Non-amide kinetic hydrate inhibitors: A review

•Non-amide kinetic hydrate inhibitors are reviewed systematically.•The inhibition performance of non-amide KHIs is related to their chemical structures.•Several non-amide KHIs are with great potential for commercial development.•The inhibition mechanisms of non-amide KHIs are discussed. Kinetic hydrate inhibitors (KHIs) have been used for several decades to solve the hydrate formation problem in oil and gas flowlines. Traditional KHIs are amide-based polymers, e.g., poly(N-vinyl pyrrolidone) (PVP) and poly(N-vinyl caprolactam) (PVCap). With the requirement of high performance, well fluid compatibility, and biodegradable KHIs in oil and gas production and transportation assurance field, more and more non-amide KHI categories have been developed. According to the functional groups, synthetic non-amide KHIs can be classified into amine-based KHIs, amine oxide-based KHIs, phosphonate-based KHIs, sulfonate-based KHIs, hydroxyl-based KHIs, acrylate-based KHIs, urethane-based KHIs, etc. Some natural non-amide polymers, e.g., polysaccharides, are also found with inhibition effect. The inhibition performance of the non-amide polymers is related to their chemical structures. Different functional groups in the polymers have different effects on their inhibition performance. However, the inhibition performance of a polymer largely depends on the type and size of the hydrophobic groups connected to the functional groups. Some of the non-amide KHIs with suitable hydrophobic groups show better inhibition performance and higher cloud point (TCl) in brines than some of the well-known commercial amide-containing KHIs, which provides a great potential for further development for field applications. In addition, aspects of the KHI inhibition mechanism related to the amphiphilic groups in the polymers and their hydrogen-bonding ability are discussed.