Patent Application
20050276733
Many processes in the semiconductor industry require a reliable source of process gases for a wide variety of applications. Often these gases are stored in cylinders or vessels and then delivered to the process under controlled conditions from the cylinder. The semiconductor manufacturing industry, for example, uses a number of hazardous specialty gases such as phosphine, arsine, and boron trifluoride for doping, etching, and thin-film deposition. These gases pose significant safety and environmental challenges due to their high toxicity and pyrophoricity (spontaneous flammability in air). In addition to the toxicity factor, many of these gases are compressed and liquefied for storage in cylinders under high pressure. Storage of toxic gases under high pressure in metal cylinders is often unacceptable because of the possibility of developing a leak or catastrophic rupture of the cylinder.
In order to mitigate some of these safety issues associated with high pressure cylinders, on-site electrochemical generation of such gases has been used. Because of difficulties in the on-site synthesis of the gases, a more recent technique of low pressure storage and delivery systems has been to adsorb these gases onto a solid support. These storage and delivery systems are not without their problems. They suffer from poor capacity and delivery limitations, poor thermal conductivity, and so forth.
The following patents and articles are illustrative of low pressure, low flow rate gas storage, and delivery systems.
U.S. Pat. No. 4,744,221 discloses the adsorption of AsH3 onto a zeolite. When desired, at least a portion of the AsH3 is released from the delivery system by heating the zeolite to a temperature of not greater than about 175° C. Because a substantial amount of AsH3 in the container is bound to the zeolite, the effects of an unintended release due to rupture or failure are minimized relative to pressurized containers.
U.S. Pat. No. 4,668,255 and U.S. Pat. No. 4,713,091 disclose the use of manganese 11 complexes having the general formula Mn(II)LX2, where L is a ligand, which includes an amine or diphosphine group, and is sensitive to oxygen, nitrogen oxides, sulphur dioxide, carbon dioxide, lower alkenes and other gases and X is an anion, e.g., Cl−, Br−, OH− and the like. The compound can be carried on a support or dissolved in a liquid solvent.
U.S. Pat. No. 6,623,659, U.S. Pat. No. 6,339,182 and U.S. 2003\0125599 disclose the separation of olefins from paraffins and di-olefins from mono-olefins using an olefin complexing metal salt dispersed in an ionic liquid. Preferred salts are Group IB salts, preferably silver salts, e.g., silver tetrafluoroborate.
U.S. Pat. No. 5,518,528 discloses storage and delivery systems based on physical sorbents for storing and delivering hydride, halide, and organometallic Group V gaseous compounds at sub-atmospheric pressures. Gas is desorbed by dispensing it to a process or apparatus operating at lower pressure.
U.S. Pat. No. 5,704,965 discloses sorbents for use in storage and delivery systems where the sorbents may be treated, reacted, or functionalized with chemical moieties to facilitate or enhance adsorption or desorption of fluids. Examples include the storage of hydride gases such as arsine on a carbon sorbent.
U.S. Pat. No. 5,993,766 discloses physical sorbents, e.g., zeolites and carbon, for sub-atmospheric storage and dispensing of fluids in which the sorbent can be chemically modified to affect its interaction with selected fluids. For example, a sorbent material may be functionalized with a Lewis basic amine group to enhance its sorbtive affinity for B2H6 (sorbed as BH3).
U.S. Pat. No. 6,277,342 discloses a method for delivering Brønsted basic gases via reversibly protonating the gases using at least one polymer support bearing acid groups. The resulting salt formed from the acid/base reaction becomes sorbed to the polymer support.
This invention relates generally to an improvement in low pressure storage and dispensing systems for the selective storing of gases and the subsequent dispensing of said gases, generally at pressures of 5 psig and below, typically at subatmospheric pressures, e.g., generally below 760 Torr, by pressure differential, heating, or a combination of both. The improvement resides in storing gases having Lewis basicity in a reversibly reacted state in a liquid containing a reactive compound having Lewis acidity.
Several advantages for achieving safe storage, transportation, and delivery of gases having Lewis basicity. These include:
The figure is a schematic perspective representation of a storage and dispensing vessel with associated flow circuitry for the storage and dispensing of gases such as phosphine and arsine.
This invention relates to an improvement in a low-pressure storage and delivery system for gases, particularly hazardous specialty gases such as phosphine and arsine, which are utilized in the electronics industry. The improvement resides in storing of gases having Lewis basicity in a liquid incorporating a reactive compound having Lewis acidity capable of effecting a reversible reaction between the gas having Lewis basicity. The reactive compound comprises a reactive species that is dissolved, suspended, dispersed, or otherwise mixed with a nonvolatile liquid.
