Hydroprocessing, residuum

Residuum Conversion This includes fluid coking, delayed coking, visbreaking, and residuum hydroprocessing. 

In Section III, commercial residuum hydroprocessing technology is discussed to establish the role and requirements of hydroprocessing in the overall refinery residuum conversion scheme. Commercial residuum hydroprocessing catalysts and residuum hydrodesulfurization (RDS)-hydrodemetallation (HDM) technology are reviewed briefly. 

In Section V, deactivation of catalyst pellets and reactor beds during residuum hydroprocessing is considered. The chemical nature of the metal deposits is described, including a discussion of the physical distribution of these poisons in aged catalysts and reactor beds. Models to predict... 

In the last section, future perspectives for the study of residuum hydroprocessing and the rational design of hydrodemetallation catalysts and processes are offered. 

This section will focus on the various hydroprocessing technologies that have been commercialized or are in a pilot stage near commercialization. Reactor design characteristics that differentiate the technologies will be highlighted. Included in this section is an overview of the properties and applications of commercial residuum hydroprocessing catalysts. 

Fig. 14. Schematic flow diagram showing multiple fixed-bed reactor residuum hydroprocessing coupled with distillation equipment for high-severity RDS (Paraskos et al., 1974).

Fig. IS. Schematic flow diagram showing residuum hydroprocessing in combination with delayed coking to produce cracking feeds and light products (Howell el al., 1985).

The distinction in Table XX between hydrotreating and hydrocracking processes is frequently misleading when residuum hydroprocessing is being considered. Hydrotreating conventionally has been referred to processes... 

Commercial Residuum Hydroprocessing Operating Capacity, Free World, January 1986 ... 

Fig. 17. Schematic flow diagram of residuum hydroprocessing unit utilizing LC-Fining expanded-bed reactor (van Driesen and Fornoff, 1985).

The variety of applications and the market growth potential have attracted numerous entries into the residuum hydroprocessing catalyst market, as indicated by the compilation of commercial vendors and catalysts in Table XXIII. Catalysts are available in an assortment of shapes, sizes, and formulations, but detailed information on catalytic metals, support composition, pore size, and pore size distribution is sketchy. 

Vanadium and Nickel Distribution Factors in Residuum Hydroprocessing Catalysts"- ... 

Fig. 40. Typical deactivation curve for residuum hydroprocessing catalyst. Arabian Heavy atmospheric residuum desulfurized to 1.10 wt. % product sulfur with a iV-in. extrudate catalyst (Tamm ei al., 1981).

Based on elemental analyses and microprobe tracing (Dautzenberg et al., 1978), metal deposits appear to be present in sulfide forms and not as adsorbed porphyrin-type compounds or as metals in the elemental or metallic state. Takatsuka et al. (1979) and Rankel and Rollmann (1983) have reported direct linear correlations of the spent catalyst sulfur content with the deposited metal content. The sulfide forms of nickel and vanadium are consistent with expectations based on thermodynamics for the conditions typically encountered in residuum hydroprocessing units (600-800°F, 1000-2200 psig, H2/H2S environment). 

Fig. 47. Pore size distribution characteristics of typical residuum hydroprocessing catalysts (Howell et ai. 1985).

The use of model compounds in reaction kinetic studies has provided valuable insight into the fundamental processes occurring in residuum hydroprocessing. The reaction of Ni and V porphyrins under commercial... 

Since residuum hydroprocessing involves both demetallation and desulfurization reactions, the residuum metal and sulfur-containing molecules and their sizes are important. As shown in Table V and illustrated in Figure 5 for the Arabian Light vacuum asphaltene, the sulfur, nickel, and vanadium compounds for the asphaltene from any given residuum have similar sizes ... 

Catalyst selectivity differences have been found for sulfur and metals removal in residuum hydroprocessing (19). Mass transfer limitations are believed to be important (20). The data reported here show that the metal-containing molecules are larger consequently, they should be more subject to diffusion restrictions than the sulfur-containing molecules. Therefore, it will be more difficult for a small pore catalyst to demetallate a residuum than to desulfurize it. 

S. J. Khang and J. F. Mosby (personal communication) have presented process models to describe the removal of sulfur, vanadium, and nickel in residuum hydroprocessing. The kinetic models are given below in Eq. (16) ... 

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