Dynamic Modelling and Optimization of Polymerization Processes in Batch and Semi-batch Reactors. Dynamic Modelling and Optimization of Bulk Polymerization of Styrene, Solution Polymerization of MMA and Emulsion Copolymerization of Styrene and MMA in Batch and Semi-batch Reactors using Control Vector Parameterization Techniques.
SupervisorMujtaba, Iqbal M.
Methyl methacrylate (MMA)
gPROMS (general PROcess Modelling System) software
The University of Bradford theses are licenced under a Creative Commons Licence.
InstitutionUniversity of Bradford
DepartmentSchool of Engineering, Design & Technology
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AbstractDynamic modelling and optimization of three different processes namely (a) bulk polymerization of styrene, (b) solution polymerization of methyl methacrylate (MMA) and (c) emulsion copolymerization of Styrene and MMA in batch and semi-batch reactors are the focus of this work. In this work, models are presented as sets of differential-algebraic equations describing the process. Different optimization problems such as (a) maximum conversion (Xn), (b) maximum number average molecular weight (Mn) and (c) minimum time to achieve the desired polymer molecular properties (defined as pre-specified values of monomer conversion and number average molecular weight) are formulated. Reactor temperature, jacket temperature, initial initiator concentration, monomer feed rate, initiator feed rate and surfactant feed rate are used as optimization variables in the optimization formulations. The dynamic optimization problems were converted into nonlinear programming problem using the CVP techniques which were solved using efficient SQP (Successive Quadratic Programming) method available within the gPROMS (general PROcess Modelling System) software. The process model used for bulk polystyrene polymerization in batch reactors, using 2, 2 azobisisobutyronitrile catalyst (AIBN) as initiator was improved by including the gel and glass effects. The results obtained from this work when compared with the previous study by other researcher which disregarded the gel and glass effect in their study which show that the batch time operation are significantly reduced while the amount of the initial initiator concentration required increases. Also, the termination rate constant decreases as the concentration of the mixture increases, resulting rapid monomer conversion. The process model used for solution polymerization of methyl methacrylate (MMA) in batch reactors, using AIBN as the initiator and Toluene as the solvent was improved by including the free volume theory to calculate the initiator efficiency, f. The effects of different f was examined and compared with previous work which used a constant value of f 0.53. The results of these studies show that initiator efficiency, f is not constant but decreases with the increase of monomer conversion along the process. The determination of optimal control trajectories for emulsion copolymerization of Styrene and MMA with the objective of maximizing the number average molecular weight (Mn) and overall conversion (Xn) were carried out in batch and semi-batch reactors. The initiator used in this work is Persulfate K2S2O8 and the surfactant is Sodium Dodecyl Sulfate (SDS). Reduction of the pre-batch time increases the Mn but decreases the conversion (Xn). The sooner the addition of monomer into the reactor, the earlier the growth of the polymer chain leading to higher Mn. Besides that, Mn also can be increased by decreasing the initial initiator concentration (Ci0). Less oligomeric radicals will be produced with low Ci0, leading to reduced polymerization loci thus lowering the overall conversion. On the other hand, increases of reaction temperature (Tr) will decrease the Mn since transfer coefficient is increased at higher Tr leading to increase of the monomeric radicals resulting in an increase in termination reaction.
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Dynamic optimisation and control of batch reactors. Development of a general model for batch reactors, dynamic optimisation of batch reactors under a variety of objectives and constraints and on-line tracking of optimal policies using different types of advanced control strategies.Mujtaba, Iqbal M.; Aziz, Norashid (University of BradfordDepartment of Chemical Engineering, 2010-07-27)Batch reactor is an essential unit operation in almost all batch-processing industries. Different types of reaction schemes (such as series, parallel and complex) and different order of model complexity (short-cut, detailed, etc. ) result in different sets of model equations and computer coding of all possible sets of model equations is cumbersome and time consuming. In this work, therefore, a general computer program (GBRM - General Batch Reactor Model) is developed to generate all possible sets of equations automatically and as required. GBRM is tested for different types of reaction schemes and for different order of model complexity and its flexibility is demonstrated. The above GBRM computer program is lodged with Dr. I. M. Mujtaba. One of the challenges in batch reactors is to ensure desired performance of individual batch reactor operations. Depending on the requirement and the objective of the process, optimisation in batch reactors leads to different types of optimisation problems such as maximum conversion, minimum time and maximum profit problem. The reactor temperature, jacket temperature and jacket flow rate are the main control variables governing the process and these are optimised to ensure maximum benefit. In this work, an extensive study on mainly conventional batch reactor optimisation is carried out using GBRM coupled with efficient DAEs (Differential and Algebraic Equations) solver, CVP (Control Vector Parameterisation) technique and SQP (Successive Quadratic Programming) based optimisation technique. The safety, environment and product quality issues are embedded in the optimisation problem formulations in terms of constraints. A new approach for solving optimisation problem with safety constraint is introduced. All types of optimisation problems mentioned above are solved off-line, which results to optimal operating policies. The off-line optimal operating policies obtained above are then implemented as set points to be tracked on-line and various types of advanced controllers are designed for this purpose. Both constant and dynamic set points tracking are considered in designing the controllers. Here, neural networks are used in designing Direct Inverse and Inverse-Model-Based Control (IMBC) strategies. In addition, the Generic Model Control (GMC) coupled with on-line neural network heat release estimator (GMC-NN) is also designed to track the optimal set points. For comparison purpose, conventional Dual Mode (DM) strategy with PI and PID controllers is also designed. Robustness tests for all types of controllers are carried out to find the best controller. The results demonstrate the robustness of GMC-NN controller and promise neural controllers as potential robust controllers for future. Finally, an integrated framework (BATCH REACT) for modelling, simulation, optimisation and control of batch reactors is proposed.
