# Patent

## Title
Accurate blending module and method

## Abstract

An accurate blending module for adjusting the pH of solutions containing therapeutic proteins includes a recirculation loop that receives the therapeutic protein solution via a feed pump and an acid solution via an adjusting pump. The recirculation loop includes a recirculation pump and a pH sensor that detects the pH of the solution in the recirculation loop. A controller communicates with the pH sensor and the adjusting pump. The adjusting pump adds acid to the recirculation loop based on the pH readings taken by the pH sensor. The recirculation pump recirculates the therapeutic protein solution and acid in the recirculation loop so that it is mixed. As a result, the pH of the therapeutic protein solution is precisely controlled and adjusted in a non-destructive fashion.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent application Ser. No. 10/688,391, filed Oct. 17, 2003, and issued as U.S. Pat. No. 7,072,742.


BACKGROUND OF THE INVENTION
The present invention relates generally to liquid blending systems and, in particular, to a module that blends two or more liquids together with high accuracy so that solutions having the desired concentrations of the components and/or other characteristics, such as pH, viscosity or optical density, etc., are created and a method for retrofitting industrial equipment and systems with the module to improve system performance.
The combining of two or more liquids together to a desired concentration and/or other characteristics, such as pH, viscosity or optical density, etc., of the constituent liquids is fundamental to many industrial processes and commercial products. This combining of liquids may be referred to as blending and is common in many industrial segments including pharmaceutical products, biopharmaceutical products, food and beverage processing products, household products, personal care products, petroleum products, chemical products and many other general industrial liquid products. In addition, blending systems find use in the field of liquid chromatography where blended liquids are provided to chromatography columns to permit the separation of mixtures for analysis or for purification purposes.
On site blending systems provide many advantages over purchasing pre-mixed chemicals. By using a blending system, a single barrel or feedstock concentrate produces many times its volume in diluted solution, depending on the desired concentration of the dilution. Thus, a single feedstock concentrate, used to produce the equivalent of many feedstocks of dilute liquid via a blending system, greatly reduces facility costs associated with fabrication of large tanks, floor space required, validation and quality control costs to confirm makeup, spoilage and disposal costs of non-compliant out of date or unused blended solutions. Freight costs associated with chemical delivery are also greatly reduced. In addition, onsite dilution and blending increases the variety of chemical concentrations and mixtures that are immediately available, without requiring a corresponding increase in the number of feedstocks and chemicals that must be purchased, thereby reducing facility and operating costs and providing the logistical and administrative advantage of reduced inventory.
High accuracy in terms of concentration for blending systems providing liquids to liquid chromatography systems is vital. In addition, quality control concerns favor increased blending accuracy for liquids that are provided to industrial processes and that are used to create commercial products. Indeed, Six Sigma quality control principles dictate that lower variability in an industrial process results in a greater percentage of higher quality products being produced by the industrial process.
It is well known, however, that it is common for different levels of a large feedstock tank filled with a solution to have different proportionate mixtures of the constituent liquids. Gradients exist in large feedstocks in terms of both concentration and temperature. As a result, liquid provided from the feedstock will vary in terms of concentration posing challenges for accurate analysis, quality control analysis, as well as uniform delivery to a process. Feedstock solvents, commercially supplied, have variations in actual concentration from batch to batch as well as innate impurities preventing 100% pure concentrations from being available in bulk supply.
FIG. 1 illustrates a prior art approach to blending a buffer or solvent solution with a diluting liquid such as water. Feedstocks, supplied from containers or tanks, are illustrated at 10a, 10b, 10c and 12. Feedstocks 10a through 10c contain different concentrations of buffer solution, for example, 0.1M, 0.5M and 1.0M buffer, respectively. Feedstock 12 contains water as a diluting liquid. It should be noted that feedstocks 10a, 10b and 10c could alternatively contain a solvent.
