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(c) 1995 John Wiley & Sons Inc. All rts. reserv.
404590000 Summary
Chapter CH=40459
Type TY=404590
Unit UN=404590000
Chapter Title: CARBON--ACTIVATED CARBON
Author: BAKER FREDERICK S., MILLER CHARLES E., REPIK ALBERT J., TOLLES E.
DONALD
Institution: Westvaco Corporation, Charleston Research Center
Source: Encyclopedia of Chemical Technology, 4th Edition, Volume 4, Pages
1015-1037
Number of Sections = 31 Tables = 6 Descriptors= 56 References = 117
Abstract:
Carbon, Activated Carbon. Activated carbon is an amorphous solid with a
highly developed internal pore structure that will adsorb molecules from
both the liquid and gas phases. The degree and selectivity of adsorption
depend primarily on the surface area and pore size distribution of the
carbon. Activated carbon is manufactured from materials such as coal,
wood, and coconut shell, and is produced in granular, powdered, and
shaped or pelletized forms. Coal and coconut shell are generally
thermally activated with steam at high temperatures, whereas wood is
activated chemically at moderate temperatures. The world production
capacity of activated carbon in 1990 was estimated to be 375,000 metric
tons. U.S. production, which represented 40% of world capacity in 1990,
is expected to increase at an annual rate of 5.5% during the early
1990s. The largest producers of activated carbon in the United States
are Calgon, American-Norit, and Westvaco. The price of most products was
0.70 to 5.50 $/kg in 1990. Activated carbon can be recycled, but the
economics depend on the specific application and the industry
regeneration capacity. Significant liquid-phase applications of
activated carbon include drinking water purification, wastewater
treatment, sweetener decolorization, and food and chemical processing.
Gas-phase applications include solvent recovery, gasoline emission
control in vehicles, and industrial off-gas treatment. Vol. 4, pp.
1015-1037, 116 refs. to January 1991.
Section Headings:
Untitled
Physical and Chemical Properties
Manufacture and Processing
Thermal Activation Processes
Chemical Activation Processes
Novel Manufacturing Processes
Forms of Activated Carbon Products
Shipping and Storage
Specifications
Economic Aspects
Analytical Test Procedures and Standards
Health and Safety
Liquid-Phase Applications
Potable Water Treatment
Groundwater Remediation
Industrial and Municipal Wastewater Treatment
Sweetener Decolorization
Chemical Processing
Food, Beverage, and Cooking Oil
Pharmaceuticals
Mining
Miscellaneous Uses
Gas-Phase Applications
Solvent Recovery
Gasoline Emission Control
Adsorption of Radionuclides
Control by Chemical Reaction
Protection Against Atmospheric Contaminants
Process Stream Separations
Gas Storage
Catalysis
Tables:
Table 1. Properties of Selected U.S. Activated Carbon Products**a
Table 2. World**a Production Capacity, Estimated 1990
Table 3. Production Capacity in the United States, Estimated 1990
Table 4. Source References for Activated Carbon Test Procedures and
Standards
Table 5. Liquid-Phase Activated Carbon Consumption**a, 10**3 t
Table 6. Gas-Phase Activated Carbon Uses**a
Figure Titles:
Fig. 1. Thermal activation of bituminous coal.
Fig. 2. Chemical activation of wood.
Fig. 3. Multistage countercurrent application of powdered activated
carbon.
Fig. 4. Adsorption zone and breakthrough curve for fixed bed of granular
or shaped activated carbon.
Descriptors:
Activated carbon [7440-44-0], #4:1015
Adsorptive properties, of activated carbon, #4:1016
Antibiotics, adsorption onto carbon, #4:1029
Atmospheric contaminants, activated carbon control, #4:1031
Beer, activated carbon treatment, #4:1029
Bituminous coal, activated carbon from, #4:1018
Catalyst supports, activated carbon, #4:1029
Catalytic properties, of activated carbon, #4:1032
Chemical processing, activated carbon treatment, #4:1028
Cigarette filters, activated carbon, #4:1032
Coal, activated carbon from, #4:1018
Coconut-based activated carbon, #4:1031
Cokes, activated carbon from, #4:1018
Cooking oil, activated carbon treatment, #4:1029
Corn syrup decolorization, #4:1028
Decaffeination, activated carbon treatment, #4:1029
Detoxification of cyanides, activated carbon, #4:1029
Eponite, #4:1015
Filtchar, #4:1015
Filters, activated carbon, #4:1029
Food purification processes, activated carbon in, #4:1029
Fuel vapors, capture by carbon, #4:1030
Gas masks, activated carbon, #4:1031
Gas-phase activated carbon, #4:1030
Gasoline emission control, by activated carbon, #4:1030
Gold recovery, activated carbon, #4:1029
Granular activated carbons, #4:1020
Groundwater treatment, activated carbon, #4:1027
HFCS decolorization, #4:1028
Hypersorption process, #4:1032
Lignite, activated carbon from, #4:1018
Liquid-phase activated carbon, #4:1026
Medical applications, activated carbon, #4:1029
Molecular sieve activated carbons, #4:1032
Natural gas storage, on activated carbon, #4:1032
Norit, #4:1015
Nuclear power plant emissions, activated carbon control, #4:1031
Nut shells, activated carbon from, #4:1018
Peat, activated carbon from, #4:1018
Pitches, activated carbon from, #4:1018
Powdered activated carbons, #4:1020
Process gas streams, activated carbon beds, #4:1032
Radioiodine emissions, activated carbon control, #4:1031
Radionuclides, activated carbon control, #4:1031
Regeneration, of activated carbon, #4:1023
Shaped activated carbon, #4:1020
Solvent recovery, by activated carbon, #4:1030
Steroids, adsorption onto carbon, #4:1029
Sugar decolorization, #4:1028
Sweetener decolorization, #4:1028
Vitamins, adsorption onto carbon, #4:1029
Vodka, activated carbon treatment, #4:1029
Volatile organic compounds, capture by carbon, #4:1030
Water treatment, activated carbon, #4:1027
Whiskey, activated carbon treatment, #4:1029
Wood, activated carbon from, #4:1018
CAS Registry Nos:
7440-44-0
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404591023 Text
Chapter CH=40459
Type TY=404591
Unit UN=404591023
Chapter Title: CARBON--ACTIVATED CARBON
Section Heading: Solvent Recovery
Text:
Most of the activated carbon used in gas-phase applications is employed
to prevent the release of volatile organic compounds into the atmosphere.
Much of this use has been in response to environmental regulations, but
recovery and recycling of solvents from a range of industrial processes
such as printing, coating, and extrusion of fibers also provides
substantial economic benefits.
The structure of activated carbons used for solvent recovery has been
predominantly microporous. Micropores provide the strong adsorption forces
needed to capture small vapor molecules such as acetone at low
concentrations in process air (87). In recent years, however, more
mesoporous carbons, specifically made for solvent recovery, have become
available and are giving good service, especially for the adsorption of
heavier vapors such as cumene and cyclohexanone that are difficult to
remove from micropores during regeneration (87). Regeneration of the carbon
is performed on a cyclic basis by purging it with steam or heated nitrogen.
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321200000 Summary
Chapter CH=32120
Type TY=321200
Unit UN=321200000
Chapter Title: Solvent Recovery
Author: Cooper, C. M.
