U.S. patent application number 10/181185 was filed with the patent office on 2003-01-02 for method for producing 1,2-dichloroethane.
Invention is credited to Eichler, Jurgen, Greve, Arend, Grumann, Helmut, Jaculi, Dieter, Lork, Winfried, Stoger, Manfred, Wilkens, Jan.
Application Number | 20030004380 10/181185 |
Document ID | / |
Family ID | 26007823 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030004380 |
Kind Code |
A1 |
Grumann, Helmut ; et
al. |
January 2, 2003 |
Method for producing 1,2-dichloroethane
Abstract
A process for the preparation of 1,2-dichloroethane that is very
pure with respect to chloral or/and chloral hydrate and carbon
dioxide is described herein. The process comprises oxychlorination
of ethylene, using hydrogen chloride and an oxygen-containing gas,
and alkali treatment of the 1,2-dichloroethane produced. In the
process, the carbon dioxide present in the
1,2-dichloroethane-containing organic phase is, in accordance with
the invention, substantially separated out from the
1,2-dichloroethane-containing organic phase before the alkali
treatment.
Inventors: |
Grumann, Helmut; (Perach,
DE) ; Stoger, Manfred; (Burgkirchen, DE) ;
Eichler, Jurgen; (Kastl, DE) ; Jaculi, Dieter;
(Burgkirchen, DE) ; Lork, Winfried; (Erftstadt,
DE) ; Greve, Arend; (Erftstadt, DE) ; Wilkens,
Jan; (Erftstadt, DE) |
Correspondence
Address: |
PITNEY, HARDIN, KIPP & SZUCH LLP
685 THIRD AVENUE
NEW YORK
NY
10017-4024
US
|
Family ID: |
26007823 |
Appl. No.: |
10/181185 |
Filed: |
July 10, 2002 |
PCT Filed: |
November 29, 2001 |
PCT NO: |
PCT/EP01/13941 |
Current U.S.
Class: |
570/224 |
Current CPC
Class: |
C07C 17/156 20130101;
C07C 17/156 20130101; C07C 17/38 20130101; C07C 19/045
20130101 |
Class at
Publication: |
570/224 |
International
Class: |
C07C 017/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 29, 2000 |
DE |
100 59 229.5 |
Feb 13, 2001 |
DE |
101 07 092.6 |
Claims
1. Process for the preparation of 1,2-dichloroethane, wherein
oxychlorination of ethylene, using hydrogen chloride and an
oxygen-containing gas, and alkali treatment of the dichloroethane
are carried out, characterised in that carbon dioxide is separated
out before alkali treatment of the 1,2-dichloroethane.
2. Process according to claim 1, characterised in that the carbon
dioxide is separated out by relieving the
1,2-dichloroethane-containing reaction mixture of pressure.
3. Process according to claim 1 or 2, characterised in that the
carbon dioxide is separated out from the
1,2-dichloroethane-containing reaction mixture in a column (2A) by
introducing an inert gas.
4. Process according to one of the preceding claims, characterised
in that the inert gas is nitrogen.
5. Process according to one of the preceding claims, characterised
in that the carbon dioxide is separated out from the
1,2-dichloroethane-containin- g reaction mixture by indirect
introduction of heat.
6. Process according to one of the preceding claims, characterised
in that separating out of the carbon dioxide is additionally or
alternatively carried out by means of a heat exchanger.
7. Process according to one of the preceding claims, characterised
in that the reaction mixture, after separating out of the carbon
dioxide, has a carbon dioxide content of less than 0.3% (w/w),
preferably less than 0.1% (w/w) and especially less than 0.06%
(w/w).
8. Process according to one of the preceding claims, characterised
in that the 1,2-dichloroethane-containing product from
oxychlorination is quenched, cooled and/or liquefied before
separating out of the carbon dioxide.
9. Process according to claim 8, characterised in that quenching is
carried out by means of introduction into a sump region of a
washing zone, which sump region is in the form of a bubble column
and contains a washing liquid.
10. Process according to one of claims 8 or 9, characterised in
that quenching is carried out by means of bringing into contact
with an aqueous solution, especially water.
