Article pubs.acs.org/EF
First Investigation of the Kinetic Hydrate Inhibitor Performance of Polymers of Alkylated N‑Vinyl Pyrrolidones Fernando T. Reyes* and Malcolm A. Kelland Department of Mathematics and Natural Science, Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway ABSTRACT: A series of water-soluble homopolymers and copolymers of 1-alkyl-vinyl pyrrolidones (1-alkyl-VPs) with alkyl groups, including methyl, ethyl, isopropyl, and n-propyl, has been synthesized. Homopolymers with larger alkyl groups had cloud points in water lower than 0 °C. The comonomers used in the copolymers were N-vinyl pyrrolidone (VP) and N-methyl-N-vinyl acetamide (VIMA). The performance of the water-soluble 1-alkyl-VP polymers as kinetic hydrate inhibitors was investigated for the first time. Tests were conducted in high-pressure rocking cells using a structure II hydrate-forming natural gas mixture and compared to poly(N-vinyl lactam)s of similar molecular weight. The best copolymer of this series was the 1:1 nPr-VP/VIMA copolymer. 1-dimethyl-VP and 1-ethyl-VP homopolymers and the 1:1 n-propyl-VP/VP copolymer also showed better performance than poly(N-vinyl caprolactam) and poly(N-vinyl azocyclooctanone) of similar molecular weights. The structure− performance analysis in this study suggests that a more lipophilic ring than PVP gives better structure II gas hydrate kinetic inhibition than PVP itself. Second, alkylation of PVP gives a better kinetic hydrate inhibitor (KHI) than expanding the PVP lactam ring with the same number of carbon atoms as used in the alkylation.
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azocyclooctanone (VACO) for the first time and showed that poly(N-vinyl azocyclooctanone) (PVACO) gave a better performance than any of the smaller ring poly(N-vinyl lactam)s (Figure 1).31 Copolymers of VACO with the smaller N-vinyl lactam monomer VP, VIMA, and N-vinyl acetamide (NVA) have also been reported (Figure 2)31 In particular, 1:1 VACO/ VIMA copolymer showed excellent KHI performance.
INTRODUCTION In upstream oilfield operations, kinetic hydrate inhibitors (KHIs) are a well-known approach to prevent gas hydrate plugs in pipelines.1−4 The best performance of KHIs has been shown by certain types of water-soluble polymers. These polymers prevent nucleation as well as the crystal growth of gas hydrates. The hold time to gas hydrate formation at the operational subcooling is of the upmost importance in upstream oilfield operations. The composition of the produced fluids will also influence the KHI performance. Another important factor affecting performance is the absolute pressure.5−8 Major classes of commercially available KHI polymers are those based on the 5- and 7-ring N-vinyl lactams, N-vinyl pyrrolidone (VP), and N-vinyl caprolactam (VCap) (Figure 1).9−16
Figure 2. Poly(N-methyl-N-vinyl acetamide) (VIMA).
The VP monomer is widely available in large quantities. It occurred to us that alkylation of VP could produce monomers and then polymers that could potentially compete at the same performance level as polymers of the larger N-vinyl lactam monomers. In this study, we have synthesized a series of 1alkyl-N-vinyl pyrrolidone monomers (1-alkyl-VPs) from VP with different alkyl groups, to modify the lipophilicity (Figure 3). Homopolymers and copolymers with VP or VIMA have been tested in high-pressure equipment as structure II hydrate KHIs against N-vinyl lactam polymers.
Figure 1. From left to right, poly(N-vinyl pyrrolidone) (PVP), poly(N-vinyl piperidone) (PVPip), poly(N-vinyl caprolactam) (PVCap), and poly(N-vinyl azacyclooctanone) (PVACO).
