Monolith reactor containing a plurality of flow passages and method for carrying out biological reactions

Biological reactions are carried out with a unitary structure, preferably formed of a ceramic material, having a plurality of flow passages including first and second sets of flow passages arranged so that individual passages of the first set are adjacent individual passages of the second set and are separated by walls formed of the ceramic material. The ceramic material is porous to provide mass transfer of gaseous oxygen and biological reaction products while containing liquid in the second set of passages. Walls of the passages may be covered with a gaseous oxygen permeable membrane. Inside walls of the second set of passages may coated with a compound adapted to immobilize biological reaction materials. In a biological reaction, the first set of passages are contacted with a fluid such as an air stream to provide gaseous oxygen, and a fluid flow such as a nutrient medium is established through the second set of flow passages whereby an oxygen flow producing gradient is produced through the porous ceramic material between the first and second sets of flow passages to supply oxygen for cells immobilized on inside walls of the second set of flow passages.

BACKGROUND OF THE INVENTION 
This invention relates generally to a method and apparatus for carrying out 
the transfer of reactants such as oxygen and/or the transfer and 
separation of products from reactions, which can be biological reactions 
or the like. Biological reactions using immobilized microorganisms have 
been the focus of much recent research and development. Notable commercial 
processes using immobilized cells include glucose isomerization, raffinose 
hydrolysis and amino acid production. Other useful reactions such as 
antibiotic modification and organic acid formation and degradation have 
been extensively studied and some are near the stage of commercial 
application. 
The widespread interest in immobilized cell systems is well justified given 
the advantages of these systems over freely suspended cells. The most 
obvious advantage is the continuous use of biomass which is retained in 
the reactor. The yield with respect to product is thus increased due to 
the decrease in the amount of biomass synthesis. Cell immobilization also 
provides the means to make batch processes continuous, and it can be 
employed with resting cells for continuous secondary metabolite 
production. The high cell densities achieved by immobilization yield 
faster reaction rates. Finally, by removing or reducing the cells 
suspended in the medium, immobilization can improve the rheological 
properties of the medium while increasing the effective densities of the 
microorganisms. For these reasons, many-fold productivity increases have 
been realized with immobilized cell reactors. 
There are, to be sure, several problems associated with immobilized cells 
systems which are due, in general, to the biological system, the 
immobilization technique, or the reactor system. Immobilization may result 
in a loss of some of the desirable catalytic activity either because of 
enzyme inactivation during immobilization, or because of diffusional 
barriers that decrease substrate access to or product removal from the 
cells. Packed beds as immobilized cell reactors have the disadvantages of 
being mass-transfer limited, being subject to plugging, and using only a 
small fraction of the available cells for biocatalysis. Hollow fiber cell 
reactors, such as those disclosed in U.S. Pat. No. 4,201,845 to Feder et 
al, have mass transfer limitations through the membrane that separates the 
nutrients from the cells. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided an apparatus 
and method for carrying out the transfer and separation of fluid reactants 
and products to and from immobilized cell biological reactions or the 
like. In the apparatus aspects of the invention, there is provided a 
unitary structure formed of ceramic or polymeric material having a 
plurality of flow passages therein which includes first and second sets of 
flow passages with material communicating means respectively so that 
different substances can be moved through the respective sets of passage 
and wherein individual passages of said first set are separated from 
individual passages of the second set by the material of the unitary 
structure. This unitary structure (or monolith structure as it is 
sometimes called) is provided with means for establishing material 
transfer through the respective sets of passages in a manner such that a 
biological reaction or the like will take place in the first set of 
passages with a reactant or a product from the reaction being transferred 
through the material of the unitary reactor from or to the second set of 
passages, a flow of said reactant or product having been produced between 
the passages of said first and second sets respectively. 
In the method aspect of the invention, a unitary ceramic structure, or 
so-called monolith, having the first and second sets of flow passages as 
outlined above is contacted with a reacting material under conditions 
giving rise to transfer of reactants and/or products to or form the first 
set of passages from or the the second set of passages. 