The system for storage and dispensing of a gas comprises a storage and dispensing vessel constructed and arranged to hold a liquid incorporating a reactive compound having an affinity for the gas to be stored, and for selectively flowing such gas into and out of such vessel. A dispensing assembly is coupled in gas flow communication with the storage and dispensing vessel, and it is constructed and arranged for selective, on-demand dispensing of the gas having Lewis basicity, by thermal and/or pressure differential-mediated evolution from the liquid mixture. The dispensing assembly is constructed and arranged:
Thus, the invention relates to a system for the storage and delivery of a gas having Lewis basicity, comprising a storage and dispensing vessel containing a liquid incorporating a reactive compound having Lewis acidity and having a readily reversible reactive affinity for the gas having Lewis basicity.
To facilitate an understanding of the storage and delivery system in terms of the general description above, reference is made to the Figure. The storage and dispensing system 10 comprises storage and dispensing vessel 12 such as a conventional gas cylinder container of elongate character. In the interior volume 14 of such vessel is disposed a liquid 16 capable of carrying a reactive compound (not shown) therein with the gas to be stored. The vessel 12 is provided at its upper end with a conventional cylinder head gas dispensing assembly 18, which includes valves, regulators, etc., coupled with the main body of the cylinder 12 at the port 19. Port 19 allows gas flow from the reactive compound and then from the liquid medium retained in the cylinder into the dispensing assembly 18. Optionally, the vessel can be equipped with an on/off valve and the regulator provided at the site for delivery.
The storage and delivery vessel 12 may be provided with internal heating means (not shown) which serves to thermally assist in shifting the equilibrium such that the gas bonded to the reactive compound, and sometimes the liquid carrier, is released. Often, the gas stored in the reactive compound is at least partially, and most preferably, fully dispensed from the storage and dispensing vessel containing the gas by pressure-mediated evolution. Such pressure differential may be established by flow communication between the storage and dispensing vessel, on the one hand, and a vacuum or low pressure ion implantation chamber, on the other. The storage and delivery vessel 12 may also be provided with a means of agitation (not shown) which serves to enhance the rate of gas diffusion from the reactive compound and liquid medium.
The storage and delivery vessel 12 may be used as the reactor itself in that a liquid medium containing the reactive compound can be transferred into the vessel and the gas subsequently added under conditions for forming the reaction complex in situ within the vessel. The reactive complex comprised of the reactive compound and gas can also be formed external to the storage and delivery system and transferred into the storage vessel 12.
A feature of the invention is that the gas is readily removable from the reactive compound contained in the liquid medium by pressure-mediated and/or thermally-mediated methods. By pressure-mediated removal it is meant that removal which can be effected by a change in pressure conditions, which typically range from 10−1 to 10−7 Torr at 25° C., to cause the gas to be released from the reactive compound and evolve from the liquid carrying the reactive compound. For example, such pressure conditions may involve the establishment of a pressure differential between the liquid incorporating the reactive compound in the vessel, and the exterior environment of the vessel, which causes flow of the fluid from the vessel to the exterior environment (e.g. through a manifold, piping, conduit or other flow region or passage). The pressure conditions effecting removal may involve the imposition on the contents within the vessel under vacuum or suction conditions which effect extraction of the gas from the reactive mixture and thus from the vessel.
By thermally-mediated removal it is meant that removal of the gas can be achieved by heating the contents in the vessel sufficiently to cause the evolution of the gas bonded with the reactive compound so that the gas can be withdrawn or discharged from the liquid medium and thus from the vessel. Typically, the temperature for thermal mediated removal or evolution ranges from 30° C. to 150° C. Because the reactant is a compound carried in a liquid medium, as opposed to a porous solid medium employed in the prior art processes, thermally-mediated evolution can be utilized, if desired.
A suitable liquid carrier for the reactive compound has low volatility and preferably has a vapor pressure below about 10−2 Torr at 25° C. and, more preferably, below 10−4 Torr at 25° C. In this way, the gas to be evolved from the liquid medium can be delivered in substantially pure form and without substantial contamination from the liquid solvent or carrier. Liquids with a vapor pressure higher than 10−2 Torr may be used if contamination can be tolerated. If not, a scrubbing apparatus may be required to be installed between the liquid mixture and process equipment. In this way, the liquid can be scavenged to prevent it from contaminating the gas being delivered. Ionic liquids have low melting points (i.e. typically below room temperature) and high boiling points (i.e. typically above 250° C. at atmospheric pressure) which make them well suited as solvents or carriers for the reactive compounds.
