Process for providing hydrogen chloride for chemical reactions

Abstract

The invention relates to an improved process for making available the coproduct hydrogen chloride obtained in the preparation of an isocyanate by phosgenation of the corresponding amine for a desired subsequent use (i.e. a chemical reaction), in which part of the total hydrogen chloride obtained is isolated in gaseous form at a pressure which is higher than the pressure desired for the subsequent use of the hydrogen chloride by lowering the pressure of the crude product from the phosgenation and the remaining part of the total hydrogen chloride obtained is separated off at a pressure lower than that desired for the subsequent use from the liquid crude product from the phosgenation remaining after lowering of the pressure and is subsequently compressed to a pressure which is higher than that desired for the subsequent use, and in which the two hydrogen chloride streams obtained in this way are, preferably together after having been combined, purified so as to give a purified hydrogen chloride at a pressure which is higher than the pressure desired for the subsequent use.

Claims

1. A process for making hydrogen chloride, obtained as coproduct in the preparation of an isocyanate by phosgenation of a corresponding amine, optionally in the presence of a solvent, available for a desired subsequent use at a desired admission pressure of the hydrogen chloride of p.sub.F, comprising: (i) single-stage depressurizing or multistage depressurizing crude product from the phosgenation, which is under a pressure p.sub.R, to a pressure p.sub.E>p.sub.F, thereby giving a gaseous stream containing hydrogen chloride and a liquid stream containing isocyanate and phosgene and also optionally solvent; (ii) separating phosgene from the liquid stream containing isocyanate and phosgene and also optionally solvent at a pressure p.sub.A<p.sub.F, thereby giving a gaseous stream comprising phosgene and hydrogen chloride and a stream containing isocyanate and optionally solvent; (iii) compressing the gaseous stream comprising phosgene and hydrogen chloride to a pressure p.sub.V>p.sub.F, thereby giving a compressed gas stream; and (iv) purifying the gaseous stream containing hydrogen chloride and the compressed gas stream at a pressure p.sub.D>p.sub.F, thereby giving purified hydrogen chloride gas and phosgene-containing liquid, wherein the subsequent use is selected from among: the preparation of chlorine by catalytic oxidation of hydrogen chloride by means of oxygen at a value of p.sub.F in the range from 1.00 bar to 25.0 bar and the reaction to form ethylene dichloride by oxychlorination of ethane or ethylene at a value of p.sub.F in the range from 1.00 bar to 15.0 bar.

2. The process of claim 1, wherein step (i) is carried out in a separator.

3. The process of claim 2, wherein the separator is configured as a cascade of a plurality of separators connected in series with a successively decreasing pressure level, where a gaseous, hydrogen chloride-containing phase is taken off from each separator and these individual gaseous phases containing hydrogen chloride are further combined to form the gaseous stream containing hydrogen chloride, the pressure of which corresponds to the pressure p.sub.E.

4. The process of claim 1, wherein step (ii) is carried out in a dephosgenation column.

5. The process of claim 1, wherein step (iv) is carried out in a distillation column.

6. The process of claim 5, wherein the gaseous stream containing hydrogen chloride and the compressed gas stream are combined before step (iv) is carried out.

7. The process of claim 6, wherein in step (iv): (1) the stream obtained by combining the gaseous stream containing hydrogen chloride and the compressed gas stream is partially condensed by indirect cooling in a heat exchanger thereby producing a resulting liquid stream and a resulting gas stream, (2) the resulting liquid stream and the resulting gas stream are fed into the distillation column, (3) a gaseous stream obtained at the top of the distillation column is partially condensed by indirect cooling in another heat exchanger, (4) a liquid phase obtained in (iv.3) is recirculated to the top of the distillation column, and (5) a gas phase obtained in the partial condensation of (3) is used as medium for indirect cooling in step (iv.1).

8. The process of claim 1, wherein the isocyanate is selected from the group consisting of methylenedi(phenyl isocyanate) as pure isomer or as isomer mixture, polymethylenepolyphenyl polyisocyanate, mixtures of methylenedi(phenyl isocyanate) and polymethylenepolyphenyl polyisocyanate, tolylene diisocyanate as pure isomer or isomer mixture, isomers of xylylene diisocyanate, isomers of diisocyanatobenzene, 2,6-xylene isocyanate and naphthylene 1,5-diisocyanate.