The system of FIG. 1 provides three blending modes, graphically illustrated at 14, 16 and 18. In the graphs illustrated at 14, 16 and 18, the x-axis represents time while the y-axis represents concentration. Graph 14 illustrates the isocratic blending mode where the buffer solution or solvent is provided to a process at a fixed concentration level or set point. Due to the inherent variability of feedstock 10a, the actual concentration delivered to the process, as illustrated at 14, will typically vary by ≧+/−2% from the set point/desired concentration.
Graph 16 of FIG. 1 illustrates the step gradient blending mode where the buffer solution is provided to the process at multiple concentration levels. In the example shown in FIG. 1, there are three concentration level steps, and thus, three set points. During the initial portion of buffer delivery, buffer of a lower concentration level is provided from feedstock 10a. After a period of time, the supply of buffer solution is switched from feedstock 10a to feedstock 10b so that a buffer solution having five times the concentration is provided. Finally, after a second period of time, the supply of buffer is switched from feedstock 10b to feedstock 10c so that a buffer solution having ten times the concentration (as compared to the buffer from feedstock 10a) is provided. As indicated at 16, such an approach passes on the innate feedstock variation of ≧+/−2% from the desired concentration levels.
Graph 18 in FIG. 1 illustrates the linear gradient blending mode where, for example, buffer solution or solvent from feedstock 10c is diluted with water from feedstock 12 so that the concentration of the buffer or solvent increases over time. In other words, the set point ramps up to a specified concentration level. As is known in the art, such blending is accomplished by adjusting the pumps or valves regulating the flow of liquid from feedstocks 10c and 12. While it is desired that the buffer concentration be increased linearly, as illustrated at 18, the resulting blend varies from the desired concentration by ≧+/−2% plus an additional variability of between +/−3% to +/−5%. In addition, due to the high variability, the buffer of feedstock 10c cannot be diluted with the water from feedstock 12 to accurately provide buffer having the concentrations of feedstocks 10a and 10b. The additional feedstocks 10a and 10b must be present in addition to feedstock 10c. In general, the variability indicated at 18 makes the linear gradient blending mode impractical for most applications.
As illustrated at 22 in FIG. 1, the variability for the three blending modes described above causes a variable and non-compliant product quality distribution. The graph 22 represents both the variability of the blend and the variability in product produced in processes relying on accurate blend makeup and delivery when the makeup blend is variable and inaccurate.
A wide range of products require pH adjustments. These include beverages, paints, specialty chemicals, cleaning solutions, buffers and chemically or biologically derived materials including various types of fermentation products, bioreactor products, cell cultures, recombinant expression systems and other natural source materials such as those with a therapeutic, nutritional or other application.
The standard prior art technique for pH adjustment uses a vessel, typically a 500 liter stainless steel or polymeric vessel or bag, containing the solution or product suspension to be adjusted. A pH probe is typically positioned at a port in the vessel wall. A mixer, such as a magnetic mixer or vortex/propeller mixer is usually inserted into the solution or product suspension in the vessel and used to facilitate the pH adjustment process. A pH adjusting solution is manually added to the vessel in portions while mixing occurs. After each manual addition, the solution or product suspension is given a few additional minutes to fully mix and then a few additional minutes for the pH reading to stabilize. The pH of the solution or product suspension is then read using the pH probe. The process is repeated with additional portions of the pH adjusting solution added until the desired pH level is reached.
The above prior art technique of pH adjustment suffers from a number of disadvantages. The process is manual and therefore does not permit automated control. Furthermore, if the desired pH set point is exceeded, the entire batch of solution or product suspension may be put at risk or even lost.
Another disadvantage of the prior art pH adjustment technique arises in the case of pH adjustment involving proteins or other labile materials. For example, when an acidic pH adjusting solution is added to the vessel, it may destroy the protein by hydrolyzing it at the point of contact with the protein in solution. As a result, the yields of protein are reduced and undesired hydrolyzed proteins become present in the product. This is particularly problematic when a very expensive protein, such as a therapeutic protein, is being treated.
Accordingly, it is an object of the present invention to provide a blending system that permits very precise control and fine tuning of the blending of liquids or solutions and product suspensions.
It is another object of the present invention to provide a blending system that is automated.
It is another object of the present invention to provide a blending system that permits a precise end point pH level to be obtained.
