Grade Transition Research Articles

Low‐density polyethylene tubular reactor control using neural Wiener model predictive control

AbstractLow‐density polyethylene (LDPE) is a valued commodity plastic with versatile applications. However, controlling the LDPE polymerization reactor is a challenging task due to its nonlinear behavior and multivariable process and operates in a board operating region. This work aims to develop and explore the neural Wiener MPC (NWMPC) application in controlling the LDPE tubular reactor process. The motivation for NWMPC development originates from its advantage in terms of lower development effort, time, resource, and computational costs compared to nonlinear MPC (NMPC) using the first principle model (FPM). In order to develop the LDPE tubular reactor model, the Aspen Plus and Aspen Dynamic software are used to simulate the process in steady‐state and dynamic form. The neural Wiener (NW) model identification is performed using state space and neural network model identification using Matlab software. The identification result shows the ability of the NW model to identify the nonlinear LDPE tubular reactor process successfully. Furthermore, the NWMPC has outperformed the state space MPC (SSMPC) in controlling grade transition, feed pressure loss, feed impurity disturbance, and heat of polymerization change during the online closed‐loop performance tests. These results signify the ability of NWMPC to handle practical LDPE tubular reactor control scenarios.

Relationships as Malleable Factors for Children’s Social-Behavioral Skills from Preschool to Grade 1: A Longitudinal Analysis

ABSTRACT Social-behavioral functioning during early childhood is associated with children’s academic and social success concurrently and over time. This study explored how concurrent, year-to-year, and sustained parent–teacher and student–teacher relationships predicted children’s social skills and problem behaviors across the preschool to Grade 1 transitions. Participants were 233 children (M = 5.32 years [SD = 0.27] in preschool), their parents, and their preschool (n = 65), kindergarten (n = 116), and first grade (n = 117) teachers enrolled in low-income public schools in rural and urban communities. Research Findings: Children’s relationships with teachers were associated with social-behavioral functioning immediately and over time. Positive, sustained relationships from preschool through first grade predicted social-behavioral benefits. Conflictual relationships related to higher problem behaviors. Parent–teacher relationships as reported by teachers predicted children’s positive social-behavioral functioning in the same year. Parents’ reports of close relationships with teachers predicted more problem behaviors in the following year. Sustained relationships between parents and teachers during the transition from preschool through first grade predicted improved social skills and fewer problem behaviors over time. Practice or Policy: Providing targeted training and support for educators to develop and maintain relationships with students and parents can improve social-behavioral outcomes for children across the preschool to 1st grade transition.

Inferential Model Predictive Control of Continuous Pulping under Grade Transition

Even though continuous pulp processes have been studied for many years, the absence of a model that can accurately describe the evolution of fiber morphology has impeded the application of advanced control techniques. In this study, a multiscale model for continuous Kraft pulping processes, which can capture the spatiotemporal evolution of wood chips and cooking liquor, is developed by integrating a macroscopic model (i.e., Purdue model) with a microscopic model (i.e., kinetic Monte Carlo algorithm). Then, an approximate model is identified to circumvent the high computational requirement of the multiscale model and to handle the input time-delay, followed by designing a soft sensor to infer state variables and primary measurements. This allows the use of an inferential model predictive control strategy in a continuous pulp digester to regulate the blow-line pulp properties (i.e., Kappa number and cell wall thickness) and achieve optimal grade transitions.

Optimization of Polyethylene Grade Transitions in Fluidized Bed Reactors with Constraints on the Polymer Sticking Temperature

In gas-phase polyolefin processes, it is important to evaluate the melting temperature of particles since exceeding this temperature may cause particle sticking and aggregation. In this work, a mod...

