Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate

Petroleum Science, Jul 2011

Based on molecular dynamics simulation results, a lauryl methacrylate polymer with drag reduction and shear resistance properties was designed, and synthesized by emulsion polymerization using 2-vinyl pyridine and methyl methacrylate as the polar polymerization monomer. After ionization of lauryl methacrylate polymer, an ion-dipole interaction based drag reduction agent (DRA) was obtained. The existence of ion-dipole interaction was proven through characterization of the drag-reducing agent from its infrared (IR) spectrum. The pilot-scale reaction yield of the DRA under optimum conditions was investigated, and the drag reduction and shear resistance properties were measured. The results show that: 1) The ion-dipole or hydrogen bonding interaction can form ladder-shaped chains, therefore the synthesized DRA has shear resistance properties; 2) The larger the molecular weight (MW) and more concentrated the distribution of MW, the better the drag reduction effi ciency and the performance of the ionomer system was superior to that of the hydrogen bonding system; 3) With increasing shear frequency, the drag-reduction rates of both the DRAs decreased, and the drag reduction rate of the ionomer system decreased more slowly than of the corresponding hydrogen bonding system. From the point of view of drag reduction rate and shear resistance property, the ionomer system is more promising than the hydrogen bonding system

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Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate

Pet.Sci. Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate Yu Ping 0 Li Changyu 0 Zhang Changqiao 0 Chen Shiwei 0 Fang Shu 0 Sun Hui 0 0 School of Chemistry and Chemical Engineering, Shandong University , Jinan 250061 , China Based on molecular dynamics simulation results, a lauryl methacrylate polymer with drag reduction and shear resistance properties was designed, and synthesized by emulsion polymerization using 2-vinyl pyridine and methyl methacrylate as the polar polymerization monomer. After ionization of lauryl methacrylate polymer, an ion-dipole interaction based drag reduction agent (DRA) was obtained. The existence of ion-dipole interaction was proven through characterization of the drag-reducing agent from its infrared (IR) spectrum. The pilot-scale reaction yield of the DRA under optimum conditions was investigated, and the drag reduction and shear resistance properties were measured. The results show that: 1) The ion-dipole or hydrogen bonding interaction can form ladder-shaped chains, therefore the synthesized DRA has shear resistance properties; 2) The larger the molecular weight (MW) and more concentrated the distribution of MW, the better the drag reduction efficiency and the performance of the ionomer system was superior to that of the hydrogen bonding system; 3) With increasing shear frequency, the drag-reduction rates of both the DRAs decreased, and the drag reduction rate of the ionomer system decreased more slowly than of the corresponding hydrogen bonding system. From the point of view of drag reduction rate and shear resistance property, the ionomer system is more promising than the hydrogen bonding system Molecular design; ion-dipole interaction; hydrogen bonding; drag reduction rate; shear resistance property Pipelines are one of the five basic transportation modes (waterway, railway, highway, pipeline and air transportation). The total mileage of pipeline transportation has exceeded that of railways worldwide. In the oil industry, about 93 percent of crude oil is transported by pipeline (Sun,1996) . However, pipeline transportation has the problems of long transportation distance, large diameter of pipelines and high energy consumption. Particularly, due to the aging and corrosion of long-term service pipelines, operation under original design pressure or increased pressure for normal transportation may cause serious safety problems. To overcome these problems, use of drag reduction technology is a good countermeasure, i.e., adding a small amount of specific compounds in the system to reduce the resistance of fluids (Motier and Prilutski, 1985) . These specific compounds are called drag reduction agents (DRA). Under the designed temperature condition, long distance pipeline transportation should be pressurized by pumps to maintain the pressure difference of the whole pipeline in a reasonable range. These pumps are usually called pipeline transportation stations, which is a standard continuous transmission mode. Oil-soluble drag reducing agents are widely used in oil transportation. They can be used to maintain the designed capacity at decreased pressure, or used to enhance the transport capacity (Liu et al, 2008) . As one important type of DRA, poly-?-alkene has been used in actual pipeline transportation for many years. However, due to its comb-like structure, the backbone chains of ?