Method for preparing thionyl chloride

The invention belongs to the technical field of chemical synthesis, and particularly relates to a method for preparing thionyl chloride. Raw material mixed gas composed of sulfur dioxide, chlorine and sulfur dichloride enters a reactor from the upper portion, a crude product thionyl chloride gas phase directly enters a rectifying tower from the lower portion of the reactor, the gas phase on the top of the rectifying tower is recycled back to the reactor, a product is produced in the middle of the rectifying tower and enters a blowdown tank so that light components in the product can be blown away by nitrogen, and a qualified product is obtained. The pressure of the reactor and the pressure of the rectifying tower are normal pressure. The process for preparing thionyl chloride through a sulfur dioxide method is simplified, normal-pressure reaction is conducted, the process is simple, energy consumption is low, system safety is high, and the product yield is improved and reaches 99.95% or above.