This invention relates to a whole cell support and a method of preparing the support. The support comprises alumina and diatomaceous earth characterized in that the support has interconnected pores which are at least 5 microns in diameter and preferably has a pore volume greater than about 0.3 mL/g. The support is prepared by forming a mixture of an aluminum sol and a diatomaceous earth forming spheres from the mixture by using the oil drop method and then calcining at a temperature of about 1000.degree. to about 1450.degree. C.

BACKGROUND OF THE INVENTION 
Enzymes have received considerable attention because of their ability to 
catalyze various reactions which occur in living organisms. The enzymes 
may also be isolated and used in industrial applications. For example, the 
enzyme glucose isomerase is extensively used to convert glucose to 
fructose in the manufacture of high fructose corn syrup. 
Because enzymes are water soluble and generally unstable, they are 
difficult to remove from the reaction mixture for reuse. Accordingly, this 
increases the cost of using enzymes on a commercial scale. A solution to 
this problem has been to immobilize the enzyme by using a porous oxide 
support on which the enzyme is deposited. 
In certain applications it is desirable to use (and immobilize) whole cells 
of micro-organism. The use of whole cells has the advantage that the cell 
acts as a carrier for the enzyme and one does not have to extract the 
enzyme from the cell. If whole cells are to be immobilized on a porous 
oxide support, the support must have pores which are large enough to 
accommodate the whole cells. If the pores are too small, the microbial 
cells or enzymes will plug the pores. Additionally, small pores may cause 
the fluid with which the whole cells are to be contacted to "hold-up" in 
the pores, thereby reducing the production rate of product because fresh 
fluid cannot reach the enzyme present in the whole cell. 
Conventional silica, alumina or silica-alumina supports are microporous 
with micropores of about 0.001 to about 0.03 microns in diameter. These 
pores are too small to accommodate microbial cells since typically 
microbial cells are larger than 1 micron. The prior art indicates that 
pore diameters of about 1 to about 25 microns are needed to adequately 
accommodate microbial cells. Thus, U.S. Pat. No. 4,581,338 discloses a 
process for preparing an enzyme support with large macropores. The process 
involves making a mixture of diatomite, a solvent, a fluxing agent and an 
organic burnout material, forming the mixture into generally spherical 
balls and then calcining the balls at a temperature of about 700.degree. 
to 2300.degree. F. Diatomite or diatomaceous earths are interchangeable 
terms which refer to sedimentary materials composed of the skeletal 
remains of single celled aquatic plants called diatoms. The resultant 
support is stated to have an average pore diameter of at least 8 microns. 
Applicant has taken a different approach to making a macroporous support by 
forming a mixture of an aluminum sol and a diatomaceous earth, forming 
spheres from this mixture by dropwise dropping the mixture into an oil 
tower, followed by calcination of the spheres at a temperature of about 
1,000.degree. to about 1450.degree. C. The resultant support has pores 
which are at least 5 microns and which are interconnected. It is important 
that the pores be interconnected; otherwise whole cells cannot enter the 
pores and the fluid which is to contact the cells will not be able to 
diffuse into the large pores. Accordingly, the use of applicant's process 
produces interconnected macropores without using a burnout material. 
Applicant's process also produces a uniform, spherical product as compared 
to the prior art's nearly spherical product. 
The prior art also reveals that alumina spheres may be prepared using a 
suspension of an alumina powder. For example, U.S. Pat. No. 4,514,511 
teaches that a mixture of an alumina powder and an aluminum salt can be 
used to form spheres with pores having a diameter from about 0.2 to 15 
microns. However, these pores are closed which would make them useless as 
a support for whole cells. Applicants are, therefore, the first to prepare 
an alumina/diatomaceous earth macroporous support, having interconnected 
pores. 
SUMMARY OF THE INVENTION 
This invention relates to a whole cell support and a method of preparing 
the support. Accordingly, one embodiment of the invention is a whole cell 
support comprising alumina and diatomaceous earth characterized in that 
the support has interconnected pores which are at least 5 microns in 
diameter. 
Another embodiment of the invention is a process for preparing a whole cell 
support comprising forming a mixture of an aluminum sol and a sufficient 
amount of a diatomaceous earth, forming said mixture into spheres by 
dropping said mixture into an oil tower, isolating the spheres and 
calcining the spheres at a temperature and for a time sufficient to form a 
catalyst support having interconnected pores which are at least 5 microns 
in diameter. 
