RU2076071C1 - Process for preparing heteropolyacids - Google Patents

Abstract

FIELD: inorganic synthesis; preparation of heteropolyacids of formula: H_8-m+nX^m+M_12-nV_nO₄₀, wherein X is P, Si, Al, Fe; M=Mo, W; n=0-6. SUBSTANCE: molybdenum or tungsten oxides or compound of general formula: M_12-nV_nO_m, wherein M= Mo, W; n=1-6; m=33-35.5. Mixture of original element oxides is subjected to mechanical and chemical activation and the resulting products are subsequently treated with water or hydrogen peroxide at 25-100 C. EFFECT: more efficient preparation process. 4 cl

Description

The invention relates to inorganic synthesis, namely, to an improvement of the method for the synthesis of heteropoly acids of molybdenum, tungsten and vanadium of the general formula H _{8-m + n} X ^{m +} M _12-n V _n O ₄₀ , where M Mo or W, n 0-6, X P , Si, Al, Fe.

These heteropoly acids are widely used as catalysts for acid and oxidation processes [1]
A common method for producing heteropolyacids is the Drexel method [2, p. 1897] Using this method, a mixture of soluble molybdates, tungstates, vanadates with a solution containing a heteroatom is prepared. After mixing, the solution is acidified to the desired pH and heated, whereby a heteropoly acid salt is obtained with an admixture of an excess of the mineral acid anion used for acidification. To isolate a heteropoly acid free of impurities, the resulting mixture is subjected to extraction with ether. After decomposition of the ether complex, the heteropoly acid is crystallized. The yield, as a rule, does not exceed 60%. The described method is laborious, fire hazardous, and environmentally dirty. This method gives H ₄ PMo ₁₁ VO ₄₀ , H ₅ PMo ₁₀ V ₂ O ₄₀ , H ₆ PMo ₉ V ₃ O ₄₀ [2, p. 1907] H ₃ PMo ₁₂ O ₄₀ [2, p. 1893] mixed tungsten-molybdenum heteropoly acids and a number of other heteropoly acids [2]
More promising is the direct synthesis of heteropoly acids by the interaction of oxides of molybdenum, tungsten and vanadium with compounds containing a heteroatom. This method cannot be implemented due to the low solubility of these oxides in acidic solutions; however, a method is known for producing phosphorus-molybdenum heteropoly acid from molybdenum oxide and phosphoric acid [2, p. 1898] According to this method, molybdenum trioxide is added to a boiling solution of phosphoric acid and boiled for 2 2.5 hours. Despite prolonged boiling, not all molybdenum oxide is dissolved, insoluble molybdenum oxide is filtered off, and ether extraction must still be used to get rid of impurity HPA . A method is described for producing a series of phosphoromolybdenum acids by reacting phosphoromolybdenum acid with vanadium pentoxide and phosphoric acid without using ether extraction [3] Stoichiometric amounts of these compounds are boiled in an aqueous solution for 5 to 10 hours, hydrazine hydrate is added and another 5 10 hours are boiled until the pentoxide is completely dissolved vanadium, then hydrogen peroxide is added, evaporated and crystallized. In the described method, ether extraction is not used, however, one of the reagents is phosphoromolybdenum heteropoly acid, already obtained through the stage of ether extraction.

Closest to the proposed is a method for producing heteropoly acids by reacting pre-ground oxides of molybdenum and vanadium with phosphoric acid. Pre-grinding allows to reduce the duration of the synthesis from 20 days to 20 hours [4]
The disadvantage of existing methods for the synthesis of heteropoly acids is the presence of acidification and ether extraction stages, which give a large amount of effluents, harmful emissions, making the production process fire hazardous, as well as a long synthesis time and low yields.

 The objective of the invention is to increase the yield, simplifying the process by eliminating environmentally harmful stages, reducing the synthesis time.

This is achieved by the interaction of compounds containing a heteroatom with new oxide compounds of molybdenum, tungsten and vanadium, formed as a result of mechanochemical activation of a mixture of these oxides in a planetary centrifugal mill. As a result of mechanical activation, new oxide compounds of the general formula M _12-n V _n O _{m are formed} , containing in the structure V ⁴⁺ , where M Mo and W; n 1 6; m 33 35.5. The formation of these compounds is confirmed by X-ray diffraction and NMR methods on the V ⁵¹ core.

