CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/257,357 filed November 19, 2015, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] Embodiments of the present disclosure generally relate to the production of drag reducing agents for use in hydrocarbon conduits, and more specifically relate to methods of making ultra high molecular weight poly(α-olefin) drag reducing agents.

BACKGROUND

[0003] In the petroleum industry, hydrocarbon fluids are transported through a conduit at a very high flow rate. This creates a lot of turbulence and wall friction, which cause fluid flow pressure drops. To overcome this pressure drop, a lot of mechanical energy is required. Thus, the transport of the hydrocarbon fluid is an economic challenge. Ultra high molecular weight (UHMW, molecular weight (MW)≥ 10 ⁶ ) poly(oc-olefin) homopolymers and copolymers, in the form of drag reducing agents (DRAs), have been used to combat this challenge. The DRAs reduce the turbulence-mediated friction and eddies, which, in turn, decrease the pressure drop. Specifically, when injected into a stream of hydrocarbon fluid flowing through a pipeline, DRAs enhance the flow of the stream by reducing the effect of drag on the liquid from the pipeline walls. This, in turn, creates better streamlining for the flow in the pipe, increases the conservation of energy, and reduces the costs of pipeline shipping.

[0004] DRAs are produced using transition metal catalytic polymerization processes; however, the catalytic activity from conventional catalysts is substandard. Moreover, other DRA synthesis processes require that the polymerization be performed at cryogenic temperatures, which is also costly and inefficient. Further, obtaining DRAs with the requisite degree of drag reduction has also been challenging. SUMMARY

[0005] Accordingly, ongoing needs exist for improved DRAs, as well as improved processes and improved catalyst systems for synthesizing DRAs.

[0006] In one embodiment, a method of producing ultra high molecular weight (UHMW) C ₄ - C ₃₀ α-olefin drag reducing agent (DRA) is provided. The method includes polymerizing in a reactor a first α-olefin monomer in the presence of a catalyst and hydrocarbon solvent to produce the UHMW C ₄ _ C ₃₀ α-olefin polymer DRA. The catalyst consists essentially of at least one tertiary monophenyl amine having a formula R ¹ R ² N-aryl, where R ¹ and R ² are the same or different, and each is a hydrogen, an alkyl, or a cycloalkyl group, where at least one of R ¹ and R 2" contain at least one carbon atom; at least one titanium halide having a formula TiX _m , where m is from 2.5 to 4.0 and X is a halogen containing moiety; and at least one cocatalyst having a formula AlR _n Y ₃ _ _n where R is a hydrocarbon radical, Y is a halogen or hydrogen, and n is 1-20. Further, the catalyst is absent of a carrier or support.

[0007] In another embodiment, a catalyst is provided. The catalyst consists essentially of at least one tertiary monophenyl amine having a formula R ¹ R ² N-aryl, where R ¹ and R ² are same or different, and each is a hydrogen, an alkyl, or a cycloalkyl group, where at least one of R ¹ and R ² contain at least one carbon atom; at least one titanium halide having a formula TiX _m , where m is from 2.5 to 4.0 and X is a halogen containing moiety; and at least one cocatalyst having a formula AlR _n Y ₃ _ _n where R is a hydrocarbon radical, Y is a halogen or hydrogen, and n is 1-20. Further, the catalyst is absent a carrier or support.

[0008] In yet another embodiment, a method of reducing drag in a conduit is provided. The method includes producing a UHMW C ₄ -C ₃₀ α-olefin copolymer DRA by polymerizing in a reactor a first α-olefin monomer in the presence of a catalyst and a hydrocarbon solvent. The catalyst consists essentially of at least one tertiary monophenyl amine having a formula R ¹ R ² N-aryl, where R ¹ and R ² are same or different, and each is a hydrogen, an alkyl, or a cycloalkyl group, where at least one of R ¹ and R ² contain at least one carbon atom; at least one titanium halide having a formula TiX _m , where m is from 2.5 to 4.0 and X is a halogen containing moiety; and at least one cocatalyst having a formula AlR _n Y ₃ _ _n where R is a hydrocarbon radical, Y is a halogen or hydrogen, and n is 1-20. The method further includes introducing the UHMW C ₄ -C ₃₀ α-olefin polymer DRA into the conduit to reduce drag in the conduit. [0009] Additional features and advantages of the described embodiments will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the described embodiments, including the detailed description which follows, the claims, as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a flow chart depicting a process for making a DRA in accordance with one or more embodiments of the present disclosure; and

