Hydrocracking, comparison with

The values defined in this manner do not represent any probability for rupture of definite carbon-carbon bonds in the feed molecule. This term is meaningless if rearrangement of the carbon skeleton precedes the cracking step. Rather, the values indicate the probability of an n-alkane for being hydrocracked according to the overall cracking reaction in question. These probabilities are useful for a comparison with the relative concentrations of the products formed by hydroisomerization (cf. Table IV). 

By comparison with a fixed-bed gas-liquid reaction, a three-phase fluidized-bed reactor offers the advantage of very high effective thermal conductivity and, therefore, a more uniform temperature distribution in the reactor. Van Driesen and Stewart139 have demonstrated this for large-scale catalytic desulfurization and hydrocracking of heavy petroleum fractions. 

Cemy, J. Pospisil, M. Sebor, G. Composition and Oxidative Stability of Hydrocracked Base Oils and Comparison with a PAO, J. Synth. Lubr., 2001,18-3,199. 

Hydrocracking. A series of experiments was carried out at a relatively low temperature and hydrogen partial pressure of 358°C and 103 atm, respectively. Comparison runs were carried out with Pittsburgh... 

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... 

The commercial Co-Mo catalysts used for hydrocracking oil sands bitumen and petroleum residua are normally supported on alumina. Several years ago hydrodesLilphuriEation (HDS) studies with thiophene (ref. 1) indicated that carbon supported catalysts were superior to alumina supported ones. However HDS of benzothiophene (ref. 2) was found to be greater on alumina supported catalysts than on carbon supported ones. Studies of these two supports were performed in our laboratory with Athabasca bitumen (ref, 3). Care was required in choosing the particular carbon support since carbons which have very large surface areas also have small pore sizes which would inhibit or perhaps exclude some of the larger molecular species in resid feedstocks, such as Athabasca bitumen The wide pore carbon that vas available, had a surface area and a rredian pore diameter that were respectively half and more than double those of the alumina support used for comparison. 

Another variant of the severe hydrotreatment process is the substitution of wax for lubricant distillate as feedstock. The wax recovered from conventional solvent dewaxing units is essentially a pure alkane feedstock containing a high proportion of linear alkanes. With this type of feedstock and under appropriate operating conditions, the isomerisation reaction can be made to predominate over cracking reactions. Unconverted wax can be removed by conventional methods to yield a base oil that is exclusively composed of isoalkanes and that resembles synthetic polyal-phaolefin base fluids more closely than the hydrocracked base oils described in Section 1.5.2. A comparison of some of these base fluid properties is shown in Table 1.4. 

More recently, British Petroleum (BP)37 39 produced two group III stocks, a 4 cSt BP HC-4 and a heavier HC-6 from the fractionator bottoms of their fuels hydrocracker at BP s Lavera, France, refinery. The total bottoms are solvent extracted to stabilize the final products, fractionated, and finally solvent dewaxed. The hydrocracker is operated in a severe mode (relative to lube hydrocracking) at a once-through conversion of 90% (in comparison, lube hydrocrackers may operate at conversions of only about 20%, and perhaps less with a very good quality feed). Like other hydrocracker-sourced group HI products, their compositions are virtually independent of feed source due to the extent of the molecular reorganization that occurs and the molecular structures that are required for those Vis. The properties of the HC-4 are compared in Table 7.26 with those of some competitive group I, II, and IV base stocks. It can be seen that the HC-4 closely resembles the more... 

Comparison of f 600 and / 800 shows that, with one exception, there is only a difference of 1 or 2 %, which implies that, above 600 °C, hardly any degradable material is left. The coke residue decreases slightly with increasing residence time, but the amount of coke is small compared to that of the vacuum residue. This indicates that the high-molecular-weight material does not undergo conversion under the reaction conditions of the hydrocracking process. 

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