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Extraction of Natural Products Using Near-Critical Solvents
Extraction of Natural Products Using Near-Critical Solvents
Edited by
M.B. KING and T.R. BOTT School of Chemical Engineering
University of Birmingham
Published by Blackie Academic & Professional, an imprint of Chapman & Hall, Wester Cleddens Road, Bishopbriggs, Glasgow G64 2NZ
First edition 1993
© Springer Science+Business Media Dordrecht 1993 Originally published by Chapman & Hall in 1993 Softcover reprint of the hardcover 1st edition 1993 Typeset in 10/12 pt Times New Roman by Pure Tech Corporation, Pondicherry, India
ISBN 978-94-010-4947-4 ISBN 978-94-011-2138-5 (eBook) DOI 10.1007/978-94-011-2138-5
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page.
The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.
A catalogue record for this book is available from the British Library
Preface
The aim of this book is to present the current state of the art of extracting natural products with near-critical solvents and to view the possibilities of further extensions of the technique. Relevant background theory is given but does not dominate the book. Carbon dioxide is the near-critical solvent used in most recent applications and inevitably receives prominence. In addition to general descriptions and reviews, the book contains three chapters by industrial practitioners who describe in detail the operation of their processes and discuss the market for their products. Sections on the design of the pressure vessels and pumps required in these processes and on the acquisition of the data required for design are included. The costing of the processes is also discussed.
There is good scope for combining a near-critical extraction step with other process steps in which the properties of near-critical solvents are utilised, for example as a reaction or crystallisation medium and a chapter is devoted to these important aspects.
It is hoped that the work will be found to contain a great deal of specific information of use to those already familiar with this field. However the style of presentation and content is such that it will also be useful as an introduction. In particular it will be helpful to those wondering if this form of separation method has anything to offer for them, whether they are engineers, chemists or managers in industry, or in academic or research institutions.
Acknowledgements
M.B. King T.R. Bott
We wish to thank the many people including postgraduate students, postdoctorate fellows. visitors and colleagues who have worked with us on near-critical fluids. We also wish to thank Distillers MG Limited for their supply of carbon dioxide and for their friendly support and encouragement.
If it had not been for the above contributions. it would not have been possible for us to have conceived this book and we dedicate it gratefully to all the above helpers and co-workers.
Contents
1 Introduction 1 M.B. KING and T.R. BOTT
1.1 Compressed and liquefied gases as solvents: the commercial applications I 1.2 The scope of the book 3 1.3 Range of solvent conditions regarded as 'near-critical' 4 1.4 Range of available solvents 5 1.5 Range of components present in natural products: typical phase behaviour with
near-critical carbon dioxide and similar near-critical solvents 10 1.5.1 Classification of phase behaviour in systems containing a near-critical
component 10 1.6 Role of solvent density 19 1.7 Possible and actual process layouts 23 1.8 Advantages in use of near-critical solvents: future prospects 26 Appendix: Some historical notes 28 References 31
2 Food legislation and the scope for increased use of near-critical fluid extraction operations in the food, flavouring and pharmaceutical industries N. SANDERS
34
2.1 Introduction 34 2.2 Solvent extraction of foodstuffs and flavourings: legal restrictions on solvents
used and residual solvent levels 34 2.3 Widening the choice of extraction solvent: compressed and liquefied gases