11. Process according to one of the preceding claims, characterised
in that the 1,2-dichloroethane-containing reaction mixture is
treated with an aqueous alkali solution after separating out of the
carbon dioxide.
12. Process according to claim 11, characterised in that the
1,2-dichloroethane-containing reaction mixture or the
1,2-dichloroethane is separated from the aqueous alkali solution
after treatment with the aqueous alkali solution and, before the
treatment, the aqueous alkali solution preferably has a pH greater
than 8.5.
13. Process according to claim 12, characterised in that the
aqueous alkali solution is recycled.
14. Process according to claim 13, characterised in that the
aqueous alkali solution is recycled to the quench.
15. Process according to one of the preceding claims, characterised
in that, after separation of the aqueous alkali phase from the
organic phase, a pH in the range of from 10.5 to 13 is set.
16. Process according to one of the preceding claims, characterised
in that the 1,2-dichloroethane-containing reaction mixture has a
chloral or/and chloral hydrate content of less than 0.02% (w/w),
preferably less than 0.005% (w/w) and especially less than 0.002%
(w/w).
17. 1,2-Dichloroethane obtainable using a process according to one
of claims 1 to 16.
Description
DESCRIPTION
[0001] The invention relates to a process for the preparation of
1,2-dichloroethane that is very pure with respect to chloral or/and
chloral hydrate and carbon dioxide, which process comprises
oxychlorination of ethylene, using hydrogen chloride and an
oxygen-containing gas such as air or oxygen, and alkali treatment
of the dichloroethane, and also to 1,2-dichloroethane prepared in
accordance with that process.
[0002] A known process for the preparation of 1,2-dichloroethane is
the oxychlorination of ethylene using hydrogen chloride and oxygen,
wherein chloral or/and chloral hydrate are formed as undesirable
by-products. Also, the product of the process often comprises
relatively large amounts of dissolved carbon dioxide formed as a
by-product of the reaction of ethylene with oxygen.
[0003] The publication DE 1 518 931 describes an oxychlorination
process for the preparation of 1,2-dichloroethane, wherein the
undesirable chloral is removed by means of a condensing step.
However, only 75 to 80% of the chloral can be separated out from
the product by means of that process step. The remaining chloral is
subsequently converted, by increasing the pH, into substances, for
example chloroform, that can be more readily separated out by means
of distillation.
[0004] Similarly, German Patent Specification 1 468 480 describes
an oxychlorination process wherein the undesirable by-products
chloral and/or chloral hydrate are converted into sodium formate
and chloroform by means of alkali treatment and can therefore be
readily separated out from the product of the process,
1,2-dichloroethane.
[0005] The disadvantage of both processes is that a large quantity
of the alkali solution, especially aqueous alkali metal hydroxide
solution, is consumed in neutralising the carbon dioxide and a
corresponding amount of alkali metal carbonate or other salts is
formed. Larger amounts of alkali solution therefore have to be used
than would be necessary purely for converting the chloral and/or
chloral hydrate. In addition, the salt charge formed in
considerable measure as a result of the neutralisation has to
removed from the production plant and disposed of.
[0006] The problem of the present invention accordingly was to
provide, for the preparation of 1,2-dichloroethane, an
oxychlorination process that avoids the disadvantages of the known
processes. The problem of the present invention was especially to
reduce, or to avoid altogether, the consumption of alkali solution,
and the salt charge, during conversion of the undesirable
by-products chloral and chloral hydrate and, at the same time, to
prepare 1,2-dichloroethane that has only a low content of the said
by-products, if any at all.
[0007] The problem is solved by a process for the preparation of
1,2-dichloroethane, which process comprises oxychlorination of
ethylene, using hydrogen chloride and an oxygen-containing gas such
as oxygen or air, and alkali treatment of the
dichloroethane-containing reaction mixture and which is
characterised in that carbon dioxide is especially removed from the
1,2-dichloroethane-containing organic phase before alkali treatment
of the 1,2-dichloroethane is carried out.
[0008] It has been found to be especially advantageous for the
carbon dioxide to be removed, to as great an extent as possible,
from the reaction mixture before alkali treatment of the
1,2-dichloroethane because the formation of large salt charges can
be avoided as a result. That spares the production plant and saves
working time and costs, because it is no longer necessary, or only
necessary to a reduced extent, to remove a salt charge from the
production plant.
