Olefin plant recovery system employing catalytic distillation

A method for treating a thermally cracked feedstream containing the hydrogen, methane, ethylene, propylene, acetylene, methyl acetylene, propadiene and other C.sub.4 and C.sub.5 and heavier unsaturated hydrocarbons produced in said thermal cracking to separate said ethylene and propylene, to saturate at least a portion of said acetylene, methyl acetylene, propadiene and C.sub.4 and C.sub.5 and heavier unsaturated hydrocarbons and to consume a portion of the hydrogen contained in said feedstream without the prior separation of said hydrogen therefrom and comprising the steps of:

• a. introducing said feedstream to a first distillation reaction column and concurrently
• (i) selectively hydrogenating at least a portion of said acetylene, methyl acetylene, propadiene and C.sub.4 and C.sub.5 and heavier unsaturated hydrocarbons while maintaining a high ratio of the total of the C.sub.4 and C.sub.5 hydrocarbons to the total of the C.sub.2 and C.sub.3 hydrocarbons in said first distillation column and without any substantial hydrogenation of said ethylene and propylene;
• and
• (ii) separating by fractional distillation said C.sub.4 and lighter hydrocarbons from said C.sub.5 and heavier hydrocarbons;
• b. removing substantially all of said hydrogen and C.sub.4 and lighter hydrocarbons as overheads and substantially all of said C.sub.5 and heavier hydrocarbons as bottoms from said distillation reaction column;
• c. separating said hydrogen from said C.sub.4 and lighter hydrocarbons in said overheads;
• and
• d. processing said overheads less said hydrogen to recover ethylene and propylene.

A method for treating a thermally cracked feedstream containing the hydrogen, methane, ethylene, propylene, acetylene, methyl acetylene, propadiene and other C.sub.4 and heavier unsaturated hydrocarbons produced in said thermal cracking to separate said ethylene and propylene, saturate a portion of the other unsaturates and consume a portion of the hydrogen without the prior separation of said hydrogen therefrom and comprising the steps of:

• a. introducing said feedstream to a distillation reaction column and concurrently
• (i) selectively hydrogenating at least a portion of the acetylene, methyl acetylene, propadiene and C.sub.4 and heavier unsaturated hydrocarbons while maintaining a high ratio of the total of the C.sub.4 and C.sub.5 hydrocarbons to the total of the C.sub.2 and C.sub.3 hydrocarbons in said first distillation column and without substantially hydrogenating said ethylene and propylene and
• (ii) separate by fractional distillation the C.sub.4 and lighter hydrocarbons from the remainder of the hydrocarbons;
• b. removing substantially all of the hydrogen and C.sub.4 and lighter hydrocarbons as overheads and all of the C.sub.5 and heavier hydrocarbons as bottoms from said distillation reaction column;
• c. separating the hydrogen from the C.sub.4 and lighter hydrocarbons in said overheads;
• d. feeding the overheads less said hydrogen to a demethanizer distillation column wherein methane is separated as overheads from the C.sub.2 and heavier hydrocarbons which are taken as bottoms;
• e. feeding the bottoms from the demethanizer to a deethanizer distillation column where the C.sub.2 hydrocarbons are separated as overheads from the C.sub.3 and heavier hydrocarbons which are taken as bottoms;
• f. feeding the overheads from the deethanizer to an ethylene/ethane distillation column where the ethylene is taken as overheads and the ethane is recovered as bottoms;
• g. feeding the bottoms from the deethanizer to a depropanizer distillation column where the C.sub.3 hydrocarbons are separated as overheads from the C.sub.4 hydrocarbons which are taken as bottoms;
• and
• h. feeding the overheads from the depropanizer to a propylene/propane distillation column where the propylene is taken as overheads and the propane is recovered as bottoms.

A method of processing a thermally cracked feedstream containing hydrogen, ethylene, propylene, and other C.sub.2, C.sub.3, C.sub.4 and heavier unsaturated hydrocarbons, to hydrogenate at least some of said unsaturated hydrocarbons with said hydrogen contained in said feedstream without hydrogenating said ethylene and propylene comprising the steps of:

• a. introducing said feedstream into the feed zone of a distillation reaction column containing a distillation stripping zone below said feed zone and a combination distillation rectifying and catalytic reaction zone above said feed zone;
• b. concurrently
• (i) contacting said feedstream in said distillation reaction column with a vertically oriented bed of hydrogenation catalyst in said combination distillation rectifying and catalytic reaction zone;
• (ii) maintaining hydrogenation conditions within said bed of hydrogenation catalyst including a high ratio of the C.sub.4 and heavier hydrocarbons to the C.sub.2 and C.sub.3 hydrocarbons whereby said ethylene and propylene remain essentially un-hydrogenated and essentially all of said other C.sub.2, C.sub.3, and C.sub.4 and heavier unsaturated hydrocarbons are hydrogenated;
• (iii) fractionating the resulting mixture of hydrogenated and un-hydrogenated products;
• (iv) recycling heavy materials from the stripping zone to the top of the enriching zone or to the top of the catalytic reaction zone or both in order to increase the temperatures in these zones and to provide additional unsaturates to be hydrogenated;
• c. withdrawing an overhead stream containing essentially all of the said C.sub.2, C.sub.3, and C.sub.4 hydrocarbons and a portion of the heavier hydrocarbons and a bottoms stream containing the remaining portion of the heavier hydrocarbons;
• and
• d. processing said overhead stream to recover ethylene and propylene.

A method of processing a thermally cracked charge gas containing the hydrogen, ethylene, propylene, and other C.sub.2, C.sub.3, C.sub.4 and heavier unsaturated hydrocarbons produced in said thermal cracking to separate said ethylene and propylene from at least some of said other unsaturated hydrocarbons and to hydrogenate at least some of said other unsaturated hydrocarbons with said hydrogen contained in said charge gas without the prior separation of said hydrogen therefrom and without significantly hydrogenating said ethylene and propylene comprising the steps of:

• a. introducing said charge gas into the feed zone of a distillation reaction column containing a distillation stripping zone below said feed zone and a combination distillation rectifying and catalytic reaction zone above said feed zone;
• b. concurrently:
• (i) contacting said charge gas in said distillation reaction column with a vertically oriented bed of hydrogenation catalyst in said combination distillation rectifying and catalytic reaction zone;
• (ii) maintaining a high ratio of the total of C.sub.4 and heavier hydrocarbons to the total of the C.sub.2 and C.sub.3 hydrocarbons at the bottom of said vertical oriented bed of hydrogenation catalyst whereby said ethylene and propylene remain essentially un-hydrogenated and at least some of said other unsaturated hydrocarbons are hydrogenated;
• (iii) fractionating the resulting mixture of hydrogenated and un-hydrogenated products;
• c. withdrawing an overhead stream containing essentially all of said C.sub.2, C.sub.3 and C.sub.4 hydrocarbons and a portion of said heavier hydrocarbons and a bottoms stream containing essentially all of the remaining heavier hydrocarbons;
• and
• d. processing said overhead stream to recover ethylene and propylene.