WO1999011857A1 - Transition-metal substituted tungstoaluminate complexes for delignification and waste mineralization - Google Patents

Transition-metal substituted tungstoaluminate complexes for delignification and waste mineralization Download PDF

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WO1999011857A1
WO1999011857A1 PCT/US1998/018462 US9818462W WO9911857A1 WO 1999011857 A1 WO1999011857 A1 WO 1999011857A1 US 9818462 W US9818462 W US 9818462W WO 9911857 A1 WO9911857 A1 WO 9911857A1
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polyoxometalate
lignocellulosic
preparation
solution
oxidant
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PCT/US1998/018462
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French (fr)
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Ira A. Weinstock
Jennifer J. Cowan
Richard S. Reiner
Craig L. Hill
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The United States Of America, Represented By The Secretary Of Agriculture
Emory University
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Priority to EP98944749A priority Critical patent/EP1017899A4/en
Priority to BR9812135-9A priority patent/BR9812135A/en
Priority to CA002301719A priority patent/CA2301719A1/en
Priority to AU92213/98A priority patent/AU9221398A/en
Priority to JP2000508848A priority patent/JP2003514127A/en
Publication of WO1999011857A1 publication Critical patent/WO1999011857A1/en

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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1063—Bleaching ; Apparatus therefor with compounds not otherwise provided for, e.g. activated gases

Definitions

  • Heteropolyoxometalates of the Keggin structural class are effective homogeneous catalysts for selective oxidations of organic and inorganic substrates by a variety of oxidants, M. T. Pope and A. Muller, Ange . Chem. Int. Ed. Encfl . 30:34 (1991) and C. L. Hill and C. M. Prosser-McCartha, Coordination Chem. Rev. 143:407 (1995).
  • POMs polyoxometalates
  • these class are remarkably stable to oxidizing conditions.
  • POM anions can be converted to organic-soluble forms for use in organic solvents.
  • the Keggin vanadotungstosilicate, [SiVW 11 O 40 ] 5 J is stable at near neutral pH values, but possesses too positive a reduction potential for rapid, spontaneous reaction with 0 2 , I. A. Weinstock, R. H. Atalla, R. S. Reiner, C. H. Houtman and C. L. Hill, Holzforschuncf, 52:304 (1998).
  • reduced forms of [PV 2 Mo 10 0 40 ] s ⁇ react rapidly with 0 2
  • this vanadomolybdophosphate catalyst is unstable at pH values above 4 , Weinstock, supra .
  • Polyoxometalate compounds capable of stability in water over wider pH values and rapid reactivity with oxygen are needed in the art of lignocellulosic material delignification.
  • One aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms of the general formula [Al 1 V m Mo n W o Nb p Ta q (TM) r 0 s ] x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron- containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0.
  • the formula of one exemplary polyoxometalate useful in the present invention is [AlVW 1:L O 40 ] 6 ⁇ .
  • a further aspect of the invention provides a method of using mixed addendum derivatives of tungstoaluminates of the above kind as delignification and bleaching agents.
  • a still further aspect of the present invention provides a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers, and lignocellulosic pulps by contacting the substance with a solution of polyoxometalate complexes of the above general formulas, wherein the pH of said solution is adjusted to 1 - 11, preferably pH 6 - pH 11, more preferably pH 6 - pH 9 and most preferably pH 7 - pH 10; the consistency of the mixture of polyoxometalates and fibers or pulp is approximately 1 to 20%; and wherein said mixture is heated in a temperature- controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and enhanced delignification occurs.
  • the reduced polyoxometalate complex is reoxidized with an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • the most preferable oxidant is oxygen.
  • Yet another aspect of the invention provides a method of wet oxidizing soluble-organic lignin or polysaccharide fragments or oxidation products using polyoxometalate complexes of the above general formulas.
  • the method involves heating a solution, which contains both the polyoxometalate and the organic fragments or products, in the presence of an oxidant, under such conditions that the dissolved organic compounds are oxidatively degraded to volatile organic compounds and water.
  • the reaction is preferably conducted in a pressure and temperature controlled vessel .
  • the reaction is conducted at between 10-2000 psi and between ambient temperature to 500°C.
  • the pH be 0-11, more preferably 6-11, and most preferably 6-9.
  • the oxidant is preferably selected from air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • the most preferable oxidant is oxygen.
  • Another aspect of the invention provides a novel method of making dodecatungstoaluminic acid, H 5 [AlW 12 O 40 ] comprising the steps of adjusting the pH of a sodium tungstate dihydrate solution to between pH 7 and pH 8 ; adding aluminum chloride hexahydrate solution to the sodium tungstate dihydrate solution under reflux where the ratio of Al to W is 2:11 to thereby obtain [Al (A1)W U 0 39 ] 6" ; converting the [Al (Al) VI l 0 39 ] 6" to H s [AlW 12 O 40 ] by adjusting the pH to about 0; heating under reflux; and isolating the H 5 [AlW 12 O 40 ] .
  • the invention also provides a salt of 9 ⁇ by reacting the H 5 [A1W 12 0 40 ] with a base.
  • a further aspect of the invention provides a salt of [AlVW 11 O 40 ] 7 ⁇ by reacting the salt of [A1W 11 0 39 ] 9 ⁇ with vanadyl sulfate .
  • the salt of 7" can then be oxidized to [AlVW ⁇ :L O 40 ] s" by using, for example, bromine, oxygen, or ozone.
  • Yet another aspect of this invention provides a method of making polyoxometalate complexes of the formula [ lM n W 1: , ⁇ 39 ] (9 ⁇ n> ⁇ by reacting a salt of [AIW.. ⁇ ,,] 9 ⁇ with M, where M is manganese (II) or cobalt (II) .
  • Yet another aspect of the invention provides a novel method of making polyoxometalate complexes of the above general formulas by reacting a defect-structure derivative of an Al-containing polyoxometalate anion (the salt of [ lW ⁇ O jg ] 9" is an example of such a defect structure) with a d-electron-containing transition- metal cation to give the corresponding d-electron-containing transition-metal-substituted polyoxometalate .
  • a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers and lignocellulosic pulps may take place in a neutral or alkaline pH environment of pH 6 - pH 11. This is an advantage because lignin is more rapidly oxidized under alkaline conditions and cellulose is less easily hydrolyzed.
  • polyoxometalates described above may be reoxidized with oxygen.
  • Fig. 1A and B shows (A) 27 A1 and (B) 183 W NMR spectra of Na 6 [A1 2 W 11 0 39 ] (mixture of ⁇ and ⁇ isomers) prepared as described in Example I.A.
  • Fig. 2A, B and C shows 27 A1 and 183 W NMR spectra and the structures (in polyhedral notation) of ⁇ - and ⁇ -H 5 [Al ⁇ :tI W 12 O 40 ] .
  • Fig. 2C shows 27 A1 NMR spectrum of a reaction mixture containing ⁇ - and ⁇ -H 5 [Al I ⁇ : ⁇ W 12 O 40 ] (see inset) and [Al (H 2 0) J 3+ .
  • Figs. 2A and B show 27 A1 and 183 W NMR spectra and structures of ⁇ - [AlW 12 O 40 ] 5" (left) and ⁇ - [AlW 12 O 40 ] 5" (right).
  • Fig. 3 is the structure (in polyhedral notation) of ⁇ - [A1W 12 0 40 ] 5 ⁇ determined by X-ray crystallography.
  • Fig. 4 shows the 7 A1 NMR spectrum of ⁇ - [A1VW 11 0 40 ] 6" .
  • Fig. 5 shows the 51 V NMR spectrum of ⁇ - [AlVW 11 O 40 ] e J
  • Fig. 6A, B and C shows 183 W NMR spectra of (A) ⁇ - [Al(Co II OH 2 )W 11 0 39 ] e" , (B) ⁇ - [AlVW xl O 40 ] 6' and (C) ⁇ - [Al (A10H 2 ) W X1 0 39 ] e" .
  • Fig. 7 shows the reduction potentials (Volts vs Normal
  • heteropolytungstates possess greater base stability than do isostructural heteropolymolybdates . This suggested that efforts to develop base-stable Keggin anions should focus on the development of new polytungstates .
  • Keggin anions with greater negative charge densities can be obtained by preparing the anions from increasingly lower-valent main-group or transition-metal heteroatoms, X n+ , i.e. [X n+ W 12 O 40 ] (8 ⁇ n) J
  • One aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms of the general formula [Al 1 V m Mo n W o Nb p Ta q (TM) r 0 x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron- containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0.
