Summarize the previous experience on vacuum distillation _ oil pump

Original Title: Brief Introduction to Titanium Alloy and Titanium Plate Summation of domestic and foreign materials


Original title: Summarize the experience of predecessors on vacuum distillation I. Basic Introduction: 1. Distillation under reduced pressure The boiling point of a liquid is the temperature at which its vapor pressure is equal to the external pressure. Therefore, the boiling point of a liquid changes with the external pressure. If the pressure in the system is reduced by means of a vacuum pump, the boiling point of the liquid can be reduced, which is the theoretical basis for vacuum distillation operation. Vacuum distillation is one of the common methods to separate and purify organic compounds. It is especially suitable for those substances that have been heated to decompose, oxidize or polymerize before they reach the boiling point during atmospheric distillation. 2. Device Vacuum distillation unit It mainly consists of four parts: distillation, air extraction (decompression), safety protection and pressure measurement. The distillation part consists of a distillation flask, a Kjeldahl distillation head, a capillary tube, a thermometer, a condenser tube, a receiver and the like. The Kjeldahl head reduces the possibility of liquid splashing into the condenser tube due to bumping, and the capillary action It is used as the gasification center to make the distillation smooth and avoid the bumping phenomenon caused by the overheating of the liquid. The distance between the capillary opening and the bottle bottom is about 1 ~ 2 mm. In order to control the air intake of the capillary, a section of soft rubber tube can be sleeved on the upper opening of the capillary glass tube, and a section of thin iron wire can be inserted into the rubber tube and clamped with a spiral clamp. In the distillate receiving section, two or three pear-shaped or round flasks are usually connected by a multi-tailed pipette. When receiving different fractions, it is only necessary to turn the pipette. Do not use cracked or thin glass instruments in the vacuum distillation system. In particular, flat-bottomed bottles (such as conical bottles) that are not pressure-resistant shall not be used to prevent internal explosion. Decompression pump is used in the air extraction part. There are two kinds of decompression pumps: water pump and oil pump. The safety protection part is generally provided with a safety bottle. If an oil pump is used, it must also be provided with a cold trap and an absorption and drying tower respectively filled with granular sodium hydroxide, block paraffin, activated carbon or silica gel, anhydrous calcium chloride, etc., so as to prevent low boiling point solvents, especially acid and water vapor, from entering the oil pump and reducing the vacuum efficiency of the pump. Therefore, all low boiling point liquids and water as well as acid and alkaline gases must be distilled under normal pressure or water pump pressure reduction before oil pump pressure reduction distillation. The pressure measuring part uses a manometer, a commonly used manometer. 3. Method of operation After the instrument is installed, first check whether the system leaks. The method is: close the capillary tube,thin film distillation, reduce the pressure until the pressure is stable, clamp the rubber tube connected to the system, and observe whether the mercury column of the manometer changes. No change indicates no leakage, and any change indicates leakage. In order to make the system airtight, all interfaces of the ground instrument must be coated with vacuum grease. After checking that the instrument is airtight, add the liquid to be distilled, and the amount should not exceed half of the distillation flask. Close the piston on the safety bottle, start the oil pump, and adjust the amount of air introduced by the capillary to emit a series of small bubbles. When the pressure is stable, start heating. After the liquid boils, pay attention to control the temperature and observe the change of boiling point. When the boiling point is stable,rotary vacuum evaporator, rotate the multi-tail liquid receiving pipe to receive the fraction, and the distillation rate should be 0.5 ~ 1 drop/S. Distillation is complete ? Remove the heat source, slowly unscrew the screw clamp of the rubber tube clamped on the capillary tube, slowly open the piston on the safety bottle after the distillation flask is slightly cooled, balance the internal and external pressures (if it is opened too fast, the mercury column will rise quickly, and it is possible to break through the manometer), and then turn off the air pump. II. Points for attention in vacuum distillation A. Capillary plays the role of gasification center, but zeolite does not play any role. Of course, for those easily oxidized substances, Capillary tube can also be filled with nitrogen and carbon dioxide for protection. And B, that oil bath pan can also be stir by magnetic force, so that the oil bath pan is convenient, the heating is stable, and the stir speed can be controlled. C. For simple vacuum distillation, a liquid nitrogen cold trap is directly added at the back. For complex distillation, as mentioned above, paraffin tower, calcium chloride and sodium hydroxide alkali tower need to be added to protect the suction filter pump. (D) in that proces of vacuum distillation and purification, if the temperature of the distillate continuously rises in the distillation