According to a number of physicochemical research methods (IR spectroscopy, electron and x-ray diffraction), vanadium pentoxide or other vanadium oxides are absent in activated mixtures. X-ray diffraction shows that the activated mixtures are homogeneous and contain one phase with a structure close to that of MoO ₃ . A study of the interplanar spacings <OK> allows us to conclude that after mechanochemical activation in the MO ₃ –V ₂ O _{5 system} , where M = Mo, W, a number of new compounds of variable composition are formed. A comparison of the X-ray diffraction data and the data obtained by the NMR ⁵¹ V method allows us to characterize the structure of the new compounds formed as having a structure close to MoO ₃ , in which layers from the MoO ₃ structure are interspersed with layers from the V ₂ O ₅ structure. In this case, depending on the concentration of vanadium, a change in the distortion of octahedral polyhedra is observed. In addition, all samples contain vanadium in a distorted tetrahedral environment. Processing a mixture of oxides in a ball mill, as this is done in the prototype, does not lead to the formation of these compounds.

 Distinctive features of the obtained compounds are the chemical composition and crystal structure. The compounds obtained are not described in the literature. In this regard, the claimed compounds and the method of their production meet the criteria of novelty, inventive step and industrial applicability.

The interaction of oxide compounds with heteroatom compounds is carried out at room temperature under conditions of mechanical activation of oxide compounds M _12-n V _n O _m , where n 1 6 with compounds containing XO ₄ groups.

A distinctive feature of the method is the use as an initial component of the oxide compounds of molybdenum and tungsten with vanadium. We have not found the use of mixed oxides for the synthesis of heteropolyacids in known technical solutions. Compounds used for synthesis are also not described in the literature. A distinctive feature of the method is the use of mechanical activation for the interaction of XO ₄ groups with oxide compounds. In this regard, the proposed methods meet the criteria of novelty and inventive step.

 Carrying out the process according to the proposed method allows to obtain a number of heteropoly acids with practically quantitative yield, to eliminate environmentally harmful stages of acidification and ether extraction, and to significantly reduce the synthesis time.

Example 1 (comparative). A mixture of 3.8 g of MoO ₃ and 0.48 g of V ₂ O _{5 was} ground in a ball mill for 30 hours. A portion of 0.89 g of this mixture was placed in a flask and a 3.45 mm solution of phosphoric acid with a concentration of 14.45 g was added / l and 6.25 ml of water. The mixture was refluxed for 4 hours. An orange-red solution formed. The NMR spectra on the P ³¹ and V ⁵¹ nuclei are characteristic of the acid H ₅ PMo ₁₀ V ₂ O ₄₀ . The solution was evaporated and crystallized to obtain a solid HPA; yield 50
Example 2. A mixture of 4.73 g of MoO ₃ and 0.27 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 minutes to form the compound Mo ₁₁ VO _35.5 . Then a solution of phosphoric acid (0.29 g of H ₃ PO ₄ ) was added to the drum of the planetary mill and activated for 5 minutes. The resulting product is dissolved in water at 100 ^o C for 5 min with the formation of a solution of HPA according to NMR spectroscopy.

Example 3. A mixture of 4.44 g of MoO ₃ and 0.56 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 minutes to form the compound Mo ₁₀ V ₂ O ₃₅ . Then, a solution of phosphoric acid was added to the drum of the planetary mill and activated for 5 minutes. The resulting product is dissolved in water at 80 ^o C for 3 min with the formation of a solution of HPA according to NMR.

Example 4. A mixture of 4.13 g of MoO ₃ and 0.87 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 minutes to form the compound Mo ₉ V ₃ O _34.5 . Then a solution of phosphoric acid (0.31 g of H ₃ PO ₄ ) was added to the drum of the planetary mill and activated for 3 min. According to IR spectroscopy, the solid product is HPA. The resulting product at 25 ^o C for several seconds is dissolved in water with the formation of a solution of HPA according to NMR spectroscopy.

Example 5. A mixture of 3.8 g of MoO ₃ and 1.2 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 minutes until the formation of the compound Mo ₈ V ₄ O ₃₄ . Then a solution of phosphoric acid (0.32 g of H ₃ PO ₄ ) was added to the drum of the planetary mill and activated for 2 min. According to IR spectroscopy, the resulting product is HPA. The resulting product at a temperature dissolves in water for several seconds to form a HPA solution according to NMR spectroscopy.

Example 6. A mixture of 3.06 g of MoO ₃ and 1.94 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 min to form the compound Mo ₆ V ₆ O ₃₃ . Then a solution of phosphoric acid (0.35 g H ₃ PO ₄ ) was added to the drum of the planetary mill and activated for 1 min. The resulting product dissolves in water in a few seconds with the formation of a HPA solution according to NMR spectroscopy
Using this method, it is also possible to obtain heteropolyacid layers, as illustrated by Examples 7.