9. The process of claim 1, wherein p.sub.R has a value in the range from 6.00 bar to 60.0 bar, p.sub.E has a value in the range from 5.00 bar to 30.0 bar, p.sub.A has a value in the range from 0.50 bar to 5.00 bar, p.sub.V has a value in the range from 5.00 bar to 30.0 bar and p.sub.D has a value in the range from 1.01 bar to 25.5 bar.

10. The process of claim 1, wherein p.sub.R has a value in the range from 12.0 bar to 45.0 bar, p.sub.E has a value in the range from 9.00 bar to 18.0 bar; p.sub.A has a value in the range from 1.00 bar to 3.00 bar; p.sub.V has a value in the range from 9.00 bar to 18.0 bar and p.sub.D has a value in the range from 5.00 bar to 17.5 bar.

11. The process of claim 9, wherein the crude product from the phosgenation has a temperature T.sub.R in the range from 80 C. to 200 C., the gaseous stream containing hydrogen chloride has a temperature T.sub.E in the range from 90 C. to 170 C., the gaseous stream comprising phosgene and hydrogen chloride has a temperature T.sub.A in the range from 10 C. to 90 C., the compressed gas stream has a temperature T.sub.V in the range from 90 C. to 170 C. and the purified hydrogen chloride gas has a temperature T.sub.D in the range from 50 C. to 20 C.

12. The process according to claim 10, wherein the crude product form the phosgenation has a temperature T.sub.R in the range from 110 C. to 170 C., the gaseous stream containing hydrogen chloride has a temperature T.sub.E in the range from 110 C. to 150 C., the gaseous stream comprising phosgene and hydrogen chloride has a temperature T.sub.A in the range from 30 C. to 70 C., the compressed gas stream has a temperature T.sub.V in the range from 110 C. to 150 C. and the purified hydrogen chloride gas has a temperature T.sub.D in the range from 30 C. to 10 C.

13. The process of claim 10, wherein the subsequent use is selected from among the preparation of chlorine by catalytic oxidation of hydrogen chloride by means of oxygen at a value of p.sub.F in the range from 1.50 bar to 17.0 bar, and the reaction to form ethylene dichloride by oxychlorination of ethane or ethylene at a value of p.sub.F in the range from 4.00 bar to 12.0 bar.

14. The process of claim 12, wherein the subsequent use is selected from among the preparation of chlorine by catalytic oxidation of hydrogen chloride by means of oxygen at a value of p.sub.F in the range from 1.50 bar to 17.0 bar, and the reaction to form ethylene dichloride by oxychlorination of ethane or ethylene at a value of p.sub.F in the range from 4.00 bar to 12.0 bar.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flowchart of an embodiment of the process of the invention in which the phosgenation reaction is also shown.

DETAILED DESCRIPTION

(2) The process of the invention is particularly suitable for use in the preparation of methylenedi(phenyl isocyanate) (MMDI) as pure isomers or as an isomer mixture, polymethylenepolyphenyl polyisocyanate (PMDI higher homologues of MMDI having three or more benzene rings), mixtures of methylenedi(phenyl isocyanate) and polymethylenepolyphenyl polyisocyanate, tolylene diisocyanate (TDI) as pure isomers or isomer mixture, isomers of xylylene diisocyanate (XDI), isomers of diisocyanatobenzene, 2,6-xylene isocyanate, naphthylene 1,5-diisocyanate (1,5-NDI), diisocyanates based on aliphatic or cycloaliphatic hydrocarbons having from 2 to 18 carbon atoms, e.g. butane 1,4-diisocyanate, pentane 1,5-diisocyanate, hexane 1,6-diisocyanate (HDI), octane 1,8-diisocyanate, nonane 1,9-diisocyanate, decane 1,10-diisocyanate, 2,2-dimethylpentane 1,5-diisocyanate, 2-methylpentane 1,5-diisocyanate (MPDI), 2,4,4(or 2,2,4)-trimethylhexane 1,6-diisocyanate (TMDI), cyclohexane 1,3- and 1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,4- or 2,6-diisocyanato-1-methylcyclohexane (H6-TDI), 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane (AMCI), 1,3(and/or 1,4)-bis(isocyanatomethyl)cyclohexane, bis(isocyanatomethyl)norbornane (NBDI), 4,4(and/or 2,4)-diisocyanatodicyclohexylmethane, and (cyclo)aliphatic triisocyanates having up to 22 carbon atoms, e.g. triisocyanatocyclohexane, tris(isocyanatomethyl)cyclohexane, triisocyanatomethylcyclohexane, 1,8-diisocyanato-4-(isocyanatomethyl)octane, undecane 1,6,11-triisocyanate, 1,7-diisocyanato-4-(3-isocyanatopropyl)heptane, 1,6-diisocyanato-3-(isocyanatomethyl)hexane or 1,3,5-tris(isocyanatomethyl)cyclohexane. The process of the invention is very particularly preferably suitable for use in the preparation of tolylene diisocyanate, diphenylmethane diisocyanate and polyphenylenepolymethylene polyisocyanate.

