Noncatalytic Thermal Hydrotreating

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. 

Thermal reactions are unavoidable phenomena that occur simultaneously during catalytic hydroprocessing of heavy oils. Depending upon the reaction conditions, type of feed, and experimental setup, the extent of thermal reactions can be such that the behavior of catalysts is masked or not interpreted properly. The composition and properties of the feed play an important role in noncatalytic hydrotreating since paraffinic material tends to be easier to crack thermally or catalytically, while aromatic feeds are more difficult to convert because the heaviest part tends to agglomerate, thus forming coke (Ancheyta and Speight, 2007). 

Modeling of Processes and Reactors for Upgrading of Heavy Petroleum 

Heavy oils and residua contain hydrocarbons that are characterized by large amounts of heteroatoms and asphaltenes. The nature and chemical structure of these complex components are also other factors that strongly affect the extent of thermal reactions. For instance, it is more feasible to convert asphaltenes with small content of aromatic rings and high number of alkyl side chains are more feasible to convert (Ancheyta et al., 2009). 

During thermal hydrotreating, heavy molecules crack into smaller ones, thereby favoring the catalytic action for sulfur and other heteroatoms removal (Kin et al., 1998). When a catalyst is present, the thermal reactions occur in the space between catalyst particles, in the liquid phase, and also in the gas phase, and they are nonsensitive to hindrance restrictions (Rahimi and Gentzis, 2003). 

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Thermal Stability of Filtrate. The thermal stability of filtrate from the SRC process to typical process conditions for hydrorefining was tested in a 40-hr, noncatalytic hydrotreating run. Filtrate was passed upflow over 3 L of Vi-in. tab alumina balls (Harshaw Chemical Company) at a nominal pump rate of 1 L/hr. Pressure was maintained at 2000 psig with once-through hydrogen during the run. Temperature at the bed inlet was varied between 600° and 800°F. Data from the run are summarized in Table II. 

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