Continuous process for preparing chlorine and a catalyst for preparing chlorine

The present invention relates to a continuous process for preparing chlorine and a production unit for carrying out said process. The present invention further relates to a monolithic catalyst for preparing chlorine, the use of said catalyst as well as the use of the aforementioned production unit for the continuous production of chlorine.

In the large-scale production of isocyanates by phosgenation of the corresponding amines, large amounts of HCI are obtained as a by-product. In addition to its use in other applications, the recovery of chlorine from the HCI and its use in phosgene synthesis is an attractive route (chlorine recycling).

Electrochemical processes are expensive both in terms of investment and operating costs. The oxidation of HCI to chlorine, the so-called Deacon process, is more economically attractive. The Ch produced can then be used to manufacture other commercially valuable products, such as phosgene and isocyanates from phosgene, and at the same time the emission of waste hydrochloric acid is curtailed. The Deacon process is based on the gas phase oxidation of hydrogen chloride. HCI is reacted with oxygen over a catalyst, for example copper chloride (CuCh), Ru- based catalyst or Ce-based catalyst as disclosed in WO 2007/134771 A1 , WO 2011/111351 A1 , WO 2013/004651 A1 , WO 2013/060628 A1 and US 2418930 A, to form chlorine and water in the gas phase at temperatures of 200 to 500 °C. It is an equilibrium reaction with a slight exotherm. Cooled reactors are used to control the temperature development and avoid hot spots. Both tube-bundle (tube-and-shell) reactors and fluidized beds are known.

To avoid corrosion damage, suitable materials are required that can withstand the aggressive substance system at high temperatures, including nickel and nickel-based alloys but also silicon carbide. These materials and their processing is comparatively expensive, which leads to correspondingly high costs for the reactor. In addition, a high-temperature cooling system is required, which causes additional costs. As a rule, a nitrate I nitrite molten salt is used as the cooling system. In the event of a leak, this can react with the reaction gas and damage the reactor. Therefore, there is a need to provide a new process for preparing chlorine which permits to avoid these problems. Further, the price in term of investment and operating costs has to be reduced to be even more economically attractive.

Furthermore, during chlorine production according to know processes, there is a pressure loss at the catalyst bed(s) and at the piping, etc. which increases expenses over time (such as operational costs for compressor).

Thus, the object of the present invention is to provide a new process for preparing chlorine which permits to improve the production of chlorine and avoid the problems of the prior art, such as excessive pressure drop, deterioration of the production unit used for such processes, leakage of the cooling systems, as well as the deterioration/destruction of the used catalyst while reducing the operating costs. Further, the object of the present invention is to provide a catalyst for the production of chlorine. Surprisingly, it was found that the process for preparing chlorine according to the present invention permits to provide chlorine at a good conversion rate while reducing greatly the overall pressure loss along the system and avoiding the deterioration of the reactor and the deactivation of the catalyst. Further, the process of the present invention permits to optimize the amount of catalyst and the conditions of operation for reducing costs. Thus, the process according to the present invention may be used for a longer period by reducing the need for changing deactivated catalysts. Further, leakage of the cooling system is also avoided in the reactor. Hence the process of the present invention is effective and permits to reduce production/operating costs.

Therefore, the present invention relates to a continuous process for preparing chlorine, comprising

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream GP from said reaction zone Z, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

(iii) dividing the gas stream GP obtained according to (ii), obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

Preferably ) is 1 or 2, more preferably 2.

Preferably the mixture consists of the at least two gas streams.

As to the reaction zone Z, it is preferred that it is an adiabatic reaction zone. This means that the reaction zone Z is operated adiabatically.

Preferably f(GR):f(G2) is in the range of from 0.5:1 to 10:1 , more preferably in the range of from 1 :1 to 8:1 , more preferably in the range of from 2:1 to 6:1. As to the amount of oxygen and hydrochloric acid in the j gas streams G0(k) used for the process of the present invention, there is no particular restrictions as far as enough chlorine is produced by said process. However, it is preferred that the mole ratio of the amount of oxygen, in mol, to the amount of hydrogen chloride, in mol, in the j gas streams G0(k) is in the range of from 0.1 :1 to 2:1 , more preferably in the range of 0.15:1 to 0.8:1 , more preferably in the range of from 0.2:1 to 0.7:1 , more preferably in the range of from 0.3:1 to 0.6:1.

During standard operation mode of the continuous process, it is preferred that providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising, more preferably consisting of, three gas streams, said three gas streams comprising the gas stream GR and two gas streams G0(1 ) and G0(2), wherein the two gas streams G0(1 ) and G0(2) in total comprise oxygen (O2) and hydrogen chloride (HCI).

During standard operation mode of the continuous process, it is preferred that providing the gas stream G1 according to (i) comprises preparing G1 , as a mixture comprising, more preferably consisting of, three gas streams GR, G0(1 ) and G0(2), G0(1 ) comprising oxygen (O2) and G0(2) comprises hydrogen chloride (HCI), which comprises combining the gas stream G0(1 ) with the gas stream G0(2), more preferably in a static mixer, and admixing the gas stream GR with the combined gas streams G0(1 ) and G0(2).

Preferably admixing the gas stream GR with the combined two gas streams G0(1 ) and G0(2) according to (i) is performed in a mixing device, wherein the mixing device is an ejector, a static mixer or a dynamic mixer, more preferably an ejector, wherein the ejector is more preferably driven by the combined gas streams G0(1 ) and G0(2).

Preferably, the continuous process for preparing chlorine according to the present invention comprises

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream GP from said reaction zone Z, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

(iii) dividing the gas stream GP, obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 , as a mixture comprising, more preferably consisting of, three gas streams GR, G0(1) and G0(2), G0(1 ) comprising oxygen (O2) and G0(2) comprises hydrogen chloride (HCI), which comprises

- combining the gas stream G0(1 ) with the gas stream G0(2), preferably in a static mixer, and

- admixing the gas stream GR with the combined gas streams G0(1 ) and G0(2), wherein admixing the gas stream GR with the combined two gas streams G0(1 ) and G0(2) according to (i) is performed in a mixing device, wherein the mixing device is an ejector, a static mixer or a dynamic mixer, preferably an ejector, wherein the ejector is more preferably driven by the combined gas streams G0(1) and G0(2).

In the context of the present invention, preferably, the combined gas streams G0(1) and G0(2) have a pressure PO and the gas stream GR has a pressure PR, wherein PO > PR, wherein more preferably the gas stream G1 has a pressure P1 and PO > P1 > PR; wherein more preferably the pressure PO ranges from 2 to 50 bar(abs), more preferably from 4 to 20 bar(abs).

As to the amount of oxygen and hydrochloric acid in the combined gas streams G0(1 ) and G0(2) used for the process of the present invention, there is no particular restrictions as far as enough chlorine is produced by said process. However, it is preferred that the mole ratio of the amount of oxygen, in mol, to the amount of hydrogen chloride, in mol, in the combined gas streams G0(1) and G0(2) is in the range of from 0.1 :1 to 2:1 , more preferably in the range of 0.15:1 to 0.8:1 , preferably in the range of from 0.2:1 to 0.7:1 , more preferably in the range of from 0.3:1 to 0.6:1.