  • the formula of one exemplary polyoxometalate useful in the present invention is [AlVW 11 O 40 ] 6" .
  • the present invention employs new, high-yield synthesis methods for H 5 [AlW 12 O 40 ] , J. A. Mair and J. L. T. Waugh, " Preparation of H 5 [AlW 12 O 40 ] (mistakenly described as 11- tungstoaluminic acid)," J ⁇ Chem. Soc . 2372, 1950; J. W. Akitt and A. Farthing, ⁇ Preparation and 27 A1 NMR spectroscopy of H s [AlW 12 O 40 ] (most likely a mixture of ⁇ and ⁇ isomers) ,” J.C.S . Dalton Trans . 1615, 1981; D. H.
  • a useful property of the aluminum heteroatom is that the 27 A1 isotope, present in 100% abundance and possessing a nuclear spin of 5/2, is easily and rapidly observed by nuclear magnetic resonance (NMR) spectroscopy.
  • NMR nuclear magnetic resonance
  • the chemical shift and line width of 27 A1 NMR signals provide readily accessible information regarding both the coordination number of the aluminum atom and the chemical symmetry of its environment, Akitt, supra .
  • Reported preparations of [AlW 12 O 40 ] 5" require the slow (20 hours) dropwise addition of solutions of Al 111 salts to mildly acidic solutions of condensed tungstate ( [W0 4 ] 2 J anions, Mair, supra; Akitt, supra .
  • Reagent grade chemicals sodium tungstate dihydrate was Folin Reagent Grade
  • Deionized water was used throughout.
  • Infrared and UV-visible spectra were obtained using a Nicolet 510 FTIR and a Hewlett-Packard 8452A spectrophotometers , respectively. pH measurements were made using an Orion model 250A pH meter.
  • Electrochemical data were obtained using a BAS CV-50W electrochemical analyzer, with a glassy carbon working electrode and Ag/AgCl reference electrode. Solutions used for cyclic and differential-pulse voltammetry were 1 M in sample, dissolved in an electrolyte solution of 0.10 M NaCl in water.
  • Spectral parameters for Al were: sweep width, 13500 Hz (wide window) or 2350 Hz (narrow window used for accurate integration); pulse width, 18 ⁇ sec; delay, 10 ⁇ sec .
  • all spectra were acquired from NMR tubes of the same quality and composition obtained from a single manufacturer: Wilmad grade 528-PP (Wilmad Glass, Buena, NJ) .
  • the NMR software package NUTS (1-D version, distributed by Acorn NMR Inc., Fremont, CA) was used to correct for "rolling" in the baselines of 183 W NMR spectra.
  • a further aspect of the invention provides a method of using mixed addendum derivatives of tungstoaluminates of the above kind as delignification and bleaching agents .
  • the present invention provides a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers, and lignocellulosic pulps by contacting the substance with a solution of polyoxometalate complexes of the above general formulas, wherein the pH of said solution is adjusted to 1 - 11; the consistency of the mixture of polyoxometalates and fibers or pulp is approximately 1 to 20%; and wherein said mixture is heated in a temperature-controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and enhanced delignification occurs.
  • Methods of delignifying wood pulps and other lignocellulosic pulps with polyoxometalates are fully described in U.S. patents 5,695,605, 5,302,248 and 5,552,019. These patents are incorporated by reference herein as if fully set forth below.
  • the pH of the solution is between pH 6 and pH 11.
  • the solution is between pH 6 and pH 9.
  • the reduced polyoxometalate complex is reoxidized with an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • a preferable oxidant is oxygen.
  • Yet another aspect of the invention provides a method of wet oxidizing soluble-organic lignin or polysaccharide fragments or oxidation products using polyoxometalate complexes of the above general formulas.
  • the method involves heating a solution, which contains both the polyoxometalate and the organic fragments or products, in the presence of an oxidant, under such conditions that the dissolved organic compounds are oxidatively degraded to volatile organic compounds and water.
  • the reaction is preferably conducted in a pressure and temperature controlled vessel.
  • the reaction is conducted at between 10-2000 psi and between ambient temperature to 500°C. It is preferred that the pH be 0-11, preferably 6-9.
  • the oxidant is preferably selected from air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone.
  • the oxidant is most preferably oxygen. Examples IC, III and IV, below, exemplify this aspect of the invention.
  • Step 1 11[W0 4 ] 2" + 2 Al 3+ + 10H + --> [Al (Al) W ⁇ O,,] 6" + 5H 2 0
  • Step 2 12 [Al (Al) W 1:L 0 39 ] 6" + 56H + --> 11 [AlW 12 O 40 ] 5" + 13A1 3+ + 28H 2 0
  • Step 1 Sodium tungstate dihydrate (NaW0 4 -2H 2 0, 100 g, 0.304 mol) was dissolved in 400 mL of H 2 0 in a 1000 mL 3 -neck round bottomed flask containing a magnetic stirring bar and fitted with an addition funnel and condenser. Hydrochloric acid (HC1, 23.0 mL, 0.276 mol) was added to the solution dropwise by pipet with vigorous stirring. By adding the acid slowly over a 20-30 minutes period, precipitation of tungstic acid is largely, but not entirely, avoided. The pH of the solution at this point should be approximately 7.7 (it is important that the pH be above 7.0) .
  • the solution was heated to reflux, and aluminum chloride hexahydrate (A1C1 3 -6H 2 0, 13.32 g, 0.0552 mol) dissolved in 80 mL water was added dropwise by means of the addition funnel over about 90 minutes (approximately 5-6 drops/min.) with constant stirring. During the addition, the solution becomes slightly cloudy. However, addition should be kept at a sufficiently slow rate so as to avoid excessive precipitation. If this should occur, however, the addition must be stopped and the solution stirred until it becomes clearer. After all the A1C1 3 had been added, the solution was kept at reflux for 1 hour, allowed to cool to room temperature and filtered through a medium sintered glass frit. The final pH should be approximately 7.
  • the solution may be filtered (if cloudy) using a medium glass frit.
  • the solution which now contains H 5 [AlW 12 O 40 ] , H + , Na + , Al 3+ , Cl " and S0 4 2 J was transferred to a 1000 mL beaker and cooled to 0°C.
  • the bottom (etherate) layer (about 20 mL in total) was collected in a 50 mL beaker and concentrated to dryness by gentle heating (4-5 hours) in a warm water bath.
  • the crude product (69.2 g, 95%) was recrystallized by dissolving in 20 mL of hot water, concentrating to a volume of 23 mL by gentle heating, and then cooling to 0°C for 16 hours. Yield: 50.46 g, 64%.
  • the acid was neutralized by adding dropwise via pipet a solution of 0.75 M Na 2 C0 3 (116 mL, 0.087 mol) to a final pH of 2.4.
  • the solution was concentrated in vacuo until precipitate began to form and cooled to 5°C.
  • the product was collected on a medium glass frit and air dried.
  • the first crop (7.15 g) impure by IR spectroscopy, was discarded.
  • the second crop (40.02 g, 39%) was mostly ⁇ - [AlW 12 O 40 ] 5" (90% ⁇ by 27 A1 NMR, along with 10% ⁇ ) .
  • vanadium is easily oxidized in solution to diamagnetic V(V) by addition of elemental bromine (Br 2 ) . Spectra may then be observed for [AlVW 11 O 40 ] 6" .
  • 27 Al NMR, ⁇ : 72.5 ppm ( ⁇ v 1/2 175 Hz) .
  • 51 V NMR, ⁇ : -535.5 ppm ( ⁇ v 1/2 220 Hz) .
  • the first experimental conditions were 0.05 M [AlVW ⁇ O ⁇ ] s" in 0.3 M acetate buffer at 125°C for 1 hour, using 0.5% pulp consistency.
  • the starting Kappa number of the pulp was 31.8, and the final Kappa number was 17.0.
  • the second experimental conditions were 0.1 M [AlVW 11 O 40 ] ⁇ " in 0.1 M sodium tungstate (pH adjusted to 7.5-7.6) at 125°C for 10 hours, using 1% or 2% pulp consistency, initial Kappa number 31.8 and viscosity 31.4 mPa-s .
  • Three samples treated at 1% consistency gave Kappa numbers of 15.0, 16.4, and 17.8 after bleaching and washing.
