2020年9月15日星期二

Green Catalytic Activity of Phosphotungstic Acid for Four Hydrogen Sulfide

Four hydrogen sulfide is a chemical intermediate of nitro spray paint, rubber and other solvents, so is often used in the protection of hydroxyl groups.

The catalysts, Lewis acid and ion exchange resin used in the preparation of the four - hydrogen catalyst, all of which have good catalytic effect. However, there are some shortcomings in these methods, such as longer reaction time, reflux, solvent, complex catalyst preparation procedure and unsatisfactory yield.

Phosphotungstates have copper phosphotungstic acid, zinc phosphotungstate and aluminum phosphotungstate. As a kind of heteropoly acid salts, phosphotungstates are widely used as catalysts. It has been proved by experiments that the catalytic activity of phosphotungstic acid for the catalytic hydrogenation of four hydrogen peroxide is better than that of the four hydrogenation of alcohol, thus, a green environmental reaction route is provided for the four hydrogen alkylation reaction better than other methods.

green catalytic activity of phosphotungstic acid for four hydrogen sulfide image

The results show that there are three kinds of phosphotungstates such as copper phosphotungstate, zinc phosphotungstate and aluminum phosphotungstate, which have good catalytic effect on tetrahydropyran. In the reaction catalyzed by copper tungstate, the reaction time of secondary alcohol and tertiary alcohol is longer, and the activity of Bibb alcohol is relatively low; the reaction of aluminium tungstate catalyzed alcohol (except n-butanol, SEC butyl alcohol and tert butyl alcohol) is in progress, the catalytic activity of alcohol is very high, and the structure of alcohol has little effect on the catalytic effect; And zinc phosphotungstate as a catalyst, regardless of which structure of the alcohol structure of its activity are very high.

It can be seen that phosphotungstic acid can provide a simple, new and efficient and environmentally friendly reaction pathway for the protection of hydroxyl groups, which is the effective catalyst for tetrahydropyran.

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Pesticide Pollution Treatment by Potassium Phosphotungstate

Chlorothalonil is an efficient fungicide absorbed in organic pesticide, organic compounds but it is also easy to cause pollution of soil.

In the process of agricultural operations, the land often contains chlorothalonil which is difficult to degrade, not only the soil ecological structure is affected, but it is often washed by rainwater to enter the river or infiltrate the ground water, causing serious pollution.

In recent years, with the tungsten based photocatalyst for environmental, economic, effective and has become a new method for the treatment of organic wastewater, some scholars have found that most of the organic pesticides is easily degraded and mineralized into H2O and CO2 and other small molecules, so the photocatalytic degradation of chlorothalonil is feasible.

.degradation of chlorothalonil by phosphotungstic acid image

Tungsten photocatalysts mainly consist of tungstate and tungsten heteropoly acids, the commonly used method is to use a combination of loading and photocatalyst to form a new composite preparation for photocatalytic work, a common load has cloth, holes, sieves, or other chemicals. Some scholars believe that phosphotungstic acid has good degradation effect on chlorothalonil, and in order to verify his opinion, potassium chloride is used to degrade phosphotungstic acid.

During the experiment, he added potassium chloride and phosphotungstic acid to 2.5:1 in proportion to H3PW12O40 water solution and stirred it to produce a white precipitate, continue to stir 10h until the precipitation is complete, centrifugal separation, washed with deionized water, white precipitate to no Cl, and then dried, baking at 300 hours, made into potassium tungstate.

Through the contrast test of two chlorothalonil solution showed that potassium phosphotungstate catalyst of chlorothalonil solution has good photocatalytic effect, not only this, have the effect of all similar pesticides, and very small amount of it. It is estimated that 1 grams of potassium phosphotungstate degradable 10L chlorothalonil solution (5mg/L), light degradation time is 4 hours, the degradation rate is 86.22%, the effect is ideal. And the use is also very convenient, that is, before the allocation of pesticides, according to the proportion of phosphorus potassium tungstate stirring can be used.

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Photocatalytic Activity of Bismuth Tungstate Upgraded by Polyester Fiber

Bismuth tungstate (Bi2WO6) is the most common Aurivillius type oxide and is a hot spot in the field of photocatalysis.

Most of the traditional photocatalytic reactions are carried out in the suspensions of bismuth tungstate catalyst powders. Although they have high photocatalytic activity, bismuth tungstate powders are easy to agglomerate and difficult to separate and recover. In practice, it was recognized that some measures had enabled bismuth tungstate to work, and some scholars had thought of loading bismuth tungstate onto the cloth.

bismuth tungstate photocatalysis image

Of course, loading bismuth tungstate on cloth is not a simple mix, and it also requires a series of chemical procedures that combine bismuth tungstate with cloth to function. Acrylic, polyester fiber and so on, have the same effect at last, and their main difference is synthetic method.