In a preferred form of the invention, the reaction can be a biological 
reaction or a reaction requiring oxygen in said first set of passages. 
In a further preferred form of the invention, the first and second sets of 
passages can be orthogonally positioned to each other. 
In an important further preferred form of the invention, a membrane, 
permeable to the reactants or products to be passed from the individual 
flow passages of said one set of passages to those of said other set of 
passages, but impermeable to other materials, is coated on, or covers, the 
inside walls of either the passages of said first set or the passages of 
said second set respectively, or is otherwise associated with said walls. 
In either the method or apparatus aspects of the invention, immobilized 
cells can be present on the walls of the individual passages of the second 
set of passages.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1 there is a shown a unitary structure, or monolithic 
reactor as it will sometimes be called herein, formed of ceramic 
materials. The unitary structure 10 comprises first and second sets of 
flow passages shown for example as element 11 that are in parallel 
arrangement to a second set of flow passage 12. Each of the flow passages 
11, in this arrangement, is adjacent to a flow passage 12 being mutually 
separated by a wall of said ceramic material. 
In FIG. 2 a different arrangement of a monolithic reactor 13 is shown 
wherein, as shown, schematically, a first set of flow passages 14 and a 
second set of flow passages 15 are disposed in orthogonal relationship to 
each other on the respective "X" and "Y" axes. 
With regard to the monolithic reactors shown in FIGS. 1 and 2, they are 
preferably made of ceramic materials by extrusion and firing and can 
consist of an array of parallel channels as shown in FIG. 1, of square, 
triangular, hexagonal or sinusoidal geometry. The result, in a preferred 
form, is a small unit, typically about 6" long by 6" diameter with a high 
flow surface area. These honeycomb structures constitute unique chemical 
reactors with high geometric external surface, structural durability, low 
pressure drop; and uniform flow distribution within the monolith matrix. 
High cell loadings can be attained in the structures shown in FIGS. 1 and 2 
by adsorption because of the high surface area to volume ratio in the 
monoliths compared to beads ina packed bed. The required pressure is very 
low as flow through the flow passages 14 and 15 is unhindered. Cell 
sloughing in passages 14 or 15 poses no plugging problems since cells can 
be readily swept from such channels by a flowing stream. 
Cross-flow monoliths such as shown in FIG. 2 offer additional advantages 
over straight-through monoliths as biological catalyst supports. The 
monolithic reactor 13 consists of two sets of flow passages 14 and 15 
respectively, running in perpendicular direction, in alternating layers. 
Such systems have been explored as reactor-heat exchangers and as solid 
electrolyte fuel cell reactors but have not heretofore been used as 
biological reactors. Two separate flow streams are contacted across the 
walls of the flow channels 14 and 15 of monolith 13 all along its length 
and width. Because the ceramic material of the monolith is porous, mass 
transfer is allowed across the walls. 
As shown in FIGS. 3 and 4, by applying an appropriately selective permeable 
membrane 16 to the walls which separate the passages of said first and 
second sets of flow passages of the reactor, mass transfer between the two 
segregated streams can be controlled. Selective mass transfer to or from a 
biofilm 17 offers a new variable which can be used to optimize bioreactor 
performance and control. 
Potential applications of the cross-flow monolithic reactor shown in FIG. 2 
include inhibitory product removal, simultaneous reaction and product 
enrichment, and infusion of limiting substrates into a biofilm. 
The material of unitary reactors 10 and 13 must be porous to biological 
reaction products and generally will have a pore size between 50 angstrom 
units and 1 millimeter. The porous material must be insoluble in water, 
nonswellable and structurally sound so that it can form a monolithic 
reactor 10. The material must be nontoxic to micro-organisms and the 
surface of the material may have functional groups capable of being 
modified according to this invention. Inside walls of the second set of 
flow passages may have a coating of a compound adapted to attach to the 
ceramic material and to immobilize biological reaction materials. 