Ionic liquids can be acid/base neutral or they can act as a reactive liquid, i.e., as a Lewis acid, for effecting reversible reaction with the gas to be stored. These reactive ionic liquids have a cation component and an anion component. The acidity or basicity of the reactive ionic liquids then is governed by the strength of the cation, the anion, or by the combination of the cation and anion. The most common ionic liquids comprise salts of tetraalkylphosphonium, tetraalkylammonium, N-alkylpyridinium or N,N′-dialkylimidazolium cations. Common cations contain C1-18 alkyl groups, and include the ethyl, butyl and hexyl derivatives of N-alkyl-N′-methylimidazolium and N-alkylpyridinium. Other cations include pyridazinium, pyrimidinium, pyrazinium, pyrazolium, triazolium, thiazolium, and oxazolium.
Also known are “task-specific” ionic liquids bearing reactive functional groups on the cation, and these ionic liquids can be used here. Task specific ionic liquids often are aminoalkyl, such as aminopropyl; ureidopropyl, and thioureido derivatives of the above cations. Specific examples of task-specific ionic liquids containing functionalized cations include salts of 1-alkyl-3-(3-aminopropyl)imidazolium, 1-alkyl-3-(3-ureidopropyl)imidazolium, 1-alkyl-3-(3-thioureidopropyl)imidazolium, 1-alkyl-4-(2-diphenylphosphanylethyl)pyridinium, 1-alkyl-3-(3-sulfopropyl)imidazolium, and trialkyl-(3-sulfopropyl)phosphonium.
A wide variety of anions can be matched with the cation component of such ionic liquids for achieving a neutral ionic liquid or one that possesses Lewis acidity or Lewis basicity. One type of anion is derived from a metal halide. The halide most often used is chloride although the other halides may also be used. Preferred metals for supplying the anion component, e.g., the metal halide, include copper, aluminum, iron, cobalt, chromium, zinc, tin, antimony, titanium, niobium, tantalum, gallium, and indium. Examples of metal chloride anions are CuCl2−, Cu2Cl3−, AlCl4−, Al2Cl7−, CoCl3−, CrCl4−, ZnCl3−, ZnCl42−, Zn2Cl5−, FeCl3−, FeCl4−, Fe2Cl7−, TiCl5−, TiCl62−, SnCl5−, SnCl62−, etc.
Other commonly used anions include carboxylates, fluorinated carboxylates, sulfonates, fluorinated sulfonates, imides, borates, phosphates, chloride, etc. Preferred anions include BF4−, PF6−, p-CH3—C6H4SO3−, CF3SO3−, CH3OSO3−, CH3CH2OSO3−, (CF3SO2)2N−, (NC)2N−(CF3SO2)3C−, CH3COO− and CF3COO−.
Examples of halide ionic liquid compounds from which other ionic liquids can be prepared include:
Other suitable liquid carriers include oligomers and low molecular weight polymers, hyperbranched and dendritic amorphous polymers, natural and synthetic oils, etc. Specific examples of suitable liquid carriers include alkylene carbonates, glymes, polyether oils, perfluoropolyether oils, chlorotrifluoroethylene oils, hydrofluorocarbon oils, polyphenyl ether, silicone oils, fluorosilicone oils, hydrocarbon (refined petroleum) oils, hyperbranched polyethylene, hyperbranched polyether, polyester polyols, polyether polyols, polycarbonates, etc. Some of these liquids suffer from excessive volatility at elevated temperatures, in which case they are not suited for thermal-mediated evolution. However, they may be suited for pressure-mediated evolution.
A suitable reactive compound for reversibly reacting with the gas to be stored and subsequently delivered therefrom must also have low volatility and preferably has a vapor pressure below about 10−2 Torr at 25° C. and, more preferably, below 10−4 Torr at 25° C. In this way, the gas to be evolved from the reactive compound and the liquid medium can be delivered in substantially pure form and without substantial contamination from the reactive species. Compounds with a vapor pressure higher than 10−2 Torr may be used if contamination can be tolerated. If not, a scrubbing apparatus may be required to be installed between the storage vessel and process equipment. In this way, the reactive compound can be scavenged to prevent it from contaminating the gas being delivered.
Reactive compounds can be derived from compounds of the empirical formula:
MaLbXcYd
The metals are selected from those which form chemical complexes with PH3, AsH3, and other Lewis bases, e.g., Cu, Ag, Al, B, Sn, Ti, Zn, Fe, Ni, Pd, Pt, Mn, Ca, Ga, As, Sb, In, Nb, Mg, Sc, Zr, Co, Ru, and V.