It is still another object of the present invention to provide a blending system that is non-destructive to proteins.
These and other objects of the invention will be apparent from the remaining portion of the application.
SUMMARY OF THE INVENTION
The present invention is directed to an accurate blending module for retrofitting existing laboratory or industrial systems or use as a standalone device and a method of use. In one embodiment, the accurate blending module includes a proportioning submodule adapted to receive and merge at least two liquid feeds. A blending submodule communicates with the proportioning submodule and blends the merged liquid stream. A detection submodule communicates with the blending submodule so that a blended liquid stream from the blending submodule flows therethrough. The detection submodule detects a composition of the blended liquid stream and communicates it to a controller. The controller is also in communication with the proportioning submodule and adjusts the proportioning submodule based upon the detected composition so that a desired composition is provided by the accurate blending module. The proportioning, blending and detection submodules are integrated together, resulting in the accurate blending module.
The accurate blending module also includes a purge valve in communication with the outlet of the detection submodule that communicates with the controller so that the controller opens the purge valve when the detected composition exceeds a predetermined tolerance. The blending submodule may optionally include a pump to blend the liquid feeds and delivers the merged stream to the detection submodule.
In another embodiment, the accurate blending module of the present invention is used for blending a supply of feed solution and a supply of adjusting solution. More specifically, the feed solution may include therapeutic proteins and the adjusting solution may include acid. In this embodiment, the module includes a feed inlet adapted to communicate with the supply of feed solution. The module also includes an adjusting solution inlet that is adapted to communicate with the supply of adjusting solution. A recirculation loop features a recirculation pump and a pH sensor. A feed pump is positioned in circuit between the feed inlet and the recirculation loop and provides feed solution to the recirculation loop. An adjusting pump is in circuit between the adjusting solution inlet and the recirculation loop and provides adjusting solution to the recirculation loop. A controller is in communication with the pH sensor so that the pH of the solution in the recirculation loop can be detected as the recirculation pump mixes the solution in the recirculation loop. The controller is also in communication with the adjusting pump so that delivery of adjusting solution to the solution in the recirculation loop can be controlled based upon the detected pH level. As a result, the pH of the protein solution is precisely controlled and adjusted in a non-destructive fashion.
The following detailed description of embodiments of the invention, taken in conjunction with the appended claims and accompanying drawings, provide a more complete understanding of the nature and scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow diagram illustrating prior art approaches to blending buffers or solvents with a diluting liquid such as water and the resulting product variability;
FIG. 2 is a flow diagram illustrating approaches to blending using an embodiment of the accurate blending module and method of the present invention and the impact on product variability;
FIG. 3 is a schematic of an embodiment of the accurate blending module of the present invention;
FIG. 4 is a schematic of the module of FIG. 3 providing greater detail of the components;
FIG. 5 is a flow chart illustrating the processing performed by the software of the PLC or PC of FIGS. 3 and 4;
FIG. 6 is a perspective view of an industrial system retrofitted with an embodiment of the blending module of the present invention in accordance with the method of the present invention;
FIG. 7 is a schematic of an embodiment of the accurate blending module of the present invention that is particularly well-suited for use in adjusting the pH level of protein suspensions;
FIG. 8 is a perspective view of the accurate blending module of FIG. 7 mounted on a cart.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to FIG. 2, an embodiment of the accurate blending module of the present invention 24 has been has placed in communication with feedstocks 10c and 12. While the buffer or solvent from feedstock 10c varies ≧+/−2% from the desired concentration levels, the accurate blending module 24 can provide a blended variability of only +/−0.1% for each of the isocratic, step gradient and linear gradient blending modes, as illustrated at 26, 28 and 32, respectively.
Due to the precision blending provided by the module 24, feedstocks 10a and 10b are no longer required as the concentrations provided thereby may be obtained instead by blending buffer from feedstock 10c and water from feedstock 12. As illustrated by the liquid chromatography results illustrated at 34, the arrangement of FIG. 2 provides consistent and compliant product quality distribution.