Preferably, the monolithic catalyst is selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst, a Cu-based catalyst and a mixture of two or more thereof, more preferably is selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst and a Cu- based catalyst, more preferably is a Ru-based catalyst. Therefore, the present invention preferably relates to a continuous process for preparing chlorine, comprising

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream GP from said reaction zone Z, the monolithic catalyst, being a Ru-based catalyst, comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

(iii) dividing the gas stream GP, obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

In the context of the present invention, it is preferred that the monolithic catalyst is a Ru-based catalyst, the Ru being supported on the surface of the internal walls of the flow-through monolith substrate and/or within the internal walls of the flow-through monolith substrate. Alternatively, it can be preferred that the catalyst be an extrudate and that Ru is preferably a component of the flow-through monolith substrate.

Preferably, the Ru-based monolithic catalyst comprises Ru in an amount, calculated as RuC>2, in the range of from 0.25 to 20 weight-%, more preferably in the range of from 0.5 to 15 weight-%, based on the weight of said catalyst.

Preferably, the cross section of the monolithic catalyst is a circle, a square, a rectangle or a triangle, more preferably a circle or a square, more preferably a circle.

Preferably, the cross section of the passages of the monolithic catalyst is a square, a circle, a rectangle or a triangle, more preferably a square.

The monolithic catalyst preferably has a honeycomb structure.

Preferably, the monolithic catalyst has a cell density in the range of from 50 to 900 cells per square inch (cpsi), more preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

Preferably the opening rate of the cross section of the monolithic catalyst is in the range of from 20 to 80 %, preferably in the range of from 50 to 70 %.

Preferably, the flow-through monolith substrate has a cell density in the range of from 50 to 900 cells per square inch (cpsi), more preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

Preferably, the opening rate of the cross section of the flow-through monolith substrate is in the range of from 20 to 80 %, preferably in the range of from 50 to 70 %.

Preferably, the flow-through monolith substrate comprises, more preferably consists of, one or more of TiC>2, AI2O3, SiC>2, ZrC>2 and Ce _x O _y , more preferably one or more of TiC>2, AI2O3 and SiC>2, wherein AI2O3 is more preferably alpha- AI2O3 or gamma- AI2O3. Preferably, the flow-through monolith substrate comprises, more preferably consists of, one or more of TiC>2 and AI2O3, more preferably one or more of TiC>2 and alpha-ALOs.

More preferably, the flow-through monolith substrate comprises, more preferably consists of, TiC>2 and alpha-ALOs, wherein from 30 to 35 weight-% of the substrate consists of TiC>2 and from 65 to 70 weight-% of the substrate consists of alpha-ALOs. Alternatively, the flow-through monolith substrate more preferably comprises, more preferably consists of, TiC>2 or alpha-ALOs.

Preferably, the flow-through monolith substrate is porous or non-porous.

Preferably, the monolithic catalyst has a cylindrical shape with a diameter in the range of from 0.5 m to 10.0 m, more preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m, and preferably a length in the range of from 1 to 7 m, more preferably in the range of from 2 to 6 m, more preferably in the range of from 2.5 to 5 m. In this respect, it is noted that the monolithic catalyst alternatively may preferably have a different shape, such as a parallelepiped shape. The shape of the monolithic catalyst will be adapted/selected by the skilled person dependent on the shape of the reactor for example.

Preferably, the monolithic catalyst consists of a catalyzed flow-through monolith substrate.

Alternatively, the monolithic catalyst preferably comprises, more preferably consists of, a plurality of catalyzed flow-through monolith substrates, wherein said catalyzed flow-through monolith substrates are stacked to each other and above one another into the reaction zone Z; wherein the catalyzed flow-through monolith substrates which are stacked above one another are more preferably vertically aligned.

Preferably, said catalyzed flow-through monolith substrates are stacked to each other and above one another with cooperation of a filler material, wherein the filler material is one or more of weave, felt and mats, more preferably one or more of mineral weave, mineral felt and mineral mats, more preferably mineral mats.

Preferably, the recycle ratio is the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(GP) of the gas stream GP, f(GR):f(GP), which is in the range of from 0.2:1 to 0.95:1 , more preferably in the range of from 0.5:1 to 0.9:1 , more preferably in the range of from 0.7:1 to 0.85:1.

Preferably, the gas stream GP has a temperature T(GP) of at most 450 °C, more preferably of at most 405 °C, wherein said temperature T(GP) is more preferably controlled by fixing the recycle ratio defined in the foregoing and by varying the temperature of the gas stream G1 . Indeed, it is preferred that the amount and the temperature of the recycle gas, namely gas stream GR, are selected to control the outlet temperature of the reaction zone which corresponds to the temperature of the gas stream GP, to a temperature of at most 450 °C, more preferably of at most 405 °C.

Preferably, the gas stream G1 has a temperature T(G1) of at least 200 °C, more preferably at least 250 °C, more preferably in the range of from 250 °C to 300 °C.

As to (II), it is preferred that it further comprises passing the gas stream GP removed from the reaction zone Z in a heat exchanger, obtaining a cooled gas stream GP, more preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C; wherein the heat exchanger more preferably is a tube-and-shell heat exchanger. Therefore, the present invention preferably relates to a continuous process for preparing chlorine, comprising

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst, more preferably a Ru-based monolithic catalyst, comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream from said reaction zone Z, passing the gas stream GP removed from the reaction zone Z in a heat exchanger, more preferably a tube-and-shell heat exchanger, obtaining a cooled gas stream GP, more preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

(iii) dividing the gas stream GP, obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

In the context of the present invention, as to (iii), it is alternatively preferred, when GP is preferably not passed into a heat exchanger, that (iii) further comprises passing the gas stream GR into a heat exchanger, obtaining a cooled gas stream GR, more preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C, prior to admixing with GO in (i.2) during standard operation mode of the continuous process; wherein the heat exchanger more preferably is a tube-and-shell heat exchanger.

More preferably, (iii) further comprises passing the gas stream G2 in a heat exchanger, more preferably a tube-and-shell heat exchanger, obtaining a cooled gas stream G2, more preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C.

Preferably, the gas stream G0(k) has a temperature T(G0(k)) in the range of from 20 to 350 °C, more preferably in the range of from 50 to 325 °C, more preferably in the range of from 100 to 300 °C, more preferably in the range of from 150 to 250 °C.

Preferably from 50 to 100 weight-%, more preferably from 70 to 100 weight-%, more preferably from 75 to 100 weight-%, more preferably from 80 to 100 weight-%, of the j gas streams G0(k) consist of HCI and O2.

Preferably, according to (iii), two gas streams are obtained, a gas stream G2 and a gas stream GR. Therefore, the present invention preferably relates to a continuous process for preparing chlorine, comprising

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream from said reaction zone Z, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

(iii) dividing the gas stream GP, obtaining two gas streams being a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

In the context of the present invention, it is preferred that the reaction zone Z comprises a reactor, more preferably a cylindrical reactor, comprising the monolithic catalyst.

Preferably, the gas stream in the reactor is of at most 450 °C, more preferably of at most 405 °C, the temperature being more preferably measured with a thermocouple.