Examples of neutral donor ligands, L, are those having a lone pair of electrons to donate and are commonly based on nitrogen, oxygen, phosphorous, sulfur, and unsaturated hydrocarbons. General classes include amines, imines, nitriles, phosphines, phosphites, ethers, aldehyes, ketones thioethers, olefins, diolefins, aromatics, etc. Examples include NH3, RNH2, R2NH, NR3, R2C═N—R, NECR, PH3, RPH2, R2PH, PR3, P(OR)3, OR2, SR2, CO, RCH(O), R2C═O, cyclooctadiene, and benzene, where R is alkyl, cycloalkyl, aryl, alkoxy, aryloxy, haloalkyl, haloalkoxy, a polymer, etc. R may incorporate additional neutral donor groups or ionic groups.
Anions, X, include organic and inorganic groups that bear a negative charge. General classes of anions include halides, alkyls, alkoxides, aryls, aryloxides, alkylates, cyclopentadienyls, acetylacetonoates, amides, sulfonates, sulfates, borates, aluminates, aluminoxides, phosphates, arsenates, etc. Examples include F−, Cl, Br−, I−, R−, RO−, cyclopentadienyl (Cp), pentamethylcyclopentadienyl, R2N−, acetylacetonoate (acac), hexafluoroacetylacetonoate (hfac), CF3SO2O−(−OTf), RSO2O−, ROSO2O−, BF4−, BR4−, AlCl4−, PF6−, PR3F3−, AsF6−, NO3−, SO4−, where R is alkyl, cycloalkyl, aryl, alkoxy, aryloxy, haloalkyl, haloalkoxy, a polymer etc. R may incorporate additional neutral donor or ionic groups.
Cations, Y, include organic and inorganic groups that bear a positive charge. Examples include Na+, K+, Li+, Ca2+, Ba2+, NH4+, R3NH+, NR4+, R3PH+, PR4+, N-alkylpyridinium, N,N′-dialkylimidazolium, pyridazinium, pyrimidinium, pyrazinium, pyrazolium, triazolium, thiazolium, oxazolium, etc, where R is typically alkyl. R may incorporate additional neutral donor or ionic groups.
Examples of Lewis acidic metal compounds with the formula MX include AgCl, AgBr, Agl, Ag(BF4), Ag(OTf), Ag(NO3), CuCl, CuBr, Cul, CuCN, Cu(OTf), Cu(PF6), Cu(AsF6), Cu(acac), Cu(O2CCH3), Cu(O2CCF3), and Cu[N(SO2CF3)2].
Examples of Lewis acidic compounds with the formula MX2 include CuCl2, Cu(BF4)2, Cu(OTf)2, SnCl2, ZnCl2, NiCl2, MgCl2, Mg(CH2SCH3)2, CaCl2, MnCl2, Ca(OTf)2, PdCl2, Pd(CN)2, (Cp)2Os, and (Cp)2Ru.
Examples of Lewis acidic compounds with the formula MX3 include AlCl3, Al(OTf)3, FeCl3, GaCl3, SbCl3, InCl3, La(OTf)3, Sc(OTf)3, Ln(OTf)3, Yb(OTf)3, tributylborane, tributylborate, and tris(perfluorophenyl)borane.
Examples of Lewis acidic compounds with the formula MX4 or MX5 include SnCl4, TiCl4, ZrCl4, PtCl4, Ptl4, SbCl5, NbCl5 and titanium compounds TiCl3(4-nitrophenoxide); TiCl3(OCH2CH3), TiCl3(OCH2CF3), TiCl2(OCH2CF3)2, TiCl3(OCH(CF3)2), (Pentafluorocyclopentadienyl)TiCl3, TiCl3(phenoxide), and TiCl3(pentafluorophenoxide).
Other examples of Lewis acidic metal compounds include TiCl3(2-phenyliminomethyl-phenoxide), TiCl3(2-[(2,6-diisopropylphenylimino)-methyl]phenoxide, TiCl3(4-Nitro-2-phenyliminomethylphenoxide) [MLX4]; bis(dibenzylideneacetone)Pd and bis(cyclooctadiene)Pd [ML2]; (bisoxazoline)Cu(OTf)2, (bisoxazoline)Mg(OTf)2, (bisoxazoline)Zn(OTf)2, (bisoxazoline)Cu(SbF6)2, and (bisoxazoline)PdCl(CH3) [ML2X2]; [PdCl(C3H5)]2, CuAlCl4 [M2X4]; [RhCl(CO)2]2 [M2L4X2]; Al2Cl7−BMIM+[M2X7Y], CuCl2−BMIM+[MX2Y], Cu2Cl3−BMIM+[M2X3Y], and [(α-diimine)—Ni(CH2CH2CH2C(O)OCH3)]+, B(3,5-CF3—C6H3)4−[ML3X2].
Reaction of a gas may occur directly with the metal center, through a ligand coordinated to the metal center (e.g., a functional group on the ligand), or through displacement of at least one ligand on the metal center. The properties of the donor ligands, anions and/or cations affect the physical properties of metal-based reactive compounds. Ligands and counterions are selected such that volatility is minimized, and so that the steric and electronic properties of the reactive compound are suitable for reversibly binding the desired gas.
