Ammonium Metatungstate Production Equipment

Ammonium metatungstate production equipment according to the different stages of production and different methods may be variety, such as pyrolysis method of AMT production, a reactor, rotary kiln, high-speed centrifugal spray drying equipment or spray atomization drying equipment may be used; In addition, other pyrolysis equipments include microwave oven, plate multiple hearth furnace and tubular multiple hearth furnace. The direct recovery AMT can be more than 95% when using tubular multiple hearth furnace.

At present, the pyrolysis equipment for producing ammonium metatungstate is mainly rotary calciner, which is a rotary kiln. A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner. The fuel for this may be gas, oil, pulverized petroleum coke or pulverized coal.

alkali decomposition furnace

plate and frame filter

Ammonium metatungstate produced by ion exchange method will probably use ion exchange resin, crystallizer, or spray dryer and other production equipments. Alkali decomposition furnace is mainly used for decomposing tungsten ore during the preparation of AMT to dissolve tungsten into a solution. A plate and frame filter press is the most fundamental design, and many now refer it as a "membrane filter plate". This type of filter press consists of many plates and frames assembled alternately with the supports of a pair of rails. It is used for the impurity removal process of sodium tungstate for preparing high purity sodium in the APT preparation.

ion exchange column

spray drying tower

Ion exchange colum is used for removal of S, Mo, P, As, Ca, Cu and Sn and other impurities. Co-current deionization refers to the original downflow process where both input water and regeneration chemicals enter at the top of an ion exchange column and exit at the bottom. Co-current operating costs are comparatively higher than counter-current deionization because of the additional usage of regenerants. Because regenerant chemicals are dilute when they encounter the bottom or finishing resins in an ion exchange column, the product quality is lower than a similarly sized counter-flow column. Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals.

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Ammonium Metatungstate Decomposition Temperature

Ammonium metatungstate decomposition temperature is the temperature of AMT coming out decomposition reaction; while in the actual production environment, ammonium metatungstate will have several different decomposition temperatures according to complete reaction or not. Decomposition temperature of a substance means the temperature at which the substance chemically decomposes, which the chemical decomposition caused by heat. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion.

ammonium metatungstate image

Ammonium metatungstate will produce different products at different decomposition temperatures. When the heat treatment temperature is 200~300°C, AMT will be removed of all crystal water and most of the ammonium ions; then phase transformation will occur at 300-350°C to generate metastable tungsten oxide species; when the heat treatment temperature rise to 500~550°C, a small amount of ammonium and bound water is still not broken down; and when the temperature rises to 600°C and above, ammonium metatungstate will completely decomposed into tungsten trioxide (WO3); when the temperature raised to 700°C and held for 2 hours, mesoporous tungsten trioxide hollow balls will be obtained.

About ammonium metatungstate:
Ammonium metatungstate (AMT) is an important intermediate compound in tungsten wet smelting process, with the appearance of white or slightly yellow crystalline, the biggest solubility in all the tungsten compound, wherein the solubility will bigger than 300g WO3/100ml H2O at 25℃. The preparation methods of ammonium metatungstate are mainly Acid neutralization, Thermal separation, electrodialysis, solvent extraction and ion exchange method and the method depends on ammonium paratungstate (APT). AMT is the important raw material of tungsten compound (such as tungsten trioxide, blue tungsten oxide, tungsten hexachloride ect.); at the same time, it is usually used in industries of petroleum, chemical, ceramic, lubrication and so on; in addition, since the continually developing of electronics industry and the constantly mining of new material, AMT is also used in film substrate, capacitor and shielding ect. of semiconductor devices.

Ammonium Metatungstate Detection Method and Equipment

atomizer photo

The detection methods of ammonium metatungstate are graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS), inductively coupled plasma emission spectrum (ICP-MS) and coprecipitation separation - hydride atomic fluorescence spectrometry (i.e. coprecipitation separation - HG - AFS method.

Graphite furnace atomic absorption spectrometry (GFAAS) is the method absorbing and analyzing atoms by atomization with current heating in an atomization device which produced by graphite and to form shapes of tubes, cups and others. Since all atoms of sample are getting involved in the atomization, and the atomic concentration diluted in the flame gas has been avoided, then the analytical sensitivity has been greatly improved. While, when that method applied in detecting trace metal element, its property is better than many of other methods, and will be used in analysis of small amount samples and detect analysis of solid sample.

Detection equipments of ammonium metatungstate are atomization device, flame atomic absorption spectrometer, and inductively coupled plasma mass spectrometer ect..
1. Atomization device is a device for sample atomization of atomic absorption spectrometry, which is used in both graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS). It converts the sample to a free atomic vapor (ground state atom) to absorb the characteristic radiation, and to calculate the element to be measured. There are many kinds of atomizers, and they can be divided into two categories of fire stuffing atomizer and electrothermal atomizer in common. The former includes pre-mixed and full consumption type; the latter includes graphite furnace, carbon wire atomizer, carbon rod atomizer, graphite increase exhaust, and graphite probes ect..
2. Inductively coupled plasma mass spectrometer consists of plasma torch (composed of three concentric quartz tube), high frequency generator (to produce high frequency current), induction coil, gas supply system and atomization system and other parts;
3. Flame atomic absorption spectrometer is composed of light source, atomization system, spectroscopic system and detection system. The principle is that the instrument emits light with the characteristic spectral line of the element to be measured from the light source, then when the sample vapor passes through, the light will be absorbed by the under measure ground state atom, and finally measured by the weakened degree of radiation characteristic spectrum of light.

