Demand for our diesel has dipped. What process steps do you recommend for increasing gasoline make?

First published in PTQ Q4 2016

David Schwalje, Business Development Manager, Axens North America

With the fall of pump prices, US consumers have responded relatively quickly by increasing gasoline demand, which has led to increased gasoline crack spreads and incentives for refiners to switch from middle distillates to gasoline in the short term. This phenomenon has been especially true in markets affected by unexpected outages.

Aside from adjusting cut points in the crude unit, FCC, and hydrocrackers, refiners have a number of processing options to shift their diesel to gasoline ratio (D/G) to favour gasoline production. One solution for refiners with cat feed hydrotreaters (CFHT) or mild hydrocrackers (MHC) upstream of the FCC is to reduce severity in those units to reduce conversion of AGO and LVGO to middle distillates. This strategy coupled with decreasing the CFHT/MHC fractionator diesel end-point to maximise the amount of FCC feed can be an attractive method for cracking heavy diesel to light gasoline in the FCC. Consequently, a robust CFHT/MHC catalytic system is required for this operation to achieve adequate HDS of the FCC feed at lower severities. Alternatively, units equipped with a robust Prime-G+™ FCC gasoline post-treater can afford to let FCC gasoline sulphur increase temporarily without sacrificing excessive octane during the post-treatment process.

Hydrocracking severity can also be increased for those units with the capacity to handle the extra light ends make and ability to reform the additional paraffinic hydrocracked naphtha for pool blending. Typically, catalyst loading philosophies (maximum naphtha or maximum diesel loads) are selected every two to three years and therefore do not provide on-the-fly solutions.

Another interesting option is the use of Axens Polynaphtha & Polyfuel oligomerisation technologies for production of transportation fuels from FCC olefins. This catalytic process operates with a regenerable solid catalyst in carbon steel fixed-bed reactors to produce C6+ olefins with feeds as light as propylene and mixed butenes through C5 and C6 olefins. Reactor severity can be adjusted on the fly, allowing the refiner to fine-tune the product yield slate from 100% gasoline boiling olefins to 60% middle distillate boiling compounds, thus providing key flexibility to adjust to shifting margins.

The gasoline blendstock produced from Axens oligomerisation units fed by FCC olefins is typically in the range of 98 RON, making it an excellent blendstock. Axens oligomerisation technologies have been commercially proven in 20 operating units worldwide.

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