Field of Invention

[0001] This invention relates to a process for the synthesis of amine oxides from tertiary amines with hydrogen peroxide in spinning disk reactors.

Technical Background

[0002] Fatty substances like tertiary amines and aqueous materials (i.e., hydrogen peroxide) are typically immiscible. Thus, reactions such as oxidation of tertiary amines to amine oxides using aqueous solutions of hydrogen peroxide require solvents that are able to compatibilize the two immiscible materials, enabling the reaction to take place in conventional stirred tank reactors. Without compatibilizing solvents, the surface area between the amine and hydrogen peroxide phases is small, significantly limiting the rate of reaction between the constituents of the two phases. Moreover, traditional techniques for making amine oxides have used batch processes and result in aqueous compositions comprising approximately 30% by weight of the aqueous composition of amine oxide. Thus, in order to achieve required levels of amine oxide in final commercial products, large quantities of such aqueous amine oxide compositions need to be added.

[0003] Of course, chemical reactions cannot occur until individual molecules of the reagents are brought together and physical interactions between components can be facilitated. Stirred tank reactors can facilitate these interactions, but only after sufficient time has elapsed to provide the necessary uniformity of interdispersion of the reagents. Furthermore, with respect to the reaction of tertiary amines and hydrogen peroxide, a stoichiometric mixture is highly viscous and generates heat that must be removed in order to control the reaction temperature. The current reactor technology (stirred tank reactors) is unable to remove the heat of reaction at a rate sufficient to maintain the desired reaction temperature if the reactants are mixed together in stoichiometric quantities.

[0004] The spinning disk reactor (SDR) is a continuous reactor able to create intimate contact between immiscible materials through physical means by creating forces that intimately mix at least two reactants together in stoichiometric (or other) ratios. The spinning disk reactor allows for the continuous mixing of the immiscible reactants without the use of a compatibilizing solvent (i.e., alcohol, glycol, etc.), while simultaneously removing the heat of the reaction at a rate sufficient to maintain the desired reaction temperature. Thus, employing a SDR allows for the continuous manufacture of fatty amine oxides in aqueous solution.

SUMMARY

[0005] Although SDR is an improvement over stirred tank reactor technology, current methods are typically limited to amine oxide production processes where a portion of the amine oxide product is recycled or a compatibilizing solvent is required. The Applicant recognized the need for an improved SDR amine oxide production process.

[0006] The Applicant has found a continuous process for making an amine oxide composition on a large scale without the need for compatibilizing solvent and little or no recycling requirement. In particular, the process includes mixing a tertiary amine composition and an aqueous oxidizing composition in a first spinning disk reactor to provide an intermediate composition and either (1) diluting and/or digesting the intermediate composition to provide the amine oxide composition or (2) mixing the intermediate composition in a second spinning disk reactor to provide the amine oxide composition, or both. Between 0% and 80% of the intermediate composition is recycled into the first spinning disk reactor, and at least about 80% by weight of tertiary amines in the tertiary amine composition are converted to amine oxides.

[0007] All publications referenced herein are incorporated by reference in their entirety to the extent they are not inconsistent with the teachings presented herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The Figure illustrates one embodiment of a spinning disk reactor.

DETAILED DESCRIPTION

[0009] The present disclosure provides a continuous process for making an amine oxide composition. The process includes mixing a tertiary amine composition and an aqueous oxidizing composition in a first spinning disk reactor to provide an intermediate composition and one of (1) diluting and/or digesting the intermediate composition to provide the amine oxide composition and (2) mixing the intermediate composition in a second spinning disk reactor to provide the amine oxide composition. Between 0% and 80% of the intermediate composition is recycled into the first spinning disk reactor, and at least about 80% by weight of tertiary amines in the tertiary amine composition are converted to amine oxides. In some embodiments, the process described herein yields a final amine oxide composition having an amine oxide concentration of greater than 80% by weight.