Institution: Michigan State University
Source: Kirk-Othmer. 3rd ed.Vol 21. 355-376
Number of Sections = 6 Tables = 1 Descriptors= 62 References = 25
Abstract:
This article reviews the present status of solvent recovery from the
viewpoint of process design techniques, relative efficiencies,
economics, energy needs, safety, and the impact of environmental and
occupational health legislation. Solvents calling for recovery include
those used as vehicle for deposition of polymeric materials, as
extractants for components of naturally occurring materials, as agents
for selective separations, as cleaners for solid products, and as media
for chemical reactions. Process design techniques of decantation,
filtration, extraction, evaporation, condensation, fractional
distillation, absorption, adsorption, and automatic control are
described. 21 refs. to November, 1981.
Section Headings:
Untitled
Solvent-Recovery Systems
Solvent-Recovery Techniques
Economic Aspects
Health and Safety Factors
Applications
Tables:
Table 1. Recovery Characteristics of Some Typical Solvents
Figure Titles:
Figure 1. Solvent flow in generalized solvent recovery system.
Figure 2. Recovery of mixed solvents in fabric coating.
Figure 3. Recovery of acetone from cellulose acetate spinning using
water scrubbing.
Figure 4. Recovery of diluent and clathrating solution in solvent
refining of oil (1-2).
Figure 5. Recovery of supercritical CO2 solvent in secondary and
tertiary petroleum recovery (3-5).
Figure 6. Recovery of methyl ethyl ketone in azeotropic process for
producing toluene.
Figure 7. Recovery of mixed solvents in antibiotic manufacture.
Figure 8. Recovery of hexane in vegetable oil extraction.
Figure 9. Recovery of furfural in butadiene purification.
Figure 10. Recovery of perchloroethylene in dry cleaning.
Descriptors:
Absorption towers, in solvent recovery, #21:369
Absorption, in solvent recovery, #21:369
Acetic acid [64-19-7], recovery in acetate mfg, #21:375
Acetone [67-64-1], explosive limits in air, #21:370
Acetone [67-64-1], recovery from cellulose acetate, #21:359
Adsorption, in solvent recovery, #21:370
Antibiotics manufacture, solvent recovery system, #21:362
Azeotropic distillation, in solvent recovery, #21:372
Benzene [71-43-2], explosive limits in air, #21:370
Butadiene [106-99-0], furfural recovery system, #21:364
Butanol [71-36-3], explosive limits in air, #21:370
Carbon dioxide [124-38-9], supercritical, recovery system, #21:361
Carbon tetrachloride [56-23-5], explosive limits in air, #21:370
Carbon, activated, in solvent recovery, #21:370
Cellulose acetate [9004-35-7], acetone recovery from, #21:357
Cellulose acetate spinning, solvent-recovery system, #21:357
Condensers, shell-and-tube, #21:368
Condensers, vapor-through-tube, #21:369
Cyclohexane [110-82-7], recovery in Pe mfg, #21:375
Distillation, fractional, of solvents, #21:367
Dry cleaning, solvent recovery system, #21:365
Dryers, for solvent recovery, #21:368
Ethanol [64-17-5], explosive limits in air, #21:370
Ethyl acetate [141-78-6], explosive limits in air, #21:370
Ethyl ether [60-29-7], explosive limits in air, #21:370
Evaporators, in solvent recovery, #21:366
Extractors, for solvent removal, #21:366
Fabric coating, solvent-recovery system, #21:358
Filtration, in solvent recovery, #21:360
Fractional distillation. See Distillation., #21:368
Hexane [110-54-3], recovery from oil extraction, #21:363
Lubricating oils, solvent refining of, #21:362
Methanol [67-56-1], explosive limits in air, #21:370
Methyl ethyl ketone [78-93-3], explosive limits in air, #21:370
Methyl ethyl ketone [78-93-3], recovery in toluene process, #21:361
Methylene chloride [75-09-2], vaporization of, #21:367
n-Butyl acetate [123-86-4], explosive limits in air, #21:370
n-Decane [124-18-5], explosive limits in air, #21:370
n-Hexane [110-54-3], explosive limits in air, #21:370
Oil-well products, separation of, #21:361
Penicillin [1406-05-6], from fermentation broth, #21:366
Perchloroethylene [127-18-4], recovery in dry cleaning, #21:365
Petroleum, product separations, #21:357
Polyethylene [9002-88-4], production, cyclohexane recovery, #21:375
Propanol [71-23-8], explosive limits in air, #21:370
Safety, in solvent recovery, #21:374
Solvent oil refining, diluent recovery, #21:360
Solvent purification (See also Solvent recovery.), #21:355
Solvent recovery, #21:355
Solvent-recovery systems. See Solvent recovery., #21:355
Solvents (See also Solvent recovery.), #21:355
Solvents, explosive limits and vapor pressures, table, #21:370
Soybeans, oil extraction, #21:375
Stills, for dry cleaning, #21:367
Supercritical extraction, CO2 recovery in, #21:361
Supercritical fluids, in enhanced oil recovery, #21:367
Tetrachloroethylene [127-18-4], explosive limits in air, #21:370
Toluene [108-88-3], explosive limits in air, #21:370
Toluene [108-88-3], MEK recovery in production, #21:361
Trichloroethylene [79-01-6], explosive limits in air, #21:370
Vegetable oil, extraction of, #21:372
Vegetable oils, hexane recovery system, #21:363
CAS Registry Nos:
56-23-5; 60-29-7; 64-17-5; 64-19-7; 67-56-1; 67-64-1; 71-23-8;
71-36-3; 71-43-2; 75-09-2; 78-93-3; 79-01-6; 106-99-0; 108-88-3;
110-54-3; 110-82-7; 123-86-4; 124-18-5; 124-38-9; 127-18-4;
141-78-6; 1406-05-6; 9002-88-4; 9004-35-7
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321201000 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201000
Chapter Title: Solvent Recovery
Section Heading: Untitled
Text:
The recovery of valuable solvents is an economically rewarding practice.
Ever since the surge in solvent manufacturing and solvent-utilizing
facilities began around 1930, processes employing solvents have generally
included solvent-recovery systems as part of the initial installation in
order to increase profitability. However, in some highly innovative and
extremely profitable processes the inclusion of solvent recovery would have
reduced the overall profitability, and solvent recovery facilities were
generally added after competition reduced profits to a normal level. There
are also operations that use an inexpensive solvent in quantities
sufficiently small in which a solvent-recovery system would not be
economically justified.
The environmental and safety hazards associated with the discharge of
organic vapors and liquids to the air or to sewers was recognized early
with the result that even marginally profitable solvent-recovery systems
were often installed to comply with industry standards or with state or
local regulations. However, the establishment of the EPA in 1970 and the
ensuing air- and water-pollution legislation have brought these
considerations more sharply into focus (see Air pollution; Water, water
pollution). The EPA has the responsibility to survey current and achievable
industrial practices, and to establish limitations on the discharge of
polluting emissions to air and effluents to waters. These limitations are
to become more stringent in a series of steps aimed at an expressed
national goal of zero pollution. For new installations the EPA is
authorized to establish guidelines for pollution-reducing equipment and
control systems to be used either at the end of a process or within the
process (see also Regulatory agencies).
