Patent Application
20180015448
In liquid-liquid reactions, an intrinsic tradeoff exists between reactivity and post-reaction separation. High interfacial surface area between two liquid phases is needed to achieve high activity. As an example, for motor fuel alkylation using ionic liquid catalysts, large ionic liquid droplets implies low surface area, which leads to slow mass transfer of olefin and isobutane from the bulk hydrocarbon phase to the ionic liquid droplets, and a mass transfer-limited reaction of olefin inside the ionic liquid droplets. Mass transfer limitations also lead to slow product mass transfer out of the ionic liquid droplets back to the hydrocarbon phase and to product degradation, hence to low C8 alkylate selectivities.
High ionic liquid inventory and/or smaller ionic liquid droplets are used to counter the mass transfer limitations of the alkylation kinetics. However, smaller droplets which are typically generated by shear force, are also more difficult to separate than larger droplets once the reaction is complete. Small ionic liquid droplets require very long or even infinite settling times for complete separation by gravity. Often, specialized equipment such as coalescers or centrifugal separation may be employed. However, coalescers are subject to fouling by pinning of ionic liquid droplets on coalescing elements and separation by centrifugal force requires a large amount of power.
The high activity of ionic liquids used for motor fuel alkylation and related processes allows for the use of relatively low ionic liquid volume fractions compared to the high acid volume fractions used in HF or H2SO4 processes. However, even at low ratios of ionic liquid catalyst to hydrocarbon, the loss rates of ionic liquid due to inefficient separation and deactivation may introduce a significant cost in ionic liquid catalyst make-up.
Alternative methods for generating liquid-liquid mixtures which allow both efficient reaction and easy separation after the reaction is over are needed for alkylation and for other liquid-liquid reactions.
One aspect of the invention is a micro-emulsion. In one embodiment, the micro-emulsion comprises polar structures and at least about 50 vol % of an oil phase. The oil phase comprises a hydrocarbon and a co-solvent. The polar structures comprise an ionic liquid. The micro-emulsion can include an optional surfactant, and an optional catalyst promoter. In some embodiments the polar structures comprise reverse micelles. The co-solvent has a polarity greater than the polarity of the hydrocarbon, and the co-solvent is miscible in the hydrocarbon. The ionic liquid comprises a halometallate anion and a cation, and the ionic liquid is at least slightly soluble in the oil phase.
Another aspect of the invention is a method of forming a micro-emulsion. In one embodiment, the method involves contacting the hydrocarbon, the co-solvent, the ionic liquid, the optional surfactant, and the optional catalyst promoter. The micro-emulsion comprising an oil phase, which comprises the hydrocarbon and the co-solvent, as well as polar structures, which comprise the ionic liquid. The hydrocarbon has a polarity less than the polarity of the co-solvent, and the co-solvent is miscible in the hydrocarbon. The ionic liquid comprises a halometallate anion and a cation, the ionic liquid being at least slightly soluble in an oil phase. The oil phase comprises the hydrocarbon and the co-solvent, and the oil phase comprises at least about 50 vol % of the micro-emulsion.
One aspect of the invention is a micro-emulsion composition composed at least partially of an ionic liquid in a mixture that contains a hydrocarbon as a major component. Rather than relying on the continuous input of force to shear the ionic liquid and create droplets, the micro-emulsion comprises thermodynamically stable polar structures in a less-polar medium. Although not wishing to be bound by theory, it is believed that the polar structures are stabilized by an amphiphilic surfactant or the ionic liquid itself. In some embodiments the polar structures are reverse micelles.
Mixtures containing ionic liquid reverse micelles have been made. See, for example, Table 5 of Correa et al., Nonaqueous Polar Solvents in Reverse Micelle Systems, C
In this invention, the ionic liquid forms a micro-emulsion comprising an oil phase and polar structures. The oil phase comprises a hydrocarbon and a co-solvent, and the polar structures comprise ionic liquid. In some embodiments, the polar structures comprise reverse micelles.
The composition can be made utilizing a surfactant that is compatible with the ionic liquid or without any additional surfactant. In the latter case, although not wishing to be bound by theory, it is believed that the ionic liquid itself acts as the amphiphile to stabilize the micro-emulsions. To generate a micro-emulsion using a hydrocarbon as a major component of the mixture, a polar aprotic co-solvent such as dichloromethane is used. The micro-emulsions are useful as high surface-area catalysts for alkylation and other hydrocarbon conversion processes, as well as separation processes.