  • the viscosity of the sample with Kappa number 15.0 was 22.5 mPa-s .
  • Two samples at 2% consistency had Kappa numbers of 22.0 and 27.7.
  • the viscosity of the 22.0 Kappa pulp was 18.0 mPa-s .
  • the [ lVW ⁇ O ⁇ ] 6" solutions were dark brown in color after delignification, indicating the presence of [AlVW 11 O 40 ] 7" , reduced by lignin during the reactions.
  • a useful characteristic of [A ⁇ VW II O 40 ] 6" is that its reduction potential is sufficiently negative such that the reduced form of the anion, [AlVW 11 O 40 ] 7" , can be readily oxidized by oxygen (0 2 ) .
  • a solution of 0.001 M [A1VW 11 0 40 ] 7" in 0.01 M sodium tungstate dihydrate (adjusted to pH 7) was purged with oxygen (by bubbling 0 2 through the solution for 3 minutes) , blanketed with a layer of oxygen, and then sealed in a Teflon liner inside a stainless steel pressure vessel. The solution was heated to 200°C for 90 minutes and then removed from the pressure vessel.
  • [PV 2 Mo 10 0 40 ] s" an excellent wet oxidation catalyst 8 (Fig. 7). Because the catalytic role of [PV 2 Mo 10 0 40 ] 5" in wet oxidation is to facilitate the transfer of electrons from the dissolved organic compounds to oxygen, it follows that the reduction potential (ease with which the anion receives and gives up electrons) is an important determinant of effectiveness. Reduction potential is a thermodynamic parameter. The rate of reaction of the reduced anion is also important in determining effectiveness as a catalyst for wet oxidation. Because the reduction potential of [AlVW ⁇ :L O 40 ] 6" is similar to that of [PV 2 Mo 10 0 40 ] 5" (Fig.

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Abstract

A method of delignifying lignocellulosic fibers is disclosed. In one embodiment, the method comprises the steps of combining a polyoxometalate complex with aluminum heteroatom of the formula [Al1VmMonWoNbpTaq(TM)rOs]x- where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron-containing transition metal ion, where l+m+n+o+p+q ≥ 4, and s is sufficiently large that x > 0, with a lignocellulosic pulp, wherein the pH of the combination is between 6 and 11 and the consistency of the combination is 1-20 %; and heating the combination in a temperature-controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and delignification occurs.

Description

TRANSITION-METAL SUBSTITUTED TUNGSTOALUMINATE COMPLEXES FOR DELIGNIFICATION AND WASTE MINERALIZATION
BACKGROUND OF THE INVENTION
Heteropolyoxometalates of the Keggin structural class, including their transition-metal-substituted derivatives, are effective homogeneous catalysts for selective oxidations of organic and inorganic substrates by a variety of oxidants, M. T. Pope and A. Muller, Ange . Chem. Int. Ed. Encfl . 30:34 (1991) and C. L. Hill and C. M. Prosser-McCartha, Coordination Chem. Rev. 143:407 (1995). Like the condensed phase metal-oxide catalysts for which they are structural and electronic models, many polyoxometalates (POMs) of this class are remarkably stable to oxidizing conditions. In addition, by introduction of organic- soluble counter cations, many POM anions can be converted to organic-soluble forms for use in organic solvents.
However, due to the susceptibility of many POMs to base hydrolysis, the use of POMs in water, the least expensive and safest solvent available, is often limited to acid pH values, T. Okuhara, N. Mizuno and M. Misono, Advances in Cat. 41:113 (1996) . In light of the increasing drive towards more environmentally benign chemical systems, it would be advantageous to develop POMs that are stable in water over a wider range of pH values . In addition, salts of several Keggin anion derivatives are candidates for anti-viral agents, (C. L. Hill, G.-S. Kim, C. M. Prosser- McCartha, D. Judd, In Polyoxometalates: From Platonic Solids to Anti-retroviral Activity, Pope, M. T.; Muller, A., Eds.; Kluwer Academic Publishers: Dordrecht, Netherlands; pp. 359-371, 1994; J. T. Rhule, C. L. Hill, D. A. Judd and R. F. Schinazi, Chemical Reviews , 98:327 (1988)) and greater stability at physiological pH values (close to neutral) might prove valuable in this context. In addition to stability in water, there is a need for POM oxidation catalysts that can function using oxygen (02) , the most cost-effective and environmentally advantageous oxidant available, R. Neumann, M. Dahan, Nature , 388:353 (1977). What is required is that the POM anion possess a reduction potential sufficiently positive for rapid reaction with target substrates and, at the same time, sufficiently negative such that reaction of the reduced POM anion with 02 will be rapid (i.e., both kinetically and thermodynamically favorable), I. A. Weinstock, Chemical Reviews , 98:113 (1998). The need for both stability in water at neutral pH values and for rapid reactivity with 02 is exemplified by reports of POM-based wood-delignification catalysts. For example, the Keggin vanadotungstosilicate, [SiVW11O40] 5J is stable at near neutral pH values, but possesses too positive a reduction potential for rapid, spontaneous reaction with 02, I. A. Weinstock, R. H. Atalla, R. S. Reiner, C. H. Houtman and C. L. Hill, Holzforschuncf, 52:304 (1998). On the other hand, although reduced forms of [PV2Mo10040] s~ react rapidly with 02, this vanadomolybdophosphate catalyst is unstable at pH values above 4 , Weinstock, supra .
Polyoxometalate compounds capable of stability in water over wider pH values and rapid reactivity with oxygen are needed in the art of lignocellulosic material delignification.
BRIEF SUMMARY OF THE INVENTION
One aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms of the general formula [Al1VmMonWoNbpTaq(TM)r0s]x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron- containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0. Another aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms with the Keggin structure and the general formula [AljVpJTM) nWo0p] x~ where 1 is 1-2, m is 0-6, n is 0-3, o is 0-12, and TM is a d-electron-containing transition- metal ion, where 1+m+n+o = 12 or 13, and p is sufficiently large that x > 0.
The formula of one exemplary polyoxometalate useful in the present invention is [AlVW1:LO40] 6~ .
A further aspect of the invention provides a method of using mixed addendum derivatives of tungstoaluminates of the above kind as delignification and bleaching agents.
A still further aspect of the present invention provides a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers, and lignocellulosic pulps by contacting the substance with a solution of polyoxometalate complexes of the above general formulas, wherein the pH of said solution is adjusted to 1 - 11, preferably pH 6 - pH 11, more preferably pH 6 - pH 9 and most preferably pH 7 - pH 10; the consistency of the mixture of polyoxometalates and fibers or pulp is approximately 1 to 20%; and wherein said mixture is heated in a temperature- controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and enhanced delignification occurs.
Preferably, the reduced polyoxometalate complex is reoxidized with an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone. The most preferable oxidant is oxygen.
Yet another aspect of the invention provides a method of wet oxidizing soluble-organic lignin or polysaccharide fragments or oxidation products using polyoxometalate complexes of the above general formulas. The method involves heating a solution, which contains both the polyoxometalate and the organic fragments or products, in the presence of an oxidant, under such conditions that the dissolved organic compounds are oxidatively degraded to volatile organic compounds and water. The reaction is preferably conducted in a pressure and temperature controlled vessel . Preferably, the reaction is conducted at between 10-2000 psi and between ambient temperature to 500°C. It is preferred that the pH be 0-11, more preferably 6-11, and most preferably 6-9. The oxidant is preferably selected from air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone. The most preferable oxidant is oxygen.
Another aspect of the invention provides a novel method of making dodecatungstoaluminic acid, H5 [AlW12O40] comprising the steps of adjusting the pH of a sodium tungstate dihydrate solution to between pH 7 and pH 8 ; adding aluminum chloride hexahydrate solution to the sodium tungstate dihydrate solution under reflux where the ratio of Al to W is 2:11 to thereby obtain [Al (A1)WU039]6"; converting the [Al (Al) VI l039] 6" to Hs [AlW12O40] by adjusting the pH to about 0; heating under reflux; and isolating the H5 [AlW12O40] . The invention also provides a salt of
Figure imgf000006_0001
9~ by reacting the H5 [A1W12040] with a base. A further aspect of the invention provides a salt of [AlVW11O40] 7~ by reacting the salt of [A1W11039] 9~ with vanadyl sulfate . The salt of
Figure imgf000006_0002
7" can then be oxidized to [AlVWι:LO40] s" by using, for example, bromine, oxygen, or ozone.