Materials for the unitary reactors 10 and 13 can be ceramic such as 
cordierite (made of a alumina, silica and magnesia), steatite (magnesia 
and silica) and others and additionally such material can be porous glass. 
The substrate material may also be a polymeric material such as 
polysulfone. Other ceramic materials well known in the art either slip 
cast or extruded can also be used. In any event, the substrate material is 
such that when in combination with a substrate treating compound according 
to the invention, it will permit passage of selected biological reaction 
products and/or reactants while preventing passages of unreacted reactants 
and nonselected by-products of the reaction. 
Many useful biological reactions are severely limited by mass transfer of 
one substrate. In particular, oxygen is the limiting reactant or substrate 
in numerous whole cell catalyzed processes, including: aceticacid 
fermentation by Acetobacter aceti, antibiotic production by Pennicillium 
chrysogenum, resolution of L-amino acids from racemic mixtures by 
Trigonopsis variabilis, L-glutamic acid production by Corynebacterium 
glutamicum, and others. The cross-flow monolithic reactor as described 
herein can be used to provide the limiting substrate to cells through a 
large surface area adjacent to the biofilm. Further, the high surface area 
and its closeness to the active cells is built into the reactor, rather 
than being maintained at the expense of high power input and high shear 
rates as in suspended cultures. Since the pressure drop of flow through 
the sets of flow passages of the reactor is very small, relatively little 
power is required to circulate air and medium at sufficiently high rates 
to achieve good substrate supply, aeration, and product removal. 
In accordance with one aspect of this invention, it is demonstrated that a 
membrane coated porous material can readily be made which retains a liquid 
stream, uncontaminated, in one set of flow passages, while allowing 
adequate oxygen supply across the material from a gas stream in another 
set of flow passages. 
Within an immobilized-cell cross-flow monolithic reactor 13, as shown in 
FIG. 2, the layers of the first set of flow passages 15 running in the 
X-direction conduct an air stream and the layers of the second set of flow 
passages 14 running in the orthogonal direction contain a nutrient medium. 
A hydrophobic, gas-permeable membrane 16 (FIG. 3) is attached or 
associated with the sides of the flow passages 15 conducting an air 
stream. The immobilized cells from the nutrients medium form a biofilm on 
the material of the wall which will penetrate into the pores of the wall 
from the liquid in flow passages 14 (FIG. 4). For the case of highly 
aerobic cells, the biofilm can be expected to develop until growth is 
limited by oxygen or nutrient supply. Therefore, oxygen will be completely 
consumed, and the concentration of oxygen will go to zero at some point 
within the ceramic (FIG. 5). 
To measure oxygen transfer rates which are realistic for the monolithic 
reactor configuration of FIGS. 1 and 2, it was necessary to design an 
experiment which simulates the consumption of oxygen of the ceramic 
material selected for such unitary or monolithic reactors. The sulfite 
oxidation system of Cooper, et al, Ind. and Eng. Chem., 36, p 504 (1944), 
was chosen as the method for measuring oxygen transfer rates. The 
enhancement of the oxygen transfer rate due to the sulfite reaction is 
analogous to the enhancement of the oxygen transfer which would occur due 
to oxygen consumption by a biofilm growing on the ceramic (FIG. 4). The 
reaction 
##STR1## 
can be catalyzed by either copper or cobalt ions. The kinetics of the 
reaction are second order to oxygen, zero order in sulfite for sulfite 
concentrations between 0.03 and 1.0N. The rate constant depends on 
temperature, pH, catalyst and catalyst concentration. The sulfite reaction 
is easily quantified by idiometric titration which allows quick, 
reproducible measurement of the oxygen transfer; whereas measurement of 
oxygen transfer rates using various immobilized cells will require much 
more time, a more elaborate eperimental apparatus, and oxygen assays 
tailored to each cell, substrate, and product system. Thus, the sulfite 
reaction provides an important simplification of the experiments to 
demonstrate the feasibility of oxygen transfer in th cross-flow monolithic 
reactor structure of FIG. 2 and to estimate a realistic range of oxygen 
transfer rates. 