Other objects and embodiments of this invention will become apparent in the 
following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
As stated, this invention relates to a whole cell support and a method of 
preparing the support. Generally, the method of preparation involves first 
making an aluminum sol by means well known in the art. For example, 
aluminum can be reacted with hydrochloric acid to provide an Al/Cl sol 
(see U.S. Pat. No. 2,620,314). A sol is a liquid composition which, when 
placed between one's line of vision and a strong light source, shows a 
bluish cast. This is known as the Tyndall effect. 
Having formed the aluminum sol, the next step involves forming a mixture of 
the aluminum sol and a diatomaceous earth powder. As stated, diatomaceous 
earths are sedimentary materials composed of the skeletal remains of 
single celled aquatic plants called diatoms. Many diatomaceous earth 
deposits were laid down by sedimentation in shallow waters many years ago. 
Subsequent geologic uplift has raised these beds to positions where they 
can be mined by conventional methods. Once mined, the diatomaceous earths 
are washed, dried and then sold or they may be treated with a fluxing 
agent such as CACO.sub.3, Na.sub.2 CO.sub.3 or K.sub.2 CO.sub.3 and then 
calcined prior to sale. These latter materials are referred to as 
flux-calcined diatomaceous earths. Typically, diatomaceous earths are 
composed of 86-90% silica, 3-4% alumina, about 1% alkaline oxides, about 
1% other oxides and the remainder water (if not flux calcined). The 
flux-calcined materials will contain 2-4% alkaline oxides. 
The particle size of the diatomaceous earths can vary considerably and can 
determine the size of the macropores of the catalyst support. When the 
diatomaceous earth is mixed with the aluminum sol one obtains a mixture 
which consists of discrete particles of the diatomaceous earth in a sol 
matrix. Accordingly, the size of the particles determines the amount of 
sol between the particles, i.e., how the particles pack, which determines 
the pore size of the final product. It has been determined that it is 
necessary that at least 10 weight percent and preferably at least 40 
weight percent of the total diatomaceous earth have a median particle 
diameter greater than 40 microns and the remainder of the diatomaceous 
earth have a median particle size smaller than 40 microns and preferably 
in the range of about 7 to about 15 microns. Because the particle size of 
diatomaceous earth varies based on the source of the earth, it may be 
necessary to blend diatomaceous earths from various sources in order to 
obtain the desired particle size distribution. Alternatively, the large 
particle diatomaceous earth can be ground by conventional means to give 
smaller diameter particles. 
The amount of diatomaceous earth which is added to the aluminum sol can 
vary considerably, but in generally chosen to give an amount in the final 
product from about 40 to about 75 weight percent and preferably from about 
55 to about 70 weight percent. Increasing the amount of diatomaceous earth 
present in the sol has the effect of decreasing the ABD (apparent bulk 
density), surface area and crushing strength, while increasing the 
attrition of the resultant product. Additionally, increasing the amount of 
diatomaceous earth increases the total pore volume of the finished 
product. This is owing to the fact that the diatomaceous earth is more 
sinterable than the alumina, thereby forming more and/or greater voids. It 
is desirable that the support have a pore volume of greater than 0.3 ml/g. 
Before the above mixture is dropped into an oil tower, it is necessary to 
add a gelling agent. One suitable gelling agent is hexamethylene 
tetrammine. (For specific details on the basic oil dropping procedure see 
U.S. Pat. No. 2,620,314 which is incorporated by reference.) The resultant 
mixture is dropped into an oil bath maintained at elevated temperatures. 
The droplets of the mixture remain in the oil bath until they set and form 
hydrogel spheres. The spheres are then continuously withdrawn from the oil 
bath and typically subjected to specific aging and drying treatments in 
oil and an ammoniacal solution to further improve their physical 
characteristics. The resulting aged and gelled particles are then washed 
and dried at a relatively low temperature of about 140.degree.-205.degree. 
C. and subjected to a calcination procedure at a temperature of about 
455.degree.-705.degree. C. for a period of 1 to about 20 hours. The 
calcined spheres are next sintered at a temperature of about 1000.degree. 
to about 1450.degree. C. and preferably from about 1350.degree. to about 
1400.degree. C. for a time from about 1 to about 4 hours. 
