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1993 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Extraction of Natural Products Using Near-Critical Solvents

herausgegeben von: M. B. King, T. R. Bott

Verlag: Springer Netherlands

Enthalten in: Professional Book Archive

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Über dieses Buch

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 indus­ trial 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.

Inhaltsverzeichnis

Frontmatter
1. Introduction
Abstract
If the pressure is raised sufficiently, many substances which are gaseous at ambient pressure either liquefy or begin to behave like liquids in that they exert appreciable solvent power, even for solutes of low volatility. For example, at temperatures up to 31.06°C (the critical temperature) carbon dioxide can be liquefied by raising the pressure (Figure 2.1) and this liquid can be used to dissolve natural oils and quite a wide range of non-polar or slightly polar materials. Many of these are natural products and several commercial processes are based on this solubility behaviour. For example liquid CO2 has been used commercially as a solvent for obtaining hop extracts since 1980 (chapter 4). Liquid propane has also been used for extracting natural products: at one time there were about five commercial plants in use for extracting natural oils by the propane-based ‘Solexol’ process. (see appendix to this chapter). Propane has the disadvantage of being a fire-hazard, but it is a more powerful solvent than carbon dioxide and the pressures required when using it as a solvent are usually lower. Although not an example of the extraction of a natural product (the natural products considered in this book are of recent vegetable origin), it is relevant to remember the existence of the propane-based process for de-asphalting petroleum. This has been widely used since the 1930s.
M. B. King, T. R. Bott
2. Food legislation and the scope for increased use of near-critical fluid extraction operations in the food, flavouring and pharmaceutical industries
Abstract
The food, flavouring and pharmaceutical industries have become increasingly safety conscious over the years and the safety of both producers and consumers is now a major requirement of any new product. This is evidenced by the complexity of the testing procedures which are now applied to new products prior to their introduction into the market-place, particularly in the pharmaceutical industry. It is not uncommon for a new pharmaceutical product to take 10 years to come to the market-place. The situation is slightly less rigorous for the food industry, but the trend is towards adopting similar standards to those presently applied to pharmaceutical products.
N. Sanders
3. Other uses for near-critical solvents: chemical reaction and recrystallisation in near-critical solvents
Abstract
The use of supercritical fluid and near-critical solvents as media for physical separation techniques has expanded significantly over the last decade and a half. Their potential application as reaction solvents, whilst often exploiting the same physico-chemical properties, is an interesting branch of technology which has taken rather longer to achieve recognition, and for which a large body of fundamental knowledge is still being acquired. Process development is nevertheless taking place in a number of countries [1] usually under conditions of confidentiality. This includes the potentially important area of the clean-up of industrial effluent in supercritical water [2], where a wide variety of compounds are found to be rapidly oxidised to simple products [3]. There is a plant now on stream in Japan, with a capacity of 40 000 tonnes per annum, for the production and separation of methyl ethyl ketone [4]. On the other hand, polymerisations such as that of ethylene, which were early examples of processes which can be classified as supercritical when carried out under high pressure, are now increasingly done catalytically at low pressure.
M. H. M. Caralp, A. A. Clifford, S. E. Coleby
4. Commercial scale extraction of alpha-acids and hop oils with compressed CO2
Abstract
By the end of the 19th century, the dual properties of the flavour and preservative value of hops had become the subjects of investigation by chemists. In the 1880s the effect of the hop resins on beer spoilage bacteria had been demonstrated [1, 2] and later their influence on some pathogenic organisms [3]. The resin fractions designated alpha and beta were separated and their bactericidal activities compared [4]. For a while, the resin content of a hop was used as an indication of preservative value (P.V.). It was found that the resins contained the bitter principles while the aroma was predominantly due to the essential (volatile) oil.
D. S. Gardner
5. Commercial scale decaffeination of coffee and tea using supercritical CO2
Abstract
Coffee and tea both contain caffeine and are the most widely used stimulants in our society. They are valued all over the world either as day-to-day drinks or as semi-luxury beverages. In consequence, raw green coffee and tea together constitute, after wheat, the world’s second largest cultivated crop. In 1990, for example, the world production for green coffee was about 5.5 million tons, the most important cultivation areas being in South America and Africa. About 70% of this production was exported to Europe (2.5 millions tons) and North America (1.5 million tons). The market in Asia is much smaller, but is increasing particularly in Japan. Agreements regulating the international coffee trade are described by McClumpha [1]. These are designed to stabilise the market which can suffer from periods of oversupply and then shortage brought about, for example, by frost or drought damage in a major producing area.