(3) The amines corresponding to the above polyisocyanates are aromatic polyamines such as methylenedi(phenylamine) (MMDA) as pure isomers or as isomer mixture, polymethylenepolyphenyl polyamine (PMDA), mixtures of methylenedi(phenylamine) and polymethylenepolyphenyl polyamine, toluenediamine (TDA) as pure isomers or isomer mixture, isomers of xylylenediamine (XDA), isomers of diaminobenzene, 2,6-xylidine, 1,5-naphthylenediamine (1,5-NDA), polyamines based on aliphatic or cycloaliphatic hydrocarbons having from 2 to 18 carbon atoms, e.g. 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane (HDA), 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 2,2-dimethyl-1,5-diaminopentane, 2-methyl-1,5-pentanediamine (MPDA), 2,4,4(or 2,2,4)-trimethyl-1,6-diaminohexane (TMDA), 1,3- and 1,4-diaminocyclohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane (IPDA), 2,4- or 2,6-diamino-1-methylcyclohexane (H6-TDA), 1-amino-1-methyl-4 (3)-aminomethylcyclohexane (AMCA), 1,3 (and/or 1,4)-bis(aminomethyl)cyclohexane, bis(aminomethyl)norbornane (NBDA), 4,4(and/or 2,4)-diaminodicyclohexylmethane, (cyclo)aliphatic polyamines having up to 22 carbon atoms, e.g. triaminocyclohexane, tris(aminomethyl)cyclohexane, triaminomethylcyclohexane, 1,8-di amino-4-(aminomethyl)octane, 1,6,11-undecanetriamine, 1,7-diamino-4-(3-aminopropyl)heptane, 1,6-diamino-3-(aminomethyl)hexane or 1,3,5-tris(aminomethyl)cyclohexane.

(4) The process of the invention is particularly suitable for use in the preparation of methylenedi(phenyl isocyanate) (MMDI) as pure isomers or as isomer mixture, polymethylenepolyphenyl polyisocyanate (PMDI), mixtures of methylenedi(phenyl isocyanate) and polymethylenepolyphenyl polyisocyanate, tolylene diisocyanate (TDI) as pure isomers or isomer mixtures, isomers of xylylene diisocyanate (XDI), isomers of diisocyanatobenzene, 2,6-xylene isocyanate, naphthylene 1,5-diisocyanate (1,5-NDI).

(5) Particular preference is given to using the process of the invention in the preparation of diphenylmethane diisocyanate (MMDI) and/or polyphenylenepolymethylene polyisocyanate (PMDI). For the purposes of the present invention, MMDI and PMDI are also referred to collectively as MDI, regardless of the degree of polymerization and isomer distribution; an analogous situation applies to MDA.

(6) The preparation of the corresponding polyamines is adequately known from the prior art and will therefore not be described in detail at this point. In the case of the particularly preferred polyisocyanate MDI, the corresponding polyamine MDA is obtained by acid-catalyzed condensation of aniline and formaldehyde. This gives a mixture of the two-ring compound MMDA (containing two benzene rings each bearing an amino group) and higher homologues PMDA (multiring compounds containing three or more benzene rings each bearing an amino group). In most industrially practiced processes, this mixture is phosgenated without prior separation into monomeric and polymeric constituents. Separation into monomeric constituents and polymeric constituents therefore usually takes place only at the stage of the polyisocyanate. Here, the two-ring compound (MMDI) and secondly a mixture of the two-ring compound (MMDI) and the higher homologues (PMDI) are obtained.

(7) Embodiments of the invention will be described in more detail below. Here, various embodiments can be combined with one another in any way as long as the contrary is not indicated to a person skilled in the art from the context.

