Part
1 Introduction
Part 2 Supercritical
extraction and other high pressure extraction
processes
Part 3 The evaluation
of new supercritical and marginally sub-critical
extraction process
Part 4 Removal of
organic contaminants from streams leaving liquid-liquid
extraction processes
Part 5 Extraction
processes for removing contaminants from effluent
streams
Part 6 Non-dispersive
contacting extraction processes
Part 7 Liquid membranes
Part 8 Safety in
liquid-liquid extraction processes
Volume
SE VII Part 1 Introduction.
This part gives an overview
of the volume and how to use it to best effect.
Volume
SE VII Part 2 Supercritical
extraction and other high pressure extraction processes.
The theoretical principles
underlying the use of supercritical or marginally sub-critical
solvents, often termed near critical, for extraction
are explained. The phase equilibria in systems involving
a near-critical component and the different classes
of systems are described. Phase equilibria in systems
involving a supercritical or near critical component
and methods for classifying the different systems are
discussed. The wide and diverse patent literature on
extraction processes using supercritical and near critical
solvents are reviewed, including such examples as the
extraction of coffee beans, hops, mineral deposits,
coal products, tar-sands and peat. The factors which
need to be considered in selecting a suitable solvent
and equipment are discussed. These include the best
operating conditions, the recovery system, the sizing
of equipment, contactor and ancillary equipment design.
Descriptions are given of methods for determining solubilities,
mass transfer coefficients, densities and viscosities.
A brief economic appraisal of supercritical extraction
processes and plant is given.
Volume
SE VII Part 3 The
evaluation of new supercritical and marginally sub-critical
extraction processes.
Extraction involving the
use of supercritical or marginally sub-critical solvents,
often termed 'near-critical' extraction operations have
aroused considerable interest over the last decade or
so. Some of the advantages to be gained from carrying
out extractions with supercritical or near-supercritical
solvents rather than with solvents in the normal liquid
range are: easier solvent recovery; use of solvents
which are not liquids under normal conditions, for example,
carbon dioxide, ethane and ethylene; a greater range
of selectivities and dissolving power; and solvents
having higher diffusivities and lower viscosities than
the common solvents. This Part recommends a logical
procedure for evaluating potential processes which utilise
supercritical or near-critical solvents. Careful attention
to the details described should provide a basis for
making sound technical decisions on the viability of
supercritical extraction processes. A flow diagram describes
the steps which need to be followed in evaluating supercritical
extraction processes and are then discussed in greater
detail in subsequent chapters. These steps include a
preliminary assessment of the process, the use of theoretical
models for predicting phase equilibrium data, solvent
selection and flowsheet design. Experimental methods
are described for determining phase equilibrium data,
mass-transfer coefficients and physical properties,
which are essential for detailed evaluation. The need
and practicalities for conducting pilot plant studies
are described and the advantages stressed. Some of the
problems which may be encountered in scaling-up equipment
for supercritical extraction processes and ways of overcoming
them are discussed. The final chapter discusses how
to assess the economic viability of supercritical extraction
processes.
Volume
SE VII Part 4 Removal of organic contaminants
from streams leaving liquid-liquid extraction processes.
Methods are described for
controlling the contaminants found in aqueous streams
leaving liquid-liquid extraction plants, so that aqueous
effluents remain within current and proposed legislative
limits. An overview is given of the UK environmental
control requirements, the impact of impending EEC environmental
policy, proposals for scheduled processes and best available
technology, the approach adopted in the USA and the
control of radioactive wastes. Different approaches
to minimise or prevent the production of dissolved contaminants
are discussed and various methods for measurement, detection
and removal are described. The latter include adsorption,
stripping, distillation, extraction, ultrafiltration,
reverse osmosis and pervaporation. Destruction of contaminants
by chemical and biological treatments are also discussed.
Another section discusses the influence of processing
conditions and type of contacting equipment on entrained
liquid and solid contaminants. General principles of
phase separation and a wide range of removal methods
for liquid and solid contaminants are described. These
include gravity separation, centrifugal separation,
coalescers, flotation, membrane processes, demulsification
and filtrations. A final section discusses the economic
aspects of dissolved and entrained contaminants in streams
leaving liquid-liquid extraction processes.