It is difficult to speculate on the ultimate impact that such
far-reaching powers are likely to have on the design of solvent-recovery
systems. Certainly formulation, revision, and enforcement of the
regulations are subjected to a variety of disparate influences, including
those of large and small operating companies, industry associations,
environmental activist groups, equipment manufacturers, agency personnel,
cooperating state and local authorities, and the courts. Assuming a
reasonable resolution of all these influences, it is expected that
solvent-recovery designs will continue to be chosen by process design
engineers on the basis of economic evaluation of a variety of
possibilities. However, it will no longer be possible to discharge large,
or even relatively small, amounts of solvents to the atmosphere, municipal
sewers, streams, lakes, or oceans. Inclusion of solvent recovery in a
process is indicated as long as the costs and credits associated with it
are more favorable than the often considerable cost of eliminating solvent
pollution at the end of the process.
The solvent that has seen the greatest recent increase in recovery and
reuse is, of course, water. However, because of its special importance and
unique purification technology, this subject is covered elsewhere (see
Water, water reuse). This article deals with the recovery of nonaqueous
solvents employed in the following industrial processes; the formation and
drying of synthetic fibers and films, plastics and rubber products,
smokeless powder, impregnated fabrics, adhesives, printing inks, paints,
lacquers, enamels, and other deposited coatings; the solvent extraction of
oils and fats from vegetable and animal products, of fossil fuel materials
from coal, shale, tar, and oil sands, of metallic compounds from treated
ores, and other solid-liquid extractions; the solvent-refining of mineral
and vegetable oils, other liquid-liquid extractions, extractive and
azeotropic distillations, and gas-absorption processes; the degreasing of
fabricated parts, dry cleaning, and other washing operations; and
polymerizations and other chemical reactions carried out in solution, and
precipitation and recrystallization from solution.
In most of these applications the recovered solvent is recycled. There
are, however, a number of applications where solvent separation takes place
at a different place and time than solvent addition. In such cases the
recovered solvent is reused in a different and usually a lower value
application.
In a number of applications, organic liquids that are potentially
solvents are purified and separated from processes in which they were not
used primarily as solvents. Except for the use to which the organic liquid
is put, such operations may resemble solvent-recovery systems in every
respect. Among such closely related applications are the recovery of
natural gasoline and light hydrocarbons from natural and casing-head gas;
vapor-recovery operations in petroleum refining; recovery of ethanol from
fermentation gases; recovery of organic liquids from wood distillation and
coal-tar distillation operations; and recovery of by-products or unused
reactants from chemical synthesis (see Gasoline; Petroleum; Ethanol; Coal;
Tar and pitch).
The solvent flow in a typical recovery system is given in Figure 1.
Fresh and recovered solvents join together and enter an industrial process.
In the separations section the products are separated from recycle streams
and a stream containing the bulk of the solvent for recovery. The last
stream is recycled after one or more purification steps in which solvent is
separated from the other gas, liquid, or solid components. Solvent that is
not recycled leaves the system as a component of the product, by-product,
or waste streams. If emissions, spills, and solvent leaving in degraded
form are included, it is obvious from Figure 1 that solvent make-up must be
equal to solvent loss. Thus, good solvent recovery means low solvent use,
and therefore low activity in the manufacture of chemicals specifically for
solvent applications.
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321201001 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201001
Chapter Title: Solvent Recovery
Section Heading: Solvent-Recovery Systems
Text:
Solvent-recovery operations may differ greatly in scale, and the way in
which they interface with the main process. This is well illustrated by the
series of flow diagrams shown below adapted from actual installations or
commercial designs. Adsorption (see Adsorptive separation), eg, plays an
important part in Figure 2, absorption (qv) in Figure 3, crystallization
(qv) in Figure 4, vaporization and recompression in Figure 5, and
liquid-liquid extraction (qv) in Figure 6. Figure 7 is exclusively a
distillation (qv) process, the system in Figure 8 uses vacuum, and those in
Figure 5 and 9 operate to a large extent under pressure. A batch process is
illustrated in Figure 10, semicontinuous processes in Figures 2 and 9, and
truly continuous processes in the other figures. Filtration, drying (qv),
refrigeration (qv), decantation, and evaporation (qv) are utilized in
varying degrees and modifications in the different applications.
Differences in design are often called for in similar or identical
applications. Thus, Figures 2 through 10 are not standard designs for the
industries in question, nor do they necessarily represent best practice for
the particular application indicated. For example, the water-absorption
system shown in Figure 3 for recovering acetone from cellulose acetate
spinning is economical only when a large supply of cooling water is
available. Where water temperatures are high, an adsorption system similar
to that shown in Figure 2 might be suitable for the same application.
The principal similarity which exists among solvent-recovery systems
lies in the approach that must be taken in order to ensure a satisfactory
design. The same techniques; ie, absorption, adsorption, extraction,
filtration, distillation, and condensation. The same factors must be taken
into account, ie, volatility, solubility, thermal stability, corrosion,
purity requirements, capacity, steam and water conditions, safety, and
economics. In general, each unit must be individually designed.
Standardization is desirable only where all factors are substantially the
same.
Solvent-recovery units may be classified according to the method used to
make the initial separation between solvent and product streams as shown in
Figure 1. This separation may be made by any one of the following:
mechanical separation, such as filtering, settling, draining, decanting,
centrifuging, or pressing; extraction, using another liquid to wash out
solvent or product; evaporation; fractional distillation; drying the
product in the absence of air or gas; or drying in the presence of air or
inert gas followed by condensation, absorption, or adsorption.
Although a solvent-recovery system may be classified by the initial
step, subsequent steps may be of a different type. Thus in Figure 10, the
mechanical separation of garments from solvent is followed by drying in the
presence of air. In Figure 2, drying the product in air is followed by
adsorption of solvent, evaporation, condensation, decantation, and
distillation.
It may also be noted that some flow diagrams show more than one type of
solvent-recovery system. Thus, in Figure 9 the separation of the furfural
solvent from butadiene and its separation from polymer may be considered
different units. The same may be said for separating hexane from
solvent-oil mixtures (miscella) and from spent flakes (marc) in Figure 8.
In Figure 4 the recoveries of volatile methylene chloride and of a
nonvolatile urea solution are accomplished by entirely different
techniques.
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321201002 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201002
Chapter Title: Solvent Recovery
Text continues in 321201003
Section Heading: Solvent-Recovery Techniques
Text:
Mechanical Separation. Draining of liquids from solids is a common
operation in solvent processes. The solids are usually retained either by
stationary or moving screens, perforated plates, baskets, belts, or chains.
Sometimes agitation by shaking, tumbling, or rotation promotes separation.
An example of draining is shown in Figure 8, where the conveyor that moves
the extracted flakes from the extractor to the dryer allows solvent to
drain back into the extractor. Another example is the draining of liquid
from fabricated parts in solvent-degreasing operations.
Filtration through screens or cloths is indicated where solids are
present in small particle sizes. Batch, semicontinuous, or continuous
filters using either pressure or vacuum are used for separating solvents
from solids. For reasons of economy and safety, filter closures should be
pressure tight or at least fumeproof. Presses or open filters are usually
avoided.
Continuous pressure-tight filters are used for solvent refining of
lubricating oils. The operation of the filter shown in Figure 4 is typical
of such equipment. The solids are first filtered and carried on a moving
screen or drum to a section where they are washed with solvent. They are
moved to sections where liquid is drawn out and the dry solids dumped into
a screw conveyor. The filters are under vacuum in order to conduct any
leakage in the rotary joints inward.