[0011] FIG. 2 is a schematic depiction of the experimental equipment set-up used to evaluate the drag reduction achieved by DRA embodiments of the present disclosure.

DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure are directed to improved catalyst systems and a polymerization process that synthesize (UHMW) C ₄ -C ₃₀ α-olefin polymer drag reducing agents (DRAs) with improved percentage drag reduction for a flowing hydrocarbon fluid.

[0013] Method embodiments for producing UHMW C ₄ -C ₃₀ α-olefin polymer DRA may comprise polymerizing in a reactor a first α-olefin monomer in the presence of catalyst and hydrocarbon solvent. The UHMW C ₄ -C ₃₀ α-olefin polymer DRA may comprise a homopolymer, copolymer, or a terpolymer. In a specific embodiment, the UHMW C ₄ -C ₃₀ α-olefin polymer DRA is a copolymer produced by copolymerizing the first α-olefin monomer with a second a- olefin comonomer.

[0014] The first α-olefin and second α-olefin comonomers may include C ₄ -C ₃₀ α-olefins, or C ₄ -C ₂₀ α-olefins, or C ₆ -C ₁₂ olefins. In one embodiment, the first α-olefin and second α-olefin comonomers are different α-olefins selected from ethylene, propylene, 1-butene, 4-methyl-l- pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, and combinations thereof.

[0015] The solubility of DRAs in hydrocarbons is an important factor which affects the efficiency of the DRA. Without being bound by theory, DRAs produced from the combination of a short chain α-olefin (for example, a C ₂ -C ₆ α-olefin) and a long chain α-olefin (for example, a C ₈ -C ₁₂ α-olefin) has demonstrated improved solubility in hydrocarbons and thereby improved drag reduction efficiency. In one embodiment, the first α-olefin comonomer is 1-hexene and the second α-olefin comonomer is 1-dodecene. Various molar ratios are contemplated for the first α-olefin and second α-olefin comonomers. In one embodiment, the α-olefin monomers are 1- hexene and 1-dodecene present in a 1:4 to 4: 1 molar ratio, or a 1:2 to 2: 1 molar ratio, or a 1: 1 mole ratio.

[0016] Embodiments of the present catalyst used in the polymerization may include a tertiary monophenyl amine, a titanium halide, and a cocatalyst. In specific embodiments, present catalyst consists of or consists essentially of the tertiary monophenyl amine, a titanium halide, and a cocatalyst. In additional embodiments, the catalyst is absent of a carrier or support.

[0017] The tertiary monophenyl amine may have the formula R ¹ R ² N-aryl, where R ¹ and R ² are the same or different, and R ¹ and R ² may each be a hydrogen, an alkyl, or a cycloalkyl group with the proviso that at least one of R ¹ and R ² contains at least one carbon atom. The aryl group may be substituted or unsubstituted. Examples of the tertiary monophenyl amine may include but are not limited to Ν,Ν-diethylaniline, N-ethyl-N-methylparatolylamine, N,N-dipropylaniline, Ν,Ν-diethylmesitylamine, and combinations thereof. In one embodiment, the tertiary monophenyl amine is N,N-diethylaniline.

[0018] The titanium halide has the formula TiX _m , where m is from 2.5 to 4.0 and X is a halogen containing moiety. In one embodiment, the titanium halide catalyst is crystalline titanium trichloride, for example, in the following complex TiCl ₃ ●l/3AlCl ₃ , which is prepared by reducing titanium tetrachloride (TiCl ₄ ) with metallic aluminum (Al).

