Hydrotreatment Hydrogenation

Table 5.28 gives the modifications in physical/chemical characteristics resulting from deeper and deeper hydrotreatment (Martin et al., 1992). The sulfur contents could thus be reduced to first as low as a few hundred ppm, then to a few ppm. The level of aromatics in the selected example drops from 39% to 7% while the cetane number increases from 49 to 60. Note here that such a treatment, possible through experimental means, does not correspond to current industrial practice because of its high cost and its very high hydrogen consumption. 

Most sulfur compounds can be removed from petroleum streams through hydrotreatment processes, where hydrogen sulfide is produced and the corresponding hydrocarbon released. Hydrogen sulfide is then absorbed in a suitable absorbent and recovered as sulfur (Chapter 4). 

Other important catalytic processes are those directed toward improving the product quality through hydrotreatment. These processes use heterogeneous hydrogenation catalysts. 

Catalysts used in hydrotreatment (hydrodesulfurization, HDS) processes are the same as those developed in Germany for coal hydrogenation during World War II. The catalysts should be sulfur-resistant. The cobalt-molybdenum system supported on alumina was found to be an effective catalyst. 

Reactions occurring in hydrotreatment include both hydrogenation and hydrogenolysis reactions. 

Hydrotreat to reduce organically bound nitrogen, sulfur, and oxygen to ammonia, hydrogen sulfide, and water, respectively. 

The catalyst s resistane to coking may also be improved by the solvent while maintaining high catalytic activity. Hydrogen pressure can, thus, be reduced to 110 atm in a two-step hydrotreatment, as shown in Table II (21, 128). The two-step hydrotreatment assisted by the proper solvent not only improves the extent of hydrocracking and heteroatom removal, but it also allows the reduction of the hydrogen pressure required for efficient upgrading. 

Fig. 14. Effect of decationizing pretreatment on the liquefaction, (a I) First-stage noncata-lytic hydrogen-transferred Morwell coal in the two-stage hydrotreatment (4(X)°C-10 min, 20 atm N>, tube bomb and molten tin bath, rapid heating) 4HFI/coal = 3.0g/3.()g. (a2) Second-stage catalytic hydrotreated Morewell coal in the two-stage hydrotreatment (400°C-20 min, 50 cc autoclave, slow heating).

TBR widely used for all sorts of hydrotreatments in petro and commodity chemicals, it is now adopted in finer chemicals. Intermediates hydrogenation includes quinones, sugars, lactones, functional aromatics, etc... Despite continuous operation, small size TBR can be adapted to batch-wise synthesis by multiple recycling of L product. Example trifluoracetic acid hydrogenation [28]. 

Figure 8.23 Hydrogen recovery from a hydrotreater used to lower the molecular weight of a refinery oil stream. Permea polysulfone membranes (PRISM ) are used [42]...

For the process engineering studies, these severity definitions were broadened, based on the hydrogen consumption required. If the hydrogen consumption for the whole oil hydrotreater was over 2750 SCF/bbl, the severity was referred to as high. If the hydrogen consumption was between 1750 and 2750 SCF/bbl, the severity was referred to as intermediate. If the hydrogen consumption was 1750 SCF/bbl or lower, the severity was referred to as moderate. 

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