AMT/SiO2 Catalyst on Orthortho-Hydroxy Anisole Production II

Ammonium metatungstate, also known as AMT, is a tungsten chemical in the form of highly soluble hydrated crystals. Global Tungsten & Powders AMT is produced as minus 10-mesh powder to meet stringent demands in the catalyst, medical, semiconductor and other high-technology industries. GTP AMT is also used in materials research and in analytical chemistry. At room temperature, aqueous solutions can be saturated up to 70% by weight of contained WO3. This equates to 1.6 kilograms per liter or 13.3 pounds per gallon.

AMT / SiO2 catalyst calcined at different temperatures has different degrees of AMT decomposition, resulting in different properties of the catalyst surface pH center, resulting in catalyst performance vary. The activity and stability of catalyst prepared at low firing temperature calcination is much better than a catalyst prepared at high firing temperature. Weak acid-weak alkali centers on the catalyst surface is the main activity center of catechol and methanol monoetherification reaction to produce ortho-hydroxy anisoles. the main reason for the reduced activity is coke on the catalyst surface during the reaction. the catalyst after inactivation was calcined at a higher temperature and regeneration treatment then the reactivity partially restored, but still significantly lower than the fresh catalyst, and the stability of the catalyst after regeneration process is poor. This may be the high temperature regeneration properties of the active center of the catalyst surface (including pH properties) has changed, so that the regenerated catalyst is more easily inactivated.

AMT/SiO2 Catalyst on Orthortho-Hydroxy Anisole Production I

Orthortho-hydroxy anisole is important fine chemical intermediates and chemical raw materials, with a wide range of applications. Pyrocatechol - Methanol Gas phase single etherification method to produce orthortho-hydroxy anisole has attracted much attention due to its advantages of economic and environmental, some effective catalyst systems of this reaction have been found including a variety of complex oxides, phosphates and zeolite.

According to preliminary studies on phosphates and phosphate multicomponent catalyst, it’s found that a weak acid - weak alkali catalyst usually shows high activity and selectivity on the reaction of pyrocatechol and methanol vapor phase synthesis of orthortho-hydroxy anisole. Recently, scholars have found that supported ammonium metatungstate (AMT) catalyst prepared by SiO2, TiO2, and Al2O3 as the carrier has good catalytic performance on this reaction. In which the tungsten loading of 7.9% of AMT / SiO2 catalyst has the best performance. Preliminary characterization results show that the weak acid - weak alkali species formed by ammonium metatungstate partial decomposition are the the active center of the catalytic reaction in roasting preparation processing. On this basis, the study focused on the influence of calcination temperature on pyrocatechol and methanol vapor single etherification performance with AMT / SiO2 catalyst and examine the stability and performance of the catalyst regeneration. Meanwhile, according to X-ray diffraction (XDR), infrared spectroscopy (IR), temperature programmed desorption (TPD), scanning electron microscopy (SEM) and differential thermal - thermogravimetric (TG-DTA), catalyst structure, surface acidity the nature and reasons for deactivation were discussed.

Morphology and Size of Ammonium Metatungstate Microsphere Prepared by Spray Drying Method

Ammonium metatungstate (AMT) is usually used as one of the precursors of tungsten carbide (WC) catalyst, and the properties of AMT precursor affect the morphology and size distribution of WC microsphere, which have a finally effect on the catalyst activity.

In this work, the mechanisms of airflow and centrifugal spray drying methods were introduced, then the AMT microspheres having different morphologies were prepared by using these two kinds of spray drying methods, and the morphology and size of the microspheres prepared were studied. The results show that the morphology of the powder prepared by centrifugal spray drying is solid sphere, and it is different from that of the powder prepared by airflow spray drying, which is hollow sphere. For the airflow spray drying method used, the effects of solution concentration, feed rate and surfactant on the particle size of products were investigated.

It was found that the solution concentration is the most important factor affecting the particle size, and under different drying conditions, the minimum median diameter (d50) of the dry products is 2.26 μm. This study might provide a referential foundation for the morphology and size control of hollow global WC microspheres prepared by the gas-solid reaction method of spray drying sphere miniaturization.

Ammonium Metatungstate(AMT) Industry China Market Research Report 2016

The China Ammonium Metatungstate(AMT) Industry 2016 Market Research Report is a professional and in-depth study on the current state of the Ammonium Metatungstate(AMT) industry.

