Method for manufacturing ammonium metatungstate

Abstract

The present invention relates to a method for producing ammonium metatungstate using a reverse osmosis cell and an apparatus for carrying out the method according to the present invention.

Description

Technology Field

[0001] The present invention relates to a method for producing ammonium metatungstate using a reverse osmosis cell and an apparatus for carrying out the method according to the present invention. Background Technology

[0002] Ammonium metatungstate (AMT) is used particularly in catalyst production. Various methods are available for the production of ammonium metatungstate, which can be categorized into solid and liquid material transformations. Generally, solid material transformation involves the thermal decomposition of ammonium paratungstate (APT), where ammonium paratungstate decomposes into metatungstate through acidification when transformation occurs in the liquid state.

[0003] DE 37 43 267 relates to a method for producing ammonium metatungstate having an ignition loss of 5.6 to 5.9 weight% by annealing ammonium paratungstate from roasting aggregate at a temperature of 150 to 400°C and then leaching the roasted product obtained with water, wherein, to obtain the desired ignition loss, a roasted product having an ignition loss of less than 5.6 weight% and a roasted product having an ignition loss of more than 5.9 weight% are mixed in proportion, so that the ignition loss of the mixture is within the claimed range and a high yield is obtained.

[0004] EP 0 193 171 discloses a method for producing ammonium metatungstate from ammonium paratungstate, comprising the steps of heating ammonium paratungstate at a temperature of 200 to 400°C, decomposing the heated ammonium paratungstate in water to form an aqueous ammonium metatungstate solution, evaporating the ammonium metatungstate solution to form a concentrated ammonium metatungstate solution, separating insoluble matter from the concentrated metatungstate solution, and crystallizing ammonium metatungstate from the concentrated ammonium metatungstate solution.

[0005] US Patent No. 7,794,686 describes a method for producing ammonium metatungstate, comprising the preparation of a mixture of solid ammonium paratungstate and water. The mixture is brought into contact with a cation exchange material to lower the pH of the mixture to a stable range for ammonium metatungstate ions and prevent the formation of insoluble tungstic acid. The mixture is then maintained at this pH until a significant portion of the ammonium paratungstate is converted into an ammonium metatungstate solution. Performing this process on an industrial scale is very complex because an ion exchanger is used, the latter must be regenerated with acid, and the resulting ammonium salt solution cannot simply be drained into receiving water but must be recycled.

[0006] EP 0 200 170 describes a method for producing ammonium metatungstate from ammonium paratungstate, wherein the method comprises roasting ammonium paratungstate at a temperature of 275 to 300°C to form a sludge. The sludge is evaporated to 20% of its original volume to obtain a concentrated metatungstate solution, from which insoluble substances are separated. As a final step, the described method comprises crystallizing ammonium metatungstate from the concentrated ammonium metatungstate solution. Within the scope of the described method, it is considered particularly advantageous to perform leaching of the roasted material at a very low concentration of less than 12 g / L to achieve a high overall yield.

[0007] These known methods for manufacturing metatungstate share a common characteristic: they require an evaporation step, which necessitates significant energy consumption. Therefore, there is a need for a metatungstate production process that reduces energy consumption within the scope of current efforts to improve the sustainability of existing production processes.

[0008] Various alternative concentration methods have been described for the production of different tungstate compounds.

[0009] Accordingly, US 5,178,848 discloses a method for producing lithium metatungstate by treating an aqueous solution of lithium monotungstate with a cation extractant to lower the pH value of the solution to 3.5 to 5.0, thereby producing a diluted solution of lithium metatungstate. In a subsequent step, the diluted solution is concentrated by removing water, and it is suggested that evaporation by heating, vacuum treatment, vacuum heating, reverse osmosis, or a combination of these methods be used in this step. The formation of undesirable lithium paratungstate is prevented by saturating the lithium tungstate solution with colloidal tungsten trioxide.

