The naphthalene separated from coal tar is called tar naphthalene. In high-temperature coal tar, naphthalene accounts for approximately 8-12%. Cut naphthalene oil fraction with a temperature range of 210-230 ℃ from the side line of the tar distillation tower, wash and dephenolize it, and then distill and separate the light components to obtain industrial naphthalene with a solidification point of 78 ℃ and a purity of 96%.
Industrial naphthalene contains impurities such as sulfur indene (1-3%), methyl naphthalene (1-2%), and a small amount of indene, tar base, and tar acid. After progressive acid washing and distillation, refined naphthalene with a sulfur content of less than 0.1% and a solidification point of 79 ℃ can be obtained. If it is necessary to improve refining so that the sulfur content is below 0.05%, a hydrofining process is required.
The raw material of petroleum naphthalene comes from the heavy aromatic components of catalytic reforming, catalytic cracking, and hydrocarbon cracking processes. In 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. Then, a catalytic hydrodealkylation method is used, using Cr2O3-Al2O3 as catalyst, to undergo hydrodemethylation reaction at 400-800 ℃ and 0.5-7 MPa. The reaction product is cooled by gas phase substances, and the light components such as benzene, toluene, and xylene are removed by distillation. Then, petroleum naphthalene products can be obtained through further distillation. The product is purified using solvent absorption and solvent washing methods, with a purity of up to 99.73%.
It is estimated that an ethylene plant with an annual production of 300000 tons using light diesel as the cracking raw material can produce 90000 tons of tar as a byproduct, with a potential of 40-50000 tons of naphthalene and naphthalene.
Industrial refined naphthalene is a basic chemical raw material mainly used in the production of water reducing agents and dispersants. It is a raw material for the production of synthetic resins, plasticizers, rubber antioxidants, surfactants, synthetic fibers, dyes, pharmaceuticals, and spices.
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