The report provides a basic overview of the industry including definitions, classifications, applications and industry chain structure. The Ammonium Metatungstate(AMT) market analysis is provided for the China markets including development trends, competitive landscape analysis, and key regions development status.

Development policies and plans are discussed as well as manufacturing processes and Bill of Materials cost structures are also analyzed. This report also states import/export consumption, supply and demand Figures, cost, price, revenue and gross margins.

The report focuses on China major leading industry players providing information such as company profiles, product picture and specification, capacity, production, price, cost, revenue and contact information. Upstream raw materials and equipment and downstream demand analysis is also carried out. The Ammonium Metatungstate(AMT) industry development trends and marketing channels are analyzed. Finally the feasibility of new investment projects are assessed and overall research conclusions offered.

With 148 tables and figures the report provides key statistics on the state of the industry and is a valuable source of guidance and direction for companies and individuals interested in the market.

Structure and Thermal Decomposition of Ammonium Metatungstate

Ammonium metatungstate, also known as AMT, is a tungsten chemical in the form of highly soluble hydrated crystals. Global Tungsten & Powders AMT is produced as minus 10-mesh powder to meet stringent demands in the catalyst, medical, semiconductor and other high-technology industries. GTP AMT is also used in materials research and in analytical chemistry. At room temperature, aqueous solutions can be saturated up to 70% by weight of contained WO3. This equates to 1.6 kilograms per liter or 13.3 pounds per gallon.

The structure and morphology of ammonium metatungstate (AMT), (NH4)6[H2W12O40]⋅4H2O, and its thermal decomposition in air and nitrogen atmospheres were investigated by SEM, FTIR, XRD, and TG/DTA-MS. The cell parameters of the AMT sample were determined and refined with a full profile fit. The thermal decomposition of AMT involved several steps in inert atmosphere: (i) release of crystal water between 25 and 200 °C resulting in dehydrated AMT, (ii) formation of an amorphous phase between 200 and 380 °C, (iii) from which hexagonal WO3 formed between 380 and 500 °C, and (iv) which then transformed into the more stable m-WO3 between 500 and 600 °C. As a difference in air, the as-formed NH3 ignited with an exothermic heat effect, and nitrous oxides formed as combustion products. The thermal behavior of AMT was similar to ammonium paratungstate (APT), (NH4)10[H2W12O42]⋅4H2O, the only main difference being the lack of dry NH3 evolution between 170 and 240 °C in the case of AMT.

Synthesis and Interfacial Electron Transfer of a Composite Film of Graphene and AMT

Solar energy is a renewable energy, hydrogen production with that is expected to solve the current common problems of energy shortage and environmental pollution, which has been widespread concerned. In many semiconductor photocatalytic hydrogen production materials, tungsten oxide become a hot research materials in the photocatalytic field due to its stable performance and low cost, but its optical electronic - holes are so easy to combine that restrict the photoelectric device performance. In order to improve the photoelectric conversion performance of the tungsten oxide, the domestic and international researchers carried out a number of explorations. Currently, common methods are semiconductor compound, noble metal deposition, surface sensitization, ion doping.

With ammonium metatungstate as tungsten source, PVP as binding agents, use dip-coating method to prepare graphene - tungsten oxide composite films, using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy methods such as composite structure were characterized by light and current test, electrochemical impedance spectroscopy (EIS), transient photocurrent spectrum and intensity modulated photocurrent spectroscopy methods to study complex film electrode interface at a photoelectric effect carriers transfer process and a charge transport behavior. The results show that the composition of the film and the tungsten oxide nanoparticles are graphene fully complex, significantly improved photoelectric properties; graphene composite after the transient time constant of the film is increased, the electron - hole pairs life expectancy; electron transport time is reduced, as 47.5% of pure tungsten oxide film.

Emulsion Liquid Membrane and APT Production Advantages

Dissolve crude sodium tungstate that obtained after alkali fusion with tungsten fine mud in water as feed solution and adjusted pH to 8-9, after removing impurities of silicon, without removal of phosphorus, arsenic, molybdenum at room temperature for a directly laboratory intermittent film migration, according to the best operating conditions of the orthogonal design, obtain ammonium paratungstate (APT) crystallization directly in inside aqueous phase within 5min . Extraction rate is 99.85%, and the purity level of product is the firsts standards. This article had depth study on various factors, and proposed A-class continuous countercurrent flow with low cost, which is a new approach with great promise.