The compositions contain an ionic liquid, a hydrocarbon and a co-solvent. The composition may optionally contain an additional surfactant and/or a catalyst promoter.
In some embodiments, more than about 90% of the reverse micelles have a diameter less than about 100 nanometers, or less than about 90 nanometers, or less than about 80 nanometers, or less than about 70 nanometers, or less than about 60 nanometers, or less than about 50 nanometers, or less than about 40 nanometers, or less than about 30 nanometers, or less than about 20 nanometers. The presence of added surfactant can be used to help control the size of the reverse micelles, as shown in
In some embodiments, the size distribution of the reverse micelles may be changed by changing the co-solvent. Not wishing to be bound by theory, using a more polar co-solvent may lead to larger reverse micelles due to the higher solubility of the co-solvent in the reverse micelles and due to the higher surface tension at the interface between the reverse micelles and the oil phase.
The micro-emulsion is substantially free of water. By substantially free of water we mean that the polar structures are not water. There is typically less than about 300 wppm water in the micro-emulsion, or less than about 250 wppm water, or less than about 200 wppm water, or less than about 150 wppm water, or less than about 100 wppm water, or less than about 75 wppm water, or less than about 50 wppm water. Water is not typically compatible with halometallate ionic liquids. Water reacts with the ionic liquid resulting in facile hydrolysis of the halometallate anion. In cases where the ionic liquid is Lewis acidic, this causes reduction in or neutralization of Lewis acidity.
The ionic liquid comprises a cation and an anion. The cation is generally a nitrogen, phosphorous, or sulfur-based organic cation. In some embodiments, the cation is amphiphilic in nature and at least slightly soluble in either the hydrocarbon component or co-solvent. If the cation and anion are both not amphiphilic, an additional surfactant may be needed. In many cases, the ionic liquid is fully miscible with the co-solvent.
Suitable cations include nitrogen-based organic cations, phosphorus based organic cations, sulfur based cations, or combinations thereof. Examples of cations include tetraalkyl phosphoniums, dialkylimidazoliums, alkylimidazoliums, pyridiniums, alkyl pyridiniums, trialkylammoniums, tetraalkylammoniums, lactamiums, alkyl-lactamiums and trialkylsulfoniums. Mixtures of cations may be used as well. Examples of suitable cations include, but are not limited to:
where R1-R3 are independently selected from alkyl groups, alkene groups, naphthene groups, and aryl groups having 1 to 12 carbon atoms, and R4 is independently selected from alkyl groups, alkene groups, naphthene groups, and aryl groups having 1 to 15 carbon atoms; and where R5-R16 are independently selected from hydrogen, alkyl groups, alkene groups, naphthene groups, and aryl groups having 1 to 20 carbon atoms, n is 1 to 8, and the alkyl, naphthene, alkene and aryl groups may be substituted with halogens, or other alkyl, aryl and naphthene groups.
The anion is a halometallate or anion with acidic character, and in most embodiments, with Lewis acidic character. In other embodiments, it can be neutral or basic in character. Halometallate anions may contain a metal selected from Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Hf, Ta, W, or combinations thereof, and a halide selected from F, Cl, Br, I, or combination thereof. The halometallate may be a simple halometallate or a composite in which more than one metal is used. For catalytic applications requiring Lewis acidity (such as alkylation, disproportionation, and isomerization), the ratio of moles of halide to moles of metal in the anion is less than 4. The anion may be formally an anion, or it may be an anion associated with a metal halide. For instance, the anion may be AlCl4− associated with AlCl3. BF4− activated with BF3 or a Brønsted acid may also be suitable. Although B is not technically a metal, for purposes of this invention, it can be considered a metal as part of a halometallate anion.
