Magnetically stabilized fluidized particles in liquid media

A method for the preparation of an ion exchange sorbent containing at least one anion exchange resin, a ferromagnetic substance, and a water permeable organic polymer binder, as well as a process for the use of said sorbent to separate removable anions from feedstreams containing said anion.

BACKGROUND OF THE INVENTION 
Recent regulations have mandated the removal of ions such as chromate ion 
from waste streams to a maximum acceptable level. One of the ways to 
capture these removable ions is to use ion exchange resins in a fixed or 
fluidized bed. The advantage that a fluidized bed offers is that of 
greater rates of flowthrough and resistance to clogging by particulate 
impurities, but small particles are carried out of the fluidized bed 
thereby contaminating the effluent and losing expensive sorbent. These 
disadvantages can be overcome through permanent magnetization of the 
sorbent particles bu resident magnetism in these particles causes 
flocculation to occur anywhere in the apparatus and its associated 
plumbing. 
In U.S. Pat. No. 4,115,927 Rosensweig discusses the prior art in which 
magnetic fields had been applied to fluidized beds of particles and then 
discloses a process for fluidizing magnetizable particles characterized by 
operating in a magnetic field at a superficial fluid velocity which avoids 
fluidization by bubbling at high velocities. While the term "fluid" is 
used, it is clear that Rosensweig's experiments were carried out with 
gases rather than liquids since only gases provide the bubbling action in 
the fluidized bed which the patentee wished to avoid. Further, the 
superficial velocities reported are typical of gases rather than liquids. 
As will be seen in the description of the present invention which follows, 
the inventors have found that carrying out a process in a bed of particles 
fluidized with liquid presents unique conditions not found in the 
Rosensweig patent. 
BRIEF SUMMARY OF THE INVENTION 
This invention provides a process for the exchange of ions between a 
sorbent particle which includes a soft magnetic material and a liquid 
medium containing unwanted ions in a magnetically stabilized fluidized 
bed. 
In one aspect, the invention relates to a process for contacting a bed of 
particles containing soft magnetic material having an average diameter of 
about 100 to 300 microns in an upwardly flowing liquid stream having a 
linear velocity of about 0.018 to about 1.0 cm/sec and in which the bed of 
particles is fluidized by said liquid stream and maintained between 
predetermined boundaries with controlled axial dispersion by maintaining a 
magnetic field from a DC solenoid surrounding said bed and providing 
between 25 to 500 gauss (in the absence of said particles). The soft 
magnetic material preferably will have a coercivity of less than 0.6 
oersteds. 
Another aspect of this invention is found in a process for the exchange of 
anions which comprises contacting an aqueous medium containing removable 
anions with sorbent particles having an average diameter of about 100 to 
300 microns, said sorbent being a homogeneous composite of an anion 
exchange resin, a soft ferromagnetic substance, and a water permeable 
organic polymer binder, in an ion exchange zone under the influence of a 
magnetic field providing about 25 gauss to about 500 gauss (in the absence 
of said particles) sufficient to stabilize said sorbent as a fluidized bed 
comprising the steps of 
a) loading said sorbent by passing an acidic aqueous feedstream at a pH 
from about 1 to 4 containing removable anions through said magnetically 
stabilized fluidized bed at a flow rate ranging from about 0.018 to about 
1.0 cm/sec that affords maximum sorption of said anions by said sorbent 
resulting in a purified feedstream; 
b) stripping said sorbent of said removable anions by passing a basic 
aqueous stream at a pH from about 8 to about 14 through said magnetically 
stabilized fluidized bed at a flow rate ranging from about 0.018 to about 
1.0 cm/sec and discarding or reusing said effluent stream; and 
c) regenerating said sorbent by passing an acidic aqueous stream at a pH 
from about 1 to about 3 through said magnetically stabilized fluidized bed 
at a flow rate from about 0.018 to about 1.0 cm/sec.

DETAILED DESCRIPTION OF THE INVENTION 
Broadly, the invention is related to the contacting of fluidized particles 
in an upwardly flowing liquid stream where the particles are stabilized in 
a fluidized bed by a magnetic field. In one aspect, the present invention 
is concerned with the removal of removable anions from liquid streams 
containing such ions using an ion exchange sorbent containing a soft 
ferromagnetic substance in a magnetically stabilized fluidized bed 
process. 
