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.

根据纯度不同，萘可分为工业萘和精萘，工业萘的纯度一般约为96%，工业萘进一步提纯脱除杂质及脱硫后，可得到高纯度的精萘，生产方法焦油萘从煤焦油中分离出来的萘称之为焦油萘，在高温煤焦油中萘约占8-12%，从焦油精馏塔侧线切取出温度区间为210-230℃的萘油馏分，经过洗涤脱酚，再精馏分离轻组分，便可得到凝固点为78℃、纯度为96%的工业萘，工业萘中含杂质硫茚1-3%、甲基萘1-2%及少量茚、焦油碱和焦油酸，经过进一步酸洗和蒸馏，可得到硫含量小于0.1%、凝固点为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.

若需要进一步精制使硫含量低于0.05%，则需采用加氢精制工艺，石油萘石油萘的原料来自于催化重整、催化裂化和烃类裂解等过程的重芳烃组分，在催化重整油中，甲基萘的含量约为55%，首先经过萃取和吸附，从原料馏分中分离出萘的各种同系物，然后采用催化临氢脱烷基的方法，以Cr2O3-Al2O3为催化剂，在400-800℃和0.5-7兆帕下进行临氢脱甲基反应，反应产物经冷却气相物质后，蒸馏除去轻组分苯、甲苯、二甲苯等，最后进一步精馏可得到石油萘产品。

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.

产品用溶剂吸收和溶剂洗涤的方法进行提纯，纯度可达99.73%。据估计，以轻柴油为裂解原料的年产30万吨的乙烯装置，可副产焦油9万吨，其中萘和萘潜量为4-5万吨。

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.