Multi-scale modelling describing thermal behaviour of polymeric materials. Scalable lattice-Boltzmann models based upon the theory of Grmela towards refined thermal performance prediction of polymeric materials at micro and nano scales.Not named; Clark, Peter G. (University of BradfordSchool of Engineering, Design and Technology, 2013-12-18)Micrometer injection moulding is a type of moulding in which moulds have geometrical design features on a micrometer scale that must be transferred to the geometry of the produced part. The difficulties encountered due to very high shear and rapid heat transfer of these systems has motivated this investigation into the fundamental mathematics behind polymer heat transfer and associated processes. The aim is to derive models for polymer dynamics, especially heat dynamics, that are considerably less approximate than the ones used at present, and to translate this into simulation and optimisation algorithms and strategies, Thereby allowing for greater control of the various polymer processing methods at micrometer scales.
Physicochemical and tableting properties of crystallised and spray-dried phenylbutazone containing polymeric additives. Effect of polymeric additives (hydroxypropyl methylcellulose and a polyoxyethylene-polyoxypropylene glycol) on the crystalline structure, physicochemical properties and tableting behaviour of crystallised and spray-dried phenylbutazone powdersYork, Peter; Al-Meshal, Mohammed A.S. (University of BradfordPostgraduate School of Studies in Pharmacy, 2010-02-03)The physicochemical properties of a drug affect to a large extent its subsequent biological absorption and bioavailability profile. Considerable pharmaceutical interest is therefore directed torwards the improvement of drug dissolution characteristics of drugs with low aqueous solubility. This thesis has considered the controlled modification of drug dissolution profiles by means of incorporating low concentrations of hydrophilic polymers by different processes into a host drug substance. In order to examine this approach and its potential use, the physicochemical, solid state, stability and tableting properties of a poorly aqueous soluble drug, phenylbutazone, in alternative polymorphic form and containing low levels of two hydrophilic polymers - hydroxypropyl methylcellulose (H. P. M. C. ) and the surfactant poloxamer 188 - prepared by both conventional crystallisation and spray drying are reported. As an integral nart of the work attempts were mado to identify the different polymorphic forms of phenylbutazone. The 6-form, the cammerdiallý 4- available stable ýorm and the a and s metastable forr. s (nomenclature after Huller, 1978).. were isolated. The a form was found to be unstable on storage. A .7 fold increase in intrinsic dissolution rate was observed for the metastable s-polymorph compared with the stable 6-polymorphic form. The effect of crystallisation rate on the formation of polymorphs of phenylbutazone was studied using a mini-spray dryer, and slower rates of crystallisation were found to favour polymorph formation. The hydrophilic polymers, H. P. M. C. and poloxamer 188 were incorporated by conventional crystallisation and spray drying into the drug crystal. Samples were subjected to a series of tests including differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy, and intrinsic dissolution and solubility. When prepared by conventional crystallisation H. P. M. C. was f8und to form a "high energy" complex with phenylbutazone which melted 10 C lower than the parent drug. When prepared by spray drying H. P. M. C. inhibited the formation of the metastable a-polymorph of phenylbutazone. A2 fold increase in intrinsic dissolution rate was observed for crystallised and spray dried samples containing 2% w/w or more added polymer. Poloxamer 188 did not form a complex witý phenylbutazone and unlike H. P. M. C. did not inhibit thejgr gation of the a-polymorph. For both crystallised and spray fo0ld increase in dissolution rate was obtained at polymer levels oý 1% w/w or above. The increase in dissolution has been attributed to facilitated wetting by lowering of interfacial tension rather than through the formation of micelles. The stability of-selected phenylbutazone: polymer samples was tested at elevated temperatures. The stability was found to be affected both by the method of sample preparation and the type of additive. Large breakdowns occurring by a hydrolytic effect were identified for the crystallised phenylbutazone samples containing poloxamer 188. The effects on compact. ion of phenylbu. tazone in alternative form and presence of polymeric additives were studied by compressing samples of similar particle sizes of phenylbutazone as supplied (67form), samples of spray dried phenylbutazone (a-form) and samples containing different concentrations of H. P. M. C. prepared both by conventional crystallisation and spray drying. Compaction data were analysed according to the Heckel relationship and by force transmission ratio as well as from the tensile strengths of prepared tablets. The presence of H. P. M. C. up to 5% w/w concentration in phenylbutazone did not change the mean yield pressure for the crystallised or spray dried samples, although a difference in mean value was observed between the crystallised and spray dried materials, 93.22 MPa and 147.02 MPa respectively. Force transmission was found to be improved for samples containing H. P. M. C. prepared by both techniques and in general, the tablet tensile strengths for crystallised samples containing H. P. M. C. were approximately three times greater than for spray dried samples at equivalent tablet porosity. Differences are attributed to variation in solid state and particulate properties between samples.