Catalysis 2023 Issue

tail gas treating unit (TGTU) may require 30 MT of tail gas catalyst and a resulting carbon footprint of 660 tons CO2 e. However, by replacing the traditional catalyst with EcoMax TG, the total carbon footprint would be reduced by nearly 500 tons CO2 e – a substantial reduction in environmental footprint. Applications in a large-scale oil refinery The EcoMax TG catalyst has been demonstrated at an oil refinery located on the US Gulf Coast (PADD 3) with a capacity of 370,000 barrels per day (17.8 MMTPA). The facility has four sulphur recovery units (SRU) with four TGTUs, with a total design capacity of 470 tons per day. The four TGTUs are conventional in design, where the tail gas reactor feed is heated using a fired direct heater or ‘reducing gas generator’ (RGG). The refinery required a mid-cycle catalyst replacement for the subject TGTU, which had a spherical conventional temperature tail gas catalyst installed. In a recent process upset, pressure drop across the existing tail gas catalyst bed had increased to an unacceptable level, which lim- ited the overall SRU and TGTU throughput. The decision was taken to replace the tail gas catalyst and complete the remainder of the cycle until the next planned turnaround. EcoMax TG was selected for this task in one TGTU based on the price of the catalyst, as well as its expected perfor- mance and pressure drop, physical properties, availability, and sustainability benefits. Once the catalyst was supplied in oxide form, it was sulphided in situ. During this process, a temperature rise was observed upon introduction of H 2 S and H 2 , which was expected by the unit operations staff given its higher quantity of metals (Co, Mo) than other tail gas treating catalysts. As a result, the total heat release due to sulphiding is higher and consequently a higher exotherm is expected compared with some other tail gas catalysts. Therefore, it is crucial to ensure that H 2 S and H 2 levels are controlled and monitored well. The unit operations staff could easily control the tem- perature rise by reducing the amount of H 2 S and H 2 feed to the reactor, increasing recirculation (start-up) blower flow rate, and holding the reactor inlet temperature fixed until the temperature ramp rate could be maintained and con- trolled. Catalyst sulphiding was completed by increasing the reactor temperature to 600°F (315°C) and holding prior to the introduction of Claus tail gas. The reactor showed the expected temperature profile and excellent conversion activity, and the catalyst performance enabled the refinery to meet the unit emissions limit. After six months of continuous operation, performance tests were carried out to assess the impact of EcoMax TG on the refinery, with the delay being taken to ensure that the catalyst had completely stabilised prior to testing (see Figure 3 ). The test results indicated very challenging conditions for the tail gas catalyst, with significant feed contamination: • Non-aromatic hydrocarbons (480 ppmv C4+ dry)

255˚C

Feed Euent

270˚C

100

150

200

ppmv (dry)

255˚C

COS

270˚C

100

ppmv (dry)

255˚C

270˚C

100

200

300

400

ppmv (dry)

255˚C

270˚C

2000

4000

6000

8000

ppmv (dry)

intensive than the process of forming particles to make a fresh catalyst. So, taken altogether, numerous ‘Scope 3’ emissions – indirect emissions associated with ‘upstream’ processes tied up in making a fresh catalyst – are effectively avoided with the more sustainable EcoMax TG catalyst. Improvements against the industry standard The important qualities of a tail gas catalyst are perfor- mance, economics, and environmental impacts. Catalyst performance is quantified by the testing of catalyst conver - sion performance under identical controlled conditions. The performance of a traditional benchmark catalyst, EcoMax TG, and Maxcel TGE-01 is shown in Figure 2 . The economics of tail gas catalysts are a function of the cost of the catalyst components itself, manufacturing cost, transportation cost, and catalyst density. To standardise the effects of different types and locations of manufactur- ing, tail gas catalyst costs may be computed per unit vol- ume. The comparison in the table below is based on actual fill cost, thereby removing the density variable: Figure 3 Component feed and effluent concentrations (ppmv) and conversion (%) measured in field testing of EcoMax TG catalyst

Catalyst type: Relative cost:

Traditional 1.00 (basis)

EcoMax TG Maxcel TGE-01

0.65

0.83

• COS (100-400 ppmv dry) • CS 2 (30-100 ppmv dry) • BTEX (60 ppmv dry)

The carbon intensity of manufacturing each type of cata- lyst has been studied extensively. For example, a typical

Catalysis 2023