as solvents: economic and other problems in their use 37 2.4 Use of carbon dioxide for dense gas extractions: 'rule of thumb' solubility rules 40 2.5 Actual and proposed applications of extractions using dense C02: tabular review
of the literature 43 2.5.1 Future applications 45
References 48
3 Other uses for near-critical solvents: chemical reaction and recrystallisation in near-critical solvents M.H.M. CARALP, A.A. CLIFFORD and S.E. COLEBY
3.1 Chemical reaction in near-critical solvents 3.1.1 Optimising physical properties and phase behaviour 3.1.2 Supercritical fluids in the critical region as reaction media 3.1.3 Supercritical fluids as continuum solvents 3.1.4 Transition state theory and supercritical fluids
3.2 Recrystallisation in near-critical solvents 3.2.1 Recrystallisation by pressure reduction 3.2.2 Recrystallisation by other methods
References
50
50 51 61 67 69 76 76 79 80
viii CONTENTS
4 Commercial scale extraction of alpha acids and hop oils with compressed CO2 84 D.S. GARDNER
4.1 Introduction, composition and brewing value of hops 4.1.1 Composition 4.1.2 Varietal differences
4.2 Convenience of hop extracts 4.2.1 Organic solvents originally used for preparing hop extracts
4.3 Advantages of compressed CO2 over conventional organic solvents for the extraction of hops: extraction plant using this solvent 4.3 .1 The advent of C02 extraction plant 4.3 .2 Extraction plant utilising liquid CO2 4.3.3 Supercritical CO2 extraction 4.3.4 Relative merits of liquid and supercritical C02 as extraction solvents
for hops 4.4 Conclusions References
5 Commercial scale decatTeination of coffee and tea using supercritical CO2
E. LACK and H. SEIDLITZ
5.1
5.2
5.3
5.4
Introduction: the extent of coffee and tea production worldwide and the need for decaffeination 5.1.1 Processing of raw coffee and tea: caffeine levels and the effects
of caffeine Present-day demand for decaffeinated products and trends in the market 5.2.1 Decaffeinated coffee consumption in the USA 5.2.2 The decaffeinated coffee market in Europe Brief description of the currently used processes for decaffeination and their history 5.3.1 Examples of processes for decaffeinating coffee using organic
solvents 5.3.2 Water decaffeination of coffee beans 5.3.3 Decaffeination processes which use compressed CO2 as solvent 5.3.4 Tea decaffeination Decaffeination with compressed CO 2 5.4.1 Advantages of supercritical CO2 as a decaffeination solvent 5.4.2 General description of the basic COz-based coffee decaffeination
84 84 87 87 89
89 91 91 95
97 99
100
101
101
101 105 105 106
107
109 110 111 111 111 112
processes 112 5.4.3 Proposed modifications to the basic coffee extraction schemes 119 5.4.4 Process for the continuous extraction of green coffee beans with
compressed C02 121 5.4.5 Decaffeination of tea with supercritical CO2 122
5.5 The patent literature for decaffeination processes 123 5.6 Comparison of economic aspects of the COz-based and ethylacetate-based
decaffeination processes 125 5.7 Technical aspects of plant design 129
5.7.1 CO2 recovery system 129 5.7.2 Caffeine recovery systems 132 5.7.3 Extractor vessel and internals 132 5.7.4 Plant safety and control 136
5.8 Conclusions 137 References 138
CONTENTS ix
6 Extraction of flavours and fragrances with compressed CO2 140 D.A.MOYLER
6.1 Introduction 6.2 The properties of CO2 as an extraction solvent
6.2.1 'Naturalness' 6.2.2 Selectivity 6.2.3 Use of entrainers to enhance solubilities in CO 2 6.2.4 Stability of extract and the role of lipids
6.3 The raw materials 6.3.1 Origins 6.3.2 Crop to crop variations 6.3.3 Storage and pretreatment prior to extraction
6.4 Equipment 6.4.1 Laboratory scale equipment 6.4.2 Equipment for extraction with liquid CO2 on a commercial scale 6.4.3 Commercial extraction with supercritical CO2
6.5 Commercial use of C02 extracts since 1982 6.6 Conclusions Appendix: COz-extracted flavour and fragrance ingredients References
7 Physico-chemical data required for the design of near-critical fluid extraction process M.B. KING and O. CATCHPOLE
7.1 The need for physico-chemical data 7.2 Phase equilibria
7.2.1 Types of phase behaviour of components typically present in natural products: typical solubilities