Preferably, the reactor is an adiabatic fixed-bed reactor. Preferably, the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst.

Preferably the reactor is a single stage adiabatic fixed-bed reactor.

Preferably, the process of the present invention comprises (i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, wherein the reaction zone Z comprises an adiabatic fixed-bed reactor, comprising the monolithic catalyst, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream GP from said reaction zone Z, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough, wherein more preferably the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst, wherein more preferably the reactor is a single stage adiabatic fixed-bed reactor, wherein more preferably the gas stream in the reactor is of at most 450 °C, more preferably of at most 405 °C, the temperature being more preferably measured with a thermocouple;

(iii) dividing the gas stream GP, obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream

G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

Preferably the process of the present invention further comprises, after (iii), passing the gas stream GR through a return means R prior to preparing G1 according to (i), during standard operation mode of the continuous process, in an ejector; wherein more preferably the return means R forms a loop external to the reactor, for recycling GR and passing it into the ejector for admixing with the j gas streams G0(k) according to (i), during standard operation mode of the continuous process.

Preferably from 20 to 100 weight-%, more preferably from 30 to 80 weight-%, more preferably from 40 to 70 weight-%, of the gas stream GP consist of chlorine. The present invention further relates to a monolithic catalyst for preparing chlorine, preferably according to the process of the present invention, the catalyst comprising: a catalyzed flow-through monolith substrate, said substrate having an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow through substrate extending therethrough.

Preferably the monolithic catalyst is selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst, a Cu-based catalyst and a mixture of two or more thereof, more preferably being selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst and a Cu- based catalyst, more preferably being a Ru-based catalyst.

Preferably the monolithic catalyst is a Ru-based catalyst, wherein Ru is supported on the surface of the internal walls of the flow-through monolith substrate and/or within the internal walls of the flow-through monolith substrate. Alternatively, it can be preferred that the catalyst be an extrudate and that Ru is preferably a component of the flow-through monolith substrate.

Preferably the monolithic catalyst comprises Ru in an amount, calculated as Ru02, in the range of from 0.25 to 20 weight-%, more preferably in the range of from 0.5 to 15 weight-%, based on the weight of the catalyst.

Preferably the cross section of the monolithic catalyst is a circle, a square, a rectangle or a triangle, more preferably a circle or a square, more preferably a circle.

Preferably the cross section of the passages of the monolithic catalyst is a square, a circle, a rectangle or a triangle, more preferably a square.

The monolithic catalyst preferably has a honeycomb structure.

Preferably the monolithic catalyst has a cell density in the range of from 50 to 900 cells per square inch (cpsi), more preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

Preferably the opening rate of the cross section of the monolithic catalyst is in the range of from 20 to 80 %, preferably in the range of from 50 to 70 %.

Preferably the flow-through monolith substrate of the monolithic catalyst has a cell density in the range of from 50 to 900 cells per square inch (cpsi), more preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

Preferably the opening rate of the cross section of the flow-through monolith substrate is in the range of from 20 to 80 %, more preferably in the range of from 50 to 70 %. Preferably the flow-through monolith substrate comprises, more preferably consists of, one or more of TiC>2, AI2O3, SiC>2, ZrC>2 and Ce _x O _y , more preferably one or more of TiC>2, AI2O3 and SiC>2, wherein AI2O3 is more preferably alpha- AI2O3 or gamma- AI2O3.

Preferably the flow-through monolith substrate comprises, more preferably consists of, one or more of TiC>2 and AI2O3, more preferably one or more of TiC>2 and alpha-ALOs.

More preferably the flow-through monolith substrate comprises, more preferably consists of, TiC>2 and alpha-ALOs, wherein from 30 to 35 weight-% of the substrate consists of TiC>2 and from 65 to 70 weight-% of the substrate consists of alpha-ALOs. Alternatively the flow-through monolith substrate more preferably comprises, more preferably consists of, TiC>2 or alpha-ALOs.

Preferably the flow-through monolith substrate is porous or non-porous.

Preferably the monolithic catalyst has a cylindrical shape with a diameter in the range of from 0.5 m to 10.0 m, preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m, and preferably a length in the range of from 1 to 7 m, more preferably in the range of from 2 to 6 m, more preferably in the range of from 2.5 to 5 m. In this respect, it is noted that the monolithic catalyst alternatively may preferably have a different shape, such as a parallelepiped shape. The shape of the monolithic catalyst will be adapted/selected by the skilled person dependent on the shape of the reactor for example.

Preferably the monolithic catalyst consists of a catalyzed flow-through monolith substrate. Alternatively the monolithic catalyst preferably comprises, more preferably consists of, a plurality of catalyzed flow-through monolith substrates, wherein said catalyzed flow-through monolith substrates are stacked to each other and above one another into the reaction zone Z; wherein the catalyzed flow-through monolith substrates which are stacked above one another are more preferably vertically aligned.

Preferably said catalyzed flow-through monolith substrates are stacked to each other and above one another with cooperation of a filler material, wherein the filler material is one or more of weave, felt and mats, more preferably one or more of mineral weave, mineral felt and mineral mats, more preferably mineral mats.

The present invention further relates to a production unit for carrying out the process according to the present invention, the unit comprising a reaction zone Z comprising

-- an inlet means for passing the gas stream G1 into Z;

-- a monolithic catalyst, the catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

-- a reaction means for bringing into contact the gas stream G1 with said catalyst;

-- an outlet means for removing the gas stream GP from Z; a stream dividing device S for dividing the gas stream GP in at least two streams, preferably two streams, comprising a gas stream GR and a gas stream G2; a means for passing the gas stream GP into said device S; a means M for preparing G1 as a mixture comprising GR and j gas streams G0(k) with k=1 , ... j, wherein j is in the range of from 1 to 3, preferably 1 or 2, more preferably 2; a return means R for passing the gas stream GR exiting from S to said means M for preparing G1 .

Preferably, the reaction means of the reaction zone Z is a reactor, more preferably a cylindrical reactor.

Preferably, the reaction means of the reaction zone Z is an adiabatic fixed bed reactor.

Preferably, the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst.

Preferably, the reactor is a single stage adiabatic fixed-bed reactor.

Preferably, the production unit of the present invention comprises a reaction zone Z comprising

-- an inlet means for passing the gas stream G1 into Z;

-- a monolithic catalyst, the catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

-- a reaction means for bringing into contact the gas stream G1 with said catalyst;

-- an outlet means for removing the gas stream GP from Z; a stream dividing device S for dividing the gas stream GP in at least two streams, preferably two streams, comprising a gas stream GR and a gas stream G2; a means for passing the gas stream GP into said device S; a means M for preparing G1 as a mixture comprising GR and j gas streams G0(k) with k=1 , ... j, wherein j is in the range of from 1 to 3, preferably 1 or 2, more preferably 2; a return means R for passing the gas stream GR exiting from S to said means M for preparing G1 ; wherein the reaction means of the reaction zone Z is an adiabatic fixed bed reactor, wherein the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst.