Advantages of the  first level film production process are: it does not need to adjust the solution to acidic after removing Si, crystalline can be directly produced in  inside aqueous phase by A-class liquid membrane process, acid saving, the process is short, fast, without evaporation and crystallization, energy saving and finer grain, without removing P, As, Mo. Solution containing tungsten material has up to 45g / L when the first extraction. The oil phase and the inner aqueous phase repeatedly reuse, less reagent consumption. According to the economic accounting of film production of mixed rare earth to calculate the operating costs be low, operating costs of liquid membrane method are generally about 1/3 than extraction method, the actual accounts of that is to be tested.

Emulsion Liquid Membrane in Ammonium Paratungstate Production

Tungsten reserves in China takes the first place in the world, occupying an important position in China's metallurgical industry. 

Ammonium paratungstate is the main raw material of metal tungsten production. Now the factories use extraction or ion exchange process in production, the former one is that the tungsten concentrate with alkali cooking (or alkali fusion) division after removing silicon, phosphorus, arsenic, adding Na2S to make Mo become MoS3 precipitation, and then adjust the pH of supernatant to 2-3, and extracted with a tertiary amine and recovering with NH4OH.

The concept of emulsion liquid membrane is proposed by N.N.Li in 1968, and it has attracted researchers from many countries. Because it simulates the activity of migration of biofilms on the migration mechanism, it enables materials highly enriched against the concentration difference. It is the combination of extraction and back-extraction process carried out in a system at the same time, the reaction takes place on the surface area of the extremely thin film interface, and there is carrier on the membrane, so its kinetic advantages are much more than the reaction takes places in solution, also the mass transfer rate, efficiency and selectivity than the extraction process. This new technology is currently developing forward unit operations. University of Graz in Austria is first one to started the international industrial application, for the recovery of zinc from waste water, followed by the Institute of Environmental Science, South China University of Technology for the removal of phenol from wastewater.

Liquid Membrane Production of Ammonium paratungstate

Tungsten reserves in China takes the first place in the world, occupying an important position in China's metallurgical industry.

Ammonium paratungstate is the main raw material of metal tungsten production. Now the factories use extraction or ion exchange process in production, the former one is that the tungsten concentrate with alkali cooking (or alkali fusion) division after removing silicon, phosphorus, arsenic, adding Na2S to make Mo become MoS3 precipitation, and then adjust the pH of supernatant to 2-3, and extracted with a tertiary amine and recovering with NH4OH. Therefore, the defecator will go through stages of pH = 6. APT will then crystallize resulting in difficulties in normal operation. This problem is difficult to resolve from the formula, it is by strengthening stirring to dissolve the crystals again clarified or improved groove geometry of the internal structure of the practice.

It’s not required in removing P, As, Si in the ion exchange method but molybdenum can not be removed, so the tungsten concentrate with low Mo-containing is often the choice. This method can use alkaline feed solution directly, but due to the amount of exchange is small, the material must first be diluted to WO3 contain 25g / L or less, and the amount of the rinse water is also large, therefore the emissions of alkaline wastewater with a pH10-13 is very large, wastewater treatment has become a burden, and tungsten in waste water of these two methods can not be recovered.

Ammonium Paratungstate (APT) Nucleation Rate

Evaporation and crystallization is a process that feed liquid and solid of ammonium tungstate to get to oversaturation, which makes the material’s phase change and precipitate purified crystals from the solution. 

APT crystals precipitate from ammonium tungstate solution can be achieved, by that to adjust the PH of solution through loss of ammonia and get into the secondary salt formation region. The loss ammonia -adjust PH process can be achieved by evaporation crystallization process and neutralization crystallization process.

The physical properties of ammonium paratungstate crystals are decided by nucleation rate and grain rate. APT nucleation rate depends on: 

(1) the velocity of APT periphery crystallized from a liquid phase, is proportional to the amount of oversaturation (difference between the solution concentration and the equilibrium concentration) of nuclei forming;

(2) the dissolution velocity of APT, that is a velocity that precipitated APT crystals goes into the solution again, it depends on the equilibrium solubility of solute. A major factor of nucleation rate is oversaturation. A new root of nucleation can only form when oversaturation up to a certain level. Growth mechanism of APT grain is still within reach. It is generally believed: After nucleation, the solute is deposited onto the lattice and gradually grow.

