Naphthalene, also known as binaphthylene, is a kind of colorless and glossy flake crystal, insoluble in water, easy to sublimate, can volatilize with water vapor and has special smell. It is the most important polycyclic aromatic hydrocarbon in industry. It can be used as raw anhydride, intermediate of dyestuff, rubber additive and insecticide. The maximum allowable concentration in air is 10ppm.

根據純度不同，萘可分為工業萘和精萘，工業萘的純度一般約為96%，工業萘進一步提純脫除雜質及脫硫后，可得到高純度的精萘，生產方法焦油萘從煤焦油中分離出來的萘稱之為焦油萘，在高溫煤焦油中萘約占8-12%，從焦油精餾塔側線切取出溫度區間為210-230℃的萘油餾分，經過洗滌脫酚，再精餾分離輕組分，便可得到凝固點為78℃、純度為96%的工業萘，工業萘中含雜質硫茚1-3%、甲基萘1-2%及少量茚、焦油堿和焦油酸，經過進一步酸洗和蒸餾，可得到硫含量小于0.1%、凝固點為79℃的精萘。
         

According to the different purity, naphthalene can be divided into industrial naphthalene and refined naphthalene. The purity of industrial naphthalene is generally about 96%. After further purification and removal of impurities and desulfurization, the purified naphthalene with high purity can be obtained. The naphthalene separated from coal tar by tar naphthalene is called tar naphthalene. In high temperature coal tar, naphthalene accounts for about 8-12%. Naphthalene with temperature range of 210-230 ℃ is cut from the side line of tar rectification tower The naphthalene with a freezing point of 78 ℃ and a purity of 96% can be obtained by washing and dephenolizing the oil fraction and then rectifying and separating the light components. The industrial naphthalene contains impurities of 1-3% thioindene, 1-2% methylnaphthalene and a small amount of indene, tar base and pyrooleic acid. After further pickling and distillation, refined naphthalene with sulfur content less than 0.1% and freezing point of 79 ℃ can be obtained.

若需要進一步精制使硫含量低于0.05%，則需采用加氫精制工藝，石油萘石油萘的原料來自于催化重整、催化裂化和烴類裂解等過程的重芳烴組分，在催化重整油中，甲基萘的含量約為55%，首先經過萃取和吸附，從原料餾分中分離出萘的各種同系物，然后采用催化臨氫脫烷基的方法，以Cr2O3-Al2O3為催化劑，在400-800℃和0.5-7兆帕下進行臨氫脫甲基反應，反應產物經冷卻氣相物質后，蒸餾除去輕組分苯、甲苯、二甲苯等，最后進一步精餾可得到石油萘產品。

If the sulfur content is lower than 0.05%, the hydrofining process should be adopted. The feedstock of petroleum naphthalene comes from heavy aromatic components in catalytic reforming, catalytic cracking and hydrocarbon cracking. In the catalytic reforming oil, the content of methyl naphthalene is about 55%. After extraction and adsorption, various homologues of naphthalene are separated from the raw material fraction, and then catalytic cracking is used In the method of hydrodealkylation, Cr2O3-Al2O3 was used as catalyst to carry out hydrodemethylation at 400-800 ℃ and 0.5-7 MPa. After cooling the gas phase, the light components such as benzene, toluene and xylene were removed by distillation. Finally, petroleum naphthalene was obtained by further distillation.

產品用溶劑吸收和溶劑洗滌的方法進行提純，純度可達99.73%。據估計，以輕柴油為裂解原料的年產30萬噸的乙烯裝置，可副產焦油9萬噸，其中萘和萘潛量為4-5萬噸。

The purity of the product can reach 99.73% by solvent absorption and solvent washing. It is estimated that an ethylene plant with an annual output of 300000 tons using light diesel oil as cracking raw material can produce 90000 tons of tar by-product, of which naphthalene and naphthalene have a potential of 40000-50000 tons.