GB1597617A

GB1597617A - Magnetically stabilized fluid bed process operated in the bubbling mode

Info

Publication number: GB1597617A
Application number: GB13522/78A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1977-04-11
Filing date: 1978-04-06
Publication date: 1981-09-09
Also published as: FR2387078B1; FR2387078A1; CA1135207A; BE865860A; NL7803839A; DE2815224A1; JPS53128573A; AU3496478A; IT1095382B; IT7822165A0; AU526944B2

Description

(54) MAGNETICALLY STABILIZED FLUID BED PROCESS OPERATED IN THE BUBBLING MODE (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a fluidized bed process. More particularly, the invention is concerned with hycrocarbon conversion processes wherein a fluidized bed containing magnetizable particles is subjected to a magnetic field.

Many chemical and physical reactions such as catalytic cracking, hydrogenation, oxidation, reduction, drying, filtering, etc., are carried out in fluidized beds. A fluidized bed, briefly, consists of a mass of a particulate solid material in which the individual particles are in continuous motion relative to each other whereby the mass or fluidized bed possesses the characteristics of a liquid. Like a liquid, it will flow or pour freely, there is a hydrostatic head pressure, it seeks a constant level, it will permit the immersion of objects and will support relatively buoyant objects, and in many other properties it acts like a liquid. A fluidized bed is conventionally produced by effecting a flow of a fluid, usually gas, through a porous or perforate plate or membrane underlying the particulate mass, at a sufficient rate to support the individual particles against the force of gravity. The minimum air flow or pressure drop required to produce the fluid-like, or fluidized, condition is known as the minimum fluidization and is dependent on many parameters including particle size, particle density, etc. Any increase in the fluid flow beyond minimum fluidization causes an expansion of the fluidized bed to accommodate the increased fluid flow until the fluid velocity exceeds the free-falling velocity of the particles which are then carried out of the apparatus.

Fluidized beds possess many desirable attributes, for example, in temperature control, heat transfer, catalytic reactions, and various chemical and physical reactions such as oxidation, reduction, drying, polymerization, coating, diffusion, filtering and the like.

However, the establishment and maintenance of a stable fluidized bed by conventional procedures is a sensitive and difficult process possessing many drawbacks and disadvantages.

Among the problems associated with fluidized beds, a most basic one is that of bubble formation, frequently resulting in slugging, channeling, spouting and pneumatic transport; this problem is most common in gas-fluidized systems. The problem necessitates critical flow control and affects design factors such as minimum fluidization velocities, pressure drops, particle sizes, etc. Bubbling causes both chemical and mechanical difficulties: for example, in gas-solids reactions gas bubbles may bypass the particles altogether resulting in lowered contacting efficiency.

Ideally, a fluidized bed should be free of bubbles, homogeneous, maintain particle suspension and manifest noncritical flow velocity control for various bed heights and bed densities. Many procedures and systems have been proposed to effect improvements, for example, by the use of baffles, gas distribution perforated plates, mechanical vibration and mixing devices, the use of mixed particle sizes, gas plus liquid flow schemes, special flow control valves, etc.

More recently it has been disclosed in a number of publications that the application of a magnetic field to fluidized beds will result in certain improvements in the operation of the fluidized bed. For example, Belgian Patent No. 834,384 describes the application of substantially uniform fields to suppress bubble formation in a fluidized bed.

U.S. Patent No. 3,440,731 is also directed to bubble suppression in a fluidized bed by the application of a magnetic field to the bed particles which are magnetizable. Patentee avoids bubble formation by the use of relatively non-uniform fields and relatively low fluidizing gas velocities.

Numerous publications disclose the application of a magnetic field produced from a direct current (nontime-varying) electromagnet to fluidized iron or iron-chromium particles such as used in ammonia synthesis or carbon monoxide conversion.

In general, the published works teach that higher gas velocities can be used in the presence of an applied magnetic field than in its absence.

The aforedescribed prior art fails to recognize that such high fluidizing gas velocities as are contemplated by this invention could be employed without significant solids backmixing in the bed and entrainment of solids in the gas leaving the fluidized bed. Such high fluidizing gas velocities without significant solids backmixing and entrainment would appear to be unattainable with the type of fluidizable particle systems studied by prior workers in this field since the higher field strengths required to maintain the particles in the bed would result in agglomeration of their highly magnetizable iron particles.

According to the aforementioned Belgian Patent No. 834,384, the use of a magneticially stabilized, fluidized bed minimizes solids backmixing and eliminates gas by-passing of the fluidized solids by preventing gas bubble formation. The elimination of backmixing in certain operations such as cat cracking, reforming, hydrofining, hydrocracking, drying, etc., is particularly advantageous since it prevents backmixing of feed and products and thereby results in a greater selectivity in conversion of feed to desirable products.