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Ammonium Metatungstate Spray Drying Tower

ammonium metatungstate spray drying tower picture

Ammonium metatungstate spray drying tower belongs to the spray equipments of ammonium metatungstate production, which is the most widely used of liquid forming process and drying industry. Spray-drying tower is suitable for preparing powder, granular solid product from liquid raw material with forms of suspoemulsions, solution, emulsion, and paste. Thus, when the finished product particle size distribution, residual moisture content, bulk density and particle shape are in line with the precision standard, the spray drying tower is supposed to be an ideal drying process.

Principle of ammonium metatungstate spray drying tower is that the air goes into the top dryer’ air distributor after filtered and heated, then the hot air will uniformly go into the drying room in the spiral. AMT feed solution through the high-speed centrifugal atomizer (rotary) at the top of the tower to be sprayed into the extremely fine mist liquid beads AMT, and dried AMT will come into being in a very short time when it in contacts with the stream of hot air. Then, ammonium metatungstate is exported continuously from the bottom of the spray drying tower and the cyclone, and the exhaust gases are vented by the fan.

Extended reading:
Spray drying tower is the equipment which can be used in drying biological pesticide, medicine and food microorganism, with the max evaporation rate of 10 kg/h, max gas drying rate of 150 kg/h; the main function of a spray drying tower is to dry the materials in solution state in it and then discharge in form of solid. There are 6 properties of a spray drying tower which show bellows:
1. The fast drying speed within seconds to finish;
2. Suitable for the heat-sensitive materials;
3. Widely apply in most of products with very huge difference;
4. The outlet product has excellent dispersion, fluidity and solubility;
5. Sample producing process and easy to operate and control;
6. The part which in contact with material is using stainless steel to protect raw material not to be polluted and extend the service life of the equipment.

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Ammonium Metatungstate to Prepare Surface Decarburized WC-Co Gradient Cemented Carbide

ammonium metatungstate crystal image

The surface decarburized WC-Co gradient cemented carbide based on impregnation liquid of ammonium metatungstate solution (AMT) can greatly enhance the comprehensive performance of cemented carbide; and with the simple process, easy to operate, it is suitable for industrial production. The preparation steps are as follows:
1. Put the conventional WC-Co carbide under vacuum conditions at 100~500°C for dewaxing, then to carry out presintering in 800~900°C to obtain presintering billet with a certain strength and porosity;
2. After them, the sample is dipped into ammonium metatungstate solution to form concentration gradient of AMT with a certain depth and distribution from the surface layer to the inner;
3. Then, after the sample is dried, put it in vacuum furnace for sintering along with slow heating in low temperature stage, to make the ammonium metatungstate decomposed, which the broken down products (tungsten oxide) will react with surface substance of WC, Co, then we can get surface decarburized WC-Co gradient cemented carbide.

Cemented carbide is a kind of metal ceramic tool material which prepared by powder metallurgy method by taking refractory metal compounds (such as WC, TiC, TaC, NbC, etc.) as the matrix, and transition of metals (like Co, Fe and Ni) as bonding phase. Due to its high strength, hardness and elastic modulus, wear resistance, corrosion resistance, low thermal expansion coefficient and stable chemical properties, etc, it in has important application in metal cutting, wood processing, oil drilling in mines, composite materials processing and other respects. Conventional class of WC-Co carbide is uniformly consisted with two phases of WC and binding phase, however it exists contrary relationship between the hardness, wear resistance and strong toughness. The WC - Co gradient cemented carbide structure with high wear-resistance and hardness surface, toughness core part was developed in the 1980s, while the appearance of surface decarburized WC-Co gradient cemented carbide makes it easier to control surface eta phase formation depth, and thereby to prepare the superior performance of WC-Co carbide.

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Silicon Dioxide Supported Ammonium Metatungstate Catalyst

It is found that the supported ammonium metatungstate (AMT) catalysts with the carriers of silicon dioxide, titanium dioxide and aluminium oxide have exhibited good catalytic activity for the synthesis of ortho - light anisole by gas - phase reaction of catechol and methanol. Among them, the AMT / silica catalyst with tungsten loading of 7.9% has the best catalytic performance; in addition, the species with weak acidity and alkalinity which formed by the partial decomposition of ammonium metatungstate in the calcination process has been indicated to be the active center of the catalytic reaction.

SiO2-AMT catalyst SEM image

Preparation of silicon dioxide supported ammonium metatungstate catalyst is using the traditional impregnation method, which is dipping carrier of silicon dioxide with ammonium metatungstate (AMT) aqueous solution in equal volume, followed by drying at 363 K for 6 hours, and then calcining at a certain temperature for 3 hours under air atmosphere to obtain SiO2/AMT catalyst. The study found that the calcination temperature affects the catalytic activity of silicon dioxide supported ammonium metatungstate catalyst; while the catalysts obtained at calcination temperatures of 533K and 573K showed the highest catechol conversion rate and selectivity of adjacent hydroxyl benzene methyl ether within 10 hours, which is respectively maintaining at about 97% and 90%.

Moreover, with the extension of reaction time, the activity of silicon dioxide supported ammonium metatungstate catalyst is decreased slowly, which is mainly attributed to the carbon deposition on the catalyst. The study of regeneration of deactivated SiO2 / AMT catalyst has proved that both the alcohol washed purging and low temperature (533k) calcination could not obviously restore the activity of the catalyst, and also the regenerated catalyst has stability no better than the fresh catalyst. This may be due to the change of the properties (including the acidity and alkalinity) of active centers on catalyst surface after high temperature regeneration treatment, and to make the easier deactivation of regenerated catalyst.