Generalized initialization for the dynamic simulation and optimization of grade transition processes using two‐dimensional collocation

AbstractOptimization modeling tools are essential to determine optimal design specifications and operation conditions of polymerization processes, especially when quality indices based on molecular weight distributions (MWDs) must be enforced. This study proposes a generalized MWD‐based optimization strategy using orthogonal collocation in two dimensions, which can capture the dynamic features of MWDs accurately. To enable the strategy, this study considers generalized initialization methods for large‐scale simulation and optimization. Here, a homotopy method based on intermediate solutions is adopted to generate initial values for general steady‐state simulation models, starting from an arbitrary known solution for any steady‐state simulation model. For dynamic simulation models, the response of a first‐order linear system is adopted to initialize the state variables. Case studies show the effectiveness of this procedure to enable systematic, reliable, and efficient solution of the optimization problem.

August 2020 Highlights.

August 2020 Highlights.

The only-child premium and moderation by social origin: Educational stratification in post-reform China

The One Child Policy initiated in the late 1970s created a birth cohort with an unusually high proportion of only children. This paper examines the relationship between being the only child in the family and educational attainment, as well as its potential variations by social origin. Drawing my sample from the China Family Panel Studies, I compare two birth cohorts born before and after the birth-control policy. Results show that in the younger cohort, being the only child in the family produces a premium in educational outcomes, including years of completed schooling and odds of progressing through critical grade transitions. In addition, I observe a pattern that the only-child premium tends to be larger for people with higher social origins in competitive grade transitions.

Thermodynamic Effects on Grade Transition of Polyethylene Polymerization in Fluidized Bed Reactors

AbstractAn off‐line dynamic optimization procedure is employed to optimize the transition between different grades of linear low density polyethylene in a fluidized bed reactor. This type of reactor is frequently operated under condensed mode, which consists of injecting induced condensing agents (ICA) to absorb part of the reaction heat. However, the presence of ICA affects the solubility of monomers in the polymer, so it is important to account for this effect in a grade transition optimization strategy. A kinetic model is combined with a thermodynamic model based on the Sanchez–Lacombe equation of state to describe the grade transitions. Simplified correlations are then suggested to predict the impact of ICA on ethylene and comonomer solubility in a quaternary system. The results highlight the importance of the thermodynamic model during grade transition.

Performance of transition metal-doped CaCO3 during cyclic CO2 capture-and-release in low-pressure H2O vapour and H2O plasma

The effects of transition metal doping of calcium carbonate on the subsequent performance of the material during CO2 release and recapture have been evaluated for calcination under low-pressure (~0.1 mbar) water vapour and water plasma conditions. The initial samples were prepared by precipitation method from analytical grade carbonate, calcium and transition metal (Fe, Co, Zn, Cu and Ni) containing precursors. The release-recapture properties of the sorbents were monitored over five cycles involving calcination at 1200 K and carbonation at 825 K. The most noteworthy effects were observed for the Zn-doped samples, which exhibited rapid CO2 recapture.Calcination in H2O plasma was tested to evaluate the potential for in-situ material processing as a means to counteract material degradation. The impact of plasma exposure during calcination on the looping performance was mixed and dependent on the specific sample composition. The performance of the Zn-doped CaCO3 was consistently improved by plasma calcination, yielding high uptake and better retention of carrying capacity over the five cycles.All samples exhibited a deterioration in carrying capacity over repeated cycles. The Zn-doped samples also performed best in this respect (least loss of carrying capacity). The beneficial effects of Zn-doping were dependent on the Zn-content of the precursor solutions used for material synthesis.

Cannabis cessation among youth: rates, patterns and academic outcomes in a large prospective cohort of Canadian high school students.

Following cannabis legalization in Canada, a better understanding of the prevalence of unprompted cannabis use reduction and subsequent effects on youth academic outcomes is needed to inform harm reduction and health promotion approaches. We analyzed a longitudinally linked sample (n = 91774) from the COMPASS prospective cohort study of Canadian high school students attending Grades 9-12 in Ontario and Alberta between 2013-2014 and 2016-2017. We investigated the prevalence of spontaneous cannabis use reduction and cessation between grade transitions (Grades 9-10, 10-11, 11-12) and the effect of cessation on academic achievement (current or recent math and English course marks) and rigour (usual homework completion and past-month truancy). Only 14.8% of cannabis users decreased their use between grades. Of these, two-thirds made only incremental downward changes, a pattern which held true for all three transitions. Cessation rates from daily and weekly use decreased every year. After cessation, students had better odds than continuing users (OR = 1.23, 95% CI: 1.03- 1.48) and worse odds than never-users (OR = 0.55, 95% CI: 0.31-0.97) for some subcategories of math performance. Students who quit cannabis universally improved class attendance (OR = 2.48, 95% CI: 1.93-3.19) and homework completion (OR = 2.32, 95% CI: 1.85-2.92) compared to continuing users. Increased academic rigour may underlie any improvements seen in academic performance after cannabis cessation. High school students who use cannabis likely need targeted support to facilitate reduction or cessation and subsequent academic recovery. This indicates that a school-based focus on cannabis harm reduction is justified.