Lewis acidic reactive compounds also include polymers, oligomers, and organic compounds containing Brønsted acid groups, e.g. carboxylic acid and sulfonic acid groups. Examples include ion exchange resins, e.g. polymeric sulfonic, perfluoroalkylsulfonic, and fluorinated sulfonic acids, cross-linked sulfonated polystyrene-divinylbenzene copolymers; poly(ethylene oxide) sulfonic acid, ptoluene sulfonic acid, dodecylbenzene sulfonic acid, dodecylsulfonic acid, benzoic acid, dimethylpropionic acid, dimethylolpropionic acid, dimethylolbutanoic acid, dialkyl sulfosuccinic acid etc. Some compounds may suffer from excessive volatility at elevated temperatures and are not suited for thermal-mediated evolution. However, they may be suited for pressure-mediated evolution.
Gases having Lewis basicity to be stored and delivered from a liquid incorporating a reactive compound having Lewis acidity may comprise one or more hydride gases, e.g., phosphine, arsine, stibine, and ammonia; hydrogen sulfide, hydrogen selenide, hydrogen telluride, isotopically-enriched analogs, basic organic or organometallic compounds, etc.
The reactive compound should be dispersed throughout the liquid medium to achieve optimum capacities for gas storage. Some of the reactive compounds may be solid and at least partially insoluble in the liquid medium. To facilitate the incorporation of the reactive compound in the liquid medium, if not soluble, it may be emulsified, stabilized with surfactants, or cosolvents may be added.
The reactive compound should be incorporated in the liquid medium in an amount sufficient to meet preselected capacity and delivery requirements of the system. In the context of the liquid carrier, a molar ratio of at least about 0.3 moles reactive compound per 1000 mL of liquid is generally acceptable.
To provide an understanding of the concepts disclosed herein the following are relevant definitions to the process: Definitions:
Total Capacity (or Capacity): Moles of gas that will react with one liter of a reactive liquid medium at a given temperature and pressure.
Working Capacity (Cw): Moles of gas per liter of a reactive liquid medium which is initially stored and is subsequently removable from the mixture during the dispensing operation, specified for a given temperature and pressure range, typically at 20 to 50° C. over the pressure range 20 to 760 Torr.
Cw=(moles of reacted gas−moles of gas remaining after delivery)/(liters of reactive liquid medium)
Percent Reversibility: Percentage of gas initially reacted with the reactive compound which is subsequently removable by pressure differential, specified for a given temperature and pressure range, typically at 20 to 50° C. over the pressure range 20 to 760 Torr.
% Reversibility=[(moles of reacted gas−moles of gas remaining after delivery)/(moles of initially reacted gas)]*100
It has been found that good Lewis acid/base systems can be established from the Gibbs free energy of reaction (ΔGrxn) for a given system. In a storage and delivery system based upon a reactive mixture and a gas having Lewis basicity, an operable ΔGrxn range exists for operable temperature and pressure and is from about 1.3 to about 4.5 kcal/mole. There also exists an optimum ΔGrxn for a given temperature and pressure range, which corresponds to a maximum working capacity for the mixture. In reference to the gas PH3, if the magnitude of ΔGrxn (and thus, Keq) is too small, the reactive mixture will have insufficient capacity for PH3. This insufficient capacity may be compensated for by selecting a reactive mixture with a higher total capacity (i.e. higher concentration of PH3 reactive groups). If the magnitude of ΔGrxn (and thus, Keq) is too large, an insufficient amount of PH3 will be removable at the desired delivery temperature. For the reaction of PH3 with a Lewis acidic group, A, at 25° C. and in the pressure range 20 to 760 Torr, the optimum value range for ΔGrxn is about from −0.5 to −1.6 kcal/mol. For all systems in solution involving the reaction of a single equivalent of gas with a single equivalent of Lewis acid/base group, the optimum ΔGrxn will be about −1.1 kcal/mol at 25° C. and between 20 to 760 Torr. The situation is more complex for other systems, e.g., if the gas and Lewis acid/base group react to give a solid complex, or if more than one equivalent of a gas reacts with a single equivalent of a Lewis acid/base group.
One of the difficulties in the development of a suitable storage and delivery system is the matching of a suitable reactive mixture with a suitable gas through prediction of the ΔGrxn. To minimize experimentation and project the viability of possible systems, quantum mechanical methods can be used to elucidate molecular structures. Density Functional Theory (DFT) is a popular ab initio method that can be used to determine a theoretical value for the change in electronic energy for a given reaction (ΔErxn=sum of Eproducts−sum of Ereactants). The following is a discussion for this determination. The calculations are assumed to have an error of approximately ±3 kcal/mol.