Sorbent Particles Composition 
In order to prepare the sorbent, a weak anion exchange resin can be 
transformed from the ordinary bead appearance to a dry powder having a 
particle size of from about 10 microns to about 150 microns, using any 
method known to a person skilled in the art. The weakly basic anion 
exchange resin comprises polymeric amines, such as crosslinked 
polyvinylbenzyldimethylamine, but other weakly basic anion exchange resins 
should function in this invention though not necessarily with equivalent 
results. It is also contemplated within the scope of this invention that 
mixtures of weakly basic anion exchange resins can also be used. 
A second ingredient is a ferromagnetic substance, preferably in powdered 
form, whose purpose is to cause the sorbent to have its movement 
restricted while under the influence of a magnetic field. Two general 
classifications of these ferromagnetic substances are known to the art and 
include the class called hard magnetic substances and the class called 
soft magnetic substances. A hard magnetic substance is a material which 
retains its magnetism after the inducing magnetic field is shut off, while 
a soft magnetic substance is a material which rapidly loses most of its 
magnetism after the inducing magnetic field is turned off, and has a high 
magnetic permeability and a low coercivity. In this application and in the 
appended claims the use of the term ferromagnetic substance is to be read 
to mean a soft ferromagnetic substance. 
The third ingredient in the sorbent is a water permeable organic polymer 
binder whose purpose is to hold together the resin and the ferromagnetic 
substance in discrete particles capable of sorbing said removable anions 
from a liquid stream containing such ions, and for this purpose is best 
chosen with smaller alkyl pendant or substituent groups so as to be a more 
polar binder. For purposes of this application and in the appended claim, 
the term sorbent will refer to particles capable of absorbing the 
removable anions from the liquid stream containing said ions. The term 
water permeable will include both water permeablility and substrate 
permeablility, thus the binder must be permeable to both water and to the 
ions to be removed. 
Soft Magnetic Materials 
Soft magnetic substances may be generally defined as materials which are 
easily magnetized and which are readily demagnetized. The are 
characterized by high permeability and low coercivity and are found within 
six major crystalline groupings including iron and low carbon steels, 
iron-silicon alloys, iron-aluminum and iron-aluminum-silicon alloys, 
nickel-iron alloys, iron-cobalt alloys, and ferrites, as well as amorphous 
soft magnetic alloys near the (Fe.sub.1 CO.sub.1 Ni).sub.80 (P.sub.1 
B.sub.1 Al.sub.1 Si.sub.1 C).sub.20 composition where the eighty and 
twenty refer to percent composition respectively. Any or all of these 
alloys types may provide a soft magnetic substance useful in sorbents 
useful in the invention, however, it should be understood that the 
performance of the stabilized fluid beds of the invention will be 
determined by various factors and the selection of the soft magnetic 
material will be only one of such factors. In general, selection of a 
material with a low coercivity , preferably less than 0.6 oersteds, is 
considered of particular importance. Iron alloys can be taken from the 
group including, but not limiting to 3% silicon, 4% silicon, 30% silicon, 
45% silicon (Permalloy), 50% nickel (Hipernik), 78.5% nickel (78 
Permalloy) 4% molybdenum and 79% nickel (Supermalloy), 5% copper, 2% 
chromium and 77% nickel (Mumetal), 3% molybdenum, 14% copper, and 72% 
nickel (1040 alloy), 50% cobalt (Permendur), 1.8% vanadium and 49% cobalt 
(Vanadium Permendur), and 5% aluminum and 10% silicon (Sendust) wherein 
all percents are by weight and enough iron is added to make 100% by weight 
of each alloy. Particularly preferred are iron-nickel alloys containing 
more than 40 wt. % nickel. 
Anion Exchange Resins 
The anion exchange resin can be either gel-type or macroreticular and 
includes, but is not limited to, resins manufactured by the Rohm & Haas 
Corporation known in the trade as "Amberlite" and as "Duolite" as well as 
those manufactured by the Dow Corporation and known in the trade as 
"Dowex.revreaction.. Other anion exchange resins manufactured by other 
corporations can also be used by not necessarily with equivalent results. 