Equipment of this type is generally expensive and its use can be
justified only where the throughput is relatively large. Batch filtration,
on the other hand, may also be expensive because of the labor required for
removing the solids. An exception is the separation of dirt, fines, or
impurities present only in small quantities. In such cases, disposable
filter mediums are often used, and the filter is made sufficiently large
that only occasional cleaning is required. Filtration is frequently
complicated by the presence of polymer-forming, sticky, or very finely
divided materials. Pretreatment with heat or chemicals and the addition of
filter aids or surface-active agents may solve these problems.
Settling followed by decantation or drawing off of the separated phases
is an obvious and frequently easy way to separate immiscible liquids,
solids, and gases. Separation drums of nominal cross-section often give
fluid velocities that are far below the free settling values, and achieve
essentially complete separation of the fluid phases with or without the use
of baffle, centrifugal-flow, or packed-type entrainment separators.
However, solutions of some materials or synthetic polymers, often contain
traces of surface-active compounds that produce relatively stable foams,
emulsions, or solids suspension. This urdesirable surface activity must be
counteracted. The appropriate technique may be very specific to a
particular solution and much ingenuity and experimentation is often needed
to devise the right treatment. The mixture of residual petroleum, carbon
dioxide, water, and fine sediment produced from the well in Figure 5
requires the expenditure of a significant amount of heat, energy, and
chemicals for the necessary phase separations.
Centrifugal filters, perforate-basket centrifuges, and solid-bowl
centrifuges use centrifugal force to increase the efficiency of filtering,
draining, and settling operations, respectively (see Centrifugal
separation). Examples may be found in the extraction step in dry cleaning,
separating crystals from solvent solutions, and the clarification of
extracts. Pressing between rolls, inside membranes, or in screw expellers
also promotes separation of solvent from fibrous or flaky materials.
Magnetic or electrostatic separators may be required in some cases.
The removal of dust, lint, or mist from air streams prevents the
following of adsorption beds. Air filters are used except where the gases
contain adhesive or varnish-forming materials. In the latter case,
entrainment separators or slat-packed towers with water-washed surfaces are
employed (see Fig. 2). Such an arrangement may also serve to remove
corrosive impurities from air.
Extraction. Solvent and product are sometimes separated by washing with
water or another solvent (6-7). In Figure 6, the solvent is washed out of
the nonaromatic hydrocarbon product with water. In other cases the product
is washed out of the solvent with an aqueous solution. Centrifugal
contactors, mixer-settlers, sieve-plates, and baffled or packed towers with
or without agitation are some of the types of equipment used in
liquid-liquid extraction. If the liquids are clean and of low viscosity,
extractors of reasonable size give effective countercurrent contact
equivalent to ten or more theoretical stages. However, if the liquids are
viscous or turbid, or if they tend to form emulsions, very low extraction
efficiencies may be expected. Sometimes the solvent must be washed out of a
solid product in which case various types of washers or solid-liquid
extractors are used.
Extraction is sometimes accompanied by a chemical reaction between a
component of the washing solution and the impurity (or product) material
being extracted. In other cases, the extraction step may be preceded by a
chemical reaction in which the material to be extracted is converted to a
more easily extractable compound. For example, in the production of
penicillin from dilute fermentation broths, a change in pH fromm 7.5 to 2.5
converts the penicillin from a preferentially water-soluble compound to a
preferentially organic-soluble one (see Antibiotics, BETA -lactams). By
alternating changing pH and extracting from one phase to the other,
hundredfold increases in concentration are possible with only minimal
expenditures of energy. Similar recovery processes may be expected in the
currently evolving biosyntheses.
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321201003 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201002
Chapter Title: Solvent Recovery
Text continued from 321201002
Text continues in 321201004
Section Heading: Solvent-Recovery Techniques (continued)
Text:
Chemical-reaction techniques are particularly prominent in
solvent-recovery systems associated with the extraction of transition metal
compounds from ores (8) (see also Extractive metallurgy). These compounds
are made preferentially soluble in organic solvents by reacting the cation
with an organic complexing agent. Changes in oxidation-reduction potential,
pH, or anionic environment converts the compound to a less organophilic
form, thus reversing the direction of extraction and regenerating the
solvent. Extraction with chemical reaction is performed in the same type of
equipment as extraction without chemical reaction, but the design
calculations are more complex.
Evaporation. Solvents are often recovered by simple evaporation and
condensation. In drycleaning, for example, grease and dirt must be removed
from the solvent (see Fig. 10). Package stills, complete with condenser,
feed preheater, and semiautomatic controls are available for this purpose.
These units are inexpensive and they are often used in industries other
than dry cleaning. For high-boiling Stoddard solvent, the operation may be
under vacuum, for lower-boiling chlorinated solvents at atmospheric
pressure. Feed may be either batch or continuous. Heating is usually with
indirect steam, but provision for gas or electricity is made in some units.
Direct steam may be added for the final removal of solvent from the sludge.
A natural-circulation evaporator is shown in Figure 8. It is followed by
a heater which is also an evaporator, but of the once-through type. The
latter has a lower boiling point at the inlet and a higher temperature
driving force than the former. Other types of evaporators may, of course,
be used. Multiple-effect evaporation and its counterpart, vapor-reuse
distillation, are growing in popularity because they effectively conserve
high cost energy. Evaporation of solvent at high dilution is particularly
advantageous in this respect because boiling and condensing temperatures
are close together, and solutions are stable over a wide range of
temperature and pressure. The double-effect vaporization of methylene
chloride is shown in Figure 4. Condensing vapors from the second, high
pressure, column supply heat to the reboiler of the first column.
Interest is growing in solvents that are high pressure
intermediate-density supercritical fluids (3-5). The solvent power of such
fluids can be changed by varying the density and less energy is required to
separate solute from solvent than with conventional vaporization of
liquids. These solvents are used in secondary and tertiary petroleum
recovery (see Petroleum, chemicals for enhanced recovery). Utilization of
CO2 in such an application is shown in Figure 5. Depending on the pressures
and temperatures in the formation, the CO2 may function at various points
as gas, liquid, supercritical fluid, solvent for petroleum fractions,
viscosity reducer, driving fluid, or a combination of these. Converison to
a low density phase is accomplished in this case by the reduction in
pressure as the production rises to the surface.
When a volatile solvent is separated from a nonvolatile liquid, the
product is saturated with solvent at the pressure in the evaporator. The
introduction of direct steam into the boiling liquid reduces the solvent
partial pressure. However, steam-stripping columns, like the one at the
lower right in Figure 9, are much more efficient. The steam not only
supplies heat and dilutes the vapor, but its condensate washes the
solvent-free polymer out of the column. In the vacuum column shown in
Figure 8, condensation of steam and consequent emulsification must be
avoided. Indirect heat is supplied to the top of the column to prevent
lowering the temperature by solvent vaporization. This piece of equipment
is in effect a falling-film evaporator with a steam purge.
Direct steam is commonly used to steam distill solvent from the surfaces
or pores of solids. Since the heat for vaporizing the solvent is provided
by steam condensation, the separated solid is wet. This moisture can be
removed by drying. Drying equipment for evaporating water is generally
simpler than that for evaporating solvent. However, the two-step
arrangement consumes more energy.
Fractional Distillation. Solvents are commonly separated from products,
water, or other solvents by fractional distillation. The mixtures to be
separated are usually nonideal and often azeotropic or partially miscible.
