by Tim Foley
The expansion of shale gas extraction and production of associated natural gas liquids (NGLs) is creating new opportunities in the petrochemical industry. NGLs production growth, especially in the US, is resulting in a lower price structure for these raw materials. This is evidenced in the several recently announced propane dehydrogenation and NGLs steam cracking projects in the US. Likewise, cost advantaged NGLs enable the economic production of aromatics from unconventional feedstock.
Cyclar Unit Flow Diagram
The Cyclar Process, produces petrochemical grade aromatics and hydrogen from propane and butane (NGLs) feedstock in a single operating unit. The Cyclar product can be used to directly feed an aromatics complex for the production of para-xylene and benzene. The Cyclar product is also suitable as a high octane gasoline blending component. Further, only fractionation is necessary to produce high purity benzene, toluene and mixed xylenes avoiding the substantial additional costs associated with solvent extraction which is required to purify reformate based aromatics.
The Cyclar process employs a series of reactions, collectively termed “dehydrocyclodimerization,” to produce a mixed aromatics stream from propane and/or butane feeds. The first reaction, the rate limiting step, is the dehydrogenation
of the paraffin feed to mono-olefins. At reaction conditions, olefins then quickly oligomerize to form large intermediates which rapidly cyclize to naphthenes. The final step is then the dehydrogenation of naphthenes to aromatics.
Because the net reactions are endothermic, multiple reaction stages, with interstage reheating, are used to achieve high per pass conversions while maintaining high selectivity to aromatics. The Cyclar process makes use of UOP’s Continuous Catalyst Regeneration (CCR) technology which removes coke, a reaction byproduct, from the catalyst and also reconditions the catalyst. The result is a stable long term operation.
The reaction products are a mixed aromatics stream and a significant amount of byproduct hydrogen. The composition of the mixed aromatics will change slightly over the possible range of feeds, from 100% propane to 100% butane and mixtures in between, while the yield of hydrogen is relatively constant. The mixed aromatics product has very low paraffin content, such that the benzene, toluene, and mixed xylenes can be recovered without the need for an extraction unit. Alternatively, the Cyclar product can be sent to an aromatics complex for the conversion of toluene and xylenes to p-xylene and benzene, valuable petrochemical precursors.
Cost advantaged NGLs can be converted to high value base chemicals using the Cyclar process. The yield of aromatics will be between 58-60 Wt%, varying slightly with feed composition. An additional benefit is the yield of approximately 5 Wt% of hydrogen, which can be recovered at very high purity if desired. The first application of the technology was a 1,000 barrel per day (BPD) unit in Scotland.
The second commercial unit was designed at ~45,000 BPD and has operated in
the Middle East from the year 1999 through 2013.