LEVEL 1 - 46 OF 739 PATENTS
5,618,432
Apr. 8, 1997
Process for solvent recovery
INVENTOR: Rewitzer, Siegfried, Ihrlerstein, Federal Republic of Germany
Roth, Peter M., Eppstein/Ts., Federal Republic of Germany
ASSIGNEE-AT-ISSUE: Hoechst Agteingesellschaft, Federal Republic of Germany
(03) APPL-N0: 183,155
FILED: Jan. 18, 1994
FOR-PRIOR:
Jan. 15, 1993 Federal Republic of Germany 43 00 921.2
INT-CL: [6] B01D 11#00
US-CL: 210#634; 210#805; 134#10; 134#13; 264#179; 203#14; 55#DIG30
CL: 210;134;264;203;55
SEARCH-FLD: 210#634, 180, 774, 767, 805; 134#10, 13; 528#501; 203#75, 77, 81,
49, 14; 264#179; 55#DIG.30
REF-CITED:
U.S. PATENT DOCUMENTS
<=3> 3,608,043 9/1971 * Reni 264#179
<=4> 3,928,517 12/1975 * Knight et al. 264#179
<=5> 4,040,913 8/1977 * Clovis et al. 203#77
<=6> 4,043,873 8/1977 * Ackermann et al. 203#77
<=7> 4,057,491 11/1977 * Bushnell et al. 203#49
<=8> 4,070,253 1/1978 * Hofen et al. 203#49
<=9> 4,303,478 12/1981 * Field 203#19
<=10> 4,436,902 3/1984 * Wood et al. 203#75
<=11> 4,484,984 11/1984 * Bannon 203#42
<=12> 4,589,957 5/1986 * Sherk 203#75
<=13> 4,793,938 12/1988 * Dayton 210#774
<=14> 4,847,057 7/1989 * Brugerolle et al. 95#169
<=15> 4,976,825 12/1990 * Iwasaki et al. 203#71
FOREIGN PATENT DOCUMENTS
1543411 8/1969 * Federal Republic of Germany
2506193 8/1976 * Federal Republic of Germany
OTHER PUBLICATIONS
European Search Report No. 94100195.0, May 30, 1994.
PRIM-EXMR: Fortuna, Ana
LEGAL-REP: Connolly & Hutz
ABST:
A process for recovery and reuse of liquids used as solvents and
diluents in a chemical reaction and/or the processing of substances, the
process include the introduction of a solvent, a diluent, and a substance
to be reacted and/or processed into a processing plant, feeding a used
mixture of solvent, diluent and residues into a recovery plant, separating
the solvent, diluent and residue resulting from the chemical reaction
and/or processing of substances, recycling the solvent and diluent back to
the processing plant, ejecting residues, and ejecting the treated
substances. The apparatus for carrying out the process is also described.
NO-OF-CLAIMS: 20
EXMPL-CLAIM: <=16> 1
NO-OF-FIGURES: 8
NO-DRWNG-PP: 8
SUM:
FIELD OF THE INVENTION
The present invention relates to a process for solvent recovery and an
apparatus adapted for carrying out this process.
DESCRIPTION OF THE PRIOR ART
In many production and processing processes, solvents are brought into
contact with the actual raw material and/or the product. Conventionally,
the solvent is contaminated in the course of this and, subsequently to the
actual process, is subjected to a purification. Frequently the individual
processes require that the solvents used be diluted by specific addition
of another liquid, whether it be to regulate a required solution viscosity
or, for cost reasons or to be able to carry out certain process steps, for
example precipitation of a dissolved substance in a precipitation bath.
Both the contaminants (waste materials) and the diluent are conventionally
ejected from a solvent recovery plant, while the purified solvent is
returned to the production process. Such previously known processes are
common practice. An example thereof is given in Kirk-Othmer: "Encyclopedia
of chemical Technology", Vol. 21, 3rd Edition, John Wiley & Sons (1983),
head word " Solvent Recovery" , p. 357.
