PTQ Q4 2023 Issue

the properties of conventional oils. The closer a renewable or recycled feedstock falls in Figure 2 relative to conventional gasoils, the more easily these feedstocks can be upgraded in existing refinery processes. The further a feedstock falls from conventional oils in Figure 2, the more challenging it will be to upgrade in existing refinery processes. For the specific case of FCC units, as hydrogen content decreases and concarbon increases, the coke yield during cracking will inevitably increase. At some position in Figure 2, there exists a minimum effective hydrogen index and maximum concarbon content, where if the feedstock were fed undiluted into the FCC unit, the coke yield would exceed what the heat balance can tolerate. At this point, the feed- stock must be diluted in conventional oil (‘co-processing’) to increase the hydrogen content and reduce the concarbon of the blend. The lower the effective hydrogen and higher the concarbon content, the more dilution with conventional oil is needed. For example, in the case of biomass pyrolysis oils that have not been hydrotreated, the maximum concentra- tion of bio-oil in gasoil is typically ~10 wt%. Circular manufacturing of plastic wastes opportunities Circular manufacturing of plastic has received significant attention over the past decade to reduce the amount of conventional oil needed for new polymer production. One approach applicable to a variety of plastics uses thermal pyrolysis to first convert the solid waste plastic into a hydro - carbon oil, followed by further conversion of the oil into a monomer using existing refinery assets. Due to its relatively high selectivity to producing light olefins and widespread availability, steam cracking is often preferred. However, two limitations of steam cracking are its need for relatively saturated feedstock and hydrocarbons lighter than ~C22 to control the coking rate. Hydrotreating and hydrocracking are possible solutions to manage these limitations, but they add cost. FCC may also be an attractive choice to improve the processability of pyrolysis oils or perhaps even be used as an alternative process to steam cracking. Polyolefins (polypropylene, LDPE, HDPE) will be the eas - iest plastic waste for circular manufacturing given its very high hydrogen effective index and very low concarbon, reflected in its location in the top left of Figure 2. During pyrolysis, polyethylene and polypropylene undergo random

Py-oil

Olen/paran ~ 1.2 100% Aliphatic hydrocarbons

Py-gas

Carbon number

scission, resulting in a broad distribution of largely aliphatic hydrocarbons (olefin/paraffin~1.25) ranging from light gases to heavier waxes (~C34 ) shown in Figure 3 for pyrolysis of LDPE. Given the properties of the pyrolysis oil, these oils could possibly be fed into the FCC unit without diluting with gasoil. For example, Figure 4 shows the case where the LDPE oil described in Figure 3 was fed undiluted into a pro - prietary ACE reactor using two commercial BASF catalysts: (1) catalyst designed to maximise conversion to naphtha, and (2) catalyst designed to maximise conversion to light olefins. An ACE reactor is the industry-accepted laboratory-scale process widely used to predict how different catalysts and feedstocks might behave in an actual FCC unit. As would be expected given the properties of the oil, the coke yield is much lower than what is typical for conventional gasoil. In both cases, the wax fraction of the pyrolysis oil is fully con- verted into naphtha and LPG hydrocarbons. In the case of the ‘Max LPG’ catalyst design, more than half of the original pyrolysis oil is converted into relatively olefinic LPG, with the remaining oil being naphtha that could be separated and separately cracked to complete the recy- cling process. It is worth noting that the coke yield observed in these experiments is so low that traditional FCC with con - tinuous catalyst regeneration may not be required. Rather, Figure 3 Composition of oil derived from pyrolysis of LDPE plastic measured using combination of chromatography and mass spectrometry

(a)

(b)

Max naphtha catalyst Max LPG catalyst

LPG Naphtha LCO HCO Coke

Dry gas

C= C

Figure 4 Comparison of (a) overall yields and (b) LPG & dry gas breakdown for catalytic cracking of undiluted pyrolysis oil derived from LDPE using catalyst designed for maximum naphtha and maximum LPG

PTQ Q4 2023