-olefins can be easily broken when they pass through the pumps in the pipeline transportation stations, and the drag reduction efficiency is greatly decreased. Therefore, developing a new type of DRA with high drag reduction efficiency and shear stability has become an important topic in study of oilfield chemicals (Mei, 2005). Based on the previous studies (Pang and Zhang, 2009) , a new type of DRA is designed and synthesized in our work in laboratory scale and scale-up (Shui et al, 2008; SY/T65782009) , in which ion-dipole and hydrogen bond interactions exist. These DRAs are expected to have high drag reduction efficiency and shear resistance. In addition, the effect of Reynolds number (Resende and Escudier, 2006) and molecular weight (Zhao et al, 2007) of the polymer on drag reduction rate were also investigated. 2 Molecular design and experimental P o l y m e r d r a g r e d u c e r i s s y n t h e s i z e d t h r o u g h copolymerization of different carbon numbers of alpha olefin. Its main and branched chains are all combined by covalent bonds, and the molecular weight is mostly more than 4 million. When the polymer drag reducer flows through a high-shear area, covalent bonds are broken under the high shear force and the drag reducer loses its efficiency. The aim of designing a shear-resistant drag reducer molecule is to synthesize a cluster system or hydrogen bond system. Because of the ion-dipole effect of a cluster system and the hydrogen bonding effect of hydrogen bond system, these both systems not only have excellent drag reduction performance but also display shear resistance properties. When the polymer drag reducer flows through a high-shear area, because the covalent bonds are stronger than those of ion-dipole and hydrogen bond, the latter are broken more easierly than covalent bonds, reducing the effect of shear strength damage on the chain structure. When the polymer drag reducer flows into a low-shear area, the ion-dipole or hydrogen bond is reassociated automatically, and its drag reduction properties are recovered. Thus the drag reducer has the dual function of shear resistance and drag reduction. The idea for designing a shear-resistant drag reducer molecule is that when good drag reduction performance is required, an ion-dipole cluster system or a hydrogen bond system should be used. Therefore, we first conducted molecular dynamics simulation to study the possible microscopic structure and dynamic properties of both systems. The molecular dynamic simulation was carried out in the isobaric-isothermal (NPT) system using the all-atom force field based on OPLS-AA/AMBER force field (Liu et al, 2010) . The pressure was 1 bar with a compressibility of 4.5?10-5 bar-1. A leap-frog algorithm was used to integrate Newton?s equations of motion, with a time-step of 1 fs and the long-range electrostatic interaction was calculated by using the particle mesh Ewald method with a cut-off radius of 1.2 nm. The model system for the MD simulations is composed of 252 cations and 252 anions, total containing 7308 atoms. These cations and anions were all arbitrarily distributed in a rectangular box with a low density and periodic boundary conditions. Using the steepest descent method for minimizing energy and the 500 ps balance simulation, the box is compressed to normal size, then the normal sized structure was used in balance simulation. All the simulations were carried out using the GROMACS 3.3.3 software package. Beginning with the dipole cross linking formed by the iondipole effect (Peiffer, 1987) , the microstructure and molecular dynamics of monovalence pyridine were calculated. Based on this, we investigated the similar structure and behavior of hydrogen bonds. When the monovalence pyridine, which has a nitrogen (N) atom, reacts with another compound to form a system, the electric behavior of nitrogen atom is related to the property of the compound. When it reacts with fluorine (F)-containing compounds whose chemical structure is very stable, the nitrogen atom can easily lose an electron to create a positive ion. When it reacts with other compounds, the nitrogen atom gains an electron and creates a negative ion. In order to simplify the calculation of molecular dynamics simulation, and conveniently obtain the calculation parameters from literature, n-Butyl pyridine (BPy) is selected as a typical representative of monovalence pyridine, and the other compound is BF4, making the system provide cationic N and BF4?. Considering the environmental factors and industrial cost of fluoride (Zhu et al, 2007) , if the monovalence pyridine is ester-olefins and the other compound is non-fluoride, then the nitrogen on the pyridine ring is negative and the nonfluoride is positive. For the system composed of ester-olefins and non-fluoride, the molecular dynamics simulation results are still suitable for the ester-olefins and non-fluoride system as that for the BPy-BF4 system, except for the difference of the cation and anion. Based on the molecular dynamics simulations, the cation cation, cation-anion, and anion-anion center-of-mass radial distribution functions (RDFs), (RDFs), g(r), are calculated and the results are shown in Fig. 1. Clearly, we can see that all RDFs show strong and