In recent years, requirements of the operation of plants in which chemical
substances are reacted or processed have become increasingly stricter. This
relates both to the emission of chemical substances which originate from the
operation of such plants and the consumption of energy in the operation of
such plants.
There is thus a requirement for processes and apparatuses with which
chemical substances can be reacted or processed with a minimum of energy
consumption and/or in the operation of which a minimum of waste substances
results.
SUMMARY OF THE INVENTION
A process is provided by the present invention in which at least a part of
the solvent and diluent used is recirculated, so that by this simple measure a
reduced consumption of solvent and diluent for this solvent is achieved. In a
preferred embodiment of the process according to the invention, a reduction of
the energy consumption in the solvent recovery is achieved.
The present invention relates to a process for recovery and reuse of
liquids which are used as solvents and for the specific dilution of the
solvent in the chemical reaction and/or the processing of substances
including the measures:
a1) introducing fresh solvent into a processing plant,
b1) introducing fresh diluent into the processing plant,
c1) introducing substances to be reacted and/or to be processed into a
treatment apparatus of the processing plant,
d1) ejecting products from the processing plant,
e1) feeding the used mixture of solvent, diluent and residues from the
reaction and/or processing of the substances to a solvent recovery plant,
f1) separating the mixture from step e1) in the solvent recovery plant
into a solvent fraction, which is primarily composed of solvent and
possibly contains a small proportion of diluent, into a diluent fraction,
which is primarily composed of diluent and possibly contains a small
proportion of solvent, and into residues from the reaction and/or
processing of the substances,
g1) returning the solvent fraction to the processing plant, so that this
fraction is again available for the reaction and/or processing of the
substances,
h1) returning the diluent fraction to the processing plant so that this
fraction is again available for the reaction and/or processing of the
substances, and
i1) ejecting residues from the reaction and/or processing of the substances
from the processing plant.
The term "chemical reaction of substances" is taken to have its
broadest meaning. In this case, therefore, these are processes in which
any substances are converted into other chemical substances with a change
in their chemical composition. These can be reactions in which a starting
material is converted to a product of a new chemical constitution or in
which two or more starting materials are reacted together to give one or
more products of new chemical constitution. Preferred examples of such
chemical reactions are polymerization reactions, such as polymerizations,
polycondensations or polyadditions.
The term "processing of substances" is likewise taken to have its
broadest meaning. In this case, therefore, these are processes in which
any substances are processed, retaining their chemical composition. These
can be purification processes which are carried out with the aid of
mixtures containing solvent and diluent, for example for degreasing
objects or for recrystallizing chemical substances, or these are shaping
processes in which a dissolved chemical substance or a mixture of such
substances is processed to give a predetermined shape. Examples thereof
are the production of films, fibers or coatings from solutions of
dissolved compounds, in particular from polymer solutions.
The term "solvent" is taken to mean all compounds, in particular
organic compounds, with which solutions of substances can be prepared
which are used in a reaction or processing of these substances.
Examples of preferred organic solvents are aliphatic or aromatic
hydrocarbons which may or may not be halogenated, such as brominated or
chlorinated hydrocarbons, and polar aprotic solvents such as amide
solvents.
Preferred examples of organic, polar and aprotic solvents are
N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl
sulfoxide.
The term "diluents for specific dilution of the solvent" is taken to
mean liquids which differ from the respective solvent used and are
specifically added to the solvent in the broadest sense before or during
the reaction or processing process, in order to achieve a desired change
of the dissolved substance, for example a change in the solubility of the
dissolved substance, or to carry out an adjustment of a required process
parameter, such as the viscosity of the solution, but also to reduce the
costs for the respective solvent used. These can therefore be mixtures of
different solvents for the substance intended to be reacted or processed
or else mixtures of solvents and non-solvents for the said substance, in
particular these are a combination of solvents and non-solvents, the
combination itself no longer acting as a solvent but as a precipitant for
the said substance.
The diluent is particularly preferably a non-solvent, in particular
water, for the substance intended for reaction or processing.
Preferred combinations of solvent and diluent in the process according
to the invention are mixtures of organic polar and aprotic solvent with
water.