Yet another aspect of this invention provides a method of making polyoxometalate complexes of the formula [ lMnW1:,θ39] (9~n>~ by reacting a salt of [AIW..^,,] 9~ with M, where M is manganese (II) or cobalt (II) .
Yet another aspect of the invention provides a novel method of making polyoxometalate complexes of the above general formulas by reacting a defect-structure derivative of an Al-containing polyoxometalate anion (the salt of [ lW^Ojg] 9" is an example of such a defect structure) with a d-electron-containing transition- metal cation to give the corresponding d-electron-containing transition-metal-substituted polyoxometalate .
It is an advantage of the present invention that a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers and lignocellulosic pulps may take place in a neutral or alkaline pH environment of pH 6 - pH 11. This is an advantage because lignin is more rapidly oxidized under alkaline conditions and cellulose is less easily hydrolyzed.
It is another advantage of the present invention that a polyoxometalate complex with aluminum heteroatoms of the general formula [Al1VJVIoJrfJS.bpTaq (TM) r0s] x~ where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d- electron-containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0 is provided.
It is another advantage of the present invention that the polyoxometalates described above may be reoxidized with oxygen.
Other advantages, features and objects of the present invention will be apparent to one of skill in the art after review of the specification, claims and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1A and B shows (A) 27A1 and (B) 183W NMR spectra of Na6 [A12W11039] (mixture of α and β isomers) prepared as described in Example I.A.
Fig. 2A, B and C shows 27A1 and 183W NMR spectra and the structures (in polyhedral notation) of α- and β-H5 [Alι:tIW12O40] . Fig. 2C shows 27A1 NMR spectrum of a reaction mixture containing α- and β-H5 [AlIι:πW12O40] (see inset) and [Al (H20) J 3+ . Figs. 2A and B show 27A1 and 183W NMR spectra and structures of α- [AlW12O40] 5" (left) and β- [AlW12O40] 5" (right). The 27A1 atom (100% abundance; I = 5/2) occupies a tetrahedral site (α- [AlW12O40] 5J Δv1/2 = 0.9 Hz 27A1 NMR signal) or pseudo-tetrahedral site (β- [AlW12O40] 5J Δv1/2 = 5.1 Hz) located at the center of the WVI 12O40 8" shell of W0e octahedra .
Fig. 3 is the structure (in polyhedral notation) of α- [A1W12040] 5~ determined by X-ray crystallography.
Fig. 4 shows the 7A1 NMR spectrum of α- [A1VW11040] 6" .
Fig. 5 shows the 51V NMR spectrum of α- [AlVW11O40] eJ
Fig. 6A, B and C shows 183W NMR spectra of (A) α- [Al(CoIIOH2)W11039]e", (B) α- [AlVWxlO40] 6' and (C) α- [Al (A10H2) WX1039] e" .
Fig. 7 shows the reduction potentials (Volts vs Normal
Hydrogen Reference Electrode, NHE) , as function of pH, of aqueous electrolyte solutions of [PV2Mo10O40] 5" (at pH 4 ) , [SiVWlxO40] 5" and
[AlVWιrLO40] 6" and of dioxygen (02) . Approximate ranges of stability of the POM anions are shown by horizontal lines .
DETAILED DESCRIPTION OF THE INVENTION In general, heteropolytungstates possess greater base stability than do isostructural heteropolymolybdates . This suggested that efforts to develop base-stable Keggin anions should focus on the development of new polytungstates . In addition, within the Keggin structural class, a correlation exists between greater base stability and greater negative charge density of the anion, D. P. Smith and M. T. Pope, "Increasing x in the series:
[PVxW12_xO40] <3+x> J results in an increase in the negative charge on the anion and greater hydrolytic stability," Inorganic Chem. 12:331, 1973; I. A. Weinstock, R. A. Atalla, R. S. Reiner, M. A. Moen, K. E. Hammel, C. L. Hill and M. K. Harrup, "While
Figure imgf000008_0001
is stable in water at pH values near 3, the silicon analog,
[SiVW11O40] 5J is stable indefinitely at reflux in water initially at pH 1 /' __ Mol. Cat. A Chemical . 116:59, 1997. Synthetically, Keggin anions with greater negative charge densities can be obtained by preparing the anions from increasingly lower-valent main-group or transition-metal heteroatoms, Xn+, i.e. [Xn+W12O40] (8~n)J The most well-studied Keggin heteropolytungstate anions are based on phosphorus (P(V), n = 5) or silicon (Si (IV), n = 4) heteroatoms, M. T. Pope, Heteropoly and Isopolyoxometalates , Springer-Verlag, New York, 1993. Based on composition and anion charge, [AlVW11O40] 6" might thus be expected to possess greater base stability than [PV2Mo10O40] 5" or [SiVW11O40] 5J At the same time, B(III) derivatives such as [BWX1039] 9~ are much less stable than their Si (IV) counterparts. The reason is that B(III) may be too small to optimally occupy the pseudo-tetrahedral site within the [WX1039] 12~ shell. Because Al(III) is larger than B(III), we thought that [AlW12O40] 5" and its derivatives might provide greater stability and versatility. Because derivatives of [AlW12O40] 5~ were unknown, however, their stabilities could not be reliably predicted.
A correlation also exists between reduction potential and anion charge density; anions with larger negative charge densities possess more negative reduction potentials . Because the reduction potential of [SiVWι:LO40] 5" is too positive to allow for rapid reaction of its reduced form, [SiVW-.JJ. 6", with 02, it followed that [AlVW11O40] 7" , the reduced form of [AΓVW1:IO40J 6" , might , by virtue of an incrementally more negative reduction potential, react with 02 at a more useful rate .
a) Polyoxometalate Complexes with Aluminum Heteroatoms
One aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms of the general formula [Al1VmMonWoNbpTaq(TM)r0 x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron- containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0.
Another aspect of the invention provides polyoxometalate complexes with aluminum heteroatoms with the Keggin structure and the general formula [Al1Vm(TM) nWo0p] x" where 1 is 1-2, m is 0-6, n is 0-3, o is 0-12, and TM is a d-electron-containing transition- metal ion, where 1+m+n+o = 12 or 13, and p is sufficiently large that x > 0.
The formula of one exemplary polyoxometalate useful in the present invention is [AlVW11O40] 6" .
In another embodiment, the present invention employs new, high-yield synthesis methods for H5 [AlW12O40] , J. A. Mair and J. L. T. Waugh, " Preparation of H5 [AlW12O40] (mistakenly described as 11- tungstoaluminic acid)," J^ Chem. Soc . 2372, 1950; J. W. Akitt and A. Farthing, ^ Preparation and 27A1 NMR spectroscopy of Hs [AlW12O40] (most likely a mixture of α and β isomers) ," J.C.S . Dalton Trans . 1615, 1981; D. H. Brown, " X-ray powder diffractometry of Css [AlW12O40] ," J^ Chem. Soc. 3281, 1962; K. Nomiya and M. Miwa, " IR spectroscopy of H [ (C4H9) 4N] 4 [AlW12O40] , " Polyhedron 2:955, 1983, and includes the first reported synthesis of its mono-lacunary derivative [A1W11039] 9~ . The latter is a precursor to a variety of transition-metal-substituted Keggin anions and the preparations of several of these, [AlVW11O40] 7J [AlMnW11039] 7" , and [AlCoW11039] 7" , are provided here by way of example .
A useful property of the aluminum heteroatom is that the 27A1 isotope, present in 100% abundance and possessing a nuclear spin of 5/2, is easily and rapidly observed by nuclear magnetic resonance (NMR) spectroscopy. The chemical shift and line width of 27A1 NMR signals provide readily accessible information regarding both the coordination number of the aluminum atom and the chemical symmetry of its environment, Akitt, supra . Reported preparations of [AlW12O40] 5" require the slow (20 hours) dropwise addition of solutions of Al111 salts to mildly acidic solutions of condensed tungstate ( [W04] 2J anions, Mair, supra; Akitt, supra . This procedure results in the formation of product mixtures, from which the desired compound is isolated in low yield after repeated baking and extraction of reaction residues. Unlike the phosphorous (P(V)) or silicon (Si (IV)) cations used to prepare [XW12O40] n~ , X = P (V) or Si (IV), aluminum
(Al(III)) can function both as a heteroatom and as an addendum atom. Thus, the product mixtures previously encountered in the preparation of [AlW12O40] 5" result from the competitive formation of
[Al (Al) W11O40] 6" during aluminum addition, Akitt, supra; M. A. Fedotov and L. P. Kazanskii, "Solution 7A1 NMR spectroscopy of reaction mixtures," Izv. Akad. Nauk SSSR, Ser. Khim. , No. 9, 2000- 2003, 1988, Eng. trans, pg. 1789.
