精萘精萘是指粗萘(工业萘或压榨萘)进一步提纯得到的含萘98.45%以上的萘产品。精萘的生产方法主要有熔融-结晶法(见萘熔融-结晶精制)、加氢法(见萘加氢精制)、酸洗蒸馏法、溶剂结晶法、升华法和甲醛法等。酸洗蒸馏法工艺简单，操作较方便，但萘损失较多，设备腐蚀严重，废酸处理困难，生产环境较差，已逐渐淘汰。升华法产品纯度较低，也不常用。酸洗蒸馏法:用96～98%的浓硫酸洗涤粗萘，将硫杂茚和不饱和化合物磺化、聚合成树脂状物质(俗称酸焦油)，碱性化合物与硫酸结合转入硫酸层，酸类则在随后的碱洗时除去，制得精萘。

Refined naphthalene refers to naphthalene products containing more than 98.45% naphthalene obtained by further purification of crude naphthalene (industrial naphthalene or pressed naphthalene). The production methods of refined naphthalene mainly include melting crystallization method (see naphthalene melting crystallization refining), hydrogenation method (see naphthalene hydrogenation refining), acid washing distillation method, solvent crystallization method, sublimation method, and formaldehyde method. The acid washing distillation process is simple and easy to operate, but naphthalene loss is significant, equipment corrosion is severe, waste acid treatment is difficult, and the production environment is poor, which has gradually been phased out. The purity of sublimation products is relatively low and is not commonly used. Acid washing distillation method: Wash crude naphthalene with 96~98% concentrated sulfuric acid, sulfonate and polymerize sulfhydrin and unsaturated compounds into resin like substances (commonly known as acid tar), combine alkaline compounds with sulfuric acid to transfer to the sulfuric acid layer, and remove the acids during subsequent alkaline washing to obtain refined naphthalene.

工艺流程为：粗萘(工业萘或压榨萘)被加热熔化，并继续升温到90～95℃，在酸洗槽中分数次加入总量为4%(对工业萘)的浓硫酸，搅拌后静置分离，从底部排出硫酸盐基，上部排出的液体萘依次用热水和10～12%的氢氧化钠溶液洗涤。从碱洗分离器流出的液体萘再进入真空精馏塔，塔顶真空度保持8.0～10.7kPa。从塔顶采出的精萘，经精萘接受槽送入萘转鼓结晶机制成片状，其结晶点在79.3℃以上。酸洗过程中萘的损失约4～5%(对压榨萘)和4～9%(对工业萘)。为提高酸洗效果和减少萘的损失，苏联采用硫酸甲醛法洗涤净化。

The process flow is as follows: crude naphthalene (industrial naphthalene or pressed naphthalene) is heated and melted, and further heated to 90-95 ℃. Concentrated sulfuric acid with a total amount of 4% (for industrial naphthalene) is added several times in the pickling tank, stirred, and then left to stand for separation. The sulfate base is discharged from the bottom, and the liquid naphthalene discharged from the upper part is washed with hot water and 10-12% sodium hydroxide solution. The liquid naphthalene flowing out of the alkali washing separator enters the vacuum distillation tower, and the vacuum degree at the top of the tower is maintained at 8.0-10.7kPa. The refined naphthalene extracted from the top of the tower is fed into a naphthalene drum crystallizer through a refined naphthalene receiving tank to form flakes, with a crystallization point above 79.3 ℃. The loss of naphthalene during the pickling process is about 4-5% (for pressed naphthalene) and 4-9% (for industrial naphthalene). In order to improve the pickling effect and reduce the loss of naphthalene, the Soviet Union adopted the sulfuric acid formaldehyde method for washing and purification.

甲醛法：粗萘中的不饱和化合物和硫茚等杂质在酸性介质中与甲醛缩聚成树脂状物质，经分离除去。熔融的粗萘先经浓硫酸脱水和缩聚，再用甲醛硫酸溶液进一步缩聚，分离除去树脂层，然后经加碱中和、水洗、精馏、切片，即得结晶点大于79.3℃的精萘。萘精制率约为90%。也可不经浓硫酸脱水和缩聚工序，直接用甲醛硫酸溶液精制。重要的化工原料萘是重要的化工原料，煤焦油中含萘10%左右，可以从煤焦油的中油馏分或石油产品裂化所得的高沸点馏分用结晶法分离获得。

Formaldehyde method: Unsaturated compounds and impurities such as thionines in crude naphthalene are condensed with formaldehyde in an acidic medium to form resin like substances, which are separated and removed. The molten crude naphthalene is first dehydrated and condensed with concentrated sulfuric acid, and then further condensed with formaldehyde sulfuric acid solution to separate and remove the resin layer. Then, it is neutralized with alkali, washed with water, rectified, and sliced to obtain refined naphthalene with a crystallization point greater than 79.3 ℃. The naphthalene refining rate is about 90%. It can also be refined directly with formaldehyde sulfuric acid solution without undergoing concentrated sulfuric acid dehydration and condensation processes. The important chemical raw material naphthalene is an important chemical raw material. Coal tar contains about 10% naphthalene, which can be separated by crystallization from the middle oil fraction of coal tar or the high boiling point fraction obtained from petroleum product cracking.

其产量多少可作为衡量有机化工发展水平的标志之一。约有80%的萘用来制取邻苯二甲酸酐，邻苯二甲酸酐是重要的有机化工原料，并进一步合成增塑剂及一些染料。其余用作染料Chemicalbook中间体及生产鞣革、表面活性剂。少量用于代替樟脑制卫生丸，利用其特殊气味供家庭衣物驱虫防蛀用。但萘蒸气或粉尘吸入人体会引起头痛、恶心，量大时会引起视角膜混浊和视神经炎、心肌炎等。萘的化学性质比苯活泼，与金属钠在沸腾的无水乙醇中还原为1，4-二氢萘;在沸腾的戊醇中则全部还原为1，2，3，4-四氢萘;被铬酸氧化为1，4-萘醌。

The output can be used as one of the indicators to measure the development level of organic chemical industry. About 80% of naphthalene is used to produce phthalic anhydride, which is an important organic chemical raw material and further synthesizes plasticizers and some dyes. The rest are used as intermediates for dye Chemicalbook and in the production of tanned leather and surfactants. A small amount is used to replace camphor in making sanitary pills, and its special odor is used to repel insects and prevent moths in household clothing. However, inhalation of naphthalene vapor or dust into the human body can cause headaches, nausea, and in large amounts, it can cause opacity of the viewing membrane, optic neuritis, myocarditis, etc. Naphthalene has more active chemical properties than benzene and is reduced to 1,4-dihydronaphthalene with metallic sodium in boiling anhydrous ethanol; In boiling pentanol, all are reduced to 1,2,3,4-tetrahydronaphthalene; Oxidized by chromic acid to 1,4-naphthoquinone.

用五氧化二钒高温催化氧化可得邻苯二甲酸酐，

Phthalic anhydride can be obtained by high-temperature catalytic oxidation of vanadium pentoxide,