Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Effecting a change in a polymerization process in response...
Reexamination Certificate
2001-11-20
2003-12-02
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Effecting a change in a polymerization process in response...
C422S109000, C422S110000, C422S111000, C714S051000, C526S335000
Reexamination Certificate
active
06657019
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for predicting the properties of a polymer latex in an emulsion polymerization process and more particularly relates to a method and apparatus of using the predicted polymer latex properties to monitor and adjust the process parameters of an emulsion polymerization process to improve the quality and productivity of the process and the emulsion polymer latices produced therefrom.
BACKGROUND OF THE INVENTION
One common method for producing polymers such as homopolymers and copolymers is emulsion polymerization. In a typical emulsion polymerization process, monomers are combined with an initiator in the presence of a surfactant in an aqueous medium and the monomers are polymerized to form the polymer. For example, the monomers can be combined with a surfactant and water to form a pre-emulsion and the pre-emulsion and initiator separately fed to a reactor where the polymerization reaction occurs to form the polymer. Alternatively, the monomers, an aqueous surfactant solution and an initiator can each be fed separately to the reactor.
It is important that the polymer latices produced in the emulsion polymerization process are consistent and of good quality. To ensure acceptable product quality, it has traditionally been necessary to take samples of the polymer latex at various stages or times during the emulsion polymerization process. Analytical tests are then conducted on the samples to verify that the samples are of sufficient quality. If the analytical tests do not produce values within certain specified limits, the process is modified to alter the product such that the product is of sufficient quality.
One drawback to the traditional method of process quality control is that it takes time to receive the results from the analytical tests. Accordingly, the emulsion polymerization process must be delayed resulting in reduced production. In addition, the sampling and testing is retrospective and does not allow the process to be proactively controlled. Furthermore, taking and analyzing samples can be expensive. Therefore, there is a need to provide a method of proactively controlling an emulsion polymerization process that produces a quality product without reducing the amount of the latex polymer produced and without increasing the cost of the process.
SUMMARY OF THE INVENTION
The present invention provides a method for predicting polymer latex properties for an emulsion polymer latex based on statistical relationships between the polymer latex properties and process parameters. The method of the invention allows for real-time control of the emulsion polymerization process and thus facilitates the production of a quality emulsion polymer without the need to stop production for sampling and analytical testing. The method of the invention also provides feedback and feed forward control of the emulsion polymerization process to ensure the production of a quality product without increasing the cost of production. Furthermore, the statistical relationships between the polymer latex properties and process parameters determined for a specific emulsion polymerization process can advantageously be used to predict the polymer latex properties for another emulsion polymerization process making generally the same polymer. The method of the invention can be used with continuous, batch and semi-batch emulsion polymerization processes.
The method for predicting one or more polymer latex properties for an emulsion polymer latex according to the invention includes conducting an emulsion polymerization process in a reactor including one or more reactor inputs to produce an emulsion polymer latex, measuring a set of process parameters for the emulsion polymerization process, performing a heat balance and a mass balance across the reactor based on the set of measured process parameters to determine a set of calculated polymer latex properties for the emulsion polymerization process, and determining one or more predicted polymer latex properties for the emulsion polymer latex being prepared in the emulsion polymerization process using process parameters selected from one or more of said set and said second set and a predetermined set of statistical relationships between the selected process parameters and the polymer latex properties to be predicted. The heat balance and mass balance are typically conducted using a set of measured process parameters including the mass of ingredients initially added to the reactor, the flow rates for the reactor inputs, the temperatures for the reactor inputs, the flow rates and temperatures for the input and output of a coolant stream communicating with the reactor, and the temperature and pressure of the reactor, to determine a set of calculated process parameters such as the monomer/polymer ratio in the reactor. The one or more predicted polymer latex properties for the emulsion polymer are preferably determined using the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and a predetermined set of statistical relationships between the reactor temperature, the flow rates for the reactor inputs, the monomer/polymer ratio and the polymer latex properties to be predicted.
In accordance with the invention, the set of statistical relationships between the process parameters and the polymer latex properties used are preferably determined by first operating the emulsion polymerization process using a plurality of varying process parameters and measuring the polymer latex properties and then calculating the set of statistical relationships between the process parameters and polymer latex properties for the emulsion polymerization process based on the process parameters and the measured polymer latex properties. In addition to the measured polymer latex properties, polymer latex properties such as the monomer/polymer ratio calculated by performing a heat balance and mass balance across the system can be used to determine the statistical relationships. Preferably, the process parameters used to provide the set of statistical relationships are selected from the group consisting of the reactor temperature and the flow rates for the reactor inputs. In addition, the measured and calculated polymer latex properties are preferably selected from the group consisting of the monomer/polymer ratio, the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size. Preferably, the monomer/polymer ratio, the flow rates for the reactor inputs, the reactor temperature, and the statistical relationships are used to predict polymer latex properties such as the number of polymer particles, the amount of polymer crosslinking, the molecular weight of the polymer, the concentration of Diels-Alder adducts and the polymer particle size.
The predicted polymer latex properties can be used in various ways to provide a more consistent emulsion polymer product. For example, the predicted polymer latex properties can be compared to predetermined upper and lower limits for the polymer latex properties. If the predicted polymer latex properties are not within the predetermined upper and lower limits for the polymer latex properties, a sample of the emulsion polymer from the emulsion polymerization reaction can be taken and the actual polymer latex properties from the sample measured to determine if the process parameters for the emulsion polymerization reaction should be adjusted. Alternatively, the process parameters for the reactor or for further processing steps downstream from the reactor can be adjusted if the predicted polymer latex properties are not within the predetermined upper and lower limits for the polymer latex properties to provide feedback or feed forward control. The predicted polymer latex properties can also be analyzed using statistical process control methods to determine whether the predicted polymer latex properties are acceptable and whether process parameter
Antonucci Jonathan P.
Racz Robert R.
Taylor Michael A.
BASF Corporation
Cheung William K.
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