Preparative Chromatography

H. Schmidt-Traub, Michael Schulte, Andreas Seidel-Morgenstern, H. Schmidt-Traub, Michael Schulte, Andreas Seidel-Morgenstern

• Publisher: Wiley-VCH
• Year: 2020
• Print ISBN: 9783527344864
• eBook ISBN: 9783527816330
• Edition: 3
• Topic: Ciencias físicas
• Subtopic: Química industrial y técnica

The third edition of this popular work is revised to include the latest developments in this fast-changing field. Its interdisciplinary approach elegantly combines the chemistry and engineering to explore the fundamentals and optimization processes involved.

1
Introduction

Henner Schmidt‐Traub ¹, and Reinhard Ditz²

¹TU Dortmund Fakultät für Bio‐ und Chemieingenieurwesen, Lehrstuhl für Anlagen‐ und Prozesstechnik, Emil‐Figge‐Str. 70, 44227 Dortmund, Germany

²Bristenstrasse 16, CH 8048 Zürich, Switzerland

1.1 Chromatography, Development, and Future Trends

Ink dripping on a blotting paper thrills children when they realize the rainbow of colors spreading out. It is chromatography, an effect first coined by Tswett (1906) in 1903 for the isolation of chlorophyll constituents. Now, more than a hundred years later, children still enjoy chromatographic effects. Chromatography has developed into an important method for chemical analysis and production of high purity product in micro‐ and macroscale, and today pharmaceuticals are unthinkable without chromatography.

Liquid chromatography (LC) was first applied as a purification tool and has therefore been used as a preparative method. It is the only technique that enables to separate and identify both femtomoles of compounds out of complex matrices in life sciences and allows the purification and isolation of synthetic industrial products in the ton range. Figure 1.1 characterizes the development of chromatography and its future trends.

In the 1960s, analytical high‐performance liquid chromatography (HPLC) emerged when stationary phases of high selectivity became available. At the same time, an essential technology push for preparative chromatography was created by the search of engineers for more effective purification technologies. The principle to enhance mass transfer by countercurrent flow in combination with high selectivity of HPLC significantly increased the performance of preparative chromatography in terms of productivity, eluent consumption, yield, and concentration. The first process of this kind was the simulated moving bed (SMB) chromatography for large‐scale separation in the petrochemical area and in food processing (Broughton and Gerhold 1961).

These improvements were closely coupled to the development of adsorbents of high selectivity. In the 1980s, highly selective adsorbents were developed for the resolution of racemates into their enantiomers. The availability of enantioselective packing in bulk quantities enabled the production of pure enantiomers by the SMB technology in the multi‐ton range. Productivities larger than 10 kg of pure product per kilogram of packing per day were achieved in the following years.

Figure 1.1 Development of chromatography.

Source: Unger et al. (2010). Reproduced and modified with permission of John Wiley and Sons.

In the 1990s, the SMB process concept was adapted and downsized for the production of pharmaceuticals. The development of new processes was necessarily accompanied by theoretical modeling and process simulation, which are a prerequisite for better understanding of transport phenomena and process optimization.

While preparative as well as analytical LC were heavily relying on equipment and engineering and on the physical aspects of their tools for advancement in their fields, the bioseparation domain was built around a different key aspect, namely, selective materials that allowed the processing of biopolymers, for example, recombinant proteins under nondegrading conditions, thus maintaining bioactivity. Much less focus in this area was on process engineering aspects, leading to the interesting phenomenon, that large‐scale production concepts for proteins were designed around the mechanical instability of soft gels (Janson and Jönsson 2010).

The separation of proteins and other biopolymers has some distinctly different features compared with the separation of low molecular weight (MW) molecules from synthetic routes or from natural sources. Biopolymers have an MW ranging from several thousand to several million. They are charged and characterized by their isoelectric point. More importantly, they have a dynamic tertiary structure that can undergo conformational changes. These changes can influence or even destroy the bioactivity in the case of a protein denaturation. Biopolymers are separated in aqueous buffered eluents under conditions that maintain their bioactivity. Moreover, these large molecules exhibit approximately 100 times lower diffusion coefficients and consequently slower mass transfer than small molecules (Unger et al. 2010). Due to these conditions, processes for biochromatography differ substantially from the separation of low molecular weight molecules. For instance, process pressure, which is in many cases much lower for bioprocesses than for HPLC, requires a different plant design. Selectivity makes another difference; due to the very different retention times of biosolutes, an effective separation is only possible with solvent gradients.