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Testing Trace Bismuth in High Purity Ammonium Metatungstate -- Co-Precipitation-HG-AFS Method

Ammonium metatungstate (AMT) is an important intermediate compound of tungsten wet smelting process, with appearance of white and little yellow crystal. In recent years, as the requirement of tungsten product purity being higher and higher, for controlling and accurate detecting of impurity content in tungsten products, the required analysis of impurity element types gas been more and more. A study has put forward a method of co-precipitation-HG-AFS to testing trace bismuth in high purity ammonium metatungstate; HG-AFS refers to hydride generation atomic fluorescence spectrophotometry, which has shown to have advantages of high sensitivity, good selectivity and small matrix interference.

atomic fluorescence spectrometer image

Steps of co-precipitation-HG-AFS method to detect trace bismuth in high purity ammonium metatungstate are as follows:
1. Weigh 0.125g (Accurate to 0001g) of high purity (99.995%) ammonium metatungstate sample  in 50mL beaker, add a small amount of water, suitable amount of coprecipitation agent and KOH (The standard addition test requires adding standard solution in advance);
2. Carry out filtration after heated for 15min at low temperature, and wash the precipitation and the beaker twice by using KOH solution, again to wash twice with water;
3. Then goes on operation of coprecipitation twice, transfer to 25mL volumetric flask and add 5.0mL HCI, 2mL tartaric acid solution after the precipitation dissolved with hydrochloric acid solution (HCl), then diluted with water to scale, shake well to get mixture solution under test;
4. Test the ready solution by atomic fluorescence spectrometer;
5. Prepare series of different concentrations of bismuth standard solution, test the fluorescence intensity according to running program, and process data with computer, draw standard curve using monadic linear regression equation to calculate the content of bismuth.

The aim of choosing hydrochloric acid (HCl) as Current-carrying medium is to obtain bismuth fluorescence with high strength and stability, while, when the solution acidity is changing among 1~6mol/L, bismuth fluorescence value changed little, however the increasing acidity will help to eliminate the interference.

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Ammonium Metatungstate Hydrotalcite Catalyst

In recent years, solid acid alkali catalysis of gas-solid-phase reaction of alkylation of catechols has attracted attention due to the environmentally friendly economy and overcoming the environmental pollution, separation and recovery difficulties and equipment corrosion and other defects, compared to conventional synthesis methods, and has shown significant advantages in saving resources and improving economic efficiency. It is found that Al-Ti-P-O, Al-Ti-Si-P-O and silica-supported ammonium metatungstate (AMT/SiO2) catalyst exhibited high catalytic activity.

AMT hydrotalcite sample XRD spectra image

Hydrotalcite is a kind of anionic clay with layered structure, because of its special layered structure and high catalytic performance in acid-base catalysis, condensation, addition polymerization, hydrogenation and alcohol conversion reaction, hydrotalcite has attracted many concerns. The exchangeable property of hydrotalcite anions make all kinds of anions (such as metatungstate ion) can be introduced into the interlayer of hydrotalcite in succession, thus to form a large class of materials - pillared hydrotalcite layered material.

A study has pointed out a preparation method of ammonium metatungstate hydrotalcite catalyst, and studied its catalytic performance, while the preparation steps are as follows:
1. synthesis of hydrotalcite material, take the raw material of magnesium nitrate hexahydrate, aluminum nitrate and sodium hydroxide, and to control the final pH value among 8 ~ 10 of the system, then go on aging, filtration and washing to get hydrotalcite NO3-MgAl;
2. Weigh a certain amount of fresh prepared hydrotalcite NO3-MgAl to disperse in distilled water, stirring at room temperature for overnight to fully expand;
3. Add dilute nitric acid dropwise to adjust the pH value of hydrotalcite slurry among 5.5~6, then rise the temperature to 348K;
4. Rapidly add ammonium metatungstate solution under the condition of stirring, and to react at 348K for 2 to 3 hours, then pumping wash the sample and dry at 348K to get the ammonium metatungstate hydrotalcite catalyst, i.e. AMT-Mg2Al.
The results showed that after changed with AMT, hydrotalcite will exhibit activity to the reaction of gas-solid phase reaction of catechol and methanol, while the conversion of catechol is 75%, the selectivity of guaiacol is 90%, but the catalytic activity decays.

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Differences among Ammonium Tungstate, Ammonium Paratungstate and Ammonium Metatungstate

The most distinctive difference between ammonium tungstate, ammonium paratungstate and ammonium metatungstate is their solubility in water.

bag of ammonium metatungstate sample photo

Ammonium tungstate is also called ammonium wolframate, its molecular formula is (NH4)6W7O24•6H2O. It is colorless trapezius crystal which is soluble in water and insoluble in alcohol. Under 100℃ it loses four molecular crystal water. Ammonium tungstate can be used as the raw material for ammonium phosphotungstate and other tungstate compound. It can also be applied in producing metallic tungsten and catalyst.

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.

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Difference Between Ammonium Paratungstate and Ammonium Metatungstate

The most apparent difference between ammonium paratungstate and ammonium metatungstate is APT insoluble in water, but AMT soluble in water.

ammonium metatungstate image

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also tungsten powder including tungsten trioxide, tungsten blue oxide. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).

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Producing Ammonium Metatungstate from Ammonium Tungstate in Silica advantages

ammonium metatungstate product picture

A particular advantage of the ammonium metatungstate (AMT) prepared from ammonium tungstate in silica is that the silica used in digestion and subsequently filtered from the digested solution of ammonium metatungstate (AMT) may be reused repeatedly, that is, its capacity to promote formation of AMT is not diminished with use. While the exact mechanism is not well understood at this time, the role of silica is to prevent the precipitation of insoluble APT and therefore to allow lowering of the pH to the ammonium metatungstate forming region, about 4 to 4.5.
After digestion is completed, the silica is removed, such as by filtering, and the solid AMT may be recovered in the conventional manner, such as by evaporation or spray drying.

