Method for increasing yield of hexanoic acid produced by straw by adding ethanol in stages

The invention discloses a method for increasing the yield of hexanoic acid produced by straws by adding ethanol in stages. The method comprises the following steps: S1, collecting the straws; s2, pretreating the straws in the step S1; s3, 4-6 g of straw powder obtained in the step S2 is weighed and placed in a reactor, then 1-1.5 g of BES is added, meanwhile, rumen fluid is collected, the rumen fluid is obtained by filtering through four layers of medical gauze, and the rumen fluid is placed in a vacuum cup to control the anaerobic condition; s4, 100-150 ml of rumen fluid in the step S3 is taken, the pH is adjusted to 6.5-7.0, then the rumen fluid is poured into the reactor in the step S3, 30-50 g/L of substrate concentration and 8-12 g/L of BES additive amount are formed, 0.3-0.45 g of ethyl alcohol is added, 15 g/L of ethyl alcohol concentration is formed, finally, N2 is used for aeration for 15 min, anaerobic fermentation is conducted for 15 days, and the rumen fluid is obtained. During anaerobic fermentat