E. Lack, H. Seidlitz
6. Extraction of flavours and fragrances with compressed CO2
Abstract
As pointed out in chapter 2, most of the organoleptic compounds, i.e. the compounds responsible for aroma, flavour and taste, are soluble in liquid CO2. (These compounds tend to be comparitively volatile with molecular weights normally below about 250.) Virtually all are soluble in supercritical CO2, though this solvent also extracts some unwanted compounds and involves the use of higher temperatures.
D. A. Moyler
7. Physico-chemical data required for the design of near-critical fluid extraction process
Abstract
Before the chemical engineering design of a proposed process can be initiated, values (or good estimates) will be required for a number of physico-chemical properties both for the pure components (these are usually comparatively easy to find) and the relevant mixtures. Extraction processes involving near-critical solvents are no more and no less demanding than other, more conventional, processes in this respect. Figures 1.16, 1.17 and 1.18, for example, and also 9.2 and 9.3 show simplified layouts for possible processes for extracting beds of solids or liquid streams with a near-critical solvent. In these cases the disengagement of the solute from the solvent gas is achieved by a throttling expansion. When carrying out the chemical engineering design of simple processes of this type, phase equilibria will be required for mixtures of the near-critical solvent with the material in the extractors and also for the solvent/solute mixtures in the separator. Mass transfer rate data will be required for sizing the continuous extractors in Figure 1.18 and 9.2. They will also be required in evaluating the performance of the extractor units (V1, V2, V3 in Figure 10.2 or 5 in Figure 9.3) used in the batch extraction of beds of solids.
M. B. King, O. Catchpole
8. Design and operation of the pressure vessels used in near-critical extraction processes
Abstract
Industrial processes proposed for the extraction of natural products with near-critical solvents work in a pressure range between 50 bar and 500 bar, and in some exceptional cases up to 1000 bar. Therefore this type of extraction must be regarded as a high pressure process. The pressure vessels are very important, since it is in these that the initial extraction takes place and also in which the saturated solvent is separated from the product. The design and operation of the pressure vessels have a decisive influence on the successful performance of equipment for extracting natural products with near-critical solvents. While the calculation of the necessary wall thicknesses is based on well-established codes of practice for pressure vessels, the mechanical design and especially the operation itself are specific to the type of extraction process considered.
R. Eggers
9. Pumps and compressors for supercritical extraction: design, characteristics and installation
Abstract
Supercritical extraction processes entail pumping, ducting and metering the flow of fluids over a very wide range of conditions. These may range from pressures not far above the vapour pressure of the subcritical fluid in the solvent recovery stage, to pressures upwards of 400 bar for the supercritical fluid in the main extraction unit. This range of conditions is almost unique to supercritical extraction processes, although there are on the horizon additional potential applications for supercritical fluids and these will require similar high pressure pumps and compressors [1–5]. These potential applications include the use of supercritical reactions and also the production of fine powders and other deposits by controlled expansion of solutions in supercritical solvents (see chapter 3). High pressure machinery, such as pumps and compressors, are at the very core of all high pressure plant, and influence the economy, safety and reliability of the plant in a most important manner [6].
G. Vetter
10. Estimation of separation cost
Abstract
Most recent papers on the economic evaluation of near-critical extraction processes have been concerned with semi-continuous processes for extracting materials from a solid matrix and the example given in the second half of this chapter is for the evaluation of separation cost for a process of this type. However, some costings have been carried out for continuous processes in which the feed is liquid (see, for example references [1, 2]. Although the process details are very different, the pressures involved are similar as are the problems involved in costing the plant and evaluating energy and other running costs.
M. B. King, O. J. Catchpole, T. R. Bott
Backmatter
Metadaten
Titel
Extraction of Natural Products Using Near-Critical Solvents
herausgegeben von
M. B. King
T. R. Bott
Copyright-Jahr
1993
Verlag
Springer Netherlands
Electronic ISBN
978-94-011-2138-5
Print ISBN
978-94-010-4947-4
DOI
https://doi.org/10.1007/978-94-011-2138-5