[0009] As a result of the process according to the invention, it
is, in addition, advantageously possible to reduce the amount of
alkali solutions to be used. The reduced lye requirement allows the
production costs to be reduced. That is also advantageous and
desirable from a health point of view as smaller volumes of lye
have to be handled by the operating staff. In addition, therefore,
less lye needs to be disposed of, which constitutes a considerable
advantage both from a cost point of view and from an environmental
point of view.
[0010] In accordance with the invention, pure or very pure EDC has,
per kg of EDC, a 2-chloroethanol content of <100 mg, especially
<50 mg, preferably <20 mg, more preferably <10 mg, even
more preferably <5 mg, and very preferably <2 mg.
[0011] In accordance with the invention, very pure EDC has, per kg
of EDC, a chloral content of <20 mg, preferably <10 mg, and
very preferably <5 mg. In accordance with the invention, very
pure EDC has, per kg of EDC, an iron chloride content of <20 mg,
preferably <10 mg, more preferably <5 mg, and very preferably
<1 mg.
[0012] In accordance with one embodiment, the process of the
invention preferably comprises the following process steps:
[0013] 1. oxychlorination of ethylene using hydrogen chloride and
oxygen,
[0014] 2. quenching, washing and/or cooling and condensing of the
reaction gases, that is to say of the products obtained from
oxychlorination,
[0015] 3. optionally, separation from the washing liquid,
[0016] 4. distillation and condensing of 1,2-dichloroethane and,
where applicable, water from the quench,
[0017] 5. separation of the aqueous phase from the organic phase
from step 4, optionally after transfer of the
1,2-dichloroethane-containing condensate into a separating vessel,
optionally recycling of the aqueous phase to the quench, and
optionally recycling of gases to the oxychlorination reaction,
[0018] 6. removal of carbon dioxide from the
1,2-dichloroethane-containing phase (the reaction mixture),
[0019] 7. alkali treatment of the 1,2-dichloroethane-containing
phase, for example using an aqueous lye,
[0020] 8. separation of the aqueous phase from the organic phase,
optionally after transfer of the 1,2-dichloroethane-containing
phase from step 7 into a separating vessel, optionally recycling of
the aqueous phase to the quench,
[0021] 9. obtaining 1,2-dichloroethane, and
[0022] 10. optionally further working up or further processing
steps.
[0023] The 1,2-dichloroethane obtained in that manner is very pure
with respect to chloral/chloral hydrate.
[0024] The process conditions of individual steps, known per se, of
the process according to the invention, especially the
oxychlorination step and the alkali treatment step, can be carried
out preferably in accordance with the process conditions described
in the publication DE 1 518 931 and German Patent 1 468 480, the
disclosures thereof being incorporated by way of reference in the
present description.
[0025] A catalyst is preferably used for the oxychlorination step,
with CuCl.sub.2 or FeCl.sub.3 catalysts having been found to be
especially suitable for the purpose.
[0026] Before removal of the carbon dioxide, the reaction mixture
is preferably blown into a washing-liquid-containing sump region,
in the form of a bubble column, of a washing or quenching zone.
[0027] In accordance with a further embodiment of the process, the
reaction mixture coming from the reaction zone, which reaction
mixture may under certain circumstances include solids, with
catalyst fragments under certain circumstances also being present
in addition to the gaseous and/or liquid products of
oxychlorination of the ethylene, is passed through a washing zone;
the washing zone may comprise, for example, a column and a lower
sump region arranged in the form of a bubble column. In the
process, the reaction mixture preferably enters the lower portion
of the bubble column, where it comes into intimate contact with the
washing liquid present therein and, at the same time, is
quantitatively freed of catalyst fragments. That process step can
also be designated quenching.
[0028] The consumed washing liquid from the sump region of the
washing zone is directed away, for example being neutralised and
sent to waste water treatment.
[0029] The gaseous portion of the reaction mixture, which has been
cooled and washed in the washing zone, is passed, by way of a gas
line, into a condensing zone, in which there preferably prevail an
elevated pressure and a low temperature.