[0010] The continuous process involves a reaction between a tertiary amine and an aqueous oxidizing agent. The tertiary amine can be of formula (I):

where R ¹ , R ² and R ³ are independently selected from linear or branched, saturated or unsaturated, cyclic or acyclic Ci-C2 ₄ alkyl, poly(alkylene oxide), poly(alkylene oxide)-Ci- Ci ₂ alkyl-OR, Ci-C2 ₄ alkyl-OR, C2-C2 ₄ amide, and Ci-C2 ₄ amine, where R is hydrogen or Ci-C ₄ alkyl.

[0011] In some embodiments, one or more of R ¹ , R ² and R ³ are independently Ci-

C ₂₄ alkyl, Ci-Ci ₈ alkyl, Ci-Ci ₂ alkyl, Ci-C ₆ alkyl, Ci-C ₃ alkyl, C ₂ -C ₂₄ alkyl, C ₃ -C ₂₄ alkyl, C ₄ - C ₂₄ alkyl, C ₅ -C ₂₄ alkyl, C ₆ -C ₂₄ alkyl, C ₈ -C ₂₄ alkyl, Ci ₂ -C ₂₄ alkyl, Ci ₆ -C ₂₄ alkyl, C ₂ -Ci ₈ alkyl, C ₂ -Ci ₂ alkyl, C ₂ -C ₆ alkyl, C ₂ -C ₂ oalkyl, C ₃ -C ₂₀ alkyl, C ₄ -C ₂₀ alkyl, C ₅ -C ₂ oalkyl, C ₆ -C ₂ oalkyl, C ₂ -C ₂ 2alkyl, C ₃ -Ci ₈ alkyl, C ₄ -Ci ₈ alkyl, C ₅ -Ci ₈ alkyl, C ₆ -Ci ₈ alkyl, C ₂ -Ci ₈ alkyl, C ₃ -Ci ₈ alkyl, G _t -Cisalkyl, C ₅ -Ci ₈ alkyl, C ₆ -Ci ₈ alkyl, C ₂ -Ci ₆ alkyl, C ₃ -Ci ₆ alkyl, C ₄ -Ci ₆ alkyl, C ₅ -Ci ₆ alkyl, Ce-Ciealkyl, C ₂ -Ci ₂ alkyl, C ₃ -Ci ₂ alkyl, C ₄ -Ci ₂ alkyl, C ₅ -Ci ₂ alkyl or C ₆ -Ci ₂ alkyl.

[0012] In some embodiments, one or more of R ¹ , R ² and R ³ are independently Ci- C ₂₄ alkyl-OR, Ci-Ci ₈ alkyl-OR, Ci-Ci ₂ alkyl-OR, Ci-C ₆ alkyl-OR, Ci-C ₃ alkyl-OR, C ₂ - C ₂₄ alkyl-OR, C ₃ -C ₂₄ alkyl-OR, C ₄ -C ₂₄ alkyl-OR, C ₅ -C ₂₄ alkyl-OR, C ₆ -C ₂₄ alkyl-OR, C ₈ - C ₂₄ alkyl-OR, Ci ₂ -C ₂₄ alkyl-OR, Ci ₆ -C ₂₄ alkyl-OR, C ₂ -Ci ₈ alkyl-OR, C ₂ -Ci ₂ alkyl-OR, C ₂ - C ₆ alkyl-OR, C ₂ -C ₂₀ alkyl-OR, C ₃ -C ₂₀ alkyl-OR, C ₄ -C ₂₀ alkyl-OR, C ₅ -C ₂₀ alkyl-OR, C ₆ - C ₂₀ alkyl-OR, C ₂ -C ₂ 2alkyl-OR, C ₃ -Ci ₈ alkyl-OR, C ₄ -Ci ₈ alkyl-OR, C ₅ -Ci ₈ alkyl-OR, C ₆ - Cisalkyl-OR, C ₂ -Ci ₈ alkyl-OR, C ₃ -Ci ₈ alkyl-OR, C ₄ -Ci ₈ alkyl-OR, C ₅ -Ci ₈ alkyl-OR, C ₆ - Cisalkyl-OR, C ₂ -Ci ₆ alkyl-OR, C ₃ -Ci ₆ alkyl-OR, C ₄ -Ci ₆ alkyl-OR, C ₅ -Ci ₆ alkyl-OR, C ₆ - Cigalkyl-OR, C ₂ -Ci ₂ alkyl-OR, C ₃ -Ci ₂ alkyl-OR, C ₄ -Ci ₂ alkyl-OR, C ₅ -Ci ₂ alkyl-OR or C ₆ - Ci ₂ alkyl-OR.