Where more than one solvent is used, several different types of compounds
may be present, and such mixtures are often very complex. The mixture
recovered in Figure 7, for example, contains two alcohols, an amine, an
alcohol ether, water, salt, and traces of hydrocarbons.
Such complex mixtures are separated into individual components by long
series of distillation operations. Additional components may be added to
serve as entrainers in azeotropic or extractive steps (9) (see Azeotropic
and extractive distillation). A partial separation of mixed solvents often
suffices to permit their reuse. In both Figures 2 and 7 additional columns
would be needed for complete separations. In Figure 7, a change in just one
of the solvents might require a complete revision in the distillation-train
arrangement.
Methods have been developed for estimating multicomponent from bianry
equilibrium and designs of this type can be calculated. Sieve-plate or
bubble-cap columns are generally specified, but packed columns and other
designs are also used. Operation is normally continuous, except for very
small quantities (see Distillation).
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Unit UN=321201002
Chapter Title: Solvent Recovery
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Section Heading: Solvent-Recovery Techniques (continued)
Text:
Drying in the Absence of Air or an Inert Gas. Drying solids by
vaporizing the solvent in the absence of circulating air or an inert gas
has many advantages (see also Drying). Explosion hazards are reduced,
mechanical circulation of air is eliminated, and the task of recovering the
vaporized solvent is greatly simplified. On the other hand, heat transfer
to the solid may be more difficult, and a higher temperature is required
for vaporization unless reduced pressure is used.
Heat is usually supplied by surfaces heated with indirect steam or other
media, or occasionally radiant lamps. In Figure 8, a rotary-shelf type is
shown. Agitation and flow of solids is obtained by rotary rakes that move
the solids inwardly and outwardly across successive steam-heated platens.
Steam-jacketed screw conveyors would accomplish the same result in a
somewhat different way. Vacuum drum dryers, cylinder, dryers, rotary
dryers, or other types of indirect dryers may also be used, provided the
solid has suitable properties. Dryers that employ forced circulation of
superheated solvent vapors through the solids give good heat transfer and
eliminate contact of solids with moving parts or heated surfaces.
At the point where granular solids flow from these dryers, solvent
vapors may leak out or air may be drawn in and overload the gas-handling
capacity of the condensing system. These problems are alleviated if the
pressure in the dryer can be kept close to atmospheric, mechanical
discharge devices are used, and the solid void volume can be compressed or
displaced with liquid. A purge stream of direct steam flowing back into the
dryer through the voids reduces solvent losses without increasing the
noncondensible gas load (see Fig. 8). If the dryer must operate at
significant pressure or vacuum, the solid can be discharged batchwise or
through locks.
Drying with Air or an Inert Gas. Drying in the presence of air or a
mixture of nitrogen and CO2 (deoxygenated air) permits vaporization of
solvent at lower temperatures than in the absence of air. In addition, hot
circulated air provides good heat transfer and does not require contact
with hot surfaces. The importance of tight closure is reduced since
additional air may be drawn into the dryer without serious consequence. Hot
air may be the sole sources of heat, or additional conducting or radiating
surfaces may be provided inside the apparatus. If combustible solvents are
present, a high rate of air circulation keeps their concentration well
below the lower explosive limit. Although flammable mixtures still exist
near the drying surface, the danger of explosion is greatly reduced.
Operation may also be above the upper limit. The use of inert-gas
generators to remove oxygen from the air is good safety practice and is
justified especially where the air stream is recirculated.
Recovery of solvent from the air may be by adsorption, absorption, or
condensation. Since recovery, particularly in the last case, is never
complete, the air from the recovery system is often recirculated back to
the dryer (see Fig. 3 and 10). Recirculation is not used when the return
duct-work is expensive, the exhaust air is relatively solvent-free, or
undesirable impurities are increased (see Fig. 2). Even with recirculation,
a small portion of air is generally discharged through a blower. The
resulting suction draws air through the dryer openings and prevents solvent
vapors from contaminating the surrounding atmosphere. If dust is present,
the air may be filtered at the dryer inlet and outlet. A similar
arrangement is used for inert gas.
Condensation. Vaporized solvents may be liquefied either in surface
condensers or direct-contact condensers. Direct contact with water is
largely restricted to solvents with very low water solubilities, but direct
contact with cold solvent may be used in any case. Shell-and-tube surface
condensers are used almost exclusively. With vertical vapor-through-tube
condensers, the condensed liquid and vent gas leave at a temperature
approaching that of the cooling water. With other types, separate vent
condensers are used or additional passes for vent gas provided inside the
main condenser. Extended surface designs are advantageous for lean air
streams where sensible heat is an appreciable proportion of the total (see
Heat-exchange technology).
The air or gas leaving a condenser contains solvent to the extent of its
vapor pressure at the condensing temperature. The vapor-pressure column in
Table 1 gives the volumetric concentration of solvent
remaining in the air after condensation at 25 DEGREES C. Comparison with
the lower-explosive-limits column reveals that condensation from
circulating air streams operating below the lower explosive limit would not
be possible for most common flammable solvents. As a consequence, the use
of condensation is restricted to high-boiling solvents, nonflammable
solvents, systems using inert gas, or systems where relatively small
proportions of air are present.
Even in these cases, solvent loss may be high if an appreciable amount
of air or gas is discharged to the atmosphere. Refrigeration of the vent
gas to 0 DEGREES C reduces the concentration of solvent to ca 20-30% of
that obtained at 25 DEGREES C (see Fig. 8). Gas compression before cooling
and condensation has been much used by the petroleum industry in gasoline
and vapor-recovery plants. In solvent recovery, however, compression is not
preferred because of the somewhat corrosive nature of many solvent-air
mixtures.
The solvent content of the condenser vent-gas stream may also be
effectively reduced with small clean-up absorbers or adsorbers. Sometimes
the volume of the vent gas can be reduced by degassing the liquid at an
earlier point in the process.
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Chapter CH=32120
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Unit UN=321201002
Chapter Title: Solvent Recovery
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Section Heading: Solvent-Recovery Techniques (continued)
Text:
Absorption. Solvents may be recovered from air or gas streams more or
less completely by scrubbing with a suitable liquid. Such operations
constitute absorption. However, although much of the theory of absorption
refers to packed or continuous-contact towers, most large absorbers in
solvent recovery plants are of the stagewise type. Bubble-cap, sieve-plate,
and baffle-plate columns are used, as are banks of spray chambers arranged
for countercurrent flow. Baffle-plate designs, spray designs, and randomly
packed towers operating well below maximum capacity give low pressure drops
and therefore tend to minimize the cost of power for circulating air.
However, after considering all factors, the more predictable sieve-plate or
bubble-cap columns with moderate pressure drop designs are usually chosen.
Water is the principal scrubbing liquid used; the amount required
depends largely on the type of solvent recovered. This is shown in the
fourth column of Table 1 , which gives the minimum
number of mol of water theoretically needed for complete absorption of the
compound from one mol of lean air at 25 DEGREES C and 101.3 kPa (1 atm).
These values would be 1% of those in the third column of Table 1 if the scrubbing liquid were not water but one forming an ideal
solution with the solvent, that is, one obeying Raoult's law. The ratio of
the values in these two columns is the activity coefficient of the compound
in dilute aqueous solution. In a homologous series of alcohols the one with
the highest vapor pressure is most easily absorbed in water. If an absorber
oil were used instead of water, the order would be reversed, and the moles
of absorbent required for the hydrocarbon solvents could be taken from the
vapor-pressure column of Table 1 .