[0030] The EDC-containing reaction mixture is substantially
condensed therein, preferably under pressure, and is separated from
the volatile by-products. The carbon dioxide is present in
dissolved form in the condensate.
[0031] The carbon dioxide, present especially in the
1,2-dichloroethane-containing organic phase, may be separated out
using any suitable procedure or apparatus. Separating the carbon
dioxide out from the 1,2-dichloroethane-containing phase is
preferably carried out by a method involving at least relieving the
phase of pressure, for example in a vessel (desorption vessel). In
that process, before the pressure is relieved, the phase has, for
example, a pressure in the region of about 4 bar abs., whereas
after the pressure is relieved it has, for example, a pressure in
the region of about 1.1 bar abs. A vessel of that kind preferably
has an outlet for drawing off the carbon dioxide (gaseous) and an
outlet for the 1,2-dichloroethane-containing phase (liquid). That
liquid phase can then be supplied to the further process steps by
way of that outlet. A further process step is alkali treatment of
the dichloroethane, which is already very pure with respect to
CO.sub.2, for the purpose of removing chloral and/or chloral
hydrate.
[0032] In a further preferred embodiment, the carbon dioxide is
separated out from the 1,2-dichloroethane phase in a column, by
introduction of an inert gas. Any inert gas that is suitable in
this process step may be used as the inert gas. The inert gas is
preferably nitrogen. 1,2-Dichloroethane and inert gas are
advantageously directed past one another in counterflow, as a
result of which the mass transfer can be improved. A process course
having concurrent flow is, however, also possible.
[0033] In yet another preferred embodiment, before the carbon
dioxide is separated out, the 1,2-dichloroethane or the
1,2-dichloroethane-containin- g phases is/are heated, by the
introduction of heat, it being possible to use the customary
procedures and apparatus known to the person skilled in the art.
Special preference is given to carrying using a heat exchanger.
[0034] The above-mentioned procedures relating to the removal of
carbon dioxide may also be combined with one another as
desired.
[0035] As a result of the separating out of carbon dioxide in
accordance with the invention, it is possible to remove, completely
or virtually completely, from the 1,2-dichloroethane-containing
reaction mixture, especially from the organic phase, the carbon
dioxide dissolved therein. After the separating out of carbon
dioxide, the 1,2-dichloroethane-contai- ning organic phase
preferably has a carbon dioxide content of less than 0.3% (w/w),
preferably less than 0.2% (w/w) and especially less than 0.06%
(w/w).
[0036] The process according to the invention makes possible, by
simple technical means and in economical manner, effective removal
of the catalyst fragments and/or the carbon dioxide from the
1,2-dichloroethane-containing phase. The process according to the
invention is first in resulting, in advantageous manner, in
significant carbon dioxide separation, allowing a reduced use of
base together with effective breakdown of chloral and/or chloral
hydrate and accordingly resulting in a reduced salt charge.
[0037] In an especially preferred embodiment, the
1,2-dichloroethane-conta- ining product from oxychlorination is
quenched before the carbon dioxide is separated out.
[0038] In the context of the invention, quenching, for example in
the form of cooling and condensing, means that unreacted starting
materials, for example hydrogen chloride, are completely or at
least substantially removed by means of suitable liquids,
solutions, gases or gas mixtures. Quenching according to the
invention has the advantage that, in the oxychlorination step, all,
or the major portion, of unreacted starting materials are removed
from the phase which is subjected to the further process steps.
[0039] The product from the oxychlorination process preferably
contains, after quenching, less than 0.010% (w/w) hydrogen
chloride, especially less than 0.005% (w/w) and most preferably
less than 0.001% (w/w). As a result, undesirable reactions
(corrosion) can advantageously be reduced or even avoided
altogether.
[0040] Special preference is given to quenching by means of
bringing into contact with an aqueous solution (washing solution),
most preferably with water or an aqueous alkali solution.
[0041] The alkali treatment of the 1,2-dichloroethane-containing
phase to be carried out after separating out the carbon dioxide may
be accomplished using any suitable procedure and by means of
customary apparatus. This process step is preferably carried out
using an aqueous alkali solution. The aqueous alkali solution
preferably has a pH of more than 8.5, especially more than 9.5.