[0013] In the foregoing embodiments, the alkyl portion of each of R ¹ , R ² and R ³ , independently of the others, can be any one of a straight or branched Ci, C ₂ , C ₃ , C ₄ , C ₅ , C ₆ , C ₇ , C ₈ , C ₉ , C ₁₀ , Ci 1 , Ci ₂ , C ₁₃ , i ₄ , C ₁₅ , Ci ₆ , C ₁₇ , Ci ₈ C ₁₉ , C ₂ o, C _2i , C ₂₂ , C ₂₃ , or C ₂₄ alkyl.

[0014] In some embodiments, poly(alkylene oxide) is a poly(alkylene oxide) chain capped with an R group. Poly(alkylene oxide) can be derived from ethylene oxide, propylene oxide or butylene oxide, and can be a combination of two or three different alkylene oxide units. In some embodiments, the poly(alkylene oxide) is poly(ethylene glycol) or poly (propylene glycol).

[0015] In some embodiments, poly(alkylene oxide) can have the structure of formula (II):

where w is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0016] In some embodiments, R ¹ and R ² are Ci-C ₄ alkyl, and R ³ is Ci-C2 ₄ alkyl or Ci- C ₂₄ alkyl-OR, where R is hydrogen or Ci-C ₄ alkyl. For example, the tertiary amine can be an alkyldimethylamine.

[0017] In some embodiments, R ¹ and R ² are poly(alkylene oxide), and R ³ is Ci- C ₂₄ alkyl or Ci-C ₂₄ alkyl-OR, where R is hydrogen or Ci-C ₄ alkyl.

[0018] In some embodiments where the tertiary amine includes an OR group, R is hydrogen. In other embodiments, R is Ci-C ₄ alkyl. For example, R can be methyl, ethyl, n- propyl, iso-propyl, n-butyl, sec-butyl, iso-butyl or tert-butyl.

[0019] In some embodiments, one of R ¹ , R ² and R ³ is an amide group (e.g., has the general formula R ⁴ (CO)NR ⁵ where R ⁴ + R ⁵ contains between 1 and 23 carbon atoms). In other embodiments, one of R ¹ , R ² and R ³ is an amine group containing between 1 and 24 carbon atoms.

[0020] In some embodiments, the tertiary amine composition does not include a solvent other than water. That is, the tertiary amine composition and the aqueous oxidizing composition do not contain a compatibilizing solvent. Compatibilizing solvents are often used in amine oxide synthesis to decrease the viscosity of the reaction mixture. But compatibilizing solvents are usually flammable, so a process that does not require compatibilizing solvents is safer than one that does, particularly on a large scale (generally 40,000 to 50,000 pound batches). Also, when used, compatibilizing solvents will also be present in the amine oxide product of the process. Typical compatibilizing solvents include, but are not limited to, ethanol, isopropanol and propylene glycol.

[0021] In other embodiments, the reaction solution contains a compatibilizing solvent.

[0022] The continuous process involves the oxidation of the tertiary amine with an aqueous oxidizing agent (present in the aqueous oxidizing composition). The oxidation can be performed using a peroxide or a source of peroxide ( e.g ., peroxide generated in situ). The oxidation can be conducted in water. In some embodiments, the aqueous oxidizing composition does not contain a compatibilizing solvent. In some embodiments, the peroxide is tert-butyl peroxide or hydrogen peroxide. Peroxides are commercially available in aqueous solutions of various strengths up to 90% by weight. In some embodiments, the aqueous oxidizing agent is hydrogen peroxide.