Representative examples of the anion exchange results of the weakly basic 
gel-type polystyrene or phenolic polyamine include Amberlite IRA-45, 
IR-48, IRA-68, IRA-60, and IRA-58, Duolite A-6, A-4F, ES-375, and A-340, 
and Dowex WGR and WGR-Z. 
Representative examples of the anion exchange resins of the macroreticular 
type include Amberlite IRA-35, IRA-93, IRA-94, IRA-99, and Amberlyst A-21, 
Duolite ES-308, ES-368, ES-366, A-7, A-374, A-378, and A-561, and Dowex 
MWA-1. 
Mixtures of the gel-type anion exchange resins with the macroreticular 
anion exchange resins are capable of functioning in this invention as are 
mixtures of the gel-type or mixtures of the macroreticular type resins. 
For instance, Amberlite IRA-68 might be mixed with Amberlite IRA-45, 
Amberlite IRA-68 might be mixed with Duolite ES-375, Amberlite IR-48 might 
be mixed with Amberlite IRA-60, and Duolite ES-375 might be mixed with 
Dowex WGR. 
Binders 
The binders are water permeable and will be found as members of the group 
consisting of polyurethanes, cellulose esters, and cellulose ethers. 
The material to make the binder can include, but is not limited to, the 
foamable hydrophilic prepolymers basically derived from toluene 
diisocyanate manufactured by W. R. Grace & Company and known in the trade 
as "HYPOL" polymers, examples of which include FHP2000, FHP3000, and 
FHP2002. Of course, other polyurethane prepolymers will function in this 
invention but not necessarily with equivalent results. 
When polyurethanes are used as a binder, preparation of the sorbent entails 
a mixing of binder prepolymer monomers in a solvent to form a solution of 
the binder. This binder solution is then mixed with the powdered anion 
exchange resin, water, and the powdered ferromagnetic substance to form a 
homogeneous mixture. Subsequent controlled polymerization forms a gel 
which is subsequently dried to a solid and formed to the desirable shape 
and size. 
An example of the third method for preparation of the sorbent involves 
adding together, with stirring, two separately prepared mixtures, the 
first one containing the prepolymer and the ferromagnetic substance and 
the second containing the ion exchange resin and water. In this manner, a 
2:1 mixture of isocyanate prepolymer FHP2000 and a 1:1 nickel-iron alloy 
is combined with a 3:8 mixture of finely ground Amberlite IRA-68 and 
water. Stirring is continued until solidification occurs, and then the 
mixture is broken into small pieces, dried, and ground to the appropriate 
size. Possible methods of drying include drying under vacuum with or 
without heating, and conventional oven drying, all performed at 
temperatures ranging from about 10.degree. C. to about 110.degree. C. 
The binder also can include, but is not limited to, cellulose ethers such 
as ethyl cellulose, methyl cellulose, propyl cellulose, butyl cellulose, 
hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, and 
diethylaminoethyl cellulose, as well as cellulose esters such as cellulose 
acetate, cellulose nitrate, cellulose sulfate, cellulose butyrate, 
cellulose propionate, cellulose isobutyrate, cellulose benzoate, and 
cellulose acetate-butyrate. 
Solvents for use with cellulose esters or ethers can include, but are not 
limited to, acetone, p-dioxane, methyl ethyl ketone, ethyl acetone, 
chloroform, benzyl alcohol, cyclohexanone, formamide, acetic acid, 
diethylketone, toluene, and acetonitrile, For purposes of this application 
and the appended claims, the word solvent will be taken to mean both a 
single solvent as well as a mixture of solvents. 
One method for preparation of the sorbent of this invention utilizes a 
mixing of the resin with the ferromagnetic substance, and then with a 
water permeable organic polymer binder prior to introduction of the 
solvent, in such a way as to minimize the stratification of these 
ingredients. Once a homogeneous mixture is achieved, a solvent is 
introduced to dissolve the binder thus resulting in formation of a 
malleable mixture which is then dried to a solid and formed to the 
desirable shape and size. Possible methods of drying include extrusion 
into water to remove the solvent followed by further drying to remove the 
water, drying under vacuum with or without heating, and conventional oven 
drying, all performed at temperatures ranging from about 10.degree. C. to 
about 110.degree. C. The resultant solid can be formed by methods 
including, but not limited to, extrusion, chopping, grinding, and 
extrusion combined with chopping or grinding. 