Unfortunately, the advantages associated with the elimination of backmixing are partially offset by the poorer heat and mass transfer due to the relatively stationary positioning of the fluidized solid particle. Such a decrease in heat transfer could, in some cases, cause hot spots on the catalyst particles and lead to deactivation of the catalyst, side reactions; selectivity loss, etc. In addition, temperature control may be more difficult in certain reactions such as catalytic cracking, catalytic reforming, hydrocracking, hydrogenation, etc., which are highly exothermic or endothermic in nature.

In accordance with the present invention it has been unexpectedly found that a magnetically stabilized fluid bed may be advantageously operated with high fluidizing gas velocities in the region where bubbling occurs in the bed because the bubbling obtained is uniform and the bubbles themselves are small and finely divided. Further, the particle movement induced is greatly restricted in direction and is without gross vertical circulation which accompanies bubbling in the non-magnetically stabilized fluid beds in use heretofore.

The restricted gross movement of solids and backmixing of gas and solids is not very significant when the bed of the invention is subjected to an applied magnetic field and operated in the bubbling mode. The disadvantages associated with the formation of bubbles in the fluidized bed may be offset by the advantages of good heat and mass transfer and solids transport.

According to the invention a fluidized bed process having reduced solids backmixing with improved heat and mass transfer characteristics, comprises subjecting a bed comprising magnetizable, fluidizable composite particles containing at least 50 volume % of a non-magnetizable material to a magnetic field and passing a gas upward through said bed at a superficial gas velocity of at least twice the minimum fluidization superficial gas velocity in the absence of a magnetic field to produce bubbling therein on a continuous basis without significant entrainment of solids in the gas leaving the bed.

The fluidizable solids which are used in the process of this invention include a composite of magnetizable materials. The magnetizable materials include ferromagnetic and ferrimagnetic substances including, but not limited to, magnetic Fe304, iron oxide (Fe2O3), ferrites of the form MO. Fe2O3, wherein M is a metal or mixture of metals such as Zn, Mn, Cu, etc.; ferromagnetic elements including iron, nickel, cobalt and gadolinium, alloys of ferromagnetic elements etc. Other magnetizable substances which are useful herein are known in the art, for example, U.S. Patents 3,439,899 and 3,440,731 and Belgian Patent 834,384, which are incorporated herein by reference.

In addition to the aforedescribed magnetizable substances, the composite particles will include 50-99, preferably 80 to 95, volume % of a non-magnetizable material. In general, the non-magnetizable material will include a vast number of conventional materials which are inert and/or known to catalyze the desired reaction or the desired mass transfer operation such as drying, separation, etc.

Examples of catalytic materials which may be combined with the magnetizable material of the invention include those catalysts conventionally employed in such processes as fluid catalytic cracking, reforming, hydrogenation, hydrocracking, isomerization, alkylation, polymerization, oxidation, etc. Examples of materials for mass transfer useful herein include drying and separation agents such as the well known molecular sieves, activated charcoals, solid metallic and organic complexing agents and other materials, such as silica gel, which are capable of adsorbing or otherwise capturing selected components of a multi-component gas stream.

The fluid catalytic cracking catalyst which may be incorporated into the magnetizable, fluidizable solids of the invention include the highly active zeolite-containing catalysts and the amorphous silica-alumina catalysts.

In general, the zeolite-type catalysts are exemplified by those catalysts wherein a crystalline aluminosilicate is dispersed with a siliceous matrix. Among the well-recognized types of zeolites useful herein are the "Type A", "Type Y", "Type X", "Type ZSM", mordenite, faujasite, erionite, and the like. A further description of these zeolites and their methods of preparation are given, for example, in U.S. Patent Nos. 2,882,243; 2,882,244; 3,130,007; 3,410,808 and 3,733,390; 3,827,968 and patents mentioned therein, all incorporated herein by reference. Because of their extremely high activity, these zeolite materials are encapsulated with a material possessing a substantially lower level of catalytic activity such as a siliceous matrix material which may be of the synthetic, semi-synthetic or natural type. The matrix materials may include silica-alumina, silica-gel, silica-magnesia, alumina and clays such as montmorillonite, kaolin, etc.

The zeolite which is preferably incorporated into the matrix is usually exchanged with various cations to reduce the alkali metal oxide content thereof. In general, the alkali metal oxide content of the zeolite is reduced by ion exchange treatment with solutions of ammonium salt, or salts of metals in Groups II to VIII of the Periodic Table or the rare earth metals. Examples of suitable cations include hydrogen, ammonium, calcium, magnesium, zinc, nickel, molybdenum and the rare earths such as cerium, lanthanum, praseodymium, neodymium, and mixtures thereof. The catalyst will typically contain 2-25% of the zeolite component and 75-98% of the matrix component. The zeolite will usually be exchanged with sufficient cations to reduce the sodium level of the zeolite to less than 5 wt. %, preferably less than 1 wt. %. Other specific examples of these types of catalysts are found, for example, in U.S. Patent Nos. 3,140,249; 3,140,251; 3,140,252 and 3,140,253, which are incorporated herein by reference.