Some scholars used polyester as the carrier of bismuth tungstate and prepared them by hydrothermal method, the polyester fabric was treated with acetone and ethanol at 50 °C for 30 min and 80 °C by ultrasonic cleaning. Then soak 40 min in butyl acrylate and dry. Twelve sodium sulfate and Bi2WO6 powder were dissolved in 50 mL deionized water, and then 2 h at room temperature and then removed and dried to obtain the load polyester fabric.

The results show that Bi2WO6 loaded polyester fabric has better UV resistance and water repellency than Bi2WO6 powder alone. The photocatalytic results show that the Bi2WO6 load of polyester fabric on the degradation of methylene blue was significantly higher than that of Bi2WO6 powder, the degradation efficiency of methylene blue reached 92%, this is because the load after Bi2WO6 got a stable platform, can play a balanced effect.

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Graphene, Bismuth Tungstate, Titanium Oxide

Bismuth tungstate is a popular new visible light catalyst, especially petal shaped bismuth tungstate.

It has good light absorption and high stability, and has broad application prospects in the field of photocatalysis.

The scholars in our country believe that the proper doping of bismuth tungstate, the preparation of semiconductor compound and assistant modification are effective ways to improve the photocatalytic property of bismuth tungstate.

treatment of methyl wastewater image

In recent years, graphene has brought tremendous changes to the material industry because of its unique two-dimensional structure, large specific surface area and high electron transmission rate. It has been recognized as the "king of new materials", Chinese scholars believe that graphene as an efficient electronic additive, and Bi2WO6 composite catalyst, will greatly improve its light capture electronic capabilities, thereby enhancing catalytic capacity. However, scholars believe that only graphene is not enough, and the number of photocatalytic holes will also be increased to improve the cavity manufacturing capacity of bismuth tungstate.

In the photodegradation process, the main active species, HO, is obtained by the reaction of holes and H2O. In recent years, adding cavity additives into photocatalyst is a popular method. Amorphous oxide amorphous TiOis a common assistant, and TiO2 is also a photocatalyst. It is found that the amorphous TiO2 film can be applied to the surface of BiVO4 and GaAs electrodes to transfer the photogenerated cavity rapidly.

With bismuth tungstate (Bi2WO6) as the main catalyst, graphene (rGO) is an electron assistant, and TiO2 (TIO2) is a hole assistant, three Musketeers combined to degrade methyl wastewater. Ti (IV) -rGO/Bi2WO6 has been prepared by hydrothermal impregnation deposition method to degrade methylene orange. The test concluded that the catalytic rate of composite catalyst are pure Bi2WO6, Ti (IV) Bi2WO6 / rGO/Bi2WO6, 88 times, 67 times and 17 times, enhance the photocatalytic performance is mainly due to the Ti (IV) and rGO double additive synergistic effect, rapidly capture and transfer of photogenerated holes and electrons promote separation between them, thus effectively reducing the recombination of photogenerated carriers.

From the cost point of view, bismuth tungstate is the most expensive, followed by graphene, titanium dioxide is the cheapest, they reduce the use of bismuth tungstate, cost a great deal of medicine, and the effect is greatly increased. Therefore, the use of new additives to modify the photocatalytic materials will be most likely to become mainstream methods in the future.

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2020年8月11日星期二

Ultrafine Ammonium Metatungstate Acquisition Strategy

Ammonium metatungstate (AMT) is one of the most important raw materials and precursors for the preparation of WC.

spray drying method image

The structure and properties of WC are affected by the physical and chemical properties of precursor. The particle size and structure of precursor will greatly influence the process of reduction and carbonization in the late stage, and then affect the catalytic activity of WC catalyst.

In order to obtain precursor with good particle size and good structure, spray drying is usually used. Spray drying has many advantages, such as simple process, no pollution, homogeneous composition, and suitable for mass production.

The basic principle of spray drying method is ammonium metatungstate solution by spray drying, in a few seconds, water quickly evaporated into powder, physical and chemical properties of homogeneous granular, hollow spherical or spherical solid products.

Many scholars have found that in the spray drying process, the concentration of ammonium tungstate solution has an important influence on the morphology of ultrafine tungsten powder, and so does ammonium metatungstate.

Some scholars have investigated the effects of different feed concentration, feed rate and the addition of surfactants on the particle size of microspheres under aerobic spray drying conditions. The results show that the feed concentration is 5% at the inlet temperature of 200 °C, the outlet temperature is 90 ~ 100 °C, the air velocity is 550 L· min-1 and the feed rate is 7 m L · min-1 (d50) was 2.26 um. The AMT was prepared by the precursor solution, and the minimum median diameter (d50) was 2.26 um; AMT with solid solution concentration of 50% (WT) is the solid microsphere, and the minimum median diameter (D50) is 6.43 mu m. The greater the solubility, the greater the particle.