Alternatively, the adiabatic fixed-bed reactor is preferably a multi-stage reactor comprising two or more catalyst beds, wherein each of the two or more catalyst beds is a monolithic catalyst, herein above, wherein the catalyst in the respective catalyst beds has the same or different chemical compositions. Preferably the reactor has an inner diameter in the range of from 1 .0 m to 10.0 m, more preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m.

Preferably the reactor has a wall thickness in the range of from 10 mm to 50 mm, more preferably in the range of from 15 to 35 mm.

Preferably the reactor is made of corrosion-resistant material, more preferably of iron-based alloys, nickel-based alloys, nickel or nickel clad, more preferably of nickel or nickel clad.

Preferably the production unit further comprises, downstream of the reaction zone Z and upstream of the stream dividing device S, a heat exchanger, wherein the gas stream GP is passed through said heat exchanger. Therefore, the present invention preferably relates to a production unit for carrying out the process according to the present invention, the unit comprising a reaction zone Z comprising

-- an inlet means for passing the gas stream G1 into Z;

-- a monolithic catalyst, the catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

-- a reaction means for bringing into contact the gas stream G1 with said catalyst;

-- an outlet means for removing the gas stream GP from Z; a stream dividing device S for dividing the gas stream GP in at least two streams, preferably two streams, comprising a gas stream GR and a gas stream G2; a heat exchanger positioned downstream of the reaction zone Z and upstream of the stream dividing device S, wherein the gas stream GP is passed through said heat exchanger; a means for passing the gas stream GP into said device S; a means M for preparing G1 as a mixture comprising GR and j gas streams G0(k) with k=1 , ... j, wherein j is in the range of from 1 to 3, preferably 1 or 2, more preferably 2; a return means R for passing the gas stream GR exiting from S to said means M for preparing G1 .

Alternatively the return means R preferably further comprises a heat exchanger for cooling GR prior to enter the means M.

In the context of the present invention, it is preferred that the heat exchanger is a tube-and-shell heat exchanger, wherein the heat exchanger is more preferably made of corrosion-resistant material, more preferably of nickel-based material or nickel.

Preferably, the return means R is a return pipe, more preferably an external return pipe to the reactor of Z or an internal return pipe to the reactor of Z, more preferably an external return pipe. Preferably, the return pipe has an inner diameter of at most 2000 mm, more preferably in the range of from 100 to 2000 mm, more preferably in the range of from 150 to 1000 mm.

Preferably, the return pipe is made of corrosion-resistant material, more preferably of iron-based alloys, nickel-based alloys, nickel or nickel clad, more preferably of nickel-based alloys, nickel or nickel clad.

Preferably, the means M is a mixing device, wherein the mixing device is more preferably an ejector, a static mixer or a dynamic mixer, more preferably an ejector.

Preferably, the production unit of the present invention comprises a reaction zone Z comprising

-- an inlet means for passing the gas stream G1 into Z;

-- a monolithic catalyst, the catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

-- a reaction means for bringing into contact the gas stream G1 with said catalyst;

-- an outlet means for removing the gas stream GP from Z; a stream dividing device S for dividing the gas stream GP in at least two streams, preferably two streams, comprising a gas stream GR and a gas stream G2; a means for passing the gas stream GP into said device S; a means M for preparing G1 as a mixture comprising GR and j gas streams G0(k) with k=1 , ... j, wherein j is in the range of from 1 to 3, preferably 1 or 2, more preferably 2; a return means R for passing the gas stream GR exiting from S to said means M for preparing G1 ; wherein the means M is a mixing device, wherein the mixing device is an ejector, a static mixer or a dynamic mixer, more preferably an ejector.

Preferably, the monolithic catalyst is as defined herein above.

The present invention further relates to a use of a production unit according to the present invention and as defined herein above for the continuous production of chlorine.

The present invention further relates to a use of a monolithic catalyst according to the present invention and as defined herein above for the continuous production of chlorine.

The present invention further relates to a process for preparing phosgene comprising preparing chlorine according to the process of the present invention; reacting the obtained chlorine with carbon monoxide in the presence of a catalyst, in gas phase, obtaining phosgene. The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3, and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

1 . A continuous process for preparing chlorine, comprising

(i) providing a gas stream G1 comprising oxygen (O2) and hydrogen chloride (HCI);

(ii) passing the gas stream G1 into a reaction zone Z, bringing the gas stream G1 into contact with a monolithic catalyst comprised in said reaction zone Z, obtaining a gas stream GP comprising chlorine (CI2) and one or more of O2, H2O and HCI, removing the gas stream GP from said reaction zone Z, the monolithic catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow- through substrate extending therethrough;

(iii) dividing the gas stream GP, obtaining at least two gas streams comprising a gas stream G2 and a gas stream GR, G2 and GR having the same chemical composition as GP, wherein the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(G2) of the gas stream G2, f(GR):f(G2), is in the range of from 0.1 :1 to 20:1 ; wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising at least two gas streams, said at least two gas streams comprising the gas stream GR and j gas streams G0(k) with k=1 , ... j, wherein the j gas streams G0(k) in total comprise oxygen (O2) and hydrogen chloride (HCI) and wherein j is in the range of from 1 to 3.

2. The process of embodiment 1 , wherein j is 1 or 2, preferably 2.

3. The process of embodiment 1 or 2, wherein the reaction zone Z is an adiabatic reaction zone.

4. The process of any one of embodiments 1 to 3, wherein f(GR):f(G2) is in the range of from 0.5:1 to 10:1 , preferably in the range of from 1 :1 to 8:1 , more preferably in the range of from 2:1 to 6:1. 5. The process of any one of embodiments 1 to 4, wherein the mole ratio of the amount of oxygen, in mol, to the amount of hydrogen chloride, in mol, in the j gas streams G0(k) is in the range of from 0.1 :1 to 2:1 , preferably in the range of 0.15:1 to 0.8:1 , more preferably in the range of from 0.2:1 to 0.7:1 , more preferably in the range of from 0.3:1 to 0.6:1.

6. The process of any one of embodiments 1 to 5, wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 as a mixture comprising, more preferably consisting of, three gas streams, said three gas streams comprising the gas stream GR and two gas streams G0(1 ) and G0(2), wherein the two gas streams G0(1) and G0(2) in total comprise oxygen (O2) and hydrogen chloride (HCI).

7. The process of any one of embodiments 1 to 6, wherein during standard operation mode of the continuous process, providing the gas stream G1 according to (i) comprises preparing G1 , as a mixture comprising, more preferably consisting of, three gas streams GR, G0(1) and G0(2), G0(1 ) comprising oxygen (O2) and G0(2) comprises hydrogen chloride (HCI), which comprises

- combining the gas stream G0(1 ) with the gas stream G0(2), preferably in a static mixer, and

- admixing the gas stream GR with the combined gas streams G0(1 ) and G0(2).

8. The process of embodiment 7, wherein admixing the gas stream GR with the combined two gas streams G0(1 ) and G0(2) according to (i) is performed in a mixing device, wherein the mixing device is an ejector, a static mixer or a dynamic mixer, preferably an ejector, wherein the ejector is more preferably driven by the combined gas streams G0(1) and G0(2).