When used in hydrotreating or hydrofining reactions the catalyst component will contain a suitable matrix component, such as those mentioned heretofore and one or more hydrogenating components comprising the transition metals, preferably selected from Groups VI and VIII of the Periodic Table. Examples of suitable hydrogenating metals which may be supported upon a suitable matrix include, among others, nickel, cobalt, molybdenum, tungsten, platinum, and palladium, ruthenium, rhenium, iridium (including the oxides and sulfides thereof). Mixtures of any two or more of such hydrogenating components may also be employed. For example, catalysts containing (1) nickel or cobalt, or the combination thereof, in the form of metal, oxide, sulfide or any combination thereof, and (2) molybdenum or tungsten, or the combination thereof, in the form of metal, oxide, sulfide or any combination thereof are known hydrofining catalysts. The total amount of hydrogenating component supported on the matrix may range from 2 to 25 wt. % (calculated as metal) usually 5 to 20 wt. % based on the total weight of the catalyst composition. A typical hydrofining catalyst includes 3 to 8 wt. % CoO and/or NiO and about 8 to 20 wt. % MoO3 and/or W03 (calculated as metal oxide).

Examples of reforming catalysts which may be used in accordance with the invention are those catalysts comprising a porous solid support and one or more metals (or compounds thereof, e.g. oxides) such as platinum, iridium, rhenium, palladium, etc. The support material can be a natural or a synthetically produced inorganic oxide or combination of inorganic oxides.

Typical acidic inorganic oxide supports which can be used are the naturally occurring aluminum silicates, particularly when acid treated to increase the activity, and the synthetically produced cracking supports, such as silica-alumina, silica-zirconia, silicaalumina-magnesia, and crystalline zeolitic alumino-silicates. Generally, however, reforming processes are preferably conducted in the presence of catalysts having low cracking activity, i.e., catalysts of limited acidity. Hence, preferred carriers are inorganic oxides such as magnesia and alumina. Other examples of suitable reforming catalysts are found in U.S.

Patent Nos. 3,415,737; 3,496,096; 3,537,980; 3,487,009; 3,578,583; 3,507,780; and 3,617,520 which are incorporated herein by reference.

The aforedescribed magnetizable material may be directly incorporated with the non-magnetizable material in accordance with well known techniques. For example, one or more of the aforedescribed non-magnetizable materials may be impregnated with a soluble precursor of a ferromagnetic or ferrimagnetic substance which is subsequently reduced to render the particles ferromagnetic or ferrimagnetic. Alternatively, the ferromagnetic or ferrimagnetic material may be incorporated into the non-magnetizable component by encapsulation of finely divided ferromagnetic or ferrimagnetic material. The particular method of preparing a fluidizable solid does not form a part of this invention.

The fluidized bed containing the magnetizable, fluidizable composite particles of the invention may include composites or other solids which are not magnetizable. In addition to the magnetizable, fluidizable composite particles of the invention, the bed may contain some particles which are 100% ferro- or ferrimagnetic materials.

An important factor in selecting or preparing the magnetizable, fluidizable composite particles of the invention is the magnetization M of the particle. The higher the magnetization M of the particle, the higher will be the superficial gas velocity at which the bed may be operated without significant backmixing of solids in the bed and significant entrainment of solids in the gas leaving the bed, all other factors such as particle size, particle density, particle size distribution, gas viscosity, gas density, etc. being held constant. The magnetization of the magnetizable, fluidizable composite particles of the invention in the bed will have a magnetization M of at least 10 gauss. Generally for high gas velocities, the particles will have a magnetization, as being imparted by the applied magnetic field, of at least 50 gauss, preferable at least 100 gauss and more preferably at least about 150 gauss, e.g. 150 gauss to 400 gauss. For those processes advantageously operated at very high gas velocities, the magnetization of the magnetizable, fluidizable composite particles of the invention may be up to about 1000 gauss or more.

The magnetization M of the particles, as is well known, is defined as B-H in the particle, where B is the magnetic induction and H is the magnetic field, the fields being defined in standard published works in electromagnetism, e.g., Electromagnetic Theory, J. A.

Stratton, McGraw-Hill (1941). The value of M may be measured in a variety of ways, all of which give the same value M since M has an objective reality.

One means for determining magnetization M of the particles in a bed under the influence of a given applied magnetic field is to measure their magnetic moment at that field in a vibrating sample magnetometer under conditions of similar voidage, sample geometry and temperatures as exist in the process to be used. The magnetometer gives a value of , the magnetic moment per gram from which magnetization M is obtained from the formula: M = 4zpo where p is the density of the particles in the test sample, a is the magnetic moment in emu/g and M is the magnetization of the particles in gauss at the applied magnetic field tested.

Generally, the magnetization M of a particle as obtained from a magnetometer when a given magnetizing field Ha is applied will not provide a value which is the same as the magnetization of the particle in response to the same intensity of magnetic field in the fluidized bed to be used in accordance with the teachings of the present invention.

The purpose of the following is to indicate a method for determining the magnetization Mp of a typical particle in a bed from those values obtained from a magnetometer.

