50% VGO + 50% Oak feed
C VGO + C Oak over E-Cat
C VGO + C Oak over JM Catalyst
91 92 93 94 95 96 97 98 99 m/z (mass/charge) or MW
91 92 93 94 95 96 97 98 99 m/z (mass/charge) or MW
Figure 3 Outcome of GC-MS analysis when a mix 50% VGO/50% oak feed is cracked over Ecat and JM Catalyst
runs provided clear boundaries where each pure feedstock was used. To explore co-processing, the micro-reactor was operated with a 50:50 wt/wt ratio of VGO and green oak feeds. However, it is recognised that such a high ratio may not be practical in a commercial FCC due to increased delta coke and other operating issues. This 50:50 feedstock was tested using standard Ecat and then tested using equili- brated purpose-made catalysts. Figure 1 shows the GC-MS spectrum for the baseline 100% VGO/standard Ecat run. The origin of the derived toluene is clearly all attributable to the C 12 source having M/Z peaks at 91 and 92. Figure 2 shows the results for the 100% green oak over standard FCC Ecat. As expected, the majority of the toluene was derived from the C 13 source with M/Z peaks at 99 and 98. Some toluene was produced with M/Z peaks lower than 98 due to successive amounts of trace C 12 incorporated because it was not practical to fully isolate all traces of C 12 when growing the green oak from the C 13- enriched CO 2 . Co-processing runs provided interesting observations that gave insight into how biogenic carbon interacts with conventional oils. Figure 3 shows that the dominant source of carbon atoms in toluene produced over standard Ecat originated from the VGO (C 12 ), despite the feedstock being a 50:50 ratio with green oak. To explain this, we consider that much of the biomass pyrolysis oil was lost to coke pro- duction and CO + CO 2 in the dry gas. Very different conclusions were made when using the purpose-made catalyst, as can clearly be seen in Figure 3. Toluene produced using the purpose-made catalyst
showed significantly higher C13 incorporation, as seen in the increase in relative abundance of M/Z peaks above 92 (having at least one C 13 atom). As expected, some toluene was derived from the C 12 VGO source, but overall, toluene from this feedstock was minor. Toluene with an M/Z peak of 99 contained exclusively C 13 , and peaks from 93 through to 98 had successive levels of C 13 incorporated in the molecu- lar structure. We refer to the mixing of grey and green carbon atoms within molecules as carbon scrambling. The purpose-made catalyst was designed to promote olefin aromatisation and aromatic transalkylation reactions to encourage carbon scrambling in the FCC. Figure 4 illustrates the reaction mechanism: it shows benzene being produced by aromatisation of two propyl- ene molecules derived from differing carbon sources (grey C 12 and green C 13). Olefin aromatisation produces aromatic rings that can contain both grey and green carbon atoms. These already carbon-scrambled aromatics can also react with other aromatic molecules to achieve further carbon incorporation through aromatic transalkylation reactions (the exchange of side chains between aromatic molecules). The results from this study provide the first step towards the development of catalysts specifically designed to improve biogenic carbon incorporation into FCC products. Increasing biogenic carbon incorporation will help refiners meet RED II mandates more easily. The focus of this research was to explore and understand key mechanisms important for biomass co-processing in the FCC and understand whether the extent of incorporation could be improved by appropriate catalyst design. Due to the expense of C 13
JM Catalyst
Ole n aromatisation
Aromatic transalkylation
Figure 4 Scrambling toluene mechanism
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PTQ Q2 2023
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