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Aug-2018

Maximising propylene and isobutylene from the FCC

A combination of recent catalyst and additive developments raised a refinery’s output of FCC propylene and isobutylene.

VALENTIN NILCA, ADRIAN IONUT TUDOSE and TIBERIU CRUDU, KMG Rompetrol
LJUBICA SIMIC and MARIA LUISA SARGENTI, Grace
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Article Summary
KMG Rompetrol is addressing current market challenges through a strategy of downstream integration with petrochemicals, taking advantage of the flexibility that the FCC unit offers for maximum light olefins production. In this article, KMG Rompetrol and Grace provide an overview on how refineries can increase the profitability of their FCC operation by maximising the production of propylene and isobutylene using the latest FCC catalyst and additive technology. Achieve technology from Grace has contributed to sustaining the refinery’s profitability and improving its competitive position in the marketplace. This technology has resulted in yields of 11 wt% propylene, which ranks the refinery’s FCC unit among the top five propylene producers in the EMEA region.

Introduction
Maximisation of propylene production has become the focus of many refineries because propylene consumption continues to grow and there is a supply shortage, resulting in a supply-demand gap. Demand for propylene is driven mainly by the global polypropylene industry, which has seen historical growth of 5.0-6.0%/year.1 As Figure 1 shows, by 2035, petrochemical products will account for almost 50% of the expected growth in demand for crude oil based products, of which a significant portion will be propylene.

In Asia-Pacific (and to a large but slightly lesser extent in the EMEA region) propylene demand is high; therefore, many refineries that have the potential to produce more propylene are enjoying a competitive edge in the industry. There are different ways for refineries to increase production of light olefins, for example through a revamping and debottlenecking of the entire FCC unit. However, using the latest catalyst and additive technology offers a reliable, quick, and flexible route.

KMG Rompetrol unit and operating focus
KMG Rompetrol operates two production facilities: Petromidia, consisting of a refinery and a petrochemical complex, as well as the Vega refinery. Petromidia is located in Constanta close to the Black Sea, which gives the company several strategic advantages. Petromidia refinery’s Nelson Complexity Index is 10.5 and it usually processes Ural crudes but also blends with other crudes such as Kirkuk, Azeri, and Siberian. The FCC unit is a 24 000 b/d UOP side-by-side design and processes 100% hydrotreated feed from a mild hydrocracking unit (see Figure 2).
 
Solomon benchmark related figures
Every two years, Rompetrol Rafinare participates in the Solomon Worldwide Fuels Refinery Performance Analysis (Fuels Study) and the information shown in Figures 3 and 4 illustrates the conversion units’ performance.

Figure 3 highlights FCC unit performance related to the first quartile/second quartile break (black line), and with respect to the world’s top 10% of performers (green line). FCC unit performance is based on Solomon methodology using a correlation between dynamic activity (measure of catalyst performance) and Feed UOP K Factor. The graph demonstrates that the Rompetrol FCC unit (red dot ‘2016’) is placed in the first quartile and close to the world’s top 10% of performers.

This gap in yield performance, as measured by a dynamic activity gap compared to the world’s top 25% of performers, can then be translated into a gap in product yields and then into a gap in $/bbl. Figure 4 shows that in both the 2014 and 2016 Solomon Fuels Studies, the Rompetrol FCC unit is placed at the border between the first and second quartiles from a total of approximately 300 FCC units.

In Figure 4, each FCC unit is placed in one of the four quartiles (the red colour represents the fourth quartile and the green colour represents the first quartile).

Improved performance through FCC catalyst optimisation
The refining market is more global and more competitive than ever, and Grace recognises the importance of providing value through new product development. The KMG Rompetrol and Grace teams have worked closely together, to better identify refinery opportunities as well as to understand challenges and limitations in more depth, which has been essential for overall success. The following objectives were identified as the main drivers to help increase FCC unit profitability:2
• Maximum propylene yield (minimum 10 wt%)
• Maximum isobutylene yield 
• Maximise LCO
• High RON
• Higher delta coke
• Minimise dry gas.

Maximum propylene is driven by demand from the nearby petrochemical plant, while maximum isobutylene is highly desired to boost MTBE unit capacity. Grace executed a rigorous process to qualify and verify selected catalyst performance, including ACE pilot plant testing, which minimises the financial risk associated with unsuccessful catalyst trials in the unit.3,4

Based on extensive ACE pilot plant testing utilising a representative feedstock from KMG Rompetrol Petromidia refinery, various new catalyst formulations were screened versus the base catalyst. This enabled Grace to identify a combination of the Achieve 100 catalyst and OlefinsUltra HZ light olefins additive as the leading formulation to provide optimum performance in terms of the desired operating targets. Figure 5 shows that this catalyst system resulted in significantly higher propylene and isobutylene yields, as well as higher LCO and lower slurry (decanted oil), which demonstrates a clear improvement in bottoms upgrading.

Achieve and OlefinsUltra HZ technologies
The Achieve catalyst series comprises state-of-the-art technologies designed to maximise refinery profitability for a wide range of FCC feedstocks and yield objectives. When processing lighter feedstocks, insufficient catalytic activity requires that the catalyst circulation rate must increase so that conversion, and thus the coke yield from the catalyst increases to satisfy the FCC heat balance. If the FCC unit cannot physically circulate enough catalyst, it will be necessary to reduce the unit charge rate or the reaction severity to stay within the FCC catalyst circulation limit. Use of a high activity catalyst can counter the effects of low delta coke, highlighting the importance of selecting a catalyst with the proper coke selectivity (coke to conversion relationship).

Achieve 100 catalyst is designed for use with hydrotreated and light VGO feedstocks, with a low to moderate level of contaminant metals. Achieve 100 catalysts are formulated with ultra high activity zeolite to support conversion and counter the effects of low delta coke, while delivering the proper coke selectivity. The high diffusivity of the catalyst increases distillate yield, while an optimised rare earth exchange results in the required hydrogen transfer activity to balance LPG and gasoline production.

Launched in 2010, OlefinsUltra HZ additive is part of Grace’s OlefinsUltra family of propylene maximisation additives. The family includes additives for moderate to high propylene yields, and OlefinsUltra MZ additive for very high propylene yields.
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