Industrial Crystallization Process Monitoring and Control

Angelo Chianese, Herman J. Kramer

• Publisher: Wiley-VCH
• Year: 2012
• Print ISBN:
  9783527331734
• eBook ISBN:
  9783527645176
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Crystallization is an important technique for separation and purification of substances as well as for product design in chemical, pharmaceutical and biotechnological process industries.

This ready reference and handbook draws on research work and industrial practice of a large group of experts in the various areas of industrial crystallization processes, capturing the essence of current trends, the markets, design tools and technologies in this key field. Along the way, it outlines trouble free production, provides laboratory controls, analyses case studies and discusses new challenges.

First the instrumentation and techniques used to measure the crystal size distribution, the nucleation and solubility points, and the chemical composition of the solid and liquid phase are outlined. Then the main techniques adopted to control industrial crystallizers, starting from fundamental approaches to the most advanced ones, including the multivariable predictive control are described. An overview of the main crystallizer types is given with details of the main control schemes adopted in industry as well as the more suitable sensors and actuators.

Chapter 1

Characterization of Crystal Size Distribution

Angelo Chianese

1.1 Introduction

Crystalline population coming out from a crystallizer is characterized by its size distribution, which can be expressed in different ways. The crystal size distribution (“CSD”) may, in fact, be referred to the number of crystals, the volume or the mass of crystals with reference to a specific size range, or the cumulative values of number, volume or mass of crystals up to a fixed crystal size. The first approach refers to a density distribution, whereas the second one to a cumulative size distribution.

However, it is also useful to represent the CSD by means of a lumped parameter as an average size, the coefficient of variation, or other statistical parameters which may be adopted for the evaluation of a given commercial product.

In this section the more usual ways to represent both the whole CSD and the lumped CSD parameters are presented.

1.2 Particle Size Distribution

The particle size distribution may be referred to the density distribution or cumulative distribution. Each distribution may be expressed in number, volume, or mass of crystals.

The cumulative variable, F(L), expresses number, volume, or mass of crystals per unit slurry volume between zero size and the size L, whereas the density distribution function, f(L), refers to number, mass, or volume of crystals per unit slurry volume in a size range, whose average size is L.

The relationship between the cumulative size variable and the density distribution size one is as follows:

1.1

or in the reverse form:

1.2

In Table 1.1 the expression of cumulative and density function variables referred to the number, volume, or mass of crystals is reported.

Table 1.1 Cumulative and density variables.

Examples of number and volume distributions are reported in Figure 1.1.

Figure 1.1 Cumulative and volume crystal size distributions (continuous line for the cumulative distribution and dotted lines for the density distribution).

In spite of the three geometric dimensions of crystals, the CSD is usually referred to just one dimension, the so-called characteristic one, which is related to the adopted measurement technique. In the case of crystal size measurement by sieving the characteristic dimension is the second one, corresponding to the wire mesh length. Otherwise, if a laser diffraction-based analyzer is used, the characteristic dimension is the length given by the instrument, falling between the first and the second crystal dimension.

The most used density distribution variable is the crystal population density, n(L). It can be used to estimate the total number, N_T, the total ...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Preface
• Scope of the Book
• List of Contributors
• Chapter 1: Characterization of Crystal Size Distribution
• Chapter 2: Forward Light Scattering
• Chapter 3: Focused Beam Reflectance Measurement
• Chapter 4: Turbidimetry for the Estimation of Crystal Average Size
• Chapter 5: Imaging
• Chapter 6: Turbidimetry and Nephelometry
• Chapter 7: Speed of Sound
• Chapter 8: In-Line Process Refractometer for Concentration Measurement in Sugar Crystallizers
• Chapter 9: ATR-FTIR Spectroscopy
• Chapter 10: Raman Spectroscopy
• Chapter 11: Basic Recipe Control
• Chapter 12: Seeding Technique in Batch Crystallization
• Chapter 13: Advanced Recipe Control
• Chapter 14: Advanced Model-Based Recipe Control
• Chapter 15: Fines Removal
• Chapter 16: Model Predictive Control
• Chapter 17: Industrial Crystallizers Design and Control
• Index