(139c) A Reactive Distillation Process for Separation of Propylene-Propane Mixtures

Propylene has been historically produced as a by-product of ethylene in the refinery gas oil or naphtha steam-cracking process, or as a by-product of motor gasoline in the fluid catalyst cracking (FCC) process.  Prior to 2005, propylene market supply/demand was in balance and no on purpose production of propylene was necessary.  However, the propylene market has continued to expand and traditional refinery-based modes of co-production can no longer meet demand.  Global consumption of propylene in 2012 was about 79 million metric tons per year (MMTA) with growth at 7% annually. It is estimated that US production of propylene must increase by 2 million tons per year by 2020 to meet the increasing demand. Expanded shale gas production in North America has recently sent a supply shock throughout the world energy picture, and is beginning to transform the global ethylene and propylene markets.  Production of ethylene by steam cracking of naphtha or gas oil is becoming non-competitive, and U.S. producers are shifting their steam crackers to lighter feedstock such as shale gas-derived liquids.  Energy-efficient separation and recovery of high-purity propylene is a crucial step in its on-purpose production.       

The design study in this project focuses on the development of a novel, reversible reaction-based process to separate and recover propylene from propylene/propane mixtures in on-purpose propylene production. Separating light olefins from paraffinic feed stocks by conventional distillation is highly energy and capital intensive because of small boiling points differences. In order to improve energy efficiency and reduce capital, alternate separation processes have been developed and implemented.  This design study focuses on an advanced reactive distillation concepts including heat integration and side reactors. In the process, propylene is hydrated to form isopropanol or esterified to form an isopropyl ester that is immediately separated from propane. The reverse reaction regenerates propylene of high purity.