METHOD FOR PREPARING ISOPRENE Russian patent published in 2004 - IPC

FIELD: organic chemistry, chemical technology. SUBSTANCE: invention proposes a method for preparing isoprene based on liquid-phase interaction of isobutylene or isobutylene-containing fractions of C₄-hydrocarbons with formaldehyde or 4,4-dimethyldioxane-1,3 an aqueous solution. Process is carried out in two reaction zones. In the first zone isobutylene hydration is carried out at 70-90^oC under pressure 15-20 atm in the presence of a solid cationite catalyst and in feeding part of the parent solution of formaldehyde or 4,4-dimethyldioxane-1,3 to this zone. The parent raw is fed to this zone as preliminary prepared liquid homogenous mixtures "trimethylcarbinol-C₄-water-hydrocarbons-formaldehyde" or "trimethylcarbinol-C₄-hydrocarbons-water-4,4-dimethyldioxane-1,3" taken in the definite ratio and taking into account the molar ratio water : isobutylene = 0.9, not less. After distilling off non-converted C₄-hydrocarbons the prepared reaction mixture is fed to the second reaction zone together with the remained part of the parent formaldehyde or 4,4-dimethyldioxane-1,3. In the second zone the process is carried out at temperature 150-170^oC under pressure 5-7 atm in the presence of water-soluble acidic catalyst and in continuous distilling off highly volatile reaction products and part of water. Isobutylene isolated from reaction mass of the second reaction zone is recirculated to the first reaction zone. Homogenous raw is prepared by mixing the parent components under pressure followed by stirring and separation of isolated aqueous phase. Utilization of this raw results to minimizing water consumption in isobutylene hydration and to enhance activity of cationite catalyst sharply that provides preparing part of isoprene and its precursors even in the first reaction zone. Except for, invention provides simplifying the process technology and enhancing its selectivity. EFFECT: improved preparing method. 2 cl, 2 tbl, 6 ex