[0023] During the reaction, the aqueous oxidizing agent can be present in a stoichiometric amount with the tertiary amine. The tertiary amine (in the tertiary amine composition) and the aqueous oxidizing agent (in the aqueous oxidizing composition) can be present in a 1 :1 mixture or as a slight excess of the aqueous oxidizing agent. For example, the ratio of the tertiary amine to the aqueous oxidizing agent can be between about 1 : 1 and about 1 : 1.25. In some embodiments, the ratio of tertiary amine to aqueous oxidizing agent is about 1 :1, or about 1 :1.05, or about 1 :1.1, or about 1 :1.15, or about 1 :1.2, or about 1 :1.25.

[0024] The tertiary amine composition and the aqueous oxidizing composition are mixed in a spinning disk reactor, which enables the mixing of thin films of reactants under high rotational shear between a rotating plate and a stationary plate. The spinning disk reactor is able to overcome the high viscosity encountered in amine oxide synthesis.

[0025] In an embodiment, the process includes mixing a tertiary amine composition and an aqueous oxidizing composition in a first spinning disk reactor to provide an intermediate composition and diluting and/or digesting part of the intermediate composition to provide an amine oxide composition and mixing the remainder of the intermediate composition in a second spinning disk reactor to provide another amine oxide composition, whereby both amine oxide compositions are optionally combined to form a final amine oxide composition. In another embodiment the intermediate composition is either diluted and/or digested or fed into a second spinning disk reactor.

[0026] In an embodiment the process is batch- wise and the same spinning disk reactor is used as both the first and second spinning disk reactor. In an embodiment the process is continuous and two separate spinning disk reactors are used.

[0027] Conventional spinning disk reactors can be used according to the present disclosure. The Figure represents a typical description and set up for a spinning disk reactor. The first spinning disk reactor includes a first rotating surface, a first stationary surface, and a first mechanically adjustable gap that extends between the first rotating surface and the first stationary surface. The Figure schematically illustrates one example of a spinning disk reactor. Spinning disk reactor 10 includes reactor housing 12, rotor 14, first rotating surface 16, stator 18, first stationary surface 20, axial feed port 22, annular feed port 24, exit port 26, gap 28 and actuating means 30. Rotor 14 is driven by a motor or other attached rotational component (not shown in the Figure) so that first rotating surface 16 rotates within reactor 10. Stator 18 remains stationary so that first stationary surface 20 is fixed (i.e. does not rotate) within reactor 10. Reactants are introduced to reactor 10 via axial feed port 22 and annular feed port 24; products are removed from reactor 10 via exit port 26.

[0028] Gap 28 is a mechanically adjustable gap that extends between first rotating surface 16 and first stationary surface 20. A mechanically adjustable gap is one in which the gap distance is adjusted using mechanical means, such as with an actuator that is controlled by electrical voltage or current, pneumatic or hydraulic pressure or human power. The first gap can be adjusted by an operator via switches, levers or computer input or by operational software or routines that communicate with the first spinning disk reactor. As shown in the Figure, actuating means 30 adjusts the position of stator 18 relative to rotor 14 within reactor 10. The end of rotor 14 within reactor housing 12 “floats” and stator 18 is moved to change the gap distance (the distance between first rotating surface 16 and first stationary surface 20. The first gap can be adjusted before introducing the tertiary amine composition and the aqueous oxidizing composition in the first spinning disk reactor and remain fixed during the reaction. Alternatively, the gap can be mechanically adjusted during the reaction process. A spinning disk reactor with a mechanically adjustable gap does not require a supply pressure to maintain the gap. That is, the gap is not adjusted based on the pressures of the reactants delivered to the reactor (e.g., the tertiary amine composition and the aqueous oxidizing composition). In some embodiments, the first mechanically adjustable gap can be about 100 microns to about 600 microns. The rotational speed of the first rotating surface of the first spinning disk reactor can be variable up to 7000 RPM.