The silica used in the invention may be any commercially available silica, provided that its impurities, both in kind and amount, are consistent with the final envisioned application for the ammonium metatungstate. For example, both sodium and phosphorus may be considered objectionable impurities for certain catalyst applications. Residual silica which cannot be removed from the digested AMT solution by filtering is generally below 1 percent by weight, and typically from 0.3 to 0.6 weight percent WO3 basis, and is compatible with many catalyst applications.

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Producing Ammonium Metatungstate from Ammonium Tungstate by Digestion in Silica

At present both ammonium paratungstate (APT) and ammonium metatungstate (AMT) are being used as tungsten sources in the catalyst industry. Since APT has a limited solubility in water (about 2 to 3 percent at room temperature), thus the user should converts APT to a more soluble peroxytungstate form by means of reaction with hydrogen peroxide in order to prepare the catalyst. While AMT is highly water soluble, and thus no need be converted, it is in general more expensive than APT, due to the complexity and/or low yields of processes for producing it.

A process for producing ammonium metatungstate (AMT) from ammonium tungstate (AT) solution is described which involves the addition of about 3.6 percent by weight of silica to an AT solution, digestion for at least about 4 hours at a temperature of at least about 98°C, followed by filtration to remove the silica from the AMT solution. Typically about 0.4 percent by weight of silica remains after filtering. The resulting AMT solution may be further processed to recover solid AMT, such as by evaporation or spray drying.

ammonium metatungstate photo

silica image

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Ammonium Metatungstate SEM Micrograph

AMT-image

Ammonium metatungstate is also named AMT, which is a kind of white crystal powder. AMT is the raw material for making tungsten product, and also widely used in alloyed steel, fireproof industries. Further more, it is a good tungsten based flux in oil chemical and ceramic industries. The manufacturing standard of AMT in China is GB/T 23368, which is also used for measuring the content of ammonium metatungstate. Based on different manufacturing degree, the products manufactured out by factories have performed different chemical contents. Standard used manufacturing ammonium metatungstate, AMT is GB/T 23368. The content of WO₃ is 90.00% in most Chinese manufacturers, but 91.4~91.5% for Chinatungsten Online. For the different crystallized conditions, AMT can be analyzed as (NH₄)6H₂W₁₂OnH₂O, (NH₄)₆H₂W₁₂O₄₀.XH₂O and (NH₄)₆H₂W₁₂O₄₀.

SEM micrograph is short for Scanning Electron Microscope, a kind of scanning equipment using for micrograph by multiplying objects, which can be metal, powder, vegetables etc. Ammonium metatungstate is one of can-be scanned products. After scanning, the powder of AMT is showing ball shape with inner empty. All the balls are gathered together when the multiply value is low, but with gap when the value large enough, which means that the molecule of AMT are separate actually.

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Ammonium Metatungstate Producing Method

ammonium metatungstate photo

Ammonium metatungstate producing method includes neutralization method, tungstic acid method, thermal decomposition method, solvent extraction method and ion exchange method.

Neutralization method uses secondary ammonium metatungstate and nitrate as the raw material to produce metatungstate.

Tungstic acid method using ammonia tungstate tungstic acid dissolved, add a boil deionized water in the stirring, heating by ammonia, Ph=8, in the boiling solution by adding acetic acid.

Thermal decomposition method combines ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h.

Solvent extraction using ammonium tungstate solution and organic extractant phosphoric acid: two (2- ethylhexyl) ester (D2EHPA) or phosphoric acid butyl ester three (TBP) and kerosene solvent to form organic phase, extract ammonium ion from ammonium tungstate solution.

Ion exchange method uses ammonium paratungstate as raw material, heating ammonium paratungstate from 1 to 8 h at 130 ~ 140 ℃, the resultant tune into a paste, to 80 ~ 100 ℃ boiling for 2 ~ 6 h, generates ammonium metatungstate solution. And then obtain the product through concentrating crystallization, filtration and drying.

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Ammonium Metatungstate Preparing Tungsten Trioxide

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, it is white or slightly yellow crystals which has no harmful components and slightly acidic. Due to its solubility in water, it can be used as raw material to produce tungsten trioxide.

ammonium metatungstate picture

Use ammonium paratungstate as raw material and heat to 220-280℃. After that it will lose ammonium and crystal water and transform into ammonium metatungstate. Continuously heat ammonium metatungstate to 600℃ until it loses all ammonium and crystal water, cool it down and crystallize, after spray drying it turns into yellow tungsten trioxide.

Ammonium metatungstate preparing tungsten trioxide is easy to operate, the finished product is of good uniformity. Tungsten trioxide can be used to made tungsten product and shielding materials which is widely used in industry.

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Ammonium Paratungstate Preparing Ammonium Metatungstate

ammonium metatungstate powder picture

Ammonium metatungstate is an important tungsten-containing compound, mainly used as catalyst in petroleum cracking, organic synthesis, nitration, and so on. With the rapid development of petroleum refining, petrochemical engineering and other industries, the ammonium metatungstate usage is increasing very fast. In the prior art, ammonium paratungstate is used as a raw material, and a crystallization process is utilized for the preparation of ammonium metatungstate; this process is expensive, costly and energy-consuming, and the obtained product is unstable in quality, particularly the solubility is poor.

A process for preparing ammonium metatungstate using ammonium paratungstate as raw material comprising: (A) leaching wet ammonium paratungstate with nitric acid to obtain a dilute solution of ammonium metatungstate; (B) concentrating the dilute solution of ammonium metatungstate to be a concentrated solution of ammonium metatungstate; and (C) spray-drying the concentrated solution of ammonium metatungstate to obtain powder of ammonium metatungstate.

