U.S. patent application number 10/134265 was filed with the patent office on 2003-02-06 for multi-temperature modular reactor and method of using same.
This patent application is currently assigned to Symyx Technologies, Inc.. Invention is credited to Hajduk, Damian A., Mansky, Paul, Matsiev, Leonid, McFarland, Eric, Nielsen, Ralph B., Safir, Adam.
Application Number | 20030026736 10/134265 |
Document ID | / |
Family ID | 46149790 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030026736 |
Kind Code |
A1 |
Hajduk, Damian A. ; et
al. |
February 6, 2003 |
Multi-temperature modular reactor and method of using same
Abstract
An apparatus and method for carrying out and monitoring the
progress and properties of multiple reactions is disclosed. The
method and apparatus are especially useful for synthesizing,
screening, and characterizing combinatorial libraries, but also
offer significant advantages over conventional experimental
reactors as well. The apparatus generally includes multiple vessels
for containing reaction mixtures, and systems for controlling the
stirring rate and temperature of individual reaction mixtures or
groups of reaction mixtures. In addition, the apparatus may include
provisions for independently controlling pressure in each vessel.
In situ monitoring of individual reaction mixtures provides
feedback for process controllers, and also provides data for
determining reaction rates, product yields, and various properties
of the reaction products, including viscosity and molecular
weight.
Inventors: |
Hajduk, Damian A.; (San
Jose, CA) ; Nielsen, Ralph B.; (San Jose, CA)
; Safir, Adam; (Berkeley, CA) ; Matsiev,
Leonid; (San Jose, CA) ; McFarland, Eric;
(Santa Barbara, CA) ; Mansky, Paul; (San
Francisco, CA) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Symyx Technologies, Inc.
|
Family ID: |
46149790 |
Appl. No.: |
10/134265 |
Filed: |
April 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10134265 |
Apr 29, 2002 |
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09417125 |
Nov 19, 1998 |
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09417125 |
Nov 19, 1998 |
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09177170 |
Oct 22, 1998 |
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60096603 |
Aug 13, 1998 |
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Current U.S.
Class: |
422/82.12 ;
374/E13.001; 422/400; 422/78 |
Current CPC
Class: |
B01J 2219/00702
20130101; B01J 2219/00585 20130101; B01L 2300/14 20130101; B01J
19/004 20130101; B01J 2219/0031 20130101; F28D 15/00 20130101; B01L
2200/026 20130101; B01L 2300/06 20130101; B01J 19/0006 20130101;
C40B 40/14 20130101; B01J 2219/00029 20130101; B01F 33/45 20220101;
B01J 2219/00745 20130101; B01L 2300/049 20130101; B01F 35/2215
20220101; B01J 2219/00335 20130101; B01L 7/54 20130101; B01J
2219/002 20130101; B01J 2219/00418 20130101; B01J 2219/0059
20130101; B01J 2219/00308 20130101; B01J 2219/00351 20130101; B01J
2219/00481 20130101; B01J 2219/00691 20130101; B01L 2300/0627
20130101; Y10T 436/10 20150115; Y10T 436/25 20150115; B01F 33/71
20220101; F28F 27/00 20130101; Y10T 436/11 20150115; F28D 2021/0077
20130101; B01J 2219/00495 20130101; G01N 21/253 20130101; B01J
2219/00283 20130101; B01J 2219/00686 20130101; B01J 2219/00689
20130101; B01J 2219/00596 20130101; B01J 2219/0072 20130101; B01L
3/50851 20130101; B01J 19/0013 20130101; B01J 2219/00722 20130101;
B01J 2219/00333 20130101; B01L 3/50853 20130101; B01F 35/2213
20220101; B01J 2219/00389 20130101; B01J 2219/00477 20130101; B01J
2219/00373 20130101; B01J 2219/00601 20130101; B01J 2219/00704
20130101; C40B 40/18 20130101; B01J 2219/00367 20130101; B01J
2219/00698 20130101; B01L 2300/1805 20130101; G01K 13/00 20130101;
B01F 35/213 20220101; B01J 19/0046 20130101; B01J 2219/00162
20130101; B01J 2219/00695 20130101 |
Class at
Publication: |
422/82.12 ;
422/78; 422/99 |
International
Class: |
G01N 021/75 |
Claims
What is claimed is:
1. A modular reactor for analyzing chemical reactions in an array
of material, comprising at least two reactor modules, each of said
reactor modules having at least two reactor vessels for receiving
material therein, and a temperature control system comprising (i) a
first temperature control device for commonly biasing said at least
two reactor modules to a first predetermined temperature, (ii) a
separate second temperature control device associated with one of
the at least two reactor modules for selectively varying the
temperature of said at least one reactor module to a second
predetermined temperature, and (iii) a separate third temperature
control device associated with another of the at least two reactor
modules for selectively varying the temperature of the another
reactor module to a third predetermined temperature, said first
predetermined temperature being different from each of said second
and third predetermined temperatures.
2. The reactor in claim 1, wherein said second predetermined
temperature is equal to said third predetermined temperature.
3. The reactor in claim 1, wherein said first temperature control
device further includes a plurality of passages for receiving a
temperature control medium.
4. The reactor in claim 3, wherein said temperature control medium
is a thermal fluid.
5. The reactor in claim 4, wherein said thermal fluid is a member
of the set consisting of water, silicone oil and halogenated
solvents.
6. The reactor in claim 1, wherein said first, second or third
temperature control device is a thermoelectric module.
7. The reactor in claim 1, wherein said first, second or third
temperature control device is an electrical heating strip.
8. The reactor in claim 1, further including temperature sensors
associated with said reactor modules for monitoring the temperature
of each of said reactor modules.
9. The reactor in claim 8, wherein said first temperature control
device has at least one of said temperature sensors associated
therewith.
10. The reactor in claim 8, further including a processor connected
to said temperature sensors for collecting and analyzing
temperature data from said reactor modules, wherein said processor
produces signals to vary the temperature of said reactor
modules.
11. The reactor in claim 11 wherein the reactor vessels are
wells.
12. The reactor in claim 11 wherein the reactor vessels are
removable liners.
13. A modular reactor for analyzing chemical reactions in an array
of material, comprising at least two reactor modules, each of said
reactor modules having at least two reactor vessels for receiving
material therein, and a temperature control system comprising (i) a
first temperature control device for commonly biasing the
temperature of both of said at least two reactor modules, (ii) a
separate second temperature control device associated with one of
the at least two reactor modules for selectively varying the
temperature of the at least one reactor module, and (iii) a
separate third temperature control device associated with another
of the at least two reactor modules for selectively varying the
temperature of the another reactor module, said second and third
temperature control devices allowing the temperature of the one
reactor module to be varied independent of the temperature of the
another reactor module.
14. The reactor in claim 13, wherein the temperature of the one
reactor module is equal to the temperature of the another reactor
module.
15. The reactor in claim 13, further including temperature sensors
associated with said reactor modules for monitoring the temperature
of each of said reactor modules.
16. The reactor in claim 15, wherein said first temperature control
device has at least one of said temperature sensors associated
therewith.
17. The reactor in claim 15, further including a processor
connected to said temperature sensors for collecting and analyzing
temperature data from said reactor modules, wherein said processor
produces signals to vary the temperature of said reactor
modules.
18. The reactor in claim 13 wherein the reactor vessels are
wells.
19. The reactor in claim 13 wherein the reactor vessels are
removable liners.
20. A method for analyzing, synthesizing or characterizing an array
of materials comprising the steps of providing a modular reactor
comprising at least two reactor modules and a first temperature
control device for commonly biasing said at least two reactor
modules, each of the reactor modules having at least two reactor
vessels, placing material in said reactor vessels, independently
controlling the temperature of the at least two reactor modules to
different predetermined temperatures by biasing the at least two
reactor modules using said first temperature control device to a
first predetermined temperature and independently varying the
temperature of said at least two reactor modules using a separate
temperature control device associated with each of the reactor
modules, and evaluating the materials in situ in each of the
reactor vessels.
21. The method of claim 20, wherein said first predetermined
temperature is below ambient.
22. The method of claim 20, wherein said first predetermined
temperature of said at least two reactor modules is maintained
constant over time.
23. The method of claim 20, wherein said step of varying the
temperature of said at least two reactor modules includes varying
the temperature of each of said at least two reactor modules to a
second and third predetermined temperature, respectively, wherein
said second and third predetermined temperatures are different from
each other and from said first predetermined temperature.
24. A method for analyzing and characterizing an array of materials
comprising the steps of: providing at least two reactor modules,
each having a plurality of reaction vessels; placing material in
said reaction vessels; biasing said at least two reactor modules to
a first predetermined temperature using a first temperature control
device for commonly biasing said at least two reactor modules;
independently controlling the temperature of the at least two
reactor modules by associating a separate temperature control
device with each of said at least two reactor modules, and varying
the temperature of each of said reactor modules to different second
and third temperatures, respectively, said second temperature of
one of the at least two reactor modules being different than said
third temperature of the other of said reactor modules; monitoring
and detecting changes in the materials in-situ after the
temperature of each of said reactor modules is varied; and
determining characteristics of the materials based on the detected
changes.
25. The method of claim 24, wherein said monitoring and detecting
step is performed at predefined intervals of time, and wherein said
determining step determines said characteristics of the materials
as function of time.
26. The method of claim 24, wherein said step of varying the
temperature of said reactor modules is performed at a predetermined
rate, and wherein said determining step determines said
characteristics of the materials as function of temperature.
27. The method of claim 24, wherein said step of varying the
temperature of said reactor modules includes varying an amount of
electrical power supplied to said temperature control devices.
Description
RELATED APPLICATION
[0001] The present application is a Continuation-in-Part of U.S.
application Ser. No. 09/177,170, filed Oct. 22, 1998, entitled
"Parallel Reactor with Internal Sensing and Method of Using Same,"
which claims the benefit of U.S. Provisional Application No.
60/096,603, filed Aug. 13, 1998. Applicant incorporates the above
applications herein by reference and claims priority from these
earlier filed applications pursuant to 35 U.S.C. .sctn.120.
BACKGROUND
[0002] 1. Technical Field
[0003] The present invention relates to a method and apparatus for
rapidly making, screening, and characterizing an array of
materials. More particularly, this invention is directed to a
multi-temperature reactor for screening and characterizing
different zones of materials in a combinatorial library.
[0004] 2. Discussion
[0005] In combinatorial chemistry, a large number of candidate
materials are created from a relatively small set of precursors and
subsequently evaluated for suitability for a particular
application. As currently practiced, combinatorial chemistry
permits scientists to systematically explore the influence of
structural variations in candidates by dramatically accelerating
the rates at which they are created and evaluated. Compared to
traditional discovery methods, combinatorial methods sharply reduce
the costs associated with preparing and screening each
candidate.
[0006] Combinatorial chemistry has revolutionized the process of
drug discovery. See, for example, 29 Acc. Chem. Res. 1-170 (1996);
97 Chem. Rev. 349-509 (1997); S. Borman, Chem. Eng. News 43-62
(Feb. 24, 1997); A. M. Thayer, Chem. Eng. News 57-64 (Feb. 12,
1996); N. Terret, 1 Drug Discovery Today 402 (1996)). One can view
drug discovery as a two-step process: acquiring candidate compounds
through laboratory synthesis or through natural products
collection, followed by evaluation or screening for efficacy.
Pharmaceutical researchers have long used high-throughput screening
(HTS) protocols to rapidly evaluate the therapeutic value of
natural products and libraries of compounds synthesized and
cataloged over many years. However, compared to HTS protocols,
chemical synthesis has historically been a slow, arduous process.
With the advent of combinatorial methods, scientists can now create
large libraries of organic molecules at a pace on par with HTS
protocols.
[0007] Recently, combinatorial approaches have been used for
discovery programs unrelated to drugs. For example, some
researchers have recognized that combinatorial strategies also
offer promise for the discovery of inorganic compounds such as
high-temperature superconductors, magnetoresistive materials,
luminescent materials, and catalytic materials. See, for example,
co-pending U.S. patent application Ser. No. 08/327,513 "The
Combinatorial Synthesis of Novel Materials" (published as WO
96/11878) and co-pending U.S. patent application Ser. No.
08/898,715 "Combinatorial Synthesis and Analysis of Organometallic
Compounds and Catalysts" (published as WO 98/03251), which are both
herein incorporated by reference.
[0008] Because of its success in eliminating the synthesis
bottleneck in drug discovery, many researchers have come to
narrowly view combinatorial methods as tools for creating
structural diversity. Few researchers have emphasized that, during
synthesis, variations in temperature, pressure, ionic strength, and
other process conditions can strongly influence the properties of
library members. For instance, reaction conditions are particularly
important in formulation chemistry, where one combines a set of
components under different reaction conditions or concentrations to
determine their influence on product properties.