[0029] In some embodiments, the first mechanically adjustable gap can be about 100 microns to about 150 microns, about 100 microns to about 200 microns, about 100 microns to about 250 microns, about 100 microns to about 300 microns, about 100 microns to about 350 microns, about 100 microns to about 400 microns, about 100 microns to about 450 microns, about 100 microns to about 500 microns, about 100 microns to about 550 microns, about 150 microns to about 200 microns, about 150 microns to about 250 microns, about 150 microns to about 300 microns, about 150 microns to about 350 microns, about 150 microns to about 400 microns, about 150 microns to about 450 microns, about 150 microns to about 500 microns, about 150 microns to about 550 microns, about 150 microns to about 600 microns, about 200 microns to about 250 microns, about 200 microns to about 300 microns, about 200 microns to about 350 microns, about 200 microns to about 400 microns, about 200 microns to about 450 microns, about 200 microns to about 500 microns, about 200 microns to about 550 microns, about 200 microns to about 600 microns, about 250 microns to about 300 microns, about 250 microns to about 350 microns, about 250 microns to about 400 microns, about 250 microns to about 450 microns, about 250 microns to about 500 microns, about 250 microns to about 550 microns, about 250 microns to about 600 microns, about 300 microns to about 350 microns, about 300 microns to about 400 microns, about 300 microns to about 450 microns, about 300 microns to about 500 microns, about 300 microns to about 550 microns, about 300 microns to about 600 microns, about 350 microns to about 400 microns, about 350 microns to about 450 microns, about 350 microns to about 500 microns, about 350 microns to about 550 microns, about 350 microns to about 600 microns, about 400 microns to about 450 microns, about 400 microns to about 500 microns, about 400 microns to about 550 microns, about 400 microns to about 600 microns, about 450 microns to about 500 microns, about 450 microns to about 550 microns, about 450 microns to about 600 microns, about 500 microns to about 550 microns, about 500 microns to about 600 microns, or about 550 microns to about 600 microns.

[0030] In some embodiments, the first mechanically adjustable gap can be about 100 microns to about 300 microns, or about 110 microns to about 300 microns, or about 100 microns to about 290 microns, or about 110 microns to about 290 microns.

[0031] The tertiary amine composition and the aqueous oxidizing composition can enter the spinning disk reactor at either of two separate points. One reactant can enter through a first inlet and the other reactant can enter through a second inlet. The rotation of the first rotating surface then causes shearing of the two reactants into thin films that mix with one another. The temperature of the reactor is maintained by an external fluid that is continuously pumped through the reactor, such as through internal cavities located within the stationary and/or rotating plates.

[0032] The tertiary amine composition and the aqueous oxidizing composition can be mixed in the first spinning disk reactor at temperatures ranging from about 30 °C to about 80 °C. In some embodiments, the temperature in the first spinning disk reactor is about 30 °C to about 75 °C, about 35 °C to about 80 °C, about 30 °C to about 70 °C, about 40 °C to about 70 °C, about 40 °C to about 60 °C, about 50 °C to about 80 °C, about 60 °C to about 80 °C, about 40 °C to about 50 °C, about 60 °C to about 80 °C, or about 35 °C to about 75 °C.

[0033] Following mixing in the first spinning disk reactor, the continuous process provides an intermediate composition that includes amine oxides. The amine oxides can be of formula (III):

RAR ²

N ©

R ³

(III)

where R ¹ , R ² and R ³ are defined above.

034 In some embodiments, one pair of R 1 , R 2 and R 3 (i.e. R 1 and R 2 , R 2 and R 3

[0 ] or R ¹ and R ³ ) can bond together following the reaction with the aqueous oxidizing agent to form a cyclic ether group, similar to morpholine ( e.g ., together R ¹ and R ² have the formula CH2CH2OCH2CH2). The above amine oxide differs from morpholine in that it contains an R ³ group instead of-H. [0035] The amine oxides can be provided at a concentration (within the intermediate composition) of greater than or equal to about 70% by weight. In some embodiments, the concentration of the amine oxide is greater than or equal to about 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84% or about 85% by weight.