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Ammonium Metatungstate Molecular Weight

Ammonium metatungstate molecular weight generally refers to relative molecular mass of ammonium metatungstate (AMT), molecular weight differences between each other depending on its moisture content; while according the formula of (NH₄)₆H₂W₁₂O₄₀.XH₂O, the anhydrous basis of molecular weight should be 2956.08.
Wherein the relative molecular mass of each element is：N=14, H=1, W=183.84, O=16;
then Mr(AMT)=14*6+1*26+183.84*12+16*40=2956.08.

AMT molecular structure picture

Sum of relative atomic mass (Ar) of each element in the formula is the relative molecular mass, which represented by symbol of Mr. Relative molecular mass equal to the molar mass in value, but in different units. The unit of relative molecular mass is "1", while the unit of molar mass is g/mol. H₂O is the oxide with the minimum relative molecular mass, however, as for the polymer, its relative molecular mass can up to tens or even hundreds of thousands.
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What Is Ammonium Metatungstate

What is ammonium metatungstate? Ammonium metatungstate is a white crystalline powder, soluble in water, insoluble in aocohol.
Chinese Name: 偏钨酸铵

ammonium metatungstate picture

Abbreviation: AMT
Molecular Formula：H₈N₂O₄W；
Chemical Formula：(NH₄)₆H₂W₁₂O_{40.XH2O；
Molecular Weight：283.9145；
CB No.：CB41411564；
EC No.：234-364-9；
CAS No.: 14311-52-5；
HS Code：28418040；
Solubility(Water)：300g/100ml；
W valance in AMT： +6
W content in AMT：72%
Ammonium metatungstate has no harmful components, it has subacidity, often used in the preparation of tungsten products, catalyst in petroluem industry, nuclear shielding material, also ceramic industry, steel alloy, fire resistant fiber and inhibiter. In recent years, it is also used in emerging industry like semiconductor and thin film.
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Ammonium Metatungstate Preparing WO3 Plate SCR Denitration Catalyst--Dry Powder Mixing Method

The main component of tungsten trioxide plate denitration catalyst is just similar to honeycomb denitration catalyst, both are based on vanadium pentoxide, tungsten trioxide as the main active substance, titanium dioxide as the carrier. Compared with cellular, it has a stronger capacity of ash anti-clogging, wear resistance, less consumption under dust and low pressure loss ect.; although its market share is only about 1/3 of the cellular, it will gradually expand with the further launch of high-dust flue gas denitration in China.

plate denitration catalyst

The process that dry powder mixing method prepares tungsten trioxide plate denitration catalyst is as follows:
1. Put the titanium dioxide powder, stearate acid, AK sugars, methyl cellulose into the kneader, stir for about 10 minutes;
2. Add pulp slurry and stir for about 10 minutes;
3. Add silica sol solution and continually stir for 10 minutes;
4. Add the lactic acid, ammonia, ammonium metavanadate and suitable amount of deionized water into the mixed solution prepared above, then stir for about 1 hour for sufficiently reacting;
5. Add glass fiber and tungsten compound containing with tungsten trioxide (ammonium paratungstate, ammonium metatungstate ect.), stirring for about 30 minutes to prepare a catalyst mud;
6. Forming to generate the wet catalyst;
7. Dry the catalyst at 100 °C to remove excess free water;
8. Roasting, the purpose of it is: at the same time titanium dioxide crystal transition does not occurred, decompose the organic matter and active ingredient precursors; studies have shown that the active ingredient precursors and organic substances are decomposed completely at 400°C, the polymerization of vanadium pentoxide has been improved as the temperature increasing, but the titanium dioxide crystalline transition may occur, thus will cause the properties of catalyst reduced; therefore, calcination at the proper temperature, we can finally get the best active tungsten trioxide plate denitration catalyst.

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Titanium Blast Furnace Slag Prepares Ammonium Metatungstate and Tungsten Trioxide Denitration Catalyst

Flue gas denitration refers to the reduction of NOx to N2, thereby removing NOx from the flue gas; it can be divided into wet and dry denitration method according to the press preparation process. Because of the high titanium content (about 20%), titanium blast furnace slag is often used in the preparation of titanium dioxide, and then as a carrier for preparing tungsten trioxide denitration catalyst.

blast furnace slag

The first one preparing method:
1. Crushing the Titanium blast furnace slag, adding the sulfuric acid for leaching out titanium dioxide, then get the solution filtered to obtain the residue and titanium-containing solution;
2. Add the burnability type porous catalyst carrier into the titanium-containing solution obtained in step 1 with stirring; besides, a basic compound is optionally added to adjust the pH value to carry out a hydrolysis;
3. Filtering, washing and drying the material after hydrolysis which is obtained in step 2 to generate the support partial titanate carrier;
4. Load precursor of tungsten source (ammonium paratungstate, ammonium metatungstate) and vanadium source (ammonium metavanadate) to the partial titanate;
5. Roasted to get the vanadium pentoxide-tungsten trioxide-titanium dioxide of SCR flue gas denitration catalyst.

The second preparing method:
1. The titanium blast furnace slag is crushed and then added sulfuric acid for the titanium dioxide leaching, finally filtered to get the residue and titanium-containing solution;
2. Add the burnability type porous catalyst carrier into titanium-containing solution under the condition of stirring, also a basic compound is added selectively to adjust the pH value for the solution hydrolysis, tungsten source precursor (ammonium paratungstate, ammonium paratungstate, etc.) is added during the hydrolysis process;
3. The materials after hydrolysis is filtered, washed and dried to get the get the partial titanate containing tungsten trioxide;
4. The product obtained in step 3 is calcined to generate the final product of vanadium pentoxide-tungsten trioxide-titanium dioxide SCR flue gas denitration catalyst; or calcine the partial titanate containing tungsten-supporting to prepare titanium-tungsten powder, then further loaded the precursor of vanadium source, firing again to prepare the vanadium-tungsten-titanium of SCR flue gas denitration catalyst.