Volume
SE VII Part 5
Extraction
processes for removing contaminants from effluent streams.
The requirement to remove
contaminants from effluent streams, where they may be
present in relatively small concentrations, becomes
more important year by year as concern and legislative
pressure for the quality of the environment grows. At
the same time, many effluent streams contain potentially
valuable constituents the recovery of which could, under
appropriate economic conditions, be advantageous. Liquid-liquid
extraction can be used to reduce the environmental impact
of waste streams and the recovery of usable materials.
The first part of this report is devoted to general
consideration of the interrelated factors involved in
the selection and design of extractive decontamination/recovery
processes, both technical and economic. Subsequent chapters
are devoted to the removal of specific solutes, grouped
by chemical categories; by far the most widely studied
have been organic contaminants, but further chapters
discuss metals and other inorganic materials. In the
final chapter the forward prospects for the application
of this technology are reviewed.
Volume
SE VII Part 6 Non-dispersive contacting extraction
processes.
This part outlines the
state of the art of the use of membranes as interphase
separators in liquid-liquid extraction. This is a recent
area of development, and its links with related technology
such as supported liquid membrane extraction and preparation
are indicated. Following an introduction to the technology,
fundamental aspects of interface stability and mass
transfer in membrane geometries are discussed and the
governing equations given. This is followed by a chapter
on membrane materials, which typically take the form
of sheets or hollow fibres; existing materials are principally
polymeric and have been developed for other applications,
but the potential of inorganic membranes is also highlighted.
Subsequent chapters are devoted to equipment and process
layout, and to inorganic and organic processes which
have been demonstrated in the laboratory. The final
chapter considers the potential for, and challenges
inherent in, further development of the technology.
Volume
SE VII Part 7 Liquid membranes and related technologies.
Liquid
membrane technology offers the potential to combine
the flexibility of solvent extraction with the inherent
energy efficiency of semi-permeable membranes for novel
liquid-liquid separation processes. Two types of liquid
membrane scheme have been proposed: the Liquid Surfactant
Membrane or Dispersed Liquid Membrane, whereby the extractant
forms surfactant-stabilised droplet capsules of double
emulsion, and the Supported Liquid Membrane in which
the extractant is supported by a porous substrate. This
report describes technical, process and economic considerations
in the development of both types of liquid membrane
and their potential applications. The essential concepts
of extraction and stripping between phases separated
by an immiscible extractant layer are discussed and
the individual components of liquid membrane systems
described. The two types of membrane system are described.
For Liquid Surfactant Membranes the management of the
membrane through the cycle of emulsion formation and
breakdown is of key concern, while for Supported Liquid
Membranes membrane geometry and longevity are important.
Potential uses of liquid membranes in hydrocarbon separations,
waste water treatment, hydrometallurgy, biotechnology
and pharmaceuticals are discussed.
Between 1983 and 1998,
the number of applications described in the technical
literature, principally by academic authors, has increased
three-fold. All major new applications have been covered,
as well as significant developments in similar technologies.
Most important among the latter are reversed micellar
extraction systems. In reversed micellar extraction,
spherical membrane entities with a hydrophobic exterior
and hydrophilic interior (the reversed micelles) are
used preferentially to extract sensitive biomolecules
from an aqueous to an organic phase.
Volume
SE VII Part 8
Safety
in liquid-liquid extraction processes.
Liquid-liquid extraction,
like other separation processes, is usually part of
a more complex system which could include storage systems,
reaction vessels, other separation processes, recovery
systems, effluent systems etc.. It is now common practice
that such systems where inflammable, corrosive, potentially
explosive and/or toxic materials are involved, are subject
to various types of safety studies. This is especially
so where the processes involved cannot rely on a long
background history of operation with associated safety
records. The requirement for these safety studies is
due to either, statutory regulations, company policy
or working permit procedures. This report describes
in general the type of safety studies presently being
used in the process industries, the type of data required
for these studies and also a very generalised assessment
of safety related aspects for the wide range of established
liquid-liquid extraction processes and equipment involved.