In the method described here, the stoichiometry of aluminum is deliberately adjusted, (2A1:11W), to give [Al (Al) W^O.jJ 6~ in quantitative yield (27A1 NMR) at neutral pH. (Aluminum is added dropwise over a 90 minute period.) This initial product is then quantitatively converted (27A1 NMR and crude yield) in si tu to
[AlW12O40] 5~ (11/12 mols per mol of [Al (Al) π039] 6") by reaction with H+ at pH 0 (preferably one week at reflux) . Tungsten-183 NMR spectroscopy of the product is consistent with a mixture of α and β isomers of the Keggin structure, in which the β isomer is the major product (80 to 95%) . Subsequent work-up and isolation of Hs [AlW12O40] , and the synthesis of mixed addendum and transition- metal substituted derivatives, follow well-established methods.
Reagent grade chemicals (sodium tungstate dihydrate was Folin Reagent Grade) were obtained from commercial sources. Deionized water was used throughout. Infrared and UV-visible spectra were obtained using a Nicolet 510 FTIR and a Hewlett-Packard 8452A spectrophotometers , respectively. pH measurements were made using an Orion model 250A pH meter. Electrochemical data were obtained using a BAS CV-50W electrochemical analyzer, with a glassy carbon working electrode and Ag/AgCl reference electrode. Solutions used for cyclic and differential-pulse voltammetry were 1 M in sample, dissolved in an electrolyte solution of 0.10 M NaCl in water. Reported 27A1 and 51V NMR spectra were collected on a General Electric GN 500 MHz spectrometer at 130.3 and 131.1 MHz, respectively. 183W NMR spectra were obtained using a Varian UNITY 400 NMR at 16.66 MHz. External references were: 27A1, 0.10 M A1C13-6H20 ( [Al (H20)6]3+, δ = 0 ppm) ; 51V, 10 mM H4 [PVMoιrLO40] in 0.6 M NaCl (δ = -533.6 ppm, relative to neat V0C13; values are reported relative to V0C13 at δ = 0 ppm), and for 183W, 2.0 M Na2W04-2H20 (W04 2~ (aq) , δ = 0 ppm) . Spectral parameters for Al were: sweep width, 13500 Hz (wide window) or 2350 Hz (narrow window used for accurate integration); pulse width, 18 μsec; delay, 10 μsec . In order to minimize the variation of the intensity of the 27A1 signal arising from Al(III) ions in the glass sample tubes, all spectra were acquired from NMR tubes of the same quality and composition obtained from a single manufacturer: Wilmad grade 528-PP (Wilmad Glass, Buena, NJ) . The NMR software package NUTS (1-D version, distributed by Acorn NMR Inc., Fremont, CA) was used to correct for "rolling" in the baselines of 183W NMR spectra.
b) Delicrnification of Wood Pulp
A further aspect of the invention provides a method of using mixed addendum derivatives of tungstoaluminates of the above kind as delignification and bleaching agents .
For example, the present invention provides a method of delignifying substances such as wood pulp, wood, lignocellulosic fibers, and lignocellulosic pulps by contacting the substance with a solution of polyoxometalate complexes of the above general formulas, wherein the pH of said solution is adjusted to 1 - 11; the consistency of the mixture of polyoxometalates and fibers or pulp is approximately 1 to 20%; and wherein said mixture is heated in a temperature-controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and enhanced delignification occurs. Methods of delignifying wood pulps and other lignocellulosic pulps with polyoxometalates are fully described in U.S. patents 5,695,605, 5,302,248 and 5,552,019. These patents are incorporated by reference herein as if fully set forth below.
In a preferable version of the present invention, the pH of the solution is between pH 6 and pH 11. Preferably, the solution is between pH 6 and pH 9.
Preferably, the reduced polyoxometalate complex is reoxidized with an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone. A preferable oxidant is oxygen.
Yet another aspect of the invention provides a method of wet oxidizing soluble-organic lignin or polysaccharide fragments or oxidation products using polyoxometalate complexes of the above general formulas. The method involves heating a solution, which contains both the polyoxometalate and the organic fragments or products, in the presence of an oxidant, under such conditions that the dissolved organic compounds are oxidatively degraded to volatile organic compounds and water. The reaction is preferably conducted in a pressure and temperature controlled vessel. Preferably, the reaction is conducted at between 10-2000 psi and between ambient temperature to 500°C. It is preferred that the pH be 0-11, preferably 6-9. The oxidant is preferably selected from air, oxygen, hydrogen peroxide, other organic or inorganic peroxides (free acid or salt forms), and ozone. The oxidant is most preferably oxygen. Examples IC, III and IV, below, exemplify this aspect of the invention.
Methods for oxidative degradation of lignin and polysaccharide fragments dissolved during polyoxometalate delignification or bleaching of wood pulp or other lignocellulosic pulps are disclosed in U.S. patent 5,549,789, incorporated by reference as if fully set forth below.
EXAMPLES I. PREPARATION AND CHARACTERIZATION OF K7 [AlVW.JJ AND RELATED
COMPOUNDS
A. Preparation of H5 [AlW12O40] (mixture of α and β isomers) .
Step 1: 11[W04]2" + 2 Al3+ + 10H+ --> [Al (Al) W^O,,] 6" + 5H20
Step 2: 12 [Al (Al) W1:L039] 6" + 56H+ --> 11 [AlW12O40] 5" + 13A13+ + 28H20
Step 1. Sodium tungstate dihydrate (NaW04-2H20, 100 g, 0.304 mol) was dissolved in 400 mL of H20 in a 1000 mL 3 -neck round bottomed flask containing a magnetic stirring bar and fitted with an addition funnel and condenser. Hydrochloric acid (HC1, 23.0 mL, 0.276 mol) was added to the solution dropwise by pipet with vigorous stirring. By adding the acid slowly over a 20-30 minutes period, precipitation of tungstic acid is largely, but not entirely, avoided. The pH of the solution at this point should be approximately 7.7 (it is important that the pH be above 7.0) . The solution was heated to reflux, and aluminum chloride hexahydrate (A1C13-6H20, 13.32 g, 0.0552 mol) dissolved in 80 mL water was added dropwise by means of the addition funnel over about 90 minutes (approximately 5-6 drops/min.) with constant stirring. During the addition, the solution becomes slightly cloudy. However, addition should be kept at a sufficiently slow rate so as to avoid excessive precipitation. If this should occur, however, the addition must be stopped and the solution stirred until it becomes clearer. After all the A1C13 had been added, the solution was kept at reflux for 1 hour, allowed to cool to room temperature and filtered through a medium sintered glass frit. The final pH should be approximately 7.
Step 2. The solution, now containing Na6 [Al (Al) W1:L039] (27A1 NMR: 73 ppm, Δv1/2 = 89 Hz; 8 ppm, Δv1/2 = 256 Hz; Fig. 1) was transferred to a 1000 mL round-bottomed flask fitted with a reflux condenser. The solution was acidified to pH 0 by careful dropwise addition of concentrated sulfuric acid (about 20 mL, 0.376 mol) . After the pH had reached 0, an additional 3 mL of concentrated sulfuric acid were added and the solution heated to reflux. Any initial cloudiness or yellow color should disappear within 16 hours. To ensure complete conversion to product, the solution should be kept at reflux for 6 days. Then, after cooling to room temperature, the solution may be filtered (if cloudy) using a medium glass frit. The solution, which now contains H5 [AlW12O40] , H+, Na+, Al3+, Cl" and S04 2J was transferred to a 1000 mL beaker and cooled to 0°C.
