W. Harmon Ray’s research while affiliated with University of Wisconsin–Madison and other places

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Publications (175)


Remarks by W. Harmon Ray - Fifty Years of Exciting Times in Chemical Engineering
  • Conference Paper

November 2009

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36 Reads

W. Harmon Ray

The excitement of 50 years of experiences by the speaker as a student, industrial intern, researcher, teacher, and industrial consultant in the evolving field of chemical engineering will provide the basis of this talk. From Sputnik in 1957 (with the resulting tremendous expansion of new ideas and opportunities in research and teaching) up to the present state of our field, there have been many exciting developments in fundamental understanding, in new tools for engineering R&D, and in engineering practice. Some of the developments leading to changes in engineering practice arising from the fields of process modeling, optimization, and control, chemical reaction engineering, and polymerization reaction engineering will be discussed. Working in these fields together with students and senior colleagues has provided a half-century of adventure, satisfaction, and tremendous fun.




Multiplicity and Stability of Chemical Reactors with Evaporative Cooling

June 2008

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70 Reads

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4 Citations

Industrial & Engineering Chemistry Research

This work characterizes the dynamic behavior of reactors with evaporative cooling. The process under consideration is a continuous stirred tank reactor used to carry out an exothermic irreversible first-order reaction with heat removal through the wall as well as by partial evaporation of the reacting liquid followed by return of the condensate to the reactor. Bifurcation analysis is used to classify the stability character and the types of multiplicity and oscillatory behavior to be expected. A variety of practical situations is examined, including cases of volatile reactant, volatile or nonvolatile product (liquid or solid), and volatile solvent. For a fixed vapor flowrate to the condenser, the dynamic structure of reactors with evaporative cooling is qualitatively similar to the case with wall cooling alone. Other cases show significantly different structures. Cases with five steady states and two regions of three steady states are found with evaporative cooling operation, and for some conditions even seven steady states may be possible. A rich variety of dynamic behavior is predicted.


Ethylene and 1‐hexene sorption in LLDPE under typical gas‐phase reactor conditions: Experiments

April 2006

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79 Reads

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69 Citations

Antonin Novak

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The sorption of ethylene and 1-hexene and their mixture in three poly(ethylene-co-1-hexene) samples is measured gravimetrically at temperatures 70, 90, and 150°C and pressures 0–30 bar. Gravimetric sorption measurements are supplemented with microscopic observations of swelling of polyethylene particles caused by sorption and the extent of swelling is found to be significant. Experimental data are compared with predictions of PC-SAFT (perturbed chain—-statistical associating fluid theory) equation of state. Comparison of sorption data in semicrystalline polymer (measured at 70 and 90°C) and amorphous polymer (at 150°C) demonstrates the constraining effect of semicrystalline structure. Solubilities of penetrants in investigated samples are not observed to depend on the content of 1-hexene in copolymers. The solubility of the mixture of ethylene and 1-hexene is smaller than the sum of solubilities of individual components at 70 and 90°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1124–1136, 2006


Dynamic Modeling of Polyethylene Grade Transitions in Fluidized Bed Reactors Employing Nickel−Diimine Catalysts

December 2005

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43 Reads

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26 Citations

Industrial & Engineering Chemistry Research

Dynamic simulations of grade transitions are conducted for an industrial fluidized bed polyethylene reactor using a nickel−diimine catalyst. The reactor process model incorporates a kinetic model that predicts polymer properties for nickel−diimine ethylene polymerization. The relationships between reactor process variables and the end polymer properties are determined to be more complex than for conventional early transition-metal catalysts. In this respect, the kinetic model is demonstrated to be an effective tool for mapping out the reactor steady-state operating regions for a range of polyethylene grades and for examining process issues specific to using these catalysts. Temperature, monomer concentration, and hydrogen composition are the primary manipulated variables for achieving grade transitions in polymer density and melt index. Transitions involving changes in temperature require continual simultaneous adjustment of hydrogen and monomer feed rates to maintain the desired gas composition. Thus, where possible, it is desirable to keep the temperature constant while only changing monomer and hydrogen concentrations when making product transitions to simplify reactor operation. Quick venting and overshoot strategies are demonstrated to aid in improving product transition times. The risk of particle melting is heightened because both temperature and monomer concentration have a large influence on the branching density and the melting point of the polymer.