The other major simplication of the cross-flow monolithic reactor of FIG. 2 
for the purpose of facilitating the experiment is to perform the 
measurements on a single layer. Selectively permeable membranes, such as 
used as element 16 (FIG. 3), are easily applied to each face of a single 
layer of flow channels simulating flow channels 14 and 15, forming a 
sandwich which is easily mounted and sealed into the test cell as shown in 
FIG. 6A. Due to the repeating structure of the cross-flow monolith, the 
results of a measurement on a single layer of flow channels may be 
linearly extrapolated to many layers. 
The test cell used for experimentation was designed and built to simulate 
the conditions in a cross-flow monolith reactor 13 such as shown 
schematically in FIG. 2. 
Corning cordierite monoliths, having a density of 300 channels/in.sup.2 
were used for this study. The 6" by 4" by 4" "race track" monoliths were 
sliced into slabs 4" by 4" by 3 or 4 layers thick. These slabs were ground 
down to a single layer of channels and polished. The ceramic material was 
washed several times with deionized water during and after grinding and 
polishing. 
The first step in developing a high oxygen transfer system is to establish 
a procedure to make the walls permeable to oxygen and impermeable to the 
nutrient medium. The method use for these experiments using the single 
layer of channels as prepared above was to apply a gas permeable, liquid 
impermeable membrane to the polished faces of the ceramic layer. W. L. 
Gore and Associates, Inc., has developed a line of Gore-Tex.RTM. membranes 
made of expanded polytetrafluoroethylene which are waterproof yet vapor 
permeable. The 0.2 micron pore size Gore-Tex.RTM., polypropylene scrim 
laminate was used in these experiments. The small pore size can prevent 
contamination of the medium by foreign microbes. 
Referring now to FIGS. 6A, 6B, and 7, there is shown a test cell 20 for 
demonstrating the invention. One half of the cell 21 contains a well 22 
into which a piece of a monolith 23, 4" by 4" by 1" layer of channels, 
prepared as previously described, is mounted between two silicone rubber 
foam gaskets 24, 4" by 4", with a 2" square opening 25. At each of this 
well there are flow ports 26 to allow fluid to be fed into one port 26, 
flow through the channels of the ceramic material 23, and exit through the 
other port 26 when the cell is assembled. The ceramic piece and gaskets 
are sandwiched in the assembled cell so that a 2" by 2" by 1/16" deep flow 
passage 27 is aligned with the opening in the gaskets; the fluid entrance 
and exit ports 28 to these passages allow fluid to be passed over both 
external faces of the ceramic material 23. In all of the experiments 
reported here, the liquid was fed through the channels of the ceramic 
material 23 and the gas stream was passed outside the ceramic in passage 
27. Although the flow in the cell is countercurrent rather than 
cross-flow, the distances within the cell 20 are sufficiently small that 
the data will reasonably predict mass transfer behavior in a cross-flow 
configuration. The halves of cell 20 are milled from 6" by 7" by 3/4" 
blocks of aluminum and are hard anodized. The gaskets and tubing used are 
silicone rubber. 
The test cell 20 is at the center of the apparatus shown in FIG. 7. The 
gases are metered through Brooks Rotoflow meters 29 and mixed in a mixing 
tee 30. The gas is circulated over the external faces of the ceramic piece 
in the cell 20, i.e. through the ports designated 28 as in FIGS. 6A, first 
through one-half of the test cell, then the other, then exhausted to the 
atmosphere as shown in FIG. 7. The bulk of the sulfite solution is in the 
reservior 31 is stirred and kept under a nitrogen blanket by continuous 
flushing with nitrogen to prevent air oxidation. The solution is 
recirculated by a peristaltic pump 32 through the channels of the ceramic 
mounted in the test cell, i.e. through the ports 26. The gas and liquid 
streams run countercurrent with respect to one another. Samples of the 
sulfite solution are pipetted from the reservior 31 through a port in its 
lid 33. 
