Ammonium Paratungstate Preparing Metatungstate Solution

Metatungstate is one of many types of tungstate, the only compound which the structures have been identified as colorless crystals. It has high solubility in water, and can be derived from metatungstate. Since the metatungstate itself is extremely unstable and easily degradable, therefore, it has a large difficulty in preparation. In the traditional way, sodium tungstate often used to prepare metatungstate crystals, but the complex process, high production costs, low productivity, poor product quality and the environmental pollution and other defects make the way no to be better. Nowadays, harmonious environment, cost savings, simplified procedures are promoted, so its necessary to develop a process which has the simplified process, low cost and environmental pollution, and also conducive to industrial producing metatungstate.

Studies have pointed out that ammonium paratungstate (APT) can be used to prepare metatungstate solution. The steps as following:
1. APT powder heated to 270℃~350℃ for 30-60 minutes to dissociate, thus to generate ammonium metatungstate;
2. Add ammonium metatungstate powder into deionized water to leaching with stirring to get an emulsion;
3. Carry out filtration to remove insoluble, and the filtrate was placed in a water bath of 60~90℃ aging for 4~24 hours;
4. Filtered again, and exchanged by Cation Resin, then we get metatungstate solution.

As we can see from the above, the method APT used as raw material to prepare metatungstate solution has the advantages like: simplify process, easy to control, and low cost; In addition, since the reaction process doesn’t introduce any impurity element, so the purity and quality of metatungstate can be ensured; finally, the production process does not use ether and other volatile organic compounds, with minimal impact on the environment, so it is suitable for industrial mass production.

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Ammonium Paratungstate Preparing Ammonium Metatungstate--Electrodialysis Method

ammonium metatungstate

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).

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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An Invention for APT/AMT Production-Examples

Ammonium tungstate, ammonium paratungstate, ammonium metatungstate or hydrated tungsten trioxide is produced by passing tungstate anions through an anion exchange membrane into an aqueous solution containing ammonium cations under the driving force of an electrical potential for a time sufficient to achieve a pH within the range in which the desired tungsten compound will form.

EXAMPLE I

An electrolytic cell is divided into positive and negative sides by placing an anion exchange membrane (111BZ6066 from Ionics Inc., Watertown, Massachusetts) between 2 platinum electrodes each having a surface area of about 6 square inches and suspended by means of a platinum wire in the cell. 450 Milliliters of a sodium tungstate solution containing 213 grams of WO3 per liter is placed on the negative side of the membrane. A solution of 400 milliliters of water with 10 milliliters of reagent grade (28% by weight) ammonium hydroxide is placed on the positive side of the membrane. A potential of about 12 volts is applied to the cell resulting in a current flow of about 1 ampere. After about 1 1/2 hours the current has increased to about two amperes, the pH has decreased from about 10 to about 9, and ammonium tungstate is formed. After about 6 hours the current has increased to about 3 amperes, the pH has decreased to about 8 and ammonium paratungstate crystals are formed. After about 12 hours, most of the ammonium paratungstate has dissolved, the pH has decreased to about 2.8, and ammonium metatungstate is formed. At this point the solution is removed from the positive side, evaporated down to form crystals, and the crystals identified by x-ray analysis as ammonium metatungstate.

 ammonium metatungstate

 

EXAMPLE II

The procedure of Example I is followed, except that 400 mls. of tungstate solution containing 317 grams of WO3 per liter is placed on the negative side of the membrane, a solution of 10 milliliters of 28% ammonium hydroxide in 400 milliliters of water is placed on the positive side, and a potential of about 10 volts is applied to the cell resulting in a current initially of about 0.5 amperes. After about 81/2 hours the current has increased to about 2.5 amperes, and ammonium paratungstate crystals have formed. After about 29 hours, the pH has decreased to about 1.5 and tungstic acid has formed. The solution is evaporated to dryness and analyzed. Results show that the product contains hydrated tungsten trioxide, and the following impurities in the total amount of less than 0.1 weight percent: aluminum, calcium, copper, iron, magnesium, molybdenum, silicon, tin, and sodium. With the exception of molybdenum, all listed impurities are present in amounts less than about 100 parts per million.

 

EXAMPLE III

The procedure of Example I is followed, except that a 400 ml solution of sodium tungstate containing about 79 grams WO3 /liter is placed on the negative side of the membrane, and 10 milliliters of 28% ammonium hydroxide in 400 milliliters of water is placed on the positive side. After about 24 hours the current had increased from 1.5 to 4.5 amperes and ammonium paratungstate crystals have formed.