The reaction of one equivalent of PH3 gas with one equivalent of a Lewis acid acceptor (A) in the liquid phase to give a reaction product in the liquid phase is represented by the equations:
The equilibrium constant for this reaction, Keq, is described by equation 1, where [PH3(gas)] is expressed as the pressure of gaseous PH3 in atmospheres. Keq is dependent upon the change in Gibbs free energy for the reaction, ΔGrxn, which is a measure of the binding affinity between PH3 and A. The relationships between ΔG, K, and temperature (in Kelvin) are given in equations 2 and 3.
ΔG=ΔH−TΔS (Equation 2)
ΔG=−RTInK (Equation 3)
The value ΔErxn can be used as an approximate value for the change in enthalpy (ΔH, see equation 2). Also, if it is assumed that the reaction entropy (ΔS) is about the same for similar reactions, e.g., reversible reactions under the same temperature and pressure conditions, the values calculated for ΔErxn can be used to compare against ΔGrxn for those reactions on a relative basis, i.e., ΔGrxn is approximately proportional to ΔErxn. Thus, the values calculated for ΔErxn can be used to help predict reactive groups or compounds having the appropriate reactivity for a given gas.
The following examples are intended to illustrate various embodiments of the invention and are not intended to restrict the scope thereof.
The following is a general procedure for establishing the effectiveness of reactive liquid mixtures for storing and delivering gases in the examples. PH3 has been used as the descriptive gas for chemical reaction.
In a glove box, a 25 mL or 50 mL stainless steel reactor or 25 mL glass reactor was charged with a known quantity of a liquid mixture. The reactor was sealed, brought out of the glove box, and connected to an apparatus comprising a pressurized cylinder of pure PH3, a stainless steel ballast, and a vacuum pump vented to a vessel containing a PH3 scavenging material. The gas regulator was closed and the experimental apparatus was evacuated up to the regulator. Helium pycnometry was used to measure ballast, piping and reactor headspace volumes for subsequent calculations. The apparatus was again evacuated and closed off to vacuum. The following steps were used to introduce PH3 to the reactor in increments: 1) the reactor was isolated by closing a valve leading to the ballast, 2) PH3 was added to the ballast (ca. 800 Torr) via a mass flow controller, 3) the reactor valve was opened and the gas pressure was allowed to equilibrate while the reactor contents were stirred. These steps were repeated until the desired equilibrium vapor pressure was obtained. The quantity of PH3 added in each increment was measured by pressure and volume difference according to the ideal gas law. The amount of reacted PH3 was determined by subtracting tubing and reactor headspace volumes.
The purpose of this example is to provide a control. No reactive compound was used in combination with the Lewis acidic ionic liquid.
Molecular modeling was used to approximate the effectiveness of BMIM+Cu2Cl3− as a reactive liquid. The ionic liquid was modeled as an ion-pair, using 1,3-dimethylimidazolium as the cation, Cu2Cl3− as the anion, and it was assumed that one equivalent of PH3 reacted with each equivalent of copper (concentration of Cu reactive groups=9.7 mol/L). Structures were calculated using Spartan SGI Version 5.1.3 based on Density Functional Theory (DFT) with minimum energy geometry optimization at the BP level with a double numerical (DN**) basis set. This Lewis acidic ionic liquid was calculated to have an average ΔErxn of −5.5 kcal/mol for its reaction with PH3. Since ΔGrxn is of higher energy than ΔErxn and the optimum ΔGrxn for the pressure range 20 to 760 Torr at room temperature is ca. −1.1 kcal/mol, the result suggests that the binding properties of BMIM+Cu2Cl3− may be well suited for reversibly reacting with PH3 (i.e., high working capacity and high % reversibility).
In a glove box, 11.6 g of CuCl was slowly added to a round bottom flask charged with 10.2 g of BMIM+Cl−(2:1 stoichiometry). (It is assumed the anion Cu2Cl3− is formed from the reaction stoichiometry 2 equivalents CuCl to 1 equivalent BMIM+Cl−). The mixture was stirred overnight. A glass insert was charged with 12.02 g of the ionic liquid (density=1.8 g/mL) and placed into a 50 mL reactor, and the general procedure for measuring PH3 reaction was followed. The ionic liquid reacted with 51 mmol of PH3 at room temperature and 736 Torr, corresponding to 7.6 mol PH3/L of ionic liquid.
The results show % reversibility=84%, working capacity=6.4 mol/L (room temperature, 20-736 Torr). The experimental ΔGrxn, is approximately −0.7 kcal/mol at 22° C. This example represents a pure liquid-based system that is well matched, as calculated by ΔErxn and measured by ΔGrxn for reversibly binding PH3.