Cold (-20°C) concentrated sulfuric acid (147 mL) was added carefully to avoid excessive heating. The solution was then cooled again to 0°C and transferred to a 2000 mL separatory funnel. Diethyl ether (500 mL) was added and the mixture shaken very gently with frequent ventilation until rapid evaporation of diethyl ether subsided. Then, the mixture was shaken more vigorously, still with frequent venting, and allowed to settle until three layers separated. The top clear colorless layer is diethyl ether, the middle somewhat cloudy layer is the aqueous phase and the bottom layer (a dense, pale yellow, viscous liquid) is the etherate of H5 [AlW12O40] (α and β isomers) . The bottom (etherate) layer (about 20 mL in total) was collected in a 50 mL beaker and concentrated to dryness by gentle heating (4-5 hours) in a warm water bath. The crude product (69.2 g, 95%) was recrystallized by dissolving in 20 mL of hot water, concentrating to a volume of 23 mL by gentle heating, and then cooling to 0°C for 16 hours. Yield: 50.46 g, 64%. IR (KBr pellet): 972, 899, 795 (broad), 747 (broad), 538, and 477 cm"1. Anal. Calculated
(found) for H5 [A1W12040] -15H20: H 1.12 (1.15) W 70.07 (70.23) Al 0.86 (0.89). White, crystalline α- [AlW12O40] 5" and pale yellow β-
[A1W12040] 5" (amorphous and more soluble) can be separated by fractional crystallization. 7A1 and 183W NMR spectra of α-
[A1W12040] 5" and β- [AlW12O40] 5" are shown in Figs. 2A and 2B .
B. Preparation of α-Na5 [AlW12O40] . A 65.9 g sample of Na5 [AlW12O40] (mixture of α and β isomers) was dissolved in 130 mL of water. The pH of the solution was adjusted to ca. 6 using 0.75 M Na2C03 (15.0 mL) . The solution was heated at reflux for 3 days: the 27A1 NMR spectrum indicated that the resonance at 72.1 ppm
(α-isomer) accounted for about 95% of the [AlW12O40] 5" in solution.
After cooling to room temperature, the solution was concentrated by rotary evaporation until precipitate began to form and then cooled in a refrigerator at 5°C. The product was collected on a coarse glass frit and air dried. Yield: 32.24 g (48.9%). 183W
NMR, δ: -107.5 ppm. 27A1 NMR, δ: 72.1 ppm (Δv1/2 = 0.93 Hz). IR
(KBr pellet) : 955 , 883 , 799 , 758 , 534 , and 498 cm"1. Anal .
Calculated (found) for Na5 [AlW12O40] -13H20 : H 0 . 81 (0 . 78) W 68 .47
(68 . 22 ) Al 0 . 84 ( 0 . 88 ) Na 3 . 57 (3 . 39 ) .
C . Stability of Hs [AlW12O40] at high pH values . In sharp contrast to the stability of [SiW12O40] 4" , which is rapidly hydrolyzed at room temperature to [SiWι:L039] 8" at pH 5 , the data in Example IB . show that [AlW12O40] 5" is stable for at least 3 days at 100°C at pH 6 . D. Isolation of β-Na5 [AlW12O40] . Crude H5 [AlW12O40] (100 g, 0.0321 mol) was dissolved in 60 mL water and filtered through a medium frit. The acid was neutralized by adding dropwise via pipet a solution of 0.75 M Na2C03 (116 mL, 0.087 mol) to a final pH of 2.4. The solution was concentrated in vacuo until precipitate began to form and cooled to 5°C. The product was collected on a medium glass frit and air dried. The first crop (7.15 g) , impure by IR spectroscopy, was discarded. The second crop (40.02 g, 39%) was mostly β- [AlW12O40] 5" (90% β by 27A1 NMR, along with 10% α) . IR (KBr pellet) : 966 (m) , 893 (m) , 799 (s) , 757 (s) , 545 (w) , and 481 (w) cm"1. Anal. Calculated (found) for Na5 [AlW12O40] -13H20: H 0.81 (0.77) W 68.47 (68.25) Al 0.84 (0.87) Na 3.57 (3.40) .
E. Preparation of α-K5 [AlW12O40] . A 5.0 g sample of H5 [AlW12O40] (mixture of α and β isomers) was dissolved in 5 mL water and 10 mL of saturated KC1 solution were added. The solution was placed in a vial, capped, and stored at room temperature in the dark for several weeks . Colorless crystals of the K+ salt of the α isomer (less soluble) formed slowly. One of the crystals was used for X-ray crystallographic analysis. Anal. Calculated (found) for K5 [AlW12O40] -19 H20: H 1.12 (1.07) W 64.68 (64.76) Al 0.79 (0.78) K 5.73 (5.68).
F. Crystal data for α-K5 [A1W12040] -17H20. Colorless crystal, dimensions of 0.31 x 0.24 x 0.21 mm, hexagonal P6222, with a = 19.0720(1) A, c = 12.5658 A, V = 3958.34(7) A3, dc = 4.223 g cm"3, Z. = 3. A total of 25389 reflections were collected on a Siemens SMART system using Mo Kα radiation (λ = 0.71073 A) and corrected for absorption, of which 3274 were above 4σ(F) . The structure was solved by direct methods and refined by full-matrix-least-square- on-F2 techniques using SHELXTL V5.03 with anisotropic temperature factors for all the atoms in the Keggin anion, except that All, Ol, 02, 03, and the oxygen atoms of crystalline water were refined isotropically. Partial occupancies and common anisotropic parameters were employed for K(3) and K(4) during final refinements. At final convergence, Rλ (I > 2σl) = 3.42%, R2 = 7.45% and GOF = 1.02 for 143 parameters. Relevant bond lengths
(A): Al(l)-0(3), 1.742(8); W(l)-0(1), 1.910(8); W(l)- 0(2) ,1.909(8) ; W(l)-0(3), 2.265(8); W(l)-0(4), 1.704(8); W(l)- 0(6) ,1.976(8) ; W(2)-0(2), 1.935(8); W(2)-0(5), 1.961(8); W(2)- 0(7), 1.710(9); W(2)-0(8), 1.896(9); W(2)-0(9), 1.901(9); W(3)- 0(10), 1.704(8); W(3)-0(l), 1.899(8); W(3)-0(9), 1.964(8). The structure (in polyhedral notation) is shown in Fig. 3.
G. Preparation of α-K9 [AlWι:ι039] . A 43.76 g sample of H5 [AlW12O40] (14.1 mmol; mixture of α and β isomers) was dissolved in 100 mL of water and heated to 60°C in a beaker fitted with a variable temperature pH meter. With constant stirring, 6.97 g of solid K2C03-1.5 H20 (42.3 mmol, 3 equiv.) were added slowly. Foaming (formation of C02) was observed and the addition was carried out slowly to prevent the reaction mixture from overflowing the beaker. Then, a solution of 11.62 g K2C03-1.5H20
(70.5 mmol, 5 equiv.) in 20 mL of water was added dropwise with care taken to keep the pH below 8 until at least 75% of the carbonate solution had been added. The product, a white powder, began precipitating during the course of the addition. During addition of the final 25% of the carbonate solution, the pH was allowed to increase to 8.5; final pH values typically ranged from 8-8.25. The mixture was then cooled to 5°C for several hours. The precipitate, α-K9 [A1W1:L039] (white powder) was collected on a medium porosity glass frit, washed with three 20 mL portions of water and air dried. Yield: 41.8 g (92%, 100% α isomer based on 27A1, B1V and 183W NMR spectra of K5 [AlW12O40] and K6 [AIV ^O^] derivatives) . As α-K9 [AlW-^O.^] is only sparingly soluble in water (2 g in 100 mL at 22°C) , reprecipitation is impractical. 27A1 NMR, δ: 63.3 ppm (Δv1/2 = 1735 Hz). IR (KBr pellet) 937, 868, 789, 756
(shoulder), 704, 524, and 493 cm"1. Anal. Calculated (found) for K9[A1W11039]-13H20: H 0.80 (0.77) W 62.05 (61.87) Al 0.83 (0.78) K 10.80 (10.92) .
H. Preparation of α-K6 [Al (Al'^OH-J WX1039] . A 5.18 g (1.58 mmol) sample of α-K9 [A1W11039] was stirred in 15 mL of water and aluminum chloride hexahydrate (A1C13-6H20, 0.38 g, 1.5 mmol) dissolved in 5 mL of water was added quickly via pipet . After stirring at room temperature for 15 minutes, the mixture was stirred in a warm (60°C) water bath until the solution became clear (ca. 5 minutes); the final pH of the solution was 6.7. The solution was cooled to room temperature, filtered on a medium glass frit, and cooled at 5°C until crystals formed. The crystals were collected and dried on a coarse frit. Yield: 3.77 g (75%) . 183W NMR (Fig. 6C) , δ (integration): -60.7(2), -103.2(2), - 132.0(1), -142.9(2), -152.0(2), -205.1(2). 27A1 NMR, δ: 74.3 (Δv1/2 = 78.5 Hz) and 8.8 ppm (Δv1/2 = 205.5 Hz). IR (KBr pellet): 948
(m) , 876 (s) , 799 (s) , 765 (m) , 735 (sh) , 685 (w) , 531 (w) , and 497 (w) cm"1. Anal. Calculated (found) for K6 [Al (AlOHJ WιrL039] -15H20: H 0.94 (0.87) W 63.10 (62.80) Al 1.68 (1.62) K 7.32 (7.04).
