Decarbonisation Technology - November 2023 Issue

• The carbon intensity of FCC catalyst and ZSM-5 additive manufacturing is the same. When additive is used, the addition rate of the catalyst decreases by the amount of additive used. • Propylene generated by the FCC is routed to petrochemical plants for the production of polypropylene. The assumption used in this LCA for emissions generated during the polymerisation of propylene is based on the work of Alsabri, et al. (Alsabri, Tahir, & Al- Ghamdi, 2021). Also, we assume there is capacity in the FCC unit propylene purification train to handle additional propylene produced. • In addition to generating propylene, the use of ZSM-5 generates other LPG olefins (butenes) and saturates, as well as a small amount of ethylene. We assume all of these components are combusted as fuels since butenes are alkylated and added into the gasoline blending pool, and propane, butane and ethylene are burned as fuel. The assumption used in the LCA for emissions generated in the combustion of fuels is 8.887 kg CO₂ per gallon of fuel consumed (Environmental Protection Agency, n.d.). • Globally, 19% of all plastics were incinerated in 2019, so it is assumed that eventually the plastics derived from ZSM-5 usage are incinerated at this rate (OECD, n.d.). An estimated emissions rate of ~3 kg CO 2 eq per kg of plastic incinerated is assumed for this LCA, in line with the estimates of others (GAIA, n.d.). Utilising ZSM-5 in the FCC unit has the following primary effects on Scope 3 CO₂ emissions: • More CO₂ generated from increased rates in petrochemical plants to produce polypropylene • More CO₂ generated from the combustion of propane, butane, and ethylene • More CO₂ generated from plastics incineration • Less CO₂ generated from the combustion of FCC gasoline in vehicles. This is a result of gasoline being converted by ZSM-5 into propylene and other lighter molecules. The results from the LCA indicate that for a 50 kbpd FCC unit, the use of ZSM-5 additive to convert 1 wt%ff of gasoline-range material translates into a 4,500 MT/year reduction in Scope 3 CO₂ emissions (this is roughly equivalent to the emissions produced by 1,000 passenger vehicles in a year) (Environmental Protection Agency, n.d.). These effects are summarised in Figure 4 .

ROT (˚C)

CO emissions (kt/a)

400

550

545 540 535

390

380

530

370

525

520

360

515

350

510

505

340

Base High ZSM-5

ZSM-5 additives are available from many suppliers but range widely in activity. Applications targeting the highest propylene yields benefit greatly from ZSM-5 additives with corresponding activity levels. Higher-activity ZSM-5 additives require lower additive usage, minimising the dilution of base catalyst activity. This affords the refiner with the flexibility to employ catalysts with low hydrogen transfer, boosting propylene yield even further. W. R. Grace has a long track record in ZSM-5 innovation: the high-activity additives currently in our portfolio include OlefinsUltra MZ technology and the latest Zavanti additive, intended for applications with the highest C 3 = yields (Hager, Nate, DeVaney, Payne, Amalraj, & Cipriano, 2023) (Serban, Ekeocha, Singh, & Cipriano, 2021). LCA: Comparison of Scope 3 emissions from the FCC unit Grace recently conducted an LCA to better understand how the use of ZSM-5 additive affects Scope 3 CO₂ emissions from the FCC unit. A calculator was developed to quantify the change in emissions that results when an FCC unit focused on gasoline production uses ZSM-5 technology to produce propylene. This comparison is made at constant operating conditions. Several assumptions were made in this LCA, including: Figure 3 Commercial FCC unit data comparing standard operation at high ROT (red) with a case for low ROT, high ZSM-5 technology (green) Adapted from (Brandt, 2010)