(8) A possible embodiment of the process of the invention in which the phosgenation reaction is also shown is depicted in FIG. 1:

(9) Amine (10) and phosgene (20) are dissolved in a solvent (30) which is inert under the reaction conditions, preferably in such a way that the resulting phosgene-containing stream has a proportion by mass of from 5% to 95%, preferably from 20% to 75%, particularly preferably from 30% to 60%, of phosgene and a proportion by mass of from 95% to 5%, preferably from 80% to 25%, particularly preferably from 70% to 40%, of an inert solvent, in each case based on the total mass of the phosgene-containing stream, the amine-containing stream has a proportion by mass of from 5% to 95%, preferably from 10% to 60%, particularly preferably from 30% to 45%, of amine and a proportion by mass of from 95% to 5%, preferably from 90% to 40%, particularly preferably from 75% to 55%, of an inert solvent, in each case based on the total mass of the amine-containing stream.

(10) Here, inert under the reaction conditions means that the solvent does not react to a significant extent with the starting materials, intermediates and end products of the reaction. The inert solvent (30) for stream (10) and stream (20) is therefore preferably selected independently from among chlorobenzene, dichlorobenzene, toluene, dioxane, dimethyl sulphoxide and mixtures of two or more of the abovementioned solvents. Chlorobenzene and dichlorobenzene are particularly preferred for both streams (10) and (20), with very particular preference being given to chlorobenzene. In the case of dichlorobenzene, the ortho isomer (ortho-dichlorobenzene) is particularly preferred.

(11) The amine- and phosgene-containing streams obtained in this way are mixed (not shown in FIG. 1) and reacted in a reactor (1000), where the mixing apparatus used can also be integrated into the reactor (1000). Any mixing apparatus known from the prior art can be used here. Examples which may be mentioned are static mixers, in particular nozzles such as annular slit nozzles (DE-A-1792660), ring-hole nozzles (DE-C1-3744001), flat jet mixing nozzles (EP-A1-0 065 727), fan jet nozzles (DE-A1-2950216), angular jet chamber nozzles (DD-A7-300.168), three-fluid nozzles (DD-A1-132340), countercurrent mixing chambers (DE-B1146872), banking-up nozzles (FR-E-69428) and Venturi mixing nozzles (DE-B1175666). Dynamic mixers, in particular rotor-stator or turbine-like systems in which the reactants are introduced in concurrent into the mixing unit are also suitable. The mixer described in EP-A-2 077 150 may be mentioned as an example.

(12) The reaction in the reactor (1000) gives a crude product (40) comprising isocyanate, solvent, hydrogen chloride, unreacted phosgene and, depending on the precise reaction conditions, proportions of carbamoyl chloride and possibly relatively small amounts of amine hydrochloride. The only prerequisite for carrying out the process of the invention is that this crude product is obtained at a pressure p.sub.R which is greater than the pressure p.sub.F desired for the subsequent use of the hydrogen chloride, and indeed at least so much greater that the gas stream (60) which is obtained in step (i) (see below for details) and, in contrast to the gas stream (80) obtained in step (ii), is not compressed further has a pressure level which allows a sufficient gas flow via the purification apparatus (5000) used in step (iv) to the subsequent use. As long as this prerequisite is satisfied, the reaction in the reactor (1000) can be carried out by any known method of the prior art. p.sub.R is preferably from 6.00 bar to 60.0 bar, particularly preferably from 12.0 bar to 45.0 bar. The crude product (40) preferably has a temperature T.sub.R in the range from 80 C. to 200 C., preferably from 110 C. to 170 C.

(13) Thus, any phosgenation reactor known from the prior art can in principle be used as reactor (1000). Preference is given to using upright tube reactors through which flow occurs from the bottom. To narrow the residence time, the tube reactor can be segmented by means of suitable internals known to those skilled in the art. The present invention also encompasses embodiments in which a plurality of reactors (1000) are connected in series or in parallel.

(14) In one embodiment of the process of the invention, the reactor (1000) is operated adiabatically, i.e. without deliberate introduction or removal of heat. In such a process, the enthalpy of reaction is, disregarding unavoidable heat losses, reflected quantitatively in the temperature difference between outlet stream and inlet stream. To avoid heat losses, the reactor is preferably insulated. The document EP 1 616 857 A1 describes the adiabatic mode of operation of polyamine phosgenation in detail, especially in paragraphs [0014] to [0018].

