Production of middle distillate range hydrocarbons by light olefin upgrading

In the continuous process for upgrading lower olefin feedstock to higher hydrocarbons including the steps of combining olefinic feedstock with a pressurized liquid diluent stream comprising C.sub.5.sup.+ olefins, contacting the diluted feedstock with a shape selective medium pore acid zeolite catalyst under reaction conditions at moderate temperature in a pressurized reactor system comprising a series of catalytic reactor beds to convert olefins and recover reactor effluent at reaction conditions;

• the improvement which comprises:
• incrementally decreasing reactor temperature from a first reactor bed in the series to last reactor bed to promote oligomerization in the last reactor bed;
• separating reactor effluent in a primary phase separation zone to vaporize light and middle distillate hydrocarbon components into a first vapor phase stream and recover from the primary separation zone a heavy liquid recycle stream, said heavy liquid stream containing at least 50% of those C.sub.16.sup.+ hydrocarbons recovered in the reactor effluent;
• passing the heavy hydrocarbon recycle stream to said first reactor bed, maintained under conditions to degrade the heavy hydrocarbons;
• condensing a light portion of the first vapor phase stream by cooling and recovering from a secondary phase separating zone the dominant portion of a light olefinic recycle stream for further reaction in a lower temperature serial reactor bed to promote oligomerization, said light recycle stream comprising a major portion of C.sub.6 to C.sub.8 hydrocarbons recovered in the reactor effluent;
• and
• recovering an intermediate liquid product stream from the secondary separation zone to obtain a distillate product stream consisting essentially of substantially linear C.sub.9 -C.sub.16 aliphatic hydrocarbons.

A continuous process for upgrading lower olefin feedstock to higher hydrocarbons, comprising the steps of combining olefinic feedstock with a pressurized olefinic recycle stream, contacting the feedstock and recycle with a shape selective medium pore acid zeolite catalyst under reaction conditions at moderate temperature in a pressurized reactor zone to convert feedstock and recycled olefins recovering reactor effluent comprising C.sub.6 -C.sub.8 lower olefins, C.sub.9 -C.sub.16 light distillate hydrocarbons and heavy liquid hydrocarbons;

• separating reactor effluent to recover a first vapor phase stream and recover a heavy liquid recycle stream, said heavy liquid recycle stream containing a major portion of hydrocarbons in the reactor effluent normally boiling above 290.degree. C.;
• condensing a portion of the first vapor phase stream by cooling and recovering the dominant portion of C.sub.9 to C.sub.16 light distillate and an olefinic light hydrocarbon recycle stream for combining with the feedstock, said light recycle stream comprising C.sub.6 -C.sub.8 low boiling hydrocarbons recovered in the reactor effluent;
• and
• further fractionating the light distillate stream to obtain a product stream consisting essentially of substantially linear C.sub.9 to C.sub.16 aliphatic hydrocarbons.