MP62-04 ONCOLOGICAL PROGNOSIS AND PATHOLOGICAL FEATURE AFTER RADICAL PROSTATECTOMY ACCORDING TO THE ZONAL ORIGIN OF HIGH GRADE PROSTATE CANCER

You have accessJournal of UrologyProstate Cancer: Staging I (MP62)1 Apr 2020MP62-04 ONCOLOGICAL PROGNOSIS AND PATHOLOGICAL FEATURE AFTER RADICAL PROSTATECTOMY ACCORDING TO THE ZONAL ORIGIN OF HIGH GRADE PROSTATE CANCER Jung Jun Kim*, Sung Kyu Hong, and Seok Soo Byun Jung Jun Kim*Jung Jun Kim* More articles by this author , Sung Kyu HongSung Kyu Hong More articles by this author , and Seok Soo ByunSeok Soo Byun More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000937.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: We assessed the impact of prostatic zone tumor origin on pathological prognostic features and subsequent biochemical outcomes after radical prostatectomy. METHODS: A total of 3,823 patients who underwent radical prostatectomy between 2003 and 2018 were divided into two grade group. A high grade group was defined as Gleason sum ≥ 4+3 and ISUP (International Society of Urological Pathology) groups 3 to 5. A low grade group was defined as Gleason sum ≤ 3+4, and ISUP groups 1/2. The patients was also classified according to the location of index lesion which is transition zone and peripheral zone. The Kaplan-Meier method was used to determine differences in biochemical recurrence-free survival. RESULTS: The presence of high grade index lesion at transition zone cancer was associated with significantly increased prostate specific antigen, tumor volume and incidence of positive surgical margins but a lower incidence of extraprostatic extension, seminal vesicle invasion, lymph node involvement and biochemical failure after radical prostatectomy compared with high grade peripheral zone cancer (Table 1&2). And the outcome was consisitent regardless of surgical margin (Figure). The zonal origin could not differ the recurrence of low grade cases(Table 2). however, the patients with low grade prostate cancer demonstrated good pathology and decent oncological prognosis regardless of tumor origin. CONCLUSIONS: Among high grade cancer, high grade transition zone index lesion independently impact better biochemical outcome in spite of some worse clinical and pathological prognostic factors. To predict prognosis of high grade cancer patients after prostatectomy, the location of index lesion is definitely one of the factor to consider. Source of Funding: None © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e946-e947 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Jung Jun Kim* More articles by this author Sung Kyu Hong More articles by this author Seok Soo Byun More articles by this author Expand All Advertisement PDF downloadLoading ...

Optimal polymer grade transitions for fluidized bed reactors

Industrial polymerization plants experience frequent changes of products, driven by end-use properties to meet various market requirements. Efficient grade transition policies are essential to save time and materials. In this study, the gas-phase catalytic polymerization is modeled in a fluidized bed reactor by a single-phase model, and dynamic optimization is implemented to determine optimal operating sequences for grade changes. Two optimization formulations, a single-stage and a multi-stage formulation, are introduced and compared. The superiority of the multi-stage formulation is demonstrated owing to a better control on each stage during the transition and a further reduction of off-grade time. Subsequently, an on-line optimal control framework is established by incorporating shrinking horizon nonlinear model predictive control with an expanding horizon weighted least-square estimator for process states and unknown parameters. The results of a case study indicate the designed framework is able to handle process uncertainty, while reducing the transition time.