9. The process of embodiment 7 or 8, wherein the combined gas streams G0(1 ) and G0(2) have a pressure P0 and the gas stream GR has a pressure PR, wherein P0 > PR, wherein preferably the gas stream G1 has a pressure P1 and P0 > P1 > PR; wherein more preferably the pressure P0 ranges from 2 to 50 bar(abs), preferably from 4 to 20 bar(abs).

10. The process of any one of embodiments 6 to 9, wherein the mole ratio of the amount of oxygen, in mol, to the amount of hydrogen chloride, in mol, in the combined gas streams G0(1) and G0(2) is in the range of from 0.1 :1 to 2:1 , preferably in the range of 0.15:1 to 0.8:1 , preferably in the range of from 0.2:1 to 0.7:1 , more preferably in the range of from 0.3:1 to 0.6:1.

11 . The process of any one of embodiments 1 to 10, wherein the monolithic catalyst is selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst, a Cu-based catalyst and a mixture of two or more thereof, preferably is selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst and a Cu-based catalyst, more preferably is a Ru-based catalyst.

12. The process of embodiment 11 , wherein the monolithic catalyst is a Ru-based catalyst, the Ru being supported on the surface of the internal walls of the flow-through monolith substrate and/or within the internal walls of the flow-through monolith substrate.

13. The process of embodiment 11 or 12, wherein the monolithic catalyst comprises Ru in an amount, calculated as RuC>2, in the range of from 0.25 to 20 weight-%, preferably in the range of from 0.5 to 15 weight-%, based on the weight of said catalyst.

14. The process of any one of embodiments 1 to 13, wherein the cross section of the monolithic catalyst is a circle, a square, a rectangle or a triangle, preferably a circle or a square, more preferably a circle; wherein the cross section of the passages of the monolithic catalyst preferably is a square, a circle, a rectangle or a triangle, more preferably a square.

15. The process of any one of embodiments 1 to 14, wherein the monolithic catalyst has a cell density in the range of from 50 to 900 cells per square inch (cpsi), preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

16. The process of any one of embodiments 1 to 15, wherein the flow-through monolith substrate has a cell density in the range of from 50 to 900 cells per square inch (cpsi), preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi.

17. The process of any one of embodiments 1 to 16, wherein the opening rate of the cross section of the flow-through monolith substrate is in the range of from 20 to 80 %, preferably in the range of from 50 to 70 %.

18. The process of any one of embodiments 1 to 17, wherein the flow-through monolith substrate comprises, preferably consists of, one or more of TiC>2, AI2O3, SiC>2, ZrC>2 and Ce _x O _y , preferably one or more of TiC>2, AI2O3 and SiC>2, wherein AI2O3 is preferably alpha- AI2O3 or gamma- AI2O3.

19. The process of embodiment 18, wherein the flow-through monolith substrate comprises, preferably consists of, one or more of TiC>2 and AI2O3, preferably one or more of TiC>2 and alpha-AhOs.

20. The process of embodiment 19, wherein the flow-through monolith substrate comprises, preferably consists of, TiC>2 and alpha-ALOs, wherein from 30 to 35 weight-% of the substrate consists of TiC>2 and from 65 to 70 weight-% of the substrate consists of alpha- AI2O3. The process of embodiment 19, wherein the flow-through monolith substrate comprises, preferably consists of, TiC>2 or alpha-ALOs. The process of any one of embodiments 1 to 21 , wherein the flow-through monolith substrate is porous or non-porous. The process of any one of embodiments 1 to 22, wherein the monolithic catalyst has a cylindrical shape with a diameter in the range of from 0.5 m to 10.0 m, preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m, and preferably a length in the range of from 1 to 7 m, more preferably in the range of from 2 to 6 m, more preferably in the range of from 2.5 to 5 m. The process of any one of embodiments 1 to 23, wherein the monolithic catalyst consists of a catalyzed flow-through monolith substrate. The process of any one of embodiments 1 to 23, wherein the monolithic catalyst comprises, preferably consists of, a plurality of catalyzed flow-through monolith substrates, wherein said catalyzed flow-through monolith substrates are stacked to each other and above one another into the reaction zone Z; wherein the catalyzed flow-through monolith substrates which are stacked above one another are preferably vertically aligned. The process of embodiment 25, wherein said catalyzed flow-through monolith substrates are stacked to each other and above one another with cooperation of a filler material, wherein the filler material is one or more of weave, felt and mats, preferably one or more of mineral weave, mineral felt and mineral mats, more preferably mineral mats. The process of any one of embodiments 1 to 26, wherein the recycle ratio is the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(GP) of the gas stream GP, f(GR):f(GP), which is in the range of from 0.2:1 to 0.95:1 , preferably in the range of from 0.5:1 to 0.9:1 , more preferably in the range of from 0.7:1 to 0.85:1. The process of any one of embodiments 1 to 27, wherein the gas stream GP has a temperature T(GP) of at most 450 °C, preferably of at most 405 °C, wherein said temperature T(GP) is preferably controlled by fixing the recycle ratio defined in embodiment 26 and by varying the temperature of the gas stream G1. The process of any one of embodiments 1 to 28, wherein the gas stream G1 has a temperature T(G1) of at least 200 °C, preferably at least 250 °C, more preferably in the range of from 250 °C to 300 °C. The process of any one of embodiments 1 to 29, wherein (ii) further comprises passing the gas stream GP removed from the reaction zone Z in a heat exchanger, obtaining a cooled gas stream GP, preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C; wherein the heat exchanger preferably is a tube-and-shell heat exchanger.

31 . The process of any one of embodiments 1 to 29, wherein (iii) further comprising passing the gas stream GR into a heat exchanger, obtaining a cooled gas stream GR, preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C, prior to admixing with GO in (i.2) during standard operation mode of the continuous process; wherein the heat exchanger preferably is a tube-and- shell heat exchanger; wherein (iii) preferably further comprising passing the gas stream G2 into a heat exchanger, more preferably a tube-and-shell heat exchanger, obtaining a cooled gas stream G2, more preferably having a temperature in the range of from 200 to 350 °C, more preferably in the range of from 250 to 300 °C.

32. The process of embodiment 30 or 31 , wherein the gas stream G0(k) has a temperature T(G0(k)) in the range of from 20 to 350 °C, preferably in the range of from 50 to 325 °C, more preferably in the range of from 100 to 300 °C, more preferably in the range of from 150 to 250 °C.

33. The process of any one of embodiments 1 to 32, wherein from 50 to 100 weight-%, preferably from 70 to 100 weight-%, more preferably from 75 to 100 weight-%, more preferably from 80 to 100 weight-%, of the j gas streams G0(k) consist of HCI and O2.

34. The process of any one of embodiments 1 to 33, wherein according to (iii), two gas streams are obtained, a gas stream G2 and a gas stream GR.

35. The process of any one of embodiments 1 to 34, wherein the reaction zone Z comprises a reactor, preferably a cylindrical reactor, comprising the monolithic catalyst.

36. The process of embodiment 35, wherein the gas stream in the reactor is of at most 450 °C, preferably of at most 405 °C, the temperature being preferably measured with a thermocouple.

