Environment-friendly shale inhibitor as well as preparation method and application thereof

The invention provides an environment-friendly shale inhibitor and a preparation method thereof. The preparation method specifically comprises the following steps: S1, preparing cotton straw powder, adding an alkaline solution, heating in a water bath, filtering, adjusting the pH value of slurry to 4-5, adding ethanol for reaction, filtering again, and collecting filtrate; s2, under a protective atmosphere and a vacuum condition, mixing [EM < iM >] CH3COO ionic liquid with the filtrate, stirring, heating, and carrying out suction filtration to obtain filter residues which are crude lignin; s3, extracting by taking tetrahydrofuran as a solvent to obtain refined lignin; and S4, dissolving the refined lignin in water, adding a p-benzenesulfonic acid solution, heating in a water bath, dropwise adding a 2, 3-epoxypropyltrimethylammonium chloride solution, carrying out a heat preservation reaction, after the reaction is finished, carrying out centrifugal separation, taking supernate, and carrying out freeze drying