From an economic point of view, the concentration of the liquid should be as high as possible, because it can reduce the water content in the solution, thereby reducing the amount of hot air used for evaporating water, and reducing energy consumption. However, the ultrafine ammonium metatungstate precursor can be obtained by analyzing the technical requirements, and the ammonium metatungstate can be obtained with lower concentration.

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How to Extract Rare Element Rubidium with Phosphotungstic Acid

 Rubidium, as a rare and weak alkali metal element, has been widely used in organic catalysts, photomultiplier tubes, special glass and anticancer drugs.

extraction of rare element rubidium by phosphotungstic acid image

Rubidium does not have independent minerals, often and other alkali metals coexist in lithium mica, cesium garnet, lithium cesium garnet, natural carnallite, salt lake brine and underground brine. Because of the coexistence of rubidium and sodium and cesium, which are closely related to the physical and chemical properties, the extraction technology of rubidium is very difficult, which results in a large amount of brine rubidium resources not being rationally utilized.

The common methods for separation of rubidium and cesium are fractional crystallization, precipitation, solvent extraction and ion exchange. In industrial production, precipitation method is used to separate rubidium and cesium, which is mainly used to separate rubidium and cesium from high content solution. Solvent extraction is easy to realize continuous operation and has great potential for application.

Extractant is the most important extractant. Some scholars believe that the salts of heteropoly acids such as phosphotungstic acid and phosphorus molybdate have higher selectivity to rubidium and cesium. However, since the powder is too fine and unsuitable for the continuous operation of the exchange column, it is difficult to be used in the actual production process. Therefore, it is an ideal way to prepare the composite adsorbent by loading the heteropoly acid salt on other carriers.

Some scholars used calcium alginate as carrier and ammonium phosphate as active component to extract rubidium and cesium directly from mother liquor, the research shows that the composite adsorbent can extract Rb+ directly from the mother liquor containing about ten thousand times of impurities. The extraction rate of RbCl is above 92%, the desorption rate is nearly 100%, and it can be reused again and again.

At present, the total reserves of rubidium (excluding rubidium in seawater) are about 10 million 770 thousand tons, of which more than 92% and about 10 million tons exist in Saline Lake, in view of the role of rubidium and the reserves of rubidium, the rubidium resources in the brine of Saline Lake will be the focus of future development, and the solvent extraction method with ammonium phosphotungstate is the most promising method of industrial application.

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Microwave Ultrasonic Method for Customizing Ultrafine Ammonium Paratungstate

Ammonium paratungstate (APT) is the main raw material for the production of tungsten powder, tungsten carbide powder, tungsten wire and tungsten products.

microwave ultrasonic machine image

As everyone knows, the tungsten particle size, crystal morphology of its APT has a great "inherited" relationship, so, if want to produce nanometer tungsten powder and tungsten carbide powder, we first need to prepare ultrafine ammonium paratungstate (APT).

It is an innovative method to prepare superfine ammonium paratungstate (APT) by microwave ultrasonic combined crystallization. Many scholars have shown that compared with traditional heating crystallization, microwave ultrasonic combined crystallization has obvious advantages in speeding up the crystallization rate, refining the particle size and improving the purity of products. So what's the difference between microwave - ultrasonic combined crystallization and traditional evaporation crystallization?

Some scholars have used microwave-ultrasonic combined crystallization method for ultra-fine ammonium paratungstate (APT) preparation test, they used a certain volume of ammonium paratungstate solution placed in the use of XH-300A computer ultrasonic microwave combination synthesis extractor, set the ultrasonic frequency of 25 K Hz, adjust the microwave and ultrasonic power, in the specified value, using ultrasonic wave with microwave heating, at 45, 65, 80, 90, 95 degrees Celsius for evaporation crystallization, after a certain period of time, while the heat filter. After filtration, the filter material was washed with deionized water for 2 to 3 times, and the filtered material was dried in an electric constant temperature oven at 100 °C for 2 h to obtain ultrafine ammonium paramate powder.

The experiment concluded that in the absence of mechanical or magnetic stirring, adding surfactant, in the optimum preparation conditions of APT ultrasonic frequency of 25 K Hz, power 1000 W, microwave power 700 W, temperature 80 °C, ammonium tungstate concentration of WO3212 g/L, CO time 15 min, fine crystal APT-4 with average particle size of 7.6 m, uniform particle size distribution and crystal integrity can be obtained by microwave ultrasonic combined crystallization method.

Microwave ultrasonic assisted evaporation and crystallization can be prepared by micro APT in high temperature and without the addition of surfactant, can influence the crystallization rate and preparation of surfactants micro APT process APT purity to overcome the disadvantages of traditional heating. However, this method is only suitable for small scale production, more suitable for the special needs of the private custom, the main reason is the large microwave - ultrasonic equipment manufacturers almost did not come out, there are also expensive.

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Green Catalytic Activity of Phosphotungstic Acid for Four Hydrogen Sulfide

Four hydrogen sulfide is a chemical intermediate of nitro spray paint, rubber and other solvents, so is often used in the protection of hydr...