The temperature of absorption determines the quantity of scrubbing
liquid required. With rich air streams the heat of absorption is sometimes
removed by indirect cooling either inside the absorption column or
externally between stages (see Fig. 3). Refrigerated scrubbing liquids are
sometimes used for the same reason (see Absorption).
Adsorption. The predominant method for removing solvent vapors from air
streams is adsorption on activated carbon (see Carbon, activated carbon)
(10-12). As commonly practiced, the air is fed alternately to one of two
adsorbing vessels, while the other is being fed with low-pressure steam
(see Fig. 2).
The steaming operation causes the solvent to be vaporized, and the
latent heat is supplied by a portion of the steam that condenses into the
bed. With some organic solvents this moisture interferes with subsequent
adsorption, but with most it does not. If water can be tolerated, its
vaporization into the air stream keeps the temperature down. In any case,
if there is a net loss of heat around the cycle the water content rises to
a point where it stops adsorption. This water balance is often an important
factor in the design of an adsorption unit. Heating, cooling, or special
drying periods may have to be included in the cycle of operations.
Although such a system has all the inherent disadvantages of
intermittent processes, it offers great advantages for many applications.
Unlike water scrubbing, it may be applied to water-insoluble solvents.
Unlike condensation, it may reduce the solvent content of the air to a
figure as low as desired.
The theoretical steam requirement for carbon adsorption is usually less
than for absorption. Heats of adsorption are high, that is, the vapor
pressure of solvent above activated carbon increases more rapidly with
temperature than it does above liquid solutions. However, since the
steaming operation in adsorption is somewhat inefficient, the actual steam
requirement may offer no advantage over a favorable scrubbing application
with water or oil. On the other hand, with mixed solvents and with those
not ideally suited to absorption, water scrubbing may require excessive
quantities of steam for reasons already noted. Low pressure drop may be
obtained in adsorption systems by reducing the linear velocity of the air
and the thickness of the bed. Beds are usually 30-100 cm thick with uniform
pellets =3 mm dia. The beds are commonly supported inside horizontal
cylinders so as to give a large flow cross section. Special devices must be
used for distributing the air.
The success of carbon adsorption depends to a large extent upon proper
control of the operating cycle. When the rate of solvent recovery is
constant, automatic time cycle controllers are often used. When flow varies
widely, cut points may be determined by bed saturation. This type of
operation is particularly well suited to guard against sudden surges in
solvent content caused by process disturbances. In large installations with
many adsorbers, operations are staggered to eliminate the peaks in steam
demand.
Some volatile compounds react chemically on the surface of activated
carbon. In the presence of air, organic compounds like aldehydes and
ketones are oxidized, and the heat of combustion added to the heat of
adsorption may raise the temperature of the active carbon to a point where
it burns. With normal well-distributed air flows through the carbon bed,
fires are not encountered because the flowing stream cools the carbon.
However, in an irregular operation or a poorly channeled bed, hot spots may
develop. Procedures and precautions have been recommended to prevent such
an occurrence (13-14). Use of inert gas is an obvious solution.
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Chapter CH=32120
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Unit UN=321201002
Chapter Title: Solvent Recovery
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Section Heading: Solvent-Recovery Techniques (continued)
Text:
Solvent vapors can also react on the surface of activated carbon to give
undesirable products or to reduce the activity of adsorption, whereas
entrained solids may foul the bed mechanically. Galvanic corrosion of metal
parts may be accelerated by the electrical conductivity of the carbon.
Sooner or later the pellets deteriorate and must be replaced. Most of the
serious problems involved in adsorption processes have been solved by the
manufacturers of activated carbon. Maintenance and operating labor has been
minimized by sound engineering of process, equipment, and controls.
Activated carbons resistant to poisoning and mechanical failure have been
produced by careful controls of the manufacturing process.
Although carbon-adsorption operations are usually conducted batchwise,
continuous contacting is feasible, especially on a large scale. Both
moving-bed and fluidized-bed designs have been used for moving carbon
particles from the adsorber to the stripper and back. In one
solvent-recovery installation, a series of shallow fluidized beds produces
countercurrent contact between the solid and gas phases (see Fluidization).
Adsorption may also be applied in a different way for solvent recovery.
Traces of high-molecular-weight compounds, undesirable because of color,
odor, or other properties, may be removed by treatment of the liquid with
active carbons, clays, or other adsorbents (11). These solids are first
slurried with the solvent until adsorption is complete. Then they are
filtered from the purified liquid. The operation can be performed
continuously, but it is usually done batchwise on a small scale (see
Adsorption separation, liquids).
Automatic Control. Instrumentation advanced the development of
satisfactory solvent-recovery units. When these units are only auxiliary to
the manufacturing operation, they require little attention. The trend has
been toward completely automatic control, including start-up and shut-down
periods. A number of fairly large installations require no manual labor
other than the operation of a start-and-stop switch. Sequenced with the aid
of cycle control, batch operations are as efficient as continuous
operations. A single piece of equipment may thus be used for a whole series
of operations. For example, in vegetable-oil extraction, a single heated
vessel with automatic control throughout is used for solvent extraction of
oil from flakes, filtration of the marc from the miscella, vacuum
vaporization of the solvent from the marc, and discharge of the dried
solids (see Vegetable oils).
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321201007 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201003
Chapter Title: Solvent Recovery
Section Heading: Economic Aspects
Text:
Solvent-recovery decisions, like most engineering and management
decisions, are based mainly on economic analysis (see Economic evaluation).
Such analysis involves careful engineering calculations, an estimate of
future prices of raw materials, utilities, and products, and of interest
rates on borrowed capital, tax rates, and government standards and
regulations with regard to pollution and occupational safety. In an
inflationary economy and with government regulation in a state of flux,
such estimates are highly tenuous and, unless great profitability is
expected, new expenditures for solvent recovery may be delayed unless they
are required by law.
For processes employing large quantities of solvents, the installation
of a solvent-recovery system is a foregone conclusion, since recovery under
any circumstances would be profitable. The type of system used may
significantly contribute to the total production cost.
For these reasons, the recovery system should be designed early in the
development of a new process. It may, eg, prove desirable to evaporate the
solvent with steam rather than air since recovery in the latter case is
more expensive and less efficient. Nonflammable, less corrosive, or easily
recovered solvent may be preferable. Mixed solvents are generally more
difficult to recover than single compounds, and individual solvents may
vary greatly in their ease of recovery. Methanol, for instance, is easily
dehydrated by straight fractional distillation. Ethanol and propanol form
constant-boiling mixtures with water, and recovery in the anhydrous form
requires azeotropic entrainers. Butanol, on the other hand, is easily
dehydrated since the two layers can be decanted and stripped. When
purification of the recovered solvent is difficult, a less pure solvent
might be acceptable for recycle.
Selection of the optimum design involves minimizing cost ofunrecovered
solvent, utilities, and labor, interest on borrowed capital and expected
return on investment. The cost of unrecovered solvent is of most concern in
an inefficient recovery system handling large volumes of solvent over a
long period of time. If only 95% of the solvent is recovered, the cost of
making up the unrecovered 5% would normally be much larger than any of the
other charges. Better engineering design aimed at recoveries >99% would
usually not increase the other costs significantly and should be sought in
every case.
