How to determine the quality of industrial naphthalene and what are the influencing factors

1、塔顶温度的影响:

1. Influence of tower top temperature:

前已述及，工业萘的生产过程是以萘洗三混馏分为原料，经过精馏过程而完成的。而精馏操作恰恰是利用混合液中各组分挥发度的不同而达到分离的目的，溶液中各组分的挥发度的差异是随温度的改变而变化的，因而温度的变化可影响精馏操作的正常进行。

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初馏塔塔顶温度的影响

1.1 effect of overhead temperature of primary distillation tower

在通常情况下，初馏塔塔顶温度需控制在185-195℃左右。主要是因为萘洗三混馏分中只有酚油的温度小于200℃，而为182℃，在这个温度下，只有酚油作为轻组分而从塔顶溢出，其余馏分作为重组分而从塔底流出;若初馏塔塔顶温度过高，则萘洗馏分中的一部分很容易作为轻组分随酚油一起从塔顶溢出，使酚油中萘含量增加从而使萘的提取率下降;若初馏塔塔顶温度过低则一部分酚油将随萘洗混合馏分流入塔底，使后续工艺过程中萘油的酚油含量升高，从而使产品质量下降。

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精馏塔塔顶温度的影响

1.2 influence of distillation tower top temperature

同理，精馏塔塔顶温度一般都应控制在218℃到220℃之间。若高于这个温度，则洗油中的一部分易作为轻组分随萘油从塔顶溢出,使萘油中洗油含量增加，从而使产品质量下降，若塔顶温度过低则萘油中的一部分易作为重组分流入塔底，因而使萘的提取率下降。

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.

故在工业萘的生产的过程中，需要严格控制塔顶温度使其在一定温度范围之内，严禁出现偏高或偏低现象，从而使柰的提取率或质量下降。

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、回流量对产质量的影响

2. Effect of return flow on Yield and quality

由蒸馏过程的原理可知，将液体混合物进行一次部分汽化(或部分冷凝)的过程，对于轻组分只能起到部分分离的效果。然而要想使混合物中的各组分都得到近乎完全的分离，需要进行多次部分汽化和部分冷凝过程，但如果采用多级分离则在分离过程中不但设备庞杂，能耗严重，同时因为得到许多中间馏分，而使纯产品的收率也很低。因而只有采用将上级液相回流与下级的气相直接接触,这样就解决了中间产品,提高了产品的收率;同时由于液相温度低于气相温度，因而高温蒸汽将直接加热低温液体，从而使液体部分汽化，而蒸汽自身则被同时部分冷凝，故省去了中间加热器和部分冷凝器。上述情况对于难挥发组分亦上如此。所以采用回流不仅可以提高收率,而且是精馏过程进行的必不可少的条件。

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.