Composition and hydrotreating process for the operation of a magnetically stabilized fluidized bed

#Recently it has been discovered that a fluidized bed of magnetizable particulate solids can be stabilized when operated under the influence of a magnetic field, and that such a bed is useful for conducting various fluid-solids contacting processes; inclusive particularly of adsorption, absorption, particulate removal and catalytic processes. Notable among these are gas-solids contacting processes primarily designed for particulate capture but which may also feature a catalytic reaction, or reactions; or the process may be primarily designed for conducting a chemical reaction, or reactions, with or without the feature of particulate capture. Processes of this type are conducted with composites wherein a ferromagnetic component is incorporated with the nonferromagnetic component, or components, to render the composite ferromagnetic.

#Like conventional fluidized processes a fluid, notably a gas, is injected upwardly at velocity sufficient to overcome the free fall velocities of the individual particles (due to gravity) and cause bed expansion and fluidization of the particles without sweeping significant amounts of the particles, catalytic or otherwise, from the bed. In conventional fluidized processes, however, the injection of gas at velocity sufficient to produce expansion of the bed (i.e., transform the fixed bed from a fixed packed bed to a fluidized bed) is accompanied by significant bubble formation whereas, in contrast, in a fluidized bed subjected to the influence of a magnetic field at conditions which does not increase the weight of the bed there exists an interim, or quiescent zone wherein there is little, if any, motion exhibited by the particles within the fluidized bed. Thus, within this zone the formatin of bubbles and slugs are virtually eliminated due to the interaction between the fluidized ferromagnetic particles and the magnetic field; operation within such zone characterizing that of a magnetically stabilized bed.

#Magnetically stabilized bed processes offer advantages over both fixed and fluidized bed operations. They provide superior operation over conventional fluidized bed operations in that they provide better counter-current contacting, low gas and solids back mixing, and lower particle attrition. They provide better operation as contrasted with fixed bed operations in that they provide lower pressure drop, better ability to transfer solids, and virtually eliminate bed plugging problems. A process disclosing a magnetically stabilized bed and its mode of operation for conducting catalytic reactions, and the capture of particulates to provide a filtering action is disclosed in U.S. Pat. No. 4,115,927 by Ronald E. Rosensweig.

#Magnetic composite materials were prepared from atomized 410 stainless steel powder in a range of concentrations, matrices, and particle sizes. Preparative techniques included: (1) mixing the 410 stainless steel powder with a silica-alumina gel or an alumina gel and spray-drying the mixture to form a composite powder, (2) spray-drying as in (1) and then calcining the resulting powder; (3) mixing the 410 stainless steel powder with alumina powder or polypropylene powder and pressing a pellet of the mixture in a hydraulic press; and (4) mixing the stainless steel powder with silica-alumina gel and allowing the entire mixture to harden in a tray, then crushing the resulting block to form a composite powder. Concentration of stainless steel in the finished composites varied form 0.4 wt. % to 78 wt. %, and from 0.09 Vol. % to 39 Vol. %. In all cases, the volume percent stainless steel in the composite was substantially less than the volume percent stainless steel in the pure stainless steel powder (47%), so that there was substantially no direct contact of stainless steel particles within any of these composites. A very fine mesh cut of the atomized stainless steel, with particle sizes from 0 to 30 .mu.m, was used in some preparations. A coarser cut, with particle sizes from 20 to 44 .mu.m, was used in the other preparations. A total of 20 different composites were prepared.

#The magnetic properties of all these samples were measured using a Princeton Applied Research Model 155 Vibrating Sample Magnetometer and a conventional laboratory electromagnet. Sample shape was varied as much as the magnetometer sample holder would permit; all samples were approximately cylindrical, with their cylinder axis perpendicular to the applied field in the magnetometer. Sample diameters could only be varied from 0.32 to 0.38 cm, but sample lengths were varied from 0.25 to 0.97 cm.

#It was found that stainless steel content was the only one of these variables that had a major influence on the magnetic properties of the composite. Magnetic moment at saturation was directly proportional to stainless steel content, with a proportionality constant of 171.5 emu/g stainless steel. In addition, the magnetic moment resulting when a given field was applied to an initially demagnetized sample was found to be principally determined by the stainless steel content. In particular, when an applied field of 200 oersteds was applied to each of the twenty initially demagnetized samples, the induced magnetic moment averaged 12.4 emu per gram of stainless steel in the sample, with a standard deviation of only .+-.1.5 emu/g.