Effect of Feedstock Variation

In commercial practice, there will be significant differences in olefin feed composition. Under the AlkyClean process cyclic operation, high RON is obtained over a prolonged time period with various feeds. The use of a refinery-sourced MTBE raffinate gave similar results (alkylate yields and product quality) to a pure cis-2-butene feed (Table 12.9). The MTBE raffinate contained about 26wt% trans-2-butene, 15 wt% cis-2-butene, 12 wt% 1-butene, 2 wt% isobutene, 40 ppmw (parts per million by weight) of various oxygenates and 3 ppmw of sulfur (balance isobutane and n-butane). 

In HE alkylation, the processing of 1-butene leads to a significantly lower RON. Therefore, to avoid this octane loss, HF units often employ upstream selective hydrogenation/isomerization to isomerize 1-butene to 2-butene. 

The addition of about 25% isobutene on olefins resulted in a loss of less than 0.5 RON. This loss may be attributed to a somewhat higher formation level of C5-C7 and Cg + compounds. For H2SO4 alkylation, the same amount of feed isobutene would lead to a loss of about 1 RON. 

Similarly, after blending about 30vol.% of propylene with cis-2-butene, the RON loss was less than 1 number. With H2SO4 alkylation, similar amounts of propylene would lead to a RON about 1.5 lower. Table 12.10 summarizes the estimated impact of feedstock variation on RON relative to a pure cis-2-butene feedstock for the AlkyClean process and liquid acid technologies. Based on these results, it can be concluded that our new SAC technology is less sensitive to feedstock variation regarding product quality than either liquid acid technology. 

According to the open literature, other solid acid alkylation catalysts are generally susceptible to poisoning/deactivation by water and other common feed impurities (e.g., oxygenates, sulfur compounds, dienes, etc.), thus necessitating (potentially costly) feedstock pretreatment for their removal. In some cases, this requirement is further mandated by the potential corrosion problems associated with the use of halogens in the catalyst system. 

---