What are the latest advances in FCC SOx reduction, and what levels can be achieved?

Responses to a question in the Catalysis 2021 Q&A feature

Various from BASF Catalysts, Johnson Matthey, & W R Grace & Co.

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Article Summary

Colin Baillie, Segment Manager, Environmental Additives, W. R. Grace & Co - Colin.Baillie@Grace.com

SOx reduction additives have long been recognised as a highly reliable and cost-effective option for controlling FCC SOx emissions. They are particularly suited for full-burn applications, where extremely low levels of SOx (<5 ppm) and high levels of SOx reduction (>98%) can typically be achieved with additive usage of less than 10% of fresh FCC catalyst rates. Although partial burn applications are more challenging due to the lack of oxygen being a rate-limiting step, high levels of SOx reduction beyond 60% can still be achieved.

The latest advance in FCC SOx reduction is the launch of the EMISSCIAN SOx additive. This was the culmination of an extensive research and development programme from Grace that included a multi-million dollar investment in SOx additive manufacturing facilities and the introduction of a new processing step. The new process modification results in a more homogeneous distribution of cerium and vanadium across the additive particle, as well as an optimised magnesium aluminate spinel content. These improved features increase the effectiveness of the SOx additive, meaning that SOx emissions can be maintained at lower additive usage rates, or if additive usage rate is maintained then SOx emissions can be reduced further. The EMISSCIAN SOx additive has gained significant momentum in the market with more than 10 refiners switching from alternative products to this new technology.

These recent successful case studies for the EMISSCIAN SOx additive versus competitor additives have been in both full and partial burn applications. For example, a full burn application in North America saw SOx emissions drop from ca. 20 ppm to 10 ppm while also using a lower additive rate, whilst a partial burn unit in Europe saw the percentage SOx reduction increase from 50% to >55% at a constant additive addition rate.

While other companies have begun to focus on investing in emerging technologies that include next generation battery materials, as well as technologies for producing hydrogen and fuel cell components, Grace remains committed to developing new FCC additive technologies for the refining industry. To highlight this, we are making another significant capital investment in our SOx additive manufacturing facilities in 2021, as we continue our research and development activities to develop the next generation of additive technologies.


Hernando Salgado, Technical Service Manager, BASF Catalysts - hernando.salgado@basf.com

There are several methods to effectively reduce SOx emissions in an FCC unit, such as feed hydrotreatment, wet gas scrubbers, and SOx reduction additives. While the first two solutions can reduce the emission by 70-95%, they also involve considerable investments and operating costs. On the other hand, the use of a SOx reduction additive, such as BASF EnviroSOx, is a cost-effective solution that can be applied when a moderate reduction is required.

EnviroSOx can capture SOx by using a MgO based material with enhanced retention, in order to maintain its SOx capturing abilities longer than other SOx reduction additives. In addition, a Ce based compound is added to promote oxidation from SO2 to SO3, together with V2O5 which assists to achieve a full regeneration of the MgO. As can be implied, the combustion mode of the unit is one of the factors affecting the additive performance; since nearly 90% of SOx is SO2 and a certain O2 excess is needed for it to be converted to SO3, partial burn units are more challenging.

Specifically, EnviroSOx has been successfully applied in a broad range of uncontrolled SOx concentrations in the flue gas up to 7000 mg/Nm3, either in full or partial burn units. One of the main parameters to monitor the additive performance is the pickup factor (PUF), defined as the amount of SOx captured per mass of additive, expressed in kg-SOx per kg-additive. In the case of EnviroSOx, the PUF can vary from 15 to 80, achieving SOx reduction rates up to 90%, with an average of 40-75%, depending on the specific process conditions and additive dosage in every FCC unit. Some examples of using EnviroSOx in FCC units are presented in Table 1.


Hongbo Ma, Technical Service Engineer, Additives, Johnson Matthey - Hongbo.Ma@matthey.com; Carl Keeley, Regional Sales & Key Account Manager – Refineries, Johnson Matthey - Carl.Keeley@matthey.com; Wayne Armstrong, Head of Commercial Sales, Johnson Matthey - Wayne.Armstrong@matthey.com.

Fluid catalytic cracker (FCC) feed contains sulphur compounds. In the riser, the feed is converted to products and coke. Part of the feed sulphur deposits in the coke on the catalyst. The catalyst is regenerated in the regenerator. In a full burn regenerator, the sulphur is oxidised to sulphur oxides (SOx). In a partial burn regenerator, where oxygen availability is limited, part of the sulphur is converted to reduced sulphur species (carbonyl sulphide, for instance). Dedicated SOx additives are needed for each situation. Johnson Matthey’s R&D has developed SOx additives specifically tailored for each application.

In full burn operation, a high concentration of sorbent is needed to capture sulphur trioxide. Johnson Matthey’s latest development has the highest concentration of sorbent available.

In partial burn, where oxygen availability is limited, a specific oxidation package is needed to maximise the conversion of sulphur to sulphur trioxide – without disturbing the CO/CO2 balance.

To control SOx emissions, refineries can reduce feed sulphur, use SOx additives, use a scrubber, or employ a combination of these. Refineries that have scrubbers can take advantage of SOx additives to reduce operating costs and reduce caustic consumption and waste handling problems.

Based on the experience of our customer base, a SOx reduction level of >90% can be achieved in full burn operation. However, in partial burn operation, where oxygen availability is limited, SOx reduction is less. SOx reduction depends on the depth of partial burn (see Figure 1). The SOx reduction shown in the plot is based on SOx concentration in the CO boiler flue gas, not the regenerator flue gas.

In addition to different regenerator types, some FCC units target maximum distillate production and operate with a low riser top temperature, for instance <950°F (<510°C). Consequently, sulphur release in the stripper is more challenging. Sulphur release is also more challenging in units with poor stripper design or performance. Johnson Matthey has optimised SOx additive release functionality to improve sulphur release in these units.

Johnson Matthey has dedicated products for each situation and continues to develop improved products for unique FCC challenges.

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