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It is well-known that VCap/VP copolymers have good profile and are commercially available;1−4 for VCap copolymers with N-methyl-N-vinyl acetamide (VIMA) in a ratio of 1:1,17 in recent years, the increase in price of the monomer VIMA has stopped their use as gas hydrate kinetic inhibitors.18−23 Recently, we showed that the 6-ring poly(N-vinyl piperidone) (PVPip) homopolymer had an intermediate KHI performance on structure II gas hydrates compared to the 5ring PVP and 7-ring PVCap. We also synthesized N-vinyl © 2013 American Chemical Society
MATERIALS AND SYNTHESIS
All common reagents and solvents from commercial suppliers were used without further purification. Samples of PVPs (PVP K15 and PVP K30) and Agrimer 904 (partially butylated PVP) were kindly donated by Ashland Chemical Co. PVIMA, VP/VIMA, VCap/VIMA, Received: April 3, 2013 Revised: June 5, 2013 Published: June 12, 2013 3730
dx.doi.org/10.1021/ef400587g | Energy Fuels 2013, 27, 3730−3735
Energy & Fuels
Article
(CDCl3) δ: 17.852, 19.445, 20.697, 28.612, 43.212, 48.370, 94.201, 129.680. 3-Propyl-1-vinylpyrrolidin-2-one. 1H NMR (CDCl3) δ: 0.926 (t, J = 7.5 Hz, 3H), 1.374 (m, 4H), 2.501−2.261 (m, 2H), 3.494− 3.356 (m, 2H), 4.399 (m, 2H), 7.092 (dd, JA = 16.2 Hz, JB = 9.3 Hz, 1H). 13C NMR (CDCl3) δ: 14.135, 20.537, 24.552, 33.435, 42.368, 43.030, 94.143, 129.746. General Procedure for the Synthesis of Polymers. The monomer or comonomers were mixed with 2 wt % of the radical initiator 2,2-azobis(2-methylpropionitrile) and 6−10 mL of 2-propanol in a Schlenk tube. The resulting solution was degassed on a highvacuum line and sealed with a glass cap under nitrogen. The reaction mixture was then stirred and allowed to polymerize at 80 °C for 24 h. Solvents were removed under reduced pressure to leave a white solid. 1 H and 13C NMR spectroscopy indicated greater than 99% monomer conversion. Polymer samples were analyzed for molecular weight by gel permeation chromatography (GPC) in N,N-dimethylformamide (DMF) solvent against poly(methyl methacrylate) (PMMA) standards. A summary of all polymers used in this study is given in Table 1.23 Cloud points for all of the new polymers are also shown. The structures of the polymers and copolymers are given in Figures 4 and 5, respectively.
Figure 3. General structure of poly(1-alkyl-vinylpyrrolidin-2-one)s [poly(1-alkyl-VP)s].
PVCap, PVPip, and PVACO were synthesized as previously described.31 All other chemicals were obtained from either SigmaAldrich Chemical Co. or VWR. Proton (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectra were recorded on a Varian Mercury instrument operating at 300 MHz for proton and 75 MHz for carbon. Chemical shifts were recorded as δ values in parts per million (ppm) using residual chloroform (δ = 7.26 ppm for proton and 77.0 ppm for carbon) as an internal standard for 1H and 13C NMR. Below is described the full synthesis of 3-methyl-1-vinylpyrrolidin-2one; according to this, all monoalkyl monomers were prepared according to this procedure, with the exception of dialkyl monomers, which are described after. Therefore, for all other monomers prepared, 1 H and 13C NMR are given.24−29 Synthesis of 3-Methyl-1-vinylpyrrolidin-2-one. VP (10.0 g, 89.9 mmol) dissolved in 20 mL of tetrahydrofuran (THF) was added dropwise to 45 mL (89.9 mmol) of a 1 M lithium diisopropylamide (LDA) solution at 0 °C. The resultant solution was magnetically stirred for 90 min. Iodomethane (14 g, 98.8 mmol) dissolved in 5 mL of dry THF was added dropwise at 0 °C over 15 min. The reaction mixture was magnetically stirred at room temperature for 24 h in inert atmosphere conditions. The mixture reaction was diluted with 50 mL of dichloromethane and 20 mL of deionized water. The aqueous layer was then extracted with further portions of dichloromethane (30 mL 3 times). The organic layer was dried over sodium sulfate and filtered off, and the solvent was removed under reduced pressure. The crude product obtained was purified by flash column chromatography (2:1 light petroleum ether and ethyl acetate). Solvents were removed under reduced pressure, giving a yellow pale oil as a product. 1 H NMR (CDCl3) δ: 1.223 (d, J = 7.5 Hz, 3H), 1.685 (m, 1H), 2.324−2.554 (m, 1H), 3.439 (m, 2H), 4.418 (d; J = 8.3 Hz, 2H), 7.076 (dd, J = 8.7 Hz, 1H). 13C NMR (CDCl3) δ: 16.252, 26.764, 37.370, 42.812, 94.238, 129.768. Synthesis of 3,3-Dimethyl-1-vinylpyrrolidin-2-one. VP (10.0 g, 89.9 mmol) dissolved in 20 mL of THF was added dropwise to 90 mL (179.8 mmol) of a 1 M LDA solution at 0 °C. The resultant solution was magnetically stirred for 90 min. Iodomethane (26.8 g, 188.8 mmol) dissolved in 5 mL of dry THF was added dropwise at 0 °C over 15 min. The reaction mixture was magnetically stirred at room temperature for 24 h in inert atmosphere conditions. The mixture reaction was diluted with 50 mL of dichloromethane and 20 mL of deionized water. The aqueous layer was then extracted with further portions of dichloromethane (30 mL, 3 times). The organic layer was dried over sodium sulfate and filtered off, and solvent was removed under reduced pressure. The crude product obtained was purified by flash column chromatography (4:1 light petroleum ether and ethyl acetate). Solvents were removed under reduced pressure, giving a yellow pale oil as a product. 1 H NMR (CDCl3) δ: 1.198 (s, 6H), 1.92 (t, J = 6.9 Hz, 2H), 3.411 (t, J = 6.6 Hz, 2H), 4.400 (dd, JA = 22.5 Hz, JB = 2.4 Hz, 2H), 7.069 (dd, JA = 16.2 Hz, JB = 9.3 Hz, 1H). 13C NMR (CDCl3) δ: 14.360, 21.228, 24.778, 33.675, 41.364, 60.555, 94.165, 129.993. 3-Ethyl-1-vinylpyrrolidin-2-one. 1H NMR (CDCl3) δ: 0.963 (t, J = 7.5 Hz, 3H), 1.44 (m, 1H), 1.891−1.755 (m, 2H), 2.443−2.377 (m, 2H), 3.525−3.331 (m, 2H), 4.402 (m, 2 H), 7.087 (dd, JA = 16.2 Hz, JB = 9.3 Hz, 1H). 13C NMR (CDCl3) δ: 11.567, 23.934, 24.283, 43.038, 43.925, 94.238, 129.702, 175.301. 3-Isopropyl-1-vinylpyrrolidin-2-one. 1H NMR (CDCl3) δ: 0.930 (dd, JA = 42.3 Hz, JB = 7.5 Hz, 6H), 1.877 (m, 1H), 2.239− 2.037 (m, 2H), 2.510 (m, 1H), 3.41 (m, 2H), 4.387 (dd, JA = 14.7 Hz, JB = 8.7 Hz, 2H), 7.107 (dd, JA = 16.5 Hz, JB = 9.3 Hz). 13C NMR
Table 1. Molecular Weights and Cloud Points for Polymers in This Studya polymer
Mn (g mol−1)
PVP PVP K15 PVP K30 PVPip PVCap PVACO PVP-Me PVP-DiMe PVP-Et PVP-Et (low Mn) PVP-iPr PVP-nPr PVP-nPr (low Mn) Agrimer 904 1:1 VP-nPr/VP-Me 1:1 VP-nPr/VP PVIMA 1:1 VP-nPr/VIMA 7:3 VP-nPr/VIMA 9:1 VP-nPr/VIMA 1:1 VP/VIMA 1:1 VCap/VIMA
3400 Mw = ca. 8000 Mw = ca. 60000 3300 2600 1700b 6900 2500 30300 6000 4300 7800 1000 Mw = ca. 18000 16200 9500 12401 8090 7680 9530 8978 7645
polydispersity index (PDI)
cloud point (°C)
1.18 not known not known 1.22 1.81 2.76 1.87 2.28 5.33 1.49 1.67 1.56 1.65
>100 >100 >100 78 33 16 65 43 25 26