Another possible method for the preparation of this sorbent utilizes the 
same ingredients as the first method but differs in that the ferromagnetic 
substance and the resin are first mixed together in powdered form and then 
this powder mixture is added to a separate mixture of the binder with the 
solvent to form the malleable mixture which is then treated as in the 
before-mentioned method. 
After forming to the desired size and shape, the sorbent particles will 
contain the ion exchange resin in a range from about 30 wt. % to about 85 
wt. %, the ferromagnetic substance in a range from about 5 wt. % to about 
30 wt. %, and the water permeable organic polymer binder in a range from 
about 10 wt. % to about 50 wt. %. In one embodiment, the sorbent particles 
range from about 100 microns to about 300 microns, which may be obtained 
by passing particles through a 50 mesh screen and onto a 140 mesh screen. 
Fluidized Bed Processing 
Ion exchange can be accomplished utilizing methods such as fixed beds, 
fluidized beds, and magnetically stabilized fluidized beds (MSFB). While 
fixed bed problems such as high pressure and low flow rate can be 
alleviated through use of a fluidized bed, this use of a fluidized bed 
introduces new problems concerning the movement of the particles of the 
fluidized bed. As reported by Rosensweig, fluidized a bed or particles 
with a gas is best done at a superficial velocity which avoids unstable 
bubbling. When a liquid is used, bubbling does not occur and no unstable 
flow regime is found. However, loss of particles will limit the velocities 
which may be used. When liquids are used as a fluidizing medium, their 
higher density and viscosity effectively entrain small particles making 
loss of particles a much more sever problem for liquids than for gases. 
Prior art (see U.S. Pat. No. 3,560,378) attempted to correct these 
problems by use of magnetic stabilization of these mobile particles but 
said art used hard magnetic substances whereas this invention incorporates 
soft ferromagnetic substances to curtail the effluent contamination by 
sorbent fines as well as to control the migration of sorbent or fluid 
throughout the bed (axial dispersion). 
The sorbent of this invention is held in place in the MSFB through use of 
an external homogeneous magnetic field which provides from about 25 gauss 
to about 500 gauss when measured in the absence of particles. The magnetic 
flux density (measured in gauss or Tesla) is related to the external field 
strength by the equation 
EQU B=.mu.(H+M) 
where H is the external field strength, M is the magnetization of the 
magnetic materials (measured in oersted or A/m) and .mu. is the magnetic 
permeability. In the absence of magnetic materials, these units are 
defined so that a field strength of one oersted (79.58 A/m) provides a 
flux density of one gauss (10.sup.-4 T). Our measurements of the magnetic 
flux density were made in the absence of particles and references to gauss 
should be understood to be on that basis. When magnetic materials are 
present, the flux densities are much higher than the gauss values given 
for an empty column. 
Such stabilization results in a diminishing of the axial dispersion 
normally present in a fluidized operation as well as in a formation of the 
sorbent particles into linear networks instead of the cross-linked network 
arrangement found in the prior art. These linear networks form with soft 
magnetic materials because the magnetic moments particles remain aligned 
with the external field. In contrast, the moments of particles with hard 
magnetic materials orient toward each other, causing three dimensional 
aggregation. Said prior art utilized hard magnetic substances that were 
magnetized externally and then utilized in a fluidized bed separation. 
Such particles required occasional external remagnetizations, and probably 
caused clogging problems due to flocculation in the associated plumbing of 
the MSFB. In this invention, the sorbents do not require external 
remagnetization as they are magnetic at any time the external magnetic 
field is applied and the sorbents do not cause flocculation problems in 
that the sorbent particles lose most of their magnetism upon cessation of 
the external magnetic field. 
Through use of the magnetically stabilized fluidized bed (MSFB) the sorbent 
of this invention is utilized in a process for the exchange of anions 
which comprises subjecting a liquid medium containing removable anions to 
contact with a sorbent, said sorbent being a composite of at least one 
anion exchange resin, a ferromagnetic substance, and a water permeable 
organic polymer binder, in an ion exchange zone under the influence of a 
magnetic field of strength sufficient to stabilize said sorbent as a 
fluidized bed comprising the steps of 
a) loading said sorbent bypassing an acidic aqueous feedstream containing 
removable anions through said fluidized bed at a flow rate that affords 
maximum sorption of said ions by said sorbent resulting in a purified 
feedstream 
b) stripping said sorbent of said removable anions by passing a basic 
aqueous stream through said fluidized bed and discarding said effluent 
stream; and, 
c) generating said sorbent by passing an acidic aqueous stream through said 
fluidized bed. 