[0009] Moreover, because the performance criteria in materials
science is often different than in pharmaceutical research, many
workers have failed to realize that process variables often can be
used to distinguish among library members both during and after
synthesis. For example, the viscosity of reaction mixtures can be
used to distinguish library members based on their ability to
catalyze a solution-phase polymerization-at constant polymer
concentration, the higher the viscosity of the solution, the
greater the molecular weight of the polymer formed. Furthermore,
total heat liberated and/or peak temperature observed during an
exothermic reaction can be used to rank catalysts.
[0010] Therefore, a need exists for an apparatus to rapidly prepare
and screen combinatorial libraries in which one can monitor and
control process conditions during synthesis and screening.
SUMMARY OF THE INVENTION
[0011] In accordance with one aspect of the present invention,
there is provided an apparatus for parallel processing of reaction
mixtures. The apparatus includes vessels for containing the
reaction mixtures, a stirring system, and a temperature control
system that is adapted to maintain individual vessels or groups of
vessels at different temperatures. The apparatus may consist of a
monolithic reactor block, which contains the vessels, or an
assemblage of reactor block modules that have individual
temperature control devices. A robotic material handling system can
be used to automatically load the vessels with starting materials.
In addition to heating or cooling individual vessels, the entire
reactor block can be maintained at a nearly uniform temperature by
circulating a temperature-controlled thermal fluid through channels
formed in the reactor block. The stirring system generally includes
stirring members--blades, bars, and the like--placed in each of the
vessels, and a mechanical or magnetic drive mechanism. Torque and
rotation rate can be controlled and monitored through strain gages,
phase lag measurements, and speed sensors.
[0012] The apparatus may optionally include a system for evaluating
material properties of the reaction mixtures. The system includes
mechanical oscillators located within the vessels. When stimulated
with a variable-frequency signal, the mechanical oscillators
generate response signals that depend on properties of the reaction
mixture. Through calibration, mechanical oscillators can be used to
monitor molecular weight, specific gravity, elasticity, dielectric
constant, conductivity, and other material properties of the
reaction mixtures.
[0013] In accordance with a second aspect of the present invention,
there is provided an apparatus for monitoring rates of production
or consumption of a gas-phase component of a reaction mixture. The
apparatus generally comprises a closed vessel for containing the
reaction mixture, a stirring system, a temperature control system
and a pressure control system. The pressure control system includes
a pressure sensor that communicates with the vessel, as well as a
valve that provides venting of a gaseous product from the vessel.
In addition, in cases where a gas-phase reactant is consumed during
reaction, the valve provides access to a source of the reactant.
Pressure monitoring of the vessel, coupled with venting of product
or filling with reactant allows the investigator to determine rates
of production or consumption, respectively.
[0014] In accordance with a third aspect of the present invention,
there is provided an apparatus for monitoring rates of consumption
of a gas-phase reactant. The apparatus generally comprises a closed
vessel for containing the reaction mixture, a stirring system, a
temperature control system and a pressure control system. The
pressure control system includes a pressure sensor that
communicates with the vessel, as well as a flow sensor that
monitors the flow rate of reactant entering the vessel. Rates of
consumption of the reactant can be determined from the reactant
flow rate and filling time.
[0015] In accordance with a fourth aspect of the present invention,
there is provided a method of making and characterizing a plurality
of materials. The method includes the steps of providing vessels
with starting materials to form reaction mixtures, confining the
reaction mixtures in the vessels to allow reaction to occur, and
stirring the reaction mixtures for at least a portion of the
confining step. The method further includes the step of evaluating
the reaction mixtures by tracking at least one characteristic of
the reaction mixtures for at least a portion of the confining step.
Various characteristics or properties can be monitored during the
evaluating step, including temperature, rate of heat transfer,
conversion of starting materials, rate of conversion, torque at a
given stirring rate, stall frequency, viscosity, molecular weight,
specific gravity, elasticity, dielectric constant, and
conductivity.
[0016] In accordance with a fifth aspect of the present invention,
there is provided a method of monitoring the rate of consumption of
a gas-phase reactant. The method comprises the steps of providing a
vessel with starting materials to form the reaction mixture,
confining the reaction mixtures in the vessel to allow reaction to
occur, and stirring the reaction mixture for at least a portion of
the confining step. The method further includes filling the vessel
with the gas-phase reactant until gas pressure in the vessel
exceeds an upper-pressure limit, P.sub.H, and allowing gas pressure
in the vessel to decay below a lower-pressure limit, P.sub.L. Gas
pressure in the vessel is monitored and recorded during the
addition and consumption of the reactant. This process is repeated
at least once, and rates of consumption of the gas-phase reactant
in the reaction mixture are determined from the pressure versus
time record.
[0017] In accordance with a sixth aspect of the present invention,
there is provided a method of monitoring the rate of production of
a gas-phase product. The method comprises the steps of providing a
vessel with starting materials to form the reaction mixture,
confining the reaction mixtures in the vessel to allow reaction to
occur, and stirring the reaction mixture for at least a portion of
the confining step. The method also comprises the steps of allowing
gas pressure in the vessel to rise above an upper-pressure limit,
P.sub.H, and venting the vessel until gas pressure in the vessel
falls below a lower-pressure limit, P.sub.L. The gas pressure in
the vessel is monitored and recorded during the production of the
gas-phase component and subsequent venting of the vessel. The
process is repeated at least once, so rates of production of the
gas-phase product can be calculated from the pressure versus time
record.
[0018] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates a parallel reactor system in accordance
with the present invention.
[0020] FIG. 2 shows a perspective view of a modular reactor block
with a robotic liquid handling system.
[0021] FIG. 3 shows a temperature monitoring system.
[0022] FIG. 4 shows a cross-sectional view of an integral
temperature sensor-vessel assembly.
[0023] FIG. 5 shows a side view of an infrared temperature
measurement system.
[0024] FIG. 6 shows a temperature monitoring and control system for
a reactor vessel.
[0025] FIG. 7 illustrates another temperature control system, which
includes liquid cooling and heating of the reactor block.
[0026] FIG. 8 is a cross-sectional view of thermoelectric devices
sandwiched between a reactor block and heat transfer plate.
[0027] FIG. 9 is a cross-sectional view of a portion of a reactor
block useful for obtaining calorimetric data.
[0028] FIG. 10 is an exploded perspective view of a stirring system
for a single module of a modular reactor block of the type shown in
FIG. 2.
[0029] FIG. 11 is a schematic representation of an electromagnetic
stirring system.
[0030] FIGS. 12-13 are schematic representations of portions of
electromagnet stirring arrays in which the ratios of electromagnets
to vessel sites approach 1:1 and 2:1, respectively, as the number
of vessel sites becomes large.
[0031] FIG. 14 is a schematic representation of an electromagnet
stirring array in which the ratio of electromagnets to vessel sites
is 4:1.
[0032] FIG. 15 shows additional elements of an electromagnetic
stirring system, including drive circuit and processor.
[0033] FIG. 16 illustrates the magnetic field direction of a
2.times.2 electromagnet array at four different times during one
rotation of a magnetic stirring bar.
[0034] FIG. 17 illustrates the magnetic field direction of a
4.times.4 electromagnet array at five different times during one
full rotation of a 3.times.3 array of magnetic stirring bars.
[0035] FIG. 18 illustrates the rotation direction of the 3.times.3
array of magnetic stirring bars shown in FIG. 17.
[0036] FIG. 19 shows a wiring configuration for an electromagnetic
stirring system.
[0037] FIG. 20 shows an alternate wiring configuration for an
electromagnetic stirring system.
[0038] FIG. 21 shows the phase relationship between sinusoidal
source currents, I.sub.A(t) and I.sub.B(t). which drive two series
of electromagnets shown in FIGS. 19 and 20.
[0039] FIG. 22 is a block diagram of a power supply for an
electromagnetic stirring system.
[0040] FIG. 23 illustrates an apparatus for directly measuring the
applied torque of a stirring system.
[0041] FIG. 24 shows placement of a strain gauge in a portion of a
base plate that is similar to the lower plate of the reactor module
shown in FIG. 10.
[0042] FIG. 25 shows an inductive sensing coil system for detecting
rotation and measuring phase angle of a magnetic stirring blade or
bar.
[0043] FIG. 26 shows typical outputs from inductive sensing coils,
which illustrate phase lag associated with magnetic stirring for
low and high viscosity solutions, respectively.
[0044] FIG. 27 illustrates how amplitude and phase angle will vary
during a reaction as the viscosity increases from a low value to a
value sufficient to stall the stirring bar.
[0045] FIGS. 28-29 show bending modes of tuning forks and
bimorph/unimorph resonators, respectively.
[0046] FIG. 30 schematically shows a system for measuring the
properties of reaction mixtures using mechanical oscillators.
[0047] FIG. 31 shows an apparatus for assessing reaction kinetics
based on monitoring pressure changes due to production or
consumption various gases during reaction.
[0048] FIG. 32 shows results of calibration runs for
polystyrene-toluene solutions using mechanical oscillators.
[0049] FIG. 33 shows a calibration curve obtained by correlating M,
of the polystyrene standards with the distance between the
frequency response curve for toluene and each of the polystyrene
solutions of FIG. 32.
[0050] FIG. 34 depicts the pressure recorded during solution
polymerization of ethylene to polyethylene.
[0051] FIGS. 35-36 show ethylene consumption rate as a function of
time, and the mass of polyethylene formed as a function of ethylene
consumed, respectively.
[0052] FIG. 37 is a schematic of an alternative embodiment of a
multi-temperature modular reactor.
[0053] FIG. 38 is top and side view of a reactor block module.
[0054] FIG. 39 is a cross-sectional view of two reactor modules in
a storage rack taken along lines 39-39 in FIG. 37.
[0055] FIG. 40 is top view of a heat transfer plate.
[0056] FIG. 41 is an exploded view of a temperature control unit
for use with the multi-temperature modular reactor.
[0057] FIG. 42 is a planar view of the interior of a top plate for
an insulating encasing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] The present invention provides an apparatus and method for
carrying out and monitoring the progress and properties of multiple
reactions. It is especially useful for synthesizing, screening, and
characterizing combinatorial libraries, but offers significant
advantages over conventional experimental reactors as well. For
example, in situ monitoring of individual reaction mixtures not
only provides feedback for process controllers, but also provides
data for determining reaction rates, product yields, and various
properties of the reaction products, including viscosity and
molecular weight. Moreover, in situ monitoring coupled with tight
process control can improve product selectivity, provide
opportunities for process and product optimization, allow
processing of temperature-sensitive materials, and decrease
experimental variability. Other advantages result from using small
mixture volumes. In addition to conserving valuable reactants,
decreasing sample size increases surface area relative to volume
within individual reactor vessels. This improves the uniformity of
reaction mixtures, aids gas-liquid exchange in multiphase reactions
and increases heat transfer between the samples and the reactor
vessels. Because large samples respond much slower to changes in
system conditions, the use of small samples, along with in situ
monitoring and process control, also allows for time-dependent
processing and characterization.
[0059] Overview of Parallel Reactor
[0060] FIG. 1 shows one embodiment of a parallel reactor system
100. The reactor system 100 includes removable vessels 102 for
receiving reactants. Wells 104 formed into a reactor block 106
contain the vessels 102. Although the wells 104 can serve as
reactor vessels, removable vessels 102 or liners provide several
advantages. For example, following reaction and preliminary testing
(screening), one can remove a subset of vessels 102 from the
reactor block 106 for further in-depth characterization. When using
removable vessels 102, one can also select vessels 102 made of
material appropriate for a given set of reactants, products, and
reaction conditions. Unlike the reactor block 106, which represents
a significant investment, the vessels 102 can be discarded if
damaged after use. Finally, one can lower system 100 costs and
ensure compatibility with standardized sample preparation and
testing equipment by designing the reactor block 106 to accommodate
commercially available vessels.
[0061] As shown in FIG. 1, each of the vessels 102 contains a
stirring blade 108. In one embodiment, each stirring blade 108
rotates at about the same speed, so that each of the reaction
mixtures within the vessels 102 experience similar mixing. Because
reaction products can be influenced by mixing intensity, a uniform
rotation rate ensures that any differences in products does not
result from mixing variations. In another embodiment, the rotation
rate of each stirring blade 108 can be varied independently, which
as discussed below, can be used to characterize the viscosity and
molecular weight of the reaction products or can be used to study
the influence of mixing speed on reaction.
[0062] Depending on the nature of the starting materials, the types
of reactions, and the method used to characterize reaction products
and rates of reaction, it may be desirable to enclose the reactor
block 106 in a chamber 110. The chamber 110 may be evacuated or
filled with a suitable gas. In some cases, the chamber 110 may be
used only during the loading of starting materials into the vessels
102 to minimize contamination during sample preparation, for
example, to prevent poisoning of oxygen sensitive catalysts. In
other cases, the chamber 110 may be used during the reaction
process or the characterization phase, providing a convenient
method of supplying one or more gases to all of the vessels 102
simultaneously. In this way, a gaseous reactant can be added to all
of the vessels 102 at one time. Note, however, it is often
necessary to monitor the rate of disappearance of a gaseous
reactant--for example, when determining rates of conversion--and in
such cases the vessels 102 are each sealed and individually
connected to a gas source, as discussed below.
