Several research centres, universities and companies have been working for years in the co-processing of renewable raw materials in FCC refining units. In the studies performed by these authors, it has been shown the technical viability of the co-processing of vegetable oils (palm, rapeseed, soybean or sunflower oils), waste cooking oil and animal fats and vacuum gasoil under FCC conditions (Bormann and Tilgner, 1994; Bormann et al., 1993; Buchsbaum et al., 2004; Carlos de Medeiros et al., 1985; Pinho et al., 2007). Not only the operation conditions registered but also the final products obtained after the catalytic cracking reactions are perfectly compatible with the conditions and products usually related to the FCC unit. However, there is a strong effect of the feedstock composition on the cracking products distribution.

Figure 15.6 illustrates the results of the co-processing of pure PO blended with vacuum gasoil in FCC conditions (Melero et al., 2010b). Data clearly show that the production of all gases (dry gas and LPG) is enhanced by the increase of the non-petrol feedstock in the feed. This fact comes from the presence of triglyceride molecules in the initial feedstock, which reduce the concentration of aromatic rings, which tend to be refractory and more difficult to be cracked. However, comparing the results obtained in the experiments performed by different authors, there is an important difference in the olefin gases production. In some studies (Bormann et al., 1993; Couch, 2007; Ramakrishan, 2004), it is claimed that the

15.6 Products yields for catalytic cracking of feedstocks with different content in palm oil. Reaction temperature of 565°C and a catalyst-to-oil ratio of 4 g catalyst/g oil. (a) Palm oil/VGO (wt.%) 0/100, (b) Palm oil/ VGO (wt.%) 30/70, (c) Palm oil/VGO (wt.%) 100/0 (Melero etal., 2010b).

presence of vegetable oils in the feedstock may enhance the olefins production in comparison with a petrol feedstock, and even UOP has patented a process for the production of olefins C2-C5 from renewable raw materials in FCC conditions (Marker, 2007). In contrast, in the work reported by Melero et al. (2010b), the olefinity of LPG is not enhanced by the presence of renewable raw materials in the feedstock, and in the case of the VGO, cracking is even slightly higher (see Table 15.3). Nevertheless, these data are in fair agreement with the increase of aromatic compounds in the liquid effluent as the vegetable oil content increases in the feed stream (see data in Table 15.3). The removal of hydrogen from the hydrocarbon molecules to form water under reaction conditions (high temperature, low pressure and high residence time) yielding olefinic hydrocarbons will suffer subsequent cyclization and hydrogen transfer reactions to form aromatic compounds (Dupain et al., 2007; Melero et al., 2010b).

As observed in Fig. 15.6, the increasing content of triglyceride-based biomass in the feed gradually diminishes the yields towards liquids, this effect being more relevant for LCO and DO fractions as compared with GLN (Melero et al., 2010b). Similar conclusions have been achieved by Bormann et al. (1993). These results are associated with the higher crackability of vegetable oils and animal fats in comparison with the petrol feedstocks. Hence, the gasoline content in the OLP is always enhanced as the percentage of vegetable oil is increased in the initial feedstock (Bormann et al., 1993; Carlos de Medeiros et al., 1985). For example,

Bormann et al. (1993) indicate that the percentage of gasoline in the liquid products rises from 60.3% to 61.1%, when they use rapeseed oil instead of vacuum gasoil in their cracking experiments. Similar results have been obtained by Carlos de Medeiros et al. (1985), whose yield to gasoline in OLP is increased by 8.6 points when they crack soybean oil instead of the typical vacuum gasoil. This better crackability of triglyceride-based biomass is also clearly confirmed by the research group of Melero et al. (2010b) in their gasoline distribution, where the medium (MN; 90-140°C) and heavy (HN; 140-221°C) naphthas yields are gradually reduced with the presence of vegetable oil in the feedstock (see data in Table 15.3).