damped oscillations with and beyond 1.8 nm, respectively, which indicate a long-range ordered structure. For further insight into the structural features of the cation and the anion, the spatial distribution of the anions and cations around a given cation are also shown in Fig. 2. Seen from this figure, the anions are mainly distributed near the N atom of the pyridine cation. The diffusion coefficients of n-butyl pyridine cations ([BPy]+) and boron tetrafluoride anions ([BF4]-) are shown in Fig. 3. MSD(A2) is the diffusion coefficients, ? is log[MSD(A2)] and ? is gauss of MSD(A2). The anions and cations of the BPy-BF4 system form a strong dipole force, and their diffusion coefficients are similar to each other. These results indicate that the monovalence pyridine with N atoms monomer is the direction for molecular design of ionomer system drag reducer. For hydrogen system drag reducer, except for the non-ionized hydroxyl, its microstructure and dynamic properties are similar to the ionomer system. 1.5 (r)g 1.0 0.5 0.0 0.43 0.48 0.74 0.80 Cation-anion Cation-cation Anion-anion 0.0 0.5 1.0 1.5 r, nm Fig. 1 Radial distribution function between [BPy]+ and [BF4] Note: g(r) is anion-anion center-of-mass radial distribution functions Pet.Sci.(2011)8:357-364 359 360 Charging valve Relief valve Oil pressure buffer tank Drain valve a 4 Drag reduction properties of ionomer and hydrogen bond systems The DRA testing and evaluation system was used according to the ?Lab test method for the performance of drag reduction agents to be applied in oil pipeline? (from China Petroleum Industry Standard SY/T6578-2009) and is shown in Fig. 8, with the 0# diesel oil as the solvent (Wilkens and Thomas, 2007). The drag reduction performance of the two systems were compared. 4.1 Effect of Reynolds number of oil fluid on drag reduction performance Drag reduction performance testing was carried out in a 15 mm diameter circular pipeline at different Reynolds numbers and pressures such as 0.05, 0.1, 0.2, 0.3 MPa. Table 1 shows the relationship between pressure and pipeline parameters and Fig. 9 shows the relationship between drag reduction and Reynolds number based on Table 1. Electromagnetic valve Emptying valve Nitrogen cylinder Nitrogen pressure tank Oil circulation tank Mass flowmeter C1 C2 C3 D1 E1 D2 D3 E3 E2 0.30 MPa Pipeline parameters Velocity, m/s Flow, L/min Re number Differential pressure transmitter Pressure measuring point A1 0.05 MPa 0.44 4.66 A2 A3 Reflux pump B1 B2 B3 Pressure 0.10 MPa 0.95 0.20 MPa 1.54 ? * ? As shown in Fig. 9, the drag reduction rate of the ionomer system and the hydrogen bonding system both increased with Reynolds number. For 1,000 ppm addition, the drag reduction performance of the both systems was similar at low Reynolds number, but the difference in their drag reduction performance became larger with increasing Reynolds number. For 2,000 ppm addition, the drag reduction performance of the both systems showed a large difference at low Reynolds number, and the situation remained unchanged with increasing Reynolds number. The relationship between drag reduction performance and Reynolds number indicated that the ionomer system is superior to the hydrogen bonding system. 4 . 2 E f f e c t o f p o l y m e r c o n c e n t r a t i o n o n d r a g reduction performance Since the drag reduction performance is strongly influenced by the polymer concentration, the throughput increasing capacity (TI) of oil with increasing concentration at a Reynolds number of 15,383 and 25 ?C between the ionomer system and the hydrogen bond system was measured. Subsequently, the drag reduction rate was calculated by TI. The relationship between drag reduction and polymer concentration is shown in Fig. 10. Fig. 10 shows that the drag reduction rate of the hydrogen bonding system increased with increasing polymer concentration, while for the ionomer system, the drag reduction rate changed very little over 2,000 ppm, although it increased with increasing polymer concentration when the polymer concentration smaller than 2,000 ppm. This is because the reduction rate increases with the drag reduction agent?s concentration increasing. When the drag reduction system reaches its critical concentration, the reduction rate no longer increases. At the experimental concentrations, the drag reduction rate of the ionomer was improved more than that of the hydrogen bond system. 4.3 Molecular weight of polymer on drag reduction performance For the functional polymers, the molecular weight and 50 45 40 35 % ,no 30 i tcu 25 d re 20 g raD 15 10 5 0 0 ? ? ? ? 500 ? Ionomer system ? Hydrogen bond system ? ? ? ? ? ? ? ? 