[0019] The cocatalyst may be an organoaluminum compound having the formula AlR _n Y ₃ _ _n where R is a hydrocarbon radical, Y is a halogen or hydrogen, and n is 1-20. Representative examples of such organoaluminum compounds which can be used alone or in combination are trimethyl aluminum, triethyl aluminum, tri-n-propyl aluminum, tri-n-butyl aluminum, tri- isobutyl aluminum, tri-n-hexyl aluminum, tri(2-methylpentyl) aluminum, tri-n-octyl aluminum, diethyl aluminum hydride, diisobutyl aluminum hydride, diisoproyl aluminum chloride, dimethyl aluminum chloride, diethyl aluminum chloride, diethyl aluminum bromide, diethyl aluminum iodide, di-n-propyl aluminum chloride, di-n-butyl aluminum chloride, and diisobutyl aluminum chloride. In one embodiment, the cocatalyst is diethyl aluminum chloride.

[0020] Various amounts are contemplated for the catalyst components. For example, the tertiary monophenyl amine may be present in an amount of from 0.1 millimole (mmol) to 2 mmol, or from 0.25 mmol to 1 mmol, or from 0.4 mmol to 0.8 mmol, or 0.5 mmol. Moreover, the titanium halide may be present in an amount of from 0.1 millimole (mmol) to 1 mmol, or from 0.2 mmol to 0.8 mmol, or from 0.2 mmol to 0.5 mmol, or 0.25 mmol. Further, the cocatalyst may be present in an amount of from 0.2 millimole (mmol) to 5 mmol, or from 0.5 mmol to 2.5 mmol, or from 0.8 mmol to 1.5 mmol, or 1.0 mmol. The molar ratio of the cocatalyst to titanium halide may be from 1: 1 to 10: 1, or 2: 1 to 8: 1, or 3: 1 to 5: 1, or 4: 1. Alternatively, the molar ratio of the cocatalyst to tertiary monophenyl amine may be from 1 : 1 to 5: 1, or 2: 1 to 4: 1, or 2: 1.

[0021] The hydrocarbon solvent may include various solvent compositions. For example, a halogenated hydrocarbon solvent such as ethylene dichloride is contemplated for the hydrocarbon solvent. Moreover, the hydrocarbon solvent may include aromatic solvents, such as toluene, or cumene. Commercial examples of suitable aromatic solvents include Koch Sure Sol® 100 and KOCH Sure Sol® 150. Other solvents may include straight chain aliphatic compounds (for example, hexane and heptane), branched hydrocarbons, cyclic hydrocarbons, and combinations thereof. As will be described in the paragraphs to follow, the addition of solvent and the timing of solvent addition may impact the final properties of the DRA.

[0022] Referring to the embodiment depicted in FIG. 1, the method 100 of producing the DRA includes the step 110 of delivering the first dried α-olefin monomer and optionally the second α-olefin monomer to a reactor or series of reactors. In specific embodiments, the reactor may include a stirring rod or a similar agitation device. In multiple embodiments, the reactor is a continuous, batch, or semi-batch stirred tank reactor. These olefin monomers may be included in the presence of solvent and optionally in the presence of a scavenger, such as triisobutylaluminum (TIBA). In specific embodiments, the reactor may be subjected to an inert gas. For example, the first α-olefin monomer and the second α-olefin may be delivered to the reactor under argon flow. [0023] Referring again to FIG. 1, the catalyst may be activated prior to delivery to the reactor. In one embodiment, the activation step 120 may involve activating the titanium halide and cocatalyst by heating prior to delivery to the reactor. Various temperatures are contemplated, for example 30 to 60 °C, or 40 °C. In another embodiment, the tertiary monophenyl amine is mixed with the titanium halide and the cocatalyst during the activation step. Alternatively, the tertiary monophenyl amine may be added to the reactor separate from the titanium halide and cocatalyst either before or after the addition of activated titanium halide and cocatalyst to the reactor.