The purpose of this example was to provide a second control using a reactive liquid in the absence of a Lewis Acid reactive compound.
A 50 mL reactor was charged with 12.56 g of TiCl4 (liquid, density=1.73 g/mol), the reactor was cooled to ca. 7° C. in and ice bath, and the general procedure for measuring PH3 reaction was followed. The liquid reacted with 100.3 mmol of PH3, corresponding to 13.8 mol PH3/L of TiCl4 at an equilibrium vapor pressure of 428 Torr and a temperature of 12° C. A bright yellow solid results upon reaction of PH3 with liquid TiCl4. As a result, the isotherm for this reaction is an S shape rather than a conventional Langmuir isotherm.
The results show % reversibility=41%, working capacity=5.6 mol/L (12° C., 44-428 Torr). The delivered gas, because of the high vapor pressure of the TiCl4, is contaminated with the volatile titanium complexes and would require scrubbing prior to use.
Molecular modeling was used to help predict potentially useful titanium compounds for reversibly binding PH3 based on comparison with the systems of Examples 1 and 2 above. Structures were determined using the DFT method described above (Spartan SGI Version 5.1.3, minimum energy geometry optimization, BP level, double numerical (DN**) basis set). The results are listed in Table 1. Most of the modeled compounds were predicted to react with 2 equivalents of PH3 (2 available coordination sites), in which case a value for ΔErxn was calculated for the first (ΔE1) and second (ΔE2) reaction. If the first reaction was calculated to be unfavorable, the second reaction was calculated to determine if favorable. For compounds containing only 1 coordination site, a value does not exist for ΔE2 (N/R).
Structures for compounds 5, 11 and 14 are shown below:
As illustrated in Examples 4-8, and as summarized in Table 2, compounds 5, 11, and 14 were tested to determine if they react with PH3.
The purpose of this example was to determine the effect of Compound 5 in the absence of a liquid carrier.
Compound 5 was synthesized under nitrogen using standard Schlenk techniques. A 100 mL round bottom Schlenk flask was charged with a magnetic stir bar and 6.84 g (0.069 mol) of CF3CH2OH. Nitrogen was bubbled through the liquid to ensure that it was deoxygenated and 5 mL of toluene was added. In a glove box, an addition funnel was charged with 13.15 g of TiCl4 (0.069 mol). The addition funnel was brought out of the glove box and attached to the Schlenk flask containing the solution of CF3CH2OH. The TiCl4 was added dropwise to the alcohol with stirring to give a red solution. The mixture was heated to toluene reflux for ˜2 hours and allowed to cool overnight. No crystallization occurred upon cooling in an ice bath, so the mixture was heated to toluene reflux for an additional 6 hours, cooled to room temperature and was allowed to stand for 4 days. The flask was evacuated to remove the volatile components, leaving a dark yellow solid. The solid was washed with ˜7 mL of toluene, the toluene was removed via cannula filtration, and the product was dried under vacuum. The product was washed with 8 mL of pentane, isolated via cannula filtration, and dried under vacuum to give 8.55 g of an off-white powder. Elemental analysis indicated that the isolated solid was 5. Anal. Calc. for C4H4Cl2F6O2Ti: C, 15.16; H, 1.27; Cl, 22.38. Found: C, 14.54; H, 1.44; Cl, 22.56.
A 50 mL reactor was charged with 1.98 g of compound 5, and the general procedure for measuring PH3 reaction was followed. The solid reacted with 0.19 mmol of PH3, corresponding to 0.096 mmol PH3/g of 5 at room temperature and an equilibrium vapor pressure of 476 Torr.
This example is similar to Example 4 except the reactive compound is dissolved in a liquid carrier.
In a glove box, 1.31 g of BMIM+BF4− was added to 0.91 g of 5 to give a yellow solution (estimated density=1.3 g/mL). A 50 mL reactor was charged with the solution, and the general procedure for measuring PH3 reaction was followed. To increase the rate of reaction, the reactor was heated to 56° C. The solution reacted with 0.55 mmol of PH3, corresponding to 0.32 mol PH3/L of solution and 0.18 mol PH3/mol Ti compound at 56° C. and 290 Torr.
The results show a significant improvement in the PH3 capacity of compound 5 compared to the process in Example 4.