In the above mentioned process, regeneration of this sorbent occurs at a pH 
of from 1 to about 3, loading of the sorbent occurs at a pH of from 1 to 
about 4, and stripping of said sorbent occurs at a pH of from about 8 to 
about 14, and the flow rate ranges from about 0.018 to about 1.0 
centimeter per second. 
Removable anions sorbed by the sorbent of this invention include, but are 
not limited to, the hexavalent oxidation state, (an oxidation number of 
plus six), a chromium, selenium, sulfur, and manganese. These removable 
anions are found in waste streams such as metal finishing streams as well 
as in cooling water blowdown and other similar operations. Other ions 
which can be removed include tetrachloroplatinate ions and 
tetrachloropalladate ions. It is contemplated as within the scope of this 
invention to run this ion exchange process in a semi-batch manner in which 
the feedstream is passed through the bed until the sorbent capacity is 
reached and then is regenerated. Alternatively, the process can be 
operated continuously with a portion of the sorbent being continuously 
removed, regenerated, and returned to the fluidized bed. 
EXAMPLE I 
In an open beaker, 3 grams (g) of finely ground Amberlite IRA-68 ion 
exchange powder, and 160 milliliter (mL) water were mixed, yielding a 
viscous suspension. In a second beaker, 20 g of HYPOL FHP2000 polyurethane 
prepolymer was mixed with 10 g of 1:1 nickel-iron alloy and stirred until 
the mixture appeared homogeneous. Subsequently, the aqueous suspension was 
added to the prepolymer mixture with rapid stirring thereby forming a 
foaming mixture which rapidly became more viscous until a slightly elastic 
dense foam was obtained. This solid foam was then crumbled into small 
pieces and heated to 110.degree. C. for 2 days. 
EXAMPLE II 
A 2.5 centimeter (cm) glass column was mounted vertically in the center of 
a water-cooled cylindrical DC solenoid magnet (length 660 cm, 152 cm 
I.D.), powered by a Hewlett Packard 6274B D.C. power supply. A small 
circle of steel mesh blocked the inlet of the column and supported 50 mL 
of 3 mm glass beads. The column was charged with 43 mL of the dry sorbent, 
a 90 gauss (G) magnetic field was applied which provided 90 Gauss in the 
column (in the absence of particles) and a feedwater stream was admitted 
at the base of the column with a velocity of 0.34 cm/sec, which is a 
velocity sufficient to fluidize the sorbent particles. The pH of the 
feedstream was acidified until the effluent stream had a pH of 2.95 at 
which time the feedstream was changed to pH 3.0 water containing 0.24% by 
weight sodium dichromate. Samples of the effluent stream were taken 
periodically for analysis wherein the concentrations were determined by 
atomic absorption spectrophotometry. The chromium (VI) concentration was 
measured by adding tartaric acid and 1,5-diphenylhydrazide to the sample, 
agitating it, and then measuring the absorption of the sample at 540 
nanometers (nm). The results of these analyses indicated that breakthrough 
of the sodium occurred almost immediately, but breakthrough of the 
chromium (VI) was delayed for 35 minutes. Once breakthrough of the 
chromium (VI) had occurred, the feed was changed to water, then to 0.5 
sodium hydroxide in order to strip the chromium (VI) from the column as a 
more concentrated stream. 
EXAMPLE III 
In an open pan, 200 grams (g) of Amberlite IRA-68 (Rohm and Haas weak anion 
exchange resin) was heated to 104.degree. C. or 3 days. The resin was then 
ground in a ball mill and screened and the fraction which passed through 
the 140 mesh screen was used in the following procedure. 