proces and the distillate cannot be purified, rotovap distillation ,50l rotovap, I, a fractionating column can be added, and if not, a rectifying column can be replaced; II. Vacuum before distillation, and then slowly heat up after the vacuum is stable. Expand the full text E. Several experiences of oil pump vacuum distillation In organic synthesis, we often use vacuum distillation, I am here to talk about my own experience, hoping to play a role in throwing out a brick to attract jade. First of all, it is only useful for novices. The connection sequence of the pressurized distillation unit is: distillation unit interface, emptying bottle, U-shaped pressure gauge, absorption bottle, cold trap, calcium chloride drying tower, alkali tower, paraffin drying tower and oil pump. The absorption bottle may not be filled if not necessary. The commonly used liquid in the absorption bottle is concentrated sulfuric acid. It can absorb a lot of water and organic matter! I think changing the absorption bottle is better than changing the calcium chloride. It is easier to use three drying towers, such as alkali, paraffin and so on, so I usually use them. Here are some of my own experiences: 1。 Do not open the vent immediately at the end of the distillation. Instead, clamp the space between the cold trap and the calcium chloride drying tower with a medical hemostatic forceps (if not, a return clamp is also available), and then slowly open the vent. The purpose of this is: A. Do not let too much air into the oil pump to protect the oil pump; B. Open directly without clamping, because the air intake speed is too fast, it is easy to wash the liquid in the gas bottle and cold trap into the next bottle. When the front part is stable, do not move the hemostatic forceps, pull it directly from the position of the calcium chloride drying tower (this position can also be connected to a tee, which is easier to operate), open the atmosphere, and immediately turn off the oil pump. 2。 If the product of your distillation is unstable, for example, acyl chloride is afraid of water, and other substances need to be protected by nitrogen, at the end of the distillation, the same operation is done as above, but before opening the vent, connect the inlet of the vent to a gas bag containing high-purity nitrogen (I use a medical oxygen bag about 55 yuan each, if filled with nitrogen, one can be used for at least one year . If a high-purity nitrogen cylinder is used directly, the pressure of the gas is not easy to control, and it is easy to break the glass stopper and thermometer. This will not happen with a nitrogen bag. It is OK to use nitrogen instead of air. At this time, hemostatic forceps (or clip) are indispensable, and they should be clamped as tightly as possible to avoid wasting nitrogen. In this way, it plays the role of cooling and nitrogen protection. 3。 If more low boiling points are easily pumped away by the oil pump, 2-3 cold traps can be installed; the cooling effect should be good Usually, the cold trap is cooled by ice salt. If the high vacuum pump needs to be well protected, it can also be cooled by dry ice-acetone (or liquid nitrogen). 4. The cold trap of the cooling system of the oil pump may be cooled by a refrigerator Economical and affordable. There is no trouble with ice salt bath or dry ice + acetone, etc. My brother next to my lab often uses high boiling point solvents such as DMSO and DMF, and uses a refrigerator to cool the cold trap. Generally, the temperature is set at -30 degrees. The effect is very good! 5. Remember to clean the cold trap in time. 。 Look at it every time you use it. If there is liquid in it, it should be cleaned in time to prevent the solvent from entering the oil pump and affecting the distillation effect. 6. The oil pump should also be changed frequently. If it is found in the experiment that the same temperature and the same oil pump are used, if the distillation effect is not good, it is likely that the oil in the oil pump is not good. A timely oil change will not affect your experiment. 7. When using the oil pump Also pay attention to the maintenance of the oil pump, do not pump for half a day. You have to let it rest in the middle. People can't stand working all the time, and so can she. F. Know well the nature of what you are distilling. The boiling point of a substance is fixed at a certain pressure. The lower the pressure, the lower the general boiling point. Therefore, the purpose of decompression is to reduce the boiling point of the substance to be treated, so that it can boil at a lower temperature and be evaporated. When you steam something, you should first check its pressure. After the pressure is determined, you can find out its corresponding boiling point. Then you can choose a temperature lower than its boiling point according to the speed of distillation and the purity of the substance to be distilled. In addition, some mixtures will form azeotropy. There is a phase diagram to consult. G. When steaming, consider the boiling point of what you want to steam and the thermal stability of what you want to leave behind. First of all, make sure that the things you want to leave are stable, and then because of the decompression steaming, the temperature is generally lower than the boiling point of the things you want to steam,cbd crystallization equipment, which can be adjusted according to your specific equipment and the speed you need, be careful not to rush out! Return to Sohu , see more Responsible Editor:. toptiontech.com