1000 1500 2000 2500 3000 Concentration of polymer, ppm its distribution of polymers are also an important factor. The accept polymer and donor polymer were dissolved in toluene with the same concentration of 0.01 g/mL. Using 515-type high-temperature gel permeation chromatography (Waters Corporation, USA), the molecular weight of polymer drag reducers was measured. The distribution of polymer of the ionomer system and the hydrogen bond system are shown in Fig.11. Fig. 11 shows that the molecular weight distribution is a single symmetrical peak. The computer data analysis shows that the polymer has a high molecular weight. For hydrogen bonding complex: the number-average molecular weight (Mn) is 298,700, the weight-average molecular weight (Mw) is 382,600 and the dispersion degree is 2.63; For the blend complex: Mn is 3,593,587, Mw is 4,607,226 and the dispersion degree is 2.32. Using the testing and evaluation system, the relationship between the polymer molecular weight and drag reduction rate was obtained and is shown in Fig. 12. As shown in Fig. 12, the drag reduction rate increased with increasing molecular weight. At low molecular weight, the drag reduction rate was quite different for different concentrations. This difference became smaller with a b M g o l d / w d 20 Elution time, min 22 Fig. 11 The molecular weight distribution of polymer of ionomer system (a) and hydrogen bond system (b) ? 2000 ppm(polymer) ? 1000 ppm (polymer) ? 500 ppm (polymer) 50 45 40 increasing molecular weight. When the molecular weight is about 5?106, the drag reduction rate of polymer with a concentration of 500 ppm was similar to that of 2,000 ppm. These results indicated that increased molecular weight and concentrated molecular weight distribution of polymer were favorable to drag reduction. 5 Shear resistance of ionomer system and hydrogen bond systems The shear resistance was tested using the tube pump transmission subsystem within the testing and evaluation system. New drag reduction tests were conducted in the diesel without addition of new DRA conditions relying on the gear pump subsystem cycle. So evaluation of the drag reduction and shear resistance of polymer system were achieved. The experimental condition for shear resistance test was that the temperature was 25 ?C and Reynolds number was 15,383. Seven numbers were achieved under different concentrations of the three types of drag reduction agent. The relationship between drag reduction change and the shear number was shown in Fig. 13. ? ?? Fig. 13 Drag reduction rate with increase of shear number ? ? ? 2 ? ? ? ? ? ? 3 4 5 Shear number ? Ionomer system ? Hydrogen bond system ? ?-alkene ? ? ? 6 ? ? ? 7 8 From Fig. 13, we can see the drag reduction rate of polymer ?-alkene decreases from 38% to 2% after first shear, and no shear resistance was observed in the end. Although both the drag reduction rates of the ionomer and hydrogen bond systems decreases with increasing shear time, they exhibit excellent shear resistance. However, the hydrogen bond system shows a mutant site at the second shear. For ionomer system, the reduction rate decreases slowly, and the drag reduction rate is much larger than the two other systems. So, we deduce that the ionomer system has better potential industrial application than hydrogen bond system. 6 Results 1) When the ionomer system is formed by blending, it has strong ion-dipole interaction to form a "ladder" chain between the first order of pyridine functional groups and ions groups, leading to the shear resistance of the ionomer system. The shear resistance function was also observed in the hydrogen bond system. There are two parts for DRA, one part is first order pyridine of the chain compounds, and the other is long chain anionic compounds produced from the polymerization. 2) The synthesis of ionomer system is as follows: Taking ionization treatment on the bc-PDP of methyl methacrylate and lauryl methacrylate with methanol dissolved NaOH, and then mixing with the tc-PDP of styrene, lauryl methacrylate and 2-vinyl pyridine at 1:1 (w/w). The hydrogen bond system was obtained by mixing the bc-PDP without the treatment with the tc-PDP at 1:1 (w/w). 3) Based on the relationship between Reynolds number and drag reduction performance, the ionomer polymer system shows advantages over the hydrogen bond system on drag reduction. The drag reduction efficiency of the ionomer is much better than that of the hydrogen bond system within the experimental concentrations. 4) Although the drag reduction rates of the two systems showed the same decreasing trend with increasing shear time, the hydrogen bond system decreases sharply at the second shear. But for the ionomer system, the reduction rate decreases slowly and smoothly. So the ionomer system may have better potential industrial application than hydrogen bond system owing to its better shear resistance and drag reduction. Acknowledgement This work is supported by the Basic Research Program of China (973 Program, Grant No. 2008CB617508). Deng L and Liang D H . Online monitoring of the aggregation and fusion of DPPC/PA by static and dynamic light scattering . Acta Phys. Chim. Sin . 2010 . 26 ( 4 ): 862 - 868 Liu H , Song G J and Guan M. Characterization of ?-olefin polymer DRA via solution polymerization . 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Ping Yu, Changyu Li, Changqiao Zhang, Shiwei Chen, Shu Fang, Hui Sun. Drag reduction and shear resistance properties of ionomer and hydrogen bond systems based on lauryl methacrylate, Petroleum Science, 2011, 357-364, DOI: 10.1007/s12182-011-0153-x