[0036] In some embodiments, the intermediate composition is not recycled (0% recycling) into the first spinning disk reactor. The spinning disk reactor used in the process is able to overcome the high viscosity encountered in amine oxide synthesis with no need for recycling the reaction mixture. Known processes in the art require that 80% or more of the amine oxide product be recycled back into the same reactor so that yields up to 80% are obtained. The present process provides amine oxides at yields that can be greater than or equal to about 80% without the need for recycling, which enables the current process to provide high yields on a large scale.

[0037] In other embodiments, some amount of recycling of the intermediate composition to the first spinning disk reactor can occur. Generally speaking, the less intermediate composition recycled, the shorter the overall reaction time. Thus, minimizing the amount of recycling of the amine oxide to the first spinning disk reactor yields faster reaction/production times. According to the instant disclosure, less than 80% of the intermediate composition is recycled to the first spinning disk reactor. Further, less than 40%, less than 20%, less than 10% and less than 5% of the intermediate composition can be recycled to the first spinning disk reactor.

[0038] In some embodiments, the spinning disk reactor is substantially free of catalysts,“substantially free” meaning that the contents within the spinning disk reactor contain less than 2% by weight of catalyst.

[0039] The intermediate composition can be diluted and/or digested to provide an amine oxide composition. Diluting can include diluting the intermediate composition with water or other solvent. The intermediate composition can be diluted with water so it is about 30 weight percent to about 50 weight percent amine oxides. In some embodiments, the intermediate composition is about 30 weight percent to about 45 weight percent amine oxide, about 30 weight percent to about 40 weight percent amine oxide, about 30 weight percent to about 35 weight percent amine oxide, about 35 weight percent to about 50 weight percent amine oxide, about 40 weight percent to about 50 weight percent amine oxide, or about 45 weight percent to about 50 weight percent amine oxide. [0040] The intermediate composition can also be digested. Digestion refers to holding the fully mixed intermediate composition at a certain temperature for a period of time necessary for the reaction between the tertiary amine and the aqueous oxidizing agent to complete. During digestion the intermediate composition can be stirred in a tank or pumped through a pipe. Digestion time can vary. In some embodiments, digestion time is between about 20 minutes and 120 minutes. In some embodiments, digestion of the intermediate composition is performed in an oven. The digestion of the intermediate composition can include heating the intermediate composition in the oven to about 40 °C to about 80 °C. In some embodiments, the temperature of digestion is about 40 °C to about 75 °C, about 40 °C to about 70 °C, about 40 °C to about 60 °C, about 50 °C to about 80 °C, about 60 °C to about 80 °C, about 40 °C to about 50 °C, about 60 °C to about 80 °C, or about 45 °C to about 75 °C. Typical digestion times for conventional stirred tank reactions can range from 4 to 12 hours. Thus, the SDR methods described herein provide significantly shorter overall reaction times even when digestion is carried out.

[0041] In some embodiments, the intermediate composition can be both diluted and digested to provide the amine oxide composition. In other embodiments, the intermediate composition can be diluted but not digested to provide the amine oxide composition. In other embodiments, the intermediate composition can be digested but not diluted to provide the amine oxide composition. In some embodiments, dilution occurs before digestion. In other embodiments, digestion occurs before dilution.

[0042] During dilution or digestion, the intermediate composition can be transferred to a holding tank that is separate from the first (or second) spinning disk reactor. In some embodiments, the intermediate composition is transferred to a holding tank that is separate from the first spinning disk reactor for both dilution and digestion. In other embodiments, the intermediate composition is transferred to a holding tank for digestion, but is diluted in a second spinning disk reactor. In other embodiments, the intermediate composition is diluted and digested in the second spinning disk reactor.

[0043] In embodiments where no dilution or digestion step is performed, the intermediate composition is mixed in a second spinning disk reactor to provide the amine oxide composition. The mixing step in the second spinning disk reactor allows tertiary amines in the intermediate composition to fully react with any residual aqueous oxidizing composition present in the composition. No additional aqueous oxidizing composition needs to be added during the mixing step. The second spinning disk reactor allows tertiary amines in the intermediate composition to be in intimate contact (thin films) with the residual aqueous oxidizing composition. The second spinning disk reactor can be identical to the first spinning disk reactor (e.g., same reactor size, same mechanically adjustable gap) or have different parameters compared to the first spinning disk reactor. The conditions used for mixing the intermediate composition (e.g., rotating surface RPM, temperature) in the second spinning disk reactor can be the same as the conditions used for mixing the tertiary amine composition and the aqueous oxidizing composition in the first spinning disk reactor.