[0042] Subsequently, further customary separation procedures known
to the person skilled in the art, such as distillation, may be
carried out in order to separate the chloral and/or chloral hydrate
breakdown products and further constituents from the
1,2-dichloroethane.
[0043] The organic and aqueous waste products of the process are
removed from the process circuit and are disposed of or recycled as
necessary. The aqueous alkali solution obtained from the final
process step is preferably recycled, especially together with
further aqueous phases to which other process steps give rise. In
the context of the invention, recycling is understood to mean that
products of the process, intermediates or auxiliaries are returned
to and used again in a process step.
[0044] In an especially preferred embodiment, the aqueous alkali
solution, alone or together with the further aqueous phases, is
recycled to the quench.
[0045] As a result of recycling the alkali solution to the quench,
the pH of the quench is increased, as a result of which it is
advantageously possible to improve the washing out of unreacted
hydrogen chloride remaining from oxychlorination. Furthermore,
additional neutralisation of the lye can, at least in some cases,
be omitted.
[0046] The product of the process, 1,2-dichloroethane, obtained
using the process according to the invention is substantially free
of chloral and chloral hydrate. It preferably has a chloral or/and
chloral hydrate content of less than 0.02% (w/w), preferably less
than 0.005% (w/w) and especially less than 0.002% (w/w).
[0047] A further aspect of the invention relates to
1,2-dichloroethane that is very pure with respect to chloral and/or
chloral hydrate and obtainable using a process as described
above.
[0048] 1,2-Dichloroethane according to the invention may
advantageously be used in applications where chloral or chloral
hydrate would have an adverse effect.
[0049] Further advantages and developments of the invention are
shown by the patent claims, the drawings, and the following
description in which exemplary embodiments of the invention are
described in detail with reference to the drawings, with:
[0050] FIG. 1 showing a flow diagram of a process of the invention
according to a first preferred embodiment;
[0051] FIG. 2 showing a flow diagram of a further preferred
embodiment of the process according to the invention; and
[0052] FIG. 3 showing a flow diagram of a further preferred
embodiment of the process.
[0053] FIG. 1 shows a flow diagram of a process according to the
invention, wherein EDC denotes the 1,2-dichloroethane being
produced and 5 denotes an oxychlorination step. The oxychlorination
is carried out in known manner under customary conditions known to
the person skilled in the art. The process gas of the
oxychlorination step 5 is transferred to a quenching step 7 by way
of a line 6. The reaction mixture obtained therefrom is transferred
into a decanter 1 by way of a line 8 provided with a heat exchanger
21, whereas the waste water is directed away from the quenching
step 7 by way of a waste water line 20. Recycle gases are recycled
from the decanter 1, by way of a line 9, to the oxychlorination
step 5.
[0054] The aqueous phase is separated off in the decanter 1 and it
is recycled to the quenching step 7 by way of a line 10 by means of
a pump 16. The 1,2-dichloroethane(EDC)-containing organic phase
from the decanter 1 is relieved of pressure in a vessel 2 by way of
a control valve 19, the carbon dioxide given off being removed by
way of a carbon dioxide take-off line 11. In accordance with the
preferred embodiment shown, an inert gas, in this instance
nitrogen, can, in addition, be fed in by way of an inert gas supply
line 13.
[0055] Then, in an apparatus 3, the 1,2-dichloroethane-containing
phase is treated by introduction of lye by way of an inlet line 12.
In a further decanter 4, the aqueous alkaline phase is separated
from the organic 1,2-dichloroethane-containing phase and recycled
to the quenching step 7 by way of a line 14 by means of a pump 17.
Finally, by that means, 1,2-dichlorothane that is very pure with
respect to chloral or/and chloral hydrate is obtained from the end
product take-off line 15.
[0056] FIG. 2 shows a flow diagram, corresponding to FIG. 1, in
accordance with a further preferred embodiment of the invention.
The difference from the process shown in FIG. 1 lies in the fact
that carbon dioxide removal is carried out by means of a column 2A
in conjunction with a heat exchanger 18, with inert gas, in this
instance nitrogen, being introduced in counterflow; the heat
exchanger 18 is situated upstream of the control valve 19.