Ammonium Paratungstate (APT) Production Conditions

Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher and higher.

For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.

WO3 Concentration’s Effect on Ammonium Paratungstate Production

Here is the disscusion about the effect of WO3 concentration in ammonium tungstate solution.

As it can be seen from Figure 1, the bulk density of the APT increases with WO3 concentration in solution decreases. When WO3 concentration is reduced to a certain extent, the bulk density of APT has no obvious change. It shows that when the WO3 concentration in solution is high, the supersaturation is high. Nucleation is fast, so it’s not easy for crystalline particles to grow. When the WO3 concentration in solution is low, oversaturation of the evaporation process does not change significantly in the solution, the oversaturation is low so it helps nuclei to grow. However, when the WO3 concentration in solution is too low, the oversaturation is too low, less chance of contact between the solute and molecule nuclei, affecting the growth of grains.

Temperature’s Effects on Ammonium Paratungstate Production

Here is temperature’s effects on Ammonium Paratungstate production.

Test results are shown on Figure. With the increase of evaporation temperature, the crystal growth rate of APT is faster than the nucleation rate, which makes a particle size enlargement and increases the bulk specific gravity of APT (see figure). The reasons are increasing temperature , faster molecular motion, more opportunities of molecules colliding with each other, which are conducive to grain growth. 

Plane grain formation rate on the grain surface is affected a lot by temperature. When temperature increases to 10 ℃, speed needs to increase 2 to 4 times, so the increasing temperature is most significant for grain growth. It was also observed in the experiment that APT crystalline grains were much coarser than other parts on the crystallizer wall. This may be due to an indirect steam heating, the temperature on wall is higher than other parts , which is conducive to grain growth. It was also found in the experiment that the crystalline particles is more regular in a higher temperature than a lower one, and size distribution is more well-distributed.

Effect of Time on Ammonium Paratungstate Production

Here is the discussion of effect of time on ammonium paratungstate production.

Evaporation and crystallization including the heating time (heating rate) and the evaporation time (evaporation rate). When the heating time is quick, most of the free ammonia in solution were expelled in a short time, so that PH of the solution decreased rapidly, and the over-saturation increases, and a lot of nuclei was formed rapidly, the particle size became finer. Long evaporation time, it will help small crystals dissolve constantly, big crystals continue to grow. the situation of crystal growth becomes more apparent when APT crystalline precipitate for a while before filtered. It was also found in the conditions of a certain degree of vacuum, evaporation speed increases, the bulk density of the resulting APT reduces significantly.

Effect of Stirring Speed on Ammonium Paratungstate Production

Here is the discussion of effect of stirring speed on ammonium paratungstate production.

The test results are shown in Figure 2. It’s complicated that stirring speed affects nucleation. On one hand, the stirring speed is accelerated, so that the newly formed crystals were minced and the form much crystal nucleus, particle size becomes fine, on the other hand, in a certain stirring speed range, increasing the stirring speed can increase the relative velocity between solid and liquid, thereby increasing the speed of nuclei grow. 

To prepare coarse APT, the best speed is when the resulting APT does not precipitate,  APT particle formed can make full contact with the solutes. It was also found  the effect is not the same with different paddles stirring or different stirring intensity. Stirring has a great impact on the preparation of the different particle size of APT, APT prepared by gas stirring is more regular . For different production conditions, it’s generally required to determine the proper form and speed of stirring through practice.

Structural Evolution of Ammonium Paratungstates during Thermal Decomposition

Mixed metal oxide systems (e.g. Mox(V,W)yO3-z) are employed for the partial oxidation of light alkenes. Ammonium paratungstate (APT) and ammonium heptamolybdate (AHM) are used as precursors for the production of WO3 and MoO3, respectively. The catalytic activity of these materials may depend on the treatment of the precursors. Therefore, studies of the decomposition process in order to identify and quantify tungsten oxide phases and their formation under various atmospheres, reveal correlation between catalytic activity and structural evolution of APT is very important. Here, we present results obtained from bulk structural studies on the thermal decomposition of APT in various reducing and oxidizing atmospheres. In this work the decomposition of APT is studied in situ by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Using these two complementary methods allows us to follow the evolution of the short-range and long-range structure of the phases formed during the decomposition of APT, to elucidate the evolution of the primary and secondary structure under different conditions. 