 

EXAMPLE IV

The procedure of Example I is followed except that in order to increase the current flow through the cell a solution of 1:1 by volume of ammonium tungstate (280 grams WO3 per liter) and 28% ammonium hydroxide is placed on the positive side of the cell, and a solution of 280 grams per liter of WO3 (sodium tungstate) is placed on the negative side of the cell. After about 61/2 hours of cell operation, solution from the negative side is analyzed to show that 86.3% of the tungsten is removed. Essentially 100% of this tungsten is recovered in the form of ammonium paratungstate crystals from the positive side of the cell. These crystals as indicated by spectrographic analysis contain a total impurity content of less than 0.1 weight percent. Such impurities include the following: Al, Ca, Cu, Fe, Mn, Mo, Si. All the listed impurities each are less than 100 parts per million except molybdenum which was about 200 parts per million.

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Ammonium Metatungstate Preparing Tungsten Trioxide

Ammonium metatungstate (AMT) is an appearance of white or slightly yellow crystalline powder, its water-soluble is 300g / 100ml, it slightly soluble in water; when the temperature reaches at 20 ℃, its solubility is less than 2%. Ammonium metatungstate is used in making metal tungsten, steel, fireproof fabric and for the ceramic industry. Usually, we take ammonium tungstate solution as raw material to obtain ammonium metatungstate solution by solvent extraction or ion exchange method, and then evaporate it to prepare crystals of ammonium metatungstate. Ammonium metatungstate is also used in the manufacture of various petrochemical catalysts and other tungsten compounds, and it is the main raw material refinery tungsten-based catalyst. According to the features of ammonium metatungstate slightly soluble in water, we prepare tungsten trioxide in this case.

AMT

Ammonium metatungstate preparing tungsten trioxide is based on taking ammonium metatungstate as raw materials, heating ammonium metatungstate to 220-280 ℃; it can be converted to ammonium metatungstate when it loses some ammonia and crystal water, and then continue to heat ammonium metatungstate to more than 600 ℃, when ammonium metatungstate loses all crystal water and ammonia, cooling and crystallization, the finished product is dried thoroughly into yellow tungsten trioxide.

There many methods of preparation of ammonium metatungstate, such as acid method, thermal decomposition method, ion exchange, solvent extraction method. The method of ammonium metatungstate preparing tungsten trioxide is simple and easy, and it meets the needs of industrial production.

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Ammonium Metatungstate Prepare WO3 Contained De-Dioxin and Denitration Catalyst

Dioxin refers to the collectively chlorine-containing organic compounds which contain one or two oxygen-bond connecting with two benzene rings, the carcinogen with most toxic, very stable and difficult to break down, besides, the dioxin has reproductive, immunity and endocrine toxicity. The main active ingredients of de-dioxin catalyst are titanium dioxide, vanadium pentoxide, tungsten trioxide, cobalt oxide and other transition metal oxides, or a noble metal (platinum, gold, etc.). The researches on an efficient, economic catalyst with both functions of de-dioxin and denitration catalyst is very necessary.

honeycomb denitration catalyst

Waste hydrodesulfurization catalyst generated by the refinery contains a lot of metals, such as aluminum, tungsten, nickel, cobalt, vanadium, which is a relatively inexpensive resource. The recycling of it can not only recycle the useful resources, but also reduce the environmental pressure, and thus become a hot topic. Experiments have shown that the waste hydrodesulfurization catalyst can be used to prepare tungsten trioxide contained of de-dioxin and denitration catalyst, and prepared as follows:

1. Waste hydrodesulfurization catalyst is carried out a pretreatment by washing with deionized water and drying;

2. Mix the carrier-titanium dioxide and the active ingredient-tungsten trioxide. The ammonium metatungstate and titanate are mixed according to mass ratio of 1: 9 to give a suspension, then filtered and the wet powder is calcined, to obtain the titanium dioxide loading with tungsten trioxide;

3. Ball grinding to mix the waste hydrodesulfurization catalyst and the carrier to obtain a raw material mixed powder, adding oxalic acid (or citric acid) and water to mix uniformly at the same time;

4. Dry and calcine the semi-finished products o give the finished-products--tungsten trioxide catalyst with the function of both de-dioxin and denitration.

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Ammonium Metatungstate for Tungsten Trioxide Denitration Catalyst with Dioxin Removable

Dioxins are a class of substances with persistent pollution, with its highly toxic, the small amount of them can cause serious damage to health or fatal, so they has become the focus of public attention in recent years. Dioxins are very stable compounds, which appear in a colorless solid at room temperature; it will accumulate in fat after entering human body with its high lipophilicity; In addition, it is extremely difficult to remove once the pollution occurs, because the strong bond between it and the soil or other particulate material.

de-dioxin and denitration catalyst

The most effective way to remove dioxins is still the selective oxidation-reduction, experimental proposed a preparing method of tungsten trioxide denitration catalyst which with dioxin removable; also the anti-sulfur poisoning is improved, and possess the good catalytic activity at the same time. It is prepared as the follow steps:

1. Successively add the equal amount of titanium dioxide powder and carbon nanotubes into the dilute ammonia to form the carrier mixture with stirring well, then transferred to the ultrasonic cleaning machine for an ultrasonic treatment;

2. Dissolve ammonium metavanadate, ammonium sulfate, ammonium metatungstate in the dilute aqueous ammonia in turns to form of a mixed solution of the active ingredient, then thoroughly stirred under heating, transferred into a rotary evaporator furnace for drying to give a mixture of the active ingredient;

3. Successively add the active ingredient mixture, glass fiber, cellulose and polyacrylic acid  into the mixed carrier to form a catalyst mixture, heat with stirring to dry and stop until the catalyst mixture of a moisture content of about 30%;

4. Get the tungsten trioxide denitration catalyst products with dioxins removable by extruding, drying, calcining the catalyst mixture.