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Ammonium Metatungstate Spray Dryer Wall Sticking Reasons and Solutions

Spray drying is a wide applied process in liquid process shaping and drying industry. It can be used to transform solution, emulsion, suspension and paste liquid into powder and granular solids. When the finished particle size distribution, residual moisture content, density and particle shape must meet with precise standards, spray drying becomes an ideal method. 

ammonium metatungstate

The types and reasons for wall sticking during spray drying were analyzed. There are three types of wall sticking: half wet materials, materials with low melting point, dry powder. The wall sticking of half wet materials is concerned to the structure, fixing and operation of spray drying tower and sprayer, the motion of hot air in tower. The melting sticking occurred when the melting point of materials is lower than the drying temperature. The wall sticking of dry powder is concerned to geometric figure of cyclone chamber, roughness of wall, velocity of air and static charge.

Ammonium metatungstate spray dryer wall sticking solutions include improve the structure and texture of drying tower, use the proper atomizer, proper installation of atomizer, proper operation process, etc.

1. Improve the structure and texture of drying tower. If the design of diameter of dry tower is smaller than the atomizer cone, it will cause a mass amount of wall sticking. In order to prevent wall sticking, the diameter of dry tower should be larger, thus the liquid material will fall down directly without making contact with wall of tower. But the diameter can not be too large because it will increase cost of equipment and occupied area, it also affects flow speed of hot air in the tower and drying quality.
2. Use the proper atomizer. Atomizer is also called nozzle, it is the key part of spray dryer. Its different structure affect the distribution of misty liquid, also diameter and property of micro grains.
3. Installation of atomizer. If there is only one atomizer in the dry tower, the axis of atomizer should be on the center line of tower. If there is more than one atomizer, then the nozzle of atomizers should not be face to face.
4. Proper operation process. For the pheumatic spray drying tower, the process parameter often refers to drying temperature, feeding velocity and pressure of nozzle. Drying temperature includes inlet air temperature and outlet air temperature. Increase inlet air temperature can promote liquid evaporation, which will solidify the liquid before it contacts the wall which will reduce the wall sticking waste rate and increase yield of product. Besides that, temperature also affects the diameter of grains. When the temperature is low, the grain size is bigger which will prolong the drying process. When the inlet air temperature stay the same, raise the outlet air temperature can reduce the temperature differences to fasten drying efficiency.
5. The movement of hot air in the dry tower. The movement of hot air in the dry tower affects wall sticking directly. When the total amount of inlet air stay the same, the proportion of the air for protection atmosphere and air for drying will affects the drying result. If the air is insufficient for drying, then the liquid will stick on the wall before getting dried.
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Ammonium Metatungstate Prepared by Electrodialysis Method

Ammonium metatungstate (AMT) is a tungsten compounds with high molecular weight and water-soluble, which is easily dissolved in water, the solubility of it can reach 100g/mL at room temperature. It can be prepared from the material of ammonium tungstate by the method of Bipolar Membrane Electrodialysis (BEMD).

AMT picture

Electrodialysis method uses the effect of electric field, makes water which is in the two sides of bipolar membrane dissociated into H + and [OH] - then directional moved to both sides of electrode, and entered into the liquid chamber (the salt chamber) and alkali chamber respectively. Electrodialysis method is widely used in the field of chemical, light, metallurgy, papermaking industry and so on.

The preparation process of AMT by the method of electrodialysis which is using ammonium tungstate or ammonium paratungstate as raw materials is performed as bellows:

1. Add ammonium paratungstate into anode chamber, when an electric current passes by, water dissociated into two forms--H+ and [OH]– and directional moved to both sides of electrode under the action of strong electric field, and then respectively enter the liquid chamber (the salt chamber) and alkali chamber;

2. H+ ions enter the salt chamber to combine with WO4- and then will not go into alkali chamber ever again; ammonium ions move to cathode chamber through the exchange membrane, thus cause the concentration of ammonium metatungstate increased;

3. OH- moves into alkali chamber through the anion exchange membrane to combine with ammonium ions which is continually moved in and no longer went into the anode chamber;

4. With the process of electrolysis carrying out, ammonium ions decreased and hydrogen ions increased continually in the salt chamber, thus cause the pH value of the solution in salt chamber decreased continuously;

5. Finally, ammonium metatungstate solution is released from the cathode chamber, and AMT generated.

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Ammonium Metatungstate for WO3-Based Oxidative Desulfurization Catalyst

Oxidative desulfurization process consists of two steps: Firstly, oxidize the organic sulfur compounds in the oil into polar sulfone substance; secondly, separate the sulfone substances to achieve the purpose of desulfurization by adsorption, extraction and distillation methods s. Wherein the transformation of sulfone substance is the key step.

Sulfone is a group organic compound which contains sulfonyl, and often combined S with two carbon atoms (e.g. two hydrocarbons or simple divalent), generally the stable crystalline compounds, can be generated by the oxidation of organic sulfides or other methods.

WO3 desulfurization catalyst photo

Supported WO3-based oxidative desulfurization catalyst is achieving deep desulfurization by the oxidation catalyzed reaction of organic peroxide and sulfur heterocyclic aromatic compounds under mild conditions. The preparation program is under a hydrogen atmosphere or an inert gas atmosphere, plasma treatment supported tungsten trioxide based catalyst.