The rate of oxygen consumption was measured by determination of the 
unoxidized sulfite-ion content of the solution, sampled at intervals 
during each run. Duplicate 10 ml samples were taken using nitrogen flushed 
pipettes. Each sample was run immediately into an excess (20 ml) of 
freshly pipetted standard (0.1N) iodine reagent, the tip of the pipette 
being slightly submerged in the iodine solution, in a glass stoppered 250 
ml erlenmeyer flask. The flasks were swirled and allowed to react for 10 
minutes for 20 minutes before analysis by back titration with 0.01N 
standard thiosulfate solution to a starch indicator endpoint. 
A series of experimental examples using Gore-Tex.RTM. 0.2 .mu.m pore size 
polypropylene laminate membranes as the perm-selective barrier on the 
ceramic were conducted. The oxygen transfer rates from gas to liquid as 
determined by sulfite oxidation range were from 1.8 to 6.6 g O.sub.2 
per.sub.l total reactor volume per hour. The data, presented as plots of 
moles of oxygen transferred, measured by iodometric titration, versus 
time, are shown in FIG. 8. 
EXAMPLE 1 
A mixture of 1 volume air to 1 volume nitrogen in the gas stream was used. 
The total gas flow rate was 440 cc/min, and the total liquid flow rate was 
95 cc/min. The liquid was a 0.1M sodium sulfite solution, 10.sup.-4 M in 
copper ion, added as CuSO.sub.4.5H.sub.2 O. The solution was adjusted to 
pH 8, and the pH was controlled to +0.02 pH units by addition of 1M NaOH 
during each run. The slope of the line shown through the data for the 
first run is 8.34.times.10.sup.-6 moles O.sub.2 min.sup.-1 ; for the 
second run it is 8.95.times.10.sup.-6 moles O.sub.2 min.sup.-1. Since the 
test cell simulates a section 2" by 2" by 1 layer of a cross-flow 
monolith, which is 7.57.times.10.sup.-3 l in volume for the monoliths used 
in this study, these oxygen transfer rates on a per volume basis are 2.12 
and 2.27 g O.sub.2 l.sup.-1 hr.sup.-1, respectively. 
EXAMPLE 2 
Air was used as the gas, again at gas and liquid flow rates of 440 and 95 
cc/min, respectively. The liquid solution was a 0.1M sodium sulfite 
solution, 10.sup.-4 in cobalt ion added as CoSO.sub.4.7H.sub.2 O. The 
solution was adjusted to pH 8, and controlled to +0.02 pH units throughout 
the experiment. The slope of the line through the data is 
2.609.times.10.sup.-5 moles min.sup.-1, corresponding to O.sub.2 transfer 
rate of 6.62 g O.sub.2 l.sup.-1 hr.sup.-1. 
EXAMPLE 3 
Air was used as the gas with a gas flow rate of 440 cc/min and a liquid 
flow rate of 95 cc/min. The liquid was 0.1M SO.sub.3 with 10.sup.-4 M 
copper ion, with no pH control. The shape of the curves through the data 
points, showing an oxygen consumption rate decreasing with time, is 
probably due to a pH effect: initially the solution is basic, around pH 
12; the reaction is known to liberate hydrogen ions, so the basic pH 
drives the reaction forward more rapidly; the effect decreases as the pH 
decreases. The later points fall on lines corresponding to 
7.76.times.10.sup.-6 and 7.16.times.10.sup.-6 moles O.sub.2.min.sup.-1, or 
1.97 and 1.82 g O.sub.2.l.sup.-1.hr.sup.-1, for the first and second runs, 
respectively. This value is much lower than the results using cobalt ions 
as the catalyst in Example 2, although the gas and flow rates are the 
same. This is largely due to the fact that cobalt is a faster catalyst for 
sulfite oxidation, resulting in a greater dissolved oxygen gradient. 
