Polymerisation of Ethylene: In Slurry Loop Reactors

by Paul Allemeersch

Overview

This book presents all information necessary to understand the functioning of a slurry loop reactor for the polymerisation of ethylene into high density polyethylene, and to operate it accordingly. All discussions are based on experimental data from the operation of full scale commercial loop reactors.
Methods for off-line modelling and scaling-up from lab to full scale are included, as well as the answers to important questions on the running of two loop reactors in series.
Building knowledge from full scale industrial experience. This highly accessible book makes one understand the functioning of slurry loop reactors for the polymerisation of ethylene, and how to operate them.
Its methods include off-line modelling, scaling-up and running reactors in series. It is inspiring for all production and process engineers, showing, for the first time, how with full scale reactor data the link is made between firm basic theory and the most practical operating guidelines.

Product Details

ISBN-13:	9783110292145
Publisher:	De Gruyter
Publication date:	01/29/2015
Pages:	206
Product dimensions:	6.69(w) x 9.45(h) x 0.03(d)
Age Range:	18 Years

About the Author

Paul Allemeersch, Tessenderlo, Belgium.

Table of Contents

Preface vii

1 Introduction 1

2 The Loop Reactor Circulation Pump Power 4

2.1 Circulating Pure Liquid 4

2.2 Circulating the Slurry 6

2.3 Upsets in Pump Power 9

2.3.1 Realistic Pump Power Curve 9

2.3.2 Reactor Fouling 10

2.3.3 Hot Spots 12

3 The Functioning of the Settling Legs 19

3.1 Functioning of the Settling Legs 20

3.1.1 Description and Definitions 20

3.1.2 The Overall Reactor Mass Balance 22

3.1.3 The Volumetric Output Equation 23

3.1.4 Solids Removal Rate Equation 24

3.2 Correlations for the Settling Velocity 25

3.2.1 General Correlation 25

3.2.2 Specific Correlations 27

3.2.3 Correlation with the Terminal Falling Velocity 28

3.3 Control of the Solids Concentration in the Loop Reactor 29

3.3.1 The Solids Concentration Control Equation 29

3.3.2 Control of the Solids Concentration 30

3.3.3 Stability of the Solids Concentration Control 32

4 The Settling of the Polymer in the Settling Legs 36

4.1 Description and Definitions 37

4.2 Kynch's Sedimentation Theory 38

4.3 Growth Rate of the Zone of Thickened Slurry 40

4.4 Settling Behaviour of the Polymer 41

4.5 Maximum Filled Fraction of the Settling Legs 45

4.6 Settling Legs with a Change in Diameter 46

5 Catalyst Activity and Productivity 51

5.1 The Polymerisation Reaction 51

5.2 Polymerisation Rate Equation 54

5.3 Catalyst Activity 56

5.4 Catalyst Reactor Productivity 57

5.5 Catalyst Reactor Productivity in a Batch Reactor 58

6 The 1/1 Hypothesis 62

6.1 Silica Gel Particles 62

6.2 Catalyst Particle Fragmentation 64

6.3 Particle Productivity 66

6.4 Balance for the Number of Particles 66

6.5 Verification of the 1/1 Hypothesis 68

7 Catalyst Residence Time Distribution 73

7.1 Definitions and Assumptions 73

7.2 Perfect Mixing of the Catalyst 75

7.3 Catalyst Activity 76

7.4 Catalyst Reactor Productivity 78

7.5 Mass of Polymer Present in the Reactor 79

7.6 Catalyst Residence Time Distribution 80

7.7 Mass Balance for the Polymer 82

7.8 Measurement of the Catalyst RTD in the Loop Reactor 83

7.8.1 Cumulative RTD and Response to a Step Signal 84

7.8.2 Experiment 84

8 Catalyst Activity Profiles 88

8.1 Catalyst Activity Profiles 88

8.2 Catalyst Productivity Curve and Activity Profile 89

8.3 Particle Productivity 91

8.4 Experimental Results for Activity Profiles 92

8.5 Induction Time 96

9 Conversions 98

9.1 Calculating Conversions from Full Scale Reactor Data 98

9.2 The Conversion of Ethylene 100

9.3 The Conversion of Hydrogen 103

9.3.1 Hydrogen to Ethylene Ratios 103

9.3.2 Calculating the Hydrogen Conversion 104

9.4 The Conversion of 1-Hexene 106

9.4.1 1-Hexene to Ethylene Ratios 106

9.4.2 Calculating the 1-Hexene Conversion 108

9.5 Conversions and Polymer Properties 110

9.5.1 Correlations for Melt Index 110

9.5.2 Incorporated 1-Hexene and Density 111

9.6 In-situ Generation of 1-Hexene 114

9.7 Optimisation of Reactor Conditions 116

10 Ethylene Concentration Profile in the Loop 120

10.1 Reactor Geometry 120

10.2 Slurry Flow in the Reactor 121

10.3 Catalyst Activity 122

10.4 Rate of Reaction along the Loop 124

10.5 Ethylene Concentration Profile 125

10.6 Increasing Production Rates 128

11 Simple Reactor Model 132

11.1 Elements to Build the Model with 133

11.1.1 Overview of the Variables 133

11.1.2 Independent Variables 134

11.1.3 Dependent Variables 136

11.1.4 The Use of Conversions 137

11.2 Simplifying Assumptions 137

11.3 Mathematical Relations 138

11.3.1 Polymer Properties 138

11.3.2 Conversions 139

11.3.3 Physical Properties 140

11.3.4 Catalyst Activity 141

11.3.5 Flash Gas Flows 141

11.3.6 Reactor Feeds 142

11.3.7 Constraints 142

11.4 A Corrective Offline Model 143

12 Correlations by Linear Regression 147

12.1 The Data Set 147

12.2 Building the Data Set 152

12.3 Establishing the Correlations 154

12.3.1 Inspection of the Data Set 154

12.3.2 Cluster Analysis 154

12.3.3 Pearson Correlation Coefficients 156

12.3.4 Establishing the Correlation by Linear Regression 157

13 Scaling-Up from Bench to Loop 161

13.1 Bench Reactor Polymerisation Tests 161

13.2 Variables in Bench Reactor Tests 162

13.3 Catalyst Activity 165

13.4 Data Set and Correlations 167

13.5 From Bench Scale Variables to Loop Conditions 168

13.5.1 Type and Composition of the Catalyst 168

13.5.2 Ethylene Concentration 168

13.5.3 Reactor Temperature 169

13.5.4 Catalyst Activation Temperature 169

13.5.5 Hydrogen Concentration 169

13.5.6 Comonomer Concentration 170

13.5.7 Dosage of the Cocatalyst 171

13.5.8 Comparing Bench Results to Full Scale Loop Data 172

13.6 Molecular Weight Distributions 172

14 Two Loop Reactors in Series 177

14.1 Mass of Polymer Present in the Second Reactor 177

14.2 Residence Time Distribution in the Second Loop 178

14.3 Total Residence Time in Two Loop Reactors 180

14.4 Catalyst Productivity in a Second Loop Reactor 181

14.5 Bimodality Distribution 183

14.5.1 Ideal Bimodality Distribution 184

14.5.2 Realistic Bimodality Distribution 186

Index 193