How to determine the quality of industrial naphthalene and what are the influencing factors
1. Influence of tower top temperature:
As mentioned earlier, the production process of industrial naphthalene is completed through distillation process with naphthalene washing three mixture fraction as raw material. The distillation operation achieves the purpose of separation by using the different volatilities of each component in the mixed liquid. The difference of volatilities of each component in the solution changes with the change of temperature, so the change of temperature can affect the normal operation of distillation.
1.1 effect of overhead temperature of primary distillation tower
Under normal circumstances, the top temperature of the primary distillation tower needs to be controlled at about 185-195 ℃. This is mainly because the temperature of only phenol oil in the naphthalene washing three mixture fraction is less than 200 ℃ but 182 ℃. At this temperature, only phenol oil overflows from the tower top as a light component, and the rest of the fraction flows out from the tower bottom as a heavy component; If the temperature at the top of the primary distillation tower is too high, part of the naphthalene washing fraction can easily overflow from the top of the tower as a light component with the phenol oil, increasing the content of naphthalene in the phenol oil and reducing the extraction rate of naphthalene; If the temperature at the top of the primary distillation tower is too low, part of the phenol oil will flow into the tower bottom with the naphthalene washing mixed fraction, which will increase the phenol oil content of naphthalene oil in the subsequent process, so as to reduce the product quality.
1.2 influence of distillation tower top temperature
Similarly, the top temperature of distillation column should be controlled between 218 ℃ and 220 ℃. If the temperature is higher than this, a part of the washing oil is easy to overflow from the tower top as a light component with the naphthalene oil, increasing the washing oil content in the naphthalene oil, so as to reduce the product quality. If the tower top temperature is too low, a part of the naphthalene oil is easy to be diverted into the tower bottom as a reorganization, so as to reduce the extraction rate of naphthalene.
Therefore, in the production process of industrial naphthalene, it is necessary to strictly control the tower top temperature to make it within a certain temperature range, and it is strictly prohibited to be high or low, so as to reduce the extraction rate or quality of Nai.
2. Effect of return flow on Yield and quality
According to the principle of distillation process, the process of partial vaporization (or partial condensation) of liquid mixture can only partially separate the light components. However, in order to achieve almost complete separation of each component in the mixture, multiple partial vaporization and partial condensation processes need to be carried out. However, if multistage separation is adopted, not only the equipment is complicated and the energy consumption is serious, but also the yield of pure products is very low because many middle fractions are obtained. Therefore, only by directly contacting the upper liquid phase reflux with the lower gas phase, the intermediate product is solved and the yield of the product is improved; At the same time, because the liquid phase temperature is lower than the gas phase temperature, the high-temperature steam will directly heat the low-temperature liquid, so as to vaporize part of the liquid, while the steam itself is partially condensed at the same time, so the intermediate heater and part of the condenser are omitted. The above situation is also true for non-volatile components. Therefore, reflux can not only improve the yield, but also be an essential condition for the distillation process.