Otherwise, the course of the process corresponds to that shown in
FIG. 1, for which reason corresponding parts and process steps are
given reference symbols corresponding to FIG. 1.
[0057] FIG. 3 shows an oxychlorination step 5, a washing or
quenching zone 7, a vessel 2, a condensing step 105, a desorption
zone 104, a separating zone 107 and a distillation zone 108 as
central zones. In two heating zones 112 and 113, the process gases
hydrogen chloride, oxygen, ethylene and recycle gas, that is to say
gas obtained by recycling, are pre-heated and fed into the
oxychlorination step 5.
[0058] 6000 Nm.sup.3/h of hydrogen chloride and 1545 Nm.sup.3/h of
oxygen are fed, through the hydrogen chloride line 117 and the
oxygen line 118, respectively, into the second heating zone 113 and
they are blown into the oxychlorination step 5 at a temperature of
140.degree. C. 10000 Nm.sup.3/h of recycle gas and 3000 Nm.sup.3/h
of ethylene are fed, through the recirculating line 120 and the
ethylene line 119, respectively, into the first heating zone 112
and they are likewise blown into the oxychlorination step 5 at a
temperature of 140.degree. C.
[0059] The oxychlorination step 5 comprises a fluidised-bed reactor
having a steam generator for dissipating the reaction heat; the
reacted reaction gas flows out of the fluidised-bed reactor at a
temperature of 210.degree. C., through the reaction gas line 6 and
into the lower region of the quenching or washing zone 7. The
washing zone 7 comprises a column (dia.: 2.2 m) having 8 valve
trays and having a sump region 7a arranged very especially in the
form of a bubble column. The reaction gas enters the lower region
of the bubble column, where it comes into contact with the washing
liquid and, at the same time, is quantitatively freed of catalyst
fragments. In the washing zone 7, the reaction gas is cooled to a
temperature of from 95.degree. C. to 100.degree. C. by the washing
solution.
[0060] The washing liquid at the base of the bubble column runs
off, through the run-off line 121, into the vessel 2 for the
purpose of neutralisation by means of sodium hydroxide solution
introduced by way of line 114 and is finally passed, by way of line
126, to the waste water plant for further treatment. The washed and
cooled reaction gases are passed from the washing zone 7, through
the gas line 122 and into the condensing zone 105.
[0061] Non-condensed recycle gas is passed, through the line 131,
to the recirculating compressor 106 and is returned, by way of the
line 120, to the oxychlorination step 5. A portion of the recycle
gas is taken away by way of the waste gas line 133. By way of the
condensate line 124, the EDC/water mixture, which is in liquid form
under a pressure of about 4 bar and which contains dissolved carbon
dioxide, at a temperature of 37.degree. C. is relieved of pressure
in the desorption zone 104, down to a pressure of about 1.6 bar,
where it separates into carbon dioxide, which leaves at the top,
and EDC/water mixture, which runs off at the base. It is also
optionally possible for separation of water and the remaining
reaction mixture to be carried out beforehand.
[0062] 2 Nm.sup.3/h of nitrogen are fed into the condensing zone
105, by way of the line 129, for thorough mixing of the condensate,
and 3 Nm.sup.3/h of nitrogen are fed into the pressure-relieving
zone 104, at the base, by way of line 132, for stabilising the
carbon dioxide flow, the addition of nitrogen also bringing about
more effective or improved removal of the carbon dioxide.
[0063] While the carbon dioxide flowing out from the desorption
zone 104 by way of line 125 is removed from the process in the form
of waste gas (33 Nm.sup.3/h), the EDC/water mixture running off at
the base is passed to the separating zone 107, by way of line 127,
after thorough mixing with 25% sodium hydroxide solution from line
115, for the purpose of separating the two-phase mixture into an
alkaline aqueous phase and an EDC phase.
[0064] Because both the aqueous phase and the EDC phase no longer
contain dissolved carbon dioxide, after the introduction of sodium
hydroxide solution the possibility of buffering in the as a result
of sodium hydrogen carbonate/sodium carbonate formation is ruled
out and excellent, constant regulation of the specified pH in the
range of from 10.5 to 13, preferably in the region of about 12, in
the aqueous phase is ensured at all times for the purpose of
chloral and 2-chloroethanol breakdown.