The details of an embodiment of the accurate blending module, indicated in general at 24, are presented in FIGS. 3 and 4. A programmable logic controller (PLC) 36, or onboard controller that communicates with an external personal computer (PC), indicated at 37 in FIG. 4, communicates with a proportioning submodule 38 and a detection submodule 42. With the latter configuration, the onboard controller communicates with the PC via an Ethernet connection or a serial port connection. Alternatively, a soft PLC approach, whereby software residing on the PC eliminates the need for an onboard PLC, could be employed. With such an arrangement, however, a hardware controller (but not a PLC) may still be required on the module skid (FIG. 6).
The sensor (57 in FIG. 4) of the detection submodule 42 of FIG. 3 is calibrated prior to use with the critical or variable feed (such as buffer or solvent) concentration tuned to the desirable sensor output level, typically 100% or full scale. The sensor output is zeroed with water.
Two customer-supplied liquid feeds 44a and 44b are connected to the proportioning submodule 38. It should be noted that while two feeds are illustrated, additional feeds are within the scope of the present invention. The proportioning submodule continuously merges the two separate incoming liquid streams (such as a salt concentrate solution and purified water) with valving into one stream. As illustrated in FIG. 3 at 46a and 46b, 46c, respectively, the valving of proportioning submodule 38 may be either a single 3-way valve or two control valves that are automated and communicate with PLC 36 or PC 37 (if the soft PLC approach is implemented) in the manner described below. The two control valve arrangement (46b and 46c) is illustrated in FIG. 4. Valves 46a, 46b and 46b may be any type of valve that may be automated. Examples include diaphragm valves, ball valves and needle valves which may be controlled in a digital or analog fashion.
The merged liquid stream 48 exiting the proportioning submodule 38 is mixed within a fixed volume (50 in FIG. 4) in blending submodule 52 to ensure that the mixture is fully blended. As illustrated at 54a and 54b in FIG. 3, the blending submodule may utilize an in-line mixer 54a or a recirculating mixer 54b, both of which are known in the art, positioned within the fixed or variable volume 50 of FIG. 4. Alternatively or in addition to dynamic mixing, static mixing may also be used in the blending submodule 52. The volume of the blending submodule is selected based upon the total flow requirement for the module (how much buffer or solvent is needed at what flow rate). It should be noted that either a fixed mixing rate or volume or a variable mixing rate or volume may be used in the blending submodule. As illustrated at 55 in FIG. 4, if dynamic mixing is used, the mixing device may be controlled by the PLC 36 or PC 37.
The blended liquid stream 56 exiting the blending submodule 52 encounters the detection submodule 42. An ionic (e.g. conductivity or pH for a salt solution) or spectral (e.g. near-infrared or ultraviolet for an alcohol or other solvent solution) measurement of the blend, as appropriate, is taken by an in-line sensor, indicated at 57 in FIG. 4, within the detection submodule 42.
As indicated in FIG. 3, the detection submodule may use a range of sensor types including NIR, conductivity, temperature, pH etc. Basically any sensor that can detect specific properties of the critical (or variable) feed and outputs a measurable signal may be used. Typically the signal is analog, but it may be digital. Examples of suitable sensors include fixed or variable wavelength near infrared or ultraviolet sensors (such as those manufactured by Wedgewood, Foss, Custom Sensors, Optek and Knauer), pH sensors (such as those manufactured by TBI Bailey and Yokagawa) and conductivity sensors (such as those manufactured by TBI Bailey and Wedgewood). The sensor 57 within the detection submodule 42 communicates the composition of the blended liquid stream with the PLC 36 or PC 37.
The outputted signal from the sensor 57 (FIG. 4) of the detection submodule 42 (FIG. 3), which is typically analog, provides the PLC 36 or PC 37 with a Process Value (PV) for a software PID (gain, integral, derivative) feedback loop. A Set Point (SP) for the software feedback loop will have been set in the PLC 36 or PC 37 by the user via a user interface 58 (FIG. 3) which may be the PC 37 of FIG. 4. Based on the discrepancy between the measured PV and the user-defined SP, the PLC's (or PC's) software PID feedback mechanism continually adjusts the signal that is sent to the automated valving of proportioning submodule 38, which are valves 46b and 46c in the embodiment of FIG. 4. This signal is called the Output. The Output signal causes constant adjustments in the proportioning submodule valves' opening/closing such that the PV continuously matches the SP. The Output signal is scaled by the software of the PLC or PC to a process value (such as molarity or concentration).
In summary:


    
    
        SP=set point=user defined value or blending percentage
        PV=process value=measured value that is coming from the measuring sensor
        Output=continuously adjusting signal that the software is programmed to send to the mixing valves that allows the measured PV to approach the user-defined SP
    
    


FIG. 5 is a flowchart illustrating the processing performed by the software of the PLC or PC in performing the above steps. While busses are not required for the PLC or PC to control the valves, etc., they provide faster speed and response for the module. As an example, Profibus may be used for valve control while Foundation Fieldbus may be used for the other signals. As advances in process control software and hardware become available, these faster speed options can be used to further improve performance and reliability.
As indicated in FIG. 5, there is also a user-specified “deadband” or acceptable tolerance for the Process Value. If the PV falls outside of the SP by a value greater than the deadband during the process, then a purge valve, illustrated at 62 in FIG. 4, will open and a delivery valve, illustrated at 63 in FIG. 4, will close to divert the out-of-spec liquid away from the rest of the system. Meanwhile, the software PID loop attempts to correct the liquid blend. Once corrected, the liquid is directed back to the system.
The precisely mixed merged stream, indicated at 58 in FIGS. 3 and 4, which has now been verified as accurate since the software has enabled the PV to match the SP, is then delivered.
As an example, after a calibration of sensor response with appropriate buffer and water, a user has purified water connected to one inlet of the module and 1 M NaCl solution connected to the second inlet of the module. The user specifies the SP as 0.1 M NaCl. The module's software will adjust the behavior of the blending valves such that the measured PV detected by, in this case, the conductivity sensor, shall be as close to the reading corresponding to 0.1 M NaCl as possible.
As illustrated in FIG. 6, an embodiment of the accurate blending module of the present invention, indicated in general at 24, includes a skid 82 upon which the components of FIGS. 3 and 4 are mounted. The skid 82 features rollers 84a, 84b, 84c and 84d so that the module may be easily rolled across a surface, although fixed installations are also possible.
The module 24 may optionally include a pump, illustrated at 86 in FIG. 6, that blends the liquid from feedstocks, such as those illustrated 10a-10c and 12 in FIGS. 1 and 2, which are delivered through the liquid feeds 44a and 44b to the proportioning submodule 38. In FIG. 6, the proportioning submodule takes the form of two control valves. After leaving the proportioning submodule, the liquid stream, 48 in FIGS. 3 and 4, travels through line 48 to the blending submodule 52. In FIG. 6, the blending submodule takes the form of a recirculating and fixed volume mixer. Blending submodule 52 optionally includes a bubble trap 92 so that the blended liquid stream (corresponding to blended liquid stream 56 in FIGS. 3 and 4) traveling through line 94 to the detection submodule 42 does not contain bubbles.
As described previously, the liquid exiting the detection submodule travels through either valve 62 or 63. If travel is through the latter valve, the liquid can be delivered to an existing process, or system, as indicated in general at 96, through line 98. The stream traveling through line 98 corresponds to the precisely mixed stream 58 in FIGS. 3 and 4. It is to be understood that the complete blending module can be connected to an existing system by means of a single tubing connection, as illustrated in FIG. 6, or alternatively can be used in a stand-alone way to generate adaptively-controlled liquid blends.
The accurate blending module integrates with the existing process in ways ranging from a simple relay switch closure which defines the module's start/stop points, to a complete renovation of any existing controller hardware and software permitting replacement with or installation of latest version hardware and software for optimized performance. For a simple switch, or contact closure, the existing system must send a digital output to the module that signals the module to initiate its blending procedure, or stop its blending procedure. For a complete hardware and software replacement, the existing controller hardware, such as a programmable logic controller, is removed and replaced with updated hardware, software and PC.