[0063] FIG. 2 shows a perspective view of a parallel reactor system
130 comprised of a modular reactor block 132. The modular reactor
block 132 shown in FIG. 2 consists of six modules 134, and each
module 134 contains eight vessels (not shown). Note, however, the
number of modules 134 and the number of vessels within each of the
modules 134 can vary.
[0064] The use of modules 134 offers several advantages over a
monolithic reactor block. For example, the size of the reactor
block 132 can be easily adjusted depending on the number of
reactants or the size of the combinatorial library. Also,
relatively small modules 134 are easier to handle, transport, and
fabricate than a single, large reactor block. A damaged module can
be quickly replaced by a spare module, which minimizes repair costs
and downtime. Finally, the use of modules 134 improves control over
reaction parameters. For instance, stirring speed, temperature, and
pressure of each of the vessels can be varied between modules.
[0065] In the embodiment shown in FIG. 2, each of the modules 134
is mounted on a base plate 136 having a front 138 and a rear 140.
The modules 134 are coupled to the base plate 136 using guides (not
shown) that mate with channels 142 located on the surface of the
base plate 136. The guides prevent lateral movement of the modules
134, but allow linear travel along the channels 142 that extend
from the front 138 toward the rear 140 of the base plate 136. Stops
144 located in the channels 142 near the front 138 of the base
plate 136 limit the travel of the modules 134. Thus, one or more of
the modules 134 can be moved towards the front 138 of the base
plate 136 to gain access to individual vessels while the other
modules 134 undergo robotic filling. In another embodiment, the
modules 134 are rigidly mounted to the base plate 136 using bolts,
clips, or other fasteners.
[0066] As illustrated in FIG. 2, a conventional robotic material
handling system 146 is ordinarily used to load vessels with
starting materials. The robotic system 146 includes a pipette or
probe 148 that dispenses measured amounts of liquids into each of
the vessels. The robotic system 146 manipulates the probe 148 using
a 3-axis translation system 150. The probe 148 is connected to
sources 152 of liquid reagents through flexible tubing 154. Pumps
156, which are located along the flexible tubing 154, are used to
transfer liquid reagents from the sources 152 to the probe 148.
Suitable pumps 156 include peristaltic pumps and syringe pumps. A
multi-port valve 158 located downstream of the pumps 156 selects
which liquid reagent from the sources 152 is sent to the probe 148
for dispensing in the vessels.
[0067] The robotic liquid handling system 146 is controlled by a
processor 160. In the embodiment shown in FIG. 2, the user first
supplies the processor 160 with operating parameters using a
software interface. Typical operating parameters include the
coordinates of each of the vessels and the initial compositions of
the reaction mixtures in individual vessels. The initial
compositions can be specified as lists of liquid reagents from each
of the sources 152, or as incremental additions of various liquid
reagents relative to particular vessels.
[0068] Temperature Control and Monitoring
[0069] The ability to monitor and control the temperature of
individual reactor vessels is an important aspect of the present
invention. During synthesis, temperature can have a profound effect
on structure and properties of reaction products. For example, in
the synthesis of organic molecules, yield and selectivity often
depend strongly on temperature. Similarly, in polymerization
reactions, polymer structure and properties-molecular weight,
particle size, monomer conversion, microstructure-can be influenced
by reaction temperature. During screening or characterization of
combinatorial libraries, temperature control and monitoring of
library members is often essential to making meaningful comparisons
among members. Finally, temperature can be used as a screening
criteria or can be used to calculate useful process and product
variables. For instance, catalysts of exothermic reactions can be
ranked based on peak reaction temperature and/or total heat
released over the course of reaction, and temperature measurements
can be used to compute rates of reaction and conversion.
[0070] FIG. 3 illustrates one embodiment of a temperature
monitoring system 180, which includes temperature sensors 182 that
are in thermal contact with individual vessels 102. For clarity, we
describe the temperature monitoring system 180 with reference to
the monolithic reactor block 106 of FIG. 1, but this disclosure
applies equally well to the modular reactor block 132 of FIG. 2.
Suitable temperature sensors 182 include jacketed or non-jacketed
thermocouples (TC), resistance thermometric devices (RTD), and
thermistors. The temperature sensors 182 communicate with a
temperature monitor 184, which converts signals received from the
temperature sensors 182 to a standard temperature scale. An
optional processor 186 receives temperature data from the
temperature monitor 184. The processor 186 performs calculations on
the data, which may include wall corrections and simple comparisons
between different vessels 102, as well as more involved processing
such as calorimetry calculations discussed below. During an
experimental run, temperature data is typically sent to storage 188
so that it can be retrieved at a later time for analysis.
[0071] FIG. 4 shows a cross-sectional view of an integral
temperature sensor-vessel assembly 200. The temperature sensor 202
is embedded in the wall 204 of a reactor vessel 206. The surface
208 of the temperature sensor 202 is located adjacent to the inner
wall 210 of the vessel to ensure good thermal contact between the
contents of the vessel 206 and the temperature sensor 202. The
sensor arrangement shown in FIG. 3 is useful when it is necessary
to keep the contents of the reactor vessel 206 free of
obstructions. Such a need might arise, for example, when using a
freestanding mixing device, such as a magnetic stirring bar. Note,
however, that fabricating an integral temperature sensor such as
the one shown in FIG. 4 can be expensive and time consuming,
especially when using glass reactor vessels.
[0072] Thus, in another embodiment, the temperature sensor is
immersed in the reaction mixture. Because the reaction environment
within the vessel may rapidly damage the temperature sensor, it is
usually jacketed with an inert material, such as a fluorinated
thermoplastic. In addition to low cost, direct immersion offers
other advantages, including rapid response and improved accuracy.
In still another embodiment, the temperature sensor is placed on
the outer surface 212 of the reactor vessel of FIG. 4. As long as
the thermal conductivity of the reactor vessel is known, relatively
accurate and rapid temperature measurements can be made.
[0073] One can also remotely monitor temperature using an infrared
system illustrated in FIG. 5. The infrared monitoring system 230
comprises an optional isolation chamber 232, which contains the
reactor block 234 and vessels 236. The top 238 of the chamber 232
is fitted with a window 240 that is transparent to infrared
radiation. An infrared-sensitive camera 242 positioned outside the
isolation chamber 232, detects and records the intensity of
infrared radiation passing through the window 240. Since infrared
emission intensity depends on source temperature, it can be used to
distinguish high temperature vessels from low temperature vessels.
With suitable calibration, infrared intensity can be converted to
temperature, so that at any given time, the camera 242 provides
"snapshots" of temperature along the surface 244 of the reactor
block 234. In the embodiment shown in FIG. 5, the tops 246 of the
vessels 236 are open. In an alternate embodiment, the tops 246 of
the vessels 236 are fitted with infrared transparent caps (not
shown). Note that, with stirring, the temperature is uniform within
a particular vessel, and therefore the surface temperature of the
vessel measured by infrared emission will agree with the bulk
temperature measured by a TC or RTD immersed in the vessel.
[0074] The temperature of the reactor vessels and block can be
controlled as well as monitored. Depending on the application, each
of the vessels can be maintained at the same temperature or at
different temperatures during an experiment. For example, one may
screen compounds for catalytic activity by first combining,. in
separate vessels, each of the compounds with common starting
materials; these mixtures are then allowed to react at uniform
temperature. One may then further characterize a promising catalyst
by combining it in numerous vessels with the same starting
materials used in the screening step. The mixtures then react at
different temperatures to gauge the influence of temperature on
catalyst performance (speed, selectivity). In many instances, it
may be necessary to change the temperature of the vessels during
processing For example, one may decrease the temperature of a
mixture undergoing a reversible exothermic reaction to maximize
conversion. Or, during a characterization step, one may ramp the
temperature of a reaction product to detect phase transitions
(melting range, glass transition temperature). Finally, one may
maintain the reactor block at a constant temperature, while
monitoring temperature changes in the vessels during reaction to
obtain calorimetric data as described below.
[0075] FIG. 6 shows a useful temperature control system 260, which
comprises separate heating 262 and temperature sensing 264
elements. The heating element 262 shown in FIG. 6 is a conventional
thin filament resistance heater whose heat output is proportional
to the product of the filament resistance and the square of the
current passing through the filament. The heating element 262 is
shown coiled around a reactor vessel 266 to ensure uniform radial
and axial heating of the vessel 266 contents. The temperature
sensing element 264 can be a TC, RTD, and the like. The heating
element 262 communicates with a processor 268, which based on
information received from the temperature sensor 264 through a
temperature monitoring system 270, increases or decreases heat
output of the heating element 262. A heater control system 272,
located in the communication path between the heating element 262
and the processor 268, converts a processor 268 signal for an
increase (decrease) in heating into an increase (decrease) in
electrical current through the heating element 262. Generally, each
of the vessels 104 of the parallel reactor system 100 shown in FIG.
1 or FIG. 3 are equipped with a heating element 262 and one or more
temperature sensors 264, which communicate with a central heater
control system 272, temperature monitoring system 270, and
processor 268, so that the temperature of the vessels 104 can be
controlled independently.
[0076] Other embodiments include placing the heating element 262
and temperature sensor 264 within the vessel 266, which results in
more accurate temperature monitoring and control of the vessel 266
contents, and combining the temperature sensor and heating element
in a single package. A thermistor is an example of a combined
temperature sensor and heater. which can be used for both
temperature monitoring and control because its resistance depends
on temperature.
[0077] FIG. 7 illustrates another temperature control system, which
includes liquid cooling and heating of the reactor block 106.
Regulating the temperature of the reactor block 106 provides many
advantages. For example, it is a simple way of maintaining nearly
uniform temperature in all of the reactor vessels 102. Because of
the large surface area of the vessels 102 relative to the volume of
the reaction mixture cooling the reactor block 106 also allows one
to carryout highly exothermic reactions. When accompanied by
temperature control of individual vessels 102, active cooling of
the reactor block 106 allows for processing at sub-ambient
temperatures. Moreover, active heating or cooling of the reactor
block 106 combined with temperature control of individual vessels
102 or groups of vessels 102 also decreases response time of the
temperature control feedback. One may control the temperature of
individual vessels 102 or groups of vessels 102 using compact heat
transfer devices, which include electric resistance heating
elements or thermoelectric devices, as shown in FIG. 6 and FIG. 8,
respectively. Although we describe reactor block cooling with
reference to the monolithic reactor block 106, one may, in a like
manner, independently heat or cool individual modules 134 of the
modular reactor block 132 shown in FIG. 2.
[0078] Returning to FIG. 7, a thermal fluid 290, such as water,
steam, a silicone fluid, a fluorocarbon, and the like, is
transported from a uniform temperature reservoir 292 to the reactor
block 106 using a constant or variable speed pump 294. The thermal
fluid 290 enters the reactor block 106 from a pump outlet conduit
296 through an inlet port 298. From the inlet port 298, the thermal
fluid 290 flows through a passageway 300 formed in the reactor
block 106. The passageway may comprise single or multiple channels.
The passageway 300 shown in FIG. 7, consists of a single channel
that winds its way between rows of vessels 102, eventually exiting
the reactor block 106 at an outlet port 302. The thermal fluid 290
returns to the reservoir 292 through a reactor block outlet conduit
304. A heat pump 306 regulates the temperature of the thermal fluid
290 in the reservoir 292 by adding or removing heat through a heat
transfer coil 308. In response to signals from temperature sensors
(not shown) located in the reactor block 106 and the reservoir 292,
a processor 310 adjusts the amount of heat added to or removed from
the thermal fluid 290 through the coil 308. To adjust the flow rate
of thermal fluid 290 through the passageway 300, the processor 310
communicates with a valve 312 located in a reservoir outlet conduit
314. The reactor block 106, reservoir 292. pump 294, and conduits
296, 304, 314 can be insulated to improve temperature control in
the reactor block 106.
[0079] Because the reactor block 106 is typically made of a metal
or other material possessing high thermal conductivity, the single
channel passageway 300 is usually sufficient for maintaining the
temperature of the block 106 a few degrees above or below room
temperature. To improve temperature uniformity within the reactor
block 106, the passageway can be split into parallel channels (not
shown) immediately downstream of the inlet port 298. In contrast to
the single channel passageway 300 depicted in FIG. 7, each of the
parallel channels passes between a single row of vessels 102 before
exiting the reactor block 106. This parallel flow arrangement
decreases the temperature gradient between the inlet 298 and outlet
302 ports. To further improve temperature uniformity and heat
exchange between the vessels 102 and the block 106, the passageway
300 can be enlarged so that the wells 104 essentially project into
a cavity containing the thermal fluid 290. Additionally, one may
eliminate the reactor block 106 entirely, and suspend or immerse
the vessels 10' in a bath containing the thermal fluid 290.
