METHOD FOR PRODUCTION OF ISOPRENE Russian patent published in 1997 - IPC

FIELD: production of high molecular weight compounds. SUBSTANCE: isoprene is prepared by interaction of formaldehyde with isobutylene and/or with trimethyl carbinol, the process is carried out in liquid phase at elevated temperature and at increased pressure in the presence of aqueous solution of acid catalyst. Process takes place in two consequent steps of contact. The second step has zone of heat supply, separation zone and contour of circulation of liquid phase in between them. Reaction products are separated from separation zone of the second step of contact and then isoprene is isolated of reaction products. After the first step of contact reaction mass is separated into aqueous and hydrocarbon streams. Hydrocarbon stream is divided in two portions, their ratio being from 3:1 to 1:3, the first portion is fed into contour of circulation of liquid phase of the second step of contact which takes place before and (or) after zone of heat supply. The second portion is separated while fractions having boiling points not more than 140 C and higher than 140 C or fractions having boiling points not higher 120 C, 120-140 C and higher than 140 C are isolated; the process takes place by rectification. At the first case the first fraction is returned into hydrocarbon stream being fed on the second step of contact. At the second case the first fraction is returned into the same stream. The second fraction is separated while preferable dimethyl dioxane fraction is isolated and is returned into hydrocarbon stream being fed on the second step of contact (quantity of said fraction being up to 100 %) and preferable fraction of unsaturated alcohol is also isolated. The third fraction is isolated or is returned into the same stream, its quantity being up to 100 %, aqueous stream being fed into contour of circulation of liquid phase before feeding of hydrocarbon stream, or into separation zone of the second step of contact. Hydrocarbon stream is fed into contour of circulation of liquid phase of the second step of contact before and (or) after zone of heat supply at ratio from 3:1 to 1:3, respectively. EFFECT: improved efficiency of the method. 2 cl, 3 dwg