[0024] Next, the activated catalyst may be added to the reactor 130 which initiates the polymerization 150. The polymerization may occur at or less than ambient temperature. In a specific embodiment, the polymerization may occur at ambient temperature. Without being limited to specific advantages, performing the polymerization at ambient temperature reduces process costs in comparison to other conventional processes which operate under cryogenic conditions.

[0025] In yet another embodiment, the polymerization may occur in an argon atmosphere for a duration of 4 to 6 hours with a reaction temperature of 15 to 25 °C. In at least one embodiment, the polymerization in argon may occur with a reaction temperature of -20 to 30 °C. Further, in at least one embodiment, the polymerization time in argon may extend for a duration of 30 minutes to 12 hours. As stated previously, the reactor may be agitated by a mechanical stirring device. For example, the stirring speed may be between 400 to 900 revolutions per minute (rpm), 600 to 800 rpm, or 700 rpm.

[0026] Referring to FIG. 1, the hydrocarbon solvent 140 may be added at once, gradually, or at multiple times during the process. For example, hydrocarbon solvent may be added in bulk 142 prior to the polymerizing step 150. Alternatively, the hydrocarbon solvent may be added gradually throughout the polymerization process, or after the start of the "rod climbing effect" 160. The rod-climbing effect refers to a phenomenon resulting from mechanical stirring in the reactor when (i) the viscosity of the reaction mixture exceeds a certain critical value, and (ii) the normal forces with respect to the surface of the reaction mixture exceed the corresponding tangential forces, thereby causing the mixture to ascend or climb the stirring rod. [0027] Referring again to FIG. 1, the reactor may be quenched with methanol 170 thereby at least partially terminating the polymerization process. At which point, the UHMW C ₄ -C ₃₀ a- olefin DRA is produced 180. In specific embodiments, the DRA may have a non-crystalline or amorphous structure. Alternative quenching procedures are contemplated as are alternative procedures to terminate the polymerization process.

[0028] Without being bound by theory, further branching, for example, long chain branching, may enhance the solubility of the DRA. This increased branching may be quantified in part by the molecular weight distribution (MWD) metric. In one or more embodiments, the UHMW C ₄ - C ₃₀ α-olefin copolymer drag reducing agent may have an MWD of at least 2.0, where MWD is defined as M _w /M _n with M _w being a weight average molecular weight and M _n being a number average molecular weight. In another embodiment, the MWD may be at least 3.25. Moreover, the UHMW C ₄ -C ₃₀ α-olefin polymer drag reducing agent has a weight average molecular weight (M _w ) of at least 1.5 x 10 ⁶ g/mol, or at least 2.0 x 10 ⁶ g/mol, or at least 2.5 x 10 ⁶ g/mol. The polydispersity index (PDI) may be at least 2.0.

[0029] For additional details regarding the embodiments of the present disclosure, the following examples are provided.

[0030] EXAMPLES

[0031] All the synthesis procedures and manipulations were done under inert environment using argon, standard Schlenk technique, and a glove box. Toluene, 1-hexene (C ₆ ), and 1- dodecene (C ₁₂ ) were dried by contacting with an activated 4A molecular sieve at room temperature overnight. The molecular sieve was activated at 230 °C.

[0032] Reference Example

[0033] 1-hexene (C ₆ ) and 1-dodecene (C ₁₂ ) were copolymerized using a computer- interfaced, AP-Miniplant GmbH laboratory- scale reactor set-up. The reactor consists of a fixed top head and a one-liter jacketed Biichi glass autoclave. The glass reactor was baked for 2 hours (h) at 120 °C. Then, it was purged with nitrogen four times at the same temperature. The reactor was cooled from 120 °C to room temperature. [0034] Specifically, the desired volume of 1-hexene (C ₆ ), dodecene (C ₁₂ ), and dried toluene dissolved in 200 milliliters (mL) of dried n-hexane and 1.0 mL of 1.0 M triisobutylaluminum (TIB A) were transferred to the reactor under mild argon flow.