[0080] FIG. 8 illustrates the use of thermoelectric devices for
heating and cooling individual vessels. Thermoelectric devices can
function as both heaters and coolers by reversing the current flow
through the device. Unlike resistive heaters, which convert
electric power to heat, thermoelectric devices are heat pumps that
exploit the Peltier effect to transfer heat from one face of the
device to the other. A typical thermoelectric assembly has the
appearance of a sandwich, in which the front face of the
thermoelectric device is in thermal contact with the object to be
cooled (heated), and the back face of the device is in thermal
contact with a heat sink (source). When the heat sink or source is
ambient air, the back face of the device typically has an array of
thermally conductive fins to increase the heat transfer area.
Preferably, the heat sink or source is a liquid. Compared to air,
liquids have higher thermal conductivity and heat capacity, and
therefore should provide better heat transfer through the back face
of the device. But, because thermoelectric devices are usually made
with bare metal connections, they often must be physically isolated
from the liquid heat sink or source.
[0081] For example, FIG. 8 illustrates one way of using
thermoelectric devices 330 to heat and cool reactor vessels 338
using a liquid heat sink or source. In the configuration shown in
FIG. 8, thermoelectric devices 330 are sandwiched between a reactor
block 334 and a heat transfer plate 336. Reactor vessels 338 sit
within wells 340 formed in the reactor block 334. Thin walls 342 at
the bottom of the wells 340, separate the vessels 338 from the
thermoelectric devices 330, ensuring good thermal contact. As short
in FIG. 8. each of the vessels 338 thermally contacts a single
thermoelectric device 330, although in general, a thermoelectric
device can heat or cool more than one of the vessels 338. The
thermoelectric devices 330 either obtain heat from, or dump heat
into, a thermal fluid that circulates through an interior cavity
344 of the heat transfer plate 336. The thermal fluid enters and
leaves the heat transfer plate 336 through inlet 346 and outlet 348
ports, and its temperature is controlled in a manner similar to
that shown in FIG. 7. During an experiment, the temperature of the
thermal fluid is typically held constant, while the temperature of
the vessels 338 is controlled by adjusting the electrical current,
and hence, the heat transport through the thermoelectric devices
330. Though not shown in FIG. 8, the temperature of the vessels 338
are controlled in a manner similar to the scheme depicted in FIG.
6. Temperature sensors located adjacent to the vessels 338 and
within the heat transfer plate cavity 344 communicate with a
processor via a temperature monitor. In response to temperature
data from the temperature monitor, the processor increases or
decrease heat flow to or from the thermoelectric devices 330. A
thermoelectric device control system, located in the communication
path between the thermoelectric devices 330 and the processor,
adjusts the magnitude and direction of the flow of electrical
current through each of the thermoelectric devices 330 in response
to signals from the processor.
[0082] Calorimetric Data Measurement and Use
[0083] Temperature measurements often provide a qualitative picture
of reaction kinetics and conversion and therefore can be used to
screen library members. For example, rates of change of temperature
with respect to time, as well as peak temperatures reached within
each of the vessels can be used to rank catalysts. Typically, the
best catalysts of an exothermic reaction are those that, when
combined with a set of reactants, result in the greatest heat
production in the shortest amount of time.
[0084] In addition to its use as a screening tool, temperature
measurement--combined with proper thermal management and design of
the reactor system--an also be used to obtain quantitative
calorimetric data. From such data, scientists can, for example,
compute instantaneous conversion and reaction rate, locate phase
transitions (melting point, glass transition temperature) of
reaction products, or measure latent heats to deduce structural
information of polymeric materials, including degree of
crystallinity and branching.
[0085] FIG. 9 shows a cross-sectional view of a portion of a
reactor block 360 that can be used to obtain accurate calorimetric
data. Each of the vessels 362 contain stirring blades 364 to ensure
that the contents 366 of the vessels 362 are well mixed and that
the temperature within any one of the vessels 362, T.sub.j, is
uniform. Each of the vessels 362 contains a thermistor 368, which
measures T.sub.j and heats the vessel contents 366. The walls 370
of the vessels 362 are made of glass, although one may use any
material having relatively low thermal conductivity, and similar
mechanical strength and chemical resistance. The vessels 362 are
held within wells 372 formed in the reactor block 360, and each of
the wells 372 is lined with an insulating material 374 to further
decrease heat transfer to or from the vessels 362. Useful
insulating materials 374 include glass wool, silicone rubber, and
the like. The insulating material 374 can be eliminated or replaced
by a thermal paste when better thermal contact between that reactor
block 360 and the vessels 362 is desired-good thermal contact is
needed, for example, when investigating exothermic reactions under
isothermal conditions. The reactor block 360 is made of a material
having high thermal conductivity, such as aluminum, stainless
steel, brass, and so on. High thermal conductivity, accompanied by
active heating or cooling using any of the methods described above,
help maintain uniform temperature, T.sub.o, throughout the reactor
block 360. One can account for non-uniform temperatures within the
reactor block 360 by measuring T.sub.o,j, the temperature of the
block 360 in the vicinity of each of the vessels 362, using block
temperature sensors 376. In such cases, T.sub.o,j, instead of
T.sub.o, is used in the calorimetric calculations described
next.
[0086] An energy balance around the contents 366 of one of the
vessels 362 (jth vessel) yields an expression for fractional
conversion, X.sub.j, of a key reactant at any time, t, assuming
that the heat of reaction, .DELTA.H.sub.r, and the specific heat of
the vessel contents 366, C.sub.P,j, are known and are constant over
the temperature range of interest: 1 M j c P , j T j t = m o , j H
r , j X j t + Q m , j - Q out , j . I
[0087] In expression I, M.sub.j is the mass of the contents 366 of
the jth vessel; m.sub.o,j is the initial mass of the key reactant;
Q.sub.in,j is the rate of heat transfer into the jth vessel by
processes other than reaction, as for example, by resistance
heating of the thermistor 368. Q.sub.out,j is the rate of heat
transfer out of the jth vessel, which can be determined from the
expression:
Q.sub.out,j=U.sub.jA.sub.j(T.sub.j-T.sub.o)=U.sub.jA.sub.j.DELTA.T.sub.j
II
[0088] where A.sub.j is the heat transfer area--the surface area of
the jth vessel--and U.sub.j is the heat transfer coefficient, which
depends on the properties of the vessel 362 and its contents 366,
as well as the stirring rate, U.sub.j can be determined by
measuring the temperature rise, .DELTA.T.sub.j, in response to a
known heat input.
[0089] Equations I and II can be used to determine conversion from
calorimetric data in at least two ways. In a first method, the
temperature of the reactor block 360 is held constant, and
sufficient heat is added to each of the vessels 362 through the
thermistor 368 to maintain a constant value of .DELTA.T.sub.j.
Under such conditions, and after combining equations I and II, the
conversion can be calculated from the expression 2 X j = 1 m o , j
H r , j ( U j A j t f T j - 0 t f Q i n , j t ) , III
[0090] where the integral can be determined by numerically
integrating the power consumption of the thermistor 368 over the
length of the experiment, t.sub.f. This method can be used to
measure the heat output of a reaction under isothermal
conditions.
[0091] In a second method, the temperature of the reactor block 360
is again held constant, but T.sub.j increases or decreases in
response to heat produced or consumed in the reaction. Equation I
and II become under such circumstances 3 X j = 1 m o , j H r , j (
M j c P , j ( T f , j - T i , j ) + U j A j 0 t f T j t ) . IV
[0092] In equation IV, the integral can be determined numerically,
and T.sub.j and T.sub.i,j are temperatures of the reaction mixture
within the jth vessel at the beginning and end of reaction,
respectively. Thus, if T.sub.f,j equals T.sub.i,j, the total heat
liberated is proportional to 4 0 t f T j t .
[0093] This method is simpler to implement than the isothermal
method since it does not require temperature control of individual
vessels. But, it can be used only when the temperature chance in
each of the reaction vessels 362 due to reaction does not
significantly influence the reaction under study.
[0094] One may also calculate the instantaneous rate of
disappearance of the key reactant in the jth vessel, -r.sub.j,
using equation I, III or IV since -r.sub.j is related to conversion
through the relationship 5 - r j = C o , j X j t , V
[0095] which is valid for constant volume reactions. The constant
C.sub.o,j is the initial concentration of the key reactant.
[0096] Stirring Systems
[0097] Mixing variables such as stirring blade torque, rotation
rate, and geometry, may influence the course of a reaction and
therefore affect the properties of the reaction products. For
example, the overall heat transfer coefficient and the rate of
viscous dissipation within the reaction mixture may depend on the
stirring blade rate of rotation. Thus, in many instances it is
important that one monitor and control the rate of stirring of each
reaction mixture to ensure uniform mixing. Alternatively, the
applied torque may be monitored in order to measure the viscosity
of the reaction mixture. As described in the next section,
measurements of solution viscosity can be used to calculate the
average molecular weight of polymeric reaction products.
[0098] FIG. 10 shows an exploded, perspective view of a stirring
system for a single module 390 of a modular reactor block of the
type shown in FIG. 2. The module 390 comprises a block 392 having
eight wells 394 for containing removable reaction vessels 396. The
number of wells 394 and reaction vessels 396 can vary. The top
surface 398 of a removable lower plate 400 serves as the base for
each of the wells 394 and permits removal of the reaction vessels
396 through the bottom 402 of the block 392. Screws 404 secure the
lower plate 400 to the bottom 402 of the block 392. An upper plate
406, which rests on the top 408 of the block 392, supports and
directs elongated stirrers 410 into the interior of the vessels
396. Each of the stirrers 410 comprises a spindle 412 and a
rotatable stirring member or stirring blade 414 which is attached
to the lower end of each spindle 412. A gear 416 is attached to the
upper end of each of each spindle 412. When assembled, each gear
416 meshes with an adjacent gear 416 forming a gear train (not
shown) so that each stirrer 410 rotates at the same speed. A DC
stepper motor 418 provides torque for rotating the stirrers 410,
although an air-driven motor, a constant-speed AC motor, or a
variable-speed AC motor can be used instead. A pair of driver gears
420 couple the motor 418 to the gear train. A removable cover 422
provides access to the gear train, which is secured to the block
392 using threaded fasteners 424. In addition to the gear train,
one may employ belts, chains and sprockets, or other drive
mechanisms. In alternate embodiments, each of the stirrers 410 are
coupled to separate motors so that the speed or torque of each of
the stirrers 410 can be independently varied and monitored.
Furthermore, the drive mechanism--whether employing a single motor
and gear train or individual motors--can be mounted below the
vessels 362. In such cases, magnetic stirring blades placed in the
vessels 362 are coupled to the drive mechanism using permanent
magnets attached to gear train spindles or motor shafts.
[0099] In addition to the stirring system, other elements shown in
FIG. 10 merit discussion. For example, the upper plate 406 may
contain vessel seals 426 that allow processing at pressures
different than atmospheric pressure. Moreover, the seals 426 permit
one to monitor pressure in the vessels 396 over time. As discussed
below, such information can be used to calculate conversion of a
gaseous reactant to a condensed species. Note that each spindle 412
may penetrate the seals 426, or may be magnetically coupled to an
upper spindle member (not shown) attached to the gear 416. FIG. 10
also shows temperature sensors 428 embedded in the block 392
adjacent to each of the wells 394. The sensors 428 are part of the
temperature monitoring and control system described previously.
[0100] In another embodiment, an array of electromagnets rotate
freestanding stirring members or magnetic stirring bars, which
obviates the need for the mechanical drive system shown in FIG. 10.
Electromagnets are electrical conductors that produce a magnetic
field when an electric current passes through them. Typically, the
electrical conductor is a wire coil wrapped around a solid core
made of material having relatively high permeability, such as soft
iron or mild steel.
[0101] FIG. 11 is a schematic representation of one embodiment of
an electromagnet stirring array 440. The electromagnets 442 or
coils belonging to the array 440 are mounted in the lower plate 400
of the reactor module 390 of FIG. 10 so that their axes are about
parallel to the centerlines of the vessels 396. Although greater
magnetic field strength can be achieved by mounting the
electromagnets with their axes perpendicular to the centerlines of
the vessels 396, such a design is more difficult to implement since
it requires placing electromagnets between the vessels 396. The
eight crosses or vessel sites 444 in FIG. 11 mark the approximate
locations of the respective centers of each of the vessels 396 of
FIG. 10 and denote the approximate position of the rotation axes of
the magnetic stirring bars (not shown). In the array 440 shown in
FIG. 11, four electromagnets 442 surround each vessel site 444,
though one may use fewer or greater numbers of electromagnets 442.
The minimum number of electromagnets per vessel site is two, but in
such a system it is difficult to initiate stirring, and it is
common to stall the stirring bar. Electromagnet size and available
packing density primarily limit the maximum number of
electromagnets.