The definition "processing plant" is taken to mean a plant in the
broadest sense in which the above-defined "chemical reaction of
substances" or "processing of substances" is carried out. This can
therefore be a plant for polymerization or a purification plant or, in
particular, a plant for producing films or fibers.
The term"treatment apparatus" is taken to mean that part of the
abovementioned "processing plant", in which the actual chemical reaction
or processing is undertaken. Whereas the term "processing plant" denotes
the entire plant, that is the "treatment installation" including all
supply units, disposal units and control units.
The process according to the invention is used particularly in the
cleaning of objects in which impurities are removed by treatment with a
solvent.
The process according to the invention is very particularly preferably
used in the shaping of substances in which polymers are converted from
solutions into a desired form, in particular into films, fibers or
coatings.
This includes very particularly preferably a shaping in which polymers
are converted from solutions into fibre form, a wet-spin process or a
dry-wet spin process being used, and a secondary treatment following in
particular directly the precipitation of the filament in the coagulation
bath.
The used mixture as described in step e1) is preferably a mixture which
originates from the coagulation bath of a wet-spin plant and which
contains an organic, polar and aprotic solvent or mixtures of such
solvents and water.
For the solvent recovery, all processes known for this purpose can be used by means of which a separation of the mixture into a solvent fraction and a
diluent fraction is possible.
Examples of such processes are the extractive, absorptive, adsorptive and,
in particular, the separation by distillation of the used mixture as
described in step e1).
The separation is preferably carried out in a rectification column.
The mixture of spinning solvent, water and residues from the
precipitation bath and the secondary treatment, originating from the
coagulation bath and, possibly, the secondary treatment apparatuses, such
as drawing baths, finishing baths and washing baths, is particularly
preferably passed to a solvent recovery plant and the mixture is separated
there by rectification into a solvent fraction, into a diluent fraction
and into residues from the precipitation bath and the secondary treatment.
In a particularly preferred embodiment of the process according to the
invention, the composition of the solvent fraction and diluent fraction
leaving the rectification column is chosen so that the coolant for the
rectification column does not have to be subjected to an additional
cooling before its use or the preheated coolant can be used for the
operation of at least a part of the rectification column. This embodiment
is based on the finding that in some cases it can be entirely sufficient
not to carry out a complete separation in the solvent fraction or diluent
fraction and to take off part of this fraction from the column via a side
take-off beneath the column head. This fraction has a higher boiling point
than the solvent fraction or diluent fraction taken off over the head and
can therefore be condensed at a higher temperature than the purer overhead
fraction. With this embodiment of the process according to the invention,
an additional energy saving or improved energy utilization can be
achieved.
A further particularly preferred variant of the process according to
the invention relates to the return of at least some of the solvent
fraction or diluent fraction via an exhaust air scrubber which is intended
to purify the exhaust air which originates from the processing plant and
is enriched with solvent vapors and diluent vapors. With this embodiment,
too, an additional coolant water saving and thus also an energy saving can
be achieved. For this purpose, e.g. the cooled diluent fraction is
conducted through the scrubber in counter-current to the laden exhaust
air, so that the solvent residues and diluent residues condense and are
returned into the treatment plant with the diluent fraction.
The invention also relates to the combination shown of apparatuses for
carrying out the process described.
In the following FIGS. 1 to 8, the present invention is described by way of
example.
DRWDESC:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a diagram of the principle of the process according to the
invention.
In FIGS. 2 and 3, an embodiment of the process according to the
invention is shown, in which the solvent reprocessing is carried out by
means of a rectification column. In the variants shown, a solvent is used
which is higher-boiling or lower-boiling than the diluent used.
In FIGS. 4 and 5, embodiments of the process according to the invention
are shown in which the production or processing process permits a certain
preloading of solvent in the diluent. In the variants shown, the preloaded
diluent is withdrawn from the rectifying column via a side take-off.
FIGS. 6, 7 and 8 show processes according to the invention in which an
exhaust air scrubber is additionally used.