A robustly model predictive control strategy applied in the control of a simulated industrial polyethylene polymerization process

This work investigates the quality control problem of polyethylene grades produced in an industrial polymerization plant. The plant is represented by a phenomenological model previously validated using industrial data. Three advanced control strategies were developed in order to propose strategies capable of dealing with different grades of products. A stability guaranteed [IHMPC (Infinite Horizon Model Predictive Control)] technique and a robust stabilized [RIHMPC (Robust IHMPC)] technique were designed and compared with a conventional MPC. The results show that RIHMPC outperformed the other techniques, providing smoother and faster grade transitions and setpoint tracking. This result provides a significative contribution, since no report of application of RIHMPC on polymerization plants was found. The RHIMPC controller seems to be a promising option for other polymerization reactor control problems in which the diversity of resins produced, coupled with the nonlinear characteristic of the system, lend themselves to the use of different linear models.

Preparation and Properties of Functionalized Lignin-Modified Polyvinyl Alcohol

AbstractA functional lignin-modified polyvinyl alcohol material was prepared by in-situ copolymerization and alcoholysis of vinyl acetate and functional lignin. We then investigated the molecular functional groups, mechanical properties, thermal properties and flame retardancy of the materials by using Fourier-transform infrared spectrometer, universal testing machine, differential scanning calorimeter, thermal gravimetric analyzer, scanning electron microscope, limiting oxygen indexer and horizontal vertical burning tester. The results show that with increase in functional lignin content, the limiting oxygen index, combustion grade and glass transition temperature of the functional lignin-modified polyvinyl alcohol film increased. Both tensile strength and elongation at break increased first and then decreased with increasing functional lignin content. When the functional lignin content was 15 %, these two indices reached their maximum values. As the functional lignin content increased, the melting temperature of the material gradually rose after a sudden drop. When the functional lignin content was 5 %, the melting temperature was the lowest.

Low density polyethylene tubular reactor control using state space model predictive control

One of the conventional commodity polymers in the world is Low density polyethylene (LDPE). LDPE is mostly produced from free radical polymerization of ethylene gas under high pressure and temperature environment. However, the control of LDPE polymerization reactor is challenging due to the complexity of the polymerization process and the nature of the reactor itself. Thus, this study explores the application statespace model predictive control (SS-MPC) in controlling LDPE polymerization tubular reactor process. SS-MPC is a type of model predictive control (MPC) scheme which utilizes state space model as its process model. In general, MPC control scheme has a wide application in the industry due to its ability to handle multivariable control and optimize process performance. In order to implement the control scheme, a dynamic model of the reactor was developed using Aspen Dynamic. The dynamic model is then linked with MATLAB Simulink for online control implementation. The LDPE polymerization process was controlled by regulating the initiator and chain transfer agent (CTA) flowrate to control reactor temperature and polymer Melt Flow Index (MFI) grade. The state space model was identified using identification technique through two approaches; MIMO model and augmented SISO model. In order to evaluate the controller performance, MFI grade transition and disturbance rejection tests are conducted along with PID controller, as a comparison. Based on the tests, MPC had presented a notable performance in handling polymer grade transition (Integral squared error, ISE = 4530) and disturbance rejection (ISE = 99.03) in MFI profile compared to PID controller respond (ISE = 7003 for set point tracking and ISE = 12.66 for disturbance rejection). Nonetheless, PID controller had also presented a comparable performance in controlling maximum reactor temperature.

Preschool transition in Mexico: Exploring teachers' perceptions and practices

This study explored the perceptions of preschool and first grade teachers regarding preschool to first grade transition practices in public schools in Mexico City. A survey was administered to a sample of 15 preschool and 15 primary school teachers, who rated twenty transition practices and answered five open-ended questions. Overall, results revealed that teachers used some practices moderately to promote school-home links but school-school links are not used. Teachers rarely carry out activities with families and other teachers. Teachers' concerns focused on children's academic and personal skills and adaptation to a new routine. Implications for policy and practice are discussed.

