Method for manufacture of isoprene

Claim 1

IN A PROCESS FOR THE MANUFACTURE OF ISOPRENE FROM A C5 PARAFFIN HYDROCARBON BY DEHYDROGENATION OF THE LATTER, THE IMPROVEMENT WHICH COMPRISES INTRODUCING A MIXTURE CONSISTING ESSENTIALLY OF BRANCHED AND STRAIGHT CHAIN C5 PARAFFIN HYDROCARBONS INTO A REACTION ZONE UNDER CONDITIONS FAVORABLE TO THE DEHYDROGENATION OF SAID HYDROCARBONS AND TO THE ISOMERIZATION OF THE OLEFINS RESULTING THEREFROM, CONTACTING SAID MIXTURE IN SAID ZONE WITH A COMPOSITE MASS CONSISTING ESSENTIALLY OF A CHROMIACONTAINING DEHYDROGENATION CATALYST AND PLATINUM-DERIVED ISOMERIZATION CATALYST, WITHDRAWING A PRODUCT MIXTURE CONTAINING A 2-METHYLBUTENE FROM SAID ZONE, RECOVERING FROM SAID PRODUCT MIXTURE BY EXTRACTION WITH AN AQEOUS SULFURIC ACID SOLUTION AN EXTRACT STREAM CONSISTING ESSENTIALLY OF A 2-METHYLBUTENE SAID A RAFFINATE STREAM CONSISTING CHIEFLY OF PARAFFINS AND STRAIGHT CHAIN OLEFINS, RECYCLING SAID RAFFINATE STREAM TO SAID DEHYDROGENATION-ISOMERIZATION REACTION ZONE NEXT BRINGING SAID EXTRACT STREAM INTO CONTACT WITH A CHROMIA-CONTAINING DEHYDROGENATION CATALYST IN A SECOND REACTION ZONE UNDER CONDITIONS FAVORABLE FOR THE DEHYDROGENATION OF SAID 2-METHYLBUTENE TO ISOPRENE, WITHDRAWING THE RESULTING PRODUCT MIXTURE CONTAINING ISOPRENE AND MONO-OLEFINS, RECOVERING ISOPRENE THEREFROM, AND RECYCLING SAID MONO-OLEFINS TO SAID SECOND REACTION ZONE.