[0010] J.-Q. Liu et al., in their study "A Study on a Novel Method for Preparing Pure Ammonium Metatungstate (AMT) Using a Combined Process of Neutralization - Nanofiltration - Crystallization" published in Journal of Membrane Science 240 (2004), 1-9, describe a method for preparing metatungstate by concentrating an aqueous metatungstate solution using nanofiltration.

[0011] Because the isopolyanionic properties of tungstate salts are fundamentally different from those of other metal salts, the experience and knowledge gained from the production of one metal salt can generally only be used very restrictively in the production of another metal salt. The problem to be solved

[0012] Therefore, the object of the present invention is to provide a method for manufacturing ammonium metatungstate that is an alternative to conventional methods and reduces specific energy consumption.

[0013] Surprisingly, it was confirmed that this objective can be achieved by performing the concentration of an ammonium metatungstate solution in the production of ammonium metatungstate using a reverse osmosis cell. means of solving the problem

[0014] Accordingly, the present invention first relates to a method for producing ammonium metatungstate (AMT) by passing an aqueous ammonium metatungstate solution (A) through one or more reverse osmosis cells to obtain a concentrate (C) and a permeate (P). Effects of the invention

[0015] Process control according to the present invention causes only very little tungsten loss, while high concentrations of ammonium metatungstate can be achieved. Brief explanation of the drawing

[0016] FIG. 1 is a drawing illustrating an apparatus for carrying out the method of the present invention. Specific details for implementing the invention

[0017] Surprisingly, it has been discovered that concentrated metatungstate solutions can be obtained using reverse osmosis cells without membrane clogging caused by equilibrium shifts, due to the differing permeabilities of various isopolytungstate ions. Therefore, the energy-intensive evaporation step, which forms an essential part of the production of ammonium metatungstate by conventional methods, can be omitted in this manner. Furthermore, eliminating the evaporation step in ammonium metatungstate production successfully removes the bottlenecks essential to the process, thereby not only lowering specific energy requirements but also improving production capacity and reducing manufacturing costs through shorter lead times. Reduced energy demand simultaneously leads to a decrease in CO2 emissions, contributing immediately to the sustainability of the production process.

[0018] The use of reverse osmosis cells is generally known to those skilled in the art. Accordingly, WO 2004 / 099087 describes a method for treating nitrate-containing wastewater in which, after preliminary washing to remove solids or suspended solids, separate alkaline earth and heavy metal ions through sedimentation and ion exchange, and remove CO2 at low pH values, the wastewater passes through one or more reverse osmosis and / or electrodialysis cells. Preferably, a NaNO3 concentration of up to 200 g / L is obtained by reverse osmosis in a multi-stage countercurrent process.

[0019] Now, within the scope of the present invention, it has been discovered for the first time that reverse osmosis can be used not only for simple inorganic salts in aqueous solution but also for metals forming isopolyanions in which partially complex equilibria exist between different species, and that this must not be hindered by the selective ion permeability of the membrane that may occur.

[0020] Simple salts such as NaCl, NaNO3, Na2SO4, NH4Cl, NH4NO3, or (NH4)2SO4 are mainly dissolved in water to form simple ions. The presence of these ions is independent of the concentration or pH of the solution. A different picture is observed for elements that form complex isopolyanions, including tungsten in addition to niobium, tantalum, and molybdenum, and especially vanadium.

[0021] Generally, monomer WO4 2- The formation of isopolytungstate proceeding in is formulated according to the following reaction scheme.

[0022] pH + + qWO4 2- = [H p-2r W q O 4q-r ] (2q-p)- + rH2O

[0023] The resulting equilibrium depends on the pH, concentration, and temperature of the solution. Therefore, due to complex interrelationships, it was assumed that when using reverse osmosis cells in the context of isopolymetallates, undesirable compounds such as tungstic acid or ammonium paratungstate would precipitate locally in the cell due to ion-selective permeability. The present invention overcomes this prejudice. Surprisingly, precipitation or clogging of the membrane used was not observed within the scope of the present invention, contrary to the suspicions of the prior art.

