Abstract:
The invention relates to an apparatus and method for testing the properties of chemicals in a reaction flow stream. In the method, chemicals from the reaction flow stream are directed to the apparatus for testing the physical properties of the chemicals, which is an indication of the state of the chemical reaction. Data measured by the apparatus is stored in a computer, and the computer may be used to analyze the data and to control the reaction parameters based on the analysis of the data. The apparatus used for the analysis comprises a rheometer having an actuated shaft and a concentric container, wherein the shear properties of the material sampled in the apparatus are measured when the actuator shaft is oscillated within the container. Various unique configurations of the apparatus are described.

Description:
This is a Divisional of Application Ser. No. 09/734,348, filed Dec. 11, 2000, presently pending. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an in-line or on-line testing device used for analyzing the state of a chemical reaction. In a specific embodiment, the testing device is a rheometer. 
     BACKGROUND OF THE INVENTION 
     Many chemical reactions are carried out in a continuous process, because of the efficiencies inherent in continuous processing related to yield and to eliminating the need to isolate intermediate products. In continuous chemical processing, it is sometimes important, in a multi-step chemical reaction, that the reaction reach a particular stage before parameters are changed, such as the addition of chemical compounds to the reaction, changes in temperature or atmospheric conditions, and the like. In the art, the status of the chemical reaction is often measured by removing a sample of material from the reaction process line, quenching the material, i.e. stopping the process of the chemical reaction, and analyzing the chemicals in the sample. The chemicals in the sample at that particular point define the status of the chemical reaction at that point, and tells the technician whether the reaction is proceeding as planned, and whether conditions are right for adding additional chemical reactants, or for changing the temperature or other parameters in the processing line. 
     A common means for determining the state of reaction of a process is to measure certain physical properties of the compound mixture which are a reflection of the nature of the material. Most chemicals, in a fluid state, exhibit rheological (flow) properties that are a function of the molecular size and structure of the material. For small chemical molecules with simple structure, the rheological properties of the material are fluid-like, independent of the rate and size of the applied deformation, and can be characterized in terms of a simple viscometric function such as a Newtonian viscosity. As molecular size and structure increases, a material&#39;s Theological properties become more complex and are dependent on the size and rate of the applied deformation. Polymeric materials are comprised of very long molecules and exhibit viscous (fluid-like) as well as elastic (solid-like) behavior, known to those skilled in the art as viscoelasticity. Although characterizing the viscosity of a polymer can be descriptive of its molecular size, a viscoelastic characterization which is more sensitive to molecular structure is required since a viscometric function is not descriptive of the elastic nature of the material. A more thorough treatment for describing the molecular mechanisms underlying the viscoelastic rheological behavior of polymeric fluids can be found in “Viscoelastic Properties of Polymers” by J. Ferry, Third Edition, John Wiley &amp; Sons, New York (1980). 
     In the chemical processing art, it is a continuing goal to completely automate the processing line. By that, it is meant that if analysis of the chemical reaction stream can be made at critical points, and the data from those critical points is fed into a computer, the computer can use the information to know when to adjust the reaction conditions as necessary, to assure that the chemical reaction goes as planned, which will improve the efficiency and yield of the chemical process. The nature of the analyzing equipment used at the critical points depends on the nature of the chemical reaction and the kind of data that will be most useful in analyzing the status of the chemical reaction. Since a chemical processing line is sometimes used for preparing more than one kind of chemical, and the materials used in the chemical processing line will change depending on the reaction, it is desirable that the analyzing equipment used be useful for a broad spectrum of chemical reactions. 
     It is an object of the present invention to provide a method and apparatus for analyzing the chemical or physical properties of a fluid in a reaction flow stream. 
     Other objects of the invention will be apparent from the following description and claims. 
     DESCRIPTION OF PRIOR ART 
     Various apparati have been developed for the use of on-line monitoring of a chemical process, most of which involve taking a side stream and pumping it through a capillary, slit, or rotating cylinder type of rheometer. These types of rheometers, however, typically provide only a viscometric and not a viscoelastic characterization of a fluid. 
     U.S. Pat. No. 4,468,953 (Garritano) describes an on-line concentric cylinder rotational rheometer for determining the vicoelastic properties of a fluid sampled from a process stream. The sampled fluid is introduced into the annular region of the concentric cylinders by means of a gear pump. The outer cylinder is made to oscillate about its axis of symmetry by means of a drive shaft and motor assembly, and the resultant torque on the inner cylinder is measured by means of a torsion tube assembly that is hermetically sealed. Flow into the rheometer is distributed uniformly through the annulus so that the introduction of fresh sample flushes the previous fluid sample out of the annulus. In order to allow free oscillation of the outer cylinder, however, the drive shaft requires the use of seals that are exposed to the thermal, chemical, and abrasive properties of the fluid. These seals require regular maintenance of the device and provide a possible source of failure during operation that could expose the surrounding environment to the hazards of the fluids being tested. 