[0035] The required amount of solid TiCl ₃ ●l/3AlCl ₃ dissolved in dried toluene was pre- activated with a calculated amount of diethyl aluminum chloride (DEALC) in a Schlenk flask by heating them at 40°C for 30 minutes (min).

[0036] The whole volume of the pre-activated catalyst solution was siphoned into the reactor under mild argon flow to start polymerization for 5 hours with reaction temperature and stirrer speed set at 20 °C and 700 rpm, respectively. Additionally, 200 mL of dried toluene was added when the rod-climbing effect started. The reaction mixture was quenched by adding methanol with vigorous agitation.

[0037] Upon completion of the polymerization trial as described previously, the reactor was opened, the resulting honey-like reaction mixture was stored in a bottle, and its weight was determined. The glass reactor vessel was cleaned using technical grade toluene for the next trial.

[0038] The synthesized C ₆ -C ₁₂ reference copolymer was characterized in terms of weight average molecular weight M _w using high temperature gel permeation chromatography (GPC) (Polymer Lab GPC 220, UK).

[0039] The following table lists properties of the DRAs produced by the prior Reference Example as well as additional examples. In transition metal-catalyzed olefin polymerization, M _w and catalyst productivity are approximately inversely related. However, catalyst productivity is a complex function of monomer and co-monomer concentration, macro-mixing and micro- mixing, and temperature in combination with thermodynamic, kinetic, and mass transfer limitations. Preferably, the catalyst productivity is maximized while maintaining the M _w above 1 x 10 ⁶ g/mol. [0040] Table 1 : Summary of DRA synthesis (polymerization) trials

[0041] When comparing Example 1 to the Reference Example, it is clear that the addition of tertiary monophenyl amine (Ν,Ν-diethylaniline) in Example 1 improves the monomer conversion and catalyst productivity. Moreover, when comparing Example 2 to Example 3, it is clear that the addition of hydrocarbon solvent such as cumene and toluene at the beginning of the rod climbing effect as in Example 3 is better at monomer conversion and catalyst productivity than Example 2 where hydrocarbon solvent is included dropwise throughout the process. Additionally, when comparing Examples 1, 3, and 4 to the Reference Example, an increase in catalyst productivity is observed. Without wishing to be bound by theory, the higher catalyst productivity in Examples 1, 3, and 4 over the Reference Example is believed to be the result of the interaction and complexation of the precatalyst Τί0 ₄ · 1/3ΑΚ¾ with N,N- diethylaniline. N-N-diethylaniline is sterically and electronically hindered. The steric hindrance originates from the ethyl substituents on the N heteroatom. Similarly, the phenyl group, which is an electron-withdrawing substituent, reduced the electron density on the basic N heteroatom and introduces electronic effect. This coherent and combined steric and electronic effect increases the catalyst productivity compared to the Reference Example by playing the role of a catalyst promoter. Increased catalyst productivity results in a greater production volume and allows for a commensurate reduction in production cost.

[0042] Adjustments to the process parameters may also adversely affect the catalyst productivity. Specifically, in Example 5 the precatalyst TiCl ₄ * 1/3 AICI ₃ , N,N-diethylaniline, and DEALC were all contacted together. This results in the Lewis base (N,N-diethylaniline) being available to coordinate simultaneously with both TiCl ₄ * 1/3 AICI ₃ and DEALC. This adversely affects the alkylation of TiCl ₄ * 1/3 AICI ₃ by DEALC and the subsequent creation of open coordination sites at the titanium to form active sites which results in a catalyst productivity drop. Further, in Example 2 the 200 mL of toluene was added dropwise throughout the polymerization trial unlike in the Reference Example and Examples 1, 3, and 4 where the toluene was added as a single bolus as soon as the rod-climbing effect was noted. The drop- wise addition allows the polymerization to turn highly viscous which restricts the desired macromixing and micromixing of the growing polymer chains which contain the active center with the unreacted monomer. This results in a comparative decrease in catalyst productivity. Finally, in Examples 6-9 benzophenone was added. The benzophenone decreased both the rates of propagation and termination, albeit the termination rate decreased more than the propagation resulting in a net decrease in catalyst productivity. However, reduction in catalyst productivity may result in a commensurate improvement in drag reduction performance. As such, through process adjustments, a process of forming a DRA with desirable drag reduction performance and acceptable catalyst productivity may be achieved.

