High-selectivity method for preparing styrene through condensation reaction of toluene and formaldehyde or trioxymethylene

The invention discloses a high-selectivity method for preparing styrene through condensation reaction of toluene and formaldehyde or trioxymethylene. The high-selectivity method comprises the following steps of: using toluene and formaldehyde or trioxymethylene as the materials under the medium of carbon dioxide or nitrogen gas, wherein the molar ratio of the toluene to the formaldehyde or trioxymethylene (based on three formaldehydes is (1.0:1.0)-(10.0:1.0) and the reaction temperature is 350 DEG C to 540 DEG C; and keeping the reaction air speed of the toluene to 0.1-4h , the reaction medium pressure is 1.0-6.0 MPa, and the molar ratio of the carbon dioxide to the toluene of (0.5:1.0)-(8.0:1.0), or the molar ratio of the nitrogen gas to the toluene of (0.5:1.0)-(8.0:1.0). The high-selectivity method provided by the invention adopts much excessive greenhouse gas carbon dioxide as the reaction medium and uses the formaldehyde and toluene as the materials, so that the selectivity of toluene-formaldehyde condensation alkylation reaction is improved when the styrene is prepared at high yield; and the selectivity and stability of the reaction reach the base requirements of industrial application.