(15) In another embodiment of the process of the invention, the reactor (1000) is operated isothermally, i.e. with introduction of heat via a thermostatable reactor by means of a suitable heat transfer medium (e.g. heat transfer oil, salt melt). The documents DE 1768439 A1, in particular paragraph [0003] on page 8 and EP 1 616 857 B1, in particular paragraphs [0021] to [0022], may be mentioned by way of example for the phosgenation of polyamines using an isothermal mode of operation.

(16) It is also possible (not shown in FIG. 1) to use a sequence of a plurality of reactors (1000) which can independently be operated isothermally or adiabatically. Preference is given to a sequence of two reactors connected in series, of which the first is operated adiabatically and the second is operated isothermally, as described in EP 1 616 857 A1.

(17) Furthermore, it is possible to branch off a substream (41) from the crude product (40) and recirculate this to the mixing of amine- and phosgene-containing stream (reaction circuit; shown by means of a broken line in FIG. 1). Such a process is described in the as yet unpublished European patent application No. EP15174217.8.

(18) The crude product (40) obtained under the pressure p.sub.R is separated by depressurization, i.e. with lowering of the pressure to a pressure p.sub.E>p.sub.F, into a liquid phase (50) containing predominantly isocyanate and phosgene and also solvent (30) and a gaseous phase (60) containing predominantly hydrogen chloride and subordinate proportions of phosgene in a separator (2000) (step (i)). The separator (2000) can also be configured as a cascade of a plurality of separators (2010, 2020, 2030, . . . ) connected in series with a successively decreasing pressure level, where the liquid phase obtained in one separator is fed into the following separator (naturally with the exception of the liquid phase from the last separator, which represents the stream (50) containing predominantly isocyanate and phosgene and also optionally solvent). The individual gas phases (61, 62, 63, . . . ) are combined to form the gas stream (60) which has a pressure p.sub.E and preferably makes up from 30% to 80%, particularly preferably from 50 to 70%, of the total hydrogen chloride obtained. Separator (2000) and reactor (1000) can also be combined in a single apparatus. It is also possible (not shown in FIG. 1) to discharge a gaseous purge stream from the reactor (1000) even during the actual reaction of amine and phosgene. Such a purge stream containing predominantly hydrogen chloride is combined with the other streams (61, 62, 63, . . . ) to form the gas stream (60). p.sub.E is preferably from 5.00 bar to 30.0 bar, particularly preferably from 9.00 bar to 18.0 bar. The gas stream (60) preferably has a temperature T.sub.E in the range from 90 C. to 170 C., preferably from 110 C. to 150 C.

(19) The liquid phase (50) leaving the last separator is freed of phosgene at a pressure p.sub.A<p.sub.F in the apparatus (3000), giving a gaseous stream (80) containing phosgene and hydrogen chloride and also a subordinate amount of the solvent and a stream (70) containing isocyanate and the major part of the solvent (step (ii)). In a preferred embodiment, the apparatus (3000) is a distillation column, hereinafter referred to as dephosgenation column. In this case, the pressure p.sub.A designates the pressure at the top of the dephosgenation column and is preferably from 0.50 bar to 5.00 bar, particularly preferably from 1.00 bar to 3.00 bar. The gaseous product (80) leaving the dephosgenation column (3000) preferably has a temperature T.sub.A in the range from 10 C. to 90 C., preferably from 30 C. to 70 C. The dephosgenation column (3000) is preferably configured as a bubble cap tray column. It is also possible for a plurality of distillation columns to be connected in series. In this case, p.sub.A designates the pressure at the top of the last distillation column.

(20) The liquid stream (70) obtained from the dephosgenation column is freed of solvent (30) as described in the prior art and worked up further (not shown in FIG. 1).

(21) In contrast to the prior art, the gas phase (80) obtained in the dephosgenation column (3000), which preferably comprises from 20% to 70%, particularly preferably from 30% to 50%, of the total hydrogen chloride obtained, is not fed to a further stage to separate off phosgene (e.g. by absorption in a falling film absorber) but instead is compressed without further purification to the pressure p.sub.V (stream (90)) in a compressor (4000) (step (iii)). Suitable compressors for compressing corrosive gases are known to those skilled in the art and are described, for example, in EP 2 021 275 B1. Examples which may be mentioned are turbo compressors, piston compressors, screw compressors or liquid-ring compressors. p.sub.V is preferably from 5.00 bar to 30.0 bar, particularly preferably from 9.00 bar to 18.0 bar. Stream (90) preferably has a temperature T.sub.V in the range from 90 C. to 170 C., preferably from 110 C. to 150 C. Particular preference is given to combining the stream (90) with the gas stream (60), as shown in FIG. 1. If present, the pressure difference between p.sub.E and p.sub.V should be selected so that it is negligibly small at the point at which the two streams are combined. Here, as is known to those skilled in the art, pressure drops as a result of distances to be overcome in pipes have to be taken into account, i.e. p.sub.E and p.sub.V should be selected so that sufficient flow of the corresponding gas streams to the combination point and from there to the purification apparatus (5000) is ensured. It is also conceivable for p.sub.E and p.sub.V to be identical. In the case of a pressure difference between the two pressures, this is preferably from >0.00 bar to 7.00 bar, particularly preferably from 1.00 bar to 5.00 bar.

