Hydroisomerization yields

There are currentiy three important processes for the production of isobutylene (/) the extraction process using an acid to separate isobutylene (2) the dehydration of tert-huty alcohol, formed in the Arco s Oxirane process and (3) the cracking of MTBE. The expected demand for MTBE wHl preclude the third route for isobutylene production. Since MTBE is likely to replace tert-huty alcohol as a gasoline additive, the second route could become an important source for isobutylene. Nevertheless, its avaHabHity wHl be limited by the demand for propylene oxide, since it is only a coproduct. An alternative process is emerging that consists of catalyticaHy hydroisomerizing 1-butene to 2-butenes (82). In this process, trace quantities of butadienes are also hydrogenated to yield feedstocks rich in isobutylene which can then be easHy separated from 2-butenes by simple distHlation. 

The co-refining synergy of natural gas liquids and Fe-HTFT was exploited for alkylate production. The natural gas liquids serve as a source of butane that can be hydroisomerized to yield isobutane that is alkylated (HF process) to produce a... 

In Figure 5 the generally accepted reaction path (14) for hydroisomerization of n-alkanes has been represented along with different possibilities for the cracking step. The n-alkane molecules are adsorbed at a dehydrogenation/hydrogenation site where n-alkenes are formed. After desorption and diffusion to an acidic site chemisorption yields secondary carbenium ions that rearrange... 

The mechanistic background for such a comparison is illustrated in Figure 10 which represents in more detail the pathway of hydroisomerization and hydrocracking of two n-alkanes. Branched carbenium ions are formed via n-alkenes and linear carbenium ions. Then, either desorption or (3 -scission may occur in parallel reactions. Desorption (followed by hydrogenation) of a given carbenium ion yields an iso-alkane with the same carbon skeleton. f3 - scission, on the other hand, yields fragments of definite carbon numbers ( (3 -scissions which would yield or C2... 

Our study was undertaken specifically to investigate the processing of a typical raffinate to produce either high yields of LPG or isobutane as well as to determine the octane improvement in the C5+ fraction due to hydroisomerization. A 0.7 wt % Pd-15 wt % Ni-SMM catalyst was used for all the experimentation. 

Laboratory studies have shown that omega (MAZ structure type) based paraffin hydroisomerization catalyst shows higher activity than mordenite based catalyst and better selectivity, i.e. higher octane due to higher yield of di-branched paraffins compared to mordenite performance (17). The isomerization of a C5/C6 cut at 15 bar results in a final calculated RON of 80.4 for the alumina bound dealuminated PtH-MOR catalyst supplied by IFP with undisclosed (most likely similar) Si/Al ratio, measured at 265 °C compared to a RON value of 80.9 for an alumina bound dealuminated PtH-MAZ catalyst with bulk Si/Al = 16, measured at 250 °C. Both measurements were performed in a bench-scale tubular reactor with a volume of 50 cm3 of 2 mm diameter extrudates with WHSV of 1.5 h and H2/HC of 4. This... 

Hydroisomerization is not only critical to the yield of base oil, but its control significantly impacts on both the pour point and the VI. Table 8.3 shows the impact of branching on the melting point of decanes and nonanes (26,27). 

Hydroisomerism Pt mordenite Converts low octane, pentane, and hexane to higher yields... 

The pyrolysis bottoms were then hydroisomerized to give a —22°C pour point, 4.4 cSt oil of 154 VI (Table 13.3). The overall 343°C- - yield, based on feed to the pyrolyzer, was 44 wt%. Adding the potential lube from oligomerizing the lighter olefinic product from the pyrolyzer would increase the 343°C- - yield to about 59 wt%. However, in this run, a significant amount of 343°C— was in the feed to the hydroisomerization step (10 wt% based on feed to the pyrolyzer). Had this been sent to oligomerization, the potential 343°C- - would be at 67 wt% (Figure 13.11), based on the PONA olefin analysis. 

A portion of the pyrolysis bottoms was hydrotreated to reduce the nitrogen from 8 ppm to less than 1 ppm. This was then hydroisomerized to give a — 15°C pour point 3.8 cSt oil with a 150 VI (Table 13.3). The overall 343°C+ yield was 40 wt%, close to that estimated for unhydrotreated feed at the same pour point. 

Potential lube yields were in the 60-70 wt% range, assuming all the olefins (almost all 1-olefins) could be upgraded to lube. About half this yield would come from hydroisomerization and half from oligomerization. 

Hydrotreating the feed prior to the hydroisomerization step did not significantly affect lube oil yield or quality. Eliminating this step could benefit the overall process economics. 

To compare the hydrogenating activity of the cation forms of mordenite with that of H-form which contains the metals of column VIII, we have studied benzene hydrogenation on the catalysts 0.5% Pd/HM and 5% Ni/HM. Under the conditions indicated in Table II, the extent of benzene hydrogenation on these catalysts is 85 and 95%, respectively. Thus, the hydrogenating activity of certain cation forms of mordenite is not inferior to that of H-mordenite, which contains palladium and nickel. Benzene hydrogenation on these catalysts is accompanied by a considerable hydroisomerization to yield methylcyclopentane 30-40%. 

Isoforming. Proprietary process for fixed-bed hydroisomerization, requiring a non-noble-metal catalyst. Claimed to give high yields of C8 (xylene) isomers with low hydrogen consumption and minimal catalyst regeneration. 

When coupled to a lubes hydrocracker, for the same VI as produced by solvent dewaxing, hydroisomerization allows hydrocracker severity to be reduced, giving higher yields of base stocks. 

FIGURE 10.29 Pour points versus yield loss for solvent dewaxing and using five hydroisomerization catalysts. 

Long chain alkanes are involved when hydroisomerizing diesel. Then, the higher the steric constrains present in a given zeolite, the lower will be the maximum isomerization yield. 

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