37. The process of embodiment 35 or 36, wherein the reactor is an adiabatic fixed-bed reactor.

38. The process of embodiment 37, wherein the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst.

39. The process of any one of embodiments 1 to 38, further comprising, after (iii), passing the gas stream GR through a return means R prior to preparing G1 according to (i), during standard operation mode of the continuous process, in an ejector. The process of embodiment 39, as far as it depends on any one of embodiments 35 to 36, wherein the return means R forms a loop external to the reactor, for recycling GR and passing it into the ejector for admixing with the j gas streams G0(k) according to (i), during standard operation mode of the continuous process. The process of any one of embodiments 1 to 40, wherein from 20 to 100 weight-%, preferably from 30 to 80 weight-%, more preferably from 40 to 70 weight-%, of the gas stream GP consist of chlorine. A monolithic catalyst for preparing chlorine, preferably according to the process of any one of embodiments 1 to 41 , the catalyst comprising: a catalyzed flow-through monolith substrate, said substrate having an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow through substrate extending therethrough. The monolithic catalyst of embodiment 42, being selected from the group consisting of a Ru-based catalyst, a Ce-based catalyst, a Cu-based catalyst and a mixture of two or more thereof, preferably being selected from the group consisting of a Ru-based catalyst, a Ce- based catalyst and a Cu-based catalyst, more preferably being a Ru-based catalyst. The monolithic catalyst of embodiment 43, being a Ru-based catalyst, wherein Ru is supported on the surface of the internal walls of the flow-through monolith substrate and/or within the internal walls of the flow-through monolith substrate. The monolithic catalyst of embodiment 43 or 44, comprising Ru in an amount, calculated as RUO2, in the range of from 0.25 to 20 weight-%, preferably in the range of from 0.5 to 15 weight-%, based on the weight of the catalyst. The monolithic catalyst of any one of embodiments 42 to 45, wherein the cross section of the monolithic catalyst is a circle, a square, a rectangle or a triangle, preferably a circle or a square, more preferably a circle; wherein the cross section of the passages of the monolithic catalyst preferably is a square, a circle, a rectangle or a triangle, more preferably a square. The monolithic catalyst of any one of embodiments 42 to 46, having a cell density in the range of from 50 to 900 cells per square inch (cpsi), preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi. The monolithic catalyst of any one of embodiments 42 to 47, wherein the flow-through monolith substrate has a cell density in the range of from 50 to 900 cells per square inch (cpsi), preferably in the range of from 80 to 600 cpsi, more preferably in the range of from 100 to 300 cpsi. The monolithic catalyst of any one of embodiment 42 to 48, wherein the opening rate of the cross section of the flow-through monolith substrate is in the range of from 20 to 80 %, preferably in the range of from 50 to 70 %. The monolithic catalyst of any one of embodiments 42 to 49, wherein the flow-through monolith substrate comprises, preferably consists of, one or more of TiC>2, AI2O3, SiC>2, ZrC>2 and Ce _x O _y , preferably one or more of TiC>2, AI2O3 and SiC>2, wherein AI2O3 is preferably alpha- AI2O3 or gamma- AI2O3. The monolithic catalyst of embodiment 50, wherein the flow-through monolith substrate comprises, preferably consists of, one or more of TiC>2 and AI2O3, preferably one or more of TiC>2 and alpha-ALOs. The monolithic catalyst of embodiment 51 , wherein the flow-through monolith substrate comprises, preferably consists of, TiC>2 and alpha-ALOs, wherein from 30 to 35 weight-% of the substrate consists of TiC>2 and from 65 to 70 weight-% of the substrate consists of alpha-AhOs. The monolithic catalyst of embodiment 51 , wherein the flow-through monolith substrate comprises, preferably consists of, TiC>2 or alpha-AhOs. The monolithic catalyst of any one of embodiments 42 to 53, wherein the flow-through monolith substrate is porous or non-porous. The monolithic catalyst of any one of embodiments 42 to 52, having a cylindrical shape with a diameter in the range of from 0.5 m to 10.0 m, preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m, and preferably a length in the range of from 1 to 7 m, more preferably in the range of from 2 to 6 m, more preferably in the range of from 2.5 to 5 m. The monolithic catalyst of any one of embodiments 42 to 55, consisting of a catalyzed flow-through monolith substrate. The monolithic catalyst of any one of embodiments 42 to 55, comprising, preferably consisting of, a plurality of catalyzed flow-through monolith substrates, wherein said catalyzed flow-through monolith substrates are stacked to each other and above one another into the reaction zone Z; wherein the catalyzed flow-through monolith substrates which are stacked above one another are preferably vertically aligned; wherein preferably said catalyzed flow-through monolith substrates are stacked to each other and above one another with cooperation of a filler material, wherein the filler material is one or more of weave, felt and mats, more preferably one or more of mineral weave, mineral felt and mineral mats, more preferably mineral mats.

58. A production unit for carrying out the process according to any one of embodiments 1 to 41 , the unit comprising a reaction zone Z comprising

-- an inlet means for passing the gas stream G1 into Z;

-- a monolithic catalyst, the catalyst comprising a catalyzed flow-through monolith substrate which has an inlet end, an outlet end and a substrate axial length extending from the inlet end to the outlet end of the substrate and comprising a plurality of passages defined by internal walls of the flow-through substrate extending therethrough;

-- a reaction means for bringing into contact the gas stream G1 with said catalyst;

-- an outlet means for removing the gas stream GP from Z; a stream dividing device S for dividing the gas stream GP in at least two streams, preferably two streams, comprising a gas stream GR and a gas stream G2; a means for passing the gas stream GP into said device S; a means M for preparing G1 as a mixture comprising GR and j gas streams G0(k) with k=1 , ... j, wherein j is in the range of from 1 to 3, preferably 1 or 2, more preferably 2; a return means R for passing the gas stream GR exiting from S to said means M for preparing G1 .

59. The production unit of embodiment 58, wherein the reaction means of the reaction zone Z is a reactor, preferably a cylindrical reactor.

60. The production unit of embodiment 59, wherein the reaction means of the reaction zone Z is an adiabatic fixed bed reactor.

61 . The production unit of any one of embodiments 58 to 60, wherein the adiabatic fixed-bed reactor comprises one catalyst bed being the monolithic catalyst.

62. The production unit of any one of embodiments 58 to 60, wherein the adiabatic fixed-bed reactor is a multi-stage reactor comprising two or more catalyst beds, wherein each of the two or more catalyst beds is a monolithic catalyst, as defined in embodiment 58, wherein the catalyst in the respective catalyst beds has the same or different chemical compositions.

63. The production unit of any one of embodiments 59 to 62, wherein the reactor has an inner diameter in the range of from 1 .0 m to 10.0 m, preferably in the range of from 2.0 m to 7.0 m, more preferably in the range of from 3.0 m to 6.0 m. 64. The production unit of any one of embodiments 59 to 63, wherein the reactor has a wall thickness in the range of from 10 mm to 50 mm, preferably in the range of from 15 to 35 mm.

65. The production unit of any one of embodiments 59 to 64, wherein the reactor is made of corrosion-resistant material, preferably of iron-based alloys, nickel-based alloys, nickel or nickel clad, more preferably of nickel or nickel clad.

66. The production unit of any one of embodiments 58 to 65, further comprising, downstream of the reaction zone Z and upstream of the stream dividing device S, a heat exchanger, wherein the gas stream GP is passed through said heat exchanger.