EXAMPLE 4 
A mixture of 1 volume air: 1 volume oxygen as the gas was used with a gas 
flow rate of 440 cc/min, a liquid flow rate of 95 cc/min. As in Example 3, 
the liquid was 0.1M SO.sub.3 with 10.sup.-4 copper ion, with no pH 
control. Again the data show a decrease in oxygen absorption rate over the 
first few hours. The later points of each run fall nicely on lines with 
slopes 12.89.times.10.sup.-6 and 9.18.times.10.sup.-6 moles 
O.sub.2.min.sup.-1 for the first and second runs respectively. These 
correspond to oxygen transfer rates of 3.27 and 2.33 g 
O.sub.2.l.sup.-1.hr.sup.-1. It is worth noting that these values differ 
considerably from triple the values for Example 3although the only 
difference in the experimental conditions is tripling the O.sub.2 
concentration in the gas stream. This demonstrates the fact that a kl a 
type of correlation for this reactor configuration is inappropriate. 
EXAMPLE 5 
This experiment was conducted using 1 volume air: 1 volume oxygen, as in 
Example 4, but with a higher gas flow rate of 660 cc/min. The liquid and 
liquid flow rate were the same as in Example 4. Again the oxygen 
consumption rate decreases with time. In the first run, from hours 1 to 4 
a slope of 17.31.times.10.sup.-6 moles O.sub.2.min.sup.-1, or 4.62 g 
O.sub.2.l.sup.-1 was observed. The second run was broken into two 
intervals: from 1 to 3 hours, with 14.95.times.10.sup.-6 moles 
O.sub.2.min.sup.-1, or 3.79 g O.sub.2.l.sup.-1 and from 3 to 7 hours, with 
10.93.times.10.sup.-6 moles O.sub.2.min.sup.-1, or 2.77 g 
O.sub.2.l.sup.-1.hr.sup.-1. Comparing these with the values for Example 4, 
it is evident that increasing the gas flow rate increases oxygen transfer 
in this range of gas flow rate and oxygen consumption. 
The economic evaluation of a fermentation process depends on the power 
dissipated in the reactor. Oxygen-transfer performance in particular can 
be associated with an oxygen-transfer efficiency as kg O.sub.2 /l.hr 
oxygenation per kW/l power dissipated in order to achieve that oxygenation 
rate. The reactor volume in the test cell was too small to measure the 
power dissipated. However, it is possible to estimate the frictional 
losses in a cross-flow monolith for the flow rates used in these 
experiments. 
The largest Reynolds number in either the gas or liquid flows in any 
experiment was below 40. The power requirement was estimated by 
approximating the channels as cylinders with the same hydraulic radius. 
The kinetic drag can be correlated as 
EQU F.sub.D =f.multidot.A*.multidot.KE* 
where A* is the wetted surface area, KE* is the average kinetic energy per 
unit volume (1/2.rho.v .sup.2, with density .rho. and fluid velocity v) 
and f is the friction factor, (64/Re, for laminar flow in tubes). From the 
drag, the power per unit volume, neglecting end effects, can be calculated 
as 
EQU P/V=F.sub.D .multidot.v 
The power required for the liquid and gas streams was calculated for a 10 
cm edge cube to arrive at the power per l reactor volume given in Table 1 
as follows: 
TABLE 1 
______________________________________ 
Power Oxygen Oxygenation 
Requirement Transfer Rate 
Efficiency 
Example 
(W/l) (g O.sub.2 /l hr) 
(kg O.sub.2 /kW hr) 
______________________________________ 
1 3.6 .times. 10.sup.-3 
2.12 588 
2.27 631 
2 3.6 .times. 10.sup.-3 
6.62 1840 
3 3.6 .times. 10.sup.-3 
1.97 550 
1.82 508 
4 3.6 .times. 10.sup.-3 
3.27 914 
2.33 651 
5 4.2 .times. 10.sup.-3 
4.62 1102 
3.79 905 
2.77 662 
______________________________________ 
As shown in the foregoing specific examples, oxygen transfer rates of 1.8 
to 6.6 g per liter total volume per hour, roughly equal to 3.6 to 13.2 g 
per liter liquid volume per hour, were observed for the experimental 
analogue to the cross-flow reactor using Gore-Tex.RTM. 0.2 .mu.m pore size 
polypropylene scrim laminate membrane. These transfer rates equal and 