Mixing effects on performance and stability of low‐density polyethylene reactors

December 2005

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150 Reads

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24 Citations

Imperfect initiator mixing greatly affects the stability and efficiency of low density polyethylene (LDPE) autoclave reactors. A combined simulation technique utilizing compartment models and computational fluid dynamics extends previous work in the literature by providing a physically detailed picture of imperfect mixing. Analysis indicates that the effective volume for chain propagation in the autoclave reactor can expand and contract in a continuous fashion as operating conditions change. As mixing becomes poor, the effective reactive volume decreases, causing a reduction in initiator efficiency, but an expansion in the stable operation region. Examples demonstrate that accurate prediction of the effective reaction volume is crucial for predicting LDPE autoclave reactor behavior. A new mixing model that represents the feed plume by a series of interconnected tanks with geometrically increasing volumes provides a favorable tradeoff between accuracy and model complexity. © 2005 American Institute of Chemical Engineers AIChE J, 2005


Methodology for modeling detailed imperfect mixing effects in complex reactors

May 2005

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151 Reads

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59 Citations

A powerful new modeling technique is presented for exploring mixing effects in reactive flow systems. The technique combines the detailed mixing representation of computational fluid dynamics (CFD) simulations with the simplicity and computational efficiency of stirred-tank compartment models. The method can be generally applied to many reactive systems, and requires only that appropriate criteria be specified to select compartment models from a single converged CFD simulation. A 1000-fold increase in computational speed is achieved by the new compartment model/CFD technique when modeling steady-state operation of low-density polyethylene (LDPE) autoclave reactors, making broad studies of operating conditions and stability possible. Results from compartment models are shown to capture the accuracy and detail of CFD simulations over a wide range of LDPE reactor operation, and the new technique provides a combination of modeling detail and computational ease not previously available for this type of reactor. © 2005 American Institute of Chemical Engineers AIChE J, 2005


Prediction of Polymer Properties in LDPE Reactors

April 2005

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186 Reads

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39 Citations

A new analysis tool is presented that uses the governing kinetic scheme to predict properties of low‐density polyethylene (LDPE) such as the detailed shape of the molecular weight distribution (MWD). A model that captures mixing details of autoclave reactor operation is used to provide a new criterion for the onset of MWD shouldering. Kinetic effects are shown to govern the existence of MWD shoulders in LDPE reactors, even when operation is far from perfectly‐mixed. MWD shoulders occur when the mean reaction environment has a relatively high radical concentration and has a high polymer content, and is at a low temperature. Such conditions maximize long chain formation by polymer transfer and combination‐termination, while limiting chain scission. For imperfectly‐mixed reactors, the blending of polymer‐distributions produced in different spatial locations has a small effect on the composite MWD. However, for adiabatic LDPE autoclaves, imperfect mixing broadens the stable range of mean reactor conditions, and thereby increases the possibility for MWD shouldering. Polymer MWD produced in an LDPE autoclave reactor by various kinetic mechanisms. magnified image Polymer MWD produced in an LDPE autoclave reactor by various kinetic mechanisms.


Kinetic Modeling and Prediction of Polymer Properties for Ethylene Polymerization over Nickel Diimine Catalysts

March 2005

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31 Reads

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16 Citations

Industrial & Engineering Chemistry Research

A kinetic model is developed for predicting the polymerization rate, chain-branching characteristics, and molecular weight from ethylene polymerization over homogeneous and supported nickel diimine catalysts. Seven dimensionless parameter groups are able to describe the polymer properties and kinetic behavior over a broad range of temperatures and pressures. Relative to existing models in the literature, the proposed model is simpler, requires fitting of fewer kinetic parameters, and can be more easily extrapolated over a wide range of reaction conditions. As such, the model can be more readily incorporated into reactor process models for performing dynamic simulations. Experimental data from the literature are used to fit the model kinetic parameters. The model is able to describe the kinetic behavior of both homogeneous and heterogeneous nickel diimine catalysts, and the results compare favorably with existing models in the literature.


Citations (81)


... So, there is a need to be more focused in this direction in order to improve the productivity and economic aspect of the process industries by minimizing the requirement of more chemicals, water IOP Publishing doi: 10.1088/1757-899X/1022/1/012010 2 and man power.This can be achieved by optimizing various design parameters by using various modern control system techniques. ...

Reference:

A Review on Control System Applications in Industrial Processes
Using Knowledge-Based Neural Network Process Models for Model-Based Control
  • Citing Article
  • May 1994

IFAC Proceedings Volumes

... As observed in our previous SMAD model, a sharp drop in the level of functional TGF-β receptors leads to a marked decrease in the activity of receptor-activated SMAD complex. From a control theory perspective, the loss of functional TGF-β receptors corresponds to a reduction in the "process gain," as a result of which only a small portion of the input signal is "transduced" into the response [47,48]. If, in addition to the loss of receptors, receptor internalization is biased toward lipid rafts, then activity of the SMAD complex is reduced even further, to an almost undetectable level. ...

Process Dynamics, Modeling, and Control
  • Citing Book
  • January 1994

... Villa et al first established the dynamics of polymerization reactors with evaporative cooling and wall heat transfer [17] . They showed that the successful design and operation of such reactors, which relies on reflux condensers for heat removal , requires careful consideration of stability issues. ...