67. The production unit of any one of embodiments 58 to 65, wherein the return means R further comprises a heat exchanger for cooling GR prior to enter the means M.

68. The production unit of embodiment 66 or 67, wherein the heat exchanger is a tube-and- shell heat exchanger, wherein the heat exchanger is preferably made of corrosion-resistant material, more preferably of nickel-based material or nickel.

69. The production unit of any one of embodiments 58 to 68, wherein the return means R is a return pipe, preferably an external return pipe to the reactor of Z or an internal return pipe to the reactor of Z, more preferably an external return pipe.

70. The production unit of embodiment 69, wherein the return pipe has an inner diameter of at most 2000 mm, preferably in the range of from 100 to 2000 mm, more preferably in the range of from 150 to 1000 mm.

71 . The production unit of embodiment 69 or 70, wherein the return pipe is made of corrosionresistant material, preferably of iron-based alloys, nickel-based alloys, nickel or nickel clad, more preferably of nickel-based alloys, nickel or nickel clad.

72. The production unit of any one of embodiments 58 to 71 , wherein the means M is a mixing device, wherein the mixing device is an ejector, a static mixer or a dynamic mixer, preferably an ejector.

73. The production unit of any one of embodiments 58 to 71 , wherein the monolithic catalyst is as defined in any one of embodiments 11 to 26 or any one of embodiments 42 to 57.

74. Use of a production unit according to any one of embodiments 58 to 73 for the continuous production of chlorine. 75. Use of a monolithic catalyst according to any one of embodiments 42 to 57 for the continuous production of chlorine.

76. A process for preparing phosgene comprising preparing chlorine according to the process of any one of embodiments 1 to 41 ; reacting the obtained chlorine with carbon monoxide in the presence of a catalyst, in gas phase, obtaining phosgene.

In the context of the present invention, it is noted that the term ”a catalyzed flow through monolith substrate” refers to a flow through monolith substrate which has been catalyzed by impregnation of a catalytic component, such as Ru for example. However, it is also noted that the “catalyzed flow through monolithic” can be a substrate prepared by extrusion wherein the catalytic component would have been mixed with the components of the substrate prior to extrusion. The first definition being preferred.

In the context of the present invention, the opening rate of the cross section of a monolithic substrate is calculated by multiplying the cross section area of one single channel (or passage) by the cell density. This can also be called cross section opening area percentage of the cross section of a monolithic substrate.

In the context of the present invention, the term “passage” used for describing the monolithic substrate or the flow-through monolith substrate has the same meaning as “channel”.

In the context of the present invention, a term “X is one or more of A, B and C”, wherein X is a given feature and each of A, B and C stands for specific realization of said feature, is to be understood as disclosing that X is either A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. In this regard, it is noted that the skilled person is capable of transfer to above abstract term to a concrete example, e.g. where X is a chemical element and A, B and C are concrete elements such as Li, Na, and K, or X is a temperature and A, B and C are concrete temperatures such as 10 °C, 20 °C, and 30 °C. In this regard, it is further noted that the skilled person is capable of extending the above term to less specific realizations of said feature, e.g. “X is one or more of A and B” disclosing that X is either A, or B, or A and B, or to more specific realizations of said feature, e.g. “X is one or more of A, B, C and D”, disclosing that X is either A, or B, or C, or D, or A and B, or A and C, or A and D, or B and C, or B and D, or C and D, or A and B and C, or A and B and D, or B and C and D, or A and B and C and D.

The present invention is further described by the following reference examples and examples.

Examples

Reference Example 1 : Production of chlorine not according to the present invention

A Deacon reaction is realized in a loop reactor set-up. A fresh stream (GO) of 23482 kg/h HCI and 10307 kg/h O2 at a temperature of 171 °C was mixed via an ejector with a recycled stream GR of 138 t/h removed from the outlet end of an adiabatic fixed-bed reactor and cooled down via an external heat exchanger to 307°C to get a feed stream G1 exiting the ejector at a temperature of 280°C. The ratio f(GR):f(G2) was of 4.1 :1 and f(GR):f(GP) of 0.8:1. The maximum gas stream temperature in the reactor and the temperature of the stream GP at the outlet end of the adiabatic fixed-bed reactor was of 390°C and the inlet pressure 5.4 bara (pressure at the inlet of the catalyst bed). The amount of HCI in G2 related to the feed flow of 23482 kg/h of HCI in GO gives a HCI conversion of about 87.5 %.

The Deacon reaction took place in a catalyst bed of 5 m diameter and 3.6 m length completely filled with cylindrical Ru-based catalyst extrudates with a mean diameter of 3 mm and a mean length of 5 mm.

The mixing done via the ejector was driven by GO at 16 bara to realize the above mentioned recycle flow at given pressure drop. The pressure drop was caused by the catalyst bed (pressure drop: 312 mbar) and by additional contributions from piping, gas distributor and heat exchanger (additional pressure drop: 434 mbar). The overall pressure drop of the system was 746 mbar.

Example 1 : Production of chlorine according to the present invention

A Deacon reaction is realized in a loop reactor set-up described in Figure 1 below. The difference with the loop reactor set-up of Reference Example 1 is the catalyst bed (cylindrical extrudates in Ref. Ex. 1 vs. a monolithic catalyst in Ex. 1 ) and the pressure of GO (16 bara in Ref. Ex. 1 vs. 9.3 bara in Ex. 1). The ratio f(GR):f(G2) was of 4.1 :1 and f(GR):f(GP) of 0.8:1.

Same process as described in Reference Example 1 was performed, except that the reaction took place in a catalyst bed of 5 m diameter and 3.6 m length being a catalyst consisting of a flow through monolith substrate impregnated with a catalytic metal (Ru), the substrate having an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the substrate and a plurality of passages defined by internal walls of the substrate extending therethrough, wherein said catalyzed flow through monolith substrate is made of a plurality of catalyzed flow through monolith substrates stacked to each other and above one another. The catalyst had a cell density of 150 cells per square inch and the opening rate of the cross section of the catalyst wasof 50%. The volume of the Ru-catalyst in Ref. Example 1 and Example 1 were the same.

Thus, the mixing done by the ejector was driven by GO at lower pressure compared to Reference Example 1 , namely at 9.3 bara. The amount of HCI in G2 related to the feed flow of 23482 kg/h of HCI in GO gives a HCI conversion of about 87.7 %. Temperatures were as in Reference Example 1 . The pressure drop across the catalyst bed was of only 14 mbar and the additional pressure drop from piping, gas distributor and heat exchanger was of 434 mbar, causing an overall pressure drop of 448 mbar.

Therefore, compared to the process and catalyst used in Reference Example 1 , the overall pressure drop has significantly been reduced from 746 mbar to 448 mbar and GO can be used as the driver in the injector at lower pressure (9.3 bara vs. 16 bara) decreasing invest and operational costs for feed flow compressor.

Example 2: Production of chlorine according to the present invention

A Deacon reaction is realized in a loop reactor set-up described in Figure 1 below.

Same process as described in Reference Example 1 was performed, except that the reaction took place in a catalyst bed of 5 m diameter and 3.6 m length being a monolithic catalyst as defined in Example 1 .