Example 7. A mixture of 3.8 g of MoO ₃ and 1.2 g of V ₂ O ₅ was subjected to mechanochemical activation for 30 minutes until the formation of the compound Mo ₈ V ₄ O ₃₄ . Then 1.1 g of Na ₃ PO ₄ • 10H ₂ O was added to the drum of the planetary mill and activated for 3 minutes. According to the NMR data, a heteropoly acid salt was formed ^on P ³¹ cores.

 In this method, heteropoly acids with silicon, iron and aluminum as the heteroatom can also be obtained (example 8).

Example 8. A mixture of 2.0 g of SiO ₂ and 4.0 g of MoO ₃ was subjected to mechanochemical activation for 30 min in a planetary centrifugal mill with a drum rotation speed of 10 s ^-1 . The activated mixture was washed with water at a temperature of 50 ^° C. and an excess of SiO _{2 was} filtered. According to IR spectroscopy, a silicon-molybdenum heteropoly acid is formed in solution. The acid yield of 80%
Example 9. A mixture of 4.5 g of WO ₃ and 0.36 g of V ₂ O ₅ was subjected to mechanochemical activation until the formation of compound W ₁₀ V ₂ O ₃₅ . Then, 1 g of SiO _{2 was} added to the drums of the planetary mill and activated for 3 min. The activated mixture was boiled. According to IR spectroscopy, a heteropoly acid H ₆ SiW ₁₀ V ₂ O _{40 is} formed in solution. Yield 20%
Example 10. Activated a mixture of 4.53 g of MoO ₃ and 0.47 g of FeOOH for 30 min in a centrifugal planetary mill at a rotational speed of the drums of 10 s ^-1 . The activated mixture was boiled in a solution of hydrogen peroxide for 30 minutes; during this time, the mixture was completely dissolved, the resulting solution had a pH of 2. To identify the resulting acid, its salt with tetrabutylammonium cation was obtained. According to IR spectroscopy, a salt of the composition (Bu ₄ N) ₉ FeMo ₆ O _{40 was} obtained, i.e. the solution was acid H ₉ FeMo ₆ O ₂₄ .

 Example 11

A mixture of 4 g of MoO ₃ and 1 g of Al (OH) ₃ was subjected to mechanochemical activation for 30 min in a centrifugal planetary mill at a rotational speed of 10 s ^-1 . The activated mixture was boiled in water for 30 minutes. The solution was filtered from aluminum hydroxide; it had a pH of 2. To identify the resulting acid, its salt with a tetrabutylammonium cation was obtained. According to IR spectroscopy, an acid of the composition H ₉ AlMo ₆ O _{24 was} obtained.

 The data of examples 2 to 11 indicate the achievement of the purpose of the invention: environmentally harmful stages of acidification and ether extraction are eliminated, almost all syntheses proceed in quantitative yield; the synthesis time of molybdenum-vanadium heteropoly acids decreases from several tens of hours to several minutes, and in some cases to several seconds; For the first time, tungsten-containing heteropoly acids were obtained by the direct synthesis reaction within 3 hours, while this reaction does not occur with the use of oxides.

 In addition, for the first time in the direct synthesis reaction, it was possible to obtain iron-molybdenum and aluminum-molybdenum acids.

Claims (4)

1. The method of obtaining heteropolyacids composition
H _{8-m + n} X ^{m +} M _12-n V _n O ₄₀ ,
where XP, Si, Al, Fe;
M Mo, W;
n 0 6,
the interaction of compounds containing vanadium and molybdenum or tungsten, with compounds containing a heteroatom, characterized in that as the starting compounds use a compound of the General formula
M _{1 2 - n} V _n O _m ,
where M Mo, W;
n 1 6;
m 33 35.5,
or oxides of molybdenum or tungsten, and the interaction is carried out under conditions of mechanochemical activation in a centrifugal planetary mill, followed by treatment of the resulting products with water or hydrogen peroxide at a temperature of 25 100 ^o C.  2. The method according to claim 1, characterized in that as compounds containing a heteroatom, use phosphoric acid or its salts, silica gel, aluminum hydroxide, iron hydroxide. 3. The method according to PP.1 and 2, characterized in that as compounds of the general formula
M _{1 2 - n} V _n O _m ,
where M Mo, W;
n 1 6;
m 33 35.5,
use compounds obtained by mechanochemical activation of a mixture of vanadium oxide and oxides of molybdenum or tungsten in a centrifugal planetary mill for 20 to 40 minutes at a drum rotation speed of 10 s ^{- 1} . 4. The method according to claims 1 and 2, characterized in that the interaction of compounds of the composition M _{1 2 - n} V _n O _m or molybdenum or tungsten oxides with compounds containing a heteroatom is carried out in a centrifugal planetary mill at a drum rotation speed of 10 s ^{- 1} within 1 30 minutes