     U.S. Pat. No. 4,643,020 (Heinz) describes a concentric cylinder process rheometer for characterizing the viscoleastic properties of a fluid that can be used either on-line or in the process stream. The sensing device consists of three concentric, thin-walled cylinders, the middle cylinder of which is made to oscillate about its axis of symmetry. The motion of the drive cylinder applies a shear to the fluid in the adjacent annular regions which causes a resultant torque on the drive cylinder that is measured on the drive shaft by means of a torsion tube and sensor assembly. Flexible bellows are used to seal the pivoting drive shaft from the fluid environment. Sample flushing out of the rheometer is uncontrolled, however, and the design does not allow for metered fluid flow into and out of the adjacent annuli to permit fresh sampling into the rheometer. 
     SUMMARY OF THE INVENTION 
     An apparatus for measuring the state of a chemical reaction in a process line comprises: (a) a cell of fixed volume for sampling and collecting material from a chemical process stream, and (b) a rheometer in which a portion of the sampled material is confined within a shearing gap where a controlled shear deformation is applied to the material and the response from the sheared material is measured. 
     In the illustrated embodiment, the rheometer cell is located external to the process stream, and material is allowed to enter and exit the cell by means of flow conduits and valves. The shearing gap is defined by the annulus of two substantially parallel concentric cylinder shafts. The inner cylinder moves axially in oscillation along its primary axis and is attached to a means of resolving (measuring) the physical material response to the applied deformation, in this case a force transducer. 
     Also provided is a method for measuring the flow response of fluids in a shear rheometer comprising the steps of a) providing an apparatus for measuring the rate of shear flow of fluids comprising a drive shaft mounted external to the rheometer cell wherein the drive shaft is connected to a moving cylinder that defines the applied shear deformation, b) confining a portion of sampled material within the defined shear gap, c) causing the material confined within the defined gap to be sheared by the motion of the moving cylinder, and d) measuring the physical response created by the shearing of the sample. 
     An oscillating shear deformation is applied in order to assess the in-phase and out-of-phase physical responses to the applied deformation that are a reflection of the viscoelastic nature of a polymeric fluid. A step shear deformation may also be applied to the fluid in the gap, as in the case of a shear stress relaxation experiment. The shear deformation may also be applied such that the rate of fluid deformation in the shear gap is steady, as in the case of a viscometric flow characterization. 
     The rheometer provides a method for measuring the viscoelastic rheological properties of a fluid chemical that are a reflection of the state of chemical reaction of that chemical based on its molecular size and structure. 
     In an alternative embodiment, an apparatus  110  for inline testing of the properties of a fluid in a reaction flow stream comprises a container  122 , consisting of container ends  122 B,  122 C and ring  122 A connected to each other by bellows  120 . An actuator shaft  124  within container  122  is connected to a shearing ring  126 , the actuator shaft  124  being adapted to move shearing ring  126  within the container  122 . A force transducer  128  is associated with the ring  122 A for measuring torque forces on ring  122 A. 
     The apparatus  110  has a shearing gap  116  which separates ring  122 A and shearing ring  126  when shearing ring  126  is positioned within container  122  for obtaining test data. Shearing ring  126  has a cross-sectional shape which includes recirculation gaps  118 . Apparatus  110  is adapted to be connected to a reaction flow stream by a tap line whereby a sample enters apparatus  110  through a first end  122 B through portal  112 , and exits apparatus  110  through portal  112 A in second end  122 C. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a cutaway side view of an apparatus of the invention. 
     FIG. 2 illustrates a cross sectional top view taken along line  2 — 2  of the apparatus of FIG.  1 . 
     FIG. 3 illustrates the apparatus of FIG. 1 in an open condition. 
     FIG. 4 illustrates a cutaway side view of an alternative apparatus of the invention. 
     FIG. 5 illustrates a cross sectional top view taken along line  5 — 5  of the apparatus of FIG.  4 . 
     FIG. 6 illustrates the apparatus of FIG. 4 in an open condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Most chemicals, in a fluid state, exhibit viscous properties. Polymeric materials exhibit viscous (fluid-like) as well as elastic (solid-like) behavior, known to those skilled in the art as viscoelastacity. Elastomers exhibit greater elastic properties than other polymers. In the conception of the invention, the inventors proposed to use the known viscous nature of a fluid as an indicator of the contents of the fluid. 
