Decarbonisation Technology - November 2023 Issue

Paving the way to low-carbon propylene from the FCC unit With the demand for propylene expected to increase in the petrochemical industry, new technology is required to process it and reduce CO 2 emissions

Bani H Cipriano, Clint Cooper and Stefan Brandt W. R. Grace & Co

P ropylene plays a critical role in the the manufacture of polypropylene, a widely used polymer in durable goods and packaging, among other uses. The demand for propylene is projected to increase by 36% through 2030 (or 4% annualised) (Wood Mackenzie, 2022). One challenge associated with meeting the increased demand for propylene is the CO₂ emitted during its production. The production of propylene and ethylene is estimated to generate 250-300 million metric tons (MTs) of CO₂ per year. Since the annual demand for propylene and ethylene combined is approximately 295 million MTs per year, the production of ethylene or propylene generates, on average, approximately 1 MT of CO₂ per MT of ethylene or propylene (Dziedziak & Murphy, 2023). Jurisdictions are continuing to implement CO₂ taxation or increase the magnitude of petrochemical industry. Approximately 70% of propylene produced is used in their CO₂ tax with the aim to reduce emissions. Countries in the Asia Pacific, such as Singapore, are implementing new carbon taxes (Gupta, Tan, Ho, & Hui, 2023). The carbon price in Europe has recently reached values of ~€100/ MT (Twidale, Abnett, & Chestney, 2023). Against this backdrop, petrochemical feedstock producers will be challenged to reduce the carbon intensity of their production processes. Propylene is made via different processes; the three most important are steam cracking, fluid catalytic cracking (FCC), and propane dehydrogenation (PDH). This article compares the carbon emissions of these processes and further examines the carbon intensity of propylene from

the FCC unit. ZSM-5 technology is discussed, including its unique ability to increase the yield of propylene from the FCC without increasing CO₂ emissions. Finally, a life cycle analysis (LCA) for producing propylene from the FCC is presented, showing how Scope 3 emissions change when a refinery shifts operation between transportation fuels and propylene modes. Carbon intensity of different processes The process to produce propylene (and ethylene) involves either cracking of larger molecules (naphtha, VGO, resid, ethane, propane, butane) in the case of steam cracking and FCC or dehydrogenation of propane in the case of PDH. These reactions are endothermic and require significant amounts of energy. Table 1 shows ranges for the carbon intensity of different processes. Note that in both steam cracking and FCC, propylene is one of several products produced, so the emissions are expressed as MT of CO₂ per MT of total product produced.

CO 2 /product,

Reaction

MT/MT

temperature,°C

Refinery/FCC

0.3-0.4

550

(Concawe, 2022) PDH (Environmental Protection Agency) Steam cracker (S&P Global, n.d.)

1.2-1.7

630

1.0-1.8

840

Table 1 CO₂ emissions generated per unit of product produced and typical reaction temperature for several processes