The hydrocarbon serves as a component of the less polar oil phase of the micro-emulsion. In embodiments in which the micro-emulsion contains reverse micelles, a majority of the hydrocarbon component is in the oil phase. The hydrocarbon may be a paraffin, an olefin, an aromatic, a naphthene, or mixtures of these four components. When reverse micelles are used to catalyze a hydrocarbon conversion process, the hydrocarbon reactants also serve as a portion of the hydrocarbon phase. In order to form a micro-emulsion, there must be at least some solubility of the amphiphile in both the oil phase and the polar structures of the micro-emulsion. Here, at least some solubility of the amphiphile in the oil phase is defined as the amphiphile being soluble in an amount of at least 0.5 mole ppm in the oil phase. If the cation and anion are both not amphiphilic, an additional surfactant may be needed to act as the amphiphile. The solubility of the amphiphile in the polar structures is generally much higher than in the oil phase and depends on the type of amphiphile and size of the structure. In cases where a non-polar hydrocarbon medium is desired (for instance, in motor fuel alkylation where the medium must contain isobutane), a co-solvent is used to modify the polarity of the hydrocarbon. The co-solvent is more polar than the hydrocarbon. The co-solvent must also be compatible with the ionic liquid and must be miscible with the hydrocarbon. Here, miscible with the hydrocarbon means that the co-solvent being soluble in an amount of at least 1 mol % in the hydrocarbon. Suitable co-solvents are any organic solvents containing at least one atom that is not carbon or hydrogen. Examples include, but are not limited to, halomethanes, other halogenated hydrocarbons, halocarbons, halogenated aromatics, or combinations thereof. Halogenated hydrocarbons are any compounds that contain carbon, hydrogen, and a halogen atom or atoms. Halomethanes are any compounds of the formula CH4-nXn where X is selected from F, Cl, Br, I, or a combination thereof. Halocarbons are any compounds that contain only carbon and one or more halogens. Halogenated aromatics are aromatic compounds containing one or more halogen atoms, such as chlorobenzene. Halomethanes, halocarbons, halogenated aromatics, and compounds with no hydrogen attached to the adjacent (beta) carbon atom are preferable to compounds with a beta hydrogen (such as halogenated hydrocarbons with more than one carbon) because of the potential to eliminate a halogen and a hydrogen to form a hydrogen halide and an olefin. Suitable co-solvents include, but are not limited to, chloroform, dichloromethane, chloromethane, chlorobenzene, dichlorobenzene, fluoromethane, difluoromethane, trifluoromethane, and 1-chloro-2,2-dimethylpropane.
In cases where the ionic liquid is not Lewis acidic or where a weaker Lewis acid is utilized, other co-solvents may be used that would otherwise be reactive with stronger Lewis acids. These include ethers (e.g., tetrahydrofuran, and diethyl ether), alcohols (e.g., butanol, propanol, and methanol), amides (e.g., dimethylformamide, and dimethylacetamide), esters (e.g., ethyl acetate), ketones (e.g., acetone), nitriles (e.g., acetonitrile), sulfoxides (e.g., dimethylsulfoxide), sulfones (e.g., sulfolane), or combinations thereof.
In some embodiments, the viscosity of the co-solvent is less than 1 centipoise at 25° C. Preferably, the viscosity of the co-solvent is less than 0.6 centipoise. This may be advantageous if the micro-emulsion is used in a process, such as alkylation, for which high viscosity may not be desirable.
In some embodiments, no additional surfactant is needed because the ionic liquid itself acts as an amphiphile to make a stable micro-emulsion. However, if a non-amphiphilic ionic liquid is used or if the use of less co-solvent is desired, a surfactant may be added. The surfactant can be cationic, anionic, or neutral. The surfactant can be amphiphilic and non-protic (i.e., it does not contain an acidic H atom bound to N, O, or S). Protic surfactants with very weakly acidic protons such as ternary ammonium salts and cyclic amides may also be suitable. Many surfactants that are not reactive with the ionic liquid are suitable. Examples of classes of such surfactants include, but are not limited to, surfactants containing functional groups such as amphiphilic quaternary ammonium salts, ternary ammonium salts, phosphonium salts, sulfonate salts, phosphonate salts, di-substituted amides (e.g., amides of the formula R—(C═O)—NR2, where R groups are generally alkyl or aryl groups but may be substituted as well), ethers, or glymes. Ideally, the anion of the quaternary ammonium salt, the ternary ammonium salt, or the phosphonium salt may be selected to match the anion of the ionic liquid or selected to be compatible with it. By compatible with the anion of the ionic liquid we mean that the anion of the additional surfactant does not neutralize the Lewis acidity of the ionic liquid anion or coordinate strongly to the ionic liquid anion such that the catalyst activity is substantially decreased. By substantially decreased we mean that the reaction rate for isobutane alkylation with olefins is decreased by more than 25% for a mole ratio of surfactant to ionic liquid of 1:1 compared to the same conditions with no additional surfactant. As an example of compatible surfactant anions, Cl−, AlCl4− or Al2Cl7− may be used as the anion with an Al2Cl7− ionic liquid (as may the bromide versions). Examples of cationic quaternary ammonium salts are cetyltrimethylammonium chloride, and benzyldimethyltetradecylammonium chloride. Anionic surfactants may also be suitable; however, most include sulfonate groups which are expected to be reactive with, or coordinate to, a Lewis acidic ionic liquid. Ideally, the cation of the sulfonate salt or phosphonate salt may be selected to match the cation of the ionic liquid or selected to be compatible with the cation of the ionic liquid. For instance, if the acidic ionic liquid is tributylhexylphosphonium heptachloroaluminate the surfactant could be tributylhexylphosphonium dodecyl sulfonate. As demonstrated below, the use of a surfactant allows use of a smaller quantity of polar co-solvent, and in some cases results in larger reverse micelles.
