# Revamping Fluid Catalytic Cracking Unit, and Optimizing Catalyst to Process Heavier Feeds
## 1 Introduction  
Over the years, fluid catalytic cracking has been extensively used and investigated as the main producer of high octane gasoline [1], middle distillate [2; 3; 4; 5; 6], ethylene and propylene [7; 8; 9; 10; 11], and bio-fuel [12; 13; 14; 15; 16], and as a waste (scrap tire, plastics) processor [17; 18; 19]. Its flexibility in the processing of feeds with a different quality has allowed the high penetration of FCC technology into petroleum refining. Worldwide, more than 350 FCC units, out of 650 refineries, are operated in petrochemical complexes, converting vacuum gas oil (VGO) and high-boiling residues into lighter fuel products and chemical feedstocks [20]. Now, when mankind has started to replace internal combustion engines with electrophoresis and a drop in passenger vehicle production using petrol-based fuel has already been registered [21], the place and meaning of FCC technology as an automotive fuel maker is going to change to it being a chemical producer [22; 23]. The most prevalent are the recent studies devoted to the role of FCC as an ethylene and propylene producer [7; 8; 9; 10; 11], and bio-fuel producer [11; 12; 13; 14; 15; 16]. In the next two decades, oil demand for petrochemicals is expected to increase by ca. 4 Mb/d per year, reaching 34% of the total oil market in 2040, in contrast to the current 15% rate [22]. In this respect, FCC technological solutions directed to process crude oils have been explored [23; 24]. However, the general trend in the extraction of petroleum has been towards heavy and low-quality oil [25; 26]. Thus, a combination of FCC and vacuum residue upgrading units seems to best utilize the potential hidden behind the refining of heavy petroleum. The vacuum gas oil generated in the vacuum residue upgrading units can be processed in the FCC unit. Unfortunately, the secondary VGOs coming from cookers or vacuum residue hydrocrackers are characterized by a higheramount of refractory poly-nuclear aromatics and nitrogen compounds [20; 27; 28; 29], which leads to a substantial decrease in the FCC unit conversion. The content of basic nitrogen compounds has an influence on hydrocarbon cracking during the secondary vacuum gas oil (coker and H-Oil VGO) FCC reaction [30; 31]. Furthermore, the compositional and structural identification of basic extracts by positive-ion electrospray Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) shows that basic nitrogen compounds in the secondary vacuum gas oils include N, N2, NO, N2O1, and NS class species [30]. The N1 class species centered at 9 \(<\) DBE \(<\) 13 with a carbon number ranging from 20 to 24 is the most abundant, and it is a key for coker and H-Oil VGO retarding performance. The effect of the structure and composition of basic nitrogen compounds was found to be much more obvious than that of content, and it was stronger with the increase in their rings plus double-bond equivalence [30]. The secondary vacuum gas oil, nitrogen, determines the ratio between available metal and acid sites of the hydrocracking catalyst. The aromatics generate coke precursors on the available acid sites. Both factors play a coupled role that promotes coke deposition on the catalyst surface, which leads to an increase in the deactivation rate [32]. Thus, both the higher polynuclear aromatic content, and the higher nitrogen content of the coker and H-Oil vacuum gas oils, make them undesirable components of the feed for vacuum gas oil hydrocarbons. That is the reason why their processing seems most suitable in fluid catalytic cracking because it is less vulnerable to the higher content of nitrogen and aromatics than fixed-bed vacuum gas oil hydrocarbons. It is a challenge to find the optimum catalyst and operating conditions to maximize conversion during the processing of secondary VGOs [28; 33; 34].