Dynamics of Polymerization Reactors with Evaporative Cooling and Wall Heat Transfer
  • Citing Article
  • February 1999

Polymer Reaction Engineering

... Although, the industrial processes are generally nonlinear yet FLC technique has proven to be very effective for it. Scott, Ray (1993) has extensively studied on applications of knowledge-based artificial neural network for various practical solutions of many intricate problems of linear model structures. He cited a comparison between conventional PID and ANN-based control and demonstrated how refining of PID controller using neural networks has been possible. ...

Experiences with model-based controllers based on neural network process models
  • Citing Article
  • December 1993

Journal of Process Control

... Meanwhile, the feed forward and back propagation is the most famous training algorithm to train the ANN [36]. The multilayer perceptron (MLP) feed forward neural network is the commonest prediction architecture [22,37]. The MLP architecture includes one input layer, one output layer and one or more hidden layers depending on the complexity of the problem being examined. ...

Creating efficient nonlinear neural network process models that allow model interpretation
  • Citing Article
  • December 1993

Journal of Process Control

... The wave model has the advantage of providing a low-order approximation that describes the property of interest directly and can be used in model-based control schemes [11,12]. Profile control strategies have also been used for control of packed bed reactors to ensure that the reactor hotspot is below the safety limit, which in turn avoids catalyst deactivation [13,14]. A full profile control of temperature in an FBR has been experimentally demonstrated by Yoshida and Matsumoto [15]. ...

A control scheme for packed bed reactors having a changing catalyst activity profile. I: On-line parameter estimation and feedback control
  • Citing Article
  • December 1992

Journal of Process Control

... Nevertheless, the theory for systems governed by differential algebraic equations (DAEs) is not so well developed and is modestly discussed in the open literature, and the main results available are usually obtained for simple cases, such as those described by index-1 DAE systems. Besides, open and public domain computational codes for nonlinear analysis of DAEs are almost nonexistent in the literature (see, for instance, Hyanek et al., 1995; Kienle, et al., 1995; Ochs et al., 1996; Mangold et al., 2000). ...

Dynamic Flowsheet Modelling of Polymerization Processes Using POLYRED
  • Citing Article
  • June 1996

Computers & Chemical Engineering

... Hence, it is required to obtain using input-output data. An example fascinating this approach is singular value decomposition (SVD) method to estimate Green's function model [97]. The disadvantage concerning this approach is that it provides lower order model only for time-invariant systems. ...

Identification and Control of Distributed Parameter Systems by Means of the Singular Value Decomposition
  • Citing Article
  • May 1995

Chemical Engineering Science

... Several mathematical models have been proposed for the free-radical polymerization of styrene (Berkenwald et al. 2016;Kalfas and Ray 1993;Kovenklioglu 1980;Seyedi et al. 2020; Soriano-Corral and Morales 2011). However, the number of publications discussing silver nanoparticles' effect on the free-radical bulk polymerization of styrene is limited (Soriano-Corral and Morales 2011; Yanagihara et al. 1999;. ...

Modeling and experimental studies of aqueous suspension polymerization processes. 1. Modeling and simulations
  • Citing Article
  • September 1993

Industrial & Engineering Chemistry Research

... Vinyl acetate Semibatch FPE Galerkin Solubility data - [13] Styrene-methyl methacrylate CSTR PB OCM Partition coefficients - [14,15] Vinyl acetate-butyl acrylate Semibatch PB OCM Partition coefficients Yes [16] Sty-butadiene, acrylonitrile-butadiene CSTR 0-1-2 Method of moments Partition coefficients - [17] Vinyl chloride CSTR 0-1-2 Finite volume (not reported) - [18] Vinyl chloride Batch 0-1-2 Finite volume Solubility data - [19] Vinyl chloride Batch 0-1 Finite volume Partition coefficient Yes [20] Styrene, butyl acrylate Batch 0-1/PB Backward finite difference Solubility data Yes [12] Styrene Semibatch FPE Finite volume Morton equation Yes [11] Styrene-butyl acrylate Batch and semibatch PB Fixed pivots Partition coefficients Yes [21] The numerical solution of hyperbolic PDE's is challenging due to the possible presence of steep fronts as in the case of the inviscid Burger's equation representing shock-waves [22]. One way to reduce the set of PDEs to a set of ordinary differential equations (ODEs) in time is using the weighted residual method (MWR) on finite elements, in which the solution in each element is approximated with either first-, second-, or third-order polynomials of the internal coordinate (mass or diameter particle) with time-dependent coefficients [23]. ...

Mathematical Modeling of Emulsion Copolymerization Reactors. I. Model Formulation and Application to Reactors Operating with Micellar Nucleation
  • Citing Article
  • January 1998

Journal of Macromolecular Science Part C- Polymer Reviews