Residuum processing

While subsequently replaced by further improved catalysts, the catalyst achieved high selectivity, was metal resistant at 7,800 ppm nickel plus vanadium, and achieved design projections during start-up and two months of commercial operation. Development of the catalyst served to stimulate research efforts by the catalyst industry to introduce other advanced residuum processing catalysts. 

With residuum processing, however, the situation changes. Metal levels rise dramatically. Figure 16 shows the metal distribution in a log/log scale plot of nickel versus vanadium for some 50 crudes. Obviously, many reduced crudes contain... 

Obviously, the structure of a catalyst surface in any reaction system is important since it defines the catalyst itself. In residuum processing the pore structure is as critical. As shown in the following section, the pore structure influences the diffusion characteristics of metal-bearing molecules and thus the spatial distribution of metal deposits in catalyst pellets. The spatial distribution in turn affects the activity of the catalyst and the useful life of the reactor bed. 

Fig. 49. Effect of catalyst particle size on vanadium deposition for an Arabian Heavy atmospheric residuum processed at 370° (700°F) under 12.59 MPa (1825 psia) of hydrogen (Tamm et al., 1981).

Fig. 50. Novel catalyst shapes for residuum processing, (a) UNOCAL s cloverleaf shape, (b) AKZO Chemie/Ketjen s asymmetric quadralobe, (c) Chevron s Bumpy Oval, (d) W. R. Grace s Minilith.

Fig. 53. Comparison of residuum processing catalyst stability for high-(Maya) and low-(Arabian Heavy) metal-content feeds (Howell et al., 1985).

Brown, E. C., Eccles, R. M., Lukk, G. G., and Rabolini, F. R., Exxon Research and Engineering Company, Florham Park, N. J., "Residuum Processing for Conversion," AM-76-38, paper presented at 1976 NPRA Annual Meeting, March 30, 1976, San Antonio, Texas. 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Refinery sludges remain after distillation and residuum processing. These include petroleum coke (64741-79-3), oils burned in the refinery, and acid sludges containing sulphuric acid used in the refining processes. Acid sludges are used commercially in fertilizer manufacture. 

Bachtel,R.W., Kramer,D.C., Scheuerman,G.L., Stangeland,B.E., and Yuan,S., (1990), Onstream catalyst replacement a breakthrough in residuum processing . Paper presented at the Japan Petroleum Institute Petroleum Refining Conference, Tokyo, October 18-19, 1990. 

Fluid coking (Fig. 4) is a continuous process that uses the fluidized soflds technique to convert atmospheric and vacuum residua to more valuable products (12,13). The residuum is converted to coke and overhead products by being sprayed into a fluidized bed of hot, fine coke particles, which permits the coking reactions to be conducted at higher temperatures and shorter contact times than they can be in delayed coking. Moreover, these conditions result in decreased yields of coke greater quantities of more valuable Hquid product are recovered in the fluid coking process. 

Fig. 11. Schematic of a residuum oil supercritical extraction (ROSE) process using compressed pentane to separate vacuum resids into asphaltenes (high...

Fractionation. Kett-McGee developed the ROSE process for separating the heavy components of cmde oil, eg, asphaltenes, resins, and oils, in the 1950s. This process was commercialized in the late 1970s, when cmde oil and utility costs were no longer inexpensive. In the ROSE process (Fig. 11), residuum and pentane ate mixed and the soluble resins and oils recovered in the supetctitical phase. By stepwise isobatic temperature increases, which decrease solvent density, the resin and oil fractions ate precipitated sequentially. 

The term tar sands is a misnomer tar is a product of coal processing. Oil sands is also a misnomer but equivalent to usage of "oil shale." Bituminous sands is more correct bitumen is a naturally occurring asphalt. Asphalt is a product of a refinery operation, usually made from a residuum. Residuum is the nonvolatile portion of petroleum and often further defined as atmospheric (bp > 350° C) or vacuum (bp > 565° C). For convenience, the terms "asphalt" and "bitumen" will be used interchangeably in this article. 

Petroleum asphalts, compared to native asphalts, are organic with only trace amounts of inorganic materials. They derive their characteristics from the nature of their cmde origins with some variation possible by choice of manufacturing process. Although there are a number of refineries or refinery units whose prime function is to produce asphalt, petroleum asphalt is primarily a product of integrated refineries (Fig. 1). Cmdes may be selected for these refineries for a variety of other product requirements and the asphalt (or residuum) produced may vary somewhat in characteristics from one refinery-cmde system to another and even by cut-point (Table 2) and asphalt content (Fig. 2) (5,6). The approximate asphalt yields (%) from various cmde oils are as follows ... 

Propane Asphalt. As noted above, cmde oils contain different quantities of residuum (Fig. 2) and, hence, asphalt. Asphalt is also a product of the propane deasphalting and fractionation process (5,6,21,22) which involves the precipitation of asphalt from a residuum stock by treatment with propane under controlled conditions. The petroleum charge stock is usually atmospheric-reduced residue from a primary distillation tower. 

Processes for hydrogen gasification, hydrogen pyrolysis, or coking of coal usually produce Hquid co-products. The Hygas process produces about 6% Hquids as benzene, toluene, and xylene. Substitution of petroleum residuum for the coal-derived process oil has been used in studies of coal Hquefaction and offers promise as a lower cost technology (104). 

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