[0024] It has been found that using a high-pressure reverse osmosis cell is particularly advantageous within the scope of the method according to the present invention. Accordingly, an embodiment of the method according to the present invention is preferred in which reverse osmosis is performed in a high-pressure reverse osmosis cell at a pressure preferably greater than 50 bar, preferably greater than 90 bar, more preferably greater than 100 bar, particularly greater than 120 bar, and particularly greater than 150 bar.

[0025] The method according to the present invention has the additional advantage of being applicable to a conventional method for obtaining metatungstate by proceeding from ammonium paratungstate. Accordingly, an embodiment is preferred in which ammonium paratungstate tetrahydrate is calcined and the calcined material is water-leached to obtain an aqueous metatungstate solution (A).

[0026] A filtration step may be performed to separate solids and suspended solids from an aqueous ammonium metatungstate solution (A). Accordingly, in a preferred embodiment of the method according to the present invention, the solution (A) undergoes a filtration step before reverse osmosis is performed.

[0027] By using a reverse osmosis cell in the process according to the present invention, the energy-intensive evaporation step typically required to produce a concentrated metatungstate solution is no longer necessary. Reverse osmosis produces a concentrated metatungstate solution with significantly reduced energy input, and the desired product can be separated in an additional process in which energy savings of more than 10% are achieved. Thus, in a preferred embodiment, ammonium metatungstate is recovered by cooling the concentrate (C) obtained after reverse osmosis. For lower quality requirements, metatungstate may also be obtained, for example, by spray-drying the solution concentrated by reverse osmosis.

[0028] The method according to the present invention is characterized particularly by energy efficiency and related sustainability. This is also reflected in process control. Accordingly, an embodiment in which the obtained permeate is returned to the process cycle is preferred. In this way, high efficiency can be ensured, while wastewater production can be reduced on the other hand. Surprisingly, it was found that after many cycles, a portion of the mother liquor must be discharged to separate the impurities, as trace impurities can become abundant in the mother liquor. The tungsten contained in these mother liquor fractions is completely recycled into the ammonium paratungstate manufacturing process, which is a starting compound for producing metatungstate. The method according to the present invention can be operated continuously or in batch or discontinuous mode. To ensure an efficient utilization of the production plant, the process according to the present invention is preferably operated continuously.

[0029] The remarkably high efficiency of reverse osmosis enables one-step process control, which is particularly advantageous in terms of saving costs and time. Accordingly, in a preferred embodiment, the process according to the present invention operates as a one-step process. Preferably, the efficiency of the process is further enhanced by the fact that the obtained permeate is completely recycled to the manufacturing process by using it for the leaching of the calcined material, i.e., for the production of an aqueous ammonium metatungstate solution (A). Thus, it has been found that the reverse osmosis cell can be operated at a very high pressure of 110 bar or higher, thereby obtaining a concentrate having an ammonium metatungstate concentration of more than 1200 g / L. Furthermore, it has been found that product loss, for example through ammonium metatungstate contained in the permeate, is prevented by the process control according to the present invention. Since the permeate is completely utilized in the leaching step, there is no need to recycle the permeate in an upstream process step for concentrating metatungstate in the permeate or for producing ammonium paratungstate.

[0030] To further improve the efficiency of the process according to the present invention, it may be operated as a multi-stage process, that is, one or more reverse osmosis cells are passed through. Accordingly, an embodiment in which the method according to the present invention operates in a multi-stage mode is preferred. In this mode, it has been surprisingly found that the general procedure of guiding the concentrate and permeate flow to a reverse flow is not required in the process according to the present invention. Preferably, multi-stage process control using multiple reverse osmosis cells connected in series has the advantage that the reverse osmosis cells can be applied individually to the corresponding requirements. Accordingly, an embodiment of the process according to the present invention in which the reverse osmosis cells operate at different pressures in multi-stage process control is preferred.

