Vacuum bottom

The reactor effluent is separated by conventional distillation into recycle solvent, light gases, to 537°C bp distillate, and a heavy vacuum bottoms stream containing unconverted coal and ash. The recycle solvent is hydrogenated in a separate reactor and sent back to the Hquefaction reactor. 

The heavy vacuum bottoms stream is fed to a Flexicoking unit. This is a commercial (125,126) petroleum process that employs circulating fluidized beds at low (0.3 MPa (50 psi)) pressures and intermediate temperatures, ie, 480—650°C in the coker and 815—980°C in the gasifier, to produce high yields of hquids or gases from organic material present in the feed. Residual carbon is rejected with the ash from the gasifier fluidized bed. The total Hquid product is a blend of streams from Hquefaction and the Flexicoker. 

The vacuum residua or vacuum bottoms is the most complex fraction. Vacuum residua are used as asphalt and coker feed. In the bottoms, few molecules are free of heteroatoms molecular weights range from 400 to >2000, so high that characteri2ation of individual species is virtually impossible. Separations by group type become blurred by the sheer mass of substitution around a core stmcture and by the presence of multiple functionahties in a single molecules. Simultaneously, the traditional gc and ms techniques require the very volatiUty that this fraction lacks. 

Vacuum distillatiou is used to remove the residue from the distillate product. Additional heavy oil may be recovered from the vacuum bottoms by employing Exxon s Flexicoldng process. 

The heaviest bottoms product from the main column is commonly called slurry or decant oil. (In this book, these terms are used interchangeably.) The decant oil is often used as a cutter stock with vacuum bottoms to make No. 6 fuel oil. High-quality decant oil (low sulfur, low metals, low ash) can be used for carbon black feedstocks. 

Crude Source API Gravity Vacuum Bottoms, vol% Total Nitrogen of Heavy Vacuum Gas Oil, PPM... 

Fig. 10 The FT-Raman spectra over the wavenumber range 10-250cm-1 ofmagnesium stearate after different drying procedures. Top, heated at 90°C to constant weight under vacuum middle, heated to 60°C to constant weight under vacuum bottom, commercially supplied sample.

Figure 6. Semicoke texture a) flow domain anisotropy in a LVB semicoke b) fine grain mosaic anisotropy in a HVB semicoke c) vacuum bottoms and carboniferous MVB coal at 554 " C (coal 30% by weight).

Residual oil Vacuum bottoms can be utilized as feedstock for the visbreaker, coker, or possibly the asphalt unit can be used as 6 fuel oil... 

C+ cold lake vacuum bottoms To MICROCAT-RC reactors ... 

Process hydrogen is produced by steam reforming light hydrocarbon gases. An alternative method for hydrogen production is partial oxidation of the heavy vacuum bottoms stream or of coal. 

Experience indicates that an important part of a normal process development is definition of solutions to operability and reliability problems that have been identified. The EDS process development is no exception. Potential mechanical problems associated with feed slurry preheat, slurry pumping, high pressure letdown valves and vacuum bottoms pumping have been identified and will be addressed in the 250 T/D pilot plant program. In addition, several process problems associated with the variety of coals processed have been identified and solutions defined. The status of both pilot plant construction and definition of solutions to process problems is presented in this paper. 

ER E discussions with Texaco and with Shell on bottoms processing are summarized herein. Texaco has indicated that its partial oxidation process could be applied to coal liquefaction bottoms on a commercial scale and that operation of their 12 T/D pilot plant with coal liquefaction bottoms representative of a projected commercial feedstock would be adequate to set the design basis for a commercial facility. Texaco indicated that three to four years after successful operation of the 12 T/D unit a commercial facility could be ready for startup. In initial discussions, Shell has indicated that development of the Shell/ Koppers partial oxidation process for coal liquefaction bottoms would involve operations of both their 6 T/D pilot plant and their 150 T/D demonstration unit. It was estimated that the 150 T/D facility might become available in the late 1980/early 1981 time frame for possible operation on vacuum bottoms. 

M(PC)]. (10) For example, [M(PC)] have been used as homogeneous catalysts for the hydrotreating of black oils (vacuum bottom). (11) The addition of [M(PC)], M = Co, Fe, V, Ni, Cu, and Pt, increases the amount of distillables when the oil is subjected to hydrogenation at 260-425°C and 1500-3500 psi H2 pressure. Hydroconversion of heavy oils is also accomplished with catalysts of powdered Fe metal and [M(PC)] where M Co, V, Ni, Cr, Mo, Pt at 420-482°C and 1000-3000 psi H2 pressure. (12) Although [M(PC)] have never been used as HDN catalysts per se, the oils have an appreciable concentration of heteroatom-containing molecules which appear to be hydrogenated. 

The percent of alkali-soluble acids varies somewhat, but not greatly, among asphaltenes, preasphaltenes, and total H-coal vacuum bottoms, but the percent of precipitable bases varies markedly. Assuming that phosphotungstic... 

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