To produce polymer-grade propylene from ethylene and butenes using Lummus’ olefins conversion technology (OCT). This technology can be used with a variety of C4 streams, including the mixed C4s produced in steam cracking, raffinate C4s from MTBE or butadiene extraction, and C4s produced in FCC units.
Two chemical reactions take place in the OCT process: propylene is formed by the metathesis of ethylene and butene-2; and butene-1 is isomerized to butene-2 as butene-2 is consumed in the metathesis reaction.
Ethylene feed plus recycle ethylene are mixed with the butenes feed plus recycle butenes and heated (1) prior to entering the fixedbed metathesis reactor (2). The catalyst promotes the reaction of ethylene and butene-2 to form propylene, and simultaneously isomerizes butene-1 to butene-2. The beds are periodically regenerated using nitrogen-diluted air. The ethylene-to-butene feed ratio to the reactor is controlled at a value to minimize C5 + olefin byproducts and maintain the per-pass butene conversion.
The reactor product is cooled and sent to the ethylene column (3) to remove ethylene for recycle. A small portion of this recycle stream is purged to remove methane, ethane and other light impurities from the process. The ethylene column bottoms is fed to the propylene column (4) where butenes are separated for recycle to the reactor and some is purged to remove butanes, isobutylenes and heavies from the process. The propylene column overhead is ultra-high-purity, polymer-grade propylene product.
This process description is for a stand-alone OCT unit that can be added into any refining/petrochemical complex. The utility requirements which include cooling water, steam, electricity, fuel gas, nitrogen and air—are typically integrated with the existing complex. The process may also be integrated into a grassroots cracker project to either reduce equipment sizes, capital cost and energy requirements; or to increase propylene-to-ethylene ratio to as high as 1.1:1.
Licensor: Lummus Technology