Analysis of the environmental impact using the waste reduction algorithm in polypropylene production by applying grade transitions strategies in Colombia.

The global manufacturing sector faces a significant challenge about minimizing environmental impacts without witnessing the adverse effects on the market competitiveness. A cleaner production methodology must involve different approaches for minimizing or recycling waste streams, obtaining at the same time economical and environmental advantages for manufacturing companies (Severo et al., J Clean Prod 142:87-97, 2017). In the polypropylene production process, more than 60 grades of polypropylene are produced. To achieve this target, changes in the process variables are carried out, due to the continuous operation process. Those changes generate a mixture of resins with intermediate properties (transition), which must be minimized. Moreover, failures during the transitions process generate a large extra amount of material that represents a significant impact on the environment, when it is considered as waste. In this paper, an environmental analysis was made by applying a waste reduction algorithm (WAR) to establish the potential impact of a polypropylene production process over the environment, applying grade transitions strategies and then to demonstrate how the improvement of transition times implies a significant reduction of plastic waste. It was found that the reduction of transitions time minimizes the environmental impact based on real industry data. Last should be considered for the real polymer plant analyzed and future projects.

Optimal grade transition of a non-isothermal continuous reactor with multi-objective dynamic optimization approach

Dynamic optimization (DO) is a useful tool for carrying out grade transitions in polymer industry. Most open literature studies on DO emphasize such grade transitions using single objective optimization. However, there are multiple criteria which must be met simultaneously for economic benefits. In this work, we solve a multi-objective DO problem for free-radical polymerization of methyl methacrylate in a non-isothermal continuous stirred tank reactor. The process objectives considered in the DO activity include minimization of off-spec, minimization of grade transition time, and minimization of the averaged feed flowrate. The manipulated variables considered for this problem are the initiator and coolant flowrates. The DO problem is solved using control vector parameterization (CVP) approach with first order interpolation. The solution of the aforementioned multi-objective DO problem is obtained in terms of a trade-off curve, pareto curve, using non-dominated sorting genetic algorithm (NSGA II). The three-dimensional pareto front is then projected to each of the three pairs of the objectives for better visualization and analysis. Furthermore, three representative pareto solution points, namely the two end points and a utopia point are further analysed for of each of the bi-objective pareto solution curves.

A Dynamic Response Surface Model for Polymer Grade Transitions in Industrial Plants

The dynamic response surface methodology (DRSM) has recently been applied to accurately model the dynamics of polymer grade transitions (Wang and Georgakis, Ind. Eng. Chem. Res. 2017, 56, 10770−10782). Following this publication, we propose here two methodological improvements that greatly reduce the required number of experiments and still achieve similar model accuracy. First, a novel design of the experiments is defined to combine the previously separate input domains incorporating transitions that increase and decrease a measure of polymer grade. This enables use of a single DRSM model, instead of the prior two separate ones, and reduces the number of experiments by half. Furthermore, a sequential modeling strategy is proposed, appending experiments to an initial simpler design to estimate a more complex DRSM model. As the desired DRSM model complexity is not known a priori, the sequential modeling strategy is critical in achieving the desired model accuracy with the minimum number of experiments. These methodological advances have been tested against an academic and an industrial process simulation.

Dynamic optimization for grade transition processes using orthogonal collocation on molecular weight distribution

To meet the demands of a competitive market, an industrial plant often produces several grades of polymer product through the same process in an economical way. As molecular weight distribution (MWD) is a crucial quality index of polymers, dynamic optimization for grade transition based on MWD is highly important, but challenging. This study considers the development of optimization models for MWD‐based grade transition. An MWD reconstruction method using orthogonal collocation in two dimensions is developed to capture the dynamic feature of MWD in time and the distributive feature in chain length. The simultaneous collocation approach is adopted to discretize the model. Two optimization formulations are proposed to describe minimizing the transition time as well as off‐spec production. Both formulations inherit the advantages of the simultaneous collocation approach. The numerical results show that the proposed methods can efficiently solve the grade transition problem with MWD specification, and obtain high performance control profiles to reduce the production cost. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1198–1210, 2019