     With reference now to FIGS. 1-3, an apparatus  40  which may be used in the invention is illustrated. The apparatus  40  comprises a sample chamber which is enclosed in sample container walls  58  which are sealed by ends  64  and  66 . An entry port  46  for the sample is provided in end  64 , and an exit port  56  for the sample is provided in end  66 . Accordingly, the sample must pass through entry port  46  into sample reservoir  62 . 
     Apparatus  40  is designed to be attached to a tap line  61  which is connected to the chemical processing line, whereby the tap line may be opened to obtain a sample. After data is obtained, the sample may be returned through another tap line  63  to the chemical processing line through exit port  56 , or the sample may be discarded, or collected for additional testing. 
     In apparatus  40 , the viscoelastic properties of the sample are measured by the shear of the sample, by trapping the sample in shearing gap  52  between shearing block  50  and step  59  in sample container wall  58 . To obtain a measurement, an actuator shaft  42  causes shearing block  50  to move back and forth in the proximity of step  59 , and the shear on the sample caused by the motion of a shearing block  50  in shearing gap  52  is measured using force transducer  44 . Bellows  48 ,  54  facilitate the back-and-forth motion of shearing block  50 , while sealing the internal components of the apparatus from the chemicals of the sample. 
     With reference specifically to FIGS. 1 and 2, when measurements are being taken on a sample, step  59  of container wall  58 , and outcropping  51  of shearing block  50  are separated by shearing gap  52  at opposed surfaces  68  and  70  of shearing block  50  and of step  59 , respectively. The viscoelastic properties of the sample dictate the shear, i.e. the force of resistance measured by force transducer  44 . In the illustrated embodiment, the cross section of shearing block  50  is part of a circle which fits within the circle of step  59  in circular container walls  58 . It should be apparent to those skilled in the art that other geometric configurations can be used for obtaining the shear properties of the sample. 
     Shearing block  50  is made with flat sides  53 , 55 , which create a recirculation gap  60  when shearing block  50  is disposed in the proximity of step  59  of container walls  58 . Recirculation gap  60  permits motion of the sample into and out of sample reservoir  62  so that hydraulic pressures in the sample container do not interfere with the shear data that is to be obtained. Those skilled in the art will recognize that sample reservoir  62  need not be completely filled with sample, i.e. an air gap can be provided, as long as the shearing gap  52  is completely filled when data is being obtained on a sample. 
     With reference now to FIG. 3, when data on a sample has been obtained, and it is desired to flush the sample from sample container  40 , shear block  50  is extended by shaft  42  into a position wherein shear block  50  is removed from the proximity of step  59  of container walls  58 . Bellows  48  and  54  facilitate this motion wherein, in the illustrated embodiment, bellows  48  are extended, and bellows  54  are compressed, while the seal between the internal components of the apparatus and the chemicals being tested is maintained. 
     Those skilled in the art will recognize that instead of extending shear block  50  toward sample exit port  56 , it is possible to build the apparatus so that shear block  50  is retracted toward entry port  46  when shear block  50  is removed from the proximity of step  59  in container walls  58 . 
     As illustrated in FIG. 3, when the shaft actuator (not shown) is activated, shearing gap  52  no longer exists, and a resampling gap  52 A is created between step  59  and shearing block  50 . Resampling gap  52 A permits flushing of the sample from the sampling device, and replacing the measured sample with a new sample of material that is to be measured. 
     In the method of the invention, when it is desired that data be obtained from a sample using apparatus  40 , the apparatus is retained in a configuration as illustrated in FIG. 3, and sample entry port  46  is opened and sample exit port  56  is closed so that sample is drawn into sample reservoir  62 . When sufficient sample has been received into sample reservoir  62 , sample entry port  46  is closed, isolating the sample from the reaction processing line. Thereafter, as illustrated in FIG. 1, the shaft actuator is activated to draw shearing block  50  into the proximity of step  59  in container walls  58 , creating a shearing gap  52 . Shaft  42  is then actuated to move shearing block  50  in a back and forth motion to create a shear in the sample between face  68  of shearing block  50  and face  70  of step  59 . Force transducer  44  measures the resistance force created by the sample, which is an indication of the sample&#39;s viscoelastic properties. 
     When the data is obtained, the collected data can be transferred to a computer, and the information will indicate the status of the chemical reaction in the chemical processing line, i.e. the state of the completion of the chemical reaction. This information will be used by the computer to maintain or change the flow rate of chemicals through the chemical processing line, maintain or change the temperature in the chemical processing line, or activate other parameters that will affect the rate of the reaction or to maintain the rate of the reaction. 