[0044] The mechanically adjustable gap of the second SDR can be mechanically adjusted before mixing the intermediate composition in the second spinning disk reactor, and can be about 100 microns to about 600 microns. In some embodiments, this second mechanically adjustable gap can be about 100 microns to about 150 microns, about 100 microns to about 200 microns, about 100 microns to about 250 microns, about 100 microns to about 300 microns, about 100 microns to about 350 microns, about 100 microns to about 400 microns, about 100 microns to about 450 microns, about 100 microns to about 500 microns, about 100 microns to about 550 microns, about 150 microns to about 200 microns, about 150 microns to about 250 microns, about 150 microns to about 300 microns, about 150 microns to about 350 microns, about 150 microns to about 400 microns, about 150 microns to about 450 microns, about 150 microns to about 500 microns, about 150 microns to about 550 microns, about 150 microns to about 600 microns, about 200 microns to about 250 microns, about 200 microns to about 300 microns, about 200 microns to about 350 microns, about 200 microns to about 400 microns, about 200 microns to about 450 microns, about 200 microns to about 500 microns, about 200 microns to about 550 microns, about 200 microns to about 600 microns, about 250 microns to about 300 microns, about 250 microns to about 350 microns, about 250 microns to about 400 microns, about 250 microns to about 450 microns, about 250 microns to about 500 microns, about 250 microns to about 550 microns, about 250 microns to about 600 microns, about 300 microns to about 350 microns, about 300 microns to about 400 microns, about 300 microns to about 450 microns, about 300 microns to about 500 microns, about 300 microns to about 550 microns, about 300 microns to about 600 microns, about 350 microns to about 400 microns, about 350 microns to about 450 microns, about 350 microns to about 500 microns, about 350 microns to about 550 microns, about 350 microns to about 600 microns, about 400 microns to about 450 microns, about 400 microns to about 500 microns, about 400 microns to about 550 microns, about 400 microns to about 600 microns, about 450 microns to about 500 microns, about 450 microns to about 550 microns, about 450 microns to about 600 microns, about 500 microns to about 550 microns, about 500 microns to about 600 microns, or about 550 microns to about 600 microns.

[0045] In some embodiments, the second mechanically adjustable gap can be about 100 microns to about 300 microns, or about 110 microns to about 300 microns, or about 100 microns to about 290 microns, or about 110 microns to about 290 microns.

[0046] Mixing the intermediate composition in the second spinning disk reactor can be performed in the same way as the mixing of the tertiary amine composition and the aqueous oxidizing composition in the first spinning disk reactor as described herein.

[0047] In some embodiments, the amine oxide composition is the product of the process (following mixing in the second spinning disk reactor). Such an amine oxide composition can contain amine oxides at a concentration of greater than or equal to about 80% by weight. In some embodiments, the concentration of the amine oxides is greater than or equal to about 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94% or about 95% by weight.

[0048] In other embodiments, the amine oxide composition is diluted and/or digested following the second spinning disk reactor. The dilution or digestion of the amine oxide composition can be performed in the same way as the dilution and digestion of the intermediate composition as described herein.

