High‐Pressure Polymerization of Ethylene in Tubular Reactors: A Rigorous Dynamic Model Able to Predict the Full Molecular Weight Distribution

Asteasuain, Mariano; Brandolin, Adriana

doi:10.1002/mren.200900013

Cited by 15 publications

(3 citation statements)

References 24 publications

(46 reference statements)

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“…Grade transition requires changes from one steady state to another to product different final products. During these changes, off‐specification, low‐value products are produced in transient states . To decrease economic losses, plant operators must implement optimal profiles of the manipulated variables.…”

Section: Introductionmentioning

confidence: 99%

A novel strategy for dynamic optimization of grade transition processes based on molecular weight distribution

et al. 2014

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To achieve different end-use properties of polymers, an industrial plant must produce several grades of the product through the same process under different operating conditions. As molecular weight distribution (MWD) is a crucial quality index of polymers, grade transition based on MWD is of great importance. Dynamic optimization of the grade transition process using MWD is a challenging task because of its large-scale nature. After analyzing the relationships among state variables during polymerization, a novel method is proposed to conduct the optimal grade transition using dynamic optimization with a small-scale moment model, combined with a steady-state calculation of the MWD. By avoiding expensive computation in dealing with dynamic MWD optimization, this technique greatly reduces the computational complexity of the process optimization. The theoretical equivalence of this simplification is also proved. Finally, an industrial high-density polyethylene slurry process is presented to demonstrate the efficiency and accuracy of the proposed strategy.

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Section: Introductionmentioning

confidence: 99%

A novel strategy for dynamic optimization of grade transition processes based on molecular weight distribution

et al. 2014

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“…High-pressure tubular reactors, like those well-established in the chemical industry for the generation of low density polyethylene (LDPE), could be an appropriate solution. These reactors consist of several tubes connected together with 180º bends which can reach a total length of 3000 m. High-pressure tubular reactors in a LDPE plant operate at pressures about 300 MPa and temperatures close to 300°C and they can render an annual output of 400,000 tons (Asteasuain & Brandolin, 2009;Kiparissides et al, 2005;Trieb, Karl, & Moderer, 2007). This concept of tubular reactor, especially adapted for high-pressure shift freezing, has been already explored by Otero et al (2007) and Urrutia et al (2007).…”

Section: Industrial Relevance and Feasibility Of The Processmentioning

confidence: 98%

Pressure-shift nucleation: A potential tool for freeze concentration of fluid foods

Otero

Guignon

Martínez

2012

Innovative Food Science & Emerging Technologies

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Pressure-shift nucleation (PSN) has been evaluated as a potential substitute of the crystallization step at the scraped surface heat exchanger in conventional freeze concentration. To do that, PSN experiments were carried out at different pressure and temperature conditions in orange juices of several concentrations. After crystallization, the final concentration reached and the size and shape of the ice crystals formed were measured. The results obtained showed that the higher the pressure and the lower the temperature employed in the PSN experiments, the higher is the final concentration in the juice and the smaller the ice crystals formed. Four important advantages of pressure-shift nucleation over conventional crystallization were found: temperature in the pressure vessel can be relatively high if pressure is increased enough, the desired concentration can be achieved in the whole sample quasi-instantaneously just after expansion, ice crystals produced are round in shape without pockets and indentations and they are homogeneously distributed throughout the sample. Industrial relevance: Freeze concentration is the most advantageous technique to obtain high quality food concentrates without appreciable loss in taste, aroma, color, or nutritive value. However, it is hardly employed in the food industry mainly due to economic aspects of the technology. In the last decades, many efforts have been made to improve the crystallization phase, the most expensive step in freeze concentration, without definitive success. The results obtained in this paper show that pressure-shift nucleation presents a number of advantages over the traditional crystallization step at the scraped surface heat exchanger which can be exploited to improve the industrial freeze concentration process.

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“…It does not assume a priori any shape of the distribution and can be applied to different systems, even those described by complex kinetic mechanisms. It has provided excellent results in terms of accuracy, simplicity of implementation, and computational effort, in models for simulation and optimization activities 15–21. In its previous state of the art, this technique employed univariate pgfs, which allowed modeling a one‐dimensional distribution.…”

Section: Introductionmentioning

confidence: 99%

Mathematical Modeling of Bivariate Polymer Property Distributions Using 2D Probability Generating Functions, 1 – Numerical Inversion Methods

Asteasuain

Brandolin

2010

Macro Theory & Simulations

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This is the first of two papers presenting a new mathematical method for modeling bivariate distributions of polymer properties. It is based on the transformation of the infinite mass balances describing the evolution of a two‐dimensional distribution using 2D probability generating functions (pgf). A key step of this method is the inversion of the transforms. In this work, two numerical inversion methods of 2D pgfs are developed and carefully validated. The accuracy obtained with both methods was very satisfactory. The inversion formulas of both methods are simple and easy to implement. A simple copolymerization example is used to show the complete procedure from the derivation of the pgf balances to the recovery of the bivariate molecular weight distribution.magnified image

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High‐Pressure Polymerization of Ethylene in Tubular Reactors: A Rigorous Dynamic Model Able to Predict the Full Molecular Weight Distribution

Cited by 15 publications

References 24 publications

A novel strategy for dynamic optimization of grade transition processes based on molecular weight distribution

A novel strategy for dynamic optimization of grade transition processes based on molecular weight distribution

Pressure-shift nucleation: A potential tool for freeze concentration of fluid foods

Mathematical Modeling of Bivariate Polymer Property Distributions Using 2D Probability Generating Functions, 1 – Numerical Inversion Methods

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