[0102] As illustrated in FIG. 11, each vessel site 444, except
those at the ends 446 of the array 440, shares its four
electromagnets 442 with two adjacent vessel sites. Because of this
sharing, magnetic stirring bars at adjacent vessel sites rotate in
opposite directions, as indicated by the curved arrows 448 in FIG.
11, which may lead to stalling. Other array configurations are
possible. For example, FIG. 12 shows a portion of an array 460 in
which the ratio of electromagnets 462 to vessel sites 464
approaches 1:1 as the number of vessel sites 464 becomes large.
Because each of the vessel sites 464 shares its electromagnets 462
with its neighbors, magnetic stirring bars at adjacent vessel sites
rotate in opposite directions, as shown by curved arrows 466. In
contrast, FIG. 13 shows a portion of an array 470 in which the
ratio of electromagnets 472 to vessel sites 474 approaches 2:1 as
the number of vessel sites becomes large. Because of the
comparatively large number of electromagnets 472 to vessel sites
474, all of the magnetic stirring bars can be made to rotate in the
same direction 476, which minimizes stalling. Similarly. FIG. 14
shows an array 480 in which the number of electromagnets 482 to
vessel sites 484 is 4:1. Each magnetic stirring bar rotates in the
same direction 486.
[0103] FIG. 15 illustrates additional elements of an
electromagnetic stirring system 500. For clarity, FIG. 15 shows a
square electromagnet array 502 comprised of four electromagnets
504, although larger arrays, such as those shown in FIGS. 12-14,
can be used. Each of the electromagnets 504 comprises a wire 506
wrapped around a high permeability solid core 508. The pairs of
electromagnets 504 located on the two diagonals of the square array
502 are connected in series to form a first circuit 510 and a
second circuit 512. The first 510 and second 512 circuits are
connected to a drive circuit 514, which is controlled by a
processor 516. Electrical current, whether pulsed or sinusoidal,
can be varied independently in the two circuits 510, 512 by the
drive circuit 514 and processor 516. Note that within each circuit
510, 512, the current flows in opposite directions in the wire 506
around the core 508. In this way, each of the electromagnets 504
within a particular circuit 510, 512 have opposite magnetic
polarities. The axes 518 of the electromagnets 504 are about
parallel to the centerline 520 of the reactor vessel 522. A
magnetic stirring bar 524 rests on the bottom of the vessel 522
prior to operation. Although the electromagnets 504 can also be
oriented with their axes 518 perpendicular to the vessel centerline
590, the parallel alignment provides higher packing density.
[0104] FIG. 16 shows the magnetic field direction of a 2.times.2
electromagnet array at four different times during one full
rotation of the magnetic stirring bar 524 of FIG. 15, which is
rotating at a steady frequency of .omega.
radians.multidot.s.sup.-1. In FIG. 16, a circle with a plus sign
532 indicates that the electromagnet produces a magnetic field in a
first direction; a circle with a minus sign 534 indicates that the
electromagnet produces a magnetic field in a direction opposite to
the first direction; and a circle with no sign 536 indicates that
the electromagnet produces no magnetic field. At time t=0 the
electromagnets 530 produce an overall magnetic field with a
direction represented by a first arrow 538 at the vessel site. At
time 6 t = 2 ,
[0105] the electromagnets 540 produce an overall magnetic field
with a direction represented by a second arrow 542. Since the
magnetic stirring bar 524 (FIG. 15) attempts to align itself with
the direction of the overall magnetic field, it rotates clockwise
ninety degrees from the first direction 538 to the second direction
542. At time 7 t = ,
[0106] the electromagnets 544 produce an overall magnetic field
with a direction represented by a third arrow 546. Again, the
magnetic stirring bar 524 aligns itself with the direction of the
overall magnetic field, and rotates clockwise an additional ninety
degrees. At time 8 t = 3 2 ,
[0107] the electromagnets 548 produce an overall magnetic field
with a direction represented by a fourth arrow 550, which rotates
the magnetic stirring bar 524 clockwise another ninety degrees.
Finally, at time 9 t = 2 ,
[0108] the electromagnets 530 produce an overall magnetic field
with direction represented by the first arrow 538, which rotates
the magnetic stirring bar 524 back to its position at time t=0.
[0109] FIG. 17 illustrates magnetic field direction of a 4.times.4
electromagnetic array at five different times during one full
rotation of a 3.times.3 array of magnetic stirring bars. As in FIG.
15, a circle with a plus sign 570, a minus sign 572, or no sign 574
represents the magnetic field direction of an individual
electromagnet, while an arrow 576 represents the direction of the
overall magnetic field at a vessel site. As shown, sixteen
electromagnets are needed to rotate nine magnetic stirring bars.
But, as indicated in FIG. 18, due to sharing of electromagnets by
multiple magnetic stirring bars, the rotational direction of the
magnetic fields is non-uniform. Thus, five of the fields rotate in
a clockwise direction 590 while the remaining four fields rotate in
a counter-clockwise direction 592.
[0110] FIG. 19 and FIG. 20 illustrate wiring configurations for
electromagnet arrays in which each vessel site is located between
four electromagnets defining four corners of a quadrilateral
sub-array. For each vessel site, both wiring configurations result
in an electrical connection between electromagnets located on the
diagonals of a given sub-array. In the wiring configuration 610
shown in FIG. 19. electromagnets 612 in alternating diagonal rows
are wired together to form two series of electromagnets 612. Dashed
and solid lines represent electrical connections between
electromagnets 612 in a first series 614 and a second series 616,
respectively. Plus signs 618 and minus signs 620 indicate polarity
(magnetic field direction) of individual electromagnets 612 at any
time, t, when current in the first series 614 and the second series
616 of electromagnets 612 are in phase. FIG. 20 illustrates an
alternate 111 wiring configuration 630 of electromagnets 632, where
again, dashed and solid lines represent electrical connections
between the first 634 and second series 636 of electromagnets 632,
and plus signs 638 and minus signs 640 indicate magnetic
polarity.
[0111] Note that for both wiring configurations 610, 630, the
polarities of the electromagnets 612, 632 of the first series 614,
634 are not the same, though amplitudes of the current passing
through the connections between the electromagnets 612, 632 of the
first series 614, 634 are equivalent. The same is true for the
second series 616, 636 of electromagnets 612, 632. One can achieve
opposite polarities Within the first series 614, 634 or second
series 616, 636 of electromagnets 612, 632 by reversing the
direction of electrical current around the core of the
electromagnet 612, 632. See, for example, FIG. 15. In the two
wiring configurations 610, 630 of FIGS. 19 and 20, every
quadrilateral array of four adjacent electromagnets 612, 632
defines a site for rotating a magnetic stirring bar, and the
diagonal members of each of the four adjacent electromagnets 612,
632 belong to the first series 614, 634 and the second 616, 636
series of electromagnets 612, 632. Moreover, within any set of four
adjacent electromagnets 612, 632, each pair of electromagnets 612,
632 belonging to the same series have opposite polarities. The two
wiring configurations 610, 630 of FIGS. 19 and 20 can be used with
any of the arrays 460, 470, 480 shown in FIGS. 12-14.
[0112] The complex wiring configurations 610, 630 of FIGS. 19 and
20 can be placed on a printed circuit board, which serves as both a
mechanical support and alignment fixture for the electromagnets
612, 632. The use of a printed circuit board allows for rapid
interconnection of the electromagnets 612, 632, greatly reducing
assembly time and cost, and eliminating wiring errors associated
with manual soldering of hundreds of individual connections.
Switches can be used to turn stirring on and off for individual
rows of vessels. A separate drive circuit may be used for each row
of vessels, which allows stirring speed to be used as a variable
during an experiment.
[0113] FIG. 21 is a plot 650 of current versus time and shows the
phase relationship between sinusoidal source currents, I.sub.a(t)
652 and I.sub.b(t) 654, which drive, respectively, the first series
614, 634 and the second series 616, 636 of electromagnets 612, 632
shown in FIGS. 19 and 20. The two source currents 652, 654 have
equivalent peak amplitude and frequency, .omega..sub.0, though
I.sub.A(t) 652 lags I.sub.B(t) 654 by 10 2
[0114] radians. Because of this phase relationship, magnetic
stirring bars placed at rotation sites defined by any four adjacent
electromagnets 612, 632 of FIGS. 19 and 20 will each rotate at an
angular frequency of .omega..sub.0, though adjacent stirring bars
will rotate in opposite directions when the electromagnet array 460
depicted in FIG. 12 is used. If, however, the arrays 470, 480 shown
in FIGS. 13 and 14 are used, adjacent stirring bars will rotate in
the same direction. In an alternate embodiment, a digital
approximation to a sine wave can be used.
[0115] FIG. 22 is a block diagram of a power supply 670 for an
electromagnet array 672. Individual electromagnets 674 are wired
together in a first and second series as, for example, shown in
FIG. 19 or 20. The first and second series of electromagnets 674
are connected to a power source 676, which provides the two series
with sinusoidal driving currents that are 11 2
[0116] radians out of phase. Normally, the amplitudes of the two
driving currents are the same and do not depend on frequency. A
processor 678 controls both the amplitude and the frequency of the
driving currents.
[0117] Viscosity and Related Measurements
[0118] The present invention provides for in situ measurement of
viscosity and related properties. As discussed below, such data can
be used, for example, to monitor reactant conversion, and to rank
or characterize materials based on molecular weight or particle
size.
[0119] The viscosity of a polymer solution depends on the molecular
weight of the polymer and its concentration in solution. For
polymer concentrations well below the "semidilute limit"--the
concentration at which the solvated polymers begin to overlap one
another--the solution viscosity, .eta., is related to the polymer
concentration, C, in the limit as C approaches zero by the
expression
.eta.=(1+C[.eta.]).eta..sub.S VI
[0120] where .eta..sub.s is the viscosity of the solvent.
Essentially, adding polymer to a solvent increases the solvent's
viscosity by an amount proportional to the polymer concentration.
The proportionality constant [.eta.], is known as the intrinsic
viscosity, and is related to the polymer molecular weight, M,
through the expression
[.eta.]=[.eta..sub.0]M.sup.+, VII
[0121] where [.eta..sub.0] and .alpha. are empirical constants.
Equation VII is known as the Mark-Houwink-Sakurda (MHS) relation,
and it, along with equation VI, can be used to determine molecular
weight from viscosity measurements.
[0122] Equation VI requires concentration data from another source;
with polymerization reactions, polymer concentration is directly
related to monomer conversion. In the present invention, such data
can be obtained by measuring heat evolved during reaction (see
equation III and IV) or, as described below, by measuring the
amount of a gaseous reactant consumed during reaction. The
constants in the MHS relation are functions of temperature, polymer
composition, polymer conformation, and the quality of the
polymer-solvent interaction. The empirical constants, [.eta..sub.0]
and .alpha., have been measured for a variety of polymer-solvent
pairs, and are tabulated in the literature.
[0123] Although equations VI and VII can be used to approximate
molecular weight, in situ measurements of viscosity in the present
invention are used mainly to rank reaction products as a function
of molecular weight. Under most circumstances, the amount of
solvent necessary to satisfy the concentration requirement of
equation VI would slow the rate of reaction to an unacceptable
level. Therefore, most polymerizations are carried out at polymer
concentrations above the semidilute limit, where the use of
equations VI and VII to calculate molecular weight would lead to
large error. Nevertheless, viscosity can be used to rank reaction
products even at concentrations above the semidilute limit since a
rise in viscosity during reaction generally reflects an increase in
polymer concentration, molecular weight or both. If necessary, one
can accurately determine molecular weight from viscosity
measurements at relatively high polymer concentration by first
preparing temperature-dependent calibration curves that relate
viscosity to molecular weight. But the curves would have to be
obtained for every polymer-solvent pair produced, which weighs
against their use for screening new polymeric materials.
[0124] In addition to ranking reactions, viscosity measurements can
also be used to screen or characterize dilute suspensions of
insoluble particles-polymer emulsions or porous supports for
heterogeneous catalysts-in which viscosity increases with particle
size at a fixed number concentration. In the case of polymer
emulsions, viscosity can serve as a measure of emulsion quality.
For example, solution viscosity that is constant over long periods
of time may indicate superior emulsion stability or viscosity
within a particular range may correlate with a desired emulsion
particle size. With porous supports, viscosity measurements can be
used to identify active catalysts: in many cases, the catalyst
support will swell during reaction due to the formation of
insoluble products within the porous support.
[0125] In accordance with the present invention, viscosity or
related properties of the reactant mixtures are monitored by
measuring the effect of viscous forces on stirring blade rotation.
Viscosity is a measure of a fluid's resistance to a shear force.
This shear force is equal to the applied torque, .GAMMA., needed to
maintain a constant angular velocity of the stirring blade. The
relationship between the viscosity of the reaction mixture and the
applied torque can be expressed as
.GAMMA.=K.sub..omega.(.omega.,T).eta., VIII
[0126] where K.sub..omega. is a proportionality constant that
depends on the angular frequency, .omega., of the stirring bar, the
temperature of the reaction mixture, and the geometries of the
reaction vessel and the stirring blade, K.sub..omega. can be
obtained through calibration with solutions of known viscosity.