surpass the maximum aeration rates observed in stirred tanks. One of the 
highest oxygen demands observed in a stirred tank is 260 mmol 
O.sub.2.sup.-1 h.sup.-1 for Azotobacter vinelandii. This is equal to 8.3 g 
O.sub.2 l.sup.-1 h.sup.-1, well within the range of transfer rates per 
liter liquid volume observed using a sulfite system. This does not 
guarantee that this transfer rate will be obtained when immobilized cells 
are used, since the gap between the membrane gas-liquid interface and the 
biofilm (FIG. 4) and the diffusivity of oxygen in the biofilm might reduce 
the effective driving force or increase the barrier to oxygen transport, 
respectively. It does indicate, however, that the membrane-ceramic 
composite can sustain the required oxygen flux. Another basis for 
comparison is the number of cells per liter which can be supported in the 
biofilm given this range of oxygen transfer rates. Assuming that oxygen is 
the limiting substrate and allowing a very high oxygen requirement per 
cell of 5.times.10.sup.-12 g O.sub.2 per cell per hour, the observed 
oxygen transfer rates could support a population density ranging from 
3.times.10.sup.11 to 13.times.10.sup.11 cells per liter reactor volume, or 
6.times.10.sup.11 to 26.times.10.sup.11 cells per liter liquid volume. 
Compared to 10.sup.9 cells per liter liquid for suspended cultures this 
represents an improvement of roughly two orders of magnitude. 
The power requirements for a cross-flow monolithic reactor consists in the 
power required to maintain the pressure drops to drive the gas and liquid 
flows through the channels. Since no liquid agitation is required and 
since the channels are unhindered, this power requirement is expected to 
be much lower than that for a stirred tank or packed column. Using an 
approximate method to estimate the power requirement for a cross-flow 
monolith operating with the same superficial gas and liquid velocities as 
used in the experiments, values of the oxygenation efficiency were 
estimated for the examples presented in Table 1. The oxygenation 
efficiencies range roughly from 500 to 1000 kg O.sub.2 per kW.multidot.hr. 
For the sake of comparison the values tabulated by Serieys, et al, 
Biotechnology and Bioengineering, XX, pp. 1393-1406 (1978), from the work 
of various researchers on gas-liquid contactors range from 0.3 to 7.5 kg 
O.sub.2 kW.multidot.hr. While a precise value of the oxygenation 
efficiency for a cross-flow monolithic reactor cannot be predicted, this 
comparison indicates that it is likely to be orders of magnitude better 
than conventional reactors. 
The results of the experimental studies reported in the previous section 
show that should an overall volumetric mass transfer coefficient (k a) be 
calculated on the basis of the obtained oxygen transfer rates, this 
coefficient would depend on the oxygen concentration in the gas phase, the 
kinetics of the reaction, and the gas flow rate. The detected trends are 
correct, i.e. the coefficient increases with the gas-phase O.sub.2 
concentration, gas flow rate and velocity of reaction, but cannot be 
quantitatively predicted by using the simple models usually employed for 
the description of k la in agitated vessels with outside aeration. This is 
not surprising because several ill-defined processes participate in the 
transport of oxygen through the membrane-ceramic composite material. 
EXAMPLE 6 
Murine-murine hybridoma cells, CRL-1606, which produce an IgG monoclonal 
antibody to human fibronectin were obtained from the American Type Culture 
Collection (ATCC, Rockville, Md.). The cells were thawed rapidly and 
passaged as necessary in DMEM (Mediatech, Washington, D.C.) supplemented 
with 5% FBS (Sigma Chemical, St. Louis, Mo.) for an unspecified period of 
time. All media used were supplemented with 100 U/mL penicillin and 100 
.mu.g/mL streptomycin (Mediatech, Washington, D.C.). 
