精萘精萘是指粗萘(工業(yè)萘或壓榨萘)進一步提純得到的含萘98.45%以上的萘產品。精萘的生產方法主要有熔融-結晶法(見萘熔融-結晶精制)、加氫法(見萘加氫精制)、酸洗蒸餾法、溶劑結晶法、升華法和甲醛法等。酸洗蒸餾法工藝簡單，操作較方便，但萘損失較多，設備腐蝕嚴重，廢酸處理困難，生產環(huán)境較差，已逐漸淘汰。升華法產品純度較低，也不常用。酸洗蒸餾法:用96～98%的濃硫酸洗滌粗萘，將硫雜茚和不飽和化合物磺化、聚合成樹脂狀物質(俗稱酸焦油)，堿性化合物與硫酸結合轉入硫酸層，酸類則在隨后的堿洗時除去，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.

工藝流程為：粗萘(工業(yè)萘或壓榨萘)被加熱熔化，并繼續(xù)升溫到90～95℃，在酸洗槽中分數(shù)次加入總量為4%(對工業(yè)萘)的濃硫酸，攪拌后靜置分離，從底部排出硫酸鹽基，上部排出的液體萘依次用熱水和10～12%的氫氧化鈉溶液洗滌。從堿洗分離器流出的液體萘再進入真空精餾塔，塔頂真空度保持8.0～10.7kPa。從塔頂采出的精萘，經精萘接受槽送入萘轉鼓結晶機制成片狀，其結晶點在79.3℃以上。酸洗過程中萘的損失約4～5%(對壓榨萘)和4～9%(對工業(yè)萘)。為提高酸洗效果和減少萘的損失，蘇聯(lián)采用硫酸甲醛法洗滌凈化。

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：粗萘中的不飽和化合物和硫茚等雜質在酸性介質中與甲醛縮聚成樹脂狀物質，經分離除去。熔融的粗萘先經濃硫酸脫水和縮聚，再用甲醛硫酸溶液進一步縮聚，分離除去樹脂層，然后經加堿中和、水洗、精餾、切片，即得結晶點大于79.3℃的精萘。萘精制率約為90%。也可不經濃硫酸脫水和縮聚工序，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，可以從煤焦油的中油餾分或石油產品裂化所得的高沸點餾分用結晶法分離獲得。

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.

其產量多少可作為衡量有機化工發(fā)展水平的標志之一。約有80%的萘用來制取鄰苯二甲酸酐，鄰苯二甲酸酐是重要的有機化工原料，并進一步合成增塑劑及一些染料。其余用作染料Chemicalbook中間體及生產鞣革、表面活性劑。少量用于代替樟腦制衛(wèi)生丸，利用其特殊氣味供家庭衣物驅蟲防蛀用。但萘蒸氣或粉塵吸入人體會引起頭痛、惡心，量大時會引起視角膜混濁和視神經炎、心肌炎等。萘的化學性質比苯活潑，與金屬鈉在沸騰的無水乙醇中還原為1，4-二氫萘;在沸騰的戊醇中則全部還原為1，2，3，4-四氫萘;被鉻酸氧化為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.

用五氧化二釩高溫催化氧化可得鄰苯二甲酸酐，

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