Generally, this will require a calculation since the effective field that a bed particle is subjected to depends on the applied field, the bed geometry, the particle geometry, the bed voidage and particle magnetization. A general expression has been derived to relate these quantities based on the classical approximation of the Lorentz cavity that is employed in analogous problems such as the polarization of dielectric molecules.

Ha = He + Mp [dp + (l--E,) (db-1/3)1 (1) Ha is the applied magnetic field as measured in the absence of the particles, He the magnetic field within a particle, Mp the particle magnetization, dp the particle demagnetization coefficient, Eo the voidage m the particle bed, and db the bed demagnetization coefficient.

The term -1/3 is due to the magnetizing influence of a (virtual) sphere surrounding the bed particle.

The expression above applies as well to a sample of particles such as used in a magnetometer measurement. In that case db is the demagnetization coefficient da corresponding to shape of the cavity in the sample holder.

Magnetometer measurement produces a graph of Mp vs. Ha. Using the above equation and known values of dp, ds, eO, Mp and Ha a corresponding value of He may be computed.

When the value of He IS small its value found in this manner is determined by a difference between large numbers, hence is subject to cumulative errors. Accordingly, a modified approach is useful as described in the following.

Thus it is useful to define a reference quantity Hs representing the calculated field in a spherical cavity at the location of the particle. It is imagined that the magnetization of surrounding particles is unchanged when the said particle is removed.

Hs = Ha - Mp [(1Eo) (db-l/3)] (2) Combining the two expressions gives an alternate relationship for Hs, in which Ha is eliminated.

Hs = He + Mpdp (3) This expression is recognized to give Hs as the change of field in passing from the inside of a particle to the outside of the particle.

Denoting Km as the following constant Km = (1Eo) (d51/3) then from (2) Km equals the quantity Mp/(HaHs) i.e.

K Mp (5) Hazes Thus, on the graph of Mp vs. H a straight lines of slope Km intersecting the measured curve and the Ha axis relate corresponding values of Mp and Hs. Accordingly, a graph may be constructed of Mp vs. Hs. For example, when the sample is contained in a spherical cavity da = 1/3, Km is infinite, and Hs equals Ha. For a long sample such that da = 0, Km is negative and Ha is less than Hs i.e. the field magnetizing a particle of the sample is greater than the field applied to the sample.

Additionally, for a process bed, a constant Kp may be defined as follows: Kp = Eo)(db 1/3)] (6) It may also be seen from Eq. (2) that a line of slope-Kp passing through a point Ha on the horizontal axis of the graph of M vs. Hs intersects the curve on the graph at a value of Mp giving the particle magnetization in the bed. Thus, the particle magnetization M in a process bed has been related to the field Ha applied to the process bed.

The relationship of Eq. (1) is an approximation more likely to be accurate for beds having high voidage than for very densely packed samples.

It is to be understood that the term "applied magnetic field" used throughout the specification and claims refers to an empty vessel applied magnetic field. The empty vessel applied magnetic field strength is that measured within the vessel if all conditions were the same except that there were no ferromagnetic material present in the vessel to direct or otherwise influence the magnetic field at the point where the measurement is made. This value is the field strength one obtains when only the coil geometry and the energizing current through the coil are used to calculate the field strength.

Thus, it can be seen from the above discussion that the fluidizing gas velocity region of operation in accordance with the invention is potentially expanded with increasing magnetization of the particles. The actual magnetization of the pArticles in the fluidization vessel will be a function of the particles themselves (the degree of magnetizability they inherently possess) and the intensity of the applied magnetic field.

As stated above the magnetizable particles should have a certain degree of magnetization M which is imparted to the particles by the intensity of the applied magnetic field.

Obviously, one would seek the lowest applied magnetic field possible because of cost.

Commonly, many of the composite particles will require at least 50 oersteds, preferably at least 100 and preferably less than 1000 oersteds to achieve the requisite magnetization M.

The determination of the applied magnetic field will take into account the type of particles fluidized, i.e., their magnetization M, particle size and distribution, the fluidizing gas velocity to be used, etc.

As stated earlier, it is contemplated that in some cases the magnetizable, fluidizable composite particles of the invention may be admixed with non-magnetic particles. For example, silica, alumina, metals, catalysts, coal, etc. may be admixed with the magnetizable, fluidizable composite particles. In the case of admixtures (as opposed to only composite materials containing the magnetizable particles) it is preferred that the volume fraction of magnetizable, fluidizable composite particles exceed 25 percent, more preferably exceed 50 volume percent. In most cases, the bed will be comprised of 100 volume percent of the magnetizable, fluidizable composite particles (i.e., it will not contain admixtures of other materials). When the non-magnetizable admixture exceeds 75 volume percent, the particle mixtures may separate analogous to liquids of limited solubility.

The particle size of the fluidizable, magnetizable composite particles will range from about 0.001 mm to 50 mm, more preferably from 0.05 to 1 mm. Often the particle size will range from about 0.1 to .75 mm. The particle size range referred to herein is that determined by the mesh openings of a first sieve through which the particles pass and a second sieve on which the particles are retained.