[0043] Drag Reduction Tests

[0044] The drag reducing performance of the C ₆ -C ₁₂ reference UHMW copolymer was evaluated using the experimental set-up shown in FIG. 2. This consists of a horizontal stainless steel pipeline of 0.5 inch outer diameter (OD = 0.01270 m) and 0.4 inch inner diameter (ID = 0.01016 m). The first pressure sensor 220 was located around 4 meters (m) from the kerosene hydrocarbon fluid inlet 216. The second pressure sensor 222 was located 1.5 m from the first pressure sensor 220. The DRA injection point 218 is located 20 cm from the kerosene fluid inlet 216. The pressure gradient was measured using a high accuracy differential pressure transducer 224 (Siemens) with a manufacturer states error of less than 0.065%. The flow of the kerosene fluid, which was stored initially in a tank 200, was delivered and controlled by ball valves 202, 209, pump 204, and flow control valve 206. The flow rate of kerosene was measured using a high accuracy vortex flow meter 208 with a manufacturer states error of less than 2%. The temperature of the liquid was measured using a resistance temperature detector (RTD) temperature sensor 226 located at the end of the test section. Downstream of the temperature sensor 226, a portion of the DRA infused kerosene fluid was separated at splitter 230 with a portion being discarded in waste tank 234 and another portion recycled to the kerosene tank 200.

[0045] Referring again to FIG. 2, the DRA polymer solution with liquid kerosene as a solvent, which were the DRAs produced in the Examples listed in Table 1, were injected into the test pipe using a diaphragm dosing pump 212. The DRA polymer solution concentration was determined using the polymer content in the reaction mixture and configured to be 120 parts per million (ppm) of DRA in the test pipe after mixing. The flow rate of the DRA polymer solution was controlled with a variable speed drive 214, lined-up with the pump 212. The pump 212 was calibrated before each experiment using different speeds. The pump speed was varied from 0 to 1,400 rpm. The pump flow rate was changed between 0.01 and 2 L/min with an accuracy of 2-4%. The DRA polymer solution was introduced into the kerosene feed at DRA injection point 218, which is a single hole at the top of the pipe having a diameter of 2 mm, located 20 cm upstream of the kerosene inlet 216.

[0046] The drag reducing performance tests of the C ₆ -C ₁₂ reference UHMW copolymer were conducted using a kerosene flow rate of 10 L/min. This makes the average velocity of kerosene in the pipe about 2.1 m/s (6.8 ft/s) with a Reynolds number about 18,850, which indicates high turbulent flow.

[0047] The effectiveness of drag reduction is expressed by percent drag-reduction (%DR) defined as follows:

where are pressure drops with and without the drag- reducing

agent, respectively.

[0048] Table 2 as follows summarizes drag reduction for the Examples of Table 1.

[0049] Table 2: Summary of DRA performance trials

[0050] When comparing Examples 1 through 9 and the Reference Example to the commercially available DRA1, a clear improvement in the percent drag-reduction is evident. Similarly, Examples 2 and 7 through 9 when compared to the commercially available DRA2 exhibit a clear improvement in the percent drag-reduction as well. Improvement in the level of drag reduction results in a reduction in required pumping energy and a commensurate savings in electricity and associated costs.

[0051] It should be apparent to those skilled in the art that various modifications and variations can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification covers the modifications and variations of the various described embodiments provided such modification and variations come within the scope of the appended claims and their equivalents.