This kind of catalyst is constituted by the following components: 1.2% of vanadium pentoxide, 7% of vanadium oxide sulfate, 1.5% of tungsten trioxide, 2.5% of glass fiber, 1.5% of polyacrylic acid cellulose, 1.1% of cerium sulfate, 14% of manganese sulfate, the rests are carriers (titanium dioxide and carbon nanotubes with the mass ratio of 1:1).

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Ammonium Metatungstate for Diesel Engined Car Exhaust WO3 Denitration Catalyst

Oxide catalyst is mainly the vanadium based catalyst, and adding co-agents like tungsten trioxide, such kind of catalyst has a high NOx removal efficiency in the temperature range of 300-400°C with excellent stability. In the past, the catalyst of diesel engined car exhaust is primarily the noble metal catalyst, but its application is limited by high cost. An invention has pointed out that a method for preparing the diesel engined car exhaust tungsten trioxide denitration catalyst which has a high catalytic activity, wide temperature window, as follows:

diesel engined car exhaust WO3 denitration catalyst

1. Calcine carrier of the titanium dioxide at 300-400°C for 2-5 hours;

2. Preparation of the active ingredient solution: dissolve the ammonium metavanadate and ammonium metatungstate in deionized water, then add the appropriate amount of oxalic acid solution and uniformly stirred, to obtain the active catalyst component solution;

3. Impregnation method to load the active component: The carrier is immersed in the calcined active component solution prepared in step 2;

4. Natural drying the catalyst obtained in step 3, then transferred to drying conditions at 80~120°C for 8~12 hours;

5. After drying, the catalyst is calcined at 300~600°C for 2 to 5 hours, then heated to 680-800°C and continually calcined for 2 to 5 hours to obtain the tungsten trioxide denitration catalyst which is suitable for diesel engined car exhaust.

Noted: wherein the carrier is titanium dioxide which takes 90-99.5% of the mass of catalyst; the main active component vanadium pentoxide takes 0.5-10%; additive- tungsten trioxide takes 0.5-10%.

The preparation method of this catalyst without introducing any chemical agent, just by changing the preparation process; by changing the calcining temperature to improve the distribution of the active component in the catalyst support surface, has the advantages of simple operation, excellent repeatability, easy to optimize the size and modifying the conventional catalyst.

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Sky-High Green Ticket Reproduced, Tungsten Trioxide Denitration Catalyst Boosts Air Purification

June 1st in the morning, Shanghai Environmental Protection Bureau said it would write a ten million Yuan of green ticket to a company; and, it was revealed that Shanghai is revising the new environmental regulations, proposed individual fines from 200,000 Yuan increased to 1 million. This may be another 10 million Yuan level green ticket since last year after the Qinhuangdao City Environmental Protection Bureau of the States (Qinhuangdao) Co., Ltd. Sewage Treatment out of nearly 13 million of ticket.

thermal power plant denitration catalyst

Some netizens commented: "Well done, if they had known today, why didn’t it take this ten million to invest in SCR denitration and desulfurization project which can also contribute to improve our living environment." Denitration catalyst is the core of SCR technology, the current widespread used is based on tungsten trioxide (or molybdenum trioxide) and vanadium pentoxide as the main active material, the titanium oxide as a carrier, and loading of other related species. Tungsten trioxide can improve the anti-sulfidation of the catalyst, and to enhance the anti-weld ability of the carrier. By the way, the nano-tungsten trioxide will exhibit better performance with its larger surface area. 

It is reported that, more than 20 units of the plants have been completed desulfurization and denitrification transformation in Shanghai, this year, more than 1,400 factories also identified to carry out VOCs transformation; in addition, tens of thousands of the old cars would be eliminated. Exhaust gas thermal power plant is one of the main sources of NOx and other pollutants, the using of SCR project using tungsten trioxide denitration catalyst to governance, is now widely recognized as the most effective way of NOx removal; at the same time, the elimination of old cars, while vigorously implement the vehicles which installed tail gas treatment unit (such as tungsten trioxide with SCR denitration catalyst), thus, the pressure on the environment will possible to greatly reduced.

I believe if everyone pay attention to the environment protection issues, what smog, water pollution ect., will be nowhere to hide, and sky-high green ticket will no longer appear.


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