Cordierite ceramic monoliths, 200 cells/in.sup.2, were provided by Corning 
Glass Works (Corning, N.Y.) in cylinders four inches long. These monoliths 
were sectioned into slabs 4".times.4".times.three layers. The slabs were 
immersed in a boiling solution of 10% nitric acid for one hour to 
precipitate any heavy metals ions which may have been introduced during 
the manufacture of the monoliths. The ceramics were washed extensively 
with de-ionized water and autoclaved in calcium- and magnesium-free 
phosphate buffered saline (PBS) to allow the pH to return to neutral. The 
slabs were sliced and polished to produce one single-layer slab and one 
double-layer slab. 
In order to separate the medium from the contacting gas stream, the ceramic 
slab was sandwiched between two vapor permeable, liquid impermeable 
Gore-Tex.RTM. membranes provided by W. L. Gore and Associates (Elkton, 
Md.). The polypropylene scrim laminate membrane had a 0.2 pore size with a 
total porosity of 78%. 
The ceramic slabs were sandwiched between two membranes in an anodized 
aluminum block using silicone rubber gaskets. A gas stream consisting of 
10% CO.sub.2 in air at a total flow rate of 30 cc/min contacted the medium 
stream across each membrane through a 2" square "window" cut from the 
rubber gaskets. Medium flowed through the ceramic monolith in a direction 
counter-current to the gas stream at an average channel velocity of 4.2 
cm/min. Since single pass conversion was so low, medium recirculated 
continuously using a medium reservoir external to the monolith. Medium was 
replaced every three days or when the pH had dropped sufficiently by 
draining all lines and aspirating spent medium from the reservoir. The 
reservoir, monolith bioreactor, and all associated pumps and tubing were 
placed in a humidified, 10% CO.sub.2 incubator. Indirect measurement of 
immobilized cell number was achieved by collecting samples of medium every 
eight to twelve hours and assaying the samples for glucose, lactate, and 
monoclonal antibody. 
Two experiments demonstrating the feasibility of culturing hybridoma cells 
in a ceramic matrix with Gore-Tex.RTM. membranes are presented below. The 
first experiment consisted of a double-layer, 4".times.4" ceramic slab in 
which cells were inoculated at a low density. The second experiment 
consisted of a single-layer, 4".times.4" slab in which cells were 
inoculated at a much higher density. 
Cumulative glucose consumption and cumulative lactate and monoclonal 
antibody production is shown in FIG. 9A for the first experiment. The 
bioreactor was inoculated with 2.0.times.10.sup.7 cells as determined by 
hemacytometer cell counts. This corresponds to an average cell density of 
1.2.times.10.sup.6 cells/cm.sup.3 wall. 
If cell growth is exponential and specific rates of consumption and 
production are constant, then total substrate consumption or product 
accumulation can be related to the growth rate. A non-linear least squares 
fit of the data gives a value for the growth rate of 0.013 hr.sup.-1 
.+-.2% for the culture, a value somewhat lower than in batch cultures but 
still reasonable. Based on this estimate, the average cell density at the 
end of the experiment was approximately 1.2.times.10.sup.8 cells/cm.sup.3 
wall. 
In the second experiment the monolith was inoculated with 
2.4.times.10.sup.8 cells, corresponding to an average density of 
2.5.times.10.sup.7 cells/cm.sup.3 wall. As shown in FIG. 9B the 
exponential growth phase occurs only in the first 100 hours, followed by a 
gradual decline in grown rate as the culture reaches what appears to be a 
state of confluency. After about 250 hours, the bioreactor produces 
monoclonal antibody at a constant rate of 1.2 mg/hr. Since the cell line 
continues to secrete antibody, oxygen must be supplied to these cells at 
sufficient levels to maintain viability and antibody productivity. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description; and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.