Feb-2021

Boosting profitability in a maximum propylene FCC

Refiner and supplier collaborated to evaluate, prepare, and execute the revamp of an FCC and an LPG olefins additive trial.

BERTA ARAMBURU LOPEZ-ARANGUREN, ELENA PEREZ GUEVARA, MIGUEL ARJONA and ELOISA SERRANO, CEPSA
MODESTO MIRANDA LOPEZ and MELISSA CLOUGH MASTRY, BASF

Article Summary

The CEPSA La Rábida refinery operates a maximum propylene fluid catalytic cracking (FCC) unit. This FCC is highly integrated with the rest of the refinery, which mainly produces fuels, asphalts, and petrochemical products. The FCC unit often runs a mixture of unconverted oil (UCO) and vacuum gasoil (VGO).
 
The revamp project
The La Rábida refinery and BASF Refining Catalysts have a long history of collaboration and continuous improvement. In a previous effort, the refinery and BASF jointly evaluated the then-new Zip additive for the La Rábida application. The result was a successful implementation of the Maximum Propylene Solution (MPS) catalyst technology and its long-term use at the refinery.1 MPS allowed the refinery to achieve high levels of propylene, up to the handling limits of the unit. The FCC was often constrained downstream with the refinery’s liquified petroleum gas (LPG) processing capacity. For this reason, the La Rábida refinery decided to investigate the potential profitability of a revamp to increase its LPG handling capacity.

In addition to utilising its own technical workforce, CEPSA regularly works with the BASF technical service team to ensure that their assets run in the most profitable manner. In order to evaluate the revamp potential, both CEPSA and BASF conducted extensive simulations to forecast future scenarios in order to find an optimum between minimum investment and maximum profitability. It was determined that a revamp to increase the LPG handling capacity could be profitable for the refinery and a formal project was started.

The turnaround ended up being more challenging and complex than expected. In order to alleviate some of the unexpected difficulties, BASF designed a customised on-site training course dedicated to emergency shutdown procedures, work preparation processes, and new project start-ups. Later, during the turnaround itself, BASF provided on-site advice and jointly discussed the inspection reports to ensure a successful, safe, and on-time project completion. Finally, in order to meet the gap of the then-current and the to-be scenarios, in which additional propylene could be handled, BASF offered a new technology to achieve the expected results from the La Rábida FCC.

High activity additive
BASF introduced CEPSA to its latest offering: the Zeal LPG olefins additive. Compared to the Zip additive that CEPSA was using at the time, Zeal was expected to generate 10% higher propylene at the same additive dosage, coming from the higher inherent activity of the additive. Figure 1 shows that Zeal is able to deliver higher propylene than the Zip LPG olefins additive at the same dosage rate.

Zeal is the result of R&D work focusing on a higher activity additive. It brings the benefits of Zip by following a similar manufacturing process to ensure additive activity and integrity, while boosting activity even higher. Higher activity is ideal for refiners and operators of FCCs, especially those in the maximum propylene segment and those with a high degree of integration into chemical plants, to find an optimal balance between additive loading and catalyst activity. Zeal is particularly advantageous when a refinery is adding the olefins additive from a hopper separate from the catalyst’s. In some FCCs, when an LPG olefins additive is supplied from a separate hopper, it becomes a diluent to the fresh catalyst, which is providing both LPG and gasoline precursors that are further converted with ZSM-5, and lowers the overall activity of the catalyst circulating in the inventory. Therefore, some refineries reach a limit in the amount of olefins additive they can add to the FCC in order to avoid the dilution effect of the base catalyst. Refineries that are operating close to the limit of the maximum additive concentration in the inventory can adopt Zeal. The new additive can be added at equivalent loading versus any incumbent additive or, in the extreme case where the refinery is already limited by the dilution effect, it can be added at a lower dosage rate while still achieving the same LPG yields. This can represent an important debottleneck to some refineries.

In addition, the in-situ manufacturing nature of BASF catalysts allows the MPS catalyst to be formulated in such a way that prevents the loss of activity when combined with olefins additives like Zip or Zeal. This was the case for the CEPSA La Rábida refinery, in which it is critically important to maintain catalyst activity at a high level. Therefore, the MPS catalyst not only includes a high activity LPG olefins additive, but delivers high catalytic cracking ability for the feed as well.

Additive testing and validation
Prior to commencing any new product trial, CEPSA R&D plans and executes a thorough and detailed laboratory evaluation.2 In a previous collaboration between CEPSA and BASF, the refiner fine-tuned the deactivation conditions needed for an FCC focused on maximum propylene.2 In a previous joint publication, CEPSA described that 1) longer deactivation times for ZSM-5 additives and 2) steam deactivation instead of deactivation involving metals were the most suitable for mimicking conditions for its refinery and equilibrium catalyst. Instead of trying to match the physical properties of equilibrium catalyst, the CEPSA laboratory aims to mimic equilibrium catalyst performance, including yield selectivities and octane response. In taking this approach, CEPSA ensures that data generated in the laboratory are the most representative of what will happen in the FCC unit.

In this recent example, BASF supplied the CEPSA laboratory with a Zeal sample. The laboratory deactivated the sample under the conditions described previously and tested it with the base MPS catalyst against the Zip additive at constant additive loading. In this evaluation, the Zeal additive gave 6% higher propylene on a relative basis, with results from CEPSA closely matching the results from BASF (see Figure 2).

The predictions showed that CEPSA’s revamp expectations and ability to handle more propylene could be fulfilled with the new technology by delivering higher LPG olefins and in particular higher propylene. After carefully evaluating the laboratory results alongside the revamp expectations, the refinery decided to trial the new product. The targets to secure a successful trial were clearly defined by CEPSA: at the same additive loading (Zip versus Zeal) and similar conversion levels, the Zeal product was expected to deliver 6-10% higher propylene yields while keeping other variables constant. A trial plan was jointly prepared and executed.

FCC refinery trial
The trial started at the end of 2019. During the trial, the feed quality changed significantly. As a result, the equilibrium catalyst became severely contaminated with sodium coming in with the feed. Sodium is a well-known poison for the active zeolite in an FCC catalyst, particularly USY zeolite, and has an irreversible effect. Therefore, with the change in feed quality, conversion in the unit also suffered and was lowered significantly. In addition to the increase in sodium, the furfural extracts stream was eliminated from the feed diet. In order to close the heat balance due to this change, slurry recycle was introduced. In summary, the feed diet was significantly changed during the trial, making monitoring of the trial much more complex. A summary of the main operating changes is shown in Table 1.