Another optional component is a catalyst promoter. In many hydrocarbon conversion reactions, such as motor fuel alkylation and paraffin disproportionation, a Brønsted acidic catalyst promoter is needed. Two common classes of promoters are anhydrous hydrogen halides (for instance, HCl) and halogenated hydrocarbons (such as 2-chlorobutane or 2-chloro-2-methyl propane (t-butyl chloride)). The halogenated hydrocarbons react in the presence of a Lewis acid to form a hydrogen halide and an olefin.
The above components are mixed in specific ratios such as to stabilize ionic liquid micro-emulsions, including reverse micelles. The ionic liquid is typically present in an amount of about 0.05 wt % to about 25 wt % of the micro-emulsion. The co-solvent is typically present in an amount of about 30 wt % to about 70 wt % of the micro-emulsion. The amount of co-solvent needed is lower when less ionic liquid is present in the composition. The molar ratio of the surfactant to the ionic liquid is typically less than about 2.5:1. When the catalyst promoter is present, the molar ratio of the catalyst promoter to the ionic liquid is typically about 0.1:1 to about 1:1. The amounts of co-solvent and surfactant needed to stabilize the polar structures depend on the amount of ionic liquid and hydrocarbon component present. When surfactant is included in the micro-emulsion, less co-solvent is needed. When more ionic liquid is included in the micro-emulsion, more surfactant or more co-solvent is needed.
The amounts of each component needed to result in a stable micro-emulsion may be determined by determination of a phase diagram. The phase diagram for a given combination of hydrocarbon component, co-solvent, ionic liquid, optional surfactant and catalyst promoter is constructed by preparing mixtures containing various known amounts of the components. A particular composition is then determined to be a micro-emulsion or consist of two distinct phases. Determination of whether a composition is a micro-emulsion or two distinct phases is generally completed by assessing turbidity of the mixture or identifying an interface between two phases, but may be accomplished by other means known in the art such as dynamic light scattering, conductivity measurement, or x-ray scattering. A mixture which is a micro-emulsion is then subjected to addition of the hydrocarbon component or ionic liquid to determine the composition at which the phase boundary between micro-emulsion and two-phase composition exists. Alternatively, a mixture which is two phases is subjected to addition of co-solvent or surfactant to determine the composition at which the phase boundary between micro-emulsion and two-phase composition exists.
The micro-emulsion can be formed by contacting or otherwise mixing the hydrocarbon, the co-solvent, the ionic liquid, the optional surfactant, and the optional catalyst promoter. The hydrocarbon has a polarity less than the polarity of the co-solvent, and the co-solvent is miscible in the hydrocarbon, at least up to the desired composition. The ionic liquid comprises a halometallate anion and a cation which is at least slightly soluble in the hydrocarbon or in the co-solvent. The oil phase, which includes the hydrocarbon and the co-solvent, comprises at least about 50 vol % of the composition.
The components can be combined in different ways. For example, the hydrocarbon and co-solvent can be combined first, and then combined with ionic liquid. Alternatively, the ionic liquid and the co-solvent can be combined first, and then combined with the hydrocarbon. The optional surfactant and optional catalyst promoter can be added at different times and to different combinations of the components. For example, the catalyst promoter and optional surfactant can be added to the hydrocarbon, the co-solvent, the ionic liquid, or any combinations of these components. Other ways of combining the components would be understood by those skilled in the art.