Even with efficient recovery, make-up solvent is always required.
Designers of solvent-recovery equipment often claim that the solvent
content of the various waste streams can be held to negligible amounts.
Although analyses of these streams usually corroborate such claims,
inventory balances general show losses to be much higher than those
calculated. Only by a careful study of spillage, venting, gauging practice,
chemical instability, etc, can this discrepancy be eliminated.
For large long-lived systems with recoveries approaching 100%, utilities
present the largest cost. Steam costs can be reduced to as little as
=$0.01/kg solvent recovered. In the recovery of acetic acid in cellulose
acetate manufacture, eg, azeotropic distillation with a volatile entrainer
reduces the steam required for straight fractional distillation of water
from acid. This operation is followed by less volatile entrainers, and then
by liquid extraction with low-boiling solvents. Steam savings are realized
in each successive step. These savings are further improved by
multiple-effect and vapor-reuse techniques. Extraction with higher boiling
solvents gives even lower steam consumption.
By comparison, interest on borrowed capital is a small charge against a
large long-lived solvent recovery system, as long as the economy in
noninflationary. With inflation interests increase several-fold, reflecting
mainly anticipated reduction in the real value of the dollar. Aside from
these considerations, solvent-recovery decisions could be made on the basis
of sound engineering rather than on concern for the future of the general
economy.
Investment and operating costs increase as the quality of solvent
increases, but not proportionally. There are many fixed costs, and
investment, labor, and overhead costs per kilogram recovered can be
unreasonably high for small or short-lived solvent-recovery systems. In the
past, most small manufacturers have simply discarded their spent solvent
and other wastes, but with increasing impact of environmental regulations
this may no longer be possible. A recent EPA publication states that as
many as 232 small paintformulating plants may have to close as a result of
a proposed regulation of plant effluents (15). Remedies like piping or
trucking effluents to a common treatment installation have been suggested.
A small combination solvent-recovery and disposal unit, if developed, might
find a sizable market.
Many larger plants are engaged in a number of small-volume solvent
applications for which individual recovery and disposal systems would not
be economical. Such solvent effluents can be collected and stored, and
periodically recovered. However, the mix of waste streams must not include
materials that produce health and safety hazards during disposal.
Indiscriminate mixing of wates, followed by sale or payment for disposal to
a private contractor does not relieve the waste generator of legal
responsibility for whatever environmental harm may result (see Wastes,
industrial).
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321201008 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201004
Chapter Title: Solvent Recovery
Section Heading: Health and Safety Factors
Text:
Safety considerations are of prime importance in the design of most
solvent-recovery processes. They may form the basis for choosing a
particular solvent and motivate the installation of the recovery system.
Safety considerations may determine important operating conditions, or call
for certain types of building designs, equipment, controls, or accessories.
Although safety is usually thought of in terms of flammable solvent,
consideration must also be given to heat and mechanical hazards, and to the
noxious properties of solvent vapors (see Plant safety).
Accepted practice with regard to the handling of flammable solvents is
governed by the UL codes and those of the National Fire Protection
Association (16). They form the basis for municipal safety laws and
insurance inspection requirements. Included are the location, design, and
ventilation of buildings; size, type, and construction of vessels;
arrangement of piping, valves, pumps, and vents; distribution of alarm and
extinguishing equipment; instruction of personnel; and many others. The
codes for dry cleaning, the solvent extraction of fats and oils, and
deposits of coatings by sprays and dip tanks include rather detailed
descriptions of the standard equipment items available to these industries.
Such standardization is in the interest of safety especially for the small
installations and operating personnel lacking in scientific and engineering
background. At the same time, it is the intent of these codes to permit
genuine improvements in design.
The use of most common flammable solvents creates conditions classified
as Class I, Group D by the National Electrical Code (17). Motors and other
electrical equipment in these locations must be explosionproof and
specifically approved for this class of service. Sources of static
electricity such as belt drives should be eliminated, and open flames such
as welding torches, should be prohibited during operation of the unit.
Vents should be protected with flame arresters. Leakage of noxious or
flammable vapors into operating rooms should be minimized and adequate
ventilation provided. Pressure-relief systems with remote catch tanks
should be used on equipment wherever there is a possibility of excessive
internal pressure.
Mixtures of air and solvent should be kept below the explosive range
whenever they are present in significant volumes. Convenient automatic
instruments are available for this purpose. It has been recommended that
concentrations inside equipment be kept below one half of the lower
explosive limit. For concentrations higher, special precautions should be
taken to guard against mishaps. Unsafe practices lead, sooner or later, to
diaster.
Concentrations of solvent vapors outside equipment and in areas
accessible to employees are limited by OSHA standards (18). Allowable
concentrations for both nonflammable and flammable vapors under these
standards are much lower than those dictated by fire safety. Compliance
with these standards may require costly additions to process equipment,
control and monitoring instrumentation, and employee training.
Increased interest in the long-range effect on human health of exposure
to solvents and other chemicals had led to the following developments:
Legislation has been enacted requiring governmental agencies to identify
and regulate health risks and requiring industrial concerns to comply with
the appropriate regulations in their operating, labeling, and reporting
practices (see Industrial hygiene and toxicology). Courts have awarded
sizeable damages against chemical manufactures and users on the basis of
exposure to a variety of substances by employees, customers, and others.
Finally, some large chemical companies in response to these developments
are accepting complete responsibilities over the chemicals they produce.
The effect of these developments on solvent-recovery design will, of
course, be an increased preference for innocuous solvents and for systems
yielding essentially complete recovery.
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321201009 Text
Chapter CH=32120
Type TY=321201
Unit UN=321201005
Chapter Title: Solvent Recovery
Section Heading: Applications
Text:
Processes for the manufacture of synthetic fibers and sheets,
impregnated articles, and related products often use solvents as volatile
vehicles for the deposition of polymeric materials. Although many resins
are deposited from water suspensions or are formed directly from fused
solid or by chemical reaction, deposition from organic solvents represents
a significant fraction of the total. Recovery of acetone from cellulose
acetate spinning and film production was the largest operation in this
group. The products in these applications are usually air-dried and the
solvent is recovered by absorption or adsorption. Superheated steam has
also been used for drying followed by condensation of the vapors. The
recovery of solvents vaporized in painting is generally avoided unless the
operation is large or continuous. The automotive industry with its very
extensive painting operations has long been reluctant to modify these
operations in order to recover the solvents. However, under a new
cooperative arrangement with the Michigan Department of Natural Resources,
the large manufacturers except to reduce their volatile organic emissions
substantially (19).
Solvent extraction of vegetable oils and other solid-liquid extraction
processes in the United States utilize solvent recovery, such as the
manufacture of oil from soybeans (qv). Recovery is principally by
evaporation from the miscella and drying the marc with indirect heat or
steam (16,20). Other oils are also extracted in quantity but the expression
process is favored for seeds of higher oil content. The pharmaceutical
industry uses solvents extensively for the extraction of both natural and
synthetic materials. Field tests have been conducted on the use of solvents
to extract petroleum in situ from oil sands, but only minor attention was
given to the solvent-recovery aspects (5) (see Oil shale; Tar sands). Other
interesting processes involving the solvent extraction of metal ores,
fossil fuel materials, and other natural resources have reached various
stages of development (8,21-22), many with government financing.