[0127] During a polymerization, the viscosity of the reaction
mixture increases over time due to the increase in molecular weight
of the reaction product or polymer concentration or both. This
change in viscosity can be monitored by measuring the applied
torque and using equation VIII to convert the measured data to
viscosity. In many instances, actual values for the viscosity are
unnecessary, and one can dispense with the conversion step. For
example in situ measurements of applied torque can be used to rank
reaction products based on molecular weight or conversion, as long
as stirring rate, temperature, vessel geometry and stirring blade
geometry are about the same for each reaction mixture.
[0128] FIG. 23 illustrates an apparatus 700 for directly measuring
the applied torque. The apparatus 700 comprises a stirring blade
702 coupled to a drive motor 704 via a rigid drive spindle 706. The
stirring blade 702 is immersed in a reaction mixture 708 contained
within a reactor vessel 710. Upper 712 and lower 714 supports
prevent the drive motor 704 and vessel 710 from rotating during
operation of the stirring blade 702. For simplicity, the lower
support 714 can be a permanent magnet. A torque or strain gauge 716
shown mounted between the upper support 712 and the drive motor 704
measures the average torque exerted by the motor 704 on the
stirring blade 702. In alternate embodiments, the strain gauge 716
is inserted within the drive spindle 706 or is placed between the
vessel 710 and the lower support 714. If located within the drive
spindle 706, a system of brushes or commutators (not shown) are
provided to allow communication with the rotating strain gauge.
Often, placement of the strain gauge 716 between the vessel 710 and
the lower support 714 is the best option since many stirring
systems, such as the one shown in FIG. 10, use a single motor to
drive multiple stirring blades.
[0129] FIG. 24 shows placement of a strain gauge 730 in a portion
of a base plate 732 that is similar to the lower plate 400 of the
reactor module 390 shown in FIG. 10. The lower end 734 of the
strain gauge 730 is rigidly attached to the base plate 732. A first
permanent magnet 736 is mounted on the top end 738 of the strain
gauge 730, and a second permanent magnet 740 is attached to the
bottom 742 of a reactor vessel 744. When the vessel 744 is inserted
in the base plate 732, the magnetic coupling between the first
magnet 736 and the second magnet 740 prevents the vessel 744 from
rotating and transmits torque to the strain gauge 730.
[0130] Besides using a strain gauge, one can also monitor drive
motor power consumption, which is related to the applied torque.
Referring again to FIG. 23, the method requires monitoring and
control of the stirring blade 702 rotational speed, which can be
accomplished by mounting a sensor 718 adjacent to the drive spindle
706. Suitable sensors 718 include optical detectors, which register
the passage of a spot on the drive spindle 706 by a reflectance
measurement, or which note the interruption of a light beam by an
obstruction mounted on the drive spindle 706, or which discern the
passage of a light beam through a slot on the drive spindle 706 or
on a co-rotating obstruction. Other suitable sensors 718 include
magnetic field detectors that sense the rotation of a permanent
magnet affixed to the spindle 706. Operational details of magnetic
field sensors are described below in the discussion of phase lag
detection. Sensors such as encoders, resolvers, Hall effect
sensors, and the like, are commonly integrated into the motor 704.
An external processor 720 adjusts the power supplied to the drive
motor 704 to maintain a constant spindle 706 rotational speed. By
calibrating the required power against a series of liquids of known
viscosity, the viscosity of an unknown reaction mixture can be
determined.
[0131] In addition to direct measurement, torque can be determined
indirectly by measuring the phase angle or phase lag between the
stirring blade and the driving force or torque. Indirect
measurement requires that the coupling between the driving torque
and the stirring blade is "soft," so that significant and
measurable phase lag occurs.
[0132] With magnetic stirring, "soft" coupling occurs
automatically. The torque on the stirring bar is related to the
magnetic moment of the stirring bar, .mu., and the amplitude of the
magnetic field that drives the rotation of the stirring bar, H,
through the expression
.GAMMA.=.mu.H sin .theta., IX
[0133] where .theta. is the angle between the axis of the stirring
bar (magnetic moment) and the direction of the magnetic field. At a
given angular frequency, and for known .mu. and H, the phase angle.
.theta., will automatically adjust itself to the value necessary to
provide the amount of torque needed at that frequency. If the
torque required to stir at frequency .omega. is proportional to the
solution viscosity and the stirring frequency--an approximation
useful for discussion--then the viscosity can be calculated from
measurements of the phase angle using the equation
.GAMMA.=.mu.H sin .theta.=.alpha..eta..omega. X
[0134] where .alpha. is a proportionality constant that depends on
temperature, and the geometry of the vessel and the stirring blade.
In practice, one may use equation VIII or a similar empirical
expression for the right hand side of equation X if the torque does
not depend linearly on the viscosity-frequency product.
[0135] FIG. 25 shows an inductive sensing coil system 760 for
measuring phase angle or phase lag, .theta.. The system 760
comprises four electromagnets 762, which drive the magnetic
stirring bar 764, and a phase-sensitive detector, such as a
standard lock-in amplifier (not shown). A gradient coil 766
configuration is used to sense motion of the stirring bar 764,
though many other well known inductive sensing coil configurations
can be used. The gradient coil 766 is comprised of a first sensing
coil 768 and a second sensing coil 770 that are connected in series
and are wrapped in opposite directions around a first electromagnet
772. Because of their opposite polarities, any difference in
voltages induced in the two sensing coils 768, 770 will appear as a
voltage difference across the terminals 774, which is detected by
the lock-in amplifier. If no stirring bar 764 is present, then the
alternating magnetic field of the first electromagnet 772 will
induce approximately equal voltages in each of the two coils 768,
770--assuming they are mounted symmetrically with respect to the
first electromagnet 772--and the net voltage across the terminals
774 will be about zero. When a magnetic stirring bar 764 is
present, the motion of the rotating magnet 764 will induce a
voltage in each of the two sensing coils 768, 770. But, the voltage
induced in the first coil 768, which is closer to the stirring bar
764, will be much larger than the voltage induced in the second
coil 770, so that the voltage across the terminals 774 will be
nonzero. A periodic signal will thus be induced in the sensing
coils 768, 770, which is measured by the lock-in amplifier.
[0136] FIG. 26 and FIG. 27 show typical outputs 790, 810 from the
inductive sensing coil system 760 of FIG. 25, which illustrate
phase lag associated with magnetic stirring for low and high
viscosity solutions, respectively. Periodic signals 792, 812 from
the sensing coils 768, 770 are plotted with sinusoidal reference
signals 794, 814 used to drive the electromagnets. Time delay,
.DELTA.t 796, 816, between the periodic signals 792. 812 and the
reference signals 794, 814 is related to the phase angle by
.theta.=.omega..multidot..DELTA.t. Visually comparing the two
outputs 790, 810 indicates that the phase angle associated with the
high viscosity solution is larger than the phase angle associated
with the low viscosity solution.
[0137] FIG. 27 illustrates how amplitude and phase angle will vary
during a reaction as the viscosity increases from a low value to a
value sufficient to stall the stirring bar. A waveform or signal
820 from the sensing coils is input to a lock-in amplifier 822,
using the drive circuit sinusoidal current as a phase and frequency
reference signal 824. The lock-in amplifier 822 outputs the
amplitude 826 of the sensing coil signal 820, and phase angle 828
or phase lag relative to the reference signal 824. The maximum
phase angle is 12 2
[0138] radians, since, as shown by equation X, torque decreases
with further increases in .theta. leading to slip of the stirring
bar 764 of FIG. 25. Thus, as viscosity increases during reaction,
the phase angle 828 or phase lag also increases until the stirring
bar stalls, and the amplitude 826 abruptly drops to zero. This can
be seen graphically in FIG. 27, which shows plots of {overscore
(A)} 830 and {overscore (.theta.)} 832, the amplitude of the
reference signal and phase angle, respectively, averaged over many
stirring bar rotations. One can optimize the sensitivity of the
phase angle 828 measurement by proper choice of the magnetic field
amplitude and frequency.
[0139] To minimize interference from neighboring stirring
bars--ideally, each set of gradient coils should sense the motion
of a single stirring bar--each vessel should be provided with
electromagnets that are not shared with adjacent vessels. For
example, a 4:1 magnet array shown in FIG. 14 should be used instead
of the 2:1 or the 1:1 magnet arrays shown in FIGS. 13 and 12,
respectively. In order to take readings from all of the vessels in
an array, a multiplexer can be used to sequentially route signals
from each vessel to the lock-in amplifier. Normally, an accurate
measurement of the phase angle can be obtained after several tens
of rotations of the stirring bars. For rotation frequencies of
10-20 Hz, this time will be on the order of a few seconds per
vessel. Thus, phase angle measurements for an entire array of
vessels can be typically made once every few minutes, depending on
the number of vessels, the stirring bar frequency, and the desired
accuracy. In order to speed up the measurement process, one may
employ multiple-channel signal detection to measure the phase angle
of stirring bars in more than one vessel at a time. Alternate
detection methods include direct digitization of the coil output
waveforms using a high-speed multiplexer and/or an
analog-to-digital converter, followed by analysis of stored
waveforms to determine amplitude and phase angle.
[0140] Phase angle measurements can also be made with non-magnetic,
mechanical stirring drives, using the inductive coil system 760 of
FIG. 25. For example, one may achieve sufficient phase lag between
the stirring blade and the drive motor by joining them with a
torsionally soft, flexible connector. Alternatively, the drive
mechanism may use a resilient belt drive rather than a rigid gear
drive to produce measurable phase lag. The stirring blade must
include a permanent magnet oriented such that its magnetic moment
is not parallel to the axis of rotation. For maximum sensitivity,
the magnetic moment of the stirring blade should lie in the plane
of rotation. Note that one advantage to using a non-magnetic
stirring drive is that there is no upper limit on the phase
angle.
[0141] In addition to directly or indirectly measuring torque, one
may sense viscosity by increasing the driving frequency
.omega..sub.D, or decreasing the magnetic field strength until, in
either case, the stirring bar stalls because of insufficient
torque. The point at which the stirring bar stops rotating can be
detected using the same setup depicted in FIG. 25 for measuring
phase angle. During a ramp up (down) of the driving frequency
(field strength), the magnitude of the lock-in amplifier output
will abruptly fall by a large amount when the stirring bar stalls.
The frequency or field strength at which the stirring bar stalls
can be correlated with viscosity: the lower the frequency or the
higher the field strength at which stalling occurs, the greater the
viscosity of the reaction mixture.
[0142] With appropriate calibration, the method can yield absolute
viscosity data, but generally the method is used to rank reactions.
For example, when screening multiple reaction mixtures, one may
subject all of the vessels to a series of step chances in either
frequency or field strength, while noting which stirring bars stall
after each of the step changes. The order in which the stirring
bars stall indicates the relative viscosity of the reaction
mixtures since stirring bars immersed in mixtures having higher
viscosity will stall early. Note that, in addition to providing
data on torque and stall frequency, the inductive sensing coil
system 760 of FIG. 25 and similar devices can be used as diagnostic
tools to indicate whether a magnetic stirring bar has stopped
rotating during a reaction.
[0143] Mechanical Oscillators
[0144] Piezoelectric quartz resonators or mechanical oscillators
can be used to evaluate the viscosity of reaction mixtures, as well
as a host of other material properties, including molecular weight,
specific gravity, elasticity, dielectric constant, and
conductivity. In a typical application, the mechanical oscillator,
which can be as small as a few mm in length, is immersed in the
reaction mixture. The response of the oscillator to an excitation
signal is obtained for a range of input signal frequencies, and
depends on the composition and properties of the reaction mixture.
By calibrating the resonator with a set of well characterized
liquid standards, the properties of the reaction mixture can be
determined from the response of the mechanical oscillator. Further
details on the use of piezoelectric quartz oscillators to measure
material properties are described in co-pending, U.S. patent
application Ser. No 09/133,171 "Method and Apparatus for
Characterizing Materials by Using a Mechanical Resonator," filed
Aug. 12, 1998, which is herein incorporated by reference.
[0145] Although many different kinds of mechanical oscillators
currently exist, some are less useful for measuring properties of
liquid solutions. For example, ultrasonic transducers or
oscillators cannot be used in all liquids due to diffraction
effects and steady acoustic (compressive) waves generated within
the reactor vessel. These effects usually occur when the size of
the oscillator and the vessel are not much greater than the
characteristic wavelength of the acoustic waves. Thus, for reactor
vessel diameters on the order of a few centimeters, the frequency
of the mechanical oscillator should be above 1 MHz. Unfortunately,
complex liquids and mixtures, including polymer solutions, often
behave like elastic gels at these high frequencies, which results
in inaccurate resonator response.
