Rectification under vacuum, developed by our company on the basis of normal pressure distillation, is the corollary equipment of pyrolysis equipment. It fundamentally solved the problem that exists in the oil refining field. The equipment possesses the features of safety, big production, good quality and convenient operation. This set of rectification under vacuum is the abbreviation of the petrochemical. In the production process, because of the function of decompression, the gasification point decreases and the temperature gets lower, hence, much fuel is saved and the cost gets lower (about 20%) and meanwhile, the content of the sulphur declines and the color of the oil is clearer.