The module is built from various components, such as valves, pumps, and sensors that are sized and specified for use with the existing system and/or the processes for which it will be used.
The present invention thus provides a portable closed-system unit that upgrades an existing pharmaceutical/biopharmaceutical/nutraceutical/fine chemical/industrial process pumping system to permit precise and reproducible buffer and/or solvent blends to be delivered from the existing system. These precise buffer and/or solvent blends can be leveraged by the equipment user to greatly enhance their particular biopharmaceutical/nutraceutical/fine chemical/industrial process of interest. In addition, the present invention offers a standalone blending system that may provide liquids containing constituents at precise concentration levels and/or desired characteristics such as pH, viscosity or optical density, etc., to any process or process equipment that may benefit from reduced variability and increased reproducibility and robustness.
FIGS. 7 and 8 illustrate an embodiment of the accurate blending module of the present invention that is particularly suited for adjusting the pH level of a solution containing proteins. For example, therapeutic proteins typically undergo a viral deactivation step that uses a base such as sodium hydroxide. As a result, the pH of the protein solution must be brought down to neutral by the addition of acid. As described previously, the acid can destroy the very high value therapeutic protein at the point of contact by hydrolysis. As a result, it is desirable for a system to add the acid continuously in a very precisely controlled fashion and in a non-destructive manner. The embodiment of FIGS. 7 and 8 accomplish this.
It should be noted that while the embodiment of FIGS. 7 and 8 will be described in connection with adjusting the pH of a solution containing a therapeutic protein, it is to be understood that the system of FIGS. 7 and 8 could be used to adjust the pH of any solution or suspension that would benefit from accurate and non-destructive pH adjustment. As will be described below, the accurate blending module of FIGS. 7 and 8 could also be used to perform other types of adjustments.
With reference to FIG. 7, a primary feed vessel 102 contains a feed solution such as a therapeutic protein solution requiring pH adjustment. The vessel may be, for example, a 500 liter tank or bag. The feed tank is connected to the accurate blending module, indicated by dashed line 104 in FIG. 7 and in general at 104 in FIG. 8, via feed inlet 106. The feed inlet 106 communicates with a variable frequency drive controlled feed pump 108. Due to its variable frequency drive, the pumping speed of the feed pump 108 may be accurately controlled. The feed pump 108 preferably is a low shear rotary lobe pump so that the delicate proteins in the solution from tank 102 are not damaged. Appropriate pumps are available from the ITT Jabsco company of Foothill Ranch, Calif.
A supply of adjusting solution, such as acid/concentrate 110, is connected to the adjusting solution inlet or acid/concentrate inlet 112 of the accurate blending module 104, which in turn communicates with a variable frequency drive controlled adjusting or acid/concentrate pump 114. Adjusting or acid/concentrate pump 114 is preferably a diaphragm-type dosing pump that provides very precise control with regard to the rate that the acid/concentrate is pumped. Suitable pumps are available from the American Lewa, Inc. of Holliston, Mass.
As illustrated in FIG. 7, the outlet streams from feed pump 108 and acid/concentrate pump 114 travel through valves 116 and 117, respectively, to recirculation mixing loop 118. Recirculation mixing loop 118 is provided with a variable frequency drive recirculation pump 122 which recirculates solution around loop 118 so that the solution becomes thoroughly mixed. Recirculation pump preferably is a sanitary disc pump so that damage to the proteins in the solution being recirculated through loop 118 is avoided. Suitable disc pumps are available from Discflo Corporation of Santee, Calif.