7.2.2 Use of equations of state and other methods for collating phase equilibrium data for systems with a near-critical component (the solvent)
7.2.3 Other correlation techniques: the Chrastil-Stahl correlation 7.2.4 Experimental determination of phase equilibria in systems containing a
near-critical component 7.3 Mass transfer rate parameters
7.3.1 Modelling mass transfer processes 7.3.2 Diffusion coefficients
Appendix: The fluid mass balance equations References
8 Design and operation of the pressure vessels used in near-critical extraction processes R. EGGERS
140 141 142 142 147 147 148 148 148 149 149 149 lSI 153 156 157 158 178
184
184 185
185
186 206
207 209 209 220 225 228
232
8.1 Introduction 232 8.2 .C1assification of pressure vessels 232
8.2.1 Influence of process type on pressure vessel requirements 232 8.2.2 Classification of pressure vessels according to method of construction 234 8.2.3 Relative merits of multilayer and thick solid-walled vessels 237 8.2.4 Examples of solid-walled and multilayer extraction vessels 240
8.3 Vessel design 241 8.3.1 Process engineering criteria: sizing the vessels 241 8.3.2 Construction 244 8.3 .3 Closure systems 247 8.3.4 Inner fittings and baskets 252
x CONTENTS
8.4 Operation of the pressure vessels in a near-critical extraction plant 254 8.4.1 Columns 254 8.4.2 Operation of the extraction vessels 255 8.4.3 Pressure release and CO 2 recovery 255
8.5 Design and development of equipment for the continuous extraction of solids 257 References 259
9 Pumps and compressors for super critical extraction G. VETTER
9.1 Introduction 9.2 Process requirements
9.2.1 Continuous extraction processes 9.2.2 Discontinuous extraction processes
9.3 Pumps for liquids 9.3.1 Pump characteristics and selection of the best type of pump 9.3.2 Reciprocating pumps 9.3.3 Centrifugal pumps
9.4 Compressors for gas recovery References
261
261 262 263 264 265 265 271 290 296 297
10 Estimation of separation cost 299 M.B. KING, O.J. CATCHPOLE and T.R. BOTT
10.1 Introduction 299 10.2 Energy and economic assessment of near-critical extraction processes 301 10.3 Extraction with a marginally subcritical solvent 301
10.3.1 Process layout 301 10.3.2 Energy consumption 303 10.3.3 Mass transfer considerations 305 10.3.4 Capital versus energy costs 305
10.4 Extraction with supercritical solvent 307 10.4.1 Separation by pressure reduction followed by recompression 308 10.4.2 Separation by temperature change 309
10.5 Energy and other costs in some typical cases 309 10.6 Example of preliminary costing 310
10.6.1 Energy consumption and heat exchanger duties 311 10.6.2 Installed capital costs of the compressor, extraction towers and
product separator 312 10.6.3 Estimation of separation cost 317 10.6.4 Discussion 317
References 319
Index 321
Contributors
Dr T.R. Bott School of Chemical Engineering, University of Birmingham, Birmingham B 15 2TT, UK
Dr M.H.M. Caralp School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
Dr O. Catchpole Industrial Research Limited, Lower Hutt, New Zealand
Dr A.A. Clifford School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
Dr S.E. Coleby School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
Professor R. Eggers Technische Universitat Hamburg-Harburg, Verfahrenstechnik II, Eissendorfer Strasse 38, Postfach 901403, 2100 Hamburg 90, Germany
Dr D.S. Gardner English Hops Ltd, Paddock Wood, Tonbridge, Kent
Dr M.B. King School of Chemical Engineering, University of Birmingham, Birmingham B 15 2TT, UK
Dr E. Lack Schoeller-Bleckmann Gesselschaft mbH, Verfahrenstechnik, Haupstrasse 2, A2630 Ternitz, Austria
Mr D. Moyler Universal Flavors Ltd, Bilton Road, Bletchley, Milton Keynes MKI IHP, UK
Mr N. Sanders Reading Scientific Services Ltd, The Lord Zuckerman Research Centre, Reading University, Whiteknights, Reading RG6 2LA, UK
Dr H. Seidlitz Schoeller-Bleckmann Gesselschaft mbH, Verfahrenstechnik, Haupstrasse 2, A2630 Ternitz, Austria
Professor Dipl.-Ing. G. Vetter Lehrstuhl fur Apparatetechnik und Chemiemaschinenbau, Universitat ErlangenNurnberg, Couerstrasse 4, 8520 Erlangen, Germany
