are formed. Currently, KHI formulations deployed in the field contain one or more water-soluble polyamides with optimized hydrophobic groups, while most commercialized AAs are cationic quaternary ammonium surfactants also with optimized hydrophobic groups. The amine oxide group is closely related to quaternary ammonium salts but has zero overall charge and is also related to the amide group as a result of strong hydrogen-bonding properties. In the past decade, small amine oxides as KHI synergists, polyamine oxides as stand-alone KHIs, and amine oxide surfactants as AAs have all been developed. This review summarizes all contributions to the development of amine-oxide-based LDHIs. This includes powerful monoamine oxide synergists for polyamide KHIs, high-salinity-compatible polyamine oxide KHIs, and bis-amine oxide surfactants that function as both KHIs and AAs.

Attempts to Improve the Performance and Biodegradation of Kinetic Hydrate Inhibitors–More Lessons Learned

“…In all KHI projects discussed in this work, a multi stainless steel rocker rig supplied by PSL Systemtechnik, Germany with cells from Swafas, Norway was used. Details of the equipment and the test methods used have been reported previously . This apparatus can rock five 40 mL cells in a cooling bath, with each cell equipped with temperature and pressure sensors.…”

“…This method has been shown previously to give comparable performance ranking as isothermal tests in autoclaves . The reader is referred to past studies for details about the test procedure and analysis. − For the SNG tests, the start pressure was 76 bar. This gave 20.5 °C as the hydrate equilibrium temperature (HET) found from calculations performed in the PVTSim software of Calsep .…”

“…Our research is also aimed at exploring other hydrophilic functional groups that are used in the vast majority of commercial KHI polymers. An example is the amine oxide group . Another goal is to improve compatibility issues of KHIs such as cloud and deposition points, without loss of performance. ,, Underpinning all of these goals is a desire to understand the KHI mechanism(s) operating and develop structure–activity relationships.…”

“…One of the main goals of our research is to improve KHI performance, with either improved KHI polymers or the addition of synergists to known KHI polymers. Recently we reported blends of polymers and synergists with much superior performance. ,, Another goal is to improve KHI environmental acceptability and sustainability. The focus is on readily and fully biodegradable KHIs (BOD28 > 60% for the polymer in OECD306 seawater tests).…”

Comparing the Kinetic Hydrate Inhibition Performance of Linear versus Branched Polymers

“…The main component in liquid KHI formulations is one or more water-soluble oligomers or polymers that contain peripheral amphiphilic groups. These groups have hydrophilic parts that have strong hydrogen bonding properties such as amide, imide, or amine oxide, although many other functional groups have been investigated. − Well-known examples of KHI polymers include homo- or copolymers of N -vinyl caprolactam (VCap), N -vinylpyrrolidone (VP), and N -isopropylmethacrylamide (NIPMAm) (Figure ). The homopolymer of VCap, PVCap, is a powerful KHI and is often used as a standard to gauge the performance of other polymers .…”