Noncatalytic Hydrodesulfurization

To evaluate the extent of NHDS reaction in the two-reactor unit, the following 

FIGURE 6.3 Total thermal hydrodesulfurization (NHDSj) of heavy crude oil and atmospheric residua as functions of temperature and pressure ( ) 13°API crude oil, (A) AR-13°API, ( ) 21°API crude oil, and (X) AR-21°API. 

At low temperature ( 390°C), the level of NHDS is relatively small however, when temperature is higher than 390°C, NHDS rapidly increases. This behavior is due to the high values of activation energy of thermal desulfurization reactions (Yang et al., 2011). These results agree with those reported by Juraidan et al. (2006) for the noncatalytic hydrothermal reaction of Boscan crude. 

The path for thermal reactions is through the mechanism of free radicals (Yang et al., 2011) therefore, it is expected that at higher hydrogen partial pressure in the reactor, the saturation reaction should be favored, and in this way hydrogen quenches 

The temperature dominates the NHDS of the four feedstocks however, the nature and composition of the feeds also affect NHDS. The heaviest feed (AR-13°API) 

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This chapter deals with the noncatalytic hydrodesulfurization (NHDS), hydrodemet-allization (NHDM), and hydrocracking (NHDC) of heavy crude oil and atmospheric residue. Some experiments were carried out in two different bench-scale units equipped with fixed-bed reactors in series operated in adiabatic and isothermal modes. The reactors were loaded with inert material (silicon carbide). Different feedstocks were used for the tests 13°API heavy crude oil, 21°API crude oil, atmospheric residue from the 13°API heavy crude oil, and atmospheric residue from the 21°API crude oil. The effects of pressure, residence time, temperature, and type of feed on noncatalytic reactions and axial reactor temperature profiles are examined. Reaction kinetics of the different noncatalytic reactions is studied by following the power-law approach. 

Chapter 6 deals with thermal hydroprocessing. The effect of different reaction conditions on the extent of noncatalytic hydrodesulfurization, hydrodemetallization, and hydrocracking is examined in detail. 

The extent of the hydrocracking is, like the hydrodesulfurization reaction, dependent upon the temperature, and both reaction rates increase with increase in temperature. However, the rate of hydrocracking tends to show more marked increases with temperature than the rate of hydrodesulfurization. The overall effect of the increase in the rate of the hydrocracking reaction is to increase the rate of carbon deposition on the catalyst. This adversely affects the rate of hydro-desulfurization hydrocracking reactions are not usually affected by carbon deposition on the catalyst since they are more dependent upon the noncatalytic scission of covalent bonds brought about by the applied thermal energy. 

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