Preparation process are as follows:
1. The equal volume dipping method to prepare supported WO3/SiO2 catalyst: Weigh 0.852g of ammonium metatungstate and dissolved in 9ml of dubbed deionized water to form a solution and dripped drop by drop into the 3g silica with stirring;
2. Static in the room temperature for 12h, and then dried at 120°C for 4 hours;
3. Raise the temperature by the rate of 2V/min to 500 ° C, calcined for 5 hours to obtain the tungsten trioxide silica supported catalyst, wherein the loaded tungsten trioxide amount is 20% of the mass fraction of (of the total catalyst mass meter);
4. Under Ar atmosphere, treating the WO3/SiO2 catalyst with plasma;
Put 2mL of catalyst in the dielectric barrier discharge plasma reactor; control the Ar gas flow rate at 100mL/min under normal pressure; discharge frequency of plasma is about 10kHz; the input voltage of 50 volts; the input power of about 15 watts for 30min, and then get the supported WO3-based oxidative desulfurization catalyst.
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Ammonium Metatungstate for Tungsten Trioxide Based Ultra-Strong Acid Desulfurization Catalyst

The sulfide in the In the fuel will unavoidable release into the air in the form of gas when in the combustion process, which will probably causes a series of issues that destroying ecosystems like acid rain, damaging buildings. As the improving of people's awareness of environmental protection and vehicle fuel emission standards, increasingly strict restrictions on the sulfur content of fuel oil index has been worked out, therefore, the production and using of ultra-low sulfur fuel oil is imperative. In deep desulfurization, the application of traditional method of hydrodesulfurization (HDS) has been limited, because of its disadvantages such as harsh reaction conditions, equipment investment and higher operating costs.

desulfurization catalyst picture

Oxidative desulfurization is using an oxidizing agent to oxidize the sulfur compounds like thiophene in the fuel which are difficult to remove to sulfoxide or sulfone sulfur-containing materials with stronger polar in normal temperature, pressure and the presence of catalyst conditions, and then removing the sulfoxide or sulfone sulfur-containing materials by the methods like extraction, thus to achieve the goal of deep desulfurization. Oxidative desulfurization is considered to be a very attractive desulfurization technology, which usually consists of two steps: first, the fuel sulfide oxidation; second, removing the oxidized sulfur compounds from fuel oil by extraction, adsorption and distillation methods.

 The key of desulfurization method is developing an oxidative desulfurization catalyst with good properties of high desulfurization rate, oil yield, and low cost. Research indicates that a kind of zirconium hydroxide as a carrier, then immerse in the aqueous solution constitute of ammonium metatungstate after finely crushed; the immersion liquid placed in an ultrasonic generator ultrasonic to promote the dipping, evaporating the water, dried, and roasting at the high temperature to generate the WO3/ZrO2 solid ultra-strong acid desulfurization catalyst. This catalyst exhibits good activity and selectivity, and high desulfurization rate when used for the deep desulfurization of diesel fuel.
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Ammonium Metatungstate for Tungsten Trioxide Based Ultra-Strong Acid Desulfurization Catalyst

The sulfide in the In the fuel will unavoidable release into the air in the form of gas when in the combustion process, which will probably causes a series of issues that destroying ecosystems like acid rain, damaging buildings. As the improving of people's awareness of environmental protection and vehicle fuel emission standards, increasingly strict restrictions on the sulfur content of fuel oil index has been worked out, therefore, the production and using of ultra-low sulfur fuel oil is imperative. In deep desulfurization, the application of traditional method of hydrodesulfurization (HDS) has been limited, because of its disadvantages such as harsh reaction conditions, equipment investment and higher operating costs.

desulfurization catalyst picture

Oxidative desulfurization is using an oxidizing agent to oxidize the sulfur compounds like thiophene in the fuel which are difficult to remove to sulfoxide or sulfone sulfur-containing materials with stronger polar in normal temperature, pressure and the presence of catalyst conditions, and then removing the sulfoxide or sulfone sulfur-containing materials by the methods like extraction, thus to achieve the goal of deep desulfurization. Oxidative desulfurization is considered to be a very attractive desulfurization technology, which usually consists of two steps: first, the fuel sulfide oxidation; second, removing the oxidized sulfur compounds from fuel oil by extraction, adsorption and distillation methods.

 The key of desulfurization method is developing an oxidative desulfurization catalyst with good properties of high desulfurization rate, oil yield, and low cost. Research indicates that a kind of zirconium hydroxide as a carrier, then immerse in the aqueous solution constitute of ammonium metatungstate after finely crushed; the immersion liquid placed in an ultrasonic generator ultrasonic to promote the dipping, evaporating the water, dried, and roasting at the high temperature to generate the WO3/ZrO2 solid ultra-strong acid desulfurization catalyst. This catalyst exhibits good activity and selectivity, and high desulfurization rate when used for the deep desulfurization of diesel fuel.
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Ammonium Maratungstate Prepared from Ammonium Tungstate by Ion Exchange

At the present time, crystalline ammonium metatungstate (AMT) is being produced from APT. Although this process overcomes some of the disadvantages of the-prior art, in practice it is somewhat difficult to control for maximum conversion. As a consequence, on crystallization of AMT from solution, the residual APT must be removed in order to produce completely water-soluble AMT products. Another disadvantage of this process is its intermittent batch nature, requiring baking, digesting, filtering and concentrating of solutions before crystallization. On a production scale, such stepwise operations tend to be time consuming and costly.

ammonium metatungstate AMT image

As an improvement over the above process, a method of ion exchange for producing ammonium maratungstate directly from ammonium tungstate (AT) solution is came up with. AT solution is contacted with a liquid extraction system consisting of Di-Z-ethyhexyl phosphoric acid (D-2-EHPA)-tri-n-butyl phosphate (TBP)- kerosene, which extracts ammonium ion and rapidly lowers the pH to the AMT-forming region. The solution is then digested to allow formation of AMT.