The process of the invention permits operation with high fluidizing gas velocities in the region where bubbling occurs without significant entrainment of solids in the gas leaving the bed. In accordance with the invention, the fluidizing gas velocity will be passed upwardly through the bed at a superficial gas velocity at least twice, e.g. 2 to 10 times and as much as 25 times, and more, the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field. In order to fluidize the solids of the invention at such high gas velocities without significant entrainment of solids in the gas leaving the bed, it is preferable to employ magnetic fields having a field strength greater than 50 oersteds, more preferably, greater than 150 oersteds, with the upper limit being determined on the basis of the amount of field which would cause agglomeration of the particles or slug formation.

The minimum superficial gas velocity to be employed in order to produce bubbling in the bed is a function of the component of magnetization of the magnetizable, fluidizable composite particles along the direction of the external force field, i.e. gravity in the verticle direction, which is imparted by the applied magnetic field. It is to be recognized that factors such as particle size, particle composition, particle density, length and shape of the bed, etc.

each affect the gas fluidization velocity to be employed to achieve the benefits of the invention at a given component of magnetization. The variation and adjustment of these factors will be apparent to those skilled in the art in practising the process of the present invention.

As is generally known, the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field is that superficial gas velocity required to transform the bed of particles at rest, i.e. a fixed bed, to a bed in the fluidized state, i.e. a fluidized bed, in the absence of an applied magnetic field. In general, this minimum fluidization superficial gas velocity is the gas velocity observed when the pressure difference of the gas passing through the fluidized bed, as measured between upper and lower surfaces of the bed, is first substantially the same as the bed weight per unit cross-sectional area. As is well known, superficial gas velocity is a measure of the linear gas velocity that would pass through an empty vessel and it is measured in feet per second, centimeters per second, etc.

As the superficial gas velocities are increased, the component of magnetization of the magnetizable, fluidizable composite particles along the direction of the external force field, i.e. gravity in the vertical direction, will at some point have to be increased so as to prevent significant entrainment of solids in the gas leaving the bed (and possibly to prevent unacceptable backmixing of the solids in the bed). It will be recognized that particles of high magnetization such as iron and steel can achieve a very high component of magnetization M at relatively low applied magnetic fields. These particles, however, have the limitation that at applied magnetic fields, e.g., above 50 or 100 oersteds, the particles tend to aggregate and take the form of a slug. Consequently, the level of superficial fluidization gas velocity that can be achieved with such particles is limited while still maintaining fluidization of the solid particles in the bed without significant entrainment of solids in the gas leaving the bed.

The maximum useful levels for the magnetization M of most particles will normally be less than about 1000 gauss, preferably less than 400 gauss, in order to achieve a reasonably fluid-like bed medium without undue agglomeration of particles. For example, it can be calculated that iron spheres in a bed subjected to an applied field of 50 oersteds has a magnetization M of bed particle of about 300 gauss. However, it will be recognized that at points of contact of the particles, the magnetization can be far greater and hence the magnetic forces of agglomeration are greater.

In the preferred embodiment of the invention, the fluidized bed is subjected to a substantially uniform magnetic field. This means that the magnetic field is applied to have a vertical component to stabilize the fluidized medium and the variation of the vertical component of the magnetic field to the mean magnetic field in the bed will be no greater than 50% and preferably no greater than 10%.

The degree of magnetic field to be applied to the fluidized solids in the reaction zone will, as indicated, depend on the magnetization of the fluidizable particles and the superficial velocity of the fluidizing gas. The type and amount of the solids will also obviously have an effect on the strength of the magnetic field to be employed. The strength of the field produced by an electromagnet can be finely adjusted by adjusting the current supplied to the electromagnet. Specific methods of applying the magnetic field are also described in U.S. Patents 3,440,731 and 3,439,899 and Belgian Patent 834,384 which are incorporated herein by reference.

In accordance with the invention, the fluidized bed process is operated to produce bubbling in the bed without significant entrainment of solids in the fluid leaving the bed.

The point of bubbling and the amount of entrainment can be controlled by adjusting particle density, particle size, particle shape, fluidizing gas velocity and viscosity, particle magnetization, strength of the field applied to the fluidized bed, etc.

Bubbling can be visually observed in an open top or, alternately, transparent wall reactor such as may be used in experimental and atmospheric pressure operation. As is known, at the point of bubbling the height of the fluidized bed begins to fluctuate and becomes difficult to measure. Significant entrainment is a point where unacceptable quantities of solids are stripped from the fluidizing medium and are carried from the bed region. And, significant backmixing refers to the condition where the lifting forces of the fluidizing medium flow result in a sufficiently great upward welling of solids at some points in the bed, together with a corresponding downflow at other points so that reactants entering the bed and reaction products returned to the reactant inlet zone by the circulating solids are comixed to an undesirable and unusable degree. All three of these conditions may be inferred by indirect measurement techniques when the process of the invention is used in typical chemical or hydrocarbon reactor systems. Such measurement means include, but are not limited to, the determination of heat transfer rates for the bubbling condition, and the modification, upon passage through the bed, of pulse shapes when pulses of a tracer component are introduced with the fluidizing medium for the backmixing condition.

