Method for preparing maleic anhydride by virtue of n-butane oxidation

The invention relates to a method for preparing maleic anhydride by virtue of n-butane oxidation. The method comprises the following steps: i) feeding cooled product gas containing maleic anhydride and flowing out of a reactor of preparing maleic anhydride by virtue of n-butane oxidation into a spiral absorber, wherein in the absorber, maleic anhydride in the product gas is absorbed by an absorbent to obtain a first absorbent material flow; and ii) feeding the preheated first absorbent material flow rich in maleic anhydride and flowing out of the absorber to a desorber, after desorbing, separating 80-99wt% of maleic anhydride from the absorbent, refining the separated maleic anhydride gas to obtain a maleic anhydride product, passing the absorbent containing impurities and residual maleic anhydride through an evaporator to obtain a second absorbent material flow, entering the second absorbent material flow and desalted water into an impinging stream-rotary filler bed extractor together, and extracting and washing the impurities and residual maleic anhydride contained in the second absorbent material flow to obtain a clean absorbent.