In an open beaker, 20 g powdered Amberlite IRA-68, 5 g powdered 1:1 
nickel-ion alloy, and 7 g powdered Eastman Kodak cellulose acetate were 
mixed until the mixture appeared homogeneous. To this mixture was added in 
small portions a total of 43 mL acetone was continuous stirring. The 
mixture darkened in color and became lumpy, then acquired the consistency 
of bread dough. After kneading this material until it appeared 
homogeneous, the paste was transferred to an evaporating dish, chopped 
into small pieces, and placed in a 50.degree. C. oven overnight. The hard 
and brittle product was then ground in a mechanical grinder to obtain 
28.65 g of 20-50 mesh material and 6.6 g of 50-140 mesh material. 
EXAMPLE IV 
In an open beaker, 30 g of finely ground Amberlite IRA-68 ion exchange 
powder, 10 g of ethylcellulose, and 20 g of 1:1 nickel-iron alloy were 
dry mixed until the mixture appeared homogeneous. To this mixture was 
gradually added a total of 70 milliliters (mL) of acetone with continuous 
stirring, resulting in a mixture with a dough-like consistency. This dough 
was broken into small pieces, air-dried at room temperature for 2 hours, 
heated to 105.degree. C. for 12 hours, and now brittle solid was ground to 
granular particles of a 50-140 mesh size. 
EXAMPLE V 
In an open beaker, 30 g of finely ground Amberlite IRA-68 ion exchange 
powder, 10 g of cellulose acetate and 20 g of 1:1 nickel-iron alloy were 
mixed dry until the mixture appeared homogeneous. To this mixture was 
gradually added 35 mL of acetone with continuous stirring resulting in a 
mixture with a dough-like consistency. This dough was extruded through a 
1/8 inch circular die into a pan of water, the resulting strands were 
soaked in water for 24 hours, allowed to dry, and ground to granular 
particles of a 50-140 mesh size. 
EXAMPLE VI 
The apparatus described in Example II was charged with 66 mL of the dry 
sorbent. A magnetic field was applied which provided 90 gauss in the 
column (in the absence of particles), and a feedwater stream was admitted 
at the base of the column with a velocity of 0.34 cm/sec, which is a 
velocity sufficient to fluidize the sorbent particles. The pH of the 
feedstream was acidified until the effluent stream had a pH of 3.16 at 
which time the feedstream was changed to pH 3.0 water containing 4.1 parts 
per million (ppm) zinc, 2.4 ppm cadmium, 3.6 ppm chromium (III), and 11.4 
ppm chromium (VI). 
Samples of the effluent stream were taken periodically for analysis wherein 
the concentrations were determined by atomic absorption spectrophotometry. 
The chromium (VI) concentration wa measured by adding tartaric acid and 
1.5-diphenylhydrazide to the sample, agitating it, and then measuring the 
absorption of the sample at 540 nanometers (nm). The results of these 
analyses indicated that breakthrough of the zinc and cadmium occurred 
immediately, but breakthrough of the chromium (VI) never occurred. After 
212 minutes the feed was changed to water and then at 242 minutes the feed 
was changed to 0.1 M sodium bicarbonate in order to strip the chromium 
(VI) from the column as a concentrated stream. 
EXAMPLE VII 
(Comparative) In a small beaker, 7.1 g of finely ground Amberlite IRA-68, 
7.9 g of finely ground IRC-84, 50 of barium ferrite (a hard magnetic 
substance), and 10 g of ethyl cellulose were mixed intimately as powders. 
To the resulting mixture was added in portions 50 mL of acetone. The 
mixture was stirred throughout the addition, resulting in a dark grey 
paste. This paste was spread in an evaporating dish, and then heated in an 
oven at 105.degree. C. for 4 hours. The material was then ground to 20-50 
mesh. 
EXAMPLE VIII 
The apparatus described in Example II was used. A thin glass tube was used 
to sample the water at various heights in the bed. This tube was equipped 
with a separate small pump to withdraw fluid from the column and pass it 
through a 1-cm flow cell in a Perkin Elmer UV spectrophotometer. The flow 
of fluid through the column was visualized by injecting a pulse of 0.5 mL 
of blue dye (a 0.001 M aqueous solution of copper 
phthalocyaninetetrasulfonic acid) into the inlet line to the column, and 
observing the flow of this dye through the column. 
Magnetic resin having a mean particle size of 438 microns was added to a 
depth of 7.8 cm. When the water pump was turned on (50 mL/min, 0.17 
cm/sec) the resin was fluidized to a depth of 17-27 cm with resin evenly 
dispersed from side to side in the column. Axially, the particle density 
was somewhat higher at the base of the fluidized column that at the top, 
but no gaps were apparent. 