In a preferred embodiment, a fluxing agent is added to the spheres to lower 
the sintering temperature. One way to do this is to impregnate the 
diatomaceous earth with a fluxing agent. Fluxing agents are usually Group 
I or Group II metal compounds which decompose on heating to give the metal 
oxide. Preferred fluxing agents may be selected from the group consisting 
of magnesium carbonate, calcium carbonate, cesium carbonate, lithium 
carbonate, potassium carbonate and sodium carbonate. Other fluxing agents 
include the acetate and nitrate salts of the Group I and Group II metals. 
The amount of fluxing agent to be added to the mixture can vary 
considerably but is usually from about 1 to about 20 weight percent and 
preferably from about 5 to about 15 weight percent of the diatomaceous 
earth. 
The support which is obtained is characterized as having pores which are at 
least 5 microns in diameter. Generally, the pores have diameters in the 
range of about 5 to about 20 microns. The pores are also interconnected, 
thereby allowing fluid to easily enter and leave the large pores. The fact 
that the pores are interconnected was shown by mercury intrusion analysis 
and scanning electron microscopy (SEM). It is preferred that the large 
pores provide a pore volume of greater than 0.3 ml/g (for pores greater 
than 5 microns) as measured by mercury intrusion. 
As stated, the support which is one of the embodiments of this invention is 
useful as a support for enzymes or microbial cells. Additionally, the 
support may be used to disperse other catalytic materials such as noble 
metals, any of the Group VIII metals, etc. Since the support has such 
large pores, it is especially suited for applications which may be 
diffusionally limited. The support may be used as is or it may be broken 
up into smaller irregularly shaped particles. This helps to increase the 
contact between the catalyst and the stream to be treated and decreases 
the back pressure. 
The following examples are presented in illustration of this invention and 
are not intended as undue limitations on the generally broad scope of the 
invention as set out in the appended claims. 
EXAMPLE 1 
A flux-calcined diatomaceous earth having a median particle size greater 
than 40 microns (obtained from Ceca SA and identified as Clarcel grade) 
was mixed with a washed diatomaceous earth having a median particle size 
of about 15 microns (obtained from Eagle Picher Co. and identified as MN-2 
grade). This powder mixture was mixed with an aluminum sol which was 
prepared by dissolving aluminum metal in hydrochloric acid to give an 
Al/Cl ratio of about 1.03. The relative amounts of materials present was 
such as to provide 41% of the flux calcined diatomaceous earth; 21% of the 
washed diatomaceous earth and 38% alumina on the finished product. 
Hexamethylene tetrammine was added to the mixture to gel the mixture into 
spheres when dropped through a tower of oil maintained at 95.degree. C. 
The amount of hexamethylene tetrammine which was added was about 105% of 
the amount required to neutralize the acid in the aluminum sol. 
After the spheres were removed from the hot oil, they were pressure aged at 
135.degree. C. and washed with a dilute (1.85 weight percent NH.sub.4 OH) 
ammonium hydroxide solution, dried at 110.degree. C. and calcined at 
650.degree. C. for about 2 hours. The calcined spheres (1/16 inch in 
diameter) were heated at 1450.degree. C. for 4 hours and analyzed by 
mercury intrusion and SEM (scanning electron microscope). The results 
obtained showed that only pores in the 5-20 micron were present, that the 
pore volume was about 0.35 mL/g and that the spheres had roughly circular 
pores homogeneously distributed throughout the sphere. These pores were 
also found to be interconnected. 
EXAMPLE 2 
Spheres were prepared as in Example 1 except that only the Clarcel grade 
diatomaceous earth was mixed with the aluminum sol in an amount sufficient 
to give 52% Clarcel and 47% alumina in the finished product. Again, the 
calcined spheres were heated at 1450.degree. C. for 4 hours and analyzed 
by SEM and mercury intrusion. Again 5-20 micron pores were present, but 
the pore volume of these pores was only 0.18 mL/g. The pore structure of 
these spheres was the same as those of Example 1. 
This example shows that increasing the amount of alumina in the product and 
using only one size of diatomaceous earth decreases the pore volume of the 
spheres.