Hydrotreating conditions

The aromatic hydrogenation reactions are reversible and at normal hydrotreating conditions, the equilibrium limits to achieve complete conversion. Low temperatures and higher pressures favor the aromatic saturation. The carbon atoms of a multi-ring system are hydrogenated in sequential steps, each one being equilibrium limited, as well. 

Figure 12. Bromine number distribution in high severity cracking products as a function of hydrotreating conditions.

Vanadyl salen is readily converted at 100°C with H2S in the absence of a catalyst to a vanadium sulfide and a free organic ligand (or decomposition products). Vanadyl phthalocyanine is more stable with respect to ring attack and demetallation. Rates relative to catalytic reactions have not been measured. If VO-salen is an appropriate model of vanadium binding in asphaltenes, asphaltenic metals are more readily converted to sulfides under hydrotreating conditions than the porphyrinic metals. This suggests... 

Authentic and synthetic solvent-refined coal filtrates were processed upflow in hydrogen over three different commercially available catalysts. Residual (>850°F bp) solvent-refined coal versions up to 46 wt % were observed under typical hydrotreating conditions on authentic filtrate over a cobalt-molybdenum (Co-Mo) catalyst. A synthetic filtrate comprised of creosote oil containing 52 wt % Tacoma solvent-refined coals was used for evaluating nickel-molybdenum and nickel-tungsten catalysts. Nickel-molybdenum on alumina catalyst converted more 850°F- - solvent-refined coals, consumed less hydrogen, and produced a better product distribution than nickel-tungsten on silica alumina. Net solvent make was observed from both catalysts on synthetic filtrate whereas a solvent loss was observed when authentic filtrate was hydroprocessed. Products were characterized by a number of analytical methods. 

Table I. Critical Properties of Solvents and Typical Hydrotreating Conditions...

It is interesting to know whether phosphorus is sulfided under conventional hydrotreating conditions. Mangnus et al (70) showed by TPS that... 

The formation of mixed Mo — P —S compounds is thermodynamically restricted at temperatures lower than 1000°C (70). This restriction implies that the sulfur atoms in M0S2 are not directly replaced by phosphorus atoms. In the same way, phosphorus does not regularly occupy the edges of the M0S2 platelets through bonds with sulfur atoms as in the case of the promoted CoMoS or NiMoS phases. The presence of P(white), P(red), and P(black) on catalysts can also be excluded because they have extremely high vapor pressures under hydrotreating conditions. 

Model 1-6 is a new hydrodearomatization (HDA) catalyst developed by ICERP to be used in aromatics hydrogenation of gas oil blends. The catalyst has been obtained by a highly improved NiO dispersion on the promoted alumina support having a bimodale pore distribution with a total pore volume of minimum 45 cmVg. 1-6 has a good HDA activity under rather moderate hydrotreating conditions i.e. 60 bar total pressure and a remarkable sulphur resistance. 

Pure component studies indicate the rate of mercaptan formation is sufficiently rapid at hydrotreating conditions compared to the saturation step which lead to alkane [8]. The exothermic reversible reaction, which shifts to the left at higher hydrogen sulfide partial pressure, is also dependent on temperature, feedstock type, total sulfiir, partial pressure of hydrogen and alkenes, space velocity and catalyst type. Furthermore the size of the reactor affect the balance between the kinetic sulfur removal and alkene saturation [9]. 

N. Nourbakhsh, T.T. Tsotsis and I.A. Webster, Model planar alumina catalyst preparation and aging under hydrotreating conditions. Appl. Catal., 50 (1989) 65. 

Another way to separate nitrogen compounds from hydrotreated shale oil products is by adsorption chromatography. Experiments have been conducted where basic and neutral alumina have been used to separate shale oil into specific nitrogen-type fractions. Both a pumped-flow and gravity-flow method were executed. However, it was determined that the pumped-flow procedure was better since it enabled more control over experimental parameters such as flow rate. This separation scheme could be very useful because it has been applied to shale oil products produced under different hydrotreating conditions... 

The Stable TMS Catalytic Phases and Their Structures. It is fundamental to determine the catalytically stabilized phases under operating hydrotreating conditions as a basis for understanding the activity and selectivity of the HDS catalysts. 

Recently, the C - N< bond was proposed to be associated with H2S in the formation of C - SH and NH3. The C - SH bond is easily eliminated under hydrotreating conditions. Prins et al. reported that 2-methylcyclo-hexylamine (MCHA) is hydrodenitrogenated through three ways (a) direct elimination of ammonia, (b) nucleophilic removal of the NH2 group by H2S followed by removal of the -SH group, and (c) direct... 

It is known that poly aromatic hydrocarbons (PAH) hydrogenate via successive steps, each of which is reversible [8]. Hydrogenation of the first ring is usually the least thermodynamically favorable step under typical hydrotreating conditions. We use the simplest mono-aromatic molecule, benzene, as our model molecule in all the related studies. 

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