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In this present study, an in vivo experiment was carried out to determine the tendencies of a naturally occurring high-phenolic compound red-onion skin extract (HPC-ROSE) and conventional N-Vinylcaprolactam (N-VCAP) kinetic hydrate inhibitors (KHIs) to bio-accumulate in offshore environment through the analysis of their uptake and depuration kinetics by a Fish-Chemical Model using Cyprinus carpio marine invertebrate. This test was performed in the laboratory in a flow through experimental set up according to the guidelines by [49] (Fish-chemical exposure test). The uptake duration was 10 days with a depuration period of twenty days. The inhibitor toxicity test was evaluated by determining the 50 % lethal concentration (LC50) as highlighted by OSPAR Commission protocols. The solubility of the inhibitors was determined by a column elution technique. Similarly, a proton-enabled nuclear magnetic resonance (1HNMR) technique was used to measure the partitioning characteristics of the inhibitors in an immiscible mixture of octanol and water (Kow) by 1HNMR spectroscopy using a benchtop low-field NMR spectrometer. OSPAR Commission and ASTM standard protocols were used for the laboratory investigation of the static sediment toxicity tests. A reference chemical substance of known BCF and solubility (Ethyl Acetate, EtOAc) was used as control to check the experimental progression. The stock solution was prepared by solid phase desorption mechanisms. The HPC-ROSE does not constitute environmentally significant risk to aquatic life owing to its lower BCF values between 215 L/kg - 251.5L/Kg, Log-Kow of 1.2 and higher lethal concentration of 25140 mg/L. Unlike the NVCAP which is very toxic with lower lethal concentration of 1280 mg/L and higher BCF values in the range of 442.5L/Kg to 485 L/kg with Log-Kow of 1.5. Furthermore, Nuclear magnetic resonance (1HNMR) is a simple and reliable method of estimating partition coefficient characteristics (Kow) because the obtained Log-Kow values showed good agreements with that of shake flask and high-performance liquid chromatography techniques. Also, the chemical concentration in water has an inverse relationship with uptake rate constant (K1) and steady-state bioconcentration factor (BCFss). Finally, the theoretically estimated BCFs were higher than the steady-state (BCFss) values that were obtained from laboratory experiments for the different inhibitor samples and at all concentrations. This is due to the route by which Log-Kow was estimated since most of the empirical models are usually one-factor model consisting of partition coefficient and BCF.

Highlights • Hydroxy-terminated PVCap with fairly low PDI value has been synthesized. • The cloud point of PVCap-OH increased 10.6 °C compared with PVCap. • PVCap-OH has improved the maximum subcooling and induction time. • PVCap-OH has reduced the hydrate growth rate and prevented the agglomeration. Abstract Hydroxy-terminated poly(N-vinylcaprolactam) (PVCap-OH) with a narrow molecular weight distribution (PDI = 1.06) has been synthesized. PVCap-OH gave a cloud point of 51.7 °C, 10.6 °C higher than that of the synthesized PVCap (41.1 °C). Its KHI performance was tested using a high-pressure stainless-steel cell with methane gas. Powder X-ray diffraction (PXRD), Raman spectroscopy, and cryo-scanning electron microscopy (cryo-SEM) were used to characterize the micro-structure of the hydrate. It was found that PVCap-OH provided a better KHI performance than PVCap in the same conditions, which gave a higher maximum subcooling and longer induction time, as well as lowered the growth rate of hydrate. The addition of PVCap-OH did not alter the hydrate crystal structure, but reduced the stoichiometric ratio of the peak intensities of the large (51262) and small (512) hydrate cages (I L /I S) and made the hydrate particles more dispersed, which further ensured the gas transportation smoothly. [ABSTRACT FROM AUTHOR]

Low dosage kinetic hydrate inhibitors play an important role in flow assurance for oil and gas industry. New polymers especially based on N-vinyl caprolactam (NVCap) are widely designed to serve as potential inhibitors. In this work, a series of random copolymers of NVCap with hydrophobic monomer isopropylacrylamide (NIPAM) were synthesized. The effect of molecular weight on inhibition performance of newly copolymers (PVCap-co-NIPAM)s on CH 4 hydrate formation were firstly examined and compared with N-vinyl caprolactam homopolymer (PVCap). The macroscopic kinetic tests indicated that all the copolymers were more powerful than PVCap as nucleation inhibitors under the same conditions. Significant reductions in the hydrate growth rates by 1.0 wt% inhibitors were also observed. Copolymers with the lowest molecular weight possessed the best suppression performance. Powder X-ray diffraction and Raman spectra indicated neither PVCap nor PVCap-co-NIPAM affected the hydrate structure due to their too large molecular size to match the hydrate cages. However, cage-dependent gas occupancy calculated from Raman data proved that the polymers preferred to hinder CH 4 molecules from being trapped by large cages (51,262). A possible inhibition mechanism of PVCap-co-NIPAM was also proposed. These results could be helpful to develop synergistic kinetic hydrate inhibitors for guaranteeing pipeline fluids transportation safety. [Display omitted] • Copolymers of N -vinyl caprolactam and isopropylacrylamide were firstly synthesized. • Introducing isopropylacrylamide yielded a synergetic kinetic inhibitory effect. • The copolymer with lower molecular weight exhibited better inhibition performance. • PXRD patterns showed the copolymer was too large to change hydrate microstructure. • The inhibition mechanism based on macroscopic and Raman measurements was proposed. [ABSTRACT FROM AUTHOR]

• Block copolymer of N -vinyl caprolactam and acrylamide was synthesized. • Higher-cloud-point PVCap- co -AM performed better than PVCap as KHIs on CH 4 hydrate. • PXRD and Raman results showed PVCap- co -AM did not alter hydrate crystal structure. • Morphology of CH 4 hydrate was clearly different between PVCap- co -AM and PVCap. In this paper, a novel block copolymer poly (N -vinyl caprolactam)- co -acrylamide) (PVCap- co -AM) was made from N -vinyl caprolactam (NVCap) with acrylamide (AM) by living radical copolymerization. The kinetic inhibitory performance of PVCap- co -AM on CH 4 hydrate formation was firstly investigated and compared with PVP and PVCap. The results indicated that higher-cloud-point PVCap- co -AM behaved better than PVCap under the same conditions. Powder X-ray diffraction (PXRD) spectroscopy and Raman spectroscopy showed structure I hydrate was formed with and without KHIs. However, compared to pure water, the presence of KHIs reduced the ratio of large to small cage occupancy by CH 4. The stronger inhibition activity, the value became lower. Cryo-SEM images illustrated the morphology of CH 4 hydrate crystals formed significantly varied by KHIs, which could be helpful for pipeline fluids safe transportation. [ABSTRACT FROM AUTHOR]