     It has been found, in creating the apparatus shown in FIGS. 1-3, that materials are not yet available that make possible the miniaturization of the hermetically sealed apparatus on the scale desired by the inventor. With materials available, the inventor estimates that the sample size for the apparatus of FIGS. 1-3 will need to be several liters due to the size and sensitivity requirements of bellows  48 ,  54 . Although usable in large reaction lines, such as those seen in refineries and synthetic rubber manufacturing, the inventor sees a need for such testing on a smaller sampling scale. 
     Accordingly, in an alternative embodiment, as illustrated in FIGS. 4-6, the same basic principles are used in an embodiment in apparatus  110  wherein actuator shaft  124 , having a shearing ring  126  is oscillated back and forth in a container  122  which comprises a first end  122 B, a second end  122 C, and a ring  122 A which are connected to each other by bellows  120 . The alternative apparatus shown in FIGS. 4-6 operates on the same principles as the apparatus shown in FIGS. 1-3 in that the shearing force of a sample trapped within shearing gap  116  is measured when shaft  124  is oscillated within container  122 . 
     The apparatus  110  has a shearing gap  116  which separates ring  122 A and shearing ring  126  when shearing ring  126  is positioned within container  122  for obtaining test data. Shearing ring  126  has a cross-sectional shape which includes recirculation gaps  118 . Apparatus  110  is adapted to be connected to a reaction flow stream by a tap line whereby a sample enters apparatus  110  through a first end  122 B through portal  112 , and exits apparatus  110  through portal  112 A in second end  122 C. 
     In the embodiment of FIGS. 4-6, bellows  120  are very stiff, and ring  122 A is stationary, or substantially stationary, within container  122  when a shearing stress of a sample acts over the internal surface of ring  122 A as shaft  124  is oscillated. Force transducer  128 , which is associated with ring  122 A, is capable of measuring forces that are applied to ring  122 A by the shearing force of the sample in shearing gap  116 . Transducer  128  is capable of measuring forces in the range of 0.001 to 500 Newtons. Those skilled in the art will recognize that alternatively the axial deflection of ring  122 A may also be measured as a means of resolving the physical response of the material to the applied shear deformation. In such a case, the measured axial deflection of the ring  122 A is governed by the spring rate of the attached bellows. 
     In the illustrated embodiment, bellows  120  are of precision construction and made of nickel which has a thickness of 0.1 mm. 
     In the construction of apparatus  110 , seals  132  are provided in first end  122 B of container  122 , and seals  130  are contained in second end  122 C of container  122  to contain a sample within sample cavity  114  of container  122 . 
     In the illustrated embodiment, seals  130 ,  132  comprise spring energized PTFE seals from Bal Seal Engineering Company. 
     The transducer  128  is the same as that illustrated with respect to FIGS. 1-3. 
     Similar to what was described with regard to the apparatus described in FIGS. 1-3, and with reference specifically to FIG. 6, when it is desired to collect a sample in apparatus  110 , a valve and tap line leading from a reaction flow line is opened to sample entry port  112 , and sample exit port  112 A is closed to permit entry and containment of the sample in sample chamber  114 . When the desired volume of sample has entered sample chamber  114 , the sample entry port  112  is closed to isolate the sample and sample chamber  114  from the reaction flow line, and shaft  124  is activated about 4 centimeters so that shearing ring  126  is opposite center ring  122 A as is illustrated in FIG.  4 . Shaft  124  is oscillated using a linear motor stage (not shown) provided by Aerotech, Inc. 
     The linear motor is one factor that makes possible the small size of the apparatus shown in FIGS. 4-6. The ALS20000 series linear motor stage by Aerotech, Inc. has a stroke range of 10 cm, which is sufficient to move shearing ring  126  clear of center ring  122 A when the apparatus is open to a new sample as shown in FIG.  6 . The motor is also capable of oscillating shaft  124  at frequencies greater than 100 Hz, which is suitable for creating a dynamic shear in a sample being tested. 
     The sheared sample in shear gap  116  between shearing ring  126  and ring  122 A applies a shear stress over the internal surface of ring  122 A, which is measured as a dynamic axial load by force transducer  128 . After the data is collected on a sample, sample exit port  112 A is opened, and the sample is permitted to return to the reaction flow line, or is collected for further testing as desired. 
     The data can be collected and used as is illustrated with respect to the apparatus described in FIGS. 1-3. 
     While the invention has been specifically illustrated and described, those skilled in the art will recognize that the invention can be variously modified and practiced without departing from the spirit of the invention.