[0031] Within the scope of the method according to the present invention, reverse osmosis is used, particularly to produce a concentrated ammonium metatungstate solution, from which the desired product, ammonium metatungstate, is recovered. There are no special requirements for the production of an aqueous ammonium metatungstate solution. Rather, surprisingly, it has been found that a highly diluted solution containing only low concentrations of metatungstate, which is described as advantageous in the prior art, can react efficiently. In this case, it has been found advantageous to initially connect several reverse osmosis cells in parallel and then connect these blocks in series stepwise. As the number of stages increases, the number of cells connected in parallel per stage can be reduced. In the method according to the present invention, a diluted ammonium tungstate solution obtained, particularly in some production methods, may also be used. To concentrate such a solution, particularly a diluted ammonium metatungstate solution containing less than 100 g / L or even less than 50 g / L or even less than 25 g / L, the method according to the present invention provides a preferred embodiment in which several reverse osmosis cells are connected in parallel and the block thus formed is connected in series upstream of the individual reverse osmosis cells.

[0032] In a preferred embodiment, the concentration of ammonium metatungstate in the aqueous solution (A) before passing through the osmotic cell is 150 to 550 g / L, preferably 250 to 500 g / L, and more preferably 200 to 300 g / L. The use of the reverse osmotic cell according to the present invention can surprisingly yield a particularly high concentration of ammonium metatungstate solution, and thus efficient process operation can be achieved. Accordingly, an embodiment in which the concentration of ammonium metatungstate in the concentrate (C) after passing through the osmotic cell is 1200 g / L or more, preferably at least 1500 g / L or more is preferred.

[0033] Within the scope of the method according to the present invention, it was further confirmed that the presence of small amounts of foreign ammonium salts, such as NH4Cl, NH4NO3, or (NH4)2SO4 obtained from some preparation methods of the aqueous solution (A), is insignificant. Surprisingly, the presence of foreign salts was found not to have any adverse effect on the method according to the present invention.

[0034] There are no specific requirements regarding the reverse osmosis cell used in the method according to the present invention. However, it has been found that using a reverse osmosis cell comprising a membrane in the form of a spirally wound membrane is advantageous. Therefore, an embodiment in which the reverse osmosis cell comprises at least one membrane in the form of a spirally wound membrane is preferred.

[0035] The present invention also relates to the use of a reverse osmosis cell in the production of ammonium metatungstate. More preferably, the reverse osmosis cell is a high-pressure reverse osmosis cell and preferably comprises at least one membrane in the form of a spirally wound membrane.

[0036] The present invention also relates to an apparatus for carrying out a method according to the present invention, wherein the apparatus comprises at least one reverse osmosis cell, preferably a high-pressure reverse osmosis cell.

[0037] The present invention is described in more detail with reference to FIG. 1 and the following examples, but this should not be interpreted as limiting the idea of ​​the invention in any way.

[0038] A storage vessel (1) equipped with a stirrer (2) and a heat exchanger (3) is first filled with an AMT solution diluted to the maximum working volume through a valve (4). After filling is complete, a metering pump (5) transfers the solution in the storage vessel (1) to a high-pressure pump (6), and the so-called feed solution is transferred to an internal cycle driven by a circulation pump (7), where the feed is mixed with recycled concentrate and supplied to a high-pressure reverse osmosis cell (8), which comprises one or more spirally wound membranes that are composed of a semipermeable membrane (9) and support the structure of a pressure pipe. Water passes through the membrane and is discharged from the entire system as a permeable stream (10) under gravity. The remaining concentrate stream (11) in the internal cycle is divided through a pressure control (12) and a control valve (13) into recycled concentrate (17) for the internal cycle and a channeled-out concentrate (14). When the plant operates in batch mode, the concentrate discharged from the internal cycle maintained by the pump (7) flows back into the storage container (1) under gravity while the valve (15) is closed and the valve (16) is open. The filling volume in the storage container is lower in batch mode because it flows out of the entire system beyond the external balance limit, so the AMT concentration increases over time to the desired preset value and increases in batch mode, and batch concentration is completed. Significant heating occurs as the internal circulation pump (7) and, in particular, the high-pressure pump supply operate in the internal cycle. Some of this excess energy is dissipated as heat along with the permeate flow of the entire system exceeding the external balance limit, and the remainder is recovered from the recycled concentrate (14) through the heat exchanger (3). A constant temperature of the internal cycle is ensured by a temperature control (18) that controls the cooling water supply.