[0065] Maintenance of the pH is monitored by means of continuous
measurement.
[0066] The aqueous phase obtained in that manner in the separating
zone 107 can therefore be introduced into the quenching or washing
zone 102 as washing liquid.
[0067] After an average dwell time, in the separating zone 107, in
the region of preferably from 0.5 to 3 hours, especially of about 1
hour, the upper, aqueous alkaline phase (having a pH adjusted to
more than 9.5) is returned, by way of the line 123, to the
washing/quenching zone 102 and the lower, 1,2-dichloroethane phase
is passed, by way of line 128, into the distillation zone. The
distillation zone 108 comprises a perforated-plate column (dia.: 2
m) having an evaporator 109, condenser 110 and separator 111.
[0068] While the low-boiling and aqueous portion is removed from
the separator 111, the purified 1,2-dichloroethane is drawn off, by
way of line 130, from the sump of the distillation zone 108 for the
purpose of obtaining vinyl chloride by EDC cracking.
[0069] A certain portion both of the aqueous phase from line 123
and of the 1,2-dichloroethane phase from line 128 are returned to
line 127 in order to achieve additional thorough mixing.
[0070] After start-up of the plant, the chloral, 2-chloroethanol
and iron chloride contents in the purified 1,2-dichloroethane (EDC)
were, at
[0071] <2 mg of 2-chloroethanol/kg of EDC
[0072] <5 mg of chloral/kg of EDC
[0073] <1 mg of iron chloride/kg of EDC,
[0074] below the limits of detection.
[0075] After a continuous production period of 6 weeks, the
analytical impurity values did not change. Analysis of the
1,2-dichloroethane yielded the same results as had been obtained
after start-up of the plant (see above).
[0076] For production of about 13500 t of EDC, a total of 327 t of
25% sodium hydroxide solution was added, corresponding to a
specific consumption of 24.2 kg/t of EDC.
[0077] The process is distinguished by the fact that, in accordance
with the invention, without a circulating procedure for the
suspension, which may possibly contain solids, and irrespective of
production changes and of the pH in the course of the washing
and/or dwell zone, after separating out carbon dioxide in the
desorption zone, the 1,2-dichloroethane/water mixture obtained from
the condensing zone at a temperature of preferably from 25 to
45.degree. as a result of its being relieved of pressure needs only
to be subjected to alkali treatment with sodium hydroxide solution
at an adjustable pH of preferably >8.5, especially >9.5, more
especially in the range from 10.5 to 13, and for a dwell time of,
for example, from 0.5 to 3 hours in the separating zone in order to
obtain effective reduction of the chloral and 2-chloroethanol
contents in the 1,2-dichloroethane and, therefore, to ensure the
desired EDC quality for a lasting period. The iron chloride content
in the product is below the limit of detection at all times.
[0078] In accordance with a preferred embodiment, a certain portion
of the separated aqueous phase and/or organic phase can be returned
to the line leading into the separating zone in order to achieve
additional thorough mixing.
EXAMPLE 1
[0079] The course of the process in this instance is as shown in
FIG. 1. The oxychlorination is carried out under customary process
conditions, which will be known to the person skilled in the art
and are therefore not explicitly mentioned here. The process gases
from the oxychlorination step 5, essentially 1,2-dichloroethane,
water and the undesirable by-products carbon dioxide, chloral
and/or chloral hydrate and possibly further by-products, are
quenched in a following process step (the quenching step 7) using
an aqueous solution. In the process, traces of hydrogen chloride
that have not been reacted during oxychlorination and, possibly,
catalyst residues are washed out from the product mixture obtained
from oxychlorination.
[0080] The 1,2-dichloroethane-containing phase, together with
water, is then distilled off from the quenching step and condensed.