Compound 11 was synthesized under nitrogen using standard Schlenk techniques. A 250 mL round bottom Schlenk flask was charged with a magnetic stir bar, 3.16 g of 4-nitrophenol (0.023 mol), and 35 g of toluene (4-nitrophenol did not dissolve in toluene). In a glove box, an addition funnel was charged with 4.53 g of TiCl4 (0.023 mol) and 46 g of toluene. The addition funnel was brought out of the glove box and attached to the Schlenk flask containing the slurry of 4-nitrophenol. The TiCl4 solution was added dropwise to the stirring mixture of 4-nitrophenol to give a dark red suspension. The mixture was heated to toluene reflux for ˜3 hours and allowed to cool overnight. 30 mL of methylene chloride was added and the mixture was heated to CH2Cl2 reflux with stirring for 2.5 hours. The mixture was cooled, and the solid was isolated via cannula filtration and dried under vacuum for 3 days. Elemental analysis of the rust colored product was consistent with 11. Anal. Calc. for C6H4Cl3NO3Ti: C, 24.65; H, 1.38; Cl, 36.38; N, 4.79. Found: C, 26.28; H, 1.87; Cl, 32.73; N, 4.86.
A 50 mL reactor was charged with 1.23 g of compound 11, and the general procedure for measuring PH3 reaction was followed. The solid reacted with 0.10 mmol of PH3, corresponding to 0.081 mmol PH3/g of 11 at room temperature and an equilibrium vapor pressure of 110 Torr.
This example is similar to Example 6 except the reactive compound is dissolved in a liquid carrier.
In a glove box, 0.64 g of compound 11 was added to a vial containing 3.71 g of 1-ethyl-3-methylimidazolium (EMIM+) BF4−. The solid titanium compound appeared to be completely dissolved in the ionic liquid. The reactor was charged with 3.88 g of the solution (estimated density=1.4 g/mL) and the general procedure for measuring PH3 reaction was followed. To increase the rate of reaction, the reactor was heated to 51° C. The solution reacted with 0.98 mmol of PH3, corresponding to 0.35 mol PH3/L of solution and 0.6 mol PH3/mol Ti compound at 51° C. and 520 Torr.
The results show a much higher PH3 capacity for compound 11 when the reactive compound is dissolved in a liquid carrier.
Synthesis of ligand 2-[(2,6-diisopropylphenylimino)methyl]phenol: a 100 mL round bottom flask containing a magnetic stir bar was charged with 5.24 g of 2-hydroxybenzaldehyde (0.0429 mol), 25 mL of methanol, 8.40 g of 2,6-diisopropylaniline (0.0474 mol), and 1 mL of formic acid. The reaction was stirred overnight and the resulting solid was filtered and washed with methanol. The isolated solid was dissolved in methylene chloride and dried over magnesium sulfate. The product was crystallized from methylene chloride/methanol, isolated via cannula filtration, and dried under vacuum.
Compound 14 was synthesized under nitrogen using standard Schlenk techniques. In a glove box, a 250 mL round bottom Schlenk flask was charged with a magnetic stir bar, 9.06 g of 2-[(2,6-diisopropylphenylimino)methyl]phenol (0.032 mol), and 20 mL of toluene (ligand dissolved in toluene). In a glove box, a 100 mL round bottom Schlenk flask was charged with 6.74 g of TiCl4 (0.036 mol) and 20 mL of toluene. The TiCl4 solution was added to the stirring mixture of 2-[(2,6-diisopropylphenyl-imino)methyl]phenol via cannula to give a dark brown solution. The mixture was heated to toluene reflux for 4 hours and allowed to cool. A solid precipitated from solution and this was isolated via cannula filtration, washed with pentane, and dried under vacuum. The dried product was a purple powder.
In a glove box, 0.50 g of compound 14 was added to a glass reactor insert containing 3.0 g of BMIM+BF4−. The solid titanium compound was partly dissolved in the ionic liquid, but some portion of the solid settled out upon standing over a period of days. The glass insert containing 3.5 g of the mixture (estimated density=1.4 g/mL) was placed into a 50 mL reactor and the general procedure for measuring PH3 reaction was followed. The mixture reacted with 1.15 mmol of PH3, corresponding to 0.46 mol PH3/L of mixture and 1 mol PH3/mol Ti compound at room temperature and 404 Torr.
The above results in the table show that a significantly higher level of Ti reaction can be achieved when the respective compound is carried in a liquid carrier. It should be noted that compound 5 had the lowest calculated ΔE1 of compounds 5,11 and 14, and compound 14 had the highest calculated ΔE1.
This example is similar to Example 8 except there is no reactive compound dispersed in a liquid carrier. The purpose was to determine whether the ionic liquid carriers in Examples 5, 7 and 8 react with PH3 gas.
A 50 mL reactor was charged with 3.99 g of BMIM+BF4- and the general procedure for measuring PH3 reaction was followed. The ionic liquid is not Lewis acidic and it does not react with the Lewis basic PH3, demonstrating that a Lewis acidic species in the carrier, as described in Examples 6-8, must be present for reaction with PH3.
