A refinery study of FCC vs Gasolfin for naphtha cracking into propylene (ERTC)
European refineries have experienced challenging market conditions over the past decade. Between 2008 and 2013, European refining capacity decreased by 3 mbpd or 15% of its total capacity, and between 2011 and 2016 Europe’s largest refiner, Total, slashed its European refinery capacity by 20%.
Bart de Graaf, Ray Fletcher and Herman van den Bold
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During the same period, refining capacity in North America increased from 17.6 mbpd in 2008 to 18.4 mbpd in 2016, with refinery utilisation rates increasing from 83% to nearly 90%.1
There were several factors contributing to this shift, including excess global refining capacity, shifting fuel demand patterns (and fewer gasoline exports to the US), relatively high costs and regulatory burdens at both national and EU levels. But probably the most important contributing factor was a lagging European demand due to slow recovery from the economic crisis. Fortunately, there are early indications of recovery, with oil demand showing a strong increase, especially in Central and South East Europe. This stems from local economic development as refineries in this part of Europe concentrate on supplying local markets and are less oriented on fuel exports, especially to the US.
An additional global trend is an increasing focus on petrochemicals. The global growth of propylene is projected to increase by 4.5% in the next few years compared with the projected fuel consumption increase in the automotive sector of 0.9% per year for the foreseeable future.3
For this purpose, a European refinery has performed a study on maximisation of propylene due to its long-term strategic goal of shifting from a fuel-based refinery to supplying petrochemical facilities. This will be achieved by either an increase in FCC severity with the use of ZSM-5 additive or by adding a separate conversion unit for post-processing of the FCC naphtha, the Gasolfin process as developed by InovaCat. For this study, the refiner sent FCC naphtha to be processed in a dedicated pilot plant at CPERI laboratories in Thessaloniki, Greece. Although no details of the economics can be presented as yet, the results clearly favoured the post-processing of naphtha in a separate conversion unit. It must be noted that this result was obtained without taking into account optimisation of all naphtha-range products available in this refinery, including light straight-run and delayed coker naphtha.
For this study, three different catalytic systems were tested in the pilot plant. The catalytic system for Gasolfin consists of a dehydrogenation catalyst and a cracking component. FCC naphtha contains a substantial concentration of olefins. This changes the concentration profile in the fixed-bed reactor system between both catalytic components. Initially, it was assumed that due to the presence of olefins less dehydrogenation catalyst would be required. Surprisingly, pilot plant studies showed that when the cracking component is the minority component of the catalyst blend, this favours the stability of the system, increases cycle length, and improves the selectivity towards LPG olefins over the formation of light gases.
In this study, the latest generation of Gasolfin catalysts have been employed. In prior studies, propylene yields up to 28 wt% have been obtained. In this study, throughout the cycle length, all three catalytic systems showed around 40 wt% propylene selectivity (on naphtha feed basis, including the non-reactive aromatics in the feed. When excluding the aromatic content propylene selectivities, up to 50 wt% is observed).
Propylene yield for these catalytic systems is 40% higher than in the first generation of Gasolfin catalysts, thus highlighting the optimisation potential in the catalytic system. Separately, the propylene selectivity approaches a linear dependency on the presence of the cracking catalytic component of the catalytic system. These selectivities are substantially higher than the 5-8 wt% propylene yield observed in the standard FCC unit or the 17% propylene typically observed in conventional naphtha steam cracking. Major improvements in the catalytic system stem mostly from improved selectivities of the dehydrogenation catalysts, reducing the aromatic by-products when operating in propylene mode.
Some considerations in the economic evaluation are: why do the economics show a clear preference for a separate conversion unit over maximising the propylene yield in the FCC unit? Although this is refinery specific, a refinery operating in a gasoline market will most often maximise profit via operation of the FCC unit in maximum gasoline mode. Combining the flexibility to operate the FCC unit at maximum charge rate with optimised motor fuels production plus the ability to shift production propylene (or butylenes for alkylation feed) to a second unit (Gasolfin) offers the refiner an additional degree of freedom. This mode of operation frequently releases existing FCC constraints.
This study shows the potential of adding an extra degree of freedom in the operation of a fuel-based refinery desiring to shift towards an integrated petrochemical platform. The most surprising result of this study next to the 50% propylene selectivity in naphtha cracking is that the simple payout of the additional capital expenditure is less than 18 months of operation.
Did you know: Inovacat invented the first catalytic process that directly converts gasoline into petrochemicals?
This short article originally appeared in the 2017 ERTC Newspaper, produced by PTQ / DigitalRefining.
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