[0146] Often, shear-mode transducers as well as various
surface-wave transducers can be used to avoid some of the problems
associated with typical ultrasonic transducers. Because of the
manner in which they vibrate, shear mode transducers generate
viscous shear waves instead of acoustic waves. Since viscous shear
waves decay exponentially with distance from the sensor surface,
such sensors tend to be insensitive to the geometry of the
measurement volume, thus eliminating most diffraction and
reflection problems. Unfortunately, the operating frequency of
these sensors is also high, which, as mentioned above, restricts
their use to simple fluids. Moreover, at high vibration
frequencies, most of the interaction between the sensor and the
fluid is confined to a thin layer of liquid near the sensor
surface. Any modification of the sensor surface through adsorption
of solution components will often result in dramatic changes in the
resonator response.
[0147] Tuning forks 840 and bimorph/unimorph resonators 850 shown
in FIG. 28 and FIG. 29, respectively, overcome many of the
drawbacks associated with ultrasonic transducers. Because of their
small size, tuning forks 840 and bimorph/unimorph resonators 850
have difficulty exciting acoustic waves, which typically have
wavelengths many times their size. Furthermore, though one might
conclude otherwise based on the vibration mode shown in FIG. 28,
tuning forks 840 generate virtually no acoustic waves: when
excited, each of the tines 832 of the tuning fork 840 acts as a
separate acoustic wave generator, but because the tines 832
oscillate in opposite directions and phases, the waves generated by
each of the tines 832 cancel one another. Like the shear mode
transducers described above, the bimorph/unimorph 850 resonators
produce predominantly viscous waves and therefore tend to be
insensitive to the geometry of the measurement volume. But unlike
the shear mode transducers, bimorph/unimorph 850 resonators operate
at much lower frequencies, and therefore can be used to measure
properties of polymeric solutions.
[0148] FIG. 30 schematically shows a system 870 for measuring the
properties of reaction mixtures using mechanical oscillators 872.
An important advantage of the system 870 is that it can be used to
monitor the progress of a reaction. The oscillators 872 are mounted
on the interior walls 874 of the reaction vessels 876.
Alternatively, the oscillators 872 can be mounted along the bottom
878 of the vessels 876 or can be freestanding within the reaction
mixtures 880. Each oscillator 872 communicates with a network
analyzer 882 (for example, an HP8751A analyzer), which generates a
variable frequency excitation signal. Each of the oscillators 872
also serve as receivers, transmitting their response signals back
to the network analyzer 882 for processing. The network analyzer
882 records the responses of the oscillators 872 as functions of
frequency, and sends the data to storage 884. The output signals of
the oscillators 872 pass through a high impedance buffer amplifier
886 prior to measurement by the wide band receiver 888 of the
network analyzer 882.
[0149] Other resonator designs may be used. For example, to improve
the suppression of acoustic waves, a tuning fork resonator with
four tines can be used. It is also possible to excite resonator
oscillations through the use of voltage spikes instead of a
frequency sweeping AC source. With voltage spike excitation,
decaying free oscillations of the resonator are recorded instead of
the frequency response. A variety of signal processing techniques
well known to those of skill in the art can be used to distinguish
resonator responses.
[0150] Alternate embodiments can be described with reference to the
parallel reactor system 130 shown in FIG. 2. A single resonator
(not shown) is attached to the 3-axis translation system 150. The
translation system 150, at the direction of the processor 160,
places the resonator within a reactor vessel of interest. A reading
of resonator response is taken and compared to calibration curves,
which relate the response to viscosity, molecular weight, specific
gravity, or other properties. In another embodiment, a portion of
the reaction mixture is withdrawn from a reactor vessel, using, for
example, the liquid handling system 146, and is placed in a
separate vessel containing a resonator. The response of the
resonator is measured and compared to calibration data. Although
the system 870 shown in FIG. 30 is better suited to monitor
solution properties in situ, the two alternate embodiments can be
used as post-characterization tools and are much simpler to
implement.
[0151] In addition to mechanical oscillators, other types of
sensors can be used to evaluate material properties. For example,
interdigitated electrodes can be used to measure dielectric
properties of the reaction mixtures.
[0152] Pressure Control System
[0153] Another technique for assessing reaction kinetics is to
monitor pressure chances due to production or consumption of
various gases during reaction. One embodiment of this technique is
shown in FIG. 31. A parallel reactor 910 comprises a group of
reactor vessels 912. A gas-tight cap 914 seals each of the vessels
912 and prevents unintentional gas flow to or from the vessels 912.
Prior to placement of the cap 914, each of the vessels 912 is
loaded with liquid reactants, solvents, catalysts, and other
condensed-phase reaction components using the liquid handling
system 146 shown in FIG. 2. Gaseous reactants from source 916 are
introduced into each of the vessels 912 through a gas inlet 918.
Valves 920, which communicate with a controller 922, are used to
fill the reaction vessels 912 with the requisite amount of gaseous
reactants prior to reaction. A pressure sensor 924 communicates
with the vessel head space--the volume within each of the vessels
912 that separates the cap 914 from the liquid components--through
a port 926 located in the cap 914. The pressure sensors 924 are
coupled to a processor 928, which manipulates and stores data.
During reaction, any changes in the head space pressure, at
constant temperature, reflect changes in the amount of gas present
in the head space. This pressure data can be used to determine the
molar production or consumption rate, r.sub.i, of a gaseous
component since, for an ideal gas at constant temperature, 13 r i =
1 R T p i t XI
[0154] where R is the universal gas constant and p.sub.i is the
partial pressure of the ith gaseous component. Temperature sensors
930, which communicate with the processor 928 through monitor 932,
provide data that can be used to account for changes in pressure
resulting from variations in head space temperature. The ideal gas
law or similar equation of state can be used to calculate the
pressure correction.
[0155] In an alternate embodiment, the valves 920 are used to
compensate for the consumption of a gaseous reactant, in a reaction
where there is a net loss in moles of gas-phase components. The
valves 920 are regulated by the valve controller 922, which
communicates with the processor 928. At the beginning of the
reaction, the valves 920 open to allow gas from the high pressure
source 916 to enter each of the vessels 912. Once the pressure
within each of the vessels 912, as read by the sensor 924, reaches
a predetermined value, P.sub.H, the processor 928 closes the valves
920. As the reaction consumes the source 916 gas, the total
pressure within each of the vessels 912 decreases. Once the
pressure in a particular vessel 912 falls below a predetermined
value, P.sub.L, the processor 928 opens the valve 920 associated
with the particular vessel 912, repressurizing it to P.sub.H. This
process--filling each of the vessels 912 with source 916 gas to
P.sub.H, allowing the head space pressure to drop below P.sub.L,
and then refilling the vessels 912 with source 916 gas to
P.sub.H--is usually repeated many times during the course of the
reaction. Furthermore, the total pressure in the head space of each
of the vessels 912 is continuously monitored and recorded during
the gas fill-pressure decay cycle.
[0156] An analogous method can be used to investigate reactions
where there is a net gain of gas-phase components. At the beginning
of a reaction, all reaction materials are introduced into the
vessels 912 and the valves 920 are closed. As the reaction
proceeds, gas production results in a rise in head space pressure,
which sensors 924 and processor 928 monitor and record. Once the
pressure within a particular vessel 912 reaches P.sub.H, the
processor 928 directs the controller 922 to open the appropriate
valve 920 to depressurize the vessel 912. The valve 920, which is a
multi-port valve, vents the gas from the head space through an
exhaust line 934. Once the head space pressure falls below P.sub.L,
the processor 928 instructs the controller 922 to close the valve
920. The total pressure is continuously monitored and recorded
during the gas rise-vent cycle.
[0157] The gas consumption (production) rates can be estimated from
the total pressure data by a variety of methods. For simplicity,
these methods are described in terms of a single reactor vessel 912
and valve 920, but they apply equally well to a parallel reactor
910 comprising multiple vessels 912 and valves 920. One estimate of
gas consumption (production) can be made from the slope of the
pressure decay (growth) curves obtained when the valve is closed.
These data, after converting total pressure to partial pressure
based on reaction stoichiometry, can be inserted into equation XI
to calculate r.sub.i, the molar consumption (production) rate. A
second estimate can be made by assuming that a fixed quantity of
gas enters (exits) the vessel during each valve cycle. The
frequency at which the reactor is repressurized (depressurized) is
therefore proportional to the gas consumption (production) rate. A
third, more accurate estimate can be obtained by assuming a known
gas flow rate through the valve. Multiplying this value by the time
during which the valve remains open yields an estimate for the
quantity of gas that enters or leaves the vessel during a
particular cycle. Dividing this product by the time between the
next valve cycle--that is, the time it takes for the pressure in
the vessel head space to fall from P.sub.H to P.sub.L--yields an
average value for the volumetric gas consumption (production) rate
for the particular valve cycle. Summing the quantity of gas added
during all of the cycles equals the total volume of gas consumed
(produced) during the reaction.
[0158] The most accurate results are obtained by directly measuring
the quantity of gas that flows through the valve. This can be done
by noting the change in pressure that occurs during the time the
valve is open--the ideal gas law can be used to convert this change
to the volume of gas that enters or leaves the vessel. Dividing
this quantity by the time between a particular valve cycle yields
an average volumetric gas consumption (production) rate for that
cycle. Summing the volume changes for each cycle yields the total
volume of gas consumed (produced) in the reaction.
[0159] In an alternate embodiment shown in FIG. 31, the gas
consumption rate is directly measured by inserting flow sensors 936
downstream of the valves 920 or by replacing the valves 920 with
flow sensors 936. The flow sensors 936 allow continuous monitoring
of the mass flow rate of gas entering each of the vessels 912
through the gas inlet 918. To ensure meaningful comparisons between
experiments, the pressure of the source 916 gas should remain about
constant during an experiment. Although the flow sensors 936
eliminate the need for cycling the valves 920, the minimum
detectable flow rates of this embodiment are less than those
employing pressure cycling. But, the use of flow sensors 936 is
generally preferred for fast reactions where the reactant flow
rates into the vessels 912 are greater than the threshold
sensitivity of the flow sensors 936.
EXAMPLES
[0160] The following examples are intended as illustrative and
non-limiting, and represent specific embodiments of the present
invention.
Example 1
Calibration of Mechanical Oscillators for Measuring Molecular
Weight
[0161] Mechanical oscillators were used to characterize reaction
mixtures comprising polystyrene and toluene. To relate resonator
response to the molecular weight of polystyrene, the system 870
illustrated in FIG. 30 was calibrated using polystyrene standards
of known molecular weight dissolved in toluene. Each of the
standard polystyrene-toluene solutions had the same concentration,
and were run in separate (identical) vessels using tuning fork
piezoelectric quartz resonators similar to the one shown in FIG.
28. Frequency response curves for each resonator were recorded at
intervals between about 10 and 30 seconds.
[0162] The calibration runs produced a set of resonator responses
that could be used to relate the output from the oscillators 872
immersed in reaction mixtures to polystyrene molecular weight. FIG.
32 shows results of calibration runs 970 for the
polystyrene-toluene solutions. The curves are plots of oscillator
response for polystyrene-toluene solutions comprising no
polystyrene 952, and polystyrene standards having weight average
molecular weights (M.sub.w) of 2.36.times.10.sup.3 954,
13.7.times.10.sup.3 956, 114.2.times.10.sup.3 958, and
1.88.times.10.sup.6 960.
[0163] FIG. 33 shows a calibration curve 970 obtained by
correlating M.sub.w of the polystyrene standards with the distance
between the frequency response curve for toluene 952 and each of
the polystyrene solutions 954, 956, 958, 960 of FIG. 32. This
distance was calculated using the expression: 14 d i = 1 f 1 - f 0
f 0 f 1 ( R 0 - R i ) 2 f , XII
[0164] where f.sub.0 and f.sub.1 are the lower and upper
frequencies of the response curve, respectively; R.sub.0 is the
frequency response of the resonator in toluene, and R.sub.1 is the
resonator response in a particular polystyrene-toluene solution.
Given response curves for an unknown polystyrene-toluene mixture
and pure toluene 952 (FIG. 32), the distance between the two curves
can be determined from equation XII. The resulting d can be located
along the calibration curve 970 of FIG. 33 to determine M.sub.w for
the unknown polystyrene-toluene solution.
Example 2
Measurement of Gas-Phase Reactant Consumption by Pressure
Monitoring and Control
[0165] FIG. 34 depicts the pressure recorded during solution
polymerization of ethylene to polyethylene. The reaction was
carried out in an apparatus similar to that shown in FIG. 31. An
ethylene gas source was used to compensate for ethylene consumed in
the reaction. A valve, under control of a processor, admitted
ethylene gas into the reaction vessel when the vessel head space
pressure dropped below P.sub.L.apprxeq.16.1 psig due to consumption
of ethylene. During the gas filling portion of the cycle, the valve
remained open until the head space pressure exceeded
P.sub.H.apprxeq.20.3 psig.