An air sensor 124 is positioned in the line 126 that runs between the outlet of feed pump 108 and mixing loop 118. The air sensor detects the absence of liquid in line 126 and communicates with the system controller, which is preferably a programmable logic controller (PLC) 128. The controller 128 shuts down the system pumps and provides the appropriate indication when the feed tank 102 is empty.
The controller 128 is housed in the electronics cabinet of the module, illustrated at 130 in FIG. 8. Controller 128 controls, as will be explained below, many of the valves and pumps of the module 104.
At start-up, valves 116 and 117 are opened, then feed pump 108, acid/concentration pump 114, and recirculation pump 122 are activated by controller 128 so that solution containing therapeutic proteins and the adjusting acid is pumped to mixing loop 118 and recirculated therein. The pH of the solution being recirculated through loop 118 is detected by a pH probe or sensor 132. As illustrated in FIG. 7, the pH sensor 132 communicates with the system controller 128 which controls acid/concentrate pump 114. Acid is continuously delivered in variable quantities as controlled by the controller 128. The speed of pump 108 is typically maintained constant. Initially, valve 142 will be open, diverting the output of the recirculation loop back to the feed tank 102. Only when the target pH has been attained will the valve 134 open and valve 142 close via controller 128 to deliver the output of the recirculation loop through outlet port 135 to the collection tank 136. The acid (pH adjusting solution) addition rate continues to be based on feedback control from the pH sensor 132.
If the solution being recirculated and mixed in the loop 118 goes out of spec, it must be reconditioned. The solution in loop 118, which contains therapeutic proteins, is too valuable to merely purge and dump. As a result, when pH sensor 132 detects that the solution in loop 118 has gone out of spec, controller 128 opens valve 142 and closes valve 134. The solution is then pumped out of loop 118, through purge port 143 (see FIG. 8) and three-way valve 144, which has been configured to direct the solution through return line 146. The out-of-spec solution travels through the return line 146 and back to feed tank 102. When recirculation loop 118 has been emptied, recirculation pump 118 is stopped and valve 142 is closed by the controller 128. Three-way valve 144 is then reconfigured so that a source of pressurized nitrogen gas 148 is place in communication with return line 146. As a result, the liquid remaining/trapped in return line 146 is flushed back to the feed tank 102. The source of pressurized nitrogen and the associated three-way valve could be, for example, user supplied.
Pressure sensor 152 is positioned in the recirculation loop 118 and detects the pressure therein. The pressure sensor 152 communicates with the controller 128 and stops the appropriate pumps to prevent overpressure within loop 118. Pressure sensor 154 detects the pressure in line 155, which runs between the mixing loop 118 and outlet port 135 and adjusts valve 156 to provide the user-specified backpressure in line 155.
The versatility of the accurate blending module of FIGS. 7 and 8 may be increased by providing mixing loop 118 with a conductivity sensor 158 (FIG. 7). As a result, a solution or suspension in loop 118 may be adjusted based upon a desired conductivity value instead of pH.
In a typical pH adjustment application, it is important that the controller software has the ability to manage the highly non-linear, 14 decades of concentration involved. Software, such as that provided by Expertune or Rockwell Automation, is used to enhance the advanced PID control features of the controller 128 in the preferred embodiment to manage this non-linearity.
The embodiment of the accurate blending module of the present invention illustrated in FIGS. 7 and 8 therefore provides precise addition of acid or other adjusting solution in an automated fashion. The addition of the adjusting solution also occurs in a non-destructive fashion which is key when treating expensive feed solutions such a solutions containing therapeutic proteins.
While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.