In one method, an ionic liquid and an optional surfactant are dissolved in a co-solvent to form an ionic liquid solution. The ionic liquid comprises a halometallate anion and a cation, and the ionic liquid is at least slightly soluble in the co-solvent. The ionic liquid solution is introduced into a hydrocarbon to form the micro-emulsion. The polarity of the hydrocarbon is less than the polarity of the co-solvent, and the co-solvent is miscible in the hydrocarbon. The oil phase comprises the hydrocarbon and the co-solvent. The oil phase comprises at least about 50 vol % of the micro-emulsion. If a catalyst promoter is included, it can be added to the ionic liquid solution, the hydrocarbon, the co-solvent, or the micro-emulsion.
Another method involves mixing the hydrocarbon with a co-solvent to form an oil phase. The polarity of the hydrocarbon is less than the polarity of the co-solvent, and the co-solvent is miscible in the hydrocarbon. The ionic liquid and an optional surfactant are added to the oil phase to form the micro-emulsion. The ionic liquid comprises a halometallate anion and a cation, and the ionic liquid is at least slightly soluble in the oil phase. The oil phase comprises at least about 50 vol % of the micro-emulsion. If a catalyst promoter is included, it can be added to the hydrocarbon, the co-solvent, the oil phase, or the micro-emulsion.
Processes using ionic liquid micro-emulsions are described in U.S. Application No. 62/141,056; U.S. Application No. 62/141,070; and U.S. Application No. 62/141,076, all filed on Mar. 31, 2015, each of which is incorporated herein by reference.
In the examples below, n-hexane is used as the hydrocarbon, tributylhexylphosphonium heptachloroaluminate is used as the ionic liquid, and dichloromethane is used as the co-solvent.
Reverse micelles were generated by preparing a mixture of ionic liquid and (in some cases) benzyldimethyltetradecylammonium chloride, referred to as “surfactant” below. Four different compositions were prepared with the following surfactant:ionic liquid mole ratios. Formulation 1 had a molar ratio of surfactant:ionic liquid of 2.1:1. Formulation 2 had a molar ratio of surfactant:ionic liquid of 1.7:1. Formulation 3 had a molar ratio of surfactant:ionic liquid of 0.83:1. Formulation 4 had no surfactant. Sufficient dichloromethane was added to dissolve the ionic liquid and surfactant. Following this, n-hexane was added dropwise, with shaking. When turbidity appeared, this composition was recorded as the boundary between the micro-emulsion region and the two-phase region of the phase diagram. A drop or drops of dichloromethane was then added to check that cloudiness disappeared. This was recorded as a second limit for the phase boundary. Additional dichloromethane was added, and the procedure was repeated. As the ionic liquid and surfactant became more dilute in the mixture, less dichloromethane was needed in the mixture to clarify the liquid. When a large amount of surfactant was added to the ionic liquid, less dichloromethane was needed to stabilize the same amount of ionic liquid. However, with little or no surfactant a phase boundary was also found. A phase diagram showing the required dichloromethane/hexane ratio to form a clear liquid (the phase boundary) for each of the formulations 1-4 as a function of total ionic liquid plus surfactant mole fraction is shown in
Compositions that were sufficiently cloudy and contained sufficient amounts of ionic liquid would eventually settle to form two liquid phases, indicating that cloudiness was due to formation of a second liquid phase. In mixtures that were not cloudy, formation of reverse micelles was presumed. This was confirmed using dynamic light scattering (DLS) for two compositions, one with and one without surfactant. Compositions were prepared as described in Example 1. A composition was prepared with 2.9 wt % tributylhexylphosphonium heptachloroaluminate ionic liquid, 2.9 wt % benzyldimethyltetradecylammonium chloride, 54.6 wt % dichloromethane and 39.5 wt % hexane. This composition had measured volume normalized average particle size of 12±2 nm. This composition is indicated with a “B” on
A composition with 6.16 wt % tributylhexylphosophonium heptachloroaluminate ionic liquid, 62.7 wt % dichloromethane and 31.2 wt % hexane had measured particle size of 3±2 nm. This composition is indicated with an “A” on
As used herein, the term about means within 10% of the value, or within 5%, or within 1%.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
This application is a Continuation of copending International Application No. PCT/US2016/025415 filed Mar. 31, 2016, which application claims priority from U.S. Provisional Application No. 62/141,087 filed Mar. 31, 2015, now expired, the contents of which cited applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62141087 | Mar 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2016/025415 | Mar 2016 | US |
| Child | 15713017 | US |