When pulses of dye were injected into the column, they dispersed evenly and 
resulted in a pulse of dye detected at the UV spectrophotometer. The width 
of this pulse depended on the strength of the magnetic field applied to 
the column. Axial dispersion coefficients were calculated from the 
observed peak widths and show that axial dispersion decreased as the field 
strength was increased to provide from 0 to 500 gauss in the column (in 
the absence of particles) as can be seen from the following Table. 
______________________________________ 
Axial Dispersion 
Coefficient (cm.sup.2 /sec) 
Gauss 
______________________________________ 
4.3 0 
1.8 140 
1.5 280 
0.8 410 
0.75 550 
______________________________________ 
The axial dispersion coefficient is a measure of the degree of back mixing 
in the particle bed and is determined by injecting dye into the column and 
measuring the shape of the pulse at the top of the bed (see O. Levenspiel 
and W. K Smith, Chem. Eng. Sci. 6, 227 (1957. It will be evident that back 
mixing is much reduced as the magnetic field strength is increased. 
EXAMPLE IX 
(Comparative). The same apparatus as that described in Example II as 
modified in Example VIII was used. A sample of 10 g of 20-50 mesh resin of 
the type described in Example VI was used. Fluidization of this resin was 
difficult, since the resin aggregated into lumps even at zero field. These 
lumps fluidized and could only be partially broken up by varying the flow 
rate. Injection of pulses of dye showed that flow through this bed was 
irregular (non-plug flow). The dye was observed to exit the top of the bed 
as several small streams rather than an even flow, and gave peaks with 
skewed shapes or multiple smaller peaks. Due to the skewed peak shapes no 
axial dispersion calculations were possible. 
EXAMPLE X 
The apparatus described in Example II was used. Magnetic resin having a 
mean particle size of 592 microns was added to a depth of 15.6 cm. When 
the water pump was turned on (210 mL/min, 0.71 cm/sec), the resin was 
fluidized to a height of 56 cm. Increasing the magnetic field strength had 
no effect on the fluidized height, but did result in a "sharpening" of the 
upper boundary. This illustrated in FIGS. 1-4 in which an increasing 
magnetic field strength was applied. Note that in FIG. 1 a magnetic field 
was employed which provided 46 gauss in the column (in the absence of 
particles) with the relatively large particles used in this experiment. 
This field strength had essentially no observed effect and appeared to be 
similar to the bed with no magnetic field applied. FIGS. 2 through 4 show 
the effect on the bed as the applied magnetic field is raised to provide 
150 gauss, 290 gauss, and then 570 gauss, in the column (in the absence of 
particles), respectively. It will be clear that the bed becomes better 
defined and entrainment is much reduced. Close examination revealed that 
at the higher field strengths, the particles in the upper portion of the 
bed were loosely aggregated into strings colinear with the column. 
EXAMPLE XI 
(Comparative). A 500 mL three neck round bottom flask was equipped with a 
Chesapeake stirrer, condenser, nitrogen inlet, and thermometer and was 
flushed with nitrogen. To this was added 1.5 g of sodium 
dioctylsulfosuccinate and 150 mL of mineral oil. The mixture was stirred 
vigorously until the succinate dissolved completely, generating a cloudy 
solution. In a separate small beaker cooled in ice, 14.8 g of sodium 
hydroxide were dissolved in 30 mL of water. To this was added 25 ml of 
acrylic acid in portions. A white slurry was obtained. Now 11.4 g of 
methylenebisacrylamide and 19.6 of magnetite (a hard magnetic substance) 
were added, and the resulting black paste was transferred to the reaction 
flask. Vigorous stirring was used to disperse the paste in the oil. A 
solution of 0.205 g of ammonium persulfate in 3 mL of water was added. The 
temperature rose immediately to 60.degree. C. External heating was then 
applied to bring the temperature to 95.degree. C. overnight. 
After cooling to room temperature, the reaction mixture was filtered with 
suction. The black product was rinsed with hexane to remove the oil, then 
with 2 N sulfuric acid, then with water. The product was then dried in an 
oven at 50.degree. C. 
When tested as in Example II, poor contacting was observed as a result of 
aggregation of the particles.