As indicated, bubbling in a fluidized bed is a well known and recognized phenomena resulting in fluctuations of the fluidized bed height. Bubbling, therefore, can be determined by a variety of techniques which measure the fluctuation of bed height (length). Thus bed height fluctuation can be ascertained by a Hall probe placed in a fluidized bed, the use of a laser beam or by pressure taps into the fluidized bed. A convenient means for detecting bed height fluctuation is by determining the pressure difference through the bed containing the magnetizable, fluidizable composite particles. Fluctuations in bed height will produce fluctuations in the pressure difference through the bed, thus indicating that the superficial fluidization gas velocity is sufficiently high to produce bubbling in the fluidized bed. With reference to Figure 1, this means that the bed is operating in the region beyond VT. Thus, fluctuations in the pressure difference in the bed is indicative of bubble formation, and it is the intent of the present invention to operate fluidized bed to produce bubbling therein as a result of a sufficiently high gas fluidization velocity. In one embodiment, therefore, the superficial gas velocity is controlled and/or monitored such that it is sufficient to cause time-varying fluctuations of pressure difference through the bed over a finite period of time, e.g. 1, 2, 10, etc. seconds, during continuous fluidization.

The upper limit on the superficial gas velocity employed in the present invention is that superficial fluidizing gas velocity which produces unacceptable carryover or entrainment of solids in the gas leaving the fluidized bed. In other words, the superficial gas velocity is controlled and/or monitored so that there is no significant entrainment of solids in the gas leaving the fluidized bed, e.g. less than 15 grains/SCF, preferably less than 1.5 grains/SCF, more preferably less than .5 grains/SCF, e.g. .02 to 0.1 grains/SCF (standard cubic feet at 60"F and 1 atmos. pressure).

Preferably, conditions in the fluidized bed zone are maintained to continuously produce bubbling therein without significant entrainment of solids in the fluid leaving the bed. The fluidized bed is preferably operated in the bubbling mode on a continuous basis as opposed to the occasional or periodic operation of a magnetically stabilized fluidized bed in the bubbling mode. It is recognized, however, that in some instances it may be desirable during operation of the fluidized bed process to occasionally operate the bed under conditions which will not produce bubbling. For example, when it is desired to initiate a reaction which requires an elevation of temperature within the bed and mixing motions would cool the bed and thus quench the reaction before the temperature is reached at which self-sustaining exothermic conditions are reached.

The feedstocks suitable for conversion in accordance with the invention include any of the well-known feeds conventionally employed in hydrocarbon conversion processes.

Usually, they will be petroleum derived, although other sources such as shale oil and coal are not to be excluded. Typical of such feeds are heavy and light virgin gas oils, heavy and light virgin naphthas, solvent extracted gas oils, coker gas oils, steam-cracked gas oils, middle distillates, steam-cracked naphthas, coker naphthas cycle oils, deasphalted residua, etc.

The application of a magnetic field to the reactor, catalyst regenerator, separation zone, drying zone, etc. in accordance with the invention is not to be limited to any specific method of producing the magnetic field. Conventional permanent magnets and/or electromagnets can be employed to provide the magnetic field used in the practice of this invention. The positioning of the magnets will, of course, vary with the solids used, degree of fluidization required and the effects desired. In the preferred embodiment of this invention, a cylindrical electromagnetic, or an a rangement of toroidally-shaped electromagnet which produces a magnetic field which is equivalent to that of a cylindrical electromagnet, is employed to surround at least a portion of the fluidized bed as this provides those skilled in the art with an excellent method of achieving near uniform magnetic field and stability throughout the bed. Such electromagnets when powered by direct current with the use of a rheostat, solid state controller, saturable core transformer, etc. are particularly desirable for applying a magnetic field to the bed particles and to provide an excellent method of maintaining the fluidization of the bed particles in response to changing flow rates of the fluidizing medium.

The process conditions to be employed in the practice of the present invention will, of course, vary with the particular physical or conversion reaction desired.

The following table summarizes typical hydrocarbon conversion process conditions effective in the present invention.

Reaction Conditions Principal Conversion Temperature Pressure Feed Rate Hydrogen Rate Desired "F psig V/VlHr. scf/Bbl Hydrofining 500-800 50-2000 0.1-10.0 500-10,000 Hydrocracking 450-850 200-2000 0.1-10.0 500-10,000 Catalytic Cracking 700-1000 0-50 0.1-20.0 0 Catalytic Reforming 800-1100 50-1000 0.1-20.0 500-10,000 The invention is described with reference to the drawings in which: Figure I is a graphical illustration of a three-phase diagram displaying a bed containing magnetizable, fluidizable solids subjected to various magnetic field intensities and fluidizing gas velocities and operated (1) in the region where the solids are unfluidized, (2) the region where the solids are fluidized and stabilized to eliminate bubbling and (3) the region where bubbling occurs in the fluidized bed (the region of the invention).

