Paraffin hydroisomerization

A refinery lubricant base stock is obtained having an viscosity index around 100, certain hydrotreatments result in Vi s of 130, and paraffin hydroisomerization provides oils with a VI close to 150. 

We have explored rare earth oxide-modified amorphous silica-aluminas as "permanent" intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides "titrates" the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions. 

Thus, under HCK conditions, and under hydrodewaxing (HDW) as well, paraffins are hydroisomerized and hydrocracked by a bifunctional mechanism involving the metallic and the acid sites. This classical mechanism involves ... 

Paracrystallinity, Cu/ZnO/AIjOj, 31 295 2"-Paracyclophanes, 32 453 Paracyclophanes, macrocycles, 29 206-208 Paraffin, see also Alkanes alkylation, 10 165, 27 98 carbon selectivity, bed residence time effects, 39 249-250 cracking, 39 283 cyclization, 28 295 rates, 28 301, 302 double cyclization, 28 312-314 in exhaust gases, 24 66, 67 hydrogenolysis, 30 43-44 hydroisomerization, 39 183 oxidation, 32 118-121 solubility enhanced hydrogeolysis, 39 285 Parahydrogen conversion rate correlations, 27 48-50... 

In addition to this, solid acid catalysts can also be used in the hydroisomerization cracking of heavy paraffins, or as co-catalysts in Fischer-Tropsch processes. In the first case, it could also be possible to transform inexpensive refinery cuts with a low octane number (heavy paraffins, n-Cg 20) to fuel-grade gasoline (C4-C7) using bifunctional metal/acid catalysts. In the last case, by combining zeolites with platinum-promoted tungstate modified zirconia, hybrid catalysts provide a promising way to obtain clean synthetic liquid fuels from coal or natural gas. 

Chao, K.-) Wu, H.-C., and Leu, L-J. (1996) Hydroisomerization oflight normal paraffins over series of platinum-loaded mordenite and beta catalysts. Appl. Catal. A., 143, 223-243. 

BRANCHING ANALYSIS OF HYDROGENATED PLATFORMING PRODUCTS OBTAINED BY HYDROISOMERIZATION OF PARAFFIN WAX... 

The hydroisomerization of light paraffins (C5-C6-C7) to produce their branched isomers is an important industrial process aimed at improving the octane number of the light straight mm stream (LSR). Reformulated gasolines with their impact on olefins and aromatics reduction [26, 27] have increased the number of LSR isomerization units. Table 5.1 gives the octane number of the different C5-C7 linear and branched paraffins. 

Hydroisomerization of C5 and C6 paraffins (250°C, Pt-H-mordenite as the catalyst) combined with separation of normal and branched paraffins (over zeolite CaA). 

Commercial zeolite based hydroisomerization catalysts comprise alumina bound and platinum impregnated dealuminated mordenite. The activity and selectivity of the hydroisomerization of n-paraffins is strongly influenced by acid leaching. The influence of silica to alumina ratio has been studied for pentane isomerization over platinum mordenite many times since one of the first papers published (6). 

Steaming usually produces extra framework aluminum, but even in the case of leaching some extra framework aluminum may be left on the mordenite. In some cases they can be removed by ammonium ion exchange, if desired, followed by calcination. However, depending on the amount and location of the extra framework aluminum, as the case may be, these species may increase or decrease the catalyst activity. An early review on the dealumination of mordenite was given by Karge and Weitkamp (14). In particular for hydroisomerization of paraffins, this effect has been studied by A. Corma et al. (15, 16). 

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 also a key process. In this process, linear paraffins are converted to isoparaffins. This reaction greatly improves the pour point of the base oil, but results in a loss in VI. The catalyst is often noble metal supported on a controlled acidity support. The catalyst formulations are often proprietary and may utilize an amorphous silica-alumina or a modified molecular sieve. 

Baltanas, M. A., and G. F. Froment, Computer generation of reaction networks and calculation of product distributions in the hydroisomerization and hydrocracking of paraffins on Pt-containing bifunctional catalysts, Comput. Chem. Eng., 9. 71-81 (1985). 

To date, crystalline zeolite catalysts have been most effective in catalyzing carbonium ion reactions such as catalytic cracking and hydrocracking. Other carbonium ion reactions such as alkylation and isomerization also are catalyzed by certain forms of zeolites. I expect to see these applications expand— provided suitable catalyst compositions are developed to allow economically viable processes. Although X- and Y-type faujasite can be used in catalytic cracking and hydrocracking, the Y-type is preferred for paraffin-olefin alkylation. Y-type faujasite is suitable for use in hydroisomerization catalysts, but synthetic mordenite is also a promising material. 

A number of hydrocarbon transformations have been shown by Haensel and Donaldson 10), Heinemann et al. 11), and by Ciapetta and Hunter 12) to be catalyzed by solid catalysts in which a transition metal, notably platinum or nickel, has been combined with an acidic oxide carrier substance such as, for example, silica-alumina, or halogen containing alumina. These include the isomerization of paraffins, the hydroisomerization of naphthene rings, and the hydrogenative cracking of paraflBns. 

Catalyst. The catalyst studied in this work was a platinum (0.205% wt) supported on an amorphous mesoporous silica-alumina, MSA (Si02/Al203=100) extrud with 50% wt alumina. The synthesis of the catalyst and the metal deposition procedure were described in detail [9]. A used catalyst, prepared as the former and containing 0.186% wt of Pt, was studied after the hydroisomerization of an n-paraffin feed containing 10 ppm S. 

Used catalysts were tested at 300°C for about 1000 h in the hydroisomerization of n-paraffin with feed containing traces of sulfur compounds (10 ppm S). The reaction was stopped and the catalyst was divided in two parts one was directly characterized, the other was cleaned as follows. The catalyst was washed with n-heptane (reflux at 100°C) and dried by a mild calcination at 300°C for 16 hours in flowing air, in order to remove the physisorbed organic compounds without changing the physico-chemical characteristics of the catalyst. 

In 1960, Weisz, Frilette, and co-workers first reported molecular-shape selective cracking, alcohol dehydration, and hydration with small pore zeolites (6,7), and a comparison of sodium and calcium X zeolites in cracking of paraffins, olefins, and alkylaromatics (8). In 1961, Rabo and associates (9) presented data on the hydroisomerization of paraffins over various zeolites loaded with small amounts of noble metals. Since then, the field of zeolite catalysis has rapidly expanded,... 

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