Several authors have pointed to the reduction of the heavier fractions with the co-processing of renewable raw materials in the FCC unit (Bromann et al., 1993; Couch, 2007; Carlos de Medeiros et al., 1985; Melero et al., 2010b). Carlos de Medeiros et al. (1985) obtained LCO and DO yields ranging from 16.98% to 11.85% and from 9.98% to 3.33%, respectively, when cracking vacuum gasoil and soybean oil in FCC conditions. Similar results have been described by Holmgren et al. (2007), and LCO and DO yields changed from 9.5% to 5.0% and from 5% to 3%, respectively, if they crack a triglyceride-based feedstock instead of vacuum gasoil in the FCC unit. LCO is obtained either by means of the heavier fractions cracking or polymerization reactions. In case of the renewable raw materials based on triglycerides, most of the fatty acids of the initial molecules have a length similar to the hydrocarbons in the LCO range as well as an easier trend to be cracked. Something similar takes place with the DO fraction, whereas in the case of petrol feedstocks, it is mainly referred to the percentage of unconverted feed, and in the case of renewable raw materials, DO is always produced via polymerization reactions of olefins and aromatic rings. Triglycerides will be decomposed in reaction conditions, leading to free fatty acids that are never longer than a C22 (DO fraction is in a range of C18-C30 approximately). Since DO is heavier than LCO, its formation by means of polymerization reactions will be more hindered, and hence this fraction being dramatically reduced with the presence of renewable feedstocks in the feed. Thus, DO yield can be remarkably reduced (even more than a 75%) by the presence of a renewable raw material in comparison with the petrol feedstocks (Fig. 15.6).

Considering that polymerization reactions play a significant role when renewable raw materials are processed in FCC conditions, it is interesting the study of the aromaticity of the final liquid product. The aromaticity of the FCC liquid product is enhanced by the presence of vegetable oils and animal fats in the initial feedstock (Bormann et al., 1993; Carlos de Medeiros et al., 1985; Melero et al., 2010b). Data in Table 15.3 also evidence that the presence of renewable raw materials in the feedstock induces changes in the distribution of aromatic rings. The presence of polyaromatic species in the untreated petrol feedstocks leads to higher yields of these refractory compounds since they remain in the final products. Vegetable oils do not have these heavy compounds in their initial composition. Therefore, the cracking product from a triglyceride-based biomass always has lower polyaromatic content than the cracking product of vacuum gasoil. A different trend is observed for the case of monoaromatic (in the range of gasoline) and diaromatic (in the range of diesel) compounds because, although they are absent in the initial vegetable oils, they are easier to form than polyaromatic compounds, especially in the presence of renewable raw materials in the feedstock (Melero et al., 2010b).

Obviously, in the same way that excessive hydrogen elimination from hydrocarbons would produce a higher yield of aromatic compounds, if the removal of hydrogen continues, an increase in the coke production will be observed (highly favoured in case of the renewable raw materials because of the water formation) (Dupain et al., 2007; Melero et al, 2010b). Therefore, coke production is enhanced with the increase of triglyceride-based biomass in the feedstock (Buchsbaum et al., 2004; Carlos de Medeiros et al., 1985; Melero et al., 2010b; Ramakrishan, 2004), as clearly stated in Fig. 15.6.

Finally, some studies of the co-processing of triglyceride-based feedstocks with different features have been performed under FCC conditions. These preliminary studies indicate that the most saturated vegetable oils and animal fats lead to higher LPG yields and lower yields to liquid products as compared with more unsaturated feedstocks (Melero et al., 2010b). On the other hand, the co-processing of crude and refined vegetable oils might induce some deactivation of the FCC catalyst. Wlaschitz et al. (2004) have reported that the conversion can be reduced to 5.4% when crude feedstock is processed. These data are in agreement with the trend depicted by Chew and Bhatia (2009), who observed a slight decrease in the final conversion from 72.9% to 70.9% when they cracked unblended crude PO and used PO, respectively, under FCC conditions.