Experimental 

Ammonium paratungstate (APT), (NH4)10H2W12O42*4H2O (OSRAM) was used as purchased. Transmission X-ray absorption spectra were measured in situ with the sample pellet in a flow reactor (4 ml total volume) under a controlled reactant atmosphere. In situ XAS experiments were performed at the W LIII edge (10.204 keV) (Hamburger Synchrotron Radiation Laboratory, HASYLAB, beamline X1), using a Si (311) double crystal monochromator. Temperature programmed decomposition was carried out at temperatures between 300 and 773 K in atmospheres of pure helium, 5 % hydrogen in helium, 20 % oxygen in helium, 10 % propene in helium, and 10 % propene/10% oxygen in helium. For the in situ XAS measurements APT was mixed with boron nitride and pressed into 5 mm in diameter pellets. Analysis of the gas phase was carried out with a quadrupol mass spectrometer, QMS 200 (Pfeifer), with a time resolution of ~ 2 s. Further details about the experimental XAS set-up used can be found in .

Metallo-Organic Deposition of Tungsten Oxide Films from Alkylammonium Tungstate Solutions

Metallo-organic deposition of tungsten oxide films from alkylammonium tungstate solutions

This paper describes a simple and inexpensive metallo-organic deposition (MOD) process for forming electrochromic tungsten oxide (WO₃) films on glass. The thin films of WO₃ were made by air firing (500–700°C) films from xylene/2-propanol solutions of bis-(di-n-octylammonium) tetratungstate, [(n-C₈H₁₇)₂NH₂]₂[W₄O₁₃]. The process coats glass with undoped films ranging in colour from faint yellow to dark brown, and can be used to make gradients of these colours. The colour is determined by the firing parameters and results from residual carbon and tungsten suboxides in the film due to incomplete firing. Increased firing temperatures or longer firing times removes the carbon and produces films with higher crystallinity. Electrochemical doping with acid (H⁺) switches the colour gradient films to a uniformly blue colour.

Processing of Ammonium Paratungstate from Tungsten Ores

To obtain highly purified, lamp grade ammonium paratungstate crystals from any of several different tungsten ores, the ore is reduced to finely divided status and slurried in heated HCl solution to convert tungsten values to WO.HO. Recovered tungstic oxide is washed and dissolved in heated aqueous solution of sodium carbonate or sodium hydroxide with the pH maintained at about 8 to 8.5 to form soluble sodium tungstate. Sodium hydroxide is added to raise the pH to about 10.5 to 11.5, and magnesium chloride is added in amount sufficient to somewhat neutralize the solution. Sodium hydroxide is added to raise the pH to about 10.5 to 11.5 to precipitate as hydroxide the magnesium and additional metallic impurities. At least one of ammonium sulfide and thioacetamide is and the heated solution is acidified to a pH in the range from about 2 to 3 to precipitate any molybdenum as MoS. The tungstate solution is then contacted with an organic, water-immiscible ion exchange liquid in which the active ingredient is an amine salt to extract the tungsten values. Tungsten values are then stripped from the ion exchange liquid with ammonium hydroxide to form ammonium tungstate solution, which in turn is separated. From the ammonium tungstate solution is crystallized highly purified ammonium paratungstate. The process is adaptable to continuous type operation.

Process for Producing Ammonium Paratungstate

Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O.

Ammonium paratungstate is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO₃, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.

A process is disclosed for producing ammonium paratungstate which involves adding hexamethylenetetramine to a first solution of ammonium tungstate, adjusting the pH to about 2 with an acid to form a precipitate which contains the major portion of the tungsten and the hexamethylenetetramine and separating the precipitate from the resulting mother liquor. The tungsten hexamethylenetetramine precipitate is then dissolved in aqueous ammonia to form a second ammonium tungstate solution which is then heated at from about 90℃ to about 100℃ to form a precipitate essentially all of which is ammonium paratungstate and a mother liquor which contains essentially all of the hexamethylenetetramine. The ammonium paratungstate precipitate is then separated from the mother liquor.

about ammonium paratungstate (APT)

Ammonium paratungstate, (APT) is a white crystalline salt of ammonium and tungsten.

APT is produced by separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO₃, tungsten oxide. At that point, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to powder, leaving behind water vapor. From there, the tungsten metal powder can be fused into any number of things, from wire to bars to other shapes.

The WO3 content of APT manufactured and supplied by Chinatungsten Online is over 88.5%.

More information, please visit: www.tungsten-powder.com