Solvent refining of lubricating oils and other solvent operations in the
petroleum industry entail the recovery of solvents in quantities far
exceeding all other applications (23). Extractive distillations or
gas-treating operations can be of similar magnitudes. If steam stripping of
absorber oils is classed as a solvent-recovery operation, the total volume
of solvent recovered by this industry is truly immense. Liquid-liquid
extraction is also being used extensively in the solvent extraction of
nuclear intermediates and of other metallic compounds from ores (8). The
organic streams in these metallurgical operations are ordinarily prepared
for reuse by chemical treatment, additional extractions, and mechanical
separations. However, evaporation and distillation are also used.
Liquid-liquid extractions of appreciable size are used in pharmaceutical
manufacture.
Washing operations using solvents, eg, dry cleaning, are small in size
but large in number. In the U.S. about 3 TIMES 10**5metric tons of solvent
is consumed each year by such operations. Statistics are not available on
the amount of redistillation practiced in this industry but 1-2 TIMES 10**6
t/yr seems a reasonable estimate. Improvements in aqueous detergents and
the increased popularity of washable fabrics account for the recent decline
in dry cleaning (qv).
The use of solvents for solution polymerizations and other chemical
reactions is a growing area for solvent recovery, and large amounts of
cyclohexane are recovered each year in the manufacture of high density
polyethylene alone. Recovery is mainly by mechanical separation and
redistillation. Polypropylene manufacture and other polymerization
processes also include large solvent recovery operations. Acetic acid used
as a solvent medium for the reaction of acetic anhydride with cellulose now
amounts to about 10**6 t/yr in the U.S..
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(c) 1995 John Wiley & Sons Inc. All rts. reserv.
321202001 Table
Chapter CH=32120
Type TY=321202
Unit UN=321202001
Chapter Title: Solvent Recovery
Table: Table 1. Recovery Characteristics of Some Typical Solvents
Table Data:
> Solvent Explosive limits Explosive limits Equilibrium mol
mol fraction in mol fraction in fraction in air
air Upper air Lower at 25 DEGREES C
> ------------------ ------------------ ---------------- ---------------
> methanol 0.360 0.073 0.16
> ethanol 0.190 0.043 0.075
> propanol 0.135 0.021 0.026
> butanol 0.112 0.014 0.009
> acetone 0.128 0.026 0.29
> methyl ethyl 0.100 0.018 0.13
ketone
> ethyl acetate 0.090 0.025 0.12
> n-butyl acetate 0.076 0.017 0.018
> ethyl ether 0.480 0.019 0.70
> benzene 0.071 0.013 0.13
> toluene 0.071 0.012 0.037
> n-hexane 0.075 0.011 0.20
> n-decane 0.054 0.008 0.002
> carbon 0.14
tetrachloride
> trichloroethylene 0.10
> tetrachlorethylene 0.025
Table Data (part 2):
> Solvent Minimum absorption requirement at 25 DEGREES C mol
water/mol air
> ------------------ -----------------------------------------------------
> methanol 0.26
> ethanol 0.33
> propanol 0.37
> butanol 0.44
> acetone 2.1
> methyl ethyl 2.3
ketone
> ethyl acetate 8
> n-butyl acetate 15
> ethyl ether 50
> benzene >100
> toluene >100
> n-hexane >100
> n-decane >100
> carbon >100
tetrachloride
> trichloroethylene >100
> tetrachlorethylene >100
1/5/15
DIALOG(R)File 302:Kirk-Othmer Encycl Chem
(c) 1995 John Wiley & Sons Inc. All rts. reserv.
321203000 Bibliography
Chapter CH=32120
Type TY=321203
Unit UN=321203000
Chapter Title: Solvent Recovery
References = 25
References:
1. H. L. Hoffman and co-workers, Hydrocarbon Process. Pet. Refiner
45(9), 220 (1966).
2. E. J. Fuller in J. J. McKetta, ed., Encyclopedia of Practice and
Design, Marcel Dekker, Inc., New York, 1979.
3. C. A. Irani and E. W. Funk, in N. N. Li, ed., Recent Developments in
Separations Science, Vol. III-A, CRC Press, Cleveland, Ohio,
1977, pp. 171-193.
4. L. W. Holm and V. A. Josendal, J. Pet. Technol. 26, 1427 (1974).
5. T. B. Reid and H. J. Robinson, J. Pet. Technol. 33, 1723 (1981).
6. R. E. Treybal in R. H. Perry and C. H. Chilton, eds., Chemical
Engineers' Handbook, 5th ed., McGraw-Hill Book Co., New York,
1973, Sec. 15.
7. L. A. Robbins in P. A. Schweitzer, ed., Handbook of Separation
Techniques for Chemical Engineers, McGraw-Hill Book Co., New
York, 1979.
8. G. M. Ritcey and A. W. Ashbrook, Solvent Extraction, Elsevier
Scientific Publishing Co., Amsterdam, 1979.
9. B. D. Smith in R. H. Perry and C. H. Chilton, eds., Chemical
Engineers' Handbook, 5th ed., McGraw-Hill Book Co., New York,
1973, pp. 13-36-13-47.
10. T. Vermeulen, G. Klein, and N. K. Hiester, in R. H. Perry and C. H.
Chilton, eds., Chemical Engineers' Handbook, 5th ed., McGraw-Hill
Book Co., New York, 1973, Sec. 16.
11. P. N. Cheremisinoff and F. Ellerbusch, Carbon Adsorption Handbook,
Ann Arbor Science Publishers, Inc., Ann Arbor, Mich., 1978.
12. J. W. Drew in P. A. Schweitzer, eds., Handbook of Separation
Techniques for Chemical Engineers, McGraw-Hill Book Co., New
York, 1979.
13. A. A. Naujokas, CEP Technical Manual, Loss Prevention 12, 128
(1979).
14. M. J. Chapman and D. L. Field, CEP Technical Manual, Loss Prevention
12, 136 (1979).
15. J. R. Berlow, Proposed Effluent Limitations for the Paint
Formulating Point Source Category, EPA 440/1-79/049-b, U.S.
Environmental Protection Agency, Washington, D.C., 1979.
16. National Fire Codes, Vol. 3, National Fire Protection Association,
Boston, Mass., 1978.
17. National Fire Codes, Vol. 6, National Fire Protection Association,
Boston, Mass., 1978.
18. R. J. Lewis and R. L. Tatken, eds., Registry of Toxic Effects of
Chemical Substances, U.S. Dept. of Health and Human Services,
Cincinnati, Ohio, 1980.
19. D. Rector, SAE Transactions, No. 790370, V. 88, 1979.
2O. D. Swern, ed., Bailey's Industrial Oil and Fat Products,
Interscience, Publishers, a division of John Wiley & Sons, Inc.,
New York, 1964, pp. 704-711.
21. R. P. Anderson, Chem. Eng. Prog. 71, 72 (Apr. 1975).
22. R. Katzen, R. Frederickson, and B. F. Brush, Chem. Eng. Prog. 76, 62
(Feb. 1980).
23. J. G. Speight, The Chemistry and Technology of Petroleum, Marcel
Dekker, Inc., New York, 1980.
General References:
''Solvent Recovery'' in ECT 1st ed., Vol. 12, pp. 641-654, by C. M.
Cooper, Michigan State College
''Solvent Recovery'' in ECT 2nd ed., Vol. 18, pp. 549-564, by C. M.
Cooper, Michigan State University.