(22) The purification apparatus (5000) for carrying out step (iv) is preferably a distillation column. The pressure p.sub.D then corresponds to the pressure at the top of the distillation column where the gaseous stream of purified hydrogen chloride (100) is taken off. A phosgene-containing liquid phase (110) is taken off from the bottom of the distillation column and is preferably recirculated to the reaction (shown by means of a broken line in FIG. 1). The liquid phase (110) is preferably mixed with the phosgene-containing stream composed of phosgene (20) and solvent (30). p.sub.D is preferably from 1.01 bar to 22.5 bar, particularly preferably from 5.00 bar to 17.5 bar. The overhead product (100) leaving the distillation column (5000) preferably has a temperature T.sub.D in the range from 50 C. to 20 C., preferably from 30 C. to 10 C. Suitable distillation columns (5000) are known to those skilled in the art and are described, for example, in Dubbel, Taschenbuch fr den Maschinenbau, Springer, 2001, p. N 11 to N 14. It is also possible for a plurality of distillation columns to be connected in series. In this case, p.sub.D designates the pressure at the top of the last distillation column.

(23) For the purposes of the present invention, step (iv) is preferably carried out as follows:

(24) The streams (60) and (90) are preferably combined and the combined stream is conveyed through a heat exchanger to give a liquid stream and a gaseous stream which are both fed into the purification apparatus (5000) configured as distillation column, preferably with the gaseous stream being introduced above the liquid stream. In this heat exchanger, the stream is preferably cooled to a temperature in the range from 0 C. to 50 C., particularly preferably in the range from 10 C. to 30 C.

(25) The gaseous stream obtained at the top of the distillation column (5000) is then conveyed through another heat exchanger in which partial liquefaction of this stream takes place as a result of indirect cooling (by means of a coolant introduced from the outside) to a temperature in the range from 50 C. to 20 C., particularly preferably in the range from 30 C. to 10 C. The liquid phase obtained in this way is recirculated to the top of the distillation column (5000). The remaining gaseous phase (the purified hydrogen chloride gas (100)) has a lower temperature than the streams (60) and (90) and is fed into the heat exchanger located downstream of the compressor (4000), in which heat exchanger it is employed for indirect cooling of the combined streams (90) and (60). As a result, the gas stream (100) is heated but its composition is not altered.

(26) The hydrogen chloride stream (100) produced by the process of the invention has a high purity and is therefore also suitable for sensitive applications such as use in a Deacon process. Furthermore, the hydrogen chloride stream (100) is at a pressure p.sub.D which is higher than the pressure p.sub.F desired for the subsequent use. In the ideal case, the pressure difference is only so great that the pressure p.sub.F desired for the subsequent use is achieved without further measures as a result of inherent pressure decreases during transport of the hydrogen chloride (100) to the subsequent use. If this is not the case, the desired pressure p.sub.F can be set by installation of a simple pressure reducer known to those skilled in the art.

(27) Preferred subsequent uses of the hydrogen chloride (100) are: Catalytic oxidation by means of oxygen to chlorine (Deacon process), which is preferably carried out at a pressure p.sub.F of from 1.00 bar to 25.0 bar, preferably from 1.50 bar to 17.00 bar, particularly preferably from 1.5 to 17 bar and in particular from 2.0 to 15 bar (absolute). The Deacon process is known to those skilled in the art and is described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, chapter 10.2.1 (pp. 597 to 599), and the literature cited therein. Here, catalysts based on metal oxides and/or chlorides (in particular of the metals ruthenium, chromium, tin, cerium or mixtures of at least two of these metals) are, for the purposes of the present invention, preferred over the use of inorganic acids as catalysts. Reaction to form ethylene dichloride (EDC) by oxychlorination of ethane or ethylene, preferably ethylene, which is preferably carried out at a pressure p.sub.F of from 1.00 bar to 15.0 bar, preferably from 4.00 bar to 12.0 bar (absolute). The EDC process is known to those skilled in the art and is described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, chapter 1.3 (pp. 12 to 17), and the literature cited therein.

