What is the difference between vacuum filtration and atmospheric filtration

The differences are as follows:

Atmospheric filtration: Filter with a conical glass funnel lined with filter paper, and the filtrate flows down through the filter paper by its own gravity to achieve separation.

Vacuum filtration: Use a Brinell funnel mounted on a suction filter bottle and lined with filter paper.

Or glass sand core funnel filtration, suction filter bottle branch pipe is connected with the suction device, filtration is carried out under reduced pressure, and the filtrate flows through the filter paper or sand core under the action of internal and external pressure difference to achieve separation.

The advantages of vacuum filtration are: fast filtration and washing speed; The separation of liquids and solids is relatively complete; The filtered solids dry easily.

Vacuum filtration process.

1. Install the instrument and check whether the connection between the Brinell funnel and the suction filter bottle is tight, and whether the connection port of the suction pump is leaking.

2. Trim the filter paper so that it is slightly smaller than the Brinell funnel, but cover all the holes and add distilled water dropwise.

Wet the filter paper and slightly open the suction valve to make the filter paper tightly connected with the funnel.

3. Turn on the switch of the suction pump, pour in the solid-liquid mixture, and start the suction filtration. Try to keep the substance to be filtered in the Brinell funnel** to prevent it from flowing down through the gap between the funnel and the filter paper without filtration.

4. After filtration, first remove the suction filter bottle and then turn off the suction pump.

5. When taking out the solid from the funnel, the funnel should be removed from the suction filter bottle, hold the funnel tube in the left hand, turn it upside down, and "pat" the left hand with the right hand, so that the solid will fall into the clean paper or surface dish together with the filter paper. Remove the filter paper and dry the solids. The solution in the suction filter bottle should be poured from the upper mouth.

Vacuum filtration (air filtration): filter with a Brinell funnel or glass sand core funnel installed on the suction filter bottle and spread with filter paper, the suction filter bottle branch pipe is connected with the suction device, the filtration is carried out under reduced pressure, and the filtrate flows through the filter paper or sand core under the action of the internal and external pressure difference to achieve separation. In addition, the two are not the same in terms of filtering objects and speeds.

Vacuum filtration: It is not advisable to filter colloidal precipitation and precipitation with too small particles, because colloidal precipitation is easy to penetrate the filter paper, and the precipitation with too small particles is easy to form a dense precipitate on the filter paper, and the solution is not easy to penetrate.

Atmospheric filtration: universally applicable, filter paper is selected according to the nature of precipitation, generally medium speed filter paper is used for coarse crystalline precipitation, slow filter paper is used for fine grain or indefinite precipitation, and fast filter paper is used when the precipitation is colloidal.

Constant pressure filtration, in the case of low pressure, its porosity decreases with the increase of pressure, and when the pressure exceeds a certain critical value, the porosity increases with the increase of pressure.

Due to the existence of the compressibility coefficient, the higher the pressure, the larger the cake volume and the smaller the void ratio. This is also very understandable, the greater the pressure, the tighter and tighter it is pressed. Moreover, in the filtration process, as the filter cake becomes thicker, its porosity is decreasing, that is to say, the resistance of Shixiao flow in the filtration process is increasing, and the amount of filtrate in each state at different times is different, that is, the filtrate is out of unstable flow.

Constant pressure filtration refers to the filtration process in which the filtration pressure is kept at a certain level during the filtration period. It can be passed into the slurry storage tank.

People compress the air to maintain a certain pressure. For example, when using a quantitative pump such as a reciprocating pump to transport slurry, the filtration pressure will gradually rise, and a pressure reducing valve is used.

Maintain a constant pressure. The filtration operation of the continuous rotary vacuum filter belongs to constant pressure filtration. Since the resistance of the filter cake increases with the filtration during constant pressure filtration, the filtration speed is bound to decrease.

<>1. Vacuum filtration is a method of filtration by reducing pressure in the suction filter bottle.

2. This method can accelerate filtration and make the precipitation suctioned drier, but it is not suitable to filter the colloidal precipitation and the precipitation with too small particles, because the colloidal precipitation is easy to penetrate the filter paper field for preparation, and the precipitation particles are too small to form a dense precipitate on the filter paper, and the solution is not easy to penetrate.

3. The circulating water vacuum pump reduces the pressure in the suction filter bottle, and the filtration speed is accelerated due to the pressure difference between the bottle and the Brinell funnel liquid surface. When installing, care should be taken to make the bevel of the funnel opposite the branch pipe of the suction filter bottle.

4. There are many small holes on the Brinell funnel, and the filter paper should be cut to a size that is slightly smaller than the inner diameter of the funnel, but can cover all the porcelain holes. Wet the filter paper with a small amount of water, turn on the pump, reduce the pressure to make the filter paper fit snugly with the funnel, and then start filtration.

5. When the suction filtration is stopped, it is necessary to unplug the rubber tube connecting the suction filter bottle and the pump, and then turn off the pump to prevent back-suction. In order to prevent the phenomenon of back-suction, a safety bottle is generally installed between the suction filter bottle and the pump.

Vacuum filtration, also known as suction filtration and suction filtration, uses a vacuum pump or air pump to pump out the air in the suction filter bottle to generate negative pressure. The pressure filtration device is composed of a vacuum pump, a Brinell funnel, and a suction filter bottle. Vacuum filtration can accelerate filtration and make the precipitation suctioned drier, but it is not suitable to filter colloidal precipitation and precipitation with too small particles, because colloidal precipitation is easy to penetrate the filter paper, and the precipitated particles are too small to form a dense precipitate on the filter paper pants, and the solution is not easy to penetrate.

When installing, care should be taken to make the bevel of the funnel opposite the branch pipe of the suction filter bottle. When stopping the suction filtration, it is necessary to unplug the rubber tube connecting the suction filter bottle and the pump, and then turn off the vacuum pump to prevent the liquid from backflowing. In order to prevent the phenomenon of liquid backflow, a safety bottle is generally installed between the suction filter bottle and the pump.

The advantages of decompression concerns are: fast filtration and washing; Liquids and solids are safely separated; The filtered solids dry easily. The decompression filtration operation is also the suction filtration, which is the operation of using the air pump to reduce the pressure in the suction filter bottle to achieve the purpose of solid-liquid separation.

Vacuum filtration operation process

1. Install the instrument and check whether the connection between the Brinell funnel and the suction filter bottle is tight, and whether the connection port of the suction pump is leaking.

2. Trim the filter paper so that it is slightly smaller than the Brinell funnel, but cover all the holes, and add distilled water dropwise to wet the filter paper, and slightly open the suction valve to make the filter paper and the funnel tightly connected;

3. Turn on the switch of the suction pump, pour in the solid-liquid mixture, and start the suction filtration. Try to keep the substance to be filtered in the Brinell funnel** to prevent it from flowing down directly through the gap between the funnel circle and the filter paper without filtering.

4. After filtration, first remove the suction filter bottle and then turn off the suction pump.

5. When taking out the solid from the funnel, the funnel should be removed from the suction filter bottle, hold the funnel tube in the left hand, turn it upside down, and "pat" the left hand with the right hand, so that the solid falls into the clean paper or surface dish together with the filter paper. Remove the filter paper and dry the solids.