February 3, 2014
Boost propylene yields from fluid catalytic crackers. Petroleum refineries are an increasingly important source of propylene for the petrochemicals business. As US-based steam cracker operators switch to inexpensive ethane for their feedstock, less and less propylene coproduct is produced.
Historically, refineries have been the major secondary source of propylene. Propylene is made in relatively small amounts, 5–6%, in fluidized catalytic crackers (FCCs). This may seem like little production, but the magnitude of the gasoline business makes refinery propylene a significant source of this petrochemical feedstock.
As propylene demand continues to outpace ethylene demand, propylene prices have risen relative to ethylene prices. These high prices make it attractive for refiners to increase revenues by intentionally making more propylene in their FCC units. Catalysts that can make >20% propylene in FCC units are now available.
L. Zheng and co-inventors found that adding a so-called inhibitor to FCC units can boost propylene selectivity to well beyond 20%. The inhibitor, hydrogen or a hydrogen donor, decreases the conversion of product propylene to other species under FCC conditions. In the patent’s examples, the inventors used the commercial zeolite MMC-2 as the catalyst and hydrogen or CO as the inhibitor.
In one example, vacuum gas oil was cracked in a once-through operation at 650 ºC and a reaction time of 1.8 s. Hydrogen was added in a H2/feedstock ratio of 0.0045:1. The propylene yield was 28.55 wt%. In a similar experiment with no inhibitor, the propylene yield was 23.14 wt%. (Research Institute of Petroleum Processing SINOPEC; China Petroleum & Chemical Corp. [Both in Beijing]. US Patent 8,608,944, Dec. 17, 2013; Jeffrey S. Plotkin)