Since the 1990s modeling and simulation tools for chromatographic separations of fine chemicals have developed considerably and are meanwhile well established, stimulating the efficiency of practical processes, while bioseparations were mainly based on empirical knowledge because of the complex nature of biomolecules. In the past regulation policies of FDA and other authorities focused on certified process schemes and process conditions as well as quality control by measuring the composition of intermediates and final products in order to guarantee drug safety. This resulted in overregulation and threatened to lead drug production into a dead end. Therefore, FDA started the process analysis technology (PAT) initiative in the 2000s and stated, “The goal of PAT is to enhance understanding and control of the manufacturing process, which is consistent with our current drug quality system: quality cannot be tested into products; it should be built‐in or should be by design” (FDA 2004). PAT implies a paradigm change in pharmaceutical industries and created a momentum for better understanding of processes and products. Meanwhile it is extended by quality by design (QbD), which in summary aims at: “a systematic approach to development that begins with predefined objectives and emphasizes product and process understanding and control, based on sound science and quality risk management” (Yu et al. 2014).

In the recent past countercurrent SMB processes have been highlights of chromatographic separations. With a focus on increased productivity and to make chromatographic separations more economical especially for bioproducts, the SMB principles are becoming a source to create new and more flexible processes with a reduced number of columns. Here the extreme case is a proposal for a SMB‐like process with only one column (Zobel et al. 2014). Process control is another example for improvements. Robust processes are essential for high‐quality products. Prerequisites for all these developments are stable and highly selective stationary phases and reliable equipment and on the other side rigorous models and increased computer power, which enables fast and reliable process simulations.

Peeking into the future reveals a technology trend toward the use of continuous process operations and downstream processing for fine chemicals and especially biopharmaceuticals. Costs and production capacities will have to be addressed, asking for better integrated and efficient approaches. Adapting countercurrent solvent gradient concepts for the isolation of antibodies from complex fermentation broths will allow for more cost‐effective downstream processing of biopharmaceuticals within the next couple of years.

Preparative and large production chromatography in their current major fields of application and scale have reached a level of maturity, which turns it from a breakthrough technology into a commodity. Major future opportunities will be in the field of continuous operation in the form of new SMB variants and especially in combination with other unit operations like extraction, crystallization, precipitation, etc. Such combinations will provide new and viable opportunities in fields like natural and renewable plant‐based products, for example, in healthcare applications and other regulated industries. Work in a variety of applications and combinations is in progress with a focus on regulated products. This, however, is outside and beyond the scope of this book.

1.2 Focus of the Book

The general objective of preparative chromatography is to isolate and purify products in high quality. During this process, the products have to be recovered in the same condition that they were in before undergoing the separation. As preparative chromatographic processes have to produce the target with a desired purity and as economical as possible, they are usually operated under overloaded (nonlinear) conditions.

In contrast to this, analytical chromatography, which is not in the core of this book, focuses on the qualitative and quantitative determination of a compound. Thus, the sample can be processed, handled, and modified in any way suitable to generate the required information, including...

Table of contents

• Cover
• Table of Contents
• Preface
• About the Editors
• List of Abbreviations
• Notation
• 1 Introduction
• 2 Fundamentals and General Terminology
• 3 Stationary Phases
• 4 Selection of Chromatographic Systems
• 5 Process Concepts
• 6 Modeling of Chromatographic Processes
• 7 Determination of Model Parameters
• 8 Process Design and Optimization
• 9 Process Control
• 10 Chromatography Equipment: Engineering and Operation
• Appendix A: Data of Test Systems
• Index
• End User License Agreement