## Claims

1. An accurate blending module for blending a supply of feed solution and a supply of adjusting solution comprising:
a) a feed inlet adapted to communicate with the supply of feed solution;
b) an adjusting solution inlet adapted to communicate with the supply of adjusting solution;
c) a feed pump in communication with the feed inlet;
d) an adjusting pump in communication with the adjusting solution inlet;
e) a continuous recirculation loop featuring a recirculation pump and a sensor, said recirculation loop in communication with said feed pump and said adjusting pump so that feed solution and adjusting solution are received by the recirculation loop and mixed therein by the recirculation pump; and
f) a controller in communication with the sensor so that a characteristic of the feed solution in the recirculation loop can be detected, said controller also in communication with the adjusting pump so that delivery of adjusting solution to the solution in the recirculation loop can be controlled based upon the detected characteristic.

2. The accurate blending module of claim 1 further comprising a return line distinct from the recirculation loop, said return line leading from an outlet of the recirculation loop and adapted to communicate with the supply of feed solution.

3. The accurate blending module of claim 2 further comprising a source of pressurized gas selectively in communication with the return line.

4. The accurate blending module of claim 3 wherein the pressurized gas is nitrogen.

5. The accurate blending module of claim 1 wherein the sensor is a pH sensor.

6. The accurate blending module of claim 1 wherein the feed solution includes proteins, the adjusting solution includes acid and the sensor is a pH sensor.

7. The accurate blending module of claim 6 wherein the proteins are therapeutic proteins.

8. The accurate blending module of claim 1 wherein the feed pump is a low shear rotary lobe pump.

9. The accurate blending module of claim 1 the adjusting pump is a diaphragm-type dosing pump.

10. The accurate blending module of claim 1 wherein the recirculation pump is a disc pump.

11. The accurate blending module of claim 1 further comprising an air sensor in communication with the feed inlet and the controller, said air sensor detecting when the supply of feed solution is exhausted and the controller providing an indication of same.

12. A method for providing an adjusted solution comprising the steps of:
a) providing a continuous recirculation loop with a recirculation pump and a sensor;
b) providing a supply of feed solution and a feed pump;
c) providing a supply of adjusting solution and an adjusting pump;
d) pumping feed solution to the recirculation loop;
e) pumping adjusting solution to the recirculation loop;
f) mixing the feed solution and the adjusting solution in the recirculation loop with the recirculation pump;
g) detecting a characteristic of the mixed solution in the recirculation loop with the sensor and controlling the adjusting pump based on the characteristic.

13. The method of claim 12 further including the step of providing a return line distinct from the recirculation loop, said return line extending between the recirculation loop and the supply of feed solution and returning feed solution from the recirculation loop to the supply of feed solution when the sensor detects that the feed solution in the recirculation loop is out of spec.

14. The method of claim 13 further comprising the step of purging the return line with a pressurized gas.

15. The method of claim 12 wherein the sensor is a ph sensor.

16. The method of claim 12 wherein the feed solution includes proteins, the adjusting solution includes acid and the sensor is a pH sensor.

17. The method of claim 16 wherein the proteins are therapeutic proteins.

18. The method of claim 12 further comprising the step of providing an air sensor in communication with the supply of feed solution and detecting the when the supply of feed solution has been exhausted with the air sensor.

19. The method of claim 18 further comprising the step of communicating to the controller from the air sensor that the supply of feed solution has been exhausted and providing a corresponding indication with the controller.

20. The accurate blending module of claim 1 further comprising:
g) a feed tank containing the supply of feed solution, said feed tank in communication with the feed inlet and having a return inlet;
h) a return valve in communication with the recirculation loop;
i) a return line distinct from the recirculation loop and in communication with the return inlet of the feed tank and the return valve so that solution in the recirculation loop is returned to the feed tank when the return valve is opened.