[0049] The process described herein provides an amine oxide with a low level of nitrosamine. In some embodiments, the concentration of nitrosamine is less than 500 parts per billion (ppb). The formation of nitrosamines can be further inhibited by the addition of a chelating agent to the tertiary amine composition. For example, the chelating agent can be etidronic acid, oxalic acid, citric acid, ammonium carbonate, EDTA, EDTA-Na or any combination thereof. The chelating agent can be present within the tertiary amine composition at 0.5 weight % or greater. Definitions

[0050] As used herein, the term“alkyl” includes alkyl, alkenyl and alkynyl groups of a designated number of carbon atoms, such as 1 to 24 carbons (i.e., inclusive of 1 and 24), 1 to 18 carbons, 1 to 3 carbons, or 1, 2, 3, 4, 5 or 6. The term“C _m -C _n alkyl” means an alkyl group having from m to n carbon atoms (i.e., inclusive of m and n). For example, “Ci-Cealkyl” is an alkyl group having from one to six carbon atoms. Alkyls and alkyl groups can be straight or branched and depending on context, can be a monovalent radical or a divalent radical (i.e., an alkylene group). Examples of“alkyl” include, for example, methyl, ethyl, propyl, isopropyl, butyl, iso-, sec- and tert-butyl, pentyl, hexyl, heptyl, 3-ethylbutyl, 3-hexenyl and propargyl. If the number of carbon atoms is not specified, the subject“alkyl” or“alkyl” moiety has from 1 to 24 carbons.

[0051] As used herein, the term“about” means ± 1% of the specified value. For example, “about 100 microns” means from 99 microns to 101 microns. Regarding percentages, for example,“about 80%” means 79.2% to 80.8%, and“about 20%” means 19.8% to 20.2%.

Examples

Example 1: Amine oxide synthesis with digestion

x + y = 11

R = C12 - C18

[0052] The tertiary amine illustrated above was fed (4.5 -4.6 mL/min) to the axial feed port of a spinning disk reactor (1.3 mL reactor volume), while a solution of 50% hydrogen peroxide in water was fed (0.4-0.5 mL/min) to the annular feed port. The amount of excess hydrogen peroxide was varied from 20 to 5 mole %. No catalyst was used in the reaction. The exiting material was collected in 2 oz. bottles and digested for 2 hours at ~70 °C on a multi-stirrer hotplate. Table 1 summarizes the process conditions and analysis of the three samples produced.

Table 1: Process conditions and analysis of amine oxide samples made by SDR

Example 2: Amine oxide synthesis using two spinning disk reactors

[0051] Ethomeen C/21 (cocoamine ethoxylate) was fed (4.6 mL/min) to the axial feed port of a spinning disk reactor (1.3 mL reactor volume), while a solution of 50% hydrogen peroxide in water was fed (0.4 mL/min) to the annular feed port. The amount of excess hydrogen peroxide was 5 mole %. No catalyst was used in the reaction. The exiting material was collected in 8 oz. bottles and digested for 20 minutes at ~55 °C on a stirrer hotplate. This material was then fed back to the spinning disk reactor (after the reactor was cleaned; only a single reactor was available so the cleaned reactor was used to simulate a second spinning disk reactor) along with water (i.e. dilution) to simulate a process scheme of reaction/digestion/dilution in a continuous process that can provide the production of an amine oxide. Table 2 summarizes the process conditions and analysis of the samples produced.

Table 2: Process conditions and analysis of amine oxide samples made by SDR

Example 3: Comparison of amine oxide synthesis using dilute hydrogen peroxide (spinning disk and stirred tank reactors)

[0052] Ethomeen C/12 (cocoamine ethoxylate) was fed (3 g/min) to the axial feed port of a spinning disk reactor (1.3 mL reactor volume), while a solution of 7% hydrogen peroxide in water was fed (7 g/min) to the annular feed port. The amount of excess hydrogen peroxide was 41 mole %. No catalyst was used in the reaction. The exiting material was collected in an 8 oz. bottle and digested at 60 °C for 30 minutes. The resulting product has an active concentration -35% greater (42.0 wt % vs. 30-32 wt %) than material made by conventional means using a stirred tank reactor and the same reagents. The spinning disk reactor product had conversion >99.5% even though dilute hydrogen peroxide solution was utilized. Table 3 summarizes the process conditions and analysis of the samples produced. It is expected that the above SDR reaction using a solution of 50% hydrogen peroxide in water would produce an amine oxide having about 92% by weight.

Table 3: Process conditions and analysis of amine oxide samples