I. Preparation of K7 [AIV^W^O^] . A solution of 0.39 g (1.80 mmol) vanadyl sulfate trihydrate (VOS04-3H20) in 5 mL of water was added rapidly via pipet to a slurry of 5.43 g K9 [AlWι039j (1.80 mmol) in 10 mL of deionized water. The mixture became deep purple immediately. The solution was stirred for 10 minutes and filtered on a medium glass frit. After cooling the filtrate for several hours at 5°C, dark purple crystals were collected and dried on a medium frit and recrystallized from a minimum of warm (60°C) water. Yield: 3.5 g (61%). IR (KBr pellet) : 942 (m) , 871 (m) , 793 (s) , 761 (m) , 697 (w) , 537 (w) , 492 (w) , and 473 (w) cm"1. Anal: Calculated (found) for K7 [AlVWιrιO40] -13H20: H 0.81 (0.76) W 62.26 (62.23) Al 0.83 (0.69) V 1.57 (1.71) K 8.43 (8.34). In solution, the V(IV) ion in [AlVW1:LO40] 7" is paramagnetic; no NMR signals were observed. However, the vanadium is easily oxidized in solution to diamagnetic V(V) by addition of elemental bromine (Br2) . Spectra may then be observed for [AlVW11O40] 6" . 183W NMR, δ (integrations): -83.1 (2), -99.1 (2), -119.5 (2), -123.0 (1), - 124.0 (2), and -144.4 (2) ppm. 27Al NMR, δ: 72.5 ppm (Δv1/2 = 175 Hz) . 51V NMR, δ: -535.5 ppm (Δv1/2 = 220 Hz) .
J. Preparation of α-K6 [AIV^O^] . VOSO4-3H20 (12.20 mL of a 0.5 M solution, 6.1 mmol) was added dropwise to a slurry of K9 [AlW^Ojg] (20 g, 6.1 mmol) in 50 mL of water to give a purple solution of K7 [AlVIVWxlO40] (ca. 0.1 M) . Two equiv. of HC1 (4 mL of a 3 M solution) were added to the solution in order to consume the hydroxide generated upon subsequent oxidation of V(IV) to V(V) by reaction with ozone . A stream of ozone was then bubbled through the solution until its color changed to bright yellow. Oxygen was then bubbled through the solution for several minutes to remove unreacted ozone, and the solution was concentrated by rotary evaporation to half its initial volume. After cooling overnight at 5°C, yellow crystalline -K6 [AlVWι:LO40] was collected on a medium frit, air dried, and recrystallized from a minimum of hot (80°C) water. Yield: 12.95 g (66%). IR (KBr pellet) : 950 (m) , 878 (s) , 794 (s) , 756 (s) , 542 (w) , and 487 (w) cm"1. Anal. Calculated (found) for K6 [AlVW^O^] -13H20: H 0.82 (0.78) W 63.02 (62.97) Al 0.84 (0.88) V 1.59 (1.88) K 7.31 (7.29). 27A1 NMR, δ: 72.5 ppm (Δv1/2 = 175 Hz, Fig. 4). 51V NMR, δ: -535.5 ppm (Δv1/2 = 220 Hz, Fig. 5). 183W NMR (Fig. 6B) , δ (integrations): -83.1 (2), -99.1 (2), -119.5 (2), -123.0 (1), -124.0 (2), -144.4 (2) ppm.
K. Preparation of α-K8 [Al (MnIX0H) WX1039] . A 10.0 g sample of K9 [A1W11039] (3.05 mmol) was stirred in 100 mL of water. Manganese sulfate hydrate (MnS04-H20, 0.516 g, 3.05 mmol) was dissolved in 10 mL of water and then added rapidly via pipet to the K9 [A1W11039] slurry. The mixture was stirred in a water bath at 80°C for about 10 minutes, until all the solid had dissolved to form a golden- colored solution. The final pH of the solution was 6.3. After cooling to room temperature, the solution was filtered and then refrigerated overnight. The product, a brownish-yellow amorphous powder, was collected and dried on a coarse frit. Yield: 8.5 g (85.7%) . The product was recrystallized from a minimum of warm water. IR (KBr pellet) : 933 (m) , 871 (m) , 796 (s) , 766 (sh) , 698 (m) , 526 (w) , and 486 (w) cm"1. Anal. Calculated (found) for K7[AlMnWxl039] -13H20: H 0.81 (0.79) W 62.49 (62.34) Al 0.83 (0.96) Mn 1.70 (1.44) K 8.46 (8.20) .
L. Preparation of α-K6 [Al (MnIΣIOH2) W11039] . A 20 g portion of K9 (6.1 mmol) was stirred in 100 mL of water. A solution of MnS04-H20 (1.03 g in 10 mL water) was added dropwise to the slurry via pipet. The reaction mixture was stirred in a hot water bath (70 to 80°C) until the solution became clear, about 10 minutes. The pH of the solution was lowered to about 3 using a 1 M solution of HCl, and a solution of household bleach (Blue Ribbon brand, 5.25% NaOCl, 4.33 g bleach diluted by about half in water) was added while monitoring the pH. When about 75% of the bleach had been added, the pH had risen to 5.3 and did not decrease, so a few more drops of 1 M HCl were added to return the pH to about 3. During the process of adding bleach, the color of the solution changed from golden yellow to deep pink-purple. The solution was concentrated in vacuo until precipitate began to form and refrigerated at 5°C overnight. The precipitate, pink-purple in color, was collected on a coarse glass frit, dried in vacuo, and recrystallized in a minimum of warm water. Yield: 12.45 g (63%) . M. Preparation of α-K8 [Al (Co^OH) WlrL039] . The procedure was similar to that used for the preparation of K8 [Al (Mnι::OH) W1:L03g] , except that Co (N03) 2-6H20 (0.888 g) was used in place of MnS04-H20 (the pH after addition was 6.2) . The resulting solution (after heating in a water bath) was dark pink, and the product was a red powder. Yield: (2 crops) 7.31 g (74%) . The two crops were recrystallized together in a minimum amount of warm (60°C) water. Recrystallized yield: 3.66 g (37%). IR (KBr pellet): 952 (m) , 935 (s) , 891 (s) , 798 (m) , 697 (m) , 533 (w) , and 486 (w) cm"1. Anal: Calculated (found) for K7 [AlCoW^O-jg] -15H20: H 0.92 (0.91) W 61.73 (62.26) Al 0.82 (0.88) Co 1.80 (1.73) K 8.35 (8.16).
N. Preparation of α-K6 [Al (CoIXI0H2) W11039] . A 20 g portion of Kg [A1W11039] (6.1 mmol) was stirred in 100 mL of water. A solution of Co (N03) 2-6H20 (2.15 g in 10 mL water) was added dropwise to the slurry via pipet . The reaction mixture was stirred in a hot water bath (70 to 80°C) until the solution became clear, about 10 minutes. After cooling to room temperature, the solution was filtered and acidified with 4.0 mL 3 M HCl to a pH of 2. A stream of ozone was passed through the solution until it became dark green in color. The solution was concentrated in vacuo until precipitate began to form and refrigerated at 5°C overnight . The crystalline product was collected on a coarse glass frit, dried in vacuo, and recrystallized in a minimum of warm water. Yield: 11.33 g (58%). 183W NMR, δ (integrations): +148.5 (2), -60.3 (2), -89.7 (2), -120.6 (l) , -146.6 (2), and -149.0 (2) ppm (Fig. 6A) . 27A1 NMR, δ: 74.7 ppm.
II. BLEACHING WITH [A1VW1:L040] 6'
Delignification of wood pulp by [A1VW11040] 6" was demonstrated under several sets of conditions . Microkappa numbers (TAPPI UM246) of the bleached pulps were determined by FT-Raman Spectroscopy, and viscosities were determined by capillary viscometry (TAPPI T230 om-89) .