[0166] FIG. 35 and FIG. 36 show ethylene consumption rate as a
function of time, and the mass of polyethylene formed as a function
of ethylene consumed, respectively. The average ethylene
consumption rate, --r.sub.C2,k (atm.multidot.min.sup.-1), was
determined from the expression 15 - r C2 , k = ( P H - P L ) k t k
XIII
[0167] where subscript k refers to a particular valve cycle, and
.DELTA.t.sub.k is the time interval between the valve closing
during the present cycle and the valve opening at the beginning of
the next cycle. As shown in FIG. 35, the constant ethylene
consumption rate at later times results from catalyzed
polymerization of ethylene. The high ethylene consumption rate
early in the process results primarily from transport of ethylene
into the catalyst solution prior to establishing an equilibrium
ethylene concentration in the liquid phase. FIG. 36 shows the
amount of polyethylene produced as a function of the amount of
ethylene consumed by reaction. The amount of polyethylene produced
was determined by weighing the reaction products, and the amount of
ethylene consumed by reaction was estimated by multiplying the
constant average consumption rate by the total reaction time. A
linear least-squares fit to these data yields a slope which matches
the value predicted from the ideal gas law and from knowledge of
the reaction temperature and the total volume occupied by the gas
(the product of vessel head space and number of valve cycles during
the reaction).
[0168] Overview of a Multi-Temperature Modular Reactor for Use in a
Parallel Reactor System
[0169] FIG. 37 shows a perspective view of one embodiment of a
multi-temperature modular reactor module 132' for use in a parallel
reactor system 100. Modular reactor 132', similar to modular
reactor 132 which has been previously described in reference to
FIG. 2, includes a plurality of reactor modules 134' and a heat
transfer plate 336'. Reactor modules 134', best seen in FIG. 38,
each include a plurality of wells 104' for receiving removable
reaction vessels (not shown) for containing therein an array of
materials to be analyzed and characterized. While wells 104' may
serve as reaction vessels, it is preferred that removable reaction
vessels are used so that one can remove a subset of reaction
vessels from reactor modules 134' for, e.g., further in-depth
characterization. Further, reaction vessels, which are considerably
lower in cost than reactor modules 134', may be discarded if
damaged after use, without incurring great cost. In FIG. 38, wells
104' are shown as being aligned along a common axis B-B. However,
it is understood that wells 104' may be arranged in any suitable
manner along reactor module 134'. Further, while reactor module
134' is shown as having twelve wells 104' formed therein, any
number of wells 104' may be provided.
[0170] To properly position reactor modules 134' in modular reactor
132', there is provided a rack 133', as shown in FIGS. 37 and 39.
Rack 133' includes a plurality of recesses 135' for selectively
storing and properly positioning reactor modules 134' therein,
where the number of recesses 135' corresponds to the number of
reactor modules 134' that may be used with modular reactor 132'.
Preferably, rack 133' is constructed of an insulating material,
such as ceramic or other suitable materials, to insulate reactor
modules 134' from one another, as best seen in FIG. 39. The
function of the insulating material rack 133' will be explained
more fully below.
[0171] Referring to FIGS. 37 and 40, heat transfer plate 336' is
positioned below and in thermal contact with reactor modules 134'
so as to subject reactor modules 134' to a first predetermined
temperature. To accomplish this, heat transfer plate 336', which is
constructed of a material having high thermal conductivity, such as
aluminum, brass, etc., is provided with a plurality of passages
300' and inlet and outlet ports 298' and 302', respectively. A
temperature control medium, such as a thermal fluid, is transported
to heat transfer plate 336' using a pump (not shown) through inlet
port 298'. Suitable thermal fluids include water, silicone oil and
halogenated solvents (e.g., fluorinated, chlorinated, brominated),
although other suitable fluids may also be employed. From inlet
port 298', the thermal fluid flows through passages 300' formed in
the heat transfer plate, eventually exiting heat transfer plate
336' at outlet port 302'. To improve the thermal contact between
rack 133' and heat transfer plate 336', rack 133' may be positioned
in mechanical contact with heat transfer plate 336' so as to
permanently fixedly secured to heat transfer plate 336'. Mechanical
contact may be achieved through the use of bolts, clips or other
suitable fasteners.
[0172] In accordance with one aspect of the invention, it is
preferred that heat transfer plate 336' is maintained substantially
at a constant first predetermined temperature. This temperature may
be above or below ambient temperature, depending upon the range of
temperature values chosen for reactor modules 134', to be explained
in greater detail below. To insure such a constant temperature,
heat transfer plate 226' is provided with a temperature sensor 202'
to monitor the temperature of heat transfer plate 336'. Suitable
temperature sensors 202' include thermocouples, thermistors or
resistance thermometric devices. Other sensors 202' may be employed
as well.
[0173] In accordance with one aspect of the present invention,
referring to FIGS. 37 and 41, each reactor module 134' has
associated with it a separate temperature control device 329', such
that the number of reactor modules 134' is equal to the number of
temperature control devices 329'. The temperature control devices
329' serve to independently vary the temperature of each reactor
module 134' to a second predetermined temperature such that each
reactor module 134' has a different second predetermined
temperature. Further, the insulating material of the rack 133' that
separates each reactor module 134' insures that heat is not
transferred between each reactor module 134'.
[0174] In one embodiment, the temperature control device 329' is an
electrical heating unit having a temperature control base plate
331', a temperature control top plate 333' and an electrical
heating strip 335' with etched stainless steel circuit paths 337'
encased in polyimide, such as those sold under the tradename
Kapton.TM.. The heating strip 335' is sandwiched between base plate
331' and top plate 333'. with base plate 331' and top plate 333'
being bolted together to form the electrical heating unit. The top
plate 333' includes a raised center section 339' having a notch
341' therein for receiving a temperature sensor (not shown) similar
to temperature sensor 202'. Leads 343' from temperature sensor 202'
extend along a lower section 345' of top plate 333' to an external
processor 186'. Wires 347' are connected to electrical heating
strip 335' to permit power from electrical sources to vary the
temperature of the electrical heating unit, and consequently the
reactor modules 134'. To insure that wires 347' are not damaged
when heating strip 335' is sandwiched between base plate 331' and
top plate 333', base plate 331' preferably includes a recessed
portion 349' through which wires 347' can safely extend.
[0175] In another embodiment the temperature control device 329' is
a thermoelectric module. The thermoelectric module is constructed
so as to be substantially identical to the electrical heating unit,
except that a thermoelectric device replaces electrical heating
strip 335'. The operation of temperature control devices 329' will
be explained in greater detail below.
[0176] Referring back to FIG. 37, temperature control devices 329'
may be fixedly secured to heat transfer plate 336', by bolting,
bonding, welding or other suitable methods, such that temperature
control devices 329' are positioned directly beneath reactor
modules 134' and sandwiched between reactor modules 134' and heat
transfer plate 336' when heat transfer plate 336' is in thermal
contact with rack 133'. In an alternative embodiment, temperature
control devices 329' may be permanently secured to each reactor
module 134' or disposed directly within each reactor module 134',
thereby resulting in an improved thermal contact between each
temperature control device 329' and reactor module 134'.
[0177] Rack 133', storing reactor modules 134', temperature control
devices 329' and heat transfer plate 336' are preferably arranged
in an insulating casing 357', constructed of ceramic material, or
other suitable insulating material, to thermally insulate modular
reactor 132' from the environment. Casing 357' is constructed with
sidewalls 359', a base plate 361' and a removable top plate 363' to
permit access to the reaction vessels disposed in wells 104', as
shown in FIG. 42. Top plate 363' includes a plurality of
trough-like sections 365' that have a width that is greater than
the diameter of wells 104' of reactor modules 134' and that are
substantially aligned with wells 104'. Trough-like sections 365'
are preferred to permit tops of the reaction vessels to extend into
casing top plate 363' such that top plate 363' rests on upper
surface 367' of rack 133', as opposed to the tops of the reaction
vessels in wells 104', as walls of reaction vessels are relatively
thin and may break under the weight of top plate 363'. Preferably,
rack 133' is removable from casing 357' such that the entire array
of materials may be removed from modular reactor 132' at one
time
[0178] Overview of the Operation of a Multi-Temperature Modular
Reactor
[0179] To analyze, synthesize or characterize an array of
materials, modular reactor 132' is assembled as described above in
casing 357' with heat transfer plate 336' in thermal contact with
rack 133'. Reaction vessels containing materials are then disposed
in wells 104' in reactor modules 134' and top plate 363' of casing
357' is secured onto casing 357' to insulate modular reactor 132'.
Heat transfer plate 336' is next brought to and substantially
maintained at a constant first predetermined temperature that is
below ambient temperature. The first predetermined temperature is
achieved by constantly circulating thermal fluid through passages
300' in heat transfer plate 336' to bias rack 133', the reactor
modules 134' and reaction vessels containing material therein to
the first predetermined temperature.
[0180] Next, the temperature control devices 329' vary the
temperature of each of the reactor modules 134' from the first
predetermined temperature to a second predetermined temperature.
Second predetermined temperature may be greater than or less than
the first predetermined temperature of heat transfer plate 336'
depending upon the characteristics of the materials under study.
Preferably, each reactor module 134' has a different second
predetermined temperature such that the characteristics of the
materials in each reactor module 134' may be compared and
contrasted with one another to determine the effect of temperature
on reactions of the materials in the array.
[0181] The reactor modules 134' and heat transfer plate 336' are
monitored by temperature sensors 202' which send signals to the
processor 186'. The processor 186' simultaneously collects and
analyzes temperature data received from all of the reactor modules
134' and heat transfer plate 336' and generates signals to a power
supply 371'. The power supply 371', which is connected to
temperature control device 329' by wires 347' produces a current in
response to the temperature data received by processor 186' to vary
the temperature of the temperature control device 329' which is
transferred to the reactor modules 134'.
[0182] Electrical heating units, which convert electric power to
heat, are desirable for use as the temperature control devices 329'
in situations where it is desired to maintain all of reactor
modules 134' at temperatures substantially greater than that of
heat transfer plate 336'. Such units are available in a wide range
of power levels, permitting the performance characteristics of the
heating units to be matched to the requirements of the materials
and reactions under study at a relatively low cost. In situations
where one or more reactor modules 134' are to be maintained at
temperatures below that of heat transfer plate 336', or in
applications where rapid heating and cooling of reactor modules
336' is necessary, thermoelectric devices may be employed.
Thermoelectric devices primarily serve as heat pumps, employing the
Peltier effect to pump heat from one side of the device to the
other when a direct electrical current is applied in a
predetermined direction. When current is directed through the
thermoelectric devices in a first predetermined direction, heat is
pumped from heat transfer plate 336' to reactor blocks 134' to
increase the temperature of reactor modules 134'. When the
direction of electrical current is reversed to a second
predetermined direction, heat is pumped from the reactor modules
134' to heat transfer plate 336', thereby reducing the temperature
of the reactor modules 134'. Once the temperature of the reactor
modules 134' are varied, temperature sensors 202' cooperate with
processor 186' to simultaneously evaluate the data collected and
changes in the material in the reaction vessels are detected. The
detecting and monitoring step may be performed at predefined
intervals of time, such that characteristics of the array of
materials may be performed as a function of time. Alternatively,
the temperature of the reactor modules 134' may be varied at a
predetermined rate such that the characteristics of the materials
may be evaluated as a function of temperature.
[0183] In an alternative embodiment, the temperature may be
independently varied over time for each reactor module 134'. One
purpose is to vary the thermal history of samples in each module.
Another purpose is to allow for different reaction times or
different conditions in different reactor modules. For example,
different modules may be maintained at the same temperature (e.g.,
the first predetermined temperature or second predetermined
temperature) for different lengths of time. Another example is
where different modules have different time/temperature profiles
(such as heating or cooling different modules at different rates).
A further example is where different modules are maintained at
different temperatures for different time periods. Those of skill
in the art will recognize different time/temperature profiles that
can be accomplished with this system. This function can be
controlled manually or automatically and may be accomplished by
simply turning control on or off at specified times to one or more
of the temperature control devices, discussed above. Thus, one or
more of the reactor modules 134' may be allowed to come to ambient
temperature or to the first or second predetermined temperature.
The first predetermined temperature may be above or below ambient
temperature. The temperature of each reactor module may be varied
independently on the basis of another measured property or
condition, such as viscosity, gas uptake, heat evolution, color
change, dielectric constant, etc.
[0184] The above description is intended to be illustrative and not
restrictive. Many embodiments as well as many applications besides
the examples provided will be apparent to those of skill in the art
upon reading the above description. The scope of the invention
should therefore be determined, not with reference to the above
description, but should instead be determined with reference to the
appended claims, along with the full scope of equivalents to which
such claims are entitled. The disclosures of all articles and
references, including patent applications and publications, are
incorporated by reference for all purposes.
* * * * *