(28) The above-described process is also of particular economic importance for the reason that the ever increasing isocyanate production capacities make the question of how to make economically purposeful use on site of the hydrogen chloride inevitably obtained more urgently.

(29) The invention is illustrated by the following examples.

EXAMPLES

(30) The examples presented below are based on a process simulation of the respective steady-state operating conditions, the essentials of which are described, for example, in U. Pleker, R. Janowsky, H. Briesen, W. Marquardt, Prozessanalyse und-synthese: Modellierung, Simulation und Optimierung, chapter 9 Stationare and dynamische Prozesssimulation in Chemische Technik, Winnacker, Kchler (editor), volume 2, 5.sup.th edition, Wiley-VCH-Verlag, Weinheim, 2004, pages 270-279. The numerical solution of the steady-state operating conditions according to the model was based firstly on the phase equilibria of the individual components and secondly on the reaction kinetics for the reaction of MDA with phosgene while maintain, ng the energy and mass balance.

(31) 72 t/h of a 55% strength by mass solution of phosgene in monochlorobenzene (MCB) and 95 t/h of a 42% strength by mass solution of a mixture of diamines and polyamines of the diphenylmethane series (MDA) in MCB are reacted, giving a crude product stream 40 (p.sub.R). Depending on the reaction conditions in the reactor 1000 (cf. FIG. 1), this stream is under a particular pressure p.sub.R. In each case, about 29.5 t/h of an HCl stream 100 containing about 1 ppm of phosgene, which satisfies the requirements of a subsequent use such as the Deacon or EDC process, are obtained after distillation and compression. The runbacks/bottom fractions of the individual process stages are recirculated to the work-up process for the isocyanate.

Example 1 (According to the Invention, p.SUB.R.=40 Bar (Absolute))

(32) The following table shows the results. Data for the streams are based on the designations in FIG. 1.

(33) TABLE-US-00001 Stream 50 60 70 80 90 100 110 Index i E A V D HCl/kg/h 3465.6 18534.5 11754.3 11754.3 29423.0 865.8 Phosgene/kg/h 1222.0 776.9 0.1 1219.0 1219.0 0.03 1995.9 MCB/kg/h 81974.4 1647.8 77388.0 668.1 668.1 2315.9 Crude MDI.sup.1) 58389.9 50446.5 Total/kg/h 141586.3 20959.2 127834.6 13641.4 13641.4 29423.03 5177.6 T.sub.i/ C. 114.6 130.6 189.7 50.0 131.9 22.6 9.8 p.sub.i/bar 3.00 12.0 3.00 3.00 12.0 11.0 11.0 .sup.1)Crude MDI consisting of MDI, carbamoyl chlorides and carbodiimides.

Example 2 (According to the Invention, p.SUB.R.=20 Bar (Absolute))

(34) The following table shows the results. Data for the streams are based on the designations in FIG. 1.

(35) TABLE-US-00002 Stream 50 60 70 80 90 100 110 Index i E A V D HCl/kg/h 3096.4 20992.7 9323.0 9323.0 29419.4 896.3 Phosgene/kg/h 987.5 963.0 0.1 1005.9 1005.9 0.03 1968.8 MCB/kg/h 81491.7 2164.2 75889.3 530.2 530.2 2694.4 Crude MDI.sup.1) 56071.5 0.1 50418.4 0.1 Total/kg/h 141647.1 24120.0 126307.8 10859.1 10859.1 29419.5 5559.6 T.sub.i/ C. 125.4 123.0 189.8 50.0 131.8 22.6 10.9 p.sub.i/bar 3.00 12.0 3.00 3.00 12.0 11.0 11.0 .sup.1)Crude MDI consisting of MDI, carbamoyl chlorides and carbodiimides.

(36) The examples show that hydrogen chloride can successfully be obtained in the desired purity without the entire hydrogen chloride formed in the isocyanate process (i.e. the sum of hydrogen chloride in stream 60 and in stream 80) having to be compressed. In contrast, the entire hydrogen chloride stream has to be compressed in the process described in EP 2 021 275 B1. In addition, secondary components which have to be disposed of are formed.