The first experimental conditions were 0.05 M [AlVW^O^] s" in 0.3 M acetate buffer at 125°C for 1 hour, using 0.5% pulp consistency. The starting Kappa number of the pulp was 31.8, and the final Kappa number was 17.0.
The second experimental conditions were 0.1 M [AlVW11O40] δ" in 0.1 M sodium tungstate (pH adjusted to 7.5-7.6) at 125°C for 10 hours, using 1% or 2% pulp consistency, initial Kappa number 31.8 and viscosity 31.4 mPa-s . Three samples treated at 1% consistency gave Kappa numbers of 15.0, 16.4, and 17.8 after bleaching and washing. The viscosity of the sample with Kappa number 15.0 was 22.5 mPa-s . Two samples at 2% consistency had Kappa numbers of 22.0 and 27.7. The viscosity of the 22.0 Kappa pulp was 18.0 mPa-s . The [ lVW^O^] 6" solutions were dark brown in color after delignification, indicating the presence of [AlVW11O40] 7" , reduced by lignin during the reactions.
III. OXIDATION OF [AlVWlrLO40] 7" BY OXYGEN
A useful characteristic of [AΓVWIIO40] 6" is that its reduction potential is sufficiently negative such that the reduced form of the anion, [AlVW11O40] 7" , can be readily oxidized by oxygen (02) . A solution of 0.001 M [A1VW11040] 7" in 0.01 M sodium tungstate dihydrate (adjusted to pH 7) was purged with oxygen (by bubbling 02 through the solution for 3 minutes) , blanketed with a layer of oxygen, and then sealed in a Teflon liner inside a stainless steel pressure vessel. The solution was heated to 200°C for 90 minutes and then removed from the pressure vessel. The solution, which was initially deep purple in color, had become bright yellow, indicating that the reduced anion, [AlVWι:,O40] 7" (purple), initially present had been oxidized to [AlVWι:LO40] 6" (yellow) . No precipitate was observed. The extent of the oxidation was quantified by UN- Visible spectrometry at 540 nm. At least 95% of the [AIVW^O^] 7" had been oxidized to [AlVW11O40] 6" .
IV. WET OXIDATION (MINERALIZATION) USING [AlVW^O^] s" AND OXYGEN. The reduction potential of [AlVW.,.,O40] 6" is similar to that of
[PV2Mo10040] s", an excellent wet oxidation catalyst8 (Fig. 7). Because the catalytic role of [PV2Mo10040] 5" in wet oxidation is to facilitate the transfer of electrons from the dissolved organic compounds to oxygen, it follows that the reduction potential (ease with which the anion receives and gives up electrons) is an important determinant of effectiveness. Reduction potential is a thermodynamic parameter. The rate of reaction of the reduced anion is also important in determining effectiveness as a catalyst for wet oxidation. Because the reduction potential of [AlVWι:LO40] 6" is similar to that of [PV2Mo10040] 5" (Fig. 7) and because [AlVW^O^] 7" is rapidly oxidized to [AIVW^O^] 6" by 02, it follows that solutions of [AlVW^O^] 6" and [AlVW^O^] 6" , or any combination thereof, would function effectively as catalysts for the wet oxidation of dissolved lignin and polysaccharide fragments .
V. OXIDATION OF [AlMn^W^O^] 7" AND [AlCo^W^O^] 7" TO [AlMn^W^O^] s" AND
Figure imgf000024_0001
6J RESPECTIVELY, BY OZONE
These reactions were accomplished by bubbling 03 (in 02) through solutions of [AlMnIIW11O40] 7" or [AlCoIIW11O40] 7", as described above in detail in Example I.L.

Claims

CLAIMS We claim:
1. A method of delignifying lignocellulosic fiber, comprising the steps of a) combining a polyoxometalate complex with aluminum heteroatom of the formula [Al-.VmMonW0NbpTaq(TM) rO x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron-containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0, with a lignocellulosic fiber preparation, wherein the pH of the combination is between 6 and 11 and the consistency of the combination is 1-20%; and b) heating the combination in a temperature- controlled and pressure-controlled vessel under conditions of temperature and time wherein the polyoxometalate is reduced and delignification occurs.
2. The method of claim 1 wherein the polyoxometalate is [Al1Vm(TM)nWo0p]x" where 1 is 1-2, m is 0-6, n is 0-3, o is 0-12, and
TM is a d-electron-containing transition-metal ion, where 1+m+n+o = 12 or 13 , and p is sufficiently large that x > 0.
3. The method of claim 1 wherein the polyoxometalate is [A1VW1104(J 6" .
The method of claim 1 wherein the pH is between 6 and
9.
5. The method of claim 1 wherein the lignocellulosic material is at least one of a lignocellulosic pulp, wood fiber and wood pulp .
6. The method of claim 1 wherein the reduced polyoxometalate complex is reoxidized by an oxidant selected from the group consisting of air, oxygen, hydrogen peroxide, organic and ozone.
7. The method of claim 6 wherein the oxidant is oxygen.
8. The method of claim 1 wherein the reduced polyoxometalate complex is reoxidized by an organic or inorganic peroxide .
9. A method for oxidative degradation of lignin and polysaccharide fragments dissolved during polyoxometalate treatment of lignocellulosic material, comprising the steps of: a) obtaining a lignocellulosic preparation; b) mixing the preparation with a solution of a polyoxometalate of the formula [Al1VmMonW0NbpTaq(TM) r0s] x" where 1 is 1-6, m is 0-18, n is 0-40, o is 0-40, p is 0-10, q is 0-10, r is 0-9, and TM is a d-electron-containing transition metal ion, where 1+m+n+o+p+q > 4, and s is sufficiently large that x > 0, wherein the preparation is of a consistency of 1-20%, wherein the preparation is delignified, the polyoxometalate is reduced, and the lignin and polysaccharide fragments within the preparation are dissolved, and wherein a liquor is obtained that contains the polyoxometalate and dissolved lignin and polysaccharide fragments; and c) heating the liquor in the presence of a gaseous oxidant, wherein oxidation takes place, under conditions wherein the polyoxometalate is oxidized and the dissolved lignin and polysaccharide fragments are catalytically and oxidatively degraded by the oxidant and the polyoxometalate to volatile organic compounds and water, i) wherein the pressure of the oxidant in the heating step is 15 to 1000 psia; ii) wherein the temperature of the heating step is between 100┬░C and 400┬░C; iii) wherein the heating step is performed at final pH of between 1.0 and 11.0; iv) wherein the time of oxidation is between 0.5 hours and 10.0 hours; and v) wherein the heating step takes place in a vessel capable of withstanding said pressure .
10. The method of claim 9, wherein the polyoxometalate is of the formula [Al1Vm(TM)nWo0p] x" where 1 is 1-2, m is 0-6, n is 0-3, o is 0-12, and TM is a d-electron-containing transition-metal ion, where 1+m+n+o = 12 or 13 , and p is sufficiently large that x > 0.
11. The method of claim 9 wherein the polyoxometalate is of the formula [AlVW^O^] 6" .
12. The method of claim 9 wherein the oxidant is oxygen.
13. The method of claim 9 wherein the lignocellulosic preparation is at least one of a lignocellulosic pulp, a wood fiber and a wood pulp.
14. The method of claim 12 wherein the lignocellulosic preparation is a wood fiber.
15. The method of claim 12 wherein the lignocellulosic preparation is a wood pulp.
PCT/US1998/018462 1997-09-05 1998-09-04 Transition-metal substituted tungstoaluminate complexes for delignification and waste mineralization WO1999011857A1 (en)

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CA002301719A CA2301719A1 (en) 1997-09-05 1998-09-04 Transition-metal substituted tungstoaluminate complexes for delignification and waste mineralization
AU92213/98A AU9221398A (en) 1997-09-05 1998-09-04 Transition-metal substituted tungstoaluminate complexes for delignification and waste mineralization
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US5552019A (en) * 1992-08-28 1996-09-03 The United States Of America As Represented By The Secretary Of Agriculture Oxidative delignification of wood or wood pulp by transition metal-substituted polyoxometalates

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US5549789A (en) * 1992-08-28 1996-08-27 The United States Of America As Represented By The Secretary Of Agriculture Oxidation of lignin and polysaccharides mediated by polyoxometalate treatment of wood pulp

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