Fluid cat cracking with high olefins prouduction

Abstract

The propylene production of a fluid catalytic cracking unit employing a large pore zeolite cracking catalyst, produces more propylene by adding a naphtha cracking riser and a medium pore zeolite catalytic component to the unit, and recycling at least a portion of the naphtha crackate to the naphtha riser. The large pore size zeolite preferably comprises a USY zeolite and the medium pore size is preferably ZSM-5. Propylene production per unit of naphtha feed to the naphtha riser is maximized, by using the 60-300.degree. F. naphtha crackate as the feed.

Description

FIELD OF THE INVENTION[0001] The invention relates to a fluid cat cracking process for high olefins production, using a combination of dual risers and a cracking catalyst containing both large and medium pore zeolites. More particularly, the invention relates to a fluid cat cracking process using a cracking catalyst having faujasite and ZSM-5 components, to produce reaction products comprising light olefins and naphtha in a first riser. At least a portion of the naphtha is recovered and passed into a second riser, in which it is catalytically cracked to produce more light olefins.BACKGROUND OF THE DISCLOSURE[0002] The demand for light olefins, such as propylene and butylenes, and particularly propylene, is increasing faster than present plant capacity. A major source of propylene is from fluid cat cracking (FCC) processes. Fluid cat cracking is an established and widely used process in the petroleum refining industry, primarily for converting petroleum oils of relatively high boilin...

AI Technical Summary

Benefits of technology

0003] The invention relates to a fluid cat cracking (FCC) process having increased production of light olefins, including propylene, using at least two risers feeding into a single separation-stripping vessel and a cracking catalyst comprising both large and medium pore, shape-selective zeolite components. The FCC feed is catalytically cracked to produce a crackate which comprises naphtha and propylene in a first riser, with recovery and recycle of at least a portion of the naphtha crackate as feed into a second riser, in which it is catalytically cracked into products comprising additional propylene. While the naphtha crackate passed into the second riser may comprise the entire C.sub.5-430.degree. F. boiling naphtha fraction in the practice of the invention, it has been found that more propylene-containing light olefins are produced per unit of the naphtha crackate feed passed into the second riser, by using the lighter, C.sub.5-.ltoreq.300.degree. F. fraction, which typically boils in the range of 60-300.degree. F. (15-149.degree. C.). While some heavier naphtha components boiling above 300.degree. F. may be present in the embodiment in which the feed to the second riser reaction zone comprises the light naphtha fraction, it is preferred that it be present in an amount of less than 50 wt. %, preferably less than 25 wt. % and still more preferably less than 10 wt. % of the naphtha feed. The large pore zeolite component is preferably a faujasite type and more preferably a Y type faujasite. The medium pore zeolite component is preferably a ZSM-5 type. It is also preferred that the catalyst contain a phosphorus component. In addition to the large and medium pore size zeolite components, the catalyst will also include at least one porous, inorganic refractory metal oxide as a binder. It is preferred that the binder have acid cracking functionality, for cracking the heavier components of the FCC feed and that the medium pore size zeolite component comprise at least 1 wt. % of the catalyst, on a total weight basis. In a particularly preferred embodiment, the large pore zeolite component will comprise an ultrastable zeolite Y, with a unit cell size no greater than 24.30 .ANG. and preferably no greater than 24.26 .ANG., and the medium pore zeolite will comprise ZSM-5. It is also preferred that the catalyst contain at least 0.5 wt. % phosphorus, typically present as P.sub.2O.sub.5. In one embodiment, which is a preferred embodiment, the catalyst will comprise particles comprising the large pore size zeolite, composited with a porous, inorganic refractory metal oxide binder and particles comprising the medium pore size zeolite, composited with a porous, inorganic refractory metal oxide binder. In another embodiment, the catalyst particles may comprise both the large and medium pore zeolite components composited with a porous, inorganic refractory metal oxide binder, in a single particle.

Problems solved by technology

Typical FCC cracking catalysts are based on zeolites, especially the large pore synthetic faujasites, such as zeolites X and Y. The olefins yield from the cracking reaction is limited by the process and cracking catalyst.

While it is possible to build a new FCC unit with additional risers and vessels for increased light olefins production, it is extremely costly to add additional vessels to an existing FCC unit.

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