While this method substantially avoids the formation of APT and is amenable to continuous processing, it has not found widespread use due to a tendency toward instability of the organic system, and resultant formation of insoluble phospho-tungstates in amounts up to percent or more of the total solid product, depending upon the conditions of formation.

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Ammonium Metatungstate Preparation-Thermal Decomposition Method

Ammonium Metatungstate Picture

The thermal decomposition method of ammonium paratungstate to prepare ammonium metatungstate: ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h. The removal of ammonia and water, ammonium paratungstate weightlessness rate was 5% ~ 6%.

The thermal decomposition products immediately after the slurry, adding proper amount of ammonia, Ph value is adjusted in the 3 to 4 range, at 90 ℃ digestion slurry. After evaporation to ammonium metatungstate content of 50% can be used as a liquid product to sell, crystallization, when the evaporation to the original volume of 20% filtering and separating, granulating product. Also can be evaporated and concentrated liquid product is prepared by spray drying. As of 45% ~ 50% ammonium metatungstate by high-speed centrifugal rotary spray dryer, imports of hot air temperature 250～300 ℃, outlet temperature 90 ～ 95 ℃, the obtained product is a spherical crystal, particle size is 200 mesh accounted for 95%, free water <1.5%.

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Ammonium Metatungstate New Producing Method

Ammonium metatungstate  new producing method is Using a coupling process of neutralization–nanofiltration–crystallization, pure ammonium metatungstate (AMT) was prepared. The effects of chemical neutralization of ammonium paratungstate (APT) by nitric acid, operating pressure, AMT concentration, the volume of washing water on the coupling process were systematically discussed. It was found that the better conditions of AMT preparation were as follows: the neutralization temperature was 80–95 °C, pH value was 2.0–3.5; the operating pressure of HDS-12-2, nanofiltration was 1.5–2.0 MPa, the density of AMT crystallization solution was 2.39 kg/L, and then cooling. APT conversion efficiency (δ) to AMT was more than 97.62%. The removal ratio of nitrate ion (NO3−) was more than 99% while AMT rejection (RAMT) was 99.9%. Besides, small-grained, even-proportioned, white-colored and high-purified AMT crystal was be obtained and analyzed. This method has several advantages such as simple technological process, short production cycle, lower environmental pollution and high quality.

ammonium metatungstate AMT picture

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Ammonium Metatungstate Properties

Ammonium metatungstate is also called AMT, it is inorganic chemical product. Its molecular formula is H₈N₂O₄W  and molecular weight is 283.9145. CAS number is 11120-25-5;14311-52-5. Ammonium metatungstate properties include white or slightly yellow crystals which has no harmful components and slightly acidic. The solubility in water is 303.99/loogH:O when 20℃, aqueous fairly stable. It is insoluble in alcohol.

Its molecular structure is listed as below:

ammonium metatungstate molecular structure

Ammonium metatungstate can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).

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Ammonium Metatungstate Preparation-Neutralization Method

Ammonium metatungstate, also known as AMT, is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃, aqueous fairly stable. It is white or slightly yellow crystals which has no harmful components and slightly acidic.

Neutralization method with secondary ammonium metatungstate and Nitrate as the raw material purchase ammonium metatungstate: secondary ammonium metatungstate deionized water and ammonium citrate with WO₃ 12%~ 30% concentration of slurry. According to =1:20: nitrate ammonium paratungstate by adding 3% ~ 5% of dilute nitric acid to ammonium paratungstate slurry, control ratio of solid to liquid 1: (3 ~ 4), the Ph value of 2 ~ 4, heating and dissolving solution, the relative density of 1.18 ~ 1.20, heating to 80 ~ 90 ℃, constant temperature and constant volume control Ph value, the stirring reaction for 4H hours, aging, concentrating the supernatant to WO₃ content is about 50-, filtration to remove insoluble, liquid concentration, cooling crystallization, continue to 80 ℃ drying.

ammonium metatungstate crystal

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Ammonium Metatungstate Modified Borated Zirconium

Samples of tungsten-modified borated zirconium were prepared to be used as catalyst in 2-phenoxyethanol acetylation. The borated zirconias were obtained by impregnation of two zirconias (S2 and S4) obtained by the micellar method using different zirconium precursor concentrations with boric acid solution containing 0.3 moles B/dm³. These solids and the parent zirconias were impregnated with two concentration levels of ammonium metatungstate solutions (0.11 and 0.22 moles W/dm³). The solids containing boron mainly have amorphous characteristics and strong acidity, while those that contain only tungsten showed stronger acidity and evidence of the presence of a crystalline phase.

The specific surface area and the pore volume slightly decreased in the solids obtained by adding tungsten to borated zirconia, and more markedly in those that contain only tungsten, and the mean pore size increased with respect to the parent support. It was observed that in the 2-phenoxyethanol acetylation using acetic acid as acylating agent and tungsten-modified borated zirconia as catalyst, the yield to acetylated product was high and it is correlated with the acid strength of the catalysts. In turn, the solids that contain only tungsten have a correlation with the acidity, but lead to low yield values due to a poorer dispersion of the tungsten species. The best yield was obtained with the catalyst prepared with the borated S4 zirconia containing 15% g B₂O₃/100 g support and 12.5% g W/100 g support. Using this catalyst and the same reaction conditions, the acetylation of different alcohols and phenols was studied, the reactivity order being as follows: primary alcohols > secondary alcohols > phenols.

Ammonium Metatungstate AMT

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