The recycle stream GR was increased from 138 t/h to 166 t/h. The ratio f(GR):f(G2) was of 4.9:1 and f(GR):f(GP) of 0.8:1 . The fresh feed of HCI and O2 (GO) at 16 bara allows a pressure buildup in the ejector of about 600 mbar with pressure drop contributions of about 14 mbar across the catalyst bed and of 586 mbar from piping, gas distributor and heat exchanger (additional contributions). The maximum gas stream temperature in the reactor and the temperature of the stream GP at the outlet end of the adiabatic fixed-bed reactor was of 390°C, the stream was cooled down to 321 °C and separated in two streams GR and G2, the feed stream G1 exiting the ejector was at a temperature of 296 °C. The amount of HCI in G2 related to the feed flow of 23482 kg/h of HCI in GO gives a HCI conversion of about 87.7 %.

The higher temperature of G1 (296°C vs. 280 °C in Ref. Ex. 1 ) increases the reaction rate at the inlet end of the reactor allowing the reduction of the catalyst bed length from 3.6 m to 2.9 m to realize the same conversion. In this way about 20 % of catalyst can be saved.

Comparative Example 1 : Production of chlorine not according to the present invention

A Deacon reaction was realized in a loop reactor set-up. The fresh stream GO was the same as in Reference Example 1. However, compared to Reference Example 1 , the recycle stream GR was reduced to fit the upper limit of the recycle ratio disclosed in US 2004/052718, thus f(GR):f(G2) was set up at 3:1 (f(GR):f(GP) was of 0.75:1). The recycle stream GR of 101 t/h was removed from the outlet end of an adiabatic fixed-bed reactor and cooled down via an external heat exchanger to 297°C (cooling step not disclosed in US 2004/052718) to get a feed stream G1 at a temperature of 265°C. The maximum gas stream temperature in the reactor and the temperature of the stream GP at the outlet end of the adiabatic fixed-bed reactor was of 400°C and the inlet pressure 5.4 bara (pressure at the inlet of the catalyst bed). The amount of HCI in G2 related to the feed flow of 23482 kg/h of HCI in GO gives a HCI conversion of about 86.7 %. The reaction took place in the same reactor as defined in Reference Example 1 with the same catalyst (cylindrical extrudates packed in the catalyst bed).

The mixing done via the ejector was driven by GO at 7.9 bara to realize the above mentioned recycle flow at given pressure drop. The pressure drop was caused by the catalyst bed (pressure drop: 196 mbar) and by additional contributions from piping, gas distributor and heat exchanger (additional pressure drop: 268 mbar). The overall pressure drop of the system was 464 mbar.

Example 3: Production of chlorine according to the present invention

A Deacon reaction was realized in a loop reactor set-up described in Figure 1 below. The difference with the loop reactor set-up of Comparative Example 1 is the catalyst bed (cylindrical extrudates in Ref. Ex. 1 vs. catalyzed flow through monolithic substrate in Ex. 3). The ratio f(GR):f(G2) was of 3:1 and f(GR):f(GP) was of 0.75:1 .

Same process as described in Comparative Example 1 was performed, except that the reaction took place in a catalyst bed of 5 m diameter and 3.6 m length being a catalyst consisting of a flow through monolith substrate impregnated with a catalytic metal, the substrate having an inlet end, an outlet end, a substrate axial length extending from the inlet end to the outlet end of the substrate and a plurality of passages defined by internal walls of the substrate extending therethrough, wherein said catalyzed flow through monolith substrate is made of a plurality of catalyzed flow through monolith substrates stacked to each other and above one another. The catalyst has a cell density of 150 cells per square inch and a porosity of 50%.

The pressure drop across the catalyst bed was of only 11 mbar and the additional pressure drop from piping, gas distributor and heat exchanger was of 268 mbar, causing an overall pressure drop of 279 mbar. The HCI conversion was comparable to Comparative Example 1 .

Therefore, compared to the process and catalyst used in Comparative Example 1 , the overall pressure drop has significantly been reduced from 464 mbar to 279 mbar and GO can be used as the driver in the injector at lower pressure (6.9 bara vs. 7.9 bara) decreasing invest and operational costs for feed flow compressor while maintaining comparable HCI conversion.

Description of the figures

Figure 1 is a schematic representation of a production unit according to embodiments of the invention. The production unit comprises a reaction zone Z comprising an inlet means, such as a pipe, for passing the gas stream G1 into Z and a reaction means for bringing into contact the gas stream G1 with a catalyst (not shown), preferably an adiabatic reactor, namely a reactor wherein the reaction is operated adiabatically. The temperature of gas stream G1 is of 280 °C in Ex. 1 , 296°C in Ex.2 and 265°C in Ex.3. The reactor comprising a monolithic catalyst, the reactor being preferably an adiabatic fixed-bed reactor. The maximum gas stream temperature in the reactor and at the outlet of the reactor was 390 °C (Ex. 1-2) or 403 °C (Ex. 3). Further, the reaction zone Z comprises an outlet means, for example a pipe, for removing the gas stream GP from Z. The gas stream GP comprises chlorine and one or more of HCI, H2O and O2. The production unit further comprises a heat exchanger H for cooling the gas stream GP prior to be divided in a stream dividing device in two streams, a gas stream GR (T(GR) in Ex. 1 = 307 °C, T(GR) in Ex. 2 = 321 °C and T(GR) in Ex. 3 = 297 °C) and a gas stream G2 (T(G2) in Ex. 1 = 307 °C, T(G2) in Ex. 2 = 321 °C and T(G2) in Ex. 3 = 297 °C), a means, such as a pipe, for passing the gas stream GP into the stream dividing device not represented in this figure. The gas streams G2 and GR have respectively the same chemical composition as GP. The amount of HCI in G2 related to the feed flow of HCI in GO gives a HCI conversion of about 87.7 % (Ex.1), of about 87.7 % (Ex.2) and of about 86.7 % (Ex.3). The production unit further comprises a means M, preferably an ejector driven by GO, for admixing the gas stream GO with the gas stream GR comprising an inlet means, such as a pipe, for feeding the gas stream GO into M and a means for feeding the gas stream GR into M. The gas stream GO consists of HCI and O2. To obtain GO two gas streams, G0(1) consisting of HCI and G0(2) consisting of O2 were combined, these streams are not shown here. The recycle gas stream GR is sucked in the ejector M. The recycle ratio is the ratio of the mass flow f(GR) of the gas stream GR relative to the mass flow f(GP) of the gas stream GP, f(GR):f(GP), which was of about 0.8:1 (Ex.1 ), 0.8:1 (Ex.2) and 0.75:1 (Ex.3) and f(GR):f(G2) was of about 4.1 :1 (Ex.1), 4.9:1 (Ex.2) and 3:1 (Ex.3). The production unit further comprises a return means R, a return pipe, for passing the gas stream GR exiting from the stream dividing device to said means M.

Cited Literature

- US 2004/0052718

- WO 2017/089231

- WO 2014/090841

- WO 2007/134771 A1

- WO 2011/111351 A1

- WO 2013/004651 A1

- WO 2013/060628 A1

- US 2418930 A