Figure 2 is a graph showing the results in terms of bed void fraction vs. fluidizing gas velocity for a fluidized bed operated at various gas fluidizing gas velocities.

Referring to Figure 1 in greater detail, this figure illustrates the operating regimes that can be achieved when a magnetic field is applied to a fluidized bed of ferromagnetic solids at various superficial fluidizing gas velocities. The region indicated as (1) is the region where the fluidizing gas velocity U is not high enough to fluidize the solids, i.e. the solids are in a settled mass analogous to a fixed bed.

The region indicated as (2) is a region above the minimum superficial gas velocity UMF required to fluidize the bed at applied field H where the bed is expanded and the solids behave like a fluid but there is essentially no bubbling or motion of the solids. The region indicated as (3) is a region above the transition superficial gas velocity UT (minimum superficial gas velocity to cause bubbling mode operation) at applied field H where the bed is expanded and the solids behave like a fluid but bubbling of the bed occurs in a very gentle quiescent manner with no gross movement of solids or backmixing of gas and solids. Region 3)is the region of the invention.

The following example further illustrates the present invention.

An open-topped cylindrical Plexiglas column having an inner diameter of 28 centimeters and a length of 55 centimeters was charged with 3,148 grams of fluidizable particles consisting of Ni on alumina containing 23 wt. % magnetizable Ni and sold under the trade name Girdler G87RS and having an average particle size of 270 microns. (The words 'Plexiglas' and 'Girdler' are registered Trade Marks). Coaxially surrounding the bed of particles was a toroidal electromagnetic coil having an inner diameter of 40 cm consisting of a stack of 10 flat coils each 2.54 cm high with an outer diameter of 60 cm. The coils were spaced in a vertical direction by 2.8 cm with each coil consisting of 170 turns of flat copper ribbon and about 0.05 cm thickness. The coil was supplied with direct current to produce a uniform, axially oriented field of 420 oersteads over the entire test region.

Air at various velocities was passed upwardly through the bed for fluidization. The fraction of the bed which was void was measured at various fluidizing velocities by measuring the increase in bed height and calculating the void fraction from the weight of catalyst, the known particle density, and the cross-sectional area of the bed. The results are shown in Figure 2.

When the bed was operating in the bubbling mode, it was observed that the bubbling was very uniform and the bubbles were smaller as compared to bubbles produced in the absence of the magnetic field. Further, the downflow of solids at the vessel wall which is normally observed in a bubbling bed in the absence of a magnetic field was minimal in the instant bubbling bed subjected to a magnetic field. In the presence of the magnetic field, the bubbling occurs without significant backmixing and results in good heat transfer characteristics. Entrainment of bed fines less than 5 microns did not occur except at very high fluidizing velocities. In this example, entrainment of bed fines (less than 5 microns) started when the air velocity was about 10 times the minimum fluidization velocity for the fluid bed, and bubbling occurred in the bed at about 3.5 times the minimum fluidization velocity.

The applied magnetic field of 420 oersteds used in this example resulted in a magnetization of the fluidizable, magnetizable composite particles of about 100 gauss when the bed was at or above the transition velocity, UT.

WHAT WE CLAIM IS: 1. A fluidized bed process for improving the contacting of a gas phase with a solid phase by reducing solids backmixing and improving heat and mass transfer characteristics, in which a bed comprising magnetizable, fluidizable composite particles which contain at least 50 volume % of a non-magnetizable material is subjected to a magnetic field and a gas is passed upward through said bed at a superficial gas velocity of at least twice the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field to produce bubbling therein on a continuous basis without significant entrainment of solids in the gas leaving the bed.

2. A process according to claim 1 in which said fluidized bed is subjected to a magnetic field of at least 50 oersteds oriented axially to the flow of gas in the fluidized bed zone.

3. A process according to either of claims 1 and 2 in which the magnetizable, fluidizable composite particles contain 1 to 50 volume % of a magnetizable material.

4. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles have a magnetization of at least 150 gauss.

5. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles contain 5 to 20 volume % of a ferromagnetic material.

6. A process according to any one of the preceding claims in which the fluidized bed is subjected to a substantially uniform magnetic field of at least 100 oersteds oriented axially to the flow of gas in the fluidized bed zone.

7. A process according to any one of the preceding claims in which the fluidizing gas has a superficial velocity in the range of 2 to 10 times the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field.

8. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles contain a zeolitic crystalline aluminosilicate and a ferromagnetic material.

9. A process according to any one of the preceding claims in which the bed is surrounded by an electromagnet powered by a direct current source.

10. A process according to any one of the preceding claims in which the variation of the vertical component of the magnetic field to the mean magnetic field in the bed is no greater than 10%.

11. A process according to any one of the preceding claims in which the fluidized bed is at an elevated temperature, said fluidizing gas comprises a vaporized hydrocarbon feedstock and said magnetizable, fluidizable composite particles are active for the catalytic conversion of said hydrocarbon feedstock.