[0039] Alternatively, the described system can also be operated in a continuous mode in which the supply solution (diluted AMT solution) is permanently supplied to the storage container (1) through the valve (4) and the formed concentrate is discharged as a permeate through the open valve (15) while the valve (16) is closed.

[0040] Examples

[0041] 1.20 g / cm² in the storage container (1) 3 500 liters of diluted AMT solution with a density of (at 20°C) was filled. The concentration was 242.5 g AMT / L. A concentrate with a density of 2.40 g AMT / L (measured at 35°C) was prepared at a predetermined pressure of 110 bar controlled by pressure control (12). The concentration of AMT was 1682 g AMT / L. Approximately 427 liters of permeate were separated. Analysis of the permeate revealed a tungsten content of 1.35 g / L (0.64%), and no change in the NH4 / W ratio was observed. The ammonium content measured by the Kjeldahl method was 0.067 g / L. As can be seen from the permeate analysis, the small loss of tungsten did not cause a significant change in the chemical composition. Since the chemical composition did not change, the permeate can be completely recycled during operation to prepare the diluted AMT solution. The small loss of tungsten through the membrane of less than 1% demonstrates the economic advantages associated with the method according to the present invention as an additional benefit.

[0042] As can be seen from the described examples, process control according to the present invention causes only very little tungsten loss, while high concentrations of ammonium metatungstate can be achieved.

Claims

Claim 1 A method for producing ammonium metatungstate, characterized by passing an aqueous ammonium metatungstate solution (A) through one or more high-pressure reverse osmosis cells and concentrating it to obtain a concentrate (C) and a permeate (P) containing ammonium metatungstate (AMT), wherein the process is performed at a pressure greater than 50 bar in the high-pressure reverse osmosis cells. Claim 2 delete Claim 3 A method for manufacturing according to claim 1, characterized in that the aqueous ammonium metatungstate solution (A) is obtained by calcining ammonium paratungstate tetrahydrate and water leaching of the calcined material. Claim 4 A manufacturing method according to claim 1, characterized in that the solution (A) undergoes a filtration step before reverse osmosis is performed. Claim 5 A manufacturing method according to claim 1, characterized in that the ammonium metatungstate is recovered by cooling the concentrate (C). Claim 6 A manufacturing method according to claim 5, characterized in that the obtained permeate is recirculated to the process cycle. Claim 7 A manufacturing method according to claim 1, characterized in that the above method is operated continuously. Claim 8 A manufacturing method according to claim 1, characterized in that the method operates continuously and in a one-step mode. Claim 9 A manufacturing method according to claim 1, characterized in that the above method operates in a multi-stage mode. Claim 10 A manufacturing method according to claim 9, characterized in that the reverse osmosis cell operates at different pressures when the above method is operated in a multi-stage mode. Claim 11 A method for manufacturing according to claim 1, characterized in that the concentration of ammonium metatungstate in the aqueous solution (A) is 150 to 550 g / L. Claim 12 A manufacturing method according to claim 1, characterized in that the concentration of ammonium metatungstate in the concentrate (C) is 1200 g / L or higher. Claim 13 delete Claim 14 delete Claim 15 delete

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