For that purpose, the quench is distilled at a pressure of from 2
to 4 bar and at a temperature of from 90 to 110.degree. C. in a
suitable distillation apparatus, is condensed and is then
transferred to a separating vessel, preferably a decanter 1. In the
decanter 1, the aqueous phase is separated from the organic
1,2-dichloroethane-containing phase. The gaseous constituents
therefrom can be recycled to the oxychlorination step 5. The
aqueous phase is recycled to the quenching step 7 and the organic
phase is relieved of pressure in a vessel 2, the carbon dioxide
being substantially evolved from the 1,2-dichloroethane and drawn
off through an outlet from the vessel. The carbon dioxide content
in the 1,2-dichloroethane phase obtained is from 0.2% to 0.3% (w/w)
carbon dioxide, based on the 1,2-dichloroethane-containing
phase.
[0081] In the process step that follows, the
1,2-dichloroethane-containing- , organic phase is transferred to an
apparatus 3 located downstream and alkali treatment is carried out.
For that purpose, a lye, preferably an NaOH solution having a
concentration of <10% (w/w) is introduced into the apparatus 3,
as a result of which the chloral and/or chloral hydrate is broken
down.
[0082] The mixture is passed into a further decanter 4, in which
the 1,2-dichloroethane and the alkaline aqueous phase are separated
from one another. The alkaline aqueous phase is recycled to the
quenching step 7, and 1,2-dichloroethane that is very pure with
respect to chloral/chloral hydrate, having a chloral or/and chloral
hydrate content of less than 0.002% to 0.005% (w/w) based on the
1,2-dichloroethane-containing phase, is obtained.
EXAMPLE 2
[0083] The course of the process is as shown in FIG. 2. The process
steps and the course of the process therein also correspond to
those of FIG. 1, with the difference that, for separating out the
carbon dioxide from the 1,2-dichloroethane-containing phase, that
phase is passed from the first separating vessel, a decanter 1,
into a column 2A in which the carbon dioxide is separated off by
means of the introduction of nitrogen by way of an inert gas supply
inlet 13. After that process step, the
1,2-dichloroethane-containing phase has a carbon dioxide content of
from 0.05% to 0.1% (w/w).
EXAMPLE 3
[0084] The process steps and the course of the process again
essentially correspond to those of FIG. 1, with the difference
that, for separating out the carbon dioxide from the
1,2-dichloroethane-containing phase, that phase from the first
separating vessel, a decanter 1, is subjected to indirect
introduction of heat by means of a heat exchanger, with nitrogen
additionally being introduced into the column 2A. After that
process step, the 1,2-dichloroethane-containing phase has a carbon
dioxide content of from <0.05% to 0.06% (w/w).
LIST OF REFERENCE SYMBOLS
[0085] 1 decanter
[0086] 2 vessel
[0087] 2A column
[0088] 3 apparatus for alkali treatment
[0089] 4 decanter
[0090] 5 oxychlorination step
[0091] 6 line for process gas from oxychlorination
[0092] 7 quenching step
[0093] 7a sump region
[0094] 8 line with heat exchanger
[0095] 9 line for recycling of gas
[0096] 10 line for recycling of aqueous solution
[0097] 11 carbon dioxide take-off line
[0098] 12 alkali solution inlet line
[0099] 13 inert gas supply line
[0100] 14 aqueous solution recycling line
[0101] 15 end product take-off line
[0102] 16 pump
[0103] 17 pump
[0104] 18 heat exchanger
[0105] 19 control valve
[0106] 20 waste water line
[0107] 21 heat exchanger
[0108] 104 pressure-relieving or desorption zone
[0109] 105 condensing step
[0110] 106 recirculating compressor
[0111] 107 separating zone
[0112] 108 distillation zone
[0113] 109 evaporator
[0114] 110 condenser
[0115] 111 separator
[0116] 112 heating zone
[0117] 113 heating zone
[0118] 114 line
[0119] 115 line
[0120] 116
[0121] 117 hydrogen chloride line
[0122] 118 oxygen line
[0123] 119 ethylene line
[0124] 120 recirculating line
[0125] 121 run-off line
[0126] 122 gas line
[0127] 123 line (return to washing zone)
[0128] 124 condensate line
[0129] 125 carbon dioxide waste gas line
[0130] 126
[0131] 127 line
[0132] 128 line
[0133] 129 line
[0134] 130 product line
[0135] 131 line
[0136] 132 line
[0137] 133 line
* * * * *