12. A process according to any one of the preceding claims in which the fluidizing gas comprises hydrogen.

13. A process according to any one of the preceding claims in which the fluidized bed is at a temperature of 500-800"F, said fluidizing gas comprises a vaporized petroleum feedstock and hydrogen and said magnetizable, fluidizable composite particles are active for the catalytic desulphurisation of said feedstock.

14. A process according to any one of claims 1 to 12 in which the fluidized bed is at a temperature of 800-1100 F, said fluidizing gas comprises a vaporized hydrocarbon feedstock and said magnetizable, fluidizable composite particles are active for the catalytic

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

ribbon and about 0.05 cm thickness. The coil was supplied with direct current to produce a uniform, axially oriented field of 420 oersteads over the entire test region.

Air at various velocities was passed upwardly through the bed for fluidization. The fraction of the bed which was void was measured at various fluidizing velocities by measuring the increase in bed height and calculating the void fraction from the weight of catalyst, the known particle density, and the cross-sectional area of the bed. The results are shown in Figure 2.

When the bed was operating in the bubbling mode, it was observed that the bubbling was very uniform and the bubbles were smaller as compared to bubbles produced in the absence of the magnetic field. Further, the downflow of solids at the vessel wall which is normally observed in a bubbling bed in the absence of a magnetic field was minimal in the instant bubbling bed subjected to a magnetic field. In the presence of the magnetic field, the bubbling occurs without significant backmixing and results in good heat transfer characteristics. Entrainment of bed fines less than 5 microns did not occur except at very high fluidizing velocities. In this example, entrainment of bed fines (less than 5 microns) started when the air velocity was about 10 times the minimum fluidization velocity for the fluid bed, and bubbling occurred in the bed at about 3.5 times the minimum fluidization velocity.

The applied magnetic field of 420 oersteds used in this example resulted in a magnetization of the fluidizable, magnetizable composite particles of about 100 gauss when the bed was at or above the transition velocity, UT.

WHAT WE CLAIM IS: 1. A fluidized bed process for improving the contacting of a gas phase with a solid phase by reducing solids backmixing and improving heat and mass transfer characteristics, in which a bed comprising magnetizable, fluidizable composite particles which contain at least 50 volume % of a non-magnetizable material is subjected to a magnetic field and a gas is passed upward through said bed at a superficial gas velocity of at least twice the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field to produce bubbling therein on a continuous basis without significant entrainment of solids in the gas leaving the bed.
2. A process according to claim 1 in which said fluidized bed is subjected to a magnetic field of at least 50 oersteds oriented axially to the flow of gas in the fluidized bed zone.
3. A process according to either of claims 1 and 2 in which the magnetizable, fluidizable composite particles contain 1 to 50 volume % of a magnetizable material.
4. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles have a magnetization of at least 150 gauss.
5. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles contain 5 to 20 volume % of a ferromagnetic material.
6. A process according to any one of the preceding claims in which the fluidized bed is subjected to a substantially uniform magnetic field of at least 100 oersteds oriented axially to the flow of gas in the fluidized bed zone.
7. A process according to any one of the preceding claims in which the fluidizing gas has a superficial velocity in the range of 2 to 10 times the minimum superficial gas velocity required to fluidize the bed in the absence of a magnetic field.
8. A process according to any one of the preceding claims in which the magnetizable, fluidizable composite particles contain a zeolitic crystalline aluminosilicate and a ferromagnetic material.
9. A process according to any one of the preceding claims in which the bed is surrounded by an electromagnet powered by a direct current source.
10. A process according to any one of the preceding claims in which the variation of the vertical component of the magnetic field to the mean magnetic field in the bed is no greater than 10%.
11. A process according to any one of the preceding claims in which the fluidized bed is at an elevated temperature, said fluidizing gas comprises a vaporized hydrocarbon feedstock and said magnetizable, fluidizable composite particles are active for the catalytic conversion of said hydrocarbon feedstock.
12. A process according to any one of the preceding claims in which the fluidizing gas comprises hydrogen.
13. A process according to any one of the preceding claims in which the fluidized bed is at a temperature of 500-800"F, said fluidizing gas comprises a vaporized petroleum feedstock and hydrogen and said magnetizable, fluidizable composite particles are active for the catalytic desulphurisation of said feedstock.
14. A process according to any one of claims 1 to 12 in which the fluidized bed is at a temperature of 800-1100 F, said fluidizing gas comprises a vaporized hydrocarbon feedstock and said magnetizable, fluidizable composite particles are active for the catalytic

reforming of said feedstock.
15. A process according to any one of the preceding claims in which the gas is passed upward through said bed at a superficial gas velocity sufficient to cause fluctuations in the pressure difference in said fluidized bed without significant entrainment of solids in the gas leaving the bed.
16. A fluidized bed process for improving the contacting of a gas phase with a solid phase substantially as hereinbefore described with reference to the Examples and the Figures.