Catalysis 2023 Issue

~22.1

~5.5

Spent catalyst Thermal ox.

Co & Mo mining/ processing

Bauxite mining/ processing

Fresh catalyst substrate mfr.

Fresh catalyst impregnation and nishing

Total for replacing spent with fresh

EcoMax TG

Fresh catalyst manufacture

Figure 1 Carbon footprint of tail gas catalysts

catalyst in this way reduces the refining industry’s depen - dence on freshly mined metals. Reusing tail gas treating catalysts Given the clear economic and environmental benefits of this tried-and-tested technology, what if it could be applied beyond hydroprocessing to Claus tail gas treating? That was the question posed against a backdrop of decades of experience in both hydroprocessing catalyst recovery and sulphur recovery catalysis. The result: a lower-cost catalyst offering the same level of performance has a lesser envi - ronmental impact and contributes to circularity and sus - tainability for refiners. Once a hydroprocessing catalyst has been successfully reactivated, the catalyst may be utilised in tail gas treat - ing processes as there are several similarities between the catalysts. Both applications generally make use of metals such as cobalt and molybdenum, supported by an alumina substrate. Moreover, in each case, the catalyst needs to be converted to a metal-sulphide state for activity toward the desired reactions, and both consume hydrogen as a reac - tant in the desired reactions. However, there are also important differences to note between the two types of catalysts and their applications. For example, the quantity of active metal applied to hydro - processing catalysts is commonly much greater than that on tail gas treating catalysts. Also, hydroprocessing cata - lysts do not typically encounter species containing oxygen atoms when processing fossil fuels, and the operating pressure is significantly higher in hydroprocessing (up to 2000+ psi/140+ bar) compared to tail gas treating. These differences influence which types of deactivation typically occur during operation, which in turn has an impact on whether the catalyst can be reused. Treating spent catalyst To counteract the differences and fully maximise the spent catalyst potential, Evonik has developed and patented a method for treating a spent catalyst from a refinery hydro - processing unit to remove contaminants from the catalyst and optimise the catalyst for use in a tail gas treating hydro - genation reactor. This catalyst, EcoMax TG, has significantly

lower costs – 20-40% – than typical tail gas catalysts but provides very high activity combined with minimal environ - mental impact. The ecological effects of using EcoMax TG compared to a freshly manufactured tail gas catalyst using virgin raw materials were evaluated using a Life Cycle Assessment (LCA) based on Evonik-internal manufacturing data as well as data from peer-reviewed publications. The LCA com - pared the carbon footprint between the two products using a ‘cradle to gate’ methodology. As shown in Figure 1 , the total carbon footprint associ - ated with manufacturing a fresh tail gas catalyst using virgin raw materials is approximately 22.1 kg per kg of catalyst. The total carbon footprint for EcoMax TG is estimated to be a significant 75% lower impact: approximately 5.5 kg per kg catalyst. This is largely because no new metal raw mate - rial (aluminum, cobalt, or molybdenum) mining is required, as is the case for a freshly manufactured catalyst, and con - sequently no additional processing or transportation. Furthermore, as previously outlined, reusing the cata - lyst reduces waste that would otherwise be disposed of in landfill. The catalyst reuse method is also less energy

100

COS

EcoMax TG

Maxcel TGE-01

Benchmark catalyst

Figure 2 Comparison of tail gas catalyst performance

Catalysis 2023